음향-구조 연성해석기법을 활용한 모형벌브수차 공진회피설계 검토
Resonance avoidance design verification of scale model bulb turbine using vibro-acoustic FSI
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초록
벌브수차를 비롯해 수중에서 운전되는 수차들은 구조물과 접하는 유체의 부가질량효과로 인해 고유진동수에 변화가 생긴다. 공진회피 설계를 위해서는 수차 실제 운용조건에서의 고유진동수를 파악해야 하며, 연성해석기법의 하나인음향-구조 연성해석을 통해 이러한 사례를 분석할 수 있다. 본 연구에서는 실물수차 설계에 앞서 축소모형수차의 수중고유진동수를 전산해석을 통해 구하고 이를 수력학적, 기계적, 전자기적 가진원들의 주파수와 비교하여 수차의 공진회피설계 여부를 확인했다. 해석결과 1~6차 수중고유진동수는 253.46~473.67Hz 범위에 분포했고, 이는 운전주파수, 깃통과주파수를 비롯한 다양한 수력학적 가진 주파수 및 전자기적 가진주파수와 최소 100% 이상 분리되어 이들 가진원에 대한공진은 발생하지 않을 것으로 예상된다. 또한 동일한 해석기법과 분석절차는 향후 벌브형 수차를 비롯한 다양한 수차설계에 적용할 수 있을 것이다.
Abstract
Hydro turbines as well as bulb turbine, which are operated in water, have different natural frequencies due to added mass effect of immersed structure in fluid compared with case of dried condition. Thus actual operational condition of turbine must be considered for resonance avoidance design and vibro-acoustic FSI can be a verifying solution of this analysis. In this study, natural frequencies of scale model turbine was attained using computational analysis then compared with frequencies of hydraulic, mechanical and electro-magnetical vibration sources in advance of real scale turbine design. As the result of FSI analysis, 1~6th natural frequencies of immersed condition were found within 253.46~473.67Hz. These frequencies have more than 100% separation with those hydraulic excitations as well as operation, blade passing, RSI, VIV, Karman vortex and electro- magnetic excitations, thus no probability of resonance will be expected in these excitations. This FE analysis method and verifying process can be applied to various hydro turbine as well as bulb turbine.
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