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Fractured soft and low permeability coalbed is commonly developed in China, which restricts the increase of single well gas production and industrial development of coalbed methane (CBM). Indirect fracturing is a kind of fracturing method to communicate with coal seams by creating vertical fractures in the neighboring layers and thus achieve effective coal seam transformation, which can solve disadvantages such as drilling collapse, coal dust production, fracturing fluid filtration loss and thin coal seam thickness. In this paper, physical simulation experiments and extended finite element numerical simulation analysis of indirect fracturing are used to reveal the factors influencing the fracture expansion of indirect fracturing in the coal seam roof and to clarify the fracture expansion mechanism in order to provide guidance for indirect fracturing technology. The indirect fracturing experiments under the influence of direct fracturing of coal seam and different fracture initiation location, vertical stress and construction displacement show that high fracture initiation pressure is more likely to produce long fractures, and the influence of primary fractures is significantly reduced; however, the farther the fracture initiation point is from the coal seam, the more energy is required for fracture initiation, and high fracture pressure will cause crushing damage to the coal seam; under large construction displacement, the fracture initiation pressure is correspondingly increased, the fracture initiation time becomes shorter, and the influence of primary fractures becomes smaller. The degree of impact of primary fracture becomes smaller. Under the condition of model parameter setting in this paper，the numerical simulation results considering the parameters of ground stress, fracture initiation location, rock mechanics and construction displacement show that the maximum horizontal principal stress and vertical stress difference is 3 MPa, and the combination of coal and roof elastic modulus difference

The Erzhuangke landslide is a typical landslide affected by the rainy season. Rainfall changes the seepage pattern with the pre-existing landslide, weakening matric suction and soil shear strength, leading to the formation of tension cracks internally. This triggers overall sliding and localized extensive deformations. Existing studies seldom considers the interaction between the seepage field and stress field of the Erzhuangke landslide. Therefore, based on the actual engineering geological disaster scenarios, supported by on-site monitoring data and terrain physical parameters, a geometric computational model is established, and hydraulic coupled numerical simulations are conducted. By investigating variations in saturation and pore pressure within the landslide, the paper explores the rainfall infiltration patterns. It examines the impact of rainfall intensity on landslide reactivation from the perspective of stress displacement. In addition, in order to validate the accuracy and feasibility of the method, selected measurement points from the landslide are matched with corresponding positions in the numerical model. Comparative analysis is performed on displacement, soil pressure, and saturation aspects, confirming that the numerical model effectively reflects the actual situation. Through coupling numerical simulations and the study of the reactivation mechanism of the old landslide under rainfall conditions, the paper interprets field data, analyzes the reactivation process, and provides theoretical foundations and technical guidance for subsequent engineering early warning and disaster mitigation works.

Objective Recently, the seismic damage of an actual bridge structure in a frozen soil area has shown that the presence of frozen soil will increase the lateral stiffness of the bridge foundation, which may cause more serious seismic damage to the bridge structure, but there is a lack of research on the frozen soil-pile interaction effect of frozen soil bridge structures under seismic loadings and the corresponding seismic responses. Methods The present paper proposed efficient nonlinear numerical models to consider the effect of the frozen soil-pile interaction on the seismic responses of structures. First, the relationship between the depth of frozen soil and surface temperature was constructed. Then, the p-y spring modelling approach was presented to simulate the seismic behavior of frozen soil. Several as-recorded ground motions were selected as the seismic input. The seismic responses of piers and bearings of regular bridges with different depths of frozen soil under seismic loadings were investigated. Results The results show that the proposed efficient nonlinear numerical model can be adopted to model the seismic behavior of bridges considering frozen soil. And the proposed p-y curves for frozen soil can accurately predict the p-y relationship from the existing tests. When the PGA is relatively small, the pier curvature increases slightly; by contrast, in the case of large PGA, frozen soil can significantly increase the curvature demands, which can make the pier enter into the inelastic behavior. When the depth of frozen soil is small (the temperature is -5℃), the bearing displacement increases significantly, which increases the probability of unseating under seismic loadings. Moreover, frozen soil can transfer to the adverse locations of structural systems under seismic loadings. Conclusion Therefore, the conclusions of this paper can provide the necessary theoretical basis and data support for studying the seismic performance and corresponding seismic design methods of frozen soil bridge structures in China, which is of great significance for promoting the development and engineering application of disaster prevention and mitigation of bridge engineering in frozen soil areas in China.

Objective Monitoring natural attenuation (MNA) is a widely used, economical and effective remediation technique for soil and groundwater contamination. The migration of nonaqueous phase liquid (NAPL) in heterogeneous strata is an important element in the assessment for the efficiency of MNA. Methods Based on three consecutive years of dynamic groundwater quality monitoring data, the purpose of this study is to accurately characterize the biodegradation processes of multiphase fluids at a typical phenol contaminated site in northern China. A multiphase flow numerical model of phenol transport considering Monod biodegradation processes based on TOUGH3/TMVOCBio software was developed and applied. The model depicted the spatial distribution and temporal variation of phenol under the current conditions well and analysed the sensitivities of the adsorption and biodegradation parameters. The paper also discussed the removal contributions of dissolution, volatilization, adsorption and biodegradation effects under uncertainty of adsorption and microbial degradation parameters and predicted two different natural attenuation scenarios for source disposal. Results The contribution of phenol removal varies over a range under the influence of parameter uncertainty, with 17.91% to 58.02% for biodegradation, and precipitation conditions affect the seasonal variation in phenol concentrations. In the future 20 years, under the conditions with complete removal of the phenol source and the present leakage model, the total mass removal rate of phenol will arrive at 98% and 80% at the end of the 20th year, respectively. Conclusion This paper identifies the biodegradation parameters with high sensitivity in the multiphase flow model, which provides a reference for the numerical simulation of the organic matter biodegradation process at petrochemical sites and can also provide a theoretical basis for the application of MNA technology in China.

[Introduction] With the development of wind power generation technology, the unit capacity of permanent magnet wind generator is increasing, and the heating power is also increasing. The heat dissipation of generator is facing unprecedented challenges. How to effectively solve the problem of generator temperature rise and heat dissipation difficulty has been the focus of our study. [Method] Based on the STAR-CCM+ software platform, an integrated numerical simulation method for generator heat dissipation and cooling was proposed in this paper. The reliability of the numerical calculation method was verified by comparing the calculated values with the experimental values. On this basis, a study was conducted on the internal temperature distribution law and the factors influencing the cooling system heat dissipation performance of the high power permanent magnet wind generator. [Result] Under the rated power, the highest temperature of the winding and stator core appear in the middle area. If the process conditions allow, the cooling water pipe should be as close to the winding as possible to take away more heat. The stator core temperature and winding temperature can be reduced significantly by increasing the total intake air volume of the generator. The intake air temperature has a linear relationship with the maximum temperature of the winding and stator core. For every 5℃ decrease in the intake air temperature, the maximum temperature will be reduced by about 1.4℃. Reducing the intake air temperature can improve the heat dissipation performance of the generator to a certain extent. The intake water temperature has a linear relationship with the maximum temperature of the winding and stator core. For every 5℃ decrease in the intake water temperature, the maximum temperature will be reduced by about 3.3℃. Reducing the intake water temperature can greatly improve the heat dissipation performance of the generator. In addition, the gap between the cooling water pipe and the stator core greatly hinders the heat transfer of the cooling water pipe. Filling the gap with materials with good thermal conductivity can effectively improve the heat dissipation performance of the generator. [Conclusion] The conclusions drawn in this paper can effectively guide the heat dissipation design of permanent magnet wind generator and ensure the safe operation of wind turbines in normal work.

Prediction of water inflow of a sub-sea tunnel under the blasting vibration effect is still a difficult subject. This paper takes the sub-sea tunnel between the Wawuzhuang Station and Guizhou Road Station of the Qingdao Metro Line 1 as the engineering background. Based on the equivalent continuum model, the mirror image method is used to deduce the calculation formula for the water inflow of the sub-sea tunnel considering the damage area factor. Through forward modeling and inversion, combined with numerical simulation results and actual engineering monitoring results, the correctness of the formula is comprehensively verified, and the influence mechanism of damage area factors on water inflow is analyzed. The results show that the squeezing effect caused by blasting vibration makes the pore water pressure of surrounding rock around the tunnel rise rapidly in a short time. After reaching the peak value, it began to decline slowly with the weakening and disappearance of blasting vibration. Under the influence of damage zone factors, the water inflow of the tunnel increases gradually with the increasing thickness of the damage zone, but it will not increase continuously with the increase of the coefficient of permeability in the damaged area. Through numerical simulation calculation, the ratio of tunnel water inflow considering blasting damage area is 1.4, and the error is only 4.1% compared with the calculation result of 1.342 deduced in this paper. The calculated results in this study are only 0.53 m3/(d·m) less than the field measured results, and are closer to the measured results than those with the traditional calculation formula, indicating that the calculation formula in this paper is suitable for the calculation of tunnel water inflow considering the factor of damage zone, and are of high engineering application value.

The study of the transient electromagnetic detection device with small sized coil and easy installation underground will offer new insights into the real-time dynamic exploration and forecast water-bearing structure in excavation roadway.By drawing on the full-space transient electromagnetic theory, this paper adopted the three-dimensional time-domain finite element method for numerical simulation to explore the characteristics of the secondary field response obtained by small coil excitation and the transient electromagnetic response received by the magnetic core coil.This study constructed a geological-geophysical model of the water-bearing fault in front of the roadway excavation working face, studied the transient electromagnetic response characteristics of the small coil device for the water-bearing fault, and compared the effects of small coil and conventional coil in advance detection.The study shows that : ①the decay law of the induced electric potential generated by the small coil source excitation is the same as that of the induced electric potential generated by the conventional transmitting coil with time, ②the magnetic core coil can effectively improve the induced signal strength, ③the application of both the small coil device and the conventional coil device can effectively explain the distribution range of the low resistance area, ④the detection results match the verification results of the roadway excavation.Combined with the underground field test, this paper verified the applicability and effectiveness of the small coil device applied to mine transient electromagnetic method advance detection.

The borehole transient electromagnetic method is used to detect the long-range water-bearing bodies around the borehole wall by using the advanced water exploration borehole in the heading roadway, which avoids the “one’s opinion in one hole” because the normal logging methods can only detect the rock layer of the borehole wall. At present, because of the whole space effect, the current borehole transient electromagnetic method cannot distinguish the orientation of abnormal bodies by the received single-component response, and it can approximate the orientation of abnormal bodies by multi-component response, but it is difficult to precisely locate and interpret the profiles by the visual and effective means such as imaging. Based on the theory of borehole transient electromagnetic method and azimuthal electromagnetic logging, this paper proposes a borehole transient electromagnetic positioning method with azimuthal coil scanning detection. The azimuth coil is used as the detection device to reduce the mutual inductance of the coil and enhance the detection effect of the borehole transient electromagnetic method. At the same time, by changing the rotation angle of the coil, the borehole wall is scanned by 360° to form a radial all-round detection of the borehole, aiming at a precise localization and profile interpretation of low-resistance abnormal bodies in the rock mass at the periphery of the borehole wall. Firstly, the authors derive an analytical expression for the mutual inductance of an azimuth coil, discuss the effect of azimuth angle on azimuth coil mutual inductance, and determine the optimum azimuth angle by numerical calculation. Secondly, a full-space 3D geological-geophysical model of the borehole with homogeneous medium and low-resistance abnormal bodies are established respectively and the numerical simulation of transient electromagnetic field is carried out. The multi-component response characteristics of the azimuthal coil scanning detection transient electromagnetic response are analyzed, and the law of transient electromagnetic response of azimuthal coil scanning detection is summarized, and the borehole transient electromagnetic positioning method with azimuthal coil scanning detection is determined. Namely, through the transient electromagnetic response characteristics of the axial and radial directions of the borehole, the position of the low-resistance abnormal bodies in the rock body at the periphery of the borehole wall is determined. Finally, by establishing the geological-geophysical model with two low-resistance bodies and using azimuth coils set to the best azimuth angle for numerical experiments, it is verified that the method can intuitively and effectively determine the orientation of low resistance abnormal bodies. The study shows that the azimuth coil scanning detection results of the borehole transient electromagnetic method can better reflect the transient electromagnetic field anomaly caused by the low-resistance abnormal bodies in the rock body at the periphery of the borehole wall, and the resolution of the full-space apparent resistivity imaging results is high. Based on the transient electromagnetic response characteristics of the axial and radial directions of the borehole, the borehole transient electromagnetic positioning method with azimuthal coil scanning detection has a high resolution and localization accuracy for the low-resistance abnormal bodies in the rock body at the periphery of the borehole wall. The research results provide a theoretical basis for the practical application of the borehole transient electromagnetic positioning method with azimuthal coil scanning detection.

ObjectivesThis papers aims to analyze the impact resistance of honeycomb structure with different Poisson's ratio. MethodsBased on the explicit dynamic finite element method, this paper analyzes the dynamic mechanical properties of honeycomb structures with different Poisson's ratios under in-plane impact load, and explores the influence laws of Poisson's ratios on their impact resistance. Three typical honeycomb structures with negative/zero/positive Poisson's ratios (reentrant hexagon, hexagon and semi-reentrant hexagon) are selected, their geometric parameters are changed to give them the same relative density and different Poisson's ratios (−2.76 – +3.63), and their dynamic mechanical properties under low/medium/high-speed dynamic displacement loads are analyzed. ResultsThe results show that the zero Poisson's ratio semi-reentrant honeycomb structure has the best structural stability without transverse deformation under compression deformation; without structural instability, the platform stress has little correlation with the Poisson's ratio; and the compact strain and total energy absorbtion increases with the absolute value of the Poisson's ratio. Negative Poisson's ratio honeycomb structures with large t/l and small θ are suitable for applications with high platform stress (strong deformation resistance), and negative Poisson's ratio honeycomb structures with small t/l and small θ are suitable for high total energy absorbtion applications, while zero Poisson's ratio semi-reentrant honeycomb structures are suitable for applications with high platform stress (strong deformation resistance). ConclusionsThis study can provide references for the type selection and geometric parameter design of side impact honeycomb structures.

The purification effect of coal mine groundwater reservoir on mine water mainly lies in the water-rock coupling between the rock mass and mine water.This paper systematically reviews the research methods of water-rock coupling in coal mine underground reservoirs, and presents the characterization methods of water quality and physicochemical properties of rock samples.It employs static simulation, dynamic leaching, cycle purification simulation and other tests to explore the purification regulation of mine water in coal mine underground reservoir, uses numerical simulation to obtain the selective adsorption trend of ions in the reaction process, and combines Piper three-line diagram, Gibbs model and correlation analysis to reveal the mechanism of water-rock coupling.The purification effect and research progress of suspended solids, specific ions and organic matter in coal mine underground reservoirs are discussed.The paper shows that underground reservoir of coal mine has a certain purification effect on mine water, and the purification effect of specific ions is mainly related to filtration and adsorption.Three research directions of coal mine underground reservoir purification technology in the future are proposed: ①developing large-scale and low-cost treatment technologies for underground mine water based on water-rock coupling purification, ②developing a "three-in-one" water quality control technology for coal mine underground reservoirs coupled with multiple water treatment technologies, and ③exploring the underground storage and resource utilization technology of concentrated salt wastewater for the future studies of water-rock coupling.

The mining of thin coal seam resources is seriously affected by the overlying coal seam gas. The detection of three zones of goaf roof is of great significance to the safety production. In this paper, we carried out loading coal and rock resistivity testing experiment, analyzed the loading damage in the process of coal and rock resistivity change and distribution, and carried on the theoretical analysis and numerical simulation of overlying strata three zones according to the actual embedded depth, and then carried out field test. Direct current method has been used to test the forward three-zone apparent resistivity distribution. The main conclusions are as follows: the resistivity changes due to the crack propagation of coal samples, and the resistivity surge point corresponds well with the failure point of coal and rock; in the process of coal and rock failure under load, there are abnormal areas in the resistivity cloud diagram under load, and it migrates with the uneven deformation of coal and rock under load; the collective subsidence of the goaf after the roof is cut in the coal seam mining will form a large sectioned area in thefracture area of the upper part of the goaf. There are large cracks in this part of the sectioned area, and it will extend to the roof rock of the return air roadway, resulting in the increase of cracks in the rock; the electrical detection results show that the horizontal distance from the working face to the caving zone is about 20 m, and the influence resistance value of the fracture zone becomes larger and its height is 17 m, which is consistent with the theoretical calculation and numerical simulation results.

At present, physical information neural network has become a new paradigm for numerical calculation of engineering mechanics. It can solve partial differential equations by integrating the physical mechanism of neural network in the case of unlabeled sample data, and solve them quickly with low computational cost. In this paper, the calculation principle of physical information neural network（ＰＩＮＮ） and the framework for solving the governing equation of coal stick-slip impact are expounded. By comparing the solution results with the explicit finite difference method, the effective accuracy of the solution results is verified. Taking the working face of No.12 coal seam in Jinhuagong Mine as the research background, the dynamic numerical simulation of coal stick-slip impact is carried out, and the occurrence time interval and fluctuation rule of coal stick-slip deformation process are obtained by means of numerical simulation. The numerical simulation results show that when the abutment pressure concentration coefficient is 2, the maximum value of coal stick-slip displacement（ｄｅｆｏｒｍａｔｉｏｎ） increases obviously; when the abutment pressure concentration coefficient is 3, the typical stick-slip phenomenon occurs, and the displacement changes quasi-periodically, the storage elastic energy of coal stick-slip system gradually increases, and the strength damage of coal-rock stick-slip process occurs. The dynamic friction factor has a great influence on the coal stick-slip dynamic characteristics. When the dynamic friction factor changes, the displacement field of the coal stick-slip system changes obviously.

