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CONTENTS
Volume 7, Number 6, December 2018
 

Abstract
In this paper, we present a numerical model for fluid-structure interaction between structure built of porous media and acoustic fluid, which provides both pore pressure inside porous media and hydrodynamic pressures and hydrodynamic forces exerted on the upstream face of the structure in an unified manner and simplifies fluid-structure interaction problems. The first original feature of the proposed model concerns the structure built of saturated porous medium whose response is obtained with coupled discrete beam lattice model, which is based on Voronoi cell representation with cohesive links as linear elastic Timoshenko beam finite elements. The motion of the pore fluid is governed by Darcy\'s law, and the coupling between the solid phase and the pore fluid is introduced in the model through Biot\'s porous media theory. The pore pressure field is discretized with CST (Constant Strain Triangle) finite elements, which coincide with Delaunay triangles. By exploiting Hammer quadrature rule for numerical integration on CST elements, and duality property between Voronoi diagram and Delaunay triangulation, the numerical implementation of the coupling results with an additional pore pressure degree of freedom placed at each node of a Timoshenko beam finite element. The second original point of the model concerns the motion of the outside fluid which is modeled with mixed displacement/pressure based formulation. The chosen finite element representations of the structure response and the outside fluid motion ensures for the structure and fluid finite elements to be connected directly at the common nodes at the fluid-structure interface, because they share both the displacement and the pressure degrees of freedom. Numerical simulations presented in this paper show an excellent agreement between the numerically obtained results and the analytical solutions.

Key Words
acoustic fluid-structure interaction; dam-reservoir system; coupled discrete beam lattice model; saturated porous media; mixed displacement/pressure based formulation; hydrodynamic pressure

Address
Emina Hadzalic:
1) Universite de Technologie de Compiegne, Laboratoire Roberval de Mecanique, Centre de Recherche Royallieu, 60200 Compiegne, France
2) Faculty of Civil Engineering, University of Sarajevo, Patriotske lige 30, Sarajevo 71000, Bosnia and Herzegovina
Adnan Ibrahimbegovic:
1) Universite de Technologie de Compiegne, Laboratoire Roberval de Mecanique, Centre de Recherche Royallieu, 60200 Compiegne, France
2) Institut Universitaire de France
Samir Dolarevic: Faculty of Civil Engineering, University of Sarajevo, Patriotske lige 30, Sarajevo 71000, Bosnia and Herzegovina

Abstract
This paper deals with numerical modeling of dynamic failure phenomena in rate-sensitive brittle and/or ductile materials. To this end, a two-dimensional continuum viscodamage-embedded discontinuity model, which is based on our previous work (see Do et al. 2017), is developed. More specifically, the pre-peak nonlinear and rate-sensitive hardening response of the material behavior, representing the fracture-process zone creation, is described by a rate-dependent continuum damage model. Meanwhile, an embedded displacement discontinuity model is used to formulate the post-peak response, involving the macro-crack creation accompanied by exponential softening. The numerical implementation in the context of the finite element method exploiting the second-order mid-point scheme is discussed in detail. In order to show the performance of the model several numerical examples are included.

Key Words
dynamics; fracture process zone-FPZ; strain-softening; localization; finite element; embedded discontinuity; mid-point scheme

Address
Xuan Nam Do and Adnan Ibrahimbegovic: Universite de Technologie Compiegne / Sorbonne Universites, Laboratoire Roberval de Mecanique
Centre de Recherche Royallieu, Rue Personne de Roberval, 60200 Compiegne, France

Abstract
In this paper, nonlinear displacements of laminated composite beams are investigated under non-uniform temperature rising with temperature dependent physical properties. Total Lagrangian approach is used in conjunction with the Timoshenko beam theory for nonlinear kinematic model. Material properties of the laminated composite beam are temperature dependent. In the solution of the nonlinear problem, incremental displacement-based finite element method is used with Newton-Raphson iteration method. The distinctive feature of this study is nonlinear thermal analysis of Timoshenko Laminated beams full geometric non-linearity and by using finite element method. In this study, the differences between temperature dependent and independent physical properties are investigated for laminated composite beams for nonlinear case. Effects of fiber orientation angles, the stacking sequence of laminates and temperature on the nonlinear displacements are examined and discussed in detail.

