Experimental Study on the Wave Loads on Monopile and Jacket Type Support of Offshore Wind Turbines

As the offshore fixed wind turbine developed, more ones will be installed in the sea field with the depth 15–50 meters. Wave force will be one of the main forces that dominate the design of the wind turbine base, which is calculated using the Morison equation traditionally. This method can predict the wave forces for the small cylinders if the drag and inertia coefficients are obtained accurately. This paper will give a series scaled tests of monopile and jacket type base of the offshore wind turbine in tank to study the nonlinear wave loads.

Accuracy of Failure Criteria Commonly Used for Ship Collision Simulations

The paper summarises observations of the fracture response of small-scale double hull specimens subjected to quasi-static impact loads by means of simulations of the respective experiments. The collision scenarios are used to evaluate the discretisation of the finite element models, and the energy-responses given by various failure criteria commonly selected for collision assessments. Nine double hull specimens are considered in the analysis so that to discuss the advantages and disadvantages of the different failure criterion selected for the comparison. Since a large scatter is observed from the numerical results, a discussion on the reliability of finite element analysis is also provided based on the present study and other research works found in the literature.

On the Array of Wave Energy Converters: The Case of the Coaxial-Duct OWC

This work focuses on the initial performance assessment of an array of coaxial-duct (CD) oscillating-water-columns (owc’s) with potential to be used as multipurpose platform for the creation of value in a diverse range of offshore economic activities. The coaxial-duct owc (CD-owc) is an axisymmetric oscillating-water-column wave energy converter that has been studied for both small-size and large-size applications. This work focuses on buoys of 12 meter diameter distributed in an array of five devices, rigidly attached to each other, to form a cluster of owc’s. The objective of the study is to assess the performance of the array with this configuration and estimate the effect of parameters such as distance between devices, various modes of movements, and other constraints on the overall power output of the array. Results of different cases are compared to the performance of an isolated device to determine the interference effect of other devices. Some results validate previous research conclusions and new findings on the behavior coaxial-duct owc are presented.

Numerical and Experimental Analysis of a Hybrid Wind-Wave Offshore Floating Platform’s Hull

This paper presents a study regarding a novel hybrid concept for both wind and wave energy offshore. The concept resembles a semi-submersible wind platform with a larger number of columns. Wave Energy Devices such as point absorbers are to be displayed around the unit, capturing wave energy while heaving and also enhancing the stability of the platform. In this paper, a first numerical study of the platform’s hull, without Wave Energy Converters, is carried out. Experiments in wave basin regarding the same unit have been conducted and the results are presented and compared to the numerical ones. Both stability and seakeeping performances are assessed and compared.

Numerical Analysis on the Response of Deck Plates Laterally Impacted by a Rectangular Indenter

Ship deck plates are often subjected to localized dynamic loads, such as the loads of landing helicopter or impacts of ice floes. In order to investigate the dynamic response of ship plates subjected to such dynamic loads, a series of numerical simulations are performed on ship plates with different thicknesses. Parametric studies are performed on the impact response of plates, including the thickness of the plates, mass and impact velocity of the rectangular indenter. The maximum permanent deflections of the plates are obtained during the simulation. The relation between maximum force and permanent deflection is obtained and the deformation modes are analyzed. A theoretical procedure is developed to predict the deformation of plates with different initial impact energies, and a good agreement between the theoretical and numerical results is obtained. It has also been observed that the thickness of plates has little effect on the dimensionless maximum permanent deformation and dimensionless maximum impact force.

