Testing new discovery

[HunterWhite]

Did you tap on the shroud of the Hatsan, or the unshrouded barrel?
. . .
The Flash doesn't seem to have a shroud, it has a pickle. I very well could be wrong about that.

Update:
Okay,  you are correct, the Flash DOES have a shroud. ⁰ The harmonic that I reported was not the harmonic of the barrel, it was the shrouded barrel.
Even with the shroud, it's still about the same size as any pb.

[rsterne]

Just out of curiousity, let's say you can accurately determine the primary frequency (Mode 1) and the first secondary frequency (Mode 2) for you barrel, either through measurement, or calculation.... Do you want the Damper to have the same resonant frequency, or something completely different, in order to cancel out the barrel resonance?....

Just asking, 'cause I haven't a clue.... 

Bob

[grand-galop]

Just out of curiousity, let's say you can accurately determine the primary frequency (Mode 1) and the first secondary frequency (Mode 2) for you barrel, either through measurement, or calculation.... Do you want the Damper to have the same resonant frequency, or something completely different, in order to cancel out the barrel resonance?....

Just asking, 'cause I haven't a clue.... 

Bob

What is MAINSTREAM in free energy talks is the RESPONDING FREQUENCIES  are the same OR 1/4 wavelength.

I have shared experience  drove by a Croatia guy with a glass of mercury and he was making reaction to a harmony tuner.

[rsterne]

Sorry, I don't understand that answer....

According to Varmint Al's website on barrel vibration, the frequency of the Mode 2 vibration (one node) is about 5 times as high as the Mode 1 (cantilever bending from the receiver) using a tapered barrel....

https://www.varmintal.com/amode.htm

Further down the page, he gives the frequency calculations for a straight cantilever beam, 1/2" sq. x 20" long.... and Mode 2 is about 6.25 times the frequency of Mode 1 (251 Hz. vs 40 Hz.)…. Nowhere do I see a relationship for 1/4 wavelength....

Here is another calculator you may find interesting, by Geoffrey Kolbe....

http://www.geoffrey-kolbe.com/articles/rimfire_accuracy/barrel_vibrations.htm

However, the chamber pressure used is 50,000 psi, with the pressure profile of a .308 Winchester (7.62 NATO) cartridge.... However, it will show what happens when you add, for example, a muzzle weight....

Bob

[HunterWhite]

I will proceed intuitively!
I guess that I wanted to get a baseline to work from. If I can measure the offending frequencies,  then I can adjust the mass until the frequencies are reduced.  I don't know if that's any better than shooting groups. Everybody's got their own way of doing things.

[grand-galop]

Sorry, I don't understand that answer....

According to Varmint Al's website on barrel vibration, the frequency of the Mode 2 vibration (one node) is about 5 times as high as the Mode 1 (cantilever bending from the receiver) using a tapered barrel....

https://www.varmintal.com/amode.htm

Further down the page, he gives the frequency calculations for a straight cantilever beam, 1/2" sq. x 20" long.... and Mode 2 is about 6.25 times the frequency of Mode 1 (251 Hz. vs 40 Hz.)…. Nowhere do I see a relationship for 1/4 wavelength....

Here is another calculator you may find interesting, by Geoffrey Kolbe....

http://www.geoffrey-kolbe.com/articles/rimfire_accuracy/barrel_vibrations.htm

However, the chamber pressure used is 50,000 psi, with the pressure profile of a .308 Winchester (7.62 NATO) cartridge.... However, it will show what happens when you add, for example, a muzzle weight....

Bob

To not confused anyone,  node1 and node 2 are at the same place for measurement?
If not, the node closer to the exit hole is the one to damped..

[rsterne]

A "node" is a point which remains stationary (relative to the position of that point at rest), while the rest of the barrel moves up and down (or sideways, or in a circular orbit)…. A "Mode" is a description of how the barrel is vibrating.... Different Modes have different numbers and locations of nodes....

Mode 1 barrel vibration has no nodes, the muzzle waves back and forth, bending from the receiver.... Mode 2 barrel vibration has a single node at roughly 1/4 of the barrel length behind the muzzle.... Mode 3 barrel vibration has two nodes, one near the center of the barrel, and the other just behind the muzzle.... The diagrams on the Varmint Al website I linked to above make the various modes perfectly clear, and also the approximate frequency relationship between them.... The actual position of the nodes of a free floating barrel will depend on the ratio of length to diameter, any taper, and how rigidly the barrel is mounted in the receiver.... and also if the receiver is held rigidly, with only the barrel vibrating (actually quite unlikely in real world shooting)….

Bob

[grand-galop]

My take on it is the mode 2 close to the muzzle. This indicate the videst AMPLITUDE  and makes more sense..
It you can register the frequencies that happen when the shot cycle occur, this frequency that need to be countered.

An app like Hunter White would give that information..

[grand-galop]

Just out of curiousity, let's say you can accurately determine the primary frequency (Mode 1) and the first secondary frequency (Mode 2) for you barrel, either through measurement, or calculation.... Do you want the Damper to have the same resonant frequency, or something completely different, in order to cancel out the barrel resonance?....

Just asking, 'cause I haven't a clue.... 

Bob

After reviewing and have a clear view on the subject I think I wasn't clear on my explanation yesterday..
 There is a reason mode 1 and mode 2 are measured..  He want to examine the correlation of the NATURAL FREQUENCY  that everything has and the REACTANCE FREQUENCY.... THE TESLA EXPERIENCE ON THE BUILDING WAS CONDUCTED THE SAME WAY...  He have found the natural frequency of some beam and he determine that by INDUCING the SYNCRONICITY the frequency it would AMPLIFIED THE INITIAL MOVEMENT'S  up to destruction..

The COUNTER EFFECT would be the  FREQUENCY OF THE  SHOT CYCLE MESURED AT 3/4 OF THE BARREL divided by 1/4 of this frequency...

I suggest the Koble link you provided would just work with firearms because he suggested many times in the document  the vibration INDUCED BY THE RECOILED RIFLE  and he mentioned the weight of the rifle is to be added to the equation..

[Lefusil]

Just out of curiousity, let's say you can accurately determine the primary frequency (Mode 1) and the first secondary frequency (Mode 2) for you barrel, either through measurement, or calculation.... Do you want the Damper to have the same resonant frequency, or something completely different, in order to cancel out the barrel resonance?....

Just asking, 'cause I haven't a clue.... 

Bob

FWIW I don't think the damper works by a natural frequency that is countering the vibration modes of the barrel.  I think it dissipates the kinetic energy of the barrel motion.  The natural frequency of an object is the frequency at which it oscillates after being subjected to an initial temporary disturbance.  This vibration always dies away eventually because there is internal damping present in most structures, or objects.  Damping makes the vibration die away more quickly.
As an analogy, a bell or a tuning fork when struck in air, will ring at some frequency.  If you put a ringing tuning fork in a pot of oil, the sound will stop quickly.  If you put the tuning fork in oil before you strike it, it will have more of a thunk sound.  This is because the oil is damping (absorbing) the amplitude of the vibration.  This may be how the damper is working on the barrel of the rifle.

[grand-galop]

Just out of curiousity, let's say you can accurately determine the primary frequency (Mode 1) and the first secondary frequency (Mode 2) for you barrel, either through measurement, or calculation.... Do you want the Damper to have the same resonant frequency, or something completely different, in order to cancel out the barrel resonance?....

Just asking, 'cause I haven't a clue.... 

Bob

FWIW I don't think the damper works by a natural frequency that is countering the vibration modes of the barrel.  I think it dissipates the kinetic energy of the barrel motion.  The natural frequency of an object is the frequency at which it oscillates after being subjected to an initial temporary disturbance.  This vibration always dies away eventually because there is internal damping present in most structures, or objects.  Damping makes the vibration die away more quickly.
As an analogy, a bell or a tuning fork when struck in air, will ring at some frequency.  If you put a ringing tuning fork in a pot of oil, the sound will stop quickly.  If you put the tuning fork in oil before you strike it, it will have more of a thunk sound.  This is because the oil is damping (absorbing) the amplitude of the vibration.  This may be how the damper is working on the barrel of the rifle.

That is Logical thinking.. . The damping  would be greater if the fluid is thicker RIGHT?

[rsterne]

I don't think the damper works by a natural frequency that is countering the vibration modes of the barrel.  I think it dissipates the kinetic energy of the barrel motion.

