“…On the boundary between the channel region and the tip region, the fluxes are evaluated to determine the volume of fluid in each tip element. These tip fluid volumes are then used to locate the fracture front by exploiting the property that, for a smooth front, the asymptotic behavior of the solution close to the tip corresponds to a one-dimensional fracture propagating in a state of plane strain [32]. For example, if the applicable asymptotic power law is of the form (ˆ ) ∼ cˆ , then the tip volume V ( ) can be expressed in the form (16) whereˆ is the distance from the local fracture front, (ˆ ) is the local dimension of the current element in a direction parallel to the front, and is the distance between the front and the opposite vertex of the tip element.…”