Search

Aim: This study aimed to measure the vertical force developed during canal instru - mentation with Neoniti rotary files at predetermined torque in relation to the oper - ator’s experience. Methodology: The research was performed on 60 human maxillary and mandibular incisors extracted for periodontal reasons. Each group of 20 teeth (10 maxillary and 10 mandibular incisors) was prepared by three different operators with different levels of experience in endodontics: a fresh dental school graduate, a postgraduate student training in endodontics and an endodontic specialist. Maxillary incisors represented the experimental model of wide root canals while mandibular incisors represented a model of narrow root canals. Root canals were prepared employing Neoniti files and TCM Endo unit at speed and torque recommended by the manu - facturer. Vertical force measurement was performed utilizing device constructed for this purpose. Statistical analysis was accomplished using Mann-Whitney U test, Kruskal-Wallis test and Spearman’s rank correlation. Results: The amount of vertical force was significantly higher in narrow than in wide root canals (P=0.001). Comparison of vertical forces developed by three different operators demonstrated significant differences (P

Various aspects of exposed ship structure have major impact on the accuracy of wind load estimation methods. Although several appropriate approaches for dealing with these issues have been proposed so far, there is still room for improvement. In that context, this paper presents an extension of previously proposed approach, which was based on Elliptic Fourier Descriptors (EFD) that are used for ship frontal and lateral closed contour representation. In previous research, the Generalized Regression Neural Network (GRNN) was trained with elliptic Fourier descriptors of a set of closed contours and non-dimensional wind load coefficients obtained from experimental wind tunnel tests. In this paper, training and testing sample is expanded with wind load coefficients derived from 3D steady RANS Computational Fluid Dynamic (CFD) analysis. In this way, the cheaper and faster calculation can bridge the gap between ship shapes for which calculations or experiments have already been made. The obtained neural network (NN) responses are well aligned with results of available experiments and obtained CFD results. Simulations used for this purpose were based on the analysis of the relationship of various container configurations on the deck of a 9000+ TEU container ship and associated wind forces and moments.

Veći broj eksperimentalno dobivenih rezultata mjerenja za opstrujavanje oko pojednostavljenog modela automobila (Ahmed body) dostupan je u literaturi. Poseban naglasak je na promjeni nagiba stražnjeg kraja modela čime se značajno mijenja karakter strujanja fluida. U radu su napravljene numeričke simulacije čiji rezultati su uspoređeni s mjerenim rezultatima iz literature kako bi se ispitao utjecaj numeričke mreže na točnost rješenja turbulentnih modela korištenih u software-u FLUENT. S obzirom da se radi o složenom turbulentnom strujanju, potrebno je pravilno prilagoditi numeričku mrežu budući da značajno utječe na vrijeme trajanja proračuna kao i na točnost rezultata. Veći broj elemenata numeričke mreže, ukoliko su raspoređeni na pravilan način, povećava točnost rezultata, ali značajno povećava vrijeme trajanja proračuna. Promatran je utjecaj smještaja i veličine volumnih elemenata strukturirane i nestrukturirane mreže na način da se minimizira broj elemenata numeričke mreže i time smanji vrijeme potrebno za izračun simulacije, a postigne zadovoljavajuća točnost rješenja, tj. odstupanje od mjerenih rezultata. Utjecaj numeričke mreže ispitan je za različite turbulentne modele.

