bluuebunny/crossref_metadata_2025 huggingface dataset:
Real-Time Prediction of Reliability of Dynamic Positioning Sub-Systems for Computation of Dynamic Positioning Reliability Index (DP-RI) Using Long Short Term Memory (LSTM)
Authors: Fernandez Charles , Bhushan Kumar Shashi , Lok Woo Wai , Norman Rosemary , Kr. Dev Arun
Published: December 2020

In this study, a framework using Long Short Term Memory (LSTM) for prediction of reliability of Dynamic Positioning (DP) sub-systems for computation of Dynamic Positioning Reliability Index (DP-RI) has been proposed. The DP System is complex with significant levels of integration between many sub-systems such as the Reference System, DP Control System, Thruster / Propulsion System, Power System, Electrical System and the Environment System to perform diverse control functions. The proposed framework includes a mathematical computation approach to compute reliability of DP sub-systems and a data driven approach to predict the reliability at a sub-system level for evaluation of model performance and accuracy. The framework results demonstrate excellent performance under a wide range of data availability and guaranteed lower computational burden for real-time non-linear optimization.

There are three main components of the proposed architecture for the mathematical formulation of the DP sub-systems based on individual sensor arrangements within the sub-system, computation of reliability of sub-systems and optimized LSTM deep learning algorithm for prediction of its reliability. Firstly, the mathematical formulation for the reliability of sub-systems is determined based on the series/parallel arrangement of the sensors of each individual equipment item within the sub-systems. Secondly, the computation of the reliability of sub-systems is achieved through an integrated approach during complex operation of the vessel. Thirdly, the novel optimized LSTM network is constructed to predict the reliability of the subsystems while minimizing integral errors in the algorithm.

In this paper, numerical simulations are set-up using a state-of-the-art advisory decision-making tool with mock-up and real-world data to give insights into the model performance and validate it against the existing risk assessment methodologies. Furthermore, we have analyzed the efficiency and stability of the proposed model against various levels of data availability. In conclusion the prediction accuracy of the proposed model is scalable and higher when compared with other model results.
Stress Concentration Factors Calculation: Analytical and Numerical Approaches for Welded Tubular Joints
Authors: Paruolo Nathalia , Mello Thalita , Teixeira Paula , Pérez Marco
Published: December 2020

In the oil and gas industry, fixed platforms are commonly applied in shallow water production. In-place environmental conditions generates cyclic loads on the structure that might lead to structural degradation due to fatigue damage. Fatigue is one of the most common failure modes of offshore structures and is typically estimated when dimensioning of the structure during design phase. However, in times when life extension of existing offshore structures is being a topic in high demand by industry, mature fields may represent an interesting investment, especially for small companies.

Concerning fixed platforms, composed mainly by welded tubular joints, the assessment of hot spot stresses is considered to predict structure fatigue. The estimation of welded joint hot spot stresses is based on the stress concentration factors (SCFs), which are given by parametric formulae, finite element analysis (FEA) or experimental tests. Parametric formulae may be defined as a fast and low-cost method, meanwhile finite elements analysis may be time consuming and experimental tests associated with higher costs. Given these different characteristics, each method is applied according to the study case, which will rely on the joint geometry and associated loads.

Considering simple joint geometries several sets of parametric equations found in the literature may be applied. On the other hand, the SCFs calculation of non-studied yet complex joints consider known formulae adapted according to the under load joint behavior and geometry. Previous analysis shows that this adaptation may furnish different results compared to those obtained by FEA. Furthermore, it is observed that even for simple joints the results derived from the different methods may differ.

Given their importance for the oil and gas industry, since they are the basis for the assessment of the fatigue life of welded tubular joints which may impact on additional costs related to maintenance and inspection campaigns, the estimation of SCFs must be the most accurate as possible. Therefore, this paper intends to investigate the differences between results derived from parametric formulae and different FEA studies.
Local Study of Jet of a Fluid Sloshing Inside a Rolling Tank
Authors: Tsao Wen-Huai , Kinnas Spyros A.
Published: December 2020

Sloshing is an important topic for the integrity of LNG tanks and the overall stability of the vessel. In the past, the interaction between the free surface and its substructure have been studied, especially where high-speed fluid jets impinge on the interior surface of the tank, and sometimes cause damage. In this paper, a boundary element method (BEM) with a fourth-order Runge-Kutta scheme is used to study the local phenomenon of nonlinear free-surface motion in a two-dimensional tank subject to roll motions. As the external excitations are nearly resonant with the fluid inside the tank, large free-surface deformations usually take place. The dynamic responses including the fluid velocity and pressure will grow drastically as the fluid is slamming on the walls. If no adequate conditions are applied, it is difficult to capture the peak physical quantities associated with strong nonlinear waves by most conventional Eulerian-Lagrangian methods. The numerical error will be accumulated and enlarged in just a few computational steps, which will eventually lead to unstable solutions. This paper will study the local phenomenon of a fast-moving jet forming on the wall of the tank, and its effect on the numerical stability and accuracy of the method overall. Some special numerical treatments are carried out for the local phenomenon approximation. The conservation of fluid mass is employed to obtain a reasonable geometry of the jet and its velocity along the wall. This provides a new set of rational boundary conditions applied on the walls, rather than using the artificial damping effect of other researchers. Results from the present method are compared with those from the volume of fluid (VOF) method implemented in ANSYS Fluent. The local free-surface shape in the vicinity of the jet and some local and global flow field patterns, including velocity and pressure, will be compared with and verified with experimental observations and measurements.
Accelerated Hydrodynamic Analysis for Spar Buoys With Second-Order Wave Excitation
Authors: Pegalajar-Jurado Antonio , Bredmose Henrik
Published: December 2020

