• 유공압시스템학회논문집
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• 제5권2호
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• pp.1-7
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• 2008

To improve the performance of the bent axis type axial piston pump driven by the tapered piston, it is necessary to know the driving characteristics and mechanism of the tapered piston and the cylinder block. Since each piston not only rotates on its axis and reciprocates in the cylinder bore, but also revolves around the axis of the driving shaft, it is difficult to analyze the driving mechanism theoretically. The theoretical mechanism far the bent axis type axial piston pump is studied by using the geometrical method. The driving range of the tapered piston is determined by theoretical equations. The results show that the cylinder block is driven by one tapered piston in a limited range and the core parameters such as driving factor of the piston and the ahead delay angle influenced performance of the bent axis type axial piston pump.

• 대한정형도수물리치료학회지
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• 제22권2호
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• pp.51-56
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• 2016

Background: The purpose of this study is to compare axis change during cervical flexion and extension according to lordosis angle to patients with scoliosis. Methods: Movement axis change was estimated during cervical flexion and extension in twenty-four scoliosis patients with hypolordosis using radiography. Subjects were divided into mild lordotic curve group (MLCG, n=12, $34{\sim}25^{\circ}$) and severe lordotic curve group (SLCG, n=12, less $25^{\circ}$) according to cervical lordosis angle. Results: During cervical flexion, both group showed movement axis change to upper part of cervical vertebra and SLCG showed greater than MLCG but there is no significant difference. During cervical extension, SLCG showed greater than MLCG and there is significant difference. Conclusion: It is considered that cervical hypolordosis acts as important factor to scoliosis and degenerative joint disease because it leads to change of movement axis and central route of joint.

• Wind and Structures
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• 제38권5호
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• pp.341-354
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• 2024

This paper presents a theoretical method to deal with the aerodynamic performance and pitch optimization of the horizontal axis wind turbine blades at low wind speeds. By considering a blade element, the functional relationship among the angle of attack, pitch angle, rotational speed of the blade, and wind speed is derived in consideration of a quasi-steady aerodynamic model, and aerodynamic loads on the blade element are then obtained. The torque and torque coefficient of the blade are derived by using integration. A polynomial approximation is applied to functions of the lift and drag coefficients for the symmetric and asymmetric airfoils respectively, where specific expressions of aerodynamic loads as functions of the angle of attack (which is a function of pitch angle) are obtained. The pitch optimization problem is investigated by considering the maximum value problem of the instantaneous torque of a blade as a function of pitch angle. Dynamic pitch laws for HAWT blades with either symmetric or asymmetric airfoils are derived. Influences of parameters including inflow ratio, rotational speed, azimuth, and wind speed on torque coefficient and optimal pith angle are discussed.

• 대한족부족관절학회지
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• 제17권3호
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• pp.189-195
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• 2013

Purpose: We investigated a statistical difference of tibial-articular surface (TAS) angles between radiographs of standing ankle anteroposterior (AP) and whole lower extremity view, and evaluated whether the tibial axis obtained from the standing ankle AP view reflects the original mechanical axis of lower extremity. Materials and Methods: Both the standing ankle AP and whole lower extremity view were taken from 60 legs of 30 healthy volunteers without a history of ankle surgery or deformity of lower limb. To determine the tibial axis, Takakura's and Hintermann's method were employed in the standing ankle AP view. To compare these results with the original TAS angle, ANOVA and multiple comparison test were used. Results: The mean TAS angle was 88.3 degrees(from hip joint to ankle), 89.5 degrees (from knee joint to ankle), 88.5 degrees (Takakura's method), and 90.2 degrees(Hintermann's method). Although there was a statistical significance (p=0.000) between these results, Takakura's method had no significant difference, compared to the results of whole extremity view by the multiple comparison test. Conclusion: The tibial axis obtained by Takakura's method reflects the original mechanical axis of lower extremity. When a surgical procedure is planned, however, it is necessary to consider that the ankle radiographs do not provide any information on the proximal deformity without the whole lower extremity view.

• International Journal of Aeronautical and Space Sciences
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• 제11권2호
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• pp.131-135
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• 2010

We report on the design of a three-axis missile autopilot using multi-objective control synthesis via linear matrix inequality techniques. This autopilot design guarantees $H_2/H_{\infty}$ performance criteria for a set of finite linear models. These models are linearized at different aerodynamic roll angle conditions over the flight envelope to capture uncertainties that occur in the high-angle-of-attack regime. Simulation results are presented for different aerodynamic roll angle variations and show that the performance of the controller is very satisfactory.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 추계학술대회 논문집
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• pp.478-481
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• 2009

As a first step for aerodynamic analysis of vertical axis wind turbine, dynamic stall characteristics of airfoil was investigated. Dynamic stall of wind turbine airfoil is caused by severe variation of angle of attack and relative velocity of flow around airfoil. Angle of attack and relative velocity can be expressed with tip speed ratio. Variation of angle of attack is strongly dependent on the tip speed ratio. For tip speed ratio, 1.4 and free stream velocity, 15m/s, dynamic stall characteristics of wind turbine airfoil is compared with those of oscillating airfoil having same angle of attack variation.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2004년도 Asia Display / IMID 04
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• pp.1182-1184
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• 2004

We have studied contrast ratio of a homogeneously aligned nematic liquid crystal (LC) display as a function of the angle between the polarizer axis and LC director. The results show that a cell configuration in which a polarizer axis facing a light source coincides with a short LC axis has a better process margin in terms of high contrast ratio than that of the cell coinciding with a long LC axis.

• 한국초전도ㆍ저온공학회논문지
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• 제19권2호
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• pp.9-13
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• 2017

This study presents a simple method to control the seed orientation which leads to the various growth characteristics of a single grain REBCO (RE: rare-earth elements) bulk superconductors. Seed orientation was varied systematically from c-axis to a-axis with every 30 degree rotation around b-axis. Orientations of a REBCO single grain was successfully controlled by placing the seed with various angles on the prismatic indent prepared on the surface of REBCO powder compacts. Growth pattern was changed from cubic to rectangular when the seed orientation normal to compact surface was varied from c-axis to a-axis. Macroscopic shape change has been explained by the variation of the wetting angle of un-reacted melt depending on the interface energy between $YBa_2Cu_3O_{7-y}$ (Y123) grain and melt. Higher magnetic levitation force was obtained for the specimen prepared using tilted seed with an angle of 30 degree rotation around b-axis.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 춘계학술대회 논문집 디스플레이 광소자분야
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• pp.150-152
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• 2004

We have studied contrast ratio of a homogeneously aligned nematic liquid crystal (LC) display as a function of the angle between the polarizer axis and LC director. The results show that a cell configuration in which a polarizer axis facing a light source coincides with a short LC axis has a better process margin in terms of high contrast ratio than that of the cell coinciding with a long LC axis.

• Journal of Mechanical Science and Technology
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• 제18권5호
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• pp.753-761
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• 2004

In this paper, an efficient method for generating 5-axis cutting data for a turbine blade is presented. The interference elimination of 5-axis cutting currently is very complicated, and it takes up a lot of time. The proposed method can generate an interference-free tool path, within an allowance range. Generating the cutting data just point to the cutting process and using it to obtain NC data by calculating the feed rate, allows us to maintain the proper feed rate of the 5-axis machine. This paper includes the algorithms for: (1) CL data generation by detecting an interference-free heel angle, (2) finding the optimal tool path interval considering the cusp-height, (3) finding the adaptive feed rate values for each cutter path, and (4) the inverse kinematics depending on the structure of the 5-axis machine, for generating the NC data.