bluuebunny/crossref_metadata_2025 huggingface dataset:
A Numerical Study on Enhancement of Heat Exchanger Performance by Inserting Static Mixer Elements
Authors: Rahmani Ramin K. , Ayasoufi Anahita , Keith Theo G.
Published: July 2008

In chemical processing industries, heating, cooling and other thermal processing of viscous fluids are an integral part of the unit operations. Static mixers are often used in continuous mixing, heat transfer, and chemical reactions applications. Generally, a static mixer consists of a number of equal stationary units, placed on the inside of a pipe or channel in order to promote mixing of flowing fluid streams. These mixers have low maintenance and operating costs, low space requirements, and no moving parts. A range of designs exists for a wide range of specific applications. The shape of the elements determines the character of the fluid motion and thus determines the effectiveness of the mixer. There are several key parameters in the design procedure of a static mixer. An ideal static mixer for heat transfer applications provides a higher rate of heat transfer and thermally homogenous fluid with low pressure drop and similar traveling history for all fluid elements. To choose a static mixer for a given application or in order to design a new static mixer, besides experimentation, it is possible to use powerful computational fluid dynamics (CFD) tools to study the performance of static mixers. This paper illustrates how static mixer can improve the performance of heat exchangers. Using different measuring tools, the global performance and costs of two popular commercial static mixers are studied in order to choose the most effective design for thermal applications.
The Robustness of a Simple Expression for Quantifying Fracture Initiation at a Blunt Flaw
Authors: Smith E.
Published: July 2008

Linear elastic fracture mechanics of cracks is well established, and is based on the stress field near a crack tip being described by the stress intensity factor, with crack extension occurring when the stress intensity factor is equal to a critical value, which is referred to as the fracture toughness of the material. This methodology has been applied to a wide range of materials and structures, with the fracture toughness being related to the micro-mechanistic fracture processes, often via the cohesive-process zone representation of these fracture processes. The author is involved in a wide-ranging research programme whose objective is to extend the fracture mechanics methodology to blunt flaws, so as to take credit for the blunt flaw geometry, the strategy being to parallel, as far as possible, the methods that have been developed for cracks. Earlier work has shown that an appropriate characterizing parameter, analogous to the stress intensity factor for a crack, is the elastic peak flaw tip stress, with fracture initiating when the peak stress attains a critical value, which is related to the flaw geometry, in particular the flaw root radius, and material parameters. A simple expression has been derived for the critical peak stress and, in this paper, we provide support for its robustness.
The Size of a Uniform Stress Process Zone at Fracture Initiation
Authors: Smith E.
Published: July 2008

The process zone description is often used to represent the micro-mechanistic processes that are operative in the immediate vicinity of a crack tip. The process zone is an infinitesimally thin strip, and the theoretical analysis is considerably simplified if the stress within the process zone is assumed to be uniform. The paper derives an expression for the size of a uniform stress process zone when fracture initiates at the tip of a sharp crack. The expression relates this size to the size appropriate to the case of a semi-infinite crack in an infinite solid, and is a two term expression in terms of the ratio of this size to a characteristic structural dimension. The expression is validated against known results for specific geometrical configurations.
High-Pressure Storage Vessels Used in Hydrogen Refueling Station
Authors: Zheng Jinyang , Li Lei , Chen Rui , Xu Ping , Kai Fangming
Published: July 2008

The storage of hydrogen in a compressed gaseous form offers the simplest solution in terms of infrastructure requirements and has become the most popular and most highly developed method. Hydrogen storage vessels are the key equipment of hydrogen refueling station. Seamless pressure vessels made from high strength steel, which are now used in hydrogen refueling stations, are more susceptible to hydrogen embrittlement, difficult in on-line safety monitoring and limited in volume. In order to solve the aforementioned problems, the authors have developed a multifunctional layered hydrogen storage vessel with volume 5m3 and design pressure 42MPa for the first demonstration hydrogen refueling station in the People’s Republic of China. This vessel is flexible in design, convenient in fabrication, safe in use, and easy in online safety monitoring. Its structure and functions are presented after giving a brief introduction of hydrogen refueling station, and analyzing risk of high-pressure hydrogen storage vessel.
Flange Assembly Bolt Load Selection Based on Leak Before Break Analysis
Authors: Brown Warren
Published: July 2008

The selection of an appropriate assembly bolt load has an upper bound limited by an actual, or perceived, maximum allowable bolt load for the joint. Often, this limit may be selected based on examination of stress levels in the flanges. Present guidelines for selection of the appropriate bolt assembly stress (ASME PCC-1, [1]) use higher bolt loads than the allowable stress levels specified in the design code (ASME VIII, Div. 1, [2]), without justification of why this is an acceptable practice. The basis is, appropriately, the lack of mechanical failure of flanges within industry when bolt loads of that magnitude are employed. Since the basis is industry practice, it is difficult for the end-user to know when it is possible to extend the limits. This is particularly important in cases of joints that are problematic to seal, which may require assembly bolt loads in excess of those found in ASME PCC-1. This paper develops a complete technical basis for why it is acceptable to load flanges beyond the limits of ASME PCC-1 without risk of mechanical failure of the joint. The limits of applicability of such a bolt load selection philosophy are also defined. The paper discusses the practical application of high bolt loads in achieving leak-free joint operation.
Evaluation of Dissimilar Socket Weld Connections
Authors: Basavaraju Chakrapani
Published: July 2008

In the power industry, stainless steel is widely utilized for instrumentation tubing, while the small bore branch piping up to the root valves is either of carbon steel (A106 Gr. B, A106 Gr. C) or low alloy steel (A335 Gr. P11, A335 Gr. P22), or intermediate alloy steel (A335 Gr. P91). Stainless steel is not widely used for small bore piping. Generally, socket weld connections are employed in small bore piping applications as well as for pipe to tube adapter locations in instrumentation for sampling and sensing line applications. In this paper, socket weld connections at pipe to tube adapter locations are evaluated to determine the acceptability for higher temperature service applications. Finite element analysis methodology, based on axi-symmetric finite element models, is utilized to obtain thermal discontinuity stresses at the dissimilar socket weld connection. Taking into account the stress and cyclic considerations, the dissimilar socket weld connection is evaluated. Limitations and guidelines are provided concerning the acceptability for higher temperature service.
SIE ASME-NH Program for the Structural Integrity Evaluations of a LMR Subjected to Elevated Temperature Operations
Authors: Koo Gyeong-Hoi , Lee Jae-Han
Published: July 2008

In this paper, SIE ASME-NH (Structural Integrity Evaluation by ASME-NH) program, which has a computerized implementation of the details for ASME Pressure Vessels and Piping Code Section III Subsection NH rules including the time-dependent primary stress limits, total accumulated creep ratcheting strain limits, and the creep-fatigue limits for the reactor structures subjected to elevated temperature operations, are described with their detailed application procedures. Using this code, the selected high temperature structures which are subjected to two cycle types are evaluated and the sensitivity studies for the effects of the time step size, primary load, numbers of a cycle, normal temperature on the creep damage evaluations and the effects of the load history on the creep ratcheting strain calculations are investigated. From the selected applications, it is verified that the developed SIE ASME-NH Program is an easy user interface program and it can be an effective tool for the high temperature structural integrity evaluations of LMR.
Prediction of Creep Crack Initiation Under Transient Stress Conditions
Authors: Davies Catrin M. , O’Dowd Noel P. , Nikbin Kamran M. , Webster George A.
Published: July 2008

A method to predict the time for creep crack initiation (CCI) from a stationary crack tip is presented. The method is relevant to situations where small scale yield or widespread plasticity conditions prevail on initial loading. Initiation is considered to occur at the attainment of a critical creep strain at a small distance from the crack tip. The model proposed here considers the integrated effects of creep strain accumulation as the stress distribution changes from that on initial loading (controlled by J) to the steady state creep stress distribution (controlled by C*). Material properties are chosen to represent Type 316H stainless steel at 550°C and plane strain conditions are considered. For the conditions examined, the CCI times predicted are significantly shorter times than those predicted using a steady state creep model.
Analysis of Creep and Stress Relaxation Data for Ultra-Supercritical Steam Turbine Materials
Authors: Ellis Fred V. , Maziasz Philip J. , Wright Ian G. , Shingledecker John P.
Published: July 2008

Development efforts are underway to qualify boiler and turbine materials for the ultra-supercritical (USC) steam conditions of 720/760°C and 31/35 MPa. An evaluation of the creep-rupture and stress relaxation data was performed for the critical turbine components of casing and bolting. The casing materials were Inconel 740, Udimet 500, and CCA617. Time-temperature parametric analysis of the rupture data was performed to determine the average rupture stress for a life of 100,000 hours at temperatures from 700 to 760°C. A multiple heat analysis was used for Inconel 740, and the average stress varied from 88 MPa to 109 MPa at 760°C. For Udimet 500, data for both cast and forged materials were used, and the average rupture stress was approximately the same, greater than 150 MPa at 760°C. The maximum useful temperature for CCA617 is about 730°C based on a 100 MPa/105 hours criterion. The bolting materials were Nimonic 105 and Udimet 500. For Nimonic 105, the initial strain was 0.15% and the calculated relaxed stress at 760°C was 32 MPa (using the Larson Miller parameter). For Udimet 500, the initial strains were 0.2% and 0.3%. The calculated time to a relaxed stress of 47 MPa depended on the time-temperature parameter used, and ranged from 50,000 to 100,000 hours at 760°C for an initial strain of 0.3%.
Engineering Analysis of the Warm Prestressing (WPS) Effect: Influence of Stress-Strain Curve, Specimen Size and WPS Level
Authors: Novak Jiri
Published: July 2008

Under WPS effect is understood ratio of stress intensity factor at fracture after WPS (Kfr) and the “usual” fracture toughness KIc. Theoretical models of WPS effects were derived for Small Scale Yielding (SSY) conditions. For comparison of experimental results with theory, classical Chell model was chosen: real Kfrexper is compared with predicted KfrChell. For characterization of pre-stress level in case of small specimens, it is convenient to use elastoplastic quantity KJWPS corrected to the equivalent KJWPS in SSY conditions; this quantity is denoted by symbol KJWPS(SSY). For material with certain stress-strain curve σ = f(ε), universal dependence of Kfrexper/KfrChell on KJWPS(SSY) was obtained, which describes behaviour of specimens of different sizes. If another stress-strain curve has the same shape (i.e. if σ = const.f(ε)), KIcfrexper/KfrChell lies (up to the accuracy of experiments) on the universal dependence curve Kfrexper/KfrChell vs. KJWPS(SSY)/σy, where KJWPS(SSY)/σy is a quantity proportional to the square root of the plastified zone size in SSY conditions. Different stress-strain curve shapes lead to smaller or greater Kfrexper/KfrChell. Stress-strain curves cannot be generally expressed by power law hardening, but the Curry-Smith model derived with the use of Ramberg-Osgood law qualitatively predicts the increase or decrease of Kfr in dependence on the strain hardening exponent.
Dynamic Analysis of Nuclear Steam Generator: Program Overview
Authors: Broc Daniel , Sigrist Jean-Franc¸ois
Published: July 2008

The present paper exposes the main directions of a R&D program that DCN and CEA are currently developing to study the dynamic response of the steam generator of a naval nuclear propulsion reactor submitted to a shock. The structure is composed of tube bundles, immersed in a two phase flow fluid (steam and water). The dynamic solicitation contains high accelerations and high frequencies. It is thus necessary to establish which kind of physical phenomena can take place, and which kind of numerical tool can be used to study the dynamic behavior of the system. If the acceleration and the frequencies are very high, it will be necessary to consider highly non linear physical phenomena, with large deformation within short time duration. If the acceleration and (or) the frequencies are lower, simpler methods can be considered, assuming a linear behavior for the structure. In the latter case, as the frequencies still remain higher than the seismic ones, it might be necessary to take into account different kind of eigenmodes, as those depending on the fluid compressibility. As the fluid is a two phase medium, the use of homogenized fluid model has to be investigated. Since the tube bundle is a periodic structure, a homogenization technique can be used. Basic principles of the method are recalled as well as potential developments of existing methods. Influence of dissipative effects has also to be evaluated. The paper exposes the various problems that have to be addressed in order to produce a physical model of the structure that takes into account the various fluid-structure interaction effects for the shock analysis of the steam generator.
Multi-Scale Simulation of Soft Material Flow
Authors: Bankhead Mark , Good Kevin , Owens Scott L. , Travis Karl P.
Published: July 2008

We describe a multi-scale modeling approach to model the rheology of soft matter, which can then be applied to simulate flow of viscous inorganic material in pipes and containers. Mesoscale methods, such as dissipative particle dynamics (DPD) are a key component of multi-scale modeling, as they bridge the gap between fundamental theory and continuum length scales. The paper describes a method for parameterizing DPD simulations for cements and inorganic sludges based on calculating a volume dependent cohesive energy interaction and compressive term from MD simulation with a generalized inorganic forcefield. By modifying the fluid properties through the interaction parameters one can simulate change of chemistry, such as pH or the introduction of chemicals to improve flow properties (super-plasticizers). Parameters obtained from mesoscale simulation can then be applied to simulate flow of soft matter inside pipes and containers using traditional CFD techniques. Two potential future applications in the nuclear industry are discussed in the areas of waste retrieval and encapsulation.
FEA of the Effects of Initial Tube-Tubesheet Clearance, Wall Reduction and Material Strain Hardening on Rolled Joint Strength
Authors: Al-Aboodi A. , Merah N. , Shuaib A. R. , Al-Nassar Y. , Al-Anizi S. S.
Published: July 2008

The tube-to-tubesheet joint strength is measured in terms of residual contact pressure between the tube’s outer surface and tubesheet hole surfaces. The joint integrity is affected by several design parameters, including the type of tube and-tubesheet materials, level of expansion and the initial radial clearance between the tube and tubesheet. In the present work, an axisymmetric finite element model based on the sleeve diameter and rigid roller concepts is developed. The model has been used to evaluate the combined effects of clearance, wall reduction level and the-strain hardening of tube and tubesheet materials on the interfacial pressure between tube and tubesheet. The FE results show that the initial clearance effect is dependent on the strain hardening capability of the tube material. For low strain hardening tube material the interfacial pressure remains almost constant well above the TEMA (Tubular Exchanger Manufacturing Association) maximum radial over tolerance of 0.0254 mm. These results are validated by the experimental data developed during the research program. As expected, a drastic reduction in joint strength is observed at high values of radial clearances. The cut-off clearance (clearance at which the interfacial pressure starts to drop) is found to vary linearly with the level tube material hardening level. The residual pressure is found to increase slightly for moderate strain hardening tube materials but shows lower cut-off clearances. Wall reductions ranging from 1% to 10% were utilized in calculating the contact pressure as a function of radial clearance. The results show that for low strain hardening materials the optimum value of residual contact stress is obtained for the industry recommended value of 5%. Finally, because of the absence plastic deformation in the ligament, the level of tubesheet material strain hardening does not have any noticeable effect to the joint strength.
Theoretical and Numerical Predictions of Burst Pressure of Pipelines
Authors: Zhu Xian-Kui , Leis Brian N.
Published: July 2008

