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Advanced wind turbine near-term product development. Final technical report

Description: In 1990 the US Department of Energy initiated the Advanced Wind Turbine (AWT) Program to assist the growth of a viable wind energy industry in the US. This program, which has been managed through the National Renewable Energy Laboratory (NREL) in Golden, Colorado, has been divided into three phases: (1) conceptual design studies, (2) near-term product development, and (3) next-generation product development. The goals of the second phase were to bring into production wind turbines which would meet the cost goal of $0.05 kWh at a site with a mean (Rayleigh) windspeed of 5.8 m/s (13 mph) and a vertical wind shear exponent of 0.14. These machines were to allow a US-based industry to compete domestically with other sources of energy and to provide internationally competitive products. Information is given in the report on design values of peak loads and of fatigue spectra and the results of the design process are summarized in a table. Measured response is compared with the results from mathematical modeling using the ADAMS code and is discussed. Detailed information is presented on the estimated costs of maintenance and on spare parts requirements. A failure modes and effects analysis was carried out and resulted in approximately 50 design changes including the identification of ten previously unidentified failure modes. The performance results of both prototypes are examined and adjusted for air density and for correlation between the anemometer site and the turbine location. The anticipated energy production at the reference site specified by NREL is used to calculate the final cost of energy using the formulas indicated in the Statement of Work. The value obtained is $0.0514/kWh in January 1994 dollars. 71 figs., 30 tabs.
Date: January 1, 1996
Partner: UNT Libraries Government Documents Department
open access

Vertical-axis wind turbines -- The current status of an old technology

Description: Vertical-axis wind turbine technology is not well understood, even though the earliest wind machines rotated about a vertical axis. The operating environment of a vertical-axis wind turbine is quite complex, but detailed analysis capabilities have been developed and verified over the last 30 years. Although vertical-axis technology has not been widely commercialized, it exhibits both advantages and disadvantages compared to horizontal-axis technology, and in some applications, it appears to offer significant advantages.
Date: December 31, 1996
Creator: Berg, D.E.
Partner: UNT Libraries Government Documents Department
open access

NREL airfoil families for HAWTs

Description: The development of special-purpose airfoils for horizontal-axis wind turbines (HAWTs) began in 1984 as a joint effort between the National Renewable Energy Laboratory (NREL), formerly the Solar Energy Research Institute (SERI), and Airfoils, Incorporated. Since that time seven airfoil families have been designed for various size rotors using the Eppler Airfoil Design and Analysis Code. A general performance requirement of the new airfoil families is that they exhibit a maximum lift coefficient (c{sub l,max}) which is relatively insensitive to roughness effects. The airfoil families address the needs of stall-regulated, variable-pitch, and variable-rpm wind turbines. For stall-regulated rotors, better peak-power control is achieved through the design of tip airfoils that restrain the maximum lift coefficient. Restrained maximum lift coefficient allows the use of more swept disc area for a given generator size. Also, for stall-regulated rotors, tip airfoils with high thickness are used to accommodate overspeed control devices. For variable-pitch and variable-rpm rotors, tip airfoils having a high maximum lift coefficient lend themselves to lightweight blades with low solidity. Tip airfoils having low thickness result in less drag for blades having full-span pitch control. Annual energy improvements from the NREL airfoil families are projected to be 23% to 35% for stall-regulated turbines, 8% to 20% for variable-pitch turbines, and 8% to 10% for variable-rpm turbines. The improvement for stall-regulated turbines has been verified in field tests.
Date: January 1, 1995
Creator: Tangler, J L & Somers, D M
Partner: UNT Libraries Government Documents Department
open access

Effect of tilt of the propeller axis on the longitudinal-stability characteristics of single-engine airplanes

Description: Report presenting the results of tests of a model of a single-engine airplane with two different tilts of the propeller axis. The results indicate that on a typical design, a 5 degree downward tilt of the propeller axis will considerably reduce the destabilizing effects of power.
Date: November 1944
Creator: Goett, Harry J. & Delany, Noel K.
Partner: UNT Libraries Government Documents Department
open access

Predicting Posttraumatic Stress Disorder Symptoms During Adolescence: A Longitudinal Study of The Role of Hypothalamic-Pituitary-Adrenal (HPA) Axis Dysfunction

Description: Posttraumatic stress disorder (PTSD) is a trauma-related disorder that may develop in response to traumatic or stressful events. Dysfunction of the Hypothalamic-Pituitary-Adrenal (HPA) axis has been implicated in the disorder. Studies support such dysfunction as being a consequence of PTSD, rather than a precursor. However, most studies of the HPA are either cross-sectional or have been carried out in adults. The aim of the present study was to identify whether HPA dysregulation interacts with stressful experiences to increase the likelihood of developing PTSD symptoms in a community-recruited sample of healthy adolescent girls. Adolescent girls (N = 550) and one of their parents participated. Adolescents’ clinical symptoms were assessed at baseline and at a nine month follow-up. Saliva samples were collected from all adolescent participants at waking, 30 minutes after waking, and 8 pm on 3 consecutive days. Flattened diurnal slope of cortisol at baseline was associated with increased PTSD symptoms nine months later. Baseline cortisol awakening response (CAR) per se was not prospectively related to developing PTSD symptoms, but its interactions with stressful experience was associated with elevated PTSD symptoms at follow-up. Effects were small and need to be replicated in samples with more severe stressors, as well as more clinical levels of PTSD. Nevertheless, findings suggest that dysregulated basal HPA functioning may be involved in the development of PTSD symptoms.
Date: May 2016
Creator: Liu, Keke, 1988-
Partner: UNT Libraries
open access

Atmospheric tests of trailing-edge aerodynamic devices

Description: An experiment was conducted at the National Renewable Energy Laboratory`s (NREL`s) National Wind Technology Center (NWTC) using an instrumented horizontal-axis wind turbine that incorporated variable-span, trailing-edge aerodynamic brakes. The goal of the investigation was to directly compare results with (infinite-span) wind tunnel data and to provide information on how to account for device span effects during turbine design or analysis. Comprehensive measurements were used to define effective changes in the aerodynamic and hinge-moment coefficients, as a function of angle of attack and control deflection, for three device spans (7.5%, 15%, and 22.5%) and configurations (Spoiler-Flap, vented sileron, and unvented aileron). Differences in the lift and drag behavior are most pronounced near stall and for device spans of less than 15%. Drag performance is affected only minimally (about a 30% reduction from infinite-span) for 15% or larger span devices. Interestingly, aerodynamic controls with vents or openings appear most affected by span reductions and three-dimensional flow.
Date: January 1, 1998
Creator: Miller, L. S.; Huang, S. & Quandt, G. A.
Partner: UNT Libraries Government Documents Department
open access

Structural health monitoring of wind turbines

Description: To properly determine what is needed in a structural health monitoring system, actual operational structures need to be studied. We have found that to effectively monitor the structural condition of an operational structure four areas must be addressed: determination of damage-sensitive parameters, test planning, information condensation, and damage identification techniques. In this work, each of the four areas has been exercised on an operational structure. The structures studied were all be wind turbines of various designs. The experiments are described and lessons learned will be presented. The results of these studies include a broadening of experience in the problems of monitoring actual structures as well as developing a process for implementing such monitoring systems.
Date: September 1, 1997
Creator: Simmermacher, T.; James III, G. H. & Hurtado, J. E.
Partner: UNT Libraries Government Documents Department
open access

Earth, Rotation of

Description: Encyclopedia article entry in the Encyclopedia of Time: Science, Philosophy, Theology, and Culture by H. James Birx. This encyclopedia article discusses the rotation of the earth.
Date: 2009
Creator: O'Toole, Erin
Partner: UNT Libraries
open access

Effect of Tilt of the Propeller Axis on the Longitudinal-Stability Characteristics of Single-Engine Airplanes

