CA2057733A1 - Sound-damping material for underwater use - Google Patents
Sound-damping material for underwater useInfo
- Publication number
- CA2057733A1 CA2057733A1 CA 2057733 CA2057733A CA2057733A1 CA 2057733 A1 CA2057733 A1 CA 2057733A1 CA 2057733 CA2057733 CA 2057733 CA 2057733 A CA2057733 A CA 2057733A CA 2057733 A1 CA2057733 A1 CA 2057733A1
- Authority
- CA
- Canada
- Prior art keywords
- sound
- damping
- damping material
- material according
- plastic
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/162—Selection of materials
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
- B63G—OFFENSIVE OR DEFENSIVE ARRANGEMENTS ON VESSELS; MINE-LAYING; MINE-SWEEPING; SUBMARINES; AIRCRAFT CARRIERS
- B63G8/00—Underwater vessels, e.g. submarines; Equipment specially adapted therefor
- B63G8/28—Arrangement of offensive or defensive equipment
- B63G8/34—Camouflage
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F41—WEAPONS
- F41H—ARMOUR; ARMOURED TURRETS; ARMOURED OR ARMED VEHICLES; MEANS OF ATTACK OR DEFENCE, e.g. CAMOUFLAGE, IN GENERAL
- F41H3/00—Camouflage, i.e. means or methods for concealment or disguise
Landscapes
- Engineering & Computer Science (AREA)
- General Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Aviation & Aerospace Engineering (AREA)
- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Multimedia (AREA)
- Laminated Bodies (AREA)
- Soundproofing, Sound Blocking, And Sound Damping (AREA)
- Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
- Pharmaceuticals Containing Other Organic And Inorganic Compounds (AREA)
Abstract
Abstract A sound-damping material for underwater use includes a layer of solid material having a thickness of at least 1 cm and an open structure. The material has open alveole structures of 2-20 alveoles per centimeter which, in use, are filled with water. The front surface of the material is preferably structured with crests and troughs. A
reticulated polyurethane foam material is suitable for this purpose.
reticulated polyurethane foam material is suitable for this purpose.
Description
A Sound-Dampina Material ~or Underwater Use Underwater sound-damping material can be put to many uses. For example, such ma~erial can be used to elimi-nate disturbances in depth sounding processes, or as protection against acts of terrorism that are directed against pipelines and offshore rig~, for example~
Those frequencies whose damping is of interest in the present context lie between about 50 and 500 Khz, corre-sponding to wavelengths in water of about 3 mm-0.3 mm.
Sound is reflected back in the arrival direction of both objects which are lighter than water and objects which are heavier than water. A principle for damping of the reflexes is conceivable in an analogous method as by ant$reflex processing, where the front and rear surfaces of a coating reflect with mutually extingui hing phase angles. The reflection ability with this type of damping is highly dependent on frequency, however.
An ob~ect of the present invention is to provide a sound-absorbent material which will primarily provide a good effect within the frequency range of 75-300 Khz, prefera-bly up to S00 Hz. Thi~ object i8 achieved with a mate-rial constructed in accordance with the invention and having the characteristic features set forth in Claim 1.
In order to achieve a good sound-damping effect, par-ticularly at lower frequencies, preferably frequencies down to 50 Khz, it is also preferred to provide a pro-filed surface structure, e.g. of the "egg-carton typen, in accordance with Claim 5. Such surface structures are al60 advantageous at high frequencies.
Surprisingly good effects have been achieved with experi~
ments in which there was used a so-called reticulated foam, which is a material known as a packaging material, filter material, and also as a material used in the construction of loudspeakers. Such commercially avail-able, known material, is normally manufactured by deto-nating gas present in the cells of the material, or by removing the partition walls between adjacent cells.
Experiments have shown that a good absorption effect for water-filled structures cannot be achieved if the materi-al i8 too pliable. Thus, natural sponges provide a poor absorption effect. Carpets or mats which have a long pile in the sound direction also give a relatively poor result, as do also different skeleton-like structures which have penetrating openings or are otherwise trans-parent. The mechanism of damping can be seen to be a combination of internal friction in water which in the undulation is forced to take different paths, wherein the different paths taken confuse the phase pattern, and the internal friction of the dampening material itself. ~he latter effect is the most important. Therefore, the material must not only have structure of mutually con-nected cavities, ~ut also a proper propensity to absorb sonar energy. In order to achieve this, it is necessary for the plastic material to be near to its glass transi-tion temperature, and it is therefore for best effect neceasary to select the material differently if it is to be used in northern winter waters (temperatures near 0 ) and if it is to be used in tropical waters. As the glass transition temperature is also different for different frequencies, the choice of material must ha~e a glass transition temperature for frequencies of 50-500 Khz which is near the intended temperature of use.
