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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.

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.

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.

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.

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.

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.

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.

[Objectives] The shock environment of a warship in an underwater explosion is the basic input for the design and shock resistance ability evaluation of ship equipment. [Methods] In this paper, a numerical simulation is used to analyze the shock environment in different regions of a ship, and the Second-order Doubly Asymptotic Approximation(DAA2)is used to solve the fluid-structure interaction. First, the appropriate calculating parameters are chosen, such as damping ratio, and then a series of Single-Degree-of-Freedom(SDOF) systems are attached at various deck locations to simulate flexible equipment. [Results] The accuracy and reliability of DAA2 is verified by the fact that the calculated shock spectrums at classic regions perfectly match the data of the ship shock trial. The shock response of the SDOF systems under the same shock input are then calculated and transformed into the shock environment. Finally, the results of shock environments in different regions are compared. [Conclusions] The conclusions of this paper can provide design reference data for the subsequent anti-shock design of equipment.

[Objectives] In order to investigate the strength of the joint structure of box girders under internal explosion, [Methods] this paper use the explicit dynamic finite software ANSYS/LS-DYNA to establish a large complex typical cabin model. Numerical investigations are then conducted to analyze the dynamic response of different forms of joint structure under internal explosion using the ALE algorithm. The whole deformation/failure mode of cabin structures with the same charge mass and detonation position is obtained. A comparison of stress level at typical positions is then carried out in detail. [Results] The results show that the arc-arc type joint has a lower stress level compared to the bracket at the broadside. In the central position where a box girder is connected to a web beam, the arc-arc joint form is better than the other two. [Conclusions] The findings of this paper can provide useful references for the engineering application of joint structures.

[Objectives] The shipboards of large surface ships are greatly threatened by anti-ship weapons, and a multicamerate defense structure (MDS) is usually established to ensure the safety of important internal cabins. In this paper, the dispersion effect of fragment-induced shockwaves in an MDS liquid tank is studied. [Methods]First, the elemental experiment of a miniature liquid tank struck by fragments is conducted, through which the free field pressure, etc. of typical positions in the tank are obtained. The numerical method used in this paper is then validated on the basis of the experimental results and the dispersion effects in a full-scale MDS liquid tank are analyzed. [Results] It is found that the amplitude and impulses of shockwaves in a liquid tank satisfy the exponential attenuation law as the spatial position changes. [Conclusions] The findings of this paper can provide useful references for the optimal design of MDS.

ObjectivesIn this paper, the numerical simulation method is used to study the anti-penetration performance and energy absorption mode of a stiffened plate, as well as the influence of different stiffened bars on the flight attitude of the projectile body.Methods Finite element software LS-DYNA is used to simulate the process of a truncated oval-nosed projectile penetrating a stiffened plate, and the results of the numerical simulation are compared with an experiment to verify the reliability of the numerical simulation method. The momentum method and mass equivalence method are used to predict the residual velocity of the projectile, and the applicability of different theoretical methods within different velocity ranges is compared. The deformation energy of different regions of the stiffened plate is then extracted to analyze the influence of the initial velocity of the projectile body on the energy absorption mode of the target plate. Finally, the structure of the stiffeners is changed and the influence of the relative position of the stiffeners on the penetration attitude of the projectile body is analyzed.ResultsThe results show that the mass equivalence method is more accurate than the momentum method in predicting the residual velocity of the stiffened plate when the initial velocity of the projectile body is in the range of 300–900 m/s. The ratio of the deformation energy of the stiffened plate to the energy loss of the projectile body decreases with the increase of the initial velocity of the projectile body. The effect of a T-stiffened plate on trajectory is greater than that of a rectangular-stiffened plate.ConclusionsThe related calculation method and research results have certain reference value for research and engineering application surrounding the anti-penetration of stiffened plates.

