bluuebunny/crossref_metadata_2025 huggingface dataset:
Current Effects on the Generation and Evolution of the Peregrine Breather-Type Rogue Wave
Authors: Lu Wenyue , Yang Jianmin , Tao Longbin , Lu Haining , Tian Xinliang , Li Jun
Published: October 2015

Rogue wave is a kind of surface gravity waves with much larger wave heights than expected in normal sea state. Since this extreme sea event always occurred in the areas with strong currents, the wave-current interaction was considered to be one of the physical mechanics of the formation of the rogue wave. Some breather type solutions of the NLS equation have been considered as prototypes of rogue waves in ocean which usually appears from smooth initial condition only with a certain disturbance. In this paper, we have numerically studied evolutionary process of the Peregrine breather rogue wave based on the current modified fourth order nonlinear Schrödinger equation (the CmNLS equation). During the generation and evolution of the Peregrine breather rogue wave, the effects of the steady current was investigated by comparing with the results without current. The differences of the focusing position/time were observed due to the current influence.
On the Influence of Atmospheric Stability on the Wave Climate in a Warm and Saline Water Body
Authors: Golestani Maziar , Jensen Palle Martin , Kofoed-Hansen Henrik
Published: October 2015

This paper presents some of the challenges faced during a project aimed at preparing long-term wave climatology in the Persian/Arabian Gulf. Using the hourly CFSR wind fields as forcing, an attempt was made to produce a comprehensive hydrodynamic and sea state conditions data set. By comparing the wave results to various in-situ and satellite measurements, an obvious seasonal difference was observed. Wave conditions were well reproduced during winter while the wave height was generally overestimated and scattered during the summer period.

After comparing the wind fields against measurements it was believed that other sources were playing an important role in wave growth and propagation. Based on available measurements, it was shown that in the summer period, where the air temperature is higher than the sea temperature, wave growth rate is lower than in the winter period. Similar real cases have been reported in some lakes, but the influence of atmospheric stability on wave climate in a relatively large sea like The Gulf has not been documented yet to the authors’ knowledge. This paper focuses on the importance of including atmospheric stability effects into wave modelling. In order to account for the stability effects, the friction velocity and surface roughness were modified in the 3rd generation wind-wave model, MIKE 21 SW, using the Monin-Obukhov similarity theory. Improvements were seen in the quality of modelled wave heights in the summer period. The Gulf is also highly affected by changes in the sea water density. The effects of varying water density on wave climate were also studied in this paper. In order to reproduce the best quality wave climatology in The Gulf, it was concluded that seasonal modelling is required and the effects of atmospheric stability should be included.
Validation of CFD+DEM Against Measured Data
Authors: Vroegrijk Erik
Published: October 2015

In this paper the author attempts to validate the ability of CFD and DEM to predict the added resistance due to brash ice. For this, a comparison is made between measured data and computational results. In addition, the paper provides details on the computational effort required. The results show that the added resistance calculated with CFD and DEM has the potential to be valid. Due to uncertainties in the measured data and inconsistencies observed in the computational results, however, no definite conclusion on its validity can be drawn.
Global In-Place System Behavior of Flexible Pipeline on Seabed
Authors: Brankovic Maša , Vervik Stian , Løken Erik , Damsleth Per
Published: October 2015

A pipeline system consists of the flexible pipe and all associated ancillary components up to the connecting components at battery limits. The global system design deals with aspects related to the overall flexible pipe system — not cross-section or component design. Key system design issues to address are specified in ISO 13628-11:2007 (API 17B) and include general system design requirements, flowline design requirements, and interfaces involving different contractors and suppliers. Unlike unbonded flexible risers that operate in tension, flexible pipe laying on the seabed will be subject to compressive forces and global buckling as for rigid pipelines.

The global flexible pipeline system design will use relevant design codes such as ISO 13628-11:2007 and API 17B / 17J. Yet, the terminology and what such design encompasses can be interpreted differently amongst the community of flexible designers, installers and operators. Failure modes, for example, are not perceived in the same way. While axial compressive force may not be allowed for a riser design, it is a normal flexible pipe response to expansion when pressurized on the seabed. Pull-in and connection forces and moments may be perceived as maximum loads by installers and subsea equipment suppliers but the pressure-induced hydrotest and operational loads may exceed these and overstress the piping leading to a HISC failure.

The system functional requirements for flexible pipelines are similar to rigid lines but when it comes to a flowline laid on the seabed, exposed to pressure and temperature, the methodology for establishing accurate predictable global behaviour is still under development in the industry.

To perform the global in-place design of a flexible flowline, a detailed understanding of the effects of pressure and temperature on the unbonded flexible construction with respect to its bending stiffness and expansion and the limiting criteria stipulated by the manufacturer is needed. The flexible’s behaviour can be simulated using a 3D FE model capturing the effects of seabed surface variations, interaction with soil, and entire load history from installation, to flooding and hydrotest to filling with product at a range of pressures and temperatures including start-up shut-down cycles. Whereas general requirements are stipulated in API 17, specific guidelines applicable to global buckling design are found in DNV-RP-F110 for rigid pipelines. This predictive analysis methodology using risk-based design criteria provides the basis for a robust design that can accommodate large variations in installation tolerances, uneven seabed, varying soils, etc., while providing all concerned with a sound understanding of the flexible behavior and interface loads throughout its design life.
Performance and Mooring Analysis of 10 KW Floating Duct-Type Tidal Current Power System
Authors: Jo Chul-hee , Rho Yu-ho , Goo Chan-hoe , Kim Do-youb
Published: October 2015

Recently, focus has been placed on ocean energy resources because environmental concerns regarding the exploitation of hydrocarbons are increasing. Among the various ocean energy sources, tidal current power (TCP) is recognized as the most promising energy source in terms of predictability and reliability. The enormous energy potential in TCP fields has been exploited by installing TCP systems. The flow speed is the most important factor for power estimation of a tidal current power system. The kinetic energy of the flow is proportional to the cube of the flow’s velocity, and velocity is a critical variable in the performance of the system. Since the duct can accelerate the flow speed, its use could expand the applicable areas of tidal devices to relatively low velocity sites. The inclined angle of the duct and the shapes of inlet and outlet affect the acceleration rates of the flow inside the duct. To investigate the effects of parameters that increase the flow speed, a series of simulations are performed using the commercial computational fluid dynamics (CFD) code ANSYS-CFX. Experimental investigations were conducted using a circulation water channel (CWC). Also, mooring system concepts are investigated using the commercial mooring analysis software WADAM and OrcaFlex. Due to other floating structures operating within a limited area, station-keeping is needed in order to keep the motions of the floating duct structures within permissible limits. In this study, methods for optimizing the mooring system of a floating duct-type tidal current power system in shallow water are investigated. Based on the performance and mooring analysis results of the 10 kW floating duct-type TCP system, a new design for a small capacity floating TCP system is introduced.
Numerical Study on the Deformation of a Net Panel in Steady and Oscillatory Flow
Authors: Shen Jing , Qin Hongde , Ma Leixin , Fu Shixiao
Published: October 2015

Based on the hydrodynamic coefficients obtained in a series of experiment on a full-scale net panel, numerical simulation is conducted to study the interaction between flow and the flexible net in waves and current. Finite element model was constructed and modified Morison Equation was adopted to estimate the deformation of the net sheet. The deformation of the net sheet was investigated quantitatively by estimating the minimum projected area and comparing the area reduction ratio under each test case. Furthermore, the relationship between the net’s area reduction ratio and the nondimensionalized parameters in the model testing, including the structure’s Reynolds number, KC number, frequency parameter and reduced velocity was discussed.
Evaluations on Ship Performance Under Varying Operational Conditions
Authors: Perera Lokukaluge P. , Mo Brage , Kristjánsson Leifur Arnar , Jønvik Petter Chr. , Svardal Jan Øivind
Published: October 2015

Various emission control measures have been introduced in the recent years for improving vessel performance in the shipping industry. That consists of: Energy Efficiency Design Index (EEDI) for new ships and Ship Energy Efficiency Management Plan (SEEMP) and Energy Efficiency Operational Indicator (EEOI) for all ships. These emission control measures enforce the shipping industry to improve operational conditions and to implement modern technology for more energy efficient shipping fleets. Therefore, this study presents preliminary data analysis of a selected vessel for monitoring its performance along the ship routes. The results consist of observing vessel performance under several navigation parameters: ship GPS speed (i.e. speed over the ground), log speed, course, fuel consumption, main and auxiliary engine power, main engine shaft RPM, loading and draft conditions with respect to the route, voyage time and wind conditions. Furthermore, these parameters have been used to analyze potential and optimal energy usage situations in ship navigation with respect to the EEOI, in which represents an important part of the SEEMP.
Integrity Assessment of a Free-Fall Lifeboat Launched From a FPSO
Authors: Ji Guomin , Berchiche Nabila , Fouques Sébastien , Sauder Thomas , Reinholdtsen Svein-Arne
Published: October 2015

The paper addresses the structural integrity assessment of lifeboat launched from floating production, storage and offloading (FPSO) vessels. The study is based on long-term drop lifeboat simulations accounting for more than 50 years of hindcast data of metocean conditions and corresponding FPSO motions. Selection of the load cases and strength analyses with high computational time is a challenge. The load cases analyzed are those corresponding to the 99th percentile of long term distribution of indicators for large slamming loads (CARXZ) or large submergence (Imaxsub). For six selected cases, the time-varying pressure distribution on the lifeboat hull during and after water impact is calculated by CFD simulations using StarCCM+. The finite element model (FEM) of the composite structure of the lifeboat is modelled by ABAQUS. Quasi-static finite element (FE) analyses are performed for the selected load cases. The structural integrity is assessed by the maximum stress and Tsai-Wu failure measure.

In the present study, the load and resistance factors are combined and applied to the response. A sensitivity study is performed to investigate the non-linear load/response effects when the load factor is applied to the load. In addition, dynamic analysis is performed with the time-varying pressure distribution for selected case and the dynamic effect is investigated.
Quasi-Static Assessment of Response to Slamming Impact on Free Fall Lifeboats
Authors: Heggelund Svein Erling , Li Zhiyuan , Jang Beom-Seon , Ringsberg Jonas W.
Published: October 2015

Design against impact loads (slamming) can be challenging and time consuming and can involve complex calculations. Application of simplified, quasi-static calculation approaches will make the design process much easier. In this paper, such simplified methods are discussed using free fall lifeboats as a case. Results from non-linear FE-analysis show that the response is non-linear due to large deformations. The impact pressure is then mainly carried by membrane stress and the dynamic response is small. A non-linear beam theory approach for hand calculation is established. As the non-linear calculation model is the most realistic, it is recommended that this is used in an initial design assessment. Although the results are on the conservative side, simple hand calculations including non-linear geometry can be used to predict the maximum strain. Linear methods are also investigated. However, these methods should be used with more rigid structures such as stiffened steel and aluminium panels.
Discussion on Hybrid Utilization for Offshore Wind and Wave Energy
Authors: Fujioka Katsunari , Nihei Yasunori , Le Boulluec Marc
Published: October 2015

In this paper, we will discuss the concept of combined utilization of offshore wind and wave energy in terms of both tank test and numerical simulation. There are some possibility that combined utilization of ocean renewable energies can avoid some disadvantages that single utilization of them may have, such as cost problem associated with the stability of power and power supply. In this study, we focus on the motion of an offshore wind turbine in waves associated to wave energy converters, are installed in the same area in order to improve its motion by reducing the effect of incident waves. We carried out wave tank test and numerical simulation, and investigated the motion of wind turbine in waves. In addition, numerical simulation allows to visualize the wave fields around those devices. Appropriate arrangement of them is discussed for the most efficient utilization of offshore wind and wave energy.
Spatial Variability of Extreme Sea States on the Irish West Coast
Authors: Clancy C. , Belissen V. , Tiron R. , Gallagher S. , Dias F.
Published: October 2015

Recent studies have revealed a long history of large waves around Ireland, which can be attributed to persistent strong winds in this area. At the same time, due to the consistently high levels of wave energy, the West Coast of Ireland has attracted a lot of interest as a prospective site for deployment of wave energy converters (WECs) farms. The design of such devices, and in fact of any offshore installation, depends crucially on the knowledge of extreme sea states they will experience during their deployment time.

With this in mind, an Extreme Value Analysis incorporating seasonality and accounting for long-term trends was performed, based on a 29 year hindcast for Ireland. The hindcast was performed using the WAVEWATCH III wave model in a 3 nested grid setup, with the largest grid covering the North Atlantic basin and the finest resolution grid (10km) focusing on Ireland. The model was forced with ERA-Interim 10m winds from the European Centre for Medium Range Weather Forecasts. The wave model was validated by comparison to buoy data from the Irish Marine Data Buoy Network.

The analysis was performed on the entire fine resolution grid. This affords a characterisation of the spatial variability in extremes both along the coast and with depth gradients. This is of interest in many marine applications, and in particular WEC design and deployment. Indeed, in the nearshore, wave energy levels can be similar to those found in the offshore. This, in conjunction with the diminished risk of extreme sea states, makes nearshore areas attractive for future ocean energy sites.
Experimental and Numerical Study of the Bending Behavior of a Flexible Riser Model
Authors: Rahmati M. T. , Norouzi S. , Bahai H. , Alfano G.
Published: October 2015

Unbonded flexible risers have become the main means of extracting hydro carbonates from deep waters. So, understanding the complex structural integrity of flexible risers has become a crucial issue for the offshore industry. In this paper, an experimental test and a detailed finite element analyses were carried out on a scaled down model of a flexible riser pipe in order to understand its bending behavior. The model used consists of four layers which include two cylindrical polycarbonate tubes and two steel helical layers. One helical layer, wounded around the pipe assembly, represents the carcass layer in an actual flexible riser whilst the other represents the riser tendon armour layers. The model was subjected to a three point bending load in order to study its bending-curvature behavior. The test data was then compared with the FE numerical results which predicted a similar nonlinear trend but under predicts the strain at tendon layers.
Behavior of the Residual Wave Components in a 3D Wave Basin After the Termination of the Wave Maker
Authors: Zaman M. Hasanat , Mak Lawrence , Millan Jim , Kuczora Andrew
Published: October 2015

