Archives for February 2013

Rush Releases Steampunk Clock, Audiobook, Rash of New Tour Dates

Given its price ($ 62.99 on Amazon), this probably isn't an easy grab even for hardcore fans, but Clockwork Angels: The Watchmaker's Edition is an audiobook
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Stingrays Invade Gaza Strip

Hundreds of bloody stingrays washed up on the Gaza coast yesterday, and were immediately carted off for sale at the local fish market. ->
Earth : Discovery News

Higher cancer risk after Fukushima nuclear disaster: WHO

GENEVA (Reuters) – People in the area worst affected by Japan’s Fukushima nuclear accident two years ago have a slightly higher risk of developing certain cancers, the World Health Organisation said on Thursday.

Reuters: Environment

Windmills at Sea Can Break Like Matches

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

(Click to enlarge) Offshore turbines. When waves above 13 metres hit wind turbines, an unfortunate force arises at the rear of the turbine. This is called ringing. John Grue is now looking for a general mathematical formula that can explain the special phenomenon. (Credit: halberg / Fotolia)

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.

(From ScienceDaily) – “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, Norway. 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.

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 to the research magazine Apollon at University of Oslo.

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 in West-Norway.

“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.

Related Posts:

Consortium for Ocean Leadership

A scaly crisis: why we must act now to save reptiles

Anna Taylor summarises the findings of the most extensive research ever conducted on the global status of reptiles, and argues that if conservation continues to focus too heavily on ‘charismatic megafuna’, we face losing countless reptile species forever.
Environment news & analysis, climate change reports –
The Ecologist

BP drilled doomed U.S. well despite early problems: expert

NEW ORLEANS (Reuters) – BP Plc took chances drilling its doomed Macondo well long before it ruptured in 2010, a well design and pressure expert said on Wednesday in the second day of testimony in the civil trial over the Gulf of Mexico oil spill.

Reuters: Environment

Greg Lake releases new live CD, 'Songs of a Lifetime'

25, 2013, legendary singer/songwriter Greg Lake released his new live CD, Both a print edition and audio book read by Lake are expected by the end of
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The temperature response of soil microbial efficiency and its feedback to climate

Soils are the largest repository of organic carbon in the terrestrial biosphere. Nevertheless, relatively little is known about the factors controlling the efficiency with which microbial communities utilize carbon, and its effect on soil–atmosphere CO2 exchange. Now research using long-term experimental plots suggests that climate warming could alter the decay dynamics of more stable organic-matter compounds with implications for carbon storage in soils and ultimately climate warming.

Nature Climate Change doi: 10.1038/nclimate1796

Nature Climate Change – AOP – science feeds

Lake Tahoe Return

Lake Tahoe is a large freshwater lake in the Sierra Nevada of the United States. Visibility in Lake Tahoe was about 100 feet in the 1970s, but has since declined. The main culprits seem to be dirt, dust and other fine particles. Lake Tahoe’s clarity improved in 2012 for the second year in a row, and its waters were the clearest in 10 years, according to University of California, Davis, scientists who study the lake. Last year’s average annual clarity level was 75.3 feet, or a 6.4-foot improvement from 2011, according to data released today by the UC Davis Tahoe Environmental Research Center and the Tahoe Regional Planning Agency.
ENN: Top Stories

Operation Infinite Patience

Taiji is a Japanese coastal town that has become infamous for its practice of drive hunting. This deeply unethical activity results in the mass slaughter of thousands of cetaceans. Sea Shepherd ‘Cove Guardians’ report on the latest from the killing shores.
Environment news & analysis, climate change reports –
The Ecologist