validation of Delft3D FM

1. Validation of Delft3D Flexible Mesh
Arthur van Dam, Herman Kernkamp, Wim van Balen,
Sander van der Pijl, Erik de Goede, Mart Borsboom, Henk
van den Boogaard, Jan van Kester, Niels Jacobsen,
Mohammed Nabi, Adri Mourits, Michal Kleczek, Robert
Leander, Gijs van den Oord.
Delft Software Days 2015

2. Validation of D-Flow Flexible Mesh
Methodology
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Example tests Current status

3. Purpose of validation
The purpose of validation is twofold:
1. Assess the quality of D-Flow FM results.
2. Guard the consistency of D-Flow FM results.

4. Validation methodology: IAHR guidelines

6. Validation methodology: IAHR guidelines
Example from D-Flow FM Validation Document

7. Regression testing: some statistics.
• Currently 249 testcases, run+checked automatically.
• Small, fast tests: Average runtime of 8.19 seconds per testcase.
• Testset runs at least once a day, but typically four times (each commit).

8. Some example validation testcases
• Analytic Thacker analytical flooding & drying.
• Schematic Riemann weakly reflective boundary conditions.
• Laboratory Stelling and Duinmeijer’s dambreak
• Real-world Frisian Inlet

9. Flooding and drying: Thacker testcase
Flooding and drying in a friction-less parabolic-shaped basin.
Analytical solutions by Thacker (1981)

10. Flooding and drying: different test grids

11. Flooding and drying: conclusions
D-Flow FM can deal computationally with flooding and drying on all
grid types.
Bed level handling needs care (wrong conveyance parameter may
cause incorrect high flow velocities).
Numerical diffusion causes some phase lag in this case, but in
practice, flooding and drying scenario’s are forced by a certain
period signal.

12. Weakly reflecting boundary cond.: Riemann testcase
Riemann (waterlevel) boundaries for non- weakly-reflecting outflow
boundaries.
• Initial Gauss pulse in a radial domain.
• Two model sizes: R=90km, R=120km.

13. Riemann-boundaries: inspect timeseries
Inspect water level timeseries at observation points.
Pulse travels at characteristic speed 10 m/sgh 
Conclusion: Riemann boundaries work well, but some weak reflections occur
for large perturbations.

14. Dam break: Stelling and Duinmeijer experiment
Stelling and Duinmeijer (1981): laboratory test of 2D dambreak.
• Both a wet bed and dry bed scenario.
• Performed in closed domain: bores and reflected bores will interact.

15. Stelling and Duinmeijer 2D dambreak: dry bed

16. Stelling and Duinmeijer 2D dambreak: dry bed
In simulations (both FM and Delft-FLS) the reservoir empties quicker:
Model: gate opens instantaneously, in lab experiment lifted at 0.16 m/s.

17. Stelling and Duinmeijer 2D dambreak: dry bed
FM similar to FLS w.r.t. front arrival times. Will also need reduced
friction to match experiments.

18. Real-world: Frisian Inlet testcase
Not this one…

19. Real-world: Frisian Inlet testcase
But this one:
Frisian inlet model with tidal flats.

20. Real-world: Frisian Inlet testcase
With almost identical settings, D-Flow FM has somewhat higher flow
velocities than Delft3D.

21. Real-world: Frisian Inlet testcase
Most important lesson-learn in this case was:
pay attention to differences in bed level handling!
D-Flow FM: cell-centered depth
based on depth of all velocity points.
Delft3D-FLOW: cell-centered depth
based on depth of all corner points.
Closest match:

22. Current status
D-Flow FM Validation Document:
• Currently focuses on 2D(+1D) hydrodynamics, plus flow-wave-
interaction.
• Has been partially reviewed and will undergo further review:
not officially published yet.
dflowfm_examples.zip
A large subset of these testcases is available to users of D-Flow FM,
serving as example models (purpose: documentation + training).

23. D-Flow FM Validation in 2016
Validation will continue!
• 3D cases are currently being added, but still largely focus on
regression testing.
• More 2D and 3D flow-wave testcases are currently being added.
• 2D and 3D morphology testcases are currently being added.