Key Words
composite laminated beams; thermal nonlinear analysis; Timoshenko beam theory; total Lagragian; Finite Element Method; temperature dependent physical properties

Address
Şeref D. Akbas: Department of Civil Engineering, Bursa Technical University, Yildirim Campus, Yildirim, Bursa 16330, Turkey


Abstract
The semi-active optimal vibration control of nonlinear torsion-bar suspension vehicle systems under random road excitations is an important research subject, and the boundedness of MR dampers and the uncertainty of vehicle systems are necessary to consider. In this paper, the differential equations of motion of the coupling torsion-bar suspension vehicle system with MR damper under random road excitation are derived and then transformed into strongly nonlinear stochastic coupling vibration equations. The dynamical programming equation is derived based on the stochastic dynamical programming principle firstly for the nonlinear stochastic system. The semi-active bounded parametric optimal control law is determined by the programming equation and MR damper dynamics. Then for the uncertain nonlinear stochastic system, the minimax dynamical programming equation is derived based on the minimax stochastic dynamical programming principle. The worst-case disturbances and corresponding semi-active bounded parametric optimal control are obtained from the programming equation under the bounded disturbance constraints and MR damper dynamics. The control strategy for the nonlinear stochastic vibration of the uncertain torsion-bar suspension vehicle system is developed. The good effectiveness of the proposed control is illustrated with numerical results. The control performances for the vehicle system with different bounds of MR damper under different vehicle speeds and random road excitations are discussed.

Key Words
stochastic nonlinear vibration; semi-active bounded optimal control; coupling vehicle system; uncertainty; random road excitation; MR damper; stochastic dynamical programming; minimax strategy

Address
Z. G. Ying and G. F. Yan: Department of Mechanics, School of Aeronautics and Astronautics, Zhejiang University,
Hangzhou 310027, P.R. China
Y. Q. Ni: Department of Civil and Environmental Engineering, National Rail Transit Electrification and Automation Engineering Technology Research Centre (Hong Kong Branch), The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong

Abstract
The recent seismic events have led to concerns on safety and vulnerability of Reinforced Concrete Moment Resisting Frame \"RC-MRF\" buildings. The seismic design demands are greatly dependent on the computational tools, the inherent assumptions and approximations introduced in the modeling process. Thus, it is essential to assess the relative importance of implementing different modeling approaches and investigate the computed response sensitivity to the corresponding modeling assumptions. Many parameters and assumptions are to be justified for generation effective and accurate structural models of RC-MRF buildings to simulate the lateral response and evaluate seismic design demands. So, the present study aims to develop reliable finite element model through many refinements in modeling the various structural components. The effect of finite element modeling assumptions, analysis methods and code provisions on seismic response demands for the structural design of RC-MRF buildings are investigated. where, a series of three-dimensional finite element models were created to study various approaches to quantitatively improve the accuracy of FE models of symmetric buildings located in active seismic zones. It is shown from results of the comparative analyses that the use of a calibrated frame model which was made up of line elements featuring rigid offsets manages to provide estimates that match best with estimates obtained from a much more rigorous modeling approach involving the use of shell elements.

Key Words
MRF buildings; codes provisions; seismic design demands; finite element modeling; modeling assumptions

Address
Shehata E Abdel Raheem:
1) Faculty of Engineering, Taibah University, Madinah 41411, KSA
2) Civil Engineering Department, Faculty of Engineering, Assiut University, Assiut 71516, Egypt
Mohamed Omar:
1) Civil Engineering Department, Faculty of Engineering, Aswan University, Egypt
2) Civil Engineering Department, Faculty of Engineering Rabigh Branch, King Abdulaziz University, KSA
Ahmed K Abdel Zaher:
1) Faculty of Engineering, Taibah University, Madinah 41411, KSA
2) Civil Engineering Department, Faculty of Engineering, Cairo University, Giza, Egypt
Ahmed M Taha: Faculty of Engineering, Taibah University, Madinah 41411, KSA

Abstract
The Ritz method is known as very successful strategy for discretizing continuous problems, but it has never been used for solving systems of algebraic equations. The Iterated Ritz Method (IRM) is a novel iterative solver based on the discretized Ritz procedure applied at each iteration step. With an appropriate choice of coordinate vectors, the method may be efficient in linear, nonlinear and optimization problems. Additionally, some iterative methods can be explained as special cases of this approach, which helps to understand advantages and limitations of these methods and gives motivation for their improvement in sense of IRM. In this paper, some ideas for generation of efficient coordinate vectors are presented. The algorithm was developed and tested independently and then implemented into the open source program FEAP. Method has been successfully applied to displacement based (even ill-conditioned) models of structural engineering practice. With this original approach, a new iterative solution strategy has been opened.

Key Words
iterative methods; conjugate gradients; successive over-relaxation; preconditioning; Iterated Ritz Method

Address
Josip Dvornik, Damir Lazarevic, Mario Uros and Marta Savor Novak: Department for Engineering Mechanics, Faculty of Civil Engineering, University of Zagreb, Kaciceva 26, 10 000 Zagreb, Croatia



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