bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Study on Mathieu Instability of DDMS Platform
Authors: Li Binbin , Ou Jinping
Published: January 2011

Deep draft multi-spar (DDMS) is an innovative platform which is specially designed for deepwater drilling and production in 2009 by Center for Deepwater Engineering, Dalian University of Technology. The hard tank of DDMS is composed of four columns at corners and a novel moonpool protecting the top tension risers at center. In addition, the top tension and self-weight of rigid risers are provided by air-cans in the moonpool. At the foot of hard tank, the pontoons and horizontal bracing are used to connect the separated columns and moonpool. It is noted that two heave plates are directly integrated with the hard tank in order to reduce the heave response. The middle section consists of 4 columns of smaller diameter which connect the hard tank and ballast tank. The early investigation indicates that the global hydrodynamic and motion behavior of DDMS are similar with Spar platform, and furthermore the heave natural period is close to the half pitch natural period. Therefore the DDMS platform may have possibility to trigger the Mathieu instability which has been validated on Spar platform through the numerical and experimental method. In this paper, a coupled heave and pitch motion equations of DDMS platform are established with accounting the time-varying restoring heave and pitch restoring stiffness. A damping case matrix is generated considering the heave plate damping, mooring line damping and hull drag damping. The damping ratios are identified by free-decay tests. The nonlinear motions under the action of regular waves of different periods and heights are numerically solved by the 4th order Runge-kutta method. The calculational results reveal that the heave damping significantly influences the occurrence of pitch instability, meanwhile the damping contribution of heave plates and mooring lines also play an important role in suppressing the instability. The phenomenon of Mathieu instability is owing to the energy exchange in this paper, and the mechanism of this phenomenon is amply studied as well as 3 different ways of instability are summarized.
Fatigue Damage Assessment of Container Ships Concerning Wave-Induced Torsion
Authors: Li Zhiyuan , Ringsberg Jonas W. , Mao Wengang
Published: January 2011

The traditional method to assess fatigue damage of ship structures assumes moderate wave amplitudes and linear responses. This method can be questioned when applied on container ships that are characterized by large deck openings, because the low torsion rigidity of this type of ship makes it sensitive to oblique waves. In this paper, the 3D hydrodynamic code WASIM is used to simulate a 4400 TEU container ship operating in the North Atlantic Ocean. Nonlinear wave loads are utilized for direct calculation of the stress histories under severe sea states. The warping stress from wave-induced torsion is separated from the stress components from vertical and horizontal bending. The contribution to fatigue damage accumulation from warping stresses is evaluated. For comparison, the results from the numerical simulations and fatigue calculations are verified with full-scale measurements made on a similar type of container vessel.
Hybrid Grid Auto-Generation Technique and Its Application on the Numerical Prediction of Ship Hydrodynamic Performance
Authors: Zhang Zhenjiang , Chen Zuogang , Deng Deheng
Published: January 2011

In order to facilitate ship CFD computation, hybrid grid auto-generation software HIGOT-V1.1 is developed. After importing the geometric shape and control data, the software may automatically create the computational domain, partition computation zones, generate structured or unstructured grid in each zone, set the boundary conditions and export the grid file for CFD computation. The model of TEU3100 container ship is employed to evaluate the software. The grid resolutions for drag and maneuverability numerical prediction are carried out. The computed results are in good agreement with the measured data. Ship stern are deformed to investigate the propulsive performance. The numerical simulation shows that CFD computation can capture the variation of hydrodynamic performance resulting from ship stern deformation. The present research is expected to facilitate ship CFD application and construct the basis of simulation based ship design.
Influence of the Bow Shape on Loads in High and Steep Waves
Authors: Clauss Gu¨nther F. , Klein Marco , Dudek Matthias
Published: January 2011

To ensure survival of floating structures in rough seas, a precise knowledge of global and local loads is an inevitable integral part for safe design. One of the key parameters is the vertical bending moment. Not only vertical forces but — as previous investigations revealed — also longitudinal forces significantly contribute to the vertical wave bending moment. Three segmented ships, equipped with force transducers, are investigated systematically in high and steep regular waves and in harsh wave environments at several cruising speeds to identify the structural loads. The model tests are carried out in the seakeeping basin of the Technical University Berlin at a scale of 1:70. To cover possible influences of the bow geometry, three different types of vessels are chosen, a bulk carrier with a full bow, a Ro/Ro vessel and a container vessel with a V-shaped frame design. For identifying the influence of the wave height and steepness on the vertical bending moment, model tests in regular waves with different crest/trough asymmetries are performed with the Ro/Ro vessel and the bulk carrier. The program can be subdivided into three parts, each characterized by the same wave lengths with varying wave steepness. The first test series includes regular waves with small amplitudes, thus linear wave theory can be applied. In the second part the same (regular) wave lengths have been generated with increased wave heights, i.e. increasing crest/trough asymmetries and wave profiles within Stokes II domain. During the last part of the experimental program the wave heights are further increased to reach wave profiles within Stokes III domain. For the evaluation of the test results in regular waves — in particular in high steep waves — the results are compared to the respective Response Amplitude Operator determined by the transient wave package technique. Here the focus lies on the asymmetry of the hogging and sagging loads with respect to the wave steepness and the bow geometry of the investigated ship models. Furthermore, the influence of the freeboard height on the vertical bending moment is analysed. For this purpose a container vessel is investigated with two different freeboard configurations in a harsh wave environment.
Wind Shielding Effects on DP System of a Shuttle Tanker
Authors: Tannuri Eduardo Aoun , Fucatu Carlos Hakio , Rossin Bruno Devoraes , Montagnini Renata Cristina B. , Ferreira Marcos Donato
Published: January 2011

