As is well known, the solution of analytical elastic contact problems [1, 2] is limited to a small number of specific contacts. For this reason, various numerical approaches were proposed to solve contact problems. The use of conventional numerical solving methods is however limited by the large volume of computation due to the use of fine meshing of the assumed area of contact with an important number of nodes. Various methods are proposed in literature to reduce the computing time and power needed to solve contact problems. In order to highlight the dependence between micro-contact parameters and the mechanical properties of the materials in contact, the present paper proposes the numerical modeling of micro-contacts using the Conjugate Gradient and Fast Fourier Transform technique (CG + FFT), [3, 4], and its adaptation to the micro-contact range. Model validation is performed by comparing the obtained results with the classical Hertz model, for various contact body shapes. The obtained results show very good agreement between the numerical and analytical results, thus validating the proposed numerical model.
The paper presents some aspects regarding the conception and construction of an experimental test rig used for studies concerning friction phenomenon of threads immersed in oil, maintained in a state of motion with constant velocity. The structure of the experimental test rig, testing methodology, experimental results and the applicability of the experimental set-up were detailed. To validate the experimental equipment and method, the obtained values were correlated with those obtained analytically. A good correlation was found, which attests the applicability of the test rig and method.
The paper purpose is to investigate the influence of some of the machining input factors and conditions on the surface texture and roughness parameters. The machining tests were carried out on a homebuilt (DIY) CNC router with a one teeth carbide flat end mills. The router movements were calibrated in order to assure three decimals precision. The spindle speed is controlled by a frequency converter that allows setting the speed ranging from 0 to 20000 rpm. Rectangular pockets were milled considering cutting across and along the grain and at a 45-degree angle. Different cutting path strategies were generated using a specialized CAM software. A Taguchi DOE method was considered and a confocal microscope type CWM 100 produced by Mahr was used to analyze the surface texture and roughness parameters.
The vast majority of suspension systems widely used in road vehicles by all major manufacturers are passive. They have a unique force - displacement or speed - force characteristic, imposed by the characteristics of the constructive elements used. However, for the suspension system of the vehicles, to optimally perform on the widest possible areas of the road unevenness, adaptive suspension systems have been developed. These systems can be either semi-active or active. The main problem that these suspension systems have to answer is the maximization of traction. This involves maintaining permanent contact between tire and road, while also ensuring increased passenger comfort. Passenger comfort, on the other hand, requires smooth damping, with as little chassis acceleration as possible. Under these conditions, it is impossible for passive systems to meet these requirements, and a compromise between comfort and safety is always necessary. For these reasons, adaptive systems have been developed that allow the shortcomings of passive systems to be eliminated, being able to ensure optimal behavior for the entire frequency range offered by runway irregularities. Semi - active systems usually use dampers with variable parameters, dictated by various controllers such as proportional, derivative, integrative or various combinations thereof. This paper aims to simulate and analyze a passive suspension by referring to the characteristics of a semi-active. The study evaluates the vertical movements of a vehicle with known parameters over different shapes of the cross section of the road. The study involves the use of the Matlab-Simulink environment in which a physical study model for the quarter machine model is made, using the predefined blocks found in Simscape. According to the obtained results, there is a substantial change in the damping characteristic when using the semi-active suspension, in order to reduce the oscillations and shorten the time to reach equilibrium.
This article will study the impact of a liquid jet with a flat surface, from a dynamic point of view. The surface where the liquid jet impact will take place has been positioned both perpendiculars to the direction of the jet and at a certain angle. To determine how the impact of the liquid jet takes place in the immediate vicinity of the plane plate, a CFD simulation is performed. The obtained results allow us to study two situations, one that concerns the occurrence of the hydraulic jump during the impact and the second will allow us to analyze the evolution of the jet symmetry. It is known that the impact of a liquid jet with a surface is quite complex. To solve this, the VOF (volume of fluid) model was used. The obtained results allow us to visualize the evolution of the liquid jet in the form of a complex geometric shape that at the extremities is followed by a hydraulic jump and the fragmentation of a part. The behavior of the impact of the jet with a surface inclined at 45°, shows that there is an asymmetry of the contact fingerprint as the jet inclines towards the normal straight-line surface. The main objective of the present simulations is to experimentally investigate the effect of the angle of inclination of the jet and of the fluid flow on the initial imprint formed at the contact and on the post-fragmentation mode of the complex geometrical structure formed.
