305 research outputs found

    Evaluation of room acoustic qualities and defects by use of auralization

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    A review on quantitative ultrasound of fast and slow waves

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    Offering inexpensive, widely available and safe method to evaluate the bone condition as a prevention step to predict bone fracture which caused by Osteoporosis disease makes ultrasound becomes an alternative method beside X-ray based bone densitometry. Conventional quantitative ultrasound (QUS) applies the analysis of attenuation and velocity to estimate bone health with several measurement techniques which analyzes different types of ultrasound waves and bones. However, most of the QUS results still does not match the accuracy of the Dual X-ray absorptiometry due to the interaction of ultrasound and bone microstructure are not fully exploited. The Biot’s theory has predicted that, porous medium like a cancellous bone supporting two types of longitudinal wave known as fast and slow wave which depends on the type of medium travelled. Both experiment and simulation were conducted to investigate the correlation of fast and slow waves individually with a variety of cancellous bone condition. Some of the analysis methods are based on conventional QUS methods. The fast and slow wave relates more to the microstructure of the cancellous bone compared to overall waves. In addition, overall waves had been proven to consist of fast and slow wave and can be separated using Bayesian methods. Overall waves also found to suffer artifact such as phase cancellation and negative dispersion that could cause confusion in analyzing the parameters of ultrasound wave with bone structure. In vivo application based on fast and slow wave analysis is able to produce results based on mass density which can be compared directly and have high correlation with X-ray based bone densitometry. The recent backscattered simulation result indicates that, fast and slow waves can be reflected inside the cancellous bone might offer a new method to evaluate bone especially in crucial skeletal parts

    Evaluation of room acoustic qualities and defects by use of auralization

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    Modelling and optimising micro-nozzle resin injection repair of impacted composites using CFD

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    Resin injection repair is identified to have a gap of knowledge and rigour in the modelling and execution of the process. We outline the strategy of our proposed predictive modelling strategy of ‘reconstruction-simulation-injection’ to simulate real cases to improve repair outcomes. We model the damage zone using Darcy’s law and determine permeability using two methods applied on the Kozeny-Carman equation. We then discuss how we evaluate porosity and detail two proposed methods on reconstructing the porosity field. We verify the model through simulation, and demonstrate verification using a novel comprehensive 2D porosity liquid-ideal gas phase flow model after deriving the analytical solution, which is a contribution of our work. Next, we apply the now-established model to reconstruct real damage cases using the two methods and compare them. We also calibrate the permeability parameter for the model by comparison to a simulation accuracy index, and also calibrate an ultrasonic scanning parameter to minimise reconstruction artefacts as well as the sensitivity of the reconstructed geometry characteristics to scan parameter variations. Then, we validate the model by simulating real repair cases and comparing them to the experimental outcomes, achieving simulation accuracy indices of about 70% or more. We demonstrate the application of the resin injection model by applying resin injection in a proof-of-concept simulation and use it for a case study, and examine the importance of hole configuration, vacuum usage as well as resin flow behaviour between inlet and outlet holes in the context of a given damage area geometry. It is important to maximise the total length of resin flow paths available, through carefully placing inlet and outlet holes, to allow resin to infiltrate the damage zone as much as possible. Vacuum increases the minimum achievable filling, and it is still invariably better to use vacuum with an optimal hole placement, instead of one or the other. In a second case study, we improve the predicted outcome by the model after intentionally changing the hole configuration to maximise resin infiltration, demonstrating that filling can be improved by placing holes intelligently (e.g. by using gathered information on the damage area, together with knowledge of how resin would flow). Using this, we conduct an optimisation study of the resin injection model by first setting up the optimisation strategy and carefully determining the methodology. The optimisation procedure is verified by using one and two degree-of-freedom optimisation cases, with known optima. Then, the optimisation strategy is applied to reconstructed repair cases to demonstrate and assess the efficacy of the optimisation procedure, with average reductions in unfilled volumes of approximately 28% compared to initial configurations.Open Acces

    Investigating the build-up of precedence effect using reflection masking

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    The auditory processing level involved in the build‐up of precedence [Freyman et al., J. Acoust. Soc. Am. 90, 874–884 (1991)] has been investigated here by employing reflection masked threshold (RMT) techniques. Given that RMT techniques are generally assumed to address lower levels of the auditory signal processing, such an approach represents a bottom‐up approach to the buildup of precedence. Three conditioner configurations measuring a possible buildup of reflection suppression were compared to the baseline RMT for four reflection delays ranging from 2.5–15 ms. No buildup of reflection suppression was observed for any of the conditioner configurations. Buildup of template (decrease in RMT for two of the conditioners), on the other hand, was found to be delay dependent. For five of six listeners, with reflection delay=2.5 and 15 ms, RMT decreased relative to the baseline. For 5‐ and 10‐ms delay, no change in threshold was observed. It is concluded that the low‐level auditory processing involved in RMT is not sufficient to realize a buildup of reflection suppression. This confirms suggestions that higher level processing is involved in PE buildup. The observed enhancement of reflection detection (RMT) may contribute to active suppression at higher processing levels
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