• Journal of Korea Water Resources Association
• /
• v.36 no.3 s.134
• /
• pp.447-454
• /
• 2003

The Bragg reflection of monochromatic waves propagating over a rectangular-typed impermeable submerged breakwaters is numerically investigated by using the finite element method. The reflection coefficients calculated from the present model are compared with those of laboratory measurements and the eigenfunction expansion method. A good agreement is observed. The finite element model is also applied to calculate reflection coefficients according to variations of length and width of submerged breakwater.

• Journal of Ocean Engineering and Technology
• /
• v.6 no.1
• /
• pp.43-51
• /
• 1992

The hydrodynamic performance of a floating-type OWC (Oscillating Water Column) chamber is studied numerically and experimentally in this study. The numerical approach based on two-dimensional linear theory of floating wave absorber was attempted to design an efficient wave energy absorber, while model test was performed in a wave basin to test a performance of designed model and validate the reliability of developed numerical code. The focus of study is placed mainly on the experimental study to evaluate the principal characteristics of the designed OWC chamber in regular waves. The effects of the variation of wave height on OWC device and of air pressure inside chamber are also presented. Finally, the measured results were compared with computed ones, and it was shown that the designed chamber works with high efficiency $(\eta_H>1$ over most of wave lengths covered by present study. It is therefore concluded that the developed code is capable of being successfully employed to design OWC chambers at various ocean environments, even though there exist some minor discrepancies between measured and computed results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.19 no.6
• /
• pp.698-705
• /
• 2008

When electromagnetic waves propagate through atmosphere, waves are affected by various factors. Atmosphere normally consists of different molecular species, water vapours, rain, fog, snow and small suspended particles called aerosols. The distributions of atmosphere molecules, water vapours, rain rate, snowfall and aerosol are dependent on geometrical regions or environment. In order to predict propagation characteristics in atmospheric environment, statistical analysis of the relevant parameters such as temperature, humidity, atmospheric pressure, wind speed, areosol and rainfall is crucial. In this paper, we performed a long-term statistical analysis for the atmospheric parameters in domestic environments and analyzed the propagation characteristics through atmosphere based on that.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.18 no.4
• /
• pp.360-371
• /
• 2006

In order to calculate waves propagating into the shallow water region, a generalized parabolic approximate model is presented. The model is derived from the modified mild slope equation and includes all the existing parabolic models presented in the paper. Numerical results are presented in comparison to laboratory data of Berkhoff et al.(1982). The existing parabolic model shows almost same accuracy against the modified parabolic model and both results of models stand in closer agreement to the laboratory data. Therefore the existing parabolic model based on mild slope equation is a useful tool to compute shallow water waves which turns out to be more fast and stable in computational aspect.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2002.05a
• /
• pp.257-262
• /
• 2002

Numerical model introduced in this study combines wave refraction-diffraction, breaking, bottom friction, lateral mixing, and critical shear stress and three sub-models for simulating waves, currents, and bottom change were briefly discussed. Simulations of beach processes and harbor sedimentation were also described at the coast neighboring Bangpo Harbor, Anmyundo, Chungnam, where the area has suffered from accumulation of drifting sand in a small fishing harbor with a wide tidal range. We also made model test for the case of a narrow tidal range at Nakdong river's estuary area to understand the effect of water level variation on the littoral drift. Simulations are conducted in terms of incident wave direction and tidal level. Characteristics of wave transformation, nearshore current, sediment transport, and bottom change are shown and analyzed. We found from the simulation that the tidal level impact to the sediment transport is very important and we should apply the numerical model with different water level to analyze sediment transport mechanism correctly. Although the model study gave reasonable description of beach processes and harbor sedimentation mechanism, it is necessary to collect lots of field observation data, including waves, tides and bottom materials, etc. for better prediction.

