Offshore Technology Research Center

 

OTRC Project Summary

Project Title:

Risk Assessment of Submarine Slope Stability - Hydroplaning

Prinicipal Investigators:

Stephen Wright

Sponsor:

Minerals Management Service

Completion Date:

February, 2007

Final Report ID#

B178(Click to view final report abstract)

OBJECTIVE:

This project is developing a model to predict the movement of submarine slides, with emphasis on slides that travel large distances once they are initiated. In particular the research seeks to develop a numerical model for predicting the initiation of hydroplaning of a slide mass and the subsequent motion of the mass once hydroplaning is initiated.

The numerical model developed in this project will be applicable to subaqueous slides of any scale, and will be able to determine if hydroplaning is likely to be initiated as well as the magnitude of movements when hydroplaning is initiated. The sliding process will be simulated based on the initial geometry of a slope failure, the geology of the nearby seafloor, and the mechanical properties of the slide material (including shear strength, stress-deformation properties and unit weight). The model will describe (1) the variation of the velocity of the slide mass in time and space, and (2) the eventual runout distance and geometry of the slide mass. This information is essential in judging the potential risk associated with submarine slides.

INTRODUCTION:

Previous research on submarine slides has consisted of numerical and physical modeling and the development of both empirical and numerical models to predict the initiation and movement of slides. This research shows that under certain conditions a moving slide mass can hydroplane on a layer of water that becomes trapped between the moving slide mass and the underlying soil. One of the most important aspects of hydroplaning is the interaction between the moving slide mass and surrounding fluid. Most of the previous work has been based on simplified assumptions regarding the interaction between the sliding mass and fluid. Often the assumptions are based on the interaction between fluid and simple structural elements that often have different geometries and are subjected to quite different motions than a slide mass moving along the ocean bottom. The assumptions have not been verified and most likely introduce errors of a large, but unknown magnitude.

BENEFITS TO MMS & INDUSTRY:

Provide a means of including the likelihood and impact of hydroplaning on submarine soil slides to better evaluate the risk of slides impacting a subsea facility or pipeline planned for a specific site in the Gulf of Mexico.

DEPLOYMENT OF RESULTS:

Results of this research will be published in Project Reports, theses, and dissertations as well as in conference proceedings and journal articles. Guidance on the likelihood and impact of hydroplaning on slides that could occur in the Gulf of Mexico will be provided, and the model will be available for application.

PROJECT ORGANIZATION & TIMING:

During the Phases 1 and 2, research focused on modeling the interaction between a moving slide mass and surrounding fluid. Various numerical models for fluid response, including the commercial software Fluent have been used for this purpose. This modeling has led to an improved understanding of the characteristics of the fluid-slide mass interaction. However, up to this point the focus of the research has been on the fluid, rather than on the motion and deformation of the slide mass. In work done to this point the motion of the slide mass has been stipulated as a boundary condition. In Phase 3 we will incorporate the understanding of the fluid-mass interaction into a numerical model that includes the moving and deforming soil slide mass. The primary scope of the work in Phase 4 is experimental. In this phase laboratory experiments will be developed, performed and used to verify and calibrate the numerical model developed in Phase 3. The model will also be compared to any available field data. The calibrated model will be applied to hypothetical situations typical of Gulf of Mexico conditions to illustrate situations in which hydroplaning is likely and its impact on the slide behavior.

Related Publications: Hongrui Hu, Stephen G. Wright, and Spyros A. Kinnas. (2006). “Hydroplaning of Submarine Slides and the Influence of Hydrodynamic Stresses”. Proceedings, 16th International Offshore and Polar Engineering Conference, San Francisco, California, USA. pp. 482-489.

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