scholarly journals Hydrostatic equilibrium preservation in MHD numerical simulation with stratified atmospheres

2019 ◽  
Vol 631 ◽  
pp. A68 ◽  
Author(s):  
G. Krause
Keyword(s):  
Variable Temperature ◽  
Hydrostatic Equilibrium ◽  
Godunov Method ◽  
Pressure Gradients ◽  
Reconstruction Scheme ◽  
Gravitational Source ◽  
Type Reconstruction ◽  
The Difference ◽  
Low Amplitude ◽  
Polynomial Reconstruction

Context. Many astrophysical processes involving plasma flows are produced in the context of a gravitationally stratified atmosphere in hydrostatic equilibrium, in which strong gradients can exist with gas properties that vary in small regions by several orders of magnitude. The standard Godunov-type schemes with polynomial reconstruction used to numerically solve these problems fail to preserve the hydrostatic equilibrium owing to the appearance of spurious fluxes generated by the numerical unbalance between gravitational forces and pressure gradients. Aims. The aim of this work is to present local hydrostatic reconstruction techniques that can be implemented in existing codes with Godunov-type methods to obtain well-balanced schemes that numerically satisfy the hydrostatic equilibrium for various conditions. Methods. The proposed numerical scheme is based on the Godunov method with second order MUSCL-type reconstruction, as is extensively used in astrophysical applications. The difference between the scheme and the standard formulations is only given by calculating the pressure and density Riemann states on each intercell face and by computing the gravitational source term on each cell. Results. The local hydrostatic reconstruction scheme is implemented in the FLASH code to verify the well-balanced property for hydrostatic equilibrium with constant or linearly variable temperature and constant or variable gravity. In addition, the behavior of the scheme for hydrostatic equilibrium with arbitrary temperature distributions is also analyzed together with the ability to propagate low-amplitude waves and to capture shock waves. Conclusions. The scheme is demonstrated to be robust and relatively simple to implement in existing codes. This approach produces good results in hydrostatic equilibrium preservation, satisfying the well-balanced property for the preset conditions and strongly reducing the spurious fluxes for extreme configurations.

Total Pressure Correction of a Sub-Miniature Five-Hole Probe in Areas of Pressure Gradients

2012 ◽  
Author(s):  
J. Town ◽  
A. Akturk ◽  
C. Camcı
Keyword(s):  
Pressure Measurement ◽  
Measurement Errors ◽  
Total Pressure ◽  
Pressure Gradients ◽  
Pressure Data ◽  
Flow Conditions ◽  
Complex Flow ◽  
Ducted Fan ◽  
The Difference ◽  
Best Fit

Five-hole probes, being a dependable and accurate aerodynamic tools, are excellent choices for measuring complex flow fields. However, total pressure gradients can induce measurement errors. The combined effect of the different flow conditions on the ports causes the measured total pressure to be prone to a greater error. This paper proposes a way to correct the total pressure measurement. The correction is based on the difference between the measured total pressure data of a Kiel probe and a sub-miniature prism-type five-hole probe. By comparing them in a ducted fan related flow field, a line of best fit was constructed. The line of best fit is dependent on the slope of the line in a total pressure versus span and difference in total pressure between the probes at the same location. A computer program, performs the comparison and creates the correction equation. The equation is subsequently applied to the five-hole probe total pressure measurement, and the other dependent values are adjusted. The validity of the correction is then tested by placing the Kiel probe and the five-hole probe in ducted fans with a variety of different tip clearances.

Abstract 15322: Trifecta vs. Mitroflow: Superior Hemodynamics Despite Similar Design

Circulation ◽  
2014 ◽  
Vol 130 (suppl_2) ◽  
Author(s):  
Mahmoud Diab ◽  
Gloria Faerber ◽  
Ivliane Tsanava ◽  
Martin Breuer ◽  
Mario Walther ◽  
...  
Keyword(s):  
Aortic Annulus ◽  
Special Consideration ◽  
Pressure Gradients ◽  
Valve Design ◽  
Innovative Design ◽  
Mean Pressure ◽  
The Difference ◽  
Different Diameters

