As in the case of the solid plug-like motion of viscoplastic materials in
pipes and slits (discussed in Chapter 3), there again exists a bounded zone of
flow associated with a sphere moving in a viscoplastic medium, and beyond
this zone, the fluid experiences elastic deformation, similar to that in elastic
solids [Volarovich and Gutkin, 1953; Tyabin, 1953]. Indeed the difficulty in
delineating the interface between the flow and no flow zones has been the
main impediment to obtaining numerical solutions to this problem. Furthermore,
even within the cavity of shear deformation, there is unsheared material
adhering to parts of the sphere surface and this suggests that the yield stress
may not act over the entire surface. The existence of such unsheared material
attached to a moving sphere has been observed experimentally, but it is rather
difficult to estimate its exact shape and size [Valentik and Whitmore, 1965;
Atapattu et al., 1995].
Using the laser speckle photographic method, Atapattu et al. [1995]
measured point velocities in the fluid near a sphere moving at a constant speed
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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