4 Joseph D. Barry et al. 0 . 06 using the definition eq. 3), consistent with experi- mental observation. In these simulations of simple shear, where there is no wall drag, either wall may be regarded as the one that moves. Recent results by Wyn [33] sug- gest that as the second moment of the bubble area dis- tribution µ$_{2}$ ( A ) is increased in such simulations to val- ues approaching 0.2 or higher, shear-banding can occur in regions away from the moving boundary. The width of these shear bands has a square-root dependence on µ$_{2}$ ( A ). This type of behaviour has yet to be observed in experiments. In this paper, we only examine the rheol- ogy of foam samples of disorder µ$_{2}$ ( A ) = 0 . 13 but will probe higher values of disorder in future work in order to search for similar effects. served when wall drag is present. For dry foams though, where low liquid fraction causes bubbles to become more polygonal in shape, this approach is no longer accurate [12]. In this paper, we adopt the 2D Viscous Froth (VF) Model [11, 21] as a more realistic model for dry 2D foam dynamics. We have performed an extensive study of shear localisation with the VF Model in a straight ge- ometry which shows realistic dynamics and a rich variety of behaviour, particularly at low λV . For a summary of the experimental and theoretical work presented in this section, see [27]. With the aid of the Surface Evolver software [4], quasi-static simulations are increasingly easy to imple- ment and, with modern computing, are certainly fast. But are they suitable for rheology? In quasi-statics, the foam is relaxed to equilibrium at each step. There is therefore no relevant time scale present and so no con- cept of shear-rate. It makes no sense to consider Herschel- Bulkley type relations or to discuss the dependence of localisation on boundary velocity. What then, are the alternatives to quasi-static sim- ulations? Bubble models [9], where a foam is modeled as a collection of interacting disks appear to represent at some level the dynamics of 2D foams. Langlois et al. [24] report a Herschel-Bulkley exponent of a = 0 . 54 ( µ$_{2}$ ( A ) ≈ 0 . 03). In addition, shear localisation is ob- The model describes the motion of a soap film in the 2D systems described above, with wall drag [21]. In the present case, bubble areas are kept constant. The foam is considered to be sufficiently dry (liquid fraction less than 0.01) so that a soap film may be accurately described by a curved line and the junctions are represented by points. In the present simulations, a soap film is approximated as a system of connected straight line segments. The motion of a point s joining these segments is given via the equation 2 The 2D Viscous Froth Model and its implementation λv $^{⊥}$( s ) = ΔP − γK ( s ) (2)