Design Optimization of a Wind Tunnel Force Balance Using Stepwise Response Surface Method

Abstract

A force balance is a device utilized in wind tunnels in order to measure the forces being applied to a body during a wind tunnel test. The balance is equipped with strain gauges that measure structural deformations for evaluation of the forces and moments being applied to the body. The force balance is required to have structural safety under a large roll moment, due to design changes with the testing apparatus. The balance must be optimized to allow for this increased roll moment while guaranteeing the balance will not fail and the gauges within the balance will generate an acceptable gauge reading. The finite element simulation-based design optimization is studied in this theses. Firstly, a finite element (FE) model of the force balance was created. To ensure the model accuracy of the force balance, a comparison of the stress values and the gauge readings was conducted while the balance experienced rated loads. Second, two response surface method (RSM) trials were run using three sampling techniques: Central Composite Circumscribed (CCC), Central Composite Face-centered (CCF), and Box-Behnken (BB). The first trial is a broad sampling centered around the original dimensions. The results of the first trial led to the second trial, which consisted of narrow sampling with a center point closer to the optimal point than the first trial. The data from these trials was then utilized in a final regression, in which a final quadratic model was generated to find a further optimized point. The result of this study shows the force balance design changes to decrease stress values with a greatly increased roll moment and provides satisfactory gauge readings. This theses successfully demonstrated the benefit of the stepwise RSM that can achieve optimal design using limited number FE analysis.