Manav Bhatia

Design Optimization of a Truss-Braced-Wing Transonic Transport Aircraft

the conventional cantilever configuration. One comparison produces a reduction of 45% in the fuel consumption while decreasing the minimum takeoff gross weight by 15%. For a second comparison, the fuel weight is reduced by 33% with a decreased minimum takeoff gross weight of 19%. Very attractive vehicle performance can be achieved without the necessity of decreasing cruise Mach number. The results also indicate that a truss-braced wing has a greater potential for improved aerodynamic performance than other innovative aircraft configurations. Further studieswillconsidertheinclusionofmorecomplextrusstopologiesandotherinnovativetechnologiesthatarejudged to be synergistic with truss-braced-wing configurations.

Structural and Aeroelastic Characteristics of Truss-Braced Wings: A Parametric Study

flexible in nature. This paper presents a set of parametric studies of truss-braced-wing configurations to understand the influence of the wing geometry parameters on the wing structural and aeroelastic characteristics. The primary parametersconsideredherearethewinghalf-span,strutsweep,spanwiselocationofwing-strutjoint,andnumberof truss members in the wing configuration. Each truss-braced-wing parametric configuration is sized based on strength considerations and studied for aeroelastic behavior. The results indicate strong influence of all the parameters considered here. For most cases, increasing the half-span monotonically increases the wing weight and reduces both the natural frequencies and the flutter speed. A larger difference between the wing- and strut sweep angles is seen to increase wing weight, but with a positive influence on flutter speed for various truss-braced-wing configurations. The spanwise intersection location has distinct optima for wing weight and flutter speed, which typically lie in between 55 and 70%. These results are expected to provide guidance for future multidisciplinary design optimization studies for truss-braced-wing configurations.

Design-Oriented Thermostructural Analysis with Internal and External Radiation, Part 1: Steady State

This paper presents a steady-state sensitivity analysis formulation covering configuration shape and structural sizing design variables for coupled linear structural analysis and nonlinear thermal analysis including the effects of radiation: in external and internal cavities. A new coupled design-oriented thermoelastic analysis capability is first presented and validated by using an available commercial analysis code. It is then used to calculate shape sensitivities and assess a number of standard approximation techniques in an effort to gain insight regarding the functional relations between design variables and thermoelastic responses. A novel approximation scheme is presented for the category of problems discussed that lead to substantial savings in central processing unit time. A hypersonic wing structure similar to a space shuttle wing is used as a test case.

Design-Oriented Thermostructural Analysis with External and Internal Radiation, Part 2: Transient Response

This is the second paper in a two-part series presenting a sensitivity-analysis formulation covering configuration shape and structural sizing design variables for nonlinear thermostructural analysis including the effects of radiation: external and in internal cavities. Part 1 presented the steady-state coupled thermal-structural formulation with results from a new coupled design-oriented thermoelastic analysis capability. The present paper considers transient heat transfer analysis problems with temperature-dependent material properties. Structural response is assumed to be quasi-steady. Because structural-thermal integration had been demonstrated earlier, the focus here is on design-oriented analysis aspects of the conduction-radiation problem. An approximation scheme is presented for the category of problems discussed that leads to a reduction of CPU cost from the order of N 3 operations to N 2 for cavity radiation analysis. A hypersonic wing structure similar to a space shuttle wing is used as a test case.

Structural Design of a Truss Braced Wing: Potential and Challenges

This paper discusses current work on STRUCTURAL ASPECTS OF the design optimization of a Truss Braced Wing (TBW) configuration. These wings offer significat potential for performance improvements in terms of fuel efficiency, but also offer challenges for a structural designer. The details of the structural analysis and design methodology are presented. Two different design methodologies are discussed: structural sizing based on beam idealization considering only bending stiffness and static analysis, and a finite element based sizing optimization approach including aeroelastic effects. The paper reports all aspects of the two approaches: design parameterization, model geometry and mesh generation, analysis and optimization. The first approach has been used in the past at Virginia Tech for Multidisciplinary Design Optimization (MDO) studies of a Strut-Braced Wing (SBW), and extensions to sizing of a more general TBW configuration are discussed. The second approach is used to perform some parametric studies presented here. Comparative studies are performed for wings designed for rigid and flexible trim subject to static stress constraints. The aeroelastic performance of some TBW configurations is investigated. Only structural sizing parameters are treated as design variables. Conclusions are drawn from these results for guidance to the ongoing MDO studies of the TBW, to be reported in future papers.

