bluuebunny/crossref_metadata_2025 huggingface dataset:
Methods for Modeling Local Fuel Rod Crud and Assessing Failure Risk
Authors: Krammen Michael A. , Wang Guoqiang , Grill Steven F. , Karoutas Zeses E. , Young Michael Y.
Published: February 2010

A code system with attendant methods has been developed for modeling local fuel rod crud. The methodology is in production use, when appropriate, in 14×14 and 16×16 CE-design fuel PWR reloads. This tool is used in making EPRI Level IV type crud and corrosion guideline assessments, where the EPRI crud and corrosion guidelines were developed in response to the INPO zero fuel failures by 2010 initiatives. The methodology is in process of being extended to other Westinghouse fuel designed reloads. The methodology involves translating very detailed relative thermal hydraulic variations determined by Computational Fluid Dynamics (CFD) computations over a fuel assembly grid span into specific local thermal hydraulic conditions over the entire axial length of every fuel rod in a reactor core over the life of the rod in reactor. The very local thermal hydraulic conditions are combined with reactor coolant crud concentrations as input to models for predicting very local fuel rod crud deposition. The reactor coolant crud concentrations are determined over each reactor cycle by reactor system wide crud mass balance calculations. The reactor coolant crud concentrations are used to calculate local crud thickness using mass transfer models which are a function of the local thermal conditions. The advanced crud deposition models also include models for calculating local crud dryout. Local crud deposition and crud dryout are strongly dependent on very local boiling or steaming which are predicted through the translation of the CFD results. The local crud thickness and degree of local crud dryout are key factors in determining the margin or risk for local fuel rod cladding crud induced fuel failure. Guideline limits were established by benchmarking the methodology to recent fuel rod crud induced fuel failures. This paper presents details on each facet of this methodology. Results for a particular application are provided to illustrate the methodology. The application is for a plant where a new fuel design was implemented with mixing grids and intermediate flow mixers. The results of the analysis demonstrated acceptable levels of local crud thickness and percent local crud dryout.
The Study of Hybrid Method in the Onset of Droplet Escaping From the Film
Authors: Guo Yun , Ishiwatari Yuki , Ikejiri Satoshi , Oka Yoshiaki
Published: February 2010

A particle-grid hybrid method for simulating the onset of droplet entrainment is described. The air and liquid phases are expressed by grid and particle separately. The effects of surface tension and wall adhesion are calculated by the continuum surface force model. The fluid film variation and the droplet disengaging procedure are analyzed. The onset of entrainment criterion is obtained and it has a good agreement with Ishii’s correlation. The influences of surface tension and gas phase density on the criterion are also studied. Several simulation flow fields are given for illustrating the efficiency of the method.
Ascertaining Directional Information From Incident Nuclear Radiation
Authors: Archambault Brian C. , Lapinskas Joseph R. , Wang Jing , Webster Jeffrey A. , Taleyarkhan R. P.
Published: February 2010

Unprecedented capabilities for the detection of nuclear particles are presented by tensioned metastable fluid states which can be attained via tailored resonant acoustic systems such as the acoustic tensioned metastable fluid detection (ATMFD) systems. Radiation detection in tensioned metastable fluids is accomplished via macro-mechanical manifestations of femto-scale nuclear interactions. Incident nuclear particles interact with the dynamically tensioned metastable fluid wherein the intermolecular bonds are sufficiently weakened such that the recoil of ionized nuclei generates nano-scale vapor cavities which grow to visible scales. Ionized nuclei form preferentially in the direction of incoming radiation, therefore, enabling the capability to ascertain information on directionality of incoming radiation — an unprecedented development in the field of radiation detection. Nuclear particle detection via ATMFD systems has been previously reported, demonstrating the ability to detect a broad range of nuclear particles, to detect neutrons over an energy range of eight orders of magnitude, to operate with intrinsic detection efficiencies beyond 90%, and to ascertain information on directionality of incoming radiation. This paper presents advancements that expand on these accomplishments, thereby increasing the accuracy and precision of ascertaining directionality information utilizing enhanced signal processing-cum-signal analysis, refined computational algorithms, and on demand enlargement of the detector sensitive volume. Advances in the development of ATMFD systems were accomplished utilizing a combination of experimentation and theoretical modeling. Modeling methodologies include Monte-Carlo based nuclear particle transport using MCNP5 and complex multi-physics based assessments accounting for acoustic, structural, and electromagnetic coupling of the ATMFD system via COMSOL’s Multi-physics simulation platform. Benchmarking and qualification studies have been conducted with special nuclear material (SNM), Pu-based neutron-gamma sources, with encouraging results. These results show that the ATMFD system, in its current configuration, is capable of locating the direction of a radioactive source to within 30° with 80% confidence.
Seismic Spans for Cold Piping Based on Simplified Dynamic Analysis in APR1400
Authors: Lee Joon-Ho , Bae Jae-Hwan , Kim In-Yeung , Jo Jik-Lae
Published: February 2010

The process piping of nuclear power plants have been seismically qualified for many years by rigorous dynamic analyses utilizing piping analysis computer programs or simplified dynamic analyses such as the constant-pitch span method or the seismic load coefficient method specified in ASME Sec. III, Appendix N-1225. In the case of OPR1000 (Korea standard nuclear power plants, e.g., Ulchin 3&4, 5&6 including Shin-Kori 1&2 and Shin-Wolsong 1&2 which are under construction), almost all of the nuclear piping have been seismically qualified by rigorous dynamic analyses to reduce the cost for the excessive number of supports required by simplified methods. Whereas, for the up-to-dated APR1400 (Korea’s advanced power plant 1400 MW-class) project, the application of simplified design approach is to be considered in depth to catch up with the growing demands in recent years for reducing engineering man-hours and the level of efforts required by rigorous piping analyses. The key to overcoming the excessive number of supports required by simplified method is how to determine the allowable range of seismic piping spans. To develop seismic piping spans for non-safety related cold piping in APR1400, some piping span models are introduced herein based on simplified dynamic analysis, and several topic studies for those models are performed. Topics studied are dead weight and seismic spans, lateral to vertical support span ratio, and span reduction factors as well as the design conditions including the pressure-temperature, pipe sizes, materials and insulations. The study results show that determined seismic spans are conducive to achieving the economical goal and complying with the prevailing code requirements.
CFD Simulation of Passive Auto-Catalytic Recombiner Operational Behaviour
Authors: Kelm S. , Jahn W. , Reinecke E.-A. , Baggemann J. , Allelein H.-J.
Published: February 2010

In order to mitigate the impact of a possible hydrogen combustion and to avoid containment failure, passive auto-catalytic recombiners (PAR) are used for hydrogen removal in an increasing number of European nuclear power plants. Hydrogen and oxygen react exothermally even below conventional flammability limits on the catalytic surfaces inside a PAR generating steam and heat. Modelling of the operational behaviour of PAR is one part of development issues in order to achieve reliable predictions of local atmosphere conditions. International research activities, e.g. in the European FP-6/FP-7 Network of Excellence SARNET (Severe Accident Research NETwork), investigate these aspects. At Forschungszentrum Ju¨lich, two strategies are pursued. First, the detailed evaluation of the reaction kinetics and heat and mass transport phenomena on a single catalyst element is performed by a direct implementation of the transport and kinetic approaches in ANSYS CFX-11. Second, in order to model the interaction of PAR with the containment, REKO-DIREKT, a detailed user model of the relevant processes inside a PAR based on Fortran 90 will be implemented in CFX. At present, validation against the available experimental database is performed. The validity of the numerical models strongly depends on the experimental data available. For this purpose, detailed experiments are performed at Ju¨lich. In the small-scale test facility REKO-3, representing a recombiner section, detailed investigations of the reaction kinetics under well-defined and steady-state conditions have been performed. In co-operation with RWTH Aachen University, a new test vessel REKO-4 is currently under preparation for testing PAR behaviour under natural convection conditions. It will provide various possibilities for instrumentation to measure temperatures and gas compositions and in particular it will be equipped with particle image velocimetry (PIV) for measuring the flow field around the PAR.
Condition Monitoring of Electrical Cables Using Line Resonance Analysis (LIRA)
Authors: Fantoni Paolo F.
Published: February 2010

This paper describes a method for cable system condition monitoring, developed initially at the IFE Halden Reactor Project and then further developed at Wirescan AS, which is based on transmission line theory and resonance analysis. This method resulted in the development of a system called LIRA (LIne Resonance Analysis), which can be used on-line to detect local or global changes in the cable electrical parameters as a consequence of insulation faults or degradation. This paper presents the latest results achieved in field experiments on signal and power cables.
Testing and Qualification of Diverse Safety Rod and Its Drive Mechanism for PFBR
Authors: Vijayashree R. , Veerasamy R. , Patri Sudheer , Suresh Kumar S. , Kumar Krovvidi S. C. S. P. , Dash S. K. , Logaiyan T. , Ravichandran N. , Chandramouli S. , Rajan K. K. , Banerjee Indranil , Dhanasekaran R.
Published: February 2010

