bluuebunny/crossref_metadata_2025 huggingface dataset:
The Development of 3D Hydroelastic Software and its Application on Platform
Authors: Ni Xinyun , Zhang Zhengwei , Tian Chao , Lu Ye , Ding Jun
Published: November 2019

In the past few decades, 3D hydroelastic theory, an important branch of ship mechanics, has been developing dramatically. It offers a fluid-structure interaction method calculating response of structure of ship or offshore platform directly, which plays an significant role in the evaluation of wave loads on maritime structures. For platform with multiple modules, it is not only referred to loads on modules themselves but also to connectors’ loads between modules for their performance prediction. Absolutely, the 3D hydroelastic method described here can solve this problem accurately and directly. In this paper, 3D hydroelastic software, named COMPASS-THAFTS, has been developed by CSSRC and CCS on the basis of 3D hydroelastic theory initially established by Wu (1984). This software is very proper for designers and researchers of offshore structures because of its convenient and fast processing function. The COMPASS-THAFTS software mainly contains two modules, frequency-domain module and time-domain module. In this paper, we will focus our attention on introduction of integrated framework and processing functions in frequency domain module of COMPASS-THAFTS. Taking a certain offshore platform as application object, the 3D hydroelastic responses are calculated and the results are processed, and finally, the internal rules of data are analyzed. In subsequent work, some new modules, such as mooring module, will be integrated into COMPASS-THAFTS.
Review of Available Probabilistic Models of the Crack Growth Parameters in Paris Equation
Authors: Amirafshari Peyman , Stacey Alex
Published: November 2019

Crack growth rate parameters of the Paris equation are crucial inputs in the engineering critical assessment (ECA) of structures containing flaws. In fracture mechanics based reliability analysis, probabilistic models of these parameters are often used. Despite the considerable body of research in this area, there is significant variability among available models. This paper reviews the current available models in the literature and addresses areas requiring further research with a view to assisting probabilistic flaw assessment. The effect of the existing variability in crack growth model parameters is investigated by fracture mechanics analysis of a case study crack.
Drained Lateral Breakout Resistance of Subsea Pipelines
Authors: Ballard Jean-Christophe , Westgate Zack
Published: November 2019

The lateral resistance between a subsea pipeline and the surrounding seabed is important for assessing stability and susceptibility to lateral buckling. The breakout, or peak, lateral resistance can exhibit undrained or drained behaviour depending on the rate of pipeline displacement relative to the permeability of the seabed. A drained response is common in coarse-grained soil but also can occur in transitional soil such as silty sands. While undrained breakout resistance is well understood, robust solutions for drained lateral breakout resistance of exposed subsea pipelines are lacking. The models currently used in practice exclude links to relevant soil properties such as the soil or interface friction angles despite their influence on the drained lateral breakout resistance. The lack of an industry-wide accepted approach for assessing drained lateral breakout resistance leads to an increase in the level of uncertainty being applied in routine design. To address this gap in pipe–soil interaction assessment, a parametric study using limit and finite element analyses is presented to illustrate the sensitivity of various input parameters on the lateral breakout resistance. The numerical results are compared to established drained lateral resistance models and model test data.
Extreme Value Estimation of Mooring Lines Top Tension
Authors: Simão Marina Leivas , Videiro Paulo Mauricio , Oliveira Mauro Costa , Sudati Sagrilo Luís Volnei
Published: November 2019

It is known that the mooring system of floating platforms responds non-linearly to environmental loads. Even though the wave-frequency excitation can be assumed as a Gaussian process, the line tension generally is not a Gaussian process due to the second-order slow-drift floater motions and the nonlinearities of the system itself. Distinct short-term time-domain analyses with the same wave spectrum excitation, i.e., distinct realizations of the response process, lead to a set of distinct values for the simulated individual maximum observed line tensions. Therefore, the ideal practice for estimating extreme tension values should be to perform a sufficiently large number of independent simulations along with an extreme statistical analysis considering the sample of the maximum line tension identified in each simulation. However, this process can be very time-consuming and cumbersome for everyday design applications. In this paper, the short-term line tension is assumed to be a non-Gaussian ergodic process. The extreme tension is then estimated based on the peaks sample of just a single simulated tension time-history. A number of known probability distributions are fitted to the peaks of the time series and classic order statistics theory is applied to determine the most probable extreme line tension corresponding to a specified short-time period (3-h) in order to identify the one with best performance. The proposed probability distribution models for the tension peaks are the 3-parameter Weibull distribution, the Weibull distribution fitted to the tail of the data (Weibull-tail) and the Shifted Generalized Lognormal Distribution (SGLD). The estimated extreme values are also prone to uncertainties due to time-domain simulation details. The effects of the major parameters in the dynamic analysis, such as simulation length and discretization level of the wave spectrum, are therefore investigated using several simulated mooring line tension time-histories. Furthermore, the effect of correlation between consecutive line tension peaks in the extreme values estimation is investigated through a Nataf transformation-based model for joint probability distribution for the peaks and the one step Markov chain condition. It is shown that this latter consideration leads to extreme value estimates that are invariably smaller than those obtained by standard order statistics. These estimates are also shown to be closer to the extreme estimates directly obtained from a sample of largest values taken from several distinct numerical simulations. Numerical examples cover two study cases for mooring lines belonging to FPSO (Floating, Production, Storage and Offloading) units to be installed in Brazilian waters.
A Comparative Study on the Dynamic Response of Three Semisubmersible Floating Offshore Wind Turbines
Authors: Shi Wei , Zhang Lixian , Ning Dezhi , Jiang Zhiyu , Michailides Constantine , Karimirad Madjid
Published: November 2019

