Applied Mechanics and Materials Vols. 138-139

Abstract: An optimal motion planning based on minimum principle is presented to address the motion problem of the mobile manipulator in a sort of experimental system. In view of the characteristic of the practical experimental apparatus, the model of the manipulator is deduced based on the kinetic analysis and mathematic method. An optimal control scheme is then investigated to deal with the optimization problem of the motion planning for the manipulator, so as to guarantee the demand of the teaching experiment. Simulation verifies the control performance of the optimal control scheme for the optimal motion planning of the manipulator, and it helps improve the teaching experiment effect.

Abstract: This paper presents a support structure for gravity-based horizontal axial tidal current energy conversion system considering factors such as strength, reliability, and costs of transportation and installation, etc. The support structure is an important part which directly affects the operation of tidal energy conversion system. ANSYS Workbench is used to determine stress and deformation of the structure subjected to current loads, wave hydrodynamic loads and inertia loads. Nonlinear contacts effects between framework and base structure are taken into account in our calculation. In order to facilitate offshore installation of framework and base structure, some work is done to explore the effects of contact height between internal and external tube and wall thickness of internal tube to the strength. The results show that the strength and stiffness of support structure comply with the design requirements, and the research work provides a valuable reference for the development of harnessing of tidal energy.

Abstract: During rehabilitative training, a 3-DOF wire-driven parallel robot driven was designed to coordinate and control the trainer pelvis movement. Based on the force balance equation of the end-effector, the stiffness problem about the robot system was analyzed and one kind of force/position parallel control strategy was proposed that the position loop would realize the end-effector motion trajectory, and the force loop would control the wire tension. The experimental results have shown that the robot systematic stiffness is related with the wire tension and can be changed to realize the compliance control of the robot system by adjusting the wire tension.

Abstract: In pressure vessels design, WRC107 provides a typical method of local stress analysis to supports and attachments. But influence of the rigidity of attachments on calculation is not considered. For fatigue analysis of round hollow attachment on cylindrical shell, equivalent stresses calculated by WRC107 were compared with those by finite element method. Three attachment thickness configurations, that half, equal, double of the shell thickness were tested. Results show that, in key point Au defined by WRC107 equivalent stress decreases while attachment rigidity increases, and in key point Cu, equivalent stress increases while attachment rigidity increases. When the thickness of attachment equals to that of shell, equivalent stress of WRC107 in Cu comes closest to FEM.

Abstract: Based on the finite volume method, the Navier-Stokes equations was used as the governing equations to develop a new module of the wave generating and absorbing function. The wave generating was introduced as the man-made source terms into the momentum equations, which was suitable for the volume of fluid method (VOF). Within the numerical wave flume, the reflected waves from the construction could be absorbed effectively. The absorbing section arranged at the end of the wave flume was for absorbing the incident wave, which allows for random and effective working time within the reletively smaller computation domain. Consequently, the computation efficiency was greatly improved. Finally, the validity of the absorbing section arranged at the front and end of the wave flume was investigated individually.

Abstract: In order to explore the application of glottis’ deformable modulation model, used to simulate the human phonation process, in high power pneumatic speaker, a simulation model was established to model the flow field in the time-dependent shape vocal tract of air-modulated speaker. Characteristics of unsteady flow field in duct under typical working conditions were analyzed. The evolution process of pulsating sound source in the vocal tract was presented. The speaker’s characteristic parameters with different chamber pressures and modulated frequencies were investigated. The simulation results provided an useful guidance for possible application of improving the acoustic characteristics of pneumatic speaker.

Abstract: According to the conditions of supercavitating vehicle stable control problems, the massive uncertain factors caused by reactions between the vehicle and cavity, and the control system real-time request, the paper presents a supercavitating vehicle stable navigation least squares support vector multiple intelligent control scheme. The scheme makes full use of the nonlinear mapping ability, self-learning adaptability and parallel information processing of the least squares support vector machine. Combining with fuzzy control method, complementary advantages, the closed-loop control has been formed. The simulation shows that the control system has good adaptive ability and robustness. The supercavitating movement stability and precise control realizes even in the situation that difficult to obtain an accurate model.

Abstract: Flow field information is very important to study hydro-performance of amphibious vehicle. However, it is difficult and expensive to measure it. To overcome the problem, CFD was used to acquire the information. The Reynolds Average Navier-Stokes equation was taken as basic mathematical model to describe flow field. Flow field region was discretized by hybrid mesh and governing equations were discretized by Finite Volume Method. Second order upwind scheme was used for spatial discretization and Euler scheme was used for temporal discretization. Result indicates that simulated flow field is consistent with experimental flow field on shape and hydrodynamic characteristic. Resistance accuracy is nearly 12%. It can be concluded that the method based on CFD is feasible to simulate the flow field around amphibious vehicle.

Abstract: The dynamic behaviors of a flexible multi-rotor system with a fault of parallel misalignment are investigated on the basis of assumptions, such as the long journal bearings, small rotor misalignment and mass disk unbalance. Firstly, based on the Lagrange equations with undetermined multiplier, the dynamic model of a rotor system under the action of the nonlinear oil film forces is developed after taking into account the holonomic constraint, which describes the misalignment relation between two rotors, and the theoretical analysis reveals that the system with eleven DOF is of strong nonlinear properties. Then the nonlinear dynamic characteristics on numerical technique, such as steady state response, rotor orbit, Poincaré section and the largest Lyapunov exponent, are paid more attention in this study. The results show that at low speed the components of the steady-state responses in lateral direction is of the synchronous frequency with rotating speed as well as its integer multiples frequencies. As the speed increases the dynamic characteristics become complicated, and the nT-period, quasi-period and chaotic oscillations occur.

Abstract: The nature of buffer system is a very important factor of determining the dynamic properties for the success of docking operation in space. The current buffer system is too large and highly complicated, which is not suitable for microspacecraft for On Orbit Servicing (OOS). In this paper, a new type of probe-cone docking mechanism with flexible docking cone as buffer system was presented, and the impact force was simulated using the explicit finite element code, LS-DYNA. Then, the time history of the impact process such as the velocity of docking probe and the docking cone’s displacement was computed under the given impact velocity and initial deviation. In the end, the influence of the wall thickness of docking cone on the impact force was analyzed. The conclusion that the flexible docking cone can greatly help to reduce the maximum impact force by more than 50% provides a basis for the engineering design of the buffer system.