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Številne raziskave kažejo, da se lahko proces kavitacije uspešno uporabi v postopkih čiščenja vode in za uničenje bakterij. Vendar se večina relevantnih študij izvaja na makro merilu, zato je razumevanje procesov na temeljni ravni še vedno slabo. Z namenom nadaljnje razjasnitve procesa čiščenja vode s pomočjo kavitacije na nivoju posameznih mehurčkov, dana disertacija numerično obravnava interakcijo med kolapsirajočim mikromehurčkom in bližnjo strukturo, ki je mehansko in strukturno podobna bakterijski celici. Uporabljena je metodologija interakcije fluid-struktura, kjer je upoštevan stisljiv večfazni tok, bakterijska celična stena pa je modelirana kot večplastna lupinasta konstrukcija. Raziskan je vpliv dveh neodvisnih brezdimenzijskih geometrijskih parametrov, in sicer razdalje ? med mehurčkom in celico ter njuno razmerje velikosti ?. Rezultati kažejo, da lahko lokalne napetosti, ki jih vzbudi kolaps mehurčka, presežejo prag poracije celičnih membran in liposomov, ter da je poškodbo bakterijskih celic mogoče razložiti zgolj z mehanskimi učinki, v odsotnosti termičnih in kemičnih mehanizmov. Mikroobtekanje je opredeljeno kot primarni mehanski mehanizem poškodbe bakterijskih celic, ki je lahko v določenih primerih okrepljen ob pojavu udarnih valov med kolapsom mehurčka. Numerous studies have already shown that the process of cavitation can be successfully used for water treatment and eradication of bacteria. However, most of the relevant studies are being conducted on a macro scale, so the understanding of the processes at a fundamental level remains poor. In attempt to further elucidate the process of cavitation-assisted water treatment on a scale of a single bubble, the present thesis numerically addresses interaction between a collapsing microbubble and a nearby structure, that mechanically and structurally resembles a bacterial cell. A fluid-structure interaction methodology is employed, where compressible multiphase flow is considered and the bacterial cell wall is modeled as a multi-layered shell structure. The contribution of two independent dimensionless geometric parameters is investigated, namely the bubble-cell distance δ and their size ratio ϛ. The results show that local stresses arising from bubble-induced loads can exceed poration thresholds of cell membranes and liposomes, and that bacterial cell damage could be explained solely by mechanical effects in absence of thermal and chemical ones. Microstreaming is identified as the primary mechanical mechanism of bacterial cell damage, which in certain cases may be enhanced by the occurrence of shock waves during bubble collapse.

Acoustic cavitation, generated by a piezo-driven transducer, is a commonly used technique in a variety of processes, from homogenization, emulsification, and intensification of chemical reactions to surface cleaning and wastewater treatment. An ultrasonic horn, the most commonly used acoustic cavitation device, creates unique cavitation conditions under the horn tip that depend on various parameters such as the tip diameter, the driving frequency of the horn, its amplitude, and fluid properties. Unlike for hydrodynamic cavitation, the scaling laws for acoustic cavitation are poorly understood. Empirical relationships between cavitation dynamics, ultrasonic horn operating conditions, and fluid properties were found through systematic characterization of cavitation under the tip. Experiments were conducted in distilled water with various sodium chloride salt concentrations under different horn amplitudes, tip geometries, and ambient pressures. Cavitation characteristics were monitored by high-speed (200,000 fps) imaging, and numerous relations were found between operating conditions and cavitation dynamics. The compared results are discussed along with a proposal of a novel acoustic cavitation parameter and its relationship to the size of the cavitation cloud under the horn tip. Similar to the classical hydrodynamic cavitation number, the authors propose for the first time an acoustic cavitation parameter based on experimental results.

V vodovodni sistemih se lahko pojavljajo veliki deleži neprodane količine vode, ki se pogosto skrijejo v vodnih izgubah. Z vzpostavitvijo merilnih območij se iz razlike med merjenim vtokom in količino obračunane vode izračuna vodna bilanca, ki upravljavcem omogoča hitrejšo identifikacijo dejanskih vodnih izgub in boljši nadzor nad delovanjem vodovodnega sistema. V magistrskem delu je predstavljena učinkovita metoda za vzpostavitev merilnih območij (MO) v vodovodnih omrežjih (VO), ki temelji na uporabi algoritmov iz teorije grafov. Metoda sestoji iz dveh glavnih delov: razbitja VO na MO in vpetja le-teh nazaj v celotno VO. Preizkusili smo jo na primeru realnega VO in med seboj primerjali tri načine spektralnega razbitja grafov, več različnih utežnih primerov in dva kriterija gručenja. Učinkovitost predlaganega algoritma za vpetje MO v primerjavi s tradicionalnim kombinatoričnim pristopom, smo prikazali za različna števila vzpostavljenih MO. Končno rešitev smo izbrali z uporabo večkriterijskega evalvacijskega modela, ki upošteva hidravlične, cenovne ter topološke metrike ter izloči subjektivni vpliv na izbiro. Rezultati so pokazali, da so vse tri preizkušene metode spektralnega razbitja, kvocientni prerez, normirani prerez in novo predlagani prirejeni normirani prerez, ustrezne za zasnovo MO in da lahko z upoštevanjem ustreznih topoloških in cenovnih informacij o VO v fazi razbitja pozitivno vplivamo na dobljeno rešitev. A high proportion of non-rewenue water can appear in water distribution systems which is often due to water losses. By establishing district metered areas (DMAs), a water balance can be calculated from the difference between the measured flow and the amount of revenue water. This allows system operators to identify the actual water losses faster and to control the functioning of the water distribution system efficiently. We present an efficient graph theoretical method for automatic design of district metered areas (DMAs) in water distribution networks (WDNs). The proposed method consists of two main parts: WDN partitioning and DMA connection, and is tested on a real-life WDN, for which three spectral partitioning methods, multiple weight cases and two clustering criteria are compared. The efficiency of the proposed DMA connection algorithm, with respect to the traditional combinatorical approach, is shown for different numbers of established DMAs. The final solution is selected according to a multi-criteria evaluation model, which was developed in order to reduce the subjective influence in the selection process and considers hydraulic, cost and topological criteria. The results show, that all three tested spectral partitioning methods, the ratio cut, the normalized cut and the newly proposed modified normalized cut, are suitable for WDN partitioning and, that we can further improve the quality of the obtained solutions by considering appropriate topological and cost based WDN information in the partitioning process.

We present an efficient graph-theoretical method for partitioning water distribution networks (WDNs) into district metered areas (DMAs). The proposed algorithm consists of two main parts, namely WDN partitioning and DMA connection, and is tested on a real-life WDN, for which different weight cases are compared. The efficiency of the proposed DMA connection algorithm, in regard to the traditional combinatorics approach, is shown for various numbers of established DMAs. The final solution is selected according to the multi-criteria evaluation model, which was developed in order to reduce the subjective influence in the selection process and considers hydraulic, cost, and topological criteria. The results show that the newly proposed spectral partitioning method, namely generalized normalized cut, is appropriate for WDN partitioning and that we can further improve the quality of the obtained solutions by considering appropriate topological and cost-based WDN information in the partitioning process. V prispevku je predstavljena učinkovita metoda za particijo vodovodnih omrežjih (VO) na merilna območja (MO), ki temelji na teoriji grafov. Algoritem sestoji iz dveh glavnih delov: razbitja VO na MO in njihovega vpetja nazaj v celotno VO. Preizkusili smo ga na primeru realnega VO in med seboj primerjali več različnih utežnih primerov. Učinkovitost predlaganega algoritma za vpetje MO v primerjavi s tradicionalnim kombinatoričnim pristopom smo prikazali za različna števila vzpostavljenih MO. Končno rešitev smo izbrali z uporabo večkriterijskega evalvacijskega modela, ki upošteva hidravlične, stroškovne ter topološke metrike ter izloči subjektivni vpliv na izbiro. Rezultati so pokazali, da je novo predlagana metoda spektralnega razbitja, tj. posplošeni normirani prerez, ustrezna za particijo VO in da lahko z upoštevanjem ustreznih topoloških in cenovnih informacij o VO v fazi razbitja pozitivno vplivamo na dobljeno rešitev.

