bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite Element Analysis of Offshore Pipelines Overlying Active Reverse Fault Rupture
Authors: Thebian Lama , Sadek Salah , Najjar Shadi , Mabsout Mounir
Published: October 2017

The paper investigates the behavior of buried offshore pipelines overlying active reverse faults using the finite element (FE) tool Abaqus. In the FE analyses, the pipeline is modeled with 3D shell elements and the soil with continuum elements. Equivalent boundary conditions are imposed at both pipeline ends to account for the elastic response in the far-field away from the fault. Nonlinear materials, nonlinear interactions, and nonlinear geometries are adopted.The Mohr-coulomb constitutive model with strain-softening is used to model the soil behavior and true stress-strain properties are incorporated to model the response of the pipeline steel material. The effects of soil properties, pipeline diameter, diameter to thickness ratio, and fault displacement are investigated. The results focused on analyzing the pipeline deformations, the axial strains, and the buckling behavior of the pipeline with increasing vertical bedrock displacement. Critical compressive strains are calculated and compared with the DNV code provisions.
Design of an Offshore Three-Bladed Vertical Axis Wind Turbine for Wind Tunnel Experiments
Authors: Roy Sukanta , Branger Hubert , Luneau Christopher , Bourras Denis , Paillard Benoit
Published: October 2017

The rapid shrinkage of fossil fuel sources and contrary fast-growing energy needs of social, industrial and technological enhancements, necessitate the need of different approaches to exploit the various renewable energy sources. Among the several technological alternatives, wind energy is one of the most emerging prospective because of its renewable, sustainable and environment friendly nature, especially at its offshore locations. The recent growth of the offshore wind energy market has significantly increased the technological importance of the offshore vertical axis wind turbines, both as floating or fixed installations. Particularly, the class of lift-driven vertical axis wind turbines is very promising; however, the existing design and technology is not competent enough to meet the global need of offshore wind energy. In this context, the project AEROPITCH co-investigated by EOLFI, CORETI and IRPHE aims at the development of a robust and sophisticated offshore vertical axis wind turbine, which would bring decisive competitive advantage in the offshore wind energy market. In this paper, simulations have been performed on the various airfoils of NACA 4-series, 5-series and Selig profiles at different chord Reynolds numbers of 60000, 100000 and 140000 using double multiple streamtube model with tip loss correction. Based on the power coefficient, the best suitable airfoil S1046 has been selected for a 3-bladed vertical axis wind turbine. Besides the blade profile, the turbine design parameters such as aspect ratio and solidity ratio have also been investigated by varying the diameter and chord of the blade. Further, a series of wind tunnel experiments will be performed on the developed wind turbine, and the implementation of active pitch control in the developed turbine will be investigated in future research.
Soil-Pipe Interaction Models for the Simulation of Buried Steel Pipeline Behaviour Against Geohazards
Authors: Sarvanis Gregory C. , Karamanos Spyros A. , Vazouras Polynikis , Dakoulas Panos , Mecozzi Elisabetta , Lucci Antonio
Published: October 2017

Hydrocarbon pipelines constructed in geohazards areas, are subjected to ground-induced actions, associated with the development of severe strains in the pipeline and constitute major threats for their structural integrity. In the course of pipeline design, calculation of those strains is necessary for safeguarding pipeline integrity, and the development of reliable analytical/numerical design tools that account for soil-pipe interaction is required.

In the present paper, soil-pipe interaction models for buried steel pipelines subjected to severe ground-induced actions are presented. First, two numerical methodologies, (simplified and rigorous) and one analytical are presented and compared, followed by an experimental verification; transversal soil-pipe interaction is examined through full-scale experimental testing, and comparisons of numerical simulations with rigorous finite element models are reported. Furthermore, the rigorous model is compared with the results from a special-purpose full-scale “landslide/fault” experimental test in order to examine the soil-pipe interaction in a complex loading conditions. Finally, the verified rigorous model is compared with both the simplified models and the analytical methodology.
Experimental Study of Viscous Cargo Behaviour and Investigation on Global Loads Exerted on Ship Tanks
Authors: Baudry Virginie , Rousset Jean-Marc
Published: October 2017

The LiquefAction project is dedicated to the study of cargo liquefaction, especially to understand the inception of this phenomenon and its effects on bulk carrier stability. Both numerical and experimental approaches are set-up to simulate the behaviour of specific ores in various modes of motions.

This paper is dealing with forced motion tests of a tank filled with two highly viscous fluids. The tank is a bulk carrier hold model and a hexapod platform is reproducing the ship motions. Free surface evolutions as well as global loads are analysed.

Some preliminary conclusions are given with respect to the filling ratio, the fluid viscosity and type of motions.
Experimental Study on the Vortex-Induced Motions (VIM) of a Semi-Submersible Floater in Waves
Authors: Maximiano António , Koop Arjen , de Wilde Jaap , Gonçalves Rodolfo T.
Published: October 2017

Recent studies suggest that the vortex-induced motions (VIM) of a semi-submersible found in model tests over-predicts the response in the field, which may lead to an over conservative design of the mooring and riser system. Within the Vortex Induced Motion Joint Industry Project (VIM JIP), run by MARIN and University of São Paulo (USP), possible reasons for this over-prediction are investigated using model tests and CFD [1–6]. A model test campaign was carried out at MARIN to test different candidates that might explain the observed differences. The results obtained with an air bearing setup regarding damping, mass ratio, draft variations and sinusoidal tow velocities, have been published elsewhere [6]. The present publication focuses on the influence of waves on the VIM response.

The model was a generic bare hull semi submersible with four rounded square columns at scale 56.5. A simplified mooring system consisting of four springs was designed to match the desired natural period in the sway and yaw direction. The model was towed at different velocities, corresponding to the range of reduced velocities where the highest response is expected. A VIM tow test campaign was carried out in calm water as a benchmark. The model was then tested at 7 different wave-current conditions, and the results are compared with the benchmark case.

The results suggest that two factors are important for VIM response in waves: the wave height, and the relation between wave and current direction. Comparing to calm water conditions, a reduction of 15% on the peak nominal response was found for a smaller sea state (HS = 2m, TP = 10s), however with a higher significant wave height (HS = 4m, TP = 10s) the peak nominal response was reduced by 30%. Depending on the combination of current-wave direction, the influence of the same sea state (HS = 4m, TP = 10s) on VIM response can be negligible (transverse seas) or result in a 30% reduction of the peak nominal response for collinear sea and current. This is a relevant finding since most research on the topic has focused on collinear conditions, and VIM tests in waves with transverse or oblique conditions are rare [7–9].

Comparing the calm water VIM response obtained with the air bearing setup, published in [6], with the soft mooring configuration reported here, the latter shows a generally smaller response, with a narrower lock in region. Nevertheless the peak response is found to be similar for both experimental setups.
Modelling the Dynamic Response and Loads of Floating Offshore Wind Turbine Structures With Integrated Compressed Air Energy Storage
Authors: Sant Tonio , Buhagiar Daniel , Farrugia Robert N.
Published: October 2017

Nowadays there is increased interest to incorporate energy storage technologies with wind turbines to mitigate grid-related challenges resulting from the intermittent supply from large-scale offshore wind farms. This paper presents a new concept to integrate compressed air energy storage (CAES) in floating offshore wind turbine (FOWT) structures. The FOWT support structures will serve a dual purpose: to provide the necessary buoyancy to maintain the entire wind turbine afloat and stable under different met-ocean conditions and to act as a pressure vessel for compressed air energy storage on site. The proposed concept involves a hydro-pneumatic accumulator installed on the seabed to store pressurized deep sea water that is pneumatically connected to the floating support structure by means of an umbilical conduit. The present study investigates the technical feasibility of this concept when integrated in tension leg platforms (TLPs). The focus is on the impact of the additional floating platform weight resulting from the CAES on the dynamic response characteristics and loads when exposed to irregular waves. A simplified model for sizing the TLP hull for different energy storage capacities is initially presented. This is then used to evaluate the dynamic response of nine different TLP geometries when supporting the NREL1 5MW baseline wind turbine model. Numerical simulations are carried out using the marine engineering software tool ANSYS Aqwa©. The work provides an insight on how TLP structures supporting wind turbines may be optimised to facilitate the integration of the proposed CAES concept. It is shown that it is technically feasible to integrate CAES capacities on the order of Megawatt-Hours within TLP structures without compromising the stability of the floating system; although this would involve a substantial increase in the total structure weight.
Heat Loss of Heated Deck Elements in Cross-Flow Wind
Authors: Peechanatt Jino , Kvamme Bjarte O. , Gudmestad Ove T. , Amith Yaaseen A.
Published: October 2017

In recent years, there has been unprecedented interest shown in the Arctic region by the industry, as it has become increasingly accessible for oil and gas exploration, shipping, and tourism. The decrease in ice extent in the Arctic has renewed the interest in the Northern Sea route, necessitating further research to evaluate the adequacy of the equipment and appliances used on vessels traversing in polar waters.

The introduction of the Polar Code by the International Maritime Organization (IMO) attempts to mitigate some of the risks endangering the vessels in Polar waters. The Polar Code is scheduled to take effect on 01.01.2017, and applies to all vessels traversing in polar waters. One of the requirements in the Polar Code is that means shall be provided to remove or prevent accretion of snow and/or ice from escape routes, embarkation areas and access points. Even though, prior to the formulation of Polar Code, the requirement for de-icing the deck surfaces on vessels already exists, the suitability of the equipment currently in use is debatable. Large amounts of energy is required to maintain an ice-free surface, which is not desirable economically or environmentally, due to the substantial increase in fuel consumption.

