bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Simulation of Ship-Ship Interactions in Waves
Authors: Xie Xueshen , Wan Yuxiang , Wang Qing , Liu Hao , Feng Dakui
Published: November 2019

A numerical simulation of the hydrodynamic interaction and attitude of a ship and two ships of different sizes navigating in parallel in waves were carried out in this paper. The study of the two ships navigating in parallel is of great significance in marine replenishment. This paper used in house computational fluid dynamics (CFD) code to solve unsteady RANS equation coupled with six degrees of freedom (6DOF) solid body motion equations. URANS equations are solved by finite difference method and PISO algorithm. Structured grid with overset technology have been used to make computations. Turbulence models used the Shear Stress Transport (SST) k-ω model. The method used for free surface simulation is single phase level set. In this paper, two DTMB 5415 with different scales are selected for simulation analysis. This paper analyzed the impact of the big ship on the small ship when the two ships were navigating in parallel. This paper also analyzed the relationship between interaction and velocity between hulls, which has certain guiding significance for the ship’s encounter on the sea.
Evaluation of the Performance of an Integrated WEC Type of Breakwater System
Authors: Ding Haoyu , Zang Jun , Ning Dezhi , Zhao Xuanlie , Chen Qiang , Blenkinsopp Chris , Gao Junliang
Published: November 2019

A new type of coastal structure is proposed to reduce construction-cost and construction-space by integrating wave energy converters (WECs) into breakwater system. To develop this type of system to be more stable and effective, this paper focuses on investigating and improving an existing concept of integrated WEC type of breakwater system using a numerical method based on OpenFOAM®. Validation of the numerical setup is conducted by comparing the numerical predictions with relevant experimental data collected in a wave tank at Dalian University of Technology. The integrated WEC type of breakwater system considered in this paper is a pile-restrained WEC-type dual-floating breakwater system. The two floating breakwaters in this system are constrained to heave motion independently and work as a heaving-oscillating buoy type of WECs driven by a linear power take-off damping system (PTO system). Two parameters including wave transmission factor and capture width ratio (which is defined as the ratio of absorbed wave power to the incident wave power in the device width) are studied and discussed in the paper. The range of effective frequencies (range with wave transmission factor KT < 0.5 and capture width ratio CWR > 0.2) is obtained to evaluate the performance of this system with regard to both breakwater and WEC. These results indicate that damping coefficient of PTO system and gap width between two floating bodies influence wave transmission factor and capture width ratio, and the range of effective frequencies can be improved by the appropriate damping coefficient and gap width.
An Arrow-Shaped Honeycomb Pedestal With Negative Poisson Ratio and its Impact Resistance
Authors: Wu Haoran , Lin Xiaobin , Zhang Jie
Published: November 2019

The ship’s pedestal is the connection structure between the ship’s equipment and the hull, and is also the basis for the installation of the equipment. The pedestal bears both the static load generated by the weight of the equipment and the dynamic load generated during the operation of the equipment, and at the same time transmits the external load received by the hull to the equipment, and the load it bears is very complicated. If there is a problem with the pedestal in an impact environment, the accuracy of the system equipment will be affected, the system equipment will not work properly. Negative Poisson’s ration structures have a unique set of properties because of their tensile expansion, such as increased shear modulus, enhanced fracture toughness, better energy absorption and co-curvature. In recent years, the negative Poisson’s ration honeycomb structure has been applied to the pedestal of marine equipment, which demonstrates good vibration damping effect. However, the pedestal has two functions: vibration damping and impact resistance, there is not much research on the impact resistance of the pedestal. In this paper, an “arrow-shaped” honeycomb pedestal is taken as the research object. Firstly, the analytical expression of the Poisson’s ration of the honeycomb pedestal is derived theoretically and the influence of each parameter on the Poisson’s ration is analyzed. Secondly, the effect of Poisson’s ration on the impact resistance of the pedestal was analyzed by ensuring that the pedestal height was constant. It was found that with the reduction of Poisson’s ration, the impact resistance of the pedestal and the output impact environment of the pedestal panel were effectively optimized. Finally, by ensuring that the height of the pedestal is constant and the Poisson’s ration is the same, the influence of the number of honeycomb layers on the impact resistance of the pedestal is analyzed.
Impact of Rotor Misalignment due to Platform Motions on Floating Offshore Wind Turbine Blade Loads
Authors: Smith Rachael E. , Pillai Ajit C. , Tabor Gavin , Thies Philipp R. , Johanning Lars
Published: November 2019

