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Articles 1 - 28 of 28

Full-Text Articles in Applied Mechanics

Effects Of Material Microstructure And Surface Geometry On Ultrasonic Scattering And Flaw Detection , Yanming Guo Jan 2003

Effects Of Material Microstructure And Surface Geometry On Ultrasonic Scattering And Flaw Detection , Yanming Guo

Retrospective Theses and Dissertations

This dissertation studies the effect of two practical attributes of structural materials on ultrasonic inspection. The effects of the material microstructure of polycrystalline aluminum alloys on propagating ultrasonic waves and the effects of surface curvature and roughness on ultrasonic scattering and flaw detectability are both addressed.;The relationships between ultrasonic properties (velocity, attenuation, and backscattering) and the microstructure are studied both experimentally and theoretically for rolled aluminum samples with highly elongated grains. Attenuation measurements show a very small anisotropy, whereas backscattering measurements show a very high anisotropy. Existing theories and related extensions are able to explain these physical phenomena. Three ...


Statistical Signal Processing For Mechanical Systems , Li Wen Jan 2003

Statistical Signal Processing For Mechanical Systems , Li Wen

Retrospective Theses and Dissertations

Random processes such as temperature and acoustic noise are found in all types of mechanical systems. Knowledge of these processes can lead to improved design and detection methods related to faulty operation. The goal of this dissertation is to contribute to the knowledge base of such processes. Specifically, we address statistical signal processing methods that are appropriate and consistent relative to the physics of these systems. Two generic problems associated with random signal measurements from mechanical systems are addressed.;Random processes associated with mechanical systems usually have complex spectral structure containing both continuous and line spectral components. Accordingly, they are ...


Extraction Methods For Multidirectional Driving Point Accelerance And Transfer Point Accelerance Matrices , Jianrong Dong Jan 2000

Extraction Methods For Multidirectional Driving Point Accelerance And Transfer Point Accelerance Matrices , Jianrong Dong

Retrospective Theses and Dissertations

To experimentally determine the multidirectional driving point and transfer accelerance matrices is a difficult task that has remained unsolved for 30 years. These matrices relate both linear and rotational degrees of freedom in three dimensions. The direct measurement of dynamic moments and rotational accelerations is very difficult. Little work exists on the subject and none includes so many DOF's. Besides, it is assumed that any test attachment is rigid and none used angular accelerometers to measure the angular acceleration;Various errors in substructure testing are studied. The study reveals that the interface DOF deficiency error is the most catastrophic ...


Ultrasonic Beam Models In Anisotropic Media , Matthias Rudolph Jan 1999

Ultrasonic Beam Models In Anisotropic Media , Matthias Rudolph

Retrospective Theses and Dissertations

This dissertation models the sound fields produced by ultrasonic transducers for immersion inspections where the sound fields pass through general curved interfaces into a general anisotropic material;The foundations for these models are discussed, including slowness surfaces for anisotropic materials and the reflection/transmission of plane waves at a planar fluid/anisotropic solid interface;Three beam models are developed. Two of these models---the boundary diffraction wave model and the multi-Gaussian model---rely on the paraxial approximation, resulting in models that are computationally very efficient. As a consequence, those models can be used to conduct parametric studies in a highly effective manner ...


A Three-Dimensional, Dynamic Model Of The Human Body For Lifting Motions , Jason Clay Gillette Jan 1999

A Three-Dimensional, Dynamic Model Of The Human Body For Lifting Motions , Jason Clay Gillette

Retrospective Theses and Dissertations

Lower back pain is prevalent in society and manual lifting has been linked as one potential cause of these types of injuries. Therefore, the 3dLift biomechanical model was developed in this research with the goal of quantitatively analyzing lifting motions. The model divided the body into fifteen segments that were connected by fourteen anatomical joints. During experimental trials, a volunteer subject lifted an object using four different lifting combinations: symmetric leglifts, asymmetric leglifts, symmetric backlifts, and asymmetric backlifts. In order to individualize the 3dLift model, anthropometric parameters were estimated using measurements taken on the subject. During the lifting trials, the ...


Thermal Stresses In Axially Symmetric Fracture Mechanics Problems For Bodies With An External Crack , Janice Sue Pawloski Jan 1998

Thermal Stresses In Axially Symmetric Fracture Mechanics Problems For Bodies With An External Crack , Janice Sue Pawloski

Retrospective Theses and Dissertations

The method of integral transforms is used in this work to solve for both the temperature distribution and the stress function for several axially symmetric fracture mechanics problems. The problems considered are symmetric in temperature and stresses with respect to the plane of the crack. Due to the mixed boundary conditions in the plane of the crack, this method leads to two sets of dual integral equations. One of these is a result of solving the conduction problem, and the other occurs in the solution of the thermoelastic problem;In this work, the problem of determining stress intensity factors for ...


