bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification and Optimization of Most Relevant Variables When Creating a Maintenance Strategy of an Offshore Wind Farm
Authors: Zanforlin Ana Beatriz Gomes , Schleder Adriana Miralles , Martins Marcelo Ramos
Published: October 2017

A lot has been researched recently in order to enable economically feasible use of offshore wind energy. Although these figures have been falling, offshore wind energy generation has in average still much higher costs associated with the inherent drawbacks of installing and operating assets at the sea’s hostile environment. As much of these costs are related to unplanned maintenance tasks, one promising approach to make wind energy more competitive is to optimize the resources involved in it. This paper was developed with the purpose of analyzing the viability of an algorithm that offers valuable information when defining a maintenance strategy for the operation of an offshore wind farm, aiming at the availability and the expected profit optimization, with a different approach than usual. Initially, an algorithm to conduct a reliability, availability and maintainability (RAM) analysis was created based on a Monte Carlo Simulation (MCS). Given a simplified wind farm model, as well as its components’ failure data and configuration, it is possible to obtain its availability and energy production costs. The algorithm was validated by comparing known failure data with the stochastically obtained after running the algorithm. A case study was defined based on extensive literature research and the simulation was executed considering restrictions typically found in modern wind farms. A sensitivity analysis was conducted in order to understand how each model’s parameter affects the energy production costs. Given this analysis, it was possible to determine the most relevant optimization variables when creating a maintenance strategy. Following, an algorithm for optimizing those parameters is presented.
Effect of Second-Order and Fully Nonlinear Wave Kinematics on a Tension-Leg-Platform Wind Turbine in Extreme Wave Conditions
Authors: Pegalajar-Jurado Antonio , Borg Michael , Robertson Amy , Jonkman Jason , Bredmose Henrik
Published: October 2017

In this study, we assess the impact of different wave kinematics models on the dynamic response of a tension-leg-platform wind turbine. Aero-hydro-elastic simulations of the floating wind turbine are carried out employing linear, second-order, and fully nonlinear kinematics using the Morison equation for the hydrodynamic forcing. The wave kinematics are computed from either theoretical or measured signals of free-surface elevation. The numerical results from each model are compared to results from wave basin tests on a scaled prototype. The comparison shows that sub and superharmonic responses can be introduced by second-order and fully nonlinear wave kinematics. The response at the wave frequency range is better reproduced when kinematics are generated from the measured surface elevation. In the future, the numerical response may be further improved by replacing the global, constant damping coefficients in the model by a more detailed, customizable definition of the user-defined numerical damping.
Collision Study Between a Ship Section Moving Sideways and an Oil Platform
Authors: Pericard Yaël , Halse Karl H.
Published: October 2017

Over the last decades, the need for overseas transportation of both people and goods has gradually increased. At the same time, several offshore activities as oil and gas exploration, wind power parks as well as fish farms have bloomed. As a consequence of the increased traffic and activities, the risk of accidents became noticeable. This paper presents a study of the collision between a Platform Supply Vessel (PSV) and an oil platform. Even if such accidents are seldom, their consequences are disastrous, for the ship owner as well as the oil-platform company. Beyond the economic consequences, some lives have been lost due to the ship - structure collisions. These problems are inducing to investigate the possibility of developing protective systems in order to save lives of the concerned persons.

Structural impact analyses can be carried out to give a scientific foundation for an evaluation of the consequences of a possible collision. This study is based on Non-Linear Finite Element Analysis (NLFEA) of the interaction between the PSV and the platform. Due to heavy calculations, only the ship section located close to the crash zone has been modelled and additional masses have been included on each side of this section in order to get the correct ship inertia. These additional masses correspond to the mass of the remaining part of the ship structure. Moreover, the sideways ship motion is modelled with a prescribed initial velocity, and does not contain hydrodynamic response calculations. The NLFEA software package HyperWorks is used to perform the numerical simulations.

As a way to reduce the consequences of a ship platform collision, a shock absorber called “crash box” is proposed mounted on the platform column to absorb the kinetic energy and thus decrease the effect in both ship and platform. 4 case studies are performed in order to compare the results with and without the crash box. Presented results are based on the deflection, resultant forces due to the contacts and absorption of the kinetic energy. The results demonstrate that penetration of the oil platform into the ship structure can be decreased by 96% if the crash box is used. Similar systems such as tires are currently used but this crash box should be investigated with an inner structure using “honeycomb” shape in order to maximise the absorption.
Time Domain Fatigue Analysis of the Pin for Offshore Bridges Considering the Nonlinear Effect of Sliding Connections
Authors: Dong Wenbin , Scherf Ingar , Sigurdsson Gudfinnur
Published: October 2017

A bridge between platforms needs to operate safely and continuously over its lifecycle. This paper focuses on the fatigue assessment of the bridge pin connection due to relative movements between platforms. A nonlinear time domain stochastic fatigue analysis of the pin connection in a bridge in the North Sea using a combined model of the jacket platforms and the interconnecting bridge is presented. The fatigue life is compared to the fatigue life from a linear frequency domain stochastic analysis.

The facility has been in operation for more than 40 years and the operator requested an update of the inspection plans for the bridge. An RBI analysis has been done according to [1] based on fatigue results from wind gusts and relative movements. Regarding the fatigue assessment due to relative movements there are uncertainties related to selection of the friction coefficient. It was assessed that a friction coefficient of 0.4 is slightly conservative in this case. The fatigue life of the pin was calculated based on a linear frequency domain stochastic analysis, assuming that the bridge was fixed at both ends and this was considered reasonable conservative for fatigue estimation. Efforts have been made in the study presented here to assess the conservatism through a nonlinear time domain stochastic fatigue analysis. The sliding connections of the bridge are simulated by nonlinear springs. The effects of assuming different friction coefficients and different nonlinear spring models for a certain friction coefficient on the fatigue damage of the pin are investigated by a sensitivity study. The fatigue lives of the pin thus computed for a series of short-term sea states for the different assumptions for the friction coefficient and the nonlinear spring model are then compared to the result from a corresponding frequency domain approach.
Scale Effects Influence on the Fatigue Crack Growth of an Offshore Steel
Authors: Micone Nahuel , De Waele Wim
Published: October 2017

Offshore tubular members are manufactured in a very wide thicknesses and diameters. The design curves considered for the fatigue design of such structures are assessed based on testing small scale laboratory specimens. A correction factor is applied to account for differences in thickness and weld geometry. However crack growth behaviour in tubular elements is complex and it is not totally clear if this can accurately be represented by testing small-scale coupons. Large scale fatigue tests aim to characterize the fatigue behaviour in a more realistic manner. However conducting such tests is very expensive. Hence, a medium scale strip type specimen with dimensions between small scale standardized specimens and a full pipe is designed. It has the same curvature and thickness as the pipe from which it is extracted and a quasi semi-elliptical notch is introduced. It is hypothesized that can account for most of the scale effects. Furthermore it can be tested in conventional test rigs at rather high frequencies.

With the objective of quantifying the scale effects between standardized ESE(T) specimens and medium size coupons, a series of crack growth based tests on a high strength offshore steel are carried out. By comparing the corresponding da/dn-ΔK curves it will be possible to evaluate possible scale effects.
A System for Automated Vision-Based Sea-Ice Concentration Detection and Floe-Size Distribution Indication From an Icebreaker
Authors: Heyn Hans-Martin , Knoche Martin , Zhang Qin , Skjetne Roger
Published: October 2017

This paper presents a ship-mounted multi-lens camera system for sea-ice monitoring and algorithms to automatically evaluate the sea-ice concentration and to indicate the floe-sizes in a radius of 100 meter around the vessel. During the SWEDARCTIC Arctic Ocean 2016 expedition, 11 camera lenses recorded the sea-ice conditions around the Swedish icebreaker Oden. As an example of the possible use of this image system, the images of six lenses are combined into one 360° panoramic image. To distinguish between water and sea-ice in the images, and thus to evaluate the sea-ice concentration around the vessel, a direct thresholding, the k-means, and a novel adaptive thresholding method are applied. Moreover, an edge detector gives the number of pixels that either form the boundary between sea-ice and water or are part of a visible ice fracture. The ratio between these edge pixels and the total number of pixels containing sea-ice gives an indication of the floe size distribution (FSD) in the image.
Design Load Measures for Vapor Cloud Explosion on Complex Systems: Review and Recommendations
Authors: Mortazavi Maryam , Heo YeongAe , Li Yue
Published: October 2017

A hydrocarbon Vapor Cloud Explosion (VCE) is one of critical hazardous events in offshore installations. Once VCE occurs in the ocean, it results in tremendous economic loss, casualties, and environmental impact. The combustion mechanism of VCE differs from HE in particular in complex geometries (e.g. offshore oil and gas production facilities) as there exist many objects which can trigger severe turbulences. Although many research efforts have been made to develop design provisions for blast resistant structures, most of those provisions are based on high-order explosives (HE) such as TNT (TriNiTrotoluene) in a free field. Therefore, typical blast resistant structural design standards were examined to address the weaknesses of standards in this study. Existing blast wave models which provide key design load parameters were also reviewed to address limitations of each approach. Finally, essential recommendations are discussed in this paper for future studies to improve blast resistant structural design provisions with the ultimate aim of protecting our lives, assets and environment from VCE in the ocean.
Experimental Study of Phase Inversion Phenomena in Electrical Submersible Pumps Under Oil Water Flow
Authors: Bulgarelli Natan Augusto Vieira , Biazussi Jorge Luiz , Castro Marcelo Souza de , Monte Verde William , Bannwart Antonio Carlos
Published: October 2017

Despite the common presence of water in oil production, just recently, the scientific community has devoted efforts to studying the influence of emulsion phenomena effects related to oil production using pumps. In the context of this study of phase inversion phenomena, the influence of viscosities and rotational speeds in Electrical Submersible Pumps (ESPs) are evaluated as part of this effort. This study is aimed at investigating the influence of viscosity in phase inversion phenomena. An 8-stage ESP was tested with three different rotational speeds and two different oil viscosities for the best efficiency point (BEP) flow rates. Initially, the total flow rate was obtained in relation to BEP using ESP performance curves for pure oil at 52 cP and 298 cP and rotational speeds of 800 rpm, 1200 rpm and 2400 rpm. The total flow rate was kept constant and the water cut was increased from zero to a hundred percent. The inversion phase phenomenon was detected by the performance improvement when the water cut increased. The factors analyzed were the head and efficiency of the ESP as a function of the water cut. The phase inversion experimental data obtained in this study was compared with literature models for horizontal pipes. The results of this comparison presented satisfactory agreement. The phase inversion phenomena occur in all 8-stage at same time. Hysteresis was observed in ESPs for oil viscosity of 52 cP and rotating speed of 800 rpm and 1200 rpm.
Comparative Study of Motions and Drift Forces in Waves and Current
Authors: Sprenger Florian , Hermundstad Elin Marita , Hoff Jan Roger , Fathi Dariusz , Selvik Ørjan
Published: October 2017

Station keeping analysis is an important activity in the early stages of any vessel/DP project that eventually determines the machinery and thruster configuration and thruster size selection. In order to obtain reliable results, it is crucial to apply engineering tools that realistically represent the flow physics and resulting hydrodynamic forces. Present computer tools are based on the assumption that wave drift- and current forces can be superimposed. However, there are also mutual interaction effects between waves, current and hulls that should be accounted for in the evaluation of the wave drift forces. In MULDIF, a 3D diffraction/radiation panel code developed by SINTEF Ocean within the framework of a JIP, this wave-current-body interaction is taken into consideration by a new potential flow numerical model. A case study with offshore vessels and general cargo ships of different main dimensions has been performed to assess the capabilities of MULDIF for station keeping purposes in wave and current environments. The first-order vessel motions as well as mean second-order drift forces for 0 kn forward speed without current have been calculated. Through an interface to SINTEF Ocean’s vessel response code VERES, MULDIF offers the possibility to include viscous roll damping due to hull friction, flow separation at bilge keels, lift effects as well as normal forces acting on bilge keels and hull pressure created by the presence of bilge keels. This reduces roll motions to a realistic extent as shown by the comparison of RAOs from MULDIF calculations and model tests. Roll reduction tank effects can currently only be considered through the external damping matrix. Model tests for the selected vessels have been performed in SINTEF’s Ocean Basin in a soft-mooring arrangement in different irregular sea states and headings in deep water. The models were equipped with two two-component force transducers, measuring the x- and y- components of the forces. The yaw moments have been calculated from the y-force measurements. In order to measure the vessel motions in six degrees of freedom, an optoelectronic position measuring system has been used. Selected cases illustrate the significant influence of wave-current interaction on motions and drift forces.
Development of the Next Generation Thermoplastic Hose Umbilical
Authors: Rutherford Alan , Dobson Alan
Published: October 2017

Thermoplastic Control Umbilicals, as shown in Figure 1, have been deployed subsea for decades globally. Typically, these have been installed in harsh dynamic environments such as the North Sea, very cold environments such as the North Atlantic and very warm environments such as the coastal waters of Middle East and Asia Pacific. The inherent fatigue and corrosion resistance of the functional components can offer significant operational advantages while umbilical make-up and manufacturing process can offer significant cost and schedule advantages.

As the industry has moved into deeper warmer water regions since the late 1990’s, such as the Gulf of Mexico and West Africa, some of the limitations of conventional thermoplastic umbilicals, such as inherent collapse resistance or design working pressures became barriers for the adoption of the technology.

In recent years there have been many new polymer materials developed that provide increased tenacity and temperature stability which subsequently have enabled an evolution in thermoplastic hose technology. This has facilitated the development of the next generation of high temperature, high pressure, collapse resistant hoses that can be deployed in deep water.

This paper defines the testing carried out on the constituent parts of the composite hose primarily focusing on the liner and details typical modes of degradation associated with high temperature, pressure or tension. The new material technologies will be benchmarked against conventional materials traditionally used in less aggressive environments.

This paper will detail the results of the development program aimed at optimising the hose design process and implementing the cutting edge materials in order to qualify a robust series of hose designs qualified to the stringent requirements of ISO 13628-5 [1].

The paper will also detail the development of the new termination coupling which has been developed in parallel with the next generation hose and which provides a reliable and robust method of coupling the hose to the subsea control system or joining two lengths of hose together.

