bluuebunny/crossref_metadata_2025 huggingface dataset:
An Investigation of the Drag Induced on a Tool in a Granular Medium
Authors: Reid Daniel , Neilson Richard , Ivanovic´ Ana
Published: January 2011

An investigation of the drag induced by pulling a tool through a granular medium is reported. The work is aimed at understanding the drag on an offshore cable-laying tool with the objective of producing a model capable of predicting the force required to pull the tool through a granular medium. Experiments were run at 1g in a laboratory rig comprising a channel, containing the granular medium and a frame, in which the tool was inserted into the sand to a fixed depth and pulled through it at a constant velocity. The width, length and depth of insertion of the tool, the shape of the tool face and velocity of towing were investigated in dry sand only. The results show little change in drag force with velocity, over the range investigated, but indicate a power law relation to the depth of insertion. Increase in face width produces a near proportional increase in drag while increases in length produce smaller increases in drag force. The use of a rounded nose on the tool reduces the drag by a factor of up to 30%. A numerical model is proposed which is matched to the data and used to predict the loads on a full-scale device.
Applications of the Ogilvie-Tuck Formulae to Ship Hydrodynamics
Authors: Bandyk Piotr J. , Beck Robert F. , Zhang Xinshu
Published: January 2011

The work of Ogilvie and Tuck [1] was critical in extending strip theory to problems with forward speed. Salvesen et al. [2] used some of those findings in their classical work to determine the hydrodynamic coefficients in five degrees-of-freedom. Other methods have also utilized the formulae with success. The original derivation makes several assumptions about the hull shape and the steady flow around it. In practice, these assumptions do not hold exactly. Other simplifications are usually made, i.e. the mean ship speed is used instead of the actual steady flow around the hull. These may violate the original assumptions, but the results are generally satisfactory. The truly elegant aspect of the Ogilvie-Tuck hydrodynamic coefficients is that they can be calculated from zero-speed results. This is a product of the approach, assumptions, and mathematics done in Appendix A of the original work [1] to derive the Ogilvie-Tuck theorem, also called Tuck’s theorem by many authors. The Ogilvie-Tuck formulae include the hydrodynamic coefficients, expressions of the mj terms, and the Ogilvie-Tuck theorem. This paper discusses the original derivation and several practical applications, including those where the assumptions may be violated. Several qualitative or quantitative statements can be made about the errors introduced by simplifications. Some computational results are presented to emphasize the significance in practical use.
Unsteady Numerical Analysis of Flow Across 2D Cylinder
Authors: Peng Yaling , Zhang Zhiguo , Wu Fangliang , Feng Dakui
Published: January 2011

2-D computational analyses were conducted for unsteady viscous flow across cylinders of different geometries and different incident angle. Circular, square and elliptic (both at 0° and 90° angles of incidence) cylinders were examined. The calculations were performed by solving the unsteady 2-D Navier-Stokes equation at Re = 100. The calculated results produce drag and lift coefficients, as well as Strouhal number in excellent agreement with published data. Calculations for unsteady, incompressible 2D flow around a square cylinder at incidence angle of 0° and 45° and for Reynolds number = 100 were carried out. Cycle independence and grid independence results were obtained for the Strouhal number. The results were in excellent agreement with the available experimental and numerical results. Numerical results show that the Strouhal number increases with fluid angle of incidence on the cylinder. The wake behind the cylinder is wider and more violent for a square cylinder at 45° incidence compared to a square at 0° this is due to the increase in the characteristic length in the flow direction. The Strouhal number is highest for elliptic geometry among all cylinders in this research. For the geometries elliptic at 0° at Re = 100, there is not vortex shedding behind the cylinder. This is due to dominance of inertia forces over viscous forces. The present study was carried out for a 2-D single cylinder at fixed location inside a channel for unidirectional velocity. To get more accurate results computation on 3-D geometry should be carried out.
Numerical Study of Unsteady Wave-Generation for Flow Around NACA 0024 Airfoil
Authors: Zhang Zhiguo , Song Weng , Feng Dakui , Wang Li
Published: January 2011

Using numerical method to study the unsteady free-surface, wave-induced flow for a surface-piercing NACA 0024 airfoil is presented here. The simulation conditions are: Froude numbers = 0.19, 0.37, and 0.55 and Reynolds number = 0.822, 1.52, and 2.26×106. The simulation includes mean far-field wave elevations for all three Fr, unsteady near-field wave elevations for medium and low Fr number, mean foil-surface pressures for all three Fr numbers, and unsteady foil-surface pressures for medium Fr number. The numerical method combined finite volume method with both VOF and reconstructing moving-interfaces of PLIC for the numerical calculation of free surface flow in the condition of Froude numbers = 0.19, 0.37, and 0.55. For Fr = 0:19, there is no separation and the expected Kelvin waves are present. The results of numerical simulation of free surface boundary-layer separation and wave-making of the airfoil have been analyzed and compared with the results with related data and figures which is provided by university IOWA U.S.A, the results of numerical simulation is in accord with that of experiment. It laid a good foundation for related research in the future.
Inflow Measurement in a Tidal Strait for Deploying Tidal Current Turbines: Lessons, Opportunities and Challenges
Authors: Li Ye , Colby Jonathan A. , Kelley Neil , Thresher Robert , Jonkman Bonnie , Hughes Scott
Published: January 2011

