bluuebunny/crossref_metadata_2025 huggingface dataset:
Third-Order Steady-State Solutions of Bichromatic Bi-Directional Water Waves
Authors: Gao Zhe , Liu Yi , Jia L. S. , Teng Yunfei , Wang Dejun , Jia Xu
Published: September 2023

In the context of potential flow theory, the resonance mechanism leads to energy transfer between primary waves, resulting in a series of dynamic physical phenomena. However, for the analytical solutions of surface gravity waves, resonance interactions become an obstacle in solving the steady-state solution of surface gravity waves, resulting in a small divisor problem. Due to the small divisor problem caused by harmonic resonances, the classical perturbation method fails when solving third-order solutions of bichromatic bi-directional water waves. In this paper, a novel method is proposed to solve third-order solutions of bichromatic bidirectional water waves, which successfully overcome the small division problem caused by harmonic resonance and is applicable to resonance and non-resonance cases. Finally, the third-order steady-state solutions provide explicit expressions for the surface elevation, surface potential and nonlinear dispersion relations.
A Computational Study to Predict Seakeeping Performance of a Surfaced Submarine in Irregular Waves
Authors: Jung Doojin , Kim Sanghyun
Published: September 2023

In general, submarines are designed to optimize operation below the water surface because they spend most of their time in an underwater condition. However, the performance in free surface condition is also important because submarines face a variety of scenarios to complete operational missions and the free surface condition is unavoidable for port departure and arrival. In case of submarine, a numerical accuracy of potential theory for seakeeping analysis is excellent in submerged condition, but it is poor in free surface condition because of nonlinear effects near the free surface area. In this study, Star-CCM+ was used as a Reynolds-averaged Navier Stokes (RANS) solver to estimate the seakeeping performance of Canadian Victoria Class submarine in irregular waves, and the results were compared to those of model tests from a published paper. In addition, the potential theory code was also used for seakeeping performance to compare with Computational Fluid Dynamics (CFD) results. From the calculation results, the motion responses in irregular waves by using CFD showed similar trends to experimental results, while motion responses from potential code showed significantly larger values than experimental results. In conclusion, CFD simulations with irregular waves can be good solution to predict the seakeeping performance of submarines in free surface condition.
Motion Response Study of the Floating Dock During the Spar Installation
Authors: Pani Soumyashree , Saha Nilanjan , Sundaravadivelu R.
Published: September 2023

Floating wind turbines are an evolving renewable energy source, but installing them offshore is difficult due to weather conditions. A new approach called the floating dock concept has been developed to address this issue. The dock makes the process more reliable by shielding the installation process from weather disturbances. This study examines a floating dock of 60 m diameter used to install a 5 MW wind turbine on a spar of 15 m diameter. The dock has a gate that allows for establishing a spar at the desired location. The system is analyzed under two conditions: with the gates closed and open since the latter has a risk of instability. The paper uses the ANSYS-AQWA software to study the heave and pitch response of the structures. Free decay tests were conducted numerically to obtain the total damping matrix, from which the viscous damping matrix was derived. This matrix was also incorporated in the analysis of the structures. The behavior of the system was analyzed, and the results ensured that the floating dock was effective in reducing the responses of the spar foundation.
Review on Feasibility of Bottom-Fixed Offshore Wind Development in the Arctic Focusing on Icing Problems
Authors: Gu Yingjie , Ong Muk Chen , Janocha Marek Jan , Blomgren Atle
Published: September 2023

The Arctic is a resource-rich region, especially concerning hydrocarbons, minerals, and fisheries abundance. Due to remoteness and harsh environment, communities in some parts of the Arctic rely heavily on diesel-based power generation. In addition to the challenge of maintaining reliable sustainable supply chains for fossil fuels, the generator emissions also have an undeniable negative impact on the vulnerable Arctic ecosystems. Low-cost, efficient, clean energy sources are required to support the sustainable development of the most remote communities. Comprehensive comparison and evaluation of the advantages and disadvantages of known energy generation and storage technologies suitable for cold climate deployment are presented in this study. Among analyzed solutions, hybrid power systems that incorporate bottom-fixed offshore wind turbines (BFOWTs) have great advantages of providing green energy and reducing land occupation and energy generation costs. Many challenges and risks require further investigation before BFOWTs can be commercially deployed in the Arctic. The main risks of BFOWTs deployed in the Arctic are the structural interaction with sea ice and ice accretion on wind turbine elements. To address issues about ice accretion, this study provides reviews of state-of-the-art research on ice detection and ice mitigation technology. Important knowledge gaps related to the BFOWT development in the Arctic are identified and future research recommendations are made.
Study on Deformation Analysis and Prediction Method of Multi-Function FPSO Hull
Authors: Yuan Hongtao , Ren Huilong , Chen Gang , Yin Yan , Wang Chao , Wu Bin
Published: September 2023

