• 시스템엔지니어링학술지
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• 제19권2호
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• pp.117-125
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• 2023

Systematic performance evaluation of the Defense Acquisition Program is very important, since they are directly related to national security. In this paper, we reviewed various performance evaluation models from a methodological perspective for pragmatic performance evaluation, and the limitations of each model. In order to evaluate the performance of the Defense acquisition program efficiently, especially for the Naval ship Projects and considering their unique characteristics, both various stakeholders' participation, standard indicators for performance measurement, and tailoring them considering the projects' circumstances are necessary. We also propose indicators, contents, and detailed criteria example for the Requirements management. This approach enables a pragmatic and consistent evaluation of defense projects, and through this, meaningful insights could be acquired with accumulate data.

• 시스템엔지니어링학술지
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• 제20권spc1호
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• pp.76-89
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• 2024

This study investigates the impact of standardized underground logistics conainers on lower body muscle activation during warehouse tasks, comparing conventional roll containers(A type) with newly developed ones(B type). Through a detailed experimental setup involving electromyography(EMG) and tensiomyography(TMG), muscle activities of the lower limbs were quantitatively analyzed during loading unloading and transporting tasks. Results indicated no significant difference in muscle activation patters between the two rolltainer types, suggesting that the dimensions of these containers do not critically affect the muscular strain and workload. Furthermore, the TMG analysis revealed that muscle contraction velocity(Vc) increased in certain muscles when using the B-type rolltainer, indicating a potential for more efficient muscle engagement without increasing fatigue. This research underscores the importance of ergonomic considerations in the design of logistics equipment and suggests that further studies should focus on optimizing the interaction between human operators and logistical systems to enhance safety and efficiency in warehouse operations.

• 대한안전경영과학회지
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• 제22권4호
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• pp.75-86
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• 2020

With the advent of the 4.0 era of logistics due to the Fourth Industrial Revolution, infrastructures have been built to receive the same services online and offline. Logistics services affected by logistics 4.0 and IT technology are rapidly changing. Logistics services are developing using technologies such as big data, artificial intelligence, blockchain, Internet of things, and augmented reality. The convergence of logistics services and various IT new technologies is accelerating, and the development of data management solution technology has led to the emergence of electronic cargo waybill to replace paper cargo waybill. The electronic waybill was developed to supplement paper waybill that lack economical and safety. However, the electronic waybill that appeared to complement the paper waybill are also in need of complementation in terms of efficiency and reliability. New research is needed to ensure that electronic cargo waybill gain the trust of users and are actively utilized. To solve this problem, electronic cargo waybill that combine blockchain technology are being developed. This study aims to improve the reliability, operational efficiency and safety of blockchain electronic cargo waybill. The purpose of this study is to analyze the blockchain-based electronic cargo waybill system and to derive evaluation indicators for system supplementation.

• 대한기계학회논문집B
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• 제27권10호
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• pp.1412-1419
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• 2003

Heat regenerator occupied by regenerative materials improves thermal efficiency of combustion system through the recovery of sensible heat of exhaust gases. By using one-dimensional two-phase fluid dynamics model, the unsteady thermal flow of regenerator with spherical particles, was numerically analyzed to evaluate the heat transfer and pressure losses and to derive the design parameter for heat regenerator. It is confirmed that the computational results, such as air preheat temperature, exhausted gases outlet temperature, and pressure losses, agreed well with the experimental data. The thermal flow in heat regenerator varies with porosity, configuration of regenerator and diameter of regenerative particle. As the gas velocity increases with decreasing the cross-sectional area of the regenerator, the heat transfer between gas and particle enhances and pressure losses decrease. As particle diameter decreases, the air is preheated higher and the exhaust gases are cooled lower with the increase of pressure losses. Assuming a given exhaust gases temperature at the regenerator outlet, the regenerator need to be linearly lengthened with inlet Reynolds number of exhaust gases, which is defined as a regenerator design parameter.

• 대한기계학회논문집A
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• 제26권8호
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• pp.1552-1564
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• 2002

Meter-in, meter-out and bleed-off circuits are widely utilized in order to adjust the speed of a hydraulic actuator by using a flow control valve and in order to regulate the pressure of a hydraulic volume by using a simple on-off valve. In these circuits, a relief valve serves either to maintain constant system pressure or to protect the system from over-pressure loading. The relief valve of a bleed-off circuit is the second case frequently undergoing on-off action during operation. It makes the analysis of the pressure control characteristics of the circuit highly difficult. In this paper, steady-state flow rate, pressure, heat loss and efficiency of the three circuits are reexamined and basic experiments far obtaining the characteristics of a pump and relief valve are conducted. Finally, simple empirical first-order dynamic models of decreasing and increasing pressure were separately proposed and verified by comparison with experiment. As the result, the basis for the theoretical analysis of the pressure control characteristics of a bleed-off circuit using a simple on-off valve is established.

