COMSOL’s New Thermoacoustics Interface and Computationally Efficient Alternative Formulations for FEM

Three efficient alternatives to the model in COMSOL’s thermoacoustics interface are presented. The higher efficiency of these models are explained from theory and are demonstrated by means of two examples

Phase-field modeling droplet dynamics with soluble surfactants

Using lattice Boltzmann approach, a phase-field model is proposed for simulating droplet motion with soluble surfactants. The model can recover the Langmuir and Frumkin adsorption isotherms in equilibrium. From the equilibrium equation of state, we can determine the interfacial tension lowering scale according to the interface surfactant concentration. The model is able to capture short-time and long-time adsorption dynamics of surfactants. We apply the model to examine the effect of soluble surfactants on droplet deformation, breakup and coalescence. The increase of surfactant concentration and attractive lateral interaction can enhance droplet deformation, promote droplet breakup, and inhibit droplet coalescence. We also demonstrate that the Marangoni stresses can reduce the interface mobility and slow down the film drainage process, thus acting as an additional repulsive force to prevent the droplet coalescence

Individual variability in the perceptual learning of L2 speech sounds and its cognitive correlates

This study explored which cognitive processes are related to individual variability in the learning of novel phonemic contrasts in a second language. 25 English participants were trained to perceive a Korean stop voicing contrast which is novel for English speakers. They were also presented with a large battery of tests which investigated different aspects of their perceptual and cognitive abilities, as well as pre- and posttraining tests of their ability to discriminate this novel consonant contrast. The battery included: adaptive psychoacoustic tasks to determine frequency limens, a paired-association task looking at the ability to memorise the pairing of two items, a backward digit span task measuring working memory span, a sentence perception in noise task that quantifies the effect of top-down information as well as signal detection ability, a sorting task investigating the attentional filtering of the key acoustic features. The general measures that were the most often correlated with the ability to learn the novel phonetic contrast were measures of attentional switching (i.e. the ability to reallocate attention), the ability to sort stimuli according to a particular dimension, which is also somewhat linked to allocation of attention, frequency acuity and the ability to associate two unrelated events

A new approach to model tyre/road contact

In the Structural Dynamics and Acoustics group at the University of Twente, we aim to develop a quantitative tyre/road noise model. An essential part of this model is an accurate contact algorithm which is fast enough to simulate tyre vibrations up to the acoustic frequencies. In this paper we present a contact algorithm, describing the contact between a tyre and a road surface, which has the potential to be made very fast using the multigrid techniques developed in the field of elasto-hydrodynamic lubrication. For the development of the algorithm a flexible ring model is used to describe the tyre. The friction model is based on Coulomb’s friction. We present (quasi-)static results obtained from the algorithm for various friction coefficients, as well as frictionless results for a rotating tyre. The vibrations of the tyre obtained by this model have been used to calculate the radiated sound field by means of a boundary element program (BEMSYS)

Influence of straw residue cover on the sprouting and yield of spring cereals in direct seeding on clay soil in Southern Finland

In normal years when there is no insufficiency of water, 2-4 t/ha is an adequate amount of straw residue to cereals on soil surface in direct seeding, but if the beginning of growth season is very dry, a thicker straw residue cover is better. The obverse is that sprouting became/becomes lower with thicker residue covers. The need of weed and disease control is obvious, irrespective of the cultivation system, especially if the weather and environmental conditions promote spreading of diseases

Optimised Sound Absorbing Trim Panels for the Reduction of Aircraft Cabin Noise

The EU project FACE (Friendly Aircraft Cabin Environment) aims to improve the environmental comfort in aircraft cabins. As part of this project, this paper focuses on the reduction of noise in aircraft cabins. For modern aircraft flying at cruise conditions, this cabin noise is known to be dominated by turbulent boundary layer noise. The purpose of this work is to reduce the resulting sound pressure levels in the cabin by means of optimised sound absorbing trim panels with quarter-wave resonators. Sound absorption with quarter-wave resonators is mainly realised by dissipation of sound energy as a result of viscous and thermal losses. The viscothermal wave propagation of the air inside the resonators is efficiently and accurately described by the so-called low reduced frequency model. By optimisation of the dimensions of the resonators, desired sound absorption characteristics can be obtained for different specified frequency ranges. This means that the panels can be tailored to different positions in the aircraft cabin with different prevailing sound pressure levels. Results of optimisations for various frequency ranges show that a very good agreement is obtained between the desired and the calculated absorption curves. With the same optimisation procedure, panels have also been tuned for the dominant frequency range of a sound spectrum measured in a modern aircraft. Experimental validation of the numerically predicted optimal configurations, by means of impedance tube measurements, shows that a fairly good agreement is obtained between the numerical and experimental results

Application of Viscothermal Wave Propagation Theory for Reduction of Boundary Layer Induced Noise

Boundary layer induced noise, i.e. noise inside the aircraft resulting from the turbulent boundary layer enclosing the fuselage, is known to dominate air-cabin noise at cruise conditions. In this paper a method is described to design trim panels containing a large number of coupled tubes to effectively reduce this type of noise. The theory of viscothermal wave propagation in tubes, as presented by Tijdeman [3], is discussed. To illustrate the procedure the absorption coefficient for a panel containing a number of non-coupled tubes is calculated. Initial results optimising the tubes’ length and radii for a desired fictive absorption coefficient are presented and prove the applicability of the method

Elliptical side resonators for broadband noise reduction: theory and experiments

Previous research of the authors pointed out that side-resonators can be applied to reduce fan noise. However, the noise reduction capabilities of most resonator geometries, e.g. tube resonators, cylindrical resonators (cylindrical air layers) and circular resonators (disc shaped air layers), are relatively narrow banded. This is disadvantageous in case resonators are used in combination with a noise source that emits broadband noise or tonal noise at varying frequencies (for instance a speed controlled fan). It was found that the choice of the resonator geometry influences the broadband reduction capabilities (circular resonators offering the best broadband reduction capabilities). In the present study, it is investigated to what extent elliptical resonators, consisting of an elliptically shaped air layer, can be used to achieve broadband noise reduction. A semi-analytical model is proposed that describes the wave propagation in the elliptically shaped air layer. This model is connected to the analytical solution for wave propagation in a tube. The dimensions of the elliptical resonator can be optimized for broadband\ud noise reduction using this model. In addition, an experimental setup was built to verify\ud the semi-analytical model of the elliptical resonator