The total longitudinal bending deformation of the hull girder will affect the static function of the ship equipments and the dynamic response of the hull girder structure, while the influence of the deformation of the FPSO hull girder on the design of the Topside module support structure can not be ignored. Therefore, in addition to the conventional design load, the influence of the displacement of the Topside module support structure caused by the hull girder deformation should also be considered in the design of the FPSO Topside module. There are cumbersome calculation steps and troublesome solution process in the calculation of FPSO Hull Beam Deformation based on the undetermined coefficient method, continuous subsection integration method proposed based on the single span beam theory and the total longitudinal bending deformation theory of ship hull girder. Aiming at the shortcomings of the traditional prediction methods of FPSO hull girder deformation, a simplified deflection calculation formula is proposed based on engineering experience, which is convenient for the rapid analysis of the FPSO hull girder deformation, and compared with the numerical simulation results of Finite Element Analysis to verify the applicability of the empirical formula in the front-end engineering design and basic design.
Ice Resistance Prediction Using Explainable Deep Learning Method
Authors: Sun Qianyang , Zhou Li , Ding Shifeng , Liu Renwei , Wang Aimin , Chen Jiaming
Published: September 2023

Accurate prediction of ice resistance plays an important role in ensuring the safety of ship navigation when sailing in ice regions. In recent years, machine learning has been widely applied in the field of ships, among which deep learning is a common method. This study combines the scientific problems of ice resistance for ice-ship design closely, focusing on the design of a deep learning network for predicting the resistance of ice-sailing ships, proposes a Graph Neural Network method to predict ship resistance in ice area based on different data preprocessing methods. The predicted response and real response of the network, the feature weight relationship of the network and the prediction error are shown in the form of a graph. This study refers to the traditional semi-empirical formula, selects appropriate input features (ship design parameters and ice mechanic properties). The neural network is trained through the ship model test data. Different data preprocessing methods are selected to analyze the error of network prediction results, and the generalization ability and fitting effect of the network are evaluated. This work will provide reference for ice-sailing ship.
Symmetry Breaking of a Rigid-Flexible Coupling System at Low Reynolds Numbers
Authors: Zhang Huanyu , Tian Xinliang , Zhao Yakun , Li Xin , Lu Wenyue
Published: September 2023

Flow past a rigid-flexible coupling system consisting of a rigid plate and a trailing closed flexible filament was simulated numerically. An immersed boundary method was developed based on OpenFOAM to solve this fluid-structure interaction (FSI) problem. Three simulations including flow past a rigid circular cylinder, a rigid plate, and two flexible loops were conducted to validate our code. The motion modes transition and dynamic performance of the coupling system were investigated at low Reynolds numbers (Re ≤ 80), where the tension coefficient and bending coefficient of the filament were fixed. According to the symmetry of the filament motion, six motion modes have been identified for different filament lengths and Reynolds numbers, i.e. symmetric and stationary (SS) mode, asymmetric and stationary (AS) mode, regular and unilateral flap (RUF) mode, transition motion (TM) mode, symmetric and bilateral flap (SBF) mode, and asymmetric and bilateral flap (ABF) mode. Moreover, symmetry breaking was discovered in the AS, RUF, and ABF modes. The positions of the filament at different times were drawn to describe its movement and distinguish motion modes. Meanwhile, the drag and lift of the coupling system were investigated and a significant drag reduction was found. In addition, The time-averaged lift directly depended on the symmetry of the filament and rapidly changed with a sudden alteration in symmetry. Our research is helpful to understand the change of motion behavior of this coupling system at low Reynolds numbers.
A Review: DC Microgrids for Sustainable Power Delivery in Offshore Industries
Authors: Indrajith Bawantha , Gunawardane Kosala , Jayasinghe Hasith
Published: September 2023

