bluuebunny/crossref_metadata_2025 huggingface dataset:
Experiments on Fluid Placement in a Confined Pipe: Fluid Mechanics Analysis for Plug and Abandonment Applications
Authors: Akbari Soheil , Taghavi Seyed Mohammad
Published: December 2020

Plug and abandonment (P&A) of oil and gas wells is an essential process to prevent the oil and gas reservoir fluids migration over time and possibly contaminating other formations and also fresh water resources. In order to plug and abandon a well, a high quality cement plug placement is required. One of the most common methods of cement plug placement is the dump bailing method. In this method, a fixed volume of cement is dumped using a bailer on a mechanical plug in the wellbore. The cement slurry occupies the wellbore and also the annular region outside the dump bailer. In the processes of cement slurry placement, an extensive range of Newtonian or non-Newtonian fluids is used to remove the in-situ fluid (drilling fluid or water) in the wellbore. Based on the large number of parameters such as the density and viscosity differences between the fluids, the geometry type (pipe, annulus, etc.), the operation conditions (velocity, geometry inclination, dumping height), various kinds of placement and mixing flows can occur, and different flow regimes (e.g. inertial, viscous) can develop. In this paper, we experimentally study the placement of a heavy fluid to replace an in-situ light fluid in an inclined closed-end pipe (representative of the dump bailing method). The two fluids are Newtonian and miscible, and they have the same viscosity. We investigate the effects of some of the flow parameters such as the dumping height, the pipe inclination, and the inflow velocity of the heavy fluid on the degree of mixing and the placement quality and efficiency. Our results show that the the most efficient displacement happens with the shortest dumping height and at lower inclination from vertical. Also, a high inflow velocity displaces the light fluid promptly with more mixing in comparison with a low inflow rate. The results can help us to develop strategies for improving the dump bailing method in the P&A of the oil and gas wells.
Performance Analysis of a Three-Axis Gyroscope Composite Anti-Rolling Device
Authors: Zhou Yuefa , Li Tao , Liu Zhiyuan , Zheng Kexin
Published: December 2020

In the ocean environment, the ship is prone to motions in six directions of roll, pitch, yaw, sway, surge, and heave under the influence of the waves. It will affect not only the airworthiness of the ship, but also have an adverse impact for the crew and the board’s equipment. In view of this situation, a new type of ship anti-rolling device has been proposed, which is based on the structural characteristics of the Stewart platform with precise adjustment of the position of the load platform and the stability of the gyroscope under the high-speed rotation of the rotor. Firstly, theoretical analysis of the device conducted with theorem of moment of momentum method shows that the device has practical feasibility and effectiveness. Then, a solid model has been established in Creo2.0 software, and the model has been imported into the dynamic analysis software MSC.ADAMS. Finally, using torque as the exciting force to simulate the impact of the wave, the dynamic simulation of the overall model has been analyzed. The simulation results show that such device has good anti-rolling performance under certain waves, indicating that the new anti-rolling device based on the Stewart platform and the three-axis gyroscope has effective reliability and practicability.
Numerical Study on the Resistance and Sinkage of Inland Vessels Passing Through Navigable Tunnel
Authors: Chen Xuehua , Wang Lizheng , Chen Shunhuai , Xiong Aokui
Published: December 2020

While passing through a navigable tunnel, a vessel usually undergoes a steady forward motion at low speed. Due to the limited size of the navigable tunnel, the restricted water conditions of small section-coefficient will have an adverse impact on vessel navigation safety. A bottom suction effect on vessels may occur for the risk of grounding and harming the maneuvering performance. Thus, it is particularly important to reveal the effect of the navigable tunnel scale on the vessel sinkage.

In this paper, a numerical model of the representative 1000-ton vessel of the Wujiang channel under construction is established. Numerical simulations of the vessel are conducted based on RANS equations in deep water, both in fixed condition and free condition (i.e. the trim and sinkage are allowed). And the validity of the method is verified by comparing the calculation results with the experimental ones. Subsequently, for diverse water depths, water widths and vessel speeds, the parameters such as the vessel resistance and sinkage are predicted and compared. The calculation results are analyzed to obtain the trend of vessel motion at different tunnel scales. In addition, the effect of the tunnel scale on vessel navigation performance is also investigated.
Numerical Simulation of Multi-Layer-Liquid Sloshing by Multiphase MPS-GPU Method
Authors: Wen Xiao , Chen Xiang , Wan Decheng
Published: December 2020

In this paper, a new multiphase MPS-GPU method is proposed through the combination of moving particle semi-implicit (MPS) method and Graphics Processing Unit (GPU) acceleration technique. The new method not only inherits the advantage of MPS method in capturing complex interface deformations, but also overcomes the limitations of huge computational cost in three-dimensional MPS simulation. By this method, both the two-layer-liquid and three-layer-liquids sloshing problems are simulated three-dimensionally on the GPU device, in which more than one million of particles are included. In simulations, the sloshing patterns of each liquid layer under different external excitations are accurately captured. From the interface elevations and impacting pressures calculated by present method, it is found that an obvious discrepancy exists between the deformations of free surface and phase interfaces. Then, the results obtained by multiphase MPS-GPU method are compared with experimental data and other numerical results in open literature and a good agreement is achieved, which validates the accuracy and applicability of the present method in three-dimensional simulations of multi-layer-liquid sloshing flows.
Study on the Architecture of a Zero Emission Hydrogen Fuel Cell Vessel Power Generating Unit
Authors: Balestra Lorenzo , Schjølberg Ingrid
Published: December 2020

This study focuses on providing design guidelines for a vessel’s power-plant in the multi-megawatt range, equipped with a hybrid fuel cell and battery system. Background information is provided on the challenges to realizing such a system, spanning from a literature review on studies looking into energy management, to the technical limitations of state-of-the-art fuel cells and batteries. The central part of the work consists of the description of the model used to calculate the size of the hybrid power generating unit, including a case study on a single, real-world scenario. The Plant Analysis Balance with Operational Profile (PABOP) model, developed by the author and presented in the paper, is used to calculate the resources needed to retrofit a vessel operating on fossil fuels with a hybrid zero-emission power-plant. The model aim is to achieve a 1:1 replacement for diesel-electric configurations, both in terms of range and power, using fuel cell and battery power. In the case study, the model is applied to analyze the operational data of a double-ended ferry operating with diesel-electric propulsion. Emphasis is put on the I/O needed and produced by the model, and how this tool can be used by shipyard engineers to estimate the footprint required, the necessary storage capacity, lifetime of components and other parameters. The presented solutions could help manufacturers estimate the economical viability of hydrogen vessels, filling a gap in current maritime fleets where zero-emission systems are gaining increasing importance.
A Stress Magnification Factor for Plates With Welding-Induced Curvatures
Authors: Mancini Federica , Remes Heikki , Romanoff Jani
Published: December 2020

The fatigue strength of thin-walled structures can be reduced significantly by non-linear secondary bending effects resulting from geometrical imperfections such as axial and angular misalignments. The welding-induced distortions can cause a critical increase of the structural hot-spot stress in the vicinity of the weld. Traditionally, the classification society rules for the fatigue strength assessment of welded ship structures suggest an analytical formula for a stress magnification factor km for axial and angular misalignment under axial loading condition. Recently, the well-known analytical solution for the angular misalignment has been extended to account for the curvature effect. The present paper analyses the effect of non-ideal, intermediate boundary conditions between fixed and pinned ends. In this regard, the fixity factors ρ (with 0 ≤ ρ ≤ 1 from ideally pinned to clamped conditions) are introduced in order to model the actual constraint on the rotation close to the ends. Under tension, a non-negligible decrease of the km factor is observed in relation to the reduction of the fixity factor at the welded end, while the fixity factor related to the loaded end has a minor effect on the km factor. Under compression, the reduction of the beam end fixity factors results into lower buckling resistance.
Feasibility Study of Lateral Buckling Using Residual Curvature Method for Deep Water Pipelines
Authors: Bai Qiang , Xu Fengbin , Brunner Mark
Published: December 2020

In recent years the residual curvature (RC) method has been used to provide buckle initiators to control and mitigate the lateral buckling of pipelines for some shallow water projects. With the appropriate planning of the controlled buckles using RC sections, an acceptable design of the pipeline in-place behavior is achieved. However, the RC method has not yet been applied to deep-water pipelines. The twist of RC sections in the sagbend during installation has been observed, and the orientation of as-laid RC section on the seabed is difficult to control in deep-water pipelines. The effects of as-laid RC-section orientation on in-place lateral buckling in deep water are unknown.

The FRIC user subroutine in the Abaqus finite-element software suite has been developed for modelling pipe-soil interactions based on uncoupled axial and lateral soil resistances that are assumed to be independent of vertical pipe penetration after initial embedment into the soil surface. However, the penetration of a twisted RC section can vary dramatically from a normal pipeline on the seabed. The UINTER user subroutine in Abaqus was selected for presenting 3D pipe-soil interactions that incorporate the variations of independent axial and lateral soil resistances as a function of pipe penetration more accurately. UINTER is used in the present study to account for the effects of soil penetration on the lateral buckling performance of a pipeline with RC sections in soft clay.

The analysis results show that the RC section twists in the sagbend area during installation, and the twist angle reaches its maximum value just prior to the RC section touching the seabed. The in-place lateral buckling analysis is carried out after the installation analysis is finished. The analysis results demonstrate the feasibility of applying the RC method as the primary buckle triggering mechanism for deep water pipelines, and it shows how the RC orientation affects the pipeline in-place performance in terms of strength and fatigue damage (only the stress ranges for use in fatigue calculations are shown in the paper).
Nonlinear Dynamic and Bilinear Fatigue Performance of Composite Marine Risers in Deep Offshore Fields
Authors: Khan Rizwan A. , Ahmad Suhail
Published: December 2020

Composite materials have drawn considerable consideration from the offshore business, basically because of their high explicit quality. Notwithstanding weight decrease, composites offer extra advantages, for example, fatigue resistance, damping, and thermal (protection) properties, and high erosion resistance. As a part of design procedure there are requirements of mechanical strength based on criteria referring to failure modes, such as rupture by over loading, fatigue failures, buckling or an unstable fracture. Three dimensional nonlinear assessment of riser is carried out in time domain using ABAQUS/Aqua. The response time histories so obtained are used for the study of fatigue safety assessment of riser. It is based on a bi-linear approach to model fatigue crack growth and incorporates a failure limit to describe the interaction between rupture and plastic failure. Using Monte Carlo Simulation, tests of fatigue reliability and fatigue crack size evolution are obtained. It is observed that bilinear S-N curve and crack growth models leads to higher estimate of fatigue life. Sensitivity behavior pertinent to limit state adopted has been thoroughly examined. These outcomes implicate assessment of components of the marine structures to ensure minimization of the surprises due to wide scatter of the fatigue phenomenon in marine environment.
Influence of Ice Floe Shape and Distribution on Ship Resistance
Authors: Cahay Marc , Fabiano de Lima Gabriel
Published: December 2020

Many ice basin tests have been performed on ships to assess the ice resistance of the hull in an ice floe field. During these tests, many parameters are studied, the most important of them being the transit speed, the thickness and the concentration of ice. Given the cost and the time required to carry out these basin test campaigns, it is imperative to keep the number of tests to the strict minimum, whilst still making it possible to draw conclusions about the sizing of the vessel. Hence, the influence of ice floe shape and their distribution in the field are generally not considered.

A way to achieve sensitivity studies regarding these parameters is to use numerical simulations in addition to a basin test. There are few advanced numerical design tools available in the market, especially those able to cope with any kind of structure geometry and a large variety of ice interaction & failure mechanisms. In 2012 TechnipFMC, Cervval and Bureau Veritas initiated a common development program to offer a new tool for the design of offshore structures interacting with ice combining a variety of models and approaches such as analytical, numerical and empirical. This numerical tool called Ice-MAS (www.ice-mas.com) uses a multi-agent technology and has the possibility to combine, in a common framework, multiple phenomena from various natures and heterogeneous scales (i.e. drag, friction, ice-sheet bending failure, local crushing and rubble stack up).

The study presented in this paper compares the simulation results for different ice floe fields not only in terms of concentration, maximum size of floe and their distribution but also in the way to generate the ice floe and its shape.
An Ontology-Based Approach for Simplified FMU Variable Connections With Automatic Verification of Semantically Correct Configuration
Authors: Nordahl Håvard , Rindarøy Martin , Skjong Stian , Kyllingstad Lars T. , Walther Dirk , Brekke Tore
Published: December 2020

Simulation is increasingly used as an engineering tool in the maritime industry. Currently, there is a particular focus on digital twins, where a supplier of equipment should also supply a simulation model of the equipment. Today, the person configuring the simulator must manually connect all required signals between these models, interpreting the meaning of each signal name to determine which signal can be connected together (e.g., connecting “pressure out” to “pressure in”, while ensuring that their units match). This is a tedious and error-prone process.

In this paper, we present a method for automatically connecting variables of different models while complying with the FMI standard in co-simulations. This also includes a method for unit conversions. The methods for both automatic connections and unit conversions are based on ontologies. The key idea is to build an ontology, based on existing ontologies, which enables structuring model input and output variables into groups and hierarchies, and assign them a defined type. This enables reasoning about connections between models, and simplifies the model connections. The focus in this paper is to present the ontology, how FMI interface signals can be connected to the ontology, and how this can be used to simplify model connections.
Study on 2nd-Order Wave Loads With Forward Speed Through Aranha’s Formula and Neumann-Kelvin Linearization
Authors: Xie Zhitian , Falzarano Jeffery
Published: December 2020

The 2nd-order wave loads consist of difference frequency, sum frequency components and a steady drift component that is also called the mean drift load. The first two components are usually not of interest, because of their small amplitudes compared with the 1st-order wave loads. The remaining mean drift load should be taken into consideration due to its steady effect on floating bodies. In the previous research, the full derivation and expression of the 2nd-order wave loads applied to a floating structure was presented. Moreover, numerically estimated quadratic transfer function was also illustrated with both off-diagonal elements and diagonal elements called the mean drift coefficients. Most research topics in this scenario consider the wave only case. In this paper, the mean drift wave loads applied to a floating structure with forward speed or current velocity has been numerically estimated through Aranha’s formula, a far field method and Neumann-Kelvin linearization, a near field method. Therefore, the effect of the floating structure’s forward speed or current velocity on the 2nd-order mean drift loads that is also called the wave drift damping has been discussed through these two methods. This work will provide a meaningful reference and numerical basis for the ongoing projects of the floating structure’s seakeeping and maneuvering problems.
Laboratory Experiment of Two-Degree-of-Freedom Vortex-Induced Vibrations of Circular Cylinder in Regular Waves
Authors: Opinel Pierre-Adrien , Srinil Narakorn
Published: December 2020

This paper presents new laboratory experiments of two-degree-of-freedom vortex-induced vibration of a flexibly mounted vertical circular cylinder in regular waves. A new experimental model has been developed and tested in the Wind, Wave & Current Tank at Newcastle University. The system mass ratio is close to 3 and the cylinder aspect ratio based on its submerged length is close to 27. The Stokes first-order wave theory is considered to describe the depth-dependent, horizontal velocity amplitude of the wave flow in the circulating water tank. This wave theory is satisfactorily validated by the wave probe measurement. The effects of cylinder stiffness affecting system natural frequencies are also investigated by using a combination of different spring setups in in-line and cross-flow directions. For each set of springs, VIV tests are performed in regular waves, with flow frequency ranging from 0.4 to 1 Hz and amplitude from 0.01 to 0.09 m. The associated Reynolds number at the water surface is in a range of 1.7 × 103–1.5 × 104. The surface Keulegan-Carpenter number (KC) is in the range of 2 < KC < 28 while the surface reduced velocity (Vr) is in the range of 0.5 < Vr < 16 depending on the implemented spring stiffness. Combined in-line/cross-flow oscillations of the cylinder are measured using two non-intrusive Qualisys cameras and the associated data acquisition system. The spring forces are also acquired using four load cells. Results reveal that, depending on KC and Vr, the cylinder primarily oscillates at the flow frequency in the in-line direction and at an integer (mainly 2, 3 and 4) multiple of the flow frequency in the cross-flow direction. Such occurrence of multi frequencies corroborates other experimental and numerical results in the literature. Several peculiar trajectories are observed, including infinity, butterfly, S and V shapes. The present experimental data of vibration amplitudes and oscillation frequencies in in-line/cross-flow directions as well as response patterns provide new results and improved understanding of VIV in oscillatory flows. These will be useful for the development of an industrial tool in predicting offshore structural responses in waves.
Future Scenarios for Arctic Shipping
Authors: Bergström Martin , Leira Bernt J. , Kujala Pentti
Published: December 2020

Maritime activity in the Arctic is on the increase, driven by multiple factors including the development of Arctic natural resources, climate change, regulatory changes, improved technology and operations, national and international policies, infrastructure developments, fuel prices, and the global economy. This article aims to identify and analyze such change drivers and to discuss how these might influence the future of three specific segments of Arctic shipping: destination-Arctic shipping (operation between Arctic and non-Arctic locations), trans-Arctic shipping (operation between non-Arctic locations through Arctic waters), and Arctic cruising. The study finds that each considered segment of Arctic shipping is subject to a unique set of significant change drivers.
Cemented Wellbore Experiments Reveals That Cement Interface Debonding Modeling Overestimate Potential Leakage Rates
Authors: Speer Zachary , Wise Jarrett , Nygaard Runar , Hareland Geir , Ford Eric , Arild Øystein , Lohne Hans Petter , Kragset Steinar
Published: December 2020

Leakage pathways may develop in wellbores during construction, production, or during and after plug and abandonment (P&A). These pathways are created due to events and conditions during cementing operations, or because of physical and chemical changes after cementing such as changes in temperature and wellbore pressures, and deterioration of the cement. Common leakage pathways develop inside the cement sheath, or as microannuli along the cement-tubing interface. Numerous evidence exists showing that wellbores leak, but there is no verified method to determine if a well will leak or not. To ensure long term wellbore integrity, leakage risks need to be evaluated for plugged and abandoned wells.

To evaluate leakage risks from plugged and abandoned wells, numerical finite element models have been developed and used to investigate leakage scenarios during the life of the well. Currently, little work has been done to verify finite element numerical models with experimental data regarding flowpath size in cement sheaths. The aim of this paper is to model previously published experimental data to determine if the finite element models can accurately predict leakage potentials.

Two lengths of cemented annuli were modeled, each with conventional and expanding cement to replicate the Aas et. al. [1] experiments. The numerical results show that the simulated microannuli overestimate flow rate compared to experimental data, indicating that flow path dimensions and/or fluid friction factor does not accurately represent the fluid flow in the experiments.
Wave Propagation in Continuous Sea Ice: An Experimental Perspective
Authors: Passerotti Giulio , Alberello Alberto , Dolatshah Azam , Bennetts Luke , Puolakka Otto , von Bock und Polach Franz , Klein Marco , Hartmann Moritz , Monbaliu Jaak , Toffoli Alessandro
Published: December 2020

Ocean waves penetrate hundreds of kilometres into the ice-covered ocean. Waves fracture the level ice into small floes, herd floes, introduce warm water and overwash the floes, accelerating ice melt and causing collisions, which concurrently erodes the floes and influences the large-scale deformation. Concomitantly, interactions between waves and the sea ice cause wave energy to reduce with distance travelled into the ice cover, attenuating wave driven effects. Here a pilot experiment in the ice tank at Aalto University (Finland) is presented to discuss how the properties of irregular small amplitude (linear) waves change as they propagate through continuous model sea ice. Irregular waves with a JONSWAP spectral shape were mechanically generated with a very low initial wave steepness to avoid ice break up and maintain a consistent continuous ice cover throughout the experiments. Observations show an exponential attenuation of wave energy with distance. High frequency components attenuated more rapidly than the low frequency counterparts, in agreement with a frequency-cubed power-law. The more effective attenuation in the high frequency range induced a substantial downshift of the spectral peak, stretching the dominant wave component as it propagates in ice.
Study on Ship Operational Effect for Defining Design Values on Ship Motion and Loads in North Atlantic
Authors: Miratsu Rei , Fukui Tsutomu , Matsumoto Toshiyuki , Zhu Tingyao
Published: December 2020

Ships are being operated under consideration of the safety for lives and properties, economical reasons and so on, therefore the sea states in natural phenomena and those actually encountered by ships are thought to be different, and the latter includes some effects of human operational factors (so called “ship operational effect”). Quantitative evaluation of the ship operational effect is important to consider rational wave design loads for the evaluation of hull structure strength.

The purpose of this study is to evaluate the ship operational effect in actually encountered sea states quantitatively for defining design values on ship motion and loads.

In this study, the quantitative evaluation of ship operational effect is carried out considering the wave heights and wave periods in the North Atlantic. It was confirmed from the results that the quantitative ship operation effects vary depending on the hindcast wave source. Furthermore, the ship speeds tend to decrease in head, bow and beam seas when the encountered significant wave heights became higher. Moreover some patterns are observed on the typical encountered wave headings in the North Atlantic, which comes from the combination of the features of the North Atlantic routes and the wave propagation directions of the natural phenomena.
On the Effect of Non-Linear Boundary Conditions on the Wave Disturbance and Hydrodynamic Forces of Underwater Vehicles Travelling Near the Free-Surface
Authors: Lambert William , Brizzolara Stefano
Published: December 2020

This study compares the effect of non-linear free-surface boundary conditions for a high-order non-linear free-surface Rankine-source boundary element method on wave disturbance and hydrodynamic forces acting on an underwater vehicle travelling near a calm free-surface. In particular, simulations for a steady nonaxisymmetric prolate spheroid using different basis flows and linearization techniques were compared to an analytical method achieved by Chatjigeorgiou using a multipole expansion of Green’s functions. It appears that at low Froude numbers, the basis flow used in the formulation contributes significantly to differences in the steady solutions for wave resistance and pitch, whereas for higher Froude numbers the linearization technique becomes a more defining feature. Upon observation of the analytical solution for wave resistance, one can see that it was formed under a Neumann-Kelvin formulation and this is supported by the Neumann-Kelvin simulations converging well to the analytical solution.

Further comparisons were made using a wave directional energy spectrum gathered from transverse wave cuts of the free wave pattern. The spectral analysis allows for a higher level of comparison between all of the different cases, establishing a direct relation between the change in wave resistance and the energy content variation of the particular wave spectrum components.
A Non Linear Finite Element Model to Analyse the Dynamics of Subsea Lifting Operation Using Synthetic Cables
Authors: Carobino Evandro Souto , Pavanello Renato , Tommasini Rodrigo Batista , Fonseca Debora Junqueira , de Oliveira Carvalho Leonardo
Published: December 2020

In the context of subsea lifting many equipment and strategies are employed in order to avoid dynamic instabilities and complex mechanical behaviors during the installation procedures. One of those strategies is the use of synthetic cables to reduce the total sustained weight on the crane and to shift the resonance frequency of the system, leading to reductions of fails risks. This work presents a numerical model intended to predict the dynamic behavior of a cable-equipment system under the influence of the sea waves. The cable is discretized in a finite element mesh which accounts for a nonlinear material model for the elasticity of the cable. The nonlinear elastic law uses a polynomial function to represent the force on the cable as a function of the strain, being able to predict the variation of the stiffness for different load conditions. Further, hydrodynamic forces are considered acting on the equipment and are modeled via Morison’s equation, which introduces a quadratic nonlinear forcing term. The equation of motion is then integrated at the time domain through a Newmark-β predictor-corrector method in order to obtain the dynamic response of the system. Furthermore, an Orcaflex model is constructed using an equivalent linear stiffness representation for the synthetic cable. The results obtained are compared, and the differences between them are highlighted for typical subsea lifting scenarios. In this case, the proposed model can predict non trivial dynamic behaviors of the system such as dependence on the amplitude of the displacement of the lifting point. It is also presented the scenarios where the equivalent linear model is accurate in comparison to the nonlinear one and how the selection of the strain point used to linearize the model affects the dynamics of the system.
Numerical Simulations and Sea Trial for Leader Follower Formation Control of Cruising-Type AUVs
Authors: Umeda Jun , Kim Kangsoo , Sato Takumi , Inaba Shogo , Fujiwara Toshifumi
Published: December 2020

With the emphasis on the utilization of rich materials in the seabed in recent years, autonomous underwater vehicles (AUVs) are valued for technology to explore the oceans. Simultaneous operations of multiple-AUVs enable to investigate a wider area in a shorter time than the use of only a single AUV. During the survey, each AUV corrects the position error due to the inertial navigation system by the acoustic communication systems. All AUVs are required to be within the acoustic-communication available area. The formation control which can keep the desired relative positions becomes the mandatory function to explore the oceans efficiently while being within the acoustic-communication available area. In this study, a simple formation control-law based on a leader-follower algorithm was developed and validated through numerical simulations and sea trials. In the numerical simulations, waypoint tracking control-law and the proposed method were applied to the cruising-type AUVs and these control performances are compared. Sea trials using two cruising-type AUVs were carried out to evaluate the performance of the control-law.
Experimental Study on Three Phase Flow in Inclined Pipe for Deep Sea Mining
Authors: Takano Satoru , Masanobu Sotaro , Yamamoto Joji , Kanada Shigeo , Ono Masao , Sasagawa Hiroki
Published: December 2020

Subsea minerals exist in the deep water within Japanese exclusive economic zone. However, the development of subsea minerals is not commercialized. The Air-lift pump is the promising method for subsea minerals transport. It is significant to estimate the amount of lifting ore when the conditions of submergence ratio and supplying air volume are changed. The estimation of the amount of lifting ore needs the void fraction in three phase flow and friction loss in pipe. Therefore, the empirical methods to estimate the void fraction and friction loss in mainly vertical pipe were proposed in the previous studies. However, the lifting system for subsea minerals has not only vertical pipe but inclined pipe. There are few works for flow assurance on three phase flow in inclined pipe. Then we conducted the scale model experiment to investigate void fraction and friction loss. The experiment was conducted in the conditions of the five kinds of inclination angles. We used the glass beads as solid particles in the experiment. The glass beads were 4mm in diameter and 2553kg/m3 in density. The internal diameter of pipe was 26mm. We applied the empirical method for vertical or horizontal pipe proposed in previous researches to the present experimental condition. Then we compared the experimental results with the calculated ones on void fraction and friction loss. As the results, the calculated results were in good agreement with the experimental ones. Therefore, it was suggested that the void fraction and friction loss in the inclined pipe could be calculated by the empirical method based on the experiment on the vertical or horizontal pipe.
Feasibility Study on Fabrication of Large-Scale Offshore Structural Steel Component Using LAAM Technology
Authors: Chew Y. X. , Ang J. H. , Sastry K. Y. , Xu D. Q. , Kuik S. , Bi G. J.
Published: December 2020

ASTM A131 Steel, grade EH36 is a high strength steel used extensively as structural parts in shipbuilding, Oil and Gas applications. In this work, additive manufacturing of a support node connecting the main platform and columns for semi-submersible offshore vessel was performed using Laser Aided Additive Manufacturing (LAAM) process to evaluate both technical feasibility and economic viability. Both coupon and component levels LAAM process study was carried out. Properties of printed EH36 steel are significantly determined by the printing process parameters. EH36 deposited with optimized LAAM process has shown better mechanical properties than conventional rolled EH36 material. A deposition strategy was developed to distribute the accumulated residual stress, to minimize substrate distortion and stress-induced cracking in the print part. A hybrid approach combining both substrate and AM, with a 60% print to hot-rolled substrate plate weight fraction was proposed to enable printability and to enhance efficiency. Near-net-shape node was printed without cracking/delamination using optimized printing strategy. Total printing weight is 70kg and total time spent is 90 hours. It was concluded that LAAM technology is feasible for fabrication of large load bearing structural steel sections.
Simulating High Mode Vortex Induced Vibration of Riser in Linear Sheared Current Using an Empirical Time Domain Model
Authors: Kim Sang Woo , Sævik Svein , Wu Jie
Published: December 2020

This paper addresses the performance evaluation of an empirical time domain Vortex Induced Vibrations (VIV) model which has been developed for several years at NTNU. Unlike the frequency domain which is the existing VIV analysis method, the time domain model introduces new vortex shedding force terms to the well known Morison equation. The extra load terms are based on the relative velocity, a synchronization model and additional empirical coefficients that describe the hydrodynamic forces due to cross-flow (CF) and In-line (IL) vortex shedding. These hydrodynamic coefficients have been tuned to fit experimental data and by considering the results from the one of existing frequency domain VIV programs, VIVANA, which is widely used for industrial design.

The feature of the time domain model is that it enables to include the structural non-linearity, such as variable tension, and time-varying flow. The robustness of the new model’s features has been validated by comparing the test results in previous researches. However, the riser used in experiments has a relatively small length/diameter (L/D) ratio. It implies that there is a need for more validation to make it applicable to real riser design.

In this study, the time domain VIV model is applied to perform correlation studies against the Hanøytangen experiment data for the case of linear sheared current at a large L/D ratio. The main comparison has been made with respect to the maximum fatigue damage and dominating frequency for each test condition. The results show the time domain model showed reasonable accuracy with respect to the experimental and VIVANA. The discrepancy with regard to experiment results needs to be further studied with a non-linear structural model.
Casing Wear Simulation by Application of Real-Time Data and Predictive Modelling
Authors: Teigland Andreas , Sangesland Sigbjørn , Dale Stein Inge
Published: December 2020

Casing wear poses a significant safety hazard during drilling and production of hydrocarbons. Failure to maintain integrity due to inaccurate casing wear estimation can cause severe accidents or preclude prospective operations. Current industry practice is to estimate casing wear during the planning phase of the well and subsequently use assumed operational parameters with inherent uncertainties. This paper aims to study how to utilize real-time data to improve the industry standard methodology and evaluate the benefit of the modification. The research was conducted by applying the model on data from a well on the Norwegian continental shelf. There were two main objectives of the research.

Firstly, the industry standard approach to casing wear estimation was expanded to include real-time data. Application of real-time data to the industry standard method for estimating casing wear caused a significant difference in results. The approach using real-time data resulted in an estimate of more casing wear compared to the standard approach. Secondly, an algorithm for continuous prediction of casing wear at the end of operation was developed. The predictive algorithm resulted in consistently more accurate estimates in relation to the final value throughout the operation.

With variations in input parameters and consecutive casing wear of this magnitude, well integrity cannot be ensured during operation without application of real-time data. The failure to maintain well integrity demonstrates the necessity of the proposed approach.
Planning and Design of Floating Offshore Architecture
Authors: Takahashi Akane , Yoshida Ikuo
Published: December 2020

Floating offshore structures are attracting increasing attention as a method for addressing problems such as rising sea levels due to global warming and the increasing global populations. However, unlike ground structures, floating offshore structures must consider the effects of waves. The movement characteristics of the floating offshore structure have been reported. However, no studies have compared variations in motion response characteristics according to the scale of floating structures or buildings atop them, so it is currently difficult during the initial planning and design stages to estimate the size of superstructures that can be designed for a given marine area. Therefore, with the aim of obtaining basic data for planning floating offshore structures, in this study we developed floating structure modules (a square 36m on a side) according to their superstructure and investigated the basic motion response characteristics for each. We furthermore derived tendencies for horizontal acceleration and inclination occurring in individual modules according to design waves for Tokyo Bay.
1300 Tons Grouted Integrity Support Installation Case Study
Authors: Alonso Castro Beatriz , Daly Roland , Becerro Francisco Javier , Vabø Petter
Published: December 2020

The North sea Yme oil field was discovered in 1987, production started in 1996 and ceased after 6 years when it was considered no longer profitable to operate. In 2007 a new development was approved, being Yme the first field re-opened in the Norwegian Continental Shelf. The concept selected was a MOPUStor: comprising a jack-up unit grouted to a subsea storage tank. Due to compromised structural integrity and lack of regulatory compliance that came to light shortly after installation, the platform was required to be removed [1]. The remaining riser caisson and the future 1050 t wellhead module required a support to allow the re-use of the facilities and tap the remaining oil reserves. The innovative tubular frame support was designed as a braced unit, secured to the existing MOPUstor leg receptacles and holding a grouted clamp larger than typical offshore clamps for which design guidance in ISO is available. The existing facilities had to be modified to receive the new structure and to guide it in place within the small clearances available.

