bluuebunny/crossref_metadata_2025 huggingface dataset:
An Advanced Thrust Allocation Algorithm for DP Applications, Taking Into Account Interaction Effects and Physical Limitations
Authors: Arditti F. , Cozijn J. L. , van Daalen E. F. G.
Published: September 2014

The Dynamic Positioning (DP) system is responsible for the stationkeeping and manoeuvrability of a vessel in offshore operations. The forces required by the DP system are distributed among the available thrusters of the vessel by a thrust allocation algorithm, which should be both accurate — i.e. the sum of the effective forces is close to the required forces — and efficient — i.e. the total consumed power is minimal.

Ideally, the thrust allocation algorithm accounts for the forbidden zones, a practical solution to avoid significant hydrodynamic interaction effects such as thruster-hull interaction, thruster-current interaction and thruster-thruster interaction. Moreover, the thrust allocation algorithm should also take into account the physical limitations of each thruster such as the maximum thrust (saturation), the maximum rate of turn (azimuth) and the maximum rate of change of RPM.

In order to include these complex requirements in the thrust allocation algorithm the hydrodynamic interaction effects are modelled as efficiency functions, which are incorporated in the (power) object function and in the (required forces) constraints.

With the purpose of solving the complete problem, including the physical limitations and the hydrodynamic interaction effects, several advanced optimization methods were investigated. The selected optimization algorithms were the Sequential Quadratic Programming (SQP) method and the Steepest Descent (SD) method.

In this paper a DP drill ship is considered, with 6 azimuthing thrusters. Results were obtained for environmental conditions of increasing strength, from benign sea states to higher sea states with large required forces, eventually leading to thruster saturation. As a final test case, the required forces are such that the thrust allocation algorithm forces the thrusters to cross large forbidden zones with significant thruster-hull interaction.

The results show that the enhanced thrust allocation algorithm can deal with both hydrodynamic interaction effects and physical limitations in a time-efficient and robust manner. Altogether, these improvements are expected to lead to higher accuracy and efficiency for DP operations.
Study of Ice Failure and Deformation Processes
Authors: Aleksandrov Anatolii V. , Platonov Viktor V. , Matantsev Roman A.
Published: September 2014

Intensive development of computer simulation technique for ice deformation and failure processes is an important problem in respect to both ice propulsion definition and strength analysis for ice vessel and ice-resistant structures. However, evaluation of applied algorithms effectiveness requires developing a procedure for verification of numerical models.

This paper presents results of experiment-calculated studies for strains in a bounded region on a specimen surface containing a point grid. Grid movement during the tests was recorded with the help of a system of three-dimensional computer vision and digital image correlation for noncontacting shape and deformation measurements. An experimental facility, test methodology, observed results and test results processing method are explained. Experimental data on freshwater field ice under uniaxial compression and bending are given.

Ice mechanical characteristics were evaluated based on inverse solution and finding ice strain characteristics as initial data for the finite element analysis. The calculated results were analyzed and compared with experimental data. Application of the proposed methodology will extend essentially a verification base for computer simulation of ice failure under contact with a structure and create prerequisites for forming a new direction in the area of ice numerical simulation.
Assessment of the Size Effect in Fatigue Analysis of Butt Welds and Cruciform Joints
Authors: Lotsberg Inge
Published: September 2014

Reduced fatigue capacity of welded structures for larger thicknesses was introduced in design standards approximately 30 years ago. A significant amount of research on this topic was performed during the following years. In general the presence of a size effect was agreed upon. The size effect is considered to be dependent on the plate thickness at the considered hot spot in addition to size of attachment plate and type of dynamic loading. Only simplified recommendations on the size effect are included in most fatigue design standards. One reason for this is normal scatter in fatigue test data and also somewhat different recommendations based on these data in the literature. This has made it difficult to arrive at full agreement on recommended fatigue analysis procedures. In this paper a review of literature and design standards are presented together with a calibration of analysis method with fatigue test data. The effect of different parameters contributing to the size effect is illustrated. An attempt has been made to use the calibrated analysis model to also quantify the size effect based on crack growth analyses. Finally some recommendations on size effect to be used in fatigue design standards are presented.
A New Recommended Practice for Inspection Planning of Fatigue Cracks in Offshore Structures Based on Probabilistic Methods
Authors: Lotsberg Inge , Sigurdsson Gudfinnur
Published: September 2014

