Mooring Line Tension Calculation and Monitoring

Discover the importance of calculating and monitoring mooring line tension for floating structures like FPSOs and learn how the RUP Excursion Monitoring System can meet this requirement with its Mooring Line Tension software module.

Understanding Mooring Line Tension Calculation

Mooring line tension calculation is an important aspect of floating wind turbine structures, as outlined in DNV standard DNV-ST-0119 and DNVGL-OSE301. In some cases, mooring line tensions can be calculated instead of measured, such as for submerged turret systems. However, this requires knowledge of the anchor positions, anchor line lengths, and continuous monitoring of the unit's position.

To calculate mooring line tension, the RUP Excursion Monitoring System offers a Mooring Line Tension software module. Before using this module, a work package must be carried out to compute the Load Response Curves. Each mooring line is analyzed using software like OrcaFlex to determine its tension for various offsets from the floating structure's neutral position. These analyses result in a set of Load Response Curves, with additional curves needed if the mooring design is sensitive to changes in water depth caused by ballast/draft and tide.

The Mooring Line Tension software module is configured with the Load Response Curve information for each mooring line. It runs in the background alongside other RUP Excursion Monitoring System software, computing the tensions at a rate of 1Hz. The output tensions are written into the realtime database as standard SCADA tags, which can be monitored, displayed, and logged.

Implementation of the RUP Excursion Monitoring System

The RUP Excursion Monitoring System is a comprehensive solution for monitoring the position and mooring line tensions of floating structures like FPSOs. With the addition of the Mooring Line Tension software module, it can meet the requirement outlined in DNV standard DNV-ST-0119 and DNVGL-OSE301.

To implement the RUP Excursion Monitoring System, a work package must be carried out to compute the Load Response Curves for each mooring line. This involves analyzing each line using software like OrcaFlex to determine its tension for different offsets from the neutral position. The resulting set of Load Response Curves provides the necessary information for the Mooring Line Tension software module.

Once implemented, the Mooring Line Tension software module runs in the background alongside other software components of the RUP Excursion Monitoring System. It computes the tensions at a rate of 1Hz and writes the results into the system's realtime database as SCADA tags. These tags can be used for alarm monitoring, display, and logging.

Load Response Curves Analysis

Load Response Curves analysis is a crucial step in calculating mooring line tensions for floating structures. By analyzing each mooring line using software like OrcaFlex, it is possible to determine the tension for various offsets from the structure's neutral position.

During the analysis, a set of Load Response Curves is generated, with one curve for each mooring line. These curves represent the load response for different conditions, such as high and low tide. The mooring line load is computed based on the offset from the neutral position and the water depth, which is used to interpolate between the curves.

The Load Response Curves analysis provides the necessary information for configuring the Mooring Line Tension software module of the RUP Excursion Monitoring System. It ensures accurate and real-time monitoring of mooring line tensions.

Monitoring Mooring Line Tension

Monitoring mooring line tension is essential for ensuring the stability and safety of floating structures like FPSOs. With the RUP Excursion Monitoring System's Mooring Line Tension software module, this monitoring can be done accurately and efficiently.

The Mooring Line Tension software module is configured with the Load Response Curve information for each mooring line. It runs in the background alongside other software components of the RUP Excursion Monitoring System, continuously computing the tensions at a rate of 1Hz.

The calculated tensions are then written into the system's realtime database as standard SCADA tags. These tags can be easily monitored, displayed, and logged, providing real-time information on the mooring line tensions. This enables operators to quickly identify any abnormal conditions and take appropriate actions.

Detecting and Responding to Failures

Detecting and promptly responding to mooring line failures is crucial for maintaining the integrity of floating structures. In a 3x2 mooring spread, a single mooring line failure can result in large mooring line loads on the lines in the failed sector.

To detect failures, the RUP Excursion Monitoring System's Mooring Line Tension software module provides load bar displays that turn red when high tensions are detected. In case of a sudden failure, there would be a step change in the load trend, which can also be monitored visually.

To ensure timely response, the Control Centre is equipped with audible and visual alarms that announce any mooring line failure. Additionally, email alerts can be configured to notify relevant personnel. These measures help minimize the downtime and potential risks caused by mooring line failures.