Finite element analysis of TMT vibrations transmitted through Telescope-Enclosure-Soil Interaction

Telescope-Enclosure-Soil Interaction could result in additional telescope movement due to two main sources: (i) enclosure windshake and (ii) vibrations of machinery located at enclosure, summit and utility facilities. To analyze and minimize these vibrations, a novel FE model was developed based on existing FE models for the TMT enclosure and telescope structures. This integrated structural model adequately represents propagation of vibrations from the source to the telescope structure through surrounding soil/rock region. The model employs 3-D linear-elastic harmonic analysis using commercial FE code ANSYS. Special attention was devoted to adequate modeling of reflecting and non-reflecting boundary conditions. Based on the FE model developed, we examined the effects of soil/rock stiffness and damping upon telescope vibrations and, ultimately, seeing quality. The effects of location, intensity and spectral content of main sources of machinery vibrations were also investigated.