bluuebunny/crossref_metadata_2025 huggingface dataset:
The State of Stress of Transportation Packages During Hypothetical Accident Free-Drop Impact
Authors: Huang S. N. , Shiraga S. S. , Hay L. M.
Published: August 2008

In general, only stress-based design criteria are used and accepted by regulatory agencies to demonstrate transportation package structural performance by analysis. However, as stated in the regulatory guidance, other criteria may be accepted on a case-by-case basis. There are efforts to develop alternate design criteria, based on strain or strain energy density, to demonstrate acceptable structural performance of packages under the HAC free drop. Prior to developing such design criteria, two elements must be understood and developed: (1) the failure mechanism from strain or strain energy density and (2) a theory of failure. However, in order to understand the failure mechanism and to develop a theory of failure, the stress state behavior (stress fields) must be known. As a first step, this paper examines and reports the stress states for free-drop impact loadings on two transportation packages currently in use.
Flaw Classification by Using Artificial Neural Network and Wavelet
Authors: Li Lingqi , Cheng Wei , Tsukada Kazuhiko , Hanasaki Koichi
Published: August 2008

This paper presents a methodology to 2-D flaw-shape recognition by combining a neural network and the wavelet feature extractor. This approach consists of three stages. First, the 2-D pattern of an object is retrieved from image and then transformed to complex contour, which is described by the coordinates of its shape. Then, feature extraction is performed to this contour representation. Fourier descriptor (FD), principal component analysis (PCA) and wavelet descriptor (WD) are employed in this stage, and their performances are compared and discussed. In the third stage, artificial neural networks, including two different types of multi-layer perceptron (MLP) and Kohonen self-organizing network, are used as the classifier based on the feature sets extracted in the second stage. The numerical experiments performed on the recognition of simulated shapes demonstrate the superiority of the WD feature extractor (both used for MLP and Kohonen network classifiers) to the other two: PCA and FD, especially when the raw data have poor signal-to-noise ratio (SNR). The application to the real ultrasonic C-scan image flaw-shape classification shows the effectiveness of the proposed approach to the field of PVP.
Design and Performance of a Broadband 10MHz Transducer for Elevated Temperature, Leave-in-Place Applications
Authors: Pedrick Michael , Tittmann B. R. , Seliga Jim
Published: August 2008

This paper describes the novel design of an ultrasonic normal beam transducer for prolonged use in elevated temperature environments. Through the use of a Carbon/Carbon composite backing layer, prolonged exposure to elevated temperature had minimal effect on transducer performance. The conductive nature of the Carbon/Carbon allowed for an innovative electrical coupling technique. A clamping mechanism combined with the use of an annealed gold quarter-wave matching layer allowed for joint-free, dry coupling. This simple design allows for easy field assembly and eliminates temperature dependencies in the acoustic coupling. The transducer was tested initially at room temperature for reference data. Further tests after 100+ hours of exposure to a 77°C environment showed little overall change in the transducer performance. The transducer showed consistent −6dB bandwidths on the order of 54–67%, along with negligible change in centerline frequency. The insertion loss as a function of temperature showed an increase from approximately 6.8dB to 8.5dB over a temperature range from 25°C to 85°C. Regression lines show bandwidth changes of −0.01% per °C and insertion loss changes of 0.03dB per °C. These results show potential use for a transducer of this design at even higher temperatures.
Application of 3D X-Ray CT to Stress Simulation Analysis of Porous Materials With Homogenization Method
Authors: Nagano Yasuo , Ikeda Yasushi , Kawamoto Hiroshi
Published: August 2008

A 3D X-ray CT method was developed using a combination of a micro-focus X-ray generator and an image intensifier camera. An image processor used produced 2D projection data for CT imaging. The channel number of the data was 1024, and the slicing number was up to 200. A micro-focus X-ray generator was used and image-magnifying method was carried out to imaging porous ceramic materials. Using obtained 3D CT images, voxel mesh method was carried out with mathematical homogenization method. Complicated structures of porous materials were taken into the simulation process as an image-based modeling. Equivalent homogenized elastic constants were calculated for the microscopic porous models, and global macroscopic stress and local stress distribution in porous materials were calculated with the simulation method. This simulation method was considered to be applicable to much larger porous materials of piping and construction.
Analytical and Experimental Approaches for the Sizing of Fatigue Cracks in Inconel Welds by Eddy Current Examination
Authors: Cheng Weiying , Komura Ichirou , Shiwa Mitsuharu
Published: August 2008

