Virtual Wind Speed Sensor for Wind Turbines

A data-driven approach for development of a virtual wind-speed sensor for wind turbines is presented. The virtual wind-speed sensor is built from historical wind-farm data by data-mining algorithms. Four different data-mining algorithms are used to develop models using wind-speed data collected by anemometers of various wind turbines on a wind farm. The computational results produced by different algorithms are discussed. The neural network (NN) with the multilayer perceptron (MLP) algorithm produced the most accurate wind-speed prediction among all the algorithms tested. Wavelets are employed to denoise the high-frequency wind-speed data measured by anemometers. The models built with data-mining algorithms on the basis of the wavelet-transformed data are to serve as virtual wind-speed sensors for wind turbines. The wind speed generated by a virtual sensor can be used for different purposes, including online monitoring and calibration of the wind-speed sensors, as well as providing reliable wind-speed input to a turbine controller. The approach presented in this paper is applicable to utility-scale wind turbines of any type.     

Effects of Long-Term Dynamic Loading and Fluctuating Water Table on Helical Anchor Performance for Small Wind Tower Foundations

The application of this study is to use helical anchors as a foundation system for small wind tower (1–10?kW) guyed cables. Helical anchors are currently used to anchor guyed cables of cell or transmission towers. However, the increased dynamic vibrations a wind turbine adds to the tower and foundation system under working loads, as well as extreme environmental conditions (e.g., straight line winds, ice load, or sudden furling shocks), require additional knowledge about the behavior of helical anchors. These field conditions were simulated in this study from tower-instrumented field data on wind speed and tower response. These tower responses were then transmitted to the helical anchors through an extensive, large-scale testing program that included monitoring the performance of the helical anchor foundation under dynamic loads, subject to natural variations in both wind regimes, precipitation (water level) and variations in helical anchor geometry. This paper compares the uplift prediction methods used in helical anchor design as well as discusses the effects of long-term dynamic loading and fluctuating water table on helical anchor performance.     

Finite-Element Analysis of Helical Piers in Frozen Ground

This paper presents a study of the behavior of helical pier foundations in frozen ground. The scope of the work presented includes developing finite-element analysis (FEA) models that simulate the stress-strain relationships in the pier and in the surrounding frozen soil. The paper also presents the results of the analysis models developed. The FEA computer program ANSYS is used to perform the computations that include three phases: The first phase is related to the instantaneous stability of piers in frozen or thawed soil under applied design loads. The second phase is related to the analysis of the pier strength during installation into frozen ground when the piers need to withstand installation torque and axial loads. The third phase is related to the long-term stability and critical loads of piers owing to creep in frozen soil. The most important finding of the analysis is that the load is not distributed into the frozen ground equally by the helixes of a multi-helix pier; instead, the bottom helix transfers most of the load.     

Experimental Investigation of Grouted Helical Piers for Use in Foundation Rehabilitation

Building rehabilitation is critical for numerous older urban areas, many of which have inadequate foundations to support new demands. Consequently, development of practical methods to strengthen existing foundations is crucial. In engineering practice, both subsurface grouting and helical piers have been widely used to address these issues by strengthening the foundation. If the solid shaft of a typical helical pier is replaced by a hollow shaft, then helical piers provide the ability to deliver grout. It is hypothesized that these grouted helical pier systems could address foundation strengthening needs. This paper presents findings from an exploratory research program where grouting and pier placement tools were developed and tested on the large geotechnical centrifuge at the University of California, Davis. Experimental methods and procedures developed are presented, and observations regarding the formation of grout bulbs under different conditions are analyzed. Physical observation of the test specimens indicates that average grout bulb diameters of 0.6–1.9 times the helix diameter (Dh) are attainable. For similar grout mixes, 20–50% larger grout bulbs can be attained by adding just a modest amount of injection pressure. Future research may use these results to develop load performance data.     

Aspects of Technological Development of Wind Turbines

The wind turbine technology has a unique technical identity and unique demands in terms of the methods used for design. Remarkable advances in wind power design have been achieved due to modern technological developments. Since 1980, advances in aerodynamics, structural dynamics, and “micrometeorology” have contributed to a five percent annual increase in the energy yield of the turbines. Current research techniques are producing stronger, lighter, and more efficient blades for the turbines. The annual energy output per turbine has increased enormously and the weight of turbine and the noise they emit have been halved over the last few years. The deployment of modern wind turbines has resulted in experience in the production and use of wind turbines, which has led to improved turbines and reduced cost of wind-generated electricity. The paper reviews the research and development of technology of wind turbines and its impact on the cost of wind energy systems. Also the important gaps between the theoretical research and practical implementation have been analyzed and the problems associated with this have been discussed. The need and areas for further research and development effort have also been outlined.     

Mode Shape Corrections for Wind Load Effects

Traditionally, wind analysis procedures based on the “gust loading factor” approach and experimental techniques involving the high frequency base balance and the “stick-type” aeroelastic model test have assumed ideal structural mode shapes, i.e., linear lateral modes and uniform torsional modes. The influence of nonideal mode shapes manifests itself through modifications in the generalized wind load, the structural displacement, the equivalent static wind load (ESWL), and the attendant influence function. This has led to the introduction of several correction procedures, each focusing on an individual feature of the overall response analysis framework. This paper presents a systematic development of correction procedures in terms of correction factors (CFs) to account for nonideal mode shapes in the formulation of generalized load, analysis of structural response, and the derivation of the ESWL. A parameter study is conducted to examine the significance of CFs in estimating various load effects. It is observed that the influence of a nonideal mode shape is actually negligible for the displacement response and the base bending moment, but not so for other load effects, e.g., the base shear and the generalized wind load. Although the existing procedures are effective in correcting the intended response component, they should not be used indiscriminately for other load effects. This paper also presents a correction procedure for the influence of mode shapes on the ESWLs, a loading format that is very attractive for implementation in codes and standards and design practice as well as for the correct interpretation of wind tunnel measurements.     

Equivalent Wheel Load Approach for Slender Cable-Stayed Bridge Fatigue Assessment under Traffic and Wind: Feasibility Study

In the current AASHTO LRFD specifications, the fatigue design considers only one design truck per bridge with 15% dynamic allowance. While this empirical approach may be practical for regular short and medium span bridges, it may not be rational for long-span bridges (e.g., span length >152.4?m or 500?ft) that may carry many heavy trucks simultaneously. Some existent studies suggested that fatigue may not control the design for many small and medium bridges. However, little research on the fatigue performance of long-span bridges subjected to both wind and traffic has been reported and if fatigue could become a dominant issue for such a long-span bridge design is still not clear. Regardless if the current fatigue design specifications are sufficient or not, a real understanding of the traffic effects on bridge performance including fatigue is desirable since the one truck per bridge for fatigue design does not represent the actual traffic condition. As the first step toward the study of fatigue performance of long-span cable-stayed bridges under both busy traffic and wind, the equivalent dynamic wheel load approach is proposed in the current study to simplify the analysis procedure. Based on full interaction analyses of a single-vehicle–bridge–wind system, the dynamic wheel load of the vehicle acting on the bridge can be obtained for a given vehicle type, wind, and driving condition. As a result, the dimension of the coupled equations is independent of the number of vehicles, through which the analyses can be significantly simplified. Such simplification is the key step toward the future fatigue analysis of long-span bridges under a combined action of wind and actual traffic conditions.     

