WO2006052146A1

WO2006052146A1 - Marine structure for a fish cage for aquaculture with a net spanned by a tensegrity structure

Info

Publication number: WO2006052146A1
Application number: PCT/NO2005/000425
Authority: WO
Inventors: Anders Sunde Wroldsen; Anne Marthine Rustad; Tristan Perez; Vegar Johansen; Arne Fredheim; Pål Furset LADER; Asgeir Johan SØRENSEN; Mats Augdal Heide
Original assignee: Ntnu Technology Transfer As
Priority date: 2004-11-12
Filing date: 2005-11-10
Publication date: 2006-05-18

Abstract

A marine structure like a fish cage (0) for aquaculture, with a net (90) spanned by a tensegrity structure, i.e. a structure comprising compressive elements (1), and tension elements (2).

Description

Marine structure for a fish cage for aquaculture with a net spanned by a tensegrity structure

Introduction The present invention relates to design concepts for flexible marine aquaculture structures. An extraordinary freedom to control shape, motion and vibration can be achieved by designing the system as a so-called tensegrity structure and by introducing appropriate actuation, sensing and control. A tensegrity structure comprises compressive elements like rods, and tensile elements like lines or wires. The invention also comprises interconnected units of flexible offshore structures.

Background of the invention

Tensegrity structures are built up by compression members (rods, bars), under compression, and tension members (strings), in tension. This structure concept emerged from structural art in the late fifties and has been applied in civil engineering, structural engineering, architecture and aerospace engineering.

Definition of a tensegrity structure. A general definition of a tensegrity structuremay is as follows: A network of interconnected compressive and tensile members, in which all structural elements experience only axial loading with no reversal of load direction, and in which the compressive members are kept in position by a network of tensile members in a stable equilibrium. Tensegrity structures are divided into several classes:

In class 1 tensegrity structures no compressive elements are connected end to end in nodes. A node is defined as being a point or portion with a transition from a compressive element to a tension element or to another compressive element. Class 2 tensegrity structures are defined by comprising two compressive elements connected end to end in nodes.

Class 3 tensegrity structures are defined by comprising three compressive elements connected end to end in nodes, and so forth. Fish farming and aquaculture installations are today located in sheltered areas close to shore or inside fjords. This is primarily due to limitations of fish farming with respect to rough weather conditions and the acceptable profits of the industry to date.

To date, the fish farming industry can be described by the following features:

• Simple technical solutions.

• Small to medium scale fish cage installations. • Limited flexibility of the marine structures.

• Need of appropriately sheltered locations.

• Lack of shape, motion or vibration control of the marine installations.

The main reasons for moving fish farming structures offshore are • Higher water quality in most open seas.

• Larger water flow-rate through the fish cages resulting in an increase in fish welfare.

• Shortage of appropriate locations for fish farming installations in sheltered waters. • Large installations can increase the quantity and profit.

The challenges of using installations offshore with respect to structural design are as follows:

• Large structures such as net-keeping ring-shaped floaters and other structures need to be very rigid and strong, or highly flexible to cope with environmental loads, i.e. waves and currents.

• Shape and motion control of the structure may be required both to improve the welfare of the fish by altering the water flow and oxygen supply, and to reduce the environmental loads as far as practically possible. • The shape of the structure is of importance also with respect to the displacement or transport of fish cage structures and the harvesting of the fish.

Prior art in the separate fields of tensegrity and fish farming, respectively.

US patent 3.063.521 to R. Buckminster-Fuller describes different aspects of the tensegrity design concept for building spherical shell structures, towers, beams and other structures. Basic elements of Buckminster-Fullers structure are generally slender rods of which one end is connected by a so-called tensile element to the end of a second rod and an intermediate portion of a third rod. Buckminster-Fuller has given name to the later carbon molecule structures C-60 called Buckminster-Fullerenes of similar structure. One possible disadvantage of attaching a tensile element to a portion intermediate the ends of a rod is the introduction of bending moments to the rods, i.e. the so-called compressive elements, which may eventually break.

US patent 3.169.611 to K. D. Snelson develops further aspects of tensegrity structures, displaying arcs and other structural art having purely compressive force fields along the bars, reducing the problem of the bending moments of some of Buckminster-Fuller's compressive elements.

The introduction of tensegrity structures, which may also be controlled, can address the environmental load challenges of marine structures including fish cages for the open sea. This is due to the following properties of tensegrity structures:

• A large strength to mass ratio. As the tensegrity structure may be designed to be flexible, a locally focused external force acting on the structure may be distributed to a plurality of elements of the structure, so as for the acting force to be dissipated in the structure. • Compressive elements (rod, bar) are subjected to compression force solely, thus no bars are subject to any torsion moment. However, if the structure is heavily loaded, one may experience that some compressive elements momentarily may be subjected to tension.

• The compressive elements may be slender and we may expect most of the external forces acting on each compressive element and also on the tensile elements, to originate from fluid flowing around, along and possibly through the bars and the tensile elements.

• Tensegrity structures may have advantageous properties with respect to shape, motion and vibration control by adjusting the tension or/and length of the tensile elements. • It is also believed that tensegrity structures may be developed in order for propulsion to be achieved by proper interaction between subelements.

Summary of the invention The present invention which may represent solutions to one or more of the above-mentioned problems, the invention being a marine structure such as a fish cage for aquaculture, with a net spanned by a tensegrity structure, i.e. a structure comprising compressive elements and tension elements.

One embodiment of the invention comprises a marine structure of in which the tensegrity structure comprises hexagonal cylindrical basic cells.

A preferred embodiment of the invention comprises a tensegrity structure forming a flexibly deformable ring for being arranged near the surface or under the surface of the sea, for spanning said net inside or around the tensegrity structure, or for hanging said net in the sea below the ring, said net arranged for enveloping a number of fish or other marine organism. A jump net may also be arranged if required.

In another embodiment of the invention the tensegrity structure may form a flexibly deformable hemispheric structure spanning said net arranged for enveloping the fish. The net may attached to the structurally outer or inner surface formed by the hemispheric structure.

In a further alternative embodiment the tensegrity structure may form a flexibly deformable and closed, preferably tube-shaped structure arranged for spanning said net.

Current marine aquaculture structures are mostly of small to medium size and do not provide active control of shape, motion or control to prevent vibration. We foresee that tensegrity structures in general would be a solution with respect to building flexible structures for rough environmental and climate conditions that may be experienced offshore. Proper sensing, actuation and control may in addition reduce environmental loads and improve the welfare of the fish. Additionally, sensing, actuation and control might prove necessary to allow the marine structure to respond to forces acting upon it in rough weather conditions.

The invention hereby presented as a plurality of marine installations comprising tensegrity structures. Proper sensing, actuation and control may be used to provide flexibility and adaptability of the structure. We introduce some novel features:

• An actuated tensegrity ring structure, please see Fig. 2a and Fig. 2b, making the offshore structure flexible. The basic elements in the illustrated structure is an arrangement of three compression members mutually crossing and kept in a fixed spatial relationship by three tensile elements extending from each compressive element in a triangular short cylindrical cage-like structure with three quadrangular side surfaces, with the compressive elements arranged diagonally in each quadrangle, please see Fig. 4. This basic element was first defined by K. D. Snelson in 1965. Other embodiments of the invention based on such a ring structure formed by other tensegrity structures are shown in Figs. 2c, 2d and 2e, and in Figs. 2f, 2g, and 2h. • A second actuated tensegrity ring structure, please see Fig. 22, may form a flexible offshore ring structure. The basic element in this structure is an octahedral cell (Fig. 19) presented by Passera & Pedretti at the Swiss Expo 2001. An interconnection between two basic elements with two joints and two tension members is shown in

Fig. 20.

• A third actuated tensegrity ring structure, shown in Fig. 23, may form flexible offshore ring structures. The basic elements in this structure is also the octahedral cell (Fig. 19). Two neighboring octahedral cells are here connected with only one joining wire or actuated line between rod ends, and four tension members connecting and controlling neighbour cells with respect to each other, please refer to Fig. 21.

• A basic hexagonal subcell, please see Fig. 12a, is presented as a subordinate part of the present invention. An interwoven pattern is made by interconnecting such basic hexagonal cells as shown in the combined hexagonal cell, ref. Fig. 13a. Actuation, primarily by use of tension members, can make the combined hexagonal cell change shape considerably between a wide and flat hexagonal prism as shown in Fig. 13b and a slender and high hexagonal prismatic bundle as in Fig. 13c.

• Energy production by using motion actuated generators also acting as actuators on the structure, may be provided. Conversely, shape, motion and vibration control is one of the main issues for the interconnected structures. • The combined hexagonal subcells, please see Fig. 13a, may be interconnected in several ways to form flexible structures. Different conceptual drawings have been made to indicate some of its various possible applications in fish farming, please see Fig. 14, Fig. 15, Fig. 16, and Fig. 17. • Interconnection of several installations built as tensegrity structures and exploit joint motion between the units to produce energy (Fig. 3). Short figure captions

The invention is illustrated in the attached drawings, which shall not be construed to be limiting for the invention, which shall be limited by the attached claims only.

Fig. 1a is an introductory illustration of a plane view of a buoyancy ring of a fish cage.

Fig. 1b illustrates a plane view of a buoyancy ring of a fish cage, said cage containing live fish, and shaped to reduce the effect of environmental loads like waves, current, and wind.

Fig. 1c illustrates a perspective view of a fish cage arranged athwart of the prevailing water current to more efficiently shift the water.

Fig. 1d illustrates one embodiment according to the invention, here a three dimensional structure that spans a net.

Fig. 2a illustrates a ring structure comprising several basic tensegrity elements, but is not illustrated to detail.

Fig. 2b illustrates the ring structures of Fig. 2a, having a general shape deviating from the shape of the ring structure of Fig. 2a, either by deformation or actively changing of shape.

Fig. 2c. shows an embodiment according to the invention, and is an isometric view of a ten rods tensegrity structure comprising ten vertical strings and twenty horizontal strings, and ten slanted strings.

Fig. 2d illustrates the same embodiment of the invention as Fig. 2c, and shows a plan view of the tensegrity structure as seen from above. Fig. 2e illustrates the same embodiment of the invention as Figs. 2c and 2d, and shows a side elevation view of the structure.

Fig. 2f shows an isometric view of an embodiment according to the invention, comprising a circular structure formed by multiple interlinked tensegrity structures comprising 40 rods and 200 strings.

Fig. 2g illustrates the same embodiment according to the invention shown in Fig. 2f, and shows a plan view of the structure as seen from above.

Fig. 2h illustrates the same embodiment according to the invention shown in Fig. 2f and Fig. 2g, and shows a side elevation view of the structure.

Fig. 3 shows a general plane view of several similarly shaped ring structures, e.g. of buoyancy rings of several fish cages, in which relative movements may be exploited for producing energy.

Fig. 4 shows a basic tensegrity element according to Snelson, as shown in US- patent 3169611. The tensegrity element has three compression members and nine tension members forming a self-supported spatial structure. Snelson combines several such basic cells to form towers, arc structures, etc., in which the compression through the combined rod elements is discontinuous, i.e. that the compression force in one rod element's length direction is not coupled directly to a successive rod element, and in which structure the tension is continuous in the tension elements, i.e. ropes, wires, lines, chains, and in which tension forces must be maintained in the tensile elements.

Fig. 5a shows two such combined basic cells according to Snelson, of which a cell is arranged end on end on a successive cell, while compression is discontinuous from a rod in a cell to a successive rod in a successive cell, in that one end of a rod in the successive cell rests on one of the tensile elements of the preceding cell, and vice versa. Figs. 5b and 5c illustrates such Snelson-tensegrity cells combined to a so-called 10 stage Snelson beam being slightly modified by adding a continuous series of strings. Each joint level between a triangular cell and a successive triangular cell forms more or less a hexagon, as is evident from the drawings. Such a modified Snelson beam may be used as a beam or rod (1) as a substructure according to the invention, or it may be bent with the ends joined to a ring structure to form a ring according to Fig. 1a, b, c or d to span a net. This Snelson beam is well known and documented and has considerable advantages for the present use for forming a fish cage.

Fig. 6 illustrates that three such triangular cells of Snelson may, when connected side-by-side, have conflicting directions, incurring mechanical contact between the compression members, i.e. the rods, constituting a risk of fatigue or mutual mechanical wear induced on crossing compression members. If used in a dynamic environment, e.g. in the sea or in shifting winds, this may incur damage to the entire structure if the structure is based on such basic elements.

Fig. 7 illustrates a hexagonal basic element previously imagined to be useful as a basic cell for building a multi-hexagonal structure, but having the above- mentioned potential risk of conflicting crossing directions between rods of adjacent cells.

Fig. 8 is a simplified illustration of combined basic hexagonal and/or pentagonal cell elements imagined to form a spherical shell of inner and outer hexagonal and/or pentagonal areas formed by tension members, and imagined to have compressive elements like those shown in Fig. 9, connecting the inner and outer hexagonal and/or pentagonal areas.

Fig. 8b illustrates part of a spherical and closed shell structure of basic Snelson prisms arranged side-by-side, each bar (1) end connected to one of the neighbour Snelson prism's "triangle-forming" wires (2). In this structure there are no crossing beams mutually touching.

Fig. 9 shows one advantageous effect of an embodiment of the present invention, the effect being the ability to compress or expand the hexagonal base area of basic hexagonal cells constituting elements of a large shell structure. The resulting dimensional change of the basic hexagonal cell may compress the shell structure. The structure may thus be prepared for displacement in the sea, or transport on a carrier like a ship. One may thereby expand the shell structure upon arrival at a desired site for deploying it in the sea, said shell structure spanning a net.

Fig. 10 is a view of the outline of a partly compressed basic hexagonal element or subcell according to the invention and is illustrated in more detail in Fig. 13c. The partly compressed hexagonal element is imagined to form a part being a subcell of a compressed spherical shell of Fig. 8. The element is redesigned here to be consistent with the basic hexagonal cell of Fig. 12a.

Fig. 11 illustrates in more detail the outline of an expanded basic hexagonal element, imagined to form a part being a subcell of an expanded spherical shell of Fig. 8. The element is now redesigned to be consistent with the basic hexagonal cell of Fig. 12a.

Fig. 12a illustrates an embodiment of a basic hexagonal subcell of a basic hexagonal tensegrity element of Fig. 13a according to the invention.

Fig. 12b, Fig. 12c and Fig. 12d illustrate how three layers of the basic hexagonal subcells displaced relative to each other may be combined to form the combined basic hexagonal tensegrity element according to the invention.

Fig. 13a shows such a combined basic hexagonal tensegrity element according to one embodiment of the invention. Fig. 13b illustrates an expanded combined basic tensegrity element according to a preferred embodiment of the invention, showing a part of a first structure comprising six compressive elements, i.e. rods, connected in a hexagonal sawtooth pattern. Also shown is a part of a second trusswork of three compressive elements in a triangular pyramid shape, having their common node or hub in the upper hexagonal plane and between three upper nodes in the sawtooth ring of said first trusswork. Further is shown part of a third, oppositely arranged triangular pyramidal trusswork of compressed elements, being a mirror image of the part of said second trusswork.

Fig. 13c illustrates the same combined basic tensegrity element as shown in Fig. 13a and Fig. 13b, now compressed about a vertical axis of the hexagonal structure.

Fig. 14 shows a set of seven interconnected combined basic tensegrity element cells, no compression members shown.

Fig. 15 illustrates one single combined basic tensegrity element cell spanning a net, to illustrate that one single tensegrity cell may be sufficient to form a fish cage when spanning a net.

Fig. 16 illustrates a tubular trusswork formed by several combined basic tensegrity element cells according to the invention, the tubular trusswork arranged in the sea and being subject to waves.

Fig. 17 illustrates a tubular trusswork formed by several combined basic tensegrity element cells according to the invention, the tubular trusswork closed at either end of the tube structure by hexagonal members of the same type of basic tensegrity element. Figs. 18a, b, c, d show several fish cages having a first shape while connected to a rigid structure like a moored float, and having a second shape adapted for being tugged by a tender.

Fig. 19 illustrates another basic tensegrity element according to another embodiment of the invention, called an octahedral cell.

Fig. 20 shows two connected octahedral cells of Fig. 19, forming part of a ring structure according to the invention as shown in Fig. 22. The two octahedral cells are joined along one side element of the four connected compressive elements.

Fig. 21 shows two octahedral cells connected in a node of the four connected compressive elements, having more freedom to move, and for forming an alternative ring structure as shown in Fig. 23.

Fig. 22 illustrates a plane view of a ring structure formed by the octahedral cells of Fig. 19 and connected as shown in Fig. 20. The ring structure may be provided with a net arranged in the frame formed by the four interconnected rods of the above-mentioned octahedron.

Fig. 23 shows a similar plane view of another ring structure formed of octahedral cells of Fig. 19 and connected as shown in Fig. 21, having more freedom to be flexibly floating in sea waves on the surface.

Fig. 24 illustrates a connection for three compression members. This can be used at the point where three compression members meet in the center of the combined basic hexagonal tensegrity element of Fig. 13a.

Fig. 25 shows three winches attached to the end of a rod, i.e. a compression member. Fig. 26 illustrates one solution to how a linear actuator can be used to adjust the length or/and tension of said tension elements.

Fig. 27a shows a nearly cubic tensegrity structure for a fish cage, in which is shown a tensegrity structure comprising 12 rods or bars (1) and 36 strings (2). The cubic structure is arranged with the ends of three rods or bars (1) arranged in each corner of said nearly cubic fish cage.

Fig. 27b illustrates the cube-like structural frame of Fig. 27a, provided with buoyancy elements (4), and a net (90) spanned by the cube-like structural tensegrity frame, a circumferential walkway (95), in order to form a complete fish cage.

Fig . 28a illustrates an embodiment according to the invention, in which a tensegrity structure comprising buoyancy or ballast elements on the tension lines of the structure is shown. This is an adaption of the ring structure of Fig. 2c.

Fig . 28b illustrates an embodiment according to the invention, in which a tensegrity structure comprising buoyancy or ballast elements on the rods or bars of the structure is shown.

Fig . 28c illustrates an embodiment according to the invention, in which a tensegrity structure spanning a net is shown, and in which buoyancy elements are arranged on the strings of the structure, and buoyancy or ballast elements are arranged on the rods or bars of the structure.

Fig. 29 illustrates an embodiment according to the invention, in which a mainly circular tensegrity structure is shown holding a generally cylinder shaped net.

Fig. 30a illustrates an embodiment according to the invention, in which a tensegrity structure is shown moored to the seafloor. Fig. 30b illustrates an embodiment according to the invention, in which is shown three interconnected ring structures and mooring lines to anchors on the sea bed or on land.

Fig. 31a illustrates a bar element (1) according to the invention, said bar element

(1) being an element arranged for being subjected to axial compressive forces in a tensegrity structure.

Fig. 31b illustrates an alternative bar element (1) according to the invention formed as a trusswork.

Fig. 31c illustrate two telescoping bar or rod elements (1), said telescoping bar element (1) comprising actuators.

Fig. 31 d illustrates a compressive element or rod (1) provided with ballast elements or ballast tanks (5), or buoyancy elements or tanks (4) arranged near the ends of said compressive element (1).

Fig. 31 e illustrates in more detail such a compressive element (1) with ballast and buoyancy tanks (4, 5) spanned by tension elements (2).

Fig. 32a illustrates a string element (2), in which said string element (2) is arranged between the ends of two bar or rod elements (1). Said string element

(2) may be implemented using any material able to withstand tension forces such as wire, rope etc..

Fig. 32b shows said string element (2) of which the tension and length is adjusted using tackles.

Fig. 32c shows another string element (2) provided with springs connected to the bar nodes, said springs for attenuating of peak tensions. Fig. 32d illustrates a tension member (2) provided with buoyancy elements (4).

Fig. 33 shows a said bar node (10) illustrating a possible way of attaching said string elements (2).

Fig. 34a shows one possible solution for actuation of said string elements (2). The said actuator (7) is in this case shown as a winch drum actuator (7). The string (2) uses here an optional tackle.

Fig. 34b shows a linear actuator (11) for pulling or releasing the string element (2), said linear actuator (11) arranged for altering the extended string length between said bar nodes (10).

Fig. 34c illustrates a bar node comprising three separate actuators (7) for separately controlling of string lengths of three different strings (2).

Fig. 35a is a three-dimensional snapshot from a simulation run of a 40-bar tensegrity ring structure according to the invention. The ring structure is shown subjected to waves. The ring structure is similar to the structure shown in Figs. 2f, 2g, and 2h.

Fig. 35b is a side view of the 40-bar tensegrity ring structure of Fig. 35a, showing a modeled instant of time.

Detailed description of the invention

The invention hereby presented pertains to marine installations using tensegrity structures with proper sensing, actuation and control to provide flexibility and adaptability to fish farming and aquaculture installations.

A fish farming installation (0) can be described as being a three-dimensional structure (101) spanning a net (90) enveloping a number of fish, either for storage or culture. Said three-dimensional structure (101) may have several shapes and only a few embodiments will be presented in the present document. In the attached figures may be found ring shaped structures, as well as a closed, e.g. tubular or spherical or similarly shaped generally closed structure.

Fig. 1a and Fig. 1b provide a rough overview of said ring shaped structure (102) arranged for changing shape either passively by flexible deformation or by using active control to reduce the effects incurred by environmental loads, i.e. wind, waves and currents. Fig. 1c is a plan view that illustrates a shape that increases the area exposed to water through-flux for improved water exchange conditions within the said fish farming installation. Fig. 1d further illustrates one embodiment according to the invention, here a three dimensional structure (101) that spans said net (90).

Fig. 2a illustrates another embodiment of said ring shaped structure (102) formed by combining a number of basic elements (110) to form a ring. The basic element (110) may in this case be almost any desired basic tensegrity element (111). Fig. 2b illustrates how a such ring shaped structure (102) may be deformed or actively change shape due to deformation or controlled shape change of said basic elements (110). Said basic tensegrity element (111) is normally a candidate for shape control that will be utilized in fish farming installations (0) according to the invention built on the further developed concept of tensegrity structures.

Fig. 2c. shows an embodiment according to the invention, and is an isometric view of a tensegrity structure comprising ten rods (1) and ten vertical strings (2) twenty horizontal strings (2) and ten slanted strings (2). This embodiment shows an upper and a lower ten-sided ring formed by horizontal strings (2) between nodes. Each upper and lower pair of nodes are connected by vertical strings (2). The rods (1) are arranged extending from one node in the lower ring to a node in the upper ring, extending two nodes to one direction, with all rods (1) inclined in the same direction along the ring structure. The number of rods (1) is not bound to be ten, but may be any number equal to or more than four. The embodiment depicted in Fig. 2c is a class 1 tensegrity structure. An important property of class 1 tensegrity structures is that there are no direct mechanical couplings between the compressive elements. This a significant advantage as such direct mechanical links pose problems when utilised in marine structures, due to the fact that such direct mechanical links are subject to continuous wear and may eventually break.

Fig. 2d illustrates the same embodiment of the invention as Fig. 2c, and shows a plan view as seen from above. Fig. 2d shows more clearly that the rods are arranged extending from one node in the lower ring to a node in the upper ring, extending two nodes to one direction.

Fig. 2e illustrates the same embodiment of the invention as Figs. 2c and 2d, and shows a side elevation view of the structure.

Fig. 2f shows an isometric view of another embodiment according to the invention, comprising a circular class 1 tensegrity structure formed by multiple interlinked tensegrity structures comprising 40 rods (1) and 200 strings (2). The illustrated ring structure comprises 20 inner and 20 outer tensegrity sub-elements similar to the triangular Snelson prism as shown in Fig. 4, except that one bar (1) being omitted in each prism, and in which two nodal points arise due to the nearest neighbour cells. The ring structure thus formed is stable, despite each sub-element being unstable. The number of rods (1) is any even number equal to or larger than six. The number of strings (2) depends on the number of rods. A walkway may be arranged on the upper part of the tensegrity ring.

Fig. 28a illustrates an embodiment according to the invention, in which is shown a tensegrity structure according to Fig. 2c, but further comprising buoyancy elements (4) on the upper horizontal strings (2) of the structure. Similar buoyancy elements (4) may be arranged on a ring structure according to Fig. 2f or other tensegrity structures. The advantage of arranging buoyancy elements (4) on the strings (2) is that no bending moments are added to the rods or bars (1). Further, the buoyancy elements arranged on the upper horizontally arranged strings contributes to the righting moment of the ring structure, in addition to the contribution to the buoyancy of the structure. Likewise, ballast elements (5) may be arranged, preferrably on the lower tension lines of the structure. Modeling of the structure's behaviour in sea indicates that a ring structure comprising 6-9 rods is favourable with respect to said structures stability. Less than 6 rods (1) leaves little space inside the structure for a fish net. More than 9 rods (1) may reduce the stability of the ring when subject to waves.

Fig . 28b illustrates an embodiment according to the invention, in which a tensegrity structure according to Fig. 2c, comprising buoyancy elements (4) and ballast elements (5) on the rods or bars of the structure is shown. The buoyancy elements (4) may also be arranged to be ballasted, and the ballast elements (5) may also be arranged to contain air to contribute to the buoyancy of the structure.

Fig . 28c illustrates an embodiment according to the invention, in which a tensegrity structure spanning a net (90) is shown, and in which buoyancy elements (4) are arranged on the strings (2) of the structure, and buoyancy elements (4) and ballast elements (5) are arranged on the rods or bars of the structure.

Fig. 29 illustrates an embodiment according to the invention, in which a mainly circular tensegrity structure similar to the ring structure of Fig. 2c is shown, the circular structure holding a generally cylinder-shaped net (90) inside the ring to form a complete fish cage (0). The fish cage (0) of Fig. 29 is provided with weights hanging in vertical weight chains to span the lower parts of the net (90). A fish cage as shown in Fig. 29 should be moored if not allowed to drift freely in the sea. Fig. 30a illustrates an example in which such a ring-shaped tensegrity structure e.g. of Fig. 29 is shown moored to the seabed similar to the mooring of a "tension leg platform". The net (90) is not illustrated in this embodiment. Fig. 30b illustrates, in the upper part, an alternative single point mooring for a ring structure. The lower part of Fig. 30b shows three interconnected ring structures and mooring lines to anchors on the sea bed or on land.

Fig. 27a shows a nearly cubic fish cage for fish farming, in which is shown a tensegrity structure comprising 12 rods or bars (1) and 36 strings (2). The cubic structure is arranged with the rods or bars (1) arranged in close proximity of the lines forming the edges of the imagined cubic shape and with the ends of the bars (1) arranged near the corners of said imagined cubic shape. The ends of three by three meeting rods or bars (1) are connected by short tension elements enveloping the corners of said imagined cubic structure. The structure according to this embodiment of the invention presents several advantages as it allows for spanning a large cube-shaped net (90) which may be attached by loops to either said rods or bars (1) or strings (2), as shown in Fig. 27b. A further advantage of this embodiment according to invention is that it allows for the attachment of buoyancy elements directly to said strings (2) or rods (1) of said tensegrity structure as shown e.g. in Fig. 32 d . This embodiment according to the invention further allows the use of existing cube-shaped nets attached by loops with metal rings to fasten said net to run alongst vertical members of said tensegrity structure, either rods (1) or strings (2), as described in the background art of aquaculture.

Fig. 27b illustrates the cube-like structural frame of Fig. 27a, provided with buoyancy elements, and a net (90) spanned by the cube-like structural tensegrity frame, a circumferential walkway (95) (also arranged for providing buoyancy) arranged on top of the upper ends of four generally vertical rods, a fence with hooks for holding the net, and mooring chains, of which only one is illustrated.

Fig. 3 illustrates an interconnected structure (105). Said interconnected structure combines several of said three dimensional structures (101) of desired shape. The individual three dimensional structures (101) may be connected by joints (80). Externally forced relative motion between said three dimensional structures (101) can be exploited by integrating energy generators arranged for converting 425

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mechanical energy e.g. due to a varying length of tensile elements or rotational relative movements about said joints (80) to e.g. electrical energy.

The length and tension of said tension members (2) can be changed by linear actuators (25) or winches (26), see Fig. 24, Fig. 25, and Fig. 26. Said linear actuators (25) may be rather slender and may be arranged within or arranged about a compression member (1). Winches (26) may be arranged at an end of a bar element (1), i.e. a so-called compression member (1), see Fig. 25, or remotely from said compression members (1) for transferring wire tension e.g. using a wire-and-hose mechanism.

In an alternative embodiment of the invention, some compression members may be arranged so as for the length of said compression members (1) to be changed by means of hydraulic pistons or linear actuators (25) using motors, see Fig. 26. This allows for the control of the fish cage so as to be able to react to enviromental loads, or for changing the shape of the fish cage structure, e.g. for unloading of fish, or for transportation of the structure in itself.

A first, overall control system (75) for the fish cage (0, 70, 72, 74) according to the invention, please refer to Fig. 27c, is arranged for receiving sensor signals (760) from first sensors (76) arranged for sensing tension force in tension elements (2), and in which said sensors are further arranged for sensing the actual length of extension for tension elements (2). Said control system (75) may also be arranged for receiving second sensor signals (770) from second sensors (77) arranged for sensing the compressive force in compressive elements (1). The overall control system (75) should have information about the actual length of all compressive elements (1) and all tensile elements (2). The overall control system (75) is then arranged for calculating the shape of all basic elements (600, 700), and thus the overall shape and size of the entire fish cage (0, 70, 72, 74). Based on measurements of external environmental loads like wind direction, wind speed, wave directions, sea state, current direction and current speed, the control system (75) may then calculate how the lengths of specific tensile elements should change length in order to change the overall shape of the fish cage (O₁ 70, 72, 74). The control system (75) may receive command signals (780) from an operator command input console (78) about how the overall shape of the fish cage should be or be changed, e.g. for a transition of the shape from a moored configuration as shown in Fig. 18a or 18c, to a more elongate and narrow shape for transport, either tugged like in Fig. 18b or to be operated as part of a vessel like in Fig.18d. The geometry of the structure may also be set to be among of several predefined structures, and the control system (75) may be arranged for selecting one of said predfined structures automatically according to the enviromental conditions as measured by the sensors. The control system (75) may calculate a shape that minimizes wave or current action of external forces acting on the fish cage (0, 70, 72, 74) to avoid damage of parts or the entire structure.

The overall control system (75) may then provide control signals (750) to actuators (25, 26) for changing the tension or length, or both, of specific tension elements (2) that should change said tension and / or length. Alternatively, said control system (75) may provide said control signals (750) to second control systems (85) arranged for changing the shape of specific cells thus changing the overall structural shape according in order to fit into the overall desired shape. Locally, in said tensile elements (2) receiving said control signals (750) for changing its tensile force or extended length, the subordinate control system (85) may be arranged for receiving said sensor signals (760) from first sensors (76) arranged for sensing the tension force in tension elements (2), and also for sensing the actual length of extension for tension elements (2), and provide control signals locally to the actuators (25, 26) in order for the local tensegrity element to achieve its shape or size commanded from the overall first control system (75).

In order to make the entire structure more rigid, all tensile elements may be tightened, or slackened in order to reduce the rigidity of the overall structure. In order to change the tension of some tensile elements, and thus the shape of a local tensegrity cell, some of the rods or bars (1), i.e. the compressive elements may be provided with actuators such as hydraulic pistons or electric motors acting on said compressive elements to change their lengths.

Signals related to the control system (75, 85), i. e. sensor signals (760, 770), control signals (750) to actuators, and command signals (780) from the operator to the control system (75) may be sent as acoustic, radio, optical or electrical signals through the water or through conductors in said tension members (2) and / or said compression members (1).

Fig. 8 illustrates a basic pentagonal cell (500) and a basic hexagonal cell (600) according to the invention, for forming part of a closed structure (74). By changing the width of a desired number of such basic hexagonal cells as shown in Fig. 9, the radius may be changed between a collapsed-state radius (r_c) and an expanded or deployed-state radius (rd). This feature may provide that a fish cage according to the invention may be contracted to a small radius, e.g. between 2 and 6 metres, for being tugged or lifted onto a ship's deck and transported to a desired site, and when positioned in the sea at the desired site, to be expanded to a radius of 10 to 20 metres or more, in order to expand an attached spanned net (90) to form a large fish cage. Fig. 10 and Fig. 11 illustrate a cell-radially contracted and expanded basic subcell (31 , 32, 33) according to the invention. This basic subcell will be explained below.

One preferred embodiment of a complete basic hexagonal cell (600) according to the invention comprises a side-shifted combination of three of the basic subcells (31 , 32, 33) is shown in Fig. 13a, and is described in detail below. This basic hexagonal cell can be contracted sidewards (and will expand radially) as shown in Fig. 13c, but the effect of the sidewards contraction is that the radius of an entire structure formed by such basic cells will contract to (r_c) as illustrated in Fig. 9 mentioned above. The basic hexagonal cell may, from a more or less contracted state as described above, be transformed to flatten in the basic cell's radial direction to be widened to a structural radius (r_d) for the entire cage as shown in Fig. 9 and in Fig. 11 and more detailed on a cell level as shown in Fig. 13b.

Below is described one of said basic tensegrity element first presented by Snelson in US-patent 3169611. This basic tensegrity element (200) is defined as having three struts and is illustrated in Fig. 4. The three-struts basic tensegrity element (200) comprises three of said compression members (1) mutually crossing in a wire tension network comprising nine of said tension members (2).

In the present invention we exploit the possibility of changing the shape of this said three struts basic tensegrity element (200), see Fig. 6, by adjusting the length of the said tension members (2) in a coordinated manner. The three struts basic tensegrity element (200) can change shape to be low (or high) by lengthening (or shortening) the horizontal tension members (5) both at the top and the bottom and shortening (or lengthening) the vertical tension members (4). Fig. 6 also show at which points (6) this three struts basic element (200) could be interconnected with equal said basic tensegrity elements (111).

Fig. 5a illustrates how two of said three struts basic tensegrity elements (200) could be connected in the points (6) axially adjacent to each other, but mutually rotated. One possible said ring shaped structure (102) can be constructed by connecting a finite number of said three struts basic tensegrity elements (200) together in a ring. The possibility of shape change in each said three struts basic tensegrity element (200) may give this said ring shaped structure (102) of said three struts basic tensegrity elements (200) an extraordinary freedom and flexibility to control shape, motion, vibrations and stiffness.

