Notation (v*gradient operator)v in Navier-Stokes

[TylerH]

Notation "(v*gradient operator)v" in Navier-Stokes

What does \left( \textbf{v} \cdot \nabla \right) \textbf{v} mean, assuming knowledge of the gradient operator? And, specifically, how would that be expanded? In general, I'm ignorant of the notation \left( f \left( y, \frac{d}{dx}, \frac{d^2}{dx^2}, \ldots \right) y \right) where, for example, f \left( y, \frac{d}{dx}, \frac{d^2}{dx^2}, \ldots \right) could be y + \frac{d}{dx}.

 

[HallsofIvy]

That is, by the way, the "del" or "nabla" operator. It is specifically only \nabla f(x,y,z, with f a scalar valued function, that is the "gradient". \nabla\cdot \vec{v} is the "gradient" or grad \vec{v} and \nabla\times\vec{v} is the curl \vec{v}.

In any case
\vec{v}\cdot\nabla= v_x\frac{\partial }{\partial x}+ v_y\frac{\partial }{\partial y}+ v_z\frac{\partial }{\partial z}
so that
\vec{v}\cdot\nabla \vec{v}= \left(v_x\frac{\partial }{\partial x}+ v_y\frac{\partial }{\partial y}+ v_z\frac{\partial }{\partial z}\right)v_x\vec{i}+ \left(v_x\frac{\partial }{\partial x}+ v_y\frac{\partial }{\partial y}+ v_z\frac{\partial }{\partial z}\right)v_y\vec{j}+ \left(v_x\frac{\partial }{\partial x}+ v_y\frac{\partial }{\partial y}+ v_z\frac{\partial }{\partial z}\right)v_z\vec{k}
= \left(v_x\frac{\partial v_x}{\partial x}+ v_y\frac{\partial v_x}{\partial y}+ v_z\frac{\partial v_x}{\partial z}\right)\vec{i}+ \left(v_x\frac{\partial v_y}{\partial x}+ v_y\frac{\partial v_y}{\partial y}+ v_z\frac{\partial v_y}{\partial z}\right)\vec{j}+ \left(v_x\frac{\partial v_z}{\partial x}+ v_y\frac{\partial v_z}{\partial y}+ v_z\frac{\partial v_z}{\partial z}\right)\vec{k}

 

[TylerH]

Oh, I didn't understand it as well as I thought I did. Thanks.

Just wondering, is \left( y + \frac{d}{dx} \right)y meaningless, or can it be expanded? If it can, what is it?

Thanks for your time.

 

[hunt_mat]

it can be expanded as:
<br /> y+\frac{dy}{dx}<br />