bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Study on the Influence of Hydraulic Fracturing on Hydrogen Sulfide Generation in Longxi Block of Daqing Oilfield
Authors: Sun Hongyu , Zhong Liguo , Liu Jianbin , Hao Tongchun , Li Shihao , Zhu Yu , Zhang Hailong , Wang Kexin
Published: October 2022

Hydraulic fracturing has a significant effect on increasing production and injection of oil and water wells in low-permeability and tight reservoirs. Hydrogen sulfide (H2S) was generated after hydraulic fracturing of oil and water wells in Longxi Block of Daqing Oilfield. The maximum hydrogen sulfide content in casing gas reached 232 ppm, far exceeding the safety critical concentration value (20 ppm), which increased the risk and difficulty of production and construction operation. In order to reveal the influence mechanism of fracturing on H2S generation in Daqing oilfield, the experimental simulations of the thermal decomposition of sulfur (TDS), thermochemical sulfate reduction (TSR) and bioreduction reaction of sulfate-reducing bacteria (SRB) with different compositions of fracturing fluid at different temperatures were conducted in this paper. The results showed that the influence mechanism of the fracturing fluid compositions on the formation of H2S was different when the formation temperature was different. The critical temperature of TDS and TSR reaction in the formation was 100°C and 140°C, respectively. The higher the temperature, the higher the amount of H2S was generated. The potassium persulfate (K2S2O8) and sodium sulfite (Na2SO3) in the fracturing fluid could promote the TDS and TSR reaction to generate H2S, but did not change the critical reaction temperature of TDS and TSR reaction. When the formation temperature was not higher than 56°C, the guar gum and sulfur-containing materials in the fracturing fluid could provide nutrition for SRB in the formation, which promoted the rapid reproduction of SRB in a short period of time, and then generated a large amount of H2S. The mechanism of H2S generation for fractured wells in the Longxi block with temperature of 30∼56°C was the proliferation of SRB in the fracturing fluid. The mechanism of H2S generation in fractured wells with temperature of 100∼120°C was that sulfur-containing materials promoted TSR reaction. This study clarifies the reasons and conditions for the generation of H2S, and plays an important role in the subsequent research on H2S prevention and control measures.
Numerical Modelling of Residual Liquefaction in the Subsoil Under a Vibrating Plate
Authors: Shanmugasundaram Ranjith Khumar , Rusche Henrik , Windt Christian , Kirca V. S. Özgür , Sumer B. Mutlu , Goseberg Nils
Published: October 2022

Seabed liquefaction is the phenomenon by which the seabed soil loses its strength and stiffness, due to applied stress, and behaves like a non-Newtonian fluid. Seabed liquefaction can lead to severe failure of marine structures, such as buried pipelines or coastal breakwaters. Numerical modelling of liquefaction can provide valuable insights into the prevailing wave-structure-soil interaction. However, the holistic modelling of seabed liquefaction, including the transition from solid to liquid and back to solid soil, is challenging, due to the prevailing hydrogeotechnical processes. As a step towards the development of such a holistic numerical model of seabed liquefaction, this paper considers the modelling of the soil under a rocking plate as an idealised representation of a caisson breakwater as presented in [1]. The numerical model has recently been presented in [2] and includes equations for the accumulation of pore pressure and a criterion to distinguish between the liquefied and non-liquefied regions. The numerical results are compared to the experimental results taken from [1]. Different numerical model setups are presented to overcome modelling challenges due to occurring punching shear failure.
Cost-Effective Optimal Solutions for Steel Catenary Riser Using Artificial Neural Network
Authors: Abam Joshua T. , Pu Yongchang , Hu Zhiqiang
Published: October 2022

Over decades, free-hanging steel catenary riser (SCR) has been regarded as a cost-effective and straightforward system for riser solutions in deepwater and ultra-deepwater by National oil companies NOCs, international oil companies IOCs, and independent players. However, the free-hanging SCR comes with its own challenges, which, if not correctly evaluated during design stages, can result in system failures. The two main challenges facing the free-hanging SCR usage are increased self-weight and high fatigue damage, especially at the touchdown and hang-off points. Fatigue damage is the failure resulting from cyclic stress accumulation over a specific duration. The involvement of technologies has improved the design method for these systems over the years. Two of such innovative contributions include the optimisation algorithm and artificial neural network ANN methods. The aim of this research is to develop an effective optimisation algorithm to search for the global optimal weight of the riser configuration while maintaining its structural integrity. The method involves the combined use of ANN and optimisation genetic algorithms (GA) to determine the optimum solution of the SCR. The GA is used because of its capability in handling a variety of complex nonlinear optimisation problems to ascertain the global optimum solution and its capacity to self-moderate the number of iterations. At the same time, the ANN method is deployed for its accurate prediction of non-linear responses. The deployed techniques have shown to be promising due to the time-saving and less computational cost compared to integrating GA and time-domain FE models. This method was illustrated using a prospective 10-inch internal diameter SCR installed in a 2000m deepwater offshore field off the oil-rich Niger Delta region, Nigeria. The obtained results have shown a 19.10 per cent reduction in the riser weight and a time reduction of 90.83 per cent.
Influence of Extreme Environmental and Deep-Sea Temperature Conditions on Silicone Oil Used for Insulating Underwater Electrical Switching Systems
Authors: Haba Yvonne , Arumugam Saravanakumar , Krohmann Sascha , Körner Gerhard , Richert Ranko , Kosleck Sascha
Published: October 2022

