• 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 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 the Society of Naval Architects of Korea
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• v.31 no.4
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• pp.51-57
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• 1994

In this study, the method for calculation of the frequency transfer function of motions based on the multi-directional waves in the analysis of a full-scale seakeeping trials is presented. 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. To confirm the validity of this method, the numerical simulation was executed. 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-scathe seakeeping trials.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.5 no.2
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• pp.76-83
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• 1993

In this study, an approximate method for calculating the directional spectrum of waves encountering a current in shallow water is developed. The wave trains in tile directional spectrum are assumed to be linear and Gaussian; development of the spectrum requires that the waves also be short crested. The Miche's breaking criterion is imposed to determine the upper limit of wave height and to establish an expression for the breaking wave elevation in terms of the ideal wave's elevation and the second time derivative of wave elevation. Two examples are given; one for a Wallops directional spectrum encountering a shear current and another with an upwelling current.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.14 no.3
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• pp.240-246
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• 2002

Hydraulic model experiments were conducted fur a series of regular and uni-directional irregular waves propagating over a submerged elliptic shoal. Two different sets of experiments have been studied； one considers regular wave transformation with no breaking, and the other considers uni-directional irregular wave with partial breaking on top of the shoal. The numerical experiments are also performed using a numerical model based on the parabolic approximation equation. The result of the numerical experiments are compared with that of hydraulic experiments.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.299-299
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• 2007

This paper presents an omni-directional piezoelectric actuator which utilizes only one actuator. The actuator has a simple structure of cone type consists of two piezoelectric ceramics of ring type and electrodes divided four segments and a stainless steel body. To find the optimal operating condition of the actuator, the frequency characteristics of the actuator are analyzed by ATILA, FEM and measured by Impedance Analyzer. We have also developed a stage using the omni-directional actuator and an actuator driver circuit to create four sinusoidal waves with a variable frequency and phase difference.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.105-112
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• 2006

Freak waves in the ocean are recently drawing much attention as a natural disaster to ocean structures and navigating ships as well. Several observation data, among them the Draupner New Year Wave, show the very impressive feature of Freak waves whose wave height is up to three times as high as the significant wave height of surrounding waves, In addition, Freak wave appears as an isolated very high crest in somewhat stationary random waves of same order in their wavelengths. Bearing such characteristics in mind, one notices its extraordinary steepness. This strongly suggests that Freak wave is not long lived but transient nature on the whole. A great number of studies to explain these natures were published from both theoretical and numerical point of view. However it is not sure if they are applicable to actual ocean environment. In this paper, we deal with the results concerning abnormal and/or Freak waves from in-situ ocean wave data and point out several remarks to the problems lain behind the contributions in this context. A physical experiment is described to reinforce the subject discussed from the observation data.

• Bulletin of the Korean Chemical Society
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• v.20 no.4
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• pp.411-416
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• 1999

A new kind of differential flow induced chemical wave is introduced by theoretical calculation. A differential flow between the counter acting species of a dynamical activator-inhibitor system may destabilize its homogeneous reference state and cause the medium to self-organize into a pattern of travelling waves through the differential flow instability (DIFI). In a chemical system, also, the differential bulk flow may change the dynamics of the system, thus it has been refered to as the differential flow induced chemical instability (DIFICI). For DlFICI experiments, one directional flow has been commonly employed, resulting in periodic wave patterns generally. In this study, we considered two directional flow for the DIFICI wave by exchanging artificially the flow direction at some period.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.3
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• pp.149-159
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• 2014

In this study, we develop an algorithm to predict swell-like high waves on the east coast of Korea using the directional wave gauge which was installed near Sokcho. Using the numerical wave model SWAN, we estimate wave data in open sea from the wave data collected by using the directional wave gauge. Then, using the wave ray method and SWAN model with the open-sea wave data as offshore boundary conditions, we predict the swell-like high waves at several major points on the east coast of Korea. We verify the prediction methods with the SWAN and wave ray methods by comparing predicted data against measured one at Wangdolcho. We can improve the prediction of the swell-like high waves in the east sea of Korea using both the real-time wave measurement system and the present prediction algorithm.