Holger Riewaldt

An integrated simulation model of the Euro50

The Euro50 is a proposed optical telescope with an equivalent aperture of 50 m. It will have a segmented primary mirror and full adaptive optics. To study the interaction of the telescope structure, the control system and the optics, an integrated simulation model has been formulated. The mechanical model is a modal version of an Ansys finite element model. The optics model is based on ray tracing and physical optics. The segments model takes the alignment servos and the segment dynamics into account. Wind variation over the primary mirror is included. Segment control system modeling is in progress. First results clearly demonstrate that a good enclosure is needed to protect the telescope well against wind. The results also suggest that the segment alignment system must have a bandwidth well above the lowest eigenfrequencies of the telescope.

Integrated modeling of the Euro50

The Euro50 is a proposed 50 m optical and infrared telescope. It will have thousands of control loops to keep the optics aligned under influence of wind, gravity and thermal loads. Cross-disciplinary integrated modeling is used to study the overall performance of the Euro50. A sub-model of the mechanical structure originates from finite element modeling. The optical performance is determined using ray tracing, both non-linear and linearized. The primary mirror segment alignment control system is modeled with the 618 segments taken as rigid bodies. Adaptive optics is included using a layered model of the atmosphere and sub-models of the wavefront sensor, reconstructor and controller. The deformable mirror is, so far, described by a simple influence function and a second order dynamical transfer function but more detailed work is in progress. The model has been implemented using Matlab/Simulink on individual computers but it will shortly be implemented on a Beowulf cluster within a trusted network. Communication routines between Matlab on the cluster processors have been written and are being benchmarked. Representative results from the simulations are shown.

Wind on the Euro50 Enclosure

The Euro50 is a European Extremely Large Telescope. Its enclosure will be among the largest buildings of the world. Determining the maximum wind load is crucial for the survival of the structure, and local forces have an impact on the detailed design such as cladding. Pressure variations on the primary mirror and the wind load on the telescope are important for the development of active optics and segment control systems. To obtain data for the survival wind load as well as for typical observing conditions, the airflow pattern has been studied both with a wind tunnel model and computational fluid dynamics (CFD). Special attention has been given to determination of pressures on the primary mirror. Results are compared for the two methods and also with data available from previous studies and from measurements on existing telescopes. Finally, a typical wind load envelope is defined for the integrated telescope model.