EP3653793B1 - Reduction of the reflection coefficient of a vertical wall in a port - Google Patents

Description

FIELD OF THE INVENTION

The invention relates generally to reducing the force of waves within a maritime infrastructure, in particular a maritime infrastructure such as a port. One objective of the invention is in particular to facilitate the loading and unloading of a boat in such an infrastructure.

TECHNOLOGICAL BACKGROUND

Boats are generally loaded and unloaded in ports. Depending on the type of boat and the unloading means used, it is preferable for the boat to be stable and substantially immobile in order to allow them to be loaded and unloaded easily. However, the waves, whether they are generated at sea and propagate in the port (swells and seas of wind), induced by the wind within the port itself (chop) or even induced by the boats in the port (wake) , then propagate by reflection against any submerged wall in the port (such as a breakwater, a quay, a slope, a beach, etc.). This results in difficulties for some boats to load or unload their cargo, or problems of comfort and safety, such as in marinas, for example.

Each submerged wall has a reflection coefficient (Cr) which depends in particular on its geometry (slope, edge level, plan shape, etc.), its texture (roughness, porosity, etc.) and the characteristics of the incident wave (period, camber, ...). In particular, vertical walls reflect incident waves almost perfectly and therefore have a reflection coefficient substantially equal to 1. However, the most common structures in a port are vertical quays - and therefore vertical walls - which can be made, in a non-limiting way, from sheet piles, diaphragm walls, caissons.

In order to reduce the reflection coefficient of these vertical walls, it has already been proposed to place in front of these walls coastal protection dykes such as perforated rigid walls of the JARLAN caisson type. These rigid perforated walls are however very expensive and require structures in complex concrete, and cannot be envisaged a posteriori on an existing quay.

It has also been proposed to create submerged embankments, such as the slopes located under open quays on piles. However, building quays on piles is expensive and this solution is only competitive when the geotechnical and/or seismic conditions are severe.

These solutions are therefore effective and effectively make it possible to reduce the reflection coefficient of the walls, and in particular of the vertical walls. However, their cost is high, they can be complex to implement, and they cannot be implemented on an already existing quay to reduce its reflection coefficient.

It has therefore been proposed to use floating structures with a low reflection coefficient. However, these structures undergo movements that are generally incompatible with the loading-unloading function, and are therefore only possible in rare areas where the waves are weak and very short (chops generated by local winds or wake waves created by the passage of boats, with a period of less than 3 s or 4 s).

It was also proposed in the document US 2009/0239645 an at least partially submerged curtain configured to damp the movements of water in front of a substantially vertical wall in a port-type infrastructure. For this, the curtain is sized so as to have a transmission coefficient which is substantially less than 1. This curtain thus makes it possible to shelter the part which is located downstream of it, that is to say between the curtain and the wall, from an upstream stress such as a propeller jet. It was also proposed in the document JP 2015-055055 a system configured to dampen waves, in particular in front of a vertical wall of a quay, comprising helical bars configured to reflect incident waves and return reflected waves. The reflected waves will then interfere, which has the effect of attenuating them.

SUMMARY OF THE INVENTION

An objective of the invention is therefore to propose a solution making it possible to reduce the agitation in front of a substantially vertical wall in a body of water of the port type under the effect of an incident wave 3i, which is simple to produce and to set up and of moderate cost, and that it is possible to install on an existing structure as a corrective measure.

• dimensionner le rideau en fonction de caractéristiques liées à la paroi verticale et aux vagues incidentes, ledit rideau étant formé d'une pluralité de blocs unitaires assemblés les uns aux autres par l'intermédiaire de liens flexibles de sorte à former une grille de blocs articulée,
• fabriquer le rideau ainsi dimensionné.
• De plus, le rideau est dimensionné de sorte que son coefficient de réflexion Cr soit inférieur à 1. Les vagues incidentes présentent par ailleurs des périodes comprises dans une plage de périodes donnée et le rideau est dimensionné de sorte son mode propre n°3 et/ou n°4 soit compris dans la plage de périodes donnée.

