radial transport
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Author(s):  
Weisheng Lin ◽  
Xiaogang Wang ◽  
Xueqiao Xu ◽  
Defeng Kong ◽  
Yumin Wang ◽  
...  

Abstract Tritium self-sufficiency in future DT fusion reactor is a crucial challenge. As an engineering test reactor, CFETR requires a burning fraction of 3% for the goal to test the accessibility to the future fusion plant. To self-consistently simulate burning plasmas with profile changes in pellet injection scenarios and to estimate the corresponding burning fraction, a one-dimensional (1-D) multi-species radial transport model is developed in BOUT++ frame. Several pellet-fueling scenarios are then tested in the model. Results show that the increased fueling depth improves the burning fraction by particle confinement improvement and fusion power increase. Nevertheless, by increasing the depth, the pellet cooling-down may significantly lower the temperature in the core region. Taking the density perturbation into consideration, the reasonable parameters of the fueling scenario in these simulations are estimated as the pellet radius r_p=3 mm, the injection rate = 4 Hz , the pellet injection velocity =1000–2000 m/s without drift or 450 m/s with high filed side (HFS) drift.


Mathematics ◽  
2021 ◽  
Vol 9 (19) ◽  
pp. 2509
Author(s):  
Ibrahim Ayuba ◽  
Lateef T. Akanji ◽  
Jefferson L. Gomes ◽  
Gabriel K. Falade

This paper reports an analytical study conducted to investigate the behaviour of tracers undergoing creeping flow between two parallel plates in porous media. A new coupled model for the characterisation of fluid flow and transport of tracers at pore scale is formulated. Precisely, a weak-form solution of radial transport of tracers under convection–diffusion-dominated flow is established using hypergeometric functions. The velocity field associated with the radial transport is informed by the solution of the Stokes equations. Channel thickness as a function of velocities, maximum Reynolds number of each thickness as a function of maximum velocities and concentration profile for different drift and dispersion coefficients are computed and analysed. Analysis of the simulation results reveals that the dispersion coefficient appears to be a significant factor controlling the concentration distribution of the tracer at pore scale. Further analysis shows that the drift coefficient appears to influence tracer concentration distribution but only after a prolonged period. This indicates that even at pore scale, tracer drift characteristics can provide useful information about the flow and transport properties of individual pores in porous media.


2021 ◽  
Author(s):  
Daniel Santos-Costa

<p>We present our latest understanding of the processes that shape the spatial distributions of energetic electrons trapped in the magnetospheres of Uranus (L < 15) and Neptune (L < 25). To determine what controls the energy and spatial distributions throughout the different magnetospheres, we compute the time evolution of particle distributions with the help of a diffusion theory particle transport code that solves the governing 3-D Fokker-Planck equation. Different mechanisms of particle loss, source and transport are numerically examined. Our theoretical modeling is guided by the analysis of particle, field and wave data collected during Voyager 2’s flyby of Uranus in January 1986 and at Neptune in August 1989.</p> <p>Our preliminary data-model comparison results at Uranus show that adiabatic transport cannot explain the radial and angular features of warm to ultra-relativistic electron populations within the ~1-15 L region. Our simulation results also suggest that, with absence of loss mechanisms inside L = 15, energetic and radiation-belt electron populations would be higher by 1-3 orders of magnitude in intensity close to the planet (L ~ 1-8). Particularly, our results confirm that moon sweeping effect is a significant loss mechanism at Uranus. Nonetheless, other radial, energy and pitch-angle dependent mechanisms seem to be missing to explain the in-situ data. We will thus present our ongoing effort to examine the role of --for instance, Uranus’ rings system, atomic hydrogen corona and wave activity inward of L ~ 8-10 to improve our modeling of Uranus’ electron populations between L values of 1 and 15.</p> <p>Our first physics-based model of energetic electrons at Neptune will be presented, emphasizing first the role of radial transport and moon sweeping effect for the 1-25 L region before investigating new processes. Our models developed for Uranus and Neptune are based on the theoretical modeling of electron distributions at Saturn, which included the modeling of radial transport and interactions of electrons with Saturn's dust/neutral/plasma environments and waves, as well as particle sources from high-latitudes, interchange injections, and outer magnetospheric region. Comparisons between the distributions of electron populations at Gas and Ice Giant systems will be discussed.</p> <p>Data analysis, theoretical modeling, and numerical computations for Uranus and Neptune are carried out by adapting the Kronian modeling tools developed at Southwest Research Institute to the Ice Giants environment. Key data analysis, theoretical modeling, and numerical computational tasks for Saturn were carried out at Southwest Research Institute under NASA GSFC grant 80NSSC18K1100.</p>


