WO2020128097A1

WO2020128097A1 - Rope for airborne wind power generation systems

Info

Publication number: WO2020128097A1
Application number: PCT/EP2019/086944
Authority: WO
Inventors: Rigobert Bosman
Original assignee: Dsm Ip Assets B.V.
Priority date: 2018-12-21
Filing date: 2019-12-23
Publication date: 2020-06-25

Abstract

A braided rope for a tethered airborne wind power generation system comprising load carrying primary strands comprising yarns with a tenacity of at least 1.0 N/tex, wherein the tensioned braided rope has an aerodynamic cross-section with an aspect ratio in the range from 1.2 to 4.0, wherein the aspect ratio is the ratio of the primary diameter D to the secondary diameter d, wherein D is the largest diameter of the cross-section and d is the largest diameter of said cross-section, wherein the primary diameter D and the secondary diameter d are perpendicular to each other and intersect each other in point c, whereby c divides the primary diameter D in two unequal segments R and r, characterized in that the ratio R to r is in the range from 1.2 to 4.0. The invention further relates to an airborne wind power generation system comprising at least a winch and an airborne unit connected by a tether, wherein the tether comprises said rope.

Description

ROPE FOR AIRBORNE WIND POWER GENERATION SYSTEMS

The present invention relates to a braided rope, which is suitable as load bearing core of the tether cable for a tethered airborne wind power generation system, the braided rope comprising load carrying primary strands comprising yarns with a tenacity of at least 1.0 N/tex. The invention further relates to airborne wind power generation system or marine trawling systems comprising such rope. The terms load bearing core and load carrying core used interchangeably herein.

In view of the limited resources of fossil fuels in the world and the need to reduce C0₂ emission, there is an increased demand for alternative sources of energy, in particular for energy from a renewable source. Different renewable energy systems are currently being developed using, among others, wind energy, solar energy or wave and/or tidal energy as a source.

Wave energy systems use the energy in the movements of water near the surface of the sea, which may result from wind streams due to solar heat. Examples of wave energy systems are power buoys, where a floating buoy is moored to the sea bed and attenuator systems, which is a floating hinged system with moving segments.

Tidal energy systems use the energy resulting from the rise and fall of tides, which may be due to gravitational forces of the moon and sun. Examples of tidal wave energy systems are submerged turbines, mounted on existing wind turbine systems and rigid panels moving with tidal streams.

An example of a wind energy system is a high-altitude wind energy system, which generally consists of a kite, balloon or airplane like structure that flies at an altitude of from 100 to 1 1.000 m, or from 100 to 2000 m, making optimal use of the high-altitude winds. Such wind energy system is often called an airborne wind energy (AWE) system.

Another example of a wind energy system is a high-altitude wind energy system, comprising a structure, which may also be referred to as air-borne unit herein, that flies at an altitude of from 100 to 1 1.000 m. Such structure typically makes optimal use of the high-altitude winds.

Examples of such structure include as a kite, balloon, airplane, glider and a drone. Alternatively, the as air-borne unit flies at an altitude of from 200 to 2.000 m. Different systems currently exist, which include systems with a ground-based generator such as described in WO2018072890, but also systems with an air-borne, or flying, generator have been suggested. An example of such a system is described in US 7,335,000.

The majority of the systems as described above will need a tether comprising a load bearing rope to anchor the system to an anchoring point, e.g. to the ground or to the sea bed. The systems may also need one or more cables to either transport power to the system for controlling the system, or to transport power from a generator to a ground station.

WO2012013659 describes tethers combining the functionality of an anchoring member with a plurality of conductors.

A tether for high-altitude wind systems is for instance know from WO09142762. This document describes a tether that is designed to have less aerodynamic drag by applying flexural skins positioned symmetrically around a circular-shaped cross-section.

A drawback of the known tethers and in particular the high-power tethers remains that they represent a significant source of drag and are heavy constructions. These result in a high catenary, reduced attainable altitude and energy losses.

A further drawback is that constructions to reduce aerodynamic drag such as described in WO09142762 are voluminous, complex, may be heavy and/or fragile making the use of such tethers in dynamic airborne wind power generation system difficult.

Thus, a tether for such a system must withstand high tension forces and at the same time be robust against transversal forces upon winding. Moreover, the tether should be lightweight because heavy cables would compromise too much the movement of the renewable energy system.

In an attempt to overcome the above mentioned drawbacks, the invention provides a braided rope that when tensioned (under a load of at least 300 MPa) has an aerodynamic cross-section with an aspect ratio in the range 1.2 - 4.0, wherein the aspect ratio is the ratio of the primary diameter D to the secondary diameter d, wherein D is the largest diameter of the cross-section and d is the largest diameter of said cross-section perpendicular in c to the primary diameter, wherein c divides D in two radiuses, R and r, characterized in that the ratio R to r is in the range from 1.2 to 4.0. The primary diameter D and the secondary diameter d are perpendicular to each other and intersect each other in point c, whereby c divides the primary diameter D in two unequal segments or radiuses R and r. In an aspect the cross-section of a tensioned rope herein is the cross section of the rope under a load of 300 MPa. In a further aspect to overcome the above mentioned drawbacks, the invention provides a braided rope, wherein the rope is a soutache braid of uneven number of from 5 to 1 1 twisted or braided primary strands, wherein at least a first elongated body extends within a non-central channel formed by the soutache braid of the primary strands. In an embodiment of the rope according to the invention, the rope is a soutache braid of 5 or 7 twisted or braided primary strands, wherein at least a first elongated body extends within a non-central channel formed by the soutache braid of the primary strands

The invention provides a braided rope for a tethered airborne wind power generation system comprising load carrying primary strands comprising yarns with a tenacity of at least 1.0 N/tex, wherein the tensioned braided rope has an aerodynamic cross-section, wherein the rope is a soutache braid of uneven number of 5 to 1 1 twisted or braided primary strands, wherein at least a first elongated body extends within a non-central channel formed by the soutache braid of the primary strands.

The invention provides a braided rope for a tethered airborne wind power generation system comprising load carrying primary strands comprising yarns with a tenacity of at least 1.0 N/tex, wherein the tensioned braided rope has an aerodynamic cross-section with an aspect ratio in the range from 1.2 to 4.0, wherein the aspect ratio is the ratio of the primary diameter D to the secondary diameter d, wherein D is the largest diameter of the cross-section and d is the largest diameter of said cross-section, wherein the primary diameter D and the secondary diameter d are perpendicular to each other and intersect each other in point c, whereby c divides the primary diameter D in two unequal segments R and r, characterized in that the ratio R to r is in the range from 1.2 to 4.0.

