Aerospace Engineering Commons^™

Free Vibrations Of A Piezoelectric Body, J. S. Yang, R. C. Batra

Mechanical and Aerospace Engineering Faculty Research & Creative Works

We present a systematic analysis of the eigenvalue problem associated with free vibrations of a finite piezoelectric body. The analysis is based on an abstract formulation of the three-dimensional theory of piezoelectricity. A series of fundamental properties of free vibrations of a piezoelectric body are proved concisely. The problem of free vibrations of a piezoelectric plate governed by the two-dimensional plate equations due to Mindlin is treated in a similar manner. © 1994 Kluwer Academic Publishers.

Experiences In The Integration Of Design Across The Mechanical Engineering Curriculum, Ashok Midha, J. M. Starkey, D. P. Dewitt, R. W. Fox

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The Faculty of the School of Mechanical Engineering at Purdue University have effected a major change in the Purdue Mechanical Engineering program by integrating design throughout the curriculum. In doing so, a significant level of faculty interaction has been achieved as well. The goals of the curriculum revision are: (1) to improve student skills in how to solve open-ended design problems, (2) to reduce the core of the curriculum to allow flexibility in course selection, and allow time for solving design problems, (3) to improve student skills in team work and communications, and (4) to improve student skills in using …

Impact On Laminated Composites: Recent Advances, Serge Abrate

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Impact damage in structures made out of composite materials is a major concern since such damage can be introduced during the life of the structure, and its mechanical properties can be drastically reduced as a result. In a previous review of the literature on impact on composite materials, this author considered 285 published before 1989. In this article over 300 articles most of which appeared after 1989 are reviewed. These figures indicate that this is a very active area of research, and the present paper seeks to present a comprehensive view of the latest developments. Taken together, these two reviews …

On The Interface Stability Of A Neck Propagating In A Sheet Reinforced With Shape-Memory Fibers, C. Q. Ru, R. C. Batra

Mechanical and Aerospace Engineering Faculty Research & Creative Works

We propose a simple model of necking in a sheet reinforced with straight fibers made of a shape-memory alloy and examine conditions under which the interface between the necked and the unnecked region is morphologically stable. We use the Mullins and Sekerka (1963, J. Appl. Phys. 34, 323-330; 1964, J. Appl. Phys. 35, 444-450) method, established for studying the stability of a moving interface in a solidification problem, to investigate the interface stability of a propagating neck. It is found that the moving straight interface is morphologically stable for several typical cases even in the absence of surface-tension effects, and …

Buckling Of A Coating Bonded To A Round Bar Subjected To Axial Extension. Mech. Mater. 15 (1993) 131-138, C. W. Bert, Victor Birman

Mechanical and Aerospace Engineering Faculty Research & Creative Works

No abstract provided.

Optimal Design Of Laminated Plates And Shells, Serge Abrate

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Designing structures made out of composite materials represents a challenging task, since not only the thickness of the element must be determined to satisfy the constraints of the problem, but, in addition, the number of plies in the laminate and their relative orientation must also be selected. Because of their strong anisotropy, a careful selection of lay-up is required to make the best use of the capabilities of the material. In this article the optimum design of laminated plates and shells subjected to constraints on strength, stiffness, buckling loads, and fundamental natural frequencies are examined. © 1994.

On The Propagation Of A Shear Band In A Steel Tube, R. C. Batra, Xiangtong Zhang

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Marchand and Duffy tested thin-walled steel tubes in a split Hopkinson torsion bar at a nominal strain-rate of approximately 1600/s and could not determine conclusively whether a shear band initiating at a point in the tube propagated around the circumference in one direction or in both directions. They estimated the speed of propagation to be 520 m/s in the former case and 260 m/s in the latter. Here we simulate their test numerically and find that the shear band propagates in both directions around the circumference of the tube. When the tube is twisted at a nominal strain-rate of 5000/s, …

Use Of Hopfield Neural Networks In Optimal Guidance, S. N. Balakrishnan, James Edward Steck

Mechanical and Aerospace Engineering Faculty Research & Creative Works

A Hopfield neural network architecture is developed to solve the optimal control problem for homing missile guidance. A linear quadratic optimal control problem is formulated in the form of an efficient parallel computing device known as a Hopfield neural network. Convergence of the Hopfield network is analyzed from a theoretical perspective, showing that the network, as a dynamical system approaches a unique fixed point which is the solution to the optimal control problem at any instant during the missile pursuit. Several target-intercept scenarios are provided to demonstrate the use of the recurrent feedback neural net formulation.

