• 국제초고층학회논문집
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• 제2권3호
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• pp.229-244
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• 2013

Twenty six pressure models of high rise buildings with various cross-sections including twisted models were tested in a boundary layer wind tunnel. The cross-sections were triangular, square, pentagon, hexagon, octagon, dodecagon, circular, and clover. This study investigates variations in peak pressures, and effects of various cross-sections and twist angles on peak pressures. To study the effects of various configurations and twist angles on peak pressures in detail, maximum positive and minimum negative peak pressures at each measurement point of the building for all wind directions are presented and discussed. The results show that peak pressures greatly depend on building cross-section and twist angle.

• 한국진공학회지
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• 제12권S1호
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• pp.33-35
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• 2003

The electrooptic properties of the reflected light in a reflective mode, $45^{\circ}C$twisted nematic liquid crystal (TNLC) cell were investigated in the voltage regions near and away from the Freedericksz transition threshold. The measured reflectivity away from the threshold voltage ($V_th$) could not be described by the model which assurnes a constant tilt angle as well as a linearized distribution of twist angle across the cell, although the data are well fitted near $V_th$. We found that in the voltage region away from $V_th$, the model considering the distributions of the tilt angle and the twist angle should be applied for the calculation of the reflectivity. The director-axis distributions were obtained from the numerical integration of the Euler-Lagrange equation.

• 한국항공우주학회지
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• 제43권9호
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• pp.765-772
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• 2015

칼새 비행의 생체모방 초소형 비행체 적용 가능성을 확인하기 위한 공력측정과 위상동기 PIV 연구가 수행되었다. 2축 회전자유도의 로봇 날개 모델과 불어내기식 풍동을 사용하였다. 비틀림 각은 ${\pm}0$, ${\pm}5$, ${\pm}10$, ${\pm}20$도의 진폭을 갖고, 스트로크각은 90도의 위상차를 갖는 단순조화함수로 변화시켰다. 비틀림 각에 따른 시간에 대한 양력계수 변화는 작은 공력감소와 지연만을 나타내며 주목할 만한 차이를 보이지 않았다. 그러나 항력은 작은 비틀림 각 변화가 큰추력을 생성할 수 있음을 보여주었다. 이러한 것들은 칼새가 비행 중에 작은 비틀림 각을 사용하는 이유를 간접적으로 설명해 준다. PIV연구 결과는 공력지연이 날개주위의 와류구조와 밀접한 관계있다는 것을 보여준다. 이러한 결과는 칼새 모방형 초소형비행체 설계에 있어 비틀림 각은 필수적인 파라미터로서 반드시 고려되어야 함을 의미한다.

• Wind and Structures
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• 제32권3호
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• pp.267-281
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• 2021

Bending-twisting coupling induced in big composite wind turbine blades is one of the passive control mechanisms which is exploited to mitigate loads incurred due to deformation of the blades. In the present study, flutter characteristics of bend-twist coupled blades, designed for load alleviation in wind turbine systems, are investigated by time-domain analysis. For this purpose, a baseline full GFRP blade, a bend-twist coupled full GFRP blade, and a hybrid GFRP and CFRP bend-twist coupled blade is designed for load reduction purpose for a 5 MW wind turbine model that is set up in the wind turbine multi-body dynamic code PHATAS. For the study of flutter characteristics of the blades, an over-speed analysis of the wind turbine system is performed without using any blade control and applying slowly increasing wind velocity. A detailed procedure of obtaining the flutter wind and rotational speeds from the time responses of the rotational speed of the rotor, flapwise and torsional deformation of the blade tip, and angle of attack and lift coefficient of the tip section of the blade is explained. Results show that flutter wind and rotational speeds of bend-twist coupled blades are lower than the flutter wind and rotational speeds of the baseline blade mainly due to the kinematic coupling between the bending and torsional deformation in bend-twist coupled blades.

• 대한기계학회논문집B
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• 제37권2호
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• pp.149-154
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• 2013

본 연구는 7kW 모터로 $18.5m^3/min$의 유량을 양정(H) 0.5m로 공급할 수 있는 고농도 폐수처리용 3엽 수중 펌프의 블레이드를 개발하는 것을 목표로 한다. 이를 위해 블레이드의 축방향 비틀림 각, 블레이드의 길이 및 반경방향 비틀림 각을 설계변수로 선정하여 이들이 블레이드 효율에 미치는 영향을 상용 해석용 프로그램을 사용한 (ANSYS BladeGen, Turbo Grid, CFX) 전산해석을 통해 수행하였다. 해석 결과 블레이드의 축방향 비틀림각(${\beta}$)가 펌프의 효율에 가장 민감한 변수임을 알 수 있었으며, 축방향 비틀림각 $({\beta})=20^{\circ}$, 반경방향 비틀림 각 $({\alpha})=110^{\circ}$ 그리고 블레이드의 길이 (l)=240 mm 일 때 펌프의 최고 효율을 가지게 됨을 알 수 있었다.

• 한국기계가공학회지
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• 제12권2호
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• pp.75-80
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• 2013

Cathode is an essential component used in plasma etching process which is to make micro pattern on the silicon wafer. The currently used cathodes produce particles at the high temperature plasma etching process. To overcome this problem, a 'Silicon Only Cathode' was developed. This 'Silicon Only Cathode' requires manufacturing process changes due to the change of shapes, material features, and machining characteristics of work materials. This research investigates the small hole drilling process. The conclusion is that PCD drills with twist angles of $20^{\circ}$ and $25^{\circ}$ were tested for small hole drilling and the experimental results indicate that the drill with $25^{\circ}$ twist angle drill causes less thrust force.

• Advances in Energy Research
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• 제6권1호
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• pp.35-54
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• 2019

A successful blade design must satisfy some criterions which might be in conflict with maximizing annual energy yield for a specified wind speed distribution. These criterions include maximizing power output, more resistance to fatigue loads, reduction of tip deflection, avoid resonance and minimize weight and cost. These criterions can be satisfied by modifying the geometrical parameters of the blade. This study is dedicated to the aerodynamic assessment of a 20 kW horizontal axis wind turbine operating with two possible airfoils; that is $G{\ddot{o}}ttingen$ 413 and NACA 2415 airfoils (the Gottingen airfoil never been used in wind turbines). For this study parameters such as chord (constant, tapered and elliptic), twist angle (constant and linear) are varied and applied to the two airfoils independently in order to determine the most adequate blade configuration that produce the highest annual energy output. A home built numerical code based on the Blade Element Momentum (BEM) method with both Prandtl tip loss correction and Glauert correction, X-Foil and Weibull distribution is developed in Matlab and validated against available numerical and experimental data. The results of the assessment showed that the NACA 2415 airfoil section with elliptic chord and constant twist angle distributions produced the highest annual energy production.

• Journal of Welding and Joining
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• 제20권5호
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• pp.93-98
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• 2002

The effect of bonding misfit on single crystallization of transient liquid phase (TLP) bonded joints of single crystal superalloy CMSX-2 was investigated using MBF-80 insert metal. The bonding misfit was defined by (100) twist angle (rotating angle) at bonded interface. TLP bonding of specimens was carried out at 1523K for 1.8ks in vacuum. The post-bond heat treatment consisted of the solution and sequential two step aging treatment was conducted in the Ar atmosphere. The crystallographic orientation analysis across the TLP bonded joints was conducted three dimensionally using the electron back scattering pattern (EBSP) method. EBSP analyses f3r the bonded and post bonded heat treated specimens were conducted. All bonded joints had misorientation centering around the bonded interface for as-bonded and post-bond heat treated specimens with rotating angle. The average misorientation angle between both solid phases in bonded interlayer was almost identical to the rotating angle at bonded interface. HRTEM observation revealed that the atom arrangement of both solid phases in bonded interlayer was quite different across the bonded interface. It followed that grain boundary was formed in bonded interface. It was confirmed that epitaxial growth of the solid phase occurred from the base metal substrates during TLP bonding and single crystallization could not be achieved in joints with rotating angle.

• 한국항공우주학회지
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• 제46권1호
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• pp.1-9
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• 2018

람다 날개 형태의 무인전투기는 동체-날개 융합익의 형태를 띄고 있어 일반적인 항공기에 비해 상대적으로 항력이 작고 레이더 반사 면적이 작아 우수한 스텔스 성능을 갖는다. 그러나 앞전 후퇴각에 의해 생성되는 앞전 와류의 영향으로 특정 받음각에서 피칭모멘트가 급격히 증가하는 현상이 나타난다. 본 연구에서는 무미익 람다 날개 형상을 기반으로 한 UCAV 1303 모델을 사용하여 풍동시험과 전산해석을 수행하였다. 실험 풍속은 50 m/s, 받음각 범위는 $-4^{\circ}{\sim}28^{\circ}$ 으로 하였으며 전산해석 또한 실험 조건과 동일하게 연구를 수행하였다. 본 연구를 통해 UCAV의 날개 비틀림이 피칭모멘트의 안정성에 미치는 영향을 확인하였다. 그 결과 날개에 음의 비틀림 각을 적용하였을 때 날개 바깥쪽에서의 유동 박리가 지연되면서 Pitch-break가 발생하는 받음각이 증가하였고, 양의 비틀림 각을 적용하였을 때 Pitch-break가 발생하는 받음각이 감소하였지만 양항비가 증가하는 것을 확인하였다.

• EDISON SW 활용 경진대회 논문집
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• 제4회(2015년)
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• pp.184-190
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• 2015

On wide variety of fields, studies on active twist control are becoming more active. For effective twist control, blades have to have low torsional stresses with high torsional deformations to the same magnitude of torque acting on its cross-section. In this study, 2D sectional analysis and 3D finite element analysis were made for 5 different blades with each having different cross - sections which have different spars. The results from 2D sectional analysis, were then put into 3D blade deformation and stress calculations which lead to analysis. Outcomes from 2D and 3D analysis, showed that on the same torque and concentrated load conditions, the blade with 'C' shaped spar was the best of all the blades which were used in this study.