(Borja Sorazu, Alan Cumming, Giles Hammond)

This entry is an informative summary of some of the work we are doing/planning to do at Glasgow related to the monolithic suspensions and their violin modes R&D:

1) Identify actual fibre profiles of the installed fibres with actual masses.

2) Model aLIGO 'real' final stage suspension (with real fibre profiles) in ANSYS, to learn about the violin frequencies distribution and see how that can inform on identifying the higher order harmonics and their associated masses. Notice that only fundamental and fist harmonics are partially identified with actual test masses.

3) Use the model to estimate D factor for first 5 or 6 harmonics, and the energy distribution along the fibre length taking into account full fibre shape including necks and hopefully welds.

4) Use these energy ratios to weight the material loss factor equations. In this case, the material loss factor equations are used independently for each segment along the length of the fibre (therefore taking into account correctly the full fibre shape), and summed together and weighted by the energy ratio of each segment of the fibre, to give the full material loss of the fibre. Most probably we are talking about 500-1000 segments or so along each fibre's length.

5) The material loss factor equations we have used previously have used conservative estimates of parameters such as surface and weld loss, and subsequent measurements here in Glasgow have shown that the losses could be better than this, so we can give a range of possible losses (and hence noise spectra) using these and the FEA analysis, for the lower glass stage of the suspension, and compare these values with the measured Q's of the fundamental and higher harmonics of the violin modes. This information may help into understand if the low frequency noise has any thermal noise source.