It is known that the Tresca yield theory predicts a lower bound of burst pressure, whereas the von Mises yield theory provides an upper bound of burst pressure of pipelines. To accurately predict the burst pressure, the present authors [1] recently developed a new multiaxial yield theory for isotropic hardening materials, based on an average shear stress criterion (ASSC). Extensive classic experiments showed that the ASSC criterion can well correlate the stress-strain relations for both initial yield and subsequent yield states. Based on the ASSC yield theory, a new theoretical solution of the burst pressure of pipelines at plastic collapse is developed as a function of pipe geometry, material hardening exponent, and ultimate tensile strength. This solution is then validated by experimental data for various pipeline steels. The ASSC yield theory is further applied to accurately determine actual burst pressure using available finite element software like ABAQUS, which currently adopts the von Mises yield criterion and the associate flow rule for isotropic elastic-plastic analysis. Four burst failure criteria: the Mises equivalent stress criterion, the maximum principal stress criterion, the Mises equivalent strain criterion and the maximum tensile strain criterion are developed as functions of the ultimate tensile stress and the strain hardening exponent. Application demonstrates that the proposed failure criteria in conjunction with ABAQUS numerical analysis can accurately determine burst pressure of pipelines.
Coupling of Lattice Boltzmann and Finite Element Methods for Fluid-Structure Interaction Application
Authors: Kwon Y. W.
Published: July 2008

In order to analyze the Fluid-Structure Interaction (FSI) between a flow and a flexible structure, an algorithm was presented to couple the Lattice Boltzmann Method (LBM) and the Finite Element Method (FEM). The LBM was applied to the fluid dynamics while the FEM was applied to the structural dynamics. The two solution techniques were solved in a staggered manner, i.e. one solver after another. Continuity of the velocity and traction was applied at the interface boundaries between the fluid and structural domains. Furthermore, so as to make the fluid-structure interface boundary more flexible in terms of the computational modeling perspective, a technique was also developed for the LBM so that the interface boundary might not coincide with the fluid lattice mesh. Some example problems were presented to demonstrate the developed techniques.
Pipe Internal Pressure Calculation Methods for Pipe With Corrosion Flow, Pitt and Crack
Authors: Bereisˇa Mindaugas , Didzˇiokas Rimantas , Zˇiliukas Antanas , Leisˇis Vitalis
Published: July 2008

There are many methods and codes for pipe design and corrosion failure assessment. It is complicated to decide which of these method is the best. The main idea is to simulate the defect geometry as close as possible to real defect geometry and evaluate it by several methods. Based on pipe operation conditions in Lithuania and other countries the main causes of fracture were found. For the pressure pipes fracture assessment the most popular codes are: R-6, SINTAP, API-RP-579. Based on these methods some calculation results have been verified and assessed. As a result of these analyses recommendations have been made to assist in corrosion failure assessment. Special attention was paid to corrosion flows, pitting and stress corrosion cracking.
Creep Fatigue Behavior and Damage Assessment for Mod 9 Cr 1 Mo Steel
Authors: Cabrillat Marie-The´re`se , Allais Lucien , Mottot Michel , Riou Bernard , Escaravage Claude
Published: July 2008

Mod 9Cr-1Mo Steel (grade 91) is a material candidate for pressure vessels and some internal structures of Gas Cooled Reactors. Some of these structures will operate in the creep range and have to be designed relatively to creep-fatigue damage. In order to characterize the creep-fatigue behavior of this steel and to validate the creep fatigue design rules proposed in nuclear design codes (mainly RCC-MR and ASME), specific fatigue-relaxation (strain controlled during hold time) and creep-fatigue (stress controlled during hold time) tests have been carried out at CEA on this steel. All these tests are conducted at 550°C, but several loading conditions are considered and the influence of the position of hold time in the cycle (either in a tensile or a compressive state) is investigated. This paper presents the experimental program undertaken and describes the main results obtained. Then the creep-fatigue life evaluations are performed using creep-fatigue design rules and material data codified in RCC-MR and ASME and the predictions are compared to experimental results.
Static and Dynamic Burst Analysis of Cylindrical Shells
Authors: Xue Liping , Cheng Cunjiang , Widera G. E. O. , Sang Zhifu
Published: July 2008

