Investigation of ship-bank, ship-bottom and ship-ship interactions by using potential flow method

The authors were inspired by the benchmark model test data in MASHCON [1, 2] and carried out some numerical studies on ship-bank, ship-bottom and ship-ship interactions based on potential flow method in the last few years. In the confined waterways, many researchers question the applicability of the classical potential flow method. The main objective of the present paper is to present some validations of the 3D boundary element method (BEM) against the model test data to exam the feasibility of the potential method in predicting the hydrodynamic behaviour of the ships in confined water. The methodology used in the present paper is a 3D boundary element method based on Rankine type Green function. The numerical simulation is based on the in-house developed multi-body hydrodynamic interaction program MHydro. We calculate the wave elevations and forces (or moments) when the ship is manoeuvring in shallow and narrow channel, or when the two ships is travelling side by side or crossing each other. These calculations are compared with the benchmark test data, as well as the published CFD results. Generally, the agreement between the present calculations and model test and CFD results are satisfactory, which indicates that the potential flow method and developed program are still capable to predict the hydrodynamic interaction involved in ship-bank, ship-bottom and ship-ship problem

ELIGMOS: time domain simulation of the maneuvering of ships in deep and shallow waters

Calm water manoeuvring simulations are commonly used at the initial design stage as they provide useful an practical insight concerning ship's manoeuvrability and compliance with the relevant IMO criteria. In this paper the authors present ELIGMOS; a time-domain numerical code utilizing a 3-DOF manoeuvring model based on the MMG method. For the validation of the code's predictions, a comparison with the experimental results on the turning ability of S-175 has been conducted. The paper presents also the investigation performed regarding the accuracy of certain empirical formulas for the derivation of the manoeuvring derivatives is also investigated, especially for the case of shallow water where experimental data and results remain scarce. The code is written in C++ programming language, adopting a modular approach for the calculation of external forces and moment (i.e. hydrodynamic hull, rudder and propeller) which allows future enhancements with the introduction of additional terms

Sensitivity analysis of the tool for assessing safe manoeuvrability of ships in adverse sea conditions

In 2013, International Maritime Organization (IMO) introduced the Interim Guidelines for determining the minimum propulsion power to maintain the manoeuvrability of ships in adverse conditions. Considering the sufficiency of propulsion system in adverse sea conditions, the European project SHOPERA has developed alternative processes and tools for assessing safe manoeuvrability of ships. The main objective of these procedures is to identify the critical conditions where the vessel maintains its course keeping and manoeuvring ability at the vessel available propulsion power by using basic ship design values as input into the simplified methods proposed. Outcomes of this project were submitted and discussed in the 70th session of IMO’s Marine Environmental Protection Committee. In this paper, a brief description of these new assessment procedures is presented and a sensitivity analysis is conducted. The analysis is performed for a range of different open water propeller and hull resistance characteristics, hull – propeller interaction factors and engine power limit values, investigating the influence of these various performance parameters on the performance of the vessel

Dynamic mooring simulation with Code_Aster with application to a floating wind turbine

This is the final version of the article. Available from Elsevier via the DOI in this record.The design of reliable station-keeping systems for permanent floating structures such as offshore renewable energy devices is vital to their lifelong integrity. In highly dynamic and/or deep-water applications, including hydrodynamics and structural dynamics in the mooring analysis is paramount for the accurate prediction of the loading on the lines and hence their dimensioning. This article presents a new workflow based on EDF R&D's open-source, finite-element analysis tool Code_Aster, enabling the dynamic analysis of catenary mooring systems, with application to a floating wind turbine concept. The University of Maine DeepCwind-OC4 basin test campaign is used for validation, showing that Code_Aster can satisfactorily predict the fairlead tensions in both regular and irregular waves. In the latter case, all of the three main spectral components of tension observed in the experiments are found numerically. Also, the dynamic line tension is systematically compared with that provided by the classic quasi-static approach, thereby confirming its limitations. Robust dynamic simulation of catenary moorings is shown to be possible using this generalist finite-element software, provided that the inputs be organised consistently with the physics of offshore hydromechanics.IDCORE is funded by the ETI and the RCUK Energy programme, grant number EP/J500847/1. The authors are grateful for the funding provided by these institutions, and to EDF R&D for hosting and supervising the industrial doctorate which expressed the present work