Furthermore, the surface of the material is preferably structured, so as to obtain reduced reflection at primar-~ly progressively lower frequencie~. one preferred method of achieving this involves pas~ing a slab of compressible material through the roll nip of rolls which are provided with patterns of obtuse studs which leave in the nip a free centre plane in whicn a knife is ~ounted.
In this way, when the cut sheet leaves the roll nip and returns to its original form, the sheet is divided along two complementary surfaces of egg-carton configuration.
The distance between the top and the bottom of each surface i5 preferably between 10 and 30 mm. Optionally, the residual flat surfaces of slabs cut in this manner may be fa~tened to flat slabs of corre6ponding material.
When the material is to be used under water for long periods of time, the material is preferably coated with an antifouling substance of the kind u~ed in boat paints.
Example~ of such suDstances are organic tin compounds or copper powder.
Reticulated plastic foam materials may be produced from different plastics. The most common plastic~ at present, however, are the polyurethane plastics, e.g. polyester or polyether-based plastics, which react with i60cyanate in a hydroxyl terminated state. Because the polyether-based pla~tic is the more water-resistant of these plastics, it is the plastic that is preferred according to the present lnvention, even though experiments have shown that the polyester-based plastic is equivalent to the polyether-based plastic from the aspect of sound absorption.
The inventive material can be bent and cut in an appro-priate manner to cover objects of different shapes, e.g.
cylindrical, conical and spherical shapes, and can be glued or mechanically fastened to th~ surfaces of the objects concerned. The invention can therewith be ap-plied advantageously to objects having metal surfaces and objects made, e.g., of construction cellular plastic, or ~ore generally expressed materials which have a higher or a lower density than water.
It may also be suitable to saturate the material with a wetting agent or the like, so that its poor structures will be readily filled with water.
A large number of experiments have been made with various materials, which can be summarized as fOllows.
open, water-filled alveolar structures having 2-20 alve-oles per centimeter have been found to function best, while so-called reticular foam has been found to function best of all. Sonar experiments have shown that the material should not be transparent, although it can be slightly transparent. When damping frequencies in the range beneath 100 Khz, it is essential that the outer sur~ace of the material is structured, whereas the inter-nal structure is of greater significance when damping higher frequsncies.
Those materials which have been tested and found highly suitable, with respect to availability, are materials which are normally used in filters, and materials which are used in the manufacture of loudspeaker constructions and the like. Other available materials are fibreboard in which the fibres are mutually connected in a space system, or appropriately positioned stacks of expanded metal with slots which together form the alveolax struc-tures.
The invention will now be described in more detail with reference to an exemplifying embodiment thereof and also with reference to the accompanying drawings. Figure 1 is a sectioned view of an absorber having a surface struc-ture of the "egg-carton type"; and Figures 2-5 illustrate absorption curves obtained with different materials.
The slab of material illustrated in Figure 1 comprises reticulated foamed plastic which has been cut in the manner described in the introduction.
In the following Examples, damping of sound reflection at different frequencies has been measured for different slabs which have been mounted on slabs of hard cellular plastic with closed cellg (thickness 20 mm, density 200 kg/m3). The test equipment was immersed in water and the absorption material well saturated. The frequency is plotted in logarithmic scale along the X-axes of the Figures, while a damping scale is plotted along the Y-axes of said Figures, approximately normalized in Db.
Exam~le 1 (Figure 2) A plain, non-patterned slab having a thickness of 20 mm and produced from a material having 15-25 alveoles per inch in reticulated plastic foam. A very good damping effect was obtained at frequencies above 80 Khz, although damping was poorer at lower frequencies.
Example 2 CFigure 3~
A slab made of the same material as in Example 1 but with an "egg-carton structure", such that the slab had a smallest thickness of 15 mm and a largest thickness of 25 mm. The pattern-repeat of the surface structure was 60/90 mm of its manufactured length and breadth dimen-sions respectively (the tested slab was square). It will be seen from the graph that damping is the lowest fre-quency range is now greatly improved in comparison with damping achieved in Example 1.
E~ (Figu~e 4) A flat slab of reticulated plastic foam having an average of 60 aveoles per inch (alveole size about 0.4 mm). It will be seen from the graph that damping was not satis-factory.
Exam~le 4 (Fiau~Q ~) An egg-carton structured slab of reticulated foam plastic having an alveole size of 7-15 alveoles per inch (1.7-3.6 mm). The structure or pattern had a pattern-repeat of 60/90 mm.
As shown by the graph, qood absorption was obtained over the whole of the range.
These preferred reticular foams are polyurethane foam. A
summary of different test results shows that open, non-transparent alveolar structures function well at frequencies which exceed 100 Khz when the average size of the alveoles is greater than 0.5 mm, and prefera~ly greater than 1 mm, and smaller than 5 mm, and preferably smaller than 2.5 mm. The material should also have a surface structure or pattern having a pattern-repeat or the like of less than 100 mm, particularly for the lower frequencies.
Ths preferred reticulated foams commercially available at present ha~e a bulk density in a dry state of 26-32 kg/m3 in the case of Examples 1 and 2, and a bulk density of 20-24 kgJm3 in the case of Examples 3 and 4. The com-pre~sibility (compressibility with 40%~ in the former case is 2.6-3.6 and in the latter case 3.0-5.0 Kpa.
Among other materials that were tested can be mentioned non-woven PVC of corresponding thickness, which when flat exhibits good results (>6 Db over 100 Khz for a thickness of 15 mm), artificial turf ("Astro Turf") with usable results above 150 Khz, and 20 mm felt (needled and fullered), which gave poor absorption.
Those frequencies whose damping is of interest in the present context lie between about 50 and 500 Khz, corre-sponding to wavelengths in water of about 3 mm-0.3 mm.
Sound is reflected back in the arrival direction of both objects which are lighter than water and objects which are heavier than water. A principle for damping of the reflexes is conceivable in an analogous method as by ant$reflex processing, where the front and rear surfaces of a coating reflect with mutually extingui hing phase angles. The reflection ability with this type of damping is highly dependent on frequency, however.
An ob~ect of the present invention is to provide a sound-absorbent material which will primarily provide a good effect within the frequency range of 75-300 Khz, prefera-bly up to S00 Hz. Thi~ object i8 achieved with a mate-rial constructed in accordance with the invention and having the characteristic features set forth in Claim 1.
In order to achieve a good sound-damping effect, par-ticularly at lower frequencies, preferably frequencies down to 50 Khz, it is also preferred to provide a pro-filed surface structure, e.g. of the "egg-carton typen, in accordance with Claim 5. Such surface structures are al60 advantageous at high frequencies.
Surprisingly good effects have been achieved with experi~
ments in which there was used a so-called reticulated foam, which is a material known as a packaging material, filter material, and also as a material used in the construction of loudspeakers. Such commercially avail-able, known material, is normally manufactured by deto-nating gas present in the cells of the material, or by removing the partition walls between adjacent cells.
Experiments have shown that a good absorption effect for water-filled structures cannot be achieved if the materi-al i8 too pliable. Thus, natural sponges provide a poor absorption effect. Carpets or mats which have a long pile in the sound direction also give a relatively poor result, as do also different skeleton-like structures which have penetrating openings or are otherwise trans-parent. The mechanism of damping can be seen to be a combination of internal friction in water which in the undulation is forced to take different paths, wherein the different paths taken confuse the phase pattern, and the internal friction of the dampening material itself. ~he latter effect is the most important. Therefore, the material must not only have structure of mutually con-nected cavities, ~ut also a proper propensity to absorb sonar energy. In order to achieve this, it is necessary for the plastic material to be near to its glass transi-tion temperature, and it is therefore for best effect neceasary to select the material differently if it is to be used in northern winter waters (temperatures near 0 ) and if it is to be used in tropical waters. As the glass transition temperature is also different for different frequencies, the choice of material must ha~e a glass transition temperature for frequencies of 50-500 Khz which is near the intended temperature of use.
Furthermore, the surface of the material is preferably structured, so as to obtain reduced reflection at primar-~ly progressively lower frequencie~. one preferred method of achieving this involves pas~ing a slab of compressible material through the roll nip of rolls which are provided with patterns of obtuse studs which leave in the nip a free centre plane in whicn a knife is ~ounted.
In this way, when the cut sheet leaves the roll nip and returns to its original form, the sheet is divided along two complementary surfaces of egg-carton configuration.
The distance between the top and the bottom of each surface i5 preferably between 10 and 30 mm. Optionally, the residual flat surfaces of slabs cut in this manner may be fa~tened to flat slabs of corre6ponding material.
When the material is to be used under water for long periods of time, the material is preferably coated with an antifouling substance of the kind u~ed in boat paints.
Example~ of such suDstances are organic tin compounds or copper powder.
Reticulated plastic foam materials may be produced from different plastics. The most common plastic~ at present, however, are the polyurethane plastics, e.g. polyester or polyether-based plastics, which react with i60cyanate in a hydroxyl terminated state. Because the polyether-based pla~tic is the more water-resistant of these plastics, it is the plastic that is preferred according to the present lnvention, even though experiments have shown that the polyester-based plastic is equivalent to the polyether-based plastic from the aspect of sound absorption.
The inventive material can be bent and cut in an appro-priate manner to cover objects of different shapes, e.g.
cylindrical, conical and spherical shapes, and can be glued or mechanically fastened to th~ surfaces of the objects concerned. The invention can therewith be ap-plied advantageously to objects having metal surfaces and objects made, e.g., of construction cellular plastic, or ~ore generally expressed materials which have a higher or a lower density than water.
It may also be suitable to saturate the material with a wetting agent or the like, so that its poor structures will be readily filled with water.
A large number of experiments have been made with various materials, which can be summarized as fOllows.
open, water-filled alveolar structures having 2-20 alve-oles per centimeter have been found to function best, while so-called reticular foam has been found to function best of all. Sonar experiments have shown that the material should not be transparent, although it can be slightly transparent. When damping frequencies in the range beneath 100 Khz, it is essential that the outer sur~ace of the material is structured, whereas the inter-nal structure is of greater significance when damping higher frequsncies.
Those materials which have been tested and found highly suitable, with respect to availability, are materials which are normally used in filters, and materials which are used in the manufacture of loudspeaker constructions and the like. Other available materials are fibreboard in which the fibres are mutually connected in a space system, or appropriately positioned stacks of expanded metal with slots which together form the alveolax struc-tures.
The invention will now be described in more detail with reference to an exemplifying embodiment thereof and also with reference to the accompanying drawings. Figure 1 is a sectioned view of an absorber having a surface struc-ture of the "egg-carton type"; and Figures 2-5 illustrate absorption curves obtained with different materials.
The slab of material illustrated in Figure 1 comprises reticulated foamed plastic which has been cut in the manner described in the introduction.
In the following Examples, damping of sound reflection at different frequencies has been measured for different slabs which have been mounted on slabs of hard cellular plastic with closed cellg (thickness 20 mm, density 200 kg/m3). The test equipment was immersed in water and the absorption material well saturated. The frequency is plotted in logarithmic scale along the X-axes of the Figures, while a damping scale is plotted along the Y-axes of said Figures, approximately normalized in Db.
Exam~le 1 (Figure 2) A plain, non-patterned slab having a thickness of 20 mm and produced from a material having 15-25 alveoles per inch in reticulated plastic foam. A very good damping effect was obtained at frequencies above 80 Khz, although damping was poorer at lower frequencies.
Example 2 CFigure 3~
A slab made of the same material as in Example 1 but with an "egg-carton structure", such that the slab had a smallest thickness of 15 mm and a largest thickness of 25 mm. The pattern-repeat of the surface structure was 60/90 mm of its manufactured length and breadth dimen-sions respectively (the tested slab was square). It will be seen from the graph that damping is the lowest fre-quency range is now greatly improved in comparison with damping achieved in Example 1.
E~ (Figu~e 4) A flat slab of reticulated plastic foam having an average of 60 aveoles per inch (alveole size about 0.4 mm). It will be seen from the graph that damping was not satis-factory.
Exam~le 4 (Fiau~Q ~) An egg-carton structured slab of reticulated foam plastic having an alveole size of 7-15 alveoles per inch (1.7-3.6 mm). The structure or pattern had a pattern-repeat of 60/90 mm.
As shown by the graph, qood absorption was obtained over the whole of the range.
These preferred reticular foams are polyurethane foam. A
summary of different test results shows that open, non-transparent alveolar structures function well at frequencies which exceed 100 Khz when the average size of the alveoles is greater than 0.5 mm, and prefera~ly greater than 1 mm, and smaller than 5 mm, and preferably smaller than 2.5 mm. The material should also have a surface structure or pattern having a pattern-repeat or the like of less than 100 mm, particularly for the lower frequencies.
Ths preferred reticulated foams commercially available at present ha~e a bulk density in a dry state of 26-32 kg/m3 in the case of Examples 1 and 2, and a bulk density of 20-24 kgJm3 in the case of Examples 3 and 4. The com-pre~sibility (compressibility with 40%~ in the former case is 2.6-3.6 and in the latter case 3.0-5.0 Kpa.