The study of the evolution of the mass of a liquid droplet and its average temperature in the case of collision between a solid surface and liquid droplet can be carried out using the Volume of fluid method VOF. The dynamics of the drops will be investigated at the moment of impact on a heated plane wall until a steady state is reached. During this transition period, the average temperature of the drop vaporization process is estimated. The lifetime of a drop of liquid is determined from a static point of view, upon contact with a hot surface. The equations applied are Navier-Stokes energy and vapor transport.
The „downsizing” phenomenon has grown and has led to the technological and efficient use of the supercharger systems. Despite this, conventional turbocharging systems have a transitional response due to the exchange of power with the engine and affect the elasticity of the engine. An electrically actuated turbocharging system can eliminate this shortfall, transient operation, without loss of interference, as the response is instant to the electric drive. A power recovery system can be added to increase overall efficiency. The study provides an overview of the influence of the compression ratio of a compression ignition engine to which an electric power-driven axial compressor has been attached. The results showed that the implementation of an electric compressor and a high compression ratio contribute to increasing yields and reducing losses in the operating cycle.
This study aimed to highlight the mass flow and boost pressure performance of an electrically operated axial compressor. This compressor proposed and developed by its authors[1] was mounted on a diesel engine, which is fitted to a VW Golf 4. A mathematical model was developed in MathCad for the overall calculation of this compressor, determining the boost pressure and the theoretical air flow. The mathematical model also highlights the increase in the boost in each stage of the compressor, but also the mechanical work consumed. The compressor was made of the following parts: fan 1 which is designed to take the air and to direct it axially into the second stage, where is the second fan with a smaller diameter and a number of higher revolutions, the control unit which allows the speed of each fan to be adjusted and the part to be protected against electrical shock. To determine the air flow, a diaphragm has been created which has been fixed by 6 screws at the compressor outlet, fitted with holes for measuring the difference in pressure. In this study, the pressure at several characteristic points of the compressor will be measured using an integrated differential sensor assembly. LabVIEW program was used to determine characteristic values according to the speed of the axial compressor and pressure variation can be seen on a laptop interface during compressor operation. After determining the mass flow, the turbocharging pressure can also be determined from the calculation.
Over the last decades, 3D printing has become more and more highly used in the production of various parts and prototypes. There are several technologies employed for 3D printing. Of these, the most widely spread and most affordable is probably the FDM (Fused Deposition Modelling) technology, which permits the use of various thermoplastic polymers to create 3D geometries by melting the material and deposing it in thin layers. Technical advances in latest years made 3D printers widely available and affordable. It is therefore of interest to investigate the properties of parts manufactured using the simplest of printers and the most usual materials. The present paper presents experimental investigations conducted regarding the influence of the printing regimes on the surface properties in 3D printed parts. Various printing parameters, such as extruder temperature, print speed and layer thickness were varied for the same part. Printing was done using a general purpose printer with a delta bot structure. The parts investigated in the present study were made using a generic PLA (poly-lactic acid) filament. Surface properties were then investigated optically by aid of a confocal microscope. Using the microscope’s dedicated analysis software, surface micro-topography was investigated and its parameters, obtained in accordance to ISO 4287 and ISO 25178, were analyzed.
This paper presents a new concept of a rotary engine, with combustion chamber at constant volume. In this context, we present a comprehensive theoretical study on the combustion process that takes place at constant volume in the combustion chamber. A mathematical model was developed to describe the combustion process. The conducted theoretical study allowed comparing the thermodynamic parameters describing the combustion process for two fuel mixtures. Air - petrol vapors mixture and additional hydrogen feed were considered. A main attention has been paid to maximum values of the pressure in the combustion chamber as it has a direct influence on engine torque. Also, the study shows the advantages of using constant volume burning and the differences that occur with the use of the two types of fuel, as well as the evolution of the pressure and temperature within the combustion chamber. This allows evaluating the thermal load and determining the mechanical stresses to which the components of the proposed rotary engine are subjected.
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