Subsea Inertial Measurement Units for Marine Riser Fatigue Analysis
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Solution Overview
Problem
The complexity and cost of distributed sensor systems make it impractical to effectively monitor the dynamics of marine riser systems, which are crucial for dynamic positioning, determining riser and wellhead fatigue, and managing cyclic loads that cause fatigue in marine riser systems.
Innovation Solution
A monitoring system comprising subsea inertial measurement units at strategic locations on the marine riser and LMRP, capable of acquiring and processing time series data for inclination and acceleration, computing frequency spectra, and transmitting data to a surface processing unit for stress level computation and fatigue analysis, reducing the need for extensive sensor networks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If distributed sensor systems are used to monitor marine riser vibrations, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent divides the marine riser monitoring into discrete measurement locations (surface, intermediate, and bottom positions) with dedicated sensors at each segment. This segmentation allows focused monitoring of critical vibration zones without requiring continuous distributed sensing along the entire riser length, reducing overall system complexity while maintaining measurement precision at key locations.
Solution Approach 2:
The patent introduces intermediate measurement devices (such as tensionometers and inclination meters) that act as mediators between the complex distributed vibration field and the simpler surface measurement system. These intermediaries capture specific vibration characteristics at strategic points and transmit simplified data to the surface, reducing the need for extensive distributed sensor networks.
2Measurement precision
If distributed sensor systems are deployed along the marine riser, then measurement precision is improved, but manufacturing and installation cost increase
Solution Approach 1:
The monitoring system is segmented into modular units located at surface, intermediate, and bottom positions. Each module contains necessary sensors and electronics, allowing independent installation and testing. This modular approach simplifies manufacturing and installation compared to deploying continuous distributed sensor systems along the entire riser length.
Solution Approach 2:
The intermediate measurement devices are designed to perform multiple functions: measuring tension, inclination, and vibration characteristics simultaneously. This multi-functionality reduces the total number of separate devices needed, simplifying both manufacturing and installation processes while maintaining comprehensive monitoring capability.
3Reliability
If multiple sensors are distributed over the marine riser length, then reliability of fatigue assessment is improved, but device complexity increases
Solution Approach 1:
The patent applies local quality by concentrating measurement resources at specific locations where vibration amplitudes are highest or where fatigue is most critical (surface, intermediate, and bottom positions). Rather than uniformly distributing sensors along the entire riser, the system places sophisticated measurement devices at strategic locations to capture the most significant fatigue-inducing vibrations, improving reliability while reducing overall complexity.
Solution Approach 2:
The system implements feedback mechanisms where intermediate measurement devices continuously monitor vibration characteristics and transmit data to the surface for real-time fatigue assessment. This feedback loop allows the system to reliably assess fatigue conditions using focused measurements at key locations rather than requiring comprehensive distributed sensing, reducing complexity while maintaining assessment reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution provides practical and economical monitoring of marine riser dynamics, enabling accurate dynamic positioning, fatigue determination, and stress level computation along the riser and wellhead, thereby improving operational safety and efficiency.
Implementation Method 1
A monitoring system includes an inertial measurement unit adapted for measuring the inclination and acceleration of a marine riser
Data Source
AI summary
A monitoring system for use in a marine riser system coupled to a rig vessel includes one or more subsea inertial measurement units adapted for mounting to a lower end of a riser, an LMRP, or both. The one or more subsea inertial measurement units may acquire time series data of inclination and acceleration. The one or more subsea inertial measurement units may transmit, to a vessel transceiver, frequency data computed from the time series data, low-pass filtered values of the time series data, or both. The monitoring system includes a surface processing unit that is in communication with the vessel transceiver. The surface processing unit may be programmed to compute, for example, fatigue along the marine riser system, the difference between the inclination of the lower end of the riser and the inclination of the LMRP, or both, by applying predetermined functions to the transmitted data.