bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-Linear Free Vibrations of a Rotating Beam Carrying a Tip Mass With Rotary Inertia
Authors: Al-Qaisia Ahmad A.
Published: August 2008

The non-linear, for each of the first three modes, of planar, large amplitude flexural free vibrations of a beam clamped with an angle to a rigid rotating hub and carrying a tip mass with rotary inertia are investigated. The shear deformation and rotary inertia effects are assumed to be negligible, but account is taken of axial inertia, non-linear curvature and the inextensibility condition. The Lagrangian dynamics in conjunction with the assumed mode method, assuming constant hub rotation speed, is utilized in deriving the non-linear unimodal temporal problem. The time transformation method is employed to obtain an approximate solution to the frequency-amplitude relation of the beam-mass free vibration, since the order of the nonlinear terms is not small which includes static and inertial geometric stiffening as well as inertial softening terms. Results in non-dimensional form are presented graphically, for the effect beam root-attachment angle, hub radius and the attached inertia element ratio on the variation of the natural frequency with vibration amplitude.
Characterization of the Performance of Coupled Heat Exchangers With an Intermediate Heat Load
Authors: Ezekoye L. Ike , Swantner Stephen R.
Published: August 2008

Heat exchanger design is both an art and a science. The science part of it is premised on the fundamentals of convective and conductive heat transfer and the art part of it is based on determining how to effectively package the design to meet the process requirements with cost constraints. This paper is not concerned with the art portion of heat exchanger design. Rather, the paper presents a method of characterizing the performance of coupled heat exchangers with an intermediate heat load in process systems. In process plants, it is not uncommon to see heat exchangers that are coupled. Determining the performance of such heat exchanger arrangements can be daunting, but not insurmountable. Using first principles equations, engineers iteratively establish the performance of the heat exchanger arrangement. This process is time consuming. In this paper, we present a specific case of two coupled heat exchangers with an intermediate heat load in the intermediate system. The resultant model allows an engineer to perform sensitivity studies of the arrangement prior to investing resources in an actual design of the system. This method is expected to facilitate the process of examining the performance of similarly configured heat exchanger arrangements. Similar techniques can be used to simplify more complex heat exchanger arrangements.
Analysis of Rotating Blade Forced Vibration Due to Torsional Excitation Using the Method of Harmonic Balance
Authors: Al-Bedoor B. O. , Al-Qaisia A. A.
Published: August 2008

This paper presents an analysis of the forced vibration of rotating blade due to torsional excitation. The model analyzed is a multi-modal forced second order ordinary differential equation with multiple harmonically varying coefficients. The method of Harmonic Balance (HB) is employed to find approximate solutions for each of the blade modes in the form of truncated Fourier series. The solutions have shown multi resonance response for the first blade vibration mode. The examination of the determinant of the harmonic balance solution coefficient matrix for stability purposes has shown that the region between the two resonance points is an unstable vibration region. Numerical integration of the equations is conducted at different frequency ratio points and the results are discussed. This solution provides a very critical operation and design guidance for rotating blade with torsional vibration excitation.
Fluid Particles Fundamental Movement in Rotating Flow Passage of Turbomachinery
Authors: Tanaka Takaharu
Published: August 2008

Hydraulic energy balance is held in radial direction at trailing edge of impeller outlet in pump and at leading edge of impeller inlet in water turbine. Hydraulic energy output at trailing edge of impeller outlet in pump and hydraulic energy input at leading edge of impeller inlet in water turbine appear in the form of product of fluid particle’s rotational and tangential movement. The rate of hydraulic energy head H and flow rate Q is equivalent to the rate of centrifugal and tangential forces, hence equivalent to rate of rotational and tangential distances of which fluid particle had moved at those sections.
On the Influence of Back Pressure and Size on the Performance of Safety Valves
Authors: Dossena V. , Gaetani P. , Marinoni F. , Osnaghi C.
Published: August 2008

The paper presents the results of an extensive experimental research programme performed on safety valves in order to clarify the effects of back pressure and valve size on the flow capacity of a valve. As well known, back pressure strongly influences valve operating characteristics and can also reduce the discharge coefficient. This flow rate reduction can be related to the occurrence of a subsonic flow regime along the flow path and to insufficient disc lift. Last mentioned features can play a different role on different valve sizes because of the non exact geometrical scaling within the same valve size range. This happens because the requirements of typical application design standards, such as the API Standard 526, are such that the valve inlet, valve outlet and face to face dimension are not exactly scaled with respect to the orifice diameter. Moreover, face to face dimension can limit the body bowl volume leading to different device performances the same operational conditions. In order to clarify and evaluate the influence of the above mentioned parameters on the flow capacity of safety valves, many tests were carried on a single valve for different pressure ratios, disc lifts and for different valve outlet areas and body volumes representing different sizes derived from API Standard 526. Test results show significant differences on the flow capacity of safety valves under back pressure regime. This would suggest testing every valve size of the considered valve size range at different expansion ratios to confirm performance. Since this procedure leads to an excessive number of experimental tests, a sensitivity analysis on the influence of the most important geometrical parameters has been carried out. In order to minimize the number of experimental tests required for characterizing the flowing capacity of the whole valve size range, the paper proposes an experimental correlation for the prediction of the above mentioned non similarity effects.
Reliability, Availability and Maintainability Analysis of Steam Turbines Used in an Oil Refinery
Authors: Sheikh Anwar Khalil , Al-Anazi Dahham Matar , Younas Muhammad
Published: August 2008

