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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