bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on the Hydrodynamic Efficiency of Flexible Foil at Different Operating Parameters
Authors: Kizhakkedath Martin Anties , Krishnankutty Parameswaran
Published: October 2017

The hydrodynamics of a flexible foil, which is inspired by the thunniform kind of propulsion system, is studied numerically. The NACA0012 foil with a chord length of 0.1m is selected for the study. The foil performance parameters such as force coefficients and efficiency are estimated for different flexibility of the foil and Strouhal numbers. The results show that oscillating foil generated thrust increases with increase in Strouhal number up to 0.4 and a maximum efficiency is achieved at St = 0.15.
Assessment on Morphological Changes due to Coastal Exploitations and Remedies for Coastal Defense
Authors: Huang Wei-Po , Chien Lien-Kwei , Ku Cheng-Yu
Published: October 2017

This study evaluates the influence of coastal structures on coastal morphology near Hsin-Chu fishery harbor in the northwest of Taiwan. As a result, the downdrift side has undergone local erosion due to the longshore sediment was impounded at updrift breakwaters resulting the enhancement of coastal flood risks as well as deterioration of the biological environment. Process and trend analyses were used to assess the effects the coastal exploitation made on the coastal morphology. Environmentally-friendly remedial measure, beach nourishment is proposed. The sediment source supply and the location of beach nourishment were also suggested for achieving the goal of sustainable use in the area.
Temperature Dependent Torque and Drag for 3-D Wells: Model Description and Field Case Study
Authors: Wiktorski Ekaterina , Tveiterå Martin , Sui Dan , Aadnoy Bernt S.
Published: October 2017

Wellbore friction represents one of the biggest limitations for drilling and completion of long 3-dimensional wells. Traditionally, wellbore friction forces calculation is performed using soft-string torque and drag models, which assume tubular to be in contact with the wellbore at any point along its length. However, precise results are needed for wells with complex geometry and high doglegs.

This paper presents a novel way regarding wellbore friction forces calculation, which takes into account both wellbore deviation and wellbore tortuosity. To locate contact points of the string and the wellbore, a Dogleg Severity filter, or DLS-filter is proposed. The DLS-filter is integrated into soft-string torque and drag models by taking into account dogleg, wellbore geometry and depth. Such simple implementation of DLS-filter makes it applicable for any case only if survey data is available.

Fundamental understanding of drillstring mechanics and drilling fluids properties is essentially required in planning phase and drilling operations. To enhance the accuracy of torque and drag calculation, thermal effects on buoyancy forces and viscous forces have been studied. Experiments using one oil-based mud (OBM) recipe and one water-based mud (WBM) recipe have been conducted to measure viscosity and density of fluids in different pressure and temperature conditions. Based on the obtained results, viscosity model and density model as functions of pressure and temperature have been developed for better model interpretation of fluids thermal effects in HPHT conditions. Friction factor is a critical parameter to affect wellbore friction, which depends on fluids composition, contact surface, rotary speed, temperature, etc. Conventionally it is set constant for friction forces calculation. Experimental results show that the friction factor is heavily dependent on the temperature. In this study, friction factor was assumed to increase linearly with temperature for torque and drag calculation.

The new approach provides more correct values for torque and drag, and gives a better understanding of the downhole environment, as cuttings transport and drillstring dynamics. The study can be further used for the evaluation and recommendation of drilling muds for HPHT wells. Such analysis will aid in the design of appropriate drilling mud in the integrated well planning phase.
The Influence of Damping on the VIV Suppression of a Circular Cylinder Fitted With Flexible Shrouds
Authors: Cicolin Murilo M. , Assi Gustavo R. S.
Published: October 2017

Experiments have been carried out with a circular cylinder fitted with four different models of flexible shrouds with variable values of structural damping. Shroud models were derived from the geometry of the suppressor called “ventilated trousers”. VIV responses are presented in a range of reduced velocities from 2 to 15 and Reynolds number from 2,000 to 25,000. Influence of structural and hydrodynamic damping is considered and, since the meshes generate more hydrodynamic damping than a bare cylinder, this effect on VIV suppression is analyzed. With the minimal structural damping, the VT mesh reduced about 55% of the amplitude peak of bare cylinder, while the thick-sparse, thin-sparse and thin-dense meshes reduced about 50%, 45% and 50%, respectively. For the case with similar levels of total damping (structural plus hydrodynamic) the same models reduced about 50%, 25%, 40% and 50%, respectively. The results show that the effect of increasing the structural damping has an important role in the VIV suppression of the thick-sparse mesh. For the other models, this effect is less significant.
Subsea Pipelines and Flowlines Decommissioning: What We Should Know for a Rational Approach
Authors: Manouchehri Soheil
Published: October 2017

Offshore and subsea decommissioning will increase in the next five years or so as many producing fields are matured and cease production while the oil price continues to remain low. This emphasizes the need for a thorough decommissioning plan to ensure a safe and technically feasible solution while it is economically viable and safeguards the environment.

