bluuebunny/crossref_metadata_2025 huggingface dataset:
The Adoption of Bottom-up Governance in China's Homeowner Associations
Authors: Wang Feng , Yin Haitao , Zhou Zhiren
Published: November 2011

Since China's marketization-featured housing reform, homeowner associations have played a greater role in neighbourhood governance. Using the theory of social movements and organizations, this article investigates how homeowner associations strategically reorganize themselves to achieve their goals. Our survey in Beijing suggests that about half of the homeowner associations have adopted bottom-up governance structures, which are not specified in governmental regulations. We find that such innovations are more likely to occur when a neighbourhood needs grassroots participation to deal with external grievances, especially developer-related issues, or to overcome its powerlessness due to little access to the polity. We also find that homeowner associations are more likely to adopt bottom-up structures when their leaders believe strongly in resident participation or actively engage in extra-organizational professional activities as a means to overcome infrastructure deficit.
A Crucial Factor in Evangelicalism’s Success in (South) Korea: Coalescence with Nationalism and Anticommunism
Authors: Lee Timothy S.
Published: November 2011

South Korea is the home of the most vibrant evangelical community in East Asia. There one of every five citizens is an evangelical. This fact calls for an explanation, given that evangelicalism has hardly made similar inroads into China or Japan, the other major nations in the region, not to mention North Korea. This study examines what may be the most compelling factor in the rise of evangelicalism in Korea, one grounded in the modern history of Korea. The study makes the case that perhaps the most crucial factor in evangelicalism’s success in (South) Korea is that unlike in China or Japan or North Korea, in South Korea evangelicalism coalesced with collective interests of the larger society: first with Korean nationalism and then with South Korean anticommunism.
Cultural Differences in the Subjective Experience of Emotion: When and Why They Occur
Authors: Scollon Christie Napa , Koh Sharon , Au Evelyn W. M.
Published: November 2011

Cross‐cultural comparisons of subjective emotional experience are common, and virtually any comparison of nations or different ethnic groups is bound to yield some differences and some similarities. While nobody doubts the considerable intercultural variability in subjective or self‐reports of emotion, more attention needs to be given to when and why and these differences occur. In this article, we explore factors that accentuate or attenuate cultural differences in the subjective experience of emotion. We propose that cultural norms shape emotional experiences to different degrees depending on the time frame of the emotional experience, the valence of the emotion, and even the specific emotion being compared. We review the research that supports this view and we highlight new avenues of research that are likely to shed light on cultural differences in the subjective experience of emotions.
The Role of Racial Identification, Social Acceptance/Rejection, Social Cognition, and Racial Socialization in Multiracial Youth’s Positive Development
Authors: Csizmadia Annamaria
Published: November 2011

Deficit‐based scholarship has suggested that multiracial youth are maladjusted due to racial identity confusion and social marginality. This paper proposes an integrative model of multiracial youth’s positive development. This model highlights the important role of social cognition in understanding multiracial youth’s development. Drawing on Spencer’s PVEST, developmental research on monoracial and multiracial youth, and the racial socialization literature, I argue that multiracial youth’s perceptions of how their racial identity choices are accepted in their social environment have implications for their adjustment. Serving as developmental resources, parents can attenuate their children’s social perceptual biases or enhance their abilities to cope with actualized negative social experiences by engaging in cultural socialization, preparation for bias, and transmitting race‐related messages that help multiracial children reframe their negative perceptions.
Conflating Apples and Oranges: Understanding Modern Forms of Racism
Authors: Carson Byrd W.
Published: November 2011

Social scientists generally agree that the post‐Civil Rights form of racism is different from that which existed in the Jim Crow‐era in the United States. However, beyond this agreement, what exactly modern racism is and “looks like” is debatable. With this in mind, a surprising and somewhat disturbing trend frequently occurs among social scientists that can have real consequences within academia and the general public: conflation. In naming a newly developed concept as “racism”, social scientists often conflate three interrelated concepts: racial prejudice, racial discrimination, and racism. This paper clarifies these three interrelated concepts and the problems with conflating them. Additionally, this paper describes many of the alternative conceptions of racism in the post‐Civil Rights era, identifying where conflation exists in each concept. In closing, the paper describes the implications of conflation for social science research and the American public.
Effects of vildagliptin on postprandial markers of bone resorption and calcium homeostasis in recently diagnosed, well‐controlled type 2 diabetes patients*
Authors: BUNCK Mathijs C. , POELMA Marieke , EEKHOFF E. Marelise , SCHWEIZER Anja , HEINE Robert J. , NIJPELS Giel , FOLEY James E. , DIAMANT Michaela
Published: November 2011

Background:  Bone metabolism is a dynamic process that is influenced by food ingestion. Endogenous incretins have been shown to be important regulators of bone turnover. The aim of the present study was to assess whether a dipeptidylpeptidase (DPP)‐4 inhibitor affects markers of bone resorption and calcium homeostasis.

Methods:  The present study was a single‐center, double blind, randomized clinical trail. Fifty‐nine drug‐naïve patients with type 2 diabetes (T2D) were randomized to either 1 year treatment with the DPP‐4 inhibitor vildagliptin (100 mg, once daily; n = 29) or placebo (n = 30). Patients received a standardized breakfast after measurement of serum concentrations of cross‐linked C‐terminal telopeptide (s‐CTx), a bone resorption marker influenced by food intake, before and after 50 weeks treatment.

Results:  Vildagliptin did not change postprandial s‐CTx concentrations compared with pretreatment levels (between‐group ratio 1.15 ± 0.17; P = 0.320). Fasting serum alkaline phosphatase, calcium, and phosphate were also unaffected y 1 year treatment with vildagliptin.

Conclusions:  Treatment with vildagliptin for 1 year was not associated with changes in markers of bone resorption and calcium homeostasis in drug‐naïve patients with T2D and mild hyperglycemia.
5‐fluorouracil arterial infusion + interferon therapy for highly advanced hepatocellular carcinoma: A multicenter, randomized, phase II study
Authors: Monden Morito , Sakon Masato , Sakata Yuh , Ueda Yoshitaka , Hashimura Etsuro ,   FAIT Research Group
Published: November 2011

Aim:  The efficacy and safety of 5‐fluorouracil arterial infusion + interferon therapy (FAIT) was evaluated in patients with hepatocellular carcinoma (HCC) with a high degree of vascular invasion associated with poor prognosis, using best salvage therapy (BST) as a reference group.

Methods:  Sixty‐nine patients with advanced HCC with a high degree of vascular invasion (Vp3, Vp4, Vv3) were randomly assigned to a FAIT group or a BST group. The FAIT group received interferon‐α and 5‐fluorouracil combination therapy; the BST group received either combination therapy of cisplatin and 5‐fluorouracil (low‐dose FP therapy) or cisplatin for arterial infusion.

Results:  Thirty patients in the FAIT group and 31 patients in the BST group were included in the efficacy analysis. The response rate (primary endpoint) was 26.7% (eight out of 30 patients) for the FAIT group and 25.8% (eight out of 31) for the BST group. The number of occurrences of adverse events of grade 3 or higher was 115 in 30 patients in the FAIT group and 113 in 29 patients in the BST group. None of the deaths were related to the study therapy.

Conclusions:  FAIT exerts modest antitumor effects and poses no particular safety concerns. FAIT may be a strategy of choice worth trying for advanced HCC with high degree of vascular invasion, which is associated with poor prognosis.
Avoiding Disasters: Evolution in Integrity and Maintenance Management
Authors: Witte Carlos C. , Ribeiro Duperron M. , Grossman Beatriz
Published: November 2011

The critical structure demands a 3D model to recreate a real situation and optimize the asset maintenance with a visual management. Since 1995, Petrobras uses software able to do the maintenance management registering the structures degradation evolution, paints, and cathodic protection in all vessels and offshore platforms. This paper regards how technology can help to avoid disasters with timeline deployed information management applied to structure maintenance.
Design of a Point Absorber Inside the WindFloat Structure
Authors: Peiffer Antoine , Roddier Dominique , Aubault Alexia
Published: November 2011

This paper summarizes the modeling and testing that was performed to integrate a point-absorber type Wave-Energy Converter (WEC) within the WindFloat hull. The WindFloat is a floating structure supporting a very large (>5MW) wind turbine. By adding a wave-energy device to the structure, one can improve the overall economic cost of the project, since both the mooring system and power infrastructure are shared. For the device analyzed here, the modeling is first described and then the Motion Response Amplitude Operators (RAOs) are computed. From these motion responses, the theoretical mechanical power available is calculated. The power values depend on empirical coefficients that need to be confirmed through model testing in the lab. The hydrodynamic forces on each device are often dependent on the interference between the device and the hull, the mooring, and the non-linear effects which are challenging to model. Therefore, these forces are approximated using a Morrison-type formulation in the numerical models. The empirical values for drag coefficients, damping coefficients, and stiffness coefficients in this report are validated against model tests, which are also described.
How to Carry Out Metocean Studies
Authors: van Os Judith , Caires Sofia
Published: November 2011

Metocean studies involve quite a lot of statistical analyses. The detail and extent of the required metocean conditions (waves, water level, currents and wind) is study dependent. Nevertheless, most of the studies involve data validation, determination of normal and extreme metocean conditions and offshore to nearshore transformation of data. All of the above aspects of a metocean study can be performed in numerous different ways, which will in a way depend on the quality and amount of the available data. Data validation, for example, can be done visually and numerically and there are several methods to perform an extreme value analysis. It is therefore needed to have best practice guidelines to execute metocean studies in an efficient and standardized way so that accurate and verifiable results can be obtained. Deltares carries out a lot of metocean studies for the industry and is presently working on a method to standardize the execution of metocean studies, by developing guidelines along with a MATLAB tool, called ORCA, which integrates the main aspects of analyzing metocean data.
What Can We Learn From Uncertainty Analysis With Respect to Survivability or Time to Capsize of a Ship Struck in Collision?
Authors: Hogstro¨m Per , Ringsberg Jonas W.
Published: November 2011

Collisions between ships contribute to ship losses even in modern time, and the International Maritime Organization (IMO) strives towards a more risk-based view on addressing the damage stability of ships. The current paper makes use of a methodology for computing the consequences of ship collisions. This methodology is comprised of structural analysis of a collision scenario followed by dynamic damage stability simulations of the struck ship. The emphasis of this investigation is on uncertainties related to structural computations of the collision event. Explicit finite element analyses are presented for a case study of a collision scenario. For comparison, the model of the bow of the striking ship is considered as either rigid or deformable in separate analyses. The consequences from the model representation of the bow, uncertainties in material properties and failure model (three different ones are presented) in terms of shape and size of the damage opening are studied. This variation also has an impact on the time to capsize of the struck vessel, which is studied in the subsequent damage stability computations for different sea states. One conclusion is that the methodology that has been used is important for future efforts in the research on safety at sea. The study presented demonstrates the importance of incorporating uncertainties in the analysis chain and studying the effect of these on the final results: the time to capsize.
Analysis of Free Vibration Characteristics and Mode Shapes of a Semi-Submersible Platform
Authors: Ringsberg Jonas W. , Ernholm Per , Hogstro¨m Love
Published: November 2011

The current investigation presents a global natural frequency and mode shape analysis of a semi-submersible platform. The purpose is to evaluate the separation in frequency between the semi-submersible’s global natural frequencies and the exciting wave spectrum. Two types of finite element models are compared: a beam element model and a shell element model. The main differences in the models are the level of resolution in details and model complexity. It is shown that both beam and shell element models can be used for the analysis. However, the beam element model is recommended for a first approximate assessment of the fundamental natural frequency and the interval/spectrum of global resonance frequencies compared to the wave spectrum. The shell element model is recommended when a more thorough analysis is required. In addition, the natural frequencies of the semi-submersible are calculated for free vibration in air. The fundamental frequency was 1.9 Hz for the beam element model and 1.5 Hz for the shell element model. When weights corresponding to a submerged structure in operation mode are considered, including the effects of added mass, the fundamental frequency for the first mode using the beam element model was decreased to 0.7 Hz, and to 0.6 Hz when using the shell element model. When compared to the DNV world wave spectrum’s highest frequency of 0.29 Hz it is concluded that the natural frequencies of the semi-submersible are at a sufficient distance from the exciting wave spectrum.
A Generic Optimization Algorithm for the Allocation of DP Actuators
Authors: van Daalen E. F. G. , Cozijn J. L. , Loussouarn C. , Hemker P. W.
Published: November 2011

In this paper we present a generic optimization algorithm for the allocation of dynamic positioning actuators, such as azimuthing thrusters and fixed thrusters. The algorithm is based on the well-known Lagrange multipliers method. In the present approach the Lagrangian functional represents not only the cost function (the total power delivered by all actuators), but also all constraints related to thruster saturation and forbidden zones for azimuthing thrusters. In the presented approach the application of the Lagrange multipliers method leads to a nonlinear set of equations, because an exact expression for the total power is applied and the actuator limitations are accounted for in an implicit manner, by means of nonlinear constraints. It is solved iteratively with the Newton-Raphson method and a step by step implementation of the constraints related to the actuator limitations. In addition, the results from the non-linear solution method were compared with the results from a simplified set of linear equations, based on an approximate (quadratic) expression for the thruster power. The non-linear solution was more accurate, while requiring only a slightly higher computational effort. An example is shown for a thruster configuration with 8 azimuthing thrusters, typical for a DP semi-submersible. The results show that the optimization algorithm is very stable and efficient. Finally, some options for improvements and future enhancements — such as including thruster-thruster and thruster-hull interactions and the effects of current — are discussed.
Modelling of the IPS Buoy Wave Energy Converter Including the Effect of Non-Uniform Tube Cross-Section
Authors: Falca˜o Anto´nio F. O. , Caˆndido Jose´ J. M. B. , Justino Paulo A. P. , Henriques Joa˜o C. C.
Published: November 2011

