bluuebunny/crossref_metadata_2025 huggingface dataset:
Manoeuvring Modelling and Control Design of Autonomous Vessels on Inland Waterways
Authors: Zhang Chengqian , Dhyani Abhishek , Ringsberg Jonas W. , Thies Fabian , Reppa Vasso , Negenborn Rudy R.
Published: August 2024

Autonomous inland shipping has great potential to enable intelligent and sustainable freight transport. At the same time, with the increasing traffic on confined waterways, ensuring safe operations of these autonomous inland vessels within limited operational spaces becomes imperative. This will require considering hydrodynamic effects during control design stages. This study presents a comprehensive analysis of an autonomous inland vessel’s manoeuvrability and controller design. The ship’s motions are modelled using an enhanced Manoeuvring Modelling Group (MMG) model to account for the hydrodynamic effects of inland waterways, including water depths, river currents, and bank effects. A verification study is conducted utilising a pusher-barge prototype model in shallow water to verify the model’s accuracy. Through the implementation of a controller, a course-keeping study is conducted to assess the vessel’s steering performance across various inland waterway scenarios, including sailing along river bends and waterway intersections. The results show that the manoeuvring model can generate fast and accurate vessel trajectory predictions. It is found that the proposed control technique proves effective in mitigating the confinement effects and countering disturbances caused by river currents, thereby ensuring efficient course-keeping suitable for the considered type of autonomous vessels on inland waterways.
Impact Loads on Ships From Breaking Waves
Authors: Rognebakke Olav , Ruth Eivind , Landet Tormod , Austefjord Håvard
Published: August 2024

Plunging breaking waves may cause large impact loads on ships. Neither the risk of such impacts nor the magnitude of the resulting loads is much studied or well understood. Breaking waves in open sea typically occur in steep non-stationary growing sea-states. Recent advances in modelling of highly nonlinear wave conditions combined with computational fluid dynamics provide a means to quantify the frequency of breaking wave events. A higher-order spectral wave model is used to initialize large-domain wave propagation analyses in OpenFOAM. Breaking wave events are identified, and the risk of hitting different part of a vessel’s hull is evaluated. This includes evaluation of relative motions between the ship and breaking wave profile. Calculating linear vessel motions using a linearized wave field provides a good approximation compared to including the vessel in the CFD calculations. The focus is on beam-sea waves impacting the side of the ship. Existing rules and design practice account for dynamic wave loads but not large impulsive loading outside of the area vulnerable to bow-or stern slamming loads. A calculation framework is established that can be used to quantify how the risk of excessive loads depends on sea-state characteristics and vessel operation. General observations are made about the risk for high impact loads from breaking waves, and mitigating actions are discussed.
On the Design, Hydrodynamic Modelling and Response Analysis of a New Concept FOWT Platform
Authors: Islam Touhidul , Venugopal Vengatesan
Published: August 2024

This paper primarily focused on the design and hydrodynamic analysis of a new concept Floating Offshore Wind Turbine (FOWT) with a capacity of 5 MW or above. The proposed concept has smaller dimensions, hence reduced material and displacement. The platform consisted of large volume cylindrical structures at its base and near the waterplane, and, this was done to increase the distance between the FOWT’s centre of gravity and buoyancy. Furthermore, the base cylinders work as containers for ballast and effectively reducing vertical motion.

For a detailed hydrostatic stability analysis, general hydrostatics (GHS) software was used to verify different loading conditions. During the stability analysis, it was found that the platform could be designed with relatively lower displacement to comply with the static stability, however, when subjected to wave loads, it exhibited reduced stability with significant motion amplitudes. Nonetheless, the sizing of the platform was primarily determined by the hydrodynamic heave and pitch natural periods, considering them to be outside the wave period range.

Once the preliminary dimensions were chosen, the radiation-diffraction tool BV Hydrostar was used to estimate hydrodynamic coefficients, transfer functions and for detailed hydrodynamic modelling and analysis of the platform. Viscous loads from the slender elements were accounted using the drag term of Morison’s equation for platform motion.

The turbine tower was modelled according to the description found in literature. Rotor-nacelle assembly was modelled as a point mass. The resulting platform has a 30% reduction in displacement and save at least 15% of material weight compared to the NREL DeepC platform. Motion RAOs for the platform in heave, roll, and pitch show peak values near natural periods, however, values were comparable to the NREL DeepC platform.
Vortex Induced Vibrations of a Lazy Wave Dynamic Power Cable Under Various Currents and Propagation Directions: Analysis of Strain
Authors: Moideen Rameeza , Venugopal Vengatesan , Chaplin John
Published: August 2024

Vortex induced vibrations (VIV) of a flexible dynamic power cable in lazy wave configurations were investigated experimentally to understand their behaviour under currents of various magnitudes. The preliminary study investigates the effect of increasing current magnitudes in the range 0.1–0.8 m/s and for three different current propagation directions (i.e. 0, 90 and 180 degrees relative to the cable’s alignment) on a model power cable of external diameter 0.031 m, 5m long. The experiments were undertaken at the FloWave combined wave-current facility of The University of Edinburgh. They fall in the subcritical range with Reynolds numbers from 103 to 104. The cable was instrumented with water-proofed strain gauges at seven locations along the its length at 0.5 m intervals to measure total bending strain at each point. The cable was also instrumented with six-component load cells while an optical system measured displacements at a large number of locations. However, these are not presented in this paper.

