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 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.

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.

Strength Assessment of Jacket Offshore Wind Turbine Support Structure Accounting for Rupture

The objective of the present work is to carry out the strength assessment of jacket offshore wind turbine support structures subjected to progressive rupture. A defect existing in a structure made during the fabrication may turn into a small-scale rupture and because of the high-stress concentration and low-cycle fatigue load. Therefore, the ultimate load-carrying capacity of the support structure is analysed accounting for the progress of the rupture until the leg component experiences a full rupture along its circumference. The effect of the severity of the imperfection is also investigated through 3 case studies that are created by varying the amplitude of the waves. The moment-curvature relationship of the structure with respect to the studied cases is presented. Furthermore, the jacket support structures, at different water depths, are also analysed and discussed. Finally, some of the leg components are removed one by one to study the redundancy of the jacket support structure at 80-m water depth.

Hydroelastic Analysis of a 3D Floating Body Considering Uncoupled Flexural and Torsional Vibrations

A semi analytic three-dimensional time domain method is developed to predict the hydroelastic effect due to wave induced loads on a floating body. The methodology being a semi analytic approach is able to capture real life scenario of bending of a ship like structure on sea taking both flexural and torsional vibrations. A prismatic beam equation with analytically defined modeshapes is taken into consideration to represent the structural response. The elastic deformation is solved using modal superposition technique. The radiation forces for elastic modes are obtained through impulse response function in time domain where frequency domain added mass, damping coefficients and wave exciting forces for the flexible modes are derived from a frequency domain panel method code. The Duhamel integral is employed in order to get the flexural and torsional deflection, velocity. A rectangular barge with zero forward speed is chosen for the analysis. Structural responses, torque, bending moments are calculated to assess the wave induced loads on the floating elastic body. The proposed technique, developed in Fortran, appears to be robust, efficient and computationally less expensive and can be used to predict the wave induced loads on a flexible structure as a first approximation in the initial design stage.

Seakeeping Prediction of a Survey Vessel Operating in the Caspian Sea

This paper presents the numerical and experimental analysis of the seakeeping performances of a survey vessel operating in the Caspian Sea. For the numerical analysis we have developed our own code, based on a linear hydro-dynamic strip theory formulation. The irregular waves are modelled by short-term power density spectra JONSWAP, for the spectral parameters significant wave height and peak period corresponding to the Caspian Sea scattering diagram. The experimental study is developed at the towing tank from Naval Architecture Faculty of Galati, using a semi-captive scaled model 1:16 of the survey vessel, made of fibre glass and wood, being recorded the heave, pitch, roll motions and wave elongation. The experimental tests are carried out for two speeds and several significant heading cases: head, follow and beam regular waves. This study delivers the prediction of the survey vessel seakeeping capabilities and the validation of the numerical response amplitude operators by experiment.