Purpose: Hemodynamic results of stented tissue valves are influenced by both valve design and sizing strategy. The Mitroflow and the Trifecta have an innovative design where the pericardium is wrapped around the stent. The goal of this study was to compare both valves giving special consideration to the suggested sizing strategies. Methods: We obtained pressure gradients from discharge echocardiograms from all patients having received an isolated Trifecta (n=104) or Mitroflow (n=246) between 01/2007 and 01/2014. We compared the results by size label and by the most likely selected size according to the suggested sizing strategy. This is important because the prostheses, despite having a similar design, have different diameters for the same size label and different sizing strategies. Results: The majority of implanted valves were size labels 21 and 23 (82.7% of the Trifecta and 74.8% of the Mitroflow). Mean pressure radients were lowest with Trifecta (Trifecta vs. Mitroflow, label-21: 11.4±4.65 vs 13.6±5.23 mmHg, label-23: 9.23±3.38 vs. 11.8±4.42 mmHg, p< 0.05, and label-25: 11.2±4.97 vs 12.0±4.46 mmHg, n.s.). The sizers for the Trifecta are metric, while those for the Mitroflow are 2-3 mm larger than the corresponding size label. It is therefore likely that for a patient with a 23 mm aortic annulus, a 23 Trifecta but often only a 21 Mitroflow is selected. Thus, comparing the Trifecta to the Mitroflow not by size label but by selected valve (e.g., 23 vs. 21) would therefore only increase the difference. Conclusion: The Trifecta shows a hemodynamic advantage over the Mitroflow which is not likely associated with the applied sizing strategy.

Predicting Turbulent Boundary Layer Wall Pressure Fluctuations in Adverse Pressure Gradients

2005 ◽  
Author(s):  
Frank J. Aldrich
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Pressure Fluctuations ◽  
Adverse Pressure Gradient ◽  
Wall Pressure ◽  
Prediction Tool ◽  
Pressure Gradients ◽  
Wall Pressure Fluctuations ◽  
The Difference

A physics-based approach is employed and a new prediction tool is developed to predict the wavevector-frequency spectrum of the turbulent boundary layer wall pressure fluctuations for subsonic airfoils under the influence of adverse pressure gradients. The prediction tool uses an explicit relationship developed by D. M. Chase, which is based on a fit to zero pressure gradient data. The tool takes into account the boundary layer edge velocity distribution and geometry of the airfoil, including the blade chord and thickness. Comparison to experimental adverse pressure gradient data shows a need for an update to the modeling constants of the Chase model. To optimize the correlation between the predicted turbulent boundary layer wall pressure spectrum and the experimental data, an optimization code (iSIGHT) is employed. This optimization module is used to minimize the absolute value of the difference (in dB) between the predicted values and those measured across the analysis frequency range. An optimized set of modeling constants is derived that provides reasonable agreement with the measurements.

scholarly journals Electronic interactions in 1D-π-assemblies from TLS analysis of thermal motion

2014 ◽  
Vol 70 (a1) ◽  
pp. C659-C659
Author(s):  
Sergey Lindeman ◽  
Marat Talipov ◽  
Shriya Wadumethrige ◽  
Oleg Dolomanov ◽  
Rajendra Rathore
Keyword(s):  
Charge Transfer ◽  
Graphical Representation ◽  
Electronic Materials ◽  
Variable Temperature ◽  
Supramolecular Assemblies ◽  
Thermal Motion ◽  
Theoretical Interpretation ◽  
Electronic Shell ◽  
Donor Acceptor ◽  
The Difference

Advanced features of TLS analysis within Olex2 program package allow for a detailed analysis of electronic redistribution in supramolecular systems. Particularly, the possibility of calculating TLS tensors in user-defined coordinate systems along with qualitative graphical representation of difference thermal motion are especially useful for analysis of atomic asphericity and intra- and inter-molecular electron redistribution. In addition, these features allow for a directional dynamic analysis of intermolecular motions from variable-temperature experiments. We explored the exciting new possibilities analyzing supramolecular assemblies closely resembling modern electronic materials for a series of electron donor-acceptor complexes and ion-radical salts based on aromatic octamethyl-anthracene and anti-aromatic octamethyl-biphenylene substrates. The difference TLS analysis revealed intimate details of chemical bond polarization and electronic shell expansion for acceptor components along with electronic shell contraction for donor components of the complexes indicative of intra- and intermolecular charge transfer. Also, the variable-temperature analysis of relative thermal motion of the complex components in the crystals revealed some widening of the potential-energy minima in direction of the electronic overlap as a result of intermolecular pi-orbital coupling both in charge-transfer and charge-resonance supramolecular assemblies. A theoretical interpretation of the observed peculiarities was undertaken supported by respective spectroscopic data.

