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Resonance waves on Canals (engineers mathematicians and physicists)


Bjarki06

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Not sure where to post this but looking out my window the last few days every now and then a sort of resonance pattern of increasing amplitude happens on the canal like when you make waves in a bath and they get higher and higher. Then it just seems to dissipate gradually even though it had been building and building.

 

Does anyone with a science background know how canals deal with this problem or if it even would be a problem? There’s a little outlet hole opposite us so I can get a good idea of the amplitude of these waves. I’ve found a couple of scientific papers on researchgate but they’re either beyond my capability to understand as a layman or too hyper specific to the canals they’re looking at.

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Soliton wave ? Is that what gets created when a boat hurtles up to a bridge 'ole then just pootles through, the wave carrying on by itself, discombobulating the slow down brigade moored on the far side?

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10 minutes ago, Jim Riley said:

Soliton wave ? Is that what gets created when a boat hurtles up to a bridge 'ole then just pootles through, the wave carrying on by itself, discombobulating the slow down brigade moored on the far side?

Nope. It is what the packet and fast passenger boats used to use to travel at ten to twelve mph down a canal, drawn by a team of horses. Once the wave was established, the boat could ride it with little effort. Any boats that got in the way had their tow ropes cut by a sword mounted on the bow.

 

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13 minutes ago, Jen-in-Wellies said:

Nope. It is what the packet and fast passenger boats used to use to travel at ten to twelve mph down a canal, drawn by a team of horses. Once the wave was established, the boat could ride it with little effort. Any boats that got in the way had their tow ropes cut by a sword mounted on the bow.

 

Soliton waves can be generated under very specific conditions of boat speed/water depth/channel width. It's difficult to make this happen in real life even if you're trying, and there's no evidence that this was ever done by fast canal boats as a routine thing, maybe it happened occasionally by accident (there are records of this implying it was an unusual phenomenon).

 

The fast boats were long and narrow with very fine bow and stern shapes, and there's no problem getting a boat like this up to such speed in a canal if the water is reasonably deep and well dredged, solitons are not needed.

 

The sword/knife on the bow was symbolic or for decoration, there's no record of it being used to cut other boat ropes -- if you think about how one fast horse-drawn boat might overtake a slower one, you'd realise it would be very difficult to actually cut a tow-rope like this...

Edited by IanD
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Is there a lock ‘upstream’?

it is surprising how far a wave can travel, created by an emptying lock.  I have often felt the boat rise as a wave passed on the Shroppie when the Hack Green lock was emptied, from some distance away.

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25 minutes ago, dor said:

Is there a lock ‘upstream’?

it is surprising how far a wave can travel, created by an emptying lock.  I have often felt the boat rise as a wave passed on the Shroppie when the Hack Green lock was emptied, from some distance away.

When one of the oil tanker barges is heading from Goole to Rotherham, loaded up, if you are moored on the route, you can feel your boat lurch against its mooring lines many minutes before the tanker arrives. 600 plus tons and drawing 7 feet.

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A friend of mine lives on an offside mooring a little North of Gayton Junction, one of my favourite hello's is to crank it up round the long bend, and then maybe 200 yards away, chunk the reverse on to stop....and watch the wave carry on.

 

I have heard the SLOW DOWN more than once, and laughed as he clambered out on to his back deck and then listen to the stream of obscenities as he sees me....150 yards away.....at slow ticker.

 

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One of my best memories of such phenomena is from when I came to a bridge hole near the top of the Ashby and realised I was travelling far too fast for the extremely shallow stretch that followed it. When I throttled back, the wave lifted the stern and the boat adopted the stance of a surfboard. Instead of letting the wave pass me, as is usual, I found that i could open the throttle and thus maintain my position riding the wave; if I throttled back at all the wave started to leave me behind, and if I opened the throttle too far the water level under the boat dropped so I slowed down, but keeping exactly the right amount of throttle and staying precisely in the centre of the channel, for over half a mile I travelled at a good 4mph along a stretch that normally barely allows tickover speed. There was absolutely no breaking wash either; the level at the banks rose and fell considerably but the water there was otherwise stationary so it made no wash. Then after half a mile I lost concentration and drifted about a foot off course; everything collapsed and I had to return to tickover speed.

 

I have tried to repeat the effect many times, and just briefly managed it for about a minute on a similar stretch of the Maccy a couple of years ago, but usually my attempts are not successful.

 

I'm sure this effect was something special, far more than the usual effect of just a wave passing through the bridge.

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22 hours ago, Bjarki06 said:

Not sure where to post this but looking out my window the last few days every now and then a sort of resonance pattern of increasing amplitude happens on the canal like when you make waves in a bath and they get higher and higher. Then it just seems to dissipate gradually even though it had been building and building.

 

Does anyone with a science background know how canals deal with this problem or if it even would be a problem? There’s a little outlet hole opposite us so I can get a good idea of the amplitude of these waves. I’ve found a couple of scientific papers on researchgate but they’re either beyond my capability to understand as a layman or too hyper specific to the canals they’re looking at.

Wavelength? Cause? Is this small waves picked up by wind or a bow wave?

 

In theory you could get resonance waves on the surface of the canal is the canal was shaking, but this seems unlikely

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6 hours ago, Keeping Up said:

When I throttled back, the wave lifted the stern and the boat adopted the stance of a surfboard.

Surely, whatever the speed over the ground, if someone isbcreating a wave of this magnitude they're going far too quickly and must be causing bank erosion. 

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9 minutes ago, Sea Dog said:

Surely, whatever the speed over the ground, if someone isbcreating a wave of this magnitude they're going far too quickly and must be causing bank erosion. 

There was no wave in the deep section before the bridge it only started (as usual) as I entered the bridge hole and, as I said, strangely although the boat was riding on a big wave it was causing none of the usual effects in even the very shallow edges at the banks. It seemed that all the water movement was close to the boat with no such movement either ahead of the boat or behind it. Certainly nothing that could cause any bank erosion. 

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Is this the basis of the ‘soliton’ wave?

As for bank erosion, whilst wash will move water quite fast, this is flow not wave action.  In a true wave, whilst the wave moves, the water itself only moves up and down ( strictly it rolls in a circle). It is only when the wave breaks that there is significant lateral movement of the water itself.

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1 hour ago, dor said:

Is this the basis of the ‘soliton’ wave?

As for bank erosion, whilst wash will move water quite fast, this is flow not wave action.  In a true wave, whilst the wave moves, the water itself only moves up and down ( strictly it rolls in a circle). It is only when the wave breaks that there is significant lateral movement of the water itself.

That's my understanding too, which is why a breaking wash does so much damage compared to a non-breaking one.

 

However a resonance wave is one induced in one body or medium by vibration in another when the vibration hits the resonant frequency. You sometimes get this in a bowl of water or soup at certain engine revs (the frequency will differ between water and soup) - in my office kitchen it happens when the washing up bowl has water in and the cafe downstairs are using their spin dryer. 

 

If the OP is observing this phenomenon without an obvious cause then they've asked a very interesting question indeed!

Edited by magpie patrick
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