• Journal of Mechanical Science and Technology
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• 제20권7호
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• pp.1077-1088
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• 2006

This paper describes a numerical investigation on the performance deteriorations of a low speed, single-stage axial turbine due to use of rough blades. Numerical calculations have been carried out with a commercial CFD code, CFX-Tascflow, by using a modified wall function to implement rough surfaces on the stator vane and rotor blade. To assess the stage performance variations corresponding to 5 equivalent sand-grain roughness heights from a transition ally rough regime to a fully rough regime, stage work coefficient and total to static efficiency were chosen. Numerical results showed that both work coefficient and stage efficiency reduced as roughness height increased. Higher surface roughness induced higher blade loading both on the stator and rotor which in turn resulted in higher deviation angles and corresponding work coefficient reductions. Although, deviation angle changes were small, a simple sensitivity analysis suggested that their contributions on work coefficient reductions were substantial. Higher profile loss coefficients were predicted by higher roughness heights, especially on the suction surface of the stator and rotor. Furthermore sensitivity analysis similar to the above, suggested that additional profile loss generations due to roughness were accountable for efficiency reductions.

• 제어로봇시스템학회논문지
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• 제10권3호
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• pp.205-215
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• 2004

The characteristic ratio assignment (CRA) method〔1〕 is new polynomial approach which allows to directly address the transient responses such as overshoot and speed of response time in time domain specifications. The method is based on the relationships between time response and characteristic ratios($\alpha_i$ ) and generalized time constant (T), which are defined in terms of coefficients of characteristic polynomial. However, even though the CRA can apply to developing a linear controller that meets good transient responses, there are still some fundamental questions to be explored. For the purpose of this, we have analyzed several sensitivities of a linear system with respect to the changes of coefficients itself and $\alpha_i$ of denominator polynomial. They are (i) the unnormalized root sensitivity : to determine how the poles change as $\alpha_i$ changes, and (ii) the function sensitivity to determine the sensitivity of step response to the change of o, and to analyze the sensitivity of frequency response as o, changes. As an other important result, it is shown that, under any fixed T and coefficient of the lowest order of s in denominator, the step response is dominantly affected merely by $\alpha_1, alpha_2 and alpha_3$ regardless of the order of denominator higher than 4. This means that the rest of the$\alpha_i$ s have little effect on the step response. These results provide some useful insight and background theory when we select $\alpha_i$ and T to compose a reference model, and in particular when we design a low order controllers such as PID controller.

• 한국항행학회논문지
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• 제23권5호
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• pp.415-423
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• 2019

본 논문에서는 유전율 측정을 위한 구부러진 슬롯이 추가된 고감도 마이크로스트립 패치 센서 안테나의 설계 방법에 대하여 연구하였다. 유전율에 대한 감도를 향상시키기 위해 단일 링 CSRR 구조와 유사한 구부러진 슬롯이 패치의 한쪽 방사면에 추가되었다. 제안된 마이크로스트립 패치 센서 안테나의 감도를 기존의 직사각형 마이크로스트립 패치 센서 안테나와 얇은 직사각형 슬롯이 추가된 마이크로스트립 패치 센서 안테나와 비교하였다. 세 마이크로스트립 패치 센서 안테나는 피 시험 상판이 없는 상태에서 전송 계수가 2.5 GHz에서 공진하도록 0.76 mm 두께의 RF-35 기판 상에 설계하고 제작하였다. 피 시험 상판으로 비유전율이 2.17에서 10.2 범위에 있는 타코닉 기판 5종을 사용하여 실험한 결과, 입력 반사계수의 공진 주파수의 이동으로 측정된 제안된 마이크로스트립 센서 안테나의 감도는 기존의 직사각형 마이크로스트립 패치 센서 안테나와 비교할 때 4.1배에서 6.1배 증가하는 것을 확인하였다.

• 한국콘텐츠학회논문지
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• 제18권2호
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• pp.216-230
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• 2018

본 논문에서는 산업연관분석을 적용하여 무인항공기 산업과 관련된 기술별 경제적 파급효과를 분석한다. 구체적으로 고용창출효과와 부가가치유발효과, 감응도 계수, 영향력 계수를 산출할 수 있으며, 분석결과에 대한 시사점을 제시하기로 한다. 분석결과, 고용유발효과는 투자액 10억원당 10.017명으로 확인되었으며, 부가가치유발효과는 1원의 예산이 투입될 경우, 0.9771원의 부가가치가 발생하여 타제조업 평균치(고용유발계수: 2.285, 부가가치유발계수: 0.581) 대비 모두 월등히 높은 수치를 보였다. 한편, 무인항공기 산업은 전방연쇄효과를 의미하는 감응도 계수는 0.7870로 제조업 평균치(감응도 계수: 1.125)보다 낮고, 후방연쇄 효과를 의미하는 영향력 계수는 각각 1.161로 제조업 평균치(영향력 계수: 1.116)보다 높기 때문에 최종 수요적 제조업형 산업으로 분류된다. 이는 무인항공기 산업이 경기변동에 영향을 적게 받는 산업임을 의미하며, 다른 부문에 비해서 투자지출대비 경제적 파급효과가 큰 산업으로 해석이 가능하다. 이러한 정략적 데이터를 기반으로 무인항공기 산업의 기술별 R&D 투자 방향 정책을 수립하는데 활용될 수 있다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 춘계학술대회 논문집
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• pp.140-145
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• 2002

At present, wind tunnel test or CFD is used for predicting aerodynamic drag coefficient in motor company. But, wind tunnel test requires much cost and time, and CFD has about 30% error. In this study a predicting program of the aerodynamic drag coefficient based on empirical techniques was developed. Also a mathematical optimization method using GRG method was added to the program. The program was applied to six cars. Aerodynamic drag coefficient values of six cars were Predicted with 4.857% average error. The optimization method was also applied to six cars. Three parameters selected from sensitivity analysis were determined to reduce the afterbody drag coefficient to the value established by a designer and when some parameters were changed for a developing automotive, optimal modifiable parameters were determined to preserve the same drag coefficient as the original automotive. It was verified that this program could predict the aerodynamic drag coefficient effectively and accurately, and this program with GRG method could determine optimal values of parameters.

• Journal of the Optical Society of Korea
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• 제15권4호
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• pp.329-334
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• 2011

We proposed a poly-dimethylsiloxane (PDMS)-coated fiber Bragg grating (FBG) temperature sensor for enhancing temperature sensitivity. By embedding the bare FBG in a temperature-sensitive elastomeric polymer, the temperature sensitivity of the proposed structure could be effectively improved by 4.2 times higher than those of the conventional bare-type FBG sensors due to the high thermal expansion coefficient of the PDMS. We analyzed the temperature-sensitivity enhancement effect with the increased Bragg wavelength shift in our structure and dependence on the temperature sensitivity with respect to the cross-section area of the PDMS.

• 소음진동
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• 제6권4호
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• pp.475-479
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• 1996

Recently, fiber optic hydrophone is a subject which has attracted as a underwater acoustic sensor. In this paper, a length of optical fiber is bonded to an end-capped hollow cylinder of some elastic material, e. g. aluminum and glass-pyres. The normalized sensitivity is derived according to the direction of polarization. Derived sensitivity equations are simulated for two different mandrel materials. The results are also compared to the McMahon's results which calculated for an average Pockel coefficient. Based on the numerical simulation normalized sensitivity is propotional to the inner to outer diameter ratio.

• 한국태양에너지학회 논문집
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• 제35권1호
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• pp.53-60
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• 2015

The ECO2 building energy simulation program is used on the assessment project for building energy certification of non-dwelling buildings in Korea. In the design of energy efficient buildings, it is beneficial to identify the most important design parameters in oder to more efficiently develop alternative design solutions or reach optimized design solutions. The sensitivity analyses will be used at a reasonable early stage of the building design process, where it is still possible to influence the most important design parameters. In this study, the sensitivity analysis is focused on building envelope parameters such as U-values, SHGC and Wall-window ration.

• Journal of Information Technology Applications and Management
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• 제21권4_spc호
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• pp.381-401
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• 2014

This study proposes the accurate economic effect (employment inducement coefficient, hiring inducement coefficient, index of the sensitivity of dispersion, index of the power of dispersion, and ratio of value added) of Korea software industry by analyzing the inter-industry relation using the modified inter-industry table. Some previous studies related to the inter-industry analysis were reviewed and the key problems were identified. First, in the current inter-industry table publishedby the Bank of Korea, the output of software industry includes not only the output of pure software industry (package software and IT services) but also the output of non-software industry due to the misclassification of the industry. This causes the output to become bigger than the actual output of the software industry. Second, during rewriting the inter-industry table, the output is changing. The inter-industry table is the table in the form of rows and columns, which records the transactions of goods and services among industries which are required to continue the activities of each industry. Accordingly, if only an output of a specific industry is changed, the reliability of the table would be degraded because the table is prepared based on the relations with other industries. This possibly causes the economic effect coefficient to degrade reliability, over or under estimated. This study tries to correct these problems to get the more accurate economic effect of the software industry. First, to get the output of the pure software section only, the data from the Korea Electronics Association(KEA) was used in the inter-industry table. Second, to prevent the difference in the outputs during rewriting the inter-industry table, the difference between the output in the current inter-industry table and the output from KEA data was identified and then it was defined as the non-software section output for the analysis. The following results were obtained: The pure software section's economic effect coefficient was lower than the coefficient of non-software section. It comes from differenceof data to Bank of Korea and KEA. This study hasa signification from accurate economic effect of Korea software industry.

• 한국대기환경학회지
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• 제5권1호
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• pp.1-10
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• 1989

The sensitivity analysis is a method to quantify to what extent the output of a model changes with the values of input parameters. This will lead to increase model accuracy through measurement validation. Three line source air quality models, HIWAY 2, PAL, and CALINE 3 were selected for this study. The input parameters analysed included wind speed, wind direction, stability, emission rate, mixing height, receptor distance, initial dispersion coefficient, surface roughness, and averaging time. It turned out that PAL model generally showed higher concentration than other two models, and that between CALINE 3 and HIWAY 2, CALINE 3 showed higher concentration than HIWAY 2 model near the line sources, but beyond a certain downwind distances HIWAY 2 model showed higher concentration. The modesl were very sensitive to wind speed especially in the range of 0 $\sim$ 1 m/s and to wind direction near the parallel wind to streets. In case of emission rate, the output concentration was directly proportional to these input parameters. And the sensitivity of the input parameters such as stability, mixing height, initial dispersion coefficient, surface roughness, and averaging time were not very significant.