Biomedical subjects

D Weaire

Publications and source records attributed to D Weaire.

11 recordsLinked to original sources

PubMed2006

The response of 2D foams to continuous applied shear in a Couette rheometer.

The continuum model that has reproduced the experimental observation of exponential shear localisation for straight-edge boundary conditions is adapted to the case of circular geometry. Essentially the same effect is found. However, the scenario of possible velocity profiles is much richer. Our calculations elucidate many recent experiments qualitatively and suggest further extensions of them. Various limits are analysed. In particular, the localisation length vanishes as the inner-boundary velocity tends to zero.

Algorithms↗

PubMed2006

Two-dimensional foam rheology with viscous drag.

We formulate and apply a continuum model that incorporates elasticity, yield stress, plasticity, and viscous drag. It is motivated by the two-dimensional foam rheology experiments of Debregeas et al. [Phys. Rev. Lett. 87, 178305 (2001)10.1103/PhysRevLett.87.178305] and Wang et al. [Phys. Rev. E 73, 031401 (2006)10.1103/PhysRevE.73.031401], and is successful in exhibiting their principal features, which are an exponentially decaying velocity profile and strain localization. Transient effects are also identified.

Biomechanical Phenomena↗

PubMed2006

Drainage induced convection rolls in foams I. Convective bubble motion in a tilted tube.

When liquid is added to a foam at sufficiently large flow rates, convective bubble motion will occur. Experiments are described in which the foam is confined in a tube which is tilted from the vertical. The theory of foam drainage is applied to this problem to show that the critical angle of tilt theta(c) at which convection occurs is related to the liquid flow-rate Q by theta(c) proportional to Q(-3/4).

Journal Article↗

PubMed2004

Two-dimensional viscous froth model for foam dynamics.

The two-dimensional viscous froth model is a simple tractable model for foam rheology and coarsening. It includes, but is not confined to, the quasistatic regime. Here we present a detailed analysis and implementation of the model, illustrated with various examples. With certain simplifying assumptions, it provides significant insight into strain-rate-dependent effects in foam rheology and elsewhere, particularly in relation to recent experiments.

Journal Article↗

PubMed2004

The foam/emulsion analogy in structure and drainage.

The often quoted analogy between foams and emulsions is experimentally tested by studying properties after settling and under forced drainage of oil-in-water emulsions of drop size similar as for bubbles generally used in foam experiments. Observations with regard to structure, water fraction and drainage wave properties confirm the expected similarity in the low flow rate range. However, while for foams a convective circulation on the scale of the container sets in for values of water fraction exceeding about 0.2, no such convection is found in emulsions. Here instabilities are only encountered at water fractions of about 0.4, close to the void fraction of random packings of spheres. These take on the form of descending pulses of increased water fraction and lead to the transition from a frozen to a locally agitated structure.

Biophysics↗

PubMed2003

Topological changes in a two-dimensional foam cluster.

Experiments on a small cluster of bubbles in a nominally two-dimensional foam show an instability in which a topological change forces one of the bubbles to be ejected to the outside of the cluster at a point where this is not predicted by a two-dimensional model of a foam. This is interpreted in terms of the energy of the initial and ejected states and of the finite liquid content of the experimental system. A description of the distribution of liquid in various experimental set-ups suggests that the exact response may depend critically upon the type of system used. This is demonstrated experimentally with reference to small clusters of bubbles undergoing a single topological change.

Journal Article↗

PubMed1995