Harry H. Robertshaw

Active suppression of acoustic radiation from impulsively excited structures

The objective is to use active control to suppress the acoustic energy that is radiated to the far field from a structure that has been excited by a short‐duration pulse. The problem is constrained by the assumption that the far‐field pressure cannot be directly measured. Therefore, a method is developed for estimating the total radiated energy from measurements on the structure. Using this estimate as a cost function, a feedback controller is designed using linear quadratic regulator theory to minimize the cost. Computer simulations of a clamped–clamped beam show that there is appreciable difference in the total radiated energy between a system with a controller designed to suppress vibrations of the structure and a system with a controller that takes into account the coupling of these vibrations to the surrounding fluid. The results of this work provide a framework for a general, model‐based method for actively suppressing transient structural acoustic radiation that can also be applied to steady, narro...

Active structural acoustic control of broadband disturbances

A control design technique is developed to actively suppress the acoustic power radiated from a structure, with negligible fluid loading, that is persistently excited by narrow‐band or broadband disturbances. The problem is constrained by the assumption that the far‐field pressure cannot be measured directly. A method for estimating the total radiated power from measurements on the structure is developed. Using this estimate as a cost function and assuming knowledge of the spectrum of the disturbance, a controller is designed using the linear‐quadratic‐Gaussian (LQG) theory to minimize the cost. Computer simulations of a clamped–clamped beam show that there is a significant difference in the total radiated power between a system with a vibration‐suppression controller and a system with an acoustic controller that accounts for the coupling of these vibrations to the surrounding fluid. In some cases, the acoustic controller increases the system vibration in order to minimize the radiated power.

Design and Wind-Tunnel Analysis of a Fully Adaptive Aircraft Configuration

This work describes the design and construction of a fully adaptive aircraft configuration used as an experimental testbed for aerodynamic modeling and flight control. The adaptive model is designed to achieve large scale shape changes in order to investigate morphing for multi-mission UAVs. There are five independent planform changes along with independent twist control for each wing. Wind tunnel testing was conducted in Virginia Techs Stability tunnel to analyze the aerodynamic characteristics and evaluate the usefulness of having a UAV with multiple configuration capability. Wind tunnel tests of various planform configurations indicate that different configurations yields minimum drag over a range of flight conditions.

A model to compare the flight control energy requirements of morphing and conventionally actuated wings

This work presents a theoretical analysis of the actuation energy requirements of a morphing aircraft. Morphing aircraft lack discrete control surfaces and use distributed actuation of the wing surface for maneuvering. An adaptive camberline is designed that generates morphed wing shapes in response to variations in leading and trailing-edge camber. Aerodynamic energy expressions are derived from the camberline functions using a unique energy computation stemming from the vortex lattice method (VLM). Beam theory is applied to morphing airfoil sections situated along the wingspan to obtain closed-form strain energy expressions. The resulting work expressions are combined and energy optimal wing deflections are found using Lagrange multipliers. In the optimization, total energy is the cost function and constraints are placed on achieving commanded changes in lift and moment coefficients. The functions are numerically implemented to compare work expressions for a wing with morphing inputs and a conventional wing, with inboard and outboard flaps. It is shown analytically that morphing aircraft have the capability to outperform conventional vehicles in terms of required flight control energy. This work also provides a theoretically sound methodology for morphing wing energy analysis that can be applied in future trade studies of morphing vehicles. Introduction Morphing aircraft are a topic of current research interest in the aerospace community. Such aircraft allow shape optimization over the entire flight regime _________________________ * Graduate Student, Department of Aerospace and Ocean Engineering, Student Member AIAA † Graduate Student, Department of Mechanical Engineering ‡ Professor, Department of Mechanical Engineering § Professor, Department of Aerospace and Ocean Engineering, Associate Fellow AIAA ¶ George R. Goodson Professor, Department of Mechanical Engineering Copyright

A Design and Analysis of a Morphing Hyper-Elliptic Cambered Span (HECS) Wing

The HECS wing, developed by NASA Langley Research Center, features a nonplanar, hyper- elliptically swept leading and trailing edge as well as spanwise camber. In this paper, we propose a single-degree-of-freedom mechanism to provide a means for the wing to continuously morph from a planar to a nonplanar configuration. The mechanism, which is something like a scissor linkage, uses a repeating quaternary-binary link configuration to translate the motion from one wing segment to the next. The mechanism is synthesized such that, with one input to the first seg- ment in the chain, the other wing segments move into their desired positions. To predict the aerodynamic loads associated with this morphing dihedral change, linear theory is applied to the HECS wing configuration at distinct morphed positions. For the structural study, a finite ele- ment representation of the mechanism is developed, and a linear static analysis at different morphed positions is performed. Using the predicted aerodynamic loads, the structural analysis investigates different materials and cross sections of the mechanism members to determine a need for redesign due to failure from buckling and bending stress. A design is finalized which, com- pared to the design of the original model, lightens the structure as well as increases its strength. These results are beneficial for the next phase of model development of the mechanism. This work shows that a relatively simple kinematic mechanism can produce the desired range of mo- tion for a variable dihedral HECS wing. It also provides insight into the aerodynamic effects of the nonplanar wing configuration with an analysis of the structural integrity of the mechanism under loading.

