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Keywords: vibration experiments, dynamic measurements, model updating, inverse analysis, numerical methods, modal analysis.

Summary

CUORE is an acronym for cryogenic underground observatory for rare events. It is an experiment in nuclear physics to be held in the Gran Sasso Laboratory (Italy) [1]. It will be constituted by an array of TeO₂ crystals (bolometers) operating at 8 to 10 milli-degrees Kelvin. The crystals are placed in a copper frame, hanging on the "cold finger" of a refrigerator. One of the major issues in the experiment is the reduction of the background noise, due also to mechanical vibrations of the structure. For this reason, a proper vibration control system should be introduced. In view of the design of such system, it is necessary to perform vibration analyses of the copper structure on the basis of a reliable model.

In view of the structural complexity and of the high degree of accuracy required, the model is tuned up after having performed some vibration tests on structural modules of the copper frame. This allows one to identify some uncertain material properties in the computational model, which is afterwards used for assessing the vibration behaviour of the whole structure. The measurements are carried out at the ENEA laboratory in Rome, making use of an electro-dynamic shaker. A horizontal sine sweep vibration (5-500Hz) is induced on a slip table, used in order to support the specimen. Several triaxial accelerometers are located on previously chosen points of the structure. Two series of tests are performed: the former with the copper structure alone, the latter with the "dummy" crystals in perfect grip conditions.

The data collected during the tests (i.e. the acceleration frequency response functions (FRF) of the measurement points [2]) are used for the identification of the mechanical properties assumed in the numerical simulation. The chosen numerical model is as simple as possible, in order to reduce the computational burden for the whole structure. The copper frame is modeled by beam elements, the crystals by three-dimensional rigid elements, the PTFE joints (located between crystals and copper) by spring elements. The model updating procedure embraces some stiffness and damping properties of the different elements, not excluding the behaviour of connections. A proper identification strategy is devised, implementing a very simple criterion for the comparison of measured and computed FRFs [3].

In view of the satisfactory agreement between computational and experimental data that is finally achieved, the updated model is extended to the whole structure, which is composed of thirteen basic modules properly connected to each other. The numerical results are of great aid in the optimal choice of some of the design features.

References

1: R. Ardito, C. Arnaboldi, D.R. Artusa, et al., "The CUORICINO and CUORE double beta decay experiments", Progress in Particle and Nuclear Physics, 57, 203-216, 2006. doi:10.1016/j.ppnp.2005.11.030
2: D.J. Ewins, "Modal Testing: Theory and Practice", John Wiley and Sons, New York, 1984.
3: M.I. Friswell, J.E. Mottershead, "Finite Element Model Updating in Structural Dynamics", Kluwer, Dordrecht, 1995.

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 88 PROCEEDINGS OF THE NINTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY Edited by: B.H.V. Topping and M. Papadrakakis Paper 100 Modal Identification and Vibration Analyses for Noise Reduction in the CUORE Cryogenic Experiment R. Ardito¹, C. Brofferio², C. Gargiulo³ and S. Morganti³ ¹Department of Structural Engineering, Politecnico di Milano, Milan, Italy ²Department of Physics, University of Milano-Bicocca, Milan, Italy ³National Institute for Nuclear Physics, Rome, Italy doi:10.4203/ccp.88.100 purchase the full-text of this paper Full Bibliographic Reference for this paper R. Ardito, C. Brofferio, C. Gargiulo, S. Morganti, "Modal Identification and Vibration Analyses for Noise Reduction in the CUORE Cryogenic Experiment", in B.H.V. Topping, M. Papadrakakis, (Editors), "Proceedings of the Ninth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 100, 2008. doi:10.4203/ccp.88.100 Keywords: vibration experiments, dynamic measurements, model updating, inverse analysis, numerical methods, modal analysis. Summary CUORE is an acronym for cryogenic underground observatory for rare events. It is an experiment in nuclear physics to be held in the Gran Sasso Laboratory (Italy) [1]. It will be constituted by an array of TeO₂ crystals (bolometers) operating at 8 to 10 milli-degrees Kelvin. The crystals are placed in a copper frame, hanging on the "cold finger" of a refrigerator. One of the major issues in the experiment is the reduction of the background noise, due also to mechanical vibrations of the structure. For this reason, a proper vibration control system should be introduced. In view of the design of such system, it is necessary to perform vibration analyses of the copper structure on the basis of a reliable model. In view of the structural complexity and of the high degree of accuracy required, the model is tuned up after having performed some vibration tests on structural modules of the copper frame. This allows one to identify some uncertain material properties in the computational model, which is afterwards used for assessing the vibration behaviour of the whole structure. The measurements are carried out at the ENEA laboratory in Rome, making use of an electro-dynamic shaker. A horizontal sine sweep vibration (5-500Hz) is induced on a slip table, used in order to support the specimen. Several triaxial accelerometers are located on previously chosen points of the structure. Two series of tests are performed: the former with the copper structure alone, the latter with the "dummy" crystals in perfect grip conditions. The data collected during the tests (i.e. the acceleration frequency response functions (FRF) of the measurement points [2]) are used for the identification of the mechanical properties assumed in the numerical simulation. The chosen numerical model is as simple as possible, in order to reduce the computational burden for the whole structure. The copper frame is modeled by beam elements, the crystals by three-dimensional rigid elements, the PTFE joints (located between crystals and copper) by spring elements. The model updating procedure embraces some stiffness and damping properties of the different elements, not excluding the behaviour of connections. A proper identification strategy is devised, implementing a very simple criterion for the comparison of measured and computed FRFs [3]. In view of the satisfactory agreement between computational and experimental data that is finally achieved, the updated model is extended to the whole structure, which is composed of thirteen basic modules properly connected to each other. The numerical results are of great aid in the optimal choice of some of the design features. References 1 R. Ardito, C. Arnaboldi, D.R. Artusa, et al., "The CUORICINO and CUORE double beta decay experiments", Progress in Particle and Nuclear Physics, 57, 203-216, 2006. doi:10.1016/j.ppnp.2005.11.030 2 D.J. Ewins, "Modal Testing: Theory and Practice", John Wiley and Sons, New York, 1984. 3 M.I. Friswell, J.E. Mottershead, "Finite Element Model Updating in Structural Dynamics", Kluwer, Dordrecht, 1995. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £145 +P&P)
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