Aerospace Engineering Commons^™

Suppression Of Post-Buckling Deflection And Panel-Flutter Using Shape Memory Alloy, Mohammad Tawfik Abo El So-Oud

Mechanical & Aerospace Engineering Theses & Dissertations

A novel concept proposed is the use of Shape Memory Alloy (SMA) to reduce the panel thermal deflection and flutter responses. SMA has unique ability to recover large prestrains completely when the alloy is heated (by aerodynamic heating in the present case) above the austenite start temperature A_s. During the recovery process, a large tensile recovery stress occurs if the SMA is restrained.

In this thesis, a panel subject to the combined aerodynamic and thermal loading is investigated. A nonlinear finite element model based on von Karman strain displacement relation is utilized to study the effectiveness of SMA …

An Improved Thermal Mass Flow Controller For Hazardous And Precision Applications, William J. Alvesteffer

Mechanical & Aerospace Engineering Theses & Dissertations

A new mass flow controller has been designed which responds very rapidly to changes in control settings. The design was evolved after carefully studying the internal flow and the sources for thermal lag and other non-linear behavior. After discussing an overview of the basic mass flow controller operating principles, data will be presented which characterize the basic building blocks of an advanced flow sensor design. Subsequently, a flow model and control strategy have been developed and tested which reduce response lag significantly. Results of the new design, obtained experimentally under various transient conditions, will be discussed.

Long-Term Aircraft Structural Integrity Prediction Under The Influence Of Feedback Control, Si-Bok Yu

Mechanical & Aerospace Engineering Theses & Dissertations

This thesis investigates the influence of feedback control, and other factors associated with loading characteristics, on fatigue damage reduction and long-term integrity of aircraft structural components. An actively controlled flexible aircraft model and a new state space modeling procedure for crack growth are utilized to uncover important factors which influence airframe crack growth. A matrix of simulation test cases is constructed to cover such variables as open-loop operation, nominal closed-loop operation, perturbed closed-loop operation (i.e., feedback gain variation), nominal maneuver profile, perturbed maneuver profile (including overload strength and frequency), atmospheric gust, and mean stress level. Simulation output data including crack …

Jet Stability And Noise Computations Using Direct Numerical Simulation, Farouk Owis

Mechanical & Aerospace Engineering Theses & Dissertations

The computations of axisymmetric jet noise with symmetric disturbances are investigated using the direct numerical simulation of the unsteady compressible Navier-Stokes equations. High order accurate numerical schemes are employed for the solution of the governing equations. The investigation shows that MacCormack schemes with operator splitting and minimum dispersion error can be used to predict noise radiated from subsonic and supersonic jets with low and high Reynolds numbers. In addition, different kinds of nonreflecting boundary conditions are used at the inflow and outflow boundaries. These boundary conditions include characteristic boundary conditions, buffer domain technique and perfectly matching layer method. The results …

Large Amplitude Pitching Of Supermaneuver Delta Wings Including Flow Control, Yahia A. Abdelhamid

Mechanical & Aerospace Engineering Theses & Dissertations

The unsteady, three-dimensional Navier-Stokes equations are solved to simulate and study the aerodynamic response of a delta wing undergoing large amplitude pitching motion up to 90° angle of attack. The primary model under consideration consists of a 76° swept, sharp-edged delta wing of zero thickness, initially at zero angle of attack. The freestream Mach number and Reynolds number are 0.3 and 0.45 × 106, respectively. The governing equations are solved time-accurately using the implicit, upwind, Roe flux-difference splitting, finite-volume scheme. Both laminar and turbulent flow solutions are investigated. In the laminar flow solutions, validation of the computational results is carried …

Development And Application Of Adaptive Dynamic Grids For Wake Vortex/Ground Interaction, Ilker Emin Türkgeldi

Mechanical & Aerospace Engineering Theses & Dissertations

An adaptive and dynamic grid approach is developed for the numerical computations of wake vortex flow problems with ground interaction. The unnecessary grid points at the far field of the original, large, single zone grid are removed for computational efficiency. Next, the grid is modified into an adaptive one, where the fine core region keeps track of the vortices and can be split into two regions when the vortex separation distance exceeds a specified limit length. In the final step a multi zonal feature is added to this grid by means of two embedded grids placed at the vortex centers …

Ls-Dyna3d Modeling And Simulation For Uncontained Engine Debris Impact On Fuselage Skins, Robin Eileen Lawson

Mechanical & Aerospace Engineering Theses & Dissertations

Impact and penetration events for uncontained engine debris on fuselage skins are simulated using the LS-DYNA3D finite element analysis code. The LS-DYNA3D code is a nonlinear transient dynamic simulation tool with contact algorithms for impact. A finite element analysis is used to simulate the penetration of aluminum plates impacted by titanium impactors on aircraft-like skin panels. By gaining a more comprehensive understanding of this dynamic impact event, this work is meant to contribute to improving designs for damage tolerance and residual strength by providing modeling and analysis guidelines for the analyst.

