FLOWS OF VISCOPLASTIC MATERIALS - MODELS AND COMPUTATIONS

Flows of materials with yield are analysed by using a continuous visco plastic equation (CVE) that eliminates the necessity of tracking mater ial yield surfaces. These flows are computed by means of the Galerkin/ finite element method and global Newton iteration. Numerical difficult ies stemming from the sigmoidal form of the CVE are avoided by appropr iate selection of the initial estimation to the Newton iteration, or b y solution continuation in the space of the exponential material param eter of the CVE. Simultaneously with the determination of the unknown velocity and pressure fields, the finite element scheme locates the ch aracteristic material lines, such as interfaces and yield surfaces. Re sults are presented for two-dimensional flows over generalized flow co nduits at driving gradients below and above yielding. It is shown that a general viscoplastic held consists of truly unyielding plug regions (UPR) carried by yielded flowing films (YFF) in contact with solid bo undaries or intervening apparent unyielded regions (AUR). (C) 1997 Civ il-Comp Ltd and Elsevier Science Ltd.