4,048 research outputs found
Wave reflection and transmission due to defects in infinite structural waveguides at high frequencies
No full textIn waveguide structures, waves may be partially reflected by local non-uniformities such as cracks and other defects. The reflection and transmission characteristics associated with the presence of a discontinuity may be used, in principle, to give some indication of both the location and size of the defect. A combined spectral element and finite element (SE/FE) method has been used previously to investigate the effects of local non-uniformities at relatively low frequencies. However, for analysis at higher frequencies, where complex deformation of the waveguide occurs, it is necessary to extend this approach. Such high frequency analysis is necessary if small defects are to be located within the waveguide cross-section. In order to investigate wave propagation at higher frequencies, a combined spectral super element and finite element (SSE/FE) method is presented. This method allows the transmission, reflection and wave conversion at discontinuities to be determined for complex waveguides. As an example of the use of this method, wave reflection and transmission in rails are estimated at frequencies between 20 and 40 kHz for various notional sawcut-like defects of progressively increasing size. This shows the feasibility of the approach for realistic waveguides. However, from these simulations it is shown that defects have to be quite large before they can be detected using a single transducer position on the rail cross-section using train-induced vibratio
Decay rates of propagating waves in railway tracks at high frequencies
No full textIn order to understand long range wave propagation in railway tracks, it is required to identify how far vibrations can travel along a rail. To answer this question, the attenuation characteristics of the main propagating waves are required as a function of distance. In this work, decay rates of propagating waves in railway tracks are investigated for frequencies up to 80 kHz. A numerical method called the wavenumber finite element (WFE) method is utilized to predict decay rates for a rail on a continuous foundation. Damping is introduced in this track model by the material damping in the rail and in the foundation. In order to improve the simulated results, the frequency dependent damping loss factor of a rail has been measured up to 80 kHz on short rail samples. From this simulation, the relative importance of the rail and support damping for the long range wave propagation is determined. In order to validate the simulated results, a field measurement has been performed on an operational railway track. From this experiment, train-induced rail vibrations have been acquired for several running trains travelling over a long section of rail. The measured results are presented for comparison with the output of the simulations and good agreement is found between them.<br/
Investigations of propagating wave types in railway tracks at high frequencies
No full textAt low frequencies waves propagate in a rail as bending, extensional or torsional waves. At higher frequencies, above about 1.5 kHz, the rail cross-section deforms and many higher order wave types exist. This cross-section deformation has to be taken into account for an accurate evaluation of the dispersion properties at high frequencies. Simulation results in the literature show that a multiplicity of wave modes is possible within this high-frequency range. In this work, wave types that propagate primarily through separate regions of the rail cross-section are investigated for frequencies up to 80 kHz. Two numerical methods are applied to obtain the dispersion properties for a railway track model including rail pads as a continuous foundation. These are a conventional finite element (FE) method and a wavenumber finite element (WFE) method, each of which can include the effects of cross-sectional deformation. In order to validate the predicted results, experiments were performed on a short test track using an impact hammer and accelerometers. Additional measurements used piezoceramic transducers to excite the rail at higher frequencies. The results are compared with simulations in terms of the group velocity and they present very good agreement. From this comparison, it is identified which wave types predominantly propagate on various regions of the rail cross-section
Direct numerical simulation of turbulent Couette-Poiseuille flow with zero skin friction
No full textThe near-wall scaling of mean velocity U(y) is addressed for the case of zero skin friction on one wall of a fully turbulent channel flow. The present DNS results can be added to the evidence in support of the conjecture that U is proportional to √yw in the region just above the wall at which the mean shear dU/dy = 0
Scaling and intermittency in ocean turbulence: analysis of coastal water optical properties and sea surface temperature (SST)
No full textWe consider here some scaling and intermittency properties of oceanic turbulence, with a general aim of considering the impact of turbulence on the bio-optical dynamics. For that purpose, we tried two different approaches, using in situ and satellite data. For the in situ study we adopted one dimensional and for the satellite two dimensional approaches. Different techniques such as Fourier power spectrum, Empirical mode of decomposition (EMD), Hilbert spectral analysis (HSA) have been used for analyzing the intermittency characteristics of the in situ data. For analyzing the multi-scale properties of the satellite images, we have considered Structure functions (SF) and Fourier power spectrum (1D and 2D). The general objective is to understand the multi-scale oceanic variability using scaling tools developed in the field of intermittent turbulence studies
Behavioural Reactivity and Real Time Programming in XML: Functional Programming meets SMIL animation
No full textXML and its associated languages are emerging as powerful authoring tools for multimedia and hypermedia web content. Furthermore, intelligent presentation generation engines have begun to appear, as have models and platforms for adaptive presentations. However, XML-based models are limited by their lack of expressiveness in presentation and animation. As a result, authors of dynamic, adaptive web content must often use considerable amounts of script or code. The use of such script or code has two serious drawbacks. First, such code undermines the declarative description possible in the original presentation language, and second, the scripting/coding approach does not readily lend itself to authoring by non-programmers. In this paper we describe a set of XML language extensions, inspired by features from the functional programming world, which are designed to widen the class of reactive systems which could be described in languages such as SMIL. The features which we discuss extend the power of declarative modeling for the web by allowing the introduction of web media items which may dynamically react to continuously varying inputs, both in a continuous way and by triggering discrete, user-defined, events. The two extensions described herein are discussed in the context of SMIL Animation and SVG, but could be applied to many XML-based languages
Early Prosthetic Complications After Uncemented Austin Moore and Cemented Thompson Hemiarthroplasty. A Multicentre Review of 1118 Patients
No full textIntroduction & Aims\ud
For displaced intracapsular fractures of the femoral neck the most frequently employed hemiarthroplasty in Australia is the Uncemented Austin Moore (UAM) prosthesis.\ud
Despite concerns regarding the poor functional outcome and increased revision rates associated with the UAM prosthesis, apprehension about the systemic effects of PMMA acrylic cement implantation in the elderly patient continues to influence prosthesis selection.\ud
This study examines the incidence early prosthesis related complications after Uncemented Austin Moore (UAM) and Cemented Thompson (CT) hemiarthroplasty implantation for the management of femoral neck fractures
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