I agree 100%, and tried to explain that many pages ago.... the difference between a TUNER and a DAMPER.... but it did no good, people are still working on the idea that a damper should be tuned.... I asked that question to make people stop and think.... If anything, IMO you want a damper "out of tune" with the barrel, so that it doesn't resonate with it and increase the vibration.... A tuner, on the other hand needs to be adjusted to change the position of the node to as close to the muzzle as possible.... BOTH will reduce the amplitude and frequency of the barrel vibration because of their mass....

Increasing the viscosity of the oil makes it more difficult for the lead shot to move, which is what it needs to do to absorb the barrel's vibrational energy.... Think about imbedding the lead shot in peanut butter and you get the idea.... you may as well just have a solid lead mass, IMO....

The more I think about it, the more I like the idea of using Mercury.... It has twice the density of lead shot, and a very low viscosity, only slightly greater than water.... and it has a viscosity index higher than water (the viscosity hardly changes over the temperatures we shoot at)…. JMO....

Bob

[Lefusil]

Just out of curiousity, let's say you can accurately determine the primary frequency (Mode 1) and the first secondary frequency (Mode 2) for you barrel, either through measurement, or calculation.... Do you want the Damper to have the same resonant frequency, or something completely different, in order to cancel out the barrel resonance?....

Just asking, 'cause I haven't a clue.... 

Bob

FWIW I don't think the damper works by a natural frequency that is countering the vibration modes of the barrel.  I think it dissipates the kinetic energy of the barrel motion.  The natural frequency of an object is the frequency at which it oscillates after being subjected to an initial temporary disturbance.  This vibration always dies away eventually because there is internal damping present in most structures, or objects.  Damping makes the vibration die away more quickly.
As an analogy, a bell or a tuning fork when struck in air, will ring at some frequency.  If you put a ringing tuning fork in a pot of oil, the sound will stop quickly.  If you put the tuning fork in oil before you strike it, it will have more of a thunk sound.  This is because the oil is damping (absorbing) the amplitude of the vibration.  This may be how the damper is working on the barrel of the rifle.

That is Logical thinking.. . The damping  would be greater if the fluid is thicker RIGHT?

In the tuning fork example, I would say yes, a more viscous (thicker) oil should damp more.  I am not so sure this can be directly extended to the case of the oil and shot damper on the rifle barrel.  If the oil gets too thick, the whole damper might act more like a solid mass attached to the barrel.   
It has been a while since I studied this stuff, and I am not really an expert in the field of vibration and damping.

[Lefusil]

Increasing the viscosity of the oil makes it more difficult for the lead shot to move, which is what it needs to do to absorb the barrel's vibrational energy.... Think about imbedding the lead shot in peanut butter and you get the idea.... you may as well just have a solid lead mass, IMO....

The more I think about it, the more I like the idea of using Mercury.... It has twice the density of lead shot, and a very low viscosity, only slightly greater than water.... and it has a viscosity index higher than water (the viscosity hardly changes over the temperatures we shoot at)…. JMO....

Sorry, didn't see your post before I replied.  We are on the same page.

Here is a good short description of damping:
https://www.britannica.com/science/damping

I think that what would be desirable for shooting would be an over damped condition.  Because I am not sure exactly what is the mechanism that makes Mike's damper work on a barrel, I am not clear on if mercury is the right damping material or not (I will defer to your intuition on this, you have a lot more experience with airguns than I).   I think the shot is resisting being vibrated by the barrel because it has inertia, and the fluid is flowing around the shot is using up energy that would be normally be stored back into the barrel. 
Not an easy problem, but those are the problems that are the most rewarding to solve.

[rsterne]

I like your idea of an "overdamped" condition, where the damping is so great that the barrel vibration is cancelled out before completing even a single cycle.... I think that is how a "no-bounce" hammer works.... and it makes sense that is what we are trying to emulate....

Bob

[Mole2017]

Back from vacation...now to try to get back into things...

I found some more information on particle dampers because I want to understand them better, and I'm a glutton for punishment!   
...
I also found a commercial particle damper for a rifle that uses tungsten powder, I believe.  Good suggestion HunterWhite!   

http://www.ezellcustomrifles.com/home-3/pdt-tuners/

It looks smaller than our designs but I have not found out if the Ezell PDT tuner is effective or not.

