• Bulletin of the Society of Naval Architects of Korea
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• v.13 no.1
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• pp.11-16
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• 1976

The effect of the bow shape on the ship motion response in longitudinal regular waves of water of finite depth is investigated by employing the strip theory. The two-dimensional hydrodynamic forces(added mass and damping) were calculated by close-fit method for water of finite depth. The models for investigation are U and V bow ship forms of block coefficient 0.8 with constant after body which were used by Yourkov [2] and recently by Kim [3] for their deep water investigations. The following results are obtained by the present numerical experiments. (1) It is confirmed that the damping coefficient of the V-bow ship is greater than that of U-bow ship and in consquence the amplitude of heave and pitch of V-bow ship is smaller than that of U-bow ship among longitudinal regular head waves in water of finite depth (2) The merit of the V-bow ship on the motion damping is more significant in heave than in pitch, and is decreasing with the shallowness of water depth. (3) The change of bow form gives little effect on the wave exciting force and moment compared with the motion responce.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.6
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• pp.286-297
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• 2018

In the present study, wave measurements at KOGA-W01 were analyzed and then the numerical wind waves simulations have been conducted to investigate the characteristics of wind waves in the Yellow sea. According to the present analysis, even though the location of the wave stations are close to the coastal region, the deep water waves are prevailed due to the short fetch length. Chun and Ahn's (2017a, b) numerical model has been extended to the Yellow Sea in this study. The effects of tide and tidal currents should be included in the model to accommodate the distinctive effect of large tidal range and tidal current in the Yellow Sea. The wave hindcasting results were compared with the wave measurements collected KOGA-W01 and Kyeockpo. The comparison shows the reasonable agreements between wave hindcastings and measured data, however the model significantly underestimate the wave period of swell waves from the south due to the narrow computational domain. Despite the poorly prediction in the significant wave period of swell waves which usually have small wave heights, the estimation of the extreme wave height and corresponding wave period shows good agreement with the measurement data.

• Journal of the Society of Naval Architects of Korea
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• v.49 no.1
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• pp.6-13
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• 2012

As ocean resources in shallow water areas are being exhausted, deep sea development is becoming common these days. Therefore floating type offshore structures are more competitive than fixed type structures, and FPSO is the most popular one these days. FPSO's are generally operated in a specific region and positioned to meet mostly head or bow waves in order to reduce roll motions. However this makes these vessels more vulnerable to green water around the bow region, and therefore the bow shape must be properly designed to mitigate green water damage. In the present study, experimental results for three different FPSO bow shapes in regular head waves were analyzed and compared to each other. Also CFD computations were carried out as a sample validation case for the database built for CFD code validation.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.3
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• pp.159-167
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• 2015

In this paper, the errors found in the existed analytical solutions described the mechanism of residual pore-water pressure accumulation were examined and a new analytical was proposed. The new analytical solution was derived by using a Fourier series expansion and separation of variables was verified by comparison with the existed both analytical and numerical solutions and experimental result. The new analytical solution is very simple that there is no need for numerical integration for deep soil thickness. In addition, the solutions of the residual pore-water pressure for finite, deep, and shallow soil thickness reveled that it is possible to approach from finite to shallow soil thickness, but not possible to deep soil thickness because there was discontinues zone between finite and deep soil thickness.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.1
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• pp.70-86
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• 2015

Short crested waves play an important role for planning and design of harbours. In this context a numerical simulation is carried out to evaluate wave tranquility inside a real harbour located in east coast of India. The annual offshore wave climate proximity to harbour site is established using Wave Model (WAM) hindcast wave data. The deep water waves are transformed to harbour front using a Near Shore spectral Wave model (NSW). A directional analysis is carried out to determine the probable incident wave directions towards the harbour. Most critical threshold wave height and wave period is chosen for normal operating conditions using exceedence probability analysis. Irregular random waves from various directions are generated confirming to Pierson Moskowitz spectrum at 20m water depth. Wave incident into inner harbor through harbor entrance is performed using Boussinesq Wave model (BW). Wave disturbance experienced inside the harbour and at various berths are analysed. The paper discusses the progresses took place in short wave modeling and it demonstrates application of wave climate for the evaluation of harbor tranquility using various types of wave models.

