• International Journal of Fluid Machinery and Systems
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• 제7권4호
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• pp.160-173
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• 2014

Surge phenomena in multi-stage axial flow compressors were studied with attention to the frequency behaviors. A new parameter "volume-modified reduced surge frequency" was introduced, which took into consideration the essential surge process, i.e., emptying and filling of the working gas in the delivery plenum. The behaviors of the relative surge frequencies at the stall stagnation boundaries, compared with the corresponding duct resonance frequencies, have demonstrated the existence of two types of surges; i.e., a near-resonant surge and a subharmonic surge. The former, which has fundamentally a near-resonance frequency, occurs predominantly at the stall stagnation boundary for the short -and-fat plenum delivery flow-path and the long-and-narrow delivery duct flow-path, and possibly in the intermediate conditions. The latter, which has a subharmonic frequency of the fundamental near-resonant one and occurs mainly in the intermediate zone, is considered to be caused by the reduced frequency restricted to a limited range. In relation with those dimensionless frequencies at the stall stagnation boundary, the surge frequency behaviors in more general situations away from the boundaries could be estimated, though very roughly.

• 한국경영과학회지
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• 제27권4호
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• pp.41-65
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• 2002

We study a multi-component production/inventory system in which individual components are made to meet various demand types. We assume that the demands arrive according to a Poisson process, but there is a fixed probability that a demand requests a particular kit of different components. Each component is produced by a flow line with several stations in which the processing times of each station follow a two-stage Coxian distribution. The production of each component is operated by an independent base-stock policy with blocking. We assume that the time needed to assemble final products follows a general distribution and the capacity of an assembling facility is sufficiently large. The objective of this study is to obtain key performance measures such as the distribution of the number of each orders for each final product and the mean time of fulfilling a customer order. The basic principle of the proposed approximation method is to decompose the original system into a set of subsystems, each subsystem being associated with a flow line. Each subsystem is analyzed in isolation using a Marie's method. An iterative procedure is then used to determine the unknown parameters of each subsystem. Numerical results show that the accuracy of the approximation method is acceptable.

• 국제학술발표논문집
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• The 6th International Conference on Construction Engineering and Project Management
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• pp.496-500
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• 2015

International construction projects are inherently more risky than domestic projects with multi-dimensional uncertainties that require complementary risk management at both the country and project levels. However, despite a growing need for systematic country evaluations, most studies have focused on project-level decisions and lack country-based approaches for firms in the construction industry. Accordingly, this study suggests data-driven approaches for evaluating countries using two quantitative models. The first is a two-stage country segmentation model that not only screens negative countries based on country attractiveness (macro-segmentation) but also identifies promising countries based on the level of past project performance in a given country (micro-segmentation). The second is a multi-criteria country segmentation model that combines a firm's business objective with the country evaluation process based on Kraljic's matrix and fuzzy preference relations (FPR). These models utilize not only secondary data from internationally reputable institutions but also performance data on Korean firms from 1990 to 2014 to evaluate 29 countries. The proposed approaches enable firms to enhance their decision-making capacity for evaluating and selecting countries at the early stage of corporate strategy development.

• 대한산업공학회지
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• 제8권2호
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• pp.3-14
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• 1982

The purpose of this study is to establish the function of a sub-system for System Alternatives Feasibility Estimation (SAFE) in R & D Project Planning Phase (RDPPL). It is the fundamental function of the RDPPL/SAFE that selected an optimal planning system alternative of all, considered at RDPPL/SAS, by logical means in view of feasibility. In this paper, improving the function of RDPPL/SAFE, mathmatical models in order to quantify methods determining and integrating the feasibility funtion in each terminal system with a multi-stage process are examined.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2011년도 춘계학술대회 논문집
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• pp.1515-1516
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• 2011

• 산업경영시스템학회지
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• 제39권1호
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• pp.73-80
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• 2016

This study focuses on the formation of input release lots in a semiconductor wafer fabrication facility. After the order-lot pegging process assigns lots in the fab to orders and calculates the required quantity of wafers for each product type to meet customers' orders, the decisions on the formation of input release lots should be made to minimize the production costs of the release lots. Since the number of lots being processed in the wafer fab directly is related to the productivity of the wafer fab, the input lot formation is crucial process to reduce the production costs as well as to improve the efficiency of the wafer fab. Here, the input lot formation occurs before every shift begins in the semiconductor wafer fab. When input quantities (of wafers) for product types are given from results of the order-lot pegging process, lots to be released into the wafer fab should be formed satisfying the lot size requirements. Here, the production cost of a homogeneous lot of the same type of product is less than that of a heterogeneous lot that will be split into the number of lots according to their product types after passing the branch point during the wafer fabrication process. Also, more production cost occurs if a lot becomes more heterogeneous. We developed a multi-dimensional dynamic programming algorithm for the input lot formation problem and showed how to apply the algorithm to solve the problem optimally with an example problem instance. It is necessary to reduce the number of states at each stage in the DP algorithm for practical use. Also, we can apply the proposed DP algorithm together with lot release rules such as CONWIP and UNIFORM.