Legacy Alternating Current (AC) based power systems, coupled with bulk-generated electrical energy from fossil fuels, are working against the achievement of sustainable development. Worldwide integration of renewable energy in power generation is growing rapidly. This is making a major contribution to the achievement of sustainable development goals and affordable clean energy. Direct Current (DC) operable products are becoming the most common type of internal power architecture in many application domains in both land and marine based systems. In these systems, power supplied from AC form is internally converted to DC within the appliance. Renewable-based power generation, including solar photovoltaics (PVs), wind, wave, and tidal generators, can generate DC power intrinsically or can be converted to DC power. In addition to that the supportive novel technologies developing around renewable energy generation such as hydrogen storages, fuel cells and associated other alternative energy storage technologies such as battery and supercapacitors all are intrinsically in DC form. Therefore, both the supply and the demand sides of power systems are in favor of moving towards DC systems called DC microgrids. With the elimination of DC/AC and AC/DC converter stages in DC grids, they create a highly efficient, low-cost platform. Also impacts such as skin effect, reactive power usage, power quality issues and grid synchronization are comprehensively reduced too. Since renewable sources like photovoltaics generate on-site DC power, eliminating the need for long distance AC transmission facilities, they are particularly attractive for remote communities and industrial and commercial sites. Since the minimum interaction on main power grids, offshore systems are more attractive to be operated as low voltage DC distribution. DC microgrids have the potential to revolutionize power systems by offering a versatile solution for a wide range of power applications. These microgrids can support various power applications including small-scale generation, energy storage backup, data centers, marine operations, and industrial facilities. With the details provided about the objectives behind the trend towards DC microgrids, their benefits and some issues, a comprehensive discussion about DC microgrid standards, components and controlling are also presented. Furthermore, this paper discusses application of offshore industries like aquaculture, oil and gas. These offshore industries are rapidly integrating with DC microgrids to have low-emission operations with reduced impact on nature. With the information illustrated on this paper, it is desirable to indicate that system and control architecture for a desired offshore application can be designed uniquely from any another industrial application to have sustainable power delivery arrangements.
A Dry Monitoring System of Mooring Lines Utilizing Artificial Intelligence
Authors: Sidarta Djoni E. , Tcherniguin Nicolas , Bouchard Philippe
Published: September 2023

Detection of mooring line failure of a floating vessel without any inputs of environmental conditions and/or directions can be made possible by measuring and analyzing vessel positions and headings, and also drafts in the case of an FPSO. This approach simplifies the required monitoring equipment and certainly helps in reducing cost and required maintenance.

In addition to changing a vessel’s mean positions and headings, mooring line failure changes natural periods of the system. Therefore, to determine the condition of mooring lines and to detect mooring line failure, a dry monitoring system can (or needs to) detect subtle changes of natural periods of the system and variations in vessel headings as a function of vessel position and draft (or mass) for an FPSO. This task that can be categorized as pattern recognition and classification is very difficult to carry out with human visualization or conventional methods/tools to get to a reasonable detection rate. Although challenging, solving this task can be rewarding. This is an area that Artificial Intelligence (AI) is very good at, and AI can be an essential component of a reliable dry monitoring system.

This paper presents several AI models, including Artificial Neural Networks (ANN), that can be used to determine the condition of mooring lines and to detect mooring line failure. This paper compares the performance of these AI models for a vessel’s loading condition (draft) that has not been included in the training of the models. This paper also discusses a method to enable an ANN model to be more tolerant and adaptive to new conditions and its applicability for other AI models.

AI models can be used in combination with conventional digital methods (numerical algorithms) to determine the condition of mooring lines and to detect mooring line failure. This approach of combining AI models and conventional digital methods for a dry monitoring system requires knowing how and when to use AI models and conventional digital methods. This important aspect is illustrated in the presented examples on how the monitoring system detects mooring line failure in real time. These examples show the importance of AI and conventional digital methods and the significant contribution from each of them.

This paper demonstrates that AI can be an important tool for a dry monitoring system of mooring lines and can be used in conjunction with conventional digital methods to increase the robustness of the solution. This application of AI is an example of the potential of AI in solving an engineering problem, which is otherwise difficult to solve using conventional methods/tools.
Reducing Containership Greenhouse Gas Emission Through Speed Optimisation by Coupling a Fast Time Manoeuvring Solver to a One-Dimensional Propulsion Model and Under Keel Clearance Predicting System in Shallow Water Under Environmental Forcing
Authors: Kazerooni Reza , Karatvuo Helena , Harkin Alex , Womersley Timothy , Jensen Bugge
Published: September 2023

Deciding the target speed profiles within harbor approach and navigational channels requires a trade-off between sufficient under keel clearance and control of the ship in different weather conditions. Rudder as the main type of steering system for conventional ocean-going vessels is considered as a passive control device leading to decreased steering performance when ship speed through water decreases. On the shallow sections of navigational channels, the ship needs to slow down to maintain safe bottom clearance margins (due to squat effects). However, once combined with strong wind or currents, this speed reduction may limit the ship controllability and course-keeping which becomes a challenge to navigation. In response to the recent pressures on the climate, another dimension has been added to this transit planning balance. It is now also important to optimize target speed profiles to minimize emissions while ensuring safety in manoeuvering and reducing grounding risk. A fast time manoeuvering solver using a PID controller for steering the ship is developed based on SimFlex 4 manoeuvering model and linked to a one-dimensional model of the ship propulsion system to estimate the actual loading on the propeller and engine during the manoeuvers. Consequently, the fuel consumption and emission of green-house gases from the engine is predicted. The ship under keel clearance is calculated based on empirical squat, turning and wind induced heel methods, and a second order panel method for evaluating vessel frequency response incorporating implicitly the effect of vessel forward speed and varying depth for the ship responses in waves. Consolidated as commercial package, NCOS ONLINE, it is of the modern generation of operational tools for navigation optimization in shallow and confined waterways. The tool is then used to find the optimum target speed resulting in minimum emissions from the main propulsor, while the manoeuvring performance and under keel clearance remain within the acceptable thresholds for safe navigation of large commercial ships.
Experimental and Numerical Analysis of Ice Crushing Tests With Different Shaped Ice Specimens
Authors: Müller Franciska , Böhm Angelo , Herrnring Hauke , von Bock und Polach Rüdiger U. Franz , Ehlers Sören
Published: September 2023

