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1991

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Articles 1 - 30 of 91

Full-Text Articles in Aerospace Engineering

An Investigation Of The Floor Attachment Assembly Of A Large Transport Aircraft Seat Subjected To Crash Dynamic Loadings, Mark William Creager Dec 1991

An Investigation Of The Floor Attachment Assembly Of A Large Transport Aircraft Seat Subjected To Crash Dynamic Loadings, Mark William Creager

Master's Theses - Daytona Beach

Accident investigations by the National Transportation Safety Board concluded that the passenger seat and restraint systems found in today's aircraft used by the airlines are inadequate to protect the occupant in airplane crashes. Computer models were developed of the seat-track assembly and finite element analyses were performed subjected to crash dynamic loadings. The seat-track interface was modeled with gap elements to accurately model the geometric interaction between the track and seat-track fittings. Results showed large deformations and stresses above yielding in both the seat and track when subjected to accelerations prescribed for certification under the Federal Aviation Administration (FAA) regulations.

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An Analysis Of Tracking And Impact Predictions, Susanne V. Lefebvre Dec 1991

An Analysis Of Tracking And Impact Predictions, Susanne V. Lefebvre

Theses and Dissertations

The accuracy of the United States Space Command's early Tracking and Impact Predictions and its OPREP-3 report initiation procedure are analyzed. The study involves satellites which decayed between 1987 and 1990. Each of the early decay predictions are compared to the final prediction with the resulting time error compared to the accuracy level asserted by the Space Surveillance Center. The results of this study indicate that the accuracy of the decay predictions is usually, but not always, within the asserted accuracy level. The results also suggest the existence of a positive bias indicating that the early decay predictions are routinely …

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High-Resolution Tvd Schemes For The Analysis Of 1. Inviscid Supersonic And Transonic Flows. 2. Viscous Flows With Shock-Induced Separation And Heat Transfer, Mark A. Driver Dec 1991

High-Resolution Tvd Schemes For The Analysis Of 1. Inviscid Supersonic And Transonic Flows. 2. Viscous Flows With Shock-Induced Separation And Heat Transfer, Mark A. Driver

Theses and Dissertations

Application of TVD schemes to both inviscid and viscous flows is considered. The mathematical and physical bases of TVD schemes are discussed. First and second-order accurate TVD schemes and a second-order accurate Lax- Wendroff scheme are used to compute solutions to the Riemann problem in order to investigate the capability of each to resolve shocks, rarefactions, and contact surfaces. Second-order finite-volume and finite-difference TVD schemes are used to obtain solutions to inviscid supersonic and transonic cascade flow problems. TVD schemes are shown to be superior to the Lax-Wendroff family of schemes for both transient and steady-state computations. TVD methodology is …

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A Top-Down Performance Analysis Of A Pegasus-Based Space Strike System, Douglas E. Collins Dec 1991

A Top-Down Performance Analysis Of A Pegasus-Based Space Strike System, Douglas E. Collins

Theses and Dissertations

The feasibility of using Pegasus launch vehicle as a conventional weapons platform is examined. Using a top-down approach, the analysis addresses the fundamental question of whether such a system should be considered for development. The measures of effectiveness considered are delivery range, probability of destroying the target, and responsiveness. Each of the measures is assessed at its top-level and analyzed only to the level of detail needed to address the fundamental question. The study indicates that attaining a high probability of destroying the target requires extremely precise control over the burnout conditions and that the system must be on constant …

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Improvement Of The Thermodynamic Model For A Flux-Difference-Splitting Algorithm For The Computation Of High Speed Flows, Mark E. Schieve Dec 1991

Improvement Of The Thermodynamic Model For A Flux-Difference-Splitting Algorithm For The Computation Of High Speed Flows, Mark E. Schieve

Theses and Dissertations

This study modifies the thermodynamic model of a previously existing first-order accurate Flux Difference Splitting (FDS) algorithm for planar, supersonic nozzles. The thermodynamic model is changed from a calorically and thermally perfect gas to a thermally perfect (imperfect) gas, where the flow field is frozen or non-reacting. The frozen flow and imperfect gas assumptions more nearly approximate the real behavior of a fluid in supersonic propulsive nozzles. The modified code can now account for specific heats that vary as a function of temperature. Using curve fittings of JANAF thermochemical data, the code can handle nine gas species, as well, to …

