Wayne O. Miller

Wind power curve modeling in complex terrain using statistical models

The simplest power curves model wind power only as a function of the wind speed at the turbine hub height. While the latter is an essential predictor of power output, wind speed information in other parts of the vertical profile, as well as additional atmospheric variables, are also important determinants of power. The goal of this work was to determine the gain in predictive ability afforded by adding wind speed information at other heights, as well as other atmospheric variables, to the power prediction model. Using data from a wind farm with a moderately complex terrain in the Altamont Pass region in California, we trained three statistical models—a neural network, a random forest and a Gaussian process model—to predict power output from various sets of aforementioned predictors. The comparison of these predictions to the observed power data revealed that considerable improvements in prediction accuracy can be achieved both through the addition of predictors other than the hub-height wind speed and the...

Status of VibroIR at Lawrence Livermore National Laboratory

Current efforts at Lawrence Livermore National Laboratory in the area of vibrothermography (VibroIR or SonicIR) are presented. The primary goals of the efforts of the NDE group at LLNL have been to demonstrate the applicability of vibrothermography to new areas, to examine the degree to which VibroIR may replace existing NDE inspection procedures, and to conduct research on the underlying processes and optimal parameters in its implementation. We report three new applications of VibroIR, in the areas of brazed tube joint inspection, evaluationtion of thick multilayer carbon/carbon composites as used in the NASA Shuttle, and the inspection of soft composite materials. The goal of the brazed joint inspection process is ultimately the replacement of a current dye penetrant inspection procedure. Therefore a direct comparison between VibroIR and dye penetrant inspection is made. Preliminary results of the analysis of a leading edge panel from a NASA Shuttle is also reported as an example of the application of VibroIR to thick composites. Finally, a comparison betweeen the effectiveness of VibroIR versus a spectrum of other NDE techniques (ultrasonic imaging, radiographic tomography) for the imaging of known ceramic defects is briefly discussed.

Thermal design and performance of the gamma-ray spectrometer for the MESSENGER spacecraft

A gamma-ray spectrometer (GRS) has been built and delivered to the MESSENGER spacecraft which launched on August 3, 2004, from Cape Canaveral, Florida. The GRS, a part of seven scientific instruments on board MESSENGER, is based on a coaxial high-purity germanium detector. Gamma-ray detectors based on germanium have the advantage of providing excellent energy resolution, which is critical to achieving the science goals of the mission. However, germanium has the disadvantage that it must operated at cryogenic temperatures (typically /spl sim/80 K). This requirement is easy to satisfy in the laboratory but difficult near Mercury, which has an extremely hot thermal radiation environment. To cool the detector, a Stirling cycle mechanical cooler is employed. In addition, radiation and conduction techniques are used to reduce the GRS heat load. Before delivering the flight sensor, a complete thermal prototype was built and tested. The results of these tests, including thermal design, radiative and conductive heat loads, and cooler performance, are described.

Evaluation of sonic IR for NDE at Lawrence Livermore National Laboratory

Sonic IR was evaluated as an NDE technique at LLNL using a commercial ThermoSoniX system from Indigo Systems Corp. The main effort was to detect small cracks in aluminum oxide, a dense stiff ceramic. Test coupons were made containing 0.2- mm cracks by surface grinding, 1-mm cracks by compression with a Vickers bit, and 4-mm cracks by 3-point bending. Only the 3-point bend cracks produced thermal images. Several parts shattered during testing, perhaps by being forced at resonance by the 20-kHz acoustic probe. Tests on damaged carbon composite coupons produced thermal images that were in excellent agreement with ultrasonic inspection. The composite results also showed some dependence on contact location of the acoustic probe, and on the method of support. Tests on glass with surface damage produced weak images at the pits. Tests on metal ballistic targets produced thermal images at the impact sites. Modal analyses suggest that the input frequency should be matched to the desired response, and also that forced resonance damaged some parts.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Coupled Mesoscale Microscale Model for Wind Resource Estimation and Turbine Aerodynamics Using an Overset Grid Approach

This study investigates the performance of a one-way grid nesting between the Weather Research and Forecasting (WRF) model framework and three di erent computational uid dynamics codes of varying complexity. WRF is run in ideal large eddy simulation (LES) mode to provide the velocity eld for a speci ed number of time steps. Slices of velocity contours from the WRF simulations are used as boundary conditions for the simulations using the CFD codes. The data interpolation between the codes are setup using an overset grid connectivity approach. The framework is parallel, automated and requires no user intervention during the simulations. The use of an automated framework allows an e cient coupling between the codes, speed-up of the calculations and the ability to add additional modules for uid-structure interaction and o -shore wind energy applications. The capabilities of the framework are demonstrated for an experimental wind farm and an operational wind farm. The results obtained from the simulations show good agreement with available data for both wind farms.

A code-independent generalized actuator line model for wind farm aerodynamics over simple and complex terrain

Abstract Actuator line model representations of wind turbines reduce the simulation cost of wind farm aerodynamics relative to blade geometry resolving simulations. However, most implementations are code specific and may not have proper load balancing when run in parallel. Here, a generalized actuator line model (GALM) is developed to overcome this implementation drawback of existing approaches. The GALM can be coupled to any existing microscale solver with minimal or no modifications. The coupling of our GALM model with the open-source microscale code CgWind is used to demonstrate both its ease of use and fidelity. The results obtained from the coupled-model simulations are validated for both isolated turbine in wind tunnel experiments and measurements in offshore wind farm. Finally, an operational wind farm over complex terrain is demonstrated. The simulations show that wake meandering and power production are strongly influenced by terrain impacts. Access information for obtaining the code is provided.

Evaluation of the effect of Realistic and Synthetic Inflow on the Power and Loading Pattern of Wind Turbine

This study is focused on investigating the differences between realistic and synthetic inflow models for the large eddy simulation (LES) of the flow field and prediction of aerodynamics in an onshore and offshore wind farm . Weather Research and Forecasting (WRF) is run in LES mode for generating the realistic inflow boundary conditions while synthetic inflow is generated using Mann’s model. WindPact and NREL 5MW turbines were used as the model turbines for onshore and offshore wind farms, respectively. The geostropic wind driving the flow field in WRF-LES was adjusted to ensure the same wind speed at hub height for onshore and offshore cases, respectively to perform a comparative study. The coupling between the mesoscale and microscale codes are performed using a mesoscale microscale coupling interface (MMCI) developed as a part of our earlier work. This framework allows the efficient interpolation of data between the different codes in an automated and parallel fashion. Three different microscale computational fluid dynamics codes were

Quantifying Flaw Characteristics from IR NDE Data

Work is presented which allows flaw characteristics to be quantified from the transient IR NDE signature. The goal of this effort was to accurately determine the type, size and depth of flaws revealed with IR NDE, using sonic IR as the example IR NDE technique. Typically an IR NDE experiment will result in a positive qualitative indication of a flaw such as a cold or hot spot in the image, but will not provide quantitative data thereby leaving the practitioner to make educated guesses as to the source of the signal. The technique presented here relies on comparing the transient IR signature to exact heat transfer analytical results for prototypical flaws, using the flaw characteristics as unknown fitting parameters. A nonlinear least squares algorithm is used to evaluate the fitting parameters, which then provide a direct measure of the flaw characteristics that can be mapped to the imaged surface for visual reference. The method uses temperature data for the heat transfer analysis, so radiometric calibration of the IR signal is required. The method provides quantitative data with a single thermal event (e.g. acoustic pulse or flash), as compared to phase-lock techniques that require many events. The work has been tested with numerical data but remains to be validated by experimental data, and that effort is underway. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.