And the published document link is broken but I think this is the document they're referencing:

https://oaktrust.library.tamu.edu/bitstream/handle/1969.1/1459/etd-tamu-2003C-AERO-Marhadi-1.pdf?sequence=1&isAllowed=y

Thanks,

Taso

Nice work tracking down that "dead" link Taso! For those of you that want to check it out, don't let the theory section scare you. Actually, it is kinda of short (and dare I say lame for those of us that have been through the thesis process) and essentially says "go see so and so for more...", but the good stuff is in the results section where he presents things in terms of a specific damping capacity (higher is better) vs dimensionless acceleration amplitude, which is just a math trick of sorts.

He tests glass, lead, steel and some tungsten carbide (he unfortunately doesn't look at tungsten carbide for all comparisons). I came away with the conclusion that none of the materials were run-away favorites, though lead tended to look better than others, especially lead dust. Which is good, because it is both dense and cheap. Interestingly, he is testing dry particles--no oil. Hmm...

I'm seeing discussion about tuning in the material that has gone up while I was out (no internet...). Let me try a few summary comments to reiterate what some of the others are pointing out to the group;

1. So far, discussions have brought up several technologies for controlling vibration. They are not all the same and work by different principles.
2. "Tuning" means different things for the different technologies.

The classic movable barrel weight and maybe the "limb saver" designs try to get a mass on particular location to change the interaction of the barrel modes.

Tuned mass dampers, especially those for car suspensions, some archery vibration controllers, power lines and buildings, are tuned for a single specific frequency and level of damping. There is also another tuned mass damper more like other archery vibration dampers and those for power lines.

Harmonic dampers like those on crankshafts seem to be a special case of tuned mass damper. I'd have to research that point.

Particle dampers, and, I believe, the devices Knife has drawn our attention to, are something else altogether. They are pretty new, and engineers are still grappling with ways to analyze them, but they are also a broadband solution that doesn't have such a narrow "tuned" range as the barrel weights and tuned mass dampers, which is good for us.

I suspect the mercury dampers are something like particle dampers in broad range applicability--not nearly as specific as the tuned mass dampers.

PS: The Ezell PDT seems to be a cross between a barrel weight and a particle damper. Hard to say if that would be useful for air rifles; seems like it would not be getting the most out the particle damper part of it, i.e. one might do better exchanging some of that adjustment hardware for more particles inside the device.

[cosmic]

Maybe magnetic damping

[KnifeMaker]

We have several members testing mercury as we speak.


I have a lot of lead dust. Perhaps I will try it next. 

[Mole2017]

Maybe magnetic damping

Magnetic damping replaces viscous fluids between the moving parts of a system. The damping is accomplished by eddy currents "heating" up the conductor, thus dissipating the energy in the system. It is essentially a generator with no wires. What is weird is how they can give resistance that is proportional to the power dissipation. The classic physics lab example is to drop a magnet down a copper or aluminum tube and compare that to a fall down a plastic tube. Very impressive.

They are especially useful as a non-contacting method of damping motion in precision equipment. The key to getting them to work is to have a conductive part that can move within a magnetic field.  In practice, a metal vane or plate is set up to swing between the poles of a strong magnet. In industrial eddy brakes, I think they set something up that looks like a disk brake: the disk rotates in the magnetic field created by an electromagnet.

Applied in a barrel damper, perhaps the simplest version would use some small rare earth magnets lightly suspended near some sort of conductive plate. The important part would be to make one that had the motion in directions that correspond to the undesired motion of the barrel. I've attached a quick sketch of one with a thin rod holding a magnet near a conductive disk. Add more rods around the barrel for more damping. The magnet on a rod becomes a sprung mass with a natural frequency, so I suppose the whole thing becomes some sort of tuned mass damper, and a rather intricate one at that. For that matter, you could leave out the magnets, add a sealed tube around the system with some sort of fluid and you'd be back to a regular hydraulic damper that looks like a strange whisk in a tube.

Note: All methods that try to dissipate energy, i.e. any damper design, require some motion in the first place. We're just trying to reduce the total amount.

[Mole2017]

Writing that up gave me another idea: fill a tube with brush bristles. Don't pack them tight--you want a little movement to dissipate the motion. This acts a little like a particle damper.

It's cute, but I suspect the particle damper would be more effective.