In this study, a heated deck element manufactured by GMC Maritime AS is subjected to cross flow wind of 5 m/s, 10 m/s and 15 m/s at various sub-zero temperatures in GMC Maritime AS’s climate laboratory in Stavanger, Norway. The deck element is rated to 1400 W / m2, and is one of the designs provided by GMC Maritime AS. The power consumption of the deck element is measured and compared to theoretical heat loss calculations. Large discrepancies between the measured power consumption and the theoretical heat loss were discovered, indicating the need for further studies on the matter.

As part of SARex Spitzbergen 2016, a search and rescue exercise conducted off North Spitzbergen, heated deck elements on board the Norwegian Coast Guard Vessel KV Svalbard were studied and are discussed in this paper. The heating elements in the deck elements were designed to specifications at the time of commissioning, but proves insufficient when the vessel is in transit or exposed to slight winds, allowing snow and ice to accumulate on the surface.

Finally, suggestions for a more energy efficient design of deck elements are made, as the current designs are found to have potential for improvement, especially due to the lack of insulation between the deck elements and the hull of the vessel.
Simulation of Passing Vessel Effects on Moored Vessel Mooring Response due to Environmental Loads
Authors: Vasudevan Nandhini , Nallayarasu S.
Published: October 2017

A critical review of literature on the mooring forces on the berthed ship together with the passing vessel effects indicates limited data, thus requiring additional studies. Four methods have been found in the literature namely (a) Seelig’s, (b) Flory’s, (c) Kreibel’s, and (d) Modified Seelig’s methods. A comprehensive review and comparison of existing methods has been carried out to verify the applicability of each method to certain conditions and also to establish the parameters for study. It has been found that displacement of the vessels, separation distance between the vessels and velocity of the passing vessel greatly influence the passing vessel forces on moored ship. The software OPTIMOOR has been used to verify Flory’s and Seelig’s methods with the experimental data of Remery and also to study the combined effect of environmental loads and passing vessel effects on mooring lines. The results indicate that the interaction of waves and passing vessel effects are too onerous. Conclusions have been arrived based on the results that for separation distance of 100 m or less between vessels has a greater influence on mooring line forces, leading to breakage of lines.
Spatio-Temporal Stress Path Prediction Under Different Deformational Conditions
Authors: Rafieepour Saeed , Miska Stefan Z.
Published: October 2017

Drilling new infill wells in depleted reservoirs is extremely problematic and costly due to low formation fracture pressure and narrow mud window resulting from in-situ stress changes due to fluid extraction. This is of paramount importance especially for drilling operations in deep-water reservoirs, which requires precise prediction of formation fracture pressure. In turn, this entails accurate prediction of reservoir stress changes with pore pressure depletion, i.e., the stress path. Currently-used models assume a transient flow regime with reservoir depletion. However, flow regime in depleted reservoirs is dominantly pseudo-steady state (PSS). Shahri and Miska (2013) proposed a model under plane-strain assumption. However, subsea subsidence measurements confirm that depletion-induced reservoir deformation mainly occurs in axial direction. We provide analytical solutions for stress path prediction under different deformational conditions namely, plane strain-traction and displacement boundary conditions, generalized-plane-stress, generalized uniaxial strain, and uniaxial-strain. For this purpose, constitutive relations of poroelasticity are combined with equilibrium equations, and pore pressure profile is described by PSS flow regime. In a numerical example, we examine the effects of different deformational conditions on depletion-induced in-situ stress changes. Interestingly, results indicates that stress path in reservoir is significantly affected by reservoir’s boundary conditions. The stress path under plane strain-displacement assumption overestimates the stress path predicted under uniaxial strain state by almost a factor of two. However, the generalized plane stress and traction plane strain conditions underestimates the results of uniaxial strain assumption. The order of stress path values for different boundary conditions can be summarized as: SPps-disp > SPuniaxial > SPps-trac > SPgps.
A Web Based Application for the Lateral Analysis of Pile (LAP) Foundations
Authors: Doherty James P.
Published: October 2017

This paper presents and discusses a new web based application for analysing piled foundations subject to lateral loads; a common problem in civil engineering. Details of the algorithm used to form and solve the non-linear system of equations are provided, along with details of the application’s deployment on Amazon Web Services cloud infrastructure. The application is particularly convenient to use as it does not require the installation of any software. The responsive web based interface scales according the screen size of the user’s device and can therefore be run on PC, tablet or smart phone.The application has been developed with both industry and the research community in mind. A particularly convenient method for specifying user defined soil springs is available. This feature is illustrated in this paper with an example that also validates the numerical implementation.
Comparison of Global Riser Analysis to Full Scale Measurements on the NCS
Authors: Grytøyr Guttorm , Hørte Torfinn , Russo Max , Gregersen Kathrine , Aronsen Kristoffer H.
Published: October 2017

Fatigue of subsea wellhead systems due to wave-induced loads from riser and rig motions has been subjected to increased attention in recent years. It is expected that calculated riser loads are conservative, as both input parameters and methodology are associated with some uncertainty. However, it is difficult to quantify the degree of conservatism in analytical results unless reference to measurements can be made.