Currently, there is a great interest to globally develop offshore wind energy due to the greenhouse effect and energy crisis. Great efforts have been devoted to develop reliable floating offshore wind energy technology to exploit the wind energy resources in deep seas. This paper presents a comparative study of the dynamic response of three different semisubmersible floating wind turbine structures. All the three platforms support the same 5MW wind turbine. The platforms examined are: a V-shaped Semi, an OC4-DeepCwind Semi and a Braceless Semi at 200 m water depth. A dynamic analysis is carried out in order to calculate and compare the performance of these platforms. The comparison is made on the rigid body motions of the semisubmersible platform and tensions of the mooring lines. The presented comparison is based on statistical values and spectra of the time series of the examined response quantities. Coupling effects are more significant for the V-shaped Semi platform. The V-shaped Semi and the Braceless Semi show a more rational motion response under the investigated load cases. The results of this analysis may help to resolve the fundamental design tradeoffs between among different floating system concepts.
Human Reliability Analysis of Ship Maneuvers in Harbor Areas
Authors: Abreu Danilo T. M. P. , Maturana Marcos C. , Martins Marcelo R. , Schenk Siegberto R.
Published: November 2019

During a ship life cycle, one of the most critical phases in terms of safety refers to harbor maneuvers, which take place in restricted and congested waters, leading to higher collision and grounding risks in comparison to open sea navigation. In this scenario, a single accident may stop the harbor’s traffic as well as incur into patrimonial damage, environmental pollution, human casualties and reputation losses. In order to support the vessel’s captain during the maneuver, local experienced maritime pilots stay on board coordinating the ship navigation while in restricted waters. Because of their shorter relative duration, harbor maneuvers accidents are more probable to occur due to human errors — reinforced by the inherent surrounding difficulties —, rather than machinery failures, for instance. The human errors are object of study of the human reliability analysis (HRA). Aiming to assess the main factors contributing to human errors in pilot-assisted harbor ship maneuvers, this work proposes a Bayesian network model for HRA, supported by a prospective human performance model for quantification. Similar works focus mainly on open sea navigation and collision accidents, which do not reflect the strict conditions found on port areas. Additionally, most of the models are highly dependent on expert’s opinion for quantification. Therefore, the novelty of this work resides into two aspects: a) incorporation of harbor specific conditions for maritime navigation HRA, including the performance of ship’s crew and maritime pilots; and b) the use of a prospective human performance model as an alternative to expert’s opinion for quantification purposes. To illustrate the usage of the proposed methodology, this paper presents an analysis of the route keeping task along waterways, starting from the quantification of human error probabilities (HEP) and including the ranking of the main external factors that contribute to the HEP.
High-Bandwidth Underwater Wireless Communication Using a Swarm of Autonomous Underwater Vehicles
Authors: Immas Alexandre , Saadat Mohsen , Navarro Jesus , Drake Matthew , Shen Julie , Alam Mohammad-Reza
Published: November 2019

We present a new method for underwater wireless communication with high bandwidth and over long distance. A swarm of Autonomous Underwater Vehicles (AUVs) is used to relay an optical signal between two points at any distance. Each vehicle is equipped with multiple attitude stabilization systems to reach the required pointing and tracking accuracy for optical communication. This technology would enable fast and efficient underwater exploration which is highly needed as only 5% of the world’s oceans have been explored so far. We carried out an experimental proof of concept to show that it is possible to relay an optical signal underwater between two points using a swarm of AUVs. The experiment took place in a 2m deep water tank. We modified and controlled two submarine models to reflect the laser beam stemming from a laser pointer at the bottom of the tank to the desired location. To know their positions, we developed an image processing technique which required the setup of a RF communication link at 315Mhz between the computers processing the camera’s videos and the units.
Optimization of a Swarm of Autonomous Underwater Vehicles for High-Bandwidth Underwater Wireless Communication
Authors: Immas Alexandre , Alam Mohammad-Reza
Published: November 2019

