Strain gage balance signal filtering with piecewise representations

Abstract

Strain gage balances provide the most important output of the supersonic wind tunnels. Typically, the time histories of the six forces/moments components must be filtered out, to provide useful results for performance assessment of the models. Various filtering models do exist, from basic regressions, to frequency domain and combinations of piecewise fit polynomials. Results with decoupled piecewise linear fit (moving window) showed the need of more suitable methods, namely piecewise, that must properly connect the neighboring fit curves, to provide continuity up to the first derivative. A polygonal line fit is derived and modified for increased smoothness. A third order cubic spline is derived, offering connectivity up to the first derivative. A fifth order spline is derived with continuity up to the second order derivative. Filtering results are shown for real and synthetic sets of data with conclusions.

Keywords

• strain gage balance
• filtering
• polygonal line
• spline fit