• Journal of Power Electronics
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• 제18권4호
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• pp.1015-1026
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• 2018

A family of dual-DC-input (DI) dual-buck inverters (DBIs) is proposed by employing a DI switching cell as the input of traditional DBIs. Three power ports, i.e. a low voltage DC input port, a high voltage DC input port and an AC output port, are provided by the proposed DI-DBIs. A low voltage DC source, whose voltage is lower than the peak amplitude of the AC side voltage, can be directly connected to the DI-DBI. This supplies power to the AC side in single-stage power conversion. When compared with traditional DBI-based two-stage DC/AC power systems, the conversion stages are reduced, and the power rating and power losses of the front-end Boost converter of the DI-DBI are reduced. In addition, five voltage-levels are generated with the help of the two DC input ports, which is a benefit in terms of reducing the voltage stresses and switching losses of switches. The topology derivation method, operation principles, modulation strategy and characteristics of the proposed inverter are analyzed in-depth. Experimental results are provided to verify the effectiveness and feasibility of the proposed DI-DBIs.

• 한국산학기술학회논문지
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• 제14권8호
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• pp.4012-4018
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• 2013

본 연구에서는 2020년까지 리모델링을 하는 국내 아파트에 에너지절약을 할 수 있는 방안을 제공하기 위하여 해외 패시브하우스에 적용된 에너지절약을 위한 기술들에 대해 알아보고 이를 통하여 우리나라에 적용 가능한 패시브적인 요소기술을 도출하였다. 또한 이를 적용 시 에너지절감율을 알아보기 위하여 국내의 건물에너지효율등급인증제도를 사용하여 선정한 5개 사례의 에너지절감율을 산출하고 등급을 부여하여 분석하였다. 그리고 이를 통하여 에너지를 절약할 수 있는 합리적인 열관류율 대안을 도출하고, 국내에서 추진되는 아파트 리모델링 프로젝트에 제시하였으며, 이 방안은 표준주택 대비 에너지를 40%이상 절약 할 수 있다.

• Journal of Power Electronics
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• 제12권4호
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• pp.519-527
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• 2012

A high step-down multiple-output LED driver is proposed in this paper. Firstly, the derivation of the driver with dual-output is presented and its operation principle and steady state performance are analyzed in detail. Secondly, a high step-down N-channel LED driver is proposed and its current auto-balance characteristic and step-down ratio are analyzed. Finally, an experimental prototype is built and the experimental results are given. The theoretical analysis and experimental results show that the proposed driver has the following virtues: First, if load balancing is achieved, the voltage gain is 1/N that of a Buck driver, where N is the number of channels. Second, each output automatically has an equal output current, without requiring more current close-loop control circuits than a Buck driver. Last, the voltage stresses of the switches and diodes are lower than those of a Buck driver, meaning that lower voltage switches and diodes can be used, and a higher efficiency can be expected.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.209-212
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• 2002

Since Berkhoff proposed the mild-slope equation in 1972, it has widely been used for calculation of shallow water wave transformation. Recently, it was extended to give an extended mild-slope equation, which includes the bottom slope squared term and bottom curvature term so as to be capable of modeling wave transformation on rapidly varying topography. These equations were derived by integrating the Laplace equation vertically. In the present study, we develop a finite element model to solve the Laplace equation directly while keeping the same computational efficiency as the mild-slope equation. This model assumes the vertical variation of wave potential as a cosine hyperbolic function as done in the derivation of the mild-slope equation, and the Galerkin method is used to discretize . The computational domain was discretized with proper finite elements, while the radiation condition at infinity was treated by introducing the concept of an infinite element. The upper boundary condition can be either free surface or a solid structure. The applicability of the developed model was verified through example analyses of two-dimensional wave reflection and transmission. .

• Journal of Mechanical Science and Technology
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• 제15권2호
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• pp.160-171
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• 2001

Depending upon the method of the surface generation and the quality of the designed boundary curves, the resulting surfaces may have global or local irregularities in many cases. Thus, it would be necessary for the designer to evaluate the surface quality and to modify the surface. This is very important because the defect of the surface causes the rework of the dies, increasing cost and delivery time significantly. To simulate the reflection line test in the actual production line, a faster algorithm for generating reflection lines is presented. In this paper, among various surface interrogation methods using reflection lines, Blinn-Newell type of reflection mapping is applied to generate the reflection lines on the trimmed NURBS surfaces. The derivation of reflection lines is formulated as a surface-plane intersection problem (Jung 1994) and is solved by surface-contouring techniques. Also, for eliminating the discontinuity of reflection lines due to the configuration of reflection map, a modified reflection map is proposed. An efficient traced contouring technique is utilized for the computational efficiency and proves to be well suited for the real-time quality-assessment task.