Using Bullet for air drag and blast waves

[bwelch]

Hello Bulleteers,

I'd like to be able to simulate the physics of an object experiencing the force from a blast. For simple cases, I can just use ApplyForce() to launch an object, but if I want a more accurate representation, I have to consider the fact that the force applied to the object varies over time (and is related to the object's relative velocity and surface area presented to the blast).

I'd also like to be able to simulate a situation like having a shape in a wind tunnel, exposed to long-duration distributed force. Again, the reaction of the object will depend on its velocity and surface area with respect to the applied force.

Have any of you seen anyone use Bullet in these ways? If not, do you have any ideas of how I might be able to implement these cases? Thanks for your input!

[Basroil]

I have to consider the fact that the force applied to the object varies over time (and is related to the object's relative velocity and surface area presented to the blast).

I'd also like to be able to simulate a situation like having a shape in a wind tunnel, exposed to long-duration distributed force. Again, the reaction of the object will depend on its velocity and surface area with respect to the applied force.

An explosion typically lasts in the millisecond range, so you can easily have good enough accuracy simply by applying an impulse. As for surface area to blast surface, you can try ray casting from the blast, or colliding the object with a sphere with radius from the blast center to the center of your object. It won't be perfect, but getting the collision manifold should be more accurate for the computation time used.

Wind would be mostly the same, but you can substitute a sphere for a plane, and apply as a force rather than impulse.

Just remember that you won't get turbulence and other secondary effects, those will require fluid calculations (like OpenFOAM) and accuracy isn't going to be great with bullet, just good enough for most things that don't require a degree in rocket science.

[bwelch]

Thanks for your response! I'm going to try to tinker with your suggestions and see if they have a level of accuracy high enough for what I'm being asked to do. Unfortunately, what I'm working on is closer to rocket science than gaming, so it might require some tweaking.