bluuebunny/crossref_metadata_2025 huggingface dataset:
Feasible Numerical Technique for Analysis of Offshore Pipelines and Risers
Authors: Trapper Pavel A.
Published: December 2020

A simple 2D numerical model for pipeline and riser configuration analyses is presented. The model considers large deformations of the pipe, pipe-seabed contact detection, pipe’s interaction with uneven inelastic seabed, environmental loading such as drag forces applied by the ocean currents, water surface level variations and incorporation of buoyancy modules.

The solution technique is based on a consistent minimization of the total potential energy of the deformed pipe discretized as a Riemann sum, which results in a system of nonlinear algebraic finite difference equations that is solved in an incremental/iterative manner. At each increment, the total potential energy is being updated, thus accounting for energy dissipation due to irrecoverable plastic deformation of the seabed and according to hydrodynamic drag forces. The whole pipe is treated as a single continuous segment.

To demonstrate the method, examples with several riser configurations and pipe-lay scenarios are presented. It is shown how on-bottom unevenness, including pits and hills, incorporation of buoyancy modules and tidal effects can affect pipeline or riser configurations and their internal forces. Results are compared to those obtained with Abaqus and appear to be in an excellent agreement.

The model presents simple and time-efficient way to analyze the pipe-lay or riser configurations with various boundary and loading conditions. The proposed model, contrary to commercial packages, which impose using time-consuming Graphical User Interface (GUI), allows for performing the series of analyses for varying geometric and/or material properties, and processing the results in reasonable time by single click.
Retracted: “Dynamic Analysis of a Subsea Spool Under Dropped Container Impact Loads” [Proceedings of the ASME 2020 39th International Conference on Ocean, Offshore and Arctic Engineering, Volume 4: Pipelines, Risers, and Subsea Systems, Virtual, Online, August 3–7, 2020, Conference Sponsors: Ocean, Offshore and Arctic Engineering Division, ISBN: 978-0-7918-8435-5, Copyright © 2020 by ASME. Paper No. OMAE2020-18578, V004T04A037; 8 pages; doi: 10.1115/OMAE2020-18578]
Authors: ASME
Published: December 2020

This paper was removed from publication at the author’s request, August 30, 2021.

Copyright © 2021 by ASME
Measurements of Low Frequency Vibration in Subsea Piping Using ROV Video Analysis
Authors: van Wijhe Andries , Buijs Lennert , Stachyra Leszek , Macchion Olivier
Published: December 2020

Vibrations in Subsea Production Systems are well recognized as a concern in the subsea industry. To identify the severity of the vibrations and potential accumulated fatigue damage, subsea vibrations need to be measured with great accuracy. Currently, accurate detection and subsea measurements are often performed by utilizing accelerometers, which have to be connected to the structure by ROV or a diver.

ROV video analysis provides an alternative solution. Video analyses are widely utilized across different applications. With the increased quality of a HD camera on ROV, the accessibility of such measurements is an attractive substitute to other techniques.

As a part of on-shore mechanical testing on a full assembled XT in St John’s Canada, a flowloop on a water injection XT was subjected to free vibrations. The vibrations were filmed using a commercial HD camera placed on a tripod.

This test was done to validate data generated using video processing in which pipe vibration of an operating subsea XT was filmed using an ROV camera.

A study that aimed to quantify the video processing accuracy, limitations and provide general guidance was conducted. For the onshore test filmed with a tripod the results of video analyses were compared with the measurements obtained by means of accelerometers. For the video of an operating subsea XT filmed by an ROV, the obtained vibration frequency and direction was compared with the free mechanical vibration obtained by a FEM model.

The results obtained by means of the video analysis matched well with the accelerometer data. A high accuracy was reached, as vibration displacements as low as 20% of the pixel were accurately determined in the video analysis. With respect to detection frequencies, the upper cut-off frequency was around 15 Hz determined by the video framerate. The video analysis utilizing ROV videos was found to be applicable for low frequency vibration measurements, opening the opportunity for easier and more cost effective vibration detection and monitoring. The method is also reliable for subsea application in which the camera is placed on an ROV and is thus not affected by ROV movements, subsea lighting condition and moving ocean debris.
Effect of Wave-Current Interaction on Structural Responses of a Very Long and Side-Anchored Floating Bridge
Authors: Dai Jian , Abrahamsen Bjørn Christian , Leira Bernt Johan
Published: December 2020

This paper is concerned with a computational study on the hydroelastic response of a long, straight and side-anchored fjord-crossing floating bridge accounting for the wave-current interaction. The effect of this interaction on a single bridge pontoon is investigated by using the three-dimensional potential solver VERES3D. The frequency-dependent hydrodynamic coefficients and excitation force transfer functions are presented and compared with WAMIT results where the current effect is ignored. Based on the frequency domain results, an approach to account for the wave-current interaction in time domain analysis is proposed. Next, a generic straight and side-anchored floating bridge model is put forward to examine the stochastic structural responses in the time domain. For the purpose of comparison, the bridge responses under waves and current without interaction are also investigated. This study attempts to quantify the wave-current interaction effect on the structural responses of a floating bridge and provide useful recommendations and suggestions to researchers and engineers for their study of similar structures.
Numerical Modelling of the Interaction of Moving Fish Nets and Fluid
Authors: Martin Tobias , Wang Gang , Bihs Hans
Published: December 2020

The significant difference in length scales between the flow around a moving fish net and the flow around each twine of the net prevents the resolution of the complete structure within a discrete fluid domain. In this paper, this issue is overcome by calculating the net and fluid dynamics separately and incorporate their interaction implicitly. The forces on the net are approximated using a screen force model, and the motion of the net is computed with a lumped mass method. Here, a linear system of equations is derived from the dynamic equilibria and kinematic relations. The net model is coupled to the CFD solver REEF3D which solves the incompressible Navier-Stokes equations using high-order finite differences in space and time. Several numerical calculations are provided, and the comparison of loads and velocity reduction with available measurements indicates the good performance of the proposed model.
Elevated Pipelay Initiation and Cost Optimized Lowering of Subsea Rigid Pipeline
Authors: Vadassery Ittyarachan , George Gregory , Sudevan Hariraj
Published: December 2020

S-lay installation methodology is an industry accepted method for the installation of subsea rigid pipelines. Pipeline initiation is a major operation during the start of S-lay and its selection is dependent on various factors including project requirements, field layout and strength of holdback.

The beachpull initiation method is utilized in shallow water regions where a barge or vessel is unable to access the initiation point due to keel clearance. For most applications, however, the dead man anchor initiation method is utilized irrespective of the water depth. For the dead man anchor methodology, the type of anchor needs to be selected based on the in-situ conditions. Near the jacket, conventional dead-man anchor initiation is not feasible due to the presence of subsea assets. The holdback method provides an acceptable alternative in such cases. There are several variations of this method such as elevated holdback, vertical bow string and horizontal bow string initiation which are chosen based on operational requirements.

During a project undertaken recently in the Middle East region, several initiation challenges were encountered due to congested fields owing to subsea assets and the best suitable methodology was determined which included dead man and elevated holdback initiation. It was observed that optimizing the initiation, reduced risk associated with subsea asset clashes and accelerate the schedule. For another fast track project in Asia Pacific region at deeper water depths, vertical bow string initiation was used to override challenges in reducing loads on the jacket. On the same project a modified initiation method was adopted to avoid a davit lift operation, shorten the target box distance and avoid saturation diving which helped the project avoid mobilization of a large anchored or DP barge and utilize available diving support vessel with a single crane or davit.

The paper explains different challenges in pipelay initiation operations of subsea rigid pipelines and the selection of the appropriate type of initiation. It also presents recent case studies of different initiation operations with the associated challenges and benefits.
Prediction of Wave-Induced Motions and Loads of Ships With Forward Speed by Matching Method
Authors: Li Hui , Deng Baoli , Liu Chunlei , Zou Jian , Ren Huilong
Published: December 2020

A novel matching method has been developed to solve the wave-induced motions and loads of ships with forward speed. The fluid domain is divided into two subdomains by a cylindrical control surface: an interior domain and an exterior domain. Unlike the conventional domain decomposition strategy, the control surface is meshless in present method, on which the physical quantities are expanded into Fourier-Laguerre series. Based on forward speed Green function, the source distribution method is adopted to solve the exterior domain. The calculations of boundary integral equation about forward speed Green function over the control surface are performed analytically, and the solution of exterior domain provides a Dirichlet-to-Neumann (DN) relation on the control surface. In the interior domain, the boundary value problem is solved by Rankine source method. In order to be consistent with exterior solution, the control surface is kept meshless. The ship hull is discretized into constant panels. The free-surface is discretized into cubic B-splines to represent the high-order derivatives of velocity potential precisely. Then, the DN relation is used to close the equation system established in the interior domain. Comparisons with known experimental measurements show that the calculations achieve good accuracy. Furthermore, the influences of numerical method used in the exterior domain are described.
Hydrodynamic Optimization of a Containership
Authors: Feng Yanxin , el Moctar Ould , Schellin Thomas E.
Published: December 2020

Using open-source software Dakota, this paper describes the process of generating an optimal parametric hull shape for a generic containership. Selected design variables defined the ship’s hull, and the influence of these variables on calm water resistance was analyzed. Computations of the flow around the hull were obtained from a validated nonlinear potential flow boundary element method. Using the multi-objective optimization algorithm Surrogate Based Global Optimization (SBGO) reduced the computational effort. The hydrodynamic calm water ship resistance defined the objective function. Compared with the original hull, wave resistance of the optimal hull was significantly reduced for the ship at Froude numbers corresponding to its design speeds.
Maneuvering and Seakeeping Performance of a Generic Tug Based on Numerical Simulations
Authors: Zheng Yingying , Jin Yuting , Yiew Lucas J. , Magee Allan R.
Published: December 2020

Autonomous tugs may play an important role in future ports, due to the shortage of qualified mariners. A digital twin (mathematical model incorporating a vessel’s hydrodynamic behavior and response, suitable for real-time control) would be needed for autonomous operations. Yet, partly because tugs are generally high-powered and very maneuverable compared to conventional vessels, there is little published data on the hydrodynamic performance of such vessels. As a first step in the development of the tug’s digital twin, the present work studies the maneuvering and seakeeping performance of a generic tug at model scale. Numerical simulations are performed for an approximately 1:10 scale model for standard resistance, static and dynamic captive and seakeeping cases. Reynolds-Averaged Navier-Stokes (RANS) k-ω model is employed for the simulations including the free surface through the Volume of Fluid approach. The hydrodynamic forces and moments on the tug model in the simulations of the standard resistance and the static and dynamic captive cases, as well as the tug model’s motions and the added resistance in headseas, are investigated. The simulation results provide data to build a mathematical maneuvering model for the tug based on 4-DoF MMG manoeuvring model, which serves as the digital twin in this case.
Characterization of Magnetic Field in Crack Propagation Stage and Application to Non-Destructive Evaluation
Authors: Bao Sheng , Zhao Zhengye , Luo Qiang , Yang Jian
Published: December 2020

Monitoring of fatigue crack propagation is very important in industrial fields. Stress-induced magnetic measurement is a newly developed non-destructive testing technique which can detect early failure of ferromagnetic materials in service. A lot of experiments demonstrate that magnetic measurement is more sensitive compared with other non-destructive testing technologies. In order to explore the correlation between crack propagation and magnetic hysteresis under cyclic stress in X70 pipeline steel, a series of stress-controlled tests were carried out and the changes in magnetic field around cracks during their propagation process were observed throughout the tension-tension fatigue tests. The variations of magnetic field and stress intensity factor K in the crack propagation stage were studied. The results obtained allowed the division of the magnetic behavior of the investigated steels into three stages corresponding to three distinct crack propagation stages. It was found that the magnetic field varies with crack propagation, and the stress intensity factor K increased with the increase of loading cycles. A strong correlation between the variation of the magnetic field and stress intensity factor was recognized, regardless of the loading conditions, maximum load or stress ratio. The results suggest that non-destructive evaluation of fatigue cracks would be possible using this relationship.
Evaluation of the Frozen Ground for Developing Construction Technology of Pipelines in Cold Regions
Authors: Kim YoungSeok , Kim Sewon
Published: December 2020

Cold regions, such as Alaska, Russia and Canada, get attention from many countries due to the tremendous amount of natural resources which are buried there. An accurate evaluation of the frozen ground is very important because the behavior of the active layer is greatly affected by the soil characteristics and water content in the active layer. It is necessary for developing a construction technology for pipelines in cold regions. This study has two objectives: 1) First one is to evaluate the characteristics of a newly-produced insulated aggregate and 2) the other one is to check the applicability of insulated aggregate. A series of laboratory experiments (specific gravity test, sieve analysis test, direct shear test, test for abrasion of coarse and aggregates by use of the Los Angeles machine) were performed to estimate the characteristics of the newly-produced insulated aggregate. In addition, the laboratory chamber tests were carried out to evaluate the applicability of frozen soil behavior using the newly-produced insulated aggregate. The chamber tests were conducted to check the laboratory model surrounded by soil mixing the insulated aggregate and ordinary soil in order to prevent the damage of structures such as pipelines due to the ground being frozen. For the laboratory chamber tests, the extreme cold engineering laboratory was built within the Yeon Cheon SOC Demonstration Research Center, of the Korea Institute of Construction Technology. The performance of the frozen ground which was installed with the insulated aggregate using vinyl was evaluated through monitoring the time-dependent distribution of temperature and earth-pressure.
Free Fall Water Entry of a Two-Dimensional Asymmetric Wedge in Oblique Slamming: A Numerical Study
Authors: Hosseinzadeh Saeed , Izadi Mohammad , Tabri Kristjan
Published: December 2020

