scholarly journals Impact of ADCP motion on structure function estimates of turbulent kinetic energy dissipation rate

2021 ◽  
Author(s):  
Brian Daniel Scannell ◽  
Yueng-Djern Lenn ◽  
Tom P. Rippeth
Keyword(s):  
Structure Function ◽  
Dissipation Rate ◽  
Function Method ◽  
Energy Dissipation Rate ◽  
Flow Speed ◽  
Angular Range ◽  
Beam Velocity ◽  
Flow Speeds ◽  
The Mean ◽  
The Impact

Abstract. Turbulent mixing is a key process in the transport of heat, salt and nutrients in the marine environment, with fluxes commonly derived directly from estimates of the turbulent kinetic energy dissipation rate, ϵ. Time series of ϵ estimates are therefore useful in helping to identify and quantify key biogeochemical processes. Estimates of ϵ are typically derived using shear microstructure profilers, which provide high resolution vertical profiles, but require a surface vessel, incurring costs and limiting the duration of observations and the conditions under which they can be made. The velocity structure function method can be used to determine time series of ϵ estimates using along-beam velocity measurements from suitably configured acoustic Doppler current profilers (ADCP). Shear in the background current can bias such estimates, therefore standard practice is to deduct the mean or linear trend from the along-beam velocity over the period of an observation burst. This procedure is effective if the orientation of the ADCP to the current remains constant over the burst period. However, if the orientation of a tethered ADCP varies, a proportion of the velocity difference between bins is retained in the structure function and the resulting ϵ estimates will be biased. Long-term observations from a mooring with three inline ADCP show the heading oscillating with an angular range that depends on the flow speed; from large, slow oscillations at low flow speeds to smaller, higher frequency oscillations at higher flow speeds. The mean tilt was also determined by the flow speed, whilst the tilt oscillation range was primarily determined by surface wave height. Synthesised along-beam velocity data for an ADCP subject to sinusoidal oscillation in a sheared flow indicates that the retained proportion of the potential bias is primarily determined by the angular range of the oscillation, with the impact varying between beams depending on the mean heading relative to the flow. Since the heading is typically unconstrained in a tethered mooring, heading oscillation is likely to be the most significant influence on the retained bias for a given level of shear. Use of an instrument housing designed to reduce oscillation would mitigate the impact, whilst if the shear is linear over the observation depth range, the bias can be corrected using a modified structure function method designed to correct for bias due to surface waves.

Speed Factors on Two-Lane Rural Highways in Free-Flow Conditions

2005 ◽  
Vol 1912 (1) ◽  
pp. 39-46 ◽  
Author(s):  
Alberto M. Figueroa Medina ◽  
Andrew P. Tarko
Keyword(s):  
Large Body ◽  
Ordinary Least Squares ◽  
Flow Speed ◽  
Free Flow ◽  
Rural Highways ◽  
Horizontal Curves ◽  
Free Flow Speed ◽  
Flow Speeds ◽  
The Mean ◽  
A Site

The mean free-flow speed and its variability across drivers are considered important safety factors. Despite a large body of research on operating speeds, there is still much to learn about the factors of free-flow speeds, especially on tangent segments of two-lane rural highways. The roadway factors of speed dispersion across drivers are largely unknown. Also, the use of the entire free-flow speed distribution suggested by other authors has not yet been addressed. Consequently, the existing models are not aimed to evaluate the speed variability at a site. This paper presents free-flow speed models that identify factors of mean speed and speed dispersion on tangent segments and horizontal curves of two-lane rural highways. