Engineering Mechanics Commons^™

An Analysis Of The Response Of A Buckled Beam With Fixed Ends To An Harmonic Base Excitation Using The Finite Element Method, Peter John O'Donoghue

Mechanical & Aerospace Engineering Theses & Dissertations

A finite element formulation is developed to analyze the large deflection vibration of a buckled isotropic beam. The beam is buckled mechanically by an applied end displacement, and the dynamic loading is derived from the forced periodic base motion. The principle of virtual work is used to derive the system equations of motion. A Newton-Raphson iteration routine modified for the case of an applied end displacement is used with the incremental equations of motion to determine static deflection. The 0l time numerical integration algorithm is applied to the system of equations of motion in physical coordinates to determine dynamic response …

A Fracture Mechanics Analysis Of A 38 Inch Diameter Hot Pressed Beryllium Telescope Mirror, Phillip L. Brown

Mechanical & Aerospace Engineering Theses & Dissertations

A 38 inch diameter hot pressed beryllium telescope mirror was analyzed for structural integrity using finite-element modeling and a fracture mechanics analysis program, ZIP3D, developed for three-dimensional (3-0) solid and cracked bodies. The calculation of stress and mixed-mode fracture mechanics parameters for the mirror critical stress area was the objective of the mirror analysis.

Finite-element modeling for ZIP3D solution was performed in two stages. The first stage modeling modeled the mirror configuration on a global basis for calculation of accurate nodal displacements. The second stage modeling reduced the modeled mirror configuration to a set of localized models for calculation of …

Elastic Buckling Of Stiffened Composite Curved Panels, Navin R. R. Jaunky

Mechanical & Aerospace Engineering Theses & Dissertations

Continuous filament grid-stiffened structure is a stiffening concept that combines structural efficiency and damage tolerance. However, buckle resistant design of such structures using finite elements methods is expensive and time consuming. An analytical model of a general grid stiffened structure is developed using a smeared theory with a first order shear deformation theory to account for transverse shear flexibilities. The solution for buckling of a simply supported panel subjected to combined loading is developed using energy method and a Rayleigh-Ritz technique. The smeared theory results are compared with finite element results. The results smeared theory compare well with the finite …

Design Considerations For An Astronaut Monorail System For Large Space Structures And The Structural Characterization Of Its Positioning Arm, Judith J. Watson

Mechanical & Aerospace Engineering Theses & Dissertations

An astronaut monorail system (AMS) is presented as a vehicle to transport and position EV A astronauts along large space truss structures. The AMS is proposed specifically as an alternative to the crew and equipment transfer aid for Space Station Freedom. Design considerations for the AMS were discussed and a reference configuration was selected for the study. Equations were developed to characterize the stiffness and frequency behavior of the AMS positioning arm. Experimental data showed that these equations gave an fairly accurate representation of the stiffness and frequency behavior of the arm. A study was presented to show trends for …

Analysis Of Impact Damage Of Composite Laminates Using Five-Point Bending, Mark Edward Robeson

Mechanical & Aerospace Engineering Theses & Dissertations

The low-velocity impact of composite laminates can induce high transverse shear strains, resulting in severe damage within the laminate. This type of damage may be studied in a quasi-static manner by use of a multi-span beam shear test in five-point bending configuration. A five-point bending arrangement induces high transverse shear strains in sections of the laminate, causing failures, such as intraply cracks and delaminations, that are similar to those caused by low-velocity impact. Stress distributions in the laminate can be calculated using a potential energy approach, and these stress distributions can be correlated with failure locations in the five-point bending …

Theoretical And Experimental Study Of Inlet Manifold Pressure Profiles Using Compensated Transducers, P Mtui

Tanzania Journal of Engineering and Technology (TJET)

Computer simulation and experimental findings on single cylinder four-stroke cycle engine were done with a view of getting more realistic inlet manifold pressures. Since there is a direct relationship between the inlet pressure profiles and the volumetric efficiency of the engine, then there is a possibility of utilizing the knowledge of these profiles to enhance better engine air flow characteristics and hence improvement of engine performance.

The simulation program is based on hometropic process with constant specific heats where the results were validated using experimental findings of the engine with varying engine speeds.

Experimental results are obtained by measuring manifold …

Modal Analysis Of Gyroscopically Coupled Sound-Structure Interaction Problems, Vijay B. Bokil

Mechanical & Aerospace Engineering Theses & Dissertations

In many practical situations we encounter sound-structure interaction between the fluid in a cavity and the flexible wall on the boundary. The aircraft cabin interacting with its fuselage and double-leaf partition walls interacting with the enclosed cavity are some of the typical examples. The vibratory behavior of the structure and the acoustical pressure inside the cavity are affected by this interaction.

In most of the cases, the governing differential equations for the coupled system can be shown to involve gyroscopic coupling. A special method has been applied to decouple the equations in terms of pairs of generalized coordinates and the …

Transfer Function Models And Control Of A Flexible Structure Using Piezoelectric Laminates, Joseph A. Colvin

Mechanical & Aerospace Engineering Theses & Dissertations

The development of piezoelectric polymer films has generated a great deal of excitement in the structural controls community because they are lightweight, durable, distributed in nature and have broad band frequency characteristics. The flurry of research inspired by piezoelectric films has primarily been dedicated to using them as distributed sensors, and to a lesser extent, as distributed actuators.

Active damping of structural vibrations using piezoelectric polymer films as sensors and actuators has primarily been directed toward taking advantage of their distributed nature and employing various types of distributed control theory. This approach does not easily yield insight into the dynamics …

Hierarchical Flux-Based Thermal-Structural Finite Element Analysis Method, Sandra P. Polesky

Mechanical & Aerospace Engineering Theses & Dissertations

A hierarchical flux-based finite element method is developed for both one- and two-dimensional thermal-structural analyses. Derivation of the finite element equations is presented. The resulting finite element matrices associated with the flux-based formulation are evaluated in closed-form. The hierarchical finite elements include additional degrees of freedom in the approximation of the element variable distributions by the use of nodeless variables. The nodeless variables offer increased solution accuracy without the need for defining actual nodes and rediscretizing the finite element model. Thermal and structural responses obtained using the hierarchical flux-based method are compared with results obtained from a conventional linear finite …

Development Of A Model Updating Technique For Controls-Structures Integrated Design Optimization, Angela Georges

Mechanical & Aerospace Engineering Theses & Dissertations

A model updating technique is developed with the intent of providing an efficient means of improving the accuracy of the modelling of the vibrational qualities of a large, flexible structure as it undergoes an integrated controls-structures design optimization. The proposed technique utilizes eigenvalue/eigenvector sensitivity information, two different model reduction methods which assign weights of importance to the vibrational modes of the structure, and modal switching based upon the modal weights determined by the model reduction methods. Issues associated with the numerical implementation of the proposed technique, such as discontinuities induced by modal switching, are also addressed.

The proposed model updating …

Comparative Study Of Inlet Manifold Tuning To Enhance Supercharge, Mtui L

Tanzania Journal of Engineering and Technology (TJET)

Computer model ing and experimental results on a single cylinder, four-stroke cycle engine for best air flow characteristic is The modeling analysis is based on hornet ropie fluid di scussed . The model n g resul s is flow w it. h constant: specific heats. included to val idat.e the s imulation program against experimental results with widely vary ing manifold lengths and engine speeds. ExperimenLal results are obtained by measuring air f low rates Lo the inlet valve during steady g Late speed Of Lhe engine. Manifold tuned lengths are Obtained for a range Of speeds by exper and …

Electrical Equivalent Method For The Calculation Of Vibrations In Transformers, D Chambega

Tanzania Journal of Engineering and Technology (TJET)

Noiselevel calculations may be done using an electrical equivalent method. So far a single mass and a double mass vibrating system may easily be represented by equivalent electrical circuits which are in turn useful for analysis. Multimass vibrating systems like transformers do not have straightforward methods which can enable analysis of noiselevels. This paper attempts to develop such a method by extending the method applicable to a double mass vibrating system. Then the validity of the method is tested using a transforme

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 …

An Experimental Investigation Of Composite Sensors For Crack Length Measurement, Manickam Ramasamy

Mechanical & Aerospace Engineering Theses & Dissertations

Structural defects such as cracks can cause catastrophic failure in engineering components or structures. There are many techniques to measure the crack growth in materials and are commercially available. In this thesis, bondable crack length measurement gages have been investigated and these gages give electrical signal as the output and measure the crack length continuously. Silver paint, nickel powder impregnated epoxy and carbon powder impregnated polymer composite gages are investigated and tests are conducted by resistance measurement method with simple instrumentation and by potential drop method with a constant current output source. Rectangular shape gages have been investigated and as …

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 …

Finite Element Analysis Of Nonlinear Panel Flutter Of Rectangular Composite Plates Under A Uniform Thermal Load, Lain Ross Dixon

Mechanical & Aerospace Engineering Theses & Dissertations

A finite element formulation is developed to analyze large-amplitude panel flutter of arbitrarily laminated composite plates subjected to a uniform temperature change. The plates considered are anisotropic composite, thin rectangular panels. The aerodynamic pressure load is modeled through the use of the first-order piston theory. The equations of motion for the oscillating plate are determined from the principle of virtual work. Two different solution procedures are given to determine the panel motions. The first procedure, which considers only the aerodynamic load, solves the panel limit-cycle motions by employing the linearized updated-mode with a nonlinear time function (LUM/NTF) approximation. The second …

Dynamic Test/Analysis Correlation Using Reduced Analytical Models, Paul E. Mcgowan

Mechanical & Aerospace Engineering Theses & Dissertations

Test/analysis correlation is an important aspect of the verification of analysis models which are used to predict on-orbit response characteristics of large space structures. This thesis summarizes the study of using reduced analysis models for performing dynamic test/analysis correlation. The reduced test-analysis model (TAM) has the same number of degrees-of-freedom (DOF) as the number of test measurements. This allows the direct comparison of modal parameters between ground vibration test results and finite element model (FEM) analysis results. The TAM can also be used for pre-test analysis and to aid in the post-test mathematical model updating process.

