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Three Dimensional Fracture Mechanics Analysis For Welded Joint Structures Using Virtual Crack Closure-integral Method
Tanaka, Satoyuki (Department of Social and Environmental Engineering, Graduate School of Engineering, Hiroshima University) | Okazawa, Shigenobu (Department of Social and Environmental Engineering, Graduate School of Engineering, Hiroshima University) | Okada, Hiroshi (Department of Nano-Structure and Advanced Materials, Graduate School of Science and Engineering, Kagoshima University)
In this study, evaluation of stress intensity factors (SIFs) has been carried out to the defects in welded joint structures. There are many welded joints in marine structures. It has possibilities that fatigue defects are initiated in the welded joint structures under severe conditions. It is important to critically examine the mechanical behaviors for the welded joint structures based on the concept of fatigue strength evaluation. SIFs are one of the important parameters to estimate the mechanical properties for the cracked bodies. Finite element analyses (FEA) are often used to calculate the SIFs. There are some difficulties to make a three dimensional FEA model to the complex shaped structures. In this study, quadratic tetrahedral finite element analyses with large scale computation and virtual crack closure-integral method (VCCM) are adopted to evaluate the SIFs for the cracks in welded joint structure. The use of tetrahedral finite elements enables us to make FEA models from 3D-CAD model directly because we are able to use automatic mesh generation software. In this paper, mathematical formulation and numerical implementation for the VCCM analysis using quadratic tetrahedral finite elements are described. Calculation of SIFs for the VCCM analysis is carried out to the three dimensional linear elastic crack problems. And, estimation and evaluation for the SIFs of the cracks in the welded joints are presented. INTRODUCTION Welded joint structures are often used to build structural members in marine structures. It has possibility that fatigue cracks are initiated in the welded joints due to the weld defects. The cracks are developing and are propagating in the welded joint structures under cyclic loads. The developed cracks will give big damage to the structural members. Then, it is important to evaluate the initial flaw in the welded joint structures based on fatigue strength evaluation.
The repair cost over the lifetime for caisson breakwaters covered with wave-dissipating blocks is estimated. The repair cost is estimated as the sum of the cost for repairing the wave-dissipating works and the cost equivalent to the amount of damage to the harbor area. In this study, it is assumed that the subsidence of the crest height of the wavedissipating works due to wave attacks causes the increase in the transmitted wave height behind the breakwater. The variations of the repair costs under several conditions are discussed. INTRODUCTION Effective repair of coastal structures is very important. The percentage of the coastal structures constructed more than 30 years ago is increasing in Japan. In general, the performances of old structures are reduced and the maintenance cost for old structures is increased. However, the budget for replacing old structures with new structures is very limited. Under these circumstances, existing coastal structures need to be effectively repaired in order to save the cost. In the repair, the maintenance costs for the coastal structures need to be minimized because too frequent repair needs high repair cost; however, insufficient repairs may lead to catastrophic damage to coastal structures and surrounding area. Repair of coastal structures, e.g., breakwaters, should be determined on the basis of the decrease in the breakwater performances; this will help reduce the maintenance costs of the breakwaters during their designed lifetime, i.e., life cycle cost. However, the repair of breakwaters is currently determined on the basis of the degree of the displacement or the deformation of breakwaters. Recently, several studies on lifecycle costs for coastal structures including repair costs have been studied. Matsubuchi and Yokota (1999) investigated the lifecycle cost of berthing facilities. Nagao and Matsubuchi (1999) estimated the lifecycle cost and allowable failure probability of composite breakwater.
Because a moored ship can be drifted and stranded when a mooring chain is broken due to a high wave, it is important to predict the movement of a moored floating object under action of such a high wave. Some of numerical prediction has been conducted, however, there is no model to simulate a floating object appropriately under a high wave. Therefore, in this study, a simulation model based on a particle method is developed. INTRODUCTION When a mooring chain is broken due to a large-scale tsunami or a high wave, a moored ship can be drifted and stranded. The mooring system, which has been researched before (ex. Takayama et al., 1979), is one of the important research themes because, especially, a large-scale floating structure like a floating airport has attracted attention in late years. The numerical simulation is required for the rational design of a floating body, however, in a popular method to predict the motion of floating body, only a linear wave can be treated. A numerical model for tracking a floating body in a nonlinear wave had been developed by Ikeno (2000) and Mizutani et al. (2004), however, there is no numerical model applied in a high wave which causes strong wave force to break a mooring chain. The reason is difficulty in calculating the interaction between a floating body and fluid around water surface accurately in a previous numerical method. Especially in a high wave such as a ship is dashed blue wave. Therefore, in this study, a model for tracking of a moored floating body by using a particle method which is applicable for a violent water surface change is developed. In a particle method, because it is easy to treat a movable object, numerical analyses on a free floating body had already been carried out by Koshizuka et al.(1998), Sueyoshi et al.(2003) and Gotoh and Ikari(2007), however, there is no example of simulation for tracking of a floating body bound by a mooring chain based on a particle method.
Refined Reproduction of a Plunging Breaking Wave And Resultant Splash-up By 3D-CMPS Method
Gotoh, Hitoshi (Department of Urban and Environmental Engineering, Kyoto University, Katsura Campus, Nishikyo-ku, Kyoto, Japan) | Khayyer, Abbas (Department of Urban and Environmental Engineering, Kyoto University, Katsura Campus, Nishikyo-ku, Kyoto, Japan) | Ikari, Hiroyuki (NEWJEC Inc., Osaka, Japan) | Hori, Chiemi (Department of Urban and Environmental Engineering, Kyoto University, Katsura Campus, Nishikyo-ku, Kyoto, Japan)
The paper presents a 3D-CMPS method for refined simulation of a plunging breaking wave and resultant splash-up. The Corrected MPS (CMPS; Khayyer and Gotoh, 2008a) has been extended to three dimensions and 3D-CMPS method has been developed on the basis of 3D-MPS method by Gotoh et al. (2005b). The enhanced performance of 3D-CMPS method with respect to 3D-MPS method has been shown by simulating a plunging breaking wave on a plane slope. Furthermore, the parallelization of 3D-CMPS method with two different solvers of linear equations has been performed to enhance the computational efficiency of the calculations. INTRODUCTION Breaking waves on beaches constitute one of the most energetic events in the coastal environments. Hence, a better understanding and modeling of the breaking waves is of central importance for coastal engineering applications. Both of experimental techniques and gridbased numerical methods have certain constraints and drawbacks when applied in the study of violent free-surface hydrodynamic flows such as the breaking waves (Gotoh et al., 2005a). On the other hand, particle methods or the Lagrangian gridless methods provide a substantial potential for a comprehensive description of the full processes associated with the breaking waves. Because of their gridless nature, particle methods are inherently wellsuited for the analysis of problems which include moving discontinuities characterized by large deformations or fragmentations as in case of breaking waves. In addition, due to their Lagrangian treatment of discrete particles, such methods are able to simulate freesurface fluid flows without the numerical diffusion (Gotoh et al., 2005a) and without the need for an interface capturing technique as in case of Eulerian grid-based methods. The Moving Particle Semi-implicit (MPS; Koshizuka and Oka, 1996) is one of the capable particle methods developed initially for the simulation of incompressible free-surface fluid flows. Despite its simplicity and capability, the MPS method has a few shortcomings including the non-conservation of momentum (Khayyer and Gotoh, 2008a).
