presence of gravity in potential energy

The "potential energy" which is saved via a FieldSaver is only the potential energy contained in the specific interaction group which is given as a parameter to the field saver - whatever "potential energy" may mean for the particular type of interaction. E.g. for something like rotational friction interaction it is essentially the elastic energy stored in the interactions. To get the gravitational "potential energy" (i.e. something like mass*height*gravitational acceleration) it would be necessary to read put the potential energy from the "gravity" interaction group (well, "interaction" is a bit misleading here, with gravity being a body force but the way the code is organized anything that generates a force on a particle is an "InteractionGroup", not matter if the force is caused by another particle or not).
However, the necessary FieldSaver classes for body forces (like gravity) are not implemented at the moment.

Steffen Abe

Thanks for the answer. But I guess that's a bit confusing. I hope I have understand your answer correctly. Because I also specify the gravitational acceleration as an interaction group in the script. So I thought, it is the gravity that pushes down the particles and that it contributes to the potential energy. So how was the particles moved by the gravity anyway?? Or where should the gravitational force be incorporated with?

Jessica

In order to have gravity in your model there needs to be something like
--
gparm=GravityPrms("Gravity",Vec3(0.0,-1.0*g,0.0))
mySim.createInteractionGroup(gparm)
--
in your modelling script, setting up an InteractionGroup called "Gravity" with the appropriate parameters which is then used to calculate the gravitational force on the particles.

Steffen

I did actually defined the gravity as a parameter (i.e. gravity = Vec3(0.0,-9.81,0.0)) and specified them in the script using:

sim.createInteractionGroup(
  GravityPrms (
     name=''earth-gravity",
     acceleration=gravity
   )
)

Now, my exact question is where did the gravity go in the simulation if I wanted to know the contribution of the gravity in a particle flow? Because the forces that is present in the potential energy here is not just elastic but also the gravitational potential energy.
I did understand that when I used the fieldsaver "potential_energy" the force calculated is only the elastic interaction of the particle but how did the gravity took effect in the simulation?

Hi Jessica,

sorry, i did not clearly understand what you mean, but the gravity applies
to all particles of the simulation. It adds an additional force F=mg to all
spheres.
And if your simulated body falls down, you should see kinetic energy
increasing.

______________________________

Anton Gladkyy

2010/3/17 Jessica <email address hidden>

> Question #104413 on ESyS-Particle changed:
> https://answers.launchpad.net/esys-particle/+question/104413
>
> Status: Answered => Open
>
> Jessica is still having a problem:
> I did actually defined the gravity as a parameter (i.e. gravity =
> Vec3(0.0,-9.81,0.0)) and specified them in the script using:
>
> sim.createInteractionGroup(
> GravityPrms (
> name=''earth-gravity",
> acceleration=gravity
> )
> )
>
> Now, my exact question is where did the gravity go in the simulation if I
> wanted to know the contribution of the gravity in a particle flow? Because
> the forces that is present in the potential energy here is not just elastic
> but also the gravitational potential energy.
> I did understand that when I used the fieldsaver "potential_energy" the
> force calculated is only the elastic interaction of the particle but how did
> the gravity took effect in the simulation?
>
> --
> You received this question notification because you are an answer
> contact for ESyS-Particle.
>

Hello sir Anton!!

My question is how to calculated or obtain the potential force with the presence of the gravity. Because I need to calculate the total energy. I already had data on kinetic and potential so my problem now is the gravitational contribution to the total energy.
Is there a way to obtain the gravitational potential part in the simulation?

Jessica

Thanks Dion Weatherley, that solved my question.