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CONTENTS
Volume 2, Number 4, December 2013
 

Abstract
The coupled free vibration of flexible structures and on-board liquid in zero gravity space was analyzed, considering the spacecraft main body as a rigid mass, the flexible appendages as two elastic beams, and the on-board liquid as a “spring-mass” system. Using the Lagrangians of a rigid mass (spacecraft main body), “spring-mass” (liquid), and two beams (flexible appendages), as well as assuming symmetric motion of the system, we obtained the frequency equations of the coupled system by applying Rayleigh-Ritz method. Solving these frequency equations, which are governed by three system parameters, as an eigenvalue problem, we obtained the coupled natural frequencies and vibration modes. We define the parameter for evaluating the magnitudes of coupled motions of the added mass (liquid) and beam (appendages). It was found that when varying one system parameter, the frequency curves veer, vibration modes exchange, and the significant coupling occurs not in the region closest to the two frequency curves but in the two regions separate from that region.

Key Words
hydroelastic vibration; space structure; coupled system; sloshing

Address
Masakatsu Chiba; Department of Aerospace Engineering, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan
Shinya Chiba; Keihin corporation, 2021-8, Hosyakuji, Takanezawa-machi, Tochigi 329-1233, Japan
Kousuke Takemura; NTN corporation, 1578, Higashi-Kaizuka, Iwata, Shizuoka 438-8510, Japan

Abstract
This study aims at observing the coupling behaviours between suspended ceilings and partition walls in terms of their global seismic performance using full-scale shake table tests. The suspended ceilings with planar dimensions of 6.0 m Χ 3.6 m were tested with two types of panels: acoustic lay-in and metal clip-on panels. They were further categorized as seismic-braced, seismic-unbraced, and non-seismic installations. Also, two configurations of 2.7 m high partition wall specimens, with C-shape and I-shape in the plane layouts, were tested. In total, seven ceiling-partition-coupling (CPC) specimens were tested utilizing a unidirectional seismic simulator. The test results indicate that the damage patterns of the tested CPC systems included failure of the ceiling grids, shearing-off of the wall top railing, and, most destructively, numerous partial detachments and falling of the ceiling panels. The loss of panels was mostly concentrated near the center of the tested partition wall. The testing results also confirmed that the failure mode of the non-seismic CPC systems was brittle: The whole system would collapse suddenly all at once when the magnitude of the inputs hit the capacity threshold, rather than displaying progressive damage. Overall, the seismic capacity of the unbraced and braced CPC systems could be up to 1.23 g and 2.67 g, respectively; these accelerations were both achieved at the base of the partition wall. Nonetheless, for practical applications, it is noteworthy that the three-dimensional nature of seismic excitations and the size effect of the ceiling area are parameters that exacerbate the CPC's seismic response so that their actual capacity may be dramatically decreased, leading to important losses even in moderate seismic events.

Key Words
suspended ceiling systems; partition walls; seismic performance; operational and functional components; shake table tests; nonstructural components; OFC

Address
Department of Civil Engineering and Applied Mechanics, McGill University,817 Sherbrooke Street West, Montreal, Quebec H3A 0C3, Canada

Abstract
In this work we propose a novel procedure for direct computation of buckling loads for extreme mechanical or thermomechanical conditions. The procedure efficiency is built upon the von Karmann strain measure providing the special format of the tangent stiffness matrix, leading to a general linear eigenvalue problem for critical load multiplier estimates. The proposal is illustrated on a number of validation examples, along with more complex examples of interest for practical applications. The comparison is also made against a more complex computational procedure based upon the finite strain elasticity, as well as against a more refined model using the frame elements. All these results confirm a very satisfying performance of the proposed methodology.

Key Words
buckling; thermomechanical coupling; geometric instability, critical load, eigenvalue problem

Address
Adnan Ibrahimbegovic and Emina Hajdo; Laboratoire de mécanique et technologie, École Normale Supérieure,61 Avenue du Président Wilson, 94230 Cachan, France
Samir Dolarevic; Faculty of Civil Engineering, University of Sarajevo, Patriotske lige 30, 71000 Sarajevo, Bosnia and Herzegovina

Abstract
Soils consist of an assemblage of particles with different sizes and shapes which form a skeleton whose voids are filled with water and air. Hence, soil behaviour must be analyzed by incorporating the effects of the transient flow of the pore-fluid through the voids, and therefore requires a two-phase continuum formulation for saturated porous media. The present paper presents briefly the Biot’s basic theory of dynamics of saturated porous media with u–P formulation to determine the responses of pore fluid and soil skeleton during cyclic loading. Kelvin elements are attached to transmitting boundary. The Pastor–Zienkiewicz–Chan model has been used to describe the inelastic behavior of soils under isotropic cyclic loadings. Newmark-Beta method is employed to discretize the time domain. The response of fluid-saturated porous media which are subjected to time dependent loads has been simulated numerically to predict the liquefaction potential of a semi-infinite saturated sandy layer using finite-infinite elements. A settlement of 17.1 cm is observed at top surface. It is also noticed that liquefaction occurs at shallow depth. The mathematical advantage of the coupled finite element analysis is that the excess pore pressure and displacement can be evaluated simultaneously without using any empirical relationship.

Key Words
2-D isoparametric continuum element; kelvin element; transmitting boundary; 2-D infinite elements; liquefaction; pastor–zienkiewicz–chan model

Address
Department of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand 247667, India

Abstract
Three-dimensional Lagrangian fluid finite element is applied to seismic response analysis of an oil storage tank with a floating roof. The fluid element utilized in the present analysis is formulated based on the displacement finite element method considering only volumetric elasticity and its element stiffness matrix is derived by using one-point integration method in order to avoid volumetric locking. The method usually adds a rotational penalty stiffness to satisfy the irrotational condition for fluid motion and modifies element mass matrices through the projected mass method to suppress spurious hourglass-mode appeared in compensation for one-point integration. In the fluid element utilized in the present paper, a small hourglass stiffness is employed. The fluid and structure domains for the objective oil storage tank are modeled by eight-node solid elements and four-node shell elements, respectively, and the transient response of the floating roof structure or the free surface are evaluated by implicit direct time integration method. The results of seismic response analyses are compared with those by other method and the validation of the present analysis using three-dimensional Lagrangian fluid finite elements is shown.

Key Words
FEM; fluid element; fluid-structure interaction; oil storage tank; seismic response

Address
Department of Engineering and Applied Sciences, Faculty of Science and Technology, Sophia University, 7-1 Kioicho, Chiyoda-ku, Tokyo 102-8554, Japan


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