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During drilling operations, naturally, fractured formations are prone to show serious mud losses, which hinder drilling and increase nonproductive time and costs. The influencing factors of dynamic fluid loss are important for optimizing drilling parameters, reducing drilling fluid loss, and protecting oil and gas reservoirs. In this study, we simulated the dynamic filtration loss of drilling fluid during drilling under formation conditions using commercial software CMG (Computer Modelling Group). The effects of filtration time, filtrate viscosity, pressure difference, internal filter cake permeability, and external filter cake permeability on filtration loss were investigated. The simulation results showed that the permeability of the external mud cake is an important factor to control the fluid loss, and the pressure consumed by the external mud cake with low permeability can account for more than 90% of the total pressure difference. When the permeability of the external mud cake is high, the permeability of the internal mud cake also has a significant influence on the dynamic fluid loss. Under formation conditions, the dynamic fluid loss of radial fluid loss is still proportional to the filtration time and pressure difference, and inversely proportional to the filtrate viscosity of drilling fluid. Under the simulated conditions, the pressure will quickly transfer to the boundary, and the formation pressure at the same position in the formation will gradually increase, while the increase is relatively small with a constant filtration rate. The results of this paper can be used to the real site for drilling optimization. This numerical analysis method can be easily applied to filtrate loss analysis, formation damage area calculation, and other radial flow-related study. [ABSTRACT FROM AUTHOR]

With the shift of coal seam mining to the deep, the in-situ stress of coal and rock mass increases gradually. High ground stress can limit the generation of rock cracks caused by blasting, and blasting usually shows different crushing states than low stress conditions. In order to study the blasting expansion rule of rock mass with cavity under high ground stress and the rock mass fracture state under different side stress coefficients. In this paper, the effective range of blasting and the stress distribution under blasting load are analyzed theoretically. The RHT (Riedel-Hiermaier-Thoma) model is used to numerically simulate the blasting process of rock mass with cavity under different ground stress, and the influence of ground stress and lateral pressure coefficient on the crack growth of rock mass is studied. The results show that when there is no ground stress, the damage cracks in rock mass are more concentrated in the horizontal direction and the fracture development tends to the direction where the holes are located, which confirms the guiding effect and stress concentration effect of the holes in rock mass, which helps to promote the crack penetration between the hole and the hole. The length difference of horizontal and vertical damage cracks in rock mass increases with the increase of horizontal and vertical stress difference. Under the same lateral stress coefficient, the larger the horizontal and vertical stress difference is, the stronger the inhibition effect on crack formation is. For blasting of rock mass with high ground stress, the crack formation length between gun holes decreases with the increase of stress level, and the crack extends preferentially in the direction of higher stress. Therefore, the placement of gun holes along the direction of greater stress and the shortening of hole spacing are conducive to the penetration of cracks between gun holes and empty holes. The research can provide reference for rock breaking behavior of deep rock mass blasting. [ABSTRACT FROM AUTHOR]

This paper is based on the proximity engineering project of the Baishiyi tunnel group passing under the Chongqing West Station track group. Considering the train load and the spatial relationship of the tunnel and track groups, the settlement patterns, horizontal displacement, and differential settlement of the tunnel–strata–tracks system during the excavation process are studied through theoretical calculations and numerical simulation methods. The results indicate that the tunnel vault, strata, and track settlement deformation patterns are similar. Throughout the tunnel construction process, the tracks underwent uplift, settlement, and eventually stabilized. The settlement trough formed by the excavation of the three tunnels below the track group has an impact range of 25–145 m. Between 35 and 75 m, the differential settlement of the double track gradually increases with excavation. As the tunnel face reaches 75 m, the track differential settlement gradually converges and tends to stabilize. To minimize the impact of underpass tunnel construction on track groups, it is recommended to use a combination of full-section hole grouting and surface reinforcement grouting for ground reinforcement. Additionally, optimizing the construction parameters, including the step length and primary support closure time, and strengthening the locking anchor can further reduce the impact. [ABSTRACT FROM AUTHOR]

The scale of propagation of hydraulic fractures in deep shale is closely related to the effect of stimulation. In general, the most common means of revealing hydraulic fracture propagation rules are laboratory hydraulic fracture physical simulation experiments and numerical simulation. However, the former is difficult to meet the real shale reservoir environment, and the latter research focuses mostly on fracturing technology and the interaction mechanism between hydraulic fractures and natural fractures, both of which do not consider the influence of temperature effect on hydraulic fracture propagation. In this paper, the hydraulic fracturing process is divided into two stages (thermal shock and hydraulic fracture propagation). Based on the cohesive zone method, a coupled simulation method for sequential fracturing of deep shale is proposed. The effects of different temperatures, thermal shock rates, and times on the scale of thermal fractures are analyzed. As well as the effects of horizontal stress difference and pumping displacement on the propagation rule of hydraulic fractures. The results show that the temperature difference and the thermal shock times determine the size and density of thermal fractures in the surrounding rock of the borehole, and the number of thermal fractures increases by 96.5% with the increase of temperature difference. Thermal fractures dominate the initiation direction and propagation path of hydraulic fractures. The main hydraulic fracture width can be increased by 150% and the length can be increased by 46.3% by increasing the displacement; the secondary fracture length can be increased by 148.7% by increasing the thermal shock times. This study can provide some inspiration for the development of deep shale by improving the complexity of hydraulic fractures. [ABSTRACT FROM AUTHOR]

As cities have grown, conductor rail power supplies have been widely used in the field of urban rail transit. In order to improve the running performance of trains and reduce the occurrence of accidents, it is necessary to understand the vibration of shoegear-rail system under different initial contact forces and explore the dynamic performance of shoegear-rail system. Therefore, according to the structure of shoegear-rail system, a coupling model of shoegear-rail system is established in this paper. On the basis of the model, the numerical simulation of the shoegear-rail system under different initial contact forces is carried out, and finally the vibration data of the shoegear-rail system under different initial contact forces are obtained. The results show that with the increase of initial contact force in the range of 70–160 N, the vibration amplitude of the electric shoegear and the fluctuation amplitude of the contact force increase, but the maximum absolute shear force value of the conductor rail decreases. It indicates that the lower initial contact force, the better the performance of shoegear-rail system. [ABSTRACT FROM AUTHOR]

Multi-stage hot forging is widely used to produce complex forged products in inFdustry. Flash after the forging should always be minimized for the material saving, and it is important to determine the preform shape minimizing the flash. The process parameters in multi-stage hot forging such as the billet temperature and the stroke have also an influence on the product quality as well as the flash, but they are still determined by a trial-and-error method. In this paper, multi-objective design optimization in three-dimensional multi-stage hot forging is numerically performed so as to minimize both the flash and the distribution of equivalent strain. The preform shape and the process parameters such as the billet temperature, the die temperature and the stroke are optimized. The three-dimensional numerical simulation is computationally so expensive that sequential approximate optimization that response surface is repeatedly constructed and optimized is adopted to identify the pareto-frontier between the flash and the distribution of equivalent strain. It is found from the numerical result that 60% reduction of flash can be achieved, compared to the conventional preform shape. In addition, the total forging energy considering the multi-stage hot forging is reduced. It is confirmed through the numerical result that the proposed approach is valid to determine the optimal preform shape and process parameters in multi-stage hot forging. [ABSTRACT FROM AUTHOR]

This paper presents a coil optimization method of the ultra-deep azimuthal electromagnetic (EM) resistivity Logging While Drilling (LWD) to obtain the best parameters of the tool for formation boundary detection by theory. First, a rapid numerical simulation algorithm, i.e. the Fast Hankel Transform (FHT) method, is developed to simulate the logging responses of the layered formation. A system of double inclined coils is selected based on the response characteristics and the depth of detection (DOD) from four common coils. Simulation results demonstrated that the optimal coils are perfectly suitable for anisotropic formation. Then, the crucial parameters of the frequency and spacing of the selected coils with a DOD of 30 m are determined using the Picasso diagram. In addition, the influences of the electrical parameter of the drilling collar and resistivity anisotropy of the formation on the response are investigated. The results show that the conductivity of the drilling collar, the thickness and the resistivity anisotropy of the formation all affect the DOD. Finally, formation models with different layers are created to verify the performance and signal intensity. The results demonstrate that the optimized coils not only have a large DOD but also possess a high signal intensity, further confirming the advantages of the preferred coils. Compared with the conventional physical experiment tests, the method of coil optimization proposed in this paper is more economical and efficient. The findings of this study can help better understand the detection characteristics of the different coils, which can provide theoretical support for designing and developing a tool with the best boundary capability. [ABSTRACT FROM AUTHOR]

Numerical simulations consist of many components that affect the simulation accuracy and the required computational resources. However, finding an optimal combination of components and their parameters under constraints can be a difficult, time-consuming and often manual process. Classical adaptivity does not fully solve the problem, as it comes with significant implementation cost and is difficult to expand to multi-dimensional parameter spaces. Also, many existing data-based optimization approaches treat the optimization problem as a black-box, thus requiring a large amount of data. We present a constrained, model-based Bayesian optimization approach that avoids black-box models by leveraging existing knowledge about the simulation components and properties of the simulation behavior. The main focus of this paper is on the stochastic modeling ansatz for simulation error and run time as optimization objective and constraint, respectively. To account for data covering multiple orders of magnitude, our approach operates on a logarithmic scale. The models use a priori knowledge of the simulation components such as convergence orders and run time estimates. Together with suitable priors for the model parameters, the model is able to make accurate predictions of the simulation behavior. Reliably modeling the simulation behavior yields a fast optimization procedure because it enables the optimizer to quickly indicate promising parameter values. We test our approach experimentally using the multi-scale muscle simulation framework OpenDiHu and show that we successfully optimize the time step widths in a time splitting approach in terms of minimizing the overall error under run time constraints. [ABSTRACT FROM AUTHOR]

The heat and mass transfer behavior of droplet transfer in the CO2 welding process plays a decisive role in weld formation, joint microstructure, and service performance. Studying the process of droplet transfer is of great significance for welding metallurgical analysis, stress deformation analysis, process control, and process optimization. In recent years, welding scholars have devoted themselves to the theoretical analysis of the dynamic information of droplet transfer through numerical simulation and combined with experimental research, so that the welding process has changed from qualitative analysis to quantitative analysis, and the theoretical research and experimental research have been upgraded to scientific research. Based on the available data, this paper takes the CO2 welding process as the object and finds that in recent years, the numerical simulation field of CO2 welding droplet transfer has developed in the direction of arc-droplet-pool integration. However, there are still some problems in the existing mathematical model, such as insufficient model accuracy, too much calculation, too many assumptions, and too large gap between the actual and other problems. It can be predicted that the future development direction of the numerical simulation of the droplet transfer will be towards refinement and high efficiency. [ABSTRACT FROM AUTHOR]

In this paper, we present a numerical finite-difference time-domain (FDTD) simulation procedure developed to quantify the frequency-dependent ground penetrating radar (GPR) spectral responses occurring in four on-site scenarios involving concrete that is dry, half-saturated, saturated and chloride- contaminated. The responses are (1) numerically simulated by making use of the real and imaginary parts of complex permittivity derived from the GPR signal's two-way travel time and rebar reflection amplitude, respectively; then (2) characterized using Nyquist and Bode plots, and (3) compared to the wavelets obtained from authentic concrete specimens. The characterization shows good correspondence with the well-established Debye's models. Experimental validation shows that the simulated dispersion model is compatible with authentic concrete specimens when an optimal centre frequency is used. The method demonstrated in this paper can be used to convert GPR into a spectral analyser for predicting the on-site variability in material properties, the expected depth ranges of targets, and levels of attenuation and scattering before actual GPR survey. [ABSTRACT FROM AUTHOR]

Cast steel nodes are widely used as important components of offshore platform, owing to their better performance than welded nodes. In this paper, the mold filling and solidification process of cast steel nodes were numerically simulated and verified by the finite element analysis commercial software package—ProCAST, and the occurrence of shrinkage porosity was quantitatively predicted based on the simulation results. The numerical simulation results of the preliminary design showed that the overall filling was stable with bottom gated system, agreeing well with the design requirements. However, the shrinkage porosities in the intersection of lower tubes and main tube were evident due to the insufficient feeding. Optimization of the casting design was carried out through repeated computer simulation. By incorporating chills in the cores, the optimized design showed that the shrinkage porosities in the intersection of lower tubes and main tube were effectively eliminated. In view of these aforementioned optimizations, the casting steel can meet the technical requirements in an actual production. [ABSTRACT FROM AUTHOR]

