When ordinary Smoothed Particle Hydrodynamics （SPH） method is used to simulate wave propagation in a wave tank, it is usually observed that the wave height decays and the wave length elongates along the direction of...When ordinary Smoothed Particle Hydrodynamics （SPH） method is used to simulate wave propagation in a wave tank, it is usually observed that the wave height decays and the wave length elongates along the direction of wave propagation. Accompanied with this phenomenon, the pressure under water decays either and shows a big oscillation simultaneously. The reason is the natural potential tensile instability of modeling water motion with ordinary SPH which is caused by particle negative stress in the computation. I＇o deal with the problems, a new sextic kernel function is proposed to reduce this instability. An appropriate smooth length is given and its computation criterion is also suggested. At the same time, a new kind dynamic boundary condition is introduced. Based on these improvements, the new SPH method named stability improved SPH （SISPH） can simulate the wave propagation well. Both the water surface and pressure can be well expressed and the oscillation of pressure is nearly eliminated. Compared with other improved methods, SISPH can truly reveal the physical reality without bringing some new problems in a simple way.展开更多
Two kinds of fractures can be observed in the SPH （smoothed particle hydrodynamics） simulations, which are the physical fracture and the numerical fracture. The physical one exists in reality, while the numerical on...Two kinds of fractures can be observed in the SPH （smoothed particle hydrodynamics） simulations, which are the physical fracture and the numerical fracture. The physical one exists in reality, while the numerical one is fictitious. This paper presents the effects of both fractures and proposes a simple adding particle technique to avoid the numerical fracture. The real physical fracture is then figured out by using an applicable fracture criterion. Firstly, the effect of the numerical fracture on the computational accuracy is investigated by introducing the artificial fracture in a model of wave propagation. Secondly, a simple adding particle technique is proposed and validated by a three dimensional bending test. Finally, the experiments of penetration on the skin of aircrafts are simulated by both the initial SPH method and the improved method with the adding particle technique. The results show that the improved SPH method can describe the physical fracture very well with better accuracy.展开更多
In this paper,the smoothed particle hydrodynamics(SPH)method is employed in modeling and numerical simulation of droplet coalescence.Considering the effect of tangential force on boundary material,besides normal force...In this paper,the smoothed particle hydrodynamics(SPH)method is employed in modeling and numerical simulation of droplet coalescence.Considering the effect of tangential force on boundary material,besides normal force,tangential force is also introduced in the continuum surface force(CSF)model.The formation of droplet,the coalescence processes of two droplets and three droplets are simulated by the modified CSF model.The validity of the modified model is verified from the aspects of the morphological change of the droplet,the smoothness of free surface and the conservation of the centroid of the system.Compared with finite element method,the results of the modified CSF model show that tangential force plays a crucial role in the CSF model when dealing with model boundary with curves and sharp angles.展开更多
This paper investigates the effects of charge parameters of the underwater contact explosion based on the axisymmetric smoothed particle hydrodynamics （SPH） method. The dynamic boundary particle is proposed to impro...This paper investigates the effects of charge parameters of the underwater contact explosion based on the axisymmetric smoothed particle hydrodynamics （SPH） method. The dynamic boundary particle is proposed to improve the pressure fluctuation and numerical accuracy near the symmetric axis. An in-depth study is carried out over the influence of charge shapes and detonation modes on the near-field loads in terms of the peak pressure and impulse of shock waves. For different charge shapes, the cylindrical charge with different length-diameter ratios may cause strong directivity of peak pressure and impulse in the near field. Compared with spherical charge, the peak pressure of cylindrical charge may be either weakened or enhanced in different directions. Within a certain range, the greater the length-diameter ratio is, the more obvious the effect will be. The weakened ratio near the detonation end may reach 25% approximately, while the enhanced ratio may reach around 20% in the opposite direction. However, the impulse in different directions seems to be uniform. For different detonation modes, compared with point-source explosion, the peak pressure of plane-source explosion is enhanced by about 5%. Besides, the impulse of plane-source explosion is enhanced by around 5% near the detonation end, but close to those of the point-source explosion in other directions. Based on the material constitutive relation in the axisymmetric coordinates, a simple case of underwater contact explosion is simulated to verify the above conclusions, showing that the charge parameters of underwater contact explosion should not be ignored.展开更多