A basic hexagonal sub-cell (300, 31 , 32, 33), according to a preferred embodiment of the present invention, please see Fig. 11 , may be used for assembling a basic hexagonal cell (600) (please see Fig. 13a) for building said spherical shaped structures (103) and hemispherical shaped structures (104). We proposed to build these structures by using hexagonal and pentagonal said basic tensegrity elements (111) interconnected like the hexagonal and pentagonal surface elements forming a soccer ball. See Fig. 8. We first tried pentagonal and hexagonal said basic tensegrity elements (111) similar to the one illustrated in Fig. 7. We call those elements pentagonal basic tensegrity element and hexagonal basic tensegrity elements respectively. By proper control of such said pentagonal basic tensegrity elements and said hexagonal basic tensegrity elements we desired to control the shape and volume of one kind of said spherical shaped structure (103) illustrated in Fig. 9.

However, it was realized that conflicts could arise, due to mechanical contact due to mechanical shocks or rubbing between the bar elements (1) both between neighboring such pentagonal basic tensegrity elements and/or said hexagonal basic tensegrity elements due to mechanical cross-contact of said compression members (1). The direction of the diagonally arranged compression member may be changed to avoid conflicting directions between two adjacent cells, but the third cell that should have been introduced adjacent to the two first cells may not satisfy the direction of both first cells simultaneously. This same kind of shortcoming is illustrated in Fig. 6 for neighboring said three struts basic tensegrity elements (200) of Snelson's US-patent 3169611 mentioned above.

A reconfiguration of said hexagonal tensegrity subelement (31, 32, 33) of a generally prismatic outline was done according to Fig 12a. Said diagonally arranged compressive members (1) in the six side surfaces are connected end- on-end in nodes (112) arranged interchangeably in the upper and the lower hexagon. Thus the rods (1) are placed in a sawtooth or crown-like pattern. This structure is not self-supporting. These hexagonal tensegrity subelements (31, 32, 33) are repeated along directions parallel to the sides of the hexagonal planes. One of each compression members doubled due to pattern repetition are removed. Thus upper nodes (52) will connect three compressive member's (1) upper ends (112), and lower nodes (51) would connect three compressive member's (1) lower ends (113).

According to one embodiment of the invention we define the new combined basic hexagonal tensegrity cell (600) by combining three such repeated patterns of the tensegrity subcell (31 , 32, 33). See Fig 12a, Fig. 12b, Fig. 12c, Fig. 12d and Fig 13a. A tensegrity structure of compressive elements (1) and tension elements (2) comprises first, second and third subcells (31, 32, 33) combined to form one or more hexagonal structures. * The three subcells (31 , 32 33 ) comprise six rods (1) arranged with a first (lower) end (113) of a next compressive element (1) adjacent to a second (lower) end (112) of a first compressive element (1) as first (lower) nodes (51) and second (upper) nodes (52) together forming a hexagonal ring, as shown in Fig. 11 and explained above. Every second node (51 , 52) is arranged in a first or "lower" or "inward-facing" hexagonal plane (41) and a second or "upper" or "outward-facing" hexagonal plane (42), respectively, forming a ring-shaped sawtooth-pattern. Each such basic hexagonal cell may then be extended to any side to form a triangular upright and upside-down open pyramid pattern (having no volume) formed by said compressive elements. * The three patterns comprising subcells (31 , 32 , 33 ) are then displaced relative to each other along said upper or lower planes (41 , 42) by a half-width of said subcell, subcell (32) in the direction of a first hexagonal side of subcell (31), and subcell (33) in the direction of a second hexagonal side of subcell (31). In this way, a first (lower) node (51_3i) of said second sub cell (32) is placed between said three first (lower) nodes (51₃₂) and between the three other lower nodes (51₃₃) in said first lower plane (41) of said first subcell (31). A second (upper) node (52) is placed between said three first (upper) nodes and the three other nodes in said second (upper) plane (42) in said first subcell (32). * The nodes (51) of said first lower plane are connected by first tension elements (21) to each six neighbour nodes (51) in said lower first plane (41). * The nodes (52) of said second upper plane are connected by first tension elements (21) to each six neighbour nodes (52) in said upper second plane (42). This completes tensile connections along the hexagonal planes.

* The nodes (51) are also connected by second tension elements (22) arranged in a direction perpendicular between said first lower plane 41 and said second upper plane (42) to corresponding nodes (52) in said second plane (42). This direction may be called "vertical" in Fig. 12 and in Figs. 13a, 13b, and 13c, and completes connection of nodes in the "lower", or "inward facing" hexagonal tile pattern with nodes in the "outer", or "outward facing" hexagonal tile pattern. * One purpose of the above mentioned structure is to form a static tensegrity elementary structure. The structure may also be arranged to change its shape, or size, or both, by changing the length of tension elements (2) or compressive elements (1).

Fig 13b and Fig. 13c. illustrate said new combined basic hexagonal tensegrity cell (600) when the length of said vertical tension members (4) have been shortened, see Fig. 13b, and lengthened, see Fig. 13c, respectively and the length of said horizontal tension members (5) have been lengthened and shortened, respectively, to provide such a flat and broad shape, or tall and slender shape, respectively.

Those new combined basic hexagonal tensegrity cell (600) can be used in several ways to form said three-dimensional structures (101). Fig. 14 illustrates seven of said new combined basic hexagonal tensegrity cells (600) connected side by side. This could for example be seven large said fish cages (0) connected together, a large said fish cage (0) or only part of a larger weave-pattern in a tube shaped structure (74) or the like. Fig. 15 shows one single new combined basic hexagonal tensegrity cell (600) used as a said fish cage (0) spanning a said net (90). Fig. 16 shows one possible such vertically arranged tube shaped tensegrity structure (74) made by connected new combined basic tensegrity cells (200, 600). Fig. 17 shows another tube shaped structure (103) of which the wall is formed by such basic hexagonal tensegrity cells (200, 600), and which may more or less flexibly deformed by external forces or controlled by actuators. Fig. 17 illustrates a tubular trusswork formed by several combined basic tensegrity element cells according to the invention, the tubular trusswork closed at either end of the tube structure by hexagonal members of the same type of basic tensegrity element. Such a closed trusswork may be arranged floating, neutral or with negative buoyancy in the sea and spanning an inside or outside arranged net for forming a fish cage that may resist environmental loads.

Fig. 18a, b, c, d show some conceptual drawings of said interconnected structures (105). The illustrations show how structures can be compressed or deformed while hauled or otherwise displaced on the sea.

Fig. 19 shows a basic octahedral tensegrity element (111) of Passera and Pedretti defined as a octahedral cell (700). This octahedral cell (700) comprises five compression members (1), of which four rods (1) are connected in the nodes (112) to form a square or rectangular shaped frame. This frame could be covered by an impermeable surface or a portion of a net (90). A fifth compression member (1) is connected by eight said tension members (2) in such a way that it is held orthogonal to the frame formed by the afore mentioned four said compression members (1).

The described said octahedral cell (700) is used as a said basic tensegrity element (111) in a said ring shaped structure (102). We have proposed two ways of interconnecting this said octahedral cell (700) with its neighboring elements to from a said ring shaped structure (102).

Fig. 20 illustrates how two said octahedral cells (700) can be connected by two of said joints (80) and two said tension members (2). A coordinated adjustment of the length and tension in the two said tension elements (2) would make the two neighboring elements move and change position with respect to one another. This can be utilized for shape, motion, vibration and stiffness control of the said ring shaped structure (102). This said ring shaped structure (102) will only be able to change shape in the horizontal plane due to the use of two said joints (80) between neighboring said octahedral cells (700). An illustration of such a said ring shaped structure (102) connected as shown in Fig. 20 can be seen from above in Fig. 22.

Fig. 21 illustrates another possible way of connecting two such octahedral cells (700), now with one said joint (80) and four said tension members (2). This provides a feasible way of controlling shape, motion, vibrations and stiffness both horizontally and vertically in an extended or ring-shaped structure formed by such octahedral cells. An illustration of such a ring shaped structure is shown in Fig. 23.

Fig. 31a illustrates a bar element (1) according to the invention, said bar element (1) being an element arranged for being subjected to axial compressive forces in a tensegrity structure.

Fig. 31b illustrates an alternative bar element (1) according to the invention formed as a trusswork. Said trusswork of said bar element (1) may in an alternative embodiment according to the invention be a tensegrity structure. This illustrates the scaling properties of tensegrity structures, as the compressive elements themselves may be built using tensegrity.

Fig. 31c illustrate two telescoping bar or rod elements (1), said telescoping bar element (1) comprising actuators. Actuators could be arranged inside said telescoping bars or rods (1) to change the length of the compressive element (1). The shape of a tensegrity structure may be altered by changing the length of the said bar elements (1). Moreover, the stiffness properties of a tensegrity structure may be altered by adjusting the pretensioning or prestressing of compressive elements or rods (1). Fig. 31 d illustrates a compressive element or rod (1) provided with ballast elements or ballast tanks (5), or buoyancy elements or tanks (4) arranged near the ends of said compressive element (1). The reason for arranging said ballast tanks (5) and / or buoyancy tanks (4) near the ends of said compressive element (1) is to reduce the bending moments on the rod (1) introduced by the static or dynamic forces from the ballast or buoyancy elements (5, 4).

Fig. 31 e illustrates in more detail such a compressive element (1) with ballast and buoyancy tanks (4, 5) spanned by tension elements (2). The tank may be arranged around a continuous pipe or rod (1) to maintain continuous strength along the rod (1), but the tanks may also be arranged as widened portions of the pipe or rod (1) as shown in Fig. 31 e. The buoyancy and ballast elements (4, 5) may be provided with valves for pressurized air supply through inlet valves, and an air outlet, and valves for inlet and outlet of water.

Fig. 32a illustrates a string element (2), in which said string element (2) is arranged between the ends of two bar or rod elements (1). Said string element (2) may be implemented using any material able to withstand tension forces such as wire, rope etc..

Fig. 32c shows another string element (2) provided with springs connected to the bar nodes, said springs for attenuating of peak tensions.

Fig. 32d illustrates a tension member (2) provided with buoyancy elements (4).

Fig. 33 shows a said bar node (10) illustrating a possible way of attaching said string elements (2). Fig. 34a shows one possible solution for actuation of said string elements (2). The said actuator (7) is in this case shown as a winch drum actuator (7). The string (2) uses here an optional tackle.

Fig. 35a is a three-dimensional snapshot from a simulation run of a 40-bar tensegrity ring structure according to the invention. The ring structure is shown subjected to waves. The ring structure is similar to the structure shown in Figs. 2f, 2g, and 2h. In this modeling the height of the ring structure is about 1 m. The outer diameter of the ring is 10 m, and the inner diameter is 8 m. The wave height is 0.2 m, i.e. the amplitude is 0.1 m and the ratio of wave height to length h/lambda is 1/30, i.e. the wavelength is about 6 m. The reason for simulating this with a ring of 10 m diameter is that the model may be verified in a model tank of moderate size. The rods in the model are hollow pipes and have 80 mm diameter and are imagined made in aluminium or steel. The 40 bars structure's tension wires are modeled as about 10 mm diameter wires having between 10⁵ and 10⁶ N/m stiffness. This model setup seems to yield slightly to the waves, as can be seen in Fig. 35b, and is somewhat out of phase with the waves. Later stages of the simulation shows improved stability. Generally, a net may be more affected by current than by waves, and adding a net to the structure should not significantly affect the behaviour of this buoyancy structure in waves.

Claims

1. A marine structure for a fish cage (0) for aquaculture, with a net (90) spanned by a tensegrity structure comprising compressive elements (1) and tension elements (2).

2. The marine structure of claim 1 , the tensegrity structure comprising one or more hexagonal cylindrical basic cells (600).

3. The marine structure of claim 1 , the tensegrity structure forming a flexible ring (70, 102) for being arranged near the surface or under the surface of the sea, for spanning said net (90) suspended in the sea below the ring (70, 102) for enveloping a number of fish.

4. The marine structure of claim 1 , the tensegrity structure forming a flexible hemisphere (72) spanning said net (90), said hemisphere for partly or entirely enveloping the fish.

5. The marine structure of claim 1 , the tensegrity structure forming a flexible closed, preferably tubular structure (74) for spanning said net (90).

6. The marine structure of claim 1 , the tensegrity structure being arranged for changing shape by adjusting the tension or length of the tension elements (2).

7. The marine structure of claim 1 , the tension elements (2) being wires, ropes or similar.

8. The marine structure of claim 6, the tension elements (2) arranged for being adjusted by linear actuators (25) or winches (26).

9. The marine structure of to claim 7, in which linear actuators (25) and/or winches (26) are arranged for tensioning/hauling or giving slack on said tension elements (2).

10. The marine structure according to claim 9, in which said actuators (25) and/or winches (26) are arranged within, on, or about said compressive element (1).

11. The marine structure according to claim 9, in which said actuators (25) and/or winches (26) are arranged remotely from said compressive element (1).

12. The marine structure of claim 1 , the compressive elements (1) being rods, bars, pipes, or similar.

13. The marine structure of claim 1 , the tensegrity structure being arranged for changing shape by adjusting the length of the compressive elements (1).

14. The marine structure of claim 10, adjusting the length of the compressive elements (1) using hydraulic or pneumatic pistons or linear actuators using motors.

15. The marine structure of claim 8, having a first control system (75) for receiving sensor signals (760) from first sensors (76) arranged for sensing tension forces and extended length of tension elements (2), and for providing control signals (750) to said actuators (25, 26) for changing the tension and / or changing the length of said tension elements (2).

16. The marine structure of claim 15, said first control system (75) being arranged for calculating the shape of some or all basic elements (600, 700), and thus the overall shape and size of the entire fish cage (0, 70, 72, 74).

