Aerospace Engineering Commons^™

Finite Element Analysis For Nonlinear Flutter Suppression Of Composite Panels At Elevated Temperatures Using Piezoelectric Materials, Run Chen Zhou

Mechanical & Aerospace Engineering Theses & Dissertations

Nonlinear coupled finite element equations of motion are derived for composite panels with embedded piezoelectric layers subjected to aerodynamic, thermal loads and applied electric fields. The nonlinear equations of motion describe the coupling between a structure and an electrical network through the piezoelectric effect. The von Karman large-deflection strain-displacement relations, quasi-steady first-order piston theory aerodynamics, quasi-steady thermal stress theory and linear piezoelectricity theory are used to formulate the nonlinear coupled panel flutter finite element equations of motion in nodal displacements. The governing equations, which are referred to actuator and sensor equations, form a basis for piezoelectric actuation and sensing. Following …

Numerical Simulation Of The Nonlinear Response Of Composite Plates Under Combined Thermal And Acoustic Loading, Jayashree Moorthy

Mechanical & Aerospace Engineering Theses & Dissertations

A time-domain study of the random response of a laminated plate subjected to combined acoustic and thermal loads is carried out. The features of this problem also include given uniform static inplane forces. The formulation takes into consideration a possible initial imperfection in the flatness of the plate. High decibel sound pressure levels along with high thermal gradients across thickness drive the plate response into nonlinear regimes. This calls for the analysis to use von Karman large deflection strain-displacement relationships. A finite element model that combines the von Karman strains with the first-order shear deformation plate theory is developed. The …

Vibration Control With Piezoelectric Actuation Applied To Nonlinear Panel Flutter Suppression, Zhihong Lai

Mechanical & Aerospace Engineering Theses & Dissertations

Panel flutter is a large-deflection limit-cycle motion excited by the airflow, which is only on one side of a panel. The objective of this research is to analytically study the panel flutter limit-cycle suppression using nonlinear vibration control techniques with piezoelectric actuation. It is well known that piezoelectric materials are characterized by their ability to produce an electrical charge when subjected to a mechanical strain. The converse piezoelectric effect can be utilized to actuate a panel by applying an electrical field. Piezoelectric actuators are driven by feedback controllers, and control the panel dynamics. For a simply supported panel with piezoelectric …

Multigrid Acceleration Of Time-Dependent Solutions Of Navier-Stokes Equations, Sarafa Oladele Ibraheem

Mechanical & Aerospace Engineering Theses & Dissertations

Recent progress in Computational Fluid Dynamics is encouraging scientists to look at fine details of flow physics of problems in which natural unsteady phenomena have hitherto been neglected. The acceleration methods that have proven very successful in steady state computations can be explored for time dependent computations. In this work, an efficient multigrid methods is developed to solve the time-dependent Euler and Navier-Stokes equations. The Beam-Warming ADI method is used as the base algorithm for time stepping calculations. Application of the developed algorithm proved very efficient in selected steady and unsteady test problems. For instance, the inherent unsteadiness present in …

Prototype Space Fabrication Platform, James A. Bessel, James M. Ceney, David M. Crean, Edward A. Ingham, David J. Pabst

Theses and Dissertations

Current plans for constructing large structures in space entail fabricating the primary components, such as truss segments, on the ground and assembling them in space. This process requires an exorbitant number of support missions, and methods to minimize the number must be considered. Whenever the space shuttle is launched, its external tank is jettisoned and destroyed prior to reaching orbit. This aerospace grade aluminum structure can be carried into orbit and utilized extrusively. The Prototype Space Fabrication Platform SFP fabricates aluminum materials, reduced from external tanks, into functional trusses. The trusses are strong and can be used as the primary …

Boundary Layer Influences On The Subsonic Near-Wake Of A Family Of Three-Dimensional Bluff Bodies, Charles Willliam Alcorn

Mechanical & Aerospace Engineering Theses & Dissertations

A study is reported on subsonic bluff body near-wake flows. It has been determined that one family of bluff bodies, namely slanted-base ogive cylinders, can experience either a closed recirculating near-wake, or a longitudinal vortex near-wake depending on the base slant-angle and the Reynolds number. This suggests a dependence of near-wake parameters on the state of the boundary layer ahead of separation. This report addresses the influence of the boundary layer on the near-wake of slanted-base bluff bodies. Experiments were conducted in two facilities, the 6-inch Magnetic Suspension and Balance System (MSBS) at NASA Langley Research Center and the Old …