The purpose of this paper is to determine whether the finite element method can be employed to accurately predict the burst pressure of a specific cylindrical shell subjected to internal pressure. Both static and dynamic analyses were carried out. The computer code ANSYS is employed to perform a static, nonlinear analysis (both geometry of deformation and material behavior) using three-dimensional 20 node structural solid elements. The “Newton-Raphson Method” (N-R method) and the “Arc-Length Method”, are both employed to solve the nonlinear equations. The finite element code LS-DYNA is used to generate a three-dimensional finite element model by use of eight-node brick elements for the dynamic analysis. Both explicit and implicit methods are used to simulate the dynamic response of cylinders. A comparison with various empirical equations shows that both static and dynamic finite element method simulations can be employed with sufficient accuracy to predict the burst pressure of a specific cylindrical shell.
Estimation of Fatigue Crack Propagation of Subsurface Cracks by “SCAN”
Authors: Nakanishi Shin , Iwamatsu Fuminori , Shiratori Masaki , Matsushita Hisao
Published: July 2008

The authors have proposed an influence function method to calculate stress intensity factor, K, of the surface cracks. This method makes the calculating task easier for arbitrarily distributed surface stresses. They have developed the database of influence coefficients, Kij, for various types of surface cracks through a series of finite element analyses.[1] They also have developed a software system “SCAN” (Surface Crack Analysis), from the database. The K values of surface cracks can be evaluated immediately, and further, fatigue crack propagation can be simulated easily with a personal computer. A fatigue crack often initiates from a defect located at the subsurface of a structural member. In this case, it is important to account for the fatigue life from the initiation of a subsurface crack to its propagation into a surface crack. However, since it is difficult to simulate this process precisely, the authors have proposed a simple model about the transition from a subsurface crack into a surface crack based upon ASME CODE SECTION XI [2] and WES 2805 STANDARD. [3] They have developed a SCAN system – Subsurface Crack Version-. They calculated the fatigue life for some models of subsurface cracks and compared the quantitative differences between two standards.
Numerical Investigation of Deformable Hydrofoils in Steady Flows
Authors: Ducoin Antoine , Deniset Franc¸ois , Damay Thomas , Astolfi Jacques-Andre´ , Laine Christian
Published: July 2008

The work is developed within the general frame of marine structure design. The study presents a numerical investigation of the hydro elastic behaviour of a deformable lifting body in a uniform steady flow. The fluid is considered as inviscid. The structure problem is solved by a finite element method and the flow problem is solved by a finite volume method using two commercial codes. Both problems are coupled through an iterative algorithm based on the exchange of boundary conditions at the flow-structure interface. The study is conducted on a cambered rectangular hydrofoil mounted in a hydrodynamic tunnel simulating the experiment that is currently performed in our laboratory. Results obtained from the fluid-structure computations including the deformation together with the hydrodynamic coefficients are presented. The influence of the fluid-structure coupling has been highlighted through comparisons with “non-coupled” simulations. Depending on the flow conditions, the twist of the hydrofoil together with the hydrodynamic loading are observed through the coupled simulation.
A Novel Approach to Evaluating Spiral-Wound Gaskets in Bolted Flange Joint Calculations
Authors: Seipp Trevor G. , Reichert Christopher , Schaeffer Mathew
Published: July 2008

In this paper, the authors introduce a compound gasket approach to performing calculations on bolted flange joints with spiral wound gaskets. The spiral windings and the solid-metal centering ring are treated independently. Using the calculation methodologies of ASME Section VIII, Division 1, Appendix 2 and EN-1591-1, the authors calculated the assembly bolt stress for multiple bolted flange joint sizes over a range of classes. The calculations assumed that the flange sealed on the solid-metal centering ring as well as on the spiral windings. This bolt stress required to achieve this seal was added to the bolt stress required to compress the spiral windings fully to the centering ring. The resulting total bolt stresses are similar to the practical bolt stresses recommended by ASME PCC-1. Thus, using this new approach to the spiral wound gasket provides a better understanding of bolt stresses required to achieve an adequate bolted flange joint.
Probabilistic Structural Mechanics Analysis of the Degraded Davis-Besse RPV Head
Authors: Williams Paul T. , Yin Shengjun (Sean) , Bass B. Richard
Published: July 2008

The Heavy-Section Steel Technology (HSST) Program at Oak Ridge National Laboratory (ORNL) performed a probabilistic structural mechanics (PSM) analysis of the damaged Davis Besse reactor pressure vessel head in support of the United States Nuclear Regulatory Commission’s ongoing forensic investigations. This paper presents a summary of the results of that PSM analysis, including a description of the Davis-Besse wastage-area damage model, the technical basis for the model, and the results of sensitivity studies based on a cladding capacity analysis (CCA) and an Accident Sequence Precursor (ASP) investigation of the wastage cavity. A companion paper describes the HSST experimental program carried out at ORNL in parallel with the PSM analysis.
A Study on the Hydrodynamic Load in a Water Pool When Discharged Air Forms a Bubble Cloud
Authors: Uchida Ken , Suzuki Seijiro
Published: July 2008

