Patent Application
20080014025
Referring to
The connecting elements 104,105,106 are joint swiveling to the carrier 103 and the foundation 5, preferably with carrier joints 107,108 and anchor joints 120,121,122. Connecting elements 104,105,106 limit motion of carrier 103 along each connecting elements longitudinal axis. Depending on to the number and orientation of the connecting elements 104,105,106 the motion in other directions remains free. Connecting elements 104,105,106 are securely attached to foundation 5 trough anchors 130,131,132.
Carrier joints 107,108 and anchor joints 120,121,122 may be ball joints, cardan joints, or any other joint know in the art to allow swiveling motion between connecting elements 104,105,106 and carrier 103, and connecting elements 104,105,106 and foundation 5. Cardan joints may be beneficial due to their ability of transferring rotational torque. Ball joints will generally not transfer torque but may be modified to do so, e.g. by employing guiding slides and pins.
Carrier joints 107,108 and anchor joints 120,121,122 may comprise elastic material which enables the swiveling of the attached parts relative to each other and may e.g. be formed as flexible.
Attached to carrier 103 are buoyancy tanks 110,111,112. The buoyancy volume of buoyancy tanks 110,111,112 is selected such that the total buoyancy is greater than the weight of structure 2, and all parts of mounting system 1. Without external forces such as wind or waves the excess buoyancy causes mounting system 1 to maintain a stable position such that the buoyancy tanks 110,111,112 rise to the highest possible position allowed by connecting elements 104,105,106.
Connecting elements 104,105 and 106 may be oriented parallel to each other and buoyancy tanks 110,111,112 and others not shown in the two dimensional drawing may be mounted concentric to the connecting elements 104,105,106. This arrangement of connecting elements and buoyancy tanks causes carrier 103 to rise to the highest position allowed by the connecting elements 104,105,106 as normal position. The length of connecting elements 104,105,106 is selected such that a large part of the volume of buoyancy tanks 110,111,112 remains below water level 100 at all times.
Mounting system 1 may be disturbed by external forces, e.g. wind or waves. Those external forces can cause carrier 103 to move like a pendulum around its normal position. The magnitude of the restoring force pushing carrier 103 back into its normal position depends on the magnitude of the excess buoyancy. The inertia of mounting system 1 is related to the mass of the structure 2 and of the mounting system 1 as well as the mass of the water which is displaced by the motion of carrier 103, buoyancy tanks 110,111,112 and connecting elements 104,105,106. The large size of buoyancy tanks 110,111,112 and resulting large volume of replaced water causes system inertia to be large. Inertia is further be influenced by the shape of buoyancy tanks 110,111,112. This form factor e.g. is two for a cylindrical body. There is also damping of the motion in the water. The large inertia of the buoyant volume acts similar to a heavy weight funding.
Connecting elements 104,105,106 may transfer pushing and pulling forces, so that horizontal torque can be transferred to the foundation 5 without the need of pretension. Wind in direction of arrow 150 may cause a horizontal force on structure 2 resulting in a horizontal torque on carrier 103. This torque causes an additional pulling force on connecting element 104 and a pushing force on connecting element 106. Connecting element 106 may carry a pushing load from carrier 103 into foundation 5. Generally there will be a pulling force on the luff and pushing force on the lee. The ability of connecting elements 104,105,106 to carry a pushing force eliminates the need for pretension to compensate external forces, as would be required for ropes or chains, which can only carry a pulling force.
The horizontal distance between the attachment of structure 2 on carrier 103 and the attachment of connecting elements 104,105,106 on carrier 103 determines an effective lever arm and thereby the force required to compensate torque acting on carrier 103. To compensate larger wind forces and torques acting on structure 2 and carrier 103 the connecting elements 104,105,106 may be placed further apart. Smaller wind forces and torques acting on structure 2 and carrier 103 allow placing the connecting elements 104,105,106 closer together thus enabling a smaller horizontal size of carrier 103.
