bluuebunny/crossref_metadata_2025 huggingface dataset:
An Elastically Moored Flexible Multibody Wave Energy Converter
Authors: Nag Chowdhury Debneil , De Chowdhury Swapnadip , Ghoshal Ritwik
Published: August 2024

This paper introduces a novel wave energy converter design that utilizes a concept for regulating displacement amplitude with an internal non-linear rotative gravity pendulum system. A standard wave energy converter, which operates as a cylindrical buoy floating in an ocean of finite depth and is tethered to a concrete foundation installed in the seabed, and subjected to regular waves. The buoy is equipped with an original internal non-linear rotative gravity pendulum system designed to control the heave motion of the buoy. This allows for the dynamic adjustment of wire tension, subsequently governing the power output of the buoy. Furthermore, this innovative design enables the buoy to adapt to a wide range of power requirements and environmental conditions. A mathematical model that employs potential theory and a linearized free-surface boundary condition is adopted to simulate the behavior of this elastically moored flexible multibody wave energy converter. The effectiveness of this design is thoroughly investigated through an extensive study. The influence of the mass and damping constants of the multibody device on the displacement response is also explored. A comparative analysis is performed numerically between devices with and without a parametric gravity pendulum exciting device. The study indicates the existence of both beat and prominent internal resonance phenomena, which warrant meticulous investigation in further studies. These findings have potentially significant implications for renewable energy production, particularly in coastal and offshore areas.
An Analytical Solution for Evaluating Structural Resistance of a Stiffened Plate Under Lateral Impact With Large Indentation
Authors: Zhang Yichi , Zhou Jiayou , Yuan Yuchao , Tang Wenyong
Published: August 2024

Ship collision accidents occur frequently despite the efforts of developing collision-avoidance technology and tools. The structural crashworthiness analysis is thus important and developing rapid prediction tools have been a hot field in the past decades. This paper presented a new analytical solution for assessing the structural resistance of a stiffened plate under lateral impact from a raked bow. Numerical simulations were firstly carried out to help identify the mechanisms of structural deformation of the stiffened plate from the side shell. The damage modes of the stiffened plate were categorized as three types with the continuous indenting of the bow. Multiple analytical formulas were derived to cover the process of damage evolution, including plate denting, plate rupture and plate tearing. Detailed analytical models for stiffeners were also developed for various deformation phases instead of using equivalent thickness method. Finally, an integrated method was developed based on the derived formulas for each single component. The integrated method innovatively considered the coupling effects and interactions between various structural members in the collision analysis by dynamically correcting some parameters. The method was verified against the numerical simulations of full-scale ship collisions through several typical scenarios and good accuracy was achieved. The newly developed method is valuable for crashworthiness design in the preliminary designing phase, especially for severe collision scenarios.
Development of a High Fidelity Multi-Agent Maritime Simulator
Authors: Ibrahim M. Mohammed , Deogaonkar Vallabh , Somayajula Abhilash
Published: August 2024

The maritime industry has experienced significant growth in autonomous systems in recent years, with substantial research dedicated to developing diverse algorithms for the autonomous navigation of surface vessels. To thoroughly gauge the credibility of such autonomy algorithms often requires evaluation across a diverse range of scenarios. Due to the vast number of potential scenarios that necessitate testing, it is impractical to conduct all these tests in a practical manner. Furthermore, these tests are not one-shot endeavors and need to be evaluated with the changing maneuvering characteristics of the vessel as it evolves over its operational years. This paper introduces the concept of a novel multi-agent, adaptive simulator designed specifically for testing various autonomy algorithms for surface vessels such as path planning and collision avoidance. The key highlight of the simulator lies in its potential to progressively improve the accuracy of the hydrodynamic models of the vessels present in the simulation.
The Effect of Post-Storm Reconsolidation on the Response of Monopile-OWT Systems in Clay
Authors: Aghedo Iwinosa O. , Charlton Tom S. , Rouainia Mohamed
Published: August 2024

Geotechnical processes related to offshore monopiles for supporting OWTs in soft clay involve intermittent episodic remoulding during storm events and reconsolidation during calm conditions. To assess the resulting response of monopiles, this study employs a three-dimensional finite element analysis. The methodology incorporates a kinematic hardening soil constitutive model within the critical state framework, calibrated against cyclic triaxial experiments and validated against the centrifuge test results on a 6m diameter monopile in soft clay subjected to multiple episodes of cyclic loading and reconsolidation. Thereafter, we investigate the performance of a reference 15MW OWT supported on a 10m diameter monopile in clay, subjected to three ten-minute storms of combined wind and wave loading representative of a 10-year return period, with reconsolidation periods between each storm. The results show a reduction in effective stress around the monopile during storms followed by recovery during reconsolidation, leading to a reduction in the level of monopile displacement accumulated in each subsequent storm event. This beneficial effect is overlooked in design practice, but can be anticipated through the approach presented here, which can form the basis for the validation of a digital twin that monitors the lifetime integrity of a monopile foundation.
On the Bending Responses of Adhesively Bonded Mechanically Lined Pipes
Authors: Yan Junhan , Yuan Lin
Published: August 2024

As a new type of CRA lined pipe, adhesively bonded mechanically lined pipe utilizes a glue layer between the inner and outer pipes to enhance the gripping between the two pipes. With the help of mechanical bonding and adhesive, the liner’s wrinkling and collapse have shown to be somewhat delayed, making this new type of product a more economical and efficient solution for offshore applications. However, the mechanical behavior and the design of key parameters of such a product are still less understood.

