Meshing with COMSOL Multiphysics 4 - Michelsen · PDF file• Automatic mesh generation...
Transcript of Meshing with COMSOL Multiphysics 4 - Michelsen · PDF file• Automatic mesh generation...
Meshing with
COMSOL Multiphysics 4.3a
General Introduction
© 2012 COMSOL. All rights reserved.
• Meshing Techniques
• Mesh Elements
• Creating Meshes
• Importing Meshes
• Virtual Geometry and Mesh Control Operations
• Mesh Adaptation During Solving
Contents
Meshing Techniques
• Automatic mesh generation adapted to the physics settings in the model
• Tuned for – Fluid flow
– Plasma
– General physics
Model of an ICP reactor created with the Plasma Module
Physics-Controlled Meshing
• Nine predefined mesh size settings
ranging from ”Extremely fine” to
”Extremely coarse”
• Starting point for manual mesh
generation
ICP reactor geometry meshed
with “Extra Fine” setting
ICP reactor geometry meshed
with “Extra Coarse” setting
Physics-Controlled Meshing
• Manually add mesh operations to
generate a mesh
• Mesh operations are saved in a
meshing sequence
• Several meshing sequences may be
saved in a model
• Nine predefined mesh size settings
• Manual control over mesh size
User-Controlled Meshing
• Add, delete, disable, move, or edit
mesh operations
• Mesh operations can be
parameterized – Use expressions with variables for mesh size
parameters
• Enables automatic regeneration of
mesh for geometric parametric sweeps
The Meshing Sequence
Mesh Elements
Triangles
Quadrilaterals
Tetrahedrons Hexahedrons
Prisms Pyramids
2D and 3D Elements
Creating Meshes
• Generate triangular, quadrilateral, or
tetrahedral meshes
• Robustness ensured by automatic or
manual choice of Delaunay and
advancing front triangulation methods
• Fully automatic meshing with 9
predefined mesh size parameters
• Manual adjustment of mesh size
parameters
Meshed geometry of a
continuous velocity (CV) joint.
The model is courtesy of Fabio Gatelli, Metelli S.p.A., Italy
Creating Unstructured Meshes
• Maximum element size
• Minimum element size
• Curvature
• Element growth
• Resolution of narrow regions
• Explicit sizing on edges
Element Size Control
Handling Small Features
• Built-in detection for small features
and narrow regions in geometry
• Automatic element size adjustment to
small features, narrow regions and
curved boundaries
• Detected edges and faces are
highlighted in the geometry and can be
used as input for further CAD
defeaturing or virtual geometry
operations
Model of a Li-Ion battery pack Swept, hexahedral mesh
Mapped mesh on end
surfaces
Tetrahedral mesh by conversion
Working with Structured Meshes
• Create mapped meshes in 2D, or 3D surfaces
• Create swept meshes, hexahedral or prismatic, in 3D
• Use a sequence of map, sweep, and convert operations to
create structured triangular or tetrahedral meshes
• Possible to sweep a source side with
N faces to a destination side with M
faces, where N≥M
• Control element distribution in the
sweep direction
• Supports triangular, quadrilateral and
mixed meshes on end surfaces
• Create sweepable domains by – Hiding geometry features with virtual
geometry operations
– Partitioning domains with geometry
operations
Partitioned source face with mixed
triangular and quadrilateral mesh
Swept mesh with prism and
hexahedron elements
Swept Meshes
• Possible to create a
continuous mesh while
keeping separate regions
(parts are bonded)
• Possible to mesh parts
individually with
compatible/incompatible
mesh on touching surfaces Continuous mesh
Incompatible mesh Compatible mesh
Meshing Several Parts (Assemblies)
• Use – In fluid flow applications to resolve boundary layers along the no-slip boundaries
– In heat transfer applications to resolve large temperature gradients close to heated surfaces
– In low-frequency electromagnetics to resolve the skin effect
• Boundary layer mesh is created automatically when needed for fluid flow
applications
Benchmark model of turbulent flow
field around a car-like object
Prism elements in the boundary
layer mesh of the above model
Boundary Layer Meshes
• The boundary layer mesh consists of – Layered quadrilateral elements in 2D
– Layered prism or hexahedron elements in 3D
• Automatic detection and treatment of
sharp corners
• Can be created for any mesh
• Manual control of boundary layer
properties
• Smooth transition to the interior mesh
• Support for boundary layers on
isolated boundaries
Creating Boundary Layer Meshes
New
New
• Use for applying periodic boundary
conditions with high accuracy
requirements, such as – Cyclic symmetry in structural mechanics
applications
– Floquet boundary condition for
electromagnetic wave propagation
• Available for domains, faces and
edges
• Automatic orientation of source mesh
on destination
• Supports copy to multiple destinations – Quick mesh generation for large periodic
geometries
Copying Meshes
• Use when creating meshes for geometric multigrid solver
• Use for convergence studies or to verify whether the solution is mesh dependent
• Different physics may have different meshes over the same region
• Duplicate, then edit mesh sequences
• Link meshing sequences by using the reference operation
– Apply scaling to the referenced mesh to create coarser or finer mesh
– Break the link to edit the meshes separately
• Use multiple imported meshes when preparing the mesh in other software
Multiple Meshes
• Quick overview of the mesh
• Minimum and maximum quality
• Histogram plot of element quality
Mesh Statistics
• Mesh plot to aid in creating good quality meshes – Plot various element types separately
– Color elements according to quality
– Show elements based on logical expressions
– Shrink elements for better visualization
Mesh Visualization
• Export the triangular surface mesh of the geometry, mesh, or deformed mesh to the
STL format (.stl)
• Create or modify designs in CAD programs based on the exported STL surface mesh
Large deformation analysis of a snap
hook. The deformed geometry can be
exported to STL format
STL Export
Importing Meshes
• Import mesh and materials
• Automatic split into domains
based on material data
• Automatic split into domains
based on element type
• Automatic or manual control
of parameters for face
partitioning
Imported Nastran
mesh of a crankshaft
Importing Nastran (.nas) Meshes
• .mphbin, .mphtxt mesh format
• Model with COMSOL Multiphysics on
meshes based on MRI and scanned
data
• The following software support export
to COMSOL mesh format • Mimics by Materialise, read more on
www.materialise.com
• +ScanFE by Simpleware, read more on
www.simpleware.com
Imported mesh, generated with
+ScanFE software by Simpleware,
of a scanned pork (bacon) side
The model is courtesy of Simpleware.
Importing COMSOL Meshes
• Create new boundaries and domains on imported meshes for assigning boundary
conditions and material properties
• Group existing mesh elements using one of the following operations:
– Ball
– Box
– Join Entities
– Delete Entities
– Create Vertex
– Logical Expression New
Partitioning Imported Meshes
Virtual Geometry and
Mesh Control Operations
• Complements CAD defeaturing and repair operations on the imported geometry
• ”Hides” geometry features from the mesher
• Use to get rid of – Sliver faces
– Short edges
– Small faces
– Undesired surface partitioning
– Small domains due to overlapping solids
• Difference from geometry defeaturing – Works on the geometry that is seen by the mesher
– Keeps the underlying shape of the geometry
Virtual Geometry Operations
• Gain precise control over mesh layout and density in regions of known rapid changes
or steep gradients, which may occur for example in CFD simulations
• Selected geometry features are available exclusively to control local mesh properties
and do not affect the subdivision of edges, faces, or domains when applying physics
settings
Domain for mesh control in benchmark model of turbulent flow field around a car-like object
Mesh Control Operations
Mesh Adaptation during Solving
Plot of sound pressure level
after shape optimization of an
initially cone shaped horn
• Automatic or manual choice of shape
function and element order
• Available shape functions include – Lagrange
– Hermite
– Argyris
– Discontinuous Lagrange
– Curl (vector) elements, etc.
• Automatic or manual choice of
geometry shape order
Model of an antenna implemented with
the Electromagnetic Wave interface
utilizing curl elements
Shape functions and Element Order
• Improve solution accuracy by adapting
the mesh to the problem’s physical
behavior
• The solver minimizes the error
according to an error criterion by
adding mesh elements to refine the
mesh
• Available for stationary, eigenvalue,
eigenfrequency or time dependent
studies
Ink droplet ejected through a nozzle
modeled with the help of transient
mesh adaptation
Adaptive Mesh Refinement
• Study the behavior of different shape
of an original object by enabling mesh
movement
• Model a process which removes or
adds material from the original
geometry, for example electrochemical
polishing or electrodeposition
• Perform optimization and sensitivity
analyses
Model of electrodeposition of
copper
Sensitivity analysis of a
structural member to
determine the effect of small
design modifications
Deformed Geometry
• Study deformation of solid
objects
• Model fluid-solid interaction,
or for example movement of
solids under electric fields
Model illustrating the principles of a MEMS
flow meter. Due to the fluid flow the
obstacle in the channel is bending, which
results in considerable change of the
shape of the flow domain
Moving Mesh
• Available for Moving Mesh
and Deformed Geometry
• Automatic remeshing,
based on user-defined
mesh quality threshold
• The simulation is
automatically continued
starting from the new
mesh
Mesh elements before and after an automatic remesh,
during the solution of a model for electrodeposition of
copper
Automatic Remeshing