Herein, four methods for …

Simulation And Measurement Of The Radiant Field Produced By Quartz Heating Systems, Travis Lee Turner

Mechanical & Aerospace Engineering Theses & Dissertations

A method is developed for predicting the radiant heat flux distribution produced by tungsten-filament tubular quartz heating systems with reflectors. The method is an application of Monte Carlo simulation, which takes the form of a ray tracing or random walk scheme. The method is applied to four systems of increasing complexity including; a single unreflected lamp, a single lamp with a flat reflector, a single lamp with a parabolic reflector, and up to six lamps in a six-lamp contoured reflector heating unit. The general methodology of the Monte Carlo method is discussed and applied to the simulation of thermal radiation. …

Finite Element Analysis Of Thermal Post-Buckling And Vibrations Of Thermally Buckled Composite Plates, Charles Clifton Gray

Mechanical & Aerospace Engineering Theses & Dissertations

The development of supersonic and hypersonic flight vehicles such as the High Speed Civil Transport and the National Aero-Space Plane has created an increased need for analysis of structures at very high temperatures. Bisplinghoff and Pian, Yang and Han, and Dokmeci and Boley have conducted experimental and analytical studies to determine the effect of elevated temperatures on the vibration characteristics of isotropic plates, Chen and Chen, and Meyers and Hyer have clone studies on thermal buckling and post-buckling of composite plates, respectively.

The thermal loads which will be imposed on the new high speed aircraft will be too great for …

Thermal Compatibility Analysis Of The Passive Damping Treatment Proposed For The Space Shuttle Remote Manipulator System (Srms), Mahesh Chowdhary

Mechanical & Aerospace Engineering Theses & Dissertations

The NASA Space Shuttle Remote Manipulator System (SRMS), due to its long reach and light weight construction has significant structural flexibility. Thus any routine use of SRMS often results in large amplitude oscillations with long settling time. A passive damping technique utilizing a constrained viscoelastic layer damping treatment has been proposed to augment the active control of these oscillations in order to enhance the system stability and the end effector positional accuracy. This thesis concerns with the thermal compatibility analysis of the proposed damping treatment. The necessity for thermal compatibility analysis arises from the fact that acceptable damping performance of …

Analytical And Experimental Investigation On Vibration Control Of Piezoelectric Structures, M. J. Tzeng, W-Z Ben Wu

Civil, Architectural and Environmental Engineering Faculty Research & Creative Works

Active vibration control of smart structural materials (beam and plate) has been achieved by using distributed piezoelectric actuators. Numerical simulation and experimental testing have been conducted to investigate vibration suppression of the advanced structures. Results from simulation and testing are in satisfactory agreement.

The Effectiveness Of Viscoelastic Damping Treatments On A Flexible Manipulator Subjected To Torsional Loads, Leah L. Remias

Mechanical & Aerospace Engineering Theses & Dissertations

The advent of new technology has led to an increasing number of missions in space. The space shuttle Remote Manipulator System (RMS) is a lightweight flexible manipulator currently used in NASA space missions. The future role of the RMS and similar flexible manipulators may include in-space construction and assembly tasks. Because these tasks require precise motion and short settling time of the end-point oscillations, effective vibration control schemes are being investigated.

Passive damping techniques have shown to provide a considerable amount of damping in controlling flexural vibrations. In this research passive damping via constrained viscoelastic damping treatments is explored as …

Finite Element Analysis Of Structures With Constrained Viscoelastic Layer Damping, Yung Chen

Mechanical & Aerospace Engineering Theses & Dissertations

It has been demonstrated that constrained viscoelastic layer damping treatments provide an effective means of passive control for structural vibration. These treatments dissipate vibrational energy by inducing shear strain in a thin layer of viscoelastic material. Our interest is in adding passive damping to a structure as an augmentation to active control. For such applications it is desirable to achieve high damping performance in a given frequency range with a minimum of added weight. Most damping treatments employ spatially continuous constraining layers over the entire viscoelastic layer. Plunkett and Lee have shown that the effectiveness of the damping treatment can …

Finite Element Formulation And Numerical Simulation Of The Large Deflection Random Vibration Of Laminated Composite Plates, Jay Howard Robinson

Mechanical & Aerospace Engineering Theses & Dissertations

A theoretical large deflection finite element formulation is developed for the purpose of simulating the random vibration of thin generally laminated composite plates. The random acoustic load is taken to be stationary and Gaussian with zero mean and uniform magnitude and phase over the surface of the plate. In­ plane inertia terms are included in the formulation however rotary inertia terms are assumed negligible.

The integration routine is derived from a set of unified single step algorithms, using a weighted satisfaction of the equilibrium equation. The algorithm is second order accurate and unconditionally stable for particular values of its free …

Numerical Investigation Of A Non-Newtonian Material Through A Sudden Pipe Expansion, V. G. Masanja

Tanzania Journal of Engineering and Technology (TJET)

A numerical method for solving two dimensional elliptic boundary-value problems of fourth order is used for finding stationary solutions of the equations of motion for a laminar flow through a sudden pipe expansion of an incompressible non-Newtonian fluid with a constitutive equation of the Reiner-Rivlin (R-R) type. Results for the Newtonian fluid, which is a special case, are in excellent agreement with those by previous investigators and they demonstrate the reliability, superiority and accuracy of the method. Results for the non-Newtonian cases could be of value for fixing ideas about visco-elastic behaviour although the R-R fluid allows only inelasticity: this …

The Influence Of Payload Dynamics On Trajectory Tracking Performance Of Robot Manipulator, Atul G. Kelkar

Mechanical & Aerospace Engineering Theses & Dissertations

Future space mission plans call for extensive use of remote manipulator systems for tasks such as assembly of lunar vehicles or space station modules, servicing of satellites, etc. These tasks demand very high precision end-effector motion control. Methods for compensating manipulator dynamics to achieve better trajectory tracking performance have been investigated by many researchers. Still, it is not always clear whether the added complexity of dynamic compensation is warranted for a given system. As an aid in evaluating when dynamic compensation is required, this thesis presents a method for the determination of maximum endpoint tracking error due to uncompensated inertial …

A Detailed Analysis Of Dynamic Robotic Simulation, Lonnie J. Love

Mechanical & Aerospace Engineering Theses & Dissertations

Future space missions may require the utilization of automation technology for assembly, maintenance, repair, and a variety of repetitive or hazardous operations. Many tasks which are likely candidates for robotic or telerobotic execution are either difficult or impossible to duplicate in the laboratory. With an accurate simulation package, many of these tasks can be evaluated by computer simulation before committing the resources required for laboratory experimentation. With this motivation, the ROBSIM robot simulation software has been developed by NASA Langley Research Center in conjunction with the Martin Marietta Corporation. ROBSIM is a versatile tool with features including the ability to …

A Systematic Procedure For The Analysis And Design Of Deployable Space Structures, Praveen Kumar

Mechanical & Aerospace Engineering Theses & Dissertations

An integrated graph theory and a symmetry-based approach have been developed for the type synthesis of deployable truss structures. Using this systematic approach, a bay of a deployable structure may be looked upon as being built around an axis or a plane of symmetry, including anti-symmetry. By providing a fictitious joint along this axis, the problem of structural design and analysis can be reduced to the study of one plane or face of the given structure. Each face is considered to be an assemblage of structural links connected by joints which form a closed kinematic chain. The conventional graph representation …

Eigensensitivity Analysis For Space Structures With Applications In Design Optimization, Sean Patrick Kenny

Mechanical & Aerospace Engineering Theses & Dissertations

Eigensensitivity analysis is concerned with the rates of changes of eigenvalues and eigenvectors with respect to design variables. Eigensolutions of space structures are found to display four distinct characteristics, three of which are related to various types of repeated eigenvalues. This study will address three cases of the real symmetric structural eigenvalue problem. The three cases that will be considered are: distinct eigenvalues, repeated eigenvalues with distinct first eigenvalue derivatives, and repeated eigenvalues with infinitely repeating eigenvalue derivatives. Analytic formulations for eigenvalue/ vector derivatives will be presented for each of the three cases. The directional differentiability of eigenvalues for the …

The Fractal Dimension As A Measure Of The Roughness Of Rock Discontinuity Profiles, Y. H. Lee, J. R. Carr, David J. Barr, Charles J. Haas

Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works

An important factor in the analysis of deformation and failure of rock masses along discontinuities is the roughness of the jointing surfaces. The fractal dimension is proposed as a method of objectively quantifying the roughness profile of such discontinuities. With this method much less engineering judgement and experience are required in determining the surface roughness,sb than is required for other methods such as the widely used joint roughness coefficient (JRC) suggested by the International Society for Rock Mechanics [1] (Int. J. Rock. Mech. Min. Sci. & Geomech. Abstr. 15, 319-368, 1978). The fractal dimension, suggested by Mandelbrot [2] (Fractals-Form, Chance …