CFD에 의한 장대교량의 플러터 해석

민원 建國大學校 大學院 2002 국내박사

Wind tunnel tests have been carried out for analysing flutter of long-span bridges, but it has disadvantages in their costs and times. This study proposes the flutter analysis of long-span bridges by using Computational Fluid Dynamics(CFD) not only for substituting wind tunnel tests, but also for improving the wind study for bridge design. This study mainly consists of non-linear analysis of aerodynamic properties, calculation of flutter derivatives, and analysis of flutter. The non-linear analysis focuses on computing aerodynamic properties for bluff bodies, and the calculation of flutter derivatives and analysis of flutter are done to evaluate the accuracy and applicability of the analysis for bridge design. A computer program for non-linear analysis of aerodynamic properties is developed using Penalty Finite Elements Method (Penalty FEM), formulated by weak-form of FEM. Picard Method is adopted in solving the non-linear equations. The program is applied to analyze the aerodynamic properties, and the flutter derivatives are mathematically approached by solving Wagner's indicial function. In the analysis of flutter, single mode analysis is used. To verify the numerical analysis suggested in this study, two rectangular sections having different aspect ratio are used. For those sections, both numerical analysis and wind tunnel test are carried out, then aerodynamic coefficients and flutter derivatives gotten from two methods. It is shown that the results are almost the same. As an example of analysis for long-span bridges, Seo-Hae Grand Bridge, a cable stayed bridge in Gyeonggi, Korea, and Nam-Hae Grand Bridge, a suspension bridge in Gyeongnam, Korea, are used, and the results of analysis are compared with those of wind tunnel tests which have been carried out during design stage. Consequently, it is proved that the results of a non-linear analysis in this study are very similar to the results of wind tunnel tests. Moreover, flutter derivatives for Seo-Hae Grand Bridge are mathematically obtained by indicial functions. It is presented that most of the derivatives are very similar to the results of wind tunnel test. A critical flutter wind velocity is gotten by a single mode flutter analysis using flutter derivatives obtained from the numerical analysis for Seo-Hae Grand Bndge and Nam-Hae Grand Bridge, and it is shown that the critical flutter velocity gotten from the numerical analysis is thus almost same as that from wind tunnel tests. From the result described above, it is proved that most results of numerical analysis in this study are equal or similar to those of wind tunnel test and wind study Therefore, the numerical analysis method by CFD, proposed in this study, is surely applicable to analysis in flutter of long-span bridges.

Indicial 함수를 이용한 플러터계수 산출

송진원 建國大學校 2006 국내박사

한글초록:장대교량은 풍동실험을 통해 플러터에 대한 내풍안정성을 평가하는 것이 일반적이다. 하지만 모형제작과 실험에 많은 시간과 자금이 소요되는 비효율성으로 인해 최근에는 전산유체역학를 통해 풍동실험을 대체하려는 노력이 계속되고 있다.본 연구에서는 풍동실험을 대체할 수 있는 효율적인 플러터 해석을 위해 CFD 프로그램인 FLUENT를 이용하여 Indicial 함수를 생성하고, 생성된 Indicial 함수의 FFT 해석을 통해 Flutter 계수를 구함으로서 Flutter 해석을 수행하는 수치해석을 수행하였다.먼저 Indicial 응답을 구하기 위해서는 순간적인단면의 변화시 일어나는 양력계수와 모멘트 계수를 구해야 하는데, 기존의 연구에서는 영각의 순간적인 움직임을 모사하기가 어려워 일정상태의 영각을 고정시킨 상태에서 양력계수와 모멘트 계수를 구하는 방법을 사용하였다. 본 연구에서는 정상상태에서 단면의 영각을 변화시키는 과정을 C++로 작성한 FLUENT 의 UDF(User Defined Function)를 사용하여 모사함으로서 Indicial 응답 의 정확성을 높였고, 이를 바탕으로 도출된 플러터 계수역시 좀 더 정확한 값을 보여주었다.해석에 사용된 단면은 NACA0012 비행날개의 단면과 단면비(B/D) 3,4,5,10,15 의 뭉뚝한 단면 그리고 비대칭 단면형상에 대해서 해석을 수행하여 풍동실험결과와 비교하였다. 또한 영각이 3도로 고정된 기존의 해석법과 영각이 0ꔆ에서 3ꔆ로 회전하는 두가지 경우에 대해 층류와 난류의 경우를 모두 해석하여 상호 비교하였다.최종적으로 실제교량에 적용하기 위해 유선형 단면을 가진 형재대교와 π형 단면을 가진 서해대교단면을 선정하여 전산해석을 수행하였으며 풍동실험 결과와 비교하였을때 영각을 회전시킨 본 연구방법이 중요 계수인 H1, H4, A2, A3 의 경우에 기존의 방법보다 더 잘 일치하고 있음을 확인하였다 영문초록:Wind tunnel tests have in general been carried out for evaluating aerodynamic stability of long-span bridges against flutter. However, recent studies are poised to substitute Computational Fluid Dynamics (CFD) for wind tunnel tests, which are regarded relatively inefficient in their costs and times spent in miniature productions and experiments.The central focus of this study is the numerical analysis of flutter which may be the alternative to wind tunnel tests, by producing indicial function with the FLUENT, a commercial CFD program to evaluate flutter derivative via FFT analysis of the produced indicial function. The first step for obtaining indicial response is to compute lift coefficient and moment coefficient at the time of abrupt change in the attitude of the body. While most previous studies used the method to compute lift coefficient and moment coefficient with fixing the angle of attack under certain conditions due to difficulties in simulating momentary motion of the angle of attack, this study shows increase in accuracy of indicial response by portraiting the changing process of the angle of attack of the body after reaching steady state using the user defined function (UDF) of the FLUENT.The results of wind tunnel tests were compared with the numerical results on the body of NACA0012 airfoil, the bluff bodies of B/D 3,4,5,10 and 15, and asymmetric body shape. The existing analytic method in which the angle of attack is fixed at three degree was compared with the case where the angle of attack is changing from zero to three degree in cases of laminar and turbulent flow respectively. In last a computational analysis based on the aforementioned method has been performed on the Hyung-Jae Grand Bridge with a streamlined body and the Seo-Hae Grand Bridge, Woodoo-Jonghwa Grand Bridge with a π-type body, and it is confirmed that the method introduced in the present study provides more identical numerical values than the existing method based on the material coefficients such as H1,H4, A2, A3

면내 곡률이 있는 날개의 공력 및 플러터 해석

조영빈 경상국립대학교 항공우주특성화대학원 2023 국내석사

Long-range international air travel has increased significantly and will continue to increase well. This trend and advances in flight technologies, such as aircraft structures, materials, propulsion, and electronics, have resulted in a renewed interest in supersonic cruise aircraft. The concept of curving the leading and trailing edges of the wings can improve aerodynamic performance and reduce the pitch-up instability associated with highly swept wings. Computational fluid dynamics (CFD) and time-domain flutter analyses have been conducted to investigate the effects of planform curvature (curving the leading and trailing edges of a wing in the x-y plane) on both aerodynamic and flutter characteristics of a series of three moderately swept-back wing models. For three-different wing models, moderate angle-of-attack conditions corresponding to cruise flight and high angle-of-attack conditions to landing are considered in this study. In addition, effective time-domain flutter analyses based on transonic small-disturbance equations have been conducted and compared with previous NASA wind-tunnel flutter test.

압축기 및 터빈 블레이드의 유동, 진동 및 플러터 해석

고승진 경상국립대학교 대학원 2026 국내석사

전산유체역학을 이용한 세장 구조물 단면의 플러터계수 추정

정승준 목포대학교 대학원 2007 국내석사

<국문초록> 장대교량은 바람의 영향에 민감하게 반응하며 장대교량의 플러터 현상은 풍동실험을 통하여 확인할 수 있다. 하지만 모형 제작 및 실험에 많은 비용과 시간이 소요된다. 본 논문에서는 풍동실험을 거치지 않고 구조물의 형상 변화에 따른 공기역학적 특성의 변화 양상을 예측할 수 있는 방법으로서 전산유동장해석에 기반한 수치해석적 방법을 제시하였다. 본 논문에서는 상용프로그램인 Fluent을 사용하여 진동체 주변의 난류 흐름으로부터 거더단면의 플러터 계수를 산정하였다. 플러터 계수는 내풍설계에 있어서 활용성이 높은 중요한 계수이다. 예제로 직사각형 거더단면에 대한 해석을 수행하였다. 구조물의 공탄성 해석을 위하여 구조물에 강제진동을 가하였다. 뭉뚝한 단면에 대하여 비교적 정확한 것으로 알려진 k- SST 모델을 적용하였다. CFD로 얻어진 구조물의 공기력 곡선과 강제진동곡선의 위상차로부터 플러터 계수를 추정하였다. 구조물과 바람의 상호작용 거동을 전산 유동해석법으로 평가함으로써 검토범위 내에서 해석적 접근의 가능성을 평가하였다. <Abstract> Long-span bridges are vulnerable to upcoming wind and wind tunnel tests usually have been carried out for estimating flutter behavior of the bridges. Wind tunnel tests, however, have disadvantages in their costs and times. The purpose of this paper is to investigate flutter-related motional properties, i.e. the so-called flutter derivatives, using the Computational Fluid Dynamics(CFD). Commercial program, the FLUENT, is utilized to model turbulence flow around oscillating structure and to obtain wind-induced force on the structure. As an example, analysis of turbulence flow around rectangular section is performed. The girder section is set to be oscillating harmonically and the aerodynamic force is measured. Turbulence of wind flow is modeled by the K-ω SST model, which is suitable to model the flow around a bluff-structure. The flutter derivatives were evaluated from the phase difference between forced vibrating motion and simulated time history of aerodynamic force. This study estimated feasibility of analytical approach of the Computational Fluid Dynamics(CFD) in estimating flutter derivatives with limited girder sections and analysis conditions.

Design of the Main Wing in Co-axial Compound Rotorcraft Considering Whirl Flutter Stability

염제완 서울대학교 대학원 2021 국내석사

Rotorcraft has been utilized in various fields thanks to its vertical take-off/landing and hover capability, but is limited in terms of the speed and range due to its aerodynamic aspects such as compressibility, aeroelastic stability, and stall. Recently, there occurs a rise and growth in the research on the compound rotorcraft which has advantages from both fixed and rotary-wing aircraft. Because those have unique configurations distinguished from that of the conventional rotorcraft, new design factors should be taken into account. whirl flutter phenomenon, which usually occurs in an aircraft with a proprotor, is also observed in the compound rotorcraft with a proprotor, such as the tiltrotor. In this thesis, the three-dimensional feature of the main wing for a compound rotorcraft is suggested. Then three configurations are suggested to find structural integrity variation concerning their composite ply thickness. To estimate its structural intergrity, NASTRAN will be used to perform the relevant static analysis. And, modal analysis is performed and the natural frequencies/eigenvectors will be obtained. With those results, whirl flutter analysis via CAMRAD II and trend analysis using one factor at a time (OAT) method will be performed. 회전익기는 특유의 수직 이착륙과 제자리 비행 기능으로 다양한 분야에서 활용되어 왔으나, 압축성 효과, 공력탄성학적 안정성, 실속과 같은 이유로 최대 속도와 운용 반경에서 제약이 존재했다. 최근에는 기존 회전익기의 장점을 유지하면서 단점을 상쇄하고 고정익기의 장점을 동시에 보유한 복합형 회전익기에 대한 연구가 활발히 이루어지고 있다. 이러한 복합형 회전익기 중에는 주익에 프롭로터가 위치한 형상들도 존재하는데, 그러한 형상들의 경우 축류에 의해 프로펠러/나셀 시스템이 섭동되거나 짐발허브의 플래핑 자유도로 인해 세차운동을 하며 공력 하중이 발생하게 된다. 그리고 이러한 하중에 의해 훨플러터가 유발되므로 주익에 프롭로터가 위치한 복합형 회전익기는 설계 시 훨플러터가 고려되어야 한다. 본 논문에서는 동축반전형 복합형 회전익기의 3차원 형상을 설계하였다. 이후 3가지 형상을 제안하여, NASTRAN을 활용한 구조적 설계 여유와 CAMRAD II를 통한 훨플러터 해석을 수행하였으며 그 중 기본 형상을 정하고 이 형상에서 각 변수를 조절하며 임계 감쇠 값의 경향을 분석하였다.

