bluuebunny/crossref_metadata_2025 huggingface dataset:
A Methodology to Assess the Downtime of a Multi-Phase Offshore Floating Bulk Transshipment Operation
Authors: Wang Yijun , van Deyzen Alex , Pauw Willemijn , Huijsmans René
Published: October 2016

Operators who want to im- or export bulk (coal, iron ore, scrap, etc.) by means of offshore bulk transshipment often want to determine the operability of their bulk transshipment configuration in an early stage to assess if offshore floating bulk transshipment is a feasible option for im- or export of the commodity. The downtime of such offshore (un)loading operations may be unacceptably large. The operational windows may become limited. This implies insufficient im- or export volumes, which may result in large and expensive storage capacity onshore.

In this paper a methodology is proposed to assess the operability of offshore floating bulk transshipment. Offshore bulk transshipment is a multi-phase operation. For offshore operations consisting of multiple phases, persistency of the environmental conditions has to be considered. Persistency analysis allows for multiple operational phases, individual phase duration and shift of sea states during the operation.

The proposed methodology shows that using persistency data of the waves (wind and current are not considered yet), the downtime of an offshore floating bulk transshipment operation can be estimated more accurately. Compared to persistency analysis, scatter analysis (using wave scatter diagrams) resulted in an optimistic estimate of the downtime. Persistency analysis is better in demonstrating the influence due to each consecutive step on the total operability. This methodology could be further extended to other multi-phase offshore operations.
Three-Dimensional Forward-Speed Seakeeping Calculation Using FINE/Marine
Authors: Chen Limin , He Guanghua , Wang Dazheng , Zhang Zihao
Published: October 2016

A time-domain seakeeping numerical model based on a computational fluid dynamics (CFD) software FINE/Marine has been developed for nonlinear steady and unsteady viscous flows. Simulation of multi-phase flows around a Wigley hull with forward speed is performed by solving the Reynolds-average Navier-Stokes (RANS) and continuity equations with k-ω (SST-Menter) turbulence model. The water free surface is captured by Blend Reconstruction Interface Capturing Scheme (BRICS). Both steady and unsteady problems including wave-making, radiation and diffraction problems are simulated. Ship waves generated by the Wigley model advancing at a constant forward speed in calm water or incident waves are computed. The numerical results including the wave-making resistance and wave patterns for steady problem, hydrodynamic coefficients and forces for unsteady problems are illustrated and compared with experimental measurements in good agreement. It is confirmed that the present numerical model has the capability of evaluating the seakeeping performance of ships.
The Compression Behaviour of Marine Clays in Malaysia
Authors: Ahmad N. R. , Harahap Indra S. H.
Published: October 2016

The paper presents results of experimental works on intact marine clay samples in Malay and Sarawak Basins, which is located in Malaysia. Recent development in economic and search of new energy has brought to the usage of areas with plenty of marine clay inshore and offshore. For offshore area, the seabed foundation support or subsurface installation often create several complexities in geotechnical design due to high compression behavior and low bearing capacity. Knowledge of seabed soils and rocks is very important in designing any structures onshore or nearshore. However, the seabed data properties in Malaysia is less and not many researches have been done to contribute to this database. Series of oedometer tests performed intact clay samples from different depths showed inconsistency patterns of compression behavior. The preconsolidation pressure for all samples ranged from 200 to 500 kPa, which can be compared with the presence literature for the compression behavior towards denser soil. The compression index, Cc ranged from 0.177 to 0.797 and Swelling index, Cs ranged from 0.133 to 0.066.
Model Test Investigation of the Influence of Damping on the Vortex Induced Motions of Deep Draft Semi-Submersibles Using a Novel Active Damping Device
Authors: Sterenborg Joost , Koop Arjen , de Wilde Jaap , Vinayan Vimal , Antony Arun , Halkyard John
Published: October 2016

Vortex Induced Motions (VIM) of semi-submersibles occur when the vortex shedding frequency is close to the natural frequency of the semi-submersible in the direction transverse to the current. Recent studies suggest that the magnitude of VIM predicted during model tests is higher than that observed in the field. Among others, the damping effect provided by the risers and mooring lines is regarded as one of the reasons for this difference. In this paper the setup and results are presented for model tests to investigate the influence of damping on VIM.

For these model tests an active damping system was developed, which introduces an actively controlled external force mimicking a damping force. This applied damping force is based on the floater sway motion and sway velocity. With this system the introduced damping level can easily be controlled and verified without changing the stiffness of the system. In this paper the advantages and disadvantages of this active damping system are presented.

The VIM tests were conducted for two semi-submersibles: a paired-column semi with eight columns and a four column semi. Reduced velocities ranged from Ur=3 to Ur=10 and different levels of additional linear damping were applied to the floaters in the direction transverse to the current direction. Damping was found to reduce the VIM motions significantly: reductions of more than 60% were observed in the nominal A/D response for 25% equivalent linear damping. This indicates that damping has a significant effect on the global VIM response and thus should be considered in the design phase of the risers and mooring lines of the semi-submersibles.

To improve the understanding of the driving mechanism of VIM and also to provide validation data for CFD analyses, forces were measured on each column of the four column semi. Column force measurements indicate that for the four column semi for 45 degrees heading, i.e. the heading with largest VIM responses, the upstream, the portside and the starboard side columns are exciting the VIM motions. For 22.5 degrees, the downstream, the portside and the starboard side columns excite the VIM motions. For all tested headings the pontoon always damps the VIM response.
A Procedure to Include Slip Damping in a VIV Analysis of an Umbilical
Authors: Passano Elizabeth , Abtahi Shahriar , Ottesen Torfinn
Published: October 2016

Ocean currents may cause vortex induced vibrations (VIV) of deep-water umbilicals. The VIV response may give significant contributions to the total fatigue damage. Good estimations of the VIV response and damage are therefore important for the design of deep-water umbilicals. As VIV response is very sensitive to the structural damping, good response and fatigue estimates will be dependent on good estimates of the damping and that they are included in the VIV response analysis in a consistent way.

A complex cross section such as an umbilical or a flexible riser will have two sources of structural damping; damping due to the strain variation in the individual materials that make up the cross sections, and damping due to the different layers slipping against one another. The first may be denoted material damping and is present at all response levels, and will be particularly important at low response levels. The second may be denoted slip damping and will contribute when the curvature exceeds the initial slip curvature.

Ideally, accurate data for both the material and the slip damping are available. Unfortunately, this is not always the case and the damping parameters must then be estimated. The material damping may be estimated from the material properties of the various layers in the cross section, taking operating conditions such as temperature into account. The slip damping may be estimated from detailed cross-sectional analyses.

As the slip damping is dependent on the curvature, iterations are needed to ensure that the applied damping and the calculated response are consistent with each other. A procedure to include these iterations within a VIV response calculation is proposed.

A case study is presented demonstrating the use of the proposed procedure for a deep-water umbilical in a lazy wave configuration. For the case studied, the maximum curvatures caused by VIV are significantly reduced.
Verifying Production Losses due to Petroleum Flow Improving Well Intervention and Design
Authors: Coca Suaznabar Paola Adriana , Miura Kazuo , Morooka Celso Kazuyuki
Published: October 2016

The purpose of this research is to identify in the literature: causes, factors, case study descriptions and adopted solutions for production losses regarding the petroleum flow in offshore oil wells. Those facts will be organized and structured to identify potential zones of intervention for planning the well maintenance during well design phase to avoid production losses.

This paper focuses on four offshore regions: Campos Basin, Gulf of Mexico, North Sea, and West Africa. These regions represent the most significant share of offshore oil production in the world.

Data set available in the last thirty five years through academic, technical and governmental reports in the literature were the basis of this study. The procedure was accomplished in three steps: (1) data research (2) analysis of the data (3) guidelines establishment.

The main cause of production loss regarding the petroleum flow is the solids deposition in the well/line system, such as hydrates, asphaltenes, wax, scales (barium sulfate, strontium sulfate, calcium sulfate, calcium carbonate, and naturally occurrence radioactive material), and calcium naphthenates.

In this work the superposition of graphics (hydrate curve, wax appearance temperature, asphaltene onset pressure, and saturation index) resulted in a region free of solids deposition, denominated as “flow assurance envelope”.

The main expected result is to propose a guideline to be used during the well design phase in order to minimize and facilitate the well intervention.

The main contributions of this paper to the oil industry are the identification of potential zones of intervention due to solids deposition in the well/line system, the foresight of well intervention before the beginning of the oilfield production, and finally, possibilities to improve the well or intervention design.
A French Application Case of Tidal Turbine Certification
Authors: Paboeuf Stéphane , Macadré Laura-Mae , Yen Kai Sun Pascal
Published: October 2016

Tidal turbines are emerging technologies offering great potential for the harnessing of a renewable and predictable oceanic resource. However, exploitation at sea comes with significant design, installation, grid connection, and maintenance operations challenges. Consequently, guidelines and standards are required to ensure safety, quality, performance and accelerate tidal turbines development and commercialisation. Standardisation is also a necessity to support and improve safety and confidence of a wide range of Marine Renewable Energy (MRE) stakeholders such as designers, project operators, investors, insurers or final users.

There are undergoing developments on guidelines, standards and certification systems within the International Electrotechnical Commission (IEC) Technical Committee TC 114 “Marine energy - Wave, tidal and other water current converters” and the IEC Renewable Energy “Marine Energy - Operational Management Committee” (IECRE ME – OMC). However, as the tidal energy concepts are only at the demonstration stage, only few guidelines and no dedicated certification scheme has been published so far within this organization, which guarantee an international, independent, non-governmental and consensus-based elaboration process.

