Revisiting the Local Scaling Hypothesis in Stably Stratified Atmospheric Boundary Layer Turbulence: an Integration of Field and Laboratory Measurements with Large-eddy Simulations

The `local scaling' hypothesis, first introduced by Nieuwstadt two decades ago, describes the turbulence structure of stable boundary layers in a very succinct way and is an integral part of numerous local closure-based numerical weather prediction models. However, the validity of this hypothesis under very stable conditions is a subject of on-going debate. In this work, we attempt to address this controversial issue by performing extensive analyses of turbulence data from several field campaigns, wind-tunnel experiments and large-eddy simulations. Wide range of stabilities, diverse field conditions and a comprehensive set of turbulence statistics make this study distinct

Modelling of reduced GB transmission system in PSCAD/EMTDC

Energy and environmental issues are two of the greatest challenges facing the world today. In response to energy needs and environmental concerns, renewable energy technologies are now considered the future technologies of choice. Renewable energy is produced from natural sources that are clean and free; however, it is widely accepted that renewable energy is not a solution without challenges. An example of this can be seen in the UK, where there is much interest amongst generation developers in the construction of new large scale onshore and offshore wind farms, especially in Scotland. The stability of electric power systems is also an important issue. It is important to have full knowledge of the system and to be able to predict the behaviour under different situations is an important objective. As a result, several industrial grade power system simulator tools have been developed in order to estimate the behaviour of the electric power system under certain conditions. This paper presents a reduced Great Britain (GB) system model for stability analysis using PSCAD/EMTDC. The reduced model is based upon a future GB transmission system model and, hence, contains different types and mix of generation, HVDC transmission lines and additional interconnection. The model is based on the reduced DIgSILENT PowerFactory model developed by National Grid

Computational Analysis of Flow Around a Scaled Axial-Flow Hydro Turbine

Water power energy harvesting has become an important and growing industry supported by research and significant interest and impetus from the government and commercial sector. Due to waters high power density, marine current energy is an attractive addition to other renewable energy technologies. That said, there is still much to be understood about the design, application, installation, operation, and maintenance of current-driven marine-hydrokinetic devices and with new designs coming out frequently it is imperative to understand the physics and dynamics involved. Recently, testing of the Sandia turbine, designed by University of California, Davis, Pennsylvania State and Sandia National Laboratories, took place at Pennsylvania State\u27s Applied Research Laboratory. The testing was performed with a 1:8.7 scale model of the Sandia turbine. The experiment successfully assessed the turbine\u27s power and cavitation performance, unsteady driveshaft loading, blade strain, unsteady tower pressure, flow field, and acoustics. Given the expense and time required for experimentation, commercial computational fluid dynamics codes, such as CD-Adapco\u27s Star-CCM+ can be used to simulate new designs both quickly and inexpensively. The goal of this research is to validate the results obtained using Star CCM+ to model the Sandia turbine as compared to the experimental results obtained by Pennsylvania State. To carry out the simulation, several unstructured grids were generated on which several unsteady simulations were run at the design point of a tip-speed ratio of 4. For this design point at 95% blade span, the chord Reynolds number is approximately 500,000 which equates to about 2,000,000 for the full scale turbine. In comparing model results to experimental data there was good agreement for power performance parameters, such as thrust and power coefficients, as well as downstream velocity profiles. With such good agreement it is optimistic that computational fluid dynamics models can be used to accurately predict the performance of future water turbine designs, thus reducing the high cost of research needed to develop novel current-driven marine-hydrokinetic devices.\u2

Determination of the Jet Energy Scale at the Collider Detector at Fermilab

A precise determination of the energy scale of jets at the Collider Detector at Fermilab at the Tevatron $p\bar{p}$ collider is described. Jets are used in many analyses to estimate the energies of partons resulting from the underlying physics process. Several correction factors are developed to estimate the original parton energy from the observed jet energy in the calorimeter. The jet energy response is compared between data and Monte Carlo simulation for various physics processes, and systematic uncertainties on the jet energy scale are determined. For jets with transverse momenta above 50 GeV the jet energy scale is determined with a 3% systematic uncertainty

Observations of the December 13 and 14, 2006, Solar Particle Events in the 80 MeV/n - 3 GeV/n range from space with PAMELA detector

We present the space spectrometer PAMELA observations of proton and helium fluxes during the December 13 and 14, 2006 solar particle events. This is the first direct measurement of the solar energetic particles in space with a single instrument in the energy range from $\sim$ 80 MeV/n up to $\sim$ 3 GeV/n. In the event of December 13 measured energy spectra of solar protons and helium were compared with results obtained by neutron monitors and other detectors. Our measurements show a spectral behaviour different from those derived from the neutron monitor network. No satisfactory analytical fitting was found for the energy spectra. During the first hours of the December 13 event solar energetic particles spectra were close to the exponential form demonstrating rather significant temporal evolution. Solar He with energy up to ~1 GeV/n was recorded on December 13. In the event of December 14 energy of solar protons reached ~600 MeV whereas maximum energy of He was below 100 MeV/n. The spectra were slightly bended in the lower energy range and preserved their form during the second event. Difference in the particle flux appearance and temporal evolution in these two events may argue for a special conditions leading to acceleration of solar particles up to relativistic energies.Comment: Accepted for publication on Astrophysical journa