Mechanics and Control
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ISSN 2083-6759
e-ISSN: 2300-7079
Issue Date
2014
Volume
Vol. 33
Number
No. 1
Description
Journal Volume
Mechanics and Control
Vol. 33 (2014)
Projects
Pages
Articles
Stochastic analysis in the acoustics of damped sounds
(2014) Banek, Tadeusz
A stochastic model of sound propagation in damping medium is proposed. It consists of: (1) Ito's stochastic differential equation describing the sound propagation, (2) a potential which models the damping effects. However, due to presence of path integrals this model is elaborate and time consuming, hence inappropriate for numerical simulations and/or model calibrations. To make it simpler we used the classical results of stochastic analysis, Feynman-Kac formula and Girsanov tansformation obtaining easy-to-use computational procedure for practical purposes.
Problems with rectification of hoist supports on the example of a semi-portal bridge-crane with a lattice structure
(2014) Ładecki, Bogusław; Matachowski, Filip
The long period and conditions of operation are the cause of various types of severe damage to cranes used in the steelworks industry. Among the more dangerous and difficult to eliminate crane damage types, there is excess durable deflection of its supports from vertical axis. The object of the study is the semi-portal grab bridge-crane with steel lattice structure, for which deflection of a fixed support was detected that several times exceeded permissible values. For this crane, rectification was performed aimed at bringing fixed supports to the vertical line by stabilisation of the corrected location of the bearing structure of the crane using additional angle braces. The analysis of periodical geodetic measurements of the crane structure showed insufficient effect of the rectification, whereas loss of stability of some rods in the fixed support was detected. The study involved the FEM strength analysis of the crane, which revealed that the applied rectification method caused redistribution of forces in the rods of the fixed support, resulting in the loss of stability of some rods of the support, thus questioning the effectiveness of the rectification method applied.
Damage localization and monitoring of load changes in truss structures
(2014) Mendrok, Krzysztof
In recent years one can observe an increasing interest of the researchers, both from academia and industry, in the development of systems for the monitoring of health structures. The main fields of application for these systems are rotating machinery, aircrafts and other means of group transport and civil engineering structures. Many of the latter, contain truss elements in its structure. That is why detection and possible localization of the fault in such a structures is crucial for the safety of its operation. In this paper the application of modal filtration to damage detection and localization in the truss structures is presented. The results of numerical simulation an laboratory experiment are shown.
Asymptotic formulae for the acoustic self-impedance of simply-supported and simply supported-clamped annular plates
(2014) Rdzanek, Wojciech; Rdzanek, Witold
This study focuses on the sound radiation of a vibrating flat annular plate. The rigorous theoretical considerations deal with some time-harmonic and axisymmetric vibrations. Three different boundary configurations are considered, i.e. one of the plate's edges is simply supported and the other one is clamped or also is simply supported. The active and reactive self-impedance of the system are presented in their Hankel's representations, valid within the whole frequency spectrum. The expressions obtained are transformed to their elementary forms, valid for the high frequencies. Low fluid loading and low internal friction of the plate are assumed. The obtained results are illustrated with sample plots in the domain of acoustic wavenumber. Elementary formulae presented can be useful for further theoretical analysis of the total sound power radiated by an excited flat plate in an acoustic fluid as well as for efficient engineering computations.
Overview of the experimental determination of acoustic flow on the basis of sound intensity measurements
(2014) Weyna, Stefan
A large variety of CFD/CAA hybrid approaches are commonly used today for aero-acoustic engineering applications using equations and the coupling between source and acoustic propagation region. The coupling is usually made using Lighthill 's acoustic analogies and Kirhchoff's acoustic boundary conditions. This paper intends to give answer how the size and shape of the source may be influence on the accuracy of the different coupling methods and their sensitivity. In this way, some experimental investigation was made using sound intensity measurement technique to the graphic presentation of the spatial distribution of the acoustic power flow over various geometrical shapes of structures located in a three-dimensional space. The results of these studies contribute to the theory of sound and general knowledge about the physics of flow acoustic phenomena, especially in the near acoustic field. As a result of research, the visualization analysis of the sound intensity flux in 3D space is shown as flow wave reactions on the presence of obstacles with different shapes. The results of vector flow fields around a rectangular and circular plate, over the cavity and inside a ducts are shown. The visualization of acoustic power flow in real-life acoustic fields can explain many particular energetic acoustic effects like scattering, vortex flow in shielding area, etc., concerning area where it is difficult to make numerical analysis.