bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Dynamic Feature of the Fluid Resonance in a Recessing-Type Moonpool
Authors: Song Zhiwei , Tang Guoqiang , Lu Lin
Published: September 2023

Two-dimensional fully nonlinear potential flow numerical analyses on the fluid resonance within moonpool are systemically performed in the time domain with the varied incident wave amplitudes and a wide range of the incident wave frequency covering the natural frequency of the piston mode. The super-harmonic resonances are found around half and one-third of the first sloshing mode natural frequency in the recessing-type moonpool, where the higher-order harmonics rather than first-order harmonic dominate the responses, and the frequencies of higher-order harmonics are almost identical to the first sloshing mode natural frequency. Such a nonlinear phenomenon, however, disappears in the response of fluid oscillation within a traditional clean moonpool. The harmonic analysis illustrates that the introduction of recess leads to the energy transferring to the sloshing mode, thus exciting the sloshing motions. The joint works of the asymmetry due to recess and the free-surface nonlinearity results in the super-harmonic resonances inside the recessing-type moonpool. The evolutions of fluid oscillations in the recessing-type moonpool, being a complex nonlinear dynamic process, are further examined through the phase dynamics by performing Hilbert Transformation on the time series. Phase trapping and phase slipping states are confirmed in the responses of fluid in the recessing-type moonpool, which reflects the nonlinear evolutions of response developing from partial synchronization to de-synchronization.
Floating Nuclear Power Plants, a Safe Way Out of the Energy and Climate Conundrum
Authors: Lim Soon Heng
Published: September 2023

Climate scientists are alarmed at the rate global temperatures are rising and its knock-on effect on biodiversity. Some believe we are in the midst of the sixth mass extinction. Even as the evidence is apparent, the extraction of coal, oil and gas continues unabated to feed an insatiable demand for energy.

Global initiatives such as COP 27 and COP15 have not made as much headway as needed. Carbon sequestration is too costly. Solar and wind energy are not the silver bullet they have been made up to be.

The deployment of solar panels and wind turbines on land and over oceans desecrates the world’s biodiversity. Its impact is no less than that of wild forest fires and droughts.

The best tool to date to produce energy is by nuclear fission. It has zero emission, virtually zero impact on climate change and biodiversity owing to its high capacity factor and energy density and hence small spatial footprint. The spent fuel is also dense and hence easy to manage compared to CO2 and carbon particulates.

Floating nuclear power plants overcome many of the challenges that land based nuclear power plants face including construction and geotechnical issues and the loss of water replenishment source.

The proposal here is to build a lagoon to surround the floating plant. This would enhance security and provide other benefits including storing spent fuel and provide a benign environment for operation and maintenance. Within the lagoon, desalination and green hydrogen production may also be carried out.
Propagation of Hydrodynamic Wave Past Two Vertically Submerged Flexible Barriers of Non-Uniform Thickness
Authors: Singh Mansi , Gayen R.
Published: September 2023

In the literature related to linear water waves, most of the works have considered thin structures to have constant or uniform thickness. This assumption is based on the fact that the thickness variations in structures that are thin have no significant impact on the hydrodynamic quantities. But in the present work, we have shown that it is not so; even for thin structures, thickness variations can cause major changes in the physical quantities like plate deflection and the hydrodynamic force experienced by the structure. Also, in general, for an intensive study of the fluid-structure interaction problems, it is necessary to include the structural variations in the models for a better understanding of the phenomena. The transition from one barrier to a pair of barriers might be interesting because they enclose a water column which leads to near-resonant motion. This feature might be helpful to engineers for the purpose of construction of breakwaters. Thus in the present paper, we assess the hydrodynamic response of a pair of completely submerged vertical flexible barriers of non-uniform thickness to incoming surface gravity waves using hypersingular integral equations. The fluid domain is considered to be of infinite depth, and further, both the barriers are assumed to have clamped-free ends. By considering Kirchhoff’s thin plate theory, the described problem is reduced into a boundary value problem, which is solved by converting it into a system of coupled Fredholm integral equations using the classical method of integration and Green’s integral theorem. Further, the obtained integral equations system is converted to a matrix system of linear equations using appropriate approximations for the unknown quantities to obtain numerical solutions. With the help of MATLAB software the matrix system is solved, whose solutions are then used to determine numerical estimates of various physical quantities. The method used and the numerical results are validated by comparing them in the limiting cases of dual flexible barriers of constant thickness which are already available in the literature. Some selective graphical results are depicted in order to show the effect of the non-uniform thickness of the two flexible barriers on their hydrodynamic response by choosing certain thickness profiles.
A Study on Tsunami Disaster Prevention Measures by Floating Tsunami Mooring Bitts for a Vessel Moored at a Wharf
Authors: Tsutsui Chiaki , Minami Kiyokazu , Masuda Mitsuhiro
Published: September 2023

