JPH05273986A - Silencer for underwater use - Google Patents

Abstract

PURPOSE: To obtain a silencer having a good effect in a prescribed frequency range by providing the silencer with a layer of an open structure of a solid material consisting of a plastic material and having an open cellular structure having cells. CONSTITUTION: This silencer is designed to be filled with water at the time of use. The layer consists of the plastic material having at least 1cm thickness and having a frequency of a glass transition temp. of 50 to 500kHz near the service temp. The layer is composed of the cellular structure having the cells of 2 to 20 pieces per 1cm which are opened and are filled with the water. More preferably the layer contains cellular plastic of open cells. This cellular plastic is preferably network plastic. Polyurethane plastic is most general as a network plastic foam material; such plastic is polyether or polyester plastic. The polyether plastic is adequate in terms of water resistance.

Description

Detailed Description of the Invention

Underwater sound deadening materials have many applications. For example, such materials can be used to remove obstructions in acoustic sounding or to defend against acts of terrorism directed at pipelines and offshore oil refineries.

The frequencies at which silencing is desired are in this context approximately 50 to 500 kilohertz and 3 to 0.3 millimeters for wavelengths in water. Sound is reflected from both lighter and heavier water bodies toward the arrival method. The principle of silencing reflections can be considered by a method similar to the anti-reflection method, in which the front and back surfaces of the coating reflect at mutually canceling phase angles. However, the reflectivity of this type of silencing is highly frequency dependent.

The object of the present invention is mainly to obtain a sound deadening material with good effect in the frequency range from 75 to 300 kilohertz, preferably up to 500 hertz. This object is achieved according to the invention by a material constructed with the features specified in claim 1.

At a particularly low frequency in order to achieve a good silencing effect, preferably below 50 kHz, it is also according to claim 5, ie an "egg box".
It is preferable to provide a surface structure with a contoured shape. Such surface structures are also advantageous at high frequencies.

Surprisingly good results have been achieved by experiments using what are known as reticulated foams, known as packaging materials, filtering materials and also used in the construction of loudspeakers. Such known commercially available materials are usually made by the explosive gas present within the cells of the material or by removing the septum between adjacent cells.

Experiments have shown that if the material is too soft, a water-filled structure will not have a good absorption effect. Thus, natural sponges have a low absorption effect. Carpets and mats with long piles in the acoustic direction also give relatively poor results, as well as various skeletal structures with through openings or otherwise clear eyes. It is considered that the sound deadening mechanism is due to the combination of internal friction in water that takes various paths in the undulation, and the various paths are confused with the phase pattern and also confused with the internal friction of the sound deadening material itself. To be done. The latter effect is the most important. But the material doesn't have to be just interconnected cavities,
Any material having a proper tendency to absorb acoustic energy may be used. In order to achieve this, it is necessary to choose the material for the plastic material depending on whether it is used in northern winter seawater (around zero temperature) or in tropical seawater. The glass transition temperature is also different for different frequencies, so the choice of material is close to the planned operating temperature, from 50 kHz to 500.
It must be done for the glass transition temperature for kilohertz.

Furthermore, the surface of the material is preferably constructed so as to keep the reflection low, mainly at low frequencies. One preferred way to reach this involves passing a slab of compressible material through the nip point of a roller with an obtuse stiletto pattern that leaves a free center plane in which the knife is installed in the nip. There is. When the sheet cut by this method leaves the roller nip and returns to its original shape, the sheet is split along two complementary surfaces in the shape of an egg box. The distance between the top and bottom of each surface is preferably between 10 and 30 millimeters. Optionally, the residual plane of the plank is cut in this manner and attached to a flat plank of matching material.

When the material is used for a long time in water, it is preferably coated with an antifouling substance of the type used as boat paint. Examples of such substances are organotin compounds or copper powder.

Reticulated plastic foam materials are made from a variety of plastics. The most common plastics today are polyurethane plastics, that is polyester or polyether based plastics, which react with isocyanates in the hydroxyl end group state. Polyether plastics are preferred plastics for this invention because they are more water resistant than these plastics, and experiments have shown that polyester plastics are comparable to polyether plastics in terms of sound absorption.

The material according to the invention can be bent and cut in a suitable manner to cover objects of various shapes, ie cylindrical, conical and spherical, and adhere to the surfaces of the objects concerned. It can be attached mechanically. The present invention may be advantageously applied to objects having a metallic surface, and objects made of cellular plastic structures, or even materials made more densely or less densely than water, which is more commonly specified.

It is also possible to suitably saturate with a surfactant or the like so that the poor structure of the material is easily filled with water.

A number of tests have been conducted on various materials, as summarized below.

Open, water-filled, vacuolar structures with 2 to 20 cells per centimeter have been found to work best, especially those called reticulated foams of all. It has been found to work well, acoustic tests have found that the material should not be transparent, but may be slightly transparent. At sound absorption frequencies below 100 kilohertz it is very important that the outer surface of the material is textured, while the internal structure is of great importance in silencing higher frequencies.

The materials tested and determined to be very suitable for practical use were those commonly used in filters and those used in loudspeaker construction and the like. Other practicable materials are appropriately arranged fiberboards interconnected in a spatial system or expanded metal stacks with elongated eyelets that together form a cell structure.

The present invention will be described in more detail with reference to embodiments by way of example and the accompanying drawings.

