scholarly journals The Effect of Surface Drag Strength on Mesocyclone Intensification and Tornadogenesis in Idealized Supercell Simulations

2020 ◽  
Vol 77 (5) ◽  
pp. 1699-1721 ◽  
Author(s):  
Brett Roberts ◽  
Ming Xue ◽  
Daniel T. Dawson
Keyword(s):  
Cross Sections ◽  
Force Balance ◽  
Surface Drag ◽  
Low Level ◽  
Relative Contribution ◽  
Frictional Forces ◽  
A New Technique ◽  
Land Surfaces ◽  
Range Of Values ◽  
Effect Of Surface

Abstract A suite of six idealized supercell simulations is performed in which the surface drag coefficient Cd is varied over a range of values from 0 to 0.05 to represent a variety of water and land surfaces. The experiments employ a new technique for enforcing a three-force balance among the pressure gradient, Coriolis, and frictional forces so that the environmental wind profile can remain unchanged throughout the simulation. The initial low-level mesocyclone lowers toward the ground, intensifies, and produces a tornado in all experiments with Cd ≥ 0.002, with the intensification occurring earlier for larger Cd. In the experiment with Cd = 0, the low-level mesocyclone remains comparatively weak throughout the simulation and does not produce a tornado. Vertical cross sections through the simulated tornadoes reveal an axial downdraft that reaches the ground only in experiments with smaller Cd, as well as stronger corner flow in experiments with larger Cd. Material circuits are initialized enclosing the low-level mesocyclone in each experiment and traced backward in time. Circulation budgets for these circuits implicate surface drag acting in the inflow sector of the supercell as having generated important positive circulation, and its relative contribution increases with Cd. However, the circulation generation is similar in magnitude for the experiments with Cd = 0.02 and 0.05, and the tornado in the latter experiment is weaker. This suggests the possible existence of an optimal range of Cd values for promoting intense tornadoes within our experimental configuration.

scholarly journals The Role of Surface Drag in Tornadogenesis within an Idealized Supercell Simulation

2016 ◽  
Vol 73 (9) ◽  
pp. 3371-3395 ◽  
Author(s):  
Brett Roberts ◽  
Ming Xue ◽  
Alexander D. Schenkman ◽  
Daniel T. Dawson
Keyword(s):  
Vertical Wind Shear ◽  
Streamwise Direction ◽  
Grid Spacing ◽  
Surface Drag ◽  
Low Level ◽  
Frictional Forces ◽  
Homogeneous Background ◽  
Horizontal Grid ◽  
Effect Of Surface

Abstract To investigate the effect of surface drag on tornadogenesis, a pair of idealized simulations is conducted with 50-m horizontal grid spacing. In the first experiment (full-wind drag case), surface drag is applied to the full wind; in the second experiment (environmental drag case), drag is applied only to the background environmental wind, with storm-induced perturbations unaffected. The simulations are initialized using a thermal bubble within a horizontally homogeneous background environment that has reached a balance between the pressure gradient, Coriolis, and frictional forces. The environmental sounding is derived from a prior simulation of the 3 May 1999 Oklahoma tornado outbreak but modified to account for near-ground frictional effects. In the full-wind drag experiment, a tornado develops around 25 min into the simulation and persists for more than 10 min; in the environmental-only drag experiment, no tornado occurs. Three distinct mechanisms are identified by which surface drag influences tornadogenesis. The first mechanism is the creation by drag of near-ground vertical wind shear (and associated horizontal vorticity) in the background environment. The second mechanism is generation of near-ground crosswise horizontal vorticity by drag on the storm scale as air accelerates into the low-level mesocyclone; this vorticity is subsequently exchanged into the streamwise direction and eventually tilted into the vertical. The third mechanism is frictional enhancement of horizontal convergence, which strengthens the low-level updraft and stretching of vertical vorticity. The second and third mechanisms are found to work together to produce a tornado, while baroclinic vorticity plays a negligible role.

scholarly journals Micrometric research results of vacuum dough divider components

2019 ◽  
Vol 19 (3) ◽  
pp. 231-241
Author(s):  
E. G. Martynova ◽  
S. A. Velichko ◽  
A. V. Martynov
Keyword(s):  
Partial Replacement ◽  
Production Volume ◽  
Efficient Technology ◽  
Research Results ◽  
Electrospark Machining ◽  
Size Distortions ◽  
A New Technique ◽  
Side Gap ◽  
Vertical Gap ◽  
Range Of Values

