Continuous-in-time approach to flow shear in a linearly implicit local gyrokinetic code

2021 ◽  
Vol 87 (2) ◽  
Author(s):  
Nicolas Christen ◽  
Michael Barnes ◽  
Felix I. Parra
Keyword(s):  
Turbulent Transport ◽  
Current Approach ◽  
Test Cases ◽  
Time Step ◽  
Flow Shear ◽  
New Approach ◽  
Step Flow ◽  
Discrete Approach ◽  
Stringent Constraint ◽  
Gyrokinetic Simulations

A new algorithm for toroidal flow shear in a linearly implicit, local $\delta f$ gyrokinetic code is described. Unlike the current approach followed by a number of codes, it treats flow shear continuously in time. In the linear gyrokinetic equation, time-dependences arising from the presence of flow shear are decomposed in such a way that they can be treated explicitly in time with no stringent constraint on the time step. Flow shear related time dependences in the nonlinear term are taken into account exactly, and time dependences in the quasineutrality equation are interpolated. Test cases validating the continuous-in-time implementation in the code GS2 are presented. Lastly, nonlinear gyrokinetic simulations of a JET discharge illustrate the differences observed in turbulent transport compared with the usual, discrete-in-time approach. The continuous-in-time approach is shown, in some cases, to produce fluxes that converge to a different value than with the discrete approach. The new approach can also lead to substantial computational savings by requiring radially narrower boxes. At fixed box size, the continuous implementation is only modestly slower than the previous, discrete approach.

scholarly journals How eigenmode self-interaction affects zonal flows and convergence of tokamak core turbulence with toroidal system size

2020 ◽  
Vol 86 (5) ◽  
Author(s):  
Ajay C. J. ◽  
Stephan Brunner ◽  
Ben McMillan ◽  
Justin Ball ◽  
Julien Dominski ◽  
...  
Keyword(s):  
Turbulent Transport ◽  
Zonal Flow ◽  
System Size ◽  
Flow Shear ◽  
Direction Parallel ◽  
Zonal Flows ◽  
Radial Extent ◽  
Modulational Instabilities ◽  
Gyrokinetic Simulations ◽  
The Magnetic Field

Self-interaction is the process by which a microinstability eigenmode that is extended along the direction parallel to the magnetic field interacts non-linearly with itself. This effect is particularly significant in gyrokinetic simulations accounting for kinetic passing electron dynamics and is known to generate stationary $E\times B$ zonal flow shear layers at radial locations near low-order mode rational surfaces (Weikl et al. Phys. Plasmas, vol. 25, 2018, 072305). We find that self-interaction, in fact, plays a very significant role in also generating fluctuating zonal flows, which is critical to regulating turbulent transport throughout the radial extent. Unlike the usual picture of zonal flow drive in which microinstability eigenmodes coherently amplify the flow via modulational instabilities, the self-interaction drive of zonal flows from these eigenmodes are uncorrelated with each other. It is shown that the associated shearing rate of the fluctuating zonal flows therefore reduces as more toroidal modes are resolved in the simulation. In simulations accounting for the full toroidal domain, such an increase in the density of toroidal modes corresponds to an increase in the toroidal system size, leading to a finite system size effect that is distinct from the well-known profile shearing effect.

scholarly journals 107 Traceability

2019 ◽  
Vol 97 (Supplement_2) ◽  
pp. 61-62
Author(s):  
John Butler
Keyword(s):  
United States ◽  
The United States ◽  
Current Approach ◽  
Animal Disease ◽  
Global Marketplace ◽  
Cattle Industry ◽  
New Approach ◽  
Traceability System ◽  
Competitive Disadvantage ◽  
Final Rule

Abstract Animal disease traceability—or knowing where diseased and at-risk animals are, where they’ve been, and when—is important to ensuring a rapid response when animal disease events take place. Although animal disease traceability does not prevent disease, an efficient and accurate traceability system reduces the number of animals and response time involved in a disease investigation; which, in turn, reduces the economic impact on owners and affected communities. The current approach to traceability in the United States is the result of significant discussion and compromise. Federal policy regarding traceability has been amended several times over the past decade based on stakeholder feedback, particularly from the cattle industry. In early 2010, USDA announced a new approach for responding to and controlling animal diseases, referred to as the ADT framework. USDA published a proposed rule, “Traceability for Livestock Moving Interstate,” on August 11, 2011, and the final rule on January 9, 2013. Under the final rule, unless specifically exempted, livestock moved interstate must be officially identified and accompanied by an interstate certificate of veterinary inspection (ICVI) or other documentation. However, these requirements do not apply to all cattle. Beef cattle under 18 months of age, unless they are moved interstate for shows, exhibitions, rodeos, or recreational events, are exempt from the official identification requirement in this rule. We can do better. Our industry must recognize how vulnerable we really are, should we be subject to a disease such as foot and mouth. We must also understand what a competitive disadvantage the United States faces in the global marketplace without a recognized, industry-wide traceability system.