Statoil has conducted drilling riser load instrumentation campaigns in several locations around the world over the last few years in order to gather high quality data for accurate assessment of the fatigue loads imposed on the subsea wellheads (see e.g. ref. /1/, /2/, /3/, and /17/). Four (4) of these measurements campaigns have been studied in more detail, with the intention to quantify the degree of conservatism to be expected from drilling riser analysis. Three (3) of these cases have direct bending moment measurements from strain sensors at the BOP connector elevation, giving high confidence in the results. For one (1) of the cases, the bending moments at the WH have been established by use of indirect methods (ref. /2/). The campaigns have been anonymized; They are from the Norwegian Continental Shelf (NCS), with water depths ranging from 110 to 400m. This paper presents the findings from our comparison of measurements and analytically derived drilling riser loads from these 4 campaigns. The analysis models have not been “tuned” to match the measurements. The goal is rather to get a measure of how well riser analyses are able to predict the real world.

The conclusion in this paper is that the global drilling riser analyses accurately predict the cyclic loads on the subsea wellheads, provided that the input data are known with high degree of detail, including e.g. riser tension setting; drill pipe tension variation over time; and hydrodynamic loads. We found that scatter in the results is due to the uncertainty inherent to several of the input parameters.

It is also shown that the accumulated fatigue damage from a full drilling campaign, can be established with sufficient degree of accuracy with somewhat lower requirement to the level of detail of the input, like e.g. using unidirectional waves instead of short crested waves. Directionality and spreading of the wave field can be handled by use of factors on the damage rate. A directionality factor is proposed, to enable comparison of directionality of the measured response to the predictions from global analysis.
Risk Management of Autonomous Marine Systems and Operations
Authors: Utne Ingrid Bouwer , Sørensen Asgeir J. , Schjølberg Ingrid
Published: October 2017

Autonomous systems may lead to smarter and more efficient operations, but emerging risks are involved, because of lack of knowledge and operational experience with such systems, and challenges related to verification of safe performance. The objective of this paper is to clarify, categorize, and classify risk related to autonomous marine systems, and establish a foundation for risk management of such systems. Autonomous systems are usually associated with unmanned systems, but several manned systems, e.g., offshore oil and gas rigs and ships with complex automation and dynamic positioning (DP) systems, have certain control functionality that may be characterized as autonomous. Therefore, this paper addresses both manned and unmanned systems with different levels of autonomy. This means that the concept of autonomy in this paper includes a range of systems and operations with increasing complexity and major hazard potential, even though autonomous ships are used to exemplify. Hence, the paper addresses a broader approach in contrast to the traditional focus on robotics.
A Comparative Study of Wave Breaking Models in a High-Order Spectral Model
Authors: Seiffert Betsy R. , Ducrozet Guillaume
Published: October 2017

We examine the implementation of two different wave breaking models into the nonlinear potential flow solver HOS-NWT. HOS-NWT is a computationally efficient, open source code that solves for surface elevation in a numerical wave tank using the High-Order Spectral (HOS) method [1]. The first model is a combination of a kinematic wave breaking onset criteria proposed by Barthelemey, et al. [2] and validated by Saket, et al. [3], and an energy dissipation mechanism proposed by Tian, et al. [4, 5]. The wave breaking onset parameter is based on the ratio of local energy flux velocity to the local crest velocity. Once breaking is initiated, an eddy viscosity parameter is estimated based on the pre-breaking local wave geometry, as described in [4, 5]. This eddy viscosity is then added as a diffusion term to the kinematic and dynamic free surface boundary conditions for the duration of wave breaking. Results implementing this wave breaking mechanism in HOS-NWT have shown that the model can successfully calculate the surface elevation and corresponding frequency spectra, as well as the energy dissipation associated with breaking waves [6–8].

The second model implemented to account for wave breaking in HOS-NWT is based on the method proposed by Chalikov, et al. [9–11]. This model defines wave breaking onset by the curvature of the water surface and defines the wave as broken if it exceeds a certain value. A diffusion term is added to the kinematic and dynamic free surface boundary conditions which dissipates energy based on the local curvature of the water surface, which is consequently not constant in space nor time.