The tsunami triggered by the 2011 Great East Japan Earthquake caused severe maritime accidents to moored vessels in Japanese ports. Some researchers have proposed the floating tsunami protection wharf (FTPW) as a new tsunami protection measure for moored vessels in wharves. FTPW is a useful tool that can prevent breaking of mooring lines and grounding at a wharf by the leading waves of a tsunami. However, it may be difficult to place the FTPW in existing ports because it occupies a large area of the port, depending on the size of moored vessels. Additionally, some concerns exist about negative effects on cargo works because cargo handling equipment is placed on the floating body of the FTPW, which can sway. In this study, we proposed the use of floating tsunami mooring bitts (FTMB) to address these FTPW problems. FTMB are pillared floating mooring bitts placed inside the digging of a wharf so that they occupy less port area compared with the FTPW and minimize negative effects on cargo works. The FTMB float when the water level increases as a result of a tsunami, preventing the vessel from grounding at the wharf and breaking of the mooring lines. In this study, we performed tsunami simulations to verify the floating and disaster prevention performance of the FTMB using the 3-dimensional moving particle simulation (MPS) method. Our study demonstrates the tsunami disaster prevention and mitigation performances of the FTMB. The pillar and slit types FTMB, which are smaller than the existing FTPW, were able to prevent the breaking of mooring lines and grounding at the wharf by the tsunami. Furthermore, the FTMB showed the effect of delay of the tsunami inflow time to the land area. In the future, the FTMB will be one of the effective tsunami disaster prevention measures to reduce tsunami damage to vessels moored at the wharf.
Two-Sided Wave Generation in a High-Order Spectral Numerical Wave Tank
Authors: Aertsens Tim , Ducrozet Guillaume , Toffoli Alessandro , Monbaliu Jaak
Published: September 2023

The Coastal & Ocean Basin (COB) is a brand-new wave-current basin in Ostend (Belgium). The basin is 30m long and 30m wide, and it is equipped with modular wavemakers on two adjacent sides. This allows generation of multi-modal seas (including the so-called crossing-sea states). A system of multiple pumps will also be installed to allow generation of currents propagating at an arbitrary angle relative to the dominant wave field. To optimally utilize this new facility, an efficient numerical equivalent of the COB has been coded based on the High-Order Spectral Method (HOSM). The first step is the addition of a secondary wavemaker to the open-source High-Order Spectral Numerical Wave Tank (HOS-NWT). This was done by calculating an additional potential for each of the wavemakers in two separate additional domains and then using them as forcing terms on the two sides of the basin where the physical wavemakers are present. The implementation was done in a generic way and is made open-source. The effectiveness of the implemented method is demonstrated by comparing three base cases: only the x-wavemaker, only the y-wavemakers and both wavemakers together. However, there still remain challenges when it comes to wave generation in the y-direction and accurately modelling the corner between the two wavemakers.
Developing an Optimal Shape for Dynamically Installed Anchor
Authors: Bae Junsik , Kim Youngho , Hossain Muhammad Shazzad
Published: September 2023

Dynamically installed anchors (DIAs) have been identified as the most cost-effective anchoring solutions for mooring floating facilities because of its simple (free-fall) installation procedure. Due to the impressive concept of DIAs, many attractive shapes of the anchor have been proposed. However, the influence of the various geometric parameters on the performance of the anchor during installation and under operational loadings is yet to be explored. This paper assesses the potential of changing each component of the geometry and through that optimising the shape aiming at reducing fabrication cost and increasing efficiency in terms of tip embedment depth during installation and diving behavior under operational loadings. Large-deformation finite element analyses were performed using the Coupled Eulerian-Lagrangian (CEL) approach with the simple elastic-perfectly plastic Tresca soil model modified incorporating strain softening and strain-rate dependency of the shear strength. Parametric analyses were conducted varying the configurations of the shaft, fins and padeye. The anchor drag coefficient during free-fall in the water column was also assessed through computational fluid dynamics (CFD) analyses. Thus far, it has been found that an anchor with (i) a 1:2 sloped cylindrical shaft, (ii) padeye offset ratio within 0.2 < ηp < 1, and (iii) enhanced middle main two fins show better performance in terms of tip embedment depth and diving upon loading. A critical factor to dive is the alignment of the loading direction at the padeye with the anchor resistance centroid.
Jellyfish Deflection From Marine Fish Pens Using Bubbler Technology
Authors: Thodi Premkumar , Talimi Vandad , Liu Lei , Thijssen Jan , Gauthier David , Paris Mario
Published: September 2023