This paper reports bending strains and the corresponding response spectra at seven locations along the length of the cable. The impact of VIV on measured strains and their effect on response frequencies (hence the Strouhal number) are illustrated over a range of current magnitudes and directions. A detailed analysis of the data collected, results and discussions are presented in the paper.
Characterization of Dynamic Pore-Throat Structure and Petrophysical Properties in an Unconsolidated Sandstone Reservoir
Authors: Ge Lizhen , Liu Guangfeng , Luo Zhoujun , Chen Xiaoming , Ma Teng , Yang Daoyong
Published: August 2024

In this study, a comprehensive and practical technique was developed to study the dynamic changes of pore-throat structure and petrophysical properties of unconsolidated sandstone reservoirs during long-term water injection. Experimentally, core samples were gathered from unconsolidated sandstone reservoirs for thin-section preparation and analyzed using laser particle size and X-ray diffraction techniques. In addition to identifying and classifying pore types and clay minerals, the size, fraction, and distribution of particles were also determined and categorized. Furthermore, a high-pressure mercury injection test was conducted on the core after waterflooding so as to quantify alterations in the microscopic pore-throat structure. The dispersion of clay minerals breaks the formation bond, leading to the fall and migration of clay and fine silt, and the content of clay and fine silt decreases, resulting in the change of pore-throat structure. Compared with the change of pores, the change of throat has a greater influence on the seepage behaviour, but such a change mainly occurs in the early stage of waterflooding. The fractal dimension of the pore-throat structures increases from 2.51 to 2.58, enhancing the heterogeneity and making the seepage channels more concentrated. The pore-throat structure was changed by 90% when water was injected to 200 PVs, gradually changed until 300 PVs of injected water, and then remained basically unchanged afterwards.
Consequence Analysis of a Bunkering Facility for Liquid Hydrogen Loading and Unloading
Authors: Schiaroli Alice , Campari Alessandro , Paltrinieri Nicola , Cozzani Valerio , Ustolin Federico
Published: August 2024

Hydrogen is widely regarded as a key option for the replacement of fossil fuels in the near future. Despite compression being the most well-known and widespread technology for hydrogen storage and transportation, liquid hydrogen (LH2) is preferable for large-scale applications where a greater energy density is crucial to reach the desired storage capacities. For instance, in 2020–2021, the HySTRA (Hydrogen Energy Supply-chain Technology Research Association) pilot project was carried out to demonstrate the feasibility of a large-scale liquefied hydrogen energy supply chain from the production site in Australia to the receiving terminal in Japan. The unloading facility, which includes a 2,500 m3 LH2 spherical storage tank, a boil-off tank, and other equipment for the transfer of LH2 from land-based facilities to the LH2 truck trailers, is located in the Port of Kobe, in the northeast section of Kobe Airport Island. This facility is the world’s first liquefied hydrogen receiving terminal for unloading of a LH2 marine carrier. Given the hazards related to hydrogen storage and handling that derive from its high flammability, safety plays a fundamental role in hydrogen applications, particularly when managing large amounts of fuel. In the present study, a risk analysis is performed to estimate the risk related to a liquid hydrogen bunkering facility. First, the most safety-critical components are identified through a preliminary risk analysis. Second, more detailed modelling is carried out to quantify the consequences of an unexpected loss of containment (LOC) from the most critical piece of equipment. The consequences are expressed in terms of separation distances and calculated by integral models from the effects of possible final events (e.g., fires and explosions).
Low Frequency Energy in Measured Waves in a Narrow Norwegian Fjord
Authors: Jena Parthasarathi , Li Lin , Haver Sverre , Xiang Xu
Published: August 2024

The E39 Coastal Highway Route project undertaken by Norwegian Public Roads Administration aims at replacing existing ferry crossings by constructing permanent road connections using bridges along the western coast of Norway. One of the bridge designs being developed is a beam bridge resting on floating pontoons. In contrast to conventional bridges, a floating bridge rests on pontoons floating on the water surface and are affected to a much greater extent by waves and currents in the waters it spans. In order to have a solid basis for taking the environmental loads into account in the bridge design a wave measurement campaign was initiated at the bridge fabrication location.