Connecting elements 104,105,106 may carry a pushing force that is transferred to the sea-bed through anchor joints 120,121,122 and anchors 130,131,132. Anchors 130,131,132 may e.g. be pile anchors or suction anchors which can carry pushing and pulling loads. The ability to transfer pushing loads from the carrier 103 into the foundation 5 allows placing the anchors closer together than would be possible with traditional rope mountings without need to increase their maximum force rating.
Connecting elements 104,105,106 may not only be able to carry a pushing or pulling force but may also be used to carry torque from carrier 103 into foundation 5. The torque applied to connecting elements 104,105,106 can restrict the tilting of carrier 103 and thereby avoid or reduce a yawing motion of structure 2. Carrier joints 107,108 and anchor joints 120,121,122 may e.g. be cardan joints or any other joint know to carry torque. If the sea-bed is used as foundation 5, the torque is transferred to the sea-bed via anchors 130,131,132. To avoid transferring torque into the seabed in one or more limited anchor areas the foundation 5 may be formed as a stiff structure, e.g. a concrete block or steel structure. The foundation itself may then be mounted to the sea-bed or stabilized in another way. An advantage of this set-up is that the torque does not affect a single point in the sea-bed or a single anchor, but can be distributed to several points in the ground, so that there are large lever arms between these points.
If three or more connecting elements are used to attach the carrier to the foundation their attachment points at the carrier and at the foundation should not be in one axis, unless movement of the carrier around that axis is desired. (In some of the drawings the joints are in one line for reasons of the perspective.)
If waves cause carrier 203 to move in the direction of arrow 250 it results in a more upright position of connecting element 206 and a more tilted position of connecting element 204. This causes carrier 203 and attached structure 2 to tilt in direction of arrow 251. Proper selection of the tilt angle between connecting elements 204,205,206 and the systems' vertical axis allows limiting the movement at the top of structure 2. This allows to for example maintain the position of the rotor and generator of a wind-electric generator essentially in place even though the carrier 203 is moving.
The sideways motion of carrier 203 can be reduced to the order of magnitude of one meter by a proper choice of excess buoyancy of carrier 203. This is short relative to the length of connecting elements 204,205,206 so that the tilt angle of structure 2 can be kept negligibly small. Tilt of structure 2 caused by motion of carrier 203 may be smaller than the bending of the mast itself by the forces of the wind. It may be useful not to compensate the sideways motion of the carrier 203 completely. Allowing wind forces to push carrier 203 in the direction of arrow 250 may be desirable, since the resulting motion of structure 2 in the direction of arrow 251 compensates bending of structure 2 in the opposite direction such that the absolute position of the top of structure 2 may be kept essentially steady.
Generally, the more sideways motion of the carrier 203 is restricted, the arger the torque transferred to foundation 5 will be. Variation of tilt angle connecting elements 204,205,206 as well as location of attachments points of connecting elements 204,205,206 at the carrier 203 provide freedom to choose the maximum force expect to be carried by connecting elements 204,205,206. The maximum force may be selected to fully utilize but not exceed strength of connecting elements, carrier joint, anchor joints, anchors and foundation.
To select the appropriate tilt angle of connecting elements 204,205,206 a mathematical treatment of first order will provide good results. This may be illustrated with respect to motion of carrier 203 along arrow 250. Carrier 203 is attached to connecting element 204 which as a length 11 and is in its normal position tilted at an angel A1 relative to the vertical axis of mounting system 1. Respectively connecting element 206 has a length 12 and a tilt angel A2. If carrier 203 is moved to the side by an angle W the absolute heights h1 and h2 of attachment points 207,208 relative to foundation 230 change. The new heights will be h1=11 cos (W+A1) and h2=11 cos (W+A2). For small angels of W a Taylor expansion of first order will give good results: h1=11 cos (A1)−11 sin (A1)*W and h2=12 cos (A2)*W. If A1=−A2 and 11=12=1 it is h1−h2=(1 sin (A1)−1 sin (A2))*W. The angle of the tilt B is given by the difference of the high h1−h2 and the distance t between the points where the connection units 4 are joint to the carrier 203: h1−h2=t sin (B). For small angles sin (B)=B can be assumed. The relation between W and B can be obtained as W (sin (A1)−sin (A2))1/t=B. The two dimensional calculation can be generalized to three dimensions. To do so one may project the three dimensional system into the plane of tilting angel W. Doing so reveals that the relationship 1 sin (A)/t remains constant.
The carrier of mounting system 1 may be connected to the foundation using more than three connecting elements. This requires that the connecting elements have the same distance from and the same tilt towards the vertical axes in the middle of the mounting system to not be blocking any additional degree of freedom. If one would take a more precise look than by Taylor expansion of first order, one may notice that a motion out of the plane of the angle W is coupled with the motion by the angle W which is so small that it is tolerable. Furthermore the use of more than three connecting elements would block more than 3 degrees of freedom. But if a defined flexibility of the material is chosen and the oscillation qualities are adjusted well, the motion can be reduced, so that the deviations can be tolerated.
Referring now to
Structure 2 is located directly above the connecting element 304, so that its weight is pushing directly on connecting element 304. The weight force is counteracted directly by the buoyancy of connecting element 304. Connecting element 304 may be a cylindrical hollow body capable of transferring torque from carrier 300 into the foundation. In this example connecting element 313 and others not shown are required only to compensate horizontal torque, carrying either a pushing or pulling force from carrier 300 into the foundation.
Connecting element 304 may be made of steel pipes. Pipes, especially when made of steel, provide high torsion strength. Their cylindrical shape provides an advantageous ratio of volume to surface, making them suitable to act as buoyancy tanks. For large conventional mounting systems the use of steel has been proven beneficial and may be applied to the disclosed invention.
Connecting element 304 may, e.g. due to external forces acting on carrier 300, be tilted. In that case the buoyancy of connecting element 304 causes a bending load in the connecting element 304 as the buoyancy force is acting at an angle relative to the connecting element's longitudinal axis. The bending moment acting on connecting element 304 is largest in the middle of connecting element 304. The connecting element may therefore be designed such that its stiffness corresponds to the distribution of bending load within it, e.g. by using a smaller pipe material strength at the ends of connecting element 304 and a thicker pipe material in the center of connecting element 304. To reduce the bending load connecting element 304 may also be shaped such that its buoyancy volume is distributed unequally along its length and concentrated in the upper part where connecting element 304 is attached to carrier 300. This may e.g. be achieved by increasing the radius of connecting element 304 from a small radius at the bottom where connecting element 304 is attached to the foundation to a larger radius at the top where connecting element 304 is attached to the carrier.
Alternatively an asymmetrical distribution of buoyancy along the connecting element's longitudinal axis may be achieved through ballast in the lower part of the connecting element 304. Ballast in the lower part of connecting element 304 is not critical due to the relatively small movements the connecting element experiences close to its foundation joint. This alternative may be beneficial when mounting system 1 is used to carry parts of a bridge.
A connecting element 304 having asymmetrical distribution of buoyancy may be shaped like a cylindrical wedge with a large diameter at the top and a small diameter at the bottom. Such a connecting element may be made of steel concrete. The bottom tip of the wedge may be solid steel concrete. To simplify transporting the connecting element to the mounting site that solid tip of the cylindrical wedge may be ballast material added to the connecting element at the construction site.
Connecting element 304 having a center of buoyancy above its center of gravity will produce the desirable effect of maintaining an upright position suitable for attaching carrier 300, even if its weight is larger than its buoyancy. In this case anchor joint 305 may only need to transfer a pushing force from connecting element 304 into foundation 5, providing a wider choice of anchor joint technologies to choose from. A connecting element 304 having a center of buoyancy above its center of gravity may for example be formed by ballast weights attached to or being part of the lower section of connecting element 304.
