The frequency-locked phenomenon commonly occurs in the vortex-induced vibration(VIV)of bluff bodies.Numerical simulation of this lock-in behavior is challenging,especially when the structure is positioned in close pro...The frequency-locked phenomenon commonly occurs in the vortex-induced vibration(VIV)of bluff bodies.Numerical simulation of this lock-in behavior is challenging,especially when the structure is positioned in close proximity to a solid boundary.To establish a robust simulator,an enhanced smoothed particle hydrodynamic(SPH)model is developed.The SPH model incorporates a particle shifting algorithm and a pressure correction algorithm to prevent cavity formation in the structure's wake area.A damping zone is also established near the outlet boundary to dissipate the vortices that shed from the structure.Additionally,GPU parallel technology is implemented to enhance the SPH model's computational efficiency.To validate the mo del,the predicted results are compared with the available refere nce data for flow past both stationary and oscillating cylinders.The verified SPH model is then employed to comparatively investigate the motion re sponse,lift characteristic,and vortex shedding mode of cylinders with and without accounting for the effect of boundary layers.Numerical analyses demonstrate that the developed SPH model is a proficient tool for efficiently simulating the vibration of near-wall bluff bodies at low Reynolds number.展开更多
A droplet undergoes spreading,rebounding or splashing when it impacts solid boundary,which is a typical phenomenon of free surface flow that exists widely in modern industry.Smoothed particle hydrodynamics(SPH)method ...A droplet undergoes spreading,rebounding or splashing when it impacts solid boundary,which is a typical phenomenon of free surface flow that exists widely in modern industry.Smoothed particle hydrodynamics(SPH)method is applied to numerically study the dynamical behaviors of the droplet impacting solid boundary,and both the spreading and rebounding phenomena of the droplet are reproduced in the simulation.The droplet deformation,flow fields and pressure fields inside the droplet at different moments are analyzed.Two important factors,the initial velocity and diameter,are discussed in determining the maximum spreading factor,revealing that the maximum spreading factor increases with the increase of the impact velocity and droplet diameter respectively.展开更多
船舶在冰区海域中航行会受到冰水环境阻力的影响,是冰区船舶快速性研究中的重要影响因素。为合理分析冰区船舶的快速性能,该文采用基于离散元(discrete element method,DEM)和光滑粒子流体动力学(smoothed particle hydrodynamics,SPH)...船舶在冰区海域中航行会受到冰水环境阻力的影响,是冰区船舶快速性研究中的重要影响因素。为合理分析冰区船舶的快速性能,该文采用基于离散元(discrete element method,DEM)和光滑粒子流体动力学(smoothed particle hydrodynamics,SPH)方法的流固耦合模型模拟船舶冰区航行过程,获得不同航速下的船舶阻力和推进力,进一步计算出螺旋桨的推力、扭矩以及定速航行所需的螺旋桨转速等参数。为研究船体结构、海冰与海水之间的流固耦合作用,文中通过SPH粒子与固定粒子边界相对运动的拟合项直接计算固体与流体之间的相互作用力,建立船体结构、海冰与海水耦合的DEM-SPH模型,并基于该模型分别对船舶在冰区的航行阻力和推进力进行模拟,通过拟合的方式匹配航行阻力和推进力,并考虑尾部流场导致的船体阻力增额,从而预报船舶在特定航速下实现自航所需的螺旋桨转速。此外,文中还模拟了DTMB 5415船模在浮冰区和层冰区中航行的阻力和不同螺旋桨转速下的推力,对船模在不同工况下实现特定航速航行所需的螺旋桨转速进行了预报。计算结果表明:DEM-SPH耦合模型对船-冰、桨-冰作用中的流固耦合过程模拟效果出色,可完整描述船体及尾部伴流场对海冰的拖曳作用;通过文中所述阻力-推力模拟算例及强制力的拟合分析,所形成的基于数值模拟方法的船舶自航下螺旋桨转速预报,可为进一步的试验验证和工程应用推广奠定基础。展开更多
The pair-wise forces in the SPH momentum equation guarantee the conservation of momentum, but they cannot prevent particle clustering and wall penetration. Particle clustering may occur for several reasons. A fundamen...The pair-wise forces in the SPH momentum equation guarantee the conservation of momentum, but they cannot prevent particle clustering and wall penetration. Particle clustering may occur for several reasons. A fundamental issue is the tensile instability, which is caused by negative numerical pressures. Clustering may also occur due to certain properties of the kernel gradient. Discontinuities in the pressure and its gradient, due to surface tension and gravity, may cause particle instabilities near the interface between two fluids. Wall penetration is also a form of particle clustering. In this paper the particle collision concept is introduced to suppress particle clustering. Here, the use of kinematic conditions (motion) rather than dynamic conditions (forces) is explored. These kinematic conditions are obtained from kinetic collision theory. Conservation of momentum is maintained, and under elastic conditions conservation of energy as well. The particle collision model only becomes active when needed. It may be seen as a particle shifting method, in the sense that the velocities are changed, and as a consequence of that the particle positions change. It is demonstrated in several case studies that the particle collision model allows for realistic (low) viscosities. It was also found to stabilise the interface between two fluids up to high, realistic density ratios (1000:1) in typical liquid-gas applications. As such it can be used as a multi-fluid model. The concept allows for real wave speed ratios (and far beyond), which, as well as real viscosities, are essential in the modelling of heat transfer applications. The collisions with walls allow for no-slip conditions at real viscosities while wall penetration is suppressed. In summary, the particle collision model makes SPH more robust for engineering.展开更多
基金financially supported by the National Natural Science Foundation of China (Grant Nos.52101312 and 51979028)the Basic and Applied Basic Research Foundation of Guangdong Province (Grant Nos.2022A1515240014 and 2023A1515011000)+1 种基金the Basic and Applied Basic Research Project of Guangzhou (Grant No.202201010240)the Project supported by SKL of HESS (Grant No.HESS-2012)。
文摘The frequency-locked phenomenon commonly occurs in the vortex-induced vibration(VIV)of bluff bodies.Numerical simulation of this lock-in behavior is challenging,especially when the structure is positioned in close proximity to a solid boundary.To establish a robust simulator,an enhanced smoothed particle hydrodynamic(SPH)model is developed.The SPH model incorporates a particle shifting algorithm and a pressure correction algorithm to prevent cavity formation in the structure's wake area.A damping zone is also established near the outlet boundary to dissipate the vortices that shed from the structure.Additionally,GPU parallel technology is implemented to enhance the SPH model's computational efficiency.To validate the mo del,the predicted results are compared with the available refere nce data for flow past both stationary and oscillating cylinders.The verified SPH model is then employed to comparatively investigate the motion re sponse,lift characteristic,and vortex shedding mode of cylinders with and without accounting for the effect of boundary layers.Numerical analyses demonstrate that the developed SPH model is a proficient tool for efficiently simulating the vibration of near-wall bluff bodies at low Reynolds number.
基金Supported by the National Natural Science Foundation of China(No.51079095)the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(No.51021004)
文摘A droplet undergoes spreading,rebounding or splashing when it impacts solid boundary,which is a typical phenomenon of free surface flow that exists widely in modern industry.Smoothed particle hydrodynamics(SPH)method is applied to numerically study the dynamical behaviors of the droplet impacting solid boundary,and both the spreading and rebounding phenomena of the droplet are reproduced in the simulation.The droplet deformation,flow fields and pressure fields inside the droplet at different moments are analyzed.Two important factors,the initial velocity and diameter,are discussed in determining the maximum spreading factor,revealing that the maximum spreading factor increases with the increase of the impact velocity and droplet diameter respectively.
文摘The pair-wise forces in the SPH momentum equation guarantee the conservation of momentum, but they cannot prevent particle clustering and wall penetration. Particle clustering may occur for several reasons. A fundamental issue is the tensile instability, which is caused by negative numerical pressures. Clustering may also occur due to certain properties of the kernel gradient. Discontinuities in the pressure and its gradient, due to surface tension and gravity, may cause particle instabilities near the interface between two fluids. Wall penetration is also a form of particle clustering. In this paper the particle collision concept is introduced to suppress particle clustering. Here, the use of kinematic conditions (motion) rather than dynamic conditions (forces) is explored. These kinematic conditions are obtained from kinetic collision theory. Conservation of momentum is maintained, and under elastic conditions conservation of energy as well. The particle collision model only becomes active when needed. It may be seen as a particle shifting method, in the sense that the velocities are changed, and as a consequence of that the particle positions change. It is demonstrated in several case studies that the particle collision model allows for realistic (low) viscosities. It was also found to stabilise the interface between two fluids up to high, realistic density ratios (1000:1) in typical liquid-gas applications. As such it can be used as a multi-fluid model. The concept allows for real wave speed ratios (and far beyond), which, as well as real viscosities, are essential in the modelling of heat transfer applications. The collisions with walls allow for no-slip conditions at real viscosities while wall penetration is suppressed. In summary, the particle collision model makes SPH more robust for engineering.
