Professor A.C. Palmer
Professor P. King
The development of Petroleum Engineering in the Department continued, with an increased number of research students, several medium-term and short-term academic visitors, and larger numbers of undergraduates selecting the Part IIB module A1. Research into several problems in pipeline engineering and ice mechanics continued(I8,I9,I10,I11,I12), and the group moved into the new areas of drilling mechanics and reliability.
Drilling raises a number of practically important problems in mechanics, and these problems are made more challenging by moves towards extended-reach drilling, where the BP Amoco Wytch Farm M-11 well has reached a record 10.7 km horizontal distance. A leading drill-bit manufacturer generously made available measurement-while-drilling (MWD) data which showed very large coupled self-excited axial and torsional oscillations of a PDC bit, largely confined to the collar string, and distinct from the better-known whirl oscillations. The data showed that the angular velocity of the bit varied from almost stationary to twice the angular velocity at the top of the hole, and that there were huge oscillations in instantaneous weight-on-bit. A research student is working on the link between these oscillations and a model of the tooth/rock interaction. There is a close link with parallel work in the Department on the excitation of violin strings through a frictional contact with the bow.
Research continued on interactions between the seabed soil, the trenching process(I11), and buried pipelines. A program supported by Coflexip Stena Offshore, a major contractor, confirmed that backfilling induces a travelling upward force under a pipeline, and that this explains the troublesome and otherwise inexplicable flotation which has been observed in some North Sea pipelines. The same program resolved a long-standing controversy about the circumstances under which "ratcheting" uplift can lead to upheaval of pipelines subject to temperature and pressure cycles. Test were carried out at full-scale and at 1/10 scale in the centrifuge, and the comparison raised questions about centrifuge modelling of displacements, with much broader implications.
BP Amoco's concerns about ruptures in pipelines through mountainous terrain in Colombia led to the development of a theoretical model of pipeline rupture, comparison with field data, and the development of a centrifuge model. A paper was published on a serious and instructive pipeline construction accident in Columbia(I12).
Professor John Dempsey spent a year with the group as a Senior Research Fellow, on sabbatical leave from Clarkson University, supported by the EU LOLEIF project under the MAST III programme, in which the Department collaborates with institutions in Germany, Finland, Sweden, Norway and France. His work focused on new high-resolution observations of contact forces between ice and structures(I1,I2,I3). A large platen indentor covered with pressure-sensitive film sensors was driven horizontally into level sea ice in a lagoon in northern Japan. The measurements show that the distribution of force is very far from uniform (as had been suspected previously, but not demonstrated with the same detail and clarity). At high indentor speeds (3 mm/s), almost all the contact force is concentrated in a ridge of high contact pressure, parallel to the surface and close to mid-way through the thickness. These observations led to the development of a fracture mechanics model of `hot spots' where most of the contact force concentrates. The model is based on simple idealisations with spherical and cylindrical symmetry, and predicts behavior in semi-quantitative terms.
A second focus of Cambridge research has been speed effects. The starting point has been edge loading of a semi-infinite floating plate by an inclined indentor, and an analytic solution has been developed for the quasi-static case. This analysis has been developed to the true hydrodynamic case, which takes account of the inertia of the water and the ice, and of the hydrodynamic conditions at the bottom. The techniques applied are based on Green's functions, which lead to computationally efficient forms for finite water depths, and on Wiener-Hopf techniques.
Several research workers made shorter visits to Cambridge to work on ice mechanics. Dr Colin Fox of the University of Auckland spent two months in Cambridge with his colleague Hyuck Chung. Dr Dev Sodhi (USA CRREL) spent April 1999 in Cambridge. The presence of these visitors in Cambridge attracted other specialists in ice mechanics for one-day visits. Those visitors included Dr Tuomo Karna (VTT, Finland), Dr Kaj Riska and Dr J. Tuhkuri (University of Helsinki), and Professor Ian Jordaan (Memorial University of Newfoundland).
Professor King's research on geostatistics and reservoir engineering continued(I4, I5, I6, I7).
Part IIB teaching in petroleum development further. Forty-one students opted for the Part IIB module, and seven submitted MEng dissertations in petroleum engineering. At least two of the dissertations will be published.
The Department is one of five which are collaborating in the BP Amoco Fluids Institute, a new development made possible by a generous benefaction from BP Amoco. The Director and the Professor of Petroleum Science were appointed during the year, and the foundation stone was laid on June 28. Four new lecturers are to be appointed.
Professor Palmer is President of the Pipeline Industries Guild for the two years 1999-2000.
I1. Dempsey, J.P., Fox, C., Palmer, A.C. Ice-slope interaction: transitions in failure mode. Proceedings, 18th International Conference on Offshore Mechanics and Arctic Engineering (ASME) St. John's, Newfoundland, Canada, Paper 99-1156 (July 1999).
I2. Dempsey, J.P., Palmer, A.C. Non-universal scaling of arctic fractures. Proceedings, 15th International Conference on Port and Ocean Engineering under Arctic Conditions, Helsinki, Finland (August 1999).
I3. Dempsey, J.P., Palmer, A.C., Sodhi, D.S. High pressure zone formation during compressive ice failure. Proceedings, 18th International Conference on Offshore Mechanics and Arctic Engineering (ASME), St. John's, Newfoundland, Canada, Paper 99-1155 (July 1999).
I4. Dokholyan, N.V., Buldyrev, S.V., Havlin, S., King, P.R., Lee, Y., Stanley, H.E. Distribution of shortest paths in percolation. Physica A: Statistical Mechanics and Its Applications, 266, (1-4), 55-61 (April 1999).
I5. Heffer, K.J., King, P.R., Jones, A.D.W. Fracture modelling as part of integrated reservoir characterisation. Society of Petroleum Engineers Paper SPE 53347 (1999).
I6. King, P.R., Andrade, J.S., Buldyrev, S.V., Dokholyan, N.V., Lee, Y., Havlin, S., Stanley, H.E. Predicting oil reovery using percolation. Physica A: Statistical Mechanics and Its Applications, 266, (1-4), 107-114 (April 1999).
I7. Lee, Y., Andrade, J.S., Buldyrev, S.V., Dokholyan N.V., Havlin S., King, P.R., Stanley, H.E. Traveling time and traveling length in critical percolation clusters. Physical Review E, 60, (3), 3425-3428 (1999).
I8. Palmer, A.C. Challenges to pipeline design. Proceedings, Subsea 98 International Conference, London (December 1998).
I9. Palmer, A.C. Innovation in pipeline construction and design: solutions and problems in search of each other. Pipes and Pipelines International, 43, (3), 5-11 (November-December 1998).
I10. Palmer, A.C. Pipeline design strategies for deep water. Proceedings, Deepwater Pipeline Technology Conference, New Orleans, LA, USA (March 1999).
I11. Palmer, A.C. Speed effects in cutting and ploughing. Geotechnique, 49, (3), 285-294 (1999).
I12. Palmer, A.C., Tebboth, L., Miles, D., Calladine, C.R. Instability of pipelines on slopes. Transactions of the ASME, Journal of Applied Mechanics, 66, (3), 794-799 (September 1999).
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Last modified: July 2000