bluuebunny/crossref_metadata_2025 huggingface dataset:
Parameters Estimation of Nonlinear Manoeuvring Model for Marine Surface Ship Based on PMM Tests
Authors: Xu Haitong , Hassani Vahid , Guedes Soares Carlos
Published: September 2018

A nonlinear manoeuvring mathematical model of marine surface ship model is briefly introduced. In order to obtain the hydrodynamic coefficients, system identification is used to estimate the parameters using Planar Motion Mechanism (PMM) test data. Usually, the obtained parameters using measured data have a large uncertainty due to the ill-conditioned processes of identification. An optimal Truncated Singular Value Decomposition (TSVD) method is exploited to reduce the uncertainty of the estimated parameters. The optimal number of retaining singular values is calculated by using the L-curve, which is a log-log plot of the norm of a regularized solution versus the norm of the corresponding residual norm. It is a graphical tool for displaying the trade-off between the estimated parameters norm and the corresponding residual error norm. The validation process is performed by comparison of the prediction values with the experimental data in the time domain.
Simulation Requirements and Relevant Load Conditions in the Design of Floating Offshore Wind Turbines
Authors: Faerron Guzmán Ricardo , Müller Kolja , Vita Luca , Cheng Po Wen
Published: September 2018

Aligned with work performed in deliverable D7.7 of the H2020 project LIFES50+, this study supports the definition of the numerical setup in the design of floating offshore wind turbines. The results of extensive simulation studies are presented, which focus particularly on determining the requirements for the load simulations in the design process. The analysis focusses on the cases of: (1) fatigue during power production and (2) ultimate loads during power production and severe sea state. For the fatigue load case, sensitivity study is performed in order to determine relevant load conditions and the expected impact of a variation in the environmental loading. Additionally, focus is put on the requirements regarding the run-in time, number of seeds and the simulation length for both fatigue and ultimate limit state (FLS, ULS) analysis. Another topic addressed is the benefit of using an increased number of seeds rather than extending the simulation time of single seeds, when a given total simulation time is required as described in the guidelines. The run-in time may be shortened when using predetermined steady states as initial conditions. Requirements for the steady state simulations are also determined and presented.
Risk-Based In-Service Inspection Framework for Offshore Concrete Wind Turbine Structures and Application of Fuzzy Inference System
Authors: Samarakoon S. M. Samindi M. K. , Ratnayake R. M. Chandima
Published: September 2018

Risk-based in-service inspection enhances structural integrity and minimizes the number of potential unwanted incidents in relation to offshore concrete wind turbine structures. Risk-based in-service inspection enables in-situ inspections, evaluation of inspection results, condition assessment of the offshore wind turbine structures and recommends optimal future inspections. The vagueness, uncertainties and variability present in the risk-based in-service planning process jeopardizes the final inspection recommendations and structural integrity of the structure under consideration. Hence, it is vital to develop methodologies for the systematic utilization of expert knowledge to minimize variability in risk-based in-service assessments. This manuscript suggests a fuzzy set theory-based approach to minimize the risk assessments’ variability and unwanted activities. The suggested fuzzy set theory-based approach enables the identification of the potential hot points that encompass high-risk regions needing priority in future inspections with optimal effort and higher productivity. This manuscript also discusses the use of available inspection methods to enhance the structural integrity of offshore concrete wind turbines subject to deterioration, as well as the use of fuzzy theory-based risk-based in-service inspection assessments for making optimal in-service inspection recommendations.
Impact on an Ice Floe With a Surface Crack
Authors: Korobkin Alexander A. , Khabakhpasheva Tatiana I.
Published: September 2018

A floating two-dimensional ice plate with a crack on its lower surface is considered. Deflection of the plate is caused by an external impulsive load. The ice floe dynamics is described by thin compound elastic plate equation. Two parts of the plate are of constant thickness and are connected by a torsional spring which models the crack effect on the elastic deflection of the plate. The stiffness of the equivalent torsional spring is given as a function of the plate parameters and the crack length. Both the motions of the ice plate and the stresses near the crack tip are determined without account for gravity and surface tension effects. In the symmetric problem, the crack is always perpendicular to the plate surface. The growth of the crack is governed by the condition of the crack equilibrium at each time instant. The conditions of the impact, the magnitude of the impact force and its duration, which lead to the crack growth are studied within the water impact theory.
Consideration of the Human Element in Cementing Operations and Well Integrity
Authors: Shenold Chad , Teodoriu Catalin , Salehi Saeed
Published: September 2018

The recent Macondo tragedy changed the health and safety landscape throughout the petroleum industry. Through such incidents, oil well cementing operations have gained widespread attention. Detailed technical reports of the Macondo well control incident outline the significance of the competent and efficient cementing operations.

The voluntary API RP 75 standard was recently modified into the current mandatory offshore Safety and Environmental Management Systems (SEMS II) regulations. The regulatory guidelines in the United States, dormant over the past 20 years, are finally being updated to meet current industry and public expectations. The human factor, overlooked for decades in the petroleum industry, serves as the catalyst behind the newly adopted offshore regulations.

This paper provides a brief overview of well integrity, and the pivotal role of cementing operations in well control. The critical role of human and organizational factors in cementing operations and well control is addressed. Furthermore. an outline of the newly implemented SEMS II regulations is also offered, with insight into adjustments that could enhance this program’s modest requirements.
Manoeuvring Study of a Container Ship in Shallow Water Waves
Authors: Ruiz Manases Tello , Mansuy Marc , Delefortrie Guillaume , Vantorre Marc
Published: September 2018

When approaching or leaving a port a ship often needs to perform manoeuvres in the presence of waves. At the same time the water depth is still limited for deep drafted vessels. For manoeuvring simulation purposes this requires a manoeuvring model which includes phenomena such as short crested waves and squat effects. The present paper addresses the manoeuvring problem in shallow water waves numerically and experimentally. The numerical study is conducted by means of potential theory, incorporating first and second order exciting wave forces, and their superposition to the calm water manoeuvring models. The applicability of such an approach is also investigated. The experimental work has been conducted at Flanders Hydraulics Research (in cooperation with Ghent University) with a scale model of an ultra large container vessel. Captive model tests comprise harmonic yaw tests and steady straight line tests with and without waves, at different forward speeds, wave frequencies and amplitudes, in head and following waves. Waves are chosen to represent conditions commonly met by ships in the Belgian coastal zone of the North Sea.
A Comparison Study on the Hydroelasticity of Two Types of Floating Bridges in Inhomogeneous Wave Conditions
Authors: Li Shuai , Fu Shixiao , Wei Wei , Moan Torgeir
Published: September 2018

Due to the interaction between elastic structural deformations and fluid motions, the responses of floating bridges should be analyzed by hydroelasticity methods. We firstly employed a linear time-domain approach, based on the discrete-module-based hydroelastic method to investigate the responses of two surface bridge concepts under first order wave forces, a straight bridge with mooring system and an end-anchored curved bridge. The results show that the displacement of the curved bridge is smaller, compared with the straight bridge. However, the reaction force and the vertical bending moment of the curved bridge are larger. Furthermore, a nonlinear time-domain hydroelasticity approach for analysis of the floating bridge under nonlinear wave forces within inhomogeneous wave conditions is established. Finally, a comparison between the linear and nonlinear responses of the moored straight bridge is made. The results show that the nonlinearity of the wave excitation forces has a significant influence on the mooring forces and horizontal displacement.
A Coupled Potential-Viscous Flow Method for Wave Impact on Semi-Submersible Platform Simulation
Authors: Liao Kangping , Duan Wenyang , Ma QingWei , Zhao Binbin , Ma Shan , Kim Jang
Published: September 2018

In rough sea conditions, Semi-submersible platform often suffers from extreme wave impact loads, which can result in structural damage. It is important to predict the wave impact loads on Semi-submersible platform. A CFD method, based on a fixed regular Cartesian grid system, has been developed by the authors for wave impact loads on semi-submersible platform (Liao et al., 2017). However, time consuming is still the bottleneck of CFD method for industry application. In this study, a coupled potential-viscous flow method is developed for improving computational efficiency. In the present method, our CFD in-house code is coupled with MrNWB dynamic libraries using the Euler Overlay Method (EOM) (Baquet et al., 2017). Comparison of the computational accuracy and efficiency between our original CFD in-house code and the present coupled method will be discussed in detail, and benchmark model test will also be used to validate the present coupled method in wave impact simulation.
Assessment of Methods for Short-Term Extreme Value Analysis of Riser Collision
Authors: Fu Ping , Leira Bernt J. , Myrhaug Dag
Published: September 2018

Risers are commonly arranged as clusters with relatively small spacing due to economic necessity. As a consequence, collision between risers becomes an essential problem. This study presents a comprehensive assessment of various methods for riser collision probability analysis. A pair of tandem arrangement risers subjected to combined current and wave loads is modelled. Three hours short-term simulation is performed in order to obtain the time history samples for the collision probability analysis. The wake effect due to the presence of the upstream riser is considered. The shortest distance between risers is calculated at each time step. Four methods for estimation of the extreme value distribution, e.g. Gumbel probability paper method, Weibull based method, average conditional exceedance rate method and moment based Hermit method, are presented, and the results obtained from different methods are compared and discussed.
Prediction of Hydrodynamic Coefficients of Coupled Heave and Pitch Motions of Heeled Planing Boats by Asymmetric 2D+T Theory
Authors: Tavakoli Sasan , Dashtimanesh Abbas , Sahoo Prasanta K.
Published: September 2018

This paper attempts to present a mathematical model to predict hydrodynamic coefficients of a heeled planing hull in vertical plane. This model has been developed by using 2D+T theory and theoretical solution of the water entry of wedge section bodies. Sectional hydrodynamic force acting on the vessel is determined and then extended over the entire length of the vessel. By simplifying final equations of heave force and pitch moment acting on a heeled planing hull, equations for prediction of hydrodynamic coefficients of the vessel are developed. Accuracy of the method is evaluated by comparing its results against previous empirical methods. It is seen that current method has reasonable accuracy in prediction of different hydrodynamic coefficients. Also, effects of heel angle on added mass, damping and stiffness coefficients are studied and discussed.
Response Study of Jacket Piles Induced by Spudcan Penetration
Authors: Li Shuzhao , Wang Zhongchang , Jia Xu , He Linlin
Published: September 2018

Mobile jack-up rigs are frequently cantilevered over production jacket platforms to drill new wells or rework existing well for the offshore oil and gas at shallow and middle water depths. The proximity of the rig to the existing fixed platform will affect the performance of pile foundations of the platform and may cause some distress to the adjacent pile foundation by spudcan penetration. With the increasing accidents with respect to the spudcan penetration and spudcanpile interaction caused severe economic losses in offshore engineering of China, solving these problems is an urgent and significance assignment at present. Since the spudcan-pile interaction is a typical offshore geotechnical large strain large deformation problem, a numerical approach based on the large strain technique is a valid solution tool for evaluating spudcanpile interaction. The paper addresses additional responses of the adjacent pile induced by spudcan penetration in single clay profile and clay overlying sand profile using two different large strain large deformation numerical approaches. One is called two-stage approach. Firstly, ALE (Arbitrary Lagrangian Eulerian) approach is used to the displacement field of soil is calculated at the free field without adjacent piles, and then bending moments of piles investigate through conventional beam-column model. Another is CEL (Coupled Eulerian Lagrangian) approach to analyze the adjacent pile responses induced by spudcan penetration through three dimensional numerical model including spudcan, soil profile and adjacent pile. The feasibility of two approaches was verified through comparison between numerically predicted and experimentally measured results. Variations of pile bending moment induced by spudcan penetration are demonstrated with different pile length, spudcan-pile clearance and soil profiles. Comparisons of the numerically predicted pile bending moment and the experimentally measured values show that the both are close agreement for the different spudcan-pile clearance at the spudcan penetration depth of less than 15m in NC soil profiles. However, an apparent discrepancy lays on that the second positive peak bending moment from the numerical calculation by the beam-column model moves up to a higher depth than the measurement for the 40m pile length.
Application of Fine Water Plugging Technology With Coiled Tubing in High Water Cut Wells
Authors: Wang Jie , Zhou Fujian , Zhang Lufeng , Fan Fan , Yang Hong
Published: September 2018

Water logging problem in late production reservoir with abundant edge-bottom water and water-gas layer stagger is one of the main factors that lead to production wells stop flow. For the water plugging problem during gas well production, the common operation is coiled tubing through casing. So, coiled tubing technology without moving production string is explored.

X oilfield is located in Sichuan basin of China southwest and belongs to the origin of gas pipeline from Sichuan to China east. Its main gas producing area is carbonatite full of edge water and controlled by structural and lithology. The relationship between water and gas is complex and water-gas system is independent of different blocks and different layers. Because the main gas producing layer is close to the water layer, lots of gas producing wells stop spray for high water cut. At the meantime, the difficulty and risk of water plugging increases for its high depth of main gas producing layer and high temperature at the well bottom.

To solve the problem above, cement slurry system with the characteristics of high temperature and sulfur resistant and channeling preventing is developed. At the same time, the cement slurry system has low friction and high liquidity and is easy to flow through the coiled tubing. Besides, cement slurry pollution is reduced and the success rate of gas well produced water plugging is improved by the combination of coiled tubing and cementing process and the construction technology optimization, software simulation and laboratory evaluation is carried out. The key step is that log analysis of water and gas distribution is done first. Then, tubing-expansion bridge plug is placed under the water layer and the cement slurry is sent to the desired location. At last, coiled tubing is put down after cement solidification and gas production is recovered.

The measurement of coiled tubing and cement slurry system is positive for water plugging in gas wells with high depth and temperature. The oilfield test results show that daily gas production is improved largely and liquid production is reduced by 90% of 4 wells with high water cut through water plugging. Besides, operation cost is reduced and the pollution problem caused by produced water is also solved, which can provide certain significance for the same type wells need water plugging operation.
Numerical Investigation of Regular Waves Interaction With Two Fixed Cylinders in Tandem Arrangement
Authors: Liu Zhenghao , Wan Decheng , Hu Changhong
Published: September 2018

The interaction of waves with fixed or floating structures involves complex wave radiation, wave diffraction and free surface deformation. In this work, the interaction of waves with a pair of cylinders in tandem arrangement is investigated using a numerical wave tank. The numerical simulation is first validated by comparing numerical results and experimental data for regular wave interaction with a single cylinder. Wave interaction with tandem cylinders is investigated for different center-to-center distances between the cylinders.

All the numerical simulations are carried out by the in-house CFD solver naoe-FOAM-SJTU which is developed on the open source platform OpenFOAM. The incompressible unsteady Reynolds averaged Navier-Stokes (URANS) equations are adopted as the governing equations. The volume of fluid (VOF) method is applied to capture the free surface. The surface elevation around the cylinders is probed by a series of wave gauges and analyzed using transfer function. The wave forces of upstream and downstream cylinder are discussed in detail. The wave forces experienced by the tandem cylinders is highly influenced by the distance between the cylinders. The local surface elevation and the scattered wave field around the cylinders are also investigated. The results show that the present CFD solver can be an alternative tool to deal with wave-structure interactions.
CFD Parametric Study of Geometrical Variations on the Vortex-Induced Motions of Deep-Draft Semi-Submersibles
Authors: Zhao Weiwen , Wan Decheng
Published: September 2018

Vortex-Induced Motions (VIM) is a key issue for deep draft column stabilized floaters (DDCSF). An example of DDCSF is the concept design called Paired-Column semi-submersible (PC-Semi) with a pair of columns instead of single column at four corners of the platforms. The complex multi-column design involves several extra design parameters such as paired-column gaps and column cross-section areas than conventional semi-submersibles. These parameters can be tuned to mitigate dynamic response to waves and currents. However, it is expensive to perform parametric study of geometric variations by means of experiments.

In the present work, CFD method is utilized to investigate the VIM characteristics for different geometrical variations of the PC-Semi. An in-house CFD code naoe-FOAM-SJTU, which is developed on top of the open source framework OpenFOAM, is used for all numerical simulations. Delayed detached-eddy simulation (DDES) is used for turbulence modeling with massively separated flow. A geometry model scaled at 1:54 from MARIN is select as the baseline model for parametric study. VIM simulations of the baseline model is firstly carried out and compared with experiments to validate the current CFD code. After that, VIM characteristics of paired-column gaps geometrical variations are numerically investigated. Motions of the platform and hydrodynamic forces on columns are compared and analyzed. The ability of CFD method in optimizing geometric design parameters on mitigating VIM response for deep-draft semi-submersibles is demonstrated.
Numerical Simulation of Three-Layer-Liquid Sloshing by Multiphase MPS Method
Authors: Wen Xiao , Wan Decheng
Published: September 2018

In the present study, three-layer-liquid sloshing in a rigid tank is simulated based on the newly developed multiphase MPS method. Firstly, the multiphase MPS method is introduced in detail, including the basic particle interaction models and the special interface treatments employed to extend single phase MPS solver to multiphase flows simulations. The new multiphase MPS method treats the multifluid system as the multi-density and multi-viscosity fluid, thus only a single set of equations needs to be solved for all phases. Besides, extra density smoothing technique, interparticle viscosity model and surface tension model are included in the present method for interface particles. The new multiphase MPS method is then applied to simulate three-layer-liquid sloshing in a rigid tank and verified through comparison with the experiment conducted by Molin et al. [1]. The predicted motion of interfaces by the present method shows a good agreement with the experimental data and other numerical results.
Experimental Study on Gravity Anchor for Optimum Design of Shear Key
Authors: Han Yun Su , Hong Jeong Woo , Oh Min Han , Jung Jong Jin
Published: September 2018

The purpose of a gravity anchor is to moor the installation barge affected by the environmental condition during installation at the offshore site. It is important to obtain the sufficient holding capacity to prevent the anchor from dragging. There are several methods to enhance the holding capacity such as increasing its self-weight or attaching the shear key at the bottom of the gravity anchor. However, increasing the self-weight of gravity anchor is a constrained approach due to the limitation of handling equipment capacity. Therefore, it is necessary that the shear key design should be optimized to maximize the holding capacity under limited handling equipment. In this paper, reduced scale model tests simulating rock condition mixed by sand, cement, and water are performed. The actual offshore mooring condition is simulated by using towing carriage. Five types of gravity anchor models which have different shear keys are assessed to examine what type of the shear key is the optimum design. The optimum shape and the number of shear keys for maximizing the holding capacity are assessed through this study. The results of this study can be utilized to design the shear key of gravity anchor.
Energy Harvesting From Waves Using Piezoelectric Floaters
Authors: Dessi Daniele , Leonardi Giorgia , Passacantilli Fabio
Published: September 2018

