bluuebunny/crossref_metadata_2025 huggingface dataset:
Serious Anaphylactic Reactions due to Protamine Sulfate: A Systematic Literature Review
Authors: Nybo Mads , Madsen Jonna Skov
Published: July 2008

Abstract:  Anaphylactic reactions caused by injection of protamine sulfate during cardiac surgery are a well‐known complication. A systematic literature review was therefore conducted to gather evidence of the knowledge concerning these side effects, and to see if any prospective randomized studies supported this. Studies investigating the effect of protamine sulfate in human beings were extracted from MEDLINE, Embase and the Cochrane Library, retrieving 487 articles. Abstracts were evaluated by both authors, and referred articles not found in the primary search were furthermore extracted from reviews and case reports, resulting in a total of 272 relevant articles. Of these, 9 retrospective studies and 16 prospective studies were performed in an evidence‐based manner. However, only 3 of the 16 prospective articles had an optimal design as far as inclusion criteria, randomization, and description of symptoms were concerned. Incidence of anaphylactic reactions in the prospective studies was 0.69% compared to 0.19% in the retrospective studies, but caution should be taken due to a pronounced heterogeneity of those studies. One study found heparinase I unsuitable as replacement for protamine sulfate. Overall, our findings support the low incidence of anaphylactic reactions reported in previous studies, but of note only few prospective investigations was conducted on the subject. Our study also emphasizes the need for critical appraisal of many routine procedures: in all aspects of medical care, systematic literature review conducted in a well‐structured, repeated manner should be given high priority.
Effects of Subchronic versus Acute in utero Exposure to Dexmedetomidine on Foetal Developments in Rats
Authors: Tariq Mohammad , Cerny Vladimir , Elfaki Ibrahim , Khan Haseeb Ahmad
Published: July 2008

Abstract:  Dexmedetomidine is a highly selective and specific α‐2 adrenergic agonist with sedative, analgesic and sympathetic activities. This study was undertaken to investigate the effects of in utero exposure of dexmedetomidine on foetal development and postnatal behaviour in the offspring. Pregnant Sprague‐Dawley rats were chronically treated with dexmedetomidine (0, 5, 10 and 20 µg/kg, subcutaneously) daily from gestation day 7 to day 19. Another group of animals received only a single acute dose of dexmedetomidine (20 µg/kg) on gestational day 19 to mimic a model for systemic analgesia during labour. Administration of dexmedetomidine did not affect the frequency of implantations. Chronic administration of 10 and 20 µg/kg of dexmedetomidine significantly reduced the body weight and crown‐rump length of pups, whereas a single acute dose (20 µg/kg) did not affect these parameters. None of the pups exhibited any external malformations or skeletal abnormalities irrespective of treatment assigned. All the pups showed a normal postnatal weight gain during the developmental phase. No significant differences were observed among any of the groups with respect to behavioural performances of offspring in beam balance, grip strength and inclined plane tests as well as motor activity. In conclusion, acute exposure to dexmedetomidine at the anticipated delivery time does not exert any adverse effects on perinatal morphology of pups, their birth weight, crown‐rump length, physical growth and postnatal behavioural performances. Since this study was conducted in rats, its clinical relevance in human beings remains to be unclear and warrants further studies.
Amelioration of Cyclosporine A‐Induced Renal, Hepatic and Cardiac Damages by Ellagic Acid in Rats*
Authors: Yüce Abdurrauf , Ateşşahin Ahmet , Çeribaşı Ali Osman
Published: July 2008

Abstract:  Treatment with cyclosporine A has significantly improved long‐term survival after organ transplantations. Cyclosporine A also causes a dose‐related decrease in body functions in experimental animals and human beings. The generation of reactive oxygen species has been implicated in cyclosporine A‐induced dysfunctions. The aim of this study was to determine the effects of ellagic acid on cyclosporine A‐induced alterations in the kidney, liver and heart oxidant/antioxidant system. The control group was treated with placebo and subcutaneous injection of 0.5 ml isotonic saline + 0.5 ml slightly alkaline solution for 21 days. The cyclosporine A group received a subcutaneous injection of cyclosporine A (15 mg/kg) + 0.5 ml slightly alkaline solution for 21 days. The ellagic acid group was treated with a subcutaneous injection of 0.5 ml isotonic saline + ellagic acid (10 mg/kg) for 21 days. The cyclosporine A plus ellagic acid group received a subcutaneous injection of cyclosporine A + ellagic acid for 21 days. Ellagic acid and slightly alkaline solution were administered by gavage. The rats were killed at the end of the treatment period. Malondialdehyde (MDA) and reduced glutathione (GSH) levels, glutathione peroxidase (GSH‐Px) and catalase (CAT) activities were determined in kidney, liver and heart tissues. While administration of cyclosporine A increased the MDA levels in kidney, liver and heart tissues, it decreased the GSH, GSH‐Px and CAT in these samples when compared to the control group. However, the simultaneously administration of ellagic acid markedly normalized the cyclosporine A‐induced liver and heart MDA levels, liver CAT activities and GSH‐Px activities of all samples. Cyclosporine A caused marked damages in the histopathological status of kidney, liver and heart tissues, which were partially ameliorated by ellagic acid administration. In conclusion, ellagic acid may be used in combination with cyclosporine A in transplantation treatment to improve the cyclosporine A‐induced oxidative stress parameters and other adverse effects.
A Silent Witness for Peace: The Case of Schoolteacher Mary Stone McDowell and America at War
Authors: Howlett Patricia , Howlett Charles F.
Published: July 2008