In this work, we developed a numerical framework to study the bending response of the adhesively bonded mechanically lined pipe (ABMLP), in which the hydraulic expansion-induced residual stresses and strains were considered for completeness. The pure bending characteristics of perfect and imperfect ABMLP, especially the evolution of local buckling of the liner, were carefully examined. Furthermore, the paper also preliminarily investigated the effect of important parameters of potential problems, such as the length of glue-free zones and the adhesive property variations.
Numerical Modelling and Analysis of a New Combined Concept of Floating Wind Turbine and Fish Farm Structure
Authors: Wan Ling , Tay Zhiyung , Shi Wei
Published: August 2024

To achieve better utilization of ocean space and energy, a new combined concept of floating wind turbine and fish farm structure is proposed. The four-pontoon semi-submersible platform is designed to support an offshore wind turbine and fish farm frames. The platform can be cost-effective, due to the sharing of the infrastructures, and the potential synergy from a proper combination. Open cage fish farm structure is designed to be modular, and can be flexible in dimension. In this work, coupled numerical model of the platform is established. Potential flow theory or panel model is used in the hydrodynamic property calculation. The slender fish farm frame structures are modelled by the Morison elements. Viscous effects are included through quadratic coefficients. Various aspects of wind turbine modelling, and fish farm modelling are discussed. Dynamic motion responses are studied, with a focus on the influences of the fish farm frames on the platform. Two scenarios, i.e., floating wind turbine with and without the existence of the fish farm frames, are specially investigated. Natural periods are presented, and dynamic performance of the two scenarios under wave conditions, wave + current condition, and wave + current + wind condition is investigated. Uncertainties in the analysis and future improvements are also discussed.
Experimental Study on the Collapse of Mechanically Lined Pipe Under External Pressure
Authors: Yuan Lin , Wang Chuangyi , Wang Xipeng
Published: August 2024

Mechanically lined pipes (MLP), known for their cost-effectiveness and reliability in transporting corrosive oil and gas, have increasing applications in offshore projects. The presence of the non-corrosive liner, although relatively thin, will increase the collapse capacity of MLP to some extent. In addition, the mechanical property changes induced by hydraulic plastic expansion during manufacturing are also expected to influence the buckling behavior of lined pipes. However, this problem is still less understood, and related studies about MLP collapse are mostly limited to numerical simulations instead of experiments.

In this work, we conducted a series of small-scale experiments on the mechanically lined tubes. The lined pipes, made of carbon steel Grade GB45 (AISI 1045) and T2 copper, are manufactured using a custom hydraulic expansion facility. The products have finished diameters of 50 mm and an overall D/t of 16.5, with 1.0 mm thickness for the liner. Afterward, intact and minorly dented specimens were collapsed under external pressure in a sealed hyperbaric chamber. The collapse pressure and final configuration of the tubes were recorded. In addition, the experimental results were reproduced by finite element models, which takes account for both the manufacture and collapse stages, and good agreement was reached.
Hydrodynamic Investigation on a Submerged Tunnel Suspended From Two Pontoons Under Various Immersion Depths
Authors: Song Yue , Sun Zhenxiang , Chen Nianzhong
Published: August 2024

In this paper, the hydrodynamic responses of a tunnel element suspended from two immersion pontoons have been studied by physical model tests in wave basin. A wide range of irregular waves is conducted on the tunnel immersing from the depth near the free surface to the depth near seabed. During each test, the six-DOF motion of the tunnel element and the immersion barge are measured in a simultaneous manner with two receiving terminals of an electromagnetic motion tracking system. Based on the measured data of scale 1:60, response spectra analysis is conducted to examine the coupled motion characteristics of the tunnel element for various immersion depths. Furthermore, to explore the coupled resonant properties of the tunnel immersion system, the coupled motion equation of the whole system is solved and the eigen modes and natural frequencies are obtained. The results showed that the mode frequencies of the coupled tunnel-barge system have a good corresponding relationship with the peak frequencies in the motion spectra. This demonstrates that the coupling mechanism between the tunnel element and immersion barges plays an important role in the motion responses of the tunnel. The increasing immersion depth have a significant effect on the coupling effects, and thus on the motion characteristics of the tunnel element.
Construction and Validation of a Two-Way Fluid-Structure Interaction Solver Under an Open-Source Framework
Authors: Sun Jia-Yu , Sun Shi-Li , Wang Shuang
Published: August 2024

