bluuebunny/crossref_metadata_2025 huggingface dataset:
Cost and Profitability Analysis of Modular SMRs in Different Deployment Scenarios
Authors: Boarin Sara , Ricotti Marco E.
Published: February 2010

The loss of economies of scale affects Small and Medium sized Reactors’ (SMRs) overnight construction costs, as compared to Large Reactors (LRs) and is particularly burdensome to the financial performance of a capital intensive project as a Nuclear Power Plant (NPP). Nevertheless, multiple SMRs projects have factors that mitigate the loss of economies of scale. Furthermore, by exploiting investment scalability, SMRs are able to limit the capital investment and to self-finance the construction of later units with operating cash flow from early deployed units. In our forecasted scenarios, SMRs lower profitability for the shareholders may be counterbalanced by savings in Equity capital investment, as compared to LR. This reduces sunk costs and investment risk of SMRs project under uncertain market conditions, in a “merchant plant” scenario where business profitability is as valuable as business risk.
A Simple and Reliable System for Detecting and Measuring Gas Voids in Safety-Related Fluid Systems
Authors: Estrada Herb , Hauser Ernest M.
Published: February 2010

Over the past 20 years there have a number of instances where nuclear power plant operators have discovered gas voids—typically air but occasionally other gases such as undissolved hydrogen—in fluid systems whose function is important to reactor safety. These systems have included emergency core cooling systems, decay heat removal systems, and containment spray systems. The amount of gas has, in some cases, been sufficient to call into question the operability of the systems; had they been needed. The automatic initiation of a system with a gas void present may lead to gas binding of its pumps, or destructive water hammer. The sources of the gas have been various and not readily controlled. The need for licensees to manage gas accumulation has been formally identified in an NRC generic letter (1). The letter points out a need for continuous monitoring, to detect and quantify gas voids in these systems, thereby to ensure their availability in accordance with design basis requirements. The letter further notes that periodic functional tests of the critical systems will not provide the required assurance of operability; if a periodic test finds a system’s functionality questionable because of gas accumulation, the question of how long its operability has been compromised is unanswered. The system described in this paper—the Linewatch Gas Void Detection System—addresses these issues definitively. It provides the means to detect the onset of void formation in any one of multiple pipes in multiple systems on a continuous basis and, following void formation, the means to quantify the amount of these voids, again continuously.
Simulation of a Once-Through, Helical-Coiled Steam Generator of High Temperature Gas-Cooled Reactor
Authors: Ye Jinliang , Zhou Yangping , Chen Xiaoming , Ma Yuanle , Li Fu , Dong Yujie
Published: February 2010

A quasi-static model of a helical coiled Once-Through Steam Generator of High Temperature gas-cooled Reactor-Pebble Bed Module (HTR-PM) is developed based on the fundamental conservation of fluid mass, energy and momentum. The steam generator is handled with single tube concept and is divided into three regions as subcooled region, boiling region and superheated region. The equations are solved by Rung-Kutta method. The steady-state simulation results agree well with the design data. Furthermore, the results are compared with the results gotten from THERMIX/BLAST program, and the difference between them is small which shows the model and the methodology are reasonable.
Power Conversion System (PCS) Options for Generation IV Nuclear Plant
Authors: Persson Jenny , Donaldson Anthony J.
Published: February 2010

The next stage of Generation IV High Temperature Gas-Cooled Reactor (HTGR) is currently under development for production of electricity and process heat. High outlet temperature of the helium coolant makes it possible to use gas turbines in future power conversion systems. This paper compares the costs and risks of various direct and indirect power conversion systems to evaluate the best commercial electricity generation option. It concludes that, although a direct cycle was predicted to be more efficient, a significant cost and risk reduction will be achieved for an indirect cycle for the near term commercial electricity generating plant. The indirect Combined Cycle Gas Turbine (CCGT) cycle offers excellent efficiency, together with lowest risk and cost for the near term commercial plant. This combines a gas turbine of low-risk design with a current technology steam system. However, the intermediate heat exchanger (IHX) represents a major development item and also introduces some major risks. The implications of the IHX risks have not been fully assessed. In the longer term, when development of high risk and high cost components such as electro-magnetic bearings are more mature, a direct cycle may merit reconsideration on the grounds of elegance and simplicity, in particular a direct Brayton cycle.
ABWR Containment Analysis Model Qualification Using the GOTHIC Code
Authors: Douglass J. , George T. , Jain N. , Barnett N. , Gallagher D. , Ofstun R. , Loehlein B.
Published: February 2010

Westinghouse is developing the capability to perform containment analyses for the advanced boiling water reactor (ABWR) design. These analyses include the following: the short-term primary containment peak pressure and temperature response, short-term suppression pool swell response, and secondary containment compartment pressure and temperature response. The GOTHIC code, developed by Numerical Applications Incorporated (NAI) with funding from the Electric Power Research Institute (EPRI) is used for the ABWR containment response analyses. The code is capable of performing multidimensional analyses for models containing mixtures of air, steam, water, and other gases. It is qualified by a wide range of experimental tests that cover the important phenomena associated with containment design analyses. It has been used extensively for existing BWR and PWR power plants and this paper focuses on the extension to ABWR designs. The GOTHIC ABWR containment modeling approach is described and the results are compared with results from other previously accepted containment analysis methods.
The Use of TOFD for Enhancement of HDPE Pipe Fusion Inspection
Authors: Smith Clayton T. , den Boer Peter , Corley Lonnie
Published: February 2010

