• 한국자동차공학회논문집
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• 제10권3호
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• pp.227-236
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• 2002

We have performed two kinds of experimental modal analyses fur a radial tire for passenger car under free-suspension. One is the modal analysis to obtain three-dimensional modes of tire using accelerometers and the other is the one to identify cavity resonance frequency using a pressure sensor. From the first analysis, we have obtained the three-dimensional natural modes, which makes it possible to grasp the features of the modes and to classify the vibrational modes into symmetric, non-symmetric, and antisymmetric modes in a simple way by using the experimental results. From the first and the second experimental analyses we have identified the cavity resonance frequency and its three-dimensional mode shape.

• Steel and Composite Structures
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• 제26권2호
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• pp.125-137
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• 2018

In this work, the bending and free vibration analysis of multilayered plates and shells is presented by utilizing a new higher order shear deformation theory (HSDT). The proposed involves only four unknowns, which is even less than the first shear deformation theory (FSDT) and without requiring the shear correction coefficient. Unlike the conventional HSDTs, the present one presents a novel displacement field which incorporates undetermined integral variables. The equations of motion are derived by using the Hamilton's principle. These equations are then solved via Navier-type, closed form solutions. Bending and vibration results are found for cylindrical and spherical shells and plates for simply supported boundary conditions. Bending and vibration problems are treated as individual cases. Panels are subjected to sinusoidal, distributed and point loads. Results are presented for thick to thin as well as shallow and deep shells. The computed results are compared with the exact 3D elasticity theory and with several other conventional HSDTs. The proposed HSDT is found to be precise compared to other several existing ones for investigating the static and dynamic response of isotropic and multilayered composite shell and plate structures.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.441-447
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• 2002

KSR-III(Korea Sounding Rocket - III), which is being developed by Space Technology R&D Division of KARI(Korea Aerospace Research Institute) will be launched in late 2002. It is a three-stage, liquid propellant rocket which can reach 250 km altitude and will carry out observation of ozone layer and scientific experiments, such as microgravity experiment, and atmospheric measurement. KSR-III is believed to be an intermediate to the launch vehicle capable of carrying a satellite to its orbit. Space Test Department of KARI performed GVT(Ground Vibration Test) fer KSR-III EM at Rocket Test Building of KARI. GVT is very important for predicting the behavior of rocket in its operation, developing flight control program and performing aerodynamic analysis. This paper gives an introduction of rocket GVT configuration and information on test procedures, techniques and results of It. In this test. to simulate free-free condition, test object hung in the air laterally by 4 bungee cords specially devised. For the excitation of test object, pure random signal by two electromagnetic shakers was used and total 22 frequency response functions were achieved. Polyreference parameter estimation was performed to identify the modal parameters with MIMO(Multi-Input-Multi-Output) method. As the result of the test, low frequency mode shapes and modal parameters below 60Hz were identified

• 대한토목학회논문집
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• 제5권3호
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• pp.31-38
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• 1985

아치의 미소요소(微小要素)에 작용(作用)하는 합응력(合應力)들의 평형방정식(平衡方程式)과 D'Alembert의 원리(原理)를 이용(利用)하여 회전관성(回轉慣性)을 고려(考慮)한 포물선(抛物線)아치의 자유진동(自由振動)에 대한 미분방정식(微分方程式)을 유도(誘導)하였다. 본(本) 연구(硏究)에서 유도(誘導)한 미분방정식(微分方程式)을 검증(檢證)하기 위하여 포물선(抛物線)아치의 미분방정식(微分方程式)을 보의 미분방정식(微分方程式)으로 수렴(收斂)시킨 결과(結果), 포물선(抛物線)아치의 미분방정식(微分方程式)이 보의 미분방정식(微分方程式)으로 수렴(收斂)되는 것을 보였다. 본(本) 연구(硏究)에서 유도(誘導)한 미분방정식(微分方程式)을 시행착오적(試行錯誤的) 고유치문제(固有値問題)와 Runge-Kutta method를 이용(利用)하여 수치해석(數値解析)하였으며, 본(本) 연구(硏究)의 수치해석(數値解析) 결과(結果)와 SAP IV의 결과(結果)가 잘 일치(一致)함을 보였다.

• Structural Engineering and Mechanics
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• 제75권6호
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• pp.747-769
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• 2020

This paper provides a semi-analytical approach to investigate the variations of 3D displacement components, electric potential, stresses, electric displacements and transverse vibration frequencies in laminated piezoelectric composite plates based on the scaled boundary finite element method (SBFEM) and the precise integration algorithm (PIA). The proposed approach can analyze the static and dynamic responses of multilayered piezoelectric plates with any number of laminae, various geometrical shapes, boundary conditions, thickness-to-length ratios and stacking sequences. Only a longitudinal surface of the plate is discretized into 2D elements, which helps to improve the computational efficiency. Comparing with plate theories and other numerical methods, only three displacement components and the electric potential are set as the basic unknown variables and can be represented analytically through the transverse direction. The whole derivation is built upon the three dimensional key equations of elasticity for the piezoelectric materials and no assumptions on the plate kinematics have been taken. By virtue of the equilibrium equations, the constitutive relations and the introduced set of scaled boundary coordinates, three-dimensional governing partial differential equations are converted into the second order ordinary differential matrix equation. Furthermore, aided by the introduced internal nodal force, a first order ordinary differential equation is obtained with its general solution in the form of a matrix exponent. To further improve the accuracy of the matrix exponent in the SBFEM, the PIA is employed to make sure any desired accuracy of the mechanical and electric variables. By virtue of the kinetic energy technique, the global mass matrix of the composite plates constituted by piezoelectric laminae is constructed for the first time based on the SBFEM. Finally, comparisons with the exact solutions and available results are made to confirm the accuracy and effectiveness of the developed methodology. What's more, the effect of boundary conditions, thickness-to-length ratios and stacking sequences of laminae on the distributions of natural frequencies, mechanical and electric fields in laminated piezoelectric composite plates is evaluated.

