Suzanne Weaver Smith

Model Refinement and Damage Location for Intelligent Structures

Intelligent Structural Systems (ISS) are structures which integrate control and computational subsystems into a single structural entity. Ideally, an ISS would adapt its dynamic characteristics to meet performance objectives at any instant. Therefore, ISS have a tremendous potential for a wide range of structural applications in which efficient integrated systems are necessary, from large space structures to low noise emission submarines. To realize this potential, however, advances are needed in several technical areas, including development of embedded sensors/actuators, algorithms for control/adaptation, techniques for health monitoring and integrated approaches for system design.

Optimal matrix approximants in structural identification

Problems of model correlation and system identification are central in the design, analysis, and control of large space structures. Of the numerous methods that have been proposed, many are based on finding minimal adjustments to a model matrix sufficient to introduce some desirable quality into that matrix. In this work, several of these methods are reviewed, placed in a modern framework, and linked to other previously known ideas in computational linear algebra and optimization. This new framework provides a point of departure for a number of new methods which are introduced here. Significant among these is a method for stiffness matrix adjustment which preserves the sparsity pattern of an original matrix, requires comparatively modest computational resources, and allows robust handling of noisy modal data. Numerical examples are included to illustrate the methods presented herein.

Underlying modal data issues for detecting damage in truss structures

Independent of the modal identification techniques employed for damage detection, use of measured modal data limits the expectations for damage location. These limitations are examined using the distribution of modal strain energy and the sensitivity of the frequency and mode shapes to structural stiffness changes. For given measured modal information of specific accuracy, this examination reveals the following: (1) damage detection is feasible for members that contribute significantly to the strain energy of the measured modes, (2) the modes which are most effective in detecting damage to certain critical members can be identified, and (3) a relationship can be drawn between the accuracy of the measured modes and frequencies and damage detection feasibility.

An experimental study of structural damage detection using incomplete measurements

In this paper, algorithmic approaches to enhance damage detection capability when faced with incomplete measurements are addressed. The incomplete measurement problem arises in part because of the mismatch in the number of degrees of freedom included in the structural math model versus the number of degrees of freedom instrumented during structural testing. Studies comparing model reduction, eigenvector expansion, and a hybrid model reduction/eigenvector expansion are performed using experimental data. These approaches to the incomplete measurement problem are evaluated within the frameworks of optimal matrix update theory (both sparsity and non-sparsity preserving algorithms) and minimum rank perturbation theory, which are both applicable for model refinement as well as damage location. Experimental evaluation of the proposed approaches utilize data from the NASA LaRC 8-bay and MDA 10-bay truss facilities.

Design of HALE Aircraft Using Inflatable Wings

Inflatable wings are examined for use in high altitude long endurance (HALE) aircraft. Due to the unique requirements for HALE flight such as high aspect ratio and and unconventional airfoil profiles due to the low density and high aerodynamic efficiency, this places significant constraints on inflatable wing designs for use in such vehicles. Since inflatable wings achieve their structural stiffness from inflation pressure, the high bending loads experienced at the root of high aspect ratio wings must be supported by either extremely high inflation pressures, mechanical means, or some combination thereof. Different inflatable designs result in different load carrying capabilities that are matched with the aerodynamic loads encountered by extremely high aspect ratio vehicles. This paper discusses the design considerations and requirements of inflatable wings under such restrictions for use in HALE applications.

An Experimental Study of Structural Health Monitoring Using Incomplete Measurements

In this paper, algorithmic approaches to enhance structural health monitoring capability when faced with incomplete measurements are addressed. The incomplete measurement problem has two aspects: (i) experimental measurement of a lesser number of modes of vibration than that of the analytical model and (ii) experimental measurement of a lesser number of degrees of freedom than that of the analytical model. Studies comparing model reduction, eigenvector expansion, and a hybrid model reduction/eigenvector expansion to address the second contribution are performed using experimental data. These approaches to the incomplete measurement problem are evaluated within the frameworks of multiple-constraint matrix adjustment (both sparsity and nonsparsity preserving algorithms) and minimum rank perturbation theory, which are both applicable for model refinement as well as damage location. Experimental evaluation of the proposed approaches utilize data from the NASA Langley Research Center 8-bay truss and McDonnell Douglas Aerospace 10-bay truss facilities.

Design and Flight Testing of Inflatable Wings with Wing Warping

The paper presents work on testing of inflatable wings for unmanned aerial vehicles (UAVs). Inflatable wing his tory and recent research is discussed. Design and con struction of inflatable wings is then covered, along with ground and flight testing. Discussions include predictions and correlations of the forces required to warp (twist) the wings to a particular shape and the aerodynamic forces generated by that shape change. The focus is on charac terizing the deformation of the wings and development of a model to accurately predict deformation. Relations be tween wing stiffness and internal pressure and the impact of external loads are presented. Mechanical manipula tion of the wing shape on a test vehicle is shown to be an effective means of roll control. Possible benefits to aero dynamic efficiency are also discussed.

Development and Flight Testing of a UAV with Inflatable-Rigidizable Wings

The present paper provides a snapshot of current work on developing and flying UAVs with inflatable-rigidizable wings. The BIG BLUE (Baseline Inflatable Glider BalloonLaunched Unmanned Experiment) project at the University of Kentucky funded under a NASA Workforce Development Grant has a primary objective of promoting aerospace careers to undergraduate students. The goal of the project is to flight-test a high-altitude aircraft with inflatable-rigidizable wings to determine concept feasibility for a Mars explorer mission. The wings are stowed in the fuselage, inflate during ascent, and rigidize with exposure to UV light. The vehicle will descend as a glider using tail control. Ease of manufacturing is the primary design constraint in choosing the wing profile and planform. Results from combined XFoil and ANSYS analyses on multiple profiles are presented. Low altitude flight tests using the inflatable-rigidizable wings is discussed, as well as a high altitude wing deployment test.

Intergenerational Transmission Attributions in Relationships With Parents and Intimate Others

This study examined the attributions of young adults about their relationships with their parents and intimate others. In addition to their attributional reports, participants also provided information about the quality of their intimate relationships. The findings indicated that higher relationship quality was related to attributions in ways that were consistent with attributional theory. In addition, attributional differences between current and past relationships suggested relationship-sustaining versus relationship-terminating attributional patterns. Attributions about intimate relationships also were associated with attributions about relationships with parents. Specifically, (a) the attributions that individuals made about the positive aspects of their relationships with their mothers and (b) and the attributions about the negative aspects of their relationships with their fathers were related to their attributions in their intimate relationship. The findings suggest some refinements in attribution theory regarding close relationships and introduce the value of exploring the intergenerational transmission of attributional patterns.

Development of a Finite Element Model of Warping Inflatable Wings

This paper presents development of a structural model of warping inflatable wings. In order to quickly and effectively analyze the effects of aerodynamic loading and to consider design options for warping actuation, a detailed finite element model is required. The methodology used to develop and initially validate a finite element model of an inflatable wing is described in this paper. The wing is a complex structural system including intricate geometry, internal pressurization and a woven fabric shell structure. This effort includes determination of material properties via laboratory tests. These are verified with finite element simulations of simple inflatable cylinders constructed of similar material. The process used to create a finite element simulation of the wing is presented, including modeling assumptions and nonlinear analysis stages. Results for various loadings of interest are included. Finally, the paper presents initial validation of the finite element model using results of static cantilever wing bending and twisting loads applied at the inflatable wing tip. Although the model represents important deformation characteristics of the inflatable wing, it is generally too stiff compared to experimental results. Future modifications to the model and further validation are also discussed.