bluuebunny/crossref_metadata_2025 huggingface dataset:
Suspension Design for Linear Toe Curves: A Case Study in Mechanism Synthesis
Authors: Raghavan Madhusudan
Published: May 2004

We present an algorithm for synthesizing the attachment point locations of the tie-rod of an automotive suspension, to achieve linear toe change characteristics with jounce and rebound of the wheel. This behavior is considered desirable for achieving good ride and handling. The algorithm reduces the synthesis problem to the computation of the center and normal of a circle, given the coordinates of 3 points on the circle. This procedure is significant because it eliminates numerous cycles of design iterations in traditional analysis-based design methods. Furthermore, the locus of acceptable solutions allows the designer to comply with suspension packaging constraints.
On the Determination of Joint Reactions in Multibody Mechanisms
Authors: Blajer Wojciech
Published: May 2004

In this paper some existing codes for the determination of joint reactions in multibody mechanisms are first reviewed. The codes relate to the DAE (differential-algebraic equation) dynamics formulations in absolute coordinates and in relative joint coordinates, and to the ODE (ordinary differential equation) formulations obtained by applying the coordinate partitioning method to these both coordinate types. On this background a novel efficient approach to the determination of joint reactions is presented, naturally associated with the reduced-dimension formulations of mechanism dynamics. By introducing open-constraint coordinates to specify the prohibited relative motions in the joints, pseudoinverse matrices to the constraint Jacobian matrices are derived in an automatic way. The involvement of the pseudo-inverses leads to schemes in which the joint reactions are obtained directly in resolved forms—no matrix inversion is needed as it is required in the classical codes. This makes the developed schemes especially well suited for both symbolic manipulators and computer implementations. Illustrative examples are provided.
Geometric Design of Cylindric PRS Serial Chains
Authors: Su Hai-Jun , Wampler Charles W. , McCarthy J. Michael
Published: May 2004

This paper considers the design of cylindric PRS serial chains. This five degree-of-freedom robot can be designed to reach an arbitrary set of eight spatial positions. However, it is often convenient to choose some of the design parameters and specify a task with fewer positions. For this reason, we study the three through eight position synthesis problems and consider various choices of design parameters for each. A linear product decomposition is used to obtain bounds on the number of solutions to these design problems. For all cases of six or fewer positions, the bound is exact and we give a reduction of the problem to the solution of an eigenvalue problem. For seven and eight position tasks, the linear product decomposition is useful for generating a start system for solving the problems by continuation. The large number of solutions so obtained contraindicates an elimination approach for seven or eight position tasks, hence continuation is the preferred approach.
On Delamination Growth in Shallow Shells
Authors: Stora˚kers B. , Larsson P.-L. , Rohart C.
Published: May 2004

A theoretical and computational study has been carried out for compressive loading of a thin circular embedded delamination located below a cylindrical surface. The delaminated member is subjected to nominally uniaxial and balanced biaxial loading with the main objective to analyze its influence on surface curvature especially as regards imminent crack growth. The analysis is based on nonlinear shell theory combined with linear fracture mechanics. A finite element program earlier developed for delaminated plates has been generalized to apply also for shells and used to determine energy release rates and mode intensities along the delaminated front. A parameter study is made of the influence of curvature of the delaminated shell in particular as regards initiation and stability of crack growth.
Sloshing Effects in Half-Full Horizontal Cylindrical Vessels Under Longitudinal Excitation
Authors: Papaspyrou S. , Valougeorgis D. , Karamanos S. A.
Published: May 2004

A mathematical model is developed for sloshing effects in half-full horizontal cylindrical vessels, under external excitation in the direction of the longitudinal vessel axis. In this geometry the problem is not separable. The velocity potential is expressed in a double series form, and after some mathematical manipulation the problem results in a series of systems of ordinary linear differential equations, one for each longitudinal mode. For the particular case of harmonic motion, a semi-analytical solution is possible. Keeping only the first two terms of the expansion in the transverse direction, an elegant formulation of remarkable accuracy is obtained. Hydrodynamic pressures and forces are calculated for harmonic excitation and for a real seismic motion event. Finally, the equivalence between the half-full horizontal cylinder and an “equivalent” rectangle is demonstrated.
Dynamics of Electrorheological Suspensions Subjected to Spatially Nonuniform Electric Fields
Authors: Kadaksham J. , Singh P. , Aubry N.
Published: May 2004

A numerical method based on the distributed Lagrange multiplier method (DLM) is developed for the direct simulation of electrorheological (ER) liquids subjected to spatially nonuniform electric field. The flow inside particle boundaries is constrained to be rigid body motion by the distributed Lagrange multiplier method and the electrostatic forces acting on the particles are obtained using the point-dipole approximation. The numerical scheme is verified by performing a convergence study which shows that the results are independent of mesh and time step sizes. The dynamical behavior of ER suspensions subjected to nonuniform electric field depends on the solids fraction, the ratio of the domain size and particle radius, and four additional dimensionless parameters which respectively determine the importance of inertia, viscous, electrostatic particle-particle interaction and dielectrophoretic forces. For inertia less flows a parameter defined by the ratio of the dielectrophoretic and viscous forces, determines the time duration in which the particles collect near either the local maximums or local minimums of the electric field magnitude, depending on the sign of the real part of the Clausius-Mossotti factor. In a channel subjected to a given nonuniform electric field, when the applied pressure gradient is smaller than a critical value, the flow assists in the collection of particles at the electrodes, but when the pressure gradient is above this critical value the particles are swept away by the flow.
The Gas Penetration Through Viscoelastic Fluids With Shear-Thinning Viscosity in a Tube
Authors: Yamamoto Takehiro , Suga Takanori , Nakamura Kiyoji , Mori Noriyasu
Published: May 2004

The penetration of a long gas bubble through a viscoelastic fluid in a tube was studied. Experiments were carried out for two Newtonian and five polymeric solutions to investigate the relation between the coating film thickness and rheological properties of the test fluids. The polymeric solutions are viscoelastic fluids having shear-thinning viscosity. A bubble of air was injected into a tube filled with a test fluid to form hydrodynamic coating on a tube wall. The film thickness was evaluated by hydrodynamic fractional coverage m. The fractional coverage was characterized using the capillary number Ca and the Weissenberg number Wi. For viscoelastic fluids, Ca and Wi were evaluated considering the shear-thinning viscosity. Two kinds of representative shear rate were used for the evaluation of Ca and Wi. The dependence of m on Ca in viscoelastic fluids was different from that of the Newtonian case. The film was thinner than that of the Newtonian case at the same Ca when Wi was small, i.e. the viscous property was dominant. The shear-thinning viscosity had a role to make the film thin. On the other hand, the film tended to be thicker than the corresponding Newtonian results at large Wi because of normal stress effect.
An Experimental Study of the Effect of Grid Turbulence on Shear Layer Evolution
Authors: Lang Amy Warncke , Gomez Begon˜a
Published: May 2004

An experiment was performed in a shear layer water tunnel to determine the effect that grid turbulence, introduced within the meeting of the two streams, had on the evolution of a free shear layer. DPIV results show that the presence of grid turbulence inhibited the growth of the large coherent structures formed in the undisturbed shear layer, and thus led to an alteration of the entrainment process of free stream fluid into the shear layer. This caused more symmetry and various growth rates in the shear layer evolution. Also, the peak Reynolds stress magnitudes increased with the presence of grid turbulence.
Isentropic Compressible Flow for Non-Ideal Gas Models for a Venturi
Authors: Cornelius Kenneth C. , Srinivas Kartik
Published: May 2004

The non-ideal gas equations and mathematical formulation developed in this work using the compressibility factor in the equation of state closely resemble the derivations used for the ideal gas mathematical formulation for a direct comparison of the differences between the ideal versus the non-ideal gas law. The local Mach number is defined for the non-ideal gas. The plenum total variables used in compressible flow are expressed in terms of the local Mach number for the polytrope and Rayleigh models. A power law relationship is derived between the thermodynamic variables that allow an analytical result for the mass flow under certain constraints.
Indentation of an Anisotropic Half-Space by a Heated Flat Punch
Authors: Lin Yuan , Ovaert Timothy C.
Published: May 2004

The two-dimensional thermoelastic contact problem of an anisotropic half-space indented by a heated rigid flat punch is studied using the extended version of Stroh’s formalism. Two cases, where the contact interface is nonslip and frictionless, have been considered. In the first case, the contact is perfect throughout the punch face. In the second case, separation is assumed to occur at the edges of the punch.
The Generalized Lame´ Problem—Part I: Coupled Poromechanical Solutions
Authors: Kanj Mazen Y. , Abousleiman Younane N.
Published: May 2004

Cylindrical geometries are known to present special problem simulation capabilities in engineering design. (For example, solid and hollow cylinder tests are routinely studied in soil and rock mechanics to gain insights into the geomechanical properties and to assess the stability of boreholes and cylindrical openings in the project design geomedia.) This paper identifies a unified and universal solution to all the three recognized right-cylindrical problem objects in poromechanics. A closed-form solution to the problem of the finite, homogeneous, isotropic, fully saturated, thick-walled hollow cylinder subjected to various loading modes is readily presented and described. The assumed loading modes encompass arbitrary temporal functions of uniformly distributed inner/outer pore pressure, inner/outer confining pressure, inner/outer deviatoric stress, and end axial compaction or extension. The time-dependent response derivations are outlined within the frameworks of the Biot’s theory of linear poroelasticity and facilitated by the governing generalized plane-strain (GPS) principle. The (as presented) solution is shown to converge asymptotically to those of the two essential problem setups in geomechanics: the finite solid cylinder and the borehole core in an infinite medium. As such, a complete/explicit solution to a generalized statement of the Lame´ problem is presented. The solution utilizes a fairly simple loading decomposition scheme which leads to two basic problem forms: a generalized poroelastic axisymmetric problem and a generalized, plane-strain, poroelastic deviatoric problem.
The Generalized Lame´ Problem—Part II: Applications in Poromechanics
Authors: Abousleiman Younane N. , Kanj Mazen Y.
Published: May 2004