Description: Report presents the results of tests of a model of a single-engine airplane with two different tilts of the propeller axis. The results indicate that on a typical design a 5 degree downward tilt of the propeller axis will considerably reduce the destabilization effects of power. A comparison of the experimental results with those computed by use of existing theory is included. A comparison of the experimental results with those computed by use of existing theory is included. It is shown that the results can be predicted with an accuracy acceptable for preliminary design purposes, particularly at the higher powers where the effects are of significant magnitude.
Date: 1944
Creator: Goett, Harry J. & Delaney, Noel K.
Partner: UNT Libraries Government Documents Department
open access

Effect of Propeller-Axis Angle of Attack on Thrust Distribution Over the Propeller Disk in Relation to Wake-Survey Measurement of Thrust

Description: "Tests were made to investigate the variation of thrust distribution over the propeller disk with angle of pitch of the propeller thrust axis and to determine the disposition and the minimum number of rakes necessary to measure the propeller thrust. The tests were made at a low Mach number for a low and a high blade angle with the propeller operating at three small angles of pitch, and some of the tests were repeated at a higher Mach number. The data obtained show that, for small angles of pitch, large changes occur in the energy distribution in the wake which prohibit the use of a single survey rake for thrust measurement in flight tests and limit the use of a single rake in wind-tunnel tests" (p. 1).
Date: December 1945
Creator: Pendley, Robert E.
Partner: UNT Libraries Government Documents Department
open access

Measurements of television interference caused by a vertical-axis wind machine. Final subcontract report

Description: The electromagnetic interference to television reception caused by the 17 m Darreius at Albuquerque, NM, has been studied by carrying out measurements at a number of sites in the vicinity of the VAWT. The rf sources used were the commercial vhf and uhf TV signals available in the area. Ambient field-strength measurements showed that the signals on all TV channels except one were strong, and provided good reception at all test sites. With the antenna (properly) oriented for maximum direct signal, unacceptable interference was observed on some channels at sites out to 33 m from the WT in the forward and backward regions. With the antenna beam directed at the WT, interference varying from slight to violent were observed at all sites on some or all TV channels. A simple theoretical model has been developed for analyzing the TVI produced by a VAWT like the Darrieus. Using the model in conjunction with measured data, an approximate expression for the equivalent scattering area A of the Darrieus has been developed. It is found that A is wavelength (lambda) dependent and varies as lambda/sup 1/2/.
Date: January 1, 1983
Creator: Sengupta, D L; Senior, T B.A. & Ferris, J E
Partner: UNT Libraries Government Documents Department
open access

Design and experimental results for the S809 airfoil

Description: A 21-percent-thick, laminar-flow airfoil, the S809, for horizontal-axis wind-turbine applications, has been designed and analyzed theoretically and verified experimentally in the low-turbulence wind tunnel of the Delft University of Technology Low Speed Laboratory, The Netherlands. The two primary objectives of restrained maximum lift, insensitive to roughness, and low profile drag have been achieved. The airfoil also exhibits a docile stall. Comparisons of the theoretical and experimental results show good agreement. Comparisons with other airfoils illustrate the restrained maximum lift coefficient as well as the lower profile-drag coefficients, thus confirming the achievement of the primary objectives.
Date: January 1, 1997
Creator: Somers, D.M.
Partner: UNT Libraries Government Documents Department
open access

Effect of an autopilot sensitive to yawing velocity on the lateral stability of a typical high-speed airplane

Description: Report presenting a theoretical investigation to determine the effect on the lateral stability of a typical high-speed fighter airplane of an autopilot sensitive to yawing velocity. The effects of inclination of the gyro spin axis to the flight path and of time lag in the autopilot were also determined. The damping of lateral oscillation of the airplane for all flight conditions studied should satisfy the Air Force-Navy criterion when the proposed autopilot is installed.
Date: September 1951
Creator: Gates, Ordway B., Jr. & Sternfield, Leonard
Partner: UNT Libraries Government Documents Department
open access

