Applied Mechanics and Materials Vol. 821

Abstract: The paper deals with a numerical analysis of wind effects on structures with perforated surfaces. The solution based on FEM model is governed by the stabilized Navier-Stokes equations for incompressible fluid. Special attention is given to perforated surface. Such a partly resistance barrier always introduces considerable numerical difficulties resulting from the complexity of a flow distortion when the fluid is passing through. For simplification, the barrier is assumed as a thin screen with specific resistance parameters where the fluid flow mechanism needs not be resolved. The general influence of the barrier on the flow field is a loss in the normal momentum component and the change in the flow direction. On the other hand, the authentic simulation of the fluid mechanics requires specifying the relevant input parameters that can be determined by an experiment or by using a corresponding handbook.

Abstract: This paper presents a co-simulation method to design of speed controller for turbojet fuel pump. Expected fuel pump is used for small turbine engine concept with reducer driven by free turbine. The amount of injected fuel into the combustion chamber is based on the speed of the fuel pump which is controlled by the engine control unit. The final flow of fuel into the combustion chamber is restricted by fuel bypass which constricts the return fuel according to pressure in the nozzles. This back fuel bypass has nonlinear and fixed characteristic determined by its structure. The only way how to control the amount of incoming fuel to the engine is the pump speed control. Effect of the bypass represents a variable component in the fuel pump load and from the view of the speed controller it is a disturbance variable. This paper describes the co-simulation model based on the use of MATLAB/Simulink and MSC Adams environment. This simulation uses interconnection of Simulink controller design and simplified model of the fuel pump dynamics in Adams (without hydraulic modelling).

Abstract: This paper deals with a new experimental approach to the analysis of radial, axial, and tilt error movements of machine tool spindles under load. The main focus is on the identification of error spindle movements under different machine operation conditions between 500 - 5000 rev / min and loads in the range of 50 - 500 N. Errors of the spindle movements are measured on the cylindrical workpiece using capacitance sensors for different loads. The analysis of measurements of radial, axial, and tilt error movements of machine tool spindle indicates a dependency of loads and measured errors. The integration of error measurements into novel multi-body dynamic models of machine tool spindles is very important for prediction of machine behaviour during a cutting process and for prediction of workpiece geometric accuracy.

Abstract: This article deals with optimization of operational parameters of an energy regeneration module for a heavy vehicle. Recently, there was developed an energy regeneration module for a pneumatic tyred roller with hydrostatic drive. It was necessary to optimize its operational parameters to achieve good results in experimental tests on the actual vehicle. The optimization process was based on a numerical model of the vehicle using a parallelized modification of the differential evolution algorithm as an optimizer. Suggested parameter values were subsequently verified experimentally on the vehicle by analysis of the fuel consumption.

Abstract: Presently, production machines and mainly contemporary machining centers are subjected to ever increasing pressure to enhance energy efficiency, both from the side of customers and also in terms of legislative regulations. A selection of drives for the individual axes is primarily a compromise between achievable dynamics, precision and price. The electrical efficiency and energy consumption is not usually taken into consideration during the design of the axis. In this paper, the electricity consumption of single drive axis actuator and redundant actuation through two drives is compared under various operating conditions. The measurement results are used to assess the benefits of redundant actuation of positioning axes with emphasis on energy efficiency, which is consistent with the current trend of the so-called Ecodesign.

Abstract: Safety is currently a widely discussed topic in the design and construction of machine tools. Similarly important is the area of functional safety. This article focuses on determining the mean time to dangerous failure and diagnostic coverage in safety function of machine tools. Legislative requirements (2006/42/EC [1]) and requirements of current standards (EN ISO 12100 [2], EN ISO 13849-1 [3], EN 62061 [4]) are discussed. The current state of calculating the mean time to dangerous failure and diagnostic coverage and the shortcomings of current approach is presented. A new methodology for determining of mean time to dangerous failure and diagnostic coverage is outlined.

Abstract: Findings are presented from the tests of balanced control valve mounted on the steam piping with experimental turbine. The forces applied on the spindle are recorded and compared to design calculation. The forces are evaluated from the pressures on a servo drive piston or they are measured directly using force transducers. The real operational characteristics are compared with characteristics defined for constant inlet pressure.

Abstract: Nowadays, the possibility of applying alternative energy sources is increasingly discussed. In terms of application, a Seebeck thermoelectric generator seems promising for the direct conversion of heat (preferably waste heat) into electricity. In order to increase the performance and thereby the effectiveness of different thermoelectric modules, especially advantageous thermoelectric properties of materials and also innovative design of thermoelectric devices are now solved. However, the achievement of maximum possible performance and operating efficiency is not determined solely by material efficiency and geometric dimensions of thermocouples connected in a thermal battery. It is also necessary to predict an optimum load of the specific source of energy in order to use material design improvements optimally and ensure longer life of thermal batteries. Their manufacturers, except the power input as a “heat consumption” and the maximum power output of a thermal battery (at a certain temperature difference between cold and heated walls), should also declare such load by an appliance, which is optimal for the given type of thermogenerator. The present paper, therefore, proposes a method for determining the optimum load of a thermal battery.

Abstract: A turning knife contacts a work piece during turning. Due to friction, heat is produced proportionally to the turning speed. The resulting temperature influences the quality of the machined surface and wear of the knife. Thus, new machine tools must be developed that minimize the production of unwanted heat. To accomplish this task, a new experimental knife was prepared with thermocouples both built into it and welded to its surface. The measurement process was supplemented by thermovision. Heat flux and surface temperatures were computed from subsurface data using a one-dimensional inverse relationship. The detailed temperature distribution on the surface of the turning knife was determined using a combination of these methods.

Abstract: The study presents a two-dimensional (2D) finite element (FE) model of the fluid-structure-acoustic interaction during self-sustained oscillation of the human vocal folds (VF). The FE model combines the FE models of the VF, trachea and a simplified human vocal tract shaped for phonation of a Czech vowel [a:]. The developed FE model comprises large deformations of the VF tissue, VF contact, fluid-structure interaction (FSI), morphing of the fluid mesh according to the VF motion (Arbitrary Lagrangian-Eulerian approach), solution of unsteady viscous compressible airflow described by the Navier-Stokes equations and airflow separation during the glottis closure. The effect of stiffness and damping of lamina propria, which can be caused by certain VF pathologies, on VF vibrations and produced sound are analyzed. The numerical simulations showed that stiffer lamina propria results in a decrease of the maximum width of glottal opening and in a decrease of the fundamental vibration frequency. Stiffer lamina propria also leads to an increase of maximum of the subglottal pressure and it causes amplitude decrease and flattening of the first and second formant in the spectrum of acoustic pressures. Higher values of lamina propria damping result in the amplitude decrease and flattening of all formants.