The Pier is a very important building block of any large optical telescope. It is very
evident that there are several sources of strong vibrations all around the optical
telescope. A large height makes it more vulnerable to low frequency oscillations, both as
surface waves, as well as bulk oscillations. These vibrations may be transferred to the
optical system, which mainly happens through the pier, since it is directly connected to
the telescope. In order to avoid enhanced transfer of energy between pier and optical
system, it is important to ensure that the resonance frequency of the pier and the
telescope fixtures are fairly separated.
Hence, the as-built structure of telescope pier was modeled and simulated using FEM
analysis in Solidworks Package for finding the resonating modes. Also various test
procedures were defined and on-site testing was done using 3C geophones as well as
Piezoelectric sensors to validate the model and to closely observe the response of the
pier. The main mode in low frequency regime was found to occur at approximately 23Hz
by both the testing and simulations. Thus a few parameters about the telescope were
fixed. Theoretical supports are also provided for observed modes.
Also, a proof of concept was demonstrated for impulse response based resonance
frequency determination. It was also demonstrated that a low-cost piezoelectric sensor
based test-bench can be used for finding the resonating modes, compared to expensive
3C geophones.