During the last 30 years a methodology for planning in-service inspection of fatigue cracks based on probabilistic methods has been developed. Due to the nature of the fatigue phenomena it is well known that minor changes in basic assumptions can have significant influence on the predicted crack growth lives. Calculated fatigue lives are sensitive to input parameters using standard design analysis procedures. Calculated probabilities of fatigue failure using probabilistic methods are even more sensitive to the analysis methodology and to input parameters to the analyses. Fracture mechanics analysis is required for prediction of crack sizes during service life in order to account for probability of detection after an inspection event. Analysis based on fracture mechanics needs to be calibrated to that of fatigue test data or S-N data. Thus, use of these methods for planning inspection requires considerable education and engineering skill. Therefore the industry has asked for guidelines that can be used to derive reliable inspection results using these methods. DNV has during the last years performed a joint industry project on use of probabilistic methods for planning in-service inspection for fatigue cracks in offshore structures. The recommendations from this project are now being included in a DNV Recommended Practice. The main background for this document is presented in this paper.
Rankine Source Method for Seakeeping Analysis in Shallow Water
Authors: von Graefe Alexander
Published: September 2014

Following Hachmann approach, Söding’s Rankine source method describes the steady perturbation potential in the body-fixed reference frame. This is beneficial for seakeeping predictions at forward speed, because error-prone m-terms do not occur in the boundary condition on the ship hull. Although similar terms arise in the boundary condition on the free surface, numerical inaccuracies in these terms have much less influence on the behaviour of the ship than in the traditional approach, where m-terms are evaluated on the hull. The periodic flow is linearised with respect to the amplitude of the incident wave, taking into account the steady ship wave.

A problem arises for shallow water problems if the Hachmann approach is used. For the shallow water problem, the boundary condition ‘no flow through the bottom’ must be fulfilled. Usually, this is done using image sources. If the steady perturbation potential is described in the body-fixed reference frame, this is not possible directly. This paper extends the Hachmann approach to treat this issue. Following the usual procedure for steady flow calculation, the boundary condition at the flat bottom of the steady problem is realised using image sources. For seakeeping computations, the steady perturbation potential is split into two parts, modelled respectively by steady sources above and below the flat bottom. The first part is assumed to be constant in the body-fixed reference frame, whereas the second part is assumed to be constant in the reference frame of the mirror image of the ship. This extended Hachmann approach fulfils the boundary condition at the flat bottom analytically.

Computed ship motions with and without forward speed in shallow water are validated by model test results from Flanders Hydraulics Research, Antwerp, and from TU Berlin.
Model Test of the STC Concept in Survival Modes
Authors: Wan Ling , Gao Zhen , Moan Torgeir
Published: September 2014

The STC (Spar Torus Combination) concept combines a Spar floating wind turbine and a torus-shaped heaving-body wave energy converter (WEC). Numerical simulation has shown positive synergy between the WEC and the Spar floating wind turbine in operational conditions. However, in extreme wind and wave conditions, it is challenging to maintain structural integrity, especially for the WEC. To ensure survivability of this concept in extreme conditions, three survival modes have been proposed.

To investigate the performance of the STC in extreme conditions, model tests with a scale factor of 1:50 were carried out in the towing tank of MARINTEK, Norway. Two survival modes were tested. In both modes, the Torus WEC was fixed to the Spar. In the first mode, the Torus WEC is at the mean water surface, while in the second mode, the Torus WEC is fully submerged to a specified position. In the tests, 6 D.O.F rigid body motions, mooring line tensions, forces in 3 directions (X, Y and Z) between the Spar and Torus were measured, wind velocity and wind force were also measured by a sensor in front of the model and a load cell installed on the wind disc.

In this paper, the model test set-up for the two survival modes are described, and then decay tests, regular wave tests and the statistical tests for wind only, irregular wave only and irregular wave plus wind are presented, compared and analyzed. In the mean water level survival mode, the Torus had a small draft and large water plane area, so slamming and green water were observed as expected. In addition, Mathieu instability phenomena were observed during the regular wave test. In some large wave conditions in the fully submerged mode, no severe wave load occurred. All the results are presented in model scale unless specified, for direct comparison with numerical simulations later.
Comparison of Model Tests and Coupled Simulations for a Semi-Submersible Floating Wind Turbine
Authors: Huijs Fons , de Ridder Erik-Jan , Savenije Feike
Published: September 2014

The GustoMSC Tri-Floater is a slender and robust three-column semi-submersible supporting an offshore wind turbine. Model tests were performed for a Tri-Floater equipped with an operational wind turbine and mooring system exposed to wind and waves in the offshore basin at MARIN. A high quality wind setup and special low Reynolds number blades were used, aiming at delivering the Froude scaled thrust. The base scope of experiments was performed with fixed blade pitch angle and generator speed. Some of the experiments were repeated with active blade pitch and generator torque control using a dedicated algorithm developed by ECN. The experiments covered typical operational and survival design conditions. Numerical simulations for the same wave and wind conditions were performed using ANSYS-AQWA coupled with PHATAS. The paper describes the setup and results of both the model tests and the simulations.

From the comparison of the numerical and experimental results, it is concluded that coupled aero-hydro-servo-elastic simulations can be used to predict the response of the floating offshore wind turbine to a sufficiently accurate level for design purposes. Furthermore, it is shown that the Tri-Floater motion response is very favorable and that the nacelle accelerations, air gap and mooring loads comply with the design requirements.
On the Numerical Prediction of the Flow Around Smooth Circular Cylinders
Authors: Eça Luís , Vaz Guilherme , Rosetti Guilherme , Pereira Filipe
Published: September 2014

The numerical prediction of the flow around a smooth cylinder is one the classical test cases of Computational Fluid Dynamics (CFD). Different mathematical models have been used to address this statistically periodic flow. Namely, ensemble-averaged Navier-Stokes equations (URANS); partially-averaged Navier-Stokes equations (PANS); space filtered Navier-Stokes equations (large eddy-simulation LES or variational multi-scale VMS) and direct solution of the Navier-Stokes equation (DNS). Although all these models deal with turbulence in a very different way, all of them require a numerical solution and so they all require a careful control of the numerical uncertainty. We present an overall view of the values of the average drag coefficient (one of the most simple flow quantities that we could select) that have been published in the open literature, which shows a worrying spread of data. Therefore, it is logical to wonder if all these results are obtained with negligible numerical errors/uncertainties, especially when the scatter in the data also applies to results obtained with the same mathematical model. In this paper, we present Solution Verification exercises for the simplest model of those mentioned above: URANS. The calculations are performed at different Reynolds numbers and with different iterative convergence criteria using the ReFRESCO solver. The two-equation SST k–ω eddy-viscosity turbulence model is used in all the calculations performed in this study. The results presented show that numerical (iterative and discretization) errors may have a strong impact in the predictions and that misleading apparent convergence may be obtained with careless iterative convergence criteria. Furthermore, it is shown that grids with similar numbers of cells but different space distributions may lead to significantly different numerical uncertainties.
Assessing Conductor and Casing Systems for Damage From Extreme Snag Loads
Authors: Arikan Yusuf , Koska Ryan , Zlokich Jess
Published: September 2014

Conductor and casing systems for subsea wells can be damaged due to excessive loads caused by vessel drift offs and snag loads. These types of accidental loads on the conductor and casing system are uncontrolled in nature and hence difficult to predict. Therefore, designing the system for these types of loads can be very challenging and economically not practical. Additionally, in the event of an incident subsea, a conductor and casing system is permanently installed and cannot readily be retrieved or inspected once the damage is done.

The decision to abandon or to produce from a well with a damaged conductor has serious financial and environmental consequences and should be fully understood. Therefore, to make a knowledgeable decision, it is necessary to understand extent of the damage and its implications for future operations by forensic analytical tools. This paper examines the methodology of a conductor and casing system damage assessment in order to support more informed decisions and provides a case example for a typical deepwater subsea well undergone excessive accidental loading. The objective of the assessment is (1) to verify wellhead system integrity and (2) evaluate the effect of any future operations on the integrity of the system. The paper outlines a process, suggested code checks, and analysis techniques which can be implemented to determine fitness for service of an excessively loaded wellhead system.
A Multi-Purpose Finite Element Model for Flexible Risers Studies
Authors: Caleyron Fabien , Guiton Martin , Leroy Jean-Marc , Perdrizet Timothee , Charliac David , Estrier Pascal , Paumier Laurent
Published: September 2014

The paper focuses on a Finite Element (FE) model developed at IFPEN, denominated 3D-Periodic, which is dedicated to flexible riser studies. It takes full advantage of the geometric and loading periodicities to reduce the model length and the CPU cost. The model is developed in a commercial FE software with dedicated pre- and post-treatment packages. The model can represent standard cyclic bending with internal pressure and axial tension as well as external pressures load cases to investigate the risk of lateral buckling of tensile armors or of pipe collapse.
Fatigue Assessment of Work-Over Risers Through Physical Testing
Authors: Gundersen Gerhard , Kirkvik Rolf Hugo , Hoen-Sorteberg Christopher
Published: September 2014

Critical sections of work over strings, with respect to integrity, are components located close to end terminations, near well heads and above drill floors, where recurring bending moments are prevalent. The lifetime of these components are strongly dependent on the stiffness in the components of the string. Connections between these components are often complex, and of a type where the stiffness is unknown, or hard to reveal based on theoretical analysis. This paper considers the feasibility of applying state-of-the-art measurement technology for testing of the physical behavior of specific connections on a landing string to be used for work over operations in harsh environmental conditions, where low fatigue life of components have proven to be a recurring problem. Behavior of joint-connections revealed through measured response from physical testing serve as input for the global finite element (FE) analysis, where accumulated fatigue damage for each sea state is calculated based on site specific met-ocean data. The present work was carried out in advance of an operation on the Norwegian shelf, where a four-point bending test of the actual landing string to be used during the offshore campaign were performed on a section containing two critical couplings, in order to reveal the actual stiffness of the connections. The test string was subject to variable internal pressure, axial tension and bending loads, representative for the applicable work-over riser operational loads. The performance of the system was monitored through strain, displacement and force sensors, in order to relate applied loads to structural response. The results from these tests where later recreated from local FE analysis, where non linear springs was implemented and modified to fit the experimental results at the connections of interest. These springs was later input to the global fatigue analysis, where the complete system, including marine riser and inner work over string, was implemented in one model. Results from the fatigue assessment where used to determine the operational criteria for the work over operations.
Plastic Mechanism Analysis of Structural Performance of Web Girders During Ship Collision and Grounding
Authors: Gao Zhenguo , Hu Zhiqiang
Published: September 2014

The behavior of web girders is of crucial importance during ship collision and grounding accidents. A new theoretical deformation model for ship web girders subjected to in-plane localized force is proposed in this paper. It is based on a summary of the existing theoretical models and progressive deformation process of the web girder in the numerical simulation, which is a reproduction of a previous experiment. From the analysis of the deformation process of the web girder in the numerical simulation it is found that there are some important features which have not been considered by any of the existing models. Based on these new features, plastic analytical method is employed, and special emphasis is placed on the folding mechanism establishing and major energy dissipation pattern identifying. Thus, a new theoretical deformation model is proposed.

The proposed model is verified by two previous experiments, one is small-scale and the other is large-scale. From the force-indentation curves in comparisons, it can be found that the results of the proposed method compare well with those of the experiments. Therefore, the proposed method can be a useful part in the quick and reliable assessment of the performance of the ship structures in the accidental collision and grounding events.
Time Domain Simulation of a Dynamic Positioning Deepwater Semisubmersible Drilling Platform
Authors: Yang Xu , Sun Liping , Chai Shuhong
Published: September 2014

DPS (dynamic positioning system) has been widely used in floating structures, especially in deepwater area. Time domain simulation of platforms with dynamic positioning system has great significance to DP capability and riser system. Motion response of a deepwater semi-submersible platform with DPS on time domain was presented in this paper. PID (proportional, integral, derivative) controller and thruster allocation method were applied in numerical simulations of DPS. Wind, current and wave environmental loads were analyzed and limited angular speed was considered as well. Thruster failure analyses were covered and discussed also. Experiments of DPS in deep-water basin of Harbin Engineering University (HEU) were presented and compared with numerical study.
The Research on Load Test Solution of Cantilever System for POD-5 Jack-Up
Authors: Ji Zeng , Gang Chen , Hongtao Yuan , Jian Mo , Chenfeng Li , Chao Wang
Published: September 2014

Cantilever structure is a very important component of Jack-up drilling rig, which improve well numbers, flexibility and efficiency of drilling operation during the preloading process. The load cases of the cantilever system are complex, whose structural strength is a key factor of whole drilling rig safely operating in offshore[1], this paper design and research a new and safe load test solution to verify the structure strength of cantilever and drilling rig body whether meet the design requirements or not[2], through simulate normal drilling operation condition by top drive hanging test barge, pipe rack and set back area piled steel blocks. This solution will apply in POD-5 Jack-up project, and the test results will prove the safety and feasibility of this test solution.
Simulation of a Free Standing Riser Model and Validation With Experimental Results
Authors: Yamamoto Marcio , Masanobu Sotaro , Takano Satoru , Kanada Shigeo , Fujiwara Tomo , Asanuma Takayuki
Published: September 2014

In this article, we present the numerical analysis of a Free Standing Riser. The numerical simulation was carried out using a commercial riser analysis software suit. The numerical model’s dimensions were the same of a 1/70 reduced scale model deployed in a previous experiment. The numerical results were compared with experimental results presented in a previous article [1]. Discussion about the model and limitations of the numerical analysis is included.
Stress Concentration Factors for Butt Welds in Plated Structures
Authors: Lotsberg Inge , Rove Harald
Published: September 2014

Geometric stress concentration factors for butt welds in stiffened plates have been investigated by finite element analysis. The purpose of these analyses has been to establish a data basis that can be used to develop an analytical expression for stress concentration factors (SCF) for butt welds in stiffened plates. The geometry investigated is that typical used in stiffened plates in floating production vessels and ships. The geometry is also considered to be in the relevant range for semisubmersibles. Stress concentration factors are derived at the butt weld in the midway between the longitudinal stiffeners and at butt welds in way of cope holes of the longitudinal stiffener. Based on the performed work an equation accounting for eccentricity of plates due to fabrication tolerances and difference in thickness is derived that also has been included in the DNV Recommended Practice for fatigue analysis.
Hydrodynamic Interaction Between Two Ships Arranged Side by Side in Shallow Water
Authors: Yuan Zhiming , Incecik Atilla , He Shi
Published: September 2014