An important class of floating wave energy converters (that includes the IPS buoy, the Wavebob and the PowerBuoy) comprehends devices in which the energy is converted from the relative (essentially heaving) motion between two bodies oscillating differently. The paper considers the case of the IPS buoy, consisting of a floater rigidly connected to a fully submerged vertical (acceleration) tube open at both ends. The tube contains a piston whose motion relative to the floater-tube system (motion originated by wave action on the floater and by the inertia of the water enclosed in the tube) drives a power take-off mechanism (PTO) (assumed to be a linear damper). To solve the problem of the end-stops, the central part of the tube, along which the piston slides, bells out at either end to limit the stroke of the piston. The use of a hydraulic turbine inside the tube is examined as an alternative to the piston. A frequency domain analysis of the device in regular waves is developed, combined with a one-dimensional unsteady flow model inside the tube (whose cross-section is in general non-uniform). Numerical results are presented for a cylindrical buoy in regular waves, including the optimization of the acceleration tube geometry and PTO damping coefficient for several wave periods.
Installation of Monopiles for Offshore Wind Turbines—By Using End-Caps and a Subsea Holding Structure
Authors: Sarkar Arunjyoti , Gudmestad Ove T.
Published: November 2011

Monopiles are commonly used as foundations for offshore wind turbines at sites with shallow to intermediate water depths (say, up to 40m water depth). The installation of a monopiles is normally carried out by using a bottom supported platform (e.g., a jack-up vessel) which holds the pile at the correct location vertically while driving it into the seabed. In this paper, a methodology for installing a monopile is described which can be applied either by a bottom supported platform or by a floating vessel. The basic philosophy behind this methodology is to support the monopile initially by buoyancy and then by a subsea holding structure. Thus the requirement for a large crane working offshore is eliminated and the marine operation is no longer dependent on the motions of the supporting vessel. Brief geotechnical calculations are presented to support the feasibility of this methodology. Some of the possible design challenges of the installation aids are listed in the conclusion.
Uncertainties, Risks and Opportunities in Development of Hydrocarbon Fields
Authors: Gu Minli , Gudmestad Ove T.
Published: November 2011

The main objectives of this paper are to contribute to change people’s attitude to uncertainty, and transform project risk management into project uncertainty management, to develop the proper project risks management processes, and to achieve a balance between exploiting opportunities and controlling risks. We will analyze the uncertainties and risks in the decision making process, in particular in the early project phases, and explore factors that cause cost and schedule savings and overruns. It is important to distinguish between positive and negative impacts of uncertainty, and then give suggestions to the manager for successful execution of the project in the later phase. We suggest that further research is needed to completely and successfully integrate the strategic risk management process into the organization. The practical challenges shall be reconciled with the organization to implement uncertainty management successfully. Emphasis should be put on the company’s adoption of HSE culture into the organizational culture.
New Concept of Port Planning for Small Ferries From the Viewpoint of Berthing Ship Motions Under Strong Tidal Currents
Authors: Sasa Kenji , Kim Kyunghoi
Published: November 2011

The working ratio of ports when the influence of waves is remarkable has been discussed in detail; however, the ratio of those not facing open sea areas has not been considered. The current port operations are clarified through a questionnaire. Because tidal currents are the main complicating factor in ferry operations, the difficulty of ferry berthing is estimated through revised numerical simulations. The working ratio due to tidal currents is newly defined to compare it with that due to waves. In a ferry terminal of the Seto Inland Sea, the working ratio due to tidal currents is lower than the standard for harbor tranquility. New port planning is required for small ferry terminals with strong tidal currents.
Probability of Occurrence of Extreme Waves in Three Dimensional Mechanically Generated Random Wave Fields: A Comparison With Numerical Simulations
Authors: Toffoli A. , Chai S. , Bitner-Gregersen E. M. , Pistani F.
Published: November 2011

Experimental and numerical investigations reveal that nonlinear modulational instability can significantly affect the probability of occurrence of extreme waves, especially if waves are sufficiently steep and narrow banded both in the frequency and directional domain. However, it is not yet completely clear whether numerical simulations can provide an accurate quantitative estimate of experimental results. Here the potential Euler equations are used to assess the ability of numerical models to describe the evolution of statistical properties of mechanically generated directional, random wave fields and in particular the evolution of the kurtosis. Results show that simulations provide a good quantitative estimate of experimental observations within a broad range of wave directional width.
Simulation of Passive Soil Failure and Cutting Processes in Sand
Authors: Rahman Mahbubur , Abdeli Morteza , Miedema Sape , Schott Dingena
Published: November 2011