Cracks by SCC (stress corrosion cracking) and high cycle fatigue were detected at the welded joints of nickel based alloy of reactor vessel, pressurizer and core internal of nuclear power plants in recent years. To ensure the integrity of plants, it is necessary to improve NDT (non-destructive testing) techniques for reliable detection and evaluation of defects in the nickel-base alloy. Basic studies on the flaw detection and characterization by eddy current examination of inconel, a typical nickel-base alloy, are carried out. Specimens made of inconel and inconel weld metal are prepared, fabricated with EDM (Electro-Discharge Machining) notches and fatigue cracks. The detecting and sizing capability of eddy current method is investigated through analytical and experimental approaches. Numerical analysis helps in choosing an appropriate probe and examination condition, and evaluating a crack from the measured signals. All or part of a planar crack is reconstructed using an inversion approach. The result from ECT (eddy current testing) is compared with that of UT (ultrasonic testing). The research presented in this paper shows that by choosing a proper testing situation, eddy current examination is feasible for the detection and sizing of surface-breaking cracks in inconel welds.
Methodology of Digital Image Acquisition and Digital Inspection for Liquid Penetrant and Magnetic Particle Testing
Authors: Taguchi Tetsuo , Mori Masako , Kurosaki Michiaki , Takagi Mikio
Published: August 2008

Liquid Penetrant Test (PT) and Magnetic Particle Test (MT) are widely used in industry to detect surface defects. It is extremely important to maintain the repeatability and reproducibility of PT and MT so that they are able to detect any defect that might affect the quality of a product, especially the weld joints of welded structures. In the present paper, calibration methods for visual conditions for PT and MT are proposed with the use of a visual resolution gauge. In addition, a “PT/MT support System” applying digital image processing techniques, which enables us to perform “Remote Inspection” is proposed. A visual resolution gauge is a transparent plate on which line pairs are printed with equivalent hue to the indications of PT and MT, which ensures proper resolution for visual testing. In Japan, the standard for calibration methods for visual conditions using these resolution gauges for PT and MT were published in the Japanese Industrial Standards (JIS) Z 2340 in 2002. By applying these visual resolution gauges, we developed a “PT/MT support system.” In this system, the PT or MT digital images, which are captured by digital camera with resolution gauges, are converted into hue and saturation data by image processing. These images are then divided into two categories of defects and false indications. This is useful in detecting defects and establishing standard evaluation criteria. Furthermore, this will also enable “Remote Inspection,” which is a method in which PT and MT digital images are observed from remote place (as opposed to direct observations). This enables the possibility of inspections being performed from remote places and manufacturers, inspectors, customers, and government inspectors in remote areas can share the inspection results as electronic data.
New Crack Detection Method by Using Electromagnetic Wave
Authors: Hashizume Hidetoshi , Shibata Takuya , Yuki Kazuhisa , Yoshioka Takahiro
Published: August 2008

The NDT method using electromagnetic waves has the possibility to detect widely and quickly inner surface crack existing in large pipes. The purpose of this study is then to demonstrate validity of the method to detect the thin crack introduced by plasma discharge fabrication. Through this study, it has been shown that both reflected and transmitted waves carry a lot of information on existence of the crack. Experimental results indicate that there exists attractive possibility in this new NDT method.
Modeling Downhole Natural Separation Using a Bubble Tracking Method
Authors: Liu Bin , Prado Mauricio
Published: August 2008

For any pumping artificial lift system in petroleum industry, the free gas significantly affects the performance of the pump and the system above the pump. A model, though not a complete two-phase flow model, has been developed for the effective prediction of separation efficiency across a wide range of production conditions. The model presented is divided into two main parts, the single-phase flow field solution and the bubble tracking method. The first part of the model solves the single-phase liquid flow field using the CFD approach. Then, a simple bubble-tracking method was applied to estimate the down-hole natural separation efficiency for two-phase flow. A comparison between the results of the model and the experimental data was conducted. It shows a very good agreement with the experimental data for lower gas void fractions (bubble flow regime).
Fully Three Dimensional Modeling of Fluid-Structure Interaction Problems Using High Order Finite Elements for the Structural Simulation
Authors: Scholz Dominik , Du¨ster Alexander , Rank Ernst
Published: August 2008

Our approach is to use fully three-dimensional models for both the fluid and the structure. For thin-walled structures, which are typically sensitive to loads resulting from the surrounding fluid, it will be shown that the use of high-order hexahedral elements with high aspect ratios is feasible. Furthermore, it will be demonstrated that three-dimensional elements of high order can be used very efficiently by choosing a high polynomial degree in in-plane direction and a low polynomial degree in thickness direction. By varying the polynomial degrees in the local directions of the elements, the choice of an appropriate structural model can be achieved in an adaptive way. This will be demonstrated by means of a numerical example.
New Mesh Relaxation Technique in Multi-Material ALE Applications
Authors: Mahmadi K. , Aquelet N. , Souli M.
Published: August 2008

The Arbitrary Lagrangian-Eulerian (ALE) method is a method that contains both pure Lagrangian and pure Eulerian formulations. It is assumed to be capable to control mesh geometry independently from material geometry. However for transient problems involving pressure wave, this method will not allow to maintain a fine mesh in the vicinity of the shock wave for accurate solution. A new mesh relaxation method for explicit multi-material arbitrary Lagrangian Eulerian finite element simulations has been developed to keep an as “Lagrange like” fluid mesh as possible as in the vicinity of shock fronts, while at the same time keeping the mesh distortions on an acceptable level. However, the relaxation parameter must be defined for general applications of high pressures, it is the objective of this work. In this paper we present numerical results of three shock waves problems. For every application, numerical results will be compared with the experimental results in order to improve to understanding how the relaxation parameter is chosen.
Shock Analysis of Underwater Explosion Using Smoothed Particle Hydrodynamics
Authors: Matsumoto S. , Itoh S.
Published: August 2008

