• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.10a
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• pp.350-357
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• 1998

Slot restrictor air journal bearing has high load capacitance and high stiffness. Stability characteristics of slot restrictor air journal bearing are studied theoretically to forecast and to prevent the whirl instability. As for the high speed rotating machinery, the instability called 'whirl' occurs when the rotor rotates at a speed more than twice the resonant speed. Once the whirl occurs, rubbing contact between the journal and the bearing occurs mostly and the bearing-rotor system is destroyed ultimately. Therefore, the forecasting and prevention of the occurence of whirl instability is a very important subject especially to develop highly efficient high speed machinery. The bearing with the slot restrictor that varies about circumferencial direction is used for the purpose of the prevention of whirl instability.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.609-613
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• 2008

The fire whirl occurring by the instability of atmosphere is a rare phenomenon, but highly destructive because it has high inhalation and lift force, caused by the rotating velocity. And it is difficult to extinguish the fire, because of increment of the spread rate with the flame height. In this study, for investigation of the flow characteristic of fire whirl for various heat release rate, numerical analysis is performed in same conditions with experiments, using the FDS which is developed at NIST. For validating of the numerical study, the results are compared with the experiment. The result shows that the relation between the characteristic length and the ratio of circulation versus the buoyancy force is $z_f$/D$^{\ast}$ = 0.304(${\Omega}/{\alpha}$)^2 - 1.334${\Omega}/{\alpha}$ + 5.516.

• Fire Science and Engineering
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• v.26 no.3
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• pp.73-78
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• 2012

This study is intended to understand flame behavior of pool and whirl fire by height of fire source. Liquid fuel was methanol which is used in many studies for pool and whirl fire. Size of vessel was $100{\times}100{\times}50$ and the vessel was made by stainless steel. Combustion time, mass loss rate, flame temperature, flame height and air entrainment rate from the outside to flame were measured, and flame behavior was visualized with video camera. Based on the experiment, it was found that combustion characteristics by height of fire source got a more effect on whirl fire than pool fire.

• Fire Science and Engineering
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• v.25 no.2
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• pp.126-131
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• 2011

This study is intended to understand mass loss rate and air entrainment rate of the whirl fire by height of fire source. Liquid fuels were methanol and n-Heptane which are used in many studies of whirl fire. Size of vessel was 100 mm ${\times}$ 100 mm ${\times}$ 50 mm and the vessel was made by stainless steel. When height of fire source changed from 0 cm to 30 cm, air entrainment rate showed the fastest in case of 0 cm. And in the same height of fire source, average and maximum air entrainment rate showed the fastest in 30 cm of anemometer. From the results of whirl fire for methanol and n-Heptane, mass loss rate and air entrainment rate of n-Heptane was found to faster 1.33 to 1.58 times and 4.38 to 5.44 times compared with methanol, respectively. Consequently, mass loss rate and air entrainment rate in whirl fire was able to identified decrease as height of fire source increases and the higher the heating value, increases the that's value.

• Aerospace Engineering and Technology
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• v.7 no.2
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• pp.205-212
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• 2008

This paper describes the modeling data and final analysis results of rotor resonance, rotor aeroelastic stability and whirl flutter stability for Smart UAV (SUAV). The effects of wing beamwise, chordwise and torsional stiffness on the whirl flutter stability were investigated considering the possibility of design change of SUAV wing structure. The parametric study showed that wing torsional and beamwise stiffness changes have much stronger influence on the wing mode damping than chordwise stiffness. It was analytically demonstrated that the final designed rotor system is aeroelastically stable and free from resonance, and that rotor/pylon/wing system of SUAV TR-S4 has enough rotor stability and whirl flutter stability margin.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.622-627
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• 2012

During helicopter rotor system development process, whirl tower test is conducted basically. For conducting whirl tower test during bearingless hub development process, design new blade or using existing blade with repair or remodeling. Because simple shape and efficient aerodynamic characteristic, BO-105 blade is used for hub system development widely. Originally BO-105 blade is used for hingeless hub, ho flap stiffness and lag stiffness on blade root area is relatively low. So applying BO-105 blade to bearingless hub whirl tower test, root area have to be reinforce. In this process, blade root area's section property will be changed. In this paper, suggest reinforcement method of BO-105 blade root area and study dynamic characteristic of bearingless rotor system with reinforcement BO-105 blade.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.6
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• pp.75-82
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• 2006

Tiltrotor aircraft can fly about twice faster and several times further than conventional helicopters. These aircraft provide advantages preventing compressibility of advancing side and stall of retreating side of blades because they take forward flight with tilting rotor systems. However, they have limit on forward flight speed because of the aeroelastic instability known as whirl flutter. First, the parametric study on the aeroelastic stability of the isolated rotor system has been performed in this paper. And the effects of pitch-link stiffness, gimbal spring constant, and precone angle on the whirl flutter stability of Smart-UAV have been investigated through CAMRAD II analysis.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.301-307
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• 2005

In this study, simplified whirl flutter analyses using quasisteady aerodynamic theory have been performed for a 2-DOF tilt-rotor system with both pitch and yaw motions of a rotor-nacelle. The present dynamic system consists of the rotor (propeller), forming the gyroscopic and aerodynamic element, supported horizontally by a pylon that is pivoted at some wing attachment point. Several design parameters (or rotor-nacelle system are considered and the effect of whirl flutter stability are also investigated for various design parameters.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.182-183
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• 2008

In this study, rotor dynamic analysis have been conducted using three-dimensional solid model. Analysis object has smaller size and higher speed than any general CNC spindle. It is important to consider the real supporting conditions and external forces for whirl behavior analysis. As a results, the bearing stiffness is higher, whirl motion is less than before.

• Journal of the Korean Society of Safety
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• v.20 no.2 s.70
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• pp.11-17
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• 2005

Rotational motion in the atmosphere around a fire may have a profound influence on the fire plume. This process underlies the occurrence of fire whirls. Fire whirls are rare but highly destructive phenomenon which were observed in a large forest, urban and building fires. The present study aims to investigate of the effect of rotation Strength on the fire whirl characteristics expeimentally. Experiments are performed for various sizes of fire source with different rotation strength. From the experimental observations, it is noted that the mean centerline temperature is gradually increased and mean radial temperature is decreased as increases rotation strength. The characteristic mean flame height of fire based on the visible observation is increased as increases of dimensionless swirl parameter, $\Omega/\alpha$, represented by swirl induced motion to buoyancy driven motion.