bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling the Impact of Abdominal Pressure on Hypoxia in Laboratory Swine
Authors: KadkhodaeiElyaderani Behzad , Leibowitz Joshua L. , Moon Yejin , Stachnik Stephen , Awad Morcos , Sarkar Grace M. , Shaw Anna E. , Stewart Shelby , Culligan Melissa , Friedberg Joseph S. , Hahn Jin-Oh , Fathy Hosam K.
Published: September 2023

This paper presents an experimentally parameterized model of the dynamics of oxygen transport in a laboratory animal that simultaneously experiences: (i) a reduction in inspired oxygen plus (ii) an increase in intra-abdominal pressure. The goal is to model the potential impact of elevated intra-abdominal pressure on oxygen transport dynamics. The model contains three compartments, namely, the animal’s lungs, lower body vasculature, and upper body vasculature. The model assumes that intra-abdominal pressure affects the split of cardiac output among the two vasculature compartments and that aerobic metabolism in each compartment diminishes with severe hypoxia. Fitting this model to a laboratory experiment on an adult male Yorkshire swine using a regularized nonlinear least-squares approach furnishes both physiologically plausible parameter values plus a reasonable quality of fit.
Non-Contacting Two-Dimensional Position Estimation Using an External Magnet and Monocular Computer Vision
Authors: Pushpalayam N. , Alexander L. , Rajamani R.
Published: September 2023

This paper develops a position estimation system for a robot moving over a two-dimensional plane with three degrees-of-freedom. The position estimation system is based on an external rotating platform containing a permanent magnet and a monocular camera. The robot is equipped with a two-axes magnetic sensor. The rotation of the external platform is controlled using the monocular camera so as to always point at the robot as it moves over the 2D plane. The radial distance to the robot can then be obtained using a one-degree-of-freedom nonlinear magnetic field model and a nonlinear observer. Extensive experimental results are presented on the performance of the developed system. Results show that the position of the robot can be estimated with sub-mm accuracy over a radial distance range of +/−60 cm from the magnet.
Social-Aware Long-Distance Trip Planner for Electric Vehicles Using Genetic Algorithm
Authors: Su Zifei , Lamantia Maxavier , Chen Pingen
Published: September 2023

In the past decade, the number of battery electric vehicles (BEVs) on the road has been growing rapidly in response to global climate change and cyclic gasoline shortages. Due to the limited driving range of most commercial BEVs, individuals who use BEVs for long-distance travel tend to spend much more time on the road than owners of traditional internal combustion engine vehicles. To reduce travel time in long-distance trips, a social-aware trip planner is necessary to coordinate driving speed, vehicle charging, and social activities (e.g., dining, visit of places of interest). This paper formulates this travel time minimization problem into a mixed-integer programming model and utilizes genetic algorithm (GA) to solve for the optimal driving speed, vehicle charging, and the schedule of dining. The proposed planner is first tested numerically based on two real-world routes. Then, Monte Carlo simulations are performed to give a thorough analysis on the performance of the proposed planner. The simulation results show that the proposed method outperforms the baseline on both routes. Additionally, real-world tests are conducted to further validate the accuracy of the mixed-integer programming model.
Mitigating Interwell Fracturing Interference: Numerical Investigation of Parent Well Depletion Affecting Infill Well Stimulation
Authors: Wang Wendong , Yu Wenfeng , Wang Sukai , Zhang Lipeng , Zhang Qian , Su Yuliang
Published: September 2023

Frac hits were not unfamiliar in tight gas development. During the hydraulic fracturing process in infill well, due to closely spaced wells and parent well depletion, operators often encounter fracture interference between the parent well and infill well, resulting in frac hits. This phenomenon typically has a significant impact on the productivity of both infill and parent wells. However, effectively mitigating and minimizing the negative effects of frac hits continues to pose a formidable challenge. Therefore, we developed a new frac hits evaluation and management workflow, aiming to investigate the mechanism of frac hits between infill well and parent well and improve the performance of the infill well while avoiding frac hits. The results indicate that an increased extent of parent well depletion leads to higher surrounding rock pressure and stress depletion. The stress deflection region near the fracture tip of the parent well attracts the propagation of infill well fractures, resulting in frac hits and significantly affecting the performance of the parent well. Consequently, optimizing the timing of hydraulic fracturing in the infill well is beneficial to mitigate parent well depletion, controlling frac hits and enhancing gas well productivity. This research provides important insights for mitigating parent–infill well interference in the development of tight gas reservoirs and establishes a solid foundation for future studies.
Vortex-Induced Vibrations of Dynamic Power Cable for Floating Wind Turbines
Authors: Elrick Peter , Venugopal Vengatesan
Published: September 2023

Dynamic power cables are important structural components of floating renewable energy converters, such as floating wind turbines and other marine energy converters. Similar to marine risers, waves and currents are expected to produce Vortex Induced Vibrations (VIV) of these dynamic power cables. VIV of power cables can lead to a significantly shorter fatigue life if they are of large amplitude and frequency. In the past, numerous studies have been conducted investigating the vortex-induced vibrations of deep-sea risers and umbilicals but as of yet, only a very few studies have focused on dynamic power cables.

This research work investigates the VIV of a dynamic power cable for a semi-submersible floating wind turbine based on the NREL offshore 5-MW baseline wind turbine. This study is conducted using the industry standard software tools, OrcaFlex and Shear7. The dynamic power cable has been modelled into a lazy wave configuration and the Milan Wake Oscillator and Iwan and Blevins oscillator models (both from OrcaFlex), and Shear7 are applied to predict the VIV behaviour under differing current conditions. Both uniform and shear currents are considered. In the numerical model simulations, the power cable is subjected to three different current propagation directions (i.e. 0°, 90° and 180°) and current speeds from 0–2.0 m/s. The results indicate that the behaviour of the cable vibrations is strongly dependent on the (i) submerged position of the cable along its length, (ii) structural and mechanical properties of the cable, (iii) current propagation direction and its magnitude, (iv) Strouhal number, and (v) choice of numerical model.
Numerical Investigation of Hull Vane on a Medium Froude Number Displacement Hull
Authors: Gopinath Sathiyamoorthy , Ashok Kumar , Rajagopalan Vijayakumar
Published: September 2023

As a result of the rise in atmospheric emissions and an effort to move toward green shipping through de-carbonization, the International Maritime Organization (IMO) decided to enact some regulations and guidelines in the form of the Energy Efficiency Design Index (EEDI) and the Energy Efficiency Existing Ship (EEXI) on newly built and existing vessels respectively. Researchers emphasized reducing frictional and wave-making resistance components acting on the ship to explore solutions that will advance the idea of green shipping. Wave-making resistance components are predominant for a displacement vessel operating at higher speeds. Until now, Energy saving devices (ESD), In particular, Hull Vane (HV) has been extensively used as a promising methodology for minimizing wave-making resistance. Several experimental and numerical research works have been carried out on high-speed ships using HV to establish favorable trim and reduce wave-making resistance. However, the benefit of an HV for a medium-speed Froude number vessel is yet to be explored where nearly fifty percent of the total resistance is due to the wave-making component. This study includes the numerical analysis of a candidate medium-speed displacement hull to estimate the hydrodynamic characteristics, by using the VOF method and RANS solver. The numerical results are discussed on reduction in the pressure resistance, wave height, sinkage, and trim of the vessel with and without HV. The experimental work on the resistance of the candidate hull was used to validate the numerical results. The comprehensive numerical study was performed at medium speeds to analyze the effect of the hull vane to understand the improved hydrodynamic behavior of the hull.
Wellhead and Well Casing Integrity During an Event of Drift-Off: A Study Case of an Integrated Riser Analysis Solution Using On-Site Conditions
Authors: Sarnáglia do Amaral Acácio , Araujo das Virgens Edmo , Venero Germain , Mussel Dias Soares da Silva Thiago , Bohan Paul
Published: September 2023

The modern oil rig uses the dynamic position system (or DP System) to maintain position and provide ways for the rig to accomplish its mission. Although the DP System has improved its reliability over the years, it can eventually fail and produce a critical incident called a drift-off. In this situation, the riser, wellhead and well casing will be subject to a fairly large amount of stress that must be properly evaluated.

It is well established in the offshore industry to perform this assessment by performing a time domain coupled analysis simulating the behavior of a riser, wellhead and well casing in the event of drift-off. This is commonly called drift-off analysis.

Over the past few years, significant improvements have been achieved in the mathematical models of these analyses, but even today we add many conservative factors to cover forthcoming operation uncertainties. Major factor are environmental conditions used on the analysis. Seeking to cover all scenarios, extreme colinear values are used as analysis input, resulting in narrow unfeasible operational watch circles for shallow waters or sensitive wells.

In this article we present the practical methodology and the results of our experience using commercial software Optima™ that performs drift-off analysis using on-site conditions. By using actual and short forecasted conditions, on-site analysis results provided valid feasible watch circles, allowing operations to take place in safely manner.
Verification of Swarm Intelligent Underwater Robot System for Marine Environment Observation With Vehicle Loss Compensation and Functionality Maintenance
Authors: Kobatake Kanako , Arima Masakazu
Published: September 2023

There are many problems facing the oceans. These problems are mainly caused by the changing marine environment. In order to understand and solve these problems, it is necessary to obtain detailed and long-term marine environment data.

In this study, we have attempted to construct a detailed and long-term marine observation method that covers a wide area. It is necessary to adopt observation equipment that can be operated for extended periods and move decisively on its own. The authors have focused on an Autonomous Underwater Glider (AUG) which is a vehicle with low energy consumption and a long operating time. However, in underwater operations, there is always the possibility of vehicle failure. We thus propose an advanced pathfinding system that is unaffected by the loss of some vehicles since each vehicle can independently decide its behavior in accordance with surrounding information from its latest observations.

Finally, the effectiveness of the proposed method is verified by operational simulations monitoring Japan’s Exclusive Economic Zone for a year and by factoring in the loss of some vehicles. In these simulations, we have evaluated the influence to an observation system when some randomly selected vehicles stop operating.
Lifecycle Assessment of Fuel Saving in Bulk Carrier With a Flettner Rotor
Authors: Sogihara Naoto , Kume Kenichi
Published: September 2023

Reduction of greenhouse gas (GHG) from shipping sector is urgent issue. International Maritime Organization (IMO) adopted the initial strategy on the reduction of GHG emissions from ships. This has accelerated researches and developments on the technologies for energy savings in design and operation stage. A lot of attentions are paid to an application of natural energy to propelling a ship and especially wind propulsion is expected as an effective system for achieving energy saving in operation.

This study focuses to a rotor ship as a ship with wind propulsion and addressed a bulk carrier having a rotor onboard. A rotor ship can obtain the thrust force from encountering winds based on Magnus effect and consequently can achieve fuel saving in operation. For spreading the use of a rotor widely, it is necessary to evaluate the fuel saving since the cost for building a rotor ship is larger than that for ordinary ship.

For evaluating the fuel saving in a rotor ship with accuracy, the external force such as added resistance in winds and waves should be predicted. For predicting the added resistance, this study applies the methods described in ITTC-RP. The lift and drag force of a rotor is estimated based on the computational studies on a rotating cylinder in uniform flow. Solving the equilibrium equations on the forces acting on a rotor ship navigating with constant speed provides the power-curves in actual seas on which the calculation of fuel oil consumption is based.

Furthermore, based on the power-curves and the calculated fuel oil consumption, the lifecycle assessment of fuel saving in a rotor ship, which is considering the effects of aging and fouling for hull and propeller, is conducted. Fuel saving throughout ship’s life based on the lifecycle assessment is reported in this paper.
Predictions of Wind Loads on FPSO With POD-Based Discrete Empirical Interpolation Methods
Authors: Xing Xiuqing , Dao My Ha , Zhang Baili , Lou Jing , Tan Wei Siang , Cui Yongdong , Khoo Boo Cheong
Published: September 2023

As the Proper Orthogonal Decomposition (POD) based Discrete Empirical Interpolation Method (DEIM) constructs specially selected interpolation indices that define an interpolation-based projection without carrying out the orthogonal projection as the POD-based Reduced Order Method (ROM) does, we apply the DEIM method to reconstruct and predict the wind load on an FPSO in this study. High-fidelity CFD simulation is adopted to collect snapshots for the reduced-order model. Effects of the number of DEIM selected interpolation points are tested. Testing results indicate that DEIM can predict the wind load on the FPSO with high accuracy even with only 5 interpolation points. Considering the limited installation locations over the scaled models in wind tunnels, DEIM’s feature of interpolation indices selection for an optimal subspace approximation could be helpful to determine the optimal sensor positions, and consequently to offer guidance for sensor positioning for wind tunnel tests and improve the prediction accuracy of the ROM-based data assimilation models.
Design Considerations on Semi-Submersible Columns and Pontoons for Floating Wind
Authors: Ivanov Glib , Hsu I Jen , Ma Kai-Tung
Published: September 2023

Floating Offshore Wind Turbine (FOWT) is an innovative technology with little industry guidance for its hull design. Various FOWT floaters with different hull shapes claim to support the same turbines. Structural integrity and material expense analyses of different pontoon shapes were conducted, and it was found that some configurations, such as those with every two columns connected by one pontoon, have advantages over others. However, it is important to note that the choice of pontoon shape should be based on the wave loading conditions the floater will be exposed to. While a T-shaped pontoon provides a cost-effective solution under certain wave loading scenarios, it may not be the best option for all conditions. Specifically, ring pontoon designs with full bracing were found to be necessary for withstanding certain wave loads. Therefore, it is important to consider different Dominant Load Parameters (DLP) and ensure that a FOWT floater can withstand all applicable DLPs. An uneven hexahedral column shape, which combines the best attributes of square and round shapes, is proposed as a better alternative. It offers ease of manufacture and relatively good hydrodynamics, while bracing is found to be necessary for withstanding the wind turbine’s incurred moment and forces. The conclusion is that column design should prioritize manufacturing costs over hydrodynamic performance.
A Statistical Approach for Estimating Sea Ice Thickness
Authors: Veber Joshua , Brown Jeffrey , Wang Jungyong , Browne Thomas , Veitch Brian , Molyneux David
Published: September 2023

Sea ice reporting and ice charts are a necessary simplification of highly variable sea ice conditions over large areas. Ice conditions are typically shown using egg codes. These codes can be used to determine an equivalent ice thickness as a method for calculating a ship’s ice resistance. This approach does not acknowledge the variability within the chosen region, such as the presence of ridges, ice pressure and snow cover. A new statistical method is proposed to use live capture data including the speed and resistance from a medium ice breaker to estimate the changing ice thickness. The thickness is calculated using the ship’s regression model for the ship’s performance based on model scale tests. Measured thrust data from the ship is used in conjunction with the thrust deduction factor and open water resistance to derive the ice resistance and subsequent thickness. The statistical ice thickness is compared against the equivalent ice thickness derived from the ice egg codes to determine the accuracy of current ice reporting and identify the variance within a defined region. This statistical approach may also assist in identifying features such as ridges, including the frequency of encountering these events. This analysis has high potential for sources of error, such as the changes in force required to bend and break ice sheets. Therefore, the data must be adequately analyzed to eliminate such noise while preserving the ability to identify changes to ice thickness. The potential implications of this research are an improved awareness of the variability in sea ice, and improvements to the methods for reporting and characterizing sea ice conditions.
A 4 Degree of Freedom Velocity / Power Prediction Program for Wind (Assisted) Vessels
Authors: Oettle Johannes , Krüger Stefan
Published: September 2023

This paper presents a velocity prediction program (VPP) respectively a power prediction program (PPP) for ships driven or assisted by wind propulsion systems named “E4-SAIL”. The program balances the forces acting on the ship in the four degrees of freedom (4DOF) surge, sway, roll and yaw. Therefore, environmental forces caused by wind, current and seastate can be considered. The VPP/PPP is embedded within the design environment “E4”, so the pediction can be refined directly within the design process whenever more information on the ship is known. Thanks to the integration into the design environment, the calculation of the transversal forces acting on the hull and the forces due to the seastate takes into account the shape of the hull instead of using only an amount of ship parameters. Because the VPP/PPP is intended for use in the early design stage, the calculations have to run very fast, so that the effect of several changes in hullform and floating position can easily be checked during the design process. The individual force components are presented and an exemplary calculation for a tall ship is shown.
A Combination of Surrogate Model and Subset Simulation Method for Long-Term Extreme Response Analysis of Marine Risers
Authors: Miao Qingqing , Cheng Ankang , Low Ying Min
Published: September 2023

Evaluating the long-term extreme response of marine risers generally involves numerous time-consuming simulations of offshore structures in the time domain. Traditionally, the most rigorous reliability analysis method — Monte Carlo Simulation (MCS) is employed to account for both varying long-term environmental loads and short-term wave dynamics through extensive sampling. The number of simulations required by MCS is impractical when targeting long return periods to meet the industry standard. Subset Simulation (SS) as a variance reduction method has been widely applied to solve low failure probability problems. It significantly improves the efficiency of MCS while preserving accuracy. However, the computational time demanded by SS is still intolerable when simulating complex numerical models of offshore structures. Many recent studies have proposed the use of surrogate models, especially artificial neural networks (ANN) to predict the dynamic response of offshore structures for more efficient reliability analysis. This paper presents a method that combines artificial neural networks and subset simulation for long-term extreme response prediction. The ANN is well-constructed using designed training data sets of varying environmental conditions for accurate prediction. The efficiency and accuracy of the proposed method are verified through a case study to predict the extreme top riser stress of a floating production system. The structure is exposed to sea states characterized by a joint-probabilistic description of significant wave height (Hs), spectral period (Tp), and wave direction (θw). The proposed method has been shown to accurately estimate the long-term extremes with a remarkable reduction in computational time.
Wake Effects on the Drag Force Estimation of Downstream Fish Cages
Authors: Cheng Hui , Aydemir Onur , Ong Muk Chen
Published: September 2023

A typical fish farm in Norway usually consists of 6 to 12 fish cages, and these fish cages are moored together in a grid shape. Due to wake effects, individual fish cages may experience different flow velocities depending on their positions in the fish farm. Hereby, the drag forces on individual fish cages can be different. Without knowing the exact flow velocity, the drag forces on the downstream fish cages are difficult to estimate. This will cause difficulties in the mooring system design, as these drag forces are important input variables. In this paper, the computational fluid dynamic (CFD) method combined with a porous media model is employed to study the flow field through and around fish cages. The drag forces on the downstream fish cages are investigated and the wake effects on fish farm design will be discussed.
Potential Root Causes for Failures in Floating PV Systems
Authors: Zhao Shengnan , Low Ying Min , Rodríguez-Gallegos Carlos David , Reindl Thomas
Published: September 2023

To mitigate climate change and reduce the dependency on fossil fuels, the adoption of renewable energy has grown significantly in the last decade. Solar energy as one of the major renewable resources is taking up more and more share of green energy in the world. However, one problem of deploying large-scale photovoltaic (PV) system is the required land usage, especially for the countries with land scarcity and high population density. To overcome this issue, floating PV (FPV) systems have emerged as an interesting option. It has been more than 15 years since the first FPV system was installed in Aichi, Japan. Since then, different FPV technologies have been developed. Despite their potential advantages, many issues arise due to the harsher environmental conditions and the more complex configuration of FPV system compared to conventional ground-mounted installations. This paper aims to conduct an analysis of potential root causes for failures in FPV systems during the operation and maintenance, which is based on FPV systems monitored by the Solar Energy Research Institute of Singapore (SERIS) and other literature sources. Besides, an introduction of the development of FPV system and a review of current float technologies are also presented. Finally, a summary of the challenges and an outlook of the opportunities for the deployment of FPV systems is provided.
Motion-Based Wave Inference With Neural Networks: Transfer Learning From Numerical Simulation To Experimental Data
Authors: Alencar Bisinotto Gustavo , Cardozo de Mello Pedro , Gagliardi Cozman Fabio , Aoun Tannuri Eduardo
Published: September 2023

The directional wave spectrum, which describes the distribution of wave energy along frequencies and directions, can be estimated from the measured motions of a vessel subjected to a particular sea condition by resorting to the wave-buoy analogy. Several methods have been proposed to address the inverse estimation problem; recently, machine learning techniques have been assessed as further alternatives. However, it may be difficult to gather large datasets of in-service motion responses and the associated sea states to train effective data-driven models.

In this work, an encoder-decoder neural network is trained with the synthetic responses of a station-keeping platform supply vessel (PSV) to estimate the directional wave spectrum. This estimation model is directly applied to perform wave inference from motion data of wave basin tests with a small-scale model of the same vessel. Furthermore, fine-tuning is also used to incorporate experimental data into the neural network model.

Results show a satisfactory match between estimated and measured values, both with respect to the energy distribution and the integral spectrum parameters, indicating that the proposed approach can be employed to obtain data-driven wave inference models when there is little or no availability of measured motion records and the corresponding sea conditions.
Unbonded Flexible Pipeline Upheaval Buckling Design and Sensitivity Analysis
Authors: Eriksen Morten , Larsen Anders Astrup , Pedersen Tommy , Ollgaard Larsen Henrik , Shanks Andrew , Gavouyere Thierry , Kristian Boe Johan , Caracol Rui , Liu Jian , Clements Richard , Pires Roberta , Zhu Linfa , Tan Zhimin
Published: September 2023

Flexible pipelines are often subjected to cover requirements on the seabed due to protection or stability issues. These requirements may be satisfied using a range of techniques, e.g. covering the pipe with rocks or soil. Due to pressure and thermal expansion in operation the pipe may be susceptible to lateral or upheaval buckling (UHB) out of the cover which may violate the cover requirements and could ultimately be detrimental to the flexible pipe.

The present paper is concerned with the design of reliable and cost-efficient cover solutions for unbonded flexible pipes. A new DNV guideline will introduce “Allowing Irreversible Displacement” design approach which allow for the pipe to move within the cover provided that the end-of-life limit states for pipe and cover are satisfied.

The paper includes a description of how a model following that approach may be defined, including considerations on load case matrix and a discussion on relevant sensitivity cases to ensure conservatism in the cover design. A case study is included to show how the principles of the guideline may be applied in UHB design.
Monitoring the Rotational Performance of a Weathervaning Mooring System
Authors: Minnebo Joerik , Chen Jiaxing , Gu Haoyuan
Published: September 2023

Within this paper, an approach to monitoring the rotational performance of weathervaning systems is proposed, by mainly looking at the so-called release events: the maximum rotation (or break-out angle) of the geostationary side of the turret, where the mooring yaw stiffness overcomes the static friction moment internal to the rotational interfaces of the floating facility. The physics of the stick-slip and release behavior are reiterated, the multiple dependencies are identified, and various performance characteristics are defined which will support long term operational monitoring of the turret’s weathervaning capacity.

Practical methods and examples are presented to individually monitor the governing dependencies. In the end, an unsupervised machine learning algorithm is proposed to identify any unwarranted increases in break-out angle: an anomaly detection method based on isolating the contribution of each of the dependencies on the release event dynamics.
Research on Deformation Characteristics of Cruise Superstructure Based on Digital Twin
Authors: Liu Siyuan , Pei Zhiyong , Yang Bin , Wu Weiguo
Published: September 2023

In order to master the structural response characteristics, a digital twin model of the cruise structural experiment model is constructed to grasp the deformation and interaction mechanism between the main hull and plump superstructure under each loading condition.

The structural matrix of the experiment model is constructed to establish the reduced order model. Furthermore, the real-time response of the cruise structural experiment model can be predicted by the kriging agent model. Subsequently, the experiment model of a cruise ship is taken as the object. Three typical cross-section measuring points are arranged in the midship area to monitor structural response. Ten groups of different working conditions are designed to compare the response characteristics. It is found that the structural response error between the results of the digital twin model and the experiment remains small under each loading condition.

The digital twin model can represent the character of the experiment model effectively. The interaction mechanism between the main hull and superstructure can be investigated using the proposed digital twin model to improve the safety and reliability of the cruise ship structure.
Impact of New Bow Shapes on FSICR Power Requirements
Authors: Matala Riikka , Suominen Mikko
Published: September 2023

In the Baltic Sea, merchant ships receive icebreaker assistance during the winter period based on their Ice Classes, which are granted based on the Finnish Swedish Ice Class Rules (FSICR). The FSICR set requirement for e.g. the ship minimum power demand to secure an adequate ice performance of ice-classed ships. The rules have been developed based on cumulative experiences on the winter navigation in the region with ships having traditional ice-going vessel design.

Recently, growing interest on sustainable transportation has led to new emission restrictions for merchant ships. This has generated new approaches for the ship bow design, especially for ships mainly operating in open water and only occasionally in ice. Some recently built ice-capable merchant ships have open-water-optimised bow shapes that substantially differ from traditional bow shapes of ice-going vessels. Instead of traditional low stem angles, the bow angle can be vertical or close to vertical.

Our recent research indicates that the current FSICR procedures may not evaluate the brash ice channel resistance of these modern bow shapes correctly. To secure the uniform ice class classification, this paper reflects the conclusions from our channel resistance research on the ice class rules power requirements and suggests improvements to current rules.
Drag Variation of a Coupled Rigid-Flexible System in Wind Tunnel Experiments
Authors: Zhao Yakun , Tian Xinliang , Zhang Huanyu , Sun Shuyue , Guo Xiaoxian , Peng Tao
Published: September 2023

A novel flow control method, by adding a closed flexible coating to a rigid body, has been proven a significant drag reduction in the two-dimensional flow in a soap film tunnel (Phys. Rev. Lett., vol. 125(3), 2020, pp. 034502). In the present study, we extend this method to three-dimensional rigid bluff body (a flat plate) flows through wind tunnel experiments. The Reynolds number (Re) based on the free-stream velocity (U∞) and the flat plate width is 24000. The length ratio of the flexible membrane (Lr) is in the range of 1.33∼3.23, and Lr = 1 represents a bare plate scenario. The effect of the length ratio on the drag of the rigid-flexible coupling system is discussed. It is found that the mean drag varies nonmonotonically to the length ratio. Benefiting from the closed flexible membrane, the coupled rigid-flexible system achieves a significant drag reduction in three-dimensional flows. The maximum drag reduction of approximately 19.1% is observed under specific conditions (Lr = 2.43). The flexible membrane self-adapts to a more streamlined shape and substantially changes the flow structures behind the plate. Controlled by the flexible membrane at Lr = 2.43, the flow separation is delayed, and the wake region changes to a narrow and shorter region, resulting in a significant drag reduction. The preliminary results obtained in the present study may shed some light on the closed flexible coating flow control method towards some real-life situations and potential applications.
Development of a Floating Dock Numerical Model and the Ballast Water Distribution Strategy
Authors: Zhang Jianan , Wen Xueliang , Ong Muk Chen
Published: September 2023

This study aims to develop a time-domain numerical model for simulating the dynamic response of a floating dock and propose a ballast water distribution strategy to help the dock reach a target draught with zero heel and trim. The floating dock is modelled as a six-degree-of-freedom (6-DOF) rigid body subjected to hydrostatic and hydrodynamic loads. A hydrostatic force model is built using Archimedes law and strip theory along the dock’s longitudinal direction. A hydrodynamic force model is made based on the effects of added mass and dynamic damping. The developed model is verified against the corresponding results obtained using HydroD, Autodesk Inventor and the theory of the dock’s free motions of heave, roll and pitch without damping. The ballast water distribution strategy provides the target water volumes in ballast tanks for a given draught and is created based on the equilibrium equations of draught, heel and trim. Vent pipes are installed in the ballast tanks to connect the air inside the tanks to the atmosphere outside the dock. Air cushions induced when the ballast water levels are higher than the bottoms of the vent pipes make the actual ballast water volumes not exceeding the target ballast water volumes at the maximum draught during ballasting operations. The relationship between the target ballast water volume and the height of the vent pipe bottom is investigated. In the case study, the freely floating processes of the dock with the ballast water distribution plans for different target draughts are simulated using the developed numerical model. The time histories of the dock’s draught, roll and pitch motions show that the proposed ballast water distribution strategy works successfully to make the dock reach its target draught with zero heel and trim. The maximum draught of the dock with the proper ballast water distribution and the corresponding vent pipe bottom heights in all ballast tanks are obtained.
A Novel Hybrid Transfer Learning Method for Bottom Hole Pressure Prediction
Authors: Zhang Rui , Song Xianzhi , Li Gensheng , Lv Zehao , Zhu Zhaopeng , Zhang Chengkai , Gong Chenxing
Published: September 2023

Accurate and efficient prediction of bottom hole pressure (BHP) is critical for safe drilling in complex formations. Recently, more and more studies have found that intelligent models have high accuracy in predicting BHP. However, most of the existing intelligent methods are limited to historical measurement, which is insufficient in processing new data. To overcome the problem of insufficient generalization ability of the model on new dataset, we propose a novel hybrid transfer learning approach to incrementally predict BHP in different well sections, combining long short-term memory (LSTM) and domain adversarial neural network (DANN). For deeper well sections, this method applies features learned from historical data in the upper well sections to boost the BHP prediction. LSTM is applied to extract temporal characteristics from the upper and deeper well sections. DANN tries to discover constant characteristics between the upper and deeper well sections. Next, LSTM-DANN model trained with data in the upper well sections can be used to support prediction of target BHP without degradation of accuracy due to data offset. Based on drilling data from the field, the performance of the proposed method is fully assessed. Results indicate that the hybrid transfer method can significantly improve the BHP prediction performance compared to models trained on data from different well sections. The mean absolute percentage error of the novel method reaches 0.15%, which is reduced by 30% compared with the original one. This study provides reference for accurate managed pressure drilling, and contributes to improve the transferability and generalization of intelligent models.
An Experimental Study on Vortex Induced Motion of a Submerged Cylindrical Buoy With a Short Tether Chain
Authors: Ledoux Thomas , Anne Florentin , Béguin Cédric , Gosselin Frédérick , Étienne Stéphane
Published: September 2023

Here we study experimentally the Vortex Induced Motion (VIM) of a cylindrical subsurface buoy tethered by a short chain. This system has 5 degrees of freedom (DOF), but can experience 3 DOF in translation (heave, surge and sway) and 3 DOF in rotation (yaw, pitch and roll). Previous studies focused on buoys with high ratio between tether line length and buoy diameter, which led to only 3 DOF motions (surge, sway and yaw). We put a reduced model buoy in the test section of a hydrodynamic loop. The mass ratio of the buoy was of 0.213, its slenderness ratio of 3.95, and the ratio between the tether line length and the diameter of the cylinder was of only 1.99, compared to around 15 in previous studies. Reduced velocity Ur ranging from 1.55 to 10.8 have been tested. The buoy was captured crosswise, and we got its surge and heave motions and the orientation of the buoy in terms of yaw, pitch and roll motions. Sway was not obtained in a satisfying way. Eventually, we found significant heave, surge, sway, yaw, pitch and roll motions above Ur ≈ 4. These motions were mostly harmonic, but with a irregular superimposed component, which was probably due to the turbulence of the flow. We did not observe any clear lock-in phenomenon, and the roll frequencies were always lower than Strouhal frequencies.
Acoustic Emission Based Damage Source Localization for Heterogeneous Structure of Wind Turbine Blades Using Long Short-Term Memory Neural Networks
Authors: Zhao Zhimin , Chen Nian-Zhong
Published: September 2023

The cost of operation and maintenance of wind farms has been increased significantly due to insufficient attention to structural damage of wind turbine blades. There is currently a great demand for structural health monitoring of wind turbine blades that could identify the location of damage source timely. The heterogeneity of the wind turbine blades poses a great challenge for damage source localization. A novel damage source localization method based on acoustic emission (AE) and long short-term memory neural networks is developed for heterogeneous structure of wind turbine blades in this paper. Two machine learning models based on long short-term memory (LSTM) neural networks, LSTM-Atten and LACNN, are pre-trained and utilized in a two-step approach to minimize the influence of propagation characteristics of AE signals. The first step is to identify the zone where the damage source is located and the second step is to determine the exact coordinates of the damage source. The time difference of arrival (TDOA) is used as the training feature. TDOA is calculated by the time of arrival (TOA), which is determined by the Akiake information criterion (AIC). Then, an example application of damage source localization for a “spar cap-trailing panel-shear web” heterogeneous structure of a wind turbine blade is performed to evaluate the performance of the method. A comprehensive comparison between the proposed method and the damage source localization method based on “L” shaped sensor cluster is carried out to verify the superiority of the proposed method. The results demonstrate the feasibility and robustness of the proposed damage source localization method for heterogeneous structure of wind turbine blades.
Coupled Hydrodynamic and Geotechnical Simulation of Floating Offshore Structures
Authors: Dyson Ashley P. , Tolooiyan Ali , Kefayati Gholamreza
Published: September 2023

Submerged and partially submerged moored structures subject to ocean conditions often require considerations regarding hydrodynamic loads impacting the behaviour of foundations and anchors attached to the seabed. Subsequent soil deformations can further affect the performance of anchored structures and, in extreme cases, result in anchor failure. This paper addresses simulation methods for assessing the response of offshore anchored structures under wave and current loading regimes with and without fluid-soil-structure interaction. Although coupled hydrodynamic-geotechnical simulation methods present a mechanism to analyse the full offshore fluid-soil-structure system, these methods are currently seldom implemented. In this research, numerical models combining rigid and deformable structural elements, fluids and soils in a single model are used to contrast the suitability and capabilities of various Finite Element (FE), Computational Fluid Dynamics (CFD) and Large Deformation Finite Element (LDFE) methods. Comparative results focus on applied mooring line loads, soil plasticity, and deformation characteristics to assess the behaviour and performance of anchors based on a range of ocean environmental loading conditions. An initial study of a four-point catenary moored floating box is presented for different numerical methods and compared with experimental scale model flume-test results. Further consideration is given to soil performance based on coupled hydrodynamic-geotechnical simulations of high-energy offshore conditions for a floating buoy and embedded pile in what is the first coupled Fluid-Structure-Seabed Interaction model of a moored floating system.
A Case Study on the Seabed Trenching Assessment and Anchor Design in Clay Based on the Hydrodynamic Calculation of the Floater
Authors: Rui Shengjie , Zhou Zefeng , Wang Baoxuan , Wang Hongyu , Zhang Haojie , Zhang Yaru
Published: September 2023

Seabed trenches near the anchors reduce anchor bearing capacity, and increase failure risks of the mooring system. However, the adverse influence is not well considered in the anchor design. This paper presents a case study on the anchor design in clay considering the seabed trenches based on the hydrodynamic calculation of the floater. The design procedure includes four steps. First, the hydrodynamic calculation of the floater coupled with mooring system is conducted under the 100-year return period to obtain the maximum mooring line tension and maximum cyclic displacement. Then, the 3-D potential trench profile is assessed by the mooring line-seabed dynamic model according to the fairlead movement. Third, the suction anchor is designed considering the calculated trench profile, and compared with that in the intact seabed. Last, the designed anchor is optimized to inhibit the potential trench development by adding a plate on the top of caisson. Some useful suggestions are concluded based on the case study results. This paper presents a systematic design from the hydrodynamic calculation of floater to the anchor design and optimization considering the potential seabed trenches.
Experimental Study on the Combination of Split Heave Point Absorber and TLP-Type Floating Turbine
Authors: Zhang Huidong , Wang Tong , Xu Cong , Shi Hongda
Published: September 2023

There are numerous wave energy resources in the ocean, and how to convert them efficiently is still a problem to be solved. Considering the waves in China sea area are characterized by short period and small height, one new model combining three split heave point absorbers with a tension leg platform (TLP) is proposed in this paper. Based on the physical model test, the hydrodynamic performance and wave energy capture efficiency of the split absorbers are investigated, and compared with those of the corresponding unsplit absorber. The experimental results reveal that the split absorber presents new hydrodynamic characteristics, and that the efficiency of the new wave energy capture device is greatly improved for small-period waves in the low sea state. However, the pitch motion of the platform is significantly increased in some cases with specific incident wave direction, which needs to be solved by further optimizing the TLP mooring system.
System Reliability Assessment of Jacket Structures Using Fault Tree Analysis Method
Authors: Renugadevi A. , Nallayarasu S.
Published: September 2023

Probabilistic methods have been used in offshore structures for individual components and whole structures based on the ultimate strength of the structural components. A new method for the assessment of system failure using individual member probability of failure using the fault tree method has been developed and demonstrated using a typical offshore platform jacket. The logical sequences of the component failure have been assessed using the importance of member for local strength, attached joint requirement and the load path required to continue the load distribution in case the other members fail. The proposed method has been used to verify the probability of failure for an existing jacket designed using the Allowable Stress Design (ASD) method and the corresponding Reserve Strength Ratio (RSR) has been computed. The critical failure path has been generated and the probability of failure of the members involved in the established failure paths and corresponding RSR is evaluated by First Order Reliability Method (FORM). The system reliability analysis is then used to identify the combined probability of failure of the individual failure paths, which in turn results in the dominant failure path that leads to the collapse of the structure. Finally, the system failure is assessed using simple bound formula.
Numerical Simulations of Three-Dimensional Scour Below Subsea Pipelines/Cables Under Steady Current Conditions
Authors: Zhang Bingchang , An Hongwei , Draper Scott , Jiang Hongyi , Cheng Liang
Published: September 2023

Scoured induced free span is one of the major engineering hazards for submarine pipelines/cables (P/Cs) in offshore oil and gas industry and offshore renewable energy industry. Due to the lack of knowledge about scour propagation along spanwise direction, conservative and costly stabilization methods are usually adopted for span mitigation. To address the concern related to free spans, great efforts have been made to establish the prediction models for scour propagation rate, most of the research is based on laboratory experiments to propose semi-theoretical equations. However, due to the limitation of present measuring techniques, it is hard to physically measure the gap flow and bed shear stress distribution under the P/C models. Thus, the physical mechanism for scour propagation is still not well understood. As a complement to laboratory experiments, numerical simulations can reproduce the whole flow fields around a P/C undergoing three-dimensional scour, which makes it a great tool to understand the interaction between flow and evolution of erodible seabed. Thus, in the present study, a scour model is used to simulate the three-dimensional scour below a P/C under steady current conditions. Two scour propagation stages are observed, the different mechanisms for the two stages are explained using the bed shear stress amplification factor. The flow fields around the scour hole are also analyzed. The present results, combined with the available laboratory experiments [1,3], will give a better understanding about the mechanism of 3-D scour.