• International Journal of Naval Architecture and Ocean Engineering
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• 제3권2호
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• pp.122-125
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• 2011

In this work, the movement pattern of a floating breakwater is numerically analyzed using Smoothed Particle Hydrodynamic (SPH) method as a Lagrangian scheme. At the seaside, the regular incident waves with varying height and period were considered as the dynamic free surface boundary conditions. The smooth and impermeable beach slope was defined as the bottom boundary condition. The effects of various boundary conditions such as incident wave characteristics, beach slope, and water depth on the movement of the floating body were studied. The numerical results are in good agreement with the available experimental data in the literature The results of the movement of the floating body were used to determine the transmitted wave height at the corresponding boundary conditions.

• 한국해양공학회지
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• 제25권4호
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• pp.18-22
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• 2011

The Ranking source panel method was used to predict the flow phenomenon of a ship with a goose-neck type bulbous bow penetrating the free surface. The non-linearity of the free surface boundary condition was fully satisfied using an iterative calculation method, and the raised panel method was adopted to obtain a more stable solution at each iteration step. The panel cutting method was applied to generate a hull calculation grid at each iteration step, including the first step. At that time, the nose of the goose-neck type bulbous bow was divided by the free surface and the free surface panel was modified at each iteration step using the variable free surface panel method. Numerical calculations were performed to investigate the validity and efficiency of the applied numerical algorithm using the 3600 TEU container carrier. The computed wave resistance coefficients were compared with the experimentally achieved residual resistance coefficients.

• Advances in materials Research
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• 제12권1호
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• pp.43-65
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• 2023

Free vibration analysis of power law and sigmoidal sandwich plates made up of functionally graded materials (FGMs) has been carried out using finite element based higher-order zigzag theory. The present model satisfies all-important conditions such as transverse shear stress-free conditions at the plate's top and bottom surface along with continuity condition for transverse stresses at the interface. A Nine-noded C0 finite element having eleven degrees of freedom per node is used during the study. The present model is free from the requirement of any penalty function or post-processing technique and hence is computationally efficient. The present model's effectiveness is demonstrated by comparing the present results with available results in the literature. Several new results have been proposed in the present work, which will serve as a benchmark for future works. It has been observed that the material variation law, power-law exponent, skew angle, and boundary condition of the plate widely determines the free vibration behavior of sandwich functionally graded (FG) plate.

• Steel and Composite Structures
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• 제38권3호
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• pp.281-291
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• 2021

An equivalent single-layer theory (EST) is put forward for analyzing free vibrations of steel-concrete composite beams (SCCB) based on a higher-order beam theory. In the EST, the effect of partial interaction between sub-beams and the transverse shear deformation are taken into account. After using the interlaminar shear force continuity condition and the shear stress free conditions at the top and bottom surface, the displacement function of the EST does not contain the first derivatives of transverse displacement. Therefore, the C0 interpolation functions are just demanded during its finite element implementation. Finally, the EST is validated by comparing the results of two simply-supported steel-concrete composite beams which are tested in laboratory and calculated by ANSYS software. Then, the influencing factors for free vibrations of SCCB are analyzed, such as, different boundary conditions, depth to span ratio, high-order shear terms, and interfacial shear connector stiffness.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 1987년도 제29회 수공학연구발표회논문초록집
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• pp.223-234
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• 1987

A weakly nonlinear solution is presented for the two-dimensional wave kinematics forced by a generic wavemaker of variable-draft. The solution is valid for both piston and hinged wavemakers of variable-draft that may be double articulated. The second-order propagating waves generated by a planar wave board are composed of two components; viz., a Stokes second-order wave and a second-harmonic wave forced by the wavemaker which travels at a different speed. A previously neglected time-independent solution that is required to satisfy a kinematic boundary condition on the wavemaker as well as a mixed boundary condition on the free surface is included for the first time. A component of the time-independent solution is found to accurately estimate the mean return current(correct to second-order) in a closed wave flume. This mean return current is usually estimated from kinematic considerations by a conservation of mass principle.

• Korea-Australia Rheology Journal
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• 제12권2호
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• pp.107-117
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• 2000

Prediction of the product shape in sheet casting process is performed from the numerical simulation. A three-dimensional finite element method is used to investigate the flow behavior and to examine the effects of processing conditions on the sheet produced. Effects of inertia, gravity, surface tension and non-Newtonian viscosity on the thickness profile of the sheet are considered since the edge bead and the flow patterns in the chill roll region have great influence on the quality of the products. In the numerical simulation with free surface flows, the spine method is adopted to update the free surface, and the force-free boundary condition is imposed along the take-up plane to avoid severe singularity problems existing at the take-up plane. From the numerical results of steady isothermal flows of a generalized Newtonian fluid, it is shown that the draw ratio plays a major role in predicting the shape of the final sheet produced and the surface tension has considerable effect on the bead thickness ratio and the bead width fraction, while shear-thinning and/or tension-thickening viscosity affect the degree of neck-in.