Offshore and subsea decommissioning is commonly considered on a case-by-case basis using the Comparative Assessment (CA) process in which the best decommissioning solution is obtained. Health, Safety and Environmental (HSE) considerations are always paramount in any decommissioning process. The aim is to significantly reduce the long term risks to other benefactors of the sea while the associated short term risks to those responsible for decommissioning operations are minimized.

A major part of any decommissioning project is subsea pipelines decommissioning (by “pipelines”, it is meant to include flowlines, trunklines and flexible too). There are a number of techniques available for decommissioning of subsea pipelines ranging from preservation for potential future use to full recovery or leaving in-situ. However, each subsea pipeline decommissioning technique should be considered on its own merit. Selection of each decommissioning technique depends on many parameters, inter alia, size of pipeline, type of pipeline (e.g. single pipe, pipe-in-pipe, piggyback), type of conveying fluid, operational environment (location), production history, Inspection, Repair and Maintenance (IRM) records, HSE considerations, connection to other facilities, technical feasibility (including potential use of advanced technologies), regulatory authorities requirements and socio-economic considerations.

This paper will look at specifics of subsea pipelines decommissioning. It will examine the procedures to be undertaken from desk top activities (e.g. planning and CA) up to operational activities (e.g. pigging, flushing, cleaning, removal or leaving in-situ). Different scenarios are discussed and potential advantages and disadvantages of each scenario are presented. In addition, a guide is proposed for future pipelines decommissioning projects to follow a rational approach.
Experimental and Numerical Models of Wave Reflection and Transmission by an Ice Floe
Authors: Nelli Filippo , Skene David M. , Bennetts Luke G. , Meylan Micheal H. , Monty Jason P. , Toffoli Alessandro
Published: October 2017

The marginal ice zone (MIZ) is the outer part of the sea-ice covered ocean, where ice can be found in the form of large floating chucks better known as floes. Since it is the area where the most part of the interaction between ice cover and ocean waves takes place, it requires careful modelling. However existing mathematical models, based on the traditional thin-plate theory, underestimate waves attenuation for the most energetic waves, since the energy dissipation occurring during the process is not taken into account. New laboratory experimental and direct numerical models are presented here. In the experimental model a thin plastic plate is tested under the action of incident waves with varying amplitudes and periods. The same experimental set-up was reproduced using a numerical model, which was developed by coupling a High Order Spectral Numerical Wave Tank with the Navier-Stokes solver IHFOAM. Data from the experiments and numerical models confirm that non-linear effects lead to a decrease of wave transmission.
Subsea-Asset Protection From Falling Objects Using Multi-Layered Shielding: A Preliminary Study
Authors: Balash Cheslav , MacLean Guy , MacLean David
Published: October 2017

Protection solutions for pipelines, umbilicals, and cables from accidentally dropped objects are generally implemented with concrete mattresses, though concrete does not effectively dissipate shock loading. The presented work investigated relative absorption properties of two materials (concrete and polystyrene), singly and in combination, with an aim to ultimately advance the protection of subsea assets from falling objects. A series of experiments were undertaken to measure the impact force from dropped objects of varied mass and height on single and stacked plates of varied thickness. It was concluded that the combination of absorptive and non-absorptive materials could be beneficial; specifically, a protection shield for a subsea asset could comprise concrete at the base, polystyrene through the middle, and a thin shell layer of concrete on the outer surface. The proposed next phase will seek the combination of concrete strength and polystyrene compression to provide optimum levels of absorption.
Effects of the Initial Consolidation on the 3D Wave-Induced Seabed Response Around a Pile
Authors: Ding Jian , Sui Titi , Zhang Chi , Li Yuan
Published: October 2017

Seabed consolidation state could be seen as the initial simulation condition for numerically simulating wave-induced seabed response. In this study, based on a three dimensional numerical model, effects of initial consolidation state on the 3D wave-induced unsaturated seabed response around mono-pile were investigated. By model application, the consolidation state of seabed around the pile foundation was described. Two common calculation approaches (seabed consolidation is considered or not) for wave-induced seabed response were compared by describing the distributions pattern of soil effective stresses and pore pressures around the pile. Significance of the consolidation state on seabed dynamic response against distances to pile was also carefully addressed. Numerical simulations indicated (1) the initial consolidation significantly increases the vertical effective normal stress in the vicinity of pile, (2) effects of the initial seabed consolidation on the wave-induced seabed response decrease with the increasing distance to the pile. This study suggests the initial consolidation should be considered in assessing the seabed stability for the design of the mono-pile foundation.
Cathodic Protection Analysis of Spools With GRP Cover
Authors: Kongstein Randi B. , Kvande Rannveig
Published: October 2017

