• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• 제6권1호
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• pp.51-59
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• 2003

This paper has developed an efficient nonlinear finite element method that covers both initial deformations and initial stresses of general distribution in calculating the ultimate strength of ring-stiffened cylinders. The developed method and two widely-used commercial codes (NASTRAN and ABAQUS) were simultaneously applied to the same analysis model within the extent of those commercial codes' coverage to check the validity of the present method. After the validity check, it was used for parametric studies for more general cases of initial stress distribution, which produced some useful information about the imperfection sensitivity of the ultimate strength of ring-stiffened cylinders.

• Journal of applied mathematics & informatics
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• 제18권1_2호
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• pp.171-182
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• 2005

An analysis of the non-homogeneous term involved in the free surface condition for second order wave diffraction on a pair of cylinders is presented. In the computations of the nonlinear loads on offshore structures, the most challenging task is the computation of the free surface integral. The main contribution to this integrand is due to the non-homogeneous term present in the free surface condition for second order scattered potential. In this paper, the free surface condition for the second order scattered potential is derived. Under the assumption of large spacing between the two cylinders, waves scattered by one cylinder may be replaced in the vicinity of the other cylinder by equivalent plane waves together with non-planner correction terms. Then solving a complex matrix equation, the first order scattered potential is derived and since the free surface term for second order scattered potential can be expressed in terms of the first order potentials, the free surface term can be obtained using the knowledge of first order potentials only.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.508-513
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• 2000

An experimental investigation has been carried out for two circular cylinders having different groove configurations(U and V-shape). The results were compared with those for the smooth circular cylinder. The drag force, mean velocity and turbulent intensity profiles of wake behind the cylinders were measured with varying the Reynolds number $Re=8000{\sim}14,000$ based on the cylinder diameter. As a results, the U-groove circular cylinder was found to be most effective riblet shape with reducing the drag up to 21%. As the Reynolds number increases, the vortex shedding frequency of the grooved cylinders becomes a little larger, compared to the smooth cylinder. The flow visualization using the smoke-wire technique was also carried out to see the flow structure qualitatively.

• 한국해안해양공학회지
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• 제1권1호
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• pp.63-70
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• 1989

단일 및 2개의 연직 불투과성 구조물이 해역에 설치되어 있는 경우 파랑의 회절 및 상호간섭 효과를 일정요소를 사용한 경계요소법에 의해 수치 해석하였다. 파랑은 2차원 선형 회절파 이론으로부터 해석하였으며 구조물 경계상에서 뿐만 아니라 구조물 주위에서의 회절계수를 계산하였다. 본 계산의 신뢰도를 검증하기 위하여 기존의 해석결과와 비교하였으며 대체로 잘 일치하고 있음을 알 수가 있었다.

• 한국기계가공학회지
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• 제7권3호
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• pp.103-109
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• 2008

The work to raise the bridge plate by using two hydraulic cylinders is very dangerous when generating the unbalance state between cylinders. For solving this problem, one cylinder is forced to follow the trajectory of another cylinder instead of applying the same trajectory to two cylinders at once. In this paper, the control method for dynamic stable on lifting the bridge plate is proposed. The simulation model is derived by using commercial software, AMESim and MatLab/simulink. The PID controller is designed on one cylinder for following the reference trajectory and the adaptive controller is designed on another cylinder for tracking the displacement of one cylinder. The performance improvement is shown by comparing the simulation results through computer simulation.

• Bulletin of the Korean Chemical Society
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• 제29권6호
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• pp.1131-1136
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• 2008

The electrical repulsive energy between two model cylinders was calculated by solving nonlinear Poission- Boltzmann (P-B) equation under Derjaguin approximation. Effects of the surface potential, Debye screening length, and configuration of cylinders on the repulsive interaction energy were examined. Due to the anisotropy of the shape of cylinder, the interaction repulsive energy showed dependence to the configuration of particles; cylinders aligned in end-to-end configuration showed largest repulsive energy and crossed particles had lowest interaction energy. The configuration effect is originated from the curvature effect of the interacting surfaces. The curved surfaces showed less repulsive energy than flat surfaces at the same interacting surface area. The configuration dependency of interaction energy agreed with the previous analytical solution obtained under the linearized P-B equation. The approach and results present in this report would be applicable in predicting colloidal behavior of cylindrical particles.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.352-357
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• 2010

A parametric study has been carried out to elucidate the characteristics of channel flow with a streamwise-periodic array of cylinders. This flow configuration is relevant to heat exchanger applications. The presence of cylinders in channel flow causes the attached wall boundary layer to separate, leading to significant change in flow instabilities. There exist two kinds of instabilities; flow undergoes a primary instability (Hopf bifurcaiton) at a lower Reynolds number, and the unsteady two-dimensional flow becomes unstable to three-dimensional disturbances at a higher Reynolds number. We report here the dependencies of the primary instability as well as the flow characteristics of the subsequent unsteady flow including flow-induced forces and Strouhal number of vortex shedding, on the distance between the cylinder and the channel wall.

• 한국전산유체공학회지
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• 제15권3호
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• pp.54-59
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• 2010

A parametric study has been carried out to elucidate the characteristics of channel flow with a streamwise-periodic array of cylinders. This flow configuration is relevant to heat exchanger applications. The presence of cylinders in channel flow causes the attached wall boundary layer to separate, leading to significant change in flow instabilities. There exist two kinds of instabilities; flow undergoes a primary instability (Hopf bifurcation) at a lower Reynolds number, and the unsteady two-dimensional flow becomes unstable to three-dimensional disturbances at a higher Reynolds number. We report here the dependencies of the primary instability as well as the flow characteristics of the subsequent unsteady flow, including flow-induced forces and Strouhal number of vortex shedding, on the distance between the cylinder and the channel wall.

• Structural Engineering and Mechanics
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• 제9권1호
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• pp.51-68
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• 2000

The paper presents theoretical and experimental investigations on three varying thickness circular cylinders, which were tested to destruction under external hydrostatic pressure. The five buckling theories that were presented were based on inelastic shell instability. Three of these inelastic buckling theories adopted the finite element method and the other two theories were based on a modified version of the much simpler von Mises theory. Comparison between experiment and theory showed that one of the inelastic buckling theories that was based on the von Mises buckling pressure gave very good results while the two finite element solutions, obtained by dividing the theoretical elastic instability pressures by experimentally determined plastic knockdown factors gave poor results. The third finite element solution which was based on material and geometrical non-linearity gave excellent results. Electrical resistance strain gauges were used to monitor the collapse mechanisms and these revealed that collapse occurred in the regions of the highest values of hoop stress, where considerable deformation took place.

• 전자공학회논문지A
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• 제33A권4호
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• pp.92-97
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• 1996

The attenuation pattern of the E-polarized electromagnetic fields scattered by two empty circular cylinders in a dielectric medium is analyzed to calculate the effects of the inhomogenuity in hte background medium. Inthe amplitude pattern of the electromagnetic field scattered by one cylinder, double dips occur at the locations corresponding to its top and bottom boundaries. The distorton of the original double dip pattern is calculated when other air cavity approaches or its size increases.