• Title/Summary/Keyword: 가속율

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Effectiveness of 32-element Surface Coil Array for Accelerated Volume-Targeted Breath-Hold Coronary MRA (체적 지향형 호흡정지 자기공명 조영술의 가속화에 대한 32채널 코일 어레이의 효용성)

  • Lee, Hyun-Yeol;Suh, Jin-Suck;Park, Jae-Seok
    • Investigative Magnetic Resonance Imaging
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    • v.13 no.2
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    • pp.137-145
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    • 2009
  • Purpose : To compare 12 and 32-element surface coil arrays for highly accelerated coronary magnetic resonance angiography (MRA) using parallel imaging. Materials and Methods : Steady state free precession coronary MRA was performed in 5 healthy volunteers at 1.5 T whole body MR scanner using both 12 and 32-element surface coil arrays. Left anterior descending and right coronary artery data sets were acquired for each volunteer. Data sets were sub-sampled for parallel imaging using reduction factors from 1 to 6. Mean geometry factor (g-factor), maximum g-factor, and artifact level were calculated for each of the two coil arrays. Results : Over all reduction factors, the mean and maximum g-factors and artifact level were significantly reduced using the 32-element array compared to the 12element array (P << 0.1). The mean g-factor was sensitive to the imaging orientations of coronary arteries while the maximum g-factor and artifact level were independent of orientation. Conclusion : The 32-element surface coil array significantly improves artifact and noise suppression for highly accelerated coronary MRA using parallel imaging. The increased acceleration factors made feasible with the 32-element array offer the potential to enhance spatial resolution or increase volumetric coverage for 3D coronary MRA.

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The Effects of Air Injection in Compressor Exit on the Response Performance of a Turbocharged Diesel Engine under the Operating Conditions of Rapid Acceleration. (터보과급디젤기관의 급가속 운전시 압축기출구에의 공기분사가 응답성능에 미치는 영향)

  • 박상규;최낙정
    • Journal of Advanced Marine Engineering and Technology
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    • v.24 no.6
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    • pp.110-119
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    • 2000
  • In this paper, an experimental study is carried out under the operating conditions of low speed and rapid acceleration in order to investigate and improve the response characteristics of a turbocharged diesel engine with radial turbine driven by exhaust gas. A rapid acceleration for investigating the response performance is applied to the fuel-pump rack of the engine from 0-10% to 0-40% in steps of 10%, and accelerating time of 1, 2 and 3 seconds is applied to the engine. Further experiment for improving the low speed torque and acceleration performance is also performed by means of injecting air into the inlet manifold at compressor exit during the period of low speed and application of a rapid acceleration. The effects of air injection on the response performance are represented at subjected engine speed with the changes of response performance factors such as air injection pressure, air injection period, accelerating rate, accelerating time and load. From the experimental results obtained throughout this study, it is shown that air injection into the inlet manifold at compressor exit is closely related to the improvement of low speed and acceleration performance of a turbocharged diesel engine.

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Onset of Inertial Oscillation in a Rotating Flow (회전유동에서의 관성진동 원인규명)

  • Park, Jun-Sang
    • Proceedings of the KSME Conference
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    • pp.2536-2539
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    • 2008
  • A study has been made on how to occur inertial oscillations in a rotating flow. The flow is considered to be induced by differentially-rotating top and bottom disks with infinite radius. The top and bottom disks are assumed to be set in motion over a finite initial start-up time duration from initial solid body rotation ($\Omega$) to each finial state, i.e., the top disk is rotating at the angular velocity (${\Omega}+{\Delta}{\Omega}$) and the bottom disk (${\Omega}-{\Delta}{\Omega}$). The system Reynolds number, which is a reciprocal of conventional Ekman number in rotating flows, is very high so that a boundary layer flow near disks is pronounced. From a strict theoretical analysis, it is clearly found the fact that inertial oscillation in a rotating flow is caused by excessive input of torque during start-up phase. Above finding comes from the following physics of theoretical result: in the case of abrupt start-up within very shorter time-duration than spin-up time scale, the inertial oscillation is magnified but it could be completely depressed in the case of mildly accelerated start-up, i.e., start-up process being established over diffusion time scale.

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Study on the effect of Jet Fuel alteration on Turbine Engine Performances through Turbine Engine Test (터빈엔진시험을 통한 제트연료 변경에 따른 엔진성능 변화 연구)

  • Kim, You-Il;Min, Seong-Ki
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.410-415
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    • 2010
  • The engine ground and altitude tests were carried out to investigate the effect of jet fuel alteration on the performance of a small turbojet engine. JP-S was supplied 8% higher than JP-8 by fuel metering system at the same command. The employment of JP-S showed the similar starting characteristic to that of JP-8, however, difference in the ignition time and acceleration rate of engine speed due to the difference of fuel flow rate by fuel metering system was observed. In spite of jet fuel alteration, the test results yield the similar Steady-State engine performance in Net thrust, Air flow, Exhaust Gas Temperature, etc. On the other hand, the Fuel consumption of JP-S increased by 5 % compared with that of JP-8. In point of Specific Fuel Consumption (SFC), SFC of JP-S was approximately 1.1~2.6 %, 5 % higher than that of JP-8 in ground and altitude tests respectively at the same thrust.

