2,183 research outputs found
Behaviour of ultrasonic waves in porous rigid materials: anisotropic Biot-Attenborough model
No full textThe anisotropic pore structure and elasticity of cancellous bone cause wave speeds and attenuation in cancellous bone to vary with angle. Anisotropy has been introduced into Biot theory by using an empirical expression for the angle-and porosity-dependence of tortuosity. Predictions of a modified anisotropic Biot–Attenboorugh theory are compared with measurements of pulses centred on 100 kHz and 1 MHz transmitted through water-saturated porous samples. The samples are 13 times larger than the original bone samples. Despite the expected effects of scattering, which is neglected in the theory, at 100 kHz the predicted and measured transmitted waveforms are similar
A review of the state of art in applying Biot theory to acoustic propagation through the bone
No full textUnderstanding the propagation of acoustic waves through a liquid-perfused porous solid framework such as cancellous bone is an important pre-requisite to improving the diagnosis of osteoporosis by ultrasound. In order to elucidate the propagation dependence upon the material and structural properties of cancellous bone, several theoretical models have been considered to date, with Biot-based models demonstrating greatest potential. This paper describes the fundamental basis of these models and reviews their performance
Discours de M. Biot; Réponse de M. Guizot.
No full textSéance de l'académie française du 5 février 1857Discours de M. Biot prononcé a sa réception à l'Académie française le 5 février 1857Discours de M. Guizot en réponse au discour prononcé par M. Biot pour sa réception à l'Académie française le 5 février 1857Europeana-GoogleBook
Wave propagation in stereo-lithographical (STL) bone replicas at oblique incidence
No full textComparisons between predictions of a Biot-Allard model allowing for angle-dependent elasticity and
angle-and-porosity dependent tortuosity and transmission data obtained at normal incidence on
water-saturated replica bones are extended to oblique incidence. The model includes two parameters
which are adjusted for best fit at normal incidence. Using the same parameter values, it is found that predictions
of the variation of transmitted waveforms with angle through two types of bone replica are in
reasonable agreement with data despite the fact that scattering is not included in the theory
Lettre de M. le duc d'Aumont-Villequier sur la chambre où était le zodiaque de Denderah (Égypte)
No full textBiot Jean-Baptiste. Lettre de M. le duc d'Aumont-Villequier sur la chambre où était le zodiaque de Denderah (Égypte). In: Comptes rendus des séances de l'Académie des Inscriptions et Belles-Lettres, 2ᵉ année, 1858. pp. 121-122
Studies into the detection of buried objects (particularly optical fibres) in saturated sediment. Part 3: experimental investigation of acoustic penetration of saturated sediment
No full textThis report is the third in a series of five, designed to investigate the detection oftargets buried in saturated sediment, primarily through acoustical or acoustics-relatedmethods. Although steel targets are included for comparison, the major interest is intargets (polyethylene cylinders and optical fibres) which have a poor acousticimpedance mismatch with the host sediment. This particular report provides a briefhistorical overview of sediment propagation models has been presented. Two theorieshave been covered: the Biot-Stoll theory; and wave scattering from random roughsurfaces. The debate surrounding the observations of, so-called, anomalous acousticpenetration has also been discussed.This series of reports is written in support of the article “The detection by sonar ofdifficult targets (including centimetre-scale plastic objects and optical fibres) buriedin saturated sediment” by T G Leighton and R C P Evans, written for a Special Issueof Applied Acoustics which contains articles on the topic of the detection of objectsburied in marine sediment. Further support material can be found athttp://www.isvr.soton.ac.uk/FDAG/uaua/target_in_sand.HTM
Vibration analysis of super-yachts: Validation of the Holden Method and estimation of the structural damping
No full textThe hull excitation generated by marine propellers constitutes one of the most significant vibration sources affecting comfort on passenger ships. Consequently, the evaluation of the propeller-generated excitation through reliable numerical tools during the preliminary stage of ship design is fundamental. The Holden Method (HM) is an empirical tool utilized to calculate the propeller-induced pressure distribution on a ship hull. The present paper validates the HM, which is applied to a twin-screw, 54-m super-yacht. Finite Element Analysis (FEA) is used to benchmark the HM numerical predictions against a set of full-scale vibration measures. The outcomes show that the magnitude of the propeller-induced dynamic excitation predicted by the HM is overestimated. Thereafter, the calibrated propeller-induced forces and the diesel engine excitation are applied to the FE model to perform a series of forced vibration analyses and estimate the global structural damping coefficient of the super-yacht. The study highlights the necessity of developing new empirical methodologies, analogous to the HM, to be applied to modern small luxury vessels
Mémoire sur les lois générales de la double réfraction et de la polarisation dans les corps régulièrement cristallisés : lu à l'Academie Royale des Sciences, le 29 mars 1819
No full textpar M. Biot ..
Vibration analysis for the comfort assessment of superyachts
No full textComfort levels on modern superyachts have recently been the object of specific attention of the most important Classification Societies, which issued new rules and regulations for evaluating noise and vibration maximum levels. These rules are named “Comfort Class Rules” and set the general criteria for noise and vibration measurements in different vessels’ areas, as well as the maximum noise and vibration limit values. As far as the vibration assessment is concerned, the Comfort Class Rules follow either the ISO 6954:1984 standard or the ISO 6954:2000. After an introduction to these relevant standards, the authors herein present a procedure developed to predict the vibration levels on ships. This procedure builds on finite element linear dynamic analysis and is applied to predict the vibration levels on a 60 m superyacht considered as a case study. The results of the numerical simulations are then benchmarked against experimental data acquired during the sea trial of the vessel. This analysis also allows the authors to evaluate the global damping ratio to be used by designers in the vibration analysis of superyachts
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