Studies On Nonequilibrium Phenomena In Supersonic Chemically Reacting Flows, Rajnish Chandrasekhar

Mechanical & Aerospace Engineering Theses & Dissertations

This study deals with a systematic investigation of nonequilibrium processes in supersonic combustion. The two-dimensional, elliptic Navier-Stokes equations are used to investigate supersonic flows with nonequilibrium chemistry and thermodynamics, coupled with radiation, for hydrogen-air systems. The explicit, unsplit MacCormack finite-difference scheme is used to advance the governing equations in time, until convergence is achieved.

For a basic understanding of the flow physics, premixed flows undergoing finite rate chemical reactions are investigated. Results obtained for specific conditions indicate that the radiative interactions vary substantially, depending on reactions involving HO$\sb2$ and NO species, and that this can have a noticeable influence on …

Fiber Enhanced Viscoelastic Damping Polymers And Their Application To Passive Vibration Control, Houchun Xia

Mechanical & Aerospace Engineering Theses & Dissertations

A new composite damping material is investigated, which consists of a viscoelastic matrix and high elastic modulus fiber inclusions. This fiber enhanced viscoelastic damping polymer is intended to be applied to light-weight flexible structures as surface treatment for passive vibration control. A desirable packing geometry for the composite material is proposed, which is expected to produce maximum shear strain in the viscoelastic damping matrix. Subsequently, a micromechanical model is established in which the effect of fiber segment length and relative motion between neighboring fibers are taken into account. Based on this model, closed form expressions for the effective storage and …

Robust Control Of Nonlinear Multibody Flexible Space Structures, Atul G. Kelkar

Mechanical & Aerospace Engineering Theses & Dissertations

A generic nonlinear math model of a multibody flexible system is developed. Asymptotic stability of such systems using dissipative compensators is established. It is proved that, under certain conditions, this class of systems exhibit global asymptotic stability under dissipative compensation. The dissipative compensators considered are static as well as dynamic dissipative compensators. The stability proofs are based on passivity approaches, Lyapunov methods, as well as a key property of such systems, i.e., skew-symmetricity of certain matrix. The importance of the stability results obtained is that the stability is robust to parametric uncertainties and modeling errors.

For static dissipative compensators, it …

Navier-Stokes Simulation Of Quasi-Axisymmetric And Three-Dimensional Supersonic Vortex Breakdown, Hamdy A. Kandil

Mechanical & Aerospace Engineering Theses & Dissertations

Computational simulation of supersonic vortex breakdown is considered for internal and external flow applications. The interaction of a supersonic swirling flow with a shock wave in bounded and unbounded domains is studied. The problem is formulated using the unsteady, compressible, full Navier-Stokes equations which are solved using an implicit, flux-difference splitting, finite-volume scheme. Solutions are obtained for quasi-axisymmetric and three-dimensional flows. The quasi-axisymmetric solutions are obtained by forcing the components of the flowfield vector to be equal on two axial planes, which are in close proximity to each other. For the flow in a bounded domain, a supersonic swirling flow …

Theoretical Results Supporting The Use Of Passive Damping As Augmentation To The Active Control Of Flexible Structures, Joseph Vincent Harrell

Mechanical & Aerospace Engineering Theses & Dissertations

One challenge of modern control technology is how to control a flexible structure with accuracy, speed, and economy of effort. Controlling a structure with many degrees of freedom by purely active means implies the implementation of inordinate sensors and actuators and creates the need for numerous calculations that must be done instantly. Experiments have shown that practical structures under active control alone can suffer instabilities due to modal vibrations beyond the bandwidth of the active controller. Furthermore, if there is a high degree of model uncertainty, instabilities can be produced by inputs of modal vibrations not occurring in the system …

An Experimental Determination Of The Effects Of Blending Collocated And Non-Collocated Sensor Measurements To Control A Flexible Structure, Richard G. Cobb

Theses and Dissertations

An experimental investigation was performed controlling a cantilevered beam in bending using proportional feedback on a blend of collocated and non-collocated sensor measurements using a single actuator. Exact transfer functions between the control input and the measurements were developed and compared to the finite element method. By analyzing the open loop pole-zero locations as a function of the measurement blending, insight into the closed loop behavior is obtained. Minimum phase behavior can be maintained for a range of the blending ratio. Results using blended control were compared to both proportional collocated feedback and compensated collocated feedback using LQG methods. The …

The Influence Of Structural Optimization On The Aeroelastic Properties Of A Vertical Tail, David G. Miller

Theses and Dissertations

The purpose of this thesis is to investigate the influence of structural optimization parameters on the structural and aeroelastic behavior of a vertical tail. The outside geometry of the tail is assumed fixed. The objective of the optimization is to reduce the structural member sizes so that the overall weight of the tail is minimized. The influence that design loads, design constraints, design variable linking has on the optimal design is observed examining several design cases. The static aeroelastic properties a flutter speeds of the various design cases are then compared. The doublet lattice method is used to calculate the …

A New Preloaded Beam Geometric Stiffness Matrix With Full Rigid Body Capabilities, Paul A. Bosela, D. G. Fertis, F. J. Shaker

Civil and Environmental Engineering Faculty Publications

Space structures, such as the Space Station solar arrays, must be extremely light-weight, flexible structures. Accurate prediction of the natural frequencies and mode shapes is essential for determining the structural adequacy of components, and designing a controls system. The tension pre-load in the 'blanket' of photovoltaic solar collectors, and the free/free boundary conditions of a structure in space, causes serious reservations on the use of standard finite element techniques of solution. In particular, a phenomenon known as 'grounding, or false stiffening, of the stiffness matrix occurs during rigid body rotation. The authors have previously shown that the grounding phenomenon is …

Grounding Of Space Structures, Paul A. Bosela, D. G. Fertis, F. J. Shaker

Civil and Environmental Engineering Faculty Publications

Space structures, such as the Space Station solar arrays, must be extremely light-weight, flexible structures. Accurate prediction of the natural frequencies and mode shapes is essential for determining the structural adequacy of components, and designing a controls system. The tension pre-load in the 'blanket' of photovoltaic solar collectors, and the free/free boundary conditions of a structure in space, causes serious reservations on the use of standard finite element techniques of solution. In particular, a phenomenon known as 'grounding', or false stiffening, of the stiffness matrix occurs during rigid body rotation. This paper examines the grounding phenomenon in detail. Numerous stiffness …

Dynamic Analysis Of Space-Related Linear And Nonlinear Structures, Paul A. Bosela, F. J. Shaker, D. G. Ertis

Civil and Environmental Engineering Faculty Publications

In order to be cost-effective, space structures must be extremely light-weight, and subsequently, very flexible structures, The power system for Space Station 'Freedom' is such a structure. Each array consists of a deployable truss mast and a split 'blanket' of photo-voltaic solar collectors. The solar arrays are deployed in orbit, and the blanket is stretched into position as the mast is extended. Geometric stiffness due to the preload make this an interesting non-linear problem. The space station will be subjected to various dynamic loads, during shuttle docking, solar tracking, attitude adjustment, etc. Accurate prediction of the natural frequencies and mode …

A Modal Analysis And Modelling Of A Lightly Damped Large Space Structure, Scott E. George

Theses and Dissertations

This study involves the modification to the PACOSS Dynamic Test Article to create a lightly damped representative large space structure with closely spaced, low frequency modes. An experimental modal analysis is performed to recharacterize the low frequency flexible vibration modes. A finite element model is created using MSC/NASTRAN to predict low frequency behavior using both real eigenvalue analysis and frequency response analysis. Then a reduced order model is created and fine-tuned to represent the dynamics of the structure for the identified low frequency modes.