Ships operating in ice covered waters are exposed to the risk of colliding with an iceberg or ice floe. Predicting the loads in ice-structure interaction is crucial for the safety of existing ships and the optimization of the ship structures in the future. The ice geometry and the interaction velocity are two parameters, among others, that have a high influence on the acting forces and pressures. There has not been much research on the influence of the ice geometry in ice-structure interaction tests in the past. This paper analyzes the failure mode, peak forces, and energy of different ice specimen geometries at different interaction velocities in small-scale crushing tests and identifies shape-dependent effects. Furthermore, a first attempt is made to numerically simulate these experiments with the Mohr-Coulomb Nodal Split (MCNS) ice model in order to extend the applicability of the model to more general ice-structure interaction problems. Overall 21 different ice shapes were tested in crushing experiments with a hydraulic piston and drop tower experiments and were simulated with the MCNS model. In addition, the influence of the interaction velocity was analyzed for 13 shapes at interaction velocities of 10, 100 and 2000 mm/s. The specimen shapes included among others a cylinder, cones, truncated cones, elliptical, dome-shaped and wedge-shaped. In the experiments, the load, the displacement, and the failure behavior were recorded. Especially the peak force, energy, and failure mode were used for the analysis and comparison with the simulation results. The results show a high dependency of the failure mode and peak forces on the specimen shape, initial contact area, and interaction velocity. The MCNS model is capable to predict trends of the peak load depending on the initial contact area and generated different failure behaviors depending on the ice geometry to some extent. However, there is potentially room for improvement, especially considering the triaxiality and the influence of the interaction velocity.
Numerical Study of the Lateral Blockage Effect on the Performance of a Novel Vertical-Axis Turbine
Authors: Wu Hao , Cao Renjing , Wang Enhao
Published: September 2023

Regarding to a novel vertical axis auto-rotation current turbine (VAACT), a detailed three-dimensional (3D) numerical study was carried out on the influence of lateral blockage on its performance using detached eddy simulation (DES) combined with the slide mesh. Firstly, time series of angular velocities during the power production stage of the turbine are given, and it is demonstrated that the increase of blockage ratio is beneficial to stabilize its rotation and power output. Also, it is found that as the lateral blockage ratio decreases, the efficiency of the turbine decreases. The fitted curve of mean power coefficient (Cp¯) as a function of lateral blockage ratio is presented. Based on the fitted curve, it is roughly predicted that Cp¯ will be about 0.145 without the lateral blockage effect. Finally, detailed flow field characteristics such as limiting streamlines and 3D vortical structures are displayed in this paper. The two rows of side-by-side vortexes are observed to periodically fall off in the wake, and the onset vortexes behind the turbine are almost two-dimensional in the spanwise direction. All in all, this study deepens the understanding of this novel vertical-axis turbine, and can provide references for its future industrial applications.
An Approximate Method for Predicting Nonlinear Time Domain Motion of Ship Taking Motion Attitude Change at Large Amplitude Into Account
Authors: Duan Fei , Ma Ning , Shi Qiqi , Gu Xiechong , Zhou Yaohua
Published: September 2023

The large amplitude motion of a ship in rough sea will lead to obvious nonlinear characteristics of the hydrodynamic loads acting on the hull, especially for shallow draft ships. Therefore, the fast and accurate prediction of nonlinear motion of the ship needs to be solved. The transformation from frequency domain to time domain is realized based on impulse response function method. And the nonlinear restoring force is calculated through pressure integration on instantaneous wetted surfaces. The instantaneous radiation and diffraction force considering the nonlinearity of hull surface are pre-calculated and stored in a database. The database includes the added mass, damping coefficient and diffraction force at different relative position of wave and the hull. According to the height of the instantaneous average wave surface on the hull at the last moment, the instantaneous value of the added mass, damping coefficient and diffraction force of the hull are obtained by invoking the corresponding steady-state solution in the database. The radiation force and diffraction force change along with the motion attitude of the ship are considered in this method. The model test has been carried out to verify the proposed method. Compared with model test, the method proposed in this paper can obtain accurate results of ship nonlinear hydrodynamic forces in a relatively short time, which is effective for prediction of the ship’s large motion response.
HDD Borehole Pull-In Analysis of Offshore CCS Pipeline
Authors: Yu Yi , Duplenskiy Stanislav
Published: September 2023

In recent years, with the increasing demand of reducing CO2 emissions, offshore pipeline found its new application in transporting CO2 offshore. Carbon capture and storage (CCS) is an effective method in the fight against climate change. This technology allows CO2 to be “captured” from large sources such as power plants and prevents release of greenhouse gas to the atmosphere. The captured CO2 has to be compressed and then transported to a safe and durable storage location, such as depleted subsea oil reservoirs. The captured CO2 is then locked away deeply under the sea floor so that it cannot escape into the atmosphere and contribute to global warming.