Cooperative field test program for wind systems. Final report

Description: The objectives of the Federal Wind Energy Program, managed by the US Department of Energy (DOE), are (1) to assist industry and utilities in achieving a multi-regional US market penetration of wind systems, and (2) to establish the United States as the world leader in the development of advanced wind turbine technology. In 1984, the program conducted a series of planning workshops with representatives from the wind energy industry to obtain input on the Five-Year Research Plan then being prepared by DOE. One specific suggestion that came out of these meetings was that the federal program should conduct cooperative research tests with industry to enhance the technology transfer process. It was also felt that the active involvement of industry in DOE-funded research would improve the state of the art of wind turbine technology. DOE established the Cooperative Field Test Program (CFTP) in response to that suggestion. This program was one of the first in DOE to feature joint industry-government research test teams working toward common objectives.
Date: March 1, 1992
Creator: Bollmeier, W. S. II & Dodge, D. M.
Partner: UNT Libraries Government Documents Department
open access

An evaluation of an empirical model for stall delay due to rotation for HAWTS

Description: The objective of this study was to evaluate the Corrigan and Schillings stall delay model for predicting rotor performance for horizontal axis wind turbines. Two-dimensional (2D) wind tunnel characteristics with and without stall delay were used in the computer program PROP93 to predict performance for the NREL Combined Experiment Rotor (CER) and a lower solidity commercial machine. For the CER, predictions were made with a constant-chord/twisted blade and a hypothetical tapered/twisted blade. Results for the constant-chord/twisted blade were compared with CER data. Predicted performance using this empirical stall-delay method provided significant increases in peak power over 2D post-stall airfoil characteristics. The predicted peak power increase due to stall delay for the CER was found to be quite large (20% to 30%) as a result of its high blade solidity. For a more typical, lower-solidity commercial blade the predicted peak power increase was 15% to 20%. As described in the paper, correlation with test data was problematic due to factors not related to the stall-delay model.
Date: July 1997
Creator: Tangler, J. L. & Selig, M. S.
Partner: UNT Libraries Government Documents Department
open access

Aerodynamic testing of a rotating wind turbine blade

Description: Aerodynamic, load, flow-visualization, and inflow measurements were taken on a downwind horizontal-axis wind turbine (HAWT). A video camera mounted on the rotor recorded video images of tufts attached to the low-pressure side of the blade. Strain gages, mounted every 10% of the blade's span, provided load and pressure measurements. Pressure taps at 32 chordwise positions recorded pressure distributions. Wind inflow was measured via a vertical-plane array of anemometers located 10 m upwind. The objectives of the test were to address whether airfoil pressure distributions measured on a rotating blade differed from those measured in the wind tunnel, if radial flow near or in the boundary layer of the airfoil affected pressure distributions, if dynamic stall could result in increased dynamic loads, and if the location of the separation boundary measured on the rotating blade agreed with that measured in two-dimensional flow in the wind tunnel. 6 refs., 9 figs., 1 tab.
Date: January 1, 1990
Creator: Butterfield, C.P. & Nelsen, E.N.
Partner: UNT Libraries Government Documents Department
open access

Low-Maintenance Wind Power System

Description: Turbines of 1, 3 and 30 kW were designed, prototyped and evaluated. A 55 kW unit has been preliminarily designed. Two 1 kW alpha units and a 3 kW alpha unit were delivered to the US in 2005 and Empire Magnetics provided custom alternators for the units. After evaluation, the 6 bladed, 3 kW unit was chosen for beta fabrication and 5 units were delivered to the US in December, 2009 while others remained for testing in Russia.
Date: September 30, 2010
Creator: Rasson, Joseph E
Partner: UNT Libraries Government Documents Department
open access

