U radu su opisane osnovne karakteristike kapilarnosti kao jedne od osnovnih svojstva kapljevina. Definiran je pojam površinskog naprezanja, značajke kohezijskih i adhezijskih sila unutar kapljevine, ...način određivanja visine kapilarnog dizanja te najznačajnije metode za mjerenje kapilarnosti u praksi. Drugi dio rada baziran je na izradi eksperimentalnih pokusa u hidrotehničkom laboratoriju Građevinskog fakulteta u Rijeci. Prvi pokus je obuhvatio eksperimentalna mjerenja visina kapilarnog dizanja kapljevine između dviju staklenih pločica, a drugi određivanje visina kapilarnog dizanja kapljevine u malim uskim cjevčicama različitih promjera za četiri različite vrste kapljevina pri njihovim različitim temperaturama.
The paper describes the basic characteristics of capillarity as one of the basic properties of liquids. The concept of surface tension, the characteristics of cohesion and adhesion forces, the method of determining the height of capillary rise and the most important methods for measuring capillarity in practice are defined. The second part of the paper is based on the creation of an experiments in the Hydrotechnical laboratory of the Faculty of Civil Engineering in Rijeka. The first experiment included experimental measurements of liquid rise heights between two glass plates and the second one was determination of liquid rise heights in small narrow tubes of different diameters for four different types of liquids at their different temperatures.
Pollution of water by plastic contaminants has received increasing attention, owing to its negative effects on ecosystems. Small plastic particles propagate in water and can travel long distances ...from the source of pollution. In order to research the settling motion of particles in water flow, a small-scale experiment was conducted, whereby spherical plastic particles of varying diameters were released in an open-channel flow. Three approaches were investigated to numerically simulate the motion of particles. The numerical simulation results were compared and validated with experimental data. The presented methods allow for deeper insight into particle motion in fluid flow and could be extended to a larger scale to predict the propagation of mesoplastics in natural environments.
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U ovom radu opisana su osnovna svojstva i značajke viskoznosti, prikazanisu najčešći instrumenti i metode za određivanje koeficijenata dinamičke ikinematičke viskoznosti te je pojam viskoznosti ...sagledan kroz reološki dijagram.Na temelju viskozimetra s padajućom čeličnom kuglicom različitih promjera imasa, u hidrotehničkom laboratoriju Građevinskog fakulteta u Rijeci provedenoje laboratorijsko određivanje dinamičkog i kinematičkog koeficijenta viskoznostina fizikalnom modelu na temelju 4 različite vrste kapljevina (voda iz gradskogvodoopskrbnog sustava, morska voda, suncokretovo ulje i mlijeko) u ovisnosti opromjeni temperature.
This paper describes the basic properties and characteristics of viscosity andpresents the most common instruments and methods for determining the dynamicand kinematic viscosity coefficients. Using a viscometer with a falling steel ball ofdifferent diameters and masses, in the hydrotechnical laboratory of the Faculty of CivilEngineering in Rijeka a laboratory determination of dynamic and kinematic viscositycoefficient was performed on physical model of 4 different types of liquids (drinkingwater, seawater, sunflower oil and milk) depending on the change in temperature.
U ovom radu obrađena je tematika primjene i svrhe Računalne dinamike fluida (RDF) u svakodnevnoj praksi te metode vizualizacije strujanja fluida. Radi lakšeg shvaćanja pojma modela turbulencije u ...radu su navedene osnovne karakteristike fluida od kojih je fokus dan na viskoznosti i kompresibilnosti. U svrhu opisa dinamike gibanja fluida definirane su osnovne vladajuće jednadžbe strujanja fluida, koje uključuju laminarani i turbulentni režim toka. Značajan fokus ovog rada posvećen je kreiranju numeričkih modela primjenom Računalne dinamike fluida, od samog predprocesiranja, definiranja domene problema, izrade numeričke mreže, sve do parametara potrebnih za definiranje pojedinih turbulentnih modela te načina vizualizacije rješenja promatranog problema kroz postprocesiranje. Drugi dio rada razmatra eksperimentalne i računalne metode vizualizacije strujanja fluida unutar kojih su dani pojedini primjeri za svaku od metoda vizualizacije.
This paper deals with application and purpose of Computational Fluid Dynamics (CFD) in everyday practice and methods of fluid flow visualization. In order to facilitate the understanding of the concept of turbulence model the paper presents the basic characteristics of the fluid, of which the focus is on viscosity and compressibility. For the purpose of describing the dynamics of fluid motion, the basic governing equations of fluid flow are defined, which include laminar and turbulent flow regimes. A significant focus of this paper is given to the creation of numerical models using CFD, from preprocessing, defining the problem domain, creating a numerical network, to necessary parameters for defining individual turbulent models and methods of visualizing the solution of the observed problem through postprocessing. The second part of the paper discusses experimental and computational methods of fluid flow visualization, within which individual examples for each of the visualization methods are given.
