Narrow Results

Permanent magnetic levitation (PML) is an innovative levitated transportation system. Examining the dynamic response of PML vehicles based on their permanent magnetic track relationship is crucial for assessing system stability and safety. In this regard, this study first established the multibody dynamic equations of PML vehicles according to their magnetic trajectory relationship. A coupled dynamic model was then developed within the Simulink environment; finally, the dynamic characteristics of the PML vehicle engineering machine were analyzed. The simulation results were in good agreement with the experimental results, further verifying the accuracy and reliability of the dynamic model. The results show that the bogie keeps a certain attitude for a long time at a low speed. The vibration acceleration of the bogie and body was much smaller than the corresponding dynamic evaluation criteria. Notably, the spectral analysis of the vertical vibration acceleration of the body shows that the axis distance of the PML, lateral and axial distances of the second suspension system, and lateral distance of the guide wheels have a significant effect on the body vibration. This study provides a relevant reference for the engineering application of PML vehicles.

Stability and dynamic modeling of the floating wind turbine (FWT) is a crucial challenge in designing of the type of structures. In this paper, the tension leg platform (TLP) type FWT is modeled as a multibody system considering the flexibility between the nacelle and tower. The flexibility of the FWT is modeled as a torsional spring and damper. It has 6 degrees of freedom (DOFs) related to the large-amplitude translation and rotation of the tower and 4 DOFs related to the relative rotation between the rotor-nacelle assembly and the tower. First, the nonlinear equations of motion are derived by the theory of momentum cloud based on the conservation of momentum. Then, the equations of motion are solved and the system is simulated in MATLAB. Moreover, the effect of flexibility between the nacelle and tower is investigated via the dynamic response. The stability of the system in three different environmental conditions is studied. Finally, the spring and damping coefficients for the system response to get near to instability are determined, by which the critical region is defined. The simulation results demonstrate the importance of the flexibility between the nacelle and tower on the overall behavior of the system and its stability.

With the rising speed of high-speed trains, the aerodynamic loads become more significant and their influences on the hunting stability of railway vehicles deserve to be considered. Such an effect cannot be properly considered by the conventional model of hunting stability analysis. To this end, the linear hunting stability of high-speed railway vehicles running on tangent tracks is studied. A model considering the steady aerodynamic loads due to the joint action of the airflow facing the moving train and the crosswind, is proposed for the hunting stability analysis of a railway vehicle with 17 degrees of freedom (DOF). The key factors considered include: variations of the wheel–rail normal forces, creep coefficients, gravitational stiffness and angular stiffness due to the actions of the aerodynamic load, which affects the characteristics of hunting stability. Using the computer program developed, numerical calculations were carried out for studying the behavior of the linear hunting stability of vehicles under steady aerodynamic loads. The results show that the aerodynamic loads have an obvious effect on the linear critical speeds and instability modes. The linear critical speed decreases monotonously as the crosswind velocity increases, and the influences of pitch moment and lift force on the linear critical speed are larger than the other components of the aerodynamic loads.

In this paper, the dynamic vibration absorber considering time delay is taken as the research object, and the effect of time delay on the vibration characteristics of the dynamic vibration absorber is studied by combining theory and experiment. In this paper, a time-varying time-delay feedback control method is proposed. Firstly, the instantaneous frequency of complex excitation is obtained by wavelet analysis. The instantaneous frequency determines the critical time-delay parameters of the dynamic vibration absorber with time-delay as the time-delay control quantity. Then, the optimal fixed time-delay feedback gain is calculated by improved particle swarm optimization. Finally, the time-varying delay gain parameter controls the time-delay dynamic vibration absorber. The vibration reduction effect of this approach under complicated excitation is investigated using a 2-DOF vibration system with a time-delay dynamic vibration absorber as an example. Based on simulation calculation, the bench test of the control strategy is carried out, and the influence of the control strategy on the control dynamic characteristics of the primary system is analyzed. The simulation and experimental results are consistent, laying the groundwork for this paper’s research on time-varying delay control.

In order to study the three jump training and competition on knee joint impact damage degree, left knee joint of one healthy male athletes is used as the research object, a complete knee three-dimensional model was established based on the jumper’s knee CT scan and magnetic resonance imaging (MRI), including the femur, tibia, fibula, patella and knee major cartilage, ligaments. The multi-body dynamics analysis (MDA) and finite element analysis (FEA) method are used to calculate the three jump, jump starting, landing process of athletes knee joint impact, the state should change the status of stress, strain and displacement. The results show that in the three jump process, the load on the lateral contact area of the knee joint is the largest, the displacement is the largest, and it increases with the impact of jump and landing. This exacerbated the degree of wear and tear of the tibia, it tends to induce knee injury in athletes. The results show that the combination of finite element and MDA can better study the knee joint’s shock and vibration during the three-level jump training and competition, and these open up a new research method for the knee joint injury. It also provides a certain reference for the prevention and treatment of knee joint injury.

This work deals with the multibody dynamics modelling of the humanoid robots. An alternative geometric method will be presented based in the screw theory. The obtained torques are used for selecting the right motors. Otherwise, this computation allows to compute the joint torques at any humanoid robot motion, those are constrained for the physical robot limits. Furthermore, the joint torque references could be obtained for doing the torque control loop and develop any motion pattern. The simulation results in order to check the joint torques are shown and discussed.

This paper deals with alternative humanoid robot dynamics modelling, using the screw theory and Lie groups called the special Euclidean group (SE(3)). The forward dynamic model is deduced analitically, which is solved by propagation method from an end-effector to the center of gravity (COG) always on the SE(3). Many tests for reference dynamic walking patterns have been carried out, which are represented in simulation and experimental results. The results will be discussed in order to validate the proposed algorithms.