Weibull reliability and maintainability analysis have been used to analyze the time between failures and time to repair data of a group of steam turbines being used in a large oil refinery. Failure history of a set of steam turbines was obtained from the Computerized Maintenance Management System of the plant. Out of 50 steam turbines in operation, 13 are identified as bad actors which have experienced ≥3 failures in five years. The Pareto analysis performed on this set of turbines further narrowed down the 10 most critical (worst performing) turbines. This group of most critical turbines is the primary target for this Weibull reliability and maintainability analysis. The Weibull reliability and maintainability analysis provides an indication of the equipment reliability and maintainability characteristics including their failure rates and repair rates. In addition to the failure and repair data, the associated maintenance cost for this group of turbines was also collected over a period of five years, and the trends in cost increase with respect to time are plotted.
Discussion of the Available Methods for Blade Vibration Measurement
Authors: Al-Bedoor B. O.
Published: August 2008

Blade vibration has been recognized as one major and costly cause of failure in turbo-machinery. Its vibration measurement has attracted many investigators where until now there is no single reliable approach can be identified. Blade vibration measurement techniques can be classified into two broad categories, namely; (1) the direct approach that includes using strain gages, optical/laser methods, etc., to monitor directly the blade motion at one or more points on the blade span, (2) the indirect approach by extracting some vibration information form the lateral main rotor vibration and the casing/bearing cap vibration, pressure fluctuations, performance monitoring and thermal changes. Recently, a new indirect method has received attention of investigators which is monitoring the torsional vibration of the main rotor. This technique has been investigated by theoretical and experimental studies. The direct and indirect techniques are described in this survey paper and advantages and draw backs are discussed. From the results of this survey it seems that the indirect approach using the torsional vibration measurement is the most promising among all indirect techniques and further theoretical and experimental investigations are recommended.
Avoiding Failure in a Hot Isostatic Press
Authors: Taylor Dan G. , Haimowitz Larry
Published: August 2008

A Hot Isostatic Press (HIP) is a thick walled vessel subject to cyclic stress from internal pressure and temperature profiles. It contains a furnace that heats a work piece to as much as 2900° F (1590° C). These furnaces are designed with a thermal barrier that keeps the inside wall of the vessel below 400° F (204° C). A break down of this thermal barrier can allow jets of hot gas to impinge on the vessel wall and allow hot gas to accumulate at the top of the vessel. Sudden heating of the wall will cause large, localized, compressive stresses and can result in yielding and cracking. The excessive local temperature can also cause a reduction in material properties. Any of these problems can lead to the failure of the vessel. This paper traces a case history of a vessel with these kinds of damage. The problem was first identified by normal, non-destructive, inservice inspection. Further inspection and testing was required to identify the extent of the problem and to verify complete removal of the affected metal. This included insitu metallography of the vessel surface, hardness testing and tensile testing of trepanned specimens. The final vessel configuration was analyzed at a reduced pressure for compliance to Section VIII, Division 2. It was then hydrotested and placed back into service, avoiding catastrophic failure.
Detection of Propagating Cracks in Rotors Using Neural Networks
Authors: Adewusi S. A. , Al-Bedoor B. O.
Published: August 2008

This paper presents the application of neural networks for rotor cracks detection. The basic working principles of neural networks are presented. Experimental vibration signals of rotors with and without a propagating crack were used to train the Multi-layer Feed-forward Neural Networks using back-propagation algorithm. The trained neural networks were tested with other set of vibration data. A simple two-layer feed-forward neural network with two neurons in the input layer and one neuron in the output layer trained with the signals of a cracked rotor and a normal rotor without a crack was found to be satisfactory in detecting a propagating crack. Trained three-layer networks were able to detect both the propagating and non-propagating cracks. The FFT of the vibration signals showing variation in amplitude of the harmonics as time progresses are also presented for comparison.
The Effect of Restraint Non-Linearity on the Instability of Growth of a Circumferential Through-Wall Crack in a Piping System
Authors: Smith E.
Published: August 2008