The cylinder is the geometry most widely used in laboratory testing procedures for rocks and other geomaterials. This paper applies a unified and universal Lame´ solution to all the three recognized right-cylindrical problems in poromechanics. As such, the solution of the hollow-cylinder features itself converging asymptotically to the exact values predicted by the solutions of the two other essential problem setups in geomechanics; namely, the finite solid cylinder case and the borehole core in an infinite medium. The time-dependent response derivations were “scripted” within the frameworks of the Biot’s theory of linear poroelasticity and facilitated by the governing generalized plane-strain (GPS) principle.
Reference Stress Based Approach to Predict Failure Strength of Pipes With Local Wall Thinning Under Single Loading
Authors: Kim Yun-Jae , Shim Do-Jun , Lim Hwan , Kim Young-Jin
Published: May 2004

This paper proposes a new method to estimate failure strength of a pipe with local wall thinning. The method is based on the equivalent stress averaged over the minimum ligament in the locally wall thinned region. The highlight of the proposed method is to propose a simple scheme to estimate the equivalent stress in the minimum ligament. Inspired by the reference stress method for approximate creep stress analysis, approximate estimation equations are proposed for the equivalent stress in the minimum ligament, which are then calibrated using detailed elastic-plastic three-dimensional FE analysis. Remarkably the resulting estimation equations are found to be insensitive not only to pipe and defect geometries but also to material. Comparison of failure loads, predicted according to the proposed method, with published test data for corroded pipes shows excellent agreement, which provides confidence in the use of the proposed method to assess local wall thinning in pipes. Furthermore, the proposed method is conceptually simple and thus easy to be extended to more complex situations.
Dynamic Stability of Flexible Bellows Subjected to Periodic Internal Fluid Pressure Excitation
Authors: Watanabe Masahiro , Kobayashi Nobuyuki , Wada Yuichi
Published: May 2004

This paper deals with the theoretical stability analysis and experimental study of flexible bellows subjected to periodic internal fluid pressure excitation. The bellows studied in this paper are fixed at both ends rigidly, and are excited by the periodic internal fluid pressure. In the theoretical stability analysis, the basic equation of the bellows subjected to periodic internal fluid pressure excitation is derived as a Mathieu’s equation. Natural frequencies of the bellows are examined and stability maps are presented for parametric instability, computed by Bolotin’s method. It is found that the transverse natural frequencies of the bellows decrease with increasing the static internal fluid pressure and buckling occurs due to high internal fluid pressure. It is also found that primary and secondary parametric vibrations occur to the bellows in transverse direction due to the periodic internal fluid pressure excitation. Parametric instability regions are clarified and the theoretical calculations of the parametric instability boundaries are in good agreement with the experimental ones. Moreover, effects of damping and static internal fluid pressure on the parametric instability regions are examined theoretically.
Stress Concentration Factors of Cross-Bores in Thick Walled Cylinders and Blocks
Authors: Dixon Ricky D. , Peters Daniel T. , Keltjens Jan G. M.
Published: May 2004

The purpose of this paper is to investigate the stress concentration in stress fields around crossbores for closed-end thick-walled square blocks and cylindrical shells using the finite element method. These stress concentration factors are presented and discussed as a function of the ratio of crossbore radius to the cylinder internal radius (HR/Ri=0.01 to 0.7) for a range of wall ratios (Y=1.5 to 5). Charts and simple expressions are provided for ease of use.
Failure Strength Assessment of Pipes With Local Wall Thinning Under Combined Loading Based on Finite Element Analyses
Authors: Shim Do-Jun , Choi Jae-Boong , Kim Young-Jin
Published: May 2004

Failure assessment of a pipe with local wall thinning draws increasing attention in the nuclear power plant industry. Although many guidelines have been developed and are used for assessing the integrity of a wall-thinned pipeline, most of these guidelines consider only pressure loading and thus neglect bending loading. As most pipelines in nuclear power plants are subjected to internal pressure and bending moment, an assessment procedure for locally wall-thinned pipeline subjected to combined loading is urgently needed. In this paper, three-dimensional finite element (FE) analyses are carried out to simulate full-scale pipe tests conducted for various shapes of wall-thinned area under internal pressure and bending moment. Maximum moments based on ultimate tensile stress were obtained from FE results to predict the failure of the pipe. These results are compared with test results, showing good agreement. Additional finite element analyses are then performed to investigate the effect of key parameters, such as wall-thinned depth, wall-thinned angle and wall-thinned length, on maximum moment. Moreover, the effect of internal pressure on maximum moment was investigated. Change of internal pressure did not show significant effect on the maximum moment.
Yield Criterion for Thin Perforated Plates With Square Penetration Pattern
Authors: Bhattacharya A. , Venkat Raj V.
Published: May 2004

Second and fourth order polynomials describing the yield criterion for perforated plates with square penetration pattern were developed following the methodology shown by Hill (1950) and later by Reinhardt (2001) for triangular penetration pattern. The inadequacy of Hill’s (1950) criterion to describe the yield surface of the equivalent solid plate was observed by Reinhardt (2001). Unlike in the case of triangular penetration pattern, the second-order polynomial satisfies the uniqueness of yield stresses after symmetric rotation in the case of square penetration pattern, even though the second order polynomial is incomplete as it cannot satisfy the yield criterion for pure shear. However, the fourth order polynomial is found to satisfy the symmetry and boundary conditions arising from biaxial loadings completely and shows closer agreement with the finite-element results obtained by the authors as compared to the second-order polynomial. Some of the finite-element results were compared with the experimental results of Litewka (1991) and the agreement between them was found to be satisfactory. The effect of out-of-plane stresses have not been considered in the present investigation as these are found to be negligible in case of thin perforated plates, for which plane stress condition was assumed in the finite element analysis.
A Method for Producing Extra-High Dynamic Pressure Due to the Efficient Use of High Explosive
Authors: Liu Zhi-Yue , Tanaka Katsumi , Itoh Shigeru
Published: May 2004

In the material processing such as shock synthesis and powder consolidation by shock waves the method for generating dynamic pressure is a vital factor for the quality of the final recovered materials. A general and convenient way for producing shock wave demanded in such applications is to take advantage of the explosion effect from high explosive. Under normal conditions, a given high explosive can only provide some kind of magnitude of dynamic pressure after its explosion. Therefore, it is whether possible to obtain the higher dynamic pressure by adequately changing the form of the explosion of high explosive. Starting from this motivation, we put forward a new method for producing high dynamic pressure from the use of the overdriven detonation of high explosive. The proposed device consists of the following configurations. A metal flyer accelerated by the high explosive is used to impact another layer of high explosive to incur an overdriven detonation in this layer of explosive. The overdriven detonation of high explosive acts on the powder materials, bringing out high dynamic pressures to the materials studied. To examine the efficiency of this combination on the improvement of dynamic pressure, a numerical computation is performed on this system. The details on the illustration of this method as well as the results of numerical investigation will be given.
High Pressure Generation Using Underwater Explosion of a Spiral Explosive in a Conical Vessel
Authors: Hamada Toru , Itoh Shigeru , Murata Kenji , Kato Yukio
Published: May 2004

An explosive configuration was studied so that the underwater shock wave converges at the tip of the explosive, and a three-dimensional spiral configuration was obtained. This spiral configuration need to be analyzed theoretically due to the relation of propagation velocity of underwater shock wave, detonation velocity of the explosive and a configuration of vessel to charge the explosive. In order to study an effect of the convergence, pressure measurement at the spiral center was carried out by using a manganin gauge. Therefore, when SEP was used in this experiment, the maximum pressure value was 17.7 GPa. This maximum pressure value is higher than the pressure value of underwater shock wave generated from the underwater explosion of a straight configuration. Furthermore, this maximum pressure value was higher than C-J pressure of SEP. An initial pressure of underwater shock water shock wave that can obtain from an isentropic expansion curve of SEP and a characteristic curve of water is 5.7 GPa, and C-J pressure of SEP is 15.9 GPa. From the above-mentioned, the effect of spiral convergence could be shown well.
Optimal Design of Trusses According to a Plastic Shakedown Criterion
Authors: Palizzolo Luigi
Published: May 2004

The optimal design of elastic-perfectly plastic truss structures subjected to quasi-statically loads variable within a given load domain is studied. The actions are given as the combination of fixed load and perfect cyclic load. Suitably chosen load multipliers are given. A minimum volume formulation of the design problem with assigned limit load multiplier is developed and it is provided on the grounds of a statical approach as well as of a kinematical approach. The incremental collapse (ratchetting) of the optimal structure is prevented, as long as the loads are not greater than some prescribed values, by special constraints suitably introduced in the search problem. The Kuhn-Tucker equations related to the above-described search problems are deduced and studied. The duality between the statical and the kinematical problem formulations is proved. A special iterative technique devoted to the solution of the above referred optimization problems is utilized for computational purposes. A numerical example concludes the paper. The comparison between different designs is effected.
Degeneracy, Derivative Rule, and Green’s Functions of Anisotropic Elasticity
Authors: Yin Wan-Lee
Published: May 2004