The paper will conclude with a case study comparing a typical deep water installation of a steel tube umbilical with an equivalent thermoplastic umbilical, highlighting the benefits of the new thermoplastic umbilical designs.
Coupling Methodology for Modelling the Near-Field and Far-Field Effects of a Wave Energy Converter
Authors: Balitsky Philip , Verao Fernandez Gael , Stratigaki Vasiliki , Troch Peter
Published: October 2017

In order to produce a large amount of electricity at a competitive cost, farms of Wave Energy Converters (WECs) will need to be deployed in the ocean. Due to hydrodynamic interaction between the devices, the geometric layout of the farm will influence the power production and affect the surrounding area around the WECs. Therefore it is essential to model both the near field effects and far field effects of the WEC farm. It is difficult, however, to model both, employing a single numerical model that offers the desired precision at a reasonable computational cost. The objective of this paper is to present a coupling methodology that will allow for the accurate modelling of both phenomena at a reasonably low computational cost. The one-way coupling proposed is between the Boundary Element Method (BEM) solver NEMOH, and the depth-averaged mild-slope wave propagation model, MILDwave. In the presented cases, NEMOH is used to resolve the near field effects whilst MILDwave is used to determine the far field effects.
Effect of Coal Loading Conditions on Elastic Behavior of Large-Scale Floating Transshipment Station (LFTS)
Authors: Eto Hiroaki , Sato Chiaki , Masuda Koichi , Ikoma Tomoki , Kubota Mitsuru , Kishida Tomoyuki
Published: October 2017

Japan imports coal from Indonesia, the main coal supplier in the Asia-Pacific region. Effective and efficient movement of coal down the Markham River in East Kalimantan, Indonesia, and onto bulk carriers is challenging because the river is shallow and generally cannot accommodate bulk carriers. The primary transportation system comprises small barges that are shuttled back and forth between the inland barge ports along the river and bulk carriers offshore. This system is very time-consuming.

This paper proposes a large-scale floating coal transshipment station (LFTS) for loading, storing, and offloading coal. It will act as a relay base for barges and bulk carriers. Installing an LFTS offshore from East Kalimantan is expected to improve coal transport productivity. The proposed LFTS can store 5 times the capacity of one bulk carrier and can accommodate 2 bulk carriers at the same time during offloading. The LFTS is compartmentalized by bulkheads to segregate coal according to quality. This paper discusses LFTS static stability and its elastic deformation characteristics during coal loading operations.

In this study, linear potential theory and the finite element method (FEM) were used to analyze the LFTS static hydroelastic motion. Due to the compartments, coal loading conditions can vary significantly and affect the local static deflection, so we modeled the overall deformation and rigidity under various operational scenarios. The results were compared to the allowable material stress to identify conditions that will produce material failure. Moreover, we evaluated operation in the shallow Kalimantan River, since the weight of loaded coal deepens the LFTS draft, reducing the clearance between the LFTS and sea bed. We found that this reduced clearance and large added mass impact the natural frequency of the LFTS.
Ice Load Calculation on Semi-Submersible Platform
Authors: Cahay Marc , Roberts Brian A. , Sadouni Sami , Béal Pierre-Antoine , Septseault Cyril , Mravak Zoran , Benoit Claudie
Published: October 2017

In 2012 TechnipFMC, Cervval and Bureau Veritas initiated a common development program to offer a new tool for the design of offshore structures interacting with ice combining a variety of models and approaches.

This numerical tool called Ice-MAS (www.ice-mas.com) is using a multi-agent technology and has the possibility to combine in a common framework multiple phenomena from various natures and heterogeneous scales (i.e. drag, friction, ice-sheet bending failure, local crushing and rubble stack up). It can simulate the ice loadings of a drifting ice-sheet (including ridge or not) on predefined structures such as conical, cylindrical, sloping & vertical wall, artificial islands or more complex geometry by user input file like semi-submersible floaters with pontoon and columns allowing to obtain the detailed results on the different parts of the structure.

This paper presents the overall functionalities of Ice-MAS and the different possibilities to model a semi-submersible floater. It will focus on the results obtained for different geometries subject to ice sheet loading through different incidence angles. The issues related to the anchoring of the platform are addressed in a simplified way.
Application of Direct Hydrodynamic Loads in Spectral Fatigue Analysis
Authors: Parihar Yogendra , Dan Saikat , Doshi Karan , Ganesan Thirunaavukarasu Shivaji
Published: October 2017

It is common practice to employ direct calculation procedures for spectral based fatigue assessment. Numerical codes are used to compute direct hydrodynamic loads. There are several complexities and nuances associated with application of loads on finite element (FE) model. It is a computationally expensive task especially when a large number of cases need to be analyzed (for e.g. spectral fatigue analysis). The present paper outlines an approach to evaluate the stress transfer function based on the direct application of moments (vertical bending, horizontal bending and torsional moments) computed using a frequency-domain based sea-keeping code. Multi-point constraint (MPC) method is utilized for application of bending moment. The structural responses computed using direct application of the bending moments (Method 1) and the panel pressures (Method 2) are compared. The evaluated stress transfer function is used for spectral fatigue analysis. Overall, the present study provides a methodology for spectral fatigue assessment using direct application of bending moments.
An Assessment of WEC Control Performance Uncertainty
Authors: Coe Ryan G. , Bacelli Giorgio , Abdelkhalik Ossama , Wilson David G.
Published: October 2017