High-bandwidth underwater wireless communication can be achieved over long-distance using a swarm of Autonomous Underwater Vehicles (AUVs) relaying an optical signal. The swarm behavior is of critical importance as it will determine the robustness and the autonomy of the communication link. Each vehicle must remain at a distance lower than the optical communication system range from each other while fighting against environmental disturbances such as ocean current. This technology could be a game changer in the deployment and supervision of future oil wells and of deep sea mining which will be deeper and deeper in the oceans. We developed an optimization program to maximize the communication link autonomy while assuring its robustness. The nonlinear optimization problem is transformed to a Second-Order Cone Problem (SOCP), a special case of convex problems that can be efficiently solved with Yalmip on Matlab. We show on two case studies that the autonomy of the swarm and thus the lifetime of the communication link is increased by more than 10% compared to a direct approach where the reference position of the vehicles is fixed.
Detection of Mooring Line Failure of a Spread-Moored FPSO: Part 1 — Development of an Artificial Neural Network Based Model
Authors: Sidarta Djoni E. , Lim Ho-Joon , Kyoung Johyun , Tcherniguin Nicolas , Lefebvre Timothee , O’Sullivan Jim
Published: November 2019

Artificial Intelligence (AI) has gained popularity in recent years for offshore engineering applications, and one such challenging application is detection of mooring line failure of a floating offshore platform. For most types of floating offshore platforms, accurately detecting any mooring line damage and/or failures is of great interest to their operators.

This paper demonstrates the use of an Artificial Neural Network (ANN) model for detecting mooring line failure for a spread-moored FPSO. The ANN model representation, in terms of its input variables, is based on assessing when changes in a platform’s motion characteristics are in-fact indicators of a mooring line failure. The output of the ANN model indicates the status condition for the mooring lines (intact or failed). This ANN model only requires GPS / DGPS monitoring data and does not require data on the environmental conditions at the platform. Since the mass of an FPSO changes with the stored volume of oil, the vessel’s mass is also an input variable.

The ANN training uses the results from numerical simulations of a spread-moored FPSO with fourteen mooring lines. The numerical simulations create the FPSO’s response to a range of metocean conditions for 360-degree directions, and they cover several levels of vessel draft (mass). Furthermore, the simulations cover both the intact mooring configuration and the full permutation where each of the fourteen mooring lines is modeled as broken at the top. The global performance analysis of the FPSO is presented in a different paper (Part 2 of these paper series).

The training of the ANN model employs a back-propagation learning algorithm and an automatic method for determining the size of ANN hidden layers. The trained ANN model can detect mooring line failure, even for vessel draft (mass), sea states and environmental directions that are not included in the training data. This demonstrates that the ANN model can recognize and classify patterns associated with mooring line failure and separate such patterns from those associated with intact mooring lines under conditions not included in the original training data.

This study reveals a great potential for using an ANN model to monitor the station keeping integrity of a floating offshore platform with changing storage, or mass status, and to detect mooring line failure using only the vessel’s mass and deviations in the platform’s motions derived from GPS / DGPS data.
Proposed Updates to the Buried-to-Surface Flaw Recharacterization Rules in Annex E of BS 7910
Authors: Bezensek Bostjan , Tkach Yuri , Sharples John , Coules Harry
Published: November 2019

BS 7910 “Guide to Methods for Assessing the Acceptability of Flaws in Metallic Structures” [1] is undergoing revision for the next edition. Updates are proposed for the Annex E flaw recharacterization guidance. The changes aim to make Annex E more applicable to real structures and to improve the synergy between the subcritical crack growth such as by fatigue and fracture of an embedded flaw. Several studies were done by WEE/37 fracture panel focusing on brittle and ductile material behaviour to support the proposed changes. These studies are summarised in the paper.

The main modifications in the proposed updated Ann ex E are in:

• Removal of use of Annex E for brittle fracture.

• Updated guidance on recharacterized surface flaw length for ductile fracture.

• Optional guidance on use of geometry-based criterion for embedded flaw break-through under ductile conditions.

• Alignment of fatigue crack growth in Section 8 with the flaw break-through in Annex E.
Large-Scale Resonant Fatigue Testing of Welded Tubular X-Joints for Offshore Jacket Foundations
Authors: Van Wittenberghe Jeroen , Thibaux Philippe , Van Poucke Maarten
Published: November 2019

Offshore wind turbines are being installed in deeper water and with more powerful generators resulting in more severe loading conditions on its foundations such as jacket structures. Because the main loading is due to wind and currents, the dominant design limit state is fatigue. The fatigue performance of the tubular joints used in jacket structures has been assessed several decades ago based on test results with limited component dimensions (diameter and wall thickness). In addition, improvements of welding methods and evolution of steel grades are not considered in the current design standards.

To provide experimental fatigue-life data on large-scale structures a test program has been carried out on 4 welded tubular X-joints. Each X-joint consists of two horizontal braces with a diameter of 711 mm welded to a central vertical tubular member with 806 mm diameter. The X-joint has a total length of 7.5 m and has two identical welds that are fatigue tested. The fatigue tests are carried out on an innovative resonant bending fatigue test rig that allows to load the specimen in in- and out-of-plane direction at a different amplitude to obtain an even stress distribution over the circumference of the welds. The tests are carried out at a speed close to the resonance frequency of the X-joint. During the test, hotspot strains are measured using strain gauges and a limited amount of water pressure is used to detect through-thickness cracks. The tests are carried out in two phases. During the crack initiation phase, the sample is loaded in both the in- and out-of-plane mode. Once cracks are detected, the test is continued in the crack propagation phase with loading in the plane where cracks had been initiated until through-thickness cracking appeared. During this phase the beach marking technique has been used to mark the shape of the fracture surface at different moments during the fatigue tests.

The testing program is part of the RFCS project JABACO that aims to reduce offshore wind cost by incrementing prefabrication of the jacket substructure.
Seismic Design Challenges of High Pressure Riser Systems on Gravity Based Structures
Authors: Sonawane Mahesh , Vaidya Rohit , Kadakia Ronak , Haeberle Hunter , Ward Phil
Published: November 2019

This paper presents two case studies of the seismic analysis of high pressure riser and conductor systems used on shallow water fixed platforms (approximately 120m water depth) offshore Newfoundland and Labrador, Canada. The case studies presented consider the Hebron and White Rose extension Husky gravity-based concrete platforms. A methodology is presented to assess the dynamic and resonant response of each conductor and riser system to seismic loading using a fully integrated conductor and platform interaction model. Seismic loading is an application of an earthquake-generated agitation to a structure. This occurs at contact surfaces either with the ground, or with adjacent structures, or with gravity waves. Nonlinear time history analyses of the riser system subjected to various ground motion records are performed to simulate the seismic load. Design considerations that drive the HP riser design are discussed.

The paper addresses the intricacies of the gravity base concrete platform-riser system interaction, initial configuration and dynamic seismic response. The riser and conductor system response is used to determine HP riser connector and centralization requirements. The learnings taken from the detailed modeling method are presented along with the advantages of this methodology.
An Improved Body-Exact Method to Predict the Maneuvering of Ships in a Seaway
Authors: Subramanian Rahul , Beck Robert F.
Published: November 2019

Over the last decade, the importance of considering the effects of waves on the maneuvering characteristics of ships has been widely recognized. This paper presents the application of a recently developed nonlinear body-exact scheme (Subramanian, Rakesh, and Beck (2018)) to directly simulate the maneuvering characteristics of a container ship in calm water and in regular waves. In the present body-exact scheme, the perturbation free surface boundary conditions are transferred to a representative incident wave surface at each station at each time. The hydrodynamic forces are computed on the exact instantaneous wetted surface formed by the intersection of the incident wave surface with the exact body position at each time. It is proposed that this model will not only improve first order sea loads but also the higher order drift force predictions which are critical for determining the trajectory of a maneuvering vessel in a seaway. The strip theory formulation has been found to be numerically stable, robust and computationally efficient, which are all critical aspects when performing long time maneuvering simulations. The hull maneuvering, rudder and propeller forces are adopted from standard systems-based approaches that are used to predict calm water maneuvers. Care is taken to ensure that ideal fluid effects are separated from viscous effects and not double counted. Results are presented for turning circle maneuvers in calm water and regular waves incident at various headings and wavelengths. The numerical results are compared with available experiments.
Numerical Modelling of a Relatively Small Floating Body’s Wave and Low Frequency Motion Response, Compared With Observational Data
Authors: Wright Christopher , Yoshimoto Haruki , Wada Ryota , Takagi Ken
Published: November 2019

Global population growth and climate change are driving a need for increased clean renewable energy generation. One such resource is wind energy and while the onshore and fixed offshore wind energy industries are mature, the floating offshore wind energy industry is still at a demonstration phase. Floating wind turbine platforms are generally of a much smaller displacement than the typical offshore structures that have been used in the oil and gas industry. This difference results in changes to the platform dynamics, especially those resulting from second order wave forces. Existing research into low frequency drift motions of small body platforms has been mainly confined to numerical modelling with some experimental work. This work expands on this knowledge by validating numerical modelling with full scale observational data.

In this paper, a numerical time-domain model of a relatively small displacement platform is developed. The platform is installed in a relatively shallow water depth of about 110 m and station keeping is provided by four equally spaced catenary mooring chains. The required fidelity for the low frequency response is compared using first order forces only and either a full QTF (quadratic transfer equation) or Newman’s approximation. The model is compared with observation data from the Fukushima FORWARD project’s floating substation, an advanced spar type, which is composed of measurements of multidirectional wave spectra, wind and current as model inputs and six DOF platform motions as outputs. In addition to this the model computational expense is reduced by decreasing the number of wave directions simulated. The accuracy of such reductions is then described. Observation data is grouped according to sea-state data. An empirical drag coefficient formula is proposed. The 50 year return period design sea-state is also modelled using a JONSWAP spectrum and the various numerical models.
Experimental Study on Friction of Steel Wires of Dynamic Umbilical for Fatigue Life Analysis
Authors: Yin Yuanchao , Lu Qingzhen , Wu Shanghua , Yan Jun , Yue Qianjin , Chen Jinlong
Published: November 2019

Dynamic umbilicals are widely used in the wet tree development of deep-water field. In the application of dynamic umbilicals, fatigue is a key failure mode which may cause severe economic consequences. The fatigue behavior of dynamic umbilical is complicated by the mechanical properties of the material, the cross-section design and the interaction of different components. Published studies have shown that the interaction friction stress of steel wires is critical for fatigue analysis. Coefficient of friction were used as a constant during the fatigue life analysis. However, the friction stress and the coefficient of friction may change during the wear of the steel wire.

This paper presents a new experiment method and device to evaluate the change of the coefficient of friction of steel wire. Different cycles of reciprocating wear were carried out on samples to simulate interaction of the steel wires during the process of fatigue. The samples are pairs of steel wires which were cut on a dynamic umbilical. The interaction stress and friction stress were measured during the test. Micro morphology on the surface of steel wire at the contract zone were measured to investigate the wear of the sample.

The test result shows that the coefficient of friction and stress changes during the test. Worn marks were found on the contact zone of the steel wires. The change of the coefficient of friction may affect the accuracy of fatigue life analysis of dynamic umbilical. Conclusions were also presented on the coefficient of friction test and theoretical calculation method to approach a more accurate fatigue life for dynamic umbilical design.
Reduced Order Model for Unsteady Fluid Flows via Recurrent Neural Networks
Authors: Reddy Sandeep B. , Magee Allan Ross , Jaiman Rajeev K. , Liu J. , Xu W. , Choudhary A. , Hussain A. A.
Published: November 2019

In this paper, we present a data-driven approach to construct a reduced-order model (ROM) for the unsteady flow field and fluid-structure interaction. This proposed approach relies on (i) a projection of the high-dimensional data from the Navier-Stokes equations to a low-dimensional subspace using the proper orthogonal decomposition (POD) and (ii) integration of the low-dimensional model with the recurrent neural networks. For the hybrid ROM formulation, we consider long short term memory networks with encoder-decoder architecture, which is a special variant of recurrent neural networks. The mathematical structure of recurrent neural networks embodies a non-linear state space form of the underlying dynamical behavior. This particular attribute of an RNN makes it suitable for non-linear unsteady flow problems. In the proposed hybrid RNN method, the spatial and temporal features of the unsteady flow system are captured separately. Time-invariant modes obtained by low-order projection embodies the spatial features of the flow field, while the temporal behavior of the corresponding modal coefficients is learned via recurrent neural networks. The effectiveness of the proposed method is first demonstrated on a canonical problem of flow past a cylinder at low Reynolds number. With regard to a practical marine/offshore engineering demonstration, we have applied and examined the reliability of the proposed data-driven framework for the predictions of vortex-induced vibrations of a flexible offshore riser at high Reynolds number.
Squall Detection and Analysis From Historical Satellite Data
Authors: Renac L. , Hurdle D. P. , Enet F. J. M. , De Vroom J.
Published: November 2019

Thunderstorms and squalls (fronts of contiguous thunderstorms) are associated with short but intense local winds that have a great impact on operability or design conditions for moored ship operations in the coastal zone. The brevity and local scale of such events makes them difficult to capture using standard measurement data and usually requires dedicated long-term measurement campaigns. Because the standard measurements available are usually based on 10-minute averages taken once an hour, such data is often not available. In the absence of conventional measured data, the use of satellite data can provide useful design data if analyzed and applied with caution. We present two case studies (West Africa and Brazil) where squalls have been identified in satellite data and used for extreme value analysis (EVA) to support the design of intermediate water depth mooring systems. The detection of squalls is confirmed with satellite imagery and the handling of this data for the EVA is presented in detail with assumptions made and the sensitivity of the results to these assumptions. The impact on design values is also discussed for both geographic locations.
Experimental Evaluation of Hydrodynamic Loads on Marine Risers
Authors: Vileti Vinicius L. , Esperança Paulo de Tarso T. , Vitola Marcelo A. , Vignoles Mario A.
Published: November 2019

As the exploration of oceans for oil and gas goes to deeper depths, understanding the riser dynamics is fast becoming a key aspect of such systems’ design. The hydrodynamic loads acting on marine risers such as inertial and drag forces due to the relative motions between the riser and fluid, is of great concern for researchers and exploration systems’ designers.

The lack of information regarding some conditions applied on risers systems nowadays, led to an experimental approach to understand the hydrodynamic loads on these conditions, to extract those information, and complement the available literature on this subject.

