If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
d) A choice of a large L/R causes a considerable backwards force initially in the eddy simulation. I can't see that in the reference force coming from FEM. You said there is a negative force. I'm puzzled.
Hmmh. Its there, but its only numerical present. Its in the Nano-Newton-Range and really its just the first few timesteps. So its ok, if you dont see it. But having the effect present is ok.
I am still convinced that the time constant changes over time, since the projectiles exposure to the magnetic field changes and therefore the region where eddy currents happen changes. this should increase the time constant when the projectile is inside the coil.
Additionally, please note that the dataset already consideres saturation effects.
ur plays a big role in the skin effect. What values are you using in FEM and FEMM?
I've looked at the FEMM.cir. It became quite obvious, that saturation plays a big role, which I had neglected in my math for simplicity purposes. I'm working on incorporating this. You're right about the time constant, but I believe it changes due to saturation effects. Skin effect becomes much less prominent for low ur. From your B-H curves ur drops from values around 10000 to 10. Projectile L also drops, but not as strongly. I'll be back once I've reworked my simulation.
Nano Newtons for the initial backwards force seems awfully low. Not really consistent with even low eddy currents.
Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
Uspring, i think in the ZIP i delivered there is a circuit thats called "RawDataTestbench.asc" This should give you an impression on the content of the FEMM extracted data. (also the saturation | current dependence and so on)
I've been working on incorporating saturation in the eddy simulation. Involved, but doable. The main problem turns out to be the shape of the eddy force time dependency curve.
Generally the eddy force is initially repulsive. When the coils input voltage changes sign, the induced voltage in the projectile also changes sign with some (short) delay due to the projectiles L/R time constant. This will cause an attractive force later on, i.e. some time before the projectile reaches the center of the coil.
This doesn't agree, though, with a comparison of the dynamical FEM simulation and the statical FEMM simulation. The difference between both should be due to eddy effects. The force in the dynamical simulation is always less than in the static simulation. The reversal of the eddy force simply doesn't happen there.
Possibly this is caused by the length of the projectile, which would smear out the force curve and thus hide the small attractive part in the eddy force curve. How long is the projectile? Also, do you have any info on the projectile current from the dynamical simulation? Does it reverse sign and when?
Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
Hi Uspring, sry i wasnt around so long. I wasnt working on electronics or simlation for a long time so i neglected the form here for a while Sry. I still think this kind of commnication is not suited for a complex problem such as this.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
Lets's Play: Model the Multistage-Coilgun
and really its just the first few timesteps. So its ok, if you dont see it. But having the effect present is ok.
Sry.