A linear dynamic model for a wave energy converter (WEC) has been developed based on the results of experimental wave tank testing. Based on this model, a model predictive control (MPC) strategy has been designed and implemented. To assess the performance of this control strategy, a deployment environment off the coast of Newport, OR has been selected and the controller has been used to simulate the WEC response in a set of irregular sea states. To better understand the influence of model accuracy on control performance, an uncertainty analysis has been performed by varying the parameters of the model used for the design of the controller (i.e. the control model), while keeping the WEC dynamic model employed in these simulations (i.e. the plant model) unaltered. The results of this study indicate a relative low sensitivity of the MPC control strategy to uncertainties in the controller model for the specific case studied here.
A Formulation for the Unsteady Aerodynamics of Floating Wind Turbines, With Focus on the Global System Dynamics
Authors: Bayati Ilmas , Belloli Marco , Bernini Luca , Zasso Alberto
Published: October 2017

This paper proposes a formulation for the assessment of the unsteady aerodynamics of floating offshore wind turbines, based on wind tunnel experiments through surge and pitch imposed motions on the 1/75 DTU 10 MW scale model. Rotor thrust and torque were analysed out of a set of different combinations of amplitudes and frequencies of the imposed mono-harmonic motion, following the idea of splitting these forces into steady and unsteady contributions, respectively through steady and unsteady aerodynamic coefficients. The latter were analysed, for different tip-speed ratios, both experimentally and numerically, with respect to a newly introduced parameter, the “wake reduced velocity”, which turned out to be effective in the description of the unsteady regime. Experimental results have shown good consistency of the formulation and put the basis for further studies on this topic, for the comprehension of this phenomenon and for the development of reduced-order models for control purposes, with the focus of the global system dynamics.
Study on Ship Manoeuvering in Adverse Sea State
Authors: Guo Bingjie , Ruth Eivind , Austefjord Håvard , Bitner-Gregersen Elzbieta M. , Gramstad Odin
Published: October 2017

IMO introduced Energy Efficiency Design Index (EEDI) to regulate the greenhouse gas (GHG) emissions from ships. The cheapest and easiest way to fulfil the EEDI requirement is to reduce installed power for most ships. Therefore, it has raised serious concerns that some ship designers might choose to lower the installed power to achieve EEDI requirements and not consider ship safety in a satisfactory way. This could induce ship manoeuvrability and safety problems in adverse seas, which needs urgent investigations on minimum power to maintain ship manoeuvrability in adverse sea.

A time domain code ‘Waqum’ has been developed based on the force superposition of unified theory to study the minimum required power for maintaining ship manoeuvring ability in adverse sea states. The code combines sea-keeping and maneuvering equations, together with an engine model to predict ship responses in waves. The code can help us to study ship responses in transit situation and give us better insight into ship maneuvering ability in adverse sea states. In order to improve the simulation speed, the time domain code does not calculate all the hydrodynamic forces directly. Thus, some precalculations should be done for some force components before launching the simulation for a new ship. Therefore, the methodology and accuracy of each force component will influence the accuracy of the manoeuvring code. The methodology for determining each force component will be discussed, especially the identification of maneuvering derivatives based on CFD simulations. The code has been improved recently, and another rudder model has been implemented. Further, the the code with new rudder model is verified in calm water. The code’s ability to capture ship maneuvering in waves is also demonstrated.
Numerical Investigation on Wave Induced Vortex Dynamics Around Cylindrical Pile With Considering Varying Keulegan-Carpenter Number
Authors: Mohammad Beigi Kasvaei M. , Kazeminezhad M. H. , Yeganeh-Bakhtiary A.
Published: October 2017

Three-dimensional numerical simulation of regular waves passing over cylindrical monopile has been conducted to investigate the vortex dynamics. To do so the rectangular wave flume and monopile is modeled on a solver, available in the open-source CFD toolkit OpenFOAM®. The solver applied RANS equations with VOF method for tracking free surface. Model validation has been done by comparison numerical results with the experimental ones and admissible agreement has been seen. Computations have been done for three cases with different pile diameters consequently for different Keulegan-Carpenter numbers (KC).

The vorticity field around the pile was investigated as well as vortices by means of Q criterion. It was seen that by increasing KC number, horseshoe vortices will be formed and vortex shedding will be happened. Moreover, Bed shear stress around the pile has been extracted and it has been seen that, the bed shear stress is influenced by KC value which result of existence of horseshoe vortices and vortex shedding.
Multidisciplinary Approach to Design and Analysis of Arctic Marine Transport Systems
Authors: Tarovik Oleg V. , Topaj Alex , Bakharev Andrey A. , Kosorotov Andrey V. , Krestyantsev Andrey B. , Kondratenko Aleksander A.
Published: October 2017

Basic principles of the multidisciplinary approach to arctic marine transport systems (MTS) design and analysis are described in the article. The main idea of the approach is to synthesize geographic information system (GIS) technologies, different shipbuilding disciplines, fleet planning instruments and agent-based dynamic simulation models in an integrated software framework on the basis of object-oriented programming. Vessel operation is described as the movement and interaction of independent ships in GIS environment within the framework of the simulation model. MTS operation combines vessel operation itself (routing, determination of speed and fuel consumption, icebreaker escort, etc.) with plenty of external entities (port infrastructure, ice channel freezing process, offshore platform operation, etc.) that could be described as systems with comprehensive logic and physical behavior. Such integration provides a new quality of MTS simulation that allows considering complex interconnection of various subsystems and all the important details of each MTS project. The outline of the program framework to realize such an approach is given, and two case studies are described to demonstrate its capabilities and feasibility.
Modelling of Nonlinear Wave-Buoy Dynamics Using Constrained Variational Methods
Authors: Kalogirou Anna , Bokhove Onno , Ham David
Published: October 2017

We consider a comprehensive mathematical and numerical strategy to couple water-wave motion with rigid ship dynamics using variational principles. We present a methodology that applies to three-dimensional potential flow water waves and ship dynamics. For simplicity, in this paper we demonstrate the method for shallow-water waves coupled to buoy motion in two dimensions, the latter being the symmetric motion of a crosssection of a ship. The novelty in the presented model is that it employs a Lagrange multiplier to impose a physical restriction on the water height under the buoy in the form of an inequality constraint. A system of evolution equations can be obtained from the model and consists of the classical shallow-water equations for shallow, incompressible and irrotational waves, and relevant equations for the dynamics of the wave-energy buoy. One of the advantages of the variational approach followed is that, when combined with symplectic integrators, it eliminates any numerical damping and preserves the discrete energy; this is confirmed in our numerical results.
Modeling and Control of Crane Overload Protection During Marine Lifting Operation Based on Model Predictive Control
Authors: Ren Zhengru , Skjetne Roger , Gao Zhen
Published: October 2017

This paper deals with a nonlinear model predictive control (NMPC) scheme for a winch servo motor to overcome the sudden peak tension in the lifting wire caused by a lumped-mass payload at the beginning of a lifting off or a lowering operation. The crane-wire-payload system is modeled in 3 degrees of freedom with the Newton-Euler approach. Direct multiple shooting and real-time iteration (RTI) scheme are employed to provide feedback control input to the winch servo. Simulations are implemented with MATLAB and CaSADi toolkit. By well tuning the weighting matrices, the NMPC controller can reduce the snatch loads in the lifting wire and the winch loads simultaneously. A comparative study with a PID controller is conducted to verify its performance.
Crane Rig: An Experimental Setup for Developing and Verifying New Control Methods for Marine Crane Operations
Authors: Evang Thomas H. , Skjong Stian , Pedersen Eilif
Published: October 2017

This paper will present the derivation of dynamic equations describing the motion of a knuckleboom crane for marine vessels. The dynamics will be derived using Lagrange’s equation, the theory of virtual work and generalized forces. Simulations of the unforced and forced system will be carried out to verify the crane behaviour. The work is part of setting up a crane lab at the Norwegian University of Science and Technology, NTNU. The rig will be used as an experimental setup available for both students and researchers and is expected to create a solid foundation for further work regarding crane control. Examples of its application are research on heave compensation and soft landing. However, before the setup can be finished a dynamical model governing the system must be derived in order to construct simple crane controllers. As part of the modeling a step by step method for describing the crane motions will be presented. Using rotation matrices and moving reference frames the position of each point on the crane will be described in an inertial reference frame. An implementation of the model in Matlab’s Simulink will also be shown, along with some simple simulations verifying system behaviour. The main result will be a state space formulation of the crane dynamics, a Simulink model for anticipating crane behaviour and a discussion of some simple simulation scenarios.
Proposed Methodology for Fatigue Testing on Umbilical Round Armor Wires
Authors: Tagliari Mariana R. , Coser Tiago B. , Campello George , Matoso Gustavo , Bertoncello João Carlos B. , Argüello Facundo , Reguly Afonso
Published: October 2017

Subsea umbilicals are a vital component for offshore operations, being responsible to provide hydraulics, fluid injection, power and/or communication services to and from subsea facilities. They can be designed for both static and dynamic applications and can be deployed in harsh environments where potentially damaging factors such as corrosion, tension, pressure, clashing, entanglement, among others are commonly present. For armored umbilicals, the tensile armor wires of these structures are responsible for the tensile strength and its fatigue life is a key design consideration for subsea umbilicals subjected to dynamic loading. Despite its considerable importance, there is no standardized methodology for conducting fatigue tests of tensile armor wires of umbilical cables. Some general guidelines are given in technical publications such as ISO 13628-5 standard and DNV’s recommended practice F401, but there is still need for more detailed information regarding fatigue testing of these components. This lack of methodology for fatigue testing of circular wires that comprise the tensile armor of these structures lead to the motivation for this study. The main advantage of using specific data from an adequate testing methodology of tensile armor wires — instead of using standard SN curves — is to reduce conservatism, mainly considering damage calculations for the overall structure. Additionally, with the increasing operating water depths, an excessively conservative design can lead to a considerably heavier structure which will induce higher topside stresses. Therefore, it is of great importance to have a well defined methodology to obtain SN curves that can be used in the design phase of umbilical cables which can lead to an optimized structure and also keep an adequate degree of conservatism. In this work, it will be presented several attempts to achieve an adequate methodology to obtain SN curves for circular tensile armor wire of umbilicals and the final methodology adopted will be described in detail. Tensile armor wires in a wide range of diameters and strength were tested in order to validate the proposed methodology. Additionally, the normalized fatigue results from several tests are also presented and compared to SN curves commonly used during the design phase of umbilical cables.
Complementarity of Data-Driven and Simulation Modeling Based on the Power Plant Model of the Offshore Vessel
Authors: Swider Anna , Skjong Stian , Pedersen Eilif
Published: October 2017

Nowadays, there are more ships equipped with on-board monitoring systems and vessels with many sensors are becoming a standard. Available measurements can be employed for system optimization which play an important role in the vessel power plant configuration. The improvements in the power system design can be based on theoretical (modeling based on physical and empirical laws — for simulation purposes, for example [1]) or data-driven modeling (machine learning, statistical approach [2]). The data-driven models can be supportive confirming theoretical assumptions or simplifications from simulations. They are also helpful to understand the real systems, including vessel dynamic behavior and interactions. Therefore, the combination of simulation and data-driven modeling will be beneficial by identifying relationships that help explain unidentified variations. This approach is recommended when aiming for a more reliable tool for design optimization and to overcome the limitation of the simulation models that all system properties and dynamic effects must be known beforehand. The scope in this work is to present a potential synergy between the simulation and the machine learning approach. A data-driven method can be complementary to a model based on physical and empirical laws. This is shown in the example of power plant model connected with a thruster and vessel model to simulate the typical transit scenario and the data-driven model. The paper proposes a simultaneous analysis of the theoretical and machine learning models to predict the vessel power/speed and study the complex systems’ interactions in more detail, which are essential while exploring the system behavior.
A Numerical Study on a Flopper Stopper for Leg Positioning of a Jack-Up Barge
Authors: Jiang Zhiyu , Guachamin Acero Wilson , Gao Zhen , Li Lin
Published: October 2017

Jack-up barges are commonly used for marine operations in the offshore oil and gas, and offshore wind industries. A critical phase within the marine operation activities is the positioning of the jack-up legs onto the seabed. During this process, large impact velocities and forces may arise from the barge’s heave, roll and pitch motions, and structural damage of the legs can occur. This paper numerically investigates the effect of a flopper stopper (FS) on the motion responses of a jack-up barge from the offshore wind industry. The FS is known as a passive roll compensation device. It is suspended from the side of the barge by means of wire ropes and cantilever beams. A simple geometry of an FS is proposed, and the working principle introduced. For the loading condition before the leg-soil impact occurs, global dynamic analyses of the coupled system are conducted. Characteristic values of impact velocities are used to establish the jack-up operational limits in terms of the significant wave height and peak period. By comparing the operational limits for the barge with and without FS, it is found that FS should be placed on the weather side. At beam seas, the current FS can lead to a maximum increase in the operational wave height limit of 35%, whereas for the other wave headings, it may not be beneficial to use FS.
AMOS DP Research Cruise 2016: Academic Full-Scale Testing of Experimental Dynamic Positioning Control Algorithms Onboard R/V Gunnerus
Authors: Skjetne Roger , Sørensen Mikkel E. N. , Breivik Morten , Værnø Svenn A. T. , Brodtkorb Astrid H. , Sørensen Asgeir J. , Kjerstad Øivind K. , Calabrò Vincenzo , Vinje Bjørn Ole
Published: October 2017

In order to validate relevant dynamic positioning (DP) control algorithms in a realistic environment, a full-scale DP test campaign, the AMOS DP Research Cruise 2016 (ADPRC’16), was organized in a collaboration between the NTNU Centre for Autonomous Marine Operations and Systems (NTNU AMOS) and the company Kongsberg Maritime onboard the research vessel (R/V) Gunnerus. To the authors’ best knowledge, closed-loop DP feedback control algorithms have never been tested full-scale on a ship in an academic research experiment before. However, we have now achieved this by coding our algorithms into a test-module of the DP system, as prepared by Kongsberg Maritime. Among the tested algorithms is an output feedback control law with both good transient and steady-state performance. In another experiment, different adaptive backstepping control laws for DP were tested to compare and contrast their performance and properties. A hybrid state observer with a performance monitoring function proposed to switch between two observers, choosing the best one at any time instant, was also part of the test scope. For this, necessary measurements (including acceleration measurements) were logged to be able to rerun and validate the observer algorithms in post-processing. Finally, several experiments were done to test a pseudo-derivative feedback control law for DP. The feedback mechanism was tested with and without a feedforward disturbance rejection term, called acceleration feedforward. This paper reports the experimental setup, test program, and an overview of results from the ADPRC’16 campaign.
Observation of Subsea BOP Response From Field Measurements and Reflections on Conductor Design Challenges
Authors: Holden Harald , Holm Heidi Gryteland , Zhang Youhu , Smith Victor , Næss Randi
Published: October 2017