Tidal energy has received increasing attention over the past decade. This increasing focus on capturing the energy from tidal currents has brought about the development of many designs for tidal current turbines. Several of these turbines are progressing rapidly from design to prototype and pre-commercial stages. As these systems near commercial development, it becomes increasingly important that their performance be validated through laboratory tests (e.g., towing tank tests) and sea tests. Several different turbine configurations have been tested recently. The test results show significant differences in turbine performance between laboratory tests, numerical simulations, and sea tests. Although the mean velocity of the current is highly predictable, evidence suggests a critical factor in these differences is the unsteady inflow. To understand the physics and the effect of the inflow on turbine performance and reliability, Verdant Power (Verdant) and the National Renewable Energy Laboratory (NREL) have engaged in a partnership to address the engineering challenges facing marine current turbines. As part of this effort, Verdant deployed Acoustic Doppler Current Profiler (ADCP) equipment to collect data from a kinetic hydropower system (KHPS) installation at the Roosevelt Island Tidal Energy (RITE) project in the East River in New York City. The ADCP collected data for a little more than one year, and this data is critical for properly defining the operating environment needed for marine systems. This paper summarizes the Verdant-NREL effort to study inflow data provided by the fixed, bottom-mounted ADCP instrumentation and how the data is processed using numerical tools. It briefly reviews previous marine turbine tests and inflow measurements, provides background information from the RITE project, and describes the test turbine design and instrumentation setup. This paper also provides an analysis of the measured time domain data and a detailed discussion of shear profiling, turbulence intensity, and time-dependent fluctuations of the inflow. The paper concludes with suggestions for future work. The analysis provided in this paper will benefit future turbine operation studies. In addition, this study, as well as future studies in this topic area, will be beneficial to environmental policy makers and fishing communities.
Computational Modeling of Interaction Between Actions and Action Effects of FPSO Topside Structures Subject to Jet Fire
Authors: Katsaounis G. M. , Katsourinis D. , Samuelides M. S. , Founti M. , Paik Jeom Kee , Kim Bong Ju
Published: January 2011

This paper presents a computational modeling of accidental fire actions on the topside structures of a floating, production, storage and offloading (FPSO) unit. According to the assumed scenario, the accident results in a jet fire, which loads the structure by temperature increments and pressures generation on their exposed surfaces. Temperature distributions were obtained by computational fluid dynamics (CFD) simulations, using the ANSYS CFX commercial code. The temperature versus time histories computed were first approximated (idealized) by smoother curves, based on fewer time-points, while retaining the maximum and minimum values. A similar procedure was also followed for the pressure variations. For the consequence (action effect) analysis the LSDYNA nonlinear finite element program was employed and the structures were modeled using shell finite elements with nonlinear (elastic-thermal plastic) constitutive relations. On the structure surfaces non coinciding grids were used for the two kinds of analyses (i.e., the CFD and FEM), in order to accommodate the diverse requirements of the different problems. The procedure of assignment the pressure and temperature loadings directly from the CFD results to the FEM model is described and representative results are given through the application of the methodology to a sample problem.
The Analysis and Application of Numerical Wave Tank Based on the Viscous Fluid
Authors: Yue Lei , Zhang Zhiguo , Feng Dakui
Published: January 2011

The so-called numerical wave tank is to use a mathematical model to simulate the process of making waves and interaction between waves and structures. Shipping water occurs when the wave height exceeds the deck level of a floating vessel. A large amount of seawater flows down onto the deck. It damages deck equipment and causes even submergence. The water on deck is called “Green Water”, and it is dangerous for ships. It is of great significance to analyze and simulate wave and green water phenomenon. This paper developed a three-dimensional numerical wave tank and presented VOF method to deal with the movement with free surface, and then simulated process of wave generation numerically. A two-dimensional numerical simulation of the green water phenomenon of a hull placed in regular wave was performed. The process of wave running up and wave deforming were obtained. The results show that the present numerical scheme and methods can be used to simulate process of wave generation and phenomenon of green water on deck, and to predict and analyze the impact forces between waves and structures due to green water.
Model Testing on Cross-Flow Vortex-Induced Vibration in Combined In-Line Current and Oscillatory Flows
Authors: Moreau Franc¸ois , Huang Shan
Published: January 2011

The cross-flow vibration of a cylinder in co-linear steady and oscillatory flows is investigated in towing tank for the inline Keulegan Carpenter number varying from 5 to 27 and for the reduced velocity varying from 3 to 19. The reduced velocity is defined by adding together the towing speed and the maximum in-line oscillating velocity. The ratio between the maximum in-line oscillating velocity and the total in-line velocity, i.e. including the towing speed, varies from 0.1 to 0.8. The Reynolds number is in the sub-critical regime. The model test results show that cross-flow vortex-induced vibration (VIV) in combined wave and current flow is significantly different from that in current or wave alone. The response is very much dependent upon the velocity ratio between the current and wave particle velocity.
Design Methodologies for Arctic Gas Pipelines
Authors: Ortega Germa´n E. , Saad Pascinthe
Published: January 2011

The need to install gas pipelines in more technically difficult locations, coupled with very tight competitive economics necessitates increased efforts to consider more refined design methodologies that provide higher levels of certainty and result in more economical designs. The design of onshore gas pipelines in arctic environment must also address a number of Geohazards which will impose various external loads on the pipeline in addition to the internal pressure and other stress inducing loads that non-arctic pipelines typically experience. These geohazards include frost heave, thaw settlement, and soil movement and will tend to deform the pipeline and induce longitudinal strain at levels well above the linear elastic limit. The different design methods must account for these loads in order to ensure a rational and fit for purpose design. Currently, a design engineer can rely on one of three distinct design methods for onshore gas pipelines: Allowable Stress Design (ASD), Load and Resistance Factor Design (LRFD) or Reliability Based Design Assessment (RBDA). Each of the methods has advantages as well as disadvantages that could limit their applicability to a specific project. Clear understanding of the loads, the operational requirements, the environmental conditions and regulatory framework are all key factors in selecting the appropriate design method. Allowable Stress Design has been the traditional design method for onshore pipelines in the US and while the method leads to safe pipelines, the degree of safety and the inherent level of conservatism incorporated can often be improved. Gas pipelines can also be designed using probabilistic methods that require the consideration of credible modes of failure (limit states) and the calculation of the probability that these limits will be exceeded. Since the design engineer must evaluate each applicable mode of failure individually, the degree of conservatism and safety can be applied where needed the most. Probabilistic design methods can be used to achieve consistency and to provide a higher degree of certainty that pipelines would perform as designed [2]. Since probabilistic methodologies are typically applied only by small group of specialized consultants, a clear understanding of their strengths and limitations is required by all key personnel involved in the design and engineering decision making process. This paper will present a definition of the design methods as well as a direct comparison of all major components associated with each. Furthermore, it will provide a definition of commonly used terminologies associated with reliability and strain based design application in order to enhance the practical knowledge of the basis for each approach.
Powering and Seakeeping Characteristics of a Displacement Vessel Hullform With Waterline Parabolization
Authors: Gould Kevin J. , Calisal Sander M. , Mikkelsen Jon , Go¨ren O¨mer , Okan Barbaros , Kim You-Taek
Published: January 2011

Waterline parabolization is a design procedure used for displacement vessels to decrease the wave resistance of the hullform through the addition of amidships bulbs. The bow and shoulder wave system of a parent hullform are interfered with by the wave system produced by the amidships bulb. Despite an overall increase in vessel beam, amidships bulbs can produce enough wave cancellations to decrease the total resistance. The designer must pay close attention to the amidships bulbs longitudinal positioning and fairing. Two design approaches can be taken: one the amidships bulbs are “retro-fit” to the existing parent hullform increasing the vessels displacement, and second the displacement is held constant producing an entirely new “optimized” design with shallower entrance and exit angles. Optimal shapes for the amidships bulbs were developed numerically using a potential flow code based on Dawson’s method coupled with a quasi-Newton nonlinear programming algorithm, Calisal et al. (2009a). Tow-tank tests at Istanbul Technical University (ITU) confirmed that amidships bulbs could reduce the effective power by 15%. Given a significant improvement in powering, this paper compares the seakeeping performance of the parent, optimized, and retro-fit hullforms at different sea state conditions and quantifies fuel consumption and acceleration levels. SHIPMO PC, a ship motion program based on strip theory is used to compare the three different hullforms. Three speeds are considered: the design speed of 12.5 knots, a reduced speed of 11 knots associated with the expected loss of speed from added resistance, and 6 knots to represent significant speed reduction. Roll, pitch and heave motions along with added resistance are estimated. Accelerations at the bridge are used to evaluate effects on the crew. For various sea states the most significant motion is roll in beam seas and is incurred at low speeds. The only significant difference in response between all models was for the retro-fit design; the increased displacement from adding the amidships bulbs and holding the draught constant increased the added resistance. Powering and acceleration levels for all models in head seas will be verified in tow-tank tests at ITU.
VIFIE-Based Prediction and Strength Analysis on Upending of Spar
Authors: Hu Di , He Yong , Jin Wei-liang
Published: January 2011

