bluuebunny/crossref_metadata_2025 huggingface dataset:
Improving the Installation Criterion for Concrete Coated Pipelines
Authors: Nguyen Ngoc , Fyrileiv Olav , Chia Chor Yew
Published: September 2018

Current design practice limits the concrete strain to approximately 0.2% in a simplified design criterion. In most standard cases, this has proved to be safe and adequate. However, in recent years, the pipeline industry is extending into more remote, harsher environments and larger diameter pipelines. The use of the simplified design criterion has, in some circumstances, resulted in too strict installation requirements which limit the number of relevant installation vessels.

This paper presents some findings on the concrete strain for submarine pipelines with concrete weight coating (CWC) derived from the numerical program performed within the scope of Phase 1 of the joint industry project “Design of concrete coating for submarine pipelines”.

Non-linearities in the concrete weight coating, anti-corrosion coating (ACC) and steel material properties, as well as large deformation and the sequence of load application were included in the numerical model. The results from the numerical analyses have been well validated against existing experimental data, and the numerical model was subsequently used in an extensive parametric study, where the behaviour of concrete coated pipelines was investigated for monotonic and reversed bending with nominal strain up to 0.4%.

These numerical results can be used to widen the applicable range of the simplified concrete crushing criterion in DNVGL-ST-F101 (2017), and to formulate a rational approach for the design of pipeline concrete weight coating under typical installation and operation conditions. The rational design approach will allow for a wider range of installation vessels to select from for installation of the pipeline, and relaxation of the installation weather window criterion.
Should Residual Stresses Be Taken Into Account in Structural Integrity Assessment of Offshore Monopiles?
Authors: Jacob Anais , de Oliveira Jeferson Araujo , Mehmanparast Ali , Hosseinzadeh Foroogh , Berto Filippo
Published: September 2018

A key challenge in the Offshore Wind industry is assuring the life-cycle structural integrity of wind turbine foundation monopiles. This is due to harsh environmental aspects as well as the loading regime (i.e. constant exposure to wave and wind forces introducing both fatigue and corrosion damage). Welding is a widely used joining technique for the manufacturing of offshore monopile structures. However, this is an aggressive process that introduces high levels of residual stress, which in turn may lead to reduced fatigue life, corrosion cracking resistance and accelerated degradation mechanisms. This study presents evidence that a measurement-informed strategy could be used towards developing a more reliable structural integrity assessment procedure for offshore monopile structures by taking into account the effect of residual stresses. A welded mock-up, 90 mm thick, 2600 mm wide and 800 mm long plate, was fabricated using a typical double-V welding procedure following current industrial practice. The contour method of residual stress measurement was employed to map residual stresses in the welded mock-up as well as in the CT specimens extracted from the weld region of the plate for future fatigue tests. Residual stress measurement results show that the mock-up plate contained tensile residual stresses above yield in the core of the weld, while the extracted CT specimens had lower though still significant residual stress levels. These results indicate that if the initial residual stresses are not carefully considered during fatigue or corrosion cracking tests, the results from the CT specimens alone will likely result in misleading structural life estimations.
Enhance Reliability of Structural Bonding: An Advance Solution of Repair for Corrosion Onboard Offshore Units
Authors: Mouton Luc , Errotabehere Xabier , Paboeuf Stéphane , Ahmad Firas Sayed
Published: September 2018

An increasing number of Floating offshore units reach maturity (> 10 years). This induces costly maintenance operations related to hull structure corrosion damage. While crop and renew operations are generally performed in dry docks for supertankers, the FPSO are maintained afloat offshore on the oil field. For obvious security reasons hot work such as welding and gauging are prohibited without a heavy set of recommendations. Naturally, FPSO’s operators have sought “cold” solutions for decades.

This paper describes the specificities of a particular structural bonded reinforcement (ColdShield developed by COLDPAD). A general description of its particularity in the fields of installation and durability is given, but this article is mainly focused on reinforcement strength criterion. Bonded reinforcement strength is known as difficult to predict, making design methodologies not compatible with industrial applications. The innovation in the design of the presented solution leads to a special behavior in terms of strength. It is revealed by the comparison of results of the qualification test campaign with results of tests realized on a standard bonded patch application. Finite element modelling computed parallelly to the tests are used to analyze the test results. The robustness of the reached strength criteria is discussed.
Boundary Layer Effects in the Modeling of Semi-Submersible Columns
Authors: Holmes Samuel
Published: September 2018