Calculations made using the two models are compared with large scale experimental measurements conducted at the Hydrodynamics, Energetics and Atmospheric Environment Lab (LHEEA) at Ecole Centrale de Nantes. Comparison of calculations with measurements suggest that both models are successful at predicting wave breaking onset and energy dissipation. However, the model proposed by Barthelemy, et al. [2] and Tian, et al. [4] can be applied without knowing anything about the breaking waves a priori, whereas the model proposed by Chalikov [9] requires tuning to specific conditions.
A Preliminary Study of a Vessel-Shaped Offshore Fish Farm Concept
Authors: Li Lin , Jiang Zhiyu , Ong Muk Chen
Published: October 2017

The aquaculture industry is aiming to move fish farms from near-shore area to open seas because of many attractive advantages in the open water. However, one major challenge is to design the structure to withstand the environmental loads due to wind, waves and current. The purpose of this paper is to study a vessel-shaped fish farm concept for open sea applications. The structure includes a vessel-shaped hull, a mooring system and fish cages. The shape of the hull minimizes the wave loads coming from the bow, and the single-point mooring system is connected to the turret at the vessel bow. Such a system allows the whole fish farm to rotate freely about the turret, reduces the environmental loads on the structure and increases the spread area of fish wastes. A basic geometry of the vessel hull was considered and the hydrodynamic properties were obtained from frequency domain analysis. A preliminary mooring system was designed to avoid possible interactions with the fish cages. Time domain simulations were performed by coupling the hull with the mooring system. A simplified rigid model of the fish cages was considered. The global responses of the system and the mooring line loads were compared in various waves and current conditions. The effects due to misalignment of waves and current directions on the responses were also studied.
On Interactions Between Wind Turbines and the Marine Boundary Layer
Authors: Siddiqui M. Salman , Rasheed Adil , Tabib Mandar , Fonn Eivind , Kvamsdal Trond
Published: October 2017

Most mesoscale models are developed with grid resolution in the range of kilometers. Therefore, they may require spatial averaging to analyze flow behavior over the domain of interest. In doing so, certain important features of sub-grid scales are lost. Moreover, spatial averaging on the governing equations results in additional terms known as dispersive fluxes. These fluxes are ignored in the analysis. The aim of this paper is to identify the significance of these fluxes for accurate assessment of flow fields related to wind farm applications. The research objectives are hence twofold: 1) to quantify the impact of wind turbines on MBL characteristics. 2) to account for the magnitude of dispersive fluxes arising from spatial averaging and make a comparison against the turbulent flux values. To conduct the numerical study the NREL 5MW reference wind turbine model is employed with a RANS approach using k-ε turbulence model. The results are presented concerning spatially averaged velocity, wake deficit behind the turbine, dispersive and turbulent fluxes.
Dynamic Response of Floating Wind Turbine Under Consideration of Dynamic Behavior of Catenary Mooring-Lines
Authors: Guo Shuangxi , Li Yilun , Li Min , Chen Weimin , Fu Yiqin
Published: October 2017

Recently, wind turbine has been developed from onshore area to offshore area because of more powerful available wind energy in ocean area and more distant and less harmful noise coming from turbine. As it is approaching toward deeper water depth, the dynamic response of the large floating wind turbine experiencing various environmental loads becomes more challenge. For examples, as the structural size gets larger, the dynamic interaction between the flexible bodies such as blades, tower and catenary mooring-lines become more profound, and the dynamic behaviors such as structural inertia and hydrodynamic force of the mooring-line get more obvious. In this paper, the dynamic response of a 5MW floating wind turbine undergoing different ocean waves is examined by our FEM approach in which the dynamic behaviors of the catenary mooring-line are involved and the integrated system including flexible multi-bodies such as blades, tower, spar platform and catenaries can be considered.

Firstly, the nonlinear dynamic model of the integrated wind turbine is developed. Different from the traditional static restoring force, the dynamic restoring force is analyzed based on our 3d curved flexible beam approach where the structural curvature changes with its spatial position and the time in terms of vector equations. And, the modified finite element simulation is used to model a flexible and moving catenary of which the hydrodynamic load depending on the mooring-line’s motion is considered. Then, the nonlinear dynamic governing equations is numerically solved by using Newmark-Beta method.

Based on our numerical simulations, the influences of the dynamic behaviors of the catenary mooring-line on its restoring performance are presented. The dynamic responses of the floating wind turbine, e.g. the displacement of the spar and top tower and the dynamic tension of the catenary, undergoing various ocean waves, are examined. The dynamic coupling between different spar motions, i.e. surge and pitch, are discussed too. Our numerical results show: the dynamic behaviors of mooring-line may significantly increase the top tension, particularly, the peak-trough tension gap of snap tension may be more than 9 times larger than the quasi-static result. When the wave frequency is much higher than the system, the dynamic effects of the mooring system will accelerate the decay of transient items of the dynamic response; when the wave frequency and the system frequency are close to each other, the displacement of the spar significantly reduces by around 26%. Under regular wave condition, the coupling between the surge and pitch motions are not obvious; but under extreme condition, pitch motion may get about 20% smaller than that without consideration of the coupling between the surge and pitch motions.
Time-Domain Analysis of Wind-Induced Response of a Suspension Bridge in Comparison With the Full-Scale Measurements
Authors: Wang Jungao , Cheynet Etienne , Jakobsen Jasna Bogunović , Snæbjörnsson Jónas
Published: October 2017