Introduction. Nowadays, vacuum-type dough dividers are used in industries with a production volume of up to 4,000 loaves per day. In the dough divider operation, due to wear of the working surfaces of the piston, chamber, and drum, the gap between them goes beyond the value equal to 50 microns, which provides vacuum in the suction chamber. As a result, the suction process becomes unstable; the dough divider disturbs the weight accuracy of bakery goods. Repair of such equipment is carried out mainly through a full or partial replacement of worn parts and assemblies with new ones. To increase their durability, there is a need to develop a new highly efficient technology with the restoration of worn part surfaces using the welding and surfacing methods.Materials and Methods. A new technique of determining the number of objects for research using the “STATISTICA” program is presented. Wear surfaces of the vacuum dough divider parts are determined.Research Results. Micrometric studies of the dough divider components were carried out. They showed the presence of appreciable size distortions due to the local wear of the working surfaces. In this case, a side gap between the suction chamber and the main piston and between the drum and the suction chamber is 6 times higher than the permissible one, and a vertical gap between the division box and the piston exceeds the permissible gap by more than 10 times. Wear of the working surfaces of the dough divider parts is local in nature, while the range of values is as follows: for the main piston, it is 10-200 microns; for the gaging piston, it is 250- 900 microns; for the suction chamber and division box, it is 300-400 microns; for the drum surfaces, it is 280-300 microns.Discussion and Conclusions. The conducted micrometric studies showed the presence of appreciable size distortions due to the local wear of the working surfaces. Based on the results obtained, it can be argued that the most productive and economically viable technique for the restoration of worn surfaces of dough divider parts is, for example, the electrospark machining.

scholarly journals Impact of Energy Dependence on Ground Level and Avionic SEE Rate Prediction When Applying Standard Test Procedures

Aerospace ◽  
2019 ◽  
Vol 6 (11) ◽  
pp. 119
Author(s):  
Matteo Cecchetto ◽  
Rubén García Alía ◽  
Frédéric Wrobel
Keyword(s):  
Cross Sections ◽  
Random Access ◽  
Ground Level ◽  
High Energy ◽  
Standard Test ◽  
Fissile Material ◽  
Test Procedures ◽  
Relative Contribution ◽  
Standard Procedures ◽  
Commercial Flight

Single event effects (SEEs) in ground level and avionic applications are mainly induced by neutrons and protons, of which the relative contribution of the latter is larger with increasing altitude. Currently, there are two main applicable standards—JEDEC JESD89A for ground level and IEC 62396 for avionics—that address the procedure for testing and qualifying electronics for these environments. In this work, we extracted terrestrial spectra at different altitudes from simulations and compared them with data available from the standards. Second, we computed the SEE rate using different approaches for three static random access memory (SRAM) types, which present a strong SEE response dependence with energy. Due to the presence of tungsten, a fissile material when interacting with high energy hadrons, the neutron and proton SEE cross sections do not saturate after 200 MeV, but still increase up to several GeV. For these memories, we found standard procedures could underestimate the SEE rate by a factor of up to 4-even in ground level applications—and up to 12 times at 12 km. Moreover, for such memories, the contribution from high energy protons is able to play a significant role, comparable to that of neutrons, even at commercial flight altitudes, and greater at higher altitudes.

scholarly journals Proton–proton, pion–proton and pion–pion diffractive collisions at ultrahigh energies

2014 ◽  
Vol 29 (15) ◽  
pp. 1450096 ◽  
Author(s):  
V. V. Anisovich ◽  
K. V. Nikonov ◽  
V. A. Nikonov ◽  
J. Nyiri
Keyword(s):  
Cross Sections ◽  
Constituent Quark ◽  
Energy Scale ◽  
Proton Proton ◽  
Black Disk ◽  
Total Cross Sections ◽  
Diffractive Dissociation ◽  
Relative Contribution ◽  
Diffractive Scattering ◽  
Dissociation Cross Section

The LHC energies are those at which the asymptotic regime in hadron–hadron diffractive collisions (pp, πp, ππ) might be switched on. Based on results of the Dakhno–Nikonov eikonal model which is a generalization of the Good–Walker eikonal approach for a continuous set of channels, we present a picture for transformation of the constituent quark mode to the black disk one. In the black disk mode [Formula: see text], we have a growth of the logarithm squared type for total and elastic cross-sections, σ tot ~ ln 2 s and σ el ~ ln 2 s and [Formula: see text]-scaling for diffractive scattering and diffractive dissociation of hadrons. The diffractive dissociation cross-section grows as σD ~ ln s, σDD ~ ln s, and their relative contribution tends to zero: σD/σ tot → 0, σDD/σ tot → 0. Asymptotic characteristics of diffractive and total cross-sections are universal, and this results in the asymptotical equality of cross-sections for all types of hadrons (the Gribov universality). The energy scale for switching on the asymptotic mode is estimated for different processes.

scholarly journals Experimental study of the wake behind a surface-piercing cylinder for a clean and contaminated free surface

2000 ◽  
Vol 402 ◽  
pp. 109-136 ◽  
Author(s):  
AMY WARNCKE LANG ◽  
MORTEZA GHARIB
Keyword(s):  
Surface Tension ◽  
Free Surface ◽  
Turbulent Flows ◽  
Cross Sections ◽  
Surface Deformation ◽  
Surface Condition ◽  
Free Surface Flows ◽  
Shear Stresses ◽  
Surface Contaminants ◽  
A New Technique

This experimental investigation into the nature of free-surface flows was to study the effects of surfactants on the wake of a surface-piercing cylinder. A better understanding of the process of vorticity generation and conversion at a free surface due to the absence or presence of surfactants has been gained. Surfactants, or surface contaminants, have the tendency to reduce the surface tension proportionally to the respective concentration at the free surface. Thus when surfactant concentration varies across a free surface, surface tension gradients occur and this results in shear stresses, thus altering the boundary condition at the free surface. A low Reynolds number wake behind a surface-piercing cylinder was chosen as the field of study, using digital particle image velocimetry (DPIV) to map the velocity and vorticity field for three orthogonal cross-sections of the flow. Reynolds numbers ranged from 350 to 460 and the Froude number was kept below 1.0. In addition, a new technique was used to simultaneously map the free surface deformation. Shadowgraph imaging of the free surface was also used to gain a better understanding of the flow. It was found that, depending on the surface condition, the connection of the shedding vortex filaments in the wake of the cylinder was greatly altered with the propensity for surface tension gradients to redirect the vorticity near the free surface to that of the surface-parallel component. This result has an impact on the understanding of turbulent flows in the vicinity of a free surface with varying surface conditions.

scholarly journals A new technique for firn grain-size measurement using SEM image analysis

2010 ◽  
Vol 56 (195) ◽  
pp. 12-19 ◽  
Author(s):  
N.E. Spaulding ◽  
D.A. Meese ◽  
I. Baker ◽  
P.A. Mayewski ◽  
G.S. Hamilton
Keyword(s):  
Grain Size ◽  
Boundary Diffusion ◽  
Ice Core ◽  
New Technique ◽  
Sem Image ◽  
Grain Sizes ◽  
A New Technique ◽  
Predicted Values ◽  
Range Of Values ◽  
Sem Image Analysis

AbstractFirn microstructure is accurately characterized using images obtained from scanning electron microscopy (SEM). Visibly etched grain boundaries within images are used to create a skeleton outline of the microstructure. A pixel-counting utility is applied to the outline to determine grain area. Firn grain sizes calculated using the technique described here are compared to those calculated using the techniques of Gow (1969) and Gay and Weiss (1999) on samples of the same material, and are found to be substantially smaller. The differences in grain size between the techniques are attributed to sampling deficiencies (e.g. the inclusion of pore filler in the grain area) in earlier methods. The new technique offers the advantages of greater accuracy and the ability to determine individual components of the microstructure (grain and pore), which have important applications in ice-core analyses. The new method is validated by calculating activation energies of grain boundary diffusion using predicted values based on the ratio of grain-size measurements between the new and existing techniques. The resulting activation energy falls within the range of values previously reported for firn/ice.

scholarly journals Mesoscale Moisture Transport by the Low-Level Jet during the IHOP Field Experiment