Elbow pipes are widely used in many industries such as petroleum, chemical, and metallurgy. Of various elbow pipe forming technology, hot pushing pipe bending process is an efficient and economical one for processing elbow pipes. This paper introduced the technological process and plastic deformation mechanism of hot pushing pipe bending. Four deformation assumptions were proposed to describe the main deformation characteristics in the bending process. The proportional relationship between the bending deformation and the diameter expansion deformation was derived and the horn mandrel was designed. The forming process of the elbow was simulated and the metal flow in the forming process of the elbow was obtained. The results showed that controlling the axial compression and circumferential expansion in proportion is the key to getting constant wall thickness. By using the horn mandrel with variable curvature axis, it benefits the metal flowing uniformity from the concave side to the convexity, avoiding the increase of the inner wall thickness and the decrease of the outer wall thickness during pipe bending. Taking the minimum change rate and good uniformity of the concave side wall thickness as goals, the optimal process parameters were obtained, that is, the heating temperature is 750° Celsius, the pushing speed is 3 mm/s, the friction factor is 0.15, the bending angle is 45° and initial bending radius is 2.0 mm. It will play a positive role in revealing the pipe forming mechanism and have a guiding effect on production practice. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation and numerical modeling of the mechanical behavior and damage of the near-surface layer of mechanical parts, pre-machined by the EDM process. The intended purpose is therefore to understand and then predict the impact of this process on the service life of machined parts. In situ mini-tensile tests under XRD were performed to characterize the mechanical behavior of the near-surface layer preloaded by the residual stress and strain-hardening gradients previously induced by the EDM process. These tests were also used to identify the parameters associated with the numerical model. The results of this study revealed that the interface between the base material and the near-surface layer is the seat of a significant incompatibility of plastic deformations, which accelerates the rate of damage in this zone and supports the development of microcracks. This cracking tendency is enhanced by the omnipresence of residual stress and strain-hardening gradients. [ABSTRACT FROM AUTHOR]

The traditional regional air pollution characteristics analysis method cannot obtain the best meteorological pollution factors, leading to air pollution characteristics analysis results and actual deviation. Therefore, a numerical simulation method of regional air pollution characteristics based on weather factors and improved Elman neural network algorithm is proposed. The best meteorological factors affecting air quality were obtained and the annual mean concentration of air pollutants was analyzed by Spearman rank correlation coefficient method. According to the structure of Elman neural network, an interval prediction model of atmospheric pollution concentration is designed. Based on this, control equations, turbulence model and boundary conditions are constructed. The characteristics of air pollution in a city are simulated to obtain the maximum contribution of air pollution. The results show that the simulated concentration of PM2.5and PM10 is close to the measured values, the relative error between the simulated values and the measured values is small, and the simulated atmospheric concentration is in good agreement with the measured values. Therefore, the numerical simulation analysis of pollution characteristics presented in this paper is more accurate and reliable. [ABSTRACT FROM AUTHOR]

In the process of internal thread cold extrusion, the extrusion tap is an indispensable tool. Therefore, it is important to improve the service life of the extrusion tap and reduce the tool wear. In this paper, using Central Composite Design response surface test, the influence of the parameters (including the guide cone angle, backhoe capacity, guide cone length and working cone length) of the extrusion tap on the forming quality of internal cold extrusion are investigated, so as to obtain the minimum extrusion torque and the minimum extrusion temperature. A polynomial regression response model of the minimum extrusion torque and minimum extrusion temperature is obtained. Using the regression model, the objective function is optimized, and a group of optimal parameters is obtained (guide cone angle: 10°, backhoe capacity: 0.32, guide cone length: 4 mm, and working cone length: 13 mm). Numerical simulation of the optimal parameters is also carried out. The results show that the measured extrusion torque and extrusion temperature are close to the predicted values with errors of 2 and 2.55%, respectively, which are well fitted by the model. [ABSTRACT FROM AUTHOR]

Mining-induced stress will cause the change of coal seam pore structure. However, most coal seam infusion simulation studies do not consider the change of pore with mining-induced stress. In order to study the impact of mining-induced stress on coal seam infusion, this paper used the triaxial compression test of coal as the basis to establish the relationship equation between volume strain and stress loading by the volume deformation table, and then introduced the relationship equation into FLUENT through Fluent Custom Function (UDF). Taking the mining time and water injection time as the axis, this paper compared and analyzed the variation law of coal seam infusion seepage parameters with coal seams with pore changes caused by mining-induced stress (model I) and traditional fixed porosity (model II). The results show that in the elastic deformation stage, the mining-induced stress makes the original pores of the coal seam compact, so that the water injection seepage pressure, seepage velocity, and water content volume of model I are lower than those of model II. In the plastic deformation and post-peak deformation stages, mining-induced stress promotes the development of coal seam pores, and the water injection seepage pressure, seepage velocity, and water content of model I gradually exceed the seepage field parameters of model II. It can be seen that mining-induced stress has an important impact on water injection seepage. The simulation method proposed in this paper can more truly reflect the impact of actual mining process on coal seam infusion seepage. [ABSTRACT FROM AUTHOR]

Thin-walled tubular parts with longitudinal ribs are important lightweight components. To manufacture the complex shape, incremental forming processes like flow forming are increasingly used. However, it is still difficult to form deep longitudinal ribs by conventional flow forming like ball spinning (BS). This paper proposes a novel flow forming process named two-stage flow forming (TSFF) to manufacture the thin-walled tubular parts with deep longitudinal outer ribs. The TSFF process includes two forming stages of preforming and final forming. During the preforming stage, the balls make axially feed movement, which force the metal to flow radially, and preform the longitudinal outer ribs. In the final forming process, the balls make axial feed movement and the blank makes rotation, which forces the metal to flow along circumferential and radial direction. Thus, the wall thickness is reduced, and the deep longitudinal outer ribs are formed. Based on numerical simulation, the forming geometrical dimension by BS and TSFF is compared, and the forming effect of TSFF is better. To make further analysis of metal flow behavior, it can be found that TSFF promotes the metal to flow along tangential and radial direction, while restraining the axial flow of the metal, and finally improve the filling effect of the longitudinal outer ribs. In addition, the key process parameters of TSFF were studied, and it was found that the reduction of preforming and ball diameter had great influence on the filling effect of the outer ribs. Finally, the TSFF experiment is carried, and the result shows that thin-walled tubular parts with deep longitudinal outer ribs formed by TSFF are feasible. This study provides theoretical and experimental support for the development of the novel flow forming process. [ABSTRACT FROM AUTHOR]