A common structural element encountered in semisubmersible designs is a rectangular vertical column with rounded corners. The time-averaged drag and oscillating lift and drag forces on such columns are strongly influenced by the location of the lines of flow separation on the column and hence the angle of attack of the incoming flow and the corner radius. In this paper we examine published wind tunnel data to illustrate these effects which include angle of attack and Reynolds number effects. This examination suggests that care must be exercised modeling flows around these elements. Also, the data suggest that Reynolds number effects and surface roughness effects may distort the results of scaled experiments. We use CFD simulations first to model the existing data and then to explore the possible changes in hydrodynamic properties due to Reynolds number and boundary layer effects. Recommendations are made regarding the physical and CFD modeling of the flow over these structures.
Investigation of an Air-Cushion Supported Solar Island
Authors: Kristiansen Trygve , Borvik Petter
Published: September 2018

A preliminary investigation of a low-weight carrying marine platform concept was conducted by means of experiments and approximate theories. The platform consists of a circular elastic tube with circular cross-section, covered with an air-supported membrane deck. A vertical skirt is added along the circumference of the model to avoid air-leakage. We refer to this concept as floating solar island. Solar islands have recently gained interest. The models were subjected to waves. Both regular and irregular wave tests were conducted. Tests with the absence of the membrane (floater only) were also conducted. The general behaviour and failure modes were investigated. Failure modes include over-topping with flooding as consequence, as well as out-of-water incidents and membrane wear with air leakage as consequence. A systematic variation of wave conditions revealed for which wave conditions flooding occured. Out-of-water incidents of the skirt were not observed. Vertical accelerations were measured at eight positions along the circumference of the model, and the heave, pitch and first flexible mode motions were re-constructed by modal theory. The modal responses were compared to theory based on linear potential flow assumption, both for the floater model only, and with simplified theory accounting for the air-cushion of the island in heave. The theory was able to predict the global behaviour reasonably well, although important discrepancies were observed. More detailed studies, involving experiments with more instrumentation and development of theory, must be conducted in case deeper understanding of this relatively complex, hydro-elastic concept is needed.
Drag Coefficients of Vertically-Mounted Full-Scale Blue Mussel Dropper Lines
Authors: Hildebrandt Arndt , Landmann Jannis , Ongsiek Thorsten , Goseberg Nils
Published: September 2018

Developments in marine aquaculture in the last 30 years indicate that the bivalve-related industry is feasible offshore and that opportunities for large-scale, industrious production of shellfish stock exists. The objective of the project “CAWX1607” is to develop, model and test such systems. However, the forces acting on suspension cultures, the most likely form of marine farm systems are unknown. Here, drag coefficients provide an efficient approach for the calculation of arbitrary complex structures by using the Morison equation. The CD-coefficients take into account vortex shedding effects as well as the surface roughness of the structure.

This paper reports on developed and conducted tests at the medium wave and towing tank “Schneiderberg” (WKS) at the Ludwig-Franzius-Institute for Hydraulic, Estuarine and Coastal Engineering of the Leibniz University Hanover, Germany. The tests were conducted for current velocities between 0.25–1.0 m/s for three samples of blue-lipped mussel specimens. During physical testing the forces and moments in x-, y- and z-direction, the elevation of the water surface, a velocity profile in the vicinity of the live-blue mussels, as well as the velocities of the towing carriage were recorded. The developed methodology, data treatment as well as the resulting CD-coefficients are presented. Further, the CD-coefficients obtained are presented in the context of natural variation of living structures and discussed in comparison to CD—curve characteristics of offshore structures, e.g. rough cylinders.
Influence of the Maximum Wave Power Extraction on the Structural Response of OWC Wave Energy Converters
Authors: Jalón María L. , Brennan Feargal
Published: September 2018

A methodology to analyse the influence of power-optimal OWC (oscillating water column) system configurations against the maximum structural response stresses is proposed. Different values of the selected control parameters are considered to represent the power-optimal and non-power-optimal configurations of the system. The wave power extraction and the structural response of the OWC with power-optimal control parameters is compared against those obtained adopting non-power-optimal control parameters. The results reveal that the control parameters have a clear influence on both the wave power extraction and the structural response stresses. This opens a line of research to investigate the trade-off between the wave power extraction and the structural response of the system, hence the potential structural reliability.
Motion Planning, Guidance and Control System for Autonomous Surface Vessel
Authors: Hinostroza M. A. , Guedes Soares Carlos , Xu Haitong
Published: September 2018

This paper presents a motion planning, guidance and control system for an Autonomous surface vessel in a practical maritime environment. The motion planning algorithm is based in the angle-guidance fast marching square method and the guidance system is based in the line-of-sight trajectory tracking algorithm. To validate the motion planning algorithm, numerical simulations were carried out to compute the optimal path in a static environment including various obstacles. The guidance system was tested with an autonomous surface vehicle tracking a pre-established trajectory including static obstacles. The autonomous surface vehicle is a self-propelled scaled ship model of 2.5 m equipped with sensors and actuators, inertial measurement unit, GNSS positioning system, propulsion DC motors, and wireless communication. From the experiments and numerical simulations, a good agreement was found.
Useful Indicators for Screening of Sea States for Wave Impacts on Fixed and Floating Platforms
Authors: Bunnik Tim , Stansberg Carl Trygve , Pakozdi Csaba , Fouques Sebastien , Somers Luke
Published: September 2018

Design approaches for wave impact on marine structures in storm sea-states are being reconsidered due to events related to the safety of North Sea offshore structures, both fixed and floating (Valhall QP extended lifetime; COSL Innovator accident). There has been a strong research and tool development within the field during the last decade, both within model testing and numerical analysis, including CFD. However, there is still a lack of efficient methods and tools to properly analyze these phenomena and their probably of occurrence.

