원형 실린더 구조물의 와류하중 모델추정법
Mathematical Model Framework for Vortex Induced Wind Load of Circular Cylinder Structure
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초록
지난 50여 년간의 연구를 통해서 와류진동의 발생메커니즘과 폭 넓은 이해를 위한 수학적 모델이 제시된바 있으나 대부분 실험적 고찰과 경험적 모델에 기반한 현상학적인 접근이 주로 이루어졌다. 와류진동과 그에 수반된 독특한 현상, 유체의 흐름과 구조물의 상호작용에 내포되어 있는 복합성과 난해성은 지금도 많은 연구자들의 관심을 불러일으키고 있으며, 와류진동에 대한 원초적인 발생원인 규명에 대한 새로운 도전이 지속적으로 이루어지고 있다. 본 연구에서는 하중식별법에 의해 와류하중을 직접 추출하고 스펙트럼분석을 통하여 와류하중을 구성하는 요소하중을 도출하는 과정을 보였다. 와류진동을 구성하는 요소하중은 구조물의 속도가 공력감쇠에 의하여 피드백되는 하중, 와의 발생에 의한 하중(스트로할 성분에 의한 순수와류하중), 버펫팅 하중으로 구분됨을 알 수 있었다. 각 요소 하중이 구조물 응답에 미치는 영향을 분석하여 본 연구에서 제시된 와류하중 모델도출법의 정합성을 보임으로서, 모델 구축방법의 타당성을 제시하였다. 이들 요소하중에 대한 정량적인 수학적 모델의 정립을 위해서는 피드백하중의 공력감쇠예측, 순수와류하중 스펙트럼의 정량적인 분포와 그 크기 예측, 버펫팅 하중의 스펙트럼 성상 예측이 이루어져야 한다. 이를 위해 풍동실험, 실계측과 같은 현상학적인 접근방법과 유체 흐름의 정형화된 수학적 모델인 나비에-스톡스 방정식과 연계된 CFD 해석을 병행하여 와류하중을 구성하는 요소하중들에 대한 정량화된 수학적 모델의 정립이 요구된다.
Abstract
Through the last 50 years of research history, mathematical models for vortex induced vibration(VIV) and its wide understanding have been developed, but mostly phenomenological approaches based on experimental investigations and empirical models have been made. The unique phenomenon associated with VIV, and the complexity inherent in fluid-structure interactions are still attracting much research interest, and new challenges for identifying the origin of VIV are constantly addressed. In this study, the vortex induced load(VIL) was directly extracted by the force identification technique and the load components constituting the VIL was illustrated through the spectrum shape analysis. From the analysis, it is found that VIL are consisted of three independent loads: the structural velocity feedback load associated with the aerodynamic damping, pure vortex induced load with respect to Strohal component, and the across-wind buffeting load. The validity of the model construction procedure provided in this study is shown by analyzing the effect of each load on the response of the structure. In order to establish a more quantitative mathematical model for these component loads, the aerodynamic damping prediction, the quantitative distribution of the pure VIL spectrum, and the spectral property prediction of the buffeting load should be performed. For this, a phenomenological approach such as wind tunnel test, and field measurement should be collaborated with CFD technique based on the Navier-Stokes equation, which is a formal physical, mathematical model of fluid motion, to construct quantitative mathematical models of VIL.
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