Journal of Engineering and Thermal Sciences
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Method of active synthesis of discrete fixed mechanical systems
Get PDFIn this work the method of active synthesis of mechanical systems in accordance with the desired frequency spectrum has been formulated and formalised. Active synthesis of a proportional regulation system has been performed in accordance with the method formulated and a verification of the correctness of the results has been carried out
Determining the torsional natural frequency of underframe of off-road vehicle with use of the procedure of operational modal analysis
Get PDFThe paper presents the example of use of the operational modal analysis procedure (OMA) to set the torsional natural frequency of underframe of off-road vehicle. Determining the natural frequency for the object of this shape is possible with the output-only data and using the peak picking technique
Wood products automatic identification based on fingerprint method
Get PDFThis paper introduces utilization of improved fingerprint method based on wood surface visual parameters for increasing wooden products identifiability for instance in wood industry and especially for automation lines. Usually the traceability of the objects in the production chain is achieved by using identification code based systems, for example visual codes, which are marked in one position and are read by a machine vision system in another position. In many cases the possible maximum readability can be quite hard to achieve due to marking problems or code background visual problems. In wood industry traceability case it is possible to exploit the fact that wood is a biological material and therefore its surface is quite volatile, each code background is unique. The parameters describing the wood branches, grain or some other specific features can be used for matching for example the saw material in different production line positions. Presuming the conditions for the vision system in the consecutive positions are similar and no processing is applied to the traceable objects between those positions, then it is possible to match most of the objects and therefore increase automatic traceability and identification of the products in different positions of the production chain
Synthesis as designing of mechatronic vibrating mixed systems
Get PDFIn this paper synthesis of mechatronic vibrating mixed systems has been studied. Mechatronic structures have been built from mechanical discrete systems connected to piezoelectric actuator and external Lx Rx Cx network. By use of non-dimensional transformations mechatronic mixed structures (branched and cascade part), which must comply with the dynamical properties in the form of frequency spectrum: resonant and anti-resonant frequencies, have been received. The problem has been presented on few different examples of four degrees of freedom
Characterization of mechanical properties by inverse technique for composite reinforced by knitted fabric. Part 1. Material modeling and direct experimental evaluation of mechanical properties
Get PDFPolymer composites reinforced with knitted fabrics are materials with high potential in aerospace and machine building industries [1-6]. Such materials are mechanically non-linear with a high dynamic energy absorption capacity. Accurate prediction of mechanical properties is of great importance for these materials when considering their applications in novel structures. Three different approaches were implemented to this aim in the reported research work and the results are presented in: Part 1- numerical structural modeling (FEM using Solid Works) based on application of experimentally measured mechanical and geometrical properties of reinforcement and matrix, accompanied by direct measurements of mechanical properties; Part 2 - application of inverse method for characterization of mechanical properties by means of vibration modal analysis. The goal was to obtain and predict mechanical behavior of a weft knitted fabric reinforced multilayered composite plate. Results of all three approaches were compared and discussed
Hopf bifurcation and stability analysis of flexible rotor-bearing system
Get PDFAnalytical model of a long bearing was used to study the self-excited vibration of a single disc flexible rotor-bearing system on sliding bearing support. A shooting method was applied to track and acquire periodic solution of flexible rotor system after the Hopf bifurcation. Stability of periodic solution was analyzed on the basis of Floquet theory. Gas film eddying, oscillation and other nonlinear features were considered. High-speed air hybrid bearing test-bed was used to verify gas film oscillation arising from coupling between natural frequency and gas film eddying frequency. The “bounded” nature of chaotic vibration and the process of rubbing caused by instability of air film were observed. Finally, a distinguishing criterion named “practical stability” was provided
An adaptive lifting scheme and its application in rolling bearing fault diagnosis
Get PDFVibration signals of rolling bearings usually are corrupted by heavy noise and it is very important to extract fault features from such signals. In this paper, an adaptive lifting scheme is proposed for fault diagnosis of rolling bearings. The kurtosis indexes of scale decomposition signals are used as the optimization indicator to select the prediction operator and update operator, which can adapt to the dominant signal characteristics, and reveal the fault feature. Fourier transform is adopted to remove the overlapping signal frequency components at every scale decomposition signal. Experimental results confirm the advantage of the adaptive lifting scheme over lifting scheme for feature extraction, and the typical features of rolling bearing in time domain are successfully extracted by adaptive lifting scheme
Investigation of straw layer movement over the walker surface
Get PDFStraw layer movement over the walker surface has been examined by measuring characteristics of elasticity and viscosity of the straw layer. For this purpose a visco-elastic model has been introduced. The examined process is represented by two stages: the first one is associated with the elastic deformation of the straw while the walker section moves upwards, and the straw layer laying on its surface is subjected to compression. Whereas the second stage involves a free throw of straw after the takeoff from the walker surface, and after the free throw, their contact onto the walker surface. The method of successive steps was used for the analysis of the movement process. The proposed model can be applied for modeling complex nonlinear characteristics of the straw layer movement by employing linear elastic and viscous elements through selection of their equivalent coefficients. Measurement of the elastic and viscous characteristics of the straw layer by their equivalent coefficients enabled to calculate rational rotation angles of the walker crankshaft at the takeoff ωt1 of the layer from the walker surface and contact ωt3 to the surface provided that during each period of crankshaft rotation a straw layer undergoes an impact. It was determined that straw movement is mainly dependent on the thickness, moisture content and viscosity of the straw layer. The takeoff of the thicker straw layer from the walker surface is delayed, since after the impact duration of its deformation is longer, resulting in a shorter time of free throw. Wet straw layer is less elastic, resulting in its longer movement jointly with the walker section, and the height of the free throw is smaller resulting in less favorable conditions for grain penetration when compared to the dry straw
Concept and methods of adaptive vibration protection and stabilization
Get PDFThe paper considers the concept, the general formulation of problems and the algorithms of adaptive real-time control of multivariate vibration protection and stabilization of multi-axis chassis position in space, which provide in general case the solution of the problems of oscillations moderation and motion stabilit
Thermaly mechanisms in electrostaticaly actuated microelectromechanical structures
Get PDFThe paper reports results of the performed research work related to the deformations and stability of Al-Si parallel-plate electrostatic microactutors fabricated on silicon-on-insulator (SOI) wafer and subjected to uniform temperature changes. Presented research includes measurements of the deformation of Si beam with deposited Al thin-film microstructures as a function of temperature changes using Electronics Speckle Pattern Interferometry (ESPI) and a custom-built thermal module that is covered by optical beam splitter window to allow optical acces