Acoustic multipole sources from the Boltzmann equation

By adding a particle source term in the Boltzmann equation of kinetic theory, it is possible to represent particles appearing and disappearing throughout the fluid with a specified distribution of particle velocities. By deriving the wave equation from this modified Boltzmann equation via the conservation equations of fluid mechanics, multipole source terms in the wave equation are found. These multipole source terms are given by the particle source term in the Boltzmann equation. To the Euler level in the momentum equation, a monopole and a dipole source term appear in the wave equation. To the Navier-Stokes level, a quadrupole term with negligible magnitude also appears.Comment: 5 pages, to be published in Proceedings of the 36th Scandinavian Symposium on Physical Acoustic

Acoustic multipole sources for the lattice Boltzmann method

By including an oscillating particle source term, acoustic multipole sources can be implemented in the lattice Boltzmann method. The effect of this source term on the macroscopic conservation equations is found using a Chapman-Enskog expansion. In a lattice with q particle velocities, the source term can be decomposed into q orthogonal multipoles. More complex sources may be formed by superposing these basic multipoles. Analytical solutions found from the macroscopic equations and an analytical lattice Boltzmann wavenumber are compared with inviscid multipole simulations, finding very good agreement except close to singularities in the analytical solutions. Unlike the BGK operator, the regularized collision operator is proven capable of accurately simulating two-dimensional acoustic generation and propagation at zero viscosity

An investigation of the relationship between texture and tyre/road noise for different types of road surfaces and passenger car tyres

-The texture of the road surface has a major influence on the generation of tyre/road noise. For dense surfaces this may be the most important factor besides the tyre characteristics themselves. Throughout several projects, SINTEF has performed measurements of the tyre/road noise of a wide range of passenger car tyres on different types of road surfaces. These road surfaces are both normally used road surfaces in Norway and road surfaces on test areas. In this paper, some results from the analysis of the relationship between the texture levels and the tyre/road noise levels are presented. In previous investigations it has been found that there is a positive correlation between texture levels at longer wavelengths (like 20–200 mm) and the noise levels, while there is a negative correlation between texture levels at shorter wavelengths (below 8 mm) and the noise levels. In our analysis, the former is confirmed and the latter is found true for some data sets, but not for others. The analysis also shows that the noise from different tyres has a similar relationship with texture, even if the overall noise levels differ

An investigation of the relationship between texture and tyre/road noise for different types of road surfaces and passenger car tyres

-The texture of the road surface has a major influence on the generation of tyre/road noise. For dense surfaces this may be the most important factor besides the tyre characteristics themselves. Throughout several projects, SINTEF has performed measurements of the tyre/road noise of a wide range of passenger car tyres on different types of road surfaces. These road surfaces are both normally used road surfaces in Norway and road surfaces on test areas. In this paper, some results from the analysis of the relationship between the texture levels and the tyre/road noise levels are presented. In previous investigations it has been found that there is a positive correlation between texture levels at longer wavelengths (like 20–200 mm) and the noise levels, while there is a negative correlation between texture levels at shorter wavelengths (below 8 mm) and the noise levels. In our analysis, the former is confirmed and the latter is found true for some data sets, but not for others. The analysis also shows that the noise from different tyres has a similar relationship with texture, even if the overall noise levels differ

Pyintegrity: An Open-Source Toolbox for Processing Ultrasonic Pulse-EchoWell Integrity Log Data

Many companies offer similarly designed wireline tools using ultrasonic pulse-echo measurements toevaluate barrier integrity in cased-hole wells. While these tools provide very similar data, differentcompanies process their data using different algorithms, typically to estimate the pipe wall thickness andthe outer material's acoustic impedance. While the algorithms themselves are public, no openly availablesoftware implementations are available. Therefore, we have developed an open-source software toolboxcalled Pyintegrity implementing many of these algorithms. In this article, we demonstrate Pyintegrity byapplying its algorithm implementations to a well integrity log from the open Volve Data Village dataset. Ourresults demonstrate that it is quite possible to process data recorded by a particular tool using processingalgorithms developed for use with other similar tools, and we find a good correspondence between thedifferent processing algorithms. Comparing the results produced by the different processing algorithms letsus confidently identify certain features in some of the results as processing artifacts that do not reflect thephysical state of the well.acceptedVersio

The lattice Boltzmann method: Fundamentals and acoustics

The lattice Boltzmann method has been widely used as a solver for incompressible flow, though it is not restricted to this application. More generally, it can be used as a compressible Navier-Stokes solver, albeit with a restriction that the Mach number is low. While that restriction may seem strict, it does not hinder the application of the method to the simulation of sound waves, for which the Mach numbers are generally very low. Even sound waves with strong nonlinear effects can be captured well. Despite this, the method has not been as widely used for problems where acoustic phenomena are involved as it has been for incompressible problems. The research presented this thesis goes into three different aspects of lattice Boltzmann acoustics. Firstly, linearisation analyses are used to derive and compare the sound propagation properties of the lattice Boltzmann equation and comparable fluid models for both free and forced waves. The propagation properties of the fully discrete lattice Boltzmann equation are shown to converge at second order towards those of the discrete-velocity Boltzmann equation, which itself predicts the same lowest-order absorption but different dispersion to the other fluid models. Secondly, it is shown how multipole sound sources can be created mesoscopically by adding a particle source term to the Boltzmann equation. This method is straightforwardly extended to the lattice Boltzmann method by discretisation. The results of lattice Boltzmann simulations of monopole, dipole, and quadrupole point sources are shown to agree very well with the combined predictions of this multipole method and the linearisation analysis. The exception to this agreement is the immediate vicinity of the point source, where the singularity in the analytical solution cannot be reproduced numerically. Thirdly, an extended lattice Boltzmann model is described. This model alters the equilibrium distribution to reproduce variable equations of state while remaining simple to implement and efficient to run. To compensate for an unphysical bulk viscosity, the extended model contains a bulk viscosity correction term. It is shown that all equilibrium distributions that allow variable equations of state must be identical for the one-dimensional D1Q3 velocity set. Using such a D1Q3 velocity set and an isentropic equation of state, both mechanisms of nonlinear acoustics are captured successfully in a simulation, improving on previous isothermal simulations where only one mechanism could be captured. In addition, the effect of molecular relaxation on sound propagation is simulated using a model equation of state. Though the particular implementation used is not completely stable, the results agree well with theory

Acoustic multipole sources for the lattice Boltzmann method

By including an oscillating particle source term, acoustic multipole sources can be implemented in the lattice Boltzmann method. The effect of this source term on the macroscopic conservation equations is found using a Chapman-Enskog expansion. In a lattice with q particle velocities, the source term can be decomposed into q orthogonal multipoles. More complex sources may be formed by superposing these basic multipoles. Analytical solutions found from the macroscopic equations and an analytical lattice Boltzmann wavenumber are compared with inviscid multipole simulations, finding very good agreement except close to singularities in the analytical solutions. Unlike the BGK operator, the regularized collision operator is proven capable of accurately simulating two-dimensional acoustic generation and propagation at zero viscosity

Speech Enhancement with Deep Learning

publishedVersio