GB1594868A - Breakwater - Google Patents

Description

(54) BREAKWATER (71) We, INDUSTRIE PIRELLI SpA, an Italian Company, of Centro Pirelli, Piazza Duca d'Aosta No 3, 20100 Milan, Italy, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to mattresstype breakwaters, i.e. to floating and flexible breakwaters having two of their dimensions predominating with respect to the third, which can be anchored to an underwater bottom in such a position as will minimise wave-motion.

Known breakwaters generally comprise two main types: fixed non-buoyant breakwaters and movable buoyant breakwaters.

A fixed breakwater comprises a rigid nonbuoyant body of relatively massive construction which provides physical separation between one area of water and another.

Breakwaters of this type are generally very expensive and give rise to serious problems when they are to be installed in deep waters and in waters in which strong undercurrents are present.

One type of movable breakwater comprises a rigid buoyant structure, moored so that it floats on the surface. It reduces the force of incident waves by means of appropriate elements, e.g. flaps.

Breakwaters of this type are not particularly effective against waves of considerable dimensions, are very expensive, and, owing to their rigid structure, are highly vulnerable to damage by waves of large dimensions.

Another type of movable breakwater comprises a flexible buoyant structure consisting of an elongate element which in use is arranged and moored so that its larger dimension is perpendicular to the prevailing direction of the wave motion. The element is partially or totally filled with a fluid.

A known mattress-type breakwater comprises a floating and flexible body in which two dimensions predominate with respect to the third. This known breakwater is formed by joining a plurality of elongate flexible elements in mutual direct contact and is partially or totally filled with a suitable fluid and provided with inflatable flotation elements of a material lighter than the liquid surrounding the breakwater.

Breakwaters of this type, as is the case for all known buoyant breakwaters, are moored so as to be in proximity to the surface of the liquid into which the breakwater is immersed. Such breakwaters follow with their whole section, both immersed and emersed, the motion of incident waves. The energy of the incident waves is absorbed and dissipated by such mattress-type breakwaters by movement of the mattress, which reflects part of an incident wave, creates a wave counteracting the incident wave, and dissipates energy from the fluid inside the mattress. These breakwaters show some disadvantages, mainly that of being ineffective against waves whose length (i.e. the distance between the crests of two successive waves) exceeds the length of the breakwater (i.e. the dimension of the breakwater in the direction of the incident waves).Moreover, manufacture of said mattress-type breakwaters requires a considerable amount of material many joints are needed to connect the various elongate elements in mutual contact. This makes the breakwaters vulnerable to damage. Finally, to obtain the best results, the known mattress-type breakwaters have to be filled with specially-selected fluids, so that a further increase in cost is involved.

The present invention aims to provide a mattress-type breakwater having a waveattenuation ratio which is very high even against waves whose length is greater than the length of the breakwater. The waveattenuation ratio (as used herein) is defined as the difference between the height of an incident wave and the height of the same wave when downstream of the breakwater, divided by the height of the incident wave.

the resulting figure being expressed as a percentage.

The present invention also aims to provide a mattress-type breakwater having a very simple structure and which is resistant and economical.

Accordingly, the present invention provides a mattress-type breakwater having two of its dimensions predominating relative to the third and exhibiting a high wave-attenuation ratio (as hereinbefore defined), the breakwater comprising an enclosed, unitary, deformable envelope made of a flexible and inextensible material, mooring means, and a plurality of float elements for rendering the breakwater buoyant, the envelope moreover containing a fluid, whereby a complementary and counteracting wave is provided to the impact of an incident wave when the breakwater is in use.

The present invention will be illustrated, merely by way of example, in the following description, and with reference to the accompanying drawings.

In the drawings: Figure 1 shows, partly in perspective and partly in section, a mattress-type breakwater according to the present invention in a state of rest; Figure 2 shows, partly in perspective and partly in section, the breakwater of Figure 1 under the action of an incident wave; Figure 3 is a sectional view of the means for providing a liquid-tight connection between the envelope and the rigid structure of a mattress-type breakwater according to the present invention.

Referring now to Figures 1 and 2, a mattress-type breakwater I is anchored by mooring means 2 to an underwater bottom in such a way that it is maintained in proximity of the surface with its larger dimensions (hereinafter indicated as "width") perpendicular to the predominating direction of the incident waves (indicated by means of arrow A in Figure 2). The mooring means may comprise, for instance one or more anchors 2 connected to the breakwater I by means of chains or ropes 2'. The upper part of the breakwater carries at least two float elements 3, for example of cylindrical form, and extending over its whole width. The float elements 3 are filled, by means known per Se, with a fluid lighter than the water in which the breakwater is floating, for example air, and provide the necessary buoyancy to give to the breakwater I the desired trim.The float elements 3 are situated along the sides of greater dimension of the breakwater 1, preferably in proximity of the waterline, and are connected to the outer side of a sheet 4, made of a flexible and inextensible material.

(for example. rubberised fabric). which closes the upper side of the breakwater relative to the water line. Alternatively, said float elements 3 can be connected to the underside of said sheet 4, so as to be inside the breakwater. Tie-rods (not shown) arranged perpendicular to the float elements 3, can be provided for example, on the outer side of the sheet 4. The sheet 4 is watertightly connected to a rigid frame structure 5 extending along the whole lateral perimeter of the breakwater. A lower sheet 6, of a flexible and inextensible material, (for example rubberised fabric) which closes the lower side of the breakwater relative to the water line, is also connected to said rigid frame structure 5. The envelope formed by said lower sheet 6 is partly or wholly filled with an appropriate fluid, for example the water in which the breakwater is immersed.The movement of the closed and deformable envelope and of the fluid with which it is at least partially filled provides, in response to the action of an incident wave, a counterwave complementary to that incident wave when the breakwater is in use.

in Figure 3, there is shown a float element 3, and part of a rigid frame structure 5 which comprises a cylindrical element 7 joined, on its inner side 8, to a tubular member 9. The means which connect the two sheets 4 and 6 to the rigid member 5 comprise, in addition to the cylindrical element 7 two rigid bars 10 and 11 around which engage respectively the ends 4' and 6' of the sheets 4 and 6, and a continuous peripheral clamp 12 which, by means of a nut 13 engaging the threaded end 14 of a rigid tie-rod 15, urges said ends 4' and 6' against the rigid bars 10 and 11 and, in turn, urges said bars 10 and 11 against the cylindrical element 7. The elements forming the rigid frame structure 5 and the means for the liquid-tight connection of the two sheets 4 and 6 thereto can be made, for example, of a metal and/or of a rigid plastics material.

The operation of a mattress-type breakwater according to the present invention, is as follows. In Figure 2, the crest 16 of an incident wave, impinging on the breakwater, encounters a considerable mass of fluid, contained in the envelope formed by the lower sheet 6 and the upper sheet 4. This mass of fluid fills completely the trough existing between the incident wave and the preceding wave.

In this way a counter-pressure is created.

Said counter-pressure facilitates the abatement of the wave crest, absorbing a relevant amount of the kinetic energy possessed by the wave itself. Said energy is then dissipated by movement of the fluid-containing envelope into the trough of the successive incident wave. More than 70% of the kinetic energy possessed by a wave is concentrated in the zone in proximity of its surface, namely in its upper zone. corresponding to 20% of the total depth of the fluid body at that point. A breakwater according to the present invention dissipates the greater part of the kinetic energy of an incident wave and consequently reduces its effect. The effect of the incident wave is also reduced because breakwaters according to the present invention have natural oscillation periods which are much longer than the oscillation period of the incident waves.Experimental tests have demonstrated that a breakwater according to the present invention has an attenuationratio of between 80% and 90% with respect to waves having a length between 0.5 and 1 times the length of the breakwater and a height smaller than or equal to the height of the breakwater. Attenuation-ratios of about 70% were obtained in respect of waves 1.5 times the length of a breakwater according to the present invention.

Moreover, the tensions inside the lower sheet 6 were found to be very low even when the fluid contained in the envelope was subjected to considerable pressures by incident waves, because the amount of fluid contained in the envelope acts on an equal amount of fluid outside the envelope, and because said sheet is free to move and to adapt itself to the form of any incident wave.

Moreover, the presence of the float elements 3 along the greater dimension of the breakwater facilitates the lifting of the latter and the consequent passage of the incident wave below said breakwater.

Breakwaters according to the present invention having a very simple structure and being built of low-cost materials, can actually protect a part of a fluid, or structures immersed in it. They can be arranged in proximity of coasts, with considerable effectiveness.

Moreover breakwaters according to the present invention can readily be disengaged from their moorings and towed to other locations. The breakwaters can also be transported to a harbour for maintenance and/or cleaning.

WHAT WE CLAIM IS: 1. A mattress-type breakwater having two of its dimensions predominating with respect to the third and exhibiting a high wave-attenuation ratio (as hereinbefore defined), the breakwater comprising an enclosed. unitary, deformable envelope made of a flexible and inextensible material, mooring means, and a plurality of float elements for rendering the breakwater buoyant, the envelope moreover containing a fluid, whereby a complementary and counteracting wave is provided to the impact of an incident wave when the breakwater is in use.

2. A breakwater according to Claim I which is provided, on its sides of greater dimension, with a rigid frame structure.

3. A breakwater according to Claim I or 2, which is elongate and comprises at least one float element situated along either side of greater dimension of the breakwater, a rigid frame structure comprising a part arranged around the perimeter of the breakwater and rigid tie-rods extending parallel to the sides of smaller dimension of the breakwater and between opposite sides of said part and to which frame structure the two float elements are connected, an enclosed, deformable envelope constituted by two sheets of a flexible and inextensible material, which are fluidtightly connected, to said rigid frame structure and which are disposed one opposite the other with respect to said rigid structure, a fluid which fills at least partially said closed and deformable envelope and mooring means.

4. A breakwater according to Claim 3, in which the means which fluid-tightly connect the sheets of flexible and inextensible material to the rigid frame structure comprise, for each side, a cylindrical element forming the peripheral part of said rigid frame structure, two tubular bars around each of which is wound an end of one of the sheets of flexible and inextensible material and a clamp which embraces said tubular bars and which is urged against said tubular bars and thus against said cylindrical element.

5. A mattress-type breakwater, substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. longer than the oscillation period of the incident waves. Experimental tests have demonstrated that a breakwater according to the present invention has an attenuationratio of between 80% and 90% with respect to waves having a length between 0.5 and 1 times the length of the breakwater and a height smaller than or equal to the height of the breakwater. Attenuation-ratios of about 70% were obtained in respect of waves 1.5 times the length of a breakwater according to the present invention. Moreover, the tensions inside the lower sheet 6 were found to be very low even when the fluid contained in the envelope was subjected to considerable pressures by incident waves, because the amount of fluid contained in the envelope acts on an equal amount of fluid outside the envelope, and because said sheet is free to move and to adapt itself to the form of any incident wave. Moreover, the presence of the float elements 3 along the greater dimension of the breakwater facilitates the lifting of the latter and the consequent passage of the incident wave below said breakwater. Breakwaters according to the present invention having a very simple structure and being built of low-cost materials, can actually protect a part of a fluid, or structures immersed in it. They can be arranged in proximity of coasts, with considerable effectiveness. Moreover breakwaters according to the present invention can readily be disengaged from their moorings and towed to other locations. The breakwaters can also be transported to a harbour for maintenance and/or cleaning. WHAT WE CLAIM IS:

1. A mattress-type breakwater having two of its dimensions predominating with respect to the third and exhibiting a high wave-attenuation ratio (as hereinbefore defined), the breakwater comprising an enclosed. unitary, deformable envelope made of a flexible and inextensible material, mooring means, and a plurality of float elements for rendering the breakwater buoyant, the envelope moreover containing a fluid, whereby a complementary and counteracting wave is provided to the impact of an incident wave when the breakwater is in use.

2. A breakwater according to Claim I which is provided, on its sides of greater dimension, with a rigid frame structure.

3. A breakwater according to Claim I or 2, which is elongate and comprises at least one float element situated along either side of greater dimension of the breakwater, a rigid frame structure comprising a part arranged around the perimeter of the breakwater and rigid tie-rods extending parallel to the sides of smaller dimension of the breakwater and between opposite sides of said part and to which frame structure the two float elements are connected, an enclosed, deformable envelope constituted by two sheets of a flexible and inextensible material, which are fluidtightly connected, to said rigid frame structure and which are disposed one opposite the other with respect to said rigid structure, a fluid which fills at least partially said closed and deformable envelope and mooring means.

4. A breakwater according to Claim 3, in which the means which fluid-tightly connect the sheets of flexible and inextensible material to the rigid frame structure comprise, for each side, a cylindrical element forming the peripheral part of said rigid frame structure, two tubular bars around each of which is wound an end of one of the sheets of flexible and inextensible material and a clamp which embraces said tubular bars and which is urged against said tubular bars and thus against said cylindrical element.

5. A mattress-type breakwater, substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.