In recent years, with continuous social and economic development, there has been an increase in the scale of reservoir impoundment and underground industrial development activities. Consequently, induced or triggered seismicity is increasing, resulting in escalating damage losses. Therefore, the impact of industrial production behaviors on regional seismicity and the safe implementation of industrial production without causing earthquakes are important topics being discussed and closely monitored by the public and scientific research community. In this paper, we provide an overview of induced or triggered earthquakes, both domestic and international, and explore their causative mechanisms. Additionally, we summarize the methods commonly used to study induced or triggered earthquakes in academia, beginning with the governing equations. With the ongoing development of science and technology, numerical simulation will present unique advantages and become an important scientific tool for studying induced or triggered earthquakes. To date, both domestic and foreign researchers have conducted meaningful studies on induced earthquakes using numerical simulation methods. The physical mechanisms that trigger earthquakes will gradually be revealed, and measures for prevention and control will be improved. This work will effectively reduce the hazards caused by industrial production and other activities, thereby reducing the risk of triggering major earthquakes. However, there are still many challenges in numerical earthquake prediction. It not only requires a flawless physical mechanism and advanced calculation methods but also necessitates comprehensive observation and the establishment of an industrial production system.

Based on the volume of fluid multiphase flow model and the overset mesh technique, a numerical method for an asynchronous parallel oblique water-entry super-cavitating projectile was established. Experimental studies of the oblique water-entry of a high-speed single-launch projectile were carried out to validate the viability of the numerical method. The paper performed the numerical simulations and analyses of cavity evolution and motion characteristics of the front and rear projectiles in different initial intervals and in two sequences of top-side water-entry projectile first and bottom-side water-entry projectile first. The results show that when the initial interval of the first launch projectile is 0.5 time the projectile length, the first launch projectile cannot produce a cavity to completely encapsulate the projectile due to the violent squeezing of the following launch projectile cavity, and its movement is seriously affected and eventually loses its trajectory stability. At the same time, the first launch projectile that enters water from top side is squeezed to a larger degree than the one from bottom side, and the wetting phenomenon occurs earlier and loses stability faster. As the initial interval increases, the influence of the following launch projectile cavity near the first launch projectile is weakened, and the first launch projectile in both water entry sequences move steadily. For the following launch projectile, due to the continuous influence of the first launch projectile cavity, its cavity is always asymmetrical, and its motion stability is affected. The following launch projectile deflects to the inner side and destabilizes when the initial interval is 0.5 times the projectile length. When the initial interval is 1 time the projectile length, it moves steadily. It deflects to the outer side and destabilizes when the initial interval is 2 and 3 times the projectile length. In addition, the motion characteristics of the following launch projectile are basically identical in two water-entry sequences.

Wave impact is a strongly nonlinear interaction between waves and structures, and its load usually has the characteristics of a large peak value and short duration. In recent years, the extreme environment has frequently led to severe wave impacts on marine structures, resulting in loss of life and property, thus making the issue of wave impact become a great concern. For the complicated impact process, the theoretical analysis and model experiments can only provide simplified analytical solution and limited information on the slamming flow field. Therefore, numerical simulation has gradually become an effective means to study the issue of wave impact. Scholars at home and abroad have conducted a large number of numerical investigations on the load characteristics of wave impact, impact process, and its influencing factors on marine structures, gaining numerous important research conclusions. In this paper, the current progress, existing methods, and important conclusions of the numerical study of wave impact on marine structures are reviewed, which can provide useful references for further research on the numerical simulation of wave impact.

The steam generator tube rupture (SGTR) accident is one of the design basis accidents of lead-cooled fast reactor (LFR). In the event of such an accident, a subcooled water jet is generated in the lead pool of primary circuit, which forms a complicated distribution of the liquid metal-gas two-phase flow. The detection of the two-phase interface and migration of steam bubbles is an significant part of reactor safety analysis. Due to the opacity, corrosiveness, high temperature of liquid metal, and the current limitations of measurement methods involving liquid metal-gas two-phase flow, a diamond-like carbon (DLC) coated wire-mesh sensor (WMS) based on electrical principles was proposed in this paper. The sensor could achieve the image of the liquid metal-gas two-phase distribution inside the flow channel, while preventing the corrosion failure of the sensor. Based on the COMSOL software, a numerical model of the DLC coated WMS was established. Selecting the materials of two phases as liquid GaInSn alloy and air, the simulation of the electric field in the liquid metal environment containing a single bubble was performed, and an electric signal value matrix representing the liquid metal-gas two-phase was output. The signal matrix was further normalized through the linear relation to obtain the two-phase distribution image, which verified the application feasibility of the coated WMS in liquid metal. In addition, a prototype of the DLC coated WMS was manufactured, and the numerical simulation results were experimentally validated in order to demonstrate the rationality of the numerical model. Furthermore, the influence of different structural parameters on the measurement accuracy of coated WMS was studied in detail by changing the transverse interval, axial interval, electrode diameter, coat thickness, and the size of air bubble. The simulation results show that the electric field distribution in the liquid metal-gas two-phase environment differs significantly from that in conventional fluid medias such as water-gas due to the high relative permittivity of liquid metal. On the other hand, considering the resolution of the WMS and the phenomenon of electric signal crosstalk, the transverse interval of electrode should be selected between 2-3 mm, and the axial interval should be selected between 1.5-2 mm to achieve high measurement accuracy. The coat thickness and electrode diameter have little influence on the measurement accuracy, but to reduce the intrusion effect of the WMS, the electrode diameter should be selected between 0.4-0.5 mm and the coat thickness should not exceed half of the electrode radius. This study could guide the practical application of DLC coated WMS in the liquid metal-gas two-phase environment and provide a technical basis for the analysis of multi-phase distribution under SGTR accidents.

In order to reveal the seepage evolution law of high-pressure water injection and improve the effect of water injection and dust suppression in coal, based on triaxial compression and coal mining practices, this paper obtains the matching relationship between coal deformation and pore water pressure through coal-rock permeability test. The user-defined function module is used to compile the relationship into Fluent to simulate the fluid pressure field, velocity field and water distribution in the process of drilling water injection, and analyze the wetting range and seepage velocity in coal around the radial direction of drilling hole under different water injection pressures. The results show that the seepage field pressure increases with the increase of pore water pressure, and the rate of pressure change gradually decreases with the increase of time, and the variation of seepage field velocity shows a similar change law. With the continuous increase of pore water pressure, the porosity of coal increases, and the water content of coal increases gradually, and the distribution range is gradually expanded from around the borehole to both sides. The wetting process around the borehole of coal seam increases rapidly and then decreases slowly to reach a stable state.

ObjectiveThe purpose of this paper is to explores the water-entry slamming load distribution of a trimaran connecting bridge.MethodsBased on OpenFOAM open source software and starting with the continuity equation and N-S equation, this paper establishes a free entry slamming numerical model of a trimaran connecting bridge. The dynamic changes of velocity, slamming pressure and free surface during the free entry slamming process of the trimaran connecting bridge are simulated. The convergence analysis of the grid is carried out, and the numerical solution is compared with the experimental solution to verify the accuracy of the numerical calculation method. ResultsThe results show that this method can effectively predict the falling body slamming load of a trimaran connecting bridge structure. It is found that the slamming pressure coefficient of the connecting bridge is largest near the outer corner. The peak value of the slamming pressure on the lower surface of the connecting bridge and the relationship between the slamming pressure coefficient and velocity are then obtained.ConclusionsThis study presents the characteristics and range of slamming pressure on a trimaran connecting bridge, providing a numerical basis for the structural strength evaluation and design of trimarans.

ObjectiveThe exhaust ejection device is an important part of a ship's gas turbine intake and exhaust system. It is very important to ensure the exhaust and ejection performance of the exhaust ejection device for the normal operation of the ship. MethodsAccording to the characteristics of this type of gas turbine exhaust ejection device, this paper selects eight relevant structural parameters and two objective functions in order to analyze the parameter correlation, and determines the two design variables that have the greatest correlation with the objective function. On this basis, the design parameters are optimized based on the multi-objective optimization genetic algorithm NSGA-II, and the selected optimization scheme is applied to a gas turbine intake and exhaust system assembly model for verification. Results The results show that, compared with the original scheme, the optimized exhaust ejection device has a significantly improved ejection flow rate of the gas turbine casing, meeting the design requirements of the exhaust ejection amount, but this also leads to an increase in exhaust back pressure. ConclusionThe research approaches and results obtained in this paper have certain reference value for the design and optimization of gas turbine exhaust ejection devices.

ObjectiveThe purpose of this paper is to study the effects of cavitation models on the simulation of full-scale propeller cavitation. MethodsThe minimum rotational speed of the propeller required for cavitation is predicted by the Bernoulli equation, and the propeller's cavitation condition is observed by full-scale experiment. After determining the boundary layer mesh thickness and establishing the hydrodynamic model, meshes are generated. In the numerical simulation, the turbulence model is selected from either the standard \begin{document}$k - \varepsilon $\end{document} model or Realizable \begin{document}$k - \varepsilon $\end{document} model, and the cavitation model is selected from either the Schnerr−Sauer (S−S) model or the Zwart−Gerber−Belamri (ZGB) model. The maximum gas volume fraction on the surface of the propeller is tracked and recorded. In the meantime, the reliability of the numerical simulation is evaluated by observing the gas distribution on the surface of the propeller. And the simulation accuracy of the related models is compared. ResultsThe simulation results show that compared with the standard \begin{document}$k - \varepsilon $\end{document} turbulence model, the cavitation region obtained with the Realizable \begin{document}$k - \varepsilon $\end{document} model is significantly more consistent with the experimental results. By monitoring the maximum gas volume fraction on propeller's surface, it is found that the choice of turbulence model has little effect on the cavitation intensity, and the cavitation intensity obtained by S−S model is significantly higher than that obtained by the ZGB model. ConclusionsThis study shows that the turbulence model has a great influence on the area of the cavitation region, and cavitation models have a great influence on cavitation intensity. In terms of the simulation of propeller cavitation, the accuracy of the Realizable \begin{document}$k - \varepsilon $\end{document} model is higher than that of the standard \begin{document}$k - \varepsilon $\end{document} model.

ObjectiveThis paper aims to study the coupled dynamic response characteristics of an integrated system of a semi-submersible wind turbine and fish farming cage under wind, wave and current actions.MethodBased on the self-designed semi-submersible wind turbine SJTU-SPIC, an integrated floating wind turbine and fish farming cage concept is proposed and numerically modeled. The dynamic response characteristics of the integrated concept under wind, wave and current actions are then studied using coupled aero-hydro-servo-elastic-mooring analysis.ResultsThe numerical simulations indicate that introducing the fish farming cage can induce slightly a larger surge motion but suppress the pitch, which is beneficial for wind power production.ConclusionThe dynamic behavior of the integrated system of a semi-submersible wind turbine and fish farming cage proposed herein is similar to that of a floating wind turbine, and the system is shown to be feasible.

The power system of heat pipe cooled nuclear reactor can be divided into dynamic conversion system and static conversion system. Thermoelectric generator (TEG) is a typical static conversion device, which can directly convert heat energy into electric energy. The combination of heat pipe cooled nuclear reactor and TEGs can bring many advantages, such as compact structure, high inherent safety, no auxiliary mechanical equipment and low noise. However, the maximum core temperature could exceed 1 000 K, and ordinary thermoelectric generators can not operate in such high temperature. To solve this problem, the use of segmented thermoelectric generator (STEG) in the power system of heat pipe cooled nuclear reactor is a method worthy of research. STEG can play an important role in the heat pipe cooled nuclear reactor. But there is not enough literature to study the application of STEG in heat pipe cooled nuclear reactor. STEG usually splices two or three thermoelectric materials with the highest power generation efficiency in different temperature ranges. In this way, STEG can obtain a high thermoelectric conversion efficiency in a wide temperature range (usually above 600 K). Therefore, a kind of STEG for heat pipe cooled nuclear reactor was designed. In this paper, a conceptual design of a heat pipe cooled nuclear reactor with STEGs was proposed. The single STEG and single channel model were explored by COMSOL software. A three-dimensional finite element model of STEG’s performance in heat pipe cooled nuclear reactor was established. STEG was designed to compose of bismuth telluride and skutterudite, and its geometric structure and performances were optimized. Numerical simulation was carried out under steady-state conditions to determine the optimal STEG’s geometry. Then, the optimized STEG was connected with the heat pipe to form a single channel model for simulation to explore its performances. When the temperature difference reaches 550 K, the maximum STEGs’ output power reaches 0.374 W, and the maximum conversion efficiency is 15.75%. In single channel model, when the heating power is 300 W, the maximum STEGs’ output power reaches 47.29 W, and the maximum conversion efficiency is 15.63%. The simulation also show that the maximum stress of single STEG and single channel model are 270 MPa and 547.5 MPa, respectively. And the maximum stress appears on the copper conductor near the hot side. This paper could provide a preliminary basis for the numerical simulation of the combination of STEG and heat pipe cooled nuclear reactor. This paper can also be used as a reference for the thermoelectric conversion of heat pipe cooled nuclear reactors.

ObjectiveThis paper aims to explore the hydrodynamic characteristics of underwater vehicles under the action of internal solitary waves.MethodsBased on the internal solitary wave mKdV theory under the strong stratification assumption, the incompressible Navier-Stokes （N-S） equation is discretized by the finite volume method. Combining the velocity entrance wave-making and overset grid methods, a numerical model of an underwater vehicle coupled with internal solitary waves in stratified flow is established. Through this model, the coupling process of internal solitary waves and fixed and suspended vehicles in different internal wave environments is simulated, and the variation law of the hydrodynamic load is obtained by numerical solution. ResultsThe amplitude of the force and moment of the underwater vehicle increases with the increase in wave amplitude. When the position of the fixed vehicle is close to the interface of two layers of fluid, it is more severely affected. When the suspended vehicle is close to the wave trough, the impact is more significant. The increase in the initial pitch angle will lead to a sharp increase in the horizontal force amplitude of the vehicle. In addition, the "falling depth" phenomenon occurs when a vehicle with initial speed is affected by the main wave and coda wave of an internal solitary wave.ConclusionThe results obtained in this paper have reference value for safe operation of underwater vehicles.

The deep roadway with broken surrounding rock has problems such as insufficient strength of surrounding rock, serious floor heave, etc. It is urgent to strengthen the surrounding rock with effective support means. With the help of COMSOL numerical simulation software, the paper constructs the grouting diffusion model of roadway coupling grouting reinforcement, takes the pressure iso-surface as the grouting diffusion index, obtains the grouting diffusion range under different grouting reinforcement methods, and imports the obtained grouting diffusion range model into 3DEC to study the grouting reinforcement characteristics. After that, taking the surrounding rock reinforcement of belt roadway in 12101 working face of Wangjialing Coal Mine as the engineering background, the different reinforcement effects of the original support mode of belt roadway and deep shallow hole high and low pressure coupling grouting reinforcement are studied. The results show that the grouting diffusion range division method is reasonable and can better meet the engineering practice; compared with the original support method, the roadway safety has been greatly improved by using the coupling grouting support method.

The marine net cage is an essential facility and equipment for deep-water aquaculture in China, and its hydrodynamic characteristics are directly related to its operational stability. This paper established a finite element model for a marine net cage with three-layer and employed a fluid-structure interaction method to simulate the hydrodynamic characteristics of the net cage under the frontal flow conditions of a level 17 typhoon. Furthermore, a comparative analysis of the variation patterns in the hydrodynamic characteristics of the net cage with and without a netting structure was conducted. The results showed that under the frontal flow of the typhoon, the main areas of stress concentration in the net cage were the lateral support points of the bait chamber, the upmost walkway board connecting pipes on the windward side, and the cross-points of the mid-level load-bearing structure. When the net cage was equipped with a netting structure, the pendulum distance decreased, but the yawing motion intensified. In other words, the netting structure contributed to the vertical stability of the net cage but increased its yawing motion intensity. With the inclusion of the netting structure, due to the improved vertical stability of the frame, the maximum stress at the lateral support points of the bait chamber, the upmost walkway board connecting pipes on the windward side, decreased by 5.1% and 3.2% respectively, while the maximum stress at the cross-points of the mid-level load-bearing structure exhibited little change. However, the maximum stress on the windward side of the mid-lower level connecting pipes decreased by 8.7%.

ObjectivesThis paper aims to analyze the influence of polar low temperature environment and ballast water capacity on the dynamic change process of the temperature field in polar ship's ballast tank. MethodsThe volume of fluid (VOF) model was used to simulate the two phases of gas and liquid, and the standard k-ε turbulence model was used to simulate the fluid movement. The numerical analysis model of heat transfer in the ballast tank of polar ships was established to analyze the dynamic change process of the temperature field of the ballast tank at low temperature, and reveal the influence mechanism of multiple ambient temperatures and multiple loading heights on the temperature field of the ballast tank. ResultsWith the continuous occurrence of heat transfer, the temperature in the area above the waterline of the side ballast tank decreases rapidly, and the cooling area extends laterally to the cabin and downward along the bulkhead respectively. When there is more ballast water, the temperature field in the cabin is relatively stable due to the large heat capacity of water, but the air heat capacity is low and the temperature field changes greatly, which is prone to cyclones and further affects the temperature field distribution in the calculation domain. Under the condition of the same ballast water capacity, the lower the external ambient temperature, the greater the difference between internal and external temperatures, the more intense the heat exchange, and the faster the temperature of the ballast tank changes. ConclusionsThe VOF two-phase flow model and the standard k-ε turbulence model can better reveal the temporal and spatial evolution characteristics of the temperature field in the ballast tank in polar low temperature environment, and analyze the influence of internal and external thermal boundary conditions on the change of the temperature field in the ballast tank, which can provide necessary technical reference for the cold/freeze protection of polar ships' ballast tanks.

