30th International Conference on Organization and Technology of Maintenance (OTO 2021)

History of operation and development of scientific conference “Organization and Technology of Maintenance” (OTO) during the three decades from regional scientific-professional conference to international scientific symposium is presented. The paper provides an overview of the number and structure of published papers, number of authors and their professional affiliation, sponsors and venues, and analyzes the structure of published papers. The conclusion points to the contributions of OTO papers to the practice of organization and maintenance technology in the region of Slavonia i.e. Central and Eastern Europe, and gives recommendations for better cooperation of scientific institutions with companies and public affairs institutions in the OTO area.

In the design process, new and creative design solutions have a goal to increase competitiveness compared to similar design solutions from other manufacturers. Material saving, easier montage and transport, by the mass reduction of the construction in design process, are a significant factors, which affect on the lower price and easier product maintenance, especially for steel made lattice prefabricated constructions. With the development of the numerical methods and computer tools, the optimization process, in the modern design process, has an increasingly important role. By clearly defining the objective function, design optimization process, makes design solutions significantly more competitive. This paper presents design process of a floating bed frame. After the design of the initial solution, this solution was optimized, in order to reduce the mass, respectively material saving. Optimization process was performed by Direct Optimization Method (DOM). Total mass of the structure, compared to the initial design solution, was reduced by 70%. According to the results obtained by the optimization process, a design solution of the floating bed frame was made.

The paper analyses the induction squirrel cage motor type 5AZ 100LA-4 product of company Konačar. As a matter of fact two version of the same motor from Končar are analysed. The old one, known under commercial label 2AZ 155-4 and the new one, labelled as H5AZ100LA-4 (IE3 efficiency class). The computer model for calculating the parameters and operating characteristics is set in software program, based on the exact cross section of laminations of iron core from the producer. The motor is calculated on the base of these data, resulting in parameters and operating characteristics, obtained as output data from the computer model. First modification is realized by changing the number of conductors per stator slot and the length of the air gap. The improvement of efficiency from 78.4% to 78.8% is observed in the first optimized model with significant improvement of power factor from 0.8 to 0.85. Second step in motor optimization was to increase the slot fill factor. Therefore the stator slot was optimized i.e. changed which resulted in bigger slot fill factor and lower core saturation. Besides the stator slot modification, the stator outer diameter was increased as well as the motor length. The final optimized model has efficiency 86.5% and power factor of 0.87 at full load.H5AZ100LA-4 has efficiency of 86.8% and power factor of 0.76 at full load.

Market demand for electrical products by standard electrical products defines the demand for stamping tools. The design of the tool is based on the requirements of easy assembly, disassembly and maintenance. The development of such tools requires the designer to meet complex requirements, some of which are only defined at the beginning, so that the most precise specifications possible are necessary right at the start of the design process. In order to meet the required complex product geometry, product tolerance and the number of products required by the customer, the development of a multi-row punching tool is shown. The tool consists of an upper and a lower part, which are appropriately positioned accordingly and fixed to the stamping machine. The force required to stamp and the force required to detach the guide plate from the sheet metal were determined. The functionality of the developed tool and the stamping process is shown in its entirety, from the entry of the sheet into the tool to the exit of the finished product. The products obtained by stepwise stamping are rotors and stators, which are the basic elements of any electrical device.

Energy efficiency has become imperative in design of vehicles. Energy efficiency can be viewed from multiple aspects like economy to environmental (from cost of transportation to carbon emissions). There are many factors that have influence on energy consumption in any type of transportation (by land, water or air) and one of them is vehicle mass. In this paper the current methods for reducing vehicle mass will be shown.