One major aspect in this is to reduce the statistical uncertainties that are naturally arising in estimates of design loads related to extreme waves. In order to estimate the design loads it is common practice not to investigate all possible sea states (i.e. long-term analysis) but to investigate a few sea states and assume that the design value occurs at a prescribed probability level in the sea states with the same probability level (i.e. contour line approach). The estimate of the design value at that probability level is then based on results from a limited number of random realizations of these sea states. For linear or weakly nonlinear response types it is possible to estimate design loads accurately with a quite limited number of realizations. For strongly nonlinear/badly behaved problems however this is not possible due to the large variations in the tail of the distribution of the impact load, and many more realizations are required. This means that much more of these extreme, rare impact-related events should be collected to reduce the statistical uncertainty in the design load. This approach is restricted by time and costs and eventually one may have to accept an estimated design load with a large statistical uncertainty and account for the uncertainty with a higher safety margin.

In this paper an improved methodology for estimating design loads related to extreme wave impacts will be presented. The methodology is based on screening many 3-hour realizations of the design sea states with simplified, fast but sufficiently accurate methods and to focus only on the potentially critical events with a model containing a more complete description of the physics. This can be either a model test or a non-linear impact simulation (i.e. CFD analysis). By doing this many more rare/critical events can be assessed, reducing the statistical uncertainty in the estimate of the design load. The main challenge is to find suitable screening methods, which may be different for different structures (fixed, floating, etc.). Several screening methods/wave impact indicators will be discussed, and their capability will be illustrated by analyzing existing model test data for fixed and floating structures, showing the correlation between indicator and actual impact events.
Station-Keeping Trials in Ice: Dynamic Positioning in Ice — Results and Learnings
Authors: Kerkeni Sofien , Liferov Pavel , Serré Nicolas , Bridges Robert , Jorgensen Finn
Published: September 2018

Dynamic Positioning Systems are used in numerous types of marine operations. Due to the important differences in the external loads acting on the vessel, standard DP systems may fail to perform in ice conditions. Moreover, specific principles and position keeping philosophies should be applied in ice covered waters. The objective of the paper is to elaborate on these aspects by presenting and analyzing full scale DP tests. These tests were a part of the station-keeping trials performed in March 2017 in drifting ice in the Bay of Bothnia. Control algorithms limitations of Standard DP Systems are presented, showing the necessity of new control principles. The importance of crew training is also demonstrated along with the approaches to keep position in ice.
Analytical Models to Estimate Temperature Profiles During Drilling and Shut-In in Deepwater Environment
Authors: Hasan A. Rashid , Xu Boyue , Fyfe Dave
Published: September 2018

Drilling operations involve significant heat transfer between the drilling mud, downhole tubulars, and surrounding formation. Such heat transfer causes changes in drilling fluid temperature that alters drilling fluid density and viscosity, as well as changes near-wellbore formation temperature. Temperature changes in the near-wellbore formation need to be understood so that useful interpretation of often available temperature data from multiple discrete temperature sensors (MDTS) may be made.

In deepwater assets, fluid circulation through cold water makes the problem more complex. Deepwater drilling operation could be viewed as consisting of four processes: (1) mud circulation in the riser affected by surrounding cold sea water; (2) mud circulation in the cased and cemented zone; (3) mud circulation through the target zone (open hole); (4) shut-in after drilling through the target zone. Forced convective heat transfer dominates in the first three processes while conductive heat transfer is dominant during the shut-in period. Estimating temperature in the wellbore during and after circulation is critical for mud rheology, tubular thermal stress, and cement design. Application of “rule-of-thumb” and/or complicated numerical simulation is often unreliable and/or impractical.

This paper presents analytic models to estimate temperature profile during and after drilling fluid circulation in deepwater environment. Steady heat transfer is assumed in during fluid circulation, and transient modeling is performed for shut-in periods. Energy balance is set up over the differential control volume to develop the models. The end of circulation would provide the initial condition for the shut-in period. The models are used to estimate bottomhole temperature distribution during and after circulation. The analytical model is verified using data from a real deepwater well that had permanent downhole gauges (PDGs) installed at the bottomhole.
An Analytical Model of Floating Offshore Wind Turbine Blades Considering Bending-Torsion Coupling Effect
Authors: Qu Xiaoqi , Tang Yougang , Gao Zhen , Li Yan , Liu Liqin
Published: September 2018

In this paper, an analytical model is proposed to describe the nonlinear vibration of blades on floating offshore wind turbine (FOWT). The bending-torsion coupling equations are derived based on Hamilton’s principle. Comparing with the classical Newtonian method, this approach is more mathematically rigorous and systematic. The flapwise and edgewise deformation, the torsion as well as axial extension of the blades are all included in the model. A set of partial differential equations governing the coupled nonlinear vibration is established, and the results are compared with the multi-body model. Some details about the solution of equations are discussed. The eigen values of a rotating blade is also calculated. The structural model proposed in this paper can be widely used in the future study. For example, it can be coupled with an aerodynamic model to study the aeroelastic properties of the wind turbine blades. The effect of platform motion on blade dynamic response can also be obtained based on this analytical model.
Increasing Performance of Smart Well Systems by Downhole Chemical Injection
Authors: Aadnøy Bernt S.
Published: September 2018

There are many different types of smart well systems such as Inflow Control Valves, Inflow Control Devices and autonomous devices of various designs. The most common inflow system is blank pipe, producing through a screen and into the control valve at the connection sub.

To control the functionalities one may use surface control lines, dropping balls or darts or simply let the valves react autonomously to changes downhole. These tools can be deteriorated by erosion, plugging of fines, plugging of of heavy oil residue or by scaling.

Scaling is a complicated issue as it often builds up near critical parts of the tool, changing the flow pattern and affecting or offsetting the flow assurance. This paper will present a new concept in chemical well injection. It is proposed to connect a capillary tube through the entire completion string to inject chemicals to prevent scaling of critical tools before the oil enters the tool, thereby increasing the time the tool will function.

A new downhole chemical injection valve is developed. It is located near the injection point to prevent U-tube pressure effects often associated with surface injection systems. This injection valve can also easily be adjusted downhole or shut off if required. The advent of water production often changes chemical injection requirements. The new system can accommodate any changes in chemical or flow rates. The system is fully mechanical and does not rely on electrical control cables. Flow regulation is performed through the capillary tube.

The paper will describe the new downhole chemical injection system and its application to smart well technology.
Model Tests and Numerical Analysis for a Floating Mega Island
Authors: Waals O. J. , Bunnik T. H. J. , Otto W. J.
Published: September 2018

About 70% of the earth’s surface area is covered with water. Due to the sea level rise and increasing population in coastal areas we need to use our oceans more for energy production, food production, working and living.

In the present paper we discuss the results of a model test for a floating mega island in large waves up to 15.5 m significant wave height. The objective of this study is to investigate the motion response and loads on the island. These results may then be used to support further innovation of these islands.

The proposed island comprises 87 large floating triangles that are connected to one another. Together they form a flexible floating island of 1.5 by 2 km in cross-section at scale 1:250. The results are presented for the motion response of the island as well as the forces between the islands triangular modules and the mooring loads. These were measured using forces transducers and motion sensors.

The present work is part of a conceptual test carried out at MARIN. The island modules are interconnected with springs and fenders. This method is much similar to what is used in side by side offshore operations in the oil and gas industry.

Due to the flexibility in the connections the island will follow the waves in high seas. The forward two rows of the island will move in phase with the sea and therefore the amount of green water is much smaller than for a rigid island.
A Novel Semi-Empirical Non-Linear Time-Domain Formulation of Wave Elevation Diffracted by a Vertical Column
Authors: Pakozdi Csaba , Reinholdtsen Svein-Arne , Stansberg Carl T.
Published: September 2018

A novel semi-empirical non-linear formulation for fast and efficient computation of the disturbed elevation time series under large-volume platform in steep irregular waves is described and validated against model test data with a single fixed circular column. The method makes use of a linear diffraction model as a basis, which is then subject to non-linear amplification derived from a previous established crest amplification formula.

The validation test data includes a large test matrix of regular waves with systematic variations in the wave period and steepness, some tests were also run in a steep irregular wave as well as various bi-chromatic waves. The simulations show a good agreement with model test time series.

