AU661128B2 - Vibration isolation module - Google Patents

Description

S F Ref: 236194

AUSTRALIA

PATENTS ACT 19906 2 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: Australia Sonar Systems Pty Ltd Innovation House West First Avenue Technology Park South Australia 5095

AUSTRALIA

Mark Adkins, Allan Lloyd Carpenter Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Nales, 2000, Australia Vibration Isolation Module ASSOCIATED PROVISIONAL APPLICATION DETAILS [31] Application No(s) [33] Country PL2301 AU [32] Application Date 8 May 1992 The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5815/3 -2- BACKGROUND OF THE INVENTION This invention relates to the construction of Vibration Isolation Modules (VIMs) which are typically used either side of an acoustic aperture of a towed acoustic array to minimise performance degradation due to transmitted mechanical vibrations.

Conventional towed arrays have consisted of a towing cable (negatively buoyant to achieve submersion to the required depit), forward Vibration Isolation Modules (to minimise the transmission of mechanical vibration from the tow cable to the acoustic array), an array of acoustic (and non-acoustic) sensors, and an aft VIM (to minimise transmission of vibration from the "flapping tail" forward to the acoustic array). To perform the required vibration isolation functions, the VIMs, like the suspension of a motor vehicle must not only provide elastic isolation (the spring function) but must also dissipate the produded vibrational energy (the damping function).

In the past, VIMs have been constructed that have provided adequate elasticity, albeit for a limited rarge of tow loads and limited damping; their effectiveness has been limited, and restricted S- 20 to a narrow range of operating conditions.

20 BRIEF SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a :Vibration Isolation Module (VIM) which will overcome or at least reduce the limitations of current art.

Accordingly, the invention provides a Vibration Isolation Module 25 for minimising the transmission of mechanical vibrations in a towed :underwater structure, the Vibration Isolation Module having two "posite ends, and comprising: first and second attachment means located at said two opposite ends, respectively, for attachment to respective parts of the towed underwater structure, spring means 30 located between the first and second attachment means for providing vibration isolation between the first and second attachment means, visco-elastic damping means located between the first and second attachment means for attenuating the transmission of low frequency vibrations between the first and second attachment means, and viscous damping means located between the first and second attachment means for attenuating the transmission of high frequency vibrations between the first and second attachment means.

1061E -3r or o oo

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r o Preferably, the Vibration Isolation Module further comprises: a fluid-tight container which defines a fluid-tight enclosure and surrounds said spring means, said visco-elastic damping means and said viscous damping means; and a low density, high viscosity fluid filling the enclosure.

Desirably, the Vibration Isolation Module further comprises a plurality of masses and a number of elongate elastic members, said masses being spaced apart within said fluid-tight enclosure so as to divide said fluid-tight enclosure into a number of sub-enclosures, and said masses being connected together by said elongate elastic members.

The invention achieves the three desirable performance aspects of spring-mass isolation, viscous damping and visco-elastic damping.

Thus, the measures here proposed increase both the elastic isolation and the damping, and significantly extend the operating range of both tow speeds and vibrational frequency over which the VIM will provide effective operation.

BRIEF DESCRIPTION OF THE DRANINGS Two embodiments of the invention will now be described, by way of example, with reference to the drawings, in which Figure 1 schematically illustrate) the 'classical' implementation of the invention, and shows a longitudinal cross-section through one end of a Vibration Isolation Module; and Figure 2 schematically illustrates an alternative embodiment, in which the 'classical' viscous damping is re'laced by a more cost effective solution.

DETAILED DESCRIPTION As shown in Figure 1, one aspect of the preferred embodiment involves the provision of cylindrical masses 1 atcached at regular spacing to a central core of visco-elastic damping material 2, which may be extruded over a snubbed elastic strength member 3. A snubbed elastic strength member is an elastic strength member which is prevented from stretching beyond a certain predetermined length.

Normally such "snubbing" is achieved by providing a nonelastic strength member, of slightly greater length than the elastic strength member, alongside the elastic strength member so as to prevent the elastic strength member from extending to a length which exceeds the length of the nonelastic strength member. Further snubbed elastic strength members 4 may be attached around the outer diameter of the masses 1.

LI IL, r /1061E rE 141 -4o r e r Viscous 'dash-pot' type dampers 5 are installed within the masses 1.

The viscous 'dash-pot' type dampers 5 are formed by apertures which pass through at least some of the masses 1. The interior of the Vibration Isolation Module is filled with a low density, high viscosity fluid 11 which, during use of the Vibration Isolation Module, passes through the apertures in order to produce viscous damping.

The space between the masses 1 is filled with open cell plastic foam spacers 6, around which is wrapped a layer of power and data cables 7. A jacket of damped thermoplastic 8 is extruded over this cable layer 7 and caps 9 containing a fluid filling valve 10 are attached at each end of the module, for filling the interior of the Vibration Isolation Module with the low density, high viscosity fluid 11. The caps 9 are also shaped so as to provide attachment points for attaching the Vibration Isolation Module to an acoustic array.

