Journal of Mechanical Engineering 53 (2007) 1

Editorial

Journal of Mechanical Engineering in Year 2007

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Parallel Effects of Acceleration and Surface Heating on Compressible Flow: Simulation of an Aerospace Propulsion Nozzle with a Medium Amount of Surface Wear

Corresponding author - A. Alper Ozalp

Abstract

Numerical simulations of aerospace propulsion nozzles are very complex due to the necessity to simultaneously handle flow acceleration, momentum heat-transfer rates, surface roughness, temperature-dependent air properties and streamwise density variations due to the compressible character of the flow. To provide an overview for a multitask consideration of the propulsion-nozzle flows, a new computational model that integrates the axi-symmetrical continuity, the momentum and the energy equations has been developed. Numerical experiments were performed with various nozzle geometries, inlet-boundary conditions, with the combined handling of the surface heat flux and roughness conditions. The computations indicated that the input and loss power values of the propulsion nozzle increase with higher inlet stagnation pressures and decrease with higher nozzle convergence half angles and surface heat flux. The ratio of the loss to the input power was found to be independent of the heat flux; however, it decreases linearly with an increase in the convergence half angles.

Keywords - propulsion nozzle, compressible flow, discharge coefficient, power losses

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)1, 3-12
UDC 62-225.5:532.525

Parallel Effects of Acceleration and Surface Heating on Compressible Flow: Simulation of an Aerospace Propulsion Nozzle with a Medium Amount of Surface Wear (pdf)

 

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Determination of the Friction Coefficient of Groove Forms Using the Stress-Function Method

Corresponding author - C. Erdem Imrak

Authors - Ismail  Gerdemeli

Abstract

The maximum traction that can be developed in sheave grooves is a function of the actual coefficient of friction between the rope and the groove. The coefficient of friction is presented in different ways for every type of groove form.  In this paper an expression for the pressure distribution on the contact surface of round and/or U-shaped groves is obtained, and the friction coefficient of the groove forms is determined by the stress-function method.

Keywords - rope groove, friction coefficient, stress function method

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)1, 13-17
UDC 621.894:539.4

Determination of the Friction Coefficient of Groove Forms Using the Stress-Function Method (pdf)

 

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Numerical Modelling of the Internal Sound in Railway Rolling Stock

Corresponding author - Jonas Bazaras

Authors - Žilvinas Bazaras - Jonas Sapragonas

Abstract

The paper presents an analysis of the sound in railway rolling stock. The speeds of trains tend to increase as railway rolling stock improves technically and becomes more sophisticated; however, the sound generated is intensified too. Noise is one of the harmful consequences of transport. As the sound level in domestic surroundings is one of the most important human-comfort indices, increasing attention is being devoted to an investigation of sound processes. The sound generated by transport vehicles, its distribution, and its variation in internal transport-vehicle spaces, and various sound sources in railway transport are considered in the paper. Engineering, organizational and administrative sound-reducing measures are discussed.  The harmful effects of sound on human health are discussed as well. Two types of Russian production locomotives - the M62 and the TEP60 - were selected for this research. Using ANSYS/Multiphysic software the acoustic sound of the different power units in the engine sector was simulated. The results of the sound calculations were compared with the acceptable levels.

Keywords - railway rolling stock, sound analysis, numerical modelling, damping parameters

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)1, 18-25
UDC 629.4:534.61

Numerical Modelling of the Internal Sound in Railway Rolling Stock (pdf)

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A Theoretical and Experimental Investigation of the Dynamics of Rolamite-Type Mechanisms

Corresponding author - Ričardas Viktoras Ulozas

Abstract

This paper looks at theoretical research of the dynamic model of the "roller-band" system of the Rolamite-type mechanism (RTM). The dynamic model of the "roller-band" system of the RTM is described by differential equations and is investigated in two ways, i.e., when the system is not influenced by the excitation of vibrations, and when it is influenced by them. We have established that with the parameters of excitation of vibration it is possible to operate the parameters of a non-slipping zone. This allows us to assume that in a real Rolamite-type mechanism it is possible to operate on the friction between the structural elements of the RTM. Experimental research on the dynamics of the Rolamite-type mechanism with vibrating elements was done in three directions: research on the dynamic processes running in the RTM roller-band system; research on the processes of friction-control between the elements of the RTM; and research on the dynamic processes running in the Rolamite vibromotors. The increase of the supply-voltage amplitude, the decrease of the force-load magnitude of the flexible band, and the decrease of the angle of the wrapping of the roller by the flexible band cause an increase in the amplitude of the roller vibrations. An RTM with rotating vibrating rollers, compared with the vibrating rollers of the other type, has a better bearing capacity and is much more sensitive. The highest synchronicity of rotation of the rotors is provided by a Rolamite vibromotor with two rotors and a piezoelectric converter of vibrations that simultaneously rotates both rotors. This is compared with the Rolamite vibromotor with two rotors and a piezoelectric converter of vibrations, which rotates only one rotor.

Keywords - Rolamite type mechanisms, slipping, vibrations, dynamic models

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)1, 26-47
UDC 62-23:681.892

A Theoretical and Experimental Investigation of the Dynamics of Rolamite-Type Mechanisms (pdf)

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Optimization of the Performance of the Continuous-Drying Process in Gravity Dryers

Corresponding author - Neven Voća

Authors - Tajana Krička - Vanja Janušić

Abstract

Technology and technological expectations are expected to develop with time; however, opportunities, needs and working conditions affect the extent of their usage. Predictions are made in all areas of human activity, and this includes the agricultural sector. Using the know-how so far applied during the drying process in gravity dryers, together with the available data on the interdependencies of a large number of parameters, this paper suggests how a system for drying could be organized by optimising the functional ensembles. A comprehensive method for drying-process optimization in gravity dryers can be built in several steps from several functional ensembles. Each step improves the process, and together they represent the complete system for performance optimization. An additional property is the possibility of realizing each step. The drying-process optimization results in the stabilisation of the dryer functions, a decrease in the specific energy consumption, and better kernel quality.

Keywords - drying process, optimization, static properties, performance, microprocessor controller

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)1, 48-58
UDC 631.365:681.5

Optimization of the Performance of the Continuous-Drying Process in Gravity Dryers (pdf)

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