DEVICE FOR SCOUR PROTECTION OF OFFSHORE STRUCTURES

Abstract

A device for scour protection of offshore structures includes one or more elastic plates made of rubber and connected to each other, and weight elements which are fastened on the plates by fasteners.

Description

FIELD OF THE INVENTION

The invention relates to an apparatus for scour protection of offshore constructions.

BACKGROUND OF THE INVENTION

Scouring is understood to be erosion phenomena of a water-covered bottom caused by currents in the region of the offshore constructions. A disadvantage of known protective measures is that they are complicated, but nevertheless insufficient with regard to their protective effect. In the offshore sector, for example in the case of monopiles of wind energy systems, it is the state of the art to pile up approximately 300 to 1000 metric tons of stones as scour protection. However, these stones produce harmful currents that prevent sedimentation of sand and in this way actually accelerate scouring. In addition, there is the risk that falling stones or stones that sink away as the result of the current might damage the ocean cable connection of the offshore wind energy system.

It is also known to use geotextile containers filled with sand, weighing about 1000 kg, as scour protection. In this connection, however, it cannot be ensured that these will maintain their position on the ocean floor once they have assumed it. They furthermore form an angle to the ocean floor and can thereby actually promote scouring. Also, these containers and stones can sink into the ocean floor as the result of flow events, and in this case must be introduced again, which causes continuous costs. Here, too, damage to the ocean cable is possible. Furthermore, both stones and containers cannot be placed precisely, in terms of location, starting from a certain water depth.

A third possibility that is frequently utilized consists in not using any scour protection at all, accepting scouring that occurs, and hoping, in this connection, that the scouring that develops will not exceed a certain depth. However, the foundation of a monopile, for example, then has to be introduced deeper into the ocean floor by this depth, which causes additional construction costs. Furthermore, the laid ocean cables of the offshore construction can be exposed by the scouring and/or its connections can be damaged or destroyed as the result of current effects.

Not only stones but also containers can form a permanent hazard location for fishing after the systems are decommissioned, since these apparatuses are generally not removed, because of the very high costs.

BRIEF SUMMARY OF THE INVENTION

The present invention was developed against the background of the state of the art described above. It is therefore the task of the invention to propose an apparatus for scour protection of offshore constructions, which offers durable, cost-advantageous, and, in this connection, effective protection.

This task is accomplished in that the apparatus comprises one or more elastic panels composed of rubber and weight elements that are fastened onto the panels by means of suitable fastening means. Fastening is understood to be permanent and secure fixation of the weight elements on the panel or panels, specifically even if the elastic panel or the elastic panels are pulled or pressed down by the weight elements, in order to thereby form an advantageous hydrodynamic shape. Suitable fastening means are, for example, screws with nuts. An advantageous hydrodynamic shape is understood to mean that the panel or the panels is/are curved downward in the edge region of the apparatus, whereby the back or underside of the panels serves as a contact surface for the subsurface, and the front or top of the panels serves as a run-up surface and as protection against eroding sand eddies and water eddies. The panels composed of rubber can be laid directly onto the sand surface or seabed surface in the region of the offshore constructions, below the water or ocean surface, or can also lie completely or partly under the seabed surface. In this connection, they have the advantage that they can adapt to the course of the seabed surface and can absorb the energy of the waves or eddies by means of their elastic properties. Furthermore, they are resistant to salt water and no corrosion occurs. Because of the strength and durability of the rubber, the apparatus is therefore maintenance-free. The rubber can be produced from natural rubber, in environmentally friendly manner. A further advantage is that the apparatus is not hazardous in the event of a collision with watercraft. The elastic panel or the elastic panels composed of rubber are fixed in place at the locations to be protected, using the securely and permanently affixed weight elements.

Advantageous embodiments of the invention, with additional characteristics, are described below.

It has proven to be optimal if the elastic panel or the elastic panels composed of rubber have a thickness of one to two centimeters. The weight elements are preferably fastened onto the top of the elastic panels in the edge region of the apparatus. The surface formed by the panels is curved by means of the force exerted on the panels by the weight elements and by means of the recovery force brought about by their elasticity, and a particularly advantageous, hydrodynamic shape is formed, which serves as a run-up surface for water waves or pressure waves. The force of the pressure waves is taken up, absorbed, and conducted away from the offshore constructions. If the ground underneath the weight element subsides or is washed away, then the weight element, together with the panel, moves downward, thereby restoring the protective effect. An ocean cable laid under the elastic panels composed of rubber is optimally protected and increases the operational reliability of the system. The proposed apparatus for scour protection further has the advantage, in the offshore sector, that it can be removed with a single crane movement, and leaves a barrier-free ocean floor behind.

