scholarly journals On the energetics of a two-layer baroclinic flow

2017 ◽  
Vol 816 ◽  
pp. 586-618
Author(s):  
Thibault Jougla ◽  
David G. Dritschel
Keyword(s):  
Vertical Shear ◽  
Water Model ◽  
Small Scale ◽  
Stochastic Forcing ◽  
Energy Transfers ◽  
Wide Range ◽  
Flow Evolution ◽  
Baroclinic Flow ◽  
The Stability ◽  
Classical Picture

The formation, evolution and co-existence of jets and vortices in turbulent planetary atmospheres is examined using a two-layer quasi-geostrophic $\unicode[STIX]{x1D6FD}$-channel shallow-water model. The study in particular focuses on the vertical structure of jets. Following Panetta & Held (J. Atmos. Sci., vol. 45 (22), 1988, pp. 3354–3365), a vertical shear arising from latitudinal heating variations is imposed on the flow and maintained by thermal damping. Idealised convection between the upper and lower layers is implemented by adding cyclonic/anti-cyclonic pairs, called hetons, to the flow, though the qualitative flow evolution is evidently not sensitive to this or other small-scale stochastic forcing. A very wide range of simulations have been conducted. A characteristic simulation which exhibits alternation between two different phases, quiescent and turbulent, is examined in detail. We study the energy transfers between different components and modes, and find the classical picture of barotropic/baroclinic energy transfers to be too simplistic. We also discuss the dependence on thermal damping and on the imposed vertical shear. Both have a strong influence on the flow evolution. Thermal damping is a major factor affecting the stability of the flow while vertical shear controls the number of jets in the domain, qualitatively through the Rhines scale $L_{Rh}=\sqrt{U/\unicode[STIX]{x1D6FD}}$.

Scattering of Low-Mode Internal Tides at a Continental Shelf

2019 ◽  
Vol 49 (2) ◽  
pp. 453-468 ◽  
Author(s):  
Shuya Wang ◽  
Xu Chen ◽  
Jinhu Wang ◽  
Qun Li ◽  
Jing Meng ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Laboratory Experiments ◽  
Internal Tides ◽  
Vertical Shear ◽  
Mean Flow ◽  
Energy Transfers ◽  
Wide Range ◽  
The Mean ◽  
Shear Structure ◽  
Incident Waves

AbstractA series of laboratory experiments are performed to investigate the scattering of low-mode internal tides at a continental shelf by varying the criticality parameter and normalized topographic height independently. A wide-range synchronized particle image velocimetery (PIV) measures the velocity fields of the internal tides. Beams radiate from both the shelf break and the bottom of the slope, indicating that energy transfers from low modes to higher modes, which is verified by the modal decomposition. Energy is also transferred to higher harmonics, whose amplitude is less than a quarter of that of the first harmonic. The fraction of energy transmitted onshore and dissipated on the topography is determined by both the criticality parameter and the normalized topographic height, while the fraction of energy reflected offshore is dependent only on the criticality parameter. Mean flow with a shear structure induced by internal tides is observed along the continental slope, with horizontal velocity generally half of the amplitude of the incident waves. A net onshore transport along the slope is caused by the onshore current with larger thickness. The strength of the mean flow is dependent on both the criticality parameter and the normalized topographic height, and a linear relationship between the energy of the mean flow and the vertical shear of internal tides is revealed.

scholarly journals Contact patch memory of tyres leading to lateral vibrations of four-wheeled vehicles

2013 ◽  
Vol 371 (1993) ◽  
pp. 20120427 ◽  
Author(s):  
Dénes Takács ◽  
Gábor Stépán
Keyword(s):  
Large Scale ◽  
Multiple Scales ◽  
Travelling Wave ◽  
Small Scale ◽  
Global Dynamics ◽  
Contact Patch ◽  
Lateral Vibrations ◽  
Wide Range ◽  
The Stability ◽  
Wheeled Vehicles

It has been shown recently that the shimmy motion of towed wheels can be predicted in a wide range of parameters by means of the so-called memory effect of tyres. This delay effect is related to the existence of a travelling-wave-like motion of the tyre points in contact with the ground relative to the wheel. This study shows that the dynamics within the small-scale contact patch can have an essential effect on the global dynamics of a four-wheeled automobile on a large scale. The stability charts identify narrow parameter regions of increased fuel consumption and tyre noise with the help of the delay models that are effective tools in dynamical problems through multiple scales.

Centrifugal, barotropic and baroclinic instabilities of isolated ageostrophic anticyclones in the two-layer rotating shallow water model and their nonlinear saturation

2014 ◽  
Vol 762 ◽  
pp. 5-34 ◽  
Author(s):  
Noé Lahaye ◽  
Vladimir Zeitlin
Keyword(s):  
Shallow Water ◽  
Initial Conditions ◽  
Vertical Shear ◽  
Water Model ◽  
Shallow Water Model ◽  
Nonlinear Saturation ◽  
Centrifugal Instability ◽  
Wide Range ◽  
Nonlinear Mechanism ◽  
Rotating Shallow Water

AbstractInstabilities of isolated anticyclonic vortices in the two-layer rotating shallow water model are studied at Rossby numbers up to two, with the main goal to understand the interplay between the classical centrifugal instability and other ageostrophic instabilities. We find that different types of instabilities with low azimuthal wavenumbers exist, and may compete. In a wide range of parameters, an asymmetric version of the standard centrifugal instability has larger growth rate than the latter. The dependence of the instabilities on the parameters of the flow, i.e. Rossby and Burger numbers, vertical shear and the ratios of the layers’ thicknesses and densities, is investigated. The zones of dominance of each instability are determined in the parameter space. Nonlinear saturation of these instabilities is then studied with the help of a high-resolution finite-volume numerical scheme, by using the unstable modes identified from the linear stability analysis as initial conditions. Differences in nonlinear development of the competing centrifugal and ageostrophic barotropic instabilities are evidenced. A nonlinear mechanism of axial symmetry breaking during the saturation of the centrifugal instability is displayed.

Influence of Geometric Scaling on the Stability and Range of a Turbocharger Centrifugal Compressor

2005 ◽  
Author(s):  
Matthias Schleer ◽  
Reza S. Abhari
Keyword(s):  
Flow Structure ◽  
Centrifugal Compressor ◽  
System Stability ◽  
Scale Model ◽  
Small Scale ◽  
Operating Characteristics ◽  
Design Features ◽  
Geometric Scaling ◽  
Wide Range ◽  
The Stability

In this work the stability behavior of small-scale centrifugal compressor is evaluated in detail and the influence of design features typical for small-scale applications is shown. The impeller used in this study represents the design features of machines typically used in small turbochargers like a low blade count, high blade loading and a large relative tip gap. The work is evaluating data obtained in an enlarged research facility and in an actual scale turbocharger application. Both facilities are using a geometrical similar impeller and all nondimensional parameter are maintained. The Reynolds number is adjusted by changing the inlet pressure and thus the density of the air. This setup allows measurements with high accuracy on the enlarged research stage and simple parameter studies on the small-scale model. Comparing the operating characteristics of both scales shows the validity of this approach. For the range of Reynolds numbers present, the stability of the compressor is not affected by the geometric scaling. As the user of the compressor system wishes to operate at a wide range and under varying load demands but always in stable condition the knowledge of the stability margin and the kind of instabilities is vital. An analysis of the instable phenomena limiting the range of the centrifugal compressors is shown. The analyses are interpreting the pressure fluctuations gained with high response pressure transducer located in the diffuser for the characterization of the system stability. A similar overall compressor characteristic and stability range is obtained for both scales investigated. The flow structure within the diffuser is shown in a time-resolved manner using a 3D Laser Doppler Anemometer. It is shown how the flow structure is affected by the leakage flow through the tip gap. It is forming a strong jet-wake pattern resulting in a non-uniform flow and sheared velocity triangles.

scholarly journals The Influence of Topography on the Stability of Shelfbreak Fronts

