• 한국해양공학회지
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• 제23권6호
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• pp.23-31
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• 2009

The interaction of incident monochromatic waves with a bottom-mounted vertical porous circular cylinder is investigated using the framework of the three-dimensional linear potential theory. The porosity of the circular cylinder is uniform vertically but varies in the circumferential direction. By adjusting the porosities of the circular cylinder, both the wave blocking performance of a porous semi-circular breakwater and the wave responses inside a circular harbor with an entrance are applied as calculation examples. It is found that the reflected waves, wave run-up, and wave forces are significantly reduced due to wall porosity, which are positive factors for a breakwater, and the amplification factor of a circular harbor at resonant frequencies is greatly reduced by a porous sidewall.

• 대한의용생체공학회:의공학회지
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• 제28권6호
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• pp.798-802
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• 2007

The synthetic focusing in the ultrasonic imaging systems has been formed in the way that one element transmits a circular wave and receives an echo signal. The amplitude of the signal transmitted from one element is too small to propagate a long distance so that the SNR(Signal to Noise Ratio) is very low in an image obtained by the synthetic focusing. To solve this problem, a defocusing method which uses several elements has been proposed. In this method, the SNR is improved due to using several elements to transmit the circular wave. But if the number of transmitting elements increases, the phase distortion is severe in the defocusing method. In this paper, we propose a new method that can generate a circular wave using a lot of elements without phase distortion. At first, we generate limited plane waves with different propagation angles and then superpose them to make a circular wave. We show that the circular wave can be used to improve SNR in the real-time 3D ultrasonic imaging as well as the synthetic focusing through computer simulation and experiments.

• 해양환경안전학회지
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• 제23권5호
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• pp.558-565
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• 2017

해양환경의 극한 환경조건에 노출 된 고정식 및 부유식 해양구조물의 안전성과 설계비용 효율성에 있어서 파랑-구조물 상호작용의 정확한 예측은 중요하다. 본 연구에서는 규칙파 중 원형 기둥에 대한 파랑-구조물 상호작용을 해석하였다. 3차원 이상유동(two-phase flow)을 해석하기 위해 오픈소스 전산유체역학 라이브러리인 오픈폼을 사용하였다. 4개의 원형기둥이 정사각형 배열을 이루고 있을 때 규칙파의 입사각도에 따른 상호작용을 해석하였다. 원형 기둥 구조물에서의 wave run-up을 입사파의 기울기에 따라 비교하였다. 원형 기둥과 입사파의 상호작용으로 인해 원형 기둥 사이에 높은 파가 생성되는 것을 확인하였다. 본 해석 결과는 구조물과 입사파의 상호작용에 의한 air gap에 대한 연구의 기초자료로 활용될 것으로 기대된다.

• Structural Engineering and Mechanics
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• 제85권5호
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• pp.645-654
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• 2023

Based on first-order shear deformation theory, a wave propagation model of graphene platelets reinforced metal foams (GPLRMFs) circular plates is built in this paper. The expressions of phase-/group- velocities and wave number are obtained by using Laplace integral transformation and Hankel integral transformation. The effects of GPLs pattern, foams distribution, GPLs weight fraction and foam coefficient on the phase and group velocity of GPLRMFs circular plates are discussed in detail. It can be inferred that GPLs distribution have great impacts on the wave propagation problems, and Porosity-I type distribution has the largest phase velocity and group velocity, followed by Porosity-III, and finally Porosity-II; With the increase of the GPLs weight fraction, the phase- and group- velocities for the GPLRMFs circular plate will be increased; With the increase of the foam coefficient, the phase- and group- velocities for the GPLRMFs circular plate will be decreased.

• Earthquakes and Structures
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• 제27권2호
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• pp.155-164
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• 2024

Studying the propagation characteristics of waves in circular plates has important engineering value. In this paper, graphene sheet reinforced foam (GPLRMF) circular plates are taken as the research object, and the propagation characteristics of shear and bending waves in the structure are analyzed. In the process of research, we assume that the material properties are closely related to temperature, and use the first-order shear deformation theory (FSDT) to establish the dynamic model of GPLRMF circular plates. Considering the simply supported boundary conditions, the relationship between phase velocity/group velocity and wave number was obtained through Laplace transform. Subsequently, the influence of material and geometric parameters on wave propagation characteristics was analyzed, and the results showed that the porosity coefficient and temperature had a significant impact on the characteristics of wave propagation in circular plates.

