Applied Mechanics and Materials Vols. 809-810

Abstract: The track vertical irregularities are the originator of the vertical vibrations in the wheelset. These vibrations are further conveyed to the suspended masses of the vehicle, thus generating and maintaining their vibrations. The study of the vibrations behavior of the wheelset plays an important role in the research dealing with the improvement of the vehicle dynamic performance, mainly at high velocities. This paper examines the vibrations behavior of the wheelset during running at speed of up to 200 km/h on a track with stochastic vertical irregularities, which are mathematically represented via the power spectral density. As underlain on numerical simulations, a series of basic features of the wheelset vertical vibrations will stand out, in correlation with the velocity, track quality and its damping. The observations herein prove that the maximum level of vibrations is visible at the frequency resonance of the wheelset on the track. Similarly, it is evident that the wheelset vibrations behavior increases during the running at high velocities on a track with weak damping and low quality.

Abstract: The Liquid Petroleum Gas can be use for diesel engine fuelling with significant result in term of pollutant emissions improvement, with important reduction of nitrous oxides and smoke for a LPG dual fuelled diesel engine. Beside this the LPG fuelling affects the combustion process inside the cylinder and also the mixture forming. High degree of homogeneity of the air-LPG mixtures will accelerate the in-cylinder mixture forming between air-LPG and diesel fuel jets, since the LPG-air mixture combustion starts. The paper presents the results of a zero-dimensional, one-zone thermodynamic model developed by authors for diesel fuel jets vaporization and combustion at dual fuelling. The model shows the diesel fuel jet characteristic, the break-up period, the mass flow of vaporized substance on the particle surface, drops vaporization time, air-fuel mixture forming speed, drops combustion time and flame position, showing a significant influence of LPG cycle dose on their characteristic parameters. The drops vaporization and combustion duration decrease for dual fuelling and the flame radius increases. Thus, based on the experimental data, an evaluation model for mixture forming was developed for an automotive diesel engine fuelled with LPG and diesel fuel by diesel-gas method.

Abstract: Some of the aspects of the vehicle suspension limiting performances from stress and vibrations point of view have been explored in this study. The vehicle is modeled as two DOF system and the suspension is considered a passive one. 3D CATIA model was built for both the spring and spring-damper ensemble, neglecting the tire influence. This can reasonably covers the studies of geometries and forces (bending or tensile stress), masses and stiffnesses (meaning vibration profiles). The theoretical analysis on the vibration behaviour of the spring-damper ensemble, regarded as the vehicle suspension, suggests a convenient operation regime at low frequencies below 15 Hz, if the damper piston displacement is limited.

Abstract: The paper presents results of tribological properties of the kinematic pair: X210Cr12 steel / CuSn10 bronze, lubricated within the friction process by engine oil SAE 20W/40, and by the same lubricant modified by chemical exploitation preparation. Research of tribological properties were carried out using the tester T-05 (type tester roll - block). Tests have been carried out in two stages. In the first order - friction force, wear of the kinematic pair and the temperature of the friction area have been determined. The objective of the second phase was to micro roentgen spectral analysis of the surface friction zone. On the basis of these studies, the analysis of the elemental composition of the surface layer in the track wear have been made. The modification purposefulness of lubricant SAE 20W/40 by chemical exploitation preparation has been shown.

Abstract: Efficient use of adhesion between wheels and rails involves a good knowledge of this phenomenon, in order to equip the vehicle with adequate facilities and systems that protect the vehicle and the rail. The loading of the vehicle's axle with dynamic loads in vertical and horizontal planes, are to be developed in the area of contact, both normal stress and shear distributed stress, their sum giving the friction force and the moment of pivoting friction (spin). This makes the wheel-rail contact problems take the two aspects of the study, namely the problem of normal and tangential contact issue. The normal contact problem involves regular geometric shape bodies, determining the size of the resulting contact surface, the distribution of the normal contact pressures and the relationship between the proximity of the bodies and the normal contact force. Solving the problem of the tangential wheel-rail contact is about to establish the correlation between the creepage, normal contact forces and friction forces, and also the ratio between the adherent contact surface and the nominal contact surface where the creepage ocurs.

Abstract: In this paper it is developed a location model for the infrastructures dedicated to non-motorized movements by bike in Oradea city, using ArcGIS geographic and information system [3]. They are taken into consideration the movements made by the target people – alternating movements (from home to school) and optional movements (made for recreation), the densities in residential areas, the type of the city arteries and the mobility need of the target people (in this case – young people aged between 15 and 25) in order to design two structures of the transport infrastructure networks (one for the alternating movements and the other for the optional movements), structures which will be realized on the actual frame of the existing transport infrastructure in Oradea city. Using Dijkstra algorithm, the minimal routes for the movements related to the alternating mobility, but also for the movements specific to the optional mobility are determined. Further on the most used arteries in the two structures of urban infrastructure networks are determined. The paper suggests as a solution the structure of the network for the non-motorized movements and also those arteries that must be used for its development, that guarantee gains for the target people (time), for the main operators who exploit the motorized systems, for the local budget of the local municipalities (less funds to sustain the public services) and especially for the environment and people’s health (attenuation of noxious and phonic pollution, reduction of the accidents’ number and health improvement).

Abstract: Impetuous multiplication of mobility and road traffic proliferation lead to concerns for increasing the attractiveness of urban public transport. Compared to private car use, urban public transport attractiveness is conditioned, in particular, by travel times and certainty of respecting the transport schedules, meaning planned traffic stability. Traffic schedules are considered to be more stable as the primary delays from the announced schedule have low probabilities and values and their propagation as repeated delays is least noticed in time and space. Solutions for assuring traffic stability must take into consideration contradictory aspects, because introducing time reserves in the schedules means time travel extensions. In order to assure the stability of planned traffic, present paper develops studies of various models and methods that aim to reduce inherent primary delays. Thereby, for studying repeated delays on a complex network, a mathematical model adequate to a Discrete Event Dynamic System (DEDS), that in MAX-PLUS algebra becomes a linear system, was used. The paper concludes with a case study on an integrated network resulted from the superposition of Bucharest’s existing suburban rail network with the underground network designed for 2030, being identified measures for improving the stability indicators. Traffic stability is assessed on the basis of two indicators: instability coefficient and delay elimination rate. Main measure for improving stability indicators is the growth of time reserves taking into consideration the quality requirements resulting from the condition of maintaining a reduced planned travel time.

Abstract: Abstract. A modal analysis of truck system was performed. Eigen frequencies and eigenmodes are described. In order to validate the model, the engine was tested with various excitations. Acceleration responses were measured and frequency spectral analyses were performed. The transmissibility was calculated as a ratio of the effective accelerations measured at M, R, Cs, Cd points on the truck structure. The eigenfrequencies of the truck structure are sensitive to the numerical parameters of the model. The influence of the thickness of chassis frame and of the geometry’s cross member on the vibrational behavior of the chassis and on the vibration transmissibility from the engine to the cab truck were studied.

Abstract: The paper investigates the effects of mechanical wheel slide protection devices (WSPD) on the braking capacity for coaches equipped with disc or cast iron block brakes. Decelerations and jerks, that affect the passengers comfort, are also analyzed. An original simulation program, based on experimentally determined air pressure evolutions in brake cylinder is used for this purpose. Results of numerical simulations show that in the case of repeated actuations of mechanical WSPDs, disc brake vehicles are more affected in terms of braking capacity. Regarding jerks during braking actions, in both normal and low adhesion conditions, vehicles equipped with high power cast iron block brake with two pressure levels prove to be more affected.

Abstract: In track curves may show deviations from the nominal dimensions, in the form of continuous or discontinuous bends which produce dynamic forces of interaction vehicle-path in the transverse direction, which, in addition to the worse ride quality can jeopardize the safety of vehicle guidance. If the vehicle is traveling at a constant speed in a curve with deviations no I cant deficiency box to the mass m will be subject to quasi-static transverse acceleration γ_T0 or uncompensated centrifugal force F_n. As a result, each axle will act a driving force of the chassis quasi-static force H. Along with the emergence occurs and elastic compression elements and the vehicle track superstructure. Considering that their total stiffness is c_y, their static deformation will be y_c = H / c_y. Therefore, the vehicle can be considered as a simple harmonic oscillator, ie a system table - arc, the arc yc is static deformation.