Control Of Low-Speed Turbulent Separated Flow Over A Backward-Facing Ramp, John C. Lin

Mechanical & Aerospace Engineering Theses & Dissertations

The relative performance and flow phenomena associated with several devices for controlling turbulent separated flow were investigated at low speeds. Relative performance of the devices was examined for flow over a curved, backward-facing ramp in a wind tunnel, and the flow phenomena were examined in a water tunnel using dye-flow visualization. Surface static pressure measurements and oil-flow visualization results from the wind tunnel tests indicated that transverse grooves, longitudinal grooves, submerged vortex generators, vortex generator jets (VGJ’s), Viets’ fluidic flappers, elongated arches +a + a (positive angle of attack), and large-eddy breakup devices (LEBU’s) +a + a placed near the …

Shape Sensitivity Analysis And Optimization Of Skeletal Structures And Geometrically Nonlinear Solids, Ching-Hung Chuang

Mechanical & Aerospace Engineering Theses & Dissertations

Formulations and computational schemes for shape design sensitivity analysis and optimization have been developed for both skeletal structures and geometrically nonlinear elastic solids. The continuum approach, which is based on the weak variational form of the governing differential equation and the concept of the material derivative, plays a central role in such a development.

In the first part of this work, the eigenvalue and eigenvector sensitivity equations for skeletal structures are derived with respect to configuration variables of joint and support locations. This derivation is done by the domain method as well as the boundary method. The discrete approach for …

Development Of A Stratified Plate Model For Composite Panels, Alan L. Lesmerises

Theses and Dissertations

A new model for composites represents a composite panel as an alternating stack of isotropic matrix and orthotropic fiber-dominated layers. An energy approach results in a set of partial differential equations and boundary conditions where the mechanical properties of the matrix and fibers appear separately. Two solution methods are developed. The first, called Strata Theory is developed for general applications, while the second, called the Exact Stratified Plate, is used as a benchmark for comparison to Strata Theory. Both solutions assume zero gradients of displacement through the thickness of a fiber layer. They are compared for an isotropic material and …

Linearized Dynamics Of Space Structures With Articulated Appendages, Gopichand Koganti

Mechanical & Aerospace Engineering Theses & Dissertations

The inherent difficulties of the conventional spacecraft design, which first considered the optimization with respect to structural variables and then with respect to control variables, have led to the concept of Controls-Structures Interactive Design. The success of the CSI design of Space structures without articulated appendages has prompted the extension of the CSI design to systems with articulated appendages. The presentation is of two parts, the first part deals with the derivations of the equations of motion and the second part deals with the eigenvalue/vector approximations.

Three approaches, namely: the multibody approach, the finite element based approach with hinge joints …

Finite Element Frequency Domain Solution Of Nonlinear Panel Flutter With Temperature Effects And Fatigue Life Analysis, David Yongxiang Xue

Mechanical & Aerospace Engineering Theses & Dissertations

A frequency domain solution method for nonlinear panel flutter with thermal effects using a consistent finite element formulation has been developed. The von Karman nonlinear strain-displacement relation is used to account for large deflections, the quasi-steady first-order piston theory is employed for aerodynamic loading and the quasi-steady thermal stress theory is applied for the thermal stresses with a given change of the temperature distribution, ΔΤ (x, y, z). The equation of motion under a combined thermal-aerodynamic loading can be mathematically separated into two equations and then solved in sequence: (1) thermal-aerodynamic postbuckling and (2) limit-cycle oscillation. The Newton-Raphson iteration technique …

The Solution Of A Singular Integral Equation Arising From A Lifting Surface Theory For Rotating Blades, Mark H. Dunn

Mathematics & Statistics Theses & Dissertations

A technique is presented for the solution of a linear, two dimensional, singular, Volterra integral equation of the first kind. The integral equation, originally developed by Farassat and Myers, is derived from the basic equations of linearized acoustics and models the lifting force experienced by an infinitesimally thin surface moving tangent to itself. As a particular application, the motion of modern high speed aircraft propellers (Advanced Technology Propellers) is considered. The unknown propeller blade surface pressure distribution is approximated by a piecewise constant function and the integral equation is solved numerically by the method of collocation. Certain simplifying assumptions applied …

Integrated System Identification And Adaptive State Estimation For Control Of Flexible Space Structures, Chung-Wen Chen

Mechanical & Aerospace Engineering Theses & Dissertations

Accurate state information is crucial for control of flexible space structures in which the state feedback strategy is used. The performance of a state estimator relies on accurate knowledge about both the system and its disturbances, which are represented by system model and noise covariances respectively. For flexible space structures, due to their great flexibility, obtaining good models from ground testing is not possible. In addition, the characteristics of the systems in operation may vary due to temperature gradient, reorientation, and deterioration of material, etc. Moreover, the disturbances during operation are usually not known. Therefore, adaptive methods for system identification …