Increased jellyfish blooms have been identified as a major cause of caged fish damage in marine aquaculture facilities as well as clogging of seawater intake systems of nuclear power plant cooling stations and desalination plants. Bubbler technology has shown great promise for protecting marine facilities from jellyfish impacts. This paper focuses on the design of apparatus, planning and execution of large scale tests using simulated silicone jellyfish in a controlled environment. The following parameters were varied during testing: water current (0.1–0.6 m/s), bubble curtain angle (5°, 30° and 45°), air flow rate (0.1, 0.3 and 0.6 cfm/ft), number of curtains (1, 2 and 3), jellyfish size (5 and 18 cm diameter), curtain spacing (15, 50, 100 and 400 cm) and jellyfish release methods (surface and subsurface). From the test results, it was concluded that effective deflection of jellyfish in marine environment with currents upto 0.6 m/s was achievable. Also, the curtain angle, number of curtains, larger spacing between curtains and air flow rate through bubbler were observed to have a positive impact on the deflection efficiency for high current speeds. A CFD model developed was used to estimate the deflection efficiency, which provided a good agreement with test results.
Decommissioning of Umbilicals and Flexible Pipes - A Sensitivity Analysis in Decision-Making Process
Authors: Nogueira Soares Luisa , Lourenço Marcelo Igor , Paranhos Pasqualino Ilson , Ribeiro Nicolosi Eduardo , Violante Ferreira Claudio
Published: September 2023

The decommissioning of subsea equipment is a reality in Brazil and worldwide, highlighting the need for the development of decision-making methodologies for application in decommissioning projects. In Brazil, the volume of umbilicals and flexible pipes to be decommissioned in the future is huge and an analysis of the best decommissioning alternative would be desirable. Based on a decision-making methodology developed by a COPPE/UFRJ research group, this work aims to present the technical criterion for decommissioning decision-making process and a sensitivity analysis regarding the approach developed for this criterion. Among five different criteria, the proposed technical approach is composed of two sub-criteria — Complexity of Operations and Technological Risk — allowing us to assess the complexity of execution and operational activities of decommissioning alternatives and the technological risk associated with them. The decommissioning alternatives were divided into two groups — leave in situ and removal — and a total of six alternatives were considered in this study. The analyses developed to show the influence of different parameters in the methodology results emphasizes the robustness of the proposed methodology. Also, this work presents a preliminary indication for various decommissioning scenarios, varying combinations of water depth, structural integrity, cleaning status, and other factors. The results obtained in this work contribute to the consolidation of a robust methodology for the application and foundation of decision-making in decommissioning projects for flexible and umbilical lines.
An Irregular Wave Approach to Fatigue Life Capacity for Flexible Risers With Severed or Corroded Tensile Armors
Authors: Doynov Krassimir , Cooke Nathan , Pasala Dharma , Majed Arya
Published: September 2023

A novel simulation-based approach for assessing the remaining fatigue life of flexible risers with damaged or broken tensile armors has been developed that can be used to challenge the need for premature replacement, and to modify risers’ Integrity Management to ensure safe operation. A series of potential corrosion or damage scenarios, such as generalized loss of thickness or number of broken wires, are evaluated using high-fidelity finite element models and computationally efficient irregular wave simulations. Results from the various damage scenarios are used to construct curves showing the timeline of the remaining fatigue life of the flexible riser as a function of the number of broken wires. These timeline curves can then be used to modify riser Integrity Management via scheduling periodic NDT inspections to check the evolution of broken wires and provide advanced warning for approaching end-of-life conditions to operation engineers.

This novel approach is demonstrated through a case study involving a 7” ID flexible riser with a known history of annulus breach and subsequent repairs near the splash zone, with the potential for tensile armor corrosion to have occurred. Several hypothetical damage configurations involving combinations of severed (broken) tensile armors are evaluated under 100-year design loading to identify the minimum number of wires lost which increases the stress utilization of both the pressure and tensile armors up to a limit that can be considered a pre-cursor of upcoming rupture or loss of containment. The results from these analyses are used to construct a timeline of the remaining fatigue life of the flexible riser as a function of the number of broken wires.

This comprehensive demonstration of accurate capture of flexible pipe damaged wire kinematics by high fidelity finite element models and nonlinear simulations has direct applications to flexible pipe integrity management and remnant life assessments. Given that the nonlinear NDS framework allows highly efficient accelerated computation, it is now feasible to execute real-time irregular wave local fatigue simulations with finite element models that include damaged wire data from physical inspections to more accurately predict remnant life.
Application of the Yield Stress Concept in Drilling Fluid Engineering
Authors: Saasen Arild , Ytrehus Jan David , Lund Bjørnar
Published: September 2023

The yield stress appears as a quantity that is frequently used to describe drilling fluid rheological properties. For the driller it is important to use a simple model to predict the pressure losses in the total fluid circulation system. A very simple model, to which good prediction models exists, is the Bingham model using the yield point (YP) and plastic viscosity (PV) as determined following API procedures. This is acceptable for the driller when looking for the drill pipe and bottom hole assembly conditions as most of the pressure losses are to be found in these components and the bit nozzles where the shear rate is high.

