서울의 PPNG 발생 빈도(1991-1992)

김재홍,윤기범,박평원,김영진,전경민,김영태,김중환,곽호,구상완,송민석,유옥,지혜구,김동원,문상은,박영립,정승호,성범진,성순제,엄주용,황정열,이기홍,이주협,전태진 대한화학요법학회 1994 대한화학요법학회지 Vol.12 No.1

The prevalence of PPNG among pretreated gonorrhea cases isolated at the STD clinic of Choong-Ku Public Health Center in Seoul has been studied and reported annually since 1981. In 1991, 123 strains of N.gonorrhoeae were isolated, among which 58(47.1%) were PPNG. In 1992, 98 starains of N.gonorrhoeae were isolated, among which 51(52.0%) were PPNG. In all, 109(49.3%) strains were found to be PPNG among 221 strains isolated between 1991-1992. The prevalence of PPNG in Seoul showed increased tendency till 1989, thereafter, it has been stationary or slightly decreasing.

Prediction of Aerodynamic Loads for NREL Phase VI Wind Turbine Blade in Yawed Condition

Ki-Wahn Ryu,Seung-Hee Kang,Yun-Ho Seo,Wook-Ryun Lee 한국항공우주학회 2016 International Journal of Aeronautical and Space Sc Vol.17 No.2

Aerodynamic loads for a horizontal axis wind turbine of the National Renewable Energy Laboratory (NREL) Phase VI rotor in yawed condition were predicted by using the blade element momentum theorem. The classical blade element momentum theorem was complemented by several aerodynamic corrections and models including the Pitt and Peters’ yaw correction, Buhl’s wake correction, Prandtl’s tip loss model, Du and Selig’s three-dimensional (3-D) stall delay model, etc. Changes of the aerodynamic loads according to the azimuth angle acting on the span-wise location of the NREL Phase VI blade were compared with the experimental data with various yaw angles and inflow speeds. The computational flow chart for the classical blade element momentum theorem was adequately modified to accurately calculate the combined functions of additional corrections and models stated above. A successive under-relaxation technique was developed and applied to prevent possible failure during the iteration process. Changes of the angle of attack according to the azimuth angle at the specified radial location of the blade were also obtained. The proposed numerical procedure was verified, and the predicted data of aerodynamic loads for the NREL Phase VI rotor bears an extremely close resemblance to those of the experimental data.

Effects of Support Structure Changes on Flow-induced Vibration Characteristics of Steam Generator Tubes

KI-WAHN RYU,CHI-YONG PARK,HUINAM RHEE 한국원자력학회 2010 Nuclear Engineering and Technology Vol.42 No.1

Fluid-elastic instability and turbulence-induced vibration of steam generator U-tubes of a nuclear power plant are studied numerically to investigate the effect of design changes of support structures in the upper region of the tubes. Two steam generator models, Model A and Model B, are considered in this study. The main design features of both models are identical except for the conditions of vertical and horizontal support bars. The location and number of vertical and horizontal support bars at the middle of the U-bend region in Model A differs from that of Model B. The stability ratio and the amplitude of turbulence-induced vibration are calculated by a computer program based on the ASME code. The mode shape with a large modal displacement at the upper region of the U-tube is the key parameter related to the fretting wear between the tube and its support structures, such as vertical, horizontal, and diagonal support bars. Therefore, the location and the number of vertical and horizontal support bars have a great influence on the fretting wear mechanism. The variation in the stability ratios for each vibrational mode is compared with respect to Model A and Model B. Even though both models satisfy the design criteria, Model A shows substantial improvements over Model B, particularly in terms of having greater amplitude margins in the turbulence-excited vibration (especially at the inner region of the tube bundle) and better stability ratios for the fluid-elastic instability.

