Modeling and Simulation of Seismic Attenuation Systems for Gravitational Wave Interferometers

In order to detect gravitational waves (GW), the displacement of the test masses has to be reduced to the challenging level of 10^(-18) m/sqrt(Hz). For second generation detectors like Advanced LIGO the requirements are even more compelling. Since the seismic noise is the dominant low frequency noise source for terrestrial GW detectors, the performance and reliability of seismic attenuation systems play a critical role. This thesis analyzes the mechanical modeling and simulation of seismic attenuators for GW interferometers. The first part of our study concentrated on HAM-SAS, a single-stage passive mechanical isolator, proposed by the California Institute of Technology SAS group, that is designed to support the Advanced LIGO HAM vacuum chambers. Several analytical and numerical simulation techniques have been used in order to determine the performance, reliability and controllability of the system and to obtain a set of linear models that can be used for the active control of the attenuator. The second part of this work is dedicated to the pre-isolator stage of Virgo suspensions. We obtained a set of state-space representations of Virgo inverted pendulum using system identification techniques and we developed a Kalman filter, based on the linear models, that is able to estimate independently every resonance mode of the pre-isolator from open loop data.