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Experimental Investigation Of Trailing Edge Crenulation Effects On Losses In A Compressor Cascade, Steven J. Decook Dec 1991

Experimental Investigation Of Trailing Edge Crenulation Effects On Losses In A Compressor Cascade, Steven J. Decook

Theses and Dissertations

The effects of blade trailing edge crenulations on wake losses in a compressor cascade were investigated at the Air Force Institute of Technology. The cascade used NACA 64-A905 blades with a turning angle of about 30 to model last row stators of an axial flow compressor. Three blade configurations were used: unmodified blades, blades with large crenulations, and blades with small crenulations. Wake losses and mixing were evaluated in four flow conditions, generated by combinations of increased freestream turbulence and sidewall boundary layer removal. Injection of air perpendicular to the inlet flow increased freestream turbulence from about 0.15% to about …

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Investigation Of A Flux-Difference-Splitting Numerical Method In Supersonic Nozzles, Danny P. Allen Dec 1991

Investigation Of A Flux-Difference-Splitting Numerical Method In Supersonic Nozzles, Danny P. Allen

Theses and Dissertations

This research investigated the effects of adding a second-order flux- difference-splitting (FDS) correction term to an existing computer code that is based on a first-order FDS algorithm. It was determined that the second-order algorithm did improve the accuracy of the code for a source flow analysis, but second-order behavior could not be confirmed by the error convergence patterns. It was also discovered that, when tested across an oblique shock wave, the second-order correction terms had minimal influence on the accuracy and shock capturing ability of the first-order accurate FDS method.

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Ground Collision Avoidance Using A Variable Incidence Altitude Measurement System For The A-7 Aircraft, Thomas A. Hartung Dec 1991

Ground Collision Avoidance Using A Variable Incidence Altitude Measurement System For The A-7 Aircraft, Thomas A. Hartung

Theses and Dissertations

This study examines the use of a forward looking sensor in the implementation of an automatic terrain following system. The effect of the incidence angle is studied as well as methodologies to include dynamic motion in the pointing of the sensor beam. The methods examined include fixed angle with respect to the aircraft, dynamics driven by a simple gain, and dynamics directed to gather the terrain information a fixed time interval ahead of the aircraft. Incidence angles of 25, 50, 75, and 90 are examined. The terrain obstacles include a single parabolic hill, a step change is terrain, and a …

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Thermal Nonequilibrium Effects On Turbine Cascade Aerodynamics, Jill L. R. Shaw Dec 1991

Thermal Nonequilibrium Effects On Turbine Cascade Aerodynamics, Jill L. R. Shaw

Theses and Dissertations

The AFIT Total Variation Diminishing Euler Code (ATEC) was modified to include a thermal nonequilibrium model to investigate high temperature effects associated with vibrational relaxation in a transonic turbine cascade. Incorporation of this model into ATEC and creating ANTEC (AFIT Nonequilibrium TVD Euler Code) was accomplished in three steps. Steady-state solutions obtained with ANTEC were compared with those obtained with ATEC for various inlet and exit conditions. The Courant-Friedrichs-Levy criterion was held constant to ATEC; however, it required variation for ANTEC. Blade temperature profiles, temperature difference contours in the vicinity of the trailing edge and the value of the ratio …

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Analysis Of An Advanced Fighter Aircraft Using Jet Flap Techniques And The Vortex Lattice Method, Steven P. Snyder Dec 1991

Analysis Of An Advanced Fighter Aircraft Using Jet Flap Techniques And The Vortex Lattice Method, Steven P. Snyder

Theses and Dissertations

A computer code using the vortex lattice method with modified boundary conditions was used to determine the induced aerodynamic characteristics of high aspect ratio, vectoring, exhaust nozzles located at the wing root of a canard configured fighter aircraft. Comparison with existing wind tunnel data verified results of the method. The exhaust was modeled as a singularly blown jet flap at deflection angles of -10, 0, 10, 20, 30, and 40 degrees. Jet momentum coefficients were based on gross engine thrust for maximum afterburner and military power settings at a Mach number of 0.6 and an altitude of 20,000 ft. Lift, …

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Experimental Investigation Into The Effects Of Riblets On Compressor Cascade Performance, James A. Rothenflue Dec 1991

Experimental Investigation Into The Effects Of Riblets On Compressor Cascade Performance, James A. Rothenflue

Theses and Dissertations

The effects of adding riblets to the blades of a subsonic, linear compressor cascade were investigated at the Air Force Institute of Technology. Three blade configurations were tested, including a set of unmodified NACA 64- A905 series blades, a set with riblets applied to the suction surface, and a set with riblets on the pressure surface. Performance was evaluated over a wide range of Reynolds numbers, and at low and high free stream turbulence levels. Cascade performance was evaluated in terms of total pressure loss coefficient, turning angle, and static pressure rise. No riblet configuration offered robust cascade performance improvements; …

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The Effect Of Angle Of Incidence And Reynolds Number On Heat Transfer In A Linear Turbine Cascade, Steven G. Meschwitz Dec 1991

The Effect Of Angle Of Incidence And Reynolds Number On Heat Transfer In A Linear Turbine Cascade, Steven G. Meschwitz

Theses and Dissertations

The AFIT linear Turbine Cascade Test Facility was used to study the effect of the small changes in the angle of incidence on turbine blade convective heat transfer. Other parameters studied were the model Reynolds number and the freestream turbulence level. Characterization tests, performed to determine the feasibility of the study were followed by a series of tests designed to separate the effects of the angle of incidence, Reynolds number, and freestream turbulence level on convective heat transfer. For any given freestream turbulence level or angle of incidence, there is an increase in the heat transfer coefficient for an increase …

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Propulsive Capability Of A Reel-In Tether With Safe Separation Between Payload And Orbiter, Jay H. Rothhaupt Dec 1991

Propulsive Capability Of A Reel-In Tether With Safe Separation Between Payload And Orbiter, Jay H. Rothhaupt

Theses and Dissertations

This study investigates the use of a massless reel-in tether for propulsion of a payload following deployment from an orbiter. The distance between the payload and orbiter at closest passage is addressed. A literature review revealed several tether concepts, extensive tether research, and numerous mathematical models. However, previous work in the area of reel-in tethers is limited to propulsion feasibility. The reel-in tether is operated following optimum ejection of the payload from the orbiter using a free arc and subsequent full arc. The free arc of zero tether tension provides initial separation. Switching to a full arc of continuously-maximum tension …

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Static Pressure Measurements Of A Low Power Arcjet, Kevin P. Talley Dec 1991

Static Pressure Measurements Of A Low Power Arcjet, Kevin P. Talley

Theses and Dissertations

The NASA Lewis 1.2 kilowatt arcjet has been used for a number of performance and lifetime studies. This design was modified to obtain static pressure measurements at several locations along the arcjet nozzle. These measurements were taken at various propellant flow rates over most of the operational envelope of the thruster. Measured static pressure distributions are considerably higher than predicted by ID models and are proportional to the arc power. A simple thermodynamic model is also compared to the data, and is shown to match the slope of the data while overpredicting the pressure.

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Perturbation Theory For Restricted Three-Body Orbits, David A. Ross Dec 1991

Perturbation Theory For Restricted Three-Body Orbits, David A. Ross

Theses and Dissertations

A perturbation theory for restricted three-body orbits, using a periodic trajectory as a reference solution, is investigated. The nearly- periodic equations of motions are derived by analogy to a linearization about an equilibrium point. In this case, the linearization produces a set of time- periodic equations of motion that, according to Floquet, are completely solved by a periodic trajectory. The four-dimensional phase space of the restricted three-body problem is the first surveyed for regions of periodic motion, via the surface of section phase plot. Upon extraction of a periodic orbit, nearly- periodic orbits are integrated. The integrated state vector is …

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Thrust Vector Control Of An Overexpanded Supersonic Nozzle Using Pin Insertion And Rotating Airfoils, Curtis R. Amble Dec 1991

Thrust Vector Control Of An Overexpanded Supersonic Nozzle Using Pin Insertion And Rotating Airfoils, Curtis R. Amble

Theses and Dissertations

An experimental study of probe thrust vector control of overexpanded supersonic flow in nozzles using movable probes as the vectoring mechanism is presented. Two type of movable probes were used. The first inserted cylindrical proves through the wall of the nozzle to set depths relative to the nozzle wall; the second used rotating airfoils, inserted within the nozzle flow, rotated to various angles of attack relative to the nozzle centerline. Effectiveness of these probe thrust vector control mechanisms was investigated for a confined jet and conical nozzle. The study objective was to evaluate performance and transient characteristics of these probe …

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The Use Of A Higher Order Kinematic Relationship On The Analysis Of Cylindrical Composite Panels, Kathleen V. Tighe Dec 1991

The Use Of A Higher Order Kinematic Relationship On The Analysis Of Cylindrical Composite Panels, Kathleen V. Tighe

Theses and Dissertations

An analytical study was performed to determine the critical buckling loads and natural frequencies for composite cylindrical shells, including transverse shear effects and constant through the thickness direct strain εz. A linearized form of Sanders shell equations are derived, including a parabolic transverse shear strain distribution. Higher order laminate constitutive relations are developed. Hamilton's Principle is applied to derive five partial differential equations of motion and the associated boundary conditions, which are then solved using the Galerkin technique. Ply layups of (0/90), (45/-45), and (0/45/-45/90) were investigated under three boundary conditions, simply supported, clamped, and a combination simple- …

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Fatigue Behavior And Failure Mechanisms Of Centrally Notched [0]8 And [0/902]S Silicon Carbide Reinforced Aluminosilicate Glass, William R. Moschelle Dec 1991

Fatigue Behavior And Failure Mechanisms Of Centrally Notched [0]8 And [0/902]S Silicon Carbide Reinforced Aluminosilicate Glass, William R. Moschelle

Theses and Dissertations

Unidirectional and bidirectional notched laminates of silicon carbides/1723 were fatigue tested under tensile-tensile loading with a load ratio of 0.1. The notch, a hole, was determined to have a significant effect on [0]8 specimens. Matrix cracking developed near the theoretical maximum stress concentration points on the hole propagating parallel to the fibers, in the load direction, followed by fiber breakage. [0/902]s specimens were found to be notched insensitive. Damage modes for this lay-up were transverse ply matrix cracking, delamination and fiber breakage in the longitudinal plies which led to specimen failure. Several existing analytical models were …

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Optimization Of Tangential Mass Injection For Minimizing Flow Separation In A Scramjet Inlet, Richard J. Kacik Dec 1991

Optimization Of Tangential Mass Injection For Minimizing Flow Separation In A Scramjet Inlet, Richard J. Kacik

Theses and Dissertations

With the reemergence of interest in air-breathing hypersonic propulsion, scramjet inlet efficiency has become an area of concern. The impingement of the engine cowl shock near the shoulder (expansion corner between forebody and combustor) may cause boundary layer separation which reduces inlet efficiency. Tangential mass injection (TMI) upstream of the shoulder has recently been tested to control this separation but without much parametric evaluation. To resolve this deficiency, a 2-D scramjet inlet model with variable length cowl, and TMI was built and tested in the WL Mach 6 High Reynolds Number Facility. Parameters varied were boundary layer thickness, TMI flow …

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Thermomechanical Fatigue Characterization Of An Angle Ply Metal Matrix Composite, Wade H. Vaught Dec 1991

Thermomechanical Fatigue Characterization Of An Angle Ply Metal Matrix Composite, Wade H. Vaught

Theses and Dissertations

An investigation was conducted to study the thermomechanical fatigue (TMF) response of a [±45]2s angle ply SCS-6/titanium-15-3 metal matrix composite (MMC). Load controlled in-phase TMF experiments were performed over the temperature range 149-427 C, with a cycle frequency of 0.02 Hz. Test equipment included a high temperature extensometer, quartz lamp radiative heaters controlled by a Micricon thermal control unit and TMF test control software, MATE263. Stress and strain hysteresis, total strain and stiffness were monitored to characterize material behavior. Large plastic deformations were observed in all specimens, with total failure strains ranging from 7 to 13 percent. It was …

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Application Of Finite Element Modeling And Analysis To The Design Of Positive Pressure Oxygen Masks, Bruce H. Bitterman Dec 1991

Application Of Finite Element Modeling And Analysis To The Design Of Positive Pressure Oxygen Masks, Bruce H. Bitterman

Theses and Dissertations

This study investigated tools and techniques for performing finite element analysis of the MBU-20/P pilot's oxygen mask. The problem which was investigated was the fit of the mask to the face at Positive Pressure Breathing (PPB) pressures. Deformed geometry of the mask and reaction forces on the face were calculated to provide a measure of the fit. The MBU-20/P mask was first digitized by 3-D digitizer. A computer program was written to translate the digitized coordinate data to a finite element format for two commercial packages. The packages targeted were SDRC I-DEAS and PDA PATRAN. Other supplementary programs were written …

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A Comparison Of Fractional Order Time Derivative Models Of The Viscoelastic Stress Relations In Thermorheologically Complex Materials, Victor B. Chambers Dec 1991

A Comparison Of Fractional Order Time Derivative Models Of The Viscoelastic Stress Relations In Thermorheologically Complex Materials, Victor B. Chambers

Theses and Dissertations

The purpose of this thesis was to examine the viscoelastic behavior of thermorheologically complex materials, a typical example of which is a soft, rubbery material. Materials such as these are very useful in damping vibrations in structures, but the relaxation moduli of these materials change significantly with temperature and frequency. In the case of space structures applications where temperatures vary greatly and a stable platform is necessary, a method to predict this changing modulus is needed. The original approach was to validate a previously developed viscoelastic model, but the task expanded to include extending the model to materials with two …

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Tensile Strength Characterization Of A Metal Matrix Composite With Circular Holes, Jeffrey Rattray Dec 1991

Tensile Strength Characterization Of A Metal Matrix Composite With Circular Holes, Jeffrey Rattray

Theses and Dissertations

Static tensile testing conducted at room temperature and 650 C shows notch sensitivity for a quasi-isotropic lay-up of a titanium alloy metal matrix composite. The specific material used was SCS-6/Beta 21S. Some unnotched specimens were tested and then the diameter-to-width ratio was varied from 0.1 to 0.4. The room temperature unnotched strength is 840 MPa, and the strength falls to less than half this value at 650 C. The off-axis plies of the (0, + or - 45, 90)s lay-up exhibit debonding of the fibers from the matrix at only ten percent of failure stress. This debonding is shown with …

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Robust Grasp Design Using Grasp Force Focus Positioning, Freddie D. Zayas Dec 1991

Robust Grasp Design Using Grasp Force Focus Positioning, Freddie D. Zayas

Theses and Dissertations

A three-finger precision grasp is used to rotate a cylindrical object about a threaded post. Three fingered grasps are unique in that the homogeneous solution for the contact forces produces a grasp force focus. Mapping of focus points which meet grasp stability and joint torque criteria results in a usable focus region. The effects of applied torque, contact location, and object position and orientation on usable regions are presented. Stability behavior about the region is also examined. Results are used to demonstrate a technique for robust grasp design. The versatility of robotic hands permit fine motion manipulation on a wide …

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An Algorithm For Robust Eigenstructure Assignment Using The Linear Quadratic Regulator, Thomas C. Huckabone Dec 1991

An Algorithm For Robust Eigenstructure Assignment Using The Linear Quadratic Regulator, Thomas C. Huckabone

Theses and Dissertations

The Linear Quadratic Regulator (LQR) can guarantee a robust closed loop eigenstructure for full state feedback. The algorithm developed here takes advantage of the stability guarantees of LQR to achieve an eigenstructure close to desired but within the allowable region of LQR. The algorithm selects the LQR weighting matrices, Q and R, that minimize the distance between the elements of the desired and LQR achievable eigenstructures. The minimization is accomplished by using a simplex based optimization routine. Specific weightings placed on the elements of the desired eigenstructure define the relative importance of each element. The algorithm is programmed in FORTRAN …

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Investigation Of The Effects Of Increased Order Compensators In Mixed H2/H∞ Optimization, Scott R. Wells Dec 1991

Investigation Of The Effects Of Increased Order Compensators In Mixed H2/H∞ Optimization, Scott R. Wells

Theses and Dissertations

The problem of minimizing the 2-norm of one transfer function subject to an infinity-norm bound on another transfer function is examined for increased order controllers. In particular, the theoretical results of the full order case are extended to the higher order case, and SISO and MIMO numerical examples are given for increasingly higher order compensators. Some of the key proofs for higher order compensators include: the global minimum 2-norm is unachievable under output feedback for certain levels of gamma regardless of compensator order; the solution to the mixed H2/H infinity problem lies on the boundary of the infinity-norm constraint for …

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Investigation Of The Influence Of Rotary Aerodynamics On The Study Of High Angle Of Attack Dynamics Of The F-15b Using Bifurcation Analysis, Ralph D. Fero Dec 1991

Investigation Of The Influence Of Rotary Aerodynamics On The Study Of High Angle Of Attack Dynamics Of The F-15b Using Bifurcation Analysis, Ralph D. Fero

Theses and Dissertations

The purpose of this research was to use bifurcation analysis to investigate the effectiveness of rotary balance data in the prediction of aircraft spin behavior as both a stand alone representation of a model's aerodynamic data and in a conventional hybrid model. using the foundation of a previously developed model of the F-15B, the rotary balance aerodynamic force and moment data were implemented as a function of angle of attack, angle of sideslip, non-dimensional rotation steady state rate and the control surface deflections. Bifurcation diagrams were developed as a function of alpha vs. deflection angles of, the rudder, stabilator, and …

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Computation Of Planar Store Trajectories Using An Adaptive Grid Procedure, William D. Hack Dec 1991

Computation Of Planar Store Trajectories Using An Adaptive Grid Procedure, William D. Hack

Theses and Dissertations

The objective of this research was to compare a quasi-analytical, potential flow/three-degree-of-freedom model to an implicit-Euler algorithm for the calculation of store trajectories. The implicity algorithm uses a cell- centered, finite-volume, spatial discretization applied to the Euler equations, written in time-dependent, curvilinear-coordinates. A flux-differencing Roe scheme is employed to find the split-fluxes and the Steger/Warming flux-vector method is used to calculate the flux-Jacobians. The potential flow and implicit- Euler algorithm are combined with a three-degree-of-freedom algorithm to evaluate the planar, freefall trajectories of a simple store shape. The research uses two different grid-modification techniques in the implicit algorithm evaluation. Data …

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Analysis Of The Effects Of Removing Nose Ballast From The F-15 Eagle, Richard L. Bennett Dec 1991

Analysis Of The Effects Of Removing Nose Ballast From The F-15 Eagle, Richard L. Bennett

Theses and Dissertations

This study investigated the results of removing lead ballast from the nose section of the F-15 Air Superiority fighter. The goal of the investigation was to determine if aircraft handling qualities remained acceptable with the ballast removed, and also to determine what improvements in aircraft nose pointing authority resulted. Actual F-15 weight reports were used to calculate the worst case aft center of gravity location shift due to the ballast removal. Several configurations with different center of gravity locations (based on various amounts of lead weights removed) were used for comparison to the baseline aircraft. Moments of inertia were calculated …

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A Formal Definition Of The Object-Oriented Paradigm For Requirements Analysis, Andrew D. Boyd Dec 1991

A Formal Definition Of The Object-Oriented Paradigm For Requirements Analysis, Andrew D. Boyd

Theses and Dissertations

This paper develops a formal definition of the Object-Oriented paradigm for requirements analysis. The literature was surveyed for both formal and informal methods for conducting an Object-Oriented Requirements Analysis (OORA). The informal methods reviewed are: Bailin's, Shlaer and Mellor's, Booch's, and Coad and Yourdon's. The formal methods reviewed are: Bralick's, Z, and REFINE. None of the methods were found to be adequate for doing an OORA. A formal definition of an OORA, based on the concept of classes, is developed. The definition itself is presented as set and relation theory. A supporting graphical representation is also developed and presented. The …

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