Table of Contents


    • Extension of geometry and investigation of deformation on crossed helical gears to increase load capacity and performance

      pg(s) 42-46

      Crossed helical gear units are used in many applications. They range from actuators and power take-offs to household appliances and functions in automotive engineering and production processes. The design is often based on a material combination of steel-worm and plastic-wheel. Based on the research on high efficient plastic materials, they already replace a large number of steel applications. In order to improve the load capacity and performance of crossed helical gears, they must be understood in detail. This article deals with a new calculation method to design optimized flank geometries and to investigate them with regard to their properties in gear mesh. In addition, the deformation and the load distribution in the gear mesh will be examined in more detail. The observation is made in the normal section. In this section, all relevant influences on the performance of the gearing can be analyzed. The pressure and deformation are verified with the help of an FEM-simulations.

    • Acoustic emission method of diagnostic of elevating rudder covering in places of lightning strikes impact

      pg(s) 47-49

      Acoustic emission (AE) is the process of emission of mechanical waves by materials caused by dynamic local restructuring of its internal structure under the influence of stresses of any kind. The source of AE is plastic deformation, the formation and growth of cracks, the outflow of a working fluid (liquid or gas) through holes. The AE method, unlike other methods of non-destructive testing (NDT), is passive, i.e. using the physical field of emission generated by the defects themselves. The acoustic emission (AE) method is based on the registration and analysis of acoustic waves arising in the process of plastic deformation and fracture (crack growth) of diagnostic objects. It makes possible to determine the places where the structure of the material changes when lightning strikes the covering of the elevating rudder for the composite laminate from which the elevating rudder of the RRJ aircraft is made.

    • Application of hardfacing arc methods in Bulgarian ship repair SME

      pg(s) 50-52

      The paper deal with methods for hardfacing used in small and medium sized ship repair enterprise. The difference between welding and hardfacing are explained. In first part of the paper are analyzed disadvantages and advantages of arc hardfacing welding methods, materials and consumables in hardfacing. After that are described two case studies from ship repair industry. In ship repair SME with restricted resource some of hardfacing methods are not applicable. In this paper are described hardfacing methods which are applicable in this type of ship repair yard.


    • Perspectives of the auto world during the pandemic – international and national view

      pg(s) 53-55

      We live in a time of the Covid pandemic, when losses are being noticed in the car industry. Experts state that stabilization of the market is not expected before 2023. Data from the European Automobile Manufacturers Association (ACEA) showed that for the first time in 2021, hybrid electric cars were equalized with “diesels” on the European Union market. Last year, 1.901.239 new hybrid electric vehicles were registered on the common market. In April 2021, our capital Belgrade was awarded for the best Urban Mobility Plan. Our city has increased the safety of traffic participants, given priority to pedestrians and cyclists, reduced emissions and improved energy efficiency, while expanding pedestrian zones. The National Association of Autonomous and Electric Vehicles has launched a project aimed at increasing environmentally friendly traffic in Serbia. Eco 2 line of electric buses works in Belgrade from January 2022. And in Serbia, parts for Audi, Porsche and BMW will be produced in the “Motherson” factory, which was opened at the end of November 2021.

    • Practical UML subset for railway engineers to support formal modeling

      pg(s) 56-59

      The acceptance and popularity of formal modeling is increasing in the development of safety-critical railway interlocking systems, because it allows the specification of the system’s functionality using mathematically rigorous rules. The goal of the research described here is to introduce a simple, easy-to-learn, and useful UML (Unified Modeling Language) subset that supports railway engineers in developing the functionality of system elements at the system planning level. The selection of this UML subset is based on our practical experience. We examine the properties and limitations of this subset through a case study using the Yakindu Statechart Tools. The components specified with the proposed UML subset can be easily transformed into timed automata that we studied using the UPPAAL framework. In the paper, we also present the UPPAAL model for the case study. We are currently working on the implementation of a transformation using the UML subset presented in this paper, which makes it possible to generate formal models from Yakindu to UPPAAL in an automated way.

