bluuebunny/crossref_metadata_2025 huggingface dataset:
Expert System Technology for Capacity Planning and Productivity
Improvement
Authors: Angelides D. , Bitran G. , Papageorge Th.
Published: November 2009

An Expert System for Capacity Planning and consideration of tradeoffs in discrete Manufacturing is applied to a fabrication facility. A description of the system and its functionality is given first, followed by presentation and discussion of results from a case study. Tradeoffs between capacity, utilization, cost, lead time and work-in-process are considered, and the implication of different technologies, throughput and product mix are demonstrated. The system proves its value as a powerful tool for understanding the critical points of a given manufacturing environment, suggesting improvements and corrective actions for better productivity of an existing facility and helping in the design of a new facility.
Effect of Reynolds Number on Vibrations of Cylinders
Authors: Sumer B. M. , Fredso̸e J.
Published: November 2009

This study reports the results of an experimental work carried out with an elastically mounted rigid cylinder exposed to an oscillating flow. The cylinder is free to vibrate in the transverse direction. The effect of Reynolds number on the vibrations has been investigated up to Reynolds numbers of about 4 × 105. The Keulegan-Carpenter number of the experiments covers the range 10 ≤ KC ≤ 100. The range of the reduced velocity is from 0 to approximately 16 in most of the cases. The tests have been conducted with both smooth and rough cylinders. The present study demonstrates that the effect of Re number on vibrations can be substantial, depending on the surface roughness of the cylinder. The effect is most pronounced when the cylinder is smooth.
Architecture of an Expert System for Oceanographic Mooring
Design
Authors: Wood S. L. , Skop R. A.
Published: November 2009

Methods for the design and analysis of oceanographic moorings are well established (Berteaux, 1976). However, as with most engineering design problems, there are certain “rules-of-thumb” or “tricks-of-the-trade” that streamline the design process and enhance the performance of the final product. These rules-of-thumb are normally known to only a small cadre of people—experts—who have deep involvement and experience in the particular engineering design problem. These rules-of-thumb and other knowledge of several experts are incorporated to develop the fundamental architecture of an expert system for the design of single-point, subsurface, oceanographic moorings. Such moorings are used worldwide to collect oceanographic and acoustic data. The projected end user of this expert system is the oceanographer or acoustician who wishes to design and/or cost out a mooring but has not the access to or support for a mooring design group.
Some Implications of a Nonlinear Viscoelastic Constitutive Theory
Regarding Interrelationships Between Creep and Strength Behavior of Ice at
Failure
Authors: Harper B. D.
Published: November 2009

This study explores several possibilities for a correspondence in the behavior of ice at failure during uniaxial creep (constant stress) and strength (constant strain rate) experiments. The usual notion of failure in ice is employed (i.e., the occurrence of a minimum strain rate during a creep test and a peak or maximum stress during a strength test), and the behavior at failure is discussed in terms of a recently proposed nonlinear viscoelastic constitutive model for ice. It is demonstrated that no correspondence between creep and strength data can be expected in general; however, several approximate interrelationships do occur for the experimentally motivated special case of a constant (independent of stress and strain rate) failure strain.
Propagation of a Hovercraft Air Cavity Under a Floating Ice
Sheet
Authors: Hinchey M. J.
Published: November 2009

An ACIB is an air cushion device being developed in Canada for icebreaking purposes. When mated with the bow of a tugboat, the ACIB currently operational can break ice sheets about 1 m thick. During ACIB operations, the water surface directly beneath the craft is sometimes depressed below the lower edge of the ice sheet, and an air cavity is formed under the sheet. This air cavity is known to have a significant effect on the icebreaking capability of the ACIB. In a study for Transport Canada, DeHavilland Aircraft of Canada used underwater explosion theory to model its propagation. This paper shows that the explosion theory is incorrect. A more realistic theory backed up with experimental data is presented herein. The new theory is based on a theory for gravity currents developed by Benjamin.
Finite-Simulation Error Bounds for Estimated K-Year
Forces
Authors: Wang A. T.
Published: November 2009

Computer simulations have been used frequently to calculate design loads associated with a specific return period for offshore structures. However, two important questions persistently confront engineers who simulate load events on computers to estimate k-year forces: 1) How accurate is the estimated k-year force (say, 100-yr force) obtained through a computer simulation of n years (e.g., n = 1000) compared to that which would result from a much longer simulation? 2) When can we stop a computer simulation? Or how many simulation years are needed to reach a specified level of reliability for a certain k-year force? This paper presents solutions to these two questions under the assumption that the input parameters are completely known and the formulas used to compute loads are one hundred percent correct. Given a confidence level C (e.g., C = 80 or 90 percent) and an arbitrary but fixed number of simulation years, a method is identified to find an estimated k-year force and an error bound α, such that Pr(|estimator−k-yearforce|<α)>C (1) In addition, when the required confidence C and error bound α are given, a procedure is given to stop a computer simulation as soon as inequality (1) is satisfied. These results are not dependent on the statistical distribution of the underlying force distribution. Therefore, one does not have to assume that forces are of a specific probability distribution (such as lognormal, exponential, etc.).
Stress Concentrations in Circular Tubular Members Containing Local
Damage
Authors: Tam C. K. W. , Croll J. G. A.
Published: November 2009

Offshore structural circular tubular members suffering from local dent damage can develop extreme stresses at locations around the dent area. An analytical method for the prediction of elastic stress concentrations in locally damaged circular tubular members is presented. The method is based upon replacing geometric errors with an appropriately chosen load function to be applied to the perfect member for analysis. A simpler approach based upon an axisymmetric analysis, suitable for speedy assessment of the damage effects, is also presented. Axially loaded tubulars containing an idealized dent under stress and displacement-controlled situations are included.
The Dynamics of Slack Marine Cables
Authors: Griffin O. M. , Rosenthal F.
Published: November 2009

Examples of the uses of slack cables in marine and offshore applications include deepwater moorings and the guy lines of towers and platforms. A brief summary is given of some of the important aspects of the linear theory for the vibration of horizontal and inclined slack cables. Then the important differences between the two cases are pointed out through the use of analytical and computational examples. These examples use typical methods which have been developed in recent years for predicting the dynamics of slack cables with and without arrays of attached discrete masses.
Interactive Design and Operations of Moorings
Authors: Oppenheim B. W.
Published: November 2009

This paper describes a stand-alone PC-based computer simulator for mooring design and operations. Both program logic and mathematics are discussed. Competing algorithms for solving several classical mooring problems are compared. The program contains a design module, static and dynamic mooring simulators, and mooring calculator modules. The design module performs an automatic optimum design of anchor deployment for any environmental condition, or allows the user to perform an interactive design. The static simulator predicts system responses in all mooring operations. The dynamic simulator is an implementation of the recent requirement of regulatory bodies for simulating slow-drifting motions of the vessel after a line failure. The calculator includes modules that compute weather forces, system stiffness, elastic catenary mechanics, and others. The program is interactive, menu-driven, and includes graphics.
Three-Dimensional Acoustic Mapping Using Small Rotating
Arrays
Authors: Bryden I. G.
Published: November 2009

This paper outlines the principles of a technique which might, under certain circumstances, be an alternative to conventional SONAR systems. The technique, known as auto by cross-correlation using varying delay times, is briefly outlined, and its strengths and limitations are investigated using computer simulations. To conclude, mention is made of progress in the construction and development of an ACVD acoustic array, and some possible applications suggested.
Experiments on Anisotropic and Rate-Sensitive Strain Ratio and
Modulus of Columnar-Grained Ice
Authors: Sinha Nirmal K.
Published: November 2009

Anisotropic and rate-sensitive characteristics of the ratio of lateral strain to axial strain in addition to the rate-sensitive effective modulus for columnar-grained freshwater ice and sea ice from the Arctic, have been investigated. Tests were carried out at −20°C, for conditions of no microcracking under uniaxial loads (normal to the length of the grains) in the stress rate range of 1 × 10−3 MN · m−2 s−1 to 1 × 102MN · m−2 s−1 or an equivalent strain rate range of 1 × 10−7 s−1 to 1 × 10−2 s−1. With increase in stress rate, the ratio increased from about 0.2 to 0.3 in the plane parallel to the columns, whereas it decreased from about 0.65 to 0.3 in the plane normal to the columns. A closed-loop controlled test system in association with foil gages, mounted directly on the specimen, was used. A clip-on displacement gage was used to evaluate the accuracy of the foil gages.
Ship/Ice Interaction Pressures and Energies During Ship
Ramming
Authors: Kivisild H. R. , Blanchet D. , Revill C. R.
Published: November 2009

This paper shows that ice interaction forces and energies can be related to the characteristics of ice such as strength, stiffness and rheological properties on the one hand, and to the parameters of the impact such as impact velocity, confinement and size of the contact area on the other hand. Mohr-Coulomb relationships are used to evaluate quasi-static loads. Initiation of cracks in ice at the end of the elastic regime is part of this process. Once initiated, the cracks in the ice in their turn affect pressures at ultimate failure of ice. This process has been related to the size of the loaded area by using fracture mechanics. Dependence on strain rate has been applied. The direct effect of collision speed has received special treatment.
A Model Study of the Wave-Induced Motion of Small Icebergs and Bergy Bits
Authors: Lever J. H. , Reimer E. , Diemand D.
Published: November 2009

