在飞行器的气动外形优化设计中,参数化方法和优化算法具有十分重要的作用,对优化的计算时间设计空间的数学特性有着深刻的影响.类别形状函数(class and shape transformation,CST)方法是一种简洁高效的参数化方法,但对于复杂曲面很难使...在飞行器的气动外形优化设计中,参数化方法和优化算法具有十分重要的作用,对优化的计算时间设计空间的数学特性有着深刻的影响.类别形状函数(class and shape transformation,CST)方法是一种简洁高效的参数化方法,但对于复杂曲面很难使用统一的CST方法进行拟合.文章首先介绍了CST方法的三维实现,分析了其数学性质,提出了分块CST参数化方法,保留CST方法的特性,实现了分块曲面之间的光滑连接.针对气动外形优化设计的复杂情况,需要根据具体的飞行任务提出设计目标,并处理不同目标的矛盾问题.其次采用Pareto策略自动寻找最优方案集,并基于分块CST参数化方法遗传算法和气动力快速计算方法,对类乘波翼身组合飞行器进行了优化设计,并改变原有问题的设定条件优化得到了全新外形.研究结果表明分块CST方法参数少,精度高,Pareto策略处理多目标准确有效,是气动外形优化设计中非常有用的工具.展开更多
A pneumatic launcher is theoretically investigated to study its natural transverse vibration in water. Considering the mass effect of the sealing cover, the launcher is simplified as a uniform cantilever beam with a t...A pneumatic launcher is theoretically investigated to study its natural transverse vibration in water. Considering the mass effect of the sealing cover, the launcher is simplified as a uniform cantilever beam with a top point mass. By introducing the boundary and continuity conditions into the motion equation, the natural frequency equation and the mode shape function are derived. An iterative calculation method for added mass is also presented using the velocity potential function to account for the mass effect of the fluid on the launcher. The first 2 order natural frequencies and mode shapes are discussed in external flow fields and both external and internal flow fields. The results show good agreement with both natural frequencies and mode shapes between the theoretical analysis and the FEM studies. Also, the added mass is found to decrease with the increase of the mode shape orders of the launcher. And because of the larger added mass in both the external and internal flow fields than that in only the external flow field, the corresponding natural frequencies of the former are relatively smaller.展开更多
In this work, a novel numerical method is developed for simulating arbitrary crack growth in pipes with the idea of enriched shape functions which can represent the discontinuity independent of the mesh. The concept o...In this work, a novel numerical method is developed for simulating arbitrary crack growth in pipes with the idea of enriched shape functions which can represent the discontinuity independent of the mesh. The concept of the enriched shape functions is introduced into the continuum-based (CB) shell element. Due to the advantage of CB shell element, the shell thickness varia- tion and surface connection can be concerned during the deformation. The stress intensity factors of the crack in the CB shell element are calculated by using the 'equivalent domain integral' method for 3D arbitrary non-planar crack. The maximum en- ergy release rate is used as a propagation criterion. This method is proved able to capture arbitrary crack growth path in pipes which is independent of the element mesh. Numerical examples of different fracture patterns in pipes are presented here.展开更多
With the speed upgrade of the high-speed train,the aerodynamic drag becomes one of the key factors to restrain the train speed and energy saving.In order to reduce the aerodynamic drag of train head,a new parametric a...With the speed upgrade of the high-speed train,the aerodynamic drag becomes one of the key factors to restrain the train speed and energy saving.In order to reduce the aerodynamic drag of train head,a new parametric approach called local shape function(LSF) was adopted based on the free form surface deformation(FFD) method and a new efficient optimization method based on the response surface method(RSM) of GA-GRNN.The optimization results show that the parametric method can control the large deformation with a few design parameters,and can ensure the deformation zones smoothness and smooth transition of different deformation regions.With the same sample points for training,GA-GRNN performs better than GRNN to get the global optimal solution.As an example,the aerodynamic drag for a simplified shape with head + one carriage + tail train is reduced by 8.7%.The proposed optimization method is efficient for the engineering design of high-speed train.展开更多
文摘在飞行器的气动外形优化设计中,参数化方法和优化算法具有十分重要的作用,对优化的计算时间设计空间的数学特性有着深刻的影响.类别形状函数(class and shape transformation,CST)方法是一种简洁高效的参数化方法,但对于复杂曲面很难使用统一的CST方法进行拟合.文章首先介绍了CST方法的三维实现,分析了其数学性质,提出了分块CST参数化方法,保留CST方法的特性,实现了分块曲面之间的光滑连接.针对气动外形优化设计的复杂情况,需要根据具体的飞行任务提出设计目标,并处理不同目标的矛盾问题.其次采用Pareto策略自动寻找最优方案集,并基于分块CST参数化方法遗传算法和气动力快速计算方法,对类乘波翼身组合飞行器进行了优化设计,并改变原有问题的设定条件优化得到了全新外形.研究结果表明分块CST方法参数少,精度高,Pareto策略处理多目标准确有效,是气动外形优化设计中非常有用的工具.
