Energy amplification in channel flows of viscoelastic fluids

2008 ◽  
Vol 601 ◽  
pp. 407-424 ◽  
Author(s):  
NAZISH HODA ◽  
MIHAILO R. JOVANOVIĆ ◽  
SATISH KUMAR
Keyword(s):  
Reynolds Number ◽  
Energy Density ◽  
Viscosity Ratio ◽  
Average Energy ◽  
Maximum Energy ◽  
Point Of View ◽  
Channel Flows ◽  
Spatially Distributed ◽  
Energy Amplification ◽  
Elasticity Number

Energy amplification in channel flows of Oldroyd-B fluids is studied from an input–output point of view by analysing the ensemble-average energy density associated with the velocity field of the linearized governing equations. The inputs consist of spatially distributed and temporally varying body forces that are harmonic in the streamwise and spanwise directions and stochastic in the wall-normal direction and in time. Such inputs enable the use of powerful tools from linear systems theory that have recently been applied to analyse Newtonian fluid flows. It is found that the energy density increases with a decrease in viscosity ratio (ratio of solvent viscosity to total viscosity) and an increase in Reynolds number and elasticity number. In most of the cases, streamwise-constant perturbations are most amplified and the location of maximum energy density shifts to higher spanwise wavenumbers with an increase in Reynolds number and elasticity number and a decrease in viscosity ratio. For similar parameter values, the maximum in the energy density occurs at a higher spanwise wavenumber for Poiseuille flow, whereas the maximum energy density achieves larger maxima for Couette flow. At low Reynolds numbers, the energy density decreases monotonically when the elasticity number is sufficiently small, but shows a maximum when the elasticity number becomes sufficiently large, suggesting that elasticity can amplify disturbances even when inertial effects are weak.

Non-Modal Instability of Core-Annular Flow

2012 ◽  
Vol 13 (6) ◽  
Author(s):  
Gennaro Coppola ◽  
Annagrazia Orazzo ◽  
Luigi de Luca
Keyword(s):  
Annular Flow ◽  
Three Dimensional ◽  
Classical Problem ◽  
Maximum Energy ◽  
Point Of View ◽  
Polar Coordinates ◽  
Tension Parameter ◽  
Two Phases ◽  
The Stability ◽  
Energy Amplification

AbstractThe classical problem of the stability of Core-Annular Flow (CAF) in pipes is reconsidered from the point of view of the linear non-modal analysis. An accurate Chebyshev pseudospectral code in polar coordinates has been developed in order to separately discretize the two phases of the flow. Transient amplifications of the energy of three-dimensional perturbations are computed by taking into account the effects of viscosity and volume ratios between the two liquids, as well as of Reynolds number and a surface tension parameter.A detailed investigation is conducted in wide regions of the parameters space and the occurrence of remarkable transient growths is found for asymptotically both stable and unstable configurations. Optimal perturbations (i.e. giving the maximum energy amplification) are determined and their structure is analyzed. It is shown that in conditions in which axisymmetric modes are expected to constitute the most dangerous exponential disturbances, spiral perturbations can provide higher levels of transient energy amplification. Growth rates and amplification levels relative to modal and non-modal mechanisms are compared in order to analyze more in depth previous disagreements between experiments and modal theory.

The Importance of Rainfall Distribution in Urban Drainage Operation

1992 ◽  
Vol 23 (2) ◽  
pp. 121-136 ◽  
Author(s):  
Fons Nelen ◽  
Annemarieke Mooijman ◽  
Per Jacobsen
Keyword(s):  
Real Time ◽  
Treatment Plant ◽  
Rain Gauge ◽  
Point Of View ◽  
Rain Event ◽  
Real Time Control ◽  
Rainfall Distribution ◽  
Statistical Point ◽  
Time Control ◽  
Spatially Distributed

A control simulation model, called LOCUS, is used to investigate the effects of spatially distributed rain and the possibilities to benefit from this phenomenon by means of real time control. The study is undertaken for a catchment in Copenhagen, where rainfall is measured with a network of 8 rain gauges. Simulation of a single rain event, which is assumed to be homogeneous, i.e. using one rain gauge for the whole catchment, leads to large over- and underestimates of the systems output variables. Therefore, when analyzing a single event the highest possible degree of rainfall information may be desired. Time-series simulations are performed for both an uncontrolled and a controlled system. It is shown that from a statistical point of view, rainfall distribution is NOT significant concerning the probability of occurrence of an overflow. The main contributing factor to the potential of real time control, concerning minimizing overflows, is to be found in the system itself, i.e. the distribution of available storage and discharge capacity. When other operational objectives are involved, e.g., to minimize peak flows to the treatment plant, rainfall distribution may be an important factor.