For this, the invention proposes a method for manufacturing a curtain configured to reduce the agitation in front of a substantially vertical wall at least partially immersed in a port-type infrastructure under the effect of incident waves, the method comprising the following steps :

• sizing the curtain according to characteristics linked to the vertical wall and to the incident waves, said curtain being formed of a plurality of unitary blocks assembled to each other by means of flexible links so as to form an articulated grid of blocks,
• manufacture the curtain thus dimensioned.
• In addition, the curtain is sized so that its reflection coefficient Cr is less than 1. The incident waves also have periods included in a given range of periods and the curtain is sized so that its natural mode n°3 and/ or #4 falls within the given period range.

• le rideau présente une hauteur donnée lorsqu'il est en condition statique et, au cours de l'étape de dimensionnement, la hauteur et une densité des blocs sont déterminés en fonction de la plage de périodes donnée
• les blocs du rideau sont séparés les uns des autres par des espaces vides et dans lequel le rideau est dimensionné de sorte qu'une porosité du rideau est comprise entre 10 % et 30 %
• la paroi verticale comprend un bord supérieur s'étendant à proximité d'une surface de l'eau et un bord inférieur immergé et opposé au bord supérieur et la hauteur donnée du rideau est inférieure à une plus courte distance entre le bord supérieur et le bord inférieur de la paroi verticale
• la hauteur donnée du rideau est au moins égale à 30 % de ladite plus courte distance.

Certain preferred but non-limiting characteristics of the manufacturing method described above are the following, taken individually or in combination:

• the curtain has a given height when in a static condition and during the dimensioning step the height and a block density are determined based on the given period range
• the blocks of the curtain are separated from each other by empty spaces and in which the curtain is dimensioned such that a porosity of the curtain is between 10% and 30%
• the vertical wall includes an upper edge extending close to a water surface and a lower edge submerged and opposite the upper edge and the given height of the curtain is less than a shortest distance between the upper edge and the edge lower vertical wall
• the given height of the curtain is at least equal to 30% of said shortest distance.

• déterminer la plage de périodes des vagues incidentes susceptibles de percuter la paroi verticale,
• obtenir un rideau fabriqué conformément à un procédé de fabrication comme décrit ci-dessus en fonction de la plage de périodes ainsi déterminée de sorte que son coefficient de réflexion soit inférieur à 1 et que son mode propre n°3 et/ou n°4 soit compris dans la plage de périodes donnée, et
• fixer le rideau à proximité du bord supérieur de la paroi verticale, de sorte que le rideau soit intégralement immergé dans l'eau et qu'il s'étende sensiblement parallèlement à ladite paroi verticale lorsqu'il est statique.

According to a second aspect, the invention also proposes a method for arranging a substantially vertical wall at least partially submerged in order to reduce the agitation in front of the vertical wall under the effect of incident waves, in which the vertical wall comprises a upper edge extending close to a water surface and a lower edge submerged and opposite the upper edge and the incident waves have periods within a given range of periods. The process then comprises the following steps:

• determine the range of periods of the incident waves likely to strike the vertical wall,
• obtain a curtain manufactured according to a manufacturing method as described above according to the range of periods thus determined so that its reflection coefficient is less than 1 and its eigenmode n°3 and/or n°4 is within the given period range, and
• fixing the curtain close to the upper edge of the vertical wall, so that the curtain is entirely submerged in water and that it extends substantially parallel to said vertical wall when it is static.

• le rideau est fixé à une distance supérieure à un mètre de la paroi verticale et/ou
• le rideau n'est fixé qu'en tête, au niveau du bord supérieur de la paroi verticale.

Certain preferred but non-limiting characteristics of the arrangement method described above are the following, taken individually or in combination:

• the curtain is fixed at a distance greater than one meter from the vertical wall and/or
• the curtain is fixed only at the head, at the level of the upper edge of the vertical wall.

BRIEF DESCRIPTION OF THE DRAWINGS

• La figure 1 illustre schématiquement la fixation d'un exemple de rideau conformément à mode de réalisation du procédé d'aménagement conforme à l'invention.
• La figure 2a illustre la fonction de Bessel Jo de première espèce et d'ordre 0.
• La figure 2b représente les 5 premiers modes propres de vibration d'un rideau pesant suspendu en tête.
• La figure 3 illustre le coefficient de réflexion (Cr) en fonction du temps de deux exemples de réalisation de rideaux, correspondant à deux longueurs de rideaux (18 m et 9 m) placés à 3 m de la paroi verticale par une profondeur d'eau de 20 m.
• La figure 4 est un organigramme illustrant les étapes d'un exemple de réalisation d'un procédé de fabrication conforme à l'invention.
• La figure 5 est un organigramme illustrant les étapes d'un exemple de réalisation d'un procédé d'aménagement conforme à l'invention.

Other characteristics, objects and advantages of the present invention will appear better on reading the detailed description which follows, and with regard to the appended drawings given by way of non-limiting examples and in which:

• The figure 1 schematically illustrates the attachment of an example of a curtain according to one embodiment of the fitting method according to the invention.
• The figure 2a illustrates the Bessel Jo function of the first kind and of order 0.
• The figure 2b represents the first 5 natural modes of vibration of a heavy curtain suspended at the head.
• The picture 3 illustrates the reflection coefficient (Cr) as a function of time for two examples of the production of curtains, corresponding to two lengths of curtains (18 m and 9 m) placed 3 m from the vertical wall in a water depth of 20 m .
• The figure 4 is a flowchart illustrating the steps of an exemplary embodiment of a manufacturing method according to the invention.
• The figure 5 is a flowchart illustrating the steps of an exemplary embodiment of a layout method according to the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

The invention proposes the installation in front of a reflecting wall 1, typically a vertical wall, of a stretched flexible vertical curtain 2 simply suspended under a structural element of the wall 1 (for example under the capping beam of a quay ), curtain 2 whose mode vibration excited by the incident swell will help to reduce the height of the reflected wave.

The figure 1 illustrates a vertical wall 1 in a maritime infrastructure, typically a port, supporting a curtain 2 configured to reduce its reflection coefficient Cr with respect to incident waves 3i and thus reduce reflected waves 3r, in order to reduce agitation in the body of water.

The vertical wall 1 has an upper edge 4 extending above or close to the surface of the water, and a lower edge 5 submerged and opposite the upper edge 4. The upper edge 4 can be above the water level or, alternatively, be submerged. By height H of the wall, we will understand here the shortest distance between the upper edge 4 of the wall and its lower edge 5. In the case where the vertical wall 1 is a vertical face of a platform, the upper edge 4 corresponds at the edge of the quay deck.

The curtain 2 has a height h, which corresponds to the vertical dimension of the curtain 2 when the latter is fixed on the vertical wall 1.

The curtain 2 is formed of a plurality of unitary blocks 6 assembled to each other via flexible links 7 so as to form a grid of articulated blocks 6.

More specifically, the blocks 6 are connected to each other via a series of vertical flexible links 7, so as to form a plurality of parallel columns of blocks 6, and a series of horizontal flexible links 7, so as to form a plurality of parallel rows of blocks 6.

Thanks to the flexible links 7, the blocks 6 are separated from each other by empty spaces to allow their relative movement, so that during the impact of an incident wave 3i against the curtain 2, the latter is able to oscillate thanks to the relative articulation of its blocks 6.

The blocks 6 each have a given density. Preferably, each block 6 of curtain 2 has the same density, in order to facilitate the sizing of curtain 2.