The water mitigation effect on the propagation of shock wave was investigated numerically. The traditional smoothed particle hydrodynamics (SPH) method was modified based on Riemann solution. The comparison of numeric...The water mitigation effect on the propagation of shock wave was investigated numerically. The traditional smoothed particle hydrodynamics (SPH) method was modified based on Riemann solution. The comparison of numerical results with the analytical solution indicated that the modified SPH method has more advantages than the traditional SPH method. Using the modified SPH algorithm, a series of one-dimensional planar wave propagation problems were investigated, focusing on the influence of the air-gap between the high-pressure air and water and the thickness of water. The numerical results showed that water mitigation effect is significant. Up to 60% shock wave pressure reduction could be achieved with the existence of water, and the shape of shock wave was also changed greatly. It is seemly that the small air-gap between the high-pressure air and water has more influence on water mitigation effect.展开更多
为研究鸟撞飞机典型结构过程中鸟体姿态对鸟撞损伤的影响规律,以某型水陆两栖飞机-机翼前缘这一典型结构为研究对象,通过光滑粒子流体动力学(Smoothed Particle Hydrodynamics,SPH)耦合有限元法(Finite Element Method,FEM)建立鸟撞数...为研究鸟撞飞机典型结构过程中鸟体姿态对鸟撞损伤的影响规律,以某型水陆两栖飞机-机翼前缘这一典型结构为研究对象,通过光滑粒子流体动力学(Smoothed Particle Hydrodynamics,SPH)耦合有限元法(Finite Element Method,FEM)建立鸟撞数值模型,并通过鸟撞试验验证计算模型的准确性。最后,以试验修正后的机翼前缘数值模型为依托,研究分析鸟体俯仰和偏航12种撞击姿态下机翼前缘的损伤变形情况和冲击响应规律。结果表明,仿真分析和试验结果通过一致性验证;蒙皮凹坑和凹陷范围随鸟体姿态角增大而增大,鸟体剩余能量随之降低;俯仰角增大,前缘结构吸收的能量更多,蒙皮高应力区增大,结构更易破坏。因此对于鸟撞威胁影响更大的重要飞机结构的抗鸟撞安全评估应计入鸟体姿态的影响。研究结果可在飞机抗鸟撞设计与适航评估方面提供重要参考。展开更多
In this paper,we study a class of contact smoothed particle hydrodynamics(SPH)by introducing Riemann solvers and using high-order limiters.In particular,a promising concept ofWENO interpolation as limiter is presented...In this paper,we study a class of contact smoothed particle hydrodynamics(SPH)by introducing Riemann solvers and using high-order limiters.In particular,a promising concept ofWENO interpolation as limiter is presented in the reconstruction process.The physical values relating interactional particles used as the initial values of the Riemann problemcan be reconstructed by the Taylor series expansion.The contact solvers of the Riemann problem at contact points are incorporated in SPH approximations.In order to keep the fluid density at the wall rows to be consistent with that of the inner fluid wall boundaries,several lines of dummy particles are placed outside of the solid walls,which are assigned according to the initial configuration.At last,the method is applied to compressible flows with sharp discontinuities such as the collision of two strong shocks and the interaction of two blast waves and so on.The numerical results indicate that the method is capable of handling sharp discontinuity and efficiently reducing unphysical oscillations.展开更多
Based on the SPH method,this paper investigates a number of key issues in shock dynamics,including the nonlinear phenomenon and its influencing factors in the propagation process of shock waves,and the process and mec...Based on the SPH method,this paper investigates a number of key issues in shock dynamics,including the nonlinear phenomenon and its influencing factors in the propagation process of shock waves,and the process and mechanism of the interaction between shock waves and the surface of an object.Through the design of the experiments and the analysis of the results,the main conclusions and contributions of this study are drawn.At the same time,deficiencies and directions for further improvement are also pointed out,and prospects and suggestions for future research on impact dynamics are presented.This study is of great significance in promoting the research of impact dynamics.展开更多
This paper applies the meshfree Smoothed Particle Hydrodynamics （SPH） method with Graphical Processing Unit （GPU） parallel computing technique to investigate the highly complex 3-D dam-break flow in urban areas in...This paper applies the meshfree Smoothed Particle Hydrodynamics （SPH） method with Graphical Processing Unit （GPU） parallel computing technique to investigate the highly complex 3-D dam-break flow in urban areas including underground spaces. Taking the advantage of GPUs parallel computing techniques, simulations involving more than 107 particles can be achieved. We use a virtual geometric plane boundary to handle the outermost solid wall in order to save considerable video card memory for the GPU computing. To evaluate the accuracy of the new GPU-based SPH model, qualitative and quantitative comparison to a real flooding experiment is performed and the results of a numerical model based on Shallow Water Equations （SWEs） is given with good accuracy. With the new GPU-based SPH model, the effects of the building layouts and underground spaces on the propagation of dambreak flood through an intricate city layout are examined.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51579038 and 51490672)the National Basic Research Program of China(Grant No.2013CB036101)
文摘When ordinary Smoothed Particle Hydrodynamics （SPH） method is used to simulate wave propagation in a wave tank, it is usually observed that the wave height decays and the wave length elongates along the direction of wave propagation. Accompanied with this phenomenon, the pressure under water decays either and shows a big oscillation simultaneously. The reason is the natural potential tensile instability of modeling water motion with ordinary SPH which is caused by particle negative stress in the computation. I＇o deal with the problems, a new sextic kernel function is proposed to reduce this instability. An appropriate smooth length is given and its computation criterion is also suggested. At the same time, a new kind dynamic boundary condition is introduced. Based on these improvements, the new SPH method named stability improved SPH （SISPH） can simulate the wave propagation well. Both the water surface and pressure can be well expressed and the oscillation of pressure is nearly eliminated. Compared with other improved methods, SISPH can truly reveal the physical reality without bringing some new problems in a simple way.
