×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Definition of co-energy

Definition of co-energy

Definition of co-energy

(OP)
Related to my previous post - Can anyone tell me the meaning of the term co-energy, with respect to a magnetic system?
It vaguely rings a bell from my school physics many years ago, but I couldn't find a definition anywhere on the web. Even Wikipedia doesn't have an opinion, which is a first!
What I really want to know is the energy stored in my electromechanical actuator when current is flowing. I am modelling it in MagNet. Magnet gives 2 energy results - Magnetic energy and co-energy. These change when I simulate current flowing in the coil. They change by almost, but not exactly, the same amount. I suspect the difference is an artifact of the modelling, and actually they should change by the same amount.
Chris

RE: Definition of co-energy

If it's a linear system, energy is equal to coenergy.

Coenergy is defined as a convenience for computing force with current held constant.

F = -dW/dx with flux linkages held constant.
F = +dW'/dx with currents held constant

where W is energy and W' is coenergy.

W' = Sum(Lamdbak * Ik) - W

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Definition of co-energy

F = -dW/dx (with lambda held constant) seems like an obvious result from conservation of energy.

If you have a linear system, we have the surprising result:

F = + dW/dx (with currents held constant).  Seems to violate conservation of energy at first glance.

But there is electrical input energy to consider

P = dWe/dt = i * v = i * dLambda/dt
dWe = i dLambda

If you hold current constant while changing x which changes L, then lambda  must change (since lambda = L*i).  That means energy is input from the elctrical system.  The amount of energy input from the electrical system is exactly twice the energy output to the mechanical system in a linear electromagnetic system.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources