PLANAR (2D) SIMULATIONS: Plane stress, Plane strain, Axisymmetric
3D SIMULATIONS: Beams, Plates or Shells, Solids
Rule of Thumb: Try to use planar techniques (2D) FIRST
2D MODELING
typically
"______" structure, no stress normal to plane of interest
Many
3D cases can be approximated as 2D plane stress (sz
= 0)
Model
the cross section (thickness is equal on both sides)
typically
"________" with
respect to cross-section
no
strain normal to the plane of interest (ez
= 0)
Water
dams, retaining walls (typical civil engineering problems)
geometry
______ boundary conditions assume "body of revolution"
ANSYS:
Y-axis is centerline, all X-coordinates positive or zero
The
loading must also be revolved around the axis also.
Constraints
must be constant around the part’s axis, as well.
Even when small features (holes) break up the body of revolution, an axisymmetric assumption may still be appropriate.
Could this body be
treated as axisymmetric ?
Allows for
______________ runs,
__________ accurate
boundary conditions, and
__________ accurate
solutions.
"STATIC" analyses must be
constrained to prevent rigid body motion. Use of symmetry constraints
simplifies your work in providing sufficient constraint to prevent rigid body
motion (indeterminate stiffness matrix = zero or negative pivot).
Geometry and
boundary conditions are (or nearly are) equal across one or more planes
Concentrated loads
which act on a symmetry cut are divided by the number of symmetry planes
which cut at that point.
Area dependent loads
are not divided (i.e., pressure). The program can determine the area
affected by the load.
Constraints prevent edges from leaving or crossing a symmetry plane.
Does this
part have reflective symmetry ?
Geometry and loads
repeat in sectors ________________ an axis
e.g., fan blades,
flywheel
Geometry and loads
repeat in identical sectors ______________ an axis
e.g., chain, finned
tube
If you choose to model the full structure, "bury" symmetry constraints at the proper cutting planes:
