fluid mechanics

In a pure liquid, molecules touch one another but change neighbors frequently.  External forces cause the liquid to change shape by viscous flow.  Thermal agitation causes  molecules to undergo self-diffusion.  The two phenomena--viscous flow and self-diffusion--often result from a single rate-limiting process:  molecules change neighbors.  This simple picture is amply confirmed by the Stokes-Einstein relation, which links the viscosity and self-diffusivity for many liquids over wide ranges of temperature.

The attached notes are written for a course on plasticity.  I will update new posts on my twitter account:  https://twitter.com/zhigangsuo.  

In the laminar mode interactions
among molecules generate friction between layers of water that slide with
respect to each other. This friction triggers the shear stress, which is
traditionally presumed to be linearly proportional to the velocity gradient.
The proportionality coefficient characterizes the viscosity of water. Remarkably,
the standard Navier-Stokes model surmises that materials never fail – the transition
to turbulence can only be triggered by some kinematic instability of the flow. This
premise is probably the reason why the Navier-Stokes theory fails to explain

Faculty Positions are available in Department of Engineering Mechanics, Southeast University, Nanjing, China

A 3-year PhD scholarship is available to work on simulation methods to treat colloidal

particles that are flowing near, or are transported within fluid interfaces (L.

Botto et al., Soft Matter, 2012, 8, 9957-9971); the focus is on fluid

mechanical aspects coupled with physical-chemistry. For details: webspace.qmul.ac.uk/lbotto