Hydromagnetic instability of a resistive hollow jet

2008 ◽  
Vol 86 (9) ◽  
pp. 1117-1124
Author(s):  
A E Radwan
Keyword(s):  
Magnetic Field ◽  
Stability Criterion ◽  
Electromagnetic Force ◽  
High Intensity ◽  
Stability Criteria ◽  
Axisymmetric Mode ◽  
Jet Instability ◽  
Hydromagnetic Instability ◽  
Mhd Stability ◽  
Capillary Pressure Gradient

The magnetohydrodynamic (MHD) stability criterion of a resistive hollow cylinder with respect to its capillary, pressure gradient, and electromagnetic forces is established. Numerous stability criteria are obtained as limiting cases from the present relation. The capillary force is destabilizing only for certain wavelengths to axisymmetric mode and stable to all other disturbances. There are three different cases for discussing the electromagnetic force (EMF) influence on the resistive hollow jet instability. As the fluid is with finite resistivity, the EMF does not have any influence on the capillary instability of a resistive hollow jet, however, the finite resistivity has a stabilizing tendency on the MHD hollow jet. As the fluid has infinite resistivity, the EMF is (de-)stabilizing according to restrictions. As the fluid is with zero resistivity, the EMF exerts an influence giving a sort of rigidity to the conducting fluid and that influence causes the bending and twisting of the lines of force in the fluid. Consequently, for a magnetic field of high intensity the capillary destabilization could be suppressed and stability arises.PACS No.: 47.17+e

Magnetohydrodynamic stability of a streaming gas jet

1993 ◽  
Vol 49 (1) ◽  
pp. 3-15
Author(s):  
Samia S. Elazab
Keyword(s):  
Magnetic Field ◽  
Capillary Force ◽  
Electromagnetic Force ◽  
Radial Distance ◽  
Gas Jet ◽  
Axisymmetric Perturbation ◽  
Mhd Stability ◽  
The Magnetic Field

The MHD stability of a gas jet surrounded by a streaming radially finite liquid cylinder (with solid cylindrical edge) is studied. The system is acted upon by capillary, electromagnetic and inertial liquid forces. The eigenvalue relation is established to all kinds of perturbations. The streaming has a strong destabilizing influence that is independent of all problem parameters. The capillary force is destabilizing only for small axisymmetric modes and stable for the rest. The electromagnetic force is strongly stabilizing whatever the intensities of the magnetic field. If the influence of the latter is sufficiently strong, the influence of the streaming can be completely suppressed. It is found that for an axisymmetric perturbation the domain of instability is the same whatever the value of the liquid radial distance.

scholarly journals HYDROMAGNETIC STABILITY OF STREAMING COMPRESSIBLE CYLINDER PERVADED BY MAGNETIC FIELD

2014 ◽  
Vol 12 (4) ◽  
pp. 3421-3427
Author(s):  
Shimaa L. Azwz
Keyword(s):  
Magnetic Field ◽  
Surface Tension ◽  
Axial Magnetic Field ◽  
Wave Length ◽  
Magnetic Intensity ◽  
Axisymmetric Mode ◽  
Small Wave ◽  
Mhd Stability ◽  
The Stability ◽  
Compressible Cylinder

The Stability of MHD compressible streaming fluid cylinder of radius endowed with surface tension and pervaded by axial magnetic field has been developed. The stability criterion is established in general form. The model is capillary unstable only in the axisymmetric mode m=0, the electromagnetic forces acting interior and exterior the fluid cylinder are stabilizing and the MHD stability is destabilizing for small wave length. In the latter case the instability shrinks with increasing the magnetic intensity. However the compressibility has a stabilizing tendency.

scholarly journals Stability of a Viscous Liquid Jet in a Coaxial Twisting Compressible Airflow

Processes ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 918
Author(s):  
Li-Mei Guo ◽  
Ming Lü ◽  
Zhi Ning
Keyword(s):  
Viscous Liquid ◽  
Axial Velocity ◽  
Liquid Velocity ◽  
Velocity Ratio ◽  
Dominant Mode ◽  
Liquid Jet ◽  
Axisymmetric Mode ◽  
Jet Instability ◽  
Jet Stability ◽  
Jet Breakup

Based on the linear stability analysis, a mathematical model for the stability of a viscous liquid jet in a coaxial twisting compressible airflow has been developed. It takes into account the twist and compressibility of the surrounding airflow, the viscosity of the liquid jet, and the cavitation bubbles within the liquid jet. Then, the effects of aerodynamics caused by the gas–liquid velocity difference on the jet stability are analyzed. The results show that under the airflow ejecting effect, the jet instability decreases first and then increases with the increase of the airflow axial velocity. When the gas–liquid velocity ratio A = 1, the jet is the most stable. When the gas–liquid velocity ratio A > 2, this is meaningful for the jet breakup compared with A = 0 (no air axial velocity). When the surrounding airflow swirls, the airflow rotation strength E will change the jet dominant mode. E has a stabilizing effect on the liquid jet under the axisymmetric mode, while E is conducive to jet instability under the asymmetry mode. The maximum disturbance growth rate of the liquid jet also decreases first and then increases with the increase of E. The liquid jet is the most stable when E = 0.65, and the jet starts to become more easier to breakup when E = 0.8425 compared with E = 0 (no swirling air). When the surrounding airflow twists (air moves in both axial and circumferential directions), given the axial velocity to change the circumferential velocity of the surrounding airflow, it is not conducive to the jet breakup, regardless of the axisymmetric disturbance or asymmetry disturbance.

Intrinsic Thermal Stability of Anisotropic Thin-Film Superconductors

1990 ◽  
Vol 112 (1) ◽  
pp. 10-15 ◽  
Author(s):  
M. I. Flik ◽  
C. L. Tien
Keyword(s):  
Thin Film ◽  
Thermal Stability ◽  
Stability Criterion ◽  
High Temperature Superconductors ◽  
Stability Criteria ◽  
Anisotropic Thermal Conductivity ◽  
Operating Current ◽  
Released Energy ◽  
The Stability ◽  
Thermal Stability Of

Intrinsic thermal stability denotes a situation where a superconductor can carry the operating current without resistance at all times after the occurrence of a localized release of thermal energy. This novel stability criterion is different from the cryogenic stability criteria for magnets and has particular relevance to thin-film superconductors. Crystals of ceramic high-temperature superconductors are likely to exhibit anisotropic thermal conductivity. The resultant anisotropy of highly oriented films of superconductors greatly influences their thermal stability. This work presents an analysis for the maximum operating current density that ensures intrinsic stability. The stability criterion depends on the amount of released energy, the Biot number, the aspect ratio, and the ratio of the thermal conductivities in the plane of the film and normal to it.

Evaluation of the Dynamic-Response-Based Intact Stability Criterion for Floating Wind Turbines

2015 ◽  
Author(s):  
Marco Masciola ◽  
Xiaohong Chen ◽  
Qing Yu
Keyword(s):  
Wind Speed ◽  
Dynamic Response ◽  
Wind Turbines ◽  
Stability Criterion ◽  
Area Ratio ◽  
Operating Conditions ◽  
Dynamic Responses ◽  
Stability Criteria ◽  
Intact Stability ◽  
Overturning Moment

As an alternative to the conventional intact stability criterion for floating offshore structures, known as the area-ratio-based criterion, the dynamic-response-based intact stability criteria was initially developed in the 1980s for column-stabilized drilling units and later extended to the design of floating production installations (FPIs). Both the area-ratio-based and dynamic-response-based intact stability criteria have recently been adopted for floating offshore wind turbines (FOWTs). In the traditional area-ratio-based criterion, the stability calculation is quasi-static in nature, with the contribution from external forces other than steady wind loads and FOWT dynamic responses captured through a safety factor. Furthermore, the peak wind overturning moment of FOWTs may not coincide with the extreme storm wind speed normally prescribed in the area-ratio-based criterion, but rather at the much smaller rated wind speed in the power production mode. With these two factors considered, the dynamic-response-based intact stability criterion is desirable for FOWTs to account for their unique dynamic responses and the impact of various operating conditions. This paper demonstrates the implementation of a FOWT intact stability assessment using the dynamic-response-based criterion. Performance-based criteria require observed behavior or quantifiable metrics as input for the method to be applied. This is demonstrated by defining the governing load cases for two conceptual FOWT semisubmersible designs at two sites. This work introduces benchmarks comparing the area-ratio-based and dynamic-response-based criteria, gaps with current methodologies, and frontier areas related to the wind overturning moment definition.

scholarly journals The Simulation and Optimization of an Electromagnetic Field in a Vertical Continuous Casting Mold for a Large Bloom

Metals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 516
Author(s):  
Lianwang Zhang ◽  
Changjun Xu ◽  
Jiazheng Zhang ◽  
Tao Wang ◽  
Jing Li ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Continuous Casting ◽  
Electromagnetic Force ◽  
Three Dimensional ◽  
Electromagnetic Stirring ◽  
Current Intensity ◽  
Continuous Casting Mold ◽  
Current Frequency ◽  
Simulation And Optimization ◽  
Electromagnetic Model

The electromagnetic model of a large-bloom continuous casting was established to simulate the magnetic field. The model 3600 digital, high-precision, three-dimensional Gaussian meter was used to measure the internal magnetic field of mold electromagnetic stirring (M-EMS). The distribution of simulated magnetic field was basically consistent with that of the measured magnetic field; the accuracy of electromagnetic stirring model was verified. With the increase of current frequency, the electromagnetic force first increases and then decreases; when the current frequency is 9 Hz, the electromagnetic force reaches its maximum value. A bipolar electromagnetic stirring model is proposed; the influence of current intensity and distance were investigated. With the increase of current intensity of lower mold electromagnetic stirring (M-EMSB), the internal magnetic intensity of upper mold electromagnetic stirring (M-EMSA) gradually increases, and the middle region is gradually filled by magnetic field. With the increase of the distance, the range of the low-intensity magnetic field expands. When the current intensity of the M-EMSB is 320 A, and the distance is 400 mm, an 8 mT uniform magnetic field in the range of 1.2 m is formed. Compared with the traditional continuous casting electromagnetic agitator, the center equiaxial crystal of bipolar electromagnetic agitator increases from 30.3% to 49.5%.

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