Real-Time Digital Twin Of Research Vessel For Remote Monitoring

Real-time digital twins of ships in operation find many applications such as predictive maintenance, climbing the ladders of ship autonomy, and offshore operational excellence. The literature describes a focus on digital twinning of individual equipment such as navigation, propulsion, engine and power system, or crane. Yet, digital twinning and virtual prototyping for offshore operations are in their infancy and the onboard digitisation hardware and the telecommunication infrastructure are becoming accessible and affordable. Previous work has failed to address the need for building a holistic model and thus contextualising the equipment with the state of the whole vessel. A prototype of an online digital twin of a research vessel is proposed, its architecture described and its suitability for virtual prototyping demonstrated in a remote control centre. The study shows a viable proof of concept for remote monitoring and crew assistance in nominal and contingency response for offshore crane operations.

Lumped, Constrained Cable Modeling With Explicit State-Space Formulation Using An Elastic Version of Baumgarte Stabilization

This paper presents a modeling approach for efficient simulation of slender structures, such as wires, cables and ropes. Lumped structural elements are connected using constraints. These are solved explicitly, using an elastic version of Baumgarte stabilization. This avoids singularities in the matrix inversions. The resulting explicit state-space formulation filters the higher order dynamics and can be solved using simple numerical integration methods. Constraints are demonstrated for modeling different aspects: Internal cable forces, one cable sliding along another cable and contact between cable and seabed. Also, a cable initialization routine is presented for rapid building of different interconnected cable geometries, ranging from cases in offshore crane operations to in-sea equipment such as seismic cables. Two case studies are presented to illustrate the effectiveness and the robustness of the proposed modeling approach; the first one being a test of two connected, sinking cables, and the last one being a larger case demonstrating the use of the cable library in an offshore seismic survey case.

A Robust Payload Control System Design for Offshore Cranes: Experimental Study

This paper presents a robust controller design of payload position control for an offshore crane facing disturbance and parametric uncertainties. The offshore operations with cranes while lifting and lowering a payload can be dangerous since safety and efficiency are affected by waves, wind and ocean currents. Such harsh sea conditions put the offshore crane and payload through unwanted disturbances and parametric uncertainties, which requires a robust control system to guarantee reliable performance of these systems. In this paper, we detail a controller designed based on uniformly ultimately bounded (UUB) theory, combined with the input-output linearization control technique (IOLC). The stability of the closed-loop system under the UUB conditions is analyzed using the energy-based Lyapunov function. To evaluate the control performance of the proposed controller, along with an IOLC and an integral sliding mode controller (ISMC), a comparison study is also conducted. The control performance and efficiency of the proposed controller are validated through experiments on an offshore crane model.