Maximum Likelihood Estimation For Distributed Parameter Models Of Large Beam-Like Structures, Ji Yao Shen

Mechanical & Aerospace Engineering Theses & Dissertations

Proposed large space structures have many characteristics that give an advantage to modeling their structural dynamics by a set of partial differential equations (PDE's). By far, the most effort put forth in studying system identification and control to date has been based on finite element models. Despite its acceptability, such lumped parameter models have inevitable deficiencies primarily because of their complexity. Both approaches are complementary and each should be used where it is most effective. But the fact is that the distributed parameter approach has not been developed to the level of maturity as for the lumped parameter approach.

Motivated …

Sensitivity Analysis For The Selection Of Linear Quadratic Regulator Weighing Parameters Q And R For Active Vibration Suppression Of A Cantilevered Beam, Steven L. Story

Theses and Dissertations

There has been much interest during the past decade to develop and launch large space structures. The high cost of launching material into orbit will require that these structures be assembled in space using light weight elements which are vulnerable to dynamic excitations. Active control may be necessary to rapidly attenuate large amplitude vibrations. The active vibration control system is usually designed after the structure has been optimized. The integrated design of the control system and the structure may provide additional weight savings. This thesis presents a sensitivity analysis of the structure/ control optimization problem. The structure used is an …

High Heat Flux Cooling For Spacecraft Electronics, Louis C. Chow, John E. Leland

Office for Research Publications and Presentations

An experimental investigation of flow boiling in a curved channel has been performed to ascertain its value in electronics cooling applications. Results have been obtained for flow velocities of 1 to 5 m/s and subcooling of 0.5 to 40 K. These results were compared to those of straight channel under identical velocity and subcooling conditions. The critical heat flux of the curved channel was found to be greater than that of the straight channel. In some cases the increase was found to be marginal, however. An unexplained temperature shift in the nucleate boiling regime was experienced during some experiments. Because …

Radiometer For The Investigation Of Infrared Emissions From Flames And Rocket Plumes, Kathy Underhill, M. Keith Hudson, Jason Willis, Mokhtar Mofidi, Matthew J. Russo

Journal of the Arkansas Academy of Science

A prototypical radiometer using standard one inch interference filters and a lead selenide detector was constructed for use in flame and rocket plume studies. This radiometer was designed to employ a 600 Hz chopper and chopper frequency/phase reference circuit for signal processing. Bandpass filters centered for either 2.7 mum or 4.45 mum were placed in the optical path. The passed carbon dioxide or water vapor band energy irradiated the lead selenide detector, resulting in an output voltage. This signal was then fed into a dedicated synchronous detector. The signal was then recorded by a computer system equipped with an analog-to-digital …

Finite Element Investigation Into The Dynamic Instability Characteristics Of Laminated Composite Panels, Walter W. Taylor Jr.

Theses and Dissertations

Dynamic instability of a laminated composite panel subjected to a transverse load is studied. Up to cubic variations in the thickness coordinate are included in the inplane displacement field, and only the constant component is kept in the transverse displacement. The transverse shear strains retain only linear displacement terms and vary parabolically through the thickness. The complete quadratic displacement functions are included in the inplane strains. A 36 degree of freedom shell element is used to obtain numerical results. The static snap through load vs displacement curve, as well as the critical collapse load, is examined by invoking the Riks …

Material Properties Of Silicon Carbide Fibers With Continuously Applied Sol-Gel Alumina Coatings, Christian C. Daehnick

Theses and Dissertations

An investigation was conducted to determine the effect of non-alpha- alumina coatings applied under varying conditions on some of the properties of silicon carbide fibers. Limited characterization of the coating by optical, scanning electron, and transmitted electron microscopy as well as energy- dispersive x-ray analysis was performed. Tensile tests were used to determine changes in elastic modulus, ultimate strength, and strain to failure of the coated fibers relative to uncoated fibers. The coatings were found to lower the mean value of the measured properties as their thickness increased, but the measurements were not accurate enough to determine if this corresponded …