Degenerate and extra-degenerate anisotropic elastic materials have repeated material eigenvalues whose multiplicity is greater than the number of independent eigensolutions. Using basic elasticity relations, a simple, direct proof is given to show that higher-order eigensolutions may be obtained from the analytical expressions of the zeroth-order eigensolutions according to the derivative rule. These higher-order eigensolutions contribute to the complexity of the general solutions of degenerate and extra-degenerate materials, and to the analytical difficulties inherent in such cases including isotropic elasticity. For all types of anisotropic materials, the general solution is given specific forms to obtain Green’s functions of several domains with straight or elliptical boundaries. These results, presented in fully explicit expressions, extend Green’s functions of nondegenerate materials to degenerate and extra-degenerate cases that have not been explored previously.
Contact Problem Involving Frictional Heating for Rough Half-Space
Authors: Pauk Volodymyr
Published: May 2004

Plane contact problem of a punch sliding over a half-space is considered. The surface of the half-space is assumed to be rough and the roughness heights have the Gaussian distribution. The heat generation due to the friction is taken into account. The problem is reduced to nonlinear integral equations which are solved approximately. The effects of the frictional heating and the roughness on the contact size and on the contact pressure are presented.
Stress Intensity Factor of a Circumferential Crack in a Thick-Walled Cylinder Under Thermal Striping
Authors: Meshii Toshiyuki , Watanabe Katsuhiko
Published: May 2004

This paper tries to explain the interesting field data that indicate a surface axisymmetric circumferential crack inside a hollow cylinder (circumferential crack) shows tendency toward crack arrest, when the temperature of the fluid inside the cylinder experiences sinusoidal fluctuation (thermal striping). For this purpose, transient stress intensity factor (SIF) range of a circumferential crack in a finite-length thick-walled cylinder with rotation-restrained edges, under thermal striping, was analyzed. It was assumed that the fluid temperature changes sinusoidally and that heat transfer coefficient is constant. First an analytical temperature solution for the problem was obtained and it was combined with our SIF evaluation method derived based on superposition principle and Duhamel’s analogy. Then we defined the maximum SIF range as the maximum value of the SIF range during thermal striping and studied the characteristic change of this maximum SIF range with the variation of crack depth to explain the crack arrest tendency. Results showed that the maximum SIF range under thermal striping decreases monotonously when crack depth is varied to become deeper than a specific value, which corresponds to the crack arrest tendency.
The Use of “Fitness for Service” Assessment Procedures to Establish Allowable Flaw Sizes in Steel Cylinders
Authors: Rana Mahendra D. , Smith John H.
Published: May 2004

As part of the U.S. Department of Transportation safety regulations, seamless steel cylinders that are used to transport high-pressure gases are required to be periodically retested during their lifetime [1]. The safety regulations have recently been revised to permit the use of ultrasonic methods for retesting steel cylinders. These ultrasonic test methods permit the quantitative determination of the size of any flaws that are detected in the cylinders. Therefore, to use these ultrasonic test methods it is required that quantitative, “allowable flaw sizes” be established to set acceptance/rejection limits for the cylinders at the time of retesting. Typical flaws that can occur in seamless steel cylinders during service are line corrosion, gouges, local thin areas of corrosion, notches, and cracks. To establish “allowable flaw sizes” for seamless steel cylinders, an assessment of typical flaws that occur in seamless cylinders was first carried out to establish the “critical flaw sizes” (e.g., depth and length or area) for selected types of flaws. The critical flaw size is the size of the flaw that will cause the cylinders to fail at either the designated test pressure or at the marked service pressure. The API Recommended Practice 579 “Fitness-for-Service” was used to calculate the critical flaw sizes for a range of cylinder sizes and strength levels [2]. Several hundred monotonic hydrostatic, flawed-cylinder burst tests were conducted as part of an International Standards Organization (ISO) test program to evaluate the fracture performance of a wide range of steel cylinders [3]. The results of these tests were used to verify the calculated “critical flaw sizes” that were calculated using the API 579 procedures. These results showed that the analysis conducted according to API 579 always underestimated the actual flaw sizes to cause failure at test pressure or at service pressure. Therefore, the “Fitness for Service” assessment procedures can be used reliably to establish the “critical flaw sizes” for cylinders of all sizes and strength levels. After the “critical flaw sizes” to cause failure of the cylinders at both the test pressure and the service were established, the “allowable flaw sizes” were calculated for a wide range of the cylinder types and strength levels. This was done modifying (reducing) the size of the “critical flaw sizes” for each cylinder by adjusting for fatigue crack growth that may occur during the use of the cylinder. This results in the final “allowable flaw size” criteria that are used for defining the acceptance or rejection of the cylinders during retesting. This paper presents the results of the analytical and experimental work that was performed to establish the “critical flaw sizes” and “allowable flaw sizes” for a wide range of high-pressure gas cylinders.
Prediction of Creep Rupture of Pressure Vessels
Authors: Bergheau Jean-Michel , Devaux Josette , Mottet Ge´rard , Gilles Philippe
Published: May 2004