Wave tank studies were conducted to determine the kinematics of “small” ice masses in storm waves typical of the Grand Banks region (10–14-s periods, 12–15-m heights). The models tested spanned the range of full-scale masses from growlers and bergy bits (10–103 tonnes), to small icebergs (104–105 tonnes). In open water, models smaller than 1/13 wavelength behaved essentially as particles of fluid. The corresponding full-scale kinetic energies associated with such motions could exceed 107 J. Models approximately 1/2 wavelength in size could attain energies in the surge direction in excess of 109 J, largely through wave diffraction effects. Significant heave resonance motions were also seen. Tank studies additionally revealed that wave-driven ice-structure impacts of substantial energy could occur, although wave diffraction from the structure could also have a considerable influence on nearby ice motion. The conclusion is reached that wave-induced motion of small ice masses represents a significant environmental hazard to the operation of offshore structures in ice-infested waters.
Wave Elevation on Large Circular Cylinders Excited by Wind-Generated Random Waves
Authors: Rao P. S. V. , Raman H.
Published: November 2009

Wave elevation on large cylinders due to irregular waves have been calculated based on the McCamy and Fuchs linear diffraction theory and on the principle of superposition. Experiments have been conducted in the Hydraulic Engineering Laboratory, Indian Institute of Technology, Madras, to examine the wave elevation excited by wind-generated irregular waves on circular cylinders of large diameter. The wave elevation around the cylinders at representative locations were measured and compared with calculated wave elevations. The spectral density functions computed from wave elevation time series measured in the laboratory were compared with calculated time elevation spectral densities on the cylinder.
Impact/Indentation Strength of Iceberg and Artificial Snow Ice
Authors: El-Tahan H. , Swamidas A. S. J. , Arockiasamy M.
Published: November 2009

The paper presents an experimental study on the indentation and the impact strengths of iceberg and artificial snow ice. Indentation and uniaxial tests were carried out under various strain rates and confining conditions. Uniaxial compression tests were carried out on cylindrical specimens. Indentation tests were carried out on confined/unconfined rectangular ice blocks through cylindrical/flat-circular indenters. For iceberg ice, the average uniaxial strength varied between 6.6 to 7.5 MPa and the indentation strength between 17.0 to 34.0 MPa, under various strain rates. Impact was achieved by dropping a steel cylindrical indenter, weighing 60.0 kg, onto the level surface of confined/unconfined ice blocks; the velocity of impact was 2.0 m/s. The maximum (average of seven values) impact strength of iceberg ice obtained was 17.35 MPa, while that of artificial snow ice was 20.54 MPa.
Structural Responses and Design Waves of Semisubmersibles
Authors: Suhara T. , Yoshida K. , Yoneya T.
Published: November 2009

This paper presents the results of comparative calculations on structural responses of a typical semisubmersible and the discussion on design waves for brace stresses. A typical semisubmersible of two-lowerhull type is adopted as a full-scale model for the comparative calculations on three-dimensional motion and structural responses. Based on the comparative calculations by eight different computer programs, standard response functions are proposed as to axial and bending stresses of major braces. Characteristic wave loading patterns, which correspond to design waves, are proposed based on the standard stress response functions. Also simplified equations of wave forces on semisubmersibles, which are useful to consider design waves, are derived based on the assumptions of taking account of only hydrodynamic inertial forces. Based on these results, maximum brace stresses during a 100-yr return period are estimated using design wave method, and are compared with statistically estimated values by short-term and long-term predictions. As a result, it is found that design wave method has a tentative ground for practical design of semisubmersibles.
Performance of a Closed-Tube Thermosyphon With Large Length-Diameter Ratios
Authors: Lock G. S. H. , Simpson G. A.
Published: November 2009

The experimental work reported here is concerned with the single-phase closed thermosyphon under conditions which are appropriate to a northern application: large length-diameter ratios and heated lengths much greater than cooled lengths. The purpose is twofold: to generate empirical heat transfer data which represent the conservative lower limit of performance (in the absence of boiling or bubbling); and to reveal the thermal and momentum exchange mechanisms which operate at the junction of the heated and cooled sections. The apparatus consisted of a 102-mm-dia, vertical steel pipe of overall length varying from 2 m to 6 m. The lower section of the pipe was heated by means of electric-resistive tape, and the upper section cooled by means of a water jacket. Heat transfer data, plotted in the usual form of Nusselt number versus the quotient of the Rayleigh number and the length-diameter ratio, show the effect of geometry. This data was obtained for 10 ≤ LH/d ≤ 50, and 1 ≤ LH/Lc ≤ 20. An empirical correlation is developed.
A Theoretical Study on the Second-Order Wave Forces for Two-Dimensional Bodies
Authors: Miao G. P. , Liu Y. Z.
Published: November 2009

Nonlinear wave forces on fixed or floating offshore structures have attracted much attention recently. This paper deals with the nonlinear effects of regular waves on fixed two-dimensional bodies up to second-order terms. The second-order diffraction potential is solved consistently and the second-order steady wave forces and the biharmonic wave forces with frequency corresponding to the double of the incident wave frequency are obtained.
Fatigue Crack Growth Analyses of Offshore Structural Tubular Joint
Authors: Rhee H. C.
Published: November 2009

Fracture mechanics fatigue life estimation procedures have been developed for offshore structural tubular joints through analyzing a K-joint under the North Sea environment. The objective of this study was to establish reliable procedures for estimating the remaining fatigue life of a tubular joint with cracklike defects. The analysis approach was the utilization of fracture mechanics methods for fatigue crack growth and failure analyses. In this study, the fully mixed mode stress intensity factors of weld toe surface flaws of the K-joint, which were calculated through detailed three-dimensional finite element analyses, were used for fatigue crack growth simulation. For the failure analyses, the failure assessment diagram method was used to predict the conditions for brittle fracture during fatigue crack propagation. The loading conditions considered in the analyses are the brace axial force, in and out-of-plane bending, and torsion.
The Characteristic Grain Size and the Compressive Strength of Ice Containing a Bimodal Distribution of Grain Sizes
Authors: Schulson E. M. , Laughlin J. L.
Published: November 2009

The purpose of this communication is to show through experiment that the compressive strength of polycrystalline ice, which contains a bimodal distribution of grain sizes, can be expressed in terms of a characteristic grain size. The work was performed in response to an awareness that grain refinement strengthens both columnar [1] and granular [2] freshwater ice deformed under compression, and that ice formed naturally often contains grains of more than one size. A detailed discussion is given elsewhere [3].
Effect of Interface Conditions on Dynamic Ice-Structure Interaction
Authors: Vipulanandan C. , Williams A. N.
Published: November 2009

Elastic wave theory is utilized to investigate the influence of interface boundary conditions on the dynamic characteristics of a circular cylindrical structure subjected to steady-state and impulsive horizontal excitation while surrounded by an elastic ice medium of infinite horizontal extent. The influence of modified interface boundary conditions relating the shear stresses to the relative displacement (slip) or relative velocity (rate of slip) on the stiffness and damping parameters are studied and the results are compared to the usual fixed and free boundary conditions on the cylinder surface.
Stiffness Study of a Parallel Link Robot Crane for Shipbuilding Applications
Authors: Dagalakis N. G. , Albus J. S. , Wang B.-L. , Unger J. , Lee J. D.
Published: November 2009

This describes the first phase of an effort to develop a robot crane for shipbuilding applications. The focus of this phase is on the study of the stiffness characteristics of this robot as a function of its geometry payload and height. A brief description of the design of the main part of the robot crane consisting of a six-wire parallel link manipulator is given. The stiffness of the manipulator to side loads and moments was studied. The nonlinear and linearized mathematical model of the manipulator stiffness matrix is derived. Stiffness measurement tests were conducted using a small size laboratory model. The results of these tests for various external loads, heights, and payloads are given. Computer simulation and theoretical results are also discussed.
Asymptotic Solutions and Radiation Conditions for Second-Order Diffracted Waves
Authors: Huang H. , Li J. , Wang X.
Published: November 2009

The far-field asymptotic solutions for the second-order diffracted waves have been developed, both in three and two-dimensional problems. The radiation conditions for the second-order diffracted waves are derived by using the asymptotic solutions. The nonlinear wave forces on a half-circular cylinder on seabed are presented by using finite element methods with the radiation conditions imposed on the artificial boundaries.
Computation of Slowly Varying Second-Order Hydrodynamic Forces on Floating Structures in Irregular Waves
Authors: Matsui T.
Published: November 2009

An exact second-order formulation is presented for computing the slowly varying second-order hydrodynamic forces on floating structures in irregular waves. The near-field approach based on direct integration of the fluid pressure on the submerged body surface is employed in conjunction with numerical first-order solutions by means of the hybrid finite element technique. Green’s second identity is exploited to evaluate the second-order forces due to the second-order velocity potential. Numerical results are presented for the slow drift excitation forces on an articulated column and a semi-submersible platform. It is shown that the contribution from the second-order velocity potential is more significant to the roll moment than to the sway and heave forces on the semi-submersible.
Motions of Articulated Towers and Moored Floating Structures
Authors: Chakrabarti S. K. , Cotter D. C.
Published: November 2009

A versatile and efficient method of analysis has been developed to analyze a mooring system composed of a floating structure, e.g., a ship, mooring lines, fenders, and an articulated tower. The floating structure is assumed to be large, but may have an arbitrary shape, and the tower is assumed to be axisymmetrical. Although the program treats the floating structure and tower as a system, each body may be examined alone in the absence of the other. The analysis is carried out in the time domain assuming rigid body motion, and the solution is generated by a forward integration scheme. This approach permits nonlinear line and fender forces to be incorporated readily into the analysis. The exciting forces in the analysis are wind, current, and waves, which are not necessarily collinear. The waves can be single frequency or composed of multiple frequency components. The vessel is free to respond to the exciting forces in six degrees of freedom—surge, heave, sway, roll, pitch, and yaw. The tower is free to respond in two degrees of freedom—oscillation and precession. The analysis has been extensively verified with several different model tests for different structure configurations in regular and random seas. These include an articulated tower, a single-point mooring tanker system, a floating caisson and an inclined mooring tower.
Random Short-Crested Wave Forces on a Pile
Authors: Isaacson M. , Nwogu O.
Published: November 2009