A 1964 television series, “Profiles in Courage,” based on the late President John F. Kennedy's Pulitzer prize-winning book, featured the life of Mary Stone McDowell, a quiet, yet strong, teacher. Within peace circles, McDowell was a well-known figure. It was not unusual to see her marching in peace demonstrations or handing out antiwar literature at street meetings in the rain, snow, sleet and hot days in the summer. It was not out of the ordinary to read her editorials urging war tax resistance and certainly not surprising to those who knew her to draw strength from her courage and convictions. Yet what captured the interest of the show's producers was the stand she took during World War I. This quiet, unassuming Phi Beta Kappa graduate from Swarthmore College, and Quaker public school teacher in New York City, became the first educator in American history to test the constitutionality of the newly enacted loyalty oaths on religious, rather than political, grounds.
Activity budget and diving behavior of gray whales (Eschrichtius robustus) in feeding grounds off coastal British Columbia
Authors: Stelle Lei Lani , Megill William M. , Kinzel Michelle R.
Published: July 2008

Abstract

Behavior and diving patterns of summer resident gray whales (Eschrichtius robustus) foraging on mysids were studied in coastal bays along the north shore of Queen Charlotte Strait, British Columbia. In this region, gray whales were found to feed primarily on planktonic prey rather than on the benthos as in their primary feeding areas further north. During the summers of 1999 and 2000, whales spent most of their time actively feeding or searching for prey (77%), whereas only 15% of their time was spent traveling and 8% socializing. The majority of the dives were short; the mean dive duration was 2.24 min with approximately three respirations per surfacing and 15 s between blows. Whales dove frequently (26.7 h−1), spending only 17% of their time at the surface with an overall blow rate of 1.14 respirations per minute. Activity states were characterized by significantly different diving and respiratory parameters; feeding whales dove more frequently, with shorter intervals between respirations, thus spending less time at the surface compared to when traveling or searching. This diving pattern differs from benthic‐feeding whales and likely optimizes capture of the mobile mysid swarms in shallow waters.
Diel variation in beaked whale diving behavior
Authors: Baird Robin W. , Webster Daniel L. , Schorr Gregory S. , McSweeney Daniel J. , Barlow Jay
Published: July 2008

Abstract

We investigate diel variation in beaked whale diving behavior using data from time–depth recorders deployed on six Blainville's (Mesoplodon densirostris) (255 h) and two Cuvier's (Ziphius cavirostris) (34 h) beaked whales. Deep foraging dives (>800 m) occurred at similar rates during the day and night for Blainville's beaked whales, and there were no significant diel differences in ascent rates, descent rates, or mean or maximum depths or durations for deep dives. Dive to mid‐water depths (100–600 m) occurred significantly more often during the day (mean = 1.59 h−1) than at night (mean = 0.26 h−1). Series of progressively shallower “bounce” dives were only documented to follow the deep, long dives made during the day; at night whales spent more time in shallow (<100 m) depths. Significantly slower ascent rates than descent rates were found following deep foraging dives both during the day and night. Similar patterns were found for the Cuvier's beaked whales. Our results suggest that so‐called “bounce” dives do not serve a physiological function, although the slow ascents may. This diel variation in behavior suggests that beaked whales may spend less time in surface waters during the day to avoid near‐surface, visually oriented predators such as large sharks or killer whales (Orcinus orca).
Maple Trees and Weeping Willows: The Role of Time, Uncertainty, and Affinity in Intergenerational Decisions
Authors: Wade‐Benzoni Kimberly A.
Published: July 2008

Some of the most important issues in business and society today involve a conflict of interest between present and future generations. In this article, I explore how resources are allocated across generations, articulate the role of psychological distance in intergenerational decisions, and develop the construct of intergenerational discounting. Intergenerational discounting is defined as the preference for smaller, highly probable benefits for oneself in the present to relatively larger but less certain benefits for others in the future. In three studies, I explore the role of three variables in intergenerational decisions, including time delay between decisions and their consequences, uncertainty about the future, and affinity with future generations.
Linguistic Style Matching and Negotiation Outcome
Authors: Taylor Paul J. , Thomas Sally
Published: July 2008