Experimental Study on Hydrodynamics of Hybrid Deep-V Monohull With Different Built-Up Appendages

The hydrodynamic characteristics of a hybrid deep-V monohull with different built-up appendages are investigated experimentally in order to improve the resistance and seakeeping performance. Model tests have been carried out to study the hydrodynamic performance between a bare deep-V vessel and a deep-V monohull with different built-up appendage configurations (i.e. a hybrid deep-V monohull). From the model test results, it is found that the existence of the appendages will reduce the amplitude of pitching angle and bow vertical acceleration compared to that of the bare deep-V vessel in heading regular waves. However, the resistances for the hybrid deep-V monohull with built-up appendages are increased 15.6% for Fn = 0.264, and 0.1% for Fn = 0.441 compared to the resistance of the bare deep-V vessel. The model test results of seakeeping performance in irregular waves show that the hybrid deep-V monohull gives a better seakeeping performance than the deep-V vessel. The pitching angle and bow vertical acceleration of the hybrid deep-V monohull containing a built-up appendage are reduced 15.3% and 20.6% compared to the deep-V monohull in irregular waves at Fn = 0.441 in 6th class sea state (H1/3 = 6m).

Grounding Experiments of a Ship Model in Water Tank

Grounding is one of the major threats to ships under operation. In this paper, the ship model grounding experiments are conducted in a water tank to study the coupling effects of both internal mechanics and external dynamics. The influence of surrounding water on ship motions during grounding is taken into account. During testing, varying rock penetrations are considered to study the grounding damage. Experimental results such as the horizontal grounding forces and damage extents are measured and analyzed. The results show that the grounding damage depends on the rock penetration. Besides, the surrounding water of the ship model has a big influence on grounding damage assessment.

A Comparative Research on Computation Methods for Wave Loads of Semi-Submersible Platform

Wave load is one of the main external loads for semi-submersible platform, which is usually calculated by design wave method. In the present research, three design wave methods are investigated and compared on design wave parameters determination of semi-submersible platforms, i.e., the deterministic design wave method, stochastic design wave method and long-term prediction design wave method. Moreover, the specified calculation methods and the detailed wave load computation procedure are summarized considering the load characteristics of global hydrodynamic response. Finally, a semi-submersible platform is regarded as objective and the design wave results of three design wave methods are compared and analyzed. The fundamental research can provide reference for rational selection of wave loads calculation method.

Fully Coupled Analysis of Ship Motion and Sloshing Tanks in Regular and Irregular Waves

Fully coupled analysis of ship motion and sloshing tank in waves is essential for floating structures which store and transports natural gas. For partially filled tanks would generate violent sloshing due to external wave excitation, and the sloshing flow can consequently affect ship motion. Therefore, how to evaluate ship motion and sloshing phenomenon in tank is of great importance, especially under real sea state, when wave induced sloshing would be more complex than that under linear wave condition. In the present work, a CFD-based method is applied to simulate both external wave field and inner sloshing tank field in regular waves and irregular waves. The ship is a simplified FPSO, with two LNG tanks. All the numerical simulations are carried out by the in-house CFD code naoe-FOAM-SJTU, which is developed on the open source platform OpenFOAM. The regular and irregular wave condition is simulated based on open source toolbox waves2Foam. The main parameters of coupling effect of ship motion and sloshing tank, such as the time history of ship motion, sloshing phenomenon in tanks are obtained by our computations. The predicted results for the coupling effects of ship motion and sloshing tank in regular waves are compared with the corresponding experimental data. The comparison is satisfactory and shows that the CFD method has the ability to simulate coupling effects of ship motion and sloshing tank in waves.

Comparison of Mooring Solutions and Array Systems for Point Absorbing Wave Energy Devices

Most of the ocean energy technologies are considered to be in a pre-commercial phase and need technical development. This study focuses on design of mooring solutions and compares array systems of a specific floating point-absorbing wave energy converter (WEC) developed by the company Waves4Power. A full-scale prototype of the WEC is installed in Runde (Norway) where it is moored with three polyester mooring lines, each having one floater and one gravity anchor. Based on this reference installation, the method of systems engineering was used to propose twenty-two conceptual mooring solutions for different array systems. They were compared and reduced to four top concepts in a systematic elimination procedure using Pugh and Kesselring matrices. The top concepts were assessed in detail by means of LCOE (levelised cost of energy), LCA (life cycle analysis) and risk analyses. The fatigue life of the mooring lines and the energy capture were calculated using results obtained from coupled hydrodynamic and structure response analyses in the DNV-GL DeepC software. Two final concepts were proposed for the water depths 75 and 200 m.