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The prediction of ultimate ship hull strength using a simplified progressive collapse method critically relies on the evaluation of the load-shortening curve of stiffened panel components. Uncertainty in the characteristics of load-shortening curves causes subsequent uncertainty in the hull girder strength calculation. The load-shortening curve shape is influenced by parameters including imperfection, residual stress, material properties and dimensional variance. To investigate this uncertainty, a sensitivity study on the ultimate strength calculation of a ship-type box girder is completed using parametrically defined load-shortening curve. The curve is formed of linear pre-and post-collapse responses and an arc to represent the nonlinear ultimate strength region. The load-shortening curve is systematically varied in ultimate strength, ultimate strain, elastic stiffness and post-collapse stiffness. A double hull box girder model under vertical bending, combined vertical/horizontal bending and cyclic bending is analysed using this parametric representation. The influence of each parameter is evaluated with a sensitivity index. The study shows that the structural component’s ultimate strength and post-collapse stiffness have the most significant influence.

The lateral load response of a monopile is often modelled by p-y curves. However, the traditional formulation of p-y curves is unable to describe the behavior of liquefied soil. This paper presents a numerical investigation of how to develop p-y curves for monopiles installed in liquefiable soil. A monopile is modelled in the 3D finite element software package PLAXIS 3D, where a soil model able to capture liquefied soil behavior is applied. The numerical results are used to extract relevant data to assess liquefaction in the soil. Based on this information, p-y curves are generated for the liquefied soil.

A structural health monitoring (SHM) program can improve the structural integrity of offshore structures, however, the SHM scheme implies extraction of linear time-invariant modal parameters by Operational Modal Analysis (OMA). Inherently, the offshore platforms are nonlinear, and in many cases, the dynamics of the platforms are involving a friction-induced coupling that stems from bearings in the bridges connecting the platforms. This mechanism is causing the platforms to interchange between acting either as one system or separate systems, depending on the sliding or sticking state of the bearings. Along these lines, the present paper proposes an identification framework employing nonlinearity optimised random decrement (NORD) and OMA parameter estimation methods to identify two sets of underlying linear modes, relative to the state of the friction-induced coupling, both from the same measurement record.

Multi-footed structures resting on suction buckets (suction caisons) comprise a promising foundation solution for next-generation 10 MW+ offshore wind turbines located in transitional water depths. For such systems, predicting the axial behavior of buckets is a critical design aspect. Load-transfer or t–z curves have been employed for decades as an efficient tool in pile design, however applying existing formulations to suction buckets bears uncertainty. This paper introduces a novel family of static t–z curves (Winkler springs) for suction buckets installed in typical marine sand. The study is based on 50 finite-element models that involve various foundation dimensions and soil properties, as well as drained uplift and compression. The non-linear springs’ properties are therefore linked to suction bucket diameter, friction angle and vertical overburden pressure. Lastly, good agreement is found between the current results and the ones from other numerical studies. Since the proposed t–z curves require only three basic parameters, they may be conveniently implemented in preliminary stages of foundation design.

In this paper a novel Data-Driven Design and Operation approach is introduced for an offshore wind energy application to account for site-specific conditions. Data from operational state of a turbine, e.g. accelerations, strain gauges, and SCADA, are intended to be used in the True Digital Twin concept to improve initial design assumptions. A calibrated numerical model combined with measured loading and response models allows to update the structural reliability and thus quantify the potential inherent conservatism. Given this additional knowledge the lifetime extension of existing structures can be assessed while for future structures their design procedures can be optimized according to a chosen cost function. The conceptual framework for including new information from measurements based on the Bayesian updating is presented in the paper. It is demonstrated how the initially assumed generic uncertainties regarding numerical models and environmental conditions can be consistently updated based on the site-specific data and hence lead to a more reliable design and operation of a structure. New information derived from data is accounted for based on the pre-posterior decision procedures supplemented with robust decision rules.

Tests were executed to analyze the behavior of disturbed foundation stiffness. Test results reveal a causal link between stiffness hysteresis loops and applied deformation amplitude. By manipulating the applied deformation amplitude, the size and position of stiffness hysteresis loops is plausible to control. The initial stiffness curve can be erased (disturbed) and reset afterwards. Also, cyclic stiffness curves of various size can be stabilized and repositioned. Such behavior is not predicted or accounted for by conventional models.

This paper addresses challenges in fatigue management of marine structural assets with a holistically approach, by jointly considering fatigue design, inspection and maintenance decisions, whilst taking into account sources of uncertainties affecting life cycle performance. A risk-informed and holistic approach is proposed for jointly optimizing fatigue design, inspection and maintenance based on the same fatigue deterioration model. The optimization parameters are fatigue design factor (FDF) and inspection intervals, while the objective is to minimize expected life cycle costs (LCC). The framework is to guide design process as well as to formulate optimal maintenance strategies. The proposed approach is exemplified for the marine industry through a fatigue-prone detail in a ship structure to obtain the life cycle optimal management solution that achieves a best compromise between structural safety and life cycle costs.

This paper presents the onboard measurement campaign for the case study of a container ship and provides a customary methodology for monitoring important machinery systems. The main principle aim of this paper is to collect important machinery data and parameters from critical systems, located in the engine room of the ship, by determining systems to be monitored, scenarios for monitoring, sensors and suitable portable equipment and physical parameters to be inspected.

A novelty floating wind turbine concept, which utilizes a newly developed triple-column spar platform to support the NREL 5MW baseline wind turbine, is proposed in this research. A modified environmental counter method is proposed to estimate the long-term extreme response of the novelty concept. Aero-hydro-servo-elastic coupled simulations are performed. Numerical simulations demonstrate that the triple-column Spar floating wind turbine has a better dynamic performance compared with a single-column concept, in terms of platform motion, tower base structural loads and mooring line tension. The critical environmental condition is identified with the modified environmental contour method, and it is shown that the 50-year return period extreme tower base structural load is reduced with the application of the three-column Spar platform. Nevertheless, the extreme mooring line tension which is dominated by the wind load, is not reduced. The present research reveals the prospect of the three-column Spar concept in the offshore wind energy application.