For realizing the precision dressing of worm grinding wheel of face gear, this paper studies the over-cutting phenomenon of worm grinding wheel in forming dressing and puts forward the solution. Combined with the forming principle of face gear worm and forming dressing method, the influence of the continuous dressing method on the grinding wheel helix and the relative position between the dresser and the worm are expounded. Based on the numerical simulation model and the actual machining phenomenon, two kinds of over-cutting phenomenon are discovered. To ensure the surface integrity of grinding wheel in continuous processing, the reasons and laws of over-cutting are deeply analyzed. The first kind of over-cutting can be eliminated by increasing the angle between the extended line and the axis on the dresser, and a method of estimating the minimum angle is proposed for a more reasonable design of the dresser. The second kind of over-cutting can be eliminated by choosing proper dressing interval while ensuring the utilization efficiency of worm, and the selection criteria of dressing interval in continuous dressing are put forward. To verify the proposed methods, digital model, Vericut, and SolidWorks are applied, and the results show that the proposed method can effectively solve the over-cutting problem. [ABSTRACT FROM AUTHOR]

5A06 aluminum alloy has good corrosion resistance and no low temperature brittleness, so it is widely used in aerospace sheet metal components. However, when forming complex thin-walled parts, the surface forming quality and accuracy of the alloy are poor, and the forming performance is limited, which has been an important problem in application. In this paper, on the basis of hydrodynamic deep drawing, the rigid-flexible composite drawing warm forming process is innovatively proposed, which improves the forming quality of 5A06 complex bottom aluminum alloy parts and fittability. Taking aluminum alloy concave-bottom cylindrical parts as the research object, the influence law of rigid-flexible composite drawing warm forming process on the forming process and the fitting accuracy of concave-bottom cylindrical parts was explored by using the method of numerical simulation and forming experiment. The results show that under the process conditions of hydraulic pressure 20 MPa, sheet forming height 50 mm, and forming speed 1.8 mm/s, the maximum thinning rate of special-shaped bottom cylinder wall thickness is 21.3%, and the fittability is 97.3%. [ABSTRACT FROM AUTHOR]

The present paper consists of designing, modeling, and simulating a Dish-Stirling photothermal concentrator. The developed system intends to satisfy the electrical needs of a small residential building in a coastal Algerian city located at the edge of the sun-belt region, with the perspective of moving toward small-scale sustainable agglomerations. The adopted approach consisted of two steps. At the first step, the energy balances were established at the collector, receiver, absorber, and Stirling engine, considering hydrogen as a work fluid. The energy flows were reported to the surface unit of the reflector optical plane with three variants of concentration ratios, namely 500, 1000, and 1500. The second step consisted of parametric analysis of the effects of optical, thermal, and Stirling engine properties. This approach allowed us to design a Dish Stirling system of 10.52 m in diameter, with a concentration factor of 1000, and using hydrogen as a working fluid. The parametric study revealed that the highest effect is due to the regeneration efficiency; its increase of an order of 10% induces an enhancement of the delivered power exceeding 40%. The designed system showed a good performance during April, June, July, August, and September, as compared to the site demand. It proved to reach 23 kW in July around solar noon, which is equivalent to satisfying the needs of the households by around 153%. [ABSTRACT FROM AUTHOR]

A new numerical approach for the time-dependent wave and heat equations as well as for the time-independent Poisson equation developed in Part 1 is applied to the simulation of 1-D and 2-D test problems on regular and irregular domains. Trivial conforming and non-conforming Cartesian meshes with 3-point stencils in the 1-D case and 9-point stencils in the 2-D case are used in calculations. The numerical solutions of the 1-D wave equation as well as the 2-D wave and heat equations for a simple rectangular plate show that the accuracy of the new approach on non-conforming meshes is practically the same as that on conforming meshes for both the Dirichlet and Neumann boundary conditions. Moreover, very small distances ( 0.1 h - 10 - 9 h where h is the grid size) between the grid points of a Cartesian mesh and the boundary do not decrease the accuracy of the new technique. The application of the new approach to the 2-D problems on an irregular domain shows that the order of accuracy is close to four for the wave and heat equations and is close to five for the Poisson equation. This is in agreement with the theoretical results of Part 1 of the paper. The comparison of the numerical results obtained by the new approach and by FEM shows that at similar 9-point stencils, the accuracy of the new approach on irregular domains is two orders higher for the wave and heat equations and three orders higher for the Poisson equation than that for the linear finite elements. Moreover, the new approach yields even much more accurate results than the quadratic and cubic finite elements with much wider stencils. An example of a problem with a complex irregular domain that requires a prohibitively large computation time with the finite elements but can be easily solved with the new approach is presented. [ABSTRACT FROM AUTHOR]

Since the deformation region involves the interaction of electric-thermal-force coupling in electric hot incremental sheet forming, the numerical simulation of the forming process is unusually difficult. Currently, the thermal-force coupling method is adopted to simulate approximately the whole forming process, and the Joule heating effect is often ignored. Therefore, the numerical simulation of the Joule heating effect is especially significant for the prediction accuracy of forming process. In this paper, a novel numerical simulation method considering electric-thermal-force parameters was proposed to update the thermal-force condition of the forming region instantly. Meanwhile, the model of contact thermal conductance was established, combining geometrical and electric-thermal parameters. Then a high-precision finite element model was obtained to predict the Joule heating effect of the forming region. In addition to this, the impact of thermal superposition on forming temperature was further analyzed, and a modified model of contact thermal conductance was established in electric hot incremental sheet forming. [ABSTRACT FROM AUTHOR]