PFBR, India’s first commercial fast breeder reactor employing fast fission is a challenging project from technological point of view to meet the energy security of the country. It is currently under advanced stage of construction at Kalpakkam, India. PFBR is equipped with two independent, fast acting and diverse shutdown systems. A shutdown system comprises of sensors, logic circuits, drive mechanisms and neutron absorbing rods. The absorber rods of the second shutdown system of PFBR are called as Diverse Safety rods (DSR) and their drive mechanisms are called as Diverse Safety Rod Drive Mechanisms (DSRDM). DSR are normally parked above active core by DSRDM. On receiving scram signal, Electromagnet of DSRDM is de-energised and it facilitates fast shutdown of the reactor by dropping the DSR in to the active core. For the prototype development of DSR and DSRDM, three phases of testing namely individual component testing, integrated functional testing in room temperature and endurance testing at high temperature sodium were planned and are being done. The electromagnet of DSRDM operates at high temperature sodium environment continuously. It has been separately tested at room temperature, in furnace and in sodium. Specimens simulating the contact conditions between Electromagnet and armature of DSR have been tested to rule out self welding possibility. The Dashpot provided to decelerate the DSR at the end of its free fall has been initially tested in water and then in sodium. The prototype of DSR has been tested in flowing water to determine the pressure drop and drop time. The functional testing of the integrated prototype DSRDM and DSR in aligned and misaligned conditions in air/water has been completed. The performance testing of the integrated system in sodium has been done in three campaigns. Based on the performance testing in the first two campaigns of sodium testing, design modifications and manufacturing quality improvement were done. Methods of drop time measurement based on ultrasonics and acoustics were also developed along with the first two campaigns. During the third campaign of sodium testing, the performance of the system has been verified with 30 mm misalignment at various temperatures. The third campaign has qualified the system for 10 years of operation in reactor. This paper describes the test setup for all the above mentioned testing and also gives typical test results.
Online Diagnostics of Reactivity Meter for Indian Nuclear Power Plants
Authors: Hada Mohit , Dixit M. Y. , Bhatnagar P. V. , Das Debashis , Mukhopadhyay P. K.
Published: February 2010

An online reactivity meter is developed for use in the Indian Nuclear Power Plants (INPP). The reactivity meter is required to generate reactor trip whenever the calculated reactivity exceeds the predefined limits. The computation of reactivity is based on inverse point kinetic model of the reactor with six groups of delayed neutrons. The recursive equations representing the change in reactivity in response to change in neutron flux have been formulated and solved online for determining the reactivity at any instant using Gate Array. The online diagnostics features have been integrated with the reactivity computation to verify its correctness and healthiness of the meter. The online diagnostic scheme encompasses checking of all the major hardware components, viz. EPROM, ADC, DAC and their interfaces with the Gate Array. It also monitors the robustness of Gate Array and the correctness of the computational cycle algorithms implemented in Gate Array by incorporating suitable checks for stuck bits, improper timings, faulty logic, range crossing, etc., including floating point exceptions. Upon detecting fault(s), limited consecutive attempts towards validation of fault are performed. On confirmation of fault the reactivity computation is halted and output goes to a failsafe state.
PWR Nuclear Power Plants Fuel Management Optimization
Authors: Zolfaghari Ahmad , Minuchehr Hamid , Noroozy Ali , Makarachi Peymaan , Koshahval F.
Published: February 2010

The objective of this paper is to develop a new hybrid mutation in genetic algorithm (GA) for designing the loading pattern (LP) in pressurized water reactors. Because of huge number of possible combinations for the fuel assemblies (FA’s) loading in a core, finding the optimum solution is truly a complex problem. In common genetic algorithm the mutation and crossover techniques are used to optimize an objective function but in this paper a new hybrid mutation is presented. In this study flattening of power inside a reactor core is chosen as an objective function. To obtain optimal FA arrangement, a core reload package code, MAKNOGA, based on well established MAKGA code is developed. This code is applicable for all types of PWR core having different geometries and designs with an unlimited number of FA types. The result is well improved in comparison with pattern proposed by designer.
Numerical Modelling of Stratified Gas-Liquid Flow in Inclined Circular Pipes
Authors: Faccini Jose´ L. H. , De Sampaio Paulo A. B. , Su Jian
Published: February 2010

In this paper, a fully developed stratified gas-liquid flow in inclined circular pipes is numerically modeled. The model is applied on a stratified gas-liquid downward flow with smooth and horizontal interface, in pipes with inclination angles varying from 0 to −10 degrees. A system of non-linear differential equations, consisting of the Reynolds averaged Navier-Stokes equations with the κ – ω turbulence model, are solved by using an inner iteration loop based on the Newton-Raphson scheme and the finite element method. Numerical solutions are obtained for the liquid height and pressure gradient which were compared with experimental and numerical data. An excellent agreement with the experimental data was obtained, leading to conclusion that the present model is adequate to simulate the stratified gas-liquid downward flow, and it can be used to estimate the flow parameters such as the liquid height and pressure gradient.
SuperCritical-Water Reactor NPP Concept: No-Reheat Cycle Option
Authors: Naidin M. C. , Pioro I. , Zirn U. , Chophla K.
Published: February 2010

Research activities are currently conducted worldwide to develop Generation IV nuclear reactor concepts with the objective of improving thermal efficiency and increasing economic competitiveness of Generation IV Nuclear Power Plants (NPPs) compared to modern thermal power plants. The Super-Critical Water-cooled Reactor (SCWR) concept is one of the six Generation IV options chosen for further investigation and development in several countries including Canada and Russia. Water-cooled reactors operating at subcritical pressures (10 – 16 MPa) have provided a significant amount of electricity production for the past 50 years. However, the thermal efficiency of the current NPPs is not very high (30–35%). As such, more competitive designs, with higher thermal efficiencies, which will be close to that of modern thermal power plants (45 – 50%), need to be developed and implemented. Previous studies have shown that direct cycles, with no-reheat and single-reheat configurations are the best choice for the SCWR concept. However, the single-reheat cycle requires a nuclear steam-reheat, thus increasing the complexity of the reactor core design. Although preliminary results show that the thermal efficiency of the no-reheat cycle is approximately 2% lower than that of the single-reheat cycle, the less complex core configuration may prove to be a major factor when selecting the most suitable design. This paper investigates the main parameters and performance in terms of thermal efficiency of a SCW NPP based on a no-reheat, direct cycle with heat regeneration. When compared to the single-reheat cycle, the no-reheat configuration has a more simplified design: the Intermediate-Pressure (IP) turbine section is eliminated and the exhaust from the High-Pressure (HP) turbine is directly routed to the inlet of the Low-Pressure (LP) turbines. The cycle also consists of a condenser, nine feedwater heaters, a topping de-superheater, associated pumps, and the nuclear source of energy, i.e., the SCWR. In general, the major technical challenge associated with a SC no-reheat turbine is the high moisture content in the LP turbine exhaust. A thermal-performance simulation reveals that the steam quality at the exhaust from the LP turbine is approximately 81%. However, the moisture can be reduced by implementation of contoured channels in the inner casing for draining water and moisture removal stages. The overall thermal efficiency of the cycle was determined to be about 50% (assumptions are made to account for turbine and pump efficiency losses). Furthermore, important safety parameters such as bulk-fluid temperature, sheath temperature and fuel-centerline temperature are calculated for a non-uniform cosine Axial Heat Flux Profile (AHFP) along a generic fuel channel of the no-reheat SCWR concept.
Bayesian Nonparametric Analysis of Single Item Preventive Maintenance Strategies
Authors: Belyi Dmitriy , Damien Paul , Kee Ernie , Morton David , Popova Elmira , Richards Drew
Published: February 2010

This work addresses the problem of finding the minimal-cost preventive maintenance schedule for a single item. We develop an optimization algorithm that reduces the computational effort to find the optimal schedule. This approach relies on the item having an increasing failure rate, which is typical, and employs a Gibbs sampling algorithm to simulate from the failure rate distribution using real data. We also analyze the case when the item has a “bathtub” failure rate; we develop techniques that lead to an algorithm that finds an optimal schedule for this case as well. We then analyze the effectiveness of our approach on both artificial and real data sets from the South Texas Project nuclear power plant.
Dealing With External Factors in the Electricity Generation Sector: Nuclear vs. Other Baseload Technologies
Authors: Mancini Mauro , Locatelli Giorgio , Tammaro Serena
Published: February 2010

The international literature presents several studies about the economics of Power Plants, however these analyses usually consider only the classical accounts related to Construction, Operation & Maintenance, Fuel and Decommissioning cost. Beside these accounts there are many factors, from now on named External Factors (e.g. social acceptability, Security of Fuel supply, etc.) able to heavily determine the profitability and the feasibility of a certain investment. This paper lists the External Factors and, under this prospective, ranks under different scenarios the following technologies suitable for the base-load: hydro, coal, oil, gas and nuclear. First the paper provides a list of these factors considering the international literature. As second step each factor is analyzed and quantified. Then an overall multi-attribute model, based on the Quality Function Deployment approach, is introduced to obtain a weight for each factor, dividing its impact into three different sustainability dimensions (economic, environmental, social), each weighted according to the investor sensitiveness. Finally the factor weights and their performances are coupled to obtain an overall ranking specific describing the specific environmental coming out by the combination of conditions and investors’ strategies. The results show that hydroelectric plants are usually the best solution, however there is a shortage of new sites for the further deployment of these plants, therefore other plants have to be considered to fulfill the energy growth. Coal and Nuclear could be a good choice even if each type of plant has its strengths and weaknesses. Nuclear technology has good performances on “fuel supply and environmental impact factors”, but his main weak is on the social acceptability. On the opposite the oil and gas -fired plants are always the worst choice. It is important to highlight that some factors are quantified using historical data (for the nuclear sector related to GEN II reactors). This assumption does not bias the analysis since the progress in nuclear energy is present as well as in other technologies. However is clear from the analysis that the innovative passive reactors could overcome other technologies and become the most suitable choice for the base load generation.
Tidal Movement Characteristics Outside the Pearl River Estuary and Its Influence on the Mouths
Authors: Kong Jun , Xue Xiaoxiao , Ye Ronghui
Published: February 2010

The hydrology of the Pearl River Estuary is controlled both by river discharge and tide, where water and sediment move through eight outlets (mouths) into the sea. Using numerical modeling, this paper examines the characteristics of tidal movement in Pearl River Estuary. Results showed an amphidromic point near Modaomen mouth, and river runoff flows down. From marine dynamics point of view, Modaomen mouth is the main channel for water and sediment transportation of Pearl River. Using the tidal energy, we discuss the change of the sediment near the several entrances during the flood and dry seasons.
The Effect of Soil Non-Linearity on VIV Response of a Free Spanning Pipeline
Authors: Ai Shangmao , Sun Liping , Ma Gang
Published: February 2010

