• Coupled systems mechanics
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• 제1권2호
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• pp.155-163
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• 2012

This paper presents analytical approximate solutions for the initial post-buckling deformation of the pipes in oil and gas wells. The governing differential equation with sinusoidal nonlinearity can be reduced to form a third-order-polynomial nonlinear equation, by coupling of the well-known Maclaurin series expansion and orthogonal Chebyshev polynomials. Analytical approximations to the resulting boundary condition problem are established by combining the Newton's method with the method of harmonic balance. The linearization is performed prior to proceeding with harmonic balancing thus resulting in a set of linear algebraic equations instead of one of non-linear algebraic equations, unlike the classical method of harmonic balance. We are hence able to establish analytical approximate solutions. The approximate formulae for load along axis, and periodic solution are established for derivative of the helix angle at the end of the pipe. Illustrative examples are selected and compared to "reference" solution obtained by the shooting method to substantiate the accuracy and correctness of the approximate analytical approach.

• 한국분무공학회지
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• 제24권3호
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• pp.122-129
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• 2019

Flow uniformity in aftertreatment system is an important factor in determining uniform catalytic reaction and filtration. In this study, variety types of DOC-DPF system design were analyzed to increase flow uniformity. For this analysis, ANSYS Fluent was used with porous media setup for DOC and DPF. Turbulent flow was modeled by standard $k-{\varepsilon}$ model excepting porous media. Uniformity index was utilized to evaluate the flow uniformity quantitatively. Reference design showed low velocity region because two large vortex were generated before baffle. When radius of DOC-DPF system was increased, exhaust pressure acting on the inlet decreases and velocity distribution was shifted to one side. When inlet pipe was set to axial center of DOC-DPF system velocity distribution was symmetric. However, flow was not dissipated until the front end of DOC and showed higher uniformity index. When the volume of DOC was reduced while fixed volume of entire DOC-DPF system and baffle plate is located downstream of the DOC-DPF system, there was improvement in uniformity index.

• 한국산학기술학회논문지
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• 제17권6호
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• pp.721-728
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• 2016

지구상에 존재하는 물의 97%는 해수로 존재한다. 따라서 해양자원을 어떻게 활용하는 가는 최근 가장 중요한 이슈 중 하나이다. 해수의 이용은 해수담수화, 원자력 발전소의 냉각수, 해양심층수 활용 등 다양한 분야로 확대되고 있다. 깨끗한 해수를 취수하기 위해 여과사를 이용한 해수취수시스템이 활발하게 사용되고 있으며 이러한 시스템에 적용되는 취수관의 경우 각 취수구 별로 균등하게 취수될 때 취수효율뿐만 아니라 여과의 효율도 높일 수 있다. 본 연구에서는 해수취수시설에 적용된 2중관 구조의 취수효율 향상 효과를 3차원 수치모의를 통해 확인하였으며 상부유공의 간격변화에 따른 구간별 취수량을 분석하였다. 그 결과 관 말단부로 갈수록 상부유공의 간격이 감소되는 경우가 전체적인 취수량은 큰 차이가 없었으나 상부유공을 통한 취수량의 구간별 표준편차가 최소로 나타났다. 또한 이 경우에 관내 흐름이 안정적이어서 취수의 효율도 향상되는 것으로 나타났다. 추후 본 연구의 결과를 바탕으로 다양한 조건 및 영향인자에 대한 민감도 분석이 수행된다면 개별 환경에 적합한 최적설계안을 도출하는데 활용될 수 있을 것이라고 생각한다.

• 한국태양에너지학회 논문집
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• 제23권3호
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• pp.15-22
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• 2003

This study deals with the collection of solar energy and its storage in evacuated tubular collector systems for different types of header design, flow passage and heat transfer devices. In order to elicit the most efficient combination of header design, flow passage, heat transfer hardware and operating conditions, a series of tests were done for the four different types of solar collectors utilizing vacuum tubes. The systems studied here either has the evacuated collector tubes with a metal cap on one end or the all-glass evacuated solar collector tubes These evacuated tubular collectors are known to be more efficient than the flat-plate ones in both direct and diffuse solar radiation. Test results show that the system comprised of the all-glass evacuated tubes with U-shaped copper pipes inside outperforms the other configurations. Especially, a rolled copper sheet tightly placed along the inner surface of each inner tube enhances heat transfer between the heated collector surface and the water contained in the U-shaped copper pipe.

