Numerical flow models to simulate tuned liquid dampers (TLD) with slat screens

The tuned liquid damper (TLD) is increasingly being used as an economical and effective dynamic vibration absorber to mitigate the dynamic response of structures. In this paper the results of two numerical flow models of TLD behaviour are compared with experimental data. These include the free surface motion, the resulting base shear forces, and the energy dissipated by a TLD with slat screens. The importance of this experimental study is that it examines TLD behaviour over a large range of normalized excitation amplitude values, covering the practical range of serviceability accelerations for buildings subjected to wind loads and larger excitation amplitudes more representative of earthquake motion. In addition, the experimental results are used to assess the models for larger fluid depth to tank length values, and for the use of modelling TLDs equipped with multiple screens. For screens consisting of a number of thin plate slats, a method for determining the loss coefficient is presented, which is a required parameter for the models used in this paper. Findings indicate that the linear model is capable of providing an initial estimate of the energy dissipating characteristics of a TLD. The nonlinear model can accurately describe the response characteristics within the range of excitation amplitudes experimentally tested.     

Two-dimensional integral equation for a thin wind turbine blade rotating in the round tunnel

The paper presents a mathematical treatment of the aerodynamic problem about a thin wind turbine blade rotating in the round tunnel. The radius of the blade is almost the radius of the tunnel. This permits formulation of the boundary condition on the tip vortex line to the simple slip condition over the surface of the tunnel. By applying a standard technique from potential theory, the problem is reduced to a two-dimensional integral equation whose kernel is connected with a special Green's function satisfying the homogeneous Neumann boundary condition on the tunnel surface. This Green's function is constructed in an explicit analytical form.     

Non-linear multimodal model for tuned liquid dampers of arbitrary tank geometry

Tuned liquid dampers (TLDs) utilize sloshing fluid to absorb and dissipate structural vibrational energy. Simple TLD tank geometries may not always be feasible due to space limitations. While the non-linear modelling of sloshing fluid is currently limited to tanks of simple geometries, this paper develops a non-linear multimodal model which describes the sloshing behaviour of a fluid in a flat-bottom tank of arbitrary geometry. The mode shapes of the sloshing fluid are found by solving the Helmholtz equation over the tank domain using the finite element method. The Bateman-Luke variational principle is used to develop a system of ordinary differential equations which account for the coupling of the sloshing modes through the non-linear free surface boundary conditions. Damping is incorporated into the model by considering the drag produced on a set of damping screens inserted in the fluid. The system of ordinary differential equations is solved using the Runge-Kutta-Gill Method to predict the wave heights and sloshing forces. In general, the mode shapes in an arbitrary tank will have components in two orthogonal (x- and y-) directions. This out-of-plane behaviour is an important consideration for TLD design. The model is validated with existing models for the special cases of rectangular and circular tanks. Lastly, new shake table tests are conducted on a tank of complex geometry.     

结构主动开闭环多重调谐质量阻尼器（AMTMD）新控制策略

提出了一种新控制策略——主动开闭环多重调谐质量阻尼器(AMTMD)。AMTMD控制系统频率呈线性分布。AMTMD中的MTMD保持相同的刚度和阻尼系数但质量变化。基于TMD的工作原理定义了AMTMD的主动控制力构成即保持相同的位移和速度反馈增益系数但变化结构和地震加速度反馈增益系数。基于结构的广义振型模型，导出了设置AMTMD时结构的动力放大系数(DMF)，于是优化准则可定义为：Min．Min．Max．DMF．通过最优搜寻，研究了反映AMTMD有效性和鲁棒性的参数。这些参数包括：频率间隔、平均阻尼比、调谐频率比、总数、质量比和标准化加速度反馈增益系数。为了比较，多重调谐质量阻尼器(MTMD)和主动开闭环调谐质量阻尼器(ATMD)也被考虑。     

Improved non-dominated sorting genetic algorithm （NSGA）-II in multi-objective optimization studies of wind turbine blades

The non-dominated sorting genetic algorithm (NSGA) is improved with the controlled elitism and dynamic crowding distance. A novel multi-objective optimization algorithm is obtained for wind turbine blades. As an example, a 5 MW wind turbine blade design is presented by taking the maximum power coefficient and the minimum blade mass as the optimization objectives. The optimal results show that this algorithm has good performance in handling the multi-objective optimization of wind turbines, and it gives a Pareto-optimal solution set rather than the optimum solutions to the conventional multiobjective optimization problems. The wind turbine blade optimization method presented in this paper provides a new and general algorithm for the multi-objective optimization of wind turbines.