Aim To analyze apical irrigant pressure developed by four needles, each at different flow rates, using an ex vivo model for endodontic irrigation. Methodology A human maxillary incisor root canal was shaped to the working length (WL) utilising rotary files up to size 40, 0.06 taper, patency size 10. The apical foramen of the root canal was sealed in closed system connected to digital manometer (PM- 9100HA, Omega Engineering, USA). Two notched open-end irrigation needles (Needle 1: Endo-EZE ; Ultradent Products, USA, and Needle 2: Appli-Vac ; Vista Dental, USA), one single side-vented (Needle 3: Appli-Vac, Vista Dental, USA) and one double sidevented (Needle 4: Calasept, Nordiska Dental, Sweden), all 27G, were used. Each needle was mounted 1 mm short of WL and constant flow rates of 0.05, 0.10, 0.15 and 0.20 mL s 1 of irrigant (3% sodium-hypochlorite) were delivered by Precision Syringe Pump (Aladdin, World Precision Instruments, USA). Apical irrigant pressure was measured (N = 20) for each flow rate. Two-way ANOVA without repetition analysis was used to determine statistical difference between needles types and the rise of irrigant flow rate. Results The highest value of apical irrigant pressure was developed by Needle 2 at 0.20 mL s 1 (68 2.66 mmHg), while the lowest by Needle 4 at 0.05 mL s 1 (2.25 0.55 mmHg). Results showed a significant difference between the notched open-end (Needle 1 and 2) and side-vented irrigation needle (Needle 3 and 4) type groups (F = 6.53, P < 0.05). Differences in needle type were not significant. The increase of irrigant flow rate resulted in a significant increase of apical pressure for all irrigation needles. Conclusions Apical irrigant pressure was influenced by both needle type and irrigant flow rate. Increase of irrigant flow rate increased apical pressure while the application of open-end needles was associated with increased apical pressure compared to side-vented.

Analiza promjene tlaka i topline u zatrpanim spremnicima UNP za refrentnu godinu na odabranoj lokaciji.

Perpendicular blade position to the trajectory, used on the caterpillar type of the water wheel mechanism of the portable hydro plant, during blade immersion in the water causes it to brake. The reason is the bad synchronisation of the blade immersion direction with the water flow. To obtain smooth blade immersion in the water, an additional rotational relative movement of the blade is proposed.

The aim o f this study was to analyze the irrigation efficiency of two needle types in a realistic root canal , odel using Computional fluid dynamics (CFD). An extracted human maxillary canine was decoronated at the enamel -cement junction. After cleaning and shaping, the prepared root canal was scaned by computed, tomography. A 3D object representing the prepared root canal was obtained using Scan IP and computer assisted design (CAD) software Catia. an open-end notched 27G irrigation needle with closed tip was measured and a CAD model created, providing a plotting template for a virtual side-vented irrigation needle with closed tip. Both 27G, virtual needles were placed at 0.9, 4.5 and 9 mm from the apical terminus of the prepared root canal model and, after merging with root canal, models were exported to comercial CFD solvent software Star-CCM. Four different irrigant inlet velocity values were set, determined by clinicaly reproducible flow rates (0.1, 0.2, 0.3 and 0.4 ml/s), for each needle type and position. CFD analysis of irrigant flow pattern, velocity and pressure was performed. Open-ended needles had satisfactory flow patterns at 0.9 and 4.5 mm for all flow rates analyzed, while side-veneted needles were effective at 4.5 mm distance only with 0.4 mL/s, and at 0.9 mm with 0.2-0.4 mL/s flow rates. Irrigant pressure in apical portions of canals was significantly increased in the case open-ended comparing to side-vented needle. On the basis of this ex vivo investigation, open-ended irrigation needles had efficent irrigation at lower flow rates compared to side-vented closed-ended needle of the same diameter, though the latter provides decreased irrigant pressure and safer irrigation.

Simulacija strujanja i izgaranja u ložištu TE Rijeka

U sklopu projekta izvršena je simulacija strujanja fluida u dovodnom dijelu crpke. Cilj projekta je u izradi prijedloga modifikacije privoda kako bi se smanjile vibracije crpke u radu pri određenim rdanim uvjetima

Prijedlog izmjene početnog dijela odvodnog kanala HE Vinodol s ciljem smanjennja lokalnih gubitaka i smanjenja razine vode u kanalu.

Simulacija strujanja u privodu voden turbine HE Zeleni vir s ciljem izmjene gemetrije privoda radi smanjenja gubitaka.