基金supported by the National Natural Science Foundation of China (No.10577016)the 111 Project (No. B07050)the program for 2008 New Century Excellent Talents in University (No.NCET080454)
文摘Two kinds of fractures can be observed in the SPH （smoothed particle hydrodynamics） simulations, which are the physical fracture and the numerical fracture. The physical one exists in reality, while the numerical one is fictitious. This paper presents the effects of both fractures and proposes a simple adding particle technique to avoid the numerical fracture. The real physical fracture is then figured out by using an applicable fracture criterion. Firstly, the effect of the numerical fracture on the computational accuracy is investigated by introducing the artificial fracture in a model of wave propagation. Secondly, a simple adding particle technique is proposed and validated by a three dimensional bending test. Finally, the experiments of penetration on the skin of aircrafts are simulated by both the initial SPH method and the improved method with the adding particle technique. The results show that the improved SPH method can describe the physical fracture very well with better accuracy.
文摘In this paper,the smoothed particle hydrodynamics(SPH)method is employed in modeling and numerical simulation of droplet coalescence.Considering the effect of tangential force on boundary material,besides normal force,tangential force is also introduced in the continuum surface force(CSF)model.The formation of droplet,the coalescence processes of two droplets and three droplets are simulated by the modified CSF model.The validity of the modified model is verified from the aspects of the morphological change of the droplet,the smoothness of free surface and the conservation of the centroid of the system.Compared with finite element method,the results of the modified CSF model show that tangential force plays a crucial role in the CSF model when dealing with model boundary with curves and sharp angles.
基金supported by the National Natural Science Foundation of China(No.51379039)the Excellent Young Scientists Fund(No.51222904)
文摘This paper investigates the effects of charge parameters of the underwater contact explosion based on the axisymmetric smoothed particle hydrodynamics （SPH） method. The dynamic boundary particle is proposed to improve the pressure fluctuation and numerical accuracy near the symmetric axis. An in-depth study is carried out over the influence of charge shapes and detonation modes on the near-field loads in terms of the peak pressure and impulse of shock waves. For different charge shapes, the cylindrical charge with different length-diameter ratios may cause strong directivity of peak pressure and impulse in the near field. Compared with spherical charge, the peak pressure of cylindrical charge may be either weakened or enhanced in different directions. Within a certain range, the greater the length-diameter ratio is, the more obvious the effect will be. The weakened ratio near the detonation end may reach 25% approximately, while the enhanced ratio may reach around 20% in the opposite direction. However, the impulse in different directions seems to be uniform. For different detonation modes, compared with point-source explosion, the peak pressure of plane-source explosion is enhanced by about 5%. Besides, the impulse of plane-source explosion is enhanced by around 5% near the detonation end, but close to those of the point-source explosion in other directions. Based on the material constitutive relation in the axisymmetric coordinates, a simple case of underwater contact explosion is simulated to verify the above conclusions, showing that the charge parameters of underwater contact explosion should not be ignored.
基金Supported by National Natural Science Foundation of China(No.50638030 and 50525825)National Science and Technology Support Program(No.2006BAJ13B02)
文摘The water mitigation effect on the propagation of shock wave was investigated numerically. The traditional smoothed particle hydrodynamics (SPH) method was modified based on Riemann solution. The comparison of numerical results with the analytical solution indicated that the modified SPH method has more advantages than the traditional SPH method. Using the modified SPH algorithm, a series of one-dimensional planar wave propagation problems were investigated, focusing on the influence of the air-gap between the high-pressure air and water and the thickness of water. The numerical results showed that water mitigation effect is significant. Up to 60% shock wave pressure reduction could be achieved with the existence of water, and the shape of shock wave was also changed greatly. It is seemly that the small air-gap between the high-pressure air and water has more influence on water mitigation effect.