Cathodic protection (CP) design of pipelines is generally described in internationally recognized standards and recommended practices. However, not all cases can be solved by conventional CP calculations as recommended approaches and methods may not be fully defined in the standards. For instance, Glass fibre Reinforced Polyester (GRP) covers can be applied for mechanical protection (e.g. from trawl and/or dropped object) of subsea pipelines and structures. These GRP covers will restrict the electrical/ionic current lines between the anode and the steel surface to be cathodically protected. For a spool with in-line components requiring a large current (e.g. painted or bare steel) and with a GRP cover it may be difficult to obtain sufficient cathodic protection when applying simple mathematical calculations. This paper describes how the Finite Element Method (FEM) in COMSOL Multiphysics can be applied to show that the potential is acceptable for such cases.
The Installation of Flexible Risers and Flowlines Systems With PLET on the Subsea End
Authors: Ting Kee Chien , Chavan Kishor , Balmford Samuel , Sullivan Daniel
Published: October 2017

Flexible riser and flowline systems used in offshore oil and gas developments in shallow and deep water are typically terminated with vertical connectors with goosenecks or with horizontal connectors. An alternative arrangement is to terminate with PLET although it is not as commonly adopted. PLETs usually have a sizeable dimension and weight compared to the vertical and horizontal connectors hence present handling and deployment issues. A number of flexible risers and flowlines terminated with PLETs recently installed in a deepwater development in Gulf of Mexico showed that with careful engineering such deployment is viable and can be performed safely by a typical flexlay vessel. The installation engineering, installation aid requirements, the deployment methodology are presented and discussed. The observations from ensuing offshore operation showed that the flexible torsion and twist during deployment need to be carefully monitored and managed offshore. Flexibles terminated with PLETs could be potentially suitable where life of field gooseneck load may be excessive or for bigger and stiffer flexible products where making the 2nd end connections might be a challenging undertaking offshore. A PLET could also be used where an intermediate structure is required along a MEG line for example where In-Line Terminations (ILTs) are needed for flying leads plug-in. This would save on requirement for an intermediate structure and connectors.
Comparison of Riser and Well System Response Predictions to Full-Scale Measurements in a Shallow Water Harsh Environment
Authors: Walker Karen M. , Agarwal Puneet , McNeill Scot , Bhalla Kenneth , Baker David A. , Zheng Haining
Published: October 2017

Well system fatigue accumulated during drilling operations from mobile offshore drilling units (MODUs) has been a topic of intensive study in recent literature. A variety of efforts from individual operator studies to industry-wide joint industry projects have been launched in an effort to improve understanding of both the load and resistance elements of well system fatigue assessment. A key uncertainty in current predictive modeling practice is the level of conservatism inherent in that modeling, as compared to real-life system response. Collection of good quality, full-scale field measurement data is a key component in evaluating this uncertainty.

A full-scale measurement campaign was recently conducted on a 6th generation MODU during drilling operations in a shallow water region with a harsh environment. The measurement system on board the vessel captured vessel, riser and lower marine riser package (LMRP) accelerations and angular rates, along with riser tensioner pressures. Concurrent environmental measurements were acquired via wave rider buoy and acoustic Doppler current profiler (ADCP) located near the mobile offshore drilling unit (MODU), capturing wave height, period and direction, and full-depth current profiles. This paper focuses on data collected for one well during the winter months where significant wave heights at the drilling site varied from 6ft to 26ft.

In this paper, a comparison between measured and predicted riser and well system loading is presented. The predicted riser and well system response is based upon global riser analyses performed in both the frequency and time domains to evaluate the effect of linearization in the modeling process.

Loading demand on the well system is also presented as cycle-range histograms. This paper also summarizes the conclusions from the comparisons of these measurements with other published measurement campaign data. While loading derived from previous riser analysis studies have been found to be “conservative” as compared to full-scale measurements, this study finds that the predicted and measured responses match quite well. Furthermore, it is also shown that the frequency domain results are adequate for this study, suggesting that the nonlinearity within the riser and well system for the conditions studied is relatively minor.
Load Reduction on Offshore Wind Turbines by Aerodynamic Flaps
Authors: Thakur Shilpa , Saha Nilanjan
Published: October 2017

This paper focuses on load reduction by implementing controllable trailing-edge flaps on an offshore wind turbine (OWT) supported on different fixed bottom structures in various water depths. The benchmark NREL 5-MW offshore horizontal axis wind turbine is used as a reference. This work utilizes the wind turbine simulation tool FAST with coupled stochastic aerodynamic-hydrodynamic analysis for obtaining the responses. The flap is controlled using an external dynamic link library through PID controller. Blade element momentum (BEM) theory and Morison equation are used to compute the aerodynamic and hydrodynamic loads, respectively. BEM theory is presently modified to account for unsteady effects of flaps along the blade span. Variation in force coefficients is shown due to unsteady effects of flaps. The present analysis results show reduction up to 8–29% in blade loads for the turbine with different support structures on implementing controllable trailing edge flaps. Also, an influence of blade load reduction on tower base and nacelle is shown. Tower loads are calculated considering aerodynamic and hydrodynamic loads individually. This study can form the basis for evaluating the performance for large-scale fixed offshore wind turbine rotors.
A Submerged Floating Tube Bridge Concept for the Bjørnafjord Crossing: Marine Operations
Authors: Engebretsen Knut Beck , Jakobsen Kristoffer Kjellså , Haugerud Stein Atle , Minoretti Arianna
Published: October 2017

