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Effect of cooling flow on thermal performance of a gas foil bearing floating on a hot rotor
심규호,이용복,송진우,김태호 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.5
This paper presents the measurements of the thermal behavior of a gas foil bearing (GFB) floating on a hot rotor in a tangential air injection cooling scheme. The cooling air was tangentially injected against rotor spinning into the inlet mixing zone of the test GFB. The hollow rotor was heated by a cartridge heater. The GFB temperatures were measured at intervals of 30 deg along the circumference of the axial center except for at 45 deg, where the cooling flow is injected. The rotor temperatures were measured near the GFB side ends using an infrared thermometer, which was calibrated with a thermocouple. Load cells measure the static load and bearing torque. The baseline rotor temperature was measured without GFB over the axial length at rotor speeds up to 15 krpm and for increasing heater temperatures up to 400 °C. The results showed relatively uniform rotor temperatures at the test journal GFB section, and severe heat convections on the rotor surfaces. The GFB and rotor temperatures were measured under a static load of 80 N for increasing heater temperatures of 100 °C, 200 °C, 300 °C and 400 °C and with increasing cooling flow rates of 100 liter/min, 150 liter/min, and 200 liter/min. The circumferential GFB temperatures showed the maximum temperatures at the loaded zone and the minimum temperatures in the unloaded zone. The increasing cooling flow effectively reduced both the rotor and GFB temperatures, showing a dramatic decrease with the smallest amount of cooling flow. GFB friction torque was measured for two test cases for the static load of 80 N at a rotor speed of 10 krpm:1) A lift-off and touch-down operating cycle for increasing heater temperatures without the cooling flow, and 2) a continuous operation for the heater temperature of 400 °C with increasing cooling flows. In test case 1, the GFB friction torque decreased for higher heater temperatures due to a larger thermal expansion of the bearing housing than the rotor’s. In test case 2, the GFB friction torque decreased with increasing cooling flows due to strong cooling effects on the rotor temperature. The results imply that the tangential air injection increased the GFB clearance by directly cooling the rotor and effectively alleviating the rotor expansion; hence, the scheme is capable of an effective cooling for high temperature GFB applications, such as micro gas turbines.
효율적 디버깅을 위한 디자인 체크포인트 기반 시뮬레이션 방법
심규호,김남도,박인학,민병언,양세양,Shim, Kyu-Ho,Kim, Nam-Do,Park, In-Hag,Min, Byeong-Eon,Yang, Sei-Yang 한국정보처리학회 2012 정보처리학회논문지 A Vol.19 No.3
디지털시스템 설계에 대한 HDL 시뮬레이션을 통한 검증 과정에서는 설계에 대한 분석 및 디버깅을 위하여 설계에 존재하는 수많은 신호선들에 대하여 시뮬레이션 실행 중에 시그널 덤핑을 통한 가시도 확보가 필요하게 된다. 그러나 이와 같은 시그널 덤핑은 일반적으로 시뮬레이션의 속도를 크게 떨어뜨리는 문제점을 가지고 있거나, 시뮬레이션의 실행 횟수를 늘리는 문제점을 초래한다. 본 논문에서는 디자인 체크포인트를 활용하여서 시그널 덤핑을 효율적이며 신속하게 수행하는 시뮬레이션 방법을 제시하고, 이를 시스템반도체급의 대규모 회로인 산업체 설계들에 적용하여 제안된 방법이 효과적임을 확인하였다. The visibility for signals in designs is required for their analysis and debug during the verification process. It could be achieved through the signal dumping for designs during the execution of HDL simulation. However, such signal dumping, in general, degrades the speed of simulation significantly, or can result in the number of simulation runs. In this paper, we have proposed an efficient and fast simulation method for dumping based on the design checkpoint, and shown its effectiveness by applying it to industrial SOC designs.