Wind turbines at sea get Wave Resonance Syndrome (Norway)

Mar 7, 2013

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Editor’s note:  Turns out ocean waves create a phenomenon called “ringing.”  Ringing makes a resonance (vibration) which can break turbines and other such structures (oil rigs) “like matchsticks.”

The problem is, turbine towers are just the right size to be “vibrated apart” (my term) by ocean wave resonance.

Thus far it has not been possible to measure the force exerted by ringing. Laboratory measurements show that the biggest vibrations in the wind turbines occur just after the wave has passed and not when the wave hits the turbine. Right after the crest of the wave has passed, a second force hits the structure. If the second force resonates with the structural frequency of the wind turbine, the vibration is strong. This means that the wind turbine is first exposed to one force, and is then shaken by another force. When specific types of waves are repeated this causes the wear to be especially pronounced. This increases the danger of fatigue.”

—Professor John Grue, University of Oslo

This is akin to what happens inside a house. Turbine infrasound creates a resonance (vibration) within certain-sized rooms, in some cases shaking the house apart.  (Witness the home of Anne & Mark Cool, Falmouth, MA, where nails are coming out of the walls in a relatively new home.  Annie Hart Cool is a Sotheby’s realtor, incidentally.  WTS.com has heard similar accounts from homeowners, elsewhere.)

Can you see the irony?  Turbines at sea being vibrated apart by a resonance from ocean waves!  Turbines getting Wave Resonance Syndrome (WRS)!

How many marine turbines do you think will want to, er, abandon ship?  I can imagine the Australian sociologist, Simon Chapman, arguing turbines are faking WRS because they’re envious of land-based turbines, which get most of the media attention.  Others might counter that marine turbines are getting WRS because of a nocebo effect.

Wind energy has entered the realm of slapstick. Three Stooges comedy. Except, it’s so tragic.

row of match sticks

“Windmills at sea can break like matches”

Medium-sized waves can destroy wind turbines at sea, causing them to break like matches. Mathematicians are trying to explain why.

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—Yngve Vogt, Apollon:  Research Magazine, University of Oslo (Norway) 2/26/13

When waves above 13 metres hit wind turbines, an unfortunate force arises at the rear of the turbine. This is called ringing.  Professor John Grue is now looking for a general mathematical formula that can explain the special phenomenon.

Medium-sized waves can break wind turbines at sea like matches. These waves occur even in small storms, which are quite common in the Norwegian Sea. “The problem is, we still do not know exactly when the wind turbines may break,” says Professor John Grue from the Department of Mathematics at the University of Oslo. Grue is one of the world’s foremost experts on wave research. In 1989 he discovered an inexplicable wave phenomenon called ringing, which is a special type of vibration that occurs when choppy waves hit marine installations. The discovery was made in a 25-metre long wave laboratory located in the basement of the mathematics building at Blindern Campus.

Prof. Grue

So far scientists have studied ringing in small and large waves, but as it turns out, ringing is more common in medium-size waves.

For wind turbines at sea with a cylinder diameter of eight metres, the worst waves are those that are more than 13 metres high and have an 11-second interval between them.

Financial ruin

The ringing problem may increase significantly in the years ahead. There are plans to build tens of thousands of wind turbines at sea.

“If we do not take ringing into consideration, offshore wind turbine parks can lead to financial ruin,” warns John Grue.

Today, the largest windmill parks at sea are outside the coasts of Denmark and Great Britain. They are nevertheless like small miniatures compared to Statkraft and Statoil’s enormous plans on the Dogger Bank outside Scotland. This windmill park is to produce as much electricity as 60 to 90 Alta power plants. A windmill park with the capacity of two Alta power plants will be built outside Møre og Romsdal.

“Thus far it has not been possible to measure the force exerted by ringing. Laboratory measurements show that the biggest vibrations in the wind turbines occur just after the wave has passed and not when the wave hits the turbine. Right after the crest of the wave has passed, a second force hits the structure. If the second force resonates with the structural frequency of the wind turbine, the vibration is strong. This means that the wind turbine is first exposed to one force, and is then shaken by another force. When specific types of waves are repeated this causes the wear to be especially pronounced. This increases the danger of fatigue.”

It is precisely this secondary force that creates ringing and that the mathematicians until now have not managed to calculate.

Unfortunate vibrations

All structures have their own vibration frequencies, whether they are wind turbines, bridges, oil rigs or vessels.

When the vibration matches the structural frequency, things get tough. This phenomenon is called resonance, and can be compared to the steady march of soldiers on a bridge. If the soldiers march in time with the structural frequency of the bridge, it can collapse.

Unrealistic calculations

The Norwegian University of Science and Technology and the Massachusetts Institute of Technology (MIT) have already made a number of calculations of ringing. Ecole Centrale Marseille and the French Bureau Veritas have also made such calculations. Det Norske Veritas is among those who use versions of these models.

“Current models are the best we have, but the estimates are too rough and erroneous. The theories are applied far outside of their area of validity. This means that we cannot calculate the fatigue adequately.”

Ringing is not related to turbulence. Ringing is systematic and is about high underpressure at back of the cylinder.

Difficult mathematics

Internationally, very little has been done on this phenomenon. John Grue now has two Doctoral Research Fellows calculating these movements. He also collaborates with the Danish research community on wind power at Risø National Laboratory and the Technical University of Denmark.

