bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Study on Flow and Heat Transfer Performance of Natural Gas in a Printed Circuit Heat Exchanger During Transcritical Liquefaction
Authors: Ma Ting , Zhang Pan , Lian Jie , Ke Hanbing , Wang Wei , Lin Yuansheng , Wang Qiuwang
Published: December 2020

The main cryogenic heat exchanger is a core piece of equipment in the liquefaction of natural gas. The printed circuit heat exchanger is gradually becoming a primary choice for the main cryogenic heat exchanger, because it has good pressure resistance, high efficiency, and compactness. In this work, a numerical simulation is conducted to examine the local flow and heat transfer characteristics of natural gas in the printed circuit heat exchanger during trans-critical liquefaction. It is found that the heat flux density reaches a minimum value and the heat transfer is the worst when the temperature difference between the hot and cold sides is the smallest. Owing to the large variations in physical properties of trans-critical natural gas, the local pressure drop exhibits an upward parabolic shape along the flow direction, and the pressure drop reaches a minimum value near the pseudo-critical point. Finally, the friction factor and heat transfer correlations for natural gas during trans-critical liquefaction are fitted.
Frictional Flexible Pipe Model Using Macroelements
Authors: Provasi Rodrigo , Geremias Toni Fernando , de Arruda Martins Clovis
Published: December 2020

Flexible pipes are structures composed by many layers varying in composition and shapes, in which the structural behavior is defined by the role it must play. Flexible pipes construction is such that layers are unbounded, allowing relative movement between them and modifying its behavior.

Many approaches are used to model such cables, both analytical and numerical, such as the macroelements model. This sort of model consists in finite elements where geometrical characteristics are taken into account by the formulation and is under development by the authors.

Previous works have shown in detail the modeled cylindrical and helical elements, as well node-to-node connection elements (bounded, frictionless and frictional), which have allowed simplified flexible pipe with bonded elements simulations.

This article will focus on modeling a simplified cable consisting in an external sheath, two armor layers and a polymeric core, since recent advances in the contact formulation opens the possibility to incorporate friction between the layers.

Taking into consideration accuracy, computational time and memory usage, results from macroelements are compared to commercial finite element software.
Drilling Fluid’s Cuttings Bed Removal Properties for Deviated Wellbores
Authors: Ytrehus Jan David , Lund Bjørnar , Taghipour Ali , Carazza Luca , Gyland Knud Richard , Saasen Arild
Published: December 2020

Results from cuttings transport tests in laboratory using different field applied oil-based drilling fluids with similar weight and varying viscosities are presented in this paper. The fluids are designed for highly deviated wells, and the cuttings transport performance at relevant wellbore inclinations was investigated.

The experiments have been performed in a flow loop that consists of a 10 meters long test section with 2″ OD freely rotating steel drill string inside a 4″ ID wellbore made of cement. Sand particles were injected while circulating the drilling fluid through the test section. Experiments were performed at three wellbore inclinations: 48, 60 and 90 degrees from vertical. The applied flow loop dimensions are designed so that the results are scalable to field applications; especially for the 12,25″ and 8,5″ sections. The selected setup provides correct shear rate ranges and equal Reynolds number to the field application when the same fluids are applied.

Results show that hole cleaning abilities of the tested fluids vary significantly with well angle, drill string rotation and flow rate. Results support field experience showing that low viscous fluids are more efficient than viscous at higher flow rates and low drill string rotation. As well as per field experience more viscous fluids are efficient in combination with high drill string rotation rates. The results show the effect of cuttings transport efficiency as function of hydraulic frictional pressure drop, demonstrating methods to achieve more optimal hydraulic design in the tested conditions. The key findings have direct relevance to drilling operations.
Parallelized Element-by-Element Solver for Structural Analysis of Flexible Pipes Using Finite Macroelements
Authors: Geremias Toni Fernando , de Arruda Martins Clóvis
Published: December 2020

Due to the number of layers and their respective geometrical complexities, finite element analyzes of flexible pipes usually require large-scale schemes, with a high number of elements and degrees-of-freedom. If proper precautions are not taken, such as suitable algorithms and numerical methods, the computational costs of these analyzes may become unfeasible to the current computational standards. Finite macroelements are finite elements formulated for the solution of a specific problem considering and taking advantage of its particularities, such as geometry patterns, in order to obtain computational advantages, as reduced number of degrees-of-freedom and ease of problem description. The element-by-element method (EBE) also fits very well in this context, since it is characterized by the elimination of the global stiffness matrix and its memory consumption grows linearly with the number of elements, besides being highly parallelizable. Over the last decades, several works regarding the EBE method were published in the literature, but none of them directly applied to flexible pipes. Due to the contact elements between the layers, problems with flexible pipes are usually characterized by very large matrix-bandwidth, making the implementation of EBE method more challenging, so that its efficiency and scalability are not compromised. Therefore, this work presents a parallelized implementation of an element-by-element architecture for structural analysis of flexible pipes using finite macroelements, consisting of an extension of a previous work from the same authors. New synchronization algorithms were developed, with scalability improvements, the methodology was extended to other finite macroelements and comparisons were made with a well-stablished FEM software, with significant gains in simulation time and memory consumption.
Safe and Fuel-Efficient Voyage Planning for the Northeast Passage by Combining Reliable Ship Performance, Weather and Ice Forecast Models
Authors: Li Zhiyuan , Ringsberg Jonas W. , Ding Li , Rita Fransisco , Fournier Nicolas , Mendes Joana
Published: December 2020