Uporabniki cest za varno in udobno vožnjo potrebujejo ustrezna navodila. Kljub sodobnim navigacijskim sistemom GPS, se večina voznikov med potjo ravna po znakih za vodenje prometa – kažipotih. Kažipoti ljudi lahko tudi zavedejo in jih pripeljejo na napačen cilj. Diplomska naloga se loteva analize predpisov kažipotne signalizacije na avtocestah in hitrih cestah, kjer je pravočasno zaznavanje pravih informacij, ki nas vodijo na končni cilj, zaradi večjih hitrosti, še kako pomembno. V prvem delu naloge smo predstavili zgodovino znakov za vodenje prometa in trenutne predpise, ki veljajo v Sloveniji. V tem delu smo predstavili tudi predpise nekaterih drugih evropskih držav in nakazali na težnje poenotenja predpisov za vso Evropo. V drugem delu naloge smo s pomočjo analize anketnih vprašalnikov predstavili kako vozniki in njihovi sopotniki zaznavajo obravnavane znake ter našteli nekaj možnosti za izboljšave. Road users need appropriate instructions for safe and comfortable driving. Despite modern navigation system GPS, the majority of drivers are guided by signs for traffic management - signposts during the journey. Signposts can also mislead people and bring them to the wrong destination. The thesis deals with the analysis of regulations direction signs on motorways and highways and lead road users to the final destination. Because of the great speed, the timely detection of the right information is extremely important. In the first part we present the history of the characters for traffic management and current regulations which are in force in Slovenia. In this thesis we present the rules of some other European countries as well, which indicate the tendency for unifying the rules for the whole Europe. In the second part of this thesis we present how the drivers and their passengers perceive the present signs and list some opportunities for improvement through the analysis of questionnaires presented.

Nevarnosti, ki jih povzročajo drobirski tokovi in snežni plazovi ni mogoče popolnoma preprečiti. Zato se razvijajo matematični modeli teh pojavov, kar nam omogoča, da lahko ustrezno načrtujemo zaščitne ukrepe na ogroženih območjih. Enodimenzijski model PLAZEM15 omogoča analizo nestalnega toka različnih vrst tekočin s prosto gladino, natančneje toka vode, drobirskega toka in snežnih plazov. V prvem delu diplomskega dela so predstavljene teoretične osnove za modeliranje nestalnega toka tekočine in udarne sile plazu. Sledijo rezultati občutljivostne analize modela na spreminjanje začetne strižne trdnosti in viskoznosti drobirskega materiala, ter na spreminjanje topografskih parametrov, ki obsegajo razširitve in spremembe v naklonu dna struge. Vpliv spreminjanja topografije je bil preverjen za drobirske tokove in snežne plazove, za katere so bili ponovljeni računi, ki so bili na Katedri za Mehaniko tekočin opravljeni leta 1980, z namenom primerjave rezultatov. V zadnjem delu naloge so predstavljeni izračuni udarne sile na objekt za izbrane primere drobirskih tokov in snežnih plazov. Končni rezultati so pokazali, da obravnavani modeli, ki opisujejo dinamiko drobirskega toka in snežnih plazov večinoma dajejo logične rezultate, vendar bi jih bilo treba za dokončno verifikacijo še nadalje preveriti. Predvsem bi bilo nujno narediti primerjavo z rezultati meritev, ki jih v tej fazi naloge ni bilo na razpolago. Due to inability to entirely prevent debris flow and snow avalanches, it is reasonable to develop mathematical models that allow us to predict and design sufficient protection measures in endangered areas. One dimensional model PLAZEM15 allows analysis of unsteady flow of fluids, such as free surface water flow, debris flow and snow avalanches. Theoretical background for mathematical modeling of unsteady flow of fluids and their impact force is described in the first part of the thesis. Further on the thesis describes results of sensitivity analysis of the model in which the initial shear stress, viscosity of the debris material and topographic parameters, including changes in the slope of the channel bed and gradual extension of channel width, were modified. The impact of changes in topography was examined for debris flow and snow avalanches. These simulations were already made in 1980 in the frame of the Chair of Fluid mechanics of the faculty, and the results were compared. In the last part of the thesis calculations of the impact force of flow were made for selected cases of debris flow and snow avalanches. The final results of the analysis showed, that tested numerical models give basically good results, however, further verification will be necessary before final applications. Comparison with results of some field measurements, not available in this study, would be very important.