This research examined the relationship between Linguistic Style Matching (LSM)—the degree to which negotiators coordinate their word use—and negotiation outcome. Nine hostage negotiations were divided into six time stages and the dialogue of police negotiators and hostage takers analyzed across 18 linguistic categories. Correlational analyses showed that successful negotiations were associated with higher aggregate levels of LSM than unsuccessful negotiations. This result was due to dramatic fluctuations of LSM during unsuccessful negotiations, with negotiators unable to maintain the constant levels of rapport and coordination that occurred in successful negotiations. A further analysis of LSM at the local turn‐by‐turn level revealed complex but organized variations in behavior across outcome. In comparison to unsuccessful negotiations, the dialogue of successful negotiations involved greater coordination of turn taking, reciprocation of positive affect, a focus on the present rather than the past, and a focus on alternatives rather than on competition.
Individual Differences and Group Negotiation: The Role of Polychronicity, Dominance, and Decision Rule
Authors: Mohammed Susan , Rizzuto Tracey , Hiller Nathan J. , Newman Daniel A. , Chen Tina
Published: July 2008

The purpose of the current study was to integrate two streams of research that have remained largely distinct: negotiation and group composition. Specifically, this experiment examined the interactive effects of two individual difference variables (polychronicity and dominance) on multi‐party negotiation performance (task conflict and joint profit) in either unanimity or majority rule contexts. Results from business students in a multi‐issue negotiation exercise revealed that personality does play a role in group negotiation, but relationships were contingent, as revealed by the presence of a significant two‐way interaction for task conflict and a three‐way interaction for joint profit. Group polychronicity resulted in higher task conflict, but only when group dominance was low. The polychronicity–dominance interaction significantly predicted joint profit under majority rule, but had little effect under a unanimity decision rule. Consistent with task conflict results, polychronicity negatively predicted joint profit, but only for lower dominance groups under majority rule. Findings reinforce the importance of examining how multiple individual differences interact with each other, as well as with situational factors, to determine group negotiation outcomes.
Multi‐Couple Reflecting Team: Preliminary Report
Authors: De Barbaro Bogdan , Drożdżowicz Lucyna , Janusz Bernadetta , Gdowska Katarzyna , Dembińska Edyta , Kołbik Ilona , Furgał Mariusz
Published: July 2008

The aim of therapeutic help in marital crisis is to break the vicious circle of mutual hurtful accusations. The method that the authors present below involves a group of couples working within a closed cycle of meetings. In the course of successive group meetings, the various couples act as reflecting teams (RTs) for each other. This achieves two objectives: the couple recounting their crisis receives nonthreatening feedback, which helps them to implement positive changes and break out of the self‐perpetuating destructive interaction. In addition, the couples acting as the RT learn nonjudgmental, nontheorizing and affirmative communication.
Investigations Into the Statistical Properties of ECN From Corroding Marine Systems
Authors: Shashikala A. P. , Ramasubramanian J. , Janakiraman G.
Published: July 2008

The random nature of sea waves and the aggressive corrosive environment of seawater make corrosion an important factor in deciding the safe operational life of offshore steel structures. The consistent rise in offshore oil exploration activities in the last 2 decades has compelled structural engineers and researchers to better understand, the process of corrosion in offshore steel structures. The various electrochemical methods available for corrosion monitoring are polarization, electrochemical impedance spectroscopy and electro chemical noise (ECN) techniques. In offshore industry, the reliable interpretation of electrochemical noise is particularly valuable since it promises new type of online monitoring device. This paper introduces ECN as an online corrosion-monitoring tool for marine structures. The paper discusses the laboratory experiments conducted on test specimens to collect data related to the electrochemical behavior of structural steel such as the polarization data, impedance measurements, electrochemical, potential, and current noise measurements. Investigations were carried out on MS coupons surface prepared and coated with anticorrosive and antifouling paints. An electrochemical workstation capable of collecting data from specimens coated with paint was used for noise data collection. Static corrosion tests have been done and the corrosion rate and corrosion resistance of the coatings were assessed using the statistical analysis. The electrochemical noise data were compared with that of polarization and impedance data and a good correlation between corrosion rates was obtained. The polarization and noise resistance were found to be similar in trend but with variation in numerical values. Statistical parameters like mean, standard deviation, skew, and kurtosis were generated from the obtained noise. These parameters were then processed to obtain noise resistance and corrosion rate. The results were compared with that of polarization and impedance values. The corrosion rate comparison showed a deviation of 10% from polarization with ECN giving the upper bound values. The damage prediction and expected life prediction of a steel jacket platform were also performed using the data collected. The experiments showed a good correlation between the noise resistances obtained from various electrochemical methods. The aim of introducing the ECN as an online monitoring tool for marine structures especially in on-life offshore structures gives valid data with good results and shows good sensitivity.
Status Review on Fatigue Performance of Fillet Welds
Authors: Maddox Stephen J.
Published: July 2008

This paper presents a critical review of current design methods, including their background and relevant experimental data, for assessing the fatigue performance of steel fillet welds with respect to failure in the weld throat. The main focus is on fillet or partial penetration welds in cruciform, T, or lap joints under transverse loading failing by fatigue crack growth across the weld throat under normal stresses. The review covers the influence of residual stress, applied mean stress, joint fit-up and alignment, weld quality, the use of coated steel, the need for a plate thickness correction, and calculation of the optimum weld size. Also considered are cases of fillet welds failing in shear or combined normal and shear stresses.
Pyroreflectometry to Determine the True Temperature and Optical Properties of Surfaces
Authors: Hernandez D. , Sans J. L. , Pfänder M.
Published: July 2008

In this paper, we present a theoretical analysis and experimental results of a pyrometric temperature measurement method based on a two-color pyroreflectometer (working wavelengths of 1.3μm and 1.55μm) equipped with an optical fiber probe. By measuring simultaneously the radiance temperature and the normal reflectivity, the true temperature of the measurement target can be determined without the previous knowledge of the optical properties of the sample. The method is based on the introduction and the definition of the diffusivity factor ηd and the assumption that it is equal for the two wavelengths. Besides the experimental results, the sources of errors and their impact on the method accuracy and the performance of the setup are discussed. The quality of the measurement results demonstrates the utility of the pyroreflectometry in a domain where fundamental parameters, such as the temperature and radiative properties, present the major measurement difficulties. The diffusivity factor appears not only a step to determine the true temperature but also as a parameter very useful to evaluate the diffusing behavior of opaque materials.
Multihull and
Surface-Effect Ship Configuration Design: A Framework for Powering
Minimization
Authors: Yeung Ronald
W. , Wan Hui
Published: July 2008

The powering issue of a high-speed marine vehicle with multihulls and air-cushion support is addressed, since there is an often need to quickly evaluate the effects of several configuration parameters in the early stage of the design. For component hulls with given geometry, the parameters considered include the relative locations of individual hulls and the relative volumetric ratios. Within the realm of linearized theory, an interference-resistance expression for hull-to-hull interaction is first reviewed, and then a new formula for hull-and-pressure distribution interference is derived. Each of these analytical expressions is expressed in terms of the Fourier signatures or Kochin functions of the interacting component hulls, with the separation, stagger, and speed as explicit parameters. Based on this framework, an example is given for assessing the powering performance of a catamaran (dihull) as opposed to a tetrahull system. Also examined is the wave resistance of a surface-effect ship of varying cushion support in comparison with that of a base line catamaran, subject to the constraint of constant total displacement.
Water Wave Interaction on a Truncated Vertical Cylinder
Authors: Garriga Octavi Sadó , Falzarano Jeffrey M.
Published: July 2008

The purpose of this paper is to combine and extend existing potential flow theory in order to analyze the linear free surface problem of an oscillating water column (OWC) device and apply it to moon pool design. Analytical results were obtained implementing the previously derived theories, and later compared to experimental results conducted at the University of New Orleans Towing Tank. The model tests consisted of a study of a cylindrical OWC. The theoretical and experimental results of the free surface for the OWC tests agree for the resonant frequency estimation response but they disagree on the amplitude of the response.
Stochastic Earthquake Analysis of Underwater Storage Tanks
Authors: Karadeniz H.
Published: July 2008

In this paper, the problem and analysis method of underwater storage tanks resting on a horizontal seabed is presented under stochastic earthquake loading. The tank is axisymmetrical and has a flexible wall/roof. The finite element method is used for the response solution. A solid axisymmetrical finite element has been formulated to idealize the tank whereas an axisymmetrical fluid element is used for the idealization of the fluid domain. The Eulerian formulation of the fluid system is used to calculate the interactive water pressure acting on the tank during the free motion of the tank and earthquake motion. For the response calculation, the modal analysis technique is used with a special algorithm to obtain natural frequencies of the water-structure coupled system. For the stochastic description of the earthquake loading, the modified Kanai–Tajimi earthquake spectrum is used. Finally, the analysis method presented in the paper is demonstrated by an example.
Understanding the Dynamic Coupling Effects in Deep Water Floating Structures Using a Simplified Model
Authors: Low Ying Min , Langley Robin S.
Published: July 2008

The global dynamic response of a deep water floating production system needs to be predicted with coupled analysis methods to ensure accuracy and reliability. Two types of coupling can be identified: one is between the floating platform and the mooring lines/risers, while the other is between the mean offset, the wave frequency, and the low frequency motions of the system. At present, it is unfeasible to employ fully coupled time domain analysis on a routine basis due to the prohibitive computational time. This has spurred the development of more efficient methods, including frequency domain approaches. A good understanding of the intricate coupling mechanisms is paramount for making appropriate approximations in an efficient method. To this end, a simplified two degree-of-freedom system representing the surge motion of a vessel and the fundamental vibration mode of the lines is studied for physical insight. Within this framework, the frequency domain equations are rigorously formulated, and the nonlinearities in the restoring forces and drag are statistically linearized. The model allows key coupling effects to be understood; among other things, the equations demonstrate how the wave frequency dynamics of the mooring lines are coupled to the low frequency motions of the vessel. Subsequently, the effects of making certain simplifications are investigated through a series of frequency domain analyses, and comparisons are made to simulations in the time domain. The work highlights the effect of some common approximations, and recommendations are made regarding the development of efficient modeling techniques.
Generation of Large Angle Bimodal Sea States Using One-Side Segmented Wavemaker
Authors: de Reilhac P. Roux , Bonnefoy F. , Ferrant P.
Published: July 2008

In the present work, we study the capabilities of a one-side segmented wavemaker to generate multidirectional sea states. We want to reproduce typical West Africa sea conditions in a rectangular basin, that is, two spectra representing swell and wind waves with ±45deg main directions relative to the basin axis. For that purpose, we study two generation techniques proposed, respectively, by Dalrymple and Molin which rely on the control of sidewall reflections in order to enlarge the testing zone. Both numerical and experimental results show that the use of such methods in combination with a one-side wavemaker provides high quality wave fields as well as large extent testing area. The Molin method appears to be more efficient in terms of wave field quality within the testing area although the tuning of its setting parameters requires more care than the Dalrymple method.
Influence of Generator Damping on Peak Power and Variance of Power for a Direct Drive Wave Energy Converter
Authors: Stålberg Magnus , Waters Rafael , Danielsson Oskar , Leijon Mats
Published: July 2008

The first offshore prototype of a wave energy converter system has been launched off the Swedish west coast. The concept is based on a point absorber directly coupled to a linear generator located on the ocean floor. The wave energy converter is part of a research project that will study the electric system of ten units forming a small farm of wave power plants as they are linked and connected to an electric grid. A full scale farm will consist of a large number of interconnected units. The chosen direct drive system reduces the mechanical complexity of the converter but has repercussions on the electric system. The output from the generator will vary with the speed of the point absorber, leading to large fluctuations of power on the second scale. This has implications on both the individual generator and on the system as a whole. The hydrodynamic behavior of the point absorber depends, to a large extent, on the damping of the generator. The damping, in turn, can be remotely controlled by changing the load resistance. It has previously been shown that this has a large influence on the power absorbed by the wave energy converter. This paper investigates the peak power, the translator speed, and the variance of the power at different sea states and for different levels of damping. The peak power has an impact on the design of the generator and the required ability, for a single unit, to handle electric overloads. The momentum of the translator is directly proportional to its speed. The speed is thus important for the design of the end stop. The variance of the power of one unit will have an impact on the farm system behavior. The study is based on two and a half months of experimental measurements on the prototype wave energy converter and a wave measurement buoy. The aim is to analyze whether load control strategies may influence the dimensioning criteria for the electric system and the generator. The results are compared to previously investigated relationships between the absorbed mean power and the load resistance as a function of sea state. In the study, it was found that the maximum power is approximately proportional to the average power, while the maximum translator speed and standard deviation decrease as the damping factor is increased.
Updating and Optimization of a Coning Rotor Concept
Authors: Crawford Curran , Platts Jim
Published: July 2008

The work detailed in this paper is focused on updating and refining a coning rotor wind turbine concept. The coning rotor combines the load shedding properties of flapping hinges with gross change in rotor area, via large coning angles, to affect increased energy capture at nominally constant system cost. Previous studies have indicated that the large cost of energy reductions is possible, compared to the state-of-the-art machines then, particularly for abundant but presently uneconomic low-wind sites. Almost ten years later, the fundamentals of the design remain sound, but bear reevaluation relative to current machines, both exploiting modern power electronics and control technology. The coning rotor was never optimized in its own right, so an integrated design tool suitable for human and computer refinement of the design has been developed. Incorporated into the tool is a corrected blade element momentum method that more properly accounts for coned rotor aerodynamics. A discussion of the development of coning rotors is presented, along with a comparison to present operational strategies. Results obtained for nondimensionalized rotors and specific machine optimization studies are presented, followed by a discussion of further issues to be addressed.
Variable Speed Control of Wind Turbines Via Memory-Based Firing Angle Sequence Adjustment
Authors: Liao X. H. , Sun Z. , Song Y. D. , Li Bin , Mei X. Y.
Published: July 2008

Maximum electric power extraction out of available wind power is directly linked to advanced variable speed wind turbine control. The paper presents a memory-based method for variable speed adjustment of wind energy conversion systems. The fundamental idea behind the method is to use certain memorized information (i.e., current rotor speed tracking error, most recent speed tracking error, and previous control experience) to directly modify the firing angle control command sequences. The salient feature of the proposed approach lies in its simplicity in design and implementation. Furthermore, the total required memory space does not grow with time and is much smaller than most existing learning control methods. It is shown that this method, when applied to firing angle control of wind turbines, is able to ensure rotor speed tracking in the presence of varying operation conditions, as verified via computer simulation.
Uncertainty Analysis in MCP-Based Wind Resource Assessment and Energy Production Estimation
Authors: Lackner Matthew A. , Rogers Anthony L. , Manwell James F.
Published: July 2008