Initial simulations in the irregular waves disclosed some steep wave events for which the model predicted too strong non-linear amplification due to high local steepness close to or beyond breaking. A threshold criterion were introduced. Leeward (shadow) effects are also addressed, and a practical model for this is proposed.
Dynamic Modeling of H-Type Floating VAWT Considering the Rigid-Flexible Coupling Motions
Authors: Deng Wanru , Gao Xifeng , Liu Liqin , Zhao Haixiang
Published: September 2018

Dynamical characteristics of the H-type floating VAWT (vertical axis wind turbine) were studied. The wind turbine blades and the tower were treated as flexible bodies, and the floating foundation was treated as the rigid body. Considering the nonlinear deformations of the flexible bodies, the Lagrangian equation was used to establish the dynamic equations of wind turbine system. The loads included the wave forces, the wind loads, the mooring forces and the damping forces of the wind turbine system. A numerical calculation code was developed and verified. The innovation of the code is the coupling of rigid-flexible-aerodynamic-hydrodynamic of the floating wind turbine system. Taking the 5MW wind turbine as an example, the directions of the wind and the wave were considered as the same. Then the dynamic responses of the floating foundation, the tower and the blades were calculated. The results show that the wave frequency is the main frequency component of the responses of pitch, heave and surge of the floating foundation. 2P frequency (P is the rotational frequency of the wind turbine) accounts for a higher proportion for the sway, roll and yaw of the floating foundation. 2P and 4P are the main frequency components of the tower motions. 1P is the main frequency component of the blades’ motions. The 2nd mode of the blades and tower are considered. In the following research, the higher modes should be considered to improve the calculation accuracy. Besides, the model test is needed to verify the model further in the subsequent work.
Numerical Study of Density Ratio Influence on Global Wave Shapes Before Impact
Authors: Etienne Stéphane , Scolan Yves-Marie , Brosset Laurent
Published: September 2018

The influence of the gas-to-liquid density ratio (DR) on the global wave shape before impact is studied through numerical simulations of the propagation of two different waves in a rectangular wave canal. Two different codes are used: the first one, named FSID, is a highly non-linear 2D bi-fluid potential code initially developed in the frame of SLOSHEL JIP (Kaminski et al. (2011)) to simulate incompressible inviscid free-surface flows without surface tension thanks to a desingularized technique and series of conformal mappings; the second one, named CADYF, is a bi-fluid high-fidelity front-tracking software developed by Ecole Polytechnique Montreal to simulate separated two-phase incompressible viscous flows with surface tension.

The first studied wave leads to a flip-through impact while the second one leads to a large gas-pocket impact. Each condition is studied with water and three different gases with increasing densities corresponding to DR = 0.001, 0.003 and 0.005. The global wave shapes are compared a few tenths of second before the impact, before free surface instabilities triggered by the shearing gas flow have developed and also before any gas compressibility matters. Both codes give precisely the same global wave shapes.

Whatever the condition studied, it is shown that DR has an influence on these global wave shapes. The trends observed from the simulations are the same as those described in Karimi et al. (2016) obtained from sloshing model tests with Single Impact Waves (SIW) in a 2D tank with a low filling level. A small part of the mechanical energy of the liquid is progressively given to the gas. The larger the DR, the larger this transfer of energy from the liquid to the gas. This explains an increasing delay of the wave front for increasing DRs.
High Geostress Advantageous for Arctic Field Developments
Authors: Aadnøy Bernt S. , Belayneh Mesfin A.
Published: September 2018

The Arctic areas of Norway has brought many new challenges. In addition to harsh weather, drilling conditions are different.

The Barents Sea is different geologically compared to the North Sea area. A considerable amount of erosion bring older rocks higher up. It is observed that leak-off tests measured in Barents Sea wells shows abnormally high values. This is interpreted as a high stress state.

The paper analyze the stresses around a number of wells and conclude that it is very likely that a reverse fault stress state exists in these areas of the Barents Sea. This can bring positive effects because such a stress state may constrain induced fractures to propagate in a horizontal plane rather than towards surface, reducing the risk for reservoir leaks to surface. Also, a high compressive state may lead to more sealed faults, indicating a higher possibility for oil in place.

The paper will present the stress model and compare Barent Sea area to the North Sea. It will also show implications for wellbore stability, leaks from reservoirs and effects on sealing of major faults. Of particular interest is that leak potential from the reservoir is reduced in the Barent Sea as compared to other Norwegian oil fields. This may encourage more development in the Arctic areas.
Dynamic Risk Assessment of Decommissioning Offshore Jacket Structures
Authors: Babaleye Ahmed , Khorasanchi Mahdi , Kurt Rafet E.
Published: September 2018

The need to develop an integrated dynamic safety and risk analysis model for decommissioning offshore jacket structures is driven by the risky, expensive and complex nature of the operation. Many of the existing risk analysis techniques applicable to offshore assets failed to recognise and capture evolving risks during different stages of the decommissioning operation. This paper describes risk-based safety model to conduct quantitative risk analysis for offshore jacket decommissioning failure. First, a bow-tie technique is developed to model the accident cause-consequence relationship. Subsequently, a Bayesian belief network is used to update the failure probabilities of the contributing elements and thus, provides a more case-specific and realistic safety analysis when compared to the static nature of a bow-tie. This paper also presents the application of experiential learning in the dynamic safety analysis. The proposed technique is tested using a real-life case study from the Shell Brent Alpha platform. An algorithm to limit the effect of generic failure data was also developed. It is observed that the proposed technique helps to identify hazards shortly before they occur and sensitivity analysis revealed the most critical elements of the operation that must be managed to prevent catastrophe and consequently, reduce associated costs of remediation.
Use of C-Mn Linepipe for High H2S Service
Authors: Baxter David , Østby Erling , Chong Steven , Venås Asle
Published: September 2018

There have been recent incidents associated with cracking and leaks in C-Mn line pipe steels exposed to high H2S service. The incidents led to pipeline replacement with very expensive CRA clad pipeline causing substantial project delays and project cost escalations.

