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Author Topic: Future Earth  (Read 12396 times)

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AGelbert

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Re: Future Earth
« Reply #240 on: June 27, 2017, 04:46:49 pm »

Climate Change, Blue Water Cargo Shipping and Predicted Ocean Wave Activity

PART TWO OF THREE PARTS

On top of the disaster for civilization that a rise in seal level of 6 meters (over 19 FEET!) represents from the loss of coastal arable land, coastal cities, shipping ports and airports, there is the problem of wave activity. 

Which brings us back to shipping and the ocean surface.  Of particular concern to ocean shipping in a ΔT = plus 2C (and greater) atmosphere are the following facts about waves.

WHY?

Because that world will have more energy both in the oceans and in the atmosphere. That world will have, not just greater average wind speeds, particularly over unobstructed surfaces like the oceans, but a greater duration of higher wind velocities (speed in a relatively constant direction) over thousands of miles. High wind velocity and duration over hundreds or thousands of miles is a recipe for giant waves.

Here's a very brief primer on waves so you can grasp the impact of giant wave characteristics on shipping.

First, the high points of the waves are called "crests" and the low points of the waves are called "troughs". The crest is the part that starts to curl over and turn foamy when waves hit the beach. The difference in height between the crest and the trough is called the wave height.

The "amplitude" is one half the wave height. So if you have "50-foot seas", you have wave crests 25 feet above calm sea level and troughs 25 feet below it. The amplitude of 50-foot seas is 25 feet.

In the ocean, the trough of a wave is just as far below sea level as the crest is above sea level. 


Quote
Energy, not water, moves across the ocean's surface. Water particles only travel in a small circle as a wave passes.

How are waves energy?

The best way to understand waves as energy is to think of a long rope laid on the ground. If you pick up one end and give it a good snap --there's a ripple effect all the way to the other end -- just like the waves on the ocean! That means that energy is applied at one end and it moves to the other end.

What provides the energy?

In the case of ocean waves, wind provides the energy. Wind causes waves that travel in the ocean. The energy is released on shorelines. Some of the energy of waves is also released against the hulls of ships at sea. The larger the vessel surface being impacted by the wave, the more force is exerted against that surface. Being hit by a single giant wave from the front of the bow or the rear of the stern is normally within the structural design limits of a large vessel. But being broadsided can either sink a ship or severely damage it.

1973: A rogue wave off the coast of Durban, South Africa, strikes the 12,000-ton cargo ship Bencrauchan. The ship is towed into port, barely floating.

http://freaquewaves.blogspot.com/2006/07/list-of-freaque-wave-encounters.html

What determines the size of the wave?

The size of a wave depends on:

1. the distance the wind blows (over open water) which is known as the "fetch",

2. the length of time the wind blows, and

3. the speed of the wind.

The greater these three, the larger the wave.



The distance waves are apart is called the "wavelength". Wavelength is typically measured between the crests of two adjacent waves, but it could be measured from trough to trough or from any point on one wave to the same point on the next wave. You will get the same distance no matter where you measure.

Finally, the "frequency" of the wave specifies how many wave wavelengths go by in a set amount of time. So this is dependent not only on the speed of the waves, but on their wavelength.

http://www.colorado.edu/physics/2000/applets/xray/wavefront.html


The "period" of a wave must also be considered. The period of a wave is the amount of time it takes for one wavelength to occur. 

Frequency and period are distinctly different, yet related, quantities. The frequency of a wave is how many wavelengths occur in a given amount of time.

http://www.physicsclassroom.com/class/waves/Lesson-2/Frequency-and-Period-of-a-Wave

Ship hulls are designed to withstand about 15 to 20 tons per square meter. They can handle up to 30 tons per square meter only if they bend to take the blow.


When a wave with a height of 30 meters (100 ft.) is spoken of, only half that much of it is what is above the sea level. That doesn't do a ship much good because the ship will ride down the 15 meter trough before it gets hit by the 30 meter monster.  And "riding" down the trough is somewhat of a misnomer.

Large ships, because of the combined weight of the ship and the cargo, have a lot of inertia. If the ship is moving forward at about 13 kts (15 mph) and a giant wave is approaching it a 45 mph (this has been documented and is routine), you have a relative speed of the wave to the ship of 60 mph. The wavelength of a 30 meter wave is about 230 meters (this has also been documented).
 
Even if the combined speed against such a wave is just 45 mph because the captain has slowed his ship to reduce hull stress, the ship experiences a drop of ocean beneath it of 50 feet in 6 seconds, followed by the a rise of 100 feet in another six seconds.

Initially the ship just dives bow first and everybody on it feels like they are in free fall. When the ship hits the trough bottom, its inertia is still driving the bow down as the seas rise 100 feet. The bridge superstructure is impacted and often the windows are blown in and the bridge, with all its electronics, is flooded.
 