Numerical simulations and laboratory tests have been carried out to investigate the effect of wave short-crestedness on the random forces on a vertical pile. Linearized expressions based on the Morison equation are derived for the spectra of the in-line and transverse forces in short-crested seas. Expressions are also derived for the probability distribution of the peak resultant force for narrow-banded short-crested seas. The experiments were conducted in the offshore wave basin of the Hydraulics Laboratory, National Research Council of Canada. The pile was segmented in order to provide data on the vertical distribution of forces. The pile was subjected to long and short-crested random waves. Comparisons are presented between experimental and numerically simulated data.
Stress Intensity Factor for Corner Cracks of Pressurized Tees
Authors: Mohamed M. A. , Schroeder J.
Published: November 2009

A method based on local stress concentration is employed to estimate stress intensity factors for corner cracks at the crotch corner of pressurized tees. The method yields results which are in good agreement with data obtained using other advanced numerical techniques.
Global Bending Response Analysis of Elastic and Viscoplastic Nuclear Shipping Cask Structures Subjected to Impact Loading
Authors: Shieh R. C.
Published: November 2009

Within the framework of lumped mass upgraded beam theory in which rotatory and elastic shear deformation effects are considered, the title analysis is made for the case of large realistic lead-shielded, cylindrical stainless steel shipping casks equipped with end impact limiters. A computerized study developed elsewhere for the dynamic response analysis of elastic and elastic/viscoplastic beams and frames is first extended to include shear deformation and rotatory inertia effects and subsequently used in the cask impact response analysis study. Three types of impact limiter reaction force pulses are considered and three simplified analysis techniques (i.e., quasi-static, dynamic amplification factor and elementary beam analysis techniques) used in shipping cask design are evaluated. In particular, effects of shear deformation and rotatory inertia on impact responses and strain rate sensitivity effects on inelastic dynamic cask response behavior are studied. Appropriate guidelines are formulated for: 1) general use of these techniques in impact design analysis, and 2) treating strain rate sensitivity effects on material strength properties in conjunction with use of elastic, limit and elastic-plastic design analysis methods.
Quasi-Eulerian Finite Element Formulation for Fluid-Structure Interaction
Authors: Belytschko T. , Kennedy J. M. , Schoeberle D. F.
Published: November 2009

A quasi-Eulerian formulation is developed for fluid-structure interaction analysis in which the fluid nodes are allowed to move independent of the material thus facilitating the treatment of problems with large structural motions. The governing equations are presented in general form and then specialized to two-dimensional plane and axisymmetric geometries. These elements have been incorporated in a general purpose transient finite element program and results are presented for two problems and compared to experimental results.
Morrison and Parry Seals for Water Pressures up to 345 MPa
Authors: Pick R. J. , Harris H. D.
Published: November 2009

The use of water in high-pressure jet cutting and machining requires seals capable of sealing reciprocating and rotating shafts with minimal leakage. Both Morrison and Parry seals are studied analytically to determine the geometric parameters influencing their behavior in water. Limited experimental evidence supports the findings. In particular, the Morrison seal is most appropriate for use with oil, while the Parry seal shows greater potential for sealing water.
Closed-End Cylindrical Shell Under Line Load Along a Generator
Authors: Chawla U. S.
Published: November 2009

This paper presents a numerical technique for elastic analysis of a thin circular cylindrical shell with end plates under uniform line load along a generator. This technique is based upon the discrete element method. An accurate set of the governing differential equations due to Vlasov is used. The derivatives with respect to the circumferential coordinate are replaced by finite difference relationships. The end plate is analyzed as a free body under unit concentrated edge loads and the resulting coefficients are used to satisfy continuity conditions at the shell-plate junction. A computer program to implement this technique is developed and results are compared with those published in the literature. A number of new results are presented.
On Wake-Induced Flutter of a Circular Conductor in the Wake of Another
Authors: Tsui Y. T. , Tsui C. C.
Published: November 2009

This paper, which is an extension of [1], treats two-dimensional aeroelastic stability of two coupled conductors. It is found that the wake-induced flutter is symmetric with respect to the horizontal axis of the wake for all cases provided that the sign of the static coupling coefficient, ε = kxy/kxx, is changed. It appears that the spacer coupling ratio, K/kxx = Ω/ωx, is the most important factor in determining stability. For practical purposes, the system is almost always stable for K/kxx = Ω/ωx = 0.8, because the frequency ratio, κ = ωy/ωx, deviates less than ten percent from unity for a typical transmission line. On the other hand, within our range of interest, damping has little or no effect on the stability of coupled conductors. When the windward conductor is fixed, i.e., K = 0, then damping does influence the stability of the leeward conductor.
Prevention and Cure of Flow-Induced Vibration Problems in Tubular Heat Exchangers
Authors: Eisinger F. L.
Published: November 2009

Various methods for predicting and solving tube and acoustic vibration problems in heat exchangers in cross flow are presented: the use of stability diagrams comprising in-service experience of heat exchangers, for a general multispan tube model; a method of selecting efficient baffle configurations for prevention of acoustic vibration, a new method of fin barriers, an alternative to conventional baffling; a new method of enhancing the vibration resistance of a tube bank based on the use of a helical spacer; these methods, singly or in combination, can be used to design against flow-induced vibration.
Vortex-Excited Cross-Flow Vibrations of a Single Cylindrical Tube
Authors: Griffin O. M.
Published: November 2009

The cross-flow vibrations of a single tube are considered in this paper, for incident flows of air and water. Recent experimental measurements of the resonant response of and fluid dynamic forces on circular cylinders as a result of vortex shedding at subcritical Reynolds numbers are presented, and different approaches to measuring and characterizing the fluid forces are compared. Based upon these experiments, a mathematical model with which to describe the flow-induced excitation and reaction (damping) forces on a vibrating tube has been developed and is presented here. These results are applicable in general not only to the resonant, vortex-excited vibrations of flexibly mounted rigid tubes, but also to a flexible tube in air, water and other similar fluids.
Small-Scale Yielding at the Tip of a Through-Crack in a Shell
Authors: Achenbach J. D. , Bubenik T.
Published: November 2009

Deformation theory is used to model plastic deformation at the tip of a through-crack in a thin shell. In the vicinity of the crack the shell is subjected to both stretching and bending, but stretching is assumed to dominate. Thus the stresses are tensile, but with a nonuniform distribution through the thickness, which depends on the material properties as well as on the geometry. The nonlinear near-tip fields (which are singular) have been analyzed asymptotically. Cracks in shallow shells and spherical shells have been investigated in some detail. It is shown that the angular variations are the same as for generalized plane-stress plate problems. Assuming small-scale yielding a path-independent integral, which is valid in a region close to the crack edge, is used to connect the nonlinear near-tip fields with the corresponding singular parts of the linear fields. It is shown that the nonlinear behavior significantly affects the through-the-thickness variations of the near-tip fields. The singular parts of the membrane stresses tend to become more uniform through the thickness of the shell with a flatter strain-hardening curve.
Estimation of Stress Intensity Factors for Embedded Irregular Cracks Subjected to Arbitrary Normal Stress Fields
Authors: Oore M. , Burns D. J.
Published: November 2009

An integral is developed for calculating opening mode stress intensity factor at any point on the front of an irregular planar crack embedded in an infinite solid and subjected to an arbitrary normal stress field. No other solutions are available for irregular cracks, therefore the integral is first used to analyze three-dimensional regular cracks for which there are solutions. An embedded square crack is used to illustrate the integral procedure for an irregular shape. The integral is also used to explain qualitatively how irregular fatigue cracks will grow.
Time History Input Development for the Seismic Analysis of Piping Systems
Authors: Lin C.-W.
Published: November 2009

In a nonlinear time history analysis of piping systems, the system response is generally highly coupled for all dynamic degrees-of-freedom. Therefore, the seismic time history input components, which are usually synthesized from the Regulatory Guide 1.60 spectra, play an important role in the piping seismic analysis. The design ground response spectra recommended in Regulatory Guide 1.60 are identical for both horizontal directions. No specific requirements are given to define their statistical relationships. As a result, the two horizontal components could either be identical or with erroneous relationships which could adversely affect the analysis. In this paper, the results of a study conducted to establish statistical relationships on 22 earthquakes are reported. These earthquakes are those used in establishing the design ground response spectra specified in Regulatory Guide 1.60. The statistical properties studied include the autocorrelation functions, crosscorrelation functions, coherence functions, and acceleration motion distribution. A set of criteria is recommended for the generation of the synthesized time histories so that analysis of the piping systems can be realistically and correctly conducted.
Influence of Flaw Shapes on Stress Intensity Factors for Pressure Vessel Surface Flaws and Nozzle Corner Cracks
Authors: Atluri S. N. , Kathiresan K.
Published: November 2009

The influence of the flaw shape on the variation of stress-intensity factors along the crack front is examined for longitudinal inner surface flaws in pressure vessels, and for corner cracks present at the intersection of a pressure vessel and a nozzle. For the inner surface flaw problem, the geometry of the pressure vessel considered is that of a commercial pressure vessel. The analyzed flaw shapes are those recommended by the ASME Boiler and Pressure Vessel Code (Section III, App. G, 1977). In the case of corner cracks at nozzle-pressure vessel junctions, natural flaw shapes obtained through experiments are considered. A fully three-dimensional linear elastic hybrid displacement finite element procedure was used to analyze these problems of practical interest in pressure vessel analysis and design. The obtained solutions are compared with those in the literature using other numerical and/or experimental procedures, and a discussion of noted discrepancies is presented.
A Simplified Approach to Creep Buckling of Structures Under Varying Loads
Authors: Chern J. M.
Published: November 2009