Improving the knowledge about the effect of pipe-seabed-interaction on VIV is quite important for free spanning pipelines, which are often highly nonlinear due to interaction with the seabed. However, the implicit requirement for frequency domain procedures is structural linearity. In this study, a time domain analysis method for nonlinear pipe-seabed-interaction analysis of free spanning pipelines under VIV conditions has been developed. The flow is modeled by a Van-der-Pol wake oscillator developed by Facchinetti et al. And the stall parameter is taken into account in the general form of the VIV amplitude and the response frequency, which can successful model the VIV response amplitude comparing with a constant. After the free spanning pipeline discretized into finite elements, the average acceleration method is chosen to integrate the equations of motion. Three types of pipe-seabed-interaction (linear spring, perfectly plastic nonlinear spring, and tension cut-off nonlinear spring) are considered. The results show that the presented time domain method can capture the non-linear interaction between the pipeline and the seabed at the free span shoulders. And the maximum response amplitude of nonlinear case is lower than the one with linear spring.
Shoulder Ice Barrier Ice Tank Testing—Part II: Estimation of Breaking Length and Block Size Using Image Analysis
Authors: Repetto-Llamazares Ada H. V. , Gudmestad Ove T. , Gu¨rtner Arne , Ho̸yland Knut V.
Published: February 2010

When studying ice interaction on sloped structures, a key parameter that is usually reported after experiments and observations either in Full Scale or Model Scale is the breaking length associated with the ice failure. Moreover, either for numerical modeling or load calculations the size of the blocks generated during ice-structure interaction that accumulates rubble is of importance. In this paper, the technique of image analysis has been used to obtain values of the breaking length and the ice block sizes generated during model tests of a Shoulder Ice Barrier (SIB)-ice interaction. The model tests were performed in the Hamburg Ship Model Basin (HSVA) during July 2007. Since the SIB represents a new concept in ice barrier structures, model tests were intended to evaluate its general performance. A brief description of the model tests and the image analysis technique used to analyze the data is done. A total of five experiments where ice thickness, ice flexural strength and shoulder inclination were varied, are analyzed. Results of the breaking length analysis show that there is a characteristic change in the breaking length associated with the transition from ice interactions on the bare structure (Phase 1) and interaction onto accumulated rubble (Phase 2). Average values of the breaking length of both phases for each experiment are presented. Since the information regarding breaking length in structures that accumulate rubble is sparse, the experimental results of Phase 1, where the rubble accumulation is still small, are compared with the predictions from three different models presented in the literature for sloped structures, under similar ice conditions, that do not accumulate rubble. The comparison allows concluding that the breaking phenomenon is being reasonably well modeled in the experiments. The block sizes of the upper layer of the accumulated rubble were analyzed and the block length and width distributions were found for each experiment. A linear trend was found between block size and ice thickness. A linear fitting of the data was performed in order to obtain simple equations which give an upper limit of the length and width of the ice blocks generated during the SIB-ice interaction as function of the ice thickness. The results may apply for ice interaction on sloped structures in general as well.
Composite Short Caisson Foundation for Soft Coastal Lowlands
Authors: Jawaid S. M. Ali , Madhav Madhira R.
Published: February 2010

Conventional shallow foundations are difficult to construct in coastal lowlands due to the flooding of the foundation pit thanks to high water table throughout the year. In order to circumvent the above problem, a new composite short caisson foundation consisting of shallow open caisson with granular core is being proposed for foundations in coastal lowlands. It consists of shallow pipes or well steining with granular core inside. The proposed foundation is analyzed using a linear stress-displacement response of the interface between the outer surface of the steining and the ground which is treated as non-homogeneous. Possible transfer of load from the steining to granular core inside or vice versa is considered in the interaction analysis. Extensive parametric studies quantify the effects of the non-homogeneity on the shear stress distribution, load sharing between the steining and the granular core, and the settlement of the proposed foundation.
Experimental Investigation Into Plugging of Open Ended Piles
Authors: Dijkstra Jelke , Broere Wout
Published: February 2010

This paper presents the results of a model pile test in a transparent photoelastic medium. This medium is composed of crushed glass particles in a refractive index matching liquid. The test setup allows for quantitative photoelastic measurements. For the measurement of the photoelastic data the phase stepping technique is used. Stresses in the granular medium located next to and in the plug were recorded at varying installation depths of the pile during monotonic jacking of the transparent pile in combination with the pile head load. The horizontal stress ratio in the plug for this particular test is found to be equal to the vertical stress. A distinct stress arch below the pile base is observed during penetration. The high local stress increase in and below the plug move with the pile as the plug travels downward into the soil and do not change much in absolute magnitude.
Hydrogen Induced Stress Cracking (HISC) of Stainless Steels Under Cathodic Protection in Seawater: Presentation of a New Test Method
Authors: Johnsen Roy , Nyhus Ba˚rd , Wa¨stberg Stig
Published: February 2010

