bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Study and Analysis of Different Air-Injecting Segment on the Separation Performance of Air-Injected De-Oiling Hydrocyclone
Authors: Jiang Minghu , Chen Dehai , Zhao Lixin , Sun Liying
Published: July 2009

Developing state-of-the-art and separating principle of deoiling hydrocyclones are introduced. By theoretical analysis, the ways to enhance hydrocyclone’s separation efficiency are described. One way is to inject air into the hydrocyclones so as to combine with oil to form oil-gas compound body, and then increase de-oiling efficiency. By means of injecting air into large cone segment, or fine cone segment of the hydrocyclone, experiments were carried out. It is found that the best injecting part is fine cone segment. Further experimental studies were continued for confirming detail part in fine cone segment, which includes one-third segment and two-thirds segment for the sake of research. Results show that the best air-injecting part is the first one-third segment of fine cone segment. This conclusion would be useful for understanding of air-injected de-oiling hydrocyclone’s separating process, and for its design and applications.
Wave Energy Resource Assessment Using Satellite Altimeter Data
Authors: Mackay Ed , Bahaj AbuBakr , Retzler Chris , Challenor Peter
Published: July 2009

The use of altimeter measurements of significant wave height and energy period for quantifying wave energy resource is investigated. A new algorithm for calculating wave period from altimeter data, developed by the authors in previous work, is used to estimate the power generated by the Pelamis wave energy converter and compared to estimates from collocated buoy data. In offshore locations accurate estimates of monthly and annual mean power can be achieved by combining measurements from six altimeter missions. Furthermore, by averaging along sections of the altimeter ground track, we demonstrate that it is possible to gauge the spatial variability in nearshore areas, with a resolution of the order of 10 km. Although measurements along individual tracks are temporally sparse, with TOPEX/Poseidon and Jason on a 10 day repeat orbit, GFO 17 days, and ERS-2 and ENVISAT 35 days, the long record of altimeter measurements means that multi-year mean power from single tracks are of a useful accuracy.
Enhanced Design Criteria for Offshore Pipeline Integral Buckle Arrestors
Authors: Lee L.-H. , Kyriakides S. , Netto T. A.
Published: July 2009

Integral buckle arrestors are relatively thick-wall rings periodically welded in an offshore pipeline at intervals of several hundred meters in order to safeguard the line in the event a propagating buckle initiates. They provide additional circumferential rigidity and thus impede downstream propagation of collapse, limiting the damage to the length of pipe separating two arrestors. The effectiveness of such devices was studied parametrically through experiment and numerical simulations in Park and Kyriakides [2]. The experiments involved quasi-static propagation of collapse towards an arrestor, engagement of the arrestor, temporary arrest, and the eventual crossing of collapse to the downstream pipe at a higher pressure. The same processes were simulated with finite element models that included finite deformation plasticity and contact. The experimental crossover pressures enriched with numerically generated values were used to develop an empirical design formula for the arresting efficiency of such devices. A recent experimental extension of this work revealed that for some combinations of arrestor and pipe yield stresses the design formula was overly conservative. Motivated by this finding, a new broader parametric study of the problem was undertaken which demonstrated that the difference between the pipe and arrestor yield stress affects significantly the arrestor performance. The original arrestor design formula was then modified to include the new experimental and numerical results producing an expression with a much wider applicability.
Nonlinear Dynamic Analysis of Flexible Riser Structures
Authors: Hosseini Kordkheili S. A. , Bahai H.
Published: July 2009

An updated Lagrangian finite element formulation of a three-dimensional pipe elbow element is presented for large displacement and large rotation dynamic analysis. In this formulation a particular linearization method is used to avoid inaccuracies normally associated with the linearization schemes. The formulation has been implemented in a nonlinear finite element code and the results are verified. It is shown that the proposed formulation generates improved results over those previously reported in the literature.
Induced Separation and Vorticity Using Roughness in VIV of Circular Cylinders at 8×103 < Re < 2.0×105
Authors: Bernitsas Michael M. , Raghavan Kamaldev , Duchene G.
Published: July 2009

Results of an experimental investigation on fluid flow past an elastically mounted circular cylinder with rectangular surface roughness strips are presented. Flow characteristics change depending on the strip width, roughness grit size, and location. Roughness size and distribution can be designed to enhance or reduce/suppress VIV amplitude and increase or reduce the range of synchronization, respectively. To the authors’ knowledge this is the first study in passive control of VIV using properly distributed roughness.
Energy Extraction Through Flapping Foils
Authors: Simpson Bradley J. , Licht Stephen , Hover Franz S. , Triantafyllou Michael S.
Published: July 2009

We demonstrate experimentally that flapping foils within an oncoming stream can efficiently extract energy from the flow, thus offering an attractive, alternative way for energy production. The greatest promise for flapping foils is to use them in unsteady and turbulent flow, where their own unsteady motion can be controlled to maximize energy extraction. The foils in this study perform a sinusoidal linear motion (sway, or heave) in combination with a sinusoidal angular motion (yaw or pitch); the effect of three principal parameters is studied systematically, yaw amplitude, the Strouhal number, and the phase angle between sway and yaw. The foils are made of aluminum, in the shape of NACA 0012 airfoils, using three different aspect ratios, 4.1, 5.9, and 7.9; they were tested at Reynolds numbers around 14,000. Efficiencies of up to 52 ± 3% are achieved with simple sinusoidal motions, thus demonstrating that foils can efficiently extract energy from unsteady flows.
Preliminary Considerations of Modified 9Cr-1Mo Steel for Gen IV Nuclear Reactor Application
Authors: Ren Weiju
Published: July 2009

Modified 9Cr-1Mo steel is currently identified as one of the leading candidate materials in the down selection for construction of the Gen IV nuclear reactor pressure vessel. Because of the stringent requirements in strength, size, safety, design life, and maintenance for the intended nuclear application, qualification of the material demands scrutiny in various aspects such as mechanical properties, data sufficiency, Codification, mechanical behavior modeling, metallurgical stability, environmental resistance, component manufacturability and transportation. In the present paper, history of the material development is briefly reviewed; requirements and challenges for the intended application are discussed; available information on the material is described. Further research and development activities are suggested to facilitate the materials selection.
Shock Reflection at Interface of Bubbly Liquid
Authors: Moody F. J.
Published: July 2009

The reflection of a shock wave at a gas/liquid interface in a pipe is a design consideration in several industries. The transmitted and reflected shock pressures at a pure liquid interface can be six or more times as large as the initial shock, and creates proportionally large loads on the piping. Calculations shows that the magnitude of the transmitted and reflected shocks from the interface of a bubbly mixture is close to the same magnitude as if reflection occurred from a pure liquid interface, until the mixture void fraction is increased to nearly 90 percent, at which the mixture is becoming a froth.
Comparison of Response of 9977 Test Packages to Analytical Results
Authors: Smith Allen C. , Wu Tsu-Te
Published: July 2009

Each of the hypothetical accident test cases for the 9977 prototypes was included in the battery of finite element structural analyses performed for the package. Comparison of the experimental and analytical results provides a means of confirming that the analytical model correctly represents the physical behavior of the package. The ability of the analytical model to correctly predict the performance of the foam overpack material for the crush test is of particular interest. The dissipation of energy in the crushing process determines the deceleration of the package upon impact and the duration of the impact. In addition, if the analytical model correctly models the foam behavior., the predicted deformation of the package will match that measured on the test articles. This study compares the impact acceleration and impact duration for the test articles with those predicted by the analyses. In addition, the deformations of the test packages with the analytical predictions are compared.
Design Parameters Effect on Load Distribution Around the Hole in Mechanically Fastened Pinned Connections
Authors: Yavari Vahid , Daneshvar Farshad , Kadivar Mohammad-Hassan , Rajabi Iraj
Published: July 2009

The pinned connection is a principal joining element in many structures. In this article, we present two-dimensional stress analyses for isotropic plate with a pinned circular hole. A study of the pin and the plate material dissimilarity was done by Iyer [6] but still different aspects of the problem are remained to be mentioned. In this work different issues of mechanical engineering interests such as stress distribution in contact area and the magnitude and location of maximum contact pressure and tangential stress are computed with the aid of commercial software ABAQUS 6.6-1 finite element code [7]. In order to have a good evaluation of the stress distribution around the hole, design factors such as plate width to hole diameter ratio (w/d), edge distance to hole diameter ratio (e/d), clearance at the connection area and the contact friction coefficient (μ) were systematically varied during analyses from 2 to 5, 3 to 6, 5% to 25% and 0 to 0.5 respectively. A Coulomb-type friction model is used to simulate the frictional contact at the pin-plate interface. The results obtained in this paper are compared to those available from the paper published by Iyer [6]. Based on the results, it is observed that higher friction at contact interface makes the joints more safe by reducing the peak contact pressure; the same is concluded by reducing the plate width.
Coupled Finite Element Based Lattice Boltzmann Equation and Structural Finite Elements for Fluid-Structure Interaction Application
Authors: Kwon Y. W. , Jo J. C.
Published: July 2009

A computational technique was developed for analysis of fluid-structure interaction. The fluid flow was solved using the lattice Boltzmann method which found to be computationally simple and efficient. In order to apply the lattice Boltzmann method to irregular shapes of fluid domains, the finite element based lattice Boltzmann method was developed. In addition, the turbulent model was also implemented into the lattice Boltzmann formulation. Structures were analyzed using either beam or shell elements depending of the nature of the structures. Then, coupled transient fluid flow and structural dynamics were solved one after another for each time step. Numerical examples for both 2-D and 3-D fluid-structure interaction problems were presented to demonstrate the developed techniques.
Modeling and Verification of Creep Strain and Exhaustion in a Welded Steam Mixer
Authors: Holmstro¨m Stefan , Laukkanen Anssi , Rantala Juhani , Kolari Kari , Keina¨nen Heikki , Lehtinen Olli
Published: July 2009

Structures operating in the creep regime will consume their creep life at a greater rate in locations where the stress state is aggravated by triaxiality constraints. Many structures, such as the welded steam mixer studied here, also have multiple material zones differing in microstructure and material properties. The 3-dimensional structure as such in addition to interacting material zones is a great challenge for finite element analysis (FEA), even to accurately pinpoint the critical locations where damage will be found. The studied steam mixer, made of 10CrMo 9-10 steel (P22), has after 100 000 hours of service developed severe creep damage in the several saddle point positions adjacent to nozzle welds. FE-simulation of long term behaviour of this structure has been performed taking developing triaxiality constraints, material zones and primary to tertiary creep regimes into account. The creep strain rate formulation is based on the logistic creep strain prediction (LCSP) model implemented to ABAQUS, including primary, secondary and tertiary creep. The results are presented using a filtering technique utilising the formulation of rigid plastic deformation for describing and quantifying the developing “creep exhaustion”.
3-D Stress Intensity Factors for Arrays of Inner Radial Lunular or Crescentic Cracks in Thin and Thick-Walled Spherical Pressure Vessels
Authors: Perl M. , Bernstein V.
Published: July 2009

Some spherical pressure vessels are manufactured by methods such as the Integrated Hydro-Bulge Forming (IHBF) method, where the sphere is composed of a series of double curved petals welded along their meridional lines. Such vessels are susceptible to multiple radial cracking along the welds. For fatigue life assessment and fracture endurance of such vessels one needs to evaluate the Stress Intensity Factors (SIF) distribution along the fronts of these cracks. However, to date, only one 3-D solution for the SIF for a circumferential crack in a thick sphere is available, as well as 2-D SIFs for one through the thickness crack in thin spherical shells. In the present paper, mode I SIF distributions for a wide range of lunular and crescentic cracks are evaluated. The 3-D analysis is performed, via the FE method employing singular elements along the crack front, for five geometries representing thin, moderately thick, and thick spherical pressure vessels with outer to inner radius ratios of η = Ro/Ri = 1.01, 1.05, 1.1, 1.7, and 2.0. SIFs are evaluated for arrays containing n = 1–20 cracks; for a wide range of crack depth to wall thickness ratio, a/t, from 0.025 to 0.95; and for various ellipticities of the crack, i.e., the ratio of crack depth to semi crack length, a/c, from 0.2 to 1.5. The obtained results clearly indicate that the SIFs are considerably affected by the three-dimensionality of the problem and by the following parameters: the geometry of the sphere-η, the number of cracks in the array-n, the depth of the cracks-a/t, and their ellipticity-a/c.
Effect of Dynamic Loading Rates on Cleavage Fracture Toughness Properties of Steels
Authors: Moskovic Robert , Joyce James A.
Published: July 2009

The effect of dynamic loading on cleavage fracture toughness of ferritic steels is an important factor in structural integrity assessments. To address this issue, statistical analyses were carried out on a cleavage fracture toughness database obtained for a range of loading rates for deeply cracked 10mm thick pre-cracked Charpy V notch specimens and nominally 25mm thick compact tension specimens. Additional analyses were performed on shallow cracked three point bend specimens, 25mm thick, to establish whether the effect of dynamic loading rates on cleavage fracture toughness varies with crack to width ratio. The statistical analyses employ a model in which logarithm of cleavage fracture toughness varies linearly with temperature. The logarithm of cleavage fracture toughness is initially modeled as being linearly dependent on the loading rate but the analyses show that a non linear dependence is more appropriate. The effect of specimen thickness on cleavage fracture toughness is found to be negligible at dynamic loading rates when displacement rate is used as a variable in the analyses. The displacement rates applied during testing were converted into stress intensity rates and statistical analyses were performed to establish the dependence of cleavage fracture toughness on stress intensity rate.
Mechanically-Based Calibration of Ductile Fracture Models
Authors: Taylor Kerry L. , Sherry Andrew H. , Goldthorpe Martin R.
Published: July 2009

Cracks in high pressure plant are often associated with welds, where residual stresses can enhance the crack driving force due to primary loading acting alone. One approach for taking account of the influence of residual stresses on defect behaviour in ductile materials is to use ductile damage mechanics. This paper presents a mechanistic study aimed at using metallographic and fractographic observations of as-received and tested material as the basis for calibrating of the Gurson ductile damage mechanics with a view to applying the calibrated model to predict residual stress effects on the ductile tearing behaviour of a high strength, low toughness 2024-T351 aluminium alloy. Detailed examination of notched tensile test specimens has clarified that two populations of second phase particles are involved in the failure process. Large intergranular intermetallic precipitates between 5 and 10 μm in diameter fracture at low strains, creating isolated microscale voids that grow under increasing plastic strain. Subsequently, a much finer array of intragranular precipitates approximately 100 to 500 nm in diameter fail at high plastic strains, leading to the formation of an almost instantaneous sheet of nanoscale voids that cause the sudden final failure of the material. Results are presented from a series of finite element analyses of these tests incorporating Gurson parameters associated with either the microscale or the nanoscale damage. These analyses demonstrate that modelling the nanoscale damage provides far better agreement with the experimental data that simulating the microscale damage. The implications of this observation on the modelling of pre-cracked specimens are discussed.
Robust Design of Passive Suspension System of Half Railway Vehicles via Control Theory
Authors: Nguyen Chi Hung , Sone Akira , Iba Daisuke , Masuda Arata
Published: July 2009

This study deals with the robust design in designing passive suspension system of half railway vehicles via feedback control theory. This design with robustness performance is examined in the change of body weight corresponding to full and empty load of vehicle. These two states of system can be described by two sets of equations of motion that can be extended as one control object, and the controller designed by feedback control theory will control this extended model. By applying feedback control theory, parameter selection and optimization of a huge class of passive suspension system becomes a structural control problem. Since minimizing ℋ∞ norm of the system implies suppressing the peak of the magnitude of frequency response of the extended system, parameters selection of passive suspension systems becomes an ℋ∞ static output feedback problem, which turns into Bilinear Matrix Inequality (BMI) problem. One of simple methods to solve BMI problem is alternative algorithm which is derived from iterative schemes of alternation between analysis and synthesis via Linear Matrix Inequalities (LMIs). The effectiveness of vibration reduction is simulated by MATLAB software.
Regulatory Aspects on the Application of the Leak Before Break Concept for Swedish Nuclear Power Plants
Authors: Brickstad B.
Published: July 2009

The SKI regulation SKIFS 2004:2 allows for the use of Leak Before Break (LBB) as one way to provide assurance that adequate protection exists against the local dynamic consequences of a pipe break. The way to demonstrate that LBB prevails relies on a deterministic procedure for which a leakage crack is postulated in certain sections of the pipe based on the leak detection capability of the plant. It shall then be demonstrated that certain margins exist against the critical crack length at which a pipe break can be expected. In certain situations, probabilistic methods can strengthen the conclusion that LBB prevails. Then it is necessary to demonstrate that the likelihood of a pipe failure is sufficiently low and that there is a sufficient margin between a detectable leak and pipe rupture. This paper provides some general regulatory aspects on the application of LBB as well as results from two recently completed research projects. The first one is investigating the influence on the deterministic LBB-margins from different assumptions of the crack morphology. The second project provides information on failure probabilities for both leak and rupture for pipes of different sizes in Swedish PWR- and BWR-plants. The interest is focused on the conditional rupture probability corresponding to when the deterministic LBB-margins are fulfilled. Finally some results of failure probability for pipes with stress corrosion cracking are discussed.
Further Studies of Multiple Co-Planar Surface Breaking Flaws for Cleavage Fracture
Authors: Sharples J. K. , Wilkes M. A. , Beardsmore D. W. , Melvin G. T. , Jackson M.
Published: July 2009

In assessing the integrity of structures, complex multiple flaws located in close proximity to each other are generally characterised as one, larger, single flaw. Guidance for the characterisation of multiple flaws is provided in procedures such as R6 and BS 7910, which are routinely used in the UK and elsewhere in the structural integrity assessment of structures and components. For this approach to be valid, the characterisation process must be conservative. That is to say, the probability of failure must be higher for the characterised flaw than for the system of multiple flaws. However, previous studies showed that the current characterisation rules may be non-conservative under some circumstances, in particular under cleavage fracture conditions. A combined experimental and analytical programme of work has been undertaken within the UK in order to further investigate this potential non-conservatism for situations where the possibility of cleavage failure may have to be taken into account when assessing structures or components containing multiple flaws. Details of early stages of the analytical programme were reported at the 2006 and 2007 ASME PVP Conferences and comprised a number of finite element analyses to evaluate cleavage failure probability, via a Master Curve-based approach, for interacting twin flaws and the corresponding characterised single flaw, under applied tensile and bending loads, at low temperatures. These analyses considered surface-breaking semi-elliptical flaws all having the same depth, but with four different aspect ratios. For each aspect ratio the separation of the twin flaws was varied. It was found that non-conservatism of the characterisation rules was indicated for flaws of high depth to length aspect ratio (a/c) in contact. This paper describes further work that has been undertaken to extend the results previously reported. The further work described has been centred on: • for the most onerous aspect ratio (a/c = 1.0) extending the experimental results to higher temperatures in the cleavage transition regime. • performing finite element analyses to complement these experiments. • revisiting the methods for calculation of cleavage failure probability to obtain improved agreement with the experimental results. • examining the rules governing the characterisation process, to determine if modification is necessary.
UK Research Programme on Residual Stresses: A Review of Progress
Authors: Bate S. K. , Hurrell P. , Francis J. A. , Turski M.
Published: July 2009

A long-term UK research programme on residual stresses was launched in 2004. It involves Rolls-Royce plc and Serco Assurance, supported by UK industry and academia. The programme is aimed at progressing the understanding of weld residual stresses and the implementation of finite element simulation and residual stress measurement for assessing the integrity of engineering structures. Following on from this, the intention is then to develop improved guidance on residual stress modelling techniques and then to provide methods and analysis tools for design in order to control and minimise residual stress. The focus of the work to date has been to develop modelling guidelines which can be used by a finite element analyst to predict the residual stresses in austenitic welded components. These guidelines are now drafted and will be incorporated into the next issue of the British Energy R6 defect assessment procedure following peer review. The guidelines have been developed based on the experience that has been attained using various modelling techniques. To support this development, a series of welded mock-ups have been manufactured. The residual stresses in these welds have been measured using various techniques (diffraction and strain relaxation). These measurements are being used to validate the predicted stresses. It is only by corroborating each other that the resulting residual stresses can be confidently used for assessment. Mock-ups are also being used to develop material models for ferritic steel which undergo phase transformations, and to investigate how various weld parameters affect the magnitude and distribution of residual stress. Similarly, mock-ups have been manufactured to investigate the effect of start-stops on residual stresses. The programme is also supported by experimental testing to develop physical and mechanical properties which are required for analysis, i.e. up to melting temperature. Both conventional and miniaturised testing has been used to measure properties in ferritic and austenitic steels. A task has also been undertaken to develop a methodology for providing upper bound residual stress profiles which can be used as an initial estimate of stress for use in structural assessment.
Effect of Ultrasonic Impact Treatment on the Stress Corrosion Cracking of 304 Stainless Steel Welded Joints
Authors: Ma Gang , Ling Xiang
Published: July 2009

High tensile weld residual stress is an important factor contributing to stress corrosion cracking (SCC). Ultrasonic impact treatment (UIT) can produce compressive stresses on the surface of welded joints that negate the tensile stresses to enhance the SCC resistance of welded joints. In the present work, X-ray diffraction method was used to obtain the distribution of residual stress induced by UIT. The results showed that UIT could cause a large compressive residual stress up to 325.9MPa on the surface of the material. A 3D finite element model was established to simulate the UIT process by using a finite element software ABAQUS. The residual stress distribution of the AISI 304 stainless steel induced by UIT was predicted by finite element analysis. In order to demonstrate the improvement of the SCC resistance of the welded joints, the specimens were immersed in boiling 42% magnesium chloride solution during SCC testing, and untreated specimen cracked after immersion for 23 hours. In contrast, treated specimens with different coverage were tested for 1000 hours without visible stress corrosion cracks. The microstructure observation results revealed that a hardened layer was formed on the surface and the initial coarse-grained structure in the surface was refined into ultrafine grains. The above results indicate that UIT is an effective approach for protecting weldments against SCC.
Probabilistic Modeling of Crack Networks in Thermal Fatigue
Authors: Male´sys Nicolas , Vincent Ludovic , Hild Franc¸ois
Published: July 2009

A probabilistic model is proposed to predict the formation and propagation of crack networks in thermal fatigue. It is based on a random distribution of sites where cracks form and on the shielding phenomenon corresponding to the relaxed stress field created around propagating cracks. The stress gradient that arises under a surface submitted to thermal shocks is accounted for as well as multiaxial stress states. Experiments using digital image correlation have been performed to introduce the hypotheses made herein, and others to identify the parameters of the crack density as a function of the stress range and the number of cycles. Simulations of the formation of crack networks in a heterogeneous biaxial state of stress are carried out. A good qualitative agreement is obtained with existing thermal fatigue experiments especially considering the effect of the stress range on the crack densities as well as on the distribution of crack sizes.
Simulation of Leakage Behavior on Bolted Flanged Connections in Elevated Temperature Service
Authors: Ando Fumio , Ido Yasuji , Oginuma Tsuneo
Published: July 2009

Many leakage troubles were reported in petroleum and petrochemical refineries for bolted flanged connections in elevated temperature service due to the effect of differential thermal expansion in flanges, bolts, gasket, and so on as an assembly. The leakages were found especially in shut down condition for petroleum refineries and chemical plants, even if the weather seal (rain cover) was installed to prevent the flange assembly from rapid cooling by wind or rain. On the other hand, the leakage mechanism of the bolted flanged connections with weather seal under the condition of wind flow is not still clearly understood. Therefore, the leakage behavior on bolted flanged connections is investigated using the latest computerized fluid dynamics (CFD) and the structural thermal analysis with nonlinear material properties in flange and gasket (FEM: Finite Element Method). The actual environmental effect such as wind is modeled by CFD, and the plasticity is also taken into account by the nonlinear material properties in flange and gasket by FEM. The case studies are performed for 6”, 12” and 18” for Class 2,500 with ring joint gasket. In addition, the two temperature and pressure cycles including first start-up, normal operation, shut-down, and the consequent start-up, normal operation, emergency shut-down conditions are considered. Thus, the leakage phenomena are able to evaluate, and the guideline is proposed for maintenance.
Buckling Characteristics of Floating Roof Pontoons in Aboveground Storage Tanks Subjected to Bending Load in Two Directions
Authors: Yoshida Shoichi , Kitamura Kazuhiro
Published: July 2009

The 2003 Tokachi-Oki earthquake caused severe damage to aboveground oil storage tanks due to liquid sloshing. Seven single-deck floating roofs had experienced structural problems as evidenced by sinking failure in large diameter tanks at the refinery in Tomakomai, Japan. The pontoons of the floating roofs might be buckled due to circumferential bending moment during the sloshing. The content in the tank was spilled on the floating roof from small failures which were caused at the welding joints of pontoon bottom plate by the buckling. Then the floating roof began to lose buoyancy and submerged into the content slowly. The authors had reported the buckling strength of the pontoons with and without ring stiffeners subjected to circumferential bending load in the previous papers. This paper presents the buckling strength of the pontoons subjected to both circumferential and radial bending load. The axisymmetric shell finite element method is used in the analysis. Linear elastic bifurcation buckling analysis is carried out and the buckling characteristics of the pontoon with and without ring stiffeners are investigated.
Repetitive Control Based Disturbance Cancellation Using Iterative Basis Function Feedback With Wavelet Filtering
Authors: Lin Jeng-Wen , Huang Chih-Wei , Wen Hao-Ping
Published: July 2009

This paper presents repetitive control laws in real time using matched basis functions. These laws adjust the command given a feedback control system in order to eliminate tracking errors, resulting from in general a periodic disturbance and a non-periodic disturbance. The periodic error can be reduced by linear basis functions while the non-periodic error by the projection algorithm along with the wavelet filtering. The control laws do not use a system model, but instead the control action is chosen to be a linear combination of chosen input basis functions, and the corresponding output basis functions are obtained, nominally by experiment. The repetitive control laws use the projection algorithm to compute the output components on the output basis functions, and then the corresponding input components are adjusted accordingly. The output signals are reconstructed via the wavelet filtering before they are feedback to the controller. Numerical experiments show that the repetitive controllers are quite effective. In particular, the output tracking errors are further reduced because of the introduction of the wavelet filtering when compared to the previous work. In general, the repetitive control laws developed here can be used for the purpose of precision machinery control.
Heat Exchanger Gaskets Radial Shear Testing
Authors: Veiga Jose´ C. , Kavanagh Nelson , Reeves David
Published: July 2009

Due to the high incidence of leaks in Shell and Tube Heat Exchanges that are in thermal cycling service, there have been studies of the suitability of gasket styles for this kind of application. This paper researches several gasket styles in a test rig developed to simulate the radial shear caused by the differential thermal expansion of the flanges in a Heat Exchanger.
Treatment of High Temperature Tensile Data for Alloy 617 and Alloy 230
Authors: Sham T.-L. , Eno D. R. , Jensen K. P.
Published: July 2009

Yield strength and tensile strength at temperature are used to set time independent primary stress limits for structural materials in various high temperature design codes. For the Ni-based Alloy 617 and HAYNES® 230® alloy (Alloy 230), the temperature trends for the yield strength and tensile strength change significantly above around 1100K and 1025K, respectively, from the lower temperature trends. It is shown that standard methods in obtaining design values for these parameters for Very High Temperature Reactor applications are not satisfactory. Improved methods for the treatment of tensile data are proposed, resulting in more consistent and quantifiable design margin over the full range of low to high temperatures.
Equivalent CTOD Ratio β for Engineering Assessment of CTOD Correction for Constraint Loss
Authors: Ohata Mitsuru , Minami Fumiyoshi
Published: July 2009

The critical CTOD δWP for structural components associated with plastic constraint loss in case of the brittle fracture over small-scale yielding condition can be corrected from CTOD fracture toughness δ by means of the “equivalent CTOD ratio β” defined as δ/δWP, which is based on the Weibull stress criterion. In this study, taking the case of specific wide plate components subjected to uni-axial tensile load, the effect on β is analyzed taking account of Weibull shape parameter m, loading level, constraint effect that can be influenced by material work-hardening and crack type/size in structural components, etc., and volumetric effect. It is found that the β-value is almost constant beyond the applied CTOD level that is lower than CTOD of small-scale yielding limit (SSY-limit) for 25mm thick toughness specimen. From an engineering point of view, the β-value at the CTOD level of 0.01mm is used in the whole loading range beyond SSY-limit CTOD, which provides to some extent conservative measure of fracture toughness of structural components. The defined β is found to decrease with increasing Weibull shape parameter m and yield-to-tensile ratio YR of steel for all type of wide plates concerned. The crack length effect on β is quasi-theoretically formulated, which can convert the β for the wide plate with reference crack size to β for target crack size. These β and quasi-theoretical equations for correction of crack size effect can be utilized for estimating the CTOD for wide plate in consideration of constraint loss effect without numerical calculation of the Weibull stress.
JEDI: A Code for the Calculation of J for Cracks Inserted in Initial Strain Fields and the Role of J and Q in the Prediction of Crack Extension and Fracture
Authors: Beardsmore David W.
Published: July 2009

When crack tip constraint is high, the crack tip contour integral J characterises the asymptotic stress, strain and displacement fields of a stationary crack in an elastic-plastic material. In other cases, the crack tip fields can be related to J and a second parameter Q which governs the crack tip constraint. These observations are the basis of J-Q fracture mechanics assessments. In the most usual procedure J is compared to an effective, constraint-corrected fracture toughness Jc which is derived from Q and the fracture toughness of the material. The difference Jc – J is a measure of the margin of safety. The assessment procedure assumes there are no initial inelastic strains in the component or the fracture toughness specimen prior to introducing the crack and subsequent loading. However, plant components may contain inelastic strains prior to cracking arising from welding and other manufacturing or fit-up processes. This initial strain field can be established by a finite element analysis that simulates the welding and/or manufacture sequence. Weld residual stresses develop due to the accumulation of incompatible, inelastic strains, including thermal, plastic and transformation strains in the material. If a crack is inserted into an initial strain field, a procedure is required to calculate J by analysis of the resulting crack tip fields. Moreover, for the fracture assessment method to remain valid, it must be demonstrated that the values of J and Q continue to govern the onset of crack extension or fracture so that a meaningful comparison of J with Jc can be made. This paper describes a domain integral for calculating J when inelastic strains exist prior to cracking, and its implementation in the JEDI computer code. The code is used to determine J for a crack inserted into a three-point bend specimen containing an initial inelastic strain field representative of one that might develop during welding. The extent to which the crack tip stress field is characterised by J and Q is examined by comparing it to the field for high constraint, small-scale yielding conditions.
Simplified Limit Load Determination Using the mα-Tangent Method
Authors: Seshadri R. , Hossain M. M.
Published: July 2009

Limit load determination of mechanical components and structures by the mα-tangent method is proposed herein. The proposed technique is a simplified method that enables rapid determination of limit loads for a general class of mechanical components and structures. The method makes use of statically admissible stress field based on a linear elastic finite element analysis to estimate the limit loads. The method is applied to a number of mechanical component configurations and the results compare well with those obtained by the corresponding elastic-plastic finite element analyses results.
The Effects of Plate Dimensions on Residual Stresses in Welded Thin Steel Plates
Authors: Davies C. M. , Wimpory R. C. , Dye D. , Nikbin K. M.
Published: July 2009

Residual stress distributions have been measured on thin (4 mm thick) plates made from a ferritic steel designated grade DH-36 using the neutron diffraction technique. The welded specimens include two large (1 m × 1 m) butt welded plates, onto one fillet welded stiffeners were also added, and a smaller (0.5 m × 0.5 m) fillet welded stiffened plates. The large butt and fillet welded stiffened plate has also been cut to smaller dimensions and the strain relaxation due to cutting quantified by strain gauges. The residual stress distributions have been re-measured after specimen cutting and the relaxation quantities compared to the strain gauge values. The influence of specimen size is also examined by comparing measurements at the base of the fillet welds in the large and smaller plates. The results are interpreted to identify plate size effects on the residual stress levels of the welds.
A Study on Vibration Control for Reheater Spray Piping
Authors: Jeon Changbin , Yi Joonseok , Shin Joongkyo
Published: July 2009

Piping vibration sometimes occurs resulting from the mechanical excitation sources like an unbalanced force of a rotating machine. But it usually occurs due to a pressure pulsation generated from vortex shedding in the piping or from pumps. Generated vibration energy is amplified according to the structural or acoustic characteristics of the piping, which cause high vibration and excessive noise in the piping. During a startup test, high frequency shell mode vibration with severe noise (96.5 ∼ 106.7 dB, RMS) was generated at the reheater spray piping, and beating was also detected in the sound and vibration signals. The function of reheater spray piping (OD 3.5 inch, Sch 80) is to control boiler temperature. It receives water from feedwater pumps and supplies it to attemperator installed in the cold reheat line. It regulates boiler temperature by injecting feed water into the reheater when the boiler is overheated, but the line is not activated during the normal operation. The object of this study is to analyze a root cause of the piping vibration and to establish possible corrective actions to mitigate high frequency shell mode vibration and associated high level sound in the reheater spray piping.
Residual Stress Relief in Post-Weld Heat Treatment
Authors: Dong Pingsha , Hong Jeong K.
Published: July 2009

This paper focuses on analysis of weld residual stress relief process during furnace-based uniform post-weld heat treatment (PWHT). Two classes of pressure vessel steels: 2-1/4CrMo and carbon steel are considered in seam weld configurations. It is found that the dominant mechanism for residual stress relief is the creep relaxation that occurs much earlier during a PWHT cycle than typically expected. This phenomenon is further confirmed by experimental data. After a large number of parametric analyses of various PWHT parameters, a simple form of relationship is proposed for relating residuals stress relief to a set of PWHT parameters for the two classes of steels. These parameters include PWHT ramp-up heating time, PWHT holding time, PWHT holding temperature, and weldment thickness.
Valve Packings Seating Stress
Authors: Veiga Jose´ C. , Cipolatti Carlos , Gira˜o Carlos , Ascenco Leandro , Castro Fabio
Published: July 2009

