## About

61

Publications

31,412

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Introduction

I am a physicist, specialising in acoustics. My main research interests are computational physics and physical acoustics.

Additional affiliations

April 2018 - November 2021

October 2013 - March 2018

**SINTEF Digital**

Position

- Researcher

Description

- In SINTEF's acoustics group, I worked on a wide range of topics, including simulations of waves and vibrations in solids and fluids, traffic auralisation, mapping methods for environmental noise, and deep learning for sound processing and analysis.

## Publications

Publications (61)

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...

This book is an introduction to the theory, practice, and implementation of the Lattice Boltzmann (LB) method, a powerful computational fluid dynamics method that is steadily gaining attention due to its simplicity, scalability, extensibility, and simple handling of complex geometries. The book contains chapters on the method's background, fundamen...

Three issues have long impeded academic research and teaching on well logging. First, real measured data has been hard to come by. This has now been alleviated by Equinor's 2018 release of the Volve Data Village dataset. Among its 5 TB of data, it contains 16.3 GB of various well log data, plots, and analyses. Second, no free and effective software...

It is well-known that vibrating surfaces generate sound waves in adjacent fluids. According to the classical radiation model, the nature of these waves depends on whether the vibration’s phase speed cv is above (supersonic) or below (subsonic) the fluid sound speed cf. The transition between these two domains is known as coincidence. In the superso...

The integrity of cement in cased boreholes is typically evaluated using well logging. However, well logging results are complex and can be ambiguous, and decisions associated with significant risks may be taken based on their interpretation. Cement evaluation logs must therefore be interpreted by trained professionals. To aid these interpreters, we...

Ultrasonic well integrity logging is an important and common procedure for well completion and plug-and-abandonment operations. Typical logging tools employ single-element ultrasound transducers. In medical ultrasound imaging, however, more flexible phased arrays are the standard. This paper presents a first set of experimental results obtained wit...

In the oil and gas industry, pulse echo measurements have for decades been used in cased holes to estimate the properties of the materials on the outside of the pipe. To investigate the methods used to analyse pulse echo measurements from pipes, we use numerical modelling in COMSOL Multiphysics. While 3D models correctly capture the real geometry,...

The Assisted Cement Log Interpretation Project has used machine learning (ML) to create a tool that interprets cement logs by predicting a predefined set of annular condition codes used in the cement log interpretation process.
The development of a cement log interpretation tool speeds up the log interpretation process and enables expert knowledge...

Surface vibrations will generate pressure waves in an adjacent fluid. It is commonly held that these waves radiate away from the surface only if the vibration is supersonic, i.e., faster than the fluid's sound speed. However, multiple articles have shown mathematically that even subsonic vibrations can yield radiating waves. Even so, the physical u...

Some systems in ultrasonic testing can be approximated as two non-parallel plates coupled by a fluid, where leaky Lamb waves propagate in each plate. This work develops a fast and accurate simulation method for such systems by extending methods based on the theory of layered media to non-parallel surfaces. The aim is to determine the presence of ce...

It is well-known that vibrating surfaces generate sound waves in adjacent fluids. According to the classical radiation model, the nature of these waves depends on whether the vibration propagation speed cv is higher than (supersonic) or slower than (subsonic) the fluid sound speed cf. The transition between these two domains is known as coincidence...

A vibrating surface in contact with a solid material will generate P- and S-waves in the solid. When the surface vibration is spatially attenuated, we must take into account that the generated waves are always inhomogeneous. In an isotropic elastic solid, such inhomogeneous waves are attenuated perpendicularly to their direction of propagation. Whe...

The Assisted Cement Log Interpretation project has used machine learning (ML) to create a tool that interprets cement logs by predicting a predefined set of annular condition codes used in the cement log interpretation process.
The development of a cement log interpretation tool speeds up the log interpretation process and enables expert knowledge...

We investigate systems to automatically interpret cement evaluation logs using supervised machine learning (ML). Such systems can provide instant rough interpretations that may then be used as a basis for human interpretation. Here, we compare the performance of two approaches, one previously published and one new. The previous approach is based on...

A fast method is presented for calculating the wavefields from initialized leaky Lamb waves on plates immersed in sufficiently light fluids. The method works by precomputing the dispersion relation and attenuation, and propagating the wavefields in the frequency domain. An angular spectrum approach is used to include leakage into surrounding fluid....

In the petroleum industry, well integrity evaluation is an essential part of maintaining the safety and sustainability of hydrocarbon production. Ultrasonic pulse-echo cased hole logging is a widely used type of measurement for well integrity evaluation. It gives insight on casing condition and cement quality through the use of an ultrasonic transd...