As a very important element of most water supply systems, valves are exposed to the effects of strong hydrodynamic forces. When exposed to large physical quantities, the valve and piping can be ...damaged, which could endanger the performance of a water supply system. This is the main reason why it is necessary to foresee and determine the maximum values of velocity, pressure and other physical quantities that can occur in the system under certain conditions. Predicting extreme conditions allows us to correctly size the valve for the expected conditions to which the valve might be exposed, which is also the main objective of this paper. One of the methods for predicting and determining extreme values on a valve is to perform a simulation with computational fluid dynamics (CFD). This is exactly the method used in the preparation of this paper with the aim of gaining insight into the physical magnitudes for models of gate valves positioned inside a pipe under characteristic degrees of valve closure. The Ansys CFX 19.1 and Ansys Fluent 19.1 software was used to simulate the hydrodynamic analysis and obtain the required results. The hydrodynamic analysis was performed for four opening degrees of gate valve
U radu je dan opis podrijetla vode na planeti Zemlji i njezino značenje u prošlosti i sadašnjosti. Analizirani su razmjeri kretanja vode na zemlji, njihove značajke, kao i glavni izvori dostupne vode ...na zemlji izraženi kroz postotni udio na globalnoj razini. Također je razmatran nastanak vode u Svemiru i proizvodnja kisika u ranoj fazi nastanka planeta. Fokus rada bazira se na održanju kvalitete vode dostupne na Zemlji te pojavi globalne varijabilnosti intenziteta oborina koje u zadnjih nekoliko desetljeća mijenjaju značajke velikih svjetskih površina kroz procese velikih suša i poplava. Kroz rad su opisani neki od najznačajnijih primjera eksploatacije pitkih voda u svijetu kroz površinske i podzemne rezerve vode. Analizirane su mogućnosti povećanja proizvodnje hrane za ljudske potrebe u pogledu povećanja zemljišta kroz tehnološki napredne metode te zaštita vodnih resursa uslijed klimatskih promjena. Dan je osvrt na značajke kvalitete prirodne vode u medicini i industriji, poboljšanje sanitarnih uvjeta, utjecaj ljudskog zagađenje na globalnoj razini, gospodarski rast i problem smanjenja vode, kao i globalni problem ispuštanja nepročišćenih otpadnih voda u recipijente i, posljedično, ugrožavanje flore i faune.
This paper gives a description of the origin of water on planet Earth and its importance in the past and the present. The paper presents the analysis of water flow extent on Earth, its characteristics, as well as the main sources of available water on the planet, expressed through a percentage share on a global scale. It also deals with the origin of water in the Universe, as well as the production of oxygen at the early stages of the planet’s formation. The focus of the paper is based on maintaining the quality of water available on Earth and the global variability of precipitation intensity that has changed the characteristics of large world surfaces through significant drought and flood processes over the last decades. Throughout the paper, some of the most important examples of exploitation of drinking water in the world through the surface and underground reserves of water are described. The possibilities of increasing the production of food for human needs in terms of increasing land through technologically advanced methods and the protection of water resources due to climate change are analyzed. At the end of the paper, there is a review of the characteristics of natural water quality in medicine and industry, sanitary conditions improvement, the impact of global pollution on human beings, economic growth and the problem of water scarcity, as well as the global problem of discharging untreated wastewater into the recipients and consequently endangering flora and fauna.
In order to improve the treatment processes of the drinking water treatment plant (DWTP) located near the Butoniga reservoir in Istria (Croatia), a prediction of the water quality index (WQI) was ...done. Based on parameters such as temperature, pH, turbidity, KMnO4, NH4, Mn, Al and Fe, the calculation of WQI was conducted, while for the WQI prediction models, along with the mentioned parameters, O2, TOC and UV254 were additionally used. Four models were built to predict WQI with a time step of one, five, ten, and fifteen days in advance, in order to improve treatment processes of the DWTP regarding the changes in raw water quality in the Butoniga reservoir. Therefore, obtained models can help in the optimization of treatment processes, which depend on the quality of raw water, and overall, in the sustainability of the treatment plant. Results showed that the obtained correlation coefficients for all models are relatively high and, as expected, decrease as the number of prediction days increases; conversely, the number of rules, and related linear equations, depends on the parameters set in the WEKA modelling software, which are set to default settings which give the highest values of correlation coefficient (R) for each model and the optimal number of rules. In addition, all models have high accuracy compared to the measured data, with a good prediction of the peak values. Therefore, the obtained models, through the prediction of WQI, can help to manage the treatment processes of the DWTP, which depend on the quality of raw water in the Butoniga reservoir.
