The Power of the Waves

Jospa Blog

October 12, 2009

Chuter improvements and adjustments – test series E, October 5th and 6th 2009 at SeaPower Ltd., Galway.

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This short video shows the newly improved Chuter anchored rather than attached to the tank as before.  Using shoestring equipment like plastic bottles, cistern floats & elastic band the Chuter performance is optimized by varying the centre of buoyancy, anchor point, etc to provide just what is required - alternate slugs of air and water at a speed which matches the wave speed.  As a remarkable bonus the slugs of water land perfectly in phase and in front of the waves at the ideal surfing position.  This latter ability will have beneficial cost implications for the Irish Tube Compressor as it will minimize the tube length.  This result is remarkable as it confirms that the chuter can cut the energetic tops of waves where the forward momentum is at its maximum and then land these same segments of the waves right in front of their respective waves in an ideal surfing position - exactly the best location.
Our verdict? We are very pleased with this performance. Next? Test of the Chuter with a longer tube in a long tank, and test of an alternative design of infeeder that may give us more options”.

August 25, 2009

Comments on the chuter and the video

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The chuter - see picture - has side walls held apart at the front by a piece of wood (brown colour). It has no bottom, and water and air are fed in to it ONLY above the ‘knife’ level. The oscillation of the chuter can be adjusted - see picture of the pivot mechanism.

The video - listen to comments and watch for the meniscus of water in the chuter from about 00.15 to 00.32 seconds on the track. The next view shows a flotation collar being used and the final view is of the output end of the tube.chuter-pivot5

The chuter

Test to assess ability of “chuter” to feed air and water

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Readers of the progress of the ITC will be aware that the principle of the waves moving the water and air along inside the tubes seems to work well, but we hadn’t found a reliable unaided way to feed the air and water into the tube. This was a critical requirement and previous attempts were not successful.

The “chuter”

So we designed and made what we call a “chuter” -a new word that we made up from chute[1].

The chuter has arms that capture a wide width of water (wave) and funnel it into a narrower section, in this case a tube. Nothing new here, this is the normal tapered channel in “overtopping” wave technology. Now remember that as waves are propagated the surface of the water looks like it goes up and down, but actually the water molecules move in a circular or oval orbital path to transfer their momentum as seen in the diagram[2].  Most of that momentum is available in the upper portion of the wave.

ChuterOvertoppers have an upward-sloping bottom section which adds to the horizontal channelling of the arms to produce potential energy (overtopping head). In contrast the chuter hasn’t any bottom, but cuts and admits the top 20 - 25% of the wave. The kinetic energy in the rotation is used to maintain the forward momentum of the wave, exactly as required by the ITC.

The chuter is pivoted to give the pitching motion that admits water and air alternately.

The test

In the test we used just 1.2m of tube, so little power was developed: the only objective was to test the infeed (feeding in) of the air and water.

The video shows clearly that this was very successful. The cutting action of the chuter clearly worked as the water jumps into the chuter funnel over the cutting blade. Varying the pivot action has a considerable control of the pitching. Water can be seen to issue from the tube in spurts: naturally the associated air spurts can’t be seen.

Next steps

We shall soon do more chuter tests to help characterise it, and later still some tests with measurements with longer tube to prove the power developed.

We also have an idea for another infeed method that may prove to be even better than the chuter as it may be useful for control by feedback. We have started on its design and hope to test it later.

[1] A chute is a passive (not powered) conveyor section to move fluid goods (normally grain, flour, aggregate, cement) forward by sliding or under gravity. Our “chuter” is to move air and water into the tube.

[2] With thanks to

May 1, 2009

An account of the April tank test is posted below - the background noise is the wave generator. This test was most encouraging and we believe we are well on the way towards a robust proof of concept. Wikipedia defines this as “Proof of concept is a short and/or incomplete realization (or synopsis) of a certain method or idea(s) to demonstrate its feasibility, or a demonstration in principle, whose purpose is to verify that some concept or theory is probably capable of exploitation in a useful manner. A related (somewhat synonymous) term is “proof of principle”.

