Abstract:
A non-contact evaluation system for evaluating a synthetic rope. The system includes a first transducer, a second transducer, and a processor. The first transducer is located at a first position and configured to convert a first electrical signal into a wave directed toward the synthetic rope under test. The wave has characteristics such that at least of a portion of the wave passes around a perimeter of the synthetic rope. The second transducer is located at a second position opposite the first position and radially aligned with the first transducer. The second transducer is also configured to receive and convert the portion of the wave into a second electrical signal. The processor is configured to determine a structural health measure of the synthetic rope based on the second electrical signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. patent application Ser. No. 13,318,447 filed Nov. 1, 2011, which claims priority to PCT International Application No. US2010/033767 and U.S. Provisional Patent Application Nos. 61/215,496 and No. 61/215,527, and PCT International Application No. US2010/033767 filed May 5, 2010, which claims priority to U.S. Provisional Patent Application Nos. 61/215,496 and No. 61/215,527, the disclosures of which are hereby incorporated by reference in their entirety. This application also claims the benefit of U.S. Provisional Patent Application No. 61/215,496 filed May 6, 2009, and U.S. Provisional Patent Application No. 61/215,527 filed May 5, 2009, the disclosures of which are hereby incorporated by reference in their entirety. 
     
    
     STATEMENT CONCERNING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       FIELD OF THE INVENTION 
       [0003]    The present invention relates to a non-contact system for evaluating acoustic signal propagation properties through high performance synthetic fiber ropes or cables. Such a system can be used for non-destructive evaluation (NDE) and structural health monitoring (SHM) of synthetic fiber ropes and cables. Such a system can be used in conjunction with application-specific operating characteristics to establish retirement criteria for the synthetic ropes and cables used in those applications. 
       BACKGROUND OF THE INVENTION 
       [0004]    The lightweight nature of synthetic fiber rope provides many performance and economic advantages over metal wire rope. For example, when used in conjunction with sheaves in applications known as cyclic bend over sheave (CBOS) applications (e.g., cranes, elevators, heave compensation systems, and pulling lines), synthetic fiber rope allows for the use of equipment having a smaller footprint, less weight, and less power consumption than similar equipment for metal wire rope. However, regardless of whether metal wire or synthetic fiber rope is used in a particular application, it is critical to be able to assess the rope&#39;s condition to provide and maintain a retirement criteria to assure safe operation of the rope. 
         [0005]    A crucial and dynamic component used for determining and maintaining an accurate retirement criteria is the structural integrity of the rope. The integrity of the rope is used in conjunction with other components including user preferences (e.g., replacement at 50% strength, etc.) and the particular application, (e.g., mooring, cranes and winches, safety lines, etc.) to determine the retirement criteria. 
         [0006]    A number of SHM and NDE systems and methods that measure rope and cable structural integrity to determine the retirement criteria of steel and other metallic wire ropes have been developed. However, there are no generally accepted methods of measuring structural integrity for synthetic ropes, and thus the general practice for determining retirement criteria for synthetic fiber ropes relies on visual inspections and/or by tracking the history of usage for each rope. Visual inspections are inherently subjective and history-of-usage tracking can be highly inaccurate, therefore current retirement criteria are not based on meaningful parameters. 
         [0007]    Responsive to the deficiencies of visual inspections and history of usage tracking, a number of objective methods for SHM and NDE for synthetic fiber ropes have been developed. The methods use secondary materials such as conductive carbon fibers and glass or polymeric optical fibers intertwined with the synthetic fibers of the rope. In theory, the secondary materials undergo the same stresses and wear as the synthetic fibers. The stresses on the secondary materials can be easily measured and from these measurements the stresses and wear on the synthetic fibers is inferred. In reality, because the materials are inherently different and due to the complicated structure of the rope, the synthetic fibers can undergo stresses and wear that the secondary materials do not. Furthermore, the secondary materials are only exposed to stresses in their immediate vicinity and, as such, there may be sections of the rope in which stresses and wear are not measured. For these reasons, measurements obtained using secondary materials directly reflect the integrity of the evaluation materials only and indirectly reflect that of the synthetic fibers that make up the rope itself. Furthermore, synthetic fiber ropes intertwined with secondary materials may be less strong, have different than expected abrasion properties, and be more difficult to manufacture than ropes formed entirely from synthetic fibers. For at least these reasons, methods for measuring the structural integrity of rope with optical fibers are not widely practiced. 
         [0008]    Another method of monitoring and evaluating synthetic fiber ropes involves longitudinal waves propagated over a length of rope. Such a method may utilize longitudinal wave propagation theory such as described by M. Ferreira et al. in “Non Destructive Testing of Polyaramide Cables by Longitudinal Wave Propagation: Study of the Dynamic Modulus”, Polymer Engineering and Science, Vol 40, No. 7, July 2000. This method calls for at least some physical contact with the rope as probes or tappers directly contact the rope to introduce the acoustic signal. Furthermore, to determine meaningful retirement criteria with data from longitudinal waves, the rope must be held under constant tension (e.g., elevator cables, antenna stays, etc.) when being evaluated. This limits the use of this method to applications monitoring a stationary length of rope. Even then, vibrations in the rope introduced by devices in the rope&#39;s environment, such as motors and sheaves, are picked up by the transducers, resulting in distorted wave measurements. A further deficiency of this method is that it measures the entire length of the rope between the transducer and receiver, which are normally placed at each end of the rope. Therefore the resolution of this system is limited by the distance between the transducer and receiver. If only a small part of the rope is damaged, the system would not be able to indicate the specific location of the damage and the entire rope would have to be considered suspect. Another limitation to this method is that it cannot be used in situations where a portion of the rope is inaccessible, such as a rope used in conjunction with an offshore crane where one end could be under thousands of feet of water. 
         [0009]    Therefore, there is a need for a system that enables structural health monitoring of synthetic fiber ropes in a way that does not need to have direct contact with the rope, access to two distinct points along the rope, or the use of secondary materials, with greater resolution, and furthermore, is able to be used on a fast moving rope, and with a variety of rope fibers and construction methods. 
       SUMMARY OF THE INVENTION 
       [0010]    According to one aspect of the present invention, a non-contact acoustic signal propagation property evaluation system for synthetic ropes includes a first non-contact transducer spaced from a side of a rope to be evaluated. A first electrical signal is generated by a signal generator. The first transducer converts the first electrical signal from the signal generator into an acoustic signal directed towards the rope. A first portion of the acoustic signal propagates through the rope in a transverse direction and a second portion of the acoustic signal passes around the perimeter of the rope. A second transducer is spaced from an opposite side of the rope and is radially aligned with the first transducer. The second transducer receives and converts the first and second portions of the acoustic signal into a second electrical signal. A signal processing circuit receives and converts the second electrical signal into a digital signal. A processor connected to the signal processing circuit and executing computer readable code attributes properties of the digital signal to the acoustic propagation properties of the rope which can then be used to determine the physical properties of the rope. 
         [0011]    The acoustic signal may be an ultrasonic waveform and the first portion of the acoustic signal may be a longitudinal ultrasonic wave. The first and second transducers may be fixed in place while the rope moves relative to the first and second transducers. Additional transducers may be used in the system, such as a third transducer spaced from the rope and the first transducer and a fourth transducer spaced from the rope and the second transducer. The first transducer and the second transducer may be positioned at a first longitudinal location of the rope, and the third transducer and the fourth transducer may be positioned at a second longitudinal location of the rope. In some embodiments, the first electrical signal is either a pulse, square, or a sinusoidal waveform. The code may further provide a structural health measure of the rope based in part on the acoustic propagation properties of the rope. The first transducer and the second transducer may be piezoelectric-based transducers. A first air gap may be disposed between the first transducer and the rope, and a second air gap may be disposed between the second transducer and the rope. 
         [0012]    According to another aspect of the present invention, a method of evaluating acoustic signal propagation properties through a rope comprises the steps of: generating, at a first location spaced apart from the rope, an acoustic signal; directing the acoustic signal in a transverse direction towards a first longitudinal location of the rope, wherein upon impinging the rope, a first portion of the acoustic signal propagates through the rope and a second portion of the acoustic signal passes around the perimeter of the rope; receiving, at a second location spaced from the rope, the first portion and the second portion of the acoustic signal; and analyzing the first portion and the second portion of the acoustic signal. 
         [0013]    The steps of generating, directing, receiving, and analyzing may be repeated at each of a plurality of longitudinal locations along the rope. The steps of generating, directing, receiving, and analyzing may be repeated at the first longitudinal location of the rope and the step of analyzing may include analyzing changes in the first portion and the second portion of the acoustic signal over time. The step of analyzing may include determining a rate of change of the first portion and the second portion of the acoustic signal. The step of analyzing may include comparing the first portion and the second portion of the acoustic signal to reference data. The step of generating the acoustic signal may include generating the acoustic signal using a first transducer spaced from the rope. The step of receiving the first portion and the second portion of the acoustic signal may include receiving the first portion and the second portion of the acoustic signal using a second transducer spaced from the rope opposite the first transducer. The method may further comprise the step of moving the first transducer and the second transducer while the rope remains stationary. The method may further comprise the step of determining a structural health measure of the rope based, at least in part, on the first portion and the second portion of the acoustic signal. The step of directing may include directing the acoustic signal through a water gap between the first location and the rope. 
         [0014]    The foregoing and other objects and advantages of the invention will appear in the detailed description that follows. In the description, reference is made to the accompanying drawings that illustrate a preferred embodiment of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1   a  shows a first exemplary embodiment of a configuration of various components of a non-contact acoustic signal propagation property evaluation system in accordance with the present invention; 
           [0016]      FIG. 1   b  shows a second exemplary embodiment of a configuration of the various components of the non-contact acoustic signal propagation property evaluation system; 
           [0017]      FIG. 1   c  shows a third exemplary embodiment of a configuration of the various components of the non-contact acoustic signal propagation property evaluation system; 
           [0018]      FIG. 2  illustrates the amplitude of the ultrasonic signals propagated through a 0.75″ diameter synthetic fiber rope at one specific location as a function of rope life percentage obtained using the configuration shown in  FIG. 1 ; 
           [0019]      FIG. 3  illustrates the arrival time of the ultrasonic signals of  FIG. 2  as a function of rope life percentage; 
           [0020]      FIG. 4  illustrates the amplitude of the ultrasonic signals propagated through a 0.75″ diameter synthetic fiber rope at one specific location as a function of rope cycle number; 
           [0021]      FIG. 5  illustrates the arrival time of the ultrasonic signals of  FIG. 4  as a function of rope cycle number; 
           [0022]      FIG. 6  shows another configuration of the non-contact acoustic signal propagation property evaluation system of  FIG. 1  including multiple angularly disposed transducer pairs; 
           [0023]      FIG. 7  shows another configuration of the non-contact acoustic signal propagation property evaluation system of  FIG. 1  including multiple, axially spaced apart, transducer pairs; 
           [0024]      FIG. 8   a  shows a perspective view of a fixture supporting three axially spaced transducer pairs for monitoring a rope passing through the center of the fixture; and 
           [0025]      FIG. 8   b  shows another perspective view of the fixture of  FIG. 8   a.    
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]    Unlike the aforementioned prior art systems that measure longitudinal or shear ultrasonic waves traveling along the length of a rope using probes or tappers in physical contact with the rope, the present invention relies on the generation and measurement of acoustic signals propagating transversely through the longitudinal axis of the rope and transversely around the perimeter of the rope using non-contact means. 
         [0027]    Referring initially to  FIGS. 1   a - 1   c , a non-contact acoustic signal propagation property evaluation system  10  according to the present invention monitors and evaluates a synthetic fiber rope  12  (or cable; only the term “rope” is used herein for simplicity) moving along a longitudinal axis  14 . The system  10  includes a first transducer pair  16  operating in a through-transmission mode with radially-aligned transducers  18 ,  20  positioned on opposite sides of the rope  12 . The system  10  further includes a combined signal generator and receiver unit  22  (e.g., an ultrasonic signal generator and receiver unit) and a signal processing circuit  24  (e.g., an analog to digital converter). The system  10  further includes a software application operating on a processor  26  (e.g., a personal computer) to collect signal propagation property data. In some embodiments, the software application uses the data, in addition to other parameters, to evaluate the structural health of the rope  12 . 
