Convergent Richtmyer–Meshkov instability of a heavy gas layer with perturbed outer interface

2019 ◽  
Vol 878 ◽  
pp. 277-291 ◽  
Author(s):  
Juchun Ding ◽  
Jianming Li ◽  
Rui Sun ◽  
Zhigang Zhai ◽  
Xisheng Luo
Keyword(s):  
Growth Rate ◽  
Layer Thickness ◽  
High Speed ◽  
Coupling Effect ◽  
Soap Film ◽  
Interface Coupling ◽  
Outer Interface ◽  
Heavy Gas ◽  
Gas Layer ◽  
Late Stages

The evolution of an $\text{SF}_{6}$ layer surrounded by air is experimentally studied in a semi-annular convergent shock tube by high-speed schlieren photography. The gas layer with a sinusoidal outer interface and a circular inner interface is realized by the soap-film technique such that the initial condition is well controlled. Results show that the thicker the gas layer, the weaker the interface–coupling effect and the slower the evolution of the outer interface. Induced by the distorted transmitted shock and the interface coupling, the inner interface exhibits a slow perturbation growth which can be largely suppressed by reducing the layer thickness. After the reshock, the inner perturbation increases linearly at a growth rate independent of the initial layer thickness as well as of the outer perturbation amplitude and wavelength, and the growth rate can be well predicted by the model of Mikaelian (Physica D, vol. 36, 1989, pp. 343–357) with an empirical coefficient of 0.31. After the linear stage, the growth rate decreases continuously, and finally the perturbation freezes at a constant amplitude caused by the successive stagnation of spikes and bubbles. The convergent geometry constraint as well as the very weak compressibility at late stages are responsible for this instability freeze-out.

The Richtmyer–Meshkov instability of a ‘V’ shaped air/ interface

2016 ◽  
Vol 802 ◽  
pp. 186-202 ◽  
Author(s):  
Xisheng Luo ◽  
Ping Dong ◽  
Ting Si ◽  
Zhigang Zhai
Keyword(s):  
Growth Rate ◽  
High Speed ◽  
Initial Conditions ◽  
Monotone Function ◽  
Flow Characteristics ◽  
Soap Film ◽  
Vertex Angle ◽  
Initial Growth ◽  
General Behaviour ◽  
Interface Width

The Richtmyer–Meshkov instability on a ‘V’ shaped air/SF$_{6}$ gaseous interface is experimentally studied in a shock tube. By the soap film technique, a discontinuous interface without supporting mesh is formed so that the initial conditions of the interface can be accurately controlled. Five ‘V’ shaped air/$\text{SF}_{6}$ interfaces with different vertex angles ($60^{\circ }$, $90^{\circ }$, $120^{\circ }$, $140^{\circ }$ and $160^{\circ }$) are created where the ratio of the initial interface amplitude to the wavelength varies to highlight the effects of initial condition on the flow characteristics. The wave patterns and interface morphologies are clearly identified in the high-speed schlieren sequences, which show that the interface deforms in a less pronounced manner with less vortices generated as the vertex angle increases. A regime change is observed in the interface width growth rate near a vertex angle of $160^{\circ }$, which provides an experimental evidence for the numerical results obtained by McFarland et al. (Phys. Scr. vol. T155, 2013, 014014). The growth rate of interface width in the linear phase is compared with the theoretical predictions from the classical impulsive model and a modified linear model, and the latter is proven to be effective for a moderate to large initial amplitude. It is found that the initial growth rate of the interface width is a non-monotone function of the initial vertex angle (amplitude–wavelength ratio), i.e. the interface width growth rate in the linear stage experiences an increase and then a decrease as the vertex angle increases. A similar conclusion was also reached by Dell et al. (Phys. Plasmas, vol. 22, 2015, 092711) numerically for a sinusoidal interface. Finally, the general behaviour of the interface width growth in the nonlinear stage can be well captured by the nonlinear model proposed by Dimonte & Ramaprabhu (Phys. Fluids, vol. 22, 2010, 014104).

scholarly journals On the interaction of a planar shock with a light polygonal interface

2014 ◽  
Vol 757 ◽  
pp. 800-816 ◽  
Author(s):  
Zhigang Zhai ◽  
Minghu Wang ◽  
Ting Si ◽  
Xisheng Luo
Keyword(s):  
High Speed ◽  
Vortex Pair ◽  
Soap Film ◽  
Remarkable Feature ◽  
Planar Shock ◽  
Shock Impact ◽  
Planar Shock Wave ◽  
Left Corner ◽  
Interface Structures ◽  
Late Stages

AbstractThe interaction of a planar shock wave with a polygonal $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}{\mathrm{N}}_2$ volume surrounded by ${\mathrm{SF}}_6$ is investigated experimentally and numerically. Three polygonal interfaces (square, triangle and diamond) are formed by the soap film technique developed in our previous work, in which thin pins are introduced as angular vertexes to connect adjacent sides of polygonal soap films. The evolutions of the shock-accelerated polygonal interfaces are then visualized by a high-speed schlieren system. Wave systems and interface structures can be clearly identified in experimental schlieren images, and agree well with the numerical ones. Quantitatively, the movement of the distorted interface, and the length and height of the interface structures are further compared and good agreements are achieved between experimental and numerical results. It is found that the evolution of these polygonal interfaces is closely related to their initial shapes. In the square interface, two vortices are generated shortly after the shock impact around the left corner and dominate the flow field at late stages. In the triangular and diamond cases, the most remarkable feature is the small ‘${\mathrm{SF}}_6$ jet’ which grows constantly with time and penetrates the downstream boundary of the interface, forming two independent vortices. These distinct morphologies of the three polygonal interfaces also lead to the different behaviours of the interface features including the length and height. It is also found that the velocities of the vortex pair predicted from the theory of Rudinger and Somers (J. Fluid Mech., vol. 7, 1960, pp. 161–176) agree with the experimental ones, especially for the square case. Typical free precursor irregular refraction phenomena and the transitions among them are observed and analysed, which gives direct experimental evidence for wave patterns and their transitions at a slow/fast interface. The velocities of triple points and shocks are experimentally measured. It is found that the transmitted shock near the interface boundary has weakened into an evanescent wave.

On shock-induced light-fluid-layer evolution

2021 ◽  
Vol 933 ◽  
Author(s):  
Yu Liang ◽  
Xisheng Luo
Keyword(s):  
Layer Thickness ◽  
Coupling Effect ◽  
Fluid Layer ◽  
Nonlinear Models ◽  
Interfacial Instability ◽  
Dimensional Theory ◽  
One Dimensional ◽  
Helium Gas ◽  
Wave Patterns ◽  
Thickness Variations

Shock-induced light-fluid-layer evolution is firstly investigated experimentally and theoretically. Specifically, three quasi-one-dimensional helium gas layers with different layer thicknesses are generated to study the wave patterns and interface motions. Six quasi-two-dimensional helium gas layers with diverse layer thicknesses and amplitude combinations are created to explore the Richtmyer–Meshkov instability of a light-fluid layer. Due to the multiple reflected shocks reverberating inside a light-fluid layer, the speeds of the two interfaces gradually converge, and the layer thickness saturates eventually. A general one-dimensional theory is adopted to describe the two interfaces’ motions and the layer thickness variations. It is found that, for the first interface, the end time of its phase reversal determines the influence of the reflected shocks on it. However, the reverberated shocks indeed lead to the second interface being more unstable. When the two interfaces are initially in phase, and the initial fluid layer is very thin, the two interfaces’ spike heads collide and stabilise the two interfaces. Linear and nonlinear models are successfully adopted by considering the interface-coupling effect and the reverberated shocks to predict the two interfaces’ perturbation growths in all regimes. The interfacial instability of a light-fluid layer is quantitatively compared with that of a heavy-fluid layer. It is concluded that the kind of waves reverberating inside a fluid layer significantly affects the fluid-layer evolution.

Modeling and Optimization Design of Signal Interconnect Channel Considering Signal Integrity in Three Dimensional Integrated Circuits

2021 ◽  
Vol 16 (5) ◽  
pp. 773-780
Author(s):  
Bing-Jie Li ◽  
Zhen-Song Li ◽  
Yan-Ping Zhao ◽  
Zheng-Wang Li ◽  
Min Miao
Keyword(s):  
Performance Optimization ◽  
High Speed ◽  
Optimization Design ◽  
Channel Model ◽  
Transmission Loss ◽  
Coupling Effect ◽  
Signal Integrity ◽  
Signal Transmission ◽  
Equivalent Circuit Model ◽  
Transmission Performance

The signal integrity (SI) analysis of a high-speed signal interconnect channel composed of through silicon vias (TSVs) and horizontal re-distribution layers (RDL) is carried out, and the problems of SI, such as transmission loss, crosstalk and coupling effect in the transmission channel, are analyzed and studied. These signal integrity issues are considered in this paper, a signal interconnect channel model is proposed and the equivalent circuit model is deduced as well. Compared with the traditional one, this interconnect channel model has better performance in SI. Further sweep frequency analysis is carried out for different material parameters to achieve signal transmission performance optimization aimed at this model. Test samples of the proposed signal interconnect channel model are designed and fabricated according to the process index, and measured to verify the actual transmission performance. The design and optimization rule of high-speed signal interconnect channel are summarized which proved that the proposed structure has more advantages in signal transmission performance, and has important guiding significance for practical design.

scholarly journals Economic Growth and Unemployment Nexus in USA

2019 ◽  
Vol 8 (4) ◽  
pp. 1317-1325
Keyword(s):  
Growth Rate ◽  
Error Correction ◽  
Unemployment Rate ◽  
High Speed ◽  
Empirical Relationship ◽  
Var Model ◽  
Output Gap ◽  
Causality Test ◽  
Vector Error Correction ◽  
Vector Error

Empirical relationship between unemployment and growth is not pronounced as we investigate the economic scenario of the nations. Author attempted to relate US unemployment rate to the growth during 1948-2016 by using bivariate and log regression models, Bai-Perron Model, Granger Causality test, Johansen cointegration test, vector auto regression and vector error correction models. Even, author also verified relationship between unemployment gap, output gap and growth in USA during the same period. Data on US unemployment rate, GDP and growth rate have been taken from Bureau of US census during 1948-2016. Data on US natural rate of unemployment was taken from Fed Bank of St.Louis from 1949 to 2016.The paper concludes that US unemployment rate is increasing at the rate of 0.507 per cent per annum and it has upward structural break in 1971.The nexus follows the Okun’s law in USA. US unemployment is negatively related with growth rate during 1948-2016.Their relationships are causal and cointegrated. VAR model is stable and stationary. Residual test showed non-normality and autocorrelations.Moreover, author showed negative relation between growth and unemployment gap in USA during 1949-2016.They have no causality and cointegration. Their VAR model is stable and stationary. The residual test proved non-normality and auto-correlation problems. Perceptible output gap influences unemployment gap negatively during 1949-2016 .It has significant bi-directional causality and one cointegrating equation. In Vector error correction model, error corrections are significant with high speed having stability, autocorrelation and non-normality. The rate of decline in unemployment rate due to increased growth rate in USA during 1948-2016 was marginal.

scholarly journals A water droplet-cleaning of a dusty hydrophobic surface: influence of dust layer thickness on droplet dynamics

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Ghassan Hassan ◽  
Bekir S. Yilbas ◽  
Saeed Bahatab ◽  
Abdullah Al-Sharafi ◽  
Hussain Al-Qahtani
Keyword(s):  
Layer Thickness ◽  
Inclination Angle ◽  
Water Droplet ◽  
High Speed ◽  
Small Volume ◽  
Transition Period ◽  
Imaging System ◽  
Hydrophobic Surface ◽  
Dust Layer ◽  
Surface Inclination

Abstract Water droplet cleaning of a dusty hydrophobic surface is examined. Environmental dust are used in the experiments and cloaking velocity of a dust layer by a droplet fluid is measured and hemi-wicking conditions for the dust layer are analyzed adopting the pores media wick structure approach. A droplet motion on dusty and inclined hydrophobic surface is analyzed using a high speed digital imaging system. Influences of dust layer thickness, droplet volume, and surface inclination angle on the mechanisms of dust removal by a rolling droplet are evaluated. The findings revealed that dust cloaking velocity decreases exponentially with time. The droplet fluid can cloak the dust layer during its transition on the dusty surface. The transition period of droplet wetted length on the dusty surface remains longer than the cloaking time of the dust layer by the droplet fluid. Translational velocity of rolling droplet is affected by the dust layer thickness, which becomes apparent for small volume droplets. Small volume droplet (20 µL) terminates on the thick dust layer (150 µm) at low surface inclination angle (1°). The quantity of dust picked up by the rolling droplet increases as the surface inclination angle increases. The amount of dust residues remaining on the rolling droplet path is relatively larger for the thick dust layer (150 µm) as compared to its counterpart of thin dust layer (50 µm).

Closed Loop Performance of a Slotless Lorentz Self-Bearing Motor

2003 ◽  
Author(s):  
Hooi-Mei Chin ◽  
L. Scott Stephens
Keyword(s):  
High Speed ◽  
Closed Loop ◽  
Coupling Effect ◽  
Cross Coupling ◽  
Motor Design ◽  
High Speed Rotation ◽  
Bearing Stiffness ◽  
Speed Rotation ◽  
Power Densities ◽  
Tangential Directions

In previous work the authors presented a Lorentz self-bearing motor design targeted for precision pointing and smooth angular slewing applications. The motor also offers potential advantages when operated as a synchronous machine at high speed including larger power densities and shorter shafts. In this paper, the closed loop performance of the motor at low transient speeds (0–588 rpm) is presented. Using these results, several challenges to achieving high-speed rotation are identified and discussed. The most significant is the heavy cross coupling within the actuator which limits bearing stiffness and stability, and is amplified at rotor natural frequencies resulting in potential loss of levitation when passing through critical speeds. Of particular interest is the discovery of a significant cross coupling effect between the radial and tangential directions. A theory is put forth explaining this effect.

Study on the interface coupling effect in PbZr0.52Ti0.48O3/Ba(Mg1/3Ta2/3)O3 thin films

2019 ◽  
Vol 30 (15) ◽  
pp. 14490-14494
Author(s):  
Zhi Wu ◽  
Wen Chen ◽  
Jing Zhou ◽  
Jie Shen ◽  
Xiong Yang ◽  
...  
Keyword(s):  
Thin Films ◽  
Coupling Effect ◽  
Interface Coupling
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