Subsea exploration well systems are subjected to complex loading due to vessel motion and hydrodynamic forces on the riser. In design of the wells, both the ULS/ALS design under extreme loading and fatigue design under operational loading are heavily dependent on the soil support along the uppermost 20 m of the conductor casing. In today’s practice, design of the conductor against extreme loading is typically performed using the soil reaction curves (p-y springs) recommended in API RP 2GEO [1].

In recent years, 4Subsea have been monitoring the BOP and riser responses during exploration drilling campaigns for Lundin Norway. The purpose of these monitoring campaigns is to track the performance of the wells with time, based on integrity parameters such as well stiffness, BOP resonance frequency and BOP motion rotational depth. This paper summarizes the monitoring results from seven well locations in the North Sea and the Barents Sea. The observed well response is compared with up-front design analyses. The discrepancy between up-front design analyses and the observed performances is discussed in light of the uncertainties associated with the geotechnical input parameters and soil reaction models. The purpose of the paper is to reflect on the challenges faced with exploration well design and highlight areas that improvements can be made.
Adaptive Composites for Load Control in Marine Turbine Blades
Authors: Barber Ramona B. , Hill Craig S. , Babuska Pavel F. , Aliseda Alberto , Wiebe Richard , Motley Michael R.
Published: October 2017

Marine hydrokinetic turbines typically operate in harsh, strongly dynamic conditions. All components of the turbine system must be extremely robust and able to withstand large and constantly varying loads; the long and relatively slender blades of marine turbines are especially vulnerable. Because of this, modern marine turbine blades are increasingly constructed from fiber reinforced polymer (FRP) composites. Composite materials provide superior strength- and stiffness-to-weight ratios and improved fatigue and corrosion resistance compared to traditional metallic alloys. Additionally, it is possible to tailor the anisotropic properties of FRP composites to create an adaptive pitch mechanism that will adjust the load on the turbine in order to improve system performance, especially in off-design or varying flow conditions. In this work, qualitative fundamentals of composite structures are discussed with regards to the design of experimental scale adaptive pitch blades. The load-deformation relationship of flume-scale adaptive composite blades are characterized experimentally under static loading conditions, and dynamic loading profiles during flume testing are reported. Two sets of adaptive composite blades are compared to neutral pitch composite and rigid aluminum designs. Experimental results show significant load adjustments induced through passive pitch adaptation, suggesting that adaptive pitch composite blades could be a valuable addition to marine hydrokinetic turbine technology.
An Experimental Assessment of the Hysteresis Behavior of Umbilical Cables Under Cyclic Traction
Authors: Santos Caio C. P. , Pesce Celso P. , Salles Rafael , Franzini Guilherme R. , Gonçalves Rodolfo T. , Morini Rafael
Published: October 2017

Umbilical cables are composed by several internal components helically disposed and externally protected by an outer polymeric sheath. With these elements wound in different directions, internal friction is a well-known structural feature, originating hysteretic loops when umbilicals are subject to cyclic loads. On the other hand, polymeric materials represent a substantial part of an umbilical composition. These materials present a viscoelastic character, introducing a second energy dissipation mechanism to these flexible structures. Therefore, this paper aims to assess the hysteresis phenomenon observed under different periodic axial loading conditions.

The study is based on experimental campaigns carried out with two umbilical cables, proposing and testing a new experimental methodology based on standard instrumentation combined with optical tracking measurement. The hysteresis loops are evaluated considering ‘slow’ and ‘very-slow’ axial cyclic loads. The results indicates that an equivalent viscoelastic damping behavior could be adopted to model the umbilical cable response under ‘slow’ axial cyclic loads. In contrast, the ‘very-slow’ tests indicate that the energy dissipation process is dominated by a dry friction mechanism.
Wear of Outer Sheath Materials in Flexible Pipes: Testing Methodology
Authors: Øren Einar , Larsen Marit , Kvilhaug Frode Andres , Melve Bjørn
Published: October 2017

Outer sheath wear of polymers in flexible risers has been experienced with risers anchored with guide tubes and bellmouths. In addition, wear damages have been observed at touch down points and on subsea arch support structures.

A wear test methodology was developed with the purpose to mimic the observations from pipes in operation. The test apparatus used was similar to a pin-on-disc measurement method, but with emphasis on reproducing the exact environment and temperature.

Comparative tests have been done between different materials, and for some conditions the differences are significant.