The effects of hydrodynamic and aerodynamic interactions on a typical shuttle tanker (ST), when offloading a FPSO moored in Spread Mooring System (SMS) configuration are being studied in an extensive research project conducted at the University of Sa˜o Paulo, in collaboration with Petrobras. The numerical models will be incorporated in the simulators in order to evaluate the impact of such effects on the dynamics of the ST and on its DP System power requirement. Present paper focuses the wind shielding effect, since current and wave wake effects were already treated in previous works (Illuminatti et al., 2009; Queiroz Filho et al., 2009). A detailed CFD model of the FPSO and ST were used to evaluate the horizontal forces and yaw moment induced in the ST by the wind when inside the shadow zone defined by the FPSO. The CFD model was calibrated using wind tunnel measurements of a similar system. Typical tandem configurations were considered for the connection and oil-transfer stages of the operation. The power requirements for each DP thruster were then calculated, considering a thrust allocation algorithm. The comparisons with the stand-alone ST configuration indicated that the wind shielding effect is important concerning DP power. Besides, it is proposed a simplified model for wind forces and moment in the ST, considering the wind velocity field in the wake of the FPSO (CFD calculation). The procedure is based on report [7] where the wind force is evaluated through de summation of forces and moment in the stern, middle and bow parts of the ST. Such procedure has the advantage of requiring only one CFD calculation (for obtaining the velocity field downstream FPSO).
Underwater Sonar Images Processing and Its Real-Time Application of Super-Mini ROV
Authors: Song Xin , Ye Jiawei , Zou Zaojian
Published: January 2011

This paper presents a novel framework for the processing of sonar images. This novel framework is applied to the designs of the image data classification and the adaptive obstacles recognition and location. A special attention for the real-time performance is given and encouraging results have been validated by ROV’s sonar experiments.
Optimal Design Methodology for Multi-Component Mooring Systems in Deep Water
Authors: Yu Long , Tan Jiahua
Published: January 2011

Multi-component mooring systems, one of the crucial equipments of offshore platforms, play an important role in deep water oil&gas production because of relative low cost and light weight. A single mooring line can be constructed by combination of wire ropes, chains, fiber ropes, buoys and connectors etc. and provide adequate restoring force at fairlead point of platforms. Although the static and dynamic analyzing approaches for a determined multi-component system have been studied already, it is still hard to design and predetermine an appropriate mooring system that can satisfy the codes with multi-component lines. Referred to the conventional mooring system design method, this paper brings out an optimal design methodology for multi-component mooring systems. According to quasi-static method, at extreme offset position of the platform, an optimization model for designing the multi-component mooring line with biggest tension in deep water has been provided. Then, with the aid of design wave method and morison equation, a finite element model has been used to calculate mooring line dynamics at each fairlead point in time domain. The nonlinear interaction of mooring lines and seabed has also been investigated. Heave and surge of the platform have also been considered. Both 2D and 3D mooring system models have been built to search the interference of the lines and directional influence of environment loads like current and wave. The paper applied this set of analyzing methods and processes into a deep water semisubmersible serving at South China Sea. Compared with the results calculated by other software, the methodology mentioned in the paper got similar result with less weight and bigger restoring force.
Dynamic Analysis for an Internally Coupled Fluid/Riser System
Authors: Cheng Yongming , Vandiver J. Kim
Published: January 2011

Risers are fluid conduits from subsea equipment to surface floating production platforms. The integrity of a riser system plays a very important role in deepwater developments. A top-tensioned riser generally consists of outer casing, inner casing and tubing. The pipes are coupled either through fluids in the annuli or through intermediate guides (centralizers) or through both. This paper investigates the dynamic analysis for such an internally coupled fluid/ riser system. This paper first presents a theoretical formulation for a general riser system coupled with fluids in the annuli and centralizers between pipes. Hydrodynamic forces associated with the viscous fluid in between concentric cylinders are considered. An effective dynamic stiffness matrix method is then developed to evaluate the added mass and damping influence of the fluid on the natural frequencies and the dynamic response of the coupled riser system. A riser example is used to illustrate the fluid coupling impact on the system’s dynamic performance. The coupling through the fluid and centralizers can be optimally designed such that an inner pipe acts as a vibration absorber to the outer casing.
Experimental Study on Hydrodynamic Characteristics of Hydrofoil of the Birds Embedded in Marine Seismic Streamers
Authors: Zhang Xiaoqing , Zhang Weijing , Chen Jun
Published: January 2011