After the termination of the wave making, the characteristics of the existing wave components in a 3D large scale Offshore Engineering wave Basin (OEB) at the National Research Council of Canada have been investigated experimentally. In the generation of any wave in the tank we get the relevant primary wave components along with bounded wave components if the incident primary wave has more than one frequency. Inevitably we also get interacted wave components, natural frequency components of the tank and other free waves. In this paper the tank’s natural frequency components, bounded wave components and other free waves after the termination of wave making were investigated using several cases of mono- and bi-chromatic waves. These component energies were then compared with the total energy of the measured primary waves. The magnitudes of the residual undulations are also investigated for mono-, bi- and multi-chromatic waves over different time segments. Several sets of wave data are analysed to perceive the energy due to natural frequency of the basin, energy transferred to the side bands and the damping rate of the residual waves in the tank with respect to the chosen incident wave conditions. In the analysis it is observed that the energy damping rate varies with the incident wave condition but seems much faster than that of 20 minutes traditional waiting time in between two runs in the OEB. The energies for tank’s natural frequency components and other free waves were found to be very small compare to the incident primary wave energies.
Multi-Scale Investigation on Residual Strength of Jacket Platform With Fatigue Crack Damage
Authors: Wang Ren Hua , Zou Xiang , Dou Pei Lin , Fang Yuan Yuan , Luo Guang-en
Published: October 2015

Fatigue crack damage caused by the wave load brings the structure of jacket platform in service potential failure risk when subjected to the extreme load. However, there is lack of efficient method to evaluate the influence of crack damage on the structural performance because of the huge scale difference between the meso-scale damage and the macro-scale structure. Based on the multi-scale finite element method (FEM), to improve the efficiency of structural analysis, the damaged region of the structure is modeled with fine FE mesh (shell element) to describe the fatigue crack, and the undamaged area is modeled with coarse FE mesh (beam element). Furthermore, the applicability and superiority of this multi-scale model was validated through comparing the results obtained from the beam, multi-scale and shell models. The influence of the time-varying crack damage on the residual strength of jacket platform is then revealed based on the multi-scale FE model. The results show that the proposed multi-scale method can accurately describe fatigue crack damage in the macro-scale structure, and be applied to investigate the influence of meso-scale structural damage under the extreme load condition.
Tubarão Martelo Field Development: Lazy S Riser Configuration Using Mid Water Arch (MWA)
Authors: Ribeiro Elton J. B. , Labanca Edson Luiz , Bartz Cesar , Iwane Andre
Published: October 2015

Mid-Water Arches (MWAs) have been used as alternative to distributed buoyancy systems in flexible riser designs worldwide. Those structures usually involve complex lifting requirements for installation, as the Buoyancy Tank Assemblies (BTAs) are lightweight compared to its volume and footprint area. Handling those odd-sized structures in the deck of a construction vessel and crossing the splash-zone are frequently challenging engineering tasks.

This paper will present a case study of MWA installation performed by GE/WSC as part of the OGX Tubarão Martelo field development, offshore Brazil. The location is prone to swell from South Atlantic and hence a flat sea is a rare event, even when no local wind generated are present. This makes any delicate and weather sensitive operation a critical schedule issue. Still, 8 MWA were installed with minor Waiting on Weather thanks to an extensive analysis envelope and to an engineered installation method aiming to minimize the time the operation was limited by weather condition.

Also, as the scope involved a large number of MWAs, a “mass production” method was developed for the operations, not only covering the offshore installation but also the mobilization and logistic aspects of handling large and heavy items ashore. To allow road transportation by trucks, the BTAs and Gravity Bases (GBs) were shipped to the mobilization port in sub-components for site integration.
Comparison of Numerical Models and Verification Against Experimental Data, Using Pelastar TLP Concept
Authors: Vita Luca , Ramachandran G. K. V. , Krieger Antonia , Kvittem Marit I. , Merino Daniel , Cross-Whiter John , Ackers Benjamin B.
Published: October 2015

The analysis of a FWT is a complex problem, which requires advanced tools. Several numerical solutions have been used to couple hydrodynamics and aerodynamics and some of the available numerical tools have been compared in code-to-code comparisons. However the code validation for analysis of FWTs is limited by the number of available experimental data.

In the present article, DNV GL and Glosten present a code comparison of four numerical tools against model test results. The design used for the analysis is the Pelastar Tension Leg Platform (TLP) by Glosten. A 1/50 downscaled model of the platform and NREL-5 MW wind turbine was tested in MARIN ocean basin. The results from the model tests are used to verify the results from the numerical codes. The FWT is modelled using four different codes: HAWC2 (by DTU and used by DNV GL), BLADED (by DNV GL and used by DNV GL), SIMA (by Marintek and used by DNV GL) and ORCAFLEX (by Orcina and used by Glosten). Although differences exist among these codes, comparable approaches have been used.

Results from the numerical codes are compared against the experimental data, in terms of:

- Natural periods

- Response in regular waves

- Response in irregular waves

- Response in irregular waves with aerodynamic loads.

In general, the results show a good agreement between the different numerical models and all the codes are capable to reproduce the main dynamics of the system. Some deviations were found and should be solved, in order to use these models for a detailed analysis. However these differences do not seem to be due to limitations of the codes and they might be solvable with a more accurate model of the system.
The Physical Behaviour of Seine Ropes for Evaluating Demersal Seine Fishing
Authors: Madsen Nina A. H. , Aarsæther Karl Gunnar , Herrmann Bent , Hansen Kurt , Jensen Jørgen H.
Published: October 2015

Demersal seining is an active bottom fishing method, which apply seine ropes and a seine net. The seine ropes and net are laid out on the fishing ground with the seine ropes encircling an aggregation of fish on the seabed. The area on the seabed encircled by the seine ropes is typical much larger than the swept area that will be covered by the seine net during the fishing process. Therefore, the catching performance of a demersal seine depends on the efficiency by which the seine ropes are able to herd the fish into and maintain them in the path of the net until they are overtaken by it in the late stages of the fishing process. This article describes flume tank experiments to validate a numerical model. This model simulates the physical behaviour of seine ropes during the fishing process. The experiments are conducted for varying physical properties of the ropes and for different layout patterns. The seine ropes are hauled back at different speeds. A motion tracking system, based on stereo vision, is applied to record the gradual change in the area encircled by the ropes. The experimental results from the flume tank are compared with data obtained using the simulation model. Finally, the validated simulation model is applied for predictions.
Thermal Behavior and Growth of Submerged Ice Blocks: Experimental and Numerical Results
Authors: Ghobadi M. , Bailey E. , Taylor R.
Published: October 2015

Ice rubble forms when flexural, shear or compressive forces cause broken ice to pile up at the interface between ice floes or during contact with a structure. The accumulation of rubble into linear features results in the formation of ridges, which are comprised of many individual blocks that are bonded with varying degrees of strength. Essential to the overall consolidation of a ridge is the bonding process that takes place at the interface between individual blocks. In this paper initial experimental and numerical simulations are presented that show the amount of new ice that will grow when an initially cold piece of freshwater ice is submerged in freshwater at 0° C. Understanding the thermal behavior of an ice block is important as the results can be used to understand the freeze-bonding processes that occur between two ice blocks, and further extended to understand the processes that occur between multiple ice blocks (i.e., pressure ridges and ice rubble). In the experiments presented herein, a cylindrical ice sample with an initial temperature of −20° C was submerged in a tank of water at 0° C. As the ice cylinder is initially colder than the surrounding water, heat is diffused from the water into the ice cylinder causing a new layer of ice to form around the samples. Wireless temperature sensors with onboard data loggers were placed inside the ice cylinder to measure temperature. The radius, length and weight of the sample were measured before and after the submersion to calculate the thickness of the new ice layer. COMSOL Multiphysics was employed to analyze the freezing rate and the radial temperature profile of the sample. An analytical method is also used to calculate the maximum thickness of the new ice layer formed around the sample once the temperature has equilibrated to the surrounding water temperature. Results obtained using the analytical method are then compared with experimental results. Temperature profile data collected at specified locations within the ice have also been compared with the numerical simulations. Good agreement between measured and simulated results was observed.
The Effect of Different Oil Based Drilling Fluids on Mechanical Friction
Authors: Ytrehus Jan David , Taghipour Ali , Golchin Arash , Prakash Braham , Saasen Arild
Published: October 2015

A very important aspect in highly inclined wellbores is the mechanical friction. For extended reach drilling (ERD) and through tubing extended reach drilling (TTERD) this can be a limiting factor. Friction caused by the contact between the drill string and the well casing or borehole is dependent to the drilling weight and fluid properties. Drilling fluids play an important role on mechanical friction and using oil based drilling fluids with higher lubricity can reduce torque and drag behavior and minimize stick and slip. Reducing mechanical friction will improve drilling efficiency in general, and will in particular enable longer reach for ERD wells.

This paper presents results from experimental laboratory tests where mechanical friction has been investigated. The experiments have been conducted as part of a project in the Tribolab at Luleå University of Technology in cooperation with Det norske Oljeselskap.

Friction behavior has been investigated for different drilling fluids; water based and oil based drilling fluids both with and without solid particles. A pin on disc setup was used for these experiments where a spherical steel pin was sliding on a rotational disc made of granite. Friction force has been measured in constant sliding speed and in presence of particles in wet condition. The test results show that mechanical friction in general is smaller with oil based than water based drilling fluids in the presence of solid particles. In addition, the friction coefficient increases when solid particles were added to the lubricants.

Such experiments in a tribology laboratory are important to identify the effect of drilling fluids on mechanical friction from a basic point of view and isolated from all other wellbore parameters. It is interesting to monitor if the results from this setup can have quantitative relevance also for field situations and such comparison should be done as follow up. Test results and the experimental approach could therefore be of value for any one working with drilling and well construction.
Comparative Review of the Established UHB Assessment Methods for Offshore Pipelines
Authors: Kumar Sajith , Smith Daniel , Jafari Hooman
Published: October 2015

Out of straightness upheaval buckling (OOS UHB) assessment considers the pipeline design and operational parameters, post-lay survey data and the properties of back-fill and rock in order to determine load and resistance factors that are applied. The factors allow for the natural variation of all parameters and are ultimately used to determine the download requirements along the route of a pipeline that is susceptible to UHB. Two methods are most commonly used in OOS UHB assessments.

The structural reliability analysis (SRA) method is the most established and explicitly considers the variation of parameters in a Monte-Carlo simulation, enabling load and resistance factors to be calculated with a defined reliability level. A more recently developed methodology is documented in DNV-RP-F110 and provides a unified approach to the calculation of safety factors. The approach was calibrated using structural reliability based methods, undertaken with target reliability levels that are compliant with DNV-OS-F101.

This paper presents a review of two key components of OOS UHB assessments. These components are the accuracy of post-lay survey data and the load resistance factor calculation method. These components are reviewed in the context of SRA and DNV-RP-F110 based assessments for a range of pipeline sizes, and ranges of soil and operational parameters. This enables characterisation of the differences between the two methodologies for ranges of design parameters that represent the majority of in-field flowlines that are installed in the United kingdom Continental Shelf (UKCS). SRA and DNV-RP-F110 derived load and resistance factors are compared and the effect of survey data smoothing upon rock-dump requirements is also discussed.
Experimental Study of Dynamics During Crushing of Freshwater Truncated Conical Ice Specimens
Authors: Habib Kashfi B. , Taylor Rocky S. , Bruneau Stephen , Jordaan Ian J.
Published: October 2015

Ice crushing dynamics in ice structure interactions can result in hazardous vibrations and potentially damaging loads on offshore structures. Ice cone crushing experiments were conducted in the lab to characterize loading and dynamics processes for compressive failure. The indentation rate, temperature and shape of the ice specimens were varied in control tests so that the sensitivity of the resultant dynamic ice load frequency and amplitude could be determined. The results indicate that all control variables had a marked effect on both the frequency and amplitude of load fluctuations. Indentation rates varying from 0.1 mm/s to 10 mm/s and ice taper angles from 13° to 30° had drastic effects. The effects of temperature also demonstrated variations in force, pressure and dynamic behavior. In addition to load measurements, video was used to observe failure mechanisms and in particular spalling and crushing. In the present paper observations are described, though a thorough quantitative assessment has been published elsewhere. Tactile pressure sensors were also used in the experiments, allowing for the correlation of loads and processes to pressure distributions. Finally, the forensic examination of crushed specimens also provided insights into the behavior of ice under various compressive failure scenarios. On the surfaces of intact specimens and revealed within through cross-polarized views of thin sections were signs of ice damage and recrystallization zones of varying extents. The effects of the variables on the dynamic processes and failure behaviors are discussed.
Rheological Properties of Oil Based Drilling Fluids and Base Oils
Authors: Oltedal Velaug Myrseth , Werner Benjamin , Lund Bjørnar , Saasen Arild , Ytrehus Jan David
Published: October 2015

Drilling fluids for oil wells must meet a number of requirements, including maintaining formation integrity, lubricating the drill string, and transporting cuttings to the surface. In order to satisfy these needs, drilling fluids have become increasingly complex and expensive. To ensure safe and efficient drilling, it is vital for the drilling operator to be able to make a qualified choice of fluid appropriate for each individual well.

API/ISO standards specify a set of tests for characterization of drilling fluids. However, fluids that are tested to have equal properties according to these standards are still observed to perform significantly different when used in the field. The aim of the full project is to provide a thorough comparison of drilling fluids in particular with respect to hole cleaning performance, in light of the issues presented above. As part of this investigation we here present results for two oil based drilling fluids, as well as for the corresponding base oil. The drilling fluids differ in composition by varying fraction of base oil, and thus density and water content.

The fluids have been tested according to the API standard, and further, viscoelastic properties have been examined using an Anton Paar rheometer. The rheological test campaign includes determination of the linear viscoelastic range (LVER), viscosity and yield point, thixotropic time test, and temperature dependence of rheological parameters.

Further, it is demonstrated how the rheological data may be used to interpret data from ongoing full scale flow loop experiments with the same fluids. In a more general context, the rheological test campaign of the drilling fluids is expected to make a crucial contribution for the petroleum industry in explaining observed differences in hole cleaning properties beyond what todays API/ISO industry standard provides.
Design and Modeling Shape Memory Actuator for Offshore Applications
Authors: da Camara Monteiro Paulo Cesar , Netto Theodoro A. , da Silva Monteiro Luciana Loureiro , Savi Marcelo A.
Published: October 2015

The use of shape memory alloys (SMA) in smart sensors and actuators is already well established in many areas such as biomedical and aerospace engineering. Likewise, SMA’s have an enormous potential for offshore oil and gas applications. They can be used, for example, in active vibration control devices or in deep water valves as actuators. In this work, two different prototypes of SMA actuation valves are developed — a linear and rotate sliding sleeve. Several tests were performed to determine the maximum force, maximum displacement of the devices. In parallel, numerical simulations using constitutive model of shape memory alloy are carried out to capture the behaviour of SMA actuators under different thermo-mechanical loadings.
Numerical Analysis of FPSO Behavior in Ocean Towing
Authors: Zhan Dexin , Spencer Don , Molyneux David
Published: October 2015

This paper presents numerical analysis of the behavior of a towed FPSO using an in-house computer code Ship Maneuvering Laboratory (SML). The background of the study was an attempt to explain some unexpected observations during a towing situation, where the position of the towed vessel was on the upwind side of the towing vessel and oscillating in yaw. The effects of rudder, wind and current were investigated initially. Then the study focused on the behavior of the towed FPSO with different hydrodynamic coefficients in an environment of steady wind varying from 1.0 to 25 knots with the wind direction on the starboard bow of the tug. The tug was assumed to move in a straight line at a constant speed.

It was found that with the calculated MMG coefficients the FPSO had large oscillations of track and yaw when the wind speed was low (1 knot). When the wind speed was increased, the FPSO moved to the starboard side of the tug (up wind) and kept oscillating and yawing but with less amplitude. This was similar to the FPSO behavior observed in the incident. This phenomenon of oscillating and yawing of the FPSO was not seen when using the measured PMM hydrodynamic coefficients. One possible explanation for the FPSO behavior in the incident was related to the specific values of the FPSO’s hydrodynamic coefficients.

Some possible methods to reduce the FPSO yaw oscillation are also provided. Numerical results showed that by adding drag created by a drogue to the FPSO or using a longer towing bridle can significantly increase the directional stability of the FPSO. A sensitivity study of the FPSO hydrodynamic coefficients is also given and some conclusions are provided.
Development of a FPSO Motion Simulator
Authors: Zhan Dexin , Thanyamanta Worakanok , McDonald Jason , Molyneux David
Published: October 2015

This paper presents the development of a motion simulator for a moored FPSO, which includes numerical prediction of the FPSO motions in wind, waves and current. It also presents the resulting mooring line tension, 3-dimensional visualization of the FPSO motion, and summary analysis of the resulting motion parameters. The FPSO motion in waves was simulated using an in-house seakeeping code, MOTSIM. A spread mooring line routine, based on catenary theory, was developed and added to MOTSIM to calculate the restoring force of each mooring line. The visualizer (or animator) was developed in-house from open source software, including Ogre, Hydrax and Skyx. It can playback a 3-dimensional view of the simulation (above and below water). The user can view the results in a movie-like format, and change viewing position during the play-back. The user can also run a new simulation from the animator by inputting the required parameters.

The program for analyzing the time dependent responses generated by MOTSIM was developed as a stand-alone program using MATLAB. The analyzer can conduct statistical analysis of time-domain response signals.

A heading control system and a DP control system were also developed in the simulator and can be activated to help control the FPSO motion if required.

A validation of the ship motion prediction and mooring tension was conducted against model experiments using 100-year return period environments with different combinations of wave, wind and current directions.

The simulator was developed as a forecasting tool to help operators predict platform performance based of forecast weather conditions.
Practical Evaluation of the Strain Rate and Temperature Effects on Fracture Toughness of Steels
Authors: Gotoh Koji
Published: October 2015

Overview of the quantitative evaluation procedure of strain rate and temperature effects on fracture toughness proposed by the authors is introduced. Important concept of former researches is that the fracture toughness is a function of the strain rate-temperature parameter (R), which enables to unify both strain rate and temperature effects for the mechanical properties of materials. Using this knowledge, the equivalent temperature shift values at arbitrary strain rate from static loading condition are proposed.
A Novel Solution to Compute Stress Time Series in Nonlinear Hydro-Structure Simulations
Authors: Bigot Fabien , Sireta François-Xavier , Baudin Eric , Derbanne Quentin , Tiphine Etienne , Malenica Šime
Published: October 2015

Ship transport is growing up rapidly, leading to ships size increase, and particularly for container ships. The last generation of Container Ship is now called Ultra Large Container Ship (ULCS). Due to their increasing sizes they are more flexible and more prone to wave induced vibrations of their hull girder: springing and whipping. The subsequent increase of the structure fatigue damage needs to be evaluated at the design stage, thus pushing the development of hydro-elastic simulation models. Spectral fatigue analysis including the first order springing can be done at a reasonable computational cost since the coupling between the sea-keeping and the Finite Element Method (FEM) structural analysis is performed in frequency domain. On the opposite, the simulation of non-linear phenomena (Non linear springing, whipping) has to be done in time domain, which dramatically increases the computation cost. In the context of ULCS, because of hull girder torsion and structural discontinuities, the hot spot stress time series that are required for fatigue analysis cannot be simply obtained from the hull girder loads in way of the detail. On the other hand, the computation cost to perform a FEM analysis at each time step is too high, so alternative solutions are necessary. In this paper a new solution is proposed, that is derived from a method for the efficient conversion of full scale strain measurements into internal loads. In this context, the process is reversed so that the stresses in the structural details are derived from the internal loads computed by the sea-keeping program. First, a base of distortion modes is built using a structural model of the ship. An original method to build this base using the structural response to wave loading is proposed. Then a conversion matrix is used to project the computed internal loads values on the distortion modes base, and the hot spot stresses are obtained by recombination of their modal values. The Moore-Penrose pseudo-inverse is used to minimize the error. In a first step, the conversion procedure is established and validated using the frequency domain hydro-structure model of a ULCS. Then the method is applied to a non-linear time domain simulation for which the structural response has actually been computed at each time step in order to have a reference stress signal, in order to prove its efficiency.
Fatigue Crack Propagation of Deepwater Structures Under Cyclic Compression Based on Extended McEvily Model
Authors: Luo Guang-en , Dong Jia-huan
Published: October 2015

The extended McEvily model is adopted to predict the fatigue life of deepwater structures under cyclic compression. The three dimensional finite element analysis is performed to estimate the residual stress distribution along the crack surface during the crack propagation under cyclic compression. Then the stress intensity factors and crack growth rate are achieved based on extended McEvily model. The doubled edged specimen under cyclic compressive loading is taken for example to illustrate the analysis procedure, including fatigue crack growth rate prediction by Artificial Neural Networks (ANN), parameters estimation method of the extended McEvily model, calculation of the stress intensity factor and numerical simulation of fatigue crack propagation. By comparing the predicted results and the experimental results, it is found that the numerical simulation of fatigue crack growth under cyclic compression based on extended McEvily model is reasonable and feasible.
Free-Span Flowlines Resistance to In-Service Fatigue Loading
Authors: Iob Francesco , Mecozzi Elisabetta , Di Vito Luigi , Darcis Philippe , Marines-Garcia Israel , Quintanilla-Carmona Hector M.
Published: October 2015

Offshore petroleum fields frequently pass over areas with uneven seafloor. In such cases the pipeline may have free spans due to depressions crossing and are subjected to complex loading spectra. A major source for dynamic stresses in free span pipelines is vortex induced vibrations (VIV) caused by steady current since wave induced velocities and accelerations will decay with increasing water depth.

The complex loading spectrum differs sensibly from the constant amplitude loading commonly adopted for qualification of the product (line pipe and its girth welds). Centro Sviluppo Materiali and Tenaris for some years are involved in the study of in-service variable amplitude fatigue loading of risers trough numerical calculations and comparison of the actual fatigue loading experienced by free span system with constant amplitude qualification typical loading. Two papers [1, 2] have been already presented in previous OMAE conferences. The present work reports a study dedicated to the free-span flow lines.

The flow line analyzed is composed by OD 273.05 mm × WT 25.4 mm pipe lying on the uneven seabed. In particular the attention is focused on the analysis of VIV and its effect on fatigue life of the line. The Ormen Lange field, located at 120 km northwest of the Mid-Norway, was selected as reference scenario for the study.

One of the most important factors influencing the pipeline response to the VIV is the free-span length. A sensitivity analysis about the influence of different parameters (free span length and fluid velocity) on system response and consequent fatigue damage has been performed.

A case study has been selected among the cases considered in the sensitivity analysis, to produce the loading spectra to be considered in a laboratory fatigue testing campaign on strip specimens.

The fatigue performance of these samples has been compared to analogous samples subjected to constant and variable amplitude loading available from previous works [1, 2] on riser systems (Steel catenary riser and Hybrid riser).
Heavy Wall Bends for Sour and Arctic-Alike Environment
Authors: Farè Stefano , Bagliani Emanuele Paravicini , Crippa Stefano , Zana Fabio , Darcis Philippe
Published: October 2015

During last decade, customers’ requirements of Line Pipes and accessories became more and more stringent. This process is led by the exploitation of fields with more severe conditions of pressure, environment and temperature. For this reason, heavy wall products (both straight pipes and bends) need to be developed.

A development program was carried out in order to satisfy more stringent requirements and higher wall thickness. The metallurgical approach to steel design aimed to improve the combination of strength and toughness and increase the control of hardness after quenching and tempering, preserving adequate weldability.

Industrial trials were performed to manufacture 60 mm thick hot induction bends in grade X65. Characterization was carried out after various post bending heat treatments (quenching, tempering and post welding).

The new low-C steel showed promising results. The full characterization of off-line Q&T bends at various locations (tangent length, transition zone, and bend body) confirmed the achievement of X65 grade, with hardness HV10 < 240, Charpy V-notch transition temperature < −60°C, Crack Tip Opening Displacement > 0.7 mm at −45 °C, and very good HIC and SSC resistance.