Distributed motion sensing on ships

A current trend is autonomous transport of goods and people in the air, at land, and at sea. For safe and reliable operations, autonomous systems require sensors that replace, or even exceed, the senses of a human operator. A system of spatially distributed inertial measurement units (IMUs) along the hull of a vessel, which allows sensing of local accelerations of a vessel or structure at sea is proposed. In contrast to classic motion sensors on ships, the sensors are not placed in a central location of the ship, but are instead mounted on the inside of hull of the vessel. This enables the system to measure local hull vibrations, which are induced by external forces or pressure gradients. The measurements can be processed to allow a spatial awareness of environmental loads or force fields acting on the vessel. After a discussion of the fundamentals of local motion sensing on a marine vessel, this paper presents two applications for distributed motion sensing. The first application is the measurement and classification of ice-induced vibrations in the hull of an Oden-class icebreaker during transit and stationkeeping in ice-infested waters. At four locations on the vessel, the local vibrations were measured and probability distribution function fitted to the motion data. It is shown, depending on the ice-conditions, that the stochastic properties of the signal change. In a second application, a model scale ship is equipped with an array of four motion sensors along the hull of the vessel and one virtual sensor in the center of gravity as a reference measurement. By this configuration, it is demonstrated how to detect local pressure zones along the hull caused by incoming waves.