• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.23-23
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• 2020

하구 관측은 조사 방법 및 주기에 따라 크게 두 가지로 구분되는데, 첫째는 현장에서 직접 주기적으로 자료를 수집하는 정기 현장관측과 다른 하나는 고정된 지점에 관측소를 설치하여 실시간으로 연속된 자료를 수집하는 실시간 관측으로 분류된다. 본 연구는 하구 관측망 체계를 확립하기 위한 기초 연구로서 금강하구역을 대상으로 모의된 수치 모델 자료를 이용하여 관측망을 설계하기 위한 대표 모니터링 지표를 선정하고, 이를 기반으로 관측 지점을 설계하기 위한 전략을 제시하였다. 대표 모니터링 지표는 실제 현장에서 일반적으로 취득할 수 있는 6가지 항목(수온, 염분, 용존산소, 클로로필a, 총질소, 총인)을 대상으로 EOF 분석을 실시하여 해역의 시공간 분포를 대표할 수 있다고 판단되는 2개의 항목을 선정하였다. 대표 모니터링 지점은 2개의 대표 모니터링 지표에 대한 고유 벡터 사이의 각도를 벡터의 내적으로 계산하고 이를 설계변수로 활용하여 도식최적화 기법을 통해 각 모니터링 항목들에 대한 공간 분포를 가장 잘 재현해 낼 수 있는 지점의 개수와 위치를 선정하였다. 선정된 모니터링 지점들을 이용하여 재구성된 공간 분포를 참값(수치모델)과 비교하여 통계적 적정성 여부를 평가하였으며, 이를 통해 금강하구의 대표 모니터링 지점들을 도출 해 내었다. 금강하구의 정기 현장 관측에 대한 대표 모니터링 지점은 7개로 선정되었으며, 이들은 6가지 관측 항목들에 대해서 매우 높은 공간분포 재현율을 확보할 수 있음을 확인하였다. 또한, 담수가 비정기적으로 방류되는 금강하구 시스템의 지역적 특성에 대한 시계열 정보를 연속적으로 가장 잘 취득할 수 있는 실시간 관측소 설치 영역을 결정하기 위하여, 7개의 대표 모니터링 지점에서의 시계열 정보를 금강하구둑 전면과 외해의 시계열 정보와 비교분석하여 설치가능 지점을 영역으로 제언하였다.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.30 no.2
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• pp.188-202
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• 1997

The seasonal variability of the sea surface winds over the last Sea of Korea (Japan Sea) is investigated by means of empirical orthogonal function (EOF) analysis. The combined representation of fields of three climatic variables by empirical orthogonal functions is discussed. The eigenvectors are derived from daily sea level pressure, wind speed and 10-day mean sea surface temperature (SST) during 15 years $(1978\~1992)$. The spatial patterns of the mean pressure are characterized by the high pressure in the western part and the low pressure in the eastern part. The spatial distribution of the standard deviation (SD) of pressure are characterized by max SD of 6.6 mb near the Vladivostok, and minima along the coast of the Japan. In Vladivostok, the maxima of SD of SST and south-north wind (WV) were also occurred. The representation of fields of individual meteorological variables by EOF shows that the first mode of the west-east wind (WU) explain over $47.3\%$ of the variance and the second mode of WU represents $30\%$. Especially, the first mode of the WV explain $70.9\%$ of the variance and their time series coefficients show 1-cpy, 0.5-cpy frequency spectrum. The spatial distribution of the first mode eigenvectors of SST are characterized by maximum near Vladivostok. The combined representation of fields of several variables (pressure, wind, SST) reveals that the first mode magnitudes of the variance of the combined eigenvectors (WU-PR) are increased. By means of this result, the 1-year peak and the 6-months peak are remarkable. In the three combined patterns (wind, pressure, SST), the second mode of the eigenvector (wind) is affected by the SST. Their time coefficients of the first mode show noticeable 1-year peak. The spectral analysis of the second mode shows broad seasonal signal with the period of 4-months and a significant peak of variability at 3-month period.

• Journal of the Earthquake Engineering Society of Korea
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• v.16 no.3
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• pp.23-33
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• 2012

Dynamic response measurements from natural excitation were carried out for three 18-story office buildings to determine their inherent properties. The beam-column frame system was adopted as a typical structural form, but a core wall was added to resist the lateral force more effectively, resulting in a mixed configuration. To extract modal parameters such as natural frequencies, mode shapes and damping ratios from a series of vibration records at each floor, the most advanced operational system identification methods based on frequency- and time-domain like FDD, pLSCF and SSI were applied. Extracted frequencies and mode shapes from the different identification methods showed a greater consistency for three buildings, however the three lower frequencies extracted were 1.2 to 1.7 times as stiff as those obtained using the initial FE models. Comparing the extracted fundamental periods with those estimated from the code equations and FE analysis, the FE analysis results showed the most flexible behavior, and the most simple equation that considers the building height as the only parameter correlated fairly well with test results. It is recognized that such a discrepancy arises from the fact that the present tests exclude the stiffness decreasing factors like concrete cracking, while the FE models ignore the stiffness increasing factors, such as the contribution of non-structural elements and the actual material properties used.