• Water for future
• /
• v.26 no.1
• /
• pp.71-79
• /
• 1993

Nonlinear characteristics of air pressure variation and wave transformation of a fixed air-chamber structure are discussed theoretically and experimentally. Two analytical methods(method I and II) based on the perturbation method and Green's formula are employed in order to evaluate nonlinearities by the submerged and semi-submerged air-chamber structure. Moreover, an air compression model is newly developed to estimate the dynamic air pressure in the air-chamber inside the structure, assuming the Boyle-Charles's law with adiabatic process in the air pressure variation. Theoretical values of the method I considering evanescent mode waves at an fictious boundary, are in good agreement with those of method II employing the fictious boundary which is not affected by evanescent mode waves. Both theoretical values are shown to agree well with experimental values.

• Journal of Korea Water Resources Association
• /
• v.36 no.5
• /
• pp.741-749
• /
• 2003

This study presents a combined experimental and numerical effort to investigate experimentally and numerically the Bragg reflection of sinusoidal waves due to trapezoidal submerged porous breakwaters. Numerical predictions of the study are verified by comparing to laboratory measurements. In the numerical model, the flow in porous structures is described by the spatially averaged Navier-Stokes equations and the volume of fluid method is employed to track the free surface displacements. Numerical solutions are agree well with laboratory measurements. The reflection coefficients of porous structures are smaller than those of non-porous structures and become stronger in proportion to the increase of number of submerged breakwaters.

• The Journal of the Acoustical Society of Korea
• /
• v.14 no.2
• /
• pp.5-15
• /
• 1995

An application of the cross correlation technique by adopting ultrasonic waves for water pipe flow measuring purpose is studied. It is a non-intrusive flow metering method by determining the time of the flight of the flow turbulent noise and its non-obstructing mechanism enables to reduce process energy loss due to the flowmeter obstruction. A digital signal processor for the purpose of the real time Fourier transform was employed for the fast time calculation of the flow velocity. The overall accuracy was found as about $1\%$ for flow velocities from 0.25 m/s up to 16 m/s and for the pipe inside diameters from 50mm to 248mm. The cross correlation technique can be used for the tap water utility including most common liquid flows.

• Journal of Ocean Engineering and Technology
• /
• v.24 no.1
• /
• pp.1-9
• /
• 2010

A series of experiments employing particle image velocimetry (PIV) technique was conducted to produce benchmark wave kinematics data for regular waves having four different wave slopes in 2-D wave tank. Water velocities and accelerations near the free surface of regular waves were computed from image pair obtained by PIV systems. With the measured wave velocity field, the wave accelerations were computed using a centered finite difference scheme. Both local and convective components of the total accelerations are obtained from experimental data. With increasing the wave slope, the horizontal velocity and the vertical accelerations near the wave crest obtained by PIV technique became larger than theoretical results, which are well-known phenomena of the wave nonlinearity. It is noted that the relative magnitude of convective acceleration to the local acceleration became larger with increasing wave slope.

• Coupled systems mechanics
• /
• v.2 no.1
• /
• pp.53-83
• /
• 2013

Sea waves induce significant pressures on coastal surfaces, especially on rocky vertical cliffs or breakwater structures (Peregrine 2003). In the present work, this hydrodynamic pressure is considered as the excitation acting on a piezoelectric material sheet, installed on a vertical cliff, and connected to an external electric circuit (on land). The whole hydro/piezo/electric system is modeled in the context of linear wave theory. The piezoelectric elements are assumed to be small plates, possibly of stack configuration, under a specific wiring. They are connected with an external circuit, modeled by a complex impedance, as usually happens in preliminary studies (Liang and Liao 2011). The piezoelectric elements are subjected to thickness-mode vibrations under the influence of incident harmonic water waves. Full, kinematic and dynamic, coupling is implemented along the water-solid interface, using propagation and evanescent modes (Athanassoulis and Belibassakis 1999). For most energetically interesting conditions the long-wave theory is valid, making the effect of evanescent modes negligible, and permitting us to calculate a closed-form solution for the efficiency of the energy harvesting system. It is found that the efficiency is dependent on two dimensionless hydro/piezo/electric parameters, and may become significant (as high as 30 - 50%) for appropriate combinations of parameter values, which, however, corresponds to exotically flexible piezoelectric materials. The existence or the possibility of constructing such kind of materials formulates a question to material scientists.