Transcript MESH, CONNECT & SET UP MY MODEL FOR FEA STUDIES

MESH, CONNECT & SET UP MY
MODEL FOR FEA STUDIES
by D Duraikannu
Graphics Systems Corporation
MESH, CONNECT & SET UP
What is SolidWorks Simulation?
• Design, Analysis Systems fully integrated within SolidWorks
• SolidWorks Simulation provides one screen solution for several
types of analysis
• Powered by fast solvers, SolidWorks Simulation enables you to
solve large problems quickly using your personal computer.
• SolidWorks Simulation comes in several bundles to satisfy your
analysis needs.
• SolidWorks Simulation shortens time to market by saving time
and effort in searching for the optimum.
2011 SolidWorks Simulation Product Bundles
Simulation Premium
Nonlinear
Flow
Simulation
•Electronics
•HVAC
Simulation Professional
SolidWorks
Premium
Frequency/
Buckling
Design Study,
Optimization
Fatigue
Static
Composites
SolidWorks
Motion
Thermal
Event Based
Motion
Drop Test
Sustainability
Pressure
Vessel
Advanced
Dynamics
Two Meshers: Standard Vs. Curvature
Standard Mesh
Curvature Based Mesh
Supports all possible
contacts/component
types
Default mesher in
SolidWorks 2011
Activates VeronoiDelaunay scheme for
subsequent operations
Activates Curvature-based
meshing scheme for
subsequent operations
Creates uniform mesh all
around the model
Creates more elements in
higher-curvature areas
automatically curved
Uses “Global Size and
Tolerance”
Uses “Min/Max size,
number of elements,
growth ratio”
Meshing Stages
• Evaluating Geometry
– Geometry errors may cause failure
• Processing boundary
– Surface meshing
• Creating mesh
– Volume filling
• Failure Diagnosis
– Complex single body component causes problems
– Improved a lot in 2011 SolidWorks
Preparing a Model for Analysis
• Simplify geometry
– Suppress cosmetic features
– Be careful in selecting stress concentration areas
– Check for rebuild errors
• Assembles: Interferences
– Often result of a poor modeling technique
– Thickness Interferences in the case of shells, use
correct “Shell offset method” – new in 2011
– Allowed only for Shrink fit
Example: Interference
• Meshing problems due to interference are quite
common
• Always check for interference in assembly
• Tools -> Interference Detection
• Interferences prevent compatible mesh
• Re-mesh failed parts with incompatible mesh is
not always a good option
Importance of Good Quality mesh
• Stress Concentrations
– Application of mesh control is a manual process
– Stress singularities: The more mesh is refined, higher
the stress valves
• Adaptive Meshing
– Available for Solids in Static Studies
– Depends on loading types
Viewing Mesh and Results
• Useful approach for checking behavior of the
model and mesh refinement level
– Settings: Mesh boundary options
– VON: Edit Definition -> Advanced Options ->
Element Valves
• Stress is calculated at Gaussian points within
element
– Element stress is an average of just the element
– Nodal stress is an average of adjacent elements
• Energy Norm Error
– Shows % difference between element and nodal
stress for each element
Importance of Tolerance
• For Standard Mesher: Tolerance is the valve below
which adjacent nodes will be merged
• For Curvature based Mesher: In 2011, it is defined
based on Min/Max size, number elements around
holes and element ratio
• Can be particularly importance for small features
being resolved
– If global tolerance is 30% greater than the smallest
element size specified in mesh control, global
tolerance value is changed to 30% of smallest element
size
Tolerance and small features
• Can be the cause of “Restraint transfer failed” or
“No loads applied” error when running a study
– Has to do with mismatch between geometry used in
actual definition (faces/edges) and mesh generated
• When getting restraint transfer failed error, check
defined restraint, and then “show mesh” to see if
area is resolved by mesh
• Beware of the model that have small features
compared to overall dimensions
Example: Mesh Tolerance
• Tolerance Too large: feature is not resolved
• Tolerance made smaller (tighter) so nodes are not
merged
Mesh Type Selection in 2011
• Treat as Beam
– Treat as Solid / Beam
– Can treat Solid Extrusion as beams
but must specify treat as beam