Dynamic Response of Suspension Bridge to High Wind and Running Train

A framework is presented for predicting the dynamic response of long suspension bridges to high winds and running trains. A three-dimensional finite-element model is used to represent a suspension bridge. Wind forces acting on the bridge, including both buffeting and self-excited forces, are generated in the time domain using a fast spectral representation method and measured aerodynamic coefficients and flutter derivatives. Each 4-axle vehicle in a train is modeled by a 27-degrees-of-freedom dynamic system. The dynamic interaction between the bridge and train is realized through the contact forces between the wheels and track. By applying a mode superposition technique to the bridge only and taking the measured track irregularities as known quantities, the number of degrees of freedom of the bridge-train system is significantly reduced and the coupled equations of motion are efficiently solved. The proposed formulation is then applied to a real wind-excited long suspension bridge carrying a railway inside the bridge deck of a closed cross section. The results show that the formulation presented in this paper can predict the dynamic response of the coupled bridge-train systems under fluctuating winds. The extent of interaction between the bridge and train depends on wind speed and train speed.     

Wind Tunnel Tests for Wind-Excited Benchmark Building

This paper presents an overview of the wind tunnel studies conducted at the boundary layer wind tunnel facility at the University of Sydney to determine across-wind forces acting on the 76-story 306 m high benchmark building. The paper briefly describes the boundary layer wind tunnel and its special features, and then presents the testing procedures and the methodology used to determine the wind loads acting on a 1:400 model of the building.     

Peak Non-Gaussian Wind Effects for Database-Assisted Low-Rise Building Design

Current procedures for estimating the peaks of the stochastic response of tall buildings to wind are based on the assumption that the response is Gaussian. Those procedures are therefore inapplicable to low-rise buildings, in which time histories of wind-induced internal forces are generally non-Gaussian. In this paper, an automated procedure is developed for obtaining from such time histories sample statistics of internal force peaks for low-rise building design and codification. The procedure is designed for use in software for calculating internal force time series by the database-assisted design approach. A preliminary step in the development of the procedure is the identification of the appropriate marginal probability distribution of the time series using the probability plot correlation coefficient method. The result obtained is that the gamma distribution and a normal distribution are appropriate for estimating the peaks corresponding, respectively, to the longer and shorter tail of the time series’ histograms. The distribution of the peaks is then estimated by using the standard translation processes approach. It is found that the peak distribution can be represented by the Extreme Value Type I (Gumbel) distribution. Because estimates obtained from this approach are based on the entire information contained in the time series, they are more stable than estimates based on observed peaks. The procedure can be used to establish minimum acceptable requirements with respect to the duration and sampling rate of the time series of interest, so that the software used for database-assisted design will be both efficient and accurate.     

Ductility Evaluation of Concrete-Encased Steel Bridge Piers Subjected to Lateral Cyclic Loading

An experimental and analytical study was conducted to investigate the ductility of concrete-encased steel piers, referred to as “steel-reinforced concrete (SRC) construction.” Based on the cyclic lateral loading tests of SRC column specimens, the restorable and ultimate limit states are defined as the point when concrete cover spalling occurs (equivalent to longitudinal bar buckling) and the point when flange buckling of the H-shaped steel occurs, respectively. To estimate the lateral displacement capacity at both the restorable and ultimate limit states, the curvature distribution of the column was calculated based on the buckling analysis of the longitudinal bar, which was restrained by a concrete cover and transverse reinforcement, and of the steel flange encased in concrete. The lateral displacement was obtained by integrating the curvature distribution. Comparison of the computed results with experimental results, including other writers’ reports, confirmed that the proposed method can appropriately estimate the lateral displacement at the restorable and ultimate limit states, and it can accurately evaluate the buckling characteristics of the longitudinal bar and steel flange components of SRC column specimens.     

Structural Response of 34‐m Darrieus Rotor to Turbulent Winds

The results of a mathematical investigation of the dynamic response of the Sandia/Department of Energy/U.S. Department of Agriculture 34‐m‐diameter Darrieus rotor wind turbine erected at Bushland, Tex., are presented. The formulation used a double multiple stream‐tube aerodynamic model combined with a turbulent airflow and included the effects of (linear) aeroelastic forces. The structural analysis was carried out using previously established procedures with the computer program MSC/NASTRAN. A number of alternative expressions for the spectrum of turbulent wind were used. The modal loading represented by each did not differ significantly; a more significant difference was caused by imposing full lateral coherence of the turbulent flow. Spectra of the predicted stresses at various locations show that without aeroelastic forces, very severe resonance is likely to occur at certain natural frequencies. Inclusion of aeroelastic effects greatly attenuates this stochastic response, especially in modes involving in‐plane blade bending. Comparison is made with preliminary field data collected at medium‐low wind speeds (11.3 m/s) from critical locations on the blade. This comparison shows generally good agreement between measured stress spectra and model predictions based on 10% turbulence intensity and including aeroelastic forces.     

Wind Loads for 19th Century Bridges: Design Evolution, Historic Failures, and Modern Preservation

This paper presents an historical survey of the basis for design wind pressure used by 19th and early 20th century engineers. Events significant to the development of current wind design standards for pedestrian bridges are explored. These include 19th century treatments of wind load, a review of bridge disasters that spurred new thinking, and historical developments of today’s standards.     

Influence of Mechanical Draft Tube Fish Barrier on the Hydraulic Thrust of Small Francis Turbines

Environmental regulations have required from hydroelectric power plants more effective means of restricting the access of fish into the draft tube of hydraulic turbines. The decline of fish populations on rivers used for electricity generation has motivated the installation of mechanical gates as fish barriers on the tailrace pipe of hydroelectric power plants as a technical solution to preserve aquatic wild life. However, variations in the flow conditions through the turbine runner may modify the performance characteristics of turbines, thus affecting their capacity for electricity production. This note presents an experimental study of the influence of draft tube gates on the hydraulic forces acting on Francis turbines. A Francis turbine test bench was specially designed to allow this investigation. Measurements of the hydraulic thrust in relation to the level of flow restriction at the draft tube exit indicate that the mechanical gates excessively increase the axial load on the runner shaft, which may shorten the hydrogenerator unit life.     

三菱重工地面燃气轮机热障涂层研究进展

燃气轮机联合循环热效率的提高,要求涡轮进口温度不断增加。目前,三菱重工(MHI)已经积极参与日本国家项目,通过发展1700℃级燃气轮机,以使联合循环热效率实现达到62%指标。在此国家项目中开发的部分组件技术适用于1600℃级燃气轮机M501J,它具有世界上最高的涡轮进口温度。而热障涂层(TBC)是实现此目标的最关键技术之一。在发展先进的热障涂层中,在MHI工厂中建立名为T点的试验电厂是有必要的。在真实热部件中制备的先进TBC可以在工厂中进行验证,并且运行后的效果可以得到反馈。本文讨论了TBC的开发以及在三菱重工实际电厂中的验证。     

Estimation of Probabilistic Extreme Wind Load Effects: Combination of Aerodynamic and Wind Climate Data

A refined full-order method is presented for estimating the extreme wind load effects of rigid structures with given mean recurrence intervals (MRIs) by combining the distributions of annual maximum wind speed and extreme load coefficients. This refined method is capable of dealing with any type of asymptotic extreme value distribution. With this full-order method, the predictions of wind load effects by using distributions of annual maximum wind velocity pressure and wind speed are compared that provide information on the sensitivity of predictions to the upper tail of wind speed distribution. The efficacy of the first-order method is examined. The influences of the type of distributions and the variations of annual maximum wind speed and extreme load coefficient on the predictions are quantified. Finally, the first- and full-order methods are extended to wind load effects of dynamically sensitive structures which facilitate a comprehensive probabilistic analysis as compared to the Monte Carlo simulation schemes used in literature. It is pointed out that 78% fractile extreme load coefficient can be used for defining the characteristic load effects of both rigid and dynamically sensitive structures. The wind load factor is insensitive to the variation of extreme load coefficient. It can be approximately estimated through the wind speed factor and the growth rate of extreme wind load effect with increasing wind speed. The result concerning the wind load factor justifies the advantage of specifying design wind speeds with various MRIs in reducing the uncertainties of design wind loading.     

Performance of Conservatories under Wind and Snow Loads

Wind and snow loads are the governing load cases for the design of conservatories. The performance of conservatories under these loads determines to a great extent the reliability and serviceability of these structures. This paper presents a study that evaluates the performance of several conservatory designs under wind and snow loads calculated according to the ASCE 7–05 standard. A full-scale model of one common conservatory design was constructed and tested under extreme wind and snow conditions. The model was able to withstand the applied loads without any signs of damage or partial failures. Measured deformations were used to calibrate the three-dimensional computer model developed to simulate the actual structure. Several other computer models were developed to structurally analyze different conservatory designs and estimate their vertical and lateral deflections. The design of critical sections in each model was checked using the load and resistance factor design of wood structures. The study concluded that the design of these conservatories is adequate and their performance is satisfactory under wind and snow loading conditions.     

Operational Requirements for Long-Span Bridges under Strong Wind Events

In the absence of intensive wind tunnel tests, this study provides an effective and accurate approach to estimate the operational driving speed limit on bridges subjected to different road conditions and wind intensities, through a convenient continuous simulation technique (CSP). A fast and vigorous simulation tool, vehicle performance simulation, is developed to effectively model the performance of vehicles traveling on bridges by considering the interactions between wind, vehicles, and the bridge. The CSP, on the other hand, dramatically reduces the data generation time and makes a reliability analysis of vehicles possible. The application of the proposed method on the Confederation Bridge in Canada is presented as a numerical example. The simulation result overrides the general impression that only high-sided vehicles are sensitive to wind attacks, and this work demonstrates that light-weighted vehicles are also likely to suffer from instability problems on bridges under relatively low wind velocity. In addition, different types of vehicle can undergo different instability mechanisms under the same wind condition and these vehicle instability mechanisms vary with wind velocity.     

Design of Low-Rise Buildings for Extreme Wind Events

Damages from hurricanes and various windstorm events represent a loss of several billions of dollars in the United States. A loss of $30 billion was attributed to Hurricane Andrew alone in Florida in 1993. In 2004 and 2005, Florida, Louisiana, Mississippi, and other locations in the southeast United States and the Caribbean saw an unprecedented wave of major hurricanes causing great destruction and property damage. This paper discusses the topic of home design for high winds and hurricanes, and sums up a recently completed practical research on this subject.     

Design Guidelines for Community Shelters for Extreme Wind Events

The design of shelter structures has received little attention from the engineering community since the days of nuclear fallout shelters, until the development of guidance for community shelters for cases of extreme wind events was released by FEMA in July 2000 (FEMA 361). To respond to the recent demand for community shelters, many states are designating existing schools or other public buildings, such as community centers or multipurpose buildings, as public shelter areas. In most cases these buildings, or portions of these buildings, were never designed for use as shelters. Most of the designated shelters were designed and constructed according to older local building codes that do not include requirements for extreme wind pressures and uplift. Even recently designed structures have been found to have inadequate features for a high-wind shelter, particularly with respect to cladding and architectural features that are vulnerable to damage from high winds and windborne debris. Damage to the cladding is often the beginning of building failure and occupant injury during an extreme wind event. This paper identifies critical issues and gaps in presently available technology for evaluating proposed shelters and providing retrofit guidance to building owners. The writers’ experience with inspections of designated shelters, proposed retrofit recommendations, and damage investigations of buildings affected by hurricanes or tornadoes is summarized. Recommendations for design considerations that include the current standards of practice as outlined in FEMA 361, ASCE 7-98, and the Florida Shelter Evaluation Guidelines are given.