The rope according to the invention has an aerodynamic shape. The aerodynamic cross-section of the rope according to the invention has an aspect ratio in the range from 1.2 to 4.0, which indicates that the cross-section is longer (primary diameter D) than wide (secondary diameter d). Further the ratio R to r is in the range from 1.2 to 4.0, which defines that the secondary diameter d is not in the middle (R=r) of the primary diameter, but closer to one end of the primary diameter D: R/r = 1.2-4.0.

Herein diameters D and d and segments R and r are distances (see also figure description).

The advantage is that when a rope according to the invention is employed as the load carrying core of a tether, the energy efficiency of the tethered system can be optimized. In such systems, the weight imposed by the tether on the air borne unit as well as the drag imposed on the tether are optimized by the low volume and low weight of the employed rope according to the invention. Furthermore, such tether is especially suited for tethered dynamic airborne wind power generation system requiring the tether to be repeatedly winched under substantial longitudinal tension and transversal compression. It was observed that tether systems comprising the rope of the invention may show a better strength efficiency and may provide longer operation of the tether before failure or preventive replacement.

The tether comprising the rope has high strength efficiency, meaning the strength of the tether is a relatively high in relation to its overall cross-section and its

aerodynamic drag. The rope according to the invention also shows improved performance on traction and storage winches; i.e. more regular winding and less burying-in. The rope according to the invention can be easily inspected on possible damage, and can be readily, if needed, repaired.

With tether according to the invention is meant a device comprising a rope, to be attached to an airborne unit to anchor and guide said airborne unit and transfer the wind force to and/or from the airborne unit to a reeling winch on the ground. The tether may also transfer energy and guiding signals from the ground to the airborne unit. Guiding signals include signals to guide the airborne unit. The tether comprises a rope as a load carrying core and may further comprise devices to enhance its performance, such as coatings, conductors, safety lights, sensors, etc. In a preferred embodiment of the invention, the rope may comprise fairings covering substantially the outside of the rope. The addition of fairings to the outside surface of the rope may provide a further optimized aerodynamic behaviour of the rope, especially by a reduction of vortex induced vibrations.

A rope in the context of the present invention is an elongated body having a length much larger than its lateral dimensions of for example width and thickness or diameter. The rope in accordance with the invention has an aerodynamic, oblong cross-section which may be rounded or polygonal or combination thereof. Preferably, the ropes have a droplet-shaped cross-section. The ropes may have symmetric cross-section with a line-symmetry, with primary diameter D being the axis of symmetry. By aerodynamic in the context of the present invention is understood that the rope provides little resistance to transversal moving fluid, e.g. air or liquid, also referred to as low drag and expressed by a low drag coefficient (c_d). Hence the rope according to the invention preferably has a drag coefficient of at most 0.3, more preferably at most 0.25 and most preferably at most 0.20. The cross-section of the braided rope, when tensioned, has an aspect ratio, i.e. the ratio of the primary to the secondary diameter (or width to height ratio), in the range of from 1.2 to 4.0. Methods to determine the aspect ratio are known to the skilled person; an example includes measuring the outside dimensions of the rope, while keeping the rope under tension. The advantage of said aspect ratio is that during the use of the rope or the tether in high wind conditions the drag of the rope or tether system is substantially reduced, allowing optimized energy recovery and operations at higher altitude. An aspect ratio greater than about 4, resulting from certain braid constructions, however, results in an aerodynamic instable behavior and detrimental resonances. Therefore, the cross-section has preferably an aspect ratio of between 1.3 - 3.0, more preferably between 1.4 - 2.0; even more preferably between 1.5 - 1 .8, and most preferably between 1.6 - 1.7. In an embodiment the cross-section has an aspect ratio of 1.3 to 3.0, in an embodiment an aspect ratio of 1.4 to 2.0; in an embodiment an aspect ratio of 1.5 to 1.8, in an embodiment aspect ratio of 1.6 to 1.7.

The cross-section having an aspect ratio of about 1 or less would mean a cylindrical cross section, which would not have the beneficial reduction of drag as the aerodynamic cross- section of the braided rope according to the invention.

Furthermore, in the context of the present invention, the primary diameter D and the secondary diameter d are perpendicular to each other and intersect each other in point c, whereby c divides the primary diameter D in two unequal segments or radiuses R and r, such that the ratio between the two radiuses, i.e. R to r, is in the range from 1.2 to 4.0, preferably the ratio R/r is between 1.3 - 3.0, more preferably between 1.4 - 2.0, and most preferably between 1.5 - 1.8.

In an embodiment the rope according to the invention has a second aspect ratio wherein the primary diameter D and the tertiary diameter d2 are perpendicular to each other and intersect each other in point e, whereby e divides the primary diameter D in two unequal segments or radiuses R’ and r2, characterized in that the ratio R’ to r2 is in the range from 1.2 to 4.0 and the ratio R to r is smaller than the ratio R’ to r2 .

Herein diameters D, d, d2 d3 and segments and radiuses R, R’, R” r, r2 and r3 are distances (see also figure description).

In an embodiment the ratio R/r is in the range from 1.3 to 3.0, in an embodiment in the range from 1 .4 to 2.0, in another embodiment in the range from 1.5 to 1.8. In an embodiment the ratio R7r2 is in the range from 1.3 to 3.0. In an embodiment according to the invention the ratio R/r has a smaller value than the ratio R7r2 to provide the beneficial reduction of drag. It was observed that ropes with cross-section properties in these ranges have increased robustness under variable wind conditions, resulting in low resonance phenomena and increase durability.

In the context of the invention, the aerodynamic cross-section of the rope is defined under tensioned conditions of the rope. It is clear that in a rope comprising a multitude of primary strands, the individual strands may shift one against the other and adopt different shapes depending upon external constraints. As the aerodynamic character of the rope cross- section is relevant during its application, it is understood that the shape under tension is a relevant feature. Accordingly, the shape of an untensioned, or even compacted rope is not subject of the present invention, although also the rope according to the invention might also have the required aerodynamic shape under such conditions. The skilled person will be aware of the fact that braided ropes when tensioned typically adopt a circular cross-section, amongst others due the competition of all the primary strand under tension to adopt a linear

configuration and hence the attempt to migrate to the center of the rope construction. In contrast, the claimed braided rope may comprise structural differences resulting in local thickening and thinning of the primary strands or avoid the primary strands taking central position. In some cases, a braided rope according to the invention may only adopt the claimed aerodynamic shape once tensioned. By tensioned or kept under tension or kept taut in the context of the present invention is understood that the rope is subjected to an extensional force, applied in the length direction of the rope. Such tension might be expressed in force per surface area, such as N/m², but is in the field of ropes more conveniently expressed in Pascal (Pa) or even MPa. In the context of the present application, a rope is considered tensioned when a tension of at least 50 MPa, preferably 300MPa is applied to it. Typically a tension of maximum 600 MPa is applied to the rope during use. A suitable average working tension includes 300 MPa. The working tension may have a peak load in the range from 50 to 600 MPa.