• 대한조선학회논문집
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• 제30권1호
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• pp.45-64
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• 1993

본 논문에서는 전 논문 주상체의 비선형운동(I)[16]의 정합방법과 비선형해법을 이용한 원형실린더의 전진동요문제와 파랑중에서의 실린더의 운동에 관한 결과를 중심으로 보고한다. 완전한 물체표면 조건의 부과에 관하여 스펙트럴방법은 잠수된 경우에 적용할 수 있으나 물체가 부유된 경우에 적용이 어렵다. 그러나 본 방법은 어떤 구속없이 완전하게 적용할 수 있고 자유표면에서는 완전한 비선형 자유표면조건을 시간적분하여 추적한다 본 논문에서는 예로 첫째는 원형실린더가 수면하에서 전진하면서 상하동요하는 경우의 동유체력을 계산하여 Grue[6], Kim[12]의 선형계산과 비교하였고 또 다른 적용으로 부유된 원형주상체의 전진동요 문제를 수치적인 어려움 없이 성공적으로 수행하였다. 두번째는 파랑 중에서 주상체의 운동문제에 관한 계산을 수행하였다. 초기조건의 부과를 위해 가상적인 조파기를 설치하여 2차원 수치수조를 만든 다음 잠수된 원형 실린더를 고정시켜서 계산을 수행하여 비선형동유체력을 구하였고 다음은 2차원 실린더가 파랑중에서 운동할 때 계산을 수행했다.

• 대한조선학회논문집
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• 제32권1호
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• pp.42-57
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• 1995

자유표면의 유동문제는 저항추진성능과 내항성능이 우수한 선박과 파랑중 작업성능이 우수한 해양구조물의 설계와 관련되어 조선해양공학분야에서 지속적으로 관심의 대상이 되어온 연구분야이다. 본 논문에서는 선체주위 유동을 정확하고 효율적으로 해석하기 위한 3차원 수치해법의 개발을 목적으로 하였다. 수치해법으로 경계요소법을 사용하였으며, 그린함수는 간단한 랜킨소오스를 사용하였다. 전 경계요소면은 8점 경계요소로 표시하여 기하학적 특성을 정밀하게 반영하고자 하였다. 자유표면에서 속도포텐셜의 변화를 정규화된 8점 경계요소에서 이중 2차 스플라인함수(bi-quadratic spline function)로 표시함으로써 자유표면에서의 수치감쇠 및 분산오차를 개선하였다. 한편 물체표면에서의 물리량은 8점 경계요소의 특성을 살려 이중 2차 다항식(bi-quadratic function)으로 근사하였다. 이와같이 계산영역에 따라 해의 특성에 부합하는 수치방법을 채택함으로써 수치해의 정확성과 효율성이 향상되도록 하였다. 개발한 수치해법의 효능을 검증하기 위해 계산예로서 정상유동 및 비정상유동의 경우 Neumann-Kelvin문제를 다루었다. 본 방법에 의한 몰수 타원체 및 Series 60선에 대한 조파저항 계산결과는 적은 파넬수를 사용하고도 기존의 계산치는 물론 실험치와 좋은 일치를 보였다. 변형된 Wigley선형에 대한 동유체력 계산결과도 기존의 실험치 및 계산치와 비교적 잘 일치하였다. 비정상 유동의 경우 랜킨소오스법에서 일반적으로 적용하는 상류방사조건은 무차원주파수가 1/4보다 큰 경우에만 유효하므로, 본 논문에서는 파동방정식 연산자를 이용하여 무차원주파수가 1/4보다 작은 경우에 적용할 수 있는 상류방사조건을 유도하였다. 수면하에서 전진하며 동요하는 소오스에 대하여 적용한 결과 본 논문에서 유도한 방사조건이 유효함을 입증하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권6호
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• pp.598-612
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• 2017

The recently developed Harmonic Polynomial Cell (HPC) method has been proved to be a promising choice for solving potential-flow Boundary Value Problem (BVP). In this paper, a flux method is proposed to consistently deal with the Neumann boundary condition of the original HPC method and enhance the accuracy. Moreover, fixed mesh algorithm with free surface immersed is developed to improve the computational efficiency. Finally, a two dimensional (2D) multi-block strategy coupling boundary-fitted mesh and fixed mesh is proposed. It limits the computational costs and preserves the accuracy. A fully nonlinear 2D numerical wave tank is developed using the improved HPC method as a verification.

• Ocean Systems Engineering
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• 제2권2호
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• pp.147-158
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• 2012

A time-domain simulation of a land-based Oscillating Water Column (OWC) with various irregular waves as a form of PM spectrum is performed by using a two-dimensional fully nonlinear numerical wave tank (NWT) based on the potential theory, mixed Eulerian-Lagrangian (MEL) approach, and boundary element method. The nonlinear free-surface condition inside the OWC chamber was specially devised to describe both the pneumatic effect of the time-varying pressure and the viscous energy loss due to water column motions. The quadratic models for pneumatic pressure and viscous loss are applied to the air and free surface inside the chamber, and their numerical results are compared with those with equivalent linear ones. Various wave spectra are applied to the OWC system to predict the efficiency of wave-energy take-off for various wave conditions. The cases of regular and irregular waves are also compared.