ObjectiveThe ice resistance of an ice breaker on the Yellow River is predicted in the context of ice disasters caused by the freezing of the river in winter. MethodsFirst, a ship-ice-water coupled numerical model is introduced on the basis of the smoothed particle hydrodynamics method (SPH), which includes the numerical process of the constitutive equation, yield criterion and coupling model of ice. The prediction results for the ice resistance of the icebreaker under different conditions are then given. ResultsThe results show that the prediction error of ice resistance in level ice cases is less than 17.6% compared with empirical formulas; the ice resistance of the ice breaker increases with the increase in bending strength and ice thickness, and the thickness of the ice layer is the most important factor for the ice load.ConclusionThe ship-ice-water coupled SPH method proposed in this paper can predict the ice resistance of an ice breaker in the Yellow River channel, providing references for the actual operation of ice breakers on the Yellow River.

ObjectiveIn order to improve the anti-shock perfomance of ships subjected to underwater explosion, this paper studies the energy absorption and impact resistance of the new protective structure consisted of carbon fiber reinforced plastic (CFRP)-lattice aluminum sandwich plates. MethodsFirst, finite element software ABAQUS is used to establish the numerical simulation model of CFRP-lattice aluminum sandwich plates under non-explosive and non-contact underwater explosion load, and its reliability is verified. Single variables are then controlled to analyze the influence of the fiber layer thickness of the upper and lower panels and the rod diameter of the sandwich lattice structure on the energy absorption characteristics and structural deflection of the CFRP-lattice aluminum sandwich plates. Finally, based on the above three design parameters, a surrogate optimization model is established using the experimental design method and numerical simulation methodology to optimize the energy absorption of the CFRP-lattice aluminum sandwich plate structure. ResultsThe results show that when the mass of the CFRP-lattice aluminum sandwich plates is constant, the specific absorption of the optimized results can be increased by 284%. In full consideration of the deformation of the lower plates, the specific energy absorption of the optimized results can be increased by 59%. ConclusionsThis study shows that the proposed optimized structure of CFRP-lattice aluminum sandwich plates can effectively improve their energy absorption capacity, and the response surface method is an optimization method that can effectively improve the energy absorption characteristics of the structure.

To predict the maneuverability of full-revolving propeller ships, this paper analyzes the propeller force and establishes MMG equations for controlling motion mathematical models that are suited to the full-revolving propeller model, in accordance with the modeling method of the separating ship motion model and taking into account the special nature of the force and flexibility of a full rotation in the horizontal plane of a full-revolving propeller. Secondly, hydrodynamic force derivatives for the ship model are obtained by simulating the model's PMM movement, and the controlling Ordinary Differential Equation (ODE) is solved using the four-stage Rung-Kuta method. Finally, the numerical simulation of a certain ship's rotating motion and its zigzag test in still water is obtained, and the prediction results are compared with that of a self-running model. It is found that the simulation results agree well with the trial results, and the effectiveness of the ship motion model for the full-revolving propeller model is validated. In brief, this paper provides a reliable and effective method of predicting the maneuverability of full-revolving propeller ships.

ObjectivesThis paper studies the transient effects, different frequencies of spectral peaks and meaningful excitation amplitudes on liquid sloshing. MethodsA numerical model is established using the computational fluid dynamics (CFD) method, and the reliability of the numerical model is validated through comparison with the analytical solution of linear potential flow and experimental data. ResultsThe transient effects of random excitation have a significant influence on the fluctuation of the free water surface of liquid sloshing in the tank. By applying the buffer function, stable results can be obtained quickly. When the peak frequency of the excitation spectrum is close to the natural frequency of the tank, the energy of the wave-height response spectrum of the liquid sloshing in the tank is mainly concentrated at the natural frequency of the tank. When the peak frequency of the excitation spectrum is far from the natural frequency of the tank, the energy of the wave-height response spectrum is concentrated near the peak frequency. With the increase of the meaningful amplitude of the excitation spectrum, the amplitude deviation of the liquid sloshing response relative to the linear wave (the deviation degree is zero) increases, and the nonlinearity of the tank increases significantly. ConclusionsFor the random excitation simulation, especially when the excitation frequency is far from the natural frequency, it is necessary to buffer the excitation duration. It is found that when the peak frequency of the excitation spectrum moves away from the first natural frequency to higher frequencies, the energy is dominant at the i-th order of the natural frequency when the peak frequency is close to it.

ObjectivesThis paper aims to study the kinetic and dynamic characteristics of an trans-media unmanned vehicle during vertical take-off from water.MethodsIts dynamic performance during the trans-media process from water to air is numerically simulated on the basis of the viscous computational fluid dynamics (CFD) approach combined with the overset grid technique, multiple degrees of freedom and dynamic fluid body interaction (DFBI) motion model.ResultsThe results show that in order to pull the vehicle up, the air propeller rotation speed should be higher than the speed at the same pull force provided by a single propeller. As the main movement of the vehicle is vertically upward, the coupling of the air propeller downwash flow velocity and the fuselage of the vehicle leads to the "quick bowing" phenomenon.ConclusionsTo ensure smooth take-off, a manual or automatic control program should be added to adjust the tilt angle of the thrusters in real time during the take-off process. This study provides a powerful evaluation method for the optimal design and control of trans-media unmanned vehicle in the future.

ObjectivesThis paper studies the hydrodynamic performance of the submarine sailing near the ice surface using numerical simulation method.Methodsthe Suboff full-appended model, RANS method, SST k-ω turbulence model and volume of field method are used to calculate the hydrodynamic performance of the submarine in the STAR-CCM+ software. The effectiveness of the calculation method is guaranteed by the method of grid independence verification and the method of hydrodynamics analysis near the ice surface.ResultsThe results show that when the submarine sails under ice surface, the total resistance coefficient of submarine decreases with the increase of the submergence depth at the same Froude number, and decreases with the increase of Froude number at the same depth. In addition, when the dimensionless depth is greater than 1.63, the submergence hardly affects the drag coefficient.ConclusionsStudies have shown that the total drag coefficient of submarine is greatly influenced by Froude number and submergence depth. With the increase of submergence depth, the influence of submergence depth on drag coefficient decreases gradually.

[Objectives] Underwater hydrofoils have the characteristics of drag reduction and energy conservation. They are often used in the design of rudder and fin stabilizers for high-performance ships. From current research on the hydrodynamic performance of hydrofoils,such improvements as opening the inner groove and adding a leading edge nodule can significantly improve their hydrodynamic performance.[Methods] In this paper,an NACA0012 hydrofoil with internal slots is improved,the influence of different internal slots on the hydrodynamic performance of the hydrofoil is studied by means of computational fluid mechanics,and the relevant action mechanism is explored.[Results] Finally,it is concluded that the hydrodynamic performance of the hydrofoil can be improved most significantly by placing the elliptical inner groove at the leading edge of the hydrofoil,and the inner groove should have a certain width to ensure a smooth flow.[Conclusions] The results of this study can play a certain role in the improvement of ship rudders.

[Objectives] When research is conducted for the centrifugal pumps' structural design and performance,the influence of the seal ring clearance is often neglected. However,the clearance of the seal ring will not only change the external characteristics of the centrifugal pump,but also affect its flow field distribution.[Methods] In this paper,a vertical centrifugal pump with medium-specific speed is used as the research object. The ANSYS CFX is used to simulate and analyze the influence of different wear-ring clearances(0,0.5,0.7,1.06 mm)on the external characteristics,pressure distribution,and velocity distribution of the centrifugal pump.[Results] The results show that the external characteristics of the centrifugal pump with different annulus clearances are consistent with the experimental data. The relative error of two is less than 5%(except 1.06 mm clearance). This verifies the reliability of the numerical simulation. With the increase of the clearance of the seal ring,the head of the centrifugal pump decreases by 20% and the efficiency by 15% under design conditions. The local pressure of the front and back cover plates of the impeller at the small clearance increases,and the overall pressure at the large clearance decreases,resulting in the radial pressure distribution of the impeller cover plate being asymmetric. The gap of the annulus leads to turbulence in the fluid and the pressure and velocity at the inlet and outlet of the centrifugal pump present an uneven gradient distribution.[Conclusions] The research results can provide a reference for the structural design and flow field analysis of the centrifugal pump.