In a first embodiment, the blocks 6 comprise a solid body made of concrete, metal, wood, plastic or a mixture of these materials. The flexible links 7 can then comprise metal cables or geotextiles. An exemplary embodiment of such a curtain 2 comprises for example an articulated concrete mattress.

In a second embodiment, the blocks 6 comprise rigid panels, for example made of plastic, concrete, metal, or a mixture of these materials. These blocks 6 are then connected to each other by fixing to a net of mooring chains, preferably metallic.

In a third embodiment, the blocks 6 can comprise masses fixed on a textile of the anti-turbidity type. Here again, the masses can be made of concrete, metal, wood, plastic, or a mixture of these materials.

In a fourth embodiment, the blocks 6 are plastic bottles filled with a material giving them a given density, for example sand. The flexible links 7 can then comprise metal cables or geotextiles.

In order to reduce the reflection coefficient Cr of the vertical wall 1 on which the curtain 2 is intended to be fixed, the invention proposes to size (step S1) the curtain 2 so that its most probable natural period of oscillation is in the range of periods of the incident wave spectrum. The objective here is to absorb part of the energy of the incident waves 3i so that these are not totally reflected towards the port despite the presence of a vertical wall 1.

For this purpose, the curtain 2 is sized so that at least one of its natural modes is included in the range of periods of the incident waves 3i.

These eigenmodes are characterized by the Bessel functions of the first kind, due to the fact that the curtain is a flexible structure stretched in permanently, suspended at the top and free at the bottom.

Given the fact that a pendulum-type oscillation would cause large added masses of water, analogously to a horizontal translational movement of a vertical plate which mobilizes a large adjoining mass of water, vibration modes 1 and 2 (see figure 2b ) are very little developed in practice. The modes which are in practice excited by the incident swell are those which minimize the masses of water added, namely the modes of order 3 and more (see figure 2b ).

The curtain 2 must therefore be dimensioned so that the natural periods of the modes 3, 4, even 5, are in the range of the period of the incident wave 3i, since they are associated with small added hydrodynamic masses.

où : T₃ est le mode propre n°3

• le facteur 8.65 correspond à la troisième solution de la première fonction de Bessel de première espèce Jo(x) = 0, comme illustré en figure 2.
• le ratio λ/λ' correspond au rapport de la masse surfacique sur la masse surfacique déjaugée du rideau 2, lorsque le coefficient de masse ajoutée est considéré comme négligeable, ce qui est le cas pour le mode propre n°3. Ce ratio λ/λ' est égal au rapport 1/(1-1/δ), où δ est la densité du matériau constitutif des blocs 6 par rapport à l'eau environnante.

For example, eigenmode n°3 is expressed as follows, neglecting the added mass: $${\mathrm{<figure-callout\; id="3"\; label="T"\; filenames="imgf0003.png"\; state="\{\{state\}\}">T</figure-callout>}}_3=2\pi \sqrt{\frac{\lambda }{\lambda \prime }}\times \frac{1}{8.65}$$

where: T ₃ is the eigenmode n°3

• the factor 8.65 corresponds to the third solution of the first Bessel function of the first kind Jo(x) = 0, as illustrated in figure 2 .
• the ratio λ/λ' corresponds to the ratio of the surface mass to the planed surface mass of the curtain 2, when the coefficient of added mass is considered to be negligible, which is the case for eigenmode No. 3. This ratio λ/λ' is equal to the ratio 1/(1-1/δ), where δ is the density of the constituent material of the blocks 6 with respect to the surrounding water.

Mode 4 (respectively 5) can be calculated with the same formula by replacing 8.65 by 11.8 (respectively 14.9).

