On Common Research Needs for the Next Generation of Floating Support Structures

The world is facing several industrial and societal challenges, such as providing enough renewable energy and enough safe and healthy food as formulated in the United Nations sustainable development goals. Using floating stationary structures, the ocean can contribute to solving several of the challenges. New applications need new types of structures, with which we have limited experience. These support structures will be diverse, but also have essential research needs in common. Design of novel floating structures need reliable descriptions of the marine environment. This is particularly challenging for semi-sheltered coastal regions, with complex topography and bathymetry. Novel structures are likely to be compliant, modular and/or multi-body, requiring increased understanding and rational models for wave-structure interaction. Structures with sustainable, safe, and cost-efficient use of materials, including untraditional ones, must be developed. Smart, affordable, and reliable mooring systems and anchors for novel applications are necessary for station keeping. Digital solutions connecting the various stages of design and operation, as well as various design disciplines, researchers, and innovators, will be necessary. Sustainability will be an integral part of any new design. To unlock the potential of novel floating structures, we need to understand the requirements of the applications, as well as the associated technology gaps and knowledge and research needs. This paper highlights research needs for innovation within floating offshore wind, floating solar power plants, novel aquaculture structures, and coastal infrastructure.acceptedVersio

3D motion dynamics of axisymmetric bodies falling through water

A new simplified method for analysis of 3D motion dynamics of axisymmetric slender bodies falling from air through water is presented. Slender-body theory for potential flow of incompressible water is combined with 2D + t theory to account for viscous cross-flow separation in the submerged phase. The effect of flow separation from the upstream end of a pipe plays an important role. Furthermore, asymmetric vortex shedding triggering important 3D motions is considered. The water impact loads are based on strip theory and empirical slamming coefficients together with added mass and buoyancy loads. The theory is validated by comparing numerical analyses with experimental drop tests of pipes performed by Aanesland (1987). Error analyses of the theoretical method are performed and compared with tests to explore the sensitivity to input variations.acceptedVersio

Evaluation of Nonlinear Material Behavior for Offshore Structures Subjected to Accidental Actions

Evaluation of the nonlinear structural response of any structure is a challenging task; a range of input parameters are needed, most of which have significant statistical variabil- ity and the evaluations require a high degree of craftsmanship. Hence, high demands are set forth both to the analyst and the body in charge of verification of the results. Recent efforts by DNVGL attempt to mitigate this with the second edition of the DNVGL-RP- C208 for the determination of nonlinear structural response, in which guidance or requirements are given on many of the challenging aspects. This paper discusses the vari- ous challenges and the direction to which the RP-C208 points compared to published research. Parameters affecting the plastic hardening, strain-rate effects, and ductile frac- ture are discussed separately. Then, the combined effect of the range of assumptions is evaluated to assess the resulting level of safety.Evaluation of Nonlinear Material Behavior for Offshore Structures Subjected to Accidental ActionsacceptedVersio

Evaluation of Nonlinear Material Behavior for Offshore Structures Subjected to Accidental Actions

Evaluation of the nonlinear structural response of any structure is a challenging task; a range of input parameters are needed, most of which has significant statistical variability and the evaluations require a high degree of craftsmanship. Hence, high demands are set forth both to the analyst and the body in charge of verification of the results. Recent efforts by DNVGL attempts to mitigate this with the second edition of the DNVGL-RP-C208 for determination of nonlinear structural response, in which guidance or requirements are given on many of the challenging aspects. This paper discuss the various challenges and the direction to which the RP-C208 points compared to published research. Parameters affecting the plastic hardening, strain-rate effects and ductile fracture are discussed separately. Then, the combined effect of the range of assumptions is evaluated to assess the resulting level of safety

LFCS Review report – Structure and mooring response - OC2018 A-073-WP3/WP4

A review is performed on structural and mooring response analysis work in relation to Large Floating Coastal Structures and the planning of long floating bridges across fjords. The review contains observations on global response methodology, environmental loading and interactions, mooring design, measurements and validation, and finally design criteria and limit states. The basis for the review is mentioned but described in detail in the LFCS Introduction and Summary report (OC2018 F-073-WP0). Tables of identified gaps are presented along with recommendations for further work.publishedVersio

Effect of modelling inhomogeneous wave conditions on structural responses of a very long floating bridge

Floating bridges are suitable for connecting land parcels separated by wide and deep waterbodies. However, when the span of the crossing becomes very long, the water environment exhibits inhomogeneities which introduce difficulties to the modelling, analysis and design of the bridge structure. The wave inhomogeneity may be described by means of field measurement and/or numerical simulations. Both approaches face complications when the resolution is much refined. It is thus important to examine the effect of the resolution related to the modelling of inhomogeneous waves on the global structural responses. In this study, a hypothetical crossing at the Sulafjord is chosen, and the wave environment in the year 2015 at 10 positions along the crossing is numerically computed. Next, different inhomogeneous wave conditions are established based on the wave data at 3, 5, and 10 positions, respectively. Time-domain simulations are conducted to examine the effect of different modelling approaches of the inhomogeneous wave condition on the global responses of a long, straight and side-anchored floating bridge

Effect of wave inhomogeneity on fatigue damage of mooring lines of a side-anchored floating bridge

Mooring systems are important structural components of very long floating bridges. They effectively limit the transverse motions of the bridge under environmental loads. They also add viscous hydrodynamic damping to the entire system. The safe and economical design of mooring systems is thus important but also challenging especially when the wave conditions are inhomogeneous. In this paper, a computational study is carried out to investigate the responses of the mooring lines for a 4.6 km long fjord crossing floating bridge accounting for inhomogeneous wave conditions. Based on the structural responses, this study also attempts to evaluate the fatigue damage in the mooring lines by using different fatigue analysis methods. The accuracy of the spectral methods is examined by comparison with the conventional rainflow cycle counting algorithm. Numerical studies are conducted to obtain an indication of the effect of various wave inhomogeneities on the fatigue damage in the mooring lines

Effect of modelling inhomogeneous wave conditions on structural responses of a very long floating bridge

Floating bridges are suitable for connecting land parcels separated by wide and deep waterbodies. However, when the span of the crossing becomes very long, the water environment exhibits inhomogeneities which introduce difficulties to the modelling, analysis and design of the bridge structure. The wave inhomogeneity may be described by means of field measurement and/or numerical simulations. Both approaches face complications when the resolution is much refined. It is thus important to examine the effect of the resolution related to the modelling of inhomogeneous waves on the global structural responses. In this study, a hypothetical crossing at the Sulafjord is chosen, and the wave environment in the year 2015 at 10 positions along the crossing is numerically computed. Next, different inhomogeneous wave conditions are established based on the wave data at 3, 5, and 10 positions, respectively. Time-domain simulations are conducted to examine the effect of different modelling approaches of the inhomogeneous wave condition on the global responses of a long, straight and side-anchored floating bridge

LFCS Review report – Structure and mooring response - OC2018 A-073-WP3/WP4

A review is performed on structural and mooring response analysis work in relation to Large Floating Coastal Structures and the planning of long floating bridges across fjords. The review contains observations on global response methodology, environmental loading and interactions, mooring design, measurements and validation, and finally design criteria and limit states. The basis for the review is mentioned but described in detail in the LFCS Introduction and Summary report (OC2018 F-073-WP0). Tables of identified gaps are presented along with recommendations for further work.publishedVersio

Hydroplastic response of a square plate due to impact on calm water

This paper investigates large, plastic deflections of a square plate due to impact on calm water. Most research in the area has examined linear elastic structural responses to such impact, but hydrodynamic responses during large, plastic deformations of engineering structures remain under-explored. A setup for an experimental drop test was designed for this purpose with equal emphasis on the hydrodynamical and structural mechanical aspects. Dual cameras were used to monitor the deforming plate from above during impact, and its deformation was tracked using a three-dimensional digital image correlation technique. The complex hydrodynamics of the impact were captured using a high-speed camera from below. The experimental results for flat impact showed a large air pocket under the deforming plate. The material properties of the plate were documented through separate tests. Hydroelastic theories were offered to account for large deformations and validated against the experimental results. Analytical hydroplastic theory shows that the maximum deflection is approximately equal to the velocity of impact times the square root of the ratio of the added mass to the plastic membrane capacity of the plate. An important source of error between the theory and the experiments was the effect of deceleration of the drop rig on deflection of the plate. This error was estimated using direct force integration and Wagner’s theory