HDPE piping has been historically used in place of steels in petrochemical, power, and mining industries to mitigate corrosion and erosion issues. Additionally as HDPE pipe is resistant to Microbiologically Influenced Corrosion (MIC) and fouling, it appears to be a perfect fit for nuclear safety related cooling water applications. To this end, HDPE was first used in an ASME Class 3 emergency service water system, in 2005 at Sizewell B, operated by British Energy, in the United Kingdom. The long successful history of non-nuclear HDPE pipe operating experience along with the successful operation at Sizewell B and other non-safety related nuclear applications has now resulted in the first use of HDPE pipe for a safety related class 3 application in the United States nuclear industry at the AmerenUE-Callaway nuclear power plant. The application of nuclear quality assurance requirements coupled with stringent procurement, manufacturing and fabrication controls create a reasonable assurance that the production fusion joint should be sound; using Ultrasonic Time of Flight Diffraction (TOFD) inspection of the fusion joints is a volumetric, nondestructive examination tool available to provide additional assurance of the fusion joint integrity.
Research Reactor VR-1 and Determination of Neutron Spatial Distribution in Its Radial Experimental Channel
Authors: Mileticˇ Marija
Published: February 2010

The research reactor VR-1 is operated by Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University (CTU) in Prague. It is a pool-type, light-water reactor, with low enriched uranium. Maximum thermal power is 1kW (equal to 1·108 impulses/second when compared with reactors with higher power). Research on VR-1 reactor is mainly used for the education of university students, preparation and testing of new educational methodologies, investigation of reactor lattice parameters, reactor dynamics study, research in the control equipment field, neutron detector calibration, etc. One of the applications performed by students is the determination of the absolute value of the neutron flux density (also known as Neutron Spatial Distribution) in the radial experimental channel in reactor VR-1. The method used for this measurement is Neutron Activation Analysis. The principle of this method consists in neutron capture in a nucleus of the material forming the activation detector which is irradiated in the experimental channel. The activity of the produced radioactive products (radioisotopes) is then measured by means of appropriate counter system (in our case, High Purity Germanium detector). For this measurement totally 34 gold foils were irradiated at different reactor power levels and various positions in radial channel in aim to determine the neutron spatial distribution in radial channel. Interesting results about symmetry, value and dependence on reactor power level of neutron flux density were obtained.
Development of WCOBRA/TRAC-TF2 Computer Code: Coupling of the 3D Module (COBRA-TF) With the 1D Module of TRAC-PF1/MOD2
Authors: Frepoli Cesare , Ohkawa Katsuhiro , Nissley Mitch
Published: February 2010

Westinghouse realistic Large Break LOCA methodology (Frepoli, 2008) is based on the use of the WCOBRA/TRAC code (Young, et. al., 1998). The original COBRA/TRAC code (Thurgood, et. al., 1983) was developed at Pacific Northwest Laboratory by combining the COBRA-TF code (Thurgood, et. al., 1980) and the TRAC-PD2 code (Liles, et al., 1981). Later the code was significantly upgraded at Westinghouse and validated for Large Break LOCA (LBLOCA) phenomena and renamed WCOBRA/TRAC. The current WCOBRA/TRAC has been shown to adequately model LBLOCA phenomena which are mainly dominated by the thermal-hydraulic phenomena in the vessel component. Westinghouse is now looking at extending the code applicability to smaller break sizes such that the same code can be applied to a full spectrum of LOCAs, from small to intermediate break as well as large break LOCAs. Several upgrades have been made to the code which has been renamed WCOBRA/TRAC-TF2. In this new code, the TRAC-PD2 module was replaced by the 1D module of TRAC-PF1/MOD2 code (Los Alamos, 1993, Spore, et. al., 2000). TRAC-PF1 is based on a two-fluid (6-equation) formulation as opposed to the 5-equation drift-flux model of TRAC-PD2. The new formulation allows a more realistic simulation of the two-phase flow features in the PWR loops during a SBLOCA scenario. This paper also describes some of the improvements added to the code and the assessment needed to extend its applicability to the full spectrum of LOCA scenarios or break sizes.
Numerical Simulation of Wind Effects on Breaking Solitary Waves by Navier-Stokes Equations
Authors: Xie Zhihua , Wen Xianyun , Ross Andrew N.
Published: February 2010

