• 한국농공학회지
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• 제38권3호
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• pp.50-57
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• 1996

A numerical method is presented to obtain the natural frequencies and mode shapes of the arbitrary tapered beams with static deflection due to arbitrary distributed dead loads. The differential equation governing free vibration of such beams is derived and solved numerically. The double integration method using the trapezoidal rule is used to solve the static behaviour of beams loaded arbitrary distributed dead load. Also, the Improved Euler method and the determinant search method are used to integrate the differential equation subjected to the boundary conditions and to determine the natural frequencies of the beams, respectively. In the numerical examples, the various geometries of the beams are considered : (1) linearly tapered beams as the arbitrary variable cross-section, (2) the triangular, sinusoidal and uniform loads as the arbitrary distributed dead loads and (3) the hinged-hinged, clamped-clamped and hinged-clamped ends as the end constraints. All numerical results are shown as the non-dimensional forms of the system parameters. The lowest three natural frequencies versus load parameter, slenderness ratio and section ratio are reported in figures. And for the comparison purpose, the typical mode shapes with and without the effects of static deflection are presented in the figure. According to the numerical results obtained in this analysis, the following conclusions may be drawn : (1) the natural frequencies increase when the effects of static deflections are included, (2) the effects are larger at the lower modes than the higher ones and (3) it should be betteF to include the effect of static deflection for calculating the frequencies when the beams are supported by both hinged ends or one hinged end.

• 한국전산구조공학회논문집
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• 제15권3호
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• pp.523-534
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• 2002

본 논문에서는 축방향 압축하중을 받는 다퐁간분리된 적층 보-기둥의 자유진동과 좌팔에 대한 해석을 수행하였다. 다층간분리된 적층 보-기둥의 고유진동수와 탄성 좌굴 하중에 대한 층간분리의 영향을 조사하기 위해 층간분리의 양단에서 기울기와 곡률이 일정하다는 가정을 적용하여 일반적인 운동학적 연속 조건을 유도하였다. 전체 다층간분리된 보-기둥을 부분으로 분할하고, 연속조건에 따른 반복관계를 각 하부 보-기둥에 부과함으로써 다층간분리된 보-기둥의 특성방정식을 구하였다. 축방향 증분 압축 하중에 따른 다층간분리된 보-기둥의 고유진동수와 탄성 좌굴 하중을 구하였으며 이는 손상되지 않은 적층 보-기둥의 최대 탄성 좌굴 하중에 한정된다 연구를 통하여 층간분리의 크기, 위치, 수가 고유진동수와 특히 탄성 좌굴 하중에 큰 영향을 미치는 것을 알 수 있었다.

• Smart Structures and Systems
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• 제15권2호
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• pp.315-334
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• 2015

A main goal of this study is to propose a damage detection technique to detect and localize damages of a top-tensioned riser. In this paper, the top-tensioned finite element (FE) model is considered as an analytical model of the riser, and a vibration-based damage detection method is proposed. The present method consists of a FE model updating and damage index method. In order to accomplish the goal of this study, first, a sensitivity-based FE model updating method using natural frequencies and zero frequencies is introduced. Second, natural frequencies and zero frequencies of the axial mode on the top-tensioned riser are estimated by eigenvalue analysis. Finally, the locations and severities of the damages are estimated from the damage index method. Three numerical examples are considered to verify the performance of the proposed method.

• 대한기계학회논문집
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• 제16권10호
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• pp.1807-1815
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• 1992

본 연구에서는 적층 복합재 원통쉘의 동적특성을 검토한다. 복합재료 원통 쉘의 설계에서 주요 관심 대상인 직교이방성 변수가 진동특성과 어떤 관계를 갖는지 알아보기 위하여 직교이방성이론으로 한정시켜 해석하였다. 지배방정식은 면내관성 항을 고려한 Donnell 운동방정식을 사용하며, 진동수방정식은 Rayleigh-Ritz법을 이용 하여 유도하였다. 임의의 경계조건에 적용될 수 있도록 보특성함수를 사용하여 고유 진동수를 간단히 구하였다. 기존의 연구자들이 채용한 복합재료의 물성치들과 복합 재 원통쉘의 고유진동수사이에 어떤관계가 있는지 규명하도록 하였다.

• 한국도로학회논문집
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• 제15권3호
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• pp.17-22
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• 2013

PURPOSES: Current theories for composite structures are too difficult for design engineers for construction. The purpose of this paper is to demonstrate to the practicing engineers, how to apply the advanced composite materials theory to the road structures. METHODS: Some laminate orientations have decreasing values of $D_{16}$, $B_{16}$, $D_{26}$ and $B_{26}$ stiffnesses as the ply number increases. The plate aspect ratio considered is from 1 to 5. In order to study the effect of $M_x$ on the equilibrium equations, two cases are considered. $M_x$ term is considered or neglected. RESULTS: Most of the road structures have high aspect ratios, for such cases further simplification is possible by neglecting the effect of the longitudinal moment terms. CONCLUSIONS: Most of the road structures have plate aspect ratios higher than 2. It is concluded that, for all boundary conditions, neglecting the longitudinal moment($M_x$) terms is acceptable if the aspect ratio (a/b) is equal to or higher than 2. This conclusion gives good guide line for design of the road structures.