In this paper a wave energy converter (WEC) based on a segmented floating structure with embedded piezoelectric devices is numerically investigated. To illustrate the idea, a concept design based on assembling existing components is considered. The investigated system is made of three identical box-shaped slender floaters, interconnected by piezoelectric beams, aligned along the wave direction and moored to the seabed. The piezoelectric beams, bent alternatively by the oscillating relative motion of the floaters, constitute the power take-off (PTO) system to generate electricity. The numerical model is divided into two parts: a hydromechanical solver, describing the coupled motion of the floaters and the dynamics of the mooring lines, and a coupled electromechanical solver, which describes the behavior of the piezoelectric benders, including the associated resistive circuit. The coupling between these subsystems is one-way, because the WEC motion deforms the piezoelectric device without any electromechanical feedback on the floating structure. The developed numerical procedure allows for describing the basic features of the WEC response, for estimating the energy that can be generated by the device, and sets the starting point to explore the energy production capability of this kind of device.
Buckling of Stiffened Panels: An Improved Linearized Approach Compared to Nonlinear Collapse Analysis
Authors: Gaiotti Marco , Rizzo Cesare Mario , Ferrari Nicole , Montella Adriano
Published: September 2018

This paper deals with the buckling assessment of stiffened panels, typical of ship and offshore structures. In particular, rather slender structures, involving very thin plates and stiffeners with limited cross section, are considered.

In order to limit the computational burden of a fully nonlinear progressive collapse analysis but, at the same time, to retain some benefits of a numerical finite element model assessment, an improved linearized buckling procedure is proposed in this work. The idea is to linearize the computation in a suitable point based on the design load of the structure, so that the results of a linearized buckling analysis are more informative in practice. Results are assessed with nonlinear collapse analyses, comprehensively considering various loading cases. Eventually, a hands-on buckling assessment procedure is suggested, which can be implemented in rules and design process if adequately validated by a suitable number of test cases and, possibly, experimental data.
The Study on Design and Ice Collision of Icebreaking Tanker
Authors: Jang Youngjae , Park June , Lim Wooram , Kim Hanbyul , Won Sunil , Park Yunki
Published: September 2018

52,000 deadweight ton class icebreaking tanker is designed to comply with Russia Maritime Register of Shipping(RMRS) ice category Arc7 and IACS CSR-H.

The ice breaking load was obtained from the DDePS of the ABS Classification Society and the limit load calculation was examined through the Abaqus nonlinear analysis.

The collision location and iceberg type selection were adopted to define iceberg-hull collision scenarios. Nonlinear analysis simulated ice breaking process by using LS-DYNA.
Realistic Design Waves for Wave-in-Deck Problems
Authors: Bøckmann Arne , Gramstad Odin , Bloch Helmers Jens , Lande Øystein
Published: September 2018

Due to subsidence, unrealistic environmental assumptions in design or other factors, many fixed offshore installations around the world are prone to large impact forces on the super-structure. Too often, unexpected damages are found, and more accurate analyses reveal the need for reinforcement to comply with the relevant rules and regulations. The common analytical practice is to compute impact forces using 5th order Stokes waves in a CFD solver, with the crest height set to the relevant return period. Using this approach implicitly introduces a series of unrealistic assumptions, and cannot necessarily be expected to produce the force of the desired return period. In the present work, we propose a framework to better estimate the true waves producing the 100-year wave-in-deck forces in a typical North Sea environment. This is done by a long-term analysis of wave-in-deck force, hierarchically using several screening filters and solvers of different complexity. The main facilitator is an efficient High-Order Spectral Method, which at the final level is used as initial and boundary conditions in CFD. The resulting waves are short crested and may break — producing very high crest velocities that are normally not accounted for in standard engineering practice.
Using Simulator Data to Facilitate Human Reliability Analysis in Offshore Emergency Situations
Authors: Musharraf Mashrura , Moyle Allison , Khan Faisal , Veitch Brian
Published: September 2018

Data scarcity has always been a significant challenge in the domain of human reliability analysis (HRA). The advancement of simulation technologies provides opportunities to collect human performance data that can facilitate both the development and validation paradigms of HRA. The potential of simulator data to improve HRA can be tapped through the use of advanced machine learning tools like Bayesian methods. Except for Bayesian networks, Bayesian methods have not been widely used in the HRA community. This paper uses a Bayesian method to enhance human error probability (HEP) assessment in offshore emergency situations using data generated in a simulator. Assessment begins by using constrained non-informative priors to define the HEPs in emergency situations. An experiment is then conducted in a simulator to collect human performance data in a set of emergency scenarios. Data collected during the experiment is used to update the priors and obtain informed posteriors. Use of the informed posteriors enable better understanding of the performance, and a more reliable and objective assessment of human reliability, compared to traditional assessment using expert judgment.
Implementing Human Factors in Oil and Gas Drilling and Completion Operations: Enhancing Culture of Process Safety
Authors: Kiran Raj , Salehi Saeed , Teodoriu Catalin
Published: September 2018

