• 한국자동차공학회논문집
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• 제8권2호
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• pp.72-80
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• 2000

This study aims at the optimal design of the screw rotor, its performance analysis, and development of a small screw supercharger which has a low noise compared with the root type supercharger. The basic theoretical equations and the basic design of the screw supercharger have been established. The optical design of the screw rotor's shape has been also performed theoretically. Also, the performance analysis technique of the designed screw rotor has been developed.

• 대한기계학회논문집A
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• 제31권1호
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• pp.11-17
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• 2007

In this paper, we present a design, analysis, fabrication and performance test of the novel DoD metal-jet system for application to the high-density and high-temperature-melting materials. The theoretical analysis of the metal-jet nozzle system is derived by using electro-mechanical analogy. Based on the theoretical analysis results, we design the metal-jet print head system and fabricate the metal-jet system, which can eject the droplet of lead-free metal solder in high-temperature. In the experimental test, we set up the test apparatus for visualization of the droplet ejection and measure the ejected droplet volume and velocity. As a result, the diameter, volume and the velocity of the ejected droplet are about 65 $\mu$m $\sim$ 70 $\mu$m, 145p1 $\sim$ 180 pl and 4m/s, which shows quite good agreement with the theoretical analysis results of the 75 $\mu$m-diameter and 220 pl-volume of droplet. In comparison with the experimental result, the errors of diameter and volume are 7% $\sim$ 13% and 18 $\sim$ 34%, respectively.

• 한국IT서비스학회지
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• 제21권5호
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• pp.51-64
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• 2022

Companies are planning and executing IT projects using information technology as a means to secure external competitiveness. However, IT projects have high risks and uncertainties due to the invisibility of outputs (systems, services, products), and changes in plans frequently occur during project execution. As a result, most IT projects are closed without achieving the target performance. This can lead to a waste of resources and money for the company, which in turn leads to the loss of opportunities to enter new markets. This study intends to analyze the effect of changes in the project plan on customer satisfaction, which is the project performance. Also, we want to find the importance of project planning so that the target performance of the IT project can be achieved. For the empirical analysis of this study, about 500 actual project data were collected. As for the analysis method, statistical analysis such as simple and multiple regression analysis and control effect was performed. Looking at the results of the analysis, it was found that the scope change affects the cost change and the schedule change. Also, changes in scope and cost were found to affect project performance. The theoretical performance of this study proved the theoretical fact that good project performance comes out if the IT project is executed as planned. The practical performance suggested the need for a change in project management by proving that thorough execution of the project planning stage can improve the project performance in the Korean project management culture, where the project planning stage is poorly performed for the rapid implementation of the IT project.

• 한국기계가공학회지
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• 제21권6호
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• pp.1-7
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• 2022

This work investigated the performance improvement of a medium-pressure fixed-displacement-type SPUR gear pump, which is mainly used in the machine tool industry. The 3D CFX analysis and IS technique were applied using ANSYS (commercial FEM code) and compared with experimental results to ensure the reliability of the analysis. In addition, the performance improvement of the pump was obtained using the theoretical volumetric displacement equation, and the gear tooth width was changed. The pressure flow performance curves were compared, and the results were analyzed according to the width of the gear teeth. This is a factor that can cause irregular flow, vibration, and noise inside the gear pump owing to friction between the housing and gear pump.

• 한국통신학회논문지
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• 제28권4C호
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• pp.413-423
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• 2003

현재 블라인드 등화기법으로 가장 많이 사용되고 있으며 비선형 비용함수를 이용하는 CMA 등화기의 경우 closed form 형태의 최적 해를 구하는 것이 어렵기 때문에 그 동안 이론적인 성능 분석에 많은 어려움이 있었다. 그런데 최근 Zeng은 가우시안 잡음 하에서 FIR 선형 채널을 가정하였을 때 이론적인 CMA 등화기의 최적해 의 한계범위를 구하고 이를 기반으로 MSE 한계범위를 제시한 주목할 만한 결과를 발표하였다. 이러한 방법을 통하여 MSE 관점에서 CMA 등화기의 성능을 최적해인 LMS (또는 Wiener) 등화기의 성능과 이론적으로 비교 분석하는 것이 가능해진다. 본 논문에서는 이러한 Zeng의 결과를 이용하여 다음의 연구를 수행하였다. 첫째, HDD, digital VCR등의 고밀도 magnetic 기록/재생 등 부분 응답 신호 방식에 CMA 등화기를 적용하였을 때 채널의 간섭량에 따른 CMA 등화기의 MSE 한계범위를 이론적으로 계산하였고 이를 컴퓨터 시뮬레이션을 통해 검증하였다. 둘째, 부분 응답 신호방식에 CMA 등화기를 그대로 사용 할 경우 부분 응답 전달 함수?l 영점들 (zeros) 이 단위 원 위에 있어 채널왜곡의 보상 시 첨가 잡음의 증폭을 초래하여 등화기의 성능이 저하되는 문제가 발생하여 이를 개선하기 위한 Modified CMA 등화기가 제안된 바 있는데, 이 등화기에 대해서도 이론 및 시뮬레이션을 통한 성능 분석을 수행하였다. 최종적으로 CMA 와 Modified CMA 등화기의 성능 분석 결과들을 비교 성능하였다.

• Journal of Information Technology Applications and Management
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• 제21권4호
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• pp.225-245
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• 2014

ICT based convergence application is one of the most prevalent industrial issue these days. Despite of criticalness and potential economic opportunities of the ICT based convergence, theoretical research to analyze the feasibility and estimate the economic impact of the application is rather limited. This paper is intended to fill this research gap. In this respect, we develop theoretical framework to quantitatively estimate the differential benefits of convergent applications, which necessarily include underling ICT technology's contribution attributes extractions, and resulting value increments engendered from user's process effectiveness when ICT based service application is adopted. The research model to assess the differential value of the ICT based service application is developed, grounded on theoretical framework of TPC (Technology-to-performance chain) and contingency fit theories. Scenario based survey method is adopted, and SmartPLS 2.0. is used for statistical analysis of the structural equation model using 312 questionnaire. Valid statistical results are presented to provide useful insight.

• Structural Engineering and Mechanics
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• 제52권5호
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• pp.857-873
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• 2014

Structural behaviors of a sustainable hybrid column with the ultra high performance cementitious composites (UHPCC) permanent form under compression and flexure were studied. Critical state and failure stage characters are analyzed for large and small eccentricity cases. A simplified theoretical model is proposed for engineering designs and unified formulas for loading capacity of the hybrid column under compression and flexure loads are derived, including axial force and moment. Non-linear numerical analysis is carried out to verify the theoretical predictions. The theoretical predictions agree well with the numerical results which are verified by the short hybrid column tests recursively. Compared with the traditional reinforced concrete (RC) column, the loading capacity of the sustainable hybrid column is improved significantly due to UHPCC confinements.

• Smart Structures and Systems
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• 제14권2호
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• pp.247-266
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• 2014

Conventional cantilevered piezoelectric energy harvesters (PEHs) are usually fabricated with continuous electrode configuration (CEC), which suffers from the electrical cancellation at higher vibration modes. Though previous research pointed out that the segmented electrode configuration (SEC) can address this issue, a comprehensive evaluation of the PEH with SEC has yet been reported. With the consideration of delivering power to a common load, the AC outputs from all segmented electrode pairs should be rectified to DC outputs separately. In such case, theoretical formulation for power estimation becomes challenging. This paper proposes a method based on equivalent circuit model (ECM) and circuit simulation to evaluate the performance of the PEH with SEC. First, the parameters of the multi-mode ECM are identified from theoretical analysis. The ECM is then established in SPICE software and validated by the theoretical model and finite element method (FEM) with resistive loads. Subsequently, the optimal performances with SEC and CEC are compared considering the practical DC interface circuit. A comprehensive evaluation of the advantageous performance with SEC is provided for the first time. The results demonstrate the feasibility of using SEC as a simple and effective means to improve the performance of a cantilevered PEH at a higher mode.

• 한국통신학회논문지
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• 제19권3호
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• pp.425-433
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• 1994

종래부터 CATV 및 MATV 시스템에서 신호전송용으로 널리 사용되고 있는 Tap-off는 단지 경험직+실험적으로 제작되러 왔으며, 이론적인 해석이나 엄밀한 설계법이 확립되어 있지 않았기 때문에 그 성능에 있어서도 대역폭이 좁거나 분기특성이 나쁜 문제점이 있었다. 따라서, 본 논문에서는 원형의 약결합형 신호분기기에 보조변성기가 부가된 변형된 약결합형 신호분기기들 제안하여 설계의 자유도를 높임으로써 대단히 조밀한 결합간격의 회로구성이 가능함을 밝히고, 또한 이들에 대한 이론적 주파수특성을 계산하여 신험치와 비교함으로써 제안한 설계법의 타당성을 확인하였다.

• Structural Engineering and Mechanics
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• 제83권1호
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• pp.19-29
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• 2022

The angle steel frame confined concrete columns (ASFCs) are an emerging form of hybrid columns, which comprise an inner angle steel frame and a concrete column. The inner angle steel frame can provide axial bearing capacity and well confining effect for composite columns. This paper presents the experimental and theoretical studies on the seismic behaviour of ASFCs. The experimental study of the 6 test specimens is presented, based on the previous study of the authors. The theoretical study includes two parts. One part establishes the section analysis model, and it uses to analyze section axial force-moment-curvature. Another part establishes the section moment-curvature hysteresis model. The test and analysis results show that the axial compression ratio and the assembling of steel slabs influence the local buckling of the angle steel. The three factors (axial compression ratio, content of angle steel and confining effect) have important effects on the seismic behaviour of ASFCs. And the theoretical model can provide reasonably accurate predictions and apply in section analysis of ASFCs.