• Wind and Structures
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• v.16 no.2
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• pp.193-211
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• 2013

This paper presents results from a wind tunnel study that examined the drag coefficient and wind flow over an asymmetric wave train immersed in turbulent boundary layer flow. The modeled wavy surface consisted of eight replicas of a statistically-valid hurricane-generated wave, located near the coast in the shoaling wave region. For an aerodynamically rough model surface, the air flow remained attached and a pronounced speed-up region was evident over the wave crest. A wavelength-averaged drag coefficient was determined using the wind profile method, common to both field and laboratory settings. It was found that the drag coefficient was approximately 50% higher than values obtained in deep water hurricane conditions. This study suggests that nearshore wave drag is markedly higher than over deep water waves of similar size, and provides the groundwork for assessing the impact of nearshore wave conditions on storm surge modeling and coastal wind engineering.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1B
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• pp.111-114
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• 2008

Explicit solutions of the wave dispersion equation are developed using the recursive relation in terms of the relative water depth. We use the solutions of Eckart (1951), Hunt (1979), and the deep-water and shallow-water solutions for initial values of the solution. All the recursive solutions converge to the exact one except that with the initial value of deep-water solution. The solution with the initial value by Hunt converged much faster than the others. The recursive solutions may be obtained quickly and simply by a hand calculator. For the transformation of linear water waves in whole water depth, the use of the recursive solutions will yield more accurate analytical solutions than use of previously developed explicit solutions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.4_1
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• pp.137-150
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• 1992

A complete solution, exact to second-order, for wave motion forced by a hinged-wavemaker of variable-draft is presented. A solution for a piston type wavemaker is also obtained as a special case of a hinged-wavemaker. The laboratory waves generated by a plane wave board are shown to be composed of two components; viz., a Stokes second-order wave and a second-harnomic free wave which travels at a different speed. The amplitude of the second-harmonic free wave is relatively large in shallow water and decreases to less than 10% of the amplitude of the primary wave in deep water. Wavemakers with relatively deeper draft (i.e., hinged near the bottom) generate the free waves of smaller amplitude in shallow and intermediate water depths than the wavemakers with shallow draft. However, the opposite is predicted by theory in deep water.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.2 no.2
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• pp.83-95
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• 1990

It can be assumed that the ocean waves consist of many independent pure sinusoidal components which progress in arbitrary directions. To analyze irregular sea waves, both the spectrum method and the individual wave method have been used. The spectral approach is valid in the region where the water depth is deep and the linear property of velocity distribution is predominent, while the individual wave analysis method in the region where the water depth is shallow and the wave nonlinearity is significant. Therefore, to investigate the irregular wave transformation from the deep water to the shallow water region, it is necessary to relate the frequency spectrum which is estimated by the spectrum analysis method to the i oint probability distribution of wave height, period and direction affected by the boundary condition of the individual wave analysis method. It also becomes important to define the region where both methods can be applied. This study is a part of investigation to establish a systematic approach for analyzing the irregular wave transformation. The region where the spectral approach can be applied is discussed by earring out the experiments on the irregular wave transformation in the two-dimensional wave tank together with the numerical simulation. The applicability of the individual wave analysis method for predicting irregular wave transformation including wave shoaling and breaking and the relation between frequency spectrum and joint probability distribution of wave height and period are also investigated through the laboratory experiment and numerical simualtion.

• Ocean Systems Engineering
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• v.12 no.1
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• pp.87-142
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• 2022

An analysis for the computation of Fatigue Damage Index (FDI) under the effects of the various combination of the ocean loads like random waves, current, platform motion and VIV (Vortex Induced Vibration) for a certain design water depth is a critically important part of the analysis and design of the marine riser platform integrated system. Herein, a 'Computer Simulation Model (CSM)' is developed to combine the advantages of the frequency domain and time domain. A case study considering a steel catenary riser operating in 1000 m water depth has been conducted with semi-submersible. The riser is subjected to extreme environmental conditions and static and dynamic response analyses are performed and the Response Amplitude Operators (RAOs) of the offshore platform are computed with the frequency domain solution. Later the frequency domain results are integrated with time domain analysis system for the dynamic analysis in time domain. After that an extensive post processing is done to compute the FDI of the marine riser. In the present paper importance is given to the nature of the current profile and the VIV. At the end we have reported the detail results of the FDI comparison with VIV and without VIV under the linear current velocity and the FDI comparison with linear and power law current velocity with and without VIV. We have also reported the design recommendations for the marine riser in the regions where the higher fatigue damage is observed and the proposed CSM is implemented in industrially used standard soft solution systems (i.e., OrcaFlex^*TM and Ansys AQWA^**TM), Ms-Excel^***TM, and C++ programming language using its object oriented features.