A two-phase flow model is addressed in this study to investigate effects of wind on breaking solitary waves, by solving the Reynolds-averaged Navier-Stokes (RANS) equations simultaneously for the flows both in the air and water, in which the free surface is calculated by the Volume-of-Fluid (VOF) method. First, the proposed model is validated with the experiment by Synolakis [1] of a breaking solitary wave without wind on a 1 : 19.85 impermeable beach. Then the wind effects are taken into account for modelling breaking solitary waves and it is found that the wind alters the air flow structure above the water wave; affects the wave breaking and runup process; increases the velocity in the water and causes the waves to break earlier, which agrees with previous laboratory experiment by Douglass [2].
Compressive Strain Limit of Aged API-X100 Linepipe
Authors: Cho Woo Yeon , Seo Dong-Han , Yoo Jang-Yong
Published: February 2010

In compressive strain capacity, high deformable linepipe steel, which is able to delay or evade local buckling, is needed. The objective of this paper is to present the results of an experimental and a finite-element investigation into the behavior of pipes subjected to bending behavior of aged API-X100 linepipe. The comparative behavior of aged and non aged specimens was recorded. The Results from numerical models are checked against the observations in the testing program and the ability of numerical solutions to predict pipe compressive strain capacity, curvatures, and buckling modes is improved. A finite-element model was developed using the finite-element simulator ABAQUS to predict the local buckling behavior of pipes. The input stress-strain relations of the material were discussed using the indexed yield point elongations. The comparison between the results of yield point elongation type material and those of material of smooth stress-strain curve near yield was done.
Modelling Techniques and Case Study of Explicit 3D FE-Simulation of Ridge Loads Against an Offshore Structure
Authors: Heinonen Jaakko
Published: February 2010

A ridge interaction with an offshore structure, Norstro¨msgrund lighthouse in the Gulf of Bothnia, was simulated by the finite element method (FEM) utilizing the explicit solution algorithm. The explicit method in a dynamic analysis enabled an efficient way to simulate the failure of a ridge. A shear-cap material model describing the ice rubble mechanical behaviour was developed for the 3-dimensional analysis and implemented into ABAQUS FEM-software as a user material subroutine. The FE-model described the ridge: the sail and keel consisting of ice rubble and the consolidated layer close to the waterline. A selected ridge-interaction event was simulated with a simplified geometry, based on measurements carried out in the STRICE project. The ridge field was idealized to have a constant thickness. The shape of a 3-dimensional structure was modelled using rigid elements. The phenomenological model can be utilized to gain an understanding of how the ridge fails during the interaction with an offshore structure, what the ridge loads are, and how they are distributed against the structure. A parametric study was carried out to study how the mechanical properties, i.e. the cohesion and friction angle of the rubble and the strength of the consolidated layer influence the forces and failure mechanisms.
Breaking Wave-Induced Dynamic Response of Rubble Mound and Seabed Under a Caisson Breakwater
Authors: Ulker M. B. C. , Rahman M. S. , Guddati M. N.
Published: February 2010

A finite element (FE) model is developed to study the breaking wave-induced dynamic response of the porous seabed and the rubble mound foundation under a composite caisson-type breakwater. The breaking wave impact pressure distributions on the front face of the breakwater are calculated using a recently proposed method. In this study the focus is on the dynamic response of the foundation materials underneath the breakwater. The impact response of the seabed and the rubble mound is presented in terms of pore pressure and shear stress induced around the breakwater. A complete formulation of the fully dynamic response requires inclusion of the inertial terms associated with both the motion of solid skeleton and that of pore fluid. However, partly dynamic and quasi-static idealizations are also possible. The objective of this study is to investigate the effects of the inertial terms on the breaking wave induced impact response of the seabed as well as the rubble. The effect of seabed saturation on the response from different formulations is also examined.
Synergistic Use of Satellite and In-Situ Current Data to Improve the Characterisation of Seasonal Trends
Authors: Harrington-Missin Liam , Calverley Mark , Jeans Gus
Published: February 2010

The synergistic use of measured in-situ current data and altimetry derived geostrophic current data provides improved seasonal characterisation of the current regime, West of Shetland. In September 2007, considerable downtime was experienced by an offshore operator, West of Shetland, as a result of unexpectedly high currents persisting for a number of days. This downtime was unanticipated following conclusions derived from one year of in-situ measured data, which suggested a most favourable current regime during the months August to October. Ten years of altimetry derived geostrophic currents were utilised in conjunction with approximately 3 years of in-situ data to assess the validity of the reported seasonal trend. The altimetry derived geostrophic currents correlated well with the dominating long period signal extracted from the in-situ data. Seasonal comparison between the altimetry derived geostrophic currents and the total measured signal showed the previously available measurement year had a relatively benign September. Based on the 10 years of satellite data, the inter-annual variability of the current regime West of Shetland does not show any clear seasonal trend.
Tidal Flat Erosional Features of the Modern Yellow River Delta
Authors: Meng Xiangmei , Jia Yonggang , Shan Hongxian , Song Jingtai
Published: February 2010