This study provides new insights into the inertial and drag hydrodynamic coefficients (Cm and Cd respectively), how they evolve for higher KCs. These findings should make an important contribution expanding the understanding of the hydrodynamic loads on a circular cylinder.

This paper first gives a brief overview of the recent research history of this subject and the theoretical background used, followed by the description of test setup and analysis method. Lastly, the results are presented and discussed in comparison with literature data.
On Environmental Contours for Marine and Coastal Design
Authors: Ross Emma , Astrup Ole Christian , Bitner-Gregersen Elzbieta , Bunn Nigel , Feld Graham , Gouldby Ben , Huseby Arne , Liu Ye , Randell David , Vanem Erik , Jonathan Philip
Published: November 2019

Environmental contours are used in structural reliability analysis of marine and coastal structures as an approximate means to locate the boundary of the distribution of environmental variables, and to identify environmental conditions giving rise to extreme structural loads and responses. There are different approaches to estimating environmental contours, some directly linked to methods of structural reliability. Each contouring approach has its pros and cons. Although procedures for applying contours in design have been reported in articles and standards, there is still ambiguity about detail, and the practitioner has considerable flexibility in applying contours. It is not always clear how to estimate environmental contours well. Over four years, DNV-GL, Shell, the University of Oslo and HR Walling-ford worked together to review current practice regarding the use of design contours. In this paper, we present a summary of our findings. We overview the motivations for different approaches to contours, and their resulting characteristics. Using different marine applications, we also explore the various sources of uncertainty present, their impact on contour estimates and the estimation of extreme environmental loads and responses.
A Fatigue Assessment Procedure for Drilling Pipes of Scientific Vessels
Authors: Aguiari Martina , Rizzo Cesare Mario , Inoue Tomoya
Published: November 2019

In recent years, many disasters due to earthquakes and tsunamis occurred in various countries, including Japan. Two triple junctions exist below the Japanese archipelago and around Japan, where three plates meet to form a complicated crustal structure. To conduct research on the Tohoku earthquake, which accompanied the tsunami that devastated northern Japan in March 2011, Japan Agency for Marine-Earth Science and Technology (JAMSTEC) constructed the scientific deep-sea drilling vessel Chikyu. To understand the mechanism of the earthquakes, a direct access to the fault zone is necessary. During drilling operations, the drill pipes are stressed by different forces and the occurrence of drill-string failures is high, which causes significant loss of money and time. This study focused on the definition of a practical fatigue assessment procedure useful to avoid failures during drilling operations. In this paper the proposed procedure is outlined, and the sensitivity analysis carried out to highlight most influencing parameters is presented.
An Experimental Investigation of Filtercake Reinforced Wellbore Strengthening and Fracture Sealing
Authors: Yang Mingzheng , Chen Yuanhang , Growcock Frederick B. , Zhang Feifei
Published: November 2019

Drilling-induced lost circulation should be managed before and during fracture initiation rather than after they propagate to form large fractures and losses become uncontrollable. Recent studies indicated the potentially critical role of filtercake in strengthening the wellbore through formation of a pressure-isolating barrier, as well as plugging microfractures during fracture initiation. In this study, an experimental investigation was conducted to understand the role played by filtercake in the presence of lost circulation materials (LCMs). A modified permeability plugging apparatus (PPA) with slotted discs was used to simulate whole mud loss through fractures of known width behind filtercake. Cumulative fluid loss upon achieving a complete seal and the maximum sealing pressure were measured to evaluate the combined effects of filtercake and LCMs in preventing and reducing fluid losses. The effects of some filtercake properties (along with LCM type, concentration and particle size distribution) on filtercake rupture and fracture sealing were investigated. The results indicate that filtercake can accelerate fracture sealing and reduce total mud loss. Efficiently depositing filtercake while drilling can reduce the concentration of LCM that is required to plug and isolate incipient fractures.
Wind Turbine Planetary Gear Fault Identification Using Statistical Condition Indicators and Machine Learning
Authors: Peeters Cédric , Verstraeten Timothy , Nowé Ann , Helsen Jan
Published: November 2019

This work describes an automated condition monitoring framework to process and analyze vibration data measured on wind turbine gearboxes. The current state-of-the-art in signal processing often leads to a large quantity in health indicators thanks to the multiple potential pre-processing steps. Such large quantities of indicators become unfeasible to inspect manually when the data volume and the number of monitored turbines increases. Therefore, this paper proposes a hybrid analysis approach that combines advanced signal processing methods with machine learning and anomaly detection. This approach is investigated on an experimental wind turbine gearbox vibration data set. It is found that the combination of physics-based statistical indicators with machine learning is capable of detecting planetary gear stage damage and significantly simplifying the data analysis and inspection in the process.
Investigation of the Effect of Block Size, Shape and Freeze Bond Strength on Flexural Failure of Freshwater Ice Rubble Using the Discrete Element Method
Authors: Afzali Soroosh , Taylor Rocky , Bailey Eleanor , Sarracino Robert , Boroojerdi Marjan T.
Published: November 2019

Understanding ice rubble strength and associated failure mechanics is important for a variety of engineering applications in marine ice environments, including the design and operation of coastal, offshore, subsea and floating structures. As part of the Mechanics of Ice Rubble project, recent experiments have been carried out to study the strength and failure behavior of ice rubble beams and the freeze bonds that form between individual ice blocks. These new results serve as an important guide for the development of improved numerical models. The discrete element method (DEM) is a direct modeling approach which has the potential to both describe and enhance understanding of the behavior of brittle granular materials, especially with regard to the evolution of damage towards failure. In this study we present results obtained from a newly developed model for the 3D DEM open-source code LIGGGHTS. The ice model contains normal and shear springs that operate between neighboring particles which are bonded or that overlap due to compressional stresses. Energy dissipation is accounted for by using a viscous damping model. Using this DEM model, medium-scale freshwater ice rubble punch tests have been simulated for ice rubble beams with nominal dimensions of 0.50m × 0.94m × 3.05m. Rubble specimens were generated by “raining” individual DEM ice pieces into a rectangular form and compacting the rubble mass to achieve the target porosity. Before the compacting pressure was removed, bonds between contacting blocks were introduced with parameter values chosen based on representative freeze bond experiments. The ice rubble beam was then deformed by pushing a platen vertically downward through the center of the beam until failure occurred. For the numerical simulations presented here, two types of block size and shapes have been considered: cuboid blocks generated based on the size distribution of the actual rubble, and rubble blocks generated by image processing of actual blocks of broken ice used in the comparison experiments. Results obtained for these two scenarios are compared with corresponding experimental test data. These results highlight that the DEM model is useful for estimating the flexural strength of the rubble, simulating the failure mechanism and for examining the extent to which the ice rubble beam failure is controlled by the strength of the freeze bonds. These results also provide valuable new insights regarding the importance of shape and size distribution of ice blocks on simulated ice rubble strength and failure behavior. Recommendations for future work are provided.
Design of Performance Monitoring System for Diesel Generators of Offshore Drilling Platform
Authors: Hu Lei , Yang Jianguo
Published: November 2019

Conditions of diesel generators on an offshore drilling platform are crucial for oil production, if diesel generators can not work, the efficiency of oil production will be reduced, even worse, it will be a crisis to the offshore drilling platform security. So it is important to reduce maintenance costs and prevent major failures of diesel generators by using some effective means, such as establishing effective monitoring methods and strategies, predicting diesel generators’ working status and managing their operation data, it also can improve convenience for Platform crews’ operation and maintenance. Some on-line or off-line monitoring methods for diesel generators are applied widely, however monitoring strategies and integration technologies for the platform are not yet available. An integration strategy of online and off-line monitoring was proposed by using the instantaneous speed method, CP method and thermal parameters method. A suitable performance monitoring system for diesel generators is composed of performance monitoring module, data management module and network communication module. The system was developed based on virtual instrument technology, by data acquisition, analysis, processing of different types of sensors and design of monitoring strategy and system interface, the status monitoring and prediction of diesel generators is realized. The method was tested on a laboratory diesel engine, the performance and function of the monitoring system were verified. Then the system is validated on a drilling platform, and results indicated that the functions of the developed system met the designed requirements and the performance was reliable.
Fatigue Assessment of Dented Rigid Risers
Authors: Santander Elvis J. O. , Pinheiro Bianca , Magluta Carlos , Roitman Ney
Published: November 2019

In the development of oil fields, submarine pipelines are used in various applications. These pipelines and risers are subject to accidents that may occur during operation, such as shocks between risers or shocks between a riser and an anchor, rock, or any equipment or heavy object, which may cause mechanical failure, such as dents. The objective of this work is to study of the effect of the introduction of plain dents on the structural integrity of rigid risers under fully reversed bending. A three dimensional finite element model was developed to estimate the stress concentration on dented risers under bending. Several numerical simulations were carried out to evaluate stress concentration factors (SCFs) for varying dimensions of dents and risers, in a parametric study. These SCFs can be used in the prediction of the remaining fatigue life of dented rigid risers.
Validation of External Moment Determination for the Shaft-Line of the S.A. Agulhas II
Authors: Nickerson Brendon M. , Bekker Anriëtte
Published: November 2019

Full-scale measurements of shaft torque have been performed on several voyages of a polar supply and research vessel, the SA Agulhas II. Previous work has looked at the determination of the externally induced ice moments on the propeller to shed light on the expected loading conditions in the harsh Antarctic environments. This has been done by making use of a lumped mass model, measurements taken on the shaft-line and an inverse prediction algorithm. Thus the externally applied loads are determined through the internal measurements on the shaft-line. The work presented here is in an effort to assess the validity of the lumped mass model parameters used in the external moment determination process. Two methods of validation have been performed. The first is through the comparison of the lumped mass model to operational modal analysis data of the shaft-line, obtained during dry-dock operations in 2017. The second validation method that is considered relies on data recorded on board the SA Agulhas II during its 2018–19 Annual Relief Voyage to Antarctica. The shaft-line measurement system has been expanded to include the measurement of torque at a second location, further down the shaft. These two measurement locations are each used to determine the external loads and their results are compared. It was found that the results of the validation show correlation, albeit with some error, and that the developed method is valid for use in determining externally induced ice moments. However, there is room for improvement of the current external moment determination method.
Solving 2-D Slamming Problems by the Higher-Order MPS Method With an Improved Pressure Gradient Model
Authors: Zha Ruosi , Peng Heather , Qiu Wei
Published: November 2019

A higher-order moving particle semi-implicit (MPS) method was developed to solve water entry problems. The Wendland kernel function was applied in the particle interaction model. Various models for pressure gradient were investigated. To overcome the inconsistency in the original MPS methods, a pressure gradient correction was implemented to guarantee the first-order consistency of gradient. The corrective matrix was modified by using the derivative of the kernel function. A particle shifting technique was also applied to improve the numerical stability. Validation studies were carried out for water entry of a rigid wedge with the tilting angles of 0°, 10° and 20°, and a rigid ship section. The solutions by the present method are generally in good agreement with experimental data and other published numerical results.
Computational Investigation of Oil Accumulation in a Subsea Deadleg
Authors: Caglar Egemen , Zeng Yi , Khodadadi J. M.
Published: November 2019

Both 2- and 3-dimensional computational studies of two-phase flow within a horizontal pipe with a vertical deadleg placed downstream of an oil/water supply source were considered as part of a model subsea petroleum production system. Two-phase continuity and momentum relations were solved using the open-source computational software OpenFOAM. The unsteady flow behavior of the two-phase dispersed mixture which consists of 90%–10% slurry of 32.8 API crude oil-water at the inlet port (Reynolds number of 2.1 × 105) was investigated. With the 2-D simulations, the effects of the average inlet velocity, diameter of the deadleg and length of the deadleg on the oil fraction within the deadleg and the stagnant zones were studied. Results of the 3-D unsteady simulations exhibited the complex vortical flow field and separation of the two phases that evolved within the deadleg leading to migration of separated oil to the top of the deadleg.
Numerical Study on the Effect of Stern Flap for Hydrodynamic Performance of Catamaran
Authors: Zhou Peng , Liu Liwei , Guo Lixiang , Wang Qing , Wang Xianzhou
Published: November 2019

This paper presents CFD simulation results of the stern flap effect with different lengths for hydrodynamic performance of catamaran moving in calm water, including resistance and sailing attitude. Inhouse viscous CFD (computational fluid dynamics) code HUST-Ship (Hydrodynamic Unsteady Simulation Technology for Ship) is used for the study. The catamaran with/without stern flap with different lengths were studied. The trim and sinkage of the catamaran were solved coupled with flow solver. Experimental studies in calm water were conducted to validate the numerical method. The comparison of hydrodynamic performance of catamaran with stern flaps of different lengths was made. The results show that the stern flap can reduce the sailing attitude and has influence for the resistance of catamaran at high-speed.
Study of the Vortex-Induced Vibration of the Marine Risers With the Buoyancy
Authors: Zhao Lin , Su Hang , Yin Yanju
Published: November 2019

Regarding the very large top tension of ocean deep water riser which is caused by the heavy self-weight, a innovated buoyancy system is designed. This system can effectively decrease the top tension and improve the performance of the riser movement. In order to study the upper and lower part of the floating system, a specialized model test is carried out, where the acceleration, amplitude, frequency and trajectory of the interested points along the risers are investigated. It has been observed that with the increase of the current speed, both the vibration acceleration and the vibration frequency are increasing but the bare riser amplitude is decreasing. At the speed of 0.2m/s, the resonance phenomenon is observed, but the same phenomenon is not observed for the middle floating riser subjecting to different flow velocities. At the speed of 0.4 m/s, the largest amplitude is captured. Due to the response differences of the floating riser at the up and down parts of the middle floating riser, when the amplitude is increasing, the vibration frequency is decreasing, both at cross flow (CF) direction and inline flow (IL) direction. Especially the vibration behavior of the interested points is most influenced by the buoyancy. Under different models, vibration at different flow velocities is presented along bare riser, the modal vibration effects of the floating riser will decrease In addition, according to the experiment condition, Orcaflex is applied to conduct the numerical simulation to get the vibration law of the corresponding feature points and compare it with the experimental results. The results indicate that the numerical analysis reasonably match with experimental results.