Entrainment and mixing dynamics of surface-stress-driven stratified flow in a cylinder

2012 ◽  
Vol 691 ◽  
pp. 498-517 ◽  
Author(s):  
A. Shravat ◽  
C. Cenedese ◽  
C. P. Caulfield
Keyword(s):  
Surface Stress ◽  
High Frequency ◽  
Rotating Disk ◽  
Disk Drive ◽  
Time Dependent ◽  
Characteristic Velocity ◽  
Cylindrical Tank ◽  
Rate Of Increase ◽  
Mixing Dynamics ◽  
Probe Measurements

AbstractWe extend previous work of Boyer, Davies & Guo (Fluid Dyn. Res., vol. 21, 1997, pp. 381–401) to consider the evolution of an initially two-layer stratified fluid in a cylindrical tank which is driven by a horizontal rotating disk. The turbulent motions induced by the disk drive entrainment at the interface, and similarly to the results of Boyeret al. (1997), the layer nearer to the disk deepens. Through high-frequency conductivity probe measurements, we establish that the deepening layer is very well-mixed, and the thickness of the interface between the two evolving layers appears to be approximately constant. Under certain circumstances, we find that the rate of increase in depth of the deepening layer decreases with time, at variance with the results of Boyeret al. (1997), and implying that the characteristic velocity in the deepening layer decreases as the upper layer deepens. We propose that such time-dependent deepening, and the associated weakening of the upper-layer velocities, occurs naturally because of the combined power requirements of entrainment and layer homogenization which inhibit, when the stratification is very strong, the characteristic velocities of the deepening layer approaching the (constant) velocities of the driving disk, as assumed by Boyeret al. (1997).

scholarly journals Entrainment and mixed layer dynamics of a surface-stress-driven stratified fluid

2015 ◽  
Vol 765 ◽  
pp. 653-667 ◽  
Author(s):  
G. E. Manucharyan ◽  
C. P. Caulfield
Keyword(s):  
Potential Energy ◽  
Mixed Layer ◽  
Surface Stress ◽  
Stratified Fluid ◽  
Balance Model ◽  
Buoyancy Frequency ◽  
Characteristic Velocity ◽  
Rate Of Increase ◽  
Mixed Layers ◽  
Entrainment Mixing

AbstractWe consider experimentally an initially quiescent and linearly stratified fluid with buoyancy frequency $N_{Q}$ in a cylinder subject to surface-stress forcing from a disc of radius $R$ spinning at a constant angular velocity ${\rm\Omega}$. We observe the growth of the disc-adjacent turbulent mixed layer bounded by a sharp primary interface with a constant characteristic thickness $l_{I}$. To a good approximation the depth of the forced mixed layer scales as $h_{F}/R\sim (N_{Q}/{\rm\Omega})^{-2/3}({\rm\Omega}t)^{2/9}$. Generalising the previous arguments and observations of Shravat et al. (J. Fluid Mech., vol. 691, 2012, pp. 498–517), we show that such a deepening rate is consistent with three central assumptions that allow us to develop a phenomenological energy balance model for the entrainment dynamics. First, the total kinetic energy of the deepening mixed layer $\mathscr{E}_{KF}\propto h_{F}u_{F}^{2}$, where $u_{F}$ is a characteristic velocity scale of the turbulent motions within the forced layer, is essentially independent of time and the buoyancy frequency $N_{Q}$. Second, the scaled entrainment parameter $E={\dot{h}}_{F}/u_{F}$ depends only on the local interfacial Richardson number $Ri_{I}=(N_{Q}^{2}h_{F}l_{I})/(2u_{F}^{2})$. Third, the potential energy increase (due to entrainment, mixing and homogenisation throughout the deepening mixed layer) is driven by the local energy input at the interface, and hence is proportional to the third power of the characteristic velocity $u_{F}$. We establish that internal consistency between these assumptions implies that the rate of increase of the potential energy (and hence the local mass flux across the primary interface) decreases with $Ri_{I}$. This observation suggests, as originally argued by Phillips (Deep-Sea Res., vol. 19, 1972, pp. 79–81), that the mixing in the vicinity of the primary interface leads to the spontaneous appearance of secondary partially mixed layers, and we observe experimentally such secondary layers below the primary interface.

Time-resolved curling-probe measurements of electron density in high frequency pulsed DC discharges

2015 ◽  
Vol 55 (1) ◽  
pp. 016101 ◽  
Author(s):  
Anil Pandey ◽  
Wataru Sakakibara ◽  
Hiroyuki Matsuoka ◽  
Keiji Nakamura ◽  
Hideo Sugai
Keyword(s):  
Electron Density ◽  
High Frequency ◽  
Time Resolved ◽  
Pulsed Dc ◽  
Probe Measurements

Vibration Measurement and Monitoring of a Rotating Disk Using Contactless Laser Excitation

2013 ◽  
Author(s):  
Itsuro Kajiwara ◽  
Naoki Hosoya
Keyword(s):  
Laser Doppler Vibrometer ◽  
Rotating Disk ◽  
Disk Drive ◽  
Vibration Characteristics ◽  
Vibration Measurement ◽  
Testing System ◽  
Rotating Disks ◽  
Vibration Testing ◽  
Structural Surface ◽  
Theoretical Analyses

This paper proposes a contactless vibration testing system for rotating disks based on an impulse response excited by a laser ablation. High power YAG pulse laser is used in this system for producing an ideal impulse force on structural surface without contact. The contactless vibration testing system is composed of a YAG laser, laser Doppler vibrometer and spectrum analyzer. This system makes it possible to measure vibration characteristics of structures under operation, such as vibration measurement of a rotating disk. The effectiveness of this system is confirmed by experimental and theoretical analyses. In this paper, a platter of hard disk drive is employed as an experimental object. Vibration characteristics of a rotating and non-rotating platter are measured and compared with the results of theoretical analysis.

Nonlinear Resonant Motion of Traveling Waves in Rotating Disks

2000 ◽  
Author(s):  
Albert C. J. Luo ◽  
Chin An Tan
Keyword(s):  
Traveling Waves ◽  
Rotation Speed ◽  
Rotating Disk ◽  
Disk Drive ◽  
Computer Memory ◽  
Rotating Disks ◽  
Resonant Wave ◽  
Linear And Nonlinear ◽  
Resonant Spectrum ◽  
Disk Drive Industry

Abstract The resonant conditions for traveling waves in rotating disks are derived. The nonlinear resonant spectrum of a rotating disk is computed from the resonant conditions. Such a resonant spectrum is useful for the disk drive industry to determine the range of operational rotation speed. The resonant wave motions for linear and nonlinear, rotating disks are simulated numerically for a 3.5-inch diameter computer memory disk.

A One Dimensional, Time Dependent Inlet / Engine Numerical Simulation for Aircraft Propulsion Systems

1997 ◽  
Author(s):  
Doug Garrard ◽  
Milt Davis ◽  
Steve Wehofer ◽  
Gary Cole
Keyword(s):  
Numerical Simulation ◽  
Gas Turbine ◽  
High Frequency ◽  
Gas Turbine Engine ◽  
Simulation System ◽  
Time Dependent ◽  
Propulsion Systems ◽  
Turbine Engine ◽  
One Dimensional ◽  
Supersonic Inlet

The NASA Lewis Research Center (LeRC) and the Arnold Engineering Development Center (AEDC) have developed a closely coupled computer simulation system that provides a one dimensional, high frequency inlet / engine numerical simulation for aircraft propulsion systems. The simulation system, operating under the LeRC-developed Application Portable Parallel Library (APPL), closely coupled a supersonic inlet with a gas turbine engine. The supersonic inlet was modeled using the Large Perturbation Inlet (LAPIN) computer code, and the gas turbine engine was modeled using the Aerodynamic Turbine Engine Code (ATEC). Both LAPIN and ATEC provide a one dimensional, compressible, time dependent flow solution by solving the one dimensional Euler equations for the conservation of mass, momentum, and energy. Source terms are used to model features such as bleed flows, turbomachinery component characteristics, and inlet subsonic spillage while unstarted. High frequency events, such as compressor surge and inlet unstart, can be simulated with a high degree of fidelity. The simulation system was exercised using a supersonic inlet with sixty percent of the supersonic area contraction occurring internally, and a GE J85-13 turbojet engine.

