Study On The Nonlinear Self- Excited Aerodynamic Force And Galloping Characteristics Of H- Shaped Cross Section Structures

The self-excited aerodynamic of bluff body showed obvious nonlinearity, and it is easy to occur the vertical and torsional galloping. This thesis emphasizes the experimental study of the galloping characteristics of H-shaped cross section model on three aspect ratios and the nonlinear aerodynamic characteristics of H-shaped cross section model by the use of CFD. In this thesis, the calculation method of the vertical galloping with non-zero wind attack angle is derived, the results are in good agreement with the experimental results, and the energy method is used to explain the phenomenon observed in the experiment.The main work of this thesis includes:1、The nonlinear self-excited aerodynamic force on H-shaped cross section model is studied by using CFD.It is found that the vortex-induced force is likely to be "captured" by a certain order self-excited aerodynamic force, which leads to a sudden increase in the amplitude of this order of self-excited aerodynamic force. The amplitude increases along with the wind speed, but the initial phase does not change regularly as the wind speed increases.2、The calculation method of galloping critical wind speed and amplitude with wind attack angle was deduced. The square column, triangular column and H-shaped column are used as examples in the critical wind speed calculation. It is found that the results of this method is very close to the ones of Den-Hartog formula under the smaller wind attack angle, however, as the wind attack angle gets larger, the difference of the results gets greater as well. Taking the H-shaped cross section model as an example into the calculation of amplitude, it is found that the results of theoretical calculation and the experiment are very close, which proves the accuracy of the calculation method.3、Test equipment for free torsional vibration of single-degree freedom is developed independently. By using this equipment, the tests on the self-excited vibration of H-shaped cross section models are done. It is found that sufficient initial disturbance is required for the models with the aspect ratios of 4.72:1 and 2.5:1 to gallop under a certain wind speed. In addition, there might be two amplitudes under a certain wind speed when the aspect ratio is 2.5:1.4、The divergence principle of the galloping on H-shaped cross section model are explored by using energy method, which explained the phenomenon happens in the torsional vibration experiment. The reason why sufficient initial disturbance is required for the model with the aspect ratio of 4.72:1 to gallop under a certain wind speed is that the negative work of the self-excited aerodynamic force on the trailing edge of the model is so much that the total work on the model is negative.