• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.10a
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• pp.3-3
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• 1998

액체추진제 로켓엔진 연소실에는 고유모드에 대응하는 음향파동이 내재되며 이러한 음향파동은 연소와의 상호작용을 통하여 불안정한 음향에너지를 공급받아 증폭되며 결국에는 연소불안정 상태에까지 이르게 된다. 이와 같은 불안정한 상태에 이르기 위해서는 연소로부터 되먹임되는 불안정 에너지의 양이 충분히 크고 구동 음향파동에 근접한 위상을 가져야 한다. 이와 같은 구동 메커니즘을 구성하는 상세한 물리적 현상들을 규명하고 예측하기 위한 많은 연구들이 보고되었으며, 이들 중 이론적인 시간 지연 모델을 사용하는 음향적인 방법은 매우 경제적인 반면 연소 현상에 대한 상세한 모사가 생략되어 연소 불안정의 구체적인 원인을 규명하는데 어려움이 있고, 파동 방정식에 의하여 연소실 내부의 파동 에너지 증가를 예측하는 방법은 연소기 내에서의 연소 메커니즘에 대한 고려 없이 연소에 의해 발생하는 에너지만을 포함하는 단점과 선형적인 연소 불안정에만 제한된다는 제한이 있다. 음향장과 커플된 기화반응 모델은 분무액적의 기화 과정이 추진제 연소의 지배과정이라는 가정 하에 연소응답을 기화반응으로 대체하는 방법으로, 역시 단시간 내에 결과를 얻을 수 있다는 장점이 있으나 기화반응으로부터 음향파동으로의 에너지 되먹임 과정이 배제되어 있어 정확한 결과를 구하기는 어렵다. 이에 대하여 최근에는 전산 모사적인 방법을 사용하는 대규모의 연소장 해석이 가능하여 짐으로써 음향파동에 의한 외란과 에너지 되먹임과정을 모두 포하마여 수치적인 방법을 사용하여 계산하는 액체추진제 로켓엔진의 고주파 연소불안정 해석방법들이 제시되고 있다.안정성 모드가 있음을 보였다. 밀도 변화가 있는 경우나 밀도 변화가 없는 경우 모두 sinuous 모드의 가장 불안정한 모드가 varicose 모드의 가장 불안정한 모드보다 더 불안정함을 보여주어 후류 유동은 자유 유동에 가까운 위상 속도를 가지는 sinuous 모드에 의해 지배될 것임을 예측할 수 있다. 연소반응이 완전연소에 가까울수록 그리고 압축성 효과가 클수록 유동내부의 온도가 증가하고 점성 또한 증가하여 후류유동은 안정됨을 알 수 있었다 유동변수들의 contour로부터 유동의 특성을 예측한 결과 baroclinic 항이 dilatational 항보다 상대적으로 크며, 중심선 상하에 생기는 vortex를 더욱 성장시킬 것으로 생각된다.냉각 홀의 막임, 연소 입자의 점착 부위 등을 예측하여 보완책을 준비할 수 있도록 하였다.$mm^2$sec였으며, 이는 다른 graphite/epixy 복합재의 확산계수와 유사한 값을 나타내고 있다. 또한 추진제가 충전된 연소관을 절단하여 밀폐한 후 95%RH 습도 조건에 보관함으로써 연소관 내부의 추진제 기계적 특성에 미치는 침투된 습기의 영향도 함께 고찰하였다. 추진제에 따라 차이는 있겠으나 추진제가 충전된 연소관은 순수 복합재 연소관에 비해 습기의 투과 정도가 작으며, 본 연소관에 충전된 RDX/AP계 추진제의 경우 추진제의 습기투과에 의한 추진제 물성 변화는 미미한 것으로 나타났다.의 향상으로, 음성개선에 효과적이라고 사료되었으며, 이 방법이 편측 성대마비 환자의 효과적인 음성개선의 치료방법의 하나로 응용될 수 있으리라 생각된다..

• Journal of the Korean Geotechnical Society
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• v.35 no.4
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• pp.15-26
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• 2019

The stability of the gravity quay wall against earthquakes is evaluated on the basis of the allowable displacement of the wall. To estimate the displacement caused by external forces, empirical equations based on the Newmark sliding block method or numerical analysis are widely used. In numerical analysis, it is possible to analyze precisely a complicated site and structure, but difficult to set the appropriate parameters and environments; there are limitations in obtaining reliable results, depending on one's level of expertise. The Newmark method, with only seismic motions, is widely used because it is simpler than numerical simulations when estimating permanent displacement. However, the empirical equations do not have any parameters for the response characteristics and sliding block of the structure, and sliding blocks being assumed as rigid bodies does not consider the nonlinear behavior of the soil and interaction with the structure. Therefore, in order to evaluate the seismic stability of the gravity quay wall, a newly-developed empirical equation is needed to overcome the above-mentioned limitations. In this study, numerical simulations are performed to analyze the response characteristics of the backfill of the structure, and to propose an optimal method of calculating the active area. For this purpose, finite element analyses were performed to analyze the response characteristics, and stress-strain relationships for various seismic motions. As a result, the response characteristics, sliding block, and failure surface of the backfill vary depending on the input seismic motions.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.2
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• pp.211-218
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• 2021

This paper addressed the problems of controlling the coupled pitch-roll motions in a marine vessel exposed to the regular waves in the longitudinal and transversal directions. Stabilization of the pitch and roll motions can be regarded as the essential task to ensure the safety of a ship's navigation. One of the important features in the pitch-roll motions is the resonance phenomena, which result in unexpected large responses in terms of pitch and roll modes in some specific conditions. Besides, owing to its inherent characteristics of coupled combination and nonlinearity of restoring terms, the vessel shows various dynamical behaviors according to the system parameters, especially in the pitch responses. Above all, it can be seen that suppression of pitch rate remains the most significant challenge to overcome for ship maneuvering safety studies. To secure the stable upright condition, a quasi-sliding mode control scheme is employed to reduce the undesirable pitch and roll responses as well as chattering elimination. The Lyapunov theory is adopted to guarantee the closed stability of the pitch-roll system. Numerical simulations demonstrate the effectiveness of the control scheme. Finally, the control goals of state convergences and chattering reduction are effectively realized through the proposed control synthesis.

• Korean Journal of Cognitive Science
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• v.12 no.3
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• pp.29-46
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• 2001

This study attempted to demonstrate that the integration of the two premises in linear syllogism is mediated by the middle term the term that is repeated in the two premises. In Experiment 1. we examined whether representing the middle term is more important than representing the end terms. We asked a question to each premise. Depending on the order of the questions either the two end terms or the middle term became the answer in both premises. Participants solved the problems better when the middle term became the answer suggesting that it is more important to represent the middle term than the end terms. In Experiment 2 we examined whether additional processing is needed for the integration beyond establishing co-referential link through the middle term. We pronominalized the middle term in the second premise and provided two kinds of information to disambiguate the pronoun. In the direct information condition we provided information about who the pronoun is whereas in the indirect information condition we provided information about the relative location of the pronoun. Participants solved the problems more quickly in the indirect information condition than in the direct information condition indicating that mere co-referential link was not enough and that the relative location of the middle term needs to be computed for the integration of the two premises.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.1
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• pp.155-161
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• 2020

In general, optimization problems are difficult to solve simply. The reason is that the given problem is solved as soon as it is simple, but the more complex it is, the very large number of cases. This study is about the optimization of AI neural network. What we are dealing with here is the relief method for constructing AI network. The main topics deal with non-deterministic issues such as the stability and unstability of the overall network state, cost down and energy down. For this one, we discuss associative memory models, that is, a method in which local minimum memory information does not select fake information. The simulated annealing, this is a method of estimating the direction with the lowest possible value and combining it with the previous one to modify it to a lower value. And nonlinear planning problems, it is a method of checking and correcting the input / output by applying the appropriate gradient descent method to minimize the very large number of objective functions. This research suggests a useful approach to relief method as a theoretical approach to solving optimization problems. Therefore, this research will be a good proposal to apply efficiently when constructing a new AI neural network.

