bluuebunny/crossref_metadata_2025 huggingface dataset:
Conditioning of Leakage Flows in Gas Turbine Rotor–Stator Cavities
Authors: Darby P. W. , Mesny A. W. , De Cosmo G. , Carnevale M. , Lock G. D. , Scobie J. A. , Sangan C. M.
Published: December 2020

Ingress is the penetration of hot mainstream fluid into the cavity formed between the turbine disk (rotor) and its adjacent casing (stator). Gas turbine engine designers use rim-seals fitted at the periphery of the disks, and a superposed sealant flow—typically fed through the bore of the stator—is used to reduce, or in the limit prevent, ingress. Parasitic leakage enters the cavity through pathways created between mating interfaces of engine components. Owing to the aggressive thermal and centrifugal loading experienced during the turbine operating cycle, the degree of leakage and its effect on ingress are difficult to predict. This paper considers the potential for leakage flows to be conditioned in order to minimize their parasitic effect on disk cooling, and ultimately engine, performance. Measurements of static and total pressure, swirl, and species concentration were used to assess the performance of a simple axial clearance rim-seal over a range of nondimensional leakage flow rates. A computational model was used to provide flow visualization to support the interpretation of flow structures derived from the experiments. Data are presented to investigate the effects of swirling the leakage flow in accordance with, and counter to, the disk rotation. The injected momentum from the leakage created a toroidal vortex in the outer part of the cavity. Coswirl was found to improve the sealing effectiveness by up to 15% compared to the axially introduced baseline and counterswirled configurations. Varying the momentum of the leakage flow was considered by passing consistent mass-flows through a range of leakage outlet areas. Increasing the momentum was seen to increase the influence of the toroidal vortex on the flow structure in the cavity, which in turn influenced the sealing effectiveness.
Methodology to Investigate the Icebreaking Process of Ships With Non-Typical Icebreaking Bow Shapes
Authors: Hisette Quentin , Myland Daniela
Published: December 2020

For non-typical icebreaking ships the hull-ice interaction process in level ice comprises a combination of many different phenomena which is difficult to be described by existing straightforward approaches. In order to gain knowledge about the level ice resistance of such non-typical hull shapes for operation in ice, a methodology is developed and presented to identify and evaluate the level ice resistance as well as its distribution along the hull of ships with non-typical icebreaking bow shapes with high stem and/or small waterline angles. For this purpose, one ship model has been manufactured and instrumented with several multi-component load cells in the bow region of the waterline as well as with one large six-component load scale between the bow and the stern. Performing resistance model tests at several loading conditions, in model ice sheets of different thickness and at multiple speed values allows obtaining relevant information to meet the goals of the study. The paper focuses on the methodology used for the ice model tests and its analysis. Instrumentation of the model is fully described, together with an overview of the testing matrix and model test observations. Analysis procedure is described in details and applied on a representative test run of the campaign.
Thick Strip Model for Vortex-Induced Vibration of Two Flexible Cylinders in Tandem Arrangements
Authors: Deng Di , Wan Decheng
Published: December 2020

The interference phenomenon among multiple flexible cylinders is an important factor in designing offshore structures, which has been extensively studied by researchers in the past decades. In this paper, Vortex-induced Vibration (VIV) responses of two flexible cylinders experiencing the stepped flow with tandem arrangement are mainly studied using the viv-Thick-SJTU solver, which is developed based on the open source toolbox OpenFOAM and the Bernoulli-Euler bending beam model combining with the thick strip model. Hydrodynamic forces are calculated in each three-dimensional (3D) fluid strip, while vibrations of the cylinder are computed using the Finite Element Method (FEM) through the Newmark-β algrithm. The dynamic mesh technique is adopted to update the computational mesh through the cubic spline interpolation algorithm at every time step. Effects of the gap ratio between two tandem cylinders on vibration characteristic are mainly studied, while gap ratios are set as 4 and 10. Firstly, the validation of the code is conducted. Then, the modal decomposition method and Fast Fourier Transform (FFT) method are used to get the dominant vibration mode and vibration features of both cylinders.
Effect of Polymer Fluid Viscoelastic Properties on the Initiation of Transition From Laminar to Turbulent Flow Regime and the Drag Reduction in the Flow Through Horizontal Pipe
Authors: Hirpa Mehmet Meric , Kuru Ergun
Published: December 2020