Steam flooding is a method of injecting steam to heat the oil and decrease its viscosity so that it will be easy to flow from injector to producer. Fula North East oil field is a massive edge and bottom water reservoir with good properties and high viscosity of crude oil. As of March 2018, the oil field has been fully commissioned in steam stimulation for 3 years and the water cut rises rapidly and the oil rate declines seriously. In this paper, through comprehensive analysis of the geological properties of reservoir, production dynamics of single well and cement quality of wellbore, the steam flooding pilot test area under different well groups is screened out. Advanced thermal enhanced oil recovery simulator has been used to build the model of 279, 888 cells to design and optimize steam flooding pilot area for this field. The best well space and development program are optimized; this paper supplies a theoretical foundation for the next step of steam flooding in the whole field. The results show that the optimum steam flooding parameters for this area are steam injection temperature of 270 °C, with 5–7 MPa injection pressure, steam injection quality of more than 0.6 and steam injection rate of 1.6 m3/day/ha/m, and the final recovery ratio will reach 32.3%. [ABSTRACT FROM AUTHOR]

Doubly curved metal plates are widely used in various industrial fields, so many efforts have been made to achieve the required doubly curved metal plates at reasonable quality and high efficiency in the last few decades. This paper presents a flexible forming process called incremental bending to achieve the doubly curved metal plates. The basic deformation behavior of the metal plates during the incremental bending process, including the loading force distribution and springback amount distribution along the whole surface of the metal plates, was investigated and analyzed based on experiments and numerical simulation. Results show that the maximum loading force and the springback amount of the metal plates are significantly influenced by the punching position while not by the incremental step. The results provide an important theoretical foundation for the practical application of the incremental bending process for achieving various doubly curved metal plates in the future. [ABSTRACT FROM AUTHOR]

The accreted ice on wind turbine blades significantly deteriorates the blade aerodynamic performance and consequently the power production. The existing numerical simulations of blade icing have mostly been performed with the Eulerian approach for two-dimensional (2D) blade profiles, neglecting the possible three-dimensional (3D) rotating effect. This paper conducts a numerical simulation of rime ice accretion on a 3D wind turbine blade using the Lagrangian approach. The simulation results are validated through previously published experimental data. The icing characteristics along the blade radial direction are then investigated in detail. Significant radial airflow along the blade is observed, which demonstrates the necessity of 3D simulation. In addition, more droplets are found to impinge on the blade surface near the tip region, thereby producing severer ice accretion there. The accreted ice increases almost linearly along the blade radial direction in terms of both ice mass and maximum ice thickness. [ABSTRACT FROM AUTHOR]

This paper compares the microstructure and mechanical evolution in a high-strength quenched and micro-alloyed steel during the austenitising bending process. Simulation results indicated a new finding that the stress neutral layer (SNL) tends to move to the tension zone during straining. The hardness gradient detected from the centre to compression/tension zones was resulted from comprehensive factors: First of all, the location of SNL revealed a prominent impact on strength. Second, the dislocation accumulation would be responsible for the hardness gradient on the surfaces. In addition, the overall strength decrease during straining was mainly ascribed to integrated effects of dynamic recovery (DRV) and dynamic recrystallisation (DRX). Apart from that, overall smaller martensite packet size and coarser prior austenite grains resulted in the increased hardness value at a lower bending degree. Also, the high consistency between experimental and simulation results is instructive for the practical forming process of railway spring fasteners. [ABSTRACT FROM AUTHOR]

This paper describes a problem of measuring a gas flow temperature using thermocouples for which the time it takes to reach an equilibrium temperature is shorter than the duration of the measurement process. Results for the numerical simulation of a gas flow in a sensor used to measure a stagnation temperature in short-duration wind tunnels are presented. The conjugate problem of a sensor in a supersonic flow is solved and the flow field inside the stagnation chamber is calculated. The temperature of the thermocouple placed on an end of a stagnation chamber is determined. The results of simulating the thermocouple readings depend on time and the oncoming flow parameters. The obtained readings of the stagnation temperature sensor are taken as virtual experiment data, which are processed using experimental aerodynamics methods. The stepwise process and two-thermocouple methods are used to recover the stagnation temperature. A difference in thermocouple readings is a normalized thermocouple instrument function. True temperature readings are recovered by deconvolution. The recovered readings are compared with the initial values of the stagnation temperature in the incoming flow to the sensor. The sources of measurement errors are determined, and the applicability of experimental methods for determining the stagnation temperature in short-duration wind tunnels (including those whose parameters decrease with time) is substantiated. [ABSTRACT FROM AUTHOR]

In this paper, the effect of the discharge gap on the arc characteristics of sheet tungsten electrode under vertical sidewall anode configuration is discussed. By changing the horizontal discharge gap and vertical discharge gap, the temperature distribution, current density distribution, flow field distribution, pressure distribution, and viscosity distribution of non-axisymmetric arc are calculated. From the point of view of the change of current density distribution caused by the change of discharge gap, the influence of Joule heat on the temperature distribution is analyzed, and the influence of cathode jet behavior on the arc temperature field is further analyzed. At the same time, the factors such as viscosity force and shear force above anode are also considered. At the same time, the experimental verification is carried out through the arc pressure and arc grayscale image. The importance of the discharge gap on the arc characteristics of sheet tungsten electrode under vertical sidewall anode configuration is emphasized. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study carried out using numerical simulation of flame front dynamics in a gaseous reacting mixture, including those in the presence of a suspended phase of liquid microdroplets. It is shown that the local effect on the flame front is one of the leading factors determining the development of combustion. Thus, the local dynamic effect of relatively large droplets on the flame front contributes to its curvature, which, in turn, determines the corresponding local acceleration of individual sections of the front. Further unstable growth of such perturbations leads to an integral acceleration of the flame. At the same time, local stretching by the flow in lean compositions can lead to combustion extinction. [ABSTRACT FROM AUTHOR]