The present study compares the buffeting response of a suspension bridge computed in the time-domain with full-scale measurement data. The in-service Lysefjord Bridge is used as a study case, which allows a unique comparison of the computational results with full-scale buffeting bridge response observed during a one year monitoring period. The time-domain analysis is performed using a finite element approach. Turbulent wind field is simulated according to the governing bridge design standard in Norway for three different terrain categories. The time-domain analysis indicates that the non-linear components of the wind loading are of limited importance in the present case, contributing by less than 5% to the standard deviation of the lateral displacement. The contribution of the buffeting loads on the main cables, hangers and towers to the lateral dynamic response of the bridge girder is about 6%. With the time-domain method, mode coupling as well as the influence of cables and towers are well captured in the simulation results. The buffeting response, estimated in terms of the standard deviation of acceleration, is found to be in good agreement with the field measurement data. Comparison suggests that the proposed numerical method, with the non-linear force model, is able to predict the bridge response reasonably well.
Large Eddy Simulations of Flow Past Two Pipelines in Tandem in Close Proximity to the Seabed
Authors: Li Zhong , Abrahamsen Prsic Mia , Ong Muk Chen , Khoo Boo Cheong
Published: October 2017

Three-dimensional Large Eddy Simulations (LES) with Smagorinsky subgrid scale model have been performed for the flow past two free-spanning marine pipelines in tandem placed in the vicinity of a plane wall at a very small gap ratio, namely G/D = 0.1, 0.3 and 0.5. The ratio of cylinder center-to-center distance to cylinder diameter, or pitch ratio, L/D, considered in the simulations is taken as L/D = 2 and 5. This work serves as an extension of Abrahamsen Prsic et al. (2015) [1]. In essence, six sets of simulations have been performed in the subcritical Reynolds number regime at Re = 1.31 × 104. Our major findings can be summarized as follows. (1) At both pitch ratios, the wall proximity has a decreasing effect on the mean drag coefficient of the upstream cylinder. At L/D = 2, the mean drag coefficient of the downstream cylinder is negative since it is located within the drag inversion separation distance. (2) At L/D = 2, a squarish cavity-like flow exists between the tandem cylinders and flow circulates within the cavity. A long lee-wake recirculation zone is found behind the downstream cylinder at G/D = 0.1. However, a much smaller lee-wake recirculation zone is noticed at L/D = 5 with G/D = 0.1. (3) At L/D = 2, the reattachment is biased to the bottom shear layer due towards the deflection from the plane wall, which leads to the formation of the slanted squarish cavity-like flow where the flow circulates between the tandem cylinders.
Qualification of Reactive Flex Joint on a Offshore Drill Rig
Authors: Ilstad Håvar , Verley Richard , Kendon Timothy , Bjørset Arve , Rørgård Ove , Ellefsen Øystein
Published: October 2017

The RFJ has been found to respond as expected, reducing well-head moments in line with the maximum predicted from global analysis simulations conducted beforehand and for all conditions experienced, i.e. for wave conditions varying from 1.3 – 6.5 m (Hs) and drill-pipe tension up to 150 T (Weight-on-Hook up to 200 T). It is in particular noted that even for chaotic response motions caused by near-quarter seas and wave spreading; the moment response in all directions is reduced by the RFJ which works equally effectively on all components. The efficiency is similar for drilling conditions tested (17 ½”, 12 ¾” & 8 ½”, without X-tree) and for completion (with X-tree). The recommended value of Efficiency of the RFJ to be used in assessment of its effect on fatigue, when using rain-flow analysis, as a function of Hs and drill-pipe tension, is given. These curves are ∼5 %points conservative (i.e. lower) compared to Efficiency based on standard deviation of response.
Experimental and Numerical Investigation of Tsunami-Like Waves on Horizontal Circular Cylinders
Authors: Tripepi Giuseppe , Aristodemo Francesco , Veltri Paolo , Pace Calogero , Solano Andrea , Giordano Carlo
Published: October 2017

This work deals with an experimental and numerical study on the horizontal and vertical hydrodynamic forces induced by tsunami-like waves on horizontal cylinders. The laboratory investigation has been performed in the wave flume of the University of Calabria. Twelve pressure transducers have been mounted along the external contour of a cylinder, while four wave gauges have been located close to the cylinder and an ultrasonic sensor behind the paddle to measure its displacement. Tests have been carried out for Keulegan-Carpenter numbers, KC, ranging from about 4 to 7. By the numerical viewpoint, a diffusive weakly-compressible SPH model has been adopted. To prevent spurious flows near the cylindrical contour, a packing algorithm has been applied before SPH simulations. The acoustic components occurring in the numerical pressure field have been filtered through the application of Wavelet Transform. By using different calibration methods, experimental and SPH forces and kinematics at the cylinder have been used to calculate the hydrodynamic coefficients in the Morison and transverse semi-empirical equations for engineering purposes.
Model Ice: A Review of its Capacity and Identification of Knowledge Gaps
Authors: von Bock und Polach Rüdiger U. Franz , Molyneux David
Published: October 2017