The incidents occurred when TMCP ACC steels were exposed to severe Region 3 environment as per domain diagram in NACE MR0175 (high partial pressure of H2S). The leaks were associated with longitudinal cracking which initiated at hard zones present on the parent pipe internal surface, and possibly also in girth welds.

The hard spots were observed to be contained within a very shallow depth of the ID surface of the pipe. The pipe microstructure beyond the thin layer of the hard zones at the ID surface did not contain hard material. However, the cracks propagated through the parent pipe normal microstructure in the through thickness direction.

Several of the operators are now concerned and uncertain on how to ensure the integrity of C-Mn pipelines in similar severe sour environments. Some operators have therefore introduced more stringent requirements for sour environment resulting in significant challenges to manufacture of line pipes and qualification of welding procedures that meet these new requirements. We also see different requirements being imposed by different operators. The use of CRA, clad/lined pipes or other exotic materials can solve the challenges, but are very expensive and can significantly reduce margins and make several sour service projects less viable.

Several R&D institutions have already started to study the phenomena. DNV GL have also initiated a broad JIP that will look into the challenges, with the objective of developing an industry guideline for use of C-Mn line pipe for high H2S service.

This paper will give background on the challenges associated with using C-Mn steel in high H2S service, describe the various uncertainties in detail, and describe how the JIP will address the challenges on a broad basis.
Research on the Velocity Attenuation Characteristics of the Fragments During High-Speed Water Entry
Authors: Zhang Ya , Li Xiaobin , Li Siyu
Published: September 2018

When fragments entering water at high speed, velocity attenuation coefficients of the fragments calculated by different scholars were quite different. Through theoretical analysis and numerical simulation, the velocity attenuation characteristics of the fragments with different head shapes, water entry angles and aspect ratios are studied in this paper. Numerical results show that for the fragments with different head shapes, the main factors affecting the velocity attenuation of the fragments are different. In particular, the influences of the pier’s rough effect on the velocity attenuation of the cylindrical fragments (aspect ratio ≥ 0.5) and pie fragments (aspect ratio < 0.5) are different. As the water entry angle is decreased, the fragment velocity attenuation is slowed down by the “deflection effect” of the fragment. Considering the reduction of drag coefficient, a modified velocity attenuation formula is presented for the pie fragments during high-speed water entry.
Performance Analysis of Wells Turbine With Radiused Blade Tip
Authors: Kumar P. Madhan , Halder Paresh , Samad Abdus
Published: September 2018

A Wells turbine is an axial flow reaction turbine, which consists of a symmetrical airfoil at 90° stagger. It is commonly used as a power take-off device in the oscillating water column. This turbine is prone to stall at higher flow coefficients and have narrow operating range. There are several parameters, which influence the stall characteristics of the turbine, one of them is the tip leakage flow. Radiused blade tip was shown to suppress separation bubble and mitigate internal gap loss. In this study, the aerodynamic characteristics of Wells turbine with radiused blade tip were investigated. The numerical analysis was done by solving three-dimensional steady Reynolds-averaged Navier-Stokes equation with k-ω SST turbulence model. The turbine with blade profile NACA 0015 was taken as the reference blade, and the numerical results were validated with the experimental data. Radiused tip blades with different fillet radius were analysed and they showed similar performance. They improved the operating range and peak torque coefficient by 25% and 37% respectively. The fluid dynamics behind the performance augmentation was also analyzed and reported.
Ductile Fracture Modeling of DH36 Grade Steels
Authors: Cerik Burak Can , Park Sung-Ju , Choung Joonmo
Published: September 2018

A Hosford-Coulomb type ductile fracture surface was developed for DH36 grade steels. The fracture experiments reported in the literature, which consist of tests with notched tensile specimens, tensile specimens with a central hole, shear specimen and disc specimens for punch specimens, were utilized in a detailed finite element analysis of each experiment to evaluate the evolution of local stress and strain fields and identify plasticity and fracture response of DH36. The developed plasticity model consists of a von Mises yield surface, an associated flow rule and a combined Swift-Voce type isotropic hardening rule. The loading paths to fracture initiation were determined in terms of stress triaxiality and normalized Lode angle parameter histories. Finally, the Hosford-Coulomb fracture surface was calibrated using the finite element analysis results and adapting a linear damage accumulation law.
Updatable Spatio-Temporal Probabilistic Corrosion Modeling for Offshore Structures
Authors: Neumann Karoline M. , Vårdal Ole Tom , Ehlers Sören
Published: September 2018