[Objectives] To meet the functional requirements of a special purpose ship,large bulbous bow should be installed at the fore-body as the carrier of special equipment. In order to overcome the adverse effect of large bulbous bow as a special appendage on ship rapidity,the optimal design of high-speed hull form fusion special type bulbous bow was carried out.[Methods] By using the method of gradual approach to analysis,The hull and its appendages were compared and analyzed,the ship with high resistance performance was selected by numerical simulation,which was verified by model test.[Results] The results show that the hull form of round bilge fused cylindrical bulbous ship is a hull form that can meet the layout requirement and has high performance.[Conclusions] Under the same calculation conditions,the numerical simulation can accurately predict the resistance differences among different hull forms,the multi-plan optimization design approach proposed in this paper is an effective method to optimize hull forms.

Objectives This study is focused on whether CFD can be used to analyze the temperature distribution in the core storage of ocean exploration vessels.Methods In the core storage of ocean exploration vessels, high-temperature storage is 4℃, low-temperature storage is -20℃ and temperature control accuracy is ±1℃. The standard k-ε turbulence model is used in this paper for CFD simulation. In the case of an empty storage ceiling, a transverse layout, a longitudinal layout and an oblique layout are separately adopted on the deployment scheme of the air cooler for high and low temperature storage. The temperature distributions of the different layout schemes are simulated to determine the optimal layout of the air cooler. Then the simulation results are compared with the experimental results.Results The result shows that when the air cooler adopts the transverse ceiling layout, the temperature deviation degree is small, and the temperature is mostly distributed in qualified areas, therefore this layout is selected. In the case of the transverse layout ceiling arrangement, the error between the simulation results and experiment results, is below 10%. This shows that the simulation results are reasonable.Conclusions CFD can accurately simulate temperature distribution in core storage, providing a strong scientific basis for the future design of core storage air coolers.

[Objectives] This paper focusses on deriving formulations to predict the ultimate strength of both intact and damaged steel ring-stiffened cylinders subjected to hydrostatic pressure. The damage scenario considered in this study can represent the collision accidents of marine ring-stiffened cylinder structures,such as submarines,semi-submersibles,spars and more recently as buoyancy columns of floating offshore wind turbine foundations with supply vessels.[Methods] To validate the numerical modelling and the analytical techniques, six small-scale ring-stiffened cylinder models were tested. Drop tests with a knife-edge indenter were conducted to generate the damage on four cylinder models. Then, all models were tested under hydrostatic pressure for assessing the ultimate strength in intact and damaged conditions. Next,the rigorous parametric studies on actual design full-scale ring-stiffened cylinder examples were performed by changing the design variables. Based on the parametric study results, the simple design equations are derived for predicting the residual strength of damaged ring-stiffened cylinders.[Results] The accuracy and reliability of the derived formulation has been compared with those of test and finite element analysis results,which has a good agreement for all cases of loadings.[Conclusions] Therefore, it can be useful for design purpose and serviceability limit state assessment of ring-stiffened cylinders in the risk conditions of marine structures.

[Objectives] During the discharging of ship-used steam power,steam jet condensation was a common physical process. In order to fully grasp the fundamental physical phenomena within steam submerged jet and condensation under open space,CFD simulation with Mixture multiphase model was carried out.[Methods] With the experimental results,heat transfer model was modified. Vapor volume fraction 0.95 was regarded as the critical value to measure the length of plume. Spatial distribution of plume,velocity,temperature and pressure fields for steam submerged jet and condensation under different inlet pressure and condensed water temperature conditions were studied.[Results] Simulation results show that different initial state would affect the plume shapes. Within stable steam submerged jet and condensation,a relatively lower temperature area is appeared in the core of plume. Pressure distribution along the axial direction is present in a fluctuating form,verifies the existence of the expand-compress wave inside the plume,amplitude and spatial wavelength of the pressure fluctuation are increased with increasing inlet pressure.[Conclusions] Study in this paper could provide guidance for the optimal design of steam submerged jet and condensation.

[Objectives]In order to analyze the deformation and energy absorption characteristics of the stiffened plate under explosive impact loads,[Methods]the finite element analysis software LS-DYNA is used to simulate and calculate the deformation and energy absorption of the clamped stiffened plate under the explosive impact loads. The one-way stiffened plate is taken as the study object,the deformation and energy absorption characteristics are analyzed,the overall deflection and the local deflection of the stiffened plate are obtained,the ratio of these two deflections is used to indicate the proportional relationship between the local energy absorption and the overall energy absorption of the stiffened plate.[Results]The results show that the overall deformation of the stiffened plate decreases as the relative stiffness increases under certain explosive impact loads. The ratio of the local deflection to the overall deflection increases as the relative stiffness increases. The ratio of the local energy absorption to the overall deformation and energy absorption increases as the relative stiffness increases.[Conclusions]The dimensionless relative stiffness and deflection ratio proposed in this paper can provide study references and ideas for the ship anti-explosion and venting structure design.