The role of Human Factors, in complex environments like the oil and gas industry, has seen a paradigm shift over a very short span of time recently. Past studies have limited focus on the human system interfacial approach. However, the repeated failures have forced the industry and academia to take a closer look at the cascading failures with human errors perspective and conduct the root-cause analysis from the cognitive aspect. Traditionally, the knowledge, expertize, and competence took the driving seat while the human factors had been on the back burner. Lack of emphasis on Human Factors in academic research could be another reason for this laxity. Consideration of human factors in the design of systems is centered on the end user. Systems are designed to fit the physiological limitations of the people tasked with managing them. The design includes features that improve comfort and productivity, minimize errors, and minimize training time.

In this paper, first a review of crucial human factors in different well cycles such as drilling, well completion, fracturing, and abandonment will be presented. Through various cases studies, it will be shown that potential challenges can be mitigated with proper implementation of various elements for human factors such as situational awareness, team working, stress management and other non-technical skills. In addition, this paper reviews the critical components and perceived gaps of existing safety management systems in use as well as those elements that would be of most value to drilling taken from other sectors or industries on a ‘first principles’ basis. The paper attempts to highlight ’the myths, misconceptions, and realities of complex well operations’ that either deter changes or demand a new approach. It is the authors premise that if either a ‘clean sheet’ approach or more ‘actual cost’ weight was given to both common problems and low probability high consequence events such as kicks or loss of well control.
Effect of Surface Curvature on the Hydrodynamics of Water Entry at High Horizontal Velocity
Authors: Iafrati Alessandro
Published: September 2018

The role played by the curvature of the body surface on the hydrodynamics of water entry with high horizontal velocity component is investigated experimentally. The study is a part of a research activity finalized at the understanding of the aircraft ditching problem. In order to avoid scaling effects which may prevent the development of ventilation/cavitation phenomena, the study is carried out at full scale velocity. Measurements are presented in terms of pressures and loads whereas some underwater visualizations are used for the interpretation of the data. Both a convex and concave body surface are considered and comparisons with the flat plate data are established.

In the case of a concave shape, a quite complicated flow with large air entrainment develops beneath the plate. The air entrainment causes a general reduction of the pressure peak at the middle, whereas the pressure peaks recorded at the side probes are about in line with those found for the flat plate in the same conditions. The total hydrodynamic load acting normal to the plate grows more regularly but the maximum load is essentially the same as that measured in the flat plate case. For the convex shape, the pressure probes located in the middle of the plate get wetted well before the ones at the side and the pressure peaks at the sides are much lower than those in the middle. The reduced pressures at the sides cause a reduction of the total loading in the normal direction compared to flat and concave plates.
Numerical Investigation of Local Scour Around Submerged Pipeline in Shoaling Conditions
Authors: Liu Ming-ming , Zhao Ming , Lu Lin
Published: September 2018

Water waves play an important role in local scour around subsea pipelines laid on the sandy seabed, especially in shallow water regions. In this paper, a two-dimensional numerical model is employed to predict local scour around submarine pipelines under water waves in shoaling condition. The motion of water under waves is simulated by solving the Reynolds Averaged Navier-Stokes (RANS) equations. The evolution of the seabed surface near the pipeline is predicted by solving the conservation of the sediment mass, which transport in the water in the forms of bed load and suspended load. The main aim of this study is to investigate the effect of the seabed slope on the scour profiles and scour depth. To achieve this aim, numerical simulations of scour around a pipeline on a flat seabed and on a slope seabed with a slope angle of 15° are conducted for various wave conditions.
Comparison of RANS Method and Discrete Vortex Method on Simulating the Roll Motion of a Ship With Bilge Keels
Authors: Jiang Yichen , Zhao Xiaojie , Zeng Zhihua , Sun Tiezhi , Li Jiawen , Zong Zhi
Published: September 2018

The prediction of roll motion of a ship section with bilge keels is particularly difficult because the flow separation and vortex shedding under the hull significantly affect the behavior of roll damping. To predict the roll damping and roll motion directly, the numerical models must simulate the fluid viscosity. Recently, Reynolds-averaged Navier–Stokes (RANS) method and Discrete Vortex Method (DVM) have been applied in this area and show promising results. In this paper, we will use both methods to simulate the free roll-decay motion of a ship section with bilge keels. The numerical predictions of the roll time histories will be compared with experimental measurements. Besides, the numerically-predicted vorticity distributions at different time instants near a bilge keel will be shown and compared. Moreover, the computation times for both numerical methods will also be reported. In this work, we will conduct the comparison for a number of cases that are with different bilge-keel heights and bilge-keel installation angles. Thus, the accuracies and the computational efficiencies will be evaluated comprehensively.
Remaining Life Assessment and Life Extension of Offshore Pipelines
Authors: Tronskar Jens P.
Published: September 2018

Cost efficient offshore field development often involves tiebacks to existing field infrastructure. Efficient field development requires life extension of existing production facilities and pipelines to accommodate the new field resources over their life expectation. For fields near the tail end of their production the pipelines may be close to the end of their design life, and it must be shown that they have potential for extended life beyond the original design life until the end of the period of operation of the new field.