A submerged floating tube bridge (SFTB) concept is one of the three alternatives for the Bjørnafjord crossing in Norway. Two SFTB designs have been developed: one pontoon-stabilized and one tether-stabilized. There are no submerged floating tube bridges yet built and installed. Consequently there is no direct practical experience with assembly and installation of such massive string-like structures. The purpose of this article is to describe possible means of fabrication, assembling, jointing and installation of SFTB elements and the tube-bridge itself. All major project activities have been divided into stages. Further, these stages have been subdivided into factual steps to demonstrate feasibility based on various criteria. The major construction challenge is to assembly fabricated SFTB elements into one 4580 m string in a floating condition and then to tow and install it in the fjord. The focus was to utilize existing technologies and experiences available from offshore industry to the fullest extent, so that conventional tools and methods could be applied to this new application. Possible solutions both for the tether-stabilized and pontoon-stabilized alternatives — with differences in the foundation/tether and pontoon installations and associated SFTB interfaces — have been developed.
Effect of Porous Baffle on Sloshing Dynamics in a Barge Mounted Container Subjected to Wave Excitation
Authors: Thuvanismail Nasar , Shah Akshay P. , Surahonne Deepak J. , Annamalaisamy Sannasiraj S.
Published: October 2017

An experimental investigation was carried out to determine the effect of porous baffle walls on sloshing dynamics of a sloshing tank that is partially filled with liquid and rigidly mounted in a barge. The experimental setup is subjected to beam sea regular wave excitations and hence the barge experiences combined sway heave and roll excitations. An aspect ratio (hs/l, where hs is still water level and l is length of tank) of 0.488 is considered which corresponds to 75% fill condition with respect to tank height. Three porosities of 15%, 20%, and 25% are considered. The barge system was subjected to regular waves of frequency (fw) ranging from 0.45Hz to 1.54Hz. The effectiveness of porous baffles on the dissipation of sloshing energy is studied in comparison with without baffle condition. The effect of wave excitation frequency on the sloshing dynamics has also been analysed and the prominent results are here in reported.
Wake Effect Assessment of a Flap Type Wave Energy Converter Farm Using a Coupling Methodology
Authors: Tomey-Bozo Nicolas , Murphy Jimmy , Babarit Aurélien , Troch Peter , Lewis Tony , Thomas Gareth
Published: October 2017

It is expected that large farms of Wave Energy Converters (WECs) will be installed and as part of the consenting process it will be necessary to quantify their impact on the local environment. The objective of this study is to improve the state-of-the-art of the methodologies to assess the impact a WEC farm has on the incoming wave field through the use of a coupling methodology. A Boundary Element Method (BEM) solver is used to obtain the near-field wave solution accounting for the wave-body interactions within the array of WECs and a Mild-Slope Equation (MSE) model is used to assess the wave transformation in the far-field. The near-field solution obtained from the BEM solver is described as an internal boundary condition in the MSE model and then propagated throughout the domain. The internal boundary condition is described by imposing the solution of the surface elevation in the area where the farm is located. The methodology is applied to flap type WECs that are deployed in shallow water conditions. The validation of the technique is done first for a single flap and then for an array of 5 flaps. Finally, a mild-slope bathymetry and the influence of the changing depth on the wave transformation is assessed in order to prove the versatility of the method to be applied to real scenarios.
Application of Wake Shielding Effects With a Finite Element Net Model in Determining Hydrodynamic Loading on Aquaculture Net Pens
Authors: Turner Adam A. , Steinke Dean M. , Nicoll Ryan S.
Published: October 2017

A net wake shielding and self shielding model has been developed to accurately estimate the hydrodynamic loading on fin-fish aquaculture installations in the dynamics simulation software package ProteusDS. The software was developed to determine the loads and motions of various ocean engineering systems in response to wave, wind and current conditions. The effect of containment net hydrodynamic wake shielding is important to avoid overly conservative estimation of loads on fish farm installations. The reduction in fluid velocity through a net can be significant in many cases, leading to decreased loading and changes in motion on downstream nets and mooring components.

