The research aimed to develop a high-efficiency plate-type heat exchanger for exhaust gas using computational fluid dynamics (CFD) thermal analysis based on the plate shape, and to identify the optimal shape. Following this, a water/air plate heat exchanger was manufactured, and its characteristics were studied experimentally. As the Re number increases on the gas (or air) side, the heat transfer rate increases significantly, whereas an increase in the Re number on the water side leads to a smaller increase in heat transfer. This is attributed to the larger convective heat resistance on the gas side, causing a substantial reduction in gas-side heat resistance as gas velocity increases, resulting in a considerable overall reduction in heat resistance. The fluid flow pressure drop showed similar results between the CFD calculations and experimental outcomes.

본 연구는 온대 낙엽활엽수림의 하층식생 변화를 구명하여 산림생태계의 체계적 보전과 효율적 관리를 위한 기초자료를 제공하기 위하여 수행하였다. 2003년 경기도 포천 광릉 숲에 1ha 크기의 영구조사구를 설치하였으며, 영구조사구는 10×10m 크기의 부조사구 100개로 구성되었다. 영구조사구의 임분동태 및 하층식생은 2003년부터 2018년까지 5년 간격으로 조사되었다. 조사구에 출현하는 관속식물은 56과 128속 176종 18변종 4품종 1아종으로 총 199분류군 이었다. 관목층과 초본층의 종수는 시간이 경과함에 따라 모두 감소하는 경향을 보였다. MRPP-test 분석 결과 관목층의 종조성은 2008년-2013년을 제외한 모든 연도에서 유의한 차이가 있는 것으로 나타났으며, 초본층의 경우 모든 연도에서 유의한 차이가 있는 것으로 나타났다. 평균 중요치에서 관목층은 참회나무(18.23%), 당단풍나무(16.48%), 작살나무(13.85%)가 우점하는 것으로 분석되었으며, 초본층에서는 단풍취(23.41%), 애기나리(9.45%), 주름조개풀(5.62%)이 우점하는 것으 로 나타났다. 관목층은 상층 임분의 흉고단면적과 임분밀도가 높을수록 청미래덩굴, 청괴불나무, 고광나무의 풍부도가 높았으며, 흉고단면적과 임분밀도가 낮을수록 당단풍나무, 물참대, 산뽕나무, 산딸나무의 풍부도가 높았다. 시간이 경과 할수록 흉고단면적과 임분밀도는 초본층에 미치는 영향이 적은 반면, 관목층의 참회나무와 당단풍나무의 피도는 초본층 종 구성에 미치는 영향이 큰 것으로 분석되었다. 결론적으로 광릉 장기생태조사지의 하층은 종수가 지속적으로 감소하고 있으며, 이 과정은 상층 임분의 종다양성과 흉고단면적, 임분밀도가 하층식생 종조성에 영향을 주는 것으로 판단되었다.

유사한 시기에 조사된 다른 위도의 저서성대형무척추동물 군집 구조의 시공간적 차이를 비교한 결과, 평창 조사지역에서는 3문 5강 12목 44과 69분류군 13,042개체, 완도 조사지역에서는 4문 5강 12목 37과 52분류군 8,887개체가 채집되었다. 평창이 완도보다 다양도와 균등도 또한 높게 나타났다. 우점종은 평창에서는 두점하루살이로 나타났고, 완도에서는 길쭉하루살이로 서로 달랐다. 집괴 분석 결과 평창과 완도 조사지역의 군집 특성이 명확하게 나누어졌으며 지역 내에서는 대체로 계절성의 영향이 컸다. 지표종 분석에서는 총 4종의 지표종이 선정되었으며 대체로 해당 조사시기 및 지점에만 나타난 종이 선정되었다. 기능적 군집으로는 주워 먹는 무리인 깔따구류를 제외하였을 때 평창 조사지점에서는 긁어먹는 무리가 가장 많았다. 완도 조사지점에서는 주워 먹는 무리가 가장 많았으며 평창 조사지역에 비해 걸러먹는 무리의 비율이 더 높았다. 군집 온도지수 산출 결과 평창이 9.8℃, 완도가 11.0℃으로 평창의 군집이 더 낮은 온도를 선호하는 것으로 나타났다. 이는 서식지 온도 특성이 저서성대 형무척추동물 군집 구성에 크게 영향을 미치고 있음을 반영해 주었다.