This paper examines the hydrodynamic problem of a two-dimensional symmetric and asymmetric wedge water entry through freefall motion. The gravity effect on the flow is considered and because of precise simulation close to the real phenomenon, the oblique slamming is analyzed. The defined problem is numerically studied using SIMPLE and HRIC schemes and by implementing an overset mesh approach. In order to evaluate the accuracy of the numerical model, the present results are compared and validated with previous experimental studies and showed good agreement. The results are presented and compared for each symmetry and asymmetry in different deadrise angles, drop heights and heel angles. Based on a comparison of the measured vertical acceleration of the experimental wedge data, it is determined that the proposed numerical method has relatively good accuracy in predicting the slamming phenomenon and wedge response. The influence of viscous regime on water entry simulations is investigated, in according to results, effect of viscosity is negligible. Results show that the heel angle dramatically affects the wedge dynamics, pile-up evolution, and pressure distribution. These results suggest evidence for a complex interaction between geometric parameters on the water entry of rigid wedges, which could finally develop our understanding of planing vessels operating in real sea conditions.
Validation of the Master Curve Approach With Various Welding Conditions: Groove Shapes, Heat Inputs and Welding Processes
Authors: Lee Jin Ho , Kim Ji Hoon , Kim Myung Hyun
Published: December 2020

Engineering critical assessment (ECA) is a procedure for evaluating the soundness of structures with flaws and has been widely applied for assessing the structural integrity. ECA procedure requires reliable fracture toughness data to assess the effect of defects. Ideal data are typically obtained from samples taken during construction of an engineering structure or from the structure afterward, but there are cases in which removal of the test samples is impossible due to the continued operation of the structure. To this end, Appendix J of the BS 7910 provides a procedure for estimating fracture toughness values from appropriate Charpy impact test data. However, the correlation between Charpy impact energy and fracture toughness is known to be overly conservative with not sufficient theoretical background in fracture mechanics perspective. In this regard, the revised BS 7910:2019 provides an improved method for calculating the reference temperature by applying the yield strength and the Charpy upper shelf energy based on empirical data.

The target of this study is to validate the master curve approach in the modified BS 7910 for two common offshore grade steels with explicit considerations for various groove shapes, heat inputs and welding processes. For the purpose, the master curves are compared in terms of the reference temperature calculated from Charpy impact test according to BS 7910:2013 and the newly revised 2019 version of BS 7910. The modified master curve resulted in less conservative fracture toughness values anticipated from the decreased reference temperature. The estimated fracture toughness values exhibited a good correlation with experimentally obtained toughness values. The influence of various groove shapes, heat inputs and welding processes in estimating fracture toughness based on the master curve approach is discussed. In addition, the effect of impact test sample locations within weld metals toward estimated fracture toughness values is evaluated.
Relation Between Atmospheric Circulation Patterns in the North Atlantic and the Sea States in the Iberian Peninsula
Authors: Lucas C. , Bernardino M. , Guedes Soares C.
Published: December 2020

A statistical analysis of significant wave height (Hs) in eight locations offshore Portugal continental coast is performed. Specifically, locations at different water depths at Aguçadoura, Leixões, Nazaré, Peniche, Sines and Faro were chosen. The spectral and parametric information from these points used in this analysis was obtained from 21-year hindcast simulations using the spectral wave model SWAN. The modelling of the climatic variability of directional spectra provides reliable information of the most relevant parameters at these locations, i.e., how the spectral parameters and their probability of occurrence change in the regions studied. The occurrences of spectral classes are estimated, and for each class, the variability of the spectral parameters is described by means of joint distributions. The classification of the different sea states provides important information about the wave conditions present in the target areas. A relation between the sea states and the Lamb weather types (WTs), a methodology for classifying atmospheric circulation patterns, is presented in this study. The results of this study provide a description of the wave climate, through the interaction between the sea states and weather patterns, relating different circulation patterns to different sea states. This study provides useful information on the wave conditions that can be used in the design of ocean engineering structures, in the assessment of the operability and safety of shipping and renewable energy devices.
Deep Sea Mining: Towards Conceptual Design for Underwater Transportation
Authors: Vamråk Solheim Astrid , Lesage Maxime , Asbjørnslett Bjørn Egil , Erikstad Stein Ove
Published: December 2020

This paper presents the first steps towards conceptual design for the underwater transportation of minerals from seabed to shore for deep sea mining (DSM). The methodology is based on conceptual design using a systematic approach. Abstraction was used to identify the fundamental entities of the problem, and a function structure containing the overall function and subfunctions was established based on the abstraction. Further, an extensive search for working principles (WP) was conducted in order to find forms associated with the functions. This was done by exploration of solutions within different industries such as the oil and gas industry, subsea industry and dredging industry. The discovered working principles were then listed and categorized based on their physical principles, i.e. classifying criteria. For each function, the working principles were combined into design catalogues with classifying criteria in the rows and columns. Further, compatibility between principles was reviewed. This led to the selection of four working structure sets: one based on ore moved as bulk, and three based on ore moved inside a container. The container-based solutions are different in how the container is moved: inside the cargo hold, carried outside, or towed by underwater vehicle. A completion of the last steps of the conceptual design process is needed to obtain a principle solution.
A Three-Dimensional FE Approach for the Fatigue Analysis of Flexible Pipes Tensile Armors Inside End Fittings
Authors: Miyazaki Marcelo N. R. , de Sousa José Renato M. , Ellwanger Gilberto B. , da Silva Vinicius R.
Published: December 2020