Offshore pipelines are designed and constructed to recognized standards, such as the widely applied DNV OS-F101 2013 Submarine Pipelines Systems and earlier versions. The latest edition of the code was recently issued as a standard with some major updates and a modified code number i.e. DNVGL ST-F101 [1].

As pipelines age, they will inevitably be exposed to various types of degradation and an Operator must be able to both assess the significance of this damage and the pipeline remaining life to ensure that the pipelines do not fail as they age before the end of their design lives. Currently, many pipelines are operated far beyond the original design life and as mentioned above for cost efficient field development the pipeline operator often needs to demonstrate that the pipeline’s useful life can be extended another 10 or in some cases up to 30 years. For some pipelines, new operating conditions will be introduced by tie-in of new fields and this will impact the future rate of degradation. Hence, it cannot be assumed that the future degradation will be similar or less severe than experienced since commissioning of the pipeline.

Extension of the life of the pipeline can be demonstrated by adopting methods of analysis that show the line is safe for an extended life under the future expected operating condition.

This paper describes the risk based approach applied for pipeline remaining life and life extension analyses based on DNV GL codes and other relevant recommended practices. For illustration of the methodology a typical case of remaining life assessment of and life extension of a gas export pipeline is presented in the Case Study.
Study on ALE Method for Simulating Spudcan Penetrating Near Piles
Authors: Jiayu Wang , Run Liu , Chao Liang , Hui Xiao , Jun Wan
Published: September 2018

Jack-up rigs are often employed in close proximity to piled platforms, therefore the penetration process of spudcan may have a certain effect on the deformation and bearing capacity of adjacent piles. Firstly, the feasibility of using explicit dynamics algorithm to calculate the bearing capacity of pile is verified in this paper. The optimal result of this algorithm is compared with the results of static implicit algorithm and API specification. Secondly, Arbitrary Lagrangian-Eularian (ALE) adaptive meshing is used to study the penetration process of spudcan. The effects of soil strength, ALE boundary size, mesh size and soil elastic-modulus on calculation results of penetration depth studied in this paper are to determine the optimal numerical scheme. Based on the above analysis, the effect of spudcan penetration on the bearing capacity of adjacent piles with different clearances and its law are under research by using the optimal numerical scheme. The simulation results showing computation efficiency and accuracy can be improved by using this numerical scheme, in which the amount of pile radial mesh is 8, the amount of pile peripheral mesh is 4 and the load speed is 0.1m/s. The spudcan penetration leads to the increment of bearing capacity and this effect reduces with the increment of edge-to-edge clearance between spudcan and pile.
Distributed Sensing of Loads Acting Against the Hull of a Stationkeeping Vessel in Ice
Authors: Heyn Hans-Martin , Skjetne Roger , Scibilia Francesco
Published: September 2018

This paper introduces the concept of distributed motion sensing for stationkeeping vessels in ice infested waters. During the SKT 2017 project, conducted in February and March 2017 in the Bay of Bothnia, five inertial measurement units were installed on the vessel Magne Viking. Four of the sensor units were installed at different positions inside the hull of the vessel, which enabled the system to locally measure ice-induced vibrations in the hull of the vessel. The fifth sensor unit was installed at a central position of the vessel and served as reference sensor for measuring the acting global load on the vessel. Under stationkeeping the global load measured on the ship should be close to zero, because the environmental load is equal to the force from the stationkeeping system. However the remaining four motion sensor units in the hull also measured locally induced vibrations. The study shows that this sensor configuration allows for the detection of changes in the acting load against the vessel. This is demonstrated with motion data obtained during the stationkeeping trials on the vessel Magne Viking.
Station-Keeping Trials in Ice: Test Scenarios
Authors: Liferov Pavel , Serre Nicolas , Kerkeni Sofien , Bridges Robert , Guo Fengwei
Published: September 2018

Station-keeping trials were undertaken in drifting ice in the Bay of Bothnia with two anchor handling supply vessels; Magne Viking and Tor Viking. This paper describes test scenarios which were performed with Magne Viking in moored, Dynamic Positioning and transit modes. An overview of the tests performed during the trials is presented, outlining the range of environmental and operational parameters. Examples of specific ice interaction scenarios are highlighted with illustrative measurement data providing observational insight into the performance and processes.
Station-Keeping Trials in Ice: Project Overview
Authors: Liferov Pavel , McKeever Thomas , Scibilia Francesco , Teigen Sigurd Henrik , Kjøl Andreas , Almkvist Erik , Lindvall Joakim K.
Published: September 2018

