• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.2
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• pp.157-163
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• 1994

An experimental study of deep-water breaking waves is performed by nonlinear wave evolution as well as superposition of different wave frequencies. Two-dimensional and three-dimensional wave instabilities and breakings are observed in nonlinear wave evolution. The wave energy evolves with almost the same initial wave energy before breaking but decreases significantly after breaking process. Large spilling and plunging waves are generated near e expected breaking location by means of faster waves overtaking slow waves at a certain point. More energy loss in vigorous plunging breakers is observed through breaking process.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.24-34
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• 2021

This paper predicts the speed-power-rpm relationship in regular head waves using various indirect methods: load variation, direct powering, resistance and thrust identity, torque and revolution, thrust and revolution, and Taylor expansion methods. The subject ship is KVLCC2. The wave conditions are the regular head waves of λ/LPP = 0.6 and 1.0 with three wave steepness ratios at three ship speeds of 13.5, 14.5 and 15.5 knots (design speed). In the case of λ/LPP = 0.6 at design speed, two more wave steepness ratios have been taken into consideration. The indirect methods have been evaluated through comparing the speed-power-rpm relationships with those obtained from the resistance and self-propulsion tests in calm water and in waves. The load variation method has been applied to predict propulsive performances in waves, and to derive overload factors (ITTC, 2018). The overload factors have been applied to obtain propulsive efficiency and propeller revolution. The thrust and revolution method (ITTC, 2014) has been modified.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.985-990
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• 2004

Leak noise is a good source to identify the exact location of a leak point of underground water pipelines. Water leak generates broadband noise from a leak location and can be propagated to both directions of water pipes. This sound propagation due to leak in water pipelines is not a non-dispersive wave any more because of the surrounding pipes and soil. However, the necessity of long-range detection of this leak location makes to identify low-frequency acoustic waves rather than high frequency ones. Acoustic wave propagation coupled with surrounding boundaries including cast iron pipes is theoretically analyzed and the wave velocity was confirmed with experiment. The leak locations were identified both by the acoustic emission (AE) method and the cross-correlation method. In a short-range distance, both the AE method and cross-correlation method are effective to detect leak position. However, the detection for a long-range distance required a lower frequency range accelerometers only because higher frequency waves were attenuated very quickly with the increase of propagation paths. Two algorithms for the cross-correlation function were suggested, and a long-range detection has been achieved at real underground water pipelines longer than 300m.

• Journal of Ship and Ocean Technology
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• v.5 no.2
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• pp.50-61
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• 2001

In this paper, nonlinear interactions between water waves and a horizontally submerged circular cylinder are numerically simulated. In this case, the nonlinear interactions between them generated a wave breaking phenomenon. The wave breaking phenomenon plays an important role in the wave farce. Negative drifting forces are raised at shallow submerged cylinders under waves because of the wave breaking phenomenon. For the numerical simulation, a finite difference method based on the unsteady incompressible Navier-Stokes equations and the continuity equation is adopted in the rectangular grid system. The free surface is simulated with a computational simulation method of two-layer flow by using marker density. The results are compared with some existing computational and experimental results.

• Journal of the Korean Society of Marine Environment & Safety
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• v.6 no.1
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• pp.57-67
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• 2000

All crude oil carries a little of water, sand, and mineral sediment molecules tightly bounded with hydrocarbons. The result is the gradual precipitation of these heavier elements into thick, granular petroleum by products known as crude oil sludge. The oily sludges in ship tanks and in storage facilities have to be treated efficiently in order to keep the security and the capacity of storage facilities, to protect a serious environmental pollution, and to retrieve lost resource. The oily sludge treatment system should be designed to satisfy requirements mentioned in safe work condition. As a basic study, in this paper, an oily sludge treatment system by ultrasonic waves was proposed. Then, the features of ultrasonic energy and recovery of sludge with ultrasonic waves are investigated by experiments. As results, we found that ultrasonic waves are a new energy to flow oil sludge environment-friendly in safe work condition. In addition, it was shown that ultrasonic energy is more efficient than thermal energy in treating oil sludge, and that the volume of wastes for disposal is reduced remarkably.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.4 no.3
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• pp.178-186
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• 1992

An experimental study of deep-water breaking waves are performed by superposition of different wave frequencies, faster waves overtaking slow waves at a certain location. Large spilling and plunging breaking waves are generated near the expected breaking location. Wave steepness in spilling and plunging breakers significantly increases as the breaking point is approached and then decreases after breaking. Larger growth rate of the wave steepness in vigorous plunging breaking is observed. The fundamental wave frequencies in a wave group are dominant through the wave evolution, even in an intense plunging breaking event.

• Journal of Ocean Engineering and Technology
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• v.23 no.4
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• pp.6-11
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• 2009

In this study, the internal waves in two-density layered fluids were analyzed using the Numerical Wave Tank (NWT) technique in the frequency domain. The NWT is based on a two-domain Boundary Element Method with the potential fluids using the whole-domain matrix scheme. From the mathematical solution of the two-domain boundary integral equation, two different wave modes could be classified: a surface wave mode and an internal wave mode, and each mode were shown to have a wave number determined by a respective dispersion relation. The magnitudes of the internal waves against surface waves were investigated for various fluid densities and water depths. The calculated results are compared with available theoretical data.

• Earthquakes and Structures
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• v.18 no.6
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• pp.743-752
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• 2020

The phenomenon of reflection and transmission of plane waves at an interface between fluid half space and orthotropic piezothermoelastic solid half-space with two-temperature has been investigated. Energy ratios of various reflected and transmitted waves are computed with the use of amplitude ratios. The law of conservation of energy across the interface has been justified. It is found that the energy ratios are the functions of angle of incidence, frequency of independent wave and depend on the different piezothermoelastic material. A piezothermoelastic material has been considered which is in welded contact with water. Variations of energy ratios corresponding to the reflected waves and transmitted waves are computed and shown graphically for the two different models. A particular reduced case of interest is also discussed.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09b
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• pp.1298-1298
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• 2005

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.1
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• pp.28-33
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• 2013

Multidirectional random waves that obliquely approach the shore were found to become directionally asymmetric due to refraction. The directional asymmetry was expressed in terms of the asymmetry parameter which is related to the maximum spreading parameter ($s_{max}$). In this study, we calculate variation of both the asymmetry and maximum spreading parameters at different water depths for various cases of incident wave angles and maximum spreading parameters in deep water. These values are different from Goda and Suzuki (1975) who neglected directional asymmetry of waves. In calculating directional asymmetry and maximum spreading parameters, we use the JONSWAP spectrum (Hasselmann et al., 1973) and Lee et al.'s (2010) directional distribution function. The processes and results are nondimensionalized with significant wave height, peak frequency and peak wave length in deep water.