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The diameter of readily available tube for test is limited: JOSPA has been using a 50mm dia tube. The question of whether this could work in the tank at HMRC had arisen, and the development had been stuck for some time on the relationships between tube diameter on the one hand and friction and/or viscosity losses and air and water separation/commingling on the other. We hoped this test would at least shed useful light on these relationships and enable us to draw up and proceed with further development; any more would be a bonus.

The results were beyond expectation in describing parameters: the ‘efficient’ parameters are described below. They were certainly encouraging enough to make us feel we are on the right track and that proper development will make the technology work. It also provided strong suggestions on what the immediate next steps and beyond in the development should be. 


NOTE: We emphasize that this test cannot be regarded as strictly scientific in the context of proof of the concept, as we introduced the external force of mains water.



PURPOSE: This test was an attempt to ascertain the band of wave frequencies and heights at which the 50mm dia tube might be suited for tank trials.

METHODOLOGY: Mains water was injected into the tube intermittently via solenoid valves and a crude venturi (the purpose of the venturi being to entrain air). The adjustable parameters were varied and the effects on the flows in the tube were observed and videoed at different settings.

PRESENT: For HMRC: Brian Holmes, Tom Walsh   For JOSPA: Joss Fitzsimons, Stan Kucek

PROCEDURE: Before starting, BH suggested doing a ‘benchmark test’ with no waves without video.  This proved to be a wise move.



No waves


1) (Benchmark) Solenoid timer was set at 0.4 seconds and Tom pressed button at (approximately) 1.5 second intervals.  The pattern of air and water inside the tube was not segmented or defined.  Little air seemed to come out the end of the tube.  No regular air, water, air, water pattern was noticeable at the exit.  There was no evidence of a regular pattern at the exit or indeed along the tube.

              Simple Waves

2) With simple waves on. Initially a few trials were tried with periods of 1.5 seconds and 2 seconds.  The solenoid opening times were varied from 0.3-0.6 seconds. A higher opening time could be expected to give a much higher flow, but as these valves were slow acting it was a trial and error matter. Especially with regard to how much air was induced by the water. At no point did the 2 second period look right or as expected.  There were not discrete air and water segments.  The jet of water from the nozzle quickly stagnated on entry to the tube and the little air induced rapidly stagnated, just moving to and fro with little drift.  The appearance was as unimpressive as the original piston trials and the OWC attempts. There was no evidence of the water surfing within the tube or what surfers call “Catching a wave”.

3) The 1.5 second period fared better. I have no written notes but the (short) video shows air and water segments, moving but not racing forward.  An improvement over 2 seconds period, but not the fast moving slugs we were to see later.  All the subsequent trials were at 1.2 or 1.1 seconds.

4) Period 1.2 second, valve opening 0.4 sec, wave height 100mm. From my notes, “Definitely much better”. By better I mean discrete air & water segments racing forward at wave speed. The air segments were clearly running at the wave crests but as they were moving so fast it is not possible to say if the wave led the air slugs or vice verse.  This was dramatic and resembled what is expected to happen at sea.

5) The same (1.2 second & valve opening 0.4sec.) but with wave height 150mm. From my notes: “Better still”.  The extra height of the waves gave further distinction between air and water segments.  Most importantly with these tests at 1.2 second period, the distinction was clear almost to the end of the functional 12m of the tube.