The simplified numerical models commonly employed for the pre-design of floaters for offshore wind only include linear wave loads, due to the higher computational effort required by second-order methods. Second-order hydrodynamics, on the other hand, need to be considered from an early stage, since they cause resonance of the moored structure. In the present study, we introduce a new method to include second-order inviscid hydrodynamic loads at a computational cost similar to linear loads. We compare the accelerated method to standard second-order diffraction theory and to second-order Rainey forcing with Sharma & Dean wave kinematics. The comparison, based on the loads and response of a spar floating wind turbine in surge and pitch, is carried out for three different sea states. We find that a good prediction of the second-order resonant response can be obtained with the accelerated method for medium and severe sea states, while the match is not as good for the mild sea state. The accelerated method is between 400 and 850 times faster than commonly used second-order approaches, for an 1-hour realization of a given sea state. This speed up allows the application of the load model in the floater pre-design, where efficient numerical models are the key to achieve optimal designs and the consequent reduction in the cost of the floater.
Using Kriging Surrogate Models to Predict the Vibration Responses of a Submerged Riser
Authors: Damasceno Marcelo , Neto Hélio Ribeiro , Costa Tatiane , Cavalini Júnior Aldemir , Aguiar Ludimar , Martins Marcos
Published: December 2020

Fluid-structure interaction modeling tools based on computational fluid dynamics (CFD) produce interesting results that can be used in the design of submerged structures. However, the computational cost of simulations associated with the design of submerged offshore structures is high. There are no high-performance platforms devoted to the analysis and optimization of these structures using CFD techniques. In this context, this work aims to present a computational tool dedicated to the construction of Kriging surrogate models in order to represent the time domain force responses of submerged risers. The force responses obtained from high-cost computational simulations are used as outputs for training and validated the surrogate models. In this case, different excitations are applied in the riser aiming at evaluating the representativeness of the obtained Kriging surrogate model. A similar investigation is performed by changing the number of samples and the total time used for training purposes. The present methodology can be used to perform the dynamic analysis in different submerged structures with a low computational cost. Instead of solving the motion equation associated with the fluid-structure system, a Kriging surrogate model is used. A significant reduction in computational time is expected, which allows the realization of different analyses and optimization procedures in a fast and efficient manner for the design of this type of structure.
Comparison of Two Versions of the MNLS With the Full Water Wave Equations
Authors: Tang Tianning , Li Ye , Bingham Harry B. , Adcock Thomas A. A.
Published: December 2020

Versions of the non-linear Schrödinger equation are frequently used for modelling the non-linear propagation of water waves. In this paper, we compare two models against the results of fully non-linear numerical simulations. We consider uni-directional versions of the non-linear Schrödinger equation of Dysthe et al. with the hybrid model of Trulsen et al. The model of Trulsen et al. is shown to have clear advantages in all situations considered including modelling wave crest statistics for highly non-linear cases. However, for very broad bandwidths this model does start to break down, presumably due to the inherent limitation of the envelope representation of water waves. This in turn leads to a small, non-physical, leakage of energy in nonlinear simulations, although, this leakage is much smaller than for the version with 5th order linear dispersion relationship.
Potential Sealing Effects of Permanent Casing Deformation
Authors: Gheibi Sohrab , Sangesland Sigbjørn , Sevillano Lucas C. , Horák Martin
Published: December 2020

Permanent plugging and abandonment (P&A) of oil- and gas wells requires proper sealing between the formation and the casing as well as proper sealing inside the casing. The cement sheath in the annulus is intended to function as an “impermeable” barrier. Typically, shrinkage of cement sheath takes place when the cement sets and a microannulus (MA) may be formed. In addition, cyclic pressure and temperature variations may result in cracks and debonding of the cement sheath. This paper investigates the possibility of improved cement sealing imposed by permanent deformation of the casing, thus providing a mechanical compression force to the cement and thus closing the MA when performing P&A.

Two experimental setups were designed in this context. The first setup termed casing/cement plug test, where the casing is contracted by an external pressure and simultaneous measurement of the flow rate through the setup. The second setup is termed casing/cement annular test where the casing is internally pressurized while the gas flow rate is measured.

