Abstract
This paper presents a new formulation for analyzing a beam on elastic supports traveling on irregular profiles. The model is a first approximation of a passenger railway vehicle car body. The main difference with previous works is the use of a complex modulus to represent structural damping rather than relying on equivalent viscous terms. The formulation groups rigid body modes with flexible modes and proposes a matrix form that is easy to interpret and solve in the frequency domain. Comfort indexes are readily obtained from weighted response spectral densities. The model is used to assess the influence of structural damping and stiffness on comfort. It will be shown that the evolution of comfort with stiffness is non-monotonic and, therefore, comfort does not always improve as stiffness increases.
Highlights
Structural Stiffness and Loss FactorThere are two current trends in passenger rail transport that may influence comfort in a negative way
Multibody (MB) analyses conducted to predict dynamic behavior and comfort often include flexible frames represented by mass, damping, and stiffness matrices derived from finite element models (FEM)
Before using the formulation presented in the previous section to assess the influence of structural damping and flexibility on comfort, it is clarifying to use it for two oversimplified cases
Summary
There are two current trends in passenger rail transport that may influence comfort in a negative way. Multibody (MB) analyses conducted to predict dynamic behavior and comfort often include flexible frames represented by mass, damping, and stiffness matrices (or condensed versions of these matrices) derived from finite element models (FEM) These combined MB–FEM analyses show the influence of many design features on comfort but, at the same time, often hide the basic relationships between the most fundamental design parameters and passenger vibration. To the best of our knowledge, no previous work on this particular subject has modeled structural dissipation by means of a complex modulus They all include a viscous term in the equation of motion of the beam that stems from cross-section stresses proportional to strain rate and in-phase with strain rate. Mean square accelerations, from which comfort indexes may be estimated, can be obtained from frequency analyses
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