HM Automeshing extract - Altair University · Title Microsoft PowerPoint -...

Copyright© 2009 Altair Engineering, Inc. Proprietary and Confidential.All rights reserved.Copyright© 2009 Altair Engineering, Inc. Proprietary and Confidential.All rights reserved.

Automeshing Introduction

Copyright© 2009 Altair Engineering, Inc. Proprietary and Confidential.All rights reserved.

Automeshing: What is it?

• The automesh panel creates shell mesh on existing surfacesAll id ti f h• Allows rapid generation of mesh

• Most parts from CAD software come in as surfaces• Automeshing allows all surfaces of a part to be meshed at the same time• Mesh on properly connected geometry assures proper connectivity of mesh


Automeshing: What is “topology”?

• Topology is how surfaces connect to adjacent surfaces of a partS f ti it i t ll d b th i t d f d• Surface connectivity is controlled by the associated surface edges

• If a surface edge is associated with more than 1 surface, those surfaces areconsidered to be connected (“equivalenced”)

• Surface edges are categorized named and colored according to the number of• Surface edges are categorized, named, and colored according to the number of associated surfaces:

Free edge (red) T-junction edge (yellow)Free edge (red)• Associated with only 1

surface• Surfaces with a free edge

between them are NOT

T junction edge (yellow)• Associated with 3 or more

surfaces• Example: surfaces forming a

T-connectionbetween them are NOT equivalenced at that edge

Sh d d ( )

T connection• Surfaces are equivalenced

Shared edge (green)• Associated with 2 surfaces

Suppressed edge (blue)• Surfaces are treated as though

• Surfaces are equivalenced combined into 1 surface


Automeshing: How topology affects the mesh

• Surface edges control how mesh created on adjacent surfaces interact:

Free edge between Shared edge between

Free edges (red) Shared edges (green)

Free edge between 2 surfaces

5

Shared edge between 2 surfaces

Nodes are placed along edge for meshing

5

5

52

2 3

3Nodes are placed along edge for meshing

5

5

52

2 3

35

Mesh is discontinuous;nodes along the free edge

5

Mesh has proper connectivity; nodes along

52

are not equivalenced (Nodes only separated for

the edge are equivalenced

illustration)


Automeshing: How topology affects the mesh

• Surface edges control how mesh created on adjacent surfaces interact:

S d d f

Suppressed edges (blue) T-junction edges (yellow)

Suppressed edgebetween 2 surfaces

Non-manifold edgebetween 3 surfaces

Edge is ignored; nodes are not placed alongth d

Nodes are placed alongedge for meshing

5

55

5

35

54

4

3the edge

Area is treated just like 1 Mesh has proper

55

53 4

3

3

jsurface; there is no line of nodes along the edge

p pconnectivity; nodes along the edge are equivalenced


Topology Refinement: What is it?

• “Topology refinement” is modifying topology in order to obtain a quality mesh• Unlike defeaturing, this generally does not change the shape of the part

• CAD geometry has topology details that interfere with mesh quality• Edges are created where ever there is a change in surface curvature• Even smooth areas can be split into several faces• The automesher will be forced to place nodes along the edges and fixed points

• This may cause small element lengths, angles, aspect ratios, etc. depending on the shape of the model

• CAD geometry can also have surfaces with a complex outline• Highly complex shapes can make it hard to get a quality mesh• Adding in edges splits the surfaces into smaller and simpler regions which can be

meshed easier• Fixed points can be added in to force a node to be placed at that location, giving

more control


Topology Refinement: Examples

Suppressingedges

Addingedges

Removingfixed points

Addingfixed points

Replacingfixed pointsedges edges fixed points fixed points fixed points

Bef

ore

Afte

r


Topology Refinement: Tools

Edge edit• Toggle – Select a shared edge to suppress it• (Un)Suppress – Select multiple edges to suppress all of them at once

Point editPoint edit• Add – Add fixed points to help control mesh pattern

• Especially helpful along edges to control node seeding• Suppress – Removes unwanted fixed points• Replace – Combines 2 fixed points together at a single location• Project – Projects fixed points onto a nearby edge

• Useful for aligning mesh between 2 edges

Surface edit – All functions add edges by cutting surfaces• Adding edges can be useful for controlling mesh patterns in large areas• Trim with nodes – Uses node locations to cut surfacesTrim with nodes Uses node locations to cut surfaces• Trim with lines – Uses lines to cut surfaces• Trim with surfs/plane – uses other surfaces or a defined plane to cut surfaces



Quick edit• Has a number of tools found in other panels• Has a number of tools found in other panels• Focused on tools with minimal user input for rapid editing

• Split surf-node: Adds an edge to or divides a surface by cutting in a straight line between 2 selected nodes

• Split surf-line: Adds an edge to or divides a surface by cutting a straight line between a nodeand perpendicular to the selected line.

• Washer split – Adds a circular edge around a hole in a surface• Mostly used for creating all quad mesh around a hole

• Toggle – Same as edge edit panel• Remove Point – Deletes a selected fixed point



Quick edit, continued,

• Replace point – Same as point edit panel

Add/ i t i t C t fi d i t t th l t d l ti• Add/remove point : point – Creates a new fixed point at the selected locations

• Add point: line – Creates a user specified number of fixed points along the selected edge

• Project point – Same as edge edit panel


Topology Refinement: Tips

• Mesh the partVi ll th t t l k f h tt• Visually scan the part to look for poor mesh patterns

• Use element checks in order to find areas of poor element quality• Check elems panel, QI Panel, etc.

