Research on characteristics of water motion and influencing factors for the flexible air chamber jig body

The air bag deformation data were obtained by high-speed dynamic videos experiments. Based on gas–liquid flow VOF model, dynamic mesh technique and deformation data, numerical simulations for different structure models were achieved, and the law of water motion and influencing factors were analyzed.The results show that the flow in the length direction of the jig is smooth, and second pulsation appears in the separation time and forms the secondary separation. The installation position of screen and the number of air bags have a great influence on the uniformity of flow and velocity. The screen height cannot be too low to avoid forming the unstable flow. At the same time, the screen height cannot be too high, otherwise water velocity will be too small and was unable to provide enough power. At the height of 1.4m,velocity unevenness is minimum and the best uniform flow can be obtained. Compared with double air bags, there are the following features of single air bag: water flow is not smooth, the time achieving the maximum velocity is too long, maximum velocity is smaller, and overall effect is worse than double air bags.

Dynamic modeling and simulation for the flexible spacecraft with dynamic stiffening

A rigid flexible coupling physical model which can represent a flexible spacecraft is investigated in this paper. By applying the mechanics theory in a non-inertial coordinate system,the rigid flexible coupling dynamic model with dynamic stiffening is established via the subsystemmodeling framework. It is clearly elucidated for the first time that,dynamic stiffening is produced by the coupling effect of the centrifugal inertial load distributed on the beamand the transverse vibration deformation of the beam. The modeling approach in this paper successfully avoids problems which are caused by other popular modeling methods nowadays： the derivation process is too complex by using only one dynamic principle; a clearly theoretical explanation for dynamic stiffening can＇t be provided. First,the continuous dynamic models of the flexible beamand the central rigid body are established via structural dynamics and angular momentumtheory respectively. Then,based on the conclusions of orthogonalization about the normal constrained modes,the finite dimensional dynamic model suitable for controller design is obtained. The numerical simulation validations showthat： dynamic stiffening is successfully incorporated into the dynamic characteristics of the first-order model established in this paper,which can indicate the dynamic responses of the rigid flexible coupling system with large overall motion accurately,and has a clear modeling mechanism,concise expressions and a good convergence.

Effect of Flexible Spine Motion on Energy Efficiency in Quadruped Running

Energy efficiency is important in the performance of quadruped robots and mammals. Flexible spine motion generally exists in quadruped mammals. This paper mainly explores the effect of flexible spinal motion on energy efficiency. Firstly, a planar simplified model of the quadruped robot with flexible spine motion is introduced and two simulation experiments are carried out. The results of simulation experiments demonstrate that both spine motion and spinal flexibility can indeed increase energy efficiency, and the curve of energy efficiency change along with spinal stiffness is acquired. So, in order to obtain higher energy efficiency, quadruped robots should have flexible spine motion. In a certain speed, there is an optimal spinal stiffness which can make energy efficiency to be the best. Secondly, a planar quadruped robot with flexible spine motion is designed and the conclusions drawn in the two simulation experiments are verified. Lastly, the third simulation experiment is carried out to explore the relationship between the optimal spinal stiffness, speed and total mass. The optimal spinal stiffness increases with both speed and total mass, which has important guiding significance for adjusting the spinal stiffness of quadruped robots to make them reach the best energy efficiency.