The hydrodynamic interaction between two ships with side-by-side arrangement is analyzed by using 3-D Rankine source panel code. The source points are distributed over the mean wetted body surface as well as on the free surface. The shallow water effect has been taken into consideration. Moreover, the influence of the distance between the vessels is also investigated. To verify the present code, two Wigley III hulls are simulated both in beam sea and head sea conditions. The wave pattern and the motion RAOs of 6-DOF are calculated by present code and compared with WADAM program which is based on Green function method. From the comparisons, good agreement is found between present calculation and Wadam results. It is found that the hydrodynamic interactions are generally important especially in beam sea case. The resonant frequency is greatly influenced by the distance between the vessels.
Proposed Rules for Fatigue in Offshore Transport Engineering
Authors: Bos A. J. , Sohns I.
Published: September 2014

In follow up on the study presented, during OMAE 2013 regarding the importance and influence of ocean transport on offshore structures and the necessity to design for ocean transportation of modules. The importance is emphasized that design engineers must take into account forces on structures induced by ocean transport. We also warned for the significant effects of fatigue damage on offshore structures prior to commissioning them on site.

The 2013 paper generated reactions from advisers of the IACS (International Association of Classification Societies) and lead EPC contractors to develop common rules for fatigue damage calculations and monitoring.

There are no unambiguous rules and regulations for fatigue assessment and monitoring in ocean transportation. Different rules are being applied and in many cases fatigue is not addressed at all. Causing discrepancies that are unwanted and potentially dangerous since tolerating such a situation leads to a gray area in which responsibilities are unclear and processes and equipment are not properly checked. Moreover, in this situation, no common and unambiguous rules are in place to check on vital safety procedures. A proposal for fatigue assessment that will lead to common rules for transport engineering will be discussed in order to provide offshore construction organizations with a realistic and workable set of rules and regulations for fatigue assessment and monitoring in ocean transport.

The development of the formal rules is on the agenda of the Dutch working group heavy lift and transport which is organized under the auspices of DNV.
Response of Mild Steel Pipes Under High Mass Low Velocity Impacts
Authors: Fareed Shamsoon , May Ian
Published: September 2014

Accidental loads, for example, due to heavy dropped objects, impact from the trawl gear and anchors of fishing vessels can cause damage to pipelines on the sea bed. The amount of damage will depend on the impact energy. The indentation will be localized at the contact area of the pipe and the impacting object, however, an understanding of the extent of the damage due to an impact is required so that if one should occur in practice an assessment can be made to determine if remedial action needs to be taken to ensure that the pipeline is still serviceable. There are a number of parameters, including the pipe cross section and impact energy, which influence the impact behaviour of a pipe. This paper describes the response, and assesses the damage, of mild steel pipes under high mass low velocity impacts. For this purpose full scale impacts tests were carried out on mild steel pipe having diameter of 457 mm, thickness of 25.4 mm and length of 2000 mm. The pipe was restrained along the base and a 2 tonnes mass with sharp impactor having a vertical downward velocity of 3870 mm/sec was used to impact the pipe transversely with an impact energy of 16 kJ. It was found from the impact tests that a smooth indentation was produced in the pipe. The impact tests were then used for validation of the non-linear dynamic implicit analyses using the finite element analysis software ABAQUS. Deformations at the impact zone, the rebound velocity, etc, recorded in the tests and the results of the finite element analysis were found to be in good agreement. The impact tests and finite element analyses described in this paper will help to improve the understanding of the response of steel pipes under impact loading and can be used as a benchmark for further finite element modelling of impacts on pipes.
Crashworthiness of Type C Tanks in LPG Ship
Authors: Rudan Smiljko , Aščić Blanka
Published: September 2014

Liquefied Petroleum Gas (LPG) ships carry a liquefied gas either pressurized, refrigerated or both at the same time. Due to that, among the other cargo containment solutions on LPG ships, type C tanks may be distinguished: they are independent tanks built as conventional pressure vessels. A single hull design of such ships is common and a question of their crashworthiness arises. In particular, the safety of the cargo may be of concern in the case of high energy collision event. In a previous study, crashworthiness of both common and novel sandwich hull design of an LPG ship was studied. In both cases, cargo tank was damaged. It is the aim of this work to study this damage in detail. An LPG ship and ferry collision event was modeled and studied by the means of nonlinear FEM. Collision parameters were altered to study their influence on the resulting collision damage on both ships. Bi-lobe cargo tank crashworthiness is analyzed and the possibility of cargo spill examined.
Moonpool Effect Assessment During Structure Installation
Authors: Perez Gabriel Vazquez , Pistidda Alessio , Smienk Henk
Published: September 2014

Heerema Marine Contractors (HMC) is entering a new era of pipe laying with the new Deep water Construction Vessel (DCV) Aegir, which is designed to be able to reel/J-lay pipelines for a wide range of pipe dimension and water depth combinations. The DCV Aegir has a moonpool close to the center of the vessel in which the Hang Off Module (HOM) for pipeline installation is positioned. The HOM is utilized to hold the pipeline and its structures during installation [1]. Pipelines and its structures will be lowered through the moonpool. When a pipeline structure is lowered through the moonpool the HOM is retracted, thus clearing the moonpool to allow the free pass of the structure.