During the end fitting (EF) assembly, the tensile armors of flexible pipes are folded and then unfolded to allow the assessment to the inner sheath and the activation of the inner sealing system. This procedure leaves residual stresses and plastic deformations on these armors, which affect their fatigue resistance and, consequently, the overall performance of the pipe. Hence, in this work, a methodology to predict the fatigue resistance of tensile armors inside an EF is proposed. This methodology relies on stresses calculated with a previously presented three-dimensional finite element (FE) approach and is employed to analyze the fatigue response of a 6” production riser in catenary configuration. This fatigue analysis not only addresses the effects from several irregular sea states but also the local stress concentrations associated with the EF assembly and pre-operational tests (e. g., Factory Acceptance Test, FAT). The results obtained indicate that the EF entrance may be a critical point for fatigue failure and, moreover, the lower fatigue resistance is related to a region where higher alternate stresses occur despite the very high mean stresses are observed in other regions along the tensile armors.
A Discrete Element Model for Brash Ice Simulations
Authors: Behnen Jonas , Hisette Quentin , Ehlers Sören , von Bock und Polach Rüdiger U. Franz
Published: December 2020

Most merchant ships operating in the cold regions are not able to break ice themselves, they can only navigate in the broken ice, the so-called brash ice channels. Today’s standard requires a model test in real brash ice conditions to be carried out and realistic additional resistances to be estimated from this. The problem is that they can only be performed at the end of the design process. The possibility of changing the ship design within the development process can only be guaranteed by using a simulation tool, based on the Discrete Element Method. The problem with the development of this numerical simulation is the correctness of the mapping of the physical behaviour of brash ice. The physical models used are often simplified and not sufficient to represent the complex mechanical behaviour of brash ice. Thus, another problem with the use of numerical simulation is the selection of the correct parameters to describe the mechanical behaviour. A concrete definition of the used material parameters does not exist and the experimental tests for the determination of the physical properties are often complex and not standardized. This paper examines the mechanical behaviour of brash ice and the descriptive parameters of each ice rubble. On this basis, the physical behaviour in nature is compared with the model used in numerical simulation. As a result, physical inconsistencies are determined and new solution approaches are proposed, for example in the form of a new contact model, an extension of the friction model or a change of the descriptive particle shape.
Artificial Intelligence Based Approach for Predicting Fatigue Strength Using Composition and Process Parameters
Authors: Keprate Arvind , Ratnayake R. M. Chandima
Published: December 2020

Accurate prediction of the fatigue strength of steels is vital, due to the extremely high cost (and time) of fatigue testing and the often fatal consequences of fatigue failures. The work presented in this paper is an extension of the previous paper submitted to OMAE 2019. The main objective of this manuscript is to utilize Artificial Intelligence (AI) to predict fatigue strength, based on composition and process parameters, using the fatigue dataset for carbon and low alloy steel available from the National Institute of Material Science (NIMS) database, MatNavi. A deep learning framework Keras is used to build a Neural Network (NN), which is trained and tested on the data set obtained from MatNavi. The fatigue strength values estimated using NN are compared to the values predicted by the gradient boosting algorithm, which was the most accurate model in the OMAE 2019 paper. The comparison is done using metrics such as root mean square error (RMSE), Mean Absolute Error (MAE), Coefficient of Determination (R2) and Explained Variance Score (EVS). Thereafter, the trained NN model is used to make predictions of fatigue strength for the simulated data (1 million samples) of input parameters, which is then used to generate conditional probability tables for the Bayesian Network (BN). The main advantage of using BN over previously used machine learning algorithms is that BN can be used to make both forward and backward propagation during the Bayesian inference. A case study illustrating the applicability of the proposed approach is also presented. Furthermore, a dashboard is developed using PowerBI, which can be used by practicing engineers to estimate fatigue strength based on composition and process parameters.
Dynamic Ship Domain Model Based on AIS Data for Inland Waterways
Authors: He Yankang , Zhang Di , Zhang Jinfen , Wu Bing , Guedes Soares Carlos
Published: December 2020

The existing ship domain models are mostly based on the navigation behavior of open water vessels, and they are not practicable to directly apply to inland rivers. Therefore, it is necessary to establish an inland ship safety domain model based on the ship traffic characteristic therein. Based on the AIS data in the Yangtze River, this paper establishes the functional relationship between these data through multiple regression analysis using data such as ship spacing, ship length, ship speed, and heading angle. Based on this, the safety distance between ships of different lengths in different situations and other ships is determined, so as to establish a dynamic ship domain model. At the same time, this paper explores the geographical relationship between ship and channel boundary and incorporates it into the ship domain model. Finally, a quantitative approach for ship collision risk is proposed, and the collision threat degree is calculated according to the relative heading of the ship and the position in the dynamic ship domain model. Two case studies, including crossing and overtaking situations, are performed to validate the proposed model.
Machine Learning Approach for Estimating Residual Stresses in Girth Welds of Topside Piping
Authors: Bhardwaj Sachin , Ratnayake R. M. Chandima , Keprate Arvind , Ficquet Xavier
Published: December 2020

