HR: 1330h
AN: OS52B-0908    [PDF]
TI: Active Heave-Compensated Coring On The New Jersey Shelf
AU: * Nielson, D L
EM: dnielson@dosecc.org
AF: DOSECC, Inc., 675 S. Arapeen Dr., Salt Lake City, UT 84108
AU: Pardey, M
EM: mpardey@qdtech.com
AF: QD Tech, Box 239 369 E. 900 S., Salt Lake City, UT 84111
AU: Austin, J A
EM: jamie@ig.utexas.edu
AF: University of Texas Institute for Geophysics, John A. and Kathern G. Jackson School of Geosciences 4412 Spicewood Springs Rd. Building 600, Austin, TX 78759-8500
AU: Goff, J A
EM: goff@ig.utexas.edu
AF: University of Texas Institute for Geophysics, John A. and Kathern G. Jackson School of Geosciences 4412 Spicewood Springs Rd. Building 600, Austin, TX 78759-8500
AU: Alexander, C
EM: clark@skio.peachnet.edu
AF: Skidaway Institute of Oceanography, 10 Ocean Science Circle, Savannah, GA 31411
AU: Christensen, B A
EM: bchristensen@gsu.edu
AF: Department of Geology, Georgia State University 340 Kell Hall, Atlanta, GA 30303
AU: Gulick, S P
EM: sean@ig.utexas.edu
AF: University of Texas Institute for Geophysics, John A. and Kathern G. Jackson School of Geosciences 4412 Spicewood Springs Rd. Building 600, Austin, TX 78759-8500
AU: Fulthorpe, C S
EM: craig@ig.utexas.edu
AF: University of Texas Institute for Geophysics, John A. and Kathern G. Jackson School of Geosciences 4412 Spicewood Springs Rd. Building 600, Austin, TX 78759-8500
AU: Nordfjord, S
EM: sylvia@ig.utexas.edu
AF: University of Texas Institute for Geophysics, John A. and Kathern G. Jackson School of Geosciences 4412 Spicewood Springs Rd. Building 600, Austin, TX 78759-8500
AU: Sommerfield, C
EM: cs@udel.edu
AF: College of Marine Studies, University of Delaware 700 Pilottown Road, Lewes, DE 19958-1298
AU: Venherm, C
EM: claudia@skio.peachnet.edu
AF: Skidaway Institute of Oceanography, 10 Ocean Science Circle, Savannah, GA 31411
AB: The continental shelves are of obvious scientific and strategic importance. However, the ability to cost-effectively collect core samples of continental shelf sediments has been limited by technical difficulties. Many sites of scientific interest are too shallow to be drilled by large drill ships, and they are too deep to be drilled economically from jack-up platforms. DOSECC has developed an Active Heave Compensated (AHC800) drilling system under sponsorship of the Office of Naval Research to overcome these obstacles by building a small active heave compensated drilling rig that can be used to collect high-quality core from selected vessels of opportunity. The AHC800 drilling rig is designed to collect continuous core to a total drill string length of 800 m. Water depths of 200 m and less are optimal; however, with some modification operation in deeper water is possible. The AHC800 senses vessel heave using a constantly tensioned low-stretch taut line attached to a seafloor weight. A linear position transducer is attached to this taut line and through the data acquisition system, the ship's distance from the bottom is communicated to the heave compensation computer running Labview RT operating system and object-based software language. This real-time control system is used to achieve a 10-ms control loop for both data gathering and output functions. The Labview RT system continuously controls two hydraulic cylinders that keep the heave carriage and the drill string at the same reference distance from the bottom. The AHC800 system was used on the R/V Knorr on the New Jersey continental shelf in water depths from 74 to 130 m from 25 Sep to 15 Oct 2002. The AHC800 system performed up to and beyond its design specifications. The rig was designed to compensate for 2.44 m of heave with an 8 s period. However, the Knorr's response was a 6 s period resulting in a significant increase in the required acceleration as well as a faster response time for the system as a whole. We believe this 6-second period resulted from rapidly changing wind and wave conditions. During times when the heave was greater than 2.44 m with a 6 s period, the response time of the system was insufficient to keep the drill bit on bottom. However, we were able to continue operation in sea states up to 2.9 m with periods greater than 8 s. The system still requires some tuning in order for it to move from a research and development stage to real production drilling; however, the concept and engineering design are sound.
DE: 4558 Sediment transport
DE: 4594 Instruments and techniques
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting