bluuebunny/crossref_metadata_2025 huggingface dataset:
The Use of Dominance, Influence, Steadiness and Compliance (DISC) Personality Test in the Assessment of Accidents Likelihood on Offshore Drilling Operations
Authors: Morais Carlos Henrique Bittencourt , Barini Filho Ulrico , Martins Marcelo Ramos
Published: December 2020

Brazilian offshore drilling operations are carried out in a highly demanding and complex working environment. The geological characteristics of the most productive Brazilian reservoirs, located on the so-called Pre-Salt basin, actually implies for their exploration the overcoming of water depths greater than 1,500 meters and the construction of wells that can reach up to 7,000 meters of length. In such environment, human reliability plays a primordial role regarding safety issues. On the same token, in the field of risk analysis, the consideration of human behavior holds a unique position and its relevance for the consubstantiation of accidents is widely recognized throughout the literature. Nonetheless, a comprehensive way to model it is still an ongoing effort. In this challenge, human error, understood both as a success or a failure probability, provided the first base for the development of techniques capable to infer the outcome towards man machine interaction (MMI). Such stand point gave birth to a series of tools and methodologies, usually called as human reliability analysis (HRA) first generation tools. In an attempt to address the perceived deficiencies of the first-generation tools, the decade of the 1990’s saw the introduction of HRA models based on cognitive assumptions, naturally called HRA second-generation tools. On its turn, the cognitive modeling perspective has demanded the adoption of more sophisticated architectures that, ultimately, have been leading to the dynamically account of the cognitive process. In this context, the present work aims to contribute for this debate analyzing the use of the Dominance, Influence, Steadiness and Compliance (DISC) personality test in the assessment of accidents likelihood on offshore drilling operations in Brazil. By means of actual data collected during the years 2016 and 2017, the paper develops a qualitative discussion of the foreseen outcomes regarding accident proneness considering the working and the under-pressure profiles advocated on DISC.
Data-Based Approach to Optimizing the Ocean Wave Energy Carpet Using Deep Neural Network
Authors: Do Ninh Hai , Alam Mohammad-Reza
Published: December 2020

In this paper, we present the Neural Network-based Optimization Method, applied to optimizing the wave energy converter “wave carpet”. The proposed method can be applied to optimizing the computationally expensive objective function that other sequential optimization approaches fail to do. The results show that, in the simple case of single-frequency unidirectional incoming waves, this optimization method achieves the optimal carpet shape that can absorb 2.18 times more energy than the baseline circular shape, and in its best performance the neural network can optimize the carpet shape that absorbs 7 times more energy than the baseline, after being trained on a medium data set. Thus, the proposed method can be considered an effective approach to solving the optimization problems involving computationally expensive objective functions.
On the Use of Artificial Neural Networks for Estimating the Long-Term Mooring Lines Response Considering Wind Sea and Swell
Authors: Gonzalez Gabriel Mattos , de Siqueira Marcos Queija , Simão Marina Leivas , Videiro Paulo Maurício , Sagrilo Luis Volnei Sudati
Published: December 2020

Nowadays, artificial intelligence algorithms are regaining visibility mainly due to the increase in computational capability. Among those, artificial neural networks (ANN) are very useful for the regression of highly nonlinear phenomena, such as the dynamic response of offshore structures. Due to the escalating demand in the oil and gas industry, offshore fields have been explored in deeper waters, which leads to more severe environmental conditions. A reliable and efficient evaluation of the long-term response of mooring systems, a crucial element of floating offshore structures, is then imperative. The estimation of the mooring long-term response is usually obtained numerically through the convolution of the short-term responses, based on short-term stationary environmental conditions (typically 3-h). Each of these short-term responses is obtained through a time-domain dynamic structural analysis from which statistical parameters of interest are calculated, such as the mean of the tension maxima sample or the maxima frequency. Such analyses tend to be quite time-consuming and a reliable estimator of these short-term statistical parameters may be of great help. In this paper, an ANN is trained to predict the short-term extreme peak response statistical parameters. The used training datasets include the wave significant height and spectral peak period for both wind sea and swell waves, generated by Importance Sampling Monte Carlo Simulation (ISMCS) method. Fixed directions of wind sea and swell are considered. It is shown that the ANN successfully predicts the short-term response statistical parameters for both cases, which are later used for the evaluation of the long-term N-year mooring response.
Dynamic Response Comparison of Mono and Dual Submerged Floating Tunnels
Authors: Chung Woo Chul , Jin Chungkuk , Kim MooHyun
Published: December 2020