Structural Acoustic Control of a Shape Memory Alloy Composite Beam

Active control of sound radiation from a clamped, baffled, composite beam with embedded Shape Memory Alloy (SMA) fibers was demonstrated using two dif ferent control strategies. The unique behavior of the SMA reinforced composites was uti lized to allow minimization of radiated sound for harmonic beam vibration and placement of peak radiation response at specified frequencies within a controllable range.

Morphing wings for unmanned aircraft

Abstract Here a computational model is presented which predicts the force, stroke and energy needed to overcome aerodynamic loads encountered by morphing wings, to perform aircraft manoeuvres. The aerodynamic load algorithms have been verified against more time-expensive codes. The overall model allows for desired flight-path inputs and variable control algorithms. The four modules that make up the model integrate well, to make a tool that enables the study of the required actuator requirements for morphing wings.

Comments on prospects of fully adaptive aircraft wings

New generations of highly maneuverable aircraft, such as Uninhabited Combat Air Vehicles (UCAV) or Micro Air Vehicles (MAV) are likely to feature very flexible lifting surfaces. To enhance stealth properties and performance, the replacement of hinged control surfaces by smart wings and morphing airfoils is investigated. This requires a fundamental understanding of the interaction between aerodynamics, structures, and control systems. The goal is to build a model consistent with distributed control and to exercise this model to determine the progress possible in terms of flight control (lift, drag and maneuver performance) with an adaptive wing. Different modeling levels are examined and combined with a variety of distributed control approaches to determine what types of maneuvers and flight regimes may be possible. This paper describes the current progress of the project and highlights some recent findings.

Rethinking the Design of Presentation Slides: Creating Slides That Are Readily Comprehended

Presentation slides, when designed well, can significantly increase the amount of information that the audience comprehends. However, when the slide has type that can not be quickly read, the audience often gives up on the slide. Moreover, when the slide does not orient well, when the slide has too much information, or when the order of information on the slide is unclear, the audience can easily become confused. Given that these mistakes can prevent the audience from comprehending the presentation’s content, presenters should strive to format slides that can be quickly read, that effectively orient, that have a reasonable amount of information, and that have a clear order of information. Unfortunately, the slide formats that many engineering presenters use do not meet these goals. Presented in this paper are recommendations for the format of presentation slides—specifically, the typography, color, and layout of presentation slides (or overheads). An assumption for these recommendations is that the purpose of the presentation is to communicate technical information efficiently to the audience. Given that assumption, the goal of a slide’s typography is to have type that can be read as quickly as possible. To obtain that goal, this paper recommends a bold sans serif typestyle such as Arial that is at least 18 points. In regard to color, the most important goal is to have colors that can be clearly distinguished from each other. To obtain that goal, this paper recommends either a dark color against a light background or a light color against a dark background. In regard to layout, the goal is to have a slide design for which the audience can quickly discern the point of the slide and then can divide attention between the presenter and the slide as the presenter discusses the slide. To obtain that goal, this paper recommends the national laboratory design of a short sentence headline supported primarily by images. Other reasons exist for choosing this national lab design. Although this paper focuses on how readily that slides following this national lab design can be comprehended, the paper does direct the reader to references that discuss two other reasons for using this national laboratory design: (1) how well the slide design helps the audience remember details, and (2) how persuasive the slide design is.Copyright

Attacking the damage identification problem

A review of the evolution of the field of damage identification is presented. Trends of research and the present state of the field are discussed and directions of future research are postulated. Ideally, an automated damage identification method incorporated into the smart structure scheme would be able to detect damage as it is incurred by the structure, determine the location and extent of the damage, predict when and if catastrophic failure of the structure will occur, and alert the operator as to how the performance of the structure is affected in order for appropriate steps to be made to remedy the situation. Obviously, this is no easy task but it is essential that it is clearly defined how the research fits into the ultimate goal of developing an automated, noninvasive damage identification method. In attempting to quantify changes in response characteristics due to damage on a structure, it is very important to be aware of the inherent variabilities one might encounter in acquiring these response characteristics. These variabilities may come from computational algorithms, sensor error, or environmental effects. A method which assumes a priori ignorance to the manifestations of damage in the response characteristics of the structure is presented. This method uses inductive learning to statistically isolate changes in response characteristics due to damage from those due to the inherent variabilities. In order to validate the method, an example is presented which identifies the existence and location of a small test mass on an aluminum plate via the measurement of the structural impedance-response of the plate.