The wave measurement was carried out using a small diameter wave buoy with a proven track record in the offshore industry. The location of the wave measurement campaign is a narrow fjord surrounded by relatively high terrain. The fjord, being sheltered from swells from the North Sea and considering the available fetch length, it was expected that the measured waves would consist of purely wind generated waves with peak wave period, Tp, between 2s to 7s. However, the observed wave signal showed spurious long period waves with Tp in the range of 20s to 30s interspersed seemingly at random throughout the measured data. This paper discusses possible reasons for the observed low frequency energy. Harbor resonance in the fjord, resonance in the mooring system of the buoy, and passing ship interaction with the buoy were investigated as possible reasons for the presence of the low frequency energy. A method for identifying the low frequency energy and filtering them out using wavelet analysis of buoy heave signal is proposed.
Performance Assessment of Safety Barriers in Liquid Hydrogen Bunkering Operations Using Bayesian Network
Authors: Tamburini Federica , Ustolin Federico , Cozzani Valerio , Paltrinieri Nicola
Published: August 2024

Liquid hydrogen (LH2) has gathered interest as an eco-friendly energy carrier for marine transportation, avoiding carbon emissions and supporting sustainable shipping. However, LH2 intrinsic flammable characteristics pose safety concerns towards people and assets. Ensuring the effectiveness of safety barriers is paramount in preventing accidents and mitigating risks associated with LH2 bunkering operations. In this regard, among several quantitative performance assessment methods, Bayesian Networks (BNs) gained momentum, offering a statistical approach able to account for multifaceted safety factors. This paper evaluates safety barriers’ performance by translating Event Tree-Fault Tree diagrams into BNs. BNs incorporate root nodes representing basic events leading to the failure of the safety barriers, assigning failure probabilities from technical literature and Human Reliability Analysis approaches. Conditional Probability Tables quantify dependencies, mapping safety barrier interconnections. A case study on ship-to-ship bunkering affected by a LH2 release is considered to illustrate the application of BNs in the context of safety barriers performance assessment. Findings highlight BNs’ utility in assessing safety barrier performance, providing a tool for regulatory agencies, industry stakeholders, and safety experts to inform LH2 bunkering best practices. This aligns with advancing environmentally responsible LH2 maritime transportation while enhancing safety measures.
Distributions and Impact Factors of Organic Carbon in the Coastal Areas of Yangtze River Estuary in the Summer of 2023
Authors: Yang Zhongyuan , Lou Sha , Chen Shizhe
Published: August 2024

Since the start of the industrial revolution, global average temperature has been increasing year by year due to the rapid increase in atmospheric carbon concentrations. Estuarine carbon cycle processes are hotpots of greenhouse gas (CHG) emissions and play multiple roles in the global carbon budget. The driving factors of organic carbon in coastal wetlands are crucial for understanding the process of estuarine carbon cycle. However, the relationship between organic carbon and surrounding environmental factors is complex, and the impact pathways of controlling factors on organic carbon remain unexplored. Therefore, this study employed field sampling and statistical techniques to study the relationships between organic carbon and primary influencing factors in seven coastal wetlands along the Yangtze River Estuary during the summer (June-August 2023). Results showed that the average of organic carbon concentration in August was higher than that in June and July. The organic carbon concentrations in Sanchagang (SCG) and Dazhihe (DZH) were higher than those in other sampling points. Salinity, total dissolved solids, electrical conductivity and resistivity had significant impacts on organic carbon. Partial least squares path modeling indicated that the effect of salinity regulation and biogeochemical environment on organic carbon is a direct and dominant pathway (path coefficient ⩾ 0.45). Hydrodynamics had the greatest indirect effect on organic carbon but the total effect of hydrodynamics was insignificant. This work offers an insightful lens for better understanding organic carbon processes in coastal wetlands. It provides a theoretical basis for better assessing blue carbon storage in the context of global change.
Vortex-Induced Vibration of Two Rigidly Coupled Cylinders in Tandem Arrangement With Low Mass Ratios
Authors: Yu Zhipeng , Wang Enhao , Wu Hao , Xu Hongteng , Gao Chenxi
Published: August 2024

Vortex-induced vibration (VIV) of two rigidly coupled cylinders in tandem arrangement with a fixed center-to-center separation of 2 (s/D = 2) is numerically investigated in a laminar flow with Re = 150. Results are examined over a domain of reduced velocities ranging from 0.25 to 100 and very low mass ratios are considered, i.e., m* = 0.02, 0.1, 0.3 and 0.9, respectively. It is found that the amplitude at the infinite reduced velocity increases smoothly as the mass ratio decreases, whereas the amplitude experiences a sharp increase for an isolated vibrating cylinder below the critical mass ratio at the same Reynolds number. Interestingly, unlike the VIV of an isolated cylinder, the time traces of the displacement is quasi-periodic in the first part of the low branch for the two-cylinder system. This so called beating phenomenon is identified as a consequence of the different flow state, particularly the presence or absence of an active gap flow. The present study highlights significant distinctions in the amplitude response associated with wake patterns between the VIV of the two-cylinder system and that of the isolated cylinder.
Hydrodynamic Force of an Obliquely Oscillating Cylinder in Steady Flow
Authors: Ren Chengjiao , Cheng Liang , Tong Feifei
Published: August 2024

