• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.4
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• pp.375-384
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• 2015

Recently, construction sites of offshore wind power tend to move from shallow water to deep water. From this tendency, the research on the support structure of offshore wind power in deep water will be a key issue. In this study, precast concrete block and suction pile are applied to existing jacket structure. In order to reduce the vibration of this structure, the tuned liquid damper is also applied in the precast concrete block. The applicability of the suggested jacket structure is evaluated by finite element analysis. And the vibration tends to decrease about 5%, when the tuned liquid damper is applied.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.12
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• pp.3594-3599
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• 2009

The train control system used in Gyeongbu-line is classified in ATC, IXL and CTC. The ATC data related to speed and space control for trains are transmitted from wayside to onboard by way of UM71 AF track circuits and BSP Loop. The information transferred by track circuits is composed of operation data which directly influence to the train operation and the information transferred by BSP Loop is used in the section which requires the additional data transmission about the particular track-side environment such as tunnel, hot box detector or insulated section. In this paper, for the BA type turning unit of the UM71 AF track circuits which is mainly used in the linking section of existing and high-speed lines from the opening of the Gyeongbu line till the present, we not only analyze the characteristics of BA but also compare and analyze baseline values and the measured values. With this analysis, we will be able to propose how to solve the problems about operation and maintenance such as track circuit malfunctions of the relevant sections.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.5
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• pp.468-474
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• 2010

In this paper, a VCHO(Voltage Controlled Harmonic Oscillator) for K-band application has been designed and implemented. The proposed oscillator has a structure of two hair-pin resonators placed on input and output of active device. Using in/out common frequency tuning structure, the VCHO yields some advantages of the enhanced fundamental frequency suppression characteristic as well as the improved output power of second harmonic. According to implementation and measurement results, it was shown that a VCHO provides an output power of -2.41 dBm, a fundamental frequency suppression of -21.84 dBc, and phase noise of -101.44 dBc/Hz at 100 kHz offset. In addition, as for the bias voltage from 0 V to -10 V for the varactor diode, output frequency range of 10.58 MHz is obtained with a power variation of ${\pm}0.19\;dB$ over its frequency range.

• Journal of Korean Society of Steel Construction
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• v.16 no.1 s.68
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• pp.73-79
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• 2004

Tuned Mass Damper (TMD) was applied to control the vibration of an offshore structure due to ocean waves. The errors caused by the linearization of the fluid-structure interaction effect and the phenomena when using the linearized equation of motion in TMD design were analyzed. To determine the performance of TMD in controlling vibration, both regular waves with varying periods and irregular waves with different significant wave heights were used. When the offshore structure received regular waves with a period similar to the first natural period of structure. TMD performed well in terms of response reduction. Such was not the case for the other periods. however, In the case of irregular waves, TMD triggered the reduction of structural response for waves with relatively small significant wave height. For irregular waves with relatively big significant wave height, however, TMD did not show any control effect. Therefore, TMD is useful in reducing offshore structural vibration due to ambient waves, thereby helping secure fatigue life.

• The Journal of the Korea Contents Association
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• v.13 no.12
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• pp.201-211
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• 2013

This study examined the effect of valence for best reply on the conformity of general reply in online environment. A total of 194 participants participated in this study, each participant assigned randomly in three experimental groups(positive, negative, and control). Participants were asked to read online news article, best reply and general 6 replies, and then, to write their own opinions in the reply section. In addition, the level of self-expression and issue commitment were measured. The contents of reply participants written was categorized three valence(positive, negative, and neutral) by the four experimenters' judgment. The mean of inter-rater reliability was 84.9%. The results indicated that the level of self-expression and issue commitment were comparable across experimental conditions. However, the result of cross-table analysis showed that there is a significant difference in the valence of general reply across experimental conditions. Specifically, there were significant difference in the valence of general reply between positive and negative experimental group and positive and control group, but there is no significant difference between negative and control group.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.10
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• pp.71-79
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• 2006

Swirl injector with multi-stage tangential entry was analyzed to suppress high-frequency combustion instability in Liquid Rocket Engines. In order to analyze the effect of swirl injector as an acoustic absorber, swirl injector was regarded as a quarter-wave resonator and it's damping capacity is verified in atmospheric temperature. It has a finite mode of vibration and natural frequencies which can be tuned to the natural frequencies of a model combustion chamber. The interior air core shape of injector is more stable in the case of using the swirl injector with multi-stage entry than with single-stage entry. Also, when the swirl injector with multi-stage entry is used, tuned-injector length for unstable mode is well agreed with the calculated length. From the experimental data, it is proved that if the interior air core shape of swirl injector is stable, the fine tuned swirl injector can decrease the unstable mode of model chamber effectively and increase the damping rate.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.8
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• pp.36-41
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• 2006

Computer Loads can be found in all of modern society. The switching mode power supplies used in personal computers are major sources of harmonic currents. Harmonic currents can cause lots of harmonic problems such as disruption in computer performance. A series resonant filter is very effective in harmonic reduction for personal computer loads. Voltage sags are short duration reductions in rms voltage. The main causes of voltage sags at faults, motor starting, and transformer energizing. Personal computers are another example of devices sensitive to voltage sags. A serious voltage sag at the terminals way lead mis-operation of the equipment. This paper presents an in depth analysis to evaluate the effect of harmonics reduction based on the IEC 61000-3-2 and the effect of voltage sag using ITI curve by applying a series resonant filter for personal computer loads.

