Car Body Flexibility And Its Coupling Vibration Of Railroad Vehicles

In contrast to the common passenger train, the electric multi-units (EMU) runs at the operation speed over 300 km/h which experience more server dynamic inputs than the common passenger vehicles which have an operation speed lower than 150 km/h. As the running speed rises, the excitation frequencies from the track increase significantly as well as the structural vibration, wheel/rail contact forces and sensitivities of hunting motion of the vehicle. In contrast, the freight vehicle experiences more dynamic loads and harsh track conditions compared with the passenger train, and the vibrating and wheel/rail wear, as well as the safety, are always the concentrating issues. The goal of this investigation is to study the flexibility of the car body and its coupling vibration of railroad vehicles based on the multibody dynamics by considering the deformations of bodies. Therefore, this investigation includes two main topics about the car body flexibility of railroad vehicles, one is about the car body flexibility of the EMU and its coupled vibration with the devices suspended on the chassis, and the other one focus on the tank flexibility of the railroad tank vehicle and the liquid sloshing problem within the tank. The scope and objectives of this investigation,(1) In order to restrain the flexible vibration of the car body of an EMU, the suspension parameters between the devices and the car body are designed and the modal matching strategies are proposed based on the dynamic vibration absorber theorem.The impact of the suspension parameters on the vehicle dynamics is also provided to illustrate the relation between these parameters on the car body vibrating and vehicle dynamics for the high-speed train. The nonlinear properties of the stiffness and damping with the frequency are discussed for the rubber element used for the connection between the suspended devices and chassis of the car body of EMUs. The physical meaning of the model parameters for various rubber elements is explained with experimental measurements validation as well as model parameters identification algorithms. Furthermore, the experimental results from the lab tests and measurements on the track are also provided to validate the simulations.(2) The nonlinear trajectory motion constraints of a flexible body negotiating a circular curve are used to develop a systematic procedure for the calculation of the centrifugal forces during curve negotiations. In the case of a rigid body negotiates a curve, the centrifugal force has a simple form which is expressed as the body mass, forward velocity and the radius of curvature of the curve. In the case a flexible body negotiating a curve, however, the inertia of the body becomes a function of the deformation, curve negotiations lead to Coriolis forces and the expression for the deformation dependent centrifugal forces becomes more complex. The nonlinear algebraic constraint equations which define the motion trajectory along the curve are formulated in terms of the body reference and elastic coordinates. The centrifugal forces obtained for a flexible body are compared with that for the rigid body in order to have a better understanding of the relation between the deformation and the centrifugal forces.(3) The floating frame of reference (FFR) formulation is used to describe the tank deformation and define the nonlinear centrifugal and Coriolis forces for a railroad tank vehicle. The flexible tank is integrated into the multibody systems of the tank car, to show the effects of the tank deformation and shell thickness of the tank on the vehicle dynamics, such as the wheel/rail contact, wheel wear, hunting motion and the balance speed definition for the curved track.(4) In order to study the liquid sloshing in the tank of railroad vehicles, the systematic procedures are developed by using the finite element (FE) floating frame of reference formulation and absolute nodal coordinate formulation (ANCF). The proposed liquid sloshing modeling algorithm are based on a total Lagrangian approach and can be used to avoid the difficulties of integrating most of the fluid dynamics formulations based on the Eulerian approach, with multibody systems (MBS) dynamics formulations. The fluid incompressibility conditions and surface traction forces are derived directly form the Navier-Stokes formulas. The ANCF brick element is used to model the fluid, therefore, regardless of the magnitude of the fluid displacement,the fluid has a constant mass matrix, leading to zero Coriolis and centrifugal forces.Numerical scenarios are provided,such as a droplet interacts with ground and liquid sloshing within a rectangular tank, to shed light on the ability to use the FE/FFR and FE/ANCF liquid sloshing formulations. The liquid sloshing model is integrated into an MBS model of the railroad tank vehicle to represent the variants of the liquid inertia and its effects on the vehicle dynamics, which shows that significant results can be found when considering the liquid sloshing problem.