In a preferred embodiment, the apparatus forms or the elastic panel forms or the elastic panels connected with one another form a disk having a circular or approximately circular contour, at the center point of which the offshore construction is disposed. The weight elements are then particularly fastened on along the edge region of the disk. The elastic panel or the elastic panels connected with one another are then curved most strongly downward along the edge region of the disk, whereby the curvature decreases in the direction toward the centrally disposed offshore construction and makes a transition into a flat surface.

It has proven to be advantageous if the radius of the apparatus is about three times as long as the radius of the offshore construction in the plane in which the apparatus is disposed or fastened onto the offshore construction.

The weight elements have an approximately rectangular base surface, the longitudinal axis of which points in the direction of the offshore construction, in each instance.

If the weight elements are made of metal, a large mass with great weight is achieved at a small volume.

The weight elements can have the shape, in longitudinal section and/or in transverse section, of an equilateral, symmetrical trapezoid, which narrows toward the top, whereby its corners are preferably rounded off.

The weight elements can have an indentation on the underside, which is domed inward, in concave manner, in cross-section.

The weight elements serve not only for weighing down a panel or multiple panels. Depending on their size and their arrangement, they have different requirements and tasks to fulfill.

The weight elements are fastened onto the panel or the panels and have the task of holding the apparatus on the ground at certain points. The mass of the weight elements, among other things, must be determined as a function of the spacing and the water depth and the wave height to be expected, as well as the flow velocity of the water. They must balance out different pore pressures caused by wave action, i.e. the panel is supposed to rise and fall between the weight elements. However, the sand remains underneath and is held in place. In order for this to be made possible, water-tight fastening onto the offshore construction to be protected must take place, and weight elements positioned at the edge must be provided on the outside, at the edge.

The edge weight elements must have a specific, flow-advantageous shape, and must be oriented in a specific manner and at a specific distance relative to one another. The correct weight size and the least possible flow resistance must be selected for the application case, in each instance. Metal weight elements having a small surface area and great weight are advantageous. Also, the distance between the weight elements, relative to one another, is important. These weight elements must be selected, in terms of weight, shape, and surface, depending on the conditions of use, in such a manner that they work themselves into the ocean floor at the edges, on their own, under the effect of currents and waves, and thereby the panel is sealed off at the edge. In this connection, no fold or opening is allowed to form. At the same time, however, this edge must adapt to any unevenness of the ocean floor. Here, the particular configuration of an advantageous hydrodynamic shape is important. For this reason, the spacing of the weight elements, among other things the shape, size, and placement, is important. The panel must sink in so that it represents a flat transition between panel and ocean floor, otherwise new scour occurs there. Folds in the panel, even if they are very small, can lead to undermining of the scour protection and to damage to the offshore construction to be protected.

The mass of the weight elements can amount to between 50 and 500 kg/m, depending on the application case, according to studies that have been undertaken. Here, too, the conditions of use are the deciding factor.

A hydrodynamically advantageous shape is understood to mean that the panel or the panels, also as the result of possible reinforcements, sink only in the intended direction, so that with reference to the current, an inclined surface or a slightly curved surface away from the offshore construction, at an incline ratio between 1:4 and 1:5, is formed. Experiments have shown that no scour occurs at this incline.

The ocean floor is not constant in terms of its height. Debris is transported. This means that the ocean floor around the offshore construction can certainly decrease in height by approximately 2 m, depending on the location. If this happens, an incline of 1:5 has been brought about over the width of the panel, to be dimensioned in advance at 2 m, sinking at 1:5=10 m. In this connection, the outside diameter at the foot of the panel, and thereby the circumference, is decreased. Any normal elastic material would develop folds in this connection, but this is not the case for the material selected. This material is able to balance out the length changes internally within the material. Vice versa, the material is able to stretch: if the ocean floor sinks only on one side of the offshore construction, the apparatus is able to adapt to the sinking ocean floor and to stretch. Also, the apparatus is able to even out depressions within the surface to be protected.

The reinforcements can be external reinforcements or reinforcements integrated into the panel. These can have a spacing of approximately 2 to 3 m on the outside, at the edge of the panel, if they are external reinforcements. All the reinforcements are disposed to run outward in star shape from an imaginary center point of the foundation to be protected, whereby the outer contour should have a round or an approximately round shape, if at all possible, if the ocean floor is known to sink, in order to prevent fold formation at the edge of the panel.

In the case of monopiles, the outside diameter of the apparatus is approximately three times as great as the diameter of the pile.