This study conducts a series of three-dimensional numerical simulations to explore the dynamics of an oscillating cylinder in steady current. Simulations are set at a fixed Reynolds number of 500 for the steady current and a small oscillation amplitude of 0.4 cylinder diameter. Seven oscillation angles θ from 0° to 90°, defining as the orientation of the cylinder oscillation relative to the current, have been investigated across various oscillation wavelengths λ*. The impact of θ on the wake characteristics can be broadly categorized into three regions. For small λ* (less than 1.5), the flow is predominantly influenced by the cylinder oscillation, with forces that vary monotonically with respect to θ. In contrast, at larger λ* (greater than 10), cylinder oscillation becomes negligible, and the wake is primarily driven by the incoming flow. Complex wake interactions exist at intermediate λ* = 1.5–10, particularly in terms of the occurrence of lock-on states. The primary lock-on at θ = 90° (period-1 wake), characterized by a repeatable vortex shedding pattern over each oscillation period, develops at all angles. Meanwhile, the primarily lock-on state at θ = 0° (period-2 wake) is only observed for θ up to about 75°. As θ increases from 0°, both lock-on states shift towards smaller λ*.
Comparison of Two Types of Wave Buoys: Linear and Second-Order Motion
Authors: Ding Yue , Taylor Paul H. , Hlophe Thobani , Zhao Wenhua
Published: August 2024

Wave data from oceanographic buoys remains indispensable in offshore and coastal engineering. Modern wave buoys can produce semi-Lagrangian time histories of motion in three dimensions (one vertical and two horizontal) in addition to the standard statistical output. A recent study (Ding et al., 2023) reveals that, while the three translational motions of a wave buoy are dominated by the linear components, there is significant nonlinearity in the horizontal plane. This study uses field data from the Southern Ocean off Albany, Western Australia, measured from four closely spaced buoys: three Sofar Spotters and a Datawell Directional Waverider-4. The measured time histories measured by the different types of wave buoys in three orthogonal directions and the relationship between them have been systematically investigated, for the first time. Significant second-order components in both vertical and horizontal directions are observed.
A Swarming System for Multiple Autonomous Surface Vehicles Using Virtual Matrix and Leader in Ocean Engineering Basin
Authors: Kim Jung-Hyeon , Choi Si-Woong , Son Hui-Hun , Kim Do-Kyun , Kim Dong-Han , Park Jong-Yong
Published: August 2024

This study focused on the development and model testing of the formation maintenance for multiple unmanned surface vehicles (ASVs). Designed as catamarans, these ASVs were equipped with a various of sensor, such as an inertial measurement unit (IMU) and 2-dimensional (2D) light detection and ranging (LiDAR) system. The robot operating system 1 (ROS) was utilized to enhance communication, conveying data such as position, orientation, and situational insights from various sensors. To sustain the formation of these ASVs, a method combining a virtual leader with a virtual matrix was instituted. ASVs were designed to follow each cell numbers, which simplified both the maintenance and modification of their formation. To validate the efficacy of this virtual matrix approach, model tests covering an array of scenarios were carried out at the Ocean Engineering Basin. The indoor Ocean Engineering Basin’s lack of GPS operability led to the integration of an ultrasonic sensor-based Beacon system for precise positioning and enhanced navigational accuracy of the ASVs. Scenarios were designed to enable rotation while preserving row and column formations, considering the basin’s dimensions. Test outcomes demonstrated that the ASVs adeptly maintained their formation, consistently aligning with the cells defined by the virtual leader and matrix.
Numerical Study on Static and Dynamic Load Inversion of Ice Class Propellers
Authors: Qin Xu , Zhou Li , Li Fang , Fu Shixiao , Ding Shifeng , Liu Chao
Published: August 2024

This paper focuses on the inverse analysis of ice loads experienced by propellers during navigation in ice-covered waters. An objective function for inverse load calculation of propellers is established using the least squares method and Tikhonov regularization, based on the characteristics of the propeller structure response equation under both static and dynamic loads. By integrating the structural feature parameters and response of the propeller, the inverse calculation of loads under ice conditions is achieved. The inverse calculated results coincide well with actual loads, which reveals that both inverse methods possess high accuracy and are capable of practical engineering applications. Furthermore, it shows how to arrange response monitoring points on propellers in this paper, which are of significant importance for enhancing the navigational safety of the polar ship.
Extreme Value Analysis of Ship Roll Motion With Consideration of Ice Accumulation
Authors: Chai Wei , Qi Jianzhang , Leira Bernt J. , Sinsabvarodom Chana , Yang Longxia , Ji Shunying
Published: August 2024