Wave Impact Calculations By Improved SPH Methods
Khayyer, Abbas (Department of Urban and Environmental Engineering, Kyoto University, Katsura Campus, Nishikyo-ku, Kyoto, Japan) | Gotoh, Hitoshi (Department of Urban and Environmental Engineering, Kyoto University, Katsura Campus, Nishikyo-ku, Kyoto, Japan)
The paper presents improved Incompressible SPH (ISPH) methods for prediction of wave impact pressure on a coastal structure. The first improvement is the employment of a corrective function for enhancement of angular momentum conservation in a particle-based calculation. The second improvement is the application of a higher order source term derived based on a higher order differentiation to provide a less fluctuating and more accurate pressure calculation. The enhanced performance of improved ISPH methods in prediction of wave impact pressure has been shown by simulating a dam break with impact and a flip-through impact. INTRODUCTION Past failures of coastal structures indicate that some of the conventional design methods based on solely static or quasi-static analysis are not entirely reliable. Furthermore, both theoretical (e.g. Cooker and Peregrine, 1994) and experimental (e.g. Hattori et al., 1994) studies highlight the essential role of the so-called wave impact pressure in design of coastal structures. Thus, development of reliable design tools for prediction of wave impact pressure becomes indispensable. The numerical models developed for calculation of wave impact pressure are mainly based on the Navier-Stokes equation which describes the motion of an incompressible, viscous fluid. In case of grid-based Eulerian solvers of Navier-Stokes equation a mathematical treatment of free surface is required. Christakis et al. (2002) and Kleefsman et al. (2005) employed refined versions of Volume Of Fluid (VOF) method (Hirt and Nichols, 1981) to treat the free surface in their wave impact calculations. Nevertheless, VOF-based models have the drawback of numerical diffusion arising from fixed-point interpolations of advection terms in both VOF function transport equation and Navier- Stokes momentum equation. A few sophisticated schemes such as the CIP method (Yabe et al., 2001) have been proposed to attenuate the numerical diffusion in an Eulerian grid-based calculation. Hu and Kashiwagi (2004) applied the CIP method in their grid-based wave impact calculations and obtained quite satisfactory results.
Vertical Riser VIV Simulation In Sheared Current
Huang, Kevin (Ocean Engineering Program Department of Civil Engineering Texas A&M University, College Station, Texas) | Chen, Hamn-Ching (Ocean Engineering Program Department of Civil Engineering Texas A&M University, College Station, Texas) | Chen, Chia-Rong (Department of Mathematics Texas A&M University, College Station, Texas)
This paper studied a vertical riser VIV under sheared current using numerical simulation and presented the results and their comparisons to published experimental data. The riser was made of a 9.63m brass pipe with an OD of 0.02m (L/D=482), and mass ratio of 1.75. In the experiment the riser was positioned inclined with top tension of 817N, and pinned at its two ends to the test rig. Rotating the rig in the wave tank would simulate the sheared current. In our numerical simulation we pinned the riser's ends to the ground, and imposed a linearly sheared far field incoming current. The riser and its surrounding fluid were discretized using 1.5 million elements. The flow field was solved using an unsteady Reynolds-Averaged Navier-Stokes (RANS) numerical method in conjunction with a chimera domain decomposition approach with overset grids. The riser was also discretized into 250 segments. Its motion was predicted through a tensioned beam motion equation with structural damping. The external force terms were obtained by integrating viscous and pressure loads on the riser surface. We then processed the critical parameters including riser VIV a/D, vorticity contours, response histories and spectra, and VIV induced fatigue. Finally, comparisons were made to the experimental data and conclusions were drawn. In general the VIV simulation results agree well with the experimental data. It is concluded that the present CFD approach is able to simulate the vertical riser VIV in sheared current. Furthermore, it can also predict the VIV induced fatigue damage as well. INTRODUCTION Riser VIV numerical simulation has been an interesting area for many years. Many of these investigations are limited to 2D. Some of the popularly used CFD tools for riser VIV simulation were discussed by Chaplin et al. (2005). Holmes et al. (2006) also published an interesting CFD approach to simulate riser VIV in fully 3D by using 10 million unstructured elements.
