Technology






The Hull Stress Monitoring System by monitoring the stress responses in the hull structure during operations, helps to prevent design stresses being exceeded. The development of hull fatigue is measured using long-life optic sensors located in various positions in the hull. This is achieved by measuring the relative deformation, strain (stress) in the hull due to loading (still water strain) and due to waves (dynamic strain). The measured stress is analysed in a distributed way inside the sensors. The analysis methods used identify the static, dynamic and slow changing temperature components from the signal and calculate different signal characteristics. The results are transmitted to the central unit, normally on the bridge, to be further analysed, datalogged and displayed to the bridge personnel to assist the navigation. The various components of a typical hull stress monitoring system are described as, strain sensors, accelerometer units, bow pressure transducers and the bridge display unit:
 




SENSFIB Hull™ Stress Monitoring Systems is based on Fiber Bragg Grating (FBG) sensors. The FBGs are an internal stripe pattern in the core of the optical fiber that strongly reflects one wavelength (or color) of light & the user interface can be configured to show current stress, fatigue accumulation, accelerations and slamming trend as well as sailing conditions in terms of sea state, wind, speed and position if such equipment are integrated.
The Fiber Bragg Grating (FBG) optical sensing technology gives SENSFIB™ a competitive edge compared to the conventional Strain Gauge based sensors. Their key advantages being:


  • Sensors are intrinsically safe requiring no ZB and no limitation to their positioning.
  • Reliable as they are immune to EMI. & the software is based on a Linux OS platform.
  • Accurate as the stress measurements are based on measurement of the wavelength of light.
  • Reduced ownerships costs. (Recalibration, maintenance, repairs and service)
  • Flexibility due to ease of installation (no hot works required for sensor installation) and
  • The basic HSM system can be easily expanded to include fatigue monitoring in the water line, bow sensors for ice load monitoring etc., as desired.


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    SENSFIB Hull™ Stress Monitoring Systems helps the navigators to monitor the current status on hull stress with online information about the load margins and provide assistance to make faster decision-making for safe voyage. The same data can be post-processed to give valuable inputs for maintenance planning and fleet utilization.
     
    Safe and cost-effective operation of a vessel requires exact knowledge of the ship's design and awareness of the operational risks and their consequences. Bulk/LNG Carriers, Tankers and Container Vessels are particularly at a risk of hull fatigue damage, induced by the stresses that can occur in the hull as a result of ballast, cargo load and sea state. Fatigue build-up in vessels leads to local cracks in the hull, which if left unrepaired, eventually endanger the structural integrity of the vessel. The hull stress is one of the major factors which cause irretraceable damage to merchant marines. Fatigue accumulated in vessels leads to local cracks in the hull, subjected to catastrophic structural failure. Then, this might call very dangerous situations - with the consequent loss of life. One of the challenges involved has been the lack of information to the bridge about the actual load on the hull/structure. In order to reduce this type of damages, a tool is required which can collect this type of information and make it easily available at the bridge for the navigator. To reduce the incidence of such failures, IMO and leading Classification Societies have recommended the use of Hull Stress Monitoring Systems.
     


    Important features about the system:
     
  • Structural integrity vs safety (HSE)
  • Fatigue management
  • Preparation ahead of lifetime extension application
  • Preparation and documentation ahead of Risk-based inspections
  • Automated monitoring has become a preferred solution compared to traditional visual inspections due to development of new technology and cost/time saving for owners.
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