When the period of the incident waves 3i approaches natural mode No. 3 of curtain 2 thus dimensioned, the reflection coefficient Cr of curtain 2 becomes substantially less than 1, as shown in Fig. picture 3 . The picture 3 indeed illustrates the oscillations of two examples of production of curtains 2 in accordance with the invention, for which the natural mode n°3 calculated in accordance with formula (1) is equal to 2.6 s for the curtain 2 whose height h is equal at 18 m, and 1.9 s for curtain 2 whose height h is equal to 9 m, when the added mass coefficient is neglected. However, it emerges from this figure that the reflection coefficient Cr is minimal when the period of the incident waves 3i is close to 2.6 s.

The parameters of the curtain 2 having an influence on its natural modes and which can be adapted during the dimensioning step S1 include, in a non-limiting manner, the height h of the curtain 2, the density of its blocks 5 and/or the porosity of the curtain 2, as well as the distance D to the vertical wall 1.

In one embodiment, the porosity of the curtain 2 can be between 10% and 30%. By porosity, it will be understood here the percentage of empty surface with respect to the total surface of the curtain 2, the total surface corresponding to the surface extending between the lateral sides and the upper sides of the curtain 2.

The height h of the curtain 2 is chosen so as to be less than the height H of the vertical wall 1 and can be between 30% and 100% of the height H of the vertical wall 1. It is in fact preferable that the curtain 2 is not fixed at the bottom or even retained by friction against the ground in order to allow its free oscillation during the incidence of a wave 3i. It also emerges from the tests carried out by the Applicant that a curtain 2 covering the entire height H of the vertical wall 1 had a reflection coefficient Cr comparable to that of an identical curtain 2 but covering only 50% of the height H of this vertical wall 1.

It should be noted that it has already been proposed to use concrete mattresses to protect walls against erosion (see for example the document US 2009/0239645 ). However, the concrete mattresses of the prior art were not sized to reduce the reflection coefficient Cr of the wall, but on the contrary to have a low transmission coefficient Ct. These concrete mattresses indeed had a transmission coefficient Ct less than 1 so as to prevent the incident waves 3i from damaging the wall they were protecting. To this end, these concrete mattresses were sized so as to obtain a mass effect, so that the concrete mattress is heavy enough so that it does not oscillate too much under the pressure exerted by the incident wave 3. It follows that, unlike the curtains 2 implemented in the invention, the concrete mattresses of the prior art were configured to reflect the incident waves 3i as much as possible in order to prevent them from reaching and damaging the vertical wall 1, since the coefficients of reflection Cr and transmission Ct vary symmetrically, if one considers only the effects dissipative near the conservation of energy results in the equation Cr ² + Ct ² = 1.

Conversely, in the present invention, the curtain 2 is dimensioned so that its natural period (and in particular its natural mode n°3 and/or n°4) approaches that of the incident waves 3i.

The vertical wall 1 can then be arranged (method S10) in accordance with the following steps using a curtain 2 as described above.

During a first step S11, the range of periods of the incident waves 3i likely to strike the vertical wall 1 is determined. This determination can be carried out by determining, over a predetermined duration, the maximum period and the minimum period of the incident waves 3i on the vertical wall 1. These maximum and minimum periods then define the limits of the range.

As a variant, the range of periods can be chosen from a series of pre-established ranges representative of periods frequently encountered in maritime infrastructures, such as ports. For example, the range can be selected from a range of low periods, a range of medium periods or a range of high periods.

During a second step S12, a curtain 2 is obtained whose reflection coefficient Cr is less than 1, in accordance with what has been described above. The curtain 2 obtained is therefore adapted to the vertical wall 1 and to the maritime infrastructure. Its parameters (density, porosity, height h, etc.) are chosen in particular according to the vertical wall 1 (in particular its height H) and the range of periods of the incident waves 3i to be absorbed (which was determined during the first step).

During a third step S13, the curtain 2 thus obtained is fixed close to the upper edge 4 of the vertical wall 1, so that it is entirely immersed in water and that it extends substantially parallel to said vertical wall 1 when it is static (see figure 1 ).

