Showing papers in "The Open Acoustics Journal in 2009"

Elastic and Acoustic Properties of Heavy Rare-Earth Metals

Abstract: In this paper, ultrasonic properties like ultrasonic attenuation, sound velocities, acoustic coupling constants and thermal relaxation time have been studied in hexagonal structured metals Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er) and Thulium (Tm) along unique axis at room temperature For the evaluations of ultrasonic properties, secondand thirdorder elastic constants have been computed also The peculiar behavior of these metals is found at 55° due their least thermal relaxation time and highest Debye average velocity Dy is more ductile, stable, perfect metal in comparison to other chosen metals due to its lowest value of attenuation So we predict that Dy is most suitable lanthanide metals for material science and engineering

Lamb Wave Detection of Delaminations in Large Diameter Pipe Coatings

Abstract: This paper describes combined experiments and simulations to automate the extraction of ultrasonic guided wave mode arrivals in order to gain quantitative information about large-diameter pipeline coatings. The dynamic wavelet fingerprint technique (DWFT) is used to show differences between unknown coatings as well as to identify the presence of delamination and grinding flaws within the Lamb wave propagation path. Combined with complex multi-layered models to help interpret the guided wave feature changes, this extraction algorithm can be used for the detection of hidden flaws under a variety of protective coatings without having to disturb the coating or pipeline flow. High-resolution supercomputer simulations are developed using the elastodynamic finite integration technique (EFIT) accounting for the 3D interaction of realistic Lamb wave beams with finite-sized coating delaminations.

FEM/SEA Hybrid Method for Predicting Mid and High Frequency Structure-Borne Transmission

Abstract: Launch Vehicles are subject, at lift-off and during flight ascent, to acoustic and aeroacoustic loads, which are random in nature. Because electronic units are very sensitive to mid and high frequency loads, it is important to numerically predict and specify the vibration levels to be applied to units for qualification test. The general objective of the activity presented in this paper is to develop a methodology to predict mid and high frequency structure-borne transmissions in launch vehicles. As the loads of interest are random, it has been chosen to investigate energy-based modeling approaches, combined with the Finite Element Method. For energy-based modeling, the structure is divided into subsystems. For high frequency predictions, the purely numerical Power Injection Method, derived from Statistical Energy Analysis, is used to estimate the Coupling Loss Factor between structural subsystems. For the mid frequency predictions, an approach close to Statistical Energy Analysis, called Statistical Energy Analysis-Like (SEA-like), is investigated. In this approach, a relation between total energies of subsystems and input powers is established, by identifying a matrix composed of Energy Influence Coefficients. The objective of the study is to establish the methodology to compute with accuracy, using the Finite Element Method, Coupling Loss Factors and Energy Influence Coefficient. It is shown that the excitation of subsystems by 'Rain on the Roof' loads defined by the 'Influence Circle' and the Optimal Latin Hypercube methods provide accurate coupling data. A validation of the methodology on academic and industrial cases is presented.

Simulations of Ultrasonographic Periodontal Probe Using the Finite Integration Technique

Abstract: Periodontal disease is one of the most pervasive dental diseases in older adults. It involves the loss of connective tissue attachment with subsequent destruction of tooth-supporting bone, leading to loss of teeth. Periodontal pocket depth is currently measured with an invasive manual probe, but adapting diagnostic ultrasound to this purpose can avoid the pain and inaccuracy inherent in manual probing. In this paper, 3D simulations of ultrasonic periodontal probe measurements are described, using a parallel finite integration technique which is adaptable enough to create realistic anatomical geometries. The outputs of the simulation include 3D pressure values distributed throughout the periodontal anatomy, 2D vertical cross sections of the acoustic pressure waves, and the pressure across the face of the transducer which is used to synthesize the ultrasonic echo. Experimental comparison with a simple phantom is also shown. Lastly, the energy values for different simulations are calculated from the 3D pressure values to describe the amount of energy reaching different zones, especially the junctional epithelium. The simulations as well as the energy studies show that only a small portion of the ultrasonic energy is reaching the junctional epithelium, and so sophisticated mathematical techniques are required to ultrasonically measure pocket depth.

