Abstract:
A system for maintaining a spaced relationship between two energetic sources is disclosed, which system including in a preferred embodiment a clamping mechanism securable to the energetic sources, a spacing system disposed between these sources, a pivot mechanism coupled to the spacing system and pivotally engageable to the clamping mechanism, and a shock absorption system coupled to the spacing mechanism and adapted to resiliently deform.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a means to maintain the position of two or more energetically moveable objects in a spaced relation vis-a-vis each other. More specifically, the present invention in a preferred embodiment relates to a system to maintain two marine seismic sources in a preferred, spaced orientation during continuous operation. 
     2. Description of the Prior Art 
     Marine seismic exploration often utilizes seismic sources, airguns or waterguns, pulled behind a boat over submarine horizons of perceived interest. Upon actuation, these sources create a strong, primary pressure pulse which is useful in interpreting the strata comprising the sea floor. 
     To enhance this primary pulse, and hence advance the geological interpretation of the sea floor, it has become common practice to simultaneously fire a number of these seismic sources. In this connection, it has been discovered that marine seismic sources selectively positioned with respect to each other optimize the creation of the primary pulse while minimizing the creation of undesired secondary pulses. This optimization, generally known as the &#34;cluster effect,&#34; relics on spacing between the sources given the parameters of volume, pressure, and depth. 
     In practice, however, realization of the benefits of the &#34;cluster effect&#34; has been difficult since seismic sources, due to the strong energy pulses created during actuation and recoil, are prone to substantial and energetic movements with respect to each other. Furthermore, the air bubbles created upon actuation of the marine acoustic generator ultimately collapses, forcing the sources together and thereby inducing significant damage on the gun lines and peripheral equipment. 
     Prior mechanical clamping systems have been designed to address this issue. Such clamping systems, however, if strong enough to prevent substantial movement of the sources with respect to each other, have generally been bulky and contribute to substantial drag on the towing source. In some instances, this drag may be of a sufficient magnitude as to foreclose their use as a towed array altogether. 
     Systems which are not as massive, and hence more streamlined, having been generally unable to achieve the rigidity and spacing necessary for optimization of the &#34;cluster effect&#34;. Moreover, such systems are readily damaged through consecutive recoils of the seismic sources during operation. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the above identified and other disadvantages of prior art coupling systems by providing a streamlined system which secures energetic sources in a fixed relation with respect to each other. Such a system is therefore suited for use as a towed seismic source. The present system also allows for controlled, resilient deformation during actuation of the seismic source, thereby enhancing the useful life of the system. 
     In a general embodiment, the present invention comprises coupling means securable to one or more energetic sources, e.g., marine seismic sources; spacing means securable to the coupling means so as to maintain the energetic sources in a substantially fixed relationship with respect to each other; rotation means; and, a shock absorption means disposed between the coupling means and the spacing means so as to allow controlled resilient deformation of the system without premature deterioration and/or fatigue of its various components. 
     The spacing system of the present invention orients two or more energetic sources at a precise distance from each other and at an optimum separation distance to accentuate the primary pulse and minimize secondary pressure pulses. This system also serves to prevent significant displacement between the sources during actuation while absorbing energy caused, in the instance of a marine acoustic source, by the explosive force, recoil and ultimate implosion of the bubble. 
     The present invention presents a number of advantages over prior art systems. One such advantage is that the system presents a low profile and hence low drag when used as a towed source. This is significant where the system is to be towed through the water such as is in the case of a marine acoustic generator. 
     Another advantage of the present invention is that the system demonstrates greatly reduced wear due to rotation means shock absorption build into the system through controlled, resilient deformation. Yet another advantage of the present invention is its ready adaptation to a conventional energy source, which adaptation facilitating inspection and disassembly. 
     Other benefits and advantages will become apparent through a review of the detailed description of the preferred embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 discloses a top view of a typical marine acoustic generator equipped with coupling points for the system of the present invention. 
     FIG. 2 discloses a top view of one preferred embodiment of the invention. 
     FIG. 3 discloses a side view of the embodiment illustrated in FIG. 2. 
     FIG. 4 illustrates a cutaway view of a preferred embodiment of the shock absorbing means of the invention. 
     FIG. 5 illustrates a detailed view of a preferred embodiment of the shock absorbing means of the invention. 
     FIG. 6 illustrates a detailed view of a preferred embodiment of the shock absorbing means of the invention, upon resilient deformation by an explosive force. 
     FIG. 7 illustrates a detailed view of a preferred embodiment of the shock absorbing means of the invention, upon resilient deformation by implosive force. 
     FIG. 8 is a top view of an embodiment of the invention upon the firing of a single seismic source. 
     FIG. 9 is a side, detailed view of a preferred embodiment of the invention upon system deformation. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Various embodiments of the present invention may be seen by reference to FIGS. 1-9. 
     FIG. 1 illustrates a top view of a conventional marine seismic generator 2 which defines a longitudinal axis 4 therethrough and a first 8 and second 10 end. Conventional air hose and peripheral equipment (not shown) are coupled to end 8 of generator 2. Seismic generators of the type illustrated at FIG. 1 are specifically adapted to operate in a marine environment when being towed at depth, either singularly or in combination with other sources. Such sources therefore generally incorporate a coupling means comprising a bracketing arrangement which is usually adapted to be secured to opposite ends of the seismic source via conventional fasteners. 
