• Steel and Composite Structures
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• 제27권1호
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• pp.109-122
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• 2018

In This work an analysis of the propagation of waves of functionally graduated plates is presented by using a high order hyperbolic (HSDT) shear deformation theory. This theory has only four variables, which is less than the theory of first order shear deformation (FSDT). Therefore, a shear correction coefficient is not required. Unlike other conventional shear deformation theories, the present work includes a new field of displacement which introduces indeterminate integral variables. The properties of materials are supposed classified in the direction of the thickness according to two simple distributions of a power law in terms of volume fractions of constituents. The governing equations of the wave propagation in the functionally graded plate are derived by employing the Hamilton's principle. The analytical dispersion relation of the functionally graded plate is obtained by solving an eigenvalue problem. The convergence and the validation of the proposed theoretical numerical model are performed to demonstrate the efficacy of the model.

• Advances in nano research
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• 제6권1호
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• pp.21-37
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• 2018

In the present article, wave dispersion behavior of a temperature-dependent functionally graded (FG) nanobeam undergoing rotation subjected to thermal loading is investigated according to nonlocal strain gradient theory, in which the stress numerates for both nonlocal stress field and the strain gradient stress field. The small size effects are taken into account by using the nonlocal strain gradient theory which contains two scale parameters. Mori-Tanaka distribution model is considered to express the gradually variation of material properties across the thickness. The governing equations are derived as a function of axial force due to centrifugal stiffening and displacements by applying Hamilton's principle according to Euler-Bernoulli beam theory. By applying an analytical solution, the dispersion relations of rotating FG nanobeam are obtained by solving an eigenvalue problem. Obviously, numerical results indicate that various parameters such as angular velocity, gradient index, temperature change, wave number and nonlocality parameter have significant influences on the wave characteristics of rotating FG nanobeams. Hence, the results of this research can provide useful information for the next generation studies and accurate deigns of nanomachines including nanoscale molecular bearings and nanogears, etc.

• 대한토목학회논문집
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• 제13권1호
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• pp.47-54
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• 1993

일반적인 기하학적 경계와 해저 지형을 가진 항만에서 해수 고유 진동 특성의 수치해석을 위하여 유한요소법이 응용되었다. 지배 방정식인 Helmholtz방정식을 일반화된 매트릭스 고유치문제로 변환하는데 표준유한요소과정을 사용하였다. 고유주기와 고유진동모우드의 수치해를 얻기위한 컴퓨터 프로그램이 개발되었고, 고유치의 수치해석과정에서 수치적 특이성을 취급하기 위해 고유치 이동기법이 고안되었으며, 수치적 악조건을 극복하기 위해서는 행렬원소의 축척화가 효과적임을 알았다. 수치예로서 먼저 해석해를 알 수 있는 경우를 해석하여 수치해와 해석해를 비교해 봄으로써 작성된 컴퓨터 프로그램의 유용성을 확인하였고, 일반적인 경계 조건과 임의 수성의 실제 항만에 유한요소 해법을 적용하여 성공적으로 고유진동의 해를 구하였다.

• 대한기계학회논문집
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• 제15권2호
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• pp.630-643
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• 1991

The hydrodynamic stability equations are formulated for buoyancy-induced flows adjacent to a vertical, planar, isothermal surface in cold pure water. The resulting stability equations, when reduced to ordinary differential equation by a similarity transformation, constitute a two-point boundary-value(eigenvalue) problem, which was numerically solved for various values of the density extremum parameter R=( $T_{m}$ - $T_.inf./) / ( $T_{o}$ - $T_.inf./). These stability equations have been solved using a computer code designed to accurately solve two-point boundary-value problems. The present numerical study includes neutral stability results for the region of the flows corresponding to 0.0.leq. R. leq.0.15, where the outside buoyancy force reversals arise. The results show that a small amount of outside buoyancy force reversal causes the critical Grashof number $G^*/ to increase significantly. A further increase of the outside buoyancy force reversal causes the critical Grashof number to decrease. But the dimensionless frequency parameter $B^*/ at $G^*/ is systematically decreased. When the stability results of the present work are compared to the experimental data, the numerical results agree in a qualitative way with the experimental data.erimental data.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.407-413
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• 2008

This paper investigates the dynamics of a HDD spindle system due to the change of FDBs. Flying height of the HDD spindle system is determined through the static analysis of the FDBs, and the stiffness and damping coefficients are calculated through the dynamic analysis of the FDBs. Free vibration characteristics and shock response of the HDD spindle system are analyzed by using the finite element method and the mode superposition method. Experimental modal test is also performed to verify the accuracy of the proposed method. This research shows that the stiffness coefficients of journal heating mostly affect the rocking frequencies because their magnitude are within the range of the stiffness of supporting structure. It also shows that the damping coefficients of thrust bearing mostly affect the axial frequency because the stiffness of thrust bearing is much smaller that that of supporting structure.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.394-400
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• 2008

This paper presents an analytical method to investigate the stability of FDBs (fluid dynamic bearings) considering the tilting motion. The perturbed equations of motion are derived with respect to translational and tilting motion for the general rotor-bearing system with five degrees of freedom. The Reynolds equations and their perturbed equations are solved by using the FEM in order to calculate the pressure, load capacity, and the stiffness and damping coefficients. This research introduces the radius of gyration to the equations of notion in order to express the mass moment of interia with respect to the critical mass. Then the critical mass of FDBs is determined by solving the eigenvalue problem of the linear equations of motion. This research is numerically validated by comparing the stability chart of FDBs with the time response of the whirl radius obtained from the direct integration of the equations of motion. This research shows that the tilting motion is one of the major design considerations to determine the stability of rotating system. It also shows that the stability of FDBs considering only translation is overestimated in comparison with the stability of FDBs considering both translational and tilting motion.

• 한국전산구조공학회논문집
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• 제17권1호
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• pp.11-20
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• 2004

본 연구에서는 직선 강상자형 거더의 단면변형에 의한 변형 및 응력계산을 위한 Matlab 해석프로그램을 개발하고자 한다. 이를 위하여 단면변형이론을 요약하고 빔유사이론을 제시한다. 이후 탄성지반위의 보-기둥부재의 지배방정식을 제시하고, 일반화된 고유치해석을 통하여 집중 및 분포하중을 받는 보요소의 엄밀한 강성행렬을 계산한다. 본 연구의 효율성과 정확성을 입증하기 위하여 격벽을 갖는 상자형 거더의 뒤틀림응력을 계산하고 유한요소해와 비교한다.

• 한국소음진동공학회논문집
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• 제25권3호
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• pp.207-215
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• 2015

This paper deals with a theoretical method to calculate natural frequencies of a fixed-free rectangular tank partially in contact with an outer water gap. Orthogonal polynomials satisfying the boundary conditions of the tank are used as admissible functions in the Rayleigh-Ritz method. A quarter model of the liquid-coupled system is constructed and it is simplified to a line supported flat plate in contact with the liquid. The liquid displacement potential functions satisfying the Laplace equation and water boundary conditions are derived, and the finite Fourier transform is accomplished in conjunction with the compatibility requirement along the contacting interfaces between the tank and water. An eigenvalue problem is derived so that the natural frequencies of the wet rectangular tank can be extracted. The predictions from the proposed analytical method show good agreement with the finite element analysis results.

• 한국콘텐츠학회:학술대회논문집
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• 한국콘텐츠학회 2004년도 추계 종합학술대회 논문집
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• pp.348-351
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• 2004

본 논문은 Haar 웨이브릿 변환과 2D PCA를 이용한 얼굴 인식 방법에 대하여 제안한다. 기존의 PCA는 1 차원 벡터들로 공분산 행렬을 구하는 반면에 2D PCA는 2 차원 영상을 직접적으로 이용하여 공분산 행렬을 구한 후 그것의 고유값에 따른 고유벡터를 구하여 특징 벡터들을 추출하였다. 제안 방법은 얼굴 데이터를 낮은 차원과 강건한 특징을 가지는 얼굴 영상을 얻기 위해 웨이브릿 변환을 이용하여 LL 대역의 영상 데이터로 2D PCA 방법을 적용하여 얼굴을 인식한다. 실험결과는 원래 크기의 얼굴 영상에 2D PCA를 적용한 인식률보다 웨이브릿 변환의 LL 대역의 얼굴 영상에 2D PCA를 적용한 얼굴 인식률이 더 좋음을 보여준다.

• Structural Engineering and Mechanics
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• 제62권6호
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• pp.759-769
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• 2017

The effect of central axial load on natural frequencies of various thin-walled beams, are investigated by some researchers using different methods such as finite element, transfer matrix and dynamic stiffness matrix methods. However, there are situations that the load will be off centre. This type of loading is called eccentric load. The effect of the eccentricity of axial load on the natural frequencies of asymmetric thin-walled beams is a subject that has not been investigated so far. In this paper, the mentioned effect is studied using exact dynamic stiffness matrix method. Flexure and torsion of the aforesaid thin-walled beam is based on the Bernoulli-Euler and Vlasov theories, respectively. Therefore, the intended thin-walled beam has flexural rigidity, saint-venant torsional rigidity and warping rigidity. In this paper, the Hamilton‟s principle is used for deriving governing partial differential equations of motion and force boundary conditions. Throughout the process, the uniform distribution of mass in the member is accounted for exactly and thus necessitates the solution of a transcendental eigenvalue problem. This is accomplished using the Wittrick-Williams algorithm. Finally, in order to verify the accuracy of the presented theory, the numerical solutions are given and compared with the results that are available in the literature and finite element solutions using ABAQUS software.