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CONTENTS
Volume 14, Number 1, July 2002
 

Abstract
Investigated in this study are the modal characteristics of the eccentric cylindrical shells with fluid-filled annulus. Theoretical method is developed to find the natural frequencies of the shell using the finite Fourier expansion, and their results are compared with those of finite element method to verify the validation of the method developed. The effect of eccentricity on the modal characteristics of the shells is investigated using a finite element modeling.

Key Words
cylindrical shell, modal characteristic, fluid-filled annulus, finite element method, eccentricity

Address
Jhung MJ, Korea Inst Nucl Safety, 19 Kusong Dong, Yusong Gu 305338, Daejeon, South Korea
Korea Inst Nucl Safety, Yusong Gu 305338, Daejeon, South Korea
Korea Atom Energy Res Inst, Yusong Gu 305353, Daejeon, South Korea
Chonnam Natl Univ, Kwangju 500757, South Korea

Abstract
A control algorithm combining viscous and non-linear Reid damping mechanisms has been recently proposed by the authors to command active friction dampers. In this paper. friction dampers and the proposed algorithm are applied to control the seismic responses of a nonlinear 20-story building. Piezoelectric stack actuators are used to implement the control algorithm. The capacity of each damper is determined by the practical size of piezoelectric actuators and the availability of power supply. The saturation effect of the actuators on the building responses is investigated. To minimize the peak story drift ratio or floor acceleration of the building structure, a practical sequential procedure is developed to sub-optimally place the dampers on various floors. The effectiveness of active friction dampers and the efficiency of the proposed sequential procedure are verified by subjecting the building structure to four earthquakes of various intensities. The performance of 80 dampers and 137 dampers installed on the structure is evaluated according to 5 criteria. Numerical simulations indicated that the proposed control algorithm effectively reduces the seismic responses of the uncontrolled 20-story building, such as inelastic deformation. The sub-optimal placement of dampers based on peak acceleration outperforms that based on peak drift ratio for structures subjected to near-fault ground motions. Saturation of piezoelectric actuators has adverse effect on floor acceleration.

Key Words
active control, piezoelectric friction damper, steel moment resisting frame, inelastic responses, control algorithm, seismic performance, near-fault effect

Address
Chen CQ, Univ Missouri, Dept Civil Engn, 111 Butler Carlton Hall, Rolla, MO 65409 USA
Univ Missouri, Dept Civil Engn, Rolla, MO 65409 USA

Abstract
In order to trace a target in deep sky. a feed cabin 20 tons in weight used for a large radio telescope is drawn with six cables. To realize a smooth tracing all the time, optimal distribution of the cable tensions is explored. A set of cable-clog systems is utilized to control the wind-induced vibration of the cable-cabin structure. This is an attempt to apply the passive structural control strategy in the area of radio astronomy. Simulations of wind-induced vibration of the structure in both time and frequency domains offer a valuable reference for construction of the next generation large radio telescope.

Key Words
large radio telescope, cable-cabin structured, optimization, wind-induced vibration, passive structural control, nonlinear analysis

Address
Qui YY, Xidian Univ, Sch Mech & Elect Engn, Xian 710071, Peoples R China
Xidian Univ, Sch Mech & Elect Engn, Xian 710071, Peoples R China
Chinese Acad Sci, Beijing Radio Astron Obser, Beijing 100012, Peoples R China

Abstract
This work presents an iterative mesh partitioning approach to improve the efficiency of parallel substructure finite element computations. The proposed approach employs an iterative strategy with a set of empirical rules derived from the results of numerical experiments on a number of different finite element meshes. The proposed approach also utilizes state-of-the-art partitioning techniques in its iterative partitioning kernel, a cost function to estimate the computational cost of each submesh, and a mechanism that adjusts element weights to redistribute elements among submeshes during iterative partitioning to partition a mesh into submeshes (or substructures) with balanced computational workloads. In addition, actual parallel finite element structural analyses on several test examples are presented to demonstrate the effectiveness of the approach proposed herein. The results show that the proposed approach can effectively improve the efficiency of parallel substructure finite element computations.

Key Words
mesh partitioning, graph partitioning, parallel finite element computations, parallel substructure method

Address
Hsieh SH, Natl Taiwan Univ, Dept Civil Engn, Taipei 10764, Taiwan
Natl Taiwan Univ, Dept Civil Engn, Taipei 10764, Taiwan
Natl Ctr Res Earthquake Engn, Taipei, Taiwan
Mil Police Headquarter, Taipei, Taiwan

Abstract
A finite element formulation for the time-domain analysis of linear transient elastodynamic problems is presented based on the weak form obtained by applying the Galerkin\'s method to the integro-differential equations which contain the initial conditions implicitly and does not include the inertia terms. The weak form is extended temporally under the assumptions of the constant and linear time variations of field variables, since the time-stepping algorithms such as the Newmark method and the Wilson theta-method are not necessary, obtaining two kinds of implicit finite element equations which are tested for numerical accuracy and convergency. Three classical examples having finite and infinite domains are solved and numerical results are compared with the other analytical and numerical solutions to show the versatility and accuracy of the presented formulation.

Key Words
transient, elastodynamic, time-integral formulation, wave diffraction, finite element

Address
Sim WJ, Kum Oh Natl Univ Technol, Sch Mech Engn, Dept Engn Sci & Mech, 188 Shinpyung, Kumi 730701, Kyungbuk, South Korea
Kum Oh Natl Univ Technol, Sch Mech Engn, Dept Engn Sci & Mech, Kumi 730701, Kyungbuk, South Korea

Abstract
The use of supplemental damping to dissipate seismic energy is one of the most economical and effective ways to mitigate the effects of earthquakes on structures. Both displacement-dependent and velocity-dependent devices dissipate earthquake-induced energy effectively. Combining displacement-dependent and velocity-dependent devices for seismic mitigation of structures minimizes the shortcomings of individual dampers, and is the most economical solution for seismic mitigation. However, there are few publications related to the optimum distributions of combined devices in a multiple-bay frame building. In this paper. the effectiveness of a building consisting of multiple bags equipped with combined displacement-dependent and velocity-dependent devices is investigated. A four-story building with six bays was selected as an example to examine the efficiency of the proposed combination methods. The parametric study shows that appropriate arrangements of different kinds of devices make the devices more efficient and economical.

Key Words
velocity-dependent devices, displacement-dependent devices, energy dissipation devices, supplemental damping

Address
Pong WS, San Francisco State Univ, Sch Engn, Dept Civil Engn, 1600 Holloway Ave, San Francisco, CA 94132 USA
San Francisco State Univ, Sch Engn, Dept Civil Engn, San Francisco, CA 94132 USA
Feng Chia Univ, Dept Civil Engn, Taichung 40724, Taiwan

Abstract
The scaled-boundary finite element method is a novel semi-analytical technique, combining the advantages of the finite element and the boundary element methods with unique properties of its own. The method works by weakening the governing differential equations in one coordinate direction through the introduction of shape functions, then solving the weakened equations analytically in the other (radial) coordinate direction. These coordinate directions are defined by the geometry of the domain and a scaling centre. This paper presents a general development of the scaled boundary finite-element method for two-dimensional problems where two boundaries of the solution domain are similar. Unlike three-dimensional and axisymmetric problems of the same type. the use of logarithmic solutions of the weakened differential equations is found to be necessary. The accuracy and efficiency of the procedure is demonstrated through two examples. The first of these examples uses the standard finite element method to provide a comparable solution, while the second combines both solution techniques in a single analysis. One significant application of the new technique is the generation of transition super-elements requiring few degrees of freedom that can connect two regions of vastly different levels of discretisation.

Key Words
scaled boundary finite-element method, similarity, plane stress, plane strain, axisymmetry, transition element

Address
Deeks AJ, Univ Western Australia, Dept Civil & Resource Engn, Crawley, WA 6009, Australia


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