• 신재생에너지
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• 제3권4호
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• pp.22-30
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• 2007

An expansion device plays an important role in optimizing the heat pumps by controlling refrigerant flow and balancing the system pressures. Conventional expansion devices are being gradually replaced with electronic expansion valves due to increasing focus on comfort, energy conservation, and application of a variable speed compressor. In addition, the amount of refrigerant charge in a heat pump is another primary parameter influencing system performance. In this study, the flow characteristics of the expansion devices are analyzed, and the effects of refrigerant charge amount on the performance of the heat pump and the variation of compressor speed are investigated at various operating conditions. Mass flow rate through capillary tube, short tube orifice, and EEV was strongly dependent on the upstream pressure and subcooling. The heat pump system is very sensitive with a variation of refrigerant charge amount. The performance of it can be optimized by adjusting the flow rate through expansion device to maintain a constant superheat at all test conditions.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.1093-1098
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• 2007

In designing the high-speed railroad track, it is important to utilize appropriate track components to maintain uniform stiffness and ensure track alignment within the tolerance set for that system. In this regard, continuous welded rails (CWRs) were introduced to the Korean railways. Yet the installation of CWRs can result in an adverse impact due to the track/structure interaction on bridge sections yielding variations in the stiffness at the expansion joints. It may also impose additional axial force, generate excessive stress or deflection on track, and loosen the ballast at the ends as a bridge deck contracts or expands owing to a thermally-induced dynamic response. The risk is even greater in a long bridge deck, resulting in track longitudinal irregularities, deteriorating passenger's comfort, and increasing maintenance efforts. This study evaluates the performance of ZLR and their impact on track longitudinal irregularities through the track measuring results on a test section installed the ZLR in order to minimize the thermally-induced responses and the maintenance efforts for the high speed railway bridges.

• 대한조선학회논문집
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• 제41권3호
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• pp.60-71
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• 2004

Nowadays, We have had a growing interest in high-speed vessels' because it is very important to save time and cost in marine transportation. The development of hull form for high-speed vessels is high priority to secure the competitive power for the transportation of cargos. Therefore, the demand of the high-speed vessels is gradually increased, but the conventional hull forms are limited by rapidly increasing resistance upon the increase of ship speed in high-speed region. Therefore, new concepts for the hull form of high-speed vessels have been requested. One of the derived hull forms for that demand is the hull form of trimaran type. Trimaran has a very slender main hull as compared with conventional single hull so that is reduced in wave resistance. The slender main hull has the undesirable characteristics of stability, but two side hulls make up for the week points in the stability. That is, trimaran is able to have desirable performances for the resistance and stability. In this paper, for the design of 200TEU class container vessel with trimaran type, which will be cruised in Yellow-Sea region, firstly a preliminary hull is designed, and the model test is carried out with the variation of side hull position. From the experience of the preliminary hull form design, an improved hull form for the 200TEU container are designed, and the model tests are carried out. Also, a numerical computation technique is adopted for the simulation of flow phenomena around the designed hull forms. The final hull form is compared with existing ships for the resistance performance from the computation with computer and ship model tests.

• 한국컴퓨터정보학회논문지
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• 제25권7호
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• pp.1-8
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• 2020

본 논문에서는 군용시험장비로 개발된 시험용 영상생성/수집 장치에 XDMA를 활용하여 고속 이미지 데이터 전송을 구현한다. 본 연구에서 제안하는 기술은 커널영역에서 시스템버퍼를 사용하여 데이터를 복사하는 방법을 FPGA내 DMA 엔진을 통한 송수신으로 대체하여 효율성을 얻는다. 본 연구를 위해 장치는 Life Cycle을 고려하여 PXIe 플랫폼으로 개발하였으며, 양산성을 고려하여 저가의 FPGA를 활용하여 퍼포먼스를 최대화하였다. 본 논문에서 구현한 영상입출력보드는 기존의 메모리복사방식을 통해 AXI 인터페이스 클럭 주파수, 링크속도를 변경하여 시험하였다. 그리고 FPGA의 DMA 엔진을 사용하여 보드를 구성하였으며, 그 결과 전송속도는 기존의 5~8Hz에서 140Hz로 증가함을 확인하였다. 제안된 방법은 PXIe 플랫폼을 이용한 장치개발의 비용절감, 기술수준을 높여 국방력 강화에 기여할 것이다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 추계학술대회논문집
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• pp.256-259
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• 2004

In the present study, AZ31B sheets has a bad formability in room temperature, but the formability is improved significantly as increasing the temperature because of rolled magnesium alloy sheet has a hexagonal closed packed structure (HCP) and a plastic anisotropy. In this paper, after tensile test in various temperatures, strain rate, show the tensile mechanical properties, yield and ultimate strength, K-value, work hardening exponent(n), strain rate sensitivity(m). As temperature increased, yield, ultimate strength and K-value, work hardening exponent(n) are decreased but strain rate sensitivity(m) is increased. As cross-head-speed increased, yield, ultimate strength and K-value, work hardening exponent(n) are increased. And according to the temperature, how change the plastic anisotropy factor R. In addition, we observed how temperatures and cross-head-speed effect on microstructure.

• 수산해양기술연구
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• 제36권4호
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• pp.274-280
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• 2000

본 연구는 실습선에서 사용 중인 6폭짜리 저층트롤 어구의 저항을 끌줄의 길이와 예망 속도별로 분석하기 위하여 그물의 저항과 전개판의 저항을 계측하고, 어구의 저항계수를 산정하였으며, 그 결과를 요약하면 다음과 같다. 1. 시험 어구의 저항은 끌줄의 길이가 길수록 증가하나, 저항 R$\sub$t-w/=3800v$^2$으로 대표할 수 있다. 2. 그물 어구의 저항은 끌줄의 길이에 따라 다소 증가하나, 그물 어구의 저항 R$\sub$n/=10R$\sub$n/=10d/lλ$\sub$a/λ$\sub$b/v$\^$1.3/의 식으로 대표할 수 있다. 3. 시험 어구의 전개판의 저항 R$\sub$b/=1810v$\^$0.8/으로 대표할 수 있다. 4. 끌줄의 길이별로 측정된 저항값과 Koyama의 저항식과 비교하면, 예망속도가 작을 때는 시험 어구의 저항이, 예망속도가 클 때는 Koyama의 저항식에 의한 저항값이 크게 나타났다.

• 대한임베디드공학회논문지
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• 제6권3호
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• pp.139-148
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• 2011

As the architecture of automotive software is complicated and LOC of software increases, there is an increasing demand for standard operating system. OSEK/VDX defines an industry standard for automotive operating system and middleware. This paper introduces an implementation of RTOS(OSCAR-OSEK) based on OSEK/VDX standard. For better speed of scheduling, we suggest a new method for ready queue implementation considering the characteristic of automotive application software. Also we introduce a method for improving the portability of RTOS on various MCUs. And, we show OSCAR-OSEK implementation and performance test results.

• Journal of Biosystems Engineering
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• 제34권6호
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• pp.411-419
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• 2009

This study was carried out to develop a shredding-burying machine for application of gramineae green manure crops that were tall and had high biomass yield such as sudan grass and rye. We made a prototype to operate both shredding and burying concurrently to attach at middle-sized tractors. Field tests were performed with the prototype to treat rye and sudan grass. The test results showed that the average cutting length became shorter and the quantity of entwined stem became obviously decreased when the PTO shaft speed was fast and running speed was slow. Also, We found, when the cut stem length became shorter, the burying ratio became more increasing and the PTO power requirement became more decreasing. Working efficiency of the prototype was better than conventional Rotary. The test results for treating rye/sudan grass with prototype showed that average cutting length was 21.2/22.5 cm and burying ratio was 98.4/98.1% when the PTO shaft speed was 1,000/1,000 rpm and running speed was 0.25/0.17 m/s. Also, the working performance of the prototype was 0.79 and 1.14 h/10 a for rye and sudan grass, respectively. Finally, we found that the prototype of shredding-burying machine was better for labor than conventional method that required at least 3 times bigger tractor.

• 한국재료학회지
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• 제15권12호
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• pp.824-828
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• 2005

In this study the effect of the content of $TiB_2$ on wear properties was investigated. $Cu-TiB_2$ composites have been fabricated by hot extrusion. Sliding wear tests were peformed by a pin-on-disk type wear test machine under dry condition and loads varied with from 20N to 80N at sliding speed 3.5Hz. The test results showed that the wear losses and the friction coefficients decreased with increasing $Cu-TiB_2$ volume fraction and increasing the size of $Cu-TiB_2$ particle. Wear property of $10{\mu}m,\;5 vol\%\; TiB_2$ specimen was excellent all of the wear specimens. It is thought that the increase of plastic flow resistivity due to uniform distribution of $10{\mu}m,\;5 vol\%\; TiB_2$ wear specimen would improve wear property. The worn surface and wear debris were examined by optical microscope and scanning electron microscope.

• Tribology and Lubricants
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• 제36권6호
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• pp.332-341
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• 2020

High-speed turbomachinery implements gas foil bearings (GFBs) due to their distinctive advantages, such as high efficiency, lesser part count, and lower weight. This paper provides the test results of the static structural stiffnesses and loss factors of bump-type foil thrust bearings with increasing preload and bearing deflection. The focus of the current work is to experimentally quantify variability in structural stiffnesses and loss factors among the four test thrust bearings with identical design values and material of the bump and top foil geometries using the same (open-source) fabrication method. A simple test setup, using a rigidly mounted non-rotating shaft and thrust disk, measures the bearing bump deflections with increasing static loads on the test bearing. The inner and outer diameters of the test bearings are 41 mm and 81 mm, respectively. The loss factor, best-representing energy dissipation in the test bearings, is estimated from the area inside the local hysteresis loop of the load versus the bearing deflection curve. The measurements show that structural stiffnesses and loss factors of the test bearings significantly rely on applied preloads and bearing deflections. Local structural stiffnesses of the test bearings increase with applied preloads but decrease with bearing deflections. Changes of loss factors are less sensitive to applied preloads and bearing deflections compared to those of structural stiffnesses. Up to 35% variability in static load structural stiffnesses is found between bearings, while up to 30% variability in loss factors is found between bearings.