The aim of this paper is to present a proposal of certification methodology, developed by Bureau Veritas for the design assessment of current and tidal turbines, and its application to a French case study. This certification procedure was developed within the French research project Sabella D10 funded by ADEME and is published in the Bureau Veritas guideline NI603 “Current & Tidal Turbines”.

The suggested certification procedure addresses prototype, component, type and project certification. Main objective, scope, intermediary steps to be completed and resulting certificates will be detailed for each certification scheme, as well as their interactions.

This methodology will be illustrated by the case study on the Sabella D10 prototype, a French tidal turbine installed in 2015 in the Fromveur Passage, off Ushant Island. Sabella D10 is a 1 MW tidal turbine fully submerged laid on the seabed with a horizontal axis and 6 blades. It is the first French tidal turbine producing electricity and connected to the electrical network.

The Sabella D10 case study will focus on prototype certification and computations performed for support structure and blades. The paper will describe the load cases that have been considered, the review procedure for the support structure and the blades design assessment, including description of a streamlined method for basic design and a detailed method for final design. In conclusion, the next steps will be introduced to continue the certification developments of tidal and current turbines.
Marine Operation Windows Offshore Norway
Authors: Kvamme Bjarte O. , Orimolade Adekunle P. , Haver Sverre K. , Gudmestad Ove T.
Published: October 2016

A study of the wave conditions in the North Sea, the Norwegian Sea and the Barents Sea is presented in this paper. For each region, one reference location for which there are buoy measurements is selected. For the selected locations, WAM10 hindcast data are obtained from the Norwegian Meteorological Institute (MET Norway). The hindcast data for each location cover the period from 1957 to 2014.

First, the hindcast datasets were validated against available buoy measurements — both for extreme value predictions and for application of hindcast data for planning of marine operations. The validation was carried out considering the winter season and the summer season separately. For each season, the datasets for two consecutive months were used. A comparison of the time-series of the hindcast datasets against the buoy measurements showed that the hindcast datasets compared relatively well with the buoy measurements.

However, a comparison of the statistical parameters of the hindcast datasets against the buoy measurements showed that the hindcast datasets are slightly conservative in the estimate of the significant wave height for the Barents Sea and the Norwegian Sea. Overall, the data compared well, and the hindcast datasets are therefore considered in the following analysis.

Hindcast data from these 57 years show that the wave conditions in the selected Norwegian Sea location is harsher than the wave conditions in both the North Sea and the Barents Sea locations. This is in agreement with the general expected spatial trend in the wave climate on the Norwegian Continental Shelf (NCS). It was also observed that the wave conditions in the selected Barents Sea location are harsher than the wave conditions in the North Sea. These findings are also reflected in the NORSOK N-003 standard on “Actions and Action effects” (NORSOK, 2015).

The weather windows for weather-sensitive marine operations, that is, operations with operational reference period not exceeding 72 hours, were established from the hindcast dataset for each of the locations. It was observed that the Norwegian Sea has shorter weather windows, especially in the winter seasons, compared to both the Barents Sea and the North Sea. It was expected that the operational windows would be shorter in the winter seasons in the Barents Sea, due to the occurrence of polar lows. However, the polar lows are few and cause more concern related to forecasting of the weather conditions to start actual marine operations. Generally, the month with the highest probability of weather windows exceeding 72 hours was found to be July for all three locations.
Application of a Speed Exclusion Zone Algorithm on a Large 10MW Offshore Wind Turbine
Authors: Smilden Emil , Sørensen Asgeir J.
Published: October 2016

To optimize tower design it is desirable to relax the constraint of having to place natural frequencies outside the rotor and blade passing frequency-bands. A speed exclusion zone algorithm is tested to assess its effectiveness on preventing tower resonance caused by 3p thrust oscillations. The effect of the speed exclusion zone algorithm on power output is also considered. A simulation model adequate for qualitative testing of the algorithm is developed and implemented in the simulation tool Simulink by MathWorks. The model is based on a 10MW offshore wind turbine and includes a simplified representation of rotor aerodynamics, drive-train and generator dynamics and a two-dimesional finite element representation of the tower and support structure. To support simulations a rotor speed controller is implemented together with wind models accounting for wind shear, tower shadow, turbulence and rotational sampling. A significant reduction in tower vibration is seen with a ±10% speed exclusion zone. A exclusion zone width of ±5% is shown to increase tower vibrations in some cases. The speed exclusion zone algorithm will lead to a reduction in power output for a ±10% and ±15% speed exclusion zone. For the ±5% speed exclusion zone no significant change in power output is observed.
Design and Analysis of a Braceless Steel 5-MW Semi-Submersible Wind Turbine
Authors: Luan Chenyu , Gao Zhen , Moan Torgeir
Published: October 2016

