Abstract
A method for accurate prediction of flexible riser behavior and component stress computations under irregular wave inputs is a subject of major interest to offshore oil and gas operators. The initial full field procurement for flexible risers can be upwards of 500M USD, with replacement costs of a single flexible riser often approaching 40M USD. The reliability of fatigue life estimates is therefore critical to the successful long term operation of flexible risers. Computational constraints, however, continue to prevent realistic simulations and meaningful fatigue life predictions.
To address this challenge, a next generation computational capability for nonlinear dynamic simulations of flexible risers has been developed. The FLEXAS solver overcomes computational constraints which limit conventional flexible riser analysis methods by implementing Nonlinear Dynamic Substructuring (NDS). This advanced multibody framework enables the incorporation of detailed finite element models into global nonlinear dynamic simulations under realistic environmental and system loads. Prior to this development, simulating these complex models for spans greater than a few pitch lengths was computationally not feasible even in static cases. The purpose of this DeepStar project is to validate the FLEXAS solver for nonlinear dynamic simulations of flexible risers against numerical and experimental references, and includes extensive local and global benchmarking.
The local benchmarking scope involves comparing FLEXAS simulations against numerical and experimental references of pitch-length and bench test configurations. These benchmarks comprise a wide array of tensile armor stress and strain comparisons made against both a commercial solver and strain gauge measurements. The global benchmarking scope involves the comparison of FLEXAS simulations of a full length flexible riser configuration against the industry accepted numerical benchmarks, which includes large displacement nonlinear statics, vessel motion nonlinear dynamics and regular wave motion nonlinear dynamics. Results from all nonlinear simulations were in excellent agreement with their respective benchmarks.
This work was initiated, technically guided and funded by DeepStar Global Deepwater Technology Development Program as part of Phase XII projects in the DeepStar X400 Floating Systems Committee. The successful completion of the project, established herein, is to build confidence within the industry, which will benefit from the validated FLEXAS simulation technology by improving decision making associated with flexible riser integrity management and continued service, with major cost savings realized across the entire flexible riser life-cycle.