     The present system contemplates the use of brackets 12 interchangeable with those conventionally used in conjunction with marine seismic sources, thereby enhancing the ease of their installation of such systems while minimizing cost. By reference to FIG. 1, one embodiment of the mounting bracket 12 of the present invention comprises a two piece assembly which is adapted to be secured to opposite ends of source 2 via conventional fasteners 13, e.g. a bolt and nut arrangement. Bracket 12 includes attachment flanges 15 which define transverse attachment bores designated 19. Bores 19 are receptive to spacing members 20 in the manner illustrated in FIGS. 2 and 3. By reference to FIG. 3, it is contemplated in a preferred embodiment of the invention that a two source system will incorporate an tipper 20A and lower 20B spacing member about each end. The length of spacing members 20, and hence the distance between sources 2, is selected to optimize the &#34;cluster effect&#34; given operating parameters of volume, pressure and depth. Hence, the dimension of these members may vary. 
     Spacing members 20 are preferably made from a high strength, non corrosive metal, e.g. a high grade stainless steel, and defines two identical attachment ends 50. (See FIGS. 4-5) Attachment ends 50 are machined to varying diameters and dimensions to incorporate the shock absorption system of the invention, as will be described below. In the embodiment illustrated in FIGS. 3 and 4, the attachment end 50 of each spacing member 20 includes a smaller diameter shank 53 defining an arcuate shoulder 54, a pin 56 having a diameter less than said shank 53 and also defining an arcuate shoulder 57, and a still smaller diameter threaded terminal end 59. 
     Attachment ends 50 of spacing elements 20 accommodate a shock absorption system 40 which upon assembly of all components is disposed between elements 20 and the energetic source, here seismic source 2, in order to dampen the torque and the axial displacement along element 20 resultant from the operation of said source. In a preferred embodiment, system 40 comprises two semirigid annular elements 31 and 32. Elements 31 and 32 are preferably comprised of an elastomeric compound, e.g. polyurethane, and define a bore therethrough to accommodate the outer diameter of shank 53. Element 31 fits in a pocket formed by shank 53 and shoulder 54, and is positioned by sliding element 31 over shank 53 during assembly. Element 32 fits in a pocket formed by pin 56 and cap element 60, as described below. 
     Resilient elements 31 and 32 are disposed on either side of a pivot element 34 formed of a very hard, non gallable material, e.g. bronze. Element 34 includes an arcuate outer surface 36 which defines a line contact with the inner bore 19 of flange 15 when assembled. In such a fashion, a controlled pivot between spacing member 20 and flange 15 is possible upon the application of torque caused by the actuation of one or more of sources 2. Pivot element 34 also includes a bore therethrough adopted to slidably fit about pin 56 against shoulder 57, as illustrated. 
     The deformation of elastomeric elements 31 and 32 at their outer edges is controlled during the actuation of sources 2 by an annular cap or cage 43 which is preferably comprised of a rigid material such as a high grade stainless steel. Cap 43 fits into an annular groove formed in each of elements 31 and 32 as illustrated in FIG. 5. 
     Elements 31, 32 and 34 are maintained in place about attachment end 50 by a cap element 60 which describes a tapered first end 63 and a flat contact face 64. End 63 is machined to define a very narrow contact face with pivot element 34, thereby promoting greater flexibility in movement of element 34 upon torquing caused by the actuation of source 2. Cap element 50 is in turn secured in place by a nut 66. In a preferred embodiment, nut 66 is provided with a nylon locking element 68 to secure nut in place and prevent loosening. 
     The shock absorption system 40 previously described is assembled by placing each constituent element about end 50, securing said elements, placing the now &#34;loaded&#34; end 50 through bore 19 and securing the placement of said end 50, and hence spacing element 20, by the application of fastener 66 as described above and prestressed by hand with the help of a standard wrench (not shown) until cap element 60 is positioned in an abutting relationship with pivot element 34. 
     The performance of the system 40 during the actuation of sources 2 may be seen by reference to FIGS. 6-9. FIGS. 6-9 illustrate an alternate embodiment of system 40 which is substantially identical to that described above except for the absence of call elements 43. FIG. 6 illustrates a detailed view of a spacing element 20, bracket 15 and system 40 when acted on by an explosive source such as when two sources 2 are fired simultaneously. In such a case, the pressure field in the water between the two sources 2 is greater than the field outside said sources 2, so that said sources 2 tend to move away from each other as illustrated in FIG. 6. In this example, resilient element 32, being at the outer edge of the field, is compressed as sources 2 attempt to move outwardly. Simultaneously, element 31 is decompressed. After several seconds, the pressure inside the bubble (not shown) becomes lower than hydrostatic pressure, the bubble reaches its maximum size and then collapses. Water rushes into the resulting void, forcing one source 2 against the other. During this implosive effect, as illustrated in FIG. 7, sources 2 are sharply urged together. As a result, element 31 is now compressed and element 32 is decompressed. No mechanical shock, however, occurs between spacing members 20 and sources 2 since energy is dampened by the shock absorbing system 40. 
     The dynamics involved in the actuation of only one source in a two source set-up may by seen by reference to FIG. 8. In FIG. 8, source 2B is actuated, thereby creating an axial displacement &#34;D.&#34; Sources 2A is not actuated and therefore experiences no such axial displacement. The shock absorption system 40 of the present invention allows for source 2B to momentarily pivot with respect to source 2A, with a corresponding deformation of the elastomeric elements, as described above. A detailed view of the dynamics of the temporary deformation of system 40 may be seen in FIG. 9. As illustrated, the arcuate outer surface of pivot element 34 allows movement of source 2 within bracket 15 subject to the deformation limits of elements 31 and 32. 
     Although particular detailed embodiments of the apparatus and method have been described herein, it should be understood that the invention is not restricted to the details of the preferred embodiment. Many changes in design, composition, configuration and dimensions are possible without departing from the spirit and scope of the instant invention.