The Fluid-Structure Interaction (FSI) issue is a complex and nonlinear process involving the interaction between a deformed structure and the surrounding fluid. In this work, we developed a novel high-fidelity, modular, open-source and user-friendly FSI simulation framework by coupling the well-established fluid solver OpenFOAM® with the structure solver CalculiX. The fluid solver solves unsteady RANS equations using a finite volume method on unstructured meshes. The hydrodynamic loads on the surfaces of the object are then passed to structural solver. The displacements and structural response of the object are efficiently computed and exchanged with the fluid solver through a finite element analysis. The coupling was implemented through the preCICE coupling library for partitioned multi-physics simulations, which treats the two dedicated solvers as ‘black boxes’ and provides data mapping between non-matching meshes. Two classical FSI test cases are presented, and the numerical results are compared with previously published laboratory tests and benchmark data, achieving a satisfactory agreement. This work provides an efficient tool under the open-source framework for Fluid-Structure Interaction simulation.
Repurposing Submarine Hydrocarbon Pipelines for Dense Phase CO2 Transport
Authors: Rulence Emilien , Husband Sean
Published: August 2024

Carbon Capture and Storage (CCS) will play a crucial role in the energy transition. Natural gas developments must continue for decades to meet growing energy demands and to concurrently enable the transition from fossil fuels to renewable energy generation. Stripping the CO2 from the natural gas and disposing it into depleted reservoirs will be essential to reduce harmful emissions during the transition. Many depleted offshore natural gas fields are planned for CCS. They will require a submarine pipeline that transports CO2 from an onshore processing facility to the field.

CO2 has been transported via onshore pipelines for several decades, however there is less global experience in the design, construction, and operation of submarine CO2 pipelines. In many cases the CO2 needs to be transported in dense phase for efficiency. The complex properties of dense phase CO2, combined with the technical and operational challenges of a carbon steel pipeline in a wet environment, create an engineering challenge that has only recently been uncovered. A potential attractive option is to repurpose existing hydrocarbon pipelines to transport dense phase CO2. This has significant benefits. There is no need to perform seabed route surveys, purchase linepipe materials, and construct a new pipeline. However, repurposing existing pipelines for dense phase CO2 transport is not always a feasible or safe option.

This paper utilizes the foundations outlined within the DNV industry standards to propose a high-level screening methodology that aims to quickly understand if existing hydrocarbon pipelines have the potential to be re-qualified for dense phase CO2 transport. Two case studies are presented to illustrate how this methodology can be applied, with different outcomes.
Optimization Study of Ship Speed Based on Membrane Computing Theory
Authors: Wang Hao , Zhang Yanbing , Xu Haoran , Wang Lizheng
Published: August 2024

In this paper, a speed optimisation algorithm based on membrane computing theory is proposed for Yangtze River bulk carriers. First, a ship energy consumption model is constructed and validated based on the improved Ayer’s method. Then a global optimization algorithm, called the membrane computing theory-based diffusion optimization algorithm (MC-DOA), is proposed, which is inspired by the double-membrane cell structure of chloroplasts and mitochondria as well as the phenomenon of particle diffusion, and makes use of a mixed-membrane structural system and four different particle searching strategies to search for global optimum values. Finally, a sailing speed optimization model is developed with the objective of optimal energy consumption and constraints such as specified sailing arrival time. In order to verify the effectiveness of the speed optimization algorithm, a 6700-ton bulk carrier on the Yangtze River is taken as the target ship, and a typical route from Chongqing to Shanghai is selected for the optimization test. The results show that the proposed speed optimization algorithm is able to solve the inland waterway speed optimization problem efficiently, and save the fuel consumption of the ship by optimizing the ship’s speed effectively.
Meshfree Model for Porous Seabed Response Under Combined Earthquake and Random Wave Loading
Authors: Han Shuang , Zhang Jisheng , Tsai ChiaCheng , Jeng Dong-Sheng
Published: August 2024

In the context of offshore structure design, the consideration of earthquake and wave loadings is paramount due to their pivotal role as natural dynamic forces. These dynamic forces can induce vibrations in the pore water pressure, thereby precipitating seabed instability. However, the investigations of the earthquake-induced seabed behaviour are limited. Furthermore, contemporary studies on seismic seabed response often neglect the concurrent impact of ocean waves. Previous research predominantly relies on conventional mesh-based methods, such as the finite element method. To address the limitations inherent in such methods, such as computational time and mathematical complexity, this study employs a meshfree method based on the “u – p” approximation. The research assesses soil response under the Japan 311 earthquake and random wave loading in both time and frequency domains. Numerical findings indicate that earthquake-induced acceleration is notably amplified by the seabed foundation, particularly in the horizontal direction. The presence of wave loading significantly alters the development of pore pressure, yet it exerts no discernible impact on earthquake-induced acceleration in the seabed. Consequently, the contribution of random waves to seismic-induced seabed response analysis cannot be disregarded.
Effect of Directional Sea Spectrum in Cyclonic Conditions on Responses of a Weathervaning Vessel
Authors: Lubis Michael Binsar , Drobyshevski Yuriy , Kimiaei Mehrdad
Published: August 2024

Accurate representation of wave spectrum is crucial for extreme response analysis of weathervaning vessels under tropical cyclone. It is a common practice to use unidirectional or symmetrical directional wave spectrum for response analysis of floating vessels. However, reported measurements of cyclonic sea states show that directional sea spectrum may be very different from the commonly assumed spectrum. Importantly, the directional wave spectrum of cyclonic sea state is typically skewed, with its higher frequency tail tending to align with predominant local wind, while the peak wave energy at lower frequencies propagates in a different direction, sometime at large angles to wind. Asymmetrical shape of the spectrum may affect responses of a floating structure in different ways. Given that responses in cyclonic conditions usually govern the structural design, there is a need to assess the significance of the directional spectrum for the behavior and extreme responses of a weathervaning vessel.

This paper examines the effect of directional wave spectrum on weathervaning behavior and responses of a generic turret-moored Floating Production Storage and Offloading (FPSO) vessel, exposed to tropical cyclones at the North-West Shelf of Australia. Cyclonic sea states chosen for the study is representative of design metocean conditions generating the 100-year wave load responses. The study compares the directional wave spectra from a hindcast cyclonic database with a commonly assumed spectrum. A parametric formulation for the directional wave spectrum in tropical storms, which was developed in oceanographic research in the last decades, is also considered in the comparison. Results of weathervaning behavior and several wave load responses of the vessel are presented and discussed.
Experimental Investigation of Offshore Wind Turbine Structure on Structural Behavior Under Lateral Loads
Authors: Choi Won Seok , Sohn Jung Min , Kim Sang Jin
Published: August 2024

Expanding renewable energy capacity is becoming increasingly important as the International Energy Agency (IEA) advises reducing carbon dioxide emissions in response to rising energy demand and environmental concerns associated with fossil fuels. Wind turbines, a powerful and efficient means of generating renewable electricity, have seen exponential growth in numbers over the recent decades. Many countries are actively promoting wind turbine construction and research, but despite numerous reports of tower collapses, there has been limited progress in the field of structural reliability studies. Generally, the structural design methods, Allowable Stress Design (ASD) and Load & Resistance Factor Design (LRFD), used for wind turbine towers. To ensure a more robust structural design, it is advisable to consider Ultimate Limit State (ULS), which considers the potential resistance for buckling and post-buckling behavior of the entire structure.

This study presents an experimental investigation of the comprehensive structural response of a structure based on the geometric characteristics and loading conditions of a wind turbine tower. The experiment was conducted on a cantilevered cylindrical shell structure subjected to lateral loading. Both load-displacement curves and strain measurements are presented for a comprehensive understand of structural behavior. The effects of the bottom boundary condition and the initial geometric imperfections of the cylindrical shell on the results are analyzed. It also discusses experiment limitations.
Local Scour Around the Touchdown Zone of a Pipeline-Riser System
Authors: An Hongwei , Hossain Muhammad Shazzad , Kim Youngho , Kim Young-Tae , Bae Kyung-Tae , Golabek Ian , Tabram Jake
Published: August 2024

This paper presents a series of physical model tests for investigating local scour around the touchdown zone of a pipeline-riser system used for liquefied natural gas (LNG) offloading. The local scour around a J-shape pipeline-riser system is influenced by several parameters, including the curvature radius to pipeline-riser diameter ratio (R/D), pipe embedment ratio (e/D), flow intensity (defined by the ratio of the Shields parameter to the critical Shields parameter, θ/θcr), and flow direction (α). The model tests were conducted using a model pipe with a diameter of D = 0.07 m and R/D = 5. Eight different flow directions (α = 0° to 180°) and six pipe embedment ratios (e/D = 0.5, 0.7, 0.9, 1.1, 2 and 3) were examined.

The results indicate that flow direction α affects the equilibrium scour depth significantly for e/D = 3.0. When α ranges between 0° and 122.5°, the curvature of the model pipe appears to intensify the local scouring process. For larger α values, the scour depth is less than that observed around a vertical pile. For e/D = 3.0, local scour is seen to be a constrained process, and the horizontal pipeline remains buried. The equilibrium scour depth diminishes as e/D reduces from 3.0 to 0.7, and no scour propagation is observed along the pipeline on the seabed for this range. For e/D = 0.5, local scour continuously expands in the spanwise direction of the pipeline, leading to the formation of free spans. Critical e/D value for the development of free spans lies between 0.5 and 0.7.
Research on Shock Load Recovery of the Marine Isolator
Authors: Wang Shuang , Guo Jun , Qiu Zhong-Hui , Zhao Xiao-Jun , Zhao Hua-Xun
Published: August 2024

