Communications – electrical: acoustic wave systems and devices – Signal transducers – Underwater type
Reexamination Certificate
1998-09-28
2001-09-18
Oda, Christine (Department: 2862)
Communications, electrical: acoustic wave systems and devices
Signal transducers
Underwater type
C114S245000
Reexamination Certificate
active
06292436
ABSTRACT:
REFERENCE TO RELATED APPLICATIONS
This application incorporates by reference the following applications:
U.S. Provisional Application No. 60/004,203, filed on Sep. 22, 1995, entitled “Electrical Power Distribution and Communication System for an Underwater Cable”;
U.S. Provisional Application No. 60/004,209, filed on Sep. 22, 1995, entitled “Acoustic Ranging Device for an Underwater Cable”;
U.S. Provision Application No. 60/004,493, filed on Sep. 22, 1995, entitled “Support Device For An Underwater Cable”;
U.S. Provisional Application No. 60/004,494, filed on Sep. 22, 1995, entitled “Depth Control Device for Underwater Cables”;
U.S. Provisional Application No. 60/005,500, filed on Sep. 22, 1995, entitled “Heading Sensor Device for an Underwater Cable”; and
International Application No. PCT/US96/15128, filed on Sep. 20, 1996, entitled “Electrical Power Distribution and Communication System for an Underwater Cable”.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an underwater cable arrangement capable of being used, for example, in seismic testing, as well as to various internal and external devices capable of being used with an underwater cable.
2. Description of the Related Art
In marine seismic exploration, an underwater cable, commonly referred to as a streamer cable, is towed through the water by a vessel such as a surface ship. An array of hydrophones is mounted within the cable, and an acoustic source or gun is fired to force an impulse of compressed air into the water, creating a bubble. The collapse of the bubble generates acoustic pulses that radiate through the water and into the earth. Reflections of the pulses off geologic structures are picked up by the hydrophones, and data representing the detected reflections are transmitted to the towing vessel. By analyzing the reflections, it is possible to discover subsea formations of oil or gas.
Various devices requiring electric power for their operation are mounted on the exterior of the underwater cable. For example, in order to accurately control the depth of the cable as it is being towed through the water, depth control mechanisms, commonly referred to as “cable-leveling birds”, are attached to the cable at intervals along its length. The depth control mechanisms are equipped with adjustable diving planes, the angles of attack of which can be varied by motors in the depth control mechanisms so as to maintain the cable at a desired depth. Another type of external device frequently mounted on an underwater cable is an acoustic ranging device, which together with other acoustic devices is used to determine the locations with respect to the towing vessel of various points along the underwater cable to permit the exact shape of the cable during towing to be determined. Yet another type of commonly used external device is a magnetic heading sensor (also referred to as a magnetic compass), which determines the heading of the underwater cable at the point where the heading sensor is attached to the underwater cable.
It is possible to connect such external devices with a source of power aboard the towing vessel by means of wires passing through the skin of the cable, but the necessity of forming holes in the skin for the wires can lead to leakage of water into the interior of the cable, which is highly undesirable. Therefore, the external devices are usually self-powered by their own internal batteries. However, batteries have a number of serious drawbacks. First, the batteries have a limited life span and must be replaced every one to three months. Not only is the replacement of the batteries time-consuming, there is also the risk of exposing electric circuitry within the external device to sea water during replacement. In addition, lithium primary batteries, which are used because of their longer operating life compared to other batteries, are expensive, and spent batteries must be retained for proper disposal and not randomly discarded. Furthermore, each time the cable is reeled in to replace batteries in the external devices, it is subjected to stresses which frequently result in damage to the cable. Therefore, it is preferable to reel in the cable as infrequently as possible.
Another shortcoming of conventional external devices used with underwater cables is that the entire device must be removed from the cable before the cable is rolled up onto a reel on the deck of a towing vessel in order to prevent damage to the external devices and the cable. When the cable is to be redeployed, the external devices must be reattached to it. In rough seas, it can be extremely difficult and often dangerous for workers to remove the external devices from or reattach them to the cable on the deck of the towing vessel. Furthermore, onboard storage space, often a precious commodity, must be provided for the external devices on board the towing vessel. In addition, the reeling in or paying out of the underwater cable must be stopped during removal or reattachment of the external devices, so deployment and retrieval of the cable are time consuming.
SUMMARY OF THE INVENTION
The present invention provides an underwater cable arrangement including an underwater cable having one or more internal devices mounted in the cable.
The present invention also provide various internal devices for installation in an underwater cable.
The present invention additionally provides methods for connecting a stress member of an underwater cable to an internal device.
According to one aspect of the present invention, an internal device, which is used in an underwater cable having a stress member, may comprise a body having an outer periphery, central bore, a passage, and a cutaway portion. The body is mountable inside the cable with the cable surrounding the outer periphery of the body. The passage extends in a lengthwise direction of the body outside of the central bore and is capable of receiving a stress member of the underwater cable. The cutaway portion is formed in the outer periphery of the body at each end of the body adjoining an end of the passage.
In many embodiments, the lengthwise end of the passage are spaced from the lengthwise ends of the internal device. The cutaway portions cutaway the regions of the internal device adjoining the ends of the passage to permit increased movement of the stress members. Such an arrangement lowers the stresses applied to the internal device as well as those applied to the stress members.
According to another aspect of the present invention, an arrangement for use in an underwater cable comprises an underwater cable and an internal device. The underwater cable includes a stress member extending in a lengthwise direction of the cable. The internal device has an outer periphery and a central bore. The internal device is disposed inside the cable with the cable surrounding the outer periphery of the internal device. The stress member is disposed radially outward of the central bore and is connected to the internal device by an interference fit.
According to another aspect of the invention, a method of connecting a stress member of an underwater cable to an internal device for use in the cable comprises inserting an object into the stress member of the underwater cable to create a region of increased diameter in the stress member. The method further comprises forming an interference fit between the region of increased diameter of the stress member and the internal device and positioning the internal device inside the cable with the cable surrounding the outer periphery of the internal device.
In many embodiments, the stress member passes through a pocket formed in the internal device. A portion of the stress member in the pocket is locally enlarged in diameter by the insertion of a retaining member into the stress member to create the interference fit between the enlarged portion of the stress member and the ends of the pocket. The interference fit prevents relative axial movement of the internal device and the stress member. If it is desired to adjust the location of the internal devic
Olivier Andre' W.
Rau Brien G.
Input / Output Inc.
Leydig , Voit & Mayer, Ltd.
Oda Christine
Taylor Victor J.
LandOfFree
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