Redesigning Mechanical Systems for Low Wear Using System Dynamics Modeling

This work describes a method of minimizing wear and extending the life of machinery components and large, complex machine structures by controlling the overall system dynamics. The method consists of the following steps: first, developing a system dynamics model for the entire machine structure using available rigid multi-body dynamic analysis computer codes; second, obtaining dynamic performance data from the system dynamics model for each sliding contact in the actual machine, and feeding this information into a suitable wear model which is either being used or developed for the particular material combination; third, matching the results of the wear prediction with actual machine wear inspection data; and last and most important, returning to the dynamic analysis model and modifying or redesigning the machine to minimize the intensity of the system dynamics, thus extending the wear life of the components. The method is being developed for application to large, complex machines which have numerous sliding contacts. Many of these contacts are at junctions between subcomponents assembled together. These junctions are often designed to accommodate relative motion due to vibration or thermal mismatches. After the initial analyses have been done, both minor and major mechanical design and material changes must be investigated to determine how effectively these could reduce wear. Each successive configuration can be evaluated using the dynamic analysis model. Application of this approach to the mechanical design of a gas turbine combustor reduced the noise level of the entire system and tripled the average machine life.