To facilitate the connection between an offshore pipeline and an onshore plant, a robust landfall method must be adopted. The benefits of using horizontal direction drilling (HDD) for offshore pipeline landfall include longer durability, potentially lower project cost, less community and environmental disruption, and fewer authorization issues.

In this paper, the analysis methods and the results of an HDD pull-in case study are presented. An analytical method for pull-in force is discussed first and then a global finite element (FE) model is developed. In the global model, a 10 km long pipeline is included. The pipeline, the pull wire and HDD borehole are simulated by using beam elements. The tube-to-tube elements are used to simulate the contact between the pipeline/wire and the borehole. The global model is used for both the pull-in and the hang-off analysis. To prevent corrosion of the pipeline in case of the coating damage, circular anodes are installed on the pipeline. In the HDD borehole, the anodes are installed for all the pipe joints. Since the anode pitch is small enough, the anodes are also used as centralisers during pull-in installation. To study of the effect of anodes on pull-in load, a local FE model is also developed. In the local model, a short pipe section and an anode with detailed geometry are included. The pipe and the HDD borehole are modelled using shell elements and the anode is modelled with solid elements. The additional pull-in load caused by the anode is predicted by using the local model. The loads acting on the hang-off structure in different phases are also obtained from the analysis, which are used as design input data for the hang-off structural design. The finite element analysis (FEA) results are compared with the results obtained from the simplified analytic calculation. It is concluded that the results obtained from the proposed FEA method are more accurate and more reliable than those from the simplified methods. In future, the proposed numerical analysis method can be used as reference or go-by for projects with HDD pull-in.
Derivation of Adapted Soil Springs for the Buckling Analysis of Suction Caissons During Installation
Authors: Ramos Juan Pablo , Widerspan Viktor , Heinrich Dariya , Böhm Manuela
Published: September 2023

The buckling capacity of suction caissons during installation must be investigated, as these are sensitive to buckling due to their thin-walled structure. A geometric material nonlinear analysis with imperfections, in which the soil is modeled using continuum elements, provides the most realistic results. Nonetheless, the modeling of the nonlinear material behavior of the soil as well as the consideration of multiple imperfection shapes are associated with a high modeling and computational effort. To avoid this, springs are often used to model the soil. However, the common approaches for determining lateral soil springs were developed experimentally for flexible piles and not short caissons. In this work finite element models are created to derive adapted soil springs for large scale tests on suction caissons. The comparison of the implemented soil springs with the soil springs from the guidelines shows that an adjustment of the commonly used springs is necessary. A factor that allows the springs to approximate the behavior of the continuum elements is formulated. Additional models that analyze the supporting effect of the soil on the buckling capacity of the suction caisson using continuum finite elements and soil springs foundations are developed. These models also compare the effect of the embedment depth and the soil bearing capacity.
Numerical Simulation to Collapse of a Carcass of a Flexible Riser Using a Dynamic Model With Quasi-Static Behavior Through of an Explicit Solve Method
Authors: Párraga Quispe José Luis , Ribeiro Rodrigo , Drumond Geovana , Nogueira Soares Luisa , Igor Lourenço Marcelo , Barata Anderson , Ramalho dos Santos Ferreira Lucas , dos Santos Cordeiro Alexandre
Published: September 2023

A flexible pipe riser is a flowline to oil transport from a subsea well to a floating unit, and it is composed of layers between these a carcass, a pressure sheath, a pressure vault, tensile armors, and anti-wear layers. A carcass or interlocked carcass is more internal layer and is projected to support radial forces. High radial forces can produce a collapse failure of an interlocked carcass. The interlocked carcass has a helical section geometry, so the pitch provides an interlock between its surfaces. These interactions between surfaces using a finite element model with an implicit method produce high non-linearity of the numerical problem for convergence of results. Therefore, a numerical model is proposed using a dynamic model with a quasi-static behavior and explicit solve method for the collapse analysis of an interlocked carcass. Numerical analysis is carried out in two steps. In the first step, the carcass pipe is generated by an angle of revolution applied to the section considering the pitch of the spiral. Therefore, a numerical model is developed to insert an imperfection in the perfect pipe. In the second step, an external vessel with stoppers is modeled where the carcass pipe is positioned internally, thus representing the pressure test with a hyperbaric chamber.
Incorporating Empirical Nonlinear Efficiency Into Control Co-Optimization of a Real World Heaving Point Absorber Using WecOptTool
Authors: Gaebele Daniel T. , Michelén Ströfer Carlos A. , Devin Michael C. , Grasberger Jeff T. , Coe Ryan G. , Bacelli Giorgio
Published: September 2023