In order to facilitate the development of the impact test and restore the original impact load effect, this paper adopts the combined sine wave method and the composite fundamental wave method to reconstruct the impact load of the marine multi-diaphragm isolator. The advantages and disadvantages of the two methods are analyzed, and the consistency of the response effect of the components under the two shock loads is studied. The results show that the diaphragm isolator demonstrates excellent shock resistance and displacement limitation. The response effect of the isolator under the combined sine wave is different from the original response, and the reduction degree of medium and high frequency load spectrum is poor, which has certain limitations. Compared to the structural response under the original impact load, the acceleration response error under the composite fundamental wave load is 9.37%, and the top vertical deformation error is 12.9%. The composite fundamental wave method effectively recovers the shock load by transforming the characteristic parameters of the base waveform.
Machine Learning Based Prediction of Buckling in Composite Cylindrical Shells Under External Pressure Using Design Code and FEM Analysis
Authors: Lee Hyung Gi , Kim Sang Jin , Sohn Jung Min , Prabowo Aditya Rio
Published: August 2024

Composite materials, known for their strength and weight advantages, find extensive use in the maritime industry. Nevertheless, predicting the buckling pressure of composite cylindrical shells, especially with specific layup patterns, is a challenging task.

This study aims to enhance buckling pressure prediction accuracy through machine learning. The model is trained using data from NASA design codes and finite element analysis in ANSYS. Twenty-four-layer composite cylindrical shells with a thickness of 2.52mm, constructed from carbon-epoxy prepreg tape (USN-125), were subjected to external pressure. Stacking patterns, denoted as [θ/θ]12, , were varied at 2-degree or 5-degree intervals for each method, ranging from 0 to 90 degrees. This variation resulted in a dataset comprising 2378 data points.

A Random Forest machine learning algorithm, which demonstrated higher prediction accuracy compared to other algorithms, was trained on this dataset., with weights assigned to NASA design equations and FEM results at a 1:2 ratio. Predictions using random angle combinations were compared to those solely based on the design equation, demonstrating higher accuracy.

This study represents an initial step in integrating machine learning to enhance buckling pressure prediction accuracy. Future enhancements may involve incorporating post-buckling test data and fine-tuning variable weights in the algorithm to further improve precision.
Real-Time Prediction of Rate of Penetration Using Multi-Gene Genetic Programming
Authors: Ma Baodong , Zhu Zhaopeng , Song Xianzhi , Zhang Chengkai , Liu Zihao
Published: August 2024

The rate of penetration (ROP) is a crucial metric for assessing drilling efficiency. However, the ROP prediction models based on conventional machine learning have high accuracy but poor interpretability, and the offline models make it difficult to capture the dynamic impact of formation and drilling condition changes on ROP. In this paper, a real-time prediction method for ROP using multi-gene genetic programming (MGGP) algorithm is proposed. First, outliers and non-drilling conditions data are eliminated. Through the multicollinearity analysis, seven mud logging variables, weight on bit, rotary speed, torque, inlet flow, inlet density, standpipe pressure, and mud pit volume, are taken as input variables and filtered. Then the explicit expression between variables and ROP is constructed based on the MGGP algorithm, and the variables sensitivity is analyzed. Finally, a real-time update framework is proposed to capture the dynamic trend of ROP, with a coefficient of determination of 0.89 and a mean absolute percentage error of 5.44%. This study verifies the effectiveness of the MGGP algorithm in the prediction of ROP and improves the interpretability of the model, which provides a basis for complex geological drilling process.
A Numerical Analysis of a Hybrid Semisubmersible and Point Absorber Wind-Wave System
Authors: Huang Yi-Chieh , Yu Yi-Hsiang
Published: August 2024

Hybrid wind-wave systems combine a floating offshore wind turbine (FOWT) with a set of wave energy converter (WEC) systems. Although the level of power production is significantly different, integrating a WEC system with the FOWT may be beneficial, such as reducing the FOWT platform motion. This study uses Matlab for Offshore Simulation Tool (MOST) and WEC-Sim to simulate the UMaine VolturnUS-S floating platform with the International Energy Agency Wind 15 MW wind turbine and a wave energy converter (WEC) array with three heaving point absorbers. Both WEC-Sim and MOST are open-source simulation tools. WEC-Sim has been developed and applied to analyze various types of WEC systems. MOST has been developed using WEC-Sim environment and implemented to analyze floating offshore wind turbines. A series of simulations are presented in this paper, including a set of decay tests to verify the MOST+WEC-Sim solutions and selected wind-wave conditions to evaluate the hydrodynamic response of the system. The primary objective is to assess the effectiveness of coupling MOST and WEC-Sim for simulating the hybrid floating wind-wave system across various design scenarios and developing benchmark cases. Finally, the system hydrodynamic response results are analyzed, and the effectiveness of using the WEC system for stabilizing the platform is discussed.
A Shock-Absorbing Non-Hydrostatic Navier-Stokes Solver on σ-GRIDS for Wave Modeling Over Irregular Topography
Authors: Bihs Hans , Ehlers Ronja , Wang Widar
Published: August 2024

