Title

Numerical analysis of torque augmentation in viscous couplings

Date of Award

1998

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical and Aerospace Engineering

Advisor(s)

Jacques Lewalle

Keywords

Humping, Finite element, Silicone oil, Torque, Viscous couplings

Subject Categories

Mechanical Engineering

Abstract

The humping phenomenon in viscous couplings is investigated by the finite element method. The possible destabilizing factors suggested by the experimental results are divided in two groups: fluid properties and plate geometry. A simple two-dimensional model capable of including these factors was devised. Both Newtonian flow and Non-Newtonian flow in the viscous coupling were solved by our Finite Element Method code. The finite element formulation based on the variational principle is discretized by the mixed interpolation functions. Within each triangular element, velocities were approximated with a quadratic function and the pressure was represented with a linear function. The non-linear system of equations resulting from the discretization process were solved by Gaussian elimination and iteration procedures. As a result, several routes to humping in viscous couplings are documented.

The plate permeability associated with the perforations was found to have no significant effect on the humping scenario. The initial loss of symmetry can be provided by random fluctuations of the axial location of the inner plates, or by the presence of burrs. Once the symmetry is broken, the left side burrs at the leading edge of the inner plates can initiate humping with a preferred direction of motion toward the burrs side of the inner plate. It was found that viscous coupling have an ability to recover from the plate torsion.

The fluid properties of the silicone oil are also associated with the humping. After examining the power law model, the visco-pseudoplastic model and the temperature-dependent viscosity model for the variable viscosity, it was found that only visco-pseudoplastic model and the temperature-dependent viscosity model can be used to explain the humping. For some transition shear rate $(233.3<\bar S\sb{tr}<816.5)$ in the visco-pseudoplastic model, the axial forces will increase the given asymmetry and initiate the humping. For the temperature-dependent viscosity model, the axial force initially stabilized the inner plate, after passing the transition time (0.028 sec), the axial force will destabilize the inner plate and initiate the humping.

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