• Suppress edges with edge edit :(un)suppress• Use various settings for break angle to suppress many edges at once

• Sometimes suppressing all edges and then unsuppressing desired edges canbe a good method.

S ll th fi d i t b f dd i• Suppress all the fixed points before add more in• Gets rid of as many fixed points as possible, leaving ones that are required

Experiment!There is no set process, so experience is a key factor in refining topology


Automeshing: The Automesh Panel

“Automesh” PanelMesh > Create > 2D AutoMesh

• Meshing Methods:•

•

mesh surfaces or re-mesh existing meshes with constant size

the surfaces are meshed to optimize the quality index (QI) of the elements

generated

set specific meshing parameters to limit how far the mesh elements can

deviate from the actual edges of the surfaces meshed•

•

•

to mesh within limits of element deviation from a surface

Rigid Body meshing produces a poor-quality mesh, but one that

accurately models the surface shapes




• Meshing Mode:

• – Creates mesh using automesh panel settings

• – As automatic; also opens the meshing module tointeractively edit the mesh




• Mesh Parameters:• - Target size of elements to create• - Type of elements to be created

• – Quad dominant mesh; will use trias if necessary

Equilateral (60 60 60) tria meshQuads Mixed

• – Equilateral (60-60-60) tria mesh

• – Quad mesh with use of trias to create as rectilinear a mesh as possible

– Only quad elements created

• – Isosceles (45-45-90) tria mesh

•

Trias R-trias

• - advanced option allows you to select mapped and free type of mesh




• Select surfaces to be meshed

• Destination component:• Elements will be created in the current component

Elements will be created in the component of the surface(s)• Elements will be created in the component of the surface(s) being meshed

• Identify and Select:••

Click to select surfaces that have not been meshed Click to select surfaces that failed to mesh in a previous operation




• Mesh Connectivity:• Keeps the re-meshed selection connected to the adjoining mesh Keeps the re meshed selection connected to the adjoining mesh

with the same connectivity Keeps the re-meshed selection connected to the adjoining mesh

but updates the connectivity Separates the re meshed selection from the adjoining mesh so

•

Separates the re-meshed selection from the adjoining mesh so that they are no longer connected

Activates all manual adjustments and options previously used to mesh

•

•




• Mesh Parameters:• will produce a more orthogonal quad dominated mesh will produce a more orthogonal quad dominated mesh

••

To keep elements roughly the same size To prevent the mesh from producing skewed elements

• Forces opposite surface edges to use consistent edge densities




• Meshing Mode:• As automatic; also opens the meshing module to interactively edit the mesh

• General Controls• Creates and updates the mesh preview using the current settings Creates and updates the mesh preview using the current settings

• User updates some mesh parameters on a surface, then clicks mesh to view the results• Accepting and Canceling

••

Cancels out of the meshing module; no mesh is created Creates the mesh as per the mesh preview and returns to the automesh panel• Creates the mesh as per the mesh preview and returns to the automesh panel Offers Fit and controls from the View panel

• Only applies to surfaces that are currently being meshed•


Automeshing: The Meshing Module

“Automesh” PanelMesh > Create > 2D AutoMesh Interactive• Density Control element density along edges• Density – Control element density along edges

• Mesh Style – Set method and type that determines mesh pattern and smoothing

• elem type Determine the type of elements to be used in the mesh



“Automesh” PanelMesh > Create > 2D AutoMesh Interactive• Mesh Style continueMesh Style continue

• mesh method:• Autodecide Automatically selects one of the

below methods• map as rectangle For rectangular shaped

areas; can sometimes be used for other shapesas well

t i l T i l h d• map as triangle Triangular shaped areas• map as pentagon Pentagonal shaped areas• free (unmapped) For areas of any shape

• Element type and method combine to determine the overall “style” of your meshThis “style” can be viewed by mesh that transitions between different density values:• This “style” can be viewed by mesh that transitions between different density values:

Mesh TypesQuad Mixed Trias R-trias

Map as

Met

hods

Rectangle

Free (Unmapped)

Mes

hM



“Automesh” PanelMesh > Create > 2D AutoMesh Interactive• Biasing – Controls the distribution of nodes during node seedingBiasing Controls the distribution of nodes during node seeding

• bias style: Biasing

• Checks – Evaluates element quality of the generated meshy g


Automeshing: Process and Strategy

• Use geometry cleanup tools to address surface connectivityA t h th f• Automesh the surfaces

• Set the approximate element size you want• Use type and algorithm to set the overall mesh “style”• Alter individual densities to find better mesh patterns• Change some biasing on problem surfaces (this can change mesh

pattern as well)• Goal: get the mesh to be approximately 80-90% good quality• Use HyperMesh’s mesh editing tools to fix the 10-20% elements that have

poor quality or bad mesh pattern• Don’t delete a mesh that is 90% good. Keep it and fix the 10% that is bad

• Experience is key: EXPERIMENT!p y

Date post:	14-Aug-2018
Category:	Documents
Upload:	phungdat
View:	213 times
Download:	0 times

HM Automeshing extract - Altair University · Title Microsoft PowerPoint -...

Documents