• Geotechnical Engineering
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• v.1 no.1
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• pp.59-72
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• 1985

This paper deals with the numerical analysis by the (mite element method introducing Biot's theory of consolidation and the modified Cambridge model proposed by Roscoe school of Cambridge University as constitutive equation and using Christian-Boehner's technique. Especially, time interval and division of elements are investigated in vies of stability and economics. In order to check the validity of author's program, the program was tested with one-dimensional consolidation case followed by Terzaghi's exact solution and with the results of the Magnan's analysis for existing banking carried out for study at Cubzac-les-ports in France. The main conclusions obtained are summarized as follows: 1. In the case of one-dimensional consolidation, the more divided the elements are near the surface of the foundation, the higher the accuracy of the numerical analysis is. 2. For the time interval, it is stable to divide 20 times per 1-lg cycle. 3. At the element which has long drain distance, the Mandel-fryer effect appears due to time lag. 4. Lateral displacement at an initial loading stage predicted by author's program, in which the load was assumed as not concentrative. but rather in grid form, is well consistent with the value of observation. 5. The pore water pressure predicted by author's program has a better accordance with the value of observation compared with Magnan's results. 6. Optimum construction control by Matsuo-Kawamura's method is possible with the predicted lateral displacement and settlement by the program.

• Korean Journal of Optics and Photonics
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• v.15 no.4
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• pp.385-390
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• 2004

In this paper, we designed a 4-bit optical true time-delay(TTD) for phased array antennas(PAAs), which is composed of a wavelength-fixed optical source, 2 ${\times}$ 2 optical MEMS switches, and fiber-optic delay lines. A 4-bit TTD with a unit time delay difference of 6 ps for 10-GHz PAAs has been implemented. Measurement results on time delay show an error of -0.4 ps at maximum, corresponding to a radiation angle error of less than 1.63$^{\circ}$. Thus, the TTD implemented in this research performs in excellent agreement with theory. Each TTD line, composed of MEMS switches and fiber-optic delay lines, connected to the corresponding antenna element has insertion loss in between 1.36 ㏈ and 2.40 ㏈ depending upon the setup of the switches. On the other hand, the insertion loss difference between TTD lines was 0.32 ㏈ at maximum for a fixed radiation angle. The TTD structure proposed in this paper might be more reliable and economical than those previously proposed using tunable wavelength sources if proper power equalization either with gain control of RF amplifiers or variable attenuators is achieved.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.4
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• pp.85-93
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• 2011

A parametric study is conducted for the design of segmented arc plasma torch with the input power and current of 0.4 MW and 300 A, respectively. For this purpose, we use the analytical relationship between input power, current condition, plasma temperature, inner diameter (R) and length (L) of the torch constrictor based on arc channel model. The results reveal that arc plasma temperatures increase monotonically as ��L increases or R decreases for the ranges of R ${\leq}$ 7.5 mm and L ${\leq}$ 1.25 m. For larger valuse of ��R and L than 7.5 mm and 1.25 m, respectively, however, they show non-linear behavior corresponding to the variations of ��L, which stands for the generation of unstable arc plasma. From this parametric study, optimum ranges of R and L are suggested as 5.5 mm ${\leq}$ R ${\leq}$ 7.5 mm and 0.25 m ${\leq}$ L ${\leq}$ 0.5 m for 0.4 MW class segmented arc plasma torch, under which stable arc plasma can be achieved at the input currents of ~300 A.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.10a
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• pp.335-341
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• 1997

운전중 노심의 출력변화를 감시하는 노외계측기(Excore Detector)는 노내계측기(Incore Detector)를 통하여 측정되어진 축방향 출력편차(Axial Offset)를 이용하여 교정되고 있다. 노외 계측기의 전류와 축방향출력편차의 선형적인 관계를 가정하여 노내계측기로 최소한 4회 노심출력을 측정한후 최소자승법(Least Square Method)으로 비례상수들을 구하는 기존의 방법을 대신하여, 단순 노외계측기 교정법은 노내계측기로 1회 측정되어진 자료들을 이용하여 계측기 반응상수(Detector Response Factor)를 계산한 후 비례상수를 계산한다. 계측기반응상수는 2차원 중성자수송모델로부터 계산된 weighting factor와 3차원 확산이론으로부터 구한 노심출력을 이용하여 계산된다. 중성자수송계산은 (R-Z)와 (R-$ heta$)모델을 합성하여 3차원 weighting factor를 계산하므로 축방향 영향뿐만 아니라 집합체별 영향을 고려하였다. 또한 노심의 복잡한 구조로 인하여 근사적인 weighting (actor와 노심출력분포의 사용은 노외계측기의 전류와 계측기반응율의 불일치를 초래하며, 이를 해결하는 상수를 소개하여 보다 정확한 교정결과를 얻도록하였다. 이와 같은 방법을 고리 3호기 9, 10주기 전주기와 11주기초에 적용하여 노심의 연소분포, 냉각수의 온도분포, 노심의 연소도, 노심출력준위등에 대한 단순 노외계측기 교정법의 오차를 분석하여 최적의 노외계측기 교정모델을 제시하였다. 2차원 중성자수송모델 합성법에 의한 단순노외계측기 교정법은 2차원 (R-Z) 중성자수송모델보다 개선된 결과와 평균오차 0.179% 최대 오차 0.624%를 보여주고 있다.하면 조사 후의 조직안정성에도 크게 기여할 것으로 기대된다.EX>O가 각각 첨가된 경우, Ar-4vol.%H$_2$ 분위기보다 H$_2$분위기에서 소결했을 때 밀도가 더 높았다. 그러나, 결정립은 $UO_2$와 $UO_2$-Li$_2$O의 경우, 수소분위기에서 소결했을 때, (U,Ce)O$_2$와 (U,Ce)O$_2$-Li$_2$O에서는 Ar-4vol.%H$_2$분위기에서 소결했을 때 더욱 성장하였다.설명해 줄 수 있다. 넷째, 불규칙적이며 종잡기 힘들고 단편적인 것으로만 보이던 중간언어도 일정한 체계 속에서 변화한다는 사실을 알 수 있다. 다섯째, 종전의 오류 분석에서는 지나치게 모국어의 영향만 강조하고 다른 요인들에 대해서는 다분히 추상적인 언급으로 끝났지만 이 분석을 통 해서 배경어, 목표어, 특히 중간규칙의 역할이 괄목할 만한 것임을 가시적으로 관찰할 수 있 다. 이와 같은 오류분석 방법은 학습자의 모국어 및 관련 외국어의 음운규칙만 알면 어느 학습대상 외국어에라도 적용할 수 있는 보편성을 지니는 것으로 사료된다.없다. 그렇다면 겹의문사를 [-wh]의리를 지 닌 의문사의 병렬로 분석할 수 없다. 예를 들어 누구누구를 [주구-이-ν가] [누구누구-이- ν가]로부터 생성되었다고 볼 수 없다. 그러므로 [-wh] 겹의문사는 복수 의미를 지닐 수 없 다. 그러면 단수 의미는 어떻게 생성되는가\ulcorner 본 논문에서는 표면적 형태에도 불구하고 [-wh]의미의 겹의문사는 병렬적 관계의 합성어가 아니라 내부구조를 지

• Journal of KIISE:Computer Systems and Theory
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• v.32 no.3
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• pp.133-147
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• 2005

Various types of ray-tracing methods are used to predict the quantity measures of radiation illumination, the uniformity of illumination, radiation performance of LCD BLU(Hack-Light Unit). The uniformity of radiation illumination is one of the most important design factor of BLU and is usually controlled by the diffusive-ink pattern printed on the bottom of light-guide panel of BLU. Therefore it is desirable to produce an improved (ideally, the optimal) ink pattern to achieve the best uniformity of radiation illumination. In this paper, we applied the Welder-Mead simplex-search method among various direct search method to compute the optimal ink pattern. Direct search methods are widely used to optimize the functions which are often highly nonlinear, unpredictably discontinuous, and nondifferentiable, The ink-pattern controlling the uniformity of radiation illumination is one type of these functions. In this paper, we found that simplex search methods are well suited to computing the optimal diffusive-ink pattern. In extensive numerical testing, we have found the simplex search method to be reasonably efficient and reliable at computing the optimal diffusive-ink pattern. The result also suggests that optimization can improve the functionality of simulation tools which are used to design LCD BLU.