• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.38 no.3
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• pp.190-196
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• 2002

In order to analyze the hydrodynamic forces on fish cage systems, made of frames and nettings, under waves and current, hydraulic model experiments for square type and circular type of fish cage system were carried out in a towing tank. Both cage systems consist of net cages supported by floating frames made of two concentric pipes and four weights hanging from the bottom corners of the nets. There was little difference in the hydrodynamic force on the square type of fish cage system by wave heading under regular waves and the peak frequency of the force on each cage system was in a good agreement with that of induced irregular wave. In addition, it was also observed that the circular type of cage system was more stable to the action of waves and current than the square type.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.36 no.1
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• pp.1-10
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• 2024

As increasing demands for a floating structure expanded from offshore industry facilities to living facilities, it has emerged that necessity of techniques to reduce motions of a floating structure. This study present a floating structure with porosity on the outer surface of the floater. Under each regular and irregular wave, responses of the floater was investigated in frequency domain. The proposed structure is composed of inner and outer floaters, which are connected to each other and the outer wall is perforated, and the heave and the pitch of floaters with different perforation rates (0~30%) were compared with at both the center and the edge. The results showed that pitch responses can be decreased by increasing of perforation rate of the floater. Comparing with responses of the non-perforated floater, those of the proposed floating structure were reduced to above 10% and 2%, respectively for regular and irregular wave conditions.

• Journal of Ocean Engineering and Technology
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• v.11 no.3
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• pp.116-123
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• 1997

세계적으로 수요가 증대하고 있는 고속선의 설계시 승선감 또는 내항성은 필수적으로 고려되어야 하는 중요요소이다. 고속선은 필연적으로 과도한 운동을 동반하며 그로 인해 승객들은 극심한 멀미와 구토 등 불쾌한 승선감을 경험하게 된다. 근래에 항공 및 육상 교통수단들의 고급화에 따라 해양 운항선사들도 선박품질의 고급화와 괘적한 승선감 확보에 비상한 관심을 보이며 승객 유치 및 승선률 제고를 도모하고 있다. 본 논문은 고속쌍동선에 대한 내항성능을 추정하고 그 해석결과를 실험과 비교하였다. 상하동요 및 종동요 간의 선형 연성 운동방정식을 사용하였고, 규칙파에 대한 상하동요의 응답특성 곡선을 구하였다. 또한 불규칙파에 대한 운동응답을 추정하기 위하여 ITTC파도 스펙트럼을 적용하였으며, 본 고속쌍동선의 운동성능에 미치는 선수 및 선수각의 영향을 고찰하였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.6
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• pp.759-768
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• 2019

The extended Tanimoto formula has been widely used to estimate the stability for the toe protection of the composite structure. However, the extended Tanimoto formula usually over-estimates armor weight when the incident waves approach the structure obliquely because the formula incident originally considered the normally incident wave cases. In this study, three-dimensional hydraulic model experiments were conducted to investigate the horizontal wave velocity under monochromatic and random wave conditions to investigate the prediction capability of the extended Tanimoto formula under the different incident wave angle conditions. The maximum horizontal wave velocity was measured near the toe for the normally incident wave condition. In the case of obliquely incident waves, the maximum horizontal wave velocity was measured under the stem wave generation condition. The results of the experiments showed a good agreement with the results by Takahashi et al.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.1
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• pp.11-16
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• 2020

The rotational stability of an interlocking caisson breakwater was studied. Using the analytical solution for the linear wave incident to the infinite breakwater, the phase difference effect of wave pressures in the direction of the breakwater baseline is considered, and Goda's wave pressure formula in the design code is adopted to consider the nonlinearity of the design wave. The rotational safety factor of the breakwater was defined as the ratio of the rotational frictional resistance moment due to caisson's own weight and the acting rotational moment due to the horizontal and vertical wave forces. An analytical solution for the rotational center point location and the minimum safety factor is presented. Stability assessment formula were proposed to be applicable to all design wave conditions used in current port and harbor structure design such as regular waves, irregular waves and multi-directional irregular waves.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.6
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• pp.424-433
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• 2015

In this study, the wave force distribution acting on a semi-infinite and vertical-type long structure is investigated considering diffraction. An analytical solution of the wave force acting on long structures is also suggested in this study. The wave forces on long structures are evaluated for monochromatic, uni-directional random, and multi-directional random waves. Diffraction effects in front of the breakwater and on the lee side of the breakwater are considered. The wave force on a long structure becomes zero when the relative length of the breakwater (1/L) is zero. The diffraction effects are relatively strong when the relative length of the breakwater is less than 1.0, and the wave forces decrease greatly for long structure when the relative length of the breakwater is larger than 0.5. Therefore, it is necessary to consider diffraction effects when the relative length of the breakwater is less than 1.0, and the relative length of the breakwater must be at least 0.5 in order to obtain a reduction of wave force on long structures.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.5
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• pp.437-444
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• 2020

This study was focused on the stabilization of surge motions of a moored vessel under irregular head seas. A two-point moored vessel shows strong non-linearity even in regular sea, owing to its inherent non-linear restoring force. A long-crested irregular wave is subjected to the vessel system, resulting in more complex nonlinear behavior of the displacement and velocities than in the case of regular waves. Sliding mode control (SMC) is implemented in the moored vessel to control both surge displacement and surge velocity. The SMC can provide a closed-loop system with performance and robustness against parameter uncertainties and disturbances; however, chattering is the main drawback for implementing SMC. The goal of minimizing the chattering and state convergence with accuracy is achieved using a quasi-sliding mode that approximates the discontinuous function via a continuous sigmoid function. Numerical simulations were conducted to validate the effectiveness of the proposed control algorithm.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.2
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• pp.238-245
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• 2008

To evaluate wave reflection and transmission from buoyant flap-typed storm surge barriers, hydraulic experiments were performed by using regular and irregular wave conditions. Buoyant flap-typed storm surge barriers consist of buoyant main body connected with foundation structure in the seabed by hinge. The characteristics of wave reflection, transmission and dynamic response of the structure were investigated for 36 regular and 4 irregular wave conditions. It was also evaluated the usage of plain plate attached on the buoyant main body as one of alternatives to control wave reflection and transmission. From the hydraulic experiments, it was found that the case of plain plate attached on the offshore side is very effective to improve the wave transmission as well as reflection. But, the effect of the case on the harbor side might be negligible.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.3 no.1
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• pp.54-64
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• 1991

To accurately estimate the rate of sediment transport in shallow water bodies, it is necessary to investigate the irregular waves transformation characteristics and nearshore currents produced by random sea waves. Most of studies on numerical models for nearshore currents are based on the theory of monocromatic waves and thus, very few nearshore models take into account the effect of irregularities in the hight, period and directional spreading of incident waves. The numerical simulation model for nearshore currents used in this paper considers the effect of irregularities of incident waves, based on Individual Wave Analysis. The computational results are compared and shown in a reasionable agreement with the experimental data.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.4 no.4
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• pp.225-230
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• 1992

An attempt is made to assemble and synthesize recent publications which may contribute to our capability for understanding the transformation of wave spectra in finite-depth water or in the presence of current. This review is limited essentially to the effects of shoaling and current on one-dimensional transformation of wave spectra and examining the adequacy of the approximation of irregular waves by a monochromatic wave in modeling of wave transformation in coastal areas.