bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on the Ship Ice Resistance Estimation Using Empirical Formulas
Authors: Park Kyung Duk , Kim Hyun Soo
Published: September 2014

The ice resistance estimation technique for icebreaking ships has been studied intensively over recent years to meet the need of arctic vessel design. Before testing in the ice model basin, the estimation of ship ice resistance with high reliability is very important to decide the delivered power necessary for level ice operation. The main idea of this study came from several empirical formulas by B.P. Ionov[1], E. Enkvist[2] and J.A. Shimanskii[3], in which ice resistance components such as icebreaking, buoyancy and clearing resistances were represented by the integral equations along the DLWL (Design Load Water Line). However, this study proposes modified methods considering the DLWL shape as well as the hull shape under the DLWL. In the proposed methodology, the DLWL shape for icebreaking resistance and the hull shape under the DLWL for buoyancy and clearing resistances are included in the calculation. Especially when calculating clearing resistance, the flow pattern of ice particles under the DLWL of ship is assumed to be in accordance with the ice flow observed from ice model testing. This paper also deals with application examples for a ship design and its ice model test results at the Aker arctic ice model basin. From the comparison of results from the model test and the estimation, the reliability of this estimation technique is discussed.
A Strong FSI Coupling Scheme to Investigate the Onset of Resonance of Cylinders in Tandem Arrangement
Authors: Kara Mustafa C. , Stoesser Thorsten
Published: September 2014

This paper considers numerical simulations of two-dimensional viscous flow past oscillating cylinders using an efficient, oscillation-free, Cartesian grid based Immersed Boundary Method (IBM). The direct forcing approach originally developed by Uhlmann [1] for fixed and moving boundaries is employed. The IBM utilizes an improved smoothing technique for the discrete delta function and a solid-domain forcing strategy. A strong-coupling scheme is employed in which both, fluid and structure, are treated as linked components of a single dynamical system and all governing equations are iterated until convergence within the same time step. The accuracy, validity and efficiency of the utilized IBM are demonstrated by a series of validation cases including Vortex Induced Vibration (VIV) of an elastically mounted single cylinder and VIV assessment of a pair of cylinders in tandem arrangement. The method provides a good estimation of the single cylinder vortex lock in regime and fairly accurate predictions of the wake interference effect on the onset of resonance in flows involving multiple cylinders in an in-line arrangement.
Immersed Boundary Method for Simulation of Oscillatory Flow Past a Submerged Cylinder Near Above a Horizontal Bed
Authors: Fonias Efstratios N. , Dimas Athanassios A.
Published: September 2014

In the present work, the oscillatory flow past a submerged cylinder near above a horizontal bed is simulated by a Navier-Stokes equations solver. The boundary conditions, i.e., the no-slip condition on solid boundaries are imposed with the immersed boundary method. A Cartesian grid with variable size is used for the spatial discretization, and a time-splitting scheme is used for the temporal discretization. The numerical method was validated simulating the unidirectional flow past a cylinder at Reynolds number ReD = 300. For the oscillatory flow past a cylinder of diameter D at a distance G above a horizontal bed, all variables were rendered dimensionless using the maximum velocity, Uo, and the amplitude of the orbital motion, αo, of the oscillatory flow. Several tests with differing values of αo/D and G/D were considered, for Reynolds number Reα = 5,000 and Keulegan–Carpenter numbers in the range from 6.28 to 62.8. Results show that the critical range for the suppression of vortex shedding at the lower side of the cylinder is G/αo<0.01, while the critical range for the generation of vorticity uplift from the bed boundary layer is G/αo<1.0. Also, as G/D decreases, both the amplitude of the drag force and the bias towards positive values of the lift force increase.
Deriving Robust Design Parameters and Design Criteria for the First Offshore Artificial Island for Electricity Conversion in the Northern North Sea
Authors: Haerens Piet , Vandenbroucke Tim , Mercelis Peter , De Wit Kathleen , Sas Marc , Steensels Marc
Published: September 2014

In support of future wind farm developments and to anticipate the intentions to create a European wide smart electricity grid, an offshore high voltage grid in the Belgian North Sea is under development to connect several wind farms to the Belgian onshore electricity grid, called Belgian Offshore Grid (BOG). This grid will contain the first artificial island (AI) to support electricity conversion and transport in the North Sea. The AI will be part of an offshore high voltage grid that shall connect a number of offshore wind farms to an onshore high voltage station.

An accurate definition of site conditions and design criteria is of utmost importance for the design, operability and exploitation of the island and is the main driver for the cost of such islands. Deriving robust, but not over conservative site conditions and appropriate design criteria was one of the first challenges for the project. Based on in-situ measurements of geotechnical, geophysical and met-ocean conditions design parameters have been derived together with design criteria. This paper focuses on the methods and numerical models used to define the appropriate design input and the sensitivity analysis of the design criteria.

