65 research outputs found
Automotive Underhood Thermal Management Analysis Using 3-D Coupled Thermal-Hydrodynamic Computer Models: Thermal Radiation Modeling
The goal of the radiation modeling effort was to develop and implement a radiation algorithm that is fast and accurate for the underhood environment. As part of this CRADA, a net-radiation model was chosen to simulate radiative heat transfer in an underhood of a car. The assumptions (diffuse-gray and uniform radiative properties in each element) reduce the problem tremendously and all the view factors for radiation thermal calculations can be calculated once and for all at the beginning of the simulation. The cost for online integration of heat exchanges due to radiation is found to be less than 15% of the baseline CHAD code and thus very manageable. The off-line view factor calculation is constructed to be very modular and has been completely integrated to read CHAD grid files and the output from this code can be read into the latest version of CHAD. Further integration has to be performed to accomplish the same with STAR-CD. The main outcome of this effort is to obtain a highly scalable and portable simulation capability to model view factors for underhood environment (for e.g. a view factor calculation which took 14 hours on a single processor only took 14 minutes on 64 processors). The code has also been validated using a simple test case where analytical solutions are available. This simulation capability gives underhood designers in the automotive companies the ability to account for thermal radiation - which usually is critical in the underhood environment and also turns out to be one of the most computationally expensive components of underhood simulations. This report starts off with the original work plan as elucidated in the proposal in section B. This is followed by Technical work plan to accomplish the goals of the project in section C. In section D, background to the current work is provided with references to the previous efforts this project leverages on. The results are discussed in section 1E. This report ends with conclusions and future scope of work in section F
Subdominant modes and optimization trends of DIII-D reverse magnetic shear configurations
Alfvén Eigenmodes (AE) and magneto-hydrodynamic (MHD) modes are destabilized in DIII-D reverse magnetic shear configurations and may limit the performance of the device. We use the reduced MHD equations in a full 3D system, coupled with equations of density and parallel velocity moments for the energetic particles (with gyro-fluid closures) as well as the geodesic acoustic wave dynamics, to study the properties of instabilities observed in DIII-D reverse magnetic shear discharges. The aim of the study consists in finding ways to avoid or minimize MHD and AE activity for different magnetic field configurations and neutral beam injection (NBI) operational regimes. The simulations show at the beginning of the discharge, before the reverse shear region is formed, a plasma that is AE unstable and marginally MHD stable. As soon as the reverse shear region appears, ideal MHD modes are destabilized with a larger growth rate than the AEs. Both MHD modes and AEs coexist during the discharge, although the MHD modes are more unstable as the reverse shear region deepens. The simulations indicate the destabilization of Beta induced AE (BAE), Toroidal AE (TAE), elliptical AE (EAE) and reverse shear AE (RSAE) at different phases of the discharges, showing a reasonable agreement between the frequency range of the dominant modes in the simulations and the diagnostic measurements (...)This material based on work is supported both by
the U.S. Department of Energy, Office of Science, under
Contract DE-AC05-00OR22725 with UT-Battelle,
LLC and U.S. Department of Energy, Oce of Science,
Oce of Fusion Energy Sciences, using the DIII-D National
Fusion Facility, a DOE Oce of Science user facility, under Award No. DE-FC02-04ER54698. This research was sponsored in part by the Ministerio of Economía y Competitividad of Spain under project no.ENE2015-68265-P. DIII-D data shown in this paper
can be obtained in digital format by following the links
at https://fusion.gat.com/global/D3D DMP.Publicad
Subdominant modes and optimization trends of DIII-D reverse magnetic shear configurations
Alfven Eigenmodes and magneto-hydrodynamic modes are destabilized in DIII-D
reverse magnetic shear configurations and may limit the performance of the
device. We use the reduced MHD equations in a full 3D system, coupled with
equations of density and parallel velocity moments for the energetic particles
(with gyro-fluid closures) as well as the geodesic acoustic wave dynamics. The
aim of the study consists in finding ways to avoid or minimize MHD and AE
activity for different magnetic field configurations and neutral beam injection
operational regimes. The simulations show at the beginning of the discharge,
before the reverse shear region is formed, a plasma that is AE unstable and
marginally MHD stable. As soon as the reverse shear region appears, ideal MHD
modes are destabilized with a larger growth rate than the AEs. Both MHD modes
and AEs coexist during the discharge, although the MHD modes are more unstable
as the reverse shear region deepens. The simulations indicate the
destabilization of Beta induced AE, Toroidal AE, Elliptical AE and Reverse
Shear AE at different phases of the discharges. A further analysis of the NBI
operational regime indicates that the AE stability can be improved if the NBI
injection is off axis, because on-axis injection leads to AEs with larger
growth rate and frequency. In addition, decreasing the beam energy or
increasing the NBI relative density leads to AEs with larger growth rate and
frequency, so an NBI operation in the weakly resonant regime requires higher
beam energies than in the experiment. The MHD linear stability can be also
improved if the reverse shear region and the q profile near the magnetic axis
are in between the rational surfaces q=2 and q=1, particularly if there is a
region in the core with negative shear, avoiding a flat q profile near the
magnetic axis
A fast low-to-high confinement mode bifurcation dynamics in the boundary-plasma gyrokinetic code XGC1
A fast edge turbulence suppression event has been simulated in the electrostatic version of the gyrokinetic particle-in-cell code XGC1 in a realistic diverted tokamak edge geometry under neutral particle recycling. The results show that the sequence of turbulent Reynolds stress followed by neoclassical ion orbit-loss driven together conspire to form the sustaining radial electric field shear and to quench turbulent transport just inside the last closed magnetic flux surface. The main suppression action is located in a thin radial layer around ψN ≅ 0.96–0.98, where ψN is the normalized poloidal flux, with the time scale ~0.1 ms
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