Objective The great demand for urban landscape improvement and reconstruction has required increasing dredging practices for waterfront buildings, particularly antique buildings. To effectively protect such antique buildings, the influence of dredging on the ground deformation of antique buildings needs to be carefully considered in the dredging operations. Methods To obtain a better understanding of the effect of dredging activities on antique buildings, the influence of dredging depth, dredging slope shoulder width and dredging slope ratio on the displacement and stress distribution of an antique stone bridge on soft ground via a three-dimensional model of the bridge body and its ground strata was studied in this paper. Based on the calculated results, mechanistic explanations of dredging on the ground deformation of antique stone bridges were proposed. Results The simulated results show the following: ① Dredging effects on the antique stone bridge mainly appeared as giving rise to the displacement of the bridge and the near strata, changing the stress distribution, and forming a plastic zone in the adjacent area of strata. As a result, dredging activities render a more complex stress and displacement distribution to the bridge and the strata around the bridge. ② Different dredging parameters have different effects on the displacement fields and stress fields of the bridge and its surrounding area. The dredging depth primarily affects the displacement magnitude of the soil, and the dredging slope shoulder width is the crucial factor affecting the scope of the dredging effect, whereas the dredging slope ratio and the dredging slope shoulder width jointly manipulate the change in the soil displacement curve and the development of the plastic zone. ③ In dredging projects, the setting of dredging parameters should not only meet the requirements of engineering practicability and economy but also reasonably determine the dredging parameters and control the impact of dredging on adjacent ancient buildings and take into account the width of the dredging slope shoulder width and the dredging slope ratio when determining the designed dredging depth. Conclusion The results in this work are of practical significance for dredging activity in antique building protection.

The coupling between solar wind and the magnetosphere and the dynamic processes in geo-space are the basic driving factors of space weather. Understanding these processes on the system level is essential to the studies of space physics and space weather. Recent solar wind charge exchange (SWCX) X-ray emission discoveries provide a novel approach to detect the large-scale magnetosphere through soft X-ray imaging. SWCX occurs when high-charge heavy ions such as C6+, N7+, O7+, and O8+ in the solar wind interact with neutral atoms or molecules, such as neutral hydrogen atoms in near-Earth space, neutral hydrogen and helium atoms in the heliosphere, and H2O and CO2 molecules on comets and other planets. Solar wind ions become excited by receiving one or more electrons, and then return to the ground state by releasing one or more photons in the soft X-ray band. The characteristics of the SWCX emissions include the X-ray spectrum showing line emissions corresponding to different species of solar wind particles and neutrons, and fast time variations closely related to solar wind variations. The SWCX soft X-ray emission of the Earth's magnetosphere mainly occurs in the magnetosheath on the dayside and the cusp regions. Therefore, the magnetosphere can be remotely imaged using large-scale soft X-ray imaging technology, allowing the fundamental modes of the interaction between the solar wind and magnetosphere to be recognized on a systematic scale.In this context, the European Space Agency (ESA) and Chinese Academy of Sciences (CAS) jointly proposed the Solar wind Magnetosphere Ionosphere Link Explorer (SMILE). SMILE was approved in 2016 and implemented thereafter. SMILE aims to provide remote sensing measurements of the magnetopause and bow shock around the subsolar region, part of the cusp regions, and the aurora, as well as simultaneous in situ observations of the solar wind plasma and magnetic field. SMILE is planned to be launched in 2024–2025. Other missions have also been proposed to image the Earth's magnetosphere, such as the GEOspace X-ray imager (GEO-X) in Japan, Lunar Environment heliospherics X-ray Imager (LEXI) in the United States, and Lunar-based soft X-ray imager (LSXI) in China.With the advent of soft X-ray imaging missions to detect the magnetopause, evaluating the expected soft X-ray images and developing appropriate techniques to extract 3-dimentional boundary information from the 2-dimentional images is essential. Global magnetohydrodynamic (MHD) and instrument simulations are used to generate expected X-ray images under different solar wind conditions with different viewing geometries. Based on these images, several approaches have been developed to analyze the signals, composing the 'arsenal' or 'toolkit' for magnetopause reconstruction. Each approach has its own advantages and disadvantages, applicable to different situations.This paper introduces the mechanism of magnetospheric X-ray emission, reviews the research on the observational evidence and characteristics of SWCX X-ray emissions, summarizes the progress of simulation studies, presents the missions (or concept) of the magnetospheric X-ray detection, and discusses the possibility of future implementation of X-ray imaging for detecting other planets.

The third generation reactors have characteristics of safety and efficiency, and the C-shaped heat exchanger is the main equipment in the design of the third generation reactor, which is widely used in the design of the passive residual heat removal system. It is of great significance on reactor safety to study on the flow and heat transfer process of Cshaped heat exchanger. To study the coupling flow and heat transfer characteristics of its primary and secondary side, and also to obtain flow distribution mechanism in heat exchange pipes for optimizing structure design, a fullsize physical model of Cshaped heat exchanger was established in this paper. It included inletoutlethousings, inletoutlet pipes and 500 heat transfer pipes as the primary side, and the heat transfer model of the secondary side was also established. Numerical simulation studies under different thermal and geometric conditions were conducted by the software FLUENT to obtain the laws of temperature, speed, pressure and flow distribution between the heat transfer tubes in primary side. At the same time, the influence of inlet flow, inlet temperature, inlet position to the flow distribution and flow resistance distribution was analyzed, and the affecting mechanism of floating force and inertial force on flow distribution was also analyzed. The calculation results show that the current design of the heat transfer tube is uneven in flow distribution, the flow of inner side is low, the flow of outer side is high, and the inner layer has the phenomenon of reverse flow. The uneven flow distribution in the current design is mainly caused by thermosiphon (density difference causing gravity pressure difference). This phenomenon is more obvious when inlet flow is low or the inlet temperature is high. During the range of the thermal parameters in this paper, the phenomenon of the thermosiphon is always dominated in the influencing mechanisms of flow distribution. Three inlet pipe positions of 0° (existing design), 90° and 180° were compared and it is found that the position of the inlet pipeline is not obvious for flow unevenness. When the flow is low, the flow distribution unevenness of the existing design (overentering and downout) is optimal on the contrary. In further study, it is possible to explore measures to reduce flow distribution unevenness. The measures include changing the connection of the heat transfer tubes and the headers, changing the distribution of the heat transfer coefficient of the primary and secondary side, and changing the installation method of the inlet headers, etc.

Due to the advantages of long service life, compact structure, strong environmental adaptability and high inherent safety, the heat pipe reactor power supply system is worth studying. The NUSTER2.0 dual-mode heat pipe reactor non-nuclear prototype built by Xi’an Jiaotong University adopts the integrated design of “simulated reactor core-high temperature heat pipe-Stirling generator-thermoelectric power generation”. The combination of the dynamic module coupled with Stirling and the static module coupled with thermoelectric power generation device can meet the diversified demands of energy. In this paper, the steady-state experiment of NUSTER2.0 was carried out to verify the design, and the system coupling simulation of the prototype was carried out by COMSOL multiphysics to analyze its operation and mechanical characteristics. In the 15 kW thermal power steady-state experiment, the generating power of the dynamic module is 2 019 W, and the static module is 493.2 W. The overall thermoelectric conversion efficiency is 16.7%, which verifies the engineering feasibility of the design. The system simulation model is coupled with the thermal resistance network model of high temperature heat pipe, the equivalent thermal conductivity model of thermoelectric power generation device and the Stirling adiabatic analysis program. The heat source of fuel rod and the heat sink of cooling water were simulated by heat flux boundary and convective boundary respectively. Under 15 kW thermal power, the steady-state simulation results are in good agreement with the experimental results on both the heat pipe temperature distribution and the main operating parameters of the dynamic and static modules, while the maximum relative error is 6.73%, which verifies that the coupled model is reliable. The variable thermal power steady-state simulation determines that the limit due to Stirling is 16.5 kW, and predicts that the static module will reach the peak efficiency near 25 kW. The system start-up transient simulation obtains the start-up characteristics under the 3.5-10.15 kW stepped power platform. The prototype start-up strategy based on the combination of power platform cold start and thermal insulation restart was also proposed. The thermal-mechanical coupling simulation indicates that the stress danger zone of the system is the coupling between the heat pipe and assembly matrix. Under 15 kW thermal power, the maximum stress at the coupling of heat pipe-core matrix and heat pipe-collector matrix are 160 MPa and 97 MPa, respectively. In the experiment, the self-adjusting function of the Stirling insulation ring can significantly relieve the 366 MPa stress between it and the Stirling matrix. The thermal expansion rate of the reactor core is 1.21%, which will cause negative feedback on the reactivity. The simulation results provide the numerical basis for the operation safety analysis and further experimental design of the NUSTER2.0 prototype.

To master the influence law of complex landform such as the surface mountain and the valley area between the mountains on the underlying coal rock stress, this study constructed a calculation model of the vertical stress of the coal strata under the mountain through theoretical analysis.Taking the 50205 working face of Hecaogou coal mine as example for analysis, This paper studied the complex landform on the underlying coal rock load characteristics and stress transfer law.Results show that: mountain load has significant stress effect on shallow coal seam.In the horizontal direction, the influence range is negatively correlated with the mountain slope, and the coefficient of influence range is positively related to the mountain slope.The effect of mountain on the vertical stress of the underlying coal seam can be divided into three stages: initial effect, intense growth effect and slow growth effect.The vertical stress superposition value of the underlying coal strata in the gully region firstly increases and then decreases with the change of depth.Moreover, when the distance between two adjacent mountains increases to more than.1.25 times of the width of the mountain bottom, the effect of stress superposition is very small and can be ignored.As the distance between adjacent mountains gradually increases, an inverted triangle area with insignificant stress superposition is formed in the coal strata under the gully area.

Purposes As a result of the ongoing replenishment of groundwater, a multifaceted system for the storage and circulation of groundwater has developed within overlying goaf and roadway. Coal mines encounter technical challenges in preventing and managing water damage in the roof goaf during the process of multiple coal seam composite mining, leading to a substantial requirement for daily roof water exploration and drainage engineering. Methods This paper focuses on the roof and floor rocks of coal seams as the subject of investigation. The study aims to analyze the fracture zone development between coal seams in the context of multiple seams mining, utilizing on-site electrical testing, numerical simulation, and theoretical analysis. Findings The findings of the experimental investigation indicate that the extraction of coal seams in close proximity facilitates the full interconnection of the goafs, resulting in the formation of a water accumulation zone composed of double coal seam goafs. The depth of the damage zone caused by the disturbance of the double coal seam floor is measured at 15.6 m. As the underlying working face is mined, the numbers of weak structural planes in the surrounding rock increas, leading to an expansion of the area of resistivity increase. Upon reaching a height of 58 m, the development of fracture zone gradually ceases. Optimal exploration and drainage of the roof empty water can be achieved to the fullest extent when the effective thickness of the key water barrier layer is no less than 20 m. Conclusions The concept of goaf water hazard prevention and coal mining under water-containing based on the coal seam spacing and key water-resisting layer is proposed. The conception of “finding out the structure, controlling the seam spacing, and mining after upper preventing” should be followed. The research results not only effectively prevent and control the threat of water inrush from the roof goaf, but also reduce the workload and production cost of water exploration and drainage in future. It can also provide reference for water-retaining mining technology in multiple coal seams affected by the water hazard in the roof goaf.

Objective The Kuncheng Tunnel of the Central Yunnan Water Diversion Project crosses the Heilongtan and Bailongtan areas, the major headwater regions in the Chenggong District of Kunming City. Methods Tunnel water inrush may seriously threaten the safety of the urban water supply. In this paper, based on hydrodynamic data and hydrochemical data during tunnel construction, the characteristics of the karst water system, the origin of the springs, and the impact of tunnel construction were analysed. Then, a three-dimensional groundwater flow model for the Heilongtan-Bailongtan Section was developed and calibrated to simulate and predict groundwater level changes during the construction of the Kuncheng Tunnel, and the water environment effect of tunnel construction was evaluated. Results The results show that both the Heilongtan and Bailongtan springs are mainly recharged by the same karst P1q+m aquifer. However, controlled by aquitard P1d and the Hunshuitang fault downstream of the Sanjiacun Depression, the two springs actually belong to two relatively independent karst water systems. In addition, the excavation of the Kuncheng Tunnel has changed the regional groundwater flow field and cut off the flow of Bailongtan, while it has negligible impact on Heilongtan. Conclusion This study discusses the genetic relationship of karst spring, and quantitatively analyzes the impact of tunnel excavation on water environment, which has reference significance for preventing water inrush in tunnel construction.

Objective Monitoring natural attenuation (MNA), as a low cost remediation method for groundwater pollution that does not produce secondary pollutants and has little impact on the polluted site environment, has high application value and development prospects, and is worth practicing and studying. Methods This paper adopts a groundwater-contaminated site in Baiyun District of Guangzhou to assess the applicability of MNA. Based on the analysis of hydrogeological conditions and pollution status, a groundwater numerical simulation program MODFLOW was used to establish a groundwater flow model for contaminated sites. The pollutant migration numerical simulation program MT3DMS was used to establish a pollutant migration model for the site. The migration processes of groundwater flow, main pollutants total petroleum hydrocarbons (TPH), and heavy metal nickel (Ni) were simulated, respectively. Based on the model, the performances of the MNA alone and the MNA combined with pump and treat methods were compared. Results The results show that TPH and Ni are both sensitive to changes in the Freundlich constant and Freundlich exponent. The TPH shows good natural attenuation effect and can be substantially attenuated by the MNA alone. The concentration of TPH decreased from the initial value of 1.52 mg/L to the target (0.3 mg/L) after 850 days. Ni decay is relatively slow and it is suitable to adopt to a natural attenuation scheme under monitoring combined with the pump & treat method. The concentration of Ni decreased from the initial value of 0.13 mg/L to the target (0.02 mg/L) after 300 days. For a contaminated site with large natural attenuation capacities and/or low groundwater flow velocities, MNA alone is an appropriate remediation strategy. In contrast, for a contaminated site with low natural attenuation capacities and/or high groundwater flow velocities, the MNA combined with pump and treat may be a better remediation strategy. Conclusion This study provides an appropriate reference for the application of MNA to groundwater pollution remediation.

Sgnificance To quantitatively study the impact of various nonlinear factors in the coastal zone on groundwater flow and solute transport processes, MARUN (Marine Unsaturated) software for simulating groundwater flow in the coastal zone was developed. Progress This paper reviews the research and application progress of MARUN from the aspects of model principles, algorithm characteristics, literature review, and case analyses. The software is suitable for numerical simulations of two-dimensional vertical profiles of groundwater flow and solute transport reactions in the coastal zone. MARUN implements a finite element algorithm for variable saturation and density flow and solute transport, mass-consistent implicit difference discretization, and Picard, Newton, and Newton-Picard numerical solution methods, covering many nonlinear factors such as tides, waves, evaporation, rainfall, and load effects. It is characterized by its high professionalism, good flexibility, and high fault tolerance, but it does not have a graphical user interface. MARUN has achieved a number of highlighted research results in scenarios such as bioremediation of crude oil pollution on beaches, seawater-groundwater circulation processes in shallow aquifers in intertidal zones, and the evolution of regional groundwater flow systems. Conclusion and Prospects In the future, MARUN needs to be further expanded into three-dimensional space and coupled with physicochemical processes with random characteristics to improve its performance level of simulating groundwater flow and solute transport in coastal aquifers.

During the process of developing and utilizing geothermal resources, various challenges are encountered. One such challenge is the decrease in temperature and pressure of the geothermal reservoir as a result of the increasing geothermal exploitation and duration. In addition, the discharge of geothermal tail water poses a risk of thermal pollution, leading to environmental concerns. To address these issues effectively, reinjection of geothermal fluids into the reservoir can be implemented as a viable solution. Prior to initiating the geothermal development and utilization, it is crucial to conduct scientifical and rational planning of the layout of production and reinjection wells. This involves exploring optimal strategies for the production-reinjection scheme that prevents the premature thermal breakthrough and maximize the efficient utilization of geothermal resources, thereby extending the lifespan of the geothermal reservoir. The Fengpei Basin, a Cenozoic rift basin that developed since the Paleogene period, exhibits a widespread distribution of geothermal reservoirs, primarily composed of the Ordovician limestone with karst and fracture characteristics. Building upon the geothermal resource exploration results in the Anguo Town in Peixian County in Jiangsu Province, this study utilizes key parameters obtained from pumping tests and reinjection experiments, such as well spacing and the reinjection-to-production ratio. This paper establishes a 3D coupled numerical model of geothermal water seepage and heat transfer by using the Feflow6.2 software. The recoverable reserves of geothermal fluid within the geothermal reservoir are simulated and predictd, specifically the Ordovician limestone formation. Furthermore, a simulated optimization of the development and utilization scheme for the production-reinjection wells is conducted. The results reveal that an appropriate well spacing of 389 m between the producing well (RPX01) and the reinjection well (RPX02) is recommended. Moreover, the reinjection-to-production ratio, namely the ratio of average aquifer hydraulic conductivity, is determined to be 1.29, supporting a sustainable approach of one-for-one pumping and reinjection. With a stabilized drawdown of 50.61 m, the production well has a capacity to recover 1000 m3/d of geothermal resources. Under the conditions of a production rate and a reinjection rate of 1000 m3/d, as well as a reinjection temperature of 40 °C, the simulation predicts a decrease in groundwater level by 45.49 m and a temperature reduction of 1.44 °C after ten heating seasons. This represents the optimal cyclic development and utilization scheme among the simulated scenarios. The above results provide a scientific basis for decision-making in the construction of the clean energy heating demonstration area in rural northern Jiangsu. They contribute to the establishment of a scientifically sound and sustainable approach for utilizing geothermal resources, while considering the challenges associated with the thermal breakthrough and the environmental impact of geothermal tail water discharge.

Restricted by the surface smoothness and topography, it is impossible for some high-speed railways on mountainous regions to avoid parts of rockfall development sections, posing great safety challenges to construction projects and railway operations. In light of that, this paper laid its focus on the rockfall situated by the entrance of Xinghuayu Tunnel along the proposed Jinan-Zaozhuang Railway project, and leveraged the power of drone-captured 3D aerial photography to perform digital geological survey and mapping so as to accurately identify the development characteristics, scale, as well as modes of deformation and failure of said rockfall. Next, by cross-referencing the results of 3DEC numerical simulation with those from analytic hierarchy process (AHP), color-coded maps highlighting the scope of influence and danger levels of potential rockfalls induced were obtained. Using said maps, zone-by-zone hazard and risk assessment were then performed, based on which corresponding prevention and control measures were put forward. The findings show that among the 12 dangerous rock belts identified from the drone-captured 3D aerial photography model, only Belt No. 5 would threaten the safety of the tunnel entrance and bridge abutments, for which the combination of anti-rockfall passive protective netting and an open-cut tunnel structure was recommended as a comprehensive solution. By virtue of the solution’s effectiveness, this study can offer reliable references for not only zone-by-zone hazard and risk assessment for rockfalls, but also railway route selection and disaster prevention and mitigation.

Numerical simulation and related experimental research on supersonic aerodynamic heating are important contents in the development of hypersonic vehicles. The boundary layer flow and heat transfer process in the supersonic aerodynamic heating phenomenon are analyzed, and the effects of the engineering model, gas model, turbulence model, grid scale, calculation scheme, and boundary conditions in aerodynamic heating simulation on the numerical simulation are discussed from the physical point of view. This paper introduces the test equipments commonly used in the research of aerodynamic heating, such as oxygebacetylene flame ablation, radiation heater and high enthalpy wind tunnel, and their advantages and disadvantages, also discusses the similar parameters in the ground simulation test, and points out the reasons for the over high heat flow of the cold wall.

Fenders play an important protective role in ship collisions, but there are few studies related to the collision simulation methods and the protection mechanism of composite fenders. First, aimed at the new composite fender design scheme proposed in this paper and based on the material properties exhibited in the test, low-density foam and hyperelastic models are selected to simulate the inner foam and outer polyurethane of the fender, respectively. Subsequently, for the hull-fender-quay collision problem, a multi-body geometry model is established and a collision simulation method is formed to analyze the fender protection mechanism from the perspective of energy conversion. It is proved that the composite material has a better protection effect on the hull structure than the rubber fender. Finally, the inner foam strength, hull stiffness, outer polyurethane thickness, and tensile strength of composite materials are varied to analyze the protection mechanism of composite materials respectively. The results show that the relative stiffness of the fender and the structure is the main factor affecting the protection performance. The inner foam of the composite fender is the main energy-absorbing structure, absorbing the kinetic energy of the hull through compression deformation to reduce the response of the structure, while the outer polyurethane mainly plays the role of protecting the core.

ObjectiveIn order to accurately assess the ice resistance experienced by an icebreaker during continuous icebreaking when sailing in a level ice zone, and understand the characteristics of different prediction methods, this paper uses the empirical formula method, numerical simulation method and ship model test method to evaluate an icebreaker's continuous sailing in smooth ice and predict the ice resistance. MethodIn this paper, the nonlinear finite element software DYNA is used to construct ice numerical simulation models based on the traditional finite element and cohesive element methods respectively, and simulations are performed of the bending fracture and interaction process that occurs when level ice interacts with an icebreaker. At the same time, using the empirical formula method, three different empirical formulas are used to calculate the ice resistance, and a sensitivity analysis of the parameters affecting the prediction results of the empirical formula method is also carried out. ResultsThe study finds that ice resistance shows an upward trend with the increase in speed, ice thickness and bending strength. Among them, ice thickness has the greatest influence on ice resistance. Among the three empirical formulas, the prediction results of the Lindqvist formula are closer to the ship model test results, while those of the Vance and Lewis formulas are more conservative. The traditional finite element and cohesive element methods obtain more accurate ice resistance prediction results when the thickness is small. When the thickness is large, the error is about 25%. In case of small ice thickness and high speed, the ice resistance value predicted by the cohesive element method is more accurate than that of the traditional finite element method, and the accuracy error is within 10% compared with the ship model test results. ConclusionIn the actual ice resistance prediction, the empirical formula method and numerical simulation method can be combined to take into account the accuracy and efficiency of the prediction results.

The physical and mechanical properties of sea ice and the failure modes of ice sheets significantly affect the ice loading of offshore structures. This paper first introduces the physical and mechanical characteristics of sea ice, then describes the physical processes of the interaction of ice sheets with offshore structures. Finally, the progress of research on the ice loading of offshore structures is briefly analyzed, including the three main approaches of formula estimation, experimental testing and numerical simulation. By discussing the applicability of formula estimation, the research focus and difficulties of experimental testing, and the development trends of numerical simulation, we find that the model testing of ice loading is an effective method. This paper covers the research trends and problems faced by ice loading on offshore structures, and it can provide certain guiding references for the related research of scholars in the field.

Autonomous underwater vehicle will be subjected to a huge impact load during high speed water entry, which will damage the structure and the internal instruments of the vehicle. Therefore, it is of great significance to study the buffer mechanism of the vehicle during the process of water-entry. In this paper, a kind of head-jetting device with disk cavitation is used. The complex cavitation forms, under the three-phase coupling of gas, liquid and solid, in the water entry process of the vehicle on which the device is installed. In this paper, the numerical simulation of high-speed water entry of the vehicle equipped with head jet device is carried out. Through the analysis of water entry cavitation under typical working conditions, the following conclusions are obtained. After the installation of head jet device, the water entry cavity of the vehicle changes gradually from cone to spindle shape. The air jet, compared with that without jet, can promote the formation of water inlet supercavitation, decrease the interaction area between the vehicle and water, and reduce the impact load during water entry. At the same water entry depth, the diameter of cavitation increases with the amount of air jet. The water entry velocity has a great influence on the difference of cavitation shape. The water entry depth closure phenomenon, when the water entry velocity is less than 100 m/s, can be observed in the depth of 3.5 times of the projectile length. The water entry angle has a significant effect on the cavitation shape. The cavity shows obvious asymmetry when the vehicle slants into the water, and the diameter and length of the bubbles decrease with the increase of the water entry angle. The research content of this paper provides technical support for the engineering practice of high-speed water entry and load reduction, and the conclusions are of great significance in related fields.

To explore the accuracy of the calculation method of the jacking force of circular curved pipe jacking under different pipe-soil contact characteristics, in combination with the curved steel pipe jacking project of Gongbei Tunnel of Hong Kong-Zhuhai-Macao Bridge, this paper adopted several commonly used jacking force calculation formulas for the curved pipe jacking at home and abroad and jacking force finite element analysis model with consideration of grouting effect and the pipe-soil contact range established with ABAQUS to calculate the jacking force. It was found by contrast with the pipe jacking force data: ①The calculated value of jacking force: JMTA formula≫Shanghai normative formula>Shimada formula, where it was considered that the calculated value of the lower limit of Shimada formula of 1/3 pipe-soil contact was relatively close to the measured value. ②Through numerical simulation, it was found that the simulated jacking force of 1/3 pipe-soil contact characteristics was gradually close to the one of 1/2 pipe-soil contact characteristics; in the grouting state, the previously measured jacking force was close to the one of 1/2 pipe-soil contact characteristics. When the jacking force tended to be stable, the measured jacking force was close to the one of 1/3 pipe-soil contact characteristics. Therefore, the numerical model could predict the jacking force of the pipe jacking under the same working condition and had a certain guiding significance for actual construction.

