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ForcePAD A New User
Interface Metaphore for 2D
Finite Element Modeling
J. Lindemann and G. Sandberg
Division of Structural MechanicsLund University
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Introduction
First version developed in 2001
Developed as a educational tool forunderstanding shape and force relationships
Used continousl in courses for architect, desi n
and engineering students
ForcePAD targets
Designers, archtitects and people without knowledgeof material, shape and force relationships.
Engineering graduate students as a tool for enhancing
their understanding of basic mechanical conceptsDivision of Structural Mechanics, Lund University 2USNCCM9 7/25/2007
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A short history
ForcePAD 1.0.5
Painting stiffness on element grid
ForcePAD 2.0.x 2.2.x
Introduced Image based modeling
ForcePAD 2.3
Task oriented
New boundary conditions Action mode with real-time updates
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Why ForcePAD?
There was a need for a tool, explaining the basic
relationships in mechanics.
Standard FE Software too complicated
Geometry modelling
Load cases
Must have knowledge to use
too many features
Often designed to be general
Solve many types of problems
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What is ForcePAD?
2D finite element model - Plane stress
Image based geometry modeling Uses the same user interface metaphores as in image
editing software (Paintbrush, Photoshop etc)
Stiffness represented as a grayscale White = no stiffness
Black = full stiffness
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What is ForcePAD?
Pixel image FE-grid
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How do we create an easy to use user
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Reducing user interface complexity
Most evolving applications adds features
Users want features => more icons/menus
Application becomes complex
Donald Normal calls this creeping featurism
many features
Solutions:
Avoidance and restrain (not allways possible) Organisation and modularisation
functions divided into modules with each a limited set offunctions
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ForcePAD 2.2 series
Many buttons
Flipouts
Property panels
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Solution?
Task oriented user interface
Show only the tools needed for the task at hand
To support this ForcePAD divided into 3 main
modes
Sketch mode
Physics mode
Action mode
Left toolbar - main tasks for the selected mode
Right toolbar - task oriented commands
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ForcePAD 2.3 series
Main tasks Task operations
Application modes
Sketch mode
Physics modeAction mode
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Sketch mode
Used to model the structure to bestudied
Modelling is done by Painting withstiffness
Select
Brush
Geometric tools
Flood fill
All tasks are the same as in aconventional image editing application
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Select
Selection marker
Cut
Copy
Paste
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Brush
Brush mode
Erase mode
Stiffness selection
Brush size
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Geometric tools
Rectangle tool
Circle tools
Line tool
Stiffness selector
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Flood fill
Stiffness selector
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Physics mode
Defines the physical constraints of the problems
Forces
Constraints
Hinges (In the final 2.3.0 release)
Cuts (In the final 2.3.0 release) Tasks:
Forces
Constraints
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Forces
Add forces
Erase forces
Enable self-weight
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Constraints
Add constraint
Erase constraint
Rotate constraint
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Action mode
Representation of the structure
subjected to loads and constraints
No Start Calculation button
Simulation is done when transitioning to
action mode Model must be consistant before entering
action mode
Visual representations of Stress
Displacements
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Action mode continued
Many parameters for the visualisation can bechanged
Transparency, Arrow size, thickness, repeat etc. Filters for compressive/tensile stress
Stress threshold
Action mode provides 3 tasks Principal stresses
Mises stresses (under development)
Displacements
Applied forces can be modified in real-time.
This applies for all visualisation tasks
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Principal stresses
Arrow size control
Stress arrow transparency
Stress arrow skip control
Stop autoscaling of result stress arrows
Show compression and tension
Show only tension
Show only compression
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Von Mises Stresses
Jet colorscale
Hot colorscale
Set treshold for max colorscale
Invert colorscale
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Displacements
Displacement scale
l d l d f
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Real-time model modification
R l i d l difi i
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Real-time model modification
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Interacting with other programs
Most designers and architects use the sketch as
the main design tool
Software tools such as Adobe Illustrator,
Photosho are also common
ForcePAD has the ability to import pictures from
files or the clipboard
Scanned sketches can be used
Sketches in Photoshop can be imported directly
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Interacting with other programs
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Implementation goals
Fast and responsive
Fast visualisations
Fast drawing
Fast solving
Hints
High-colored icons
Standard toolset Platform independent
Mac OS X, Linux and Windows
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Implemenation
Language C++
User interface Fast Light Toolkit (FLTK 1.1.x)
Available for Linux, Mac OS X and Windows
Ver ood erformance on all latforms
FLTK OpenGL
X11 WIN32Cocoa
ForcePAD
Hardware
Solver Implemeted using the NEWMAT11 library
Graphics OpenGL
Interface to hardware accelerated 3D and 2D
Fast rasterisation interface
Platform independent
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Conclusions
ForcePAD is an effective and easy to use
educational software
ForcePAD can be used in both engineering and in
design science education
FE modeling without geometry definition forquick and eady modeling
Visualisation and understanding of internal
forces, part of the design process
Task based user interface for reduced complexity
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Future work
More constraints types with intuitive userinterface metaphors
Eigenmodes
Enable real-time constraint modification in-
Take advantage of multi-core for even moreeffective solvers
Open the ForcePAD application, enabling customapplication types and solvers
Current source available on sourceforge via subversion
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Getting ForcePAD
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