In the automotive industry there is a requirement for quick and clean brake oil maintenance. Since braking oils (DOT 4, DOT 5.1) are hygroscopic, it is recommended that braking oil should be changed every two years. Modern cars are made with intention of making service in specialized workshops which is related to OBD compliant information exchange (date of oil change, factory reset of service interval, special activation of brake servo-motors for oil bleeding etc.). Older cars and especially motorcycles are often serviced in DIY variants and there is a requirement for various kinds of vacuum pumps. Most often used vacuum pumps in automotive service are hand-driven pumps. In this paper, the small electric membrane-operated vacuum pump is utilized for the brake line oil bleeding of cars and motorcycles. The technical data (voltage, running current, operating vacuum) is shown, as well as the technical drawings and bill of materials for the build.

Dragline excavator EŠ 5/45 is used in the exploitation of coal in open-pit mines RB Kolubara. It is a complex technical system consisting of a larger number of subsystems, assemblies, and elements. Therefore, the maintenance of this machine implies a set of complex procedures, methods, and various repair activities that need to be undertaken to keep the excavator in good (working) condition and to work with the allowed level of reliability and the optimal level of productivity and economy during its life cycle. The paper presents an algorithm and description of activities undertaken during the repair of the machine part - the jaws of the jaw clutch coupling of the electric motor on the excavator EŠ 5/45, including the techno-economic analysis of the justification of this reparation procedure.

Previous passive electricity consumers by the integration of the renewable energy sources in their possession are becoming consumers with their own generation, or so-called prosumers. Current market conditions stimulate the prosumer to use the produced electricity from his own power plant mainly for his own needs because the surplus electricity that he delivers to the power network is paid at a much lower price than the one at which the customer pays for the consumed electricity. Owning an electric vehicle gives the prosumer an additional opportunity to optimally use the produced electricity from their own sources. This paper presents two models for maintaining the battery charge level of an electric vehicle in combination with expected electricity generation from photovoltaic system. The first model enables optimal maintenance of the battery storage level of the electric vehicle by applying only charging process, while the second model enables the charge and discharge of the electric vehicle battery while being connected to household power network. The models have the possibility of single-level and two-level charging power. The model with two levels of charging power gives better results in terms of optimal maintenance of the charge level of the battery storage. The charging and discharging model shows the advantages of maintaining the charge level in terms of savings. The simulations are conducted for one summer and one winter day.

Technical systems are inconceivable without documentation describing their implementation, use and maintenance. Documentation is usually based on three languages - the manufacturer’s domicile language, English and mathematics. Mathematics is not only the first foreign language that we learn, but it is also the only foreign language that everyone learns. By mastering mathematics, we often focus on the result and over the years we may forget about proper notation. This can be overcome by means of the ISO 80000 standard. A standard is a document issued by one or more organizations whose goal is to bring order into a certain field. Standards are transferred to lower instances through a hierarchical structure. The ISO 80000 standard consists of fourteen documents under the general title Quantities and units. This paper provides an analysis of the requirements of Part 2 of the standard called “Mathematical signs and symbols to be used in the natural sciences and technology”, and exemplifies its application in scientific journals and Master’s theses at engineering faculties. The presence of the standard was assessed by analyzing the elements described by the standard in papers published in 2018 in the following five scientific journals: Tehnički vjesnik/Technical Gazette, Engineering Review, Acta Polytechnica Hungarica, the American Journal of Electrical Power and Energy Systems and the International Journal of Renewable Energy Research. In addition to these journals, the presence of the standard was also analyzed in Master’s theses at two engineering faculties, i.e. the Faculty of Electrical Engineering, Computer Science and Information Technology in Osijek and the Mechanical Engineering Faculty in Slavonski Brod, and the results are presented in a clear and concise graphical format. The conclusions of the performed analyses indicate that the standard is generally only partly implemented, with the exception of Tehnički vjesnik/Technical Gazette, where the standard is fully implemented, and the importance of adhering to normative documents is stressed in its Instructions for Authors.

In real-life power system, optimization methods are used on a daily basis to obtain optimal dispatch for various types of power plants. In this paper, the existing optimization method is used to maximize profit of three cascaded Hydro Power Plants (HPP) and to co-ordinate HPPs dispatch according to Wind Power Plants (WPP) production forecast. A two-stage optimization method was used with first stage design to obtain optimal HPPs dispatch plan and to maximize profit by selling electricity on a day-ahead market. First optimization stage is defined as mixed-integer liner programming (MILP) problem. Obtained dispatch plan together with the WPPs production forecast is used to check power flows in the transmission network and if line congestion occurs, second optimization stage is needed, and it is defined as quadratic programming (QP) problem. The objective of second optimization stage is to find re-dispatch plan that would be minimal deviation from an initial dispatch but it would eliminate line congestions. Proposed optimization strategy is tested using IEEE 14 Bus Test System and the results are presented in this paper.

Electric motors today are represented in all branches of industry and their supervision is a very complex task to research. Improper maintenance and proper checking of electric motors can cause great damage to the drive. In order to determine the condition of electric motors, it is necessary to perform diagnostics of basic parameters in order to determine the reliability and thus the service life of the motor. This is why fault diagnosis is important for the maintenance of electrical machines. The assessment of the condition of the correctness and reliability of the electrical machine is carried out by the method of measuring the basic parameters. The measured data is compared with the nominal data of the correct motor provided by the manufacturer. Diagnostic measurements are performed on the measurement of winding operating resistance, winding impedance, temperature, current, voltage, power, torque, speed of noise and vibration. The measurement is performed for all three operating conditions: no load, nominal and maximum load. Spectral analysis of these quantities gives a picture of the electromechanical state of the motor. For example, the mechanical state of a motor can be determined from the frequency spectrum of noise and vibration, and the condition of each mechanical part can be estimated on the basis of individual harmonics. The analysis of the measured data provides an assessment of reliability and suggests the method and time of servicing. By applying the appropriate sensors and placing them in the right places, the required sizes can be measured quickly and efficiently, and thus the condition of the motor can be assessed. Non-contact measurement of parameters such as temperature, noise, vibration, current, voltage, speed creates a basis for the development of an automated measuring system, which significantly speeds up and facilitates the assessment of reliability and correctness, especially when it comes to a large number of motors. Proper and periodic measurement as well as proper maintenance can extend motor life and result in increased productivity and financial savings. This paper presents the procedures for measuring the required quantities and making an assessment of reliability and correctness on the same type of motor with a different number of operating hours.

Even though electrical and thermal conditions of any electrical machine are interconnected, in the most cases these conditions are separately analyzed. On the other hand, electrical machines are designed to achieve desired operating point with minimal material cost. Due to increase of load or reduced cooling possibilities, in industrial surrounding electrical machines thus can easily be overheated, shortening the machine life cycle and increasing maintenance costs. With the development of sophisticated control principles, induction motors became the most widely used machines in industry. For all these reasons, in this paper the simple electro-thermal model of induction motor for prediction of motor temperature in different operating conditions is presented. Further on, dynamical behavior of presented model is analyzed through simulations and experimental measurements.

The power transformer is the main and the most expensive component of the power substation, so successful fault diagnostic and protection is an essential part of its maintenance. Protection engineers doing the scheduled maintenance and protection testing need to be familiarized with transient phenomena that can occur in normal operation. Substations with two parallel transformers sharing a common grounding resistor are very frequent in high-voltage networks since a common grounding resistor limits the single-phase to ground-fault current. However, the unfavorable aspect of this type of transformer grounding system is the increased probability of unwanted trips of the transformer protection during the transient operational states, which has the consequence of a supplied low-voltage network outage. Under transformer energization, an appearance of the inrush current can trigger the transformer differential protection as well as circulating current between transformers in parallel operation caused by sympathetic inrush. A single-phase to ground fault in a high-voltage network can cause circulating currents between neutrals of transformers and trip the differential protection too. The paper presents a simulation model of two transformers grounded with a common grounding resistor adequate for transformer transient operational states analysis. Performed simulations of the inrush and sympathetic currents emphasized the diagnosing of the second harmonic distortion dominance in the current spectrum as an efficient tool in the prevention of unwanted trips of differential protection. The analysis of the simulated circulating currents between transformer neutrals in the paper has examined and discussed the proposed solutions for avoidance of unnecessary transformer outage caused by the single-phase to ground fault in a high-voltage network.