This paper presents a mathematical framework to properly account for uncertainty in wind resource assessment and wind energy production estimation. A meteorological tower based wind measurement campaign is considered exclusively, in which measure-correlate-predict is used to estimate the long-term wind resource. The evaluation of a wind resource and the subsequent estimation of the annual energy production (AEP) is a highly uncertain process. Uncertainty arises at all points in the process, from measuring the wind speed to the uncertainty in a power curve. A proper assessment of uncertainty is critical for judging the feasibility and risk of a potential wind energy development. The approach in this paper provides a framework for an accurate and objective accounting of uncertainty and, therefore, better decision making when assessing a potential wind energy site. It does not investigate the values of individual uncertainty sources. Three major aspects of site assessment uncertainty are presented here. First, a method is presented for combining uncertainty that arises in assessing the wind resource. Second, methods for handling uncertainty sources in wind turbine power output and energy losses are presented. Third, a new method for estimating the overall AEP uncertainty when using a Weibull distribution is presented. While it is commonly assumed that the uncertainty in the wind resource should be scaled by a factor between 2 and 3 to yield the uncertainty in the AEP, this work demonstrates that this assumption is an oversimplification and also presents a closed form solution for the sensitivity factors of the Weibull parameters.
The Influence of the Joint Wind-Wave Environment on Offshore Wind Turbine Support Structure Loads
Authors: Agarwal Puneet , Manuel Lance
Published: July 2008

Our objective here is to establish long-term loads for offshore wind turbines using a probabilistic approach. This can enable one to estimate design loads for a prescribed level of return period, generally on the order of 20–50years for offshore wind turbines. In a probabilistic approach, one first needs to establish “short-term” distributions of the load random variable(s) conditional on the environment; this is achieved either by using simulation or field measurements. In the present study, we use field data from the Blyth offshore wind farm in the United Kingdom, where a 2MW wind turbine was instrumented, and environment and load data were recorded. The characteristics of the environment and, hence, that of the turbine response at the site are strikingly different for wind regimes associated with different wind directions. Here, we study the influence of such contrasting environmental (wind) regimes and associated waves on long-term design loads. The field data, available as summary statistics, are limited in the sense that not all combinations of environmental conditions likely to be experienced by the turbine over its service life are represented in the measurements. Using the available data, we show how distributions for random variables describing the environment (i.e., wind and waves) and the turbine load of interest (i.e., the mudline bending moment) can be established. By integrating load distributions, conditional on the environment with the relative likelihood of different environmental conditions, long-term (extreme/ultimate) loads associated with specified return periods can be derived. This is demonstrated here by carefully separating out the data in different wind direction sectors that reflect contrasting wind (and accompanying wave) characteristics in the ocean environment. Since the field data are limited, the derived long-term design loads have inherent uncertainty associated with them; we investigate this uncertainty in such derived loads using bootstrap techniques.
Statistical Extrapolation Methods for Estimating Wind Turbine Extreme Loads
Authors: Ragan Patrick , Manuel Lance
Published: July 2008

With the introduction of the third edition of the International Electrotechnical Commission (IEC) Standard 61400-1, designers of wind turbines are now explicitly required, in one of the prescribed load cases, to use statistical extrapolation techniques to determine nominal design loads. In this study, we use field data from a utility-scale 1.5MW turbine sited in Lamar, Colorado to compare the performance of several alternative techniques for statistical extrapolation of rotor and tower loads—these include the method of global maxima, the peak-over-threshold method, and a four-moment process model approach. Using each of these three options, 50-year return loads are estimated for the selected wind turbine. We conclude that the peak-over-threshold method is the superior approach, and we examine important details intrinsic to this method, including selection of the level of the threshold to be employed, the parametric distribution used in fitting, and the assumption of statistical independence between successive peaks. While we are primarily interested in the prediction of extreme loads, we are also interested in assessing the uncertainty in our predictions as a function of the amount of data used. Towards this end, we first obtain estimates of extreme loads associated with target reliability levels by making use of all of the data available, and then we obtain similar estimates using only subsets of the data. From these separate estimates, conclusions are made regarding what constitutes a sufficient amount of data upon which to base a statistical extrapolation. While this study makes use of field data in addressing statistical load extrapolation issues, the findings should also be useful in simulation-based attempts at deriving wind turbine design load levels where similar questions regarding extrapolation techniques, distribution choices, and amount of data needed are just as relevant.
Numerical Site Calibration Over Complex Terrain
Authors: Brodeur Philippe , Masson Christian
Published: July 2008

