dsd-nl 2014 - nghs flexible mesh - technital pilot modeling venice lagoon, katherine cronin,...

Friday, June 20, 2014

NEXT GENERATION MODELLING APPLIED TO THE VENICE LAGOON

G.T. Menel Lemos, E. Jeradi

Next Generation Hydro Software Symposium – 2014



2nd Batch Pilot case

New Venice lagoon D-Flow-FM model:

• Set-up of the grid

• Test runs

• Verification of the results both with the measurements and 3D-Flow model

• Evaluate the performance

DELWAQ:

• Coupling of the FM version of the Venice lagoon model (converted during the 1st phase pilot study)

• Test runs with simple water quality process • Comparison of results with the 3D-Flow Venice lagoon


Next Generation Modelling applied to the Venice Lagoon

VENICE LAGOON: SENSIBLE ENVIRONMENT

Venice Town



EXISTING 3DFLOW VENICE MODEL

Existing 3DFlow Venice Model version:

• Need to use Domain Decomposition even in the “single domain” version: internal boundaries used to avoid too much cells in the seaside

• Useless cell concentration in deep areas potentially create problems – see area in front of the inlets

• Low resolution in marginal areas (northern and southern part of the lagoon) don’t allow a good representation of morphological structures

• Need many different schematizations : each different intervention have its own model…

Good representation (small cells) → small time step → long time run



1st batch pilot case :

• Conversion of the old model • Run of the FM version of the old model

• Comparison of results both with the measurements and 3D-Flow model

• Evaluate performance


Next Generation Modelling applied to the Venice Lagoon - 1ST BATCH PILOT CASE

D-FLOW VERSION



3DFLOW VERSUS D-FLOW: WATER LEVELS



3DFLOW VERSUS D-FLOW: FLUXES



PERFORMANCE

CPUtime steps / Nr of TimeSteps

TtimeStep FM/ TtimeStep 3DFlow

Run time FM/Run time 3DFlow



PERFORMANCE: CPU usage

D-Flow Flexible Mesh was run in OpenMP mode.

Delft3D-FLOW D-Flow Flexible Mesh

Delft3D-FLOW does not have the possibility to use OpenMP.

100% usage of the four cores for D-Flow Flexible Mesh does not mean that the simulation went a factor of four faster because the algorithm is for a large part sequential but this explains why D-Flow Flexible Mesh was about a factor of two faster.



2nd Batch Pilot Case

New Venice lagoon D-Flow-FM model:

• Set-up of the mesh

• Test runs

• Verification of the results both with the measurements and 3D-Flow model

• Evaluate the performance


Next Generation Modelling applied to the Venice Lagoon – 2nd BATCH PILOT CASE

1. Define curvilinear grid for all the main channels

D-FLOW VENICE MODEL: MESH CREATION


Next Generation Modelling applied to the Venice Lagoon - 2nd BATCH PILOT CASE

1. Define curvilinear grid for all the main channels 2. and inlets and sea (with different resolutions)




1. Define curvilinear grid for all the main channels 2. and sea area (with different resolutions) 3. Define grid of marshlands (based on samples)




D-FLOW VENICE MODEL: COMPLETE MESH

1. Define curvilinear grid for all the main channels 2. and sea area (with different resolutions) 3. Define net of marshlands (based on samples) 4. Define net in the shoals area



~ 170.000 nodes 400.000 links

D-FLOW VENICE MODEL: COMPLETE MESH



D-FLOW VENICE MODEL: NORTHERN PART



NEW D-FLOW VENICE MODEL: BATHYMETRY



1. Define curvilinear grid for all the main channels

2. and sea area (with different resolutions)

3. Define grid of marshlands (based on samples)

4. Define grid of the flat areas

NEW D-FLOW VENICE MODEL: ORTHOGONALITY



NEW D-FLOW VENICE MODEL: RESULTS

Water level



Node velocity

NEW D-FLOW VENICE MODEL: RESULTS



Velocity field – northern lagoon



Velocity field – central lagoon



Velocity field – southern lagoon



COMPARISON BETWEEN MODELS AND MEASUREMENTS

Fluxes Water levels



PERFORMANCE

CPUtime steps / Nr of TimeSteps

TtimeStep FM/ TtimeStep 3DFlow

Run time FM/Run time 3DFlow

3DFlow - 5 domains DFlow-FM-new

Timestep (s) 3 auto (CFL)

Simulation period (s) 604800 604800

Nr of timesteps ( ) 201600 223262

CPUtime steps (s) 125815.88** 88787.97

Run time (hh:mm:ss) 22:46:14 18:01:20

TtimeStep 0.624087 0.397685

SpeedFactor TimeStep 0.637227

SpeedFactor Wall Clock 0.791470

**Average cpu time of the 5 domains (not considering ddmodule wait time)



OPTIMIZATION OF THE NEW MESH

remove unnecessary links to save computational time (wagon wheels)

De-refine the mesh in the marshlands and shoals



2nd Batch Pilot case

DELWAQ:

• Coupling of the FM version of the Venice model (curvilinear grid)

• Test runs with simple water quality process • Comparison of results with the 3D-Flow Venice lagoon



DELWAQ

Coupling procedure

Using offline coupling (communication file) and ddbound option to account for dd internal boundaries Pros: • hydro run can have different duration and save only

last cycle • to communication file • It is possible to aggregate the grid before coupling it

Cons: • Communication file can be enormous • Coupling with ddmodel can be tricky (need manual

modifications of the *.hyd files)

Using online coupling by activating WaqInterval option in the mdu file Pros: • No communication file: creation of WAQ files

(.are, .vol, .flo, etc.) directly • Simple procedure

Cons: • hydro run must have the same duration of

the cycle for WAQ • It is not possible to aggregate the net ** (**for the moment but it will be possible to create the WAQ files on an aggregated grid)

3D-FLOW ddmodel D-FLOW



DELWAQ: TEST RUN

Hydrodynamic conditions: • Average tide : semidiurnal +- 35 cm • No wind • Average river flows

WAQ conditions: processes initial sea/river bnd

• Continuity (g/m3) 1 1/1 • Salinity (g/kg) 33 33/0 • Cons. tracer (g/m3) 1 1/0

• Duration: 20 days, time-step 5 min • Dispersion: 5 m2/s • Numerical scheme: 15 Iterative solver, backward diff.



DELWAQ: TEST RUN RESULTS - CONTINUITY

3D-FLOW D-FLOW

After the coupling procedure for the 3D-Flow model a utility called “flocheck” has been used. This utility makes a kind of “dredging” to increase the volume and/or lateral surface of isolate segments in order to keep the residence time below the user-defined integration time-step.



DELWAQ: TEST RUN RESULTS - SALINITY

3D-FLOW D-FLOW

Rivers are defined in different way in the two hydro models and so different in the WAQ: • 3D-Flow - as discharges • D-Flow - discharges boundaries Same dispersion coefficient: 5 m2/s



DELWAQ: TEST RUN RESULTS – CONSERVATIVE TRACER

3D-FLOW D-FLOW

Rivers are defined in different way in the two hydro models and so different in the WAQ: • 3D-Flow - as discharges • D-Flow - discharges boundaries Same dispersion coefficient: 5 m2/s

3D-Flow seems to have more long time response than the D-FLOW model



FURTHER DEVELOPMENTS

D-FLOW:

1. Complete the optimization the new grid: marshland and shoal areas

2. 3D simulations

DELWAQ:

1. Go further with the analysis of water quality parameters

2. Make comparisons with measurements



COMMENTS

D-FLOW:

• There was no easy way to de-refine the triangular mesh. The existing method

involves making a polygon and merge nodes and than smooth/orthogonalize

again. The procedure is very time consuming in such complex system

• It will be nice to have some kind of filter (like neighborhood) function to cleaning up

the samples before using it for the net generation

DELWAQ:

• The new WAQgui save the *.inp file with an error in the 7# block: the line that

starts with MASS/m2 have to be deleted otherwise WAQ1 gives an error and

doesn’t work

• It is not possible to defined an spatial varying initial condition using the FM mesh

Quickplot (April version):

• It is not possible to define a manual color scale limit

we plan the world of tomorrow

we plan the world of tomorrow

www.technital.it

THANK YOU!!

[email protected]

dsd-nl 2014 - nghs flexible mesh - technital pilot modeling venice lagoon, katherine cronin,...

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