In order to derive robust but not over conservative design parameters not only in-situ measurements are required, but also a combination of statistical analysis, numerical models and sensitivity analysis of design criteria and functional requirements. One of the driving design criteria for such works is the allowable overtopping discharge and related hydrodynamic forces on the infrastructure on the island, which largely influences the cost.
van der Pol-Duffing Modeling for Torsional Galloping
Authors: Fernandes Antonio Carlos , Armandei Mohammadmehdi
Published: September 2014

This study is a continuation of the study presented in OMAE 2012 entitled: “Stability Analysis of a Yawing Flat Plate into the Water Current”[1]. The structure in the aforementioned study consists of a rectangular flat plate with an elastic axis in its mid-chord length. The elasticity is provided by torsion spring. The flat plate has only one degree of freedom which is angular oscillation about its axis. It is observed that as the current speed exceeds a critical velocity, the flat plate becomes unstable. The instability leads to torsional galloping occurrence, as a result of which the flat plate begins to oscillate angularly about the elastic axis. Through the present study, a phenomenological model is developed based on van der Pol-Duffing equation, in order to explain the instability leading to the torsional galloping.
Model-Based Risk Assessment of Offshore Operations
Authors: Läsche Christoph , Pinkowski Jan , Gerwinn Sebastian , Droste Rainer , Hahn Axel
Published: September 2014

Safety and dependability are major design objectives for offshore operations such as the construction of wind farms or oil and gas exploration. Today processes and related risks are typically described informally and process specification are neither reusable nor suitable for risk assessment. Here, we propose to use a specification language for processes. We integrate this specification language in a generic modeling approach in combination with an analysis tool and a tool to construct health, safety and environment (HSE) plans — a mandatory document for granting a construction/operation permit. Specifically, for each planned scenario a process is modeled, describing the detailed operation of the involved actors as well as the interaction with resources and environmental conditions. We enrich this process model with hazardous events which is facilitated by integration with an offshore operation generic hazard list, thereby giving access to expert knowledge for the specific situation to be planned. This in turn allows us to perform an automatic quantitative risk assessment using fault tree analysis. We exemplify our approach on a standard offshore operation of personnel transfer from an offshore building to another naval unit by modeling, annotating with hazards, performing the fault-tree analysis, and finally generating HSE plans.
A Bond Graph Approach to Improve the Energy Efficiency of Ships
Authors: Jafarzadeh Sepideh , Pedersen Eilif , Notti Emilio , Sala Antonello , Ellingsen Harald
Published: September 2014

High fuel consumption coupled with increasing fuel prices, emission regulations and increasing concern about the environment, act as incentives to reduce the energy consumption of ships. However, different barriers hinder the adoption of cost-effective energy saving measures by ship owners and operators. These barriers are the reason for the existence of an ‘energy efficiency gap’ between the current level of energy efficiency and the potential for development of higher order efficiency. Imperfect information regarding the current level of energy consumption of vessels, availability and application of energy saving measures, and the impact of adopting these measures, form a group of so called ‘information barriers’.

The main objective of this article is to reduce those information barriers, as faced in shipping and more specifically in the fishing sector. The bond graph methodology is presented as a potential solution to these issues. It is utilized as a modeling and simulation method by which to visualize energy flow in a fishing vessel. The bond graph method is employed to estimate the fuel consumption of the vessel under different operational conditions: steaming, trawling and hauling of the fishing gear. It is also applied in pinpointing the major energy consuming apparatuses onboard the vessel. In this way knowledge regarding the current levels of energy consumption can be increased. The main energy consumers can then be studied to further improve energy efficiency knowledge and subsequently reduce the energy efficiency gap of the fishing vessel. Finally, the effectiveness of implementing a slow steaming strategy as a possible energy saving mechanism is studied.
Offshore Code Comparison Collaboration Continuation Within IEA Wind Task 30: Phase II Results Regarding a Floating Semisubmersible Wind System
Authors: Robertson Amy , Jonkman Jason , Vorpahl Fabian , Popko Wojciech , Qvist Jacob , Frøyd Lars , Chen Xiaohong , Azcona José , Uzunoglu Emre , Guedes Soares Carlos , Luan Chenyu , Yutong Huang , Pengcheng Fu , Yde Anders , Larsen Torben , Nichols James , Buils Ricard , Lei Liu , Nygaard Tor Anders , Manolas Dimitris , Heege Andreas , Vatne Sigrid Ringdalen , Ormberg Harald , Duarte Tiago , Godreau Cyril , Hansen Hans Fabricius , Nielsen Anders Wedel , Riber Hans , Le Cunff Cédric , Beyer Friedemann , Yamaguchi Atsushi , Jung Kwang Jin , Shin Hyunkyoung , Shi Wei , Park Hyunchul , Alves Marco , Guérinel Matthieu
Published: September 2014