A “bird” is a device usually being used to control the depth and position of marine seismic streamers. Exact position of the streamers can effectively promote the precision, reduce the measured times and save the costs for marine seismic exploitation. So the “birds” have important significance to marine oil exploitation. A Hydrodynamic characters test concerning a new embedded bird has been introduced in this paper. And some useful hydrodynamic character-data of the hydrofoil are obtained, such as lift-attack angle diagram, resistance-attack angle diagram, torque-attack angle diagram. These data and diagrams are more helpful for studying on the embedded bird, including the control method and control strategy etc. Above all, the results of the test have significant reference value for the control of birds and marine seismic streamers.
Strake Design and VIM-Suppression Study of a Cell-Truss Spar
Authors: Wang Ying , Yang Jianmin , Peng Tao , Lu Haining
Published: January 2011

Along with the development of offshore technology, Spar platforms have been widely used in deep-sea oil and gas exploitation. Due to the deep draft cylinder hull piercing into the water, Spar platforms could be subjected to Vortex-Induced Motions (VIM) in certain current conditions. To mitigate VIM, helical strakes are used on the Spar hulls, and they have been proved to be effective. Cell-Truss Spar is a new concept of Spar platform which has recently been put forward by State Key Laboratory of Ocean Engineering (SKLOE) of Shanghai Jiao Tong University. It combines some good qualities of the Cell Spar and Truss Spar designs, aiming to bring in the lighter truss section and heave plate damping feature of the Truss Spar to obtain satisfactory heave motion performances, while reduce manufacture and installation difficulties by means of cell concept. Since the Cell-Truss Spar is a new design concept that has physical characteristics which are different from the existing Spars, the global motion performance should be carefully studied and verified. Researches about the VIM performance of the Cell-Truss Spar have been carried out recently (see Wang Ying et al, 2008, etc). Since it is still at the concept design stage, the Cell-Truss Spar configuration is considered without detail strake design in these studies. For the Cell-Truss Spar, which is still on concept design stage at the present time, the design and optimization of the helical strakes is very important to control the VIM response and improve the hydrodynamic performance. In this paper, strake design and VIM-Suppression Study of the Cell-Truss Spar is carried out. As a result of the unique characters on the hull, the outer surface of the Cell-Truss Spar does not form a regular cylinder. Hence, the strakes should be designed more carefully. In this study, four different configurations of strake groups are put forward and studied, and the one with the highest efficiency is chosen to be applied on the Cell-Truss Spar. The fluid field around the hard tank of the hull, the vortex disturbance near the strakes, and the forces acting on the hard tank with different strakes are simulated by CFD method, and the strake efficiency is assessed through model test combining with CFD computation. The optimized strake configuration is finally chosen, and the VIM performance of the strake-equipped Spar is studied.
Simplified Combination of Still Water and Wave Loads With the Emphasis in Considering a General Weibull Characteristics of Wave Loads
Authors: Huang Wenbo
Published: January 2011

Based on up-crossing rate analysis of the combined still water and wave loads and the first order reliability method, a simplified analytical combination method is developed, by which a general Weillbull characteristic of wave loads can be incorporated in the prediction of extreme values of the combined still water and wave loads acting on ocean-going ships. The results predicted by the developed analytical method agree very well with those by the existing numerical methods. Further, based on type II extreme value distribution and developed load combination method, a probabilistic model for the extreme value of the combined loads is established, which would be very convenient to use in reliability analysis of a ship hull girder. Finally, numerical analysis is carried out to demonstrate the established combination method and probabilistic model.
Ultimate Strength and Fatigue Durability of Steel Reinforced Rubber Loading Hoses
Authors: Lassen Tom , Eide Anders L. , Meling Trond Stokka
Published: January 2011

Loading hoses in an offshore loading buoy system in the North Sea were investigated with respect to extreme load resistance and fatigue durability. Both experimental work and fatigue life analyses were carried out. The FLS test is based on the principle of a service simulation test according to the American Petroleum Institute (API) 17B guidelines. The test results given in number of endured cycles from the laboratory test are scaled to the in-service conditions. Although the life estimate is based on one full scale test only, an attempt has been made to account for the inherent scatter in fatigue life. Furthermore, the results are validated by large test series with small scale test specimens for the critical reinforcement components in the composite structure of the hose wall. Test series with steel wires and samples of the steel helix were carried out. Statistically based S-N curves with characteristic scatter are established. Finally, all experimental facts were assembled and fatigue life predictions made. Redesign is considered and a scheduled inspection and replacement program is presented. The rubber-steel composite structure has sufficient strength for both the ULS and FLS case. For a planned replacement interval of 10 years the thickness of the standard steel end fittings has to be increased and the shape of the fitting should be optimized with respect to fatigue.
Characteristics of Wave Groups for the Evaluation of Ship Response in Irregular Seas
Authors: Bassler Christopher C. , Belenky Vadim , Dipper Martin J.
Published: January 2011