This study focuses on understanding the influence of extreme environmental conditions on silicone oil applied as an insulating material in underwater electrical switching systems. The extreme environmental conditions imply adverse operating temperatures of the underwater electrical systems which must be effectively handled by the silicone oil. For this purpose, a standard high voltage (HV) relay is selected and is immersed in a silicone oil thereby enhancing its operating voltage to 20 kV. First, the geometry of the modified relay switch is captured and converted into a CAD model. Subsequently, the developed CAD model is imported into the simulation software and converted into a numerical model and subjected to AC/DC, electrostatic and stationary case simulation. The adverse temperature conditions are varied i.e., from −50 °C, 0 °C, 20 °C, 40 °C and 120 °C respectively. The potential and electric field displacement at the electrodes of the high voltage relay is recorded and analyzed. Following this, high voltage experiments are carried out on an actual high voltage relay constructed based on the simulation model and the respective parameters such as discharges. Thus, the dielectric quality of the silicone oil under wide range of temperature is studied. The simulation and experimental results obtained altogether validate the design modifications made on the standard relay converted to meet the high voltage requirements of underwater electrical switching systems.

Once this is identified, the chosen relay is compared with the experimental findings to validate the design modification.
Numerical Investigation of Mean Drift Forces Acting on Restrained FPSO in Regular Waves by Linear and Nonlinear Tools
Authors: Pakozdi Csaba , Fonseca Nuno
Published: October 2022

State of the art ULS/ALS mooring analysis is based on potential flow calculated wave drift forces. However, it is acknowledged that higher order effects in steep sea states increase the wave drift forces as compared to the potential flow 2nd order models. This is the background for the EXWAVE 2 JIP where semi-empirical methods to correct wave drift forces were implemented and checked, which shows the significance of this problem to the industry.

This publication aims at applying CFD simulations to better understand the physics of wave drift loads in steep sea states and to identify higher than 2nd order effects.

Calculations are performed with a RANSE-VOF based CFD code and with a linear potential flow code for a floating production storage and offloading (FPSO) unit in deep water regular waves with three periods and three wave steepnesses. The vessel is restrained from moving to make a simple and a consistent comparison between the results from the two approaches. Comparisons for small amplitude waves provide an assessment of the quality of the CFD simulations, while increasing wave steepness conditions are used to identify higher than second order effects on the wave drift forces.

CFD simulation resulting force time series are decomposed into mean value and harmonics by means of a Fourier analysis and compared against potential theory estimated mean and first order forces.

The comparisons for small wave amplitudes show a good agreement, which proofs the correctness of the applied CFD setup. Further, the CFD results show an increasing trend of the mean wave forces normalized by the wave amplitude squared with increasing wave steepness for the two shorter wave periods. The trend is unclear for the longer wave period.
Adhesively Bonded FRP Reinforcement of Steel Structures: Surface Preparation Analysis and Influence of the Primer
Authors: Sourisseau Quentin , Leprêtre Emilie , Chataigner Sylvain , Chapeleau Xavier , Mouton Luc , Paboeuf Stéphane
Published: October 2022

In tropical areas, with marine environment, high temperature and humidity, corrosion is a constant threat. The maintenance of steel structures (like FPSO’s) is becoming a challenge. The current technique of “crop and renewing” repair involves a certain number of major issues for project owners such as: “hot work”, that is to say welding; temporary weakening of the structure; need to empty, clean and purging the oil tanks of the FPSO’s, resulting in long downtime and an expensive solution. “Cold repair”, such as composite repair, is a promising solution. However, surface preparation and the influence of the primer are crucial issues to be addressed to ensure the strength and reliability of this type solution based on bonded patch.

The paper presents an experimental study of the influence of the surface preparation and the primer on the strength of small steel bonded specimens which have been deliberately degraded by corrosion and pollution. Several surface preparation methodologies were investigated and the quality of these preparations was assessed using methods that can be implemented on site. Two main aspects were investigated: the detection of the residual presence of pollutants through the use of a portable infrared spectrometer; and the determination of surface energy after preparation using contact angle and wettability measurement equipment. To study the impact of the primer on the adhesion capacity of the steel surface, critical toughnesses measurements was performed with End notch flexure tests. Three configurations have been tested: bonding with the epoxy resin without initial application of primer and bonding with the Epoxy resin with initial application of two Primer A and B. The results shown clearly that the type of primer and the quality of its application are paramount importance to ensure the strength of steel bonded patches.
Weight Optimisation of Steel Catenary Riser Using Genetic Algorithm and Finite Element Analysis
Authors: Abam Joshua T. , Pu Yongchang , Hu Zhiqiang
Published: October 2022

Steel catenary risers (SCR) are a good candidate for deepwater exploration due to their relatively low cost, less demand for subsea intervention, and compliance with the floating structures motions. However, SCR deployment in deepwater faces tremendous challenges such as increased top tension and concern over fatigue performance. This paper aims to search for the global optimal solution of a riser system through the application of genetic algorithm (GA) and finite element analysis. The process method will, in turn, automate the design process, with the implementation of an optimisation routing as a critical resource for initiating and finalising the acceptability of a riser system. The method involves the deployment of GA as the optimiser because of its capability in handling a variety of complex non-linear optimisation problems to ascertain the global optimum solution and the capacity to self-moderate the number of iterations. The total structural weight is the objective function, while bursting criteria, buckling (collapse) criteria, buckling propagation criteria, yielding criteria, and fatigue limit state (FLS) criteria are non-linear constraints. To accurately assess the strength requirements, time-domain approach through OrcaFlex is used to predict the dynamic responses and fatigue life/damage of the SCR. An interface between GA in MATLAB and ORCAFLEX has been programmed to exchange data. The wall thickness, length and declination angle at the hanging-off point are chosen as design variables due to their strong influence on the configuration and dynamic responses of a SCR.

This method was illustrated using a prospective 10inch SCR installed in a 2000m deepwater offshore field off the coast of the oil-rich Niger Delta region, Nigeria. The obtained results have shown a significant reduction in the riser weight.
Effects of Nonlinearity on the Formulation of the Crest Elevation and the Crest Width of Extreme Waves in Random Seas
Authors: Spiliotopoulos George , Katsardi Vanessa
Published: October 2022

This work highlights the effects of nonlinearity on extreme events that rise during directional focused and random wave simulations in finite water depths. For this purpose, the fully nonlinear model “HOS-Ocean” by Ducrozet et al. (2016) [1] is considered and compared with linear simulations. Large waves are formed through a series of linear and nonlinear focused and random simulations. The effect of water depth and directionality is considered by applying different directional spreadings relative to a range of short crested to long crested sea states. The results offer transparency in understanding the physics underlying such extreme events. It is shown that “walls of water” are also formulated infinite water depth, as is the case for deep water [2]. Indeed, the sea-state becomes more long-crested during the formulation of the extreme events in both focused and random simulations; all highly dependant on the directionality of the wavefield. The above is highlighted in the substantially increased crest width measured in the nonlinear simulations despite the decreased maximum crest elevations.
A Monte Carlo Approach for Fatigue Analysis of Mooring Lines Subjected to Simultaneous Environmental Actions
Authors: Seabra Pedro de Amorim , de Oliveira Mauro Costa , Simão Marina Leivas , Videiro Paulo Mauricio , Sagrilo Luis Volnei Sudati
Published: October 2022

Fatigue damage assessment of mooring lines components is one of the main issues in the design and life extension monitoring of deepwater floating production units mooring systems. Floating units operating at several ocean regions, as in the Brazilian southeast coast and Africa west coast, are almost permanently subjected to wind-sea waves and remote waves (swell), besides wind and marine current actions. Fatigue assessment of mooring systems operating under these environmental conditions shall consider an extensive number of simultaneous environmental action load cases or rely on some simplification of the load cases. In the first case, the fatigue assessment may require a large amount of computer resources and time, making it unfeasible, for example, in the early phases of the mooring system design, where normally the analysis of several configurations is necessary. In the second case, some important aspects of the actual behavior of the environmental actions may not be considered in the fatigue analyses.

This paper presents a new engineering approach for the fatigue assessment of mooring systems based on a Monte Carlo Simulation resampling using a set of simultaneous environmental conditions available in a database, sampled every 3 hours during several years. Studies show that damage estimates considering just a few resampled cases, say 5 to 10% of the cases in the database, compare very well to estimates considering the entire database. Finally, the paper also presents how to define confidence intervals of the damage estimates.
Influence of Grease Lubrication on Fretting-Fatigue Damages of Steel Wire Ropes
Authors: Montalvo S. , Fouvry S. , Martinez M.
Published: October 2022