Direct ink writing (DIW) is an extrusion-based additive manufacturing (AM) technique. One of the required factors for printing quality in DIW is to extrude continuous and tubular freeform extruded filaments (FEF) with diameters close to the nozzle inner diameter. This paper established a simulation model of FEF with volume of fluid (VOF) method and then evaluated the FEF based on the simulation results. First, ink properties including density, surface tension coefficient, and rheological properties were determined by properties tests. Then, the model of FEF was established using VOF simulation method with the software OpenFOAM and two evaluation indicators, mean diameter and stability, were proposed to evaluate the FEF. Two inks, a cellulose ink and a Nivea Crème, were used under three levels of piston velocity to verify the method universality for different inks and variable process parameters. The prediction accuracy of the established simulation model was verified as the relative error between simulation and experimental results of diameter was less than 10.22%. In this work, it was found that (1) piston velocity needed to be set higher than a minimum value to overcome yield stress and surface tension to successfully extrude filaments; (2) mean diameter of FEF decreased while stability of FEF decreased firstly and then increased as piston velocity increased. The proposed model and evaluation indicators gave an accurate and effective framework to analyze effect of the piston velocity on FEF, characterize the ink printability, and find suitable printable windows for process parameters in DIW. [ABSTRACT FROM AUTHOR]

Fatigue failure is defined as the progressive degradation of the strength of a structural component during the manufacturing of machine tools. As the increasing demands for high product quality result in a continuing need to achieve improvements in fatigue reliability on machining tools, many researches have been focused on it in recent decades with a result of many valuable contributions. However, current researches always focus on the fatigue analysis of rigid components, and the dimension change, necessary design, and optimization are lacked, while the component of a product is always a rigid-flexible coupling multi-body system, which could affect the accuracy and reliability of fatigue analysis, and parameterization help designers see each dimension change. This paper proposed a process of component fatigue analysis based on rigid-flexible coupling virtual prototyping. In this paper, a crankshaft in the cold heading machine is taken as an example to show the rigid-flexible coupling fatigue analysis process in detail. After the parameterization of the crankshaft is proposed, the static analysis and optimization of the crankshaft is carried out. The dynamics analysis for rigid-flexible coupling of the cold heading components is also proposed. The fatigue analysis for the crankshaft is discussed in detail. The crankshaft in the cold heading machine is given as an example, which demonstrates that the methodology is obviously helpful to fatigue analysis and simulation. The physical prototyping is also carried out to demonstrate the fatigue reliability. The crankshaft of cold heading machine is given as an example, which demonstrates that the methodology is obviously helpful to fatigue analysis and simulation. [ABSTRACT FROM AUTHOR]

A coupled nonlinear prey–predator system is presented. The system formulation is based on nonlinear ordinary differential equations with imprecise parameter values. In this paper, we find the equilibrium point and conduct a stability analysis of the prey–predator model using a Lyapunov functional. A comparison of our approximate analytical expressions with numerical simulation using MATLAB software is also presented. Furthermore, the proposed mathematical model is solved analytically by using the VIM and HPM for all possible parameter values in their specified ranges. Excellent agreement is noted on comparisons between the analytical and numerical results. [ABSTRACT FROM AUTHOR]

The work considers the deformation and fracture of a reinforced concrete slab under the effect of an air shock wave. The research involves data from the "Blind Blast Test" experimental case. The slab is loaded by detonating an explosive in a shock tube. The numerical and experimental results are compared quantitatively and qualitatively. Quantitative comparison is made for the history of movement of key points of the reinforced concrete slab during deformation. Qualitative comparison is made for photographs of the destruction of a real reinforced concrete slab and distribution of the damage fields obtained by calculation. The numerical simulation is carried out using LS-DYNA code and the finite element method with an explicit time integration scheme. The CSCM (Continuous Surface Cap Model) model is used to model the concrete material. This model assumes that that the material is isotropic and has a three-invariant yield surface. The strength characteristics of the material depend on the rate of loading, and its damage is considered separately for compressive and tensile loads, which allows taking into account the partial recovery of compressive strength. The mathematical description of the model is given as part of the paper. Steel reinforcement of the concrete slab is modeled explicitly with beam finite elements. Finite element meshes of the concrete volume and reinforcing elements are coupled by means of kinematic dependences, automatically created by the design code. The properties of the reinforcement material are specified within the classical theory of elastoplastic flow with the criterion of limiting states in the Huber–Mises form and taking into account viscoplastic effects. The influence of boundary conditions, practical mesh convergence, and the capability of the mathematical model to predict the location of zones of material failure, displacement, and deformation of the structure are studied. [ABSTRACT FROM AUTHOR]

Numerical simulation approaches have been widely applied to study mining induced subsidence, and they are potential methods to study the flooding induced uplift for abandoned mines. This paper gives an overview about different numerical approaches to simulate uplift induced by flooding abandoned underground mines, including three different hydraulic conditions, considering both unconfined and confined water conditions. Four basic simulation schemes using 1-dimensional rock column models verified by analytical solutions demonstrate these procedures. The results reveal that flooding induced uplift is mainly related to the pore pressure in the mine goaf. The parameter study documents that height and stiffness of the mine goaf have the strongest influence on maximum surface uplift. [ABSTRACT FROM AUTHOR]

Large ellipsoid parts are prone to wrinkle when forming by using traditional stamping. Aiming to solve the wrinkling problem in large parts, the EMIF method with a variable blank holder is proposed in this paper. The numerical simulation has shown that the sheet material near the blank holder is, as a consequence of stamping, subjected to circumferential compressive stress. When the drawing height was 100 mm, the sheet metal was notably wrinkled. In the electromagnetic forming (EMF) process, the sheet region facing the coil becomes thinner. However, the sheet metal thickness corresponding to the coil edge increases with the increase in forming height. If the EMF forming height is 150 mm, the sheet, which is in contact with the smooth mold, is deformed without a wrinkle. Compared to traditional stamping, the EMF can significantly reduce the sheet metal wrinkling, improving the deformation height of the sheet metal smooth area. [ABSTRACT FROM AUTHOR]

In this paper, a type of numerical simulation of a three-dimensional (3D) bionic bird with flapping wings in a viscous flow is studied. The model is a self-propelled flying bird capable of free rotation and translation whose flying motion follows the laws of conservation of momentum and angular momentum. The bird is propelled and lifted through flapping and rotating wings and most of thrust force and lift force are exerted on both wings. Both the vortex structures and the flight characteristics are also presented. The relationship between both wings' movement and the vortex structures as well as that between both wings' movement and flight characteristics are also analyzed in this paper. The study uses a 3D computational fluid dynamics package that includes the combined immersed boundary method, volume of fluid method, adaptive multigrid finite volume method, and control strategy for swimming and flying. [ABSTRACT FROM AUTHOR]

Reasonable selection of process parameters can adjust the temperature and velocity fields of the metal liquid in the mold cavity to obtain the desired casting organization. In this paper, the temperature and flow fields of the high molybdenum cast iron casting were simulated at different casting temperatures and mold preheating temperatures, respectively. The results show that casting temperature has little effect on the filling rate, but it has a strong effect on the movement state of the metal liquid. When the casting temperature is 1430 °C, the flow field is smooth. At higher or lower casting temperature, the metal liquid appears to split strands or splash, and it is prone to defects such as cold gap after solidification. The higher casting temperature and mold preheating temperature, the slower the solidification rate. Mold preheating temperature is the key influencing factor for the solidification rate and cooling time of the casting. There is a nearly linear relationship between cooling time and mold preheating temperature, and the cooling time of the casting increases with every 50 °C increase in mold preheating temperature, but the magnitude of the increase has been decreasing. [ABSTRACT FROM AUTHOR]

In this paper, the method of limit analysis is adopted, and three kinds of self-bending extrusion dies controlled by combined function are presented. They are the sin-atan self-bending extrusion die, the sin-erf self-bending extrusion die, and the sin-tanh self-bending extrusion die. Through numerical simulation, self-bending profiles can be obtained from all three kinds of dies. These dies can make the billet flow closer to the real billet flow path and maximize the billet utilization rate. They also can reduce the extrusion load and reduce the local damage of the die and then prolong the die life. It is very effective to predict the bending deformation of the billet by analyzing the central flow line of the billet. It provides a theoretical reference for the design of the actual streamlined self-bending die. [ABSTRACT FROM AUTHOR]

This paper presents a comparative computational analysis of the penetration of shaped charges with copper liners in the form of a cone of progressive thickness with a cone angle of 60°, a hemisphere of constant thickness, and a hemisphere and a semi-ellipsoid of degressive (decreasing from apex to base) thickness. The polar semi-axis of the semi-ellipsoidal liner slightly exceeded the equatorial semi-axis. The parameters of the generated shaped-charge jets were determined by numerical simulation within the framework of a two-dimensional axisymmetric problem of continuum mechanics, and the depth of their penetration into a steel target was determined using an engineering technique that takes into account the influence of the manufacturing precision of the charges. The parameters of the liners of degressive thickness were selected so that the tip velocity of the jets formed from them was close to the velocity provided by the conical liner. In this case, the penetration of the shaped charge with a hemispherical liner of degressive thickness was significantly lower than that of the charge with a conical liner, and the latter, in turn, was slightly inferior in the maximum depth of penetration to the charge with a semi-ellipsoidal liner. The physical reasons of the results are discussed. [ABSTRACT FROM AUTHOR]

In the shipbuilding industry, the traditional manufacturing method for the complicated ship hull metal plates is line heating method, which is not only labor intensive but also inefficient. Considerable efforts have been taken to develop the new automated manufacturing processes at a reasonable quality, efficiency and price during the last few decades. This paper presents a novel flexible forming process called incremental bending to achieve complicated plates. In this method, the initial metal plate is supported by some rotatable hydraulic cylinders and the punches move according to the given path, which is decided by minimum energy method and springback compensation method, to achieve the final plate. Taking one variable curved metal plate as one example, this paper investigates the formability of this novel process based on experiment and numerical simulation. During the numerical simulation, the implicit method is used and the gravity of the plate is considered mainly for the automatic positioning of the plate during each springback process. Results show that the incremental bending process can achieve variable curved metal plates with good accuracy, high efficiency, and relatively small punch load. In comparison with the existing methods, the new process has greater potentiality in the ship hull manufacturing industry. [ABSTRACT FROM AUTHOR]

On August 20, 2019, many catastrophic debris flows broke out in meizoseismal area of Wenchuan M s 8.0 earthquake in China under the influence of continuous heavy rainfall. This paper takes the Chutou gully debris flow event occurred on August 20, 2019 as an example. The 3-D numerical simulation software, RAMMS, is used to back calculate the event and predict the future hazard. Coulomb and viscous turbulent friction, μ and ξ are calibrated in RAMMS. Numerical simulation reveals the movement process of Chutou gully from the aspects of flow depth, velocity, discharge, and run-out solid materials volume. The simulation results show that more than two-thirds of the solid materials are still deposited in the main channel, which could provide material basis for the re-occurrence of high hazard debris flow. In addition, based on the intensity and probability of debris flow, the hazard of debris flow is divided into high, middle, and low degrees. According to the simulation results and hazard assessment model, the hazard map of Chutou gully debris flow in various rainstorm return periods (20, 50, 100, and 200 years) is established, which can provide guidance for the future land-use planning and debris flow prevention works. [ABSTRACT FROM AUTHOR]

Background: Since the high-rise buildings and deep underground structures dramatically increases in urban area, the decent design and construction of deep excavations is essential before these structures are actually built up. The building area is very susceptible to the changes of their geo-environment, and even minor insecurity of a deep excavation may lead to a catastrophic failure of structures and deformation of the ground. Therefore, the adverse influence of deep excavation on the surrounding environment should be monitored and controlled stringently. Results: Based on the real case of deep excavation in Xuzhou, China, a FDM numerical model, which was accomplished by FLAC-3D, was developed to evaluate the deformation of retaining piles and ground surface under various excavation support systems. The original pile-anchor support system was simulated as well as the proposed quincunx double-row piles support system. For the original support system, the deformations were discussed by comparing the numerical results with monitoring data. For the proposed support system, orthogonal tests were designed to evaluate the influence of multiple factors on the effectiveness of excavation support. The optimum solution for the proposed support system was obtained through orthogonal tests. Conclusion: Results show that the pile space is the primary factor for the excavation-induced deformations, which can be reflected by the lateral displacement of retaining piles and the settlement around the excavation, while the row space has insignificant influence on the deformations. The conclusions of this paper can contribute to the design of similar projects and avoid excessive deformation of the ground during excavation in the future. [ABSTRACT FROM AUTHOR]

