• Geomechanics and Engineering
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• 제15권2호
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• pp.755-767
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• 2018

This paper uses a finite element based approach to provide a comprehensive understanding to the behaviour and the design performance of buried uPVC pipes with different diameters. It also investigates pipes with good and poor haunch support and proposes minimum safe wall thicknesses for these pipes. The results for pipes with good haunch support showed that the maximum pipe wall stress and deformation increase as the diameter increased. The results for pipes with poor haunch support showed an increase in the dependency of the developed vertical displacement on the haunch support as the diameter or the backfill height increased. Additionally, poor haunch support was found to increase the soil pressure, with the effect increasing as the diameter increased. The design of uPVC pipes for both poor and good haunch support was found to be governed by critical buckling. A key outcome is a new design chart for the minimum wall thickness, which enables the robust and economic design of buried uPVC pipes. Importantly, the methodology adopted in this study can also be applied to the design of flexible pipes manufactured from other materials, buried under different conditions and subjected to different loading arrangements.

• 한국경영과학회:학술대회논문집
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• 한국경영과학회 1998년도 추계학술대회 논문집
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• pp.263-266
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• 1998

Several constraints in machine duplication cost, machining capability, cell space capacity, intercell moves and exceptional elements(EEs) are main problems that prevent achieving the goal of ideal Cellular Manufacturin System (CMS) environment. Minimizing intercell part traffics and EEs are the main objective of the cell formation problem as it's a critical point that improving production efficiency. Because the intercell moves could be changed according to the sequence of operation, it should be considered in assigning parts and machines to machine cells. This paper presents a method that eliminates EEs under the constraints of machine duplication cost and cell space capacity attaining two goals of minimizing machine duplications and minimizing intercell moves simultaneously. Developing an algorithm that calculates the machine duplications by cell-machine incidence matrix and part-machine incidence matrix, and calculates the exact intercell moves considering the sequence of operation. Based on the number of machine duplications and exact intercell moves, the goal programming model which satisfying minimum machine duplications and minimum intercell moves is developed. A linear programming model is suggested that could calculates more effectively without damaging optimal solution. A numerical example is provided to illustrate these methods.

• 한국위성정보통신학회논문지
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• 제10권1호
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• pp.22-28
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• 2015

본 논문에서는 연판정 간섭 소거 최소 자승-오류(soft interference cancellation and minimum mean squared-error; SIC-MMSE) 방법을 이용한 새로운 에너지 효율적 다중안테나(multi-input multi-output; MIMO) 검출 기법을 소개한다. SIC-MMSE 방법의 가장 큰 계산 복잡도는 복소 행렬에 대하여 안테나 개수 만큼의 여러 번 역행렬 계산을 해야 하는데 있다. 본 논문에서는 행렬에 대한 테일러 시리즈 확장(Taylor series expansion) 기법을 이용하여 안테나 개수에 상관없이 단 한번의 역행렬 계산만을 필요로 하는 방법을 제안하며, 이와 같은 방법을 이용하여 계산의 복잡도를 감소시킬 수 있다. 본 논문에서 제안한 기법의 복잡도 감소 효과는 안테나 개수가 증가함에 따라 더 크게 나타난다. 본 논문에서 제시한 시뮬레이션 결과를 통하여 제안한 기법이 기존의 SIC-MMSE 기법에 비하여 더 적은 복잡도로 거의 동일한 성능을 도출할 수 있음을 알 수 있다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.881-886
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• 2003

In spite of its simple design, structure and operating mechanism, swing check valves are one of the critical components which adversely affect the safety of the nuclear power plants if they fail to function properly. Therefore, it is important to evaluate the performance condition of the swing check valves in safety-related systems. The performance characteristics of swing check valves include opening characteristics, the minimum required flow velocity, the pressure drop at design flow, the disc stability, and the effect of the upstream disturbances. Among factors to identify the performance of a swing check valve, a method to evaluate the opening characteristics and the minimum required flow velocity, which guarantees to fully open the disc and hold the disc without motion, are presented to determine the operating region of the swing check valve, such as stable, tapping, or oscillation. Based on the determined operating region and opening characteristics, the simple methods of wear and fatigue analyses of the specific parts of the valve are also described.

• 한국농공학회논문집
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• 제49권1호
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• pp.35-42
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• 2007

This paper develops a Sustainable Regional Economic Growth Model (SREG) which estimates the relation of labor population change and employment increase in each occupation and maximum limits and minimum requirements of employment increase by labor population change in a specified region using multiplier theory. To develop the proposed model, sustainable regional economic growth is defined as a steady increase of labor population over a long term period and the limit of employment increase is defined as the estimated labor population change in the region with no need for commutation from the surrounded areas. Developed model was applied to 67 county in Pennsylvania State and the results revealed that the investment in infrastructure occupations, such as transportation, warehousing, utilities, information, communication, and other public utilities, maximizes the effects for increasing employment, whereas finance, insurance, and real estate occupations have minimum effects for increasing employment. Calculated minimum requirements of occupations show that infra-structure occupations is a critical factor for labor population change and maximum limits of occupations show that agriculture and finance occupations are difficult to increase independently.

• 대한교통학회지
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• 제17권1호
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• pp.19-28
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• 1999

본 논문은 고속도로의 오르막차로 구간을 대상으로 종점부의 설계기준을 제시하고자 하는 목적으로 미시적 관점에서 교통행태를 규명할 수 있는 임계간격 모형과 합류확률 모형식을 개발하였다. 오르막차로 종점부 최저허용속도의 분석결과는 2차로 고속도로에서는 60km/hr, 4차로 고속도로에서는 75km/hr로 나타나 2차로에서는 현행기준과 동일하고 4차로의 경우는 현행기준 보다 약 15km/hr정도 높게 적용하는 것이 바람직한 것으로 분석되었다. 또한 오르막차로 종점부 부가길이 산출결과는 오르막차로 종점부 최저허용속도 기준과 비교해볼 때 4차로 고속도로의 경우, 부가길이가 약 200m 정도 필요한 것으로 나타나 오르막차로 종점부 최저허용속도를 상향시킬 필요가 있는 것으로 분석되었다.

• 국제학술발표논문집
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• The 3th International Conference on Construction Engineering and Project Management
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• pp.800-807
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• 2009

The limited public funds available for infrastructure projects have led governments to consider private entities' participation in long-term contracts for finance, construction, and operation of these projects to share risks and rewards between the public and the private. Because these projects have complicated risk evolutions, diverse contractual forms for each project member to hedge risks involved in a project are necessary. In light of this, Build-Operate-Transfer(BOT) model is considered as effective to accomplish Public Private Partnerships(PPPs) with a characteristic of an ownership-reversion. In BOT projects, the government has used such an incentive system as minimum revenue guarantee(MRG) agreement to attract the private's participation. Although this agreement turns out critical in success of BOT project, there still exist problematic issues in a financial feasibility analysis since the traditional capital budgeting theory, Net Present Value(NPV) analysis, has failed to evaluate the contingent characteristic of MRG agreement. The purpose of this research is to develop real option model based on option pricing theory so as to provide a theoretical framework in valuing MRG agreement in BOT projects. To understand the applicability of the model, the model is applied to the example of the BOT toll road project and the results are compared with that by NPV analysis. Finally, we found that the impact of the MRG agreement is significant on the project value. Hence, the real option model can help the government establish better BOT policies and the developer make appropriate bidding strategies.

• Environmental Engineering Research
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• 제13권2호
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• pp.73-78
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• 2008

For a given soil-contaminated site, a level of soil contamination is characterized and decisions on risk may be made from the risk assessment. The study evaluated critical design factors for the determination of sample size in the sampling design plan and the assessment of soil contaminant- leaching to groundwater. Two variables, the minimum relative detectable difference (T) and coefficient of variation (CV) were evaluated for the sample size determination. The minimum number of samples can be appropriately determined by CV under a T value greater than or equal to 0.2. Soil-contaminant leaching to groundwater was evaluated by using the Soil Screening Level equation of U.S. Environmental Protection Agency and the Risk Based Screening Level equation of American Society for Testing and Materials, with the same input parameters. The groundwater concentrations estimated from soil contaminant concentrations were significantly affected by the Darcy velocity of groundwater and the organic content of soil.

• International Journal of Safety
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• 제1권1호
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• pp.47-51
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• 2002

This study was performed by measuring the minimum ignition temperature of polyurethane form recovered from the recycling process of the end-of-life home appliances. The critical ignition temperature of polyurethane form was lower as the size of the sample vessel was increased, and that of polyurethane form using cyclopentane as the forming agent was relatively lower than the polyurethane form using CFC and the combustion of cyclopentane-polyurethane form occurred fiercely. It is considered that the recycling process of end-of-life home appliances using cyclopentane-polyurethane form as the insulator would require a special fire and dust explosion prevention measures since there exists a high potential hazard of fire and dust explosion during crushing and storage processes.

• Structural Engineering and Mechanics
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• 제13권1호
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• pp.35-52
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• 2002

It was shown in the previous study (Lee and Bertero 1993) that incremental collapse can lead to the exhaustion of the plastic rotation capacity at critical regions in a structure when subjected to the number of load cycles and load intensities as expected during maximum credible earthquakes and that this type of collapse can be predicted using the shakedown analysis technique. In this study, a minimum-weight design methodology, which takes into account not only the prevention of this incremental collapse but also the requirements of the serviceability limit states, is proposed by using the shakedown analysis technique and a nonlinear programming algorithm (gradient projection method).