태백산맥 풍하측 대기 물뜀 발생에 관한 수치 실험

이재헌(Jaeheon Lee),강성락(Song-lak Kang) 한국방재학회 2022 한국방재학회논문집 Vol.22 No.6

태백산맥 풍하측 대기 물뜀에 대한 큰 에디 모사는 온난이상 이류와 음의 와도 대기 역류를 잘 보여주었다. 대기 물뜀은 상층 대기를 하층 대기로 유입한다. 모의된 물뜀 발생은 장애물의 유효 고도와 폭의 함수로 정리될 수 있었다: â > 10에 대해 ĥ ≥ 0.74, 이는 장애물의 고도와 폭으로 정의된 프루드 수로 Fra < 0 .1에 대해 Frh ≤ 1.35에 해당한다. 수치 실험에서, 부력 진동수(N) = 0.009 s-1에 대해 풍상측 평균 바람(U) ≤ 12 ms-1일 때 물뜀이 발생하였다. 물뜀 현상이 발생할 때 풍속은 30분 내외로 급격한 상승을 보였고, 초기 풍속이 강할수록 보다 강한 온난이상과 돌풍이 발생하였다. 본 연구는 산불 발생환경 조성 측면에서 대기 물뜀 현상을 이해하고, 이를 장애물 폭과 장애물 높이를 사용한 프루드 수의 함수로 설명하였다. 결과적으로 대기는 물뜀 현상이 발생할 시 보다 산불에 취약한 대기 환경을 형성할 수 있었고, 프루드 수의 함수로는 대기 물뜀과 관련된 산악파 파쇄가 잘 설명될 수 있었다. Large-eddy simulation of the lee-side hydraulic jump at the downwind side of the Taebaek Mountains demonstrates the advection of a warm anomaly and the atmospheric reverse roller of negative vorticity. The lee-side hydraulic jump entrains the upper-level atmospheric air into the lower-level atmosphere. The simulated lee-side hydraulic jump occurs under the following conditions on the effective height ĥ and width â of an obstacle: ĥ ≥ 0.74 for â > 10, which are equivalent to Frh ≤ 1.35 for Fra < 0 .1, where Frh and Fra are the Froude numbers defined in terms of the height and width of the obstacle, respectively. In detail, the hydraulic jump occurs when the upwind-side mean wind (U) ≤ 12 ms- 1 for the buoyancy frequency (N) = 0.009 s- 1. The wind speed dramatically increases within the 30-minute period when the hydraulic jump occurs. The stronger upwind causes a warmer anomaly and stronger downslope wind gust. This study situates the atmospheric hydraulic jump phenomenon with regard ro wildfire occurrence, and describes it using the Froude number for the width and height of the obstacle. It is shown that a more vulnerable atmospheric environment can be formed when the hydraulic jump occurs, and the wave-breaking of mountain waves related to the hydraulic jump can be predicted by the Froude number.

Estimation of the Change Point in VSS X Control Charts

Lee, Jaeheon,Park, Changsoon 한국통계학회 2003 Communications for statistical applications and me Vol.10 No.3

Knowing the time of the process change could lead to quicker identification of the responsible special cause and less process down time, and it could help to reduce the probability of incorrectly identifying the special cause. In this paper, we propose a maximum likelihood estimator of the process change point when a Shewhart $\bar{X}$ chart with variable sample size (VSS) scheme signals a change in the process mean. Also we build a confidence interval for the process change point by using the likelihood function.

Statistical Process Control Procedure for Integral-Controlled Processes

Lee, Jaeheon,Park, Cangsoon 한국통계학회 2000 Communications for statistical applications and me Vol.7 No.2

Statistical process control(SPC) and engineering process control(EPC) are two strategies for quality improvement that have been developed independently. EPC seeks to minimize variability by adjusting compensatory variables in order to make the process level close to the target, while SPC seeks to reduce variability by monitoring and eliminating causes of variation. One purpose of this paper is to propose the IMA(0,1,1) model as the in-control process model. For the out-of-control process model we consider two cases; one is the case with a step shift in the level, and the other is the case with a change in the nonstationarity. Another purpose is to suggest the use of an integrated process control procedure with adjustment and monitoring, which can consider the proposed process model effectively. An integrated control procedure will improve the process control activity significantly for cases of the proposed model, when compared to the procedure of using either EPC or SPC, since EPC will keep the process close to the target and SPC will eliminate special causes.

The Estimation for the Expected Cost Function in Automatic Process Control

Lee, Jaeheon 광주대학교 1996 産業技術硏究 Vol.7 No.-

자동공정관리의 목적은 품질특성치가 가능한 한 목표치에 근접하게 유지하도록 공정을 관리하는데 있다. 이러한 자동공정관리의 절차는 기대비용함수를 최소화하도록 설계되기 때문에, 기대비용함수의 추정에 관하여 많은 연구가 되어지고 있다. 본 논문에서는 간단하면서 개선된 기대비용함수의 추정식을 제안한다. 모의실험으로 이 추정식의 정확성을 비교한 결과, 제안된 추정방법은 기대비용함수를 추정하는데 있어서 충분히 좋은 결과를 주는 것으로 나타났다. The purpose of automatic process control(APC) is to regulate the process under study and to keep the quality characteristic to be as close to its target as possible. Because procedures for APC were designed to minimize the overall expected cost, many estimation methods for the expected cost function have been studied. In this paper, a simple and improved approximation method for this function is proposed. From simulation studies, it may be noted that the proposed method gives good performances in estimating the expected cost function.

Internal impingement of the shoulder in sports activity: common overuse injury

Jaeheon Lee,Hwa Pyung Kim,Min Soo Shon 대한정형외과 스포츠의학회 2023 Arthroscopy and Orthopedic Sports Medicine Vol.10 No.2

Sports-related shoulder injuries are a common condition and are particularly prevalent as an overuse injury caused by repeated microtrauma. This study aimed to provide updated information on pathophysiology, clinical diagnosis, effective treatment, and the importance of preventing internal impingement of the shoulder as a common overuse shoulder injury. Current literature indicates multiple factors that can contribute to developing internal impingement, including anatomical, biomechanical, and other pathologic lesion-associated factors. Internal impingement is diagnosed based on a thorough patient history and physical examination. Magnetic resonance imaging is a gold standard imaging to confirm the diagnosis and rule out other causes of shoulder pain. Treatment, and especially, shoulder internal impingement rehabilitation in athletes should be comprehensive, integrative, and systematic. The best way to prevent internal impingement is to strengthen and stretch the rotator cuff muscles and avoid overhead activities that cause pain. The first-line treatment option is nonsurgical treatment, while patients with more severe symptoms may require surgical treatment.

A VSR Χ￣ Chart with Multi-state VSS and 2-state VSI Scheme

Lee, Jaeheon,Park, Changsoon 한국품질경영학회 2004 품질경영학회지 Vol.32 No.4

Variable sampling interval (VSI) control charts vary the sampling interval according to value of the control statistic while the sample size is fixed. It is known that control charts with 2-state VSI scheme, which uses only two sampling intervals, give good statistical properties. Variable sample size (VSS) control charts vary the sample size according to value of the control statistic while the sampling interval is fixed. In the VSS scheme no optimal results are known for the number of sample sizes. It is also known that the variable sampling rate (VSR) X￣ control chart with 2-state VSS and 2-state VSI scheme leads to large improvements in performance over the fixed sampling rate (FSR) X￣ chart, but the optimal number of states for sample size is not known. In this paper, the VSR X￣ charts with multi-state VSS and 2-state VSI scheme are designed and compared to 2-state VSS and 2-state VSI scheme. The multi-state VSS scheme is considered to achieve an additional improvement by switching from the 2-state VSS scheme. On the other hand, the multi-state VSI scheme is not considered because the 2-state scheme is known to be optimal. The 3-state VSS scheme improves substantially the sensitivity of the X￣ chart especially for small and moderate mean shifts.

