• 대한족부족관절학회지
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• 제17권2호
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• pp.121-129
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• 2013

Purpose: To evaluate the radiographic characteristics of the tarsometatarsal osteoarthritis with hallux valgus deformity and report the clinical results of the operative treatment. Materials and Methods: This is a retrospective study of 20 patients, 22 feet who had been operated for non-traumatic tarsometatarsal osteoarthritis with hallux valgus (TMT group) and control group of hallux valgus patients without tarsometatarsal osteoarthritis (26 patients, 28 feet) from April 2004 to July 2011. Radiographic characteristics were compared between the groups, using hallux valgus angle, $1^{st}-2^{nd}$ intermetatarsal angle, metatarsal length ratio, metatarsus adductus angle, talonavicular coverage angle, talus-$1^{st}$ metatarsal angle, calcaneal pitch angle and medial cuneiform height. Pre- and postoperative difference of $1^{st}-2^{nd}$ metatarsal declination angle and distance between the $1^{st}-2^{nd}$ metatarsal head were evaluated. The clinical results were evaluated by American Orthopaedics Foot and Ankle Society (AOFAS) midfoot scale and visual analogue scale (VAS). Results: Metatarsal length ratio was significantly larger in TMT group (p<0.001). Metatarsus adductus angle, talonavicular coverage angle, talus-$1^{st}$ metatarsal angle on lateral radiograph, calcaneal pitch angle and medial cuneiform height were different from control group (p<0.001, p<0.001, p=0.001, p=0.010, p=0.006). Postoperative declination of the $2^{nd}$ metatarsal and distance between the $1^{st}-2^{nd}$ metatarsal head were increased (p=0.009, p=0.001). The AOFAS and VAS score were improved (p<0.001, p<0.001). Conclusion: Non-traumatic osteoarthritis of the tarsometatarsal joints seems to be associated with long 2nd metatarsal length, metatarsus adductus and flatfoot deformity. Spur excision may be successful to relieve symptoms when the arthritis was diagnosed in early stage.

• Journal of Astronomy and Space Sciences
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• 제30권2호
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• pp.91-94
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• 2013

We use the outer gap model to explain the spectrum and the energy dependent light curves of the X-ray and soft ${\gamma}$-ray radiations of the spin-down powered pulsar PSR B1509-58. In the outer gap model, most pairs inside the gap are created around the null charge surface and the gap's electric field separates the opposite charges to move in opposite directions. Consequently, the region from the null charge surface to the light cylinder is dominated by the outflow current and that from the null charge surface to the star is dominated by the inflow current. We suggest that the viewing angle of PSR B1509-58 only receives the inflow radiation. The incoming curvature photons are converted to pairs by the strong magnetic field of the star. The X-rays and soft ${\gamma}$-rays of PSR B1509-58 result from the synchrotron radiation of these pairs. The magnetic pair creation requires a large pitch angle, which makes the pulse profile of the synchrotron radiation distinct from that of the curvature radiation. We carefully trace the pulse profiles of the synchrotron radiation with different pitch angles. We find that the differences between the light curves of different energy bands are due to the different pitch angles of the secondary pairs, and the second peak appearing at E > 10 MeV comes from the region near the star, where the stronger magnetic field allows the pair creation to happen with a smaller pitch angle.

• Wind and Structures
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• 제32권5호
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• pp.471-485
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• 2021

Onshore wind turbines may experience substantially different wind loads depending on their working conditions, i.e. rotation velocity of rotor blades, incoming freestream wind velocity, pitch angle of rotor blades, and yaw angle of the wind-turbine tower. In the present study, aerodynamic loads acting on a horizontal axis wind turbine were accordingly quantified for the high tip speed ratio (TSR) at high yaw angles because these conditions have previously not been adequately addressed. This was analyzed experimentally on a small-scale wind-turbine model in a boundary layer wind tunnel. The wind-tunnel simulation of the neutrally stratified atmospheric boundary layer (ABL) developing above a flat terrain was generated using the Counihan approach. The ABL was simulated to achieve the conditions of a wind-turbine model operating in similar inflow conditions to those of a prototype wind turbine situated in the lower atmosphere, which is another important aspect of the present work. The ABL and wind-turbine simulation length scale factors were the same (S=300) in order to satisfy the Jensen similarity criterion. Aerodynamic loads experienced by the wind-turbine model subjected to the ABL simulation were studied based on the high frequency force balance (HFFB) measurements. Emphasis was put on the thrust force and the bending moment because these two load components have previously proven to be dominant compared to other load components. The results indicate several important findings. The loads were substantially higher for TSR=10 compared to TSR=5.6. In these conditions, a considerable load reduction was achieved by pitching the rotor blades. For the blade pitch angle at 90°, the loads were ten times lower than the loads of the rotating wind-turbine model. For the blade pitch angle at 12°, the loads were at 50% of the rotating wind-turbine model. The loads were reduced by up to 40% through the yawing of the wind-turbine model, which was observed both for the rotating and the parked wind-turbine model.

• 대한기계학회논문집
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• 제16권7호
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• pp.1381-1390
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• 1992

본 연구에서는 경사원주에서 발생하는 소용돌이 여기진동을 억제하기 위한 방 법으로 원주구조물 주위에서 발생하는 규칙적인 소용돌이 방출에 의한 여진력을 감소 시키도록 원주표면에 fin이나 wire를 부착시켜 단면형상을 바꾸는 방안을 실험적으로 검토한다. 즉, 밀폐순환식 유로을 이용하여 흐름에 경사되도록 탄성지지된 원주에 나선상의 fin과 wire를 감아, 경사각(.theta.)을 45, 60, 75, 90도, 나선피치각(.alpha.)을 30, 35, 40, 45, 50, 55, 60도, 나선권수(n)를 1,2,3으로 하여, 진동특성을 실험적으로 조사하고, plain원주와 비교하여 제진효과를 확인하며, 더우기 나선핀 원주의 최적형 상을 구하는 것을 목적으로 한다.

• 한국생산제조학회지
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• 제26권1호
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• pp.137-143
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• 2017

An axial fan has competitive advantages that can make air flow more straight and longer and produce larger air volume than the other kinds of fans. In those reasons, axial fans are widely used for ventilator, 4D cinema, duct, and so on. But, as it was designed and manufactured without any mathematical analysis or computer simulations, it is difficult to develop the performance of axial fans. Actually the axial fan is designed and manufactured in industry by imitation or traditional method. Flow velocity and volume of axial fan are changed by pitch angle, frame, the number of blade, camber angle, and chord length. In this paper, the performance of axial fan was analyzed and by computer program known as CFD. Finally, we have designed a new axial fan whose velocity and volume is improved. The performance of new axial fan is also compared with the of conventional fans experimentally.

• 한국항공우주학회지
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• 제39권6호
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• pp.498-504
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• 2011

속도와 샤프트각 그리고 피치 변화에 따른 토크 평형상태의 자동회전에서 플래핑 거동 특성과 전진비의 변화를 조사하였다. 속도 증가에 따른 압축성 효과를 모사하기 위해 압축성 Navier-Stokes 솔버로 해석된 2차원 데이터를 Pitt/Peters 유도흐름 이론과 함께 사용하였고 토크 평형상태에 대한 세 변수의 조합을 찾기 위해 과도모사법(TSM)을 이용하였다. 토크 평형상태에서 최대 플래핑각을 속도, 샤프트각, 피치와의 관계로 나타내고 전진비 변화와 비교함으로써 후진깃의 역풍영역 확대가 로터의 자동회전 특성에 관여하는 현상을 정성적으로 고찰하였다.

• 현장농수산연구지
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• 제26권2호
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• pp.25-30
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• 2024

This study was conducted to develop the hanging type circular-patterned system that at maximizing the spatial efficiency of strawberry cultivation to increase yields, while also reducing labor and improving energy efficiency. The system consists of a cultivation bed units, longitudinal moving device, bed lifting device, front and rear transfer devices, lateral transfer device, nutrient supply device, and control unit. Performance testing revealed that the operational motor for longitudinal movement should have a torque of at least 0.1Nm based on the design weight and traction force of the cultivation bed unit. The power consumption required to move one cycle was calculated to be approximately 149Wh when performing harvesting or maintenance tasks for all 10 cultivation beds. Vibration angles measured during bed movement showed that the lateral transfer resulted in a roll angle ranging from -0.62° to 0.68° and a pitch angle ranging from -3.79° to 5.26°. For longitudinal transfer, the roll angle ranged from -3.37° to 3.36°, and the pitch angle ranged from -0.45° to 0.49°.

• ETRI Journal
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• 제41권1호
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• pp.23-31
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• 2019

Since the late 20th century, there has been rapid development in the display industry. Only 30 years ago, we used big cathode ray tube displays with poor resolution, but now most people use televisions or smartphones with very high-quality displays. People now want images that are more realistic, beyond the two-dimensional images that exist on the flat screen, and digital holography-one of the next-generation displaysis expected to meet that need. The most important parameter that determines the performance of a digital hologram is the pixel pitch. The smaller the pixel pitch, the higher the level of hologram implementation possible. In this study, we fabricated the world-smallest $3-{\mu}m$-pixel-pitch holographic backplane based on the spatial light modulator technology. This panel could display images with a viewing angle of more than $10^{\circ}$. Furthermore, a comparative study was conducted on the fabrication processes and the corresponding holographic results from the large to the small pixel-pitch panels.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2011년도 전력전자학술대회
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• pp.285-286
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• 2011

Wind turbine system is converting wind energy into electric energy. In nature, torque of the blade is nonlinear function. To get a high quality electric power, system needs control of blade angle. The control of a blade is divided into a stall regulation type and a pitch control type. Pitch control type is more expensive and complicated, but it can make torque of the blade in accordance with variable wind. This paper shows 2MW pitch control system's hardware and electric part.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 춘계학술대회 논문집
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• pp.831-836
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• 2011

The study described in this paper is aimed to maintain a constant output of wind turbine system via pitch control of wind turbine using Advanced PID(APID) controller. In order to improve dynamic response characteristic in terms of pitch angle and disturbance reject, the APID controller is developed. The structure of the APID is composed with derivative P controller and new type of integral control action. This new improved integral control has concept of error window and weight function concept. The performance of the APID control technique is compared with those of conventional ones via simulation. Simulation results show that the proposed method is effective and enhanced the dynamic performance of the system.