The Shuitoushang landslide in Ershe in Qijiagou Village of Xinchang Town in Tongjiang County is a typical red-bed terrace landslide in eastern Sichuan. There are few studies on the seepage analyses of such landslides in this area, but similar slopes are widely distributed in the area. In this paper, on the basis of a large number of field investigations, surveys and data collection of disaster sites, the satellite remote sensing, UAV aerial photography, airborne LiDAR, indoor tests and other technical means are comprehensively used to analysis the landslide. Based on the mathematical model of Fredlund & Xing soil-water characteristic curve, the SEEP/W module in Geo-Studio is used to conduct the seepage analysis, and the analysis results at different time stages are coupled with the SLOPE/W module. Then the dynamic relationship between the stability coefficient, rainfall and time is obtained, revealing the deformation process and formation mechanism of the landslide. The results show that: (1) the continuous rainfall causes the groundwater level to rise and the slope stability to decrease, eventually leading to the overall instability and failure of the Shuitoushang landslide. (2) The deformation process of the landslide and the characteristics of groundwater exposure are basically consistent with the results calculated by Geo-Studio, indicating that the results based on Fredlund & Xing model can provide more accurate simulation results in similar areas. (3) Reclamation of terraced fields (paddy fields) will reduce slope stability. The results can provide theoretical support for hidden danger investigation and active prevention of similar landslide disasters in mountainous areas of Sichuan, and provide a reference for disaster prevention and mitigation.

The No.7 typhoon Higos in 2020 caused strong wind and torrential rain in Guangdong Province. A detailed study of its multi-scale energy distribution and transformation characteristics will help us better understand and prevent similar typhoon disasters. In this paper, the WRF regional numerical model is used to simulate typhoon Higos. The simulation results were separated into large scale background field (> 2 000 km), meso-α scale (200~2 000 km) and meso-micro-β scale (< 200 km) by Barnes filtering method. The distribution of kinetic energy, effective potential energy and their changes are calculated for the three scale components. Here are the results. (1) During the active period of typhoon Higos, the large scale background field kinetic energy first increases and then keeps constant. Meso-α scale kinetic energy first increases and then decreases. The change of meso-micro-β scale kinetic energy is not obvious. The main source of kinetic energy is the conversion of effective potential energy and the work done by the pressure gradient force, and the main dissipation is horizontal transport and cross scale conversion. All three scales of kinetic energy are mainly distributed in the lower troposphere. (2) The effective potential energy of large scale background field repeats the process of first increasing and then decreasing twice. Meso-α and meso-micro-β scale effective energy first increases and then decreases. The main source of effective potential energy is diabatic heating, and the main dissipation is converting into kinetic energy, horizontal transport and cross scale conversion. All three scales of effective potential energy are mainly distributed in the upper troposphere. (3) The energy conversion areas of typhoon Higos are mainly the upper troposphere of the typhoon eye wall and the central dense overcast area within 200 km from the typhoon center, the upper troposphere around typhoon in 200-700 km from the typhoon center, and the lower troposphere within 400 km from the typhoon center.

In order to study the slope deformation law during and after the construction of the sandstone bed-cut high slope support project and the effect of the treatment project, this paper relies on a slope support project in Beijing to analyze the axial force of the anchor cable and the slope during the construction process. The slope displacement is monitored and analyzed, and the results show that the change of the axial force of the anchor cable is mainly divided into the acceleration loss stage, the fluctuation stage and the continuous stable trend stage; the change of the axial force of the anchor cable can well reflect the change of the internal force of the slope; the change of horizontal displacement and vertical settlement can reflect the change law of the deep displacement of the slope and the stability of the slope, has a better support effect. The finite element analysis software was used to simulate the excavation and support process of the sandstone-layered high slope. It was found that with the excavation of the slope, the displacement of the slope developed along the slope angle of the weak sliding surface, and the stability of the slope decreased. The monitoring results and the simulation results are compared and analyzed, and it is found that the change trends of the two are basically the same, which proves that the slope support system can effectively control the deformation of the slope. The research results can provide reference for the design and construction of similar slopes in the future.

The accurate division of the disturbance space of abandoned mine methane(AMM) reservoir is an important basis for the evaluation, development and utilization of AMM resources. In this paper, taking the No. 2 coal 12501 working face of Tunlan Mine in the Xishan mining area of Shanxi as an example, numerical simulation of stress field, numerical simulation of fracture field and physical similarity simulation are used. The distribution law of stress field and fracture field during the mining process and after the goaf is stabilized is comprehensively studied. The research results show that the physical similarity simulation and the numerical simulation have a high degree of agreement. Combining the above three methods, the CBM disturbance reservoir space in the abandoned working face 12501 is finally divided into floor fracture area, recompaction area, gas conduction fracture area and bearing fracture area. The floor fissure area is located just below the working face in the coal seam. The overall mining fissure development area presents an inverted trapezoidal platform with the bottom surface close to the mined coal seam. The numerical simulation results of the fissure field show that its vertical depth is 22.3 m, Its depth is 5.58 times the thickness of the coal mined. The pressure-bearing area is located in the unexploited coal reservoir around the working face. It extends 70 m outward from the boundary of the working face inclination and 100 m from the boundary of the working face strike. The numerical simulation results show that the peak value of vertical stress of coal reservoir in the pressure bearing zone is much larger than the stress value of the original state of the coal seam, but smaller than the average compressive strength of the coal sample in the vertical seam. The main part of the gas-conducting fissure area is located at the edge of the coal seam working face. The bottom is a rock caving zone with a height of about 13.2 m, and the upper part of the caving zone is a rock stratum fault zone with a height of about 33.6 m. The vertical cracks in the fault zone continue to expand and penetrate through. Separation cracks. The overall shape of the gas-conducting fracture area is a trapezoidal platform, Its height is 11.7 times the thickness of the coal mined.. The main body of the recompaction area is distributed in the middle part of the goaf of the mining face, with a dip width of 110 m and a strike length of 1 268 m. This area is mainly composed of curved and caving overlying rocks, and the overall shape is a trapezoidal platform, which is located inside the gas-conducting fracture area. The gas-conducting fracture area is a favorable area for the development of legacy coalbed methane resources.

ObjectivesThis paper investigates the main dimensions of ROPAX ship in the aspect of energy saving and resistance reduction.MethodsBy using ship model tests and numerical simulations, the effects of changes in the main dimension ratio of a ROPAX ship on its resistance performance are studied.ResultsThe results show that the maximum difference in effective power between different L/B schemes is only 150 W at lower speeds, increasing to 1 300 W at higher speeds, while the maximum difference in effective power between different B/T schemes is only 170 W at lower speeds, increasing to 300 W at higher speeds.ConclusionsThis paper shows that increasing the L/B value can significantly reduce the model resistance and effective power of the ship, and there is no significant difference in effective power with different B/T values.

This paper selects SST k-w turbulence model and VOF wave to construct a numerical calculation model of moving body planning on a flat free surface based on STAR-CCM+ numerical simulation software. The construction model is checked through foreign classic literature, and the numerical simulation results are in good agreement with the experimental results. The hydrodynamic numerical errors are less than 5%, which is within the engineering error range. The model can be used for the numerical simulation of the planning cylinder. In this paper, it is used to simulate the planing process of cylinder with different speeds and different submerged depths, and the flow field characteristics and hydrodynamic characteristics in the planing process are obtained. The results show that waves appear at the tail and the tail liquid splashes to form a water splash during the planing process of the cylinder on a flat surface. The higher the speed of the planning cylinder is, and the deeper the submersion depth, the more pronounced waves at the tail. When the cylinder has a Fr number Cv≥8, the hydrodynamic force of the cylinder is almost unchanged, and it is not affected by the speed. But when Cv=3, the hydrodynamic characteristic coefficient is higher. The drag coefficient is 20% higher than that in the high-speed (Cv≥8) planing process. The lift coefficient is 3 times of high-speed planing lift coefficient. It is related to the surface pressure and frictional force distribution of cylinder during the low-speed planing. There is a linear relationship between the drag coefficient and the submerged depth during the cylinder planing at different submerged depths.

In the process of steelmaking, improving the flow field in ladle plays an important role in improving the purity of molten steel, homogenization of chemical composition and temperature, and shortening mixing time. Alternate stirring in ladle can improve the mixing process. In this paper, the water model of 1/5 scaled down 130 t ladle was numerically simulated by the STAR-CCM+ software. The changes of flow field, tracer transport process, and mixing time after alternate stirring at different time points were investigated. The results show that when alternating stirring is used, the flow field eventually forms a mirror image of single plug stirring, and the time required to achieve stable flow field is 55-76 s. After alternating stirring, owing to inertia, the tracer still transfers to ladle surface by counterclockwise circulation. After the formation of alternating flow field, the tracer transfers in clockwise main circulation. In this case, the dead zone is located at the front and rear parts at the bottom of ladle. The timing of alternate stirring affects the distribution ratio of tracer to participate in the counterclockwise circulation caused by inertia and the formed clockwise main circulation. Compared with single plug stirring, alternating stirring shortens the mixing time at the top monitoring points of ladle and increases the mixing time at the bottom monitoring points.