Ice accumulation poses a significant threat to ship stability, potentially leading to capsizing if the roll angle surpasses a certain threshold. Investigating the impact of ice accumulation on the extreme roll angle is crucial for the safety and stability of ship sailing in Arctic regions. This article presents a study that aims to evaluate the effects of ice accumulation on ship stability in waves. Specifically, the standard ship model CEHIPAR 2792 is selected, and the dead ship condition is considered. Calculation of the roll damping coefficients via CFD method has been verified with the experimental data. Then, single-degree-of-freedom (SDOF) models for roll motions with and without ice accumulation are established to calculate the roll response in random seas. The influence of ice accumulation on the roll damping term as well as on the restoring term are incorporated into the SDOF model. Finally, extreme value analysis is executed to evaluate the influence of ice accumulation on the roll response and ship stability in waves. This Research has shown that predicting extreme values of roll motion response is a more effective approach in capturing the impact of ice accretion on the stability of vessels in waves, surpassing conventional measures such as restoring lever arm. This methodology enables an enhanced assessment of the hazards associated with icing conditions.
Azimuthing Propulsion in Ice Management
Authors: Hänninen Samuli , Kujala Pentti , Määttänen Pirjo , Heideman Torsten , Korsström Andrei , Viheriälehto Sampo , Koponen Jorma
Published: August 2024

Year-round operations in ice covered areas result in increasing need for specially designed icebreaking vessels. An important characteristic of these vessels is their ice management capabilities. Azimuth thruster propeller wake can be effectively used in ice management (IM) both in stationary Dynamic Positioning (DP) operation and icebreaking. The ice management performance depends on the thrust of the propeller, propeller wake angle and thickness of the ice. Various ice management experiments have been done both in full-scale and model tests to study and demonstrate IM capabilities.

Recent tests were carried out with icebreaker “Polaris”, a Finnish icebreaker with ice class PC4. The novel diesel-electric propulsion system consists of three powerful azimuth propellers, two at the stern and one at the bow. This paper will present results of propeller wake effect on ice management and ice clearing. Ice clearing area depends on the ice thickness, power, heel of the ship and wake angle.

This paper will also discuss the characteristics of azimuth propulsion as well as full-scale test results from the use of Azipod units in ice management operations. These results will show how Azimuth propulsion offers improved ice management performance and greater vessel design flexibility. They will also offer further insight into different possibilities, for example, selection of most suitable azimuth angles for various tasks.
Numerical Study on the Influence of Wettability on the Sphere Surface During Water Entry
Authors: Wu Yanyuan , Guo Chunyu , Han Yang , Li Ruoxin
Published: August 2024

The water entry of objects is a fundamental physics problem and has a wide range of engineering applications, such as ship slamming, spacecraft landing on water, and anti-submarine missiles. Due to large nonlinear deformation, and strong unsteady flow and cavity characteristics caused by large-scale motions at the free surface, it is very difficult to simulate the process of water entry using a numerical approach. In this study, based on the open-source computational fluid dynamics (CFD) code library OpenFOAM, the continuum surface force (CSF) model is introduced into the volume of fluid (VOF) multiphase flow model, and the object motion is realized by overlapping grid technology. A three-dimensional sphere water entry numerical calculation model considering the wettability of the object surface is established. The reliability and accuracy of the numerical method in this paper are verified by comparing with the results of the motion displacement and cavitation morphology evolution of the sphere in the experiment. On this basis, the vertical water entry of hydrophilic and hydrophobic spheres with different initial impact velocities was numerically simulated. The effects of surface wettability and initial impact velocity on cavity evolution and motion characteristics during water entry are analyzed in detail, and the formation mechanism of water entry cavity is revealed.
Analyzing Experimental Data of 6-DOF Motions and Sloshing Impacts In LNG Carriers
Authors: Ahn Yangjun , Choi Mun-Gwan , Park Cheonjin , Kim Sang-Yeob , Park Taehyun , Shim Woohyeon , Ryoo Gyeongbin
Published: August 2024

This research delves into the intricate relationship between the 6-degree-of-freedom (DoF) motion of LNG-related vessels and the sloshing impact loads. Conducted by HD Hyundai Heavy Industries, over a decade of sloshing model tests at Seoul National University’s facility has led to a comprehensive study. The tests involve more than 30 ship models under 5,000 varied maritime conditions. A sophisticated array of over 100 Piezo electric sensors collect data on sloshing impact pressures, alongside the vessels’ 6-DoF irregular motions, across five-hour test periods at real-ship scale. Post-processing utilizes the three-parameter Weibull distribution to extract the three-hour most probable maximum peak pressures as the sloshing loads from the time series data. Subsequently, the study examines the correlation between 18 features of the ship’s 6-DoF motion — encompassing displacement, velocity, and acceleration — and the measured sloshing impact peak pressures. Machine learning techniques are pivotal in determining the significance of each feature, employing both linear and nonlinear analyses including Generalized Additive Models (GAMs). By using elimination methods based on the Light Gradient-Boosting Machine (LightGBM), the research identifies and elucidates the key parameters among the eighteen features that significantly influence sloshing loads. This comprehensive investigation not only deepens understanding of the intricate interplay between ship movements and sloshing impacts but also provides a useful dataset that could potentially inform future navigational strategies and contribute to enhancing safety and efficiency in maritime operations and hull form design.
Numerical Study of Propeller Vibrations and Radiated Noises in the Rudder-Propeller Interaction
Authors: Zhang Weipeng , Wan Qingyuan , Li Xusheng , Hu Jian
Published: August 2024

The inhomogeneous inflow amplifies the loading fluctuations on the propeller which strengthen vibrations. As a significant source of noises, these vibrations of propeller result in more severe noises on the vessels which are detrimental to the health of crews and marine organisms. The study aimed on the vibrations and radiated noises of propeller is beneficial to ideal design of vessels and better comfort. Hence, the vibrations of blades and radiated noises of 5479 propeller operating in inhomogeneous inflow are numerical predicted in present study. The hydrofoils located upstream of propeller are employed to generate inhomogeneous inflow. Firstly, the loading fluctuations on blades are studied with full-rigid propeller. The vibrations on the trailing edge of blade are compared under different rotational speed. The distributions of vibration are also compared under different rotational speed. Then the radiated noises of the propeller are predicted considering the vibrations of the propeller. Results show that the loading fluctuations on the blade are more intense at leading edge. The vibrations on the blades are dominant at shaft frequency (SF), 4SF and 12SF in the inhomogeneous inflow. Several humps of vibrations are observed at the natural frequencies of the blades. The vibrations at 12SF reaches its maximum when the 12SF approaches the first natural frequency. The deformations and vibrations of blades results in weaker tonal noises but more intense broadband noises.
Strength Analysis of Icebreak Ramming Sea Ice With Extreme Thickness Along the Northern Sea Route
Authors: Bian Anqi , Chai Wei , Dong Haibo , Yu Zhaolong , Leira Bernt J. , Xiong Fanghuai
Published: August 2024

In recent years, as a great increment in energy, the Arctic has become a focus for its abundant resources. However, the ice conditions are complex in this area, ships sailing along the Northern Sea Route (NSR) may collide with iceberg, ice sheet, ice ridges, etc. and resulting in structural deformation and damage of the hull. Therefore, the structural safety of the ice capable ships should be mainly considered. In order to estimate the structural safety of icebreakers encountering the sea ice with extreme thickness, numerical modeling calculation has been conducted in the simulation software LS-DYNA. Specifically, four representative sites are selected to predict the extreme thickness of sea ice, based on the statistics of yearly extreme sea ice thickness along the NSR. The ice-breaking conditions and bow stress patterns of icebreakers ramming the sea ice with extreme thickness at different speeds are simulated by numerical methods, and the extreme stresses of the bow ramming area are extracted. On the basis of the results above, the strength of icebreaker bow structure is checked with regulations to provide valid reference for icebreaker design.
Optimisation of the Main Hull Subdivision and Layout Based on Topology-Geometry Co-Characterisation
Authors: Yu Lei , Wang Hao , Luo Junting , Chen Shunhuai
Published: August 2024

The subdivision and layout of a ship’s main hull is a critical aspect of ship design as it directly determines the layout of the ship’s space. To enhance design efficiency and quality, an intelligent optimization method for main hull subdivision is proposed. This method aims to reduce the traditional manual subdivision design process, which heavily relies on mother ship data, and address issues such as long design cycles and high costs. The text describes the sorting and analysis of the mutual influence relationship between ship compartments and equipment. A topological characterization model of the influence relationship and an automatic identification method are proposed. The topological objective function of favourable influences between compartments and equipment is constructed, and the geometrical constraint model is proposed based on the design specifications and design experience. The Diffusion Algorithm Based on P Systems (DAPS) is then employed to achieve the optimization solution, resulting in a collection of intelligent optimization methods for main hull compartmentalization. The test for optimizing the main hull subdivision design was conducted on a scientific research vessel. The iteration curve for the optimization objective showed good convergence, and the optimization had a positive impact on the parent ship subdivision scheme. The test results demonstrate the method’s rationality.
Fatigue Test Geometries Used for Girth Welds and Assessment of Residual Stress: State of the Art
Authors: Englund Even , Chandima Ratnayake R. M.
Published: August 2024

