Hydro Turbine in a Venturi Tube

U radu su prikazani rezultati istraživanja hidroturbine u Venturijevoj cijevi za zadani broj okretaja i zadanom brzinom vode na ulazu u cijev. Rezultati su dobiveni komercijalnim softverom za numeričku dinamiku fluida. Ispitivanje je obuhvatilo usporedbu snage koju daju jedna i dvije suprotno smjerno rotirajuće hidroturbine u Venturijevoj cijevi. Numeričke simulacije za dvije turbine koje se okreću u suprotnim smjerovima s jednakim kutnim brzinama pokazale su da se javlja znatan pad snage na prednjoj turbini, dok je ukupna snaga nešto veća nego za jednu turbinu.This paper presents results of a research hydro turbine in a Venturi tube for given revolutions per minute and velocity of water at the entry of the tube. The results were obtained with commercial software for numerical fluid dynamics. The research was included comparison of power obtained with one and two contra-rotating hydro turbine in a Venturi tube. The numerical simulations, for two turbines rotating in opposite directions with equal angular velocities, showed that a considerable power drop occurred, whereas the total power is somewhat larger than for the one turbine

Determination of air and hydrofoil pressure coefficient by laser doppler anemometry

Some results of experiments performed in water cavitation tunnel are presented. Pressure coefficient (Cp) was experimentally determined by Laser Doppler Anemometry (LDA) measurements. Two models were tested: model of airplane G4 (Super Galeb) and hydrofoil of high speed axial pump. These models are not prepared for conventional pressure measurements, so that LDA is applied for Cp determination. Numerical results were obtained using a code for average Navier-Stokes equations solutions. Comparisons between computational and experimental results prove the effectiveness of the LDA. The advantages and disadvantages of LDA application are discussed. Flow visualization was made by air bubbles

The effects of laser light interactions with materials of cultural heritage

The effects of laser light and material interaction during the process of testing, processing and conservations of cultural heritage objects are very important concerning of the material characteristics preservation. Ruby and Nd3YAG lasers are very often used as light sources in a variety of optical recording and testing methods of cultural heritage items (eg interferometry). Special emphasis is give on the undesirable effects that may occur in the tests due to local laser beam focusing and to energy density increasing, as well as on the application of the laser processing, corrosion cleaning and material sintering

The analysis of damage threshold in ruby laser interaction with copper and aluminium

U radu su prikazani rezultati delovanja laserske svetlosti, talasne dužine λ = 694,3 nm (rubinski laser, Q-switch mod), na uzorke od bakra i aluminijuma. Cilj ispitivanja je bio da se odrede maksimalne gustine energije laserskog snopa koje mogu da se koriste u dijagnostičke svrhe (interferometrijska snimanja, lasersko skeniranje, itd), kao i u uklanjanju depozita, a da pri tome snop ne stupa u interakciju sa osnovnim materijalom. Odabrani uzorci od bakra i aluminijuma bili su dugi niz godina izloženi atmosferskim uticajima. Rezultati delovanja laserske svetlosti ispitivani su skenirajućim elektronskim mikroskopom. Istraživanja su pokazala da je bezbedna granica gustine energije rubinskog lasera za dijagnostičke metode za oba metalna uzorka do 20×103 J/m2.Nondestructive methods are dominant in diagnosing the status and protection of all kinds of contemporary industrial objects, as well as objects of industrial heritage. Laser methods open wide possibilities of research in the field of diagnosis and metal processing. This paper presents the results of laser radiation interaction (wavelength λ = 694.3 nm, Ruby laser, Q-switch mode) with metal samples covered with a deposit. The goal of the examination was to determine the maximum energy density of the ruby laser beam, that can be used in diagnostics purposes (interferometric methods; 3D scanning) and as a tool for safe removal of deposits, without interacting with the basic material. Microscopic examination performed with SEM coupled with EDX allowed the determination of the safe laser light energy density levels, which caused the removal of the deposite from the surface of the sample, without degradation of the surface. The energy density up to 20 kJ/m2 is the maximum allowed for diagnosis or deposit removal

Laser beam Induced Structural Changes in Multicomponent Nickels Alloys

Multicomponent nickel alloy, alloyed with: Mn, Cr, Al, Fe, B, Zr and others, was subjected after mechanical under the vacuum heat treatments: solution heat treatment at 1080oC for 1 hour, primary precipitation at 840 oC for 4 hours, secondary precipitation heat treatment at 760 oC for 3 hours and stress relief annealing at 700 oC for 1 hour. After heat treatment, laser surface treatment was applied and was related to the material deformation and damage formation on the material surface. Preliminary investigations were carried out by laser drilling and resulting traces on material were recorded by scanning electron microscope to find out the influence of different energies and pulse length on structural changes in the material

Workability conditions determination of network distribution with overhead lines power transmission with the 6-35 kV

The principal of identification of isolation workability in relation to a ground was proposed. It is based on the electrosafety criteria usage and a minimum current flow to a ground. The conditions of workability of isolation of distribution network is calculated in look of changes of isolation workability restrictions in relation to regulations and standards. A mathematical model for the calculation of isolation workability in a look of a relation of workability indicators to the isolation parameters according to a ground. By analyzing the adequacy it as set that introduced formed models assumptions result in the appearance of a method error to 3,5 %

Determination and analysis of the dynamic loaded screws by structural analysis, fractography and numerical simulation

This paper analysis the cause's dynamically loaded screws failure, using the structural analysis of mechanical properties and numerical simulation. The comparison with the new unbroken screws, which were not in use, has been done to determine the condition of the broken (dynamically loaded) ones. Analysis was performed, according to the following test methods and activities: non-destructive testing, visual inspection, radiographic testing, chemical analysis of screws sample materials, mechanical properties of screws' materials. Structure analysis of screws materials: Testing macrostructure (light optical microscope, SEM-EDS) examination of the microstructure (light optical microscope, SEM-EDS), fractographic examination. Numerical simulation of the stress state of the dynamically loaded screws was done in CATIA software package, and it was identical to the bolt loads, during service exploitation. The results between numerical simulation and structural analysis were quite coinciding - the difference is about 8-10%, which is pretty good for these types of experiments. Such an overlap, says that the stress value at the very screws is reliable and give us a true picture of loadings. Structural mechanical tests have shown a very pronounced effect of dynamic loads, that large shear stress shows also as a good agreement, where between the stresses, obtained by numerical simulation and structural mechanical testing. Analysing the results, obtained by numerical simulation and structural mechanical testing were performed with the redistribution of critical stresses, and proposal for the structure optimization. The comparative analysis methods have been provided the precise prediction of fracture appearance and made possible to define the preventive measures