TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA riser fatigue monitoring strategy and implementation on a deepwater Gulf of Mexico Spar top tensioned riser is presented. The paper explains why a fatigue monitoring program is considered necessary to provide the operator with assurance of the riser system performance and integrity in service, the considerations that led to the selection of an appropriate monitoring system and describes in detail the standalone motion logger system adopted.The principles and methods of measurements that permit the monitoring of motions at discrete locations on the riser are presented along with the methods of processing this data such that fatigue damage along the riser can be interpreted.The paper describes how a standalone logger monitoring system has been successfully installed entirely using a ROV, eliminating the need to run the monitoring system during critical path riser installation activities.
Riser VIV response due to ocean current loading is a complex phenomenon governed by both the hydrodynamic and structural properties. In order to obtain better understanding of the global riser VIV response and assist in the improvement of riser VIV design, riser monitoring is being increasingly used. An optimization technique to identify the number of sensors required and the sensor locations for monitoring riser VIV fatigue is presented. The optimization technique has been developed using modal decomposition and linear regression. The paper explains why monitoring at selected locations with limited instrumentation is sufficient to capture global riser response. The principles and methods of using multiple measurement quantities in the optimization technique are also presented along with the adopted methodology, limitations and key conclusions.
Steel Catenary Risers (SCR) are critical dynamic structures with a complex fatigue response. The offshore industry lacks verification of analytical models with full-scale response measurements. Only a small number of installed SCRs have any instrumentation to monitor dynamic response. This paper describes an on-line monitoring system deployed on one of the Tahiti infield (production) SCRs. Tahiti is a Truss Spar Floater located in 4,000 ft water depth in the Gulf of Mexico. The system is configured with localized strain and motion measurement devices. Emphasis is placed on the selection of number and location of the monitoring devices to characterize vessel induced riser response, VIV induced riser response, riser-seabed interface, and discontinuities at the riser hang-off locations. Monitoring device sensitivity requirements and qualification programs are also discussed. The monitoring system configuration drivers are reviewed in detail such as; monitoring objectives, instrumentation requirements, specification and architecture, field development integration, and installation. Information provided in this paper would be helpful for configuration of complex monitoring systems for deepwater steel catenary rises.
This paper presents two numerical methods, a vortex lattice method (MPUF-3A) coupled with a finite volume method (GBFLOW-3D) and a boundary element method (PROPCAV), which are applied to predict time-averaged sheet cavitation on rudders, including the effects of the propeller as well as of the tunnel walls. The coupled MPUF-3A and GBFLOW-3D determines the velocity field due to the propeller within the fluid domain bounded by tunnel walls. MPUF-3A solves the potential flow around the propeller by distributing the line vortices and sources on the blade mean camber surface and determines the pressure distributions on the blade surface. GBFLOW-3D solves Euler equations with the body force terms converted from the pressure distributions on the blade surface and determines the total velocity field inside the fluid domain. The tunnel walls are treated as a solid boundary by applying the slip boundary condition, and the propeller blades are modeled via body forces. The two methods are solved iteratively until the forces on the blade converge. The cavity prediction on the rudder is accomplished via PROPCAV, which can handle back and face leading edge or mid-chord cavitation, in the presence of the three-dimensional flow field determined by the coupled MPUF-3A and GBFLOW-3D. The present method is validated by comparing the cavity shapes and the cavity envelope with those observed and measured in experiment and computed by another method.
Steel catenary risers (SCRs) in deepwater environment exhibit complex dynamic dynamic response governed by various factors such as environmental conditions, vessel motions, soil-structure interaction and material degradation. Uncertainties in the SCR design exist in the design data, analysis methodologies, fabrication, and hence a conservative approach has been adopted to overcome these shortfalls. Recent advances in monitoring systems installed on SCRs provide operator the assurance of the integrity of the SCRs in service, verify the SCR design, and enhance basic understanding of the SCR response. This paper outlines a strategy for monitoring the SCRs to characterize the response due to vessel motions, vortex induced vibrations (VIV), and soil-structure interaction. A detailed example of real-time SCR monitoring system with optimized array of motion and strain measurements is presented. The methodology for sensor selection and optimization is based on linear regression analysis. The measured data processing methods include shape matching the response amplitudes with correlating response frequencies. The principles and methods of measured data interpretation to capture global response shape due to wave and vessel motions induced and VIV are presented. The pipe-soil interaction such as soil stiffness, suction, softening and trenching effects characterized using the strain measurements in the touch down zone are presented. In addition, the methods to calibrate the individual vertical, lateral and axial models for pipe-soil interaction are presented.
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