If the ocean floor sinks, undermining of the panel, at certain points or on the circumference, is intended. However, this will only happen until the sand under the panel no longer withstands the weight pressure of the panel with the weight elements, as the result of liquefaction of the sand, and sinks. In this connection, curvature of the panel, as shown, is also permissible. This can take place at certain points or completely. The elasticity of the rubber adapts to the ocean floor and forms a seal on the outside, at the row of weights, once again. The foundation is therefore protected once again. If the ocean floor sinks by 2 m, the expanse of the panel from the foundation body into the ocean is 10 m at an incline of 1:5. If this dimension suffices to absorb scour eddies of the foundation under the above conditions, the size of the panel has thereby been established.

The scour protection panel must be affixed on the body to be protected, in water-tight manner. If this does not happen, and if a gap of only one centimeter is formed, enormous scour develops through this gap and damages the stability of the foundation to be protected.

The weight elements at the edge consist essentially of metal. The weight elements have the task of weighing down the edge of the panel in such a manner that the panel sinks into the ocean floor at the ends, without causing any scour there. The greatest possible weight can be implemented with the metal weights, in relation to the flow cross-section. This also means that the smallest possible flow resistance is present at the required weight size. Among other things, this is the reason why the weight elements are disposed in such a manner, viewed from the edge in the direction of the center of the foundation. The longitudinal axis of the weight elements always points in the direction of the foundation.

However, the special shape of the weight elements, together with their dimensions, also has other reasons. The panel or the panels connected with one another have the task of adapting to every contour of the ground, at least at the edges. Therefore the weight is not allowed to become too broad. On the other hand, the apparatus, with the weight elements screwed onto it, must still be so flexible that it adapts to any unevenness of the ground, specifically to both positive and negative changes or bumps in the ground. Depending on the conditions of ocean depth, current velocity, wave stress, and ground composition, the weight elements have a mass of 50 to 500 kg/m.

The weight elements can be shaped. However, if the panel is smaller in diameter, development of a fold is unavoidable. In order for this not to cause damage, the fold is predetermined in the downward direction. This is achieved by means of the special shape of the weight elements with a lower indentation. In this connection, the panel is stretched, at first. As it sinks, the panel relaxes. As it sinks further, it will develop many small folds as a result of the predetermined shape, but these are directed downward and will press themselves into the sand. This effect suffices to obtain an incline as desired, if the panel has been designed correctly. If the distance between the weight elements becomes too great, the fold is pushed upward as the result of sand pressure. The scour protection then becomes non-tight at the edge. If sinking of the ocean floor is not expected, the weight elements can be used without an indentation, and reinforcements are also not necessary. However, these reinforcements can also be used to fold up the scour protection for transport at sea, and thereby to obtain logistical advantages.

One or more flexible reinforcements can be provided for the apparatus, the rigidity of which is preferably adjustable. A reinforcement comprises a reinforcement profile composed of flexible plastic, a reinforcement wall composed of rubber, disposed above the reinforcement profile, which wall preferably has a woven fabric insert and forms a closed cavity that is filled with a medium such as water or air. The rigidity of the flexible reinforcement can be changed or adjusted by means of the selection of the thickness of the reinforcement profile and/or the reinforcement wall, as well as by means of the selection of the medium and/or its pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures of the drawing show, in detail:

FIG. 1 a top view of the apparatus 1 with a monopile 2;

FIG. 2 partial views of another embodiment of the apparatus 1′ in vertical section;

FIG. 3 a weight element 4 in longitudinal section a, in cross-section b, and in a top view c;

FIG. 4 a weight element 4 with an indentation 9 in longitudinal section a, in cross-section b, and in a top view c;

FIG. 5a a vertical section through the apparatus 1 with weight elements 4 with an indentation a and with weight elements without an indentation 9;

FIG. 5b a vertical section through the apparatus 1 with weight elements 4 without an indentation; and

FIG. 6 a perspective detail view, horizontally cut, of a further embodiment of the apparatus 1 with a flexible reinforcement 18.

DETAILED DESCRIPTION OF THE INVENTION

In the following, a best embodiment of the invention will be described in detail, making reference to the drawings, whereby further advantageous characteristics can be derived from the figures of the drawing. Functionally equivalent parts are provided with the same reference symbols.

FIG. 1a shows a top view of the apparatus 1 with a monopile 2. This apparatus consists of elastic panels 3 composed of rubber, connected with one another, having a thickness of one to two cm. The panels 3 can be connected with one another by means of vulcanization or by means of suitable fastening means (not shown) that have a shape-fit effect. The elastic panels 3, connected with one another, have the shape of a disk having a circular contour and a circular, central opening 11. The offshore construction 2 to be protected, namely a monopile of a wind power plant, is disposed in the central opening 11. In this connection, the radius of the apparatus 1 is about three times as long as the radius of the offshore construction 2, specifically with reference to the horizontal plane in which the apparatus 1 is fastened onto the monopile 2, namely at the level of the ocean floor 8.

