Nonlinear Transient Seismic Analysis of Magellan Telescopes

CLIENT

Las Campanas Observatory (LCO)

Analysis, Dynamics, Optical Systems & Telescopes

CHALLENGES

The Magellan Telescopes have been in commission for over a decade and have experienced many earthquakes with little to no damage. The telescopes’ response to a survival level earthquake was unknown. The telescopes sit on a set of hydrostatic bearings that carry only compressive force – they will lift up if the preload due to gravity is overcome. Due to this nonlinearity, typical modal solutions would not produce accurate results and would not be able to predict nonlinear events such as bearing lift off.

SOLUTIONS

A nonlinear transient survival level seismic analysis was performed on the Magellan Telescopes using Abaqus/Standard 6.14. Stresses, strains, forces, displacements, and accelerations were monitored throughout the solution. Three different models were analyzed representing enveloping configurations of the telescope as well as both zenith and 60º off zenith pointing angles. A peak acceleration of 2.7g was calculated at the secondary mirror (peak input acceleration was 0.27g). Most of the peak responses were due to a modal excitation of the model, further exacerbated by the hydrostatic bearing nonlinearity. Accelerations at instrument locations will be used by LCO for instrument analysis and future instrument design. Displacements in the primary mirror were large enough that LCO is investigating their displacement envelope to insure that contact does not occur. Stresses were low everywhere but the adjustable anchors, where the telescope is attached to the pier. The adjustable anchors should be inspected after a seismic event. Hydrostatic bearings experience nonlinear lift off, but displacements were low and did not warrant a retrofitted retainer design.

ENGINEERING DISCIPLINES

  • Optical Systems & Telescopes

SOFTWARE & TOOLS

  • Hyperworks 13.0

  • Abaqus.Standard 6.14

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