• 한국공간구조학회논문집
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• 제20권4호
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• pp.73-81
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• 2020

In this study, a tuned mass damper(TMD) was installed to control the displacement response to earthquakes by generalizing to six analysis models according to the shape of the upper structure based on the case of various large spatial structures around the world. The six analysis models are ribbed type, latticed type, elliptical type, gable type, barrel type, and stadium type composed of 3D arch trusses. In this paper, ribbed type, latticed type and elliptical type were analyzed. The mass of each TMD was set to 1% of the total structural mass. Result of analyzing the optimal number and position of the analysis model, the displacement response control was the most excellent in the model with 6 and 8 TMDs, and the displacement response decreased in most cases. The displacement response control was better with installing the TMD at the edge point than focusing the TMD at the center of the analysis model. However, when 10 or more TMDs are installed or concentrated in the center, large loads intensively act on the structure, resulting in increased displacement. Therefore, although it is slightly different depending on the shape, it is judged that the displacement response control is the best to install 6 and 8 TMDs at the close to the edge point.

• 한국지열·수열에너지학회논문집
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• 제17권4호
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• pp.79-90
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• 2021

This paper presents a study to reduce the effect of blast pressure on the blast valves installed in protection tunnels, where the shape of the tunnel entrance and the blast pocket is optimized based on the predetermined basic shape of the protective tunnels. The reliability of the numerical tunnel models was examined by performing analyses of mesh convergence and overpressure stability and with comparison to the data in blast-load design charts in UFC 3-340-02 (DoD, 2008). An optimal mesh size and a stabilized distance of overpressure were proposed, and the numerical results were validated based on the UFC data. A parametric study to reduce the blast overpressures in tunnel was conducted using the validated numerical model. Analysis was performed applying 1) the entrance slope of 90, 75, 60, and 45 degrees, 2) two blast pockets with the depth 0.5, 1.0, and 1.5 times the tunnel width, 3) the three types of curved back walls of the blast pockets, and 4) two types of the upper and lower surfaces of the blast pockets to the reference tunnel model. An optimal solution by combining the analysis results of the tunnel entrance shape, the depth of the blast pockets, and the upper and lower parts of the blast pockets was provided in comparison to the reference tunnel model. The blast overpressures using the proposed tunnel shape have been reduced effectively.

• 수산해양기술연구
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• 제59권1호
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• pp.44-54
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• 2023

In this study, the second-order Nomoto's nonlinear expansion model was implemented as a Tagaki-Sugeno fuzzy model based on the heading angular velocity to design the automatic steering system of a ship considering nonlinear elements. A Tagaki-Sugeno fuzzy PID controller was designed using the applied fuzzy membership functions from the Tagaki-Sugeno fuzzy model. The linear models and fuzzy membership functions of each operating point of a given nonlinear expansion model were simultaneously tuned using a genetic algorithm. It was confirmed that the implemented Tagaki-Sugeno fuzzy model could accurately describe the given nonlinear expansion model through the Zig-Zag experiment. The optimal parameters of the sub-PID controller for each operating point of the Tagaki-Sugeno fuzzy model were searched using a genetic algorithm. The evaluation function for searching the optimal parameters considered the route extension due to course deviation and the resistance component of the ship by steering. By adding a penalty function to the evaluation function, the performance of the automatic steering system of the ship could be evaluated to track the set course without overshooting when changing the course. It was confirmed that the sub-PID controller for each operating point followed the set course to minimize the evaluation function without overshoot when changing the course. The outputs of the tuned sub-PID controllers were combined in a weighted average method using the membership functions of the Tagaki-Sugeno fuzzy model. The proposed Tagaki-Sugeno fuzzy PID controller was applied to the second-order Nomoto's nonlinear expansion model. As a result of examining the transient response characteristics for the set course change, it was confirmed that the set course tracking was satisfactorily performed.

• 한국식생활문화학회지
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• 제23권5호
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• pp.621-628
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• 2008

The principal objective of this study was to develop the optimal recipe for muffins containing dried broccoli powder. In this study, broccoli powder was substituted for wheat flour in order to reduce its content. The study was conducted by determining the optimal sensory composite recipe, by preparing muffins with different levels of broccoli powder (A), sugar (B), and butter (C), by C.C.D (Central composite design) and performing sensory evaluation and analysis via RSM (Response surface methodology). The sensory measurements yielded significant values for appearance, flavor (p<0.01), texture (p<0.05), overall quality (p<0.05) and color (p<0.05), whereas instrumental measurements yielded significant values in lightness (p<0.01), redness (p<0.05), yellowness, baking loss rate (p<0.05), hardness (p<0.05), cohesiveness (p<0.01) and gumminess (p<0.05). The optimum formulations processed by numerical and graphical optimization were determined as 13.58g of broccoli powder, 92.02g of sugar, and 71.97g of butter.

