Study On The Characteristic And Spanwise Correlation Of Vortex-induced Focrce On Bluff Body

The main problem of this thesis is the character of vortex-induced force of the bluff body section and its spanwise correlation. The vortex-induced vibrations are caused by vortex shedding of the fluid through the surface of the bluff body, this process has not been fully understood. Due to the complexity of fluid - solid coupling problems, it is difficult to obtain the theoretical solution. The research methods for vortex-induced vibration mainly include the establishment of simplified model, computational fluid dynamics, wind tunnel test and field measurement. In the process of engineering practice, the wind tunnel test of segment model is usually used as the main means to evaluate the vibration performance of bridge structure.However, the segmented model test failed to incorporate the effect of the three-dimensional effect of vortex-induced vibration and the structural vibration mode into the consideration.given that the issue has not yet been universally recognized, so in the design of the bridge the vortex-induced force will still be regarded as completely correlatived, which is biased in the process of judging the vortex response and not conducive to the development trend of light weight of bridge structure. In this paper, two typical bluff body sections of rectangle and trapezoid are selecte, by analyzing the surface wind pressure coefficient of the segment model,the distribution of the vortex force in the cross section and the spanwise correlation are analyzed. The main contents include:1. This paper reviews the early development of bridge wind engineering, the research methods and research progress of vortex - induced vibration are briefly summarized and sorted out. Examples of projects such as the Rio de Janeiro Bridge in Brazil, the Second Severn Bridge in the United Kingdom, the Fourth Yangtze River Bridge in Nanjing, and other examples which suffered vortex-induced vibration have been introduced and some vibration suppression measures are also introduced.2. The phenomena and problems of vortex vibration are introduced from two aspects of 2D and 3D. The important factors such as Reynolds number, aerodynamic shape,turbulence, Scruton number and other vortex-induced vibration are discussed respectively. The three-dimensional vortex shedding in the flow around the bluff body is systematically collated. Some results of the three-dimensional analysis of vortex - induced vibration are summarized.3. A rectangular model and trapezoidal model with width to depth ratio B/D=5 were fabricated, in the elastic suspension and multi-point loading two support mode. The surface pressure coefficient of the model was measured using electronic pressure scanner valve. The distribution of wind pressure coefficient mean, root mean square and power spectral density along the cross section is studied in detail, and the distribution of vortex excitation is obtained. A method to identify flow separation points and reattach points is proposed, which would be used to explore the flow field characteristics..4. On the basis of the two - dimensional distribution of vortex, the spanwise correlation of vortex-induced force in different regions is studied. Useing the multi-point loading system to control the vibration form, the effects of frequency and amplitude on the spanwise correlation of vortex-induced force were studied, and the correlation function was fitted.In this thesis, the wind tunnel test of vortex-induced vibration of two typical bluff bodies is studied, the relationship between wind pressure coefficient and vortex velocity and the flow field in the wake is analyzed, the cross-correlation of vortex force is studied and the correlation function is fitted. It is helpful to further optimize the wind resistance design of large span bridge and calculate the vortex force and vortex vibration response reasonably.