In this paper the simulation of the battery storage system connected to the grid with the possibility of active and reactive power control is presented. Considered battery storage system has the ability to inject the active power when there is a lack of active power and the reactive power when there is a lack of reactive power in the grid. Amount of the active and the reactive power injected to the grid are defined according to the active and reactive power demand. Battery storage system is connected to the grid over the two-way DC-AC converter with the IGBT switches. Model of the battery storage system is based on Typhoon HIL grid connected battery storage, but some improvements have been made on the model. Model is consisted of two parts. The first part is the battery storage model in the schematic editor and the second part is the monitoring and the control interface in SCADA. Model in the schematic editor is consisted of electric and signal parts and all used components are described in the paper. Simulation of the battery storage system with the possibility of active and reactive power control in Typhoon HIL is done and the impact on the grid voltage and the frequency is visible according to the simulation results.

Today’s technology allows remote control of industrial processes, which can include distributed energy sources such as solar or wind power. As these remote control systems age, security updates for them will eventually cease. This means that any vulnerabilities found after end of service life cannot be patched, often requiring physical replacement of the equipment. The second problem is the fact that these systems are usually integrated with other devices and cannot be easily replaced. Looking at the lifespan of industrial systems, it is clear that IT devices used for remote control usually have a shorter lifespan than the rest of the system. Inspiration to investigate how poor maintenance of IT devices could be abused in the future was taken from the cyber-attacks on the Ukrainian power grid, where attackers took control of power switches relays equipment and gave the command to open circuit breakers, disconnecting loads from the power grid, resulting in regional blackouts. Using a similar approach, it was hypothesised that distributed power sources may become vulnerable to cyber-attacks as they age. Since the installed power of distributed power sources per unit is relatively small, it is plausible for the attacker to identify multiple closely located distributed systems and conduct a parallel cyber-attack by disconnecting them from the power grid simultaneously during peak demand periods, with the goal of disrupting the power grid. In this work, distributed power sources that are connected to the Croatian distribution network are identified, mapped and the spatial correlation of the sources was analysed using GIS software. The goal is to develop methodology which enables easy identification of power sources that are spatially close to each other and have similar age, which makes them a likely target for potential attacks. This information can be used to prevent such attacks in the future, as it would help identify critical groups of such sources and focus maintenance efforts.

Today's industrial production, with the constant growth of the world's population, has a great impact on the environment loading and human health in the world. With the development of the industry, the need for large amounts of energy and materials have increased sharply, which has led to an increase in greenhouse gas emissions, which are the main cause of global warming on Earth. To reduce the impact of harmful gas emissions and global warming in the product life cycle, a new approach called LCA (Life-cycle assessment) has emerged. In the experimental part of the paper, the analysis of the impact of the product life cycle on the environment and human health was performed on the example of two household appliances using the software tool SimaPro. The conducted LCA analysis of two household appliances showed a significant impact of proper material selection at an early stage of construction on reducing the impact of production and products on the environment and human health.

The paper presents the surface drainage of a part of Jelas polje, a field that is situated in the Croatian part of the Sava River valley. It is a complex hydrotechnical system with two safeguarding segments: the subsystem of reception and evacuation of runoff from hills, and the subsystem of flood risk management of the Sava River. The agricultural production in this part of the Jelas polje is mainly oriented towards field crops, which are most endangered by excess water during spring. According to farmers, in this century they are faced with problems they have not experienced before, situations where soil hold the water for an extended period of time and there is no adequate drainage. Direct consequence of such a situation is the decline of agricultural yields. All these problems farmers attribute to “bad and insufficient” maintenance of the channel network, which is under the jurisdiction of Hrvatske vode, legal entity for water management. The deeper hydrological and hydraulic analysis indicates extreme weather events and climate change, as well as the need for better adaptation to such a change. This paper analyzes the rainfall in the first vegetation months, April and May, during the long period from 1963 to 2020. In addition, these rainfalls are analyzed in correlation with the extreme water levels of the Sava River, when sluice gates are closed and drainage was provided by pumping stations. The performed analysis shows that in the last twenty years the amount of spring precipitations has significantly increased, as well as the danger of high Sava River water levels. Unlike in previous forty years, in this period there have been several coincidences of the threat from external and internal waters, which have adversely affected agricultural production for a long time. It all points out to a need for all stakeholders to join in, and with coordinated efforts find a better way to adapt maintenance of agricultural drainage system to the new climate conditions.

Software simulations allow the interior composition of buildings to be graphically analysed. Thus, it is possible to make an approximation related to very diverse parameters such as the comfort or earthquake resistance of the buildings. From the perspective of traditional architecture, this work aims to rigorously examine the characteristics of the construction systems used in Órgiva, a town of Las Alpujarras, in Granada, one of Spain's most seismically hazardous regions. Hence, using graphical interpretation, objective values are obtained to better understand the intrinsic performance of the materials. For this purpose, the simulation of a masonry wall is created by interpreting data related to heat and vapour flow, temperature, humidity and partial pressure. By means of internal analysis, and including the climatic conditions of the territory, we can observe how the construction systems affect the comfort of the users, causing condensation dampness in joints between walls and pathologies in the systems. In addition, the results are valuable for the maintenance of the building as they foresee future problems and guide the technician in the resolution of architectural encounters, benefiting the strong points and optimising the performance of the construction, even in terms of earthquake resistance.

The post-occupancy evaluation (POE) is an overview of the architectural and technical performance of the building during its use. The purpose of POE is to improve future construction, based on previous experiences in the use of the building by immediate users. We primarily explored the architectural aspect of buildings (site, function, interior design) and the methods in which it should be valorized by users, primarily by a questionnaire. The article gives an overview of the benefits that investors and architects can have from POE and highlights obstacles to more POE procedure. We are focused on the long-term benefits that POE can provide if adopted as a standard method of valuing higher education buildings by users. POE focus in higher educational buildings is whether the physically constructed structure of the building with its architectural elements results in quality use by end-users. We found that the implementation of POEs procedures is the most necessary in educational buildings.

Reinforcements used in RC structures lose their load-bearing capacity by suffering from various deteriorations due to external effects. Insufficient cover thickness is one of these reasons. The topic of this study consists of the concept of inadequate concrete cover. Concrete cover values with different thicknesses were chosen, and it was aimed to show how these values affect the performance of a building. Base shear forces, stiffness values and target displacement were obtained for each different concrete cover. A reduction in concrete cover resulted in an increase in the base shear force and stiffness values. Insufficient concrete cover layer will reduce the strength of the reinforcement over time. This will negatively affect the earthquake performance of the building. It should be kept in mind that the main function of a concrete cover is to prevent external effects which adversely affect the strength of the reinforcement. In this study, information was also provided about corrosion caused by the lack of concrete cover, and solutions to the corrosion were presented.

Proper modeling of the durability of cementitious composite elements is necessary to schedule maintenance and servicing of civil engineering structures. Knowing when the elements need their repair is a high-demand necessity in order to avoid sometimes very serious damage. It has been very often done using nondestructive testing (NDT) or other methods suitable for evaluation of the technical state of the buildings. However, the fact that there is an increasing number of research topics considering prediction of durability of cementitious composites structures using soft computing techniques indicates that this approach might also be effective solution for this purpose.In this research, the authors would like to present a review of the latest research on the modelling of the durability of the cementitious composites with different admixtures using different machine learning algorithms. In this review, the most commonly used soft computing techniques for this purpose will be described and compared. Also, the main potential threats to loss of the durability of these elements such as wear of the material due to temperature (e.g. frost), mechanical (e.g. abrasion) and chemical (e.g. chloride concentration) will be recognised. Thanks to this review, an alternative approach to the evaluation of the technical state of buildings and its durability will be emphasized.