Parametric studies are performed to determine the influence of …

Stability Of Three-Dimensional Compressible Boundary-Layers, Samarasingham Jeyasingham

Mechanical & Aerospace Engineering Theses & Dissertations

The failure repair process of a continuously operating device is studied in this research. Different cases that incorporate modeling of equipment deterioration, inspection, and maintenance for optimal maintenance policy are proposed. Markov processes are used to determine state probabilities, and the optimal value of the mean time to preventive maintenance is determined by maximizing the availability of the equipment with respect to the meantime preventive maintenance. The approach uses models that assume that equipment can fail due to both deterioration and random failures. Preventive maintenance can be performed from each working state to avoid deterioration failure. Economic effects are integrated …

Aeroelastic Load Alleviation Using Shunted Piezolectrics, Anna-Maria Rivas Mcgowan

Mechanical & Aerospace Engineering Theses & Dissertations

Several analytical and experimental studies clearly demonstrate that piezoelectric materials (piezoelectrics) can be used as actuators to actively control vibratory response including aeroelastic response. However, two important issues in using piezoelectrics as actuators for active control are: 1) the potentially large amount of power required to operate the actuators, and 2) the complexities involved with active control (added hardware, control law design and implementation). Active or passive damping augmentation using shunted piezoelectrics may provide a viable alternative. This approach requires only simple electrical circuitry and very little or no electrical power. Shunted piezoelectrics have been shown to provide an efficient …

Assessment Of A Higher Harmonic Control System For Minimizing Vibrations On A Dynamically Scaled Tiltrotor Model, David J. Piatak

Mechanical & Aerospace Engineering Theses & Dissertations

The performance of a higher harmonic control system called the Multipoint Adaptive Vibration Suppression System (MA VSS) at reducing 3/rev wing vibratory loads and fuselage vibrations on a dynamically-scaled tiltrotor model is presented. Previous wind tunnel tests on a semispan aeroelastic tiltrotor model have demonstrated the effectiveness of MAVSS for reducing wing vibratory loads using both an active flaperon and swashplate. The primary goal, however, of such a vibration suppression system is to reduce tiltrotor fuselage vibrations in order to improve passenger comfort. The present study addresses the reduction of both wing and fuselage vibrations using MA VSS active flaperons …

Continuous Adjoint Sensitivity Analysis For Aerodynamic And Acoustic Optimization, Kaveh Ghayour

Mechanical & Aerospace Engineering Theses & Dissertations

A gradient-based shape optimization methodology based on continuous adjoint sensitivities has been developed for two-dimensional steady Euler equations on unstructured meshes and the unsteady transonic small disturbance equation. The continuous adjoint sensitivities of the Helmholtz equation for acoustic applications have also been derived and discussed.

The highlights of the developments for the steady two-dimensional Euler equations are the generalization of the airfoil surface boundary condition of the adjoint system to allow a proper closure of the Lagrangian functional associated with a general cost functional and the results for an inverse problem with density as the prescribed target. Furthermore, it has …

Efficient Dynamic Unstructured Methods And Applications For Transonic Flows And Hypersonic Stage Separation, Xiaobing Luo

Mechanical & Aerospace Engineering Theses & Dissertations

Relative-moving boundary problems have a wide variety of applications. They appear in staging during a launch process, store separation from a military aircraft, rotor-stator interaction in turbomachinery, and dynamic aeroelasticity.

