• Wind and Structures
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• 제38권2호
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• pp.147-160
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• 2024

The aerodynamic force is a significant component that influences the stability and safety of structures. It has unstable properties and depends on computer precision, making its long-term prediction challenging. Accurately estimating the aerodynamic traits of structures is critical for structural design and vibration control. This paper establishes an unsteady aerodynamic time series prediction model using Long Short-Term Memory (LSTM) network. The unsteady aerodynamic force under varied Reynolds number and angles of attack is predicted by the LSTM model. The input of the model is the aerodynamic coefficients of the 1 to n sample points and output is the aerodynamic coefficients of the n+1 sample point. The model is predicted by interpolation and extrapolation utilizing Unsteady Reynolds-average Navier-Stokes (URANS) simulation data of flow around a circular cylinder, square cylinder and airfoil. The results illustrate that the trajectories of the LSTM prediction results and URANS outcomes are largely consistent with time. The mean relative error between the forecast results and the original results is less than 6%. Therefore, our technique has a prospective application in unsteady aerodynamic force prediction of structures and can give technical assistance for engineering applications.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 춘계 학술대회논문집
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• pp.17-22
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• 2004

A space launch vehicle departs the ground in a low speed, soon reaches a transonic and a supersonic speed, and then flies in a hypersonic speed into the space. Therefore, the design of a launch vehicle should include the prediction of aerodynamic characteristics for all speed regimes, ranging from subsonic to hypersonic speed. Generally, Empirical and analytical methods and wind tunnel tests are used for the prediction of aerodynamic characteristics. This research presents considerable factors for aerodynamic analysis of a launch vehicle using CFD. This investigation was conducted to determine effects of wake over the base section on the aerodynamic characteristics of a launch vehicle and also performed to determine effects of the sting which exist to support wind tunnel test model.

• 한국군사과학기술학회지
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• 제11권4호
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• pp.20-28
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• 2008

Missile operating at supersonic conditions experiences considerable high temperature environments that is caused by aerodynamic heating as a result of the temperature gradient through boundary layer that surrounds it. This is one of important problems to the designer due to temperature limitation of structural materials. Because prediction of aerodynamic heating on missile needs unsteady calculation according to a flight trajectory, approximate method approach is efficient at design stage. In this paper, improved aerodynamic heating analysis scheme is introduced, which calculates heat flow and temperature by simple pressure field prediction on a missile body and fin. The prediction results are compared with measured data and MINIVER codes results.

• Wind and Structures
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• 제38권6호
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• pp.445-459
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• 2024

To model the aeroelasticity in vortex-induced vibrations (VIV) of slender tubular towers, this paper presents an approach where the aerodynamic damping distribution along the height of the structure is calculated not only as a function of the normalized lateral oscillation but also considering the local incoming wind velocity ratio to the critical velocity (velocity ratio). The three-dimensionality of aerodynamic damping depending on the tower's displacement and the velocity ratio has been observed in recent studies. A contour map model of aerodynamic damping is generated based on the forced vibration tests. A sectional calculation procedure based on the spectral method is developed by defining the aerodynamic damping locally at each increment of height. The proposed contour map model of aerodynamic damping and the sectional calculation procedure are validated with full-scale measurement data sets of a rotorless wind turbine tower, where good agreement between the prediction and measured values is obtained. The prediction of cross-wind response of the wind turbine tower is performed over a range of wind speeds which allows the estimation of resulting fatigue damage. The proposed model gives more realistic prediction in comparison to the approach included in current standards.

• 한국음향학회지
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• 제36권2호
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• pp.89-99
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• 2017

멀티로터형 무인항공기는 군사용 목적뿐 아니라 항공 촬영 및 무인 택배 수단 등 민간 산업까지 그 활용 범위를 넓혀가고 있다. 무인항공기의 보다 폭넓은 활용을 위해서는 추진체인 프로펠러의 공력 효율 개선과 소음의 저감을 위한 연구가 선행되어야 하며, 이는 주어진 환경에서 공력 성능 및 소음을 예측할 수 있는 기술이 바탕이 되어야만 가능하다. 본 연구에서는 소형 무인항공기 프로펠러를 대상으로 공력 및 소음 예측 기법을 개발하고, 실제 측정을 통한 결과와의 비교를 통해 검증하였다. 분당 회전수의 변화에 따른 추력 및 토크와 주어진 위치에서의 주파수 스펙트럼 예측에서 모두 예측 기법의 신뢰성을 확보하였으며, 이를 통해 프로펠러의 형상 설계에 기반이 될 수 있는 기틀을 마련하였다.

• 항공우주기술
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• 제11권1호
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• pp.19-26
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• 2012

무베어링 로터 허브시스템 개발에서 할당된 공기역학적 허브 항력 요구도를 분석하여, 요구도에서 제시된 방법으로 입증 가능하도록 요구도를 구체화 시켰다. 초기 허브 형상에 대해 공력계수에 기반하여 항력 예측을 수행하였으며, 요구도 충족을 위한 설계 변경안을 제시하였다. 최종 형상에 대해 전산유체기법을 사용하여 항력 예측을 수행하였으며, 그 결과 구체화된 요구도를 만족시킴을 확인할 수 있었다. 또한 기 개발된 헬리콥터의 추세선으로부터 유추할 수 있는 허브 항력의 범위 내에 있음을 확인할 수 있다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 춘계학술대회
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• pp.414-419
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• 2007

This paper describes the prediction of aerodynamic performance and wake of HAWT in normal and yawed flow operation using potential based methods. In order to analyze aerodynamic performance of wind turbine WINFAS program is used, which is based on VLM(Vortex Lattice Method) and CVC(Constant vorticity contour) Free wake model. Some problems of CVC vortex filament method are investigated arid to improve these problems vortex ring wake are introduced in behalf of CVC vortex filament. The prediction results using the vortex lattice wake are compared to experimental data.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 춘계학술대회논문집; 경주코오롱호텔; 22-23 May 1997
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• pp.581-587
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• 1997

Numerical predictions of aerodynamic noise radiated by subsonic rotors are carried out. A time domain approach for Ffowcs-Williams Hawkings equation of acoustic analogy is used in developing a comprehensive rotor/fan noise prediction program to handle both arbitrary blade shapes and loading conditions. Since only the aeroacoustic aspects of rotors are considered here, the calculations are carried out for rotors with simple aerodynamic characteristics. Broadband noise from ingestion of turbulence is also considered. By incorporating discrete frequency noise prediction of steady loading with broadband spectrum, much better correlation at the low frequency region with experimental data is obtaind. The contributions from different noise mechanisms can also be analysed through this method.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
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• pp.59.2-59.2
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• 2011

Although there are many activities on the construction of wind farm to produce amount of power from the wind, in practice power productions are not as much as its expected capabilities. This is because a lack of both the prediction of wind resources and the aerodynamic analysis on turbines with far wake effects. In far wake region, there are velocity deficits and increases of the turbulence intensity which lead to the power losses of the next turbine and the increases of dynamic loadings which could reduce system's life. The analysis on power losses and the increases of fatigue loadings in the wind farm is needed to prevent these unwanted consequences. Therefore, in this study velocity deficits have been predicted and aerodynamic analysis on turbines in the far wake is carried out from these velocity profiles. Ainslie's eddy viscosity wake model is adopted to determine a wake velocity and aerodynamic analysis on wind turbines is predicted by the numerical methods such as blade element momentum theory(BEMT) and vortex lattice method(VLM). The results show that velocity recovery is more rapid in the wake region with higher turbulence intensity. Since the velocity deficit is larger when the turbine has higher thrust coefficient, there is a huge aerodynamic power loss at the downstream turbine.

• 한국소음진동공학회논문집
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• 제14권4호
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• pp.310-318
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• 2004

For many industrial problems originating from aerodynamic noise, noise prediction techniques, reliable and easy to apply, would be of great value to engineers and manufacturers. General algorithm is presented for the prediction of internal flow-induced noise from quick opening throttle valve in an automotive engine. This algorithm is based on the integral formula derived by using the General Green Function, Lighthill's acoustic analogy and Curle's extension of Lighthill's. Novel approach of this algorithm is that the integral formula is so arranged as to predict frequency-domain acoustic signal at any location in a duct by using unsteady flow data in space and time, which can be provided by the Computational Fluid Dynamics Techniques. This semi-analytic model is applied to the prediction of internal aerodynamic noise from a throttle valve in an automotive engine. The predicted noise levels from the throttle valve show good agreement with actual measurements. The results show that the dipole noise is dominant in this phenomena and the origin of noise sources is attributed to the anti-vortex lines formed in the down-stream from a throttle valve. This illustrative computation shows that the current method permits generalized predictions of flow noise generated by bluff bodies and turbulence in flow ducts.