The paper is concerned with the criterion for the instability of growth of a circumferential through-wall crack in a piping system. A simple approach involves representing the cracked section behaviour by a moment (M)–rotation (φ) relation. The criterion for unstable crack growth is then L* > EI |dφ/dM| where E is Young’s modulus and I is the second moment of area of the piping at the cracked section. L* can be viewed as a crack-system compliance length parameter or an “effective” pipe length. If the piping system, apart from the cracked system, behaves in a linear manner, L* is dependent on the system’s characteristics but most importantly, is independent of the magnitudes of any applied loadings and the characteristics of the cracked section. This paper is concerned with the effect of system non-linearity, and in particular restraint non-linearity, on the instability criterion, the considerations being based on the analyses of a simple model which contains a restraint which behaves non-linearly. In this case, we show that L* is no longer dependent only on the system’s characteristics, as is the case when the restraint behaves linearly.
Integrated Leak Rate Testing of Containments: A Regulatory Perspective
Authors: Ashar Hans , Imbro Eugene , Terao David
Published: August 2008

Appendix J of 10 CFR 50, “Primary Reactor Containment Leakage Testing for Water-Cooled Power Reactors,” sets the testing requirements for preoperational and periodic verification of the leak-tight integrity of the primary reactor containment, including systems and components which penetrate containment of light water-cooled power reactors, and establishes the acceptance criteria for such tests. The purposes of the tests are to assure that leakage through the primary reactor containment and systems and components penetrating primary containment would not exceed allowable leakage rate values as specified in the plants’ technical specifications. The current Appendix J requirements provide two options for performing the tests. Option A (fully deterministic) requires that after the preoperational leakage rate tests, a set of three integrated leak rate tests (ILRT — termed as Type A tests) shall be performed, at approximately equal intervals during each 10-year service period. Option B does not provide a quantitative requirement for scheduling the periodic Type A tests. However, NEI 94-01, “Industry Guideline for Implementing Performance-Based Option of 10 CFR Part 50, Appendix J,” and NRC Regulatory Guide (RG). The containment is a vital engineering safety feature of a nuclear power plant. It encloses the entire reactor and reactor coolant system and serves as a final barrier against the release of radioactive fission products to the environment under various accident conditions. Containment design is based on pressure and temperature loadings associated with a loss-of-coolant-accident resulting from a double-ended rupture of the largest pipe in the reactor coolant system. Recently, it has been reported that in certain 1.163, “Performance-Based Containment Leak Test Program,” provide guidelines for determining the frequencies of preoperational and periodic leak rate tests using a performance based approach. The Option B requirements and NEI 94-01 guidance are based on NUREG-1493, “Performance Based Containment Leak-Test Program.” Based on the information provided by the operating data and their risk significance, the study calculated the change in risk (in person-rem) to public for the 15 alternatives considered in the study. However, recognizing the non-sensitivity of risk to change in Type A leak rate testing frequencies, as depicted in NUREG-1493, a number of licensees are proposing changes to their Type A test frequencies using NRC risk-informed guidance in RG 1.174, “An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis.” The paper discusses certain key deterministic aspects of the risk-informed decision for the plant-specific changes in the ILRT frequencies.
In-Situ Measurement of Thermowell Vibration During Production Train Pressurization
Authors: Finch Paul N. , Hamblin Michael G. , Constable Damien C.
Published: August 2008

Fatigue failure of intrusive fittings such as erosion probes, sample quills and thermowells, has occurred in Woodside’s offshore and onshore operations. The mechanism of failure is generally thought to be resonant vibration caused by vortex shedding. The consequence of these failures can be severe, in particular for thermowells, as they form part of the pressure envelope, and hydrocarbon release can result. Thermowells on the Goodwyn Alpha platform flow lines were designed to withstand the maximum normal operating flow velocities. During production train pressurisation, however, the thermowells can experience velocities higher than the design limit, albeit for a limited time. These start up flow velocities are likely to cause vortex shedding frequencies exceeding flowline thermowell resonant frequencies. If a vortex shedding frequency occurs that is close to a thermowell natural frequency, a vortex “lock on” resonance can occur, resulting in large amplitude thermowell vibration transverse to the flow direction. In order to determine if thermowell replacement was warranted, a study was undertaken to measure the thermowells in situ. The specific aims were: to determine if vortex “lock on” was occurring; and to determine what cyclic stresses are present. To do this, a novel vibration measurement probe was developed and commissioned. The probe is capable of measuring bidirectional acceleration in thermowells without the need for the thermowell to be taken offline. This paper presents the development of the probe and the results of the measurements during flowline pressurisation.
Elastic Shakedown in Pressure Vessel Components Under Non-Proportional Loading
Authors: Muscat Martin , Hamilton Robert
Published: August 2008

Bounding techniques for calculating shakedown loads are of great importance in design since this eliminates the need for performing full elasto-plastic cyclic loading analyses. The classical Melan’s lower bound theorem is widely used for calculating shakedown loads of pressure vessel components under proportional loading. Polizzotto extended the Melan’s theorem to the case of non-proportional loading acting on a structure. This paper presents a finite element method, based on Polizzotto’s theorem, to estimate the elastic shakedown load for a structure subjected to a combination of steady and cyclic mechanical loads. This method, called non-linear superposition, is then applied to investigate the shakedown behaviour of a pressure vessel component — a nozzle/cylinder intersection and that of a biaxially loaded square plate with a central hole. Results obtained for both problems are compared with those available in the literature and are verified by means of cyclic elasto-plastic finite element analysis.
Plastic Limit Solutions for Cracked Pipes Based on 3-D Finite Element Limit Analyses
Authors: Shim D. J. , Kim Y. J.
Published: August 2008

Based on detailed 3-D FE limit analyses, the present paper provides tractable approximations for plastic limit pressure solutions for axial through-wall cracked pipe; axial (inner) surface cracked pipe; circumferential through-wall cracked pipe; and circumferential (inner) surface cracked pipe. In particular, for surface crack problems, the effect of the crack shape, the semi-elliptical shape or the rectangular shape, on the limit pressure is quantified. Comparisons with existing analytical and empirical solutions show a large discrepancy in circumferential short through-wall cracks and in surface cracks (both axial and circumferential). Being based on detailed 3-D FE limit analysis, the present solutions are believed to be the most accurate, and thus to be valuable information not only for plastic collapse analysis of pressurized piping but also for estimating non-linear fracture mechanics parameters based on the reference stress approach.
Cross Property Correlations for Metals Subjected to Fatigue Damage Accumulation
Authors: Bogarapu Mahesh C. , Sevostianov Igor
Published: August 2008

A new method of evaluation of elastic property deterioration due to accumulated damage is suggested and experimentally verified. It is based on the explicit correlations between two groups of anisotropic properties – conductivity and elasticity, recently established for porous/microcracked materials with anisotropic microstructures. An experimental study of fatigue has been done to verify the theoretical predictions. The electrical resistance and Young’s modulus are measured as functions of the number of loading cycles in the standard fatigue tests. The agreement between the theoretical predictions and the direct experimental data is better than 10% in all cases. The results allow one to use the measurement of electric resistance to estimate the damage accumulated in metal structures and decrease in the elastic modulus.
Application of Surface Crack Analysis System ‘SCAN’ to Cracks at Hole
Authors: Seki Nagatoshi , Shiratori Masaki , Miyoshi Toshiro , Yamashita Youichi , Sakano Kenji
Published: August 2008

The authors have proposed an influence function method by which stress intensity factor, K, of surface cracks can be calculated easily 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. And they also have developed a software system “SCAN”, based upon the above developed database, by which K-values of surface cracks can be evaluated promptly, and further, fatigue crack propagation can be simulated easily by a personal computer. In this paper the authors have studied how they can apply the SCAN system to the problem of the surface cracks initiated from the edge of a circular hole of a rectangular plate. Since circular notches have various radiuses of curvature, the concentrated stress distribution at the notch root is different depending upon the radius of curvature. Therefore, strictly speaking, K-values have to be evaluated for each case, one by one, which means enormous amount of FEM analysis are necessary. But the authors have found that the database of a surface crack in a flat plate already installed in the SCAN system can be applied to this problem with satisfactory accuracy, which means the K-values of this problem can be evaluated promptly by the SCAN system.
Influence of Pad Reinforcement on the Limit and Burst Pressures of Large Diameter Cylindrical Shell Intersections
Authors: Xue L. , Widera G. E. O. , Sang Z. F.
Published: August 2008

The purpose of the paper is to provide some experimental results for the limit pressure of a vessel-nozzle intersection under internal pressure with a large pad-reinforced opening (d/D = 0.526). It is expected that the data obtained from the burst test will serve as the basis for the development of more accurate design guidelines for this type of reinforced intersection. A comparison of the limit and burst pressures with and without pad reinforcement is also carried out. The present test results indicate that pad reinforcement yields an effective improvement of the limit and burst pressures of a vessel.
Utilization of Micro-Electronic-Machine Systems (MEMS) to Possible Future Use in the Enhanced Analysis of Safety in Nuclear Power Plants
Authors: Bhavnani Anmol
Published: August 2008

The focal point of this paper is to go in-depth in to the potential utilization of MEMS to further enhance safety measures within nuclear power plants. Robots, which are being researched and developed in Sandia National Laboratories, sometimes built as small as the size of a pollen grain, can be utilized to constantly monitor the stress analysis within all aspects of running a Nuclear Power Plant. From cooling towers to detecting miniscule cracks within pipes, MEMS can be utilized to constantly detect and even possibly repair minor faults within the overall structure of a nuclear power plant. MEMS technologies provide the ability to reliably produce micro actuators and sensors to meet these mission requirements. MEMS technologies are also attracting an increasing interest from the commercial sector for various applications. Currently, Sandia National Laboratories has been developing MEMS technologies to support its core missions of weapon surety, stockpile maintenance, and national security interests. Already, the project has been responsible for numerous electromechanical systems in nuclear weapons, which ensure nuclear safety and provide reliable arming, fusing and firing. With these factors in consideration, the main idea of this paper is to present ideas for producing sensors and robots on a micro scale, which could be programmed to communicate and work within each other to have enhanced safety and efficiency within a nuclear power plant.
Determination of the Regional Function of the Heart
Authors: Azeloglu Evren U. , Gaudette Glenn R. , Krukenkamp Irvin B. , Chiang Fu-Pen
Published: August 2008

