1sphere_derror.sldprt at 100MPa pressure

Should be zero

Should be zero

Should be 78540N

Should be zero

Should be zero

Should be 78540N

2sphere_derror.sldprt

100MPa pressure 100MPa pressure

3

4

VERIFICATION AND VALIDATION

OF FEA RESULTS

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

8

TYPICAL DISCLAIMER NOTE

9

MODELING TECHNIQUES

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

11

2(1 )

EG

12

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

13

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

14

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

15

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

16

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

17

Displacements results confirm that symmetry boundary conditions have been correctly defined.

ec044 ALUMINUM PULLEY

Max. von Mises stress 84 MPa

18

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

19

ec043 STAMPED STEEL PULLEY

Solid geometry suitable for solid element meshing

Shell geometry suitable for shell element meshing

20

ec043 STAMPED STEEL PULLEY

Symmetry boundary conditions defined for shell elements (6 D.O.F.)

21

ec043 STAMPED STEEL PULLEY

Bottom of shell elements (green)

Top of shell elements (gray)

22

ec043 STAMPED STEEL PULLEY

P1 stress on bottom of shell elements P3 stress on top of shell elements

23

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