The open-source WecOptTool was developed to make wave energy converter (WEC) control co-design accessible. WecOptTool is based on the pseudo-spectral method which is capable of efficiently dealing with any linear or nonlinear constraints and nonlinear dynamics by solving the WEC optimal control problem in the time domain using a gradient based optimization algorithm. This work1 presents a control co-optimization study of the AquaHarmonics Inc. heaving point absorber WEC sized for ocean deployment to solve practical industry design problems. Components such as the specific type of generator, the hull shape, and the displaced volume are pre-determined. We co-optimize the WEC’s mass versus mooring line pretension in conjunction with the controller. The optimization is subject to the power-take-off (PTO) dynamics and the rated constraints of the components. In particular, the continuous torque rating is implemented as an explicit constraint, a novel approach for WEC optimization. The PTO dynamics are incorporated into the optimization algorithm via a combination of first principle methods (linear drivetrain model) and empirical efficiency maps (electrical generator) represented as a power loss map. This is a practical method applicable to a variety of PTO architectures and transferable to other WECs. A discussion between using an efficiency coefficient versus a power loss map and their implication for the optimization method is presented. This application of WecOptTool represents a real world WEC by combining simplified models with empirical efficiency data. The WEC, as a dynamically coupled, oscillatory system, requires consideration of the time trajectory dependent power loss for optimizing the average electrical power. This objective function, the modelling approach, and the realistic loss terms makes the common practice of artificially penalizing the reactive power needless.
Augmented Adaptive Filter for Real-Time Sea State Estimation Using Vessel Motions Through Deep Learning
Authors: Majidiyan Hamed , Enshaei Hossein , Howe Damon
Published: September 2023

Given the recent rise of autonomous shipping, the knowledge of environmental seaway awareness has become imperative for automated control systems onboard and autonomous units in general. The real-time wave data enables the decision-maker to evaluate dynamic wave loads on the marine structure and efficiently monitor/operate the vessel’s conditions on and off-site. To this end, the wave buoy analogy (WBA) aims to benefit from 6 DOFs ship responses to estimate the induced wave specifications. Although this concept has been extensively scrutinized, the integration of AI and its subsets, machine and deep learning in this field is new. So, the objectives of the current research are twofold; the first is to take advantage of temporal and spectral information for seaway estimation in a deep learning model. The second is to propose a solution addressing two significant issues of WBA: the time lag between the exciting wave and corresponding estimation and stabilizing outputs. The study uses a setup to integrate an ARIMA-EMD predictive filter to adjust sampling window size adaptively on the upcoming data based on the anticipated fluctuations. A major advantage is that filter helps to reduce time lag while improving estimation stability. The response data is synthesized according to a tested semi-submersible platform at Shanghai Jiao Tong University (SJTU) research institute, where the time series is transformed into the pictorial presentation through several processing stages to feed a deep learning network. For training, the concept of transfer learning has been utilized by a pre-trained network, AlexNet. The result is promising and provides a foundation for attaining real-time wave updates in operational scenarios.
A New Approach for Natural Gas and Hydrogen Blast Loading Analysis: A Fixed Mass Perspective
Authors: Lee Hyun Ho , Seo Jung Kwan
Published: September 2023

A fixed mass perspective signifies a concept of which the mass of flammable or combustible gas is fixed but the volume and concentration could be different depending on leak conditions such as location and size of leak hole, ventilation conditions, etc. This phenomenon could make the explosion level different, even if the total amount of combustible/flammable material is the same. Nevertheless, most of related studies on the gas explosion have been conducted in a fixed volume perspective which is a concept with fixed volume and variable mass of combustible/flammable material. In this study, therefore, the blast loading analysis in the fixed mass perspective on the natural gas which is being used in the maritime transport industries and hydrogen which will be used as eco-friendly energy in the future was performed by CFD simulations. The upper deck, where the fuel storage tank could be located, and compartment, where the engine and pipe could be positioned, were selected as geometrical conditions of explosion simulations because these spaces have the relatively high possibility for leak and explosion accidents in ships.
NeMo: A Multi-Draft Mooring Line Failure Detection System Based on FPSO Predicted Motion
Authors: Sa'ad Amir Muhammed , Cunha Rodrigo Da Silva , Barreira Rodrigo Augusto , Tannuri Eduardo Aoun , Gomi Edson Satoshi , Costa Anna Helena Reali
Published: September 2023