• Structural Engineering and Mechanics
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• 제76권4호
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• pp.551-559
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• 2020

On the basis of nonlocal strain gradient theory, considering the material properties of porous FGM changing with thickness and the influence of moment of inertia, the wave equation of FG nano circular plate is derived by using the first-order shear deformation plate theory, by introducing dimensionless parameters, we transform the equations into dimensionless wave equations, and the dispersion relations of bending wave, shear wave and longitudinal wave are obtained by Laplace and Hankel integral transformation method. The influence of nonlocal parameter, porosity volume fraction, strain gradient parameters and power law index on the propagation characteristics of bending wave, shear wave and longitudinal wave in FG nano circular plate.

• International Journal of Naval Architecture and Ocean Engineering
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• 제3권3호
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• pp.201-207
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• 2011

In this paper, we focused on computing the higher-harmonic components of the transmitted wave passing over a submerged circular cylinder to show that it is causing a horizontal negative drift force. As numerical models, a circular cylinder held fixed under free surface in deep water is adopted. As the submergence of a circular cylinder decreases and the incident wavelength becomes longer, the higher-harmonic components of the transmitted wave starts to increase. An increase of the higher-harmonic components of the transmitted wave makes the horizontal drift force be negative. It is also found that the higher-harmonic amplitudes averaged over the transmitted wave region become larger with the increase of wave steepness and wavelength as well as the decrease of submergence depth.

• 한국해안·해양공학회논문집
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• 제32권5호
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• pp.307-321
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• 2020

기존 케이슨방파제의 안정성을 높이기 위해 케이슨 전면 또는 후면에 추가로 신규 케이슨을 설치하여 보강하는 설계 및 시공사례가 발생되고 있다. 본 연구에서는 기존 원형케이슨 전면 또는 후면에 신규 원형케이슨이 추가 설치될 경우 파와 구조물간의 상호작용 영향을 분석하기 위해 고유함수전개법을 이용하여 수치해석을 수행하였다. 수치해석의 신뢰성을 확보하기 위해 Williams and Li의 수치 해석결과와 비교를 수행하였으며, 추가로 설치되는 원형케이슨의 다양한 변수에 따른 개별 원형케이슨에 작용하는 파력 및 파처오름 특성을 분석하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제2권3호
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• pp.146-154
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• 2010

In the present study, the wave excitation forces acting on an array of porous circular cylinders are examined based on diffraction problems. To calculate the wave forces, the fluid domain is divided into three regions i.e. a single exterior region, N interior regions and N beneath regions, and the diffraction in each fluid region is expressed by an eigenfunction expansion method with using 3-dimension liner potential theory (Williams and Li, 2000). Especially, the present method is extended to the case of an array of truncated porous circular cylinders to calculate the heave forces as well as surge and sway forces. To verify this method, the numerical results obtained by eigenfunction are compared with these results obtained by higher order boundary element method (Choi et al., 2000). The numerical results obtained by this study are in good agreement with those results. By changing the numbers of porous circular cylinders, the angle of incident wave and the porosity rate of circular cylinders, the wave excitation forces such as surge, sway and heave on an array of truncated porous circular cylinders are investigated.

• 한국해양공학회지
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• 제7권2호
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• pp.9-18
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• 1993

Numerical wave tank is a robust tool by which the nonlinear interactions between the body and the free-surface can be treated in time-domain. In this paper, a two-dimensional numerical wave tank based on the Spectral/Boundary-Element Method is developed, and applied successfully to the study of nonlinear wave diffraction around a submerged circular cylinder. Particularly, it is shown that the high-order wave components of significant wave height are developed in the lee-side of the cylinder and that these waves result in a negative drift force on the circular cylider.