This study investigated the flow of viscoelastic fluids through horizontal pipeline mainly focusing on the effect of fluid elasticity on drag reduction and onset of transition to turbulent flow regime. In order to be able to see the sole effect of fluid elasticity (independent from shear viscosity), three non-Newtonian fluids having the same shear viscosity but different viscoelastic properties were tested in the horizontal flow loop. Those fluids were the dilute solutions of partially hydrolysed polyacrylamide (HPAM) and they were prepared by using three polymer grades of HPAM (i.e. 5 × 105, 8 × 106, 20 × 106 g/gmol) in different compositions. Experiments have shown that increasing fluid elasticity resulted in higher drag reduction in pipe flow. Moreover, fluid elasticity affected the onset of turbulent flow and an earlier transition to turbulent flow regime (as compared to water flow) was only observed for the flow of fluid having the highest elastic properties. So, understanding effects of fluid elasticity on flow dynamics might improve the performance of fluids engineered for hole cleaning/cuttings transport in oil and gas well drilling or proppant transport in hydraulic fracturing operations. Also, field efforts to find solutions to problems caused by excessive dynamic pressure losses encountered in drilling horizontal or extended reach wells or in transporting hydrocarbons through pipeline might benefit from the findings of this or further extended research on this subject.
Full Year Drilling Season for MODU in Arctic Area
Authors: Cahay Marc
Published: December 2020

Exploitation of the Arctic’s resources requires the mastery of the risks caused by extreme ice conditions. The design of offshore structures subjected to extreme ice conditions is a challenge for engineers since there are very few advanced numerical design tools available in the market. Especially those able to cope with any kind of structure geometry and a large variety of ice interaction & failure mechanisms.

For developments in arctic shallow water between 50m to 200m water depth it is not possible to use conventional drilling rigs as it is either too deep for fixed or too shallow for floating operations. The other possibility is to have drilling equipment on the platform such as on Prirazlomnaya but then, with a drilling campaign of 5 to 7 years this represents a significant CAPEX compared to the remaining operations time and could imperil the economics of the project.

A smart solution would be to use a MODU for full year operations in Arctic regions. Such a solution would not only place the rig into OPEX but also reduce the living quarters on the platform to the minimum strictly necessary for the operations of the platform, the drilling staff being housed on the MODU. Such a solution could reduce the weight of the platform by nearly 50%.

This paper presents how it is possible to use an Arctic class MODU such as Arcticheskaya for full year operations in ice infested water.
Drilling Dataset Exploration, Processing and Interpretation Using Volve Field Data
Authors: Tunkiel Andrzej T. , Wiktorski Tomasz , Sui Dan
Published: December 2020

In 2018 Equinor made an unprecedented step for an energy company and made a multi-terabyte dataset from Volve field open. However, there is a long way from downloading data to executing meaningful analysis. With no way of quickly evaluating the data due to its size and unfamiliar file formats the use of Volve data was so far limited.

This paper presents our exploratory work related to the realtime drilling part of the dataset. We provide description of common obstacles and approaches for overcoming them. We also describe specific contents of the dataset for others to gauge the potential for case studies. We hope that this will lower the bar for Volve field data accessibility, promote research, and become a catalyst for other data science projects.
Experimental Investigation of Flow-Induced Vibration in Gas/Shear-Thinning Liquid Flows in Vertical Pipe
Authors: Lin Ruinan , Wang Ke , Li Qing , Srinil Narakorn , Shi Fangjun
Published: December 2020

The non-Newtonian shear-thinning fluid widely exists in the industrial process and the rheology exerts a significant influence on the flow pattern transition and flow-induced vibration (FIV). However, studies on the rheology effect of the liquid phase in the vertical upward two-phase flows are quite lacking due to the complexity of non-Newtonian fluid properties. In the present study, the vertical upward gas/shear-thinning liquid flows experiments are conducted on a rigid acrylic pipe with an internal diameter of 20 mm. Three different Carboxymethyl Cellulose (CMC) solutions are used as the non-Newtonian fluid, aimed at capturing a two-phase flow regime transition including the vertical slug, churn and annular flows. The results indicate that the maximum energy spectral densities of vibration occur at the slug-to-churn flow transition boundary at low liquid velocities and the annular flow region under high liquid velocities, respectively. The effects of the rheology of the shear-thinning fluid in terms of the flow patterns and FIV are also presented and discussed.
Detailed Finite Element Modeling of a High Capacity Mooring Steel Wire Rope: Calculation of the Stress Concentration Near the Connection
Authors: Martinez Michaël , Montalvo Sébastien
Published: December 2020

The mooring of floating platforms is an important challenge for the offshore industry. It is an important part of the design engineering and, often, a critical point for the fatigue life assessment. A solution that could improve the fatigue life is to directly connect the mooring rope to the platform, without an intermediate chain. However this solution is not widespread and the behavior of a rope near such a connection is little known. The present paper proposes to better understand this behavior, thanks to a detailed finite element model of the rope. The study case is a steel wire rope directly connected to a floating wind turbine.

A local finite element model of the rope has been built, where the wires are individually modeled with beam elements. One end of the rope is clamped, simulating the connection, while tension and cyclic bending oscillations are applied to the other end. A localized bending takes place near the connection, leading to stress concentration in the wires. The stress concentration and the local contact forces are calculated for each wire. These data are important entry parameters for a local failure or fatigue analysis. This latter is however not presented here. Despite IFPEN experience in the development of local finite element models of steel wire ropes, it is the first time that such a high capacity rope (MBL = 12 500 kN) is modeled. This is challenging because of the large diameter of the rope and the large number of wires. However this modeling approach is very valuable for such ropes, because the experimental tests are rare and very expensive.
Experimental Investigation of Large Particle Slurry Transport in Vertical Pipes With Pulsating Flow
Authors: Masanobu Sotaro , Takano Satoru , Kanada Shigeo , Ono Masao , Sasagawa Hiroki
Published: December 2020

For subsea mining, it is important to predict the pressure loss in oscillating pipes with pulsating flow for the safe and reliable operation of ore lifting. In the present paper, the authors focused on the pulsating internal flow in static vertical pipe and carried out slurry transport experiment to investigate the effects of flow fluctuation on the pressure loss. The alumina beads and glass beads were used as the solid particles in the experiment, and the fluctuating periods and amplitudes of pulsating water flow were varied. The time-averaged pressure losses calculated by the prediction method for the steady flow proposed in the past by the authors agreed well with the experimental ones. As for the fluctuating component of pressure loss, the calculation results using the quasi-steady expression of a mixture model were compared with the experimental data. The calculated results were different from experimental ones for alumina beads of which densities are almost same as those of the ores of Seafloor Massive Sulfides. It suggests that the expression is insufficient to predict the pressure loss for heavy solid particles. The calculated ones, however, provided those in the safety side. On the other hand, the calculated results for light solid particles such as glass beads agreed well with the experimental ones. It means that the expression would be applicable to the prediction of pressure loss for the mining of manganese nodules which are lighter than the ores of Seafloor Massive Sulfides.
A Preliminary Study on the Site Selection of Offshore Wind Power Generation
Authors: Miki Koki , Tabeta Shigeru , Mizuno Katsunori
Published: December 2020

In Japan, which has a wide EEZ, there are high expectations for the potential of MRE. The spread of MRE may produce various effects such as eliminating dependence on other countries for energy supply and revitalizing local economies through business entry. On the other hand, consensus building with various stakeholders at the time of project development is considered a major obstacle to dissemination. In order to promote commercialization of the MRE development, not only the evaluation of economic feasibility but also various aspects such as environmental conservation and coexistence with other industries should be integrated and evaluated. A rational system should be established to select suitable sites that all stakeholders can be convinced. In this study, especially on offshore wind power generation, existing studies on selecting suitable sites in consideration of economic, environmental, and social aspects were investigated as well as the related efforts of each country to review the current status of marine spatial planning and extract issues for MRE deployment in Japan. A preliminary economic evaluation for offshore wind power generation around Japan was also carried out.
Drilling in Karstified Carbonates: Early Risk Detection Technique
Authors: Maksimov Danil , Pavlov Alexey , Sangesland Sigbjørn
Published: December 2020

Heterogeneous nature and complex rock properties of carbonate reservoirs makes the drilling process challenging. One of these challenges is uncontrolled mud loss. Caves or a system of cavities could be a high-risk zone for drilling as the mud losses cannot always be controlled by conventional methods, such as mud weight (MW) / equivalent mud weight (ECD) optimization, or by increasing concentration of lost circulation material (LCM) in the drilling mud. Seismic-based detection of such karstification objects is inefficient due to relatively small size, various shapes and low contrast environment. In this paper we, based on drilling data from the Barents sea, analyzed possible patterns in real-time drilling data corresponding to drilling through karstification objects. These patterns can serve as real-time indicators of zones with higher risk of karsts and can be used as an online tool for decision support while drilling in karstified carbonates.
On the Validity of CFD for Simulating Extreme Green Water Loads on Ocean-Going Vessels
Authors: Bandringa Henry , Helder Joop A. , van Essen Sanne
Published: December 2020

The amount of green water and the associated loads that an ocean-going vessel may encounter during its service life are important aspects to consider in the vessel’s design and classification. As green water is typically a highly non-linear phenomenon, commonly the maritime industry relies on model tests to predict green water loads and their occurrence. In recent years, however, a lot of progress with Computation Fluid Dynamics (CFD) has been made in predicting non-linear flows and associated loads at a high level of accuracy. Especially in the field of wave impacts on (moored) offshore structures at zero speed, significant progress has been made and documented using CFD. A natural extension of this progress is to expand the obtained confidence in the applicability of CFD for simulating extreme wave events to applications involving vessels at forward speed. To that end, this paper presents a validation study towards the prediction of green water loading on a (typical) container vessel at forward speed by CFD.

For validation, two extreme green water events were selected from a model test campaign carried out at MARIN within the context of the CRS (Cooperative Research Ships) working group ‘green water dynamics’. In these tests a KRISO Container Ship (KCS) is sailing in head seas when encountering severe green water. As CFD tool, the Cartesian-grid based Volume-of-Fluid CFD solver ComFLOW was selected. Furthermore, a deterministic approach is taken for the validation, by reconstructing the non-linear incoming wave in a high amount of detail and imposing the 6 degrees of motion of the vessel using the wave basin measurements. Time traces of the green water flow on deck and local- and global impact loads on the breakwater are presented and compared against the experimental data. Detailed visualizations of the CFD results are presented to further illustrate the obtained match with the model test results and emphasize the additional value of complementing model tests with deterministic CFD analysis.
A New Type of Device Used on Submarine Landslides Monitoring
Authors: Ge Yongqiang , Chen Jiawang , Cao Chen , Gao Qiaoling , Zhang Peihao , He Jiamin
Published: December 2020

Submarine landslides in gas hydrate areas are a significant geo-hazard that can cause considerable damage to offshore infrastructures, dramatically change the marine environment and seriously threaten human lives and property. Gas and gas hydrate disassociation was considered to be a main factor inducing submarine landslide. However, the processes and mechanism of submarine landslides caused by gas and gas hydrate dissociation are not clearly understood. Therefore, we design a Micro-Electro-Mechanical Systems (MEMS) accelerometer array to study and monitor the deep displacement of submarine landslides. The MEMS accelerometer array consists of several gravity acceleration-sensing units that are connected to an I2C-communication bus. By sensing the three-axis tilt angles, the direction and magnitude of the displacement for a measurement unit can be calculated. In the end, the laboratory model test was designed to verify the operation of the device in landslide monitoring, which demonstrated the capacities of the monitoring system for collecting real-time and in-situ information during the slope failure.
Hybrid DP Simulations
Authors: Rindarøy Martin , Selvik Ørjan , Ross Andrew
Published: December 2020

Large offshore windfarm development has driven the need for next-generation simulators. These tools are of great utility in both analysis and design. Firstly, they offer the ability to combine advanced dynamic positioning and gangway simulation to evaluate operational safety limits across a large spectrum of weather conditions. Secondly, they can be used as a design tool, in which many variants of design parameters can be altered and simulated, evaluating the design choices with highest efficacy.

This paper presents SINTEF Ocean’s vessel simulator, VeSim, and its results in a numerical DP3 study of a windfarm support vessel operating in DP mode near a platform. These results are presented with a thorough validation against model-scale test results, also performed by SINTEF Ocean in its Ocean Basin Laboratory. In these tests, VeSim used SINTEF Ocean’s in-house DP algorithm to control the model-scale vessel in a realtime hybrid testing environment, which is extensible to arbitrary controller designs. Through this validation task, the simulator’s value is demonstrated as an effective tool for dynamic positioning simulation in its own right. Additionally, the approach taken is shown to emphasise VeSim’s use in both a hardware-in-the-loop and software-in-the-loop testing environment.

The simulation framework is described, including its modelling of environments, propulsion and hydrodynamics, and its implementation of SINTEF Ocean’s in-house DP algorithm. The model test are described in detail, with especial focus on the use of VeSim and how its DP-controller was used as a controller in a hybrid testing environment. The tools and approaches described in the paper offer designers a variety of approaches, both computational and computational-experimental, aiding them in making the best design choices for future offshore vessels.
Residual Stresses and Stress Intensity Factor Calculations for an Orthotropic Steel Deck
Authors: Qiang Bin , Wang Xin
Published: December 2020

The welding residual stress in an orthotopic steel deck is investigated through experimental measurements and finite-element simulations. The simulated residual stress fields are in reasonable agreement with the measured results. The weight function method are used to investigate the stress intensity factors (SIFs) at the surface and deepest points of the semi-elliptical surface cracks, subjected to a combination of external load and through-thickness welding residual stress. Different crack aspect ratios and relative depths are analyzed. The results reveal that the transverse residual stress is always tensile through the plate thickness at the middle section, which makes the SIFs of the surface and deepest points larger than those without considering the residual stress. However, the non-linear reduction for transverse residual stress through the thickness causes the SIFs to decrease for aspect ratios of 0.4, 0.6 and 1.0.
Operational Challenges for Drilling Shallow Water Wells With Dynamically Positioned Rigs
Authors: Vaidya Rohit , Sonawane Mahesh
Published: December 2020

Traditionally, shallow water wells have been drilled from fixed platforms, jack-ups or moored drilling rigs. Recently there has been increased interest in performing operations on these wells using new generation of Dynamically Positioned (DP) rigs, driven by available capacity of these rigs and environmental regulations that restrict laying anchors on the seabed. Shallow water offshore drilling operations present a set of unique challenges and these challenges are further amplified when operations are performed on older wells with legacy conductor hardware with newer DP vessels and larger BOPs.

The objective of the paper is to present challenges that occur during drilling in shallow water and discuss mitigation options to make these operations feasible through a series of case studies.

Key challenges to optimizing riser operability and rig uptime are discussed. Potential modifications to the upper riser stack-up and rig deck structure for maximizing operational uptime are discussed. Riser system weak point assessment is presented along with solutions for mitigating risks in case the wellhead or conductor structural pipe is identified as the weak link. Selection of the drilling rig can have significant impact on wellhead fatigue response. Some criteria for rig selection based on drilling riser and wellhead system performance is presented with the objective of optimizing the fatigue performance of the wellhead and conductor system. Wellhead fatigue monitoring solutions in combination with physical fatigue mitigation options are presented to enable operations for fatigue critical wells.
Second-Order Correlation of Klinkenberg-Corrected Permeability and its Experimental Verification on Heterogeneously-Stressed Gas Shale
Authors: Chen Yufei , Jiang Changbao , Leung Juliana Y. , Wojtanowicz Andrew K. , Zhang Dongming , Zhong Chuanyao
Published: December 2020

Shale is an extremely tight and fine-grained sedimentary rock with nanometer-scale pore sizes. The nanopore structure within a shale system contributes not only to the low to ultra-low permeability coefficients (10−18 to 10−22 m2), but also to the significant gas slippage effect. The Klinkenberg equation, a first-order correlation, offers a satisfying solution to describe this particular phenomenon for decades. However, in recent years, several scholars and engineers have found that the linear relation from the Klinkenberg equation is invalid for most gas shale reservoirs, and a need for a second-order model is, therefore, proceeding apace. In this regard, the purpose of this study was to develop a second-order approach with experimental verifications.

The study involved a derivation of a second-order correlation of the Klinkenberg-corrected permeability, followed by experimental verifications on a cubic shale sample sourced from the Sichuan Basin in southwestern China. We utilized a newly developed multi-functional true triaxial geophysical (TTG) apparatus to carry out permeability measurements with the steady-state method in the presence of heterogeneous stresses. Also discussed were the effects of two gas slippage factors, Klinkenberg-corrected permeability, and heterogeneous stress. Finally, based on the second-order slip theory, we analyzed the deviation of permeability from Darcy flux.

The results showed that the apparent permeability increased more rapidly as the pore pressure declined when the pore pressures are relatively low, which is a strong evidence of the gas slippage effect. The second-order model could reasonably match the experimental data, resulting in a lower Klinkenberg-corrected permeability compared with that from the linear Klinkenberg equation. That is, the second-order approach improves the intrinsic permeability estimation of gas shales with the result being closer to the liquid permeability compared with the Klinkenberg approach.

Analysis of the experimental data reported that both the first-order slippage factor A and the second-order slippage factor B increased with increasing stress heterogeneity, and that A was likely to be more sensitive to stress heterogeneity compared with B. Interestingly, both A and B first slightly increased and then significantly as the permeability declined. It is recommended that when the shale permeability is below 10−18 m2, the second-order approach should be taken into account. Darcy’s law starts to deviate when Kn > 0.01 and is invalid at high Knudsen numbers. The second-order approach seems to alleviate the problem of overestimation compared with the Klinkenberg approach and is more accurate in permeability evolution.
Numerical and Experimental Study on Ultimate Strength of Stiffened Column Under Axial Compression
Authors: Mei Hongyuan , Wang Deyu , Wan Qi
Published: December 2020

Six specimens with one Tee-bar stiffener and its attached plating were tested under axial compression to investigate the ultimate strength. The specimens have one longitudinal span and the simply supported boundary conditions at the end edge of loading were produced based on a horizontal test fixture. The initial geometrical imperfections were measured and tensile tests of high tensile steel used in the specimens with different thickness were conducted. The results calculated by FE analysis with true stress-strain curves, average measured thickness and measured initial geometrical deformation could reach a good agreement with experimental results. The ultimate strength calculated with elastic/perfectly plastic curve is approximately 10% larger than that with true stress-strain curve. The reason is that the proportional limit stress of material is significantly lower than 0.2% proof stress for the high strength steel used in specimens. And the occurrence of buckling is earlier than the time that the material enters into plastic stage. As a result, the ultimate strength assessed with elastic/perfectly plastic curve doesn’t always the lowest result and it should be adopted carefully.
Application of Machine Learning Algorithm in Optimization of PSV for 110000Dwt Oil Tanker
Authors: Xiyang Liu , Jingpu Chen , Wenyu Sun , Wei Xu
Published: December 2020

The pre-shrouded vane (PSV) in front of propeller is a kind of energy-saving device which can change the inflow to improve the received power of the propeller. The device needs to be optimized according to the flow field of the stern. Most of the existing design methods rely on the experience of the designer. In order to improve the design efficiency of PSV and obtain a design scheme with higher energy-saving effect, this paper presents an optimization and analysis method for PSV in front of propeller based on agent model.

Aiming at an 110000dwt oil tanker, 11 design parameters such as stator angle and duct radius are determined by means of parameterization. The design parameters are sampled by Latin hypercube sampling method (LH), and the sample space with 300 samples is generated. The energy-saving effect of each sample is analyzed by CFD method. The data set is formed and next divided into training set and test set. Then, machine learning methods are used to build the agent model of sample space. The error of each model in the test set is analyzed. To obtain the best model, the performance of several models in the test set and training set is considered. The applicability of different models is also highly considered. On this basis, the sensitivity analysis method is used to analyze the sensitivity of each design parameter. Then, the main influencing parameters are found. Finally, particle swarm optimization and genetic algorithm are compared to optimize the design parameters of PSV for 110000dwt oil tanker. The optimization results are verified by CFD method.

The results show that the artificial neural network model is better on this dataset, and the model error on test set is less than 1% compared with the CFD result. The optimal solution by genetic algorithm method is better than all the sample points, and a better design scheme of PSV is obtained.
Swept Blade for Performance Improvement on a Vertical Axis Wind Turbine
Authors: Su Jie , Chen Yaoran , Zhou Dai , Han Zhaolong , Bao Yan
Published: December 2020

The vertical axis wind turbine (VAWT) is considered an important device to utilize the renewable and sustainable wind energy. However, the relatively lower power coefficient has hampered its development. Therefore, this paper attempts to investigate the effect of swept blade employed in a VAWT on the enhancement in aerodynamic performance. A series of swept blades were studied in a small VAWT rotor, and the RANS SST k-ω turbulence model was utilized to simulate the flow field. The numerical model was validated against experimental data, and the aerodynamic performance was investigated with respect to force coefficients, vorticity distribution, static pressure distribution, and wind turbine wake, respectively. The results indicated that the swept blade could effectively increase power outputs by about 20% for the wind turbine. By reducing the drag coefficient, a high lift-drag ratio was achieved. And this configuration prevented the blade from suffering severe dynamic stall. Besides, the swept blade changed the distribution of low wind speed area in the wind turbine wake, which should be considered in the wind farm. It was concluded that this work provided a new way for the practical design and optimization of wind turbine.
Hydrodynamic Response of Tethered Underwater Robot by Feed-Forward and Incremental PID Control Techniques
Authors: Wu Jiaming , Chen Dongjun , Lin Jinhua , Chen Yan , Dou Yizhe
Published: December 2020

The trajectory of tethered underwater robot is usually controlled by actuating the rotating speeds of control propellers attached to the robot and/or adjusting the length of umbilical cable. When the trajectory control problem of a tethered underwater robot is studied, it is necessary to couple the main body of underwater robot, umbilical cable and control propellers together forming an integrated hydrodynamic model so that the robot is in a comprehensive dynamic equilibrium condition, suitable control algorithms are then jointed into the hydrodynamic model constructing a hydrodynamic and control model for the tethered underwater robot system. Only in this way the hydrodynamic and control nature of a tethered underwater robot during different kinds of control manipulations can be numerically revealed objectively.

In this paper, a hydrodynamic and control model to simulate the trajectory following control of a tethered underwater robot system is proposed, and the hydrodynamic performances of the robot and the umbilical cable are observed. To achieve this goal, three-dimensional hydrodynamic model of tethered underwater robot system is first introduced, feed-forward control technique for adjusting the length of umbilical cable and incremental PID algorithm for regulating the rotating speeds of propellers are then incorporated into the hydrodynamic model forming the hydrodynamic and control model. Based on the established hydrodynamic and control mode, relationships between the thrusts from the propellers and the rotating speeds of the propellers, and those among the trajectory following of the underwater robot and the control actions of adjusting the length of umbilical cable and governing the rotating speeds of the propellers are analyzed, and also the hydrodynamic performances of the tethered underwater robot system under the control manipulation are observed. In the research, the amplitude limit filtering method is applied in solving the governing equations of the umbilical cable, this technique is applied to avoid the chattering effect in the cable tension computation, so that a successive and stable computation process is maintained. The main factors affecting the singular nature of coefficient matrices during the numerical solutions of the proposed model are also investigated in the paper.
Topology Optimization Design of the Cantilever Pedestal on a Stiffened Cylindrical Hull
Authors: Yuan Siming , Wang Yue , Cheng Yuansheng , Zhang Pan , Liu Jun
Published: December 2020

The impedance value of the pedestal on a stiffened cylindrical hull directly reflects its resistance to the transmission of vibration waves. In this study, the topology optimization is used to obtain the pedestal with improved impedance and reduced weight. Taking a cuboid with the given dimensions as the research object, the mathematical model of topology optimization is established, in which the element densities is taken as the design variables. According to the optimization results, a new type of cantilever pedestal is obtained. On this basis, the position, size and shape of the main components of the new pedestal are further optimized. Then, the strength and vibration characteristics are calculated and compared. The final optimization results show that the optimized cantilever pedestal with three brackets and a closure plate can effectively improve the minimum impedance of the base. And the thickness of the middle bracket should be much larger than that of the two sides and the closure plate. Compared with the original scheme, the minimum impedance of the optimized pedestal increases by 8.67% while the weight of the structure decreases by 25.69%. The research work provides a good reference for the design of the pedestal.
Neural Network-Based Method for Structural Damage and Scour Estimation Using Modal Parameters and Dynamic Responses
Authors: Wang Shuqing , Jiang Yufeng
Published: December 2020

Wind energy is the most promising clean, renewable energies to the power industry in the world. More and more wind turbine structures equipped with the larger capacity, taller towers, and longer blades were installed at the offshore/onshore wind farms. But these structures face many harsh environmental conditions, and structural damage and foundation scour are continuously accumulated. It could alter the modal parameter and dynamic response and further reduce the safety of structures. It is a significant challenge on how to accurately estimate the structural states if there is structural damage or foundation scour.

For addressing these limitations, a One Dimensional Convolutional Neural Network (1D CNN) method is developed to estimate the structural state. After the Fast Fourier Transform of the acceleration signals, these frequency responses are used as the input to train the 1D CNN, while these states are estimated as the output. A simplified spring-beam model is introduced to simulate the pile-soil interaction, and the effects of the damage and scour on natural frequencies are investigated and compared. The effectiveness and robustness of the proposed 1D CNN method have been numerically investigated by several scenarios associated with the wind turbine structure. Results demonstrate that the 1D CNN method can accurately estimate the structural states, even under a noisy environment. Further, the 1D CNN method can identify the location of damage and scour depth with very high accuracy. This approach may be useful in the on-site structural health monitoring in the wind turbine structure.
Relation Between Cyclone Evolution and Fetch Associated With Extreme Wave Events in the South Atlantic Ocean
Authors: Gramcianinov C. B. , Campos R. M. , de Camargo R. , Guedes Soares C.
Published: December 2020

Extreme wave generation in middle and high latitudes is mainly associated with extratropical cyclones. The wave generation process depends on the size and orientation of the fetch associated with each cyclone, which is usually not taken into account in traditional statistical approaches. A better understanding of the combined effect of the fetch orientation, displacement, and position within the extratropical cyclone can contribute with more accurate wave hindcasts and forecasts, which are crucial to marine operations. The main goal of this work is to investigate the fetch patterns and configurations associated with extratropical cyclones that promote extreme wave events in the western portion of the South Atlantic Ocean. Cyclones are tracked using an objective algorithm and linked to winter extreme Hs events in 10 years of ERA5. The results show the occurrence of 11.4 ± 2.8 storms per winter associated with extreme waves within the domain. Among these extreme events, the maximum and mean Hs was 10.3m and 6.1m respectively. The analysis of the fetch evolution during the lifecycle of the cyclones associated with the 10 most extreme events showed that the surface winds present its maximum usually 12h to 24h before the maximum Hs. The spatial pattern of the most severe events shows the development of a large fetch along the continental shelf, usually within the cold sector of the cyclone.
Numerical Model of a Vertical-Axis Cross-Flow Tidal Turbine
Authors: Zhao Ruiwen , Creech Angus C. W. , Borthwick Alistair G. L. , Nishino Takafumi , Venugopal Vengatesan
Published: December 2020

An array of close-packed contra-rotating cross-flow vertical-axis tidal rotors, a concept developed to maximize the fraction of flow passage swept, has potential advantages for hydrokinetic power generation. To predict the commercial feasibility of such rotors in large-scale application, a numerical model of a vertical-axis turbine (VAT) with a torque-controlled system is developed using an actuator line model (ALM). The open-source OpenFOAM computational fluid dynamics (CFD) code is first coupled with this ALM model, and efficiently parallelized to examine the characteristics of turbulent flow behind a vertical axis tidal turbine. The numerical model is validated against previous experimental measurements from a 1:6 scale physical model of a three-bladed reference vertical axis tidal turbine at the University of New Hampshire (UNH-RM2). Satisfactory overall agreement is obtained between numerical predictions and measured data on performance and near-wake characteristics, validating the numerical model. Details of the model setup and discussions on its output/results are included in the paper.
Application of Structural Monitoring Data for Fatigue Life Predictions of Monopile-Supported Offshore Wind Turbines
Authors: Petrovska Elize , Le Dreff Jean-Baptiste , Oterkus Selda , Thies Philipp , McCarthy Edward
Published: December 2020

Support structure fatigue is a key component in determining the structural lifetime of an offshore wind turbine (OWT). As the currently installed assets age, turbine operators are exploring options for lifetime extension to potentially increase the long-term financial return. Strain monitoring at critical points on a turbine is commonly performed to improve understanding of structural integrity and ultimately reassess its remaining useful life. Reliable application of the findings of a time-limited structural monitoring programme in predicting structural response over a turbine’s lifetime requires a good understanding of the representativeness of the dataset.

Uncertainties arise in fatigue damage estimations due to the stochastic nature of the environmental loading. Statistical treatment of the environmental loads and the corresponding structural response is made by defining measured load cases (MLCs), within which the turbine operational state and associated range of environmental parameters are specified. For OWTs, this leads to a multi-dimensional problem, as both wind and wave parameters need to be accounted for. The complexity of the analysis is thus increased, requiring identification of the critical external and operational parameters that influence overall fatigue. The associated statistical uncertainty can then be estimated by considering repeated measurements throughout the monitoring period.

The work presented in this paper investigates the application of statistical resampling techniques in evaluating the uncertainty in total measured fatigue damage experienced by an offshore wind turbine. Direct fatigue computation over the given measured dataset has been contrasted with statistical approaches applying probability distributions of MLCs to give indication of the influence of the key environmental parameters. Strain monitoring data from a 2.3MW OWT was utilised in conjunction with the corresponding operational and environmental measurements.

The methods and outcomes of this study can be used to improve the remaining fatigue life prediction of installed turbine foundations, by assessing the representativeness of strain measurements. As structural design uses industry defined safety margins, comparison of design predictions against operational measurement data will allow verifying that these safety margins are not exceeded, within the bounds of the given uncertainties. Finally, an understanding of data uncertainties will allow estimates to be made regarding the reliability of the consequent fatigue lifetime reassessment or of the numerical model validation procedures. Such information is useful to wind turbine operators as it provides the first step towards data-driven lifetime extension and informs on measurement campaign utilisation.
Low-Frequency Oscillations Within the Hambantota Port During the Southwest Monsoon, 2019
Authors: Zheng Zhenjun , Ma Xiaozhou , Huang Xuezhi , Dong Yujin , Dong Guohai
Published: December 2020

Long waves with periods greater than tens of seconds propagating into a harbor may be trapped and significantly amplified, thereby resulting in detrimental effects on port operations. The water surface elevation in the Hambantota Port, Sri Lanka, was measured to investigate the low-frequency oscillations and their forcing mechanisms. Results show that the port is protected well from short waves with periods less than 30 s; however, the protection against long waves with periods larger than 30 s is inadequate. The spectral analyses identified four dominant periods within the low-frequency wave range. Modal analysis based on the extended mild-slope equation shows that the measured spectrum density for some dominant periods is low because the measurement point is close to the corresponding modal lines. Correlation analysis shows that low-frequency oscillations inside the Hambantota Port are excited directly by the low-frequency waves contained within the incident waves. The low-frequency waves outside the Hambantota Port are generated from the higher-frequency gravity waves (swell and wind waves) due to nonlinear interactions. Empirical formula is adopted to estimate the low-frequency wave height outside the Hambantota Port.
Validation of Predictions of Wire Stress of Flexible Pipe With Damaged Tensile Armor Wires Under Combined Tension and Bending
Authors: Doynov Krassimir , Rombado Gabriel , Cooke Nathan , Majed Arya
Published: December 2020

The nonlinear kinematic response of a damaged 2.5” flexible pipe under combined tensile and bending cyclic loads is simulated and compared to experimental results. High fidelity finite element model substructures are constructed for intact and broken outer and inner armor wire configurations and assembled in a nonlinear dynamic substructuring (NDS) framework to efficiently simulate the full-scale test configurations. Overall, 12 analysis configurations involving all intact wires, up to 4 broken outer wires, and 2 and 4 broken inner wires combined with 4 broken outer wires are constructed. Each analysis configuration is first preloaded axially and then subject to multiple cycles of (i) pure tension and (ii) combined tension and bending. For each case, tensile armor wire strains are extracted from the simulations and compared to strain measurements from the test. For all cases, numerical predictions and test measurements agree well accurately capturing the redistribution of strains into the adjacent intact wires which result in stress concentration factors.

This comprehensive demonstration of accurate capture of flexible pipe damaged wire kinematics by high fidelity finite element models and nonlinear simulations has direct applications to flexible pipe integrity management and remnant life assessments. Given that the NDS framework allows highly efficient computation, it is now feasible to execute real-time irregular wave local fatigue simulations with finite element models that include damaged wire data from physical inspections to more accurately predict remnant life.
A Study on the Thermal Deformation of Fillet Joint Friction Stir Welding
Authors: Kang Sungwook , Kim Jaewoong , Kim Donghyun , Lee Kwangjin , Jung Yoonchul
Published: December 2020

In this study, experiments and simulations were performed for fillet joint friction stir welding according to tool shape and welding conditions. Conventional butt friction stir welding has good weldability because heat is generated by friction with the bottom of the tool shoulder. However, in the case of fillet friction stir welding, the frictional heat is not sufficiently generated at the bottom of the tool shoulder due to the shape of the tool and the shape of the joint. Therefore, it is important to sufficiently generate frictional heat by slowing the welding speed as compared to butt welding. In this study, experiments and simulations were carried out on an aluminum battery housing made by friction stir welding an extruded material with a fillet joint. The temperature of the structure was measured using thermocouple during welding, and the heat source was calculated through correlation analysis. Thermal elasto-plastic analysis of the structure was carried out using the calculated heat source and geometric boundary conditions. It is confirmed that the experimental results and the simulation results are well matched. Based on the results of the study, the deformation of the structure can be calculated through simulation even if the tool shape and welding process conditions change.