In recent times, there has been the introduction of various numerical wave tanks (NWT) based on computational fluid dynamics (CFD) that provide detailed information on wave propagation and associated wave hydrodynamics. Faster solutions for nonlinear wave propagation are desirable for a wide range of ocean and coastal engineering scenarios. High-order spectral (HOS) wave models and fully nonlinear potential flow (FNPF) models are potential options for efficient wave propagation simulations in deep water. In the design of offshore wind substructures, it is often necessary to identify significant wave events, currents, and sediment transport processes together. The dynamics of each phenomenon are interrelated and greatly influence offshore structures. For pure wave propagation problems, a potential flow model is highly effective. However, when simulating wave-current interactions and sediment processes, a viscous flow model that considers turbulence effects is more suitable. This research presents a three-dimensional non-hydrostatic model called REEF3D::NHFLOW, which operates on a moving σ-coordinate grid. By solving the non-hydrostatic Navier-Stokes equations, this model provides detailed results. The grid used in REEF3D::NHFLOW follows the surface and bottom topography, allowing for grid refinement near the water surface or bottom while maintaining low computational effort. Developed within the open-source hydrodynamics framework REEF3D, the new model is fully parallelized and utilizes the domain decomposition strategy and MPI communication between processors. This paper showcases the capabilities of this new and efficient one-phase flow model through the implementation of a free surface and bottom following σ-grid approach.
AL – A Prototype Autonomous Ship Model for Navigating in Ice Conditions
Authors: Bolbot Victor , Sandru Andrei , Saarniniemi Ture , Freter Jan Hendrik , Puolakka Otto , Kujala Pentti , Valdez Banda Osiris A.
Published: August 2024

This paper introduces a scaled-down model of an Unmanned Surface Vessel (USV) named “AL,” designed specifically for navigating ice-covered waters. The development involved utilizing Computer-Aided Design and Computer-Aided Manufacturing (CAD CAM) tools, employing 3D printing in a modular fashion, and assembling the components into an icebreaking hull prototype. Watertightness examinations ensured the vessel’s integrity. AL was then equipped with advanced electronics, sensors, and state-of-the-art positioning algorithms in the ROS 2 environment. Systematic model tests identified critical ship hull parameters, enabling the establishment of basic controllers. These controllers contributed to the development of a basic navigation and control system for AL. The result is a ship model capable of autonomously following a predefined trajectory, guided by waypoints, while maintaining the desired speed in ice channels. The AL model serves as a platform for future research in autonomous navigation within ice-covered environments.
Methodology to Define the Probability of Detection of Failures In Subsea Equipment Considering Multiple Influencing Factors
Authors: Cuba João Pedro B. , Schleder Adriana M. , Martins Marcelo R. , de Barros Leonardo O. , Orlowski Rene Thiago C.
Published: August 2024

Cost optimization of asset management is a central issue in the offshore oil and gas strategy, and risk based approaches has been more and more employed to assist the segment in the concretization of that goal. In this sense, the use of Risk Based Inspection by the petroleum industry has significantly increased. The inspection procedure aims at mitigating the uncertainty related to the asset degradation state, enabling a better quantification of the actual damage, and, consequently, increases the accuracy of remaining life projections. However, information related to the capacity of the inspections methods to detect the failures and the degradation in equipment is scarce in the literature.

The effectiveness of an inspection method is commonly associated with the probability of detection function of the failure modes and the development of PoD curves is highly complex. Thus, in this study, a methodology is proposed to obtain detection probability values for different scenarios associated with inspections carried out in offshore environment. Several factors may influence the detection probabilities, in addition, a factor may have greater influence on one method than on another. Therefore, in this paper, it is proposed a new methodology to define the probabilities of detection, which is an evolution of the method proposed by Cuba et al [1] considering the influence of these factors; the methodology consist of four steps: the definition the probability of detection for standardized scenarios, the definition of the influencing factors impact, the definition of the correlation between the probability of detection for standardized scenarios and the influencing factors and, finally, the update of the probabilities according to the scenario analyzed.
Study on the Performance of Anti-Collision Sandwich Structure for Underwater Vehicles
Authors: Han Enquan , Yuan Siming , Chen Liyuan
Published: August 2024

Underwater unmanned vehicles (UUVs) predominantly operate in deep-sea environments characterized by complex terrains, which increases the risk of collision accidents and consequent significant losses. Enhancing UUV impact protection is therefore crucial. Traditional protective shells for UUVs rely on large-scale plastic deformation of structures to absorb impact energy, but these conventional designs often fall short in meeting impact resistance requirements. This paper introduces an innovative sandwich structure, the annular cylindrical shell chain (ACSC), designed to offer improved anti-impact performance for UUVs. The mechanical response of the ACSC under impact loading is studied, focusing on impact force and stress distribution. By employing an equal-mass design approach, the ACSC cells were arranged at varying angles, with the equal-mass homogeneous cirque serving as a control. This methodology facilitated the identification of the most effective ACSC configuration. Findings reveal that the ACSC configuration with a constant relative density and cells oriented at a 5° angle demonstrates superior impact buffering capabilities. This research contributes valuable insights to the development of new energy-diverting protective structures in the realm of UUV impact protection.
Long-Period Wave Propagation and its Influence on Sediment Transport Over a Typical Beach in West Africa
Authors: Luo Mengyan , Wang Guangsheng , Tong Linlong , Chen Ning , Zhang Jisheng
Published: August 2024