Particle method, which is a solver of Navier-Stokes equation without using a computational grid, has excellent robustness in analyzing a violent water-surface change accompanied with a fragmentation and a coalescence of water. Therefore the particle method is an optimum tool for the analysis of the process of wave breaking and runup. Herein, calculation fundamentals of the particle method are outlined. The stateof- the-art of the particle method, including highly-precise particle methods by improving momentum conservation in discretization of governing equations and the new methods for a control of pressure fluctuation, is briefly introduced. Finally few of significant issues for promoting substantial contribution of the particle method to numerical wave flume, which is the computer-aided resistive design tool of coastal structures against wave action, are shown as prospective studies on the particle method. INTRODUCTION To describe nonlinear wave transformation, the Boussinesq(1872) theory and its extension (e.g. Nwogu, 1993) are popular and reliable. However these models are unable to describe wave breaking directly, because these models are derived under the assumption of potential flow, namely irrotational flow with neglecting viscosity. In extended models of the Boussinesq theory, wave breaking was described empirically as an energy damping effect with using ad-hoc energy dissipating schemes (e.g. Svendsen, 1984). Computations based on analytical governing equations of wave motion, such as Boussinesq equation, must be replaced by numerical solutions of Navier-Stokes equation to analyze a wave breaking and a runup process without ad-hoc sub-models of energy dissipation. In the wave breaking phenomena, there exist one more difficulty, namely existence of multiply connected flow domain, or topological change of free surface, due to plunging jet striking the toe of the wave. Under this condition, Lagrangian grid methods, which track a free surface with using moving grid, break down. The Maker-And-Cell (MAC) method (Harlow and Welch, 1965), which captured water surface by tracking markers existing in the vicinity of water surface, was the first computational approach to overcome this difficulty.
DRBEM Solution of Extended Mild-Slope Equation For Waves Around a Circular Island On a Polynomial Shoal
Hsiao, Sung-Shan (Department of Harbor and River Engineering, National Taiwan Ocean University Keelung, TAIWAN, China) | Chang, Chun-Ming (Department of Civil Engineering, National Kaohsiung University of Applied Science Kaohsiung, TAIWAN, China) | Wen, Chih-Chung (Department of Safety, Health and Environmental Engineering, Hungkuang University Taichung, TAIWAN, China)
In this paper, the extended mild-slope equation was adopted to be the governing equation and solved by dual reciprocity boundary element method. This model improves the accuracy of former papers caused by neglecting the curvature and slope-squared terms in their models. Due to the former works focusing on the long wave, the extended terms become very small and were omitted. Recently, the extended terms was considered that cannot be omitted even the long wave. A series of numerical experiments were conducted including conical island, Homma's island. The Homma's island was the case studies and the results were compared with the analytical results derived by Homma (1950) and/or Jonsson et al. (1976). Excellent agreements were obtained. INTRODUCTION To simulate linear wave propagation from deep to shallow water, the use of the mild-slope equation derived by Berkhoff (1972) can be a proper and valid method. The classical mildslope equation is based on the assumption of a slowing varying bathymetry, linearzing the scattering of surface waves on variable water depth by approximating the vertical structure of motion and averaging over depth. Thus, the dimension of the problem can be reduced by one. Due to the assumption of ∇h / kh << 1 on mild-slope equation, the higher-order bottom effect terms are neglected during the original derivation procedure of Berkhoff. Motivated in part by the significant engineering applications, much of the relevant existing literature has concentrated on rapidly-varying or steep topography. Booij (1983) compared the numerical results of mild-slope equation with the finite element model results in terms of the reflection coefficients for the case of monochromatic wave propagation over a plane slope. He made a conclusion that the mild-slope equation is sufficiently accurate up to a bottom slope of 1:3. However, it has been pointed out in a lot of investigations that the classical mild-slope equation fails to produce adequate approximations for certain type of bathymetry, such as off-shore reef or bars.
