The paper presents a true digital twin concept, which is a general and novel methodology that significantly improves the fatigue prediction models of existing marine structures. The actual structural condition of existing marine platforms can often change after several years in operation due to degradation mechanisms and/or other structural changes. It is within this context, the true digital twin concept has been developed and the general idea is to create a coupling between the digital twin and measurements. The measurements are performed by Structural Health Monitoring Systems (SHMS). This coupling facilitates a direct performance evaluation of the digital twin against measurements and most importantly creates the basis for improving the performance of the digital twin to accurately capture the actual condition of the structure, and thus become a true digital twin. The full concept of creating a true digital twin encompass novel advanced analysis methods ranging from linear system identification, expansion processes, Bayesian FE model updating, wave load calibration, quantification of uncertainties from measured data, and Risk- and Reliability Based Inspection Planning (RBI) analysis, [1]. This paper presents the first 3 levels for establishing a true digital twin. The levels are illustrated by 3 case stories.

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This paper introduces a general, finite-element-based optimisation tool for improving the material layout of concrete structures. The application presented is general and exemplified by material optimisation of reinforced concrete slabs. By utilising the optimisation tool, it is possible to determine the optimal material layout of a slab at the ultimate load state based on simple inputs such as outer geometry, boundary conditions, multiple load cases and design domains. The material layout of the optimal design can either be fully orthotropic or isotropic, or a combination with a predefined coupling between design domains and reinforcement directions. The implementation is a lower bound formulation, resulting in a convex optimisation problem that consists of a number of linear constraints from the equilibrium equations and a number of convex non-linear constraints from the yield criteria. By utilising the capabilities of the non-linear interior point method, the non-linear convex yield criteria can be handled directly in the optimal solution process. Further, a graphical user interface is introduced, providing the design engineer with a practical tool for designing optimal structures. Finally, a number of reinforced concrete slab examples validate the method described and show the potential to save large amounts of material in constructions.

The scope of this paper is to connect a nonlinear WEC numerical model with a structural response model. The numerical WEC model takes into account the nonlinear hydrostatic restoring moment of the Wavestar float. A parameterized structural model of the Wavestar arm is developed in ANSYS APDL. Based on the assumption that the structural displacements remain small, linear first order theory is used to calculate the structural response. The section moments and forces are thus superimposed according to the superposition law. The effect of the nonlinear hydrostatic restoring moment on the structural response is investigated. Moreover, an analysis is carried out which shows that reactive control, applied as a closed loop control, increases the section moments and shear forces.