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Rajiv Sampath Nicholas Zabaras 《International journal for numerical methods in engineering》1999,44(9):1227-1265
This paper focuses on the numerical simulation of phase‐change processes using a moving finite element technique. In particular, directional solidification and melting processes for pure materials and binary alloys are studied. The melt is modelled as a Boussinesq fluid and the transient Navier–Stokes equations are solved simultaneously with the transient heat and mass transport equations as well as the Stefan condition. The various streamline‐upwind/Petrov–Galerkin‐based FEM simulators developed for the heat, flow and mass transport subproblems are reviewed. The use of classes, virtual functions and smart pointers to represent and link the particular simulators in order to model a phase change process is discussed. The freezing front is modelled using a spline interpolation, while the mesh motion is defined from the freezing front motion using a transfinite mapping technique. Various two‐ and three‐dimensional numerical tests are analysed and discussed to demonstrate the efficiency of the proposed techniques. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
965.
Nicholas G. Garafolo Christopher C. Daniels 《Research in Nondestructive Evaluation》2014,25(2):125-149
The mass point leak rate technique is often the methodology of choice for quantifying leak rates as it uses simple elementary measurements, applies to gas systems of low mass, proves effective for low leak rates, and does not rely on test-gas conversions. In this methodology, a number of instantaneous mass measurements are calculated through samples of volume, pressure, gas composition, and temperature measurements over time. A regression analysis of the corresponding mass-time sample set yields the leak rate of the system. A detailed uncertainty analysis is paramount for a complete, experimental characterization of the leak rate and previously was not fully implemented in the mass point leak rate method. Recent advancements in regression uncertainty analysis by propagation of errors afford the ability to quantify the uncertainty with estimates of covariance in the regression results. The mass point leak rate technique with the associated detailed measurement uncertainty analysis offers the ability to quantify both the leak rate and the uncertainty associated with the leak rate value. Detailed herein is the development of the methodology and a detailed uncertainty analysis that includes both precision (repeatability) and bias (systematic) error. Alternative leak rate methods are also discussed for comparison purposes. An example in the methodology is presented. 相似文献
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Nicholas S. Bowden 《Natural Gas u0026amp; Electricity》2013,29(9):23-25
Job creation appears to be priority number one for the Obama administration in its second term, and investments in renewable electricity infrastructure are seen as a means to achieve this goal while also meeting social concerns about the environment. In order to continue federal government support for these investments, the American Taxpayer Relief Act of 2012 extended the production tax credit (PTC) for utility-scale wind farms. 相似文献
968.
Nicholas S. Bowden 《Natural Gas u0026amp; Electricity》2014,30(9):29-32
The nationwide participation of residential customers in natural gas retail choice programs has grown from less than 0.5 percent of total US residential customers in 1997 to over 10 percent in 2012. Seventy percent of the 2012 total comes from three states: Georgia, New York, and Ohio. Add Illinois, Maryland, Michigan, New Jersey, and Pennsylvania, and the eight states constitute nearly 95 percent of the total residential retail choice market participation. 相似文献
969.
Model wind turbine arrays were developed for the purpose of investigating the wake interaction and turbine canopy layer in a standard cartesian and row‐offset turbine array configurations. Stereographic particle image velocimetry was used to collect flow data upstream and downstream of entrance and exit row turbines in each configuration. Wakes for all cases were analyzed for energy content and recovery behavior including entrainment of high‐momentum flow from above the turbine canopy layer. The row‐offset arrangement of turbines within an array grants an increase in streamwise spacing of devices and allows for greater wake remediation between successive rows. These effects are seen in exit row turbine wakes as changes to statistical quantities including the in‐plane Reynolds stress, , and the production of turbulence. The recovery of wakes also strongly mitigates the perceived underperformance of wind turbines within an array. The flux of kinetic energy is demonstrated to be more localized in the entrance rows and in the offset arrangement. Extreme values for the flux of kinetic energy are about 7.5% less in the exit row of the cartesian arrangement than in the offset arrangement. Measurements of mechanical torque at entrance and exit row turbines lead to curves of power coefficient and demonstrate an increase in efficiency in row‐offset configurations. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
970.
Ismail Dweikat Clifford Weil Stephen Moose Leon Kochian Nathan Mosier Klein Ileleji Patrick Brown Wendy Peer Angus Murphy Farzad Taheripour Maureen McCann Nicholas Carpita 《Biofuels, Bioproducts and Biorefining》2012,6(4):376-386
Corn grain ethanol production is a mature industry built on a Midwestern agricultural infrastructure. Second‐ and third‐generation biofuels and bio‐based products industries could take advantage of this robust framework. Significant but not insurmountable barriers remain for grower acceptance of bioenergy crop plants and capital investment in transitioning from grain to lignocellulosic biomass at scale. The existing infrastructure in the Midwest provides a model for implementing an environmentally responsible and sustainable next‐generation biofuels industry into the agro‐economy. © 2012 Society of Chemical Industry and John Wiley & Sons, Ltd 相似文献