bluuebunny/crossref_metadata_2025 huggingface dataset:
Fatigue Reliability Assessment for Flexible Riser Armour Wires
Authors: Silva Vinícius Ribeiro Machado da , Sagrilo Luis V. S. , Vignoles Mario Alfredo
Published: October 2015

Oil and gas exploitation in regions of ultra-deep water has already been started and there is a great expectation of growth in the coming years, mainly in the region known as Pre-Salt, at Brazilian’s coast. Operators, which have the concession to exploit this region, have adopted different solutions with different configurations using rigid and flexible pipes for this initial phase. However, the last structural type mentioned shows to be much more versatile, providing attractive cost/benefit solutions to the operators, in which, only in Brazil, it is forecasted a demand about 4.000 km of flexible pipes in the next years [1]. With new challenges coming, one may ask the following question: What is the structural reliability of each failure mode of these flexible pipes? Motivated by this question, this paper has the objective to do a preliminary analysis, under the structural reliability view, of the critical failure mode for the design of flexible pipes faced in Brazil, represented by the fatigue phenomenon on metallic layers. The work assesses the fatigue reliability of the armour wires, located in the bend stiffener region, for two 6″ flexible risers configurations, free-hanging and lazy-wave. They are considered to be installed in ultra-deep water (2140m depth) and are submitted to the same external environmental loads. The fatigue reliability methodology used is based on that presented in Ref. [2] including new random variables. Sensitivity analyses are also performed for the variables that most contributes to the quantified probability of failure. Calibrated safety factors (SF) are obtained for different target failure probabilities.
Effect of the Cooling Rate on Crystallinity and Tensile Strength of Two PVDF Grades
Authors: Velloso Caroline Slikta , de Oliveira Geovanio Lima , Nascimento Christine Rabello , Costa Neto Celio Albano da
Published: October 2015

The PVDF (poly(vinylidene fluoride)) is the recommended material for pressure barrier application when the temperature is above 90 C and below 130 C (API Specification 17J). Two grades of PVDFs used in flexible raisers were processed. The grades selected were those for extrusion, but they were compression molded instead. The processing conditions were the same for each grade, from slow to fast cooling rate. The results allowed the evaluation of their performance using a simpler processing technique and, also, to observe how the mechanical properties varied with the cooling rate applied.
Fluororubber Aged Under Continuous Compression Set at Elevated Temperatures
Authors: Mello Carolina C. , Costa Marysilvia F.
Published: October 2015

Fluororubbers are cured copolymers based on fluorolefins. Their high thermal and chemical stability added to their mechanical strength lead them to be used in aggressive environments as hoses, seal elements and pipelines for transport of fluids. Studies are needed to evaluate the material behavior under an operating environment due to degradation susceptibility of general elastomers. But the most of these studies are of long duration making them unworkable. So, short term tests under operating simulated environment are required, and some models can be applied to estimate the material behavior under the work conditions at long term. In this work, specimens of a fluororubber were aged under compression in different temperatures. Arrhenius model was used to study their behavior. An increase of stress relaxation was observed by increasing temperature. Weight change and infrared spectroscopy were also employed to evaluate chemical ageing. It was verified that the association of different ageing agents such as chemical, mechanical and thermal is crucial for correct understanding of the material global behavior. Meanwhile, the complex phenomena in a material under multiple agents make it very difficult to reliably predict lifetime.
Rheological and Wall-Slip Behaviors of Polymer Based Drilling Foams
Authors: Sherif Testi , Ahmed Ramadan , Shah Subhash , Amani Mahmood
Published: October 2015

This paper present experimental study conducted on rheology of hydroxyethyl cellulose (polymer) based foams. The effects of foam quality, wall-slip, and polymer concentration on foam rheology have been experimentally investigated using a circulating flow loop. Foam quality and flow rate were varied from 50 to 80 percent and 1 to 52 L/min, respectively. To identify the existence of wall-slip, tests were performed using different diameter (13.4, 19.6 and 31.8 mm ID) pipe viscometers.

Experimental results show expected trends; pressure loss increased with increasing flow rate and reduced with increasing pipe diameter. Slight wall-slip was observed in the small diameter viscometer. However, the measurements obtained from other viscometers do not indicate wall-slip. All tested foams exhibited strong non-Newtonian behavior, which increases with foam quality and polymer concentration. The rheology of foams best fits the power-law fluid model. Applying regression analysis, new correlations have been developed to predict rheology of polymer-based foams.
The Analysis of the Extrapolation Method Used in Typical Structures of Jacket Platforms
Authors: Zhu Yifei , Fu Shixiao , Wu Jianqiao
Published: October 2015

Acquiring the hot spot stress (HSS) in dangerous points of the structure (normally the welding seams of the structure) is the foundation of the offshore platform fatigue strength design. Because of the fact that it is very difficult and unpractical to install sensors in the welding seams, the most widely used method of acquiring the HSS currently is extrapolation, a method that obtains the HSS by extrapolating from stress of distant points. In order to figure out the feasibility of the method of extrapolation as well as the best ways to implement extrapolation in real practice, it is important to carry out numerical calculation of welded tubular joints in advance. To study the tubular joints, the finite element method (FEM) is the most widely adopted approach. In previous studies, shell elements are utilized to simulate tubular joints instead of solid elements concerning the difficulty. However, shell element simulation merely simulates the mid-surfaces of the tube walls so that shear stress in the direction of tube thicknesses are ignored, making the calculation of the stress concentration factor (SCF) inaccurate. In this study, the recommended ways of simulating the tubular Y- and T-joints are displayed and then the comparison of calculation results between different weld type, different mesh situations as well as different elements are given in order to bring up advice on numerical calculation for the study of extrapolation. The results of numerical calculation show that the extrapolation results are more accurate when we only consider the change of parameter α (chord length-to-chord radius ratio) and also, it is suggested to do the fitting in the area of 2t-4t away from the welding seam. These suggestions are verified by applying the method of extrapolation to a real jacket platform, which turns out that the fitting degree of extrapolation is very pleasant.
Characterization of Stress-Induced Residual Magnetic Field in Ferromagnetic Steels
Authors: Bao Sheng , Lin Li , Zhang Da , Fu Meili
Published: October 2015

In this research, tensile tests of three different steels were carried out to characterize the variation of the residual magnetic signals. To reduce the impact of initial magnetic field, all of the specimens were demagnetized before loaded. It was observed that the variations of magnetic signals along the surface of these steels demonstrate different characteristics both in the elastic and plastic stages. In the elastic stage, the magnetic field variation of Q235 and 45# steels had a nonlinear relationship with the applied stress and a simple linear relationship between stress and magnetic field appeared in Q345 steel. In the plastic stage, the magnetic field variation of Q235 was very complex and the magnetic field variations of Q345 and 45# steels demonstrated a process of systematic evolution. In addition, there existed a local dent of the magnetic curve in the necking position of the sample. When the sample was finally ruptured, one may evaluate the fracture position according to the features of the magnetic curve. Possible reasons were given for the different characteristics of magnetic field variations in different steels.
Zero Speed Rankine-Kelvin Hybrid Method With a Cylinder Control Surface
Authors: Li Hui , Lizhu Hao , Ren Huilong , Chen Xiaobo
Published: October 2015

The solution of hydrodynamic problem with forward speed still has some well-known problems such as high oscillation and slow convergence of the wave term when using a moving and oscillating source as the Green function. Recently, Ten and Chen (2010) has come up with a new method to benefit the merits of both the Rankine source and moving and oscillating source by taking a hemisphere as the control surface which separates the fluid region into two domains, but some troubles have been induced in the process of solution. Therefore, in this paper, a cylindrical surface instead of a hemisphere is selected to be the control surface to make the solution easy, and in this method, the control surface isn’t divided into panels. In the interior domain near the ship, the Rankin Green function is used to simplify the calculation. In the exterior domain some distance from the ship, there is no panels representing the free surface by using the Green function which satisfy the free surface boundary condition. The whole fluid region matches by the condition that the velocity potentials and their normal derivatives in the interior domain and exterior domain are equal on the control surface separately. In this paper, we have validated the Rankine-Kelvin hybrid method is applicable by adopting it to solve the zero speed problem in this work.
Analysis on the Mechanical Properties of the Plastic Pipe Reinforced by Cross Helically Winding Steel Wires (PSP) Under Internal Pressure
Authors: Xiong Haichao , Bai Yong , Qiao Hongdong , Ruan Weidong
Published: October 2015

This paper describes the analysis of the mechanical behavior of the plastic pipe reinforced by cross helically winding steel wires (PSP) under pure internal pressure. PSP is a new kind of composite pipe developed rapidly in China recently and it consists of an inner high-density polyethylene (HDPE) layer, several steel wire layers over wrapping the liner and an outer polyethylene coating. To investigate the mechanical properties of steel wire layers, the elastic parameters of the composite monolayer plate are considered as transverse isotropic and derived based on Halpin-Tsai Equations. The stress and strain functions of each layers are obtained using anisotropic elastic mechanical theory and the unknown constants are determined by equilibrium equations and interface conditions. Using ABAQUS, a finite element model (FEM) is established to study the mechanical behavior and failure mode. Results derived from the theoretical method and FEM are presented and compared. Simplified engineering formula of burst pressure is also obtained. The effect of winding angle on PSP is also discussed by parametric analysis. Values of burst capacity predicted from the theoretical method, FEM and simplified engineering formula are in great agreement with the experimental results.
Preliminary Design of Floating Point Absorber Offshore Rio de Janeiro
Authors: Shadman Milad , Estefen Segen F. , Castillo Claudio Alexis Rodriguez , Lourenço Marcelo I.
Published: October 2015

The Rio floating point absorber (FPA) is designed for a reference site located near an island offshore Rio de Janeiro. According to the reference site characteristics, a two-body floating point absorber concept design is chosen to convert ocean wave energy into electrical power. An innovative procedure aiming at finding an optimal shape adapted to predefined wave climate conditions, using the Design of Experiments (DOE) method, is applied. A simple linear damper model is used to represent the Power Take-Off (PTO) mechanism. The optimization procedure is divided into Buoy and support (spar/plate) steps, so the optimized buoy is determined first and then a proper support is determined to reach a satisfactory two-body FPA system. The nonlinearities are not considered in this study and linear Numerical models are developed using AQWA/ANSYS and Minitab software in frequency domain. Finally, a preliminary optimized model of the two-body FPA is determined in accordance with the particular sea site information of the Rio de Janeiro.
Analysis of Wind Energy Potential With a Mobile Floating Structure Around Sulawesi and Maluku Islands of Indonesia
Authors: Mahmuddin Faisal
Published: October 2015

The present study uses Quikscat data to assess the offshore wind energy potential at the Eastern part of Indonesia, around the Sulawesi and Maluku Islands. Weibull distribution with two parameters is used to represent the characteristics and distribution of the wind model. In order to confirm the accuracy of computations, statistical and numerical methods are used to compute the Weibull parameters which are regression analysis, maximum likelihood method and moment method. The obtained power density is used to draw monthly wind power maps for the sea areas around the islands. The maps are used to determine the most suitable location of a mobile conversion system every month. Moreover, by assuming that a NM72/2000 NEG Micon is installed, Monte Carlo Simulation is performed to determine the expected power percentage produced by the system every month.
Numerical Modelling of the Aerodynamic Characteristics of a Floating Offshore Wind Turbine Under Yawed Rotor Conditions
Authors: Sant Tonio , Cuschieri Kurt
Published: October 2015

The aerodynamic characteristics of floating wind turbines in yaw are more complex than those of turbines with fixed foundations as a result of the floating platform dynamics under wave action. This paper applies numerical simulation tools to investigate the time varying rotor thrust and shaft power characteristics of offshore floating wind turbines (OFWTs) under different rotor yaw angles and regular sea wave conditions. The study is based on the NREL1 5 MW baseline OFWT installed on the MIT2 tension-leg platform (TLP). Both the wind speed and rotor speed are maintained constant throughout the analysis, though different sea wave heights and periods are considered. The predictions from three different aerodynamic models are compared. These include the Blade-Element-Momentum (BEM) and the General Dynamic Wake (GDW) methods and a higher fidelity Free-Wake Vortex model (FWVM) that is capable of modelling the unsteady skewed helical wake development of the yawed rotor. Initially the motions of the OFWT under both axial and yawed rotor conditions are estimated in a time domain using FAST, an open source software developed by NREL. These motions are then prescribed to WInDS, a FWVM developed by the University of Massachusetts Amherst, to determine the aerodynamic rotor thrust and power as a function of time. The three models have consistently shown that the TLP motion under the modelled wave states exhibits a negligible impact on the time-averaged rotor shaft thrust and power of the yawed rotor. On the other hand, the cyclic component of rotor thrust and power are found to be significantly influenced by the wave state at all yaw angles. Furthermore, significant discrepancies between the predictions for this cyclic component from the three models observed.
Applicability of Current Remotely Operated Vehicle Standards and Guidelines to Autonomous Subsea IMR Operations
Authors: Hegde Jeevith , Utne Ingrid Bouwer , Schjølberg Ingrid
Published: October 2015

This paper employs a combination of literature review and case study methodology to assess the gap between current remotely operated vehicle (ROV) standards and future autonomous IMR operation requirements. With advent of autonomous subsea and underwater vehicle systems, current ROV standards and guidelines may not offer the same benefit in designing and setting guidelines for safe autonomous operations. The reasons for this claim are two-fold. Firstly, the literature review shows that existing requirements in the ROV standards lack specifications related to autonomous subsea interventions. Secondly, the results from the case study demonstrates existence of knowledge and technology gaps, which pose challenges in development of future autonomous IMR operations.
Wave Steepness and Rogue Waves in the Changing Climate in the North Atlantic
Authors: Bitner-Gregersen Elzbieta M. , Toffoli Alessandro
Published: October 2015

Wave steepness is an important parameter not only for design and operations of marine structures but also for statistics of surface elevation as well as occurrence of rogue waves. The present study investigates potential changes of wave steepness in the future wave climate in the North Atlantic. The Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) uses four scenarios for future greenhouse gas concentrations in the atmosphere called Representative Concentration Pathways (RCP). Two of these scenarios with radiative forcing of 4.5 and 8.5 W/m2 by the end of the 21st century have been selected to project wave conditions in the North Atlantic. The analysis includes total sea, wind sea and swell. Changes of wave steepness for these wave systems are shown and compared with wave steepness derived from historical data. Long-term probability description of wave steepness variations is proposed. Consequences of changes in wave steepness for statistics of surface elevation and generation of rogue waves are demonstrated. Uncertainties associated with wave steepness projections are discussed.
Manoeuvrability in Adverse Conditions
Authors: Shigunov Vladimir
Published: October 2015

Slow steaming and regulatory drive towards more energy efficient ships have raised a problem of ensuring sufficient manoeuvrability of ships under adverse weather conditions when installed power is reduced. This paper discusses possible criteria for sufficient manoeuvrability in adverse conditions and proposes practical assessment procedure and examples of its application. Further, the paper outlines necessary developments.
The Tele-Operation Experiment of the Hybrid Remotely Operated Vehicle Using Satellite Link
Authors: Takahashi Takashi , Yoshimura Naoko , Akaishi Akira , Katayama Norihiko , Toyoshima Morio , Kadowaki Naoto , Ishibashi Shojiro , Fukuda Tatsuya , Yoshida Hiroshi
Published: October 2015

Communication via satellite is the only method for communicating between the ocean and land. However, present commercial satellites cannot provide sufficient bandwidth to transmit the requisite volume of data. The National Institute of Information and Communications Technology (NICT) and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) conducted broadband satellite communication experiments with the Wideband Inter-Networking engineering test and Demonstration Satellite (WINDS). Using WINDS, the tele-operation of a hybrid remotely operated vehicle (HROV), Otohime, was also carried out successfully.
Artificial Neural Networks Applied to Flexible Pipes Fatigue Calculations
Authors: Chaves Victor , Sagrilo Luis V. S. , Silva Vinícius Ribeiro Machado da , Vignoles Mario Alfredo
Published: October 2015

Flexible pipes play an important role in offshore oil exploitation activities nowadays. However, time-domain flexible pipe irregular wave dynamic analyses are extremely computational expensive. One of the various existing methods to reduce computational costs in dynamic analyses is the hybrid methodology that combines dynamic Finite Element Analyses (FEA) and Artificial Neural Networks (ANN). This paper presents a novel application of this methodology for flexible pipes fatigue calculations. In order to decrease computational cost involved in these analyses the proposed hybrid methodology aims to predict tension and curvatures in the bend stiffener region. Firstly using short FEA simulations to train the ANN, and then using only the ANN and the prescribed floater motions to get the rest of the response histories. With the predicted tension and curvatures, a local analysis is applied to calculate stresses in tensile armour wires and the corresponding fatigue lives. To evaluate the optimal ANN a sensibility study is developed for some key parameters as: training time length, neurons on hidden layer and delay length. A full FEA is also performed in order to evaluate the accuracy of the proposed hybrid methodology, comparing both full FEA flexible pipe fatigue results and those obtained using the hybrid methodology.
New Semi-Submersible Floating Wind Turbine for South China Sea
Authors: Li RongFu , Qi Xiaoliang , Gao Wei , Li Hui
Published: October 2015

With the demand of renewable energy due to the pressure from environmental pollution and global warming, the wind industry has been growing rapidly over the past decades during which the offshore wind innovation is becoming more and more attractive because of vast offshore wind resources.

In this paper, a novel tapered-column semi-submersible floating foundation with economical mooring system is developed to support 6MW wind turbine in South China Sea. The coupled aero-hydro-servo-structural analysis is done in GH-Bladed software to obtain the global dynamic response of the whole floating wind turbine. By combining the derived wind loads with the wave and current induced loads, the global performances of the foundation and attached mooring system under both extreme conditions and normal operation conditions are analyzed in AQWA software. The result reveals that the floating foundation complies with the design standard and meets requirements of wind turbine.

This novel patent-pending floating foundation with tapered columns is proved as a successful design with high material efficiency and good seakeeping performance. Also a reliable and efficient design methodology of floating foundation based on optimal cost is provided in this paper which can be used as design reference of floating foundations.
Directional Stability of a Neutrally Buoyant Joukowsky Foil
Authors: Schultz William W. , Bapat Shounak Vinayak , Webb Paul W.
Published: October 2015

We examine the directional stability of a two-dimensional neutrally buoyant foil in an ideal fluid. To take advantage of the greatest simplicities we consider a symmetric Joukowsky airfoil and use the method of images. J.N. Newman in Marine Hydrodynamics [1] states, “For a nonlifting body with a pointed tail ... the vessel is always unstable. This situation results from the destabilizing effect of the Munk moment; in general an elongated nonlifting body will be stable only when moving broadside to the flow. Directional stability of a streamlined body depends on a tail fin, as in the case of an arrow or wind vane.” While the Munk moment on an ellipse leads to broadside stability, it does not have a Kutta condition. This Kutta condition causes many challenges to the analysis and simple computations. A symmetric Joukowsky has a “tail fin” and it is a lifting body when inclined to the flow. Instability is prevalent for many cases. We show that the stability depends on how the Kutta condition and the wake are implemented and indicate how stability may be increased by mass redistribution or manipulation of body motion. We demonstrate this with some simple experimental demonstrations and computations.
The Underwater Laser Ranging for Dynamics Measurement Around Subduction Zone
Authors: Yoshida Hiroshi , Ishibashi Shojiro , Sakaguchi Hide , Saito Takashi , Denou Motoi , Tashiro Masatoshi , Tanaka Kiyotaka , Suzuki Minoru
Published: October 2015

An underwater laser ranging system to capture microscopic fluctuations in relative plate motion around subduction zone has been developed since 2010. We believe that direct detection of the fluctuations resulted from plate motion suggests the degree of interplate mechanical instability for long-term prediction of oceanic intraplate earthquake.

In April 2011, sea trial using the first prototype was carried out in shallow water zone in Okinawa. Distance measurements could be performed in the distance of 10 meters but results included large error variation of 0–10 cm. To improve measurement resolution and accuracy of the sub-millimeter fluctuations, we have developed the second prototype of laser ranging system based on the first one.

The main part of the system consists of a transmitting unit (Tx) and a receiving unit (Rx). One of the units is composed of a transparent acrylic cylindrical pressure hull (PH), a main PH, a battery pack, and sensors, which are installed on an aluminum alloy frame. The transparent PH of Tx is equipped with a 1 Watt semiconductor blue laser, a modulator and a driver which are set on a horizontal turntable with elevation adjustment. Its Rx has an avalanche photo diode as detector and a demodulator on a same type turntable. A controller and an optical communication device are installed in each main PH. The Tx is connected with the Rx via thin optical glass fiber to transmit reference signal.

We carried out a sea-trial in Okinawa by the second prototype in February 2014. We received optical signal at distance between the Tx and the Rx of up to 20 meters. The ranging was performed at 10 meters and measurement raw data errors were within a range of millimeters. On the other hand, automatic optical alignment at 20 meters was completely failed. These results show that measurement accuracy is closer to a goal but system completion is away from the goal. We need review not only the algorithm but also optical hardware of the alignment.
Comparison of AQWA, GL Rankine, MOSES, OCTOPUS, PDStrip and WAMIT With Model Test Results for Cargo Ship Wave-Induced Motions in Shallow Water
Authors: Gourlay Tim , von Graefe Alexander , Shigunov Vladimir , Lataire Evert
Published: October 2015

A benchmarking study is carried out concerning wave-induced ship motions in shallow water, predicted with commercially available codes AQWA, GL Rankine, MOSES, OCTOPUS, PDStrip and WAMIT. Comparison is made with experiments for three cargo ship models tested at Flanders Hydraulics Research. The same IGES models of the ship hulls were used in all codes to ensure consistent representation of the model geometry. The comparisons may be used to assess the suitability of each code for zero-speed applications such as berthed ship motions and under-keel clearance, as well as forward-speed applications such as under-keel clearance in navigation channels. Another, quickly developing, application area that requires analysis of seaway-induced ship motions in shallow water, is analysis of motions, accelerations and loads on cargo transport, installation and service vessels for offshore wind parks.
Energy Harvesting Using Flapping Dynamics of Piezoelectric Inverted Flexible Foil
Authors: Gurugubelli Pardha S. , Jaiman Rajeev K.
Published: October 2015

This paper presents a numerical study on the self-induced flapping dynamics of an inverted flexible foil in the context of energy harvesting using piezoelectric elements. The inverted foil considered in this study is clamped at the trailing edge and the leading edge is free to oscillate. To simulate the nonlinear flapping dynamics of an inverted flexible foil, a high-order coupled fluid-structure solver based on the combined field with explicit interface (CFEI) has been developed. Additionally, a simplified piezoelectric model has been presented to determine the electric energy that can be harvested through flapping. The coupled solver is validated over a flexible foil fixed at the leading edge and trailing edge free to oscillate. A systematic study on the flapping response of an inverted flexible foil has been performed for a wide range of non-dimensional bending rigidity for a fixed Reynolds number of 1000 and mass ratio of 0.1. As a function of decreasing bending rigidity, four flapping regimes have been observed: (i) fixed-point stable, (ii) inverted limit-cycle oscillations, (iii) deformed flapping and (iv) flipped flapping. The inverted limit-cycle oscillations are characterized by low-frequency large amplitude oscillations which generate O(103) times greater strain energy than a flexible foil fixed at the leading edge, which has a profound impact on the development of ocean current based energy harvesting devices.
Experimental Study on a Motion of “Underwater Platform” Including Hydro-Elastic Deformation in Waves
Authors: Murai Motohiko , Haneda Ken , Yamanoi Jun , Abe Yuta
Published: October 2015

A new type of floater for floating offshore wind turbine (FOWT) was proposed. The floater, named an “underwater platform”, aims at high economic efficiency of energy generation of floating wind farm. The underwater platform is a large scale submerged structure which has small water plane area and can support several wind turbines. It is expected that the platform has small motion characteristics in waves because of its small water plane area, and it contributes for FOWT to generate energy safety.

In this study, the feasibility and usefulness study about the platform was carried out through experiments and numerical simulations. The first experiment was conducted with partial rigid model of the platform to verify the feasibility. From the experiment, it was confirmed that the model has small motion characteristics in waves. The experimental results were compared with numerical simulations of potential theory and they were well matched. Besides, the coupling analysis with aero-hydro dynamics was also carried out and it was confirmed that the stability of the platform was enough in steady wind condition.

The second experiment was conducted with elastic body model to study the elastic deformation of the platform in waves. From the experiment, it was confirmed that the deformation is small when the draft was 250mm (50m in the actual model).
Comparison of Experimental Data of a Moored Multibody Wave Energy Device With a Hybrid CFD and BIEM Numerical Analysis Framework
Authors: Nematbakhsh Ali , Michailides Constantine , Gao Zhen , Moan Torgeir
Published: October 2015

In the present paper, a hybrid Computational Fluid Dynamics (CFD) and Boundary Integral Element Method (BIEM) framework is developed in order to study the response of a moored Multibody wave Energy Device (MED) to a panchromatic sea state. The relevant results are the surge and heave responses of the MED. The Numerical Analysis Framework (NAF) includes two different models; the first model uses Navier-Stokes equations to describe the flow field and is solved with an in-house CFD code to quantify the viscous damping effect, while the second model uses boundary-integral equation method and is solved with the tool WAMIT\SIMO\RIFLEX. By studying the free decay tests with the Navier-Stokes based model, the uncoupled linear and quadratic damping coefficients of the MED in surge and heave directions are calculated. These coefficients are given as input to the WAMIT\SIMO\RIFLEX model and the responses of the MED to different wave conditions are determined. These responses are compared with the experimental data and very good agreement is obtained. The MED responses calculated by the presented NAF have been obtained in connection with a hydrodynamic modeling competition and selected as one of the numerical models, which well predict the blind experimental data that were unknown to the authors.
The Influence of Drilling Fluid Rheological Properties on Primary Solids Control
Authors: Saasen Arild , Hodne Helge
Published: October 2015

Throughout the last decades, the design and performance of the primary solid control devices have changed significantly. Some five decades ago, the circular motion shakers dominated the marked. These shakers operated by sending the drilling fluid downhill a vibrating screen. Thereafter appeared the elliptical motion or linear motion shakers where the cuttings particles were vibrated upwards a tilted screen. Onto these shakers, the use of double screen decks and finally triple screen decks became common. Within the last years also the vacuum devices appeared.

Throughout the last two decades, there has been an effort to increase the g-forces on these shakers and the industry seems to have preferred the high g-force devices recently. Laboratory studies, however, has indicated that the very high g-forces are not necessary to perform proper solids control. Instead, different vibration modes interacts with the gel structure of the drilling fluid and remove yield stresses. Hence, the fluid becomes mobile for flow through the screen.

Flow through screens is strongly dependent on the extensional properties within the drilling fluid rheology. Drilling fluids with high extensional viscosity seldom has a very strong gel structure, and are generally not affected equally much by vibrations. This explains why solids control is more difficult using a KCl/polymer water based drilling fluid than if using an oil based drilling fluid.

This article focuses on describing how the drilling fluid rheological properties alter during primary solids control. It is based on theoretical analysis, rheological studies in the laboratory and finally on practical applications in two recent exploration drilling operations. The solids control efficiency resulting from using different screen configurations is outside the scope of this article, as this topic requires a higher focus on separation technology.
Numerical Simulations for the Response of a Submerged Horizontal Cylinder Moored in Waves: COER Hydrodynamic Modeling Competition
Authors: Lim Dong-Hyun , Kim Taeyoung , Kim Yonghwan
Published: October 2015

The hydrodynamic behavior of a submerged horizontal cylinder moored in waves was studied through numerical methods as a participant of the COER Hydrodynamic Modeling Competition. The potential theory with additional viscous damping has been used to model the problem. Three different simulation cases have been constructed to identify (i) the general behaviors of the cylinder subjected to the input wave, (ii) the effect of the second-order hydrodynamic forces, and (iii) the effect of exact wetted surface issue. Computational results were compared to the experiment, and a reasonable degree of accuracy has been confirmed.
Numerical Simulation on Hydrodynamic Behaviors of Ducted Propeller in Yawing Motion of an Underwater Vehicle
Authors: Wu Jiaming , Zhang Chengwei , Ye Zhijian , Xu Ying , Feng Weiwen , Liang Huiqun
Published: October 2015

A practical approach to simulate hydrodynamic performance of ducted propellers attached in an underwater vehicle under the influence of flow field of the vehicle is proposed, hydrodynamic characteristics of the propeller when the vehicle in a dynamic yawing motion is studied numerically. In the research, 3D geometric models of the duct, propeller and underwater vehicle are first constructed according to their geometrical features. Computational fluid dynamics (CFD) technique based on the finite volume method and multi-sliding mesh technique are applied to solve the Navier-Stokes equations which govern the fluid motions around the duct, propeller and underwater vehicle when the vehicle are in a yawing motion. These equations are solved numerically with the CFD code FLUENT. With the proposed numerical simulation approaches, the hydrodynamic phenomenon of thrusts generated from the ducted propellers in the vehicle system under the flow field influence of the vehicle’s yawing motion are analyzed. Results of our numerical simulation indicate that the influence of flow field caused by the underwater vehicle on the thrusts of the ducted propellers is not negligible; when studying the thrust characteristics of a ducted propeller in an underwater vehicle system, the thrust nature of the propeller can only be evaluated objectively on the condition that the vehicle and the ducted propeller are combined together into an integrated system, and the numerical simulation are conducted in such an integrated system.
Research on the Dynamic Response of Stiffened Plates Laterally Impacted by Falling Weight Impact Tester
Authors: Liu Kun , Zhang Yanchang , Wang Zili
Published: October 2015

A proper numerical simulation method is developed to simulate the structure impact problems that consider the effect of strain rate. The high-speed tensile tests are carried out to obtain the strain-stress relations of different strain rates, and used as material inputs to analyze the dynamic response of laterally impacted stiffened plates. The simulation results are compared with falling weight impact experiment, and good agreements are obtained. The strain-stress relations obtained from high-speed tensile tests and Cowper-Symonds constitutive (CS) model are compared. It shows that curves gotten from CS model are higher than those gotten from high-speed tensile test; with the strain rate increasing the distance will became obverse, and the validation of the numerical simulation is verified and can fit the experiment result very well.
Optimal Control Parameter Determination for an Oscillating Body Type Wave Energy Converter for Japan
Authors: Kamio Takeshi , Iida Makoto , Arakawa Chuichi
Published: October 2015

The purpose of this study is to determine the optimal parameters for a control strategy of an oscillating body type wave energy converter (WEC) for a WEC development and demonstration project in Japan. We plan to use a reactive control strategy for calm sea states, because wave heights in the seas near around Japan is about 1 m in summer. We also developed a combined and tuned control strategy with both reactive and resistive controls, in which the control parameters are changed to sea states. The proposed control system achieves both better performance and safer operation. In this numerical study, we determine the control parameters for the sea states by the time-domain simulation using the Newmark–β method.
Numerical Prediction of the Hydrodynamic Performance of a Horizontal Tidal Turbines
Authors: Liu Cheng , Hu Changhong
Published: October 2015

Tidal current energy is one of the most promising renewable energy resources. The prediction of the hydrodynamic loads and power efficiency are the critical issues for verifying the new designs. Besides, Optimization of turbine arrangement is important for a tidal turbine farm. The hydrodynamic behavior of a turbine operating in the wake of an upstream turbine needs to clarify. In this paper we present a CFD approach in which the CFD library of OpenFOAM is utilized for prediction of the performance of a three bladed horizontal axis tidal turbine (HATT) in a test tunnel environment. The Reynolds Average Navier Stokes (RANS) equation with Shear Stress Transport (SST) turbulence model is applied. The steady-state solver is tested for present numerical simulation. The Multi Reference Framework (MRF) method is adopted for dealing with grid relative rotation. Turbulence models effects and the mesh generation are well described. The resultant power and thrust coefficients of these simulations are compared with experimental results at various tip speed ratios (TSRs).
Steel Lazy Wave Riser Configuration for Turret Moored FPSO With Disconnectable Turret in Deepwater
Authors: Karunakaran Daniel , Subramanian Sankar , Baarholm Rolf
Published: October 2015

Recently turret-Moored FPSOs have been used in many deep water developments worldwide, with consideration of disconnectable turrets for harsh environment applications. This trend makes the interactions between FPSO and risers system more important. Further, Steel Lazy Wave Risers (SLWR), which is a compliant variant of the mostly commonly used Steel Catenary Risers (SCR), is becoming an attractive riser option.

The paper provides a review of the various riser systems that can be considered for turret-moored FPSOs, and specific emphasis on Steel Lazy Wave Risers. A detailed case study of Steel Lazy Wave Risers for a typical turret moored FPSO with disconnectable turret is presented. This system is described in terms of design and functionalities, the fabrication and installation methods are presented. The case study shows clearly that SLWR are an attractive alternative to be used for FPSO with disconnectable turret and is very efficient to fabricate and install in a very cost effective manner.

Pros and Cons for SLWR are discussed, with consideration of the particular challenges of turret-moored FPSOs with large floater motions, hang-off geometry constraints at turret, hang-off loads, riser interferences, risers pre-installation, and turret disconnection constraints.
Ship Roll Behaviour in Large Amplitude Beam Waves
Authors: Liang Jiaming , Lin Zhiliang
Published: October 2015

In this paper, the Homotopy Analysis Method (HAM) is applied to obtain high accuracy series solutions of roll motions of a ship, which encounters a nonlinear wave of large amplitude. Comparisons are made between roll responses in linear and nonlinear beam waves with identical wave slope and frequency. Furthermore, Floquet theory is applied to analyze the stability of HAM series solutions. Besides that, numerical simulation is used to verify the analytical solution and study the behaviors of the system under disturbance. All the results demonstrate that the proposed scheme is an effective analytic technique to study nonlinear ship rolling equation, and the stability analysis reveals the significance of researching ship roll motion in large amplitude nonlinear wave.
Probabilistic Design Load Method for the Northern Sea Route
Authors: Tõns Tõnis , Ralph Freeman , Ehlers Sören , Jordaan Ian J.
Published: October 2015

A probabilistic design method allows us to link statistical data from the operational area of the vessel with design loads providing the availability for more precise safety level assessment, which is important to ensure safe and sustainable ship transit in ice covered waters. Statistical design methods are well used for open water using spectral analysis. Wave induced loads are estimated by linking statistical load parameters to the sea state parameters. Statistical methods to estimate ice-induced loads are also available, however, current Polar Class rules are not considering probabilistic methods for determining ice-induced loads. This paper shows how developed probabilistic methods can be used for the design of ice going ships, especially for ships operating along the Northern Sea Route (NSR). The method presented in this paper will combine available data from full-scale measurements performed in the Arctic with ice conditions defined using historical data from satellite sources. The full-scale measurements are used to develop the parent distribution, which forms the basis for the extreme load prediction based on the number of excepted interactions along the NSR. Satellite data from history will be used to model ice conditions, e.g. ice type and ice concentration, along the route.
A Human Factors Analysis Method for Marine Accident Evolution Using HFACS-EI Model
Authors: Wei X. Y. , Wang Y. , Yan X. P. , Wu B. , Tian Y. F.
Published: October 2015

The study on marine accidents has been a keen subject in ocean engineering for long. This paper develops an HFACS-EI Framework based on the original HFACS Framework. The framework is further combined with Cognitive Map (CM) in marine accident evolution analysis which is divided into four stages. A hybrid accident analysis approach combining HFACS-EI Framework and CM not only provides classification of human factors under six levels, but also judges if there is a positive relation between every two human factors. This paper further analyzes the positive relations between human factors at different accident evolution stages and specifies what human factors are of more significance in a certain accident phase. A serious marine accident of capsized ship is chosen as a typical case to illustrate how the hybrid approach is applied in practice. Consequently, the proposed method can effectively identify and analyze human factors under six levels at different accident evolution stages and help to reduce human errors in marine accidents.
Reliable, Low Footprint and Cost-Effective Monitoring of Wellhead Loads Using Autonomous IMUs for Fatigue Estimates
Authors: Authen Kristian , Grytøyr Guttorm , Melbø Hallgeir
Published: October 2015

Wellhead systems in the North Sea are frequently subjected to large bending loads, due to shallow waters, heavy seas and semi-submersible drilling rigs. This makes fatigue of wellhead systems a challenge.

The fatigue estimates of such wells are often conservative when based on global FE riser simulations. To reduce the conservatism from such simulations, measurements of the actual wellhead loads have been performed on certain occasions. This is often a costly and intricate process that usually require a subsea cable from the rig. This paper presents an alternative method for measuring WH loads by the use of autonomous motion sensors (IMUs) on the BOP and lower end of the drilling riser.

Measured inclinations from the IMU on the riser are used to capture the loads acting from the riser onto the BOP. The inclinations from the sensor on the BOP are used to capture the dynamic response of the BOP and well system. The combination of the measured excitation load and the measured dynamic behavior, makes it possible to reliably estimate the WH bending moment, without the use of riser simulations.

The accuracy of the proposed methodology is demonstrated in a FE riser simulation. The model acts as a controlled environment where both input parameters and WH loads are known. The sensor data is extracted from the analysis at the relevant locations, run through the proposed methodology and then compared with the WH loads in the model.

As a final verification, the method is tested on data from an actual measurement campaign where both IMU and strain gauge measurements are available. The WH loads will be calculated based on the proposed method and IMU data, and the results will be compared to the data from the strain gauge based load sensors.
Numerical Simulation of Ice Ridge Gouging
Authors: Liu Lei , Bailey Eleanor , Sarracino Robert , Taylor Rocky , Power Colin , Stanbridge Christopher
Published: October 2015

In coastal regions throughout the Arctic, the seabed is frequently scoured or gouged by sea ice ridges and icebergs. This presents an environmental hazard to pipelines or subsea infrastructures operating in the area and therefore a greater understanding of these processes is needed. This paper describes a three dimensional (3D), numerical model that was developed to simulate the failure behavior of a ridge keel as it interacts with the seabed. The simulation was conducted in Yade, an open-source code, which uses the Discrete Element Method (DEM) to model particle motions. The ice blocks in the ridge keel are modeled as spheres, which are initially bonded to contacting blocks via freeze-bonds. A Cohesive Frictional Model (CFM) which has cohesive bonds in tension and shear was used to simulate the freeze-bonds between ice blocks. In addition to normal and shear bonds, the model features springs which resist compression, shear, bending and torsion. Once the bonds are broken the material is assumed to behave like a Mohr-Coulomb material with a constant friction angle. Since the main focus of this paper is the failure behavior of the keel, the seabed is simplified as being rigid. Numerical simulation is compared with data collected from the Pipeline Ice risk Assessment and Mitigation (PIRAM) test program.