A First Principle Engine Model for Up-Front Design: Bearing Models and Example Results

The design of new engine concepts requires an engineering tool that can quickly estimate noise, vibration and durability metrics at the very onset of the engine design cycle. In (Ma et al., 2000), we presented an engine modeling template (EMT) to support up-front engine design. The engine models generated from the EMT use the minimum set of generalized coordinates to represent engine dynamics. This is achieved by employing a pre-selected set of relative coordinates. The resulting engine model is cast as a (minimum) set of ordinary differential equations in lieu of the differential-algebraic equations that result from using commercial multibody dynamics codes. The resulting models then enjoy greater computational efficiency. In (Ma et al., 2000), we formulate the equations of motion for the engine and its major components. The objective of this paper is to review the numerical results obtained from sample engine designs and to discuss several tradeoffs between model accuracy and efficiency. Attention focuses on the trade-offs resulting from several bearing models, including linear and nonlinear spring-damper bearing models, and hydrodynamic bearing models based on the Reynolds equation. Results computed using these bearing models are critically compared.