Development and implementation of heat exchanger mathematical model-based digital twin

Digitalni blizanci zauzimaju sve značajnije mjesto u industriji, omogućujući prediktivno održavanje, optimizaciju performansi i povećanje pouzdanosti sustava. Ovaj rad usmjeren je na razvoj i implementaciju digitalnog blizanca izmjenjivača topline kapaciteta do 10 kW. Cilj rada je stvoriti funkcionalan sustav koji može analizirati i optimizirati rad izmjenjivača topline korištenjem senzorskih podataka, što omogućuje efikasnije analiziranje procesa izmjene topline. Razvoj digitalnog blizanca počinje izradom detaljnog matematičkog modela koji opisuje fizikalne procese prijenosa topline unutar pločastog izmjenjivača. Implementacija modela izvršena je pomoću mikrokontrolera Raspberry Pi 4, koji omogućuje obradu senzorskih podataka u stvarnom vremenu i njihovu integraciju u simulacijsko okruženje. Hardverska arhitektura sustava uključuje i senzore temperature, koji osiguravaju kontinuirano praćenje uvjeta rada izmjenjivača. Softverska komponenta izrađena je u programskim jezicima Python i C, omogućujući akviziciju podataka, njihovu analizu i prediktivne simulacije rada sustava. Tako razvijen digitalni blizanac procesa validiran je na razvijenom eksperimentalnom sustavu.Digital twins are taking an increasingly important place in the industry, enabling predictive maintenance, performance optimization and increased system reliability. This work is focused on the development and implementation of a digital twin heat exchanger with a capacity of up to 10 kW. The goal of the work is to create a functional system that can analyze and optimize the operation of the heat exchanger using sensor data, which enables a more efficient analysis of the heat exchange process. The development of the digital twin begins with the creation of a detailed mathematical model that describes the physical processes of heat transfer inside the plate heat exchanger. The implementation of the model was carried out using the Raspberry Pi 4 microcontroller, which enables the processing of sensor data in real time and their integration into the simulation environment. The hardware architecture of the system also includes temperature sensors, which ensure continuous monitoring of the exchanger's operating conditions. The software component was created in Python and C programming languages, enabling data acquisition, their analysis and predictive simulations of system operation. The thus developed digital twin of the process was validated on the developed experimental system

Procjena i korekcija greške bočnog položaja vozila unutar cestovne mreže na temelju podataka s kamere.

The general approach to creating virtual scenarios required for validation and testing of automatic systems in vehicles typically involves equipping the vehicle with a certain sensor configuration. This sensor configuration can include cameras, radars, LiDARs etc. After the sensor configuration is picked, data is collected through real driving on certain road segments. The collected data is then processed/annotated in order to reconstruct the trajectories of moving/dynamic objects, which are then used as input data in the process of generating virtual scenarios from the recorded driving data. Throughout this process of data annotation and processing, and due to noisy sensor data trajectories can be incorrectly determined which consequently leads to possible errors in the generated scenarios. Within the scope of this Master Thesis, it is necessary to develop an algorithm for the localization of accompanying („fellow“) vehicles within the road network with an emphasis on the estimation and correction of the lateral position of the vehicle within the lane using a set of recorded camera images and GPS data. The algorithm will use AI modules for line and object detection to estimate vehicle position on the road. Then detected vehicles have to be matched with the vehicles from the recorded trajectories. Finally, a method for lateral offset estimation needs to be developed, and data has to be corrected. The algorithm needs to be verified. Aim is to reduce lateral position inconsistencies between the recorded trajectories and the corresponding road network so that in the simulation we have the same situation as it happened in the real world.Generalni pristup kod kreiranja virtualnih scenarija potrebnih za validaciju i testiranje automatskih sustava u vozilima tipično se sastoji od opremanja vozila s nekom senzorskom konfiguracijom. Konfiguracije mogu uključivati, kameru, radar, LiDAR itd. Nakon što se odabere senzorska konfiguracija, podaci se prikupljaju vožnjom na stvarnim cestovnim segmentima. Podaci koji su sakupljeni su nakon toga procesuirani/anotirani kako bi se rekonstruirale trajektorije vozila u pokretu, koje se koriste kao ulazni podatak u procesu generiranja virtualnih scenarija iz snimljenih podataka. Tijekom procesa anotacije podataka i procesuiranja i zbog netočnih senzorskih podataka, trajektorije mogu biti netočno određene što dovodi do mogućih grešaka u generiranim scenarijima. Unutar ovog diplomskog rada, potrebno je razviti algoritam za lokalizaciju popratnih vozila unutar cestovne mreže s naglaskom na estimaciju i ispravljanje lateralne pozicije vozila unutar vozne trake koristeći set snimljenih slika i GPS podataka. Algoritam će koristiti module umjetne inteligencije za detekciju linija i objekata kako bi se estimirao položaj vozila na cesti. Detektirana vozila će zatim biti uparena s vozilima iz snimljenih trajektorija. Finalno, metoda za procjenu lateralnog pomaka mora biti razvijena, a podaci ispravljeni. Algoritam također mora biti verificiran. Cilj je smanjenje nedosljednosti lateralnog pomaka između snimljenih podataka i pripadajuće cestovne mreže tako da u simulaciji imamo istu situaciju koja se dogodila u stvarnome svijetu