• 한국컴퓨터정보학회논문지
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• 제12권1호
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• pp.155-160
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• 2007

고속 데이터 전송에 적합한 Multi-Code CDMA 시스템은 출력이 Multi-Level이 됨으로써 출력신호의 복잡성과 출력단에 선형적인 증폭기를 사용하므로 고가, 고복잡성 등의 단점을 가진다. 이러한 단점을 보완하고자 기존 CDMA 기술에 기반을 둔 Binary CDMA 기술이 제안되었다. Binary CDMA 시스템에서 고속 데이터 연산 시 병목현상이 발생되는 코릴레이터는 동기획득시 매우 중요한 파라미터이다. 기존의 코릴레이터는 전력소모가 작다는 장점이 있지만 코릴레이션의 값을 얻기 위해 여러단의 가산을 거쳐야 하므로 연산량이 많아 처리 속도가 낮은 단점을 가지고 있다. 그러므로 본 논문은 Binary CDMA 시스템에서 고속의 데이터를 처리할 수 있으며 데이터 량이 증가하더라도 칩 면적이 독립적이며 전력소모가 일정한 구조를 가지는 코릴레이터를 제안하였다.

• International Journal of Fluid Machinery and Systems
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• 제7권3호
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• pp.110-124
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• 2014

Surge phenomena in the zone of reduced speeds in a system of a nine-stage axial flow compressor coupled with ducts were studied analytically by use of a surge transient simulation code. Main results are as follows. (1) Expansion of apparently stable, non-surge working area of the pressure vs. flow field beyond the initial stage-stall line was predicted by the code in the lower speed region. The area proved analytically to be caused by significantly mismatched stage-working conditions, particularly with the front stages deep in the rotating stall branch of the characteristics, as was already known in situ and in steady-state calculations also. (2) Surge frequencies were found to increase for decreasing compressor speeds as far as the particular compressor system was concerned. (3) The tendency was found to be explained by a newly introduced volume-modified reduced surge frequency. It suggests that the surge frequency is related intimately with the process of emptying and filling of air into the delivery volume. (4) The upstream range of movement of the fluid mass having once passed through the compressor in surge was found to reduce toward the lower speeds, which could have caused additionally the increase in surge frequency. (5) The concept of the volume-modified reduced surge frequency was able to explain, though qualitatively at present, the behaviors of the area-pressure ratio parameter for the stall stagnation boundary proposed earlier by the author.

• 한국산학기술학회논문지
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• 제18권12호
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• pp.57-64
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• 2017

오늘날 EU환경규제로 포장용 완충재로 사용되는 EPS(스티로폼) 대체용 공기 충진 완충재는 출시 이후 점진적으로 시장이 확대되는 포장업계 블루칩이다. 공기충진형 완충재는 뛰어난 완충능력과 친환경성으로 EPS를 대체하여 빠르게 시장을 확장하고 있다. 기존 공기 충진 완충재에 대비하여 원료절감과 공정향상, 직관적 미관 향상을 모두 충족하는 새로운 선택 충진형 공기 충진재 제조기술이다. 본 연구는 다단 에어셀 충진 밸브성형기술은 선택충전 기술을 바탕으로, 밸브형성 구조기술을 적용하여 선택적으로 다양한 형태로 충진이 가능한 기술이다. 다단 에어셀 충진 밸브성형기술의 구조도는 밸브단이 구분된 제1주입필름, 밸브필름, 제2주입필름 등 3겹의 필름을 적층하여 복수의 주입구를 형성한 기술이다. 기존의 기술은 연결된 다수의 공기주머니에 공기를 주입하기 위한 별도의 외부 공기주입로가 필수적으로 구성되어야 하나, 본 연구는 공기 주머니의 내부에 외부 공기주입로가 형성되어 공기를 주입하기 위한 외부 공기주입로가 외견상 없어짐으로써 그에 따른 원재료 및 공정이 감소하고, 공기가 주입되어 원형 튜브로 팽창하는 과정에서 단면의 길이가 63~66%로 축소되는 공기주머니와 다르게 공기주입 후 내부 공기가 배출되고 단면이 원래의 길이를 유지하여 불필요하게 접힌 채 붙어 있는 외부 공기주입로를 내부에 일체화 하여 완충재의 미관이 향상되는 기술적 특징과 다수의 연속된 공기주머니에 선택적으로 공기를 충전할 수 있는 선택충전에 관한 것으로 기존 기술대비 뛰어난 차별성을 갖는 스마트한 공기충전형 완충재 제조 기술이다.

• 터널과지하공간
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• 제29권5호
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• pp.292-304
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• 2019

완만한 거칠기를 갖는 석회암 자연절리면에 대하여 KSRM 표준시험법에 의거한 개별적 직접전단시험과 수직응력을 단계별로 조절하는 다단계 직접전단시험을 실시하였다. 각 시험을 통해 전단시험 전후의 절리면 거칠기 변화를 알아보았고, 두 가지 시험에서 얻은 전단특성 값의 차이를 분석하였다. 두 가지 시험에서 모두 절리면의 거칠기가 클수록 전단저항은 증가하였으며, 수직응력이 증가할수록 절리면의 전단에 필요한 최대전단응력 값은 증가하였다. 다단계 직접전단시험으로 구한 최대마찰각은 개별적 직접 전단시험으로 구한 것의 63% 수준에 불과하였다. 다단계시험은 절리면 요철부의 초기 맞물림이 단계적인 전단과정에 따라 시험 중 수시로 변화되어 원래의 거칠기가 변형되기 때문에 암석 절리면의 마찰각을 구할 때는 개별적 직접전단시험이 더 유효한 방법으로 판단된다. JRC값 4~8의 완만한 거칠기를 갖는 석회암 절리면의 물성값은 최대마찰각 $47^{\circ}$, 잔류마찰각 $38^{\circ}$, 점착력 37 kPa으로 평가되었다.