초음속 유동에서의 판넬의 플러터 해석에 관한 연구

박경민 서울대학교 대학원 1994 국내석사

有限要素法에 의한 三次元 平板 플러터 解析

김영국 仁荷大學校 1986 국내석사

대형 풍력 블레이드 진동, 다이버전스 및 플러터해석

윤수희 경상대학교 항공우주특성화대학원 2016 국내석사

Wind power system produces electrical energy through the blade rotation due to wind flow in the atmosphere. Among wind, wave, and ocean current exposed to various external environments, marine nature involves a relatively large movement of the wind power system. It is essential to predict the power generation performance with the help of analysis techniques. The analysis techniques are also used to estimate the loading of the system. In addition, the fundamental structure of the rotor blades in the system is directly involved in the rotation which is determined to the capacity and efficiency of the generator. An accurate analysis method for the wind turbine system is required in accordance with its design. In this study, the modal analysis of a typical large offshore wind power system model, the NREL 5MW baseline wind turbine was performed using an equivalent modeling technique. The natural frequencies and model shape conducted by a multi-body dynamics solver was verified and compared to the reference data. Furthermore, the proven model of flutter analysis was performed in parking conditions of the wind turbine. The result of flutter analysis performed in this study would be expected to be utilized very useful in wind turbine design. The aeroelastic analysis techniques can provide the stability of structures for the future massive wind power systems. 풍력시스템은 대기 중 바람의 유동에 의한 로터 블레이드(rotor blade)의 회전력을 이용하여 전기에너지를 발생시킨다. 바람과 함께 파도, 해류, 조류 등 다양한 외부환경에 노출되고, 시스템의 특성상 비교적 큰 운동을 동반하는 해상풍력시스템은 하중, 운동, 발전 성능 등을 예측할 수 있는 해석기법의 도움이 필수적이다. 또한 시스템의 핵심 구조인 로터 블레이드는 회전에 직접적으로 관여하고, 자체 설계에 따라 발전기의 용량과 효율이 결정되므로 시스템 개발에 있어 정확도가 높은 해석기법이 필요하다. 본 연구에서는 대표적인 대형 해상풍력시스템 모델인 NREL 5MW Baseline Model Phase IV을 이용하여 등가 모델링을 수행한 후, 고유진동수와 모드형상을 실제 데이터와 비교 및 검증하여 등가 모델링 기법(equivalent beam modeling technique)을 이용한 해석결과의 타당성을 검증해보았다. 또한, 검증된 모델을 통해 정지 조건(parked condition)에서의 플러터 해석(flutter analysis)을 수행하였다. 본 연구에서 수행한 진동해석기법 및 플러터 해석결과는 향후 초대형 풍력터빈시스템의 설계 및 안정성 해석과 공탄성 해석기법 구축에 매우 유용하게 활용될 것이라 기대한다.

고속 공기유동 속에서 진동하는 압전 보의 출력 전압 해석 및 실험

박창민 경북대학교 대학원 2018 국내석사

Energy harvesting technology is attracting much attention as a new type of renewable energy technology. Although the energy density is not large, the total amount can be used as a considerable energy source. It can be easily obtained from nature, there is no environmental pollution problem, and it is highly applicable because it uses abandoned energy in daily life. In this study, to develop a piezoelectric energy harvesting system that generates high voltage in high-speed flow, the wind pressure applied to the piezoelectric beam in the flow is calculated and applied to the surface, and the output voltage is obtained through an analytical method. the wind tunnel test and the actual vehicle test with this model is proceeded to validate the analysis. Experimental results show that the output voltage tends to increase with decreasing the thickness of piezoelectric beam. The output voltage of a piezoelectric beam composed of a single piezoelectric polymer was measured by a wind tunnel test and 60 V can be obatained at 90 km/h of wind speed. We developed a piezoelectric beam that produces 60 V(211 V/cm3) and 18.7 mW(65 mW/cm3) at a high velocity of 90 km/h.