Submerged floating tunnel (SFT) concept has been studied by many researchers as an alternative of conventional or floating bridges, especially in the fjord or as a connection between island and land. One of the major challenges is large dynamic responses under extreme wave and earthquake excitations. In this regard, two different types of SFT, which are mono and dual SFTs, are suggested in this study, and the global performance of them is compared through tunnel-mooring fully-coupled time-domain numerical simulations. The tunnel and mooring lines are modeled by the lumped-mass-based line model. The Morison equation is utilized for hydrodynamic load estimations of the tunnel and mooring lines at their instantaneous positions. To check dynamic response of SFT under operating condition, 10-yr waves with the current are considered as an environmental condition. Dynamic responses, mooring tensions, and inertial and drag forces are systematically compared.
Evaluation of a Hybrid Representation to Model the Wind Turbine, Platform and Mooring Lines in the Analysis of Floating Offshore Wind Turbines
Authors: de Araújo Neto Elói Daniel , Mendez Rodriguez William Steven , Nogueira Correa Fabricio , de Souza Leite Pires de Lima Beatriz , Pinheiro Jacob Breno , Ortega Arturo
Published: December 2020

This work presents and evaluates a hybrid methodology for the analysis of FOWT, taking advantage of the SITUA-Prosim code developed by LAMCSO/COPPE/UFRJ, and the NREL FAST code. SITUA-Prosim has been originally developed for the coupled analysis of floating platforms for oil production. It fully couples a validated hydrodynamic model, which represents the hull motions, with a full nonlinear dynamic Finite-Element based structural model, which represents mooring lines and risers.

The first step of the methodology is to employ the FAST code to generate time-series of forces on the bottom of the tower. These forces are then applied as input for an analysis with the SITUA-Prosim code where the platform and mooring lines are fully coupled, the latter being represented by a full nonlinear dynamic FE model. This may be considered as a “hybrid” methodology since it uncouples the platform motion response from the forces from the wind turbine, but couples the platform motions with the nonlinear dynamic structural response of the mooring lines.

The methodology is applied to analyze the OC4 DeepCwind semisubmersible, taking different wind velocities, and evaluating the influence of the elastic behavior of the blades on the global motion and line tension responses. The results are compared with a standard procedure where the whole system is analyzed entirely by the FAST program.

Due to its simplification, this hybrid methodology can be employed for preliminary or intermediate design stages. The main goal of the studies presented here is to comprise an initial step toward a full integration between the Prosim and FAST programs. In future works a full coupling between the wind turbine forces and the platform motions will be implemented.
High Temperature Flowline Thermal Design Using Rotating Buoyancy Modules
Authors: Yu Shenkai , Chapman Tracey , Rich Sharon , Harbison Austin
Published: December 2020

A rotating buoyancy modules (RBM) system was developed as an improvement to the non-rotating buoyancy from the collaboration between a major oil company and Trelleborg Offshore. In this system, a finned external shell rotates around an inner core strapped to pipeline. The rotating buoyancy reduces berm build-up, decreases friction for pipe-soil interaction, and ensures the robustness of buckling mitigation for HPHT thermal design. In the contrast, for a non-rotating buoyancy module, seabed soil berms can build up after the initial flowline lateral movement which can limit further lateral movement. As result of berm build-up, the effectiveness of non-rotating buoyancy modules to control pipeline buckling reduces.

RBM was applied for the first time in a tie-back flowline for a Gulf of Mexico (GOM) deepwater development project. In this paper, flowline thermal design using RBM for the project is presented.

The project field conditions that impacted the tie-back flowline design included existing crossings and limited space for subsea structures and flowlines. The pipe-seabed interaction and RBM-seabed model is presented along with the axial and lateral friction parameters used for peak and large displacement on normal pipe sections and RBM sections. The main loads for the flowline were from the operational conditions in term of temperature and pressure profiles. Lateral buckling mitigation results include the RBM location configurations, buckling locations, effective axial forces and von Mises stresses. Recommendations for situations when RBM should be used for high temperature high pressure thermal design are presented.
Sensitivity Analysis in Parametric Rolling of a Modern Cruise Ship Using Numerical Simulations in 6-DOF
Authors: Düz Bülent
Published: December 2020

Parametric roll is a nonlinear phenomenon that can result in large roll angles coupled with significant pitch motions. These motions might induce large loads on the ship structure, and compromise the safety of the crew and the cargo. The severity of the motions might reach to such levels that capsizing might occur. In this study sensitivity analysis in parametric rolling of a modern cruise ship is investigated using numerical simulations. Several parameters were considered as sources of uncertainty such as the combined effect of GM and roll radius of gyration, roll damping, ship speed, and fin characteristics. In terms of fin characteristics, fin angle rate and maximum angle, fin area and aspect ratio, and fin gains were investigated. Additionally, the non-ergodicity of parametric roll was studied as well as the effect of simulation duration on the statistics of parametric roll. The simulations were carried out with a hybrid time-domain seakeeping and manoeuvring code. The time-domain code was used in combination with a strip-theory based frequency-domain program in order to calculate diffraction and radiation forces as well as added-mass. The time-domain code was able simulate the dynamic behavior of a steered ship in 6-DOF, where the motions can be large up to the moment of capsize.
Impact of a Wind Turbine Blade Pitch Rate on a Floating Wind Turbine During an Emergency Shutdown Operation
Authors: Louazel Pauline , Son Daewoong , Yu Bingbin
Published: December 2020

During the shutdown of a wind turbine, the turbine blades rotate from their typical operating angle to their typical idling angle (approximately 90 degrees) at a specific speed, called the blade pitch rate. This operation leads to rapid loss of thrust force on the turbine resulting in a corresponding heel response of the floating structure. This rapid variation of loads at the turbine also leads to large nacelle accelerations which are transferred to the bottom of the tower and consequently to the floating structure, making the turbine shutdowns, and specifically emergency shutdowns, of significance in the design and certification of the turbine, tower and floating structure.

In case of an emergency shutdown (for instance due to a grid loss), the blades typically pitch from 0 degree to 90 degrees in approximately 20–35 seconds, whereas this time period can be more than 100 seconds in the case of a normal shutdown [6]. For fixed-bottom wind turbines, increasing the blade pitch rate leads to an increase of instantaneous loads at the nacelle and tower, leading to the emergency shutdown pitch rate being usually chosen to be as low as possible. In the case of a floating wind turbine, however, water/platform interaction effects such as wave induced damping on the floating platform, challenge this approach. Indeed, increasing the blade pitch rate can increase the effect of wave-induced damping on the floater and therefore reduce the loads on the overall structure. On the other hand, reducing the blade pitch rate during an emergency shutdown can reduce this damping effect and increase those loads, meaning that an optimal blade pitch rate for a fixed bottom turbine is not necessarily optimal for a floating wind turbine.

This paper will examine the behavior of a floating offshore semi-submersible platform, the WindFloat, during turbine shutdown operations, with an emphasis on the blade pitch rate during an emergency shutdown.
Subsea Pipeline Engineering Challenges in Sand Wave Area: The Lufeng Feed Project
Authors: Jun Huang , Xing Zou , Liwei Li , Igland Ragnar Torvanger , Zhenhui Liu , Bijker Romke
Published: December 2020

Lufeng oilfields are located in the Pearl River Mouth Basin, South China Sea, where significant sand wave is located. The water depth of the area is 140 to 330 m. Sand waves are present around LF15-1. A study on the sand waves is required to assess the impact of the sand waves on the pipeline design. Due to its special seabed characteristic, it is challenging for the subsea pipeline engineering. This paper presents the Lufeng sand wave pipeline project on general basis. Collect and review available information including metocean, bathymetric data and soil data and carry out general morphological analysis for the project area including seabed erodibility assessment and analysis of sediment transport potential. Identify morphological features and bed forms in the project area and analyze characteristics of the sand waves. Sand wave migration and mobility are predicted and the pipeline route (least dredging/trenching and least free spans) is optimize considering on-bottom stability, in-place strength, global buckling and installation. Determine burial (dredging/trenching) requirements assuring pipeline stability/integrity. The main challenges faced are summarized, some preliminary results are also presented. Discussions about the solutions are also included, which may shed light to similar projects.
Prediction of Performance of Tip Loaded Propeller and its Induced Pressures on the Hull
Authors: Kim Seungnam , Kinnas Spyros A.
Published: December 2020

In this paper, a boundary element method (BEM) is applied to a tip loaded propeller (TLP) to predict its open water characteristics and induced hull pressures under fully-wetted and uniform inflow. Tip of a TLP blade has a winglet-like tip plate on the pressure side to improve the overall propeller efficiency over the traditional open tip propellers by preventing circulation loss toward the tip region. TLPs are also used to reduce the tip vortex strength and thus free from the trade off the propeller efficiency against the cavitation performance; therefore, predicting their performance early in the designing stage via numerical applications can provide the initial knowledge on the loading distributions and cavitation performance. In the present method, the trailing wake is first aligned using the full wake alignment (FWA) scheme by aligning the wake surface to the local stream in order to satisfy the force free condition. The FWA is shown to improve the open water characteristics of the TLPs compared to the simplified alignment scheme that ignores the details of the flow behind the trailing edge due to the simplicity of the method. Afterwards, a pressure-BEM solver is used to solve for the diffraction potentials on the hull and estimate the propeller-induced hull pressures. In this case, both the FWA and the unsteady wake alignment scheme (UWA), which considers the time dependency of the problem, produce the same results as the testing flow is assumed to be uniform. This paper briefly introduces the model TLP, proper ways to consider the viscous effect on the blade surface, wake alignment scheme, and the pressure-BEM solver. Then, the predicted open water characteristics of the benchmark TLP and its induced hull pressures are compared to the experimental data, as well as the results from unsteady full-blown Reynolds-Averaged Navier-Stokes simulations for validations of the numerical predictions.
Detailed Study on the Behavior of Ships in Very Short Waves
Authors: Yokota Saori , Kuroda Mariko , Fukasawa Ryohei , Ohba Hiroki , Tsujimoto Masaru
Published: December 2020

Considering the sea conditions in which a large ship encountered in operation, the ship’s behavior in very short waves is important. However, the evaluation of the ship performance in very short waves was not enough validated by tank tests. Because it is difficult to generate waves with enough accuracy due to the performance of the wave generator.

In this paper, it is shown that tank tests of added resistance in the regular waves including the very short waves are conducted in the Actual Sea Model Basin at National Maritime Research Institute, MPAT for DTC container ship and accurate results are obtained. The test results are compared with the benchmarks published by SHOPERA (Energy Efficient Safe SHip OPERAtion). In addition, three curves of the added resistance in the regular waves based on the results of the tank test are compared and the sensitivity analysis of energy efficiency is discussed. In the sensitivity analysis, the performance simulator for ships in actual seas (VESTA) is used, and a comparison is carried out for the fuel consumption calculated from the frequency response of each added resistance in waves. As a result, it is found that the tendency in added resistance in very short waves affects the fuel consumption and the decrease of ship speed.
A Coupled SPH-FEM Solver for Modeling Surface Effect Ship (SES) Bow Seal Dynamics
Authors: Gilbert John , McCue Leigh
Published: December 2020

The life of Surface Effect Ship (SES) bow and finger seals are often short-lived due to a combination of environmental effects and dynamic loading due to high-speed operation. Improving SES seal robustness requires a deeper understanding of the dynamics and loads seen by SES skirt seals during operation. In this work, we present the results of a validation study performed for a coupled, smoothed particle hydrodynamics (SPH) - finite element method (FEM) solver developed to study fluid-structure impact and free-surface flow interaction with hyper-elastic structures. This work continues and extends the earlier coupled SPH-FEM approach of Yang et al. [1]. Numerical predictions for skirt seal displacement are compared against the experimental observations of Zalek and Doctors performed by the Marine Hydrodynamics Laboratory at the University of Michigan [2].
A New Rigid Jumper VIV Response Model: JIP Development
Authors: Nair Aravind , Jaiswal Vivek , Fyrileiv Olav , Vedeld Knut , Zheng Haining , Huang Jerry , Tognarelli Michael , Goes Rafael , Bruschi Roberto , Bartolini Lorenzo , Vitali Luigino
Published: December 2020

Recognizing the need to address the challenges associated with the VIV assessment of rigid jumpers, a joint industry project (JIP) was launched in December 2014. The JIP was based on the model test data supplied by ExxonMobil. Through the JIP study, measured responses from tow tests were used to develop new response curves for jumper systems and compared against the existing DNV GL-RP-F105 curves.

This paper presents details of the validation of model test data; processing of test data for response curve development; classification and interpretation of jumper response and; the two new response models developed for VIV assessment of rigid jumper systems.

The response model developed through the Jumper VIV JIP forms the first of its kind for the VIV of non-straight (complex) pipe systems.
Experimental Investigation on Hydrodynamic Effectiveness of a Wave Energy Converter Using Floating Breakwater
Authors: Peng Wei , Ma Junwei
Published: December 2020

Wave energy is favored by more and more people because of its wide distribution, pollution-free, renewable and many other advantages. Among numerous wave energy converting devices, the converters using floating breakwaters are recognized to be quite promising as the construction and maintenance cost can be shared. In this study, a shoreline wave energy converter (WEC) is proposed which consists of a floating breakwater arranged along the wave direction and restricted to only have vertical degree of motion. Making use of the motion of breakwaters, a dynamo is able to convert the wave power to electricity. At the same time, the incoming waves can be attenuated due to the complex interaction between waves and the floating structure. A scale model was built in the laboratory at Hohai University, and then employed to investigate the performance of developed wave energy device. In the physical model, dynamos and resistance were employed as the power take-off (PTO) system, and the instantaneous output power could be calculated using the measured data. Experimental results show that the resonance state of float plays an important role for the wave energy extraction, and the hydrodynamic efficiency of the device under the resonance state can be up to 41.8% for single breakwater, counting in the internal energy converted by the dissipative force. When subjected to shorter waves, the PTO damping encourages the wave reflection; whereas, more wave energy is dissipated or transformed to power for longer waves. Meanwhile, the PTO damping is also a negative factor for the wave overtopping reduction as the motion of float may be restrained considerably. Last but not the least, the PTO load is proved to be a significant parameter for the optimization the output power, and a strategy must be found to achieve the best power conversion under the dominant wave conditions.
Gulf of Mexico Hurricane Single Event Fatigue Method for Riser Analysis
Authors: Mesa Jose D. , Santala Markku J.
Published: December 2020

Deepwater steel catenary risers (SCRs) are designed considering strength under extreme loads and long-term fatigue of the riser from installation through the full range of conditions anticipated over the service life of the riser. Short-term single event fatigue is also checked to ensure that a single extreme storm or current event does not consume an excessive amount of fatigue capacity. For Gulf of Mexico SCRs, single event fatigue can be a governing case for the riser hang-off. The requirement imposes a relatively modest number of higher stress range cycles and may bias the selection of the hang-off option (titanium, steel, and flex joints) since the three common choices have widely different sensitivity to this case.

Assessing a single event hurricane is problematic because the evolution of storms which generate an extreme 100-year significant wave height at a site can vary considerably from storm-to-storm. Simplistic representations of the extreme hurricane event could lead to either non-optimal hang-off option or a unconservative design. This study documents a response-based analysis simulating fatigue damage accumulated in differing risers over a broad set of extreme hurricanes. The extreme hurricanes are gathered from hundreds of years of hindcast storms to develop a statistical assessment of the amount of damage accumulated per event. Since the response-based analysis would be cumbersome in the design process, a simplified method benchmarked to the response-based analysis is proposed for design. The simplified method consists of accumulating fatigue damage from multiple seastate cases that are already developed to assess riser strength.
Coupling Response Analysis of Deep-Water Pipeline Based on Rapid Regulation of Stinger Radius
Authors: Ma Gang , Yang Jie , Wang Hongwei , Zhang Zizhao
Published: December 2020

High strain/stress is easy to occur in the overbend section of S-lay pipelines which are supported by stinger, leading to excessive deformation and buckling failure of the pipelines. In order to ensure the safety of pipelines and evaluate the maximum laying capacity of the pipelay vessel in 1600 meter, this paper uses the curvature radius method to automatically adjust the four angles and roller positions of the articulated stinger fixed on the pipelay vessel, then analyzes the pipeline strain and effective tension in static configuration and finally calculates the timedomain coupling response by establishing a nonlinear contact model of the pipelay vessel, stinger and pipelines. The adjustment speed, which is based on the curvature radius method using Python to call OrcFxAPI, is efficient remarkably. The results show that the stinger radius and roller locations are the major influential factors on the pipeline strain and anchor positions affect the detachment point strain of pipelines on overbend section. The static and dynamic strains of the overbend section are less than 0.25% and 0.305% respectively, which meet the DNV specifications.
Numerical Study of Large Pendulum Ice Impact Loads
Authors: Andrade Sthefano L. , Quinton Bruce W. T. , Daley Claude G. , Gagnon Robert E.
Published: December 2020

The large pendulum ice impact experiments performed at the Memorial University of Newfoundland recorded pressure distributions using a novel high-fidelity measurement device, the Impact Module, which is capable of fine spatial and temporal resolutions — effectively 2 cm2 at 500 Hz. These experiments achieved impact energies approaching 29 kJ, velocities of 4.7 m/s, and loads reaching 620 kN. The data obtained by the device are unique, as the Impact Module is capable of recording ice pressure data with both high spatial and high temporal resolution over a large contact area. Until recently, there was no ice load measurement technique capable of excelling in all these aspects. This work aims to study the simulation of a numerical test panel model under the action of the loads measured during the ice impact experiments. This is done by using a non-linear numerical model with explicit time integration capable of simulating the dynamic transient ice loads and comparing their effects to a quasi-static approach.
Analysis of a Floating Wave Energy Converter With Hydraulic-Mechanical Power Take-Off Using WEC-Sim and SIMSCAPE
Authors: Chandrasekaran Srinivasan , Sricharan V. V. S.
Published: December 2020

A novel multibody ‘self-reacting’ floating wave energy converter, which constitutes a set of ‘bean’ shape tubular floats which pitch relative to the central spar (CS) resulting in net heave, is introduced in the present study abbreviated as BFWEC. The frequency-domain modeling is performed assuming potential wave theory (PWT) to obtain the fundamental building blocks viz., hydrodynamic parameters of BFWEC. The unique configuration of BFWEC with a set of four floats around CS projects it to be a novel attribute. The relative motion between CS and floats is enabled using a connecting frame and the hinge joint to each bean float. Time-domain wave-WEC interactions, along with free-decay tests, are modeled and conducted using a highly established and reliable open source MATLAB-Simulink module called WEC-Sim (Wave Energy Converter SIMulator). The CS of six degrees BFWEC with a dominant heave degree is first restricted to be fixed and later enabled to three and six degrees of freedom (D-o-F) to understand the influence of its compliance. The device is restrained and kept in position by fastening four tethers (taut mooring) to the CS by coupling it to a lumped mass stand-alone mooring line feature known as MoorDyn. A hydraulic-mechanical Power take-off (PTO) unit is coupled with BFWEC in SIMSCAPE to understand its overall performance characteristics, which is later compared with linear damping virtual PTO. The performance ratio of the device is then obtained under 0° and 45° regular waves. The critical outcome of the research is to establish a robust green channel by promoting wave energy extraction in the sea states of the Indian sub-continent with a unique and suitable design.
On the Stability of Oil-Based Drilling Fluid: Effect of Oil-Water Ratio
Authors: Ofei Titus Ntow , Cheng Itung , Lund Bjørnar , Saasen Arild , Sangesland Sigbjørn
Published: December 2020

Drilling fluids are complex mixtures of natural and synthetic chemical compounds used to cool and lubricate the drill bit, clean the wellbore, carry drilled cuttings to the surface, control formation pressure, and improve the function of the drill string and tools in the hole. The two main types of drilling fluids are water-based and oil-based drilling fluids, where the oil-based also include synthetic-based drilling fluids.

Many rheological properties of drilling fluids are key parameters that must be controlled during design and operations. The base fluid properties are constructed by the interaction of the emulsified water droplets in combination with organophilic clay particles. The rheological properties resulted from this combination, along with the particle size distribution of weight materials are vital in controlling the physical stability of the microstructure in the drilling fluid. A weak fluid microstructure induces settling and sagging of weight material particles. The presence of sag has relatively often been the cause for gas kicks and oil-based drilling fluids are known to be more vulnerable for sag than water-based drilling fluids. Hence, the shear-dependent viscosity and elasticity of drilling fluids are central properties for the engineers to control the stability of weight material particles in suspension.

In this study, we examined the stability of typical oil-based drilling fluids made for North Sea oilfield drilling application with oil-water-ratios (OWR) of 80/20 and 60/40. The structural character of the fluid samples was analyzed both at rest and dynamic conditions via flow and viscosity curves, amplitude sweep, frequency sweep, and time-dependent oscillatory sweep tests using a rheometer with a measuring system applying a grooved bob at atmospheric conditions. A high precision density meter was used to measure the density of the drilling fluid samples before and after each test. The measurement criteria used to rank the fluids stability include the yield stress as measured from flow curves and oscillatory tests, flow transition index, mechanical storage stability index, and dynamic sag index.

We observed that between the two drilling fluids, the sample with OWR = 60/40 showed a stable dispersion with stronger network structure as evidenced by higher yield stress and flow transition index values, while the mechanical storage stability index and dynamic sag index recorded lower values. The results of this study enable drilling fluid engineers to design realistic oil-based drilling fluids with stable microstructure to mitigate settling and sagging of weight material particles for North Sea drilling operation.
Study on Applicability of FEMA Formula in Prediction of Impact Load by Tsunami Drifting Vessels on Coastal Zone Structures
Authors: Masuda Koichi , Ikoma Tomoki , Eto Hiroaki , Aida Yasuhiro , Murata Kazuki
Published: December 2020

In this study, we consider and evaluate the applicability of the FEMA’s formula which is one of the main simple formulas for calculating impact forces through the comparison with our proposed numerical simulation model. We investigated the situation of collision with a thin structure such as a pillar by numerical experiments based on the particle method, in particular, we focus on the case where the drifting speed is fast in targeting the quay of Shimizu Port, Shizuoka prefecture.

We compared the results of numerical experiments obtained by detailed simulations with FEMA’s formula and evaluated the applicable range of FEMA s formula for huge vessels.

As results, it was suggested that the overestimation was occurred with FEMA’s formula for large vessel using the inundation height and its velocity. FEMA’s formula calculates the impact force of large vessel on the safe side if the drifting vessel speed is used: the condition of added mass coefficient changes the results, but these indicate the safe side in this study. On the other hand, the results of safety sides are fluctuated depending on the height of the action point of force. Therefore, we confirmed that there is a need to examine the height of the impact point when using FEMA’s formula for large vessels.
Suction Pile Splash Zone Crossing Modelling
Authors: Pelerin Jean-Luc , Terribile David , Sergent Emmanuel , Fernandez Gerard
Published: December 2020

One of the critical phases that drive allowable seastates during suction pile installation is the splash zone crossing (SPZC). Offshore experience shows that anticipated loads and slack events are often over predicted, which directly affect installation vessel operability. If conservatism is required to prevent damaging installation assets, a better risk balance is required to avoid unnecessary asset stand-by. Despite the above, basin tests have shown that the peak load/slack criteria can also be under-estimated with the current methodology which may lead to a dangerous situation offshore.

Because the applicable methodology is regardless of the installation crane capacity (i.e. slack) and because it does not account for the entrapped water dynamics, it cannot accurately predict the loads on the crane. We present here a physics based model of the free surface inside the suction pile that provides the loads applied on the crane while crossing the splash zone. This allows mitigation to be incorporated from day-1 of design phase and avoid late change from installation contractor while pile are fabricated and increase their vessel operability in the meantime. The model accounts for the entrapped air compressibility, the air/water flow through the pile openings, the vessel motion and the surrounding wave field. The numerical implementation has been performed in Python and packaged as an Orcaflex module. Some of the model physical parameters such as the opening pressure drop coefficients have been derived with the help of CFD. The impact of the free surface on the pile top cap is modelled as a polynomial function of the impact velocity and the coefficients values have been derived using CFD. The model has been validated against model tests and compared to field measurements and observations.

The numerical results have shown good agreement with both model tests and offshore measurements at a qualitative level (the observed phenomenon are properly reproduced) and at a quantitative level. The application of the validated model to projects will allow broadening of the operating envelope and the optimization of the installation vessel planning by reducing the standby time.

This new methodology shows some high potential and could be applied to projects on a more regular basis.
From Soft Mooring System to Active Positioning in Laboratory Experiments
Authors: Sauder Thomas , Tahchiev Galin
Published: December 2020

This paper presents an active positioning system aimed at replacing the classical “passive” soft horizontal mooring system used in seakeeping tests of floating structures. We discuss the limitations of the passive approach, present the main components of the active system, and demonstrate its ability to reproduce results obtained with the passive system. We then show how the active system allow controlling the low-frequency damping applied to the floater. We conclude on the possibilities offered by this apparatus.
Basic Study on Positioning of Autonomous Underwater Vehicle Based on Acoustic Ranging From One Reference Device
Authors: Watanabe Yoshitaka
Published: December 2020

An autonomous underwater vehicle (AUV) equipped with some navigational devices, such as an inertial navigation system (INS), a Doppler velocity log (DVL), and a depth sensor. This integrated system is typical and accurate, however, have drift error in position output. Then an acoustic positioning, which is one of absolute positioning, is necessary to compensate the drift error. As acoustic positioning, ultra-short baseline (USBL) is frequently used, however, not accurate especially in deep water. Long baseline (LBL) is very accurate, however, spends much time to operate. In this paper, acoustic positioning method of AUV based on ranging from only one reference device is considered with simulations. One-way travel time (OWTT) is measured for ranging assuming use of chip scale atomic clock (CSAC). And the ranging signal is continuous and modulated direct sequence spread spectrum (DSSS). Ranging is executed at each symbol peak, then period of the ranging is very small. In process of the method, the drift error of position output of the INS is estimated with extended Kalman filter (EKF). Simulation with two models, constant-position-error, and constant-velocity-error models, were performed. The later was obviously unstable. Circular cruising track of the A UV makes the estimation more stable. Moreover, when the AUV cruises near the reference, the estimation is more stable. It may good that at final phase of descending of the AUV, the AUV cruises near the seabed and spirally, and the estimation process may be performed stably.
Turbulent Flow Simulation of Power-Law Fluid in Annular Channel
Authors: Gavrilov Andrey , Ignatenko Yaroslav , Bocharov Oleg , Aragall Roger
Published: December 2020

Transient three-dimensional flow simulations of power–law fluid in a long axisymmetric annular channel considering 0.5 diameter ratio were performed. An in–house CFD code considering URANS (Unsteady Reynolds Averaged Navier–Stokes), 2D RANS (steady-state axially uniform 2D RANS) and LES (Large Eddy Simulation) approaches were compared to perform the simulations. Flow structure was analyzed. Numerical experiments showed that rotation of the inner cylinder (drill pipe) leads to two effects: decrease of apparent viscosity in the region close to the rotating cylinder, thus decreasing viscous shear stresses; development of secondary vorticity structures increasing energy loss. First mechanism decreases pressure losses and dominates when Re < 300. At Re ∼ 300 the mechanisms compete with each other and pressure losses depends on power–law index n. At Re > 300 mechanism of second vortex structured dominates and increases pressure loss with rotation. Pressure losses for two-dimensional steady-state and three-dimensional transient problems were compared. Pressure losses using a two-dimensional approach can be underestimated by up to 30%.
Guidance Model Representing an Ice Field for Path-Planning in Ice Management
Authors: Bjørnø Jon , Marley Mathias , Skjetne Roger
Published: December 2020

In the work presented in this paper, the problem on how to represent a simplified ice field in a guidance model, enabling path and maneuver planning for IM operation, has been studied. The use of B-splines and other basis functions are considered to represent relevant guidance information over the 2D drifting ice field. A weight value is computed and updated at locations that represents broken ice (visited by an icebreaker) versus unbroken ice. The guidance model will ensure that there is a continuous representation of the state of the ice field during the operations. The drifting behavior of the ice field is incorporated into the guidance model. The model will be updated with new (solid) ice that is formed at the beginning of the ice field, and it will continuously be updated in the path where the icebreaker moves. To simulate the maneuvers of the icebreaker, a dynamic model is used, and the ice breaking effect where the ice field is continuously broken into smaller ice floes is included in the model. This representation of an ice field can be used in a path-planning algorithm to determine the icebreaker path in a moving ice environment in order to reduce the ice field into small enough ice floes and reduce the load on the protected structure.
Numerical Invertigation of Water Entry of a Subsea Module With Deflated Cavity Shells
Authors: Zan Yingfei , Guo Ruinan , Yuan Lihao , Huang Fuxiang , Kang Dongchun
Published: December 2020

In subsea installation operations, the hydrodynamic forces on the subsea module are important considerations when designing the structure and choosing slings. In this paper, the hydrodynamic forces and flow field of a subsea module with deflated cavity shells during forced water entry operation were investigated numerically. The numerical simulation was carried out based on Reynolds-averaged Navier–Stokes equations, with a constant lowering velocity of the module. The results of the numerical simulation were validated by experimental data and they showed good agreement. The relationship between hydrodynamic forces and draft was presented. Furthermore, the slamming positions, free surface variation, pressure variation in deflated cavity shells, slamming coefficient and the influence of holes were studied based on flow field scenes. It was found that the hydrodynamic forces varied with draft non-linearly. Moreover, the change of draft altered the form of the free surface due to the complex steel frame structure of deflated cavity shells. The present study can be further extended to assess the operating conditions of lifting operations and to advise on the design of the subsea module.
Offshore Drilling: Extending the Weather Window for Operations by Optimal Use of Simulations and Probabilistic Machine Learning
Authors: Eldevik Simen , Sætre Stian , Katla Erling , Aardal Andreas B.
Published: December 2020

Operators of offshore floating drilling units have limited time to decide on whether a drilling operation can continue as planned or if it needs to be postponed or aborted due to oncoming bad weather. With day-rates of several hundred thousand USD, small delays in the original schedule might amass to considerable costs. On the other hand, pushing the limits of the load capacity of the riser-stack and wellhead may compromise the integrity of the well itself, and such a failure is not an option.

Advanced simulation techniques may reduce uncertainty about how different weather scenarios influence the system’s integrity, and thus increase the acceptable weather window considerably. However, real-time simulations are often not feasible and the stochastic behavior of wave-loads make it difficult to simulate all relevant weather scenarios prior to the operation.

This paper outlines and demonstrates an approach which utilizes probabilistic machine learning techniques to effectively reduce uncertainty. More specifically we use Gaussian process regression to enable fast approximation of the relevant structural response from complex simulations. The probabilistic nature of the method adds the benefit of an estimated uncertainty in the prediction which can be utilized to optimize how the initial set of relevant simulation scenarios should be selected, and to predict real-time estimates of the utilization and its uncertainty when combined with current weather forecasts.

This enables operators to have an up-to-date forecast of the system’s utilization, as well as sufficient time to trigger additional scenario-specific simulation(s) to reduce the uncertainty of the current situation. As a result, it reduces unnecessary conservatism and gives clear decision support for critical situations.
Offshore Wind-Powered Oil and Gas Fields: A Preliminary Investigation of the Techno-Economic Viability for the Offshore Rio de Janeiro, Brazil
Authors: Shadman Milad , Estefen Segen F. , Nunes Kleber , Maali Amiri Mojtaba , Tavares Luiz Filipe , Rangel Priscilla , Assad Luiz Paulo
Published: December 2020

The electricity demand of offshore oil and gas platforms are traditionally supplied by gas turbines operating with natural gas extracted from the field or fossil fuels emitting CO2 and NOx. Offshore wind power is an interesting alternative to supply such a demand as it can be produced close to the oil and gas field and providing clean and renewable electricity. The objective of this research is to investigate, as a preliminary approach, the techno-economic viability of supplying electricity demand of an oil and gas field by a floating offshore wind farm. An oil and gas field locates in the southeast of the State of Rio de Janeiro, Brazil, with a distance of about 130 km from the shoreline, is selected as a case study. The wind resource at the local is obtained using in-situ measured data. Four wind turbines are studied and compared through their capacity factor and energy production. Afterward, four wind farms composing of the selected turbines are proposed based on the available wind energy and the field demand. The cost of energy produced by the wind farm is calculated, and the results are compared to the conventional method of the electricity supply.
Genetic Optimization of Shape and Control of Non-Linear Wave Energy Converters
Authors: Song Jiajun , Abdelkhalik Ossama , Zou Shangyan
Published: December 2020

This paper presents an optimization approach to design ax-isymmetric wave energy converters (WECs) based on a nonlinear hydrodynamic model. This paper shows optimal nonlinear shapes of buoy can be generated by combing basic shapes in an optimal sense. The time domain non-linear Froude-Krylov force can be computed for a complex buoy shape, by adopting analytical formulas of its basic shape components. The time domain Forude-Krylov force is decomposed into its dynamic and static components, and then contribute to the calculation of the excitation force and the hydrostatic force. A non-linear control is assumed in the form of the combination of linear and nonlinear damping terms. A variable size genetic algorithm (GA) optimization tool is developed to search for the optimal buoy shape along with the optimal control coefficients simultaneously. Chromosome of the GA tool is designed to improve computational efficiency and to leverage variable size genes to search for the optimal non-linear buoy shape. Different criteria of wave energy conversion can be implemented by the variable size GA tool. Simulation results presented in this paper show that it is possible to find non-linear buoy shapes and non-linear controllers that take advantage of non-linear hydrodynamics to improve energy harvesting efficiency with out adding reactive terms to the system.