MET 415 - FEA Applications I

Prof. Dave Johnson, psuprofdj@psu.edu, Penn State - Erie, The Behrend College

Workbench: Using Simulation Features

ANSYS Help System > Mechanical Applications
                 > The Mechanical Application  User's Guide > Features

Geometry: Assemblies, Parts and Bodies

• Parts: one or more bodies (multi-body parts)
• When meshed, multi body parts will share nodes where the bodies touch one another, that is, they will have common nodes at the interfaces.  This means that Contact Regions are NOT needed to connect the bodies.
• Parts/Bodies can be assigned different material ID, and can be hidden or suppressed.
• Parts/Bodies can be displayed with different color (See Details Area for “Geometry”)
• Surface Bodies - can represent the mid-plane or top or bottom surfaces of a "thin" part
• Line Bodies - mesh with beam or pipe elements
• Rigid Bodies – can be used in static structural analysis, but most often apply to rigid or flexible dynamics
• Rigid bodies must be single parts, are not meshed, but maintain c.g. and MOI
• 2-D
• Symmetry
• Named Selections - grouping
• Path (construction geometry) - scope results to path through body
• Surface (construction geometry) - scope results to surface
• Remote Point - scoping method for remote boundary conditions
• Point Mass – “Idealize” (simplify) some component of no interest attached to a model we are interested in.
• Gaskets bodies

 Coordinate Systems Overview

• User-defined, local coordinate systems can be used to define joints, springs, loads, constraints, and results.
• Can be fixed in space or can be tied to faces or edges of bodies.
• Use “Transformations” to orient/position the coordinate system.
• Coordinate systems will or can be imported from CAD programs.
• Use coordinate systems: select in “Details area” for loads, constraints, etc.

  Graphics

• Annotations: tags, colored/highlighted faces, probe tags (not saved).

 Connections

·       Contact

·       Joints

·       springs, beam connections, spot welds, end releases, etc.

 Analysis Settings

·       Analysis Settings are different for different Analysis Types

·       Steps and Step Controls for Static and Transient Analyses

o   Role of Time in Tracking

§  In a transient analysis time represents actual, chronological time in seconds, minutes, or hours.

§  In a static analysis, however, time simply becomes a counter that identifies steps and substeps  

·       Steps, Substeps, and Equilibrium Iterations

o   Steps (or LOAD STEPS)

o   When do you need steps ?

§  To change analysis settings

§  To change loads: delete or add

§  To separate load cases/scenarios

§  To establish initial conditions for transient simulation

o   What are substeps and equilibrium iterations ?

§  Nonlinear problems require gradual loading which is solving the problem at intermediate load values (SUBSTEPS)

§  At each substep – equilibrium iterations are performed to arrive at “convergence” (equilibrium)  

·       Automatic Time Stepping (aka. Time Step Optimization)

o   Activate Automatic Time Stepping

o   Set: Initial / Min. / Max. number of substeps

o   While the solution is running, step size is adjusted

o   If convergence is NOT reached, the program can BISECT (retreat to the previous “good” solution and take a smaller increment of load)

o   Some dynamic problems do NOT perform better with Automatic Time Stepping, e.g., seismic, kinematics, etc.

·       In dynamic simulations: a proper integration time step size can be estimated based on expected response and model characteristics.  

o   Guidelines for Integration Step Size (apply to transient dynamics)
    ITS (Integration Time Step) suggestions

·       Step Controls 

o   settings can change for each load step

o   set in the “Details Area” for Analysis Settings

·       The “Program Chosen” step controls are listed

·       Can set either increments of TIME or number of SUBSTEPS

·       “Carry Over” (w/multiple load steps) means: 1st substep in next load step is the same size as the last substep in the previous load step (To avoid sudden change/instability)

·       Time Integration: applies to transient simulations

·       Some loads may be activated / deactivated at load step intervals

·       Restart Analysis:

o   go back to, and continue from, a previous solution

o   make changes/adjustments (in nonlinear controls, substep controls, output controls) to an unconverged substep and continue the solution

o    to interrupt a running solution (stop - check results - continue running

·       Restart Controls - control creation of restart "points"

·       Output Controls – default: All time points (can make large results file)
    Number of results sets is limited (default: 1000). Change, if needed.

 Applying Loads

·       Types of supports

·       Types of loads

·       Conditions: coupling, constraint equations, pipe idealization

·       Spatial Varying Loads and Displacements - vary with x, y, or z

·       Load Values: constant, tabular, function

Structural Results

·       Deformation, Stress, Strain

·       Contact Tool

·       Beam Tool

·       Stress Tool, Probes

Solving Overview

·       Settings, Restarts, Adaptive Convergence, file management, UNITS

 Commands Objects

·       Details > Invalidate Solution: Yes [to force fresh solution when changed]

 Report Preview

 Customize Report Content

Meshing in Simulation

 Parameters

 Design Assessment