bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Aerodynamic Performance of Offshore Twin Vertical Axis Wind Turbines With Deflector
Authors: Jiang Yichen , Zhao Peidong , Zou Li , Zhang Guiyong , Zong Zhi 
Published: November 2019

Abstract
A novel design of offshore twin counter-rotating vertical axis wind turbines (VAWTs) with deflector is proposed in this paper. We investigate the performance of the twin VAWTs by the two-dimensional computational fluid dynamic method with the Spalart-Allmaras turbulence model. Then, the performances of twin VAWTs with three kinds of deflectors are compared. The results show that installing the front deflector leads to significant improved aerodynamic performance. To better understand the simulation results, we introduce a simple and effective method to obtain the blade’s angle of attack. The mechanism of enhanced performance by deflector is pointed out, based on the information of the blade’s local angle of attack and flow field. Finally, a guideline on the design of deflector for the twin vertical axis wind turbines is provided.
Extreme and Fatigue Analysis of a Dynamic Subsea Power Umbilical
Authors: Yan Qu , Hong Guo , Lei Zhang , Zhenqin Yuan , Juyue Li 
Published: November 2019

Abstract
This paper presents an analysis procedure and results of extreme loading effect and fatigue damage of a dynamic subsea power umbilical. The umbilical was proposed by Hengtong submarine power cable Co., Ltd intended for a FPSO in south China sea at a water depth of 400 m. The umbilical cross section consists of three copper conductor strands and two layers of steel amour wires. A pliant wave configuration is used to accommodate large offset of the FPSO in the harsh environmental condition. Orcaflex is used to verify the tension and curvature of the umbilical in extreme condition against the umbilical capacity curve. UFLEX is used to estimate the mechanical properties and local stress of the umbilical. Fatigue damage is estimated by using results from the global analysis and local stress analysis. The results show that the umbilical cross section design satisfices the acceptance criteria for both extreme and fatigue damage.
Development of a Low-Cost Autonomous Underwater Vehicle for Irrigation Canal Monitoring
Authors: Masud Mamoon , Mazhar Suleman 
Published: November 2019

Abstract
Indus river basin’s irrigation system in Pakistan is extremely complex, spanning over 90,000 km. Maintenance and monitoring of this extensive network demand enormous resources. This paper describes the development of a streamlined and low-cost autonomous underwater vehicle (AUV) for the monitoring of irrigation canals including water quality monitoring and water leak detection. The vehicle is a hoveringtype AUV, designed mainly for monitoring irrigation canals, with fully documented design and open source code. It has a length of 0.43 m, and a radius of 0.09 m with a depth rating of 4m. Multiple sensors have been installed onboard the AUV for monitoring water quality parameters including pH, turbidity, total dissolved solids, temperature, and electrical conductivity. A 9-DOF IMU, GY-85, is used, which incorporates an accelerometer, a gyroscope, and a magnetometer. The readings from these three sensors are fused together using direction cosine matrix algorithm, providing the AUV with the roll, pitch and yaw angles. A water pressure sensor, MS5837, gives the depth of the AUV. Four thrusters control the vehicle’s surge and heave, providing 3 DOF. The thrusters are controlled using a proportional-integral-derivative feedback control system, with IMU data and water depth being the controller’s input and the thruster’s speed as the output. The AUV is controlled by a single onboard processor, Arduino Mega 2560.
A flow sensor has been installed beneath the main hull, for monitoring the changes in canal water flow and detecting potential water theft in the irrigation system. For recording underwater sounds, an indigenously developed hydrophone is placed on the AUV. The vehicle also provides information on water quality, providing the capability to identify the potential source(s) of water contamination. Detection of such events can provide useful policy inputs for improving irrigation efficiency and reducing water contamination. The AUV, being low cost and of small size, is suitable for autonomous maneuvering and water quality monitoring in the irrigation canals and can be used for monitoring irrigation networks at a large scale.
Eliminating the Uncertainties in Hydraulic and Ice Loads on Berm Breakwaters
Authors: Pontiki Maria , Leira Bernt Johan , Høyland Knut Vilhelm 
Published: November 2019

Abstract
A model for the computation of failure probabilities for partly reshaping mass-armored berm breakwaters in the Arctic is presented. The model consists of a reliable tool for the design of port structures in the rapidly changing Arctic environment and considers the simultaneous effects of wave and ice forces.
The applied probabilistic approach was based on Bayesian inference. Hydrodynamic and ice historical data from Prudhoe Bay, Alaska were collected and analyzed to supply the Bayesian network with a large pool of information for the analysis. The model performed real-time predictions based on historical data and the user’s prior knowledge and assigned relevant values to load and resistance parameters. The predictive skill of the Bayesian network was validated with log-likelihood tests. Furthermore, the main outputs were applied for a Level III (fully probabilistic) reliability assessment of the structure.
The study shows that a well-formulated Bayesian network can be a powerful tool in the design process and for the purpose of reliability analysis of coastal structures in highly unpredictable environments, such as the Arctic. The model can represent the dependencies between wave and ice loads in relation to the characteristics of the breakwater, as well as, its response. The average deviation of computed probabilities of failure relative to the prior estimates was 58.7%.
Numerical Solutions and Model Test Design for Anti-Typhoon Drilling Riser
Authors: Wang Jinlong , Li Lihui , Lim Frank , Zhang Hui , Xu Liangbin , Sheng Leixiang , Jin Ruijia 
Published: November 2019

Abstract
Anti-typhoon drilling riser, a solution to overcome high time cost of offshore drilling riser emergency retrieval under the situation of imminent arrival of a typhoon, is to modify the existing drilling riser to make it disconnectable closer to the surface and leave the long riser string below (and subsea blowout preventer (BOP)) in a safe and freestanding mode to survive the typhoon. The freestanding riser is held up by a buoyancy can system. And during the normal drilling operation, the buoyancy can maintain neutral thus it has limited effect on the riser overall global performance. However, locally the buoyancy can system will have some effect on the riser system nearby. To study these effects, numerical analytical methodology and results of anti-typhoon drilling rise under connected mode and freestanding mode are proposed, and a model test of 1:21 scale factor is designed. Three configuration modes: freestanding mode, connected mode and disconnecting mode are simulated in the tank test. A series of load cases under various current and wave, buoyancy upthrust are conducted in the experimental test to evaluate the hydrodynamic and strength performance of the riser near buoyancy can. The numerical solution and model test design can be a significant basis of water tank test for anti-typhoon drilling riser and a valuable reference for deepwater drilling engineering.
An Energy-Maximising MPC Solution to the WEC Control Competition
Authors: Tona Paolino , Sabiron Guillaume , Nguyen Hoai-Nam 
Published: November 2019

Abstract
The WEC Control Competition is a benchmark devised to compare energy-maximising controllers for wave energy converters, first in simulation, then in real time, using a scale device in a tank test situation. For the first round of the competition, the evaluators have provided a model of a leg of a Wavestar-like device, in the WEC-Sim simulation environment. The evaluation is based on an energy-related criterion computed on six irregular waves.
IFPEN’s solution is an energy-maximising model predictive control (MPC), composed of an estimation algorithm for wave excitation force moment, using measurements (or estimations) of float displacement and velocity and PTO moment; an algorithm for short-term wave force prediction from present and past wave excitation force estimates, where no information about wave elevation is used; a real-time compatible MPC algorithm using wave force prediction, which maximises the average produced electric energy, taking into account the nonlinear PTO efficiency law.
The Aerodynamic Analysis of Helical-Type VAWT With Semi Empirical and CFD Method
Authors: Guo Ying , Liu Liqin , Lv Xinxin , Tang Yougang 
Published: November 2019

Abstract
Comparing to Φ-type and H-type VAWT (Vertical Axis Wind Turbine), the amplitude changes of the aerodynamics acting on Helical-type VAWT are much smaller, so Helical-type VAWT has advantages in steady output power and avoiding fatigue of structure. Considering the characteristic of helical-type VAWT, this paper modifies the semi empirical method of calculating aerodynamic loads and compares with CFD results. A comparison is presented between CFD results and experiment results to confirm the model used in CFD. Single parameter analysis and muti-parameters analysis are carried out to study the influence of structural parameters on the dynamic torque. Based on an objective output power as 5MW, the parameters of wind turbine are adjusted, and optimal values of these parameters are determined.
Numerical Modelling and Sensitivity Analysis of Gas Kick Migration and Unloading of Riser
Authors: Gomes Dalila , Bjørkevoll Knut S. , Fjelde Kjell K. , Frøyen Johnny 
Published: November 2019

Abstract
In deepwater wells there is a risk of gas entering the riser. This can be caused by gas being trapped by the BOP after a well kill operation, or it can be that the BOP was not closed quickly enough upon kick detection. With oil-based mud (OBM), gas is dissolved, and larger kicks may go undetected and circulated up in the riser by accident.
If a gas kick comes into the riser, a rapid unloading event can occur. This can in worst case lead to a blowout scenario. In addition, the riser may be subject to a collapse load due to reduced liquid level inside. The unloading behavior will be different when comparing kicks in oil-based and water-based mud (WBM).
For water-based muds, field experience and experiments have shown that gas can be trapped by the mud. This effect is the same that causes mud to capture cutting particles, and it is related to the non-Newtonian and time-dependent rheology behavior of the mud. The suspended gas can only be removed from the riser by circulation. The kick must therefore be of a certain volume to be able to unload the well.
Modelling of the mentioned complex phenomena, with the violent transient phase seen when a large volume of gas expands as it moves towards the liquid surface in the riser, is still a challenge for numerical algorithms to do accurately and reliably. Robust handling of numerical diffusion in two-phase flow is one of the key topics, as are slippage and extension of gas in the liquid.
The paper describes how an explicit numerical scheme (AUSMV) is used as a numerical solver with the application of the slope-limiter technique to handle numerical diffusion. This has not yet been done for unloading of gas in riser.
A simulation case will be constructed considering gas migration and expansion in a long riser. A sensitivity analysis will be performed where both the kick volumes and the threshold for gas suspension will be varied to study when kicks will start to unload the well vs. situations where they will become fully suspended. The phenomena mentioned will be studied for water-base drilling fluids.
The paper will review previous work on the subject and highlight how transient flow models can be useful for gaining more insight into how the gas behaves in risers and what can be done to mitigate the consequences.
Removal of Viscoplastic Gels From Conduits
Authors: Alba Kamran , Oladosu Olamide , Brown Paris , Bhakta Jai , Frigaard Ian 
Published: November 2019

Abstract
There exist many industrial processes in which it is necessary to remove a gelled material from a duct. Some examples include mud removal in oil and gas well cementing, waxy crude oil pipeline restarts, and Enhanced Oil Recovery (EOR). Here, the dynamics of the removal of a viscoplastic fluid by a Newtonian fluid are investigated experimentally in an inclined pipe. We focus on both miscible and immiscible fluids mimicking wells drilled using water-based as well as oil-based mud. Under the miscible limit two major flow regimes, namely center-type and slump-type, are observed depending on the density difference between fluids. These flows are explored in great details through displacement front speed measurement which is inversely related to the efficiency of removal process. Displacement flows in the immiscible limit are accompanied by interfacial instability, gel fracture, and droplet formation. These flows are quantified through flow visualisation and spatiotemporal diagrams of fluids concentration. The findings of our study can help improve well cementing operations worldwide.
Downtime Technique Using Artificial Intelligence: A Case Study for an Exposed Berthing Facility
Authors: El Chahal Ghassan , Morel Peter A. B. , Mole Sindhu , Saadali Nadjib 
Published: November 2019

Abstract
Hydrodynamic modelling is significantly improved in the last decade, however, the coupling of these hydrodynamic models with methods to estimate berth downtime due to environmental conditions (wind, waves, currents) is less developed. The large number of environmental inputs (wind speed, wind direction, wave height, wave period, wave direction, current speed, current direction) and mooring outputs (vessel motions in six degrees of freedom, mooring lines, fender forces) to be considered in a downtime study requires major simplifications as the full wind-wave time series cannot be calculated. Downtime assessment is normally simplified by calculating a limited number of wind-wave combinations.
A new approach is developed and presented in this paper by calculating the downtime for the long-term environmental time series using artificial neural networks. Neural networks are some of the most capable artificial intelligence tools for solving very complex problems like the present case. The approach has been applied for a bulk terminal project located in the Arabian Sea. The terminal has no shelter and is totally exposed to wind and swell waves. The wave climate for a 15 years period is established at the project site using spectral wave modelling software MIKE 21 SW. A large set of combined environmental conditions is selected for the dynamic mooring analysis of the vessel at berth. The time domain mooring analysis software MIKE 21 MA is used in this study. An inhouse Matlab code/program is developed using neural network to calculate the downtime for the long-term environmental time series based on the dynamic vessel response for the set of selected environmental combinations. This approach provides a more accurate downtime estimate which is important for the operability of such exposed facilities. The downtime tool is also tested for a different set of environmental combinations and mooring layouts in order to assess the sensitivity of these parameters on the downtime estimate.
Up to the authors’ knowledge, this is the first published work applying artificial intelligence techniques for downtime studies.
Wave Load and Response Predictions Combining HOSM, CFD and Machine Learning
Authors: Oberhagemann Jan , Kaufmann Jan , Ervik Anna Kringlen , Gramstad Odin , Helmers Jens Bloch , Sireta Francois-Xavier 
Published: November 2019

Abstract
We present efforts to progress on numerical predictions of extreme wave loads of ships by combining a variety of state-of-the-art numerical tools. Aims are the generation of wave scenarios to represent the wave excitation and corresponding structural response associated with a pre-defined probability of, e.g., one expected exceedance per life cycle, as well as the further development of numerical methods to predict the ship response to the selected wave events.
Nonlinear Generation of Narrow-Banded Wave Trains
Authors: Khait Anatoliy , Shemer Lev 
Published: November 2019

Abstract
Analytic method for nonlinear wave generation by a wavemaker that is somewhat different from the nonlinear theory of Schäffer is proposed. The method that is based on the Nonlinear Schrödinger (NLS) equation and the nonlinear boundary condition at the wavemaker is free of 2nd order limitation inherent to the existing wavemaker theories. Advantages offered by the NLS model allowed simplification of the expressions for determination of the wavemaker driving signal and thus made them easily applicable in practice. The nonlinear correction to the wavemaker driving signal is calculated from the complex surface elevation envelope obtained as a solution of the NLS equation at the prescribed location in the wave flume. The domain of applicability of the generation method was determined on the basis of numerous experiments in the wave flume. A very good generation of the required wave train shape was obtained for sufficiently narrow-banded wave trains.
Identifying Higher-Order Interactions in Wave Time-Series
Authors: Ewans Kevin , Christou Marios , Ilic Suzana , Jonathan Philip 
Published: November 2019

Abstract
Reliable design and reanalysis of coastal and offshore structures requires, amongst other things, characterisation of extreme crest elevation corresponding to long return periods, and of the evolution of a wave in space and time conditional on an extreme crest.
Extreme crests typically correspond to focussed wave events enhanced by wave-wave interactions of different orders. Higher-order spectral analysis can be used to identify wave-wave interactions in time-series of water surface elevation.
The bispectrum and its normalised form (the bicoherence) have been reported by numerous authors as a means to characterise three-wave interactions in laboratory, field and simulation experiments. The bispectrum corresponds to a frequency-domain representation of the third order cumulant of the time-series, and can be thought of as an extension of the power spectrum (itself the frequency-domain representation of the second order cumulant). The power spectrum and bispectrum can both be expressed in terms of the Fourier transforms of the original time-series. The Fast Fourier transform (FFT) therefore provides an efficient means of estimation. However, there are a number of important practical considerations to ensuring reasonable estimation.
To detect four-wave interactions, we need to consider the trispectrum and its normalised form (the tricoherence). The trispectrum corresponds to a frequency-domain (Fourier) representation of the fourth-order cumulant of the time-series. Four-wave interactions between Fourier components can involve interactions of the type where f1 + f2 + f3 = f4 and where f1 + f2 = f3 + f4, resulting in two definitions of the trispectrum, depending on which of the two interactions is of interest. We consider both definitions in this paper. Both definitions can be estimated using the FFT, but it’s estimation is considerably more challenging than estimation of the bispectrum. Again, there are important practicalities to bear in mind.
In this work, we consider the key practical steps required to correctly estimate the trispectrum and tricoherence. We demonstrate the usefulness of the trispectrum and tricoherence for identifying wave-wave interactions in synthetic (based on combinations of sinusoids and on the HOS model) and measured wave time-series.
Study on the Generated Power Changes by the Relation Between an Arrangement of an Array of Point Absorber Type WECs and an Incident Wave Angle
Authors: Murai Motohiko , Li Qiao , Funada Junki 
Published: November 2019

Abstract
Using marine renewable energy can contribute providing the energy instead of using fossil fuel. There are some types of marine renewable energy. Wave energy is one of these and no one doubts its vast potential once they glance the sea. The object of this paper is an array of Point Absorber Wave Energy Converters (PA-WECs). In the array, complex hydrodynamic interactions among the array will occur. The interaction influences the wave power density among the array both increase and decrease. When we consider the maximization of generated electric power of the array, the suitable choice of the control force of the generator taken into a positive effect of the hydrodynamic interactions is the key. In the past research, as for a detection of the suitable control force of a single PA-WEC it has been shown the analytical solution within linear system. In this paper, we show the numerical solution of the control force parameter for maximizing the generated electric power of the array taking the hydrodynamic interaction among the array both in diffraction and radiation problem into account. Then we carried out the numerical examination and discussed the good arrangement of an array in waves based on the proposed method and an effect of the choice of the best and better control force.
Evaluation Adaptability of Nano Wetting Fluid for Releasing Tight Sandstone Gas Reservoir Water Locking Effect
Authors: Yao Erdong , Wang Jie , Xue Yanpeng , Zhou Fujian , Zhang Le , Li Yafei 
Published: November 2019

Abstract
At present, the most effective means of releasing the “water blocking damage” in the near-well zone is to change the wettability of the rock surface from liquid wetting to gas wetting. In this study, a novel nano wetting fluid was used to change the sandstone surface wettability aqueous phase from wetting phase to non-wetting phase. The adaptability of 0.5 wt% nano wetting fluid at different aging times, pH, salinity type, salinity and temperature was evaluated. The results show that 0.5 wt% nano wetting fluid has better adaptability under different conditions. The aqueous phase of the core surface can be changed from wetting phase to non-wetting phase; after adding nano wetting fluid, the drainage rate increased by 19.09%; at the same time, SEM characterization experiments showed that nano wetting fluid could achieve hydrophobic effect by changing the surface roughness of illite and chlorite.
Numerical Hull Resistance and Hydrodynamic Characteristics of an Independently Rotating Multi-Hull Vessel
Authors: Srinivasamurthy Sharath , Sakamoto Hiroshi , Nishikawa Tatsuo , Nihei Yasunori 
Published: November 2019

Abstract
In this study, an attempt is made to understand the hydrodynamic characteristics of an automated multi-hull vessel named as Quadmaran. Firstly, a single hull of the Quadmaran vessel is considered and numerical CFD simulation is performed using OpenFOAM. Hull resistance predictions are compared with the experimental findings and numerical simulation is validated. After validating the simulation scheme, further CFD simulations are performed on two hulls with varying distance between them to understand the hydrodynamic characteristics of different configurations. Pressure distribution and wave patterns around the hulls are also summarized and discussed in the paper. Further, efforts are made to optimize the distance between the hulls for reducing hull resistance. A basic framework is suggested to carefully consider the hydrodynamic effects for multi-hull vessels.