Predictions of creep rupture of a reactor pressure vessel in a severe hypothetical accident needs to accurately take into account the interactions between creep and damage phenomena. This paper presents an approach based on a model coupling elasto-visco-plasticity and damage, formulated within the framework of continuous damage theory. The model and its implementation in a finite element software are presented and special attention is devoted to the procedure enabling the identification of the parameters of the model. The approach is validated on two tests of the program “RUPTHER” which concerns A508 cl3 steel cylinder and on the EC-FOREVER experiment (A533 steel mockup) developed as part of the European Commission Program “Assessment of Reactor Vessel Integrity.”
Buried Pipe Modeling With Initial Imperfections
Authors: Villarraga Junes A. , Rodrı´guez Jose´ F. , Martı´nez Cora
Published: May 2004

A formulation using the finite element method is presented in this paper to analyze stresses and displacements of underground pipelines with initial imperfections. The formulation includes both thermal expansion of the pipeline and internal pressure. The method is based on large deformation beam theory with the finite element formulation based on Euler-Bernoulli beam elements of constant cross-section. The pipe-soil interaction is modeled as a nonlinear elastic foundation in the problem formulation. The resulting nonlinear finite element model with appropriate boundary conditions is solved using full Newton-Raphson as the iterative procedure. Numerical examples are provided to show the application of the methodology and to demonstrate the effect of the initial imperfections in the stress distribution of a buried pipe. The results show that initial imperfections have a considerable influence on the stress distribution of buried pipelines, leading in some cases to stress levels above the allowable limit established by the design codes. The results also help to identify the critical temperature at which buckling of the buried pipe might occur.
Creep Ovalization and Buckling of a Linear Viscoelastic Externally Pressurized Pipe
Authors: Popelar Carl H. , Evans Donald
Published: May 2004

An analysis model is developed for the creep ovalization and buckling of an imperfect plastic pipe subjected to a uniform external pressure. The pipe’s cross section is assumed to have a known initial out of roundness or ovality and to be composed of a linear viscoelastic material. The governing equations are transformed using Laplace and Carson transforms. The transformed deviation of the cross section from its initial shape is inverted exactly by evaluating the Bromwich integral and approximately by the simpler direct inversion method. The two inversion methods, which yield nearly identical results, are compared with the quasi-elastic method wherein the elastic modulus in the solution to the equivalent elastic problem is replaced by the relaxation modulus. The model predictions are quite sensitive to the viscoelastic material parameters for small values of the relaxation exponent and this sensitivity has direct implications with respect to the reliability of the predicted life expectancy for the pipe. Predictions and measurements made in creep ovalization tests of a high density polyethylene (HDPE) pipe at 50°C and different pressures are compared. Very good agreement is obtained between predicted and measured response in short-term tests and in an extended test. Bi-directional shifting is used to translate inferred material parameters at 50°C to 35°C for making comparisons of predictions with measurements at the latter temperature. While the predicted ovalization overestimates the measurement, very good agreement is obtained when one material parameter is decreased by 10% and the other is increased by 7%; thereby demonstrating the sensitivity of the predictions to small changes in the material parameters for small values of the relaxation exponent. The efficacy of a simple estimate for the limiting creep buckling or collapse pressure as a function of the design life is presented and compared with measurements.
Nondestructive Evaluation of FRP Design Criteria With Primary Consideration to Fatigue Loading
Authors: Ramirez Guillermo , Ziehl Paul H. , Fowler Timothy J.
Published: May 2004

Design of FRP tanks and pressure vessels is based on criteria developed in the late 1960s using materials and procedures that represented the state of the art at the time. Maximum strain has been the controlling factor selected for the design of these vessels at an allowable level of 0.001. With the development of newer materials and systems with recorded performances of better than 0.001 this is now an inefficient limit in the design. Tests performed in the programs described in this paper indicate that newer materials perform well at higher strains. Results of strength tests performed here indicated that strains of 0.002 to 0.003 or better are possible in the safe design of tanks and pressure vessels. In addition, more accurate determination of design limits is possible if methods like acoustic emission are incorporated in the design process.
Lower Bound Limit Load Determination: The mβ-Multiplier Method
Authors: Seshadri R. , Indermohan H.
Published: May 2004

The existing lower bound limit load determination methods, that are based on linear elastic analysis such as the classical and mα-multiplier methods, have a dependence on the maximum equivalent stress. These methods are therefore sensitive to localized plastic action, which occurs in components with thin or slender construction, or those containing notches and cracks. Sensitivity manifests itself as relatively poor lower bounds during the initial elastic iterations of the elastic modulus adjustment procedures, or oscillatory behavior of the multiplier during successive elastic iterations leading to limited accuracy. The mβ-multiplier method proposed in this paper starts out with Mura’s inequality that relates the upper bound to the exact multiplier by making use of the “integral mean of yield.” The formulation relies on a “reference parameter” that is obtained from considering a distribution of stress rather than a single maximum equivalent stress. As a result, good limit load estimates have been obtained for several pressure component configurations.
Experimental and Numerical Analysis of Transient Liquid Slug Motion in a Voided Line
Authors: Bozkus Zafer , Baran O¨zgu¨r Ugˇras¸ , Ger Metin
Published: May 2004