Nonlinear finite element analyses were carried out to simulate the two test setups. The numerical results showed an acceptable agreement with the observations in the lab. The second setup was not tested in the lab, but simulated using the FEM code. The numerical analyses indicated that the same concept of casing permanent deformation is also relevant for the annular test. It is shown that the micro-annulus formed due to cycles of pressurization/depressurization as a result of inelastic deformations in the cement can be repaired by inducing permanent deformation in the casing to some extent. Finally, we concluded that permanent casing deformation could play a positive role in favour of closing the micro-annuli in P&A operations.
Crushing of a Steel Tube Umbilical (STU) Cable During Laying Operation: A Finite Element Method Assessment at the Entry/Exit Regions of Tensioner Shoes
Authors: Guttner William C. , Santos Caio C. P. , Pesce Celso P.
Published: December 2020

Umbilical cables are fundamental equipment used in deep and ultra-deep waters oil and gas production systems. The complexity of this kind of structure leads structural analysis to be currently performed with numerical tools. This paper presents a nonlinear three-dimensional finite element model of a typical armored Steel Tube Umbilical Cable (STU) subjected to crushing loads imposed to the umbilical cable during laying operation. The study focuses on the analysis of the stress distribution in the steel tubes at caterpillar shoes, mainly at the entry/exit transition regions. With the use of a commercial software, the finite element model is constructed, considering geometric and materials nonlinearities. Crushing loads are imposed by two rigid plates. Focus is given on the duplex tubes, with the material stress-strain curve modeled from a specific crushing experiment with a single tube and by using a classic Ramberg-Osgood fitting. Firstly, comparisons at mid-length of the three-dimensional model are made with the results from a simpler and planar finite element model. Then, the localized three-dimensional effects are analyzed. The results show a considerable increase of the stress levels in the steel tubes at these transition regions, with the occurrence of stress field redistribution after the onset of plastic deformation.
A Fundamental Study on Plastic Strain Accompanying Deformation in Large-Scale Floating Coal Transshipment Station
Authors: Nishigochi Ryo , Eto Hiroaki , Iizuka Koji , Ikoma Tomoki , Aida Yasuhiro , Masuda Koichi
Published: December 2020

Indonesia is the main country supplying coal in the Asia-Pacific region, and in order to secure a stable supply of coal to neighboring countries, efficient coal transportation is required. East Kalimantan Island in Indonesia is the main coal-producing area, but the sea around the island is very shallow and bulk carriers for transporting coal cannot approach the coast. And then, Large-scale Floating Transposition Station for Loading Coal (hereafter LFTS) was proposed, which will be used as a transposition station between small coal barge coming down the river and bulk carriers that stays offshore. LFTS has a two-dimensional extent, and because the bulkheads for separating coal according to quality are installed on the floating body, the rigidity is partially different, and the draft also changes greatly according to the coal loading condition. In this way, LFTS has different characteristics from Mega-Float, which was built in Japan in the late 1990s with the aim of realizing a floating airport, so it is important to clarify its structural characteristics. In order to grasp the stress distribution acting on the structural member in consideration of the influence of the interaction between the overall deformation and the local deformation of LFTS, an analysis in which the entire structure is modeled in detail is desired. However, because members such as the internal bulkheads are arranged in a complicated manner in LFTS, a model in which the entire structure is modeled in detail requires enormous calculation costs in both capacity and time, it is difficult to perform the analysis. In existing research, various models have been studied, but there remains a problem in setting boundary conditions that reproduce the interaction between global and local deformations. And then, in this paper, a new modeling method of LFTS that can be analyzed efficiently was proposed. And the occurrence of stress concentration in the structural members of the LFTS was identified by systematically changing the external force conditions such as the coal loading condition and wave load assumed during the operation of the LFTS, and performing LFTS oscillation analysis and stress deformation analysis. Furthermore, the occurrence of plastic strain due to large deformation was investigated. The stiffening method that efficiently suppresses the occurrence of plastic strain was studied for the locations where the plastic strain was identified by the above analysis. These results demonstrate the importance of modeling large floating structures with complex structures.
Modeling Spatio-Temporal Characteristics of Metocean Conditions During Hurricanes Using Deep Neural Networks
Authors: Qiao Chi , Myers Andrew T.
Published: December 2020

Surrogate modeling of the variability of metocean conditions in space and in time during hurricanes is a crucial task for risk analysis on offshore structures such as offshore wind turbines, which are deployed over a large area. This task is challenging because of the complex nature of the meteorology-metocean interaction in addition to the time-dependence and high-dimensionality of the output. In this paper, spatio-temporal characteristics of surrogate models, such as Deep Neural Networks, are analyzed based on an offshore multi-hazard database created by the authors. The focus of this paper is two-fold: first, the effectiveness of dimension reduction techniques for representing high-dimensional output distributed in space is investigated and, second, an overall approach to estimate spatio-temporal characteristics of hurricane hazards using Deep Neural Networks is presented. The popular dimension reduction technique, Principal Component Analysis, is shown to perform similarly compared to a simpler dimension reduction approach and to not perform as well as a surrogate model implemented without dimension reduction. Discussions are provided to explain why the performance of Principal Component Analysis is only mediocre in this implementation and why dimension reduction might not be necessary.
Numerical Simulation of Elastic Deformation Based on Peridynamic Differential Operator
Authors: Hu Yumeng , Liu Fan , Feng Guoqing , Zhang Dongxu
Published: December 2020

The methodology of Peridynamics has been proposed for years and widely used in various engineering fields. The evolution of this theory is always in process, and two major branches appears, namely bond-based and state-based peridynamic method. Recently, a novel concept, peridynamic differential operator, was proposed and adopted in simulation of Newtonian fluid and analysis of structure strength. Just like the intrinsic idea in peridynamic theory, this new operator could convert the partial differential into its integral form so that it would enable the numerical differentiation through integration and avoid difficulties such as discontinuities or singularities encountered in the simulation. Also, unlike the traditional method that the higher order partial differential items are derived from the lower ones, peridynamic differential operator could easily provide differential items with any desired order thus it makes calculation process more efficient and convenient. In this study, the accuracy of peridynamic differential operator is tested by comparing with a given analytical formula. Then, this operator is embedded into the framework of Galerkin method and adopted for elastic deformation analysis in 2D case. The results are compared with those obtained from finite element method and its efficiency and feasibility are verified.
Caisson Breakwater for LNG and Bulk Terminals: A Study on Limiting Wave Conditions for Caisson Installation
Authors: Lin Yu , El Chahal Ghassan , Shao Yanlin
Published: December 2020

As the worldwide oil and gas market continues to grow and environmental concerns with respect to in-port offloading of gas have increased, there has been a boom of interest in new liquefied natural gas LNG terminals in the past years. Loading - offloading operations at LNG and bulk terminals are generally protected by a breakwater to ensure high operability. For these terminals, caisson breakwaters are generally a preferred solution in water depth larger than 15 m due to its advantages compared to rubble mound breakwaters. The caisson installation is generally planned to be carried out in the period where sea conditions are relatively calm. However, many of these terminal locations are exposed to swell conditions, making the installation particularly challenging and subject to large downtime. There is no clear guidance on the caisson installation process rather than contractors’ experiences from different projects/sites. Therefore, studies are required in order to provide general guidance on the range of acceptable wave conditions for the installation operations and to have a better understanding of the influence of the caisson geometry.

This paper presents a numerical study to determine the limiting wave conditions for caisson installing operations at larger water depth of 30–35 m for a confidential project along the African coast. Three caisson sizes/geometries are considered in order to assess and compare the wave-structure hydrodynamic interaction. The linear frequency-domain hydrodynamic analysis is performed for various seastates to determine the limiting wave conditions. Viscous effects due to flow separation at the sharp edges of the caisson are considered by using a stochastic linearization approach, where empirical drag coefficients are used as inputs. Parametric studies on caisson size and mooring stiffness are also presented, which can be used as a basis for future optimization. The uncertainty in the applied empirical viscous drag coefficients taken from the literature is examined by using a range of different drag coefficients. Further, the use of clearance-independent hydrodynamic coefficients (e.g. added mass and damping) may be questionable when the caisson is very close to the seabed, due to a possible strong interaction between caisson bottom and seabed. This effect is also checked quantitatively by a simplified approach.

The findings of the study are presented in the form of curves and generalized to be used by designers and contractors for general guidance in future projects.
Effect of Rheological Properties of Yield Pseudoplastic Fluids on Slugs Characteristics in an Upward Vertical Pipe: Experiments and Modeling
Authors: Ihmoudah Abdalsalam , Awad Mohamed M. , Rahman Mohammad Azizur , Butt Stephen D.
Published: December 2020

Two-phase flow of gas/yield Pseudoplastic fluids can be found in different industrial applications like the chemical processes, oil industry, and petroleum transport in pipelines. In this study, experimental and numerical investigation of the influence of Rheological properties of non-Newtonians fluids in two-phase flow (gas/yield Pseudoplastic fluids) on slug characteristics in an upward vertical flow were performed. Different concentrations of Xanthan gum solutions (0.05%, 0.10%, and 0.15%, by w/w), which are referred to as non-Newtonian, yield Pseudoplastic behavior used as the working liquids and air as a gas. The experiments were conducted in an open-loop re-circulating system has a total length of 65 m to ensure phase mixing, and authorize flow regime patterns to develop. The vertical pipe has a diameter of 76.3 mm. API-compliant 8-speed rotational viscometer model 800 was used to measure the rheological properties of non-Newtonian fluids. Flow visualization and recording videos were achieved by A high-speed camera to a comparison between behavior of Newtonian and non-Newtonian fluids in the two-phase model. Pressure transducers used to measure high-response pressure. Computational fluid dynamics software (ANSYS fluent 2019 R3) was used for the numerical investigation. The volume of fluid (VOF) model has been chosen for tracking immiscible fluids. CFD simulation results compared to the experimental data. The slug behavior and shape were noticed to be affected by changing the rheological properties of the liquid phase. with increasing XG concentration at the same operations conditions, we found that non-uniform and random distribution of small bubbles due to the effective viscous force of a liquid phase.
Blowing the Top on Parametric Resonance: Relief Valve Control for the Stabilisation of an OWC Spar Buoy
Authors: Davidson Josh , Gomes Rui P. F. , Galeazzi Roberto , Henriques João C. C.
Published: December 2020

An active control method, to suppress the onset of pitch/roll parametric resonance on an oscillating water column (OWC) spar buoy, is proposed in this paper, which utilises a pressure relief valve at the top of the OWC air chamber. The paper examines the hypothesis that by opening the relief valve, to reduce the air chamber pressure difference and to decouple the dynamics of the spar buoy and the OWC within, the natural pitch/roll frequencies of the system will be shifted, allowing parametric resonance to be cancelled when its onset is detected. The paper reports on experiments, performed to test the stated hypothesis, with a small-scale model OWC spar buoy in a wave flume. Two configurations are considered and tested in a range of monochromatic waves (1) fully closed air chamber; (2) fully open chamber. The results partially confirm the hypothesis, demonstrating that the occurrence of parametric resonance observed for certain wave frequencies when the chamber is closed does not occur when the chamber is open. However, the change in the natural pitch/roll frequencies between the two configurations is very small, and parametric resonance occurs in both confurations for waves with twice this frequency.
Experimental Investigation of Tip Vortex Influence on VIV of a Circular Cylinder at High Reynolds Numbers
Authors: Youssef M. , Tödter Simon , Neugebauer Jens , el Moctar Ould , Schellin Thomas E.
Published: December 2020

Lower aspect ratio cylinders are of interest as these are used for, e.g., wind turbine towers. We present a study predicting the vortex-induced vibration (VIV) characteristics of a cantilever circular cylinder with an aspect ratio (length-to-diameter ratio) of 10. The free end condition caused tip vortices to generate end-cell-induced vibration (ECIV) occurring at wind speeds higher than the threshold wind speed for VIV. Wind tunnel experiments were conducted at Reynolds numbers ranging from 3.6 × 104 to 3.26 × 105. The cantilever circular cylinder was made of a polypropylene pipe mounted on a six-degree-of-freedom load cell. Its upper end was free to oscillate in the streamline and transverse directions. An accelerometer was placed at the top of the cylinder to measure accelerations and, via twofold integration, retrieve cylinder motions at its free end. Down-wash tip vortices occurred. The response amplitude with vortex shedding was finite, even at the synchronization point. It increased with flow velocity and affected the synchronization behavior. Results suggested that nonlinearities occurring when vortices were Shedd were due to free end conditions and higher Reynolds numbers.
Study on Data Analysis of On-Board Measurement Data for Ship’s Speed Power Performance
Authors: Kim Sang-Yeob , Kim Min-Su , Han Ki-Min , Kim Joon-gyu , Seo Dae-Won
Published: December 2020

Present paper deal with data analysis of on-board measurement data from operating ship. The main purpose of the study is estimating speed-power performance of target ship which are in service now. Various kinds of on-board measured data are considered such as ship speed, engine RPM, brake power, draught, rudder angle, etc. Also, in order to estimate the added resistance, weather forecast data about wind, wave and current was considered. What this study found was that the onboard measurement data and weather forecast data have a lot of uncertainty, so the data need to be post-processed in order to derive reliable speed power performance curve. For this reason, current study proposed three-step filtering procedure. The filtering schemes are based on 1) absolute threshold value, 2) moving window, 3) derivative threshold value. The paper compared the performance estimation results of ship with and without filtering technique and some conclusions could be drawn.
Virtual Prototyping of a Low-Height Lifting System for Offshore Wind Turbine Installation
Authors: Xu Jiafeng , Ataei Behfar , Halse Karl Henning , Hildre Hans Petter , Mikalsen Egil Tennfjord
Published: December 2020