In July and October of 2008, selected physical-mechanical sediment properties were measured at 20 tidal flat experiment stations of 8 regions along the seashore of the modern Yellow River delta. At the same time, the environmental characteristics were observed. Seabed properties were compared with measurements of sediment erodibility made at the same stations to gain insight into the bioturbation and physical-mechanical sediment properties’ controls on sediment erodibility. Results indicate that crabs obviously alter the surface roughness of seabed, which makes the sediment more easily eroded than the neighboring area without crabs. Sediment erodibility along the seashore of the modern Yellow River delta varies in different stations. The critical erosion shear stress varies between 0.088 Pa and 0.254 Pa for all measurements. The factors influencing sediment erodibility are complicated. No clear relationship was found between distinct physical-mechanical sediment properties parameters and the critical erosion threshold except that there’s a positive correlation between shear strength and critical erosion shear stress. Further studies are needed to more accurately resolve the relationship between erodibility and sediment properties.
Pipe-in-Pipe Substructure Modeling in Deepwater Riser Design Analysis
Authors: Luk C. H. , Yiu F. , Rakshit T.
Published: February 2010

Substructure modeling using pipe-in-pipe (PiP) elements in a finite element program allows representation of dynamic interaction between riser components. This modeling technique is especially useful when it comes to the design of a complex riser system in deepwater applications. In this paper, the ABAQUS finite element program was used to illustrate the substructure models and the results for dynamic analysis of a classic Spar top tension riser (TTR) system in the Gulf of Mexico subjected to a given Hurricane Rita sea state. Nonlinear contacts between the buoyancy can and compliant guides are represented by two different substructure models: compliant guide surface model with friction and frictionless compliant guide spring model. The effects of centerwell hydrodynamic forces were considered. ABAQUS dynamic results were compared between the PiP substructure model and a conventional structure model treating the buoyancy can and the riser inside as a composite beam. The PiP guide friction surface model with centerwell hydrodynamics theoretically is the most representative model for riser analysis. However, the PiP guide spring model is more computationally efficient. It generates comparable guide loads but produces lower riser fatigue damage than the PiP guide friction surface model. The composite beam model leads to guide loads comparable to the PiP model, but cannot be used to determine the spacer loads between the buoyancy can and riser. The composite model also could underestimate riser stresses and riser fatigue damage within the buoyancy can region. The riser guide loads and riser damages from the calculation models without centerwell hydrodynamics are generally higher than those by the same calculation models with such consideration. It was concluded the PiP guide spring model can be used for riser design in lieu of the PiP guide surface model. The additional fatigue damage contribution from axial tension variation due to guide surface friction could be accounted for by adding a damage factor to the total fatigue damage along the riser.
Spacing Effect on Hydrodynamics of Two Adjacent Offshore Caissons
Authors: Tao Longbin , Song Hao , Chakrabarti Subrata
Published: February 2010

In this paper, scaled boundary finite-element method (SBFEM) is extended to study wave interaction with two adjacent rectangular cylinders. In addition to the advantages in accurate and efficient representation of singularities and unbounded domains, the modified SBFEM shows distinct capability in dealing with wave diffraction including adjacent multiple structure interactions. Comparisons of wave runup and wave forces on each cylinder of the two adjacent offshore caissons with traditional panel method demonstrate a high accuracy achieved with excellent computational efficiency. Detailed results and discussion of the spacing effect on the hydrodynamics of the two cylinder system are presented. Design recommendations are made based on the maximum wave forces on both caissons.
Wave Scattering From Multiple Horizontal Plates as a Breakwater
Authors: Wang Guoyu , Wang Yongxue
Published: February 2010

The multiple horizontal plates breakwater is proposed in this article, which mainly consists of several horizontal plates. The regular wave test results demonstrate that it has good performance of dissipating waves. Based on the linear potential wave theory, the scattering of waves normally incident on the multiple horizontal plates in a channel of finite water depth is investigated. The velocity potential is split to the symmetric and antisymmetric part, and the method of eigenfunction expansions is used to obtain the unknown constant coefficients determined from the matching conditions. The thickness of the plates is considered in the theoretical analysis. The present solution is compared with the existing theoretical, numerical and experimental results with good agreements. The parameters such as the relative water depth, relative plate width, relative plate thickness and number of plates, those identified with the performance of the breakwater are investigated and discussed. The variation of reflection and transmission coefficients alone with the above mentioned parameters are also presented.
Field Test on Quasi-Impermeable Seawalls Using Clayey Materials for Coastal Waste Disposal Sites
Authors: Ueno Kazuhiko , Yamada Koichi , Watabe Yoichi
Published: February 2010

A waste disposal site to be constructed in a coastal area is generally surrounded by seawall structures to accommodate waste reclaimed. In case that the seawalls are required to prevent substances contained in waste from leaking out to the sea, they are constructed as quasi-impermeable structures. The quasi-impermeability of the structures is required to be retained by self-sealing performance even in their deformed conditions to be possibly caused by deformation of soft ground or actions of earthquake, wave, tide etc. In addition, it is preferable for quasi-impermeable material to have the features of long durability and adjustability in its fabrication to suit for various construction conditions. We have developed a new quasi-impermeable material with the features of self-sealing, long durability and adjustability in its fabrication by main use of dredged marine clay taking advantage of its low impermeability. In the relevant standard of ministerial ordinance, quasi-impermeable seawall structures are required to have the thickness of 0.5m or more and equivalent hydraulic conductivity of 1.0×10−8 m/s or less. In this study, proposed is a quasi-impermeable seawall structure with steel frame by jointing H-steel sheet piles and such clayey quasi-impermeable material filled inside the frame. The overall performance of the proposed structure was examined in a field test exposing it to a natural sea condition for more than one year. The self-sealing performance of the structure was also examined in the test after intentionally deforming it. Regarding the quality of filling clayey material, the homogeneity of filling was investigated by sounding and sampling tests. It has been confirmed that the structure realizes quasi-impermeability with equivalent hydraulic conductivity of the order of ke = 10−9 m/s, which satisfies the design criteria prescribed by a ministerial ordinance in Japan to allow for practical use in the sea.
Estimation of Local Ice Pressure Using Up-Crossing Rate
Authors: Li Chuanke , Jordaan Ian J. , Taylor Rocky S.
Published: February 2010

Ice load estimation is required for offshore structures designed for arctic and sub-arctic conditions. This paper focuses on the estimation of local ice pressures. The ‘event-maximum’ method for local ice pressure analysis is based on the maximum pressure of a given event; other local peaks in the data are not included. To study how this may affect local ice pressure estimates, a method based on the up-crossing rate was developed. Field data from 1982 Polar Sea arctic trials in the Beaufort Sea are processed as a time series. Up-crossing rates at different local pressure levels are obtained for local areas of interest. A relationship between up-crossing rate and local pressure-area results is established. Results from the analysis of full-scale data using the event-maximum method are presented in a companion paper. For a sample case, local ice pressure estimates obtained using the up-crossing rate method are compared with those presented in the companion paper, based on analysis using the event-maximum method. The local pressure-area relationship is found to be similar for both the up-crossing rate method and the event-maximum method. Both methods and corresponding analysis results are compared.
A Methodology for Calculating the Hydrodynamic Forces for Structural Analysis Using the High-Order Method
Authors: de Menezes Fabio Gouveia Telles , de Souza Silva Rodrigo
Published: February 2010

In the design of floating production units, the wave loads play an important role in the structural sizing as a function of pressure distribution around the hull. The main dificult from the computatinal point of view is the existing difference between the elements for the structural analysis mesh and the traditional flat panels distributed on the hull surface: the low order approach, in which source strengths are located at each panel centroid. Such dificult takes the interpolation proccess between adjacent panels mandatory in order to obtain the potential value and then the pressure acting on a given structural element. The objective of this work is to demonstrate the feasibility of calculating the hydrodynamic forces acting on a floating system by using the high-order capabilities of WAMIT. In such approach the body surface as well as the potential function is represented by B-Spline tensor functions. The advantages of this methodology are the improved accuracy in the results and the reduced computational cost. The B-Spline representation is polinomial and for this reason continuous up to (degree-1)th derivative. This caracteristic permits the definition of the pressure distribution on the body continuously, and then a structural mesh can be projected on the body and the hydrodynamic forces on that precisely defined. Finally, the loads can be exported easily to a FEM solver in order to achieve the strutural requirements properly. A FPSO is considered as the study case. The hydrodynamic forces are obtained at each structural node using both methods (high-order and low-order) and a comparison is made in order to validate the results obtained as well as to evaluate the performance of the mentioned approaches.
Steel Catenary Riser Response Characterization With On-Line Monitoring Devices
Authors: Karayaka Metin , Ruf Wolfgang , Natarajan Shreenaath
Published: February 2010

Steel Catenary Risers (SCR) are critical dynamic structures with a complex fatigue response. The offshore industry lacks verification of analytical models with full-scale response measurements. Only a small number of installed SCRs have any instrumentation to monitor dynamic response. This paper describes an on-line monitoring system deployed on one of the Tahiti infield (production) SCRs. Tahiti is a Truss Spar Floater located in 4,000 ft water depth in the Gulf of Mexico. The system is configured with localized strain and motion measurement devices. Emphasis is placed on the selection of number and location of the monitoring devices to characterize vessel induced riser response, VIV induced riser response, riser-seabed interface, and discontinuities at the riser hang-off locations. Monitoring device sensitivity requirements and qualification programs are also discussed. The monitoring system configuration drivers are reviewed in detail such as; monitoring objectives, instrumentation requirements, specification and architecture, field development integration, and installation. Information provided in this paper would be helpful for configuration of complex monitoring systems for deepwater steel catenary rises.
Benchmarking of SHEAR7v4.5: Comparisons to Full-Scale Drilling Riser VIV Data and Legacy Analyses
Authors: Tognarelli Michael A. , Yin Fengjie , Campbell Mike , Achanta Vamsee
Published: February 2010