The rotor of a horizontal-axis floating offshore wind turbine is more frequently misaligned with the oncoming wind than that of a fixed offshore or onshore wind turbine due to the pitch and yaw motions of the floating support structure. This can lead to increased unsteady loading and fatigue on the components beyond those considered in the standard load cases. In this work, the Simulator fOr Wind Farm Applications (SOWFA) tool within the CFD toolbox OpenFOAM is used to perform simulations of a wind turbine at different stationary angles to the oncoming wind flow that a floating wind turbine may experience, so that the impact of misaligned flow on power production and blade loading can be studied. The turbine is modelled using an actuator line method which is coupled with NREL’s aeroelastic code FAST to compute the structural response. The results of this study will be used in future work to optimise the rotor geometry of a floating offshore wind turbine.
Study on Gust Parameters and Wind Spectrum of South China Sea
Authors: Xie Botao , Ren Xuhe , Li Jiagang , Duan Wenyang , Wang Junrong , Zhao Binbin
Published: November 2019

Wind loads are one of the main loads on offshore structures during typhoons in the South China Sea (SCS). The accuracy of wind turbulence characteristic parameters were very important for the calculation of wind load of these large structures and floating platforms. The parameters of the gust factor and wind spectra are studied in this paper. Characteristics of the gust factor and the turbulence during typhoon and monsoon period were analyzed by using the observational data of long-term wind on a platform in South China Sea. The relationships among the gust factor, mean wind speed and turbulence intensity were described. The most suitable wind spectrum for SCS had been compared for the different wind speed conditions. The results can provide reference and technical guarantee for the offshore constructions of SCS.
An Experimental Investigation of the Trim Effect on the Behaviour of a Containership in Shallow Water
Authors: Elsherbiny Khaled , Tezdogan Tahsin , Kotb Mohamed , Incecik Atilla , Day Sandy
Published: November 2019

A new division of the Suez Canal in Egypt, termed the New Suez Canal, was opened for international navigation in August 2015. It is therefore important to ensure the safety of ships navigating this new section of the canal. Measures to avoid grounding and/or drifting to the canal banks are necessary. Additionally, accurate prediction data for ship squat and under keel clearance is crucial.

This paper presents the results of experimental work carried out at the Kelvin Hydrodynamic Laboratory at the University of Strathclyde, Glasgow, to study the effect of trim on containership sailing characteristics in shallow waters using Kriso Container Ship (KCS) model.

A series of model tests were conducted to measure the resistance, sinkage variations with speed, water depth and loading conditions under different trimming angles at 1:75 scale. The objective of this work is to examine the range of ship trim for safe and efficient sailing in restricted water in both depth and width. The study also aimed to provide data to be used in validating numerical computations to be carried on the same type of vessel to detect the best trim angle for ships during sailing in restricted waters to reduce resistance and therefore fuel consumption.

For depth Froude numbers higher than 0.4, the results show that the ship model sinkage is less for aft trim than for level trim or forward trim. Concurrently, it can be observed that there is less water resistance for aft trim than for forward trim, albeit level trim shows the least resistance. The test was conducted for one value of model draft which was 0.144 m. Side bank effect were also examined.
Characterizing Impacts of Atmospheric Turbulence on Wind Farms Through Large Eddy Simulation (LES)
Authors: Alam Jahrul M. , Afanassiev Anton , Singh Jagdeep
Published: November 2019

Wind farms extract energy from the lowest part of the atmospheric boundary layer (ABL). Thus, characterizing the impacts of atmospheric turbulence — precisely, which aspect of it enhances or hinders the capacity factor of wind farms — is currently the least understood and the most demanding topic of wind energy research. This article demonstrates a Large Eddy Simulation (LES) of atmospheric turbulence around an array of 41 full-scale wind turbines with a rotor diameter of 126 m. A wall-adaptive subgrid-scale (SGS) model for atmospheric turbulence around wind farms has been examined. For a moist-free atmosphere in the afternoon, the spectra of kinetic energy are compared with Kolmogorov’s energy spectrum. The power production is discussed with respect to staggered arrangements of turbines. Results show that the LES model has the potential to account for atmospheric turbulence for optimizing tower placements in wind farms.
Active Control of Flexible Riser Vibration by Boundary Control Based on LQR Controller
Authors: Yu Jinxin , Chen Weimin
Published: November 2019

The lateral displacement and the rotational angle of marine riser are likely to get larger as it is in stronger ocean current and, particularly, undergoes the consequences such as vortex-induced vibration or collisions between individual risers. The riser vibration with large amplitude value will lead to fatigue or coating damage of the structural body. In this study, the active vibration control, in terms of its angle and the displacement reductions, of a flexible riser under time-varying distributed load are considered using boundary control. The governing equations of the structural dynamics involving the control system of a flexible riser are built. The riser is modeled as an Euler-Bernoulli beam under the actions of ocean loads and the feedback controller. A torque actuator is introduced at the upper riser boundary, and the control law is employed to generate the required signal for riser angle control and displacement reduction. The feed-back control law is designed in state space, and the optimization of the control law is implemented based on the LQR approach. The linear quadratic regulator is used to determine the gain matrix, which can calculate the boundary control law by solving the Recatti equation. Based on the numerical simulations, the responses of the open-loop system and closed-loop system are presented and compared. The effectiveness of the vibration suppression of the flexible riser is examined.
Investigation of the 2D Behavior of a Rotating Cylinder in Flow Using the Discrete Vortex Method
Authors: Rheem Chang-Kyu
Published: November 2019

The influence of rotation on the behavior of a two-dimensional rotating cylinder in flow was investigated by using the discrete vortex method combined with the 4th order Runge-Kutta method. There are three stages for rotational speed dependence of hydrodynamic force on a fixed rotating cylinder, the stage where lift force increases and drag force decreases, the stage where lift and drag forces increase in proportion to the square of rotation ratio, and the stage where lift and drag forces increase in proportion to rotation ratio. As a fixed rotating cylinder begins to rotate and the rotational speed increases, the vortex train that causes VIV weakens and disappears. When the cylinder is mounted on a spring, the vibration frequency of the spring mounted rotating cylinder becomes lower. This indicates that the added mass of the rotating cylinder is increasing as the rotation ratio increases.
CFD Investigations of 2D Greenwater Overtopping of a Floating Offshore Vessel
Authors: Zhang Xiantao , Draper Scott , Wolgamot Hugh , Zhao Wenhua , Chen Lifen , Cheng Liang
Published: November 2019

In this paper, 2D greenwater overtopping of a floating box is numerically investigated using CFD. The incident waves used are compact wave groups which correspond to the maximum relative wave elevation at the edge of the box according to linear theory. The motion of the box for which only heave and pitch modes are considered is calculated using linear potential flow theory and then prescribed in the CFD simulation. It is found that the normalized maximum horizontal momentum flux of greenwater overtopped onto the moving box is consistent with that for a fixed box when the incident wave length is much smaller than the box length. For longer incident wave lengths there is arguably more scatter in the momentum flux compared with that of a fixed box, although the result is still bounded by a value of 1.5 times that predicted by a classical dam break solution. This additional scatter is shown to be due to the effect of box motion.
Development of a New, Correlated FEA Method of Assessing Mooring Chain Fatigue
Authors: Farrow Gary H. , Potts Andrew E. , Kilner Andrew A. , Kurts Phillip P. , Dimopoulos Simon , Jal Eric
Published: November 2019

The first phase of the Chain FEARS (Finite Element Analysis of Residual Strength) Joint Industry Project (JIP) aimed to develop guidance for the determination of a rational discard criteria for mooring chains subject to severe pitting corrosion which, based on current code requirements, would otherwise require immediate removal and replacement. Critical to the ability to evaluate the residual fatigue life of a degraded chain, is to have an accurate estimate of the chain in its as-new condition, thereby providing a benchmark for any loss in fatigue life associated with severe corrosion or wear.

A large collection of fatigue test data was collated for comparison and to establish underlying trends in as-new mooring chain fatigue response. A non-linear multi-axial Finite Element Analysis (FEA) fatigue assessment method was developed to correlate against available as-new chain link fatigue test data and underlying failure trends as part of the JIP achieving this critical requirement.

It was established that the linear FEA fatigue method currently employed in the industry is too simplistic and does not correlate with the fatigue test data, whereas an alternative method of assessing fatigue based on FEA, developed with respect to the DNV B1 material curve, correlates well with the available physical fatigue test data.

The FEA method uses a non-linear chain link FEA and multi-axial stress fatigue calculation method to determine an equivalent Stress Magnification Factor (SMF). This method achieves good correlation of predicted utilisations and associated cycles-to-failure with fatigue test data and in respect of critical locations with evidenced failure locations. The method of equivalent SMF calculation accounted for the significant effects on fatigue performance including proof load induced residual stress, mean stress levels and the increase in material fatigue endurance associated with increased steel UTS (i.e. increased offshore mooring chain grade). The analytical method developed in this study achieved a high degree of correlation with as-new chain fatigue test data, and should enable the accurate prediction of fatigue stresses around a link and in particular for irregular geometry associated with corrosion degraded chain links.
Simplified Numerical Simulation of the Dense Sand Progressive Failure Involved in Spudcan Punch-Through Failure
Authors: Zhao Jun , Sun Futai , Jin Wenbo
Published: November 2019

In the dense sand-over-clay strata, there is a potential for an installing spudcan to experience a sudden uncontrolled punch-through failure. Such a punch-through failure would seriously threaten safety of the rig structure, even cause casualties. To estimate the potential spudcan punch-through failure, this paper presents a simplified numerical method to calculate the full load-penetration resistance profile. The present approach allows the progressive failure of the overlying dense sand to be properly simulated by using an extended Mohr-Coulomb model. A series of large deformation finite-element (LDFE) analyses are carried out, varying the strength parameters. A fairly good performance of the present approach is verified by validating against groups of centrifuge tests data. Additionally, comparisons with the typical existing LDFE analyses in which both the simple and sophisticated constitutive models are conducted, show that the present approach performs fairly well to calculate the penetration resistance of a spudcan on dense sand overlying clay.
Enhancement of Structural Redundancy of Hull Structure in Accidental Condition by Applying Highly Ductile Steel
Authors: Nakayama Shin , Ueda Keiji , Aoki Masahiro , Matsumoto Kazuyuki
Published: November 2019

Application of steel plates with highly ductile is beneficial for ship owners, in order to improve structural redundancy and prevent environmental burden in accidental condition such as collision or grounding. Highly ductile steel, in which breaking strain is improved by 20% in comparison with conventional steels has developed, by optimizing microstructure. Excellent ductility was achieved selecting ferrite-perlite dual phase structure of ferrite phase which is advantageous for stable actual production. Morphology of ferrite phase control which consists of optimization of volume fraction and strengthening of ferrite phase itself by adding Si plays an important role to enhance ductility. The highly ductile steel of YP315 grade had acquired Class approval, and for ships to which high ductile steels are applied, ClassNK would assign the notation “Hull Protection by Highly Ductile Steel” (HP-HDS). MITSUBISHI SHIPBUILDING has evaluated the effect of highly ductile steel by numerical simulation for LPG (Liquefied Petroleum Gas) Carrier owned by Astomos Energy Corporation and Iino Kaiun Kaisha, Ltd. It has been confirmed that highly ductile steel can improve the structural redundancy by 20% in accidental condition by being applying to side structure.
A Research on Predicting Method of the Damage by Tsunami Drifting Objects in Urban Port
Authors: Masuda Koichi , Ikoma Tomoki , Aida Yasuhiro , Takada Masayuki , Fukunaga Yuta
Published: November 2019

When a tsunami arrives at an urban port, the most serious concern is the damage caused by tsunami drifting objects. In other words, the damage caused by tsunami drifting objects was also enormous, even in previous disasters. Containers, automobiles, timber, and other objects drifted, resulting in a blockade of the port of the harbor, which required a great deal of time and expense to restore. Therefore, estimating the scale and damage of the occurrence of drifting objects in harbors is extremely important in the early restoration and reconstruction of the port. Therefore, the purpose of the present paper is to develop a practical numerical simulator capable of quantitatively predicting the scale and damage of tsunami drifting at a port. In the present paper, we select containers as representative drift objects at ports and quantitatively predict the magnitude of drift damage by containers and other objects. According to the proposed simulator, prediction of the occurrence of the drifting of the container by the tsunami propagation calculation and the MPS method is predicted, and the subsequent drifting behavior of the container is predicted by the individual element method. The occurrence of tsunami drifting, drifting range, drifting speed, and collision force, etc., can be estimated by the proposed simulator. As an example, we present a case of drift damage prediction in the container yard of Shimizu Port in Shizuoka Prefecture.
Cement Plug Sealing Studies of Silica Cement Systems
Authors: Corina Anisa Noor , Opedal Nils van der Tuuk , Vrålstad Torbjørn , Sangesland Sigbjørn
Published: November 2019

A cement plug is widely applied for permanent abandonment phase to provide long-term zonal isolation against fluid flow. Maintaining cement plug integrity is a challenging task, and loss in cement sealing poses risks to the surrounding environment and surface safety. It is well-known that the cement performance is affected by cement material and downhole conditions. Nevertheless, investigations linking these influencing factors with the sealing of cement plugs are still limited, especially with the lack of proper equipment in the past.

In the present work, a small-scale laboratory setup has been constructed to test the sealing ability of a cement plug. It has unique features that can simulate plugging operations at the downhole conditions and preserve the cement curing condition. By testing using this setup, it is possible to measure the minimum differential pressure required for gas to flow across the cement plug and the gas leak rate. The silica cement mixture was selected as the plug material, prepared using silica flour. Investigation of silica cement under the influence of expanding agent additive and various curing temperature was carried out. It was found that adding an expanding agent improved the sealing of cement plugs. Moreover, samples cured at a high temperature were less resistant to gas flow with the leak path observed at the cement/steel interface, indicating debonding.
Optimization of Insulation and Heating System of Derrick for Arctic Mobile Offshore Drilling Unit
Authors: Liu Dahui , Wang Zhiyuan , Zheng Kaibo
Published: November 2019

The Arctic region contains abundant oil and gas resources. Due to the harsh environment of extremely low temperature and strong wind, it has a great impact on drilling activities. Therefore, it is necessary to carry out insulation measures for drilling equipment such as drilling derricks.

This paper analyzes the heat transfer mechanism of the derrick insulation wall of the drilling platform in the polar ice region. Based on the theory of computational fluid dynamics, the insulation materials of derrick on the polar drilling platform are investigated by numerical simulation. The number and position distribution of the heaters are selected, the effect of wind speed on insulation effect is explored, and the heating power of the derrick under the thermal insulation conditions is obtained. The simulated results are compared with those calculated by theoretical analysis.

The results show that in the polar environment, polyurethane can be used as the insulation material for the derrick of polar drilling platform. Five heaters can be arranged in the derrick, wherein three heaters are arranged on the bottom layer, and two heaters are arranged on the second floor of the derrick. When the heating time is short, the external wind speed has a relatively large influence on the temperature of the air inside the derrick, but when the heating time is long, the influence of the external wind speed is small. Under the thermal insulation conditions, according to the heat transfer equation and the heat balance theory, the required heating power is similar to the heating power obtained by the fluent software simulation.
Prediction of Hydrodynamic Damping of Moored Offshore Structures Using CFD
Authors: Jiang Changqing , el Moctar Ould , Schellin Thomas E.
Published: November 2019

Usually, mooring system restoring forces acting on floating offshore structures are obtained from a quasi-static mooring model alone or from a coupled analysis based on potential flow solvers that do not always consider nonlinear mooring-induced phenomena or fluid-structure interactions and the associated viscous damping effects. By assuming that only the mooring system influences the restoring force characteristics, the contribution of mooring-induced damping to total system damping is neglected. This paper presents a technique to predict hydrodynamic damping of moored structures based on coupling the dynamic mooring model with a Reynolds-averaged Navier-Stokes (RANS) equations solver. We obtained hydrodynamic damping coefficients using a least-square algorithm to fit the time trace of decay tests. We analyzed a moored offshore buoy and validated our predictions against experimental measurements. The mooring system consisted of three catenary chains. The analyzed response comprised the decaying oscillating buoy motions, the natural periods, and the associated linear and quadratic damping characteristics. Predicted motions, natural periods, and hydrodynamic damping generally well agreed to comparable experimental data.
In-Line VIV Based on Forced-Vibration Tests
Authors: Yin Decao , Wu Jie , Passano Elizabeth , Lie Halvor , Peek Ralf , Sequeiros Octavio E. , Ang Sze Yu , Bernardo Chiara A. , Atienza Meliza
Published: November 2019

Excitation and added mass functions determined from forced vibration tests of a rigid cylinder undergoing harmonic motion in the flow are used in the semi-empirical software VIVANA to predict the VIV response of pipelines.

An advantage of this approach, as opposed to the more-commonly-used response function approach, is that it can account for changing conditions along the length of the pipe, like changing current velocity, seabed proximity, and/or pipe diameter. This makes it useful for pipelines as well as for risers when such changes occur. Further, for pipelines, travelling wave effects play less of a role than for risers, so the VIVANA approach can be simplified by assuming the phase angle of the harmonic response is constant along the span.

The interactions between cross-flow and in-line response that complicate the prediction of cross-flow VIV by the excitation function approach, do not arise for pure inline VIV. For the latter case, using the pure in-line forced vibration test data of Aronsen (2007), it is found that both VIVANA approach and simplified ‘SIVANA’ approach thereof predict VIV amplitudes consistent with experiments on flexible pipe (Ormen Lange umbilical VIV tests), and the DNVGL-RP-F105 response function for a range of structural and soil damping values.

In a companion paper, this approach is applied partially strake-covered pipeline spans, to show that a relatively small fraction of well-placed strake coverage is enough to suppress in-line VIV.
Geometrical Optimization of U-Oscillating Water Columns in Random Waves
Authors: Scialò Andrea , Malara Giovanni , Arena Felice
Published: November 2019

This paper deals with the problem of designing an optimal U - Oscillating Water Column (U-OWC) device equipped with a Wells turbine. Specifically, the paper proposes the implementation of a genetic algorithm for designing a U-OWC exposed to the typical sea states available in the Mediterranean Sea. The first challenge encountered in this problem is the efficient calculation of the U-OWC hydrodynamic parameters. The second challenge relates to the fact that the U-OWC dynamics is governed by two coupled nonlinear ordinary differential equations with no closed-form solution. For reducing the computational cost, the genetic algorithm is combined with a semi-analytical approach used for determining the U-OWC hydrodynamic parameters and with a statistical linearization based approximate solution of the equations governing the U-OWC dynamics. Such a procedure allows estimating efficiently, albeit approximately, the power output of the system.

Numerical results compare a design based on a conventional “design sea state” vis-à-vis a design based on a “design wave climate”. For this purpose, the case study of the Roccella Jonica marina (Reggio Calabria, Italy) is considered, as relevant wave data are available to characterize the most energetic seas as well as depicting the global wave climate available at that location. The numerical results highlight the fact that an optimization conducted on the basis of a design sea state does not lead to an optimal design in a wave climate.
Experimental Analysis of Reduced-Scale Jumper for Deep-Sea Mining
Authors: Yamamoto Marcio , Fujiwara Tomo , Kanada Shigeo , Ono Masao , Takano Satoru , Yamamoto Joji
Published: November 2019

In the Deep-Sea Mining, the seafloor mining tool is connected to the subsea slurry pump by a piece of flexible pipe named jumper. The jumper’s shape is similar to a steep-wave flexible riser. Compared to a flexible riser, the jumper is a reinforced hose and has a shorter length. Numerous studies shed light on the dynamic behavior of flexible riser; however, all studies were carried out by the way of numerical analysis. We carried out, in the Deep-Sea Basin, an experiment using 1/5 reduced scale model of the jumper. Unhappily, the model’s bending stiffness had to be distorted. During the experiment, an oscillator generated harmonic motion on the top end of the model and a centrifugal pump circulated water throughout the model. In addition, we installed load cells on the top and bottom ends of the model. Our Basin is equipped with a visual measurement system. Thus, we measured the displacement of targets attached to the model. The initial results show that axial tension amplitude increases with the frequency of the top end oscillation. This response is due to the drag force on the lower bend increases with the frequency of top motion. We also could observe that the internal flow may increase the vertical motion amplitude. The jumper’s motion generates an oscillation on the internal differential pressure between both ends and the flow velocity. The differential pressure amplitude increases with the top oscillation frequency, but it is proportional to the top end oscillation amplitude. We will use these experimental results to validate our numerical models. Further, it is important to understand the internal flow effects to design the actual pump used to convey the slurry through the jumper.
Hydrate Remediation Philosophy for a New Flowline Intervention System Based on Active Heating
Authors: Guindeuil Geoffrey , Sanchis Arnaud , Harchambois Stephanie , Vivet Romain , Palermo Thierry , Pasquet François-Xavier , Tosi Guillaume
Published: November 2019

The Electrically Trace Heated Blanket (ETH-Blanket) is a new offshore intervention system currently in development by TechnipFMC for the efficient remediation of plugs due to hydrates or wax deposit in subsea production and injection flowlines. The ETH-Blanket consists of a network of heating cables placed underneath an insulation layer which is laid onto the seabed above the plugged flowline. By applying electrical power to the cables, heat is generated by Joule effect which warms up the flowline content until hydrate dissociation or wax plug remediation through softening or complete melting. The ETH-Blanket is currently developed within a Joint Industry project (JIP) between TechnipFMC and Total.

The dissociation of hydrate plugs using active heating incurs a number of risks for the integrity of the flowline and for the restoration of production to nominal conditions. As the flowline content is warmed up from ambient to hydrate dissociation temperature and during the dissociation of the hydrate plug, the pressure inside the flowline may potentially increase above design limits due to hydrate degassing and fluid volume expansion. Also, plug run-away scenarios may occur if a large pressure difference exists between both sides of the plug. The remediation operation may fail because of insufficient power or misplacement of the ETH-Blanket. Lastly, even following successful operation of the ETH Blanket, new flowline blockage may occur during subsequent operations such as cold re-start.

To mitigate those risks, a hydrate remediation philosophy has been developed specifically for the ETH-Blanket Service. It is based on the development of in-house tools and procedures and builds upon experimental and modelling work performed as part of a previous JIP focusing on the dissociation of hydrate plugs using an ETH-Pipe-in-Pipe [1]. This paper introduces the different elements of the hydrate remediation philosophy, including the development and experimental validation of the dedicated tools used to define the appropriate heating sequence for the safe and efficient dissociation of hydrate plugs.
Predicting Extreme Waves From Wave Spectral Properties Using Machine Learning
Authors: Gramstad Odin , Bitner-Gregersen Elzbieta
Published: November 2019

An important question in the context of rogue waves is whether the statistical properties of individual waves, and in particular the probability of extreme and rogue waves, can be linked to the properties of the underlying wave spectrum of the relevant sea state.

It has been suggested that a narrow wave spectrum (in frequency or direction) combined with a large wave steepness may lead to increased occurrence of extreme waves. Parameters based on the ratio of the wave steepness to the spectral band-widths have therefore been suggested as indicators of increased probability of extreme waves. However, for realistic ocean conditions the success of such parameters seems to be questionable.

In this paper, we investigate relations between short-time wave statistics and wave spectral properties by using machine learning methods that can take a much wider range of spectral properties, or even the entire directional wave spectrum, into account. Numerical simulations with a nonlinear wave model that provides phase-resolved wave information are combined with wave spectra from a spectral wave model. Machine learning methods are then employed to investigate how well the wave statistics can be predicted from knowledge about the wave spectrum.

The results are discussed in the context of existing parameters suggested as indicators of rogue waves, as well as with respect to potential warning against sea states in which extreme waves are expected to occur, based on wave-forecast from spectral wave models.
Numerical Investigation of Scour Around Subsea Pipelines Near the Seabed
Authors: Yin Guang , Cheng Zhen , Liu Shengnan , Ong Muk Chen
Published: November 2019

In the present study, two-phase flow simulations using SedFoam (an open-source multi-dimensional Eulerian two-phase solver based on OpenFOAM) are employed to investigate the scour phenomenon around pipelines in the vicinity of the seabed. A complete transport profile from the immobile bed, to slowly moving quasi-static bed and upper transport layers can be captured by the present model. The fluid Reynolds stress is modeled using the two-phase k-ε model. The particle stresses due to binary collisions and enduring contacts are modeled by kinetic theory for granular flow and a phenomenological frictional model, respectively. The model is first validated through a two-dimensional (2D) simulation of scour around a single pipeline near the seabed. The predicted time-dependent scour profiles as well as the scour depth are compared with the simulation results of Lee et al. (2016) and the experimental data reported by Mao (1986). A numerical experiment is then carried out to investigate the scour around the piggyback near the seabed. The effects of different locations of the small pipeline on the scour depth are studied.
Support of Operational Decisions for Prelude’s Side-by-Side LNG Offloading
Authors: Auburtin Erwan , Miliante Thiago , van Haaften Ewoud , McPhail Finlay
Published: November 2019

Prelude floating liquefied natural gas (FLNG) facility reached a significant milestone in June 2018 when gas was introduced onboard for the first time as part of the facility startup process, loaded from an LNG Carrier (LNGC) moored in side-by-side (SBS) configuration. This first offshore LNG SBS operation allowed Prelude’s utilities to switch from running on diesel to running on gas.

SBS mooring is the base case configuration for offloading both LNG and Liquefied Petroleum Gas (LPG) into product carriers using Marine Loading Arms (MLA) once the Prelude FLNG facility is fully operational. These complex and weather sensitive operations are expected to take place on a weekly basis. This means critical decisions about weather-window and timing should be supported as much as possible by predictive analysis and modelling of forecast environment to reduce the risks.

There are multiple criteria for evaluating the operability of LNGC or LPGC SBS offloading. These criteria cover the various phases of an operation, such as personnel transfer to the visiting carrier, Terminal Team Leader (TTL) transfer, spool fitting and fender lowering, approach and mooring, connection and testing of the loading arms, ramp-up of product transfer, full rate cargo transfer, loading arm purging and recovery, de-berthing, and people and hardware recovery. The criteria have been tailored to be appropriate to the phase of the operation. They comprise both environment-based criteria (maximum acceptable wind and waves conditions), and criteria related to motion or mooring (carrier roll, MLA envelope, mooring line tension, fender deflection). Motion and mooring criteria are evaluated through dynamic time-domain simulations. This allows an accurate modelling of non-linear effects, including mooring characteristics and partially filled cargo tanks. Thrusters can be used to control Prelude FLNG facility position if needed. The required thruster force to maintain the selected heading is calculated with frequency-domain calculation for all possible headings.

This paper presents a visual reporting tool, developed by TechnipFMC in partnership with Shell. This tool has been used to support operational decisions during commissioning and startup, for SBS LNG and LPG import to Prelude FLNG facility. The daily reports used weather forecasts, in combination with numerical simulations, to predict the maximum motion and mooring criteria which contribute to determine both the timing and the decision to proceed with the operation. The format of the report has been designed to be user friendly for offshore operational staff, summarizing efficiently and in a visual manner the usage factors for each criterion separately. An overall operability is also presented for a quick overview. This paper also presents the details of numerical simulations, summarizes the different studies carried out to ensure the reliability of these simulations and discusses the possibilities for future development.
Plastic Accumulation in Front of a Plate in Cross Flow: Model Scale Test and CFD-DEM Modelling
Authors: Wrenger Hendrik , Sainte-Rose Bruno , Goniva Christoph , Hilbert Renan
Published: November 2019

Results of a flume experiment and numerical model of plastic accumulation in front of a plate are presented. The single phase CFD-DEM model formed a successful benchmark case to model plastic accumulation inside an ocean cleanup system.

A fixed wooden plate was placed in a steady cross flow and plastic was released upstream of it. We recorded the evolution of the plastic accumulation profiles under slowly increasing plastic load. Experimental parameters were the flow velocity, draft of the plate (varying the plate Froude number) as well as three different types of plastic particles. The accumulation of oil in front of barriers and parallels to the phenomena of plastic accumulation were reviewed.

As a second part of the project we used the open source CFD-DEM code CFDEM® to reproduce the flume experiment. It couples the discrete element method (DEM) software LIGGGHTS® and the open source computational fluid dynamics (CFD) software OpenFOAM®.

A linear relationship of the relative depth of the accumulation with the Froude number of the plate was found for a given type of particle and reproduced in the numerical model. We identified limitations of the experimental setup, calibration experiments and the single phase CFD-DEM approach and outlined the steps for further research.
Effect of Seabed Trenching on Holding Capacity of Suction Anchors in Deepwater Gulf of Guinea Clays: A Numerical Study
Authors: Castillo Garcia Pablo , Wallerand Regis , Hong Doan Dinh
Published: November 2019

