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An analysis of the geomechanical processes in coal mining using the Velenje mining method
Gregor Jeromel, Milan Medved, Jakob Likar, 2010, original scientific article

Abstract: With in-depth geomechanical analyses of sub-level mining using the longwall mining method we can identify the relationships between the physical and mechanical parameters of geological materials, depending on the intensity of the coal extraction. The extent and the intensity of the mining operations impose impacts on the stresses and cause deformation changes in the rocks and in the coal seams on a broader area of excavations. The method of sub-level coal extraction requires multi-caving of the hanging-wall layers, which are recompressed, and in sub-level stoping each represents a hanging wall. The repeating processes of caving-in and compression, from the aspect of the theory of plasticity, have been relatively little researched because every such process brings about structural changes in natural, multi-caved and recompressed materials in the hanging wall. The intensity of the coal extraction has direct impacts on the surrounding and distant mining areas. Extensive stress and deformation changes in the surrounding area, and in the mine, represent a safety hazard for the employees, since the supporting system in the mine roadway could collapse. Therefore, a controlled excavation of the coal, and a good understanding of the geomechanical properties of all the materials and processes involved, is extremely important for planning and managing economic production, while also ensuring safe mining operations. A numerical model that allows for in-depth analyses of the geomechanical processes that occur in the hanging wall, the footwall and in the coal seam during sub-level coal excavation, is broadly applicable and highly relevant for analysing the intensity and the level of the caving processes in sub-level coal mining, and for making realistic plans for coal excavation with workers’ safety in mind.
Keywords: coal mining, sub-level mining method, longwall coal mining method, carving processes, finite-difference method, FLAC, mathematical model
Published: 11.06.2018; Views: 411; Downloads: 64
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The costs of container transport flow between Far East and Serbia using different liner shipping services
Vladislav Rajkovič, Nenad Đ. Zrnić, Đorđe Stakić, Borut Mahnič, 2015, original scientific article

Abstract: Liner shipping is the most efficient mode of transport for goods. International liner shipping is a sophisticated network of regularly scheduled services that transports goods from anywhere in the world to anywhere in the world at low cost and with greater energy efficiency than any other form of international transportation. Liner shipping connects countries, markets, businesses and people, allowing them to buy and sell goods on a scale not previously possible. Today, the liner shipping industry transports goods representing approximately one-third of the total value of global trade. Ocean shipping contributes significantly to international stability and security. Considering the large and constant struggle in the market in terms of competitive pricing of products, a very important and indispensable role represents the container transport with a clear task to define the final price of the product. This paper analyzes the costs of container transport flow between Far East and Serbia, using different liner shipping services, observing the six world’s largest container operators (Maersk Line, Mediterranean Shipping Company, CMA CGM, Evergreen Line, China Ocean Shipping Company and Hapag-Lloyd) and inland (truck-rail-river) transport corridors. These corridors include distance between selected Mediterranean ports (Koper, Rijeka, Bar, Thessaloniki, Constanta) and Serbia. As a result, in this paper is considered a mathematical model that provides a comparative analysis of transportation costs on the different routes. It is observed already existing transport routes and it is also given hypothetical review to the development of new transport routes. The main goal of this research is to provide an optimal route with lowest transportation cost during container transport. Selection of the best route in the intermodal network is a very difficult and complex task. The costs in all modes of transport and the quality of their services are not constant parameters and changes depending on a number of conditions and characteristics. The analysis of this model within combined maritime and land-based networks would prove helpful for the study of logistics chains, the hinterland-foreland continuum, intermodal transport systems, and market competitiveness.
Keywords: costs, container transport, liner shipping, mathematical model
Published: 17.11.2017; Views: 1023; Downloads: 283
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Probabilistic behaviour of joints on joint forces in mechanisms
Boštjan Harl, Nenad Gubeljak, Marko Kegl, 2015, original scientific article

Abstract: This paper discusses the influence of the clearance in joints on the joint reaction forces in mechanisms. By using mathematical programming, the optimal parameters of kinematic chains can be efficiently obtained by using the deterministic approach. However, the situation becomes more sophisticated if random effects of tolerances of the arm lengths and the random pin positions have to be considered. In this work the influence of clearances on joint forces is calculated by using the Taylor approximation and the Monte Carlo method. The implementation of the model is illustrated with two examples. The first example considers a closed loop chain, representing a four-bar mechanism being an actual part of a hydraulic support, employed in mining industry. The second example considers joint reaction forces of car wiper mechanism.
Keywords: joint forces, kinematic chain, mathematical programming, stochastic model
Published: 12.07.2017; Views: 420; Downloads: 336
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Casting process optimization by the regression analysis applied on the wear resistant parts molding
Radomir Slavković, Slavko Arsovski, Aleksandar Veg, Zvonimir Jugović, Aleksandar Jovićić, Nedeljko Dučić, 2012, original scientific article

Abstract: Conducting a comprehensive research of the casting process of wear resistant parts (white hard casting), a significant correlation is established between the technological parameters (temperature, aging time in the mold and coolant flow) and the final product hardness. The fundamental theory of Box-Wilson's gradient method marked the baseline for the foreseen researches. The method defines the coherence of the process parameters, since their dispersion in the examined process is relatively small. Main target of the experiment was a definition of the optimal casting conditions. Therefore the different technological routes are identified and the casting process is modified until the best outcome is achieved. Target function was initially in a hypothesized form, while later on evolved into a consistent form due to the application of experiment-statistics, process optimization and process management based on empirical feedback.
Keywords: casting, mathematical model, quality management, wear resistance
Published: 11.07.2017; Views: 525; Downloads: 71
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A sensitivity model and repeatability of recipe colour
Boris Sluban, Olivera Šauperl, 2001, original scientific article