    • Unaccompanied combined transport with rail legs in Romania

      pg(s) 60-70

      The paper deals with the development of the unaccompanied combined transport (UCT), in Romania. Firstly, it presents statistics and performs a quantitative analysis, depicting a sharp decline of the UCT after 1990, its low weight in the total freight transport volumes and the main characteristics of the domestic traffic which has had a higher weight than in the neighbouring countries and is almost completely connected with the Port of Constanta. The qualitative analysis indicates a great weight of the empty boxes (generating higher costs and prices), the disappearance of several type of services during the time and the fact that the Port of Constanta has not become a real engine for UCT yet. The paper identifies as reasons for these evolutions the changes in the economy, the cancelation of the support measures implemented before 1990, the route competition, the competition with other ports at the Black Sea, the constraints for the transit through the Bosphorus Strait and the lack of practical support measures. It is interesting that the policies and the strategies before and after 1990 are practically identical, but the measures implemented before 1990 are not compliant with the European legislation. Secondly, th e paper performs a comparison between the UCT with rail legs and the road transport. The analysis depicts several structural, technical, and operational issues (poor status of the railway infrastructure and container terminals, the charges for the use infrastructure that are higher in the railway case and the investments in the roads) making UCT not attractive on the market. On the other hand, the calculations based on the method used in the Marco Polo Programme, respectively using the EcoTransit application indicate lower external costs and important savings in CO2 and other polluting gases. Thirdly, the paper deals with the possible support measures, emphasizing that the measures implemented in Austria could be models for the Romanian authorities. European legislation related to the state aids also need s revisions, so that it would not embarrass the transport policies. The main conclusion is that UCT could develop only if subsidies and other appropriate support measured would be implemented.

    • Comparative Analysis of Methods for Defining the Speed of the Vehicle in Vehicle- Pedestrian Collisions

      pg(s) 71-76

      Pedestrians are the most vulnerable road users and traffic accidents involving pedestrians are the most complex type of traffic accident to analyse. The paper describes the kinematics of traffic accidents involving pedestrians and presents statistical data on pedestrian traffic accidents. The main element which needs to be calculated regarding a pedestrian collision is the impact speed of the vehicle involved in the collision. This paper aims to present various models of vehicle impact speed calculation. As a part of this paper, several crash tests were conducted using a pedestrian dummy to determine the reliability of the models. Additionally, the PC-Crash simulation software was also used to calculate the impact speed of the vehicle.

    • Using algorithms to solve problems in urban transport optimization Case study: Prishtina

      pg(s) 77-80

      The scope of this paper is using Dijkstra algorithm in Python to get the urban transport optimization one step further, by finding the best route, besides analysing the shortest one. Studying urban transport routes has been first analysed by Dijkstra algorithm taking into consideration two parameters, the number of stations and distances between stations. After this, the code of Dijkstra algorithm has been implemented in Python, adding the demand for travelling in each station.


    • Energy analysis of two-cylinder steam turbine from nuclear power plant

      pg(s) 81-84

      In this paper, two-cylinder steam turbine, which operates in nuclear power plant is analyzed from the energy viewpoint. Along with the whole turbine, energy analysis is performed for each turbine cylinder (High Pressure Cylinder – HPC and Low Pressure Cylinder – LPC). A comparison of both cylinders shows that the dominant mechanical power producer is LPC, which also has much higher energy loss and much lower energy efficiency. Therefore, any potential improvement of this steam turbine should be based dominantly on th e LPC, which also has a dominant influence on energy analysis parameters of the whole observed turbine. The whole turbine produces real (polytropic) mechanical power equal to 1247.69 MW, has energy loss equal to 352.70 MW and energy efficiency equal to 77.96%. According to obtained energy efficiency value it can be concluded that the whole analyzed steam turbine is comparable to main marine propulsion steam turbines, while its energy efficiency is much lower in comparison to steam turbines from conventional steam power plant s which operates by using superheated steam.