Unlike many other engineering designs, the heart, a pressure vessel, shows variations within its chambers and surface in terms of mechanical function. This necessitates a whole field technique with high spatial resolution. Computer aided speckle interferometry (CASI), a nondestructive examination technique, is herein developed for this purpose. A speckle pattern was created on the surface of isolated rabbit hearts. Images of the beating hearts werc acquired with a charge-couple device (CCD) camera for one second at a rate of 50 frames per second. CASI was used to determine the 2-D displacement vectors over regions of approximately 4 × 6 mm. Regional area stroke work (the integral of the left ventricular pressure with respect to area), the first invariant of the 2-D strain tensor, and the principle strains were used to determine the regional function. After occluding the blood supply to a region of the heart, significant changes were detected in all the previously mentioned parameters. Commonly used techniques cannot determine 2-D strain and lack the high spatial resolution of CASI. Determination of the 2-D strain can provide useful data on the functionality of the heart.
Probabilistic Site Identification Analysis Using NUPEC Recorded Free-Field Motions
Authors: Xu J. , Costantino C. , Hofmayer C. , Murphy A. , Kitada Y.
Published: August 2008

This paper describes a probabilistic site identification analysis performed by BNL, using the free-field earthquake motions recorded at the NUPEC test site. The BNL analysis was intended to provide adequate characterization of the soil properties for the test site to be used for the SSI analyses. The free-field data were provided by NUPEC. The methodology employed in the BNL probabilistic analysis of site identification includes the Monte Carlo process in conjunction with equivalent linear convolution analyses for generating a large number of site profiles for use in convolution studies from which mean estimates of response can be generated. The random variable selected to characterize the site profile is the shear wave velocity in each soil layer of the site profile. A lognormal distribution was assumed with the standard deviation determined from available site data and applicable regulatory requirements. The convolution analyses were performed using an appropriate soil degradation model and the outcrop input motions generated from the recorded in-rock motions. The BNL analysis produced results in terms of the mean, median and various fractiles of free-field soil properties at the test site, and the corresponding surface response spectra, which are presented in this paper.
The Best Practice Guidelines for CFD: A European Initiative on Quality and Trust (Keynote)
Authors: Wintergerste Torsten , Casey Michael , Hutton Anthony G.
Published: August 2008

In the industrial application of Computational Fluid Dynamics (CFD), the quality of simulations and the level of reliability of the results have emerged as major issues of concern. This paper describes a recent initiative of ERCOFTAC (European Research Community on Flow Turbulence and Combustion), involving European code developers, code vendors, academics and industrial users, to set up a practical set of standard guidelines to improve the quality of CFD simulations and to help in the assessment of the trustworthiness of the CFD results. The initiative led to the publication of the first edition of the ERCOFTAC Best Practice Guidelines (BPG) in January 2000. The BPG provide generic advice on how to perform quality CFD calculations. Some examples of typical guidelines from the BPG are provided in this paper.
A Technique for Specifying Region of Interest in the Vector Field Based on 3D LIC
Authors: Sakai Koji , Koyamada Koji , Kamisawa Kazuma , Doi Akio
Published: August 2008

Line integral convolution (LIC) is an effective and powerful technique for generating images from vector fields. In the 3D-LIC, it is very important to select an adequate region of interest (ROI) in the vector field. One way for specifying ROI is to use a surface defined in the vector field. Another way is to use a significance map that defines an ROI related value at each point in the vector field. To represent an anisotropic vector field around a vortex center in an understandable way, we introduced a time-oriented significance map. Our technique for specifying ROI is to use a passage-time for a mass-less particle to travel from nearby vortex center to a pixel location. In our technique, what we call “restricted LIC technique (RLIC),” refers to the passage-time buffer before we start the convolution process at a pixel location. The original RLIC technique is 2-D based. In this paper, we extend this technique to 3-D. To confirm the effectiveness of our technique, we use an anisotropic swirl vector field and construct two types of significance maps, a dlstance-oriented map and a time-oriented map. We will show the difference in the resulting images that are generated from these significance maps.
CFD-Code Evaluation for Complex Interior Flows
Authors: Herwig H. , Mocikat H. , Gu¨rtler T.
Published: August 2008

Measurements in a test facility for a complex interior flow are provided as a data basis for CFD code evaluation. For forced convection flows the three time averaged components of the velocity vector and all components of the Reynolds stress tensor are measured in selected cross sections. Special attention is given to the inflow into the main flow section since it is the important part of the boundary condition for a numerical solution.
A Technique for Skeletonizing a Scalar Field Using a Critical Point Graph: Application to a Weather Simulation
Authors: Kamisawa Kazuma , Sakai Koji , Koyamada Koji , Doi Akio
Published: August 2008