SHEAR7 [4], industry’s most widely-used vortex-induced vibration (VIV) fatigue damage software analysis tool, has been recently revised to include a fundamental change in methodology based on observations from Deepstar’s high-aspect-ratio, slender pipe towing tests in the Gulf Stream near Miami, Fla. The key revision pertains to the way in which VIV excitation zones (or “power-in” zones) are calculated along the length of the riser. Namely, it is no longer assumed that multiple structural modes are excited simultaneously by a given current profile along the length of the riser in a manner known as multi-mode response. Rather, based on the towing tests, it is assumed that potentially excited modes participate in the response one-at-a-time in a time-sharing fashion. The fraction of the total event time accorded to each responding mode is proportional to the input power of its exciting force, or, may be set to be uniformly distributed among all responding modes. This fundamental change can have a significant effect on the fatigue damage calculated for a given riser and current profile and direct comparisons to previous analyses are not straightforward as the input parameters of the software have been altered along with the analysis methodology itself. In a recent paper [1], BP utilized measured data that it had collected from risers in the field during several of its worldwide drilling campaigns to calibrate SHEAR7v4.4 to yield an average safety factor of ten on fatigue damage when VIV occurs. Given the extent of the changes to the analysis method, it was important to revisit that study and ascertain whether the latest software version similarly captured the trends of the full-scale data and could be calibrated to maintain an appropriate factor of safety. Furthermore, where measured data were not available it was important for consistency to identify and rationalize differences between analyses with the current and penultimate versions of the software. This paper describes BP’s benchmarking of SHEAR7v4.5. Comparisons are made between predicted and measured VIV fatigue damage for several full-scale drilling risers to demonstrate the efficacy of a calibration for the latest version. In addition, comparisons are made between VIV fatigue damage predictions using SHEAR7 versions 4.4 and 4.5 for drilling risers as well as for a typical deepwater SCR in typical design Gulf-of-Mexico loop currents. The version-to-version differences are illustrated and explained. Finally, results of sensitivity studies conducted with respect to the new parameters in SHEAR7v4.5 are presented. A key finding is that while the predictions, on average, are similar from version to version; the scatter in predictions — which leads to requirements for large safety factors — is largely unimproved.
An Approach to Include Observed VIV Likelihood in Drilling Riser Fatigue Analyses
Authors: Tognarelli Michael A. , Gabbai Rene D. , Campbell Mike
Published: February 2010

Field measurements of the response of a number of drilling risers indicate that vortex-induced vibration (VIV) occurs significantly less often than predicted by the industry-standard fatigue analysis computer program SHEAR7 V4.4. Several comparisons to model tests and field data, including one published by BP and 2H in 2007 [1], demonstrate that this analysis program is generally quite conservative, given that VIV occurs. Furthermore, this conservatism does not take into account those situations in which VIV fatigue is predicted but none is observed in the field, which adds yet another layer of “hidden” conservatism to design analyses. In an effort to address this and reduce conservatism to a more appropriate level, the probability of occurrence of vortex-induced vibration (VIV) is examined using full-scale measured data. The data has been collected over the past several years from five drilling risers without VIV suppression devices. These risers are on rigs under contract to BP at high-current-susceptible sites worldwide. Collectively, the data correspond to 9,600 10-minute field measurements, equivalent to 0.18 years of continuous monitoring. The riser response is obtained from motion loggers placed at selected positions along the riser as described in [1]. Each logger measures 3D accelerations and 2D angular rates. Through-depth currents are measured via Acoustic Doppler Current Profilers (ADCP). By comparison of measurements to computer predictions based on the observed current profile, a relationship is developed between the intensity of the fatigue damage predicted and the probability that VIV is observed in the field. Subsequently, an approach is proposed for scaling analysis predictions to reflect the relative likelihood of VIV. The database of measured and SHEAR7 maximum predicted fatigue damage rates is statistically characterized to determine how it may be used to determine factors of safety (FOS) for VIV design. A worked example for a deepwater drilling riser in the GoM is used to show how the FOS methodology can be applied in the case of multiple design currents each with a different annual probability of occurrence.
Development of a Hydrodynamic Optimization Tool for Stall-Regulated Hydrokinetic Turbine Rotors
Authors: Sale Danny , Jonkman Jason , Musial Walt
Published: February 2010

This paper describes the adaptation of a wind turbine performance code for use in the development of a general use design tool and optimization method for stall-regulated horizontal-axis hydrokinetic turbine rotors. The rotor optimization tool couples a modern genetic algorithm and blade-element momentum performance code in a user friendly graphical-user-interface that efficiently automates the arduous design process for stall-regulated rotors. This optimization method calculates the optimal chord, twist, and hydrofoil distributions which maximize the hydrodynamic efficiency while ensuring that the rotor exhibits power regulation via hydrodynamic stall and avoids cavitation. Optimizing a rotor for maximum hydrodynamic efficiency does not necessarily create a turbine with the lowest cost of energy, but maximizing the efficiency is an excellent criterion to use as a first pass in the design process. With satisfactory results, two conceptual rotors were designed to test the capabilities of this optimization method.
Parameters Affecting the Buckling and Post-Buckling Behaviour of High Strength Pipelines
Authors: Fatemi Ali , Kenny Shawn , Sen Millan , Zhou Joe , Taheri Farid , Paulin Mike
Published: February 2010

Using the finite element methods, a parametric study was conducted to examine the influence of pipeline diameter, internal pressure, girth weld offset misalignment amplitude and modeled length on the local buckling of high strength pipelines. The numerical procedures were calibrated from full-scale tests on high strength pipelines subject to internal pressure and end rotation. The peak moment decreased with increasing pressure and girth weld offset misalignment amplitude. The limit curvature increased with increasing pressure and decreased with increasing girth weld offset misalignment amplitude. The effect of reducing the modeled pipeline segment length, from 5.5 D to 3.5 D, was to increase the limit curvature at the peak moment and to delay the onset of nonlinear ovalization response to higher curvature amplitudes. The influence of girth weld offset misalignment on the local buckling response was examined in terms of a strain capacity reduction parameter known as the girth weld factor. This study has determined current practice, based on DNV OS-F101 standard, was appropriate; moreover, the potential for reduction in this conservative approach is identified.
Motion Response of a Rotating Cylinder in Currents
Authors: Kloven Anders , Huang Shan
Published: February 2010

Model tests were carried in a towing tank to examine the motion response of a rotating cylinder in currents. The cylinder model diameter is 0.10 m and its length 1 m. It is supported on a vertical cantilever rod and a DC motor is used to rotate the cylinder. The reduced velocity is in the range from 3 to 9 and the ratio between current velocity and cylinder surface velocity is between 0.5 and infinity. Both VIV and orbiting motions were observed and some measured motion results are presented and discussed in the paper.
Model Tests on a Spar in Level Ice and Ice Ridge Conditions
Authors: Murray John , LeGuennec Stephane , Spencer Don , Yang Chang K. , Yang Wooseuk
Published: February 2010

1:30 and 1:50 model-scale ice tests of an ice-resistant Spar design were carried out to determine the loads on the Spar in level ice and ice ridges. Due to limitations in the depth of the ice test facility, the hull draft and mooring system were truncated. The 1:30 scale model was towed through the ice on a fixed and compliant dynamometer. The stiffness characteristics of the compliant dynamometer matched the horizontal stiffness of the full-scale mooring system. The purpose of these tests was to compare the mooring and ice loads measured in fixed and compliant conditions. The 1:50 scale model was truncated by 70 m. Its mooring system was modeled using a four-line system designed to give the same global restoring forces as the full-scale mooring system. The model was fitted with vertical plates on the exterior of the hull to compensate for loss of added mass and added moment of inertia. A limited number of tests were carried out at the two model scales in the same ice conditions to investigate scaling effects. The mooring and ice loads measured in the fixed and compliant conditions were found to be similar, indicating that loads estimated, assuming the structure is fixed, provide good estimates. Good agreement between the two models was also found for the tests carried out in the same ice conditions, suggesting that the scaling effects may be negligible.
Numerical Simulation of Dynamic Response of Structure Caused by Wave Impact Pressure Using an Eulerian Scheme With Lagrangian Particles
Authors: Mutsuda Hidemi , Doi Yasuaki
Published: February 2010

This study focuses on the development of computational techniques for computing fluid-structure interaction with wave breaking. This is of practical relevance in both ocean, and ship hydrodynamics. This paper also presents a prediction of the local highly pressure load impacting on a rigid and elastic structure caused by fluid force including impact pressure. We have developed a new numerical scheme that combines a Eulerian scheme with Lagrangian particles, i.e. free surface particles and SPH particles, to compute fluid-structure interaction caused by impact pressure. In this model, we employed two kinds of particles. One is free surface particle located near the free surface to capture air-water interface accurately. The other one is SPH particle to compute solid motion and elastic deformation. The air-water mixing flow is treated on a fixed Eulerian grid with the free surface particles to rebuild the density function for capturing the interface in filamentary regions that are under-resolved. Conversely, the structure is solved using the particle method, SPH. These Lagrangian particles are useful and available to capture the interface between different phases. In this paper, the proposed method was applied to the water entry problems of a V-shaped wedge, a horizontal flat-plate, a circular cylinder, an elastic cylindrical shell and impact pressure acting on an elastic wall caused by wave breaking. The free surface and elastic deformation are compared with both numerical and experimental results. The pressure and strain predictions are also compared with experimental results obtained by other researchers.
Numerical Modeling of Vortex-Induced Vibrations of Two Flexible Risers
Authors: Springer Marlow , Jaiman Rajeev K. , Cosgrove Steve , Constantinides Yiannis
Published: February 2010

Due to the complex interactions of vortex-induced vibrations (VIV) and downstream wake dynamics, the design of riser arrays has been an area of great uncertainty in the offshore industry. Numerical methodology can play an important role in predicting the hydrodynamic forces and motion of riser arrays from both design and operational standpoints. The focus of this study is to investigate the VIV response of two flexible risers in cross-flow using a CFD solver. Bare and straked geometries are simulated, and the results are successfully compared against experimental results. The basic hydrodynamic features are well captured and the numerical technique is an improvement over the existing empirical and experience-based methods.
CTOD Fracture Toughness Tests and Numerical Simulation for Welded Joints of Q370qE
Authors: Yu Qiming , Wu Weiguo , Gan Jin
Published: February 2010

