• 한국전산유체공학회지
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• 제13권2호
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• pp.55-61
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• 2008

The Reynolds-Averaged Navier-Stokes(RANS) analysis of the 3-D steady flow around the NREL Phase VI horizontal axis wind turbine(HAWT) rotor was performed. The CFD analysis results were compared with experimental data at several different wind speeds. The present CFD model shows good agreements with the experiments both at low wind speed which formed well-attache flow mostly on the upper surface of the blade, and at high wind speed which blade surface flow completely separated. However, some discrepancy occurs at the relatively high wind speeds where mixed attached and separated flow formed on the suction surface of the blade. It seems that the discrepancy is related to the onset of stall phenomena and consequently separation prediction capability of the current turbulence model. It is also found that strong span-wise flow occurs in stalled area due to the centrifugal force generated by rotation of the turbine rotor and it prevents abrupt reduction of normal force for higher wind speed than the designed value.

• 한국생산제조학회지
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• 제24권6호
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• pp.632-638
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• 2015

Many failures have been reported in gas turbine facilities owing to repeated startups and prolonged use of the turbines. In this study, the causes and mechanism of fatigue failure in the first blade of a gas turbine were analyzed using a finite element method to calculate the centrifugal force, bending force, and a modal analysis based on the stress-stiffening effect and harmonic response under the operating conditions. The results show that, fatigue damage was caused by the resonance conditions encountered, in which the first natural frequency declined along with an increase in the metal temperature of the blade. The position of the expected fatigue damage was shown to match the actual position of the cracking at the root area of the blade, which was on the concave side. In addition, the equivalence fatigue stress was observed to approach the fatigue limit.

• 한국산학기술학회논문지
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• 제10권12호
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• pp.3533-3539
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• 2009

에어컨 임펠러는 에어컨에 장착되어지는 부품으로서 모터 구동에 의하여 차가운 바람을 실내로 유입되도록 해주는 부분이다. 본 연구에서는 임펠러의 파손 원인을 수치적인 방법에 의하여 규명하고, 공진에 의한 파손 여부를 평가한다. 임펠러의 공진 여부를 판단하기 위하여 임펠러의 고유진동수와 Aerodynamic force에 의한 특성 주파수를 비교한다. 먼저, 임펠러의 고유진동수를 알기 위하여 모드 실험과 수치 계산을 병행한다. 즉, 구조 해석용 상용 소프트웨어인 ANSYS를 이용하여 고유진동수와 모드 형을 계산하고, 이를 확인하기 위하여 실험적 주파수 분석을 수행한다. 공진 현상의 원인이 되는 외력에 대하여 임펠러 Blade에 작용하는 Aerodynamic force를 구하여야 하며, 본 연구에서는 V.E.M.(Vortex Element Method)에 근거한 유동 해석 프로그램을 수행하여 Aerodynamic force에 의한 특성 주파수를 얻는다.

• Tribology and Lubricants
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• 제14권2호
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• pp.26-34
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• 1998

This paper presents a high-speed performance analysis of ball bearings with ceramic balls under thrust loads. The sliding velocity profiles between a ball and raceways were obtained by the 3-D quasi-dynamic equations of motion including both centrifugal force and gyroscopic moment derived by vector matrix algebra. The friction at the contact areas was obtained by the Bair-Winer's non-Newtonian rheological model and the Hamrock-Dowson's central film thickness in EHL analysis. The nonlinear equations were solved by the Newton-Raphson method and the underrelaxation iterative method. The friction torques and ball behaviors with various loads, ball materials, and contact angles were predicted by this model. It was shown that the friction torque was sensitive to thrust load and contact angle, and that the friction torque and the pitch angle of the bearing with ceramic balls are smaller than those of the bearing with steel balls.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.763-768
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• 2002