The rope according to the invention can have an equivalent diameter that varies between wide limits for example depending upon the operation conditions and size of the power generation system. Smaller equivalent diameter ropes, for example in the range of from about 2 to 20 mm, may typically be applied as cords in experimental, mobile or consumer devices. Large equivalent diameter, or heavy-duty ropes typically have a diameter of at least 20 mm. For the ropes with oblong cross-section, it is more accurate to define its size as a round rope with an equivalent diameter; that is the diameter of a circular rope of same mass per length as the non-round rope. The diameter of a rope in general, however, is an uncertain parameter for measuring its size, because of irregular boundaries of ropes defined by the strands. A more concise size parameter is the linear density of a rope, also called titer or linear weight; which is its mass per unit length. The titer can be expressed in kg/m, but often the textile units denier (g/9000 m) or dtex (g/10000 m) are used. Diameter and titer are interrelated according to the formula d = (T/(10*p*v))^{0 5}, wherein T is the titer (dtex), d is the diameter (mm), p is the density of the filaments (kg/m³), and v is a packing factor (normally between about 0.7 and 0.9). Nevertheless, it is still customary in the rope business to express rope size in diameter values. Preferably, the rope according to the invention is a heavy-duty rope having an equivalent diameter of at least 20 mm, more preferably at least 30, 40, 50, or even at least 60 mm, since the advantages of the invention become more relevant the larger the rope. Largest ropes known have diameters up to about 300 mm, ropes used in airborne win energy installations typically have a diameter of up to about 200 mm, preferably of up to 100 mm. In an aspect the rope, which may also be referred to as working cord, has an equivalent diameter of from 50 to 140 mm.

By primary diameter of the rope is herein understood the largest distance between two opposite locations on the periphery of a cross-section of the rope. The primary diameter of the rope used in accordance with the invention can vary between large limits, e.g. from length of 5 mm or less, to up to 200 mm and even up to 500 mm. Although not a limiting factor, it was observed that the rope and tether operate best when said primary diameter of said rope is at least 10 mm, more preferably at least 20 mm, most preferably at least 30 mm.

In the present invention with primary strands is meant those strands that are the first strands that are encountered when the rope is opened up. In general these are the outermost strands of the rope, but may also include a core strand, if present. The primary strands may be made up of further secondary strands.

The strands, e.g. the primary strands, of the strength member of the rope of the invention contain high strength yarns that comprise high strength fibers, also referred to in the present context as high tenacity fibers. By fiber is herein understood an elongate body, the length dimension of which is much greater than the transverse dimensions of width and thickness. Accordingly, the term fiber includes filament, ribbon, strip, band, tape, and the like having regular or irregular cross-sections. The fibers may have continuous lengths, known in the art as filaments, or discontinuous lengths, known in the art as staple fibers. Staple fibers are commonly obtained by cutting or stretch-breaking filaments. A yarn for the purpose of the invention is an elongated body containing at least 2 fibers, preferably at least 25 fibers. By high strength yarns, also referred to as high performance yarns, are understood in the context of the present invention yarns with a tenacity of at least 1.0 N/Tex, preferably of at least 1.2 N/Tex, more preferably at least 1.5 N/Tex, eve more preferably at least 2.0 N/Tex, yet more preferably at least 2.2 N/Tex and most preferably at least 2.5 N/tex. When the high performance yarns are UHMWPE yarns, said UHMWPE yarns preferably have a tenacity of at least 1.8 N/Tex, more preferably of at least 2.5 N/Tex, most preferably at least 3.5 N/Tex. Preferably the high performance yarn has a modulus of at least 30 N/Tex, more preferably of at least 50 N/Tex, most preferably of at least 60 N/Tex. Preferably the UHMWPE yarn has a tensile modulus of at least 50 N/Tex, more preferably of at least 80 N/Tex, most preferably of at least 100 N/Tex. N/Tex and N/tex are used interchangeably herein thus the synthetic filaments, present in the rope of the invention have a filament tenacity of at least 1.0 N/tex, preferably of at least 1.2 N/tex, more preferably at least 1.5 N/tex, eve more preferably at least 2.0 N/tex, yet more preferably at least 2.2 N/tex and most preferably at least 2.5 N/tex. When the high performance filaments are UHMWPE filaments, said UHMWPE filaments preferably have a tenacity of at least 1.8 N/tex, more preferably of at least 2.5 N/tex, even more preferably at least 3.0 N/tex and most preferably at least 3.5 N/tex. Preferably the high performance filaments have a modulus of at least 30 N/tex, more preferably of at least 50 N/tex, most preferably of at least 60 N/tex. Preferably the UHMWPE filaments have a tensile modulus of at least 50 N/tex, more preferably of at least 80 N/tex, most preferably of at least 100 N/tex. In the context of the present invention tensile strength and tensile modulus are defined and determined on multifilament yarns as specified in ASTM D885M, using a nominal gauge length of the fibre of 500 mm, a crosshead speed of 50 %/min and Instron 2714 clamps, of type“Fibre Grip D5618C”. The modulus is determined as the gradient between 0.3 and 1 % strain.

Ropes comprising the high strength yarns may provide ropes with high strength. Therefore embodiments of the present invention concern rope and tether systems wherein the rope has a tenacity of at least 0.50 N/tex, preferably the rope has a tenacity of at least 0.60 N/tex, more preferably of at least 0.70 N/tex, even more preferably 0.80 N/tex and most preferably at least 1.00 N/tex. In a further embodiment of the invention, the strength member has a tenacity of at least 0.9 N/tex, preferably at least 1.1 N/tex, more preferably at least 1.3 N/tex and most preferably at least 1.5 N/tex.

Preferably the ropes of the invention have high tenacity and high diameters. The combination of these features provides ropes or tethers with a breaking strength, also called minimum break load (MBL) of at least 10 kN, more preferably of at least 50 kN and most preferably of at least 100 kN. The MBL may be obtained by testing according to ISO 2307, whereby the tenacity of the rope is calculated by dividing said MBL by the titer of the rope.

Preferrably the high strength fibers, also referred to as high performance fibers, are fibers manufactured from a polymer chosen from the group consisting of polyamides and polyaramides, e.g. poly(p-phenylene terephthalamide) (known as Kevlar®);

poly(tetrafluoroethylene) (PTFE); poly{2,6-diimidazo-[4,5b-4’,5’e]pyridinylene-1 ,4(2,5- dihydroxy)phenylene} (known as M5); poly(p-phenylene-2, 6-benzobisoxazole) (PBO) (known as Zylon®); liquid crystal polymers (LCP); poly(hexamethyleneadipamide) (known as nylon 6,6), poly(4-aminobutyric acid) (known as nylon 6); polyesters, e.g. polyethylene terephthalate), poly(butylene terephthalate), and poly(1 ,4 cyclohexylidene dimethylene terephthalate); polyvinyl alcohols; and also polyolefins e.g. homopolymers and copolymers of polyethylene and/or polypropylene. The preferred high-performance fibers are polyaramide fibers and high or ultra- high molecular weight polyethylene (HMWPE or UHMWPE) fibers. Preferably the HMWPE fibers are melt spun and the UHMWPE are gel spun, e.g. fibers manufactured by DSM

Dyneema, NL. In an aspect the high strength fibers are e-PTFE fibers (known as Omnibend®). Liquid crystal polymers (LCP) are known as Vectran®.

In a preferred embodiment, the primary strands comprise ultra-high molecular weight polyethylene (UHMWPE) fibers, more preferably gel spun UHMWPE fibers.

In a further preferred embodiment, at least 50, more preferably at least 80 and even more preferably at least 90 wt% and most preferably all of the fibers present in the primary strands are UHMWPE fibers.

In an embodiment the braided rope for a tethered airborne wind power generation system comprises load carrying primary strands comprising yarns, wherein the yarns comprise ultra- high molecular weight polyethylene fibers. In a further embodiment, at least 50, more preferably at least 80 and even more preferably at least 90 wt% and most preferably all of the fibers present in the yarns are UHMWPE fibers.

Preferably the UHMWPE present in the UHMWPE fibers has an intrinsic viscosity (IV) of at least 3 dl/g, more preferably at least 4 dl/g, most preferably at least 5 dl/g. Preferably said IV is at most 40 dl/g, more preferably at most 30 dl/g, more preferably at most 25 dl/g. The IV may be determined according to ASTM D1601 (2004) at 135°C in decalin, the dissolution time being 16 hours, with BHT (Butylated Hydroxy Toluene) as anti-oxidant in an amount of 2 g/l solution, by extrapolating the viscosity as measured at different concentrations to zero concentration.

Examples of gel spinning processes for the manufacturing of UHMWPE fibers are described in numerous publications, including WO 01/73173 A1 , EP 1 ,699,954 and in“Advanced Fibre Spinning Technology”, Ed. T. Nakajima, Woodhead Publ. Ltd (1994), ISBN 185573 182 7.

The primary strands are braided with each other to form the rope of the invention. The primary strands may be of multiple constructions such as laid, twisted or braided from sub-strands or yarns.

In order to be suitable for tethers in renewable energy systems, especially high altitude wind energy systems, the rope of the invention preferably has a length of at least 50 m, preferably at least 100 m, more preferably at least 200 m, but lengths up to 5000 m can also be envisaged. Preferably the tether has a length of 100 m to 2000 m.

According to a preferred embodiment, the rope and/or the primary strands are pre-stretched before constructing the tether. This pre-stretching step is preferably performed at elevated temperature but below the melting point of the (lowest melting) filaments in the strands (also called heat-stretching or heat-setting); preferably at temperatures in the range 80-150°C. Such a pre-stretching step is described in EP 398843 B1 or US 5901632.

In a preferred embodiment, the rope according to the invention further comprises a coating, preferably the yarns of the rope are at least partially coated with a thermoset or thermoplastic polymer. The coating is preferably a thermoset or thermoplastic polymer able to form a suitable composite with the yarns, whereas silicone resins and ethylene crystalline plastomers are the preferred thermoset or thermoplastic polymers, respectively. A rope according to this embodiment may form a tether with optimized aerodynamic or reeling properties. The yarns embedded in the coating will be subject to less internal friction upon the cyclic loading of the tether. This is advantageous when tethers are being employed under cyclic load conditions such as airborne wind power generation system comprising a power generating winch as a ground unit. The coating also offers further protection against damage development during dynamic loading conditions for instance and limit the deterioration of properties during long term use. It is observed that tethers comprising such ropes may not need any further components, in other words the ropes may be used as tether as such.

The rope according to the invention comprises primary strands, also referred to as strands. The strands may be of multiple constructions. For example the strands may be braided, laid, parallel or twisted rope strands. The rope according to the invention can be of various braid constructions. There is a variety of types of braids known, each generally distinguished by the method that forms the rope. Suitable constructions may include soutache braids, tubular braids, and 3D braids. The soutache braid is typically known as flat fabric which can be easily deformed; and is commonly used for wicking, ornamental fabrics, embroidery and trimmings. The soutache braid can be made with a braiding machine having two or more horngears/horndogs, each having an odd number of slots typically designed for 3 - 17 carriers (and thus 3 - 17 primary strands).

The number of primary strands in the rope according to the invention is at least 3. An increasing number of strands results in increased braiding flexibility to achieve optimal aerodynamic cross-section of the rope. A higher number of strands, however, tends to lower the strength efficiency of the rope. The number of strands is therefore preferably at most 17, depending on the type of braid. Preferably, the rope is a soutache braid, and the number of strands is 3, 5, 7, or 9; more preferably 5 or 7. Such ropes provide a favourable combination of tenacity and resistance to flex fatigue, and can be made economically on relatively simple machines.

The braided rope according to the invention can be of a construction wherein the braiding period (that is the pitch length related to the width of the rope) is not specifically critical; suitable braiding periods are in the range of from 4 to 20. A higher braiding period results in a more lose rope having higher strength efficiency, but which is less robust and more difficult to splice. Too low a braiding period would reduce tenacity too much. Preferably therefore, the braiding period is about 5 - 15, more preferably 6 -10.

A preferred embodiment of the invention is a construction for a braided rope according to the invention being a soutache braid of 5 or 7 primary strands, wherein the primary strands are twisted and have either Z- or S-twist, preferably at least 4, more preferably at least 5 and most preferably all primary strands have same twist direction.

An embodiment of the invention is a construction for a braided rope according to the invention being a soutache braid of 3 primary strands, wherein all primary strands are twisted and have same twist direction. An embodiment of the invention is a construction for a braided rope according to the invention being a soutache braid of 5 or 7 primary strands, wherein all primary strands are twisted and have same twist direction.

An embodiment of the invention is a construction for a braided rope according to the invention being a soutache braid of 9 or 1 1 primary strands, wherein all primary strands are twisted and have same twist direction. It was observed that such constructions, when tensioned inherently result in a rope cross-section with the aerodynamic shape according to the invention. It is postulated that this effect is achieved by the movements and rotation of the horngears combined with the unbalanced character of the primary strands. The shape of the rope cross- section may amongst others be influenced by the number of primary strands, the ratio of twist direction (S or Z) between the strands, their twist length as well as the pitch of the braided rope.

In another preferred embodiment of the invention the braided rope is a soutache braid of an uneven number of between 5 and 11 twisted or braided primary strands, wherein at least a first elongated body extends within a non-central channel formed by the soutache braid of the primary strands. In contrast to the earlier embodiment, the herein described construction does rely on at least one elongated body that is embedded in the soutache braiding construction. In an embodiment of the invention the braided rope is a soutache braid of an uneven number of twisted or braided primary strands, wherein the number of strands is 5, 7, 9 or 1 1 , wherein at least a first elongated body extends within a non-central channel formed by the soutache braid of the primary strands. In an embodiment of the invention the braided rope is a soutache braid of an uneven number of twisted or braided primary strands, wherein the number of strands is 5, 7, 9 or 1 1 , wherein at least a first elongated body extends within a non-central channel formed by the soutache braid of the primary strands.

In an embodiment of the invention the braided rope is a soutache braid of an uneven number of twisted primary strands, wherein the number of strands is 5, 7, 9 or 1 1 , wherein at least a first elongated body extends within a non-central channel formed by the soutache braid of the primary strands, and wherein all primary strands are twisted and have same twist direction.

The non-central channel has its longitudinal axis perpendicular to the primary diameter D and perpendicular to the secondary diameter d. The non-central channel has its longitudinal axis along the longitudinal axis of the braided rope according to the invention. Typically point c is located within the non-central channel in which the first elongated body extends. In other words typically the first elongated body extends in the non-central channel that encloses point c.

In an embodiment of the braided rope according to the invention the rope is a soutache braid of 5 primary strands having 2 channels formed by the braid of primary strands wherein one channel comprises an elongated body, such as a rope, having a diameter that ensures the cross section of the rope obtains a droplet like shape while under tension and provides an aerodynamic cross section with reduced drag during use. In an embodiment of the braided rope according to the invention the rope is a soutache braid of 7 primary strands having 3 channels formed by the braid of primary strands wherein at least one channel comprises an elongated body, such as a rope, having a diameter that ensures the cross section of the rope obtains a droplet like shape while under tension and provides an aerodynamic cross section with reduced drag during use.

In an embodiment of the braided rope according to the invention the rope is a soutache braid of 7 primary strands having 3 channels formed by the braid of primary strands wherein at least one channel comprises an elongated body, such as a rope, and wherein at least one further elongated body extends within a further channel, the elongated bodies having a diameters that ensure the cross section of the rope obtains a droplet like shape when tensioned (under a load of at least 300 MPa). This way an aerodynamic cross section with reduced drag during use is provided

A characteristic of known oblong soutache braids is that they define channels over their primary diameter, said channels may be populated by an inserted elongated body, like a rope, a polymeric core or conductive element. The presence of an elongated body within such a non central channel will increase the primary and secondary diameter of the rope cross-section and result in an aerodynamic shape of said rope cross-section. The dimensions of said elongated body may be optimize to increase the aerodynamic performance of the rope. Preferably the elongated body may be a primary strands from which the soutache braid is formed, without being part of the braided construction. Alternatively the elongated body is a polymeric rod or tube whereby dimensions and properties are chosen to optimize aerodynamic and mechanical behaviour of the rope of the invention.

In an embodiment of the invention the braided rope is a soutache braid of an uneven number of from 5 up to and including 1 1 twisted or braided primary strands, wherein at least a first elongated body extends within a non-central channel formed by the soutache braid of the primary strands, and wherein the first elongated body is selected from a rope, a polymeric core or conductive element. In an aspect the first elongated body is a rope.

In a preferred embodiment the braided rope comprises at least one further elongated body extending within a further channel formed by the soutache braid of the primary strands, wherein the ratio of the cross-sectional areas of the first to the further elongated body is at least 1.5, preferably 2.0 most preferably at least 3.0. Such further elongated body is preferably located in a channel adjacent to the first elongated body. The presence of two or more elongated bodies of different size in the channels of the soutache braid allow for substantial design flexibility in achieving optimal aerodynamic and mechanical behaviour of the rope of the invention. Preferably the elongated body or the elongated bodies may each comprise one or more conductors capable to transmit signals or current from the ground to the airborne unit or the other way around. With“conductor” is herein meant a material able to conduct a signal such as an electrical or optical signal and preferably able to conduct power (electricity) from a generator where the power is generated, to a point where signal needs to be transported or the electricity can be collected. By“conducting a signal” may be understood within the spirit of the invention also as“transporting a signal”. A conductor may also contain a single or a plurality of cables suitable for the intended purpose of conducting or transporting a signal, wherein said cables may contain or be free of an insulation jacket.

In a yet preferred embodiment of the invention, the braided rope is a 3-D braid, braided from between 25 and 500, preferably between 50 and 400 and most preferably between 75 and 250 primary strands to provide a rope with the aspect ratio of 1.2 to 4.0 and R to r ratio of 1.2 to 4.0. In an embodiment of the invention the braided rope is a 3-D braid, which is braided from 25 to 500, in an aspect from 50 to 400 and in another aspect from 75 to 250 primary strands to provide a rope with the aspect ratio in the range of 1.2 to 4.0 and R to r ratio in the range of 1.2 to 4.0. Herein is understood that the inventive rope contains primary strands, wherein said strands may be rope yarns or strands comprising one or more rope yarns, forming a continuous three-dimensional (3D) network structure, such ropes being hereinafter referred to as a 3D ropes. By strands forming a continuous 3D network structure is herein understood that strands are continuously interlaced, i.e. without interruption, with each other forming the rope, and they are arranged to form a 3D network along and across the rope. A 3D network structure is typically obtained by consolidating and binding at least three sets of strands, one set of said forming a multi-layer warp structure, and the other two sets being positioned horizontally and vertically in respect to the warp structure forming therefore a weft structure; preferably the at least three sets of strands are orthogonal. Preferably, the 3D network structure is a 3D-woven structure, more preferably a 3D-woven multi-shuttle loom structure, since ropes comprising thereof provide a more stable rope structure under varying loads, in particular dynamic loads, maintaining its original shape in an effective way. A 3D-woven multi-shuttle loom structure is herein understood a structure wherein the binding of the at least three, preferably orthogonal, sets of strands is carried out on a multi-shuttle loom machine. Such machines are well known in the art of 3D weaving. A 3D woven rope may also allow for a more efficient and higher responsive transfer of mechanical power across its mass, in particular over prolonged time periods. The 3D structure may also be chosen from the group consisting of a 3D-braided, a 3D- knitted, a 3D-stiched, and 3D-noobed structure.

An alternative way to prepare a rope with an aerodynamic cross-section according to the invention is to combine at least two sub-ropes with dissimilar diameters into a rope construction. Diameters of the sub-ropes may vary widely but should have a difference in diameter such to provide a rope according to the invention with the aerodynamic cross-section. Therefore a preferred embodiment of the invention is a rope comprising at least 2 adjacent sub ropes whereby the ratio of the cross-sectional areas of the first to the second sub-rope is at least 1.5, preferably 2.0 and most preferably at least 3.0. In a yet further preferred embodiment of the invention, the braided rope comprises a third sub-rope adjacent to the second sub-rope, wherein the ratio of the cross-sectional areas of the second sub-rope to the third sub-rope is at least 1.5, preferably 2.0 most preferably at least 3.0. Corresponding rope constructions have the advantage that by judicious choice of diameters, the rope may have further reduced drag. The constructions of the present embodiment can be prepared by for example jacketing or overbraiding said at least two sub-ropes positioned side by side. In such a construction the at least two sub-ropes might independently move from each other or be interconnected. Such interconnection might for example be realized by stitching or interlace during the braiding process of the sub-ropes. Therefore a further preferred embodiment of the invention concerns a braided rope wherein the adjacent sub-ropes are interlaced and/or overbraided. An optional feature of such construction is that the individual sub-ropes may comprise a central conductor as earlier defined, embedded in a laid or braided construction of the sub-rope.

The rope according to the invention is utmost suitable to be the load bearing core of a tether system for airborne wind power generation systems. The rope can be used for anchoring, and optionally providing an electrical current to or from, a high-altitude wind energy system. The rope is suitable for tethers of high altitude wind energy systems which are provided with a ground generator but also systems wherein the tether transports power from an airborne generator to a ground station. The present invention hence also relates to airborne wind power generation system comprising at least a winch and an airborne unit connected by a tether, wherein the tether comprises the rope according to the invention. In an embodiment of airborne wind power generation system according to the invention, such system comprises a ground station comprising a winch for storing excess length of the tether and a power generator. The winch may be a drum winch or a traction winch combined with a storage winch connected to it. The power generator may be part of the ground station or part of the airborne wind unit. In the latter case a conductive tether will be used to transport the generated energy from the airborne unit to the ground station. A suitable average working tension includes 300 MPa. The working tension may have peak load in the range from 50 to 600 MPa.

In a preferred embodiment, the tether of said airborne wind power generation system comprises at least 2 sections, wherein at least one section comprises the aerodynamic braided rope according to the invention and a second section comprising a further braided rope with a circular or oblong cross-section with an aspect ratio of between 1.2 to 4.0, wherein the aerodynamic braided rope is installed to the airborne unit and the further braided rope is installed to the winch. Typically, the 2 sections of the tether are connected via a connector.

In an embodiment, the tether of said airborne wind power generation system comprises at least 2 sections, wherein at least one section comprises the aerodynamic braided rope according to the invention and a second section comprising a further braided rope with a circular or oblong cross-section with an aspect ratio in the range of 1.2 to 4.0, wherein the aerodynamic braided rope is installed to the airborne unit and the further braided rope is installed to the winch.

Although the rope of the invention is substantially suited for the described airborne energy systems, its aerodynamic shape opens a multitude of applications where a rope is subjected to transversal flows, whereby the flowing fluid is not limited to gases or gas mixtures like air but may also be liquids. Applications of ropes where the present inventive rope may be use are for example kite lines, riggings, buoys, barges and others in high current waters, but also rope or rope systems that are hauled through water such as seismic arrays. Therefore the invention also relates to marine trawl system comprising the rope according to the invention.

The invention further relates to the use of the rope according to the invention for generating electrical power.

The invention further relates to the use of the rope according to the invention for reducing drag of the rope while being hauled through water.

The invention further relates to a method of power generation comprising the step of

connection a tether comprising the rope according to the invention to an airborne unit. Examples of an airborne unit include without limitation a kite, a balloon, an airplane and a glider. FIGURE DESCRIPTION

Figure 1 schematically depicts a circumference of an aerodynamic cross-section of an embodiment of a braided rope (1) according to the invention. The cross section has a droplet like shape. The cross section has a primary diameter D and a secondary diameter d. D is the largest diameter of the cross-section and d is the largest diameter of said cross-section perpendicular to the primary diameter D. The primary diameter D and the secondary diameter d are perpendicular to each other and intersect each other in point c. Point c divides the primary diameter D in two unequal segments R and r. In an embodiment of the braided rope according to the invention the ratio R to r is in the range from 1.2 to 4.0. In an embodiment of the braided rope according to the invention the ratio D to d is in the range from 1.2 to 4.0.

Figure 2 schematically depicts depicts another circumference of cross-section of an embodiment of a braided rope (10) according to the invention.

The cross section has a droplet like shape. The cross section has a primary diameter D and a secondary diameter d. D is the largest diameter of the cross-section and d is the largest diameter of said cross-section perpendicular to the primary diameter D. The primary diameter D and the secondary diameter d are perpendicular to each other and intersect each other in point c. Point c divides the primary diameter D in two unequal segments R and r. The ratio R to r is in the range from 1.2 to 4.0. The ratio D to d is in the range from 1.2 to 4.0.

The central point (W) is located central in the cross-section of the rope. Point W divides the primary diameter D in two equal segments and has equal distance between the primary diameter D and the outer circumference (O).

In this embodiment the braided rope is a soutache braid of 5 primary strands (strands not shown). A non-central channel (1 1) is formed by the soutache braid of the 5 primary strands, it is present inside the soutache braided rope. Point c is located at the centre of the cross section of the non-central channel (1 1). The primary strands are typically twisted or braided primary strands.

The non-central channel (11 ) may also be referred to as the largest channel of the 5 strand soutache braid, it is present at one longitudinal edge of the soutache braid. During use the non central channel is present at the windward side (15) of the rope. The wind direction is indicated with an arrow named V.

A further non-central channel (12) is also formed by the 5 strand soutache braided rope.

The cross section of the rope has a tertiary diameter d2 which is perpendicular to the primary diameter D.

D and d2 intersect each other in a point e, which e is located at the centre of the cross section of the further non-central channel (12).

Point e divides the primary diameter D in two unequal segments R’ and r2. In an embodiment of the rope according to the invention the ratio R’ to r2 is in the range from 1.2 to 4.0. In an embodiment of the rope according to the invention the ratio D to d2 is in the range from 1.2 to 4. The further non-central channel (12) may also be referred as the smallest channel of the 5 strand soutache braid, it is present at the other longitudinal edge of the soutache braid. During use the further non-central channel is present at the leeward side (15) of the rope.

In an embodiment according to the invention the further non-central channel (12) has a smaller surface area than the non-central channel (11), this results in an aerodynamic shape of the rope cross-section and optimizes the aerodynamic performance of the rope.

In an embodiment of the braided rope according to the invention a first elongated body

(elongated body not shown) extends within the non-central channel (1 1 ), which may also be referred to as first non-central channel. The presence of the first elongated body results in a further pronounced aerodynamic shape of the rope cross-section and further optimizes the aerodynamic performance of the rope.

In an embodiment the further channel (12) may comprises a further elongated body (elongated body not shown). In case a further elongated body extend inside the further channel, such elongated body results in the diameter d2 being smaller than d such that the ratio d to d2 is in the range from 1.2 to 4 to ensure the aerodynamic performance of the rope.

The non-central channels (1 1) and (12) have their longitudinal axis along the longitudinal axis of the braided rope according to the invention, which axis is perpendicular to diameters D (shown parallel along the x-axis) and perpendicular to diameter d (shown parallel to the Y axis). This means that in the 3D orthogonal axis system (100) if diameters D is depicted along the x- axis and diameter d is depicted along the y axis the non-central channels (1 1 , 12) have their longitudinal axis parallel to the Z axis.

In an embodiment the rope according to the invention comprises a fairing (14) present at the leeward side of the rope to further optimize the aerodynamic performance of the rope.

Leeward side and windward side herein are in relation to the rope during use as load bearing core of a tether in a tethered airborne wind power generation system.

Figure 3 schematically depicts depicts another circumference of cross-section of an

embodiment of a braided rope (20) according to the invention. The cross section has a droplet like shape. The cross section has a primary diameter D and a secondary diameter d. D is the largest diameter of the cross-section and d is the largest diameter of said cross-section perpendicular to the primary diameter D. The primary diameter D and the secondary diameter d are perpendicular to each other and intersect each other in point c. Point c divides the primary diameter D in two unequal segments R and r. The central point (W) is located central in the cross-section of the rope. Point W divides the primary diameter D in two equal segments and has equal distance between the primary diameter D and the outer circumference (O).

In this embodiment the braided rope is a soutache braid of 7 primary strands (strands not shown). The primary strands are typically twisted or braided primary strands.

Such 7 strand soutache braid rope typically comprises three channels. A first non-central channel (21 ) is present inside the soutache braided rope. A second non-central channel (22) and a third non-central channel (23) are also present inside the soutache braid of 7 primary strands. The non-central channels (21 ,22,23) have their longitudinal axis along the longitudinal axis of the braided rope according to the invention. This axis is perpendicular to diameters D (shown parallel along the x-axis) and perpendicular to diameter d (shown parallel to the Y axis). This means that in the 3D orthogonal axis system (100, see fig 2) if diameters D is depicted along the x-axis and diameter d is depicted along the y axis the non-central channels

(21 ,22,23) have their longitudinal axis parallel to the Z axis.

Typically point c is located within the first non-central channel (21). The first and third non central channels are present along the longitudinal edges of the rope ate the windward and leeward (26) side respectively.

The rope has a quaternary diameter d3 which is perpendicular to the primary diameter D. D and d3 intersect each other in point f. Point f is located at the centre of the cross section of the third non-central channel (23).

Point f divides the primary diameter D in two unequal segments R” and r3. In an embodiment of the rope according to the invention the ratio R” to r3 is in the range from 1.2 to 4.0. In an embodiment of the rope according to the invention the ratio d to d3 is in the range from 1.2 to 4.

In an embodiment the rope according to the invention comprises a fairing (24) present at the leeward side of the rope to further optimize the aerodynamic performance of the rope.

Leeward side and windward side herein are in relation to the rope during use as load bearing core of a tether in a tethered airborne wind power generation system. The wind direction is indicated with an arrow named V.

Figure 4 schematically depicts an embodiment of airborne wind power generation system according to the invention comprising a winch (203) and an airborne unit (204) connected by a tether (202), wherein the tether comprises the rope (201 ) according to the invention. The winch

(203) is part of a ground station (205). The ground station is connected to the ground, the deck of a ship, typically the bow of the ship or an off-shore platform (collectively referred to as 206)

Figure 5 schematically depicts an embodiment of the airborne wind power generation system according to the invention. In this embodiment the tether (202) comprises at least 2 sections, wherein a first section (208) comprises the rope according to the invention and a second section (209) comprises a further rope with an oblong cross-section with an aspect ratio of between 1.2 to 4.0. The rope according to the invention (208) is installed to the airborne unit

(204) and the further braided rope (209) is installed to the winch (203) and the first (208) and second section (209) are connected via a connector (207) such that the winch and airborne unit are connected.

Figure 6 schematically depicts a cross section of a further braided rope (209) with an oblong cross-section having a larger diameter (D) (or width) and a smaller diameter (d) (or thickness). The oblong cross-section preferably has an aspect ratio, i.e. the ratio of the larger to the smaller diameter (or width to thickness ratio), in the range of from 1.2 to 4.0. The present invention includes the following embodiments

1. A braided rope for a tethered airborne wind power generation system comprising load carrying primary strands comprising yarns with a tenacity of at least 1.0 N/tex, wherein the tensioned braided rope has an aerodynamic cross-section with an aspect ratio in the range 1.2 - 4.0, wherein the aspect ratio is the ratio of the primary diameter D to the secondary diameter d, wherein D is the largest diameter of the cross-section and d is the largest diameter of said cross-section perpendicular in c to the primary diameter, wherein c divides D in two radiuses, R and r, characterized in that the ratio

R to r is in the range from 1.2 to 4.0.

2. Braided rope according to embodiment 1 , wherein the cross-section has an aspect ratio of about 1.3 - 3.0.

3. Braided rope according to any one of embodiments 1 or 2, wherein the rope has an equivalent diameter of at least 20 mm.

4. Braided rope according to any one of embodiments 1 -3, wherein the primary strands comprise ultra-high molecular weight polyethylene fibers.

5. Braided rope according to any one of embodiments 1 -4, wherein the rope further

comprises a coating.

6. Braided rope according to any one of embodiments 1 -5, wherein the rope is a

soutache braid of 5 or 7 primary strands, wherein the primary strands are twisted and have either Z- or S-twist, preferably at least 4, more preferably at least 5 and most preferably all primary strands have same twist direction.

7. Braided rope according to any one of embodiments 1 -5, wherein the rope is a

soutache braid of uneven number of between 5 and 11 twisted or braided primary strands, wherein at least a first elongated body extends within a non-central channel formed by the soutache braid of the primary strands.

8. Braided rope according to embodiment 7, wherein at least one further elongated body extends within a further channel formed by the soutache braid of the primary strands, wherein the ratio of the cross-sectional areas of the first to the further elongated body is at least 1.5, preferably 2.0 most preferably at least 3.0. 9. Braided rope according to any one of embodiments 1 -5, wherein the rope is a 3-D braid, braided from between 25 and 500, preferably between 50 and 400 and most preferably between 75 and 250 primary strands to provide a rope with the aspect ratio of 1.2 to 4.0 and R to r ratio of 1.2 to 4.0.

10. Braided rope according to any one of embodiments 1 -5, wherein the rope comprises at least 2 adjacent sub-ropes whereby the ratio of the cross-sectional areas of the first to the second sub-rope is at least 1.5, preferably 2.0 and most preferably at least 3.0.

1 1 . Braided rope according to embodiment 10, comprising a third sub-rope adjacent to the second sub-rope, wherein the ratio of the cross-sectional areas of the second sub rope to the third sub-rope is at least 1.5, preferably 2.0 most preferably at least 3.0.

12. Braided rope according to embodiments 10 or 11 wherein the adjacent sub-ropes are interlaced and/or overbraided.

13. An airborne wind power generation system comprising at least a winch and an

airborne unit connected by a tether, wherein the tether comprises the rope according to any of the preceding claims.

14. The airborne wind power generation system of embodiment 13 wherein the tether comprises at least 2 sections, wherein at least one section comprises the aerodynamic braided rope according to embodiments 1 to 10 and a second section comprising a further braided rope with a circular or oblong cross-section with an aspect ratio of between 1.2 to 4.0, wherein the aerodynamic braided rope is installed to the airborne unit and the further braided rope is installed to the winch.

15. Marine trawl system comprising the rope according to any of the preceding

embodiments.

Claims

1. A braided rope for a tethered airborne wind power generation system comprising load carrying primary strands comprising yarns with a tenacity of at least 1.0 N/tex, wherein the tensioned braided rope has an aerodynamic cross-section with an aspect ratio in the range from 1.2 to 4.0, wherein the aspect ratio is the ratio of the primary diameter D to the secondary diameter d, wherein D is the largest diameter of the cross-section and d is the largest diameter of said cross-section, wherein the primary diameter D and the secondary diameter d are perpendicular to each other and intersect each other in point c, whereby c divides the primary diameter D in two unequal segments R and r, characterized in that the ratio R to r is in the range from 1.2 to 4.0.

2. Braided rope according to claim 1 , wherein the cross-section has an aspect ratio of about 1.3 - 3.0.

3. Braided rope according to claim 1 or 2, wherein the rope has an equivalent diameter of at least 20 mm.

4. The braided rope according to any one of claims 1 to 3 , wherein the rope has a second aspect ratio wherein the primary diameter D and the tertiary diameter d2 are perpendicular to each other and intersect each other in point e, whereby e divides the primary diameter D in two unequal segments R’ and r2, characterized in that the ratio R’ to r2 is in the range from 1.2 to 4.0 and the ratio R to r is smaller than the ratio R’ to r2 .

5. Braided rope according to any one of claims 1 -4, wherein the yarns comprise ultra-high molecular weight polyethylene fibers.

6. Braided rope according to any one of claims 1-5, wherein the rope is a soutache braid of 5 or 7 primary strands, wherein the primary strands are twisted and have either Z- or S-twist, preferably at least 4, more preferably at least 5 and most preferably all primary strands have same twist direction.

7. Braided rope according to any one of claims 1 -5, wherein the rope is a soutache braid of uneven number of from 5 to 11 twisted or braided primary strands, wherein at least a first elongated body extends within a non-central channel formed by the soutache braid of the primary strands.

8. Braided rope according to claim 7, wherein at least one further elongated body extends within a further channel formed by the soutache braid of the primary strands, wherein the ratio of the cross-sectional areas of the first to the further elongated body is at least 1.5, preferably 2.0 most preferably at least 3.0.

9. Braided rope according to any one of claims 1 -5, wherein the rope is a 3-D braid,

braided from 25 to 500, preferably from 50 to 400 and most preferably from 75 to 250 primary strands to provide a rope with the aspect ratio in the range of 1.2 to 4.0 and R to r ratio in the range of 1.2 to 4.0.

10. Braided rope according to any one of claims 1 -5, wherein the rope comprises at least 2 adjacent sub-ropes whereby the ratio of the cross-sectional areas of the first to the second sub-rope is at least 1.5, preferably 2.0 and most preferably at least 3.0.

1 1 . Braided rope according to claim 10, comprising a third sub-rope adjacent to the second sub-rope, wherein the ratio of the cross-sectional areas of the second sub-rope to the third sub-rope is at least 1.5, preferably 2.0 most preferably at least 3.0.

12. Braided rope according to claim 10 or 1 1 wherein the adjacent sub-ropes are interlaced and/or overbraided.

13. An airborne wind power generation system comprising at least a winch and an airborne unit connected by a tether, wherein the tether comprises the rope according to any of the preceding claims.

14. The airborne wind power generation system of claim 13 wherein the tether comprises at least 2 sections, wherein at least one section comprises the aerodynamic braided rope according to claims 1 to 10 and a second section comprising a further braided rope with a circular or oblong cross-section with an aspect ratio in the range of 1.2 to 4.0, wherein the aerodynamic braided rope is installed to the airborne unit and the further braided rope is installed to the winch.

15. Marine trawl system comprising the rope according to any of the preceding claims.