• International Journal of Fluid Machinery and Systems
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• 제6권2호
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• pp.75-86
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• 2013

The effects of acoustic resonance and volute geometry on phase resonance are studied theoretically and experimentally using a centrifugal fan. One dimensional theoretical model is developed taking account of the reflection from the discharge pipe end. It was found that the phase resonance occurs, even with the effects of acoustic resonance, when the rotational speed of rotor-stator interaction pattern agrees with the sound velocity. This was confirmed by experiments with and without a silencer at the discharge pipe exit. The pressure wave measurements showed that there are certain effects of the cross-sectional area change of the volute which is neglected in the one dimensional model. To clarify the effects of area change, experiments were carried out by using a ring volute with a constant area. It was demonstrated that the phase resonance occurs for both interaction modes travelling towards/away from the volute. The amplitude of travelling wave grows towards the volute exit for the modes rotating towards the volute exit, in the same direction as the impeller. However, a standing wave is developed in the volute for the modes rotating away from the volute exit in the opposite direction as the impeller, as a result of the interaction of a growing wave while travelling towards the tongue and a reflected wave away from the tongue.

• 한국지열·수열에너지학회논문집
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• 제8권2호
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• pp.36-47
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• 2012

Time-series variation of groundwater temperature in Mongolia shows that maximum temperature is occured from end of October to the first of February(winter time) and minimum temperature is observed from end of April to the first of May(summer time). Therefore ground temperature is s a good source for space heating in winter and cooling in summer. Groundwater temperatures monitored from 3 alluvial wells in Ulaabaatar at depth between 20 and 24 m are $(4.43{\pm}0.8)^{\circ}C$ with average of $4.21^{\circ}C$ but mean annual ground temperature(MAGT) at the depth of 100 m in Ulaanbaatar was about $3.5{\sim}6.0^{\circ}C$. Bore hole length required to extract 1 RT's heat energy from ground in heating time and to reject 1 RT's heat energy to ground in summer time are estimated about 130 m and 98 m respectively. But in case that thermally enhanced backfill and U tube pipe placement along the wall are used, the length can be reduced about 25%. Due to low MAGT of Ulaabaatar such as $6^{\circ}C$, the required length of GHX in summer cooling time is less than the one of winter heating time. Mongolia has enough available property, therefore the most cost effective option for supplying a heating energy in winter will be horizontal GHX which absorbs solar energy during summer time. It can supply 1 RT's ground heat energy by 570 m long horizontally installed GHX.

• 한국수자원학회논문집
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• 제53권9호
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• pp.661-670
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• 2020

최근 지진재해의 규모가 점차 증대됨에 따라 세계적으로 개별 시설물에 대한 내진성능평가와 관련한 연구가 다수 진행되고 있다. 상수도 시스템은 타 기반 시설에 비해 설치범위가 광범위하고 그 구성요소가 다양해 고려할 것이 많아 지진에 대한 안정성을 정확하고 효과적으로 확보하기 힘든 실정이다. 따라서 지진을 대비한 상수도 시스템의 내진성능 평가 방안을 연구하고 개발할 필요가 있다. 지진에 의한 상수도 시스템의 내진성능을 평가하기 위해 지반운동예측식(Ground Motion Prediction Equation, GMPE)이 활용된다. GMPE는 지진 규모 등과 같은 독립변수 와 PGV (Peak Ground Velocity), PGA (Peak Ground Acceleration)와 같은 지반운동 등을 고려하여 산정하게 된다. 우리나라에서 발생된 높은 강도의 지진 데이터는 현재까지 많이 축적되지 않아 특정 지진에 국한된 데이터를 활용하여 GMPE를 결정하는 등의 연구가 진행되었다. 본 연구에서는 우리나라에서 계측된 지진 데이터를 활용하여 국내 지진 모의에 적합한 GMPE를 선정하고자 하였으며, 이를 위해 기존 국내 지진을 기반으로 산정된 GMPE식을 분석하고 그 결과를 제시하였다. 본 연구를 통해 결정된 적정 GMPE는 상수도관망의 수리학적 내진성능 평가에 직접적으로 활용 가능하다. 즉, 파손확률 모형과의 연계를 통한 지진시 관로 파손률의 정량화가 가능하며, 파손 및 누수에 의한 단수지역 파악 등과 같은 피해범위 산정시 보다 객관적이며 합리적인 결과 도출이 가능하다. 최종적으로 이와 같은 내진 성능 정량화 결과는 지진재해가 발생하였을 경우 그 피해를 최소화할 수 있는 최적 복구방안 마련과 선제적 관망 내진설계의 기준 자료로 활용될 수 있다.