This paper presents a review of the state of the art of model-scale ice with a focus on mechanical behavior, mechanical testing and scaling. The goal of the model-scale ice production is the generation of a material that can represent sea ice in as many aspects as possible. The question therefore is, to what extent model-scale ice complies with this high level requirement and what possible limitations of model-scale ice are encountered. A part of the answer lies in the history of model-scale testing in ice as model ice was originally designed to test ships in ice. The interaction of ships with ice, when breaking level ice, differs from other interaction scenarios in terms of triggered failure processes and consequently in the relevant mechanical properties of the ice. The significance of the forces in particular interaction scenarios is reflected in the applied scaling laws. The standard scaling laws are presented together with published alternatives and their limitation and practicality is evaluated. The relevant interaction forces and ice properties are compiled for level ice breaking, ships in brash ice and offshore structures in slow ice drift. In the production of model-scale ice, the mechanical properties and their measurements play a significant role, as they determine how well the full-scale scenario is scaled. However, latest research in context with earlier published findings indicates that state of the art measurement procedures may not be able to capture the actual ice properties, as the mechanical behavior of model-scale ice might be different than generally presumed. Consequently, this paper presents alternative measurement procedures and highlights existing knowledge gaps which are worthwhile to be addressed in future.
Numerical Simulation of Motion-Controlled Fishery Boat With Harvesting Wave Energy
Authors: Kanno Sota , Han Jialin , Maeda Teruo , Yoshida Takero , Kitazawa Daisuke
Published: October 2017

Numerical simulation of a motion-controlled ship was conducted. This ship is a catamaran, the motion of which is controlled with motors by an active control system, called Skyhook control. In addition, this ship can harvest wave energy by converting relative displacement between a cabin and floats to rotational motion, and then, to electrical energy by generators. Energy harvesting efficiency can be maximized by a technique, called MPPT (Maximum Power Point Tracking). The model of the ship was constructed on a circuit diagram with SPICE (Simulation Program with Integrated Circuit Emphasis) based on a mechanical-electrical analogy, called Mobility method, because mechanical system and electrical system are coupled through a motor/generator as a transducer in this ship. The results of the simulation based on this model were compared to those of the tank test already done by some of the authors, and its performance was evaluated. The results showed good agreement between the simulation and the experiment qualitatively, while quantitative gap could be found. There are some problems to be solved such as considering precise hydrodynamic force. Thus, the model needs to be improved more. It will be possible to design a new concept of fishery boats using the simulation based on this model in the future. This concept of fishery boats can be aimed at coastal fishery and offshore aquaculture.
Wellhead Fatigue Analysis: How Conservative Is Conservative Enough?
Authors: Macke Michael , Hørte Torfinn , Aronsen Kristoffer Høyem , Grytøyr Guttorm
Published: October 2017

In wellhead fatigue analysis, results are quite often sensitive to input parameters that are associated with considerable uncertainty. Such parameters may, e.g., be the cement level in the annulus between surface casing and conductor, the soil and template support, friction and down weight on the landing shoulder, etc. A common approach in deterministic design to deal with such problem is to use worst case assumptions on sensitive parameters. However, this may result in unreasonable short fatigue lifetime estimates.

In this paper, it is shown how existing fatigue design equations using the concept of design fatigue factors can be augmented with characteristic design values for additional uncertain variables such that the overall safety level obtained is comparable to the recommended target levels for typical uncertainties in load effect calculations. Results from sensitivity analysis and SRA are compared to investigate to what extent sensitivity analysis results can be utilized as part of the design analysis. The intention of the proposed approach is to be reasonably conservative but to avoid being overly conservative.
Application of a Boundary Element Method for Wave-Body Interaction Problems Considering the Non-Linear Water Surface
Authors: Ferreira González Daniel , Bechthold Jonas , Abdel-Maksoud Moustafa
Published: October 2017

In this paper an existing time domain panel method, which was originally developed for propeller flow simulations, is extended by implementing the mixed Eulerian-Lagrangian approach for the computation of the non-linear free water surface. The three-dimensional panel method uses a constant source and doublet density distribution on each panel and a Dirichlet boundary condition to solve the velocity potential in every time step. Additionally, a formulation for the acceleration potential is included in order to determine the hydrodynamic forces accurately. The paper gives an overview on the governing equations and introduces the numerical approach. Validation results of the developed method are presented for the wave resistance of a submerged spheroid and a wigley hull. Additionally, the wave diffraction due to a surface piercing cylinder in regular waves is validated regarding the forces and the water surface elevation around the body. Here, the computations are compared with other numerical methods as well as tank test results. Apart from this, the paper deals with an application example showing simulations of an artificial service vessel catamaran in waves. The forces on the hull with and without forward speed are presented. The paper concludes with a discussion of the presented results and a brief outlook on further work.
An Integrated Environment for Design and Analysis of Umbilical Cables
Authors: Provasi Rodrigo , Garcez Leonardo Riccioppo , Cardoso Meirelles Christiano Odir , de Arruda Martins Clovis , Freitas Barbosa Andre , Otte Filho Olaf Oswaldo
Published: October 2017

The design of an umbilical cable begins with the definition of the operational functions it must implement and the environmental conditions to that it will be subjected to. Those functions suggest the components that it must have, usually chosen from a pre-defined set. Also, structural elements must be added, based on project and manufacture requirements, so the cable can withstand the environmental conditions of use. All the components must be geometrically arranged and the cross section of the cable must be defined, usually with the help of CAD software.

But the structural behavior of the designed cable must be analyzed under several environmental conditions, using numerical and analytical tools. If this behavior does not fulfill the desired structural requirements, the cable must be redesigned: structural and functional components must be changed and the cross section of the umbilical must be rearranged in an iterative process.

This article presents an environment that integrates a CAD tool dedicated to the design of the cross section of an umbilical cable with structural analysis tools, both analytical (Utilflex) and numerical (UFLEX2D). The CAD tool architecture is based on a component-instance model that enables both drawing and reusing of components. It also can export the designed cross-section to AutoCAD using AutoLISP language. Finally, it automates the generation of the data-sheet of the designed umbilical both in AutoLISP and Microsoft Word, including the basic structural properties calculated by means of analytical formulae.
Trim Influence on Kriso Container Ship (KCS): An Experimental and Numerical Study
Authors: Shivachev Emil , Khorasanchi Mahdi , Day Alexander H.
Published: October 2017

There has been a lot of interest in trim optimisation to reduce fuel consumption and emissions of ships. Many existing ships are designed for a single operational condition with the aim of producing low resistance at their design speed and draft with an even keel. Given that a ship will often sail outside this condition over its operational life and moreover some vessels such as LNG carriers return in ballast condition in one leg, the effect of trim on ships resistance will be significant. Ship trim optimization analysis has traditionally been done through towing tank testing. Computational techniques have become increasingly popular for design and optimization applications in all engineering disciplines. Computational Fluid Dynamics (CFD), is the fastest developing area in marine fluid dynamics as an alternative to model tests. High fidelity CFD methods are capable of modelling breaking waves which is especially crucial for trim optimisation studies where the bulbous bow partially emerges or the transom stern partially immerses. This paper presents a trim optimization study on the Kriso Container Ship (KCS) using computational fluid dynamics (CFD) in conjunction with towing tank tests. A series of resistance tests for various trim angles and speeds were conducted at 1:75 scale at design draft. CFD computations were carried out for the same conditions with the hull both fixed and free to sink and trim. Dynamic sinkage and trim add to the computational cost and thus slow the optimisation process. The results obtained from CFD simulations were in good agreement with the experiments. After validating the applicability of the computational model, the same mesh, boundary conditions and solution techniques were used to obtain resistance values for different trim conditions at different Froude numbers. Both the fixed and free trim/sinkage models could predict the trend of resistance with variation of trim angles; however the fixed model failed to measure the absolute values as accurately as the free model. It was concluded that a fixed CFD model, although computationally faster and cheaper, can find the optimum trim angle but cannot predict the amount of savings with very high accuracy. Results concerning the performance of the vessel at different speeds and trim angles were analysed and optimum trim is suggested.
Modeling, Parameter Identification and Thruster-Assisted Position Mooring of C/S Inocean Cat I Drillship
Authors: Bjørnø Jon , Heyn Hans-Martin , Skjetne Roger , Dahl Andreas R. , Frederich Preben
Published: October 2017

A thruster-assisted position mooring (TAPM) system includes different control functions for stationkeeping and motion damping for a moored offshore vessel with assist from thrusters. It consists of a conventional mooring system and a dynamic positioning (DP) system. The thrusters are used to provide damping and some restoring to the vessel motion and compensate if line breakage occurs. The mooring system absorbs the main loads to keep the vessel in place. This paper presents a complete modeling, parameter identification, and control design for a 1:90 scaled TAPM model vessel. The numerical values for the different model parameters are identified from towing tests.

State-of-the-art TAPM control algorithms have been tested on the vessel in the Marine Control Laboratory (MC Lab), to see the behavior resulting from the different control algorithms. The presented experiments focus on the setpoint chasing algorithm, where the position setpoint slowly moves to the equilibrium position where the environmental loads are balanced by the mooring loads. This avoids conflicts between the mooring system and the control actions. If the environmental loads are too large so that the setpoint exceeds a user-defined safety radius, the setpoint is set to this radius and thruster forces grow to support the mooring system in counteracting the environmental loads to avoid line breakage. The experiments show that the vessel and setpoint chasing control algorithm behaves as expected, minimizing thruster usage and maximizing utilization of mooring system.