In the flow phenomena occurring in the annulus is different. The concept of YP and PV cannot generally be used to describe the necessary properties of the fluid. A low shear yield point (LSYP) is frequently used by drilling engineers to describe the yield stress of a Herschel-Bulkley fluid. When the LSYP is used it is possible to select measurement data from relevant shear rate regions to be able to produce estimates of frictional pressure losses and to determine the fluids equivalent circulating density (ECD) during circulation.

In oscillatory tests yield stresses are determined as the stress where the linear viscoelastic strain region ends. Also, a flow point is measured, being the stress at the amplitude where the viscoelastic loss modulus becomes equal to the elastic storage modulus. These two viscoelastic yield stress properties relate to interactions in particle suspensions, emulsions and polymer solutions. Thus, these properties are of importance when dealing with shelf life of fluid properties.

In the article the different application of the yield stress concept is outlined. It is shown that these values have a real significance for any flow phenomenon when used correctly. It is also shown that there is no reason for these different yield stress estimates to be equal. Still, none of these estimates are incorrect or correct, but reflects the physical conditions the yield stress is meant to describe.
Experimental Observation on Chaotic Vortex-Induced Vibration of Circular Cylinder in Turbulent Flow
Authors: Aye Yan Naung , Srinil Narakorn
Published: September 2023

The subject of vortex-induced vibration (VIV) in a steady flow has been extensively studied throughout the past decades. There is limited experimental research presenting the influence of incoming turbulent flow on the VIV of circular cylinders which may be useful in studying real-life structural responses in ocean currents. In this study, we experimentally investigate the effect of the incoming turbulence on VIV through a pivoted rigid circular cylinder with an elastically mounted pendulum and universal joint setup in a water flume at Newcastle University, where repeatable turbulent flow can be generated. The measured flow turbulence intensity is about 13–15%. This experimental system allows the vertical cylinder’s free movement in two degrees of freedom with the horizontal springs attached to the in-line (X) and cross-flow (Y) directions, with an aspect ratio (submerged length over diameter) of 22.67, a mass ratio of 4.38, a damping ratio of 0.06 and a maximum reduced velocity of 20 associated with the Reynolds number of about 11,100. The cylinder X-Y motions and the influence of cylinder inclination during VIV are captured using the Qualisys motion capture, and the load cells are equipped to monitor the spring dynamic forces. The effects of flow turbulence are observed through the measured response time histories exhibiting chaotic features with high modulations, especially in the in-line responses and at higher flow velocities. Although a typical transition of response amplitudes from an initial branch to an upper and then lower branch with a jump and hysteresis phenomenon as well as a 2:1 dual resonance is found when varying the flow velocities, chaotic responses with irregular X-Y trajectories and highly fluctuating frequencies associated with the lower branch are remarked. Wavelet signals are used to quantify the time-varying and dominant oscillation frequencies. Understanding of such chaotic VIV features in free-stream turbulent flow may be useful in estimating structural fatigue or in enhancing the renewable energy harvesting from natural flow-induced vibration phenomena.
FSI Simulations and Analyses of a Non-Resonant Buoyant Wave Energy Converter
Authors: Shao Xinyuan , Yao Hua-Dong , Ringsberg Jonas W. , Skjöldhammer Jan , Lin Jianfeng
Published: September 2023

Deploying wave energy converters (WECs) in wave parks into the ocean requires detailed planning and numerical analyses to maximize the wave energy capture and keep the LCoE at the lowest possible level. High-fidelity simulation models can accurately simulate the fluid-structure interaction (FSI) between the WECs and the ocean’s waves. However, the computation cost is too high for simulations and analyses of large-scale WEC parks. This study presents fully coupled hydrodynamic-structure response simulations and analyses using the high-fidelity CFD software STAR-CCM+, which is compared with the DNV software package SESAM that adopts potential flow theory to model environmental loads. A novel non-resonant heave-point buoyant WEC called NoviOcean is investigated. The first case study, where only one WEC was modelled, showed that both simulation approaches/software gave comparable WEC motion results for moderate sea state conditions, but the SESAM software required significantly less computation cost. Hence, the SESAM model was used in systematic simulations of two WECs to investigate the effect of FSI on the energy capture by both WECs by varying the distance between the WECs and the wave direction. The results show which WEC distances and wave directions should be preferred to maximize the wave energy capture.
The Dynamic Optimization of Lower Completion Configurations Based on the Liquid/Gas Flow Streamline in a Middle East Oilfield
Authors: Shi Shuzhe , Wu Bohong , Nie Zhen , Li Yong , Li Xin , Zhang Lufeng
Published: September 2023

Barefoot horizontal completion is the main technology that applied in the N oilfield Middle East, and several production problems have occurred at the barefoot horizontal wells in the past few years, for example, the water coning, the gas breakthrough, and the uneven production profile, which could be resulted from the edge-bottom water, gas cap or the adjoining injection wells. These production problems will result in a low sweep efficiency and low final oil recovery. In the meantime, poor design of lower completion configuration would not only lead to a lower final oil recovery but also cost a lot in the installation and operation.

Therefore, the fit-for-purpose lower completion technologies and well-designed lower completion configuration need to be studied for the purpose of high sweep efficiency and high net profit value. In this work, the production wells were classified into several categories according to the seriousness and reasons of the production problem. Then, the detailed factor analysis of water coning and gas breakthrough is carried out from the numerical simulations based on the liquid/gas flow streamline, which can find out the water coning issue and the gas breakthrough issue whether are caused by the injection wells or the edge-bottom water. At last, the well-designed lower completion configuration study for the production well and injection well is conducted in the dynamic model simulations. By applying the optimized lower completion configurations and deploying the tools accurately based on reservoir property and production performance, the highest oil recovery and net profit values can be achieved in the oilfield development.

This work can give guidance to the problem classification of production wells, and establish a more accurate optimization method of designing the lower completion to better develop the oilfield.
Hydroelastic Response of Submersible Open Net Fish Pens Under Wave Action
Authors: Chu Yun Il , Wang Chien Ming , Zhang Xinyu , Zhang Hong , Savage Leigh
Published: September 2023

Submersible fish pens are a cost-effective solution for storm proofing fish pens at offshore sites against strong surface waves and winds. This paper examines the hydroelastic responses of submersible open net fish pens and the mooring forces under wave action for various submergence depths. For the hydroelastic analysis, a single cylindrical open net fish pen and mooring system were considered. A regular wave reflecting the worst wave condition observed in an exposed farm site in Tasmania’s Storm Bay, Australia was used for the analysis. A numerical software package AquaSim was adopted for the hydroelastic analysis of the fish pen and mooring system. The analysis results show that the vertical displacement of submerged pen and mooring force are reduced significantly when compared to the corresponding results of the fish pen floating on the water surface. It is shown herein that after a particular submerged depth, the hydroelastic results do not decrease significantly with deeper depths. A future study will investigate the relationship between the optimal submerged depth, fish pen dimensions and wave conditions with the view to save ballasting costs and time to re-float the fish pens.
On Wear Thickness of Rust Layers of Steel Structure due to Ice Impact Load
Authors: Takeuchi Takahiro , Kioka Shinji , Miyazaki Hitoshi
Published: September 2023

Rust layers on the surface of corroded steel are removed due to sea ice action in ice-infested sea, subsequently leading to increased wear due to further corrosion. Damage to coastal structures and training levees comprising steel sheet pile seawalls on the Sea of Okhotsk occurred sooner than expected, since large wear rates had not been considered in their design. This paper investigates the degradation mechanism of steel structures through indoor tests focusing on sea ice impact. The effect of wear thickness is examined based on parameters such as sea ice temperature, sea ice impulse, sea ice momentum, ice impact load, sand inclusion in sea ice, angle of ice impact load, and real contact area of ice impact load. It is shown that wear thickness can be estimated from maximum ice impact pressure on the real contact area between sea ice and rust layer. This implies that the uni-axial compressive strength of sea ice, which relates to maximum ice impact pressure, plays an important role in the estimation of wear thickness. These results also lead to the estimation of thickness of sacrificial (additional) steel walls in addition to the original steel structure as a countermeasure against wear.
Study on the Axial Tension Reduction of a Dual-Bore Vertical Riser System for Deep Sea Mining
Authors: Yamamoto Marcio , Yamamoto Joji , Masanobu Sotaro
Published: September 2023

Exploiting polymetallic nodules in the Clarion-Clipperton Zone shall require a vertical riser with two separate lines. First, the ore-lift line shall convey the slurry composed of seawater and nodules from the seafloor up to the floating platform. The second line is the water-return line that shall bring this seawater to be discharged on the seafloor. One issue of this mining riser is that its top end has the highest axial tension, which may overcome the material’s yield strength resulting in structural failure.

For instance, the drilling riser used in the Petroleum Industry must have buoys attached along its length to address the same issue. The problem with the attached buoy is the hydrodynamic loads increase linearly with the buoy diameter. Thus, we aim to reduce axial tension without attached buoys and keep the internal diameter as constant as possible to avoid flow assurance issues. Our approach is to assemble the mining riser using riser joints with the same external diameter but different wall thicknesses. The pipe’s outer diameter and wall thicknesses assumed in our analyses are defined in the standards API Spec 5CT. Next, we proposed four different optimized configurations for the mining riser. Then, we carried out numerical simulations in the time domain, assuming a 4,000 m riser system. As external loads, we adopted a current profile and irregular waves typical for the Clarion-Clipperton Zone. Our reference is a riser composed of all joints with the same diameter and thickness.

Our results show that the riser with the best-optimized structure had an axial tension reduction of 15% compared to the reference. However, this riser has the highest risk of structural failure criteria defined as Method 1 of API ST 2RD in case of worse external loads.
ASSIST Observations 2017–2021: Uncertainty, Comparison With Sea Ice Charts, and Ice Concentration From Deep Learning Model
Authors: Panchi Nabil , Kim Ekaterina , Skjetne Roger , Hughes Nick
Published: September 2023

The Arctic Ocean is undergoing significant changes, leading to a surge in research and commercial activity in the region. As a result, the number of manual observations of ice conditions, known as ASSIST observations, has dramatically increased in recent years. These observations provide valuable information on the state of the Arctic ice cover and have been used as a source of ‘ground truth’ for other satellite products. However, their manual nature raises concerns about the associated uncertainty. To address these concerns, the present study evaluates the uncertainty of total ice concentrations, partial ice concentrations, ice types, and ice thicknesses reported in ASSIST observations. First, the study compares ASSIST observations from 2017 to 2021 against sea ice charts from the Norwegian Meteorological Institute, the US National Ice Center, and the Arctic and Antarctic Research Institute. Second, as a test case, the study evaluates simulated ASSIST observations conducted on optical images by an ice expert, three non-experts, and a deep learning model. Results from the comparisons indicate a good agreement between ASSIST observations and the sea ice charts, with ∼80% of comparisons resulting in a difference of less than ±10% in total ice concentration. Analysis of the remaining 20% reveals high underestimation in summer and overestimation in winter compared to sea ice charts. Groupwise comparison of ice types reveals an accuracy of ∼50% and a good match between the ice thickness reported by ASSIST observations and ice thickness associated with ice types reported by the ice charts, with ∼70% of comparisons resulting in a difference of ±10 cm. Results from the inter-comparison of simulated ASSIST observation point to an agreement between experts and novices in simple scenes with a single type of ice and disagreement in the case of complex scenes.
Towards Developing a Code of Practice for Offshore Aquaculture Vessels
Authors: Mohajernasab Saeed , Abdussamie Nagi , Harris Andrew , Shearer Chris , Tighe Nick , Bhaskar Prashant , Chin Chris , Islam Rabiul , Binns Jonathan , Enshaei Hossein
Published: September 2023

In recent years, fish farming facilities and the aquaculture industry are gradually moving towards more offshore (or exposed) locations, bringing new opportunities to increase their value creation through better production conditions regarding the aquatic environment due to space availability and water quality which can be extremely beneficial, resulting in more stable farming conditions. This study is focused on the demand for a code of practice for the design, operation, and survey of aquaculture vessels, particularly in offshore regions.

However, offshore aquaculture requires the vessels to operate in more severe sea states, which require the farming structure, station-keeping systems, and vessel-farming site interaction to be more robust. On the other hand, the specific operations demanded from a fish farm vessel, such as net handling, anchoring, mooring, towing, delousing, feeding and live fish transporting, require specific guidelines that can cover the vessel and system design as well as their safe operation.

Relevant rules and regulations from national and international guides and standards, including the Australian National Standard for Commercial Vessels (NSCV), and rules and guidelines of classification societies, are reviewed. Furthermore, the study discusses the current research studies centred around aquaculture vessel design and operations, including crew transfer vessels for fish farms, bunkering and alternative fuel sources. Finally, this paper aims to identify the current gaps and similar guidelines and research concepts towards developing a code of practice for aquaculture vessels. A framework for developing such a novel code of practice for offshore aquaculture service vessels in line with the other current efforts on the safety of aquaculture operations will be discussed.
Evaluation of Seakeeping Model Tests in Open Waters Using Two Submarine Hull Forms
Authors: Büsken Wiebke , Krüger Stefan
Published: September 2023

In this paper, the experimental procedure of seakeeping model tests in open waters with two free-running, remotely-controlled submarine hull forms as realized on Eckernförde Bay from October 2021 to April 2022 is presented. The objective of performing such model tests with surfaced submarines at various conditions of stability, speeds and encounter angles in natural seaway is explained. A summary of the qualitative observations concerning the different identified phenomena, which lead to large motion amplitudes, is given in this paper along with a quantitative evaluation of the model tests by statistical analysis of selected test runs. As part of the results, different heeling moments, which were observed to attack the surfaced submarine during these model tests, are discussed, especially in regard to their inclusion in the recently developed new stability standard for the intact surface stability of submarines of the German Navy.
A Joint Probability Distribution Model for Multivariate Wind and Wave Conditions
Authors: Vanem Erik , Fekhari Elias , Dimitrov Nikolay , Kelly Mark , Cousin Alexis , Guiton Martin
Published: September 2023

This paper presents a joint statistical model that has been fitted to data of wind and wave conditions for an offshore location at South Brittany. The data are from a numerical model and contain hourly values for several wind and wave variables over a period of 32 years. The joint distribution presented in this paper considers the variables wind direction, mean wind speed, significant wave height, wave direction and peak period. A conditional model for turbulence given wind speed is introduced to yield an additional variable for the joint model. The joint model is constructed as a product of marginal and conditional models for the various variables. Additionally, the fitted models will be used to construct environmental contours for some of the variables. For significant wave height, various models are used to obtain different extreme value estimates, illustrating the uncertainties involved in extrapolating statistical models beyond the support of the data, and a discussion on the use of non-parametric copulas for the joint distribution is presented. Such joint distribution models are important input for design of offshore structures, and in particular for offshore wind turbines and the influence of the joint model in design is illustrated by a simple case study.
Numerical Simulation of a Ship Advancing in Pack Ice Area Based on CFD-DEM Method
Authors: Zou Ming , Tang Xiang-Jie , Zou Lu , Zou Zao-Jian , Zhang Xin-Shu
Published: September 2023

The greenhouse effect has caused significant changes in polar ice conditions, and the pack ice condition is expected to become the most common environment of the future polar transportation. Study of the ship-ice interaction in the pack ice area is of great significance for ensuring the safety of polar transportation. In this paper, the numerical simulation models of a ship advancing in pack ice area are established by using the Hertz-Mindlin contact model and Linear Spring contact model, respectively. Taking the KCS ship as study object, the CFD-DEM (Computational Fluid Dynamics - Discrete Element Method) method is used to conduct numerical simulations, and the reliability of the simulation models is verified by comparing the simulation results with those of empirical formula and experimental measurements. On this basis, the effects of the two contact models on the simulated phenomena, ship-ice contact force, mean ice resistance and peak ice resistance are studied. This study provides a reference for the selection of contact model in numerical simulation.
A Simulation-Based Approach for Evaluating Merchant Fleet Decarbonization Strategies
Authors: Bergström Martin , Gosala Vaidehi , Depken Jorgen , Fitz Annika , Euskirchen Frederik , Ehlers Sören
Published: September 2023

The International Maritime Organization (IMO) aims to reduce the annual greenhouse gas emissions from international shipping by at least 50 % by 2050, compared to 2008. To this end, the organization has adopted a set of regulations, including the Energy Efficiency Design Index (EEDI), the Energy Efficiency eXisting ship Index (EEXI), and the Carbon Intensity Indicator (CII), which will require the maritime industry to transition to lower carbon operations. However, the issue of how this transition is to be achieved remains unresolved. Against this background, this paper proposes a simulation-based approach for predicting how a selected fleet of merchant ships may develop over time under various decarbonization strategies. The aim is to make it possible to identify and evaluate feasible decarbonization strategies, accounting for potential bottlenecks, for instance in terms of the supply and availability of individual low-carbon fuels and technologies. A case study is presented in which the approach is applied to a fleet of 254 ships, which is assumed to be roughly representative of ships above 400 gross tonnage serving German ports.
Numerical Study on the Hydrodynamic Characteristics of a Small High-Speed Craft
Authors: Lv Huizi , Wei Chengzhu , Liang Xiaofeng , Yi Hong
Published: September 2023

Small high-speed crafts cannot resist adverse waves by using their displacement. In order to improve their ability to execute tasks in heavy sea conditions, a concept of a small highspeed craft, the shuttle vessel (SV-SJTU) is proposed by Shanghai Jiao Tong University. The angle freeboard is adopted to control hull wetness at high speed, and the slim wave-piercing design is utilized to produce smaller lift force.

Validated CFD methods were employed to calculate hull resistances and motions. The SV-SJTU hull is tested in the model scale of 1/6. Hull resistances and motions were predicted by using the overset mesh method and solving the URANS equations closed by the SST k-ω turbulence model. The VOF method is utilized to capture the complicated free surface.

Hence, the resistances and hull motions of SV-SJTU in calm water and waves at different speeds were obtained. With satisfying running attitudes and small resistances in calm water, the SV-SJTU experiences soft motions in harmful sea conditions at high speeds without slamming or instantaneous large acceleration, which is different from normal crafts. Accordingly, the concept of a small high-speed craft that performs well in calm water and maintains in waves for soft motions at adverse sea conditions is validated.
First Principle Design Load Estimation for LH2 Fuel Tanks by Means of 0D Approach
Authors: Lampe Tobias , Roß Lukas , Okpeke Bright Ebikemefa , Ehlers Sören
Published: September 2023

Within the framework of the Sustainable Development Goals, the United Nations (UN) General Assembly has declared its firm intention to combat climate change and the associated changes in the environment. Shipping is an important factor since its exhaust gases account for just over two percent of global greenhouse gas (GHG) emissions. This is reflected in the GHG Strategy of the International Maritime Organization (IMO), which forces the maritime industry to move away from fossil fuels towards zero-carbon alternatives. Liquid hydrogen is a promising candidate to enable this transition. As of now, class approval for the required technology is based on an alternative design approach which entails operational scenario development. In this work, a simulation-based approach for the estimation of design loads with respect to liquid hydrogen fuel tanks is presented. The MATLAB software is employed to implement a 0-dimensional approach for the calculation of the bulk thermodynamic behavior. Necessary thermodynamic quantities are obtained via internal energy by means of the CoolProp package. Vapor and liquid phases are treated separately under the assumption of a saturated liquid state while the vapor is allowed to superheat. There is good correlation between validation data and simulation. In order to provide a realistic load assessment during a ship voyage, an exemplary cruise ship and corresponding power-demand profiles are utilized. The results are then analyzed with regard to occurring loads and operational efficiency.
Data Informed Model Test Design With Machine Learning – An Example in Nonlinear Wave Load on a Vertical Cylinder
Authors: Tang Tianning , Ding Haoyu , Dai Saishuai , Chen Xi , Taylor Paul H. , Zang Jun , Adcock Thomas A. A.
Published: September 2023

Model testing is common in coastal and offshore engineering. The design of such model tests is important such that the maximal information of the underlying physics can be extrapolated with a limited amount of test cases. The optimal design of experiments also requires considering the previous similar experimental results and the typical sea-states of the ocean environments. In this study, we develop a model test design strategy based on Bayesian sampling for a classic problem in ocean engineering — nonlinear wave loading on a vertical cylinder. The new experimental design strategy is achieved through a GP-based surrogate model, which considers the previous experimental data as the prior information. The metocean data are further incorporated into the experimental design through a modified acquisition function. We perform a new experiment, which is mainly designed by data-driven methods including several critical parameters such as the size of the cylinder and all the wave conditions. We examine the performance of such a method when compared to traditional experimental design based on manual decisions. This method is a step forward to a more systematic way of approaching test designs with marginally better performance in capturing the higher-order force coefficients. The current surrogate model also made several ‘interpretable’ decisions which can be explained with physical insights.
Experimental Study of the Draft on the Flow-Induced Motions (FIM) of a Semi-Submersible Platform With Four Square Columns
Authors: Gonçalves Rodolfo , Marques Matheus , Silva Leandro , Hirabayashi Shinichiro , Suzuki Hideyuki
Published: September 2023

This article aims to understand the effect of the draft condition on the FIM of a semi-submersible platform (SS) with four square section columns. Model tests of a floating system supported elastically utilizing four springs were performed in a towing tank. A parametric study based on three main dimensions: the draft, H, the pontoon height, P, and the length of the square column face, L. Two studies were conducted for different H/L conditions: first, for a constant column aspect ratio, C/L = 1.00, where C = H-P; and second, for a constant P/L = 0.25. The spacing ratio of the columns was S/L = 4; where S is the distance between column centers. Two incidence angles of the current were carried out, namely 0 and 45 degrees. The results could be summarized using the column-pontoon ratio, C/P. The amplitudes in the transverse direction decreased by decreasing the C/P.
Weakly Nonlinear Surface Wave Prediction Using a Data-Driven Method With the Help of Physical Understanding
Authors: Chen Jialun , Zhao Wenhua , Mline Ian A. , Gunawan David , Taylor Paul H.
Published: September 2023

Accurate surface wave prediction can potentially improve the safety and efficiency of various offshore operations, such as heavy lifts and active control of wave energy converters and floating wind turbines. Prediction of surface waves, even if only for a few periods in advance, is of value for decision-making. This study aims to predict weakly nonlinear surface waves (up to the 2nd-order) in real-time using a data-driven model based on Artificial Neural Networks (ANN), where the application of physics is investigated to aid the development of a data-driven model. Based on numerically synthesized nonlinear wave records calculated using exact 2nd-order theory, ANN models were trained to separate the nonlinear bound components at an up-wave location, propagate the linear waves and reintroduce the nonlinear components as a correction to the prediction at a down-wave location. The results show that the optimal approach is to predict each stage separately following the basic physical structure of weakly nonlinear water waves using a series of ANN rather than direct prediction in a single step using ANN. Further, the generalization of the models for different sea states and the impact of the 2nd-order bound waves on prediction accuracy is investigated.
Numerical Simulation of Chain-Reaction Implosions and Analysis of Different Implosion Beginning Positions
Authors: Shengxia Sun , Zhao Min
Published: September 2023

Hollow ceramic pressure hulls in the deep-sea underwater vehicles have potential risk of destructive chain-reaction implosions. A numerical simulation method for the chain-reaction implosions of multi-ceramic pressure hulls is developed. The underwater implosion in the ultra-high pressure is solved by the compressible multiphase flow theory. This method has been verified by the comparison with implosion experiments. The structure finite element method (FEM) is used to solve the response of ceramic pressure hull under implosion flow field loads and is combined with the failure criterion of ceramic materials as the judgment basis for inducing implosion. It is found that the pressure drop caused by the expansion wave generated by the implosion of the ceramic pressure hull triggers the implosion of the adjacent pressure hull. The implosion shock waves overlap each other, and generate shock wave pressure peaks larger than the implosion of a single pressure hull. Finally, three ceramic pressure hulls are arranged in a straight line, and the influence of different beginning positions of implosion on the flow field is also compared and analyzed.