文摘为研究鸟撞飞机典型结构过程中鸟体姿态对鸟撞损伤的影响规律,以某型水陆两栖飞机-机翼前缘这一典型结构为研究对象,通过光滑粒子流体动力学(Smoothed Particle Hydrodynamics,SPH)耦合有限元法(Finite Element Method,FEM)建立鸟撞数值模型,并通过鸟撞试验验证计算模型的准确性。最后,以试验修正后的机翼前缘数值模型为依托,研究分析鸟体俯仰和偏航12种撞击姿态下机翼前缘的损伤变形情况和冲击响应规律。结果表明,仿真分析和试验结果通过一致性验证;蒙皮凹坑和凹陷范围随鸟体姿态角增大而增大,鸟体剩余能量随之降低;俯仰角增大,前缘结构吸收的能量更多,蒙皮高应力区增大,结构更易破坏。因此对于鸟撞威胁影响更大的重要飞机结构的抗鸟撞安全评估应计入鸟体姿态的影响。研究结果可在飞机抗鸟撞设计与适航评估方面提供重要参考。
文摘泥石流作为高破坏性混合流体,其携带的块石对框架结构的冲击机制尚未得到充分研究。为揭示含块石泥石流冲击框架结构的动力响应与损伤机制,基于光滑粒子流体动力学-离散元法-有限元法(smoothed particle hydrodynamics-discrete element method-finite element method,SPH-DEM-FEM)耦合数值方法,构建流体-块石-结构的多耦合数值模型,模拟不同冲击速度和角度下框架结构的损伤过程,并结合两相溃坝试验来验证模型有效性。研究表明:泥石流冲击导致结构损伤经历“接触-扩散-反弹-堆积/冲击”四个阶段,当冲击速度超过6.00 m/s时,结构产生不可恢复损伤,且块石阻隔作用使流体上部冲击力大于下部,引发结构中部最先发生集中损伤;此外,冲击力峰值随速度和角度增大呈非线性增长,10.00 m/s与90°工况下框架柱底冲击力达497.17 kN,超过结构抗冲击承载力;最后,数值模拟与经验公式所得冲击力结果误差在13.95%~29.00%,数量级一致,验证了模型可靠性。研究结果可为泥石流高发区框架结构的抗冲击设计提供参考。
基金supported by the Fundamental Research Funds of Central University(B103093)Key Laboratory Foundation of Coastal Disasters.
文摘In this paper,we study a class of contact smoothed particle hydrodynamics(SPH)by introducing Riemann solvers and using high-order limiters.In particular,a promising concept ofWENO interpolation as limiter is presented in the reconstruction process.The physical values relating interactional particles used as the initial values of the Riemann problemcan be reconstructed by the Taylor series expansion.The contact solvers of the Riemann problem at contact points are incorporated in SPH approximations.In order to keep the fluid density at the wall rows to be consistent with that of the inner fluid wall boundaries,several lines of dummy particles are placed outside of the solid walls,which are assigned according to the initial configuration.At last,the method is applied to compressible flows with sharp discontinuities such as the collision of two strong shocks and the interaction of two blast waves and so on.The numerical results indicate that the method is capable of handling sharp discontinuity and efficiently reducing unphysical oscillations.
文摘Based on the SPH method,this paper investigates a number of key issues in shock dynamics,including the nonlinear phenomenon and its influencing factors in the propagation process of shock waves,and the process and mechanism of the interaction between shock waves and the surface of an object.Through the design of the experiments and the analysis of the results,the main conclusions and contributions of this study are drawn.At the same time,deficiencies and directions for further improvement are also pointed out,and prospects and suggestions for future research on impact dynamics are presented.This study is of great significance in promoting the research of impact dynamics.
基金Project supported by the National Basic Research Development Program of China(973 Program,No.2012CB719705)the National Natural Science Foundation of China(Grant Nos.91024032,70833003)
文摘This paper applies the meshfree Smoothed Particle Hydrodynamics （SPH） method with Graphical Processing Unit （GPU） parallel computing technique to investigate the highly complex 3-D dam-break flow in urban areas including underground spaces. Taking the advantage of GPUs parallel computing techniques, simulations involving more than 107 particles can be achieved. We use a virtual geometric plane boundary to handle the outermost solid wall in order to save considerable video card memory for the GPU computing. To evaluate the accuracy of the new GPU-based SPH model, qualitative and quantitative comparison to a real flooding experiment is performed and the results of a numerical model based on Shallow Water Equations （SWEs） is given with good accuracy. With the new GPU-based SPH model, the effects of the building layouts and underground spaces on the propagation of dambreak flood through an intricate city layout are examined.