Approximate Analytical Guidance Schemes For Homing Missiles, S. N. Balakrishnan, Donald T. Stansbery

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Closed form solutions for the guidance laws are developed using modern control techniques. The resulting two-point boundary value problem is solved through the use of the state transition matrix of the intercept dynamics. Results are presented in terms of a design parameter.

Vortex Developments Over An Accelerated Airfoil At High Angles Of Attack, Jacopo A. Frigerio

Opportunities for Undergraduate Research Experience Program (OURE)

Proper control of unsteady separated flow developments over the lifting surfaces of an aircraft may prove to be an effective method of enhancing aerodynamic lift and producing better aircraft performance. Due to the complexity of unsteady flow separation and subsequent flow developments, experimental exploration and observation are essential in providing a source for comparison and verification with theoretical and computational models. In light of these motivations, a new experimental system that is capable of generating wide of range of unsteady flow histories has been developed and employed to visualize flow developments over an airfoil in accelerated-decelerated motion. The paper presents …

Experimental Investigation On The Longitudinal Stability Of A P51 Mustang Aircraft Model, Erich Fitzpatrick

Opportunities for Undergraduate Research Experience Program (OURE)

This project involved the development of a test model of the P-51 Mustang aircraft and an experimental investigation of its stability. The model was developed to investigate the influence of the main horizontal tail parameters ( tail incidence, position of c.g., stabilizer moment arm,etc.)on the pitching moment around the aircraft’s center of gravity. To accomplish such a task, a test model was designed and fabricated with flat plate and airfoil wing configurations. The tail incidence of the flat plate stabilizer is adjustable over the entire range of positive and negative angles. A rechargeable, electric motor mounted in the fuselage adjusts …

Aerodynamics Of Solar Vehicles, Richard R. Pardun

Opportunities for Undergraduate Research Experience Program (OURE)

The purpose of this research project is to design the shape of a fully road worthy vehicle operating under nothing but the power of the sun. This vehicle was to meet all racing regulations of The Sunrayce and the World Solar Challenge. Because of the specific use of this vehicle, this project provides a chance to explore the aerodynamically ideal vehicle. Little attention has to be paid to practicality. The result is a very streamlined, highly aerodynamically efficient car, that is still stable and safe.

Analysis Of A Thrust Vectoring Fighter Aircraft Using Realtime Flight Simulation, Clinton A. Thessen

Opportunities for Undergraduate Research Experience Program (OURE)

A real-time flight simulation model based on the McDonnell Douglas F/A-18 Hornet was created. This model was then modified with two different styles of thrust vectoring so that a study of each system's effect on the aircraft's pitch performance could be conducted in order to determine the best system. At present, work is proceeding on the development of active flight controls for the aircraft. After that effort is completed the thrust vectoring study can begin.

Development Of A Data Acquisition System For Common Velocity Anemometers, Dane P. Drefke

Opportunities for Undergraduate Research Experience Program (OURE)

The objective of this project was to develop a software package that would allow more efficient, accurate, and easier use of wind tunnel data. The software was to receive an analog signal from an array of hot wire anemometers, convert the signal to a digital format, and then process the raw data, converting it into values of properties which have practical value to the user. Unfortunately, due to scheduling conflicts, this project never left the software development stage. The user interface was successfully designed. The signal conversion portion of the package was not completed and the package was never tested.

Analytical Guidance Laws And Integrated Guidance/Autopilot For Homing Missiles, S. N. Balakrishnan, Donald T. Stansbery, J. H. Evers, J. R. Cloutier

Mechanical and Aerospace Engineering Faculty Research & Creative Works

An approach to integrated guidance/autopilot design is considered in this study. It consists of two parts: 1) recognizing the importance of polar coordinates to describe the end game in terms of problem description and measurement acquisition, the terminal guidance problem is formulated in terms of polar coordinates; 2a) through the use of the state transition matrix of the intercept dynamics, a closed form solution for the transverse command acceleration is obtained; and 2b) through a commonly used approximation on time-to-go and a coordinate transformation, a family of proportional navigation optimal guidance laws is obtained in a closed form. A typical …

Computer Simulation Of Three-Dimensional Mechanical Assemblies: Part I - General Formulation, Yong Fang, Frank W. Liou

Mechanical and Aerospace Engineering Faculty Research & Creative Works

In Part I of this paper, a dynamic modeling system for the simulation of three-dimensional mechanical assemblies is presented. With this simulation tool, a designer can interactively create an assembly of mechanical components ready for dynamic analysis. The modeling system presented in this paper include» the derivation of the equations of motion of spatial multi-body systems, and the formulation of the equations to model the associated collision detection and collision responses. Part II of this paper is to introduce the geometry modeling and computer simulation of 3D systems.

On The Use Of Levy's Method For Symmetrically Laminated Composite Plates, Serge Abrate

Mechanical and Aerospace Engineering Faculty Research & Creative Works

For rectangular plates with two opposite edges simply supported and no bending twisting coupling, Levy's method can yield exact solutions for static deflections, free vibrations and buckling loads. However, three distinct solutions are obtained, depending on the relative magnitude of the plate rigidities, which in turn are functions of material properties, laminate thickness and lay-up. In this communication a stiffness invariant formulation is used to identify those laminates which fall under the three cases defined. © 1993.

On Minimizing Thermal Deflections Of Laminated Plates, Serge Abrate

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Thermal deflections of symmetrically laminated plates that are continuous over many line supports are determined using the Rayleigh-Ritz method. The constitutive equations and the thermal loads are expressed in terms of four non-dimensional lamination parameters. Layups that minimize thermal deflections are determined for several types of composite plates subjected to temperature increases that vary linearly through the thickness.

Computer Simulation Of Three-Dimensional Mechanical Assemblies: Part Ii - Computer Simulation, T. C. Chou, Frank W. Liou

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Computer simulation of the kinematic and dynamic behaviors of mechanical assemblies has become a very important tool in design and manufacturing, because the designer can foresee how a product is going to perform before the product is actually fabricated. However, up to now, the most current simulation modules are based on analysis from another kinematic or dynamic module by specifying the mating conditions between components, and then displaying the motion on the screen. This computer simulation actually performs similarly to a movie and can only provide visual checking. The drawback of this simulation approach is that designers are forced to …

Procase: A Prototype Of Intelligent Case-Based Process Planning System With Simulation Environment, Hao Yang, Wen F. Lu

Mechanical and Aerospace Engineering Faculty Research & Creative Works

An intelligent case-based process planning system with interactive graphic simulation environment, PROCASE, is developed lo demonstrate an integrated methodology of case-based process planning system. In PROCASE, both the mechanical part features and the machining operations are represented with a frame-based scheme. PROCASE contains a retriever, a modifier, a simulator and a repairer. It distinguishes itself from traditional rule-based process planning systems by representing the process planning knowledge through previous process planning cases instead of production rules. It therefore can overcome some problems in the traditional rule-based expert systems. PROCASE currently resides in IRIS Indigo workstation. With a user-friendly graphic environment, …

Second Law Analysis Of Active Magnetic Regenerative Hydrogen Liquefiers, L. Zhang, S. A. Sherif, T. N. Veziroglu, John W. Sheffield

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Recent published work in the area of magnetic refrigeration reports on its potential for greater efficiency and high reliability. This paper presents an exergy analysis of a three-stage active magnetic regenerative (AMR) hydrogen liquefier which cools a hydrogen gas stream at 77 K and 1 atm to hydrogen liquid at 20 K. Ortho - para conversion of hydrogen is accomplished in a heat exchanger employing a 10 atm helium fluid that cycles in the refrigerator. The performance of the system is described in terms of the cooling capacity and exergy losses as functions of the magnetic material type, magnetic bed …

Observations On Higher-Order Beam Theory, A. Bhimaraddi, K. Chandrashekhara

Mechanical and Aerospace Engineering Faculty Research & Creative Works

A parabolic shear-deformation beam theory assuming a higher-order variation for axial displacement has been recently presented. In this theory, the axial displacement variation can be selected so that it results in a suitable admissible transverse shear-strain variation across the depth of the beam. This paper examines several transverse shear-strain variations that can go with the aforementioned higher-order theory. Apart from the usual simple parabolic variation, six other shear-strain variations are considered: the sinusoidal variation, cubic, quartic, quintic, and sixth-order polynomials. All these variations for transverse shear-strain satisfy the requirement that the shear strain be zero at the extreme fibers (z …

A Parametric Investigation On Aeroelastic Behavior Of An Airfoil In Steady Flow, Edward J. Feltrop

Opportunities for Undergraduate Research Experience Program (OURE)

A parametric study is performed to investigate the influence of a number of aerodynamic, inertia and damping parameters upon the dynamic response of an elastically-supported rigid wing in steady flow. The dimensionless equations governing the vertical and angular motion of this wing are solved by an interactive computer program which facilitates the systematic analysis of the effects of changes in these parameters upon the dynamic response of the system. This investigation demonstrates the coupling of the vertical and angular motion of the wing, and illustrates the strong influence of damping, spring stiffness, initial spring deflection, and initial angular velocity upon …

Physical And Numerical Experiments On Flat Plate Boundary Layers, Scott A. Atterberry

Opportunities for Undergraduate Research Experience Program (OURE)

The results of an interactive computer program developed to predict the boundary layer flow over a flat plate with suction or injection are presented. The results include the solutions for the Blasius function and its derivatives, the velocity profiles, the shear stress distribution, and the temperature distribution. The program can be used for predicting steady, two-dimensional, laminar, viscous flow fields with temperature gradients.