Mooring line breakage of a moored offshore Floating Production Storage and Offloading (FPSO) platform results in an increased load on the remaining lines, worsening their degradation rates. Furthermore, a line break causes the FPSO to change its motions and move away from the desired location. In addition, platform motions differ depending on its draft and environmental conditions, making it difficult to detect mooring line failure. In this paper, we propose a system based on machine learning called Neural Motion Estimator (NeMo) composed of (i) a multilayer perceptron network capable of forecasting the horizontal motions of a FPSO with 18 mooring lines under 14 draft configurations, from ballasted (8 meters) to full load (21 meters), and (ii) a multinomial logistic regression classifier that provides the associated probability of failure for each line group in the mooring system. The results of several tests show that NeMo was able to identify the occurrence of line breakage in all draft configurations with a minimum percentage of false classification.
Assessing Underwater Noise Impact From Marine Projects
Authors: Lenchine Valeri V.
Published: September 2023

A substantial number of marine infrastructural projects result in increased environmental impact on marine fauna during the construction and operational stages of the projects. A significant part of this impact is due to excessive noise. The absence of standard methods of underwater noise assessment and prediction increase the risk of unacceptable change to the marine environment as a result of offshore anthropogenic activities. Generally, the auditory systems of marine species are different from that of humans, however it is typical to attempt to extend the same approaches as used for human settings to marine ecosystems. The justification of such approaches is not provided, however it is well understood from a practicability perspective.

Construction operations such as pile driving and dredging may result in significant noise increase and irreversible impact on marine species. This paper reviews relevant regulatory documents and summarizes considerations that are typically used to setting relevant underwater criteria for construction and operational noise. It also suggests approaches to groups of acoustic criteria that may be used to control and minimize underwater noise impact.

General methods of modelling underwater noise impact are reviewed as a part of planning for marine projects and identifying the need for noise mitigation measurements and preparation of relevant construction and operation plans. These approaches may be used to identify relevant noise criteria and submit environmental effect statements to attain regulatory approvals.
Probabilistic Methods for Estimation of the Extreme Air Temperature Along the Northern Sea Route
Authors: Huang Yuexiang , Chai Wei , Zeng Jiayan
Published: September 2023

In recent years, as a great increment in the demand for energy resources, the Northern Sea Route (NSR) has received increasing attention as a potential shortcut for connecting East Asia and Europe. For ships sailing in the Arctic regions, many hazards could be encountered due to the low air temperature, such as ship icing phenomenon, brittle-fracture of steel structures and freezing of liquids within pipes, etc. Therefore, an accurate estimation of the extreme values for the air temperature could provide valuable information for the selection of steel material as well as for the winterization strategies for the ships sailing along the NSR. In this work, a collection of 40-year (1981–2020) historical air temperature data is obtained from the Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2), which is an atmospheric reanalysis tool developed by NASA and four representative sites along the NSR are selected for the investigation. Subsequently, the traditional block maxima method and the proposed average conditional exceedance rate (ACER) method are applied in order to estimate the extreme air temperatures at the four representative sites. The block maxima method is executed by application of the parametric distribution functions, while the ACER method is based on a sequence of nonparametric distribution. The accuracy, efficiency and robustness of the proposed methods are compared and studied in details.
A Mechanistic Model for Predicting the Formation of the Riser Blockage
Authors: Sun Deping , Liu Haixiao
Published: September 2023

A riser blockage is a possible risk in hydraulic transport for deep-sea mining, which seriously affects transport efficiency and safety. To avoid blockages in pipes, it is crucial to predict the conditions of the blockage formation. The present work aims to develop a theoretical model to predict the appearance of the riser blockage based on mechanism analyses. The theoretical model is set up as follows. Firstly, the friction force between the pipe wall and particles at high concentrations is analyzed. Secondly, the deceleration and acceleration processes of target particles are investigated, considering the particle-particle, turbulence particle and wall-particle interactions. Finally, a dynamic equilibrium is established based on the above analysis. The solution of the equation is less than or equal to zero when the blockage is formed, which implies that the critical condition of the blockage formation in vertical pipes is obtained. The validation work is then performed by comparing the predicted results with experimental data available in the literature. To acquire further knowledge of the formation of the riser blockage, the effects of six parameters of the model are investigated in detail, including the ratio of particle diameter, the fluid velocity, the volume concentration, the pipe diameter, the particle density, and the fluid density.
The Effect of LNG and Diesel Fuel Emissions of Marine Engines on GHG-Reduction Revenue Policies Under Life-Cycle Costing Analysis in Shipping
Authors: Taghavifar Hadi , Prasad Perera Lokukaluage
Published: September 2023

The fuel life cycle involves different phases of extraction/refinery (well to tank: WtT), transport (tank to propeller: TtP), and storage where each of these processes can add a specific amount of emissions to the overall LCCA inventory. During the extraction or operation of machinery on the raw material, the released amount of GHG components is undergoing a change in the generated emissions per functional unit of the consumed fuel. As a result, the machinery efficiency, electricity share, and resources mix during the extraction or refinery would impact the emission factor and subsequent carbon credit plans. Additionally, the transportation characteristics such as the traveled distance, multi-model transportation share, and ship engine fuel efficiency can make difference in the emitted GHGs into the atmosphere. The GHG credit rate and duration under different carbon allowance scenarios in the LNG-powered vessel are considered for the current life-cycle carbon emission cost analysis. For the life-cycle costing, the inflation rate, and the discount rate along with the emission reduction incentives are going to be emphasized in the project’s feasibility indicators and its profitability. The results have shown to what extent the LNG use in marine transportation can favor green shipping and how the legislated carbon incentives encourage the shipping industry for the LNG infrastructure development. The methane slip (evaporation) during the liquefaction of LNG will also be addressed, i.e., during the LNG production phase, and its effect on the emission factor of GHGs to have a better understanding of the challenges and outlook on the LNG production industry and its utilization in shipping.
Design Assessment of Mechanical Wavemakers: A Comprehensive Study Towards Wave-Structure Interaction Applications
Authors: Gamaleldin Muhannad W. , Babanin Alexander V. , Chabchoub Amin
Published: September 2023

The development of novel marine installation concepts and physical wave modeling rely on experimental testing in water wave facilities. A crucial element in such experiments is mechanical wavemakers, which are ubiquitous in many experimental wave tank tests, ranging from shallow to deep water applications such as wave structure interactions, coastal processes, and shore protections. The present study introduces and investigates the influence of geometrical modifications to the classical piston-type mechanical wavemaker on surface wave generation. To achieve this, theoretical models based on the classical linear potential flow hydrodynamics were derived, predicting wave height and power requirements of the proposed wavemaker designs. Moreover, several two and three-dimensional numerical CFD simulations, using the Open-Source Field Operations and Manipulations (OpenFOAM) CFD numerical package, were conducted to validate and assess the proposed theoretical analysis. Finally, experimental tests were performed for a rigidly fixed cylinder subject to monochromatic wave trains to validate the outcomes of the numerical models. Overall, free surface profiles and hydrodynamic-induced forces of the theoretical, numerical, and experimental observations are in very good agreement, indicating the validity of the presented theoretical analysis. The proposed geometrical modifications are relatively straightforward to be applied and extend the versatility of the conventional piston-type wavemakers for different target design wave conditions.
An Experimental Study on the Responses of a Spar-Type Floating Structure Integrated With Aquaculture Systems
Authors: Li Qiao , Dong Shuchuang , Zhou Jinxin , Kitazawa Daisuke
Published: September 2023

The development of floating offshore wind turbines that combine aquaculture has potential economic benefits for both industries. In this study, the heave and pitch dynamic responses of a spar-type floating offshore wind turbine with aquaculture system are investigated by an experimental tank, as a feasibility study. A 1/56 model of a 2MW Spar floating wind turbine is used in the experiment. First, the Spar with an aquaculture feeding system is tested. The feeding system is built above the waterline, which can feed 300 tons of fish for one week. When attaching an additional structure such as a feeding system to the Spar, the structure’s center of gravity is raised, which might affect the stability of the floating structure. By the experiment, there is no noticeable increase in accelerations or motion displacements. Under a particular wave period, the motion of the Spar may be reduced. In addition, the dynamic responses of Spar are investigated when aquaculture cages are set near the Spar model. The target cage is silver salmon farming cage, and it has dimensions of around 25 m in diameter and 9 m in depth. Three model cages are set in front of the Spar facing the wave direction. When comparing the Spar-only testing results, the heave motion is increased but the pitch motion is reduced, because of the interference effects of the cages.
Reliability Analysis of Crack Growth Occurrence for a Secondary Structural Component due to Vibration Excitation
Authors: Kolle Kleivane Siri , Leira Bernt Johan , Steen Sverre
Published: September 2023

Ship hull vibration is a significant contributor to fatigue crack growth and the major sources of vibrations are found to be the main engine vibration excitation, the wave-induced springing and whipping loads, and the action of the propeller. In the midship region, wave-induced loads and the main engine are the major contributors, whereas propeller excitation dominates in the aft region of the ship hull. The vibration problems onboard a ship are very complex and are found at both global and local levels. No general method exists to solve all kinds of vibration problems and hence they need to be evaluated through a cost-by-case approach. The complex and uncertain aspects of hull vibration and fatigue crack growth motivate the need for a reliability-based scheme for assessing the resulting fatigue crack propagation of secondary components and structural details. In the present paper, a probabilistic formulation for the failure probability of the occurrence of crack propagation of a secondary hull component is outlined. A generic cargo hold model is analyzed with engine excitation and wave-induced loading as vibration sources, and a stochastic model for vibration response is obtained based on this. The limit state is presented as the possible occurrence of crack growth. The secondary structural component considered is a pipe stack support, and different initial crack sizes are evaluated. The adequacy of the applied stochastic model for vibration response is evaluated and the accuracy of the estimated failure probability is assessed.