bluuebunny/crossref_metadata_2025 huggingface dataset:
Simplified Strength Reliability and Integrity Analysis of TTRs
Authors: Mousavi Mir Emad , Upadhye Sanjeev , Haverty Kevin
Published: September 2014

The design of riser systems can be improved if structural reliability methods are used to assess their safety and integrity and confirm that such design meets a target annual probability of failure. TTRs are typically multi–bore assemblies involving several sub-assemblies. The failure of any of the components of a TTR under extreme or service environmental conditions can lead to an immediate failure of the entire assembly and impose a direct risk of damaging the wellheads, conductors, casing and tubing hangers, or other subsea equipment, because they are installed directly on top of the wellhead. However, the actual strength safety of the TTR cannot be examined unless after it is installed and examined under extreme events. Because of the numerous uncertainties associated with the design of TTRs, a probabilistic approach based on structural reliability methods can account for many of those uncertainties and serve as a basis for their reliable and cost-effective design. In turn, a comprehensive reliability assessment of a TTR requires extensive analysis that is considerably more complex and time consuming compared to a conventional deterministic-based analysis. This paper presents a probabilistic-based simplified methodology for the strength reliability assessment of TTR systems. In this method, marginal values on some uncertain model inputs are considered similar to the conventional analysis methods but, some key random variables related to environmental demands and component capacities are considered with their associated probability distributions. As a result, this method can be used to estimate the minimum level of safety of the TTR under extreme events. Additionally, results of the proposed method are discussed for integrity analysis and integrity-based optimal design of the TTR system, which compare the safety of the TTR components and estimate the component Optimality Factors for improving the design integrity and meeting a target minimum annual probability of failure.
Numerical Simulation of Short Duration Hydrodynamic Impact
Authors: Fu Thomas C. , O’Shea Thomas T. , Brucker Kyle A. , Judge Carolyn Q. , Ikeda Christine M. , Wyatt Donald C. , Dommermuth Douglas G.
Published: September 2014

Numerical simulations of wedge impact experiments, undertaken by the Naval Surface Warfare Center, Carderock Division, NSWCCD, and more recently by the United States Naval Academy, USNA, Hydromechanics Laboratory, were performed using the computational fluid dynamics code Numerical Flow Analysis, NFA, to assess its capabilities in simulating the short duration hydrodynamic loading associated with free-surface impact. NSWCCD performed experiments using drop heights of 15.24 cm (6 in) and 25.4 cm (10 in), while the Naval Academy used drop heights of: 7.94, 12.7, 15.88, 25.4, 31.75, 38.1, and 50.8 cm (3.125, 5.0, 6.25, 10.0, 12.5, 15.0, and 20.0 in), measured from the keel of the wedge to the calm water surface. Simulations and comparisons were made at heights of 15.24 cm (6 in) and 25.4 cm (10 in) with the NSWCCD data, and 12.5 inches for the USNA data providing for a detailed examination of NFA’s ability to simulate and predict short duration hydrodynamic impacts.
Probabilistic Performance Assessment of Fiber Optic Leak Detection Systems
Authors: Aljaroudi Alireda , Khan Faisal , Akinturk Ayhan , Haddara Mahmoud
Published: September 2014

Leak Detection Systems play a major role in enhancing reliability and operability of oil and gas pipelines. They have the functional capabilities to detect, locate and quantify leaks before they can cause drastic effects to environment and operation. The performance of Leak Detection Systems is typically affected by three different failures that have severe consequences, namely, delayed detection, missed detection and false detection of a leak. These failures pose a financial burden on operating companies. Missed detection leads to oil spill and exposes operating companies to financial risk and destroyed image while false detection results in unnecessary deployment of personnel and equipment. To insure operation continuity and maintain safe environment, Leak Detection Systems should be assessed at regular basis. To fulfill this need, a probabilistic performance assessment scheme based on limit state approach for Fiber Optic Leak Detection System (LDS) has been developed. The inherent uncertainties associated with leak detection and reporting capabilities are modeled to determine the LDS detection failure probability that combines two failure events, missed detection and delayed detection. Moreover, the probability of false detection is derived in terms of the lowest detectable change, the threshold. These three parameters establish the basis for an overall assessment scheme that can be used at any time to provide an up to date assessment about the Leak Detection System. The results will serve as the basis for deciding the actions that need to be taken to upgrade, repair or replace the system components or the system as a whole. The proposed assessment scheme has been applied to a case study to demonstrate its usefulness and feasibility.
Experimental Study of the Effects of Different Floating Breakwater on Wave Absorbing
Authors: Zhou Lilan , Chen Keqiang , Zhai Shihong , Niu Zhao , Hu Xiaoming
Published: September 2014