Steel wire ropes can be used as mooring lines for Floating Offshore Wind Turbines. Swell induces tension and bending in the line. Investigating the effects of combined loads on rope lifetime is necessary. In these cases, fretting-fatigue damage is considered to be one of the main causes of failure. To prevent corrosion, grease is injected in the rope. The effect of grease on the fretting-fatigue damage of two wires in contact was investigated. A multi-scale approach was applied to calculate representative local loads in the mooring ropes. Global tension and bending were applied to a detailed model of the rope to calculate the local stress and contact forces in the steel wires. These are the fretting-fatigue loads applied in the laboratory tests. Two series of fretting-fatigue tests were conducted, each one with clean and greased wires. A two actuators hydraulic rig was used, allowing for complete decoupling of the fretting and fatigue loads. In the first series, the fatigue load was kept constant, and the fretting load was changed. In partial slip regime, for small fretting amplitudes, greased wires have longer lifetimes than non-greased wires. In a second series of fretting-fatigue tests, this most critical fretting condition was used and kept constant, and the fatigue load was changed. Results show that the fatigue limits of clean and greased wires are equal.
Wave Impact Pressures on U-OWC Breakwater
Authors: Romolo Alessandra , Timpano Bruna , Laface Valentina , Fiamma Vincenzo , Arena Felice
Published: October 2022

A small-scale field experiment was conducted on a U-OWC incorporated into a model of caisson breakwater at the NOEL laboratory of Reggio Calabria (Italy). The U-Oscillating Water Column (U-OWC) or REWEC (REsonant Wave Energy Converter) is a device belonging to the family of OWCs. Such a device is very innovative, being able to absorb a very percentage of incoming sea waves and to produce electrical energy via proper PTO. The focus of the paper has been the analysis of the impact wave loads acting on the modified U-OWC structure during extreme wave events. It has been observed the occurrence of both “quasi-standing wave” loads due to non-breaking waves and “impulsive wave loads” with different wave impacts exerted by a wave breaking against the U-OWC model.
The Likely Cause of Loss of Position for Dynamically Positioned Semi-Submersibles Under Moderate Wave Conditions
Authors: Kaasen Karl E. , Ludvigsen Halgeir , Fonseca Nuno , Lie Halvor , Bjørheim Lars Geir
Published: October 2022

A number of incidents of wave-induced loss of position for dynamically positioned semi-submersible under normal operating conditions have occurred in the Norwegian offshore sector in recent years. A study has been carried out to seek their cause. One hypothesis for the cause has been slamming load from an extremely tall and steep wave that is not effectively counteracted by the DP system due to delays in signal filters and thruster response. Another cause could the loads from a train of tall and steep waves.

A linear single-degree-of-freedom numerical model is made for a vessel with DP. The model is essential in that it represents the basic characteristics of the DP system: State observer/filter and feedback control. The model is used to calculate the frequency response and the impulse response of the dynamically positioned semi-submersible. By calculating extreme impulsive load based on published theory it is established that slamming will not cause great vessel excursion. Still, due to delays, the DP system gives more than twice as large excursion as a mass-spring-damper system with identical restoring stiffness and damping.

Using an advanced model for vessel with DP, three-hour simulations of stochastic vessel response are carried out for five steep wave states of moderate significant height, The likely cause of large vessel excursion is found to be wave-drift. Due to additional viscous loads on the semi’s columns the wave-drift loads will be significantly larger than predicted with potential theory.
Joint-Industry Effort to Develop and Verify CFD Modeling Practice for Predicting Wave Impact
Authors: Pakozdi Csaba , Croonenborghs Eloise , Kim Jang , Peric Milovan , Ducrozet Guillaume , Bouscasse Benjamin , Xu Haihua , Califano Andrea , Akselsen Andreas , Loubeyre Sebastien
Published: October 2022

In 2020, a modeling practice was presented to perform numerical simulation of waves, where waves generated by a numerical wave tank (NWT) were used as input to a CFD simulation. This paper presents an extension of those practices in the context of wave impact on a gravity-based structure (GBS). It focuses on capturing accurate wave loads for a prescribed wave event, reproduced from a measured time series. This modeling practice serves the purpose that if it is followed by a CFD practitioner, the CFD results are reproducible.

The modeling practice is validated for two regular wave cases and one irregular wave event. The validation data are based on experiments performed at MARINTEK in model scale 1:54 with the water depth 2.81m. During the validation the wave time series are compared against model test without and with GBS at scale 1:54. Further, relative wave height time series, global forces and moments acting on the deck as well as slamming forces are compared against model test records. The modeling practice is validated with Simcenter STAR-CCM+ as the main CFD solution but the modeling strategy can be applied to other CFD software.

Thanks to the initialization of the CFD solution with user defined waves (UDW), the NWT-CFD coupling shows two advantages. First, the size of the CFD domain can be reduced to a minimum. Second, it is sufficient to start the CFD simulation shortly before the impact event.
Wave Riding Through Time – The Contributions of Günther F. Clauss to the Field of Ocean Wave Research
Authors: Sprenger Florian , Kosleck Sascha , Klein Marco
Published: October 2022

Günther F. Clauss is one of the most influential and distinguished international experts in the field of ocean engineering. With 50 years of activities in the field, often in collaboration with national and international colleagues, he has contributed significantly to the visibility and progress of ocean engineering as a research discipline. In his scientific contributions, he has repeatedly established new ideas and set standards. His research contributions include the design, installation and decommissioning of offshore structures, the analysis of loads and motions on floating structures and ships, the development of SAR and oil spill response systems and deep-sea technology.