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Study on the effect of Jet Fuel alteration on Turbine Engine Performances through Turbine Engine Test (터빈엔진시험을 통한 제트연료 변경에 따른 엔진성능 변화 연구)

  • Kim, You-Il;Min, Seong-Ki
    • Journal of the Korean Society of Propulsion Engineers
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    • v.15 no.2
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    • pp.23-28
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    • 2011
  • The engine ground and altitude tests were carried out to investigate the effect of jet fuel alteration on the performance of a small turbojet engine. JP-S was supplied 8% higher than JP-8 by fuel metering system at the same command. The employment of JP-S showed the similar starting characteristic to that of JP-8, however, difference in the ignition time and acceleration rate of engine speed due to the difference of fuel flow rate by fuel metering system was observed. In spite of jet fuel alteration, the test results yield the similar steady-state engine performance in net thrust, air flow, exhaust gas temperature, etc. On the other hand, the fuel consumption of JP-S increased by 5 % compared with that of JP-8. In point of specific fuel consumption (SFC), SFC of JP-S was approximately 1.1~2.6 %, 5 % higher than that of JP-8 in ground and altitude tests respectively at the same thrust.

Effects of the Temporal Increase Rate of Reynolds Number on Turbulent Channel Flows (레이놀즈 수의 시간 증가율에 따른 난류 채널유동의 변화)

  • Jung, Seo Yoon;Kim, Kyoungyoun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.40 no.7
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    • pp.435-440
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    • 2016
  • Effects of the increase rate of Reynold number on near-wall turbulent structures are investigated by performing direct numerical simulations of transient turbulent channel flows. The simulations were started with the fully-developed turbulent channel flow at $Re_{\tau}=180$, then temporal accelerations were applied. During the acceleration, the Reynolds number, based on the channel width and the bulk mean velocity, increased almost linearly from 5600 to 13600. To elucidate the effects of flow acceleration rates on near-wall turbulence, a wide range of durations for acceleration were selected. Various turbulent statistics and instantaneous flow fields revealed that the rapid increase of flow rate invoked bypass-transition like phenomena in the transient flow. By contrast, the flow evolved progressively and the bypass transition did not clearly occur during mild flow acceleration. The present study suggests that the transition to the new turbulent regime in transient channel flow is mainly affected by the flow acceleration rate, not by the ratio of the final and initial Reynolds numbers.

Performance Evaluation of Sliding Mode Control using the Exponential Reaching Law for a Magnetic Levitation System (자기부상 시스템을 위한 가속율도달법칙기반의 슬라이딩 모드 제어 성능 평가)

  • Moon, Seok Hwan;Lee, Ki Chang;Kim, Ji Won;Park, Byoung Gun;Lee, Min Cheol
    • Journal of Institute of Control, Robotics and Systems
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    • v.20 no.4
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    • pp.395-401
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    • 2014
  • Magnetic levitation systems using the attraction force of electromagnets have many constraints according to the variation of air gap and the nonlinearity of electromagnetic force and inductances. As a result of these constraints, the nonlinear control of a magnetic levitation system has been improved by the latest advanced processors and accurate measurement system which can overcome problems such as many constraints and nonlinearity. This paper concentrates on the modeling of a nonlinear magnetic levitation system and an application of an exponential reaching law based sliding mode controller using the exponential reaching law which is one of the most robust controllers against external unexpected disturbances or parameter fluctuations. Controllability of a magnetic levitation system using the sliding mode control algorithm and robustness against parameter fluctuations have been verified through the experimental results.

The Effect of Electrochemical Performance and Safety by Surface Modification of Anode Materials for Lithium Secondary Battery (리튬 이차 전지를 위한 음극 활물질 표면의 코팅으로 인한 전기화학적 특성 및 안전성)

  • Heo, Yoon-Jeong;Ko, Sung-Tae
    • Journal of the Korean Electrochemical Society
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    • v.12 no.3
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    • pp.239-244
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    • 2009
  • This paper aims to report the effect of surface treatment on graphite and its effect on the improvement of $Al_2O_3$ and $nano-Li_4Ti_5O_{12}$. The structure and property of surface treatment on graphite were determined by scanning electron microscopy, transmission electron microscopy and electrochemical property and safety were determined by charge/discharge cycler, accelerating rate calorimeter. The composite with different metallic oxide exhibited the first efficiency of 82.5% and specific capacity of 350 mAh/g. Although the composite showed same efficiency and specific capacity at first cycle, surface treatment on graphite by $nano-Li_4Ti_5O_{12}$ exhibited a higher charge/discharge rate, cycle life and thermal stability.