Seite - 1192 - in Book of Full Papers - Symposium Hydro Engineering

To simulate the dynamic behavior of Cabril dam the coupled model was used, considering a dynamic elasticity modulus (Edyn) of 32.5 GPa and a Poisson coefficient (ʋ) of 0.2 for the dam. Various water levels are assumed, and a fluid velocity of 1440 m/s is used. Regarding Modal_ID2.0, the main modal parameters were obtained based on acceleration records measured on April 1st of 2014, between 10 and 11 a.m., in which the reservoir water level (Hw) was of 291.45 m. As for Modal_ID_auto2.0, automatic modal identification was carried out for measured accelerations between February and October of 2014, corresponding to a water level variation between 266 and 296 m. In this work, the modal identification outputs were obtained using the FDD(RD)-SV technique. First a comparison between Modal_ID2.0 and DamDySSA2.0 is performed (Fig.6a). A graphic representing the evolution of the computed natural frequencies in function of the reservoir water level is shown (colored lines), which also contains the modal identification frequencies for Hw = 291.45 m. Second, the outputs obtained from automatic modal identification are presented and compared with DamDySSa results (Fig.6b)). A different graphic is presented, containing the natural frequencies obtained from automatic modal identification over time (green and red circles), which are compared with lines representative of numerical natural frequencies, for the referred water level variation (266-296 m). In both cases, identified and computed mode shapes are compared. By analyzing the presented study, one can note that an excellent agreement was achieved between the results obtained from interactive and automatic modal identification software and the numerical results calculated with a 3D FE program, concerning both natural frequencies and vibration mode shapes. Also, the implemented numerical model enables to compute non-stationary vibration modes, as can be measured in situ. Finally, it is relevant to state that such a close agreement between numerical and experimental results was not possible in previous studies, performed using classic added water mass models [3,4]. 6. CONCLUSIONS A comparative study regarding the dynamic behavior of Cabril dam was presented, namely in terms of the dam’s natural frequencies and vibration mode shapes, for different reservoir water levels. The excellent agreement achieved between modal identification outputs and numerical modelling results demonstrates the value of Cabril dam’s monitoring system and associated software (Modal_ID_auto2.0 and Modal_ID2.0), and simultaneously proves the reliablity of the state space formulation implemented in the 3D FE program DamDySSa2.0. Therefore, as intended, this work has proven the importance of vibrations monitoring systems in the scope of dam safety control, which must comprise quality hardware (e.g. accelerometers, data concentrators, etc.) and appropriate software for data analysis and management, as well as the potential of their combined use with numerical models of dam-reservoir-foundation systems. 1192