• Ocean Systems Engineering
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• v.3 no.4
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• pp.309-325
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• 2013

Ocean Thermal Energy Conversion (OTEC) systems utilize the temperature difference between the surface water and deep ocean water to generate electrical energy. In addition to ocean surface waves, wind and current, in certain locations like the Andaman Sea, Sulu Sea and the South China Sea the presence of strong internal waves may become a concern in floating OTEC system design. The current paper focuses on studying the dependence of the CWP hydrodynamic drag on relative velocity of the flow around the pipe, the effect of drag amplification due to vortex induced vibrations and the influence of internal waves on the floating semi and the cold water pipe integrated OTEC system. Two CWP sizes are modeled; the 4m diameter pipe represents a small scale prototype and the 10m diameter pipe represents a full commercial size CWP. are considered in the study.

• Journal of Ocean Engineering and Technology
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• v.19 no.4 s.65
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• pp.1-8
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• 2005

A nonlinear time-domain strip theory for vertical wave loads and ship responses is to be investigated. The hydrodynamic memory effect is approximated by a higher order differential equation without convolution. The ship is modeled as a non-uniform Timoshenko beam. Numerical calculations are presented for the S175 Containership translating with the forward speed in regular waves. The approach described in this paper can be used in evaluating ship motions and wave loads in extreme wave conditions and validating nonlinear phenomena in ship design.

• International Journal of Ocean System Engineering
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• v.4 no.1
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• pp.49-56
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• 2014

A three-dimensional multidirectional nonlinear numerical wave tank (NWT) based on the Navier-Stokes equations and the Finite Volume Method (FVM) is developed by using the two-phase hydrodynamic flow solver naoe-FOAM-SJTU based on the open source toolbox OpenFOAM. The free surface is capturing with the Volume Of Fluids (VOF). The directional wave including Stokes wave, solitary wave and nonlinear wave are simulated and verified. The multi-directional waves are also simulated with particular wave spectral such as JONSWAP and wave directional spreading function. The obtained numerical results show the capability of the solver to generate different type of multidirectional nonlinear waves accurately. Meanwhile, it implies that the presented NWT can easily extend to model the wave-structures interactions, which will be great help to the offshore structures design.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.4
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• pp.407-413
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• 2015

Research for renewable energy is being performed since it has the merits of little pollution of the environment and sustainable energy resources. Microalgae is attractive as a renewable energy resource. Biomass of the microalgae can be produced by mass culturing, and bulk harvest technology of is needed to produce biomass continuously. Recently, ultrasonic waves were used to harvest the cultivated microalgae continuously. In this study, the separation process using ultrasonic waves was performed to effectively harvest the microalgae. An ultrasonic wave separation resonator was designed and manufactured based on the acoustic field analysis. Separation experiments using design of experiment were carried out, and the influence of experimental variables from the ultrasonic wave separation process was investigated. Mixing conditions of variables were estimated to obtain high separation efficiency and a large microalgae harvest. Experimental results for suitable mixing conditions were compared with simulation results calculated from the state equation.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.11
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• pp.132-139
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• 1995

Turbulent boundary layer pressure fluctuation exerted on the surface of a structure can give rise to a elastic stress wave on the surface of the structure. The stress wave so called surface wave, will not only propagate along the surface of structure but also penerate into the structure. To reduce the transmission of stress wave into the structure the elastomer layer is usually attactched on the surface of structure. The transfer function, which is defined herein as the ratio of stress waves at the surface and bottom of the elastomer layer, is derved by use of the cylindrical coordinates system. The elastodynamics of the elastomer layer subjected to the turbulent boundary layer pressure fluctuation is represented by the simplified one degree-of-freedom model for easy prediction of the stress wave transmission as well as efficient design of the elastomer layer.

• Journal of Power System Engineering
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• v.8 no.4
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• pp.49-56
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• 2004

To design very large ships, such as very large drillships, we have to estimate the hydroelastic responses of the very large ships in waves. A numerical procedure is described for estimating the hydroelastic responses of very large ships advancing with slow speed in waves. The developed numerical approach is based on a combination of the three-dimensional source distribution method and the finite element method, including fluid-structure interaction by regarding a very large ship as many hull elements connected with elastic beam elements. Numerical results are compared with experimental and numerical ones obtained in the literature. The results of comparison confirmed the validity of the proposed approach.

• Water for future
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• v.9 no.1
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• pp.70-80
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• 1976

The efficient breakwater design requires a knowledge of the behaviour of the waves passing the breakwater. Wave Diffraction is an important factor and phenomeon in this behaviour. The diffraction ocean waves entering a gap in a breakwater normal to the incident wave direction in water of uniform depth has been investigated, applying a solution previously given in the author's paper, based on the theory of light diffraction by Sommerfeld. The wave profiles and heights on both the leeward side of the breakwater and the gap side have been studied and summarized in the form of diagrams with diffraction coefficients in range of x/L, y/L 0∼100, b/L=0.5∼12, with some extension of the diagrams made previously. The results of the theoretical approaches have not been experimentally verified. The theory ad computation methods with computer program in Fortran IV developed in this study make an efficient use for estimating the diffraction about a breakwater gap.

• Journal of the Korean Society of Safety
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• v.5 no.3
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• pp.8-26
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• 1990

It is important to have exact information about the contact pressure distribution in the design of connected parts of machines and structures. In previous works, stress analyses on a two body contact problem have been carried out in large numbers. Besides, the measurement of contact stress is important to confirm the adequateness of the theoretical analysis, to verify appropriateness of Hertzian contact theory and to know the practical pressure distribution, but an excellent measuring method con't be found at present. Therefore, a quantitative measurement of contact pressure by means of ultrasonic waves using a normal probe and an angle has been proposed to measure the contact pressure distribution between two rough flat surfaces. At first, in a new proposed calibration method, the relation between mean contact pressure and sound pressure of reflected waves is obtained by using calibration blocks with various surface roughnesses made of the same material as the rectangular section beams And then, this experimental results are compared with the analytical ones, and the utility of this method is discussed.

• Water for future
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• v.7 no.1
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• pp.55-64
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• 1974

The knowledge of the waves passing through the breakwater makes an important role in the efficient breakwater design. Wave diffraction is an important factor in this role, but some usable development about it have not been made in our country as yet. The diffraction of sea-water waves round the end of a semi-infinite impermeable breakwater has been investigated, applying a solution of the water wave diffraction problems given by Penney & Price. The wave pattern and heights on both the leewardside and the windward-side of the breakwater have been calculated and summarized in the form of diagrams with diffraction factors between $r/{\lambda}=0~50$. This involves some extension of the diffraction diagrams made previously. The theory and computation methods with computer program in fortran IV developed in this study make an efficient use for estimating the diffraction effects at a semi-infinite breakwater.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.6
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• pp.951-963
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• 2015

The water wave characteristics of Bragg reflections from a train of fixed floating pontoon breakwaters was studied numerically. A numerical model of boundary discretization type was developed to calculate the wave field. The model was verified by comparing to analytical data in literature and good agreements were achieved. Series of parametric studies were conducted systematically to investigate the dependence of the reflected coefficients by the Bragg scattering on the design variables, including the spacing between the breakwaters, the total number of installed breakwaters, the draft and width do the breakwater, and wave length. Certain wave characteristics of the Bragg reflections were observed and discussed in details which might be of help for practical engineering applications in shoreline protection from incident waves.