As the development of ocean engineering, safety construction is becoming a significant aspect that attracted more and more attention. The general aims of this paper were to present the effects of different floating breakwater on wave absorbing and provide a basis for the design of floating breakwater of an offshore project. Three different kinds of floating breakwater were studied; they are soft wall-sided pontoon, solid wall-sided pontoon and a circular cross-section breakwater filled with water. Various factors including wave period, wave steepness and geometrical characteristics were considered. The results had shown that the three proposed floating breakwater revealed favorable performance and the geometrical configuration could impact wave attenuation significantly. The circular cross-section breakwater had greater effects on wave absorbing compared with two other floating breakwaters, more detailed experiments were conducted to the circular cross-section breakwater, a V-shaped floating breakwater consists of two single circular cross-section breakwater were studied, the effects of angle of the two singles, wave period and wave height were considered. The results revealed that the geometrical configuration and water depth could impact wave attenuation and mooring force significantly. Researches are expected to offer some information for the design of floating breakwater for an offshore project.
Development of a Probabilistic Ice Load Model Based on Empirical Descriptions of High Pressure Zone Attributes
Authors: Taylor Rocky S. , Richard Martin
Published: September 2014

During an ice-structure interaction, the localization of contact into high pressure zones (hpzs) has important implications for the manner in which loads are transmitted to the structure. In a companion paper, new methods for extracting empirical descriptions of the attributes of individual hpzs from tactile sensor field data for thin first-year sea ice have been presented. In the present paper these new empirical hpz relationships have been incorporated into a probabilistic ice load model, which has been used to simulate ice loads during level ice interactions with a rigid structure. Additional aspects of the ice failure process, such as relationships between individual hpzs and the spatial-temporal distribution of hpzs during an interaction have also been explored. Preliminary results from the empirical hpz ice load model have been compared with existing empirical models and are discussed in the context of both local and global loads acting on offshore structures.
Numerical Simulations in the Design of a New Tension-Tethered Marine Current Turbine
Authors: Fernandez David , Moreu Jaime , de Guzman Santiago , Yeung Ronald W. , Moreu Manuel
Published: September 2014

This paper focuses on the applicability of different Computational Fluid Dynamics (CFD) software for the design of marine current turbines. As part of the conceptual design process, Seaplace has carried out a detailed numerical and experimental hydrodynamic program to optimize a new Tension-Tethered Turbine concept for harnessing energy from marine currents. Three different codes have been assessed, based on the demands from each phase: OpenProp, TurbProp, and ANSYS® CFX®. The paper provides an extensive summary of the main outcomes from the turbine optimization process to achieve highest efficiencies. A description of the tested geometries and the implementation of TurbProp to account for inline turbine solutions is included. Simulations for the test-model and prototype scales have been performed, with the pressure distributions, flow streamlines and power coefficients presented as primary results. The influence of simulation results on the final turbine configurations is discussed.
Influence of Hydrodynamic Modeling Assumptions on Floating Wind Turbine Behaviour
Authors: Ledru Rémi , Le Cunff Cédric , Heurtier Jean-Michel , Perdrizet Timothée , Poirette Yann
Published: September 2014

This paper aims to highlight the key physical aspects that govern the dynamic behavior of a trifloater based floating wind turbine and the modeling assumptions — with a focus on hydrodynamics modeling and platform/tower interface flexibility — required to properly take into account the coupled hydrodynamics and aerodynamics effects in the fatigue analysis. Three selected load cases are simulated with different hydrodynamics models and the results are compared to each other. On this specific floating structure, Morison formulation seems to provide very similar results compared to other hydrodynamic modeling approaches based on potential flow theory and a more consistent way to model the floater damping. The use of a hybrid formulation including Morison damping on the columns instead of a quadratic damping matrix is an interesting alternative since it gathers the advantages of the different models.
Modular Mathematical Model for a Low-Speed Maneuvering Simulator
Authors: Tannuri Eduardo A. , Rateiro Felipe , Fucatu Carlos Hakio , Ferreira Marcos Donato , Masetti Isaias Q. , Nishimoto Kazuo
Published: September 2014

This paper presents the mathematical model of the real-time ship simulator for low-speed maneuvering developed by the University of São Paulo, Transpetro and Petrobras, with the technical collaboration of Brazilian Pilots Association (CONAPRA). The software is based on the TPN (Numerical Offshore Tank) numerical code which had several modifications, in order to perform real-time simulations.