What to expect from the hydrodynamic energy saving devices

Many retrofitting technologies have been proposed to improve the hydrodynamic performance of existing fleets with the aim of reducing the fuel consumption and consequently CO2 emission. The magnitudes of savings predicted by manufacturers are very promising however ship owners are often still doubtful whether they can achieve what is claimed in operations. This study evaluates the performance of four energy saving devices (ESDs) at ship scale with the aim of assisting ship owners with the decision of selecting suitable devices for their ships. Due to the uncertainties associated with extrapolation of viscous flows from model to full scale it is proposed that investigations must be carried out at full scale; hence a full-scale com putational model was adopted as the only feasible method at the design stage. Two vessels representing di fferent types of ship were selected: a gas carrier and a container ship. Various retrofitting technologies to reduce resistance or to improve the propulsive efficiency were considered. The latter group is subdivided into devices located before, at and aft of the propeller. The resistance induced by large openings on the hull, such as a bow thruster tunnel was quantified and several devices designed to streamline the flow in this region were evaluated. Pre-swirl fins technology was the ESD investigated from preswirl devices. The existing propeller of the gas carrier was replaced with a new type profile propeller which improved the propulsive efficiency. Twisted rudder was the technology investigated from post-swirl ESDs. The level of savings obtained from these technologies was generally less than the values published in the literature. It was concluded that this discrepancy arose for one of three reasons: either the metric used to evaluate the savings was inappropriate, or that the method used to quantify the measure was in accurate, or finally, because the designs examined in the case studies were not suitable optimised. However if some of these devices did not deliver the expected savings because the designs considered in this study were not sufficiently optimised, then the question arises as to whether these devices must be optimised for a specific operational conditions and how well these ESDs behave when the vessel is not operating in the design conditions

An experimental study of hull girder loads on an intact and damaged naval ship

The study reported in this paper is focused on experimental investigation of the hull girder loads on an intact and damaged naval ship DTMB 5415 at zero speed. The experimental campaign was carried out in head and beam regular waves at the University of Strathclyde. The effect of the use of moorings in the model experimental setup was investigated in the context of loads assessment, and the moorings are shown to influence the measured hull girder loads at some wave frequencies compared to the free drift case. Therefore the tests in beam seas are performed with free drifting model while the moored model setup was adopted for head seas. The results for ship motions are compared with those from a previous campaign giving an insight into repeatability and uncertainty of measurements. The roll decay of the ship in both intact and damaged conditions is analysed and the linear and quadratic extinction coefficients for the model and the ship scale are reported and detailed discussion on intact-versus-damaged ship roll damping behaviour is given. The results for the hull girder loads are presented for intact and damaged ship. An investigation of the nonlinear effects due to wave height variation in the range wave height to wave length from 1/50 to 1/22 on the shear force and bending moment values was carried out for a range of wave lengths to ship length ratios from 0.8 to 1.4. The results of the extensive campaign are compared against similar experimental studies forming a benchmark data for validation of numerical methods

Experimental determination of the roughness functions of marine coatings

The aim of this paper is to determine the roughness functions of different marine coatings, including two novel FOUL-X-SPEL paints and two existing commercial coatings, and two control surfaces, using the overall method of Granville (1987). An extensive series of towing tests of flat plates coated with different antifouling coatings was carried out at the Kelvin Hydrodynamics Laboratory (KHL) of the University of Strathclyde. The tests were designed to examine the as applied drag performances of FOUL-X-SPEL paints and compare them with two existing reference paints and two control surfaces. The surface roughness amplitude parameters of all of the test surfaces were measured using a hull roughness analyser. In total over 150 runs were carried out, including a series of repeat tests designed to quantify the uncertainty in the results. The drag coefficients and roughness function values of each surface were evaluated along with the uncertainty limits

The influence of nonlinearities on the symmetric hydrodynamic response of a 10,000 TEU Container ship

The prediction of wave-induced motions and loads is of great importance for the design of marine structures. Linear potential flow hydrodynamic models are already used in different parts of the ship design development and appraisal process. However, the industry demands for design innovation and the possibilities offered by modern technology imply the need to also understand the modelling assumptions and associated influences of nonlinear hydrodynamic actions on ship response. At first instance, this paper presents the taxonomy of different Fluid Structure Interaction (FSI) methods that may be used for the assessment of ship motions and loads. Consequently, it documents in a practical way the effects of weakly nonlinear hydrodynamics on the symmetric wave-induced responses for a 10,000TEU Container ship. It is shown that the weakly nonlinear FSI models may be useful for the prediction of symmetric wave-induced loads and responses of such ship not only in way of amidships but also at the extremities of the hull. It is concluded that validation of hydrodynamic radiation and diffraction forces and their respective influence on ship response should be especially considered for those cases where the variations of the hull wetted surface in time may be noticeable

Global wave loads on a damaged ship

A computational tool was applied based on a two dimensional linear method to predict the hydrodynamic loads for damaged ships. Experimental tests on a ship model have also been carried out to predict the hydrodynamic loads in various design conditions. The results of the theoretical method and experimental tests are compared to validate the theoretical method. The extreme wave induced loads have been calculated by short term prediction. For the loads in intact condition, the prediction with duration of 20 years at sea state 5 is used, while for loads in damaged conditions the prediction in 96 hours exposure time at sea 3 is used. The maximum values of the most probable extreme amplitudes of dynamic wave induced loads in damaged conditions are much less than those in intact condition because of the reduced time. An opening could change the distribution of not only stillwater bending moment but also wave-induced bending moment. It is observed that although some cross sections are not structurally damaged, the total loads acting on these cross sections after damage may be increased dramatically compared to the original design load in intact condition