• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.439-442
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• 2008

Diffraction of multi-directional random waves passing semi-infinite breakwater is investigated by using analytic solution derived by Penny and Prices(1952). An irregylarity of period and incident angle of waves and regular periods for regular waves are considered in addition by expanding from the past study which used only monochromatic wave in general. The Bretschneider-Mitsuyasu frequency spectrum and Mitsuyasu directional spectrum are used for incident waves. And diffraction of multi-directional random waves is reappeared by decomposing numerical results of several monochromatic waves which have variable period and incident angle. Analytic solution on the diffraction of regular waves and multi-directional random waves calculated in this study.

• Journal of Ocean Engineering and Technology
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• v.12 no.1
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• pp.135-142
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• 1998

In this study, the frequency transfer function of motions are predicted from the result of a full-scale seakeeping trials. Because the real sea has the characteristics of multi-directional waves,we compare the results in the one directional waves with ones in the directional waves. For calculation of the frequency transfer function in the directional waves, Takezawa's inverse estimation method was introduced and the frequency ranges were divided into three parts in order to consider following seas. The full-scale seakeeping trials was executed in the south sea of Korea using the stern trawler. Those results show that analysis method of the multi-directional waves is more reliable than that of one directional waves, and confirm the possibility of applying this method to the full-scale seakeeping trials.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.6
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• pp.429-436
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• 2010

Hydraulic experiments were conducted to analyze the characteristics of stem waves due to multidirectional random wave incidence with the different incident angles of main wave direction. Both multi-directional and uni-directional random waves were used to generate the stem waves and their results were compared with each other. The experiment shows multi-directional random waves developed along the vertical wall tend to increase as the incident angle increases similar to the uni-directional waves. Moreover, the stem wave widths were almost same as those in uni-directional random wave cases. However, the experiment demonstrate the stem wave heights were significantly smaller in multi-directional random wave cases than in uni-directional random wave cases.

• Journal of the Society of Naval Architects of Korea
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• v.60 no.4
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• pp.266-277
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• 2023

In this study, fundamental research is conducted for the generation technique and analysis of multi-directional irregular waves in the Deep Ocean Engineering Basin (DOEB). A three-dimensional boundary element method-based numerical tank is implemented to perform wave generation simulations, and directional spectrum estimation is carried out using the results of simulations. The wave generation technique of the Snake type wave maker, generating multi-directional irregular waves, is implemented using the Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (IFFT) algorithms. The wave generation technique is validated by comparing the wave spectrum from simulations and experiments. A Maximum Likelihood Method (MLM) based estimation code is developed for estimating the directional wave spectra. The multi-directional irregular waves are tested in the DOEB and the numerical tank, and directional wave spectra obtained from two methodologies are estimated and compared. A correction procedure for the directional distribution of multi-directional waves is established, and the possibility of correcting the directional spreading function using the numerical tank is validated.

• Journal of Ocean Engineering and Technology
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• v.7 no.2
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• pp.114-120
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• 1993

Responses of marine vehicles and ocean structures in a seaway can be predicted by applying the probabilistic approach. When we consider a linear system, the responses in a random seaway can be evaluated through spectral analysis in the frequency domain. But when we treat nonlinear system in irregular waves, it is necessary to get time history of waves. In the previous study we introduced one-directional waves (long crested waves)as wave environment and carried out calculations and experiments in the waves. But the real sea in which marine vehicles and structures are operated has multi-directional waves (short crested waves). It is important to get a simulated random sea and analyse dynamic problems in the sea. We need entire sample function or probabillty density function to infer statistical value of random process. However if the process are ergodic process, we can get statistical values by analysis of one sample function. In this paper, we developed the simulation technique of multi-directional waves and proved that the time history given by this method keep ergodic characteristics by the statistical analysis.

• Journal of Ocean Engineering and Technology
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• v.11 no.4
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• pp.76-89
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• 1997

The hydrodynamic interaction characteristics between multiple floating bodies of semisubmersible type are examined to present the basic data for the design of huge offshore structures supported by a large number of the floating bodies in multi-directional irregular waves. The numerical approach is based on a combination of a three-dimensional source distribution method, the wave interaction theory and the spectral analysis method. The effects of wave directionality on the wave exciting forces acting on multiple floating bodies in multi-directional irregular waves also have been pointed out.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.9 no.2
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• pp.97-104
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• 1997

A hyperbolic numerical model with multi-directional waves has been used to investigate harbor tranquility in Pohang New Harbor. Comparing numerical results with field data measured at two stations in the harbor, it was found that use of input condition of multi-directional waves is superior to the use of uni-directional waves. Calculations with unidirectional wave input give errors of about 12% at St. P2 and 26% at St. P3, while calculations with multi-directional wave input give errors of 4 % at St. P2 and. 14% at St. P3. Using the input condition of multi-directional waves, we investigate the tranquility of Pohang New Harbor with two layouts : the condition in 1994 when the downtime at the 7th pier was often reported and the condition in 1996 when the 4th disposal site was constructed. The numerical results show that the problem of downtime at the 7th pier cannot be solved by the construction of the 4th disposal site.

• Journal of Ocean Engineering and Technology
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• v.20 no.5 s.72
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• pp.36-41
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• 2006

The main object of this study is to develop an accurate and convenient method for the response analysis of offshore structures in real sea states. A numerical procedure is described for predicting the motion responses and tension variations of the ISSC TLP in multi-directional irregular waves. The developed numerical approach in the frequency domain is based on acombination of the three dimensional source distribution method, the dynamic response analysis method, and the spectral analysis method. Frequency domain analysis in the multi-directional irregular waves is expanded to a time domain analysis by using a convolution integral after obtaining the impulse response by Fourier transformation. The results of the comparison between responses in the frequency and time domain confirmed the validity of the proposed approach.

• Journal of Ocean Engineering and Technology
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• v.20 no.4 s.71
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• pp.70-75
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• 2006

A numerical procedure is described for estimating the effects of the multi-directional irregular waves on the motion responses and tension variations of the ISSC-TLP. The numerical approach is based on a three-dimensional source distribution method and a spectral analysis technique of directional waves. The spectral description for the linear system of ISSC-TLP in the frequency domain is sufficient to completely define the motion responses and tension variations. This is because both the wave inputs and responses are stationary Gaussian random processes, of which the statistical properties in the amplitude domain are well known. The numerical results for the linear motion responses and tension variations in regular waves are compared with the experimental and numerical ones, which are obtained in the literature. The results of comparison confirmed the validity of the proposed approach.

• Journal of Ocean Engineering and Technology
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• v.26 no.2
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• pp.68-78
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• 2012

This study proposes an improved 3-D model that includes a new non-reflected wave generation system for oblique incident and multi-directional random waves, which enables us to estimate the effect of the various wave-types on 3-D wave fields in a coastal area with permeable submerged breakwaters. Then, using the numerical results,the three-dimensional wave field characteristics around permeable submerged breakwaters are examined in cases of oblique incident and multi-directional random waves. Especially, the wave height, mean surface elevation and mean flow around the submerged breakwaters are discussed in relation to the variation of incident wave condition.