Characteristics of Flow-induced Vibration for CE Type Steam Generator Tube with Various Column and Row Number

Ki-Wahn Ryu(유기완),Bong-Ho Cho(조봉호),Chi-Yong Park(박치용),Su-Ki Park(박수기) 한국소음진동공학회 2002 한국소음진동공학회 학술대회논문집 Vol.2002 No.11(영문초록)

CE형 증기발생기 전열관의 행열 변화에 따른 유체유발진동 특성

유기완(Ki-Wahn Ryu),조봉호(Bong-Ho Cho),박치용(Chi-Yong Park),박수기(Su-Ki Park) 한국소음진동공학회 2002 한국소음진동공학회 심포지엄 Vol.2002 No.1

Prediction of Aerodynamic Loads for NREL Phase VI Wind Turbine Blade in Yawed Condition

Ryu, Ki-Wahn,Kang, Seung-Hee,Seo, Yun-Ho,Lee, Wook-Ryun The Korean Society for Aeronautical and Space Scie 2016 International Journal of Aeronautical and Space Sc Vol.17 No.2

Aerodynamic loads for a horizontal axis wind turbine of the National Renewable Energy Laboratory (NREL) Phase VI rotor in yawed condition were predicted by using the blade element momentum theorem. The classical blade element momentum theorem was complemented by several aerodynamic corrections and models including the Pitt and Peters' yaw correction, Buhl's wake correction, Prandtl's tip loss model, Du and Selig's three-dimensional (3-D) stall delay model, etc. Changes of the aerodynamic loads according to the azimuth angle acting on the span-wise location of the NREL Phase VI blade were compared with the experimental data with various yaw angles and inflow speeds. The computational flow chart for the classical blade element momentum theorem was adequately modified to accurately calculate the combined functions of additional corrections and models stated above. A successive under-relaxation technique was developed and applied to prevent possible failure during the iteration process. Changes of the angle of attack according to the azimuth angle at the specified radial location of the blade were also obtained. The proposed numerical procedure was verified, and the predicted data of aerodynamic loads for the NREL Phase VI rotor bears an extremely close resemblance to those of the experimental data.

피치각 변화에 따른 헬리콥터 로터에서의 두께 및 하중소음 방사

유기완(Ki-Wahn Ryu) 한국항공우주학회 2007 韓國航空宇宙學會誌 Vol.35 No.10

정지비행시의 헬리콥터 로터 모형의 블레이드의 피치각 변화가 소음방사에 미치는 영향을 수치해석을 통해 파악하였다. 공력 자료는 비정상 패널법과 경험후류 방법을 이용하여 구하였으며, 0°에서 9°까지 등간격으로 1.5° 씩 피치각을 증가시키면서 블레이드 표면상의 공력 하중 분포를 얻어내었다. 수치해석을 통해 얻어낸 두께 소음은 피치각에 무관한 결과를 보였으나, 하중소음은 피치각이 1.5° 씩 증가할 때 마다 대략 3~4㏈A정도로 소음의 세기가 증가하는 경향을 보였으며, 이정도의 증가분은 소음이 더 커졌음을 감지할 수 있는 충분한 크기라 할 수 있다. 또한 하중소음의 방향성 결과로부터 블레이드의 윗면 보다는 아랫면에서의 소음의 세기가 더 크게 나옴을 알 수 있었다. Noises from the helicopter rotor model are calculated numerically at various pitch angles. The aerodynamic data are calculated by using prescribed wake model and unsteady panel method. The distribution of aerodynamic loads on the blade surface are obtained from 0° to 9° pitch angles with equiangular increments of 1.5°. Although thickness noise is not related to the change of pitch angles, loading noise level increases about 3~4㏈A every 1.5° increment of pitch angle. The additive noise level shows sufficient value to perceive the loudness. From the result of directivity pattern the sound level at the lower region of the blade disc plane is higher than that of the upper region.

