• Computational Structural Engineering
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• v.10 no.4
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• pp.117-130
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• 1997

In this paper, a modified 10-node equivalent solid element(MQM10 element), which has smallest degrees of freedom among 3-dimensional solid elements accounting bending deformation as well as extensional and shear deformations of isotropic plates, is proposed. The proposed MQM10 element exhibits stiffer bending stiffness due to the reduction of degrees of freedom from 20-node element or Q11 element. As an effective way to correct the relative stiffness stiffening phenomenon, the modification equation of Gauss sampling points is proposed. The quantity of modification is a function of Poisson's ratio. The effectiveness of MQM10 element is tested by applying it to several examples. It is noted that the results of static and free vibration analysis of isotropic plates using MQM10 elements show a good agreement with those using 20-node element.

• Computational Structural Engineering
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• v.8 no.1
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• pp.30-38
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• 1995

이방향 천공 발파공법의 실용성을 입증하여 실시공에 착수하기 위해서는 수치해석을 통하여 사전에 종방향 및 방사방향 천공발파에 따른 지표면에서의 지반진동의 영향을 알아보는 것이 필요하였다. 정확한 현장조건과 발파하중이 주어진 상태에서의 정밀해를 구하기 위해서는 시공상의 발파패턴대로 전체 발파공을 모형화하는 것이 필요하나 앞서 언급한 바와 같이 해석목적상 기존공법과 신공법의 지반응답의 차이를 비교하는 것이 주목적이였기 때문에 해석조건을 동일하게 가정하고 발파공도 대표적인 방향성을 가지는 1개공만을 선택하여 해석을 수행하였다. 기존 종방향 천공 발파공법과 신공법인 이방향 천공 발파공법의 상대적 비교를 위한 3차원 동적 해석결과, 관심의 대상이 되는 터널 직상부의 경우 기존의 종방향 천공 발파에 비해 이방향 천공발파는 진동이 두드러지게 감소함을 알 수 있었으며 이는 발파공의 방향성에 따라 지반응답이 크게 영향을 받는다는 것을 의미한다. 따라서 터널굴착시 문제시 되는 지상구조물의 위치에 따라 발파공의 위치를 적절히 조절함으로써 문제발생 예상지역의 진동치를 감소시킬 수 있을 것이라 판단된다. 그러나 이러한 잇점은 확대발파전 파이롯트 터널이라는 자유공간이 존재할 때만 가능하므로 이방향 천공 발파공법은 TBM의 효용성을 극대화시킨 것이라 할 수 있다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6A
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• pp.379-387
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• 2012

This study investigates free vibration characteristics of new energy harvesting multi-layer block structures with different geometrical shapes using solid and shell finite elements and evaluate their piezoelectric effect on experiments. The two and three-dimensional finite element (FE) delamination models for block structures described in this paper is attractive not only because it shows excellent accuracy in analysis but also it shows the entire vibration mode shape. The FE model using ABAQUS is used for studying free vibrations of multi-layer block structures for various tip mass and PZT. In particular, new results reported in this paper are focused on the significant effects of the global and local vibration modes for various parameters, such as size of block shape, existence of tip mass and hole, and location of tip mass and PZT. In addition, we evaluate the power generation capacity of developed energy block structures through a laboratory-scale experiment.

• Journal of Korean Society of Steel Construction
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• v.19 no.4
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• pp.367-381
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• 2007

A transmission tower was designed using the structural methodology to assume a simple truss behavior. However, there is a big difference between a simple truss behavior and a real one. A suitable explanation of structural stability is that it is a semi-rigid connection and not the assumed hinged connection. This study proposes an alternative structural-analysis modeling strategy for the transmission tower design. The element models that were considered were the truss element model, the beam element model, and the combined beam-truss element model. This study includes linear static analysis, free-vibration analysis, and elastic buckling analysis with respect to the design load. The results of the analysis indicate that the axial forces, axial stresses, and maximum displacements of the three analytical models are very similar. However, the bending moments and stresses of the beam element model and of the combined beam-truss element model are significantly high. The results of the free-vibration and elastic buckling analyses show that the beam-truss model can be conservatively used for the transmission tower design.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.2
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• pp.119-129
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• 2004