A method to evaluate ship response in heavy seas is presented. A ship maneuvering in a stochastic environment is difficult to model because of the rarity and significant nonlinearity of the large motion responses. In the proposed method, critical wave groups are defined and used to separate the complexity of the nonlinear dynamics of ship response from the complexities of a probabilistic description for the response. In this formulation, wave groups may be considered as a possible method to solve the problem of rarity. With the characteristic information about the wave groups, the problem of rarity can be solved in a deterministic manner. Characteristics, including the distributions for the number of waves in a group and wave amplitude, period, and steepness for the waves in a group are presented.
Preliminary Economic Feasibility Analysis of Cobalt-Rich Manganese Crust Mining for Rare Metal Recovery
Authors: Goto Koji , Yamazaki Tetsuo , Nakatani Naoki , Arai Rei
Published: January 2011

The importance of cobalt-rich manganese crusts on the Pacific seamounts for possible future rare metal sources has currently been recognized. The thin layer-type deposit characteristics affect not only the excavation efficiency but also the economy of mining venture. Considering the thin layer-type distribution and the utilization of some rare metals in cobalt-rich manganese crusts, a preliminary economic feasibility of the mining venture is evaluated. Under some preliminary technical assumptions, the possibility of cobalt-rich manganese crusts for future rare metal sources for Japan is examined. The important role of utilization of rare metals in the crusts is highlighted.
Dynamic Ice Forces Analysis of Conical Structure Based on Direct Measurement
Authors: Xu Ning , Yue Qianjin
Published: January 2011

The dynamic ice force is produced by failure process during ice interaction with structure. The best way for describing and modeling this process is using directly measured ice force on full scale structure in situ. In this paper, the ice force variation and corresponded failure process of ice sheet were recorded by ice load panel and video camera. It is demonstrated that when ice acting on upward narrow cone and in bending failure and well clearing by side of the cone. The form of ice force history looks like impulse signal.
Moving Performance of Crawler Driven ROV on the Inclined Sea Bottom
Authors: Katsui Tokihiro , Murakami Hisataka , Kajikawa Satoshi , Inoue Tomoya
Published: January 2011

The crawler driven ROV is considered as one of the probable systems for seafloor exploration or seabed resources development [1][2][3][4]. However the movability of crawler driven ROV on the sea bottom is not explained clearly compared with the ones on the land [5][6][7][8][9]. The experimental investigation on the crawler based ROV’s movability suggests that light weight ROV are easy to run in bow up condition and sometimes are possible to turn over. Therefore it is important to make it clear what kind of condition is to be satisfied for the normal run when the ROV moves on the sea bottom with crawlers. In this study, a simple dynamic model for the ROV which runs steadily on the inclined smooth sea bottom has been developed and the condition which should be satisfied for normal running has been derived. We consider that the forces acting on ROV are gravity, buoyancy, reaction from sea bottom, thrust and hydrodynamic resistance and treat them as concentrated loads. From the balance condition of forces for longitudinal and vertical direction and pitching moment, three kinds of relation are obtained. We consider that force reaction point from sea bottom should be inside between the fore and rear wheels for the normal operation. With this condition, the relation to be satisfied between the location of gravity center and center of buoyancy is obtained. To validate this conditional equation, the model experiments are carried out. The ROV model contains several weights and floating materials so that the longitudinal center of gravity and buoyancy can be changed by moving the weights and floats. Changing the longitudinal location of buoyancy center of the model from backward to forward, the limiting normal running condition for each longitudinal location of gravity center are measured. The obtained experimental results agree well with the theoretical ones. The presented conditional equation to be satisfied for normal running is considered to support the basic planning of a crawler driven ROV.
A Study on the Optimization for the Arrangement of Two Types of Supporting Columns for VLFS Using GA
Authors: Nishi Tatsunori , Murai Motohiko
Published: January 2011

