Economical Construction of Floating Wind Turbines
One-at-a-Time Turbine Installation:
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Sequencing: Considering the specialized equipment required, we assume the seabed anchorages would be installed first. Loops of rope would connect each anchorage point to a float bobbing above. To minimize cost the concrete foundations would be towed directly from their place of manufacture straight to the wind turbine array location.
At each turbine site, the rope loops from the seabed anchorages would be used to draw in loops of permanent anchorage cables. Because the securing cables are in loops, both the top and bottom of the foundation can be tensioned. We note that loops simplify later anchor cable replacement.
For land based wind turbine installations, transporting giant wind turbine components is formidable. Not so much at sea. Transporting huge components by ship is more straightforward. But assembling the large components, in the wind, onto floating foundations, with a floating crane, is a challenge. The giant ship-born crane method is expensive and is limited in windy conditions.
In the following we suggest an easier method. The suggestion is to assemble the wind turbine horizontally at dockside and transport it to final location in the horizontal position. Arriving at the pre-anchored floating foundation, the wind turbine would be connected to the foundation, raised to the vertical, and bolted down (see Wind Turbine Erection at Sea sketch).
For stability and speed the transport vessel carries the wind turbine horizontally.
A temporary hinge guides the raising of the tower.
Erection at Sea synopsis:
The details of the proposed at-sea installation process are of interest. What follows is intended to only offer a suggestion. Every detail could have many variations. Successful implementation could bring significant economies. Cheaper offshore floating wind could help avert the Climate Crisis.
1. Anchorages would be pre-installed on location. A float with a loop of rope would be connected to each seabed anchor point. For maximum stability, economy, and longevity we are suggesting concrete floating foundations.
2. If possible, the foundations would have no internal poisons such as rebar, or steel imbeds of any sort. The anchor bolts and the top edge prestressing bands could be stainless, synthetics, or even carbon fiber. But no rebar. Planned “service life” is an abomination. Years from now, long after wind power has become obsolete, these concrete floats could still be useful.
3. The concrete floating foundations would be manufactured at an aggregate quarry next to deep water. They would be jacked off the launch slab directly into deep water and stored floating.
4. Singly, or in file, the foundations would be towed directly to their final locations. The anchorage floats and their loops of rope would be used to pull in the permanent heavy anchor lines. These would also be loops to facilitate easy subsequent replacement. Each line would be tensioned to lock the foundation into its permanent location.
5. Turbine towers, nacelles, and blades generally will come from all over the world, transported by ship. A harbor with a large dockside assembly area and lots of space is required for storage and assembly. Also, skilled help is needed.
6. For our suggested “erection at sea”, a customized transport vessel would be required (see sketch above). The turbine tower would be welded together in a special fixture either outdoors on the dock or inside an adjacent shelter. It would be craned, in the horizontal position, onto the padded carrying cradle on the vessel. The nacelle, with its axis vertical, would be bolted to the top of the tower. With the hub axis vertical, the blades would be added in the horizontal position.
7. For the purpose of onsite erection, three additional machined parts would be bolted to the tower base using alternate threaded holes around the base plate. These are the two halves of a male hinge and a panel of “catcher bars” that will facilitate the field erection. The three parts are bolted to each other to form a strong ring.
8. With the completed wind turbine in the horizontal position, the transport vessel would provide transport stability. The vessel, with its complete wind turbine, could pass beneath harbor spanning bridges.
9. Easy erection at the site is key. We suggest here a detailed procedure, but this is just a suggestion. There should be, hopefully, many variations and improvements.
a. At the site we would have two independently floating massive objects, the foundation and the loaded transport vessel. Totally uniting them into one object would greatly simplify installation, but, because of the massiveness involved, that seems too daunting. Instead, let us compromise and try to lock them together just for roll. They can still pitch independently.
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b. At foundation construction, an extra-large tower mounting plate was concreted in place with a ring of anchor bolts (see Mounting Plate sketch).
In the center hole beneath the mounting plate a bolt-up cage has been installed. If there are, say, thirty-six anchor bolts then the transport vessel skipper, considering wind and waves, could position the transport vessel optimally at any of thirty-six orientations. At this point the transport vessel is nosed up to the foundation.
c. With the desired orientation determined, six centering cones would be swung aboard the foundation and bolted down across from each other (yellow on sketch).
Guided by the six cones, a small crane on the transport vessel places the two halves of the female hinge assembly and a rack of “catcher cylinders” onto the ring of anchor bolts. Bolting the two hinge halves and the rack together and bolting all three down would be sequenced. At this point, these two massive objects, the concrete foundation and the transport vessel, are still floating independently.
A rotary laser mounted midway on the female hinge is mounted to project a vertical plane of laser light exactly perpendicular to the hinge axis. This would be the reference line for aligning the transport vessel and the carried turbine.
d. We need to get the transport vessel axis as square as possible to the hinge axis. The transport vessel swings its two mega grip arms and takes a squeeze on both sides of the foundation. The two clamping arms are huge. Self-centering bearings in these mega-arms establish a pitch axis between these two massive objects. Immediately the foundation and the vessel are locked together for roll. But the two still pitch independently about the axis established by the bearings in the mega grippers.
e. The next step is key. There are perhaps many options to effect the detailed squaring up. We note the whole process could be automated. Our goal is that the centerline of the vessel bisects and is square to the female hinge axis on the foundation. Using the plane of laser light as reference, differential gripper squeeze can shift the vessel left or right. Hard rubber powered wheels in the grippers could inch the grippers along. Hydraulic cylinders could slide the grippers. Separate cylinders could make final angular adjustments.
When the vessel and the foundation are aligned, the mega grippers go to maximum and all hydraulics are locked. The vessel and the foundation are locked for roll. But they are pitching independently.
After transport, the turbine's position on the cradle may not be exactly as desired in either rotation or alignment, or both. Two more phases of fine alignment are required. These too could be automated.
The tower is supported on air cushions on the cradle. Air bags along the sides of the cradle bed could nudge the tower left or right until the plane of laser light is centered on both the bottom and the top of the tower.
The foundation and the vessel are rolling in sync. The male hinge halves bolted to the tower base would have an installed electronic slope readout device. The female hinge assembly on the foundation would have the same. For a harmonious joining, the two slopes, although varying, must be continuously the same. Only slight fine adjustment would be possible. By varying the air pressures in the air bags supporting the nacelle a small tower rotation could be induced to make the slopes the same.
f. To review: due to waves and wind, the pitch angle between our two massive floating objects is oscillating, alternately opening and closing. The entire turbine, male hinge half attached, sits on the cradle that is pitching on the vessel. The female hinge is bolted in exact aligned position on the foundation which is, in turn, pitching independently. The cradle can slide on its chassis longitudinally. After adjustments, the male hinge assembly will be aligned with the female. We are ready for erection. The giant sea water hydraulic cylinder is released. It swings down into start position.
g. To initiate union, the giant cylinder lifts the cradle a little. The cradle is off the front support. The slide actuates and brings the male hinge-half close to the female, but not in contact. The two parts, on different oscillating objects are waving at each other. When everything is ready, during an oscillation opening, the cradle slides forward and the male hinge pins land on the female hinge guide aprons. Immediately, the rear cradle support falls away. The turbine on the cradle is supported by the lift cylinder connection and the male hinge pins in the female hinge guide funnels.
h. Here a discussion of “Squirm” is appropriate. The vessel’s grab on the foundation will not be perfect; close, but not exact. The lift cylinder trunnion bearing and the lift cylinder rod-end to cradle connection will have tolerance. The turbine’s bed on the cradle is air cushions. (Perhaps like those used at ship launches). Cushions along the sides of the cradle can nudge the tower left or right. Adjusting pressures in the air cushions under the nacelle can induce slight rotation of the tower.
Aligning the male hinge-halves to the female hinge-halves is critical. The male hinge halves are advanced slowly into the female. Any remaining misalignment is gradually corrected as the male hinge pins rub along the guide surfaces in the female hinge funnels. The turbine “squirms” as necessary on its air cushion bed. When the male parts reach bottom, the female hinges lock on. Whew! Two huge bodies are now locked together within machine tolerances.
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i. With the tower and the foundation pinned together, the lift cylinder is further actuated. The entire wind turbine is lifted to near vertical. If carried all the way to closure, the ongoing mutual pitch oscillation could cause the tower base plate and the foundation mounting plate to come together too forcefully. The tower is near vertical. Its own weight could possibly affect closure. But that could be violent. Also, it’s now up in the wind with resulting extraneous forces. So movement must remain controlled. We employ a row of cushioned “catch cylinders”, like large shock absorbers, to engage with the catcher ring on the back of the tower base.
j. As soon as the catch cylinders get a grip, the tower-to-cradle bindings are released and the cradle pulls back. The catch cylinders lower the tower the rest of the way into final position. Working from the work platform beneath the mounting plate, the first half of the permanent tower bolts are made all around. The tower is secure. The catch cylinders are released and removed. The male hinge halves and the catcher rack are unbolted from the tower base ring and craned aboard the vessel. The other half of the tower bolts are installed.
k. The female hinge halves and the catcher cylinder assembly are unbolted from the anchor bolts. Those bolts are re-nutted. The parts are craned aboard the vessel. The lift cylinder is retracted and stowed. All done, the mega-grippers are released freeing the vessel to return to port.
10. Recap: only a few extras are required for this methodology: an enlarged mounting plate with a bolt-up cage mounted below and the tower base plate must have threaded holes.
The three machined parts bolted to the tower base and the three machined parts bolted onto the foundation can be re-used indefinitely. The transport vessel would be a special and expensive one-of-a-kind ship. But probably cheaper than a giant crane ship, and with a smaller crew.
Logistics would be minimized by delivering the foundations straight from their place of manufacture to their final locations. Assembling the turbines horizontally at dockside in port would be easier than at sea. Express delivery while horizontal, and rapid erection at sea, would prove economical, especially for the ever-larger turbines of the future.
Floticity
Economical Installation of Floating Wind
Wind turbines floating at sea offer interesting advantages. The wind is steadier and stronger at sea. That means more revenue. Objections from next door neighbors will be less. But still, it’s uphill. Boaters, commercial fishermen, shipping lines, whale migration worriers, native tribes, and the Navy, may all have concerns. And even when all concerns are abated, construction costs may be excessive.
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It is said that the generating potential of floating wind could power the earth many times over. That huge potential is motivating. Possibly, the cost of construction of floating wind turbines at sea could be less. Here are a few ideas that might reduce the cost of floating wind.
Anchorages
First, we need to anchor our turbines to the sea floor. The present method uses steel chain and heavy steel anchors that dig into the seabed. Steel making requires lots of energy. And steel rusts. Both the following options minimize use of steel. A submersible drill rig could install deep hold-downs in the seabed (see Submersible Drill Rig sketches). With each anchorage requiring no more than a bulb of grout and a drill rod, these anchorages could be most economical.
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Submersible Drill Rig - Figure 1
Made from large OD pipe. Four multi-directional propulsion units. Outriggers for stability while drilling.
For buoyancy and orientation, each chamber has air and water connections.
Submersible Drill Rig - Figure 2
Umbilical contains power, control, air, water, grout and accelerator lines.
Grout down and back lines keep grout circulating. (Not shown: drill tilt mechanism.)
With drilled-in anchors the floating foundations would be, in effect, held in place by the weight of the seabed. Each turbine would need three or four drilled-in anchors.
Another option is rock-filled concrete buckets. Until a submersible underwater drill rig is proven, concrete buckets are a simple, straightforward option. Each bucket could secure four anchor lines (see sketches below).
Anchorage Bucket Fabrication 1
Concrete printed upside down on a form/float on a jacking slab.
Embedding details would be varied to suit sea bottom conditions.
1. Grease jacking slab concrete surface and position form/float upside down on slab.
2. Print concrete anchor bucket upside down with sea floor embedding structure on top.
3. Attach 4 anchor lines and floats.
4. Jack the bucket off the slab into deep water. It spontaneously flips.
5. Tow to site - several at once.
6. Allow water to slowly enter. Guide into exact position as bucket slowly sinks.
7. Release form/float. Heap bucket with rock. Habitat!
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Anchorage Bucket Fab 2
Short heavy abrasion resistant starter lines with large thimbles.
Rock fill especially selected to make good habitat.
Concrete Foundations
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A rowboat in a storm is tossed about. An aircraft carrier less so. Inertia matters. Concrete can provide economical inertia. Some massive oil drilling platforms float on concrete foundations. Concrete made at waterside aggregate quarries (see Glensanda in Scotland) could be most economical.
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(Parenthetical note: many Roman structures built with Roman concrete stand today. Whereas steel reinforced bridge railings are everywhere crumbling. So, no rebar. Add silica fume or other admixtures. We are designing our concrete floaters to last forever. May they be useful for other purposes long after fusion takes over.)
Design of concrete floating foundations is wide-open. Very tentatively, just to move along, let’s assume a foundation made from a heavy bottom slab and five or six round flotation chambers. The top would have a surrounding post-stressing band. Lightweight structural covers would seal the chambers.
Extra Parts Required:
Large, heavy mounting plate with full circle of anchor bolts.
Tower baseplate mounting holes must be threaded.
Bolt-up cage installed beneath baseplate center hole.
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Additional Sections:
These foundations could be built in their entirety on a flat waterside “launch slab”. The flotation chambers could be built using Slipform or Jumpform construction methods. The completed foundation would be jacked off the launch slab into adjacent deep water. They would be stored floating, ready to be towed to sea.
Addenda 1:
The through center hole could allow a further stabilizing restraint. A round column or truss structure could be installed in the center hole before turbine erection. It would be added to and extended as desired below the foundation base. Each anchor loop line could then tie to both the top edge of the foundation and the bottom tip of the cantilevered extension (see sketch). Stability would become a function of the elasticity of the lines. For maximum stability, hydraulic cylinders within the extension column could dynamically adjust tension in each loop line to closely maintain verticality.
Addenda 2:
Another interesting innovation is wood towers (see Modvion.com). The carbon sequestration advantages are substantial. Perhaps the elaborate work required in joining Modvion's wood tower sections could be avoided by manufacturing wood towers in one piece. Using a technology similar to that used to make spiral-wound pipe, sheets of plywood could be wound in many successive layers onto a tapered form.
The winding facility would be at a harbor. The resulting multi-layer single-piece tapered towers would be launched into the bay where they would float. They could be towed to outfitting facilities or the finished wind turbines could be completed at the harbor of tower manufacture.
Turbine Installation