• Define Shell By Selected Faces
–
–
–
–
At mid surface
At Top Surface
At Bottom Surface
Specify Ratio
• Treat as Remote mass
Automatic Shell Realignment
• Uses an algorithm to
attempt to line up shell
top and bottom surfaces
so they are consistent
• Option to turn OFF / ON
is available through
“Simulation Options”
dialog
• Note: Having option
enabled may cause
meshing to take longer
time if there are many
elements – possible to
flip shells manually
Detecting Bad Geometry
• Use SolidWorks Utilities
Geometry Analysis tool
– Requires SolidWorks Premium
– Short edges, sliver faces, etc will
often cause mesh failure
– Does not work on imported
geometry
• Try exporting into IGES file and
importing into SolidWorks
– Can often heals problems areas
(gaps / faces)
Compatible / Incompatible Mesh
• Affects solid/solid, solid/shell or shell/shell that are
touching
• Compatible mesh with touching surfaces
– ‘Imprint’ of each face on the other – nodes line up at the
surface
• Incompatible mesh with touching surfaces
– Each component is mesh as if other is not there
• “Improve accuracy for contacting surfaces with
incompatible mesh” option – mortar bonding
Contact / Gap Elements
• No Penetration contact
– Node to Node
• Must touch initially
• No sliding – forces applied
parallel to contact normal
force
• Requires compatible mesh
– Node to Surface
• Each source node is assigned
a target element
• Slower than node to node
– Surface to Surface
• Most general option
• Most resource intensive
• Supported for Nonlinear
studies
Contact Analysis tips
• Direct Spare solver is preferred for
Contact problems
• Set global contact to free to ensure
no undesired bonding occurs –
contact hierarchy
• Node to Surface is default option
• Shell thickness is taken into account
for No penetration or virtual wall
contact
Bonding Diagnosis
• Two possible error messages
– Direct Sparse: “Model is unstable. Restraints may not
be adequate”
– FFEPlus: “Iterative solver stopped”
• Analysis fails – no results
• Enable soft spring option
• Large displacement flag may be thrown
– Say “No” (do not rerun this large displacement option
on) and save the results and check the animation
Locating a node or element
• Helpful for error messages referencing a
node/element
• In Nonlinear Analysis check *.OUT file
– Problems with convergence can have to do with specific
region and that can be due to meshing or contact
definition
– Solver places a notes that reference specific
nodes/elements in *.OUT file
• Right click on Mesh -> List selected
– Node / Element location is annotated
– Alternative approach: export as *.geo and search for node
number in notepad and get coordinates then insert a point
Beam Contact
• Beam to beam contact is defined
by joints
– No contact sets for beam to beam
contact
• Can bond a beam joint or beam to
a shell / solid face
– Beam joint or beam as set 1
– Shell / solid face as set 2
• Joints created at intersections of
neutral axes and free ends
• Joint colors
– Purple: joint connecting two or
more beams
– Olive: free or disconnected joint
Additional contact analysis tips
• If vertices and edges are involved in contacts, use
node to Surface
• Mesh should be finer on set1 entity than on set 2
– Can have convergence problems if set2 has finer mesh
• Split lines reducing the source area can help speed up
the convergence
• For nonlinear contact problems with nonlinear
material models, try draft quality
• In linear static analysis, remember that only initial
and final positions are saved – animation may show
interference
Diagnostics using “Frequency Study”
• Test for Rigid body motion (RBM)
– FFEPlus with soft spring enabled
– Combinations of restraints and
bonding with improper contacts
could result in RBM
– Rigid body mode shows frequency
valves as closes to zero
• Test for bonding behavior
– Look at mode shapes animations
– Loads can be suppressed for this
study
– Copy study information from ‘static’
to ‘frequency’ or vice-versa
Thank You
• For any questions/comments/feedbacks
– [email protected] & [email protected]
– Phone: 1-800-454-2233
• Many thanks to WIILSSUG Leader: Brain Kinnune
and Ruud Lighting, Inc.
• See you all in Nov 2011 for next WI/IL Simulation
User group (WIILSSUG) meeting