基金Foundation item： Supported by the National Natural Science Foundation of China （51379083） and the Specialized Research Fund for the Doctoral Program of Hiher Education （20120142110051）.
文摘A pneumatic launcher is theoretically investigated to study its natural transverse vibration in water. Considering the mass effect of the sealing cover, the launcher is simplified as a uniform cantilever beam with a top point mass. By introducing the boundary and continuity conditions into the motion equation, the natural frequency equation and the mode shape function are derived. An iterative calculation method for added mass is also presented using the velocity potential function to account for the mass effect of the fluid on the launcher. The first 2 order natural frequencies and mode shapes are discussed in external flow fields and both external and internal flow fields. The results show good agreement with both natural frequencies and mode shapes between the theoretical analysis and the FEM studies. Also, the added mass is found to decrease with the increase of the mode shape orders of the launcher. And because of the larger added mass in both the external and internal flow fields than that in only the external flow field, the corresponding natural frequencies of the former are relatively smaller.
基金supported by the National Natural Science Foundation of China (Grant No. 11011140335)
文摘In this work, a novel numerical method is developed for simulating arbitrary crack growth in pipes with the idea of enriched shape functions which can represent the discontinuity independent of the mesh. The concept of the enriched shape functions is introduced into the continuum-based (CB) shell element. Due to the advantage of CB shell element, the shell thickness varia- tion and surface connection can be concerned during the deformation. The stress intensity factors of the crack in the CB shell element are calculated by using the 'equivalent domain integral' method for 3D arbitrary non-planar crack. The maximum en- ergy release rate is used as a propagation criterion. This method is proved able to capture arbitrary crack growth path in pipes which is independent of the element mesh. Numerical examples of different fracture patterns in pipes are presented here.
基金supported by the National Basic Research Program of China ("973" Project) (Grant No. 2011CB711100)the National Hi-Tech Research and Development Program of China ("863" Project) (Grant No.2009BAQG12A03)Computing Facility for Computational Mechanics,Institute of Mechanics,Chinese Academy of Sciences
文摘With the speed upgrade of the high-speed train,the aerodynamic drag becomes one of the key factors to restrain the train speed and energy saving.In order to reduce the aerodynamic drag of train head,a new parametric approach called local shape function(LSF) was adopted based on the free form surface deformation(FFD) method and a new efficient optimization method based on the response surface method(RSM) of GA-GRNN.The optimization results show that the parametric method can control the large deformation with a few design parameters,and can ensure the deformation zones smoothness and smooth transition of different deformation regions.With the same sample points for training,GA-GRNN performs better than GRNN to get the global optimal solution.As an example,the aerodynamic drag for a simplified shape with head + one carriage + tail train is reduced by 8.7%.The proposed optimization method is efficient for the engineering design of high-speed train.