In the recent years, there are many researches about hydroelastic responses of Very Large Floating Structure (VLFS). As a result, we are now in a position to say that VLFSs can be used as airport, city base, energy facilities and so on. There are several supporting structures of VLFS. In this paper, we shall focus only on the column type and the pontoon type. These two types of supporting structures have different hydroelastic behavior. For example, wave-induced elastic responses of column type are usually smaller than the response of the pontoon type. On the other hand, large amplitude responses at both ends of the column type VLFS are expected in certain frequencies. Then we thought that combining the two types of supporting structures could increase or decrease the VLFS hydroelastic response. Because there is uncountable number of combinations, we could not evaluate the hydroelastic responses of all combinations. In order to achieve the optimum combination in realistic calculation load, the Genetic Algorithm (GA) is applied. In this research, we discuss the combination of the two types of supporting structures in order to achieve smaller hydroelastic response of the VLFS in regular and irregular waves. GA is implemented as a computer simulation in which a population of abstract representations for the supporting structures are generated (in this case, the representations are the combination of pontoons and columns), then these abstract representations are recombined creating a new generation. At each generation, the best individual (the VLFS with the minimum hydroelastic response) is chosen. After run several generations, the optimum solution is reached.
Steel Catenary Riser Dynamic Analysis for Deepwater Applications in South China Sea
Authors: Lin Jinbao , Wang Dongbao , Qi Tao
Published: January 2011

This paper first describes the functional requirements of the Steel Catenary Risers (SCRs) for the deepwater applications in South China Sea. Spar is assumed to be the floating platform for the study in this paper. SCR wall thickness is preliminarily selected according to the industry codes. Dynamic strength analysis is preformed to verify the riser wall thickness. Fatigue analysis is then carried out to evaluate fatigue strength for the riser. The fatigue analysis covers different sources such as wave motion, ambient current, and Spar Vortex-Induced Motion (VIM). The metocean data in South China Sea are used for the vessel global motion generation. The current data are used for computing the riser fatigue caused by Vortex-Induced Vibration (VIV). Total fatigue damage for the risers is evaluated. Conclusions are finally drawn from the work in this paper.
Structural Safety Ensuring System of Offshore Platforms in Bohai
Authors: Zhang Dayong , Yue Qianjin , Wang Yanlin , Li Huihui
Published: January 2011

Nowadays, many existing offshore platforms which exceed or approach their design life are still carrying on with producing in the ice zone, so the safety operation is the key issues. In winter, sea ice is the controlling load. Full scale measurement for many years shows the design of some ice-resistant platforms is not so sophisticated, the most significant is that ice induced vibration is the main which has caused harmful accidents in Liaodong bay of Bohai. In order to ensure security operation, structural safety ensuring in winter becomes key problems. In this paper, sea ice management system oriented structural safety ensuring of oil or gas ice-resistant platforms in ice zone is presented. By combining structural monitoring, safety assessment and risk forecast, the system belays and incorporates high safety, cost-benefit, alternative emergency measures.
In-Situ Estimation of Surface Crack Shape From Crack Opening Displacement by Use of NCOD Database System
Authors: Yue Jingxia , He Zheng , Fujimoto Yukio , Wu Weiguo
Published: January 2011

This paper proposes an in-situ estimation of crack shape from crack opening displacement (COD) by using of a visualized database system consisting of numerical calculation data of normalized crack opening displacement (NCOD) for some kinds of crack types. The relation between crack depth and corresponding NCOD is discussed based on FE analysis results, from which a crack shape estimation principle is deduced. Visualized software named NCOD Database System was developed to facilitate convenient in-situ estimation of crack shape. Shapes of three kinds of surface crack, partial circle crack in plate, fatigue cracks in gusset weld joint and in large-scale member, are successfully estimated by this system. The paper is supported by the Programme of Introducing Talents of Discipline to Universities (B08031).
Practicability Research and Design of the Underwater Plane
Authors: Wu Chao , Wang Qiang , Yan Hui , Liu Jianmin , Zhuang Guangjiao , Ge Tong
Published: January 2011

When traditional underwater vehicles (TUV), including AUVs, ROVs, submarines and underwater gliders, cruise, they are neutral in buoyancy normally and their buoyancy are produced by buoyancy materials or big ballast tanks, thus these components take up the major part of the vehicles’ volumes. Differently, an underwater plane (UP) cruises in the condition of negative buoyancy. Its wings bear the residual gravity, which makes its resistance and volume decreased drastically at the same speed and with the same payload. To prove the practicability of the UP, we find the advantages of the UP in the velocity or resistance and volume compared with the TUV on the same premise through theoretical arithmetic. So far, a model, we designed in the similar way of designing an airplane, has been manufactured to make sure that the UP could work in water. In a model trial in the tank, the model completed regular motions well and shown good maneuverability and stability. So, the concept of the UP is not only practicable but valuable.
Numerical Simulation of Rogue Waves Based on the Fourth-Order NLS Equation for Laboratory Experimental Investigation
Authors: Hu Hanhong , Ma Ning , Wang Xuefeng , Gu Xiechong
Published: January 2011

