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

Effect of the Beam Element Geometric Formulation on the Wind Turbine Performance and Structural Dynamics

In this paper, the original double symmetric cross section beam formulation in RIFLEX used to model the blades is compared against a newly implemented generalised beam formulation, allowing for eccentric mass, shear and elastic centres. The generalised beam formulation is first evaluated against an equivalent ABAQUS beam model (Using the generalised beam formulation implemented in ABAQUS) which consists of DTU 10MW RWT (reference wind turbine) blade in static conditions. A static displacement is applied to the tip, which is close to an operating load. The results appear very similar and ensure that the implementation is correct. The extended beam formulation is afterwards used on the Land-based 10MW turbine from DTU with external controller. This case study aims at evaluating the effect of the newly implemented formulation on realistic, flexible structure. During the study, the blades were discretised using both the old and new formulation, and dynamic simulations were performed. The effect of the beam formulation was evaluated using several wind conditions that are thought to be characteristic of operating conditions. Results show slight difference between two formulations but could be more significant for next generation flexible blades.acceptedVersio

Dynamic response of a monopile wind turbine in waves: Experimental uncertainty analysis for validation of numerical tools

The responses of a monopile offshore wind turbine subjected to irregular wave loads are investigated numerically and experimentally, considering a range of sea states. An extensive experimental campaign was carried out on a fully flexible model, representative of a 5 MW offshore wind turbine, at 1:40 scale. An assessment of the experimental results for the response amplitude operator for regular waves and the 90th percentile seabed bending moment in long-crested irregular waves is carried out using two models (analytical and numerical) for uncertainty propagation, suggesting that bias errors in the model properties and in the wave elevation contribute the most to the total uncertainty. The experimental results are also compared to a numerical model using beam elements and Morison-type wave loads with second order wave kinematics. The numerical model does not capture all of the responses within the level of uncertainty of the experiments, and possible reasons for the discrepancies are discussed.publishedVersio

Numerical/experimental impact events on filament wound composite pressure vessel

Impacts on pressure vessels, produced by winding glass fibre with vinyl ester resin over a polyethylene liner, were numerically and experimentally investigated in the current work. Pressure vessels were experimentally tested under low velocity impact loads. Different locations and incident energies were tested in order to evaluate the induced damage and the capability of the developed numerical model. An advanced 3-D FE model was used for simulating the impact events. It is based on the combined use of interlaminar and intralaminar damage models. Puck and Hashin failure theories were used to evaluate the intralaminar damages (matrix cracking and fibre failure). Cohesive zone theory, by mean of cohesive elements, was used for modelling delamination onset and propagation. The experimental impact curves were accurately predicted by the numerical model for the different impact locations and energies. The overall damages, both intralaminar and interlaminar, were instead slightly over predicted for all the configurations. The model capabilities to simulate the low velocity impact events on the full scale composite structures were proved.acceptedVersio

Material characterisation and failure envelope evaluation of filament wound GFRP and CFRP composite tubes

The full procedure for material characterisation of filament wound composite pipe is reported. Two different typologies of composite were used in order to evaluate the performance of the developed test methodology. Test samples were produced with glass/vinylester and carbon/epoxy in tubular section by filament winding. Split disk and biaxial tests were used to evaluate the basic in plane material properties. A new design for the biaxial test was developed. The end tabs and fixture were made in order to reduce the stress concentration at the edges of the samples and to remove any possibility of sample misalignment. The influence of the sample length as well as the sample preparation was investigated and the best solution reported. Moreover, an innovative optical method was developed for the evaluation of the void content of the produced material. In addition to the basic strength data, the complete failure envelopes in the plane s2 t12 were also evaluated for both materials by the use of the biaxial test procedure here developed. The experimental failure envelopes were also compared with the prediction made with some of the most common failure theories currently available. The results clearly showed the ability of the Puck criterion to accurately predict the failure envelope (especially when torsion plus axial compressive loads were applied to the samples).acceptedVersio

Dynamic response of a monopile wind turbine in waves: Experimental uncertainty analysis for validation of numerical tools

The responses of a monopile offshore wind turbine subjected to irregular wave loads are investigated numerically and experimentally, considering a range of sea states. An extensive experimental campaign was carried out on a fully flexible model, representative of a 5 MW offshore wind turbine, at 1:40 scale. An assessment of the experimental results for the response amplitude operator for regular waves and the 90th percentile seabed bending moment in long-crested irregular waves is carried out using two models (analytical and numerical) for uncertainty propagation, suggesting that bias errors in the model properties and in the wave elevation contribute the most to the total uncertainty. The experimental results are also compared to a numerical model using beam elements and Morison-type wave loads with second order wave kinematics. The numerical model does not capture all of the responses within the level of uncertainty of the experiments, and possible reasons for the discrepancies are discussed

Material characterisation and failure envelope evaluation of filament wound GFRP and CFRP composite tubes

The full procedure for material characterisation of filament wound composite pipe is reported. Two different typologies of composite were used in order to evaluate the performance of the developed test methodology. Test samples were produced with glass/vinylester and carbon/epoxy in tubular section by filament winding. Split disk and biaxial tests were used to evaluate the basic in plane material properties. A new design for the biaxial test was developed. The end tabs and fixture were made in order to reduce the stress concentration at the edges of the samples and to remove any possibility of sample misalignment. The influence of the sample length as well as the sample preparation was investigated and the best solution reported. Moreover, an innovative optical method was developed for the evaluation of the void content of the produced material. In addition to the basic strength data, the complete failure envelopes in the plane s2 t12 were also evaluated for both materials by the use of the biaxial test procedure here developed. The experimental failure envelopes were also compared with the prediction made with some of the most common failure theories currently available. The results clearly showed the ability of the Puck criterion to accurately predict the failure envelope (especially when torsion plus axial compressive loads were applied to the samples)

Coupled fluid-solid modelling of the valve dynamics in reciprocating compressors

A novel method coupling computational fluid dynamics (CFD) and finite element method (FEM) was developed to account for the complex physics of the reciprocating compressor. The developed method is based on data exchange between the two solvers at each time step. We address the challenges related to valve dynamics, where the motion of solid components is not prescribed as for pistons, but result from the combined interactions between pressure, velocity, spring forces and impact forces during each revolution. The coupling method enables accurate computation of the solid-fluid interaction, where at each time step the pressure acting on the valve computed by CFD is transferred to the FEM simulation, and the three-dimensional valve motion computed by FEM is transferred to the CFD simulation. It is demonstrated on the dynamics of a ring plate discharge valve in a reciprocating ammonia compressor to quantify the effect of impact damping which arises from the gas dynamics, leading to reduced forces on the valve. The results from the coupling simulations are compared against novel experimental measurements obtained by instrumenting a real compressor. The coupled CFD-FEM simulation gives detailed insights into the valve behaviour and was used also to investigate pressure inhomogeneities, which can lead to tumbling motion of the valve ring.Coupled fluid-solid modelling of the valve dynamics in reciprocating compressorsacceptedVersio

Coupled fluid-solid modelling of the valve dynamics in reciprocating compressors

A novel method coupling computational fluid dynamics (CFD) and finite element method (FEM) was developed to account for the complex physics of the reciprocating compressor. The developed method is based on data exchange between the two solvers at each time step. We address the challenges related to valve dynamics, where the motion of solid components is not prescribed as for pistons, but result from the combined interactions between pressure, velocity, spring forces and impact forces during each revolution. The coupling method enables accurate computation of the solid-fluid interaction, where at each time step the pressure acting on the valve computed by CFD is transferred to the FEM simulation, and the three-dimensional valve motion computed by FEM is transferred to the CFD simulation. It is demonstrated on the dynamics of a ring plate discharge valve in a reciprocating ammonia compressor to quantify the effect of impact damping which arises from the gas dynamics, leading to reduced forces on the valve. The results from the coupling simulations are compared against novel experimental measurements obtained by instrumenting a real compressor. The coupled CFD-FEM simulation gives detailed insights into the valve behaviour and was used also to investigate pressure inhomogeneities, which can lead to tumbling motion of the valve ring