A blasting process includes large deformations and inhomogeneities caused by shock waves as well as the detonation gases generated by explosives. Smoothed Particle Hydrodynamics (SPH) is a meshless and complete Lagrangian method. The properties of SPH method can overcome the difficulty of a simulation in a blasting process. In this study, the simulation of an underwater explosion using SEP (Safety Explosives) as a cylindrical high explosive is carried out to confirm the advantage of SPH method for the analysis in a blasting process. The Euler equations are used for the governing equations of both water and the detonation products of the explosive. The Jones-Wilkins-Lee (JWL) equation and the Mie-Gru¨neisen equation are used as the equation of states for the detonation products and water, respectively. The two-dimensional and axisymmetrical simulation in cylindrical coordinate system is adopted to analyze the underwater explosion. The simulation result is compared with the experimental result and shows that SPH method can well simulate the underwater explosion.
Exact Solution of the Base-Isolated Structure With Sliding Type Base Isolator
Authors: Tsai C. S. , Chiang Tsu-Cheng , Chen Bo-Jen
Published: August 2008

The use of base isolation for enhancing the seismic resistibility has been proved as an efficiency way from experimental efforts and theoretical studies. It is usual to insert a flexible device in horizontal direction to permit the most relative deformation at this level. Because of the rigidity of the superstructure is much higher than that of the base isolator underneath the structure, therefore, the behavior of the superstructure can be idealized as a rigid body during earthquakes. In general, hundreds of degrees of freedom and a step-by-step time history analysis are the basic requisitions for calculating the seismic response of a base isolated structure under earthquakes. In order to develop a simple tool which can be easily adopted for calculating the sliding displacement and the shear force of the base isolator, an exact solution for predicting the seismic responses of base isolated structures has been derived in this study. The comparison between the experimental results conducted at National Center for Research on Earthquake Engineering (NCREE) in Taiwan and the analytical results obtained from the exact solution show that the exact formulation derived in this study can predict the seismic response of the base isolated structure with very good accuracy.
Experimental Verifications on Seismic Response Control of Tall Structures by Multiple Tuned Liquid Dampers
Authors: Li Hong-Nan , Jia Ying , Wang Su-Yan
Published: August 2008

The focus of this paper is on the use of multiple Tuned Liquid Dampers (TLDs) as passive control devices to reduce the multi-modal responses of tall buildings and high-rise structures to earthquake ground motion excitation. A model of a 3-story building with one and two TLDs was installed on a shaking-table. The system was subjected to three earthquake time histories. Then the mechanical models and the equations of motion for the systems of tall buildings and high-rise structures with TLDs are established. Here, the solution of the dynamic liquid pressure is based on the method of the Volume of Fluid and the seismic responses are obtained by use of the state equation. The comparisons show that theoretical results are generally in good agreement with experiments. It is observed that the approach presented in this paper proved to be quite effective both in the numerical example and in the seismic simulating tests.
Vibration Test of 1/10 Scale Model of Cylindrical Water Storage Tank
Authors: Maekawa Akira , Shimizu Yasutaka , Suzuki Michiaki , Fujita Katsuhisa
Published: August 2008

Large-scale cylindrical water storage tanks have a large ratio of radius to thickness, which means their thickness is relatively thin compared with the radius. Regarding seismic responses, the deformation of a tank frame is significantly influenced by the sloshing of the water inside the tank and by the bulging vibration of the tank structure, therefore it is important to consider such deformation theoretically and experimentally. This paper describes the results of a vibration test with a 1/10 reduced scale model of a large-scale industrial cylindrical water storage tank, conducted particularly to clarify the dynamic behavior of the tank during a seismic excitation. First a sinusoidal wave excitation experiment was performed for the scale model tank, which measured axial distributions of dynamic fluid pressures, strains and accelerations. Ovaling vibration of the scale model tank also was examined by measuring the circumferential distribution of strains. Furthermore, the dependence of dynamic fluid pressure on the acceleration magnitude of the input excitation was investigated. Secondly, a seismic excitation experiment was conducted using typical seismic waves. Finally, the measuring results were compared with the values calculated using common seismic-proof design methods based on the Housner method or velocity potential theory and the finite element method. Considering the differences between the experiment values and numerical design ones, it became obvious that there was inconsistent between the positive and the negative pressures of the dynamic fluid pressure and that the dynamic fluid pressure was dependent on the acceleration magnitude. And it was suggested that such phenomena were caused by ovaling vibration. They, however, had little effect on the seismic-proof design of the tank in the range of acceleration used in this study.
An Overview of the Seismic Verification Analyses Performed for Natural Gas Pipeline Networks
Authors: Botsis Ch. , Sariyiannis A. , Anagnostides G. , Kokavesis N.
Published: August 2008

