Vectors for velocities

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PLA
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Vectors for velocities

PLA
Hi,
Is there a way to extract, export,… the static arrows for velocities ?
Thanx
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Re: Vectors for velocities

cameron
In the HDF file you can obtain the Vx and Vy values which could be used to generate arrows in ArcMap or other software.  
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Re: Vectors for velocities

HGoodpasture
How do you get the Vx and Vy from the hdf file?
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Re: Vectors for velocities

cameron
You have to turn on the option in the output options and then open up the HDF file with a HDF viewer to extract or use python to extract.
Max
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Re: Vectors for velocities

Max
Yes, But WHICH tables in the HDF are the ones with the velocity data.
The Face Velocity table gives a value for a single face at a particular time slice, but how would one go about finding the velocity vector for a cell ? I can picture adding the vectors for each face of a cell to get a cell velocity, but it is unclear how to get the vectors (i.e direction of the face velocity) from the hdf files. Would one use the Faces NormalUnitVector and Length table?

On a bigger topic, where are all these tables in HECRAS HDF tables defined. What is the relationship between them? How does one go about understanding how to use the information in the HDF files? Is there documentation or examples of how to use them? I have not found anything in multiple internet searches.
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Re: Vectors for velocities

jarvus
Computing the velocity vector at a cell is not straight forward.  The finite volume solution has a method that does this by computing a velocity field.  The RAS hydraulic reference manual discusses this.

I don't know that the RAS HDF tables are documented anywhere.  For the most part, I have found them pretty self evident.  I think if you want to use them, you are mostly on your own.
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Re: Vectors for velocities

cameron
In reply to this post by Max
It would be under Results|Unsteady|Output|Output Blocks|Base Output|Unsteady Time Series|2D Flow Areas|Perimeter 1

If you your mesh is named something different than perimeter 1 then it will be that name.

Each table in the HDF file has an attribute that tells you what each row represents.

It will be broken down by Vx (Node X Vel) and Vy (Node Y Vel) tables with values of time (rows) based on output interval and Vx/Vy in the columns.  The columns will represent the cell vertices.

If you don't know what your output interval is, there is a Time table that tells you.  

The Face Points Coordinate table in the Geometry|2D Flow Areas|Perimeter 1 contains the x/y points for each cell face.

This means you can create a point from the vertices and associate the Vx/Vy values with it in ArcMap or something else to display the vectors.

Important to note that velocities are calculated at the cell vertices, not cell center. That means each cell can have up to 8 vertices.