• Steel and Composite Structures
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• 제48권3호
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• pp.275-291
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• 2023

This paper has focused on presenting vibration analysis of trapezoidal sandwich plates with 3D-graphene foam reinforced polymer matrix composites (GrF-PMC) core and FG wavy CNT-reinforced face sheets. The porous graphene foam possessing 3D scaffold structures has been introduced into polymers for enhancing the overall stiffness of the composite structure. Also, 3D graphene foams can distribute uniformly or non-uniformly in the plate thickness direction. The effective Young's modulus, mass density and Poisson's ratio are predicted by the rule of mixture. In this study, the classical theory concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube random contact, which explicitly accounts for the progressive reduction of the tubes' effective aspect ratio as the filler content increases. The First-order shear deformation theory of plate is utilized to establish governing partial differential equations and boundary conditions for trapezoidal plate. The governing equations together with related boundary conditions are discretized using a mapping-generalized differential quadrature (GDQ) method in spatial domain. Then natural frequencies of the trapezoidal sandwich plates are obtained using GDQ method. Validity of the current study is evaluated by comparing its numerical results with those available in the literature. It is explicated that 3D-GrF skeleton type and weight fraction, carbon nanotubes (CNTs) waviness and CNT aspect ratio can significantly affect the vibrational behavior of the sandwich structure. The plate's normalized natural frequency decreased and the straight carbon nanotube (w=0) reached the highest frequency by increasing the values of the waviness index (w).

• 한국전산구조공학회논문집
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• 제16권4호
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• pp.419-429
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• 2003

두꺼운 축대칭 쌍곡형 쉘의 고유진동수를 결정하는 3차원 해석법이 제시되었다. 수학적으로 2차원적인 전통적인 쉘 이론과는 달리, 본 연구의 해석법은 3차원적인 동탄성방정식을 근간으로 하였다. 반경방향, 원주방향, 축방향으로의 변위성분인 u/sub r/, u/sub θ/, u/sub z/를 시간에 대해서는 정현적으로, θ에 대해서는 주기적으로, r과 z방향으로는 대수 다항식으로 표현하였다. 쌍곡형 쉘의 위치(변형률)에너지와 운동에너지를 정식화하고 리츠법을 사용하여 고유치문제를 해결하였으며, 진동수의 최소화과정을 통해 고유진동수를 엄밀해의 상위경계치로 구하였다. 대수 다항식의 차수가 증가하면 진동수는 엄밀해에 수렴하게 된다. 축대칭 쌍곡형 쉘의 하위 5개의 진동수에 대해서 유효숫자 4자리까지의 수렴성 연구가 이루어졌다. 쌍곡형 쉘의 서로 다른 2개의 두께 비, 3개 의 축비(axis ratio), 3개의 shv이 비를 가진 총 18개의 형상을 지닌 자유 경계의 축대칭 쌍곡형 쉘의 수치결과를 도표화하였다. 프와송 비( ν)는 0.3으로 고정하였다. 본 연구의 해석법은 매우 두꺼운 쉘 뿐만 아니라 얇은 쉘에도 적용이 가능하다.

• Coupled systems mechanics
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• 제9권3호
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• pp.201-217
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• 2020

This paper employs differential quadrature method (DQM) and nonlocal strain gradient theory (NSGT) for studying free vibrational characteristics of porous functionally graded (FG) nanoplates coupled by visco-elastic foundation. A secant function based refined plate theory is used for mathematical modeling of the nano-size plate. Two scale factors are included in the formulation for describing size influences based on NSGT. The material properties for FG plate are porosity-dependent and defined employing a modified power-law form. Visco-elastic foundation is presented based on three factors including a viscous layer and two elastic layers.The governing equations achieved by Hamilton's principle are solved implementing DQM. The nanoplate vibration is shown to be affected by porosity, temperature rise,scale factors and viscous damping.

• Composites Research
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• 제29권6호
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• pp.347-352
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• 2016

적층 복합재료 주름판에 대한 진동특성을 이론적 방법을 이용하여 분석하였다. 고려된 주름 형상은 사다리꼴을 기본으로 삼각형, 사각형 및 요각 사다리꼴형이다. 3차원 주름 구조물을 해석적으로 기계적 거동을 표현하는 것이 매우 어렵기 때문에 본 해석에서는 주름판의 진동특성을 분석하기 위해 등가균질모델을 적용하였다. 이를 위해 단위 주름을 직교이방성재료로 등가시켰으며, 해석에서 등가 신장 강성 및 굽힘 강성이 모두 고려되었다. 이론해석 결과의 타당성을 검증하기 위해 셸요소를 적용한 3차원 유한요소해석을 수행하였으며, 두 방법을 이용해 얻은 고유진동수 및 진동형상을 비교하였다. 주름판의 기하형상에 따른 영향을 분석하기 위해 다양한 수치예가 제시되었다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 춘계학술대회 논문집
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• pp.94-99
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• 2002

Increasing demands on precision machining of 3D free-form surface have necessitated the tool smoothly varying feedrates. This paper presents on of algorithm for adaptive feedrate on NURBS curve. Since the algorithm for calculating variable feedrate depends on the curvature of curve, it permits to get constant material tool can be protected un terms of tool chipping vibration, etc.