Page - 1189 - in Book of Full Papers - Symposium Hydro Engineering

The uniaxial accelerometers (prepared to measure vibrations in a radial direction) are distributed in the upper part of the dam by two galleries, above and below the cracked zone. As for the triaxial accelerometers, one is located in the central cantilever (upper gallery), while the other two are installed near the insertion of the dam base, in both banks. The accelerometers are connected to a modular system composed by acquisition/digitalization units, which in turn are controlled by 4 data concentrators that receive the recorded data. This data is sent through an optical fiber local network (intranet) to a computer in the observation and control station (OCS), located at the dam power station. In total 25 accelerograms are recorded and stored every hour, continuously. The storage and management of the collected data is carried out at the server located in the OCS using appropriate software developed in LNEC. Regarding the remote control of the system, it is important to refer that the server can be accessed via internet from LNEC by computer or even by smartphone, using suitable software, which is of great relevance given that it allows to control and analyze such important data from a distance. As previously mentioned, the hardware for measuring accelerations and the corresponding data acquisition software must be complemented with suitable software for automatic analysis and management of the collected data, to ensure the efficiency of the dynamic monitoring system and hence accurate results. For the case of Cabril dam, two programs were developed using MATLAB: Modal_ID_auto2.0 and Modal_ID2.0 (Fig. 4). Modal identification is performed using a frequency domain method [4], Frequency Domain Decomposition (FDD), including three variants, namely: a) by implementing a Random Decrement technique (FDD(RD)); b) using a Singular Value Decomposition (FDD-SVD); and d) considering the combined use of the previous techniques (FDD(RD)-SV). As the name indicates, Modal_ID_auto2.0 is a software that carries out automatic continuous data analysis based on specific outputs defined in advance (e.g. the modal identification technique or the measuring points to analyze). Besides the analysis and management of the data, it automatically generates and sends (via e-mail) files with a synthesis of the obtained results, to be analyzed by the engineers and technicians. Given its continuous analysis of the acceleration records, the results allow to study the evolution of the modal parameters over the year, taking into account water level and thermal variations. On the other hand, Modal_ID2.0 is an interactive program that performs the modal identification of the main modal parameters for a certain data file, which is associated to the hour-day-year input chosen by the user. Its interactive feature enables to carefully observe the records and modal identification outputs for a certain water level, and it facilitates the comparison with numerical results. In terms of the results obtained from the collected data, both programs present as outputs: a) the acceleration records for each installed accelerometer and the corresponding amplitude spectrum; b) the medium spectrum, as obtained by applying modal identification techniques; and c) the natural frequencies, which correspond to the main spectral peaks, and the respective vibration modes, including 3D mode shapes and harmonic waves representing the oscillatory movements in each measuring point, all associated to the measured water level. 1189