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L2-1ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Introduction to ANSYSRigid Body Dynamics
Customer Training Material
Lecture 2
Rigid Dynamics
Procedure
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Introduction to ANSYS Rigid Body Dynamics
L2-2ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialSteps in Case setup
A. Add rigid body analysis to project page
B. Geometry definition
C. Material definition
D. ConnectionsE. Meshing
F. Solution settings
G. Boundary condition/Loading
H. Solve
I. Post processing
J. Motion load export
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Introduction to ANSYS Rigid Body Dynamics
L2-3ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialPoints to Remember
Inputs and outputs are forces, moments, displacements, velocities
and accelerations.
All parts are rigid such that there are no stresses and strain results
produced, only forces, moments, displacements, velocities and
accelerations.
The solver is tuned to automatically adjust the time step. Doing it
manually is often inefficient and results in longer run times.
Viscous damping can be taken into account through springs or joints
(bushing, revolute, cylindrical joints)
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Introduction to ANSYS Rigid Body Dynamics
L2-4ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialAnalysis of Multibody Systems
Dynamic Analysis
Study of time-dependent response of the system due to the action of
time-varying loads/boundary conditions.
The time-scale of the loading is such that inertia and/or damping effects
are considered to be important.
Equation of motion to be solved:
( )Ma Cv Ku F t
Inertial Force
Damping Force
Elastic Force
External Force
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Introduction to ANSYS Rigid Body Dynamics
L2-5ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training Material
For Rigid Dynamics analysis where all bodies are rigid bodies the
Equation of Motion can be represented as:
Rigid Dynamic Solvers
Explicit 4th and 5th order Runge-Kutta method
If some components are assumed rigid while other components are
assumed flexible then
The inertial force term in the above equation applies to all components
while the damping force and the elastic force terms refer only to the
flexible components
FEA Solvers
Implicit (Newmark method, HHT method)
( )Ma F t
( )Cv KM tua F
Analysis of Multibody Systems
Where the force vector includes Ku +Cv
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Introduction to ANSYS Rigid Body Dynamics
L2-6ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialA. Add Rigid body analysis
From the Toolbox, drag a Rigid Dynamics
template to the Project Schematic.
The analysis tree will be configured for
rigid dynamic analysis.
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Introduction to ANSYS Rigid Body Dynamics
L2-7ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialB. Geometry
Geometry:
Rigid dynamic analysis can handle 2D / 3D bodies.
3D bodies can be shells and/or solids.
Multibody parts (DesignModeler concept) are supported.
All parts are assumed rigid (no stress/strain).
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Introduction to ANSYS Rigid Body Dynamics
L2-8ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialC. Material definition
Solid geometry is used to define the model.
Parts are considered rigid so density is the only required material
property.
To begin a rigid dynamic analysis parts must have their stiffnessbehavior flagged as rigid.
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Introduction to ANSYS Rigid Body Dynamics
L2-9ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialD. Connections
Joints are automatically created as per the proximity of the part.
Unlike flexible analyses, rigid bodies are related to one another and
to ground using joints/springs and/or contacts.
The body is represented by mass elements at the centroid.
Joints are represented by their respective coordinate systems.
Motions at each joint are defined with respect to a local reference
coordinate system associated with each joint.
Mass
Joint
Mass
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Introduction to ANSYS Rigid Body Dynamics
L2-10ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialE. Meshing
Apart from node ( Mass21 element) at the centroid of the
rigid bodies, mesher will create mesh on the
surface/edges of the contact.
Rigid body meshing can be used for 3D contact. Similarly, for 3D models, only the faces of the rigid body in
contact are meshed because the volume mesh is not needed.
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Introduction to ANSYS Rigid Body Dynamics
L2-11ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialF. Solution settings
The Analysis Setting branch contains
the controls for setting up the analysis:
Number of steps
Time step controls
Output controls
Solver tolerances
Note, additional steps are generally used
when loads are applied or removed orwhen load histories undergo abrupt
changes. Output controls allow the
number of solution points to be specified
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Introduction to ANSYS Rigid Body Dynamics
L2-12ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialSolution settings
Rigid dynamic solutions employ explicit time integration, whereas
flexible analyses use implicit integration.
Required time step sizes are dictated by the highest frequencies of
the system.
Auto time stepping is usually recommended since determination of
the optimum time step size is often problematic:
Initial time step: an initial time step that is too large will result in a
message indicating accelerations are too high. If the time step is only
slightly large (or too small) auto time stepping will correct this. Minimum time step: stops solution if the required time step is below this
value.
Maximum time step: places a limit on how large time steps can become in
the auto time stepping routine. Usually used to insure time steps do not
increase to where desired results are stepped over.
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Introduction to ANSYS Rigid Body Dynamics
L2-13ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialG. Boundary condition/Loading
For rigid dynamic analysis, inertial loads (acceleration and/or
gravity) are used.
Joint conditions are used to apply all other loads as constants or
time varying using tabular or functional definitions.
Once inserted each joint in the model is available via the drop down list
in the joint condition details.
A joint can be dragged and dropped from the connections folder to
automatically specify a joint condition.
Remote force
Support: Remote displacement
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Introduction to ANSYS Rigid Body Dynamics
L2-14ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialBoundary condition/Loading
Joint conditions can be defined as
constant, tabular or as a function.
Tabular and functional data can be
input in the details window, the tablein Simulation or in the Engineering
Data application.
Once entered in Simulation the data
can be saved to the Engineering Data
application.