Corrosion models are important to assess how the corrosion influences current and future structural strength. For this purpose it is desirable to describe the uneven corrosion diminution of the irregular surface (i.e. space) and progression (i.e. time) in various corrosive environments. Thickness measurements give an indication of the current state, and should be considered in the corrosion model. The inherit uncertainty in corrosion argues for a probabilistic type of corrosion model. Probabilistic models to describe corrosion in time and space, and that can be updated with observations exist, but are typically too complicated for practical engineering use for in-service corrosion assessment. Simpler models exist, that do not describe all of the mentioned aspects (probabilistic, updatable, describe corrosion in time, space and various environments). Here, a simple model covering these aspects is described in two parts. First bayes updating is used to estimate the parameters of the corrosion distribution for each unique environment. The second part uses this resulting distribution and describes how this distribution develops with time. The model is demonstrated with an example and compared to similar spatio-temporal models. The model is promising for improvement from simplistic uniform description of surface and linear progression used in current industry practice.
Coupled Dynamics Simulation of Submerged Floating Tunnel for Various System Parameters and Wave Conditions
Authors: Jin Chungkuk , Kim Joseph Moo-Hyun , Choi Junho , Park Woo-Sun
Published: September 2018

Coupled dynamic analyses of 900-m-long SFT (submerged floating tunnel) are conducted for various system parameters and random waves. The SFT dynamics between the clamped-clamped fixed-end conditions are caused by elastic modes, and thus hydro-elasticity simulation program has been modeled, from which various elastic modes and wet natural frequencies are identified. Parametric studies are conducted to investigate SFT horizontal and vertical motions and mooring tensions with varying SFT bending stiffness, mooring interval, mooring material, and 100-yr-storm-wave conditions. The BWR (buoyancy to weight ratio) and water depth are fixed to be 1.3 and 80 m. Various nonlinear phenomena including larger downward motion and the corresponding mooring snap loading are observed and discussed.
Experimental Investigations of Hydroelastic Effects on Loads During Flat Water Entry
Authors: Toedter Simon , el Moctar Ould , Neugebauer Jens , Schellin Thomas E.
Published: September 2018

Extensive water entry experiments were performed to identify the influence of elasticity on impact-induced loads acting of flat bottom structures. Two bodies were tested. One body was fitted with stiffened, rigid bottom plating; the other body, with thin elastic plating. Bottom pressures and forces acting on the flat bottom plating and impact-induced elastic bottom strains were measured. High-speed videos of water entry sequences were evaluated to investigate hydroelastic effects on air trapping.
Fluid-Fluid Displacement for Primary Cementing in Deviated Washout Sections
Authors: Lund Bjørnar , Ytrehus Jan David , Taghipour Ali , Divyankar Shreyansh , Saasen Arild
Published: September 2018

One of the most critical operations during well construction is the cementing procedure, where drilling fluid is displaced by cement, normally with one or more spacer fluids in between. Due to the curing nature of the cement slurry there will be only one opportunity to cement the well properly. Although one for top hole cases can fill cement in from the top in a remedial operation, this possibility cannot fully compensate for a non-optimal initial cement job. Furthermore, it cannot be applied to other well sections. In those sections, complex squeeze cementing operations may be necessary. Consequences of improper annular cement can be leakage during production phase and extensive costs when the well is to be plugged for abandonment after the production phase. To ensure that the risk of poor cement is minimised it is important to use the best procedures to place the cement properly. Most models in use assume that the annulus is homogeneous. This is not always the case since washout sections appear during drilling. The effects of these on cementing are not sufficiently studied and considered in models and procedures.

Here we present and discuss results from fluid displacement experiments in a laboratory flow loop, illustrating annular displacement of drilling fluid by spacer (or spacer by cement). Model fluids with realistic densities and rheological properties have been used in a test setup with a transparent annular section. The wellbore is represented by a 10 m long test section, where the annulus has a 6,5” outer diameter and an inner string of 5” that can rotate. A washout section is represented by a 2 m long section of the outer pipe with a larger diameter of 11”. These diameters are representative for the lower parts of a well were high wellbore inclinations are common. In these sections the inner pipe cannot be assumed concentric at all times, so both concentric and eccentric positions have been tested. Experiments reported here were conducted at 60 degrees inclination. The test section was instrumented with conductivity probes in an array around the perimeter at 4 separate positions along the pipe, including the inlet and outlet of the washout section. Together with a camera along the test section, this provided information about the motion and shape of the liquid-liquid interface through the test section.