The developed wake shielding model uses a wake volume approach to estimate a reduction in flow velocity and hydrodynamic loading on downstream components within the wake volume. Self shielding effects of adjacent twines within a net are also considered, as interactions between netting twines can reduce hydro-dynamic loading on nets at certain angles of incidence to the oncoming flow. This paper presents the developments both of the wake shielding and self shielding models and demonstrates the capability to accurately predict current forces acting on successive net pens by comparing simulation results with published results from tank tests, as well as a comparison of measured tensions on mooring lines at a full scale fish farm. A method for determining netting drag coefficients based on Reynolds number variations is also presented and compared to experimental drag tests on planar nets to confirm its validity.
Co-Occurrence Probability Analysis of Sea Ice at Yingkou and Huludao Observation Stations of China
Authors: Tao Shanshan , Wang Zhifeng , Zhang Ri , Dong Sheng
Published: October 2017

Co-occurrence probability analysis of sea ice between adjacent areas is very helpful for the hazard prevention and protection strategy making of coastal and offshore engineering. Yingkou and Huludao with similar latitudes are located on the opposite sides of Liaodong Bay of China. Their sea ice conditions are both apparent in winter and early spring, so it is useful to study on the co-occurrence situations of sea ice conditions between these two areas. Based on the annual maximum sea ice thickness of Yingkou and Huludao observation stations, the co-occurrence probability analysis of sea ice thickness is conducted. The joint probability distributions of sea ice thickness between these adjacent areas are constructed by using univariate maximum entropy distributions and four bivariate copulas. Both marginal curve fittings are very well, and the model determined by Gumbel-Hougaard copula describes the bivariate sea ice thickness data best. Then different cases of co-occurrence probabilities of sea ice thickness between Yingkou and Huludao are presented, and they can provide references to the hazard protection of the coastal and offshore structures between these two areas.
Calculation of the Hydrostatic and Structural Integrity of Docking Sequences
Authors: Dankowski Hendrik , Weltzien Charlott
Published: October 2017

The conditions of competition within ship yards are changing. The current market situation requires a new orientation of the Pella Sietas ship yard with flexible solutions for new ship types. Complex, heavy and ice-going ships show one way for future designs. In view of all the technical difficulties involved in such challenging projects, the first question must be how to handle these heavy constructions with the yards building facilities available. The Pella Sietas yard is using a floating platform for newbuildings. The question arises whether or not this platform is still capable and suited for this kind of ship types.

The docking procedure is a complex multi-body interaction that copes with hydrostatic and structural challenges. The docking operation is regulated by the sequence of flooding and emptying ballast water tanks of the dock. At any time of this dynamic operation the hydrostatic stable equilibrium of ship and dock must be ensured.

When the ship becomes afloat the keel block system transfers the ships weight on the structure of the dock. It must be ensured that the resulting tensions and deformations do not exceed the maximum permissible values.

This paper describes a fast calculation method that determines the mentioned hydrostatic as well as the structural investigations during the docking procedures.

The method implies a numerical progressive flooding simulation that calculates the hydrostatics of ship and dock under consideration of their interaction by dock blocks together with the ballasting sequence in the time domain. Furthermore it calculates the block forces distribution by applying the deformation method. In the calculation process ship and dock are modeled as Timoshenko beams and the dock blocks as non-linear spring elements. Moreover the shear force and bending moment distributions of ship and dock are calculated and the deflection lines are presented.

Therefore, the described method enables the ship yard to evaluate quickly the possibility of building new types of ships on the existing building platform and allows evaluating which modifications are useful to enlarge the capacity of the platform even further.

It provides a useful tool to minimize local and global stresses and deformations of the interacting bodies during the whole docking procedure by fast optimization of the block system arrangement and the ballasting sequences.

As a result the described method could expand the range of flexibility of a given floating dock structure. In addition, the whole hydrostatic and structural integrity of docking sequences can be computed faster and more accurate even at a very early project stage.
An Improved Approach for Modelling Reliability of Buckle Formation for Subsea Pipelines
Authors: Haghighi Ali , Rai Jitender , Le Maout Yann , Oliphant John
Published: October 2017

Lateral buckling (LB) design for subsea pipelines generally requires reliability analysis to evaluate the probability that a lateral buckling mitigation system will behave as expected, which means that the engineered initiators will trigger buckles sequentially before any uncontrolled buckle can form in between. As various parameters involved in the buckle formation process are uncertain (soil characteristics, residual horizontal and vertical Out of Straightness (OOS) after pipelay), a probabilistic approach is used to assess the likelihood that the pipeline will buckle at the intended locations. The Safebuck JIP has developed a structural reliability model of the pipeline expansion process to calculate the probable virtual anchor spacing (VAS). This model can be used to assess the reliability of buckle initiation on the design of pipelines susceptible to lateral buckling.

The buckling response of a pipeline will always be inherently uncertain because project specific OOS information is not known prior to pipelay. The Safebuck guideline focus is on horizontal OOS whereas the impact of bathymetry is addressed in a high level fashion, with no clear methodology. This paper presents an alternative approach to account for the effects of bathymetry on the reliability of buckle formation. The model is a significant advance on the current method for estimating buckle formation reliability and brings other important benefits such as capability for modelling any transient profiles of pressure and temperature.

In this paper the difference between the horizontal residual OOS in pipelines for different pipelay methods is discussed, and it is shown that the method of pipelay can have a significant effect on pipeline horizontal residual OOS. The impact of change in horizontal OOS on reliability of buckle formation has been assessed.
Qualification and Certification of Polyester Rope for Seabed Contact
Authors: Gabrielsen Øystein , Larsen Kjell
Published: October 2017

The Aasta Hansteen spar in the Norwegian Sea is designed to be moored with a taut polyester rope mooring system.

The water depth at the field is 1300 meters, and due to the short installation season the most efficient hookup is with pre-installed mooring lines, which require the mooring lines to be laid down on the seabed.

DNV certification does not allow seabed contact for polyester ropes unless proven that no soil ingress and damage takes place. To be able to certify the ropes Statoil developed a test method including contact with soil, rope movement and forced water flow through the filter construction. Full scale tests were performed with actual rope and Aasta Hansteen soil, both in laboratory and at site.

This paper discusses the certification requirements and presents adequate qualification test together with results from testing.
Fuzzy Logic Controller for Dynamic Positioning of an Offshore Supply Vessel
Authors: Tiwari Kunal N. , Krishnankutty Parameswaran
Published: October 2017

The purpose of this paper is to examine the performance of fuzzy controller applied to a dynamic positioning system of ship by numerical simulation. By definition, dynamic positioning system is computer controlled system which uses the active thrusters to automatically maintain the position and heading of the ship. The proposed control scheme consist of low pass filter in cascade with three proportional derivative type fuzzy controller with Mamdani type inference scheme. Feed-forward compensation decoupling scheme is employed to reduce coupling between sway and yaw. Robustness of control scheme is assessed for Cybership II in presence of wave disturbances.
Emission Reduction in Shipping Using Hydrogen and Fuel Cells
Authors: Jafarzadeh Sepideh , Schjølberg Ingrid
Published: October 2017

Despite various technical and operational improvements, shipping remains a contributor to global emissions of greenhouse gases, nitrogen oxides, and sulphur oxides, among others. As a part of its efforts to limit adverse health and environmental impacts of shipping, the International Maritime Organization (IMO) has enforced regulations to control these emissions. In addition, some countries, such as Norway have imposed additional regulations to control emissions further. Environmental regulations and concerns call for an improved environmental profile within shipping, which motivates this study.

Alternative fuels and power systems are required for a substantial reduction in emissions from shipping. Hydrogen and fuel cells are among the most promising solutions from an environmental perspective. A fuel cell is an electrochemical conversion device, which produces electricity through the reaction of an oxidant with hydrogen or another hydrogen-rich fuel, such as a hydrocarbon fuel. Since the electricity production does not entail fuel combustion, emissions are reduced substantially. When hydrogen gas is used as the fuel, only water is formed as the byproduct. In addition to emitting ultralow or zero emissions, fuel cells offer high energy conversion efficiency, low noise level, and low vibration.

The Norwegian energy system is based on electricity from renewable energy sources and mainly hydropower. Renewable energy output is strongly affected by the weather conditions, among other factors, and the supplies fluctuate accordingly. There is a need for a means to store and use the renewable energy surplus. In addition, from a technical point of view Norway still has potential to further develop hydro and wind power. Excess power can be used for production of hydrogen through water electrolysis, which in turn can fuel different means of transportation, such as shipping.

This paper aims at contributing to the research body on the use of hydrogen and fuel cells in shipping. First, a short introduction to hydrogen fuel and fuel cells is given. Then, an elaboration on pros and cons of powering vessels with fuel cells is presented. After providing an overview of current marine applications of fuel cells, the paper discusses potential vessels, which can benefit from this technology. Finally, the environmental benefits of using fuel cells are shown through a preliminary case study. Data from the Automatic Identification System (AIS) in the Norwegian waters is used for estimating operational profile of a vessel, its current emissions, and potential emission reduction by using hydrogen and fuel cells. The results of this study show the potential of hydrogen and fuel cells in reducing emissions of shipping and set forth the research gaps.
Wave-in-Deck Impact Loads in Relation With Wave Kinematics
Authors: Scharnke Jule , Lindeboom Rene , Duz Bulent
Published: October 2017

Breaking waves have been studied for many decades and are still of interest as these waves contribute significantly to the dynamics and loading of offshore structures. In current MARIN research this awareness has led to the setup of an experiment to determine the kinematics of breaking waves using Particle Image Velocimetry (PIV). The purpose of the measurement campaign is to determine the evolution of the kinematics of breaking focussed waves. In addition to the PIV measurements in waves, small scale wave-in-deck impact load measurements on a fixed deck box were carried out in the same wave conditions. To investigate the link between wave kinematics and wave-in-deck impact loads, simplified loading models for estimating horizontal deck impact loads were applied and compared to the measured impact loads. In this paper, the comparison of the model test data to estimated loads is presented.
Wave-Induced Oscillatory Soil Response Around Circular Rubble-Mound Breakwater Head
Authors: Tong Dagui , Liao Chencong , Wang Jianhua , Jeng Dongsheng
Published: October 2017