Development of non-woven carbon felt composite bipolar plates using the soft layer method

Lee, Dongyoung,Choe, Jaeheon,Nam, Soohyun,Lim, Jun Woo,Choi, Ilbeom,Lee, Dai Gil ELSEVIER (APPLIED SCIENCE) 2017 COMPOSITE STRUCTURES -BARKING THEN OXFORD- Vol.160 No.-

<P><B>Abstract</B></P> <P>Carbon fiber reinforced polymer composites are ideal substitutes for brittle graphite for electrically conductive bipolar plates because of their high mechanical property and productivity. Early composite bipolar plates suffered from high electrical contact resistance due to the resin-rich area formed on the surface. To decrease the electrical contact resistance, the “soft layer method” was developed, which exposed bare carbon fibers on the composite surface. This method significantly improved the electrical as well as mechanical properties of composite bipolar plates. The remaining problem for wider commercialization of composite bipolar plates is their high fabrication pressure.</P> <P>In this work, a non-woven carbon felt composite bipolar plate was developed to obtain improved electrical properties with low fabrication pressure. The soft layer method was also used to expose bare carbon fibers. Compared to conventional high fiber volume fraction composite bipolar plates, the developed bipolar plate exhibited superior electrical properties.</P>

궤간가변 철도차량의 곡선주행 시 피로특성

이재헌(Jaeheon Lee),강용수(Yongsoo Kang),장승호(Seungho Jang),구정서(Jeongseo Koo),김현규(Hyungyu Kim),정성균(Seongkyun Cheong) 한국자동차공학회 2007 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

In the present paper, to evaluate the stability of curve travelling gauge-variable system which is in the process of developing, gave the lateral force which was operating on locker and the wheel fitting holder. The stress analysis had accomplished by load past record which obtains from UIC code-518. And the stress analysis had accomplished on condition of broad gauge and the standard gauge. From the resultant which evaluate fatigue life with finite element method. fatigue life which evaluates on low temperature sees increased from normal temperature. From above results, we know that the fatigue life on normal temperature and low temperature was finite. And we will be able to decide the duration of maintenance with these results.

하이브리드 자동차의 효율적 배기열회수시스템 개발을 통한 연비 개선

이재헌(Jaeheon Lee),온형석(Hyungseok Ohn),최재형(Jaeyoung Choi),김석준(Seokjoon Kim),민병순(Byungsoon Min) 한국자동차공학회 2011 한국자동차공학회 학술대회 및 전시회 Vol.2011 No.11

Since the propulsion systems of vehicle have changed from a single energy source based on conventional internal combustion engine to hybrid system including more electrical system such as full type of hybrid electric vehicle or plug-in hybrid electric vehicles, a new transition associated with vehicle thermal management arises. The success of improved fuel economy is the proper integration of thermal management components which are appropriately performed to reduce friction and wasted energy. The thermal management systems of vehicle are able to balance the multiple needs such as heating, cooling, or appropriate operation within specified temperature ranges of propulsion systems. More efficient thermal management systems are required to improve the fuel economy in the hybrid electric vehicles because of the driving of electric traction motor and the increase of engine off time. The decrease of engine operation time may not sustain the proper temperature ranges of engine and gearbox. As an engine starts at low ambient temperature, heat from the wasted heat of exhausted gas can be supplied to engine and gearbox at initial warm-up. This research describes the one of cost effective thermal management solutions recovering exhaust gas heat exchanging system with coolant and gear box oil simultaneously. It is more advantageous to increase the temperature of the engine oil or gear box oil rather than to increase the coolant temperature. Consequently, the experimental result of this system improved 2.5% of fuel economy at UDDS drive cycles. The main benefit using exhaust gas heat recovery system is fuel economy improvement. However, to practically apply recent thermal management technologies in commercial use, not only improved performance for the low energy density but also cost in a viable vehicle package are necessary in general. Developed exhaust gas heat recovery system of integrated heat exchanger type is 6 times more competitive than coolant only type’s and more effective solution than Rankine cycle type’s in passenger vehicle.

Sedflume을 이용한 armor layer의 수리학적 안정성 평가

이제헌(Jaeheon Lee),최용주(Yongju Choi),이아름(Aleum Lee) 대한환경공학회 2021 대한환경공학회 학술발표논문집 Vol.2021 No.11