Vibrations of Elastically Restrained Circular Plates Resting on Partial Winkler Foundation

Abstract: This work describes a study of vibration characteristics of thin circular plates with elastic edge support and resting on partial Winkler-type elastic foundation. The foundation is described by the Winkler model, which is called as single parameter foundation. The exact analytical method is used to derive the frequency equation of the circular plate with elastic edge support-conditions and resting on partial elastic foundation system. Parametric investigations on the behavior of circular plates with elastic edge support and resting on partial elastic foundation have been carried out with respect to various values of transverse stiffness parameter, foundation parameter for a variety of boundary conditions. Extensive data is tabulated so that pertinent conclusions can be arrived at on the influence of translational edge restraint, and the foundation modulus parameters of the Winkler foundation on the natural frequencies of uniform isotropic circular plates. A comparison of the results obtained here in this paper with those available in the literature shows an excellent agreement.

Comparative Study of Optimal Design Strategies of Reverberators

Abstract: Artificial reverberator is a key element in spatial audio reproduction. This paper compares various optimal design strategies of artificial reverberators for room response simulation. From the comparison, it is hoped that guidelines for design of natural-sounding reverberators can be found. Infinite impulse response (IIR) filters such as allpass filters or comb filters are used as building blocks for the design. Early reflections of room responses are modeled by three different approaches: the traditional image method, the exponential truncation method, and network approximation method. On the other hand, comb/nested allpass filter networks are exploited for modeling late reverberations, with parameters predetermined by a genetic algorithm (GA)-based procedure. Up/down-sampling and spectral band replication (SBR) techniques are also employed to save memory storage and recover the lost high frequency portion of the reverberation. Subjective listening tests were conducted to compare the proposed artificial reverberator modules. The test results revealed that the reverberator in which early reflections are modeled by network approximation and late reverberations are modeled by comb/nested allpass filter network is superior in delivering natural-sounding reverberation among all methods.

Adaptive BEM for Low Noise Propeller Design

Abstract: A potential-based Boundary Element Method is presented for the aerodynamic and acoustic design of propel- lers at on- and off-design point conditions. Using an adaptive method, a family of airfoil sections is selected to produce the required performance (thrust, torque and efficiency versus advance ratio) at different cruise flight levels. Climb condi- tions are also considered in order to check the off-design point performance. Once the available airfoil data have been stored in a database, the code processes the families of airfoils to generate a complete geometry for a propeller of the specified performance with an optimized noise emission. The computational scheme adjusts the blade geometry (radial distribution of chord, local sweep angle and thickness) under the control of an optimization routine. The geometric data and pressure distribution are then used in the acoustic calculation, based on the Ffowcs Williams-Hawkings equation. Re- sults are presented demonstrating the application of the technique and the resulting aerodynamic performance and noise output.

Ocean Ultrasonic Shear and Compression Viscosities

Abstract: A comprehensive description of ocean molecular flow and deformation is provided with the help of hydrodynamic and ultrasonic principles. Hydrodynamic computation of true or natural viscosities shows that ocean shear viscosity (� G), compression viscosity (� K), and extensional viscosity (� E) are interrelated. There are no experimental methods available for the in situ measurement of these viscosities. Sound absorption coefficients (� obs) allow to know the ultrasonic shear (� UG), compression (� UK), and longitudinal (� L) viscosities, which decrease with increasing frequency and increase with increasing temperature, the flow activation energies having nearly equivalent values; pressure (depth) increase/decrease them at low/high frequencies. The viscosities � * UG, � * UK, � * L are approached at about 1000 KHz. They decrease with temperature and pressure, and increase with salinity. The � *UG becomes equal to the true shear viscosityG at the viscosity ratio � = � UK / � UG = 0.