Predrag Jovančić

Effectiveness assessment of agricultural machinery based on fuzzy sets theory

Highlights? The concept of effectiveness - exact indicator of the quality of service of machine. ? New structure of max-min composition - outcomes as represent of If-Then rules. ? Evaluation of tractors - on the base of expertise judgment. The quality of service of agricultural machinery represents one of the basic factors for successful agricultural production. In this sense, there is a clear need for defining the exact indicator of the quality of these machines, according to which it could be possible to determine which machine is optimal for different working conditions. The concept of effectiveness represents one of synthesis indicators of the quality of service of the technical systems. In this paper the effectiveness is defined using the fuzzy set theory, and reliability, maintainability and functionality are used as influence indicators of the effectiveness. In that sense the model for assessing the effectiveness of tractor as a typical representative of agro machinery has been formed. The model is based on integration of linguistic description of the above mentioned influence indicators using fuzzy set theory and max-min composition. The model was tested on the example of three tractors of the same category, which are exploited in climatic and soil conditions in the wider Belgrade (Serbia) area. Even if the conditions in this experiment were approximately equal, the difference of the achieved effects was attained and very significant, compared to other operation parameters.

Impact of the Bucket Wheel Support at Technical Parameters of the Block and Bucket Wheel Excavator Capacity

Bucket wheel excavators are machines that on the current level of surface mining development have gained the widest application. Its work consists of the main movements (slewing of the bucket wheel and superstructure) and auxiliary movements (moving of the excavator toward advance direction and modification of the height position for the bucket wheel in the vertical plane).

Energy resources in the Republic of Serbia: Development policy

ABSTRACT By joining the Energy Community and obtaining candidate status for accession to the European Union (EU), Serbia has committed to harmonize its energy policy to the legislation of the EU. The backbone of this policy is the power sector, which will continue to be the foundation of future development. In fact, the power sector is probably the closest to EU standards. This paper presents the energy resources in Serbia and the potentials that can be used to define the power sector policy. It is expected that lignite and large hydropower plants (HPPs) will become the basis of the energy system in the future, but with a significant increase in the share of renewable sources, primarily wind energy and biomass. One of the main objectives is to reach a 50:50 ratio of electricity produced from renewable and non-renewable sources in the period 2020–2030.

Behavior Diagnostics of Bucket Wheel Support Structure Using Finite Elements Method: Optimization of Structures

Most common types of bucket wheels were analyzed by finite elements method in this paper. Also, relevant diagnostics parameters are defined for various constructions (stress concentration, deformation energy, distribution of potential and kinetic energy for main oscillation shapes). This approach enabled identification of weak spots and selection of such types of bucket wheel which are most suitable for specific working conditions on open cast mine.

Study of Dependability Evaluation for Multi-hierarchical Systems Based on Max–Min Composition

This article presents the model for calculating the performance of dependability for complex technical systems. According to ISO-IEC 300, dependability is an overall indicator for the quality of service and considers simultaneously reliability, maintainability, and maintenance support. For a proper understanding of the quality of service for any technical system, it is important to define dependability performance at the level of single component as well as at the upper levels—levels of subsystems and entire system. As dependability indicators (reliability, maintainability, and maintenance support) have been defined as linguistic variables, the fuzzy max–min composition has been used for the dependability determination and integration of its indicators. A procedure for the synthesis of single components dependability performance to upper levels in complex technical system is proposed. Max–min composition is again used as a tool for fuzzy synthesis because it enables obtaining the comprehensive and synergetic effect in a process of dependability evaluation. A practical engineering example (mechanical systems at bucket wheel excavator) has been used to demonstrate the proposed dependability synthesis model. Copyright