After the complete description of the mathematical model, some illustrative results of simulations executed with pilots are exposed.
Hydrodynamic Analysis of Flapping Foils for Propulsion of Shallow-Water and Near-Surface Underwater Vehicles
Authors: Ananthakrishnan Palaniswamy
Published: September 2014

Hydrodynamic performance of flapping foils for the propulsion or station keeping of near-surface underwater vehicles is examined numerically. The objective of the project is to determine effects of momentum fluxes associated with the vortex wake, radiating waves and their interactions on the thrust and efficiency of the flapping foils. The fully nonlinear viscous flow problem is solved using a finite difference method based on boundary-fitted coordinates. Various flapping foil mechanisms, such as of a single foil, twin foil and hinge-connected double foil, are considered. Results are obtained for a range of key variables such as the Strouhal and Froude numbers, unsteady parameter, and the depth of foil submergence. New results obtained in this work reveal complex interactions between the flap-motion generated waves and vortices, in particular, how the deforming free surface above the vehicle and radiating surface waves could affect the generation and evolution of shed vortices and the thrust-generating capacity of flapping foils. Necessary conditions for high propulsive efficiency are found to be (i) Strouhal number between 0.25 and 0.35 and (ii) oscillation at supercritical frequency, i.e., τ > 0.25. At the critical frequency τ = 0.25 the efficiency is found to be low particularly when the body is very to the free surface. Upstream wave propagation at sub-critical frequency τ < 0.25 results in the loss of propulsive efficiency. Mechanisms affecting the efficiency are amplified by the foil proximity to the surface. In the case of flapping hinged double foil, in-phase oscillation of the foils results in high thrust while out-of phase flapping produces nearly null mean thrust. Flapping of twin foil in the “clapping mode” results in a pulsating wake jet yielding a large thrust but requiring large torque and hence at low efficiency. Efficiencies upto 80% are found in the simulations with single foil.
A Numerical Code for Waves in a Two-Layer Shallow Fluid
Authors: Tahvildari Navid , Lynett Patrick J. , Kaihatu James M.
Published: September 2014

The preliminary results from a two-dimensional two-layer nonlinear shallow water model are presented. The system is composed of two inviscid, incompressible, and immiscible fluids of constant density. The waves are assumed to be nonlinear and non-dispersive and the water depth is assumed to be constant. A high order predictor-corrector algorithm with a high order finite difference discretization, accurate to O(Δx4) is developed. The numerical algorithm and the boundary conditions are outlined and the model is compared with the analytical solution of internal solitary waves.
Effects of Strake Coverage and Marine Growth on Flexible Cylinder VIV
Authors: Resvanis Themistocles L. , Rao Zhibiao , Vandiver J. Kim
Published: September 2014

In this paper we present some results from the recent SHELL tests at the MARINTEK basin. The tests involved towing densely instrumented flexible cylinders at Reynolds numbers up to 220,000. The main objective is to present the experimental results describing the effectiveness of different amounts of strake coverage and to explore the influence of simulated marine growth.

The data is presented in terms of CF response amplitudes and rainflow-counted damage rates due to the combined CF and IL bending stresses. All results are compared with the bare cylinder cases which will be used as a reference to determine how effective the strakes are in suppressing VIV and how this effectiveness can be affected by marine growth. The results show that even small bare sections (missing strakes) can lead to significant VIV response. We also observe that moderate amounts of marine growth can quickly negate any suppression coming from the strakes.
FEA Analysis of Subsea PLET Installation and Operation
Authors: Wang Shuqin , Zhang Jiaping , Malachowski Jim , Schattenberg Diane , Ji Jason
Published: September 2014

Pipeline end termination (PLET) has been widely used in subsea field development. One challenge in the deployment of a PLET is monitoring the real-time stress condition in different components at different phase. Those components include mudmat, piping pipe system, yoke and upper structure. From load out on a barge to the field, to be settled for normal operation condition as well as recovery process, finite element analysis (FEA) could be utilized to simulate this process, minimize the material cost and optimize the design.

The scope of the current paper is to proposal a FEA simulation methodology to analyze this PLET loading process. This basic idea is to use one CAD model with all details to cover the entire simulation process, for all loading phases. The result has been approved to yield reasonable prediction of the real project with major clients. The methodology showed great potential value to be shared with the entire industry.
Viscous Flow Past a Circular Cylinder Below a Free Surface
Authors: Bouscasse Benjamin , Colagrossi Andrea , Marrone Salvatore , Souto-Iglesias Antonio
Published: September 2014

Flow past a circular cylinder close to a free surface at low Reynolds and large Froude numbers is investigated numerically using the Smoothed Particle Hydrodynamics model. This meshless method allows for a non-diffusive computation of the free surface evolution, even while breaking and fragmentation may occur. The distance of the cylinder to the free surface, submergence, is varied in order to investigate the detached flow patterns dependence with this factor. Vorticity shed by the cylinder, vortex generation due to free surface breaking, mixing processes, and drag and lift coefficients behavior are discussed. It has been found that, for small submergences, the classical Von Karman vortex shedding from the cylinder does not take place. In turn, moderate vortex shedding occurs, departing not from the cylinder but from vorticity generated at the free surface. This shedding takes places simultaneously with the transport of free surface fluid elements into the bulk of the fluid. It has been also found that for even smaller depth ratios, a vorticity layer remains spatially localized between the cylinder and the free surface, and a stagnation recirculating area develops behind the cylinder. Results are compared with literature finding reasonable qualitatively agreement with experimental works conducted with similar geometrical configuration but larger Reynolds number.
Performance Specifications for Real-Time Hybrid Testing of 1:50-Scale Floating Wind Turbine Models
Authors: Hall Matthew , Moreno Javier , Thiagarajan Krish
Published: September 2014