Methodology Development Of An Engineering Design Expert System Utilizing A Modular Knowledge-Base Inference Process , Steven John Winter Jan 1998

Methodology Development Of An Engineering Design Expert System Utilizing A Modular Knowledge-Base Inference Process , Steven John Winter

Retrospective Theses and Dissertations

Methodology development was conducted to incorporate a modular knowledge-base representation into an expert system engineering design application. The objective for using multidisciplinary methodologies in defining a design system was to develop a system framework that would be applicable to a wide range of engineering applications. The technique of "knowledge clustering" was used to construct a general decision tree for all factual information relating to the design application. This construction combined the design process surface knowledge and specific application depth knowledge. Utilization of both levels of knowledge created a system capable of processing multiple controlling tasks including; organizing factual information relative ...


Boundary Element Strategies And Discretized Green's Functions: Applications In Composite Materials And Wave Mechanics , Lingyun Pan Jan 1997

Boundary Element Strategies And Discretized Green's Functions: Applications In Composite Materials And Wave Mechanics , Lingyun Pan

Retrospective Theses and Dissertations

In this thesis, it is explicitly shown that the exact Green's function and the unknown boundary variables on the boundary, in a given boundary value problem (BVP), satisfy the same boundary integral equation (BIE) but with a different known vector. Indeed, it is made explicit here that in using the BIE method to solve a given boundary value problem, one has in fact constructed the Green's function for the domain. This observation provides a way to construct a library of numerical approximations to exact Green's functions (discretized Green's functions) for problems for which analytical Green's ...


The Effect Of Stiffener Parameters On The Farfield Sound Radiation From Composite Beams: Experiment And Theory , Julie Cathleen Slaughter Jan 1997

The Effect Of Stiffener Parameters On The Farfield Sound Radiation From Composite Beams: Experiment And Theory , Julie Cathleen Slaughter

Retrospective Theses and Dissertations

The effects of spatial and material variations on farfield sound radiation from carbon/epoxy composite beams were investigated. Specifically, the geometry of a single stiffener of carbon/epoxy embedded in a beam, periodically spaced stiffeners along the length of a beam, and single stiffeners of different materials embedded in beams were all investigated. Because of a lack of methods to sufficiently model the details of spatially varying material properties, experimental data were used to identify important parameters that needed to be included in a model. Vibration testing was performed for three frequency ranges: 500 Hz to 1500 Hz, 1500 Hz ...


Numerical Solution Of Inverse Problems In Nondestructive Evaluation Using The Boundary Element Method And Multivariate Adaptive Regression Splines , Sinniah Balakrishnan Jan 1996

Numerical Solution Of Inverse Problems In Nondestructive Evaluation Using The Boundary Element Method And Multivariate Adaptive Regression Splines , Sinniah Balakrishnan

Retrospective Theses and Dissertations

Flaw identification is an important inverse problem that underlies techniques for nondestructive evaluation (NDE). In this study, a known steady state thermal field is used to identify multiple flaws in a material. The problem is to determine locations and sizes of the multiple flaws if the number of flaws and the temperature at certain probe locations on the boundary are known. The boundary element method (BEM) is used as a computational tool in this task;Earlier work in this area has dealt with the case of a single flaw, while we address the case of multiple flaws. The identification of ...


The Effect Of Rib Attachment Properties On Structural Acoustics , Matthew Scott Carney Jan 1996

The Effect Of Rib Attachment Properties On Structural Acoustics , Matthew Scott Carney

Retrospective Theses and Dissertations

Sound Pressure measurements were taken of several 2.44m long thin beams which had 0.635cm wide t-ribs centered on them. The beams were excited by a chirp signal with the frequency range of 500Hz to 1500Hz. Two rib attachment methods were used on the beams. One group of beams were machined out of thick stock to the geometry of a rib welded to a beam to ensure that the rib and attachment were one continuous media. The other group of beams had ribs that were welded on. Fillets from the welding process were subjected to heat-treatment and machining to ...


Development Of An Acoustic Microscope To Measure Residual Stress Via Ultrasonic Rayleigh Wave Velocity Measurements , Jane Carol Johnson Jan 1995

Development Of An Acoustic Microscope To Measure Residual Stress Via Ultrasonic Rayleigh Wave Velocity Measurements , Jane Carol Johnson

Retrospective Theses and Dissertations

High stress in a crucial instrument part can cause failure. Stress detection is one of the aims of nondestructive testing. The velocity change of acoustic waves can be used to detect stress in a material. An acoustic microscope is an instrument which induces and detects acoustic waves and in one mode of operation, is able to measure the velocity of acoustic surface waves. It does this over a very small area and is capable of high spatial resolution;One of the challenges in the measurement of stress is the achievement of high spatial resolution. Since the stress induced velocity shifts ...


Ultrasonic Scattering From Decorated Grain Boundaries , John Mittleman Jan 1995

Ultrasonic Scattering From Decorated Grain Boundaries , John Mittleman

Retrospective Theses and Dissertations

The microstructure of polycrystalline materials is manipulated in many ways to create materials with superior engineering properties. Alloying pure materials, for example, can alter crystallographic structure to strengthen or stiffen the material, but when impurities collect along grain boundaries, the material may become embrittled. This undesirable condition is generally associated with improper heat treatment during fabrication, but it may also occur during the service life of alloys exposed to penetrating radiation or severe thermal conditions. This dissertation studies scattering from decorated grain boundaries theoretically and experimentally, and ties results for isolated scatterers to grain noise measurements on materials composed entirely ...


Numerical Investigation Of Type Ii Non-Newtonian De/Anti-Icing Fluid Effects On Take-Off Performance For General Aviation Aircraft , Dennis James Cronin Jan 1995

Numerical Investigation Of Type Ii Non-Newtonian De/Anti-Icing Fluid Effects On Take-Off Performance For General Aviation Aircraft , Dennis James Cronin

Retrospective Theses and Dissertations

Ground icing, while preventable with glycol based freezing point depressant fluids, accounts for nearly 40-50 civil accidents a year according to one account. More viscous than Type I fluids, Type II fluids are inherently non-linear in their shear stress-rate of strain relationship having smaller relative viscosity at higher shear rates. The non-linearity makes properly scaled wind-tunnel testing difficult and computational methods are employed in this study to look at the aerodynamic effects of the deicing fluid on global performance during typical take-off maneuvers for general aviation. The method is tested on a two-dimensional NACA 0012 airfoil under typical take-off simulation ...


Efficient Inversion Of Fourier And Laplace Domain Boundary Element Solutions For Elastodynamic Scattering , Joel Kevin Ness Jan 1994

Efficient Inversion Of Fourier And Laplace Domain Boundary Element Solutions For Elastodynamic Scattering , Joel Kevin Ness

Retrospective Theses and Dissertations

In ultrasonic nondestructive testing, the actual time domain signature of a scattered wave due to a pulsed input is the common observable (via oscilloscope) quantity. Numerically simulated solutions are thus desirable in the time domain. These can be obtained by working directly in the time domain or by inversions of integral transform solutions in the frequency (Fourier) or Laplace domains. Direct time solutions are suitable for short times but generally deteriorate for longer times. Alternately, the transform techniques generally require solutions over a wide spectrum in the transform variable to provide accurate inversions back to the time domain. However, without ...


Application Of Displacement And Traction Boundary Integral Equations For Fracture Mechanics Analysis , Seungwon Youn Jan 1993

Application Of Displacement And Traction Boundary Integral Equations For Fracture Mechanics Analysis , Seungwon Youn

Retrospective Theses and Dissertations

A general formulation by dual boundary integral equations and a computational solution algorithm for the general mixed-mode crack in a linearly elastic, isotropic medium is presented. Traction boundary integral equations are collocated at the points on one crack surface while displacement boundary integral equations are collocated at the opposite points on the other surface to ensure a unique solution. The hypersingular and strongly singular integrals in the traction and displacement boundary integral equations are regularized before the numerical implementation. The singular integration elements on both crack surfaces are replaced by smooth curved auxiliary surfaces to avoid the direct integration over ...


Vibrational And Acoustic Response Of Ribbed Plates , Ten-Bin Juang Jan 1993

Vibrational And Acoustic Response Of Ribbed Plates , Ten-Bin Juang

Retrospective Theses and Dissertations

A self-consistent mathematical formulation, using the Fourier transform method and a direct Gaussian numerical integration scheme, is developed and verified for analysis of both vibrational and acoustic responses of infinite submerged ribbed plates. Further steps developed from standard theories make structural intensity, acoustic intensity, and acoustic power calculations possible in the nearfield and farfield, and are demonstrated in this work;The direct numerical integration scheme adopted to obtain responses has proved to be straightforward and reliable. Although the double integration expression in some responses makes the technique infeasible, a practical way to overcome that difficulty is demonstrated using a standard ...


Solution Of Second Order Non-Linear Boundary Value Problems By The Boundary Element Method , Ravichandran V. Jan 1993

Solution Of Second Order Non-Linear Boundary Value Problems By The Boundary Element Method , Ravichandran V.

Retrospective Theses and Dissertations

In this work a procedure has been developed which makes it possible to use the boundary element method to solve non-linear partial differential equations of the second order in two variables. The problems solved are boundary value problems, and the non-linearity can be of any kind. A mathematical formulation is given which makes it unnecessary to have a knowledge of the fundamental solution for every type of non-linear equation. For second order partial differential equations, the use of Green's function for the Laplace equation as the fundamental solution has proved adequate to solve a wide variety of non-linear problems ...


An Experimental Method For Structural Intensity And Source Location , Yong Zhang Jan 1993

An Experimental Method For Structural Intensity And Source Location , Yong Zhang

Retrospective Theses and Dissertations

This study investigates the structural intensity and the force distribution function as tools to study vibrating plates. A laser Doppler vibrometer is used in measuring the plate normal velocity for the calculation of the structural intensity and the force distribution function. Several examples show the possibility of locating sources and studying the influence of ribs and damping material attached to the plate surface;There have been many studies on structural intensity. This thesis shows that the differences between two commonly used formulations are the assumptions that are used in deriving the formulas;The force distribution function is introduced in this ...


Solution Of Viscous Flow Problems By Using The Boundary Element Method , Abdel-Magid Abdel-Latif Abdalla Jan 1992

Solution Of Viscous Flow Problems By Using The Boundary Element Method , Abdel-Magid Abdel-Latif Abdalla

Retrospective Theses and Dissertations

A scheme based on the Boundary Element Method (BEM) for solving the problem of steady flow of an incompressible viscous fluid is presented in this thesis. The problem is governed by both Navier-Stokes (N-S) equations and the continuity equation. The fundamental solution of the two-dimensional N-S is derived, and the partial differential equations are converted to an integral equation;The computer code is flexible enough to handle a variety of boundary and domain elements with different degrees of interpolation polynomial. Boundary and domain integrals over corresponding elements are evaluated analytically. The Newton Raphson iteration scheme accompanied by a relaxation factor ...


Effects Of Stinger Axial Dynamics And Mass Compensation Methods On Experimental Modal Analysis , Ximing Hu Jan 1992

Effects Of Stinger Axial Dynamics And Mass Compensation Methods On Experimental Modal Analysis , Ximing Hu

Retrospective Theses and Dissertations

A longitudinal bar model that includes both stinger elastic and inertia properties is used to analyse the stinger's axial dynamics as well as the mass compensation that is required to obtain accurate input forces when a stinger is installed between the excitation source, force transducer, and the structure under test. Stinger motion transmissibility and force transmissibility, axial resonance and excitation energy transfer problems are discussed in detail;Stinger mass compensation problems occur when the force transducer is mounted on the exciter end of the stinger. These problems are investigated theoretically, numerically, and experimentally. It is found that the measured ...


Ultrasonic Flaw Classification And Sizing , Sung-Jin Song Jan 1991

Ultrasonic Flaw Classification And Sizing , Sung-Jin Song

Retrospective Theses and Dissertations

Flaw classification (determination of the flaw type) and flaw sizing (prediction of the flaw shape, orientation and sizing parameters) are very important issues in ultrasonic nondestructive evaluation of materials. In this work, new techniques for both classification and sizing are described;In the area of flaw classification, a methodology is developed which can solve classification problems in weldments using probabilistic neural networks. In the area of flaw sizing, four new approaches are presented including (1) the determination of distance-gain-size (DGS) curves and frequency response curves for flat-bottom holes based on a theoretical ultrasonic scattering model, (2) a time-of-flight equivalent (TOFE ...


Application Of The Boundary Element Method To Coupled Fluid-Structure Interaction Problems , Partha P. Goswami Jan 1991

Application Of The Boundary Element Method To Coupled Fluid-Structure Interaction Problems , Partha P. Goswami

Retrospective Theses and Dissertations

The direct boundary element method (BEM) is used to formulate and numerically simulate the interaction of acoustic waves with submerged elastic structures and subsequently specialized to model finite beam transmission through locally curved elastic surfaces. These are structural-acoustic or fluid-solid interaction problems coupling scalar (acoustic) and vector (elastic) media. The problem is formulated in the frequency domain and modelled in three dimensions, and the elasto-acoustic phenomenon described by the acoustic and elastodynamic boundary integral equations (BIE) with pressure and displacement serving as the primarily variables;The general problem deals with a closed solid domain surrounded by an unbounded fluid medium ...


Numerical Solution Of Inverse Problems In Mechanics Using The Boundary Element Method , Shuvra Das Jan 1991

Numerical Solution Of Inverse Problems In Mechanics Using The Boundary Element Method , Shuvra Das

Retrospective Theses and Dissertations

Due to the ill-posed nature of inverse problems, it is difficult to obtain solutions using well known analytical and numerical techniques. The use of boundary element method as a numerical technique to solve inverse problems is quite new. In this work, the algorithms for the solution of two kinds of inverse problems are examined in detail. For the first kind, the shape and location of a part of the boundary is unknown; and for the second kind, the boundary condition is not specified on a part of the boundary;Boundary value problems with partially unknown boundary are ill-posed. To solve ...


Application Of The Boundary Element Method To Elastic Wave Scattering Problems In Ultrasonic Nondestructive Evaluation , Paul Jay Schafbuch Jan 1991

Application Of The Boundary Element Method To Elastic Wave Scattering Problems In Ultrasonic Nondestructive Evaluation , Paul Jay Schafbuch

Retrospective Theses and Dissertations

The boundary element method (BEM) is used to numerically simulate the interaction of ultrasonic waves with material defects such as voids, inclusions, and open cracks. The time harmonic formulation is in 3D and therefore allows flaws of arbitrary shape to be modeled. The BEM makes such problems feasible because the underlying boundary integral equation only requires a surface (2D) integration and difficulties associated with the seemingly infinite extent of the host domain are not encountered. The computer code utilized in this work is built upon recent advances in elastodynamic boundary element theory such as a scheme for self adjusting integration ...


Modeling Of Ultrasonic Scattering Experiments With Applications To System And Transducer Characterization , David Duane Bennink Jan 1990

Modeling Of Ultrasonic Scattering Experiments With Applications To System And Transducer Characterization , David Duane Bennink

Retrospective Theses and Dissertations

The voltage signal output by the receiver electronics, which represents the observable quantity in an ultrasonic scattering experiment, is written as a product, in the frequency domain, of two factors: the system efficiency and the scattering coefficient. The system efficiency represents the combined electrical properties of both the generator and receiver electronics and is a function of frequency only. The scattering coefficient represents the acoustic nature of the experiment (the radiation, propagation, scattering and reception of ultrasonic waves) and depends on the distributed field properties of the transducers involved and their locations and orientations, on the number and type of ...


Application Of Ultrasonic Guided Waves To The Characterization Of Texture In Metal Sheets Of Cubic And Hexagonal Crystallites , Yan Li Jan 1990

Application Of Ultrasonic Guided Waves To The Characterization Of Texture In Metal Sheets Of Cubic And Hexagonal Crystallites , Yan Li

Retrospective Theses and Dissertations

Texture (preferred grain orientation) of polycrystalline metal sheets is an important material property which influences the process of making products such as aluminum cans and automobile and aircraft components. Traditionally, the texture is determined by X-ray or neutron diffraction techniques which are often destructive and time-consuming in nature. Over the last decade, ultrasonics has been found to provide an alternative way to characterize texture nondestructively and quickly. This dissertation makes an in-depth study of the fundamental physical principles of ultrasonic characterization of texture in metal sheets of cubic and hexagonal crystallites. The foundation is laid by investigations of wave propagation ...


Computer Simulation Of Arterial Blood Flow , Nikolaos Stergiopulos Jan 1990

Computer Simulation Of Arterial Blood Flow , Nikolaos Stergiopulos

Retrospective Theses and Dissertations

Computer models have been widely used to simulate pressure and flow propagation in the arterial system. While experimentation involving the human arterial system is difficult and impractical, computer models offer an attractive alternative for the study of arterial hemodynamics. The purpose of the present study was to develop a computer model of the whole systemic circulation and to use this model to study pressure and flow propagation under normal flow conditions, as well as under conditions of arterial disease;The mathematical model used to describe flow in an arterial segment was based on the one-dimensional continuity and momentum equations. The ...