The purpose of this paper is to present an overview of the various seismic analyses performed and the measures taken to ensure the mechanical integrity of the natural gas pipeline networks in Greece. Design of large pipeline networks in an open countryside is a complicated issue and involves many disciplines and works, such as, preliminary geological investigation, topographical investigation, detailed geotechnical investigation, adjustment of pipeline routing (if necessary) according to the detailed investigation results and finally pipeline stress verification due to stresses induced by seismic loading caused either by soil lateral spreading during a seismic event or by the rupture of active faults. Engineering judgment and previous experience are important to determine the best pipeline routing, however, due to the large seismic events occurring in Greece, measures are always necessary to improve the seismic response of pipeline networks. Loading of buried pipelines, due to earthquake induced permanent ground displacements (active fault rupture and lateral spreading) is displacement controlled. Various analyses were performed to evaluate the maximum ground surface acceleration and its reduction with depth, which control the outcome of the liquefaction potential. The results of the liquefaction analyses were used to compute permanent ground displacements. These displacements as well as the active fault displacements were applied to critical parts of the pipeline network and elasto-plastic analyses were performed to compute the resulting pipeline stresses and strains. Various mitigation measures have been taken to release pipeline stresses, such as changing (where possible) the pipeline routing, widening the pipeline trench in critical areas, using a light-weight backfill material, increasing the pipeline thickness, etc. The paper will present an overview of the various analyses performed and will summarize the measures taken to improve the seismic response of the pipeline network.
Application of Earthquake Experience Data as Part of the Seismic Verification of Modified Main Steam Isolation Valve Leakage Pathway Piping
Authors: Adams Timothy M. , Quiggle Scott
Published: August 2008

The Monticello Nuclear Generating Plant made modifications to the turbine island in 1998 to achieve a 5% power uprate. The radiological analysis conducted for power uprate took credit for deposition and holdup of radioactive iodine in the steam lines downstream of the Main Steam Isolation Valves (MSIV’s) and in the main condenser. The original design basis of certain main steam system piping, equipment, and components that comprise the MSIV Leakage Pathway was not in accordance with Seismic Category I requirements. As part of the original program seismic verification walkdowns were performed to demonstrate the main steam system piping, equipment, and components were seismically rugged. The walkdowns were done using the methodology suggested to seismically evaluate this pathway in the Boiling Water Reactor Owners’ Group report, entitled “BWROG Report of Increasing MSIV Leakage Rate Limits and Elimination of Leakage Control Systems”. In 2001, Monticello made significant changes to improve the performance of the plants hydrogen recombiner process. The hydrogen recombiners are part of the off gas system a portion of which was in the original MSIV Leakage Pathway. These modifications significantly redefined MSIV Leakage Pathway and required an updated assessment of the seismic ruggedness of piping and associated equipment in the MSIV Leakage Pathway. This paper describes the approach and methodology used to update and expand the seismic evaluations and seismic verification walkdowns. It also summarizes the results of these walkdowns and the steps necessary to demonstrate the seismic adequacy of the piping and equipment.
Procedures on Fracture Toughness Estimation Safety Assessment and Life Extension for In-Service High Pressure Vessels
Authors: Chen Guohua , Chen Bonuan
Published: August 2008

Based on the typical in-service high pressure vessels made of PCrNi3MoVA for producing synthetic crystal, a systematic technology of material fracture toughness estimation, structural integrity assessment, and life extension is carried out for the in-service equipment with the following aspects: macroscopically and microscopically analyzing, the tests including KIC, AKV, FATT (50%), the predicting method of fracture, system safety assessment, and the life extension technology. Some practical conclusions can be obtained from the test and analysis as follows: The main failure factors for this kind of high pressure vessels include heat treatment processes, temper brittleness, and stress corrosion; It is found that the value of FATT (50%) increased very significantly; The comparison between the test results and the predicted results of the value of KIC is also performed, and it is shown that the value of KIC of in-service equipment can be estimated by the formula presented by Barsom-Rolfe or in API 579 with the value of AKV, The test temperature is recommended at least to reach 25 C (or room temperature) for the repaired vessels; The life extension technologies are put forward for this kind of in-service super-high pressure vessels.
Optimizing Neural Networks for Leak Monitoring in Pipelines
Authors: Kassem Ayman H. , Adam Ihab G.
Published: August 2008