“Ringing is very difficult to calculate. There is great uncertainty. We want more precise descriptions of the physics of ringing. We are now trying sophisticated surface elevation models and complex calculations to reproduce these measurements accurately. We want to show that the ringing force arises systematically according to a general mathematical formula.”

Saga Petroleum has previously conducted an extensive set of measurements of the ringing force in waves.

“These fit our measurements very well”, says Grue.

Differences between deep and shallow waters

The scientists must also consider whether the installations are in deep or shallow waters.

“The structural frequency also depends on the conditions on the seabed.

You can compare it to a flagpole in a storm. The flag pole vibrates differently depending on whether the pole is fixed in concrete or on softer ground.”

“There has been no research on the connection between vibrations and the conditions on the seabed.”

Oil rig damaged

Ringing does not just harm wind turbines. Ringing has already been a great problem for the oil industry. The designers of the YME platform did not tak ringing into account, and lost NOK 12 billion.

“It is possible to build your way out of the ringing problem by strengthening the oil rigs. However, it is not financially profitable to do the same with wind turbines”, says John Grue.

Improves the models

Arne Nestegård, Chief Specialist in hydrodynamics at Det Norske Veritas, confirms to Apollon that wind turbines at moderate depths may be exposed to high-frequency resonant oscillations if the waves are extreme, but they safeguard against this. Nestegård says that in the past twenty years, Veritas has developed ringing models and that they now work on improving the models for wind turbines at sea.

  1. Comment by Marshall Rosenthal on 03/07/2013 at 6:24 pm

    Ask not for whom the bell tolls. It tolls for thee, Marine Windzillas.

  2. Comment by Bill Carson on 03/07/2013 at 6:27 pm

    Could this be an easier way to explain wave action? Other industries already deal with wave actions.

    When you have electric poles set at 300 feet apart, the cables in between the poles can go up and down like waves. When the wind goes above too many miles per hour, the cables can actually start to spin around like a jump rope between the poles.

    When you go by beach areas or wide open spaces, you’ll sometimes see several large weights on the telephone cables between the telephone sections. This prevents the cables from spinning like a jump rope.

    If you allow the wave action to happen between electric or telephone cables, it can break a 40 foot pole like a tooth pick. Here is how it happens without the weights on the cables between poles. Let’s say you have 10 sections cable with telephone cable between, and the cables start to move like waves. The cables all move together but, like everything in the world, one section of cable isn’t getting as much wind as the last section.

    When one section of cable is out of sync with the others, the two forces meet, one section going up, the other down. The weight change where the waves meet out of sync breaks the top of that pole.

    This is common in outside aerial plant construction.

    null

  3. Comment by Tom Whitesell on 03/07/2013 at 7:20 pm

    How about a good old fashioned hurricane? The turbines cost, what, $1,000,000 to replace? (The land based ones.)

  4. Comment by Itasca Small on 04/09/2013 at 3:27 am

    A month late seeing this article, but I’d like to comment anyway.

    Hubris blinds Man to Truth. It is fascinatingly ironic that the Norwegian company involved is named “Veritas!” Latin for truth.

    Irony, indeed! The industry should adopt the name, “Wave Resonance Syndrome!” It’s great!

    I wonder what happens to the infrasonic and other waves being generated by these marine turbines, when they are overwhelmed by the monster ocean like twigs crushed by an elephant’s foot. Or, like the organs in a human body are destroyed by the IWT’s own insidious wave production. If they had consciousness, I’m sure they would desperately cry for help, just as their own victims are doing to little avail. They would hope for their blades to turn into wings and for their roots to release them to fly away from death and destruction.

    Actually, it sounds very much like what happens inside a living organism, too. It is all the same basic mechanism, manifested on different micro to macro scale. It does sound like the standing waves infrasound creates within a constructed room.

    Here in Arizona, Wind Energy Victims, the Housels, own a geodesic dome house that was featured in a national magazine in its better days before Dry Lake Wind Power Plant IWTs began to turn. Very soon after the turbines about 11.25+ miles distant were turned-on, the dome experienced vibrations that caused glasses in the kitchen cupboards to vibrate audibly. It wasn’t long before the dome’s seams began to pull apart. The county finally intimidated the couple into silence by threatening to send an engineer to inspect the home to see what was inherently wrong with it, rather than investigating the standing wave propagation that is occurring inside the structure. Standing waves that can only be coming from the IWTs.

    I find it amazing that mathematicians can calculate origins for the universe with steadfast confidence, but they can’t calculate the waves overwhelming monstrous IWTs! [Hmm, I wonder how the former calculations would fare if they could be put to real-world empirical tests?]

    Where is Nikola Tesla’s heir when Big Wind desperately needs him? (Or, her?) Tesla could have explained WRS to them. Seems to me the ocean configuration, volume and surface tension are big factors in the whole dynamic. Wonder if there is a correlation between the waves and the phases of the moon, considering its great effect on the ocean dynamic?

    The most glaringly obvious fact is that certain human beings need to take a reality check and purge hubris and profound ignorance.

    This story brings to mind the lesson I learned early-on in my involvement fighting as a Warrior Against the Wind, we must do what we can do while realizing and trusting that God is working in the Big Picture to effect hindrances to the juggernaut in His perfect timing and will. I see this as a very big hindrance to the Wind Invasion on the Oceanic Front! May God save the ocean and its creatures from Man’s Madness.

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