The Northeast Passage in the Arctic between Europe and Asia offers a significantly shorter voyage compared to the Southern route through the Suez Canal. In 2017, the EU research project “Safe maritime operations under extreme conditions: the Arctic case (SEDNA)” was established to perform a comprehensive analysis of Arctic transit shipping and to promote technical solutions for this purpose. This paper is based on the deliverables of the SEDNA project. A voyage planning tool (VPT) for Arctic applications was developed to plan the optimal route regarding ship’s fuel consumption and safety. One of the most advanced metocean and ice forecast model is utilized to provide comprehensive environmental conditions that are synchronized and will be updated frequently during the voyage. The ship energy system model takes into account the various environmental variables as well as ship’s operational conditions to compute the ship performance in both open and ice infested waters. For Arctic operations, specific ice resistance models are implemented in the VPT, and a user has the options of either relying on icebreaker assistance or going for unassisted navigation in part of the entire Arctic passage. Case study voyages of different ship types, route options, staring time, home/destination ports are simulated to demonstrate how various optimal routes are planned and how the transit time and fuel consumption vary. This information is considered being crucial for ship owners for planning their voyages in advance. The continuously updated voyage information from the VPT is particularly helpful for the ship crew if there are specific ship operations and risk mitigation actions that need to be taken care of during the voyage. In addition, this study underlines that a safe and fuel-efficient Arctic passage requires viable voyage planning tools that combine reliable ship performance with weather and ice forecasts.
Influence of Combined Empirical Functions on Slug Flow Predictions of Pipelines With Variable Inclinations
Authors: Zanganeh Hossein , Kurushina Victoria , Srinil Narakorn , Matar Omar K.
Published: December 2020

Prediction of internal multiphase flows in subsea pipelines is an integral part of the oil and gas production system design. High mass and pressure fluctuations are often encountered during the operation with a liquid-gas slug flow regime exhibiting a sequence of long gas bubbles and aerated liquid slugs. It is important for industry to realistically identify the slug flow occurrence and predict slug flow characteristics, depending on several multiphase flow-pipe parameters. These may be achieved using a one-dimensional, steady-state, mechanistic model accounting for a mass and momentum balance of the two liquid-gas fluids within a controlled volume often referred to as a slug unit. By reducing a 3-D flow problem to a 1-D one, several empirical or closure correlations and associated empirical coefficients have been introduced in the literature and used in commercial software predicting slug flows in subsea jumpers, pipelines and risers with variable inclinations.

This study aims to investigate the influence of combined 25 closure functions on the predictions of slug flows in horizontal and inclined pipes based on a steady-state mechanistic model for a wide range of superficial liquid and gas velocities. The model with studied closures is implemented by the authors of this study as the numerical tool iSLUG. The model performance is verified with respect to the estimated film liquid holdup, film length and pressure drop per length of a slug unit for an empirically specified translational velocity, slug liquid holdup, slug liquid length and pipe wall wettability. Closure combinations are analyzed using the relative performance factors and compared against available experimental data in order to identify a set of functions suitable for upward, downward and horizontal flows, and the effect of diameter and inclination on the model prediction is considered. The present method and analysis outcomes may further contribute to the improvement of transient liquid-gas flow models to predict more practical cases.
Fracture Behavior of X65 Q&T Seamless Pipeline Steel Under Different Strain Rates and Stress States
Authors: Fudlailah Pratiwi , Paredes Marcelo
Published: December 2020

Dynamic crack propagation in pressurized pipelines is usually investigated by means of lab-scale specimens due to its economic feasibility and material saving. More recently, new generation of pipeline steels have incredibly shown a combined fracture toughness and plastic strength capabilities with even more heavier wall thickness, for which current design standards and practice codes underpredict largely the actual material response under different strain rates. The Drop-Weight Tear Test (DWTT) is commonly used to characterize dynamic fracture behavior of pipeline steel and its numerical implementation with appropriate constitutive equations has become essential in the fundamental understanding of the interaction between fracture process and local stress-strain fields. In the present study, a X65 Q&T seamless pipeline steel is fully characterized under different strain rate levels and stress states for dynamic fracture initiation. A rate dependent phenomenological fracture criterion is proposed in the form of Modified Mohr-Coulomb (MMC) fracture model coupling with a multiplicative decomposition of the hardening law to describe strain rate effect on post-necking behavior. The model implementation is then validated through a drop-weight tearing analysis on standard and non-standard specimen configurations including different wall thickness.
Sea Ice Thickness Forecast Performance in the Barents Sea
Authors: Hume-Wright Laura , Fiedler Emma , Fournier Nicolas , Mendes Joana , Blockley Ed , Martin Matthew , Eik Kenneth
Published: December 2020