As illustrated the buoyancy required to carry structure 2 is essentially generated by connecting element 304. Carrier joint 305 therefore only transfers a pushing force and need not be able to transfer pulling forces.
A cost effective variation of the mounting system of
The beneficial effects of using slightly tilted connecting elements as described before with respect to
The ability of connecting elements 504,505 and 506 to carry a pushing force provides advantages over designs that only carry pulling forces. A wind-electric generator mounted on a carrier similar to the one illustrated in
By using torsionally fixed connecting elements 504,505,506 the size of carrier 500 may be reduced while increasing its ability to resist yawing motions. Only a small amount of excess buoyancy is needed to obtain the desired natural oscillation frequency and maintain the system's upright position.
Utilizing anchor's 520,521,522 with a maximum force rating equivalent to that of a traditional rope mounted systems allows placing anchors 520,521,522 closer to each other, roughly cutting their distance from each other in half relative to the traditional system. The reduced size of carrier 500 also reduces its weight, thereby reducing the required buoyancy. If parts of the buoyant volume are mounted at the connecting elements 504,505,506 the coupling of the wave motion is reduced, because the wave motion is decreasing with the depth below the water line.
By selecting the distances between the parts of the mounting system 1 such that they are about half of the wave-length expected in the area where the system is used, wave induced motion will be reduced. Other distances allow reducing the forces between the parts of the system. This provides the designer with a high degree of freedom to optimize the overall system dimensions for the desired mounting locations' environmental conditions, e.g. wave height and frequency.
In
Motion of connecting element 604 in direction of arrow 650 causes joint 621 to move in direction of arrow 623, which is opposite to the motion of carrier 600. Carrier 600 moves as indicated by arrow 651. By the proper choice of the length of lever arms 622 and 620 one can achieve that essentially no sideways motion of the structure 2 occurs.
At least two position control bars are required to control the structure's orientation. The lower ends of two position control bars may be mounted to same connecting element are to two different connecting elements. The position control bars are preferably flexurally rigid elongated elements.
As discussed with respect to
In an alternative design buoyancy tanks 726,727 may be firmly attached directly to foundation 724, i.e. without joints 751,752, thereby simplifying the design.
In a variation of the described the whole semi submersible system can be mounted by a tensionleg mounting to the seabed. The pretension of these tensionlegs is much smaller than the sum of the excess buoyancy of the mounting systems 810-814. This design allows limited use of material in deep waters.
Another useful application of mounting system 1 is illustrated in
The tower can also support the bridge directly. In this case it is useful to locate the resting point close to the way of the bridge and also locate the center of mass of the bridge there. A swiveling joint can be employed to de-couple the bridge from tilting. In order to get stability against tilt several towers may be used. Alternatively the stability can be produced by the mountings on the land on the end of the bridges.
The described bridges are particularly useful for deep waters like a fjord, because a grounding would be particularly expensive. Also the resistance against waves can more easily be achieved. Especially at deep waters the embodiment of the present invention can be carried out with a semi submersible system as illustrated in
To attach the mounting systems to the seabed various alternative anchor technologies are available. Driven pile anchors provide a reliable and cost effective connection to the seabed. These anchors can transfer pushing as well as pulling forces. If the expected pulling forces are larger than the pushing forces, friction anchors may be preferred since friction works into both directions. Driven pile anchors are advantageous as the motion of the pile can be recorded while it is driving into the seabed. The recorded motion allows predicting the stability of the anchor. Alternatively piles can be made of concrete which is put inside holes that are dug into the sea-bed. To handle the torque anchors which are able to be torque can be used. Such anchors are known in the state of the art.
Alternatively the mounting system may be attached to the seabed by heavy weight anchors. These anchors are less sensitive to the quality of the ground. Heavy weight anchors can be made using caisson mounting. If there are hollow cavities in the anchors, they can be brought to the place of the installation floating. After the installation the hollow spaces can be filled with water, sand or concrete.
For use in deep water suction anchors may be useful. Their size generally decreases with increasing depth under water, because the suction effect depends on the water pressure. However, suction anchors may also be used in shallow water, if the suction bell is large enough. Several connecting elements may be mounted to one suction bell. The position of distance between the connecting elements 4 on the suction bell can be defined before the installation of the suction bell. Furthermore the forces transferred by the different connecting elements 4 to the suction bell can compensate each other partially instead of putting load onto the anchor. Suction bells of that adequate size already have been developed for wind-electric generators with stiff mounting. This technique could be used. This common suction bell can be seen as foundation 5.
Also for anchoring with piles it may be useful to have a foundation 5, which consists of a common frame, which positions the connecting elements 4 at the lower side with respect to each other. This frame can be mounted by the driven piles to the sea-bed like a grid mast or a tripod used in wind energy technology. By such a frame as foundation 5 the forces transferred by the connecting elements can compensate each other partially, before they are transferred to the anchors. Especially the torque can be transferred to several anchors.
Alternatively it is also possible to anchor each connecting element 4 directly in the sea-bed. To transfer the torque to the ground either single anchors can be used. Alternatively a frame which takes more than one anchor can be used for those connecting elements 4 that are able to transfer torque.
As connecting elements 4, that can only take pulling load, ropes from steel or plastic or changes can be used. They have sufficient flexibility to obtain swiveling. Alternatively also material like bunches of parallel wires (like at suspension bridges) or steel pipes can used. In these cases it can be useful to introduce joints to allow the swiveling. For producing such connecting elements there is a state of the art in maritime technology which can be referred to.
Depending on the special design of the embodiment of the present invention it can be brought to the mounting position in parts or as a whole. For a set-up from parts one can proceed as follows: At first the foundation is prepared at the designated location. In the next step the connecting elements 4 are mounted at the foundation 4. If the foundation is hollow, it can partly be filled with water, so that they sink. Now they can be handled with a crane. As they are fully submerged it is also possible to lower them down from a ship. The foundation and the connecting elements 4 are mounted preferably by putting the joint together. In order to position the lower part of the connecting element 4 under water robots can be used. Alternatively it may be controlled from support ships via ropes. The carrier 3 is afterwards put onto the connecting elements 4. The carrier 3 can be transferred as a whole to the designated location together with the construction mounted on it. For this an additional pontoon is useful for stabilization, because the carrier 3 has no stability as a float. The buoyancy of the carrier can be utilized during the transport. For connecting carrier and connecting elements 4 it can be useful to reduce the excess buoyancy by filling ballast into the buoyant bodies. For the lowering of the carrier winches of the pontoon, which is stabilizing the carrier, can be used. It is useful to get rid of the ballast in the connecting elements 4 not before but after the mounting is ended, because the buoyancy excess makes them difficult to handle. If ropes are in use as connecting elements, they can be fixed by divers. It is useful to manufacture ropes such that the weight is compensated almost exactly by the buoyancy. That way the handling is easier and they will not hang down (in the state of the art of maritime technology there is a large amount of possibilities for that).
If mounting system 1 is part of a semi submersible, it can be mounted to the structure as described above.
There is one last thing to be stated: As the mounting system 1 according to the present invention does not gain floating stability neither by the weight distribution nor by the distribution of the buoyant volume, one characteristic is that the center of mass is far above the center of weight. Also the water line is short, because no floats at the surface are required. While the present invention has been described with reference to exemplary embodiments, it will be readily apparent to those skilled in the art that the invention is not limited to the disclosed or illustrated embodiments but, on the contrary, is intended to cover numerous other modifications, substitutions, variations and broad equivalent arrangements that are included within the spirit and scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| DE102006033215.6 | Jul 2006 | DE | national |