The main purposes of investigating the generation of the rogue waves in offshore engineering include: 1) prediction of its occurrence to protect the offshore structure from attacking; 2) the experimental investigation of rogue waves/structure interaction for the structure design. The latter one calls high requirement of wave generation and calculation. In this paper, we establish a spatial domain model of fourth order nonlinear Schro¨dinger (NLS) equation for describing deep-water wave trains in moving coordinate system. For the first purpose mentioned above, this paper presents the evolution of random wave trains in real sea state described by the Joint North Sea Wave Project (JONSWAP) power spectrum numerically, which is governed by the NLS equation. The parameters of the spectrum are evaluated to discuss their effect on the occurrence of rogue waves. For the second purpose to generate rogue waves in experimental tank efficiently, the transient wave is focused for its allowance of precise determination of concentration place/time. First we simulate the three-dimensional transient waves in the numerical tank modeling the deepwater basin with double-side multi-segmented wave-maker in Shanghai Jiao Tong University (SJTU) with linear superposing theory. To discuss its nonlinearity for the guidance of experiment, the transient wave is set as the initial condition of the NLS equation and the difference from the linear simulation is presented, which could be given as the suggestion to the preparation of experiment.
Effects of Strain Rate on Fracture Toughness in Sour Environment
Authors: Yuan Wen Guo , Xu Da Qin , Wu You You , Tronskar Jens P.
Published: January 2011

Fracture toughness testing in sour environment using Single Edge Notch Tensile (SENT) and Single Edge Notch Bend (SENB) specimens has been developed and applied by authors’ laboratory for Engineering Critical Assessment (ECA) of pipeline girth welds. The method of testing and application of fracture toughness result for ECAs of pipeline girth welds for sour service has been presented at a previous OMEA conference (paper OMAE2009-79305). The current paper presents the results of further experimental work carried out to evaluate the effect of strain rate on the fracture toughness value. A series of fracture toughness tests using SENT specimens was carried out in artificial brine sour environment (NACE solution “A” saturated with H2S) at ambient temperature. For comparison, the result from test in air condition are also presented and discussed. Following the test, the J-integral and the CTOD values were calculated and assessed. As expected, the results show significant effect of strain rate on the J integral value and the CTOD, especially for the strain rate range between 10−6/s to 10−7/s. Further experiments and studies are suggested to establish appropriate procedures and guidelines for selection of suitable strain rates for sour environment fracture toughness testing of pipeline girth welds.
Numerical Calculation of the Dynamic Responses of Vessel Mast Structure Under Air Explosion
Authors: Li Xiaobin , Zhang Peng , Wei Xing , Wu Weiguo
Published: January 2011

Mast is defined as Grade A equipment which is essential for the safety and continued combat capability of the ship. Therefore, it is very necessary to evaluate the mast shock resistance under air explosion. However, it is very difficult to get the shock loading on the structure aroused by air explosion since it is varied with time and space. Flux-Corrected-Transport (FCT) algorithm is a high-order, monotone, preserving positive finite-difference algorithm. In this paper, a program is presented for air explosion load calculation based on FCT algorithm. Taking the coupling of air and mast into consideration, the pressure time history of each element on the surface of the mast is computed according to the program. A data file about the pressure load is written to integrate the commercial finite element software of LSDYNA. Furthermore, the dynamic responses of the mast are calculated based on LSDYNA. The capability of shock resistance under air explosion of the mast can be evaluated according to the calculation results, which can provide references for mast anti-explosion design.
Effect of Variations in Calibrated Wave Parameters on Wave Crest and Height Distributions
Authors: Hennig Janou , Scharnke Jule
Published: January 2011

In common model test practice, wave power spectra are calibrated prior to the actual model tests. The resulting wave crest and height distributions can be determined from the measured wave time traces at different reference location in the basin but they are not calibrated purposely. The corresponding wave group spectra follow from the wave power spectra together with arbitrarily chosen wave seeds applied to the wave trains. As an alternative approach, the seeds which give the highest and lowest wave group spectra can be applied in the tests. In this paper, results of wave measurements in MARIN’s Shallow Water Basin are presented which include a variation in water depth, wave seed (group spectrum) and location of measurement for the same initial wave power spectrum. The resulting wave crest and height distributions at different wave basin locations are analyzed and compared to theoretical distribution functions. A discussion of possible reasons for differences between theory and measurement concludes the investigation.
Active Vanning Device and Maintenance System for Horizontal Axis Tidal Current Turbine
Authors: Jo Chul-hee , Lee Kang-hee , Rho Yu-ho
Published: January 2011

