FR2524029A1 - PROTECTION OF WALLS IN CONTACT WITH LIQUIDS AGAINST QUICK PRESSURE FLUCTUATIONS - Google Patents

Abstract

THE INVENTION CONSISTS OF CREATING GAS POCKETS 4 IN THE WALLS, ON THE WALLS OR IN THE NEIGHBORHOOD OF THE WALLS TO BE PROTECTED FROM PRESSURE FLUCTUATIONS TRANSMITTED BY THE LIQUID 2. THE ENERGY OF THE OSCILLATIONS OF THE GAS POCKETS IS OPTIONALLY ABSORBED BY DEVICES SUCH AS THE PERFORATED PLATE 5. THE OPERATION OF THE GAS POCKET AND ENERGY ABSORBER ASSEMBLY IS ANALOGUE TO THAT OF A SPRING AND SHOCK ABSORBER ASSEMBLY IN AN AUTOMOTIVE SUSPENSION, IT IS A LOW-PASS FILTER FOR THE TRANSMISSION OF FLUCTUATIONS OF PRESSURE BETWEEN THE LIQUID AND THE WALL. AMONG THE MAIN APPLICATIONS, WE CAN Cite the protection of dams against the effect of explosions in the tank or against the effect of earthquakes and the protection of tanks containing liquids against rapid pressure fluctuations of any origin.

Description

The present invention relates to a device reducing the amplitude of

  rapid pressure fluctuations that can be exerted by masses

  liquids on a structure, structure or apparatus wall.

  only to walls of relatively large dimensions and relatively short frequency fluctuations. More precisely, the dimensions of the walls concerned must not be much smaller than the lengths of the compression waves in the liquid corresponding to the frequencies which are

wants to reduce '.

  One of the features of the invention is that its implementation, in the

  immediate settlement of the wall concerned, does not require the identification and

  the location of the origin of the pressure fluctuation This is parti-

  particularly interesting when it comes to an accidental, random or exceptional origin

  In the current state of the art, there is no method that allows

  reduce the pressure fluctuations transmitted by a liquid to

  a wall with this characteristic Once exhausted, when

  the possibilities of reducing these fluctuations at source, all that remains is to reinforce the structures or structures involved to enable them to withstand the foreseeable residual pressure fluctuations, which is sometimes very costly. what follows, we will designate the wall to be protected by "the wall",

  it being understood that the invention may apply simultaneously to different

  walls or fractions of walls in each particular case We designate the liquid in contact with the wall and likely to exert pressure fluctuations by "the liquid" The invention consists in creating in the wall, on the wall or near the wall, a number of pockets of gas that communicate widely with the liquid so that the latter can compress the gas, or allow it to expand, blood have to circulate in narrow and long ducts to make the necessary displacements

  According to an optional arrangement of the invention, absorbers of

  energy are arranged to dampen the volume oscillations of the pockets of

  This can be, for example, obstacles such as perforated walls.

  porous or arranged so as to brake, in the liquid, in the gas

  or in both, the fluid movements that accompany these oscilla-

  These absorbers may be useless if one only wants to guard against very rapid pressure fluctuations, such as shockwaves due to an explosion, for example. The operating mode of the device can be easily understood from the following: invention, because of its mechanical analogy with the systems

  Conventional suspension of vehicles The liquid, not very compressible and

  latively dense, can transmit very hard "shocks" to the wall while

  the ground can transmit shocks to a vehicle by means of solid tire wheels for example the pockets of gas, distributed on the

  tension of the wall, play a role similar to that of the springs

  mechanical sinks, or even better gas pockets of the hydro-

  The energy absorbers play a similar role to the damping

incorporated in suspensions

  The comparison would be even clearer if we could achieve

  by maintaining a layer of continuous gas on the wall that separates it

  Completely liquid

  this provision is possible, it will generally be more convenient to

  center the gas in a number of pockets The effect will be sensi-

  the same if the distances between the pockets remain much shorter than the wavelengths which correspond, in the liquid, to the frequencies which one wants to attenuate

  For each application, a number of parameters must be determined.

  very specific of the invention, namely the general distribution of gas volumes, which can be likened to a distribution of equivalent thickness over the entire wall The effective locations of the gas pockets and their shapes and the ways in which they communicate with the liquid The choice of the energy-absorbing devices that may be used There are many known types that have

  braking or friction (varying linearly or not with

  valves, valve systems, flaps, etc.) The choice will therefore be

  times about a type of law and the value of the parameters that characterize it.

  Known mathematical methods make it possible to calculate the reduction of pressure fluctuations obtained at the different points of the wall by the

  implementation of most embodiments of the present invention.

  Therefore, those skilled in the art can evaluate the effectiveness of the embodiments of the invention.

  of its choice and thus determine those that best suit all the technical and economic data of the problem to be solved. In addition, the analogy with vehicle suspension systems offers

  a valuable guide, not only for the choice of certain technical

  such as those concerning the choice of energy absorbers, but also for the execution of the necessary calculations. In fact, in both cases, it is the implementation of mechanical "filters" that are "low" and the general theory of these filters is highly developed in the literature

  FIG. 1 represents a vertical sectional view of a portion of the

  upstream king of a dam designed to incorporate a device according to the invention

  FIG. 2 represents an embodiment which makes it possible to ensure the

  protection according to the invention to a pre-existing dam by using

  FIG. 3 shows one of the possible embodiments of one of these submerged bells. FIGS. 4 and 5 show embodiments of the invention applicable to the metal walls of a tank containing a liquid.

  It is not possible to define a preferred embodiment of the invention.

  In view of the wide variety of circumstances in which this can be applied, the examples given below may be considered as preferred embodiments for each of the cases to which they refer: dam nine, old dam, metal tank In Figure 1, the body of the dam (1) is on the left and the tank (2) is on the right Sloping slabs (3) hold pockets of air (4) which constitute the gas pockets According to the invention During the volume oscillations of these air pockets, the water must pass through a perforated plate (5) which constitutes an energy absorption device according to the invention

  We will notice the very large passages made for the water in its

  airflow to the air pockets Longer and narrower passages would reduce the efficiency of the device for the higher frequencies but could improve it for lower frequencies

  Small holes (6) and (7), made in sloping slabs sta-

  balance the levels at rest under the air pockets They are not placed exactly one above the other so that the air that escapes

  a pocket that is too "full" (air) feeds the next upper pocket.

  It is thus possible to maintain or restore the levels at rest by feeding

  The devices according to the invention shown in this figure can extend horizontally, with or without variations of section, on all or part of a series of pockets arranged one above the other.

  part of the width of the dam, or this width may be occupied by

  independent devices at the same level Devices with a

  long horizontal length can be subdivided by transverse walls.

  solid, perforated or porous, occupying or not the entire section between the lower and upper slabs To mitigate pressure fluctuations of up to 1 second, the equivalent "spread" thicknesses of the air pockets shall be

  be of the order of a few decimetres for a dam of a hundred meters

  For example, in such a case, the inclined slabs (3) would have an overhang of the order of 2 meters. Moreover, the total surface / perforated surface area of the plates could be of the order of 10. of magnitude are given for information only, they must be optimized in each case by technical calculations Figure 2 shows an embodiment particularly well suited to the protection of a structure already built It represents a dam

  (10), in vertical section, at the immediate upstream of which are arranged clo-

  submerged beds (11) and (12) containing the gas pockets according to the invention Only two of these bells are shown to simplify the drawing

  but, in reality, several tens will be needed to ensure a good

  distribution of protection on a dam of any importance Figure 3 shows one of the possible embodiments of one of these

  bells It shows the bell proper (21), of cylindrical shape

  than flattened enough so that its perforated underside (22) offers a large section of passage to the water

  The gas pocket, let's say air here, is retained in the upper part.

  the bell (23) and, as before, a hole with too much air

  (24) stabilizes the level at rest when the level in the bell

  to this hole, it is said to be "in equilibrium"

  The bell is weighted by a mass (25) The whole bell at the

  balance and this ballast must maintain a slightly positive buoyancy A cable (27) connects the ballast (25) to a second ballast (28) resting on the bottom in equilibrium The weight of the ballast is such that the set of the

  bell and the two weights only assume positive buoyancy if the bell

  Che is almost completely full of air A flexible or articulated hose (29) can breathe compressed air

  in the bell to "redo" the level, it leads to a float (30) itself

  even connected by a cable (31) to the bell When, for any reason, the volume of air in the bell has

  decreased by more than a certain percentage (eg 30%), ballast (25)

  drag the bell down until the bottom is reached or until

  the cable (31) is stretched and depresses the float (30) which gives the

  This float is calculated not to sink completely even if the bell has lost all its gas The upper end of the pipe (29) and remains always accessible and allows the inflation of the air pocket with a mobile compressor for example To raise the bell and its two weights, it suffices to blow compressed air faster than it can escape through the orifice (24). There are other ways to make these bells.

  for example, consist of enclosures made of a flexible material, such as

  can be anchored by a cable on a sufficient ballast or on any other

  The advantage of this embodiment is that the interaction surface of water and gas is as large as possible

  The disadvantage for some applications is that it is difficult to introduce

  A certain absorption can result from the choice of the material of the enclosure, which can have a high coefficient of internal friction, it can also be obtained by placing finely divided materials, glass fibers for example in the gas bag, finally, we can also place these soft bells inside rigid cages with perforated walls

  Figure 4 shows a very simple embodiment that can be applied to

  for example, to the protection of the vertical walls of a metal vessel containing a liquid, is welded from place to place on the wall (40) of the triangular plates (41) and (42) welded together on their common edge (43) One forms

  thus a sort of pyramidal hood that Figure 4 has shown in

  perpendicular to the wall and that Figure 4b shows in elevation

  The gas pocket is formed under this hood during filling. FIG. 5 shows an embodiment adapted to the protection of a bottom of the tank. Among the possible applications of the invention, mention may be made of Protection of dams against the effect of seisms or explosions in the tank Protection of the walls of any enclosure containing a liquid against sudden fluctuations in pressure, due, for example, to an explosion, a water hammer, thermal instability (calefaction) etc

  Protection of maritime structures against the effect of earthquakes,

plosions and shocks due to waves

Claims (4)

  1) Device for protecting a wall, in contact with a liquid, against rapid pressure fluctuations transmitted by this liquid characterized in that gas pockets, distributed over the entire surface of the wall to be protected, are created in this wall, on said wall or in the vicinity thereof, said gas pockets being in direct contact or via a flexible wall with the liquid 2) Device according to claim 1 characterized in that means for absorbing the mechanical energy of the oscillation movements of the gas pockets are implemented 3) Device according to claim 2 o means for absorbing energy   formed by perforated or porous plates that gas or liquid   must pass through the back and forth movements due to the oscillations of the gas pockets   4) Device according to one of claims 1 to 3 characterized in that   means are installed to inject gas into the pockets according to the invention) Device according to claim 4 o the gas injection means are constituted by pipes, one end of which opens into the pockets   gas according to the invention or under these gas pockets and the other ex-   tremity leads to a station where fixed or removable compressed gas