2021 ◽  
Author(s):  
Guozhong Deng ◽  
Xueqiao Xu ◽  
Xiaoju Liu ◽  
Jichan Xu ◽  
Lingyi Meng ◽  
...  

Author(s):  
Sebastian Pfautsch ◽  
John Drake ◽  
Mike Aspinwall ◽  
Victor Resco de Dios ◽  
Craig Barton ◽  
...  

It is easy to measure annual growth of a tree stem. It is hard to measure its daily growth. The reason for this difficulty is the microscopic scale and the need to separate processes that simultaneously result in reversible and irreversible stem expansion. Here we present a model that separates reversible from irreversible cell expansion. Our model is novel, because it explains reversible expansion as consequence of longitudinally and, importantly, radially transmitted changes of hydraulic and osmotic pressures in xylem and bark. To capture and quantify these changes, we manipulated daily stem growth by applying a phloem girdle to stems of 9-m tall trees. The model was informed by measurements of radial movement in stem tissues and sap flow before and after and positions below and above the girdle. Additional measurements of whole-crown fluxes of H2O and CO2, leaf water potentials, non-structural carbohydrates and respiration were used to document the physiological impacts of girdling. This work sheds new light on the role of radial transport processes underpinning daily growth of tree stems. The model helps explain diel patterns of stem growth in trees.


2021 ◽  
Vol 78 (5) ◽  
pp. 1411-1428
Author(s):  
Tsz-Kin Lai ◽  
Eric A. Hendricks ◽  
M. K. Yau ◽  
Konstantinos Menelaou

AbstractIntense tropical cyclones (TCs) often experience secondary eyewall formations and the ensuing eyewall replacement cycles. Better understanding of the underlying dynamics is crucial to make improvements to the TC intensity and structure forecasting. Radar imagery of some double-eyewall TCs and a real-case simulation study indicated that the barotropic instability (BI) across the moat (aka type-2 BI) may play a role in inner eyewall decay. A three-dimensional numerical study accompanying this paper pointed out that type-2 BI is able to withdraw the inner eyewall absolute angular momentum (AAM) and increase the outer eyewall AAM through the eddy radial transport of eddy AAM. This paper explores the reason why the eddy radial transport of eddy AAM is intrinsically nonzero. Linear and nonlinear shallow water experiments are performed and they produce expected evolutions under type-2 BI. It will be shown that only nonlinear experiments have changes in AAM over the inner and outer eyewalls, and the changes solely originate from the eddy radial transport of eddy AAM. This result highlights the importance of nonlinearity of type-2 BI. Based on the distribution of vorticity perturbations and the balanced-waves arguments, it will be demonstrated that the nonzero eddy radial transport of eddy AAM is an essential outcome from the intrinsic interaction between the mutually growing vortex Rossby waves across the moat under type-2 BI. The analyses of the most unstable mode support the findings and will further attribute the inner eyewall decay and outer eyewall intensification to the divergence and convergence of the eddy angular momentum flux, respectively.


2021 ◽  
Vol 910 (1) ◽  
pp. 70
Author(s):  
Elishevah van Kooten ◽  
Martin Schiller ◽  
Frédéric Moynier ◽  
Anders Johansen ◽  
Troels Haugbølle ◽  
...  

Author(s):  
B.R. Neupane ◽  
Peter A. Delamere ◽  
X. Ma ◽  
C.‐S. Ng ◽  
B. Burkholder ◽  
...  

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