If that causes the engines to fail, the ship will probably sink. That is because the waves and wind will then turn the ship broadside to the waves. When a ship is broadside to the waves, it will either get rolled and sink or get holed by the force of a giant wave. Whether it sinks  or not depends on how long the severe sea state continues. This ship was hit broadside by a "rogue" wave, but survived.


Thirty meter waves have a force of about 100 tons per square meter, depending on the frequency and period of the wave. Waves of the same height with a higher frequency and shorter period are traveling faster, so they have much more force.

1976: The oil tanker Cretan Star in Indian Ocean off Bombay radios for help: “Vessel was struck by a huge wave that went over the deck.” The ship is never heard from again. The only sign of the vessel's fate was 6 km oil slick.

http://ycaol.com/demons_of_the_deep2.htm

1980: A huge wave was reported to have slammed into the oil tanker Esso Languedoc off the east coast of South Africa. First mate Philippe Lijour, aboard the supertanker Esso Languedoc, took this rare photo.

http://www.theartofdredging.com/roguewaves.htm



1981: A giant wave seemed to want to teach a crude oil tanker named "Energy Endurance" (Gross tonnage, 97,005 tons. DWT, 205,808 tons) what REAL energy endurance is all about.

http://migciao.blogspot.com/2007/10/vagues-scelerates.html


There is no amount of cargo that a large vessel can safely carry under these conditions, regardless of the design claims about "safe" DWT tonnage for cargo and tanker ships you read about earlier in this article. 

Where are the largest waves found?

The largest waves are found in the open ocean. Waves continue to get larger as they move and absorb energy from the wind.
 
http://www.angelfire.com/crazy2/nur_filzah/new_page_2.htm

Waves at Sea

Waves at sea are created by winds blowing across the water surface and transferring energy to the water by the impact of the air. Small ripples develop first, and frictional drag on their windward side causes then to grow larger, or to collapse and contribute part of their expended energy to larger waves.

Consequently, large waves capture increasing amounts of energy and continue to develop as long as the wind maintains sufficient strength and constant direction.

As more and more energy is transferred to the water surface. waves become higher and longer, and travel with increasing velocities; 50-foot waves are not uncommon in the open ocean, and waves more than 100 feet high have been reported.

http://www2.fiu.edu/~kpanneer/lab_assignment/Lab8_Waves.pdf

2002: December 15, 2002, MS Hanseatic of the Radisson Seven Seas was struck by a large rogue wave while on a coastal cruise of New Zealand.
http://freaquewaves.blogspot.com/2006/07/list-of-freaque-wave-encounters.html



Above you see a scale simulation of two small vessels in 50 ft. seas. The wavelength is fairly large, so these vessels are handling a very dangerous sea state okay. The wave is 50 feet from crest to trough. The danger increases when the wind gets stronger. That is because the wind increases the wave height and the wave frequency while the wavelength gets shorter.

When large waves are present, the shorter the wavelength, the steeper and more dangerous the wave. And, as mentioned earlier, a higher frequency of large waves makes them even more dangerous because they have much more energy to be delivered as a force against the hull of a ship. It is simple physics that getting hit with a wall of water at 44 mph is potentially far, far more than twice as damaging as the same wall of water hitting you at 22 mph.

Larger vessels, while generally more sea worthy, have weaknesses that small vessels do not have. A small vessel with properly battened hatches can bob like a cork in a storm. In the above situation, the sail boat would probably have the sails reefed (taken in). It will survive as long as it isn't smashed against a reef or a rock. 

But a large vessel, because it is much longer than it is wide, is weakest in the middle and along the sides from bow to stern. The bow and stern act as giant levers moved by the wave crests and troughs with the fulcrum located somewhere in the middle.

The middle either sags or it "hogs" (bends up instead of down). There is no ship that can be made strong enough to handle the massive metal fatigue inducing stresses of repeated sagging and hogging that would occur in seas populated with 30 meter waves. Here is an example of a container ship that hit a reef. It did not sink right away. But you can see that it buckled and cra cked on the side from the up, down and sideways wave movement of the ends of the ship.


Individual "rogue waves" (also called "freak waves", "monster waves", "killer waves", and "king waves") much higher than the other waves in the sea state can occur.

NOAA ship Delaware II in bad weather on Georges Bank.
Quote

... the largest ever recorded wind waves are common — not rogue — waves in extreme sea states.


For example: 29.1 m (95 ft) high waves have been recorded on the RRS Discovery in a sea with 18.5 m (61 ft) significant wave height, so the highest wave is only 1.6 times the significant wave height.
Quote
The biggest recorded by a buoy (as of 2011) was 32.3 m (106 ft) high during the 2007 typhoon Krosa near Taiwan.

https://en.wikipedia.org/wiki/Wind_wave


Giants of the Oceans

Naval architects have always worked on the assumption that their vessels are extremely unlikely to encounter a rogue. Almost everything on the sea is sailing under the false assumption that rogue waves are, at worst, vanishingly rare events. The new research suggest that’s wrong, and has cost lives. Between 1969 and 1994 twenty-two super carriers were lost or severely damaged due to the occurrence of sudden rogue waves; a total of 542 lives were lost as a result.

G. Lawton. Monsters of the deep. New Scientist, 170(2297):28–32, 2001.

Freak, rogue or giant waves correspond to large-amplitude waves surprisingly appearing on the sea surface. Such waves can be accompanied by deep troughs (holes), which occur before and/or after the largest crest.

There are several definitions for such surprisingly huge waves, but the one that is more popular now is the amplitude criterion of freak waves, which define them as waves with heights that exceed at least twice the significant wave height. The significant height is the height of at least one third of the largest waves in a given area being traversed by a ship.


According to orthodox oceanography, rogue waves are so rare that no ship or oil platform should ever expect to encounter one. But as the shipping lanes fill with supercarriers and the oil and gas industry explores ever-deeper parts of the ocean, rogue waves are being reported far more often than they should.

The most spectacular sighting of recent years is probably the so-called New Year Wave, which hit Statoil’s Draupner gas platforms in the North Sea on New Year’s Day 1995. The significant wave height at the time was around 12 metres. But in the middle of the afternoon the platform was struck by something much bigger. According to measurements made with a laser, it was 26 metres from trough to crest.

Hundreds of waves been recorded by now that are at least twice the significant wave height, and several waves at larger than three times the significant wave height. Waves with an "Abnormality index" (Ai) larger than three (Ai > 3) are known.

Alexey Slunyaev Christin Kharif, Efim Pelinovsky. Rogue Waves in the Ocean. Springer Berlin Heidelberg, 2009.


The New Year Wave is an example of a wave with an Ai = 3.19.


Christian Kharif and Efim Pelinovsky. Physical mechanisms of the rogue wave phenomenon. European Journal of Mechanics - B/Fluids, 22(6):603 – 634, 2003.

I obtained the above information from a paper submitted to the mathematics department of the University of Arizona. Here is a summary:

"In this project, the rogue wave phenomenon is introduced along with its importance. The main equations governing both linear and nonlinear theory are presented. The three main linear theories proposed to explain the rogue rave phenomenon are presented and a linear model reproducing rogue waves due to dispersion is shown. A nonlinear model for rogue waves in shallow water is also exhibited."

I have skipped the math. The information is state of the art and the references are impeccable.

References
[1] Alexey Slunyaev Christin Kharif, Efim Pelinovsky. Rogue Waves in the Ocean. Springer Berlin Heidelberg, 2009.

[2] K.B. Dysthe, HE Krogstad, H. Socquet-Juglard, and K. Trulsen. Freak waves, rogue waves, extreme waves and ocean wave climate. Mathematics Departments in Bergen and Oslo, Norway. Available at: www. math. uio. no/-karstent/waves/index_ en. html, July, 2007.

[3] R.S. Johnson. A modern introduction to the mathematical theory of water waves. Cambridge Univ Pr, 997.

[4] Christian Kharif and Efim Pelinovsky. Physical mechanisms of the rogue wave phenomenon. European Journal of Mechanics - B/Fluids, 22(6):603 – 634, 2003.

[5] G. Lawton. Monsters of the deep. New Scientist, 170(2297):28–32, 2001.

[6] Pengzhi Lin. Numerical Modeling of Water Waves. Taylor and Francis, 2008. 13

And that is why the conclusions are so unsettling.

Conclusions

1. Precise physical mechanisms causing the rogue waves phenomenon remain unknown.

2. Rogue waves should be considered when designing ships and marine platforms to reduce the number of vessels sunk worldwide.

http://math.arizona.edu/~gabitov/teaching/101/math_485_585/Midterm_Reports/RogueWaves_Midterm.pdf

Ocean Ranger severely listing in a storm after being hit by a "rogue" wave.

Ironically, the first industry that started to feel the effects of an angrier ocean was the fossil fuel industry. You've already read about some oil tanker damage and losses. They continue to this day despite alleged vessel "design improvements".

But the 120 million dollar "unsinkable" Ocean Ranger, a giant ocean going oil platform damaged from a "rogue" wave, really got their attention. All hands perished. This was a wake up call to the scientists that studied waves and was of much concern to the fossil fuel industry.

The wave hit too high and damaged some electronics. The platform began to list. The operator made the right moves but the valves that should have closed, opened more. The last that was heard from them was that they were listing at about 15 degrees and going to the lifeboat stations.