Among other materials that were tested can be mentioned non-woven PVC of corresponding thickness, which when flat exhibits good results (>6 Db over 100 Khz for a thickness of 15 mm), artificial turf ("Astro Turf") with usable results above 150 Khz, and 20 mm felt (needled and fullered), which gave poor absorption.
Claims (11)
1. A sound-damping material for underwater use, c h a r a c t e r i z e d by a layer of an open struc-ture of solid material which presents open alveole struc-tures having 2-20 alveoles per cm which are intended, in use, to be filled with water, said layer having a thick-ness of at least 1 cm, and being a plastic material having a glass transition temperature for frequencies of 50-500 Khz which is near to a temperature of use.
2. A sound-damping material according to Claim 1, c h a r a c t e r i z e d in that the layer includes an open-cell cellular plastic.
3. A sound-damping material according to Claim 2, c h a r a c t e r i z e d in that the cellular plastic is a reticulated-type plastic.
4. A sound-damping material according to Claim 3, c h a r a c t e r i z e d in that the material in the cellular plastic is a polyurethane-type material.
5. A sound-damping material according to Claim 4, c h a r a c t e r i z e d in that the polyurethane material is a polyether-type material
6. A sound-damping material according to Claim 4, c h a r a c t e r i z e d in that the polyurethane material is a polyester-type material.
7. A sound-damping material according to Claim 1, c h a r a c t e r i z e d in that the layer is substan-tially non-transparent.
8. A sound-damping material according to Claim 1, c h a r a c t e r i z e d in that the material has an undulating structure on one side thereof.
9. A sound-damping material according to Claim 5, c h a r a c t e r i z e d in that the structure has a thickness of from between 10 and 40 mm calculated between the crests and troughs of said undulations.
10. A sound-damping material according to Claim 5, c h a r a c t e r i z e d in that it is composed of a flat material and a surface structured material affixed to said flat material.
11. A sound-damping material according to Claim 1, c h a r a c t e r i z e d in that when dry and not filled with water, said solid material has a modulus of elasticity such that compression of the material to 40%
in a dry state requires a pressure of 2-6 Kpa.
in a dry state requires a pressure of 2-6 Kpa.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE9000794A SE500795C2 (en) | 1990-03-06 | 1990-03-06 | Sound absorbing material for underwater use |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2057733A1 true CA2057733A1 (en) | 1993-06-17 |
Family
ID=20378780
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2057733 Abandoned CA2057733A1 (en) | 1990-03-06 | 1991-12-16 | Sound-damping material for underwater use |
Country Status (5)
| Country | Link |
|---|---|
| CA (1) | CA2057733A1 (en) |
| DE (1) | DE4200773A1 (en) |
| FR (1) | FR2686725A1 (en) |
| GB (1) | GB2263281A (en) |
| SE (1) | SE500795C2 (en) |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1088671A (en) * | 1963-09-21 | 1967-10-25 | Bostik Ltd | Improvements in or relating to sound-deadening material |
| FR2528474A1 (en) * | 1982-06-14 | 1983-12-16 | Fabrikant Luc | Cutting cellular board into acoustic absorption panels - using lateral slicing to produce two or more panels simultaneously |
| ATE67038T1 (en) * | 1982-06-15 | 1991-09-15 | Raychem Corp | SONAR SYSTEM CONTAINING HIGH DAMPING POLYMER COMPOUNDS. |
| US4584232A (en) * | 1983-01-20 | 1986-04-22 | Illbruck Gmbh Schaumstofftechnik | Foam material sound absorption |
| GB2167425B (en) * | 1984-09-22 | 1988-04-27 | Wardle Storeys Plc | Vibration damping and sound insulation materials |
-
1990
- 1990-03-06 SE SE9000794A patent/SE500795C2/en not_active IP Right Cessation
-
1991
- 1991-12-16 CA CA 2057733 patent/CA2057733A1/en not_active Abandoned
-
1992
- 1992-01-13 GB GB9200602A patent/GB2263281A/en not_active Withdrawn
- 1992-01-15 DE DE19924200773 patent/DE4200773A1/en not_active Withdrawn
- 1992-01-24 FR FR9200756A patent/FR2686725A1/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| FR2686725A1 (en) | 1993-07-30 |
| SE9000794D0 (en) | 1990-03-06 |
| SE500795C2 (en) | 1994-09-05 |
| SE9000794L (en) | 1991-09-07 |
| GB2263281A (en) | 1993-07-21 |
| GB9200602D0 (en) | 1992-03-11 |
| DE4200773A1 (en) | 1993-07-22 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |