Session: 10-04-01 Bucket, Gravity Foundations and Caissons

Paper Number: 79853

79853 - A Computational Framework for Integrated Analysis and Hybrid Testing of Mooring Line Foundations 

Positional restraint of floating structures can be achieved using mooring systems anchored to the seafloor. Lifecycle assessment of these foundation systems is challenging; engineers need to account for both the variability in wave and wind loading as well as the large uncertainty associated with the load-displacement behavior and bearing capacity of anchors. In response to this challenge, new analytical models must be developed and validated against experiments. For this, a hybrid testing (HT) framework for mooring line foundations is being developed across Aarhus University (AU) and the Karlsruhe Institute of Technology (KIT).

HT testing is conducted using a hybrid model, which comprises a physical and a numerical subsystem (PS and NS, respectively). The former is tested in the laboratory while the latter is numerically simulated. A closed control loop simulates the interaction between the two subsystems subjected to a realistic excitation [1]. In offshore engineering, HT testing is extensively used for the identification of hydrodynamic models. In this case, the floater (PS) is installed in an ocean basin in station-keeping mode and subjected to artificially generated waves. A control system adjusts the mooring line tension forces in real-time based on the floater velocity response. As a result, the dynamic interaction between the tested floater (PS) and a virtual mooring system (NS) of given stiffness and damping is accurately reproduced [2].

The same HT paradigm can be reasonably adapted to study geotechnical and structural aspects of mooring line foundations. In this case, one or multiple anchors are tested in the laboratory (PS) while mooring lines and floater (NS) are numerically simulated. The advantage of using HT is twofold. First, the tested load cases are more representative of the actual loading scenario experienced by the anchor and, thus, experimental results are more meaningful. Second, parametrization of loading and NS enable designing experimental campaigns that cover the entire range of loading scenario experience by the anchor with measurable statistical significance. However, to the authors’ knowledge, the capability of the HT of mooring line foundations has not been demonstrated yet.

This paper presents a computational framework suitable for HT, consisting of computationally efficient numerical models of the floater, mooring lines, and anchor elements. This is the first outcome of the joint AU-KIT research on HT aiming to improve the design and assessment of foundations for floating offshore structures.   

References

[1].  Pan, P., T. Wang, and M. Nakashima, 2016, Development of Online Hybrid Testing: Theory and Applications to Structural Engineering. Oxford [England]; Waltham, MA: Elsevier / Butterworth Heinemann.

[2].  Vilsen, S.A., T. Sauder, A.J. Sørensen, and M. Føre, 2019, Method for Real-Time Hybrid Model Testing of Ocean Structures: Case Study on Horizontal Mooring Systems. Ocean Engineering 172: 46–58.

Presenting Author: Giuseppe Abbiati Aarhus University

Authors:

Giuseppe Abbiati Aarhus University
Andrea Franza Aarhus University, Department of Civil and Architectural Engineering
Zili Zhang Aarhus University, Department of Civil and Architectural Engineering
Lars Vabbersgaard Andersen Aarhus University, Department of Civil and Architectural Engineering
Hans Henning Stutz Karlsruhe Institute of Technology, Institute of Soil Mechanics and Rock Mechanics