Residual stresses are internal self-equilibrating stresses that remain in the component even after the removal of external load. The aforementioned stress when superimposed by the operating stresses on the offshore piping, enhance the chances of fracture failure of the components. Thus, it is vital to accurately estimate the residual stresses in topside piping while performing their fitness for service (FFS) evaluation. In the present work, residual stress profiles of girth welded topside sections of P91 pipes piping are estimate using a machine learning approach. The training and testing data for machine learning is acquired from experimental measurements database by Veqter, UK. Twelve different machine learning algorithms, namely, multi-linear regression (MLR), Random Forest (RF), Gaussian process regression (GPR), support vector regression (SVR), Gradient boosting (GB) etc. have been trained and tested. In order to compare the accuracy of the algorithms, four metrics, namely, Root Mean Square Error (RMSE), Estimated Variance Score (EVS), Maximum Absolute Error (AAE), and Coefficient of Determination (R^2) are used. Gradient boosting algorithm gives the best prediction of the residual stress, which is then used to estimate the residual stress for the simulated input parameter space. In the future work authors shall utilize the residual stress predictions from Gradient boosting algorithm to train the Bayesian Network, which can then be used for estimating less conservative through-thickness residual stresses distribution over a wide range of pipe geometries (radius to thickness ratio) and welding parameters (based on heat input). Furthermore, besides topside piping, the proposed approach finds its potential applications in structural integrity assessment of offshore structures, and pressure equipment’s girth welds.
Experimental Investigation of Pressure Drop of Gas/Non-Newtonian Flow in Horizontal Pipes
Authors: Ben Rajeb Faraj , Odan Mohamed , Imtiaz Syed , Zhang Yan , Awad Mohamed M. , Rahman Mohammad Azizur
Published: December 2020

Two-phase flow of gas/non-Newtonian fluid through pipes is commonly occurred in chemical industry and oil and gas refinery. Many correlations have been developed to evaluate pressure drop for non-Newtonian fluids. Based on that, these systems are not governed by Newtonian law of viscosity. However, only little experimental work has been devoted to study non-Newtonian flow behavior. In this present work, experimental setup has been conducted to investigate non-Newtonian two-phase (gas/ liquid) flow through pipes. Several concentrations of Xanthan Gum have been used as non-Newtonian liquid in the experiments and compressed air has been used as a gas. The flow rate and pressure of liquid and gas are changed by using a pump placed ahead of the mixing point. Pressure and temperature values are recorded by pressure sensors and thermocouples fixed at specific points along the pipe loop. Results of theses experiments are leaded to come up with experimental model for pressure drop of gas/non-Newtonian flow in pipes. Moreover, the flow regimes of two-phase gas/non-Newtonian flow at different conditions have been visualized through transparent tubes using a high-speed camera.
A Numerical Study of TAD and TLP Platforms Operating Side by Side
Authors: Tong Bo , Chang Rui , Kang Zhuang , Sui Haibo , Li Shaojie
Published: December 2020

A Tender Assisted Drilling (TAD) is typically a support vessel that serves support of a drilling rig, by offering comfortable accommodation for crew and providing additional space where the Drilling Equipment Set is stored and transported. The operation with TAD provides an economical and flexible way for offshore drilling, especially with TLP. Dynamic response of tender-assisted drilling system is crucial due to the safety concern. However, some urgent issue has not been thoroughly studied in tender assisted drilling operation like the hydrodynamic interaction and the impact of nonlinearity cable used. In this paper, a tender assisted drilling system which was taken as the research object was investigated under the metocean conditions of West Africa. The numerical model was established in frequency domain using 3D multi-body diffraction/radiation wave theory and the hydrodynamic interaction is studied in this part. Then two kinds mull-body system with different hawsers arrangements are analyzed by the time domain simulation was performed considering hydrodynamic interaction and the impact of nonlinearity of mooring lines and hawsers. The Time history results of floating body motion and the force on mooring line is compared between two schemes. The results obtained is also investigated by spectral analysis to clearly understand the coupled behavior of such system under these two arrangement.
Estimating Wave Induced Kinematics Underneath Measured Time Histories of Surface Elevation
Authors: Johannessen Thomas B.
Published: December 2020

The present paper is concerned with the accurate prediction of nonlinear wave kinematics underneath measured time histories of surface elevation. It is desired to develop a method which is useful in analysis of offshore measurements close to wind turbine foundations. The method should therefore be robust in relatively shallow water and should be able to account for the presence of the foundation and the shortcrestedness of offshore seastates.

