bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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 &lt; 300. At Re ∼ 300 the mechanisms compete with each other and pressure losses depends on power–law index n. At Re &gt; 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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.
Feasibility Study on Enhanced Oil Recovery Using Fuzzy-Ball Fluid in Offshore Heterogeneous Sandstone Reservoir
Authors: Wang Chao , Zheng Lihui , Wei Panfeng , Yang Mingzheng , Zhang Wang , Wu Tong 
Published: December 2020

Abstract
The heterogeneity of reservoirs in offshore oilfields, which causes low utilization of low-permeability reservoirs and poor exploitation of crude oil, is usually serious. Till date, fuzzy-ball fluids have been used to improve oil recovery of terrestrial heterogeneous reservoirs, but it is still uncertain whether it could enhance the recovery of offshore oilfields, because of high cost and special operating environment in offshore oilfields. To this end, laboratory core flooding experiments and field tests were conducted. The results of the feasibility analysis show that: (1) Fuzzy-ball fluid has good injection and plugging performance, which means fuzzy-ball fluid has great potential to be applied in enhancing recovery. (2) Fuzzy-ball fluid can greatly improve oil recovery, especially the recovery of low-permeability cores. Compared with polymer, surfactant and microsphere, fuzzy-ball fluid led to 30% higher recovery of low-permeability cores. (3) The application of fuzzy-ball fluid in enhancing recovery has good economic feasibility. The input-output ratio of fuzzy-ball fluid is 1:4.3. It is concluded that the use of fuzzy-ball fluid in the heterogeneous sandstone reservoirs for enhanced oil recovery is feasible.
Estimating Loads From Breaking Waves Using Operational Modal Analysis
Authors: Vigsø Michael , Georgakis Christos 
Published: December 2020

Abstract
Load effects from breaking waves on offshore structures may be a driving point for the design. It is hence important to assess the likelihood of occurrence along the magnitude of the loads in the event of an impact. Traditionally, loads are predicted using wave theory combined with a load model such as the Morison. This paper features an alternative approach in determining the loads from wave breaking. It is demonstrated how the structural response can be used for (indirectly) estimating the magnitude of the loads caused by wave breaking. The theory is applied to an experimental setup in a wave flume, where a flexible model is subjected to loads from breaking waves. The dynamic properties are mapped using operational modal analysis and it is consequently shown that the loads can be identified using the vibration measurements.
Stationary Intervals for Random Waves by Functional Clustering of Spectral Densities
Authors: Rivera-García Diego , García-Escudero Luis Angel , Mayo-Iscar Agustín , Ortega Joaquin 
Published: December 2020

Abstract
A new time series clustering procedure, based on Functional Data Analysis techniques applied to spectral densities, is employed in this work for the detection of stationary intervals in random waves. Long records of wave data are divided into 30-minute or one-hour segments and the spectral density of each interval is estimated by one of the standard methods available. These spectra are regarded as the main characteristic of each 30-minute time series for clustering purposes. The spectra are considered as functional data and, after representation on a spline basis, they are clustered by a mixtures model method based on a truncated Karhunen-Loéve expansion as an approximation to the density function for functional data. The clustering method uses trimming techniques and restrictions on the scatter within groups to reduce the effect of outliers and to prevent the detection of spurious clusters. Simulation examples show that the procedure works well in the presence of noise and the restrictions on the scatter are effective in avoiding the detection of false clusters. Consecutive time intervals clustered together are considered as a single stationary segment of the time series. An application to real wave data is presented.
Impact of Forced Roll Motion on the Ice Resistance of Modern Icebreaking Bow Geometries
Authors: Daniel Johanna Marie , Romu Tuomas , von Bock und Polach R. U. Franz , Abdel-Maksoud Moustafa , Skogström Toni 
Published: December 2020

Abstract
Following the development of low friction hull coatings and azimuthing propulsion for icebreaking vessels, the development of auxiliary systems for reducing ice resistance fell from focus of research. One of these systems is comprised of active heeling tanks which induce a forced roll motion on the icebreaker. Today it is not fully understood how effective or even useful such systems would be for the icebreaking performance in combination with a modern icebreaking hull form. In this study, the impact of active heeling systems on level ice resistance is investigated by performing ice model tests with an icebreaker representing the latest design generation. The level ice thickness used in the model tests corresponds to the maximum continuous icebreaking capability of the evaluated vessel in multi-year ice conditions. Additionally, a calculation method is developed to predict the impact of forced roll motion on the ice resistance. The calculated prediction is evaluated against the model-scale data. Finally, the effectiveness of the active heeling system is evaluated from an engineering perspective: does the active heeling system reduce the power demand, or would the same result be achievable by increasing the propulsion power accordingly. It was found that the roll motion impacts the ice resistance in level ice. The main influence in this regard lies with the tank volume and metacentric height of the icebreaker. Additionally, it was observed that an optimum heel angle dependent on the ice condition can be determined which is not necessarily the highest one achievable. The case study predicts a reduced power demand for a modern icebreaker hull form in harsh ice conditions.