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Finite Elements Analysis Basics

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Finite Elements Analysis Basics Analysis Foundation In designing the gear shafts below, what quantities would we examine? Stress Strain Displacement Rotation ... – PowerPoint PPT presentation

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Title: Finite Elements Analysis Basics


1
Finite Elements Analysis Basics
2
Analysis Foundation
  • In designing the gear shafts below, what
    quantities would we examine?
  • Stress
  • Strain
  • Displacement
  • Rotation
  • Temperatures

3
Analysis Foundation
  • In designing a valve, burner, or heat sink, what
    quantities would we examine?
  • Pressure drop
  • Temperatures
  • Mass flow rate
  • Velocities
  • Fluid mixing

4
Analysis Foundation
  • Hand calculations are easily applied to simple
    geometries.
  • Cylinders
  • Blocks
  • Beam structures
  • They are not easily or accurately applied to
    general (complex) shapes.

? To analyze complex shapes we break them into
many simple shapes and compute the combined
response.
5
FEA Analogy Area
  • Suppose we want to compute the area of a generic
    shape.

6
FEA Analogy Area
  • What do we do to improve the accuracy of the area
    measurement?

7
FEA Mesh
  • The pieces we divide the model into are called
    ELEMENTS. Equations are generated for each
    element. These are combined into a system of
    equations for the entire structure. Matrix
    algebra is used to solve the system of equations.

8
FEA Mesh Elements
  • Each element is a simple solid.
  • Elements are connected together at locations
    called NODES.

9
FEA Mesh Elements
  • A BRICK element model often must be created
    MANUALLY.
  • A TETRA element can be created AUTOMATICALLY.

10
Brick Elements vs. Tetra Elements
  • Brick Models
  • Usually have many fewer elements than a Tetra
    model (Quicker Solution).
  • - Time-consuming to generate.
  • - Very difficult to create a brick model for
    complex parts.
  • Tetra Models
  • Quick to generate the model (with Automatic
    meshing).
  • The same accuracy can be achieved as with
    Bricks.
  • Can mesh very complex parts.
  • - Usually have more elements than a Brick model.

11
Brick Elements vs. Tetra Elements
12
Brick Elements vs. Tetra Elements
13
Analysis Accuracy
  • Fewer elements will solve more quickly.
  • More elements will be more accurate.
  • You need to strike a balance between model size
    and run time.

14
Accuracy vs Mesh Size
15
Accuracy vs Mesh Size
16
Mesh Transition
  • Many times different locations in the model do
    not require the same accuracy.
  • Use mesh control and transition capabilities to
    focus the computational effort in the areas where
    the most accuracy is required.

17
Design Analysis Steps
  • Geometry definition.
  • Define component materials.
  • Define physical situation with boundary
    conditions.
  • Mesh the model.
  • Run the analysis (solve the system of equations).
  • View and evaluate the results.
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