intro story Coast / Estuary

Coast / Estuary

Coastal systems are among the most dynamic physical systems on earth and are subject to a large variety of forces. The morphodynamic changes occurring to coastlines worldwide are of great interest and importance. These changes occur as a result of the erosion of sediments, its subsequent transport as bed load or suspended load, and eventual deposition. 
 
Estuaries are partly enclosed water bodies that have an open connection to the coast. Estuaries generally have one or more branching channels, intertidal mudflats and/or salt marshes. Intertidal areas are of high ecological importance and trap sediments (sands, silts, clays and organic matter).
Within the Delft3D modelling package a large variation of coastal and estuarine physical and chemical processes can be simulated. These include waves, tidal propagation, wind- or wave-induced water level setup, flow induced by salinity or temperature gradients, sand and mud transport, water quality and changing bathymetry (morphology). Delft3D can also be used operationally e.g. storm, surge and algal bloom forecasting. 
 
On this discussion page you can post questions, research discussions or just share your experience about modelling coastal and/or estuarine systems with Delft3D FM. 
 

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Sub groups
D-Flow Flexible Mesh
DELWAQ
Cohesive sediments & muddy systems

 

 

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Delft3D-WAVE: Non-stationary mode parameters

U
Anonymous Anonymous, modified 7 Years ago.

Delft3D-WAVE: Non-stationary mode parameters

I'd appreciate some clarity on calculation points when running a Delft3D-WAVE model in non-stationary mode.

With a standalone WAVE model the calculation points are set by the 'Time' parameter in each [Time Point] section of the .mdw file.

In a non-stationary mode, additional parameters must be set, namely 'Time Interval' and 'Time Step' in GUI. These parameters appear in the .mdw file as the 'COMWriteInterval' and 'TimeStep' parameters respectively.

Then during a non-stationary model run, the screen output shows evaluation at each 'Time' specified in each [Time Point] with calculations stepping forward from each 'Time' in 'TimeSteps' over the 'Time Interval' (aka the 'COMWriteInterval').

My questions are:
1) In non-stationary mode, should 'Time Interval' ('COMWriteInterval') be set equal to the interval between the 'Time' specified in each [Time Point] which presumably should be regularly spaced.
2) Is there a good reference text describing non-stationary calculations?

[As an aside, in a coupled FLOW-WAVE model the calculation points for the WAVE module are set by the Communication File parameters (Start Time, Stop Time, and Interval) set in the FLOW GUI (or .mdf file). Indeed in the WAVE GUI the reference to the 'Time Interval' parameter changes to 'Coupling Interval' and cannot be amended.]

Once again, many thanks in advance
Ruairi
AA
Anonymous Anonymous, modified 6 Years ago.

RE: Delft3D-WAVE: Non-stationary mode parameters

Jedi Master Posts: 333 Join Date: 7/30/20 Recent Posts
Looking for answers for the same problem. How is that "time interval" really used in nonstationary mode?

Any suggestion is appreciated!

Ruairi MacIver:
I'd appreciate some clarity on calculation points when running a Delft3D-WAVE model in non-stationary mode.

With a standalone WAVE model the calculation points are set by the 'Time' parameter in each [Time Point] section of the .mdw file.

In a non-stationary mode, additional parameters must be set, namely 'Time Interval' and 'Time Step' in GUI. These parameters appear in the .mdw file as the 'COMWriteInterval' and 'TimeStep' parameters respectively.

Then during a non-stationary model run, the screen output shows evaluation at each 'Time' specified in each [Time Point] with calculations stepping forward from each 'Time' in 'TimeSteps' over the 'Time Interval' (aka the 'COMWriteInterval').

My questions are:
1) In non-stationary mode, should 'Time Interval' ('COMWriteInterval') be set equal to the interval between the 'Time' specified in each [Time Point] which presumably should be regularly spaced.
2) Is there a good reference text describing non-stationary calculations?

[As an aside, in a coupled FLOW-WAVE model the calculation points for the WAVE module are set by the Communication File parameters (Start Time, Stop Time, and Interval) set in the FLOW GUI (or .mdf file). Indeed in the WAVE GUI the reference to the 'Time Interval' parameter changes to 'Coupling Interval' and cannot be amended.]

Once again, many thanks in advance
Ruairi
U
Anonymous Anonymous, modified 6 Years ago.

RE: Delft3D-WAVE: Non-stationary mode parameters

The following contains a lot of 'appears' as it reflects my present understanding and isn't definitive by any means ...

It appears that the "Time Interval" parameter principal purpose is to control the period between writing the communication files that are used to pass wave information to the FLOW module. It appears to be more relevant to coupled FLOW-WAVE models than standalone WAVE models [see my aside in the original posting].

It appears to be used to set the end time ([tendc]) for the COMPUTE command in the SWAN input file that is created by DELFT3D. The generic command looks like COMPUTE NONSTAT [tbegc] [deltac] [tendc], which in a specific example for a nonstationary computation with a time step of 60 mins starting at 12:00 27/4/12 and ending at 15:00 27/4/12 looks like COMPUTE NONSTAT 20120427.120000 60.00 MIN 20120427.150000.

The [Time Point] entries in the MDW file for a standalone WAVE model appear to control the start times at which the wave model is executed and output files produced. For a non-stationary model, the "Time Step" parameter controls the 'delta t' between internal calculation steps while the "Time Interval" parameter controls the duration of the computation (i.e. the end time). Creating a HOTFILE captures the state of the computation at the end time which can then be used to initialize a subsequent model execution. In my opinion, this is why the "Time Interval" parameter should equal the spacing between [Time Point] entries in the MDW file.

I hope this helps
Ruairi
AA
Anonymous Anonymous, modified 6 Years ago.

RE: Delft3D-WAVE: Non-stationary mode parameters

Jedi Master Posts: 333 Join Date: 7/30/20 Recent Posts
Ruairi, Thanks for your reply! They are really very helpful.

But I am not sure whether"time interval" has to be the same as spacing between "time point", if we don't need to save HOTFILES. Output will be written at every "time point" in my test.

Ruairi MacIver:
The following contains a lot of 'appears' as it reflects my present understanding and isn't definitive by any means ...

It appears that the "Time Interval" parameter principal purpose is to control the period between writing the communication files that are used to pass wave information to the FLOW module. It appears to be more relevant to coupled FLOW-WAVE models than standalone WAVE models [see my aside in the original posting].

It appears to be used to set the end time ([tendc]) for the COMPUTE command in the SWAN input file that is created by DELFT3D. The generic command looks like COMPUTE NONSTAT [tbegc] [deltac] [tendc], which in a specific example for a nonstationary computation with a time step of 60 mins starting at 12:00 27/4/12 and ending at 15:00 27/4/12 looks like COMPUTE NONSTAT 20120427.120000 60.00 MIN 20120427.150000.

The [Time Point] entries in the MDW file for a standalone WAVE model appear to control the start times at which the wave model is executed and output files produced. For a non-stationary model, the "Time Step" parameter controls the 'delta t' between internal calculation steps while the "Time Interval" parameter controls the duration of the computation (i.e. the end time). Creating a HOTFILE captures the state of the computation at the end time which can then be used to initialize a subsequent model execution. In my opinion, this is why the "Time Interval" parameter should equal the spacing between [Time Point] entries in the MDW file.

I hope this helps
Ruairi
U
Anonymous Anonymous, modified 6 Years ago.

RE: Delft3D-WAVE: Non-stationary mode parameters

You are correct - "Time Interval" doesn't have to be the same as the spacing between [Time Points].

However for non-stationary calculations ...
1) I can't see why you would choose to not use HOTFILES, and
2) I can't see why you would choose "Time Interval" to be anything other than equal to the spacing.

Not using a HOTFILE to initialise the domain for each [Time Point] will mean the calculation starts from cold at each [Time Point]. Thus it will not benefit from the evolution of the wave field determined from preceding calculations at earlier [Time Points] and will require longer to converge.

Using a "Time Interval" longer than the [Time Point] spacing means a non-stationary calculation will terminate each calculation after the following [Time Point]. That is, the calculation for a particular [Time Point] specified in the .mdw file will move forward in time-steps (set by the "Time Step" parameter) from that [Time Point] until the "Time Interval" has been reached which will be after the following [Time Point]. Then the calculation for the next [Time Point] in the .mdw file is initiated and executed, effectively moving back in time and resulting in unnecessary calculations and longer run times.

Again I hope this helps
Ruairi