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CONTENTS
Volume 5, Number 2, March 1997
 

Abstract
Importance sampling methods have been developed with the aim of reducing the computational costs inherent in Monte Carlo methods. This study proposes a new algorithm called the adaptive kernel method which combines and modifies some of the concepts from adaptive sampling and the simple kernel method to evaluate the structural reliability of time variant problems. The essence of the resulting algorithm is to select an appropriate starting point from which the importance sampling density can be generated efficiently. Numerical results show that the method is unbiased and substantially increases the efficiency over other methods.

Key Words
importance sampling, adaptive kernel method, structural system reliability, time variant problems, random dynamic loadings, uncertain nonlinear hysteretic structures

Address
Wang GS, UNIV CALIF IRVINE,DEPT CIVIL & ENVIRONM ENGN,IRVINE,CA 92697

Abstract
Patch recovery attempts to derive a more accurate stress filed over a particular element than the finite element shape function used for that particular element. Elements that have a free edge being the boundary to the structure have particular stress relationship that can be incorporated to the stress field to improve the accuracy of the approximation.

Key Words
finite element, stress, errors

Address
Stephen DB, UNIV SYDNEY,FAC ENGN,FINITE ELEMENT ANAL RES CTR,BLDG J07,SYDNEY,NSW 2006,AUSTRALIA

Abstract
In computing eigenvalues for a large finite element system it has been observed that the eigenvalue extractors produce eigenvectors that are in some sense more accurate than their corresponding eigenvalues. From this observation the paper uses a patch type technique based on the eigenvector for one mesh quality to provide an eigenvalue error indicator. Tests show this indicator to be both accurate and reliable.

Key Words
finite elements, natural frequence, error estimation

Address
Stephen DB, UNIV SYDNEY,FAC ENGN,FINITE ELEMENT ANAL RES CTR,BLDG J07,SYDNEY,NSW 2006,AUSTRALIA

Abstract
A dynamic time-history analysis of the coupled internals and core in the vertical direction is performed as a part of the fuel assembly qualification program. To reflect the interaction between the fuel rods and grid cage, friction element is developed and is implemented. Also derived here is a method to calculate a hydraulic force on the reactor internals due to pipe break. Peak responses are obtained for the excitations induced from earthquake and pipe break The dynamic responses such as fuel assembly axial forces and lift-off characteristics are investigated.

Key Words
reactor internals, fuel assembly, pressurized water reactor, pipe break, earthquake

Address
Jhung MJ, KOREA INST NUCL SAFETY,MECH ENGN GRP,TAEJON 305338,SOUTH KOREA

Abstract
A new seismic energy dissipation shear wall structure is proposed in this paper. The new shear wall is one with purposely built-in vertical slits within the wall panel, and various seismic energy dissipation devices are installed in the vertical slits so that the dynamic characteristics of the structure (for instance, lateral stiffness, ductility and fundamental period) can be controlled. In order to verify this concept, shaking table tests of two 10-story shear wall models were carried out, and the seismic behavior of the two models are studied by analyzing the test data and computing the nonlinear seismic response of the models.

Key Words
structural control, shear wall, shaking table test, seismic energy dissipation

Address
Lu XL, TONGJI UNIV,RES INST ENGN STRUCT,SHANGHAI 200092,PEOPLES R CHINA

Abstract
In the paper, a fractional derivative Kelvin-Voigt model describing the dynamic behavior of a special class of fluid viscous dampers, is presented. First of all, in order to verify their mechanical properties, two devices were tested the former behaving as a pure damper (PD device), whereas the latter as an elastic-damping device (ED device). For both, quasi-static and dynamic tests were carried out under imposed displacement control.

Secondarily, in order to describe their cyclical behavior, a model composed by an elastic and a damping element connected in parallel was defined. The elastic force was assumed as a linear function of the displacement whereas the damping one was expressed by a fractional derivative of the displacement. By setting an appropriate numerical algorithm, the model parameters (fractional derivative order, damping coefficient and elastic stiffness) were identified by experimental results.


The estimated values allowed to outline the main parameter properties on which depend both the elastic as well as the damping behavior of the considered devices.

Key Words
fractional derivative Kelvin-Voigt model, pure damper (PD device), elastic damper (ED device), fractional oscillator

Address
Gusella V, UNIV PERUGIA,FAC ENGN,INST ENERGET,STRADA S LUCIA CANETOLA,I-06125 PERUGIA,ITALY

Abstract
Experimental tests are described on three ring stiffened machined circular cylinders and three ring stiffened machined circular cones, which were tested to destruction under uniform external pressure. All six vessels failed by inelastic general instability. The experiments showed that the vessels initially deformed plastically at mid-bay in the circumferential direction, and this caused the circumferential tangent modulus to become much less than the elastic Young\'s modulus, causing the vessels to fail through plastic general instability at pressures much less than that predicted by elastic theory. Based on a thinness ratio, two semi-empirical design charts are provided, which are intended to be used for design purposes in conjunction with the finite element method and a plastic reduction factor.

Key Words
cylinders, cones, instability, external pressure

Address
Ross CTF, UNIV PORTSMOUTH,DEPT MECH & MFG ENGN,PORTSMOUTH PO1 2UP,HANTS,ENGLAND

Abstract
The dynamic equations for an arbitrary cluster comprising rigid spheres or assemblies of spheres (subclusters) encountered in granular-type systems are considered. The system is treated within the framework of multibody dynamics. It is shown that for an arbitrary cluster topology the governing equations can be given in an explicit scalar from. The derivation is based on the D\'Alembert principle, on inertial coordinate system for each body and direct utilization of the path matrix describing the topology. The scalar form of the equations is important in computer simulations of flow of granular-type materials. An illustrative example of a three-body system is given.

Key Words
discrete systems, governing equations, granular materials

Address
Vinogradov O, UNIV CALGARY,DEPT MECH ENGN,CALGARY,AB T2N 1N4,CANADA


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