This paper presents the development and assessment of a numerical method for simulated site calibration. The wind flow over complex terrain is predicted with a small length scale resolution. The flow field is resolved with the Reynolds averaged Navier–Stokes equations, complemented by the k‐ϵ turbulence model, with special treatment of the ground boundary to account for very large roughness lengths such as forest. The computational model is solved using FLUENT. A complex site, Riviere au Renard, located in Gaspesie, QC, Canada, has been selected and data have been collected from five met masts installed on this site. An experimental data analysis has been undertaken with emphasis on uncertainty evaluation. Three sets of results are presented. First, the numerical method is validated over flat terrain by comparing the simulation results with Monin–Obukhov similarity theory. Second, the assessment of the numerical method over complex terrain is done by comparing the wind velocity profiles at three of the met masts for three different wind orientations. Finally, traditional and numerical site calibrations for Riviere au Renard are presented for two wind directions. The numerical results are within the experimental data uncertainty.
Dynamic Prescribed Vortex Wake Model for AERODYN/FAST
Authors: Currin Hugh D. , Coton Frank N. , Wood Byard
Published: July 2008

A new aerodynamic wake model has been developed for horizontal axis wind turbines. The aim is to develop an engineering tool for investigation and design of furling turbines. The prescribed vortex wake code HAWTDAWG, developed at the University of Glasgow, has been extended for dynamic flow conditions. This dynamic prescribed wake model is built into the aerodynamic code AERODYN and linked to the structural dynamics code FAST. The new model has been compared to unsteady aerodynamic experiment Phase VI wind tunnel data. Comparisons are also made to blade element momentum and generalized dynamic wake models built into AERODYN. Results are encouraging and justify further investigation.
Adaptive Pitch Control of Variable-Speed Wind Turbines
Authors: Johnson Kathryn E. , Fingersh Lee Jay
Published: July 2008

The aerodynamic efficiency of a variable-speed wind turbine operating in Region 2, or below-rated wind speeds, is greatly affected by the identification of accurate parameters for the controller. In particular, the power coefficient (Cp) surface must be well known for optimal efficiency to be achieved with a constant-gain controller. However, adaptive control can overcome the inefficiencies caused by inaccurate knowledge of the Cp surface. Previous work focused on adaptive torque gain control to cause a variable-speed turbine to operate, on average, at the tip-speed ratio λ* for which the maximum Cp occurs. This paper considers the effects of adaptive blade pitch angle control on a turbine’s aerodynamic efficiency. Computer simulations and tests on a field turbine are used to verify the adaptive pitch control scheme. Simulation and field test results demonstrate that the adaptive pitch controller causes the pitch angle to approach its optimal value. Adaptive pitch control can be used to seek the optimal pitch angle for energy capture in Region 2 operation. Additional field operation is required before a statistically significant improvement in energy capture can be demonstrated.
Three-Dimensional and Rotational Aerodynamics on the NREL Phase VI Wind Turbine Blade
Authors: Gonzalez Alvaro , Munduate Xabier
Published: July 2008

This work undertakes an aerodynamic analysis over the parked and the rotating NREL Phase VI wind turbine blade. The experimental sequences from NASA Ames wind tunnel selected for this study respond to the parked blade and the rotating configuration, both for the upwind, two-bladed wind turbine operating at nonyawed conditions. The objective is to bring some light into the nature of the flow field and especially the type of stall behavior observed when 2D aerofoil steady measurements are compared to the parked blade and the latter to the rotating one. From averaged pressure coefficients together with their standard deviation values, trailing and leading edge separated flow regions have been found, with the limitations of the repeatability of the flow encountered on the blade. Results for the parked blade show the progressive delay from tip to root of the trailing edge separation process, with respect to the 2D profile, and also reveal a local region of leading edge separated flow or bubble at the inner, 30% and 47% of the blade. For the rotating blade, results at inboard 30% and 47% stations show a dramatic suppression of the trailing edge separation, and the development of a leading edge separation structure connected with the extra lift.
Analysis of the Flow Characteristics of Two Nonrotating Rotor Blades
Authors: van Rooij R. P. J. O. M.
Published: July 2008

The investigation focuses on the analysis of the airfoil segment performances along rotor blades in the parked configuration. In this research, wind tunnel experiments on two twisted blade geometries with different airfoils played a dominant role. These measurements were carried out by the Swedish Aeronautical Research Institute, former FFA, and by the American National Renewable Energy Laboratories (NREL) during the Unsteady Aerodynamic Experiment. The spans of the blades were 2.375m and 5m, the STORK 5 WPX and the NREL Phase VI blade, respectively. Five span locations (inboard, midspan, outboard, and tip regions) were considered and compared with the 2D airfoil characteristics. Wing model experiments with similar blade aspect ratio were included in the research. Furthermore, the commercial computational fluid dynamics code FLUENT was used for the validation and analysis of the spanwise lift and drag coefficients at four different pitch settings, 20deg, 30deg, 45deg, and 60deg. The computed pressure distributions compared reasonably well, but the derived lift and drag showed quite some differences with the blade measurements. The lift coefficients for the sections beyond the leading-edge stall angle of the STORK blade were larger than for the NREL blade and were close to that of a wing model with similar airfoil and aspect ratio. Lift and drag coefficients for the sections of the two blades were always much smaller than the 2D results. The drag values for both blades showed quite some agreement, and airfoil and blade dependency seemed to be small.
A Modified Dynamic Stall Model for Low Mach Numbers
Authors: Sheng W. , Galbraith R. A. McD. , Coton F. N.
Published: July 2008

The Leishman–Beddoes dynamic stall model is a popular model that has been widely applied in both helicopter and wind turbine aerodynamics. This model has been specially refined and tuned for helicopter applications, where the Mach number is usually above 0.3. However, experimental results and analyses at the University of Glasgow have suggested that the original Leishman–Beddoes model reconstructs the unsteady airloads at low Mach numbers less well than at higher Mach numbers. This is particularly so for stall onset and the return from the fully stalled state. In this paper, a modified dynamic stall model that adapts the Leishman–Beddoes dynamic stall model for lower Mach numbers is proposed. The main modifications include a new stall-onset indication, a new return modeling from stalled state, a revised chordwise force, and dynamic vortex modeling. The comparisons to the Glasgow University dynamic stall database showed that the modified model is capable of giving improved reconstructions of unsteady aerofoil data in low Mach numbers.
Robust Multivariable Pitch Control Design for Load Reduction on Large Wind Turbines
Authors: Geyler M. , Caselitz P.
Published: July 2008

This paper deals with multivariable pitch control design for wind turbines, including load reducing control objectives. Different design approaches, including collective and cyclic pitch, and robustness aspects are discussed. A control design with decoupled controllers for collective and cyclic pitch is worked out in detail, based on the H∞ norm minimization approach. The control design is verified by simulations with a full nonlinear model of the wind turbine, showing the potential of multivariable pitch control to actively increase damping of the first axial tower bending mode and to reduce 1p fluctuations in blade root bending moments. Multivariable control design provides a convenient way of including additional load reducing objectives into the pitch controller of wind turbines. Fatigue loading of certain components, as tower and blades, could be reduced significantly.
Relevant Criteria for Testing the Quality of Models for Turbulent Wind Speed Fluctuations
Authors: Frandsen Sten , Jørgensen Hans E. , Sørensen John Dalsgaard
Published: July 2008

Seeking relevant criteria for testing the quality of turbulence models, the scale of turbulence and the gust factor have been estimated from data and compared with predictions from first-order models of these two quantities. It is found that the mean of the measured length scales is approximately 10% smaller than the IEC model for wind turbine hub height levels. The mean is only marginally dependent on trends in time series. It is also found that the coefficient of variation of the measured length scales is about 50%. 3s and 10s preaveraging of wind speed data are relevant for megawatt-size wind turbines when seeking wind characteristics that correspond to one blade and the entire rotor, respectively. For heights exceeding 50–60m, the gust factor increases with wind speed. For heights larger than 60–80m, present assumptions on the value of the gust factor are significantly conservative, both for 3s and 10s preaverages. The usually applied value of kp≈3 should probably be reduced.
Statistical Extreme Load Extrapolation With Quadratic Distortions for Wind Turbines
Authors: Natarajan Anand , Holley William E.
Published: July 2008

Extrapolation of extreme loads using turbulent wind samples of various mean speeds and random starting points is addressed using probability distribution functions that are suitably distorted to fit the peak extremes. The tail of the extreme value distribution of the simulated loads is required to fit accurately and this tail is extrapolated to a 50‐year exceedance probability to determine the characteristic load. The Gumbel distribution with a quadratic distortion is especially addressed due to its asymptotic theoretical validity for Gaussian loads. The blade root moments and the hub moments are studied here with respect to their behavior under extrapolation using a quadratic Gumbel distribution. Verification with a large number of random seeds at various mean wind speeds is done, so as to assess the accuracy of the extrapolation and the convergence of the extrapolated load. Methods of accounting for the variance in the extrapolated load with changes in the random wind seeds are proposed.
Rotor Blade Sectional Performance Under Yawed Inflow Conditions
Authors: Maeda Takao , Kamada Yasunari , Suzuki Jun , Fujioka Hideyasu
Published: July 2008

This study shows the results of pressure distribution measurements on a rotor blade of a horizontal axis wind turbine under various yawed operations. The experiments are carried out in a wind tunnel with a 2.4m diameter test rotor. In the measurements, the power curve and pressure distributions are measured for different azimuth angles. By increasing yaw angle, the maximum value of power coefficient of the rotor decreases. The sign of the yaw angle does not have any effect on power performance. The aerodynamic forces are discussed using the axial and rotational force coefficients for each azimuth angle. In the case of higher tip speed ratios, the blade section passing on the upstream side in yawed operations has a greater contribution to the rotor torque than that on the downstream side. In this tip speed range, the aerodynamic forces at the 70% radius section appear proportional to the angle of attack. In the case of the lower tip speed ratios, the blade on the downstream side does not contribute to rotor torque, which appears to result from separation.