Modeling railroad track structures using the finite segment method |
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Authors: | Martin B Hamper Khaled E Zaazaa Ahmed A Shabana |
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Affiliation: | 1.Department of Mechanical and Industrial Engineering,University of Illinois at Chicago,Chicago,USA;2.Applied Technology and Engineering Div.,ENSCO Inc.,Springfield,USA |
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Abstract: | In the finite segment method, the dynamics of a deformable body is described using a set of rigid bodies that are connected
by elastic force elements. This approach can be used, as demonstrated in this investigation, in the simulation of some rail
movements. In order to ensure that the rail geometry is not distorted as the result of the finite segment displacements, a
new track model that consistently integrates the absolute nodal coordinate formulation (ANCF) geometry and the finite segment method is developed. ANCF finite elements define the track geometry in the reference
configuration as well as the change in the geometry due to the movement of the finite segments of the track. Using ANCF geometry
and the finite segment kinematics, the location of the wheel/rail contact point is predicted online and used to update the
creepage expressions due to the finite segment displacements and rotations. The location of the wheel/rail contact point and
the updated creepage expressions are used to evaluate the creep forces. A three-dimensional elastic contact formulation (ECF-A) which allows for wheel/rail separation is used in this investigation. The rail displacement due to the applied loads
is modeled by a set of rigid finite segments that are connected by a set of spring-damper elements. Each rail finite segment
is assumed to have six rigid body degrees of freedom. The equations of motion of the finite segments are integrated with the
railroad vehicle system equations of motion in a sparse matrix formulation. The resulting dynamic equations are solved using
a predictor–corrector numerical integration method that has a variable order and variable step size. The finite segments may
be used to model specific phenomena that occur in railroad vehicle applications, including rail rotations and gauge widening.
The procedure used in this investigation to implement the finite segment method in a general purpose multibody system (MBS)
computer program is described. Two simple models are presented in order to demonstrate the implementation of the finite segment
method in MBS algorithms. The limitations of using the finite segments approach for modeling the track structure and rail
flexibility are also discussed. |
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