This paper introduces the design data and numerical analysis of a braceless steel semi-submersible wind turbine. The hull of the semi-submersible wind turbine is designed to support a reference 5-MW horizontal axis wind turbine at a site in the northern North Sea. The hull is composed of a central column, three side columns and three pontoons. The side columns and pontoons are arranged radially outward from the central column which is used to support the wind turbine. The side columns form the corners of a triangle on the horizontal plane and are connected by the pontoons to the central column at the bottom to form an integrated structure. Numerical analysis has been carried out to analyze the intact stability, natural periods and modes and global dynamic responses in winds and waves. Results of the numerical analysis show that the design has very good intact stability, well designed natural periods and modes, moderate rigid-body motions in extreme environmental conditions and a reasonable structural design. This paper emphasizes the structural responses of the hull considering both the global and local load effects. The global forces and moments in the hull are calculated by carrying out time-domain global analysis and used as inputs for simplified ultimate limit state design checks for structural strength of the hull. The design can be used as a reference semi-submersible wind turbine.
Advanced Pipeline Impact Design
Authors: Igland Ragnar T. , Alsos Hagbart S. , Kvarme Stig Olav
Published: October 2016

The safety of pipelines and subsea structures are key elements in subsea field developments. As part of the safety engineering, protection from dropped objects and third party impact actions is required. This article addresses this aspect.

Dropped object from a platform or a vessel is one of the design scenarios. The fall-pattern of the object is essential for the impact velocity and corresponding energy, model of the path and the effects of hydrodynamic behavior is outlined.

In lieu of accurate information, the design code use energy band for energy estimates and may give extremely conservative impact energy. The falling objects structural flexibility and properties are discussed and evaluated regarding the energy dissipation and possible damage of the pipeline.

The pipeline combined response from global deflection and denting regarding impacts are investigated. Analysis and testing methods applied in pipeline design are presented. Focus is placed on the overall interaction between the impacting object, the deformed pipeline and energy dissipation by coating and soil.

Typically, pipeline damage from design codes provides conservative cross sectional damage estimates. This is confirmed from both simplified and detailed FE analyses, as well as fullscale impact experiments performed by REINERTSEN AS.

One of the main objectives promoted by the authors is the importance of both impact velocity and mass during impact, and not only the kinetic energy of the impact. The kinetic energy from a dropped object is unlikely to be fully dissipated as cross sectional deformation of the pipeline.

Global deformations will be triggered, which implies that the dissipated energy going into local denting is reduced to a fractional value. The effect is more pronounced for small diameter pipelines than for pipelines with large diameter. This paper discusses the impact mechanics and seeks to estimate the fractional value by using simplified element analysis.
Numerical Simulation for Typhoon and Wave of Qiongzhou Strait
Authors: Xu Yanan
Published: October 2016

Southern China has been subject to some of the deadliest typhoons in history with records going back over a thousand years. Before the large waves associated with a typhoon reach the mainland of China there is a delay between the typhoon reaching landfall and the time of the extreme waves arriving. This paper focuses on an approach to simulate this lag in the waves reaching landfall in the Qiongzhou Strait in southern China. A numerical approach has been adopted to simulate the typhoon and wave processes using a parametric typhoon model and the SWAN wave model. Two typhoon events are simulated (typhoon Kai-Tak in 2012 and typhoon Jebi in 2013) and used to tune the parameters for the numerical models. The simulated wind speeds and significant wave heights of the typhoon are compared with measured data. For the simulation of typhoon Kai-Tak, the correlation coefficient gives an 87% agreement between the simulated and measured values of wave height with a standard deviation of 0.29 m. For typhoon Jebi the fit is less good (66%). However, the simulation results have provided insight into improving the parametric typhoon model.
Fatigue Assessment of Pipeline With Plain Dents Under Cyclic Pressure Loading Using Finite Element Method
Authors: Durowoju Michael , Pu Yongchang , Benson Simon , Race Julia
Published: October 2016

One of the major challenges faced in fatigue assessment today is determining the stress concentration factor ‘SCF’ associated with the dents, which are used with appropriate SN curves to determine the fatigue life. This historically has been determined empirically or by using finite element analysis.

This paper presents finite element analysis on a parametric range of industry pipes (both offshore and onshore) to extract SCF data used for fatigue assessment. The parametric dataset focuses on the effects of pipe geometry, dent geometry, material properties and pressure cycling on the prediction of the fatigue life. This parametric dataset will eventually be used to develop an algorithm for fatigue prediction using an artificial neural network.

Two types of indenters (Dome and Bar) are used to simulate circumferential and longitudinal dents. Four different dent depths ranging from 2% d/D to 10% d/D are also simulated to investigate the effect of dent geometry. Four different pipe grades (X42, X65, X80 and X100) are analyzed to investigate the effect of pipe materials on dent fatigue. Similarly, eight pipes with different diameter to thickness ratio D/t ranging from 18–96 are analyzed to investigate the effect of pipe geometry. Stresses are computed at both 50% SMYS and 72% SMYS to investigate the effect of pressure variation.

The results from this study indicate that longitudinal dents have higher stress concentrations compared to circumferential dents of similar dent depth. Results also indicate that the re-round dent depth (i.e. dent depth after pressurization) increases with increasing D/t and increasing dent depth. Similarly, the pipe material has a major effect on the fatigue life. Pipes with higher material strength have higher stress concentration compared to pipes with lower strength of similar dent depth. The stress concentration factors SCF associated with the dents are then computed.
A Coupled VOF-Eulerian Multiphase CFD Model to Simulate Breaking Wave Impacts on Offshore Structures
Authors: Tomaselli Pietro D. , Christensen Erik Damgaard
Published: October 2016

Breaking wave-induced loads on offshore structures can be extremely severe. The air entrainment mechanism during the breaking process plays a not well-known role in the exerted forces. This paper present a CFD solver, developed in the Open-FOAM environment, capable of simulating the wave breaking-induced air entrainment. Firstly the model was validated against a bubble column flow. Then it was employed to compute the inline force exerted by a spilling breaking wave on a vertical cylinder in a 3D domain at a laboratory scale. Results showed that the entrained bubbles affected the magnitude of the force partially. Further analyses on the interaction of the bubble plume with the flow around the cylinder are needed.
A Fuzzy Event Tree Model for Accident Scenario Analysis of Ship Stuck in Ice in Arctic Waters
Authors: Fu Shanshan , Zhang Di , Montewka Jakub , Zio Enrico , Yan Xinping
Published: October 2016

Arctic waters have historically been regarded as harsh environments because of the extreme weather conditions and remoteness from land. The advantages of shorter sea routes and hydrocarbon energy exploitation have recently led to increased marine activities in such harsh environments. Nevertheless, the risks therein need to be systematically identified and assessed. Specifically, the potential consequences of major incidents in Arctic waters should be studied. However, research in this domain is scarce, mainly due to the lack of knowledge and information related to the Arctic marine transportation system (AMTS). In this paper, we present an event tree analysis (ETA) model to illustrate the possible accident scenarios and calculate the probabilities for the associated consequences of ship stuck in ice in Arctic waters. The probability of occurrence of the initiating event and intermediate events in the scenarios are extracted by experts’ elicitation and, then, the probabilities of the potential outcome events are computed from the ETA model. Fuzzy set theory is incorporated into the ETA model to handle the epistemic uncertainties in the probability values.
Feasibility Study of the Floating Medical Support System to Operate as a Dialysis Treatment Center
Authors: Eto Hiroaki , Sato Chiaki , Masuda Koichi , Ikoma Tomoki , Nakajima Mayumi
Published: October 2016

This paper presents a feasibility study for a floating medical support system, and describes its basic concept with regards to the installation location, its primary function and patient capacity. In 2011, Japan experienced a major catastrophe: the Great East Japan Earthquake and subsequent tsunami. After the tsunami struck, overland transport routes were cut off, and consequently emergency supplies and people requiring medical attention could not be transported very efficiently. Many hospitals and other emergency facilities were destroyed or were operating with reduced capabilities during this period, meaning victims could not receive treatment within a reasonable timeframe. Therefore, we need to consider emergency facilities, particularly for medical support, which are resilient and versatile for use in such situations. Floating bases for disaster relief and support ships are already available for deployment along coastal regions or on rivers near affected areas. A medical support floating base has also been proposed, which is called the Medi-float hereafter, in preparation for the anticipated Tokyo Inland Earthquake. The original proposal was deemed inadequate in terms of its choice of deployment area, and its maximum capacity for patients. The objectives of this paper are to decide the Medi-float’s primary function, the location where it should be installed, and to determine its capacity and a floor plan which adheres to the relevant regulations. It is determined that the primary function of the Medi-float should be as a dialysis treatment center during normal operation and primarily for the treatment of crush syndrome patients during a disaster. A location in Sumida ward is chosen for the installation area. In the floor plan, the Medi-float has 55 beds in dialysis treatment rooms. Also, there are areas of open space in the Medi-float to be used for coordinating the distribution of emergency supplies. The maximum capacity for patients is approximately 5,300 people, and the Medi-float can treat up to 130 patients with crush syndrome every 2 days. There is estimated to be around 106 patients with crush syndrome around the installation area in the event of a major earthquake. Therefore, this study clearly demonstrates the usefulness of the Medi-float.
Virtual Prototyping of Maritime Systems and Operations
Authors: Hassani Vahid , Rindarøy Martin , Kyllingstad Lars T. , Nielsen Jørgen B. , Sadjina Severin Simon , Skjong Stian , Fathi Dariusz , Johnsen Trond , Æsøy Vilmar , Pedersen Eilif
Published: October 2016