• 현장농수산연구지
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• 제21권1호
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• pp.149-157
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• 2019

패류 인공종자생산에서 모패관리의 중요성이 커져가고 있으며 최적의 모패 관리 조건과 원하는 시기에 종자생산을 할 수 있는 성숙유도 조건을 구명하는 하는 것이 매우 중요하기 때문에 본 연구에서는 왕우럭 조개의 모패관리 최적조건과 성숙 촉진을 위한 가온 효과를 조사하였다. 모패관리는 실내사육에 비하여 실외사육이 비만도와 생존율 측면에서 더 효과적인 것으로 나타났으며 관리 측면에서도 인위적인 먹이생물 공급이 없으며 자연환경 조건에서 사육하기 때문에 관리가 수월하다는 장점이 있는 것으로 나타났다. 그리고 동계가온을 통한 성숙촉진 유도는 비만도와 생식소 관찰 등을 통하여 수온 18℃ 이상에서 2개월 정도 사육하였을 경우 성성숙이 이루어지는 것으로 나타나 성숙관리가 다른 패류에 비해 용이하다는 것을 알 수 있었다.

• 한국축산식품학회지
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• 제44권1호
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• pp.146-164
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• 2024

Owing to the residual toxicity and adverse health effects of chemical preservatives, there is an increasing demand for using natural preservatives in food. Although many natural extracts have been evaluated, research on their antibacterial effects remains insufficient. Therefore, this study aimed to explore the possibility of developing Psidium guajava, Ecklonia cava, and Paeonia japonica (Makino) Miyabe & Takeda extracts as natural food preservatives. Further, the effect of mixing these extracts on microbial growth and quality was evaluated during the refrigeration of sausages. Optimal mixing ratios were determined based on the minimum inhibitory and bactericidal concentrations of each mixed extract against the Listeria monocytogenes, Salmonella spp. and Escherichia coli. D-optimal mixing design optimization tool was further used to obtain an optimum mixing ratio of Formulation 1 (F1). The antibacterial activity of F1 increased with increasing concentration, with similar activities at 0.5% and 1%. The sausages with synthetic or natural preservatives showed significantly lower lipid oxidation than those of the control and grapefruit extract-treated sausages after 4 wk of refrigeration. Total plate counts were observed only in the control and treatment groups stored for 3 wk, and no significant effect of ascorbic acid was observed. Compared to the other samples, sausages with added natural extracts showed the highest overall acceptability scores initially and after 4 wk. Therefore, similar amounts of grapefruit seed and natural extracts had the same effect on microbiological analysis and lipid rancidity during sausage storage. Hence, this mixture can serve as a potential natural preservative in meat products.

• 한국전자파학회논문지
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• 제19권1호
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• pp.15-22
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• 2008

본 논문에서는 전송 선로 이론을 기반으로 분산형 증폭기의 역방향 전류 성분을 수식적으로 분석하고, 역방향 전류 성분을 상쇄시켜 최소화하기 위한 최적의 전송 선로의 길이를 구하는 방법을 제시하였다. 기존의 설계방법에서는 역방향 전류 성분을 종단 부하를 통해 단순히 소모시키는 형태이므로 게이트와 드레인 전송 선로의 길이 결정 기준이 설계상에서 뚜렷하게 주어져 있지 않았지만, 제안하는 방법에서는 역방향 전류 성분들이 서로 상쇄가 일어나도록 하는 전송 선로의 길이를 결정하는 이론적 바탕을 제시함으로써 좀 더 체계적인 설계 방법을 제시하고 있다. 제안하는 이론의 검증을 위하여 회로 시뮬레이션을 수행하였고, pHEMT 트랜지스터를 이용하여 차단 주파수가 3.6 GHz인 최적 전송 선로를 이용한 분산형 증폭기를 제작하였다. 측정을 통해 얻은 결과로서 동작 주파수 범위 내에서 최대 이득은 14.5 dB, 최소 이득은 12.8 dB로 측정되었다. 또한, 제안하는 분산형 증폭기의 측정된 효율은 3 GHz에서 25.6 %로 기존의 일반적인 분산형 증폭기에 비해 약 7.6 % 개선되었다. 출력 전력은 일반적인 분산형 증폭기에 비해 약 1.7dB 개선된 10.9 dBm을 얻었다. 이러한 성능 개선은 역방향 전류의 상쇄로 인한 것으로 분석된다.