Feedforward neural networks can be used for nonlinear dynamic modeling. Although the basic principle of employing such networks is straightforward, the problem of selecting the training data set and the network topology is not a trivial task. This paper examines the use of genetic algorithm optimization techniques to optimize the neural network. The paper presents the results of studies on the effect of number of neurons and input combination method on the performance of neural networks and the application of this study to improve leak monitoring in pipelines. The neural networks examined in this study do not use the sensor reading directly as in conventional neural networks but combine it using polynomial type laws to produce hybrid inputs. The optimization technique tries to find the best polynomial laws (input combination) to reduce network size, head variation effect, and optimize network performance. The resulting networks show superior performance and use fewer numbers of neurons.
Analysis on the Dynamic Load in a Water Pool During Air Discharge From Submerged Sparger
Authors: Uchida Ken , Shimizu Takeshi , Komuro Mitsuo , Kuroda Masatomo , Suzuki Seijiro
Published: August 2008

This paper presents a study of the applicability of the VOF (Volume of Fluid) method to estimation of dynamic load in a water pool induced by oscillation of bubbles that are ejected through sparger holes. We choose the VOF method to simulate this phenomenon, and the pressure of a bubble is given by entropy change in order to consider the compressible effect of the bubble and the effect of gas coming into the bubble. In calculation of air flow rate passing through the holes, the effect of two-phase pressure drop is incorporated. In order to investigate applicability of this method, a simplified blowdown test is carried out. According to the numerical results, the pressure-time history inside the sparger and that in a water pool are both generally reproduced well with analysis except that the magnitude of first peak pressure in a water pool is overestimated. The most likely reason is that the bubble cloud has especially low void fraction at the early stage of bubble formation, and small bubbles around a major bubble work as a buffer, which is discussed in detail in this paper.
Transient Heat Transfer Analysis to Evaluate the Voiding of the Containment Emergency Cooling Units of PWR (Pressurized Water Reactor) Nuclear Plant Following a Pipe Break Accident
Authors: Husaini S. Mahmood , Qashu Riyad K.
Published: August 2008

The U.S. Nuclear Regulatory Commission (NRC) issued the Generic Letter GL-96-06 requiring the utilities to evaluate in their Nuclear plants the operability of the Containment Emergency Cooling Units (ECUs) when the Component Cooling Water (CCW) pumps restart after a hypothetical Loss Of Coolant Accident (LOCA) or Main Steam Line Break (MSLB) accompanied by the Loss Of Offsite Power (LOOP). Normally, the ECUs are at high elevation and are susceptible to boiling when their cooling coils are exposed to the high temperature steam following a MSLB or LOCA. In a closed loop system, after the onset of boiling, the voiding is governed by the amount of water that can flow from the ECUs to the surge tank. When the CCW pumps restart, water hammer will occur due to the filling of the void. EPRI (Electric Power Research Institute) along with a number of utilities undertook an experimental research study that proposed a methodology to mitigate the water hammer by accounting for the cushioning effects of hot steam and released air. However, the EPRI study did not provide any guidance for evaluating the occurrence of boiling and the size of the void when the CCW pumps restart. Some of the utilities have used cfd based computer programs that require setting up complex models of the ECU cooling coils, which is very time consuming and costly. This paper presents a methodology based on first principles to evaluate the onset of boiling and the growth of steam void in the ECU coils of a typical PWR closed loop CCW system with a surge tank. It includes the effects of system parameters and accounts for condensation in the presence of air, natural convection, boiling heat transfer, etc. The system parameters have a very significant effect on the results of the analysis. The predictions of the calculations were compared with the predictions using the GOTHIC computer code and were found to be in reasonably good agreement. The methodology is shown to be very cost effective and reliable because it avoids the complexity of modeling the entire cooler and is based on first principles. After the water in the ECU coils reaches the saturation temperature, the void formation is dependent on the paths available from both the inlet and the outlet sides of the ECUs to the surge tank. The procedure for calculating the drainage is also illustrated. Various fixes for avoiding/mitigating the water hammer are also discussed.
Dynamic Analysis of a Coupled Fluid Structure Problem With Fluid Sloshing
Authors: Sigrist Jean Franc¸ois , Laine Christian , Peseux Bernard
Published: August 2008

The present paper is related to the study of a generic linear coupled fluid/structure problem, in which an elastic beam is coupled with an inviscid fluid, with or without sloshing effects. A previous study [18] focussed on added mass effects; the present study is devoted to the coupling effects between fluid sloshing modes and structure with fluid added mass modes. The discretization of the coupled linear equations is performed with an axisymmetric fluid pressure formulated element, expanded in terms of a FOURIER series [14]. Various linear fluid model are taken into account (compressible, uncompressible, with or without sloshing) with the corresponding coupling matrix operator. The modal analysis is performed with a MATLAB program, using the non-symmetric LANCZOS algorithm [16]. The temporal analysis is performed with classical numerical techniques [10], in order to describe the dynamic response of the coupled problem subjected to a simple sine wave shock. The coupling effects are studied in various conditions represented by several non-dimensionnal numbers [12] such as the dynamic FROUDE number and the mass number, based on the geometrical and physical characteristics of the coupled problem. Comparisons are performed on the coupled problem with or without free surface modeling, with a model and temporal analysis. Coupling effects are exhibited and quantified; the numerical results obtained in the modal analysis here are in good agreement with other previous studies, carried out on different geometry [3,15]. The temporal analysis gives another point of view on the importance of the coupling effects and their importance at low dynamic FROUDE numbers. The present study gives and will be completed with a non-linear analysis (for both fluid and structure problems) of the coupled problem, using a finite element and finite volume explicit coupling procedure [19].
Irradiation Hardening of Austenitic Stainless Steels: From Field Experience to Modeling
Authors: Pokor C. , Thebault Y. , Pujol C. , Massoud J.-P. , Loisnard D. , Lemaire E. , Dubuisson Ph. , Brechet Y.
Published: August 2008

Materials for the core internals of Pressurized Water Reactors (austenitic stainless steels) are submitted to neutron irradiation. To understand the ageing mechanisms associated to irradiation and propose life predictions of the component, a multi step iterative approach consisting in particular in modeling the evolution of the hardening has been undertaken. Combination of characterization and modeling of simplified situations and field expertise is proposed.
Aging Management Strategies for Pressurized Water Reactor Vessel Internals
Authors: Griesbach Timothy J. , Nickell Robert E. , Tang H. T. , Gilreath Jeff D.
Published: August 2008

Management of materials aging effects, such as loss of material, reduction in fracture toughness, or cracking, depends upon the demonstrated capability to detect, evaluate, and potentially correct conditions that could affect function of the internals during the license renewal term. License renewal applicants in their submittals to NRC have identified the general elements of aging management programs for Pressurized Water Reactor (PWR) internals, including the use of inservice inspection and monitoring with the possibility of enhancement or augmentation if a relevant condition is discovered. As plants near the license renewal term, plant-specific aging management programs will be implemented focusing on those regions most susceptible to aging degradation. A framework for the implementation of an aging management program is proposed in this paper. This proposed framework is based on current available research results and state of knowledge and utilizes inspections and flaw tolerance evaluations to manage the degradation issues. The important elements of this framework include: • The screening of components for susceptibility to the aging mechanisms, • Performing functionality analyses of the components with representative material toughness properties under PWR conditions, • Evaluating flaw tolerance of lead components or regions of greatest susceptibility to cracking, loss of toughness, or swelling, and • Using focused inspections to demonstrate no loss of integrity in the lead components or regions of the vessel internals. The EPRI Material Reliability Program (MRP) Reactor Internals Issue Task Group (RI-ITG) is actively working to develop the data and methods to quantify an understanding of aging and potential degradation of reactor vessel internals, to develop materials/components performance criteria, and to provide utilities tools for extending plant operations. Under this MRP Program, the technical basis for the framework will be documented. Then, based on that technical basis, PWR internals inspection and flaw evaluation guidelines will be developed for plants to manage reactor internals aging and associated potential degradation.
A Probabilistic Approach to Heatup and Cooldown Operating Limits for a Nuclear Pressure Vessel
Authors: Lott Randy G. , Server William L.
Published: August 2008

During plant heatup and cooldown, the stresses in a nuclear pressure vessel are the membrane stress associated with system pressure and the stress caused by the thermal gradient across the vessel wall. The system pressure and the rate of temperature change (heatup or cooldown) must be controlled in a manner that protects against failure of the vessel. The current basis for setting these pressure-temperature operating limits is a deterministic fracture mechanics analysis that conservatively applies a safety of factor of two to the system pressure and assumes a large flaw corresponding to 1/4 of the thickness of the vessel. This calculation produces an upper bound estimate of the stress intensity at the flaw tip, which is compared to a lower bound estimate of the material fracture toughness to set the pressure-temperature operating limits. This methodology results in restrictive operating limits that correspond to an extremely low probability of vessel failure. The development of state-of-the art probabilistic fracture mechanics for the FAVOR Code has made it possible to determine the risk of vessel failure associated with these restrictive limits. Relaxation of these limits may be possible with negligible impact on the risk of vessel failure. Overall plant risk may be reduced by eliminating other potential challenges to plant integrity that are associated with the current restrictive operating limits.
Behavior of Localized Bottom Depression in Aboveground Oil Storage Tanks Under Liquid Pressure
Authors: Yoshida Shoichi
Published: August 2008

When constructing the bottom of aboveground oil storage tanks, the bottom plates are first laid out on the flat foundation, and they then are joined by welding the joints in sequence. As the foundation is difficult to be made completely homogeneous over the bottom area, the settlement of the bottom plates is not uniform under liquid pressure. The depressions of the bottom plates are sometimes found at the first internal inspection which is usually made about 10 years after the oil storage. This paper presents plane strain finite element analysis for the localized bottom depression in aboveground oil storage tanks. Load-incremental, elastic-plastic large deformation analysis is carried out considering contact with the foundation. The relationship of the stress at the depressed bottom plate to the liquid pressure is discussed together with the deformation of the depression.
Plastic Collapse Assessment of Unequal Wall Joints in Pipeline Transitions
Authors: Zhu Xian-Kui , Leis Brian N.
Published: August 2008