The wave-structure-seabed interaction (WSSI) around circular rubble-mound breakwater head is investigated using a three-dimensional (3D) numerical scheme. The result reveals that the presence of breakwater has strong effect on wave motion and seabed response. The turbulence induced by the breakwater head gives rise to extensive pore pressure around the breakwater head, which could further lead to liquefaction or scour and might eventually result in breakwater failure.
Fracture Testing of Existing Structures Without the Need for Repairs
Authors: Walters C. L. , Bruchhausen M. , Lapetite J.-M. , Duvalois W.
Published: October 2017

It is sometimes necessary to find the toughness of existing structures without damaging them. Examples of this scenario include situations in which the material is suspected of being brittle or service life extensions. However, fracture testing is inherently destructive. Removing material for Charpy or Crack Tip Opening Displacement (CTOD) specimens can result in expensive repairs. The Small Punch Test (SPT), which has been developed for monitoring programs in the nuclear industry, offers a test method that requires such small amounts of material that the test can be performed in a practically non-destructive way.

A pilot project was conducted to determine if the SPT can be applied to steels of use in maritime and offshore applications. The results of the pilot project showed that the SPT can identify behavior related to the ductile to brittle transition for an example S355 steel. Therefore, the SPT can provide valuable information for predicting fracture properties relevant to structural-level behavior of steel, such as Charpy transition and estimates of CTOD values in the lower shelf and lower portion of the ductile to brittle transition curve.

In the end of this paper, a theoretical framework for transferring results from SPT to CTOD or Charpy testing is outlined.
Fatigue Capacity of Wellhead Housings
Authors: Kuzmichev Sergey , Rodriguez Garcia Javier , Aronsen Kristoffer H. , Grytøyr Guttorm , Kirkemo Finn , Simonsen Erik
Published: October 2017

The issue of wellhead fatigue has been given significant attention during recent years. The complexity of the wellhead system in terms of interactions betwe[en conductor (low pressure) and wellhead (high pressure) housings leads to various analysis methods being proposed to evaluate fatigue damage in the system. Most of the critical base material hotspots are located in the wellhead housing region where the loads start to distribute between the high- and low pressure housing and the load paths are highly complex varying for different input parameters. Due to this, detailed fatigue analyses are typically performed on a project to project basis for the same wellhead geometry. This paper proposes an approach that simplifies the analysis of the base material hotspots in the housings and makes it independent of where the specific type of the wellhead system is used. It is suggested to consider the housings of the wellhead system as one component with a single characteristic M-N curve, or a few M-N curves if complexity requires so. The M-N curve is a specialization of the standard S-N curves provided in rules and standards. They are generated by combining the calculated load-to-stress curve at a given hotspot with the applicable S-N curve. The load used as a reference is typically a cross-sectional moment at the top of high pressure housing.

For these purposes 3D FE models have been developed for two principal wellhead types, rigid lock and non-rigid lock. The models are used to investigate the effect of different boundary conditions and applied loading on M-N curves for each hotspot analysed. Sensitivity studies have been performed for several parameters that are considered important in wellhead fatigue analysis. Based on the sensitivity studies, the effect of each parameter on typical base material hotspots is presented.

This paper provides estimates for the spread in the M-N curves for each individual base material hotspot in the wellhead housings. Results indicate that a single characteristic M-N curve per wellhead system type can be selected to represent the wellhead housings. In addition, based on results from the analyses carried out, recommendations regarding generalized boundary conditions to obtain a characteristic M-N curve for a specific wellhead type have been given.
Efficient Evaluation of Long-Term Response for Design of Components of Offshore Structures
Authors: Videiro Paulo Mauricio , Sagrilo Luis Volnei Sudati
Published: October 2017

This paper compares two approaches for the estimation of long-term response of wave load effects on offshore structures. These approaches are applied to estimate the extreme value of the cross section interaction ratio of a tubular component of the bracing system of a semisubmersible platform. The tubular component is subjected to axial loads and bending moments due to static loads and wave effects. The iteration ratio in the ultimate limit state is defined by applying design criteria derived from API RP-2A LRFD [6]. The approaches are also applied to estimate the long-term response of a single degree of freedom system due to wave actions.