The Spar platform has become one of the most attractive development concepts as the offshore industry moves towards deep and ultra-deep water frontiers for new oil gas discovery. Upending is critical in the spar endures motion and structural loading which is substantially different from the motion and loading during the exploratory life. The paper presents a method for prediction the motions of the Spar during upending operation. Vector form intrinsic finite element (VFIFE) is good on analyzing large displacement problem, for taking advantage of it, an analysis program is written basing on it. This program predicts the upending process of spar successfully, providing elaborate information about structure motion characteristic during the process. By input the motion characteristic into software ANSYS, a detailed strength analysis is made. This method has the ability to make a detailed analysis both on time-domain motion response and strength of structure. An actual upending analysis of a spar is utilized for demonstration the feasibility and highlight of the method.
Study on Advanced Use and Social Value of Existing Fishing Port Space
Authors: Okuzawa Bungo , Kato Shimpei , Kondo Takeo , Yamamoto Kazukiyo , Kimoto Masaharu , Ikuma Takao
Published: January 2011

In recent years, the fishery population in Japanese fishing ports has halved with a decline of the fishery industry, and the use of fishing port facilities has also been declining. Because of this, there is a demand for effective use of existing fishing ports, which have thus far served only for the primary industry, and there is a transition in their use to higher order industries, indicating a change in the social value of fishing ports. In this study, the social value for realizing the higher order use of fishing port space was analyzed based on the locations of the port, the value of the land, and social needs. Although, with the current classification, 2921 existing fishing ports can be classified into 5 categories, designated class III fishing ports (13 ports), class III fishing ports (114 ports), class II fishing ports (496 ports), class I fishing ports (2210 ports), and class IV fishing ports (101 ports), the findings of this study were applied to develop a new classification which incorporated new social conditions. In this paper, the social value of fishing ports in modern society is shown, and a new classification of fishing ports which differs from the current system based solely on the port size is discussed, taking their social value into consideration.
Controlling Parameter for Wave Types of Long Flexible Riser Undergoing Vortex-Induced Vibration
Authors: Zhang Liwu , Chen Weimin
Published: January 2011

The aspect ratio of slender underwater structures of deep sea platforms such as riser, oil pipelines, tension legs and anchor chains increases with the mining depth increasing, the values of which often approach to 103 order. Investigation results in recent years show that the vortex-induced vibration of the flexible marine risers with large aspect ratio reveals some new phenomena, for example, the vortex-induced wave, multi-mode competition, wide band random vibration, which have brought new challenges to the study of vortex-induced vibration of long flexible risers. In this paper, the dimensionless parameter controlling the wave types of dynamic response of slender risers undergoing vortex-induced vibration is investigated by means of dimensional analysis and finite element numerical simulations (MSC Nastran). Our results indicate that there are three types of response for a slender riser, i.e. standing wave vibration, traveling wave vibration and intermediate state. Based on dimensional analysis the controlling parameter is found to be related to the system damping including fluid damping and structural damping, order number of the locked-in modes and the aspect ratio of riser. Furthermore through numerical simulations and function fitting, the expression and the critical value of the controlling parameter is presented. At last the physical meaning of the parameter is analyzed and discussed.
A Calculation Model for Deteriorated Members of 3D Frame Structures in the Static and Dynamic Analyses
Authors: Karadeniz H.
Published: January 2011

Jacket type structures in offshore structural industry consist of a large number of tubular members with various dimensions, which are joined to each other by welding that makes connections to be rigid. Diagonal members have relatively small dimensions, legs or chords have larger dimensions in general. Although the connections at joints are made rigidly, the actual joint behaviors under wave loadings are not fully rigid in the vicinity of connections due to local deformations of members having large diameters. In the short term, due to ultimate wave and earthquake loadings, some plastic deformations can also occur in members at some critical joints so that related members cannot be behave as rigidly connected and some releases of member forces occur. In the long term, fatigue damages can be observed at some joints that damaged members loose their functionality partly or fully as depending on damage rates. All these phenomena can be considered as member deterioration. A special treatment of deteriorated members can be used in the structural analysis by using a computation model that allows flexibility of damaged members at joints. The solution of this problem can be achieved by introducing a fictitious member concept, which can be derived as depending on actual member dimensions and joint configurations. The technique of using fictitious members introduces additional degrees of freedom that are not desirable in the analysis. A procedure which uses modified stiffness and mass matrices for flexibly connected members are more practical and attractive since a) no additional degrees of freedom are introduced, b) member-release and fixed-connection conditions can be directly obtained, c) a general member-end condition in any direction can be easily specified, d) a failure mechanism can be easily determined, e) in the fatigue damage calculation the load carrying capacity of the member can be used until the whole member cross-section is damaged and f) natural frequencies and mode shapes of damaged structural system can be estimated in terms of the natural frequencies and mode shapes of the undamaged structural system. The paper introduces a general formulation of a partly connected member to be used in structural analysis. For this purpose, a spring-beam element is defined using massless spring systems at member ends. An algorithmic procedure is presented to update member stiffness and mass matrices as well as member consistent load vector.
Fatigue Analysis on Key Components of Semi-Submersible Platform
Authors: Cui Lei , Xu Jia-nan , He Yong , Jin Wei-liang
Published: January 2011

Fatigue damage is one of the main reasons of the failure of Semi-Submersible platform. As the complex of random loading, it is difficult to analyze fatigue life accurately and determine the sensitivity of parameters. In this paper, the fatigue life on key-components of semi-submersible platform is analyzed with Spectral-based analysis method. Firstly, the stress responses of whole model platform under the random wave loads are calculated. The calculation results of whole model platform for cut-boundary interpolation are used in local model to calculate the key-component stress responses of local model. Generating the fatigue stress energy spectrum by scaling the wave energy spectrum and the complex fatigue stress transfer function in detail local model is described next. The stress response of short-term sea-state is assumed to obey Rayleigh distribution, and the spectral moments are calculated. Finally, the fatigue life of key components is analyzed according to S-N curve and Palmgren-Miner’s rule. The results show that the fatigue life of the connection meets the specification requirements, and the key components are the fatigue sensitive areas of semi-submersible platform.
Numerical Simulation of Wave Transformation Across the Surf Zone Over a Steep Bottom
Authors: Hsu Tai-Wen , Lin Ta-Yuan , Hwung Hwung-Hweng , Toledo Yaron , Roland Aron
Published: January 2011

The combined effect of shoaling, breaking and energy dissipation on a sloping bottom was investigated. Based on the conservation principle of wave motion, a combined shoaling and bottom slope coefficient is included in the mild-slope equation (MSE) which is derived as a function of the bottom slope perturbed to the third-order. The model incorporates the nonlinear shoaling coefficient and energy dissipation factor due to wave breaking to improve the accuracy of the simulation prior to wave breaking and in the surf zone over a steep bottom. The evolution equation of the MSE is implemented in the numerical solution which provides an efficient scheme for describing wave transformation in a large coastal area. The model validity is verified by comparison to accurate numerical models, laboratory experiments and analytical solutions of waves travelling over a steep sloping beach.
Improving Operating Window for Disconnect Operations of CWO Risers
Authors: Gryto̸yr Guttorm
Published: January 2011

The term ‘riser recoil’ refers to the situation when the lower end of a top tensioned riser is released, and the riser is lifted up by the riser tensioner and/or top motion compensator system on the supporting vessel. The elastic energy stored in the riser is then released, and the riser ‘recoils’. This paper focuses on the case of planned disconnect, and builds on ref. [1] which was based on a simplified riser analysis using a rigid body to represent the riser. In the present paper, the methodology has been applied to an elastic riser model in the riser analysis software RIFLEX, from MARINTEK in Trondheim, Norway, which includes axial damping elements required for modeling of the tensioner systems. Completion and Work Over (CWO) risers are unique in the sense that they may be simultaneously connected to both the riser tensioner system and the top motion compensator system of a drilling vessel. A Marine Drilling riser, on the other hand, is only connected to the riser tensioner system. Typically the riser tensioner system has a stroke of ± 8–9 m, whereas the top motion compensator system has only ± 3.5–4 m. It is imperative that the connector is lifted clear of the subsea structure in order to avoid damage to the equipment after the riser has been disconnected. The operating window for planned disconnect of CWO risers is severely limited by the available stroke of the top motion compensator. One of the purposes of the disconnect analysis is to establish the maximum wave height at which there is still sufficient clearance between the connector and the subsea structure after disconnect. Previous experience has shown that this may be the governing limitation for workover operations. The analysis may also establish a maximum tension level, and seastate, to avoid hard stroke-out of the top motion compensator cylinders. This requires an elastic riser model, since a rigid body will yield unphysically large impulse loads in case of stroke-out. The current industry practice is to use a regular wave approach in the analysis. In accordance with ref. [1], the present analysis is performed with irregular wave analyses. The results are documented through a case study of a typical CWO riser system connected to a semi-submersible in typical North Sea environmental conditions. The semi-submersible and the CWO riser system are exposed to irregular waves. Comparison of the resulting allowable wave height shows that using the approach presented here with an elastic riser model yields less conservative results than the previous methodology with a rigid body model. This should be coupled to the findings with the rigid riser model, ref. [1], that irregular waves yield a considerable increase in the operating window, and the resulting operability, compared to a regular wave analysis. Hence, using a regular wave approach combined with a simplified riser model that neglects the flexibility of the riser is expected to yield overly conservative results for the EQDP elevation after disconnect.
Material Softening Effect on Ultimate Strength of Stiffened Aluminium Panels
Authors: Chen Qiaofeng , Moan Torgeir
Published: January 2011

The material strength of aluminum alloys can be seriously deteriorated by the heat-affected zones (HAZ) caused by welding. The reduction of material strength in HAZ may lead to a serious reduction of the aluminium structural strength. The present paper is mainly concerned with the investigation on the ultimate capacity and the collapse behaviour of three types of aluminium stiffened panels (i.e., closed-stiffened panels, T-stiffened panels and flatbar-stiffened panels) considering the effects of various types of welds, the residual stresses induced by the related welds, and the combination of welds and the induced residual stresses, under axial compression and transverse compression, respectively. The investigations are carried out by nonlinear finite element (FE) analysis using ABAQUS. Based on the FE results, the material softening effects on structural capacity with respect to the parameters (i.e.: plate slenderness β and column reduced slenderness λ) are addressed. Finally, conclusions based on the investigation are made.
Effect of Lu¨ders Bands on the Bending Capacity of Steel Tubes
Authors: Hallai Julian F. , Kyriakides Stelios
Published: January 2011

In several offshore applications hot-finished pipe that often exhibits Lu¨ders bands is bent to strains of 2–3%. Lu¨ders banding is a material instability that leads to inhomogeneous plastic deformation in the range of 1–4%. It can precipitate structural instabilities and collapse of the pipe. Experiments and analysis are used to study the interaction of the prevalent structural instabilities under bending with Lu¨ders banding, with the objective of providing guidance to the designer. Pure bending experiments on tubes of various D/t values reveal that Lu¨ders bands result in the development of inhomogeneous deformation in the structure, in the form of coexistence of two curvature regimes. Under rotation controlled bending, the higher curvature zone(s) gradually spreads while the moment remains essentially unchanged. For relatively low D/t tubes with relatively smaller Lu¨ders strain, the whole tube eventually is deformed to the higher curvature, subsequently entering the usual hardening regime where it continues to deform uniformly until the expected limit state is reached. For higher D/t tubes and/or for materials with longer Lu¨ders strain, the structure collapses during the inhomogeneous deformation regime. This class of problems is analyzed using 3D finite elements and an elastic-plastic constitutive model with an up-down-up material response. It will be demonstrated that the solution procedure followed can simulate the experiments with consistency.
Advanced Lateral Stability Analyses for Lightweight Pipelines on Clay: A Case Study
Authors: Sollund Ha˚var , Vedeld Knut , Aamlid Olav
Published: January 2011

In 2007 DNV issued the new recommended practice DNV-RP-F109 On-Bottom Stability Design of Submarine Pipelines which replaced RP-E305 from 1988 with the same title. The new DNV-RP-F109 describes three different design approaches; full dynamic analysis, absolute static stability, and the generalized method with design curves for virtually stable pipes (allowing up to 0.5 diameters lateral displacement) and for up to 10 pipe diameters displacement in an extreme storm condition. DNV-RP-F109 recommends limiting the sum of the lateral displacement in the temporary condition and during operation to 10 diameters. For larger displacements one should perform a full dynamic analysis and special considerations with respect to bending and fatigue should be made. This paper is concerned with the consequences of exceeding the 10-diameter displacement criterion described in DNV-RP-F109, and how to use different methodologies in accordance with DNV-RP-F109 to ensure limited lateral displacements, acceptable environmental loads/strains and limited/acceptable fatigue damage accumulation. The methodologies covered in this paper include advanced assessments of passive resistance in soil, and account for increased vertical penetration due to laying and lateral fixation of the pipe at regular intervals. For the laterally restricted pipe, studies on reaction forces and reaction moments are made in addition to fatigue estimations at the points of maximum local longitudinal stress. Variations in environmental conditions, soil conditions and levels of effective axial force have also been considered.
Winterization Techniques for Semi-Submersible Rig Operating in the Arctic Ocean
Authors: Koo Myung-jun , Choi Jae-woong , Ha Mun-keun
Published: January 2011

Samsung Heavy Industries (SHI) has been developed many useful design concepts and procedures for offshore platforms operating in cold regions. In comparison with normal platforms, winterization for outfitting systems can be considered as an essential difference in design process to guarantee safe operation in cold environments. This study selected a Semi-Submersible Drilling Floating Rig ordered by LLC Gazflot, and shows an effective design procedure and its performance of winterization. A dominant area for winterization should be derrick and drilling deck space that have large opening areas to transport drilling, subsea equipments, risers and which have many those equipments required minimum temperature of about minus 20 degree of Celsius to guarantee normal operation under the lowest operating ambient weather condition of minus 30 degree of Celsius. The possible optimum solutions were proposed by suggesting wind wall design with openings for ventilation and by finding locations and quantities of heaters and blowers considering local temperature and air change rate to satisfy hazardous guide. Those solutions were verified by CFD (Computational Fluid Dynamics) approaches with suitable boundary conditions.
Stochastic Chaotic Roll Motion of Ship With Water on Deck
Authors: Liu Liqin , Tang Yougang , Zhang Ruoyu
Published: January 2011

The stochastic chaotic motion of ship rolling is studied considering the static effect of water on deck. The wave excitation is treated as periodic excitation perturbed by white noise and the parameter region for chaotic motion is determined by Melnikov mean-square criterion. The Poincare’ maps are constructed and the probability density functions are calculated using path integral method. It is found that the chaotic motion can be restrained by increasing ship damping and ship rolling response converges to two attraction regions. In the non-chaotic parameter region, ship rolls within one attraction region. In the chaotic parameter region the probability density function has two connected peaks and ship rolling jumps randomly from one attraction region to another.
Extreme Vertical Deepwater Current Profiles in the South China Sea, Offshore Borneo
Authors: Sheikh Rizwan , Brown Alison
Published: January 2011

This paper details a study of extreme oceanographic currents at deepwater locations offshore Borneo in the South China Sea. With the global demand for oil and gas set to rise steadily over the long-term, oil and gas operators are ever more exploring deeper waters in search of reserves. Often, these finds are economically marginal and challenging from an engineering perspective. Offshore Borneo is a typical example of this, where one such challenge is the prediction of extreme current speeds. Indeed, currents in deepwater are more complex and less constant with depth. As a consequence, the vertical profile associated to an extreme event is integral in the design and safe operation of deepwater facilities. Until recent exploration little measured full-depth deepwater current data has been available. With new datasets for multiple offshore locations, current speeds through the water column are approximated using Empirical Orthogonal Functions (EOFs) and their extreme profiles derived using the inverse First Order Reliability Method (FORM). These profiles are then compared with consideration of different types of current events and used as a basis to formulate idealised deepwater design vertical current speed profiles for locations offshore Borneo that are application specific.
Multiscale Modelling of Flexible Pipes With Nonlinear Homogenisation
Authors: Edmans Ben , Alfano Giulio , Bahai Hamid
Published: January 2011

A multi-scale framework for the analysis of flexible pipes and risers is presented, consisting of (1) a new corotational, elastoplastic beam element for flexible pipe modelling, (2) a representative volume element (RVE) consisting of a detailed shell-element model with interlaminar friction, and (3) a scale-linking scheme for a multiscale analysis using (1) and (2), justified using homogenisation theory. This enables wire stress-history data to be recovered by postprocessing the results of a large-scale dynamic analysis using (1). We develop a form of nonlinear homogenisation appropriate for flexible pipe RVEs, recognising the primacy of curvatures and handling the discontinuities in the local displacement field due to interlaminar slip. The enforcement of the Hill-Mandel condition and attention to appropriate boundary conditions ensure that the micro- and macro-scale models are dynamically compatible. We demonstrate the effectiveness of the method with a simple analysis.
Flexible Epoxy Syntactic Foam Thermal Insulation for High Temperature Deepsea Reelable Pipelay Installations
Authors: Wang Wen-Tsuen , Watkins Lou
Published: January 2011

Epoxy syntactic foam, a composite material combining glass microspheres with other fillers in an epoxy binder, has been used with increasing success in insulating offshore pipelines and subsea equipment for the past decade or more. The advantages of epoxy include excellent resistance to high temperature and high pressure sea water as well as good thermal insulting properties. The exceptional strength of epoxy has made service at great depth possible. However, the rigidity of conventional epoxy-based material has so far limited its application to subsea equipment and J-Lay or S-Lay pipelines. As the offshore industry moves into deeper water and larger fields, the desirability of making advanced epoxy insulation flexible and extending its use to more efficient reeled deployment methods is becoming obvious. This paper describes research directed toward identifying new, highly flexible insulating materials suitable for service up to 300°F (150°C) and as deep as 10,000 ft (3000m). A critical part of the research program has been to develop a methodology for testing affording confidence for very long periods of service. Preliminary test data are presented, along with predictions of how this new class of products will be further developed.
Towards the Improvement of Autonomous Glider Navigational Accuracy Through the Use of Regional Ocean Models
Authors: Smith Ryan N. , Kelly Jonathan , Chao Yi , Jones Burton H. , Sukhatme Gaurav S.
Published: January 2011

Autonomous underwater gliders are robust and widely-used ocean sampling platforms that are characterized by their endurance, and are one of the best approaches to gather subsurface data at the appropriate spatial resolution to advance our knowledge of the ocean environment. Gliders generally do not employ sophisticated sensors for underwater localization, but instead dead-reckon between set waypoints. Thus, these vehicles are subject to large positional errors between prescribed and actual surfacing locations. Here, we investigate the implementation of a large-scale, regional ocean model into the trajectory design for autonomous gliders to improve their navigational accuracy. We compute the dead-reckoning error for our Slocum gliders, and compare this to the average positional error recorded from multiple deployments conducted over the past year. We then compare trajectory plans computed on-board the vehicle during recent deployments to our prediction-based trajectory plans for 140 surfacing occurrences.
The Application of Non-Sinusoidal Mode Shape Function in the Identification of Modal Weight
Authors: Rao Zhibiao , Fu Shixiao , Yang Jianmin , Li Runpei
Published: January 2011

The main objective of this paper is to study the effect of non-sinusoidal mode shape on the identification of modal weights. The simplified analytical solution of the transverse vibration equation of uniform tensioned long flexible riser was presented, and the corresponding non-sinusoidal but orthogonal mode shape function is deduced. Then the data from the VIV model tests of long flexible riser conducted by ExxonMobil at MARINTEK are analyzed by the mode superposition method. Modal weights calculated by two different mode shape functions, sinusoidal and non-sinusoidal function, with two methods, namely direct method and indirect method are compared. The comparison shows the good performance of the non-sinusoidal mode shape in the identification of modal weights.
Full Scale Fatigue Performance of Pre-Strained SCR Girth Welds: Comparison of Different Reeling Frames
Authors: Darcis Philippe P. , Marines-Garcia Israel , Ruiz Eduardo A. , Marques Elsa C. , Armengol Mariano , Quintanilla Hector M.
Published: January 2011

The current work aims to point out the influence of plastic strain history, due to reel-lay installation, on the fatigue resistance of welded SMLS (seamless) steel pipes used for fabrication of Steel Catenary Risers (SCRs) for oil and gas development. A C-Mn steel X65 pipe 10.75″ (273.1 mm) outside diameter (OD) and 25.4 mm wall thickness (WT) was chosen for this program. The Welding Procedure designed for girth welds manufacturing involved the use of Lincoln STT-GMAW™ (Surface Tension Transfer–Gas Metal Arc Welding) process for the root pass and SAW (Submerged Arc Welding) process with twin wire configuration for the fill and cap passes. This welding procedure presents a special post-weld finishing treatment, which consists in flapping the inner and outer weld overfills to produce a flush profile between weld metal and outer/inner pipe surfaces. The experimental approach was focused on quantifying the effect of accumulated plastic deformation using two different reeling frames simulating the same laying vessel: the Technip’s Apache. In this program, two reeling trials were performed at Heriot Watt University, Edinburgh, U.K., and two other trials at Stress Engineering Services, Houston, U.S.A. Then, the strained specimens were full scale fatigue tested at TenarisTamsa R&D facilities. Those results have been compared with fatigue results obtained on unstrained specimens. Post-tests fractographic investigations were systematically performed on all samples to identify the causes for fatigue initiation. The results were statistically analyzed to determine which standard fatigue design curves best represent the measured S-N fatigue endurance. Finally, the results were also compared with the available literature.
Experimental Study on the Dynamic Characteristics of Saturated Soft Clay Under Bi-Directional Cyclic Loading
Authors: Liu Gong-xun , Luan Mao-tian , Tang Xiao-wei , Yang Qing
Published: January 2011

A series of stress-controlled bi-directional cyclic shear tests under isotropic consolidation conditions were conducted for simulating the cyclic stress induced by wave loading. The area bounded by the elliptical stress path was kept unchanged, while the ratio (R) of the axial cyclic shear stress and the torsional cyclic shear stress was changed in order to research the effect of varied two cyclic stress components on the pore water pressure, strength and deformation behaviors of saturated soft clay. The test results show that with a decrease in R, the residual pore water pressure decreases at first and then increases, and it reaches the lowest at R=1 at the same cycle number, while the amplitude of fluctuated pore water pressure decreases all along. The relationship curves between normalized ratio of pore water pressure and ratio of cycle number have significant differences with different R. The cycle number at failure increases at first and then decreases with decreasing R. It reaches the maximum at R=1, indicating that the dynamic strength is the highest when the stress path is close to a circle. The dynamic stress-strain relationship curves with different R indicate that both the axial and the torsional strains caused by the bi-directional cyclic loadings are mainly the cyclic strains, at the same time, the residual strains appear. With decreasing R, the amplitude of axial cyclic strain decreases and the ratio of axial residual strain and cyclic strain increases firstly and then decreases, while the amplitude of torsional cyclic strain increases. The cyclic shear strain is basically symmetric at R=1, while the residual shear strains appear under other conditions.
Analysis of Erosion and Failure in the Sudden Expansion Fracturing Tubing of Deep Gas Wells
Authors: Xu Yan , Wang Zunce , Li Sen , Lv Fengxia , Yan Yuejuan , Wen Houzhen
Published: January 2011

With the increasing of flow rate during fracturing in deep gas well, the erosion of fracturing tubing is an issue of immense concern to the industry. Based on the Euler-Euler two–fluid theory, the numerical simulations have been performed to predict the flow field in the sudden expansion fracturing tubing. The velocity distributions and sand concentration profiles are obtained, and the simulation results show that separation and reflux come into being in the sudden expansion fracturing tubing when pumping sand slurries at high rate, and the sand concentration increases at some regions. The erosion and failure of the fracturing tubing are relevant to the sand concentration, the velocity and the impact angle. The erosion model was established with the erosion experiment, and the numerical simulation results were used to describe the erosion rate of sudden expansion fracturing tubing according to the established erosion models. The mainly erosion region obtained through the simulation is basically agree with the failure region of tubing during fracturing in deep gas wells.