Effect of the Liquefaction On Structure Safety of Buried Pipe During Earthquake
Darn-Horng, Hsiao (Department of Civil Engineering, National Kaohsiung University of Applied Science Kaohsiung, TAIWAN, China) | Lin, M.D. (Department of Civil Engineering, National Kaohsiung University of Applied Science Kaohsiung, TAIWAN, China)
A simplified procedure is developed to evaluate dynamic behavior of buried pipe during earthquake. In the procedure, an empirical method developed by Seed, Tokimatsu et al. (1985, 1987) is used to evaluate soil liquefaction with Iwasaki et al. (1982). Pressure on the pipe is calculated by Iimura (2004) method and the bending stress can be calculated by Hetenyi (1946) method. Based on the research outcome, postliquefaction flexural displacement and bending moment of buried pipe are successfully estimated. This newly developed method is applied to predict movements and stresses of underground structure associated with the same background of a tunnel case history from Taipei. The predictions show up to 14cm of differential displacement and 6×10 N-m of bending moment of tunnel might be caused by soil liquefaction. In the meantime effects of liquefaction on structure safety are also concerned in this paper. At last, a small- scale shaking table test was applied to study seismic uplift safety factor (FS). Through the experimental works, it is concluded that friction resistance surrounding the pipe and fluid drag should be included for calculation of FS. INTRODUCTION Liquefaction or lateral spreading may generate subsequently differential settlement and thus causes flexural deflection of pipe and even induce severe damage of the structure. In order to mitigate liquefaction, Chin (1997) treated a deep-sea tunnel foundation with using cement clinker stabilization. Chou et al. (2001) indicated that basic design specification of the buried pipe has to pay attention to uplift displacement and settlement during liquefaction. Sumer et al. (1998) presented similar opinions for buried pipe near coastal shore subjected to strong wave loadings. In the past, the design of pipe during earthquake is too complicated to use easily for engineers.
- Reservoir Description and Dynamics (0.49)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers (0.47)
- Management > Professionalism, Training, and Education > Communities of practice (0.34)
- Data Science & Engineering Analytics > Information Management and Systems > Knowledge management (0.34)
A Coupled Eulerian Lagrangian Finite Element Model of Ice-Soil-Pipe Interaction
Abdalla, Basel (Advanced Engineering Group, J P Kenny Houston, TX, USA) | Pike, Kenton (Advanced Engineering Group, J P Kenny Houston, TX, USA) | Eltaher, Ayman (Advanced Engineering Group, J P Kenny Houston, TX, USA) | Jukes, Paul (Advanced Engineering Group, J P Kenny Houston, TX, USA)
In ice environments, pipelines must be buried to provide protection from the keels of gouging ice features. A pipeline must not only be buried to avoid contact, but also to mitigate the effects of strains induced by soil displacement below gouge level. Previous studies have shown that the pipe should be buried in an intermediate zone below the scour depth and above the zone where soil only deforms elastically. There remains, however, uncertainty in the extent of this intermediate zone and in the determination of an economical minimum burial depth with acceptable risk. In this paper, the current state of the art, the Coupled Eulerian Lagrangian (CEL) method was adopted to make further advancements in ice gouge numerical modeling and to solve some of the uncertainty regarding pipeline burial depth. A three-dimensional (3D) finite element (FE) model was developed using the CEL formulation in ABAQUS, providing direct and explicit estimation of pipe stresses and strains. Simulation results from the developed model were validated by comparing the free field subgouge soil displacement to measured centrifuge test data and to results of FE models developed by others. Preliminary study of pipeline response to the forces generated by subgouge soil displacement was then presented. Trends were established between pipeline burial depth and pipeline strain for varying pipeline D/t ratios. INTRODUCTION The future of the oil and gas industry will see frontier oil and gas developments in Arctic regions. According to a recent report by the U.S. Geological Survey (USGS) the total mean undiscovered conventional oil and gas resources of the Arctic are estimated at approximately 90 billion barrels of oil, 1,669 trillion cubic feet of natural gas, and 44 billion barrels of natural gas liquids. These resources account for approximately 22% of the undiscovered, ‘technically recoverable’ resources in the world, where technically recoverable means able to be produced using currently available technology.
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.75)
- North America > Canada > Quebec > Arctic Platform (0.93)
- North America > Canada > Nunavut > Arctic Platform (0.93)