Numerical modeling of 1-D transient poroelastic waves in the low-frequency range

Propagation of transient mechanical waves in porous media is numerically investigated in 1D. The framework is the linear Biot's model with frequency-independant coefficients. The coexistence of a propagating fast wave and a diffusive slow wave makes numerical modeling tricky. A method combining three numerical tools is proposed: a fourth-order ADER scheme with time-splitting to deal with the time-marching, a space-time mesh refinement to account for the small-scale evolution of the slow wave, and an interface method to enforce the jump conditions at interfaces. Comparisons with analytical solutions confirm the validity of this approach.Comment: submitted to the Journal of Computational and Applied Mathematics (2008

Sealbhú neamhiomlán na Gaeilge mar chéad teanga sa dátheangachas dealaitheach

Anailís atá sa taighde seo ar fhaisnéis a taifeadadh ó dhátheangaithe óga i gceithre aoisghrúpa sa Ghaeltacht chomhaimseartha. Léiríonn an staidreamh, na samplaí teangeolaíochta agus an anailís sochtheangeolaíochta go n-imríonn sealbhú an Bhéarla mar dhara teanga (T2) tionchar dealaitheach ar shealbhú na Gaeilge mar chéad teanga (T1) i measc chainteoirí óga na Gaeltachta. Is sealbhú neamhiomlán a dhéanann daoine óga ar an nGaeilge mar chéad teanga ach sealbhú iomlán ar an mBéarla mar dhara teanga. De réir mar a théann na cainteoirí in aois, is forás mall a thagann ar shealbhú na Gaeilge agus forás bisiúil tréan ar shealbhú an Bhéarla. Is sna blianta idir aois 4 agus aois 8 is mó atá an chodarsnacht idir shealbhú an dá theanga le sonrú sa taighde seo. Is ag aois 8, thar aon aois eile, atá an acmhainn is ísle ar an nGaeilge i gcomparáid leis an mBéarla, de réir na faisnéise. Cé gur sealbhú neamhiomlán a dhéantar ar an nGaeilge, is teanga mhaitríse ag na faisnéiseoirí i gcónaí í. Leis na bearnaí sa Ghaeilge a líonadh, tarraingíonn na cainteoirí ar fad i ngach aoisghrúpa ar struchtúir Bhéarla. Tá an fhorbairt léacsach ar cheann de phríomhshlata tomhais an taighde agus léiritear ann go gcúitítear easnaimh san fhoclóir bunúsach Gaeilge le focail Bhéarla. Léirítear impleacht an easnaimh sin sa chomhghaolúchán suaithinseach idir sealbhú foclóra Gaeilge agus cumas gramadaí sa Ghaeilge. Léirítear sa taighde freisin go bhfuil an phragmataic Ghaeilge agus an Ghaeilge Thraidisiúnta nach mór mífheidhmiúil go sóisialta i bhfianaise an chódmheasctha aontreoch a bheith fite go dlúth i dteanga mhaitríse na Gaeilge. I bhfianaise fhorfheidhmiúlacht shóisialta an Bhéarla sa saol sár-iarnua-aoiseach, ní léir go bhfuil sé d\u27acmhainn shocheolaíoch ag an bpobal Gaeilge sa Ghaeltacht cur in aghaidh imtharraingt na mórtheanga agus shealbhú neamhiomlán na Gaeilge

An integrated model of rolling tyre vibrations on a smooth road

We describe new results on the vibrations of rolling tyres, aimed at noise prediction for tyres of given design on a smooth road surface. This new approach incorporates our existing models, of smooth road-tyre interaction and belt vibration but includes additional features that are required for real tyre patterns. To this end, the model allows variable tread block size and grooves along the belt circumference; the density and angle of these grooves may also vary laterally. The key innovation is to treat the tyre belt as a laterally stacked series of rings, each of which is equipped with a set of viscoelastic springs around its circumference. It is shown how to use this construction to mimic the details of actual tyre patterns and, in conjunction with existing models, predict belt vibrations. The construction is applied to develop a ring discretisation for a real tyre that shows strong lateral variations. It is shown that the vibration amplitude is concentrated on a set of parallel lines in frequency-wavenumber space and that the tread pattern dictates the occurrence and spacing of these lines. Linkage to a boundary element calculation then allows quantification of the influence of tread parameters on radiated noise. Keywords: Vibration, tread pattern, tyre noise. Copyright © (2011) by the Institute of Noise Control Engineering