Aeroelastic Topology Optimization of Blade-Stiffened Panels

Metallic blade-stiffened panels are optimized for various eigenvalue metrics of interest to the aerospace community. This is done via solid isotropic material with penalization-based topology optimization: the stiffeners are discretized into finite elements, and each element is assigned a design variable, which may vary from 0 (void) to 1 (solid). A known issue with eigenvalue-based optimization is discontinuities due to mode switching, which may be avoided through a series of eigenvalue separation constraints, or (more challenging, but less restrictive) a bound method with mode tracking. Both methods are demonstrated to obtain optimal stiffener topologies for panel buckling, but only the former is used for aeroelastic panel-flutter problems. Satisfactory flutter optimal results are obtained, but the work concludes with a discussion of the challenges associated with the use of a bound method for aeroelastic problems, with specific complications posed by the advent of hump modes.

Optimization and Postbuckling Analysis of Curvilinear-Stiffened Panels Under Multiple-Load Cases

Recent studies have indicated that panels with curvilinear stiffeners offer a strong potential for structural tailoring. However, the design complexity requires use of numerical analysis and optimization techniques. This paper considers the problem of optimal design of a stiffened panel with cutouts and curvilinear stiffeners, under multiple-load cases. Multiple failure modes are considered: buckling, damage tolerance, stress, and crippling. An optimization framework is presented to minimize mass of the stiffened panel by a combined shape and sizing optimization subject to constraints on the individual failure modes. Different panel thicknesses are allowed for each region bounded by stiffeners or panel boundaries. The framework uses Python scripts to couple ABAQUS-based analysis with VisualDoc optimization package. A design example is presented to illustrate the capability, and the optimized design is compared with that obtained using industry-standard practices. A postbuckling analysis of the optimal design with four curvilinear stiffeners is carried out and discussed in detail.

h-Adaptive Stabilized Finite-Element Solver for Calculation of Generalized Aerodynamic Forces

A finite-element method based on the streamline-upwind/Petrov–Galerkin stabilization technique is developed to solve the compressible Euler equations. The method is extended for computing unsteady small disturbances in the flow domain as a result of boundary motion, which is applied through the linearized solid-wall boundary condition. The method is able to calculate the frequency-dependent generalized aerodynamic forces without any need for deformation of mesh inside the flow domain. Error estimates are used to drive automated h-refinement of mesh for steady-state and frequency-domain calculations. Steady-state solutions and generalized aerodynamic forces are compared to benchmark data for transonic and supersonic Mach numbers. The results show that the presence of shocks in the flow makes it difficult to use a single mesh for all computations, including the linearized flow. The h-refinement procedure is shown to be an effective way of ensuring reliable computations for the nonlinear and linearized solve...

Progress Towards Multidisciplinary Design Optimization of Truss Braced Wing Aircraft with Flutter Constraints

on multidisciplinary design optimization (MDO) of truss-braced wing airplanes. The primary focus has been to include utter constraints for structural sizing of the wing. The structural sizing uses a gradient-based optimization procedure along with an analytically calculated response function sensitivity with respect to the thickness design variables. It is shown that using the updated routine leads to lower structural mass in comparison with the fully-stressed structural design procedure used in the previous MDO studies. The primary reasons for the lower mass is that inertial weight relief due to secondary structure is now included in the sizing process, and the buckling analysis is now based on a linearized eigenvalue problem, as opposed to a simple beam Euler buckling criteria used for the previous study which was signicantly conservative. However, the results show that for a wing with lower mass the utter constraint becomes active for both strut-braced and truss-braced wing congurations. Hence, it is important to include those in the MDO studies to maintain feasibility of designs. Two challenges encountered during the process of including structural optimization with the utter constraint within the system-level MDO architecture are discussed along with the strategies devised to overcome them: convergence of structural optimization and the resulting numerical noise. A response surface methodology is used to integrate the structural optimization and system-level MDO and some initial results for the design of a truss-braced wing transonic transport airplane for minimum fuel consumption and emissions are presented.

Comparative Study on Optimal Stiffener Placement for Curvilinearly Stiffened Panels

Recent studies have shown that curved stiffeners offer potential for structural tailoring of metallic panels. However, the optimal placement of the stiffener curves has remained a challenge, due to both the presence ofmultiple localminima in the design space as well as the associated CPU cost to solve the problem. This paper presents two new approaches to design the stiffener curves by decomposition of the design space into size and shape variables. The approaches are built on a heuristic concept of effectiveness of a stiffener configuration, which argues that the most effective configuration will also provide the lowest optimized panel mass. The first approach estimates the best stiffener configuration, based purely on the first buckling mode of the unstiffened panel. The approach defines a heuristic metric for the effectiveness of a stiffener in increasing the buckling load capacity of a panel. The second approach uses optimization methods on both the sizing and shape variable subspaces. Mass is minimized over the sizing variable subspace, with constraint on buckling, while the buckling eigenvalue is maximized over the shape design variable subspace by varying the stiffener curves. The results are compared with optimization over a unified design space using a global optimization procedure, and it is shown that the proposedmethods lead to better designs at lower CPU cost.