There has been an increasing trend in the use of stainless steel alloys instead of carbon steel for subsea flowlines and production systems during the last 15 years in the oil industry. Even if this normally is a more robust solution compared to the use of carbon steel insofar as internal corrosion problems are concerned, the use of stainless steels has led to leakage, production shutdown and expensive repair work. The reported failures were associated with hydrogen entrapment resulting from welding and/or external cathodic protection (CP), combined with a certain stress/strain level. Atomic hydrogen entering the alloy can weaken the mechanical strength of the alloy, cause cracks and destroy the integrity of equipment or a system. Such failures attributed to hydrogen induced stress cracking (HISC) are clearly not acceptable from the perspective of safety, environmental hazard and cost. Leading oil and engineering companies and supplier industry have pointed out HISC as one of the major obstacles against safe operation of stainless steel subsea pipelines and production systems. It is important for the oil industry to have design guidelines and reliable test method(s) for qualification and safe utilization of subsea pipelines and components made from the actual stainless steels. This paper describes a test method that has been developed through a Joint Industry Project (JIP) executed by SINTEF and Det Norske Veritas (DNV) with support from leading oil companies and material suppliers. The method has been qualified for use on 13% Cr super martensitic (SMSS) and 22% Cr / 25% Cr duplex stainless steels (DSS/SDSS). The link to DNV-RP-F112 [1] will also be described.
Local Design Pressures for Structures in Ice: Analysis of Full-Scale Data
Authors: Taylor Rocky S. , Jordaan Ian J. , Li Chuanke , Sudom Denise
Published: February 2010

The design of structures for ice conditions requires knowledge of local ice pressures to allow for appropriate levels of structural strengthening. Full-scale field data are key to enhancing our understanding and modeling of ice behavior. Data collected during icebreaker ramming events represent an important source of information for use in the evaluation and validation of design methodologies. This paper examines several ship-ice interaction datasets using the ‘event-maximum’ method of local pressure analysis developed by Jordaan and co-workers [1]. In this method, the local pressure is obtained from a normalized curve which contains two parameters, α and x0. Local pressure analysis results for data from the USCGS Polar Sea, CCGS Terry Fox, CCGS Louis St. Laurent, and Swedish Icebreaker Oden are presented. For all data considered the calculated values of α fall below the design curve. A discussion of panel exposure, event duration and the effect of these factors on x0 is given. New design curves are presented. A comparison of results with those obtained using an alternative approach, the up-crossing rate method, is presented in a companion paper [2].
Reynolds Number Effects on Hydrodynamic Coefficients for Pure In-Line and Pure Cross-Flow Forced Vortex Induced Vibrations
Authors: Szwalek Jamison L. , Larsen Carl M.
Published: February 2010

In-line vibrations have been noted to have an important contribution to the fatigue of free spanning pipelines. Still, in-line contributions are not usually accounted for in current VIV prediction models. The present study seeks to broaden the current knowledge regarding in-line vibrations by expanding the work of Aronsen (2007) to include possible Reynolds number effects on pure in-line forced, sinusoidal oscillations for four Reynolds numbers ranging from 9,000 to 36,200. Similar tests were performed for pure cross-flow forced motion as well, mostly to confirm findings from previous research. When experimental uncertainties are accounted for, there appears to be little dependence on Reynolds number for all three hydrodynamic coefficients considered: the force in phase with velocity, the force in phase with acceleration, and the mean drag coefficient. However, trends can still be observed for the in-line added mass in the first instability region and for the transition between the two instability regions for in-line oscillations, and also between the low and high cross-flow added mass regimes. For Re = 9,000, the hydrodynamic coefficients do not appear to be stable and can be regarded as highly Reynolds number dependent.
Influence of a Varying Vertical Velocity Profile on Turbine Efficiency for a Vertical Axis Marine Current Turbine
Authors: Goude Anders , Lalander Emilia , Leijon Mats
Published: February 2010

Water currents in e.g. unregulated rivers and tides are a considerable renewable energy resource. The technology needed to harness the energy in these streams has not yet matured, but research and development are ongoing. In the present paper the power coefficient of marine current turbines using vertical axis turbines is considered. When the width and height of the turbine are kept constant, the Cp-λ curve will depend mainly on the solidity. However, since all natural channels have vertical velocity variations due to friction against the sea floor, this will also affect the efficiency. The double multiple streamtube model was used to study the power coefficient as a function of solidity and vertical shear profile. Three turbine cases were studied: one turbine vertically aligned, and two horizontally aligned turbines rotating with opposite direction. The results show that the difference depends both on how much the velocity varies over the velocity profile, and on the shape of the velocity profile, where a linear profile causes a lower Cp compared to a logarithmic profile. The difference was especially prominent at low tip speed ratios for the horizontally aligned turbines with different rotational direction.
The Effect of Wave Directionality on Low Frequency Motions and Mooring Forces
Authors: Waals Olaf J.
Published: February 2010