In the repetitive cyclic extension, the multiple spring mass system as obtained provides vibration isolation, the cyclic distortion of the visco-elastic core provides low frequency damping, and the repetitive transfer of the high viscosity fluid 11 through the apertures in the masses 1 provides the high frequency damping.

In an alternative preferred embodiment, shown in Figure 2, the general arrangement of the Vibration Isolation Module is as before, except that the 'dash-pot' type dampers (item 5 of Figure 1) are removed. In their place is a braided flexible, open-weave stocking 12 25 which surrounds the open cell foam spacers 6, and is clamped to the central core 2 by the masses 1. Under repetitive cyclic extension the braided stocking 12 pulls down, compressing the foam spacers 5 and forcing fluid out through the foam pores. This action simulates that of the classic dash-pot damper action of the first embodiment, and hence provides the required viscous damping: it is however, a much more cost-effective implementation. It should be noted that, in Figure 2, although the foam spacer 6 is shown, for consistency with Figure 1, in an uncompressed configuration, the stocking 12 is shown in its pulled down position.

The foregoing describes only some aspects of an embodiment of the present invention, and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention. ,:2 r'h/161

Claims (12)

1. A Vibration Isolation Module for minimising the transmission of mechanical vibrations in a towed underwater structure, the Vibration isolation Module having two opposite ends, and comprising: first and second attachment means located at said two opposite ends, respectively, for attachment to respective parts of the towed underwater structure, spring means located between the first and second attachment means for providing vibration isolation between the first and second attachment means, visco-elastic damping means located between the first and second attachment means for attenuating the transmission of low frequency vibrations between the first and second attachment means, and viscous damping means located between the first and second attachment means for attenuating the -ransmission of high frequency vibrations between the first and second attachment means.

2. A Vibration Isolation Module according to claim 1, wherein said visco-elastic damping means comprises a central core of visco-elastic damping material.

3. A Vibration Isolation Module according to claim 1 or 2, further comprising: a fluid-tight container which defines a fluid-tight enclosure and surrounds said spring means, said visco-elastic damping means and said viscous damping means; and a low density, high viscosity fluid filling the fluid-tight enclosure.

4. A Vibration Isolation Module according to claim 3, wherein said fluid-tight container comprises an elongate jacket having two opposite ends which define two openings, and two end caps attached to said two ends so as to cover said two openings respectively.

A Vibration Isolation Module according to claim 4, further comprising power and data cables, wherein said power and data cables run spirally within said jacket.

6. A Vibration Isolation Module according to any one of claims 3 to 5, which further comprises a plurality of masses and a number of elongate elastic members, said masses being spaced apart within said fluid-tight enclosure so as to divide said fluid-tight enclosure into a number of sub-enclosures, and said masses being connected together by said elongate elastic members. -6-

7. A Vibration Isolation Module according to claim 6, wherein said masses are cylindrical in shape.

8. A Vibration Isolation Module according to claim 6 or 7, which further comprises a plurality of elongate nonelastic strength members of greater length than said elongate elastic members, said elongate nonelastic strength members being arranged parallel with, and alongside, said elongate elastic members so as to prevent extension of the elongate elastic members to a length which exceeds the length of said elongate nonelastic strength members, thus effectively snubbing extension of the elongate elastic members.

9. A Vibration Isolation Module according to any one of claims 6 to 8, wherein at least some of said masses define apertures which pass through said at least some of said masses so as to provide a path between adjacent sub-enclosures for said high visocity fluid, and wherein, in use, passage of said high viscosity fluid through said apertures produces viscous damping, said apertures and said high viscosity fluid together forming said viscous damping means.

A Vibration Isolation Module according to any one of S,,claims 6 to 9, further comprising a plurality of open cell foam spacers filling said sub-enclosures.

11. A Vibration Isolation Module according to claim 10, when also ultimately dependent on claim 2, wherein said viscous damping means comprises a braided, open-weave stocking surrounding said open cell foam spacers, said stocking being attached to said central core of visco-elastic damping material at the locations of said masses.

12. A Vibration Isolation Module substantially as hereinbefore described with reference to Figure 1 or 2 of the accompanying drawings. DATED this FIFTH day of MAY 1995 Australia Sonar Systemt Pty Ltd Patent Attorneys for the Applicant SPRUSON FERGUSON Vibration Isolation Module ABSTRACT A Vibration Isolation Module (VIM) for a towed acoustic streamer includes cylindrical masses attached at regular spacing to a central core of viscoelastic damping material which may be extruded over a snubbed elastic strength member Further snubbed elastic strength members may be attached around the outer diameter of the masses Viscous 'dash-pot' type dampers are installed within the masses The space between the masses is filled with open cell plastic foam around which is wrapped a layer of power and data cables A jacket of damped thermoplastic is extruded over this cable layer and caps containing a fluid filling valve are attached at each end of the module, and the interior void is filled with a low density, high viscosity fluid (11). Figure 1 S Iiii* rhk/0664E