Across all areas, from fundamental to application driven research, one topic always stood out — the investigation, simulation and experimental modelling of natural waves aiming at a comprehensive deterministic analysis of offshore structures and ships in natural sea states and extreme waves.

From linear superposition of regular waves to the generation of highly nonlinear wave phenomena, from wave-structure interaction to marine oil spill response technologies this paper attempts the almost impossible task: to deliver an overview over 50 years of research by highlighting selected topics, telling the story of Günther F. Clauss who has conquered the inner space.
Structural Optimization of Ships: Benchmark Study of Metaheuristic Algorithms and Constraint Handling Approaches
Authors: Cai Yuecheng , Jelovica Jasmin
Published: October 2022

Optimization of ship structures can be performed using swarm and evolutionary algorithms in search for global optima, which is useful to maximize performance and minimize costs. There is a wide variety of such algorithms available and some have been proposed recently, but tested on mathematical problems. Thus, a benchmark study is performed here to assess their performance on structural optimization of a 180 m long chemical tanker which needs to fulfil class society’s requirements. Main frame is optimized considering firstly structural weight as a single objective and secondly weight and deck adequacy as two concurrent objectives. Optimization of deck adequacy leads to decrease of stresses in the deck. Artificial neural network is used as surrogate model to reduce the computational time. Following swarm and evolutionary algorithms are considered: PSO, NSGA-II, MOEA/D, MVO, MOMVO, MOGWO, IGWO and GSA. Following constraint handling techniques (CHTs) are used within: static and dynamic penalty, adaptive threshold and repair method. All algorithms are run for 30 times and the statistical results are presented. Results are compared in terms of objective values and speed of convergence. Results reveal that recently proposed swarm algorithms perform worse than well-known evolutionary algorithms in terms of the convergence rate and spread of the non-dominated front. In addition, algorithms’ performance is strongly influenced by CHT used. Among the ones tested, the best CHT is the repair method.
Safety Distance During Escort and Convoy Based on Channel Breakout Simulation and Model Tests
Authors: Li Fang , Puolakka Otto , Goerlandt Floris , Kujala Pentti
Published: October 2022

Escort and convoy are typical operations when a merchant ship navigates in ice beyond its own ice-going capability. In such scenarios, a safety distance between the front ship and the following ship is maintained. The leading vessel may suddenly decelerate or even come to a halt if it encounters a heavy ridge or thick ice floe. When this happens, the following ship needs to take actions to avoid collision with the leading vessel. An evasive operation for such collision avoidance is to break out of the channel. The safety distance can be defined as the minimum distance which is needed for successful collision avoidance. This depends on various parameters such as ice thickness, ship speed, channel width, the ship’s icebreaking capability and its manoeuvrability in ice. This paper investigates safety distance during escort and convoy by model-scale experiments and numerical simulation of a ship breaking out of ice channel. The experiments are carried out at Aalto Ice Tank and the numerical simulations are conducted via the in-house simulation software package of Aalto University Marine Technology group. The dependencies of the safety distance on ice thickness, channel width and initial speed are identified via multiple experimental and simulation runs. The simulation proves to provide accurate estimation on breakout distance through comparison with model test results, and reveals the influence of ice thickness, channel width and initial speed on the breakout distance.
Compressive Failure of Ice During Indentation by Rock Particles
Authors: Fitzpatrick Thomas , Taylor Rocky S. , Thijssen Jan
Published: October 2022

The indentation of rock particles into ice is an important aspect of understanding subsea interactions involving ice features and gravelly soil. This paper investigates the indentation of rock particles into an ice specimen, where observations are made to study the effect of changes in indentation rate and the relative spacing from previously formed damage zones on resulting force and pressure trends. Experiments were conducted for three indentation rates: 10 mm/s, 0.5 mm/s, and 0.01 mm/s. Observations were also completed for three unique spacing distances (as multiples of mean rock diameter) between the rock particle and previous damage zones. These setpoint spacings were taken as 2D (26 mm), 5D (65 mm), and 7D (96 mm), where the diameter D was based on a mean rock diameter of 13 mm. Maximum observed forces and pressures exerted onto the ice by the rock particles are examined and compared based on changes in the noted test parameters. The behavior observed during these tests is also compared with results from prior ice indentation tests with steel spherical indenters. The research outlined in this paper will additionally inform future research on the nature of subsea interactions of icebergs with the ocean floor, and how this may affect potential risks related to subsea installations.
A Trawl Net Model Tailor-Made for Simulation of Pipeline and Trawl Board Pull-Over Interaction
Authors: Longva Vegard , Levold Erik , Ilstad Håvar
Published: October 2022