Due to the ever higher demands from the energy market, the quantity, dimension and power capacity of newly installed offshore wind turbines are continuously increasing. In terms of logistical management, economic feasibility and engineering difficulty, the traditional installation methods, predominantly represented by using Jack-up vessel and offshore cranes, will hit their limitations soon in the future. Offshore turbines have a relatively fixed geometric profile and physical characteristics: a slender cylindrical tower with huge blades attached on the top end. In this work, we exploited these features and designed a low-height lifting system for deploying wind turbine onto a floating spar platform. The low-height lifting system lifts the wind turbine with wires attached to the bottom of the tower, and keeps the balance of the tower with extra tug lines on the mid-section. The wires and tug lines are controlled by an active 6DOF compensation system. The low-height lifting system removes the necessity of a huge offshore crane onboard and can scale well to even larger wind turbines. The design is virtual prototyped in the simulator of Offshore Simulator Centre using FATHOM simulation software. Different design configurations are discussed in terms of the general arrangement, system dimensions and control methods.
Barrier Analysis of Emergency Disconnect on DP Mobile Offshore Drilling Units
Authors: Chen Haibo , Bauge Tommy , Reinås Lorents , Landeråen Paul
Published: December 2020

Technical, operational and organization barrier elements related to the emergency disconnect on dynamically positioned mobile offshore drilling units on the Norwegian Continental Shelf are identified. Position loss scenarios are analyzed based on the published station-keeping incidents by IMCA (International Marine Contractors Association). How these barrier elements may fail in different types of position loss scenarios are addressed qualitatively and quantitatively in an event tree model. A case study is provided in the paper and notational probability of failure to disconnect given position loss is calculated. Risk reduction effect of various barrier elements are investigated by sensitivity studies. The paper provides insights into risk given position loss and failure of emergency disconnect on DP MODUs. It offers decision support for risk management of DP drilling and well operations in shallow water and harsh environment.
Offshore Topside Weight Prediction Using Data Science
Authors: Ahmadian Reza , Tcherniguin Nicolas , Tiberti Jean-François
Published: December 2020

The history of engineering shows many design solutions undergoing further improvements over time to optimize the system and eventually perfect it. However today, with a tendency for design specifications to be much stricter and with ever increasing commercial pressure to save time, materials and cost, there is a need to reach perfectible limits of an engineering system in the first step of the design process. It is therefore increasingly necessary to anticipate the design in a shorter time to maintain the schedule and therefore the competitiveness of the project. This emerging reality is most evident during the early phase of projects when the time is very short to prepare a robust budget in a competitive situation (either between solutions or providers). In this scenario, precise estimation of weight (which is strongly correlated to cost) and a prediction of its evolution during the course of all phases of an offshore project is critical when considering the overall economics, and hence the viability, of a development.

The objective of this paper is to provide a summary of a digital initiative, sponsored by the Onshore/Offshore Global Business Unit (GBU) of TechnipFMC, with the aim of using data science and data mining techniques to improve the operational efficiency of our activities. This digital initiative aims to better understand the evolution of the weight of offshore industrial projects that TechnipFMC designs and identify the impact of each influencing variable.

During the first phase, data mining algorithms are developed to automatically extract the influencing variable data from past project documentation including graphs from scanned documents using data science techniques such as transfer learning. In the second phase, the extracted data is automatically stored in a data base allowing analysis for specific causes of variance in weights. During the third phase, statistical models are used to highlight the influencing variables and their impact on the evolution of weight, giving trends which lead to an understanding of the increase or decrease of the weight. Finally, the developed algorithms can provide an estimation of the topside weight according to the design basis variables of a new project using machine learning techniques.
The Study on Flow Past a Static Hydrofoil Using Deep Neural Network
Authors: Wu Xia , Tian Xinliang , Kou Yufeng , Li Xin , Lu Wenyue
Published: December 2020

The study on flow around a hydrofoil has been performed using various methods experimentally and numerically. Here we use a purely data-driven model using deep neural networks (DNNs) to reconstruct the flow fields. Its results are also compared with that obtained by traditional methods. The datasets of flow fields around a static hydrofoil obtained from computational fluid dynamics (CFD) are used for training the DNNs and then the trained data-driven model is utilized to make reconstructions and predictions. 9 different physics informed loss functions, which contain the prediction error and the error measuring the violation of the conservation law, are proposed to train the parameters of DNNs. Effects of the proposed loss functions on reconstruction of velocity field and pressure field are analyzed. Lift and drag forces predicted during the training time are also analyzed. However, the data-driven model based on DNNs with the optimum loss function works well in the interpolation but fails in the extrapolation. The reasons causing the errors are discussed.
Design Optimisation of a Multi-Mode Wave Energy Converter
Authors: Sergiienko Nataliia Y. , Neshat Mehdi , da Silva Leandro S. P. , Alexander Brad , Wagner Markus
Published: December 2020

A wave energy converter (WEC) similar to the CETO system developed by Carnegie Clean Energy is considered for design optimisation. This WEC is able to absorb power from heave, surge and pitch motion modes, making the optimisation problem nontrivial. The WEC dynamics is simulated using the spectral-domain model taking into account hydrodynamic forces, viscous drag, and power take-off forces. The design parameters for optimisation include the buoy radius, buoy height, tether inclination angles, and control variables (damping and stiffness). The WEC design is optimised for the wave climate at Albany test site in Western Australia considering unidirectional irregular waves. Two objective functions are considered: (i) maximisation of the annual average power output, and (ii) minimisation of the levelised cost of energy (LCoE) for a given sea site. The LCoE calculation is approximated as a ratio of the produced energy to the significant mass of the system that includes the mass of the buoy and anchor system. Six different heuristic optimisation methods are applied in order to evaluate and compare the performance of the best known evolutionary algorithms, a swarm intelligence technique and a numerical optimisation approach. The results demonstrate that if we are interested in maximising energy production without taking into account the cost of manufacturing such a system, the buoy should be built as large as possible (20 m radius and 30 m height). However, if we want the system that produces cheap energy, then the radius of the buoy should be approximately 11–14 m while the height should be as low as possible. These results coincide with the overall design that Carnegie Clean Energy has selected for its CETO 6 multi-moored unit. However, it should be noted that this study is not informed by them, so this can be seen as an independent validation of the design choices.
Treatment of Bending Deformations in Maritime Crash Analyses
Authors: Kõrgesaar Mihkel , Storheim Martin
Published: December 2020

This paper focuses on the bending deformation experienced by metallic materials and its characterization during the crash analysis of ship structures. These analyses are conducted with plane stress shell elements for computational reasons. The inherent nature of through thickness plane stress poses restrictions on how the bending associated stress and strain distribution are resolved. Namely, fracture criteria used in crash analysis account bending damage accumulation differently. Most criteria do not specifically address the issue as element erosion is activated once all through thickness integration points have reached the predefined failure condition. However, when elements are bent, material layers (top and bottom) display strong variations in mechanical field variables that are commonly used to control element deletion. Therefore, the focus of current analyses is to show how different fracture criteria account bending deformation and how sensitive are the results depending on the chosen element size.
Risk Assessment and Reliability Analysis of Subsea Production Systems
Authors: Ali Liaqat , Jin Shan , Bai Yong
Published: December 2020

In past years, offshore oil and gas accidents have often occurred. Environmental hazards have the capability of turning into very difficult to manage in addition with the modern technology limits and lack of a fail-safe operation that can identify, control and terminate the accidents. However, the offshore crude oil also natural gas search and development is expanding to deep-water and moving promptly to the subsea production systems. (SPS). Though, the complicate subsea equipment material besides frequency offshore disasters stimulated the consideration onto the risk analysis of subsea systems. Detection of the impact of deep-water oil and gas reserves in the subsea production system. However, loss of SPSs can contribute to massive industrial failure, severe natural pollution, and indeed serious disasters. Therefore, the reliability analysis and safety of SPS have turned into a dominant consideration.

This study addresses on the hazards and risk conditions which must be concentrated in the subsea machinery associated within surface equipments. Furthermore, the risks identification also the risk investigation onto subsea “Xmas tree” system is brought out. An over-all risk avert procedure of subsea “Xmas tree” system is represented, also the reliability evaluation method. Moreover, several recommendations on subsea production maintenance and detection are given in this research. This paper is reviewing the following section, subsea production system, hazards or risk identification, environmental issues, hydrate problems, corrosion problems, safety issues, risk assessment on subsea “Xmas tree”, reliability issues of a subsea system.
Improved ITTC Uncertainty Analysis Method of Ship Model Self-Propulsion Tests
Authors: Zhang Li , Chen Jianting , Zhou Chuanming , Chen Weimin
Published: December 2020

In this paper, the uncertainty analysis method of ITTC (2017) for ship model self-propulsion tests was studied, and the defects of the ITTC method were analyzed, which didn’t provide the method to analyze the tests results at different temperatures. Combined with the ship model self-propulsion tests carried out by SSSRI, an improved uncertainty analysis method was proposed. First of all, the ship model self-propulsion test process was combed to determine the error sources of uncertainty, and then according to the test principle of self-propulsion tests, an conversion method of test data at different temperatures was put forward. Furthermore, this improved method can be an additional procedure of ITTC on the uncertainty analysis of self-propulsion tests. At the same time, the steps and methods of uncertainty analysis of ship model self-propulsion tests can be used as a reference for other towing tank tests. At last, an example of the uncertainty analysis of self-propulsion results in SSSRI was presented. The results show that at the nominal temperature of 15°C, at 95% confidence level, the expanded uncertainty of rotational speed n is less than 0.4%, and the expanded uncertainty of thrust T and torque Q is less than 1.0%. The expanded uncertainty of thrust deduction factor t is less than 5.5%, wake fraction w 1.1%, which shows that the test in this paper has achieved high accuracy.
Numerical Simulation on Oblique Towing Tests and Pure Yaw Tests of a Containership in Surf-Riding Condition
Authors: Ma Chengqian , Ma Ning , Gu Xiechong
Published: December 2020

Maneuvering in waves is a complex and critical issue that confuses researchers for the last several decades. Among the existing methods for predicting the maneuverability in waves, the widely-used mathematical model approach (MMG model) is considered to be efficient and accurate in large wavelength and small wave steepness conditions. However, based on the assumption that the maneuvering forces in waves are the same as those in calm water, the wave effect on the hydrodynamic derivatives is neglected in most mathematical model approaches. According to the previous theoretical analysis and experimental data, this assumption is flawed. Therefore, several experiments and some numerical simulations have conducted to research the wave effect on hydrodynamic derivatives. In the present study, oblique towing tests and pure yaw tests will be simulated using the state-of-the-art CFD techniques to obtain the linear hydrodynamic derivatives in waves. The simulation cases in the present study are set according to previous PMM tests of S175 containership in surf-riding conditions. And the simulation results are in good agreement with experimental ones. Based on that, the wave effect on hydrodynamic derivatives is obtained and some discussions are made. Finally, the course stability of the containership on the different relative position of the wave are calculated to analyze the preliminary reason for the broaching-to phenomenon.
Ultimate Strength and Collapse Behavior of Ring-Stiffened Cylindrical Shells Under External Pressure With Shell Buckling or Stiffener Torsional Buckling
Authors: Shiomitsu Daisuke , Yanagihara Daisuke
Published: December 2020

A series of ultimate strength analyses of ring-stiffened cylindrical shells with various dimensions and scantlings is carried out applying the nonlinear finite element method. The detailed buckling/plastic collapse behavior including the influence of initial deflection applied in the ultimate strength analyses is investigated. In most past studies, detailed classification of collapse modes and investigation of the influence of the initial deflection mode have not been sufficiently conducted. In this study, firstly the ultimate strength analyses of 288 cases varying the dimensions of the ring-stiffened cylindrical shell and the attachment direction of the stiffeners, inside or outside, are performed. From the results, the collapse modes are classified into five modes, which are stiffener-torsional buckling collapse (localized deformation mode and mode to keep strength after the ultimate strength), shell buckling collapse (localized deformation mode and mode with kinking lines), and combined collapse of the buckling modes. A slenderness ratio is proposed using elastic buckling strength and pressure when the circumferential stress reaches the yield stress, and the possibility of estimating the ultimate strength is indicated.
Impacts of the Madden-Julian Oscillation on South China Sea Monsoon
Authors: Zhou Qun , Wei Lixin
Published: December 2020

It is of great practical importance to understand the variability of the South China Sea (SCS) monsoon on intraseasonal time scales, since the anomalous enhancement of the SCS monsoon may exert serious impacts on the safety of offshore engineering and marine transportation. Our composite analysis shows that the SCS surface wind anomalies are considerably varying with the Madden-Julian Oscillation (MJO) eastward propagation. The SCS summer southwest monsoon tends to be stronger (weaker) in phases 5–8 (1–4) of MJO with the largest positive (negative) wind-speed anomalies when the MJO convection is centered in the western Pacific (far western Indian Ocean), suggesting the highest (lowest) probability of the gale over the SCS. The variation of the western Pacific Subtropical High (WPSH), induced by the variations of the local meridional circulation, is shown to play a crucial role in the MJO-SCS summer monsoon linkage. The SCS winter monsoon is also shown to be modulated by the MJO with strengthened (weakened) surface northeasterly in phases 5–6 (1–2). The extra-tropical East Asian trough and East Asian westerly jet associated with the local meridional circulation can well explain the changes of the MJO-SCS winter monsoon relationship. The opposite responses of the wind direction during the same phases of the MJO between summer and winter may be attributed to the discrepancy of meridional circulation related to the wintertime equatorward shift of the MJO convection. The present study indicates that the MJO could be taken into consideration when applying extended-range weather forecast over the SCS as the predictability of the MJO activity is up to 15–20 day currently.
A Coupled Harmonic Polynomial Cell and Higher-Order Spectral Method for Nonlinear Wave Propagation
Authors: Hanssen Finn-Christian W. , Helmers Jens B. , Greco Marilena
Published: December 2020

The present work deals with wave generation in fully nonlinear numerical wave tanks (NWT). As an alternative to modelling a moving (physical) wavemaker, a two-dimensional (2D) potential-flow NWT is coupled with an external spectral wave data (SWD) application programming interface (API). The NWT uses the harmonic polynomial cell (HPC) method to solve the governing Laplace equations for the velocity potential and its time derivative, and has previously been extensively validated and verified for numerous nonlinear wave-propagation problems using traditional wave-generation mechanisms.

Periodic waves of different steepness generated with a stream-function theory as reference solution in the SWD API are first considered to investigate the method’s numerical accuracy. Thereafter, with a higher-order spectral method (HOSM) as the SWD API solution, irregular waves with different wave heights and water depths relevant for e.g. aquaculture and offshore structures are simulated. Differences between the HPC and HOSM solutions in and near steep crests are investigated.

The study aims to demonstrate a robust method to generate and propagate general wave fields for further studies of nonlinear waves and wave-body interaction in both two and three dimensions.