We build systems to automatically interpret cement evaluation logs using supervised machine learning (ML). Such systems can provide instant rough interpretations that may then be used as a basis for human interpretation. Here, we compare the performance of two approaches: A previously published approach based on deep convolutional neural networks (...

The Scandinavian Symposium on Physical Acoustics is arranged every year by the Acoustics group of the Norwegian Physical Society. This 43rd symposium was held at Geilo on January 26–29 2020, and was organised by Geir Pedersen, Erlend Magnus Viggen, and Lars Hoff. It gathered 56 participants holding 26 full presentations as well as two short present...

[The proceedings are found at https://arxiv.org/html/1904.12488.] The 42nd Scandinavian Symposium on Physical Acoustics was held at Geilo, Norway from January 27 to January 30, 2019. It was arranged by the Acoustics and Optics group of the Norwegian Physical Society, and was coordinated by Geir Pedersen and Lars Hoff. The symposium gathered 52 regi...

The 42nd Scandinavian Symposium on Physical Acoustics was held at Geilo, Norway from January 27 to January 30, 2019. It was arranged by the Acoustics and Optics group of the Norwegian Physical Society, and was coordinated by Geir Pedersen and Lars Hoff. The symposium gathered 52 registered participants, holding a total of 31 presentations covering...

Speech enhancement systems aim to improve the quality and intelligibility of noisy speech. In this study, we compare two speech enhancement systems based on deep neural networks. The speech intelligibility and quality of both systems was evaluated subjectively, by a Speech Recognition Test based on Hagerman sentences and a translation of the ITU-T...

After reading this chapter, you will be familiar with how the “lattice units” usually used in simulations and articles can be related to physical units through unit conversion or through dimensionless numbers such as the Reynolds number. Additionally, you will be able to make good choices of simulation parameters and simulation resolution. As these...

After reading this chapter, you will be familiar with the basics of lattice Boltzmann boundary conditions. After also having read Chap. 3, you will be able to implement fluid flow problems with various types of grid-aligned boundaries, representing both no-slip and open surfaces. From the boundary condition theory explained in this chapter together...

After reading this chapter, you will understand the fundamentals of high-performance computing and how to write efficient code for lattice Boltzmann method simulations. You will know how to optimise sequential codes and develop parallel codes for multi-core CPUs, computing clusters, and graphics processing units. The code listings in this chapter a...

After reading this chapter, you will be able to add forces to lattice Boltzmann simulations while retaining their accuracy. You will know how a forcing scheme can be derived by including forces in the derivation of the lattice Boltzmann equation, though you will also know that there are a number of other forcing schemes available. You will understa...

After reading this chapter, you will be familiar with many in-depth aspects of the lattice Boltzmann method. You will have a detailed understanding of how the Chapman-Enskog analysis can be used to determine how the lattice Boltzmann equation and its variations behave on the macroscopic Navier-Stokes level. You will know a number of such variations...

After reading this chapter, you will understand how the lattice Boltzmann equation can be adapted from flow problems to advection-diffusion problems with only small changes. These problems include thermal flows, and you will know how to simulate these as two interlinked lattice Boltzmann simulations, one for the flow and one for the thermal advecti...

After reading this chapter, you will have a working understanding of the equations of fluid mechanics, which describe a fluid’s behaviour through its conservation of mass and momentum. You will understand the basics of the kinetic theory on which the lattice Boltzmann method is founded. Additionally, you will have learned about how different descri...

After reading this chapter, you will understand the fundamentals of sound propagation in a viscous fluid as they apply to lattice Boltzmann simulations, and you will know why sound waves in these simulations do not necessarily propagate according to the “speed of sound” lattice constant. You will have insight into why sound waves can appear spontan...

After reading this chapter, you will have a solid understanding of the general principles of multiple-relaxation-time (MRT) and two-relaxation-time (TRT) collision operators. You will know how to implement these and how to choose the various relaxation times in order to increase the stability, the accuracy, and the possibilities of lattice Boltzman...

After reading this chapter, you will have insight into a number of other fluid simulation methods and their advantages and disadvantages. These methods are divided into two categories. First, conventional numerical methods based on discretising the equations of fluid mechanics, such as finite difference, finite volume, and finite element methods. S...

After reading this chapter, you will be able to expand lattice Boltzmann simulations by including non-ideal fluids, using either the free-energy or the Shan-Chen pseudopotential method. This will allow you to simulate fluids consisting of multiple phases (e.g. liquid water and water vapour) and multiple components (e.g. oil and water). You will als...

After reading this chapter, you will have insight into a large number of more complex lattice Boltzmann boundary conditions, including advanced bounce-back methods, ghost methods, and immersed boundary methods. These boundary conditions will allow you to simulate things like curved boundaries, flows in media with sub-grid porosity, rigid but moveab...