The dominant wave in the west coast of Africa is bimodal spectrum wave consisting largely of long-period swell, where the spectral peak period is large (Tp = 8∼22s). The speed of long-period swell is also great, so the interaction mechanism of long-period wave with seabed is very complicated, which causes strong sediment transport and dramatic beach evolution. Therefore, the water-sediment movement characteristics are very different from those along the coast of China. However, there are few studies on the hydrodynamic processes in West Africa, and the propagation and deformation law of this kind of low frequency swell in the nearshore area and its influence on sediment transport and beach evolution are still unclear, which has caused serious problems to the design and construction of overseas projects, and needs to be studied urgently.

In this paper, according to the characteristics of the west coast of Africa, the typical beach of Benin Bay is selected to establish a physical model test of beach profile, and the shallow water deformation and breaking of waves, the response characteristics of pore water pressure and the changes of nearshore topography are studied. In the experiment, two-peak spectra wave groups and long-period regular wave groups with different incident conditions were set up. Wave height meter, Particle Image Velocimetry (PIV) technology, pore water pressure sensor array and Sony Alpha 3 high-speed camera were used to observe the changes of free liquid surface, boundary layer velocity, pore water pressure gradient and nearshore topography during wave propagation. This study reveals the evolution of wave propagation and sediment transport mechanism under long-period waves in the West African coast, and the results can provide scientific and theoretical basis for beach protection and restoration in Benin sea area.
Numerical Simulation Study on the Ice Load and Ship Motion Response in Formation Navigation in Brash Ice Channels
Authors: Zhang Bihui , Zhao Jiancheng , Wu Chenzhen
Published: August 2024

In recent years, the melting of Arctic ice has intensified due to the continuous increase in the global average temperature, which has made it possible to open Arctic channels. Predicting ice resistance during ice breaking is a crucial issue for navigating polar ships in ice-covered waters. However, studies on the dynamic ice resistance hydrodynamics and ship motion response of subsequent polar ships in channels after ice breaks are rare. This paper employs CFD-DEM technology to investigate the impact of a channel on a polar ship after icebreaking. The contact of discrete particles is simulated with a variant of the spring-damper model. The fifth-order Stokes wave is introduced to simulate wave action based on nonlinear wave theory. The simulation uses overlapping grid technology to model the ship’s motion response under the combined effects of nonlinear waves, currents, and brash ice. The fluid control equation is discretized using the finite volume method, while the volume of fluid method is used to capture the free surface. Finally, the grid independence is verified and compared with that of the direct sailing resistance test of the bare hull. The numerical simulations of the ice impact force, nonlinear wave action, and ship-ship coupling state were found to be in good agreement. The coupling of CFD-DEM methods can enhance the reliability and efficiency of simulating collisions between structures and brash ice. The model developed in this study can be used to investigate the coupling between dual structures and brash ice collisions.
Arrangement Effects on Flow Through an Array of Cylinders
Authors: He Fei , An Hongwei , Draper Scott , Ghisalberti Marco , Branson Paul , Cheng Liang
Published: August 2024

Although elements in natural and engineered systems, such as patches of aquatic vegetation, groups of pile foundations, and arrays of tidal stream turbines, are arranged in uniform or random configurations, there is a lack of understanding of hydrodynamic differences between these two arrangements. This paper presents results from two-dimensional direct numerical simulations of flow through a circular array of cylinders that have been undertaken to examine the hydrodynamic differences. It is shown that a random array has higher average drag coefficient and lower spatially averaged velocity within the array than these of a uniform array with the same diameter ratio. The lower drag coefficient for the uniform array is associated with the formation of characteristic flow structures, including two-row structure and shear layer reattachment and channelized flow in between adjacent lines of cylinders. As increasing perturbation of the array, these characteristic flow structures and the channelized flow progressively break down and hence the average drag coefficient increases and the spatially averaged velocity decreases. This paper provides guidelines for optimizing hydrodynamics of obstacle arrays through altering arrangement in real systems.
Analysis of Static, Dynamic, Global, and Local Load Effects for Ultimate Limit State Assessment of Semi-Submersible Hulls of Floating Wind Turbines
Authors: Wang Shuaishuai , Moan Torgeir , Gao Shan , Li Wei , Gao Zhen
Published: August 2024