Internally Pressurized Machined Domed Ends—a Comparison of the Plastic Buckling Predictions of the Deformation and Flow Theories

1990 ◽  
Vol 204 (3) ◽  
pp. 169-186 ◽  
Author(s):  
G D Galletly ◽  
J Błachut ◽  
D N Moreton
Keyword(s):  
Failure Mode ◽  
Deformation Theory ◽  
Flow Theory ◽  
Shell Buckling ◽  
Incorrect Prediction ◽  
Bifurcation Buckling ◽  
Initial Geometric Imperfections ◽  
The Difference ◽  
Flow Theories ◽  
Low Amplitude

The present series of tests, involving six machined steel torispherical shells subjected to internal pressure, was designed to highlight the difference in the buckling predictions of the deformation and the flow theories of plasticity. For the geometries selected, deformation theory predicted that bifurcation buckling would occur for all the domes tested, whereas flow theory predicted buckling in only two of them. In the tests, low-amplitude waves (detected by probes) appeared in all six of the domes. In four of the domes, the low-amplitude waves grew with increasing pressure and became buckles which were visible to the naked eye. Assuming that the occurrence of low-amplitude waves can be considered as buckling of a dome, then deformation theory predicted the failure mode correctly in all six cases. Flow theory was correct in only two cases. The agreement between the initial experimental buckling pressures and those predicted by deformation theory was reasonably good, the ratios varying between 0.71 and 0.94. For three of the domes, the buckling pressures were also found by the Southwell plot technique. These latter agreed best with the deformation theory predictions. The shell buckling program used for analysis purposes was BOSOR 5 and its predictions were checked using five other independent shell buckling programs. One reason for the incorrect prediction of the failure mode by flow theory may be the neglect of initial geometric imperfections in the analysis. Some preliminary calculations including them seem to confirm the hypothesis.

Energetic materials: variable-temperature crystal structures of γ- and ∊-HNIW polymorphs

2004 ◽  
Vol 37 (5) ◽  
pp. 808-814 ◽  
Author(s):  
Nadezhda B. Bolotina ◽  
Michaele J. Hardie ◽  
Richard L. Speer Jr ◽  
A. Alan Pinkerton
Keyword(s):  
Thermal Expansion ◽  
Energetic Materials ◽  
Variable Temperature ◽  
Mean Field ◽  
Field Potential ◽  
Atomic Displacement ◽  
Linear Temperature Dependence ◽  
Linear Temperature ◽  
The Difference ◽  
Atomic Displacement Parameters

Crystals of γ- and ∊-hexanitrohexaazaisowurtzitane (γ- and ∊-HNIW, space groupP21/nfor both crystals) have been investigated in the 100–298 K temperature range using single-crystal X-ray diffraction techniques. Temperature-dependent changes of their crystal lattices have been evaluated from the second-rank thermal expansion tensors. Both lattices undergo anisotropic thermal expansion, that of γ-HNIW being more anisotropic than that of the ∊ phase. Comparison with previously reported predictions from molecular dynamics calculations indicates significant differences. Although there are many short (less than van der Waals) intermolecular interactions in both polymorphs, there is no obvious relationship between the short distances and the difference in thermal expansion behavior. Non-linear temperature dependence of the atomic displacement parameters is indicative of anharmonicity of the crystal mean field potential.

scholarly journals Invasive and Doppler Transvalvular gradients after transcatheter aortic valve replacement

2021 ◽  
Vol 42 (Supplement_1) ◽  
Author(s):  
S Fugar ◽  
K Deka ◽  
C Anderson ◽  
C Lama Von Buchwald ◽  
R Geroux ◽  
...  
Keyword(s):  
Aortic Valve ◽  
Valve Replacement ◽  
Pressure Gradients ◽  
Entire Cohort ◽  
Funding Sources ◽  
Transcatheter Aortic Valve ◽  
The Mean ◽  
The Difference ◽  
Transcatheter Valve ◽  
The Relationship

Abstract Background Differences in mean gradients after Transcatheter valve replacement (TAVR) vary depending on the valve type and the modality used to measure the gradients. Currently there is a paucity of data on the relationship between invasive and doppler derived gradients after TAVR. Purpose We sort to assess the difference in doppler, and catheter derived aortic valve gradients after TAVR Methods This is a single center retrospective study using consecutive patients who presented for TAVR on account of native aortic valve stenosis at our institution from May 2012 till December 2020. Patients with both intraoperative invasive and postoperative doppler derived pressure gradients were included in the analysis. Student T-test were used to compare mean gradients. Pearson's correlation test was used to examine the correlation between measured gradients. Results A total of 587 patients were included in our study. Fifty one percent were male and 462 (78.7%) underwent TAVR with a balloon expandable valve. In the entire cohort the mean gradient measured invasively was significantly lower than those measured by echo doppler (4.48±3.25 vs. 5.57±3.11, P&lt;0.001). There, however, was a positive correlation between invasive and doppler measured gradients (figure 1). In those who received balloon expandable valves, the invasive gradient was 4.39±3.30 and the doppler derived gradient was 5.47±3.04 (P&lt;0.001), while in those self-expanding valves, the invasive gradient was 4.81±3.04 and doppler derived gradient was 5.94±3.36 (P&lt;0.001). Conclusion Post TAVR gradients were all significantly lower when measured invasively as compared to those measured using doppler. Self-expanding valves overall had higher residual gradients. Further studies are needed to assess the correlations between invasively measured gradients and clinical outcomes post TAVR. FUNDunding Acknowledgement Type of funding sources: None.