In recent years, there has been an increasing issue of seabed trenches developing around mooring lines attached to suction anchors in West Africa, likely related to relatively large motions of the mooring lines. These trenches are recognised by means of numerical modelling and of centrifuge testing program as significant concern to the in-place holding capacity, the integrity of the anchor and the safety of the floating facility. Conservative trench geometries and complete absence of soil and of soil resistance in front of the anchor above the padeye depth (in the loading direction) were essential assumptions due to lack of observation. Results suggested that a reduction in holding capacity of 20% to 40% for typical mooring line load angles of 30° to 45° can be expected and that the presence of the trench does not affect the portion of holding capacity developed by passive suction at the pile tip. Nevertheless, recent survey data has evidenced a wedge of soil remaining within trenches in front of suction anchors leading to a new problem-solving approach. Consequently, this paper describes a Plaxis 3D Finite Element modelling in a parametric study as a reliable tool for the assessment of the holding capacity of the suction anchors in presence of seabed trench taking into account the presence of residual soil within the trench in front of the anchor pile. Analyses were performed under 30° inclined loading (actual case of taut deep water mooring systems) with various scenarios of trench shapes, padeye depths and anchor geometries in very soft highly plastic Gulf of Guinea clays. Thus, the consideration of the residual wedge of soil in front of the anchor leads to a much less reduction in holding capacity compared to initial studies done with too pessimistic assumptions on the final trench shape. In addition, this study aims at looking at changes in the pile geometry, including the position of the attachment point, to compensate the unavoidable formation of a trench for taut moorings.
Uncertainty Analysis in the Multi-Objective Optimization of Hydraulic Fracture
Authors: Baioco Juliana Souza , Jacob Breno Pinheiro , Mazadiego Luis Felipe
Published: November 2019

Unconventional reservoirs have become an important resource for hydrocarbons. The production of this type of reservoir is only feasible from massive stimulation. In this context, the study of hydraulic fracturing becomes important. The present work has the objective of evaluating the influence of reservoir parameters that are uncertain, in the optimization of hydraulic fracturing. The parameters that will be evaluated are: drainage radius, permeability, net-pay, temperature and pressure of the reservoir. The optimization model uses evolutionary algorithms to maximize the production of the fractured well and minimize the fracture cost.
New Engineering Approach for the Development and Demonstration of a Multi-Purpose Platform for the Blue Growth Economy
Authors: Lagasco F. , Collu M. , Mariotti A. , Safier E. , Arena F. , Atack T. , Brizzi G. , Tett P. , Santoro A. , Bourdier S. , Salcedo Fernandez F. , Muggiasca S. , Larrea I.
Published: November 2019

Aquaculture is currently the fastest growing food sector in the world and the open oceans are seen as one of the most likely areas for large-scale expansion [1], [2], [3]. The global demand for seafood is continuing to rise sharply, driven by both population growth and increased per capita consumption, whilst wild-capture fisheries are constrained in their potential to produce more seafood. A recently funded EC project, the Blue Growth Farm – BGF (GA n. 774426, 1st June 2018 – 30th September 2021) aims at contributing to this world need with an original solution. The Blue Growth Farm proposes an efficient, cost-competitive and environmentally friendly multi-purpose offshore farm concept. It is based on a modular floating structure, moored to the seabed, meeting requirements of efficiency, cost-competitiveness and environmental friendless, where automated aquaculture and renewable energy production systems are integrated and engineered for profitable applications in the open sea. In the present paper, the overall engineering approach developed to carry out the research work is presented, described and justified. Different technical and scientific challenges are addressed through an integrated industrial engineering design approach, where all disciplines are tuned to achieve the Blue Growth Farm main targets. These are represented by: i) guaranteeing expected nominal fish production thanks to advanced automation and remote control capabilities; ii) minimizing the pollution introduced at marine ecosystem level when exploiting the marine natural resources, whilst increasing the social acceptance and users community agreement; iii) maximizing the electricity production in the Blue Growth Farm potential installation area ecosystem to provide energy supply to the on-board electrical equipment and to dispatch the extra produced electric energy to the land network. Preliminary engineering design results are promising to demonstrate effective increase of safety and efficiency by reducing on-board human effort and consequently risks at offshore, thus to make commercial-scale open ocean farming a reality.

The present paper introduces overall concepts and design methodology whilst other companion works submitted at OMAE2019 [4], [5], [6] provide insight of specific aspects of the Blue Growth Farm project elaborated during the first six months activity.
Influence of Different Pile Installation Methods on Dense Sand
Authors: Spill Severin , Quiroz Tulio , Foglia Aligi
Published: November 2019

A current investigation subject of geotechnical modelling is the realistic representation of the installation process of offshore piles and its influences on the surrounding soil. Depending on the soil conditions piles can be installed with different installation technologies like impact driving, vibratory driving or jacking. The soil disturbances produced as a consequence of the pile installation affect the pile capacity. The dimension of the affected region depends on the installation process itself and its parameters as well as the soil initial state and the pile geometry. Currently, there are no general approaches which can predict the effects of pile installation on the soil conditions. In this contribution a brief summary of published data describing installation effects for impact driven, vibratory driven and jacked piles is given. Secondly, the influences of different pile installation methods on the surrounding soil are presented based on experimental results for non-cohesive soils from various projects. These will be analyzed by means of a comparison of dynamic probe light (DPL) and cone penetration tests (CPT) executed before and after the pile installations. Additionally the area of influence will be quantified with respect to their relative distance to the pile axis. Finally, based on these results recommendations for future works will be given.