This paper presents performance requirements for a real-time hybrid testing system to be suitable for scale-model floating wind turbine experiments. In the wave basin, real-time hybrid testing could be used to replace the model wind turbine with an actuation mechanism, driven by a wind turbine simulation running in parallel with, and reacting to, the experiment. The actuation mechanism, attached to the floating platform, would provide the full range of forces normally provided by the model wind turbine. This arrangement could resolve scaling incompatibilities that currently challenge scale-model floating wind turbine experiments.

In this paper, published experimental results and a collection of full-scale simulations are used to determine what performance specifications such a system would need to meet. First, an analysis of full-scale numerical simulations and published 1:50-scale experimental results is presented. This analysis indicates the required operating envelope of the actuation system in terms of displacements, velocities, accelerations, and forces. Next, a sensitivity study using a customization of the floating wind turbine simulator FAST is described. Errors in the coupling between the wind turbine and the floating platform are used to represent the various inaccuracies and delays that could be introduced by a real-time hybrid testing system. Results of this sensitivity study indicate the requirements — in terms of motion-tracking accuracy, force actuation accuracy, and system latency — for maintaining an acceptable level of accuracy in 1:50-scale floating wind turbine experiments using real-time hybrid testing.
Design and Analysis for a Floating Oscillating Surge Wave Energy Converter
Authors: Yu Yi-Hsiang , Li Ye , Hallett Kathleen , Hotimsky Chad
Published: September 2014

This paper presents a recent study on the design and analysis of an oscillating surge wave energy converter (OSWEC). A successful wave energy conversion design requires balance between the design performance and cost. The cost of energy is often used as the metric to judge the design of the wave energy conversion (WEC) system, which is often determined based on the device’s power performance; the cost of manufacturing, deployment, operation, and maintenance; and environmental compliance. The objective of this study is to demonstrate the importance of a cost-driven design strategy and how it can affect a WEC design. A set of three oscillating surge wave energy converter designs was analyzed and used as examples. The power generation performance of the design was modeled using a time-domain numerical simulation tool, and the mass properties of the design were determined based on a simple structure analysis. The results of those power performance simulations, the structure analysis, and a simple economic assessment were then used to determine the cost-efficiency of selected OSWEC designs. Finally, we present a discussion on the environmental barrier, integrated design strategy, and the key areas that need further investigation.
Predicting the Second-Order Resonant Roll Motions of an FPSO
Authors: Matsumoto Fabio Tadao , Simos Alexandre Nicolaos
Published: September 2014

This paper aims at summarizing the results obtained in a recent research project concerning the prediction of wave-induced resonant behavior of new FPSO concepts. The analysis was based on a conceptual hull designed to operate in deep water fields off the Brazilian coast. Throughout this project, several configurations of the hull were proposed, some of them leading to relatively large natural periods. As a consequence, the resonant behavior of roll motions induced by second-order wave effects was clearly observed in small-scale model tests performed with some of these configurations, providing also good results for the verification and validation of numerical models that aim at predicting such wave forces. From the numerical standpoint, the hydrodynamic excitation forces can be estimated using well-established techniques for solving the second order diffraction problem, usually adopting a BEM approach. In terms of the computational time required for this analysis, however, this procedure is not so trivial since, in principle, the contribution of all pair of frequencies used to represent the wave spectrum must be computed. In face of the large computational effort tha is required and depending on the characteristics of the resonant problem, some approximations are consolidated and largely used by designers. One example is the approximation used to model the horizontal drift of the vessel, based on the very low natural frequencies that characterize the problem. Taking advantage of the asymptotic behavior of the second order horizontal force, good results can be obtained by computing the QTF (Quadratic Transfer Function) only in zero frequency. For the present case, however, this kind of approximation is not so effective. Even though the roll natural frequency of the FPSO is certainly lower than the usual values, it is not low enough for considering this asymptotic behavior. On the other hand, some other approximations can be envisaged and tested aiming at reducing the computational burden. In fact, the low viscous damping leads to a narrow-band transfer function for the roll motion and therefore enables modeling the resonant roll dynamics by means of an white-noise approach. In this case, the second order force spectrum needs to be computed only for one particular difference frequency, which is equal to the natural period of roll. This approach was investigated for different waves and draft conditions and the numerical results compared to those measured in the wave basin. Important aspects such as the influence of the viscous damping on the computation of the second-order wave forces and the change in the bandwidth of the response spectrum with the vessel draft are also discussed in the analysis, in view of the experimental results.
Fatigue of Combined Drag and Inertial Forces
Authors: Huang Wenbo
Published: September 2014

Based on the rain-flow counting technique, a frequency domain method is developed for calculating the fatigue damage caused by the combined drag and inertial loads. Firstly, by observation of the combined signal simulated, the combined load can be considered as the oscillation of the high frequency inertial force around the low frequency drag force with the random amplitudes, which makes it possible to identify the rain-flow large and small cycles. The cyclic range of rain-flow small cycles are determined by considering the reduced effect of the low frequency drag forces on the cyclic range of high frequency inertial forces. The cyclic ranges of rain-flow large cycles are determined by means of Turkstra’s rule of load combination. The numerical analysis show that the damages estimated by the developed method are very close to the rain-flow damages.
Bilge Keel Influence on the Free Decay of Roll Motion of a Three-Dimensional Hull
Authors: Yeung Ronald W. , Jiang Yichen
Published: September 2014

The prediction of roll motion of a ship with bilge keels is particularly difficult because of the nonlinear characteristics of the viscous damping. Flow separation and vortex shedding caused by bilge keels significantly affect the roll damping and the magnitude of the roll response. To predict free response of roll, the Slender-Ship Free-Surface Random Vortex Method (SSFSRVM) developed in Seah & Yeung (2008) [1] was employed. It is a fast free-surface viscous-flow solver designed to run on a standard desktop computer. It features a quasi-three dimensional formulation that allows the decomposition of the three-dimensional hull problem into a series of two-dimensional computational planes, in which the two-dimensional free-surface Navier-Stokes solver FSRVM [2] can be applied. This SSFSRVM methodology has recently been further developed to model multi-degrees of freedom of free-body motion in the time domain. In this paper, we will first examine the effectiveness of SSFSRVM modeling by comparing the time histories of free roll-decay motion resulting from simulations and experimental measurements. Furthermore, the detailed vorticity distribution near a bilge keel obtained from the numerical model will also be compared with the experimental PIV images. Next, we will report, based on the time-domain simulation of the coupled hull and fluid motion, how the roll decay coefficients and the flow field are altered by the span of the bilge keels. Plots of vorticity contour and vorticity iso-surface along the three-dimensional hull will be presented to reveal the motion of fluid particles and vortex filaments near the keels.

It is appropriate and an honor for me to present this roll-damping research in the Emeritus Professor J. R. Paulling Honoring Symposium. It was from “Randy” that I first acquired the concept of equivalent linear damping. Even more so, I am very grateful for his teaching, guidance and friendship of many years. — R. W. Yeung
Test Validation of Finite Element Analysis Results of Carcass Axial Capacity
Authors: Skeie Geir , Skjerve Håvard , Axelsson Gunnar , Pettersen Sune , Engh Bjørn , Vethe Stine
Published: September 2014

Recent incidents on the Norwegian shelf showed that the inner steel structure of a flexible riser, the carcass, can experience extensive axial loading. These events resulted in carcass overload followed by a spin-out and tear-off at the carcass end, eventually followed by shutdown of production. The carcass axial tension capacity has previously not been considered a critical design issue for flexible pipes. The incidents resulted in an extensive program, initiated by Statoil, to find the root cause of the problem. Both analytical and computational efforts validated through extensive testing of carcass axial capacity has been conducted. Advanced finite element analysis was used to establish both the carcass capacity and also the carcass load level as a function of pitch length. The numerical results are compared and validated towards experimental data. The results form a basis to suggest operational policies to mitigate the risk of new failures.
Validation of Floating Behavior of a Robinson R66 Helicopter After a Water Landing
Authors: Peiffer Antoine , Taft Dale , Lum Alan , Roddier Dominique
Published: September 2014

This paper summarizes the hydrodynamic work that was performed on the Robinson R66 helicopter’s water emergency landings as part of the roadmap to obtain FAA approval. The emergency system consists of two floats that are rapidly inflated as soon as the helicopter touches the water using gas from a high pressure cylinder. This type of design is common in the helicopter industry and is known as a “pop out” float system. The floats have already been shown to provide enough buoyancy to keep the helicopter afloat in calm water.

Recognizing that once the helicopter is in the water, it is subjected to wave forces and behaves as a small water craft, a numerical study was performed using OrcaFlex. Over 500 numerical simulations, each lasting 10 minutes, of the helicopter floating in different wave environments were performed. The helicopter’s 6 degree-of-freedom (DOF) motions were monitored throughout. At the end of the run, if the helicopter had not capsized, the run would report: “no capsizing”. Sensitivity studies were performed by varying parameters individually. This led to an understanding of each parameter’s effects on the overall helicopter floating performance. These parameters included: wind, wave period, initial helicopter relative heading against the waves, wave height, and simulation seed (different random wave sets with the same spectral characteristics). The FAA expects floatation characteristics to be evaluated in “reasonably probable” water conditions and has issued guidance that World Meteorological Organization (WMO) sea state 4 is one acceptable definition of reasonably probable. A wind speed of up to 21 knots is also associated with sea state 4.
Experimental Investigation on the Role of Entrapped Air on Solitary Wave Forces on a Coastal Bridge Deck
Authors: Seiffert Betsy , Ertekin R. Cengiz , Robertson Ian N.
Published: September 2014

