Iskanje po katalogu digitalne knjižnice

Ključne besede: accuracy, analytic hierarchy process, approximation method, pairwise comparisons, priority, simulation
Objavljeno v DKUM: 09.05.2025; Ogledov: 0; Prenosov: 2
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Opis: Cavitation is the phenomenon of fluid evaporation in hydraulic systems, which occurs due to a pressure drop below the value of the vapor pressure. For numerical modelling of this generally undesirable phenomenon, which is often associated with material damage (erosion), there are various mathematical vapor transfer models that have been validated in the past. There are different approaches to predicting cavitation erosion, which have mostly been experimental in the past. Recently various numerical models have been developed with the development of numerical simulations. They describe the phenomenon of cavitation erosion based on different theoretical considerations, such as Pressure wave hypothesis, Microjet hypothesis, or a combination of both. In the present paper, an analysis of the Schnerr-Sauer transport cavitation model was used, upgraded with an erosive potential energy model based on pressure wave hypothesis for cavitation erosion prediction. The extended numerical model has been applied to the case of a radial divergent test section in three different mathematical formulations. The results of simulation were compared and validated to experimental work performed by other authors. The study shows that the distribution of surface accumulated energy agrees with the experimental results, although certain differences exist between formulations. The applied method appears to be appropriate for further use, and to be extended to materials response modelling in the future.
Ključne besede: kavitacija, erozija, erozivna potencialna energija, numerične simulacije, cavitation, erosion, erosive potential energy, numerical simulation
Objavljeno v DKUM: 26.03.2025; Ogledov: 0; Prenosov: 3
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Opis: In this work, we developed a numerical approach based on an experimental platform to determine the working conditions on a cryoplatform and to predict and evaluate the cryogenic printing of hydrogels. Although hydrogels have good biocompatibility, their material properties make it difficult to print them with high precision and shape fidelity. To overcome these problems, a cryogenic cooling platform was introduced to accelerate the physical stabilisation of each deposited layer during the printing process. By precisely controlling solidification (crystallisation), each printed material can withstand its own weight to maintain shape fidelity, and the porosity of the scaffolds can also be controlled more selectively. The thermophysical properties of gelatine hydrogels were investigated to gain a better understanding of the phase change upon freezing. The corresponding material properties and experimental observations of gelatine solidification served as the basis for developing a computational fluid model (CFD) to mimic the solidification of gelatine hydrogels using a cryoplatform at different process conditions and extruder speeds. The goal was to develop a tool simple enough to predict acceptable process conditions for printing gelatine hydrogels using a cryoplatform.
Ključne besede: gelatine, hydrogel, cryoprinting, CFD simulation, solidification modelling
Objavljeno v DKUM: 20.03.2025; Ogledov: 0; Prenosov: 7
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Opis: The significance of the agricultural sector in the economy of Republika Srpska, as well as the importance of dairy cattle farming within agriculture, determined the thematic field of the research, which had several key research objectives. The first objective of the dissertation was to determine the economic efficiency of the investment in milk production and sales on family farms with 8-15 dairy cows in Republika Srpska. The second objective was to assess the risk, or volatility, of such investment projects. The third objective was to calculate the additional value of diversification in transitioning from selling milk to milk processing into cheese on the same farm and determine the additional project's strategic value. The final objective was to compare the case studies of the analyzed farms based on selected indicators. Primary data were collected by interviewing five farmers who produce milk and process it into cheese while secondary data were obtained from various sources. Key data processing methods included Cost-Benefit Analysis, Monte Carlo simulations, and Black-Scholes and Binomial methods for evaluating real options. Based on the results of the analysis of milk production projects on small farms in Republika Srpska, it was concluded that these projects are economically unsustainable due to their negative and insufficiently satisfactory indicators. Through Monte Carlo simulations, it was determined that changes in input and output prices have an impact on such projects. Diversification of milk production into cheese processing on small farms is economically efficient, as the option values of the additional project are satisfactory and the NPVS, representing the total value of the additional project, ranges from €28,000 to €143,000 for all five analyzed farms. Based on the farm analysis, the conclusion is that the farm with the highest number of dairy cows implements an extensive feeding method, and sells its products at a prominent tourist location in rural areas has the best indicators and represents the best business model for small milk farms in the territory of Republika Srpska.
Ključne besede: Agriculture, Milk farming, Cheese production, Cost-Benefit Analysis, Real Options Approach, Monte Carlo Simulation
Objavljeno v DKUM: 13.03.2025; Ogledov: 0; Prenosov: 14
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Opis: Measurements are of paramount importance in industry and other areas of importance to society. They are used to determine the characteristics of processes and products, to control and regulate processes, to decide on the acceptable quality of products, etc. To ensure the quality of measurements, we have to calibrate measuring devices regularly. In our laboratory – the holder of the national length standard, we mainly calibrate high-precision standards from accredited laboratories. As the demands on the accuracy of measurements are constantly increasing, we are also forced to continuously improve the accuracy of our calibration procedures. This article presents the development of methods for calibrating the diameter of ring gauges, which represent an important standard for calibrating measuring instruments for measuring internal dimensions. The main objective of this development is to reduce the measurement uncertainty based on a scientific investigation of all influencing parameters. The presented study focuses in particular on the control and reduction of the influence of geometric anomalies of the calibrated rings on the measurement uncertainty during calibration.
Ključne besede: measurement traceability, calibration, measurement uncertainty, error simulation
Objavljeno v DKUM: 11.03.2025; Ogledov: 0; Prenosov: 3
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