A critical strain approach to the prediction of creep buckling time in structures under varying loads is investigated and its relationship with the conventional linear cumulative damage (life-fraction) approach is established under condition of constant temperature. The latter approach is shown to be inconsistent in some special cases and may result in overprediction or underprediction of creep buckling time depending on whether the loads are monotonically increasing or decreasing. Numerical results obtained with the present approach are compared with incremental solutions for columns, and with recently available theoretical and experimental results of cylindrical shells under axial compression. These comparisons indicate that the critical strain approach is suitable for use in design analysis. Further investigations are needed to assess the effect of varying temperature, which is excluded in the numerical examples because no test results are available for comparison.
Simulation of Partial Autofrettage by Thermal Loads
Authors: Hussain M. A. , Pu S. L. , Vasilakis J. D. , O’Hara P.
Published: November 2009

The effect of favorable residual stresses of an autofrettaged tube is well known [1]. In many instances there is redistribution of these stresses due to changes of geometrical configurations such as the presence of keyways, riflings, cracks, etc. The problem, in general, can be studied by discretization carrried out either by finite elements or by finite differences; however, it is usually not possible to incorporate the redistributed residual stress patterns due to the presence of such geometrical changes. This difficulty is overcome by simulation of residual stresses by certain active loadings. The simulation by dislocation and equivalent thermal loading for a fully autofrettaged tube is well known. In this paper we extend the thermal loading to simulate a partially autofrettaged case. Thermal stresses due to the simulated thermal loading computed from finite elements (NASTRAN) and finite differences are in excellent agreement with residual stresses for various degrees of overstrain. The simplicity of the method to incorporate the redistribution of residual stress due to the presence of geometrical discontinuities is illustrated by a finite element (APES) computation of stress intensity factors at an OD crack tip in a partially autofrettaged, thick-walled cylinder.
An LEFM Analysis for the Effects of Weld-Repair-Induced Residual Stresses on the Fracture of the HSST ITV-8 Vessel
Authors: Rybicki E. F. , Stonesifer R. B.
Published: November 2009

A fracture mechanics analysis for an intermediate size pressure vessel is described. The vessel was tested as part of the Heavy Section Steel Technology program at Oak Ridge National Laboratory. The purpose of the test was to evaluate the effects of residual stresses on the fracture of the vessel. Residual stresses were due to a half-bead weld repair located near the fabrication seam weld of the vessel. An external part-through flaw was placed in the seam weld near the weld repair. The test was conducted at −23.3°C to cause nonductile fracture behavior and thus accent the effects of residual stresses. The vessel was loaded with internal pressure. Test results showed that crack growth initiated at a significantly lower internal pressure than would be expected if there were no residual stresses. The crack arrested before growing through the thickness of the vessel. The pressure was increased until crack growth was reinitiated. The crack arrested after causing the vessel to leak but not break. The fracture analysis of the test presented here is based on static linear elastic fracture mechanics. Stress intensity factors were evaluated for a range of crack depths using a finite element representation and an energy release rate computation. The effects of residual stresses due to the weld repair were included in the fracture analysis based on residual stress data. There are two important findings of this study. First, good agreement was obtained between the results of the computational fracture analysis and the test data for three characteristics of the test; the pressure at which crack growth initiated, the amount of crack growth at crack arrest and the increase in pressure required to reinitiate crack growth. Thus the observed effects of residual stresses are predictable. The second finding is that the combination of laboratory data and computational results indicate a significant effect of residual stresses on both the crack growth initiation pressure and the crack arrest behavior for these particular test conditions. Estimates are that residual stresses reduced the critical pressure for flaw initiation to 25 percent of the value for the case with no residual stresses. These results are discussed in terms of available data and the computational model.
Stress-Intensity Factors for Internal Surface Cracks in Cylindrical Pressure Vessels
Authors: Newman J. C. , Raju I. S.
Published: November 2009

The purpose of this paper is to present stress-intensity factors for a wide range of semi-elliptical surface cracks on the inside of pressurized cylinders. The ratio of crack depth to crack length ranged from 0.2 to 1; the ratio of crack depth to wall thickness ranged from 0.2 to 0.8; and the ratio of wall thickness to vessel radius was 0.1 to 0.25. The stress-intensity factors were calculated by a three-dimensional finite-element method. The finite-element models employ singularity elements along the crack front and linear-strain elements elsewhere. The models had about 6500 degrees of freedom. The stress-intensity factors were evaluated from a nodal-force method. An equation for the stress-intensity factors was obtained from the results of the present analysis. The equation applies over a wide range of configuration parameters and was within about 5 percent of the present results. A comparison was also made between the present results and other analyses of internal surface cracks in cylinders. The results from a boundary-integral equation method were in good agreement (± 2 percent) and those from another finite-element method were in fair agreement (± 8 percent) with the present results.
Fluid Mass Matrices for Thin Shell-of-Revolution Tanks
Authors: Ball R. E. , Citerley R. L.
Published: November 2009