This paper presents modeling work carried out using a finite-element modeling approach. The physical models implemented for HgCdTe infrared photodetectors are reviewed. In particular, generation-recombination models such as Shockley-Read-Hall through a trap level in a narrow bandgap and Auger recombination are included. These well-established models are described using widely published analytical expressions. This paper highlights both the unique set of trap parameters found to fit the dark current as a function of temperature and composition for mercury-vacancy p-type-doped photodiodes and their use in a finite-element code. An equivalent set of trap parameters is also proposed for indium n-type-doped material in a p-on- n photodiode simulated in three dimensions. Device simulations also include the impact ionization process to fine-tune the saturation dark current. Finally, excess dark current is also modeled with the help of nonlocal band-to-band tunneling, which requires no fitting parameters. [ABSTRACT FROM AUTHOR]

Die service life improvement is an important problem in high-pressure die-casting industry. Die service life, which is defined as the maximum product number produced before it fails, and die performance directly determine the production cost and quality of die-casting product. To reduce the repair and maintenance costs, an approach to prevent die from thermal damage and prolong the die lifetime is required. Biomimetic laser-remelting process (BLRP) provides a promising method to improve the service life of die-casting mold. However, the laser processing regions can only be determined by experiences. In order to determine the exact laser processing regions for a set of new die before BLRP, a combination system of CAE and BLRP is proposed in this paper. Through analyzing the mold filling process and the temperature distribution, potential thermal cracks are worked out by numerical simulation system, which are the laser processing regions. The method proposed in this paper advances the efficiency of the BLRP. And practical production validates the veracity and the reliability of the method. [ABSTRACT FROM AUTHOR]

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Cracking behavior of flawed samples has been extensively studied in rocks and rock-like materials using experimental and numerical approaches. However, the existing research mainly focuses on the effects of flaw length l and inclination angle α on rock mechanical behavior, a limited attention has been given to understand the role of flaw width b on crack initiation and propagation in relation to mechanical parameters of rocks. In this paper, a two-dimensional particle flow code (PFC2D)-based synthetic rock model, which is calibrated by the laboratory sandstone properties, is used to investigate the effects of flaw width on cracking behavior of single-flawed rock samples under uniaxial compression tests. Numerical simulation results show that the flaw width b has significant effects on the crack geometrical parameters (crack initiation location d and crack initiation angle θ). The values of θ and d significantly decrease with the increase of flaw width when b < 1.0 mm and their values tend to be stable with the further increase of flaw widths. It is also found that the mechanical properties (uniaxial compressive strength UCS and deformation modulus Es) of flawed rock samples are related to the crack geometrical parameters (θ and d) and the effects of flaw width on the values of UCS and Es of single-flawed rock specimens is significant when b < 1.0 mm for lower crack inclination angle (α < 60°). [ABSTRACT FROM AUTHOR]

This paper describes the study of the stress-strain state in the elements of a non-spherical shell of variable thickness arising during the pulse action. The effect of the radii of inserts used as reinforcing elements on the magnitude of stresses in the non-spherical bottoms is investigated. The relationship between the stress-strain state in the shell pole and the radius of the inserts is studied. It is shown that the use of an insert with the optimal radius allows creating an equally strong explosion chamber. [ABSTRACT FROM AUTHOR]

Large and thick-walled aluminium forgings exhibit shape distortions induced by residual stresses. To restore the nominal geometry, a series of highly manual and time-consuming reshaping operations need to be carried out. In this paper, we are concerned with the development of efficient computer simulation tools to assist operators in bending straightening, which is one of the most common reshaping operations. Our approach is based on the computation of reshaping diagrams, a tool that allows selecting a nearly optimal bending load to be applied in order to minimize distortion. Most importantly, we show that the reshaping diagram needs not to account for the residual stress field, as its only effect is to shift of the reshaping diagram by some offset. That is, the overall behaviour including a realistic 3D residual stress field in a forged part can be retrieved by shifting the residual stress free reshaping diagram by the appropriate offset. Finally, we propose a strategy in order to identify the offset on-the-fly during the reshaping operation using simple force-displacement measures. [ABSTRACT FROM AUTHOR]

Jet pulse assembly is one of the main components of jet hydraulic oscillator. The pressure wave characteristics produced by jet pulse assembly have an important influence on the performance of the tool. In this paper, the structure and working principle of jet pulse assembly are studied, the mechanical analysis model of piston rod is established, the dynamic resistance ratio formula of jet pulse assembly is deduced, and the numerical simulation test of 89-mm jet pulse assembly structure parameters is carried out. The results show that the piston rod downward stroke is driven by both the jet element driving force and the throttle plate load driving force, and can stably descend. The driving force of the piston rod upward stroke jet element is opposite to the load acting force of the throttle disc, and the jet driving force needs to be greater than the load resistance of the throttle disc to stably ascend. The dynamic resistance ratio formula is deduced. When the area of the end of the piston rod is reduced, the resistance of the throttle disc is reduced and the jet power is increased, thus solving the problem of insufficient power of the piston rod in the upstroke and ensuring the normal operation of the tool. Ten groups of numerical simulation tests were carried out, and it was found that the pressure amplitude and pressure drop of the tool decreased significantly with the increase of the tool size, and the error between the numerical simulation value and the theoretical calculation value was less than 9%, which verified the correctness of the theory. It is suggested to select tools on site according to the drilling construction situation to ensure the drilling effect. [ABSTRACT FROM AUTHOR]

As the computation power of modern high performance architectures increases, their heterogeneity and complexity also become more important. One of the big challenges of exascale is to reach programming models that give access to high performance computing (HPC) to many scientists and not only to a few HPC specialists. One relevant solution to ease parallel programming for scientists is domain specific language (DSL). However, one problem to avoid with DSLs is to mutualize existing codes and libraries instead of implementing each solution from scratch. For example, this phenomenon occurs for stencil-based numerical simulations, for which a large number of languages has been proposed without code reuse between them. The Multi-Stencil Framework (MSF) presented in this paper combines a new DSL to component-based programming models to enhance code reuse and separation of concerns in the specific case of stencils. MSF can easily choose one parallelization technique or another, one optimization or another, as well as one back-end implementation or another. It is shown that MSF can reach same performances than a non component-based MPI implementation over 16,384 cores. Finally, the performance model of the framework for hybrid parallelization is validated by evaluations. [ABSTRACT FROM AUTHOR]