bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigations on Hull-Ice Frictional Effects
Authors: Hisette Quentin , Myland Daniela
Published: October 2022

A study is performed to establish and enlarge the knowledge on the factors influencing the friction between ice and ship hulls. A set of experimental friction tests with a newly designed testing apparatus with computer controlled stroke, speed and acceleration is conducted. The testing involves the determination of the friction coefficient between an ice sample and a reference plate representing a ship hull with ice resistant coating. Results show a characterized, mostly decreasing evolution of the friction coefficient with an increasing number of testing cycles, especially at medium to large testing speed values. The influence of the normal load is significantly smaller and varies with the sliding speed. The friction coefficient tends to increase with a decreasing ice temperature. Finally the paper gives the basis to transfer the influence of these parameters (or others) at the laboratory level to the total ship resistance in ice.
Transitions in Charpy Energy and Splitting for X70 and X80 Pipe Steel
Authors: Mohr William , McGaughy Tom
Published: October 2022

Using data obtained for a standard production 42-inch X80 pipe with a 19.6-mm wall thickness produced around 2006 and a 24-inch diameter X70 pipe having a 0.5-inch (12.5-mm) wall thickness produced in 2016, the transition between fully brittle and fully ductile fracture behavior has been examined to assess any effects of transverse splits or delaminations. This is compared with a 48-inch X80 pipe from recent production. The 24-inch diameter pipe split more than the others, but all three showed splitting in the transition. The additional surface area formed at the splits can increase or decrease the Charpy energy by expending energy to form more fracture surface but also reducing constraint on the propagating crack as it extends through the unnotched Charpy ligament. Fitting of full Charpy energy transition curves using standard hyperbolic tangent functions does not represent the behavior well. An important transition is noted in the behavior between splitting that initiates at the initial notch tip and splitting that occurs further down in the ligament. Spitting across the notch tip increases Charpy energy by releasing constraint on crack initiation at the machined notch and occurs at temperatures just above the lower shelf temperature, where brittle fracture dominates. Splitting across the notch tip also decreases Charpy energy as compared to splitting across the ligament only. The Charpy splitting behavior also correlates to similar effects in crack tip opening displacement (CTOD) specimens for the same specimen orientation in the base material, both for conditions where unstable fracture and fully ductile response occurs.
Comparative Verification of Numerical Analysis and Model Experiments for Oyster Farming
Authors: Tamura Hiroki , Nihei Yasunori
Published: October 2022

Motion analysis of the oyster hanging ream using the numerical analysis software Orcaflex was conducted to prevent typhoon damage in oyster farming facilities. First, a model experiment was performed, and the calculation accuracy of Orcaflex was then verified by comparison with the result. Consequently, the amount of horizontal displacement was in good agreement. Therefore, it is considered that the motion of the hanging ream could be evaluated by Orcaflex. In addition, in order to verify the phenomenon of entanglement of adjacent hanging reams, the motion of multiple hanging reams is evaluated by numerical analysis. Consequently, it is suggested that there may be a wave-periodic zone in which the hanging reams are more likely to be entangled.
Numerical Simulation of Ship-Ice Interaction in Pack Ice Area Based on CFD-DEM Coupling Method
Authors: Zou Ming , Tang Xiang-Jie , Zou Lu , Zou Zao-Jian
Published: October 2022

Global warming has caused significant changes in the environment of the Arctic. Due to the shipping economy and efficiency, the number of ships sailing in the Arctic region has been increasing recently. Since pack ice is a common ice condition in the Arctic, studying the ship-ice interaction in the pack ice area is significant to the ship navigation in this area. This paper applies the fluid-ice coupling method combining Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) to establish the numerical model for investigating the ship-ice interaction in the pack ice area, considering the influence of flow field. Based on the CFD-DEM coupling method, the ship-ice interaction is simulated for the KRISO Container Ship (KCS). Through the comparison with the results of empirical formulae and experimental measurements, it is found that the numerical model can not only predict the ice resistance more accurately, but also simulate the typical phenomena of ship-ice interaction. Besides, the influences of ice concentration and ship speed on the ice resistance, and the impact of ship-generated waves on the motion of pack ice are studied.
Risk Assessment of Collision Between Dynamically Positioned Vessel and Offshore Installation
Authors: Chen Haibo , Nygård Bjørn , Hasund Nils
Published: October 2022

DP vessels are serving offshore installations for various purposes, but they may also bring major accident risk during the operation if a collision between vessel and installation happens. A quantified collision risk assessment methodology for DP vessels visiting offshore installations is developed. The methodology is based on the risk assessment framework defined in ISO31000:2018, and it consists of three elements: risk identification, risk analysis in terms of collision likelihood and collision consequence, and risk evaluation. The methodology accounts for the physics of DP vessels, the reaction time characteristic of human operators and other aspects in position loss and collision scenarios. The likelihood of collision and the consequence of collision, in terms of exceedance probability distribution of impact energy relevant for collision damage, are interrelated and calculated by using a Monte Carlo simulation model. The methodology provides a more accurate risk picture and better support for risk treatment than the collision risk study purely based on the historical collision frequency and the historical collision energy distribution. For risk evaluation the methodology proposes an alternative way of presenting the risk results in terms of “Risk Density”. It is essentially an hourly, instead of yearly, averaged risk level during the marine operation. It helps better visualization and communication of the collision risk between vessel and installation to stakeholders and decision makers. A case study is presented to illustrate the methodology and concept. It assesses the collision risk between a DP shuttle tanker and an FPSO during offshore loading operations.
Wave Drift Forces and Low Frequency Drift Motions for Mooring Analysis of a Spread Moored FPSO
Authors: Zhang Min , Xu Nuoya , Yang Tianen , Fonseca Nuno , Mood Fredrik
Published: October 2022

This paper presents a comparison study on wave drift models as well as corresponding low frequency (LF) drift motions for mooring analysis of a spread moored FPSO in moderate seastates with and without current. There are four wave drift force models applied in this study, including two numerical models from potential theory with Newman’s approximation and full quadratic transfer functions (QTFs), two combined models determined from cross bi-spectral (CBS) analysis of model test data and merged with two numerical potential flow wave drift force models at low and high frequencies, respectively. The comparison is performed in terms of both diagonal and off diagonals with constant difference frequency.

The equations of motion are solved in the time domain with a fully coupled method, accounting for different wave drift forces models. Both the LF motion response spectra and the time domain series are presented and discussed. The LF damping is adjusted by comparing simulations to the corresponding model test data and tuning the results. The results show the underestimates of wave drift forces as well as the corresponding LF motions by second order potential flow theory, especially in the cases with current. Application of full QTFs can improve the simulation results in terms of phasing of LF responses.
Finite Element Modeling of the Effect of Different Post-Weld Heat Treatment on Strength of Welded AISI 4130 Steel Pipe
Authors: Englund Even
Published: October 2022

AISI 4130 steel is a low-alloy strength steel and is a popular choice for fabrication of drilling fluid pipes in the oil and gas industry. One of the drawbacks of this low-alloy steel is that it can form martensite at relatively low cooling rates during welding, which is why the welds in this steel require post-weld heat treatment (PWHT) to temper the martensite in the heat-affected zone (HAZ). While tempering martensite in the HAZ, the heat treatment might also lead to weakening of the base material near the weld in cases where the heat-treatment temperature is too high. In 2014 the PWHT procedure for welded pipes in the ASME Code (ASME B31.3) was changed and the maximum allowed PWHT reduced. Hence, according to the new standard, older welds have been heat treated at temperatures that are too high.

The present article investigates the strength of AISI 4130 steel undergone different PWHT and uses the finite element method to model pipe failure in order to investigate the possible effects of the old heat-treatment procedure on pipe strength. The effect of the different PWHT temperatures on the base material strength is investigated through tensile tests of samples undergone different heat treatments. Then, from the extracted material data from the tensile tests the pipe is modeled and analyzed through explicit finite element method to evaluate what effect the anticipated material weakening from the old PWHT procedure has with regard to pipe strength and integrity.
Calibration for Interpretation Parameter Nkt of CPTU in Offshore Wind Farm at Coast Area of the Mekong River Delta
Authors: Wang Kuanjun , Liu Gang , Shen Kanmin , Gao Shan
Published: October 2022

Sample disturbances during drilling work in offshore wind farms are inevitable due to the marine environment, and much higher than those in onshore projects, which would lead to an underestimate of soil strength, especially for soft clay. Piezocone penetration test (CPTU) is now widely used in the geotechnical investigation in offshore wind farms, which has slight the disturbance on soil. But the soil parameters cannot be directly obtained by CPTU, and the interpretation process should be carried out, while the parameters for interpretation are site-specific. Based on an offshore wind farm at the coast area of the Mekong River Delta in Vietnam, laboratory tests and CPTU results are analyzed to calibrate the cone factor Nkt, which is used for CPTU interpretation of undrained shear strength su. The calibrated Nkt from the triaxial UU test, which ranges from 10.82 to 57.89, is much higher than the calibrated Nkt values from DSq and triaxial CU test. A possible reason is that the soil samples for triaxial tests were disturbed during drilling and transportation, the triaxial UU tests might underestimate the strength of in-situ clay. The cone factor Nkt calibrated from the DSq test and triaxial CU test respectively range from 15.65 to 25.86 and 12.51 to 30.50, with the total average value of 22.29 and 20.44, which are more accurate compared to the Nkt values calibrated from the triaxial UU test. Finally, a negative correlation between pore pressure ratio Bq and Nkt is established based on triaxial CU test results, which can be used to choose the appropriate Nkt value for interpretation. The CPTU interpretation by Bq-Nkt correlation and the total average value 20.44 of Nkt both show good agreement with the measured soil strength. For simplicity, the total average value of Nkt calibrated from triaxial CU test results is recommended to be used for the CPTU interpretation in engineering projects, which is more convenient.
Cyclonic Wave Field in the Bay of Bengal Region Under Changing Climate Scenarios
Authors: Bhavithra R. S. , Sannasiraj S. A.
Published: October 2022

Wind-wave plays a major role in the planning and designing of important coastal structures. The study on wave characteristics is considered necessary for the routing of ships, wave hindcasting and forecasting. Climate change is one of the major threat that has been occurring over the years and the impact of climate change on wave climate results in increased storm effects and rough sea conditions. Bay of Bengal (BOB), an active cyclonic region along the North Indian Ocean experiences severe storms every year during the north-east monsoon season. Hence, an understanding of wind-wave climate under cyclonic storms in the BOB region is essential. The present study considers three severe cyclonic storms in the BOB region: Phailin which occurred during October 2013; Hudhud during October 2014; and, Vardah during December 2016. The study further details about the impact caused by these cyclone when projected to the future under the climate change scenarios. The wave climate of the three considered cyclones is projected for the Representative Concentration Pathway (RCP) scenarios of RCP4.5, RCP6.0 and RCP8.5 under both for the Near-Future (2035) and Far-Future (2075) categories. The domain covering the BOB region is discretized with a resolution of 0.25°x0.25°. The surface wind of the chosen domain for the projected scenarios is obtained from the Weather Research and Forecasting (WRF) model and then these winds are forced into the WAve Model (WAM) to predict the corresponding wave climate. The significant wave height (Hs) obtained from the WAM model for the projected scenarios has been compared to the present scenario of the respective cyclones and the results show an increase in intensity for all the three cyclones under the Far-Future categories of RCP6.0 and RCP8.5 scenarios. The wave climate under Hudhud cyclone has the greatest intensity of about 21% under the Far-Future category.
Consistency Assessment of Wave Directional Spectrum Predictions From Machine Learning Based Ship-As-a-Wave-Buoy Methods
Authors: Scholcz T. P. , Düz B. , Hageman R. B. , Mak B.
Published: October 2022

Real-time knowledge of the ocean wave directional spectrum is valuable for maritime safety and navigation. When end-to-end machine learning is used to learn ocean wave directional spectra from ship motions, the spectrum predictions may be inconsistent with measured ship motions from a physical point of view. In order to assess this consistency, a method is proposed that makes use of a numerical seakeeping code to recalculate ship motions from predicted wave spectra. The recalculated ship motions are subsequently compared to the measured ship motions. The method is applied using data from three different vessels, each having a different level of data completeness. For these cases it is concluded that the consistency can be assessed when the sea state is not too extreme. The method may be improved by using higher fidelity seakeeping codes.
Motion Characteristics of a Floating Model With Moonpools for VAWTs
Authors: Ikoma Tomoki , Fujishima Katsuhide , Aida Yasuhiro , Lei Tan , Masuda Koichi
Published: October 2022

This paper describes motion behaviors of a floating body and water regions of moonpools. The floating model to be focused in this study has moonpools and is for offshore wind turbine system with two vertical axis wind turbines. Motion behaviors of water region in moonpools strongly affect on motion characteristics of a floating body itself. Often the effects lead to non-linear motion of the floating body. Besides, when the floating body is a system of vertical axis offshore wind turbines, the system becomes more complicated.

This study conducted theoretical calculations and model experiments in a wave tank. Behaviors of moonpools were measured in regular waves and we measured wave exciting forces, radiation forces on heave and motion responses of the floating model. Also, the study considered effects of Vertical Axis Wind Turbine (VAWT) model’s rotation on the motion.

From the results behaviors of moonpools were often nonlinear to incident waves and the behaviors affected on motion responses of the floating model. The experimental results were compared with the calculation results. When non-linearity due to overtopping of water from moonpools was found, the calculations could not reproduce hydro forces but they are able to estimate motion responses. The study confirmed reduction effects due to the moonpools on motion responses comparing with a conventional pontoon with identical displacement.
Numerical Analysis of the Efficiency of Corroded Pressure Vessels With Composite Repair
Authors: Drumond Geovana , Ribeiro Rodrigo , Pasqualino Ilson , Lourenço Marcelo Igor , Perrut Valber , Lana Luiz Daniel
Published: October 2022

This paper is part of a research project that is concerned with the assessment of the efficiency of composite repair in corroded metallic pressure vessels. The focus is to evaluate localized repairs in corroded areas near nozzles. A numerical model was developed, and the results were validated against experimental tests. 50%, 70%, and 80% wall loss defects were manufactured into small-scale metallic vessels in two different positions and the failure pressure of the repaired vessels was determined using hydrostatic tests. The numerical results show that the failure pressure of the repaired vessel is close to the non-defective vessel, showing that the repair system was efficient.
Full Scale CFD Validation Using Ship Performance and Wave Pattern Measurements of a Mega Cruise Ship
Authors: Schouten D. R. , Drouet A. , Birvalski M. , Morand L.
Published: October 2022

The shipping industry is directly impacted by the global challenge of reducing greenhouse gas emissions. Improvements can be achieved by hull form optimization when designing new ships. Computational Fluid Dynamics (CFD) is nowadays regularly applied for basic resistance simulations as well as for e.g. self-propulsion with rotating propellers or maneuvering in waves. In order to avoid scale-effects, it is increasingly common to perform ship scale CFD calculations. Unfortunately, the available full scale data that can be used for validation are limited. Specifically, flow velocity and radiated wave pattern data are rare at full scale because of the complexity of performing such measurements. Nevertheless, in the current work, full scale wave pattern measurement were performed on a 330 meter long cruise ship sailing at 20 knots using the Digital Image Correlation technique. This is an image analysis method capable of measuring deformations of a surface in space. The approximate size of the field of view was 75 m by 30 m. The ship’s speed, shaft power, propeller rate, motions and environmental waves were measured as well. Additionally, Reynolds Averaged Navier-Stokes (RANS) simulations were performed using STARCCM+. The propeller was modelled both as an actuator disk as well as a rotating propeller with a sliding interface. The turbulence closure model was k-ω SST and the free surface was modelled using the Volume of Fluid method. The balance between hull resistance and propeller thrust was verified as a first step, showing less than 4.0% difference. The power determined by CFD was validated against the one measured during the sea trials with less than 3.6% difference. Finally, the comparison of the stern wave pattern resulting from full scale CFD simulations with the pattern measured using DIC showed excellent agreement with good accuracy.
Challenges in the Implementation of the Air Injection EOR Method: The Venezuelan Experience
Authors: Rodriguez M. Fernancelys
Published: October 2022

Air Injection, or in-situ combustion (ISC), is one of the oldest thermal EOR methods that has been applied in Venezuela to increase the production of highly viscous crude oils, with a first field application in 1959 in the Tia Juana Field-Lake Maracaibo Basin. This method, which is characterized by a high energy efficiency, consists of injecting air into the reservoir where exothermic oxidation reactions are initiated to increase the mobility of the oil by reducing its viscosity and increasing the API gravity. Compared to other thermal EOR methods such as steam injection, the air injection method has a lower environmental impact in terms of water and fuel consumption, and emission of gases, as the produced gases can be reinjected or stored.

According to the literature, several air injection projects have been carried out in Venezuela in Tia Juana, Morichal, Miga and Melones fields. Although the technical results have been satisfactory in terms of viscosity reduction and improved crude oil properties (such as °API), other important aspects of project evaluations have not been convincing due to the following factors: operational problems, high temperatures in producing wells, corrosion, and high CAPEX and OPEX costs in low oil price environment, among others. Nevertheless, a recent literature survey has shown that additional research works have been conducted on process optimization, using solid and liquid catalysts to better address the other factors mentioned.

Due to the great need to increase hydrocarbon production in Venezuela, and to the advantages of air injection as an upgrading technique where low-carbon fuels and hydrogen as by-products are generated, this paper presents a review of the air injection projects in Venezuela from research aspects and field applications. This paper seeks to identify the main insights on success and failure of ISC projects and make substantiated recommendations in case of future application of this technology.
A Green and Environmentally Friendly Chelated Retarding Acid for Acidification of Sandstone Reservoirs
Authors: Wei Liu , Qing Wang , Changfeng Xu , Mengchuan Zhang , Xinmin Kong , Erdong Yao , Junren Que
Published: October 2022

Matrix acidizing is the main method to relieve formation damage in sandstone reservoirs. However, many problems in conventional mud acid acidification need to be carefully considered, such as fast acid-rock reaction, short effective action time, excessive dissolution near the well zone, and the secondary sedimentations from fluorosilicic acid, aluminosilicate, calcium fluoride and other pollution of the reservoir.

In this paper, a green and degradable amino acid chelating agent is investigated. This new type of sandstone chelating retarded acid system have features of chelating metal ions and slow proton release. The chelating ability of new retarder acid to calcium and iron metal ions was determined by complexometric titration. The retarding performance of chelating retarder acid were studied by core flow instrument and microscopic scanning electron microscopy. The results show that the new acid system is manifested by strong chelating ability to iron and calcium ions, low corrosion rate, good retarding performance. The permeability is increased by 225% after acidification. The results of electron microscopy scanning of the core surface before and after acidification show that the new acid solution acidification can effectively enlarge the pore-throat without generating secondary precipitations, which is a good choice for sandstone acidification practice.
Methodology for Defining Risk Indices Applicable to Subsea Equipment
Authors: Maturana Marcos Coelho , Schleder Adriana Miralles , Frutuoso e Melo Paulo Fernando Ferreira , Martins Marcelo Ramos , de Barros Leonardo Oliveira
Published: October 2022

As offshore operations explore deeper and deeper reserves, there may be an increase in the number of accidents and failures, resulting in greater challenges for the sustainability of these operations. In this sense, the planning of inspections and maintenance of subsea equipment assumes a central role, both in terms of costs and in relation to the risks involved. Risk Based Inspection (RBI) appears as possibility to address these challenges, and have been more and more employed to assist the operators in finding cost-effective solutions while considering safety aspects.

For the effective application of RBI tools, it is necessary to calculate the risk in order to facilitate the comparison of inspection plan alternatives, also allowing the comparison of each possible solution risk with a Risk Acceptance Criteria (RAC) accepted by society. In this sense, this paper discusses a risk calculation method that can be used in the quantitative optimization process (aimed at improving subsea equipment inspection plans), considering the inspection plan as a whole, the general characteristics of the equipment and its operation, and a RAC.
Fracture Toughness Characterization of LSAW UOE Pipes in Sour Media and Implications on Burst Pressure
Authors: Cravero S. , Coloschi M. , Valdez M. , Arroyo F. , Darcis Ph.
Published: October 2022

Large diameter Sour Service Pipelines are designed for the safe and efficient transportation of production fluids containing H2S. This service condition exposes the pipe to hydrogen embrittlement mechanisms and demands a material with high Sulfide Stress Cracking (SSC) resistance, and thus, a high fracture toughness in a representative sour environment.

Engineering Critical Assessment (ECA) procedures are usually employed to determine the suitability of a pipeline design, these procedures require the correct determination of the material fracture mechanical properties.

Although Method D of NACE TM0177_16 [1] using DCB specimens is currently a recognized testing methodology to evaluate SSC pipe performance, other type of tests could be employed for the purpose of an ECA.

In the present paper, a fracture mechanics experimental program in sour environment is presented. Parent Pipe and Weld Material of Longitudinal Submerged Arc Welded (LSAW) large diameter pipes in H2S were studied. Fracture Toughness Parameters, such K-limit from standard DCB tests and K-threshold from Single Edge Notch Tension (SENT) specimens under constant loading, are compared and discussed. Furthermore, the fracture toughness values obtained from SENT specimens in sour environment are used to estimate the burst pressure using an ECA procedure.
Development of Design Procedure for LNG Carriers With IMO Type-B Independent Tank
Authors: Kim Beom-il , Islam Md Shafiqul
Published: October 2022

There is a growing interest in applying the technology to small and medium-sized Liquefied Natural Gas (LNG) carriers to meet the recent increase in demand for LNG as an ecofriendly fuel and for expanding LNG bunkering infrastructure. The purpose of this study is to apply the IMO Type B tank to small and medium-sized LNG carriers and verify the safety and suitability of the design. One of the key technical issues of Type B LNG tank is heat transfer analysis and selection of hull steel grade. In this study, a heat transfer analysis was performed for hull temperature calculation and steel grade selection. Also, the stress levels and the thermal movements of the tank were checked through thermal stress analysis applying thermal and mechanical loads. Another key technical issue of a Type B tank is to determine the size of a partial secondary barrier based on fracture mechanics. For the accurate analysis, a procedure was developed and verified based on direct analysis and international regulations. Finally, the related safety and suitability of the IMO Type B for LNG cargo tanks required by International Gas Carrier (IGC) code were verified. Two key technical issues with applied examples are thoroughly analyzed in this study, could be applied in the design of independent Type B LNG carrier.
UiS Subsea Freight-Glider: Controller Design and Analysis
Authors: Nawaz Ahmad Usman , Xing Yihan
Published: October 2022

The UiS subsea freight-glider (USFG) is a novel 785 DWT large cargo-carrying underwater autonomous vehicle. It uses variable buoyancy propulsion, i.e., it glides forwards using generated lift and drag forces at the hydrofoils while ascending and descending in water. This propulsion method is ultra-efficient and can transport cargo over long distances with minimal energy consumption. For USFG to operate with maximum speed and enhanced range, a robust, reliable, and accurate control is important as this results in a precise navigation system that would allow for its gliding motion to be extremely efficient. During long-distance voyages, a robust control system based on a feedback loop provides enhanced utility against any external uncertainties or environmental disturbances. The purpose of this work is to implement a control methodology that is based on feedback from the model. This approach removes the need for excessive tuning of controllers for any changes in operating conditions. Moreover, dynamic states, i.e., velocities, can be determined by designing an observer which can be used to predict the motion of the USFG in a planar axis. The gliding paths of USFG in the vertical plane are analyzed along with the observability and controllability of the steady equilibrium glides. For this purpose, the control system is designed with two different controllers, PID and LQR, which control the heave and pitch of the vehicle. Finally, a comprehensive comparison study is presented, which highlights the key differences for the controllers for tunning and rise time. This can also help in designing the ideal control for the required application.
Quantification of Pitting and Stress Concentration Factors on Steel Coupons Exposed to Seawater in the North Sea
Authors: Thibaux Philippe , Vanden Haute Cedric
Published: October 2022

Offshore structures are exposed to a harsh environment. Normally they are protected against corrosion by a combination of excess thickness, cathodic protection, paints and / or oxygen depletion. However, the corrosion protection system can also become ineffective leading to a thickness loss and a degradation of the surface, generally by pitting. The present investigation reports the characterization of the surface of corrosion coupons exposed to free corrosion inside monopiles. Three dimensional scans of the surfaces were performed, providing information about roughness data, identification of separate pits and their individual characteristics. The statistical distribution of the pits for a given coupon can then be extrapolated towards a complete structure and linked to an increased probability of failure by computing the stress concentration factor caused by the individual pits.
Derivation of Vessel Motions as Operational Limits and Motion Forecasting With 2D Wave Spectra: Case Study of Inter-Array Subsea Cable Installation in the North Sea
Authors: Riverola Calavia Javier , Paalvast Mark , Ledoux Bart , Kymmell Jelte
Published: October 2022

The conventional approach for estimating vessel operability for offshore installation operations relies on numerical results from discrete sea state simulations (tabulated operability) and wave forecasts simplified into a set of statistical parameters (Hs, Tp, direction, etc.), leading to an important loss of operability and reliability. Recently, the potential of using vessel motions as cable installation limits has been explored due to the evidence of strong correlations between the vessel motions and the dynamic response of the cable or pipe. This paper presents an end-to-end analysis methodology for calculating operational limits of cable installation operations based on vessel motion criteria using statistical modeling and estimating vessel operability using 2D wave spectra for motion forecasting. This response-based forecasting method mainly benefits from more accurate and realistic wave forecast input, more reliable probabilistic model of the system response (vessel and cable) and avoids the conservative sea state discretization. The method is then applied to the entire sequence of inter-array cable installation in a North Sea offshore windfarm using 2D wave spectral hindcast data, including a weather downtime comparison with the conventional method. Heave velocity was found to be a great and simple predictor of cable response in shallow water applications. Response-based method results showed a significant reduction in vessel weather downtime for array cable installation. This approach could help to reduce the cable installation costs in offshore windfarms considerably, while also increasing the confidence and understanding of the risks involved in the operations.
Real-Time Prediction of Incoming Wave Profile Surrounding Floating Offshore Wind Turbine Using Kalman Filter
Authors: Isnaini Rodhiatul , Toichi Kenta , Iijima Kazuhiro , Tatsumi Akira
Published: October 2022

The present research discusses the possibility of employing a Kalman filter algorithm to predict a real-time data of the incoming wave elevations over a floating offshore wind turbine (FOWT). This is suggested to address some problems in the existing safety management system of FOWT’s operation and maintenance, from the perspective of personnel safety. In this case, knowing immediate wave elevation from a couple cycle ahead is very beneficial to elevate the safety factor during the crew transfer process from the boat to the FOWT. This can be done when the incoming waves are able to be predicted. This time, the prediction is carried out centering around the elementary wave coefficients estimation. Hence, these coefficients are prescribed to be the state variables in the Kalman filter. Meanwhile, two types of observation data are introduced. The first one retrieved its values from numerically generated data, while the other one is data from experiment. Transfer functions that are particular over some specific measurements are used as the bridge between the state model and observation model. Filter capability to predict wave profiles from unidirectional and bidirectional spectrum is explored. Overall, prediction results obtained through numerically generated data show a good agreement with its references. Experiment-based prediction results however, exhibit less favorable results.
Introducing Observation-Based Physics Into the WAM Wave Model
Authors: Kousal Joshua , Liu Qingxiang , Staneva Joanna , Behrens Arno , Günther Heinz , Bidlot Jean-Raymond , Babanin Alexander V.
Published: October 2022

Third generation spectral wave models predict the growth, decay and transformation of wind-generated waves. WAM is one of the two dominant third-generation spectral wave models covering the global ocean. The standard representation of deep-water wave physics in WAM is the semi-empirical approach of Ardhuin et al. (2010; hereafter ARD). The other modern package of wave physics for spectral models, available in WAVEWATCH-III and SWAN, but not in WAM, is the observation-based approach developed by A. V. Babanin, I. R. Young, M. A. Donelan, M. L. Banner and W. E. Rogers (hereafter BYDBR). Its source functions were measured and therefore are not subject to tuning (within confidence limits of the measurements). Furthermore, the observations revealed and/or quantified physical phenomena missing or neglected in other source packages for spectral wave models such as non-linear airflow separation (hence relative reduction of wind input at strong winds), steepness-dependent wave growth (making the wind input a weakly non-linear function of the wave spectrum), negative wind input under adverse winds, two-part wave dissipation consisting of a local in wavenumber space term and a cumulative term (which is an integral of the spectrum), a wave breaking threshold below which no breaking occurs, and swell decay due to interaction with and production of oceanic turbulence. This work documents the implementation of BYDBR physics into WAM. We find that the performance of WAM using BYDBR physics is comparable to the standard with respect to the mean-based metrics. The mean differences between BYDBR and ARD are most prominent in Boreal winter, with widespread reductions in the N. H. of ∼10cm and ∼0.2s for significant wave height and mean wave period respectively.
Discretization Challenges in Crash Simulations: Mesh, Geometry and Failure Criterion Effects From the Energy Perspective
Authors: Coppejans Okko , Werter Noud
Published: October 2022