2005 ◽  
Vol 35 (6) ◽  
pp. 1023-1036 ◽  
Author(s):  
M. Susan Lozier ◽  
Mark S. C. Reed
Keyword(s):  
Bottom Topography ◽  
Three Dimensional ◽  
Vertical Shear ◽  
Primitive Equations ◽  
Instability Mode ◽  
Bottom Slope ◽  
Flat Bottom ◽  
Baroclinic Flow ◽  
The Stability ◽  
Frontal Instability

Abstract In an attempt to understand the degree to which the stability of a shelfbreak front, characterized by continuous horizontal and vertical shear, is affected by topography, a linear stability analysis was conducted for a range of frontal jets and bottom-slope configurations. Three-dimensional perturbations superposed on a continuously stratified shelfbreak front were investigated using linearized, hydrostatic primitive equations. For all model runs in the study, the frontal instability mode, which is the fastest-growing mode for a baroclinic flow, was not influenced by the bottom: Retrograde, prograde, and flat-bottom jets all share the same stability characteristics. In contrast, weakly baroclinic jets are strongly influenced by bottom topography. The presence of a bottom slope stabilizes prograde jets and destabilizes retrograde jets, a difference attributed to the orientation of the isopycnals relative to the bottom slope. Temporal and/or downstream changes in the bottom slope and/or background stratification are shown to produce sizeable changes in the instability of a weakly baroclinic jet.

scholarly journals Vortex multipoles in two-layer rotating shallow-water flows

2002 ◽  
Vol 460 ◽  
pp. 151-175 ◽  
Author(s):  
JEAN-MICHEL BAEY ◽  
XAVIER CARTON
Keyword(s):  
Shallow Water ◽  
Internal Gravity Waves ◽  
Linear Instability ◽  
Water Model ◽  
Striking Similarity ◽  
Mean Flow ◽  
Shallow Water Flows ◽  
Energy Transfers ◽  
Rotating Shallow Water ◽  
The Stability

The stability of elliptically perturbed circular vortices is investigated in a two-layer shallow-water model, with constant background rotation. The fluid is bounded above and below by rigid and at surfaces. The linear stability analysis shows that elliptical perturbations are most unstable for moderate Burger numbers and vorticity shears. Shorter waves dominate for more sheared vortices. Shallow-water and quasi-geostrophic growth rates exhibit a striking similarity, except at each end of the Burger number domain. There, cyclones (anticyclones) with finite Rossby numbers are more (less) unstable than their quasi-geostrophic counterparts. A simple model gives a first-order trend for this bias.Nonlinear model runs with initially perturbed vortices also show the similarity between the two dynamics. In these runs, elliptically deformed vortices stabilize as stationary rotating tripoles for moderate linear instability; on the other hand, strongly unstable vortices break as dipoles. During these nonlinear processes, energy transfers indicate that barotropic instability is at least as active as the baroclinic one. For tripole formation, the modal analysis of the perturbation exhibits a dominant contribution of the original wave and of the mean flow correction. The ageostrophic and divergent parts of the flow are respectively weak and negligible. The Lighthill equation proves that few internal gravity waves are generated during tripole formation or dipolar breaking. Finally, the effects of triangular perturbations on circular vortices and the formation of quadrupoles are briefly addressed.

scholarly journals Parameter Sweep Experiments on a Spectrum of Cyclones with Diabatic and Baroclinic Processes

2019 ◽  
Vol 76 (7) ◽  
pp. 1917-1935 ◽  
Author(s):  
Wataru Yanase ◽  
Hiroshi Niino
Keyword(s):  
Tropical Cyclone ◽  
Parameter Space ◽  
Large Scale ◽  
Vertical Shear ◽  
Small Scale ◽  
Extratropical Cyclones ◽  
Asymmetric Structures ◽  
Multiscale Dynamics ◽  
Wide Range ◽  
Large Scale Vortex

