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Title: Use of Imploding Spheres: An Alternative to Explosives as Acoustic Sources at Mid-Latitude SOFAR Channel Depths

Abstract

The hydroacoustic nuclear explosion monitoring regime, like it's counterpart in seismic monitoring, requires ground truth calibration. Model predictions of traveltimes, blockages, reflections, diffractions, and waveform envelopes need to be verified with ground truth experiments, particularly in the high latitudes where models often fail. Although pressure detonated explosives are a simple, reliable, and flexible method to generate an impulsive hydroacoustic calibration source at a desired depth; safety procedures, specialized training, and local regulations often preclude their use. This leaves few alternatives since airgun and other seismic marine sources are designed for use only at shallow depths and hence do not effectively couple into the SOFAR channel, a necessary requirement for long range propagation. Imploding spheres could be an effective source at mid-ocean depths and below but development of a method to reliably break such spheres has been elusive. We designed and tested a prototype system to initiate catastrophic glass sphere failure at a prescribed depth. The system firmly holds a glass sphere in contact with a piston-ram assembly. The end cap on the cylinder confining the piston and opposing the ram has a rupture disk sealed to it. The rupture disk is calibrated to fail within 5% of the calibrated failuremore » pressure, 1000 psi in our tests. Failure of the rupture disk results in a sudden inrush of high pressure water into the air-filled piston chamber, driving the piston--and attached ram--towards the glass sphere. The spherecracker was first tested on Benthos Corp. flotation spheres. The spherecracker mechanism successfully punched a hole in the Benthos sphere at the nominal pressure of 1000 psi or at about 700 meters depth in each of four tests. Despite the violent inrush of high pressure water the spheres did not otherwise fail. We concluded that the Benthos spheres were too thick-walled to be used as an imploding source at nominal SOFAR channel depths (500 meters-1200 meters in mid-latitudes). A much thinner walled sphere, a special order modification of a standard 22 liter laboratory boiling flask made by the Kontes Glass Company, was also tested and found to fail in the desired manner, i.e. catastrophically. A test off the coast of California successfully initiated implosion of a Kontes sphere at 685 meters depth. The recorded signal showed a peak pressure slightly larger than that from 1 lb of high explosive detonated at the same depth. The signal spectra showed relatively broad band higher frequency energy with little signal below about 50 Hz and a broad peak in the amplitude spectra between about 200 and 800 Hz, similar to that from an explosive source detonated at the same depth. Although additional testing and development is needed, an imploding sphere source for hydroacoustic calibrations appears viable. Since the source spectra frequencies are generally higher than the frequency band used for nuclear explosion monitoring, low frequency signals (1-50 Hz) will be absent from the implosion source spectra. Calibration will have to be accomplished with frequencies above 50 Hz unless larger spheres, multiple spheres, or shallower implosion depths are used.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab., CA (US)
Sponsoring Org.:
USDOE Office of Defense Programs (DP) (US)
OSTI Identifier:
793868
Report Number(s):
UCRL-ID-139032
TRN: US200302%%666
DOE Contract Number:  
W-7405-Eng-48
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 12 May 2000
Country of Publication:
United States
Language:
English
Subject:
45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEFENSE; 54 ENVIRONMENTAL SCIENCES; ACOUSTICS; CASKS; CHEMICAL EXPLOSIVES; EXPLOSIVES; GROUND TRUTH MEASUREMENTS; IMPLOSIONS; MONITORING; NUCLEAR EXPLOSIONS; REGULATIONS; SAFETY; SPECTRA; WAVE FORMS

Citation Formats

Harben, P E, Boro, C, Dorman, L, and Pulli, J. Use of Imploding Spheres: An Alternative to Explosives as Acoustic Sources at Mid-Latitude SOFAR Channel Depths. United States: N. p., 2000. Web. doi:10.2172/793868.
Harben, P E, Boro, C, Dorman, L, & Pulli, J. Use of Imploding Spheres: An Alternative to Explosives as Acoustic Sources at Mid-Latitude SOFAR Channel Depths. United States. doi:10.2172/793868.
Harben, P E, Boro, C, Dorman, L, and Pulli, J. Fri . "Use of Imploding Spheres: An Alternative to Explosives as Acoustic Sources at Mid-Latitude SOFAR Channel Depths". United States. doi:10.2172/793868. https://www.osti.gov/servlets/purl/793868.
@article{osti_793868,
title = {Use of Imploding Spheres: An Alternative to Explosives as Acoustic Sources at Mid-Latitude SOFAR Channel Depths},
author = {Harben, P E and Boro, C and Dorman, L and Pulli, J},
abstractNote = {The hydroacoustic nuclear explosion monitoring regime, like it's counterpart in seismic monitoring, requires ground truth calibration. Model predictions of traveltimes, blockages, reflections, diffractions, and waveform envelopes need to be verified with ground truth experiments, particularly in the high latitudes where models often fail. Although pressure detonated explosives are a simple, reliable, and flexible method to generate an impulsive hydroacoustic calibration source at a desired depth; safety procedures, specialized training, and local regulations often preclude their use. This leaves few alternatives since airgun and other seismic marine sources are designed for use only at shallow depths and hence do not effectively couple into the SOFAR channel, a necessary requirement for long range propagation. Imploding spheres could be an effective source at mid-ocean depths and below but development of a method to reliably break such spheres has been elusive. We designed and tested a prototype system to initiate catastrophic glass sphere failure at a prescribed depth. The system firmly holds a glass sphere in contact with a piston-ram assembly. The end cap on the cylinder confining the piston and opposing the ram has a rupture disk sealed to it. The rupture disk is calibrated to fail within 5% of the calibrated failure pressure, 1000 psi in our tests. Failure of the rupture disk results in a sudden inrush of high pressure water into the air-filled piston chamber, driving the piston--and attached ram--towards the glass sphere. The spherecracker was first tested on Benthos Corp. flotation spheres. The spherecracker mechanism successfully punched a hole in the Benthos sphere at the nominal pressure of 1000 psi or at about 700 meters depth in each of four tests. Despite the violent inrush of high pressure water the spheres did not otherwise fail. We concluded that the Benthos spheres were too thick-walled to be used as an imploding source at nominal SOFAR channel depths (500 meters-1200 meters in mid-latitudes). A much thinner walled sphere, a special order modification of a standard 22 liter laboratory boiling flask made by the Kontes Glass Company, was also tested and found to fail in the desired manner, i.e. catastrophically. A test off the coast of California successfully initiated implosion of a Kontes sphere at 685 meters depth. The recorded signal showed a peak pressure slightly larger than that from 1 lb of high explosive detonated at the same depth. The signal spectra showed relatively broad band higher frequency energy with little signal below about 50 Hz and a broad peak in the amplitude spectra between about 200 and 800 Hz, similar to that from an explosive source detonated at the same depth. Although additional testing and development is needed, an imploding sphere source for hydroacoustic calibrations appears viable. Since the source spectra frequencies are generally higher than the frequency band used for nuclear explosion monitoring, low frequency signals (1-50 Hz) will be absent from the implosion source spectra. Calibration will have to be accomplished with frequencies above 50 Hz unless larger spheres, multiple spheres, or shallower implosion depths are used.},
doi = {10.2172/793868},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2000},
month = {5}
}

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