The disk formed from the rubber panels 3 is fastened onto the monopile 2 in water-tight manner, so that no sea water can penetrate through the central opening 11 underneath the apparatus 1. The elastic panel 3 or the elastic panels 3 composed of rubber lie on the ocean floor 8, whereby uneven areas of the ocean floor 8 can be evened out by means of the elasticity.

Weight elements 4 are fastened onto the panels 3 at the edge region along the circumference of the apparatus 1, which elements press the panels 3 downward into the ocean floor at the edges, and thereby seal them off. In this way, effective scour protection is achieved. For reasons of a clear illustration, the weight elements 4 are shown only on two opposite circle segments, but in fact weight elements 4 are provided along the entire disk edge 13.

The weight elements 4 have an essentially rectangular base surface. The weight elements 4 are oriented on the panels 3 in such a manner that the (imaginary) longitudinal axis 12 of each weight element 4 extends in the direction of the offshore construction 2 and therefore all the longitudinal axes 12 meet in the center of the apparatus 1 or the monopile 2.

FIG. 1b shows a detail from FIG. 1a in a detailed view. Five weight elements 4 are shown, which are disposed at the edge of a circle segment of the panels 3, whereby the circumference 5 of the circle segment amounts to about one meter. The weight elements 4 have a width of about seventeen centimeters, in each instance, and a distance 6 between them of about three centimeters. The total mass of the weight elements 4 amounts to about fifty to five hundred kilograms per meter of circumference 5, in other words about ten to one hundred kilograms per weight element 4.

FIG. 2 shows partial views a, b, c, of another embodiment of the apparatus 1 in vertical section. This apparatus has reinforcement elements 7 on the underside. It is shown that the rubber panels 3 should be fastened onto the foundation body of the offshore construction 2 in tight manner.

FIG. 2 b shows an ocean floor that has sunk away by about two meters.

In FIG. 2 c, it is shown how the elastic panels 3 are pressed downward by the weight elements 4, so that sealing takes place and the offshore construction 2 is protected against scouring. If the ocean floor sinks by two meters, the length of the panel from the foundation body 2 out amounts to about ten meters at an optimal incline of about 1:5.

In FIG. 2 d, an apparatus 1 without reinforcement elements 7 is shown. This results in a curved shape 14 of the panels, which is fundamentally hydrodynamically advantageous. However, in the case shown, the curvature 14 is overly marked, so that scour-promoting eddies are formed. A lesser curvature 14′ as shown with a broken line in FIG. 2 c is more advantageous. This can be adjusted by means of the selection of the mass of the weight elements 4.

FIG. 3a shows a weight element 4 in longitudinal section, FIG. 3b in cross-section, and FIG. 3c in a top view. The weight element 4 has the basic shape of a block that narrows upward, which has the shape of an equilateral, symmetrical trapezoid in longitudinal section and in cross-section. The weight elements 4 shown have a length of 3.80 m and a width of the of 1.70 m, with reference to their base surface. The block narrows quantitatively in such a manner that a deviation from the vertical of about 15 degrees occurs. The corners are furthermore rounded off. This results in an advantageous hydrodynamic shape, on the one hand, because no eddies and disadvantageous currents of the ocean water occur at the weight elements 4. A further, significant advantage of the shape that narrows upward consists in that sections of the panels 3 can elastically sink downward without the weight elements 4 then coming into contact in the region of a curvature.

The weight elements 4 furthermore have two continuous openings 15 for the introduction of fastening elements (not shown). In this way, the weights can be permanently fastened onto the rubber panels 3. Even if the rubber panels 3 sink down and if a slant or curvature forms, as shown in FIGS. 2c and 2d, secure fixation is guaranteed.

Furthermore, two lower recesses 17 are provided for a weight element 4, in each instance. These serve as an assembly aid and facilitate gripping of the weight element 4 when it is supposed to be transported and afterward fastened onto the elastic panels 3.

FIG. 4a shows another embodiment of the weight element 4 in longitudinal section, FIG. 4b in cross-section, and FIG. 4c in a top view. In the case of this embodiment, the weight element 4 has an indentation 9 that is curved inward or upward, in concave manner, on its underside.

FIG. 5a shows a vertical section through an apparatus 1 having weight elements 4 having a lower indentation 9. The weight elements 4 therefore correspond to the embodiment shown in FIGS. 4a, 4b, and 4c. The weight elements 4, which are shown in cross-section, are fastened onto the top of the elastic panels 3 and permanently fixed in place.

Experiments have shown that in the case of the weight elements 4 shown in FIG. 5b, without a lower indentation 9, folds that face upward, in other words elevations in the elastic panels 3 (not shown) can be formed under certain conditions, if the panels 3 sink down, as the result of the sand pressure between the weight elements 4. The scour protection then becomes non-tight at the outer edge 13 of the apparatus 1, as a result of the folds or elevations.

It is true that fold formation 10 between the weight elements 4 occurs also as the result of the indentations 9 shown. However, the folds 10 in the elastic panels 3 between the weight elements 4 point downward, in other words they are bent in the direction toward the ocean floor in the region of the interstices 16, so that depressions 10 are formed as a result. This occurs in that the indentations 9 form a concave guide for the rubber panels 3, thereby shaping the rubber panels 3 in wave-like manner, as shown in FIG. 5a. In this way, harmful fold formation upward is avoided in the region of the interstices 16, and the apparatus 1 forms a seal also in the edge regions, and protects offshore constructions 2 against scouring.

FIG. 5b shows weight elements 4 without indentation. If greater sinking of the ocean floor and thereby fold formation downward is not expected, this embodiment of the weight elements 4 can be used.

FIG. 6 shows a perspective detail view, horizontally cut, of a further embodiment of the apparatus 1 having a flexible reinforcement 18. The latter comprises a reinforcement profile 19 composed of flexible plastic. The reinforcement profile 19 is fastened onto the elastic panels 3 using suitable fastening means. A reinforcement wall 20 composed of rubber is disposed above the reinforcement profile 19, which wall can have a woven fabric insert and is tightly fastened onto the panels 3. Fastening can take place, in each instance, by means of adhesives or vulcanization.

The upper reinforcement wall 20, together with the elastic panels 3, forms a closed cavity 21 that is filled with a medium. Water or air, for example, is a possible medium. The rigidity of the flexible reinforcement 18 can be changed or adjusted by means of the selection of the thickness of the reinforcement profile 19 and/or reinforcement wall 20, as well as by the selection of the medium and/or its pressure.

REFERENCE SYMBOL LIST

• 1. apparatus
• 2. offshore construction
• 3. elastic panels
• 4. weight elements
• 5. circumference
• 6. distance between the weight elements
• 7. reinforcements
• 8. ocean floor
• 9. indentation
• 10. fold
• 11. central opening
• 12. longitudinal axis
• 13. edge region
• 14. curvature
• 15. fastening openings
• 16. interstice
• 17. recess
• 18. reinforcement
• 19. reinforcement profile
• 20. reinforcement wall
• 21. cavity with medium

Claims

1. Apparatus (1) for scour protection of offshore constructions (2), which comprises one or more elastic panels (3) composed of rubber and weight elements (4) that are fastened onto the panels (3) by means of fastening means.

2. Apparatus (1) according to claim 1, wherein the elastic panel (3) or the elastic panels (3) composed of rubber have a thickness of one to two centimeters and/or the weight elements (4) are fastened onto the elastic panel (3) or the elastic panels (3) at the edge region of the apparatus (1).

3. Apparatus (1) according to claim 1, wherein the elastic panel (3) or the elastic panels (3) connected with one another form a disk with a circular or approximately circular contour, at the center point of which the offshore construction (2) is disposed.

4. Apparatus (1) according to claim 1, wherein the radius of the apparatus (1) is about three times as long as the radius of the offshore construction (2) in the plane in which the apparatus (1) is disposed.

5. Apparatus (1) according to claim 1, wherein the weight elements (4) have an essentially rectangular base surface, the longitudinal axis of which points in the direction of the offshore construction (2), in each instance.

6. Apparatus (1) according to claim 1, wherein the weight elements (4) consist essentially of metal.

7. Apparatus (1) according to claim 1, wherein the weight elements (4) have the shape, in longitudinal section and/or in transverse section, of an equilateral, symmetrical trapezoid, wherein its corners are preferably rounded off.

8. Apparatus (1) according to, wherein the weight elements (4) have an indentation (9) on the underside, which is domed inward, in concave manner, in cross-section.

9. Apparatus (1) according to claim 1, wherein at least one flexible reinforcement (17) is provided, which comprises a reinforcement profile (19) and a reinforcement wall (20) disposed above the reinforcement profile (19), wherein the reinforcement wall (20) forms a closed cavity (21) that is filled with a medium.