Discrete-Time H-Infinity Synthesis of Frequency-Shaped Sliding Mode Control for Suppression of Vibration With Multiple Peak Frequencies

2016 ◽  
Author(s):  
Minghui Zheng ◽  
Masayoshi Tomizuka
Keyword(s):  
High Frequency ◽  
Sliding Mode ◽  
Disk Drive ◽  
Sliding Surface ◽  
Surface Dynamics ◽  
H Infinity ◽  
High Frequencies ◽  
Multiple Peak ◽  
Significant Performance ◽  
The Stability

Vibration with multiple large peaks at high frequencies may cause significant performance degradation and have become a major concern in modern high precision control systems. To deal with such high-frequency peaks, it is proposed to design a frequency-shaped sliding mode controller based on H∞ synthesis. It obtains an ‘optimal’ filter to shape the sliding surface, and thus provides frequency-dependent control allocation. The proposed frequency-shaping method assures the stability in the presence of multiple-peak vibration sources, and minimizes the weighted H∞ norm of the sliding surface dynamics. The evaluation is performed on a simulated hard disk drive with actual vibration sources from experiments, and the effectiveness of large vibration peak suppression is demonstrated.

A New Direct Measurement Method of Time Dependent Dielectric Breakdown at High Frequency

2020 ◽  
Vol 41 (10) ◽  
pp. 1460-1463
Author(s):  
Melissa Arabi ◽  
Xavier Garros ◽  
Jacques Cluzel ◽  
Mustapha Rafik ◽  
Xavier Federspiel ◽  
...  
Keyword(s):  
Direct Measurement ◽  
High Frequency ◽  
Measurement Method ◽  
Dielectric Breakdown ◽  
Time Dependent ◽  
Time Dependent Dielectric Breakdown ◽  
Direct Measurement Method

scholarly journals Mitotic waves in the early embryogenesis of Drosophila: Bistability traded for speed

2018 ◽  
Vol 115 (10) ◽  
pp. E2165-E2174 ◽  
Author(s):  
Massimo Vergassola ◽  
Victoria E. Deneke ◽  
Stefano Di Talia
Keyword(s):  
Cell Cycle ◽  
Accumulation Rate ◽  
Stable State ◽  
Reaction Diffusion ◽  
Early Embryogenesis ◽  
Time Dependent ◽  
Molecular Diffusivity ◽  
Reaction Diffusion Model ◽  
Rate Of Increase

Early embryogenesis of most metazoans is characterized by rapid and synchronous cleavage divisions. Chemical waves of Cdk1 activity were previously shown to spread across Drosophila embryos, and the underlying molecular processes were dissected. Here, we present the theory of the physical mechanisms that control Cdk1 waves in Drosophila. The in vivo dynamics of Cdk1 are captured by a transiently bistable reaction–diffusion model, where time-dependent reaction terms account for the growing level of cyclins and Cdk1 activation across the cell cycle. We identify two distinct regimes. The first one is observed in mutants of the mitotic switch. There, waves are triggered by the classical mechanism of a stable state invading a metastable one. Conversely, waves in wild type reflect a transient phase that preserves the Cdk1 spatial gradients while the overall level of Cdk1 activity is swept upward by the time-dependent reaction terms. This unique mechanism generates a wave-like spreading that differs from bistable waves for its dependence on dynamic parameters and its faster speed. Namely, the speed of “sweep” waves strikingly decreases as the strength of the reaction terms increases and scales as the powers 3/4, −1/2, and 7/12 of Cdk1 molecular diffusivity, noise amplitude, and rate of increase of Cdk1 activity in the cell-cycle S phase, respectively. Theoretical predictions are supported by numerical simulations and experiments that couple quantitative measurements of Cdk1 activity and genetic perturbations of the accumulation rate of cyclins. Finally, our analysis bears upon the inhibition required to suppress Cdk1 waves at the cell-cycle pause for the maternal-to-zygotic transition.

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