Particle Adhesion

This is work that I am doing with Josh Colwell comparing simulations to experiments. Josh is largely interested in relating this work to the early stages of planetary formation. He will be performing low velocity collision experiments that we can compare to the numerical simulations to try to pin down parameters that provide a match.

Adhesive forces are modeled in these simulations in two basic ways. One is a step function that has a constant value up to a certain critical distance, at which the force frops to zero. The second is a smooth 4th order polynomial that is zero when the particles are touching and at the critical distance, and peaks midway between those. In both cases, the magnitude of the force is set as a multiple of the gravitational force when the particles are in contact.

There are several different types of simulations that we are performing. These pages will be updated and more types of simulations will be added as work is completed.

• Sphere Collision - These were simulations in which we set up a packed sphere and then hit it with a fast moving particle.
• Particle Patch - These simulations follow a collection of particles in a patch that orbits the Sun to see how they stick together.
• Granular - These simulations are the first tests with the code to put in events other than particle-particle collision events. They include having a surface for the particles to bounce off of as well as a cylinder that confines the particles.
• Cluster Impacts - We have done a number of simulations showing clusters of particles impacting at between 0.1 and 10 cm/s with different levels of adhesion. Without adhesion, self-gravity can not hold small clusters of particles together at these velocities. The adhesion must be many orders of magnitude larger than the force of gravity to prevent the clusters from being blown apart.