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Intro to FEM

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by

Wenx Hansen

on 12 August 2013

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Transcript of Intro to FEM

FEM = Finite Element Modelling OR - Method
FEA = Finite Element Analysis
Finite Element Modelling
Dipl.-phys., M.E. Wenx Hansen
Many elements together resemble the original shape of the object - and form a
mesh
!
Finite Element Analysis
Applications
FEM
Segmentation
Meshing
my PhD
Finite Elements
Based on the idea of building a complicated object with many simple blocks, or, dividing a big problem into little ones:
Divide and Conquer!
(Even complicated) Shapes can be represented by simple geometries!
Mesh Generation
Aerodynamics
Structure Analysis
Geosciences
Thermodynamics
Continuous Fluid Mechanics
Electromagnetics
...
Methodology
Preprocessing
- build model and set boundary conditions
Solver
- solve system of equations
Postprocessing
- visual and numerical display of results
stacks of MRI images (DICOM files)
segmentation (click click click)
point cloud
Elements are connected by
nodes
.
tetrahedral mesh
hexahedral mesh
It might be necessary to optimise the mesh by
locally adjusting
the element size and mesh structure, depending on the object and goal.
Surface mesh
or
Volume mesh
?
It depends on the purpose...
Mostly, the created volume mesh is defective.
It requires
repair
and
smoothing
while maintaining the geometry!

Multiple meshes require contact definitions.
A first approach:
Abstract finite element model of the Achilles tendon-calcaneus unit.
displacement
total stress
Meshes of healthy & degenerated Achilles tendon
Boundary conditions
Static / quasi static FEA
Dynamic boundary conditions (motion analysis)
Dynamic FEA
healthy
inflammation / thickening
Stress / strain behaviour around lesions?
Injury prediction?
Achilles tendon behaviour during gait/run/sports?
Achilles tendon behaviour differences between young/old/..?
3D stress distribution
Achilles tendon lab data: material/ mechanical properties and boundary conditions
step 1
step 2
step 3
needs connectors
needs smoothing
needs a waterproof check
FEM of the Achilles Tendon
Procedure
Divide
structure into pieces
Describe physical and mechanical properties for each element (
boundary conditions
)
Connect the elements to form
system of equations
for whole mesh
Solve
the syst. of eq.
Calculate
desired quantities (stress, strain, heat, flux, ...) at nodes / elements
case example: Simao's Achilles tendon
stress. strain. volume change. Poisson ratio. Young's modulus.
after rendering
Insight into lesion development
Full transcript