Offshore wind turbines are designed and analyzed using comprehensive simulation tools (or codes) that account for the coupled dynamics of the wind inflow, aerodynamics, elasticity, and controls of the turbine, along with the incident waves, sea current, hydrodynamics, mooring dynamics, and foundation dynamics of the support structure. This paper describes the latest findings of the code-to-code verification activities of the Offshore Code Comparison Collaboration Continuation project, which operates under the International Energy Agency Wind Task 30. In the latest phase of the project, participants used an assortment of simulation codes to model the coupled dynamic response of a 5-MW wind turbine installed on a floating semisubmersible in 200 m of water. Code predictions were compared from load case simulations selected to test different model features. The comparisons have resulted in a greater understanding of offshore floating wind turbine dynamics and modeling techniques, and better knowledge of the validity of various approximations. The lessons learned from this exercise have improved the participants’ codes, thus improving the standard of offshore wind turbine modeling.
Simulation-Based Analysis of Arctic LNG Transport Capacity, Cost and System Integrity
Authors: Erikstad Stein Ove , Ehlers Sören
Published: September 2014

This paper presents a design case for arctic LNG transport, where liquefied gas is shipped from the Kharasevey terminal in Northern Russia to markets in US and Europe. Based on a fleet simulation model, the trade-off between the two main performance issues related to arctic transport are investigated; namely how to maintain transport system integrity in the harsh ice conditions, while maximizing the capacity utilization in a situation with considerable seasonal variations.

The fixed contract, single destination base case shows that meeting the requirements for a robust solution implies a low degree of utilization in the summer season. To improve upon this situation, several mitigating strategies are evaluated, including vessel speed and size changes, fixed and seasonally varying contract and market mix schedules, revision stop rescheduling, storage capacity extensions and backhauling.

The results indicate a high payoff from renegotiating the initial fixed schedule contract to allow for a higher degree of seasonal variations in the LNG deliveries. Further, increased storage capacity in loading port, combined with winter revision stops will have a significant impact on both fleet utilization and total system integrity. Flexible contracts that implies seasonal deliveries to the UK will help ensure continuous production and deliveries in winter season. Finally, surplus capacity gives opportunities for seasonal spot cargoes that could be exploited to increase fleet utilization rate.
Reel-Lay Method to Control Global Pipeline Buckling Under Operating Loads
Authors: Endal Geir , Giske Stein R. , Moen Kjetil , Sande Stian
Published: September 2014

This paper presents a simple and cost effective method to control pipeline thermal buckling in the operational phase. The method is based on active use of the straightener system during reel-lay installation in order to create intermittent residual curvature sections in the pipeline. These residual curvature sections form ‘expansion loops’, in which deflection of the pipeline appears, and the result is controlled pipeline deflection and acceptable utilization at these locations under operational loads.

The method was first applied on Statoil’s Skuld project in 2012, using Subsea 7’s reel ship “Seven Oceans” for installation of a 26 km long 14″–16″ dual diameter pipeline in the Norwegian Sea. Implementation was performed at a small cost related to making the straightener adjustments and the effect on vessel time, and eliminated the need for other measures to control thermal buckling of the pipeline. For the Skuld project, engineering analysis demonstrated that the method would be superior to other methods with regards to both robustness and load controlled utilization in the pipeline under operating loads. Inspection survey during operation has verified the suitability of the method. The technique therefore has the potential to become a vitally important reel-lay method to control global pipeline buckling under operating loads.
Model Scale Analysis of a TLP Floating Offshore Wind Turbine
Authors: Zamora-Rodriguez Ricardo , Gomez-Alonso Pablo , Amate-Lopez Juan , De-Diego-Martin Victor , Dinoi Pasquale , Simos Alexandre N. , Souto-Iglesias Antonio
Published: September 2014

This paper discusses the experimental campaign conducted by CEHINAV-UPM research group as request of IBERDROLA within the OCEAN LIDER RD project framework. The purpose of the campaign has been the hydrodynamic performance of a tension leg platform to support a wind energy turbine (TLPWT). The turbine chosen in this study has been the 5MW reference WT of NREL, the location depth has been 80m and the operation area is Estaca de Bares in the north-west of Spain. Regular waves, operational, survival, failure and transport experiments have been conducted. All tests have been performed in CEHINAV (UPM) model basin, except survival tests performed in CEHIPAR ocean basin. This document presents the experimental setup and results from decay tests, regular wave motion RAOs, irregular wave responses, tendon loads and accelerations. Experimental results are compared with available in-house numerical simulations and other numerical and experimental results found in literature.
Effect of Ship Speed on Level Ice Edge Breaking
Authors: Sazidy Mahmud , Daley Claude , Colbourne Bruce , Wang Jungyong
Published: September 2014

This paper presents a numerical model of ship ice-wedge interaction to study the effect of ship speed on level ice edge breaking. The interaction process is modeled using LS-DYNA. The developed model considers ice crushing, ice flexural failure and the water foundation effect. For the ice, two different plasticity-based material models are used to represent ice crushing and ice flexural behaviors. The water foundation effect is modeled using a simple linear elastic material. The analysis is performed for a ship speed range of 0.1 to 5 ms−1 and ice thickness of 0.5 to 1.5 m. The analysis indicates that both ship speed and ice thickness significantly affect the ice breaking process. The model results are in good agreement with a number of analytical and empirical models. The model can be useful in establishing a rational basis for safe speed criteria, improving ship structural standards and tools for ice management capability assessment.
A Case Study of the Influence on Crashworthiness From the Implementation of Ice Strengthening
Authors: Aga Halvor Larsson , Leira Bernt Johan , Ehlers Sören , Blomvågnes-Bakke Hans Arne
Published: September 2014

This paper presents a study of the influence from ice strengthening on the crashworthiness with regards to placement of LNG fuel tanks. First a brief introduction to the ship collision research as well as an assessment of the state of the art regarding nonlinear finite element analysis for use in ship collision analysis are given. Secondly the implications from the introduction of LNG fuel tanks on ships in context of collision safety are discussed. Thirdly how to quantify and compare energy absorption for different ship designs is discussed. This is followed by the presentation of a study regarding the horizontal placement of LNG fuel tanks. The study starts with presenting the variables chosen and the models made for the analysis. Energy versus indentation curves are presented for three different designs, where a standard cargo carrier is compared with two different design solutions where the cargo carrier is equipped with either vertical or longitudinal ice strengthening. It is concluded that in this case the benefit in terms of reduction of the minimum distance from the outer skin to the LNG fuel tank, as given in the current rules, is around 39%.
Full-Scale Measurements on a Polar Supply and Research Vessel During Maneouver Tests in an Ice Field in the Baltic Sea
Authors: Bekker Anriëtte , Suominen Mikko , Peltokorpi Oskari , Kulovesi Jakke , Kujala Pentti , Karhunen Jouko
Published: September 2014

Full-scale measurements were performed on the Polar Supply and Research Vessel, the S.A. Agulhas II during ice-trials in the Baltic Sea. Ice loads on the ship hull and propulsion system were measured concurrently with ice-thickness and whole-body vibration comfort for controlled maneuvers in a level ice field. These measurements were aimed at establishing the links between ice-properties, hull- and shaft loads and the vibration feedback received by the operator of the vessel. Results indicate that maneuvers significantly increase the frequency and magnitude of ice loads at the stern shoulder area as well as the ice impacts on the propellers. The number of ice impacts on the instrumented port side shaft line increased for turning maneuvers in a starboard direction. Occupants on the Bridge did not receive feedback through vibration transmission from ice impacts on the hull as a time-history of discrete events. Instead, ice passage excites the global bending modes of the vessel. Blade impacts between ice debris and the propellers are however perceivably transmitted to vessel operators. Although vibration exposure on the bridge is increased by operations in ice subjective experiences of vibration did not reach levels that caused discomfort.
CFD Modeling of Moonpool Behavior
Authors: Pistidda Alessio , Ottens Harald
Published: September 2014

Vessels equipped with a moonpool are frequently used in the offshore oil and gas industry. They are used to lay pipelines, risers, structures, cables, and for drilling. These operations are generally possible if the water motion inside the moonpool remains within workable limits. Water oscillations are generated by waves and forward speed. The water motion in the moonpool is characterized by two dominant modes, sloshing and pumping. Both modes are usually present during sailing, while during installation phase, where the vessel is kept in a fixed position, the pumping mode is dominant and sloshing is negligible. The behavior of the water column in the moonpool can either be predicted numerically (CFD and potential code) or by model tests. In this work we focus on modeling the behavior of the DCV Aegir moonpool in operational conditions via CFD. The work presented in this paper consist on the validation of the available experimental results. Results show that CFD is an adequate tool to predict the pumping mode of the water inside the moonpool and outperforms predictions of potential codes.
Collapse Resistance Enhancement in UOE SAWL Line Pipes During Coating Heat Treatment for Ultra Deepwater Applications
Authors: Arroyo Fábio , León Harold R. , Silva Ronaldo , Mantovano Luciano , Solano Rafael F. , Azevedo Fabio B.
Published: September 2014

Large diameter UOE pipes are being increasingly used for the construction of offshore pipelines and in the last few year, since oil discoveries are moving towards ultra-deepwater areas, such as Pre-Salt in Brazil, collapse resistance is a key factor in the design of the pipelines the demand for pipes with high thickness near the limits for fabrication and installation capacity. It is known that the cold forming, and the final expansion in the UOE line pipe manufacturing process, reduces the elastic limit of the steel in subsequent compression. Due to this, the DNV collapse formula includes a fabrication factor that de-rates by a 15% the yield strength of UOE Pipes. However, DNV also recognizes the effect of thermal treatments and the code allows for improvement of the fabrication factor when heat treatment or external cold sizing (compression) is applied, if documented. In previous work [1] it was presented the qualification of UOE pipes with enhanced collapse capacity focusing the use of a fabrication factor (alpha-fab) equal to 1. A technology qualification process according to international standard has been performed. The main aspects of the qualification process were presented and included significant material, full scale testing and final analysis. In this paper, we compare those results with the ones of the new qualification tests analyzing the more important variables affecting the collapse resistance such as ovality, compressive material strength, thermal treatment control, etc. This new qualification obtained even better results than the previous one, which will allow the use of a fabrication factor equal to 1 directly in deepwater and ultra-deepwater offshore pipeline projects with a possible reduction in material and offshore installation costs and also potentially enhancing the feasibility of many challenging offshore projects.
Passive Pitch Control of Horizontal Axis Marine Hydrokinetic Turbine Blades
Authors: Motley Michael R. , Barber Ramona B.
Published: September 2014

