• Smart Structures and Systems
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• 제19권3호
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• pp.299-307
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• 2017

The magneto-electro-elastic (MEE) material under thermal environment exhibits pyroelectric and pyromagnetic coefficients resulting in pyroelectric and pyromagnetic effects. The pyroelectric and pyromagnetic effects on the behavior of multiphase MEE sensors bonded on top surface of a mild steel beam under thermal environment is presented in this paper. The aim of the study is to find out how samples having different volume fractions of the multiphase MEE composite behave in sensor applications. This is studied at optimal location on the beam, where the maximum electric and magnetic potentials are induced due to pyroelectric and pyromagnetic effects under clamped-free and clamped-clamped boundary conditions. The sensor which is bonded on the top surface of the beam is modeled using 8-node brick element. The MEE sensor bonded on mild steel beam is subjected to uniform temperature rise of 50K. It is assumed that beam and sensor is perfectly bonded to each other. The maximum pyroelectric and pyromagnetic effects on electric and magnetic potentials are observed when volume fraction is ${\nu}_f=0.2$. The boundary conditions significantly influence the pyroelectric and pyromagnetic effects on electric and magnetic potentials.

• 한국해안·해양공학회논문집
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• 제34권4호
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• pp.93-99
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• 2022

본 연구에서는 바닥 조파장치가 설치된 3차원 조파수조에서 재현된 규칙파에 대한 해석해를 유도하였다. 바닥 조파장치로 삼각형 형상, 사각형 형상 및 두 형상이 복합된 형상이 적용되었다. 선형파 이론과 움직이는 바닥에 대한 경계조건, 동역학적 및 운동학적 자유수면 경계조건을 이용하여 조파수조 내의 3차원 속도포텐셜을 유도하였다. 그리고, 이로부터 각 방향 성분의 유속과 자유수면변위에 대한 해석해를 구하였다. 유도된 해석해는 바닥 조파장치가 설치된 조파수조에서 규칙파의 전파 특성에 대해 물리적으로 타당한 결과를 보였다. 바닥 조파장치가 snake 형태로 움직이는 경우의 비스듬히 전파하는 파랑의 조파에 대해서도 해석해를 유도하였으며, 해석 결과는 이론적으로 예측한 결과와 일치하였다.

• 한국기계가공학회지
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• 제16권5호
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• pp.134-140
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• 2017

Shape-from-shading (SFS) or stereo vision algorithms can be utilized to measure the shape of an object with imaging techniques for effective sensing in non-contact measurements. SFS algorithms could reconstruct the 3D information from a 2D image data, offering relatively comprehensive information. Meanwhile, a stereo vision algorithm needs several feature points or lines to extract 3D information from two 2D images. However, to measure the size of an object with a freeform surface, the two algorithms need some additional information, such as boundary conditions and grids, respectively. In this study, a stereo vision scheme using the depth information obtained by shape-from-shading as patterns was proposed to measure the size of an object with a freeform surface. The feasibility of the scheme was proved with an experiment where the images of an object were acquired by a CCD camera at two positions, then processed by SFS, and finally by stereo matching. The experimental results revealed that the proposed scheme could recognize the size and shape of freeform surface fairly well.

• Steel and Composite Structures
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• 제18권1호
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• pp.187-212
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• 2015

In this paper, various four variable refined plate theories are presented to analyze vibration of temperature-dependent functionally graded (FG) plates. By dividing the transverse displacement into bending and shear parts, the number of unknowns and governing equations for the present model is reduced, significantly facilitating engineering analysis. These theories account for parabolic, sinusoidal, hyperbolic, and exponential distributions of the transverse shear strains and satisfy the zero traction boundary conditions on the surfaces of the plate without using shear correction factors. Power law material properties and linear steady-state thermal loads are assumed to be graded along the thickness. Uniform, linear, nonlinear and sinusoidal thermal conditions are imposed at the upper and lower surface for simply supported FG plates. Equations of motion are derived from Hamilton's principle. Analytical solutions for the free vibration analysis are obtained based on Fourier series that satisfy the boundary conditions (Navier's method). Non-dimensional results are compared for temperature-dependent and temperature-independent FG plates and validated with known results in the literature. Numerical investigation is conducted to show the effect of material composition, plate geometry, and temperature fields on the vibration characteristics. It can be concluded that the present theories are not only accurate but also simple in predicting the free vibration responses of temperature-dependent FG plates.

• 한국안전학회지
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• 제17권1호
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• pp.99-104
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• 2002

아크축(arch axis)의 연장(extensibility) 및 회전관성(rotatory inertia)을 고려한 곡선보(curved beam)의 평면내(in-plane) 자유진동을 미분구적법(DQM)을 이용하여 다양한 경계조건(boundary conditions)과 굽힘각(opening angles)에 따른 진동수(frequencies)를 계산하였다. DQM의 결과를 다른 수치해석결과와 비교하였으며, DQM은 적은 요소(grid points)을 사용하여 정확한 해석결과를 보여주었다.

• 대한조선학회논문집
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• 제34권2호
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• pp.27-38
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• 1997

본 논문에서는 Rankine Source 분포법에 의해 SWATH선의 조파저항 계산을 시도하였다. 자유표변조건은 이중모형근사형(Dawson형)의 자유표면조건과 free stream에 의한 근사형(Kelvin형)을 사용하고, 각각의 경우에 유한 차분법이 아닌 해석적인 방법을 사용하여 수치해석을 하였다. 위 두 가지 패널방법에 의한 수치계산결과, 얇은배 이론과 수정 세장체이론에 의한 계산결과 및 시험 탠값과의 비교를 통하여 각 방법의 특성을 논하였다. 저항실험은 단독형 스트러스와 탠덤값(tendem) 스트러트 SWATH선에 대해서 하였으며, 두 선체간의 거리변화에 따른 결과도 포함시켰다. 개발된 프로그램의 검증을 위해서 Wigley 단독선형 및 쌍동선형에 대해서 계산을 수행하여 발표된 시험결과와 비교하였다. Wigley 단독선형, 쌍동선형 및 SWATH 선형에 대해서 계산한 조파저항 값과 시험값, 관측한 파형과 계산한 파형을 비교하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권2호
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• pp.206-218
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• 2014

The wave attenuation by floating breakwaters in high amplitude waves, which can lead to wave overtopping and breaking, is examined by numerical simulations. The governing equations, the Navier-Stokes equations and the continuity equation, are calculated in a fixed Cartesian grid system. The body boundaries are defined by the line segment connecting the points where the grid line and body surface meet. No-slip and divergence free conditions are satisfied at the body boundary cell. The nonlinear waves near the moving body is defined using the modified marker-density method. To verify the present numerical method, vortex induced vibration on an elastically mounted cylinder and free roll decay are numerically simulated and the results are compared with those reported in the literature. Using the present numerical method, the wave attenuations by three kinds of floating breakwaters are simulated numerically in a regular wave to compare the performance.

• 대한토목학회논문집
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• 제33권6호
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• pp.2267-2275
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• 2013

기존의 천수흐름 해석 상용모형에서는 내부 경계조건을 단순히 완전활동조건으로 가정하여 유체의 흐름을 해석함으로써 구조물 주위에서의 유속, 와도, 수위, 전단력의 분포, 항력 및 양력의 시간에 따른 변화 등을 올바르게 해석하지 못하였다. 본 연구에서는 구조물 주위에서의 흐름특성을 정확하게 예측할 수 있는 유한요소모형을 개발하고, 구조물에서의 경계조건을 활동길이를 이용한 부분활동조건으로 묘사하여 내부경계조건에 따른 원형 실린더 후면에서의 층류 흐름특성을 분석하였다. 종횡방향 유속 및 와도의 시간에 따른 변화, 후류길이, 활동길이에 따른 와류열의 변화와 질량보존율을 비교한 결과 완전활동조건을 부여한 경우에는 와류열이 전혀 형성되지 않고 완전한 층류흐름이 발생하였다. 부분활동조건을 입력한 경우 실린더 표면에서의 유속분포가 변화되어 전단력의 크기와 와도의 발생에 영향을 미치므로 무활조건을 부여한 경우에 비해 와류열의 발생 주기가 짧아졌다. 최대 질량보존 오차는 무활조건을 적용한 경우 0.73%로 나타났으며, 무활조건에 비해 부분활동조건을 부여한 경우의 오차율이 최대 0.21% 감소하였다.

• International Journal of Ocean System Engineering
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• 제3권1호
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• pp.1-9
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• 2013

A design procedure for a ship with minimum resistance had been developed using a numerical optimization method called SQP (Sequential Quadratic Programming) combined with computational fluid dynamics (CFD) technique. The frictional resistance coefficient was estimated by the ITTC 1957 model-ship correlation line formula and the wave-making resistance coefficient was evaluated by the potential-flow panel method with the nonlinear free surface boundary conditions. The geometry of the hull surface was represented and modified by B-spline surface modeling technique during the optimization process. The Series 60 ($C_B$=0.60) hull was selected as a parent hull to obtain an optimized hull that produces minimum resistance. The models of the parent and optimized hull forms were tested at calm water condition in order to demonstrate the validity of the proposed methodolgy.

• Ocean Systems Engineering
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• 제2권3호
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• pp.229-238
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• 2012

We discuss the bi - stability that is possibly exhibited by a liquid free surface in a parametrically - driven two-dimensional (2D) rectangular tank with finite liquid depth. Following the method of adaptive mode ordering, assuming two dominant modes and retaining polynomial nonlinearities up to third-order, a nonlinear finite-dimensional nonlinear modal system approximation is obtained. A "continuation method" of nonlinear dynamics is then used in order to elicit efficiently the instability boundary in parameters' space and to predict how steady surface elevation changes as the frequency and/or the amplitude of excitation are varied. Results are compared against those of the linear version of the system (that is a Mathieu-type model) and furthermore, against an intermediate model also derived with formal mode ordering, that is based on a second - order ordinary differential equation having nonlinearities due to products of elevation with elevation velocity or acceleration. The investigation verifies that, in parameters space, there must be a region, inside the quiescent region, where liquid surface instability is exhibited. There, behaviour depends on initial conditions and a wave form would be realised only if the free surface was substantially disturbed initially.