A framework for modal analysis in the field of computer graphics
Computer Graphics and Visualization
Student: Daniel Höhne (alternativ: dh [at] zesem.de)
Betreuer: Prof. Dr. rer. nat. Stefan Gumhold
Verantwortlicher Hochschullehrer: Prof. Dr. rer. nat. Stefan Gumhold
Motivation
Nowadays, softbody objects are simulated using the mass-spring-damper approach. This is true for real-time graphics, where simplicity and speed are trade off for accuracy and physical foundation. Special care must be taken in choosing the right integration schema since stability is crucial in unforeseen environments.
Although modal analysis is not the swiss army knife that will solve all problems it can be used to combine the best of both worlds. But this comes at the cost much more complexity in data preparation. A finite element analysis has to be done. But the resulting 2nd order ODE can be solved without the help of numerical integration, fast and stable.
To overcome the more involved FEM data preparation, a framework has been developed. A GUI tool assists you in every step necessary to do modal analysis of your (triangulated surface) data.
Description
At first a FEM-Maple library was developed, capable of generating mass (M), damping (C), stiffness (K) and modal matrix out of a tetrahedra model and material parameters. These are saved using a xml project file and can be used in one of the provided simulation programs immediately. What's more, the developed c++ framework provides...
- materials: an editor/db for isotropic materials
- mesh generation: a Tetgen-plugin, exposing most important parameters
- models: visualization at the stage of import, mesh generation and modal simulation
- FEM: FEM preprocessor for the linear tetrahedra
- math data: visualization of the produced matrices and vectors (math data)
- solver: modes (eigenvalues) abd eigenvetors are computed using LAPACK
- modal analysis: visualization of mode influence on the 3d object, phase portrait, oscillograph curve
all made available through a graphical user interface for easy access. Extending the gui/framework is straightforward. One only needs to write a new plugins for one of the main parts of the frameworks (see above).
Furthermore, modal simulation has been combined with a regular rigid body physics engine
Open Dynamics Engine (ODE). This is demonstrated by two (simple) samples programs.
Results
The first pictures show the main application with the gui-windows for the individual modules. Namely the material editor, mesh generator, fem preprocessor, eigenproblem solver and modal stimulation.
material editor |
create material |
tetgen plugin |
surface model |
meshed cube |
FEM preprocessor |
assign materials |
vis. mass matrix |
vis. stiffness matrix |
eigen-solver |
xt-portait mode 7 |
phase-portait mode 7 |
mode assembly |
simulation ctrls |
sim. of mode 6+9+12 |
OpenDE (static) |
OpenDE (dynamic) |
mode (de)composition
Videos
Some example videos of the gui and the sample applications. To watch them you can use VideoLanClient.
OpenDE (static) means, that the object is treated as static geometry in OpenDE. In contrast, OpenDE (dynamic) is modeled using a dynamic, tri-meshed, rigid object.
Mode 6 |
Mode 7 |
Mode 8 |
Mode 9 |
Mode 10 |
Mode 11 |
Mode 9 |
OpenDE (static) |
OpenDE (dynamic) |
Perspective
The most improvements are to be expected from implementing state-ot-the-art in modal simulation - constraints and modal-warping which will greatly enhence the useability and visual quality of the simluation.
More frames per second can be achieved if the matrix-vector computations are ported to dedicated hardware e.g. the gpu.
Downloads
3rd Party Software
Related papers (some)