• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.940-941
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• 2006

We developed a new tooth profile designed for P/M internal gear pump rotors. The theoretical discharge volume of the new tooth profile internal gear rotors is more than 10% higher than that of the same size conventional rotors. Our new profile rotors can achieve a decrease in torque, and fuel-efficiency will also be improved.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.139-142
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• 1999

Screw rotors are core parts of screw type air compressors, compressors in refrigerating machines and super chargers of automobiles etc. They are composed of a female and a male rotors which have complex section profiles and helically swept geometry. Screw type compressors have advantages of low noise, high efficiency, less needs in maintenance etc. Usually, machining process of screw rotors requires long machining time using CNC machine designed only for screw rotors, which increase the cost of production. In this work, the screw rotors for air-compressors were manufactured with fiber reinforced epoxy composite materials by resin transfer molding process. The mold for the RTM process was made of aluminum and silicon rubber and was designed for release of helical shape products. Composite screw rotors, manufactured by RTM process, have advantages of lightweight, less cost of production, good characteristics of vibration etc.

• Wind and Structures
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• v.25 no.6
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• pp.551-567
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• 2017

Studies of unsymmetrical blade H-Darrieus rotors at low wind speeds in terms of starting time, static torque, and power performances for different blade parameters: thickness-to-chord (t/c), camber position, and solidity are scarce. However these are required for knowing insights of rotor performances to obtain some design guidelines for the selection of these rotors. Here, an attempt is made to quantify the effects of these blade parameters on the performances of three different H-Darrieus rotors at various low wind streams. Different blade profiles, namely S815, EN0005 (both unsymmetrical), and NACA 0018 (symmetrical blade for comparison) are considered. The rotors are investigated rigorously in a centrifugal blower apparatus. Firstly the dynamic and static performances of the rotors are evaluated to determine the best performing rotor and their optimum solidity. Generalised performance equations are developed based on selected blade parameters which are validated for the unsymmetrical rotors. Further, the starting time is quantified with respect to the rotor inertia to determine the suitable range of inertia that helps the unsymmetrical blade rotor to self-start earlier than the symmetrical one. This study can work as a benchmark for the selection of optimum blade parameters while designing an unsymmetrical blade rotor at low wind speeds.

• International Journal of Fluid Machinery and Systems
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• v.7 no.4
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• pp.130-141
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• 2014

As a high specific speed pump, the contra-rotating axial flow pump with two rotors rotating reversely has been proved with higher hydraulic and cavitation performance, while in our previous researches, the potential interaction between two blade rows was distinctly observed for our prototype rotors designed with equal rotational speed for both front and rear rotors. Based on the theoretical and experimental evidences, a rotational speed optimization methodology was proposed and applied in the design of a new combination of contra-rotating rotors, primarily in expectation of the optimized blade pressure distributions as well as pertinently improved hydraulic performances including cavitation performance. In the present study, given one stationary and two rotating frames in the contra-rotating rotors case, a pressure measurement concept taking account of the revolutions of both front and rear rotors simultaneously was adopted. The casing wall pressure data sampled in time domain was successfully transferred into space domain, by which the ensemble averaged blade-to-blade pressure distributions at the blade tip of two contra-rotating rotors under different operation conditions were studied. It could be seen that the rotor pair with the optimized rotational speed combination as well as work division, shows more reasonable blade-to-blade pressure distribution and well weakened potential interaction. Moreover, combining the loading curves estimated by the measured casing wall pressure, the cavitation performance of the rotor pairs with new rotational speed combination were proved to be superior to those of the prototype pairs.

• International Journal of Fluid Machinery and Systems
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• v.5 no.4
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• pp.161-167
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• 2012

Small-sized axial fans are used as air coolers for electric equipment. There is a strong demand for higher power of fans according to the increase of quantity of heat from electric devices. Therefore, higher rotational speed design is conducted, although, it causes the deterioration of the efficiency and the increase of noise. Then, the adoption of contra-rotating rotors for small-sized fans is proposed for the improvement of the performance. In the case of contra-rotating rotors, blade row distance between the front and the rear rotors influences on the performance and the noise. Therefore, it is important to clarify the optimum blade row distance between front and rear rotors. The performance curves of the contra-rotating small-sized axial fan under the condition of different blade row distances are shown and the blade row interaction between the front and the rear rotors are discussed by the numerical results. Furthermore, the optimum blade row distance of the contra-rotating small-sized axial fan is considered.

• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.741-743
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• 2000

In this paper the relationship between the pressing force applied to rotors and the characteristics of ultrasonic motor are discussed. The characteristics of ultrasonic motor using a piezoelectric vibrator were systematically studied. And these were applied to the construction of a card forwarding device. The principle of ultrasonic motor is to use an elliptical motion generated on the side of the vibrator, and the elliptical motion of the ultrasonic motor was obtained by complex oscillation of $L_1-B_4$ mode. As the experimental results. the forwarding speed of the card increased linearly as the pressing force applied to rotors increased. The forwarding speed of the card was 16.0 cm/s when the pressing force applied to rotors was 1 N. The forwarding force of the card increased linearly as the pressing force applied to rotors increased. The forwarding force of the card was 398 mN when the pressing force applied to rotors was 1 N. Therefore, this ultrasonic motor can be expected to be used for card-forwarding device and so on.

• International Journal of Aeronautical and Space Sciences
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• v.10 no.2
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• pp.63-76
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• 2009

A study on the interference effects of overlapping tandem rotors in forward flight is conducted using the time-marching free-wake panel method which adopts field velocity boundary integral formulation. The conventional boundary integral formulation is numerically unstable for the cases when the blade and the wake are in close proximity to each other. In order to avoid this problem, this study applies the field velocity method and modifies the boundary integration formulation. The improved method is used for the parametric study on the advance ratio and the distance between the rotors. These are the parameters that most affect the interference of the tandem rotor in forward flight. Comparison of the aerodynamic performance shows that the horizontal distance between the rotors negligibly influences the overlap-induced power factor for high advance ratio. In addition, it shows that the overlap-induced power factor is inversely proportional to the squared vertical distance between the rotors, and that the overlap-induced power factor increases to a certain extent and decrease back as the advance ratio increases.

• Journal of Ocean Engineering and Technology
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• v.35 no.3
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• pp.229-237
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• 2021

A numerical hydrodynamic performance analysis of the pitch-type multibody wave energy converter (WEC) is carried out based on both linear potential flow theory and computational fluid dynamics (CFD) in the unidirectional wave condition. In the present study, Salter's duck (rotor) is chosen for the analysis. The basic concept of the WEC rotor, which nods when the pressure-induced motions are in phase, is that it converts the kinetic and potential energies of the wave into rotational mechanical energy with the proper power-take-off system. This energy is converted to useful electric energy. The analysis is carried out using three WEC rotors. A multibody analysis using linear potential flow theory is performed using WAMIT (three-dimensional diffraction/radiation potential analysis program), and a CFD analysis is performed by placing three WEC rotors in a numerical wave tank. In particular, the spacing between the three rotors is set to 0.8, 1, and 1.2 times the rotor width, and the hydrodynamic interaction between adjacent rotors is checked. Finally, it is confirmed that the dynamic performance of the rotors slightly changes, but the difference due to the spacing is not noticeable. In addition, the CFD analysis shows a lateral flow phenomenon that cannot be confirmed by linear potential theory, and it is confirmed that the CFD analysis is necessary for the motion analysis of the rotor.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1993.04a
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• pp.107-112
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• 1993

The effect of the applied direction and magnitude of loads on the stability and natural frequency of flexible rotors is analyzed, when the rotors are subject to nonconservative torque and force. The stability criterion derived from the energy and variational principle is discussed and a general Galerkin's method which utilizes admissible functions is employed for numerical analysis. Illustrative examples are treated to demonstrate the analytical developments.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.485-491
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• 2001

This paper describes the development of simulation program which is able to design cutter profiles and 3-dimensional geometry for rotors in screw compressor. Based on the symmetric rotor profiles developed previously, cutters are designed and 3-dimensional geometries of rotors are generated used by simulation program. Symmetric rotors are manufactured by a universal milling machine, and surface geometries of them are measured by a 3-dimension scanner. It is shown that simulation program developed is useful to design cutter for rotor manufacturing and to generate the 3-dimensional helicoid geometry of rotor in screw compressor.