• Journal of Navigation and Port Research
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• v.41 no.1
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• pp.1-8
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• 2017

The estimation of non-linear ship motion is one of the most important issues in recent studies of ship stability. In this paper, bispectral analysis and bicoherence analysis were introduced in order to analyze the non-linear ship motion. In addition to the previously observed non-linear pitching motion in following seas, this study observed the non-linear phase coupling of pitching motion in following & quartering seas, and starboard beam seas. By comparing phase coupling between each frequency quantitatively via the bicoherence analysis, it was confirmed that non-linear phase coupling was much stronger in frequency regions other than the peak frequencies of a power spectrum. Furthermore, it was found out that the results of bicoherence calculation were analagous to each other, although the different normalization methods were applied.

• Journal of Korean Society of Rural Planning
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• v.1 no.1
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• pp.99-110
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• 1995

이 연구는 한국 쌀생산의 효율성을 경영규모별로 파악하고, 영농규모 확대를 통한 쌀생산의 효율성 중대 가 가능하다는 가설을 검정해 보고자 하였다. 이 분석에 필요한 기술적 선도농가들의 생산함수인 프런티어(frontier) 생산함수를 구하기 위해서는 교 란항의 정보를 이용할 수 있는 확률(stochastic) 모형아 바람직하고, 아울러 경영규모별로 규모의 효율성을 파악하기 위해서는 레이 동조(ray-homothetic) 함수가 적절하다. 따라서 여기에서는 농림수산부의 1992년도 쌀생산비 자료에서 임의로 추출한 1,203호의 표본 자료를 이용해 앞에서 언급한 두가지 요소를 동시에 감안 할 수 있는 $\ulcorner$레이 동조 확률 생산함수(ray-homothetic stochastic production function)$\lrcorner$를 최우추정법 (Maximum likelilood estimation method)으로 추정하였으며, 이를 토대로 쌀생산의 경영규모별 비효율성 을 순수 기술적 비효율성과 규모의 비효율성으로 나누어 계측하였다. 게측결과에 의하면 쌀생산의 비효율성은 굉균 35.loyo에 이르고 있다. 이 가운데 순수 기술적 비효율성은 12.0%이고, 규모의 비효율성은 24.l%에 달했다. 기술적 비효율성과 규모의 비효율성 모두 경지규모 확대와 더불어 감소하는 것으로 나타나, 경영규모 확대와 더불어 미곡생산의 효율성이 증대될 수 있다는 가설은 기 각되지 않았다. 그러나 대농의 경우에도 규모의 비효율성이 여전히 높은 것으로 나타나 영농규모 확대를 저 해하는 제도적 장벽이 아직도 높다는 것을 알 수 있다. 아울러 대농과 소농과의 효율성 격차가 현저하지는 않은 것으로 나타나 단순히 경지를 중심으로 한 경영규모 확대만으로는 효율성 제고에 한계가 있음을 보여 주고 있다. 이 연구의 결과는 다음과 같은 정책적 함의를 가지고 있다. 첫째, 한국 미곡생산의 효율성 중대 잠재력이 결코 과소 평가되어서는 안된다. 둘째, 영농규모 확대가 쌀생산의 효율성 증대를 위해 필요한 것은 사실이지 만 단순한 경지규모의 확대에 치중하는 것보다 영농규모 확대를 저해하는 제도적 기술적 장애요인을 제거해 나가는 것이 더욱 중요하다. 마지막으로, 새로운 영농기술의 개발은 물론이고 현행 선진영농기술의 보급도 쌀생산의 효율성 중대에 상당한 역할을 할 수 있다는 사실이 간과되어서는 안된다.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.2 s.48
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• pp.21-29
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• 2006

It is impractical to install sensors on every floor of a tall building to measure the full state vector because of the large number of degrees of freedom. This makes it necessary to introduce reduced order control. A kind of system reduction scheme (dynamic condensation method) is proposed in this paper. This method is iterative and Guyan condensation is looked upon as an initial approximation of the iteration. Since the reduced order system is updated repeatedly until a desired one is obtained, the accuracy of the reduced order system resulting from the proposed method is much higher than that obtained from the Guyan condensation method. An eigenvalue shilling technique is applied to accelerate the convergence of Iteration. Two schemes to establish the reduced order system by using the proposed method are also presented and discussed in this paper. The results for a tail building with active tuned mass damper show that the proposed method is efficient for the reduced order modelling and the accuracy is very close to exact only after two iterations.