Validation of computational fluid-structure interaction models by comparison with collapsible tube experiments.

The objective of this thesis was to assess the validity of the fluid-structure interaction
(FSI) facilities in LS-DYNA for the analysis of highly deformable structures
interacting with flowing viscous fluids. The collapsible tube experiment was chosen
as a validation tool for FSI since its three-dimensional computational modelling
would have been impossible if the viscous internal fluid flow were not considered.
An explicit three-dimensional finite element model of a collapsible-tube was
constructed and solved using LS-DYNA. The fully coupled model included internal
fluid flow; external, inlet and outlet pressures; tube wall tension; pre-stressing; and
contact. The finite element boundary conditions were taken as the recorded values of
flow rate and pressure from a standard collapsible-tube experiment for both steady
and unsteady flows.
The predicted tube geometry in the steady LS-DYNA model showed good agreement
with the experiment for operating points in the highly compliant region of the
pressure-flow characteristic curve. The comparative position of the pinch at the
outlet end differed by only 5.6% of the outlet diameter in the worst case.
This analysis represents an advance on other published work in that previously no
comparison with experiments have been drawn for FSI models involving high
Reynolds number flowing viscous fluids interacting with highly deformable three dimensional
structures. This analysis successfully made that comparison and the
experimental and computational results have combined to form a more detailed
picture of the collapsible-tube phenomenon by including detailed stress results of the
tube walls and views of the internal fluid flow.
The collapsible tube model exhibited uncertainty errors due to the use of a coarser
than desirable mesh and a reduced fluid speed of sound. Although both these
approximations caused significant error in the model both were necessary in order to
achieve acceptable solution times. Because of these errors a thorough quantitative
validation could not be achieved although LS-DYNA has been proven to be
qualitatively accurate. Increases in computing speed are required before thorough
quantitative validation of FSI can be achieved by comparison with the collapsible tube
experiments.