Discrete Element Modeling (DEM) is a method which is designed to simulate the behavior of a material by modeling the interactions between discrete elements i.e. particles. The mechanical interactions between particles and also between particles and the walls in are modeled by springs, dash-pots and friction sliders. The properties of the material and interactions (Poisson’s ratio, shear modulus and density, coefficients of restitution, rolling and static friction) relate to the particle properties and not to the bulk properties. If DEM (using software like EDEM™ & PFC™) is reliable by validation with analytical models, it will have many applications in dredging, specifically for investigating underwater cutting processes in sand, clay and rock. Since people have no real experience with this method in dredging, the first step is to model a number of well-known examples like passive earth pressure and the cutting of dry sand and compare the simulation results with the analytical solutions. During this first step the relation between particle and bulk properties has also been investigated. Since the EDEM™ software does not yet contain a code to calculate porosity changes and pore water pressure (without coupling with CFD), this is implemented during a second step. The final target of this study is to use the DEM software to possible modify Miedema and Evans analytical solutions for sand and rock cutting at 3000 m water depths, but in the future the modeling of erosion could also be a topic of research. The current research consisted of becoming acquainted with the software and carrying out basic tests to verify the outcomes. During the research it emerged that the shape of the particles determines whether the expected behavior of sand can be replicated. Also the relation between micro and macro properties, i.e. the static friction of particle and the angle of internal friction, was investigated. Using a particle consisting of a number of spheres with an irregular shape did give very good results. Passive earth pressure simulations gave a very good match with the analytical solution, as did cutting tests in dry sand with a number of cutting angles. Using a cutting angle of 90 degrees resulted in the occurrence of a wedge in front of the blade with a wedge angle corresponding to literature.
Submerged Towing Performed by a Monohull Vessel
Authors: Jacobsen Tore , Leira Bernt
Published: November 2011

During a submerged towing operation of a subsea module, the vessel motions combined with the hydrodynamic properties of the considered module will induce drag forces and dynamic loads on the towing configuration. These loads are important when evaluating different submerged towing concepts and will have implications for structural design with respect to the relevant limit states. However, since it is difficult to quantify the hydrodynamic properties of the towed module, model tests are useful for verifying coefficients which are further used in dynamic analyses of the towing configuration. The objective of this paper is to present an analysis methodology for determination of dynamic forces and hydrodynamic properties of a marine structure during a submerged towing operation. Emphasis is made on a simple analytical model of the dynamic forces based on DNV-RP-H103, and a detailed multibody time integration by means of the MARINTEK computer program SIMO (Simulation of complex marine operations). In order to model the submerged towing operation in SIMO, hydrodynamic properties of the considered towed structure are determined based on analytical formulas presented in DNV-RP-H103. The results from the SIMO model are in addition compared with measured response obtained from an experimental investigation. In general it is found that there is good agreement between experimental and calculated values when the hydrodynamic properties of the components have been identified.
Simulation of Weather and Ocean for Numerical Ship Navigation
Authors: Soda Taisuke , Shiotani Shigeaki , Makino Hidenari , Shimada Yoichi
Published: November 2011

For safe navigation, high-resolution information on wind and waves is very important. In coastal areas in particular, the weather and ocean situation changes dramatically in time and place according to the effects of geography and water depth. In this paper, high resolution wave data are generated using SWAN [1][2] as a numerical wave model. To estimate waves, wind data is necessary. By using the mesoscale meteorological model of WRF-ARW, detailed wind data was generated. We simulated wind and ocean waves for the duration of a typhoon passing over Japan in September of 2004. Secondly, we simulated ship maneuvering using simulated wind and wave data. For the ship maneuvering model, the MMG (Mathematic Modeling Group) was used. Combining high-resolution wind and wave data with the numerical navigation model, we studied the effects of wind and waves on a ship’s maneuvering. Comparing the simulated rhumb lines of a ship with the dead reckoning tracks, it was recognized that the effects of the wind and waves on a moving ship were significant.
Development of Method/Apparatus for Close-Visual Inspection of Underwater Structures (Especially Pipelines) in Muddy and Unclear Water Condition
Authors: Agbakwuru Jasper A. , Gudmestad Ove T. , Groenli John G. , Skjaveland Helge
Published: November 2011

Ordinarily, the Remotely Operated Vehicles and underwater divers, even with modern illuminating lamps, would be unable to observe objects clearly in muddy or unclear underwater condition. Efforts have therefore been made to demonstrate that in such underwater condition, it is possible to perform visual inspections and observations adequately and reliably for underwater leaking structures using novel equipment. The novel equipment works by simply supplying a clear laminar flow of water which flows over the surface of the structure to be observed. A camera eye is then placed to observe through the steady flowing clear water. Different configurations of the equipment were checked and it was found that the equipment with fitted valves installed in the flooding box in-line with flowing clear water produced the best result. The volume of water required for the observations appears constant and independent of the depth of water except during the first initial stage of flooding. On the other hand, the period of time required for clear observations increases with increase in water depth. The performance of the equipment was found independent of the nature of underwater visibility. The benefits of this work ranges from leaking structures’ close-visual inspection including leaking pipelines, to subsea pipeline field joint wrap damage inspection for beach pulls in cofferdams. This technique is considered cheap, robust and flexible.
PSI Armour Wire for High Collapse Performance of Flexible Pipe
Authors: Paumier Laurent , Mesnage Olivier
Published: November 2011