17. The marine structure of claim 16, said first control system arranged for receiving measurement of external environmental loads like wind direction, wind speed, wave directions, sea state, current direction and current speed, the control system (75) may then calculate how the lengths of specific tensile elements should change length in order to change the overall shape of the fish cage (0, 70, 72, 74) to a desired new shape.

18. The marine structure of claim 17, said first control system (75) arranged for receiving command signals (780) from an operator command input console (78) about how the overall shape of the fish cage should be or be changed.

19. The marine structure of claim 17, said control system (75) arranged for providing said control signals (750) to second control systems (85) arranged for specific cells for changing shape according in order to fit into the overall desired shape, said actuators (25, 26) receiving said control signals (750) for changing its tensile force or extended length, said second control system (85) arranged for receiving said sensor signals (760) from first sensors (76) arranged for sensing tension force in tension elements (2), and also for sensing the actual length of extension for tension elements (2), said second control system (85) for providing control signals locally to said actuators (25, 26) in order for said tensegrity element to achieve its shape or size commanded from the overall first control system (75).

20. The marine structure of claim 15, said sensor signals and command signals (750, 760) for being sent as acoustic, radio, optical or electrical signals through the water or through signal conductors in said tension members (2) and/or said compression members (1).

21. The marine structure according to claim 2, comprising a tensegrity structure of compressive elements (1) and tension elements (2) comprising first, second and third basic cells (31, 32, 33) combined to form one or more hexagonal structures, in which * said basic cells (31 , 32, 33) comprising six rods (11) arranged with a first end (111) of a next compressive element (11) adjacent to a second end (112) of a first compressive element (11) as first and second nodes (51, 52) forming a hexagonal ring;

* in which every second node (51 , 52) is arranged in a first plane (41) and a second plane (42), respectively, forming a ring-shaped sawtooth-pattern;

* said three basic cells (31 , 32, 33) being displaced relative to each other along said planes (41 , 42) by a half-width of said basic cell;

* in which a first node (51) of said second basic cell (32) is placed between said three first nodes (51) in said first plane (41) of said first basic cell (31), and in which a second node (52) is placed between said three first nodes in said second plane (42) in said first basic cell)

* said nodes (51) of said first plane connected by first tension elements (21) to each six neighbour nodes (51) in said first plane (41); and

* said nodes (52) of said second plane connected by first tension elements (21) to each six neighbour nodes (52) in said second plane (41);

* said nodes (51) connected by second tension elements (22) arranged in a direction perpendicular between said first and second planes (41 , 42) to corresponding nodes (52) in said second plane (42);

* so as for said structure being arranged to change its shape or size by changing the length of tension elements (2) or compressive elements (1).

22. The marine structure according to claim 1 , said tensegrity structure comprising octahedral basic cells (700) comprising four first compressive elements (1) arranged in a quadrangular pattern forming generally a plane frame, and arranging a second compressive element (1) generally normal to said frame, and connecting a first end of said second compressive element (1) using four first tension elements (2) extending to the four corners of said quadrangle, and connecting a second, opposite end of said second compressive element (1) also using four second tension elements (2) extending to said four corners of said quadrangle.

23. The marine structure according to claim 22, said quadrangle frame spanning a net (90) or a portion of said net (90).

24. The marine structure of claim 22, said octahedral cells combined to a flexibly deformable ring (70, 102) by a letting a side compressive element (1) of said quadrangle of one octahedral cell forming an adjacent side compressive element (1) of an adjacent quadrangle of an adjacent octahedral cell (700), and connecting said first ends of said second compressive elements (1) by a third tension element (2) for controlling the relative orientation of said second compressive elements (1) and thus the relative orientation of said connected quadrangles.

25. The marine structure of claim 22, said octahedral cells combined to a flexibly deformable ring (70) by connecting a comer of said quadrangle of one octahedral cell with an adjacent corner of an adjacent quadrangle of an adjacent octahedral cell (700), and connecting said first ends of said second compressive elements (1) by a third tension element (2) for controlling the relative orientation of said second compressive elements (1) and thus the relative orientation of said connected quadrangles.

26. The marine structure of claim 1 , said tensegrity structure being mainly circular, and in which said structure forms two mainly regular polygonal rings with tension elements (2) forming the sides of each polygonal ring, one arranged above the other, and in which said structure comprises rods (1) extending from one node in the lower ring to a node in the upper ring.

27. The marine structure according to claim 26 in which said rods (1) extend two nodes to one direction.

28. The marine structure according to claim 26 in which said rods (1) extend three or more nodes to one direction.

29. The marine structure according to claim 1 or claim 26, said structure comprising buoyancy elements (4) arranged on the upper strings (2) of said structure.

30. The marine structure according to claim 1or claim 26, said structure comprising buoyancy elements (4) or ballast elements (5) arranged on said rods or bars (1).

31. The marine structure according to claim 1 , comprising a circular class 1 tensegrity structure formed by multiple interlinked tensegrity structures.

32. The marine structure according to claim 31 , comprising a plurality of tensegrity sub-elements similar to the triangular Snelson prism (200) but having only two bars (1), in Which said sub-elements are arranged so that for each sub- element two nodal points are formed by the bar nodes from flanking sub elements, and in which all sub elements are connected by inner and outer, upper and lower generally regular polygons.

33. The marine structure according to claim 32 in which the number of rods (1) is any even number equal to six or above six, and in which the number of strings (2) depends on the number of rods.

34. The marine structure according to claim 1 in which a nearly cubic fish cage for fish farming, comprising a plurality of rods or bars (1) and strings (2), in which said rods or bars (1) are arranged in close proximity of the lines forming the edges of the imagined cubic shape and with the ends of said rods or bars (1) arranged near the corners of said imagined cubic shape, and in which the ends of three by three meeting rods or bars (1) are connected by short tension elements (2) enveloping the corners of said imagined cubic structure.

35. The marine structure according to claim 34, further provided with buoyancy elements (4), and a net (90) spanned by the cube-like structural tensegrity frame, a circumferential walkway (95) arranged near the top of the upper ends of the four generally vertical rods (1), a fence with hooks for holding the net (90).

36. A method for changing the shape of a marine structure like a fish cage (0) for aquaculture, with a net (90) spanned by a tensegrity structure, i.e. a structure comprising compressive elements (1), and tension elements (2), said method comprising the steps of:

* using a first control system (75) for receiving sensor signals (760) from first sensors (76) sensing tension forces and extended length of tension elements (2),

* said first control system (75) using said sensor signals (760) and the size of said compressive elements (1) to calculate the shape of all basic elements (600, 700), and thus an overall present shape and a desired new shape and size of the entire fish cage (0, 70, 72, 74),

* said control system (75) providing control signals (750) to actuators (25, 26) for changing the tension and / or changing the length of said tension elements (2), so as for changing the overall shape of said fish cage (0, 70, 72, 74) to said desired new shape.

37. The method of claim 36, said first control system (75) arranged for receiving measurement of external environmental loads like wind direction, wind speed, wave directions, sea state, current direction and current speed, for calculating how the lengths of specific tensile elements should change length in order to change the overall shape of the fish cage (0, 70, 72, 74) to a desired new shape.