bluuebunny/crossref_metadata_2025 huggingface dataset:
Axial In-Place Behaviour of Unbonded Flexible Pipes
Authors: Norland Kristian , Larsen Anders A. , de la Cour Dorthe , Larsen Henrik Ø. , Pedersen Tommy , Eriksen Morten
Published: October 2022

The axial behaviour of an unbonded flexible pipe is highly non-linear and may change throughout the load history and along the pipe. The axial stiffness and expansion coefficients (pressure and temperature) of a flexible pipe are given as two sets: one for the tension state and one for the compression state. Previously the typical interpretation has been that this tension/compression classification referred to the true wall axial force in the pipe. However, this approach is incomplete in several aspects:

• The determining physical factor is whether the tensile armour layers are in contact with the underlying layers.

• An unbonded flexible pipe consists of different layers with different axial force and orientation. It can be argued that the term “true wall axial force” does not make sense for an unbonded flexible pipe.

• To determine the axial force for a given condition, a set of expansion coefficients and axial stiffness must be selected. Hence, it becomes a circular argument.

Based on detailed analysis by the product supplier, a transition plane can be defined. The “Transition Plane Concept” offers an efficient way of implementing a realistic axial behaviour in the in-place design (incl. upheaval buckling). The axial behaviour during the in-place phase can be consistently defined by a transition plane and this can be implemented in the in-place analysis. Reduced risk for upheaval buckling of flexible pipes and removal of excessive conservatism can be achieved.
Numerical Simulations for Impacts of Offshore Wind Power Facilities on Currents and Water Quality
Authors: Miki Koki , Tabeta Shigeru , Mizuno Katsunori
Published: October 2022

When selecting a suitable site for offshore wind farm, the impact on the marine environment is one of the most important issues. However, in most cases of the suitable sites selection, the distances from protected areas, spawning and wintering grounds of marine creatures are taken into account as environmental indicators, and there are few which explicitly consider the impact of the offshore windfarm on marine ecosystem including current field and water quality which could be affected by the construction of offshore power plants. In this study, the impacts of offshore wind farms on the flow field and water quality were investigated by numerical simulations, introducing models of offshore wind farms facilities and sessile organism on the structure into a three-dimensional coupled hydrodynamic-ecosystem models. A nesting grid system were employed which combines a farm-scale grid and a local-scale grid. The large-scale simulation results showed that the changes in current due to a foundation structure of wind turbine could affect the flow field around the downstream structures. It is also found that water quality change in this scale is mainly caused by the changes in current field and the effects of sessile organisms on the structures are small. On the other hand, the small-scale results shows that the effects of sessile organisms may also appear in the very near vicinity of the structure. By using the developed model, it is possible to visualize the extent of the changes in currents and water quality caused by the offshore wind farm facilities.
HSVA Model Ice – A Status Report
Authors: Ziemer Gesa , Stange Timo , Hisette Quentin
Published: October 2022

The development of HSVA’s current standard model ice dates back to 1993 when Evers and Jochmann introduced a new production process [1]. Since that time, a lot of experience has been gained in numerous ice sheets, regarding both, the process of production itself and the properties of the resulting model ice. Meanwhile, requirements on ice model tests, and also on the model ice itself, have changed during the past decades. This relates to more diversified test types, which do not only concentrate on ice-breaking ship designs with typical flat bows, but also on a variety of structures and hull designs that include different failure modes. Also, the typical property range of model ice regarding strength and thickness has significantly widened. This paper summarizes the changes that have been made over the years, leading to the standard model ice that is available at HSVA today. Its properties are presented and discussed, showing limitations regarding absolute property values and their uncertainty, as well as the ability for correct representation of specific interaction scenarios. Further, methods to modify the model ice for different specific test scenarios are suggested and discussed. This includes for instance global and local crushing against vertical structures.
Assessment of Uncertainty in Sea Ice Charts and Its Impact on Operational Planning in the Kara Sea Region
Authors: Panchi Nabil , Verma Uttam , Kim Ekaterina , Hughes Nick , Bhattacharyya Anirban
Published: October 2022

Ice charts play an important role in the planning of marine operations, including navigational guidance among other use cases (e.g., climate monitoring and model validation). With a growing number of vessels operating in dynamic sea ice cover and considering the November 2021 events when several ships were stuck and delayed in the Arctic waters, it becomes ever more important to have accurate and timely ice information as well as to account for the underlying uncertainties in the sea ice products. To this end, the present study evaluates the variability in estimated total sea ice concentration in ice charts of the Russian Arctic and Antarctic Research Institute (AARI) and the Norwegian Meteorological Institute (MET Norway). The weekly ice charts from AARI were compared with several daily charts from MET Norway for the corresponding week to discover any discrepancies in the reported sea ice concentration. Preliminary results of this study indicate seasonal as well as spatial trends in the absolute difference in total ice concentration between the two sea ice products. A higher difference in concentrations was observed in the western and the central regions of the Kara Sea which see a lot of ship traffic. Sensitivity of the results to the comparison approach is conducted and the found discrepancies between the two ice products are placed in the context of operational route planning.
A Hybrid Time-Frequency Domain Approach for Estimating Mooring Lines Dynamic Response
Authors: Leivas Simão Marina , Queija de Siqueira Marcos , Gonçalves de Lacerda Thiago Ângelo , Videiro Paulo Maurício , Sudati Sagrilo Luis Volnei
Published: October 2022

It is known that, for a given short-term environmental condition, mooring lines fatigue damage assessment can be made from the tension cycles counting using a sufficiently long tension time series. This can be obtained through coupled floater-lines time domain analyses where lines are modeled with the catenary equation, leading to faster simulations but also to quasi-static line responses that do not take line dynamics into account. On the other hand, a coupled floater-lines analysis where the lines are modeled with finite elements (FE) can assess line dynamics effects since it considers dynamic amplifications of the system in the wave frequency range. Such dynamic effects can greatly impact fatigue damage calculations and should be considered. However, while more accurate, coupled FEA-based models can become very expensive in time and computer resources when the number of environmental conditions to be evaluated is high. In this context, an approximate and efficient hybrid solution was developed for the assessment of dynamic tension series, taking advantage of quasi-static coupled analyses. In the solution, it is assumed that the line dynamic response can be roughly estimated in the frequency domain from linearized tension transfer functions for the segment of interest and from motion series at the floater-line connection point, obtained with previous quasi-static analyses. The linearized tension transfer functions are previously obtained by applying unitary amplitude motions in the line axial direction at the top connection point for different excitation frequencies and also for different line pretension levels. The methodology is validated for a spread-moored FPSO installed in Brazilian deep waters. When compared to complete FEA-based dynamic analyses, it is shown that the simplified solution provides good estimates for the lines dynamic tension response and can be a powerful tool to save computer time in fatigue damage assessments.
Investigation on Fiber Assisted Multistage Fracturing of Horizontal Well in Tight Low Permeability Sandstone Reservoirs
Authors: Zhang Lufeng
Published: October 2022

Tight sandstone reservoirs, widely distributed in the world, are the important oil and gas exploration and exploitation area in the future and have a favorable development prospect. Multistage fracturing of horizontal well is a necessary technology to inspiring the production potential and enable commercial productivity for tight reservoirs. Due to the multiple functions, degradable fiber is widely applied during hydraulic fracturing. On the one hand, fiber can enhance the sand patch profile when it was injected into the fracture with the carrier fluid; On the other hand, fiber aggregation can accelerate the formation of temporary plugging agent, which is conducive to the uniform propagation of fractures. In this paper, we conducted a series of experiments to evaluate the properties of fiber in detail. Moreover, the pilot application of fiber which was injected during the whole hydraulic fracturing was also carried out. The laboratory evaluation experiments mainly achieved the following findings: 1. The length, diameter and density of fibers are approximately 6mm, 10μm and 1.24 g/cm3, respectively. 2. The fiber can be well dispersed in high viscosity slick water with almost no settlement. 3. Under high closure pressure, the conductivity of fiber and proppant mixture is higher than that of pure proppant. Furthermore, the field case shows that the fiber assisted fracturing makes the permeability-challenged formations economically recoverable, which deepens the understanding the effect of fibers and provides fundamental for field treatment design.
Data-Driven Propeller and Rudder Modeling for Maneuvering Analysis of the ONR Tumblehome
Authors: Knight Bradford G. , Silva Kevin M. , Maki Kevin J.
Published: October 2022

The accurate prediction of ship maneuvering characteristics requires accurate representation of the forces on the propellers and rudders. Computational Fluid Dynamics (CFD) can accurately predict the maneuvering characteristics of a vessel, but the expense is dominated by the discretization of the propellers, and long-time simulations are too expensive for practical use. Propeller and rudder models can reduce the computational cost, but can also reduce the accuracy. The objective of this work is to accurately model the Office of Naval Research (ONR) Tumblehome performing both turning circle and zig-zag maneuvers with high-fidelity data-driven propeller and rudder models. The use of the data-driven propeller and rudder models significantly reduces the computational cost of performing a maneuver. The forces of the propeller and rudder are calculated as a function of the propeller revolution rate, the rigid body velocity of the vessel, and the rudder angle. The propeller and rudder models are trained with a select number of CFD simulations with the discretized propeller and rudder operating in the behind condition. The propeller and rudder models maintain the accuracy of using a discretized propeller and rudder with respect to CFD simulations used for validation. The models calculate the multi-degree of freedom force acting on the propellers and rudders of the vessel. For comparison, the maneuvering characteristics of the vessel are also analyzed with a simplified body-force propeller and a Whicker and Fehlner rudder model.
Numerical Simulation of Dynamic and Static Mechanical Response of Sinusoidal Sandwich Structure
Authors: Yao Houqi , Qu Jia
Published: October 2022

Based on the design characteristics of corrugated sandwich structure and pyramid lattice sandwich structure, this paper proposes a sinusoidal beam sandwich structure with different amplitude-period ratio, curved beam cross-sectional area and cross-section adjacent side length ratio. Three variables were used to analyze the quasi-static compression performance and impact resistance of different variable structures by numerical simulation. The three-dimensional modeling of the sinusoidal beam sandwich structure is briefly introduced, and the relative density calculation formula is derived based on the theory of mechanical characterization of the sandwich structure. Using Abaqus/Standard for quasi-static compression numerical simulation, the deformation process and failure modes of the sinusoidal beam sandwich structure under quasi-static compression are mainly presented as the bending of the two beams and the plastic hinge expansion at the peaks and valleys. The influence of the cross-sectional area and the length of the adjacent side of the curved beam on the anti-pressure performance is greater than that of the curved beam amplitude-period ratio. Using Abaqus/Explicit to simulate the SHPB impact test of the sinusoidal beam sandwich structure, it is concluded that the impact resistance of the sinusoidal beam sandwich structure is approximately irrelevant to the strain rate, and the amount between the transmitted wave and the incident wave occurs. The reduction in grades reflects excellent impact and flameproof properties and good energy absorption characteristics.
Sensitivity Analysis of a Corrosion Prediction Model Using Monte Carlo Simulation
Authors: Santos Stephane S. M. , Souza Gilberto F. M. , Barros Leonardo Oliveira de , Orlowski Rene Thiago Capelari , Martins Marcelo R. , Schleder Adriana M.
Published: October 2022

Obtaining a realistic prediction of the corrosion rate of equipment employed in the oil and gas industry is vital for safe operations. During the last few years, several corrosion prediction models have been and are being developed by oil companies and research institutes. The corrosion prediction models are usually made to meet a specific type of corrosion scenario, such as corrosion in the presence of H2S, corrosion in the presence of organic acid, corrosion in the presence of CO2, among others. Because of the distinct philosophies of these models, different results can be obtained for the same cases. The corrosion rates predicted by different models have a great influence on the selection of materials, definition of inspection plans, among other important decisions; therefore, on the total cost of the project. Reliable predictions of the corrosion rate are vital to controlling the degradation, ensuring the integrity of the operation at an optimized cost. This paper presents partial results of a research project that aims to evaluate the variability of corrosion rate prediction obtained by applying different corrosion models. This information could support oil and gas companies in selecting the most suitable model for carrying out the expected corrosion rate in new installation projects, considering the expected operational condition. In this paper, a sensitivity analysis of the NORSOK corrosion prediction model, using Monte Carlo simulation, is presented. In order to perform the Sensitivity Analysis, a methodology composed of 4 phases was followed: Selection of parameters, Monte Carlo Simulations, Obtaining Corrosion Rates and Analysis. It was found that, for the analyzed cases, the parameters with the highest and lowest impact on the prediction of corrosion rates, respectively, were pH and total pressure.
A Comparison of Design Wave Methods for Flexible Fish Farms
Authors: Jansen Markus B. , Aspelund Leiv , Fristedt Tim , Skjulstad Christoffer
Published: October 2022

Conventional floating fish farms are deployed in increasingly larger arrays and in exposed locations with challenging environmental conditions. Hydrodynamic analysis of such structures requires models with numerous coupled flexible elements. Therefore, analysis with irregular sea states is usually considered impractical. Today, the established practice in the aquaculture industry is to approximate the irregular sea state with regular waves with the most probable largest wave height. Previous numerical work on single-cage fish farms has suggested that this method produces the appropriate design forces if the simulations are run for two wave periods plus one wave period ramp-up. In this paper, the results of an extensive numerical study on floating flexible fish farms of varying sizes from 1 × 1 to 8 × 2 cages exposed to environmental loads from 4 different directions are presented. The forces found using the industry-standard regular design-wave methodology are compared to forces based on their respective irregular sea states. A new alternative regular-wave method is also proposed and compared to the other approaches. The results show that the current industry-standard method often underpredicts the dimensioning forces in larger fish farms. The new method appears to be a significant improvement, but more refinement and testing is necessary before irregular simulations can be completely omitted.
Modeling of Thermo-Mechanical Behavior of Laser Powder Bed Fusion of Nickel-Based Super Alloy Parts Used in Oil and Gas Industry
Authors: Beiranvand Zeinab Malekshahi , Ratnayake R. M. Chandima , Rasoulinia Mehdi , Moradiani Amir
Published: October 2022

Nickel-based alloys are used for a broad range of applications in oil and gas (O&G) production and marine engineering because of their good corrosion resistance and mechanical properties. The future of laser AM in the O&G industries is highly promising due to the ability to deliver cheaper and better parts quickly. As it is in the initial stages, rigorous research needs to be done to enhance the fabrication speed and parametric optimization to improve the thermo-mechanical properties of the fabricated components by laser powder bed fusion AM. Simulation methods provide financially viable and the least resource-consuming approach for the qualification of produced parts, enabling metallurgical and mechanical characterization in a short time. In this research study, a three-dimensional finite element model is developed to predict the temperature, residual stress, and distortion in nickel-based super alloy parts fabricated by a multi-layer laser powder-bed fusion (LPBF) process, to analyze the thermal and residual stress distributions. For this purpose, a FEM model of LPBF was applied that includes a thermal model representing the scanning laser thermal input, a material model to define the temperature-dependent material property in the cyclic heating and cooling environment, and a physics-based method to describe the layer build-up process. For validation of the results, the experimental results were used, and the validation results were presented.
Small Size Steel Catenary Riser S-Lay Installation With Flexible Joint as 2nd End: Difficulties and Solutions
Authors: Liu Song , Du Yongjun , Yu Wentai
Published: October 2022

S-lay installation of a 6-inch small-sized SCR with flexible joint assembly in the 2nd end is investigated in this paper. Due to the huge difference in external dimensions, weights and bend stiffnesses between the riser pipe and the flexible joint, passing through the S-lay vessel stinger of the flexible joint assembly poses a big challenge to the strength integrity of the overbend section of the SCR, especially the steel pipe at the connection with the flexible joint body. This paper summarizes the engineering approach and FE analysis work that were carried out in order to reduce the maximum strain in the critical riser overbend section. These engineering approach options include design of a long tapered stress joint type shroud, an extended upper shroud, or an installation aid in large diameters, to facilitate installation of flexible joint assembly travelling along the stinger. The latter approach is selected for detailed design which lays the engineering groundwork for successful pre-laid operation of the 6-inch SCR with flexible joint.
Image Processing to Extract Ice Features to Aid Modelling of Ice Force
Authors: Akter Shamima , Islam Mohammed , Zaman Hasanat , Ahmed Salim , Imtiaz Syed , Gash Robert
Published: October 2022

Sea-ice observation and estimation of ice forces are becoming increasingly important with the increased activities in arctic water. Proper modelling of ice properties and forces is crucial in such cases to ensure safe operations, for example, Dynamic Positioning (DP). This work, therefore, aims at developing algorithms for image processing to extract useful ice properties and subsequently aid the modelling of ice load exerted on a floating platform or a ship. A robust algorithm capable of detecting closely connected and overlapped ice floes with various sizes and shapes is presented, which is the first step for accurate modelling of ice forces. To demonstrate the effectiveness of this approach, image frames processed from videos produced during an experiment using a model ship performed at the National Research Council’s Ocean Coastal and River Engineering Research Centre (NRC-OCRE) in Canada are used. Simulated ice floe images are also used to show the efficiency of the proposed model and compare it with other published work. The model will be extended further to extract and correlate other ice properties with the ice forces and develop a machine learning based ice force prediction model. The predicted force from that model will then be used as a feedforward to Dynamic Positioning (DP) controller with an aim to improve the performance of the controller.
Simulation Tool for Evaluation of Investment in Sustainable Technology
Authors: Gullaksen Joannes
Published: October 2022

Sustainable technology enables valuable use of natural resources and reduced ecological impact, whereas impact management is the ongoing practice of measuring, assessing and improving impacts on sustainability issues. The aims are to achieve the balance between economic, environmental and social impacts through the effective management of resources whilst maximising organisational profitability. A financial evaluation helps an investor to take rational decision about an analyzed investment, whereas an economic analysis broadens this perspective to include effects of the investment imposed on other stakeholders and the environment. Changing technology landscapes, development risks and new opportunities are characterized by a need of innovative financing and investment models in order to adequately assess the uncertainty and risks. Traditional quantitative analysis calculates measures of risk and financial return for hypothetical investments based on some time series for the analysis, that also should account for market dynamics. The shortcomings with this approach could be a single constituent dominate a risk and return profile, where noise is a random variation, including any variation that is not predicted, except in terms of a statistical distribution function. Simulation, however, improves on this by looking at the impact of many variables changing at the same time. The simulation process consists of successively generating random numbers, used to select from the probability distribution of each uncertain input parameter. The process continues repeatedly to obtain a sufficient number of variable values for statistical analysis and a sufficient number of output parameters, where probability curves are used to determine the likelihood of the outcome and create a picture of risk.
A Weibull Distribution-Based Parametrization for Encounter Wave Spectra
Authors: Zago Lariuss , Kawano Alexandre , Simos Alexandre Nicolaos , Gonçalves Rodolfo Trentin
Published: October 2022

The continuous monitoring of sea states is important for many activities, from gathering oceanographic data to the planning of ship operations. There are several means to infer sea conditions, with variable levels of accuracy. Among these, the methods based on on-board measurements of vessel motions have been addressed by many researchers, attracted mainly by its practicality regarding installation and maintenance issues. However, the idea of using vessels as wave sensor also brings restrictions, mainly associated with the filtering of short waves that causes no significant motions of the hull, and, furthermore, the vessel speed introduces considerable complexity in the mathematical inference procedure. A significant part of this complexity is associated with the triple-value problem related to stern wave conditions. In the context of a research that addresses an alternative method for the parametric estimation of sea waves based on vessels with forward speed, this article deals with the problem of devising a proper parametric representation of the wave energy distribution as seen in the ship’s reference frame, i.e., the encounter wave spectrum. A Weibull-distribution parametrization is proposed, for its ability to handle the significant variations of encounter wave spectrum shapes. Analyses performed for several combinations of wave directions, peak frequencies and vessel’s speed show that this approach is indeed capable of providing proper representation of the spectral shapes based on few parameters, both for bow and stern waves.
Drilling Performance Evaluation Through Bit Cutters Reconfigurations and Micro Fractures Initiation
Authors: Abugharara Abdelsalam , Tytler Oluwafemi , Butt Stephen
Published: October 2022

Drilling operations of petroleum wells are primarily applied to create channels through subsurface formations for oil and gas production. For best drilling performance, drilling parameters including weight on bit (WOB), rotary speed in Revolutions per Minute (rpm), drilling Fluid Rates (FR), etc. need to be applied optimally to enhance drilling performance, to reduce cost, and to minimize wear of downhole tools. In this research, the drilling performance was evaluated based on examining the Drilling Rate of Penetration (ROP) in granite blocks through changing the face of a multi diameter Polycrystalline Diamond Compact (PDC) bit into three different design scenarios including the Flat Base bit (FB), Drilling Hole Opener bit (DHO), and Coring Hole Opener bit (CHO). All input drilling parameters were kept constant and the only variable was the bit configuration.

The purpose of this research was to evaluate the change in the ROP and to establish an investigation on why ROP varies when bit is reconfigured just by repositioning cutters. By linking the ROP variation to the bit configuration, a possible phenomenon of creating micro fracturing could be the reason for the ROP enhancement. Taking the FB as a baseline, results showed an increase in ROP using DHO and CHO over FB bit. The idea behind this could lay behind initiating micro fractures resulting a weaker rock portion by the 1st drill path to be drilled by the upper part of the bit.

Based on the averaged results, ROP of DHO increased by 37.5 % at 5 kN and by 47.1 % at 10 kN. Similarly, the ROP of CHO increased by 12.5% at 5 kN and by 11.8 % at 10kN indicating that initiation of micro fractures could play a role in the enhancement of the ROP.
Plug Cementing Stability
Authors: Vogl Anastasia , Waldal Nile , Sarmadi Parisa , Fershtman Adam , Mitishita Rodrigo S. , Frigaard Ian A.
Published: October 2022

Off bottom plugs are set in both well drilling (kick-off plugs) and in well decommissioning (abandonment plugs). In both cases a dense fluid (cement slurry) is placed over less dense well-bore fluids. In the case of kick-off plugs, viscous pills are commonly used, which can help stabilize this mechanically unstable situation. Abandonment plugs however are often set on top of the freshwater that is used to clean the well prior to abandonment. This is the current practice for many wells in Northwestern Canada. It is a mystery how such cement plugs are able to stay in place for a time sufficient for the cement to thicken and hydrate, but field evidence suggests they do.

In this paper we explore the mechanically unstable scenario of a heavy yield-stress fluid placed on top of a less dense Newtonian fluid in a cylindrical pipe, dimensionally scaled to represent an off-bottom plug. We present details of the experimental setup and its calibration. We then explore the buoyancy-driven exchange flows that occur in transitional parametric regimes between flow and no-flow states, by using both computer modelling and physical experimentation. 3D numerical simulation, using a Volume of fluid method, is carried out to capture the interface between the fluids. The 3D model provides us with a more detailed analysis of the concentration and velocity profiles, along with comparisons to snapshots of the experimental results. The aim is to explore the phenomenology of these unstable flows and be able to estimate timescales of the destabilization. Preliminary results are presented.
The Impact of Extreme Turbidity Flow on Subsea Pipeline Design in a Deepwater Canyon Crossing
Authors: Bai Qiang , Qi Xinhai , Pearl William , Shen Siyuan , Brunner Mark
Published: October 2022

In this paper, finite element (FE) analyses are performed with the commercial software Abaqus to investigate the turbidity-flow-induced behavior of a pipeline crossing the bottom of a deep-water canyon. A general hybrid geotechnical-fluid dynamics approach considering the contributions of fluid drag and soil bearing resistance is used to simulate the hydrodynamic loads imparted to the pipeline due to turbidity currents. By applying an active flow loading over specific lengths while axial and lateral soil resistances are applied to the zones just outside of the turbidity flow region, assessments of the pipeline are performed. Assessments include the following checks: local buckling, lateral deflection, stress/strain in the pipe wall, and the increase in anchor loads at subsea structures in the vicinity.

Although the solution is somewhat limited by modeling idealizations, this sensitivity-based approach, which focuses on a small number of key parameters, provides a useful starting point for pipeline design. Different analytical techniques are suitable for various turbidity flow mitigation options. Both static and dynamic non-linear FE models are utilized to investigate the behavior of the pipeline when subjected to the turbidity flow both with and without mitigation, and an appropriate methodology is established for detailed pipeline design.
Fatigue Analysis of Wind Turbine Blade Coating Considering Uncertainty Due to Voids Subjected to Impact Fatigue
Authors: Kuthe Nikesh , Ahmad Suhail , Mahajan Puneet
Published: October 2022

Wind Turbine Blade (WTB) coating is a protective layer that experiences repetitive raindrop impact. The impacts cause cyclic stresses, fatigue, and erosion of the leading edge of the blade coating which leads to the damage of the WT blade. The presence of voids (manufacturing defects) in the coating leads to local stress concentration and enhances erosion. This erosion can cause an increase in the drag coefficient and reduction in lift coefficient resulting in reduced performance of the WT. In India, the annual monsoon with high-intensity rain makes the problem more critical. FE model was developed using Coupled Eulerian and Lagrangian (CEL) method to calculate stress field due to raindrop impact. In the present case, stress-time histories are random in nature as observed. The stress histories are transformed into respective spectra. The spectrum obtained is converted into simpler cycles using the rain flow cycle counting method. The method is well suited for the fatigue life assessment due to random stresses in the coating of the wind turbine blades under raindrop impact. The cycles thus obtained from the spectrum can be used to estimate the cumulative fatigue life using the Palmgren-Miner rule. This rule assumes that the damage carried out by the sections of a stress signal having a particular range can be estimated and aggregated to the total damage separately from that done by other ranges. Damage evaluation in the coating with the randomly distributed void due to stochastic raindrop impacts is computed from fatigue analysis. The main novelty of this work is fatigue assessment of WTB coating, taking explicit account of uncertainties due to the presence of voids in the erosion phenomenon. Simultaneously reliability analysis is carried out considering the probabilistic distribution of droplet diameter, the velocity of impact, and occurrence of maximum stress due to raindrop impacts in the coating. This model predicts the accurate and reliable life of the coating.
On the Influence of the Soil Stratigraphy on the Monopile Deflection Investigated With FEM in a PISA Framework
Authors: Kanitz Manuela , Mesa Carlos Molina , Berenguer Todo Bom Luís , Dührkop Jan
Published: October 2022

Large diameter monopiles are the most commonly used foundation type for offshore wind farms. The accurate representation of their response to lateral loading to optimise the required pile penetration plays a crucial role in the design of offshore wind farms. Recently, the PISA method proposed by Burd et al.[6] and Byrne et al. [5] has gained importance in the design of monopiles as it more accurately represents the interaction between the monopile and the soil than standard methods. In the PISA project, sand as well as soft and stiff clay were investigated through monotonic pile tests and the PISA parameters to represent the monopile-soil interaction curves were calibrated for each soil type investigated. Normally, the PISA parameters are derived separately for each soil type and then combined in a 1D model to include the soil stratigraphy. However, soil conditions on site are typically heterogeneous and the interaction between different soil layers with different strengths and stiffnesses should be captured. In order to gain a deeper understanding of the influence of soil stratification on pile deflection curves, this paper presents numerical simulations of a large diameter laterally loaded monopile embedded in layered soil using the finite element method (FEM) including a combination of soft clays and dense sands. Based on the FEM results, PISA parameters for the monopile-soil interaction curves are derived and implemented in a 1D beam model to calculate the pile deflection. The results are compared with a 1D model where the PISA parameters are first derived for the individual soil types and then combined to include the same soil stratigraphy. It is shown that the influence of soil stratification on pile deflection is significant. This paper highlights the need for calibration of PISA parameters considering the actual soil stratigraphy present on site.
Empirical Evaluation of Influence of pVARD on Drilling Performance Through Static, Dynamic, and Drilling Applications
Authors: Abugharara Abdelsalam , Jamil Shafaet , Butt Stephen
Published: October 2022

The research of this paper is a continuation on the evaluation of Belleville Springs and Dampening for the passive Vibration Assisted Rotary Drilling (pVARD) tool optimization for drilling operations. The research involves a set of mono versus dual compression tests through involving rotational loading on Belleville Springs and Damping to simulate the rotational drilling performance using pVARD. The reason for involving rotational compression loading during rock drilling is to capture the associated bit-rock interactions and evaluate its relation to the implementation of pVARD versus conventional rotational drilling (no-pVARD). Comprehensive experimental sets on natural isotropic rock drilling using pVARD vs. no-pVARD are conducted under the same conditions of weight on bit (WOB), revolution per minute (rpm), rock type, water flow rate, drill bit. All drilling experiments were conducted at atmospheric pressure using a large-scale and fully instrumented rotary drilling simulator. At first, a full set of static compression tests on Belleville Springs and dampening in combination as well as in individual sets were conducted and displacement versus load relationships were generated. Dynamic motions of pVARD while drilling were also captured and reported. Relationships between pVARD static and dynamic compressions were linked to the drilling performance resulted from pVARD vs. no-pVARD drilling.
Numerical Study of an Alternative Way of Evaluating the Remaining Volume of a Fish Cage
Authors: Tang Hung-Jie , Yeh Po-Hung , Yang Ray-Yeng , Nan Fan-Hua
Published: October 2022

At present, the technology of measuring the net volume of a net cage in the real sea is still rare and limited. This study proposes an alternative way of accessing the remaining volume of an aquaculture net cage in both model and full scales. This new approach is called the alternative reduction coefficient (ARC), which is the ratio of the deformed height between a floating collar and a tube sinker to its original height. Its counterpart is the volume reduction coefficient (VRC), which is the ratio of deformed volume to undeformed volume. In the comparison against the existing experimental studies in the model scale, the maximum error of the current-only case is about 11.6%, and that of the wave-current case is about 23%. For the full-scale fish cage subjected to regular waves and current, the simulated results show that the maximum gap of the remaining volume between ARC and VRC is about 13.6% and 15.3% for current-only and wave-current conditions respectively. The results also show that the greater the wave steepness, the larger the error. Finally, in the simulation of the full-scale net cage subjected to irregular waves and current, the results show that the probabilities of the two methods are both a normal distribution and they are very similar, and the Pearson correlation coefficient of the two methods is about 0.937, the bias of the minimum value is only about 0.73%, that of the maximum value is about 7.18%, and that of the standard deviation is about 5.43%. Therefore, we concluded that ARC is an acceptable method of evaluating the remaining volume of fish cages in the real sea.
Probabilistic Design of Thin-Walled Cylindrical Structures for Application In Large Cargo Submarines
Authors: Jamissen Philip Lundberg , Xing Yihan , Ma Yucong
Published: October 2022

Collapse failure is the dominating failure mode of submarine pressure hulls due to the large hydrostatic pressure, which brings about a low collapse pressure capacity unless thick plates with closely spaced stiffeners are used. However, because cargo submarines require a high payload capacity to be economically attractive, an optimal design with low structural weight is vitally important. This makes thin-walled structures with a high strength-over-weight ratio favourable. Therefore, one crucial challenge relates to the research of large underwater cargo submarine concepts is to propose a cost-effective design for the collapse of the submarine pressure hulls. From experience, the collapse pressure capacity of thin-walled structures is susceptible to the geometric imperfections generated during manufacturing. For a safe design, a common practice used by the design-by-rule approach is introducing a very conservative safety factor. However, such an approach is not structurally efficient. This paper proposes a probabilistic design approach for cylindrical thin-walled structures for application in cargo submarine hulls. The initial imperfections are represented by the Fourier series. Stochastic realisations of the imperfections are made using the Monte Carlo method, and the corresponding collapse pressures are calculated using finite element analysis. The collapse pressures are then collected to plot the cumulative distribution function (CDF). Finally, the collapse pressure capacity can be defined from the CDF based on the desired failure probability. The results show that axial buckling of the thin-walled cylinder is sensitive to the initial imperfection and the distribution of critical buckling force follows Gumbel distribution. In contrast, SST structures subjected to external pressure load are not sensitive to initial imperfections. Gumbel distribution would overpredict the buckling pressure in this case. Also, it is shown that the collapse pressure capacities calculated using probabilistic design are significantly higher than the design-by-rule method.
Experimental Investigation on a Cabin-Suspended Catamaran for Wave Energy Harvesting
Authors: Han Jialin , Li Qiao , Mochizuki Akito , Maeda Teruo , Itakura Hiroshi , Kitazawa Daisuke
Published: October 2022

Wave energy can be a significant factor in the progress towards a carbon-free society. This paper demonstrates the wave energy harvesting performance of a 1/2 scale cabin-suspended catamaran in regular head waves. The catamaran has a twin-seater, the length is 3.28m, and the width is 2.10m. It consists of a suspended cabin, a suspension unit, and a twin-hull. One brushed DC Motor/Generator (M/G) coupled with one gearhead is set at each of the four corners of the cabin’s deck. The shaft of the gearhead connects to a shaft of a pinion gear which meshes with a rack that is fixed on a hull through a ball joint. In this way, the vertical motion of the rack can be transferred into the rotational motion of the pinion causing the M/G generates electrical power. The power generation of the catamaran is experimentally investigated using a Maximum Power Point Tracking (MPPT) technique in a towing tank. Two control algorithms are developed: indirect MPPT and direct MPPT. It is found that the wave energy capture width ratio (CWR) obtained at the direct MPPT is approximately 11% higher than the indirect MPPT when their control parameters are having equal magnitude.
Numerical Investigation of the Effect of Vortex Induced Vibrations (VIV) Parameters on the Behavior of Submarine Power Cables: A Comparison With Scaled Down Experimental Results
Authors: Delizisis Panagiotis , Grivas Konstantinos , De Wilde Jaap , De Ridder Erik-Jan , Resvanis Themistocles L. , Georgallis George
Published: October 2022

