# Upper-convected time derivative

In continuum mechanics, including fluid dynamics, an **upper-convected time derivative** or **Oldroyd derivative**, named after James G. Oldroyd, is the rate of change of some tensor property of a small parcel of fluid that is written in the coordinate system rotating and stretching with the fluid.

The operator is specified by the following formula:

where:

- is the upper-convected time derivative of a tensor field
- is the substantive derivative
- is the tensor of velocity derivatives for the fluid.

The formula can be rewritten as:

By definition the upper-convected time derivative of the Finger tensor is always zero.

It can be shown that the upper-convected time derivative of a spacelike vector field is just its Lie derivative by the velocity field of the continuum.[1]

The upper-convected derivative is widely use in polymer rheology for the description of behavior of a viscoelastic fluid under large deformations.

## Examples for the symmetric tensor *A*

*A*

### Uniaxial extension of incompressible fluid

In this case a material is stretched in the direction X and compresses in the directions Y and Z, so to keep volume constant. The gradients of velocity are:

Thus,

## See also

## References

- Macosko, Christopher (1993).
*Rheology. Principles, Measurements and Applications*. VCH Publisher. ISBN 978-1-56081-579-2.

- Notes

- Matolcsi, Tamás; Ván, Péter (2008). "On the Objectivity of Time Derivatives". doi:10.1478/C1S0801015. Cite journal requires
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