The present method employs measurements of surface elevation time histories at one or a small number of locations and solves the associated velocity potential by minimizing the error in the free surface boundary conditions. The velocity potential satisfies exactly Laplace’s equation, the bed boundary condition and (optionally) the boundary condition on the wall of a uniform surface piercing column. This is achieved by associating one wavenumber with every wave frequency thereby sacrificing the possibility of following the nonlinear wave evolution but ensuring a good description of the wave properties locally. For shortcrested waves, the direction of wave component propagation is drawn from a known or assumed directional spectrum. No attempt is made to calculate the directional distribution of the wave field from the surface elevation measurements since this is usually not realistically possible with the available data.

The method is set up for analysis with or without a uniform current, for shortcrested or longcrested waves and with or without a surface piercing column in the wave field. It has been compared with laboratory data for steep longcrested and shortcrested waves. The method is shown to be in good agreement with measurements. Since the method is based on a Fourier series of surface elevation, however, it cannot model overtopping breaking waves and associated wave impact loading. For problems where wave breaking is important, the method may serve as a screening analysis used to select wave events for detailed analysis using Computational Fluid Dynamics (CFD).
Dimensioning of Rudder Systems for Ice Class Ships
Authors: Hindley Rob , Adams Jillian , Valtonen Ville , Sung Chi-Hyun
Published: December 2020

Rudder systems (rudder control surfaces and steering gear) are a safety critical element of ships operating in ice-covered waters. Icebreaking ships equipped with single rudders are particularly vulnerable considering the remote and often isolated locations in which they operate. The IACS Polar Class Rules were developed as a set of harmonized requirements for ships operating in polar waters. First published in 2006 the rules contain requirements for dimensioning the hull structure and propulsion machinery to resist ice loads. There are however no specific requirements for rudders — the rules simply require appendages to be dimensioned using the hull ice load. This paper presents a series of studies aimed at providing guidance on dimensioning rudders and steering gear systems for operation in ice. Using existing ship reference cases and rudder ice loading scenarios found in previous rules and guidelines a simplified set of design approaches are presented. These approaches are evaluated with Finite Element Analysis and compared with selected measured full-scale data and damage incidents. Guidance is provided on system protection mechanisms for the steering gear under these design and over-load cases. In addition, a comparison is made between the results and those derived from using the hull area design pressures in the current IACS rules.
Collapse Failure Analysis of Subsea Corroded Pipeline Under Combined External Pressure and Axial Force
Authors: Chen Yanfei , He Guoyan , Dong Shaohua , Hou Fuheng , Ma Shang , Hu Dong , Gao Modi
Published: December 2020

The subsea pipelines are usually located in a corrosive external and internal environment. Corrosion presents to be the most common defect type in subsea pipelines, and it is regarded to be one of the main causes of subsea pipeline failure. Due to subsea subsidence, mudslides, and seismic activities, the pipeline is presented under combined external pressure, bending moments and axial force combined loading cases. The accurate determination of the collapse pressure of corroded pipelines under combined loading is important in engineering practice.

On the basis of the finite element method, collapse failure of subsea corroded pipelines under combined loads is investigated. The influence of corrosion length, corrosion width, corrosion depth and diameter-thick ratio on the collapse failure pressure is studied. It is observed that corrosion depth has the most significant impact on pipelines’ collapse capacity. Furthermore, regression equations for predicting the collapse pressure of subsea corroded pipelines are proposed based on numerical results. The solution can be referred to in structural integrity assessment of subsea corroded pipelines.
Fracture Assessment of Flaws in Undermatching Welds
Authors: Vasilikis Daniil , Tkaczyk Tomasz , Pepin Aurelien
Published: December 2020

The criticality of girth weld flaws in subsea pipelines, installed by methods introducing plastic strains such as reel-lay, is usually evaluated through an engineering critical assessment (ECA). Most ECA methodologies require weld overmatch for pipes subjected to plastic deformation. This, however, is not always achievable for corrosion resistant or even carbon steel pipelines. In this case, a material and geometry-specific ECA is often applied.

However, this ECA approach necessitates many 3D finite-element (FE) fracture analyses to be performed. Therefore, the authors propose a simpler screening assessment, which requires undertaking only a limited number of 3D FE fracture analyses. If the significance of a weld undermatch is shown to be negligible then a material and geometry-specific FE-based ECA is deemed unnecessary. Instead, flaw acceptance criteria can be determined under the assumption of weld evenmatch using a material-specific analytical ECA.

