# [aspect-devel] boundary velocity function expressions

John Naliboff jbnaliboff at ucdavis.edu
Mon Oct 10 09:25:29 PDT 2016

```Hi Payman,

Specifying the velocity on the boundaries works a bit differently than
what you have outlined below.

In 2D you need to specify velocity components for x and y, which you do
via the function.  You can control how the velocity on different
boundaries (ex: left & right) by including conditional statements in
your functions based on the position (defined by 'x' and 'y' in 2D).

You can also specify that only certain components of the function apply
to a certain boundary (i.e. only x velocity from functions is applied to
left/right boundary).

If there is a specific setup you are thinking of, can you sent over a
basic parameter file that we can look over?

Cheers,
John

*************************************************
John Naliboff
Assistant Project Scientist, CIG
Earth & Planetary Sciences Dept., UC Davis

On 10/09/2016 03:08 PM, Payman Janbakhsh wrote:
>
> Hi,
>
> I’m trying to implement the following for a 2D problem:
>
> Set Prescribed velocity boundary indicators = left : function  ,
> right : function
>
> But get error when trying to give  Function expressions in:     set
> Function expression =
>
> I have tried separating 2 velocity components with semicolon and
> separate function expressions with comma .
>
> Example:
>
>                                              Left boundary
> function                  right boundary function
>
> Set Function expression =             if(z>=1000 , 1, 0) ; 0
>           ,           if(z>=1000, -1,0) ; 0
>
> I’ve tried many ways including below but all give errors or
> nonsensical velocity Glyphs:
>
> Set Function expression =          left: if(z>=1000 , 1, 0) ; 0
>           ,     right: if(z>=1000, -1,0) ; 0
>
> Set Function expression =           left =   if(z>=1000 , 1, 0) ; 0
>           ,    right= if(z>=1000, -1,0) ; 0
>
> Set Function expression =           ( if(z>=1000 , 1, 0) ; 0     )
>  ,       ( if(z>=1000, -1,0) ; 0 )
>
> …
>
> How can I separate multiple function expressions each for its
> corresponding boundary indicator ?
>
> Thanks
>
> Payman
>
>
>
> _______________________________________________
> Aspect-devel mailing list
> Aspect-devel at geodynamics.org
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