Yan Bao

Semi-Active Direct Velocity Control Method of Dynamic Response of Spatial Reticulated Structures Based on MR Dampers:

In this paper, a semi-active optimal control strategy for spatial reticulated structures (SRS) with MR dampers subjected to dynamic actions was proposed. The motion equation of SRS embedded with MR dampers was set up. The performance function of the optimal control strategy including both the structural responses and the control efforts was constituted for the optimization of feedback gain and MR damper placement in SRS, and an integrated method of genetic-gradient based algorithm was developed to solve this optimization problem. The clipped-optimal semi-active control strategy in the conjunction of velocity output feedback was applied to compute the desired control force from the MR dampers. Finally, a numerical example of SRS dealing with optimal placement of MR dampers and feedback gains of control system demonstrates the validity of the present semi-active optimal control strategy.

Modification of turbulent wake characteristics by two small control cylinders at a subcritical Reynolds number

In this paper, the flow around a main circular cylinder with two small control cylinders is numerically investigated at a subcritical Reynolds number of 3900. Two small control cylinders with diameter ratio of d/D = 0.04 (d and D are the diameters of the control cylinders and the main cylinder, respectively) are symmetrically placed inside the separated shear layers emanating from the main cylinder. The computation is performed with highly resolved direct numerical simulations employing a high-order spectral/hp element method. For validation purposes, the results of the flow over a single cylinder are presented at first, and the current simulation is in good agreement with the existing experiments and large eddy simulations. For the main cylinder with the two control cylinders, the dynamics of shear layers is found to be modified strongly owing to the disturbance from the small control cylinders. As a consequence, the recirculation length is decreased by 89% as compared to that of a single cylinder. The presence of the small control cylinders further leads to a significant increase in the fluctuating lift and the mean drag exerting on the main cylinder. Furthermore, the statistical analysis and turbulent wake visualization imply that the turbulent intensity is amplified in the near wake region and becomes weaker further downstream. This study then suggests that the small control cylinders located in the near wake region of the main cylinder may work differently in the turbulent wake against that in the laminar wake.In this paper, the flow around a main circular cylinder with two small control cylinders is numerically investigated at a subcritical Reynolds number of 3900. Two small control cylinders with diameter ratio of d/D = 0.04 (d and D are the diameters of the control cylinders and the main cylinder, respectively) are symmetrically placed inside the separated shear layers emanating from the main cylinder. The computation is performed with highly resolved direct numerical simulations employing a high-order spectral/hp element method. For validation purposes, the results of the flow over a single cylinder are presented at first, and the current simulation is in good agreement with the existing experiments and large eddy simulations. For the main cylinder with the two control cylinders, the dynamics of shear layers is found to be modified strongly owing to the disturbance from the small control cylinders. As a consequence, the recirculation length is decreased by 89% as compared to that of a single cylinder. The p...