The simulation of collisions of ships using FEA has a long history of rules and guidelines to which such simulations should conform. Nevertheless, there are still subjects that lack thorough understanding in literature and standards. With the rise in popularity of stress state dependent failure criteria and the ability to simulate with smaller element sizes, new questions arise. This paper is part of an ongoing sensitivity study of the effect parameters such as element size, choice of failure criterion, geometric placement of the striking vessel and friction have on the dissipated energy in a collision simulation. It is shown that the use of different mesh sizes and different failure criteria results in different failure mechanisms and deformation patterns and have a great effect on dissipated energy. The stress states in which most of the plastic work is performed (and therefore energy is dissipated) are shown to be in the triaxiality range of 0.27–0.35. The energy contributions of the regions above that, towards equi-biaxial tension, and below that, towards pure shear, are very significant on first contact and shape the initial deformation mechanism. Furthermore it is shown that the placement of the incoming V-bow with respect to element boundaries significantly influences the energy absorption. The parameters influencing energy dissipation are numerous and just a very small selection is discussed in this paper. No perfect deterministic approach is presented in this paper, but a base for a probabilistic approach is given.
A Physical-Based Damping Model of Gap and Moonpool Resonance in WAMIT
Authors: Ravinthrakumar Senthuran , Ommani Babak , Kristiansen Trygve , Olimb Idunn , Lyngvær Bernt Karsten
Published: October 2022

An engineering model to estimate and incorporate quadratic damping of the piston-mode moonpool responses in the proximity of the piston mode period is proposed. The model provides a physical-based equivalent linearized damping coefficient. The method is not limited to forced motion, but applicable to freely floating moonpool vessels. Further, it is not limited to moonopools, but can be generalized to gap resonance problems, such as side-by-side operations. The soundness of the proposed physical-based method is demonstrated using the panel code WAMIT with a linear damping term in the free-surface boundary condition inside the moonpool using two existing moonpool experiments as case studies; (1) a two-dimensional rectangular box with a moonpool subject to forced heave, and (2) a freely floating offshore vessel in incident waves. The WAMIT computations using the proposed method reconstructs the experimentally obtained piston-mode and vessel responses well. We suggest that the proposed method can be used with fair degree of confidence in an early design or operational analysis phase, in the (often) case that the quadratic damping is not known from either experiments or CFD. To our knowledge, this is the first general, physical-based piston-mode damping model that does not require any tuning from experiments.
A Bayesian Networks Approach for Safety Barriers Analysis: A Case Study on Cryogenic Hydrogen Leakage
Authors: Lenti Manuel , Balestra Lorenzo , Schjølberg Ingrid
Published: October 2022

One of the main concerns, when considering hydrogen storage systems, is the possibility of an unwanted leak, which can result in potential fire, explosions, or detonation, potentially affecting both structures and passengers safety. Safety barriers can be implemented with respect to the storage system design to prevent, mitigate and control unwanted events or accidents. After the identification of the relevant failures, and hazards inherent in the system, a quantitative safety barrier analysis can be performed to assess the safety barriers reliability and quantify with numerical values the overall risk. Typically, the SB’s performances can be quantified using recorded historical failure data, applying well-known modeling tools (e.g. fault tree and event tree). This paper illustrates how the use of Bayesian networks can overcome the limitations of conventional static-structured techniques improving the flexibility in the cause-consequences representation and evaluation of potential accident scenarios. The aim of this work is to test the application of Bayesian networks for a quantitative risk analysis considering a leakage of cryogenic hydrogen from a storage tank installed on a fuel cell powered maritime vessel. A case study for liquid hydrogen release inside the tank connection space of a maritime storage vessel has been proposed. The safety barrier performances have been evaluated calculating their failure probability and assessing the possible consequences. The results indicate the advantages of Bayesian networks for quantitative assessment of safety barriers in critical accident scenarios, increasing the confidence towards hydrogen as a safe energy carrier for maritime applications.
Numerical Simulation of Nonlinear Wave Interaction With Floating Solar Platforms With Double Tubular Floaters Using Viscous Flow Model
Authors: Baruah Gautam , Karimirad Madjid , Abbasnia Arash , MacKinnon Pauline , Sarmah Nabin , Moghtadaei Abdolmajid
Published: October 2022

The development of a numerical model for the simulation of wave interaction with floating solar structures is presented in this paper. A twin-cylinder platform representing the floating structure of the floating solar is used in the simulation. To evaluate the response of the structure under waves that affects the integrity of solar panels, a numerical model is developed. Taking account of the viscous effects is essential for reliable estimation of the exciting loads and structural responses of the platform. Hence, the RANS (Reynolds-averaged Navier-Stokes equations) model is established to simulate this structure under a range of wave frequencies. The viscous model takes advantage of the finite volume solver to accomplish computational fluid dynamic (CFD) analysis. Convergence and stability of the model are evaluated for different mesh resolutions and correspondingly the computational cost is demonstrated. Numerical solutions are compared with experimental data for verification and validation. Therefore, the range of validity of the viscous model is evaluated for strong nonlinear incident waves.
A Deep Learning Approach for Underwater Leak Detection
Authors: da Silva Viviane F. , Netto Theodoro A. , Ribeiro Bessie A.
Published: October 2022

The increase in costs in the exploration and production of oil and gas in deep waters has led companies in the sector to invest in innovative technologies to detect, locate and correct faults in their production systems.

This research aims to develop a methodology for monitoring and detecting leaks in subsea structures based on deep neural networks, allowing automated, efficient, and less costly monitoring than conventional monitoring methodologies.

A set of monitoring data will be pre-processed for noise elimination, resolution improvement and resizing, to obtain a better performance of the algorithm. The next step consists of extracting relevant characteristics from the dataset to clearly identify the leak.

The results show the metrics used to evaluate the performance of the neural network as the accuracy and efficiency of the algorithm to detect leaks in the underwater structures and equipment.

Images of the Gulf of Mexico oil spill were used to test the methodology and the successful detection of the leak demonstrates the potential of the methodology for underwater leak detection.
Influence of Sail Design Parameters on Unsteady Propeller Thrust for Underwater Vehicles
Authors: Takahashi Kenshiro , Arai Jun , Mori Takayuki
Published: October 2022

To realize covert missions, submarines and other underwater vehicles must satisfy strict requirements pertaining to their acoustic signatures. However, marine propellers produce unsteady forces, resulting in undesirable noise. In this work, a parametric study was performed on the sail design under unsteady propeller thrusts by using computational fluid dynamics (CFD). The CFD procedure was validated for multiple propeller models and wake profiles and used to compute the unsteady propeller thrust of an underwater vehicle. The DARPA SUBOFF submarine and INSEAN E1619 propeller were adopted as benchmarks. The axial location of the sail and the sail width were varied, and the unsteady propeller thrusts were determined. Dominant harmonics of the computed propeller thrusts were analyzed via Fourier series. Furthermore, a correlation analysis was performed between the harmonics of the unsteady propeller thrust and inflow wake. The amplitude of the thrust fluctuation for the aft-fitted sail model was nearly two times that for the original fore-fitted sail model. The dominant 7th harmonic was significantly lowered by altering the sail width. Positive correlation coefficients were obtained at several harmonics that did not match the number of blades.
Low Cycle Fatigue Evaluation for High Strength Welded T-Joint Based on Structural Strain Method
Authors: Kim Ji Hoon , Kim Myung Hyun , Moon Won Ki , Lim Jong Il , Kim Seong Min , Yun Kwang Hee
Published: October 2022

In design process of welded structures, fatigue failure is one of the main issues to be carefully considered in the assessment of the structural integrity. In general, fatigue failure typically occurs at locations structural discontinuities. In particular, welded structures inevitably contain structural discontinuities during manufacturing process and those locations are vulnerable to fatigue loads. The 2007 ASME Div.2 Code suggests a master S-N curve approach based on structural stress that is insensitive to the size of element with improved accuracy in stress calculation [1]. Structural stress method has been validated based on numerous experimental data and studies in the high-cycle fatigue regime. However, these methods cannot be applied in low-cycle fatigue regime, and validations of the structural stress method in the low-cycle regime are insufficient so far. In this regard, an extension to the master S-N curve, structural strain method was introduced to evaluate the low-cycle fatigue performance by Dong et. al [2].

The target of this study is to validate the structural strain method in low-cycle fatigue regime of welded joints. For that purpose, low-cycle fatigue test was performed on high strength steel welded T-joints. Pseudo structural stress can be calculated through the derived structural strain, and the equivalent structural stress is expressed in consideration of the shape and thickness effects. Fatigue life evaluation using structural strain method exhibited a good correlation with the master S-N curve not only in the elastic region but also in the low-cycle regime accompanied by plastic deformation. By using structural strain method, it is possible to comprehensively evaluate the fatigue life both in high and low-cycle fatigue regime.