JPS63242529A - Underwater sound absorber - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention is directed to an underwater sound absorber that is attached to the surface of an underwater structure and used to absorb and attenuate sounds from inside and outside. do.

(Prior art) As a conventional underwater sound absorber of this type, for example,
There is one shown in Japanese Patent No. 55859.

This conventional underwater sound absorber is made by sequentially laminating a surface protective layer made of chloroprene rubber (CR) or the like, a sound absorbing layer made of a plurality of laminated rubber elastic plates having recesses on one side or cavities inside, and an adhesive layer. It is composed of

(Point to be solved by the invention) In such an underwater sound absorber, since the sound absorbing layer has a recess or a cavity, as shown by line a in FIG.
It has a good sound absorption effect for sound sources with frequencies exceeding 0KH2 (kilohertz).

However, there is a problem in that the sound absorption effect is drastically reduced for sound sources in the fisI frequency range of 30 KHz or less.

Therefore, the present invention was made in order to solve such conventional problems, and an object of the present invention is to provide an underwater sound absorber that can exhibit a good sound absorbing effect even for sound sources in the frequency range of 30 KHz or less. shall be.

[Structure of the Invention] (Means for Solving the Problems) The underwater sound absorbing body of the present invention comprises: - a sound absorbing layer formed by laminating a plurality of rubber-like viscoelastic bodies each having a concave portion or a cavity inside; and this sound absorbing layer. The underwater sound absorber is provided with a surface protective layer covering the outer surface of the underwater sound absorber, characterized in that an extremely soft and highly attenuating gel-like substance is sealed in the recess or cavity.

The gel-like substance is sealed in all four parts of the sound-absorbing layer and in all or part of the cavity, but in some cases, it is better to seal it on the side closer to the sound source of absorption*N to reduce the reflection of sound by the air inside the cavity. This is preferable because it can be suppressed.

The gel-like substance used in the present invention has a penetration rate (JIS K 2530-1976), which indicates hardness, of 60 to 200 at room temperature, and a mechanical loss coefficient (tan δ), which indicates rebound resilience, of 0. There are 5 or more silicone gels. For example, "Industrial Materials" Vol. 35 No. 2, No. 6
Silicone GEL shown on pages 7 to 71 has a substantially uniform sound absorbing effect on sound sources with a wide range of frequencies, and is therefore suitable.

The gel-like substance is a metal powder such as lead, iron, or aluminum, or a metal oxide such as iron oxide or alumina, or a microballoon such as a glass microballoon or an organic microballoon, and is in the form of particles with a particle size of 50 μml to 2-2. Alternatively, it may contain a hollow filler.Such a filler is agitated by the incidence of sound waves in the silicone gel and absorbs sound by friction with the sound-absorbing layer, so it exhibits an even greater sound-absorbing effect. do. It is also desirable to use fillers with different particle sizes as appropriate depending on the frequency range of the sound you want to absorb.

In addition to rubber with low acoustic reflectance and high acoustic transmittance such as CH, the surface protective layer used in the present invention is made of FRP (fiber reinforced plastic) with high rigidity and acoustic impedance close to that of water. Good too.

Further, as the elastic body forming the sound absorption layer, CR is used.

There are acrylonitrile-butadiene rubber (NBR), natural rubber, polyurethane, etc., but CR is preferable from the viewpoint of manufacturing processability, weather resistance, etc.

The ratio of recesses and cavities in the sound absorber (porosity of the entire sound absorber) is preferably 2 to 20%, particularly preferably 3 to 10%. This is because if the porosity is less than 2%, the sound absorption coefficient will be low, and if it exceeds 20%, the sound absorption coefficient will decrease due to increased reflection in the sound absorption layer, and the mechanical strength will also tend to decrease.

(Function) In the present invention, a damping effect is produced by the dispersion and differentiation of sound waves by the gel-like substance within the sound absorption layer.

As a result, it exhibits an excellent sound absorption effect even for sound sources in the frequency range of 30 KH2 or less.

(Example) Examples of the present invention will be described below.

FIG. 1 and FIG. 2 show one embodiment of the present invention and fl!, respectively. ! It is a figure showing an example of. In these figures, common parts are given the same reference numerals.

In Fig. 1, reference numeral 1 indicates a surface protective layer, 2 indicates a sound absorbing layer made of laminated rubber-like viscoelastic materials, 3 indicates an adhesive layer, 4 indicates an adherend, and 5 indicates a cavity provided in a sound absorbing layer N2. The resulting gel-like substances are shown in each figure. This gel-like material M5 has a penetration degree (JIS K2530-1976) of 60 at room temperature.
~200, and a mechanical loss coefficient (tan δ) of 1.0 or more.