The application of TCP (Tidal Current Power) on the west and south coastal regions in Korea seems to be very suitable. There are many potential sites with high current speed up to 6.5m/s. Not like other renewable energy sources, TCP is very reliable and predictable and continuous energy as the tidal current pattern can be predicted throughout the year. One of the essential components in TCP device is the rotor that can convert the inflow current into the rotational energy. The design and optimization of rotor are very important to maximize the power production. The performance of rotor can be determined by various parameters including number of blades, shape, sectional size, hub, diameters and etc. The attack angle also affect significantly on the efficiency of the system. It is very important to maintain the 90 degree of attack angle to the rotor. In Korea, there are distinguishable flow direction changes from high and low tides. To cope with this environmental, a new device so called “Active vanning HAT (horizontal axis turbine) system” is introduced to accommodate the change of incoming flow direction. The experiment results and the performances of the device are introduced in the paper.
Effect of Applying 2nd Order Wave Theory on Pipeline Dynamic Response
Authors: Zeitoun Hammam , To̸rnes Knut , Oldfield Stuart , Cumming Gary , Pearce Andrew , Sabavala Hosi , Stroud Stan , McConochie Jason
Published: January 2011

Ensuring subsea pipelines on-bottom stability by determining the stabilisation requirements which will limit pipelines movement under extreme waves and currents is an essential aspect of subsea pipelines design. These requirements can be a major project cost driver in some locations around the world, where the designer is faced with severe metocean conditions. This is particularly the case when the selected design solution is associated with costly stabilisation requirements such as trenching, anchoring [14], rock dumping, or mattressing. An appreciation of the pipeline structural response, when exposed to waves and steady currents kinematics is fundamental to optimise the stabilisation solution. An advanced approach used to optimise stabilisation requirements is to use transient dynamic finite element analysis. The analysis is used to simulate the dynamic response of subsea pipelines exposed to near-seabed kinematics, due to a combination of steady currents and waves. Wave kinematics at the seabed are therefore an essential input to the analysis and will significantly affect both the hydrodynamic loads on the pipeline and the pipeline response. The typical method for generating the wave kinematics in a dynamic analysis has been based on calculating the near-bed velocities corresponding to a randomly generated seastate, using linear wave theory. It has been acknowledged that this calculation is likely to produce a conservative estimate of the positive wave velocities. An improved prediction of seabed kinematics can be achieved by using higher order wave theories. Application of higher order wave theories, results in changing the velocity magnitude under wave crests and troughs. This change in kinematics may result in a change of pipeline response. This paper investigates the effect of using 2nd order wave theory for predicting the kinematics on the pipeline dynamic response. Dynamic finite elements analysis is used for determining the pipeline response and to compare the pipeline response when using 2nd order wave theory and linear wave theory. The work presented in this paper was commissioned by Woodside and performed by J P Kenny Pty Ltd.
An Experimental Analysis of the Interaction Between Hanged Pipe and Internal Flow
Authors: Yamamoto Marcio , Murai Motohiko , Uto Shotaro , Fujiwara Tomo , Kanada Shigeo , Quadrante Luis A. R. , Haneda Ken
Published: January 2011

The pipes are playing an important role in the offshore environment. Risers and pipelines are widely deployed by the petroleum industry for the well drilling and hydrocarbons production. Whereas during drilling, a mixture of drilling mud and solids in suspension (rock cuttings) flows through the drilling riser; during the production, mono or multiphase flow (comprising oil, water and gas) takes place within the production system. However up till now, most of investigations on offshore pipelines and risers have neglected the effects of the internal flow and have focused mainly on the interaction among pipe’s structure, hydro-dynamic forces and offshore platform’s motion. This paper deals with the interaction between the pipe structure and its internal flow. An experimental analysis was carried out, in the Deep Sea Basin of the National Maritime Research Institute (Japan), using a model of 10 m length. In this experiment, a mono-phase fluid of liquid and another bi-phase fluid of liquid and solids in suspension are used as the internal flow fluid and a parametric analysis using the internal flow rate and pipe’s oscillating frequency was carried out. Discussion about the experimental results is also included.
Plastic Collapse Load Investigation for Safety Assessment of Cracked Square Hollow Section (SHS) T-, Y- and K-Joints
Authors: Lie Seng Tjhen , Zhang Baofeng
Published: January 2011

The plastic collapse load play a critical role in the entire procedure of constructing Failure Assessment Diagrams (FADs) of cracked tubular structures. In this study, the models of square-to-square hollow section (SHS) T-, Y- and K-joints with the actual 3D surface cracks obtained from previous fatigue tests are generated, and their general plastic collapse behavior has been studied carefully using the elastic-plastic finite element analysis. Based on the extensive FE analyses, the fully plastic collapse load solutions for the cracked SHS joints under brace end axial loads are proposed and derived. The load-displacements curves are plotted for predicting the plastic collapse loads based on the twice-elastic compliance criterion. Compared with formulae proposed in BS7910 [1], it was found that a conservative plastic collapse load for the SHS joints under brace end axial loads is produced using the proposed formulae. Future works are recommended for validation of BS7910 [1] FADs for damaged SHS T-, Y- and K-joints based on the numerically calculated plastic collapse load.
Numerical and Experimental Study of Natural Backfill of Pipeline in a Trench Under Steady Currents
Authors: Wu Di , Cheng Liang , Zhao Ming , Wang Yongxue
Published: January 2011