The behavior of the water in the moonpool will induce loads on the structures when these are being lowered. These loads will induce motions and bending moments on the attached pipeline. The effect of the moonpool on the structure has to be known in order to assess the integrity of the pipe (fatigue and local buckling limit state) and the optimal procedure for structure installation.

The assessment of the moonpool effect on the structure during the lowering through the splash zone is complex because it is governed on one side by the motions of the vessel and on the other side by the motion of the water inside the moonpool.

This paper will focus on the moonpool effect assessment in a Pipe Line End Termination (PLET) installation analysis. Two different software packages are utilized; Flexcom of MCSKenny and STAR-CCM+ of CD-Adapco.

Flexcom is used to reproduce the vessel motions which affect the PLET motion behavior. Pipe properties (OD, WT and length) and PLET together with pipelay equipment; such as Upper Tensioner (UT), HOM, Pipe Wire Centralizer (PWC) and winch, are modelled.

To assess the hydrodynamic loads on the PLET inside the moonpool a Computational Fluid Dynamics (CFD) approach is required. STAR-CCM+ is a CFD program which uses Finite Volume Method (FVM) to solve the flow field motion equations. With this software it is possible to accurately model the geometry of the PLET and simulate the interaction between water in the moonpool and the PLET.

The paper will present an overview of the models and the analyses performed, together with the methodology used to combine the outcome of both software packages.
Underwater Sound and Vibrations due to Oil and Gas Activities
Authors: van Beek Pieter , Binnerts Bas , Nennie Erik , von Benda-Beckmann Sander
Published: September 2014

In the oil & gas industry there is a trend towards more subsea activities. To improve gas recovery from existing and new fields at greater depths, the produced gas will be compressed, processed and transported via subsea templates and underwater networks (pipelines, flexible risers, etc.). Besides the huge consequences for the subsea installation itself (reliability, maintenance, etc.), it also has consequences for underwater wildlife through the underwater source vibrations leading to sound radiation. Regulations aimed at managing the impact of underwater sound on marine life have been put in place by different nations [e.g. 1,2]. Many offshore operations require an assessment of the potential impact of underwater noise on the environment, which requires knowledge of the sound transmitted by the subsea components.

Until now very little is known about the underwater source mechanisms, the acoustic strength of these underwater networks, the coupling of the emitted source sound to the surrounding medium and the impact of the sound on the underwater wildlife. The dynamic behavior of networks for compressing and transporting gas, and the translation into emitted noise into air are rather well understood. However, due to the presence of the water the dynamic behavior from such subsea installation is very different than in air. To predict the dynamic behavior, the presence of the water cannot be neglected and has to be taken into account.

This paper presents a simplified model for a subsea high speed turbo-compressor coupled to the KrakenC normal mode propagation model. With this combined model the noise at remote locations can be predicted and compared with the ambient noise and other anthropogenic noise sources such as for instance shipping, dredging and wind farm operation noise.
Development of a Scaled-Down Floating Wind Turbine for Offshore Basin Testing
Authors: de Ridder Erik-Jan , Otto William , Zondervan Gert-Jan , Huijs Fons , Vaz Guilherme
Published: September 2014

In the last years MARIN has been involved in an increasing number of projects for the offshore wind industry. New techniques in model testing and numerical simulations have been developed in this field. In this paper the development of a scaled-down wind turbine operating on a floating offshore platform, similar to the well-known 5MW NREL wind turbine is discussed.

To simulate the response of a floating wind turbine correctly it is important that the environmental loads due to wind, waves and current are in line with full scale. For dynamic similarity on model scale, Froude scaling laws are used successfully in the Offshore industry for the underwater loads. To be consistent with the underwater loads, the winds loads have to be scaled according to Froude as well. Previous model tests described by Robertson et al [1] showed that a geometrically-scaled turbine generated a lower thrust and power coefficient with a Froude-scaled wind velocity due to the strong Reynolds scale effects on the flow. To improve future model testing, a new scaling method for the wind turbine blades was developed originally by University of Maine, and here improved and applied. In this methodology, the objective is to obtain power and thrust coefficients which are similar to the full-scale turbine in Froude-scaled wind. This is obtained by changing the geometry of the blades in order to provide thrust equality between model and full scale, and can therefore be considered as a “performance scaling”. This method was then used to design and construct a new MARIN Stock Wind Turbine (MSWT) based on the NREL 5MW wind turbine blade, including an active blade pitch control to simulate different blade pitch control systems.

MARIN’s high-quality wind setup in combination with the new model scale stock wind turbine was used for testing the GustoMSC Tri-Floater semi-submersible as presented in Figure 1, including an ECN active blade pitch control algorithm. From the model tests it was concluded that the measured thrust versus wind velocity characteristics of the new MSWT were in line with the full scale prediction and with CFD (Computational Fluid Dynamics) results.
Pressure Fluctuations on a Vertical Wall During Extreme Run-Up Cycles
Authors: Brennan J. , Viotti C. , Dias F.
Published: September 2014

The run-up of long, strongly nonlinear waves impinging on a vertical barrier can result in remarkable amplification of the far-field amplitude of incoming waves [1,2]. Such an extreme run-up is the result of an evolution process in which long waves experience strong amplification under the action of nonlinear steepening followed by the formation of undular bores, consisting of nonlinearly dispersive wave trains.

Rather than addressing the genesis of such extreme run-ups in any detail, this article describes a specific aspect of the problem; the associated pressure fluctuations at the wall. Numerical computations of the near-wall pressure field show that non-hydrostatic effects can strongly affect the dynamic loads exerted on the wall, and consequently, the high-frequency component of the pressure loads results is significantly enhanced with respect to that of the wave spectrum itself. This observation suggests that also long oceanic waves, at least in some conditions, can be a source of seismic noise.
Assessment of the Surge Effects in a Heaving Point Absorber in the Mediterranean Sea
Authors: Miquel Adrià Moreno , Antonini Alessandro , Archetti Renata , Bozzi Silvia , Passoni Giuseppe
Published: September 2014

In the present paper, the feasibility of wave electricity production in Italian seas is investigated through the implementation of a variant of the Seabased point absorber WEC. A numerical model of the coupled buoy-generator system is presented, which simulates the behavior of the WEC under different significant wave heights and periods. The WEC scheme is an improvement of the modeling of a three-body device, taking into account several aspects (independence among the bodies, heave and surge) ignored in previous studies for simplification of the scheme.

One WEC composed by three bodies is simulated, with two different hydrodynamic numerical model schemes: a floating buoy and a submerged sphere placed at 25 meters below the water surface. The third body is the translator of the linear generator, which is located at the sea bottom and attached to the submerged sphere by a steel wire.

For the hydrodynamic numerical model, the two bodies are allowed to move independently; heave and surge modes have been taken into account. The first scheme consists in the modeling with only three degrees of freedom, one per body only in the vertical direction (heave) and the other with five degrees of freedom, adding the horizontal component of movement for the buoy and the submerged body (surge). The results are compared with previous results of a WEC modeled as a single body system, with only one degree of freedom along the vertical axis. Preliminary results show that the produced energy in a simplified 1 DoF scheme is higher than results produced by the 3 DoF scheme, and is then approximately equal for the 5 DoF. The power matrixes present similar shapes. So the simplification made by neglecting the surge mode, in order to have a simpler dynamic model, doesn’t give a significant improvement in the capture width and energy production assessment.
CFD Analysis of Waves Over a Submerged Cylinder in Close Proximity of the Free Surface
Authors: Ottens Harald , Pistidda Alessio , van Dijk Radboud
Published: September 2014

Diffraction programs using potential theory are a quick and effective method in calculating wave forces and ship motions. However in cases where a small layer of water is present on top of a submerged body diffraction calculations overpredict motion and wave force RAOs. This shortcoming of diffraction programs is observed after conducting model tests on a captive submerged cylinder and a free floating SSCV. Unrealistic high wave elevations were predicted by diffraction programs on top of the submerged body. In a previous study a damping lid is implemented [1], to decrease the water elevation to realistic values.

In this study CFD is used to simulate the captive submerged cylinder in regular waves with different wave heights, wave periods and different submerged drafts. In addition irregular waves are used in the simulation matching the wave spectra used in the model tests. The simulations are transient and require high CPU usage, therefore the influence of numerical settings on wave propagation is investigated. Turbulent, laminar and inviscid flow are applied to evaluate which flow phenomena are important. The forces in heave and surge direction are validated with model test data of the captive cylinder. The numerical water elevation on top of the captive cylinder will be used to gain insight in the fluid flow and can be used as a guideline for the use of damping lids in diffraction programs.

This paper will focus on the CFD simulations and the validation with available forces obtained by model tests of the captive submerged cylinder. It will address the use of regular and irregular waves constructing the force RAO for this non-linear phenomenon. Lessons learnt to improve the CFD simulations as well as limitations of constructing RAOs using CFD from an engineering perspective will be addressed as well.
A Novel Approach for Modelling a FPSO Riser Turret Mooring (RTM) System for Mooring Design
Authors: Pistani Fabrizio , Brooker Daniel
Published: September 2014

The design approach for the analysis of a riser turret mooring system (RTM) connected to a FPSO is presented here. The design was carried out with the use of numerical models developed with Ariane and Orcaflex software packages. Ariane has been used as a screening tool while the model developed with Orcaflex was used for detailed analysis. The succesful validation of the models against existing experimental tests helps to avoid the repetition of a model test campaign for design of new systems. An original solution to overcome the limitations of the mooring software Ariane has been developed and used for mooring analysis.

This paper describes the development of the numerical models highlighting the original features, the validation with the model tests and discusses some of the main results.
A Fast Sea-Keeping Simulation Method for Heavy-Lift Operations Based on Multi-Body System Dynamics
Authors: Hatecke Hannes , Krüger Stefan , Christiansen Jakob , Vorhölter Hendrik
Published: September 2014

This paper presents a fast numerical method to analyze heavy-lift operations of ships in short crested waves. For this purpose, a sea-keeping simulation method for the coupled motions of a heavy-lift vessel and a freely suspended load is developed. The method considers the motions of the ship in six degrees-of-freedom and the suspended load as a point mass. The coupling of the multi-rigid-body system of the ship and the suspended load is considered by solving the equation of roll motion together with the Euler-Lagrange equations of the load. This approach allows the simulation of several hours of real time motion in short crested waves within only a few seconds. Consequently, the method is particularly suitable when very long or numerous sea-keeping simulations or statistical results are required. Moreover, the method is applied to evaluate the sea-keeping capabilities of a heavy-lift vessel during a lifting operation conducted offshore in 2013.
Dynamic Behaviour of the Loads of Podded Propellers in Waves: Experimental and Numerical Simulations
Authors: Queutey Patrick , Wackers Jeroen , Leroyer Alban , Deng GanBo , Guilmineau Emmanuel , Visonneau Michel , Hagesteijn Gerco , Brouwer Joris
Published: September 2014

The paper focuses on the hydrodynamic flow around a ship with pods in waves and compares the results of an experimental campaign with numerical simulations conducted during the EU-funded STREAMLINE project. It was the first project for which the effect of waves on cavitation and ventilation was explored in both experimental and numerical ways for a ship with pods. The measurements were carried out in MARIN’s Depressurized Wave Basin (DWB) with a fully instrumented podded ship model, in sailing condition, in waves and depressurised conditions. In this way, the correct representation of cavitation and possible ventilation bubbles and vortices is ensured, resulting in a correct physical behaviour. The discretisation of the Reynolds-Averaged Navier-Stokes Equations (RANSE) is based on the unstructured finite-volume flow solver ISIS-CFD developed by ECN-CNRS. An essential feature for full RANSE simulations with this code is the use of a sliding grid technique to simulate the real propeller rotating behind a ship hull. The computational study in operational service conditions considered here has been conducted to evaluate the instantaneous flow distribution around the podded propellers and to analyse and to compare the unsteady behaviour of the forces induced by the rotating propeller in waves with the measurements from omnidirectional propeller loads as well as the blade forces and moments. The computational study has been done in model and full scale to evaluate the scale effects.
Analysis of Octagonal Pile Supporting Offshore Wind Turbines Under Wave Loads
Authors: Lim Serena , Tao Longbin
Published: September 2014

Offshore wind energy development has gained considerable momentum around the world as wind is stronger and steadier offshore compared to land. This has led to a significant increase in production in recent years, especially offshore wind turbine embedded in shallow waters, such as the recent large scale offshore wind farms in the Northern Europe region. Being at the offshore waters, the wind turbines are subjected to harsh environment. The pile supporting the wind turbine must be reliable and able to withstand such sea condition. It is an important part of the design to study the structural behaviour of the piles under the wave loads.

Due to the significant capital cost associated with the fabrication of the large circular cylinders, a new recommended innovative design to overcome such problem is to substitute the circular cylinder with a vertical monopile of octagonal cross-sectional shape. This paper describes the development of an efficient numerical model for structural analysis of wave interaction with octagonal pile using a modified semi analytical Scaled Boundary Finite Element Method (SBFEM). In contrast to the existing solutions obtained using the traditional methods such as the Finite Element Method (FEM) which typically suffer from high computational cost and the Boundary Element Method (BEM) which faces limitation from fundamental equations and problems with singularities. The most prominent advantage that SBFEM has over the FEM is in terms of the number of elements used for calculation and hence a reduction in computational time. When compared with BEM, the SBFEM does not suffer from computational stability problems.
Universal Crane Model for the Ship Design System E4
Authors: Vorhölter Hendrik , Christiansen Jakob , Hatecke Hannes
Published: September 2014

For the ship design system E4 a universal crane model was developed. With the help of this model the design of crane vessels and cranes can be harmonised better and lifting operations can be analysed more precisely. The model is able to handle any type of cranes which are used in the shipping and offshore industry and provides the input for every simulations method within E4 which needs to consider crane operations. Special focus was given on keeping a common user interface both for the designer of a crane vessel and the planning engineer for lifting operations independently of the type and functionalities of the crane. Such a universal crane model has not been implemented in any other ship design software until now.

In this article the motivation for the development of the model is described together with the requirements for a universal crane model. The principle of the model explained and its functionality is demonstrated in several examples.