High field tunneling as a limiting factor of maximum energy density in dielectric energy storage capacitors

2008 ◽  
Vol 92 (14) ◽  
pp. 142909 ◽  
Author(s):  
Qin Chen ◽  
Yong Wang ◽  
Xin Zhou ◽  
Q. M. Zhang ◽  
Shihai Zhang
Keyword(s):  
Energy Storage ◽  
Energy Density ◽  
High Field ◽  
Maximum Energy ◽  
Limiting Factor

Performance of Plain Journal Bearings Operating Under Vortex Flow Conditions

1974 ◽  
Vol 96 (1) ◽  
pp. 145-149 ◽  
Author(s):  
J. Freˆne ◽  
M. Godet
Keyword(s):  
Reynolds Number ◽  
Friction Torque ◽  
Point Of View ◽  
Taylor Vortex ◽  
Experimental Program ◽  
Frictional Torque ◽  
Taylor Vortices ◽  
Attitude Angle ◽  
Relative Eccentricity ◽  
High Reynolds

An experimental program conducted on an original device was undertaken to study the performance of plain bearings operating at sufficiently high Reynolds number to introduce Taylor vortices. Curves of relative eccentricity, attitude angle, and friction torque were obtained versus speed and load. Experimental results conducted for Reynolds number smaller than 1100 indicate that both laminar and Taylor vortex regimes are encountered. The occurrence of the vortices is identified by a break in the slope of the friction torque versus speed curves. The position of the break is in good agreement with the theoretical predictions of Di Prima and Ritchie. From the practical point of view, the data show that for constant viscosity the occurence of Taylor vortices does not alter the curves of eccentricity versus either speed or load but modifies the attitude angle and frictional torque. In turn, the increase in frictional torque, and subsequently of temperature may cause a decrease in viscosity and thus a drop in load carrying capacity for fluids such as oils whose variations of viscosity with temperature is large.

Stability of Viscoelastic Channel Flow

2007 ◽  
Author(s):  
Nariman Ashrafi
Keyword(s):  
Reynolds Number ◽  
Viscosity Ratio ◽  
Weissenberg Number ◽  
Base Flow ◽  
Galerkin Projection ◽  
Large Reynolds Number ◽  
One Dimensional ◽  
Stress Effects ◽  
The Stability ◽  
The One

The nonlinear stability and bifurcation of the one-dimensional channel (Poiseuille) flow is examined for a Johnson-Segalman fluid. The velocity and stress are represented by orthonormal functions in the transverse direction to the flow. The flow field is obtained from the conservation and constitutive equations using the Galerkin projection method. Both inertia and normal stress effects are included. The stability picture is dramatically influenced by the viscosity ratio. The range of shear rate or Weissenberg number for which the base flow is unstable increases from zero as the fluid deviates from the Newtonian limit as decreases. Typically, two turning points are observed near the critical Weissenberg numbers. The transient response is heavily influenced by the level of inertia. It is found that the flow responds oscillatorily. When the Reynolds number is small, and monotonically at large Reynolds number when elastic effects are dominated by inertia.

scholarly journals Dielectric elastomer generator with diaphragm configuration

2018 ◽  
Vol 192 ◽  
pp. 01032
Author(s):  
Zhen-Qiang Song ◽  
Sriyuttakrai Sathin ◽  
Wei Li ◽  
Kazuhiro Ohyama ◽  
ShiJie Zhu
Keyword(s):  
Energy Density ◽  
Energy Conversion ◽  
Conversion Efficiency ◽  
Energy Conversion Efficiency ◽  
Dielectric Elastomer ◽  
Maximum Energy ◽  
Constant Voltage ◽  
Low Viscosity ◽  
65 J ◽  
Low Efficiency

The dielectric elastomer generator (VHB 4905, 3M) with diaphragm configuration was investigated with the constant-voltage harvesting scheme in order to investigate its energy harvesting ability. The maximum energy density and energy conversion efficiency is measured to be 65 J/kg and 5.7%, respectively. The relatively low efficiency indicates that higher energy conversion efficiency is impeded by the viscosity of the acrylic elastomer, suggesting that higher conversion efficiency with new low-viscosity elastomer should be available.

The high energy density and efficiency of PVDF-based composites with double-shell Nd-BaTiO3 particles as fillers

2020 ◽  
Vol 13 (06) ◽  
pp. 2051042
Author(s):  
Zhong Yang ◽  
Jing Wang ◽  
Long He ◽  
Chaoyong Deng ◽  
Kongjun Zhu
Keyword(s):  
Energy Storage ◽  
Energy Density ◽  
Vinylidene Fluoride ◽  
Composite Films ◽  
High Energy ◽  
Maximum Energy ◽  
Dielectric Constants ◽  
High Energy Density ◽  
Element Simulation ◽  
Poly Vinylidene Fluoride

Flexible dielectric capacitors are becoming shining stars in modern electronic devices. Ceramic particles with large dielectric constants and benign compatibility are attractive candidates to enhance the energy storage density of pristine polymer capacitors while guaranteeing their flexibility. In this work, double-shell structure of Al2O3 (AO) and dopamine (PDA) were successively coated on the Nd-doped BaTiO3 (NBT) particles and then introduced into the Poly(vinylidene fluoride) (PVDF) matrix. Obvious enhancement in dielectric constants was observed while the dielectric loss remained nearly constant. For the composite films with 1–4[Formula: see text]vol.% NBT@AO@PDA NPs, the maximum energy density of 9.1[Formula: see text]J/cm3 and energy efficiency of 65% was achieved at 430[Formula: see text]MV/m in the sample with 1[Formula: see text]vol.% filling ratio, which are 1.4 and 1.3 times larger than those of pristine PVDF at 450[Formula: see text]MV/m. The finite element simulation reveals the effective relief of the electric field concentration in the composite film induced by the AO and PDA layers. The greater improvement in the energy storage performance could be anticipated if the dispersity of NBT@AO@PDA NPs was further improved.

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