This paper analyzes the fluid flow and heat exchange on the air side of a multi-row fin-and-tube heat exchanger. The CFD procedure, validated by comparing the numerical simulation results with the experimental results, was further improved by including the fluid solid interaction in the form of heat conduction through exchanger tubes. Simulation results correspond well with measured data and show parts where shape optimization could be beneficial.

Analiza strujanja u turbinama HE Jajce II. Analiza rada kod nadvišenja brane.

Numerical analyses, performed as a part of a redesign project for an air-conditioning system of a sport hall, have been presented. The existing and redesigned air-duct arrangements as well as different types of air supply outlets have been analyzed using three dimensional steady-state numerical simulations of air flow. Commercial CFD software Star-CCM+ has been used for fluid flow simulations based on the finite volume method. It was determined that the use of special diffuser type with variable outlet flow patterns for winter and summer operation produced better thermal environmental conditions in air-conditioned space, as compared to existing air grilles. The application of computational fluid dynamics (CFD) methods for air distribution analysis has proven to be a very useful tool in design of modern air distribution systems.

U radu su prikazane značajke sustava niskotemperaturnih grijanja i visokotemperaturnih hlađenja - hlađenja pothlađenom vodom (podnih, stropnih i zidnih). Na primjeru hotelske sobe izračunate su distribucije temperatura i brzina strujanja zraka za slučaj primjene sustava podnih i stropnih grijanja i hlađenja u usporedbi sa sustavima grijanja i hlađenja ventilatorskim konvektorima. Simulacije su provedene za trodimenzionalno strujanje korištenjem CFD (Computational Fluid Dynamics) softwarea FLUENT. Dan je osvrt na specifične uvjete primjene pojedinih sustava i utjecaj na osjećaj lagodnosti osoba koje borave u prostoru. Opisane su neke mogućnosti korištenja obnovljivih izvora energije bilo korištenjem dizalica topline ili neposredno. Međusobno je uspoređena potrošnja energije kod različitih sustava grijanja i hlađenja.

This paper gives an overview of the optimization process for deflector shape design. The task was to lower the water level in the S-shaped outflow channel of HPP Vinodol by steadying the flow and reducing energy losses. Parameterized designs of ten deflectors were optimized using a genetic algorithm that evaluated each setup by running a 2D fluid flow simulation. After analyzing total pressure losses in channel segments, optimal designs were chosen according to total pressure loss and flow uniformity throughout the channel. The resulting best case design set showed a 37% reduction in energy losses over the worst-case representation of the actual channel. This provides a solid basis for further simulations using a 3D fluid flow numerical model of the channel. The 3D simulation based on the best 2D case design set showed a significant decrease in spillage through the channel ceiling into the above engineering room.

U radu su prikazane mogućnosti poboljšanja sustava hlađenja zrakom hidro-generatora. Poboljšanje se temelji na minimalnim izmjenama postojeće konstrukcije, a koje u konačnici rezultiraju s bitnim smanjenjem gubitaka strujanja zraka ("gubici ventilacije"). Osnovna ideja promjene konstrukcije se temelji na hidraulički povoljnijem („glađem“) projektiranju tokova zraka kroz generator čime se bitno smanjuju dužinski i lokalni gubici strujanja. Rekonstrukciju je moguće izvesti i na već postojećim generatorima što je dijelom napravljeno na generatoru HE Vinodol i time dokazana mogućnost smanjenja gubitaka. Provedene računalne simulacije strujanja fluida kroz zračne kanale hidro-generatora potvrdile su izmjerenu vrijednost gubitaka kod postojeće konstrukcije i ukazale ne bitno smanjenje gubitaka kod rekonstruiranih konstrukcija. Ušteda na smanjenju gubitaka strujanja zraka opravdava rekonstrukciju te ju je razumno izvesti na postojećim generatorima, a kod projektiranja novih konstrukcija generatora treba voditi računa o pravilnom oblikovanju tokova zraka kako se ne bi nepotrebno povećali gubici strujanja.

This paper analyzes the fluid flow and heat exchange on the air side of a multi-row fin-and-tube heat exchanger. A comparison is given between fin-and-tube heat exchanger characteristics with flat and louvered fins in a wider range of operating conditions defined by Reynolds number (based on fin spacing and air frontal velocities). The detailed representation of calculated data for the louvered heat exchanger shows significantly better heat transfer characteristics and a slightly higher pressure drop. The CFD procedure was validated by comparing the numerical simulation results with the experimental results showing minimal average Nusselt number deviation and almost perfectly corresponding pressure drop.

This paper compares data from calculated and measured results covering the whole operating range for a 20 MW Francis turbine in order to validate the CFD simulation. Computed hydraulic characteristics are determined for each analyzed operating point by running numerical simulations of turbulent fluid flow through a complete Francis Turbine model using the commercial fluid flow solver Fluent. The measured hydraulic characteristics were defined by on-site measurements according to the IEC 41 international field acceptance test standard. The computed characteristics show very good conformity of values and trend-lines with measured characteristics over the whole operating range. The deviations are lowest around the optimum and increase towards the boundaries of the operating range where the vorticity in the turbine diffuser is more significant. The aim was to analyze the behavior of the existing turbine and fine-tune the whole numerical experiment to achieve the level of accuracy necessary for a concept design of a revitalized turbine.

Numerical analyses, performed as a part of a redesign project for a heat pump and air-conditioning system in a sport hall, have been presented. The project goal was to reduce the energy consumption and costs for heating and cooling the building as well as to increase the thermal comfort inside the building. All year round simulations of the building energy consumption have been performed for different building insulation levels. The numerical dynamic model with concentrated parameters has been used to simulate the dynamic behavior of the heat pump system using the sea water as a heat source. The heat pump system model has been built as the modular framework, with subroutines representing equipment, pipes, tanks and controllers. Equipment data acquired from manufacturers (heat pumps, heat exchangers, controllers and pumps) have been implemented into a model in order to simulate the analyzed system. Hourly values have been evaluated for temperatures within the system, heating and cooling energy supplied by the heat pump, as well as compressor electric energy consumption during the entire year. The choice on the building insulation level has been done by using the simulation data. The proper air distribution was achieved by using numerical simulations of air flow inside the building for different air-duct arrangements, with CFD software FLUENT, based on a finite volume method.

U sklopu projekta izvršena je simulacija strujanja fluida kroz hidrauličku turbinu jednaku onoj instaliranoj u HE Senj. Prvi dio projekta odnosi se na simulaciju strujanja fluida kroz postojeću turbinu HE Senj. Simulacije strujanja trebalo je izvršiti za zadane kote gornje vode te za pomake hoda klipa servo motora određene projektom.

Analizira se utjecaj numeričke mreže na efikasnost numeričkog modela i na kvalitetu rezultata kroz matematički model plitkih voda u 2D slučaju, odnosno Navier-Stokesov model strujanja fluida u 3D slučaju. U obama slučajevima koristi se implicitna numerička shema koja pretpostavlja rješavanja linearnog sustava u svakom vremenskom koraku. U 2D slučaju predložena je upotreba numeričke mreže konačnih volumena centriranih po ćeliji jer ona daje matricu linearnog sustava pogodne strukture, a u 3D slučaju prednost se daje poliedarskom tipu mreže.

Modeliranje onecišcenja zraka postalo je esencijalno za razumijevanja nacina kojim emisije onecišcujucih tvari iz industrijskih kompleksa, cestovnog transporta i ostalih izvora emisija utjecu na dinamiku okoliša. Korištenjem standardiziranoga modela disperzije ISCST3 izraden je sustav za kontinuirano procjenjivanje prizemnih koncentracija onecišcujucih tvari. Opisan je automatizirani pristup prikupljanju emisija i meteoroloških podataka te izvršena evaluacija za odabrano vrijeme na temelju analize cjelogodišnjih mjerenih podataka emisija i meteoroloških podataka.

