Fault Detection for Shipboard Monitoring and Decision Support Systems

Abstract

In this paper a basic idea of a fault-tolerant monitoring and decision support system will be explained. Fault detection is an important part of the fault-tolerant design for in-service monitoring and decision support systems for ships. In the paper, a virtual example of fault detection will be presented for a containership with a real decision support system onboard. All possible faults can be simulated and detected using residuals and the generalized likelihood ratio (GLR) algorithm. INTRODUCTIONThe SeaSense system (Nielsen et al., 2006) has been installed on several containerships and navy vessels. The system provides an estimation of the actual sea state, information about the longitudinal hull-girder loading, seakeeping performance of the ship, and decision support on how to operate the ship within acceptable limits. It is able to identify critical forthcoming events and to give advice regarding speed and course changes to decrease the wave-induced loads. The system, sketched in Figure 1, includes a number of sensors all of which are used to estimate hull girder responses and predict wave loads, with the purpose of avoiding critical levels of hull stresses and ship motion(s). In this paper, it is suggested to improve the system by converting the system into a faulttolerant monitoring and decision support system. All the changes are on the software side, but the hardware remains the same. The wave elevation could be obtained using SeaSense system by combining the relative wave height and the vertical acceleration. The wave elevation has been -artificiallyincluded in the sensor fault detection procedure as a virtual (non-existent) sensor. The sensor fault detection is performed using several measurements: vertical acceleration, heave, pitch,

Fault Isolation and Quality Assessment for Shipboard Monitoring

“…The residuals were evaluated by the GLR test, and all the faults were detected and isolated. Using the model presented in the paper, we are able not only to detect, as in case of previous models given by [7] and [8], but also to isolate all the faults. Having fault isolation is very important for the design of a fault tolerant monitoring and decision support system.…”

“…Several papers deal with fault-tolerant monitoring and/or control of ship responses to the waves. Fault detection and fault-tolerant approaches for the SeaSense system have been presented in [7] and [8] using a different model than the model described in this paper. With the "old" model, purely based on the ship kinematics, it was possible to detect, but not to isolate all the faults.…”

Towards fault-tolerant decision support systems for ship operator guidance

“…In the original work by Lajic [15] two models for fault diagnosis are discussed: the time domain model based on ship kinematics, and the frequency domain model based on linear spectral analysis.…”

“…However, recently research has been initiated, e.g. Lajic [15], Lajic and Nielsen [17], Lajic et al [16,18], and it is foreseen that many improvements in this area will be made in the future. [22].…”

“…The present article summarises important findings made in a recent Ph.D. work, Lajic [15], on faulttolerant monitoring and decision support systems. Specifically, work was carried out to improve the reliability and dependability of decision support systems applied for matters of ship safety.…”