본 연구는 일본잎갈나무림의 벌채유형을 대조구, 보잔목작업구, 모수작업구, 군상개벌작업구, 대상개벌작업구로 구분하여 벌채 처리 전·후의 하층식생 변화를 분석하기 위해 수행되었다. 경북 봉화 지역에서 2014년부터 2016년까지 벌채유형별로 각 9개씩 총 45개 조사구를 대상으로 방형구법을 이용하여 하층식생을 조사하였다. 군상개벌작업구의 총 피도가 지속적으로 높게 나타났으며, 벌채를 실시한 처리구에서는 광선호성 종들이 우점하고 있는 것으로 나타났다. 보잔목작업구와 군상개벌작업구, 대상개벌작업구에서는 노출된 임분에 잘 적응하는 소형지상식물 (Microphanerophyte)의 비율이 가장 높게 나타났으며, 이는 지속적으로 증가할 것으로 판단되었다. 종조성 변화에서는 다른 처리구들과 다르게 보잔목작업구가 가장 큰 변화를 보인 것으로 나타났다. 처리구 간 분석 결과, 대조구와 군상개벌작업구의 두 처리구 간 종조성 차이는 이질적인 것으로 나타났다. 결론적으로, 일본잎갈나무 조림지에서 수행한 4가지 벌채 처리는 모두 대조구에 비해 식물다양성이 증가하는 경향을 보였다. 그러나, 하층식생의 발달 뿐 만 아니라 일본잎갈나무의 천연갱신을 유도하기 위해서는 5년∼7년의 결실주기를 가진 일본잎갈나무 특성상, 지속적인 모니터링 연구가 필요할 것으로 판단된다.

Headwater streams provide various microhabitats, resulting in high diversity of macroinvertebrate community. In this study, we compared the differences of communities between two adjacent headwater streams (Jangjeon stream (GRJ; GRJ1-GRJ5) and Haanmi stream (GRH; GRH1-GRH3)) in Jungwang and Gariwang mountains, Gangwon-do and evaluated the effects of habitat condition to the macroinvertebrates community composition. In order to characterize the macroinvertebrate communities and extract influential environmental factors, we applied to Cluster analysis (CA), Indicator species analysis and Non-metric multidimensional scaling (NMDS). Total 33,613 individuals in 3 phyla, 5 classes, 13 orders, 51 families, and 114 taxa (genera or species) were collected. Gammarus sp. was dominant at the upper stream of GRJ, whereas Chironomidae spp. was abundant at GRH and the downstream of GRJ. The CA classified samples into six clusters (1-6) reflecting spatial and temporal variation of benthic macroinvertebrate communities. Benthic macroinvertebrate community composition was significantly different between two adjacent streams. Sweltsa sp. 1, Psilotreta kisoensis, Rhyacophila shikotsuensis and Serratella setigera were identified as representative indicator species for clusters 1, 2, 3 and 5, respectively. Similar to CA results, NMDS revealed the spatial and temporal differences of benthic macroinvertebrate communities, indicating the difference of community composition as well as microhabitat condition. Forest composition, proportion of boulders (>256 mm), and water velocity were main factors affecting the macroinvertebrate community composition.

Recently, as demand for Electric Car has been increasing, it has been a main factor that maximizing performance and ensuring the stability of the Electric Car battery to increase the reliability of Electric Car. Above all the study on thermal control in a big influence on the performance and battery life is growing in parallel. This study has compared cooling effect of an Electric Car battery between battery with Heat Sink and without Heat Sink for optimum design of Electric Car battery. Battery is simply modeled into four cells, divided into two cases of battery with Heat Sink that attached on the cell's side and without Heat Sink. And this research was conducted on forced convection. The battery which is designed by this way was numerically analyzed by CFX 14.5. Numerical results, revealed that the battery with Heat Sink was superior in terms of cooling effect. According to the numerical analysis by battery cell's temperature variations, the battery with Heat Sink turned out to be superior in cooling effect to the battery without Heat Sink.

