Creating Models of Truss Structures With Optimization

Homestead Hilevel Bridge
Truss structures are a type of building that is ubiquitous in the industrialized world. Common examples include railroad ridges, radio towers, roof supports, and building exoskeletons. However, these structures are sufficiently complex that modeling them by hand is time consuming and tedious. In this project, I developed a method for designing truss structures automatically using non-linear optimization. To do this, I represent trusses as a set of rigid bars connected by pin joints, which may change location during optimization. By including the location of the joints as well as the strength of individual beams in the design variables, we can simultaneously optimize the geometry and the mass of structures, and generate realistic, physicaly stable models of truss structures.

This work was presented at SIGGRAPH 2002.

SIGGRAPH 2002 paper: PDF (2926 Kb)

Source code: tar.gz (506 Kb)

Fast and Controllable Simulation of the Shattering of Brittle Objects

Shattering glass table
The fracture of brittle objects, such as glass or ceramics, is a complex phenomonon to model realistically. Even fairly simple geometris, such as a pane of glass, when broken can result in hundreds of irregularly shaped shards. Further, people have a fairly good visual intuition on how brittle objects should break, which makes the task of modeling this phenomonon even harder. For this project, which I undertook in my second years of graduate school, I developed a method for the rapid and controllable simulation of the shattering of brittle objects under impact. I represented the objects to be shattered as a set of point masses connected by distance-preserving linear constraints. This use of constraints, rather than stiff springs, yeilds a significant advantage in speed while still retaining fine control over the fracturing behavior. The forces exerted by these constraints during impact are computed using Lagrange multipliers. These constraint forces are then used to determine when and where the object will break, and to calculate the velocities of the newly created fragments.

This work was first presented at Graphics Interface 2000, and republished in Computer Graphics Forum.

GI 2000 paper: PDF (2893 Kb)

Source code: tar.gz (506 Kb)


Voxel model of a user in the CAVE
Traces explores the aesthetics of physical presence in telecommunication processes in networked CAVEs. A CAVE is a four-sided stereo display system creating the illusion of immersion within a computer generated virtual environment. Traces is concerned with the development of intuitive interfaces involving whole the body and its movements. The focus is spatialbodily interaction between distant participants via real-time 3D image and sound traces. As more of our social and cultural lives occur in wider bandwidth online settings, questions arise about embodiment, virtuality and the possibility to 'be' in two locations at once. Traces gives users direct experience of having a dispersed body. The user interacts with the dynamics and volumes of simulated bodies, but they are translucent and ephemeral. In Traces, the user's body acts as a three dimensional brush. Traces is an outstanding CAVE application as it defines the virtual space as a comnunication space rather than a geometric one, emphasing on the state of being networked.

This work was first presented at Ars Electronica, 1999.

Simon Penny's web page about this work

International Conference on Artificial Reality and Tele-existence, 1999 paper: HTML

Convergence (The Journal of Research into New Media Technologies) paper: PDF (266 Kb)