Solenoidal vector field
In vector calculus a solenoidal vector field (also known as an incompressible vector field) is a vector field v with divergence zero at all points in the field:
\[ \nabla \cdot \mathbf{v} = 0.\, \]
Properties
The fundamental theorem of vector calculus states that any vector field can be expressed as the sum of an irrotational and a solenoidal field. The condition of zero divergence is satisfied whenever a vector field v has only a vector potential component, because the definition of the vector potential A as:
\[\mathbf{v} = \nabla \times \mathbf{A}\]
automatically results in the identity (as can be shown, for example, using Cartesian coordinates):
\[\nabla \cdot \mathbf{v} = \nabla \cdot (\nabla \times \mathbf{A}) = 0.\]
The converse also holds: for any solenoidal v there exists a vector potential A such that \(\mathbf{v} = \nabla \times \mathbf{A}.\) (Strictly speaking, this holds only subject to certain technical conditions on v, see Helmholtz decomposition.)
The divergence theorem, gives the equivalent integral definition of a solenoidal field; namely that for any closed surface, the net total flux through the surface must be zero:
- x45px\(\mathbf{v} \cdot \, d\mathbf{s} = 0 \),
where \(d\mathbf{s}\) is the outward normal to each surface element.
Etymology
Solenoidal has its origin in the Greek word for solenoid, which is σωληνοειδές (sōlēnoeidēs) meaning pipe-shaped, from σωλην (sōlēn) or pipe. In the present context of solenoidal it means constrained as if in a pipe, so with a fixed volume.
Examples
- the magnetic flux density B is solenoidal (see Maxwell's equations);
- the velocity field of an incompressible fluid flow is solenoidal;
- the vorticity field is solenoidal
- the electric flux density D in regions where there is no charge (ρe = 0);
- the current density J where the charge density is unvarying, \(\frac{\partial \rho_e}{\partial t} = 0\).
See also
References
- Aris, Rutherford (1989), Vectors, tensors, and the basic equations of fluid mechanics, Dover, ISBN 0-486-66110-5bs:Solenoidalno vektorsko polje
ca:Camp solenoidal de:Quellfrei es:Campo solenoidal fr:Champ solénoïdal it:Campo vettoriale solenoidale kk:Құйынды өріс nl:Divergentievrij vectorveld pt:Campo solenoidal ru:Соленоидальное векторное поле sh:Solenoidalno vektorsko polje sv:Solenoidalt fält zh:螺線向量場