A three dimensional (3D) method of analysis is presented for determining the free vibration frequencies and mode shapes of thick, circular and annular plates with nonlinear thickness variation along the radial direction. Unlike conventional plate theories, which are mathematically two dimensional (2D), the present method is based upon the 3D dynamic equations of elasticity. Displacement components u/sub s/, u/sub z/, and u/sub θ/ in the radial, thickness, and circumferential directions, respectively, are taken to be sinusoidal in time, periodic in θ, and algebraic polynomials in the s and z directions. Potential (strain) and kinetic energies of the plates are formulated, and the Ritz method is used to solve the eigenvalue problem thus yielding upper bound values of the frequencies by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Convergence to four digit exactitude is demonstrated for the first five frequencies of the plates. Numerical results we presented for completely free, annular and circular plates with uniform linear, and quadratic variations in thickness. Comparisons are also made between results obtained from the present 3D and previously published thin plate (2D) data.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.5
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• pp.1023-1031
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• 1994

The closed forms of consistent mass matrix with rotational inertia matrix are developed for free vibration analysis in space sutructures containing linearly tapered members with cross section of thin-walled I-sections. The exact displacement functions are used for formulating mass matrices. The very small slopes of the tapered member are used in usual practice, such that the series expansion forms of these are also developed to avoid numerical failure in vibration analysis. Significant improvements of accuracy and efficiency of free vibation analysis are achieved by using the mass matrices developed in this study. Frequencies of free vibation of tapered members are compared with solutions based upon stepped representation of beam element in the ANSYS. The mass matrices presented in this study can be used for the free vibration analysis of tapered and prismatic members.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.4
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• pp.419-429
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• 2003

A three-dimensional (3-D) method of analysis is presented for determining the free vibration frequencies of thick, hyperboloidal shells of revolution. Unlike conventional shell theories, which are mathematically two-dimensional (2-D), the present method is based upon the 3-D dynamic equations of elasticity. Displacement components u/sub r/, u/sub θ/, u/sub z/ in the radial, circumferential, and axial directions, respectively, we taken to be sinusoidal in time, periodic in θ, and algebraic polynomials in the r and z directions. Potential(strain) and kinetic energies of the hyperboloidal shells are formulated, and the Ritz method is used to solve the eigenvalue problem, thus yielding upper bound values of the frequencies by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Convergence to four digit exactitude is demonstrated for the first five frequencies of the hyperboloidal shells of revolution. Numerical results are tabulated for eighteen configurations of completely free hyperboloidal shells of revolution having two different shell thickness ratios, three variant axis ratios, and three types of shell height ratios. Poisson's ratio (ν) is fixed at 0.3. Comparisons we made among the frequencies for these hyperboloidal shells and ones which ate cylindrical or nearly cylindrical( small meridional curvature. ) The method is applicable to thin hyperboloidal shells, as well as thick and very thick ones.

• Journal of the Korean Society for Marine Environment & Energy
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• v.13 no.1
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• pp.47-52
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• 2010

The wave energy absorption efficiency and the first-order and the time-mean second-order wave loads of a three-dimensional bottom-mounted oscillating water column (OWC) chamber structure are studied. The potential problem is solved by making use of a hybrid Green integral equation associated with the finite-waterdepth free-surface Green function outside a twin chamber and the Rankine Green function inside taking account of the fluctuating air pressure inside the chamber. Numerical results of the primary wave energy converting efficiency and the oscillating and steady wave loads of a three-dimensional bottom-mounted OWC pilot plant have been presented.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.2
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• pp.25-32
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• 1988

A formulation of an isoparametric quadrilateral higher-order plate bending finite element is presented. The 8-noded 28-d.o.f. plate element has been degenerated from the three-dimensional continuum by introducing the plate assumptions and considering higher-order in-plane displacement profile. The element characteristics have been derived by the Galerkin's weighted residual method and computed by using the selective reduced integration technique to avoid shear-locking phenomenon. Several numerical examples are given to demonstrate the accuracy and versatility of the proposed quadrilateral higher-order plate bending element over the other existing plate finite elements in both static and dynamic analyses.

• Journal of the Earthquake Engineering Society of Korea
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• v.2 no.2
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• pp.23-34
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• 1998

This research proposes on effective analytical methodology for vertical vibration of three dimensional frame structures including slabs. The consideration of slabs, although allows more precise results, requires large amount of computer time and memory space due to the use of plane stress elements. In consideration of these problems, a method to properly manage nodal points and degrees of freedom is proposed based on matrix condensation technique. Also studied is the use of super elements to obtain fast and reliable results with simple input data when they are applied to conventional building structures.