         [0028]    Suitable non-contact transducers include commercially available ultrasonic transducers. A preferred non-contact transducer has an active area of one inch by one inch, a 100-300 kHz resonant frequency, a 200 kHz nominal frequency, and is positioned a quarter inch from the rope  12 . An alternative preferred non-contact transducer has an active areas of four inches by two inches, a 50 kHz resonant frequency, and is positioned four inches from the rope. A suitable signal generator, receiver, and converter includes a commercially available ultrasonic testing PCI board mounted in a PC chassis with an ultrasonic toneburst pulser/receiver unit and high speed analog to digital converter. A preferred pulser/receiver unit has a 0-300 V peak to peak sinusoidal or square wave output, a 20 kHz to 6.5 MHz pulse frequency, and a 0-15 pulse cycles capability. If additional signal strength is needed to overcome environmental noise or highly attenuative synthetic media, an amplifier can be used to increase the pulsing voltage to 1200 V. A preferred analog to digital converter has up to a 100 MHz sampling resolution. A suitable software application for collecting and extracting rope data includes the UTerminal or Utomography software package commercially available from FBS, Inc. of State College, Pa. Other suitable software applications can be off the shelf data acquisition programs that can be configured to acquire and interpret ultrasonic data in accordance with known phenomena, such as found in “Ultrasonic Waves in Solid Media” 1999 by Joseph L. Rose, the contents of which are fully incorporated herein by reference. 
         [0029]    In the embodiments described in the previous paragraph, the software application running on the PC  26  triggers the pulser/receiver unit  22  to generate an electrical pulse which is transmitted to the first air-coupled transducer  18 . Alternatively, a windowed sinusoid of a particular frequency may be used. The first transducer  18  converts the electrical excitation pulse into an acoustic energy wave, i.e., ultrasonic pulse signal  28 , directed towards the rope  12 . The ultrasonic pulse signal  28  travels through an air gap  30  surrounding the rope  12 , reaches a near surface  32  and propagates into the rope  12 . 
         [0030]    A large acoustical impedance mismatch between the air gap  30  and the rope  12  causes a portion of the ultrasonic signal  28  to be reflected back from the rope  12  and another portion to travel around the rope  12 . Signal losses are minimized by reducing the size of the air gap  30 , using focused transducers, matching the size of the transducer  18  with the width of the rope  12 , adjusting the signal frequency or amplitude of the pulse signal  28 , and using high resolution receiving hardware (e.g., hardware having a high sample rate, a high digitizing rate, etc.). 
         [0031]    The portion of the ultrasonic signal  28  that propagates into the rope  12  is further divided into various elastic waveforms including shear waves, not illustrated, travelling through the rope  12  along the axis  14  and surface waves, not illustrated, that travel circumferentially along the surface of the rope  12 . Some of the energy traveling around the rope does not interact with the rope  12  and only travels through the air. All of these ultrasonic signals, the waves traveling through the rope, on the surface of the rope, or in the air around the rope, can be received by the receiving transducer  20 , recorded, and analyzed to aide in predicting the structural health of the rope  12 . Of particular interest, however, is the pulse signal  28  that propagates through the rope  12  laterally, or transverse to the rope&#39;s longitudinal axis  14 . Upon reaching a far surface  34  of the rope  12 , the propagating pulse signal  28  continues through the air gap  24  and is received by the second, receiving air-coupled transducer  20 . 
         [0032]    The receiving transducer  20  is triggered to collect the ultrasonic signal  28  by the pulser/receiver unit  22  at a predetermined time interval or when the portion of the rope  12  of interest is at a particular position to allow for measurement. In a preferred embodiment, ninety-nine pulse signals  28 , occurring over one and a half seconds, are received over a given length of the rope  12  and spatially averaged together. The averaged analog signal is filtered and amplified by the pulser/receiver unit  22  and converted into a digital signal by the analog to digital converter  24 . The digital signal, representing the data point for one cycle, or, alternatively, one particular position, is collected and stored in memory of the PC  26 . 
         [0033]    The software application extracts information, including amplitude and arrival time, from each data point and can be plotted against a measure of the cycle life of the rope  12 . To extract the amplitude of each data point, a time-based window of the received radio frequency (RF) waveform is selected and the peak value of the signal is extracted.  FIG. 2  is an exemplary graph of the signal amplitude of each data point at one specific location of the rope plotted as a function of rope life percentage. To extract the arrival time of each data point, a time window in the RF waveform is first selected for evaluation. The peak of the signal in this window is then determined and followed back to the preceding “zero crossing”. The time corresponding to that zero crossing is extracted and plotted as a function of cycle number or position along the rope.  FIG. 3  is an exemplary graph of the arrival time of each data point plotted as a function of rope life percentage. Other data point properties that may be further analyzed include the total received energy and signal frequency content. 
         [0034]    The above data can be used in variety of manners. In some embodiments, the software application measures changes in the signal propagation property data of the rope  12  to evaluate the structural health of the rope  12 . One key physical property of the rope  12  is the elastic modulus which is known to change over time in response to fiber fatigue. The amount of energy transmission and speed of the propagating pulse signal  28  is a factor of the density and modulus of the rope  12 . Accordingly, the change in travel time of ultrasonic pulse signals over a range of frequencies can be used to determine the change in the modulus of the rope  12 . Changes in the properties of the ultrasonic signals passing through and around the rope  12  over time can also be used to determine changes in the modulus, and thus the fatigue or wear of the rope  12 . Alternatively, in the case where there is no previously collected data for a particular rope, the data can be compared to a known reference value to approximately determine the modulus, and thus the fatigue or wear of the rope  12 . 
         [0035]    Two other parameters known to affect ultrasonic signal propagation properties are “thinning”, or diameter reduction, and the temperature of the rope. Rope diameter reduction could cause changes in the ultrasonic wave arrival time and amplitude at the receiving transducer  20 . Likewise, the modulus of the rope  12  is affected by the internal rope temperature, which could change the ultrasonic signal propagation properties. Non-contact methods for measuring these variables include, but are not limited to, an infrared thermometer or an optical pyrometer for measuring temperatures and air-coupled transducers in pulse-echo mode to measure the diameter of the rope  12 . These and other physical parameters may be monitored, with these or other measurement techniques, and used to establish correction factors, if needed, for the received ultrasonic pulse signals. 
         [0036]    The software application may operate in a rope health mode whereby an initial reference data set acquired for the rope  12  prior to, or immediately after, being put in service is used as a reference data set. Subsequent data sets are then compared to the reference data set. The health of the rope  12  is determined based on changes in the signal properties over time. The software may also operate in a non-destructive testing mode whereby the data sets are compared to predetermined threshold values to determine the health of the rope  12 . The threshold values are stored in a database and may be determined by scanning a set of rope samples under known conditions. 
         [0037]    Furthermore, the software application may provide the ultrasonic signal propagation data as another parameter for the retirement criteria for a rope  12  in a particular application. That is, the ultrasonic signal propagation properties of a rope may be monitored, along with other parameters, such as, but not limited to, the tension the rope has been under, the number of cycles over a sheave, the time the rope has been in service, to determine when a rope should be taken out of service. In such a case, the software application may operate in one or both of the above modes, and the rope  12  is taken out of service and replaced based on a predetermined retirement criteria based on all the factors listed herein. 
         [0038]    Pattern recognition routines may be employed by the software application to help analyze the received signals, evaluate ultrasonic signal propagation properties, and, in some cases, monitor the health of the rope. Signal properties and features can be statistical or probabilistic in nature such as the skewness, Kurtesis, or mean. Properties can also be drawn from time and/or frequency domains and from other sources such as a Hilbert transform, pulse duration, and/or rise or fall time. In addition, physical based properties derived from wave mechanics, e.g., wave velocity or arrival time as a function of frequency or at a particular frequency, frequency shifting compared to reference data, attenuation as a function of frequency, and the like, could be evaluated by the routines. In cases in which the software application evaluates the structural health of the rope, the benefit of using pattern recognition routines depends on the selection of meaningful signal properties for monitoring. Pattern recognition algorithms utilizing a linear discriminate approach, nearest neighbor rule, or measured neural net could be used. 
         [0039]    The system  10  described above may be modified without departing from the scope of the invention. For example, instead of using piezoelectric-based transducers, other non-contact transducers may be used, such as electromagnetic and laser-based acoustic transducers. As another example, the system  10  could be water-sealed and use water-coupled transducers (e.g., hydrophones), particularly for underwater applications including subsea rope inspections and evaluations. Further still, acoustic transducers can be designed to work in other types of mediums, e.g., oil, and could also be considered depending on the application. 
         [0040]    An alternative transducer arrangement for the system  10  is shown in  FIG. 6 . As shown, additional transducer pairs  16  are provided and angularly spaced about the rope  12  to provide a “ring” arrangement. Such an arrangement may provide enhanced single point or spatial averaging via pulsed array operation. Another alternative transducer arrangement for the system  10  is shown in  FIG. 7 . As shown, additional transducer pairs  16  are provided and longitudinally spaced along the rope  12 . With such an arrangement, multiple data values may be obtained for a single point of the moving rope  12  and averaged together. In each of these alternative arrangements, each transducer pair  16  could operate at a different frequency. Furthermore, these alternative arrangements could be combined to provide transducer rings at multiple longitudinal locations along the rope  12 . 
         [0041]    Referring to  FIGS. 8   a  and  8   b , the above transducer arrangements may be used in connection with a support fixture  40  having a passageway  42  through which the rope extends. The support fixture  40  includes a plurality of elongated supports  44  (e.g., extruded aluminum bars) that connect to angle bracket mounts  46  to support the transducers  18 ,  20 . The transducers  18 ,  20  may be supported by different elongated supports  44 . Furthermore, each transducer pair may be angularly offset (e.g., by 120 degrees) and longitudinally spaced from the other transducer pairs (i.e., positioned in different planes). The support fixture  40  also includes end plates  48  (e.g., aluminum plates) that mount the elongated supports  44 . Two of the elongated supports  44  are preferably connected by hinges  50  that permit the fixture  40  to open, be placed around the rope, and connected to rope handling hardware (not shown). 
         [0042]    In each of the above embodiments the transducer pair  16  may be fixed in place while the rope  12  moves relative to the transducers  18 ,  20 . This suitable for applications such as, but not limited to, cranes and winches, where the rope  12  moves during use. Alternatively and in each of the above embodiments, the transducers  18 ,  20  are fixed relative to each other and move relative to a stationary rope  12 . This suitable for applications such as, but not limited to, mooring, where the entire rope  12  is stationary. 
         [0043]    Although the illustrated system  10  utilizes a through-transmission arrangement, other non-contact setups, such as a pulse/echo or shear wave arrangement, may be utilized. For example, a pulse/echo arrangement would allow for a reflection-coefficient evaluation method. In this case, a correlation between the amount of reflected ultrasonic waves and the integrity of the rope  12  could be developed and utilized. Such a method may be preferred in applications with significant rope thinning or if fewer transducers are desired. 
       Experimental Results 
       [0044]    Several 0.75″ diameter high-modulus polyethylene (HMPE) fiber ropes were cycled at six cycles per minute at a load of 7,000 pounds using a setup substantially as illustrated in  FIG. 1 . The rope typically failed and broke after 3,800 cycles. All the data was collected at the same location in each of the ropes used for the experiments.  FIGS. 2 and 4  shows the amplitude of the data points of two separate samples. The data shows a consistent and predictable pattern.  FIGS. 3 and 5  shows the arrival time from the data points for the same ropes as used for  FIGS. 2 and 4 , respectively. As with amplitude, arrival time changed in a consistent and predictable pattern. Given that the plots are generated using thousands of data points, the patterns are statistically significant. 
         [0045]    From the above description, it should be apparent that the system according to the present invention uses non-contact ultrasonic transducers to measure the acoustic propagation properties through a synthetic rope. Furthermore, the acoustic propagation properties change in a measurable way as the rope or cable wears. This data can be used in conjunction with other factors to adjust retirement criteria for synthetic fiber rope. The system can be deployed in an onboard environment, such as on a marine vessel or oil rig, to measure changes to the physical properties, such as modulus, of the ropes used thereon. In some embodiments, the system includes a waveform generator, a first transducer for generating ultrasonic signals, a second transducer for receiving longitudinal ultrasonic signals propagated transversely through the rope and around the perimeter of the rope, and a processor utilizing algorithms to evaluate the acoustic propagation properties of the rope. In some embodiments, the non-contact and real-time measurements obtained by the system enables high-speed and reliable rope integrity determinations not possible with conventional visual inspection and history-of-use methods. 
         [0046]    In some embodiments, the present invention provides a system that transmits, measures, and analyzes ultrasonic signals propagated transversely through the rope and around the perimeter of the rope. Specific features of the ultrasonic signal may be monitored over time to detect flaws or measure changes in the physical properties of the rope to, among other things but not limited to, predict remaining service life. Alternatively, specific features of the ultrasonic signal may be extracted and compared to a known reference value to detect flaws or estimate the current state of physical properties of the rope to, among other but not limited to, predict remaining service life. Signal features that could be used include, but are not limited to, signal amplitude, total received energy, signal arrival time or rope wave velocity, and signal frequency content. The use of one feature, or combinations of several features, may also be used to evaluate the physical properties of synthetic rope. 
         [0047]    Preferred embodiments of the invention has been described in considerable detail. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention is not limited by the above disclosure.