After reading this chapter, you will know the basics of the lattice Boltzmann method, how it can be used to simulate fluids, and how to implement it in code. You will have insight into the derivation of the lattice Boltzmann equation, having seen how the continuous Boltzmann equation is discretised in velocity space through Hermite series expansion...

Recent literature indicates increasing interest in deep neural networks for use in speech enhancement systems. Currently, these systems are mostly evaluated through objective measures of speech quality and/or intelligibility. Subjective intelligibility evaluations of these systems have so far not been reported. In this paper we report the results o...

Poster that shows how one could use Deep Learning for Speech Enhancement purposes. More information and related soundfiles are published at: http://acousticsresearchcentre.no/speech-enhancement-with-deep-learning/

Current methods for ultrasonic pitch-catch well logging use two receivers to log the bonded material outside a single casing. For two casings separated by a fluid, we find by simulation that increasing the number of receivers provides a better picture of the effect of the bonded material outside the second casing. Inverting simulated measurements w...

Cased petroleum wells must be logged to determine the bonding and hydraulic isolation properties of the cement. Ultrasonic logging of single casings has been widely studied and is commercially available. However, ultrasonic logging in multiple-casing geometries is an unexplored topic despite its importance in plug and abandonment operations. Theref...

Cased petroleum wells must be logged to determine the bonding and hydraulic isolation properties of the sealing material and to determine the structural integrity status. Although ultrasonic pitch-catch logging in single-casing geometries has been widely studied and is commercially available, this is not the case for logging in double-casing geomet...

(The proceedings are found at http://arxiv.org/html/1604.01763)
The 39th Scandinavian Symposium on Physical Acoustics was held at Geilo, Norway from January 31 to February 3, 2016. It was arranged by the Acoustics and Optics group of the Norwegian Physical Society, and was coordinated by Ulf Kristiansen and Erlend Magnus Viggen. This year, there w...

Auralisation of outdoor sound has a strong potential for demonstrating the impact of different community noise scenarios. We describe here the development of an auralisation tool for outdoor noise such as traffic or industry. The tool calculates the sound propagation from source to listener using the Nord2000 model, and represents the sound field a...

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 surf...

The lattice Boltzmann (LB) method typically uses an isothermal equation of state. This is not sufficient to simulate a number of acoustic phenomena where the equation of state cannot be approximated as linear and constant. However, it is possible to implement variable equations of state by altering the LB equilibrium distribution. For simple veloci...

As the numerical resolution is increased and the discretisation error decreases, the lattice Boltzmann method tends towards the discrete-velocity Boltzmann equation (DVBE). An expression for the propagation properties of plane sound waves is found for this equation. This expression is compared to similar ones from the Navier-Stokes and Burnett mode...

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 sou...

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....

Acoustic wave propagation in lattice Boltzmann Bhatnagar-Gross-Krook simulations may be analysed using a linearization method. This method has been used in the past to study the propagation of waves that are viscously damped in time, and is here extended to also study waves that are viscously damped in space. Its validity is verified against simula...

The lattice Boltzmann method, a method based in kinetic theory and used for simulating fluid behaviour, is presented with particular regard to usage in acoustics. A point source method of generating acoustic waves in the computational domain is presented, and simple simulation results with this method are analysed. The simulated waves' transient wa...

An introduction is given to the lattice Boltzmann method and its background, with a view towards acoustic applications of the method. To make a larger range of acoustic applications possible, a point source method is proposed. This point source is applied to simulate cylindrical waves and plane waves, and is shown to give a very good numerical resu...

When using music and music-like signals to find the transfer function of a system, problems specific to this type of measurement occur. These problems stem from varied sources, such as the continuous nature of the signal input to the system, the energy distribution of the signal being uneven over different frequencies, noise in the measurement, del...

## Questions

Question (1)

Using compressible CFD methods such as the lattice Boltzmann method, it is easy to set up initial conditions that result in sound waves.

One example is a Gaussian density distribution in an otherwise quiescent fluid, which results in an outgoing sound pulse. Another example is Poiseuille flow initialisation of the flow field in a simple 2D channel with an obstacle; sound waves will propagate until the flow is stabilised.

My intuition suggests that if Ma << 1 then it should be possible to decompose a given initial condition into an incompressible flow part and a sound wave part. For instance, we know for an initial condition with ∇

^{2}p ≠ 0 that it must contain a sound wave component. This must be true because ∇^{2}p = 0 is a defining characteristic of incompressible flow, and because the wave equation tells us that ∇^{2}p ≠ 0 means that a wave will be propagating.Understanding this decomposition would be essential for setting up pure sound simulations or pure flow simulations in compressible CFD methods. However, I have not been able to find anything about this in the literature. Would anyone here have any relevant references for me?