We present a visualization technique which a large scale detects the structure at all scales removing from the user the responsibility of extracting information implicit in the data, and presenting the structure explicitly for analysis and retrieval. In typical scientific applications, data is represented at the nodes of a mesh of elements and interpolated linearly across the interior of the elements. A critical point exists in the gradient field of the Scalar filed. It is possible at few cost to express the Scalar field using the graph which connected the critical point. In past, we proposed a technique for calculating isosurfaces efficiently using an extrema skeleton, which consists of elements and connects all extrema points [3]. In this algorithm, extrema points in a scalar field are first extracted. A graph is then generated in which the extrema points are taken as nodes. And our work can be regarded as an extension of our original technique, because our new skeleton connects saddle points in addition to extrema points. To confirm the effectiveness of our technique, we extract features skeletons of CFD results for forecasting weather and determine linear correlation between multiple scalar variables such as wind velocity, temperature, and humidity.
Convergence Acceleration of k-ω Turbulence Equations With Multigrid
Authors: Park Soo Hyung , Sung Chun-ho , Kwon Jang Hyuk
Published: August 2008

An efficient implicit multigrid method is presented for the Navier-Stokes and k-ω turbulence equations. Freezing and limiting strategies are applied to improve the robustness and convergence of the multigrid method. In this work, the eddy viscosity and strongly nonlinear production terms of turbulence are frozen in the coarser grids by passing down the values without update of them. The turbulence equations together with the Navier-Stokes equations, however, are consecutively solved on the coarser grids in a loosely coupled fashion. A simple limit for k is also introduced to circumvent slow-down of convergence. Numerical results for the unseparated and separated transonic airfoil flows show that all computations converge well to nine order of magnitude of error without any robustness problem and the computing time is reduced to a factor of about 3 by the present multigrid method.
Flow Visualization of the Evolution of Taylor Instabilities and Comparison With Numerical Simulations
Authors: Braun M. J. , Kudriavtsev Vladimir , Corder Rajka Krstic
Published: August 2008

The authors are presenting in this paper combined experimental and numerical results that bring up some less explored aspects the Taylor fluid instability. In fact the paper will concentrate on issues that explore flow formations on the road to the fully developed Taylor instability (500–1800 rpm). The experimental investigation uses the Full Flow Field Tracking {FFFT) method, developed at the University of Akron, to visualize the flow in longitudinal cross sections and at the same time correlate flow pattern observations to torque measurements. The experimental results indicate that incipient flow instabilities appear at lower speeds than the ones predicted by the critical Taylor number, and include formation of incipient Taylor cells that occupy only a part of the gap. The cells are separated by axially flowing narrow rope-like flowing streams that twist in a corkscrew fashion around the circumference, while separating the incipient cells. As the rotational velocities increase the Taylor cells keep growing until they occupy the entire gap. Three-dimensional CFD studies were also performed for the matching set of conditions and for the higher rotational velocities (above <1500 rpm), where experimental studies were not possible. The torque computed by the numerical model was compared with the experimentally obtained torque and the two results compare very favorably. Numerical simulation studies allowed an in-depth study of the flow mechanisms and trajectories inside the fully formed vortical Taylor instabilities. Computational studies were performed using CFD-ACE+ software package (CFD Research Corp, Huntsville, USA).
Simulation of Artificial Turbulence by the Vortex Method
Authors: Ogami Yoshifumi , Nishiwaki Kazuie , Yoshihara Yoshinobu
Published: August 2008

First, a simple and accurate numerical method is presented to produce velocity fluctuations that are determined by the prescribed physical quantities and qualities of turbulence such as longitudinal and lateral spectra, and integral scales. The fluctuations are obtained by solving a system of nonlinear equations that are derived from the equations of energy spectra and of root mean square of the fluctuations. This method requires as many computer memories and computations as one-dimensional case even for the three dimensional calculations. It is shown that there is a strong resemblance of the simulated velocity fluctuations and experimental data. The energy spectra of these velocity fluctuations are quite accurate with less than 0.01% relative errors to the prescribed spectra. Secondly, these solutions are used to examine the capability of the vortex methods to produce turbulent flows with the prescribed parameters. It is found that although the energy spectra by the vortex method scatter to some extent, they are distributed along the prescribed spectra. It can be said that the vortex methods are able to simulate the target turbulence fairly well. Also it is found that the solutions with the LES model increase and deviate from the target spectrum at the higher frequency regions. This may suggest the nonessentiality of the LES model for the vortex method.
A Three Dimensional Simulation Model for Liquid Phase Electroepitaxy Under Magnetic Field
Authors: Liu Yoncai , Sheibani Hamdi , Sakai Susumu , Okano Yasunori , Dost Sadik
Published: August 2008