Fatigue testing of girth welds in large tubes plays a crucial role in ensuring the structural integrity and safety of various structures such as oil and gas pipelines, raisers, monopiles, and wind turbines towers. The selection of appropriate test sample geometry and the influence of sample preparation is of utmost importance as it directly influences the accuracy and reliability of the fatigue test results. This review article highlights the significance of fatigue testing of girth welds and the importance of choosing the correct test sample geometry. Another critical aspect highlighted is the assessment of stress concentrations, along with the evaluation of the effects of residual stresses in fatigue testing of girth welds and welds done in close proximity. The choice of sample geometry should be representative of the actual structures being tested and should consider factors such as pipe diameter, wall thickness, weld bead profile, and potential stress concentrations. Improper selection of sample geometry can result in inaccurate fatigue life predictions and limit the practical application of test results. By conducting a literature survey on the geometry for fatigue test specimens of girth welds from large tubes, this study aims to provide insights into the significance of varying sample geometries when testing girth welds and their effects on residual stress and fatigue performance. The survey will include a comprehensive analysis of existing research, guidelines, methods, and standards related to fatigue testing of girth welds. The selection of correct test sample geometry and test method is a key factor in obtaining reliable and accurate fatigue test results. This article highlights the importance and challenges of fatigue testing of girth welds and emphasizes the significance of choosing the appropriate test sample geometry. This is conducted in form of a literature survey to further explore this crucial aspect of girth weld fatigue testing. A framework for future research and testing on girth welds, including welds performed at close proximity, and further assessment of residual stresses is also presented.
Numerical Simulation of the Decay Motion of a Water Column for the Oscillating Water Column Type Wave Energy Converter Using the Particle Method
Authors: Sasahara Yutaro , Morito Makoto , Masuda Mitsuhiro , Tahara Junichiro
Published: August 2024

The floating oscillating water column-type wave energy converter (OWC-WEC) is highly maintainable and safe because it has no moving parts under water. Estimation of water column’s motion in the air chamber is required to develop a high-performance floating OWC-WEC. The traditional approach is to model the system as an equivalent rigid body. The final goal of the present study is to reveal the details of the motion mechanism as fluid by Computational Fluid Dynamics (CFD). In this study, a high-accuracy two-phase flow moving particle simulation method was developed by combining existing and unique models to improve unstable numerical oscillations. Numerical simulations and water tank experiments were conducted for a free-motion test of the water column to validate the proposed method and analyze the fundamental motion of the water column in the air chamber of a floating OWC-WEC. A comparison between the calculated and experimental results showed that the proposed method developed reliably replicated the phenomena, although the three-dimensional effect was important, and the fundamental applicability of the method was clearly demonstrated.
Ocean Wave Spectrum Estimation Using Wave Buoy Analogy
Authors: Son Jaehyeon , Kim Yooil
Published: August 2024

The application of digital twin technology, which combines real-world measurement data with a digital model of the ship, is gaining attention in the field of structural integrity management. Considering the limited number of sensors that can be installed on a ship, the incorporation of a digital twin concept, which combines measurement data with the ship’s digital design model, can play a crucial role in ensuring structural integrity management. This study presents a methodology to estimate local responses at locations where measurements are not available, utilizing both measurement and design data. To estimate the response at unmeasured locations, the directional wave spectrum was first estimated using the least square method, minimizing the error between the estimated response spectrum and the measured response spectrum. In this process, the measured spectrum is obtained by filtering and Fourier transforming the measured time series acquired from the sensor. And the estimated spectrum was obtained through the product of the directional wave spectrum and the Response Amplitude Operator (RAO), followed by integration. And B-spline was introduced to represent the directional wave spectrum. To validate the methodology, artificially generated pseudo-measurement data using wave spectrum and RAO of 13,000 TEU container ship was employed. Subsequently, the directional wave spectrum was estimated using pseudo-measurement data, and the estimated directional wave spectrum, along with the Response Amplitude Operator (RAO), was utilized to estimate the response spectrum.
Experimental Study of the Waves-Induced Flows Inside a Liquefied Silty Seabed
Authors: Chen Ning , Tong Linlong , Huang Zhen , Yang Chen , Zhang Jisheng
Published: August 2024

Silty seabeds are widely distributed around the world and liquefy easily under periodic wave loads, which may significantly affect wave motion and soil dynamics. Laboratory experiments have been conducted to study the wave-induced flows inside the silty seabed, as well as the wave-induced soil dynamic and wave kinematics. Silt particles with a median diameter of 0.06mm are selected to model the seabed, and in the seabed preparation, the Froude-Cauchy similarity criterion is required to satisfy. The free surface elevation, excess pore pressure, and soil motion velocity are measured to study the wave motion and the flow dynamics over and inside the seabed. The experimental results show that: (1) Liquefaction in the silty seabed contributes to a rapid wave damping, manifested as a significant decrease in wave height; (2) Liquefaction occurs when the accumulated pore water pressure in the silty seabed exceeds the vertical initial effective stress. The liquefaction depth develops in a top-down manner; (3) The flow velocity inside the seabed varies periodically. The dimensionless horizontal velocity component of the soil particles in the liquefied seabed is smaller than the vertical velocity component but has a longer period; (4) The instantaneous velocity field of the liquefied soil particles reaches its peak when the water-mud interface moves to the lowest or highest point. When liquefaction just occurs, the instantaneous velocity field is likely to be disturbed by the discharge of bubbles from the unsaturated seabed.
Deep Learning’s Role in Transforming Offshore Asset Corrosion Monitoring
Authors: Bobadilla Roberto Bore , Miranda Barbosa Nicholas , Vera Muñoz Sergio Oscar Alejandro , Lourenço de Souza Marcelo Igor , Caprace Jean-David
Published: August 2024