Results show that the displacement front changes significantly when entering the washout zone compared to the regular annular section. Due to the larger flow area the density differences between displaced and displacing fluids become more important in the washout section, while momentum effects dominate in the regular section.
Station Keeping Trials in Ice: Ice Load Monitoring System
Authors: Nyseth Håvard , Hansson Anders , Iseskär Johan Johansson
Published: September 2018

In connection with the Statoil SKT project, DNV GL have developed a method for estimating ice loads on the ship hull structure and mooring tension of the anchor handling tug supply (AHTS) vessel Magne Viking by full scale measurements. In March 2017, the vessel was equipped with an extensive measurement system as a preparation for the dedicated station-keeping trial in drifting ice in the Bay of Bothnia. Data of the ice impacts acting on the hull were collected over the days of testing together with several other parameters from the ship propulsion system. Whilst moored, the tension in the mooring chain was monitored via a load cell and logged simultaneously to the other parameters. This paper presents the processes involved in developing the measurement concept, including the actual installation and execution phases. The basic philosophy behind the system is described, including the methods used to design an effective measurement arrangement, and develop procedures for estimation of ice loads based on strain measurements. The actual installation and the process of obtaining the recorded data sets are also discussed.
Assessing the Impact of Riser-Soil Interaction Model on the Fatigue Life of Large Diameter SCRs
Authors: Hejazi Rasoul , Grime Andrew , Randolph Mark , Efthymiou Mike
Published: September 2018

This paper investigates the effect of riser-soil interaction model selection on the assessment of steel catenary riser (SCR) fatigue life for realistic environmental conditions at a deep-water Australian North west shelf (NWS) site. Using a fatigue wave scatter diagram consisting of 100 metocean conditions at the site (combining irregular seas, swell and current), a dynamic time-domain finite element analysis is coupled with the rain-flow cycle counting algorithm in order to determine the fatigue life of SCRs due to first-order motions of the host floater. Rigid, linear elastic and nonlinear riser-soil interaction models are used in order to assess the impact of model selection on the fatigue life of example deep-water SCRs of varying diameter. It is shown that the use of a nonlinear riser-soil interaction model for a representative deep-water NWS site can give an almost two-fold increase in SCR fatigue life over a stiff linear seabed assumption, albeit at a significant computational expense. It is further shown that a recently developed method for calculating equivalent linear soil stiffness may be used in place of the computationally expensive nonlinear approach in order to estimate SCR fatigue life to a reasonable level of accuracy. A methodology for applying the equivalent linear stiffness method to irregular sea-states is proposed and general insight into the selection of the most appropriate soil-riser interaction model for the fatigue analysis of large diameter deep-water SCRs is provided.
Effects of Mooring Line Design Parameters on the Line Dynamics and Fatigue Response of Subsea Mooring Lines
Authors: Sedghi Hamid , Kimiaei Mehrdad
Published: September 2018

Dynamic characteristics of mooring lines play an important role in overall structural response and fatigue design of mooring systems. Full dynamic analysis including line dynamics is a vital part of fatigue design process although in time domain it needs excessive computational efforts. For fatigue analysis of mooring lines where hundreds of different environmental loads have to be checked, alternative analysis approach such as quasi-dynamic analysis with implicit inclusion of the line dynamic effects are used widely in engineering practice. This paper presents the results of series of case studies on the effects of various mooring line design parameters on the line dynamics as well as the mooring line dynamic fatigue response. Various mooring line composition types (all chain and chain-polyester-chain) used in different mooring configurations (catenary, semi-taut and taut) with variable range of mooring line pretensions connected to a floater in shallow and deep water depths are studied. Ratios of fatigue damage results between dynamic and quasi-dynamic results as well as the relation between fatigue damage and statistical characteristics of the line dynamic responses for different line configurations and load cases are investigated in detail.
Numerical Investigation of the Collision Damage and Residual Strength of a Floating Bridge Girder
Authors: Sha Yanyan , Amdahl Jørgen , Dørum Cato , Yu Zhaolong
Published: September 2018

For bridges across wide and deep waterways, fixed foundation structures are not possible to be built due to technical restrictions. Alternatively, pontoon supported floating bridges which do not require fixed foundations can be installed. As the girders of floating bridges may have a low clearance from the sea level, a critical design consideration is the capability of the girder to resist the collision of passing ships. It is hence important to investigate the collision response of the bridge girder and evaluate girder residual strength after the collision. In this paper, finite element (FE) models of a ship deckhouse and a floating bridge girder are established. The girder response to ship deckhouse collision is investigated through integrated numerical simulations. Parametric studies are conducted to compare the girder response for various girder designs and collision scenarios. The residual strength of the girder after in damaged condition is also investigated. Based on the numerical results, a residual strength index (RSI) is proposed for fast prediction of the girder damage level based on the absorbed energy.