MS2.7 - Advances in Control of Structural Vibrations

Ground-borne vibration due to railway traffic is an increasingly important environmental concern. As it may cause malfunctioning of sensitive equipment and discomfort to people. Following earlier developments of metamaterials in the field of electromagnetics, photonics, and phononics, the aim of this research is to design an array of resonators installed between buildings and a railway track for vibration reduction. We develop an optimization method to enhance the performance of the metamaterials constrained by the vibration reduction in a wide frequency range (1-80 Hz) and in an extended volume of soil. The optimization relies on a 3D coupled finite element – boundary element method. The resonators are modeled as a single degree of freedom on top of square concrete foundations while the soil is considered to be a horizontally layered elastic halfspace. In order to develop an optimization method for metamaterials, the dynamic properties of the resonators and their geometrical configuration (distance between the resonators) are considered as design variables. Varying the dynamic parameters of the resonators, uniform and nonuniform configurations are studied. At present, a simplified formulation of the problem is considered, where the vibration reduction at a single point is targeted for a harmonic source, as this is expected to lead to a design that can be interpreted more easily. Local and global optimization methods using a gradient-based algorithm are explored. As expected, the performance in vibration reduction increases with the mass of the resonators. It is also observed how vibration reduction for a harmonic source requires the natural frequency of the resonators to be slightly higher than the frequency of the source. This is due to the fact that dynamic soil-structure interaction results in a lower natural frequency of the oscillator interacting with the soil. Next, the formulation of the optimization problem can be adapted to target vibration reduction over a larger area and in a wider frequency range.

This paper presents an optimal design of a passive-adaptive Pendulum-Tuned Mass Damper (PTMD) to mitigate the structural vibrations of Offshore Wind Turbine (OWT) with a flexi-ble monopile foundation considering the Pile-Soil Interaction (PSI). The OWT basis on the 5-MW baseline proposed by the National Renewable Energy Lab (NREL). The PSI is de-signed by a pile modeled as beam-column elements supported by nonlinear springs for lat-eral loads (p-y curves) and axial loads (t-z and Q-z curves), applied at the nodal points be-tween the elements. The estimation of wind and wave spectra, as well as the hydrodynamic and aerodynamic loads, are conducted by using an in-house built MATLAB® routine working together with an ANSYS® 3-D finite element (FE) global model for evaluating the resultant peak displacement response at the OWT hub by a power spectral density (PSD) analysis. Op-timum design cases of PTMD parameters are obtained by a Genetic Algorithm (GA) optimi-zation minimizing the structural response of the tower. A static analysis procedure evaluates the monopile displacements and stresses over the foundation, then the stresses along the pile and the structural responses of the tower are evaluated in function of the wind velocity at the hub.