• 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.

  • The vehicle that can move on an accidental field

    pg(s) 7-10

    The designed vehicle can move on rough terrain (with multiple bumps); also (the vehicle) can climb a sloping terrain (with a relatively large angle).
    The movement (of the vehicle) is not continuous; contact with the ground (tread) takes place periodically, simulating the steps taken by a moving man; this movement is obtained by generating a hypocycloid.
    The vehicle will move with the help of four wheels; they (wheels) will lift and move the vehicle when they come in contact wi th the road (ground).

  • Simulation of the hobbing process of enveloping wormwheels for the calculation of contact pattern and contact lines

    pg(s) 3-6

    The contact pattern and contact line calculation is an essential part of the design of worm gears. The existing calculation algorithms are based on the law of gearing. For this reason, cases like meshing interferences can only be analysed to a limited extent. The simulation of the hobbing process of enveloping wormwheels, introduced here, makes it possible to generate any wheel flank precisely. For the contact pattern calculation, one wheel flank is generated from the cutter geometry and one from the worm geometry. These two generated flanks are brought into contact. For each flank coordinate, the distance to the opposite flank is obtained. The graphical
    application of this distance over the wheel coordinates results in a contour diagram that is known as the contact pattern. The contact linecalculation of worm gears also shows on which part of the flanks power is transmitted at a certain rotational position. For this calculation, the wheel flank generated from the cutter is brought into contact with the worm flank at any angular positions.

  • Fixed joints applied in car construction

    pg(s) 127-130

    The paper deals with the problem of joints of car parts of the car construction. The construction of the car must meet the emission standards, in order to meet them it is necessary to reduce the weight of the car while maintaining strength and durability. Therefore, different materials are used in the design of car construction, such as different types of steels, aluminum alloys, composites and plastics. This increases the demands on the car construction and on the type of sheet metal joining technology used. The paper deals mainly with glued and welded joints in the design of car construction. The suitability of individual types of joints is solved using the finite element method.