2008 ◽  
Vol 136 (10) ◽  
pp. 3781-3795 ◽  
Author(s):  
Edward I. Tollerud ◽  
Fernando Caracena ◽  
Steven E. Koch ◽  
Brian D. Jamison ◽  
R. Michael Hardesty ◽  
...  
Keyword(s):  
Great Plains ◽  
Cross Sections ◽  
Moisture Transport ◽  
Large Scale ◽  
Wrf Model ◽  
The United States ◽  
Small Scale ◽  
Low Level ◽  
Convective Scale ◽  
Low Level Jet

Previous studies of the low-level jet (LLJ) over the central Great Plains of the United States have been unable to determine the role that mesoscale and smaller circulations play in the transport of moisture. To address this issue, two aircraft missions during the International H2O Project (IHOP_2002) were designed to observe closely a well-developed LLJ over the Great Plains (primarily Oklahoma and Kansas) with multiple observation platforms. In addition to standard operational platforms (most important, radiosondes and profilers) to provide the large-scale setting, dropsondes released from the aircraft at 55-km intervals and a pair of onboard lidar instruments—High Resolution Doppler Lidar (HRDL) for wind and differential absorption lidar (DIAL) for moisture—observed the moisture transport in the LLJ at greater resolution. Using these observations, the authors describe the multiscalar structure of the LLJ and then focus attention on the bulk properties and effects of scales of motion by computing moisture fluxes through cross sections that bracket the LLJ. From these computations, the Reynolds averages within the cross sections can be computed. This allow an estimate to be made of the bulk effect of integrated estimates of the contribution of small-scale (mesoscale to convective scale) circulations to the overall transport. The performance of the Weather Research and Forecasting (WRF) Model in forecasting the intensity and evolution of the LLJ for this case is briefly examined.

scholarly journals Longpath DOAS tomography on a motorway exhaust gas plume: numerical studies and application to data from the BAB II campaign

2004 ◽  
Vol 4 (3) ◽  
pp. 2435-2484 ◽  
Author(s):  
T. Laepple ◽  
V. Knab ◽  
K.-U. Mettendorf ◽  
I. Pundt
Keyword(s):  
Cross Sections ◽  
Measurement Data ◽  
Optical Absorption Spectroscopy ◽  
Reconstruction Process ◽  
3 Dimensional ◽  
Numerical Studies ◽  
Error Estimations ◽  
A New Technique ◽  
Inversion Techniques

Abstract. This paper presents a procedure for performing and optimizing inversions for DOAS tomography and its application to measurement data. DOAS tomography is a new technique to determine 2- and 3-dimensional concentration fields of air pollutants or other trace gases by combining differential optical absorption spectroscopy (DOAS) with tomographic inversion techniques. Due to the limited amount of measured data, the resulting concentration fields are sensitive to the inversion process. Therefore detailed error estimations are needed to determine the quality of the reconstruction. In this paper we compare different row acting methods for the inversion, present a procedure for optimizing the parameters of the reconstruction process and propose a way to estimate the error-fields by numerical studies. The procedure was applied to data from the motorway emission campaign BAB II. Two dimensional NO2 cross sections at right angles to the motorway could be reconstructed qualitatively well at different meteorological situations. Additionally we present error fields for the reconstructions which show the problems and skills of the used measurement setup. Numerical studies on an improved setup for future motorway campaigns show, that DOAS tomography is able to produce high quality concentration maps.

scholarly journals Inelastic Collisions in the Townsend?Huxley Diffusion Experiment

1971 ◽  
Vol 24 (4) ◽  
pp. 841 ◽  
Author(s):  
JLA Francey ◽  
PK Stewart
Keyword(s):  
Distribution Function ◽  
Energy Loss ◽  
Cross Sections ◽  
Electron Distribution ◽  
Electron Distribution Function ◽  
Inelastic Collisions ◽  
Diffusion Experiment ◽  
Inelastic Energy Loss ◽  
The Mean ◽  
Range Of Values

The Boltzmann equation, including density gradients, is solved for the electron distribution function in the Townsend-Huxley experiment. Elastic and inelastic collisions with constant cross sections are assumed to occur, the inelastic energy loss per collision being small compared with the mean energy. The inelastic energy loss and the electron mean energy are calculated and tabulated over a range of values of EIP.

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