• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.1
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• pp.61-71
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• 1994

A modified method obtained by expanding Longuet-Higgins and Stewart's method (1964) is proposed. which can easily derive the group-bountied long wave due to the irregular were group as well as the regular wave group. The result of the proposed method agree well with those of both second order nonlinear theory and radiation stress theory. Particularly in the shallow water region, three equations from the proposed method, the second order nonlinear theory and the radiation stress theory become identical.

• Korean Journal of Hydrosciences
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• v.6
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• pp.1-11
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• 1995

A plunge pool is often employed as an energy-dissipating device at the end of a spillway or a pipe culvert. A jet from spillways or pipes frequently generates a scour hole which threaten the stability of the hydraulic structure. Existing scour prediction formulas of plunge pool of spillways or pipe culverts give a wide range of scour depths, and it is, therefore, difficult to accurately predict those scour depths. In this study, a new experimental method and new sour prediction formulas under submerged circular jet for large bed materials with shallow tailwater depths were developed. A major variable, which was not used in previous scour prediction equations, was the ratio of jet size to bed material size. In this study, jet momentum acting on a bed particle and jet diffustion theory were employed to derive scour prediction formulas. Four theoretical formulas were suggested for the two regions of jet diffusion, i.e., the region of flow establishment and the region of established flow. The semi-theoretically developed scour prediction formulas showed close agreement with laboratory experiments performed on movable bed made of large spherical particles.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1995.10a
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• pp.250-257
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• 1995

The properties of Tuned Liquid Damper are investigated theoretically. In this study, numerical model is a nonlinear model for a rectangular TLD under horizontal motion on the basis of the shallow water wave theory, where the damping of the liquid motion is included semianalytically. For TLD subjected to harmonic external force, the liquid motion of TLD is simulated. Analysis result is showed that liquid motion in TLD is strongli nonlinear even under small excitation.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.2
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• pp.1-12
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• 1996

Hydrodynamic characteristics of shipping water on deck are investigated by using a simplified two-dimensional model. Formulation of the shipping water on deck leads to a nonlinear hyperbolic system of equations based on the shallow-water wave theory. Time-domain solution of these equations are obtained numerically using a finite difference method which adopts predictor-corrector method for time-marching and 2nd upwind differencing method for convection term calculation. To confirm the validity of the present numerical method, we calculated some shallow-water wave problems accompanying a bore and compared the obtained results with the analytic solutions. We found good agreements between them. Though the calculation results of shipping water on deck, we show that the shipping water flows into the deck as a rarefying wave arid grows into a bore after colliding with a deck structure. Also we examined the effects of acceleration and slope of deck and found that they have significant influences on the flow of shipping water.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.22 no.2
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• pp.31-35
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• 1986

A bore is a transition between different uniform flows of water. If a long wave of elevation travels in shallow water it steepens and forms a bore. The bore is undular if the change in surface elevation of the wave is less than 0.28 of the original depth of water. This paper describes the growth of an undular bore from a long wave which forms a gentle transition between a uniform flow and still water. A physical account of its development is followed by the results of numerical calculations. Finite-difference approximations are used in the partial differential equations of motion. For undular bores, numerical calculations show that (i) the relationship between relative elevation and relative velocity given by long wave theory is approached for an undular bore, (ii) the amplitude of first crest of an undular bore approaches a finite limit approximately at an exponential rate, and (iii) the distance between the first two crests increases without bound, approximately logarithmically.

• The Journal of the Acoustical Society of Korea
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• v.15 no.2
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• pp.101-104
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• 1996

The pressure field for the Pekeris model which is consisted of a surface layer of fresh water overlying a thick (essentially semi-infinite) bottom layer of coarse sand is investigated experimentally in a anechoic tank scaled down 1/1,000. The water depth and frequency have been controlled so that the continuous mode integrand has not a resonance close to cut-off, and the experimental results relatively well agree with the theory which is represented as the sum of the discrete modes over a range about 10 times the water depth.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.3
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• pp.281-289
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• 1994

An equation set of nonlinear model for regular/irregular waves presented in this study can be applied to waves travelling from deep water to shallow water, which is different from the Boussinesq equations. The presented equations completely satisfy the linear dispersion relationship and when expanded, they are proven to be consistent with the Boussinesq equation of several types. In addition, the position of averaged velocity below the still water level is estimated based on the linear wave theory.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.3
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• pp.47-58
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• 1994

Theoretical calculations are carried out for the estimation of linear maneuvering coefficients of a ship moving in shallow water region. Hydrodynamic forces and moments acting on a maneuvering ship are modelled based on a slender body theory, from which integro-differential equation for the unknown inner stream velocity is derived. Numerical algorithms fur solving this equation are described in detail. By considering water depth effects in the mathematical model, variations of maneuvering coefficients with water depth are studied. Programs are developed according to this method and calculations are done for Mariner, Series 60 and Wigley hull forms. For the verification of the programs, calculated results are compared with some analytic solutions and with published experimental results, which show good agreements in spite of many assumptions included in the mathematical model. It is expected that this method can be used as a preliminary tool for the estimation of maneuverability coefficients of a ship in shallow water region at its initial design stage.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.47 no.5
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• pp.229-234
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• 2010

This paper proposed the acoustic signal processing techniques, which are applicable even in the shallow river, and will enhance the frequency resolution of the ADCP (Acoustic Doppler Current profiler). ADCP is a device that measures the velocity of a moving fluid. ADCP, in general, can be operated at ~300 Khz of center frequency due to no depth limit in the sea. However, it can hardly be used due to water depth of 30cm or shallower during the dry season in the river. Therefore, existing signal processing methods are not suitable to use in the shallow river. We are proposing an alternative acoustic signal processing method using Zoom FFT. Simulation results show that errors are reduced ${\pm}62\;cm/s$ in theory, and ${\pm}93\;cm/s$ in the experiment. The existing algorithm could not estimate the current speed at the shallow river below 30 cm, but proposed algorithm estimated the current speed that was faster than 20 cm/s at the shallow river below 30 cm.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1B
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• pp.111-114
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• 2008

Explicit solutions of the wave dispersion equation are developed using the recursive relation in terms of the relative water depth. We use the solutions of Eckart (1951), Hunt (1979), and the deep-water and shallow-water solutions for initial values of the solution. All the recursive solutions converge to the exact one except that with the initial value of deep-water solution. The solution with the initial value by Hunt converged much faster than the others. The recursive solutions may be obtained quickly and simply by a hand calculator. For the transformation of linear water waves in whole water depth, the use of the recursive solutions will yield more accurate analytical solutions than use of previously developed explicit solutions.