Abstract A wide range of environments that prevail over the globe generate various types of cyclones such as tropical, extratropical, and hybrid cyclones. In this paper, idealized numerical experiments are used to explore a spectrum of cyclones ranging from the diabatic type to the baroclinic type in a parameter space consisting of three environmental factors: temperature, vertical shear, and planetary vorticity. The experiments reproduce not only typical dynamics of tropical and extratropical cyclones but also their modified dynamics, which are consistent with theoretical studies; tropical cyclones are suppressed by vertical shear, while extratropical cyclones are intensified by condensational heating. The experiments also reproduce hybrid cyclones in environments with high temperature and large baroclinicity. The hybrid cyclones show multiscale dynamics in which synoptic-scale baroclinic systems spawn smaller-scale tropical cyclone–like convective cores. The spectrum of cyclones is found to be nonmonotonic in the parameter space because of a two-sided effect of the vertical shear: moderate shear weakens a tropical cyclone by tilting the small-scale vortex to the downshear, while strong shear develops a large-scale vortex of an extratropical cyclone or a hybrid cyclone through warm-air advection from the south. The indices based on the energetics and the symmetric and asymmetric structures overview the different types of cyclones in the parameter space. These parameter sweep experiments provide useful information on what environment is favorable for cyclones, particularly for intermediate environments where cyclone mechanisms are yet to be fully defined.

Performance of Electronic Structure Methods for the Description of Hückel-Möbius Interconversions in Extended π-Systems

2019 ◽  
Author(s):  
Tatiana Woller ◽  
Ambar Banerjee ◽  
Nitai Sylvetsky ◽  
Xavier Deraet ◽  
Frank De Proft ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Basis Set ◽  
Dft Methods ◽  
Molecular Switching ◽  
Wide Range ◽  
Electronic Structure Methods ◽  
Explicitly Correlated ◽  
Relative Errors ◽  
The Stability ◽  
Basis Set Expansion

<p>Expanded porphyrins provide a versatile route to molecular switching devices due to their ability to shift between several π-conjugation topologies encoding distinct properties. Taking into account its size and huge conformational flexibility, DFT remains the workhorse for modeling such extended macrocycles. Nevertheless, the stability of Hückel and Möbius conformers depends on a complex interplay of different factors, such as hydrogen bonding, p···p stacking, steric effects, ring strain and electron delocalization. As a consequence, the selection of an exchange-correlation functional for describing the energy profile of topological switches is very difficult. For these reasons, we have examined the performance of a variety of wavefunction methods and density functionals for describing the thermochemistry and kinetics of topology interconversions across a wide range of macrocycles. Especially for hexa- and heptaphyrins, the Möbius structures have a pronouncedly stronger degree of static correlation than the Hückel and figure-eight structures, and as a result the relative energies of singly-twisted structures are a challenging test for electronic structure methods. Comparison of limited orbital space full CI calculations with CCSD(T) calculations within the same active spaces shows that post-CCSD(T) correlation contributions to relative energies are very minor. At the same time, relative energies are weakly sensitive to further basis set expansion, as proven by the minor energy differences between MP2/cc-pVDZ and explicitly correlated MP2-F12/cc-pVDZ-F12 calculations. Hence, our CCSD(T) reference values are reasonably well-converged in both 1-particle and n-particle spaces. While conventional MP2 and MP3 yield very poor results, SCS-MP2 and particularly SOS-MP2 and SCS-MP3 agree to better than 1 kcal mol<sup>-1</sup> with the CCSD(T) relative energies. Regarding DFT methods, only M06-2X provides relative errors close to chemical accuracy with a RMSD of 1.2 kcal mol<sup>-1</sup>. While the original DSD-PBEP86 double hybrid performs fairly poorly for these extended p-systems, the errors drop down to 2 kcal mol<sup>-1</sup> for the revised revDSD-PBEP86-NL, again showing that same-spin MP2-like correlation has a detrimental impact on performance like the SOS-MP2 results. </p>

Insights into Potent Therapeutical Antileukemic Agent L-glutaminase Enzyme Under Solid-state Fermentation: A Review

2020 ◽  
Vol 21 (3) ◽  
pp. 211-220 ◽  
Author(s):  
Chandrasai Potla Durthi ◽  
Madhuri Pola ◽  
Satish Babu Rajulapati ◽  
Anand Kishore Kola
Keyword(s):  
Solid State ◽  
Solid State Fermentation ◽  
Food Industry ◽  
Energy Requirement ◽  
Production Studies ◽  
Wide Range ◽  
Hybridoma Technology ◽  
Bacteria And Fungi ◽  
The Stability ◽  
Glutaminase Activity