In this paper, the hydrodynamics of a single transient slug in a voided line was investigated numerically and experimentally. In the experiments, the liquid slugs of various lengths were propelled into an inclined smooth steel pipe under several different driving air pressures. The pipe segment terminates in an open ended elbow; the pressure time histories are recorded at this elbow. The recorded peak pressures are correlated to the tank pressures and pipe and slug geometry. Dimensionless parameters are developed to present the experimental data. Moreover, the flow is investigated numerically using several Godunov type schemes, namely, basic Godunov Scheme, Total Variation Diminishing (TVD), based Weighted Average Flux (WAF) method and two different Monotone Upstream Schemes for Conservation Laws (MUSCL) methods. These schemes employ Godunov’s approach facilitating exact and Harten, Lax and van Leer’s modified approximate solver (HLLC) type solution methods solving the Riemann problem of gas dynamics equations. Furthermore, the recorded peak pressures at the elbow are compared with the results of the numerical analysis and results of two earlier studies.
Fluid-Elastic Instability in a Tube Array Subjected to Uniform and Jet Flow
Authors: Feenstra Paul , Weaver David S. , Abdullah Zia
Published: May 2004

A wind tunnel study was carried out to investigate the fluidelastic stability of a model heat exchanger tube array subjected to a uniform cross-flow of air and a concentrated jet flow of air directed down a tube lane. The latter experiments were intended to simulate the effects of a soot blower on the dynamic response of tubes which had apparently been the cause of catastrophic tube failure in a heat exchanger. The experimental results showed that the model tube array experienced fluidelastic instability when subjected to a uniform cross-flow beyond a dimensionless pitch flow velocity which was substantially above the maximum design flow velocity of the heat exchanger. These experiments established that normal operating conditions could not have been responsible for the tube failures. Additional experiments showed that a continuously translating nozzle dispensing a jet of air at the tubes caused some static deflection of the tubes but no serious vibrations were observed. However, when the nozzle was fixed at one location, whereby the jet of air issued directly down a tube lane, fluidelastic instability occurred in the first few tube rows. A simplified analysis showed that the jet could cause fluidelastic instability. It can be inferred that, for heat exchangers equipped with steam soot blowers, normal soot blower operation should not cause fluidelastic instability but that a parked soot blower can cause fatigue failure of the tubes adjacent to the impinging jet in a relatively short period of time.
A Critical Examination of Sachs’ Material-Removal Method for Determination of Residual Stress
Authors: Parker Anthony P.
Published: May 2004

Sachs’ method is an experimental procedure used primarily in the determination of residual stresses in autofrettaged thick cylinders. In its usual form it involves fixing axial and hoop direction strain gauges to the OD of a tube; strain readings are then obtained after each incremental removal of material from the bore. Sachs’ analysis assumes that the remaining tube unloads in linear-elastic fashion throughout the process and that superposition may therefore be employed to quantify the residual stresses within the original tube. By numerical simulation of two complete Sachs’ experimental sequences with “open end” conditions it is demonstrated that the assumption of elastic unloading is invalidated by the Bauschinger effect. Sachs’ method thereby overestimates compressive residual bore hoop stresses in a typical tube by between 24% and 43%. If used as the basis for cyclic pressurization fatigue lifetime predictions with pre-existing cracks, such discrepancies will cause overestimates in fatigue lifetime of an order of magnitude. Sachs’ experimental procedure is therefore not recommended as a reliable or conservative method for determination of residual stress.
Stress Intensity Factors for a Curved-Front Internal Crack in an Autofrettaged Tube With Bauschinger Effect
Authors: Tan Choon-Lai , Parker Anthony P. , Cassell Chantz W. V.
Published: May 2004

Pressure vessel steels exhibit the Bauschinger effect that significantly reduces post-autofrettage residual compressive hoop stresses in the near-bore region in comparison with ‘ideal’ (elastic-perfectly plastic) behavior. These reduced hoop stress profiles were calculated using Von Mises’ criterion via a nonlinear analysis for the case of open-end (engineering plane strain) autofrettage. These profiles were then used to obtain stress intensity factor solutions via the Boundary Integral Equation (BIE) method, commonly known as the Boundary Element Method (BEM). Results are presented for tubes of diameter ratio 2 and 2.5 with an internal semi-elliptical surface crack having a maximum depth/surface length ratio of 0.4 (i.e., an eccentricity of 0.8). Crack depths range from 20% to 80% of wall thickness and results are presented for seven locations on the crack front from maximum depth to free surface. For crack depths up to 20% of wall thickness there is a significant reduction in magnitude of autofrettage stress intensity factor due to Bauschinger effect. For typical overstrain levels this reduction is approximately 30% of “ideal” values. Such a reduction may, in turn, cause an order of magnitude reduction in the fatigue lifetime of the vessel.
Optical‐CT gel‐dosimetry II: Optical artifacts and geometrical distortion
Authors: Oldham Mark , Kim Leonard
Published: May 2004

There is a clear need for technology that enables accurate, high‐resolution, three‐dimensional (3D) measurement of intricate dose distributions associated with modern radiation treatments. A potential candidate has emerged in the form of water‐equivalent “3D gel dosimetry” utilizing optical‐computed‐tomography (optical‐CT). In a previous paper we presented basic physical characterization of an in‐house prototype optical‐CT scanning system. The present paper builds on that work by investigating sources of optical artifacts and geometric distortion in optical‐CT scanning. Improvements in scanner design are described. Correction strategies were developed to compensate for reflection and refraction, imperfections in the water‐bath, signal drift, and other effects. Refraction and reflection were identified as the principal factors causing inaccurate reconstruction of absolute attenuation coefficients. A correction specific to a given flask was developed utilizing prescans of the flask when filled with water‐bath fluid, thereby isolating the refractive and reflective components for that flask. Residual artifacts were corrected by fitting a theoretical model to the well‐behaved portion of these prescans and extrapolating to regions of lost data, enabling reconstruction of absolute optical‐CT attenuation coefficients to within 4% of corresponding spectrophotometer values. Needle phantoms are introduced to quantify geometric distortion under a range of conditions. Radial distortion of reconstructed needle positions was reduced to (0.27% of the field of view) through adjustment of the water‐bath refractive index. Geometric distortion in polymer gel due to radiation‐induced refractive index changes was found to be negligible under the conditions examined. The influence of scattered light on reconstructed attenuation coefficients was investigated by repeat optical‐CT scans while varying the aperture of a scatter‐rejecting collimator. Significant depression of reconstructed attenuation coefficients was observed, particularly under conditions of poor scatter rejection collimation. The general conclusion is that the first‐generation optical‐CT technique can be made insensitive to geometrical distortion, but can be susceptible to scatter effects. For accurate reconstruction of absolute attenuation coefficients, correction strategies are essential.
Determination of shielding requirements for mammography
Authors: Okunade Akintunde Akangbe , Ademoroti Olalekan Albert
Published: May 2004

Shielding requirements for mammography when considerations are to be given to attenuation by compression paddle, breast tissue, grid and image receptor (intervening materials) has been investigated. By matching of the attenuation and hardening properties, comparisons are made between shielding afforded by breast tissue materials (water, Lucite and 50%–50% adipose‐glandular tissue) and some materials considered for shielding diagnostic x‐ray beams, namely lead, steel and gypsum wallboard. Results show that significant differences exist between the thickness required to produce equal attenuation and that required to produce equal hardening of a given incident beam. While attenuation equivalent thickness produces equal exposure, it does not produce equal hardening. For shielding purposes, equivalence in exposure reduction without equivalence in penetrating power of an emerging beam does not amount to equivalence in shielding affordable by two different materials. Presented are models and results of sample calculations of additional shielding requirements apart from that provided by intervening materials. The shielding requirements for the integrated beam emerging from intervening materials are different from those for the integrated beam emerging from materials (lead/steel/gypsum wallboard) with attenuation equivalent thicknesses of these intervening materials.
Ideal observer estimation and generalized ROC analysis for computer‐aided diagnosis
Authors: Edwards Darrin C.
Published: May 2004

The research presented in this dissertation represents an innovative application of computer‐aided diagnosis and signal detection theory to the specific task of early detection of breast cancer in the context of screening mammography. A number of automated schemes have been developed in our laboratory to detect masses and clustered microcalcifications in digitized mammograms, on the one hand, and to classify known lesions as malignant or benign, on the other. The development of fully automated classification schemes is difficult, because the output of a detection scheme will contain false‐positive detections in addition to detected malignant and benign lesions, resulting in a three‐class classification task. Researchers have so far been unable to extend successful tools for analyzing two‐class classification tasks, such as receiver operating characteristic (ROC) analysis, to three‐class classification tasks. The goals of our research were to use Bayesian artificial neural networks to estimate ideal observer decision variables to both detect and classify clustered microcalcifications and mass lesions in mammograms, and to derive substantial theoretical results indicating potential avenues of approach toward the three‐class classification task. Specifically, we have shown that an ideal observer in an N‐class classification task achieves an optimal ROC hypersurface, just as the two‐class ideal observer achieves an optimal ROC curve; and that an obvious generalization of a well‐known two‐class performance metric, the area under the ROC curve, is not useful as a performance metric in classification tasks with more than two classes. This work is significant for three reasons. First, it involves the explicit estimation of feature‐based (as opposed to image‐based) ideal observer decision variables in the tasks of detecting and classifying mammographic lesions. Second, it directly addresses the three‐class classification task of distinguishing malignant lesions, benign lesions, and false‐positive computer detections. Finally, it develops important theoretical results for N‐class classification tasks that should prove of value in the development of a three‐class extension to ROC analysis methods.