The work was undertaken to define and validate the screening assessment process. Subsequently, DNV-GL endorsed the proposed approach which has since been successfully applied on several projects allowing optimization of the project cost and schedule. This paper describes the screening assessment methodology and discusses its application range and limitations. The conclusions and recommendations from a validation program are also provided.
Hydroelastic Analysis of the Bending-Torsional Coupling Vibrations of an Ultra-Large Container Ship
Authors: Li Hui , Lu Lin
Published: December 2020

Springing is a resonance phenomenon between the waves and the ship hull, and the high frequency vibration will threaten the safety of hull structures. With the development of economy, the size of ultra large container ships has been increasing, and the resulting springing and whipping response and their effects has been paid more and more attention. The structure of an ultra large container ship is essentially U-shaped with a low shear center, which results in strong coupling between horizontal bending and torsion. On the other hand, the actual response of hull structures will have an apparently dynamic amplification phenomenon under the effect of springing. In this paper, the wave-induced loads on the hull structure is estimated in the framework of the 3D linear hydroelastic theory, which coupling horizontal and torsional vibration. The vibration characteristics are investigated by using finite element method (FEM), which can get a better calculation accuracy than the simplified calculation method such as the Transfer Matrix Method. And the mode shape of displacement and section loads of the whole ship can be obtained and processed, which is needed for the analysis of hydroelasticity. Finally, in order to consider the effect of the dynamic amplification effect, the dynamic response analysis approach is used for the stress calculation. A 21000TEU is calculated by this method, and the difference between wave-induced and springing-induced section load in frequency domain is shown. Then the results of the frequency response analysis is compared with the quasi-static methods. And the effect of the springing and the dynamic magnification is analyzed.
Experimental Study of Drill Cuttings Transport in Horizontal Well With Newtonian Fluid
Authors: Huque Mohammad Mojammel , Imtiaz Syed , Butt Stephen , Zendehboudi Sohrab , Rahman Mohammad Azizur
Published: December 2020

Transport of cuttings is crucial in a horizontal drilling operation. Effective removal of cuttings is necessary for efficient drilling. An experimental investigation has been carried out to analyze the flow behaviour of solid cuttings in different drilling environments with visualization techniques.

This study investigates the cuttings transport mechanism in a horizontal annulus section. A 6.16 m long and 4.5″ × 2.5″ annulus section was used to model the real-time drilling behaviour with different flow rates, drill pipe rotations and eccentric positions. Water as a Newtonian fluid was used as drilling mud and 2–3 mm solid glass beds were used to simulate the drill cuttings. The in-situ volume fraction of cuttings in the annulus was estimated by Electrical Resistivity Tomography (ERT) analyzer. Visualization technique used to estimate the moving bed velocity in the horizontal annulus section. A highspeed camera was used to capture the transport phenomena of the moving solid particle at 2000 frames per second. The highspeed camera can effectively track each particle in the system. Analysis of high-speed camera revealed different cuttings transport phenomena like rolling of cuttings, stationary cuttings bed and cuttings suspended into the drilling mud.

Experimental investigation revealed that drill pipe rotation helps in cuttings bed movement and resist the formation of large cuttings dune in the annulus formation. Also, this study revealed that eccentric annulus shows less annular solid volume compared to a concentric annulus; however, an eccentric annulus is harder to clean compared to a concentric annulus section.
Flow Induced Vibration Analysis of Topside Piping at High Pressure
Authors: Emmerson Paul R. , Lewis Mike J. , Barton Neil A. , Orre Steinar , Lunde Knud
Published: December 2020

Flow induced vibration (FIV) from high velocity multiphase flow is a common source of vibration concern in process piping, potentially leading to fatigue failures and hydrocarbon leaks. FIV screening methods tend to be conservative for multiphase flows and are typically only validated for simple single bends at low pressure. FE can predict the response of a system if a sensible forcing function is provided. CFD can be used to predict realistic forcing functions in complex combinations of bends and tees, typically seen in process piping systems.

FIV studies were performed on a topside production system operated by Equinor, carrying multiphase flow at high pressure (∼69 bara) conditions, where significant vibration was measured. The study assessed different vibration simulation methodologies, combining FE analysis with forcing functions based on both correlations and CFD simulations. The aim was to gain a better understanding of the accuracy and limitations of calculation methods typically used to assess fatigue.

CFD simulations predicted similar force magnitudes but higher frequency forcing at 69 bara compared to equivalent simulations at atmospheric pressure (at the same liquid and gas superficial velocities). The forcing function correlations used do not predict higher frequency forcing at high pressure, which has a significant impact on the predicted vibration.

Care is required when undertaking this type of analysis. It is important to have an accurate FE model of the as-built pipework and supports as well as a forcing function which accurately represents the fluid forces on the bends. For the case simulated here the magnitude and peak frequency of the forcing function had a significant influence on the response of the structure. Forcing functions based on correlated data from tests at low pressure should be used carefully for high pressure systems. In addition, the inclusion of phasing of the forces at each bend can influence the structural response, and simulations performed in the frequency domain do not consider this.

A combination of CFD and FE modelling offers a potentially powerful tool for assessing and diagnosing multiphase FIV problems in hydrocarbon production piping systems.