A three-dimensional numerical simulation for the Liquid Phase Electroepitaxial (LPEE) growth of GaAs under a vertical stationary magnetic field was carried out. The effect of magnetic field intensity on the flow field in the liquid solution was investigated. Numerical results show that the flow patterns exhibit three distinct stability characteristics: a stable flow field up to a magnetic field level of Ha = 150, a transitional flow between Ha = 150 and Ha = 220, and an unstable flow above Ha = 220. In the stable region, the applied magnetic field suppresses the flow field, and the flow intensity decreases with increasing magnetic field. In the transitional region, the flow intensity increases dramatically with increase in the magnetic field strength. The flow patterns are significantly different from those in the stable region. The flow field is no longer axisymmetric but still stable. In the unstable region, the flow structure and intensity change with time. Under a strong magnetic field, the flow cells are confined to the vicinity of the vertical wall and exhibit significant non-uniformity near the growth interface. Such strong flow fluctuations and non-uniformities near the growth interface may have an adverse effect on the growth process and lead to an unsatisfactory growth.
Three-Dimensional Numerical Analyses on Liquid-Metal Magnetohydrodynamic Flow in Magnetic-Field Inlet-Region
Authors: Kumamaru Hiroshige
Published: August 2008

Three-dimensional numerical calculations have been performed on liquid-metal magnetohydrodynamic (MHD) flow through a rectangular channel in the inlet region of the magnetic field, including a region upstream the applied magnetic field section. The continuity equation, the momentum equation and the induction equation have been solved numerically by the finite difference method. Along the flow axis (i.e. the channel axis), the pressure decreases slightly as normal non-MHD flow, increases once, thereafter decreases sharply and finally decreases gradually as fully-developed MHD flow. The sharp decrease in the pressure in the inlet region is due to increase in the induced electric current in this region comparing with that in the fully-developed region. The flow velocity distribution also changes gradually from a parabolic profile of a laminar flow to a flat profile of a fully-developed MHD flow.
Numerical Analysis of Air Convection in a Vertical Cylindrical Container With and Without a Gravitational Field Under a Gradient of a Magnetic Field
Authors: Akamatsu Masato , Higano Mitsuo , Takahashi Yoshio , Ozoe Hiroyuki
Published: August 2008

Two-dimensional numerical computations were carried out for natural convection of air in a vertical cylindrical container with and without a gravitational field under a gradient of a magnetic field. The magnetic field and the magnetizing force were induced in the cylinder area and the strength and the vectors of the magnetizing force were dependent on the axial location of the electric coil. Sample computations were carried out by changing the relative orientation of an electric coil and container. In a gravitational field, air in a cylindrical container was driven by both gravitational and magnetizing forces. On the other hand, the air flow was induced by the magnetizing force even in a non-gravitational field. Flow pattern and the heat transfer rate greatly depended on the axial position of the electric coil under both gravitational and non-gravitational fields.
Multi-Scale and Multi-Hierarchy Modeling in Electronic Materials Processing (Keynote)
Authors: Masi Maurizio , Cavallotti Carlo , Valente Gianluca , Di Stanislao Marco
Published: August 2008

Modern material science and engineering rely on models based on fundamental laws to link material structure and properties to the many parameters that control the adopted production process. Unfortunately, the full comprehension of the main features characterizing the synthesis of these materials is complicated by the fact that chemical and physical events occur at length scales differing for even some orders of magnitudes. An example well suited to illustrate these aspects is represented by the solid films deposition by means of chemical vapor deposition processes. There, the characteristic length ranges from the nanometers up the centimeters, going by through the microns. The former is the scale at which the chemical phenomena can be described through quantum chemical methods, the latter is that where the overall reactor behavior can be depicted. The meso-scales are instead of interest to describe aspect interesting the collective surface behavior, like the description of the trench filling, the obtained film morphology or the various types of defects formation. Here, different mathematical models suitable to study the mentioned multi-scale phenomena and the hierarchy that can be adopted to their link will be reviewed with particular reference to silicon film deposition processes of interest for the microelectronic industry.
Simulation of Silicon Dioxide Deposition in a Vertical 300 mm LPCVD Furnace
Authors: Schoof G. J. , Kleijn C. R. , Van den Akker H. E. A. , Oosterlaken T. G. M. , Terhorst H. J. C. M. , Huussen F.
Published: August 2008

Combining the chemical reaction mechanism for silicon-dioxide LPCVD from TEOS, as proposed by Coltrin and coworkers, and the commercially available CFD program CFD-ACE+, 2-D and 3-D models have been constructed for the gas flow, multi-component transport phenomena, gas phase chemistry and deposition chemistry in a vertical LPCVD reactor for batches of 120 wafers with 300 mm diameter. Deposition rates and uniformities on different wafers in the batch have been studied for various temperatures, pressures and flowrates, and simulation results have been validated against experimental data. Silicon-dioxide deposition from TEOS is found to be strongly influenced by gas-phase reactions, producing a reactive intermediate that is responsible for the majority of deposition. The amount of intermediate formed depends on reactor geometry and on process conditions. Large amounts of intermediate are found in regions with large local volume-to-surface ratios. Our 2-D simulations were capable of accurately predicting wafer averaged growth rates, as well as trends in deposition uniformities, for various process conditions. Intra-wafer uniformity was found to improve for reduced pressure, reduced temperature and increased TEOS flowrate. Increasing the volume-to-surface ratio by increasing the reactor diameter at fixed wafer packing density and fixed wafer diameter was found to lead to strongly increased growth rates and non-uniformities, due to increased intermediate formation. The quantitative disagreement between predicted and and experimental radial growth profiles is probably due to simplifications in the 2-D representation of the reactor geometry. Better agreement was found in preliminary 3-D simulations.
A Newton-Krylov Based Solver for Modeling Finite Rate Chemistry
Authors: Wang David H. , Bockelie Michael J. , Cremer Marc A. , Chen J.-Y.
Published: August 2008

To date, computational fluid dynamics (CFD) codes aimed at solving practical engineering problems involving chemically reacting flow have incorporated relatively simple descriptions of the chemical mechanisms involved. Techniques are now available to create reduced mechanisms that faithfully represent detailed chemical descriptions over an appropriate range of conditions using many fewer species. However, including reduced mechanisms into a CFD analysis typically leads to numerical difficulties. In a recent project, a new modeling tool was created that utilizes a combination of state-of-the-art techniques used by Reaction Engineering International (REI) for modeling finite rate chemistry in chemically reacting flows using reduced mechanisms with emerging Newton-Krylov methods for solving systems of non-linear equations. For tests problems ranging from geometrically simple combustion problems to full-scale utility boiler simulations, the Newton-Krylov solver has reduced the CPU time to achieve a solution by up to 60% compared to our traditional Picard iteration method. This paper discusses the implementation of the Newton-Krylov solver into the REI combustion code, the impact of parameters on the performance of the Newton-Krylov solver for solving problems using reduced mechanisms, and demonstration of the Newton-Krylov solver on full-scale utility boiler NOx simulations.
Numerical Modeling of Combustion Processes and Pollutants Formation in Direct Injection Diesel Engine
Authors: Kim Hoo-Joong , Heo Nam-Il , Kim Yong-Mo , Kang Sung-Mo , Ahn Jae-Hyun
Published: August 2008

The Representative Interactive Flamelet (RIF) concept has been applied to numerically simulate the combustion processes and pollutant formation in the direct injection diesel engine. Due to the ability for interactively describing the transient behaviors of local flame structures with CFD solver, the RIF concept has the capabilities to predict the auto-ignition and subsequent flame propagation in the diesel engine combustion chamber as well as to effectively account for the detailed mechanisms of soot formation, NOx formation including thermal NO path, prompt and nitrous NOx formation, and reburning process. Special emphasis is given to the turbulent combustion model which properly accounts for vaporization effects on the mixture fraction fluctuations and the pdf model. The results of numerical modeling using the RIF concept are compared with experimental data and with numerical results of the commonly applied procedure which the low-temperature and high-temperature oxidation processes are represented by the Shell ignition model and the eddy dissipation model, respectively. Numerical results indicate that the RIF approach including the vaporization effect on turbulent spray combustion process successfully predicts the ignition delay time and location as well as the pollutant formation.
Multiscale Analysis of Nonequilibrium Rarefied Gas Flows (Keynote)
Authors: Matsumoto Yoichiro , Sakiyama Yukinori
Published: August 2008

The practical method for solving the nonequilibrium rarefied gas flows is introduced in this paper. This method based on the multi-scale analysis connects the thermofluid phenomena that occur in the different time scale and spatial scale by constructing the reasonable physical model among them. As a example of the analysis, the molecular collision of silane gas, which is widely used in the semiconductor manufacturing process, is considered here. First, the new site-to-site intermolecular potential model is determined from the accurate ab initio molecular orbital (MO) calculations. Next, the collision models such as the collision cross section and the scattering angle are constructed by the statistical analysis of classical trajectory (CT) calculations using the new potential model. Finally, these collision models are applied into the direct simulation Monte Carlo (DSMC) calculation. In this way, this multi-scale model does not require the empirical parameters such as the transport coefficients and widely applicable to the various rarefied gas flows including the nonequilibrium of flow filed.
Density Distribution in Stagnation Region of Saffman Equation for Dusty Gas
Authors: Tsuboi Kazuhiro
Published: August 2008

We investigate the behaviour of flow field around an obstacle placed in uniform particle flow based on two-fluid Saffman equation. Particle density in the vicinity of the front stagnation point is, in particular, the primary interest in the present study. In the case of small Stokes number, in which particle impingement does not occur, there exists the exact solution of the flow field of particle phase is obtained. Perturbed solution is also obtained in the reciprocal of Stokes number when Stokes number is large enough. Comparison between numerical results and these solutions shows good agreement and the peak of particle density appears near the threshold of partide impingement to the body surface.