Aim & objective: To review the applications and production studies of reported antileukemic drug L-glutaminase under Solid-state Fermentation (SSF). Overview: An amidohydrolase that gained economic importance because of its wide range of applications in the pharmaceutical industry, as well as the food industry, is L-glutaminase. The medical applications utilized it as an anti-tumor agent as well as an antiretroviral agent. L-glutaminase is employed in the food industry as an acrylamide degradation agent, as a flavor enhancer and for the synthesis of theanine. Another application includes its use in hybridoma technology as a biosensing agent. Because of its diverse applications, scientists are now focusing on enhancing the production and optimization of L-glutaminase from various sources by both Solid-state Fermentation (SSF) and submerged fermentation studies. Of both types of fermentation processes, SSF has gained importance because of its minimal cost and energy requirement. L-glutaminase can be produced by SSF from both bacteria and fungi. Single-factor studies, as well as multi-level optimization studies, were employed to enhance L-glutaminase production. It was concluded that L-glutaminase activity achieved by SSF was 1690 U/g using wheat bran and Bengal gram husk by applying feed-forward artificial neural network and genetic algorithm. The highest L-glutaminase activity achieved under SSF was 3300 U/gds from Bacillus sp., by mixture design. Purification and kinetics studies were also reported to find the molecular weight as well as the stability of L-glutaminase. Conclusion: The current review is focused on the production of L-glutaminase by SSF from both bacteria and fungi. It was concluded from reported literature that optimization studies enhanced L-glutaminase production. Researchers have also confirmed antileukemic and anti-tumor properties of the purified L-glutaminase on various cell lines.

Integrated Design and Multi-Objective Optimization of a Single Stage Heat-Pump Turbocompressor

2013 ◽  
Author(s):  
J. Schiffmann
Keyword(s):  
Design Optimization ◽  
High Efficiency ◽  
Integrated Design ◽  
Heat Pumps ◽  
Small Scale ◽  
Multi Objective Optimization ◽  
Design Constraints ◽  
Multi Objective ◽  
Wide Range ◽  
Standard Design

Small scale turbomachines in domestic heat pumps reach high efficiency and provide oil-free solutions which improve heat-exchanger performance and offer major advantages in the design of advanced thermodynamic cycles. An appropriate turbocompressor for domestic air based heat pumps requires the ability to operate on a wide range of inlet pressure, pressure ratios and mass flows, confronting the designer with the necessity to compromise between range and efficiency. Further the design of small-scale direct driven turbomachines is a complex and interdisciplinary task. Textbook design procedures propose to split such systems into subcomponents and to design and optimize each element individually. This common procedure, however, tends to neglect the interactions between the different components leading to suboptimal solutions. The authors propose an approach based on the integrated philosophy for designing and optimizing gas bearing supported, direct driven turbocompressors for applications with challenging requirements with regards to operation range and efficiency. Using previously validated reduced order models for the different components an integrated model of the compressor is implemented and the optimum system found via multi-objective optimization. It is shown that compared to standard design procedure the integrated approach yields an increase of the seasonal compressor efficiency of more than 12 points. Further a design optimization based sensitivity analysis allows to investigate the influence of design constraints determined prior to optimization such as impeller surface roughness, rotor material and impeller force. A relaxation of these constrains yields additional room for improvement. Reduced impeller force improves efficiency due to a smaller thrust bearing mainly, whereas a lighter rotor material improves rotordynamic performance. A hydraulically smoother impeller surface improves the overall efficiency considerably by reducing aerodynamic losses. A combination of the relaxation of the 3 design constraints yields an additional improvement of 6 points compared to the original optimization process. The integrated design and optimization procedure implemented in the case of a complex design problem thus clearly shows its advantages compared to traditional design methods by allowing a truly exhaustive search for optimum solutions throughout the complete design space. It can be used for both design optimization and for design analysis.

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