# How to use unstructured open boundaries?

**URL:** <https://nemo-ocean.discourse.group/t/how-to-use-unstructured-open-boundaries/703>\
**Category:** Uncategorized\
**Tags:** BDY\
**Created:** [24 May 2024 09:07 UTC](https://nemo-ocean.discourse.group/t/how-to-use-unstructured-open-boundaries/703 "2024-05-24T09:07:26Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![avelina](https://yyz2.discourse-cdn.com/free1/user_avatar/nemo-ocean.discourse.group/avelina/32/140_2.png) [@avelina](https://nemo-ocean.discourse.group/u/avelina)\
**Post date:** [24 May 2024 09:07 UTC](https://nemo-ocean.discourse.group/t/how-to-use-unstructured-open-boundaries/703/1 "2024-05-24T09:07:26Z")

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Hello!

I’m having trouble using unstructured open boundaries without a `coordinates.nc` file in NEMO 4.2.2. I have a configuration that includes both ice and ocean modules. Despite reviewing previous discussions on BDY input data, I am still encountering several issues.

Here’s what we have tried so far:

- We use `nambdy_index` to identify boundaries and then trim the data according to these identified boundaries.
- We set a rimwidth of 10 cells.
- For the W/E and S/N boundaries, we used different types of input data, ensuring that the dimensions in the .nc file matched the dimensions in the variables: x, y, z, time, and y, x, z, time (cross boundary and along boundary).
- We tried both consistent ordering for all boundaries (x, y, z, time) and different orders for each boundary, but neither approach has worked.
- We’ve tested several schemes, but nothing works.

Some problems, that we’ve noticed:

1. After reading ice concentration boundary, nothing reading more in output file, why?  

2. Problem with boundary produces NaN-values (T-points are good, but velocities produces NaN, so you can see on step 0 T-points are good, then on step 1 there are NaN-values like on velocities from step 0), on this picture we’ve tested only short W-bdy:  

I’ll greatly appreciate if anyone could send a working file of bdy data and explain how it works.

Thank you!

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<div class="post-metadata">

**Author:** ![Saeed](https://avatars.discourse-cdn.com/v4/letter/s/e8c25b/32.png) [@Saeed](https://nemo-ocean.discourse.group/u/Saeed)\
**Post date:** [16 June 2024 06:11 UTC](https://nemo-ocean.discourse.group/t/how-to-use-unstructured-open-boundaries/703/2 "2024-06-16T06:11:06Z")

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Hi.  
Yes, when you delfine coordinate file for BDY, you cannot use index for T point for U and V point. The problem is that even if T point is in the sea, U and V for the same index can end up on the land and you will get None or your solution will blow up.

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**Author:** ![smasson](https://avatars.discourse-cdn.com/v4/letter/s/eb9ed0/32.png) [@smasson](https://nemo-ocean.discourse.group/u/smasson)\
**Post date:** [28 June 2024 08:46 UTC](https://nemo-ocean.discourse.group/t/how-to-use-unstructured-open-boundaries/703/3 "2024-06-28T08:46:18Z")

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There is and example of [nambdy\_index and nambdy\_dta](https://nemo-ocean.discourse.group/t/new-regional-configuration-setup-open-boundaries/37/6) here. It you still have problems, could you upload your namelist\_cfg ?