bluuebunny/crossref_metadata_2025 huggingface dataset:
Three-Dimensional Physical Environment Modelling for Integrated Multi-Trophic Aquaculture (IMTA) Implementation in Onagawa Bay, Japan
Authors: Zhou Jinxin , Yoshida Takero , Zhang Junbo , Park Sanggyu , Kitazawa Daisuke
Published: November 2019

Continually increasing demands on aquaculture products drive the current monoculture to upgrade and upscale because of not only economic but environmental sustainability reasons. Over the past decade, open water integrated multi-trophic aquaculture (IMTA) practiced as a potential alternative has been demonstratively illustrated from both scientific and public attention. Basing on previous studies of this synergistic aquaculture system, we, here, studied the physical environment in Onagawa Bay as the cornerstone for further IMTA implementation. Onagawa Bay locates in Miyagi Prefecture, Japan, and because of its mature practice on polyculture, it is recognized as a suitable site for IMTA. Unfortunately, the earthquake and tsunami in 2011 caused a huge uncertainty on physical environment changes. Still insufficient researches have been conducted on physical environment study, especially through modelling method. Here, adopting the three-dimensional Marine Environmental Committee (MEC) ocean model, we described the setup and validation for Onagawa Bay in this research. At the present stage, simulation results can best fit observation data on the tidal elevation with the correlation coefficient between observed and simulated tidal elevation reaching 0.96, captured the main characteristic of flow velocity, and exhibited homogenous tendency towards water temperature. Furthermore, through the plot of the residual velocity field and statistical seasonal velocity distribution, potential aquaculture configuration has been discussed spatio-temporally on the hypothesis that high current speeds contribute to the further implementation.
A Simulation Program for Load-Out Operation Using Self-Propelled Modular Transporters
Authors: Du Zunfeng , Zhu Haiming , Xu Dong
Published: November 2019

Self-propelled modular transporters (SPMTs) are special vehicles designed for transporting massive objects. It is becoming popular to transport offshore structure modules onboard using SPMTs in recent years. The operation is a high-risk task which needs to be carefully planned. This paper aimed at developing a load-out simulation program that can be utilized to improve the existing planning method. To achieve this goal, the risks in load-outs were addressed, and an analysis procedure was established based on the principle of SPMT hydraulic system and ship hydrostatics. We built the simulation program on the basis of the analysis procedure. It enables users to practice load-out operations in a virtual environment. By using the program, engineers can obtain an overview of the load-out process and a clear knowledge of the risks that will arise. The load-out plan can be made, verified, and optimized beforehand, which is quite beneficial to minimize the risks and get well prepared for the operation.
New Spar Design for Floating Offshore Wind Turbine With Damping Plates
Authors: Ishida Shigesuke , Imai Yasutaka
Published: November 2019

Spar is one of the promising floating structures which support wind turbine at sea. In general, some lower part of spar is used as a ballast tank. It is possible to replace this part with other shapes without water-tightness because this part does not contribute to buoyancy nor stability to support the weight or heeling moment of wind turbine. In the field of oil and gas production, truss spar has been developed with this concept and the lower part consists of heave plates. However, for wind turbine, pitching motion is more important than heaving. The authors changed this part to four vertical damping plates to reduce this motion. The effect of the central gap and holes in the damping plates were investigated because these parameters have effects on flow separation and hydrodynamic forces. The motions in waves of the new spars were compared with a classic spar of the same dimensions and stability. The proposed vertical damping plates, with central gap or holes, work to reduce the pitching motion in wide range of wave frequency. Considering the expected cost reduction and some motion reduction, the promising nature of the proposed spar revealed.
Validation of Pack Ice Resistance in Oblique Condition by the Comparison With Ice Model Test Results
Authors: Kim HyunSoo , Ozden Erinc , Lee Jae-bin
Published: November 2019

Countries around the world are increasingly interested in resource development in the Arctic due to global warming. Recently, Arctic coastal states (Russia, USA, Canada, etc.) are pursuing infrastructure construction projects for resource development in the Arctic region. Because the offshore structures in the Arctic are exposed to the sea ice, in order to ensure the safety of the structures, the calculation of the ice resistance is of paramount importance for offshore structures. In general, studies on the ice resistance have been carried out for the breaking and clearing performance of icebreakers. However, in the case of fpu (floating production unit) for resource development in the Arctic region, it is necessary to estimate the ice resistance in the oblique condition to ensure safety. Thus, despite estimation of the ice resistance in the oblique condition is significant, there has not been enough research until recently. In this paper, we suggest algorithms for estimating the ice resistance in the oblique condition. For the estimation process, an in-house code software program is used and an ice resistance estimation module is implemented for the oblique condition using empirical formula. This paper shows results of the ice resistance which was calculated in the oblique condition, and the change of the ice resistance is shown according to various oblique angles in pack ice. In addition, the results are compared to the model test result of a fpu in pack ice of 80% concentration.
Mechanical Analysis of Fiber Glass Reinforced Bonded Flexible Pipe Under External Pressure
Authors: Zhang Xiaojie , Bai Yong , Liu Chang , Wang Zhao , Zhao Jiannan
Published: November 2019