• 한국산학기술학회논문지
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• 제22권6호
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• pp.460-468
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• 2021

본 연구는 multi fan 방식의 "공랭식 연소설비"의 공정관리상의 문제점을 single F.D. fan 으로 대체하여 개선시키기 위해 CFD 진행하였고, 연소로 내 유동조건 변화를 분석하여 문제점을 확인하였다. 이를 개선하기 위해 연소공기 주입구조를 변경하였고, 구조 변화에 따른 연소효율 개선을 수치해석으로 평가하였다. 또한 실제 연소설비에 수치해석결과를 반영하여 구조개선을 한 후 개선 전·후의 연소효율을 실험적으로 측정하였다. 먼저 기존 Single F.D fan 이 적용된 연소설비에 대한 수치해석을 통해, 2개의 유로로 공급되는 연소공기가 각 유로의 마찰력 차이와 압력의 변화로 인해 연소로 내에서 공급비율이 불규칙하게 되어 선회방식의 연소조건을 위한 축 형태의 난류형성이 어려움을 확인하였다. 이를 개선하기 위해서 연소로에 주입하는 공기 공급 방식을 두 가지로 나누어 수치해석을 하였다. 첫 번째 방식은 연소공기를 외벽에서 180 ~ 360° 회전 후 예열된 연소공기가 주입되는 구조에 대하여 검토하였고, 두 번째는 연소로 내에는 선회할 수 있는 베인(vane) 구조를 적용하여 연소로 밖에서 1차 열교환 후 연소로 내부에 접선방향으로 연소공기가 주입되는 구조에 대하여 검토하였다. 그 결과, single F.D. fan을 가진 공랭식 연소로에 선회방식으로 공기를 주입할 경우, 연소로 외벽의 냉각과 연소로 내부의 완전혼합 유지를 위해 이중 냉각벽을 가지는 덕트 구조를 적용하는 것이 연소조건을 최적화하는데 바람직한 것으로 나타났으며, 실제 운영중인 설비에 적용하여 개선 전·후의 연소효율을 비교한 결과 연소효율이 개선되는 것을 확인할 수 있었다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.115-116
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• 2002

This study was carried out as one of efforts to overcome difficulties in air bearing design due to low stiffness and low damping. Hydrodynamic effects on hydrodynamic stiffness of a fluid film in a high speed air bearing with tow-row air sources are investigated. The hydrodynamic effects by the high speed over DN 1,000,000 and eccentricity of a proceeding which are not considered in conventional design of an air bearing need to be reconsidered. The hydrodynamic effects, which dominantly influence on the load capacity of air bearing, are caused mainly by proceeding speed, eccentricity, and the source positions. The two-row source arrangement in the air bearing produces quite unique hydrodynamic effects with respect to pressure distribution of the air film. Optimal arrangement of the two-row sources improves performance of an air bearing in film reaction force and loading capacity of high speed spindles. This study compares the pressure distribution by numerical simulation as a function of eccentricity of proceeding and the source positions. The air source position 1/7L form one end of an air bearing was found to be superior to source position of 1/4L. The dynamic stiffness were obtained using a two-dimensional cutting method which can directly measure the cutting reaction forces and the displacements of the spindle in two directions using a tool dynamometer and transducer sensors. Heat generation in the air film can not be negligible over the speed of DN 2,000,000. In order to analysis effects of heat generation on the characteristics of air bearing, high cooling bearing spindle and low cooling bearing spindle were tested and compared. Characteristics of the frequency response of shaft and motion of run out errors were different for the spindle. The test results show that, in the case of low cooling bearing spindle, the stiffness became smaller due to heat generation. The results, which were obtained for high speed region, may be used as a design information for spindle which can be applied to precision devices such as ultra precision grinding and ultra high speed milling.

• 한국전산유체공학회지
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• 제19권4호
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• pp.86-93
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• 2014

Increased demand of power-transformer's capacity inevitably results in an excessive temperature rise of transformer components, which in turn requires improved radiator design. In this paper, numerical simulation of the cooling performance of an ONAN-type (Oil Natural Air Natural) radiator surrounded by air was performed by using CFX. The natural convection of the air was treated with the full-model. The present parametric study considers variation of important variables that are expected to affect the cooling performance. We changed the pattern and cross-sectional area of flow passages, the fin interval, the flow rate of oil and shape of flow passages. Results show that the area of flow passage, the fin interval, the flow rate of oil and shape of flow passages considerably affect the cooling performance whereas the pattern of flow passages is not so much influential. We also found that for the case of the fin interval smaller than the basic design, the temperature drop decreases while a larger interval gives almost unchanged temperature drop, indicating that the basic design is optimal. Further, as the flow rate of oil increases, the temperature drop slowly decreases as expected. On the other hand, when the shape of flow passages are changed, temperature drop is increased, indicating that the cooling performance is enhanced thereupon.