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cjh

Simulation Failure

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Hi Everyone.

I'm reviewing an ESTRY/TUFLOW model which results in a simulation failure - quite a catastrophic one, but having gone through the usual diagnostic checks I'm coming up at a loss of what would cause such a significant instability to manifest so quickly.  I have attached some outputs for failure and failure-1 showing the devastation.

I've gone through the geometry, linking, materials and all the standard checks which yield nothing interesting or out of the usual.  My prime suspects are:

  1. The bridge downstream surcharging (at 12.86mAOD) as the simulation fails when water level is 12.78mAOD during the last output so assuming that it has reached surcharge before the next output interval.
  2. High velocities.  Velocity in the 2d domain is >6m/s in a 3m grid
  3. A nice big flat water surface across the channel and floodplain causing a few wobbles.

In the images, I've labelled the mmQ estry layer with peak flow - which is enormous compared to the upstream sections and downstream sections, as an indication of the volumes that have magically appeared. Also added a DTM shot showing that there is nothing funky going on there, this is confirmed from checking the zpt-check files.

 

However I'd love to hear if anyone has any thoughts.  The mystery water fountain is 435m high and is a bit of a pest.

failure.PNG

failure-1.PNG

dem.PNG

tlf.PNG

depths1d2d.PNG

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Hi CHJ,

 

Pretty spectacular model pop!

I see that in your tlf the instability is first registered in the 2D, does it start there or can you see it propagate from the 1D or another 2D location? Can you see earlier oscillations in either the 1D or 2D before this originating from somewhere?

Your list of things to check is very sound, and would cover most of the causes of these types of issues.  I would add a couple of things to your checklist to investigate:

- Look for changes in the flow patterns just before the instability. For the 1D, review the flow regime in the channels (in the EOF).  In the 2D, it looks like the channel is starting to seriously break out just before the instability occurs. This is also the low point of HX line. Just double check that the boundary and elevations sit as best they can here.

-  You're right that the high velocities hitting the bridge just stating to surcharge could be causing issues. If you can, it would be good to drop your output interval (or use an output zone) to see exactly where the instability starts and if indeed its the bridge. If it is looking like this, then you might need to check how you've schematised it, maybe look for big changes in conveyance or flow area.

- For 1D sections, I like to visualise conveyance (nwk_C_check). This helps look at big changes in channel geometry and section length, Ideally, you want this to be fairly gradually changing, no big jumps.

If you're still having trouble finding the cause of the instability, feel free to post again here with more information or send us through the model to support@tuflow.com and we'll take a look.

Regards,

 

 

 

Rachel

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