Maintenance and continuous monitoring of offshore structures and ships are essential in ensuring the integrity and safety of these high-value assets. Manual inspection methods are labor intensive, time-consuming, and often dangerous. Unmanned Aerial Vehicles (UAVs) also called drones equipped with cameras offer a promising solution for efficient data collection. This research addresses the need for automated corrosion detection and classification in images captured by UAVs, revolutionizing asset maintenance practices. Despite advances in computer vision and deep learning, the development of a robust and accurate deep learning algorithm for the automatic detection and classification of corrosion in UAV-captured images remains an underexplored area. Existing methods lack the precision and adaptability required to meet the rigorous demands of offshore asset management. The primary objective of this research is to develop a state-of-the-art deep learning algorithm that can automatically detect and classify corrosion in images of offshore structures and ships, acquired through UAVs. By achieving this goal, we aim to enhance the efficiency and accuracy of corrosion monitoring, thus extending the service life and safety of these critical assets. We employ YOLOv8 (You Only Look Once), a cutting-edge object detection model, as the core of our approach. The model is fine-tuned using transfer learning, leveraging pre-trained weights from a vast dataset to adapt to our specific corrosion detection task. The algorithm is trained on a diverse dataset of corrosion images. Our deep learning algorithm demonstrates good performance in corrosion detection and classification. Through extensive testing on UAV-captured images, it consistently achieves high accuracy, sensitivity, and specificity. The algorithm’s real-time processing capabilities enable swift responses to corrosion-related issues, ensuring timely maintenance interventions. In conclusion, our research presents a novel deep learning approach for automatic corrosion detection and classification in UAV-captured images of offshore structures and ships. The utilization of YOLO V8 with transfer learning significantly improves the accuracy and efficiency of corrosion monitoring. This result contributes to the continuous improvement of asset management practices, offering enhanced safety and extended service life, ultimately minimizing costs and environmental impact in the offshore industry.
Quasi-Static Fluid Structure Interactions for Ship Advancing in Waves With Constant Forward Speed
Authors: Nguyen Minh Quan , De Hauteclocque Guillaume , De Lauzon Jerome , Malenica Sime , Chen Xiao Bo
Published: August 2024

Evaluation of structural stresses for ships advancing with constant forward speed U in waves, represents a particularly important practical problem. Depending on the wave conditions and the structural properties of the ship, different types of fluid structure interaction procedures might be needed to evaluate these stresses. In the present work, the accent is on the so-called quasi static structural response which is relevant when structural vibrations are not likely to occur. Due to relatively high structural natural frequencies of the hull structure, when compared to wave frequencies, the quasi-static structural response is most often of major practical concern. The exceptions are some particular problems such as for example whipping where the structural vibrations might occur due to important impulsive loading induced by slamming or other sources. For those cases, a more complex coupling procedures, based on full hydro-elastic coupling principles, are necessary. These issues are not discussed here but will be considered in the future.

Within the quasi-static assumptions for the structural response, the main technical difficulty concerns the pressure transfer from the hydrodynamic model to structural model. In the present work, Boundary Integral Equation Method (BIEM) is used to solve the hydrodynamic problem and the Finite Element Method (FEM) is used to solve for the structural response. When compared to the seakeeping problem without forward speed, the solution of the hydrodynamic Boundary Value Problems (BVP) is much more complex and the different coupling strategies are required.
Intelligent Identification Workflow of Drilling Conditions Combining Deep Learning and Drilling Knowledge
Authors: Liu Zihao , Song Xianzhi , Ye Shanlin , Ma Baodong , Zhang Chengkai , Wang Zheng , Yao Xuezhe , Zhu Zhaopeng , Wang Yifan
Published: August 2024

Oil and gas drilling is a complex construction process, drilling conditions as the key parameters of the construction process, efficient and accurate identification of drilling conditions is the basis for statistical drilling efficiency and analysis of drilling status. With the continuous development of integrated logging technology and sensor technology, field operators and researchers have access to large amounts of realtime data. The existing methods mainly include logical judgment and manual judgment, which have the problems of insufficient accuracy and low efficiency, respectively. In recent years, more and more scholars have adopted data-driven methods such as machine learning to identify drilling conditions, but pure data-driven models have the problem of high false positive rate. This paper proposes an intelligent identification method for drilling conditions based on a combination of deep learning and drilling experience knowledge. First, abnormal fluctuations in the logging data are removed through an efficient real-time data cleaning process, and then the most critical parameters that characterize the drilling conditions during the drilling process are selected. Three deep learning algorithms, Gate Recurrent Unit (GRU), Long short-term memory (LSTM), and Convolutional Neural Networks (CNN), are used to build the intelligent identification model for drilling conditions and compare them. Then, according to the expert knowledge of drilling condition judgment, the logical constraint is formed, and it is added to the identification process. The final workflow can effectively realize real-time intelligent identification of 10 drilling conditions. The recognition precision and recall rate of various conditions are both above 94%, providing a basis for drilling efficiency analysis and risk prevention.