Melike Nikbay

Coupled Analytical Sensitivity Analysis and Optimization of Three-Dimensional Nonlinear Aeroelastic Systems

We consider the problem of optimizing for steady-state conditions a given nonlinear aeroelastic system, by varying both aerodynamic and structural parameters. We model the structure by e nite elements and predict the aerodynamic loads by a three-dimensional e nite volume approximation of the Euler equations. We present a complete optimization methodology whose key components are a computer aided geometric design method for representing the design, an analytical approach for sensitivity analysis, a gradient-based optimization algorithm and two staggered schemes for evaluating the aeroelastic responses and solving the coupled sensitivity equations. We illustrate our methodology and demonstrate its potential with various aeroelastic optimizations of idealized and builtup wing structures.

Shape optimization methodology for reducing the sonic boom initial pressure rise

A shape optimization methodology for reducing the initial shock pressure rise on the ground of a supersonic aircraft is presented. This methodology combines elements from the linearized aerodynamic theory, such as the Whitham F function, with elements from the nonlinear aerodynamic theory, such as the prediction of lift distribution by an Euler or a Navier-Stokes flow solver. It is applied to the optimization of two different airplane concepts developed by Reno Aeronautical and Lockheed Martin, respectively, for the Defense Advanced Research Projects Agencys Quiet Supersonic Platform program. For Reno Aeronauticals laminar-flow supersonic aircraft, the initial shock pressure rise on the ground is reduced by a factor close to 2, from 1.224 psf (58.605 N/m 2 ) at a freestream Mach number of 1.5 to 0.671 psf (32.127 N/m 2 ), while maintaining constant lift For Lockheed Martins point of departure aircraft, a tenfold reduction of the initial shock pressure rise on the ground is demonstrated, from 1.623 psf (77.71 N/m 2 ) at a freestream Mach number of 1.5 to 0.152 psf (7.278 N/m 2 ), also while maintaining constant lift.

Multidisciplinary Code Coupling for Analysis and Optimization of Aeroelastic Systems

This paper presents a practical methodology for static aeroelastic analysis and aeroelastic optimization via coupling of high-fidelity commercial codes. A finite-volume-based flow solver FLUENT is used to solve three-dimensional Euler equations, Gambit is used to generate mesh in the fluid domain, and CATIA is used to model parametric solid geometry. Abaqus, a structural finite element method solver, is used to compute the structural response of the aeroelastic system. The mesh-based parallel-code coupling interface MpCCI is used to exchange the pressure and displacement information between FLUENT and Abaqus to perform a loosely coupled aeroelastic analysis by a staggered algorithm, and modeFRONTIER software is used as the optimization driver for scheduling a nondominated sorting genetic algorithm initiated with design of experiments. First, an AGARD 445.6 wing configuration is optimized with objectives of maximum lift/drag ratio and minimum weight. Optimization variables are chosen as sweep angle at the quarter-chord and the taper ratio of the wing. Second, a more realistic wing model, ARW-2, is optimized for thickness values of the inner ribs and spars. Aeroelastic analysis produce consistent results with experimental data, and the applied optimization methodology results in Pareto-optimal solutions.

Analytically Based Sensitivity Analysis and Optimization of Nonlinear Aeroelastic Systems

We consider the sensitivity analysis of a coupled aeroelastic system in steady—state conditions and the related aeroelastic optimization problem. We present the global sensitivity equations for a three-field formulation of the fluid/structure interaction problem, construct a computational framework that features analytical derivations of the gradients of semi-discrete operators and addresses both the direct and adjoint solution methods, and design efficient staggered procedures for solving all intermediate coupled systems of equations. We apply this computational framework to the aeroelastic optimization of three-dimensional wing structures that are modeled by finite elements, and for which the aerodynamic loads are predicted by the three-dimensional finite volume approximation of Euler flows.

Shape optimization with F-function balancing for reducing the sonic boom initial shock pressure rise

A shape optimization methodology for reducing the initial shock pressure rise (ISPR) on the ground of a supersonic aircraft is presented. This methodology combines elements from the linearized aerodynamic theory such as Whithams F-function with elements from the nonlinear aerodynamic theory such as the prediction of lift distribution by an Euler or a Navier-Stokes flow solver. It also features a concept of F-function lobe balancing that locates suitable positive and negative lobe pairs of the F-function, and modifies the shape of the aircraft to balance the areas of these lobes. The latter feature accelerates the convergence of the optimization procedure and forces it to generate an aircraft shape with a multi-shock ground signature, which reduces further the ISPR. This shaping technology is illustrated with an application to the Point of Departure aircraft developed by Lockheed-Martin for Phase I of DARPAs Quiet Supersonic Platform program. At M∞ = 1.5, a twenty-fold reduction of the ISPR on the ground, from 1.616 psf to 0.083 psf, is demonstrated while maintaining constant length, lift (weight), and inviscid drag. At M∞ = 2.0, a six-fold reduction of the ISPR on the ground, from 1.866 psf to 0.324 psf, is also demonstrated while maintaining constant length, lift (weight), and inviscid drag.

