• Journal of Hydrospace Technology
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• v.2 no.1
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• pp.18-26
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• 1996

It is normal practice to consider bending wave modes only, when one applies SEA (Statistical Energy Analysis) to ship structures because of complexities in SEA modeling and evaluation of coupling loss factors for inplane modes. According to the result of Tratch[1], the inplane wave modes becomes important for the analysis of a foundation structure as the distance from the source and receiver increases. In this paper, the effect of inplane wave modes on structure-borne noise propagation in ship structures is presented. It is shown that the inplane wave could increase the noise level more than 10 dB compared with the results without inplane wave modes at high frequency bands for compartments far from the source location.

• Journal of KSNVE
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• v.2 no.3
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• pp.181-192
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• 1992

A method of measuring the transmission loss of silencer using two microphone technique is described. Two microphone methol is used to elliminate the measurement error due to reflected wave spectra in inlet/outlet duct of silencer. Errors associated with the measurement method are studied. Henceforth the methods to effectively supress the influence are presented. Based on these considertions, the appropriate procedure of experimental set-up to measure the transmission loss a silencer is described with experimental verifications.

• Journal of Satellite, Information and Communications
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• v.11 no.2
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• pp.69-73
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• 2016

In order to derive reliable propagation models for future millimeter-wave frequency indoor pico-cellular communications systems, accurate reflectivity data of building materials is necessary. The broad variety of building materials and construction codes makes accurate attenuation prediction very difficult without the support of specific construction data or measurements. This paper derives a transmission and reflection coefficient based on 13 GHz to 28 GHz measurement data. Transmission and reflection is measured by applying change in the reception angle of each building material, such as plasterboard. The transmission and reflection coefficient derived shows a correlation between frequency dependence and angle. As a result, as the reception angle is reduced, the reflected angle from the transmitter that could be received increases, showing that there is a correlation. In addition, the fundamental investigations carried out lay the foundation for radio channel-related research, which is essential for the development of future millimeter-wave communications systems.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.1
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• pp.113-122
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• 1992

When predicting shipboard noise levees, the accuracy depends largely on the value of the structureborne noise transmission loss. Although empirical formulars are frequently used because of their simplicities, researches on the analytical methods to estimate the transmission loss of structureborne noise such as wave guide theory and SEA has long bean one of the major topics in shipboard acoustics to overcome the inherent limiations of empirical ones. This paper describes an application of SEA to predict the transmission loss of the structureborne noise of a simple shiplike structural mode1 consisted of 22 flats plates. The result shows trial discrepancies between experimental and theoretical transmission losses are less than 3 dB.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1637-1640
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• 2005

This paper presents a technique for electromagnetic field analysis on surge response due to Mid-span back-flashovers effects in lightning protection system of 500 kV EHV single circuit transmission tower by the neural networks method. These analyses are based on modeling lightning return stroke as well as on coupling the electromagnetic fields of the stroke channel to the line. The ground conductivity influences both the electric field as well as the coupling mechanism and hence the magnitude and wave shape of the induced voltage. The technique can be used to analyzed the corona voltage effect, the effective of stroke to the span tower, the surge impedance of transmission lines. The maximum voltage from flashovers effects in the lines. The model is compatible with general electromagnetic transients programs such as the ATP-EMTP. The simulation results show that this study analyses for time-domain with those produced by a cascade multi-section model, the surge impedance of a full-sized tower hit directly by a lightning stroke is discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.311-318
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• 1998

In this paper, the power flow analysis(PFA) method is applied to the prediction of the vibrational energy density and intensity of coupled co-planar plates. To cover the energy transmission and reflection at the joint of the plates, the wave transmission approach is introduced with the assumption that all the incident waves are normal to the joint. By changing the frequency ranges and internal loss factors, we have obtained the PFA results, and compared them with the analytical exact solutions.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.16 no.3
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• pp.121-129
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• 2004

The different types of coastal souctures have been constructed for the protection of coastal region from the incident waves. Among them. the permeable submerged breakwater has been widely used as a wave dissipater and sediment transport controller because of its excellent advantages in scenery effects, construction efficiency and environment aspects. This study numerically investigated the characteristics of wave energy variations and transmission coefficient at the rear of the permeable submerged breakwater installed in the irregular wave field. To analyze it's performance numerically, a two-dimensional numerical wave flume based on VOF method was used. A frequency spectral analysis showed that the spectral peak moved to the short-period in the one-row submerged breakwater, and the wave energy was distributed evenly for the whole period in the two-row submerged breakwater in the case of breaking on the submerged breakwater. The spectral peak was shown to be converged within the significant wave period at the rear of the permeable submerged breakwater in the case of non-breaking conditions. From the result of transmission coefficients analysis. it was confirmed that a considerable quantity of wave energy was transmitted to the rear of the permeable submerged breakwater in the case of non-breaking rather than breaking.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.1
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• pp.1-8
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• 2014

In this study, a field monitoring on Namae beach erosion countermeasure in the east coast of Korea is conducted to verify its efficiency and effectiveness. The Namae Beach project has been carried out for six years with three years for planning and three years for actual construction. The planning phase of numerical model tests and investigations had been reported by Kim et al. (2008, 2011). The field monitoring confirms increase in the beach width after the submerged artificial reefs construction and is due to its wave energy dissipation effects. The field monitoring is performed at the seaward and landward of the countermeasures. The wave height reduction from the seaward side (depth h = 10.5 m) to the landward side (h = 3.7 m) of the reef is measured for wave transmission coefficient (Kt) analysis. The analysis shows 60% of deduction in wave energy due to the submerged artificial reefs.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.14 no.1
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• pp.19-33
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• 2002

A numerical method to efficiently secure necessary design informations of the hydraulic characteristics of rubble mound breakwater was attempted here. The method combines the exterior wave field with the interior wave field which is formulated incorporating porous media flow inside the breakwaters. An approximate method based on the long wave assumption was used for the exterior wave field while a boundary element method was used for the interior wave field. A hydraulic experiment was also performed to verify the validity of the numerical analysis. The numerical results were compared with experimental data and results from existing formulae. They generally agreed in both reflection and transmission coefficients. The calculated pore pressures also showed a similar pattern with experimental data, even if they gave some significant differences in their values fur some cases. The main cause of such differences can be attributed to the strongly nonlinear wave field occurring on the frontal slope of the breakwater. The direct input of dynamic pressures(measured from hydraulic experiment) into the numerical method was suggested as a promising method to enhance the predictability of pore pressures.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.6
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• pp.356-367
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• 2019

This study evaluates the variation characteristics of irregular wave fields for two-dimensional Low-Crested Structure (LCS) by olaFlow model based on the two-phases flow by numerical analysis. The numerical results of olaFlow model are verified by comparing irregular wave profile of target wave spectrum and measured one, and their spectra. In addition, spacial variation of irregular wave spectrum, wave transmission ratio, root-mean square wave height, time-averaged velocity and time-averaged turbulent kinetic energy by two-dimensional LCS are discussed numerically. The time-averaged velocity, one of the most important numerical results is formed counterclockwise circulating cell and clockwise nearshore current on the front of LCS, and strong uni-directional flow directing onshore side around still water level.