• Magazine of the Korea Concrete Institute
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• v.11 no.2
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• pp.261-270
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• 1999

In these days, construction activities have caused civil petitions associated with vibration-induced damages or nuisances. Therefore, it is strongly needed to develop a remedial technique to mitigate unfavorable effects. The objective of this experimental research is to investigate material and structural dynamic characteristics of vibration-controlled concretes which have been proportionally mixed with various vibration reducing material, such as latex, rubber powder, plastic resin, polystyrofoams and etc. Normal and high strength concrete specimens are also prepared for corresponding comparison. As part of the recycling research for obsolete rubber and plastic materials, 32 concrete cylinders and 10 concrete flexural beams have been made for material and structural dynamic properties, respectively. In accordance with the resonance test on concrete cylinders, it can be concluded that concrete with vibration-reducing material have relatively larger material damping ration than normal or high strength concrete. Styrofoam is determined to be very effective vibration-reducing mixtures. From the vibration test on 10 concrete flexural beams, meamwhile, of importance observations was that material damping ratio is very smaller than structural damping ratio of corresponding specimen. But further vibration test on more flexural beams should be strongly needed by varying support conditions.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.4
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• pp.419-429
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• 2003

A three-dimensional (3-D) method of analysis is presented for determining the free vibration frequencies of thick, hyperboloidal shells of revolution. Unlike conventional shell theories, which are mathematically two-dimensional (2-D), the present method is based upon the 3-D dynamic equations of elasticity. Displacement components u/sub r/, u/sub θ/, u/sub z/ in the radial, circumferential, and axial directions, respectively, we taken to be sinusoidal in time, periodic in θ, and algebraic polynomials in the r and z directions. Potential(strain) and kinetic energies of the hyperboloidal shells are formulated, and the Ritz method is used to solve the eigenvalue problem, thus yielding upper bound values of the frequencies by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Convergence to four digit exactitude is demonstrated for the first five frequencies of the hyperboloidal shells of revolution. Numerical results are tabulated for eighteen configurations of completely free hyperboloidal shells of revolution having two different shell thickness ratios, three variant axis ratios, and three types of shell height ratios. Poisson's ratio (ν) is fixed at 0.3. Comparisons we made among the frequencies for these hyperboloidal shells and ones which ate cylindrical or nearly cylindrical( small meridional curvature. ) The method is applicable to thin hyperboloidal shells, as well as thick and very thick ones.

• The Journal of the Korea institute of electronic communication sciences
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• v.4 no.3
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• pp.224-229
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• 2009

In this paper, an efficient signal interference control technique to improve the convergence speed of Adaptive transversal filter with LMS algorithm is introduced. The convergence characteristics of the proposed algorithm, whose coefficients are multiply adapted in a symbol time period by recycling the received data, are analyzed to prove theoretically the improvement of convergence speed. According as the step-size parameter ${\mu}$ is increased, the rate of convergence of the algorithm is controlled. Increasing the eigenvalue spread has the effect of controlling down the rate of convergence of the adaptive equalizer and also increasing the steady-state value of the average squared error and also demonstrate the superiority of signal interference control to the filter algorithm increasing convergence speed by (B+1) times due to the data-recycling LMS Algorithms.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2008.04a
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• pp.228-233
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• 2008

In this paper, peak acceleration for horizontal vibration of buildings was estimated from the results of vibration tests using a shaking table. Human comfort of occupants is supposed to be satisfied according to the peak acceleration in NBCC and ISO6897, which have been used by Korean structural engineers. In the paper, we used a one-dimensional shaking table for horizontal vibration tests, which was mounted with a vibration house similar to a living space. Experimental results were obtained according to increasing accelerations in the range of 0.2Hz through 1.2Hz of frequency with five experimental groups, each of which was composed of eight persons. We obtained performance curves by dividing the distribution of perception from horizontal vibration tests into the ranges of 0${\sim}$25%, 26${\sim}$50%, 51${\sim}$75%, 76${\sim}$100% and then fitting the curves. Also we made a questionnaire based on human comfort criteria of foreign countries, and examined the feelings of subjects. From the results of horizontal vibration tests, it was found that acceleration of perception was low when frequency was high, and that visual and auditory senses affect the human perception for horizontal vibration of buildings.

• Journal of Ocean Engineering and Technology
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• v.28 no.5
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• pp.371-377
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• 2014

In this study, the hydrodynamic characteristics of various types of jack-up legs for a wind turbine installation vessel were analyzed. Using the modified Morison equation, the wave and current excitation forces on the jack-up legs were calculated. A modal analysis was performed to predict the dynamic responses for various types of jack-up legs. The Newmark-beta time integration scheme was used to solve the equation of motion in waves in the time domain. The maximum displacement and maximum bending stress were computed for four different types of legs, and their results were compared to select an optimum leg type. Finally, a six-leg jack-up rig with the selected optimal legs was modeled, and its natural period and hydrodynamic behaviors were evaluated.

• Proceedings of the Korea Contents Association Conference
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• 2006.11a
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• pp.528-532
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• 2006

In a cyber aquarium, the behavior of fish objects is the most important factor in respect of visual effects. In this paper, we analyze the principal habits of fish objects such as the vitality, the range of movement, the maximum depth of water they can live, and the cycle of eating. Then, we suggest a method for simulating the stable marine ecosystem with controlling the behaviors, the interaction with other species, the average span of life, and all that sort of thing based on the result of analysis. Because we can freely modify the behavior of fish object by altering the values of attributes, it can be utilized in the dynamic cyber aquarium, the 3D aquarium screen saver, and the cyber fish game, and so on.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.2
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• pp.26-32
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• 2001

In this paper, elastic responses of a floating structure in waves with a breakwater are presented. The method of source-dipole distribution is used to analyze the velocity potentials for the fluid region. The deflections of structure are expanded approximately in terms of natural mode functions of free-free beam. The model for present calculation is a floating plate with an length of 1000m and the hydroelastic responses for a floating structure with a straight breakwater are shown. The effects of distance between breakwater and structure, bending rigidity and relative length of regular waves are examined.