Iwan and Blevins wake oscillator model

This wake oscillator model is as published by Iwan and Blevins. In their paper the model is developed from theoretical considerations of momentum, and the hidden wake degree of freedom is such that its rate of change is a measure of the fluid momentum in the transverse direction.

In the resulting model, the wake degree of freedom obeys a Van der Pol equation. This is a type of equation that has been used in other wake oscillator models, and it is known to have VIV-type characteristics such as frequency lock-in.

The authors calibrated the model against experimental results for fixed and forced cylinders, and then compared the model's predictions against experimental results for spring-mounted cylinders.

Note that the force generated by the Iwan and Blevins model (unlike the Milan wake oscillator) includes the standard Morison drag force in the transverse direction. When the Iwan and Blevins model is used, OrcaFlex therefore suppresses the transverse component of the usual drag force, so the drag coefficient specified for the transverse direction is not used.

Data

There are no data specific only to the Iwan and Blevins model. See instead

Results

The vortex force is available as a line force result which reports the total lift and drag force. This is the sum of the force generated by the wake oscillator model (which is in the transverse direction but doesn't include the drag force in that direction) and the standard Morison drag force in the inline, transverse and axial directions.

Transverse VIV offset is also available as a line position result.