Abstract:
An apparatus for measuring the force applied to a thin-line towed array having a towed array hose formed as part of a thin-line towed array. Coupling components divide the interior of the towed array hose into compartments. Axial tension measurement devices are located within one compartment, and bend measurement devices are located in another compartment. These measurement devices are electrically connected to a digitization and encoding module which is in turn connected to a processing device for providing measurements of the forces on the array.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefore. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates generally to thin-line towed-arrays, and more particularly to an apparatus that measures tension on thin-line towed-arrays during towed-array deployment and retrieval processes. 
     (2) Description of the Prior Art 
     Submarines deploy thin-line towed-arrays using mechanical handling systems. A thin-line array element includes an outer sheath or hose that contains hydrophones and supporting electronics. When the towed-array is deployed or retrieved, it is fed through a guide tube by a handling system. There is a great interest to quantify the handling system effects on the thin-line towed-array and its internal elements. Such quantitative information is useful for thin-line towed-array maintenance scheduling and design. By knowing the amount of stress applied to the thin-line towed-array during a typical deployment or retrieval process, faults may be predicted more accurately. Additionally, new sensor and material durability may be evaluated against existing designs. 
     There is currently no reliable method to evaluate the tension applied to a thin-line towed-array by the handling system during deployment and retrieval. 
     What is needed is an apparatus and method that measure the forces exerted upon a thin-line towed-array by the handling system during deployment and retrieval. 
     SUMMARY OF THE INVENTION 
     It is a general purpose and object of the present invention to provide an apparatus and method to measure the force applied to a thin-line towed-array by the handling system that deploys and retrieves the towed-array. 
     It is a further object to use a combination of tension and bending measurements to evaluate the handling system. 
     It is another object to provide such measurement device as part of a module that can be incorporated within a thin-line towed-array hose or outer-sheath. 
     It is yet a further object to integrate the measurement device to a tow cable for communication to a data processing system for evaluation. 
     Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings. 
     These objects are accomplished with the present invention by several modules that are incorporated within the standard thin-line towed-array configuration and positioned within the thin-line towed-array hose. The modules comprise tension sensors, bend sensors, and system electronics. Tension sensors are configured to measure axial tension applied to the towed-array during the deployment and retrieval processes, while bending sensors measure the bending load applied to simulated telemetry canisters. The sensor outputs are encoded and digitized by system electronics before transmitted through a towline for further data conditioning and processing. The tension and bending sensor data provide information to evaluate the force exerted by the handling system on the thin-line towed-array and its elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the invention and many of the attendant advantages thereto will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts and wherein: 
     FIG. 1 is a diagram of a basic thin line towed array system; 
     FIG. 2 is a cross-sectional view of the basic tension and bend sensor configuration within the thin-line towed-array; 
     FIG. 3 is an exterior view of the tension sensor container showing the interior arrangement with hidden lines; and 
     FIG. 4 is an exterior view of the bend sensor container showing the interior arrangement with hidden lines. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, there is shown a basic system configuration. A surface or undersea vessel  2  tows the thin-line array  8  at or below the surface  4  of a body of water. Test module  10  is positioned at the forward end of the towed array  8 . The tow cable  12  provides an electrical connection between the test modules and the signal conditioning electronics  14  that amplify and filter the signals before interfacing to a computer  16 . The computer  16  collects the system sensor data and performs the processing to evaluate system performance. The computer  16  and signal conditioning electronics  14  are positioned on the vessel  2 . 
     FIG. 2 provides a cross-sectional detail view of two thin-line towed-array measurement module compartments that house tension and bend sensors. Couplings  30   a  and  30   b  separate the two measurement module compartments from the remainder of the thin-line towed array  8 . The tension and bend compartments are similarly coupled  32  to allow electronic signals to pass between the two test module regions. 
     The test module  10  has a tension compartment  34  located closest to the front of the towed-array and containing two tension sensor modules  36 . The test module  10  compartment, hereinafter referred to as the bending compartment  40 , contains two bending sensor modules  42 ,  44  and two electronics canisters  46 ,  48 . The electronics digitize and encode the tension and bend measurements before transmitting them to the signal conditioning electronics for filtering and amplification. 
     The tension compartment  34  is filled with synthetic oil. The two tension sensors  36  each have two ends. The tension sensors are connected together by a steel cable  50 , with the remaining end of each tension sensor connected to coupling  30 ,  32  by nylon rope  52   a ,  52   b . While nylon is specified for ropes  52   a ,  52   b , this material can be any material with suitable elasticity, corrosion resistance and durability. The steel cable  50  can be made from any material relatively inelastic in comparison to the ropes  52   a ,  52   b . Each tension sensor  36  is electronically connected to a different electronics canister  46 ,  48  to provide redundancy. Strain gages  120  are mounted on two sides of the tension sensor&#39;s rectangular sensor mounting section  64 , and the strain gages  120  are configured in a wheatstone bridge to measure tension. 
     As the thin-line towed array measurement module section  34  passes through towed array handling sheaves, the tension compartment  34  experiences tension that is transferred to the nylon ropes  52   a ,  52   b  securing the tension sensors  36 , thereby transferring the tension to the strain gages  120  that measure the forces exerted by the handling system. Nylon ropes  52   a ,  52   b  stretch with the array to allow bending. Steel cable  50  does not allow a significant amount of stretching thereby ensuring that the sensors  36  are subject to the same forces. The tension measurements are received in the bend compartment  40  by the electronic canisters  46 ,  48  for digitizing and encoding. 
     Similarly, the two bend sensors  42 ,  44  are electronically connected to a different electronic canister  46 ,  48  for redundancy; however, the bend sensors  42 ,  44  and electronic canisters  46 ,  48  are secured within the bend compartment  40  using foam rubber  54 . Strain gages are also utilized in wheatstone bridge configurations to measure bend in the bend compartment  40 . Redundancy in the bend measurements is achieved with two identical bend canisters  42 ,  44  that provide orthogonal bend measurements. 
     Each bend canister  42 ,  44  includes four strain gages  124  comprising two orthogonal wheatstone bridges. Because each bend sensor further comprises two sensor mounting sections, the first sensor mounting section of each bend sensor comprises one wheatstone bridge configuration of two strain gages, while the second sensor mounting section of each bend sensor comprises a distinct second wheatstone bridge configuration of two strain gages. As the bend compartment  40  passes through the mechanical handling sheaves, the redundant bend sensors  42 ,  44  record the bending force applied to the bend canisters to quantify the towed-array distortion. The bend measurements are transferred to the electronic canisters  46 ,  48  for digitization and recording. The electronic canisters  46 ,  48  transfer the digitized and encoded tension and bend measurements to signal conditioning electronics for filtering and amplification. 
     Referring now to FIG. 3, there is a diagram of a tension sensor  36 . The sensor  36  comprises three sections: end sections  60   a ,  60   b , pins  62   a ,  62   b , and sensor mounting section  64 . The two end sections  60   a ,  60   b  are rectangular with two smooth sides and two sides containing a u-shaped indentation  66   a ,  66   b . The rectangular cross-section sensor mounting section  64  connects the end sections such that the end section u-shaped indentations  66   a ,  66   b  face away from the sensor mounting section  64 . Each end section additionally contains a circular, oblong pin  62   a ,  62   b  that traverses the u-shaped indentation  66   a ,  66   b . The u-shaped indentation section  66   a ,  66   b  and pin  62   a ,  62   b  combination allow the steel cable and nylon rope to attach to the tension sensor pin. The cable or rope is inserted into the end section u-shaped indentation  66   a ,  66   b,  around the pin  62   a ,  62   b , and thence out of the u-shaped indentation  66   a ,  66   b  to secure the cable or rope to the tension sensor. 
     The tension sensor&#39;s sensor mounting section  64  contains four smooth rectangular sides to provide sensor mounting surfaces. A sensor  120  is indicated by hidden lines as mounted on one side of sensor mounting section  64 . The sensor mounting section is connected directly to the end sections  60   a ,  60   b  such that tension on the nylon rope or steel cable translates to the sensor mounting section  64 . 
     Referring now to FIG. 4, there is shown a bend sensor canister  42 . The bend sensor canister has the same external shape as a telemetry canister in a typical thin-line towed-array configuration. Although the bend sensor canister  42  may have different configurations, the goal of the preferred embodiment is the provision of orthogonal bend measurements within a single bend sensor canister. The bend sensor canister  42  is preferably an aluminum canister having three support sections  80   a ,  80   b ,  80   c  and two sensor sections  82   a ,  82   b . A rectangular bridge  90 ,  92  traverses the interior of each sensor section  82   a ,  82   b , respectively. The bridge orientation alternates in the two bend sensor sections to allow orthogonal bend sensor positioning and measurements. The rectangular bridge surfaces allow sensor  124  mounting directly on the bridge surfaces. Sensor wiring from the first bend sensor section  82   a  travels through an outlet  94  in the middle support section  80   b  to the second bend sensor section  82   b . Electronic wiring from the first and second bend sensor sections  82   a ,  82   b  is then transferred out of the second bend sensor section  82   b  using outlets  96  in the end support structure  80   c , whereupon the wiring is connected to the electronics canisters. 
     In the preferred embodiment, the tension and bend sensors are strain gages, and all strain gages are affixed to the respective sensor mounting sections using epoxy. 
     The advantage of the present invention over the prior art is that the disclosed invention provides a novel method of measuring the force applied to a thin-line towed-array during the deployment and retrieval processes. 
     What has thus been described is an apparatus and method to measure the force applied to a thin-line towed-array during the deployment and retrieval processes. The invention includes several modules that are incorporated into the standard thin-line towed-array configuration. The modules comprise tension sensors, bend sensors, and system electronics. Tension sensors are configured to measure axial tension applied to the towed-array during the deployment and retrieval processes, while bending sensors measure the bending load applied to a simulated telemetry electronics canister. The sensor outputs are encoded and digitized by the system electronics before transmitted through a towline for further data conditioning and processing. The tension and bending sensor data provide information to evaluate the force exerted by the handling system on the thin-line towed-array and its elements. 
     Obviously many modifications and variations of the present invention may become apparent in light of the above teachings. For example, although strain gages were used as the sensors in the preferred embodiment, other sensing elements may be utilized. The strain gages may be configured differently than the wheatstone bridge configurations described, and a different number of sensors may be utilized. The sensors may be secured other than by epoxy. The digitizing and encoding electronics may be located within the thin-line towed-array hose, in the bend or tension compartments, or at another location. Although foam rubber secured the electronics canisters and bending sensors, other material to secure the canisters and bend sensors may be used. Substitutes for cable or rope may similarly be made to couple the axial tension sensors to each other and the coupling. A material other than aluminum may be used to form the tension and bend sensors. Although sensor redundancy was utilized, redundancy can be eliminated or increased. The electronics canisters may include filters and amplifiers as necessary to process the measurements before transmitting the measurements for processing. 
     In light of the above, it is therefore understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.