The aim of this paper is to describe the solutions developed to prepare and verify the substructure for installation; to predict the dynamic behavior of a subsea heavy lift operation with small clearances around existing assets (down to 150 mm); and to place large volume high strength grouted connections, exceeding the height and thickness values from any project ever done before. In order to avoid early age degradation of the grout, a 1 mm maximum relative movement requirement was the operation design philosophy. A reliable system to stabilize the caisson, which displacements were up to 150 mm, was developed to meet the criteria during grouting and curing. In the stabilizer system design, as well as the plan for contingencies with divers to restart grouting in the event of a breakdown, the lessons learned from latest wind turbine industry practices and from the first attempt to re-develop the field using grouted connections were incorporated. Currently the substructure is secured to provide the long term integrity of the structure the next 20 years of future production in the North Sea environment.
A Novel Approach to Improving the Structural Reliability of a Fixed Offshore Platform Subject to Wave-in-Deck Loading Using a Holistic Structural Integrity Management (SIM) TRIAD Approach
Authors: Kimiaei Mehrdad , Mirzadeh Jalal , Dev Partha , Efthymiou Mike , Khan Riaz
Published: December 2020

Fixed offshore platforms subject to wave-in-deck loading have historically encountered challenges in meeting target reliability levels. This has often resulted in costly subsea remediation, impacted platform occupancy levels or premature decommissioning of critical structural assets due to safety concerns. This paper addresses the long-standing industry challenge by presenting a novel structural reliability approach that involves converging the analytical behavior of a structure to its measured dynamic response for assessment. In this approach, called the Structural Integrity Management (SIM) TRIAD method, the platform model is calibrated based on the measured in-field platform natural frequencies using a structural health monitoring (SHM) system, so that the reliability assessment can be performed on a structural model whose stiffness is simulated as close to reality as possible. The methodology demonstrates the potential of unlocking structural capacity of offshore structures by removing conservatism normally associated with traditional reliability assessment methods, thus significantly improving the ability to achieve target structural reliability levels in a cost effective manner. The SIM TRIAD method has been implemented while assessing an existing fixed offshore platform subject to wave-in-deck loads, which is located in East Malaysian waters. It has enabled the facility operator to achieve acceptable target structural reliability and has assisted in developing an optimized risk-based inspection (RBI) plan for ensuring safe operations to end of asset field life. The methodology and findings of the assessment are presented in this paper to illustrate the benefits of the SIM TRIAD method.
Time Domain Structural Fatigue Analysis of Floating Offshore Platforms: A Response Based Technique
Authors: Kyoung Johyun , Samaria Sagar , Kim Jang Whan
Published: December 2020

This paper presents a response-based, time-domain structural fatigue analysis of a floating offshore platform. The conventional technique for structural fatigue assessments of offshore platforms uses a linear, frequency-domain analysis based on the spectral method. Although this conventional method is computationally efficient, there is a room for improving accuracy and reducing uncertainties because it cannot accurately address non-linear loadings on the offshore platform. Such non-linear loads arise from the wave, wind, and current as well as from the riser and mooring systems; these non-linearities necessitate large factors of safety that lead to conservative design and frequent inspection.

As an extension of previous work (Kyoung et al.[12]), this study presents the development of a time-domain, structural fatigue analysis that explicitly addresses non-linear loading on the platform. The external load time-histories are directly mapped onto the structure at every time interval to create a stress-based response with the varying environment. In each time step, the load mapping accurately captures the phase relationship between the external loading and hull inertial response. Therefore, present method reduces uncertainties in the fatigue damage computation and overcomes the assumptions of spectral method. Present load component-based approach is applied onto a finite element structural model, which provides unit structural response at locations of interest. Time history of structural response is obtained by synthesizing the obtained unit stress-based structural response with environmental loading and platform motion response. Fatigue damage can be computed from the obtained time series of structural response using rain-flow counting.

As an application, a conventional semisubmersible platform is used to evaluate structural fatigue damage for a given wave scatter diagram. A comparison between results from this response-based time-domain approach and the conventional spectral method is presented.