# Visualizing Boundary Traction

**URL:** <https://community.geodynamics.org/t/visualizing-boundary-traction/3106>\
**Category:** ASPECT\
**Created:** [September 9, 2023, 4:51pm UTC](https://community.geodynamics.org/t/visualizing-boundary-traction/3106 "2023-09-09T16:51:38Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![chameerasilva](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/chameerasilva/32/1160_2.png) [@chameerasilva](https://community.geodynamics.org/u/chameerasilva)\
**Post date:** [September 9, 2023, 4:51pm UTC](https://community.geodynamics.org/t/visualizing-boundary-traction/3106/1 "2023-09-09T16:51:38Z")

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Hi everyone,

When we apply a traction force to a boundary, which field should i look to track it ?. I checked both pressure and stress, but it will change with time. So, Should the applied traction ( for example from a ASCII file) be constant over the model run time ? 🙂 👋

Best,  
Chameera

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**Author:** ![bobmyhill](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/bobmyhill/32/38_2.png) [@bobmyhill](https://community.geodynamics.org/u/bobmyhill)\
**Post date:** [September 9, 2023, 5:27pm UTC](https://community.geodynamics.org/t/visualizing-boundary-traction/3106/2 "2023-09-09T17:27:48Z")

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Hi Chameera,

A traction is a force applied across a specific surface. A single traction does not uniquely define the pressure or the stress.

To answer your Question 1: You can calculate the traction \boldsymbol{t} across any given surface from the (Cauchy) stress tensor \boldsymbol{\sigma} via the equation t\_i = \sigma\_{ij} n\_j, where \boldsymbol{n} is the unit normal to the surface. You can get paraview (for example) to do this calculation.

To answer your Question 2: You can apply a constant or time-dependent traction condition to your model. See [Boundary traction model — ASPECT 2.6.0-pre](https://aspect-documentation.readthedocs.io/en/latest/parameters/Boundary_20traction_20model.html)

Does this answer your questions?

Best wishes,  
Bob

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**Author:** ![chameerasilva](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/chameerasilva/32/1160_2.png) [@chameerasilva](https://community.geodynamics.org/u/chameerasilva)\
**Post date:** [September 9, 2023, 6:09pm UTC](https://community.geodynamics.org/t/visualizing-boundary-traction/3106/3 "2023-09-09T18:09:56Z")

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Hi Bob,

Thank you for the reply 👋 . Just to clarify, because I apply traction from an ASCII file ( Now i think this represent constant traction 🙂 ) which has values defined for Y coordinate. When i calculate traction from Cauchy stress tensor, i should be seeing constant value for each depth level ( @ y = 200e3 should have a constant value ) for every time step forward from applied traction time step.

calculated traction will be represented by 2 by 1 matrix [stress[0,0] stress[1,0] ] where normal vector is [1 0] for the right boundary.

Is this the right way of understanding your answer to the question 1 ? Or can you explain a little bit more about the traction values that i should be getting over the model time considering the model depth, if you think i did not understand your answer 😅 ?

Best,  
Chameera

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**Author:** ![bobmyhill](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/bobmyhill/32/38_2.png) [@bobmyhill](https://community.geodynamics.org/u/bobmyhill)\
**Post date:** [September 9, 2023, 6:45pm UTC](https://community.geodynamics.org/t/visualizing-boundary-traction/3106/4 "2023-09-09T18:45:21Z")

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Yes, that is correct - the boundary traction model constrains one or more elements of the traction vector at every point on the prescribed boundary/boundaries ([Boundary conditions — ASPECT 2.6.0-pre](https://aspect-documentation.readthedocs.io/en/latest/user/methods/basic-equations/bc.html))

Best wishes,  
Bob

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**Author:** ![chameerasilva](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/chameerasilva/32/1160_2.png) [@chameerasilva](https://community.geodynamics.org/u/chameerasilva)\
**Post date:** [September 9, 2023, 7:07pm UTC](https://community.geodynamics.org/t/visualizing-boundary-traction/3106/5 "2023-09-09T19:07:24Z")

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Thank you Bob.

Best,  
Chameera