1. Numerical simulation
of wave propagation
Arnaud Bourdillon
Supervisor: Carol Armitage
School of Engineering
Cranfield University
Work area
Numerical simulation of bodies in
incident wave field
Numerical simulation of wave
propagation through variable
bathymetry
Using the control of diffusive effects process, numerical
simulations performed have led to satisfactory results, close
to experimental data for both [2] (Evaluation of reflection
effects caused by the propagation of the wave over a
submerged bar) and [3] for computation of diffraction
effects caused by wave propagation over a submerged
bump.
The process has permit to compute drag forces acting on a
fixed cylinder in incident wave field with results identical to
experimental data [4]. It has been found more difficult to
use for the computation of a box displacements in free
motion in incident wave field [5]
Conclusions
Numerical simulation by the use of free surface VOF codes
remains possible for several hydrodynamic engineering
fields as long as a process to manage the diffusive effects,
inherent to these codes, is used.
Other numerical simulations of wave propagation in variable
bathymetry and with bodies in free motion in incident wave
field will finalize the validation of the VOF software Isis-CFD
[1] B.D.Nichols and al (1981), Volume of fluid (vof) method for the dynamics of free boundaries.
J.computational physics volume 39.
[2] T.Ohyama and al (1995), Applicability of numerical models to nonlinear dispersive waves.
Coastal engineering volume 24.
[3] F.Ropert. (1999). Modélisation numérique du comportement hydraulique des caissons Garlan.
PhD thesis.
[4] L. Gentaz and al (2004), Numerical simulation of the 3D viscous flow around a vertical
cylinder in non-linear waves using an explicit incident wave model. 24th International
Conference on Offshore Mechanics and Arctic Engineering
[5] M.Peric and al (2001) Predictions of Floating-Body Motion in viscous flow. In 4th Numerical
Towing Tank Symposium.
With the improvement of computer capacity, numerical
simulation has become a standard to investigate
hydrodynamic engineering problems. The VOF [1] method
capacity (known to provoke several diffusive effects) to
compute wave propagation is investigated here, through
Isis-CFD flow solver.
MSc Computational and Software Techniques in Engineering 2012 (Computer aided engineering )
Control of the diffusive effects
Diffusive effects caused by the discretization schemes used
in VOF codes, can damp the maximal height of the wave
and lead to the appearance of phases differences. A process
to render VOF computations comparables to experimental
data has been extracted here:
Damping of the signal
caused by diffusive effects
1. Listing of wave
parameters for the problem
(Technical specifications)
2. Estimation of the damping
of the signal due to the
diffusive effects. Process
based on error data table
calculated. Errors are function
of the steepness of the wave
and the position of a body in
the computational domain
3. Computation of the
corrected wave parameters
to use at the inlet boundary
to avoid these errors
through a mathematical
algorithm
4. Numerical simulation
of wave propagation in
a domain without body.
Verification that the
correct wave amplitude,
is , now, coming on the
expected body position.
5. Listing of the
corrected wave
parameters to use, as
an inlet condition, to
avoid the diffusive
errors.
6. Numerical simulation
with a body in a domain
can then be compared,
in the most accurate
way, to experimental
data.