6) We tried to change the solenoid opening time on the run but this seemed to distract from the button pressing for the solenoids, and both notes and video are poor due to stoppages. Over the next few trials it became clear that we were not improving things by changing significantly from a solenoid opening time of 0.4 seconds.  The useful solenoid opening time range for the solenoids lies in the range of 0.3-0.5 seconds, on these 1.2 second waves.  Shorter opening times delivered too little water and induced too little air.  Above 0.5 seconds the flow from the nozzle is almost continuous when using wave periods of 1.2 seconds, but would suit longer wave periods.
7) A few attempts were made at a period of 1.1 seconds. Some success is evident from the videos but there were problems due to unusual wave behaviour which seem to have resulted from reflections.  An attempt with a wave height of 200mm does not show the expected improvement with this higher wave. In fact at 200mm the behaviour worsened, with a lot of break up of the air/water segments. At 50mm wave height the behaviour was better but best at 100mm.  We had already established during setting up that a period of 1.1 seconds was at the lower limit of what our modified solenoid valves could do.  That was one problem.  We seem to have also had a problem with reflections, but I am not sure that this is the case with low amplitude 1.1 second waves.  For whatever combination of these reasons, the results using 1.1 second waves were not as good as with 1.2 second.

Panchromatic waves

8)  TEST WITH PANCHROMATIC WAVES.  This was tried without the expectation of an immediate positive result. But this is what happened.  Tom judged when to activate the solenoids while watching the oncoming waves. The air water definition and flow looked surprisingly good, just as well as with the simple waves at 1.2 seconds. The main difference was that with ‘lulls’ in the wave train the speed of flow dropped but never stalled, then as the oncoming waves increased the flow speed increased in response.  This was an unexpectedly good outcome.  A second panchromatic trial was then tried but this time with the solenoids operated on a regular time basis with no reference to the oncoming waves.  The result was very poor by comparison resulting in an almost immediate stall at the entry to the tube.  Clearly there is a case for monitoring oncoming waves and controlling an ‘intelligent’ feed system.



We got consistent ‘good results’ using a period of 1.2 seconds, wave heights of 100mm and 150mm, and solenoid opening times of about 0.4 seconds.  By good results I mean discrete segmented water & air moving rapidly along to the exit, with the air segments running near the wave crests. There was some variation, but this is explained by the rough & ready in-feed system and the fact that the timing & phase were manually controlled.  In all cases a higher ratio of air would have been better, but we were already aware of flow limitations through the solenoids.  The fact that the water and air segments were not inclined to mix, but remain discrete, is evidence that while friction within the tube is indeed serious it is less than feared.  This is a valuable result of this trial. 

Longer and shorter periods both showed substantially poorer results than the 1.2 second period.




These conditions define a small operating window to be sure, but one where the surfing behaved impressively and at speed.  The only available explanation for the big difference between a 2 second period and a 1.2 second period is the difference in tube friction resulting from the difference in wave speed. A visible difference resulting from the change in wave period was expected in advance but fortunately the period at which the change happened was longer than feared. The attempts at shorter periods of 1.1 second were not so successful and are probably attributable to the slowness of the solenoids, manual timing and the crudeness of the venturi design. These trials provide evidence that we can indeed use a 50mm bore tube in tank tests, but within only a small window of these variables.  The tube friction at 1.1 or 1.2 second may still be too high to clearly demonstrate an increase in head due to the waves alone.  However, with this new knowledge we are now in a good position to open this operating window so that tube friction becomes less of a worry.  Small changes aimed at reducing the period could make a big difference.  Quicker solenoid speed, automatic solenoid switching and better venturi design could permit us to use a substantially shorter period – perhaps less than 1 second. This would result in lower speeds within the tube and substantially reduced friction (which is roughly proportional to the square of the velocity). This is critically important in whether we can ever achieve a demonstrable pressure increase due to waves alone within this tank using this 50mm bore tube.  With a better air/water feed system we can be reasonably confident that tube friction will not wipe out any gain in head produced by the waves.E. FEED SYSTEM REQUIREMENTS:

There are many ways of feeding air & water into the tube, whether using pistons, an OWC, solenoids or a revolving or other arrangement.  Regardless of what method we use we will have to ensure that the total flow air & water is even and not stop/start (even if the two are independently stop/start).  So what would be the ideal system?  The combined flow of air and water should be variable around a small range to ‘tune’ to a particular linear wave speed.  Control of the ratio of air to water would also be desirable.  A pressure sensor (or perhaps a damped manometer) should be located at the entry to the tube.  This would be the reference, above which any pressure gain within the tube would be a positive.  This pressure reference will become very important as it is difficult to know what pressure we are putting into the tube by any other means.


1. REVOLVING FEED: A revolving feed similar to early revolving demo. unit was planned last Christmas, but fear of tube friction led us down this long road of testing with solenoids.  A revolving feed would not have the delayed action of the solenoids and so shorter periods would be possible.  The quantity of air taken in by a revolving feed would be much better defined than with the solenoids, and variations due to manual timing of the solenoids would be eliminated.

A revolving feed would however bring some new difficulties to be overcome.  As a revolving tube dips in and out of the water surface the amount of air and water it takes in will vary greatly if the timing is not exactly in phase with the waves.  If the rotating tube dia is the same as the working tube dia, we must have a circumference length of approximately one wavelength in the tank.  Thus any simple revolving feed design will be tied to one, invariable, wavelength, quite a limitation.  To overcome this we may need to have a wave-free chamber located within the tank so that the speed of the revolving feeder can be varied without causing a mismatch with the tank waves.  This wave-free chamber could extend from near the bottom of the tank, where the wave movement is minimal, to above the wave crests. The chamber could be designed to present a narrow obstacle to the oncoming waves, if the axis of rotation is perpendicular to the wave direction and has a 90 degree elbow following the rotating seal and leading to the working tube. It would allow a steady water supply from below the wave movement.

We will also need to consider centrifugal force.  Centripetal force will tend to suck the air/water slugs back out of the tube and into the swirling inlet.  To reduce this effect we may use a larger dia tube for the rotating in-feed and a smaller radius of rotation.  For example if the cross section of the rotating tube is double the area of the working tube, we can halve the radius of rotation and still match the flows.  This would halve the centripetal force.  It may even be possible to have two separate rotating in-feeds to the one working tube; this would halve the rotating speed and quarter the centripetal force.

Another idea is to mount an in feed tank with an independent water supply above the top of the wave surface. This would pressurize the working tube by about 0.8m but the differential at the exit should remain the same.  A difficulty we need to be aware of in mounting the wave free chamber above or to the side of the wave tank is the tendency of the air to separate from its associated water.  Siphoning from a wave free tank over the side of the main tank would present this problem.  Whatever method we use, it would be desirable to measure the pressure at the start of the working tube using a fixed manometer of small bore to minimize fluctuations in the reading.

2. LONG REVOLVING DEMO UNIT: Also discussed with Brian Holmes is an improved revolving demo unit.  The present unit is neat and simple but it does not scale well to a realistic situation.  The angle at which waves rise from the horizontal are invariably less than 30 degrees, but our demo unit has steepness up to 90 degrees on some loops.  By stretching out the axis of the roller and gradually spiraling the tube along the length a much more realistic comparison could be made.  Furthermore by choosing all three - the roller diameter, the tube diameter and the roller length in proper scale proportions - a highly representative model could be made.  It would be far easier to feed than a tank set-up.  While far longer and more expensive than the present revolving unit it would be much more representative and would undoubtedly provide very good research information upon which to base a successful sea trial.  Indeed it poses the question as to whether conducting a sea trial without first building such a unit would be wise.


: Every approach has its own drawbacks. For example we could feed both air and water at an even flow through two flowmeters.  Then the waves themselves would sort out the segments as the air rises to the crests and the water to the troughs.  However this even input, while attractive, would use up some of the short tank length as the water & air sort themselves out as well as presenting the difficult problem of measuring the pressure in a tube which is flexing up and down. 

A possibility suggested by Brian Holmes involves the use of a long (270m) UK - based towing tank.  With such a length we could get much closer to actual scale, with all its attendant advantages.  It would involve much greater expense than heretofore.