This paper presents a numerical and qualitative study on the expected hydrodynamic load-reducing effect of bubbly media near a volumetrically oscillating bubble. In this study, the bubble or bubble cloud is assumed to be spherically symmetric, and its motion is analyzed as a one-dimensional compressible two-phase flow in the radial direction in spherical coordinates. We adopted the CCUP (CIP-Combined Unified Procedure) method, which is a unified analysis method for both compressible and incompressible fluids proposed by Yabe et al. (1991) in order to treat interaction among gas, liquid, and two-phase media, and to avoid large numerical dissipation at density discontinuities. To verify the analysis program we developed, we analyzed free oscillations of a bubble with a unity void fraction and of a bubble cloud with an initial void fraction of 0.5, and found that the natural frequency from numerical results are well reproduced with an error of 0.9% for the bubble and 5% for the bubble cloud as compared to those obtained on a theoretical basis. Using this method, we analyzed the free oscillation of a bubble cloud in which a bubble with a unity void fraction is covered by a bubbly media layer with an initial void fraction of 0.5. Numerical results show that the amplitude of pressure oscillation inside the bubble is about halved, and that a higher mode of oscillation appears when a bubbly media layer covers the bubble. The measured results from a blowdown test we previously reported also shows a similar higher mode of oscillation. The amplitude of pressure oscillation in the water region was apparently reduced when a thick bubbly media layer covers the bubble. Thus, if the bubbly media is ejected from sparger holes prior to the ejection of a high-pressure bubble, the bubbly media might reduce the hydrodynamic load induced in a water pool made by volumetric oscillation of the bubble.
Image of Defects in Pipe by Guided Wave Technique
Authors: Wu Bin , Deng Fei , He Cunfu , Li Longtao
Published: July 2008

Based on a guided wave technique and a dispersive waveform prediction method, this paper presents a method which can be used to image defects in pipes. According to this method, a non-axis symmetrical end loading transducer can be used to excite an L (0, 2) mode and receive its echo at one end of the pipe. By rotating the said transducer with a specific space in the circumferential direction of said end and then operating the said transducer, twenty-four received signals can be obtained so as to image and locate those defects. Finally, we concluded that it is effective to image and recognize defects in two kinds of pipes including a one-holed pipe and a two-partially-circumferential-notched pipe using the presented method.
Creep Strength Assessment and Review of Allowable Tensile Stress of Creep Strength Enhanced Ferritic Steels in Japan
Authors: Kimura Kazuhiro
Published: July 2008

A committee at Japan Power Engineering and Inspection Corporation was organized to evaluate long-term creep strength and to review current allowable tensile stress of creep strength enhanced ferritic steels. In FY2005, allowable tensile stresses of KA-STPA29 type steels (ASME Gr.92), KA-STPA24J1 type steels (ASME Gr.23) and KA-SUS410J2TB steel regulated in METI (Ministry of Economy, Trade and Industry) Thermal Power Standard Code has been reviewed. Creep rupture data of those materials have been analyzed by means of region splitting method in a similar way to that applied for a previous review on a modified 9Cr-1Mo steel (ASME Gr.91) and KA-SUS410J3 type steels (ASME Gr.122). It has been concluded that the allowable tensile stresses in a creep regime of KA-STPA29 type steels and KA-SUS410J2TB steel should be revised to the lower values.
Micro Mechanical Model of Filament Wound Composite Pipe With Damage Analysis
Authors: Zhou Chuwei , Xia Zihui , Yong Qiaoling
Published: July 2008

Filament winding (FW) is one of the most common techniques for manufacturing composite pipes. The material properties and failure mechanism of composite pipes depend largely on winding pattern. In this study a micro mechanical approach for filament wound composites (FWCs) is pursued. A diamond-shaped repeated unit cell (RUC) is first constructed which characterizes the micro architecture of FWC pipe, such as winding angel, shift between successive circuits and the area of local undulation region. The micro mechanical model is embedded into commercial FEM code of ABAQUS as user-defined subroutine thus the link between the analyses in macro engineering structural scale and in micro material structural scale is established. By averaging micro stiffness constants over the cell macro ones needed for engineering structural analysis can be obtained. On the other hand, the macro structural analysis provides average stresses/strains of the cell locating at any concerned region of the macro structure for local stress and damage analysis. Effects of tow undulation caused by tow crossover on micro stresses are taken into accounted. The model is applied to glass/epoxy wound pipes with various winding angles and winding shifts. Mechanical properties are predicted and damage evolutions are simulated. The effects of delamination damage, usually introduced by lateral low velocity impact, on stiffness and ultimate strength of FWC pipe are also investigated.
DAMAGE-2005: A Post-Processor for High Cycle Fatigue Under Complex Thermomechanical Loading
Authors: Desmorat Rodrigue , Pauget Fre´de´ric , Sermage Jean-Philippe
Published: July 2008

On the idea that fatigue damage is localized at the microscopic scale, a scale smaller than the mesoscopic one of the Representative Volume Element (RVE), a three-dimensional two scale damage model has been proposed in the past decade at LMT-Cachan for High Cycle Fatigue applications. It consists in the micromechanics analysis of a weak micro-inclusion subjected to plasticity and damage embedded in an elastic meso-element (the RVE of continuum mechanics). The consideration of plasticity coupled with damage equations at microscale, altogether with Eshelby-Kro¨ner localization law, allows to compute the value of microscopic damage up to failure for any kind of loading, 1D or 3D, cyclic or random, isothermal or anisothermal, mechanical, thermal or thermomechanical. A robust numerical scheme makes the computations fast and the new programming of a graphical user interface gives a software simple to use with facilities for material parameters identification: DAMAGE-2005. Examples of thermal and thermomechanical fatigue as well as applications on E.D.F. FATHER and INTHERPOL structures subjected to complex thermo-mechanical fatigue are detailed.
Destruction of Concrete Block Using Underwater Shock Wave Generated by Electric Discharge
Authors: Otsuka Masahiko , Itoh Shigeru
Published: July 2008

In this study, the destruction of concrete block using underwater shock wave generated by electric discharge was studied. Initially, the shock wave generated by electric discharge was investigated by optical observation using a high-speed camera and pressure measurement. A comparison of the underwater shock wave generated from the electrode with and without connecting a metal wire was made. A metal wire was connected to an electrode and a high voltage impulsive current was passed through it to generate the underwater shock wave. A hole was made in the concrete block, filled with water and an electrode was inserted into the hole, which acts as a pressure vessel. The electric current was passed through this electrode to generate underwater shock wave for the destruction of concrete block.
Stress Intensity Factors for Defects in Two Common Weld Joints
Authors: Cheng Wing , Itoh Shigeru
Published: July 2008

Defects are commonly in weld joints depending on the process condition and workmanship of the welding process. Under good control environment, the amount and size of the defects can be very small and do not compromise the integrity of the weld joints. In other cases, the amount and size of the defects in the weld joints can be large and, therefore, can limit the integrity of the structure. Determination of critical flaw sizes of the welds requires accurate calculation of stress intensity factors of cracks of various lengths at different locations for their use in crack growth evaluation under cyclic loading. Two commonly used welded joints, namely butt and corner weld joints, were investigated. Three crack configurations for each of the two welded joints were considered. Finite element method was used in conjunction of the M-integral to obtain the stress intensity factors for various lengths of the cracks. Results were then used to perform the fitness-for-purpose assessment of these welds under spectral loading. Methodology and results of the stress intensity factor calculation for the above-mentioned cracks are covered in this paper.
A New Method of Explosive Welding Performed by Effective Application of Reflected Underwater Shock Wave
Authors: Shiramoto Kazumasa , Fujita Masahiro , Iyama Hirofumi , Ujimoto Yasuhiro , Itoh Shigeru
Published: July 2008

In this report, we propose a new explosive welding method, and the welding is performed at employing underwater shock pressure produced by the underwater explosion of an explosive placed at one side almost vertical to the specimen to be welded. In order to prevent the reduction of the shock pressure with the distance away from explosive, a steel reflector is placed over the area of the specimen. The effects of the reflector are investigated based on the experimental results and the process is numerically analyzed results.
Phased Array UT Application for Boiling Water Reactor In-Vessel Inspection
Authors: Yuguchi Yasuhiro , Hirasawa Taiji
Published: July 2008

This paper describes development and application of Phased Array Ultrasonic Testing (UT) and Remotely Operated Vehicles (ROV) for In-Vessel Internals Inspection. Stress Corrosion Crack (SCC) on reactor internals is one of the most important issues since 1990s, and demand to inspect the reactor internals is increasing. Instrument manufactures and inspection venders have developed and applied 1) Phased Array UT technologies and technique as one of our Non-Destructive Examination (NDE) technologies, 2) several kinds of ROVs and special tools for probe delivery and positioning. They are available and effective in In-Vessel Inspection (IVI) and maintenance, which shall be conducted in the narrow room under water. Furthermore, the UT technique for Alloy 182 weld that used to be difficult to detect and size flaws was developed and deployed in the BWR IVI. UT experiences in reactor vessels are increasing in recent years. An immersion technique by Phased Array UT is a key to perform the In-vessel UT on a complex geometric surface to be inspected, and to achieve very wide accessible range by ROVs or simple special tools efficiently. Advantages of the water immersion method and a ROV development result are shown in this paper. Particularly, TOSHIBA developed a flat type ROV for Shroud (Shroud ROV), which can be held against the surface of the shroud by thrusting propellers and scan mechanically through narrow gap within 2 inches {50mm}. The ROV’s positioning accuracy and applications for Shroud UT are shown. As the field experience, this introduces the UT results for CRD Stub tube Alloy 182 weld that is located on the vessel bottom head in Hamaoka UNIT 1 of Chubu Electric Power Company in Japan. An axial SCC flaw was detected by underwater visual testing, after the CRD stub tube leakage was detected. Then UT examination for the flaw was accomplished on the Alloy 182 weld in the vessel. We evaluated that the flaw penetrated into the weld metal of the CRD stub tube-pat weld and didn’t propagate into the low alloy of Reactor Pressure Vessel base metal. After UT sizing, the CRD stub tube was removed and replaced. The examination result was proven to have a good agreement with the actual crack depth. As a result, the efficiency of our Phased Array Technique was confirmed. As the other immersion method application, UT coverage example and accessible range for Shroud inspection are shown.
A Numerical Study of Particle Flow and Mixing on Conveying Equipment in Two and Three Dimensions by the Discrete Element Method (DEM)
Authors: Kruggel-Emden Harald , Simsek Erdem , Wirtz Siegmar , Scherer Viktor
Published: July 2008

Based on LEAT’s discrete element codes, granular flow and mixing on conveying equipment is studied in two and three dimensions. Discrete element simulations, which are briefly introduced, provide detailed information on particle positions and velocities over time. This information is used to derive quantities characterizing the dynamic process of mixing. The main focus of the study presented is the mixing process of inhomogeneous particle ensembles on different grate types. For this purpose the introduced mixing parameters are used to compare the mixing in a 3D situation with the corresponding 2D approximation on identical grates and to compare different grate designs in two dimensions.
Simulation of Axisymmetric Forming Processes, With Friction, Coupling Finite Elements and Boundary Elements
Authors: Bigot Dominique , Kebir Hocine , Roelandt Jean-Marc
Published: July 2008

Nowadays, the simulation of forming processes is rather well integrated in the industrial numerical codes. However, to take into account the possible modifications of the tool during cycle of working, we develop dedicated numerical software. This one more particularly will allow the identification of the fatigue criteria of the tool. With the view to conceiving the optimal shapes of tool allowing increasing their lifespan while ensuring a quality required of the part thus manufactured. This latter uses coupling with friction finite element method — for modelling the axi-symmetric part — and boundary element method — for modelling the tool. For the validation, we modeled forming process.
Capabilities of Ultrasonic Phased Arrays for Far-Side Examinations of Austenitic Stainless Steel Piping Welds
Authors: Anderson Michael T. , Cumblidge Stephen E. , Doctor Steven R.
Published: July 2008

A study was conducted to assess the ability of advanced ultrasonic techniques to detect and accurately determine the size of flaws from the far-side of wrought austenitic piping welds. Far-side inspections of nuclear system austenitic piping welds are currently performed on a “best effort” basis and do not conform to ASME Code Section XI Appendix VIII performance demonstration requirements for near side inspection. For this study, four circumferential welds in 610mm (24inch) diameter, 36mm (1.42inch) thick ASTM A-358, Grade 304 vintage austenitic stainless steel pipe were examined. The welds were fabricated with varied welding parameters; both horizontal and vertical pipe orientations were used, with air and water backing, to simulate field welding conditions. A series of saw cuts, electro-discharge machined (EDM) notches, and implanted fatigue cracks were placed into the heat affected zones of the welds. The saw cuts and notches ranged in depth from 7.5% to 28.4% through-wall. The implanted cracks ranged in depth from 5% through-wall to 64% through-wall. The welds were examined with phased array technology at 2.0 MHz, and compared to conventional ultrasonic techniques as a baseline. The examinations showed that phased-array methods were able to detect and accurately length-size, but not depth size, the notches and flaws through the welds. The ultrasonic results were insensitive to the different welding techniques used in each weld.
Corotational Analysis of Elastic-Plastic Hardening Materials Based on Different Kinematic Decompositions
Authors: Ghavam Kamyar , Naghdabadi Reza
Published: July 2008

In this paper, two corotational modeling for elastic-plastic, mixed hardening materials at finite deformations are introduced. In these models, the additive decomposition of the strain rate tensor as well as the multiplicative decomposition of the deformation gradient tensor is used. For this purpose, corotational constitutive equations are derived for elastic-plastic hardening materials with the non-linear Armstrong-Frederick kinematic hardening and isotropic hardening models. As an application of the proposed constitutive modeling, the governing equations are solved numerically for the simple shear problem with different corotational rates and the stress components are plotted versus the shear displacement. The results for stress, using the additive and the multiplicative decompositions are compared with those obtained experimentally by Ishikawa [1]. This comparison shows a good agreement between the proposed theoretical models and the experimental data. As another example, the Prager kinematic hardening equation is used instead of the Armstrong-Frederick model. In this case the results for stress are compared with the theoretical results of Bruhns et al. [2].