This paper presents the equations for thin shell-of-revolution tanks containing an arbitrary level of fluid. The mass matrix can be used with any finite element or finite difference digital computer program that computes either the dynamic response or the natural frequencies and modes of a thin shell of revolution and that has provision for a nondiagonal mass matrix. The method does not require a numerical finite difference or finite element discretization of the fluid, but instead provides, in series form, a mass matrix that exactly satisfies the governing field equations for the fluid and satisfies the fluid-shell interface condition with a least-squares fit.
Simplified Inelastic Analysis Methods for Bounding Fatigue and Creep Rupture Damage
Authors: O’Donnell W. J. , Porowski J. S. , Badlani M.
Published: November 2009

Bounds on inelastic strain ranges and maximum residual stresses introduced by transient operating conditions are obtained. These strain ranges and maximum residual stresses can be used to determine fatigue damage and creep rupture damage. Methods for integrating creep rupture damage during relaxation of surface stresses are also included. The solutions are based on uniaxial models.
Comparison of Experimental and Simplified Analytical Results for the In-Plane Plastic Bending and Buckling of an Elbow
Authors: Sobel L. H. , Newman S. Z.
Published: November 2009

Predictions obtained from a simplified finite element analysis are compared with experimental results on the plastic in-plane bending and buckling of a 16-in-dia Type 304 stainless steel piping structure which consists of a 90-deg elbow and two straight tangent pipes. The large displacement analysis is based on the widely used MARC pipe-bend element 17, and on a stress-strain curve obtained from coupon specimens taken from the tested elbow. The simplified analysis predictions are found to be in reasonably good agreement with the experimental results. The analysis underestimates the experimental buckling load by 10 percent and overestimates the deformation at a given load, particularly at the higher load levels.
Approximate Elastic Stresses in Pipe Junctions with Chamfer Corners
Authors: Updike D. P.
Published: November 2009

Elastic stress analysis of a right angle tee branch pipe connection of two pipes of identical diameter and thickness connected through 45-deg chamfer corner sections is developed for internal pressure loading. Stresses in the crotch portion of the vessel are determined. These results are presented in the form of a table of factors useful for rapid calculation of approximate values of the peak stresses. The existence of a structurally optimum size of chamfer is demonstrated.
Three-Directional Fluid Pool Seismic Sloshing Analysis
Authors: Li T. F. , Lin C. C. , Luk C. H.
Published: November 2009

Liquid sloshing in pool due to three-directional earthquake ground motion is analyzed. The liquid pool is represented by a rigid annular circular cylindrical tank. Analytical and numerical solutions are presented and their limitations are discussed. For a given seismic ground excitation time-history, the free surface and the pressure and velocity fields in the pool are calculated by superposition of modal responses. The results show that container vertical acceleration is of secondary importance in determining the free surface displacement, but has a major effect on the pressure load on the container boundary.
Approximate Elastic-Plastic Analysis of Intersecting Equal Diameter Cylindrical Shells
Authors: Updike D. P.
Published: November 2009

Design of connections of pipes and pressure vessels on the basis of a calculated maximum elastic stress often proves to be too conservative in the case of ductile materials. Elastic-plastic analysis by the finite element method proves to be too costly. This paper presents an alternative method which reduces the calculations to those of a rotationally symmetric shell subjected to axisymmetric loading. Using this approach approximate elastic-plastic deformations on the meridian passing through the crotch of a tee branch connection of cylindrical shells of equal diameter and thickness are determined. The method is limited to cases of the normal intersection of very thin shells of identical diameter, thickness, and material and to internal pressure loading. Numerical results for the intersection of two shells of R/t equal to 100 are given for an elastic-perfectly plastic material satisfying the von Mises yield condition.
Nonlinear Dynamic Analysis of a Structure Subjected to Multiple Support Motions
Authors: Shah V. N. , Hartmann A. J.
Published: November 2009

A modal superposition method for the nonlinear dynamic analysis of a structure subjected to multiple support motions is presented. The nonlinearities are due to clearances between the components and their supports. The finite element method is used to derive the equations of motion with the nonlinearities represented by a pseudo force vector. The displacement response may be divided into two parts: elastic deformation and rigid body motion. The presence of rigid body motion necessitates the inclusion of the higher modes in the transient analysis. The modal superposition method is used to analyze the dynamic response of one loop of the nuclear steam supply system. This loop has nonlinear supports and is subjected to nonuniform seismic excitations at the supports. It is shown that the computational cost of the modal superposition method is lower than that of the direct integration.