This paper presents a mathematical model predicting the temperature distribution in rotating GMA welding. The bead width increases with rotation frequency at the same rotation diameter because the molten droplets are deflected by centrifugal force. The numerical solution is obtained by solving the transient three-dimensional heat conduction equation considering the heat input from the welding arc, cathode heating and molten droplets. Generally in GMA welding the heat input may be assumed as a normally distributed source, but the droplet deflection causes some changes in the heat input distribution. To estimate the heat flux distribution due to the molten droplet, the contact point where the droplet is transferred on the weld pool surface is calculated from the flight trajectory of the droplets under the arc plasma velocity field obtained from the arc plasma analysis. The numerical analysis shows a tendency of broadened bead width and shallow penetration depth with the increase of rotating frequency. The simulation results are in good agreement with those obtained by the experiments under various welding conditions.

• 한국신뢰성학회지:신뢰성응용연구
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• 제16권4호
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• pp.263-271
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• 2016

Purpose: A slurry pump for flue gas desulfurization system performs a role that discharges the slurry of a plaster shape in a thermal power plant. Since a slurry pump transfers the slurry by the centrifugal force, it has the friction wear in the impeller and liner because of the slurry. Methods: In this study, failure analysis and test evaluation on the slurry pump have been proposed and the process that reliability of the product improves through design improvement has been presented. And failure cause of typical failure case has been investigated and improvement design has been presented. Results: Reliability improvement is established by analysis of the test results of before and after acceleration test. Conclusion: This study can be provided to improve the product reliability through failure analysis of a slurry pump.

• 한국소음진동공학회논문집
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• 제16권9호
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• pp.982-989
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• 2006

The centrifugal force acting on a rotating disk creates the in-plane loads in radial and circumferential directions. Application of fiber reinforced composite materials to the rotating disk can satisfy the demand for the increment of its rotating speed. However, the existing researches have been confined to lamina disks. This paper deals with the stress and vibration analysis of rotating laminated composite disks. The maximum strain theory for failure criterion is applied to determine the strength of the laminate disk from which the maximum allowable speed is obtained. Dynamic equation is formulated in order to calculate the natural frequency and critical speed for rotating laminated disks. The Galerkin method is applied to obtain the series solution. The numerical results are given for the cross-ply laminated composite disks.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.848-853
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• 2001

A study about the shrink fits of rotor and retaining ring in generator was performed for the cases of three radial interference. The shrink-fitted retaining ring used to restrain the end turns of the winded coils in the rotor against centrifugal force requires very careful attention during design and manufacture because it has traditionally been the highest-stressed component of the generator. The contact pressures and residual stresses were obtained by the finite element analysis for each radial interference at zero, 100% rated, and 120% rated speeds, respectively. The results of analysis show that the radial interference in use needs to be increased carefully.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 춘계학술대회 논문집
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• pp.2151-2155
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• 2008

The tilting train express (TTX) is able to tilt its body toward to the center of the turning radius on curved railways. TTX can travel at higher speed than the existing normal railway vehicles due to the tilting mechanism decreasing centrifugal force. Also, a new suspension system is required for TTX which has proper stiffness constants and damping ratios because it has different suspension characteristics with the others. Therefore, the suspension systems need to be optimized to maximize dynamic characteristic of the railway vehicle. To optimize the dynamic characteristics of TTX, sensitivity analysis should be onde to identify design variables. In this paper, Design of Experiments(DOE) is used for the sensitivity analysis of TTX.

• 한국초전도ㆍ저온공학회논문지
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• 제8권3호
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• pp.63-69
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• 2006

This paper describes the effect of rotating frequency on the pulse tube of Stirling type pulse tube refrigerator. Various conditions were analyzed by two-dimensional analysis with several dominant non-dimensional parameters. With the additional pressure term influenced by centrifugal force in rotating condition, the linearized conservation equations of mass, momentum, energy of the gas were solved to obtain the first order variables and calculate the enthalpy flow in rectangular coordinates. The rotational effect in pulse tube for the refrigerator's performance were quantitatively evaluated. According to the first order analysis, the enthalpy flow decreases with the rotating speed.