• Computational fluid dynamics (CFD) analysis of the divergent part of the Formula Student car restrictor

    pg(s) 9-13

    The FSAE competition is a student engineering competition that involves designing, constructing, and building a small racing car. Students from different universities compete on auto-moto sports tracks. The competition’s judges are eminent experts in marketing, automotive engineering, and racing car engineering. In class IC, engines are used as power units. One of the main limitations is that all intake air must pass through a diameter of 20 mm. One of the main challenges facing student competitors is solving this problem, and the convergent-divergent jet is one of the possible solutions to the problem. In this paper, CFD simulations were used to examine the influence of the divergent part of the restrictor on the total mass flow at the nozzle exit. A diagram of the dependence of the mass flow on the half-angle of the divergent part was obtained. For the CFD simulation, ANSYS Fluent was used, which proved to be very good for examining the mentioned influence.

  • Analysis of planetary gear trains applied in vehicles

    pg(s) 5-8

    The paper presents a theoretical analysis in the field of the application of planetary gear trains in vehicles. The following main areas have been considered: design features of planetary gear trains, specific aspects of the application use of planetary gears in vehicles and possibilities of increasing the efficiency coefficient of these drives. An analysis of the option for investigating these gear sets has been implemented as well. Special attention is dedicated to the options of minimizing energy consumption, taking into account the relevant limitations and operating conditions of planetary gear trains. Conclusions have been deduces. Ideas for future scientific work are presented

  • Surface treatment – effect on spring parts in the automotive industry

    pg(s) 3-4

    In modern automotive engineering, a particular car is composed of various parts that are manufactured using a wide variety of materials and technologies and that meet the high demands of modern customers and environmental norms. In the production process of a specific article for assembling cars, a problem with springs of a certain type is found. During the planned production, assembled products began to show the same defect. The mounted springs fall spontaneously. An analysis of the possible causes was made. A visual examination was made which showed a lack of plasticity, a change in geometry and raised doubts about the thermal surface treatment. Based on the results of the performed measurements and analysis, the possible causes of the problems during production were recognized. Several conditions could have caused this:
    – Two different tools were available at the manufacturer, respectively two different technologies for the production of the springs;
    – The manufacturer used two different sub-suppliers for surface treatment;
    – insufficient corrosion protection;
    The results of the measurements show that despite the geometric deviations of the dimensions, the springs lose their function due to lack or improper surface treatment.

  • Disturbance rejection in a one-half vehicle suspension using a fuzzy controller

    pg(s) 98-102

    Generally, passenger ride comfort can be interpreted as an attenuation of sprung mass acceleration or as peak minimization of sprung mass vertical displacement, while good handling can be characterized as an attenuation of unsprung mass acceleration. This effort devoted to passive suspension design is ineffective because improvements to ride comfort are achieved at the expense of handling and vice versa. Instead, the best result can be achieved by active suspension, i.e. when an additional force can act on the system and simultaneously improve both of these conflicting requirements. Another important goal of the control design is to maintain robustness of the closed loop system. In the paper, fuzzy logic is used to simulate active suspension control of a one-half-car model. Velocity and acceleration of the front and rear wheels and undercarriage velocity above the wheels are taken as input data of the fuzzy logic controller. Active forces improving vehicle driving, ride comfort, and handling properties are considered to be the controlled actuator outputs. The controller design is proposed to minimize chassis and wheels deflection when uneven road surfaces, pavement points, etc. are acting on tires of running cars. As a result, a comparison of an active suspension fuzzy control and a spring/damper passive suspension is shown using MATLAB simulations.

  • Optimal length of a railway curve for a given design speed

    pg(s) 94-97

    The majority of railway projects in our country aim at the maximum utilization of existing railway infrastructure, increase of the operation parameters, frequently at the condition of achieving interoperability. Increasing permissible speeds of trains invariably requires increasing the radii and lengths of curves. However, at small delta angles the use of the minimum design speed radius gives suboptimal results in terms of the total length of the curve. The report presents a parametric method for optimizing the railway curves at small delta angles in view of the necessity of achieving higher speeds on existing lines.

  • LNG fueled ship type “C” storage tank pressure rise particularities related to the bunkering flow

    pg(s) 91-93

    In the proposed publication it is conducted simulation-based experiment with the bunkering process of type “C” LNG containing tank. According to the specific features of the LNG bunkering process it is analysed the nature of the boiling off mechanism of the cryogenic fluid during bunkering transfer. The attained data by the experiment is analysed including the specific condition of heat ingress simulation. On the base of the results there are stated conclusions and recommendations to the ship operators related to the limiting conditions of the pressure vessels operation as it is the type “C” tank.

  • Influence of profile modifications on the scuffing load capacity of high contact ratio gears

    pg(s) 85-89

    Scuffing is a spontaneous gear failure mechanism resulting in a disrupted surface. Scuffed gears are more sensitive to dynamic excitation and friction. Besides the lubricant and the material, the scuffing load capacity is mainly dependent on the gear geometry. High contact ratio gears exhibit a lower load carrying capacity due to an increased dissipation of frictional heat in the outer mesh positions. In this paper this phenomenon is addressed with experiments and simulative analysis. Based on these works, recommendations for adequate profile modifications are derived to maximize the load carrying capacity regarding scuffing of high contact ratio gears.

  • 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.

  • 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.

  • 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.

  • Research on loading-transport machine parts in order to determine the causes of defects

    pg(s) 15-18

    Possible defects in the system: piston-cooling jacket occur for various reasons. This system work in severe conditions: heat load; variable gas pressure and mechanical friction, which requires high strength, good wear resistance with limited lubrication and overall high resistance to abrasion, corrosion and other wear.The operation of the cylinder-piston group with insufficient or poor quality oil is the most common cause of overheating or engine blockage. Seizing of one or more pistons leads to major engine repairs or even scrappin g. Damaged fuel injectors, inaccurate injection or ignition timing can also cause the mechanism to melt or puncture. Therefore, it is essential to identify the exact causes of defects in the system and look for ways to prevent them.
    Studied details were functioned under the identical conditions of good lubrication and no overheating. The reason, apart from the ones mentioned above, which led to their destruction, has been established.

  • Determination of the quality of welds produced by robotic welding

    pg(s) 11-14

    The paper focuses on the evaluation of the quality of fillet welds produced robotically by the method of impulse synergic welding MAG. This welding technology is used in the automotive industry in the production of rear seat backs for passenger cars. In the process of automated production, the speed of the process, accuracy, and quality of the made joints are important. Several factors affect the accuracy and quality of welded joints. The paper presents the results of research where the influence of filleting of fillet welds on their quality was confirmed. Visual and capillary methods were used to determine the quality of welds, metallographic analysis for evaluation depth of weld root penetration, strength properties of welds were evaluated by static tensile test. Statistical ANOVA methods were used to process the obtained values. Experimental work confirmed that the depth of welding of the weld root into the base material has the greatest influence on the final quality of fillet welds. It is this parameter that results in the elimination of the weld and thus the entire produ ct.