Suspension design of military off-road vehicle

U ovom diplomskom radu koncipiran je i konstrukcijski razrađivan sustav ovjesa na visokomobilnom višenamjenskom vozilu na kotačima HMMWV. U radu su definirani osnovni zahtjevi za vozilo i ovjes, te su analizirane uobičajene konfiguracije ovjesa sličnih vozila. Nakon detaljne analize, odabrana je konfiguracija ovjesa koja zadovoljava navedene zahtjeve. Odabrana konfiguracija uključuje neovisni ovjes sprijeda i straga s dvostrukim poprečnim vodilicama, koji se preko podkonstrukcije povezuje na šasiju vozila. Analizirana je kinematika ovjesa i dinamika vozila kroz specifične ispitne procedure izvancestovne vožnje te su određeni osnovni parametri ovjesa i vozila, kao što su širina traga, međuosovinski razmak i klirens. Na temelju provedenih analiza, izrađeno je konstrukcijsko rješenje i kontrolni proračun kritičnih komponenata.In this thesis, a suspension system for the high-mobility multipurpose wheeled vehicle HMMWV was conceptualized and structuraly develpoed. The study defines the fundamental requirements for the vehicle and its suspension and analyzes common suspension configurations used in similar vehicles. After a detailed analysis, a suspension configuration was selected that meets the specified requirements. The chosen configuration includes independent suspension at the front and rear with double wishbones, connected to the vehicle chassis through a subframe. The kinematics of the suspension and the dynamics of the vehicle were analyzed using specific off-road driving test procedures, and key parameters such as track width, wheelbase, and ground clearance were determined. Based on the conducted analyses, a structural solution was developed, and a verification calculation of critical components was performed

Selection of a commercial battery energy storage system to ensure uninterrupted power supply for a pumping station

Održavanje kontinuiteta rada kritične infrastrukture, kao što su izolirane crpne stanice za vodoopskrbu, zahtijeva robusna rješenja za pomoćno napajanje. Sustavi neprekidnog napajanja (UPS) obično koriste baterijske sustave za pohranu energije (BESS), koji, osim što osiguravaju pričuvno napajanje, omogućuju energetsku arbitražu kako bi se smanjili troškovi električne energije iz mreže. Ovaj Završni rad ispituje izvedivost komercijalno dostupnog BESS-a za povećanje autonomije rada vodocrpne stanice opremljene glavnim elektromotornim pogonom pumpe nazivne snage 350 kW. Koristeći povijesne podatke o potrošnji komunalne vode za Cresko-Lošinjsko otočje, dobivene iz javno dostupnih izvora, provedene su simulacije za modeliranje rada crpnih stanica sa i bez integracije BESS-a tijekom kontinuiranog rada. Dobiveni podaci pružaju sveobuhvatnu analizu potencijalnih ušteda energije, smanjenja troškova i procijenjenog povrata ulaganja (ROI).Maintaining the continuity of critical infrastructure, such as isolated water pumping stations, requires robust backup power solutions. Uninterruptible power supply (UPS) systems typically use battery energy storage systems (BESS), which, in addition to providing backup power, enable energy arbitrage to reduce electricity costs. This thesis examines the feasibility of a commercially available BESS to increase the autonomy of a water pumping station equipped with a main electric motor pump drive with a nominal power of 350 kW. Using historical data on municipal water consumption for the Cres-Lošinj archipelago, obtained from publicly available sources, simulations were conducted to model the operation of pumping stations with and without BESS integration during continuous operation. The obtained data provide a comprehensive analysis of potential energy savings, cost reductions, and estimated return on investment (ROI)

Equivalent: Glucagon-like peptide-1 receptor agonists decrease total and LDL-cholesterol in obese type 2 diabetic patients.

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are increasingly utilized in the management of type 2 diabetes mellitus (T2DM). GLP-1 RAs have been associated with improvements in serum lipid profiles in clinical trials. Their long-term cardiovascular safety and benefit have also been confirmed in the recently published LEADER trial. In the current study, we assessed the effects of GLP-1 RAs (exenatide and liraglutide) on serum lipid profiles (total, LDL, HDL-cholesterol and triglycerides) of obese patients with T2DM. A total of 85 patients were included in the study (43 on exenatide and 42 on liraglutide) and followed up for 22 and 13 months, respectively. Treatment with exenatide was associated with a significant decrease in total cholesterol from 5.1±1.3 to 4.9±1.2 mmol/L (p=0.02) and LDL-cholesterol from 3.0±1.1 to 2.6±0.8 mmol/L (p=0.01). Treatment with liraglutide was also associated with a significant decrease in total cholesterol from 4.8±1.2 to 4.2±0.8 mmol/L (p=0.001) and LDL-cholesterol from 2.5±0.8 to 2.1±0.5 mmol/L (p=0.006). Treatment with liraglutide and exenatide did not significantly affect HDL-cholesterol and triglyceride levels. The results of our study suggest that treatment with exenatide and liraglutide may significantly reduce total and LDL-cholesterol in obese patients with T2DM

Motherhood and Gender Roles in Mai Zetterling's movies

Iako generalno percipirana kao dio mladog feminističkog filmskog pokreta 70-ih, Mai Zetterling se ne ograničava samo na feminističke ideje, reprezentaciju ženske seksualnosti, neheteronormativnih odnosa i rodnih uloga već seže u problematike dominantno vezane uz muške auteure. Između ostalog razvija izražen individualistički stil usporediv s onim njezinih modernističkih suvremenika poput Ingmara Bergmana spram kojeg je bila viđena inferiornom. Rad će se baviti usporednom analizom filmova Älskande par (1964), Nattlek (1966) i Flickorna (1968) promatrajući kako su prezentirane majke u podlozi prividno napredne socijaldemokratske države. Promatrat ću kako Zetterling u filmovima problematizira antagonističke odnose žena i muškaraca i kako kroz filmski jezik iznosi osjećaj izopćenosti i otuđenosti žena dekonstruirajući rodne uloge. Rodna perspektiva ponavljajući je motiv u njenim filmovima, posebice izraženo u filmu Flickorna gdje se manifestira kao stanje trajnog rata među spolovima. Analizirat ću kako opisom izopačene dekadencije bogatih u Nattlek i položajem ukočene aristokracije u Älskande par Zetterling iznosi na vidjelo konzervativnu stvarnost Švedske i kritizira državu blagostanja zbog njenog nedostatka stvarne progresivnosti. Rad će tumačiti uporabu modernističkih tehnika snimanja u svrhu razvijanja središnjih tema filmova – seksualnosti, reprodukcije i roda. Sagledat ću kako Zetterling pristupa tabu temama i eksplicitno prikazuje scene poroda, seksa te odabirom žene kao subjekta radnji izaziva pristran svijet filmske kritike i pomiče granice švedske kinematografije.Although generally perceived as part of the young feminist film movement of the 70s, Mai Zetterling does not limit herself to feminist ideas; the representation of female sexuality, non-heteronormative relationships and gender roles, but she also touches on issues dominantly related to male auteurs. Among other things, she developed a pronounced individualistic style comparable to that of her modernist contemporaries such as Ingmar Bergman, compared to whom she was seen as inferior. The paper will deal with a comparative analysis of the films Älskande par (1964), Nattlek (1966) and Flickorna (1968), observing how mothers are presented in the context of an apparently advanced social democratic state. I will observe how Zetterling problematizes the antagonistic relations between women and men in the films and how she conveys the feeling of exclusion and alienation of women through the film language by deconstructing gender roles. The gender perspective is a recurring motif in her films, especially expressed in the film Flickorna, where it manifests itself as a state of permanent war between genders. I will analyze how, by describing the perverse decadence of the rich in Nattlek and the position of the rigid aristocracy in Älskande par, Zetterling exposes the conservative reality of Sweden and criticizes the welfare state for its lack of real progressiveness. The paper will interpret the use of modernist filming techniques for the purpose of developing the central themes of the films - sexuality, reproduction and gender. I will look at how Zetterling approaches taboo topics and explicitly shows scenes of childbirth and sex, and by choosing a woman as the subject of film, she challenges the biased world of film criticism and pushes the boundaries of Swedish cinematography

Knowledge, Awareness, and Influence of the COVID-19 Pandemic on Students of Biomedical Faculties: A Cross-Sectional Study

Background/Objectives: The COVID-19 pandemic has had a profound impact on physical, mental, and social aspects of life worldwide. This study aimed to explore and compare differences in knowledge, awareness, behavior, and the psychological impact of the pandemic among students of biomedical faculties at the University of Zagreb. Methods: A cross-sectional study was conducted between 27 November 2020 and 19 January 2021 involving 518 students from the School of Dental Medicine, School of Medicine, Faculty of Pharmacy and Biochemistry, and Faculty of Veterinary Medicine. An anonymous online questionnaire was distributed, assessing participants’ knowledge about SARS-CoV-2, information sources, attitudes, and psychological responses. Data were analyzed using descriptive statistics and appropriate statistical tests. Results: The median knowledge score was 61.54%, with senior and female students demonstrating significantly more knowledge (p < 0.001 and p = 0.044, respectively). Students who consulted the scientific literature and official websites had higher knowledge levels (p < 0.001). Most participants used media and social networks for pandemic information, while scientific sources were underutilized. Psychological impacts were evident, with 46.3% expressing fear about the future and 25% reporting anxiety if they were to be infected. Additionally, those who engaged with the scientific literature were more likely to accept vaccination and showed lower levels of COVID-19 stigma. A majority (64.5%) believed that the media exaggerated the pandemic’s risks. Conclusions: Biomedical students demonstrated moderate knowledge about COVID-19, with a clear link between scientific literacy and more informed, less stigmatizing attitudes. This study underscores the importance of reliable information sources in shaping public health awareness and highlights the need for further education on COVID-19 symptoms and preventive measures

Comparison of ferrate(VI) and Fenton process for removal of microplastics from aqueous media

Plastični materijali nezamjenjivi su u današnjem svijetu. Zbog svoje jednostavne proizvodnje i ekonomske isplativosti, jednostavnog oblikovanja te odličnih mehaničkih i kemijskih svojstava, koristi se u svim aspektima našega života. Primjena i proizvodnja iz godine u godinu raste, ali raste i problem zbrinjavanja plastičnog otpada. U okolišu plastični otpad pod utjecajem prirodnih sila fragmentira se na manje čestice veličine do 5 mm, koje zajednički nazivam mikroplastikom. U okviru ovoga rada ispitano je uklanjanje modelne mikroplastike, odnosno čestica poli(etilen tereftalata) i polipropilena, iz vodenog medija primjenom dva usporedna procesa: oksidacije/koagulacije feratima(VI) te Fenton procesom. Uzorci su karakterizirani pomoću infracrvene spektroskopije s Fourierovom transformacijom (FTIR) kako bi se identificirale kemijske promjene uzoraka. Temeljem dobivenih rezultata ustanovljena je degradacija uzoraka polipropilena, pri čemu je identificiran nastanak dvostrukih veza kod polipropilena. Međutim, kod poli(etilen tereftalata) FTIR analizom nisu ustanovljene jednoznačne promjene.Plastic materials are irreplaceable in today's world. Due to their ease of production and economic viability, ease of shaping and excellent mechanical and chemical properties, the use of plastics is widespread in our lives. The use and production of plastics is increasing year by year, but so is the problem of disposing of plastic waste. In the environment, under the influence of natural forces, plastic waste is fragmented into smaller particles up to 5 mm in size, which I call microplastics. In this work, the removal of model microplastics, i.e., particles of poly(ethylene terephthalate) and polypropylene, from an aqueous medium was investigated using two comparative methods: oxidation/coagulation with ferrate (VI) and the Fenton process. The samples were characterized using Fourier transform infrared spectroscopy (FTIR) to determine chemical changes in the samples. Based on the obtained results, degradation of polypropylene samples was identified due to the formation of double bonds in polypropylene. However, for poly(ethylene terephthalate) FTIR doesn’t reveal significant changes

Polyseme somatische Lexeme im Kroatischen und Deutschen

U ovome diplomskome radu analizira se pojava polisemije u somatskih leksema, odnosno leksema koji označavaju dijelove ljudskog tijela u hrvatskome i njemačkome jeziku. Polisemija ili višeznačnost ostvaruje se trima osnovnim mehanizmima: leksičkom metaforom, leksičkom metonimijom i leksičkom sinegdohom. Sastavljen je dvojezični katalog sekundarnih, odnosno izvedenih značenja hrvatskih i njemačkih polisemnih somatskih leksema na temelju proučavanja jednojezičnih rječnika hrvatskoga i njemačkoga jezika te dvojezičnih hrvatsko-njemačkih i njemačko-hrvatskih rječnika. Na osnovi toga kataloga analizira se kojim su leksičkim mehanizmom sekundarna značenja nastala, koji su načini prijenosa imena najčešći te, konačno, koje su sličnosti i razlike među sekundarnim značenjima polisemnih somatskih leksema u hrvatskome i njemačkome.This paper analyzes the phenomenon of polysemy in somatic lexemes, i.e. lexemes denoting parts of the human body, in Croatian and German languages. Polysemy (multiple meanings) is achieved through three basic mechanisms: lexical metaphor, lexical metonymy and lexical synecdoche. A bilingual catalog of secondary or derived meanings of Croatian and German polysemous somatic lexemes has been compiled based on the study of monolingual Croatian and German dictionaries as well as bilingual Croatian-German and German-Croatian dictionaries. Based on that catalog, an analysis is made of the mechanism by which the secondary meanings have arisen, which modes of transfer are most frequent and, finally, what similarities and differences there are between the secondary meanings of polysemous somatic lexemes in Croatian and German.In dieser Diplomarbeit wird das Phänomen der Polysemie in somatischen Lexemen, d.h. Lexemen, die Teile des menschlichen Körpers bezeichnen, in der kroatischen und deutschen Sprache analysiert. Polysemie (Mehrfachbedeutung) wird durch drei grundlegende Mechanismen erreicht: lexikalische Metapher, lexikalische Metonymie und lexikalische Synekdoche. Auf der Grundlage des Studiums einsprachiger kroatischer und deutscher Wörterbücher sowie zweisprachiger kroatisch-deutscher und deutsch-kroatischer Wörterbücher wurde ein zweisprachiger Katalog sekundärer oder abgeleiteter Bedeutungen polysemer somatischer Lexeme des Kroatischen und Deutschen erstellt. Auf der Basis dieses Katalogs wird analysiert, durch welchen Mechanismus die sekundären Bedeutungen entstanden sind, welche Übertragungsarten am häufigsten vorkommen und schließlich, welche Ähnlichkeiten und Unterschiede es zwischen den sekundären Bedeutungen polysemer somatischer Lexeme im Kroatischen und im Deutschen gibt

Bora wind turbulence above complex coastal terrain

Tema ovog rada su mikro- i submezoskalna svojstva bure u zavjetrini sjevernog dijela Dinarida. Rad je podijeljen u tri cjeline, pri čemu se dvije cjeline odnose na turbulenciju bure u prizemnom sloju atmosfere, specifično, njene statističke značajke i numeričku simulaciju. Treća se cjelina odnosi na horizontalne rotacijske značajke pulsacija bure – njihov opis i numeričko modeliranje. U prvoj cjelini proučavam razlike u statističkim značajkama turbulencije bure u prizemnom sloju atmosfere, i to na dvjema bliskim postajama, Senju i Vratniku (jedna u podnožju, a druga na grebenu planine), za skup podataka u trajanju od približno 6 mjeseci. Slična analiza značajki turbulencije bure do sada nije provedena za ovako dug vremenski period. Analiza potvrđuje neka saznanja prijašnjih radova temeljenih na usporedbi ove dvije postaje za jedan izdvojen događaj bure, npr. da je kinetička energija turbulencije (TKE) u Senju dvostruko veća u odnosu na Vratnik. Raspodjela viskozne disipacije TKE () na dvjema postajama približno je jednaka, što je u suprotnosti s prethodnim zaključcima utemeljenim na jednom događaju bure. Dvije vremenske skale koriste se za odvajanje turbulencije od mezoskale – konstantna (15 min) i varijabilna; potonja je korištena s ciljem odvajanja submezoskalnih gibanja od lokalne turbulencije. Zaključci su u pravilu nepromijenjeni s obzirom na odabir vremenske skale. Podaci na postajama uspoređeni su s obzirom na teoriju sličnosti neutralnog prizemnog sloja (NPS). Odstupanja od NPS-a na Vratniku su manja od onih u Senju, što znači da je ravnoteža TKE na Vratniku bliža NPS-u (tj. smično-disipacijskoj ravnoteži). Određena odstupanja karakteristična su za utjecaj sloja hrapavosti (SH), s obzirom da je visina mjernih uređaja na objema postajama usporediva s visinom elemenata hrapavosti u njihovoj blizini. Ovo je posebice zamjetno u pomacima spektralnih maksimuma prema nižim frekvencijama. Utjecaj SH također pomaže objasniti neočekivanu jednakost na dvjema postajama. Naime, jedna od značajki SH nelokalni su ponori TKE koji smanjuju , a koja uobičajeno samostalno uravnotežuje izvore TKE. Utjecaj SH je prisutan i kod ovisnosti statističkih momenata o azimutu prizemnog vjetra, što se može objasniti anizitropijom površinske hrapavosti. Izračunate su integralne duljinske skale turbulencije i intenzitet turbulencije. Postignute vrijednosti intenziteta u skladu su s preporučenim vrijednostima, ali odstupaju od vrijednosti izmjerenih na srednjem Jadranu. Druga cjelina usredotočena je na izračun mikroskalnih svojstava bure (preciznije, TKE) numeričkim modelom. Za validaciju simulacije korišten je skup podataka prikupljen u zaleđu grada Rijeke na 100-m tornju s anemometrima na 5 visina. Ovo predstavlja dosad najviša neprekidna toranjska mjerenja brzine vjetra i turbulencije bure u prizemnom sloju atmosfere. Osim 10-min usrednjenih vrijednosti horizontalne brzine i smjera vjetra, anemometri su mjerili i standardne devijacije, što omogućava procjenu TKE i usporedbu sa simulacijom. Ovo je značajno jer je usporedba dosad provedenih simulacija, izuzev avionskih ili indirektnih mjerenja, u pravilu provedena s mjerenjima na relativno niskoj razini iznad tla. Simulacija koraka mreže 0,3 km je provedena za slučaj ekstremno dugotrajnog niza jakih do orkanskih bura iz siječnja i veljače 2012. godine, a kojeg su mjerni uređaji na tornju zabilježili u cijelosti. Točnost simulacije usrednjene vrijednosti brzine i TKE je u rasponu od razumne do izvrsne, ovisno o brzini vjetra i dubini bure. Periodi s izvrsnim podudaranjem su zabilježeni pri brzini vjetra većoj od 20 m s-1 i tijekom plitke bure, dok je podudaranje tijekom duboke bure te pri početku i kraju događaja lošije. Podudaranje je usporedivo sa simulacijama bure na južnom Jadranu, također relativno kratkog koraka mreže, dok odstupanja zabilježena kod većeg koraka mreže naglašavaju važnost reprezentacije reljefa u brdovitom terenu. U trećoj cjelini proučavam rotacijske značajke pulsacija bure u horizontalnoj ravnini – njihovu strukturu, orijentaciju i smjer rotacije – koristeći rotacijsku spektralnu analizu. Metoda je primijenjena na događaje bure iz istog skupa podataka u Senju kao u prvoj cjelini. Struktura pulsacija je kvazilinearna, tj. česti zraka osciliraju duž izduženih elipsa, a os oscilacije nije jednaka smjeru prizemnog vjetra, već je bliža smjeru vektora smicanja. Doprinos predstavlja rotacija pulsacija u horizontalnoj ravnini, a koja je gotovo isključivo pozitivna, tj. u smjeru suprotnom od kazaljke na satu. Ove značajke ukazuju da su na promatranom skupu događaja bure najvjerojatniji uzroci nastanka pulsacija Kelvin-Helmholtzova nestabilnost ili horizontalno propagirajući zavjetrinski valovi, iako ne nude objašnjenje prevladavajućeg smjera rotacije. Numerička simulacija ljetnog događaja bure je provedena s ciljem proučavanja ovog zapažanja. Simulacija je uspješna s obzirom na period, prevladavajući smjer rotacije i kut između smjera prizemnog vjetra i osi oscilacije pulsacija. Amplituda pulsacija osjetljiva je na vertikalni i horizontalni korak mreže, ali rotacijske značajke nisu. Uzrok pulsacija u simulaciji je Kelvin-Helmholtzova nestabilnost. Ohrabren podudaranjem simulacije i mjerenja, proučio sam prostornu raspodjelu rotacijskih značajki u Velebitskom kanalu. Pozitivna rotacijska komponenta nadjačava negativnu na gotovo čitavom području kanala, iako je njihova relativna jakost vremenski promjenjiva. Iznad Senja i u blizini planinskih vrhova, prevladavajući smjer rotacije pulsacija koreliran je s poljem vremenski usrednjene vertikalne komponente vrtložnosti, a iznad otvorenog mora sa smicanjem smjera vjetra na vrhu niske mlazne struje. Predlažem da je rotacija na frekvenciji pulsacija uzrokovana naginjanjem vrtložnih linija lateralne komponente vrtložnosti unutar ili ispod vrhova Kelvin-Helmholtzovih valova. U prisustvu smicanja smjera vjetra, naginjanje može imati prevladavajući smjer. Budući rad trebao bi se usredotočiti na analizu polja vertikalne komponente vrtložnosti u simulacijama sa stvarnim i idealiziranim reljefom.EXTENDED ABSTRACT 1 Introduction Bora is a strong, gusty wind that occurs along the eastern coast of the Adriatic. It belongs to the category of downslope windstorms (e.g., Ólafsson and Ágústsson 2007), and it develops due to synoptic disturbances which pull or push air over the Dinarides. Interest in the study of bora is driven mainly by its gustiness (over 60 m s-1; e.g., Grisogono and Belušić 2009) and spatial heterogeneity, which causes a myriad of problems in tourism, architecture and traffic (e.g., Keresturi 2014). Bora research started at the end of the 19th century (Mohorovičić 1889). It initially focused on the spatial and temporal variability of the mean wind speed and duration (e.g., Poje 1992). The analysis of synoptic charts and radiosoundings yielded two classifications of bora events, one with respect to the synoptic disturbance causing the cross-mountain flow, and the second with respect to the flow depth. As a result, bora event can be cyclonic, anticyclonic or frontal (e.g., Yoshino 1976; Jurčec 1988; Heimann 2001), and shallow or deep. Several subjective and objective weather-type classifications have been developed as a prognostic aid (e.g., Poje 1965; Vozila et al. 2021), newest of which claim that the winter cyclonic bora events (associated with the highest wind speed) will become less frequent in the future warming scenarios (Vozila et al. 2021). When it comes to the understanding of the physical causes of severe bora, the most important development occured as a result of ALPEX (Kuettner and O’Neill 1981) and MAP (Bougeault et al. 2001) projects. Works by Smith (1987) and Klemp and Durran (1987) did away with the notion of bora as a katabatic wind, showing instead that the flow speedup can be caused by two mechanisms, hydraulic transition from sub- to supercritical flow (can be described by two-layer shallow water models), and nonlinear amplification and breaking of mountain waves (the stratified fluid case). Both mechanisms can be present at the same time, and their relative importance depends on the stratification profile, presence and height of the critical level (level where the cross-mountain flow component is zero) and other effects (e.g., Smith and Skyllingstad 2011). In both cases, the resulting lee flow structure is similar – a strong low-level jet (LLJ) develops, topped by a layer of low wind speed and near neutral static stability (the stagnation zone). The breaking mountain wave and the LLJ present a „stage“ of sorts for this thesis. It is split into three chapters; two deal with the turbulence developed at the lower boundary of the LLJ, and the third aims to describe the horizontal rotational characteristics of bora pulsations (submesocale motion originating from the wave breaking region or the boundary between the LLJ and the stagnation zone; Figure 3) using point measurements and a numerical model simulation. The next three subsections summarize the relevant literature and motivation for each chapter, while the fourth presents the goals and structure of the rest of the text. 1.1 Bora turbulence measurements As a result of strong shear at the LLJ top and bottom, strong turbulence is developed in the lee of the mountain. Turbulence strength in the lower layer is characterized by a handful of statistical properties like the turbulence kinetic energy (TKE), its dissipation rate () and turbulent fluxes of heat, momentum, moisture, etc. Specialized fields like wind engineering use different but related statistical properties like the turbulence intensity, gust speed and integral turbulence length scales. How these properties relate to each other and vary with height is published in engineering compendia as benchmarks in calculating wind loads on structures. The first high-frequency measurements of bora-related turbulence were undertaken within ALPEX and MAP projects (aircraft-mounted instruments sampled alongshore and cross-shore profiles of TKE; Smith 1987; Večenaj 2012). First mast-mounted instrument was installed in 2001 at the town of Senj (cup anemometer; 1 Hz sampling rate); Belušić et al. (2006) used these measurements to distinguish local turbulence and low-frequency pulsations. From 2004 to 2006, a pair of 3D anemometers (4 Hz sampling rate) was mounted at Senj and at the Vratnik pass (~10 km to the east of Senj). Using this data, Belušić and Klaić (2006) show that TKE at Senj can reach values as high as 40 m2 s-2. Večenaj (2012) compared a single bora event that occured simultaneously at the two stations, and concluded that both TKE and are twice as large at Senj; therefore, turbulence strength grew along the downslope (Senj is located at the foothill, and Vratnik at the mountain ridge). The importance of turbulence averaging interval selection was emphasized; overly large averaging interval can include motions such as pulsations into turbulence, inflating TKE and related statistics by as much as ~30%. Belušić et al. (2013) also used this dataset to identify simultaneous flow regimes between the two stations via clustering. Sustained interest in bora turbulence lead to further experiments. Within the frame of the WINDEX project (Horvath et al. 2010a, b), a tower with ultrasonic anemometers at several heights was installed in the hinterland of the city of Split. This dataset was used to point out the error in applying established engineering codes (mostly developed from data measured over flat, homogeneous terrain) to areas under the influence of bora (Lepri et al. 2015; 2017), to test the applicability of the Monin-Obukhov (MOST) similarity theory (Babić 2013; Babić et al. 2016b; Lisac 2014), to evaluate higher statistical moments (Večenaj et al. 2021) and the TKE balance, etc. Further instruments were installed at the Maslenica bridge (Večenaj et al. 2015), and used to show that the distributions of the turbulence statistical properties do not depend on the bora synoptic type (Šoljan et al. 2018) and to study jugo wind turbulence (Zajec 2022). The most recent measurement campaign – project SESAR – focused on the effect of the bora turbulence on the air traffic at the Dubrovnik airport (e.g., Jurković et al. 2018). Within the context of the bora turbulence properties, these studies fall into one of the two categories. In the first, a large dataset at a particular station is analyzed (e.g., Lepri et al. 2017; Lepri 2023). In the second, two measurement locations are compared for a single simultaneous bora event (Večenaj 2012). A long-term comparison of bora turbulence statistics for two or more stations was not undertaken thus far. This represents the main motivation for this chapter. Best candidates for this comparison are the stations in Senj and at the Vratnik pass; the first is located at the foothill of the coastal mountain range, and the second one is located atop the ridgeline, ~10 km to the east of Senj. Both stations have recorded a large amount of simultaneous bora events spanning the 9-month interval from September 2004 to June 2005. 1.2 Numerical modeling of bora turbulence Measurement campaigns outlined in the previous section were followed by numerical experiments with steadily decreasing numerical grid spacing. Along-coast jet and wake distribution was successfully reproduced even with ~3 km grid spacing (Enger and Grisogono 1998; Grubišić 2004; Belušić and Klaić 2006). Decreasing the spacing to ~1 km enabled study of submesoscale structures such as pulsations, rotors and lee waves (Belušić et al. 2007; Stiperski et al. 2012; Horvath et al. 2013). This decrease was especially important for the reproduction of near-ground wind in the immediate lee of coastal mountains. A good recent example is the well-reproduced wind speed at the Dubrovnik airport (ZLD) in Večenaj et al. (2019); they used a 0.5 km grid spacing and achieved substantial improvements with respect to coarse 8- and 4 km simulations (Simić 2019). A good example of errors caused by coarse grid spacing in the study of downslope windstorms is provided in e.g., Águstsson and Ólafsson (2014). Micrometeorological measurements described in the previous section also sparked interest in studying the ability of numerical models and planetary boundary layer (PBL) schemes to reproduce bora turbulence statistics. Here as well, the errors tend to decrease with grid spacing, although it depends on the vicinity of complex terrain. Offshore, even coarse grid spacing may yield good agreement with the measurements of TKE and its dissipation rate (Večenaj et al. 2012). This is not true in the immediate lee of the mountains, e.g., Belušić and Klaić (2006) and Simić (2019) compared surface TKE measurements at, respectively, Senj and Vratnik and at the ZLD (~10 m instrument mounting height) with simulations with 3 and 4 km grid spacing. TKE is in both cases underestimated by a factor of 3–4. Večenaj et al. (2019) simulated a bora event at the ZLD, but they instead used a 0.5 km grid spacing and obtained very good agreement with the TKE measurements. Even finer simulations (in the so-called large-eddy mode) were used to study TKE balance in the hinterland of Split (Horvath et al. 2013); the model output was verified using measurements at 10 m, 22 m and 40 m above the ground. One of the main issues regarding the simulation of turbulence in downslope windstorms, except the terrain representation which in principle can be solved by using more computational resources, concerns the parametrization schemes of the momentum, heat and moisture exchanges in the surface layer and the PBL. Most of these schemes were developed using data above flat and homogeneous terrain, often underestimating turbulence length scales (Grisogono and Belušić 2009; Večenaj et al. 2010; Večenaj 2015). Consequently, surface wind speed can be overestimated and position of the lee rotor can be misjudged (e.g., Muñoz-Esparza et al. 2016). These discrepancies are, in part, due to a lack of measurements, especially at heights above a few dozen meters above the ground level (a.g.l.). From the measurement campaigns outlined in the previous section, only the WINDEX campaign delivered high-frequency measurements above 20 m a.g.l., although this was partially supplemented by airplane (MAP project; Bougeault et al. 2001), sodar (Stiperski et al. 2012; Horvath et al. 2013) and lidar measurements (Jurković et al. 2018). Therefore, additional measurements of the mean wind speed and turbulence are needed, especially above ~20 m a.g.l. Using such measurements, the ability of the numerical model to reproduce vertical wind and turbulence profiles can be evaluated. In January 2012, a 100-m tower with anemometers at five heights was installed in the hinterland of the city of Rijeka. Besides the mean wind speed and direction, the instruments also recorded their standard deviations, thus enabling the estimation of the TKE and its comparison to numerical model results. In January and February of 2012, the instruments recorded a three-week series of strong to severe bora events. Presenting this dataset and comparing it to the model output presents the main motivation of this chapter. 1.3 Bora pulsations Pulsations, i.e., quasi-periodic motions with periods of 1–20 min represent a type of secondary instability caused by the strong shear in the wave breaking region and at the LLJ-stagnation zone interface (e.g., Figure 1). They were first studied in the famous Boulder windstorm (e.g., Zipser and Bedard 1982), where structures with decoherence length of ~10 km could be observed (via lidar) moving with the mean wind (Neiman et al. 1988). In numerical experiments, three pulsation generation mechanisms were identified, Kelvin-Helmholtz instability (KHI; Scinocca and Peltier 1989; Peltier and Scinocca 1990), tilting of the base-state vorticity associated with the breaking mountain wave (Clark and Farley 1984), and the trapped, travelling lee waves (Clark and Hall 1994). A schematic view of all three mechanisms is shown in Figure 3. Pulsations exist in bora as well. First measurements and theoretical considerations originate in the late 1980s (Rakovec 1987; Petkovšek 1987). Further development occured at the start of 2000s due to the installation of a high-frequency (1 Hz) anemometer at the town of Senj. In a series of papers, Belušić et al. (2004; 2006; 2007) reveal the underlying phenomena regarding the cessation of pulsations and the appearance of a high-level jet. They simulate the pulsations using COAMPS model, identifying KHI as the generating mechanism for that particular bora event. Furthermore, Orlić et al. (2005) use 3D anemometer data (mounted at Senj in 2004) to point out the difference in pulsations and turbulence. Pulsations were studied at other locations at the Adriatic cost as well, e.g., Horvath et al. (2013) observed pulsations with periods of 3–15 min. They found that the latter are connected to the upstream variation in profiles of wind speed and static stability. The research focus in the past was the period, wavelength and phase speed of the pulsations, as well as their numerical simulation. The aim of this chapter is to study the characteristic structure of pulsations in the horizontal plane using the rotational spectral analysis method – RSA (Gonella 1972; O’Brien and Pillsbury 1974). RSA (described in the Section 4.3.3) decomposes the 2D vector time series (at a certain frequency) into a positively and negatively rotating component, and can give insight into properties such as the preferred sense of rotation, coherence and the type of motion (rectilinear, circular or elliptical). RSA was previously used at the Adriatic coast in the study of diurnal rotation of sea breeze (Prtenjak et al. 2008) and the rotational characteristics of bora in the vertical plane (Orlić et al. 2005). Latter example is notable since RSA showed that pulsations and local turbulence exhibit different structures, and thus have different generating mechanisms. The choice of the subject and the method was motivated by observing a large set of bora events recorded by a 3D anemometer at the town of Senj. After the rotation of the data into the mean-wind system, I noticed large variability in the ratio of the pulsation energy in the along-wind and cross-wind directions, even within a single bora event. This variability implies change in either the orientation of the structure, or its type (i.e., from rectilinear to circular). Since different pulsation generation mechanisms produce different structures in the horizontal plane (Section 3.2), RSA can be used to deduce the dominant one. Finally, a numerical model (WRF-ARW) can be used to reproduce these characteristics and (if successful) study their spatial and temporal variability. 1.4 Objectives and structure The aim of the first chapter is to compare the statistical properties of the bora turbulence at two nearby stations, one at the foot of the mountain and the other at a ridgeline, for a large number of bora events. The combination of length of the analyzed dataset and the comparison of turbulence statistical properties at two stations represents the original contribution of this chapter. After the selection of an appropriate turbulence averaging interval (constant or variable), I will calculate the TKE, , momentum flux and other relevant parameters. Because of the differences in the surface cover and instrument mounting height (Section 4.1.2), the data is compared in the context of the statically neutral surface layer similarity (Section 3.1). The deviation of the nondimensional statistical properties from theoretical values can point towards possible differences in the TKE balance between the two stations. In the second chapter, I intend to verify the ability of the WRF-