• 청정기술
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• 제2권2호
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• pp.51-59
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• 1996

Billions of tons of industrial waste are generated annually in industrialized countries. Managing and legally disposing of these wastes costs tens to hundreds of billions of dollars each year, and these costs have been increasing rapidly. The escalation is likely to continue as emission standards become even more stringent around the world. In the face of these rapidly rising costs and rapidly increasing performance standards, traditional end-of-pipe approaches to waste management have become less attractive. The most economical waste management alternatives in many cases have become recycling of the waste or the redesign of chemical processes and products so that wastes are prevented or put to productive use. These strategies of recycling or reducing waste at the source have collectively come to be known as pollution prevention. The engineering challenges associated with pollution prevention are substantial. This presentation will categorize the challenges in three levels. At the most macroscopic level, the flow of materials in our industrial economy, from natural resource extraction to consumer product disposal, can be redesigned. Currently, most of our raw materials are virgin natural resources that are used once, then discarded. Studies in what has come to be called industrial ecology examine the material efficiency of large-scale industrial systems and attempt to improve that efficiency. A second level of engineering challenges is found at the scale of individual industrial facilities, where chemical processes and products can be redesigned so that waste is reduced. Finally, on a molecular level, chemical synthesis pathways, combustion reaction pathways, and other material fabrication procedures can be redesigned to reduce emissions of pollution and unwanted by-products. All of these design activities, shown in Figure 1, have the potential to prevent pollution. All involve the tools of engineering, and in particular, chemical engineering.

• 상하수도학회지
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• 제35권2호
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• pp.121-133
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• 2021

This study set up the estimates of leakage management efficiency evaluation and leakage management goal that could be used in local water distribution networks efficiency business and modernization business. The data were analyzed using data envelopment analysis and multiple regression analysis. To this end, with leakage management input indices concerning leakage reduction activities (e.g., aged pipe replacement, water meter replacement, leakage restoration, and leakage detection) and leakage management calculation indices (e.g., the increase of revenue water ratio and the reduction of leakage ratio), the data on 22 K-water consignment local water supply systems were analyzed for the years from 2004 through 2018. Using the results of efficiency analysis by data envelopment analysis, the other DMUs (Decision Making Unit) benchmarked the DMU with the highest efficiency to maximize the leakage management efficiency for all DMUs. Through this, leakage management goal estimates were drawn with the input indices of four leakage reduction activities and calculation indices of the increase of revenue water ratio and the reduction of leakage ratio by multiple regression analysis for each group based on the revenue water ratio and leakage ratio. The correlation coefficients of the leakage management goal estimate for the criteria for the revenue water ratio amounted to 0.553 and 0.771. The correlation coefficients of the leakage management goal estimate for the criteria for leakage ratio were 0.397 and 0.865. Accordingly, we estimated the quantity and priority of four leakage reduction activities for the target leakage ratio and revenue water ratio.

• Ocean Systems Engineering
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• 제2권2호
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• pp.99-113
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• 2012

Steel Catenary Risers (SCR) are the simplest and often the most economic solution compared to other riser types such as flexible pipe, riser towers, top tensioned risers, etc. The top of a SCR is connected to the host platform riser porch. The other end of the SCR connects to flowlines from subsea wells. The riser touchdown point (TDP), which is the location along the riser where contact with the sea floor first occurs, exhibits complex behaviors and often results in compression and fatigue related issues. Heave dynamic responses of semisubmersibles in extreme and operating sea states are crucial for feasibility of SCR application. Recent full field measurement results of a deep draft semisubmersible in Hurricane Gustav displayed the considerable discrepancies in heave responses characteristics between the measured and the simulated results. The adequacy and accuracy of the simulated results from recognized commercial software should be examined. This finding raised the awareness of shortcomings of current commercial software and potential risk in mega investment loss and environmental pollutions due to SCR failures. One main objective of this paper is to attempt to assess the importance and necessity of accounting for viscous effects during design and analysis by employing indicator of viscous parameter. Since viscous effects increase with nearly third power of significant wave height, thus newly increased metocean criteria per API in central Gulf of Mexico (GoM) and even more severe environmental conditions in Western Australia (WA) call for fundamental enhancements of the existing analysis tools to ensure reliable and robust design. Furthermore, another aim of this paper is to address the impacts of metocean criteria and design philosophy on semisubmersible hull sizing in WA and GoM.