| Project Engineer: Dan Reudelhuber |
| Staff Liaison: Jamie Allan |
The Diamond Coring System, or DCS, combines a secondary heave compensator, slimhole diamond coring tools, and subsea/seafloor hardware into a slimhole coring package. The greatest challenge in adapting the mining technology for offshore use has been the problem of providing adequate heave compensation from a ship (as opposed to a semi-submersible). A highly specialized secondary active hydraulic heave compensation system is used to remove the heave that remains below the vessel's primary drill string compensator system. This active heave compensation has not yet been fully developed.
The Phase II effort was continued by parvus, including low-level and mid-level controller development, and initiated work on high-level control Man-Machine Interface (MMI) description in preparation for Phase III.
ODP/TAMU and TEDCOM made presentations on the status of the DCS at the annual PCOM meeting during the first week of December. The DCS outlook is positive.
Report planning has begun and a definition of the final test suite is underway. Improvements in the performance of several of the candidate controllers have been made since the late November progress meeting. At least one non-velocity-based controller is now functional and meets specifications for all but the 4500-m test case. Development of low-level controllers is nearly complete.
A Creare consultant was under contract to parvus and is working on development of yet another controller scheme using a Least Mean Squares noise reduction algorithm. Repairs were made to the test stand position sensors by parvus to remove significant noise that was present in the sensors (noisy pots). The pump was replaced on the heave input hydraulic unit due to wear.
ODP/TAMU and Stress Engineering visited parvus for a status review on January 24 and 25. parvus has made substantial progress since the TEDCOM/PCOM/ODP/TAMU meeting at parvus at the end of November. Strategies for implementing an Internal Model Control (IMC) scheme were discussed, based on using the model of the API drill string.
Amendment 3 to the SES contract was finalized and mailed in January. The amendment covers added costs for the Creare consultant to parvus, parvus software changes to parvNet since August 1994, changes to the work scope for Phase II, and the revised Phase II completion date (now March 4, effectively adding one month to Phase II as decided at the late November meeting at parvus).
SES completed seal testing in November 1995 and issued their report in late December. In summary, the alternate seal that was tested exhibits much less friction, and has equivalent longevity compared to the existing UTEX packing ring seal design. Proper cylinder finish is crucial, however, to the life of the low-friction seal (32 rms was used on the test cylinders). Westech Gear's specification for the primary heave compensator cylinder finish was also 32 rms, and this formed the basis for the finish specification chosen for the test cylinders. Nevertheless, if any alternate seal is installed on the vessel, a measurement of the existing surface finish on the cylinders is required. This will require disassembly and measurements at a port call, and the outcome of the inspection will dictate whether the original seal design should be reinstalled as is, or whether one of two alternate seals should be substituted. The two alternates are the low-friction CDI lip seal/carrier and a modified (lower friction) packing design as a compromise. ODP/TAMU is presently investigating measurement tools and costs.
SES's final report has been internally reviewed at ODP/TAMU, and copies are on their way to TEDCOM DCS Subcommittee members.
Installation of the instrumentation and data recording system was an item discussed at the late November status meeting at parvus. The subcommittee made a similar recommendation to what had been previously discussed by the design team, that is, to install the DCS sensor system now (instead of waiting until the DCS is fielded) in order to accurately measure the parameters needed for control. This is an intermediate test, the success of which will greatly increase confidence in the performance of the final system.
ODP/TAMU had planned to install instrumentation on the heave compensator previously, but for a different reason: to better quantify the actual seal friction levels both before and after seal change, if any. Because this would have required fielding an equivalent sensor/recording system than the one now envisioned for the DCS Controller Design work, it was decided that the two measurement efforts would be combined, saving funds and effort.
This effort will begin as soon as possible after the start of Phase III. Planning is already underway because convenient opportunities have presented themselves in the transit legs scheduled for April and August.