Regulations define the basic requirements for buildings, which ensure the safety and comfort of users. Fulfillment of these requirements depends on the buildings’ condition, i.e. its elements, which are affected by the use and various planned and unplanned effects. In addition to physical wear and tear, the service life often is shortened due to the lag of the building behind technological and economic progress. Therefore, proper and timely maintenance is required, and sometimes capital renewal and reconstruction. The article provides an overview of maintenance measures for the main building elements, from control to repairs and eventually to replacement. Availability of financial resources dictates how and when these measures will be conducted. In this respect, the costs of measures for maintenance and improvement of building properties in line with the new requirements are analyzed. Lifelong maintenance costs should be taken into account from the conception and design stage, because then the basic characteristics of the building are determined and, as a rule, increasing capital investment in construction can reduce the maintenance costs that will be required for numerous years. In some cases, major renovations on buildings that are already in use are also cost-effective. By time-linking the reconstruction and renovation with regular building maintenance multiplication of some works and the costs required would be avoided, leading to higher profitability of such projects.

The December 29, 2020, Petrinja earthquake highlighted the significance of maintenance of buildings in seismically active regions. Many family houses in rural parts of central Croatia were damaged by the Petrinja earthquake. During the earthquake, the insufficient response of the buildings in the rural regions resulted in the majority of human injuries and fatalities. These deaths and catastrophic property losses in rural areas have underlined the importance of earthquake prevention and mitigation in these communities. A study of the seismic performance of structures in rural areas, as well as an evaluation of seismic risk and susceptibility, were conducted with the aim to improve the overall capability to prevent seismic disasters in rural areas. The structural characteristics, construction method, and application of seismic codes and building rules of two rural villages in the Osijek-Baranja County were researched, and they can be considered representative of the continental area of Croatia and surrounding countries. GIS technology is used to process and present information on the location, distribution, and other characteristics of structures.

The state-of-the-art techniques of machine learning for assessing material consumption in the construction of prestressed concrete (PC) road bridges are described and analyzed in this paper. For model training and evaluation, a database of material consumptions and design features for 75 PC bridges is compiled. The achieved accuracy of the model for estimating prestressed steel consumption per $${\text{m}}^{2}$$ m 2 was 6.55%, calculated as the mean absolute percentage error. Based on the proposed model, a MATLAB-based software with a graphical user interface was developed to allow for the input of basic variables and the calculation of estimated prestressing steel quantities. The use of such software to determine the ideal amount of steel will, in most cases, result in the construction of higher-quality structures that require less maintenance.

It is not correct to produce the necessary information for structuring, especially in environments such as Çanakkale, which exhibit a basin structure, without determining the bedrock or the strict ground conditions in bedrock. This approach is the basis of earthquake resistant building design. In this study, which was carried out to determine the bedrock/seismic foundation depth for the central settlement of Çanakkale and to define the basin structure to a certain extent, microgravity measurements were taken on a large scale, and the study area was modelled in three dimensions based on the obtained gravity data. By taking long-term microtremor measurements, one-dimensional depth-shear wave (Vs) velocity models were obtained using the Rayleigh ellipticity method. A depth map of the engineering bedrock was created, in which the velocity Vs reached to 2500 m/s.

Today design industry relies heavily on stylish and feature-rich designs applied to everyday applications. That is especially emphasized in the furniture industry where new trends are rising thus making it, so-called, smart furniture. This paper deals with paradigms and conceptual ideas in the enrichment of furniture with added value but with a stressed focus on furniture longevity and maintainability. The following case study will provide an insight into current smart furniture solutions and key characteristics that ensure the longevity of smart furniture.

There is a high and constant thrive to utilize a variety of wireless communication systems to achieve some sort of remote monitoring and/or controlling processes and systems overall. The wood processing industry is no exception but there is still an ultimately low presence of such systems, either in automated or semi-automated form, but their rise and presence has become inevitable and is constantly growing. Such an exemplary system is set up and adjusted in the Spačva wood processing industry where wireless devices are used for constant monitoring of environmental parameters and wood structural moisture in a wooden plank during the phase of naturally aspired drying process and forced one in a controlled environment.However, because of fact that such devices must be tightly incorporated into a pack of planks a new problem arises regarding wireless signal propagation that becomes significantly affected. This paper deals with the problem in a way that we describe and propose a technique to strengthen measurement device and receiving unit wireless signal propagation to maintain quality communication link. Also, we define some practical guidelines for keeping good signal and their maintenance propositions.

This paper addresses the problem of creating a large image set with artificially inserted biscuit tile surface defects. Those defects commonly occur in real-life ceramic tile production. However, the occurrence rate of a defected tile is neglectable to the rate of a non-defected tile. To overcome the gap in the size of the two sets of images, with defects and without defects, artificial image generation increases the number of images with defects. This paper enables the future use of machine learning algorithms, which require a relatively equal size of the two image sets. The analysis of surface defects pointed to a similarity of the surface defect to an inverted Gaussian curve. The Gaussian distribution model is proposed for modeling a biscuit tile surface defect. Captured images with surface defects are compared with corresponding artificially created images. Image set without defects is used to create the image set with defects.

Due to the growing number of micro-enterprises and their contribution to the national economy, there is a need to research the human and IT impact on their performance and maintenance. The aim and purpose of this paper are to emphasise the importance of the successful business of micro-enterprises by presenting the results of empirical research on the presence of continuous education of employees and their use of modern information technology in maintaining and measuring the success of microenterprises. There is a comparison of two surveys, one from 2020 on 121 micro-enterprises and the other from 2016 on a sample of 112 micro-enterprises. The companies included in both surveys are from Slavonia and Baranja and three activities: production, construction and agriculture, fishing and forestry. By applying appropriate statistical and mathematical methods, it was determined that in 2020, compared to 2016, there was an increase in investment in training and education of employees and an increase in monitoring financial performance indicators.

Viscous characteristics of a Newtonian fluid is described by the dynamic (absolute) and the kinematic viscosity coefficients. The dynamic viscosity coefficient expresses the required applied force per unit area of the one laminar plane of the fluid in order to move it with respect to the adjacent, at an unit velocity. The Kinematic viscosity coefficient is the ratio of dynamic viscosity coefficient and the density of the fluid. This paper presents two simple software procedures for determination of the kinematic viscosity coefficient of real fluids. In addition, the laboratory experimental measurements of some oils’ viscosities were done to confirm the proposed procedures, and are presented in the paper as well. The authors intended for the procedures to be used for educational purposes at the college level entry.

This paper provides a conceptual overview of the existing solutions for monitoring the conditions for wine production and product quality maintenance in the winery environment. The biggest challenge for developing such monitoring system is to measure the essential parameters of wine during and after production. Monitoring systems are designed to allow winemakers monitoring and control the wine transformational processes, in real-time. Also, it enables and helps to make right constructive decision during the period when parameters changing have effect on a production. This article provides a comprehensive summary of the evolution of winery monitoring systems that helps to maintain wine quality during its production. In particular, the paper reviews different IoT-based monitoring systems along with required communication technologies. This paper investigates and contrasts the numerous monitoring systems for the same purpose thus giving comprehensive overview to such system conceptual composition and giving emphasis to the maintenance-product quality relations.

To ensure the demanded quality for malting barley, each season a number of quality indicators have to be determined and evaluated. Depending on the variety, location and growing conditions (precipitation, temperature, soil type, and agro-technical measures), the achieved quality indicators have to fulfil a certain theoretical value to set the variety into an end-purpose group. End purpose can be designated as feed or malting. However, based on their intended end-use and in respect to their characteristics, barley varieties in Croatia can also be classified as dual, namely malting-feed varieties. Most important parameters that have to be analyzed every year include total protein content, soluble proteins, moisture, malt extract, extract difference, friability, viscosity, Kolbach index, wort color, wort pH. For malting barley varieties, these values have to be within the set and recommended values, taken from different literature sources. The aim of this work was to present a five-year long, continuous examination of all mentioned quality control indicators. All indicators are prone to variations due to the variety, location and growing conditions, so a five-year continuous study can provide mean values for the tested indicators important for growers, maltsters and brewers. Expressed variations can be noted in protein content. Namely, 2018 resulted with the lowest protein content in comparison to other years, for almost all varieties.