This paper proposes a new trawl net model tailor-made for simulation of trawl board and pipeline pull-over interaction. The trawl net is connected to the trawl board by a steel rope referred to as the sweepline. It is crucial that the correct tension level is simulated for the sweepline during the trawl board and pipeline interaction phase. In previous work, this was achieved by using a single node with quadratic drag properties for the trawl net. However, it was necessary to apply a time-consuming approach where the drag properties were tuned on a case-to-case basis and also stepwise changes of the drag properties throughout the analysis had to be applied in some cases. These drawbacks were avoided in the present work by developing a new trawl net model consisting of 4 nodes and 4 lines. The number of degrees of freedom (DOFs) is very small which makes the proposed model an attractive alternative compared to detailed net structure models consisting of numerous DOFs. Further, the model is applicable for use in standard commercial software since it employs basic structural elements and a quadratic Morison load model. This paper also presents a numerical study where the developed model is validated against model test results of trawl board and pipeline interaction. The trawl net model was found to predict sweepline tension levels in very good agreement with the model tests performed for velocities of 1.5 m/s and 2.06 m/s. The trawl net model was further applied to study the validity of a flume tank test method that applies a constant sweepline tension during trawl board and pipeline interaction. The study showed that non-conservative pipeline interaction loads resulted for the constant sweepline tension model. It is therefore recommended to include the complete trawl net in flume tank testing of trawl board and pipeline pull-over interaction.
Indentation Test Implementation for Rock Strength Correlation by Experimental Method and Simulation Using Distinct Element Method
Authors: Premraj Prajit , Li Zijian , Abugharara Abdelsalam , Butt Stephen
Published: October 2022

Rock strength is an important parameter for the drilling penetration estimation, which is usually determined through standard destructive strength tests, which are known to be sophisticated, expensive, and time-consuming. In addition, the accuracy of these tests has a high standard on the rock sample dimension. As a non-conventional method, the rock indentation test is reviewed and conducted in this study to solve these problems. The sample preparation and test method of the rock indentation test are validated to standardize the test. Based on the stress-strain behavior of the test samples, the correlation between the rock indentation hardness index (IHI) and the rock UCS strength is developed based on different lithology. Then the rock indentation test is simulated in the distinct element method (DEM) in PFC2D software. The robustness of the DEM simulation is validated, and the sample failure pattern is studied. The significance of the process is that it very closely matches with the process a rock fails under the cones of a roller cone drilling bit penetrating the rock.
Development of an Online Ship Simulator to Represent the Dynamic Ship Responses in Regular Waves Using an Inertial Measurement Unit
Authors: Zorrilla Gomez Luis A. , Miranda Sandoval Beatriz K. , Hinostroza Miguel A. , Ramos Quiñonez Saida M. , Ramos Alvarez Nain M.
Published: October 2022

Nowadays, it has been observed a vertiginous growth of technological implementations in the naval and offshore industry, implementations such as online ship simulators that represent the state of the vessel in real-time for a certain sea condition, motion amplification methods to monitor vibrations of the ship propulsion system, virtual shore stations to control autonomous vessels, among others. This work presents the implementation of an inertial measurement unit (IMU) in a scaled-down vessel to observe the dynamic responses of a ship in an online simulator called ShipSim. The implementation considers the responses of the ship in its six degrees of freedom and its behavior in regular waves. The simulator responds to a parametric variation, which considers the direction, amplitude, period of the waves, among other geometric parameters. The scaled-down model of the vessel is fabricated on a 3D printer and is designed to place the IMU system at the geometrical center of the vessel. The IMU is a 6DOF OCTANS surface which is used to measure the ship motions. In addition, real-time results of the different movements of the scaled-down vessel in the time domain are displayed, which are observed in the simulator in the form of time-series graphs.
Offshore Wind Power Construction Efficiency Assessment in Fujian Sea Area Based on the Mixed Integer Linear Programming
Authors: Yang Zihao , Lin Yifan , Dong Sheng
Published: October 2022

China has become the world second largest energy consumer, and IEA predicted that its primary energy demand will double from 2025 to 2030. Offshore wind power construction is difficult and carries high risk. It is extremely difficult to control the cost, of which the construction period is the biggest variable. As to meet the requirements of cost reduction and efficiency increase in the coming era of flat rate, the construction procedures, primary vessels, and equipment need to be properly planned prior to the project startup. For this purpose, an algorithm based on Mixed Integer Linear Programming (MILP) for accurately calculating weather window and construction efficiency of offshore wind power was firstly proposed in this study, which comprehensively takes the complex construction procedures, duration of each link and environmental restrictions into account. Focusing on the offshore seas of Fujian province, utilizing the 1-hour hindcast wind and wave data respectively from the validated reanalysis wind field and SWAN model with a time span of 25 years (1996–2020), the weather window and construction efficiency for monopile foundation construction and offshore wind turbine installation were evaluated both on spatial and temporal scope. With respects to the specific wind farms that will be constructed, the detailed analysis and construction suggestions were provided.
An Experimental Study on the Wave Force on the Slope of Smoothed Mound Breakwater With and Without Crown Wall Under Medium-Long Period Waves
Authors: Han Xinyu , Dong Sheng
Published: October 2022

A Mound breakwater is a common coastal defence against waves. The wave force has greatly related to the stability of the armour blocks. Medium-long period waves have greatly impact on coastal structures and are attracting more and more attention. In this work, the wave force and pressure distribution on the slope of smoothed mound breakwater were studied by experiments. Total of 140 tests were carried out, in which 70 sets are breakwaters with crown wall, and the other 70 sets are breakwaters without crown wall. In the scope of medium-long period waves, the wave force on slope of the breakwater with crown wall is similar to that without crown wall. Neelamani method is more suitable for the breakwater without crown wall and its top submerged. Under short period waves, the maximum pressure on the slope is different. The pressure on the slope with and without crown wall is similar. Pressure at berm with crown wall is greater than that without crown wall. The maximum ratio of the horizontal velocity in front of breakwater with and without crown wall is about 2. A formula was proposed to predict the difference of pressure at the berm with and without crown wall through the difference of reflection coefficient Cr.
Automatic Tsunami Barrier
Authors: Hamada Eigai
Published: October 2022

The Anti-Tsunami Laboratory (ATL) invented and developed the Anti-Tsunami Door (ATD) barrier as an automatic tsunami barrier. In September 2018, ATL and Kyoto University tested a mid-scale model of a three-stage ATD unit and confirmed its performance: (1) functioning automatically (refer to Figure 9); (2) achieving reasonable wave height reduction, which is approximately 40%–80% that of a solid barrier of the same height; and (3) demonstrating reasonable strength for a wooden structure under the mid-scale model test conditions. ATL had firstly planned to test a large-scale model of an ATD unit in Oregon State University (OSU) in May 2020, but that test has been delayed owing to the COVID-19 pandemic. Currently ATL plan to do it in March 2022. Because the wave pressure on the ATD unit is expected to be high during the large-scale model test, ATL requested that the Explosion Research Institute (ERI) simulate the wave pressure on a large-scale model ATD unit, and based on the results, ATL will reinforce the ATD unit. After testing the large-scale model unit, ATL will install ATD barriers along the coast of Japan, customizing the barrier for specific tsunami hazards.
A Study on the Construction of the Tsunami Hazard Database for Mooring Vessels in the Ports
Authors: Masuda Mitsuhiro
Published: October 2022

When a tsunami attacks a coastal area, vessels moored at the wharf suffer serious damage. In fact, more than 20,000 vessels have been damaged, such as landing on a wharf, drifting, or colliding due to the tsunami caused by the Tohoku earthquake in 2011. Tsunamis are significant disasters in Japan. Many researchers have studied the prediction of tsunami damages and the tsunami damage protection measures. However, there are various approaches for studying tsunami damage prediction and tsunami protection measures for each researcher. This means that the tsunami damages and tsunami protection measures are evaluated using various methods in each area and port. Accordingly, when tsunami damages are evaluated, there is currently no unified evaluation method in Japan as a whole. This study proposes a tsunami hazard database for major Japanese ports using the unified evaluation method. The moving particle simulation (MPS) method was used as a tsunami hazard simulation method. Target ports are 23 major Japanese ports. The landing on a wharf and breakage of mooring lines were evaluated as hazard cases for the mooring vessel. In evaluating the landing of vessels on a wharf, the tsunami height in each port, the draft of vessels, and the crown heights by the difference in tidal levels were considered. The tsunami hazard database was constructed based on these results. Finally, tsunami hazards in major Japanese ports were evaluated using the tsunami hazard database.
Integrity Assessment of Electrically Heat Traced Pipe-in-Pipe Plug Weld
Authors: Zhou Daowu , Cao Lingjun
Published: October 2022

To ensure the integrity of three recent electrically heat traced flowline (EHTF) projects, an innovative engineering critical assessment (ECA) of the vacuum plug weld has been performed. Vacuum plug welds are used to seal the annulus of the EHTF pipe in pipe (PiP) after vacuum draw down operations. Plug welds are a high focus area for the EHTF system study.

EHTF PiP in offshore application is installed by a reel-lay method. The plug weld in the carrier pipe is subjected to large plastic deformation, followed by cyclic fatigue in lay-down and operation. These loading conditions pose significant challenges to plug weld integrity management. Due to the unique design and function of the EHTF plug weld, a fit-for-purpose ECA is crucial for demonstrating the weld quality is sufficient to guarantee the integrity of the carrier pipe throughout the entire EHTF life cycle. The allowable defect size from the ECA is also crucial to validate the accuracy of the inspection method.