Due to the recent advances in technology, the systems are becoming more demanding in terms of functionality and implementation complexity. Therefore, when system failures are involved in such complex systems, the effects of the related safety issues can also be more serious, thereby causing in the worst case irrecoverable hazards on both human being and properties. This fact can be witnessed in the recent rail systems accidents. In general, the accidents can be attributed to the systematic failure or the random failure. The latter is due to the aging or unsatisfied quality of the parts used in implementation or some unexpected external cause that would otherwise result in accidents whereas the former is usually related to incomplete systems design. As the systems are becoming more complex, so are the systematic failures. The objective of the paper is to study an approach to solving the systematic failure. To do so, at first the system design process is augmented by the functional safety activities that are suggested in the standard IEC 61508. Analyzing the artifacts of the integrated process yields the traceability, which satisfies the requirements for reduction of systematic failure as provided in ISO 26262. In order to reduce systematic failure, the results are utilized in the conceptual design stage of systems development in which systems requirements are generated and functional architecture is developed.

Recent trends in rail industry can be characterized by the multifunctionality and very high-speed modes of operations. In particular, the adoption of the unmaned or operatorless operations has been getting increased attention in which case ensuring systems safety is crucial. On the other hand, according to the result of analyzing rail accidents, the human/operator errors have turned out to be one of the key causes of the accidents. Therefore, the effort of improving the work environment of locomotive cabs is quite necessary in order to decrease the accidents. The objective of this paper is studying on how to incorporate the factors related to the train operators in the design of the locomotive cabs and also on how to evaluate the design results obtained, which is subsequently reflected in the generation of the test and evaluation procedure. The approach taken is based on systems engineering, yielding the procedure document as a result. The results obtained in the paper can be useful in confirming the design of locomotive cabs utilizing the domestic human/operator measure. Also, the way of achieving the objectives can be utilized to cover the expanded rail systems development with appropriate design activities added.

Recent technological advances in the domestic railway industry have turned out to deliver a profound impact on the forefront of other industries as well. Furthermore, the introduction of the high-speed railway systems has made it possible to travel around our country in a day, thereby changing our life styles a lot. However, it has been well recognized that many factors can cause unanticipated accidents during the operation. One of the causes is known to be the human errors made by the train operators in locomotive cabs. The problem is getting more serious as the trains run at high speed. As such, the objective of this paper is on how to improve the work environment of the locomotive cabs. Our approach is based on the systems engineering methodology. Specifically, we first identify the context and scope of the problem to be solved. We then continue our effort in deriving the requirements set to accomplish the improvement. These results are utilized in constructing a computer-aided management system for test and evaluation intended for the improvement. The approach taken and the results obtained in this paper is expected to make a contribution on the route to keeping our nation's technologies on the competitive edges in the high-speed railway systems industry.

The work environment of locomotive cabs has long been an important issue in the design of railload systems since it is quite critical in terms of system's operational safety. It is getting more attention as the running speed of the trains goes up these days. To this end, this paper describes how to systematically construct a DB for the requirements set in the course of the improvement process for the aforementioned cab work environment. As a solution approach, we have adopted the requirement architecture concept to cover the whole activities required to do such as in requirements generation, DB construction, change management, and traceability management. Specifically, based on the requirement architecture framework a requirement process to collect requirements for improvement is discussed, and the guide lines are suggested for verification and validation of the developed requirements. In addition, a base schema and requirements templates are developed, which will be used in generating requirements and constructing a DB. Finally, it is demonstrated how the requirements DB for locomotive cabs can be constructed using a computer-aided tool in an integrated fashion.