Operability of offshore moored ships can be affected by low frequency wave loads. The low frequency motions of a moored ship may limit the uptime of an offshore structure such as an LNG offloading terminal. The wave loads that cause the main excitation of these low frequency motions are usually computed using second order wave drift theory for long crested waves, which assumes that the low frequency components are only related to waves coming from the same direction. In this method short crested seas are dealt with as a summation of long crested seas, but no interaction between the wave components traveling in different directions is usually taken into account. This paper describes the results of a study to the effect of 2nd order low frequency wave loads in directional seas. For this study the drift forces related to the interaction between waves coming from different directions is also included. This is done by computing the quadratic transfer functions (QTF) for all possible combinations of wave components (frequencies and directions). Time traces of drift forces are generated and compared to the results without wave directional interaction after which the motions of an LNG carrier are simulated. A sensitivity study is carried out towards the number of direction steps and the water depth. Finally the motions of an LNG carrier in shallow water (15m water depth) are simulated and mooring forces are compared for various amounts of wave spreading.
Adaptive Stretching of Dynamic Pressure Distribution in Long- and Short-Crested Sea States
Authors: Clauss Gu¨nther , Kosleck Sascha , Sprenger Florian , Boeck Florin
Published: February 2010

During their lifetime, marine structures and ships are frequently exposed to severe weather and rough, sometimes extreme sea states. To ensure survival, the precise knowledge of global and local loads is an inevitable integral prerequisite for the design of safe offshore structures and marine vessels. Wave-structure interaction and the associated pressure induced wave loads are key parameters for the definition of design load cases. Once the complete surrounding sea state for the identified load condition is known, the pressure induced loads can be computed by calculating the pressure distribution along the hull, using an appropriate wave theory. As 1st-order AIRY-Theory as well as 2nd- and 3rd-order STOKES-Theory excessively overestimate the dynamic pressure above still water level, especially in high wave crests, a variety of stretching terms has been applied to common wave theories to correct the pressure distribution. This paper presents a second-order stretching approach to describe the distribution of the dynamic pressure in regular wave crests. In combination with FFT (Fast Fourier Transformation), the applicability of this method can be extended to irregular sea states and even extreme waves. Calculations for several regular and irregular sea states are shown and compared to calculations with existing stretching methods. The results are validated by measurements conducted in a wave tank at the Technical University Berlin. The paper concludes with an example for the calculation of the wave induced pressure field along a ship hull operating in a short-crested, multidirectional sea state.
Direct Adaptive Rejection of Vortex-Induced Disturbances for a Powered Spar Platform
Authors: VanZwieten Tannen S. , VanZwieten James H. , Balas Mark J. , Driscoll Frederick R.
Published: February 2010

The Rapidly Deployable Stable Platform (RDSP) is a novel vessel designed to be a reconfigurable, stable at-sea platform. It consists of a detachable catamaran and spar, performing missions with the spar extending vertically below the catamaran and hoisting it completely out of the water. Multiple thrusters located along the spar allow it to be actively controlled in this configuration. A controller is presented in this work that uses an adaptive feedback algorithm in conjunction with Direct Adaptive Disturbance Rejection (DADR) to mitigate persistent, vortex-induced disturbances. Given the frequency of a disturbance, the nominal DADR scheme adaptively compensates for its unknown amplitude and phase. This algorithm is extended to adapt to a disturbance frequency that is only coarsely known by including a Phase Locked Loop (PLL). The PLL improves the frequency estimate on-line, allowing the modified controller to reduce vortex-induced motions by more than 95% using achievable thrust inputs.
Model Test of a Steel Catenary Riser in a Towing Tank
Authors: Morooka Celso K. , Tsukada Raphael I. , da Silva Sergio , Franciss Ricardo , Matt Cyntia G. C.
Published: February 2010

The objective of the present work is the study of the dynamic behavior of steel catenary risers (SCRs), focusing on the contribution of vortex-induced vibration (VIV), through model test in a towing tank. Nowadays, a great deal of effort is being spent in order to better understand VIV’s contribution in the dynamics of riser structures through experiments, analytical analysis and numerical predictions. In the present work, the design of a SCR model test, along with its setup in a towing tank, will be described in detail and discussions of main results from the experiments will be presented. The experiment has been conducted under several simulated environmental condition combinations, varying the towing speed, riser top forced oscillation amplitudes, waves amplitudes and periods. Very promising results have been observed from the experiment. Riser oscillations due to high harmonics of vortex shedding were observed. Analysis of the experimental results, coupled with the support of numerical tools, showed the influence of the phenomena of traveling waves in the cross-flow response as is reported from the literature.
Stress Based Design Guidelines for Hydrogen Induced Stress Cracking (HISC) Avoidance in Duplex Materials
Authors: Vargas Pedro M. , Wa¨stberg Stig , Woollin Paul
Published: February 2010