In March 2017, Statoil performed station-keeping trials in drifting ice in the Bay of Bothnia with two anchor handling tug supply vessels, Magne Viking and Tor Viking. The primary objective of the Station-keeping Trials in Ice project (SKT) was to gather full-scale data on a stationary floating structure in ice. The data will be used for validation of numerical and physical models, that will in turn increase confidence in modelling tools for design and operation in ice-covered waters. The principal requirement of the project was to safely collect the maximum amount of data meeting the quality requirements within the available budget and timeframe. This paper presents the overall project planning and execution, while more details are provided in the companion papers.
Simulator for Arctic Marine Structures (SAMS)
Authors: Lubbad Raed , Løset Sveinung , Lu Wenjun , Tsarau Andrei , van den Berg Marnix
Published: September 2018

As offshore activities in the Arctic constitute a relatively new field with only a handful of relevant operations to draw experience from, and since full-scale trials are extremely expensive, there is an expressed need for much more extensive, detailed and cost-efficient analysis of concepts based on numerical simulations. However, until recently simulation tools of sufficient quality to perform such numerical analysis have not existed. The only verification available has been through a limited set of experiments in ice model basins. Today, this has changed, partly through the efforts at the Norwegian University of Science and Technology (NTNU) hosting SAMCoT (Centre for Research-based Innovation - Sustainable Arctic Marine and Coastal Technology), laying the foundation of a versatile and highly accurate high-fidelity numerical simulator for offshore structures in various ice conditions such as level ice, broken ice and ice ridges.

Arctic Integrated Solutions AS (ArcISo) is a spin-off company from NTNU established in 2016 with the vision of increasing the technology readiness level of SAMCoT’s numerical models to become a professional software package for the analysis of sea ice actions and action effects on Arctic offshore and coastal structures. This software package is called Simulator for Arctic Marine Structures (SAMS) and it was first released in 2017. This paper introduces the software implementation and the theoretical basis of SAMS, and it discusses the use of full-scale data to validate the simulator.
Modelling Results With a New Simulator for Arctic Marine Structures - SAMS
Authors: Tsarau Andrei , van den Berg Marnix , Lu Wenjun , Lubbad Raed , Løset Sveinung
Published: September 2018

The Simulator for Arctic Marine Structures (SAMS) has emerged on the foundation of a number of scientific models developed at SAMCoT – Centre for Research-based Innovation - Sustainable Arctic Marine and Coastal Technology hosted by NTNU – as a versatile numerical tool for the analysis of sea ice actions and action effects on Arctic offshore structures. The current capabilities of SAMS allow engineers to analyse icefloe impacts and ice loads on arbitrary marine structures in various environmental conditions; simulations may involve both fixed and floating structures, non-rigid multi floe interactions, ice breaking and ice rubbling, wind, current and propeller-flow effects on both structures and ice. All these capabilities can be combined to model also complex marine operations in the Arctic and subarctic regions.

As SAMS can be applied in both full- and model scales, a number of available experimental case studies from the field and ice tanks can be reanalysed with the new simulator to ensure the high fidelity of the simulations and to establish a validation basis. This paper presents several of such case studies and discusses further validation possibilities.
Validation Exercises for a Free Falling Wedge Into Calm Water
Authors: Muralha João , Eça Luís , Maximiano António , Vaz Guilherme
Published: September 2018

This paper presents the assessment of the modelling error (Validation) of a Navier-Stokes solver using Volume of Fluid (VOF) and moving grid techniques in the simulation of a free falling wedge into calm water. This problem has been studied experimentally to determine the time histories of six pressure probes located on the wedge surface and the acceleration of the wedge. The simulation is restricted to the first 100ms after the impact of the wedge on the water (t = 0 at the impact) and the mathematical model uses the following assumptions: incompressible fluid; two-dimensional, laminar flow, negligible shear-stress at the surface of the wedge and deep water. The selected quantities of interest are the peak pressures at the six sensors, time intervals between peak pressures at the sensors, sensors pressures and acceleration of the wedge at six different time instants and integrated pressure signals for 80ms after the pressure peak at the first sensor.

The application of the ASME V&V 20 standard to local quantities is presented, including the estimation of experimental and numerical uncertainties. Furthermore, a multivariate metric is used to evaluate quantitatively the overall performance of the mathematical model. The results show significant comparison errors (mismatches between simulations and measurements) for the accelerations, which may be a consequence of the assumptions of a deep water boundary condition at the bottom. However, such conclusion is hampered by some doubts about the accuracy of the experimental data. On the other hand, modeling errors are significantly smaller for the pressure measurements at the six sensors for which the main challenge is to reduce the validation uncertainty Uval. In many of the selected flow quantities, Uval is dominated by the experimental uncertainty.