A wind tunnel setup that can be used in addition to the computer program is described. The setup description includes a description of the flat plate, the wind tunnel test section, and the suction/injection unit. The experimental …

Development Of An Experimental System For Steady And Unsteady Aerodynamic Testing, Jacopo Frigerio

Opportunities for Undergraduate Research Experience Program (OURE)

This paper discusses the design and development of a new experimental system designed to produce a variety of steady and unsteady flows. Accelerating, decelerating and oscillating flows over lifting surfaces are primary examples of the unsteady flow configurations that can be generated. Also this report presents details of preliminary tests performed to determine the performance of this system. These include quantitative and qualitative testing on two-dimensional and three-dimensional flow configurations.

Determining The Chemical Composition Of Cloud Condensation Nuclei, Allen L. Williams, Jane E. Rothert, Kent E. Mcclure, Darryl J. Alofs, Donald E. Hagen, Daniel R. White, A. R. Hopkins, Max B. Trueblood

Mechanical and Aerospace Engineering Faculty Research & Creative Works

This second progress report describes the status of the project one and one-half years after the start. The goal of the project is to develop the instrumentation to collect cloud condensation nuclei (CCN) in sufficient amounts to determine their chemical composition, and to survey the CCN composition in different climates through a series of field measurements. Our approach to CCN collection is to first form droplets on the nuclei under simulated cloud humidity conditions, which is the only known method of identifying CCN from the background aerosol. Under cloud chamber conditions, the droplets formed become larger than the surrounding aerosol, …

Planning And Control Of A Robotic Manipulator Using Neural Networks, Xavier J. R. Avula, Heng Ma, Anil Malkani, Jay-Shinn Tsai, Luis C. Rabelo

Chemical and Biochemical Engineering Faculty Research & Creative Works

An architecture which utilizes two artificial neural systems for planning and control of a robotic arm is presented. The first neural network system participates in the trajectory planning and the motion decision-making process. The second neural network system provides the correct sequence of control actions with a high accuracy due to the utilization of an unsupervised/supervised neural network scheme. The utilization of a hybrid hierarchical/distributed organization, supervised/unsupervised learning models, and forward modeling yielded an architecture with capabilities of high level functionality.

Hydration Behavior Of Laser Dye Aerosols Of Mixed Composition Having High Critical Supersaturations, Max B. Trueblood, Donald E. Hagen, Darryl J. Alofs

Mechanical and Aerospace Engineering Faculty Research & Creative Works

This Study Concerns Aerosol Particles of Mixed Composition. the Particles Contain a Water Insoluble Core (Polystyrene Latex), Surrounded by a Water Soluble Shell (Various Fluorescent Dyes). a Collison Nebulizer and an Electrostatic Aerosol Classifier Are Used to Prepare the Aerosol; its Critical Supersaturation Spectrum is Measured with a Diffusion Cloud Chamber. Experiments Were Done using Four Different Dyes (Disodium Fluorescein, Sulforhodamine 640, Sulforhodamine B and Rhodamine 560 Chloride) with Five Different Polystyrene Latex Sphere Sizes. the Results Indicate that a Kohler-Type Behavior is Obeyed. This Technique of Putting a Soluble Coating Onto an Insoluble Core is Found to Be a …

A Complete Model Characterization Of Brushless Dc Motors, N. Hemati, Ming-Chuan Leu

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The authors address the modeling problem associated with brushless DC motors (BLDCMs) with nonuniform air gaps that operate in a range where magnetic saturation may exist. The mathematical model includes the effects of reluctance variations as well as magnetic saturation to guarantee proper modeling of the system. An experimental procedure is developed and implemented in a laboratory environment to identify the electromagnetic characteristics of a BLDCM in the presence of magnetic saturation. It is demonstrated that the modeling problem associated with the class of BLDCMs can be formulated in terms of mathematically modeling a set of multidimensional surfaces corresponding to …

Use Of Time Varying Dynamics In Neural Network To Solve Multi-Target Classification, S. N. Balakrishnan, J. Rainwater

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Several types of solutions exist for multiple target tracking. These techniques are computation-intensive and in some cases very difficult to operate online. The authors report on a backpropagation neural network which has been successfully used to identify multiple moving targets using kinematic data (time, range, range-rate and azimuth angle) from sensors to train the network. Preliminary results from simulated scenarios show that neural networks are capable of learning target identification for three targets during the time period used during training and a time period shortly after. This effective classification period can be extended by the use of networks in coordination …