The presence of sea ice has a major impact on the safety, operability and efficiency of Arctic operations and navigation. While satellite-based sea ice charting is routinely used for tactical ice management, the marine sector does not yet make use of existing operational sea ice thickness forecasting. However, data products are now freely available from the Copernicus Marine Environment Monitoring Service (CMEMS). Arctic asset managers and vessels’ crews are generally not aware of such products, or these have so far suffered from insufficient accuracy, verification, resolution and adequate format, in order to be well integrated within their existing decision-making processes and systems.

The objective of the EU H2020 project “Safe maritime operations under extreme conditions: The Arctic case” (SEDNA) is to improve the safety and efficiency of Arctic navigation. This paper presents a component focusing on the validation of an adaption of the 7-day sea ice thickness forecast from the UK Met Office Forecast Ocean Assimilation Model (FOAM). The experimental forecast model assimilates the CryoSat-2 satellite’s ice freeboard daily data.

Forecast skill is evaluated against unique in-situ data from five moorings deployed between 2015 and 2018 by the Barents Sea Metocean and Ice Network (BASMIN) Joint Industry Project. The study shows that the existing FOAM forecasts produce adequate results in the Barents Sea. However, while studies have shown the assimilation of CryoSat-2 data is effective for thick sea ice conditions, this did not improve forecasts for the thinner sea ice conditions of the Barents Sea.
Effects of Thickness and Winding Angle of the Laminate on Internal Pressure Capacity of Thermoplastic Composite Pipes
Authors: Xia H. , Shi C. , Wang J. , Bao X. , Li H. , Fu G.
Published: December 2020

Thermoplastic composite pipes (TCPs) are increasingly used to transport hydrocarbons and water in the oil and gas industry due to their superior properties including corrosion resistance, thermal insulation, light weight, etc. The cross-section of TCPs generally consists of three layers: inner liner, composite laminate, and outer jacket. Three layers are bonded together and form a solid-wall construction. Inner liner and outer jacket made of thermoplastic polymer provide protective barriers for the laminate to against the inner fluid and outer environment. The laminate is constructed by an even number of helically wounded continuous fiber reinforced thermoplastic composite tapes. In this study, mechanical behaviors of a TCP under an internal pressure were investigated by using analytical and finite element analysis (FEA) methods. The analytical method which is based on the three-dimensional (3D) anisotropy elastic theory can take account of non-uniformly distributed stress and strain through the thickness of the pipe wall. FEA models were setup by using the software ABAQUS to predict the stress distribution of the pipe. 3D Tsai-Wu failure criterion was used to predict the maximum internal pressure of the pipe. Effects of some critical parameters, such as the winding angle of composite tapes and the number of reinforced plies, on the internal pressure capacity of TCPs were studied. Results obtained from the analytical and FEA methods were fairly agreed with each other, which showed that with the increasing of the number of reinforced plies the internal pressure capacity of a TCP gradually increases and approaches to an extreme value. In addition, the optimal winding angle which results the maximum internal pressure is not a constant value, instead, it varies with the increasing thickness of the laminate layer. This study provides useful tools and guidance for the design and analysis of TCPs, and is currently under validation through experiments.
Load-Carrying Characteristics of Foam Core and Joint Geometry in Sandwich Structures
Authors: Ringsberg Jonas W.
Published: December 2020

Composite sandwich ships have laminated joints that contribute to a significant part of the ship’s weight. Their construction requires an extensive number of man-hours. There is great potential for weight and production-time-reduction through alternative joint designs. According to class rules, one is not allowed to benefit from the load-carrying capability of the core, i.e. the strength characteristics of the core shall be disregarded and geometry at the joint location is disregarded as well. The objective of the current investigation was to investigate the possibility of constructing a joint where the load-carrying capability of the foam core is accounted for, leading to a reduction in weight and production time. One specific joint in a 23 m composite sandwich catamaran was selected for study — a side wall-wet deck T-joint. This joint is considered to be crucial for the structural integrity of the current vessel. A global finite element (FE) model of the catamaran was designed and analysed in ANSYS. The loads and boundary conditions were applied to the global model according to DNV GL’s HSLC rules. Two local FE models of the joints (2D and 3D) were utilized for a parametric analysis with respect to structure response (stress concentrations and compliance with failure and fracture criteria). Finally, the results and conclusions from the study show the possibilities and advantages of incorporating the foam core material as a load-carrying member in joint design without compromising safety.
3D SPH Simulation of Wave Interaction Between Wave Energy Converters: Towards Optimum Wave Power Absorption in Wave Farms
Authors: Sasikala N. , Sannasiraj S. A. , Manasseh Richard
Published: December 2020

Ocean waves are one of the sustainable resources of renewable energy for carbon-free electricity. For cost-effective commercial-scale projects, Wave Energy Converters (WECs) are deployed in arrays with optimum spacing as an alternative for a large (oscillatory) device in isolation. It has been found that when the wave excitation frequency is close to the resonant frequency of the WEC, the efficiency factor of energy farms, called q-factor, increases with the oscillation amplitude of the device. It has been found that the maximum absorbed energy of WECs depends directly on array configuration as that the radiated and incident wave fields interfere to direct the energy flux in the ocean towards the floating bodies. In this paper, the fully nonlinear interaction between two 3D floating bodies in close proximity and excited near its’ resonance is studied using Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH). Apart from the calculations of q factor, hydrodynamic forces acting on the floating bodies and their dynamic responses are also calculated. An optimum array of WECs is proposed.
Design Considerations of a Subsea Shuttle Tanker System for Liquid Carbon Dioxide Transportation
Authors: Xing Yihan , Ong Muk Chen , Hemmingsen Tor , Ellingsen Kjell Einar , Reinås Lorents
Published: December 2020

Subsea pipelines and umbilicals are used for the transportation of fluids and electrical power between subsea installations and floating production systems (FPUs). The installation and maintenance of these systems can be expensive. In a conventional subsea field development, the produced fluids can be transported from the well to a FPU where they can be offloaded to a tanker (surface ship). In the case of carbon dioxide (CO2) injection into the well, the direction of flow is reversed, i.e., CO2 flows from the tanker to the FPU, down the riser base and through the subsea pipelines to the well. This offloading process is weather-dependent and cannot be performed in severe weather conditions, i.e., strong winds and large waves. This paper presents a novel subsea shuttle tanker system proposed by Equinor ASA designed to be a possible alternative to subsea pipelines, umbilicals and tanker ships. The subsea shuttle is intended to operate submerged under the sea surface to transport liquid CO2 from an existing offshore/land facility where CO2 is captured to a subsea well where the CO2 is injected into the reservoir. As the shuttle is subsea, it can operate under any type of weather conditions. Even though the subsea shuttle is proposed as a vehicle for liquid CO2 transport, it can also transport other types of cargo such as hydrocarbons, injection fluids, electrical power or subsea tools. The paper will discuss the most important design considerations surrounding the subsea shuttle tanker.
Numerical Analysis of Aeroelastic Responses of Wind Turbine Under Uniform Inflow
Authors: Huang Yang , Wan Decheng
Published: December 2020

With wind turbine blades becoming longer and slender, the influence of structural deformation on the aerodynamic performance of wind turbine cannot be ignored. In the present work, the actuator line technique that simplifies the wind turbine blades into virtual actual lines is utilized to simulate the aerodynamic responses of wind turbine and capture downstream wake characteristics. Moreover, the structural model based on a two-node, four degree-of-freedom (DOF) beam element is adopted for the deformation calculation of the wind turbine blades. By combing the actuator line technique and linear finite element theory, the aeroelastic simulations for the wind turbine blades can be achieved. The aeroelastic responses of NREL-5MW wind turbine under uniform wind inflow condition with different wind speeds are investigated. The aerodynamic loads, turbine wake field, blade tip deformations and blade root bending moments are analyzed to explore the influence of blade structural responses on the performance of the wind turbine. It is found that the power output of the wind turbine decreases when the blade deformation is taken into account. Significant asymmetrical phenomenon of the wake velocity is captured due to the deformation of the wind turbine blades.
Numerical Study of Yawed Wind Turbine Under Unstable Atmospheric Boundary Layer Flows
Authors: Wei Dezhi , Wan Decheng
Published: December 2020

Turbine-wake interactions among wind turbine array significantly affect the efficiency of wind farms. Yaw angle control is one of the potential ways to increase the total power generation of wind plants, but the sensitivity of such control strategy to atmospheric stability is rarely studied. In the present work, large-eddy simulation of a two-turbine configuration under convective atmospheric boundary layer is performed, with different yaw angles for the front one, the effect of turbine induced forces on the flow field is modeled by actuator line. Emphasis is placed on wake characteristics and aerodynamic performance. Simulation results reveal that atmospheric stability has a considerable impact on the behavior of wind turbine, wake deflection on the horizontal hub height plane for yawed wind turbine is relatively small, compared with the result of the empirical wake model proposed for wind turbine operating in the neutral stratification, which is attributed to the higher ambient turbulence intensity and large variance of wind direction in the convective condition. And associated with the smaller wake deflection, the total power production does not increase as expected when yawing the upstream turbine. In addition, due to the existence of great quantities of disorganized coherent turbulent structures in the unstable condition, the yaw bearing moment experienced by the downstream wind turbine increases dramatically, even if the rotor plane of the first turbine is perpendicular to the inflow direction.
Research on Real-Time Calculation Method of Load Response in FPSO Soft Yoke Mooring System Based on Long and Short-Term Memory Network
Authors: Sun Yu , Sun Liping , Li Peng , Ma Gang
Published: December 2020

Due to the complex marine environment factors such as wind and waves, FPSO (Floating Production Storage Offloading) relies on the mooring system for positioning and reducing the serious consequences when excessive hull movement happens. Therefore, the production, storage, and unloading operation of FPSO are directly affected by the safety of the mooring system. At present, installing the fiber grating strain sensor on the mooring system of FPSO is the primary way of system condition monitoring. However, the problems of sensors like dropping, deformation and short circuit reduce the reliability and increase costs in monitoring. In view of the above considerations, this paper proposes a real-time calculation method for motion response of mooring system of FPSO, basing on LSTM (Long and short-term memory) algorithm. In the case where the shipborne GPS (Global Positioning System) provides six degree of freedom, the force at the specific position on SYM (Soft Yoke Mooring) system can be directly calculated.

The feasibility of the load response calculation involving the critical position like pendant-hull interface and of YOKE head in FPSO SYM system is proved by comparison with the numerical simulation, providing a new method support for gradually replacing the force sensor based mooring response acquisition method, and an economical and efficient way for the real-time calculation of the key position response in the FPSO mooring system.
Numerical Investigation on Suction Pile’s Holding Capacity Installed in Carbonate-Type Soils
Authors: Cao Jianchun , Zhong Zhibin , Budhiraja Ashish
Published: December 2020

Suction piles have not been widely used in carbonate-type soils (i.e., muds/silts) because the pile skin frictions in this type of soils are only about 5% of that in normal clayey soils. The holding capacity of a suction pile installed in these types of soils may be affected by its lower friction. Moreover, pile designers have concerns not only on the development of the Reverse End Bearing (REB) but also on how long the REB can sustain. This paper presents the development of a three-Dimensional Finite Element Analysis (3D FEA) model and the analysis results to investigate the behavior of suction pile for different levels of skin frictions. Firstly, the FEA model is used to investigate the development of the Reverse End Bearing (REB) of a suction pile by assigning two different levels of pile external skin frictions, i.e., 5% and 100% (full skin friction). A vertical load is applied at the center of the pile top. Secondly, the FEA model is used to investigate the behavior of a suction pile for a very low level of pile skin friction (i.e., 5% skin friction). An inclined load with various load angles from horizontal is applied at the padeye (i.e., 16m below seabed). Thirdly, the load carrying (failure) mechanism has been checked by examining the total displacement vectors of soil masses around the pile. Fourthly, a sensitivity study is carried out to investigate the capacity of a suction pile for different usage factors of REB. Finally, suction pile design requirements for carbonate-type soils (i.e., low level of pile skin frictions) are recommended.
Estimating Swelling in Oil-Based Mud due to Gas Kick Dissolution
Authors: Manikonda Kaushik , Hasan Abu Rashid , Kaldirim Omer , Rahmani Nazmul , Rahman Mohammad Azizur
Published: December 2020

Gas kick is an ever-present hazard whose importance is magnified for offshore drilling situations. Modeling gas kick is a complex problem that requires an understanding of the relevant fluid dynamics as well as the solubility of natural gas in oil-based muds (OBM). Drilling fluid swelling due to natural gas solubility in OBM significantly affects the extent of pit gain — one of the primary indicators of a kick in progress. This paper specifically addresses the issue of drilling fluid swelling from gas dissolution in OBM.

Drilling fluid swelling due to gas dissolution is generally expressed the same way as oil swelling due to dissolved gas, by the volume factor, Bo. Many correlations for estimating Bo as a function of temperatures and pressures are available. We have developed a rigorous thermodynamic approach for estimating Bo. Our approach uses the Peng-Robison (1976) equation of state (EOS), van der Waals mixing rules, and binary interaction coefficients appropriate for drilling fluids to account for gas solubility. Solving the cubic form of the Peng-Robinson EOS yields a z-factor for the liquid phase of the mixture. The model uses this z-factor to estimate the liquid-phase volume of dissolved methane and, consequently, Bo. This paper validates the results of estimated Bo from this method with volume factor calculations obtained from Aspen HYSYS. Finally, this paper also presents a section where the methane mole fraction data at different P&T conditions, obtained from HYSYS simulations, is used to validate the solubility model previously developed by Manikonda et al. (2019).
Application of Experimental Design on Small Surface Boat for Resistance and Payload Study
Authors: Lin Chun-Cheng , Hsaio Yu-Chi
Published: December 2020

With commercialization, marine science and military applications in offshore and shallow waters is increasing, the development of the small surface vessels are getting greater, and that design targets are focus on multi-functional platforms, smart navigation and autonomous, etc. Therefore, the goals of multi-purpose small surface vessels such as the coastal patrol, offshore observation and data collection, intelligence reconnaissance, anti-mine warfare, marine shooting training targets, and so on. In currently, to achieve these missions, the length of most small surface vessels were designed less than 10 meters. Furthermore, based on these multi-propose requirements, this study will explore the configuration design of monohull and trimaran, combine the research source of the Horizontal Circulating Water Channel (HCWC), through the ship model test to acquire experimental data. In addition, to promote the study quality and experimental efficiency, we applied Taguchi design of experimental (DOE) and the variance of analysis (ANOVA) to compare the resistance and payload of various configurations ship design. In this study, we defined two control factors (such as factor-A is Longitudinal distance, factor-B is Lateral distance) and set up three-level factorial design, and planned factorial experiment based on Taguchi orthogonal array L9 (34). Also used the neural network and training metamodeling. This metamodeling was decided by relative coefficient (R) and decision coefficient (R2). According to this metamodeling, and then, applied the genetic algorithm to search the best solution such as A2B3. The results of this study showed that the resistance performance of the trimaran is better than the monohull while the volume Froude number Fr∇ > 0.95, and the optimum configuration has greater resistance performance at both higher and lower speed fields to achieve robust design. In the other hand, this paper will also discuss the feasibility and effectiveness of the installation space and multi-function performance on platform. Hence, for payload study, we also applied ANOVA to analyze these nine different configurations, and indicated a significant main effect for factor-B. However, no significant main effect for factor-A and interaction effect were found. To conclude, this study may be of importance in explaining small surface vessel design, as well as in providing ship designer with a better understanding of trade-off about speed and payload. While this study has its limitations (such as HCWC characteristic dimension), it is hoped that it could as a basis for further study in the multi-functional small surface vessel.
Non-Linear Wave Run-Up Along the Side of Sailing Ships Causing Green Water on Deck: Experiments and Deterministic Calculations
Authors: van Essen Sanne , Bandringa Henry , Helder Joop , Buchner Bas
Published: December 2020

Experiments with a flat plate in oblique waves at different speeds, wave conditions, headings and drift speed were done to evaluate non-linear wave run-up along a sailing ship. Both the incoming and diffracted part of the run-up were highly nonlinear in all test conditions. The run-up was larger at 135 than at 150 deg heading, the influence of speed was small, wave steepness increased run-up up to the point of breaking and a drift speed decreased the run-up. Most of the observed differences were larger than the seed and basin variability. (Semi-) linear diffraction methods are not sufficient to predict the highest runup crests, but applying them to screen for critical events could be further studied. CFD is able to accurately predict the nonlinear run-up in such selected events. Combining different levels of tools seems the most efficient way to predict extreme wave events such as green water due to run-up.
Second-Order Difference-Frequency Loads on FPSOs by Full QTF and Relevant Approximations
Authors: Engebretsen Espen , Pan Zhiyuan , Fonseca Nuno
Published: December 2020

This paper investigates three different approximations of the full Quadratic Transfer Function (QTF) for calculating horizontal plane second-order difference-frequency loads on FPSOs, namely Newman’s approximation, full QTF without free surface integral and the white-noise approximation.

Second-order excitation loads obtained from approximated QTFs are compared in frequency-domain with those obtained by the full QTFs computed from second-order diffraction/radiation analysis in WADAM. The comparison is performed for a new-build FPSO in a range of water depths and environmental combinations. The full QTFs from second-order diffraction/radiation analysis are further compared to empirical QTFs as identified from cross bi-spectral analysis of model test results in irregular waves.

A mesh convergence study is presented for calculating full QTFs by the near-field approach in a second-order diffraction/radiation analysis. The importance of including viscous damping in heave, roll and pitch is illustrated for the mean wave-drift force in surge and sway.

FPSO motions and mooring line tensions from fully-coupled time-domain analysis in OrcaFlex is compared when using approximated QTFs and full QTFs from second-order diffraction/radiation analysis.
Experimental Study on the Behavior of a Bubble in the Vicinity of an Air Bubble Attached to a Fixed Structure
Authors: Wang Jia-xia , Liu Kun
Published: December 2020

The interaction between a spark-generated bubble and a non-oscillating air bubble attached to a horizontal rigid plate is investigated using a low-voltage spark-discharge setup. Large numbers of fascinating and complicated interactions are given rise during two bubble coupling pulsation due to the deformation property endowed to the plate through an air bubble attached. It is found that, under the combined influence of the cavitation and the structure, some complex phenomenon likes the bubble coalescence, air bubble skirt phenomenon, bubble splitting are given rise during the two bubble interaction procedure. The coupling phenomenon between the spark generated bubble, air bubble and the structure are discussed in detailed The mainly attention are paid to the coupled response of an attached quiescent bubble under oscillating bubble, the effect of the distance parameter and volume ratio parameter on the air bubble shapes are analyzed in detail, and the mechanism behind these phenomenon are investigated. Our study can be a useful scheme in the protection of a naval structure from threats induced by an explosion bubble impact loading.
Damping of Regular Waves in Model Ice
Authors: Hartmann Moritz C. N. , von Bock und Polach R. U. Franz , Klein Marco
Published: December 2020

Wave characteristics change significantly when the waves propagate in a solid ice field. The damping of the incident waves due to the presence of the ice sheet has a significant impact on the modification of wave propagation and dispersion.

In this study the interaction of waves with solid ice are investigated by means of model tests. The objective of the study is to measure wave and ice characteristics and analyze the data regarding wave damping and the change of wave parameters in model ice.

The experiments were performed in the ice tank of the Hamburg ship model basin (HSVA) with a set of regular waves with varying wave number and steepness. The surface elevation of the waves is recorded by acoustic and motion capturing measurement devices.

By comparing the measurements of the incident open water waves with the waves in ice, the change in terms of wave amplitude and dispersion due to the presence of ice is analyzed.

It is shown that once the waves travels through the ice the angular frequency remains unchanged while the wave amplitude exponentially decays, with an increasing decay coefficient at smaller wave length. Furthermore, the dispersion relation in ice, represented by the measured angular frequency and wave number, is consistent with the theoretical dispersion relation.
Continuous Drilling Sensor Data Reconstruction and Prediction via Recurrent Neural Networks
Authors: Tunkiel Andrzej T. , Wiktorski Tomasz , Sui Dan
Published: December 2020

There is an ever-increasing amount of data being recorded in oilfield operations. During drilling a well a large number of parameters is being monitored and saved, often reaching several hundreds. We are seemingly monitoring everything, from basic parameters such as Weight on Bit, Torque, and Rate of Penetration (ROP), to the exhaust temperature of engine no. 3. Unfortunately, the quality of collected data does not match the quantity. Critical sensors, such as gamma and inclination, are often lagging many meters behind the bit. Despite best efforts, sensors stop working, hard drives corrupt files, and data mud pulse telemetry uplinks fail. Methods of infilling data spanning many meters or minutes are necessary. We present a novel approach that enables reliable prediction of data lagging behind the bit through deep neural networks by merging trend-based prediction with traditional neural network approach. We were able to predict continuous inclination data in a curved section of a well with an average absolute error of only 0.4 degrees up to 20 meters from last known value.
Representation of Breaking Wave Kinematics in the Fully Nonlinear Potential Flow Model REEF3D::FNPF
Authors: Pakozdi Csaba , Kamath Arun , Wang Weizhi , Bihs Hans
Published: December 2020

Robust simulations over three-hours are essential to represent a stationary sea state and derive wave statistics and structural response of marine structures in a reliable manner. This means that the numerical model used for the simulation of the sea state should be computationally efficient, stable and accurate. The fully nonlinear potential flow (FNPF) model solving the Laplace equations is found to be a good tool for this application. The drawback of using the FNPF model is the representation of wave breaking. Due to the assumptions of irrotational flow, it is not possible to represent an overturning free surface which occurs as a result of wave breaking. Therefore, there is a need to investigate a method to represent the effect of wave breaking in an efficient yet accurate manner. In this paper, the open-source model REEF3D::FNPF is used. The model demonstrates good robust performance and stability even in the presence of breaking waves in the domain. However, it is noticed that the free surface in the aftermath of wave breaking is slightly over predicted. This results in waves in the post-breaking region that are higher and steeper than expected after wave breaking. This difference can be avoided by incorporating techniques to correctly reduce the wave energy in the post-breaking region by the means of a reasonable damping mechanism.

Breaking waves generated in the facility at SINTEF Ocean/NTNU are simulated in REEF3D::FNPF. Earlier presented results of Star-CCM+ [1] are used in the comparison. The free surface measured at several different locations in the Small towing tank are compared to the numerical results. As published earlier, the CFD model represents the model test data well. Further, the effect of wave breaking in the numerical models is investigated by comparing the numerical results from both models. The difference in the free surface representation is used to analyze the damping factor required in the FNPF model, compared to the wave kinematics represented in the CFD model. Further, REEF3D::FNPF is used to carry out three-hour long simulations with the JONSWAP spectrum in intermediate water depth conditions in order to identify the influence of the breaking model parameters on the statistical properties of the generated waves and compared against model test data.
Effect of a Passive Tuned Mass Damper on Offshore Installation of a Wind Turbine Nacelle
Authors: Jiang Zhiyu , Skrudland Trond Kvia , Karimirad Madjid , Michailides Constantine , Shi Wei
Published: December 2020

Although the installation of offshore wind turbines takes place in calm seas, successful mating of wind turbine components can be challenging due to the relative motions between the two mating parts. This work investigates the effect of a passive tuned mass damper on the mating processes of a nacelle for a 10-megawatt (MW) offshore wind turbine. A nacelle with lifting wires and a monopile with a mass damper are respectively modelled using the multibody formulation in the HAWC2 program. A single mass damper is tuned to target at the first natural period of the monopile and is coupled to the main program using a dynamic link library. Afterwards, numerical simulations were carried out in turbulent wind conditions and irregular wave conditions typical of offshore installation scenarios. Important response variables including the tower-top motions, nacelle motions, and their relative motions are examined in the analysis. By comparing the time series and response statistics, we found that the tower-top motion is more crucial to the installation process than the lifted nacelle motion. For the relative motions and velocities between the nacelle and the tower top, the tuned mass damper can reduce the short-term maximum values by more than 50% for the examined sea states with spectral period between 4 to 12 seconds. This implies that the weather window for marine operations can be expanded if the tuned mass damper is applied.
Leading Edge Erosion of Wind Turbine Blades: Effects of Environmental Parameters on Impact Velocities and Erosion Damage Rate
Authors: Verma Amrit Shankar , Jiang Zhiyu , Ren Zhengru , Teuwen Julie J. E.
Published: December 2020

Leading edge erosion (LEE) of a wind turbine blade (WTB) is a complex phenomenon that contributes to high operation and maintenance costs. The impact between rain droplets and rotating blades exerts cyclic fatigue stresses on the leading edge — causing progressive material loss and reduced aerodynamic performance. One of the most important parameters for erosion modelling and damage prediction is the relative impact velocity between rain droplets and rotating blade and depends upon the environmental conditions. The environmental condition, in general, could vary for onshore and offshore wind turbines (OWTs) — for instance, the presence of wave-induced loads along with less turbulent wind and varying rainfall conditions in the offshore environment. The present paper tries to provide guidelines whether all these parameters need to be included for LEE modelling. Aero-hydro-servo-elastic simulations are carried out for a rotating blade based on the NREL 5 MW turbine by considering realistic environmental conditions for a land-based wind turbine and monopile-supported OWT. Further, the impact velocities and erosion damage rate, evaluated using a surface fatigue model, are analysed and compared for different environmental conditions. It is found that rainfall intensity and turbulence intensity influences the impact velocity minorly, however, has a substantial effect on the overall erosion damage rate. For instance, for the investigated load cases, an 8% increase in the impact velocity is observed when the turbulence intensity increases from 6% to 26%, which indicates an increase of erosion damage rate by more than 40%. Furthermore, no substantial influence is found due to the effects of wave-induced loads on the wind turbine.
Wavetank Tests With a 1:20 Scale Model of a Distensible Tube Device for Wave Power Harnessing in the Azores
Authors: Mendes António C. , Braga Francisco P. , Chaplin John R.
Published: December 2020

The present research focuses on the performance assessment of a wave power system targeted for electrical supply of small communities in the Azores Archipelago. Firstly, the wave power potential and wave directionality in the region is assessed. The data collected points to a device capable of withstanding severe wave climate. The device considered herein incorporates a long rubber tube filled with water, floating head to waves, connected to an oscillating-water-column (OWC) in a shaft. The shaft and power take-off system (PTO) are to be mounted on an offshore jacket platform. By interacting with the incoming ocean waves the tube excites the OWC at its stern, thereafter forcing air in and out of the pneumatic chamber through a turbine-generator set. It has been observed that this device performs as a multiresonant attenuator that couples the tube’s surging motion and longitudinal pressure bulges with the water column oscillations. In our physical model the power take-off’s nonlinear impedance is emulated by means of a set of calibrated orifice plates with different diameters, connecting the pneumatic chamber to the atmosphere. A series of tests have been carried out with a 1:20 scale physical model in wave-tank, undertaken in regular waves that translate to 5 to 9 seconds wave period in full-scale. Two sets of waves were launched, whose wave heights cover a range from 1 to 5 m in real sea conditions, in deep water as well as in intermediate water depths. The pressure inside the chamber and the free-surface displacement in the shaft have been monitored, as well as the wave field. They provide estimates of the extracted power and energy capture efficiency of the system as a function of incident wave period. Scale effects are also addressed by comparison with previous experiments at different scales. Moreover, the amplification coefficient with the tube in position is quantified and compared with typical values for OWCs alone. It is worth noting that the accuracy of the power and energy capture predictions is greatly dependent on the volume flow calculations. Miller’s algorithm for compressible flow has been applied to reduce the uncertainty of volume flow calculations across the PTO orifice. The influences of the resonant operating modes and PTO impedance upon the capture-width are also discussed. The results obtained so far enable us to provide reliable estimates of absorbed power and energy capture efficiency, in prototype dimensions, under the wave climate in the Azores namely at Corvo Island.