Recent devastations caused by tsunami and hurricanes and the inevitability of future hurricanes making landfall have focused attention on the need to assess the vulnerability of coastal structures, and bridges in particular. Findings from a series of experiments conducted on an 1:35 scale bridge model with girders under a solitary-wave flow are presented here. Side panels are added to the bridge model to trap air pockets between the girders. A range of elevations is considered, including cases where the bottom of the deck is just above the water surface and girders are submerged, to where girders are fully elevated above the water surface. Wave parameters tested include four water depths and five wave amplitudes. A qualitative comparison is made between results for forces on the trapped-air model and results from the same set of wave parameters on a model where the side panels are removed and air is allowed to escape. Results show effects of water particle velocity, buoyancy, air compression and sloshing all have effects on both horizontal forces in the direction of wave propagation and vertical uplift forces. In particular, in the case where air is trapped between girders and cannot escape, uplift forces are considerably larger when bridge elevation is such that the girders are fully elevated above the still water level or are slightly submerged.
Impact of Physical and Chemical Mud Contamination on Cement-Formation Shear Bond Strength
Authors: Oyibo Arome , Radonjic Mileva
Published: September 2014

The purpose of this experimental study is to investigate the impact of physical and chemical mud contaminations on cement-formation bond strength for different types of formations. Physical contamination occurs when drilling fluids (mud) dries on the surface of the formation forming a mud cake while chemical contamination on the other hand occurs when drilling fluids which is still in the liquid form interacts chemically with the cement during a cementing job. Wellbore cement has been used to provide well integrity through zonal isolation in oil & gas wells and geothermal wells. It has also used to provide mechanical support for the casing and protect the casing from corrosive fluids. Failure of cement could be caused by several factors ranging from poor cementing, failure to completely displace the drilling fluids to failure due to casing. A failed cement job could result in creation of cracks/micro annulus through which formation fluids could migrate to the surface which could lead to sustained casing pressure, contamination of fresh water aquifer and blow out in some cases. To achieve proper cementing, the drilling fluid should be completely displaced by the cement slurry. However, this is hard to achieve in practice, some mud is usually left on the wellbore which ends up contaminating the cement. This study focuses on the impact of contamination on the shear bond strength and the changes in the mineralogy of the cement at the cement-formation interface.
Influence of Low Confining Pressure in Modeling of Lateral Pipeline/Soil Interaction in Dense Sand
Authors: Roy Kshama , Hawlader Bipul , Kenny Shawn
Published: September 2014

Buried pipelines are extensively used for transporting water and hydrocarbons. Geohazards and associated ground movements represent a significant threat to pipeline integrity that may result in pipeline damage and potential failure. Safe, economic and reliable operation of pipeline transportation systems is the primary goal of the pipeline operators and regulatory agencies. The pipes are often buried at a shallow depth and therefore the behaviour of soil at low stress level need to be considered for proper modeling of the response of pipelines. In this study, finite element (FE) modeling of pipeline/soil interaction is presented, where the stress-stain behaviour of soil at low stress level is implemented. At first, triaxial test results are simulated to validate the proposed model and numerical techniques. Pipeline/soil interaction in plane strain condition is then simulated for lateral loading. The Arbitrary Lagrangian-Eulerian (ALE) method available in Abaqus/Explicit is used for FE modeling. One of the main advantages of this method is that it can simulate large deformation behaviour. The variation of non-dimensional lateral force with non-dimensional displacement is examined for different depth of embedment of pipeline and soil conditions. Finally, shear band formation in soil due to lateral movement of the pipe is presented.
Analysis of Vertical Bending Moment on an Ultra Large Containership Induced by Extreme Head Seas
Authors: Rajendran Suresh , Fonseca Nuno , Guedes Soares C.
Published: September 2014

This paper discusses the numerical analysis of an ultra large containership model in severe head seas. A body nonlinear time domain code based on the strip theory is used for the calculation of the rigid body response of the vessel. The radiation, diffraction, Froude-krylov and hydrostatic forces are calculated for the exact wetted surface area of the ship at each time step. A practical engineering approach is followed to calculate the body nonlinear radiation and diffraction forces. The numerical vertical bending moment is compared with the experimental results. The experiment was conducted on a flexible model in both regular and irregular waves. The model comprised six segments that were joined with an aluminum backbone of variable stiffness characteristics in order to replicate the hydroelastic behavior of the real ship. The model was tested for two ship speeds, 15 and 22 knots. For the first three harmonic values of the vertical bending moment, a good agreement between the numerical and the experimental results are found. However, higher harmonics significantly contributed to the total experimental vertical bending moment, in regular waves with 8m wave height and a ship speed of 15 knots. Similarly, the value of the fourth harmonic was 32% of the first harmonic values when the ship encountered a 5m regular wave with 22 knots speed. On comparison of the rigid body response in irregular seas, the hydroelastic loads resulted in 49% increase in the maximum value of the vertical bending moment.
Heavy Wall Linepipe Girth Weld Fatigue Strength: Investigating Weld Root Performance
Authors: Marines-Garcia Israel , Mota Noe , Darcis Philippe P. , Quintanilla Hector M. , Kan Wan C. , Ghosh Rupak , Visco Tyler
Published: September 2014

The feasibility of Heavy Wall (HW) Seamless Line pipe application for high pressure/high temperature deep and ultra-deep field developments must be experimentally demonstrated to establish acceptable performance. Detailed mechanical, corrosion and fatigue qualification programs are required for validation of heavy wall line pipe and the associated girth welds for riser and flowline systems, especially those in fatigue-critical applications.

Pipe manufacturers and Operators share a common interest in developing new technologies to economically and safely produce from challenging reservoirs. In OMAE 2013, Tenaris and ExxonMobil jointly presented the Phase 1 qualification effort performed on HW line pipe and associated girth weld via mechanical and full scale fatigue testing. The results confirmed the mechanical properties were acceptable and the fatigue performance of the associated girth welds was reasonable. As expected, most of the fatigue failures originated at the outer pipe surface. As such, the focus of the present work is to further examine the fatigue performance considering fatigue failure initiation at inner pipe surface. This would provide a better assessment of riser and flowline fatigue performance for applications where the inner pipe surface is subjected to degradation from potential aggressive components in produced fluids.

To investigate the root girth weld fatigue performance, the adopted plan was to create an outer surface free of stress raisers/imperfections at weld cap toe which would help “push” the fatigue initiation to the root weld toe at the inner pipe surface. To achieve this, an enhanced grinding and flapping technique on the fatigue test specimen external surface was applied to remove the cap overfill and produce the desired flush profile. The same surface treatment technique was also applied on the pipe body in the proximity of the girth welds.

This program utilized identical pipe and girth weld used for the Phase 1 qualification effort. The heavy wall pipe was an X65, 10 ¾″ OD × 46 mm WT. The welding procedure was a narrow-groove bevel, STT® process for the root pass and the GMAW process for hot, fill, and cap passes. Four full scale fatigue tests were conducted for this investigation, two girth welds per fatigue specimen. In the end, the enhanced surface treatment technique was successful in “pushing” the fatigue failure initiation to the inner pipe surface. This paper presents the fatigue performance results due to crack initiation at the inner pipe surface as well as post-mortem analyses of the failure surfaces.
Prototype Data Analysis on LH11-1 Semisubmersible Platform in South China Sea
Authors: Du Yu , Wu Wenhua , Wang Yanlin , Yue Qianjin
Published: September 2014

There are still uncertainties and challenges by using floating platforms as the main oil exploitation mode due to lake of actual drilling experience in South China Sea. In order to ensure the safety of platform operation, large amounts of prototype data are needed for environment and structure analysis. From 2011 till now, a prototype measurement project is carried out on a semisubmersible platform “NanHaiTiaoZhan” FPS. Large amounts of data have been collected including parameters of ocean environmental loading, motions of floater and underwater responses of mooring and risers.

In this paper, statistical analysis of floater responses together with marine environmental conditions are carried out for deep understanding of the characteristics of semisubmersible floating platform. In order to study the motion behaviors of floater under harsh storm, the data recorded in a typical typhoon “Nock-ten” are chosen to perform the deep analysis. The measured data, wind, wave, current and floater motions, are analyzed in time-domain and frequency-domain separately. The comparison study of theoretical prediction and prototype measurement result in typhoon weather has been carried out. The data recorded by standalone sensors are processed by program MoorForce. The result of frequency-domain analysis of measured mooring force proves that the significant wave frequency dynamic behavior of mooring line during typhoon weather should be considered in design.
Ultimate Strength of Stiffened Plates Subjected to Longitudinal Compression and Lateral Pressure
Authors: Doshi Karan , Vhanmane Suhas
Published: September 2014

This paper presents a non-linear finite element analysis (FEA) and subsequent formula development for ultimate strength of stiffened panels of ship structures. A review of studies on ultimate strength of ship plating subjected to lateral pressure was carried out. The present work takes into account, the influence due to the lateral pressure on the ultimate strength of stiffened plates with initial imperfections subject to longitudinal compressive loads. ANSYS non-linear FE software was used for non linear finite element analyses of stiffened panels (864 cases) considering VLCC hull. Based on regression analysis, a set of semi-analytical formulae were proposed and described. It is observed that depending upon the failure mode, scantlings of the stiffened panel and magnitude of lateral pressure, ultimate strength of the stiffened panels in compression is affected.
The Strength Analysis of Adhesive Joints of Pipe Lines in Deep Sea Environment by FEM
Authors: Zhang Yu , Chu Gui , Wu Pei Zhen , Duan Meng Lan
Published: September 2014

Considering the adhesive joint widely used in industry, and its successful use in repairing systems in offshore pipelines, its application for pipe lines in deep sea is proposed. As pipe lines underwater are subjected to tension, bending, internal and external pressure, and adhesive joints have the singular stress fields at the end of interfaces of different materials, adhesive joints of pipes lines are the weakest parts in term of strength. This research studied the strength of adhesive joints of pipe lines under tension, bending, internal and external pressure, and the combination of these loadings using finite element analysis. It was determined that the adhesive joints of pipe lines are more prone to failure along the adhesive-pipe interface under bending compared to other loadings. Moreover, the effects of adhesive thickness and cover length on the strength of adhesive joint are investigated in this paper.
A Comparative Study of Motion Performance of Four Different FOWT Designs in Combined Wind and Wave Loads
Authors: Nihei Yasunori , Iijima Kazuhiro , Murai Motohiko , Ikoma Tomoki
Published: September 2014

This paper summarizes our recent collaborative/competitive works on floating offshore wind turbines (FOWTs) among four universities including Osaka Prefecture Univ., Osaka Univ., Yokohama National Univ., and Nihon Univ. The tasks assigned to each member were to develop the respective FOWT designs which could support 5MW class wind turbine, then to fabricate a scale model based on their own concept, and finally to evaluate the performance by tank tests under prescribed environmental (wind and wave) conditions. Osaka Prefecture Univ. adopted TLP concept, Yokohama National Univ. semi-submersible concept, Nihon University SPAR concept while Osaka Univ. also adopted semi-submersible, however, with single-point mooring. All the measured data were collected and compared among the four designs. It turned out that: (1) All the proposed deigns suffice criteria in terms of motion performance which were assumed at the beginning of the study. (2) The TLP type shows the most favorable performance among the four while the SPAR type shows largest acceleration in almost all the range of environmental conditions. The large acceleration may pose a problem of maintainability. (3) The SPAR type suffers the gyration effects more than the other types. (4) The RAOs of motions under combined wind and wave loads are almost the same as those under only wave loads for all the concepts but the single-point moored semisubmersible. (5) The difference of the RAOs for the single-point moored semisubmersible may be ascribed to the larger coupling effects between the main floater and the mooring system under the combined loads.
Parametric Estimation in the Wave Buoy Analogy: An Elaborated Approach Based on Energy Considerations
Authors: Montazeri Najmeh , Nielsen Ulrik Dam
Published: September 2014

An accurate estimation of the ocean wave directional spectrum at the location of an advancing ship is very useful for the ship master to improve operation and safety in a seaway. Research has been conducted to obtain sea state estimates by the Wave Buoy Analogy. The method deals with processing the ship’s wave-induced responses based on different statistical inferences including parametric and non-parametric approaches.

This paper considers a concept to improve the estimate obtained by the parametric method for sea state estimation. The idea is illustrated by an analysis made on full-scale response measurements carried out on a 9400 TEU container ship. The process of fitting a standard JONSWAP spectrum takes into account an analysis of residuals formed by the difference between measured and estimated amount of energy of the response(s).

A couple of motion responses and also bending moment are considered as the input of the estimation process. A comparison is made between the results and also with some inhand outputs from other estimation sources, e.g., wave radar measurements and sea surface elevation by microwave sensors. The discussed and analyzed procedure could also lead to an automatic selection of response combinations for sea state estimation.
Coupled Inline-Cross Flow VIV Hydrodynamic Coefficients Database
Authors: Zheng Haining , Dahl Jason M. , Modarres-Sadeghi Yahya , Triantafyllou Michael S.
Published: September 2014

Vortex Induced Vibrations (VIV) cause major fatigue damage to long slender bodies and have been extensively studied in the past decades. While most of the past research focused on the cross flow direction, it was recently shown that the inline motion in the direction of the flow has a major impact on the fatigue life damage due to its higher frequency (second harmonic) and more importantly, its coupling with the crossflow motion, which triggers a third harmonic stress component in the cross flow direction. In this paper, the coupled inline-crossflow VIV problem is addressed from semi-empirical modeling of fluid forces. Extensive fine grid forced inline-crossflow VIV experiments were designed and carried out in the MIT towing tank. An inline-crossflow VIV hydrodynamics coefficients database was newly constructed using the experimental results and it is expected to be useful for other semi empirical programs predicting coupled inline-crossflow VIV in the field. Several key hydrodynamic coefficients in the database, including lift force coefficients, drag force coefficients and added mass coefficients, were systematically analyzed. The coefficients in the crossflow and the inline directions were found to have strong dependency on the phase between the inline and crossflow motions.