bluuebunny/crossref_metadata_2025 huggingface dataset:
Backbone for Escape, Evacuation and Rescue From Arctic Facilities: A Systematic Approach
Authors: Longrée Mark , Hoog Sven
Published: September 2014

In turn of the global warming and driven by the constant need for resources an increasing number of commercial and scientific activities conquer the Arctic in order to benefit from almost untouched resources like oil and gas but also from the overwhelming nature. These activities are accompanied by a steadily increasing number of vessels transporting goods but also operating personnel, scientists or tourists. Especially the number of tourists visiting the Arctic can reach far more than 1000 per vessel, resulting in growing headaches for the responsible safety and security authorities in the Arctic surrounding countries. Up to now no suitable Escape, Evacuation and Rescue (EER) concept is in place to cope with these challenges when it comes to hazardous situations.

In this context IMPaC ([1]) developed a new and appropriate EER concept for the Arctic, exceeding the currently dominant small and isolated settlements along the coastlines in Denmark (Greenland), Norway, Russia, Canada and the US. One question seems to be central: Is there any requirement and benefit beyond the currently used small rescue station?

Yes, we strongly believe that there is a growing demand for suitable infrastructure coming from various industries. Beyond rescue objectives there is a demand for people working and living in this area all year long, for a few days, weeks or months using these settlements for their specific needs. This led us to the idea of the provision of a common-use infrastructure for multiple industries. The commonly used infrastructure maximizes the use of the remote and very expensive infrastructure and minimizes the impact on the environment in this part of the world.

Potential users of this infrastructure would be:

• Oil & Gas Industry, driven by the increased world energy demand

• Marine Transport & Tourism Industry, driven by declined arctic ice and new sea routes via the Arctic sea

• Fishery Industry

• Scientific community

Any EER concept for the Arctic has to cope with several specific environmental and spatial challenges as addressed by the EU joint research project ACCESS ([2]), where IMPaC participates. The paper introduces the new EER concept and focuses especially on its beneficial, efficient and safe operability in the Arctic recording an increasing number of commercial and scientific activities.
Lessons Learned From Norwegian Mooring Line Failures 2010–2013
Authors: Kvitrud Arne
Published: September 2014

15 failures of offshore mooring lines have occurred in the period 2010–2013 on the Norwegian Continental Shelf. The failures are cause by a mixture of overload, fatigue and mechanical damages.

Failure statistics from the period 2010–2013 are presented and compared it with earlier statistics. In the period 1996–2005 a high number of cases were observed. The industry reacted reasonably, and the number of incidents was clearly reduced for several years. In 2010 the number of cases started to increase again, rising questions on how to improve again. Some of the old failure modes have disappeared, as dragging of anchors and failures of chains above 20 years of age. But several other failure modes have appeared or reappeared. Differences between different types of units are found. The failure frequencies are highly uncertain, but the failure rate from 2010–2013 have been in the order of magnitude

• single line failures: 92*10−4 per line year and

• double line failures: 12*10−4 per line year.

No triple line failures have occurred in 2010–2013, but using data from 2000–2013, the failure rate have been in the order of magnitude 2*10−4 per line year.

The paper discusses possible changes in practice, regulations and standards, on quality of materials, maintenance, ALS-, FLS- and ULS-design.
Selection of Leak Detection Systems by Aggregation of Experts’ Judgment
Authors: Yasseri Sirous
Published: September 2014

Numerous leak detection systems (LDS) using a variety of technologies are on the market. Since LDS are designed for a particular use, then the evaluation and selection process requires suitable metrics and involvement from all stakeholders. This paper proposes to use15 criteria for selection of LDS. Each criterion is first rated for their importance by a number of experts. Then, the same experts are asked to rate a list of candidate LDSs. Fuzzy TOPSIS is used to aggregate Experts’ judgment. A case study is presented to demonstrate the application of the method. This method would indicate how a good compromise might look like. This could aid the decision-maker to weigh options and set priority and decide on a system.
Second Order Wave Force Effects on Tension Leg Platform Wind Turbines in Misaligned Wind and Waves
Authors: Bachynski Erin E. , Moan Torgeir
Published: September 2014

Although the majority of studies of tension leg platform wind turbines (TLPWTs) have focused on aligned wind and wave conditions, it is not uncommon for the wind and waves to be significantly misaligned. Wind-wave misalignment is expected to influence both ultimate and fatigue loads. The present work compares the dynamic response of a representative TLPWT in both aligned and misaligned wind and wave conditions, with and without second order sum-frequency potential forces. The contribution of the second order loads to the maximum stress and to the short-term fatigue damage at the tower base, tower top, and tendon fairleads is examined for several operational conditions. The same TLPWT with softened tendons is also studied in order to examine the sensitivity of the results to the system natural frequencies. The fatigue damage decreased in misaligned wind and wave conditions, but the effect of second order forces increased. For the soft TLPWT design, second order forces had an important effect on fatigue in both aligned and misaligned conditions. Despite the increase in side-side loading in misaligned conditions, aligned conditions were associated with larger maximum stresses (in operational conditions).
Estimates of the Number of Vibration Cycles From Frequency Locked-in Ice Loads
Authors: Bjerkås Morten , Alsos Hagbart S. , Wåsjø Kasper
Published: September 2014

