• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.61.2-61.2
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• 2011

The spanwise aerodynamic loads of the wind turbine blade are investigated numerically. The blade shape such as twist and chord length along the blade span is obtained from the procedure of aerodynamically optimal design. The rated tip speed ratio and the rated wind velocity are set to 7 and 12m/s respectively. The BEM method is applied to obtain both the aerodynamic performance of the wind turbine (Fig.1) and the spanwise aerodynamic loads along the blade span including Prandtl's tip loss factor. The maximum running power coefficient is occurred around 90% radial position from hub (Fig.2). The distributed aerodynamic loads along the blade span can be used for structure analysis.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.12
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• pp.841-847
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• 2019

Time series data of 6-component loads were computed for a horizontal axis wind turbine rotor in yawed operating conditions with both rotating and non-rotating coordinate systems fixed at a center of a rotor hub. In this study, a well-known 20 kW class of the NREL Phase VI rotor was used for a model wind turbine, and this paper focuses on the yaw moments and over-turning moments for the operating wind speed range between 6 to 25 m/s. Unsteady blade element momentum theorem was adopted to get the aerodynamic loads acting on the wind turbine rotor. Computed 6-component loads using the developed UBEM code were compared with those using the NREL FAST program. From the computed results, both yaw and over-turning moments would be basic inputs to determine not only the specification of yawing mechanism but also the design condition of foundation.

• Tribology and Lubricants
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• v.32 no.2
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• pp.61-66
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• 2016

Total thickness variation (TTV), BOW, and surface roughness are essential characteristics for high quality sapphire substrates. Many researchers have attempted to increase removal rate by controlling the key process parameters like pressure and velocity owing to the high cost of consumables in sapphire chemical mechanical polishing (CMP). In case of the pressure approach, increased pressure owing to higher deviation of pressure over the wafer leads to significant degradation of the TTV. In this study, the authors focused on reducing TTV under the high-pressure conditions. When the production equipment polishes multiple wafers attached on a carrier, higher loads seem to be concentrated around the leading edge of the head; this occurs because of frictional force generated by the combination of table rotation and the height of the gimbal of the polishing head. We believe the skewed pressure distribution during polishing to be the main reason of within-wafer non-uniformity (WIWNU). The insertion of a hub ring between the polishing head and substrate carrier helped reduce the pressure deviation. Adjusting the location of the hub ring enables tuning of the pressure distribution. The results indicated that the position of the hub ring strongly affected the removal profile, which confirmed that the position of the hub ring changes the pressure distribution. Furthermore, we analyzed the deformation of the head via finite element method (FEM) to verify the pressure non-uniformity over the contact area Based on experiment and FEM results, we determined the optimal position of hub ring for achieving uniform polishing of the substrate.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.5
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• pp.364-370
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• 2019

In this paper, an individual blade control (IBC) methodology is applied to find the best input scenario for vibratory hub loads reduction of XH-59A co-axial rotorcraft in high speed flight. A comprehensive aeromechanics analysis code CAMRAD II is employed to analyze the aircraft. A parametric study is conducted for optimum IBC inputs leading to the maximum vibration reduction. Numerical results demonstrate that up to 50% reduction in the hub vibration index is obtained for an IBC input at 3/rev frequency with the amplitude and phase angle of 0.5 deg. and 300 deg., respectively. The upper rotor exhibits as much as 6% more vibration reduction as compared to that of the lower rotor due to a clean inflow characteristic of the rotor. It is found that further vibration reduction gain is reached for IBC inputs with advancing-side only control. The hub vibration becomes reduced by up to 17% in reference to that with full rotor disk control. It is noted that the additional gain is obtained with significantly less power input with the advancing-side only control.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.6
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• pp.440-447
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• 2013

In this paper, a higher harmonic control (HHC) methodology is applied to find the optimum input scenario for the vibratory hub loads reduction. A comprehensive aeroelastic analysis code, CAMRAD II, is used to model the HART (Higher-harmonic-control Aeroacoustic Rotor Test) II rotor, and parametric study is conducted for the best HHC inputs leading to a minimum vibration (MV) condition. The resulting outcomes are compared with the earlier HART II test results. It is indicated that the control input adopted in the MV condition showed less satisfactory results. The new MV condition obtained in the present investigation can achieve 45% lower vibration level than the baseline uncontrolled condition. The optimum HHC input results lead to 3/rev harmonic input having $0.8^{\circ}$ amplitude and $350^{\circ}$ phase angle. About 5% reduction in the required power is possible but accompanies with the increase of vibration level.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.5
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• pp.399-406
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• 2016

The large scale wind turbine blades usually experience periodic change of inflow speed due to blade rotation inside the ground shear flow region. Because of the vertical wind shear, the inflow velocity in the boundary layer region is maximum at uppermost position and minimum at lowermost position. These spatial distribution of wind speeds can lead to the periodic oscillation of the 6-component loads at hub and low speed shaft of the wind turbine rotor. In this study we compare the aerodynamic loads between two inflow conditions, i.e, uniform flow (no vertical wind shear effect) and normal wind profile. From the computed results all of the relative errors for oscillating amplitudes increased due to the ground shear flow effect. Especially bending moment and thrust at hub, and bending moments at LSS increased enormously. It turns out that the aerodynamic analysis including the ground shear flow effect must be considered for fatigue analysis.

• Journal of the wind engineering institute of Korea
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• v.22 no.4
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• pp.163-169
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• 2018

In this study, wind loads exerted on the offshore wind turbine rotor in parked condition were predicted with variations of wind speeds, yaw angles, azimuth angle, pitch angles, and power of the atmospheric boundary layer profile. The calculated wind loads using blade element theorem were compared with those of estimated aerodynamic loads for the simplified blade shape. Wind loads for an NREL's 5 MW scaled offshore wind turbine rotor were also compared with those of NREL's FAST results for more verification. All of the 6-component wind loads including forces and moments along the three axis were represented on a non-rotating coordinate system fixed at the apex of rotor hub. The calculated wind loads are applicable for the dynamic analysis of the wind turbine system, or obtaining the over-turning moment at the foundation of support structure for wind turbine system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.85-92
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• 2007

This paper presents a design optimization of a new Advanced Active Blade Twist (AATR-II) blade incorporating single crystal Macro Fiber Composites (MFC) and conducts vibratory loads reduction analysis using an obtained optimal blade configuration. Due to the high actuation performance of the single crystal MFC, the AATR blade may reduce the helicopter vibration more efficiently even with a lower input-voltage as compared with the previous ATR blades. The design optimization provides the optimal cross-sectional configuration to maximize the tip twist actuation when a certain input-voltage is given. In order to maintain the properties of the original ATR blade, various constraints and bounds are considered for the design variables selected. After the design optimization is completed successfully, vibratory load reduction analysis of the optimized AATR-II blade in forward flight condition is conducted. The numerical result shows that the hub vibratory loads are reduced significantly although 20% input-voltage of the original ATR blade is used.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.1
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• pp.29-36
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• 2008

In this paper, the orbital forming analysis of an automotive hub bearing was studied to predict forming performances using the explicit finite element method. To find an efficient solution technique for the orbital forming, axisymmetric finite element models and 3D solid element models were solved and numerically compared. The time scaling and mass scaling techniques were introduced to reduce the excessive computational time caused by small element size in case of the explicit finite element method. It was found from the numerical simulations on the orbital forming that the axisymmetric element models showed the similar results to the 3D solid element models in forming loads whereas the deformations at the inner race of bearing were quite different. Finally the strains at the inner race of bearing and the forming forces to the peen were measured for the same product of the numerical model by test, and were compared with the 3D solid element results. It was founded that the test results were in good agreements with the numerical ones.

• Composites Research
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• v.29 no.2
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• pp.73-78
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• 2016

In this paper, The concept of a wheel with carbon fiber composite is to replace the conventional material used for a wheel hub, such as plastic, with a disk-type hub made of carbon fabric and epoxy resin. The impact load from the ground under real conditions was considered; a low-velocity impact test was conducted to evaluate the impact performance of the carbon wheel and compare it with that of a conventional plastic wheel. This study applied a 70 J impact load as a test condition. The impact energy was controlled in the test by adjustment of height and weight of impactor. The use of a carbon disk wheel hub was confirmed to reduce weight and generate an excellent repulsive force at low energy under conditions similar to real driving conditions. The results showed that the maximum load increased proportionally depending on the impact load, but the growth of the maximum load was reduced at a 20 J impact load and tended to decrease at a 45 J impact load. The carbon wheel showed excellent properties ; the level of rebounding was 35.3% and 19.1% of the total impact energy at impact loads of 5 J and 10 J, respectively. On the other hand, the carbon disk wheel rebounded less than 5% of the total energy due to crack generation of the thin carbon hub for impact loads of more than 20 J.