FIG. 1 shows a cross-sectional view of an absorbent material having a "chicken egg box-shaped" surface structure.

FIG. 2 is a diagram showing a sound absorption curve obtained for a certain sound deadening material.

FIG. 3 is a diagram showing a sound absorption curve obtained for a similar sound deadening material.

FIG. 4 is a diagram showing a sound absorption curve obtained for a similar sound deadening material.

FIG. 5 is a diagram showing a sound absorption curve obtained for a similar sound deadening material.

The slab of material shown in FIG. 1 consists of reticulated foam plastic cut by the procedure described in the introduction.

In the examples below, sound-rejection silencing at various frequencies was measured for rigid cellular plastic slabs with enclosed cells (thickness 20 mm, density 200 Kg / m ³ ). The measuring instrument was submerged in water and the sound absorbing material was well saturated. Frequencies were plotted on a logarithmic scale along the X-axis of the figure and silencing scales were approximately normalized in decibels along the Y-axis of the figure and plotted approximately normalized.

Example 1 (FIG. 2) A flat, textured plank made of reticulated plastic foam material having a thickness of 20 millimeters and having 15 to 25 cells per inch, very A good silencing effect was obtained in the frequency range of 80 kHz or higher, but the silencing property was poor in the low frequency range.

Example 2 (FIG. 3) A slab made of the same material as Example 1 but having a "egg box structure" with a minimum thickness of 15 mm and a maximum thickness of 25 mm. The surface structure has a repeating pattern of 60 for each of the manufactured length and width dimensions.
/ 90 millimeters (measured slab is square). From the graph it will be seen that the silencing in the lowest frequency range is significantly improved compared to the silencing achieved in FIG.

Example 3 (FIG. 4) An average of 60 air bubbles per inch (the air bubble size is about 0.4).
Flat slab of reticulated plastic foam with millimeters. The muffling is judged to be unsatisfactory.

Example 4 (FIG. 5) Vesicles having a cell size of 7 to 15 per inch (1.
7 to 3.6 mm) reticulated foam plastic egg structure planks. Structure or pattern is 60/90
Has a repeating pattern of millimeters.

As shown in the graph, good sound absorption was obtained over the entire area.

These preferred reticulated foams were polyurethane foams. The various test results are open, and the structure of the air cells that is not transparent has an average size of the air cells of 0.
100 if greater than 3 mm mail, preferably greater than 1 mm, less than 5 mm, and more preferably less than 2.5 mm.
It has been shown to work well in the frequency range above kilohertz. The material is more particularly 10 for low frequencies
It should have a surface structure or texture with a repeating texture of 0 mm or less or the like.

The preferred reticulated foams have a volume density of 26 to 36 Kg / m ³ in the dry state in the cases of Examples 1 and 2 and are currently commercially available and in the cases of Examples 3 and 4 Is 20 to 24 Kg / m ³ . The compression ratio (compression ratio of 40%) is 2.
6 to 3.6 kPa, and in the latter 3.0 to 5.0 kPa.

Other materials tested were described as follows:
PVC non-woven fabrics of matching thickness show good results when flat (more than 6 decibels above 100 kilohertz for a thickness of 15 mm) and artificial grass ("Astroturf") can be used above 150 kilohertz. The results are shown, the 20 mm felt (needle punched and brushed) showed poor sound absorption.

[Brief description of drawings]

FIG. 1 shows a cross-section of an absorbent material having a “chicken egg box” shaped surface structure.

FIG. 2 is a diagram showing a sound absorption curve obtained for the sound deadening material of one example.

FIG. 3 is a diagram showing a sound absorption curve obtained for a sound deadening material of another example.

FIG. 4 is a diagram showing a sound absorption curve obtained for a sound deadening material of still another example.

FIG. 5 is a diagram showing a sound absorption curve obtained for a sound deadening material of still another example.

Claims (11)

[Claims] 1. A plastic material intended to be filled with water in use, the layer having a thickness of at least 1 centimeter and having a frequency of the glass transition temperature of 50 to 500 kilohertz near the temperature of use. A sound deadening material for underwater use characterized by an open-structured layer of solid material exhibiting an open-air structure with 2 to 20 air-holes per centimeter consisting of. 2. The sound deadening material of claim 1, wherein the layer comprises open cell cytoplasmic plastic. 3. The sound deadening material according to claim 2, wherein the cytoplasmic plastic is a reticulated type plastic. 4. The sound deadening material according to claim 3, wherein the material of the cytoplasmic plastic is a polyurethane type material. 5. The sound deadening material according to claim 4, wherein the polyurethane material is a polyether type material. 6. The sound deadening material according to claim 4, wherein the polyurethane material is a polyester type material. 7. The sound deadening material according to claim 1, wherein the layer is substantially opaque. 8. The sound deadening material according to claim 1, wherein the material has an undulating structure on one side thereof. 9. The sound deadening material of claim 5, wherein the structure has a thickness calculated between the top and bottom of the undulations of between 10 and 40 millimeters. 10. The sound deadening material according to claim 5, wherein the sound deadening material is composed of a planar material and a material that textures a surface attached to the planar material. 11. The solid material, when dry and not filled with water, has a modulus of elasticity such that it requires a pressure of 2 to 6 kilopascals to compress the material 40 percent in the dry state. The sound deadening material according to claim 1.