A method is proposed to estimate the number of vibration cycles caused by frequency locked-in ice loads on a bottom fixed structure. Studies of the onset of frequency lock-in have been performed and based on that, different onset criteria are studied. It is shown in this work that most existing onset criteria significantly overestimate the vulnerability to frequency locked-in ice loads. The method described proposes a 90 % reduction in the number of vibration cycles in a winter season. The 2002–2003 winter at Norströmsgrund lighthouse is compared with the proposed method. The comparisons show that all available methods overestimate the number of vibration cycles significantly.
Fatigue Analysis of Subsea Jumpers due to Slug Flow
Authors: van der Heijden Bob (H. E. J. ) , Smienk Henk , Metrikine Andrei V.
Published: September 2014

Rigid steel jumpers are used in a subsea flow line system to connect subsea components. They provide a certain flexibility with respect to installation and operating conditions. This flexibility makes the jumper susceptible to slug flow induced vibrations. Slug flow can be described as an alternating flow of long oil and gas bubbles which flow at the gas velocity. The alternation between oil and gas density causes loads on the jumper which causes the jumper to vibrate. Two excitation mechanisms can be identified; 1) The variation in weight along the straight sections and 2) the difference in impact loads on the bends. Due to the cyclic nature of these loads fatigue can cause the jumper to fail.

As a main contractor of SURF-projects (Subsea Umbilicals Risers and Flowlines) Heerema Marine Contractors (HMC) is responsible for the engineering, procurement, construction and installation (EPCI) of the entire project scope, including the design of the subsea jumpers. Hence this paper has been set up by HMC and the Delft University of Technology to study slug flow induced fatigue in subsea jumpers and in order to find new design considerations.

In the early design phase of a subsea jumper the offshore industry commonly uses, to authors knowledge, a static analysis to predict the fatigue damage caused by slug flow. Since the vibrations caused by slug flow are not incorporated in a static analysis an accurate tradeoff between flexibility and fatigue lifetime cannot be made during the design phase. As this tradeoff during the design phase is desirable, a new dynamic and more accurate analysis method has been developed which takes these vibrations into account. A comparison between this new methodology and the common industry method is made in order to quantify the difference in analyzed fatigue damage due to slug flow induced vibration. Additionally the effects of a pressure drop over a passing slug is also investigated to determine if a pressure drop should be incorporated as a design factor for slug flow induced fatigue. The new dynamic method will also be used to investigate the relation between jumper configuration and high slug flow velocity. It will show what excitation mechanisms are dominant and how this affects the fatigue behavior. Since is be the first time, to authors knowledge, such an extensive analysis of geometries and velocities is undertaken it will provide new insights into slug flow induced fatigue in subsea jumpers in general. The newly found amplification and attenuation of the vibration by the successive impacts on the bends of a subsea jumper are investigated.
Waves’ Numerical Dispersion and Damping due to Discrete Dispersion Relation
Authors: Ommani Babak , Faltinsen Odd M.
Published: September 2014

In linear Rankine panel method, the discrete linear dispersion relation is solved on a discrete free-surface to capture the free-surface waves generated due to wave-body interactions. Discretization introduces numerical damping and dispersion, which depend on the discretization order and the chosen methods for differentiation in time and space. The numerical properties of a linear Rankine panel method, based on a direct boundary integral formulation, for capturing two and three dimensional free-surface waves were studied. Different discretization orders and differentiation methods were considered, focusing on the linear distribution and finite difference schemes. The possible sources for numerical instabilities were addressed. A series of cases with and without forward speed was selected, and numerical investigations are presented. For the waves in three dimensions, the influence of the panels’ aspect ratio and the waves’ angle were considered. It has been shown that using the cancellation effects of different differentiation schemes the accuracy of the numerical method could be improved.
Design and Optimization of Scour Protection for Offshore Wind Platform DolWin Beta
Authors: de Sonneville Ben , van Velzen Greta , Wigaard Jan
Published: September 2014

DolWin Beta is a large offshore power converter platform, which will be used to connect multiple offshore wind farms off the German coast to the main land. It will be located in a water depth of 29m, where tidal currents and harsh wave conditions may cause soil erosion (scour) and possibly undermining of the foundation if not protected properly. Laboratory experiments were conducted in order to investigate the scouring around the foundation and provide an optimized layout for scour protection. This paper summarizes the initial scour assessment, the design approach for scour protection, the experimental set-up, test program, monitoring techniques and results of the experiments.

The test results revealed which zones of the scour protection around the foundation were most sensitive to shear failure and edge scour. In steps, the scour protection was strengthened in these zones and reduced in the more sheltered areas. The tests showed that the magnitude of rock displacement, apart from wave height and direction, was significantly influenced by the superimposed current velocity. Based on a test without scour protection, the sequence of installation was adjusted to minimize risks of scour during installation. Finally, a stable scour protection layout was obtained that was fully verified under extreme storms and long-term effects of edge scour.
Omnidirectional Return Values for Storm Severity From Directional Extreme Value Models: The Effect of Physical Environment and Sample Size
Authors: Randell David , Zanini Elena , Vogel Michael , Ewans Kevin , Jonathan Philip
Published: September 2014

Ewans and Jonathan [2008] shows that characteristics of extreme storm severity in the northern North Sea vary with storm direction. Jonathan et al. [2008] demonstrates, when directional effects are present, that omnidirectional return values should be estimated using a directional extreme value model. Omnidirectional return values so calculated are different in general to those estimated using a model which incorrectly assumes stationarity with respect to direction. The extent of directional variability of extreme storm severity depends on a number of physical factors, including fetch variability. Our ability to assess directional variability of extreme value parameters and return values also improves with increasing sample size in general. In this work, we estimate directional extreme value models for samples of hindcast storm peak significant wave height from locations in ocean basins worldwide, for a range of physical environments, sample sizes and periods of observation. At each location, we compare distributions of omnidirectional 100-year return values estimated using a directional model, to those (incorrectly) estimated assuming stationarity. The directional model for peaks over threshold of storm peak significant wave height is estimated using a non-homogeneous point process model as outlined in Randell et al. [2013]. Directional models for extreme value threshold (using quantile regression), rate of occurrence of threshold exceedances (using a Poisson model), and size of exceedances (using a generalised Pareto model) are estimated. Model parameters are described as smooth functions of direction using periodic B-splines. Parameter estimation is performed using maximum likelihood estimation penalised for parameter roughness. A bootstrap re-sampling procedure, encompassing all inference steps, quantifies uncertainties in, and dependence structure of, parameter estimates and omnidirectional return values.
An Efficient Direct Calculation Approach for Fatigue Assessment of Container Ships Concerning Bending and Warping Stresses
Authors: Li Zhiyuan , Mao Wengang , Ringsberg Jonas W.
Published: September 2014

Container ships are particularly susceptible to torsional loads. The distribution of torsion-induced warping stress in a container ship hull is more complicated and difficult to be expressed by beam theory formulas. In practice, finite element (FE) analysis is typically used to calculate the stress response to wave-loading conditions. However, it is time consuming to compute hull girder stresses for all relevant sea conditions through FE analyses. In this paper, an efficient and robust approach is proposed by combining beam theory and FE analyses in the determination of hull girder stresses. The parameters required by beam theory can be regressed through matching stress records from a FE analysis with the corresponding sectional and pressure loads from the hydrodynamic simulation. Stress records obtained using the proposed method are utilized in fatigue assessment of a case study container vessel. The results show that the accuracy of the regression approach is satisfactory compared with the full FE analyses.
Viscoelastic Behaviour of Bitumen in Dynamic Control Umbilicals
Authors: Olsen Elise , Hansen-Zahl Kay André , Karlsen Stian
Published: September 2014

By combination of elements like hydraulic tubes, electrical and optical signal cables and electrical power cables, umbilicals provide remote control of subsea oil and gas wells. For extra tensile strength and outer protection the umbilicals may be armoured by galvanized steel wires. Dynamic umbilicals are terminated at offshore platforms or vessels. They are exposed to tension and bending variations caused by waves and vessel motions. As such a project specific analysis is normally required to verify that a given dynamic umbilical design with all its elements is able to withstand a service life of typically 20–30 years [5].

Understanding how forces are transmitted between the elements in an umbilical is vital for correct calculation of a dynamic umbilical design life. Cross section analysis is therefore performed by a finite element method program specially designed for this purpose. This software takes into account all effects in an umbilical cross section, including friction between elements. For solid elements, commonly known friction factors may be applied. However, for the steel wire armour which is corrosion protected by bitumen, the friction factors may not be valid. The force transmission between the steel wires may not be governed by friction but by the viscoelastic properties of bitumen. In such a case the transition force is not only a function of contact pressure but also of sliding velocity and dimensions.

A project was therefore initiated with the aim of describing such force transmission between bitumen and steel wires for typical umbilical conditions. Material testing has included characterization by a controlled stress rheometer and cyclic tensile testing at various temperatures, speeds and geometries. On basis of these tests, a calculation model describing the mechanical behavior of bitumen in cyclic movement is suggested. This model may later be implemented in the umbilical cross section analysis program.
Dynamic Responses of a Semi-Type Offshore Floating Wind Turbine
Authors: Li Liang , Hu Zhiqiang , Wang Jin , Hu Qiuhao
Published: September 2014

This paper deals with wave-wind induced global motion and mooring system responses of a semi-type offshore floating wind turbine. The analysis in this paper is conducted in time domain, using an aero-hydro-servo-elastic simulation code-FAST. Due to the limitation of the initial drag force model in FAST, a quadratic damping model is developed to gain a better consideration of viscous performance. Simulations involve free-decay in still water, dynamic responses in moderate sea states with and without wind. Aerodynamic effects on platform dynamic responses are investigated.

Analysis indicates that wind force would accelerate platform’s decay motion and increase natural periods of surge and pitch, while heave motion is little influenced. Pitch motion is decreased at wave frequency range under joint wave-wind loads condition. Little wind-induced pitch resonant response has been observed. Nevertheless, instabilities are induced for surge motion due to negative aerodynamic damping. A typical mooring line force is found to be greatly excited by wind force.
A Study for Statistical Characteristics of Riser Response in Global Dynamic Analysis With Irregular Wave
Authors: Zhang Yanqiu , Tan Zhimin , Hou Yucheng , Yuan Jiabei
Published: September 2014

A study was conducted to have a deeper understanding to the statistical characteristics of response of flexible riser in global dynamic simulation with irregular wave. If consider the numerical simulation model as a system and the input wave train as an excitation to it, the time histories of riser load should be the response of the system to the excitation. In order to look the effect of riser configuration and water depth, the study was conducted with three kinds of configuration: Free-Hanging, Lazy-S and Tethered-Wave, which were in different water depths. In order to examine the stationarity and ergodicity of riser response, 100 simulations were performed. Each simulation was performed with a 3-hours-long storm. Except the seeds used to generate the random phases to the wave components, the 100 irregular wave processes for each riser are completely the same. When the number of wave components is enough large, the input irregular wave train should be a stationary normal process. Since the software used for the dynamic simulation is high nonlinear, however, the time history of riser response may not be perfectly stationary normal process. Then different probability distribution theories were applied to fit these time histories and the most fitting one was found out for different riser responses and for different riser configurations. The ensemble autocorrelation functions and the time autocorrelation functions were also examined for both irregular waves and the riser responses. Then the study indicated that both irregular waves and riser responses as random processes should be ergodic stationary. Finally the cross correlations between the irregular waves and riser responses were also examined and it was found that the irregular wave for each riser should be jointly stationary with each response of the riser.
Code Verification of ReFRESCO With a Statistically Periodic Manufactured Solution
Authors: Eça Luís , Vaz Guilherme , Hoekstra Martin
Published: September 2014

This paper presents a Code Verification study performed with the unsteady ensemble-averaged Navier-Stokes (URANS) solver ReFRESCO using the Method of Manufactured Solutions. The study uses a statistically periodic manufactured solution including the un-damped eddy-viscosity of the Spalart & Allmaras turbulence model. Three main aspects of the numerical calculations of unsteady flows are addressed in this study: iterative errors; discretization errors (space and time) and the determination of the observed order of (space and time) convergence.

The availability of an exact solution allows the determination of the numerical error and so the effects of iterative and discretization errors can be addressed. The paper presents grid and time refinement studies with different (iterative) convergence criteria and demonstrates that grid and time resolution are strongly connected when attempts are made to minimize the numerical uncertainty in the calculation of unsteady flows.

The paper also addresses error estimation based on power series expansions in the calculation of unsteady (space and time dependent) flows. Simultaneous grid and time refinement is compared to grid refinement with fixed time step and time refinement with fixed grid. The advantages and limitations of both options are discussed in the context of Code Verification (error evaluation) and Solution Verification (error estimation).
A Comparison of Two Coupled Model of Dynamics for Offshore Floating Vertical Axis Wind Turbines (VAWT)
Authors: Borg Michael , Wang Kai , Collu Maurizio , Moan Torgeir
Published: September 2014

As part of the deployment of floating offshore wind turbines (FOWTs) in deep sea, robust coupled dynamic design codes based on engineering models are being developed to investigate the behaviour of FOWTs in the offshore environment. The recent re-emerging interest in vertical axis wind turbines (VAWTs) for floating foundation applications has resulted in a number of design codes being developed concurrently by different researchers. In this study, two such design codes for floating VAWTs developed at Cranfield University and the Norwegian University of Science and Technology are compared through a series of increasingly complex simulation load cases.

A floating VAWT design was specified to be used in this study. The rotor is based on the Darrieus Troposkein shape and is the same used within the DeepWind VAWT spar concept, with a 5MW rated capacity. The floating support structure is a semi-submersible that is being used in the Offshore Code Collaboration Continuation (OC4) Phase II project for floating horizontal axis wind turbines.

A series of load cases were set out to assess and compare the two different design codes. A comparison of the performance of the two design tools is presented, illustrating their level of maturity and areas of improvement.
CFD Simulation of Propeller and Tunnel Thruster Performance
Authors: Lu Ping , Wang Sue
Published: September 2014

In the present study, the hydrodynamic performance of a typical North Sea dynamic positioning (DP) shuttle tanker consisting of two main propellers, two rudders, and two bow tunnel thrusters is investigated by solving Reynolds-averaged Navier-Stokes (RANS) equations for a viscous flow. The focus of the numerical simulation is on the performance of propellers/rudders and bow tunnel thrusters considering the hydrodynamic interactions between propellers/thrusters, hull and current. The numerical model includes hull, propeller, rudder, bow tunnel thruster and flow field.

First, an analysis of a propeller performance in open water is carried out by calculating the coefficient of thrust, torque, and propeller efficiency. Then, rudders are included in the analysis for the assessment of propeller/rudder performance. The pressure distribution on rudders, rudder’s drag and lift coefficients for different angles of attack, and flow field around the rudder are obtained. The interaction effects between propeller, rudder, ship hull, as well as bow tunnel thruster and ship hull are analyzed by adding detailed ship hull geometry in the computational domain. The tunnel thruster efficiency reduction due to current and ventilation is also analyzed. The presence of current leads to significant changes in the flow velocity and distribution of pressure in the tunnel outflow area as well as significant deflection of the propeller jet emitting from the tunnel. A comparison between Computational Fluid Dynamics (CFD) and model test results of flow features near the tunnel area with various current speeds is presented.
Fluid Structure Interaction Study on Dynamic Response of a Capped Drilling Riser Filled With Mud
Authors: Paczkowski K. W. , Zhang P. , Rogers R. , Richardson N.
Published: September 2014

In the offshore drilling, during emergency disconnect scenario the drilling operation must not be maintained and forced LMRP disconnect procedure takes place [1,2]. Such procedure allows drilling mud to interact with seawater. The paper presents hydrodynamic behavior of a drilling riser when mud is retained and not interacted with seawater. A two-way coupled fluid-structure interaction (FSI) model between a simplified drilling riser structure and mud fluid was studied through techniques of computational fluid dynamics (CFD). The volume of fluid (VOF) hydrodynamics model was used with commercially available software STAR-CCM+ [3]. A 3D finite element (FE) model of a drilling riser was created in FE software ABAQUS [4] to determine the stress and deflection of structural parts of the model due to hydrodynamic loads. In the model, the compressibility [5] and non-linear behavior of the mud was included. The dynamic frequencies of the two domains and possible resonance of the coupled system were investigated. The aim of the study was to verify the dynamic behavior of a riser system with a drilling mud enclosed within the system. The authors of this paper know no similar study of such a problem.
Dropped Object Analysis Using Non-Linear Dynamic FE Analysis
Authors: Ahn Kwanghyun , Chun Minsung , Han Sangmin , Jang Kibok , Suh Yongsuk
Published: September 2014

For the last few decades, necessity of direct non-linear FE analysis has been increasing for the accidental events at the vessel/offshore structures. One of major areas for the accidental design, dropped object analysis using non-linear analysis is indispensable for the verification of structural safety at the design process. This paper is concerned with the methodology, conditions, and design consideration of dropped object analysis using dynamic FE analysis. By comparing the results from direct FE analyses to those from simplified energy method described in DNV-RP-C204, necessities and advantages of direct non-linear analysis can be verified.

In this paper, the effect of analysis condition is investigated using parametric study. The results are influenced by the application of failure criteria according to the rule requirements, application of material properties, dropping position, condition of the object, and so on. This study can suggest appropriate determination of the methodology and condition for the dropped object analysis using direct FE analysis.
Marine Growth on North Sea Fixed Steel Platforms: Insights From the Decommissioning Industry
Authors: Mallat Chadi , Corbett Alistair , Harris Glyn , Lefranc Marc
Published: September 2014

It is reputed in the Oil & Gas industry that marine growth is overestimated in the North Sea. Can we quantify this overestimation to better tackle the challenges marine growth incurs?

This paper provides insight into the intrinsic and diverse nature of marine growth. It documents the biofouling development and the factors that affect it globally. Focus is made on fixed steel platforms in the North Sea approaching the end of their economic lives. A methodology to quantify the weight of marine growth is proposed and illustrated. 28 years after its installation, the weight of marine growth accumulated on Valhall 2/4G jacket located in Southern North Sea is evaluated based on the proposed method. It is confirmed that the current regulations overestimate the weight of marine growth in the North Sea.
Sloshing Forces on a Tank With Two Compartments, Application of the Pendulum Model and CFD
Authors: Manderbacka Teemu L. , Jacob Vincent , Carriot Thomas , Mikkola Tommi , Matusiak Jerzy E.
Published: September 2014

Two different methods, pendulum model and computational fluid dynamics (CFD), to predict the forces on the ship caused by the flooded water are compared against the model test results. Calculations were performed for a tank in forced motions at different frequencies, for which experimental results were available. The tank had a dividing wall with an opening. The overall behaviour of the force time history was well captured with the pendulum model. In particular at lower frequency the agreement of the force range is very good. Some small force peaks due to the sloshing were predicted in a good correspondence with the CFD simulations. At a higher frequency slight discrepancy is shown also in the CFD calculations. The free surface behaviour is captured in detailed level by the CFD calculations, but the overall motion of the water is captured also with the pendulum model with plane surface model. Comparison to the model tests shows the applicability of the pendulum model in simulating sloshing case with the exchange of water between the compartments. These comparisons show that the pendulum model is a sufficiently accurate and calculation time wise efficient method. It provides a tool to perform a great amount of simulations in order to study the impact of different parameters and the statistical probabilities of ship survival under different accident scenarios.
Performance of a Ship Powered Purely by Renewable Energy
Authors: Bøckmann Eirik , Steen Sverre , Myrhaug Dag
Published: September 2014

A ship harnessing all its required energy from the wind, waves and sun is proposed. The ship employs five wingsails and two spring-loaded wavefoils — one ahead of the bow and the other astern of the stern. In addition, the deck is covered with solar panels, which generate electricity for use aboard the ship. The wind speed is calculated from wave scatter tables, by finding the wind component of the waves from the two-peaked Torsethaugen wave spectrum and assuming unlimited fetch and fully developed sea. Wingsail and wavefoil forces are calculated using a dynamic stall model and implemented in a time-domain ship simulator. Statistical estimates of the ship speed are calculated for the route Ponta Delgada, Azores - Funchal, Madeira, round-trip, for all four seasons. The expected ship speeds are about 6 knots, and the standard deviations are about 5 knots.
Residual Stress Measurement in an Ultrasonic Peened Specimen
Authors: Ficquet Xavier , Hedmar Malcolm , Kingston Ed J.
Published: September 2014

Plastic deformation from peening induces a compressive residual stress on the treated surface which provides resistance to metal fatigue. Hence, peening is often used to extend the fatigue lives of welded components by reducing the effective tensile residual stress. This paper describes the influence of ultrasonic peening on the residual stress. For this study a four point plastically bent beam specimen, similar to the reeling process, was used. The specimen was made from 50D steel a material often used in offshore structural components. The residual stresses in the specimen were measured before ultrasonic peening with 5 different measurement techniques. After the ultrasonic peening treatment the residual stress was measured using the Incremental centre hole drilling and the ring core techniques. Measurements were carried within the homogeneously bent section location as well as outside. In order to see the variation of the results influenced by the gauge volume, strain gauges of three different sizes were used to provide results within 0.5mm, 1mm and 2mm depth. The measurements show that the ultrasonic peening surface treatment carried out induced high compressive residual stresses up to 2mm deep inside the specimen. Finally a compendium of residual stress profiles using different peening processes and materials is presented and discussed.
The Significance of Storm Avoidance on Macroscopic Fatigue Crack Growth
Authors: Hodapp David P. , Collette Matthew D. , Troesch Armin W.
Published: September 2014

Ship weather routing is routinely employed to assist ship-masters in avoiding storms. During these storms, however, both material and hydrodynamic nonlinearities grow with the significant wave height (Hs). Hence, to fully understand the importance of weather routing, it may be necessary to go beyond a conventional spectral-based fatigue analysis which incorporates a linear damage hypothesis (i.e., the Palmgren-Miner rule).

To this end, the present paper examines macroscopic fatigue crack growth in which the nonlinear phenomena omitted in current design practices are included. We start by considering time-dependent ship structural loading sequences which include non-linear wave-induced bending and whipping responses taken from time-domain seakeeping simulations. These stresses are then analyzed using a fatigue crack growth model previously developed by the authors [1] in which material hysteresis is included using a mechanistic rather than phenomenological approach based on numerical simulations requiring only experimentally measured fatigue crack growth rates under constant amplitude cyclic loading (e.g., ASTM E647-13) and a full material constitutive model defined through experimental push-pull tests for the same material. Using this approach, we quantify the importance of weather routing by systematically substituting storms above a certain threshold with more moderate sea conditions.
A Procedure for Non-Linear Structural Collapse Analysis
Authors: Zhang Shengming , Jiang Lei
Published: September 2014

It is a normal practice nowadays in structural engineering, including ships and offshore industry, to perform non-linear finite element analysis to assess the structure’s capacity for design or evaluation purposes. However, experience has shown that the quality and accuracy of the non-linear FE analysis results are highly dependent on the skill of the person performing the analysis and the analysis procedure used. The difference between results obtained by different people can be significant. In some cases, the results can be misleading. It is considered that a unified procedure is necessary. This paper is moving a step further and trying to develop a standard procedure which can provide a guideline for structural collapse analysis of stiffened panels under any load combinations. The paper provides the technical background on the analysis procedure and the key steps such as model extent, mesh density, initial imperfections, and boundary conditions. Analysis examples are provided in the paper for reference and discussions.
A Numerical Model to Initiate the Icebreaking Pattern in Level Ice
Authors: Erceg Sandro , Ehlers Sören , von Bock und Polach Rüdiger , Leira Bernt
Published: September 2014

Ships navigating in ice-covered waters experience local and global ice loads due to ice-hull interaction. The design of a ship with good ice performance requires adequate assessment of these forces. Recently, an increased activity in developing numerical models of ice-hull interaction in level ice has been observed, owed to the increased computational capabilities. However, certain semi-empirical icebreaking patterns inevitably influencing the interaction process have been implemented in the majority of interaction models used for the assessment of ice performance of ships. Therefore, an attempt using a quasi-static numerical approach to model the initiation of icebreaking pattern in level ice has been made and is presented in this paper. The term initiation herein denotes the creation of circumferential cracks, disregarding thus the succeeding radial cracks.

The concept used in the model features a set of radially oriented ice beams at the interaction zone. The model accounts for the bow geometry and the properties of the encountered ice. The icebreaking pattern for a case study ship is simulated using the developed model. Lastly, this paper discusses the sensitivity of the model with respect to the bow shape.
Movability Study of a Small Crawler ROV Deployed From a Launching Station to Operate on the Seafloor
Authors: Katsui Tokihiro , Inoue Tomoya , Kyo Masanori , Suzuki Hiroyoshi
Published: September 2014

A crawler system is an advanced function that can potentially allow remotely operated vehicles (ROVs) to operate on the seafloor. A quasi-static theoretical motion model for a crawler ROV was established to facilitate evaluation and design that incorporate the characteristic parameters in water, including hydrodynamic forces and the effect of an underwater cable, that are expected to affect mobility. The results confirmed that these parameters considerably affect and decrease the mobility of crawler ROVs. The established motion model was applied to examine the mobility of a sample small-size crawler ROV deployed from a launching station.
Long-Term Stochastic Dynamic Analysis of a Combined Floating Spar-Type Wind Turbine and Wave Energy Converter (STC) System for Mooring Fatigue Damage and Power Prediction
Authors: Ren Nianxin , Gao Zhen , Moan Torgeir
Published: September 2014

In this work, a combined concept called Spar-Toru-Combination (STC) involving a spar-type floating wind turbine (FWT) and an axi-symmetric two-body wave energy converter (WEC) is considered. From the views of both long-term fatigue damage prediction of the mooring lines and the annual energy production estimation, a coupled analysis of wind-wave induced long-term stochastic responses has been performed using the SIMO-TDHMILL code in the time domain, which includes 79200 one-hour short term cases (the combination of 22 selected mean wind speeds * 15 selected significant wave heights * 12 selected spectral peak wave periods * 20 random seeds). The hydrodynamic loads on the Spar and Torus are estimated using potential theory, while the aerodynamic loads on the wind rotor are calculated by the validated simplified thrust force model in the TDHMILL code. Considering the long-term wind-wave joint distribution in the northern North Sea, the annual fatigue damage of the mooring line for the STC system is obtained by using the S-N curve approach and Palmgren-Miner’s linear damage hypothesis. In addition, the annual wind and wave power productions are also obtained by using hourly mean output power for each short-term condition and the joint wind-wave distribution.
Assessment of Extreme Rolling of Ships in Random Seas
Authors: Dostal Leo , Kreuzer Edwin
Published: September 2014

The goal of our analysis is to improve intact stability criteria for ships. For this, we develop analytical formulas for mean first passage times of critical roll amplitudes of ships travelling in long crested random seas with an arbitrary wave encounter angle. Starting from a model for coupled heave-pitch-roll motion, we average the fast oscillatory dynamics of roll over the roll period, which yields equations for drift and diffusion of roll energy. The results are used to calculate the desired mean first passage times. Finally, we apply the proposed theory to a sample ship design.
Phase Resolved Wave Prediction From Synthetic Radar Images
Authors: Naaijen P. , Wijaya A. P.
Published: September 2014

A method is presented for the inversion of images of the sea surface taken by nautical radar into wave elevation that is specifically suitable for the prediction of the wave elevation outside the observation domain covered by the radar. By means of a beam-wise analysis of the image obtained by a scanning radar, the image information is translated into wave elevation. Subsequently a 2D FFT is applied in order to obtain the directional wave components required for a linear propagation of the wave field. Assuming knowledge of the significant wave height, a method to obtain the correct scaling of the wave prediction is proposed. The proposed method is verified using synthetic radar images which are modelled by applying shadowing and tilt effect to synthesised short crested linear waves.
Calculation of Horizontal Sectional Loads and Torsional Moment
Authors: Shigunov Vladimir , von Graefe Alexander , el Moctar Ould
Published: September 2014

Horizontal sectional loads (horizontal shear force force and horizontal bending moment) and torsional moment are more difficult to predict with potential flow methods than vertical loads, especially in stern-quartering waves. Accurate computation of torsional moment is especially important for large modern container ships. The 3D seakeeping code GL Rankine has been applied previously to the computation of vertical loads in head, following and oblique waves; this paper addresses horizontal loads and torsional moment in oblique waves at various forward speeds for a modern container ship. The results obtained with the Rankine source-patch method are compared with the computations using zero-speed wave Green functions and model experiments.
A Novel Strategy for the Identification of Radiation Force Models
Authors: Janssen Roman M. , Jansen Henk , van Wingerden Jan-Willem
Published: September 2014

A novel frequency domain identification (FDI) strategy for the identification of radiation force models from frequency domain hydrodynamic data is proposed. First, a subspace identification method is augmented with a convex constraint that guarantees a stable solution. Then, in a second convex optimization problem, constraints on low- and high frequency asymptotic behavior and passivity are enforced. This novel method, constrained frequency domain subspace identification (CFDSI), is validated by comparing both SISO and MIMO CFDSI results with the state-of-the-art FDI toolbox, which is part of the Marine Systems Simulator MATLAB toolbox. In two test cases, it is shown that the novel algorithm can successfully identify a model with either a SISO or MIMO structure, where stability, passivity and the desired low- and high-frequency asymptotic behavior are guaranteed. For the two test cases presented, the quality of the CFDSI models matches the quality of the state-of-the-art FDI models.
Comparison of Full-Scale and Numerical Model Dynamic Responses of Norströmsgrund Lighthouse
Authors: Popko Wojciech
Published: September 2014

This paper compares dynamic response of the Norströmsgrund lighthouse and its numerical implementation in Abaqus software. The dynamic response of the full-scale structure was analyzed based on the accelerometers data, which were correlated with ice loading time histories that were recorded from the load panels surrounding the structure. The full-scale measurement data come from the Measurements on Structures in Ice (STRICE) project. A 3D numerical model of the lighthouse, based on the solid elements was setup in Abaqus. Such aspects as soil stiffness and sand filling of caissons were accounted for to more accurately mimic behavior of the real structure. The eigen-frequency response of the numerical model was tuned to correspond with the structural response of the full-scale lighthouse. The numerical model was equipped with a set of load panels on which pre-defined time histories of the full-scale loading were applied. Then, its response was compared with the response of the Norströmsgrund lighthouse.
A Comparison of Time Domain Methods for Asymmetric Roll Predictions
Authors: Seah Robert , Bigot Fabien , Tom Nathan , Roddier Dominique
Published: September 2014

Unlike ocean going vessels, FPSOs often have appendages, such as bilge keels or riser porches, at or below the waterline in an asymmetric configuration. In addition, the riser and mooring systems impose asymmetric loads on the hull. As a result, the expected roll motion response to a wave environment is asymmetric and traditional methodologies cannot be used to predict it. Morison drag elements can be incorporated to represent the asymmetric condition and are easily implemented in time domain simulations. The limitation to this engineering approach is that the drag coefficient can only be calibrated to produce accurate motions or accurate appendage loads but not both. In this paper we compare the response using two time domain approaches, the first being adapted from a commercial marine dynamics analysis tool [9] and the other being a specialized hydrodynamics motion prediction tool [4]. Here, the commercial tool utilizes constant coefficient drag elements in conjunction with traditional linear equivalent roll damping to model the effect of unequal port and starboard bilge keels as is typical when a riser balcony are present. In contrast, the newly developed hydrodynamic model relies solely on a Keulegan-Carpenter (KC) number dependent drag relation to represent the asymmetric drag contributions. The different calibration procedures will be discussed and a comparison for a design environmental condition between the two methodologies will be presented.
Semi-Active Hydropneumatic Heave Compensator
Authors: Cuellar William H. , Fortaleza Eugenio
Published: September 2014

A hydropneumatic heave compensation system and a semi-active control are proposed according to the requirements drilling offshore of 6 km deep. The goal of this semi-active control is to maintain an acceptable performance of the system when the drill string mass changes, which also changes the performance of the hydropneumatic system. The control action is executed just by a servo valve, which modifies the system damping to optimize the compensator performance. This servo valve is the only moving part of the control system and therefore, this system is more robust regarding mechanical/ electrical failures and it has low consumption energy. The results show a satisfactory frequency response of semi-active control when the drill string mass is changed.
Simulation of Multi-Liquid-Layer Sloshing With Vessel Motion by Using Moving Particle Simulation
Authors: Kim Kyung Sung , Kim Moo Hyun , Park Jong-Chun
Published: September 2014

For oil/gas production/processing platforms, multiple liquid layers can exist and their respective sloshing motions can also affect platform performance. To numerically simulate those problems, a new multi-liquid MPS (Moving Particle Simulation) method is developed. In particular, to better simulate the relevant physics, robust self-buoyancy model, interface searching model, and surface-tension model are developed. The developed multi-liquid MPS method is validated by comparisons against Molin et al’s (2012) three-liquid-sloshing experiment and the corresponding linear potential theory. The verified multi-liquid MPS program is subsequently coupled with a vessel-motion program in time domain to investigate their dynamic-coupling effects. In case of multiple liquid layers, there exist more than one sloshing natural frequencies, so the relevant physics can be much more complicated compared with the single-liquid-tank case. The numerical simulations also show that liquid cargo can function as a beneficial anti-rolling device.