• Numerical simulation of heat transfer and hydrodynamics under transverse flow of compact bundles of tubes in shell-and-tube heat exchangers

    pg(s) 27-29

    By using the application package ANSYS Fluent, the numerical simulation of heat and mass transfer processes in the channels of shell-and-tube heat exchanger with compact placement of tube bundles has been carried out. The fields of velocities, temperatures and pressures in the heat exchanger channel were obtained and the conditions of hydrodynamic flow in the channels and the processes of heat transfer in these channels were analyzed. A new construction of shell-and-tube heat exchanger with compact arrangement of tubes in tube bundles is proposed and developed.

  • A new high-quality dynamic identification structure for im parameters

    pg(s) 23-26

    In the presented work a new identification method of difficult measured internal quantities of IM, such as components of magnetic flux vector and electromagnetic torque, is proposed. Commonly measurable quantities of IM like stator currents, stator voltage frequency and mechanical angular speed are used for identification to determine a feedback effect of the rotor flux vector on vector of stator currents of IM. Stability of the identification structure is guaranteed by position of roots of characteristic equation of its linear transfer function. Results obtained from simulation in MATLAB measurements confirm quality, effectivity, feasibility, and robustness of the proposed identification method.

  • On Transfer Functions Limitations to Active Vehicle Suspension

    pg(s) 18-22

    It is often assumed that if practical difficulties are neglected, active suspension systems could produce in principle arbitrary ideal behavior. This paper presents the factorization approach that is taken to derive limitations of achievable frequency responses to active vehicle suspension systems in terms of invariant frequency points and restricted rate of decay at high frequencies. The factorization approach enables the determination of complete sets of such constraints on various transfer functions from the load and road disturbances for typical choices of measured outputs and then chooses the optimal vector of the measurements from the point of view of the widest class of the achievable frequency responses. Using a simple linear two-degree-of-freedom car suspension model, it will be shown that even using complete state feedback and in the case in which the system is controllable in the control theory sense, there are still limitations to suspension performance in the fully active state.

  • Simulation study of the effect of coolant temperature on injection molding quality

    pg(s) 14-17

    As plastic products shrink during cooling, so knowledge of shrinkage factor for different materials is required. The main objective of the study is to examine the influence of mold cooling process on subsequent deformation of finished part. To achieve the goal, simulations were carried out at different temperatures of the cooling agent. Statistical processing was performed and a regression model was derived describing the relationship between temperature, time and deformation during cooling.

  • Determination Of Zipline Tightening Weight Travell Distance

    pg(s) 11-13

    This paper shows the determination of tightening weight travelling distance for the zipline. A rope for a zipline can be fixed at both ends, or it can be fixed at one end and tightened with a weight at the other. A both-sided anchorage is simpler to perform, but there is a problem with large changes in the rope force due to temperature differences and due to the movement of the load on it. With a rope that is fixed at one end and tightened with a weight at the other end, there are no such problems, because the force in the rope is always the same, but care must be taken to ensure sufficient travel of the tightening weight. The required travel of the weight is affected by temperature changes, ice buildup and snow, but also by the movement of passengers on the rope itself. Formulas based on which the weight movement is calculated are derived in the paper.

  • Dynamic stability of a fluid-immersed, cracked pipe conveying fluid and resting on a Winkler elastic foundation

    pg(s) 8-10

    The dynamic stability of a cracked pipeline resting on a Winkler elastic foundation and immersed in fluid that is moving with a particular velocity is investigated. The Galerkin method is employed to approach numerically the problem. Conclusions are drawn on the influence of the rigidity of the Winkler elastic foundation on the critical flow velocity of the pipe.

  • Planning and analysis of materials handling processes in production company using modelling and simulations

    pg(s) 121-126

    In this paper is presented the method of planning and analysis of the materials handling line in one production company. The method consists of design, simulations, and analysis with the support of Arena simulation software. The design of the line is accomplished using modular modelling with interconnected modules and blocks, and simulations will be carried out to view the flow of boxes with materials and the functionality of main units and processes. The modelled line contains all the necessary units of the input processes, production and output processes, warehouses, materials handling vehicles, and the process flow of packages. Analysis will investigate key performance parameters and evaluate the functionality of the line. Production and logistics companies are implementing various software to plan and design their materials handling line, internal transports and production processes prior to the implementation and development of their plant. This enables them to plan the work, determine influential parameters and identify problems in the functionality. Results will be given in the graphical and tabular forms, which will represent the analysis of performance parameters and line efficiency.

