Gwanghun Gim

Systematic construction of the equations of motion for multibody systems containing closed kinematic loops

This papers presents a systematic method for deriving the minimum number of equations of motion for multibody system containing closed kinematic loops. A set of joint or natural coordinates is used to describe the configuration of the system. The constraint equations associated with the closed kinematic loops are found systematically in terms of the joint coordinates. These constraints and their corresponding elements are constructed from known block matrices representing different kinematic joints. The Jacobian matrix associated with these constraints is further used to find a velocity transformation matrix. The equations of motions are initially written in terms of the dependent joint coordinates using the Lagrange multiplier technique. Then the velocity transformation matrix is used to derive a minimum number of equations of motion in terms of a set of independent joint coordinates. An illustrative example and numerical results are presented, and the advantages and disadvantages of the method are discussed.

A semiphysical tyre model for vehicle dynamics analysis of handling and braking

A semiphysical model presented in this paper first includes the transient steer effect characterized by both the time delay of steering application and the stress relaxation of friction due to the tyre’s viscoelastic property. The model experimentally formulates the vertical force as a function of the tyre deflection, camber angle and lateral force. In order to describe the longitudinal and lateral forces as functions of the tyre’s characteristic parameters such as stiffness and friction, the basic formulations of the UA tyre model are reused. For self-aligning and overturning moments, first the application points of three forces are experimentally formulated, and then the moments are expressed as functions of the three forces and their application points. All characteristic parameters are experimentally determined as functions of the load, camber angle, slip angle, slip angle sweep rate and/or slip ratio for cornering and/or driving–braking. For the purpose of validation, the model is implemented into ADAMS and then its simulation results are compared with measurement data for various test conditions.

A two-dimensional tire model on uneven roads for vehicle dynamic simulation

This study proposes a comprehensive analytical tire model for handling and ride comfort in low frequency ranges. A contact algorithm that is developed in this study provides a two-dimensional contact pressure distribution on even and uneven road surfaces with reasonable computational cost. Shear stresses and strains during cornering and braking are estimated by direct measurement of tread deformations. The model is validated against experimental force and moment data for general handling simulations. Cleat tests are also conducted and validated under different forward velocity and vertical load conditions for a tire vibration study.

Ride and stability analysis of a sports car using multibody dynamic simulation

This paper summarizes the joint coordinate formulation for automatic generation of the equations of motion for dynamic analysis of multibody systems. A computer program based on this formulation is used to model a sports car and simulate its dynamic response in several driving scenarios. The model contains necessary elements of the suspension system such as the leafsprings, shock absorbers, bushings, tie rods, and roll stabilizer bars. An analytical model of the pneumatic tires is incorporated in the model to determine all of the necessary interacting forces and moments between a tire and the road. Results from some selected simulations are shown.