Force actuated real-tme hybrid model testing of a moored vessel: A case study investigating force errors

This paper presents a study where real-time hybrid testing is used to emulate a moored barge. The barge is modelled physically while the mooring forces are simulated numerically and actuated onto the physical substructure. Assuming no errors in modelling of the numerical substructure, we investigate what separates the instantaneous forces acting on the physical substructure, from the forces that would be acting on it in the ideal, non-substructured case that we are trying to replicate. Four different types of errors are identified, discussed, and partly quantified.publishedVersion© 2018, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd

Numerical Models in Real-Time Hybrid Model Testing of Slender Marine Systems

This paper presents a study of numerical models used in Real-Time Hybrid Model (ReaTHM) testing, conducted in a still water basin at SINTEF Ocean. ReaTHM testing is a method where a system is divided into physical and numerical substructures to study complex hydrodynamics on the physical system. Basin infrastructure limitations are handled by numerically modeling structural components with large geometrical extent. The numerical and physical substructures are coupled in real-time through a system of sensors and actuators. The emulated system under consideration in the study is a moored axisymmetric cylindrical buoy. The physical substructure is the buoy in model-scale ratio 1:144, while the numerical substructure is the full-scale mooring system consisting of twelve mooring lines. The time scale ratio requires the numerical models to run twelve times faster than real-time. To potentially reduce computational cost, a study is performed of three variations of numerical models, varying from low to high fidelity. The models are evaluated based on the sensitivity to jitter, induced time delays and clock drift imposed on the system

Controller Analysis in Real-Time Hybrid Model Testing of an Offshore Floating System

This paper presents an experimental study using Real-Time Hybrid Model (ReaTHM) testing of a moored floating cylindrical buoy, conducted in a wave basin. ReaTHM testing is a method for studying the dynamics of marine structures by partitioning the system into numerical and physical substructures that are then coupled in real-time using a control system. In this study, the floating cylinder buoy is modelled physically, and the mooring system modelled numerically. In this paper, the effect of selected controller parameters on the performance of the control system is studied, for both wave frequency and low-frequency ranges. The architecture/design of the control system is presented in the first part of the paper, while results from experimental tests with wave excitation on the physical substructure are presented in the second part of the paper.acceptedVersio

Controller Analysis in Real-Time Hybrid Model Testing of an Offshore Floating System

This paper presents an experimental study using Real-Time Hybrid Model (ReaTHM) testing of a moored floating cylindrical buoy, conducted in a wave basin. ReaTHM testing is a method for studying the dynamics of marine structures by partitioning the system into numerical and physical substructures that are then coupled in real-time using a control system. In this study, the floating cylinder buoy is modelled physically, and the mooring system modelled numerically. In this paper, the effect of selected controller parameters on the performance of the control system is studied, for both wave frequency and low-frequency ranges. The architecture/design of the control system is presented in the first part of the paper, while results from experimental tests with wave excitation on the physical substructure are presented in the second part of the paper

Method for Real-Time Hybrid Model Testing of ocean structures: Case study on horizontal mooring systems

This paper presents a method for Real-Time Hybrid Model testing (ReaTHM testing) of ocean structures. ReaTHM testing is an extension to traditional hydrodynamic model-scale testing, where the system under study is partitioned into physical and numerical substructures. The physical and numerical subsystems are connected in real-time through a control system. Based on experience with various ReaTHM tests, a general method for ReaTHM testing of ocean structures has been proposed. An experimental case study was carried out to illustrate the proposed method. The study was conducted in a state-of-the-art hydrodynamic laboratory, where a physical cylindrical buoy was placed in a still-water basin. Horizontal mooring loads from a numerical mooring system, which were modelled using the nonlinear finite element software RIFLEX were actuated onto the physical substructure. System performance was verified through comparison with a physical horizontal mooring system consisting of physical springs.publishedVersion© 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/)