• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.364-379
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• 2019

Wave-induced ship motion and load responses are usually investigated on the assumption that the incident waves are long-crested. The realistic sea waves are however short-crested irregular waves. Real practice reveals that the ship motion and load responses induced by short-crested waves are different from those induced by long-crested waves. This paper aims to conduct a comprehensive study on ship motions and loads in different wave fields. For this purpose, comparative studies by small-scale model towing tank test and large-scale model sea trial are conducted to experimentally identify the difference between ship motions and loads in long-crested and short-crested irregular waves. Moreover, the influences of directional spreading function of short-crested waves on ship motions and loads are analyzed by numerical seakeeping calculation. The results and conclusions obtained from this study are of great significance for the further extrapolation and estimation of ship motions and loads in short-crested waves based on long-crested wave response results.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.3 s.147
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• pp.384-391
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• 2006

RCS effects of long-crested wave surfaces to marine targets are numerically analyzed using a 4-path model and a direct analysis method, developed based on physical optics and a combined method of physical optics/geometric optics, respectively. Reflectivity of long-crested wave surfaces is described with 'Fresnel reflection coefficients' The MPM(modified Pierson-Moskowitz) ocean spectrum is adopted to simulate long-crested waves in the direct analysis method. A numerical analysis of a benchmark model assures the validity of both methods. The direct analysis method is applied to the RCS calculation of electromagnetically large marine targets, which are vertically oriented or slanted to the long crested wave surfaces randomly generated with various significant wave heights. The long-crested wave surface much highly increases the RCS of the marine target, but those effects are decreased as the significant wave height grows up. At low elevation angle, the vertical model has entirely high RCS comparing slanted model, and the RCS of vertical flat plate is the highest on the calm sea surface, while those of slanted flat plates are the lowest on the calm sea surface. The RCS of marine targets on continuously-varying sea surface is more coherent at lower elevation angles, as well.

• Ocean Systems Engineering
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• v.2 no.4
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• pp.257-269
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• 2012

This paper provides a practical stochastic method by which the maximum equilibrium scour depth around spherical bodies exposed to long-crested (2D) and short-crested (3D) nonlinear random waves can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Forristall (2000) wave crest height distribution representing both 2D and 3D nonlinear random waves, and using the regular wave formulas for scour and self-burial depths by Truelsen et al. (2005). An example calculation is provided.

• Ocean Systems Engineering
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• v.4 no.1
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• pp.21-37
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• 2014

This paper provides a practical stochastic method by which the burial and scour depths of truncated cones exposed to long-crested (2D) and short-crested (3D) nonlinear random waves can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Forristall (2000) wave crest height distribution representing both 2D and 3D nonlinear random waves. Moreover, the formulas for the burial and the scour depths for regular waves presented by Catano-Lopera et al. (2011) for truncated cones are used. An example of calculation is also presented.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.6
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• pp.867-873
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• 2011

The transportation of a truss-spar hull from a transport barge of 6000 ton topside module on the spar hull is investigated in the present study. Two possible routes from a fabrication yard in Teeside, England to the Gulf of Mexico are considered in the paper. The results of motion responses of the transport barge obtained from a spectral analysis and the limiting criteria of sea fastening, deck wetness and lateral acceleration are compared and the route selection is discussed. Long-crested waves and short-crested seas as well as the joint probabilities of significant wave heights and wave periods in different sea areas are considered. Generally speaking, the results for long-crested seas are higher than those for short-crested waves.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.3
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• pp.212-219
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• 2005

Real sea waves in a towing wave basin have been generated using random periodic motion of the segmented wave makers and the wave reflections of sidewalls. Theoretically, the real sea waves can be described by the superposition of many random oblique waves. This paper introduces numerical real sea wave generation in a rectangular wave basin using spectral method that uses a superposition of orthogonal functions which have to satisfy the Laplace equation. Oblique regular waves, long crested irregular waves and real sea waves were simulated and met the requirement of sidewall wave reflection and wave absorption. MLM (Maximum Likelihood Method) and Spatial Fourier Transform were used in order to obtain propagated wave direction characteristics. The estimated results proved the usefulness of the method and the performances showed reasonable directional patterns comparing with generating patterns.

• Journal of Ocean Engineering and Technology
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• v.37 no.1
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• pp.20-30
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• 2023

Modeling a nonlinear ocean wave is one of the primary concerns in ocean engineering and naval architecture to perform an accurate numerical study of wave-structure interactions. The high-order spectral (HOS) method, which can simulate nonlinear waves accurately and efficiently, was investigated to see its capability for nonlinear wave generation. An open-source (distributed under the terms of GPLv3) project named "HOS-ocean" was used in the present study. A parametric study on the "HOS-ocean" was performed with three-hour simulations of long-crested ocean waves. The considered sea conditions ranged from sea state 3 to sea state 7. One hundred simulations with fixed computational parameters but different random seeds were conducted to obtain representative results. The influences of HOS computational parameters were investigated using spectral analysis and the distribution of wave crests. The probability distributions of the wave crest were compared with the Rayleigh (first-order), Forristall (second-order), and Huang (empirical formula) distributions. The results verified that the HOS method could simulate the nonlinearity of ocean waves. A set of HOS computational parameters was suggested for the long-crested irregular wave simulation in sea states 3 to 7.

• Journal of the Society of Naval Architects of Korea
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• v.61 no.4
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• pp.258-266
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• 2024

It is necessary to predict the ship's manoeuvrabilities in waves for its safe operations in adverse weather. At the early design stage, free-running model tests can be performed to estimate the ship's manoeuvring performance in irregular wave conditions. The wave elevations are randomly varied with times in irregular waves, large deviations of the manoeuvring performance indices are likely to occur depending on the start time of steering scenarios. In this study, a KSUPRAMAX model ship's manoeuvres in long-crested irregular waves are reproduced in the equivalent regular waves. The equivalent regular waves are searched from the energy flux relations between long-crested irregular and regular waves. But there are differences of forward speeds in the model tests, regular wave height and period are modified so that both the forward speed and the trajectory drift in regular waves are similar to those in irregular waves. In addition, low speed course-keeping tests are performed with various wave incident angles in irregular and regular waves. It is confirmed that check helms, drift angles, and speeds as well as trajectories in irregular waves are similar to those in equivalent regular waves.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.2
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• pp.1-9
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• 2001

Based on the linear potential theory with the side wall reflection. the directional spectrum waves are numerically simulated by a source distribution method and these together with long-crested irregular waves are also generated at the towing tank of Pusan National University by considering the transfer function of the wave maker obtained from the regular waves. In the numerical simulation, the characteristics of the directional spreading function are investigated by changing the breadth of the wave-maker unit. the width of the towing tank and the wave period. In the experimental generation, the statistical properties and the power spectrums of the long-crested irregular and directional waves are compared along the towing tank length. The directional spreading functions are also investigated at various positions in the tank.

• 한국기계연구소 소보
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• s.9
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• pp.193-208
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• 1982

Flap type wave-maker, wave absorber, motion measuring equipment and related instruments were newly installed at Ship Experimental Towing Tank, Ship Research Station, KIMM. The model tests in regular head and following waves were successfully carried out and the motion and wave loads in regular and long crested irregular waves were calculated for a container ship model which was adopted as the hull form for the comparative calculations of the ITTC Seakeeping Committee. The results of model tests show good agreement with calculated results and the latter are generally in good agreement with the results of the comparative calculations.