Steady and Unsteady Aeroelastic Computations of HIRENASD Wing for Low and High Reynolds Numbers

We perform static and dynamic aeroelastic analyses of the HIRENASD wing based on NASA’s reference data delivered for two test cases with dierent ight conditions. The tests have been conducted in cryogenic medium to investigate steady and unsteady aeroelastic responses in transonic regime for low and high Reynolds numbers. For computational studies, the latest structural model of NASA is used. First, a free vibration analysis is performed in Nastran. Then, the modal solution is imported from the nite element solver to ZEUS, where the aerodynamic model and uid structure interaction parameters are constructed. Steady and unsteady aeroelastic results are examined for the specied stations along the wing span, and interpolated for chordwise direction so as to match them with the wind tunnel test points. The designated output parameters such as steady aerodynamic lift, moment and drag coecients, and steady and unsteady pressure distributions along the chordwise direction are compared to the experimental results.

Sonic boom mitigation via shape optimization using an adjoint method and application to a supersonic fighter aircraft

This paper describes a computational method for the analysis and mitigation via shape optimization of the sonic boom associated with supersonic flight. The method combines a CFD approach for determining the near-field pressure field and an acoustic scheme for predicting the initial shock pressure rise at the ground. Two venues are considered for computing the ground signature. The performance of both approaches is evaluated using flight test data of two different configurations of an F5 fighter aircraft.

Reliability-based aeroelastic optimization of a composite aircraft wing via fluid-structure interaction of high fidelity solvers

We consider reliability based aeroelastic optimization of a AGARD 445.6 composite aircraft wing with stochastic parameters. Both commercial engineering software and an in-house reliability analysis code are employed in this high-fidelity computational framework. Finite volume based flow solver Fluent is used to solve 3D Euler equations, while Gambit is the fluid domain mesh generator and Catia-V5-R16 is used as a parametric 3D solid modeler. Abaqus, a structural finite element solver, is used to compute the structural response of the aeroelastic system. Mesh based parallel code coupling interface MPCCI-3.0.6 is used to exchange the pressure and displacement information between Fluent and Abaqus to perform a loosely coupled fluid-structure interaction by employing a staggered algorithm. To compute the probability of failure for the probabilistic constraints, one of the well known MPP (Most Probable Point) based reliability analysis methods, FORM (First Order Reliability Method) is implemented in Matlab. This in-house developed Matlab code is embedded in the multidisciplinary optimization workflow which is driven by Modefrontier. Modefrontier 4.1, is used for its gradient based optimization algorithm called NBI-NLPQLP which is based on sequential quadratic programming method. A pareto optimal solution for the stochastic aeroelastic optimization is obtained for a specified reliability index and results are compared with the results of deterministic aeroelastic optimization.

A Multi-disiplinary Code Coupling Approach for Analysis and Optimization of Aeroelastic Systems

We consider the static aeroelastic analysis and optimization of aircraft wings for steadystate conditions while both aerodynamic and structural parameters can be used as optimization variables. The core eort of this work lies on developing a robust methodology to couple commercial codes for a full aeroelastic optimization purpose to yield a convenient adaptation to engineering applications in industry. A commercial nite volume based ow solver Fluent-6.3.26 is used to solve inviscid 3D Euler equations, Gambit as the uid domain mesh generator and Catia-V5-R16 as a parametric 3D solid modeler. Abaqus-6.7.1, a structural nite element method solver, is used to compute the structural response of the aeroelastic system. Mesh based parallel code coupling interface MPCCI-3.0.6 is used to exchange the pressure and displacement information between Fluent and Abaqus to perform a loosely coupled aeroelastic analysis by employing a staggered algorithm. Modefrontier-4.0 is used as a multi-objective and multidisiplinary optimization software with both gradientbased and gradient-free optimization algorithms. Aeroelastic optimization is performed for a basic experimental wing model based on AGARD 445.6 elastic wing conguration with multi-objectives of maximum lift over drag ratio and minimum weight of the wing. Static aeroelastic criteria on maximum tip deection are given as design constraints. Optimization variables are chosen as sweep angle at the quarter chord and the taper ratio of the wing. A genetic algorithm NSGA-II is used to control the optimization process. The aeroelastic analysis results produced a good agreement with the experimental data given in literature and the the aeroelastic optimization study resulted with a set of pareto optimal values.

Linear-Theory-Based Shape Optimization for Sonic Boom Minimization

An overpressure ground signature with more than two shocks is proposed for sonic boom minimization. A procedure coupling linear-theory-based sonic boom theory with a state-of-the-art optimization tool is presented. The method is used to reshape a candidate supersonic aircraft for a reduced initial shock pressure rise.