Simulation software development for multibody systems / Desenvolvimento de uma ferramenta computacional para simulação de sistemas mecânicos multicorpos

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The mathematical simulation is a very important tool to reduce production costs in new projects of agricultural machines. This work consists of a simulation software development for multibody systems (MBS), called FSSM (tool for simulation of mechanical systems), with appropriate functionalities for manufacturers of agricultural machines, using the AutoCAD graphic programming resources. A computational algorithm, capable to generate the equations that automatically describe the rigid bodys movement (displacement, velocity and acceleration) in MBS is presented. The system of equations generated is solved using numeric methods. It was used the Newton-Raphson method to solve the linear system of equations, and then fourth-order Runge- Kutta method to differentiate ordinary equations. To assist the most usual demands, a set of force elements was modeled and implemented, to make possible simulations of a greater variety of problems. The FSSM allows static, kinematics and dynamics analyses in MBS. In the static analysis it is obtained the forces in the MBS joints considering the gravitational forces and users forces applied on the bodies. In the kinematics analysis, at any time, previously defined, it is obtained the displacement, velocity and acceleration of each body. In the dynamic analysis the joint efforts are solved, as well as the displacement, velocity and acceleration of the body at any instant of time. Points of interest attached to the bodies can be defined for kinematics and dynamic analysis. Forcetype spring-damping, constant, impact and harmonics are implemented, as well as a pair of spur gears and belt kinematics. The interaction forces between tire and soil are also implemented. It makes possible the simulation of off-road vehicles working on the soil. The FSSM implementation is composed by three different modules: pre-processing (VBA language), processing (executable program in VB language) and after-processing (also in VBA language). Some tests were accomplished to validate the FSSM. The tests are basically the comparison between the analytical and simulated results. Simple systems were modeled in order to obtain a set of equations that could be solved analytically. The first system was a static truss structure, used to validate the static analysis module. The second was a four-bar mechanism to validate the generation of the equations that simulate the revolution joint and validate the FSSM kinematics analysis. The third system was a set of planetary gears that allowed the simultaneous validation of relative restrictionsof pairs of gears and revolution joints usage in kinematics analysis. The fourth system was the mass-spring type with vertical movement that was used to validate the spring and gravitational forces generation and dynamic analysis. The fifth system was mass-spring-damping system with horizontal movement, used to validate the spring and damping forces generation, translation joint and dynamic analysis. Field tests using an agricultural tractor were also made. During the tests, the vertical vibration in two points were measured one located in the front and other at the rear of the tractor. The measurements were done using an automatic data acquisition system, installed on the tractor. The vertical acceleration values measured were compared to the simulated values using FSSM. The results were satisfactory showing that FSSM simulated the system appropriately in the five tests performed.

ASSUNTO(S)

dinâmica machine projects kinematic analysis sistemas mecânicos dynamics análise cinemática mechanical systems projeto de máquinas maquinas e implementos agricolas

ACESSO AO ARTIGO

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