March 4, 2009

Picture of the home-made oscillating water column used

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The home-made oscillating water column

Here’s a picture of our home-made oscillating water column

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December 29, 2008

A test to prepare for the important test - conducted ‘by hand’ to improve the chances of success of a more engineered test - mixed results.

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Preliminary report Test (3a) HMRC flume tank UCC

We (Tom and I) ran a very simple trial today in the flume tank. It was crude and preliminary and the method was simply to splash water at regular intervals, synchronizing as well as we could with the passing of the waves, into a sloped pipe connected to the tube. The idea with the sloped pipe was to get air and water into the tube with an initial starting velocity to replicate waves. The ideal result would have been if the water slugs splashed out the opposite end having surfed the whole length of the tank. We did not get such a good result, but we got surfing for a distance of about 7m before the water started to slow down and block the tube. The greater the amount of water we put in the further it traveled. We were on this occasion shorthanded with just Tom to concentrate on splashing the water, using a 10 litre bucket, in time with the waves. I was observing, so I have little good video footage. We tried 1.5 second periods and then 1 second periods. Both had the same amplitude. The tube is only 50mm dia. and 15m long. The water surfed somewhat further with the 1 second period than the 1.5m. Following both of these we stopped the waves completely and tried splashing in the water at the same rate and timing. This was to check how far the water would go under its own initial momentum, unaided by the surfing effect of the waves. In both these cases the water flowed, rather than surfed, which is not surprising. It also moved less quickly, with none of the rapid movement of the bubbles that was evident when the waves were ‘on’. It is difficult to describe at what point the movement started to stall, as the general appearance differed in both cases, with and without waves. However, with the waves on the water moved a few meters further for both periods, before the leading water seemed to break up and stall. The speed of movement seemed significantly higher with the waves than without.

While the trial was crude, and the result not all that we would have liked, I feel reasonably confident that with a regular feed of air & water, and the latter not limited to just 10 litres, or about 5 splashes, we will get surfing all the way and out the end of the 15m long tube. My aim now is to make up such a feed system. It will consist of a driven, transparent winding like the first round of the Revolving demo unit. The aim is to achieve water flowing out the end of the tube, and a pressure difference between the outflow end and a point just after the water & air infeed.

Why introduce this external drive, which will perhaps complicate the proof of concept? Wouldn’t a wave-driven-only device be more convincing and easy to understand? Yes, it would, but my gut feeling is that a single OWC (oscillating water column) will not give enough initial momentum for surfing to happen. Perhaps two OWC’s, one pumping air, the other overtopping water, and both feeding the tube might work, but we could waste a lot of time only to find that we can’t get them to work either. What we need to prove most is that we can get a pressure increase as the air locks travel the length of the tube, and an external drive seems the most certain way of getting to that stage. I see the tube as a pressure amplifier, which will only work if there is a minimum starting energy input for the tube to magnify. I am not sufficiently confident I can get this minimum starting momentum using an OWC.

I have one concern however, and that is the tube diameter of 50mm. With a water speed of 1.5m/sec inside the tube and the tube flexing we might expect a pressure loss of perhaps up to 0.5m head. If the pressure loss in the tube is as much as this, we will not get a positive result. Changing to a larger tube diameter is possible but it would make the length of the HMRC tank an even bigger scaling limitation than it already is. A suitable larger tube may not be easy to source. I will try to get a better estimate of what pressure loss to expect, but I fear intermittent air & water slugs might have a pressure loss almost equivalent to if water alone were flowing.

Both the OWC and today’s trial jig have one problem in common: the transition from the solid part of the jig to the flexible is not very streamlined, so causing unnecessary loss of pressure. I propose fixing both of these problems (more laminar flow of the water and tube diameter) over Christmas, so that if we try either again we will have an improved chance of success.

Joss Fitzsimons

Monday 22nd December 2008

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