• Smart Structures and Systems
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• 제26권1호
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• pp.1-10
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• 2020

Turkey is a transcontinental country located partly in Asia and partly in Europe, and hosted by diverse civilizations including Hittite, Urartu, Lydia, Phrygia, Pontius, Byzantine, Seljuk's and Ottomans. At various times, these built many historic monuments representing the most significant characteristics of their civilizations. Today, these monuments contribute enormously to the esthetic beauty of environment and important to many cities of Turkey in attracting tourism. The survival of these monuments depends on the investigation of structural behavior and implementation of needed repairing and/or strengthening applications. Hence, many countries have made deeper investigations and regulations to assess their monuments' structural behavior. This paper presents the dynamic behavior investigation of a monumental masonry mosque, the "İskenderpaşa Mosque" in Trabzon (Turkey), by performing an experimental examination with non-destructive testing. The dynamic behavior investigation was carried out by determining the dynamic characteristic called as natural frequencies, mode shapes and damping ratios. The experimental dynamic characteristics were extracted by Operational Modal Analysis (OMA). In addition, Finite Element (FE) model of masonry mosque was constructed in ANSYS software and the numerical dynamic characteristics such as natural frequencies and mode shapes were also obtained and compared to experimental ones. The paper aims at presenting the non-destructive testing procedure of a masonry mosque as well as the comparison of experimental and numerical dynamic characteristics obtained from the mosque.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권3호
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• pp.252-261
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• 2016

A spar-type floating substructure that is being widely used for offshore wind power generation is vulnerable to resonance in the heave direction because of its small water plane area. For this reason, the stable dynamic response of this floating structure should be ensured by accurately identifying the resonance characteristics. The purpose of this study is to analyze the characteristics of the combination resonance between the excitation frequency of a regular wave and natural frequencies of the floating substructure. First, the nonlinear equations of motion with two degrees of freedom are derived by assuming that the floating substructure is a rigid body, where the heaving motion and pitching motions are coupled. Moreover, to identify the characteristics of the combination resonance, the nonlinear term in the nonlinear equations is approximated up to the second order using the Taylor series expansion. Furthermore, the validity of the approximate model is confirmed through a comparison with the results of a numerical analysis which is made by applying the commercial software ANSYS AQWA to the full model. The result indicates that the combination resonance occurs at the frequencies of ${\omega}{\pm}{\omega}_5$ and $2{\omega}_{n5}$ between the excitation frequency (${\omega}$) of a regular wave and the natural frequency of the pitching motion (${\omega}_{n5}$) of the floating substructure.

• Structural Engineering and Mechanics
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• 제64권4호
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• pp.461-472
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• 2017

The dynamic tests of recycled aggregate concrete (RAC) are carried out, the rate-dependent mechanical models of RAC are proposed. The dynamic mechanical behaviors of RAC frame structure are investigated by adopting the numerical simulation method of the finite element. It is indicated that the lateral stiffness and the hysteresis loops of RAC frame structure obtained from the numerical simulation agree well with the test results, more so for the numerical simulation which is considered the strain rate effect than for the numerical simulation with strain rate excluded. The natural vibration frequency and the lateral stiffness increase with the increase of the strain rate. The dynamic model of the lateral stiffness is proposed, which is reasonably applied to describe the effect of the strain rate on the lateral stiffness of RAC frame structure. The effect of the strain rate on the structural deformation and capacity of RAC is analyzed. The analyses show that the inter-story drift decreases with the increase of the strain rate. However, with the increasing strain rate, the structural capacity increases. The dynamic models of the base shear coefficient and the overturning moment of RAC frame structure are developed. The dynamic models are important and can be used to evaluate the strength deterioration of RAC structure under dynamic loading.

• 대한기계학회논문집B
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• 제30권6호
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• pp.523-530
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• 2006

One of the fascinating prospects is the possibility of new hydrodynamics technology on micro-scale system since oscillations of micro-droplets are of practical and scientific importance. It has been widely conceived that the lowest oscillation mode of a pendant droplet is the longitudinal vibration, i.e. periodic elongation and contraction along the longitudinal direction. Nonlinear and forced oscillations of supported viscous droplet were focused in the present study. The droplet has a free contact line with solid plate and inviscid fluid. Natural frequencies of a pendant droplet have been investigated experimentally by imposing the acoustic wave while the frequency is being increased at a fixed amplitude. It is found that a pendant droplet shows the resonant behaviors at each mode similar to the theoretical analysis. The rotation of the droplet about the longitudinal axis is the oscillation mode of the lowest resonance frequency. This rotational mode can be invoked by periodic acoustic forcing and is analogous to the pendulum rotation. It is also found that the natural frequency of a pendant droplet is independent of the drop density and surface tension but inversely proportional to the square root of the droplet size.

• 대한조선학회논문집
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• 제30권1호
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• pp.134-144
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• 1993

샌드위치 구조는 두층의 얇고 밀도가 크며 높은 강도와 강성을 갖고 있는 면재와 이에 비해 상대적으로 두껍고 밀도, 강도, 강성이 낮은 심재로 구성되어 서로의 단점을 보완하는 경량의 특수한 형태이다. 본 연구에서는 등방성의 심재에 2장의 면재가 대칭으로 적층된 샌드위치 평판 모델에 대해 Rayleigh-Ritz 방법으로 해석한 후, 고유진동수를 구하였다. 면재는 G.R.P.의 일종인 E-glass Woven Roving 외에 2종류를 사용하였고 심재는 foam core로서 P.V.C. 외에 3종류를 사용하여 면재와 심재의 종류, 두께, 지지조건 등의 변화에 따른 각 모우드의 고유진동수와 모우드 형상들을 구하고 각 조건들이 고유진동수에 미치는 영향을 비교 분석하였다. 본 연구의 해석결과를 유한요소 program인 ADINA의 결과와 비교하였다.