While in aerospace and automotive industry, airplanes and cars are built in quantity, in maritime industry ships and offshore platforms are built uniquely such that even sister ships can be significantly different from each other. Hence, building a full scale prototype to test, verify, and demonstrate effectiveness of new innovative solutions, is not an option in maritime sector. Model testing and simulation of separate modules have been practiced in many applications successfully, however, capturing the complete interaction of different modules in a maritime system is not straight forward. To best of our knowledge, the modeling and simulation of a maritime system to the extent where the complete system, including the mutual interactions, is not accomplished yet. A maritime system incorporates a wide variety of components from different engineering fields and in order to develop a simulation framework for such a complex system, an interdisciplinary effort is needed from different branches of science including but not limited to hydrodynamics, machinery and power systems, structural engineering, navigation and control. This paper aims to introduce a joint effort from different research institutes, universities, and industrial partners to shed a light on the different issues in virtual prototyping in maritime systems and operations. It summarizes some of the available frameworks for virtual prototyping, and ends with a numerical simulation of a generic hull model coupled with propellers, propeller actuators, DP controller, thrust loss calculations, wind, waves and current, performed with the current implementation of our Virtual Prototyping Framework (VPF).
Finite Element Analysis of Flexible Pipes Under Compression: Influence of the Friction Coefficient
Authors: Ribeiro Malta Eduardo , de Arruda Martins Clóvis
Published: October 2016

In order to study the compressive behavior of flexible pipes, a nonlinear Finite Element model was developed. This fully tridimensional model recreates a five layer flexible pipe with two tensile armor layers, an external polymeric sheath, an orthotropic high strength tape and a rigid inner nucleus. The friction coefficient is known as a key parameter in determining the instability response of flexible pipes tensile armor. Since the featured model includes all nonlinear frictional contacts between the layers, it has been used to conduct several experiments in order to investigate its influence on the response. This article includes a description of the Finite Element Model itself and a case study where the friction between the layers of the pipe is changed. The procedure of this analysis is here described, along with the results.
The Study on the Risk Analysis of Submarine Landslide in the Continental Slope Region of Northern South China Sea
Authors: Yan Zhiduo , Ding Weichen , Pang Liang
Published: October 2016

Abundant oil and gas resources are stored in the continental slope region of northern South China Sea. However, due to the submarine landslide disasters, submarine pipelines and cables and other submarine facilities were damaged, which seriously affected the development of oil and gas resources, leading to a huge economic losses. In order to ensure the safe operation of the submarine gas pipeline, it is necessary to carry out some researches in the submarine slope stability. In this paper, an uncertainty analysis method is applied and a distribution model which is suitable for slope stability influencing factors of this region is put forward. In addition, the risk of submarine slope is analyzed, plotting submarine landslide risk evaluation maps. Different stochastic characteristics of variables such as water depth, angle of slope, shear strength and earthquake acceleration etc can be reflected reasonably, which is helpful for the safety of oil and gas transportation.
Comparing a Fracture Mechanics Model to the SN-Curve Approach for Jacket-Supported Offshore Wind Turbines: Challenges and Opportunities for Lifetime Prediction
Authors: Ziegler Lisa , Muskulus Michael
Published: October 2016

Accurate lifetime predictions are needed for support structures of offshore wind turbines to optimize operation and maintenance and to decide about lifetime extension of aging wind farms. A comparison of a facture mechanics model to the SN-curve approach for jacket supported offshore wind turbines shows that it is attractive for lifetime extension decisions; however major challenges are calibration of material parameters and assumptions for initial crack size. Crack growths on a Y-joint connecting brace and jacket leg was analysed with simulations of structural response to aero- and hydrodynamic loading and Paris’ law for crack propagation. The model was calibrated to yield an identical fatigue life as obtained from the SN-curve analysis. The effect of weather seasonality on crack growth was evaluated with a Markov weather model and Monte Carlo simulations. Results show that crack growth is sensitive to parameter calibration and follows seasonal weather trends.
Progressive Collapse Approach Compared to the Traditional Temperature Screening on Structural Assessment of Offshore Structures Against Fire
Authors: Nascimento Paula T. , Rosas Marco A. P. , Brandão Leonardo , Castanheira Fernando
Published: October 2016

The present study compares the progressive collapse approach with the traditional temperature screening method on determination of PFP requirements at topside offshore structures. The advantage to evaluate the consequences of fire scenarios on the global integrity and stability of topside modules can be revealed by a substantial reduction of the required amount of PFP, and consequently significant cost savings for operators, when compared to the traditional approach. In the case study presented in this paper, there is a reduction of 79% in PFP allocation.
Multi-Scale Numerical Analysis of the Field Efficiency of an Ocean Plastic Cleanup Array
Authors: Sainte-Rose Bruno , Lebreton Laurent , de Lima Rego Joao , Kleissen Frank , Reisser Julia
Published: October 2016

The impact of plastic pollution on marine ecosystems and global economy has been drawing public concern since the end of the 20th century. To mitigate this issue, The Ocean Cleanup (TOC) Foundation is developing technologies to extract, prevent, and intercept plastic debris from coastal and oceanic environments. The core technology being optimized is the use of floating booms placed perpendicular to the main ocean plastic flow so it can concentrate plastic debris to a point where it can be extracted, shipped and processed in a cost-effective manner.

In order to optimize the system’s field efficiency (i.e. mass of ocean plastic captured per length of floating boom), a multi-scale approach has been elaborated, where temporal and spatial scales span over several orders of magnitude. Here we introduce this general multi-scale method alongside its assumptions and multi-scale models. We then describe two application examples, the first corresponding to our coastal pilot in the Japanese island of Tsushima and the second related to our main cleanup target area: the so-called Great Pacific Garbage Patch, situated between Hawaii and the US west coast.
Airgap and Wave in Deck Impact Statistics
Authors: Hagen Øistein , Johannessen Thomas B. , Birknes-Berg Jørn
Published: October 2016

As offshore reservoirs are depleted, the seabed may subside. Bottom fixed installations which have previously had sufficient clearance between the deck and the sea surface may be in a situation where wave impact with the deck must be considered at relevant probability levels. Some statistical aspects associated with the calculation of a deck impact load with a prescribed probability of occurrence are the subject of the present paper.

The Short Crest JIP addressed the distribution of the crest height in extreme sea states, the properties of the largest crests and the deck impact loading on a closed deck. It was concluded that the largest waves in the sea may be in the process of breaking and thus have properties which deviate significantly from estimates found from weakly nonlinear irregular or regular wave theory.

The present paper addresses findings from the Short Crest JIP regarding

• long-term analysis of wave heights and crest, including the effect of wave breaking

• air gap analysis for jacket, TLP and semisubmersible using 2nd order time domain simulations over the platform area

• statistics for horizontal wave-in-deck impacts for short crested sea versus for long crested sea

• structural reliability analysis of jackets for some simple limit states that are governed by loads caused by impact of extreme crests
Hull Girder Ultimate Strength of Intact and Damaged Double Hull Tankers
Authors: Amante Diogo do Amaral M. , Chujutalli John Alex , Estefen Segen F.
Published: October 2016

The aim of this work is to accomplish an assessment of the hull girder ultimate strength of intact and damaged double hull tankers. First, the paper presents the validation of the numerical model through comparisons with experimental tests of small-scale box girders. The numerical models are represented by shell elements assuming finite membrane strains and large rotations, considering both geometric and material nonlinearities. Simulation results show very good agreement with experimental tests. Then, a numerical model of a double hull tanker was developed and analyzed in the intact and damaged conditions. Several damage scenarios were investigated.
CFD Modeling and Validation of Steel Lazy-Wave Riser VIV
Authors: Constantinides Yiannis , Stover Maeanna , Steele Amanda , Santala Markku
Published: October 2016

The steel lazy wave riser is an emerging solution for deepwater applications in harsh conditions. The addition of buoyancy to provide the unique “lazy wave” shape reduces the dynamic stresses at the touchdown zone due to vessel motions and waves and results in improved performance. However, as the buoyant region cannot be easily fitted with VIV suppression, VIV becomes a critical aspect of the design. The present study progresses the modeling effort presented in [2] to model and understand the global response of a deepwater lazy wave riser using computational fluid dynamics (CFD). An industry first CFD simulation of a steel lazy wave riser under in-plane currents is presented and validated against experiments with two different configurations. Results show good agreement between CFD and experiments and provide an initial understanding of the riser response under in-plane currents. The CFD method developed has been validated and will be an important tool for the design of lazy wave risers.
Fundamental Study on Elastic Behavior of Large-Scale Floating Coal Stockyard
Authors: Eto Hiroaki , Sato Chiaki , Masuda Koichi , Ikoma Tomoki , Kishida Tomoyuki , Kubota Mitsuru
Published: October 2016

This paper proposes a large-scale floating coal stockyard (LFCS) and discusses its elastic behavior. Indonesia has recently become the main country supplying coal in the Asia-Pacific region. However, there is concern that export to Japan will decrease as coal demand increases. Therefore, the trend of coal transport in Indonesia is a very important matter in ensuring the continued stable import of coal to Japan. It is difficult for bulk carriers to traverse the shallow terrain of the seabed of the Markham River in East Kalimantan to reach coastal areas. Additionally, an LFCS can be operated as a relay base for barges, and large coal carriers have been proposed for use in offshore areas. The LFCS is capable of loading, storing, and offloading coal. Installing an LFCS offshore Kalimantan is expected to improve coal transport productivity in the region.

Under such circumstances, the design plan proposed in this paper can simultaneously perform independent loading and unloading without interference. The partial mass distribution and local rigidity of the LFCS varies depending on the coal loading conditions. In addition, because the structure has a planar shape, the response of the LFCS showed elastic behavior. Design example of such a huge floating structure with the great difference of the displacement is unparalleled, it is very important to clarify a design fundamental subject.

The objectives of this study are to provide a preliminary LFCS design and investigate the impact of varying the mass distribution and local rigidity on not only the distribution of the distortion and internal stress but also on the dynamic hydroelastic motion of the LFCS when it is impacted by waves. Therefore, the wave response of the LFCS was analyzed under different loading conditions.
A Novel Tension-Leg Application for Floating Offshore Wind: Targeting Lower Nacelle Motions
Authors: Melis Cécile , Caille François , Perdrizet Timothée , Poirette Yann , Bozonnet Pauline
Published: October 2016

A novel concept of wind turbine floater based on tension-leg technology is introduced. This floater, dedicated to support wind turbines up to 10 MW, aims at minimizing weight and operations while decreasing the level of motions at the nacelle, hence reducing the loading on the turbine and the need for maintenance. The lightness and modularity of the concept allows for use of typical construction means, flexible procurement and building. The self-installability, meaning towing on site by means of standard anchor handling vessel (AHV) with the turbine already installed, facilitates and accelerates the towing and maintenance procedures. Regarding motions, especially tilt angle and nacelle accelerations, excellent floater performance in both operational and extreme conditions, is ensured through an innovative mooring system and reduced wave loads. The latter are kept low thanks to a high transparency of the floater to wave excitation.
Reeling Analysis and Limit State Criteria
Authors: Xu Jianfeng , Vishnubhotla Srinivas , Aamlid Olav , Collberg Leif
Published: October 2016

Reeling has been an attractive offshore installation method for rigid flowlines and steel catenary risers due to its fast speed, cost effectiveness and reliability. Over years of evolution, it has become a proven technology, and the understanding to the engineering fundamentals is greatly improved as well. Due to the reeling process, the pipeline is plastically deformed; residual stresses, pipe ovality, and pipe out of straightness are increased. The strength, fatigue, and fracture performance of the pipe and the girth weld have to be closely evaluated to insure the pipeline integrity during and after the installation. As part of the installation design, different types of analyses are generally carried out to demonstrate the reelability, and the pipeline responses against all limit states. However, the methods adopted by different contractors can vary greatly.

In this paper, the engineering fundamentals of reeling process are reviewed. A few typical reeling analyses, both analytical and finite element based, are demonstrated with examples. The local buckling limit state criteria based on DNV-OS-F101 for different stages of reeling are also illustrated.
An Experimental Consideration on Accuracy of Inverse Super Short Baseline Underwater Positioning Using Acoustic Data Transmission
Authors: Watanabe Yoshitaka
Published: October 2016

Authors are developing a test system of new type acoustic positioning system (APS) using inverse super short baseline (ISSBL) method. In this method, the vehicle is equipped with hydrophone array. Direction of arrival (DOA) of acoustic signal from mother ship is detected, and relative position between the mother ship and the vehicle is calculated with the measured DOA and the depth. Information of ship’s position is included in the transmitted acoustic signal, then absolute position of the vehicle can be calculated with the relative position and the included information. The vehicle position can be obtained in the vehicle in real-time and be used directly to navigate. No reply from the vehicle is necessary.

Five ocean experiments were conducted in various depth points. In the experiments, an experimental device was moored at sea bottom, and the ship cruised around above the moored device with transmitting acoustic signal including the ship’s information.

In consideration about random scattering of positioning result, followings were found. Random scattering is much suppressed with EKF using high rate symbol value. On the other hand, estimation error of ship’s position, which is about 0.5–1 meter, is not negligible. When the DOA measurement for each symbol is accurate, the estimation error of the ship’s position becomes dominant in output of EKF as a consequence of random scattering suppression. Therefore, this method is more advantageous in case the DOA measurement have larger random error. Then this method is useful in deeper case and small array can be adopted to the system. On the other hand, this method do not perform well when the elevation angle from the target to the ship is shallow. Moreover convergence percentage seems to touch the lowest value at around 10%.
A Novel Spudcan for Easing Spudcan-Footprint Interaction Issues
Authors: Jun Minjung , Kim Youngho , Hossain Muhammad Shazzad , Cassidy Mark , Hu Yuxia , Won Jonghwa , Park Jongsik
Published: October 2016

The interaction between a spudcan and an existing footprint is one of the major concerns during jack-up rig installation, especially in the surface clay layer. No guidance was provided in the recently finalised version of ISO guidelines 19905-1 [1] in regards to mitigating spudcan-footprint interaction issues except some proposed considerations due to the lack of detailed investigations. This paper reports a measure for easing spudcan-footprint interaction issues, with the efficiency of a novel spudan shape tested through 3D large deformation finite element (LDFE) analyses. The LDFE analyses using the Coupled Eulerian-Lagrangian (CEL) approach in the commercial finite element package ABAQUS. The soil conditions tested simulate soft seabed strength profiles close to the mudline. A critical reinstallation locations of 0.55D (D = spudcan diameter) and existing footprint depth (of 0.33D) were investigated. The main aim was to investigate if the spudcan shape itself can be used to mitigate potential footprint interaction when compared to a conventional spudcan. The results from this study indicated that the novel spudcan had the potential to ease spudcan-footprint interaction issues.