bc
Although called boundary condition, here we only deal with trivial Dirichlet boundary condition.
Syntax
There are currently several commands to define boundary conditions.
To apply BCs to node groups, it is possible to use the following commands.
Remark
Both
fix
andfix2
serve the same purpose but with different approaches. Thefix
command modifies the corresponding main diagonal term by multiplying a large number, for example . Thefix2
command erase the column and row of target DoF and set the main diagonal to unity. In both case, the corresponding right hand side entry is erased.The
fix2
andmultiplierbc
commands requires more operations but the final matrix is well conditioned.The performance difference is almost negligible. Either one can be used with direct solvers. The error won't accumulate as there is a special mechanism to prevent it.
The DoF identifier
(2)
takes the following string input:1
,2
,3
,4
,5
,6
,pinned
,encastre
,xsymm
,ysymm
,zsymm
and the corresponding initialsp
,e
,x
,y
,z
. The names do not actually reflect their meaning, instead, following DoFs would be restrained when string input is given.pinned
: 1 2 3encastre
: 1 2 3 4 5 6xsymm
: 1 5 6ysymm
: 2 4 6zsymm
: 3 4 5
The nontrivial Dirichlet boundary condition is treated as displacement load.
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