Determination of stability and control derivatives using computational fluid dynamics and automatic differentiation

Abstract

With the recent interest in novel control effectors there is a need to determine the stability and control derivatives of new aircraft configurations early in the design process. These derivatives are central to most control law design methods and would allow the determination of closed-loop control performance of the vehicle. Early determination of the static and dynamic behavior of an aircraft may permit significant improvement in configuration weight, cost, stealth, and performance through multidisciplinary design. The classical method of determining static stability and control derivatives-constructing and testing wind tunnel models-is expensive and requires a long lead time for the resultant data. Wind tunnel tests are also limited to the preselected control effectors of the model. To overcome these shortcomings, computational fluid

Multidisciplinary design optimization techniques - Implications and opportunities for fluid dynamics research

“…Contributions from second derivatives may also be needed. Park et al 40 reached a similar conclusion in their use of sensitivity derivatives to estimate control effectiveness. Second derivatives may be obtained fairly easily by combining the complex variable technique with use of ADIFOR or by exploiting the forthcoming Hessian capability of ADIFOR, although the computational expense will be high.…”

“…When ADIFOR 3.0 is officially released in 1999, it will also contain the capability to produce the adjoint code. 37 Recent experience 37,40 indicates that a complete multigrid, multiblock, turbulent CFD code can be equipped with sensitivity analysis capability in less than a week by using ADIFOR (assuming that the code is written in the Fortran 77 ANSI standard). The typical time for equipping by hand a laminar Navier-Stokes code with quasi-analytic sensitivity analysis appears to be about a year.…”

“…Why not use sensitivity analysis to solve the exact equations that govern the stability and control coefficients? 40,90 Aerodynamic Design Methods There has been significant progress this decade in gradient-based aerodynamic design methods, with the most efficient methods utilizing hand-coded sensitivities and adjoints (although no one has yet been masochistic enough to produce a hand-coded adjoint that includes the turbulence model). The next challenge in this line is to adapt these methods to multidisciplinary problems, e.g., to aerodynamicsstructures problems.…”

Decision Support Methods and Tools

“…This process usually involves some kind of sensitivity analysis, which may be performed manually by trade studies, or by automated tools, such as the ADIFOR 3.0 tool [36][37][38][39][40][41] which takes standard Fortran code and a specification of independent and dependent variables to produce direct (forward-mode) or adjoint (reverse-mode) Fortran code that is compiled and executed to evaluate the gradient and/or Hessian matrices of the simulation code, in lock-step with the function evaluation.…”

Computing Stability Derivatives and Their Gradients for Aerodynamic Shape Optimization

“…Godfrey and Cliff [10] explored the use of analytic sensitivity methods-in particular, the direct method-for the computation of static stability derivatives. Park et al [11] applied ADIFOR [12], an automatic differentiation (AD) tool, to a three-dimensional viscous flow solver to compute the static derivatives of various configurations.…”