Ocean Ranger reported experiencing storm seas of 55 feet (17 m), with the odd wave up to 65 feet (20 m), thus leaving the unprotected portlight at 28 feet (8.5 m) above mean sea level vulnerable to wave damage. Some time after 21:00, radio conversations originating on Ocean Ranger were heard on the Sedco 706 and Zapata Ugland, noting that valves on Ocean Ranger's ballast control panel appeared to be opening and closing of their own accord. The radio conversations also discussed the 100-knot (190 km/h) winds and waves up to 65 feet (20 m) high. Through the remainder of the evening, routine radio traffic passed between Ocean Ranger, its neighbouring rigs and their individual support boats. Nothing out of the ordinary was noted.


At 00:52 local time, on 15 February, 1982, a Mayday call was sent out from Ocean Ranger, noting a severe list to the port side of the rig and requesting immediate assistance. This was the first communication from Ocean Ranger identifying a major problem. The standby vessel, the M/V Seaforth Highlander, was requested to come in close as countermeasures against the 10–15-degree list were proving ineffective.

The onshore MOCAN supervisor was notified of the situation, and the Canadian Forces and Mobil-operated helicopters were alerted just after 1:00 local time. The M/V Boltentor and the M/V Nordertor, the standby boats of the Sedco 706 and the Zapata Ugland respectively, were also dispatched to Ocean Ranger to provide assistance.

At 1:30 local time, Ocean Ranger transmitted its last message: "There will be no further radio communications from Ocean Ranger. We are going to lifeboat stations." Shortly thereafter, in the middle of the night and in the midst of severe winter weather, the crew abandoned the rig. The rig remained afloat for another ninety minutes, sinking between 3:07 and 3:13 local time.

All of Ocean Ranger sank beneath the Atlantic: by the next morning all that remained was a few buoys. Her entire complement of 84 workers – 46 Mobil employees and 38 contractors from various service companies – were killed.
https://en.wikipedia.org/wiki/Ocean_Ranger

It turns out that the math formulas for wave action were incorrect. But it took over a decade to get some proof that they were incorrect. The fossil fuel industry apparently filed the tragedy away as a freak incident. They certainly did not seem that concerned, considering they did everything possible to keep from having to build more sturdy (i.e. double hulled) tankers with the help of the Reagan and the first Bush Administration.

Scientists, up until the 1980's, had believed that it was impossible for an ocean wave on this planet to be higher than 80 feet. This, despite eye witness accounts from mariners to the contrary. As usual, the non-credentialed folks could not convince the scientists that there were waves out there that exceeded 100 feet.

AND that those waves appeared in seas that were only half as high (or less) as the giant wave(s) (sometimes they came in a group of three - they call them the three sisters - the women always get the blame - lol!). Impossible, proclaimed the scientist worthies. Fish tales! 

But in 1995, a laser wave height measuring device on an oil platform provided the first concrete evidence that the happy math was wishful thinking. :P You saw the graph of the 1995 New Year Wave earlier in this article. In this video it is modelled in 3D.


As you all know, when the fossil fuel industry wants action, it gets action. And it gets government funded action that you and I pay for and they don't pay a penny for. But I digress. ;D Faster that you can say fossil fuel profits are threatened, a three week satellite survey of the oceans was undertaken. Four giant waves were observed and measured in just three weeks! 

Not only was the math wrong, but, as referenced earlier in this article, "rogue" waves were not really "rogue" at all!

Of course, at that time, no connection to wave activity and global warming had been established.

Snark alert. ;D Yes, it's true that scientists are taught, like all the rest of us that cook every now and then, that warmer waters can be a bit more turbulent, but it's a big ocean out there, right?

Well, the attitude of the scientific community is changing, at least in regard to these giant waves.

The cause of rogue waves is still an area of active research. One theory under investigation cites “constructive interference,” which is a result of several smaller waves overlapping in phase, combining to produce one massive wave. Another working hypothesis is based on the “non-linear Schrödinger effect,” in which energy is “soaked up” from neighboring waves to create a monster wave. Still other researchers are looking into the possibility that wave energy is being focused by the surrounding environments, or that wind action on the surface is amplifying existing effects.

http://www.damninteresting.com/monster-rogue-waves/
 

Suggested mechanisms for the formation of freak waves include the following:


http://www.theartofdredging.com/roguewaves.htm

End of PART TWO.

If you missed PART ONE, you may read it HERE.

I updated Part three on September 9, 2019.

Climate Change, Blue Water Cargo Shipping and Predicted Ocean Wave Activity: Part 3 of 3 parts
« Last Edit: September 09, 2019, 06:41:52 pm by AGelbert »
Hope deferred maketh the heart sick: but when the desire cometh, it is a tree of life. Pr. 13:12

 

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