Submersible Generator for Marine Hydrokinetics

Description: A submersible generator was designed as a distinct and critical subassembly of marine hydrokinetics systems, specifically tidal and stream energy conversion. The generator is designed to work with both vertical and horizontal axis turbines. The final product is a high-pole-count, radial-flux, permanent magnet, rim mounted generator, initially rated at twenty kilowatts in a two-meter-per-second flow, and designed to leverage established and simple manufacturing processes. The generator was designed to work with a 3 meter by 7 meter Gorlov Helical Turbine or a marine hydrokinetic version of the FloDesign wind turbine. The team consisted of experienced motor/generator design engineers with cooperation from major US component suppliers (magnetics, coil winding and electrical steel laminations). Support for this effort was provided by Lucid Energy Technologies and FloDesign, Inc. The following tasks were completed: • Identified the conditions and requirements for MHK generators. • Defined a methodology for sizing and rating MHK systems. • Selected an MHK generator topology and form factor. • Completed electromechanical design of submersible generator capable of coupling to multiple turbine styles. • Investigated MHK generator manufacturing requirements. • Reviewed cost implications and financial viability. • Completed final reporting and deliverables
Date: September 1, 2011
Creator: Cinq-Mars, Robert S.; Burke, Timothy; Irish, Dr. James; Gustafson, Brian; Kirtley, Dr. James & Alawa, Dr. Aiman
Partner: UNT Libraries Government Documents Department
open access

Modal parameter extraction from large operating structures using ambient excitation

Description: A technique called the Natural Excitation Technique or has been developed to response extract response parameters from large operational structure when subjected to random and unmeasured forces such as wind, road noise, aerodynamics, or waves. Six applications of NExT to ambient excitation testing and NExT analysis are surveyed in this paper with a minimum of technical detail. In the first application, NExT was applied to a controlled-yaw Horizontal-Axis Wind Turbine (HAWT). By controlling the yaw degree of freedom an important class of rotating coordinate system effects are reduced. A new shape extraction procedure was applied to this data set with good results. The second application was to a free-yaw HAWT. The complexity of the response has prompted further analytical studies and the development of a specialized visualization package. The third application of NExT was to a parked three-bladed Vertical-Axis Wind Turbine (VAWT) in which traditional modal testing could not excite all modes of interest. The shape extraction process used cross-correlation functions directly in a time-domain shape-fitting routine. The fourth application was to ground transportation systems. Ongoing work to improve driver and passenger comfort in tractor-trailer vehicles and to refine automobile body and tire models will use NExT. NExT has been used to process ambient vibration data for Finite Element Model correlation and is being used to study Structural Health Monitoring with ambient excitation. Shape fitting was performed using amplitude and phase information taken directly from the cross-spectra. The final application is to an offshore structure. This work is on-going, however initial studies have found a high-modal density, high noise content, and sparse data set.
Date: December 31, 1995
Creator: James, G.H. III; Carne, T.G. & Mayes, R.L.
Partner: UNT Libraries Government Documents Department
open access

Effects of Defensiveness on the Reporting of Personality Disorder Symptoms

Description: Personality disorders are not granted the same clinical attention accorded Axis I disorders despite their instrumental role in treatment and outcome. Even when standardized assessments are used, their clinical utility may be limited by an overly favorable self-presentation. The current study focused on defensiveness, the intentional denial of symptomatology, by examining individuals’ ability to minimize their presentation on personality disorder diagnostic measures. Using a within-subjects simulation design, dually diagnosed inpatients were assessed under both honest and defensive conditions. The study used self-report (Structured Clinical Interview for DSM-IV – Axis II – Personality Questionnaire, SCID-II-PQ) and interview-based (Structured Interview for DSM-IV Personality, SIDP-IV) diagnostic measures and a self-report measure of favorable self-presentation (Paulhus Deception Scales, PDS). The inpatients were quite capable of hiding maladaptive personality traits on diagnostic measures, with similarly large effect sizes on both the SCID-II-PQ and SIDP-IV. In addition to the PDS, two new detection strategies for identifying defensiveness showed promise.
Date: December 2011
Creator: Fiduccia, Chelsea E.
Partner: UNT Libraries
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