Monitoring system of extreme loadings of propulsion system’s foundation : design assumptions

Project of on-line diagnostic (monitoring) system of marine propulsion system working parameters is the authors' general target. Proper propulsion system’s foundation is one of the most important parameters for its reliable operation. Different types of quasi-static loadings and dynamic excitations can be observed during ships exploitation. Presented research has been limited to extreme loadings. Underwater explosions or ship groundings are considered examples of extreme foundation loadings. Analysis of the physical parameters of the extreme forces has been presented in the first part of the paper. Water pressure spatial and non-spatial (time) distribution during underwater explosion has been analysed as an example. Short overview of the dynamic mathematical models of underwater explosions is presented. Time function of vibrations acceleration of ship construction is important design assumption of planned Structural Health Monitoring (SHM) system. Propulsion system's foundation loading measurements should take into account general ship hull deformation (in the aft part of the ship) as well as reactions changes of main engine and shaft line bearings. Ship hull deformation should be monitored as quasi-continuous measurements, along whole propulsion system. Optical Time-Domain Reflectometer method (OTDR) is planned for hull deformation monitoring. Propulsion system bearings' reactions are a source of local foundation pads' strain changes. Fibre Bragg Grating (FBG) sensors are the best for that kind of measurements, in authors opinion. Both techniques (OTDR and FBG) have been shortly described in the paper. Scheme of monitoring system of marine propulsion systems foundation's loadings are proposed in the end of the article.