GTT LOOKS TO EXTEND DIGITAL TWIN MODEL FUNCTIONALITY

GTT announced that it has been awarded an Approval in Principle (AiP) by Lloyd’s Register for the use of its ‘Sloshing Virtual Sensor’ to optimise LNG membrane tank maintenance

The AiP has validated the use of GTT's ‘Sloshing Virtual Sensor’ for sloshing activity assessment to optimise the LNG membrane tank maintenance frequency.

The solution will allow the survey frequency for membrane containment tanks aboard LNG carriers to be extended, potentially by up to from 5 years to 7.5 years, subject to the approval of the request for a Tank Alternative Survey Plan by GTT, the classification society and the flag state.

GTT noted that the latest AiP for the sensor had been awarded after a project including Lloyd’s Register and Shell International Trading and Shipping Company Limited (STASCO), as well as multiple ship owners and flag states. GTT identified the contribution made by Shell as particularly valuable in helping to refine the use cases and validate the value proposition.

The project demonstrated that the predictive functionality of the Sloshing Virtual Sensor was accurate by validating the design methodology of GTT’s digital twin solution, and subsequently by comparing the predictions produced by the digital twin with real-time operational data from a Floating Storage and Regasification Unit (FSRU), a Floating Liquefied Natural Gas (FLNG) facility and an LNG carrier.

“All the technology aspects were thoroughly assessed, including the design, the validation methodology and the implementation details,” a GTT representative told The Motorship.

Upgrade requirements

For existing GTT Digital customers, the upgrade effort depends on the initial solution they already have on-board. Otherwise, the Sloshing Virtual Sensor can be applied for new building as well as vessels in-service. The only difference is that we may need to conduct a past-life study for vessels inservice to set up the initial fatigue and/or damage risk state.

The physical requirements for the installation on board are comparatively limited. The solution requires the installation of a motion reference unit (MRU) on board the vessel to measure the ship motions, along with an “edge” computer that collects the relevant data signals and performs some preliminary computations before sending the data to the shore for further analysis and computations.

The AiP did not approve the individual sensors but it did define the specification of the sensors when used for the envisaged application. The system was designed to be able to continue to operate in case the MRU unit fails, using hindcast data to compute the sloshing activity in the tank as an interim measure until the sensor is returned to operation.

GTT notes that it is currently working with all of the major classifications societies to allow all the LNG vessel owners and charterers to benefit from this technology. “We believe that this technology has the potential to become an industry standard,” a GTT representative said, adding that it plans to develop a similar technological solution for LNG-fuelled vessels fitted with a membrane tank.

The company is also seeking to extend the scope of the predictive functionality to cover LNG sloshing prediction inside the tank. “By reducing the LNG evaporation caused by the LNG sloshing, we can help the owners better manage the cargo and the charterers reduce the loss of cargo.”

Extended Survey Frequency

By moving to a Tank Alternative Survey Plan, the survey frequency for LNG carriers could be extended from 5 years to 7.5 years, according to GTT’s base case. For stationary units like FLNGs and FSRUs, the base case is 10 years, but it could be even more depending on the classification society involved.

For both the stationary vessel types, GTT notes that the extension period depends not only on the vessel’s type but also upon the weather conditions experienced at the site as the exposure impacts sloshing activity.

The extension of the survey period is expected to have a significant effect on the availability of LNG carriers, as well as FLNGs and FSRUs. The Motorship notes that physical tank surveys involve dry-docking, with knock-on effects on schedules, while entry into the containment vessel increases the risk of additional off-hire times.

8 GTT has received AiPs from Bureau Veritas and Lloyd’s Register for the use of ‘Sloshing Virtual Sensor’ for class surveys of its membrane tanks, and is currently working with all of the major classifications societies for this technology

By reducing the frequency of physical surveys, it is expected that shipowners will benefit from reduced maintenance time and costs, while charterers will benefit from enhanced uptime, and increased cargo deliveries within a charter contract.

“In a survey cycle, the potential savings for the ship owner is in the range of hundreds of thousands of US dollars, while [additional profits for] the charterers is in the millions of US dollars.”