10/31/2014

Rotordynamics with ANSYS Mechanical Solutions

Pre-processing:
Appropriate element formulation for all geometries
Gyroscopic moments generated by rotating parts
Bearings
Rotor imbalance and other excitation forces
Rotational velocities
Structural damping
Solution:
Complex eigensolver for modal analysis
Harmonic analysis

Transient analysis
Rotordynamics simulation can be performed in two different reference frames:
Stationary reference frame:
Applies to a rotating structure (rotor) along with a stationary support structure
Rotating part of the structure to be modeled must be axisymmetric
Rotating reference frame:
The structure has no stationary parts and the entire structure is rotating
Consider only the Coriolis force 
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ICEM CFD Introductory Course Introduction to Hexa –Workshop 4 Elbow Junction

§Blocking Strategy
In this Elbow geometry there is an cylindrical hole through the geometry.
Such Elbow can not be captured well with single Ogrid through out the elbow pipe. This is because grid lines need to be align with hole
To resolve this we will be creating an L-shaped blocking initially with an O-grid only in one straight section to capture the cylindrical hole.
Then we create final ogrid through out the elbow pipe which align well with elbow surface
§Begin blocking
Select Blocking > Create Block > Initialize Blocks
Change Type to 3D Bounding Box
Click Apply
This creates one block which encloses the entire geometry
Curves automatically change color (colored separately instead of by part) to allow you to see where the ends of curves are
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ICEM CFD Introductory Course Introduction to Hexa –Workshop 3 3D Pipe Junction O-grid Creation

§Set Working Directory
File > Change Working Directory
This will pop up a window. Select the directory 3DPipeJunct where initial project file has been saved.
It provides access to selected directory directly

All output files will be saved in same folder until user change the location
§Blocking strategy
We have created Cartesian grid in 3D pipe junction in previous workshop.
To improve the mesh quality and capture the geometry we  will be creating the Ogrid in this workshop and compare both the

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ICEM CFD Introductory-Introduction to Hexa

A hexa mesh is created by first making a “blocking”
A blocking breaks down a geometry into large brick-shapes and structures the direction of grid lines by the arrangement of the blocks
Each “block” is easily meshed with a pure Cartesian mesh
Some blocks can be defined as “swept” and be unstructured along one face
Block entities (faces and edges) are projected onto the geometry

The blocking is saved to an independent file, and can be loaded onto a different geometry

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ICEM CFD Introductory Course Introduction to Hexa –Workshop 2 3D Pipe Junction

§Begin blocking
Select Blocking > Create Block > Initialize Blocks
Change Type to 3D Bounding Box
Click Apply
This creates one block which encloses the entire geometry

Curves automatically change color (colored separately instead of by part) to allow you to see where the ends of curves are
§Splitting selected blocks only
Select Split Block > Split Block
Click on Selected button
Select the blocks to split then middle click to confirm selection
Left click on the edge to split
The new edge will be normal to the edge that you select
Hold left mouse button and drag the split to desired location
Middle mouse to complete or Apply
Repeat the procedure for second split
Delete unwanted blocks


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ICEM CFD Introductory Course Introduction to Hexa –Workshop 1 2D Pipe Junction

Associating vertices to points:
Turn on Points in the model tree
Select Associate > Associate Vertex
Entity type is already Point:  Can proceed directly with selecting from screen
Select one vertex, middle mouse, then select (left mouse) point, and it will jump there
Note change in color of vertices

White (boundary) to red (fixed – constrained to point)

Select Associate > Associate Edge to Curve
Select 3 edges as shown
Select 3 inner curves as shown to left
Middle mouse or Apply
Curves automatically grouped to one
Note single color of grouped curve
Note color change of edges
White (boundary) to green (constrained to curve)
Repeat for 3 edges and 3 outer curves as shown below left
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ICEM CFD Introductory Course-Mesh Preparation and Output to Solver



To diagnose mesh associativity problems
Errors – most likely to cause problems in:
Solver translation
Solver input
Solution convergence/run
Possible Problems – “Unclean surface mesh”
Unwanted elements
Unwanted holes/gaps
May result in incorrect solution 
Can check any combination of errors/possible problems at any one time
Individually select
Click on Error or Possible Problems tabs will select all options in column – selecting again will de-select all
Set Defaults will select most commonly seen/detrimental diagnostics
Check Mode
Create Subsets – creates a subset of elements that fit each criteria
Check/Fix Each – offers automatic fixing of indicated problem