For an installed submarine power cable, fatigue is one of the main causes of failure. For static power cables there are cases such as free spans, spans between touch-down point (TDP) and J/I-Tube bell mouth and repair/sea joint procedures that may lead to failure due to fatigue as a result of Vortex-Induced Vibrations (VIV). Similar failure modes are applicable to dynamic cables since they are exposed to current flows for their expected operational life of more than 25 years. Although much research has been done in the field of oil and gas for VIV phenomena on flexible pipe lines, there is no extended and in-depth corresponding literature on submarine power cables. The scope of the present work is to investigate and demonstrate the effect of parameters such as Strouhal number, reduced bandwidth and added mass coefficient on the predicted VIV behavior of submarine power cables, both static and dynamic. The standard industry software SHEAR7 is used in order to assess the effects of each of these parameters. Finally, a comparative study was performed with the results of a scaled down experiment, which took place in the basin of Maritime Research Institute of Netherlands (MARIN) within the scope of the Horizon 2020 (H2020) FLOTANT project and studied the response of a towed dynamic power cable.
Ship Gyroscopic Roll Stabilisation
Authors: Ribeiro e Silva S. , Varela J. M.
Published: October 2022

A thorough understanding of the interaction of waves with ships is a vital factor in the safe and economical technology design. Considerable advances have been made recently in the modelling of wave hydrodynamics and wave-structure interaction. Wave diffraction analysis using 2D Strip Theory (ST) or 3D Boundary Element Methods (BEM) based on potential flow theory is now standard with linear and second-order theory in the frequency domain. In case an assessment of a new ship roll stabilisation system of the gyroscopic type is seen as desirable, no ready to use numerical tool to predict the performance of the wave-structure interaction is available. Therefore, for smaller vessels with a certain advance speed, such a patrol boats or pleasure crafts further developments must be applied to a BEM method to take into account speed corrections plus a standard ST tool in order to include the roll stabilisation effect that could be attained using a dedicated gyroscopic roll stabilisation system installed aboard.

In this framework, the proposed work consists of exploring the application of an adapted BEM method with speed corrections, plus a standard ST to study the wave-structure interactions of an unstabilised ship and a ship fitted with a Gyroscopic Roll Stabilisation (GRS) system by considering the case study of a small patrol boat in a seaway. The main objective of this study is to assess the performance of this GRS concept and calculate the operability index of this class of vessels (percentage of time the vessel complies with user pre-defined limiting criteria) for a certain design point using long term statistics, so that complex non-linear responses in waves will be neglected at this stage.
A Contrastive Study of Two-Time Scaled Method and Unified Method in Maneuverability-in-Waves
Authors: Ma Chengqian , Ma Ning , Gu Xiechong
Published: October 2022

Maneuverability in waves, which is associated with navigation safety and overall operational efficiency, is attracting more and more attention recently. In addition to the experimental method and the pure CFD method, there are two widely used theoretical methods on this topic, the two-time-scale method, and the unified method. However, both methods have theoretical limitations. The two-time-scale method is based on the assumption that the maneuvering frequency varies a lot from the seakeeping frequency. This assumption is not achieved when the ship navigates in following wave conditions or extreme waves. Meanwhile, it is also based on the hypothesis that the total ship motions can be considered as the linear superposition of the maneuvering motion and the seakeeping one. For the unified method, the wave forces rely on the interpolation of the precalculated force coefficients or semi-empirical results in general. Therefore, the comparison between the predicted results using these methods and the experimental results is necessary and valuable to assess the error and advantages of these methods. In the present study, two in-house codes using these methods are developed and utilized to predict the motions of S175 containership in regular waves. The results are obtained and compared with the experimental ones. Finally, the conclusions and assessments on these methods are obtained.
Ultimate Strength Characteristics of Cylindrical Shell in Combined Compression and Bending Moment
Authors: Li Shen , Kim Do Kyun , Benson Simon
Published: October 2022

Many countries have set out their commitments for net-zero emission in order to address the increasingly detrimental impact caused by greenhouse gas and the consequent climate change. To accelerate the ambitious net-zero target while ensuring a sufficient energy supply, the exploitation of wind energy is one of the sustainable and clean solutions. Thus, it is foreseen that the investment in the offshore wind will continue worldwide in the coming years. For a successful deployment of offshore wind turbines, an adequate safety margin of their foundation supporting structures is of paramount importance. Prevailing design codes require a rigorous assessment against the ultimate limit state for the foundation supporting structures of offshore wind turbines. These structures are typically in the form of cylindrical shells, which are subjected to a combination of axial compression and overturning bending moment. In this paper, a numerical study is presented in the light of gaining better insights into the catastrophic collapse behaviour of cylindrical shells under combined loads. Nonlinear finite element analyses considering geometric and material nonlinearities are completed on a parametric range of structural models with different length-to-radius and radius-to-thickness ratios. A matrix of axial compression and bending moment combinations are analysed. The numerical results are compared with prediction by prevailing code formulae.