가변 피치형 수평축 풍력 터빈의 공력 최적설계 및 피치제어 성능 연구

유기완(Ki-Wahn Ryu) 한국항공우주학회 2007 韓國航空宇宙學會誌 Vol.35 No.10

피치 제어형 수평축 풍력터빈에 대한 공력최적 설계 형상과 피치 변화에 따른 공력 성능 특성을 수치적으로 계산하였다. 수치적 방법은 날개 요소이론을 적용하였으며, Prandtl의 팁 손실 효과, 에어포일의 분포 효과, 후류의 회전 효과 등을 고려하였다. 블레이드 설계에는 총 6개의 서로 다른 에어포일을 사용하였으며, 구조적 강성을 갖기 위해서 허브 측에는 최대 40% 두께비의 에어포일을 분포시켰다. 최적 설계에서 얻어진 비선형 코드 길이는 제작성과 무게 등을 고려하여 선형화 시켰고, 선형화에 따른 공력성능 변화는 무시할만하다는 결과를 얻어내었다. 피치각 변화에 따른 동력성능, 추력성능, 토크 성능 곡선을 비교한 결과 3°의 피치각 변화에도 민감한 공력 값의 변동이 생김을 알 수 있었고, 정밀한 피치 제어를 위한 각도 제어는 증분이 3°보다 작은 값으로 피치 제어 알고리즘과 피치 구동장치가 필요함을 알 수 있었다. 또한 최대 토크는 설계속도비보다 작은 속도비에서 발생되는 결과를 보여주었다. Optimal aerodynamic design for the pitch-controlled horizontal axis wind turbine and its aerodynamic performance for various pitch angles are performed numerically by using the blade element momentum theory. The numerical calculation includes effects such as Prandtl's tip loss, airfoil distribution, and wake rotation. Six different airfoils are distributed along the blade span, and the special airfoil i.e. airfoil of 40% thickness ratio is adopted at the hub side to have structural integrity. The nonlinear chord obtained from the optimal design procedure is linearized to decrease the weight and to increase the productivity with very little change of the aerodynamic performance. From the comparisons of the power, thrust, and torque coefficients with corresponding values of different pitch angles, the aerodynamic performance shows delicate changes for just 3° increase or decrease of the pitch angle. For precisive pitch control, it requires the pitch control algorithm and its drive mechanism below 3° increment of pitch angle. The maximum torque is generated when the speed ratio is smaller than the designed one.

소형 UAV 프로펠러 형상에 따른 소음 방사

유기완(Ki-Wahn Ryu) 한국소음진동공학회 2019 한국소음진동공학회 학술대회논문집 Vol.2019 No.10

풍동실험을 통한 수평축 풍력터빈 모델의 공력성능 연구

유기완(Ki-Wahn Ryu),윤성준(Seong-Jun Yoon),이창수(Chang-Su Lee),최성옥(Seong-Ok Choy) 한국항공우주학회 2007 韓國航空宇宙學會誌 Vol.35 No.11

공기역학적으로 최대동력계수를 얻을 수 있도록 최적화된 블레이드를 장착한 수평축 풍력터빈 모델을 아음속 풍동에 장착하여 공력특성을 실험하였다. Upwind 방식과 downwind 방식의 풍력 터빈 로터의 공력 특성을 비교하였을 때, 후자가 전자에 비해 측정토크의 교란이 더 크게 나타났으며, 이는 지지대에서 발생된 후류와 블레이드의 상호간섭이 원인으로 작용한다고 여겨진다. 블레이드 설치각이 0°인 경우에 설계 속도비 6에 해당하는 위치에서 최대 동력계수를 보여주고 있어 설계 조건을 잘 만족함을 알 수 있었다. 또한 음의 피치각 변화가 같은 값의 양의 피치각 변화에 비해 더 커다란 동력 감소가 발생되는 결과를 보여주었다. Wind turbine experiment was carried out for the horizontal axis wind turbine with the aerodynamically optimized blade. From the comparison of aerodynamic performance between upwind and downwind type wind turbine rotor, the measured torque fluctuation of the latter is larger than that of the former. This phenomenon is owing to the interaction of wake generated from support column and blades. The wind turbine model satisfies the design condition in that the measured result of the power coefficient at zero pitch angle shows maximum peak at the designed tip speed ratio, λ= 6. It also shows that the decrease in aerodynamic power due to negative pitch change is more sensitive than that of the same positive pitch change.