A Novel Approach to Nanoscale Materials Synthesis Using Industrial Laser Processing of Organosilazane Liquid Precursors

1990 ◽  
Vol 206 ◽  
Author(s):  
Tongsan D. Xiao ◽  
Peter R. Strutt ◽  
Kenneth E. Gonsalves
Keyword(s):  
Ceramic Powder ◽  
Average Diameter ◽  
Current Approach ◽  
Powder Materials ◽  
Materials Synthesis ◽  
Laser Plume ◽  
New Approach ◽  
Novel Approach ◽  
Liquid Precursors ◽  
Short Time

ABSTRACTA new approach has been developed for the synthesis of nanoscale ceramic powder materials from liquid organosilazane precursors. This technique, by exploiting fast kinetic chemical and physical reactions, makes it possible to synthesize significant quantities of material in a relatively short time. In the current approach aerosols of a silazane monomer, (CH3SiHNH)n, (n = 3 or 4), of mol. wt. 280–320, are injected into the beam of a cw industrial CO2 laser to obtain nanoscale ceramic powders. Injection of the aerosol into the laser-beam results in a high-temperature plume. Rapid condensation of the molecular precursor species emerging from the laser plume results in the formation of preceramic polymer particles, with an average diameter of 62 nm. One attractive feature of this process is that 70 wt.% of the liquid precursor is converted into nanoscale powders. Another feature is that only a further 10 wt.% loss occurs during post thermal treatment to form the end-product.

scholarly journals Theory of the tertiary instability and the Dimits shift within a scalar model

2020 ◽  
Vol 86 (4) ◽  
Author(s):  
Hongxuan Zhu ◽  
Yao Zhou ◽  
I. Y. Dodin
Keyword(s):  
Turbulent Transport ◽  
Plasma Phys ◽  
Magnetized Plasma ◽  
Radial Coordinate ◽  
Flow Shear ◽  
Zonal Flows ◽  
Drift Wave ◽  
Zonal Velocity ◽  
Instability Growth ◽  
Traditional Paradigm

The Dimits shift is the shift between the threshold of the drift-wave primary instability and the actual onset of turbulent transport in a magnetized plasma. It is generally attributed to the suppression of turbulence by zonal flows, but developing a more detailed understanding calls for consideration of specific reduced models. The modified Terry–Horton system has been proposed by St-Onge (J. Plasma Phys., vol. 83, 2017, 905830504) as a minimal model capturing the Dimits shift. Here, we use this model to develop an analytic theory of the Dimits shift and a related theory of the tertiary instability of zonal flows. We show that tertiary modes are localized near extrema of the zonal velocity $U(x)$ , where $x$ is the radial coordinate. By approximating $U(x)$ with a parabola, we derive the tertiary-instability growth rate using two different methods and show that the tertiary instability is essentially the primary drift-wave instability modified by the local $U'' \doteq {\rm d}^2 U/{\rm d} x^2 $ . Then, depending on $U''$ , the tertiary instability can be suppressed or unleashed. The former corresponds to the case when zonal flows are strong enough to suppress turbulence (Dimits regime), while the latter corresponds to the case when zonal flows are unstable and turbulence develops. This understanding is different from the traditional paradigm that turbulence is controlled by the flow shear $| {\rm d} U / {\rm d} x |$ . Our analytic predictions are in agreement with direct numerical simulations of the modified Terry–Horton system.

Temporal gradient in shear-induced signaling pathway: involvement of MAP kinase, c-fos, and connexin43

2000 ◽  
Vol 278 (5) ◽  
pp. H1598-H1605 ◽  
Author(s):  
Xuping Bao ◽  
Craig B. Clark ◽  
John A. Frangos
Keyword(s):  
Shear Stress ◽  
Mrna Expression ◽  
Signaling Pathway ◽  
Steady Shear ◽  
Flow Shear ◽  
Temporal Gradient ◽  
Step Flow ◽  
Shear Component ◽  
Flow Shear Stress ◽  
Impulse Flow

The effect of a temporal gradient in shear and steady shear on the activity of extracellular signal-regulated protein kinases 1 and 2 (ERK1/ERK2), c- fos, and connexin43 (Cx43) in human endothelial cells was investigated. Three laminar flow profiles (16 dyn/cm2), including impulse flow (shear stress abruptly applied for 3 s), ramp flow (shear stress smoothly transitioned at flow onset), and step flow (shear stress abruptly applied at flow onset) were utilized. Relative to static controls, impulse flow stimulated the phosphorylation of ERK1/ERK2 8.5- to 7.5-fold, respectively at 10 min, as well as the mRNA expression of c- fos 51-fold at 30 min, and Cx43 8-fold at 90 min. These high levels of mRNA expression were sustained for at least 4 h. In contrast, ramp flow was unable to significantly induce gene expression and even inhibited the activation of ERK1/ERK2. Step flow, which contains both a sharp temporal gradient in shear stress and a steady shear component, elicited only moderate and transient responses, indicating the distinct role of these fluid shear stimuli in endothelial signal transduction. The specific inhibitor of mitogen-activated protein kinase kinase PD-98059 inhibited impulse flow-induced c -fos and Cx43 mRNA expression. Thus these findings implicate the involvement of ERK1/ERK2, c -fos, and Cx43 in the signaling pathway induced by the temporal gradient in shear.

A Control-Volume Model of the Compressible Euler Equations with a Vertical Lagrangian Coordinate

2013 ◽  
Vol 141 (7) ◽  
pp. 2526-2544 ◽  
Author(s):  
Xi Chen ◽  
Natalia Andronova ◽  
Bram Van Leer ◽  
Joyce E. Penner ◽  
John P. Boyd ◽  
...  
Keyword(s):  
Euler Equations ◽  
Control Volume ◽  
Test Cases ◽  
Riemann Solver ◽  
New Approach ◽  
Vertical Coordinate ◽  
Low Mach Number ◽  
Atmospheric Flows ◽  
Lagrangian Coordinate ◽  
Control Volume Approach

Abstract Accurate and stable numerical discretization of the equations for the nonhydrostatic atmosphere is required, for example, to resolve interactions between clouds and aerosols in the atmosphere. Here the authors present a modification of the hydrostatic control-volume approach for solving the nonhydrostatic Euler equations with a Lagrangian vertical coordinate. A scheme with low numerical diffusion is achieved by introducing a low Mach number approximate Riemann solver (LMARS) for atmospheric flows. LMARS is a flexible way to ensure stability for finite-volume numerical schemes in both Eulerian and vertical Lagrangian configurations. This new approach is validated on test cases using a 2D (x–z) configuration.

scholarly journals Predicting the Operability of Damaged Compressors Using Machine Learning

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
J. V. Taylor ◽  
B. Conduit ◽  
A. Dickens ◽  
C. Hall ◽  
M. Hillel ◽  
...  
Keyword(s):  
Machine Learning ◽  
Current Approach ◽  
Training Data ◽  
Physical Parameters ◽  
Test Cases ◽  
Rapid Testing ◽  
Exciting Opportunity ◽  
Intractable Problems ◽  
High Uncertainty ◽  
Better Than

Abstract The application of machine learning to aerospace problems faces a particular challenge. For successful learning, a large amount of good quality training data is required, typically tens of thousands of cases. However, due to the time and cost of experimental aerospace testing, these data are scarce. This paper shows that successful learning is possible with two novel techniques: The first technique is rapid testing. Over the last 5 years, the Whittle Laboratory has developed a capability where rebuild and test times of a compressor stage now take 15 min instead of weeks. The second technique is to base machine learning on physical parameters, derived from engineering wisdom developed in industry over many decades. The method is applied to the important industry problem of predicting the effect of blade damage on compressor operability. The current approach has high uncertainty, and it is based on human judgement and correlation of a handful of experimental test cases. It is shown using 100 training cases and 25 test cases that the new method is able to predict the operability of damaged compressor stages with an accuracy of 2% in a 95% confidence interval; far better than is possible by even the most experienced compressor designers. Use of the method is also shown to generate new physical understanding, previously unknown by any of the experts involved in this work. Using this method in the future offers an exciting opportunity to generate understanding of previously intractable problems in aerospace.

Effects of edge biasing on blob dynamics and associated transport in the edge of the J-TEXT tokamak

2022 ◽  
Author(s):  
Wei Li ◽  
Yuhong Xu ◽  
Jun Cheng ◽  
Hai Liu ◽  
Zhipeng Chen ◽  
...  
Keyword(s):  
Electric Field ◽  
Large Scale ◽  
Turbulent Transport ◽  
Radial Electric Field ◽  
Plasma Confinement ◽  
Flow Shear ◽  
Theoretical Predictions ◽  
Outward Motion ◽  
Electrode Biasing ◽  
Particle Confinement

Abstract Effects of edge radial electric field Er and Er × B flow shear on edge turbulence and turbulent transport, in particular, on large-scale blobs and blobby transport have been investigated in the positive and negative biasing discharges in the J-TEXT tokamak. The results show that under certain conditions, the positive electrode biasing induces better plasma confinement than the negative biasing. Further studies reveal that in addition to flow shear effects on blob dynamics, the local radial electric field at the edge region plays a significant role in repulsion of the blobs and associated transport, leading to improvement of particle confinement when the outward motion of the blobs is blocked. The results are in accordance with theoretical predictions.

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