Ultra Deep Water (UDW) developments are now a reality with several fields below 2 000 m water depth now ready for production. Within the domain of flexible pipe technology for UDW, Technip identified a number of technical challenges such as flow assurance, riser tension capacity and hydrostatic collapse resistance. These challenges have been addressed through the qualification of various flexible pipe products/components and riser configurations. This paper will focus on one of the solutions developed which addresses the hydrostatic collapse resistance of the pipe, namely the dynamic PSI wire. The dynamic PSI wire was developed primarily as structurally optimized pressure armour. Based on the efficient structural cross section of the I-beam, the dynamic PSI wire provides a weight/strength optimized configuration for internal pressure capacity of the pipe. It also provides increased crushing strength for installation of the pipe in Ultra Deep Water and significantly increases the hydrostatic collapse resistance of the pipe. The objective of the development of the dynamic PSI wire was to propose a 12″ riser for 2 500 m water depth and smaller diameter down to 3 000 m. This objective has been reached, without impacting the dynamic and sour service capacity of the riser. The dynamic PSI wire has succeeded all the qualification process (industrial procurement & manufacturing, full scale dynamic test, full scale collapse tests, full scale offshore installation test down to 3 000m water depth, NACE test, etc) and is now deemed fully qualified for project application. This paper will present the qualification program and also some field case studies showing the potential applications of flexible risers integrating this new design. The availability of dynamic PSI wires provides operators with the opportunity to develop flexible riser production systems in UDW fields with larger diameters and therefore enhance the subsea production and export systems.
Statistical Uncertainty Analysis in the Long-Term Distribution of Wind- and Wave-Induced Hot-Spot Stress for Fatigue Design of Jacket Wind Turbine Based on Time Domain Simulations
Authors: Dong WenBin , Moan Torgeir , Gao Zhen
Published: November 2011

The statistical uncertainty of the long-term distribution of wind- and wave-induced hot-spot stress ranges in multi-planar tubular joints of a fixed jacket offshore wind turbine designed for a North Sea site in a water depth of 70m has been assessed in this paper. The dynamic response of the jacket support structure due to wind and wave loads is calculated using a decoupled procedure. Hot-spot stresses at failure-critical locations of each reference brace for 4 different tubular joints (DK, DKT, X-type) are derived by summation of the single stress components from axial, in-plane and out-plane action. The effects of planar and non-planar braces are also considered. A two-parameter Weibull function is used to fit the long-term statistical distribution of hot-spot stress ranges by combination of time domain simulation for representative environmental conditions (wind / sea states) in operational condition of the wind turbine. The statistical uncertainty of the Weibull distribution of hot-spot stress ranges and the two parameters defining the Weibull distribution is assessed, based on 20 simulations for each representative environmental condition. The contributions to the uncertainty from wind loads and wave loads are analyzed by considering 3 different load cases: wind loads only, wave loads only and combination of wind and wave loads. The sensitivity of the long-term distribution of hot-spot stress ranges due to their stress components is also assessed.
A Fatigue Design for Large Container Ship Taking Long-Term Environmental Condition Into Account
Authors: Oka Masayoshi , Ogawa Yoshitaka , Takagi Ken
Published: November 2011

In order to promote the reliable evaluation for the fatigue strength of ships, the validation of a direct load and strength computation was performed based on the tank test and the full scale measurement. The fatigue damage in short term sea state under various operation parameters was indicated quantitatively by the tank test in irregular wave utilizing the elastic model. The long term fatigue damage was evaluated based on the full scale measurement [1]. The fatigue damage inferred from the measured stress on deck structure is quite small compared with the direct computation utilizing a full ship finite element model. That is mainly caused by the difference of environmental wave condition. Moreover, the effect of operational condition through whole life was indicated by the direct computation quantitatively. To make more rational fatigue design, it is important to take the long-term wave condition into account.
A Whole Ship Finite Element Analysis With the Input of Nonlinear Wave Loads in the Irregular and Multi-Directional Waves
Authors: Ogawa Yoshitaka , Oka Masayoshi
Published: November 2011

Authors developed a whole ship finite element analysis system from a nonlinear wave loads to a structural strength at real sea state. A methodology for the rational analysis of structural strength is examined. Firstly, wave pressure, which is the input for the present whole ship finite element analysis and has much effect on the accuracy of a whole ship analysis, is validated through the comparison with experiments. It is confirmed that the present computation can estimates wave pressure in various wave condition accurately. Secondly, the whole ship finite element analysis system by the combination with the computation of nonlinear wave pressure is verified. It is verified that the present method can evaluate a structural response in irregular waves with taking account of the nonlinear effect of ship motions and slamming induced impact loads explicitly. Finally, through the structural analysis in various ship forward speed and wave condition by means of the present computation, the importance to assess a structural strength taking account of the effect of operational condition is clarified.
Safety Level of a Probabilistic Admittance Policy
Authors: Bos Mark , Koop Olger , Bolt Ernst
Published: November 2011

The main factor restricting admission of deep-draught ships to ports is the risk of bottom contact. In the approach channels to Rotterdam and IJmuiden such ships are subject to tidal windows because of the limited depths in the approach channels. Some decades ago probabilistic methods were introduced for the allocation of tidal windows for the Euro-Maas channel to Rotterdam and later also for the IJ channel to IJmuiden. These methods are being further developed. The increased accuracy of computational methods and of forecasted wave conditions and water levels may lead to an increased accessibility of the port. Recent developments have resulted in the new tidal window advice program Protide (PRObabilistic TIdal window DEtermination). The objective of the work presented in this paper is the verification and validation of Protide for the Euro-Maas channel to Rotterdam and for the IJ channel to IJmuiden. The probability of bottom contact during channel transit is simulated for time series of ten years of measured wave data and water levels. The fleet of ships is represented by a limited number of ships and for each ship all possible tidal windows for the ten year period are determined with Protide. A database is developed with motion response characteristics for each of the representative ships. For all possible arrival times in the ten-year period, indicated as safe by Protide, a channel transit is simulated. The probability of bottom contact during the simulated transit is computed from the motion response characteristics of the ship and with the measured wave spectra and the measured water level. Two safety criteria are applied. Firstly the probability of bottom contact during a single channel transit should not be excessive. Secondly the total probability of bottom contact during a long period of application of the admittance policy should be limited. To determine the probability that a certain ship is in a certain section of the channel some elements from queuing theory are applied. The probability that the ship is present in each channel section combined with the probability of bottom contact results in the probability of bottom contact for the ship in the channel. This leads to a long term probability of bottom contact for the channel. This paper presents the analysis method and selected simulation results for Euro-Maas channel in detail.
Pressure Measurement on the Surface of a Rigid Cylindrical Body During Slamming Wave Impact
Authors: Van Nuffel Diederik , Vepa Sridhar , De Baere Ives , Degrieck Joris , De Rouck Julien , Van Paepegem Wim
Published: November 2011

Among all kinds of loads that floating and fixed marine constructions experience, water wave slamming can be considered as one of the most critical. To prevent naval constructions from failing due to slamming impact, slamming loads should be carefully investigated. Besides analytical and numerical calculations, experimental data is of crucial importance. Slamming loads can be measured by performing pressure measurements on the surface of the object during impact. Previous publications showed that precise and correct measurements are very difficult to perform, especially for slamming events with small deadrise angles. Large scatter mostly characterizes these measurements. This research focuses on improving the accuracy and reproducibility of the pressure recordings. Therefore, slamming drop tests are performed on a rigid cylindrical body. Most attention is paid to the bottom of the cylinder where the deadrise angle is 0°.
An Example of Code Verification in the Simulation of Wave Propagation
Authors: Fathi Fahd , Ec¸a Lui´s , Borsboom Mart
Published: November 2011

Thanks to advances in modeling and hardware the range of applications available to CFD modeling is continuously increasing. As CFD has moved from demonstration of capability to production of engineering results of practical value, there is an increased awareness in the field that Verification and Validation are systematically required. Verification deals with the numerical accuracy of a given set of results. Its object is the assessment of the numerical uncertainty due to discretization and iterative errors of a numerical solution (Solution Verification) performed with a Code that has been previously checked to be free of errors (Code Verification). Both activities are required to ensure that errors are controlled and that quality of the results is maintained. Complementarily, Validation addresses the modeling error, i.e. the comparison of the mathematical model with the (physical) reality. Therefore, it requires comparison with experimental data. Validating CFD results is only meaningful when preceded by carefully verified calculations (Solution Verification) with verified codes (Code Verification). The topic of Verification and Validation is developing and standardized procedures are still under discussion. Nevertheless, there are techniques available to perform careful Code and Solution Verification for flows with engineering relevance. This paper presents a Code Verification exercise for the simulation of wave propagation with a VOF code. Systematically refined grids and time steps are applied in the calculation of waves with a known analytical solution to assess the convergence properties of the numerical solution. The aim of the exercise is to demonstrate the advantages of such exercises for the knowledge of the numerical properties of a code that is applied in complex flows. The study is not a pure Code Verification exercise. Modeling errors introduced by approximate outlet boundary conditions (allowing wave reflections) are also quantified for a linear and a high-order wave. However, these are still based on (numerical) error evaluations for known analytical solutions and so they can still be classified as Code Verification.
Multi-Cylinder Flow-Induced Motions: Enhancement by Passive Turbulence Control at 28,000<Re<120,000
Authors: Kim Eun Soo , Bernitsas Michael M. , Kumar R. Ajith
Published: November 2011

The VIVACE (Vortex Induced Vibration for Aquatic Clean Energy) Converter was introduced at OMAE2006 as a single, smooth, circular-cylinder module. The hydrodynamics of VIVACE is being improved continuously to achieve higher density in harnessed hydrokinetic power. Inter-cylinder spacing and Passive Turbulence Control (PTC) through selectively located roughness are effective tools in enhancement of Flow Induced Motions (FIMs) under high damping for power harnessing. VIVACE Converters consist of multi-cylinder modules. Single cylinders harness energy at high density even in 1knot currents. For downstream cylinders questions are raised on energy availability and sustainability of high-amplitude FIM. Through PTC and inter-cylinder spacing, strongly synergetic FIM of 2/3/4 cylinders is achieved, harnessing hydrokinetic energy with increased footprint density. Two-cylinder smooth/PTC and four-cylinder PTC systems are tested experimentally. Using the “PTC-to-FIM” map developed in previous work at the Marine Renewable Energy Laboratory (MRELab), PTC is applied and cylinder response is measured for the following parameter ranges: In-flow center-to-center distance 1.63•D–5.00•D (D = diameter), transverse center-to-center distance 0.5•D–1.5•,D, Re ∈[28,000–120,000], m* ∈[1.677–1.690], U ∈[0.36m/s–1.45m/s], aspect ratio l/D = 10.29, and m*ζ ∈[0.0283–0.0346]. All experiments are conducted in the Low Turbulence Free Surface Water (LTFSW) Channel of MRELab. Amplitude spectra and broad filed-of-view (FOV) visualization help reveal complex flow structures and cylinder interference undergoing VIV, interference/proximity/wake/soft/hard galloping.
Assessing the Use of Composite Materials in Reinforcing Offshore Risers and Pipelines
Authors: Alexander Chris
Published: November 2011

Composite systems are a generally-accepted method for repairing corroded and mechanically-damaged onshore pipelines. The pipeline industry has arrived at this point after more than 15 years of research and investigation. Because the primary method of loading for onshore pipelines is in the circumferential direction due to internal pressure, most composite systems have been designed and developed to provide hoop strength reinforcement. On the other hand, offshore pipes (especially risers), unlike onshore pipelines, can experience significant tension and bending loads. As a result, there is a need to evaluate the current state of the art in terms of assessing the use of composite materials in repairing offshore pipelines and risers. The paper presents findings from a joint industry effort involving the Minerals Management Service, the Offshore Technology Research Center at Texas A&M University, Stress Engineering Services, Inc., and several composite repair manufacturers was undertaken to assess the state of the art using full-scale testing methods. Loads typical for offshore risers were used in the test program that integrated internal pressure, tension, and bending loads. This program is the first of its kind and likely to contribute significantly to the future of offshore riser repairs. It is anticipated that the findings of this program will foster future investigations involving operators by integrating their insights regarding the need for composite repair based on emerging technology.
Mechanical Behavior of Buried Steel Pipelines Crossing Strike-Slip Seismic Faults
Authors: Vazouras Polynikis , Karamanos Spyros A. , Dakoulas Panos
Published: November 2011

The present paper investigates the mechanical behaviour of buried steel pipelines, crossing active strike-slip tectonic faults. The fault plane is vertical and perpendicular to the pipeline axis. The interacting soil-pipeline system is modelled rigorously through finite elements, which account for large strains and displacements, nonlinear material behaviour and special conditions of contact and friction on the soil-pipe interface. Steel pipelines of various diameter-to-thickness ratios, and typical steel material for pipeline applications (API 5L grades X65 and X80) are considered. The paper investigates the effects of various soil and pipeline parameters on the mechanical response of the pipeline, with particular emphasis on pipe wall failure due to “local buckling” or “kinking” and pipe wall rupture. The effects of shear soil strength and stiffness, are also investigated. Furthermore, the influence of the presence of pipeline internal pressure on the mechanical response of the steel pipeline is examined. Numerical results aim at determining the fault displacement at which the pipeline failure occurs, and they are presented in a graphical form that shows the critical fault displacement, the corresponding critical strain versus the pipe diameter-to-thickness ratio. It is expected that the results of the present study can be used for efficient pipeline design in cases where active faults are expected to impose significant ground-induced deformation to the pipeline.
Efficient Derivation of the Probability Distribution of the Extreme Values of Offshore Structural Response Taking Advantage of Its Correlation With Extreme Values of Linear Response
Authors: Abu Husain M. K. , Najafian G.
Published: November 2011

Offshore structures are exposed to random wave loading in the ocean environment and hence the probability distribution of the extreme values of their response to wave loading is required for their safe and economical design. To this end, the conventional simulation technique (CTS) is frequently used for predicting the probability distribution of the extreme values of response. However, this technique suffers from excessive sampling variability and hence a large number of simulated response extreme values (hundreds of simulated response records) are required to reduce the sampling variability to acceptable levels. A more efficient method (ETS) was recently introduced which takes advantage of the correlation between the extreme values of surface elevation and their corresponding response extreme values. The method has proved to be very efficient for high-intensity sea states; however, the correlation and hence the efficiency and accuracy of the technique reduces for sea states of lower intensity. In this paper, a more efficient version of the ETS technique is introduced which takes advantage of the correlation between the extreme values of the nonlinear response and their corresponding linear response values.