[Objectives] In response to the need for improved habitability arising from the harsh environment of submarine accommodation, this paper studies the conditioned air distribution for submarine accommodation equipped with spherical air distributors,and evaluate the thermal comfort of the accommodation.[Methods] A high-precision three-dimensional model of accommodation is constructed with CATIA,and according to the actual boundary conditions,the numerical simulation of air distribution in the accommodation under surface and underwater conditions in summer and winter,and the numerical simulation of the conditioned air distribution in the accommodation with spherical air distributors under summer surface condition are carried out by using the Computational Fluid Dynamics(CFD)technology. Besides,the distribution of the air temperature and velocity in the accommodation under each working condition is analyzed and compared,and the PMV value of the accommodation is calculated and analyzed.[Results] It is shown that the PMV values of the accommodation are -1-1 under each working condition, the air velocity distribution in most areas of the accommodation is uniform,with the average air velocity of less than 0.3 m/s,and the temperature distribution in most areas of the accommodation is uniform,with average air temperature of about 24.5-26℃ in summer,and about 22-23.5℃ in winter.[Conclusions] The typical air conditioning comfort of the submarine accommodation equipped with spherical air distributors is up to the standard.

[Objectives] In order to study the performance of Jet Blast Deflector(JBD)and its influence on the surrounding flow field during the takeoff or ground testing of the fighter,this paper studies the typical axisymmetric convergent-divergent nozzle and the JDB with fold angle of the engine.[Methods] Through FLUENT software,the numerical simulation of the upstream and downstream flow fields of the JDB after the jet flow is carried out with different horizontal distance from the nozzle exit section to the spindle of JDB,and different deflection and fold angles of JDB,to analyze the thermodynamic parameters of JDB surface and the distribution of the surrounding flow field.[Results] It is shown that the longer the horizontal distance from JDB to the rear of the nozzle is,and the smaller the deflection angle is,the lower the airflow pressure and temperature on the JDB will be. And the farther the horizontal distance is,and the larger the deflection angle is,the lower the velocity and temperature of surrounding flow field will be. The fold angle of JDB can effectively strengthen the role of JDB in controlling and guiding the air flow and increase the safe area after the JBD.[Conclusions] The calculation results provide guidance for the research and development of JDB.

[Objectives] Due to its excellent seakeeping, rapidity and stability, Trimaran Small Waterplane Area Center Hull(TriSWACH)has an increasing number of applications in both civil vessels and warships. However, the laws of resistance of different submerged body shapes and side-hull configurations at different speeds still require research. As model tests are time-consuming and expensive, and cannot cover all potential hulls, numerical calculation based on STAR-CCM + is becoming increasingly preferred.[Methods] With the free surface effect consideration,STAR-CCM+ is validated to be practical for TriSWACH resistance prediction. The resistance performance is calculated with different side-hull configurations,including longitudinal and transverse,of circular submerged body shapes under the Fr series.[Results] As the results indicate,with the increase of speed,when the side-hull is arranged behind and moves closer to the main hull,the total resistance of TriSWACH is significantly lower than that of traditional trimarans,in the range of Fr=0.338~0.494.[Conclusions] The findings in this paper can provide useful references for future TriSWACH design.

[Objectives] Blast loads differ according to whether the blast takes place in a free field or cabin. [Methods] Dynamic software is used to simulate different explosive charge blasts in a free field, closed cabin and open cabin. The numerical results are then compared with the Henrych formula results, and the load characteristics of the open cabin and closed cabin are analyzed. [Results] The research shows that the shockwave gathers in the corner of the closed cabin. The total impulse of the shockwave in the corner is about 1.45 times greater than the total impulse at the center of the plate, while the pressure in the corner of an open cabin is not obvious. The peak values of the reflected pressure and quasi-static pressure in a closed cabin are smaller than those in an open cabin. The total impulse of the shockwave in the open cabin is about 20% that of the closed cabin. The pattern of plate damage in the closed cabin is mainly the plastic deformation of the plate frame along the stiffeners and the plate tearing along the corner; the tear does not occur in the closed cabin corner, but valgus deformation occurs at the edge of the open cabin; the maximum deformation value of the plate center obtained by the numerical simulation method is close to that obtained by the simplified method when only the impact of the shockwave is considered. When both the impact of the shockwave and quasi-static pressure are considered at the same time, the error margin is larger. [Conclusions] The results of this paper can be used to predict the characteristics of blast loading and stiffened plate damage.

[Objectives] The FE method cannot accurately simulate crevasse patterns and the crevasse forming process when dealing with a projectile penetrating into a ship's plate because of mesh distortion. [Methods] To this end, this paper establishes a numerical simulation model of a projectile's penetrating shell structure based on the Material Point Method (MPM) and successfully simulates the failure process of crevasses. A comparison is made between the simulation results and the experimental results, showing that the MPM simulation results match the experimental results more closely, thus verifying the effectiveness of researching the crevasse failure process in the context of a projectile penetrating a ship's plate and providing a new approach to researching missiles penetrating a ship's shell plate. On the basis of the simulation model, simulations are made of a projectile penetrating 5 mm and 10 mm target plates with various velocities. [Results] The findings indicate that the crevasse size and plastic deformation area of the target plates are basically unchanged, and the crevasse size is slightly larger than the diameter of the projectile, with a ‘washing crevasse’ fracture mode. The target plate exhibits a plugging failure mode when hemispherical head projectiles penetrate such as the hull of shup at low, medium and high speed, and the speed has little influence on the size of the crevasses in the target plates while having a great influence on the height of the bump at the crevasse. [Conclusions] The results of this study can provide useful references for the protection design of ship structures.

[Objectives] The petaling of a ductile metal plate penetrated by a sharp-nosed missiles is a common damage mode. In order to analyze its formation process, numerical simulation is carried out. [Methods] First, a simulation model of striking the metal plate by sharp-nosed missile is established on the basis of experiments involving missiles perforating targets, and the material constants are acquired from material mechanical characteristic experiments. The petaling procedure is then studied, as well as the stress states of typical elements in the petaling cracking area. The influence on the simulation results is subsequently contrasted by different failure criteria. [Results] The results show that the petaling process is complex and can be mainly divided into four distinct stages:butterfly heaving, hole enlargement, petal appearance and expansion, and entire movement of damaged region. The stress states of the cracking area are complicated and the petaling shape cannot be sufficiently predicted by the constant strain criterion; this requires the introduction of the JC failure model which considers the influence of stress triaxiality. [Conclusions] The results of this paper can provide references for the modification of typical petaling cracking theory and evaluation.

[Objectives] This paper aims to analyze the protective performance of different broadside protection structures subjected to semi-armor-piercing missile warheads. [Methods] Single-layer homogeneous steel armor structures and double-grid protection structures are designed, and the protective performance of different broadside protection structures in blocking medium subsonic semi-armor-piercing missile warheads is compared via numerical simulation. [Results] The results show that it is easy to design single-layer homogenous steel armor for use as broadside protection structure, but high strength steel with excellent mechanical properties should be used and the thickness should be more than 50 mm. In addition, consideration should be given to the construction of thin plates and thick plates, as well as the electrochemical corrosion of different types of steel. The above problems can be avoided by using a double-layer structure as the broadside protection structure. For double-grid protection structures, the weight resources should be allocated to the inner plate by increasing its thickness, thereby improving the overall protective ability of the double-grid protection structure. [Conclusions] The results of this study can provide useful references for the design of broadside protection structures capable of withstanding semi-armor-piercing missile warheads.

[Objectives] The cone-toroid-cone structure is a new type of structure to solve the problem of stress concentration at the joint of two conical shells with different angles in a pressure hull of submarine. The pupose of this paper is to discuss the effects of the cone-cone shell transition on its connection structure,as well as the feasibility of the cone-toroid-cone structure and applicable range of conical angle.[Methods] A series of ring-stittened cone-toroid-cone and cone-cone structural model are established using ANSYS finite element method. The typical stress and elastic stability of the two above mentioned transition sections at different cone angles are obtained using the models. Through comparative analysis, the influence of the toroidal transition on the mechanical properties of cone-cone structures with different angles is obtained.[Results] The results show that the greater the difference in conical angle between the left and right conical shells,the greater the effect of reducing peak stress using toroidal shells. When the conical angle different on both sides (γ1-γ2

[Objectives] This paper involves the propagation and attenuation of the velocity and energy of air-blast waves and high-velocity fragments while taking their combined effects into account.[Methods] With ANSYS/LS-DYNA software, a simulation model of a columnar TNT air blast is built with prefabricated fragments affixed to its end. When the total quality of fragments is constant, the effects of a single fragment's size on the propagation of the air-blast wave and fragments are studied by changing the size of the single fragment.[Results] The results show that fragments greatly reduce the intensity and velocity of a shockwave, and block the air-blast waves behind them. When the total quality of the fragments remains constant, the effects of single fragment size on blast shockwave propagation characteristics show little difference. The smaller the single fragment, the more kinetic energy the fragments will have and the faster that energy will dissipate.[Conclusions] As a result, more attention should be paid to the combined effects of air-blast waves and high-velocity fragments. Such research can provide reference points for the deeper study of blast loads and their interaction.

[Objectives] This paper aims to study the effects of initial cracks on the dynamic response of aluminum alloy plate under repeated impacts.[Methods] Through the repeated impact test and finite element simulation of the aluminum alloy plate, we analyze the dynamic response characteristics of the aluminum alloy plate under repeated impacts, and compare the impact loads and failure modes of the aluminum alloy plate with and without initial cracks.[Results] The test results are in good agreement with the simulation calculations. The results show that the aluminum alloy plate is sensitive to initial cracks under repeated impacts;the initial cracks can reduce the load carrying capacity of the aluminum alloy plate,resulting in the reduced impact load and the reduced number of the repeated impacts for failure; the failure modes are also influenced by the initial cracks under repeated impacts.[Conclusions] The research in this paper provides a certain basis and reference for calculating and evaluating the structure strength of aluminum alloy hull plate.

[Objectives] In order to study how dynamic motion of explosive, initial interface disturbance and grid size affect the overpressure load of internal explosion,[Methods] the spatial and temporal terms of the two-dimensional compressible Euler equations are discretized numerically using the fifth-order WNEO finite difference scheme and the third-order TVD Runge-Kutta scheme. Based on Fortran platform, an in-house high-precision numerical calculation program of blast wave in confined space was developed. The impacts of the overpressure load of the internal explosion were preliminarily discussed adopting the developed program.[Results] The results show that, increasing charge movement speed, selecting a specific interface disturbance and decreasing the size of the grid can significantly increase shock wave peaks of internal explosion, but has little effect on quasi-static overpressure load.[Conclusions] The research in this paper can provide certain reference and basis for the design of anti-explosion structure and the evaluation of internal explosion damage.

[Objectives] The maneuverability prediction of small saildrone plays a key role in achieving intelligent tracking and navigation. In order to study the relationship between rudder angle and hull motion, and to predict the maneuverability accurately,[Methods] in this paper, the numerical simulation method is used to systematically study the ship-rudder oblique viscous flow field model and hydrodynamic properties of saildrone. Before simulation of hydrodynamic properties of ship-rudder system, the numerical calculation results and theoretical method of the hull and open water rudder are preliminarily validated. Then the numerical calculation of ship-rudder oblique viscous flow field of saildrone is carried out. Finally,the MMG (ship manoeuvring mathematical model group) method is used to establish the maneuver motion model of the saildrone. The fourth-order Runge-Kutta method is used to solve the differential equation. The influence of the rudder on the maneuverability of the hull is analyzed by simulating the hull zigzag navigation.[Results] The results show that it is feasible to predict the maneuverability of the saildrone with CFD method.[Conclusions] The maneuverability of the hull is applicable for the safe navigation of saildrone in defined conditions.