  • Optimization of Cooling Performance of Horizontal Commercial Refrigerator Prototype with Mathematical Modeling

    pg(s) 118-120

    In recent years, the problem of food safety and traceability has been one of the difficulties faced by restaurant and hotel businesses. Food spoilage can occur at any stage of the food chain; most of all food spoilage is due to improper storage conditions in refrigerators. Increasing attention to food quality and safety requires the development of sensitive and reliable analysis methods as well as innovative technologies for maintaining freshness and food quality. Freshness is a factor that has both health qualities and features that affect customer satisfaction and business profitability. Within the scope of this study, simulation studies were carried out to improve the cooling performance with mathematical modeling on a horizontal commercial refrigerator (operating temperature: -2/+8°C) prototype. Along with the original design, evaluations were made with mathematical modeling according to many different variables (temperature, airflow distribution, etc.) that affect the cooling performance, and R&D gains were achieved in developing the prototype according to the most suitable working conditions.

  • Irrigation Scheduling for Some Crops Under Arid Environment of Rosso, Mauritania

    pg(s) 114-117

    The study was performed to identify irrigation scheduling of some common crops such as seed-maize, tomato, carrot, rice, alfalfa, and tomato plants at arid Rosso province, Mauritania. In that purpose, crop water requirement, ETc, for those crops were calculated by Cropwat software computer program. In results, ETc values for Rice, Alfalfa, Carrot, Maize (grain), and Tomato crops were calculated as about 1378 mm, 1542 mm, 814 mm, 705 mm, and 956 mm respectively. The irrigation water requirements, I, for the examined crops were found as 1677 mm, 1535 mm, 811 mm, 699 mm, and 950 mm, respectively. In accordance with our findings, the following suggestions can be considered; crop pattern should be designated in accordance with current water resources; water delivery systems should be converted to modernized systems; deficit irrigation can be applied for some crops; farmers should be educated about correct water management, and there should be strong relationships between landowners and water managers.

  • A mathematical pathway to achieve sustainable design and friendly management of combined biodiesel/dairy supply chain

    pg(s) 110-113

    This study proposes a mathematical pathway to achieve sustainable design and resource-friendly management of a biodiesel supply chain produced from dairy waste scum. In the work, the features of a combined biodiesel/dairy supply chain are outlined and a set of design and management tools is developed, which is formulated in MILP terms. The optimization criterion is defined in terms of economic sustainability and environmental assessment data is applied as part of it. The purpose of the defined mathematical model is to obtain optimal operating conditions of the considered combined supply chain. A test example based on a case study from Bulgaria was considered. The results of the toolbox implementation can be used as a decision-making tool.

  • Employment of machine learning techniques for crop yield forecasting based on climate parameters

    pg(s) 86-89

    The ability to forecast the annual crop production is of crucial benefit for any country by providing the capability to define their import and export policies, as well as to estimate the economic gain of their agriculture planning. The weather conditions during the year significantly influence the growth of the crop, and the crop yield quantity is highly affected by the climate conditions in the different development cycles of the plant. Recently, the availability of historical climate data benefits the studies in the sector of agricultural sciences and food, and in particular the use of Artificial Intelligence methods in the big data analysis offers a significant opportunity to provide practicable information and actions. The present work aims to develop Machine Learning (ML) model to forecast the wheat yield based on historical climate data in a specific time frame in the Pelagonia valley in North Macedonia, as one of the most important regions for wheat production in the country. After pre-processing and selecting the input features, LS Boost regression model was employed as a ML method for estimation of the wheat yield from climate data, which resulted in high accuracy of wheat yield prediction even with limited dataset, both on the training and on the testing dataset. The research study proved the feasibility of using ML methods to complement the existing models for accurate wheat yield forecasting, providing significant advantage due to the ease of calibrating the ML model parameters.

  • An Engineering Approach to Solve Headbox Slice Opening Control Problem

    pg(s) 84-85

    A headbox of a machine producing a paper sheet has a slice opening controlled in response to signals indicative of total head of fluid in the headbox, the rate of flow of a paper slurry into the headbox and the speed of a inclined wire headbox receiving a jet of slurry emerging from the headbox slice. The slice opening is controlled to affect formation of the paper sheet on the wire. Consistency of the slurry being fed into the headbox is varied to control the position of a dry line on the wire or formation of fibers on the wire. The level of liquid in the headbox is maintained at a predetermined level by a controller. The slice opening is controlled in an anticipatory manner to compensate for the slow response of the total head in the headbox to changes occurring in response to the slurry mass flow rate into and out of the headbox. Since the double flap structure used as the control mechanism is hinged to each other, they move relative to each other, which creates an obstacle in keeping the flap positions constant. Forward kinematic calculations were tried to be made using the angle sensor, but since the sensor resolutions could not respond to small movements due to the size of the flap lengths, the final flap positions were determined by performing inverse kinematic calculations according to the servo motor positions.