Joshua D. Deaton

A Multidisciplinary Design Optimization Framework for Design Studies of an Ecient Supersonic Air Vehicle

A modular multidisciplinary analysis and optimization framework tool has been built with the goal of optimally designing a supersonic aircraft. This paper addresses the specic challenge of designing an ecient long range supersonic bomber aircraft. This framework includes all the disciplines normally required for supersonic aircraft design and it also includes disciplines specically required by an advanced military aircraft that is tailless and has embedded engines. Results from running the analysis framework for a B-58 supersonic bomber test case are presented as a validation of the methods employed.

Thermal-Structural Design and Optimization of Engine Exhaust-Washed Structures

Structures located aft of embedded engines on low observable aircraft, known as engine exhaust-washed structures (EEWS), are exposed to a combined loading environment that includes transient thermal effects in addition to conventional structural loading. Design in this environment is often complicated by non-intuitive, configuration-specific thermoelastic structural responses to elevated temperature and combined loading that result from design dependent thermal loads. In this work, the basic thermal-structural responses of EEWS components are explored to demonstrate the need for multidisciplinary optimization in EEWS design. A gradient-based thermal-structural optimization framework is developed to aid in the design of these components where thermal effects exhibit transient behavior. The framework involves properly updating both spatial and temporal design dependent thermal loads in structural optimization while managing transient thermoelastic responses as constraints. The framework is demonstrated on two structures that are subjected to combined thermal-structural loading where thermal effects are time varying.

Topology Optimization of Thermal Structures with Stress Constraints

It is known in topology optimization, that in the presence of thermal loading, the conventional maximum stiffness design objectives generally do not lead to maximum strength structures due to the design dependency of thermoelastic loads. In this paper we present the application of stress constraints to structural topology optimization problems with thermal loading in an effort to develop a new technique for the design of hot structures where thermal stresses are of primary concern. A modern stress-relaxation technique is employed to circumvent the singularity phenomena in the stress constraints. In addition, we utilize stress aggregation functions to reduce the number of constraints in the optimization problem. We note that pre-existing formulations for thermoelastic topology optimization and stress-constraint handling are employed, but for the first time they are combined to consider thermal stresses. Preliminary numerical results indicate that the stress-constrained problem leads to different designs with superior thermoelastic performance when compared to the minimum compliance problems. In today’s aerospace industry, a number of practical examples are evident where the capability developed in this work is desirable. These include the design of engine exhaust-washed structures (EEWS) on embedded engine aircraft and integrated thermal protection systems (TPS) on hypersonic vehicles. In both cases, structural components are subjected to an extreme combined loading environment that is characterized by elevated temperatures and design against thermal stresses is of paramount concern.

Thermal-Structural Analysis of Engine Exhaust-Washed Structures

Structures located aft of embedded engines on low observable aircraft, known as engine exhaust-washed structures (EEWS), are exposed to a combined loading environment that includes thermal effects in addition to conventional structural loading. Design in this environment is often complicated by non-intuitive, configuration-specific structural responses to elevated temperature and combined loading. In addition, effective analysis of exhaust-washed structures requires a coupled analysis procedure to determine accurate structural response. In this work, the history and design considerations of EEWS are briefly discussed and a coupled framework using finite element analysis has been developed and used to analyze a conceptual composite embedded engine exhaust nozzle and surrounding structure. A parametric analysis is then performed that investigates applied loading and structural parameters to gain insight into the EEWS system. The analysis framework presented in this work is extendable to alternate EEWS configurations and will also facilitate future structural optimization and structural reliability analysis.

Effectiveness of Different Model-Form Quantification Techniques as Applied to Thermal Physics-Based Simulations

In the past, the majority of work in the uncertainty quantification field has focused on parametric uncertainties inherent in design parameters within engineering problems. Current work has begun to incorporate model form uncertainties into the uncertainty quantification process. Model form uncertainty arises as a result of the uncertainty present in not knowing which model within a model set used to predict a system response is the best approximating model. Thus it becomes necessary to develop and utilize techniques for quantifying this uncertainty. This work presents a design scenario in which multiple models defining a single model set are used for predicting the same system response, and thus representing the presence of model form uncertainty. Four different model form uncertainty techniques are presented and applied to the model set consisting of three models, each used for predicting the transient temperature response at different locations within a corrugated-core sandwich panel used in thermal protection systems subject to thermal loading and boundary conditions to demonstrate the challenges inherent in each of the quantification techniques. The effectiveness of each technique is weighted against those of the other techniques.

Design of Engine Exhaust-Washed Structures for an Efficient Supersonic Air Vehicle MDO Application

Structural components located aft of embedded engines on low observable aircraft, known as engine exhaust-washed structures (EEWS), are exposed to an extreme, configuration specific, combined thermal/structural loading environment. As a result of this operating environment, and the unique design challenges it poses, the effectiveness of EEWS designs is a key factor in the overall performance of an embedded engine aircraft. This means that design requirements and effects of overall configuration variability on exhaust structures must be addressed in early stages of a new embedded engine aircraft design to ensure that the final system can continue to meet performance requirements as development progresses. This paper highlights the design considerations for engine exhaust-washed structures design, steps taken to incorporate EEWS design requirements into a configuration-level design process of an efficient supersonic air vehicle (ESAV), as well as multidisciplinary design optimization methods developed that focus directly on structural design in a thermal/structural environment.

Topology Optimization of Thermoelastic Structures using Stress-based Design Criteria

The design of thermal structures in the aerospace industry, including exhaust structures on embedded engine aircraft and hypersonic thermal protection systems, poses a number of complex design challenges that can be particularly well addressed using the material layout capabilities of structural topology optimization. However, no topology optimization methods are readily available with the necessary thermoelastic design capabilities as a significant portion of work in the topology optimization field is focused on cases of maximum stiffness design for structures subjected to externally applied mechanical loads. In addition, in the limited work on thermoelastic topology optimization, a direct treatment of thermal stresses, which are a primary consideration in thermal structures design, has not been demonstrated. Thus, in this paper, we present a method for the topology optimization of structures with combined mechanical and thermoelastic (temperature) loads that are subject to stress constraints. We present the necessary steps needed to address both the design-dependent thermal loads and accommodate the challenges of stress-based design criteria. A modern stress relaxation technique is utilized to remove the singularity phenomenon in stresses and the large number of constraints that result in the optimization problem are handled using a scaled aggregation technique that is shown to satisfy prescribed stress limits. Finally, the stress-based thermoelastic formulation is applied to two numerical example problems to demonstrate its effectiveness.