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                      Fuzzy Controller for Ocean Drilling
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Togai InfraLogic's Technology Systems Division has teamed with Paul Munroe
Engineering and GE Government Services in Houston, Texas, to work on a project
for the Ocean Drilling Program (ODP) at Texas A&M University.  The current
phase of the project is a complete engineering review and analysis of TAMU's
existing Diamond Coring System (DCS) motion compensation system.  TIL will be
designing a fuzzy controller for the DCS (see Figure 4 [not included in this
text-only version].)  The goal of the project is to improve the current motion
compensation system performance, particularly for heavier seas and longer
lengths of drill pipe.  Such improvements could allow the oil drilling industry
to operate in deeper water depths while maintaining the most productive use of
their drilling equipment.

Specialized drilling and coring techniques and equipment have been developed by
the ODP to recover fractured basalt cores in deep water.  Cores have been
retrieved in water depths as great as 1800 m using equipment and methods
similar to that used in the mining drilling industry.  In addition, unique
heave compensation modifications have been made to the mining-type coring
system to allow its use on a floating drilling vessel.  This project was
initiated in 1988.  Thus far the coring system has been deployed and operated
at sea on three occasions.  

Due to complete unobservability under the ocean, it is not possible to use
model-based adaptive control based on high fidelity simulation and to verify
such a model using traditional methods.  Fuzzy logic will be used to build an
approximate model to serve as the basis of the controller for both passive-
active and fully active secondary compensators.  This secondary compensator
operates in conjunction with a passive primary compensator.  The ideal behavior
is for the secondary compensator to leave no heave effect of wave motion on the
drill bit.

The ship's primary heave compensator is passive, but does not remove 100% of
the vertical motion, or heave, of the ship.  The behavior of the compensator
can be highly nonlinear due to friction, mechanical imperfections in the
fielded device, and heating effects on gas and hydraulic fluid properties.
The DCS platform is not held stationary relative to the seafloor, and secondary
compensation must be supplied to the DCS system to minimize motion of the DCS
drill string, a long length of pipe, and the drill bit.  The fuzzy controller
is intended to remove this residual motion.

After using TILShell+ to develop and initially test the fuzzy controller, the
team will use the Fuzzy-C Development System to produce C code which will be
integrated with Fortran output of CSSL models of the system for improved tuning
and testing of controller concepts.  If the simulations are successful, TIL's
FC110 based AT Accelerator Board may be used to provide a capable, fieldable
control system incorporating the fuzzy controller. 
  
The computer controlled heave compensation/automatic drilling system presently
has two basic modes of active operation.  Heave compensation, when the bit is
not in contact with the bottom of the hole, is termed the  STANDBY mode and is
an open loop controller using up to two sensor inputs.  The other mode uses
weight-on-bit or a feed-rate feedback control in addition to the open loop
signal to maintain a constant drilling force or constant drill rate.

The Ocean Drilling Program is funded through the U.S. National Science
Foundation and 19 member nations, and it is managed by the Joint Oceanographic
Institutions, Inc.  Through this drilling program, samples are obtained from
rock beneath all of the oceans to provide information about the earth's basic
geological processes. 
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Copyright (c) Togai InfraLogic, 1992.  All rights reserved.
Permission to freely distribute this document, provided that it remains
complete and intact, is hereby granted.
