Modeliranje metamaterialov s poenoteno večnivojsko metodo

With monitoring of dynamic properties of dams we can continuously observe the ageing process of the structure, while by vibration monitoring we can estimate the condition of the built-in material. Every structure has unique modal characteristics and its unique vibrational signature that change only in case when the structure\u27s mass, stiffness, or geometry is altered. Therefore, if the structural damage causes a decrease in stiffness, the vibration patterns as well as modal properties of the structure will change. Dams represent an important infrastructure and the ageing of dams and preservation of their structural health is rapidly becoming one of the major challenges of the entire dam engineering community. This research focuses on the analysis of operational loads and their effect on the ageing process of a hydropower dam. Shortly after the construction of the Brežice dam and during the start-up tests of hydro-mechanical equipment, we performed vibration monitoring, using state-of-the-art non-contact measurement techniques in combination with traditional contact technologies. The thesis is divided into two parts. In the first part, the motivation and fundamentals of structural health monitoring, vibration based monitoring, dam surveillance, and Laser Doppler Vibrometry (LDV) are presented, followed by the review of peer literature. Experimental work lies at the core of this research. In the second part of the thesis we present the experimental site, the equipment, the procedure and the numerical models of the powerhouse and its overspilling section. Our research confirmed the susceptibility of the concrete dam structure to the effect of operational loads, which is supported also with numerical results in experimental findings. With the beginning of our work during the construction of the dam we were able to capture the initial reference state of the dam, which will serve as a baseline for future diagnostic work. Furthermore, by adopting a corrective procedure of the LDV output, we are now able to use the LDV during regular operation of the powerhouse, when the instrument is placed inside the structure under observation and excited as well. LDV can be used as part of regular vibration monitoring activities on dams during operation.S spremljanjem dinamičnih lastnosti konstrukcije lahko opazujemo tudi proces staranja objekta, saj lahko preko spremljanja vibracij sklepamo na stanje vgrajenega materiala. Vsak objekt ima zanj značilne modalne lastnosti, ki so posledica njegove zasnove in togosti ter se odražajo v načinu, kako se objekt odzove na mehansko vzbujanje. Če se torej zaradi staranja vgrajenega materiala spremeni njegova togost, se bo posledično spremenil tudi odziv konstrukcije in njegove modalne lastnosti. Staranje pregrad trenutno predstavlja enega glavnih izzivov pregradnega inženirstva. S to raziskavo smo se osredotočili na prepoznavanje in analizo obratovalnih obtežb na konstrukcijo pregrade pretočnega tipa, namenjene za proizvodnjo energije. Stalno prisotna obtežba, ki jo povzroča hidro-mehanska oprema, namreč vpliva na pospešeno staranje betonskih konstrukcij. V okviru raziskave smo izvajali meritve vibracij na pregradi Brežice. Z eksperimentom smo pričeli že v času gradnje. Prvi odziv konstrukcije smo zabeležili kmalu po zaključku glavnine konstrukcijskih del, takrat smo izmerili odziv mlade konstrukcije in zabeležili t.~i. referenčno stanje, ki predstavlja osnovo za vse nadaljnje spremljanje kondicijskega stanja objekta. Pri meritvah smo uporabljali sodobne nekontaktne metode kot tudi tradicionalne kontaktne merilne tehnike. Naloga je razdeljena v dva dela. V prvem delu predstavimo teoretično ozadje spremljanja kondicijskega stanja konstrukcij, meritve vibracij, opazovanja pregrad in laserske vibrometrije. Eksperimentalno delo predstavlja bistvo te naloge. V drugem delu predstavimo eksperiment, opremo, metode dela in izdelana numerična modela. Obratovalna obtežba ima vpliv na pregrado. Vpliv obratovalnih manevrov smo z meritvami med zagonskimi testi zaznali na vseh eksperimentalnih mestih. Precejšnji del naše pozornosti smo usmerili v uporabo laserske vibrometrije v tako zahtevnem okolju, kot je hidroelektrarna med rednim obratovanjem. Vpeljali smo metodologijo, kjer z izvedbo dodatnih meritev na optični merilni napravi izločimo napako zaradi gibanja stojišča, kar omogoča uporabo vibrometra znotraj elektrarne med njenim rednim obratovanjem