Today’s brewing industries rely on continuous and reliable analytical methods in order to control the quality of produced beer, but also to respect the legislation related to beer quality. To achieve the wanted quality control it is important to bear in mind several things, such as size and age of the brewing industry, process automation and skills of the workers, availability of laboratory and technical evaluation of the laboratory equipment (calibration and general maintenance). Brewing process quality control involves a lot of indicators, but some of the most important are gravity of wort and beer, wort and beer pH, air injection into wort, yeast cell counts, yeast culture and propagation control, yeast viability, dissolved oxygen, carbon dioxide, sulfur dioxide, aerobic and anaerobic bacteria counts, microbiological culturing media, turbidity, color, alcohol, foam quality, sensory evaluation. Considering that beer can be packaged into cans, glass bottles, kegs or PET, many factors should be taken into an account. For example, PET packaging has the shortest storage time, 4 months in comparison to other kinds of packaging, such as kegs, cans or glass bottles. Sensory quality control evaluates the consumers’ perception and often beer bought in store is not as the one tested in the brewery. However, the input of efforts and resources involved in beer quality control is continuous and important for the overall quality of beer.

The objective of this research was maintenance of the quality parameters of homemade kulen during a three-year period. Homemade kulen is a dry fermented sausage with specific sensorial characteristic (smell and taste) which originates from the use of the high quality pig meat, specific spices, smoking (use of open fire) and long ripening time (at least four months). The production of this indigenous dry sausage take place on small farms and it is conditioned by the climatic conditions. Namely, to produce a good quality kulen it is necessary to start the production during winter months, when the slaughter and production take place. After the smoking, fermentation and drying, the ripening takes place. The physical-chemical parameters (pH, aw, moisture content, fat content, protein content and collagen content) of 25 samples of homemade kulen were determined each year. The current Croatian legislative prescribes only the moisture content (40%) and protein content (22%) for this kind of dry sausage. The results of this study showed variation in investigated parameters between the samples and between the production year. Variations can be contributed to different recipes used by producers, different climatic conditions and to different production technologies (smoking with different wood, ripening time, pig meat quality, etc.).

In this paper mobile version of the system for mentoring graduation theses (MAK) is presented. The goal of application is to enable the Students, Mentors and Reviewers to do their tasks inside of the MAK system. After successful authentication application sends token to user. Token and user name are used for further requests to decide if the user is a Student or Mentor. With that in mind, the user gets the appropriate interface. Inside every activity the user can do various activities in the MAK system, where users input is the input to the system. After an action, the user gets a Toast message which is used as an output from the system. The messages show the state of the procedure or an error which is related to the state of the Student’s paper, and disables the navigation to the next activity. The application lifecycle management is proposed and explained in further chapters.

One of the most important parts of product lifetime management is maintaining the knowledge that was implemented during product design. However, the problem occurs when the design knowledge has been lost or it is left written in the old form. In this work, the design knowledge is presented by the traditional drawing of an object using descriptive geometry. The aim is to present an approach to refresh the drawing with traditional CAD software and preserve the design knowledge. The line segment and the pentagon pyramid were drawn on paper using the traditional drawing technique with a pencil considering descriptive geometry rules. As a part of the traditional drawing method, they were never processed by conventional CAD software. They are imported as an image file, scaled, and processed with the aim to extract the written knowledge for further maintenance in a new CAD form. With such an approach, the design knowledge is refreshed and ready to be used again. This approach can help save time in much more complex applications such as in a redesign or reverse engineering process of products and their life-cycle management overall.