# Understanding Boundary Conditions

**URL:** <https://calculix.discourse.group/t/understanding-boundary-conditions/2187>\
**Category:** Uncategorized\
**Created:** [March 30, 2024, 8:00am UTC](https://calculix.discourse.group/t/understanding-boundary-conditions/2187 "2024-03-30T08:00:47Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![thapelo861](https://avatars.discourse-cdn.com/v4/letter/t/3d9bf3/32.png) [@thapelo861](https://calculix.discourse.group/u/thapelo861)\
**Post date:** [March 30, 2024, 8:00am UTC](https://calculix.discourse.group/t/understanding-boundary-conditions/2187/1 "2024-03-30T08:00:47Z")

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Good day please assist in explaining the boundary conditions listed below.

\*BOUNDARY  
nall,3,3,0.0 i,e explain this condition\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_  
1,1,3,0.0 i,e explain this condition\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_  
2,1,3,0.0 i,e explain this condition\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

\*BOUNDARY  
1,1,6,0.0 i,e explain this condition\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_  
2,3,3,0.0 i,e explain this condition\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_  
3,3,3,0.0 i,e explain this condition\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_  
4,3,3,0.0 i,e explain this condition\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_  
5,3,3,0.0 i,e explain this condition\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

I have read the CalculiX manual, the difference between homogeneous and inhomogeneous boundary conditions

In my understanding

homogeneous boundary conditions can be defined as follows.

\*BOUNDARY  
1,1,2,3 (This means node 1, is fixed in x(1), y(2) & z(3) direction

inhomogeneous boundary conditions can be defined as follows.

that’s where i get confused how to prescribe a displacement, temperature etc.

I,e i see  
\*BOUNDARY  
LINE3,1,1,0.0 (On line3 what does 1,1,0.0 mean? same as below)  
LINE1,2,2,0.0

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**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\
**Post date:** [March 30, 2024, 1:47pm UTC](https://calculix.discourse.group/t/understanding-boundary-conditions/2187/2 "2024-03-30T13:47:03Z")

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It’s rather simple because it’s always just:

`node/nset, first DOF, last DOF, magnitude`

Of course, magnitude applies only to BCs within steps since you can prescribe their non-zero values.

DOF numbers are 1,2,3 for x,y,z displacement and 4,5,6 for x,y,z rotation. Then there are non-mechanical DOFs like 11 for temperature.

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**Author:** ![thapelo861](https://avatars.discourse-cdn.com/v4/letter/t/3d9bf3/32.png) [@thapelo861](https://calculix.discourse.group/u/thapelo861)\
**Post date:** [March 30, 2024, 9:02pm UTC](https://calculix.discourse.group/t/understanding-boundary-conditions/2187/3 "2024-03-30T21:02:04Z")

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@Calc_em, Thank You for clarifying this part … node/nset, first DOF, last DOF, magnitude.