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# Intro to FEM

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## 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
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