U ovom radu opisana su osnovna načela i vladajuće jednadžbe za opis strujanja podzemne vode kroz porozni materijal. U svrhu dobivanja mjerodavnih vrijednosti pojedinih karakterističnih fizikalnih ...veličina kod strujanja podzemne vode u pjeskovitom poroznom materijalu (brzina procjeđivanja, ekvipotencijal u određenoj točki unutar prostora, hidraulički gradijenti, protok i sl.) korišten je fizikalni model GUNT HM169 koji čini sastavni dio hidrotehničkog laboratorija Građevinskog fakulteta Sveučilišta u Rijeci. U radu je opisan princip rada za navedeni fizikalni model te način pripreme samih eksperimentalnih pokusa. U tom pogledu, izrađeno je nekoliko hidrodinamičkih analiza strujanja podzemne vode u odnosu na varijabilnost potencijala gornje i donje vode, analiza strujanja ispod vertikalnog čeličnog žmurja (dijafragme) te analiza opstrujavanja podzemne vode ispod prostorno trapezno izmodelirane prirodne nasute brane. Za potrebe provođenja pokusa, nasuta brana ručno je izrađena od pleksi stakla. Svrha istraživanja kroz fizikalni model HM169 bila je dobivanje jasnije slike strujnog polja ispod pojedinih hidrotehničkih objekata i, posljedično, dobivanje simulacijskih prikaza propagacije toka podzemne vode koja je praćena žutim fluorescin traserom.
This paper describes basic principles and governing equations for describing groundwater flow through porous material. In order to obtain the relevant values of some of the characteristic physical quantities of groundwater flow in the sandy porous material (infiltration velocity, equipotential at a certain point within the space, hydraulic gradients, flow, etc.), the physical model GUNT HM169 was used, which is an integral part of the hydro technical laboratory of the Faculty of Civil Engineering, University of Rijeka. The paper describes the working principle for the mentioned physical model and the preparation of the experimental trials themselves. In this respect, several hydrodynamic analyzes of groundwater flow regarding the upper and lower water variability potential were made as well as the flow analysis below the vertical steel diaphragm and the analysis of groundwater depletion under the spatially trapezoidal modified natural sloping dam. To carry out the experiment, the sloping dam was manually made of Plexiglas. The purpose of the research through the physical model HM169 was to obtain a clearer picture of the streamline field below the individual hydroelectric objects and consequently to obtain a simulation of the propagation of the groundwater flow which was followed by a yellow fluorescence tracer.
Voda (H2O) je polarni anorganski spoj, koji je na sobnoj temperaturi tekućina bez okusa i mirisa, gotovo bezbojna. Količinski je daleko najzastupljeniji spoj na Zemlji i među rijetkim je tvarima koje ...na Zemljinoj površini postoje u krutoj, tekućoj i plinovitoj fazi. Kao relativno jednostavan kemijski spoj, opisana je kao „univerzalno otapalo“ ili „otapalo života“. Ujedno je i treća najzastupljenija molekula u Svemiru. Molekule vode međusobno tvore snažne vodikove veze, što joj definira specifična fizikalna i kemijska svojstva. Vodikove veze zaslužne su za mnoga jedinstvena svojstva vode, poput anomalije vode (činjenice da je kruti oblik – led – manje gustoće od tekuće vode), relativno visoke temperature vrenja (100 °C) i velikog toplinskog kapaciteta, što su ključni preduvjeti za očuvanje života na Zemlji. Voda je amfoterna molekula, što znači da može pokazivati svojstva i kiseline i lužine, ovisno o kemijskom okruženju u kojem se nalazi. U radu je provedena strukturna analiza molekule vode i njenih najvažnijih fizikalnih svojstava, s naglaskom na anomaliju vode. Jedno od važnih fizikalnih svojstava tekućine, a koja uvelike utječu na naš okoliš, je niska gustoća leda u odnosu na tekuću fazu vode te fenomen negativnog koeficijenta ekspanzije hladne vode. Također je opisano rješenje nuklearne Schrödingerove jednadžbe, koja daje informacije o unutarnjim gibanjima (vibracijama i rotaciji) molekule vode.
Water (H2O) is a polar inorganic compound that is almost colorless at room temperature. It is by far the most common substance on Earth and among very few substances, which exists on the Earth’s surface as a solid, liquid and gaseous substance. As a relatively simple chemical compound, it has been described as a “universal solvent” or “solvent of life”. It is also the third most common molecule in the Universe. Water molecules form strong polar hydrogen bonds with each other, which, in turn, define its specific physical and chemical properties. Hydrogen bonds are responsible for many unique properties such as the anomaly of water (the fact that its solid form, the ice, is less dense than the liquid form), a relatively high boiling point (100 °C) and a high heat capacity. Water is an amphoteric molecule, which means that it can show properties of both acids and alkaline solutions, depending on the chemical environment. In this paper, a structural analysis of a water molecule and its most important physical properties was carried out in detail with regard to its anomalies. One of the important physical properties of a liquid that strongly influences our environment is the low density of ice in relation to the liquid phase of water, and the phenomenon of the negative expansion coefficient of cold water. This work also describes the solutions of the nuclear Schrödinger equations, which provide information about the internal motions (vibrations and rotations) of a water molecule.
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