This paper presents the results of extensive numerical and analytical analyses considering the many differences in the flow properties of today’s steels with a view to determine if the code design basis developed for early steels remains appropriate in light of these changes. These analyses involved parametric study of steel grade, tensile strength, yield-to-tensile (Y/T) strength ratio, and joint geometry, for a range of transitions within as well as beyond current ASME code allowables. The numerical results indicate that the plastic-collapse failure conditions of unequal wall joints are controlled by the pipe or fitting remote to the weld, as would occur for high-quality slightly over-matched welds. Mismatch location, taper angle and anisotropy of unequal wall joints have limited influence on such failures. Based on trends in these results, a closed-form plastic collapse solution to predict internal pressure was developed as the pipe geometry, material hardening and tensile properties for both end opened and end capped pressurized pipes in reference to deformation instability, finite strain theory and deformation theory of plasticity. A plastic collapse criterion and the corresponding plastic collapse assessment diagram (PCAD) were then developed as a function of the wall thickness and tensile strength mismatch conditions to ensure plastic collapse failure in the thinner-wall, higher strength line pipe. General procedures to use the PCAD are outlined in this paper. Application of PCAD indicates that the high yield strength grades with high Y/T can be used within as well as beyond current code limitations on the transition wall-thickness mismatch for a wide range of strength mismatch.
Neuro-Fuzzy Approaches for FRP Oil and Gas Pipeline Condition Assessment
Authors: Kumar S. , Taheri F.
Published: August 2008

Recent advances in ultrasonic, optical and piezoelectric sensors, and computing technologies have led to the development of inspection systems for underground and off-shore structures such as water lines, oil and gas pipes, and telecommunication conduits. It is now possible to use inspection technologies that require no human intervention (i.e., having had to go underground or off-shore); moreover, the inspection process can be fully automated, from data acquisition to data analysis, and eventually to condition assessment and repair. This paper describes the development of an automated data interpretation system for fiber-reinforced polymer composites (FRP) oil and gas pipelines, which would also be applicable to metallic pipes. The interpretation system obtains C-scan image data from so-called “smart pigs” and maps data using Geographic Information System (GIS) and Global Positioning System (GPS). Assessment of health of pipelines using neural networks is then performed to identify the high-risk locations in each pipeline or pipeline network, thus allowing the inspection to be properly targeted. The proposed system utilizes artificial neural networks and genetic algorithm to recognize various types of defects in FRP oil and gas pipelines. Image processing and wavelets techniques are used to find the detail of the damage geometry. An expert system is also developed, using fuzzy Logic, to perform damage condition assessment and suggest an optimum repair protocol. The framework of the developed system, thus includes GIS, risk map, modification of digital images for preprocessing, image feature segmentation, utilization of multiple neural networks for feature pattern recognition, the fusion of multiple neural networks via the use of fuzzy logic systems, and the proposed expert system for suggested repair.
Drag on a Confined Cylinder in Axial Flow
Authors: Kritzinger H. P. , Kleijn C. R. , Van den Akker H. E. A.
Published: August 2008

Bluff body drag prediction remains a challenging subject for numerical investigators, with important industrial applications in aero- and hydrodynamics. A typical configuration of general interest is that of a confined axial cylinder. Experimental data for this geometry is scarce. In this paper, drag forces on this configuration were investigated using the commercial CFD solver Fluent 6. The work includes results with various mesh densities and different Reynolds numbers. Several common turbulence models as available in Fluent were applied. Good agreement to experiments was obtained with the realizable k-ε model and with the Reynolds stress transport model. The standard k-ε model was found to be inappropriate. Increased blockage (confinement) of the cylinder resulted in a corresponding increase in the drag force. This increase is shown to be a function of the mean velocity at the smallest cross-section of the channel.
Basal plane dislocation reduction for 8° off-cut, 4H-SiC using in situ variable temperature growth interruptions
Authors: VanMil B. L. , Stahlbush R. E. , Myers-Ward R. L. , Lew K.-K. , Eddy C. R. , Gaskill D. K.
Published: August 2008

In situ growth interrupts were executed during the growth of 8° off-cut 4H-SiC epitaxial layers to determine the dependence of the efficiency for converting basal plane dislocations (BPDs) to threading edge dislocations (TEDs) on the interrupt temperature. Three samples were grown with 15min growth interrupts executed near the middle of a 30–40μm thick, n-type doped layer at 1400, 1500, and 1580°C. Ultraviolet photoluminescence (UVPL) mapping of these layers reveals the BPDs and permits the observation of how these defects extend into and through the epilayer. From the lateral length of the BPDs in the UVPL wafer map, it was determined whether or not the BPD converted into a TED at the growth interrupt interface. The percentage of BPDs that converted for the 1400, 1500, and 1580°C interrupts were 20%, 28%, and 51%, respectively. The proposed cause for the higher conversion rate at the interrupt temperature of 1580°C is the higher etching rate that occurs at this temperature, and it is presumed that there is an enhanced etch rate where the BPD intersects the surface which will result in etch pit decorations. It was also observed that no new in-grown stacking faults formed at the growth interrupt interface, as has been observed for ex situ growth interrupts.
Steady state and transient behavior of currents in AlGaN∕GaN planar Schottky diodes and mechanism of current collapse
Authors: Hasegawa Hideki , Akazawa Masamichi
Published: August 2008

To get information on the current collapse mechanism under gate bias stress in AlGaN∕GaN heterostructure field effect transistors, this article investigates the steady state and transient behavior of current in a planar Schottky metal contact formed on a standard AlGaN∕GaN high electron mobility transistor wafer. Schottky contacts with reduced reverse leakage currents were prepared by using an oxygen gettering process, and their electrical characteristics were studied by current-voltage, capacitance-voltage, and current-time measurements at various temperatures. When the voltage pulse was applied into the pinch-off region, an excess current flew, showing very slow nonexponential transients covering six orders of magnitude of time from millisecconds to thousand seconds. Turn-off transients were also slow and highly nonexponential. The current transients are shown to be due to charging and discharging of the virtual gate capacitor with the electrons in and out of surface trapping states where the rate limiting process is the hopping process of electrons. The process can be described by a dispersive hopping transport, leading to charging behavior with a stretched exponential dependence on time and discharging behavior with power law dependence on time. Theoretical formulas showed good agreements with experiments, and provide ample description of the transients processes directly related to the current collapse.
Structural and electrical properties of Bi1.5Mg1.0Nb1.5O7 thin films deposited on Pt/TiO2/SiO2/Si substrates by rf-magnetron sputtering
Authors: Ahn Jun-Ku , Cuong Nguyen Duy , Yoon Soon-Gil , Kim Chang-Soo
Published: August 2008

Bi 1.5 Mg 1.0 Nb 1.5 O 7 thin films were deposited at various temperatures by rf-magnetron sputtering on Pt/TiO2/SiO2/Si substrates. The structural and electrical properties were investigated as a function of deposition temperature. The films deposited below 400 °C show an amorphous state and a dielectric constant of approximately 31–51. On the other hand, films deposited at 500 °C exhibit well-developed crystallinity and a high dielectric constant of approximately 104. However, for crystallized films deposited at 500 °C, the leakage current density is higher than that of the films deposited below 300 °C.
Highly reliable growth process of carbon nanowalls using radical injection plasma-enhanced chemical vapor deposition
Authors: Kondo Shingo , Hori Masaru , Yamakawa Koji , Den Shoji , Kano Hiroyuki , Hiramatsu Mineo
Published: August 2008

Two-dimensional carbon nanostructures, carbon nanowalls (CNWs), were fabricated on a Si substrate using radical injection plasma-enhanced chemical vapor deposition, employing fluorocarbon (C2F6) and hydrogen (H2) mixtures. The influence of the surface conditions of the chamber wall on CNW growth was investigated in order to determine the optimum conditions for CNW growth with high stability and reproducibility. In order to monitor the surface conditions of the chamber wall, optical emission spectroscopy in the plasma was measured, and the correlation between CNW growth and the surface conditions in the chamber wall was investigated. The growth rate and morphology of grown CNWs were determined to be influenced by the surface conditions of the chamber wall. Furthermore, O2 plasma chamber cleaning followed by predeposition for passivation was found to be effective for maintaining steady conditions to attain CNWs with high reproducibility.
Smooth sidewall in InP-based photonic crystal membrane etched by N2-based inductively coupled plasma
Authors: Lee K. H. , Guilet S. , Patriarche G. , Sagnes I. , Talneau A.
Published: August 2008

The etching for InP photonic crystal (PhC) hole structure using Cl2∕BCl3∕N2 and BCl3∕N2 inductively coupled plasmas has been investigated for the fabrication of membrane devices. The addition of N2 into Cl2-based plasma is shown to enhance the anisotropic etching and to suppress the sidewall roughness compared to the Cl2∕Ar plasma. The profile verticality of PhC structures is improved by the introduction of BCl3. The smooth sidewalls and the vertical hole profiles are obtained when N2 ratio (N2 mass flow rate/total gas flow) is superior to 65%. Positive ion fluxes are measured with the variations of gas flow rates for the plasma characterization. It is found that the addition of N2 to the Cl2∕BCl3 plasma can cause a decrease in positive ion density when the N2 ratio is more than 20%. Chemical identification of the InP surface after etching by a N2-based plasma is characterized by transmission electron microscopy, and no nitrogen element is observed along the sidewalls, which indicates a low probability of surface passivation through N2. By the time-resolved photoluminescence measurement, free-carrier lifetime of 1400ps is obtained on InP∕InGaAsP quantum wells with PhC structures etched by an inductively coupled plasma Cl2∕BCl3∕N2 plasma, which is beneficial for active devices fabrication. Furthermore, InP photonic crystal membrane defect waveguide with one missing row (W1) is fabricated and shows a low propagation loss value of 25dB∕cm while operating below the air-light line.