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CONTENTS
Volume 1, Number 4, December 2012
 

Abstract
As a result of the medium coupling, propagation characteristics of ultrasonic waves guided by a multi-phase medium can be different from those in a homogeneous system. This phenomenon becomes prominent for a medium consisting of phases with considerably distinct material and physical properties (e.g., submerged structures or human bones covered with soft tissues). In this study, the coupling effect arising from both fluid and soft tissues on wave propagation in engineering structures and human bone phantoms, respectively, was explored and calibrated quantitatively, with a purpose of enhancing the precision of ultrasonic-wave-based non-destructive evaluation (NDE) and clinical quantitative ultrasound (QUS). Calibration results were used to rectify conventional NDE during evaluation of corrosion in a submerged aluminium plate, and QUS during prediction of simulated healing status of a mimicked bone fracture. The results demonstrated that with the coupling effect being appropriately taken into account, the precision of NDE and QUS could be improved.

Key Words
medium coupling; guided waves; non-destructive evaluation; quantitative ultrasound

Address
Jiangang Chen : Department of Biomedical Engineering, Columbia University, New York, NY, The USA
Zhongqing Su and Li Cheng : Department of Mechanical Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong

Abstract
Previous investigations have demonstrated that strong earthquakes can cause severe damage or collapse to storage tanks. Theoretical studies by other researchers have shown that allowing the tank to uplift generally reduces the base shear and the base moment. This paper provides the necessary experimental confirmation of some of the numerical finding by other researchers. This paper reports on a series of experiments of a model tank containing water using a shake table. A comparison of the seismic behaviour of a fixed base system (tank with anchorage) and a system free to uplift (tank without anchorage) is considered. The six ground motions are scaled to the design spectrum provided by New Zealand Standard 1170.5 (2004) and a range of aspect ratios (height/radius) is considered. Measurements were made of the impulsive acceleration, the horizontal displacement of the top of the tank and uplift of the base plate. A preliminary comparison between the experimental results and the recommendations provided by the liquid storage tank design recommendations of the New Zealand Society for Earthquake Engineering is included. The measurement of anchorage forces required to avoid uplift under varying conditions will be discussed.

Key Words
storage tanks; uplift; fluid-structure interaction; hold-down force; standard

Address
Miguel Ormeno, Tam Larkin and Nawawi Chouw : Department of Civil and Environmental Engineering, The University of Auckland, Faculty of Engineering, 20 Symonds St, Auckland 1142, New Zealand

Abstract
We present different numerical methods for solving the shallow shelf equations with basal drag (SSAB). An alternative approach of splitting the SSAB equation into a Laplacian and diagonal shift operator is discussed with respect to the underlying eigenvalue problem. First, we solve the equations using standard methods. Then, the coupled equations are decomposed into operators for membranes stresses, basal shear stress and driving stress. Applying reasonable parameter values, we demonstrate that the operator of the membrane stresses is much stiffer than the operator of the basal shear stress. Here, we could apply a new splitting method, which alternates between the iteration on the membrane-stress operator and the basal-shear operator, with a more frequent iteration on the operator of the membrane stresses. We show that this splitting accelerates and stabilize the computational performance of the numerical method, although an appropriate choice of the standard method used to solve for all operators in one step speeds up the scheme as well.

Key Words
partial differential equations; operator-splitting methods; laplacian operator, diagonal shift operator iterative methods; eigenvalue approach; ice streams; membrane stress; shallow shelf approximation

Address
Jurgen Geiser : Department of Physics, Ernst-Moritz-Arndt University of Greifswald, Felix-Hausdorff-Str. 6, D-17489 Greifswald, Germany
Reinhard Calov : Potsdam Institute for Climate Impact Research, PO Box 60 12 03, D-14412 Potsdam, Germany

Abstract
In this article we have presented a unique representation for interval arithmetic. The traditional interval arithmetic is transformed into crisp by symbolic parameterization. Then the proposed interval arithmetic is extended for fuzzy numbers and this fuzzy arithmetic is used as a tool for uncertain finite element method. In general, the fuzzy finite element converts the governing differential equations into fuzzy algebraic equations. Fuzzy algebraic equations either give a fuzzy eigenvalue problem or a fuzzy system of linear equations. The proposed methods have been used to solve a test problem namely heat conduction problem along with fuzzy finite element method to see the efficacy and powerfulness of the methodology. As such a coupled set of fuzzy linear equations are obtained. These coupled fuzzy linear equations have been solved by two techniques such as by fuzzy iteration method and fuzzy eigenvalue method. Obtained results are compared and it has seen that the proposed methods are reliable and may be applicable to other heat conduction problems too.