The dynamic unstructured technology (DUT) is potentially a strong approach to simulate unsteady flows around relative-moving bodies, by solving time-dependent governing equations. The dual-time stepping scheme is implemented to improve its efficiency while not compromising the accuracy of solutions. The validation of the implicit scheme is performed on a pitching NACA0012 airfoil and a rectangular wing with low reduced frequencies in transonic flows. All the matured accelerating techniques, including the …

Computational Modeling Of Airborne Noise Demonstrated Via Benchmarks, Supersonic Jet, And Railway Barrier, Moumen Idres

Mechanical & Aerospace Engineering Theses & Dissertations

In the last several years, there has been a growing demand for mobility to cope with the increasing population. All kinds of transportation have responded to this demand by expanding their networks and introducing new ideas. Rail transportation introduced the idea of high-speed trains and air transportation introduced the idea of high-speed civil transport (HSCT). In this expanding world, the noise legislation is felt to inhibit these plans. Accurate computational methods for noise prediction are in great demand.

In the current research, two computational methods are developed to predict noise propagation in air. The first method is based on the …

Setpoint Tracking Predictive Control In Chemical Processes Based On System Identification, Sinchai Chinvorarat

Mechanical & Aerospace Engineering Theses & Dissertations

A Kraft recovery boiler in a pulp-paper mill provides a means for recovery of the heat energy in spent liquor and recovery of inorganic chemicals while controlling emissions. These processes are carried out in a combined chemical recovery unit and steam boiler that is fired with concentrated black liquor and which produces molten smelt. Since the recovery boiler is considered to be an essential part of the pulp-paper mill in terms of energy resources, the performance of the recovery boiler has to be controlled to achieve the highest efficiency under unexpected disturbances.

This dissertation presents a new approach for combining …

Studies Related To The Design Of A Magnetic Suspension And Balance System For An Ultra-High Reynolds Number Flow Facility, Oscar Magno Michael Gomeiz

Mechanical & Aerospace Engineering Theses & Dissertations

The basic design principles for a magnetic suspension and balance system applied to the test section of an ultra-high Reynolds number facility are defined. The design of the cross-sectional area to be used in the test section is analyzed. The parameters of the permanent magnet to be used in the model inside the test section are investigated. The testing of magnetic fields at the center of a test pipe and validation of data by computer finite element analysis is described with the purpose of finding common results. The performance of the magnet configuration is evaluated with relation to the magnetic …

Skin-Stiffener Separation In Buckled Composite Plates And Shallow Shells, Mark Edward Robeson

Mechanical & Aerospace Engineering Theses & Dissertations

The development of an approximate analysis for predicting stresses in the skin-stiffener interface region of composite plates and shallow shells is presented. The analysis determines interlaminar normal stress and transverse shear stresses in the direction of the stiffener axial coordinate and the direction of the inplane coordinate perpendicular to the stiffener axis. The analysis accounts for skin-stiffener interfaces with nonzero thickness and for curvature in the skin and stiffener. The interlaminar normal stress and transverse shear stresses at the interface are applied to the lower face of the skin and the upper face of the stiffener flange as unknown functions, …

Design Optimization Of Magnetic Bearings And Magnetic Suspension Systems, V. Dale Bloodgood Jr.

Mechanical & Aerospace Engineering Theses & Dissertations

Magnetic suspension systems were first demonstrated as practical by Holmes and Beams in the 1930's. Since then, numerous academic researchers have worked with various types of these systems. Commercial applications have largely been limited to magnetic bearings for rotating machinery. Other applications that have held considerable promise include wind tunnel model suspensions, space payload pointing and vibration isolation systems, satellite momentum storage and control devices and electromagnetic launch systems. However, none of these have progressed significantly beyond the prototype stage. Maglev trains have not reached serious commercial service but are being aggressively developed in Germany and Japan.

Design methods for …

Saturation Control For Reduction Of Rotor Blade Lag Vibration, Sayam Saguanrum

Mechanical & Aerospace Engineering Theses & Dissertations

Within the context of this research, the performance of saturation control for reduction in the vibratory lag motion of helicopter rotor blades is investigated. The single-degree-of-freedom plant, which consists of a spring and damper attached to the rotor blade, is perturbed by an aerodynamic force, and produces the unwanted vibration. To restrict this vibration, the second-order controller is provided to couple with the blade system. It works adaptively, when the system is excited and the controller frequency is set at half of the blade lag frequency in accordance with the relationship of both natural frequencies. The nonlinear terms from the …

Approximate Analytical Relationships For Linear Optimal Aeroelastic Flight Control Laws, Ayman Hamdy Kassem

Mechanical & Aerospace Engineering Theses & Dissertations

This dissertation introduces new methods to uncover functional relationships between design parameters of a contemporary control design technique and the resulting closed-loop properties. Three new methods are developed for generating such relationships through analytical expressions: the Direct Eigen-Based Technique, the Order of Magnitude Technique, and the Cost Function Imbedding Technique. Efforts concentrated on the linear-quadratic state-feedback control-design technique applied to an aeroelastic flight control task. For this specific application, simple and accurate analytical expressions for the closed-loop eigenvalues and zeros in terms of basic parameters such as stability and control derivatives, structural vibration damping and natural frequency, and cost function …

Vortex Wake And Exhaust Plume Interaction, Including Ground Effect, Ihab Gaber Adam

Mechanical & Aerospace Engineering Theses & Dissertations

Computational modeling and studies of the near-field wake-vortex turbulent flows, far-field turbulent wake-vortex/exhaust-plume interaction for subsonic and High Speed Civil Transport (HSCT) airplane, and wake-vortex/exhaust-plume interaction with the ground are carried out. The three-dimensional, compressible Reynolds-Averaged Navier-Stokes (RANS) equations are solved using the implicit, upwind, Roe-flux-differencing, finite-volume scheme. The turbulence models of Baldwin and Lomax, one-equation model of Spalart and Allmaras and two-equation shear stress transport model of Menter are implemented with the RANS solver for turbulent-flow modeling.

For the near-field study, computations are carried out on a fine grid for a rectangular wing with a NACA-0012 airfoil section and …

Nonlinear Stability And Control Of Three-Dimensional Boundary Layers, Erik Janke

Mechanical & Aerospace Engineering Theses & Dissertations

The linear and nonlinear evolution of steady and traveling disturbances in three-dimensional incompressible boundary layer flows is studied using Parabolized Stability Equations (PSE). Extensive primary stability analyses for the model problems of Swept Hiemenz flow and the DLR Transition experiment on a swept flat plate are performed first. Second, and building upon these results, detailed secondary instability studies based on both the classical Floquet Theory and a novel approach that uses the nonlinear PSE are conducted. The investigations reveal a connection of unstable secondary eigenvalues to both the linear eigenvalue spectrum of the undisturbed mean flow and the continuous spectrum, …

Reduction Of Thermal Deflection And Random Response Of Composite Structures With Embedded Shape Memory Alloy At Elevated Temperature, Zhiwei Zhong

Mechanical & Aerospace Engineering Theses & Dissertations

A feasibility study on the reduction of thermal deflection and random response of the composite structures using shape memory alloys (SMA) at elevated temperatures is presented in this dissertation. The characteristics of SMA are introduced and the structural problems, static and dynamic, of SMA fiber reinforced composites are investigated. The stress-strain relations are developed for a composite lamina with embedded SMA fibers. The finite element system equations including shape memory effect are derived. A consistent two-step solution procedure is developed for solving the static and dynamic problems of composite structures with embedded SMA fibers subjected to combined acoustic and thermal …

Experimental Geometry Optimization Techniques For Multi-Element Airfoils, Drew Landman

Mechanical & Aerospace Engineering Theses & Dissertations

A study is reported on geometry optimization techniques for high-lift airfoils. A modern three-element airfoil model with a remotely actuated flap was designed, tested, and used in wind tunnel experiments to investigate optimum flap positioning based on lift. All the results presented were obtained in the Old Dominion University low-speed wind tunnel. Detailed results for lift coefficient versus flap vertical and horizontal position are presented for two airfoil angles-of-attack: 8 and 14 degrees. Three automated optimization simulations, the method of steepest ascent and two variants of the sequential simplex method, were demonstrated using experimental data. An on-line optimizer was demonstrated …

The Design And Testing Of An Inlet-Airfoil For A High Altitude Remotely Piloted Aircraft, Preston Bradley Martin

Mechanical & Aerospace Engineering Theses & Dissertations

The following work describes and validates a methodology for the aerodynamic design of a low drag, efficient inlet-airfoil to be used on the cooling installations of a high altitude remotely piloted aircraft. Owing to the primary aircraft design requirement of subsonic endurance at high altitude (85,000 ft), the flight conditions present an aerodynamically unfavorable combination of low chord Reynolds number (500,000) and high subsonic Mach number (0.5). At this flight condition, the inlet-airfoil must meet the heat exchanger cooling flow requirements while maintaining the aerodynamic performance of the airfoil. As a result, the design method is closely coupled with not …

Placement Of Piezoelectric Actuators For Active Control Of Vibration Using Modal Parameters, Xuegeng Zhu

Mechanical & Aerospace Engineering Theses & Dissertations

An equation is derived to model the piezoelectric actuators incorporation with flexible structures. This equation permits the comparison of the performance indices over the entire structure for a piezoelectric actuator with constant area, which is unachievable if the Finite Element Method is used for complicated structures.