Fiber glass reinforced bonded flexible pipe (FGRFP) is one kind of new type composite pipe. However, the mechanical properties of FGRFP are not so clearly at present. Therefore, this article aims at studying the buckling pressure of FGRFP under external pressure by using external pressure test, numerical method and finite element method. Three kinds of buckling pressure have been obtained by using three methods as aforesaid. According to compare the buckling pressure of three methods, the relative error of the numerical method and the finite element method relative to external pressure test ranges from 4.09% to 14.51%. According to the result of finite element method, the first layer’s stress at the topside of FGRFP’s cross section and the final layer’s stress at the horizontal position of FGRFP’s cross section is the max stress. The numerical method and finite element method came up with in this article can be used to analyze the buckling pressure of FGRFP. These methods can also provide a guidance to pipeline engineers to design and production of FGRFP.
Numerical Manoeuvrable Tank on Wave Based Moving Domain
Authors: Feng Dakui , Cai Xiao , Sun Yue , Zhang Zhiguo , Huang XiaoWei
Published: November 2019

The maneuvering motion simulation of ship in waves needs large space, the simulation based static domain requires a large amount of mesh. On the contrary, the moving domain can reduce the grid amount and improve the simulation speed. This paper studies the establishment of numerical wave tank based moving domain. The wave-generation method of defining inlet boundary conditions is proposed. The level set method is used to solve the free surface. The URANS equation is solved by finite difference method and the projection algorithm. For the wave-generation method of defining inlet boundary conditions, the velocity inlet direction is always fixed because the direction of incident wave is always fixed. Specifically, the yaw should be turned off avoid the disturbance of wave in the y direction. Comparing the simulated wave with the target wave, the numerical results show that the simulated value is coincident with the theoretical value in the moving domain, and there are no obvious signs of dissipation over time. The established moving domain can produce a continuous and qualified wave, which provides a theoretical basis for the study of maneuvering simulation of ship in waves.
Numerical Investigation of an Optimised Horizontal Axis Tidal Stream Turbine
Authors: El Sheshtawy Hassan , el Moctar Ould , Schellin Thomas E. , Natarajan Satish
Published: November 2019

A tidal stream turbine was designed using one of the optimised hydrofoils, whose lift-to-drag ratio at an angle of attack of 5.2 degrees was 4.5% higher than that of the reference hydrofoil. The incompressible Reynolds-averaged Navier Stokes equations in steady state were solved using k-ω (SST) turbulence model for the reference and optimised tidal stream turbines. The discretisation errors and the effect of different y+ values on the solution were analysed. Thrust and power coefficients of the modelled reference turbine were validated against experimental measurements. Output power and thrust of the reference and the optimised tidal turbines were compared. For a tip speed ratio of 3.0, the output power of the optimised tidal turbine was 8.27% higher than that of the reference turbine of the same thrust.
Effect of Spectrum Tail Length on Modulational Instability and Freak Wave Occurrence in JONSWAP Sea States
Authors: Kirezci Cagil , Babanin Alexander V.
Published: November 2019

In this study, probability of freak wave occurrence due to modulational instability in JONSWAP sea states are investigated. This investigation has been conducted based on the quantitative indicators of instability in wave spectrum, which are two Benjamin-Feir index (BFI) [1,2] with different spectral bandwidth definitions and Π number [3]. Evolution of wave field are simulated using fully nonlinear phase-resolving Chalikov-Sheinin (CS) numerical model [4,5]. Initial sea surface is controlled with JONSWAP shape parameters (α and γ) and random initial phases. Effect of high frequency end of spectrum on modulational instability and freak wave evolution are discussed by considering 4 different tail lengths.

According to simulation results, all parameters that are considered here perform as an indicator for the occurrence of extreme events which makes it possible to define a certain interval for indicators, where freak wave occurrence probability is the highest and potentially dangerous, to be possibly used in extreme wave forecasting. Another key finding is that, modulational instability increases when high frequency part of spectrum is present (longer tail) as expected. Nevertheless, after certain nonlinearity, modulational instability is more prone to result in breaking which significantly decreases the probability of occurrence of freak events. Therefore, spectra with shorter tail length result in more dangerous sea states.
Vortex-Induced-Vibration of Jack-Ups With Cylindrical Legs in Regular Waves
Authors: Ramadasan Sudheesh , Tao Longbin , Dev Arun Kr
Published: November 2019

A simple mathematical model is developed based on the single-degree-of-freedom analogy and principle of conservation of energy evaluating various modes of Vortex-Induced-Vibration (VIV) of a jack-up with cylindrical legs in regular waves. Similar to uniform current, mass ratio, damping ratio and mode factor are found to be the important parameters controlling the cross-flow VIV and radius of gyration also for the yaw VIV. Criteria for the initiation of the mentioned VIV modes are developed for the cases of a single 2D cylinder experiencing planar oscillatory flow, four rigidly coupled 2D cylinders in rectangular configuration experiencing planar oscillatory flow and jack-up experiencing regular waves. The newly developed VIV model is validated by a set of experiments conducted in a wind, wave and current flume. The importance of mass damping parameter is further demonstrated in suppressing VIV in regular waves. The mathematical method will equip engineers to consider the effect of VIV due to regular waves in jack-up designs.
Implementation of Tidal Stream Turbines and Tidal Barrage Structures in DG-SWEM
Authors: Schnabl Andrea M. , Moreira Tulio Marcondes , Wood Dylan , Kubatko Ethan J. , Houlsby Guy T. , McAdam Ross A. , Adcock Thomas A. A.
Published: November 2019

There are two approaches to extracting power from tides — either turbines are placed in areas of strong flows or turbines are placed in barrages enabling the two sides of the barrage to be closed off and a head to build up across the barrage. Both of these energy extraction approaches will have a significant back effect on the flow, and it is vital that this is correctly modelled in any numerical simulation of tidal hydrodynamics. This paper presents the inclusion of both tidal stream turbines and tidal barrages in the depth-averaged shallow water equation model DG-SWEM. We represent the head loss due to tidal stream turbines as a line discontinuity — thus we consider the turbines, and the energy lost in local wake-mixing behind the turbines, to be a sub-grid scale processes. Our code allows the inclusion of turbine power and thrust coefficients which are dependent on Froude number, turbine blockage, and velocity, but can be obtained from analytical or numerical models as well as experimental data. The barrage model modifies the existing culvert model within the code, replacing the original cross-barrier pipe equations. At the location of this boundary, velocities through sluice gates are calculated according to the orifice equation. For simulating the turbines, a Hill Chart for low head bulb turbines provided by Andritz Hydro is used.

We demonstrate the implementations on both idealised geometries where it is straightforward to compare against other models and numerical simulations of real candidate sites for tidal energy in Malaysia and the Bristol Channel.
3D Printing Miniature Marine Structures Models for Structural Analysis Purpose: Is it Possible?
Authors: Calle Gonzales Miguel Angel , Kujala Pentti
Published: November 2019

In the last few years, additive manufacture techniques — also known as 3d printing — are gaining more applications in the maritime sector including the production of functional large ship components in compliance with demanded operational and quality standards. By contrast, 3d printing miniature models of marine structures with the aim to reproduce structural responses brings along a higher degree of complexity. On the one hand, miniature thin-walled structures entails different manufacturing challenges when compared with large-size ship components. On the other hand, modeling structural events that comprise extreme reduction scales (around 1:100), material deformation and fracture at high loading rates, among other aspects, require purpose-designed scaling laws to handle all these effects adequately. The aim of this work is to present a wide panorama in the development of miniature 3d printed marine structures aiming to model experimentally ship collision and grounding events in reduced scale. Some preliminary experimental tests in miniature marine structures are also presented.
On the Selection of an Appropriate Consolidation Coefficient for Offshore Geotechnical Design
Authors: White David , Chen Jinbo , Gourvenec Susan , O’Loughlin Conleth
Published: November 2019

This paper addresses the selection of an appropriate consolidation coefficient for the analysis of drainage beneath foundations and pipelines in offshore geotechnical design. An emerging trend in the design of subsea infrastructure is the consideration of ‘whole life’ effects — namely the changes in soil properties and geotechnical capacity over the operating life.

Seabed pipelines that undergo repeated thermal expansion and contraction cause shearing and consolidation in the underlying soil, leading to significant changes in the available seabed friction. Also, foundations that are either fixed or designed to slide on the seabed, are subjected to intermittent loads interspersed with periods of consolidation. These also cause a change in seabed strength and geotechnical capacity.

To assess the time over which these effects occur, and therefore their influence on the response and the reliability of the system, it is necessary to perform consolidation calculations, using an appropriate consolidation coefficient. This paper presents observed operative consolidation coefficients drawn from recent model testing measurements and numerical analyses. It is shown that the consolidation rate can vary by more than an order of magnitude for the same soil profile under different loading conditions, due to the differences in stiffness and permeability. Meanwhile, design parameters are commonly drawn from one-dimensional oedometer compression tests.

This compendium of data highlights the potential variation in consolidation coefficient for different loading types and through the ‘whole life’ of infrastructure. A key conclusion is that consolidation effects generally occur faster than is commonly assumed, meaning that changes in strength and stiffness — that are commonly beneficial in design — may be more readily relied on than is done so in current practice.
Life Extension of Deepwater Risers Used for a Spar Application in Gulf of Mexico
Authors: Cheng Yongming , Yu Chenteh Alan , Yang Guangqiang , Carballo Manuel R.
Published: November 2019

Deepwater development in Gulf of Mexico (GoM) started about two decades ago. It is the time to evaluate the global integrity of the offshore production unit and riser system and explore the possibility of life extension. This paper investigates life extension of deepwater risers used for a spar application in GoM.

A spar in GoM has been put into service for the past 17 years since it was installed in 2000. It was expected to extend the riser design life of 20 years by 10 more years. This paper first introduces the configuration of Steel Catenary Risers (SCRs) and Top Tensioned Risers (TTRs) used for the Spar platform. It then discusses the philosophy for life extension of deepwater risers by assessing the integrity of the riser system. Latest technology and monitored data are used for the assessment.

The TTRs and SCRs are modelled using latest analysis programs that were not readily available when the risers were designed. The interaction between the TTR and buoyancy can tensioning system is modelled as a pipe-in-pipe system that considers the function of centralizers with a gap size. The contact interaction between buoyancy can / stem and supporting guides of the hull platform is modelled as non-linear spring elements. The spring elements connect normally to the hull centerline and allow vertical sliding movement of the buoyancy can tension / stem system with friction. The base line inspections of the vessel, SCRs, and TTRs was carried out in the same inspection campaign with the spar hull structure. As-built information, production and operational data was also used for a continuous service assessment. Environmental condition data to the state of the art, including measured spar VIM data, was used in the assessment of VIM fatigue damage to the risers. The investigation was based on the up-to-date analytical tools including latest FEA program ABAQUS and VIV prediction Shear7. It further computes the riser global performance including dynamic strength and fatigue damage with the contributions from wave fatigue, VIV and VIM. This paper finally draws a conclusion for the life extension of the risers for the application in GoM.
Explosion Response of Cold Bond Corrosion Repairs Applied to Offshore Living Quarters
Authors: Turner Trey N. , Kumar Abhimanyu
Published: November 2019

Maintaining the integrity of an aging offshore facility often requires the repair of corrosion. With advances in adhesive technology, epoxy adhesives (cold bond repairs) are increasingly being adopted to repair corrosion damage on offshore structures. Structural elements, protection barriers, and occupied buildings, for example a platform living quarters, designated as safety critical often must comply with project or facility performance standards that specify minimum design accidental loading (e.g., from fire, explosions, or impact). In addition to satisfying conventional structural design criteria, a corrosion repaired structure must also perform within acceptable limits when subjected to accidental loads. The present study outlines approaches to assess the performance of cold bond repairs subjected to accidental explosion loads. The living quarters considered in this study featured approximately 50 individual cold bond repairs; each arbitrarily located over the building’s external surfaces. Under accidental blast conditions, failure of a cold bond repair was deemed unacceptable due to the threat of pressure leakage into the building’s interior. As such, the study demanded an analysis capable of considering both the global response of the living quarters as well as the local response of cold bond repairs. There have been several studies conducted by researchers around the globe to evaluate the response characteristics of adhesive bonds. However, these studies are largely focused on experimental, local, and micromechanical analysis of adhesively bonded materials. Numerical analysis of adhesive bonds, for purposes of global structural system response assessments, especially in the case of accidental loading, appear to be nonexistent in available literature. Inspired by this gap, we present a case study involving an assessment of global structural performance of a living quarters building repaired with cold bond adhesives subject to loading due to accidental and rare events. In this study, the local behavior of cold bond adhesives was calibrated using numerical simulations of the ASTM tests specified by the adhesive vendor. The calibrated properties were implemented in finite element analyses used to validate cold bond seal plate repairs at various locations on the living quarters building. The study includes a discussion about the methods and approaches used to model cold bond repairs in a practical and efficient manner. The approach outlined herein provides a useful framework that can be adapted to similar assessments by a practicing engineer responsible for blast analysis of marine structures.
Control Strategy for a Point-Absorber Wave Energy Converter
Authors: Li Qiao , Murai Motohiko
Published: November 2019

Linear driving wave energy converter (WEC) system need to control the electric generator to obtain more power generation. Electric power is consumed by control, but it is possible to control the natural period of the floating motion. By resonating the movement of the float part with wave, it is possible to obtain the power generation more than the control power consumption, the total power generation performance will be improved.

In this study, to ensure the WEC safety and performance for various wave condition, especially high wave height, the electrical control algorithms are changed for different wave condition. A control strategy is proposed for various wave condition considering the control force limitation and motion amplitude limitation. Basis on the control strategy, the range of operation by electric control is estimated. In addition, by estimating the expected value of power generation in the set sea, the setting parameters of the WEC can be discussed according to the wave situation.
Experimental Study on the Mechanics of a Coiled Tubing Working Within a Marine Riser Under the Affection of Marine Loads
Authors: Chen Yingchun , Wang Chang , Wang Xinhua , Wang Wenming , Wang Wenda
Published: November 2019

Due to its unique advantages, coiled tubing is now widely used in marine oil and gas exploitation operations, while the mechanical behavior of coiled tubing working within a marine riser affected by marine loads is still unknown. By building an indoor simulation experimental system, the mechanics of this pipe-in-pipe system was studied, and the effect of the lateral excitation on the axial force transmission of inner pipe was clarified. It was found that, when the external excitation frequency was within the first natural frequency range of the outer pipe, the external excitation would increase the axial load transfer efficiency of the inner pipe, and the axial force transfer efficiency of the inner tube would reach the maximum when the resonance of out pipe occurred. The results can be helpful on the understanding of mechanics of a coiled tubing working within a marine riser.
Material Design of Offshore Linepipe Steels for Ultra Deep Water Application
Authors: Yasuda Kyono , Shimamura Junji , Igi Satoshi , Muraoka Ryuji
Published: November 2019

Offshore pipeline projects have been expanded to deeper water region and the linepipes are required to have higher resistance against collapse by external pressure. The collapse resistance is mainly dominated by pipe geometry and compressive yield strength. For deep water application, diameter to thickness ratio (D/t) and pipe roundness are key factors. On the other hand, the mechanical properties in each circumferential position is dramatically changed by cyclic deformation through a pipe forming process. Therefore, in order to improve compressive yield strength of pipes, it is important to consider the Bauschinger effect caused by pipe expansion. The mechanism of this effect is understood that internal stress is generated by accumulation of dislocation and it reduces reverse flow stress. In this study, the microscopic deformation behavior was analyzed from FEM calculation, it was found that multi-phases microstructure enhanced the microscopic heterogeneous deformation adjacent to the boundary between soft and hard phases. Therefore, homogenized microstructure inhibits the Bauschinger effect. In addition, the materials of offshore pipeline should have other properties such as low temperature toughness and sour resistance. It is well known that fine grained microstructure improves the lower temperature toughness. For achieving high compressive yield strength and good lower temperature toughness, the effect of chemistry and rolling condition were investigated to obtain fine and homogeneous microstructure. Based on laboratory results, mill trial tests were carried out for Grade X65 linepipes with heavy gauge by TMCP. Full scale collapse test was also conducted after pipe coating heating. In this paper, material design concept and its mechanical properties of developed pipes were introduced.
Numerical Analysis of Tidal Turbine Performance for Floating Platform
Authors: Xing Xiuqing , Kang Chang Wei , Xu George , Lou Jing , Takagi Ken , Sinclair Jarrod
Published: November 2019

A three dimensional Computational Fluid Dynamics (CFD) model solving Reynolds-averaged Navier-Stokes (RANS) equations with k-ε turbulence model has been developed based on OpenFoam to investigate a tidal turbine performance. The CFD model is validated by comparing the simulation results with the performance characteristic data. Simulation results match the measured data with discrepancies less than 5.4%. The well validated model is then adopted to predict the turbine performance with a current heading angle of 30 degree. The simulated turbine power coefficient and flow field details from OpenFoam are compared with those obtained from commercial software ANSYS FLUENT for verification. The two simulated results match each other with a difference of only 3%. Simulated results indicate that the turbine power output drops significantly when the tidal turbine operates with a current heading angle of 30 degree. The performance loss due to a misalignment between the current and the turbine axis is analyzed with the aim to identify main causes and provide recommendations to tidal turbine operation.
Experimental Study of Wave Loading by Internal Solitary Waves on a Semi-Submersible Platform
Authors: Zhang Jingjing , Chen Ke , You Yunxiang , Zhang Xinshu
Published: November 2019

The experimental measurements presented here describe the major features of the loads exerted by internal solitary waves (ISWs) on columns and caissons of a semi-submersible platform in a two-layer fluid system. Particular attention is paid on the forces acted on the platform under different layer thickness ratio. By use of the dynamometer for forces of three degree of freedom (DOF), the wave forces exerted by the ISWs on the columns and caissons of the model are measured quantificationally, so the variations of forces with ISW’s amplitude and upper layer depth are derived. Comparisons are made between the experimental results and calculations based on the modified Morison equation and pressure integral method. The calculated results are well consistent with the measurements, so the method is capable of providing satisfactory predictions on the forces. Besides, the results show that the wave height has a considerable influence on the wave loads produced by the ISWs, and the forces varies with the different locations of the interface between the upper and lower layer.
CFD Study of Propeller Cavitation With Hull-Propeller Interaction
Authors: Kang Chang Wei , Xing Xiuqing
Published: November 2019

Propeller cavitation is the root cause for noise, hull vibration, as well as erosion on the propeller blades and appendages. Although it is a common practice for marine industry to predict the propeller cavitation by model tests, numerical simulation of propeller performance and the hull-propeller interaction has become feasible with the advancement of high performance computing. In this study, numerical studies of the flow field details around the ship hull with a rotating propeller are performed using Computational Fluid Dynamics (CFD) method by solving the unsteady Reynolds Averaged Navier-Stokes (RANS) equations. The numerical model is developed with commercial software package STAR-CCM+ for the cavitation prediction by considering the hull/propeller interactions and the free surface. Rotating propeller is modeled with an overset mesh, while κ-ω turbulence model is chosen instead of large eddy simulation (LES) or detached eddy simulation (DES) for higher computational efficiency while maintaining satisfied simulation accuracy. Cavitation bubble growth and collapse are estimated using Schnerr-Sauer cavitation model based on Rayleigh-Plesset equation. Simulation results suggest that the model developed in this study is capable to capture the flow field details under the effect of hull-propeller interactions and the free surface. This includes the cavitation emerging position, extinction position, as well as the cavitation patterns on the blade surface at various angular positions. The cavitation induced pressure oscillations on the hull at 1st to 3rd harmonics of Blade Passing Frequency (BPF) are also analyzed. The pressure fluctuation result can provide pressure load information for hull vibration evaluations in future.
Fatigue Evaluation of Drill Pipes for Scientific Drilling Program by Applying Non-Stop Driller Concept
Authors: Inoue Tomoya , Fujikubo Masahiko , Nakano Kenji , Sakurai Noriaki
Published: November 2019

The scientific drilling vessel Chikyu is performing Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), a challenging deep drilling activity, for scientific purpose. We faced difficulty to drill deep during past NanTroSEIZE operations due to unstable sediments and insufficient cutting removal. Non-Stop Driller concept is, therefore, applied for the operation of NanTroSEIZE scheduled to start Oct. 2018 to enable continuous circulation of drilling fluid circulation. The Non-Stop Driller concept requires an additional, specially-designed sub called an “NSD sub” with a ball valve for drilling fluid inlet.

Generally, the fatigue strength of a drill pipe is a critical factor governing the performance of challenging deep drilling. This study, therefore, focused on the fatigue failure of the NSD sub due to the bending stress caused by interference with risers including flex joints, ship structure, or drilling equipment resulting from ship motions. The bending stress leads to cyclic stress caused by rotation of the drill pipe. This is especially the case at the Nankai Trough where ocean currents are very strong reaching or sometimes exceeding 4 knots, a high bending stress is assumed to be exerted on the NSD sub.

Full-scale fatigue tests of the NSD sub were first conducted to acquire the actual fatigue curve. Further, the bending stress distribution of a drill pipe, which refers to the locus of the bending stress during the drilling operation, was analyzed by considering interference of the drill string with the structure, drilling equipment, and risers that are deformed by the ocean current.

Time-series ship motions is prepared using the response amplitude operators of the Chikyu for the sea states at Nankai Trough area, and then time-series stress response is obtained by considering the operational conditions such as rate of penetration and rotational velocity of drill pipe. The numbers of occurrence of each stress amplitude can be counted from the time-series stress response. Consequently, the cumulative damage ratio is calculated for evaluating the fatigue of the NSD sub. The results confirmed that the cumulative fatigue is within a safe range.

This study focused on the evaluation of the fatigue strength of the specially designed NSD sub for the challenging scientific drilling operation at Nankai Trough, a harsh environment because of the presence of strong ocean currents. This paper presents the overview of NanTroSEIZE including the Non-Stop Driller concept, and the results of fatigue evaluations.
An Experimental Apparatus for Investigating the Unsteady Aerodynamics of a Floating Wind Turbine
Authors: Wen Binrong , Zhang Qi , Liu Haoxue , Tian Xinliang , Dong Xingjian , Peng Zhike , Zhao Yongsheng , Kou Yufeng
Published: November 2019

In our prior investigations, extensive numerical simulations have been conducted to reveal the unsteady aerodynamics of Floating Wind Turbine (FWT). To validate the simulation results and further deepen the corresponding topics, a dedicated experimental apparatus has been developed by the State Key Laboratory of Mechanical System and Vibration (SKL-MSV) and State Key Laboratory of Ocean Engineering (SKL-OE) at Shanghai Jiao Tong University (SJTU). The main modules of the test bed include a dedicated Wind Generation System (WGS), a Model Wind Turbine (MWT), a 6-DOF (Degree Of Freedom) Motion Control Platform (MCP) and an integrated measurement system. The WGS is able to generate controlled flows with different wind speeds, turbulence intensities, and horizontal/ vertical wind shears. The MWT is equipped with Fiber Bragg Grating (FBG) sensors on the blade surface to monitor the operating conditions. The MCP is developed to generate controlled oscillations to the MWT aiming to model the oscillation of the FWT in offshore environments. The measurement system includes a torque sensor, two 6-DOF load cells, a 3-DOF accelerator, 2 FBG-fibers each with 3 FBG sensors, and a Wake Detection System (WDS) consisting of 6 hot-wire probes. Extensive calibrations are conducted for the WGS and the transducers. Some primary results about the unsteady aerodynamics of the FWT are presented. In the future, the MCP will be replaced by a floating platform to conduct the tests in the wave tank at SKL-OE to reveal the fully coupled dynamics of FWTs.
An AIS-Based Multiple Trajectory Prediction Approach for Collision Avoidance in Future Vessels
Authors: Murray Brian , Perera Lokukaluge P.
Published: November 2019

This study presents a method to predict the future trajectory of a target vessel using historical AIS data. The purpose of such a prediction is to aid in collision avoidance in future vessels. The method presented in this study extracts all trajectories present in an initial cluster centered about a vessel position. Features for each trajectory are then generated using Principle Component Analysis and used in clustering via unsupervised Gaussian mixture modeling. Each resultant cluster represents a possible future route the vessel may follow. A trajectory prediction is then conducted with respect to each cluster of trajectories discovered. This results in a prediction of multiple possible trajectories. The results indicate that the algorithm is effective in clustering the trajectories, where at least one cluster corresponds to the true trajectory of the vessel. The resultant predicted trajectories are also found to be reasonably accurate.
Development of Wireless Control System With Underwater Fish-Eye Camera to Monitor Fish at the Test Site of Marine Renewable Energy
Authors: Yoshida Takero , Mizukami Yoichi , Zhou Jinxin , Kitazawa Daisuke
Published: November 2019

Environmental impact assessment is important when marine renewable energy device is installed. Fishermen concern the effect of device on local fish. To confirm the effect before and after installation of marine renewable energy device, we developed wireless monitoring system using an underwater fish eye camera. The camera system is composed of a dome-shaped fish eye lens, a container, and a float. Two thrusters are attached on the container to change the monitoring directions. In the current research, this system was developed to monitor underwater situation around device remotely and in real time. We tested to monitor a target and fish in a fish case at the site off Kamaishi city. The recorded video showed the target and fish. Effectiveness of this system was shown through the field test for real time monitoring around marine renewable energy device.
A New Approach for Environmental Contour and Multivariate De-Clustering
Authors: Derbanne Quentin , de Hauteclocque Guillaume
Published: November 2019

When the long term behaviour of a floating unit is assessed, the environmental contour concept is often applied together with IFORM (Inverse First Order Reliability Method). This approach avoids direct computation on all sea-states, which is computationally very demanding, and most often simply not feasible. Instead, only a few conditions (the contour) are assessed and results in an accurate estimate of the long term extreme. However, most of available methods to derive the contour require the knowledge of the joint distribution of the different random variables (waves, wind, current...), which is often difficult to derive accurately. In fact, some complex dependences exist and are attempted to be simplified in too few coefficients. Another limitation of current environmental contour is its difficulty to deal with the dependence issue. Indeed, extreme sea-states arise by groups (storms, hurricanes...) and are not independent. While de-clustering techniques exist and are quite straightforward in univariate problems, this becomes difficult when the number of dimension increases.

In an attempt to tackle those challenges, this paper presents a novel approach to derive IFORM contours. The method does not require any joint distribution and makes use of much more degrees of freedom to capture the dependence between variables. It also allows for an easy de-clustering. The approach is illustrated on two locations, using actual hindcast data of significant wave height and period; the resulting contours are compared to the ones obtained with more traditional methods.
Influence of Microstructural Variation in Thick Section Steels on the Characterisation of Fracture Toughness Using Sub-Size Specimens
Authors: Moore Philippa , Yordanova Borislava , Lu Yong , Janin Yin Jin
Published: November 2019

The challenges of performing full-thickness fracture toughness tests on steel plates of 100mm thickness and greater means that the use of sub-size specimens is desirable. In this work, 100mm thick parent plate of S690 high strength steel was characterised using SENB fracture toughness specimens with thickness of 12mm, 25mm, 50mm and 100mm. Sub-size specimens were extracted at two different locations through the plate thickness; mid-wall and quarter wall. Sufficient specimens were tested to apply the Master Curve method in ASTM E1921 to predict the behaviour of 100mm thick material from each set of sub-size specimens. The through-thickness microstructural variation in these heavy-wall steel plates meant that significantly different predictions of full-thickness fracture toughness were obtained from the two sampling locations. However, when sampled from the mid-wall location, sub-size specimens down to 25mm thick were able to conservatively predict full-thickness fracture toughness using Master Curve methods.
An Actuator Disc Analysis of a Ducted High-Solidity Tidal Turbine in Yawed Flow
Authors: Borg Mitchell G. , Xiao Qing , Incecik Atilla , Allsop Steven , Peyrard Christophe
Published: November 2019

This work elaborates a computational fluid dynamic model utilised in the investigation of the hydrodynamic performance concerning a ducted high-solidity tidal turbine in yawed inlet flows. Analysing the performance at distinct bearing angles with the axis of the turbine, increases in torque and mechanical rotational power were acknowledged to be induced within a limited angular range at distinct tip-speed ratio values. Through multiple yaw iterations, the peak attainment was found to fall between bearing angles of 15° and 30°, resulting in a maximum power increase of 3.22%, together with an extension of power development to higher tip-speed ratios. In confirmation, these outcomes were subsequently analysed by means of actuator disc theory, attaining a distinguishable relationship with blade-integrated outcomes.
Assessment of the Reliability of the Moorings of a Floating Structure Against the Extreme Cyclone Hazard
Authors: Manzocchi Mark , Kejriwal Vikas , Hoo Eric
Published: November 2019

This paper describes the methodology adopted for an analysis performed to assess the reliability of the moorings of a free weathervaning FPSO against the cyclone hazard. A joint distribution characterizing the long-term cyclone metocean conditions was fitted to a database of environmental conditions at the site of interest. A series of archetype cyclone histories were selected from the cyclone database to capture the evolving relationships between key environmental parameters during a cyclone. A response-surface model for extreme tension in the vessel moorings was developed for the short-term extreme vessel response as a function of environmental conditions by fitting the surface to an extensive series of time-domain vessel response analyses. The reliability of the mooring system was evaluated using Monte Carlo simulation by sampling from the fitted joint distribution of long-term cyclone characteristic and generating simulated cyclone time histories by scaling the archetype cyclones. The response model for short-term exceedance probability is used to develop the probability of exceedance within each simulated cyclone, and the probability of exceeding a given response is derived from the simulation.
Assessment of Latching Control for the Hemispheric Heaving Buoy Type Point Absorber With and Without Nonlinear Froude-Krylov Force Acting on the Buoy
Authors: Kim Sung-Jae , Koo Weoncheol , Jo Chul H.
Published: November 2019

In this study, a latching control strategy was utilized to increase the efficiency of a heaving buoy-type point absorber with a hydraulic Power take-off (PTO) system. For this purpose, the hydrodynamic performance of a floating buoy was analyzed based on the potential flow theory and Cummins equation. Nonlinear Froude-Krylov (FK) force according to instantaneous wetted surface of a buoy was calculated by a theoretical solution. The effect of the latching control on a point absorber was evaluated by considering PTO performance with hydrodynamic coefficients including nonlinear FK force. The hydraulic PTO system was modeled as an approximate coulomb damping force.
Optimal Control for Response Reduction of Single Hinged Articulated Tower Using MR-Damper
Authors: Solomon Kushal , Kumar Deepak
Published: November 2019

Articulated tower is a compliant offshore structure deployed in deep waters for oil and gas exploration. The base of the tower is connected to the sea bed through universal joint, which allows the tower to rotate about horizontal axis (pitch). Articulated towers attain stability due to large buoyancy forces acting on it. Under extreme wave loads, the response of ALP can exceed the design limit causing discomfort to the occupants and create unfavourable working conditions. Structural control systems can be implemented in order to reduce the response of ALP, thereby protecting the structure from damages and to increase its life span. In this paper, a semi-active optimal control strategy using Magneto-Rheological damper is adopted to reduce the responses of ALP. Bouc-Wen model is used to describe the force generated by MR-Damper. For achieving the optimal performance of the control system, the applied voltage is varied according to the measured feedback at any moment to change the damping force using linear quadratic regulator technique. Several parametric studies have been conducted and the performance of the controller is evaluated. It is observed that the response of ALP is reduced considerably by using MR-damper as a semi-active control device. However, the capacity of the damper required for achieving the desired control is huge.
Decisional Criteria for Off-Shore Operations Interruption due to Adverse Weather
Authors: Drago Michele , Vitali Luigino , Del Guzzo Andrea , Gaggiotti Federico
Published: November 2019

Off-shore operations and installations can be occasionally delayed or interrupted due to the arrival of severe metocean conditions which could put human safety or structural integrity of the work at risk. In particular, the motion and loads induced by wind, waves and current on the vessel and on the installing structure could exceed the allowable limit for a safe and correct installation.

Whatever the operation that is being carried out, it is necessary to have a favorable window with a duration longer than the time necessary to complete the job or to interrupt the operation in order to carry out the work safely, e.g. pipe abandonment for pipe laying.

Predicting when these windows will occur is not an easy task and the decision-making process shall be correctly managed by a reliable balance between safety, first of all, and efficiency, to not unduly increase time and the cost of operations. These two aspects, safety and efficiency, respectively, tend to cause unnecessary/anticipated interruptions to the work with consequent delays or to cause late interruptions of an operation with risks to assets integrity and/or human safety.

The available information for managing the decision-making process is the monitoring of the actual conditions, both weather and installation vessel motions, and the weather forecast bulletins. Valuable information can be found also in the metocean hindcasted time series, mainly wind and waves, nowadays available for any off-shore area which the oil&gas industry is interested in with a typical duration of 30 years, for the determination of the typical characteristics of the metocean conditions of the area of interest.

This paper presents a comparison between the performances of different criteria for interruptions of long duration operations based on monitoring and on forecast, proposing an improved method based on the combination of the two kinds of information. A preliminary analysis of the metocean conditions of the area based on hindcasted time series is considered as well.

It should be noted that the same principle can be adopted for short operations to be completed within favorable weather windows. In this case the time for completing the operation is equivalent to the time necessary to safely interrupt the operations.