After a sub-sea pipeline is laid in a trench excavated on a sandy sea bed, the sand around the trench will be washed into the trench by the flow, leading to natural backfill. Natural backfill is beneficial to the stability of the pipeline and cost saving. In this study, natural backfill of pipeline trench under steady currents was investigated experimentally and numerically. Experimental tests were carried out in a water flume of a size of 0.4 m in width, 0.6 m in height and 25 m in length. The model pipeline with a diameter of 5 cm was placed in a V-shape trench. The direction of steady current was perpendicular to the pipeline. Tests were carried out in both clear-water scour and live-bed scour conditions. The bed profiles at different stages of backfill process were measured by a laser profiler. It was found that the upstream part of the trench was backfilled faster than the downstream part. In the early stage of the backfill process, sand in front of the pipeline was washed into the trench very fast. The top part of the sand behind the pipeline was washed away faster while the lower part moved towards the pipeline due to strong vortices. Two-dimensional scour model developed by Zhao and Cheng (2008) was used for simulating the backfill process numerically. This model was validated against van Rijn’s (1986) navigation channel migration experiments and good agreement between experimental data and numerical results was achieved. Numerical simulation of the pipeline trench evolution was carried out under the same conditions used in the laboratory tests. The process of the backfill simulated by the numerical method agreed qualitatively with the test results. The comparison between the numerical and the test results showed that: (1) the simulated backfill rate was greater than the measured one in the upstream side of the pipeline; (2) the sand dune downstream the pipeline was washed away slower than the experimental results, and no backfill was observed. The discrepancy between the experimental and numerical results may be attributed to the fact that the empirical formulae used for predicting the bed load and the reference concentration of suspended load were derived from fully-developed straight channel flow tests, while the velocity varied dramatically along the bed in the cases of this study.
Variation of the Short Term Extreme Ice Loads Along a Ship Hull
Authors: Suyuthi Abdillah , Leira Bernt J. , Riska Kaj
Published: January 2011

This paper focuses on the short term probabilistic analysis of ice loads acting on a ship hull. The ice load data was obtained from full scale measurement onboard the Norwegian coast guard vessel KV Svalbard during the winter of 2007. The available data corresponds to discrete peak amplitude time histories of estimated ice impact loads as well as corresponding measurements of ice thickness in addition to ship speed and course. There were several number of sensors installed along the hull, either on the port side and starboard side of the bow part. The present paper focuses on the variation of the predicted extreme ice loads acting on the ship hull for a short time duration. The short term prediction of ice loads as an integral part of an Ice Loads Monitoring (ILM) system is very important in relation to the tactical navigation plan. An inexpensive ILM system would requires less number of sensors mounted on the hull. By addressing the variation of the extremes along the hull, it will be possible to make decisions regarding the minimum number of sensors and their location without loosing the accuracy of the predicted extremes. Three different approaches for predicting the short term extremes are considered, i.e. the classical extreme value distribution approach, the time window approach, and the up-crossing rate approach. In general, all the approaches involve the following two steps: (i) establishment of the estimated distribution model, (ii) calculation of the expected largest extreme ice impact load for an extrapolated duration. Comparison of the results obtained by the three different approaches is made, and some limitations of the various approaches are discussed.
Estimation of Hydrodynamic Coefficients for VIV of Slender Beam at High Mode Orders
Authors: Wu Jie , Larsen Carl M. , Lie Halvor
Published: January 2011

The Hano̸ytangen test program was caried out by MARINTEK for Norsk Hydro in 1997. One purpose of this research effort was to investigate VIV response of deep sea risers subjected to sheared current. A densely instrumented 90 meter long riser model was tested in shear current, and bending strains along the riser was measured. Oscillatory part of both in-line (IL) and cross-flow (CF) displacements can be obtained by applying modal analysis on the bending moment measurements. The primary results from the analysis are that the riser is vibrating at high modes in cross-flow direction (10th–30th mode). The response is dominated standing waves for the lowest speed cases and gradually is influenced by traveling waves for increasing speed. For highest speed cases, it is dominated by traveling waves. The vibration amplitude is significantly smaller than for a rigid cylinder under equivalent conditions. Inverse force analysis estimates hydrodynamic forces from measured response of a slender beam. The method has previously been applied to rotating rig test data. The response was for these cases dominated by relatively low mode orders and standing wave responses. To understand the stochastic behaviour of high mode VIV response, the method is applied to Hano̸ytangen test in the present study to provide valuable insights by estimating CF hydrodynamic forces and coefficients from displacement time series found from modal analysis of measured strains. The results from this work are presented in terms of CF hydrodynamic force coefficients, excitation region and their variations in time and space. New excitation database is extracted based on the analysis results. They are used in VIVANA to predict the displacement and stress against experiment results.