1 sphere_derror.sldprt at 100mpa pressure should be zero should be 78540n should be zero should be...
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1sphere_derror.sldprt at 100MPa pressure
Should be zero
Should be zero
Should be 78540N
Should be zero
Should be zero
Should be 78540N
5
REALITY
verification
validation
MATHEMATICAL
MODEL
FEA
MODEL
RESULTS
Discretization error
Modeling error
Solution error
VERIFICATION AND VALIDATION OF FEA RESULTS
6
Sinking of Sleipner A platform
Failure occurred due to discretization error; model was not verified.
http://www.ima.umn.edu/~arnold/disasters/sleipner.html
VERIFICATION AND VALIDATION OF FEA RESULTS
7
Hartford Civic Centre Arena roof collapse.
Failure occurred due to modeling error; model was not validated.
http://www.eng.uab.edu/cee/faculty/ndelatte/case_studies_project/Hartford%20Civic%20Center/hartford.htm#Top
VERIFICATION AND VALIDATION OF FEA RESULTS
10
REALITY
MATHEMATICAL
MODEL
FEA
MODEL
RESULTS
Discretization error
Modeling error
Solution error
FEA MODELING PROCESS
Modeling error is controlled by
out understanding of the
analyzed problem
Modeling error is controlled by
using good modeling practices
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Credo
•A model can never be accepted as a final and true description of the system. Rather, it can at best be regarded as
a good enough description of certain aspects that are of particular interest to us.
Our objective is to make the design decision. FEA model should be only good enough to make that decision with a
reasonable confidence.
Modelling tips
• Spend enough time preparing and planning your analysis.
Define restraints and loads before working on geometry.
Keep it in mind that very detailed representation of geometry is often not worth the effort.
Concentrate modelling detail in the regions of most structural concern.
Do not make solid elements your first choice, consider using shells or beams in the place of solids
• Understand your structure and understand elements you use, create the mesh so it can model the real stress field
MODELING PHILOSOPHY
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Before meshing, the following should be known:
Geometry
required modelling approach (solids, shells) required element types (first order, second order, …) required element size (global, local) any symmetries or anti- symmetries?
Loads and restraints
elastic support spring stiffness? restraints in local coordinate systems? any rigid body motions?
Required results (each analysis type may require a different mesh)
global displacements ?local stress concentrations ? modes of vibration ?temperature distribution ?
Stress distribution in the structure to be meshed
•That exact stress distribution is, of course, unknown prior to analysis. However, we should have some idea of stress pattern to create the proper mesh
BEFORE YOU MESH
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MODELLING APPROACHES DICTATED BY ANALYSIS OBJECTIVE
Shell model can be used fordisplacement and modal analysis
Solid model should be used for analysis of stress concentrations
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MODELLING APPROACH DICTATED BY THE NATURE OF GEOMETRY
Stamped steel pulley requires shell element modeling
Injection molded pulley requires solid element modeling no matter what is the objective of analysis
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model file ec044
model type solid
material aluminum alloy 1060
restraints fixed to I.D.
symmetry boundary conditions
load pressure to produce 1,000N reaction force
objectives
• use symmetry boundary conditions for solid elements
• pressure load
• reaction forces
Pressure 10,000,000Pa
Fixed support
ec044 ALUMINUM PULLEY
Symmetry boundary conditions
Symmetry boundary conditions
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Displacements results confirm that symmetry boundary conditions have been correctly defined.
ec044 ALUMINUM PULLEY
Max. von Mises stress 84 MPa
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ec043 STAMPED STEEL PULLEY
model file ec043
model type shell
material Alloy steel
shell thickness 3mm
restraints built-in to I.D.
symmetry boundary conditions
load pressure to produce 1,000N
objectives
• symmetry boundary conditions for shell elements
• meshing surface geometry with shell elements
• properties of shell elements
Pressure applied
Symmetry boundary conditions
Symmetry boundary conditions
Built-in support
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ec043 STAMPED STEEL PULLEY
Solid geometry suitable for solid element meshing
Shell geometry suitable for shell element meshing
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ec043 STAMPED STEEL PULLEY
P1 stress on bottom of shell elements P3 stress on top of shell elements
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TORSION BAR
Model file TORSION BAR.sldprt
Model type solid
Material Alloy Steel
Restraints fixed to the far end
anti - sym. b.c. to the axial cross-section
Load couple of forces 1,000 N
Objectives
• demonstrate the need for defeaturing
• modeling simplifications
• demonstrate anti - symmetry boundary conditions
• limitations of linear analysis
Anti symmetry boundary conditions
1000 N
Fixed restraint
1000 N
1000 N
Note: shaft is shown shorter than in model
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