Key Words
finite element method; uncertainty; interval arithmetic; fuzzy number; fuzzy finite element method

Address
S. Chakraverty and S. Nayak : Department of Mathematics, National Institute of Technology, Rourkela, Odisha-769008, India

Abstract
This paper presents a fully coupled three-dimensional solver for the analysis of interaction between pulsatile flow and large deformation structure. A partitioned time marching algorithm is employed for the solution of the time dependent coupled discretised problem, enabling the use of highly developed, robust and well-tested solvers for each field. Conservative transfer of information at the fluidstructure interface is combined with an effective multi-predict-correct iterative scheme to enable implicit coupling of the interacting fields at each time increment. The three-dimensional unsteady incompressible fluid is solved using a powerful implicit time stepping technique and an ALE formulation for moving boundaries with second-order time accurate is used. A full spectrum of total variational diminishing (TVD) schemes in unstructured grids is allowed implementation for the advection terms and finite element shape functions are used to evaluate the solution and its variation within mesh elements. A finite element dynamic analysis of the highly deformable structure is carried out with a numerical strategy combining the implicit Newmark time integration algorithm with a Newton-Raphson second-order optimisation method. The proposed model is used to predict the wave flow fields of a particular flow-induced vibrational phenomenon, and comparison of the numerical results with available experimental data validates the methodology and assesses its accuracy. Another test case about three-dimensional biomedical model with pulsatile inflow is presented to benchmark the algorithm and to demonstrate the potential applications of this method.

Key Words
fluid-structure interaction; pulsatile flow; partitioned analysis; multi-predict-correct iterative; arbitrary lagrangian-eulerian; experimental test

Address
Wenquan Wang, Zhang Li-xiang and Yan Yan : Department of Engineering Mechanics, Kunming University of Science and Technology, Kunming 650051, China
Yakun Guo : School of Engineering, University of Aberdeen, Aberdeen AB24 3UE, UK

Abstract
Dynamic response of Pile Supported Structures is highly depended on Soil Pile Structure Interaction. In this paper, by comparison of experimental and numerical dynamic responses of a prototype jacket offshore platform for both hinge based and pile supported boundary conditions, effect of soil-pilestructure interaction on dynamic characteristics of this platform is studied. Jacket and deck of a prototype platform is installed on a hinge-based case first and then platform is installed on eight skirt piles embedded on continuum monolayer sand. Dynamic characteristics of platform in term of natural frequencies, mode shapes and modal damping are compared for both cases. Effects of adding and removing vertical bracing members in top bay of jacket on dynamic characteristics of platform for both boundary conditions are also studied. Numerical simulation of responses for the studied platform is also performed for both mentioned cases using capability of ABAQUS and SACS software. The 3D model using ABAQUS software is created using solid elements for soil and beam elements for jacket, deck and pile elements. Mohr-Coulomb failure criterion and pile-soil interface element are used for considering nonlinear pile soil structure interaction. Simplified modeling of soil-pile-structure interaction effect is also studied using SACS software. It is observed that dynamic characteristics of the system changes significantly due to soilpile- structure interaction. Meanwhile, both of complex and simplified (ABAQUS and SACS, respectively) models can predict this effect accurately for such platforms subjected to dynamic loading in small range of deformation.

Key Words
steel jacket type offshore platform; soil-pile-structure interaction; dynamic characteristics; experimental modal analysis

Address
Behrouz Asgarian, Hamed Rahman Shokrgozar, Davoud Shahcheraghi and Hasan Ghasemzadeh : Civil Engineering Faculty, K.N.Toosi University of Technology, Tehran, Iran


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