Abstract: The paper briefly describes a mathematical model of the colorant mixture colour sensitivity to concentration errors and the numerical estimates of the related quantities. Features of the theoretical model are illustrated with the results of a number of numerical experiments in which the optical data of a few basic dyes applied to textile fabric were used to predict the sensitivities of recipes for sets of target colours spaced regularly in the colour solid. The rest of the article deals with the question whether the predicted values of recipe colour sensitivity provide useful information about the repeatability of recipe colour. The results of a few groups of laboratory experiments involving the textile fabric dyeing with basic dyes have been analysed with this question in mind.
Keywords: textile dyeing, basic dyes, recipe colour, colour, color repeatability, colour sensitivity, concentration errors, mathematical model
Published: 05.07.2017; Views: 495; Downloads: 85
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Intellectual capital - developmental resource of logistic companies for the 21st century
Ratko Zelenika, Drago Pupovac, 2003, review article

Abstract: On the basis of relevant scientific research this paper systematically and concisely elaborates the interaction between intellectual capital and logistic services production. Full attention is given to intellectual capital as a factor in effective creation of the logistic processes or in other words, to prove the statement that the first place for achieving competitive advantages in the global and/or regional market of logistic services belongs to knowledge used to produce or improve the existent logistic systems and to create new ones.Further, the paper deals with the tasks of creative logistic managers as open, dynamic and stochastic systems based on knowledge or the creation of universal logistic model determined by the fact that intellectual capital and technological paradigm create the way to new logistic paradigm.Special attention is paid to building and presenting a mathematical model for measuring the intellectual capital as well as the success of its use in different logistic companies.
Keywords: traffic, transport, logistics, developement, intellectual resources, logistic model, mathematical model
Published: 02.06.2017; Views: 429; Downloads: 89
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Adaptive control for power system stability improvement
Jožef Ritonja, 2010, independent scientific component part or a chapter in a monograph

Keywords: synchronous generator, control functions, mathematical model, voltage control
Published: 31.05.2012; Views: 3015; Downloads: 87
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The combined analysis of phonon and electron heat transfer mechanism on thermal conductivity for nanofluids
Jurij Avsec, 2008, original scientific article

Abstract: The paper features the mathematical model representing the analytical calculation of phonon and electron heat transfer analysis of thermal conductivity for nanofluids. The mathematical model was developed on the basis of statistical nanomechanics. We have made the detailed analysis of the influence of temperature dependence on thermal conductivity for nanofluids. On this basis are taken into account the influences such as formation of nanolayer around nanoparticles, the Brown motion of solid nanoparticles and influence of diffusive-ballistic heat transport. The analytical results obtained by statistical mechanics are compared with the experimental data and they show relatively good agreement.
Keywords: statistical nanomechanics, phonons, electron heat transfer, nanofluids, thermal conductivity, thermodynamic properties, mathematical model, statistical nanomechanics
Published: 31.05.2012; Views: 1700; Downloads: 87
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Analysis of growth models for batch kefir grain biomass production in RC1 reaction system
Marko Tramšek, Andreja Goršek, 2008, original scientific article

Abstract: This work describes the statistical analysis of three mathematical models, modified for describing the kefir grain biomass growth curve. Experimental data of time-dependent kefir grain mass increase were used. The propagation was performed in RC1 batch reaction system under optimal bioprocess parameters (temperature, rotational frequency of stirrer, glucose mass concentration) using traditional cultivation in fresh, high-temperature, pasteurized whole fat cow's milk. We compared values of biological parameters obtained by applying the nonlinear regression of experimental data in logistic, Gompertz and Richards models. The most statistically appropriate model was determined using the seven statistical indicators. We established that the kefir grain biomass growth curve during batch propagation under optimal bioprocess conditions can be most successfully described using the Gompertz growth model.
Keywords: chemical processing, milk products, kefir grain growth, process parameters, design of experiments, modeling, mathematical models, Gompertz growth model, RC1
Published: 31.05.2012; Views: 2148; Downloads: 113
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Diesel and biodiesel fuel spray simulations
Primož Pogorevc, Breda Kegl, Leopold Škerget, 2008, original scientific article

Abstract: This paper deals with the investigation of the influential parameters of a mathematical spray breakup model using different fuels. Beside injection system measurements, fuel physical properties and injection process characteristics were measured, because they are necessary for the spray simulation input. For validation purposes, spray was injected into motionless air at atmospheric pressure and room temperature and filmed with a high-speed camera. Spray macrocharacteristics have been determined on the recorded images. Using the simulation program, the injection processes for diesel, biodiesel, and their 50% blend B50 have been simulated. Spray mathematical model parameters were tuned based on the experimentally gained results. Primary breakup model parameters showed the biggest impact on the spray characteristics and were therefore expressed using the fuel physical properties, the injection process characteristics, and the working regime parameters. Spray simulations into the combustion chamber were made in the end. All of these results are presented and discussed in this paper.
Keywords: fuel spray, spray breakup, biodiesel fuel, fuels, numerical simulations, mathematical model
Published: 31.05.2012; Views: 1220; Downloads: 68
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