FR2602012A1 - SWELL GENERATOR - Google Patents

Abstract

1. System for generating an artificial surge or swell in an ocean engineering experimental basin or dock, of the type having a beater constituted by a cylindrical float parallel to the rear wall of the basin, characterized in that the section of said float, i.e. the generatrix of said cylinder, has a substantially vertical rear side, i.e. substantially parallel to said rear wall, and a nose-shaped front side, and said float is associated with mechanical means imparting to it a horizontal alternating movement, the mean distance between the rear wall of the float and the rear wall of the basin being chosen in such a way that a resonance phenomen is created between the swell train produced by the oscillations of the water column between said walls and that created by the movement of the float, the superimposing of these two trains giving rise to a very high transfer function in a chosen swell period interval.

Description

- 2l 6 2602012 The present invention relates to a new system

  wave generator, intended in particular for pools

  ocean engineering experiment.

  We know that currently there are essentially two types of wave generators, which can be identified according to the nature of the "beater" element exerting its dynamic action on the body of water in which the artificial swell

must be created.

  Firstly, we can speak of beaters of the "shutter" type, which can be presented as a vertical shutter animated by an alternating translational movement, or as an inclined shutter, animated by an alternating tilting movement, said shutter being able to itself be articulated and / or coupled to a device for

  translation of its tilting axis (double-acting flaps).

  Studies carried out on these systems show that they provide a transfer function (ratio between the amplitude of the swell produced and the amplitude of the angular elongation of the beater) satisfactory only for double-effect systems and for short swell periods. In addition, 20 technically, such systems are unattractive in

  because of the importance of the masses to be set in motion, of the difficulties of simultaneously controlling two jacks (translation and tilting) and of the technical complexities resulting from the means necessary for sealing between the flaps and the side walls of the channel.

  Secondly, there are known beaters of the "plunger wedge" type, constituted by a prism with a triangular section facing downwards, a large face of which slides in an alternating movement along the rear vertical wall of the channel. The transfer function of these beaters is also not very satisfactory and, moreover, these beaters are not adaptable to the case of very deep swell, swell and current pools. A new and more satisfactory solution has recently been suggested by the Applicant. It consists in using as a "beater" a horizontal cylindrical float, actuated in sinusoidal tilting according to one or the other of its three degrees

of freedom.

  Although this system leads to more satisfactory transfer functions 40, it still has the disadvantage of being

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  expensive, due to complex means (cylinder and connecting rod assembly)

  used to operate the mixer.

  Now, it has been made the interesting observation that the same float, this time simply animated with a horizontal reciprocating movement 5, therefore much less costly, and placed at an appropriate distance from the rear wall of the channel, created swells having much transfer functions. more

  still satisfactory than all known systems.

  In addition, it is advantageous, to create a phenomenon of resonance, favorable to these results, that the rear of said

float is vertical.

  The invention therefore relates to a wave generator constituted by a cylindrical float, mounted transversely in a basin, - a short distance from the rear vertical wall of this basin, the generator of said cylinder having a substantially vertical rear part and a front part in beak shape, this cylinder being associated with hubs imparting a

  alternative horizontal translation.

  Thanks to this arrangement, the mechanical members are very simplified, since they are reduced to a horizontal jack, and

  the efforts they have to exert are very reduced.

  The invention will be described in more detail thanks to and with reference to the attached drawing in which: FIG. 1 is a schematic cross section of a system according to the invention, and FIG. 2 is a diagram showing the variations of the transfer function obtained with the system

  according to the invention, according to the swell period.

  Referring first to FIG. 1, it can be seen that, according to the invention, a cylindrical float 1 parallel to the wall

  vertical rear 2 of a swell basin, in a manner known per se, is animated, by means of a jack 3 of a so-called rippling movement, that is to say of alternative horizontal translation.

  The section of this cylinder, that is to say its generator, has the general shape shown in the figure, namely: its rear face 4, that is to say facing the wall 2, is substantially vertical as this wall. We will see below the effects of this peculiarity, as well as those of the

  distance o between the two vertical surfaces.

  - its front part 5 is in the shape of a beak, making with the

3 2 6 2602012

  surface S an angle o, the value of which is a compromise between the highest possible value, to obtain good performance with regard to wave generation, and a low value, to obtain good regularity of circulating current in the vicinity of said spout, in the case shown, where a current exists in the channel, in the direction F, the beater 1 thus creating a convergent for this current with the difference in level

between bottoms 6 and 6 '.

  Experience shows that, thanks to this system, it is possible to achieve very high transfer functions,

  especially for swell periods of the order of 2 to 3 seconds. FIG. 2 illustrates the influence, on the values of these transfer functions, of the distance from the rear of the mixer to the wall of the basin, that is to say the effects due to the phenomenon, of resonance resulting from the cyclic variation. of this distance.

  On this diagram, the curves I to VI correspond to different values of the time average of the distance d, for a drummer conforming to that of FIG. 1, having a width L at the waterline of 1.9 m, immersed by lm in a basin whose bottom 20 6 is 7m and bottom 6 'is 3m, distance D being 10m: Average curve (m)

I 0.6

II 0.7

III 0.8

IV O, 9

V 1.9

VI 2.0

  These curves are to be compared to curve A, illustrating the variations in the transfer function obtained with a similar float, but animated by an oscillating movement around a transverse axis X. It can be seen that the transfer functions obtained with the system according to the invention are the most favorable in the field of the desirable periods for the 35 basins considered; this also shows that the hydrodynamic performance of this system is quite different from that of the most comparable prior systems from the point of view of

geometric view.

  It should also be noted that, although these 40 results follow d. aforementioned resonance phenomenon, itself

4 2602012

  created by the piston effect played by the float on the body of water located between its rear face and the wall of the basin, which implies the verticality of this rear face, it is possible, within the framework of the invention, to produce a float whose said rear face is slightly inclined towards the front relative to the vertical. We then obtain as an additional result a limitation of the chop between the wall and the float, without

  as much decrease the transfer function.

  It follows from the above that the new wave generator system 10 according to the invention has a set of new and interesting characteristics: - high transfer function - simplicity of the mechanical system

  - good compatibility with the requirements linked to the generation of the current in the basin.

  - low hydrodynamic forces exerted by the float on the cylinder, due to a negative mass of added water in the vicinity of the resonance period (2 to 30), which makes it possible to

  limit the inertia forces that the jack must develop in order to actuate the float.

2602012

Claims (4)

  1. An artificial wave generator system in an ocean engineering experimental basin, of the type comprising a beater constituted by a cylindrical float parallel to the rear wall of the basin, characterized in that, the section of said 5 float is that is to say the generator of said cylinder, has a substantially vertical rear side, that is to say substantially parallel to said rear wall, and a beak-shaped front side, and said float is associated with mechanical means.   printing a horizontal reciprocating motion.   2. System according to claim 1, characterized in that the average distance between the rear wall of said float and the rear wall of said basin is chosen so that a resonance phenomenon is created between the swell train caused by the oscillations of the water column included between said 15 walls and that created by the proper movement of the float, the superposition of these two trains giving rise to a very high transfer function in a chosen interval of period of the swell.   3. System according to claims 1 and 2, characterized in   that, in order to limit the chop between the wall and the float, the rear face of the float is slightly inclined   forward relative to the vertical.   4. System according to claims 1 to 3, characterized in that   that it is installed in a swell and current basin. 25