The first approach is based on the proposals of Videiro and Moan [3]. The results of the first approach are compared with a new model of long-term response estimation, based on the up-crossing rate distribution of the response process.
Elastic Deformations of Floaters for Offshore Wind Turbines: Dynamic Modelling and Sectional Load Calculations
Authors: Borg Michael , Bredmose Henrik , Hansen Anders M.
Published: October 2017

To achieve economically and technically viable floating support structures for large 10MW+ wind turbines, structural flexibility may increase to the extent that becomes relevant to incorporate along with the corresponding physical effects within aero-hydro-servo-elastic simulation tools. Previous work described a method for the inclusion of substructural flexibility of large-volume substructures, including wave-structure interactions through linear radiation-diffraction theory. Through an implementation in the HAWC2 simulation tool, it was shown that one may incorporate the effects of additional modes on substructure and wind turbine response as well as predict the excitation of substructure flexible modes. This work goes one step further and describes a method to calculate internal substructural stresses that includes dynamic effects. In dynamic calculations, the substructure flexibility is considered through a reduced set of modes, selected based on their relevance to the external load frequency range, and represented with a superelement. The implementation of this method in aeroelastic simulation tool HAWC2 and wave-structure analysis program WAMIT is described, highlighting the practical challenges. A case study of the DTU 10MW Reference Wind Turbine installed on the Triple Spar concept is presented to illustrate the method. The results show that the substructure flexible modes, global platform motion and wind turbine loads can influence sectional loads within the substructure.
Design of Conventional and Assembled Bulkhead for a Flowline Bundle
Authors: Achani Dasharatha
Published: October 2017

A bundle, in general, comprises flowlines enclosed with carrier pipe and bulkheads at each end. Under operational load conditions, bundle expands in each end and releases forces from inner pipe and induces forces in outer pipe. The bulkheads that try to restrict the bundle expansion are subjected to interface forces on both sides and shall be designed and manufactured against the codes in compliance with DNV-OS-F101. A conventional bulkhead, referred as forged Bulkhead, is typically manufactured by a hot forging process as per the specified standard. For the forged bulkhead, the main body, surface and nibs shall be of specified material grade and the material shall be quenched and tempered after forging. Previous experience from different projects shows that it is sometimes hard for the forged bulkhead to achieve the results from mechanical testing to meet standard requirements and it is even expensive.

A bulkhead manufactured by assembled method can be considered as an alternative. The assembled bulkhead, in the present work, comprises of a plate with boreholes. The small pipe inserts of the respective borehole sizes are fitted through boreholes and circumferentially welded to the bulkhead plate. The ends of each pipe inserts are further welded with the ends of respective size of flowlines of the bundle in one side and the spools on the other side.

The work in this paper presents general design and methodology for the forged bulkhead of 4-line bundle. Further, the work also presents an alternative design for a conventional forged bulkhead. The design is based on FE analyses performed using finite element (FE) tool ANSYS and 3D FE models established by using advanced solid elements from ANSYS. For the same load conditions, the results from analyses show that the assemble bulkhead meets the acceptance criteria from the design methodology and can be considered as an alternative provided that appropriate welding techniques and NDE procedure are ensured in the weld root area of the welds between the pipe inserts and bulkhead plate.
Hydrodynamic Damping and Added Mass of Modern Screw Propellers
Authors: Krüger Stefan , Abels Wilfried
Published: October 2017

The operation of ships with “slow-steaming” poses new problems for the torsional vibration analysis of the drive train. It is well known that the propeller determines the essential part of the mass moment of inertia and the system damping. Both values are determined during the initial design phase by semi-empirical methods with have originally been developed by Schwanecke and Grim between 1970 and 1980. Since then, propeller designs have changed significantly and it is unclear if modern propeller designs are still covered by these calculation methods. The paper suggests an extension of Grim’s and Schwanecke’s method for modern screw propellers in homogeneous and unsteady flow.
New Drilling Muds for Drilling in Clay Rocks
Authors: Wysocki Sławomir , Wiśniowski Rafał , Gaczoł Magdalena
Published: October 2017

The paper describes studies on the development of the new formulas of water-based drilling mud for drilling in clays and shales. The research were undertaken as a part of the OPTIDRILTEC project. First stage of the project included studies related to selection of ionic inhibitors of hydration. The tests of inorganic agents with various concentrations influence on technological parameters of the developed drilling muds was undertaken. The disintegration and linear swelling tests under influence of developed muds with different ionic inhibitors were conducted on the rock samples. Miocene shale was used as the model rocks. Within a framework of the project, it was conducted selection of the polymeric inhibitors of hydration. Subsequently, different polymers were tested for the influence on technological parameters of drilling muds as well as on disintegration and linear swelling of model rocks. Studies also consists of synthesis of short-chained cationic polymers (with primary amine groups in the side chains) and cationic-anionic polymers (with, apart amine groups, sulfonic amine groups). Synthesized polymers are characterized by low molecular masses (about 10.000 – 20.000 atomic mass unit) and small steric hindrance of side chains. The studies allowed development of new water-based mud formulas for drilling in clay rocks. Developed drilling muds are characterized by good technological parameters, resistance to temperature and to salts along with effective preservation against disintegration and swelling of clay rocks. Moreover, based on the research results it can be observed that synthesized cationic polymers are efficient inhibitors of clay rocks hydration. Newly developed drilling muds could be successfully applied in the oil and gas industry causing improved drilling conditions and decreased drilling costs.