This paper studies the seating stress required to assure the sealability in valve stems used in high pressure steam service. A test device that simulates the valve stuffing box and a test protocol are proposed. Actual field tests conducted according to a procedure developed from the laboratory tests are also reported.
Experimental Determination of J-R Curves Using SENB Specimens and P-CMOD Data
Authors: Zhu Xian-Kui , Leis Brian N.
Published: July 2009

Fracture toughness and J-R curves of ductile materials are often measured under the guidance of ASTM standard E1820 using the single specimen technique and the elastic unloading compliance method. For the standard single-edge notched bend [SENB] specimens, the load, load-line displacement (LLD), and crack-mouth opening displacement (CMOD) are required being measured simultaneously. The load-CMOD data are used to determine the crack extension, and the load-LLD data together with the crack extension are used to determine the J-integral values in a J-R curve test. Experiments have indicated that the CMOD measurement is very accurate, but the LLD measurement is difficult and less accurate in a fracture test on the SENB specimen. If the load-CMOD records is used to determine the crack extension and the J-integral values, experimental accuracies for the J-R curve testing would be increased, and the test costs can be reduced. To this end, this paper develops a simple relationship between LLD and CMOD that is used to convert the measured CMOD record to the corresponding LLD data, and then to calculate the J values for a growing crack in a J-R curve test on the SENB specimen using one single specimen technique. The proposed method is then verified by the experimental data of J-R curves for HY80 steel using the SENB specimens and the load-CMOD data only. The results show that the proposed method is more accurate and more cost-effective for the J-R curve testing.
Elastic-Plastic Finite Element Simulation and Fatigue Damage Analysis of Wrinklebends
Authors: Zhu Xian-Kui , Leis Brian N.
Published: July 2009

The elastic-plastic finite element analysis (FEA) is performed in this paper to simulate the complicated plastic deformation of wrinklbends during bending and operation. The effects of element types, mesh sensitivity, and material input data of a stress-strain curve on the FEA results are discussed in details. To characterize the work hardening and Bauschinger effect on cyclic plastic deformation, three plastic hardening models: isotropic, kinematic and combined isotropic/kinematic hardening models are used and compared in the FEA simulation. Based on these investigations, a reliable nonlinear FEA model is developed, and then detailed FEA calculations are conducted for a wide range of wrinkle sizes under the cyclic pressure of 72% to 10% of SMYS (specified minimum yield stress) of X42 pipeline steel. Using the numerical results and an energy-based fatigue damage parameter, fatigue damage is quantified and a criterion is formulated as an H/L-N curve for wrinklebends. In the criterion, the wrinkle aspect ratio H/L is a key parameter that is directly related to the fatigue life. The results show that the proposed criterion and the H/L-N curve are simple and can be effectively used to evaluate integrity and estimate service life for wrinklebends.
A Comparative Study of Ke Factor in Design by Analysis for Fatigue Evaluation
Authors: Gurdal Robert , Xu Steven X.
Published: July 2009

ASME Section III Design by Analysis rules provide a “Simplified Elastic-Plastic Analysis” approach for the fatigue usage evaluation when the primary plus secondary stress range exceeds the limit of 3Sm. A penalty factor Ke is applied to the alternating peak stress calculated by assuming elastic material behavior. There is general consensus that the Ke factor determined using current code equations can be overly conservative for some conditions, and can lead to severe design limitations. The ASME code committees have been actively working on revising the Ke equations. The work in this paper intends to assess the conservatism of the Ke procedure in current ASME NB-3228.5, and to evaluate the two proposed alternative ASME Code Ke procedures through a comparative study. The evaluation focuses on the Ke procedure related to the effect of through-wall temperature gradient induced stresses on fatigue life for austenitic stainless steel. The conservatism of current ASME NB-3228.5 rules for the Ke factor is demonstrated through the comparison of predicted fatigue life with the test result of a stainless steel stepped pipe. In view of the technical background that the Ke factor represents the ratio of the actual strain range to the elastically calculated strain range, the theoretically accurate Ke factor can be calculated from elastic and elastic-plastic analyses. This directly calculated Ke factor is found to be in good agreement with the fatigue life from the test. A comparative study of procedures for calculating the Ke factor using current ASME NB-3228.5 rules and its counterparts in various codes is then conducted. B31.7 code, French RCC-M code and Japanese JSME code are considered. The two proposed alternative ASME Code Ke methodologies are evaluated. The differences in calculated Ke values are illustrated through the sample stepped pipe problem with various thermal transients. The directly calculated Ke factor using elastic and elastic-plastic analyses is used as reference value for comparison and conservatism assessment.