In Tosca Structure.bead,
the displacement direction of the design nodes (optimization displacement
vector) is normally determined as the surface normal (see Update of Optimization Displacement Vectors (VECTOR)). A
restriction of the displacement direction in bead optimization might be
necessary due to two reasons:
- Standardly, the displacement direction in bead optimization is determined
in the initial model and is not modified during optimization (OPT_PARAM,
VECTOR = FIRST). In order to define own displacement directions, the original
displacement directions might be restricted.
- Some areas in the design domain should not be modified during optimization,
for example, the boundary of the design domain. These areas might be restricted
using the
CHECK_DOF
or CHECK_BC
parameters.
Loading Node Fixations through the Interface from the FE Program
The full or partial fixation of nodes is the most common and most
important type of restriction, it is practically used in every optimization
model. The most efficient method is to define the displacement restrictions
in the FE preprocessing as an extra load case
in the transition model and then to load it through the FE interface in the
optimization preprocessor.
In order to do this, the interface must
first be activated with OPTIONS, READ_BC=...
. In this way, all node fixations for
the optimization model can be defined in advance in the FE preprocessor.
The fixation is always based on the FE displacement coordinate system
of the node.
The parameter
CHECK_BC = ALL
activates the node fixations of the node group (ND_GROUP
parameter) which are loaded through the FE interface. Fixations that
reference nodes not contained in the node groups are not activated.
To prevent loaded fixations from being activated, enter:
CHECK_BC = NO
Definition of the Displacement Direction by Command
The CHECK_DOF
parameter can be used to restrict other
displacement directions if necessary as an addition or at a later stage.
When entering node fixations by command and in contrast to load the
node fixations through the FE interface, it is necessary to first compile
all nodes that should be assigned a certain attribute to a node group.
The coordinate system must also be defined or loaded.
With the parameter
CHECK_DOF = cs_name,[FIX|FREE],[FIX|FREE],[FIX|FREE]
all the displacements of all nodes in the node group selected with ND_GROUP
are fixed (FIX
) or free (FREE
) relative to the specified
coordinate directions of the coordinate system, cs_name. Either FREE
or FIX
is allowed for each coordinate direction.
Note:
The main difference between CHECK_BC
and CHECK_DOF
is: CHECK_BC
is read in through the FE interface whereas
CHECK_DOF
is defined in the optimization preprocessor.
Generally, with CHECK_BC
each node has its own fixation
in its own displacement coordinate system, whereas all nodes of the node
group are all fixed in the same coordinate system with CHECK_DOF
.