bluuebunny/crossref_metadata_2025 huggingface dataset:
Grounding Experiments of a Ship Model in Water Tank
Authors: Zhu Ling , Zhou Qingwen , Chen Mingsheng , Chen Xiaoqi
Published: September 2018

Grounding is one of the major threats to ships under operation. In this paper, the ship model grounding experiments are conducted in a water tank to study the coupling effects of both internal mechanics and external dynamics. The influence of surrounding water on ship motions during grounding is taken into account. During testing, varying rock penetrations are considered to study the grounding damage. Experimental results such as the horizontal grounding forces and damage extents are measured and analyzed. The results show that the grounding damage depends on the rock penetration. Besides, the surrounding water of the ship model has a big influence on grounding damage assessment.
Scale Effects on Heave Plates for Floating Offshore Wind Turbines
Authors: Bezunartea-Barrio Ana , Fernandez-Ruano Sergio , Maron-Loureiro Adolfo , Molinelli-Fernandez Enrique , Moreno-Buron Francisco , Oria-Escudero Julio , Rios-Tubio José , Soriano-Gomez Cristina , Valea-Peces Alvaro , Lopez-Pavon Carlos , Souto-Iglesias Antonio
Published: September 2018

An essential aspect of experimental campaigns in ocean basins is the extrapolation of results to prototype scale. In the case of “spar” or semi-submersible platforms for floating wind turbines, it is customary to use heave plates that reduce the heave motion and/or tune its period. As part of the Hiprwind project, it was decided to study the scale effects on the hydrodynamics of these elements. To this aim, models of one column of the platform, equipped with a plain heave plate, were built. This model is a simplified representation of the actual one, which incorporates an edge vertical flap. The scales were 1:20, 1:27.6, and 1:45.45, with the former leading to added mass values of the order of 300kg, becoming one of the largest model for which experiments with heave oscillations have been carried out. Decay tests starting from various amplitudes and forced oscillations tests were performed at a range of frequencies and operational and extreme KCs (range of motion). Results related to these tests will be discussed in the paper.
Non Linear Simulation of a Wave Energy Converter With Multiple Degrees of Freedom Using a Harmonic Balance Method
Authors: Novo Riccardo , Bracco Giovanni , Sirigu Sergej A. , Mattiazzo Giuliana , Mérigaud Alexis , Ringwood John V.
Published: September 2018

Computationally efficient simulation methods for wave energy converters (WECs) are useful in a variety of applications. The simulation task is particularly challenging when non-linearities are present in the WEC model. Using a Fourier projection of the system inputs and variables, harmonic balance (HB) is a computationally-efficient method to solve for the steady-state motion of a non-linear system, preserving an accurate representation of the non-linear effects. In previous work, HB has been used for the simulation of WECs with one degree of freedom (DoF). Here, HB is presented for WEC systems with an arbitrary number of DoFs. A non-linear, 2-DoF model of the ISWEC wave energy device is used as an example of application. The HB implementation of the ISWEC model is described in detail. Through numerical applications, chosen in both regular and irregular waves, general features of the HB method are exemplified, in particular the exponential convergence rate to the actual mathematical solution, and the sensitivity, in some cases, to the starting point of the HB algoritm.
Structural Investigation of the Log Accumulation Effect in a Debris Containment Grid Through Towing Tank Experiments
Authors: de Castro Felipe Santos , Katsuno Eduardo Tadashi , Assi Gustavo Roque da Silva , Dozzi Dantas Joao Lucas
Published: September 2018

The large-scale presence of debris is a recurrent issue in the Madeira River, located on Amazon rainforest, North of Brazil, and it is a major concern for the Santo Antonio hydropower plant, located at this region. In order to avoid the abundant amount of debris, floating structures called log booms are installed across the river to retain and deflect them. This paper aims to present the methods used to investigate the structural characteristics of a truncated scale model of a log boom line, through water proof strain-gauges and load cells in hydrodynamic experiments. For that, the model was towed along the model basin of the Institute for Technological Research and wooden scale logs were included to simulate the log jam phenomenon. The paper covers experiment methods, from model design to setting of data acquisition devices and system, characteristics of the experimental runs, and further data analysis. The influence of the scale debris on the structural elements are presented, which can leads to develop a correlation model to scale the fluid-structure interactions in the real prototype.
Numerical Simulation of Shear Ram Performance
Authors: Zhu Lei , Estefen Segen F. , Jorge Nilo de Moura , Chujutalli John H. , Souza Marcelo Igor Lourenço
Published: September 2018

A subsea Blowout Preventer system plays an extremely important role in providing safe working conditions for drilling activities in deepwater oil exploration. However, estimating the performance of Shear Ram Blowout Preventeris still a challenge for the industry.

This paper considers different scenarios that may influence the shear capability of a typical subsea Blind Shearing Ram: the pipe size, ram shape, preload of pipe, off-center distance and tool joint of pipe. Element method analysis is conduct on the Abaqus software to calculate the maximum required shearing force for each scenario. Results of those simulations are collected and analyzed according to mechanic theories and oil field experience.

Furthermore, some recommendations are offered both in theoretical and practical aspects to build the criterion for the shear ability of a specific type of Blind Shearing Ram. Factors influencing shearing capabilities have been listed according to the result of the numerical simulation.
Maneuverability Towing Tank Experiments With Manifold Models: Part II — PMM Oscillation Tests
Authors: Guedes Danyllo de Lima , Kleine Felipe Augusto de Souza , de Castro Felipe Santos , Carvalho Daniel , Dozzi Dantas João Lucas
Published: September 2018

This work is the Part II of a two-part work, where the influence of geometrical simplifications and modifications in the maneuverability of a manifold were investigated by three 1:13 scaled models in a towing tank. In this work is presented the adopted methods that were used to obtain the hydrodynamic derivatives from forced oscillations motions in a towing tank using a planar-motion-mechanism. In the part I was presented the static drift tests, which were used to complement the tests presented in this paper. The maneuvering hydrodynamic derivatives are obtained by a two part analysis. First, the measured forces, moments and motions time series signals are filtered and decomposed in harmonic functions. Second, regression analysis techniques are applied to the amplitude of these harmonic functions in order to estimate the hydrodynamic derivatives. The results have showed that the simplification of the manifold geometry has a low influence in the hydrodynamic derivatives in contrast to the installation of a larger plate, which modified the manifold maneuverability significantly. The presented investigation in both papers will be used to form a data base for numerical simulation studies for manifolds installation.
Influence of Viscosity and Non-Linearities in Predicting Motions of a Wind Energy Offshore Platform in Regular Waves
Authors: del Águila Ferrandis José , Rodríguez Ricardo Zamora , Chryssostomidis Chryssostomos , Bonfiglio Luca
Published: September 2018

Motion prediction of floating bodies in waves represents one of the most challenging problems in naval hydrodynamics. The solution of the seakeeping problem involves the study of complex non-linear wave-body interactions that require large computational costs. For this reason, over the years many seakeeping models have been formulated in order to predict ship motions using simplified flow theories, usually based on potential flow theories solved within the linear assumption.

Neglecting viscous effects in the computation of radiation forces might largely underestimate the energy dissipated by the system while moving at the free surface. This problem is particularly relevant for unconventional floating bodies at resonance. In these operating conditions the linear assumption is no longer valid and conventional Boundary Element Methods, solved in the frequency domain, might predict unrealistic large responses if not corrected with empirical damping coefficients.

The application considered in this study is an offshore platform to be operated in a wind farm requiring operability even in extreme meteorological conditions. In this paper, we compare heave and pitch Response Amplitude Operators, predicted for an offshore platform using three different seakeeping models of increasing complexity; namely a frequency-domain BEM, a high-order BEM solved in time-domain and a non-linear fully viscous model based on the solution of the Unsteady Reynolds Averaged Navier-Stokes equations (URANS). Results are critically compared in terms of accuracy, applicability and computational costs.
Comparing Fracture Toughness Transition Curves for Girth Welds in X70 Pipe
Authors: Mohr William , McGaughy Tom
Published: September 2018

Most materials for offshore applications are tested for brittle fracture resistance at a single temperature related to the minimum design temperature and by a single fracture test method. It is much rarer to perform tests at multiple temperatures to compare the fracture performance across a range of temperatures and testing methods. EWI recently compared the fracture toughness transition behaviors for an X70 steel pipe across Charpy V-notch (CVN), single-edge notched bending (SENB) crack-tip open displacement (CTOD), and single-edge notched tension (SENT) CTOD test geometries. This showed variability of the material behavior better described by the inhomogeneous behavior models considered for welded joints. It also suggested the possibility that near the ductile-to-brittle transition temperature, the toughness under SENT CTOD may be higher than for SENB CTOD testing where the failure mode is brittle fracture.

The testing methods used full-size CVN and nearly full-thickness CTOD specimens in bending, as limited by the pipe curvature of the 219-mm diameter pipe with 35.4-mm wall thickness. The SENT CTOD specimens were pre-cracked in bending with the same dimensions as the SENB specimens, but are then cut down to place the pre-cracked crack tip at approximately one quarter of the thickness through the resulting specimen. This modification places the tip in the higher constraint region for the tension test.

Girth welds in the same X70 pipe were prepared using a pulsed GMAW process with ER80S-D2 welding wire. Similar testing was performed with weld centerline notches for the CVN and CTOD specimens. The transition behavior was related between the three testing methods for the weld centerline at the mid-wall of the pipe thickness.

Using representative values equivalent to the minimum of three tests, the SENT values were 4.8 to 4.9 times the values for the SENB tests.
Proof of Concept of a Novel Hybrid Wind-Wave Energy Converter
Authors: Perez-Collazo Carlos , Greaves Deborah , Iglesias Gregorio
Published: September 2018

In a global scenario of climate change and raising threats to the marine environment, a sustainable exploitation of offshore wind and wave energy resources is not only crucial for the consolidation of both industries, but also to provide a reliable and accessible source of renewable energy. In this context, and with the shared challenge for both industries to reduce costs, the combination of wind and wave technologies has emerged. In particular, this research deals with a novel hybrid system that integrates an oscillating water column, wave energy converter, with an offshore wind turbine substructure. In this paper, the novel hybrid wind-wave energy converter is studied in a three steps process. First, assessing a preliminary concept by means of a concept development methodology for hybrid wind-wave energy converters. Secondly, an OWC WEC sub-system is defined, on the basis of the results from the first step. Finally, the proof of concept of the WEC sub-system is carried out by means of a physical modelling test campaign at the University of Plymouth’s COAST laboratory.
Evaluation of Existing Semi-Empirical Models of Scour at a Submarine System
Authors: Rego Valeria S. , Santos Claudia M. P. M.
Published: September 2018

Assessment of scour below pipelines and gravity based structures in a submarine system is revisited with evaluation of data from two inspections and results for semi-empirical simplified models. Usually semi-empirical models are based on small scale experimental data that normally consider uniform and noncohesive sediments and have been questioned as to their practical applications. Recent local metocean data is used to revisit predictions of onset of scour and scour depth for the system, which are compared to survey statistics.
Numerical Analysis on Hydraulic Power Take-Off for Wave Energy Converter and Power Smoothing Methods
Authors: Yu Yi-Hsiang , Tom Nathan , Jenne Dale
Published: September 2018

One of the primary challenges for wave energy converter (WEC) systems is the fluctuating nature of wave resources, which require the WEC components to be designed to handle loads (i.e., torques, forces, and powers) that are many times greater than the average load. This approach requires a much greater power take-off (PTO) capacity than the average power output and indicates a higher cost for the PTO. Moreover, additional design requirements, such as battery storage, are needed, particularly for practical electrical grid connection, and can be a problem for sensitive equipment (e.g., radar, computing devices, and sensors). Therefore, it is essential to investigate potential methodologies to reduce the overall power fluctuation while trying to optimize the power output from WECs. In this study, a detailed hydraulic PTO model was developed and coupled with a time-domain hydrodynamics model (WEC-Sim) to evaluate the PTO efficiency for WECs and the trade-off between power output and fluctuation using different power smoothing methods, including energy storage, pressure relief mechanism, and a power-based setpoint control method. The study also revealed that the maximum power fluctuation for WECs can be significantly reduced by one order of magnitude when these power smoothing methods are applied.
Prediction of Extreme Wave Slamming Loads on a Fixed Platform
Authors: Filip Grzegorz P. , Xu Wenzhe , Maki Kevin J.
Published: September 2018

Design of offshore oil platforms requires accurate prediction of the maximum wave loads due to slamming on horizontal decks. The physical processes that influence the load are the propagation of irregular short-crested wind-driven storm seas, wave breaking, and wave-structure interaction. Furthermore, the ocean is a stochastic environment, so the load and its maximum can be considered as random variables. Ideally, the designer would like to know not only the most probable extreme load, but also the extreme load distribution.

In this paper we will use a novel technique to prescribe wave environments that lead to extreme responses so that high-fidelity simulations of the highly-nonlinear process can be investigated in detail. Specifically, the dynamics of the relative motion of the sea surface and the platform will be assumed via the selection of a sea spectrum, and the extreme-value probability distribution function (PDF) will be calculated for a given exposure window. The novel aspect of the work is in the way that a set of deterministic sea environments will be generated that are amenable for simulation with a state-of-the-art computational-fluid dynamics (CFD) software. The resulting wave environments will be simulated to estimate the extreme-value PDF.
Analysis of Hydrophobic Painting in Model-Scale Marine Propeller
Authors: Katsuno Eduardo Tadashi , Dozzi Dantas Joao Lucas , Nelli Silva Emilio Carlos
Published: September 2018

This paper aims to perform a numerical analysis of application effects of a superhydrophobic paint by completely coating the blades of a model-scale marine propeller in order to make it a superhydrophobic surface (SHS). First, a two-dimensional study was conducted. Two foils were analyzed for several hydrophobic conditions, varying the slip length. Pressure and skin friction distributions were shown. There is an increase of lift-to-drag ratio with hydrophobicity, but followed by an increase in suction pressure. In three-dimensional case, a propeller was simulated for several hydrophobic conditions, comparing thrust, torque and efficiency coefficients and pressure and friction distribution. Results with propeller showed that an increase in slip length is not always followed by an increase in efficiency, with an apparent efficiency gain limit. For the imposed simulation conditions, from the limit of gain, efficiency no longer increases with hydrophobicity, but its area of low pressure continues to grow.
A Surrogate Modeling Approach for Fatigue Damage Assessment of Floating Wind Turbines
Authors: Müller Kolja , Cheng Po Wen
Published: September 2018

Fatigue analysis for floating wind turbines poses a novel challenge to calculation workflows if a probabilistic load environment is to be considered. The increased complexity of the structure itself as well as its interaction with the environment require a coupled and more detailed analysis with respect to resolution of environmental conditions compared to fixed bottom systems.

Different approaches to address the computing challenge for floating turbines are possible to support engineering judgement and have been investigated in the past, with conservative binning on the one end of the accuracy scale and computation intensive Monte Carlo simulations on the other end. This study investigates the feasibility of regression based surrogate models based on radial basis functions. The investigation performed here is aligned with work performed in the H2020 project LIFES50+. Consequently, the considered system is the DTU 10MW Reference Wind Turbine installed on the LIFES50+ OO-Star Wind Floater Semi 10MW. The site under investigation is the LIFES50+ Site B (Gulf of Maine) medium severity representative site.

Results show a similar convergence of lifetime fatigue load prediction as with Monte Carlo simulations indicating that this technique may be an alternative if a response model of the considered system is of interest. This may be interesting if damage loading is to be calculated at a different site and if a classification of met-ocean conditions is available.
Improved Design of Multi-Rotor Tidal Energy Converters
Authors: de la Portilla Marina Pérez , Piñeiro Amable López , Núñez Rivas Luis Ramón , Guerra Enrique Tremps
Published: September 2018

There is currently an increasing interest in developing devices that can be used to exploit renewable energy in general and marine renewable energy in particular. Several sources of energy can be obtained from oceans, such as the energy produced by waves, tides, oceanic currents or thermal gradients, etc. It is important to stress that one of the most predictable sources of renewable energy is that derived from tidal and marine currents.

Several manufactures are developing devices with which to harness energy from ocean currents, and there is an extended trend towards the development of horizontal axis rotor turbines (HAT-TEC). There is, however, also a considerable amount of debate regarding both the use of fixed or controllable pitch rotors and the use of one or several rotors per device.

The decisions made in this respect have a great effect on the behaviour of the devices and the viability of the park as regards whether or not it will be technically and economically feasible. It is, therefore, necessary to be able to compare models and tools in order to design and choose the best and most feasible option. The tools most commonly used for metric comparison are: LCOE (Levelized Cost Of Energy), TRL (Technology Readiness Level) and TLP (Technology Performance Level).

This paper presents a formal procedure with which to compare various alternatives: On the one hand, previous results obtained by the GITERM-UPM Research Group as regards mono-rotor and multi-rotor fixed-pitch devices will be shown, together with their general characteristics. The possibilities of controlling them, which is achieved with the group’s own design of a ballast control system that is employed to carry out automatic emersion and immersion maneuvers to reduce the high economic cost of maintenance tasks and repairs, will also be explained.

On the other hand, the challenges involved in improving the design of the multi rotor will be listed, including the increase in the power of the rotor, the simplification of the structure, the improvement of the ability to control the device, etc. A new design for a multi-rotor device will also be presented, which takes advantage of the strengths of previous models and manages to substantially improve the amount of annual energy produced. This new device uses controllable pitch rotors, and its size and the amount of power produced by each generator have been improved.

Finally, an economic comparison is carried out by means of a series of cost-benefit indicators, and a formal procedure with which to compare their benefits through the use of LCOE is also proposed.
Real-Time Parameter Estimation of Nonlinear Vessel Steering Model Using Support Vector Machine
Authors: Xu Haitong , Hassani Vahid , Hinostroza M. A. , Guedes Soares C.
Published: September 2018

The Least-square support vector machine (LS-SVM) is used to estimate the dynamic parameters of a nonlinear marine vessel steering model in real-time. First, manoeuvring tests are carried out based on a scaled free-running ship model. The parameters are estimated using standard LS-SVM and compared with the theoretical solutions. Then, an online version, a sequential least square support vector machine, is derived and used to estimate the parameters of vessel steering in real-time. The results are compared with the values estimated by standard LS-SVM with batched training data. By comparison, sequential least square support vector machine can dynamically estimate the parameters successfully, and it can be used for designing a dynamic model-based controller of marine vessels.
Cement Hydration in the Presence of Nano Magnesium Oxides With Controlled Reactivity
Authors: Jafariesfad Narjes , Skalle Pål , Geiker Mette R.
Published: September 2018

In order to effectively compensate for bulk shrinkage of cement systems, the reaction of expansive additives must be regulated taking into account the development of cement hydration. In this study, nano-MgO particles (NM) with controlled reactivity were added to a cement system. The reactivity of NM was regulated via heat-treatment and the cement systems were investigated using isothermal calorimetry. Our results showed that increase in heat-treatment temperature resulted in coarsening of the NM and retardation of the NM reaction. We demonstrated that the addition of NM, heat-treated at low temperature, to a cement system caused significant reduction in the induction period compared to the reference system without NM. Controlling the reactivity of NMs might be a promising method in designing zero-shrinkage cement systems.
Risks to Marine Pipelines From Drifting Ice: Gathering the Evidence
Authors: Barrette Paul , McGonigal David , Pike Kenton
Published: September 2018

Marine pipelines in ice-prone waters are exposed to a number of environmental threats that do not exist in warmer waters. Of particular concern is the damage from ice features such as pressure ridges that drift into shallow areas. The ice keel comes in contact with the seabed and, as the ice feature keeps drifting, it may gouge the seabed to some depth and for considerable distances. Trenching and burial are seen as the best means of protecting these structures, but adequate depth relies on adequate knowledge of these events. This is obtained in various ways. Actual, real-scale events provide valuable information. Seabed mapping allows an appreciation of gouging activity in the target sector. Physical experiments can generate a nearly complete picture of these events, and can be used to validate numerical models. A description is presented of an abandoned marine pipeline in Northern Canada, which represents a rare test case scenario. Plans to conduct field investigations on that pipeline are being considered.
A 3D Coupled Fluid-Flexible Multibody Solver for Offshore Vessel-Riser System
Authors: Joshi V. , Gurugubelli P. S. , Law Y. Z. , Jaiman R. K. , Adaikalaraj P. F. B.
Published: September 2018

Precise position and motion control of offshore vessels is often challenging, especially in harsh environment due to highly nonlinear dynamic loads from free-surface ocean waves and currents. In addition, coupled nonlinear effects of risers and mooring cables connected to the vessel can lead to unexpected responses, thus justifying the significance of modeling these nonlinear coupled effects for safer and cost-effective design and operation of offshore structures. In this study, a fully coupled multi-field fluid-structure-interaction (FSI) solver is developed to simulate the wave- and flow-induced vibration of the flexible multibody system with constraints (viz., vessel-riser system) in a turbulent flow. The structural domain with multibody systems is solved using nonlinear co-rotational finite element method, whereas the fluid domain is solved using Petrov-Galerkin finite element method for moving boundary Navier-Stokes solutions. A partitioned iterative scheme based on non-linear interface force corrections is employed for coupling of the turbulent fluid-flexible multibody system with nonmatching interface meshes. Delayed Detached Eddy Simulation (DDES) via the Positivity Preserving Variational (PPV) method is employed for modeling turbulence effects at high Reynolds number. The free-surface ocean waves are modeled by the Allen-Cahn based phase-field method. We address two key challenges in the present variational coupled formulation. Firstly, the coupling of the incompressible turbulent flow with a system of nonlinear elastic bodies described in a co-rotated frame. Secondly, the two-phase coupling based on the phase-field approach to model the air-water interface. We then present the dynamics of coupled vessel-riser system studied in harsh environmental conditions with a view of developing a robust station keeping system. The proposed fully-integrated methodology based on the first principles of variational continuum mechanics removes many assumptions and empirically assigned parameters (e.g. drag and inertia coefficients) for modeling the surrounding fluid flow at high Reynolds number.
Propagation of Steep and Breaking Short-Crested Waves: A Comparison of CFD Codes
Authors: Lande Øystein , Johannessen Thomas Berge
Published: September 2018

Using the computational fluid domain for propagation of ocean waves have become an important tool for the calculation of highly nonlinear wave loading on offshore structures such as run-up, wave slamming and non-linear breaking wave kinematics.

At present, there are many computational fluid dynamics (CFD) codes available which can be employed to calculate water wave propagation and wave induced loading on structures. For practical reasons, however, the use of these codes is often limited to the propagation of regular uni-directional waves initiated very close to the structure, or to investigating the properties and loading due to measured waves by fitting a numerical wave to a measured wave profile.

The present paper focuses on the propagation of steep irregular and short crested wave groups up to the point of breaking. Indeed, this is challenging because of the highly nonlinear behavior of irregular wave groups as steepness increases and they approach the point of breaking. The complexity further increases with the introduction of short-crestedness requiring computation in a large 3-dimentional domain.

Two CFD codes are used in this comparison study which are believed to be well conditioned for wave propagation, the commercial code ComFLOW (available through the ComFLOW JIP project) and the open-source code BASILISK. The primary objective of this paper to show the two CFD codes capability of recreating measured irregular wave groups, using the known linear wave components from the model test as input to fluid domain. Wave elevation is measured at several locations in the close vicinity of the focus point. The comparison is carried out for a selection of events with variation in steepness, wave spreading and wave spectrum.
Optimization of the Structural Performance for Corrugated Blast Panels on Offshore Platforms
Authors: Voorde John Vande , Van den Abeele Filip , Cooreman Steven
Published: September 2018

Blast panels are integral structures in offshore topside modules to protect personnel and safety critical equipment by preventing the escalation of events due to hydrocarbon explosions. As such, blast panels are expected to retain their integrity against any blast loading and subsequent hydrocarbon fire. Most of the blast panels currently installed in offshore structures have been designed using simplified calculation approaches such as the Single Degree of Freedom (SDOF) models, as recommended by offshore design codes and industry recommended practices.

In this paper, the Non-Linear Finite Element Analysis (NLFEA) technique is used to simulate the structural response of corrugated panels subjected to blast loading. Detailed numerical analyses allow identifying the limits of the SDOF approach, and exploring different design options to optimize the structural response of corrugated blast panels.

The blast load profile corresponding to an explosion is one of the most important factors to consider in the structural analysis. The mechanism of hydrocarbon explosions is very complex, and the corresponding blast load profile intimately depends on the type of explosion, the congestion and the structural confinement. A sensitivity analysis is performed to investigate the influence of the blast pulse shape, and in particular to evaluate the effect of the maximum peak pressure and the exposure time.

To explore the benefits of introducing higher strength steels in demanding offshore applications, pressure-impulse diagrams have been derived for different high strength steel grades. In our analysis, (ultra)high strength cut-to-length plates from hot rolled coil are proposed to optimize the design of the blast panel whilst preserving the structural performance under demanding load conditions.
Real-Time Wellhead Bending Moment Measurement Using Motion Reference Unit (MRU) Sensors and Machine Learning
Authors: Srikonda Rohit , Haakonsen Rune , Russo Massimiliano , Periyasamy Peri
Published: September 2018

In order to facilitate real-time monitoring of accumulated wellhead fatigue damage, it is necessary to measure the wellhead bending moment in real-time. This paper presents a novel method to estimate the wellhead bending moment in realtime using acceleration and inclination data from the motion reference unit (MRU) sensors installed on BOP and LRJ, riser tension data and a trained neural network model. The method proposed in this paper is designed with a Recursive Neural Network (RNN) model to be trained to estimate the wellhead bending moment in real-time with high accuracy based on motion MRU sensor data and riser tension time series of a few previous cycles. In addition to the power of modeling complex nonlinearities, RNNs provide the advantage of better capturing the dynamic effects by learning to recognize the patterns in the sensor data and riser tension time series.

The RNN model is trained using virtual sensor data and wellhead bending moment from a finite element (FE) model of the drilling riser subjected to irregular wave time domain analyses based on a training matrix with limited number of significant height (Hs) and peak period (Tp) combinations. Once trained, tested and deployed, the RNN model can make real-time estimation of the wellhead bending moment based on MRU sensor data and riser tension time series. The RNN model can be an efficient and accurate alternative to a physical model based on the indirect method for real-time calculation of wellhead bending moment using real-time sensor data. A case study is presented to explain the training procedures for the RNN model. A set of test cases that are not included in the training dataset are used to demonstrate the accuracy of the RNN model using Root Mean Squared Error (RMSE), Normalized Root Mean Squared Error (NRMSE) and coefficient of determination (R2) as a metrics.
On Technologies for Shale Barrier Evaluation in the North Sea
Authors: Strand Geir-Ove
Published: September 2018

Cement evaluation tools have been used in the oil industry for decades to examine the integrity of cement bonding to the well casing and openhole. It has been suggested that such tools also can be used to verify the presence of a crept shale formation that has formed a barrier outside the casing. However, the ability of these tools to help determine an acceptable leakage risk level, which results from sufficient hydraulic isolation outside and between casing remain a subject of dispute from experiences in the industry. In this paper we present results from ongoing research that may help contribute to resolving this dispute. The research objective is to design and build a ’shale as barrier’ reference calibration cell. The reference cell is to be designed and made accessible to existing and emerging annulus barrier evaluation methods. The purpose is to help increase the quality of decisions made from such barrier evaluation technologies in an explicit well plug and abandonment context. The technical complexity of dispute coupled to the voice of business and stakeholder interests have been identified as a factor that could make project execution challenging. As result, a method to assist the execution of the project has been developed to systematically assure necessary stakeholder and end-user involvement. In this paper we present the method and demonstrate its application as an useful basis for project decision making and documentation. The method focuses on the capture and treatment of stakeholder preference elicitation, which is framed by traditional stages defined in the reference cell development process by adopting the concept of quality function deployment.
Suppression of Vortex Shedding With Rotating Wake-Control Cylinders: Numerical Investigation at a Moderate Reynolds Number
Authors: Assi Gustavo R. S. , Orselli Reinaldo M. , Silva-Ortega Mariana
Published: September 2018

This paper presents an investigation of the suppression of vortex shedding of a larger circular cylinder by the interference of smaller rotating wake-control cylinders positioned around its center. Three-dimensional numerical simulations have been conducted at a moderate Reynolds number of 10,000, thus complementing the previous experimental results by offering a better understanding of the physical mechanisms behind the suppression. Visualization of the vortex wakes revealed a complex disruption of the vortex tubes for the higher rotation speeds, with consequent reduction in the mean drag of almost 52% when compared with that of a bare cylinder. Fluctuating lift has also been drastically reduced in 90%. Configurations of control cylinder that can suppress vortex shedding may produce more efficient suppressors for flow-induced vibrations.
Impact of Sampling Variability on Sea Surface Characteristics of Nonlinear Waves
Authors: Bitner-Gregersen Elzbieta M. , Gramstad Odin
Published: September 2018

The restricted duration of wave records, usually 20 or 30 minutes, introduces sampling variability, the statistical uncertainty due to limited number of observations, in estimates of sea surface characteristics. This uncertainty may have significant impact on derived wave parameters commonly used in design and marine operations, and quantifying it is also of importance for wave forecasting purposes as well as for investigations of extreme wave events such as rogue waves. The study shows, using numerical simulations, effects of sampling variability on the measures of wave field nonlinearity, the skewness and kurtosis coefficients of sea surface elevation, and on the wave crest. Wave data are simulated by the nonlinear wave model HOSM (Higher Order Spectral Method). The Pierson-Moskowitz and the JONSWAP spectrum with different gamma parameters and different directional energy spreading functions are used in the analysis and their effect on sampling variability estimates is demonstrated. Sea states where rogue waves were recorded in nature are considered. The results are compared with the ones obtained from linear wave model simulations. Consequences of sampling variability on description of sea surface nonlinearity are discussed.
A Summary of the Recent Work at NTNU on Marine Operations Related to Installation of Offshore Wind Turbines
Authors: Gao Zhen , Verma Amrit , Zhao Yuna , Jiang Zhiyu , Ren Zhengru
Published: September 2018

In this paper, a summary of the recent work at NTNU on the installation of offshore wind turbines using jack-up and floating vessels will be reported. The wind turbine components considered here are the monopile foundations and the blades. The detailed discussions are given to the crane operations for installing wind turbine blades as well as novel installation methods for pre-assembled rotor-nacelle-tower. It includes numerical modelling and analysis for global dynamic responses of the installation system (installation vessels plus wind turbines) and for local structural responses of the blades in case of contact/impact. In particular, the stochastic nature of the environmental conditions (mainly wind and waves) and their influence on the global dynamic responses of the installation system will be assessed based on time-domain simulations. In addition, tugger line tension control is introduced for the final connection to the hub in order to reduce the motions of the blade and therefore the potential damages to the blades. It is then followed by a discussion about nonlinear structural analysis of the blade in contact with tower or surrounding structures using ABAQUS. Damages in the composite plies and sandwich core materials of the blade due to contact/impact for a given initial velocity are then estimated. The obtained damage distribution formulates the basis for a probabilistic assessment of structural safety during installation. Novel installation methods in which the rotor-nacelle-tower structure is pre-assembled onshore and installed on top of the foundation offshore, and the corresponding installation vessels are discussed at the end of the paper. Finally, the main conclusions and the recommendations for future work are drawn.
The Application of Extreme Value Calculation Model Based on Deductive Method in South China Sea
Authors: Botao Xie , Xuhe Ren , Jiagang Li , Bigui Huang
Published: September 2018

The marine environmental conditions of typhoon affected area in South China Sea (SCS) in China are complicated. The parameters of wind, wave and current speed of different return period are the basis of the selection of oilfield project and the important role of development cost evaluation. Based on the deduction method of API specification, the design criteria of the typhoon in SCS oil and gas regions with the two-layer nested model combined with typhoon numerical model is proposed in this paper. The statistical analysis of typhoon characteristics were presented, then wind speed of all the blocks in north part of SCS induced by typhoon with long return period was calculated. The prediction accuracy of the design parameters of long return period is improved by this model.
A Novel Deep Learning Method for the Predictions of Current Forces on Bluff Bodies
Authors: Miyanawala T. P. , Jaiman Rajeev K.
Published: September 2018

Unsteady separated flow behind a bluff body causes fluctuating drag and transverse forces on the body, which is of great significance in many offshore and marine engineering applications. While physical experimental and computational techniques provide valuable physics insight, they are generally time-consuming and expensive for design space exploration and flow control of such practical scenarios. We present an efficient Convolutional Neural Network (CNN) based deep-learning technique to predict the unsteady fluid forces for different bluff body shapes. The discrete convolution process with a non-linear rectification is employed to approximate the mapping between the bluff-body shape and the fluid forces. The deep neural network is fed by the Euclidean distance function as the input and the target data generated by the full-order Navier-Stokes computations for primitive bluff body shapes. The convolutional networks are iteratively trained using a stochastic gradient descent method to predict the fluid force coefficients of different geometries and the results are compared with the full-order computations. We have extended this CNN-based technique to predict the variation of force coefficients with the Reynolds number as well. Within the error threshold, the predictions based on our deep convolutional network have a speed-up nearly three orders of magnitude compared to the full-order results and consumes an insignificant fraction of computational resources. The deep CNN-based model can predict the hydrodynamic coefficients required for the well-known Lighthill’s force decomposition in almost real time which is extremely advantageous for offshore applications. Overall, the proposed CNN-based approximation procedure has a profound impact on the parametric design of bluff bodies and the feedback control of separated flows.
Workflow for Oil Recovery Design by Polymer Flooding
Authors: Ferreira Vitor Hugo de Sousa , Moreno Rosangela B. Z. L.
Published: September 2018

Polymer flooding dates from the 1960s. Early applications targeted onshore medium-to-heavy oils up to 100 cP, with limited reservoir temperature and water formation salinity. The number of implemented polymer flooding projects followed oil prices. Since its early days, polymer flooding had overcome many technical obstacles. Advances in polymer manufacturing technology, cost reduction and the use of horizontal wells have pushed polymer flooding as a feasible EOR method. A better understanding of the physical phenomena associated with polymer flow through porous media and technology advancement have extended polymer flooding applications to more viscous oil, higher salinity, and temperature level, as well as to offshore prospects. Meaningful advantages of polymer flooding over conventional methods are consolidated in the literature, such as oil recovery anticipation, incremental oil recovery and reduced volumes of injected and produced water to reach a target recovery factor. Despite all technological advances, polymer flooding needs to be tailored for the specific conditions of the target reservoir. Collect and integrate laboratory, simulation, and field information are essential for a successful polymer flooding application. This paper aims to correlate critical information to the various stages necessary for polymer flooding evaluation and production forecast. First, successfully implemented field cases allow the establishment of ranges for the method application. Once the applicability of polymer flooding is certified, the polymer solution to be injected is designed according to the reservoir characteristics and target conditions. Laboratory tests are performed to determine phase mobilities, polymer retention, and polymer degradation. These parameters are assessed through different experiments, and normalized variables provide data integration. Once the required parameters are determined, it is possible to build a base simulation model. History matching this base model to the laboratory data certifies its validity. An upsized analysis of this model is required to include some degradation phenomena. The 1D laboratory model is extended to a 3D model that incorporates permo-porosity distributions to analyze well characteristics in their radius of influence. The final step is large scale simulation and production forecast. Data integration along each stage and among then all allow the tailoring of the polymer flooding to EOR. The use of normalized parameters to evaluate the results is useful for analysis at different scales, from the laboratory to the reservoir. The proposed workflow can contribute to the design, planning, evaluation, and implementation of polymer flooding in a target field.
Fully-Coupled Aero-Hydrodynamic Simulation of Floating Offshore Wind Turbines by Different Simulation Methods
Authors: Cheng Ping , Wan Decheng
Published: September 2018

To accurately predict the critical loads due to wind and wave is one of the common challenges in designing a floating offshore wind turbine (FOWT). The fully-coupled aero-hydrodynamic simulation of a floating offshore wind turbine, the NREL-5MW baseline wind turbine mounted on a semi-submersible floating platform, is conducted with two methods. Firstly, the in-house code naoe-FOAM-os-SJTU, which is developed on the open source platform OpenFOAM and coupled with the overset grid technique, is employed for the directly CFD computations. And another in-house code FOWT-UALM-SJTU developed by coupling the unsteady actuator line model (UALM) with naoe-FOAM-SJTU is also utilized for coupling simulations. In both models, the three-dimensional Reynolds Averaged Navier-Stokes (RANS) equations are solved with the turbulence model k-ω SST, and the Pressure-Implicit with Splitting of Operations (PISO) algorithm is applied to solve the pressure-velocity coupling equations.

Both two solvers provide reasonable results of main aerodynamic loads as well as the main hydrodynamic forces. The FOWT-UALM-SJTU solver achieves better computational efficiency by simplifying the blade structure as actuator line models, while the naoe-FOAM-os-SJTU solver provides more accurate detailed flow information near the turbine blades.
CFD Simulations of Helical Strakes Reducing Vortex Induced Motion of a Semi-Submersible
Authors: He Jiawei , Wan Decheng , Hu Zhiqiang
Published: September 2018

This paper describes a set of VIM CFD simulations for a semi-submersible with and without helical strakes. The numerical investigations are conducted under low Reynolds number (Re) using naoe-FOAM-SJTU, a solver developed based on the open source framework OpenFOAM. The self-developed six degree-of-freedom (6DoF) motion module and mooring system module are applied to model motions of semi-submersible and the constraint of mooring lines, respectively. To carry out the calculations, turbulence closure has been chosen the Shear Stress Transport (SST) based Delay Detached eddy simulation (DDES), which uses the RANS model inside the boundary region and LES model outside the boundary area. This allows a realistic simulation within the boundary region where the vortex shedding is taking place, while not using unnecessary amounts of computational power. The Vortex Induced Motion (VIM) of semi-submersible with and without helical strakes was compared against each other for different reduced velocities (Ur). The flow characteristics of the semi-submersible platform is studied based on the characteristics of vortex shedding. For different current incident angles, time histories, trajectories and vorticity of the semi-submersible at different reduced velocities are reported. The result shows our CFD solver naoe-FOAM-SJTU is applicable and reliable to study VIM of semi-submersibles.