In this investigation, Based on BS7448 fracture toughness test experiment standard and DNV-OS-C401, three-point crack tip open displacement (CTOD) bending tests were made using Q370qE base steel, weld seam and heat-affected zone (HAZ) samples at different sample thicknesses and at different temperature to study the elasto-plastic fracture toughness of the materials frequently used in ocean engineering structure, and the results were calculated using the p-V curves. The results show that different CTOD values corresponding to the occurrence of brittle fracture before yield strength, brittle fracture after yield strength, and ductile fracture are related to different material types, thicknesses, temperature; and the CTOD value is made up of elastic part and plastic part, the value of plastic part greatly influence the CTOD value. Finally, using ANSYS commercial software, bending test models all of base steel, welded joint, HAZ with various center through crack sizes were computed by three-dimensional finite element method, from the results of the finite element analysis, the simulated p-V curve was obtained. It could be found that the simulated curve was close with the experimental curves, so the finite element analysis was accurate. And these works also have important project practical value to the ocean engineering structure designer.
Sound and Electromagnetic Wave Scattering by a Compact Circular Pore With a Finite Depth
Authors: Kuo Chih-Yu , Chern Ruey-Lin , Change Chien-Cheng
Published: February 2010

The three dimensional wave scattering of an oblique wave incident on a flanged circular compact pore of finite depth is solved analytically by the method of matched asymptotic expansion. We assume smallness of the product of the incident wave number and the pore radius and divide the scattering field into an inner region and an outer radiation region. For the wave system, the physical variables, e.g. sound pressure, electric/magnetic fields, satisfy the Laplace equation in the inner region. For the circular shaped pores, they can be solved by the method developed by Fabrikant. Then via the matching processes, the wave radiation in the outer field is determined. The theory is developed first for sound wave scattering. Both rigid and pressure-release boundary conditions are investigated. For a pore with a finite depth, the leading radiation terms for both conditions are at the same order of magnitude. They contain one monopole and one dipole for the former and one dipole for the latter. Quadrupoles and an octupole are found in the next higher order. Subsequently, the theory is applied to the electromagnetic wave scattering. The problems are formulated based on the duality property of the source-free Maxwell equations. A multipole expansion for the scattering wave similar to the acoustic counterpart is obtained. A few residue multipoles arising from the higher order inner region are found. The leading dipoles and their orientation are demonstrated.
VIV Response of a Flexible Cylinder Under Locally Strong Sheared Flow
Authors: Kim Yoo-Chul , Suzuki Fumihiro , Rheem Chang-Kyu
Published: February 2010

The vortex-induced vibration (VIV) analysis of a flexible riser under locally strong sheared flow is presented. The riser model is made of Teflon and has 9.5m length, 0.0127m diameter, and 0.001m thickness. 11 2-dimensional accelerometers are installed along the riser. The experiment is conducted at the model basin in the University of Tokyo whose width is 10m, depth is 5m, and length is 50m. The model is installed at about 30 degree of slope and submerged by 99% of the overall length. Locally strong sheared flow is made by adding accelerated flow generated by an impeller-type accelerator submerged by 0.72m to uniform current. The applied top tensions are 2–8kgf by 2kgf interval. The results of CFD calculation in the similar condition using discrete vortex method (DVM) are also presented.
Lateral Walking and Feed-In of Buckled Pipelines Due to Interactions of Seabed Features
Authors: Cumming Gary , Druzynski Alicja , To̸rnes Knut , Rathbone Andrew
Published: February 2010

The increasing demand for subsea pipeline tie-back systems operating at high temperatures and pressures has introduced new challenges for pipeline design. In particular, a pipeline designed to buckle laterally, may displace both laterally and axially over time when subjected to repeated heat-up and cool-down cycles. Depending on changes in local seabed slopes and the direction and severity of passing thermal transients, a combination of pipeline walking drivers with differing responses may occur along the pipeline route. In this case, both lateral and vertical features such as buckles, spans or route bends may act as sites which: • Accumulate axial feed-in over heat-up and cool-down cycles (‘collectors’). • Experience decreasing axial feed-in over heat-up and cool-down cycles (‘givers’). • Maintain buckle shape with little change in axial feed-in during heat-up and cool-down cycles. To̸rnes et al. [1] explained the mechanism in which thermal transients can lead to axial creep or walking and Carr et al. [2] demonstrated how global seabed slope and tensile loads can also cause walking as a result of repeated heat-up and cool-down cycles. This paper discusses the complex interactions of multiple features potentially present along a pipeline route, including thermal transients, slope, route bends and tensile load effects. The resultant combinations may manifest themselves in the through-life distribution of axial movement along the pipeline.