Note that this silicone gel may contain metal powders such as lead, iron, aluminum, etc., metal oxides such as iron oxide, alumina, etc., or microballoons such as glass microballoons, organic microballoons, etc. with a particle size of 50.
Particulate or hollow fillers of 11Im to 211II are contained.

The surface protection layer 1 is made of CR rubber with a hardness of 45° (JIS). The sound absorbing Fj2 is made by laminating a total of four layers of two types of rubber-like viscoelastic bodies 2a and 2b.

One rubber-like viscoelastic body 2a is provided with a dome-shaped cavity. jli! The rubber-like viscoelastic body 2b is provided with dome-shaped cavities and cylindrical cavities alternately. The materials of these rubber-like viscoelastic bodies 2a and 2b both have a hardness of 6.
It has a CR of 3°.

The adhesive N3 is made of CR having the same hardness as the sound absorbing layer material. The sound absorber M2 is bonded to an adherend 4 (mainly an underwater structure to be attached) via this adhesive layer 3.

Another embodiment will be explained with reference to FIG.

In the figure, the sound absorbing FJ2 is formed by alternately laminating a rubber-like viscoelastic body having a plurality of cylindrical cavities and a non-porous rubber-like viscoelastic body. The surface protection 11JI, in which silicone gel is sealed in the cavity of the sound absorbing layer 2, is made of FRP, such as epoxy resin 11FR'P or polyester resin UFRP, which is highly rigid and has an acoustic impedance close to that of water.

According to the underwater sound absorber of this embodiment, the surface can be maintained! By constructing the ill from FRP with high rigidity and acoustic impedance close to that of water, the sound absorption layer 2 is prevented from deforming under water pressure, and furthermore, the incident sound is guided to the sound absorption FJ2 without being reflected, which allows it to be used even under higher water pressure. It also shows excellent sound absorption effects against sound sources in the low frequency range.

FIG. 3 is a diagram showing still another embodiment. In the figure, the sound absorbing layer 2 is one layer, and the silicone gel 5 is the sound absorbing layer 2.
The sound absorber is particularly flexible when enclosed within a relatively thin rubber section provided in the housing.

FIG. 4 is a diagram showing actual measured values of the sound absorption characteristics of the conventional example and each embodiment of the present invention. In this figure, the a-line is the characteristic of the conventional underwater sound absorber described above, and the b-line and C-line are the case where no filler is contained in the gel-like substance and the case where no filler is included in the gel material in the embodiment shown in FIG. 1 or 2, respectively. The characteristics of each underwater sound absorber when it contains are shown below.

From line b and line C in the same figure, the underwater sound absorber of the present invention has a temperature of 30K.
It is clear that it exhibits an excellent sound absorption effect even for sound sources in the low frequency range below H2.

[Effects of the Invention] As explained above, according to the underwater sound absorber of the present invention, extremely soft and highly attenuating gel-like f is provided in the four parts of the sound absorbing layer or in the air conditioner.
By enclosing IJJ quality, it exhibits an excellent sound absorption effect not only for sound sources of 112 or more in 30 but also over a wide R-circuit frequency range below that.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing one embodiment of the underwater sound absorber according to the present invention, FIGS. 2 and 3 are longitudinal sectional views showing other embodiments of the present invention, and FIG. FIG. 3 is a diagram showing each sound absorption characteristic of an underwater sound absorber. Reference numeral 1 indicates a surface protection layer 11Fj, 2 indicates a sound absorbing layer, 2a and 2b indicate a rubber-like viscoelastic body, and 5 indicates a gel-like substance. Figure 1 Figure 2 Figure 3

Claims (4)

[Claims] (1) In an underwater sound absorber comprising a sound absorbing layer formed by laminating a plurality of rubber-like viscoelastic bodies having recesses or cavities on one surface and a surface protective layer covering the outer surface of the sound absorbing layer, the recesses or An underwater sound absorber characterized by having an extremely soft and highly attenuating gel-like substance sealed in a cavity. (2) The gel-like substance has a penetration degree (JIS K 2530
-1976) is 60 to 200, and the underwater sound absorber according to claim 1, which is a silicone gel having a mechanical loss coefficient (tan δ) of 0.5 or more. (3) The gel-like substance is a metal powder such as lead, iron, or aluminum, or a metal oxide such as iron oxide or alumina, or a microballoon such as a glass microballoon or an organic microballoon, and has a particle size of 50 μm to 2 mm. The underwater sound absorber according to claim 1 or 2, which contains a hollow or hollow filler. (4) The surface protective layer is made of FRP (fiber reinforced plastic) which has high rigidity and has an acoustic impedance close to that of water.
Underwater sound absorber as described in section.