Very limited research has been conducted on structural load effect analysis and design checks of large semi-submersible floating wind turbines (FWTs). Determining the combined static, dynamic, global, and local load effects in FWT is essential for the ultimate limit state (ULS) assessment of the floaters. This paper deals with the complex structural load effects for ULS analysis of column structures of a 10-MW semi-submersible FWT. First, a multi-body numerical modeling approach is employed to develop the floater model in a fully coupled FWT system to capture the time domain internal loads of column cross-sections under wind and wave conditions. Then, a high-fidelity approach and a simplified approach are developed to estimate lateral pressures on columns. With the obtained global cross-sectional loads and the corresponding lateral pressure, the ULS design check considering buckling for hull panels are performed for representative load cases. Detailed analysis results are presented and discussed, including perspectives of permanent and environmental load effects, as well as global and local lateral pressure load effects for buckling analysis of column structures. Moreover, comparisons of lateral pressures estimated by the high-fidelity and simplified approaches for buckling assessment of the outer column are made. Finally, the main conclusions are summarized. This study shed light on the importance of different structural load effects on ULS design checks. In addition, the simplified approach for lateral pressure estimate can be well used in the preliminary design stage of floaters to save large computational costs while obtaining acceptable results.
Immiscible Displacement of Oil by Water: An Experimental Investigation
Authors: Lund Bjørnar , Taghipour Ali , Saasen Arild , Ytrehus Jan David
Published: August 2024

Deviated well sections are common in modern well construction. In mature areas like the North Sea region, practically all producers or injector wells will have highly deviated sections. These wells must be completed in an optimal manner especially with respect to annular barrier integrity. The zonal isolation is important through all stages of the well’s life cycle. Since all wells must be permanently plugged before abandonment it is vital to ensure that annular barriers are designed with a long-term perspective and not only to minimize construction time and cost. Controlled laboratory environments with various fluid compositions and flow parameters are important to develop, validate and improve models and practices. Laboratory testing may often require significant simplifications to fit available resources, premises etc. and will not always be optimally designed to match relevant practical operations. Cement displacement is the objective for many such studies, while due to selection of fluids, in reality casing cleaning operations are investigated.

Most laboratory-scale experiments are conducted with water-based fluids for both the displaced and the displacing fluid. However, during cementing and clean-out operations the fluids are commonly immiscible, i.e. one fluid is water-based and the other fluid is oil-based. As a consequence, effects like immiscibility and wettability are important and will play a role for the displacement process.

We present results from displacement experiments where oil-based fluids are displaced by water-based fluids. Four experiment series were conducted. In the first series a commercial base oil was displaced by tap water with 3% NaCl. In the other three experiment series a real oil-based drilling fluid was displaced with three different brines with different viscosities and densities.

The experiments have been performed in a flow loop that consists of a 10 meters long test section with 5″ OD transparent pipe inside a 6,5″ transparent pipe. We investigate the effects of flow rate, string rotation speed, wellbore inclination, wellbore eccentricity and fluid properties on the displacement process. The displacement front is tracked using video recordings and electrical conductivity probes. Differential pressure and temperature transient measurements provide data which give additional information about the displacement process. The data can be used for validation of simulators as well as for designing cementing and wellbore cleanout operations.
Experimental Study on Added Resistance in Waves of KLNG at Design Speed and Low Speed
Authors: Kwon Yong-Ju , Park Dong-Min , Nam Bo Woo
Published: August 2024

In this study, experimental investigations were conducted to estimate the added resistance of KLNG in regular and irregular waves, with a specific focus on the effects of ship speed. A series of model tests were performed in ocean engineering basin of KRISO. The test model, with a scale ratio of 1:69, was towed with a soft spring in a diamond shape and two-axis load cells to measure the added resistance. Experimental conditions were established to examine the added resistance under various wavelength ratios and two ship speed conditions. At the design speed condition, it was found that the added resistance in waves exhibited peak values within the radiation dominant region, while under the low-speed condition, diffraction became more crucial to the added resistance. Additionally, a high correlation was found between added resistance and relative wave motion responses of bow sections. In irregular waves, a discussion was made on a comparison between the results obtained by the direct and spectral methods.
Integration of a Novel Wave Power Generator Into Vehicle Charging System
Authors: Alawur Hadeel , Alkuhily Njood , Mutawakkil Sadil , Zayane Chadia
Published: August 2024

This paper emphasizes the potential role of electric vehicles (EVs) in reducing carbon footprints. It introduces the “Mauja” wave energy conversion device, designed to harness ocean wave energy for EV charging. The system integrates a multi-panel flap and a rotary generator, directing generated electricity to charge EVs through control electronics. Utilizing SOLIDWORKS, ANSYS AQWA, and WEC-Sim, the study explores the Mauja device’s technical design, fluid dynamics, and simulations under various wave conditions. It investigates the impact of factors like device dimensions, inertia, and wave types on power absorption, highlighting the device’s adaptability to different waves. The research underscores the importance of design in optimizing power absorption from ocean waves. Ultimately, this study emphasizes the significance of innovative wave energy conversion systems in mitigating CO2 emissions and highlights the need for adaptable designs to effectively utilize ocean wave energy for sustainable power generation and EV charging.