# [aspect-devel] boundary velocity function expressions

Payman Janbakhsh payman.janbakhsh at mail.utoronto.ca
Mon Oct 10 19:22:09 PDT 2016

```Thank you John,
Actually the continental extension prm file that you sent to Mohamed helped me to figure out the velocity prescription to different boundaries using functions.

However, how can I prescribe velocity to a segment of a boundary and let the rest of that boundary be tangential?
For instance, considering a right boundary, a mantle lithospheric slab having its own westward prescribed velocity, but the rest of that boundary (mantle) be tangential.

Thanks again

Payman

From: Aspect-devel [mailto:aspect-devel-bounces at geodynamics.org] On Behalf Of John Naliboff
Sent: October 10, 2016 12:25 PM
To: aspect-devel at geodynamics.org
Subject: Re: [aspect-devel] boundary velocity function expressions

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

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