An index has been developed for placement of piezoelectric actuator for control of vibration of a flexible structure. This index is derived from the definition of H2norm. Computation of the proposed index requires only the natural frequencies and corresponding mode shapes of the structures of interest. The method is well suited to large …

Thermal And Mechanical Behavior Of Cryogenic Propellant Tank Concepts For Advanced Launch Vehicles, H. Kevin Rivers

Mechanical & Aerospace Engineering Theses & Dissertations

An important step in developing a cost-effective, fully-reusable, launch vehicle is the development of durable, lightweight, insulated, cryogenic propellant tanks. Current cryogenic tanks are expendable, and much of the technology that exist is not usable on future vehicles. As part of the Reusable Launch Vehicle/ X-33 Program, an experimental apparatus for evaluating the effects of both thermal and mechanical loading on cryogenic-tank concepts was developed at the NASA Langley Research Center. Studies to determine the behavior of various liquid-oxygen- and liquid-hydrogen-tank concepts under simulated mission conditions were performed as part of this research and are reported. Selected analytical studies of …

Interactive Approach For Geometry Definition With Automatically Differentiated Sensitivities For Practical Airplane Design, Yvette Cordero

Mechanical & Aerospace Engineering Theses & Dissertations

First, a newly developed interactive surface generation tool is described for the conceptual design phase and aerodynamic shape optimization of aircraft. The new design tool is called Interactive Rapid Airplane Parametric Input Design (IRAPID) for fuselage and wing body configurations, and Blended Wing Body (BWB) generator for flying wing configurations. The development of the software is based on the RAPID methodology, which incorporates a partial differential equation approach to surface design. By incorporating physical airplane design parameters into the boundaty conditions of the partial differential equation, the solution surface of a wing configuration is generated. The construction of fuselage components …

A Comparison Between Simulated And Measured Free-Flight Vortex Encounter Behavior In The Nasa Langley Full-Scale Wind Tunnel, Robert A. Pfouts

Mechanical & Aerospace Engineering Theses & Dissertations

An examination of the use of static measurements in simulating dynamic aircraft­ wake encounters is presented. By comparing dynamic aircraft-wake vortex encounter measurements obtained in free-flight wind tunnel tests to data obtained from computer­ simulated encounters based on static wind tunnel data, a determination is made concerning the validity of static vortex models in a dynamic flight environment. The development and testing of specialized elements of a flight simulation code are presented and dynamic free-flight measurements and predicted results are compared.

This study shows that static modeling provides reasonable estimates for lateral encounter trajectories when the following aircraft model is …

Three-Dimensional Aerodynamic Design Optimization Using Discrete Sensitivity Analysis And Parallel Computing, Amidu Olawale Oloso

Mechanical & Aerospace Engineering Theses & Dissertations

A hybrid automatic differentiation/incremental iterative method was implemented in the general purpose advanced computational fluid dynamics code (CFL3D Version 4.1) to yield a new code (CFL3D.ADII) that is capable of computing consistently discrete first order sensitivity derivatives for complex geometries. With the exception of unsteady problems, the new code retains all the useful features and capabilities of the original CFL3D flow analysis code. The superiority of the new code over a carefully applied method of finite-differences is demonstrated.

A coarse grain, scalable, distributed-memory, parallel version of CFL3D.ADII was developed based on "derivative stripmining". In this data-parallel approach, an identical copy …

Aerodynamic Gradient-Based Optimization Using Computational Fluid Dynamics And Discrete Sensitivities For Practical Problems, Mohagna Jayendrarai Pandya

Mechanical & Aerospace Engineering Theses & Dissertations

A gradient-based shape optimization methodology based on quasi-analytical sensitivities has been developed for practical three-dimensional aerodynamic applications. The flow analysis has been rendered by a fully implicit, finite-volume formulation of the Euler and Thin Layer Navier-Stokes (TLNS) equations. The flow equations and aerodynamic sensitivity equation have been solved using an alternating-direction-implicit (ADI) algorithm for memory efficiency. A wing geometry model based on space-surface and planform parameterization has been utilized. The present methodology and its components have been tested via several comparisons.

Initially, the inviscid flow analysis for a wing has been compared with those obtained using an unfactored, Preconditioned Conjugate …