Following the failure of several subsea components made of duplex steel, two JIPs were formed, one by TWI and another by DNV and Sintef to address the failure mechanism and to formulate design guidance for the industry. (TWI: The Effects of Notches and Welds on Hydrogen Embrittlement Stress Cracking of Duplex Stainless Steels, Sintef/DNV: HISC) Hydrogen charging from the cathodic protection system in the presence of creep strains embrittles the duplex steel, making the duplex susceptible to cracking (hydrogen-induced-stress-cracking, HISC). Creep effects focused on strain measurements in the test specimens from early work at TWI, favoring a strain based approach in the development of early versions of the design guidance for the industry. This paper summarizes the relevant content from the two JIPs to formulate a stress based design criteria, and provides new FEA assessment of the Foinhaven Hubs to better quantify the effect of residual stresses. The basis for the stress-based design guidelines in DNV-RP-F112 is presented that promises to be easier to apply and equally robust as the strain-based approach.
Investigation of VIV Fatigue Prediction for a Top Tensioned Riser
Authors: Cheng Yongming , Xu Lixin , Lambrakos Kostas F. , Muriby Karl
Published: February 2010

Top tensioned risers (TTRs) have been widely used with floating production systems such as Spars and TLPs in deepwater field developments. A TTR system provides direct access to subsea wellheads from a floating platform for drilling, workover, and completion operations. It is often subjected to Vortex-Induced Vibrations (VIVs) caused by ambient ocean currents. This paper investigates the VIV fatigue prediction for a TTR used with a Spar in deep water. The riser VIV predictions are mainly based on the frequency domain program SHEAR7 that is widely used in the offshore industry. The nonlinear finite element program ABAQUS is used to model the riser for the generation of modal data, including natural frequencies, mode shapes and mode curvatures. The riser is modeled using generic beam elements with equivalent section properties. The model considers the lateral supports from the keel guide and hard tank. The riser tensioner is modeled with non-linear springs. The riser VIV is predicted using different SHEAR7 versions. This paper investigates the sensitivity of the results to key parameters such as the type of lift coefficients, mode bandwidth, mode cutoff, and the Strouhal number. In addition, the time domain VIV prediction program ABAVIV is used to compute the VIV response for a few governing current profiles. The results by SHEAR7 are compared with those by ABAVIV.
Stability and Frequency Response of Top-Tensioned Risers and SCR’s: The L/D Ratio in Perspective
Authors: Todd William
Published: February 2010

Stability is closely linked to the dynamic behavior of risers and SCR’s. This paper reviews the L/D criterion as used to categorize offshore structural elements and places this criterion in perspective when used in VIV calculations to compare slender beams, beam-columns and cable behavior to anticipated results for top-tensioned risers with like L/D ratios. The stability of beam-columns with various end conditions and loadings are compared to that of an in-service 2400m top-tensioned riser. An analytic solution for the frequencies and mode shapes of top-tensioned risers at varying top-tension is given and factors which influence the dynamic behavior detailed. The analysis demonstrates that loads and representation of the load distribution are vital to obtaining valid results. Close-coupling of displacement and slope with loading are essential to the analysis. Results are shown of the effects of varying top-tension factor (TTF) on the stability and dynamic response of risers and SCR’s.
A Numerical Investigation of a Wave Energy Harness Device-Water Interaction System Subject to the Wave Maker Excitation in a Towing Tank
Authors: Xing Jing Tang , Xiong Ye Ping , Tan Ming Yi , An Huai Yu
Published: February 2010

This paper investigates numerically a wave energy harness device-water interaction system excited by a wave maker motion in order to extract maximum wave energy. The model of the energy harness device consists of a moving coil connected to a magnetic body floating on the water surface of the towing tank. At one end of the towing tank, a wave maker produces waves to excite the device-water interaction system. The motion of the coil relative to the magnetic body produces an electromagnetic induction voltage added to an energy collection circuit, so that the kinetic energy of the coil motion is transformed to electric energy. To extract maximum energy from the wave requires a large relative motion between the coil and the magnetic body of the energy harness device. To this end, the natural frequency of the wave energy harness device should be so close to the wave frequency that a resonance of the wave energy device can be reached. Since the wave energy device floats on the water surface, its dynamic behaviour is affected by the water motion. Therefore, it is necessary to consider fluid-structure interactions to design an effective wave energy device. This problem is addressed in this paper. In this numerical simulation, the water is considered as a compressible fluid satisfying a wave equation in the water domain in association with the boundary conditions on the free surface, wall and bottom of the towing tank. The wave maker motion is simulated by a given boundary acceleration on the wet interface of the wave maker. The energy harness device is treated as a two masses connected by four springs between them. The spring stiffness can be adjusted to obtain an effective energy extraction device. On the interface between the magnetic body and the water, the equilibrium and motion consistent conditions are required. The governing equations describing the fluid-structure interaction dynamics of the integrated system are presented. A corresponding variational principle is formulated and a mixed finite element model is established. The developed computer program-FSIAP is used to complete the numerical simulations. Suitable parameters of the energy harness device are obtained. The dynamic responses of the integrated fluid-structure interaction system excited by the wave maker motions are calculated. It is shown that the designed energy harness device can extract maximum wave energy using the resonance principle. The results obtained are compared and discussed. Some guidelines for engineering applications are provided.