In order to allow the curtain 2 to oscillate and absorb the incident waves 3i without coming into contact with an element likely to disturb its natural modes, the curtain 2 is fixed at a distance from the vertical wall 1, for example via of arms 8 extending substantially perpendicularly from the vertical wall 1. In other words, over the entire height h of the curtain 2 and at any point on its surface, the curtain 2 extends at a distance D of at least one meter from any structure likely to disturb its natural modes.

Preferably the curtain 2 is fixed at a distance D greater than two meters from the vertical wall 1, more particularly at a distance D greater than or equal to three meters, for example between three meters and six meters.

In one embodiment, the curtain 2 is fixed only at the head, that is to say only at the level of its upper side, in order to leave it free to oscillate along the vertical wall 1 (see figure 1 ).

Claims (8)

1. A method (S0) for manufacturing a curtain (2) configured to reduce agitation in front of a substantially vertical wall (1) which is at least partially submerged in a port-type infrastructure under the effect of incident waves (3i), the method comprising the following steps:

   - dimensioning (S1) the curtain (2) according to features related to the vertical wall (1) and to the incident waves (3i), said curtain (2) being formed of a plurality of unit blocks (6) assembled together by means of flexible links (7) so as to form an articulated grid of blocks (6),

   - manufacturing (S2) the curtain (2) thus dimensioned,

   the manufacturing method (S0) being characterised in that the curtain (2) is dimensioned so that its reflection coefficient (Cr) is less than 1 and in that the incident waves (3i) have periods comprised within a given range of periods, the curtain (2) being dimensioned so that its natural mode n°3 and/or n°4 is comprised within the given range of periods.
2. The manufacturing method (S0) according to claim 1, wherein the curtain (2) has a given height (h) when it is in a static condition and, during the dimensioning step (S1), the height (h) and a density of the blocks (6) are determined according to the given range of periods.
3. The manufacturing method (S0) according to one of claims 1 or 2, wherein the blocks (6) of the curtain (2) are separated from each other by empty spaces and wherein the curtain (2) is dimensioned so that a porosity of the curtain (2) is comprised between 10% and 30%.
4. The manufacturing method (S0) according to one of claims 1 to 3, wherein the vertical wall (1) comprises an upper edge (4) extending in the proximity of a surface of the water and a lower edge (5) which is submerged and opposite the upper edge (4) and the given height (h) of the curtain (2) is less than a shorter distance (H) between the upper edge (4) and the lower edge (5) of the vertical wall (1).
5. The manufacturing method (S0) according to claim 4, wherein the given height (h) of the curtain (2) is at least equal to 30% of said shortest distance (H).
6. A method (S10) for arranging a substantially vertical wall (1) which is at least partially submerged in order to reduce the agitation in front of the vertical wall (1) under the effect of incident waves (3i), wherein the vertical wall (1) comprises an upper edge (4) extending in the proximity of a water surface and a lower edge (5) which is submerged and opposite the upper edge (4) and the incident waves (3i) have periods comprised within a given range of periods,
   the method comprising the following steps:

   - determining (S11) the range of periods of the incident waves (3i) likely to strike the vertical wall (1),

   - obtaining (S12) a curtain (2) manufactured in accordance with a method according to one of claims 1 to 5 according to the range of periods thus determined so that its reflection coefficient (Cr) is less than 1 and that its natural mode n°3 and/or n°4 is comprised within the given range of periods, and

   - fixing (S13) the curtain (2) in the proximity of the upper edge (4) of the vertical wall (1), so that the curtain (2) is fully submerged in the water and extends substantially parallel to said vertical wall (1) when it is static.
7. The arrangement method (S10) according to claim 6, wherein the curtain (2) is fixed at a distance (D) greater than one meter from the vertical wall (1).
8. The arrangement method (S10) according to one of claims 6 or 7, wherein the curtain (2) is only fixed at the head, at the upper edge (4) of the vertical wall (1).

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