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Introduction to ANSYS Rigid Body Dynamics
L2-15ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialBoundary condition/Loading: Joint Conditions
Position, Velocity, Rotation and Angular velocity tabular joint
conditions are fit using a cubic spline interpolation. In some cases
it may be necessary to add additional steps to resolve differences
between the actual input and the interpolated curve. Note, no slope continuity is enforced between load steps.
Load
Time
Tabular
Points
Interpolated
Curve
Potential additional steps
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Introduction to ANSYS Rigid Body Dynamics
L2-16ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialBoundary condition/Loading: Joint Conditions
To Control joints during multiple steps:
Analysis settings details allow the number of steps
to be specified.
Individual joint conditions can then be specified.
A timeline and a table can be displayed for each
joint condition.
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Introduction to ANSYS Rigid Body Dynamics
L2-17ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialBoundary condition/Loading: Joint Conditions
Joint conditions can be deactivated or activated from the
timeline/table using a right mouse click.
Place cursor in desired step on the timeline or
in the table and RMB
Note: anywhere within the step is fine
RMB either
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Introduction to ANSYS Rigid Body Dynamics
L2-18ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialBoundary condition/Loading
Various mathematical functions and arithmetic operators can beused to construct functions using time as an independentvariable.
The function is displayed in function and graphical formats. Help manual link,, can provide information // Mechanical User's
Guide // Features // Applying Loads // Specifying Load Values //Constant Load Expressions about additional functions
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Introduction to ANSYS Rigid Body Dynamics
L2-19ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialBoundary condition/Loading:
Changes in position or angle in a joint condition result in forces and
accelerations in the body which are calculated internally.
Changes in velocities (translational or rotational) result in
accelerations which are calculated internally.
Changes in joint conditions can result in discontinuities in force,
acceleration, velocity or position (see below).
Translation
Velocity
Time Time
VelocityDistance
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Introduction to ANSYS Rigid Body Dynamics
L2-20ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialBoundary condition/Loading
Discontinuities in forces or accelerations are acceptable and the rigid
solver will generally handle these with no problems.
Positional or angular discontinuities are non physical and will usually
result in no solution or non physical results.
It is recommended that prescribed rotations be limited to 2or less.
Where larger rotations are desired change to angular velocity over
time.
It is generally not recommended to apply multiple joint conditions on
a single joint.
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Introduction to ANSYS Rigid Body Dynamics
L2-21ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialH. Solve
Once setup is complete the solution can be
initiated.
During (and following) the solve the solution
information branch can be highlighted to check
the solver output information.
If warning or error messages are
produced they will be indicated in the
status bar and can be reviewed via
the message window.
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Introduction to ANSYS Rigid Body Dynamics
L2-22ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialI. Postprocessing
Rigid dynamic results are presented in either graphical, tablular or
animation formats.
Only result objects under Deformation and Probe are used.
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Introduction to ANSYS Rigid Body Dynamics
L2-23ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialI. Postprocessing :User defined results
User defined results can be obtained
from worksheet or can be entered
using User defined result tab
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Introduction to ANSYS Rigid Body Dynamics
L2-24ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialPostprocessing
Desired result displays are highlighted in the tree
as with other analysis types.
The timeline displays graphically the same
information as the table.
Note: check boxes above each column control the
graphical content.Toggle
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Introduction to ANSYS Rigid Body Dynamics
L2-25ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialPostprocessing
Results can be scoped to entire assemblies
or individual bodies.
For results from a specific time, place the
cursor in the timeline/table and RMB to
retrieve results.
RMB at
specificlocation in
timeline
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Introduction to ANSYS Rigid Body Dynamics
L2-26ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialPostprocessing- Probes
Probes can be inserted into the Solution branch allowing results to
be extracted for specific locations or connections.
Probes are scoped using joints, geometry or coordinate systems.
A shortcut for setting up joint and spring Probes is to drag and drop
the item into the Solution branch.
Drag and Drop
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Introduction to ANSYS Rigid Body Dynamics
L2-27ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialPostprocessing - Joint Output
A variety of joint output is available:
Constraint forces and moments
Stop and lock status
Relative position
Constitutive displacements and rotations
Joint elastic forces, and damping forces
Relative displacement and rotations (cumulative), velocities, and
accelerations
The components of the bases vectors at the two nodes in the deformedconfiguration
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Introduction to ANSYS Rigid Body Dynamics
L2-28ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialPostprocessing
Charts allow further refinement to
graphical/tabular data displays.
Select the desired result(s) from the tree to
include in the chart.
Use CTRL or Shift key to make multiple
selections from the tree.
Charts will be inserted in the tree as children of
the Environment.
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Introduction to ANSYS Rigid Body Dynamics
L2-29ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialPostprocessing
Chart display for position result.
Note: activate/deactivate chart legend via a RMB.RMB
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Introduction to ANSYS Rigid Body Dynamics
L2-30ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialPostprocessing
Chart showing Velocity probe and position result plotted on the same
chart.
Note, the Y axis is normalized when dissimilar results are plotted.
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Introduction to ANSYS Rigid Body Dynamics
L2-31ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialPostprocessing
Animation controller:
Animation results may be distributed evenly over the entire result
or actual result points can be used for the animation.
The more frames used the smoother the animation but time to display animation
is increased.
Start/Stop Number of
Frames
Animation
Speed
Results
Distribution
Save .avi
animation file
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Introduction to ANSYS Rigid Body Dynamics
L2-32ANSYS, Inc. Proprietary
2010 ANSYS, Inc. All rights reserved.Release 13.0
December 2010
Customer Training MaterialJ. Export of motion loads as static loads
Export a motion load file containing joint and
inertial loads at a given time
Allows creation of static loads on selected parts,
made flexible
For further detail of this feature download theanimated tutorial available on customer portal