Toward an Improved Understanding of Thruster Dynamics for Underwater Vehicles

This paper proposes a novel approach to modeling the four quadrant dynamic response of thrusters as used for the motion control of ROV and AUV underwater vehicles. The significance is that these vehicles are small in size and respond quickly to commands. Precision in motion control will require further understanding of thruster performance than is currently available. The model includes a four quadrant mapping of the propeller blades lift and drag forces and is coupled with motor and fluid system dynamics. A series of experiments is described for both long and short period triangular, as well as square wave inputs. The model is compared favorably with experimental data for a variety of differing conditions and predicts that force overshoots are observed under conditions of rapid command changes. Use of the model will improve the control of dynamic thrust on these vehicles.The authors wish to recognize the valuable insights and enthusiasm of Mike Lee (MBARI) and the financial support of the MBARI summer program as well as the support from the Naval Postgraduate School Direct Research Fund

Nationale campagne valpreventie bij ouderen : Resultaten van de nameting 2007

B&G, PZ

Restoration of annular zonal isolation using localized casing expansion (LCE) technology: A proof of concept based on laboratory studies and field trial results

Sustained casing pressure (SCP), surface casing vent flow (SCVF) and other expressions of annular fluid migration are widely encountered zonal isolation issues. Conventional solutions for SCP/SCVF include perforate and squeeze cementing, or section milling and recementing. Regrettably, the former approach shows only limited success rates, while the latter involves time and cost intensive operations that require a drilling rig. We will show that localized casing expansion (LCE) technologies offer promising alternatives, enabling rigless remediation of annular fluid migration. The LCE concept involves imposing permanent deformation on the casing pipe to locally enlarge its diameter. The associated annular volume reduction causes closure of defects such as micro-annuli and cement fractures, plus potentially even larger voids, and results in an overall densification of the cement microstructure. The Shell-developed Local Expander tool is e-line deployable and imposes the required casing deformation in a mechanical, fully controlled manner. Tailored-shaped energetic charges offer valuable supplementary means for achieving expansion. We will demonstrate the sealing effectiveness of LCE in both laboratory experiments and field trials, describe how the radial deformation impacts the casing and cement, and generally discuss the current state of knowledge, capabilities and limitations of LCE with respect to SCP/SCVF remediation

Restoration of annular zonal isolation using localized casing expansion (LCE) technology: A proof of concept based on laboratory studies and field trial results

Sustained casing pressure (SCP), surface casing vent flow (SCVF) and other expressions of annular fluid migration are widely encountered zonal isolation issues. Conventional solutions for SCP/SCVF include perforate and squeeze cementing, or section milling and recementing. Regrettably, the former approach shows only limited success rates, while the latter involves time and cost intensive operations that require a drilling rig. We will show that localized casing expansion (LCE) technologies offer promising alternatives, enabling rigless remediation of annular fluid migration. The LCE concept involves imposing permanent deformation on the casing pipe to locally enlarge its diameter. The associated annular volume reduction causes closure of defects such as micro-annuli and cement fractures, plus potentially even larger voids, and results in an overall densification of the cement microstructure. The Shell-developed Local Expander tool is e-line deployable and imposes the required casing deformation in a mechanical, fully controlled manner. Tailored-shaped energetic charges offer valuable supplementary means for achieving expansion. We will demonstrate the sealing effectiveness of LCE in both laboratory experiments and field trials, describe how the radial deformation impacts the casing and cement, and generally discuss the current state of knowledge, capabilities and limitations of LCE with respect to SCP/SCVF remediation