In the present paper, the lateral dynamic flight stability properties of two hovering model insects are predicted by an approximate theory based on the averaged model, and computed by numerical simulation that solves ...In the present paper, the lateral dynamic flight stability properties of two hovering model insects are predicted by an approximate theory based on the averaged model, and computed by numerical simulation that solves the complete equations of motion coupled with the Naviertokes equations. Comparison between the theoretical and simulational results provides a test to the validity of the assumptions made in the theory. One of the insects is a model dronefly which has relatively high wingbeat frequency （164Hz） and the other is a model hawkmoth which has relatively low wingbeat frequency （26 Hz）. The following conclusion has been drawn. The theory based on the averaged model works well for the lateral motion of the dronefly. For the hawkmoth, relatively large quantitative differences exist between theory and simulation. This is because the lateral non-dimensional eigenvalues of the hawkmoth are not very small compared with the non-dimensional flapping frequency （the largest lateral non-dimensional eigenvalue is only about 10% smaller than the non-dimensional flapping frequency）. Nevertheless, the theory can still correctly predict variational trends of the dynamic properties of the hawkmoth＇s lateral motion.展开更多
The mined-out area of a gypsum mine is right un-derneath civil constructions of a township, threatening the safety of the latter. To evaluate the long-term stability of the mined-out area, a visco-elastic plastic fini...The mined-out area of a gypsum mine is right un-derneath civil constructions of a township, threatening the safety of the latter. To evaluate the long-term stability of the mined-out area, a visco-elastic plastic finite element analysis is carried out,combined with in situ measurements. The visco-elastic plastic coefficients have been determined through laboratory rock creep tests. Noticing the lim-itations of conventional element failure criteria,the authors proposed a new method to evaluate the stability of the element.i. e. ,by a si-multaneous control of the energy density and strain of the element. Computation showed that at stable state,one third of the pillars are in the visco-plastic state,the rest of the pillars ,the roof and floor are still in the visco-elastic state. The stress concentration coefficient at the boundary of pillars and roof is 2. 3,and the maximum verti-cal stress on the pillars is 11. 8 MPa. Data measured on site are con-sistent with the computation results, indicating that the proposed cal-culation method is correct. Therefore, the current mined-out area is stable,and the dimension of pillars is reasonable. The next-step ex-traction work should be carried out maintaining the current parame-ters,with only a moderate increase in pillar sizes to enhance the sta-bility of the pillars.展开更多
The initial-boundary value problem for a class of nonlinear hyperbolic equations system in bounded domain is studied. The existence of global solutions for this problem is proved by constructing a stable set, and obta...The initial-boundary value problem for a class of nonlinear hyperbolic equations system in bounded domain is studied. The existence of global solutions for this problem is proved by constructing a stable set, and obtain the asymptotic stability of global solutions by means of a difference inequality.展开更多
基金supported by the National Natural Science Foundation of China (10732030)the Foundation for the Author of National Excellent Doctoral Dissertation (2007B31)
文摘In the present paper, the lateral dynamic flight stability properties of two hovering model insects are predicted by an approximate theory based on the averaged model, and computed by numerical simulation that solves the complete equations of motion coupled with the Naviertokes equations. Comparison between the theoretical and simulational results provides a test to the validity of the assumptions made in the theory. One of the insects is a model dronefly which has relatively high wingbeat frequency （164Hz） and the other is a model hawkmoth which has relatively low wingbeat frequency （26 Hz）. The following conclusion has been drawn. The theory based on the averaged model works well for the lateral motion of the dronefly. For the hawkmoth, relatively large quantitative differences exist between theory and simulation. This is because the lateral non-dimensional eigenvalues of the hawkmoth are not very small compared with the non-dimensional flapping frequency （the largest lateral non-dimensional eigenvalue is only about 10% smaller than the non-dimensional flapping frequency）. Nevertheless, the theory can still correctly predict variational trends of the dynamic properties of the hawkmoth＇s lateral motion.
文摘The mined-out area of a gypsum mine is right un-derneath civil constructions of a township, threatening the safety of the latter. To evaluate the long-term stability of the mined-out area, a visco-elastic plastic finite element analysis is carried out,combined with in situ measurements. The visco-elastic plastic coefficients have been determined through laboratory rock creep tests. Noticing the lim-itations of conventional element failure criteria,the authors proposed a new method to evaluate the stability of the element.i. e. ,by a si-multaneous control of the energy density and strain of the element. Computation showed that at stable state,one third of the pillars are in the visco-plastic state,the rest of the pillars ,the roof and floor are still in the visco-elastic state. The stress concentration coefficient at the boundary of pillars and roof is 2. 3,and the maximum verti-cal stress on the pillars is 11. 8 MPa. Data measured on site are con-sistent with the computation results, indicating that the proposed cal-culation method is correct. Therefore, the current mined-out area is stable,and the dimension of pillars is reasonable. The next-step ex-traction work should be carried out maintaining the current parame-ters,with only a moderate increase in pillar sizes to enhance the sta-bility of the pillars.
基金supported by National Natural Science Foundation of China(61273016)The Natural Science Foundation of Zhejiang Province(Y6100016)The Public Welfare Technology Application Research Project of Zhejiang Province Science and Technology Department(2015C33088)
文摘The initial-boundary value problem for a class of nonlinear hyperbolic equations system in bounded domain is studied. The existence of global solutions for this problem is proved by constructing a stable set, and obtain the asymptotic stability of global solutions by means of a difference inequality.
基金Supported by the National Natural Science Foundation of China(11371048)the Plan Project of Science and Technology of Beijing Municipal Education Committee(KM201610016018)the Central Support Local Projects(21147515602)
