• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.5
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• pp.292-302
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• 2016

In this study, shallow-water design waves are estimated for various return periods based on statistical analysis of extreme waves observed 13 years at four stations on the Korean east coast (Sokcho, Mukho, Hupo, Jinha). These values are compared with the results from SWAN simulation by using the deep water design waves conventionally used in Korea (KORDI, 2005). It was found that the simulated values of the shallow-water design waves are comparatively smaller than the values from the extreme value analysis, expecially below 30 years frequency, which implies possible under-estimation of the deep-water design waves on the Korean east coast.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.3
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• pp.430-439
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• 1999

In this paper, we have chosen Inchon International Airport as an area for estimating flutter interference to estimate and analyze the flutter Interference. We have proposed a method to overcome flutter interference. The simulation has been performed considering the received power of a direct wave, the height of an antenna, the ERP of a transmitting point, and the reflection coefficients as an estimation function for the flutter. From the simulation results, we have found that the flutter Interference from flights is very serious, and the degree of flutter interference can be changed according to the distance between an airplane and a transmitting point, the profile between transmitting and receiving points, and the reflection coefficients of an airplane.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.26 no.1
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• pp.31-40
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• 1993

This paper deals with static tension analysis method for Floating Tire Breakwater(FTB). FTB can be used for the limited wave height. It is especially focused on Goodyear type FTB easily applied to the breakwater for the fisheries cultivating region. The numerical examples for FTB design procedure was reviewed. It is also studied the static analysis method of offshore catenary spread mooring system. The general calculation procedure for the tension versus excursion curves for the multi-line system using the basic catenary relationship was studied. Calculation results showed good agreement with some existing mooring results. To extend this mooring force calculating method to the floating fisheries caitivating cages, the strength of synthetic fiber was considered. This analysis method can be used to the estimation of the mooring force for the floating structures such as floating breakwaters and floating artificial reefs.

• Advances in concrete construction
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• v.14 no.1
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• pp.35-43
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• 2022

Based on novel Galerkin's technique, the theoretical study gives a prediction to estimate the vibrations of FG rotating cylindrical shell. Terms of ring supports have been introduced by a polynomial function. Three different laws of volume fraction are utilized for the vibration of cylindrical shells. Variation frequencies with the locations of ring supports have been analyzed and these ring supports are placed round the circumferential direction. The base of this approach is an approximate estimation of eigenvalues of proper functions which are the results of solutions of vibrating equation. Each longitudinal wave number corresponds to a particular boundary condition. The results are given in tabular and graphical forms. By increasing different value of height-to-radius ratio, the resulting backward and forward frequencies increase and frequencies decrease on increasing length-to-radius ratio. There is a new form of frequencies is obtained for different positions of ring supports, which is bell shaped. Moreover, on increasing the rotating speed, the backward frequencies increases and forward frequencies decreases.

• Journal of the Korean Society for Environmental Technology
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• v.18 no.2
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• pp.165-172
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• 2017

In current stage, it is hard to predict the scale of damage caused by natural disaster and it is hard to deal with it. However, in case of disaster planning level, if it is possible to predict the scale of disaster then quick reaction can be done which will reduce the damage. In the present study, therefore, function of wind wave damage estimation among various disaster is developed. Damage of wind wave and typhoon in eastern and Jeju coastal zone was collected from disaster report (1991~2014) published by Ministry of Public Safety and Security and to reflect inflation rate, 2014 damage cost was converted. Also, wave height, wind speed, wave direction, wave period, etc was collected from Meteorological Administration and Korea Hydrographic and Oceanographic Administration web site. To reflect the characteristic of coastal zone when wave damage occurs, CODI(Coastal Disaster Index), COSI(Coastal Sensitivity Index), CPII(Coastal Potential Impact Index) published by Korea Hydrographic and Oceanographic Agency in 2015 were used. When damage occurs, function predicting wind wave damage was developed through weather condition, regional characteristic index and correlation of damage cost.

• Journal of Korea Water Resources Association
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• v.46 no.4
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• pp.327-334
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• 2013

In this study, the optimal slit length of perforated wall with single chamber below the still water level (SWL) is studied through the two dimensional test. The relationship between the reflection coefficient and the shape of structures such as chamber width(B) and slit length(S) are investigated by applying the various wave conditions. The random waves were used for the test by using Bretschneider-Mitsuyasu frequency spectrum. Minimum reflection coefficient is obtained at $B/L_s{\approx}0.15$ condition, this result is different from the regular wave condition. Also the minimum reflection coefficients are measured at $S/H_s{\approx}2.5$. This means that the optimal slit length below the still water level is 2.5 times of the incident wave height.

• Journal of electromagnetic engineering and science
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• v.17 no.4
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• pp.241-243
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• 2017

In this paper, we have presented an equation for estimating the gain of a Fabry-Perot cavity (FPC) antenna with a finite dimension. When an FPC antenna has an infinite dimension and its height is half of a wavelength, the maximum gain of that FPC antenna can be obtained theoretically. If the FPC antenna does not have a dimension sufficient for multiple reflections between a partially reflective surface (PRS) and the ground, its gain must be less than that of an FPC antenna that has an infinite dimension. In addition, the gain of an FPC antenna increases as the dimension of a PRS increases and becomes saturated from a specific dimension. The specific dimension where the gain starts to saturate also gets larger as the reflection magnitude of the PRS becomes closer to one. Thus, it would be convenient to have a gain equation when considering the dimension of an FPC antenna in order to estimate the exact gain of the FPC antenna with a specific dimension. A gain versus the dimension of the FPC antenna for various reflection magnitudes of PRS has been simulated, and the modified gain equation is produced through the curve fitting of the full-wave simulation results. The resulting empirical gain equation of an FPC antenna whose PRS dimension is larger than $1.5{\lambda}_0$ has been obtained.

• Earthquakes and Structures
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• v.24 no.4
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• pp.237-245
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• 2023

Based on novel Galerkin's technique, the theoretical study gives a prediction to estimate the vibrations of FG rotating cylindrical shell. Terms of ring supports have been introduced by a polynomial function. Three different laws of volume fraction are utilized for the vibration of cylindrical shells. Variation frequencies with the locations of ring supports have been analyzed and these ring supports are placed round the circumferential direction. The base of this approach is an approximate estimation of eigenvalues of proper functions which are the results of solutions of vibrating equation. Each longitudinal wave number corresponds to a particular boundary condition. The results are given in tabular and graphical forms. By increasing different value of height-to-radius ratio, the resulting backward and forward frequencies increase and frequencies decrease on increasing length-to-radius ratio. There is a new form of frequencies is obtained for different positions of ring supports, which is bell shaped. Moreover, on increasing the rotating speed, the backward frequencies increase and forward frequencies decreases.

• Journal of Advanced Navigation Technology
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• v.3 no.1
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• pp.20-31
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• 1999

In this paper, we have chosen KimPo International Airport as an area for estimating the flutter interference, in order to analyze the flutter interference. The field test at 25 points around KimPo International Airport and the simulation have been performed for estimating the flutter interference. We consider the received power of a direct wave, the height of an antenna, the ERP of a transmitting point, transmit frequency, and the reflection coefficients of an airplane, the transmit/receive point coordinates as estimation functions for the flutter. From the results, we have found that the flutter interference from flights is very serious around the route of flight circumference, and often occurs when the height of an airplane is low, range from 40 to 240 m. Besides, the degree of the flutter interference can be changed according to the distance between an airplane and a transmitting point, elevation angle, and the reflection coefficients of an airplane.

• Journal of The Korean Astronomical Society
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• v.41 no.6
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• pp.173-180
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• 2008

Using the MHD coronal seismology technique, we estimated the magnetic field for three spicules observed in 2008 June. For this study, we used the high resolution Ca II H line ($3968.5\;{\AA}$) images observed by the Hinode SOT and considered a vertical thin flux tube as a spicule model. To our knowledge, this is the first attempt to estimate the spicule magnetic field using the Hinode observation. From the observed oscillation properties, we determined the periods, amplitudes, minimum wavelengths, and wave speeds. We interpreted the observed oscillations as MHD kink waves propagating through a vertical thin flux tube embedded in a uniform field environment. Then we estimated spicule magnetic field assuming spicule densities. Major results from this study are as follows : (1) we observed three oscillating spicules having durations of 5-7 minutes, oscillating periods of 2-3 minutes, and transverse displacements of 700-1000 km. (2) The estimated magnetic field in spicules is about 10-18 G for lower density limit and about 43-76 G for upper density limit. (3) In this analysis, we can estimate the minimum wavelength of the oscillations, such as 60000 km, 56000 km, and 45000 km. This may be due to the much longer wavelength comparing with the height of spicules. (4) In the first event occurred on 2008 June 03, the oscillation existed during limited time (about 250 s). This means that the oscillation may be triggered by an impulsive mechanism (like low atmospheric reconnection), not continuous. Being compared with the ground-based observations of spicule oscillations, our observation indicates quite different one, i.e., more than one order longer in wavelength, a factor of 3-4 larger in wave speed, and 2-3 times longer in period.