As the need for clean and renewable energy becomes greater, alternative energy technologies are becoming more and more prevalent. To that end, there has been a recent increase in research on marine hydrokinetic turbines to assess their potential as a reliable source of energy production and to expedite their implementation. These turbines are typically constructed from fiber reinforced composites and are subject to large, dynamic fluid forces. One of the benefits of composite materials is that the bend-twist deformation behavior can be hydroelastically tailored such that the blades are able to passively change their pitch to adapt to the surrounding flow, creating a nearly instantaneous control mechanism that can improve system performance over the expected range of operating conditions. These improvements include increasing energy capture, reducing instabilities, and improving structural performance. Practical constraints, however, lead to limitations in the scope of these performance enhancements and create tradeoffs between various benefits that can be achieved. This paper presents a numerical investigation into the capability of passive pitch control and combined active/passive pitch control to modify the performance of horizontal axis marine turbines with proper consideration of practical restrictions.
Findings From Dissection and Testing of Used Flexible Risers
Authors: Skjerve Håvard , Kristensen Claus , Muren Jan , Søfferud Mario , Engelbreth Knut Inge
Published: September 2014

During Statoil’s recent riser replacement project more than 30 used risers have been dissected onshore [1]. The main objective has been to reveal the root cause of carcass axial tearing failures. However, this also gave the opportunity to investigate details of other carcass damages, armor corrosion, annulus environment, external sheath breaches and polymer ageing as described in [5], [6] and [7]. This paper discusses some of the new knowledge obtained from the dissections.

New tools and methods have been developed for carcass pitch measurements in order to determine axial movements, maximum load level seen by the carcass and determine the utilization against tearing.

Offshore free-volume annulus testing and gas sampling is compared to liquid sampling and actual liquid found when dissecting, with significant deviations observed. Expected annulus environment is assessed in light of actual observed corrosion, with generally less corrosion than expected, however at some few selected areas significant corrosion attacks are found. Residual stresses and condition of polymer layers is quantified, with generally more degeneration and larger changes than anticipated before riser recovery.
Handling of Partially Filled Tank Containers by Means of Cranes
Authors: Hansen Andreas , Kreuzer Edwin , Radisch Christian
Published: September 2014

Tank containers are widely used to transport a variety of liquid goods such as food products, oil, and different kinds of fuel including liquefied natural gas. Due to the unpredictable dynamic behavior of partially filled tank containers, regulations limit the containers to be either almost full (> 80%) or almost empty (< 20%), when handled by cranes. In order to provide arguments to ease these restrictions, the system is analyzed and control methods for assisting the crane operator are proposed. We deduce a very accurate and computationally favorable mathematical description of the coupled crane and fluid dynamics. The fluid is modeled by a potential flow approach resulting in a low dimensional approximation of the liquid dynamics. Coupling the fluid dynamic model with the load system model of a container crane leads to a nonlinear formulation of the overall system. The state estimation algorithm exclusively relies on the measured rope forces as well as the known motion parameters of the trolley and the rope winches. A nonlinear state feedback controller based on sliding modes for underactuated systems provides a stabilizing control signal for the system. Experimental results for validation of the model, the observer, and the control design are included.
Hydrodynamic Forces and Pressure Loads on Heave Plates for Semi-Submersible Floating Offshore Wind Turbines: A Case Study
Authors: Lopez-Pavon Carlos , Garrido-Mendoza Carlos A. , Souto-Iglesias Antonio
Published: September 2014

Hydrodynamic forces on heave plates for a semi-submersible floating offshore wind turbine are discussed in this paper. Results from experiments in which added mass and damping coefficients have been measured are presented. A model which allows the fitting of a plain plate and the real reinforced one has been built. The experimental campaign comprised as well the direct measurement of dynamic pressure on the heave plates, important for the heave plates structural design. Numerical simulations have been conducted both with a frequency domain panel method and a RANS CFD commercial code. Results have been compared with literature and consistent nondimensionalizations have been sought so that such results can be useful for preliminary design purposes.
Importance Rating of Riser-Soil Interaction Effects
Authors: Voie Per Erlend , Skeie Geir , Bergan-Haavik Jens
Published: September 2014

The fatigue life of risers loaded by wave kinematics, vessel movements, and vortex-induced vibrations, is one of the critical issues when designing floating production systems comprised of a large floating structure attached to the seabed by vertical tethers or mooring lines. It is especially difficult to estimate fatigue stresses due to the interaction between the seabed/soil and the riser because of the high non-linearity of soil response. Adding to the complexity the touchdown zone where the riser contacts the soil often proves to be the critical location for the fatigue life, since the maximum bending stresses usually occur in this part of the riser. Previous studies have also shown fatigue damage to be sensitive to soil stiffness. Although linear elastic soil models provide very useful insights about pipe-soil interaction, they cannot fully describe the complex interaction problem including: trench formation, non-linear soil properties, soil suction, detachment of the pipe from the soil, pipe re-contact with the soil and degradation of soil stiffness, which are evident from full-scale experimental testing and field surveys.

The background for this study is to explore the effect of going beyond the common linear soil model, calculate the riser-soil interaction effects in more detail and identify which interaction effects are the most important for riser response.

Based on consolidating knowledge from conference publications, joint development projects and bearing capacity theory a pipe-soil interaction model accounting for the seemingly most important interaction mechanisms is developed and implemented in ABAQUS. The importance of the many interaction effects is explored through sensitivity studies. Based on the importance rating recommendations are given on what level of model sophistication to choose for different applications e.g. fatigue analysis.
Experimental Investigation of Compressive Failure of Truncated Conical Ice Specimens
Authors: Habib Kashfi B. , Taylor Rocky S. , Jordaan Ian J. , Bruneau Stephen
Published: September 2014

A series of small-scale ice indentation tests has been carried out to study the compressive failure of polycrystalline ice during indentation and explore the link between various parameters that influence the ice failure processes. In total, twenty-eight experiments were completed using ice specimens having a truncated conical geometry to investigate the nature of crushing, spalling and high pressure zones. Variables considered in this series include: grain size, indenter shape, indentation rate, temperature, and taper angle. Two grain size ranges (0–4 mm and 4–10+ mm) were considered, along with two indenter shapes (a flat plate and a spherical indenter). Indentation rates of 0.1 mm/s, 1 mm/s and 10 mm/s have been used for these tests. Experiments were conducted at temperatures of −10°C and −5°C and three geometric configurations (with taper angles of 13°, 21°, 30°) have been considered. Crushing and spalling events have been observed from the regular and high-speed videos, synchronized with tactile pressure sensor data and load cell data. To observe the microstructural modification, horizontal and vertical thin-sections of the damaged ice adjacent to the indenter have been collected and examined. Ice particles were collected from the testing area following each experiment to observe the influence of different factors. Particle size distributions and post-experiment image analyses were also conducted after each test. The effect of the variables on observed failure processes and associated loads are discussed.
Comparison of Single and Overset Grid Techniques for CFD Simulations of a Surface Effect Ship
Authors: Clark Colton G. , Lyons David G. , Neu Wayne L.
Published: September 2014

Overset, or Chimera meshes are used to discretize the governing equations within a computational domain using multiple meshes that overlap in an arbitrary manner. The overset mesh technique is most applicable to problems dealing with multiple or moving bodies. In order to extend existing full craft CFD (RANS) simulations of a surface effect ship (SES) into shallow water and maneuvering cases, an overset mesh is needed. Deep water simulations were carried out using both single and overset grid techniques for evaluation of the overset grid application. The single grid technique applies a hexahedral mesh to the fluid domain and SES geometry. An adequate mesh resolution was determined by performing a grid convergence study on a series of systematically refined meshes. An overset mesh of the same resolution was then constructed and was fixed to the body. Drag and pitch results are compared among the two simulations. Free surface elevations around the craft and under the air cushion for simulations with the single and overset meshes are compared. Steady-state simulations using the overset mesh and the single mesh show general similarities in drag, pitch, and free surface elevations.
Modeling and Analysis of a 5 MW Semi-Submersible Wind Turbine Combined With Three Flap-Type Wave Energy Converters
Authors: Luan Chenyu , Michailides Constantine , Gao Zhen , Moan Torgeir
Published: September 2014

Semi-submersible floating structures might be an attractive system to support wind turbines and wave energy converters (WECs) in areas with abundant wind and wave energy resources. The combination of wind turbines and WECs may increase the total power production and reduce the cost of the power.

A concept of a semi-submersible with a 5 MW horizontal axis wind turbine combined with three flap-type WECs is presented in this paper. The concept is named as Semi-submersible Flap Combination (SFC). The WECs of the SFC are inspired by an optimized bottom-fixed rotating flap-type wave energy absorber. Each WEC of SFC includes an elliptical cylinder, two supporting arms, a rotational axis and a power take off (PTO) system.

A time domain numerical modeling method for the SFC is presented. The numerical model is using the state-of-the-art code Simo/Riflex/Aerodyn. Linear rotational damping is introduced to model the effects of the PTO system. The choice of a PTO damping coefficient and of the mass of the elliptical cylinders has a significant effect on the power generated by the WECs. Such effects have been addressed and discussed in the paper through a sensitivity study.
On the Prediction of Fatigue Damage From VIV
Authors: Passano Elizabeth , Larsen Carl M. , Wu Jie
Published: September 2014

Empirical methods for calculation of response from vortex shedding are based on a set of coefficients that determines response frequencies, excitation force and damping, but also how competing frequencies will appear in time and along a structure. It is easy to formulate a mathematical model for Vortex Induced Vibrations (VIV), but the key challenges are to find the necessary hydrodynamic coefficients and a model for how the active frequencies appear in time and space.

Since the original version of VIVANA was released more than ten years ago, new information has been become available through new test techniques, as well as from new methods for analysis of old tests.

In this study, recent re-examination of the results of the NDP 38 m tests is presented. The observed response behavior is compared to predicted VIV response and fatigue. The consequences of assuming that response frequencies will be active concurrently or consecutively are investigated and predicted response and fatigue are compared to results based on the measurements.

Another method that has provided valuable information has been inverse analysis, by which forces on a flexible beam are estimated from measured strains and/or accelerations. When forces are known, the underlying coefficients can be calculated from the standard equations.

Inverse analysis has been carried out from a set of experiments, and a new set of coefficients has been estimated for use in coefficient based programs such as VIVANA. Initial comparisons between measured and predicted response show that the new coefficients give an improved agreement with regard to amplitudes and frequency composition.
Numerical Model of Towing Line in Sea Transport
Authors: Ćatipović Ivan , Degiuli Nastia , Werner Andreja , Čorić Većeslav , Radanović Jadranka
Published: September 2014

Towing as a specific type of sea transport is often used for installing objects for drilling and exploitation of underwater gas and oil wells. Also, towing proved to be a cost-effective solution for the installation of the offshore wind turbine electric generators at sea locations. Because of the mass of these objects the need for towing increases progressively. Time domain numerical model for the wave-induced motions of a towed ship and the towline tension in regular head seas is presented in this paper. For the sake of simplicity, one end of the towing line is attached to ship’s bow and another end has prescribed straight line motion. All considerations are done in the vertical plane so the ship is modeled as a rigid body with three degrees of freedom. Hydrodynamic loadings due to waves are taken into account along with added mass and damping. Dynamics of the towing line is described by finite elements. Due to the nonlinear properties of the problem calculations are done in time domain. Comparison of the obtained numerical results is made with previously published results.
Extended Porosity Rate Function for Frost Heave
Authors: Abdalla Basel , Fan Chengye , Mckinnon Colin , Gaffard Vincent , Audibert-Hayet Annie , Coche Edmond , Eltaher Ayman
Published: September 2014

Frost heave is a common phenomenon in the Arctic, where soil expands in the direction of heat loss due to ice lens growth upon freezing. It also occurs if a refrigerated structure is buried in unfrozen frost heave-susceptible soil, and thus special considerations are required when designing chilled or LNG pipelines in the Arctic. In the past decades, many theoretical and numerical methods have been developed to predict the frost heave of freezing soil. Among them, the rigid ice model, segregation potential model, and porosity rate function model are the most popular. These frost heave models work well in predicting the soil response during a pure freezing process, but none of these methods consider a thawing and consolidation of soil, which is the opposite but integrated process when the system undergoes the annual temperature cycle.

In this study, efforts are made to extend the porosity rate function to the thawing branch based on reasonable assumptions. With the extended model, a fluctuating surface temperature can be applied on top of the soil surface to simulate a continuous changing ambient temperature. The extended model is realized in ABAQUS with user defined subroutines. It is also validated with test data available in the public domain. As an application example, the extended model is utilized to simulate a chilled gas line buried in frost-susceptible soil to estimate its frost heave over a multi-year operation.
Fatigue Reliability Assessment for Brace-Column Details in a Semi-Submersible Hull
Authors: Schmidt Dilnei , Manuel Lance , Nguyen Hieu H. , Sagrilo Luis Volnei Sudati , de Lima Edison Castro Prates
Published: September 2014

Semi-submersible floating platforms used in the offshore deepwater environment have hull structures that are comprised of vertical cylinders (columns) connected by braces, pontoons, etc. Several of the connections between these various members are susceptible to fatigue damage. In fatigue damage assessment or fatigue reliability analysis, a global structural response analysis is typically carried out using a finite element model where internal forces or stresses in the various members are evaluated for specified sea states of interest at the site. Of specific interest in this study is the fatigue reliability analysis of brace-column connection details in a semi-submersible hull unit for selected Brazilian environmental conditions. Stress concentration factors for the selected critical hot spots are applied to the nominal component stresses due to axial forces and biaxial bending. The hot-spot stress response spectra are used with various spectral methods — referred to as Rayleigh, Modified Rayleigh (with bandwidth correction), and Dirlik — to estimate fatigue damage using Miner’s rule. Uncertainty estimates in fatigue damage rates and life based on the various methodologies are discussed and critical sea states are identified, highlighting dynamic and quasi-static influences on the predicted fatigue.
A Parametric Study on the Influence of Imperfections on Pipe Mechanical Response During Bending in Reel-Lay Installation Using Finite Element Method
Authors: Dawood Ali A. , Kenny S.
Published: September 2014

Finite element modelling procedures were developed to examine the effect of pipe diameter, ovality, wall thickness, imperfection formulations, joint-to-joint material strength variation and radial weld offset on the pipe mechanical response through numerical simulation of the reeling process. This study examines the pipe deformation, stress concentration, and strain discontinuity developed during simulation of the pipe reeling process. The key parameters influencing the pipe mechanical response are identified and recommendations on future work provided.
Hydrogen Induced Stress Cracking on Superduplex Stainless Steel Under Cathodic Protection
Authors: Fonseca José , Renck Tiago , Abreu Eliakin , Santos Fabrício P. , Diehl Bruno , Kwietniewski Carlos E. Fortis
Published: September 2014

The optimized and secure operation of oil and gas floating production units depends essentially on the performance of their devices, components and structures. Rigid pipelines are key equipment used in the offshore industry commonly employed as flowlines and risers. Carbon steel such as API 5L X65 is the material of choice for those applications due to its low relative cost and availability. However, for the Brazilian pre-salt it seems unlikely that carbon steels can be applyed, since the oil is contaminated by high concentrations of CO2, which causes generalized corrosion. Therefore, operators in Brazil should consider an alternative solution, such as lined or clad pipes as well as corrosion resistant alloys (CRA). Duplex and super duplex stainless steels (SDSS) have emerged in the last decade or so, as an alternative material for harsh environments. Nevertheless, according to recent studies, SDSS when cathodically protected against corrosion are prone to hydrogen induced stress cracking (HISC). The aim of this investigation is to evaluate through fracture toughness measurements the susceptibility of welded SDSS samples to HISC for two different levels of cathodic protection. For fracture toughness evaluation the step loading test method was selected. This practice is believed to be more realistic because samples are exposed to hydrogen during the entire tests instead of simple hydrogen pre-charging before performing the test in air, as recommended by some procedures. Fracture toughness values are given in terms of both CTOD and J-integral for crack initiation and maximum stress for SENB specimens. The results given here indicates that SDSS are quite susceptible to HISC especially in the heat affect zone even for potentials as negative as −650 mVsce.
Effect of Anti-Wear Tape on Behavior of Flexible Risers
Authors: Zhou Chongyao , Ye Naiquan , Sævik Svein
Published: September 2014

The service life of a flexible riser is often dominated by the metallic layers under cyclic bending loads, particularly the tensile armor layers. The effect of the anti-wear tapes is normally omitted during cross section modelling, where a plane-remain-plane assumption is usually used for stick condition. Significant differences have been observed between numerical analysis assuming plane surfaces remain plane and laboratory measurements studying the bending moment versus curvature for a flexible riser which has anti-wear tapes between the two tensile armor layers.

A new shear interaction algorithm has been developed in the numerical model to improve the modeling of the anti-wear tapes by taking the thickness and shear modulus of the anti-wear material into account. The impact of these parameters on the bending behavior of the flexible riser is demonstrated by comparing the numerical analysis results with the laboratory measurements.
Flexible Hybrid Reinforced Pipe-Bend Stiffener Interface Design With Optimized Thermal Performance
Authors: Salimi Amirhossein , Kalman Mark , Yu Liang
Published: September 2014

Flexible pipe risers are often protected from over-bending with a bend stiffener at the lower end of an I-tube in FPSO installations. Due to the high thermal resistance of the polyurethane bend stiffener, there is a potential risk for both riser and bend stiffener to exceed their temperature limits. This paper presents classical and computational fluid dynamics thermal models and analyses to confirm that free convection heat transfer from the pipe wall to the water in the gap between the pipe and bend stiffener, and buoyancy driven flow along the gap is sufficient to maintain the temperature of the pipe layers and bend stiffener within allowable values. Details of the models and solutions for an example riser with 120 °C design temperature in a Gulf of Mexico installation is presented.
Uncertainty Analysis for Inclining Tests
Authors: Sales Joel S. , Esperança Paulo de Tarso T. , Sphaier Sergio H. , Machado Christiane
Published: September 2014

In this paper, we addressed the qualitative consequences on uncertainty for the execution of a inclining test of a Semi-submergible platform with mooring system and risers at production site and compared the results to the ones taken from typical inclining test procedures at sheltered waters, as defined by ASTM F1321. To accomplish that, we applied Uncertainty Analysis according to ISO procedures, by evaluating propagation of uncertainties from the measurements until the final calculations. We discussed the use of measurement devices for the variables of concern and performed some numerical simulations to address the mooring system restoring effects and its implications on uncertainty analysis. We used data from two semi-subs with different displacements and found small influence on final uncertainty from the addition of mooring system and risers. At end, we discussed how new technologies on data acquisition and filtering of signals can become an important tool to help in the safety of the offshore floating production units, by facilitating the verification of the updated center of gravity of them after important interventions.