Korištenjem računalnih modela strujanja fluida moguće je opisati realna strujanja kao što su strujanja zraka i onečišćujućih tvari u okolici industrijskih i izrazito prometnih područja te komplicirana turbulentna strujanja vode u hidrauličkim turbinama. Zahtijevane točnost rezultata simulacija nameću nužno korištenje superračunala uslijed velikog broja potrebnih računskih operacija koje je potrebni izvršiti, a koje proističu iz kompleksnih fizikalnih i kemijskih modela, nepravilne geometrije te nestacionarnosti strujanja. Potrebu za primjenom superračunala nameće i što kraći vremenski rok unutar kojeg je potrebno doći do rezultata kao što je slučaj sa kontinuiranim procjenjivanjem onečišćenja zraka. Provedene računalne simulacije su vrlo bliske mjerenim rezultatima što potvrđuje opravdanost upotrebe simulacija strujanja kao numeričkog eksperimenta, a nasuprot skupim mjerenjima in situ ili u ispitnim stanicama.

U ovoj doktorskoj disertaciji se predlože učinkovit postupak revitalizacije Francisove vodne turbine. Rad započinje matematičkim modelom turbulentnog strujanja fluida te pripadajućim numeričkim modelom zasnovanim na metodi konačnih volumena. Slijedi pregled postupaka opisa geometrije lopatice rotora i rotorskog kanala te optimizacijskih metoda potrebnih za odabir optimalnog oblika rotora. Validacija primijenjenog matematičkog i numeričkog trodimenzionalnog modela strujanja fluida izvršena je usporedbom izračunatih energetskih značajki s in-situ izmjerenim podacima u pojedinačnom i paralelnom radu turbina. Povećanjem nazivnog protoka turbine, predložena revitalizacija zahtjeva modifikaciju hidrauličkog oblika predprivodećih lopatica te proširenje izlaznog presjeka rotora. Novi oblik rotorskog kanala u meridionalnoj ravnini te oblik lopatice rotora dobiveni su optimizacijom združivanjem genetskog algoritma, predprocesora i programa za simulaciju strujanja fluida. Optimizacije oblika su provedene za više radnih uvjeta turbine. Odabrana varijanta revitalizirane turbina u usporedbi s postojećom ima značajno bolje energetske karakteristike u području viših protoka fluida omogućujući dodatno iskorištenje vodnog potencijala koji se tijekom vodnih valova, radi nemogućnosti značajnijeg akumuliranja, gubi prelijevanjem. Sve simulacije strujanja fluida su izvođene na višeprocesorskim računalima čime je višestruko smanjeno vrijeme računanja. U zaključku je dana ocjena uspješnosti istraživanje te smjernice daljnjeg istraživanja.

This work was motivated by a need for validation of commercial CFD fluid flow solver for hydraulic turbine flow simulations. For the same reason, the ERCOFTAC draft tube has been used for many years as a base for evaluating the state-of-the-art CFD (Computational Fluid Dynamic) codes in the field of hydropower generation. Probably one of the most interesting parts, from the aspect of efficiency, is a hydraulic turbine draft tube. Its role is to increase the pressure head by converting outlet kinetic energy into static pressure and therefore impacts directly on the total efficiency of the hydropower plant. Draft tube fluid flow is difficult to predict numerically due the highly swirled, fluctuating and non-uniform flow that leaves the rotating runner and enters the draft tube. Without visualization of the fluid flow simulation results, only pure intuition existed of what the fluid flow in hydraulic turbines looks like. From the flow simulations results the fluid flow behavior inside draft tube can be understood in sufficient detail and this knowledge can be used to designe new generation of the draft tubes or revitalize old ones.

Efficient two-dimensional numerical model for free surface flows is defined on the basis of two-dimensional mathematical shallow water model. Shallow water equations are solved using implicit numerical methods with a number of additional numerical procedures for simulation of two-dimensional general, steady and unsteady flow problems. The simulation of unsteady problems with implicit numerical scheme includes simulation of flooding wave propagation over dry terrain, efficiently calculated by employing flexible numerical domain that changes as flooding front advances. The computer code for two-dimensional flow simulations is developed and implemented on Toce river standard test case.

Izvršena je preliminarna analiza zamjene više postojećih niskih industrijskih dimnjaka jednim višim dimnjakom u cilju smanjenja onečišćenja pri nepovoljnim uvjetima u okolici industrijskog objekta. Kroz novi dimnjak prolazit će ista količina dimnih plinova uvećana za planirano povećanje industrijskih kapaciteta u bliskoj budućnosti. Analiza onečišćenja zraka u okolici novog industrijskog dimnjaka provedena je u cilju određivanja minimalne visine dimnjaka kojom bi onečišćenje zraka na četiri unaprijed zadane lokacije bilo unutar zakonom dozvoljenih vrijednosti za bilo koje meteorološke uvjete. Razvijeni računalni program zasnovan na Gaussovom modelu dima je korišten za simulaciju disperzije onečišćenja na realističnom kompleksnom terenu uz standardne meteorološke uvjete. Genetski algoritam je korišten za pronalazak maksimalnih vrijednosti onečišćenja pri različitim meteorološkim uvjetima. Dobivena ovisnost maksimalno izračunatog onečišćenja o visini dimnjaka poslužila je za odabir minimalne visine dimnjaka nužne za očuvanje zakonom propisane kvalitete zraka.

Mjerenja obavljena na odvodnom kanalu HE Vinodol u Triblju pokazuju da je visina zbirnih gubitaka na dionici kanala, koja uključuje dva zavoja i središnji ravni dio, oko 10-15 cm. Slike strujanja pokazuju znatno odvajanje struje od stjenke na unutarnjoj strani oba zavoja. Spoznaje o smanjenju gubitaka ugradnjom skretnih limova za zatvorene kanale na skoro polovični iznos navode na korisnost analize smanjenja gubitaka za kanal sa slobodnom površinom preciznijim metodama uporabom Računarske dinamike fluida (CFD). Potrebno je stoga ovim projektom izračunati gubitak strujanja bez i sa skretnim limovima i to na tzv. klasičan način, uporabom u literaturi dostupnih podataka za koeficijent gubitaka, koje se odnose na ispitivanja u zatvorenim kanalima, potpuno ispunjenim fluidom i procijeniti moguće smanjenje gubitka. Nakon toga treba primjenom FLUENT-a, komercijalnog softvera za simulaciju strujanja vode sa slobodnom površinom, dobiti simuliranu sliku strujanja sa svim potrebnim detaljima za procjenu gubitaka za oba slučaja: bez i sa skretnim limovima, te izračunati smanjenje gubitaka primjenom skretnih limova.

The paper describes numerical analyses performed during the redesign of a heat pump and air-conditioning system of a sport hall, with heat pumps utilizing the sea water as a heat source. Dynamic models of building energy consumption and a heat pump system were used in order to evaluate energy consumption and costs, as well as to make decision about additive insulation of the building. Computational fluid dynamics (CFD) methods were used to analyze and improve the air-distribution inside the hall.

U sklopu projekta izvršena je simulacija strujanja fluida kroz hidrauličku turbinu jednaku onoj instaliranoj u HE Rijeka. Prvi dio projekta odnosi se na simulaciju strujanja fluida kroz postojeću turbinu HE Rijeka. Simulacije strujanja trebalo je izvršiti za zadane kote gornje vode (visine vode u akumulaciji Valići) te za pomake hoda klipa servo motora određene projektom.