If Create Subsets was selected
Will go through all checked criteria at once
Elements that have a particular error/problem are put into a subset with that diagnostic type name
Subsets activated in Model Tree
Turn off all parts or shells to view subsets
If Check/Fix Each was selected
Will be prompted with options one criteria at a time
Fix:  Automatically fix the error/problem
Recommended only for Duplicate Elements, Volume Orientations, Periodic Problems, Overlapping Elements
Create Subset
Ignore

For example, multiple edges may be legitimate t-junctions; single edges – legitimate free edges

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ICEM CFD Introductory Course Prism Meshing – Workshop 2 Wingbody

First, extrude prism mesh from standalone surface mesh
“Bottom up” approach
Could also extrude into existing volume mesh (traditional method), “top down” approach
Generate rest of grid
Farfield volume
Delauney
Use density region
Define mesh size for refinement
In area where no geometry exists
Create Hexa core
For majority hex fill in far field
Choose File > Open Project
To load previously saved surface mesh and geometry
Browse to Wingbody working directory

Load previous project
Set global prism parameters
Mesh > Global Mesh Setup > Prism Meshing Parameters
Set Growth law to exponential (default)
Initial height = 0
Height determined automatically so that last prism is similar volume to adjacent tetra
Proportional to size of triangle
Height ratio = 1.2
Number of layers = 5
New volume part = LIVE
Scroll down to access
We will create prism from a surface-only mesh
The volume part is necessary when extruding from surface mesh
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ICEM CFD Introductory Course Prism Meshing – Workshop 1 Waterjacket Section

File > Change Working Dir…
Choose WaterjacketSection
OK
Use the quick icon to open geometry
Choose WaterJacketExtraction.tin

Open


Mesh > Compute mesh > Volume Mesh
Leave all the defaults
Mesh Type = Tetra/Mixed
Mesh Method = Robust(Octree)
Create Prism Layers = off
Better to run prism separately so you can check quality/errors in the input mesh
Compute
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ICEM CFD Introductory Course-Prism Meshing

Inflation layers
To better simulate boundary layer effects
Mesh orthogonal to surface with faces perpendicular to boundary layer flow direction
Procedure
Set Global Prism Parameters
Select Parts to grow layers from
Typically wall boundaries
Set Local Parameters for each part
Local overrides global
Zero or blank entries will defer to global settings
Run mesher
From existing mesh
Extrude into tetra/hexa mesh
Extrude from surface tri mesh, then fill volumes
Run automatically during Volume Mesh creation
Global Prism Parameters
Growth law
exponential:   height = h(r)(n-1)    [n is layer #]
linear:                 height = h(1+(n-1)(r-1))
Initial height of first layer – h in formulae above
Auto calculated if not specified
Based on factor of edge length of base triangle/quad
Height determined so that top layer volume is slightly less than that of tetra/hex just above it
Number of layers   n
Height ratio   r
Total height  of all layers
Usually specify 3 of the above 4 parameters
Compute params will calculate the remaining parameter (total height usually left blank)
Or specify only Height ratio and Number of layers for auto calculation of initial height
These are the defaults.  Individual surface/curve height/ratio/layers will override these defaults if set
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ICEM CFD Introductory Course Volume Meshing – Workshop 3 Femur BF Cartesian Meshing

File -> Workbench Readers
Select the file LeftFemur.agdb (Design Modeler Geometry)
Push the “Open” button
Before importing the Geometry, the user is presented with options
Keep Workbench defaults
Import Geometry
Create Subset from Named Selection
Named Selections can be setup in DM, Simulation or CAD packages such as UG, Pro/E or SolidWorks
We are not setting any Named Selection Prefixes
Accept the Defaults and apply

Each Body comes in as a Part
The named Selections appear as Geometry Subsets
These can be used to control display or selection
These can be turned into Parts
Make sure all the Subsets are active
Right Click on “Subsets” and choose “Create Part”
The new parts can be displayed
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ICEM CFD Introductory Course Volume Meshing – Workshop 2 Valve Meshing

Set working directory
File > Change Working Dir…
Choose Valve
OK
To Import The Geometry
File -> Import Geometry -> ParaSolid
Select: Valve.x_t using File Browser and Open

Set Units to Millimeter in the DEZ and Apply
Geometry > Repair Geometry > Build Diagnostic Topology
Accept all defaults
Apply
Display the geometry
Display: activate Surfaces by left mouse clicking in the check box
Display: Solid & Wire mode thru right mouse click on Surfaces in Display Tree

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