Abstract:
A method and system are provided to optimize filtering of compressional wave energy in the wavenumber domain for a given frequency range using a fluid-filled elastic cylinder. The fluid is selected based on its fluid density .rho..sub.i and dilatational wave phase velocity c.sub.i. The selected fluid must satisfy the relationship ##EQU1## for the given frequency range where P.sub.i is the magnitude of the pressure field in the fluid at a point within the fluid defined by a distance r.sub.1 from the cylinder's central longitudinal axis and P.sub.o is the magnitude of the impinging compressional wave, and must control at least one of the breathing wave response, the extensional wave response and the fluid P-wave response.
Abstract:
The present invention provides an acoustic sensor having one or more segments that are electrically coupled to provide a response corresponding to a hydrodynamic pressure applied to the segments. Each segment contains a substrate of a desired shape with a concavity on an outer surface that is sealingly enclosed by an active member made from a flexible, resilient piezoelectric material. PVDF material is preferably used as the piezoelectric active element. The active member is covered with a protective layer of a suitable material, preferably a polyvinyl material. A single segment may be used as a sensor or a plurality of suitably configured segments may be suitably coupled to form the sensor. The sensor may be used as a hydrophone on a hydrophone cable commonly used for performing seismic surveys for geophysical exploration. In such applications, a plurality of hydrophones are placed equally spaced along the cable. In the preferred embodiment, two hydrophone segments are securely be placed around the cable. The segments are electrically coupled to each other and to a conductor in the cable. In operation, the hydrophone cable is placed at the bottom of a water-covered area or towed behind a seismic vessel to conduct seismic surveys.
Abstract:
Method and apparatus for carrying out seismic survey includes a plurality of spaced apart seismic detecting sensors each having a geophone unit for detecting seismic activities. The sensors are linked serially with a cable. One end of each geophone unit is flexibly linked to a carrier frame so that the geophone units pivotally move freely relative to the carrier frames. The cable passes through the carrier frames so that the carrier frames are spaced apart serially. Each geophone unit carries a vibrator, a plurality of geophones, a compass, and an inclinometer. The vibrator is positioned on the free end portion of the geophone unit, for embedding the geophone into the ground, while the compass is positioned farthest away from the vibrator. The free pivotal movement of the geophone units enables them to dig into the ground.
Abstract:
A semi-dry marine seismic streamer cable (5) consists of a number of connected streamer cable sections (5a) which each comprises a mechanical jacket (10) surrounding a hollow core (11) enclosing seismic sensor (15) and signal transfer (16) means. Elongated axial stress elements (18) for transmitting axial loads and a radial reinforcement member (12) for relieving radial loads are provided in the jacket (10). The core (11) is filled with a fluid or a fluid-saturated foam and the sensor means (15) are mounted in the core (11) by vibration isolating elements (14).
Abstract:
A cluster of seismic streamer cable utility modules is provided with a set of hinged latching members. The hinged latching members are adapted secure the cluster to the steamer cable by closing the hinged latches around corresponding collars mounted on the streamer cable. The collars form an inner race while the closed hinged latches form an outer race to allow free relative rotation between the streamer cable and the cluster of modules.
Abstract:
An elongate towed acoustic array is improved by the inclusion of a speciflly configured tensile load bearing strength member disposed within a hose-shaped sheath. The member has a plurality of longitudinally extending high strength cords formed of braids or strands of high tensile strength fibers. The cords are held in a longitudinal juxtaposed relationship by a transverse weave to define a hollow interior for non-compressively containing sensor elements. Thusly configured, the strength member possess a softness and flexibility that does not create damage inducing crimps while not overly interfering with the sensors' acoustic sensing capabilities. The hose-shaped sheath contains the tubular-shaped strength member in a non-compressive relationship to reduce the problems normally associated with flow noise. The cords are braided together in an eye-splice where they are wrapped about towing pins so that the cords' tensile strength is not compromised at the point of attachment. Optionally, a twill weave is used to hold the longitudinal cords in their juxtaposed relationship to assure softness and flexibility for the wall of the strength member.
Abstract:
Disclosed is a programmable data collection and relay circuit for a towed hydrophone array. The circuit is designed to prepare data concerning operation of the array to be interleaved with substantive data produced by the hydrophones to produce a single data stream for transmission to recording equipment. The circuit comprises (1) a plurality of sensor inputs, each of the sensor inputs adapted to be coupled to a sensor capable of sensing a physical characteristic within the towed hydrophone array, (2) a circuit for polling at least a portion of the plurality of sensor inputs to determine values of the inputs, (3) a circuit for storing programmed data concerning which of the plurality of inputs is to be polled and (4) a circuit for serially placing the input values in condition for insertion into a data stream transmitted along the towed hydrophone array.
Abstract:
An integrated module coupler for a towed hydrophone streamer and a method of transmitting towing forces and electrical signals therethrough. The coupler comprises: (1) a coupler body having a plurality of axial bores and a plurality of tension member apertures therethrough, (2) a plurality of electrically-conductive pins disposed through the bores, (3) an insulating material, disposed between the plurality of pins and walls of the plurality of bores, for insulating the pins from the coupler body to thereby allow electrical signals to pass via the plurality of pins through the body, (4) means for retaining tension members within each of the tension member apertures, the retaining means allowing the tension members to terminate within the tension member apertures in an eye, the retaining means passing through each of the eyes to thereby engage the tension member and (5) a coupler shell, coaxial with and capturing the coupler body to engage a mating coupler shell of another coupler, towing forces transmittable between the coupler shell and the tension members via the coupler body and the retaining means.
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 the 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. The "dash-pot" type dampers can be replaced by a stocking which, under extension, compresses the foam and forces fluid through pores of the foam, thus simulating the viscous damping of the "dash-pot" type dampers.
Abstract:
A marine seismic streamer cable retriever is activated promptly when the cable and its attached retriever exceed a pre-selected safe depth. In an alternative scenario, an electronics module in the cable retriever monitors the presence of through-cable communications traffic between a mother ship and the various sensors in the cable. If an interruption in communications traffic is detected, a clock starts a count-down and sends a warning to the operator aboard ship. At the end of a count-down period, absent prior operator intervention, the cable retriever is activated.