This paper presents the development of the plug weld ECA methodology. The complexity of the plug weld requires a bespoke ECA to address defect tearing during plastic deformation from reeling, as well as fracture check against operational conditions. In terms of fatigue crack growth for installation and operational phases, there is no off-the-shelf empirical stress intensity factor (SIF) solutions for a plug weld. A bespoke SIF solution for plug weld was developed and verified via 3D FEA. A case study of plug weld ECA in an EHTF using the developed methodology is presented. Segment testing of plug weld to ascertain the reeling defect growth is also described in case study.
Experimental Strain Field Assessment of Pressure Armor Profiles Subjected to Compression Loads via Digital Image Correlation
Authors: Santos Caio C. P. , Pesce Celso P. , Savioli Rafael G. , Burgos Diego S. , Carneiro Campello George , Brun Coser Thiago , de Souza Rodolfo F.
Published: October 2022

The pressure armor layer of a flexible pipe is designed mainly to resist radial loads. Despite the diversity of analytical and numerical studies, some absence of experimental results to evaluate the behavior of this reinforcement layer may be noted. One of the reasons for this lack of experimental studies is the difficulty in accessing and instrumenting this structural layer, particularly when internal contact strain fields are concerned. This study proposes a simple experiment to assess the strain fields of typical pressure armor wire profiles subjected to compressive loads. Using a DIC (Digital Image Correlation) system, the experimental campaign aims to map the strain distribution in a 2:1 scaled sample of a typical wire profile. This technique allows identifying maximum strain values in the cross-sections and more specifically in the contact regions between the pressure armor wires. The obtained experimental results are not yet conclusive. Nonetheless, they provide some interesting insights for a better understanding of the structural behavior of the pressure armor layer. Its findings are valuable for academia and the industry and could serve as a starting point to assess the complex problem of determining cross-sectional strains (and stresses) in pressure armors.
Experimental Investigation of Roughness Effect on Flow Field Around Cylinder in Steady Flow
Authors: Suzuki Masahiro , Ikoma Tomoki , Rheem Chang-Kyu , Aida Yasuhiro
Published: October 2022

In this paper, the velocity distribution around a rotating cylinder in a flow is investigated, and the effect of the roughness of the cylinder surface on the flow field is also investigated. As a research method, we measure the fluid force acting on a rotating cylinder and the flow velocity around the cylinder in a water tank experiment. The tank experiment was conducted under two conditions: in static fluid and in flow. In the flow, we measured both the speed-up side and the speed-down side due to the rotation of the cylinder. For the roughness of the cylinders, the roughness of the cylinder surface was changed by attaching water-resistant abrasive paper to the cylinder. Calculate mean flow velocity, Reynolds stress, and eddy kinematic viscosity from the measured flow velocity. In the case where only the cylinder is rotating in a stationary fluid, the effect of the cylinder surface roughness is strongly observed, the coarser the cylinder surface grain size, the stronger the velocity gradient in the circumferential mean flow velocity, and the overall Reynolds stress increases. In the flow, the effect of the cylinder surface roughness is small and the flow field does not change much.
Advanced Data Analytics Based Hybrid Engine-Propeller Combinator Diagram for Green Ship Operations
Authors: Perera Lokukaluge P. , Belibassakis Kostas , Filippas Evangelos , Premasiri Maneesha
Published: October 2022

Ship owners should comply with the forthcoming IMO legislations that mandates a reduction of ship emissions of at least 40% by 2030 compared with the 2008 baseline. However, it is unlikely that the shipping industry will be able to achieve its 2030 and 2050 emission reduction targets relying only on existing vessel technologies. Hence, the required green ship technologies that relate to industrial digitalization and AI applications should be utilized onboard vessels to achieve these emission reduction targets. This study proposes to analyze a hybrid engine-propeller combinator diagram from both theoretical calculations, i.e. from the vessel hull design, as well as data driven calculations, i.e. from ship performance and navigation data sets, to compare their performance in a single model framework. That would consist of various machine learning applications to create AI. It is expected that such combinations will support to understand the variations among system-model uncertainties in vessels and ship systems as a system of systems and that can also support industrial digitalization in shipping. Furthermore, the hybrid engine-propeller combinator diagram can be utilized to establish the basis for advanced data analytics that will be used to identify optimal vessel navigation and ship system operational conditions.
Time Series Prediction of the Trend of Hydrate Risk Using Principal Component Analysis and Deep Learning
Authors: Lee Nayoung , Kim Hyunho , Seo Yutaek
Published: October 2022

Hydrate risk strategy is a critical concern in offshore gas and oil production systems. Several empirical models were employed to predict the hydrate formation behaviors related to plugging risk. However, these empirical approaches have limitations in becoming universally used due to their dependency on geometries and fluid characteristics. Also, hydrate kinetic behaviors are statistical and nonlinear relationships on the dependent variables, which means it is difficult to develop the model to describe its behavior.

In this work, time series prediction using data-driven methods is applied rather than these model-based methods to analyze the kinetic experimental data during the hydrate formation. Deep learning models, specifically LSTM (Long Short-Term Memory) were used to be trained based on the lab-scale experiment data to make the real-time prediction. The transition trend of hydrate formation from homogenous to heterogeneous particles was predicted by using the model. The prediction was made on hydrate risk indicator, which is PCA (Principal Component Analysis) treated sensor data including pressure, temperature, relative torque, and others. The results suggested that the deep learning techniques incorporated with time series prediction could be a promising method for hydrate risk management.