Visualisation of Turbulent Wedges Under Favourable Pressure Gradients Using Both Shear-Sensitive and Temperature-Sensitive Liquid Crystals

2002 ◽  
Author(s):  
S. Zhong ◽  
T. P. Chong ◽  
H. P. Hodson
Keyword(s):  
Liquid Crystals ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Turbine Blades ◽  
Temperature Sensitive ◽  
Shear Stresses ◽  
Pressure Gradients ◽  
Surface Shear ◽  
The Difference ◽  
Thermal Boundary Layers

Turbulent wedges induced by a 3D surface roughness placed in a laminar boundary layer over a flat plate were visualised for the first time using both shear-sensitive and temperature-sensitive liquid crystals. The experiments were carried out at three different levels of favourable pressure gradients. The purpose of this investigation was to examine the spreading angles of the turbulent wedges indicated by their associated surface shear stresses and heat transfer characteristics and hence obtain further insight about the difference in the behaviour of transitional momentum and thermal boundary layers when a streamwise pressure gradient exists. It was shown that under a zero pressure gradient the spreading angles indicated by the two types of liquid crystals are the same, but the difference increases as the level of favourable pressure gradient increases. The result from the present study could have an important implication to the transition modelling of thermal boundary layers over gas turbine blades.

TEST AND QUALIFICATION OF A VARIABLE TEMPERATURE VIBRATING SAMPLE MAGNETOMETER SYSTEM FOR THE MEASUREMENT OF MAGNETIZATION CYCLES UP TO +/-12T IN THE 4.2K-300K TEMPERATURE RANGE

2000 ◽  
Vol 14 (25n27) ◽  
pp. 2914-2919
Author(s):  
M. CLOTTI ◽  
P. GISLON ◽  
M. MORONI ◽  
M. SPADONI ◽  
T. PETRISOR ◽  
...  
Keyword(s):  
Measurement Accuracy ◽  
Variable Temperature ◽  
Reference Signal ◽  
Calibration Procedure ◽  
Vibrating Sample Magnetometer ◽  
Sensor Reading ◽  
Magnetization Data ◽  
Order Of Magnitude ◽  
The Difference ◽  
Made In

A complete characterisation of an Oxford Instruments Vibrating Sample Magnetometer (VSM) has been made in order to check the limits and the reproducibility of the system as well as the measurement accuracy. Several measurement cycles have then been carried out to check the extent of the difference between the actual sample temperature and the sensor reading, and the weight of this difference on the magnetization data as a function of the temperature. Moreover an unexpected lowering of a reference signal has been observed at low temperatures, most probably due to shielding currents in the structure; this effect influences the sample signals, and has to be taken into account during data analysis. Being the magnetization a relative measurement, a great attention must be paid to the calibration procedure. Calibrations with 99.999% pure Nickel and Palladium, which have magnetization signals two order of magnitude apart, give comparable calibration constants. We observed that in order to have high accuracy measurements, the calibration has to be performed on samples geometrically identical to the test ones, and periodically repeated. The repeatability of the measurements has been found to be ±1%; once corrected the image current effect, the accuracy of the measurements, at 4.2 K, is ±3%. This value was also confirmed by the direct comparison of our results with those obtained at National Institute of Standards and Technology (NIST) on the same Nb 3 Sn samples

Observations and Modeling of Banded Orographic Convection

2005 ◽  
Vol 62 (5) ◽  
pp. 1463-1479 ◽  
Author(s):  
Daniel J. Kirshbaum ◽  
Dale R. Durran
Keyword(s):  
Numerical Simulations ◽  
Vertical Shear ◽  
Convective Precipitation ◽  
Small Scale ◽  
Radar Images ◽  
Topographic Roughness ◽  
Roughness Elements ◽  
Orographic Convection ◽  
The Difference ◽  
Low Amplitude

Abstract Radar images and numerical simulations of three shallow convective precipitation events over the Coastal Range in western Oregon are presented. In one of these events, unusually well-defined quasi-stationary banded formations produced large precipitation enhancements in favored locations, while varying degrees of band organization and lighter precipitation accumulations occurred in the other two cases. The difference between the more banded and cellular cases appeared to depend on the vertical shear within the orographic cap cloud and the susceptibility of the flow to convection upstream of the mountain. Numerical simulations showed that the rainbands, which appeared to be shear-parallel convective roll circulations that formed within the unstable orographic cap cloud, developed even over smooth mountains. However, these banded structures were better organized, more stationary, and produced greater precipitation enhancement over mountains with small-scale topographic obstacles. Low-amplitude random topographic roughness elements were found to be just as effective as more prominent subrange-scale peaks at organizing and fixing the location of the orographic rainbands.

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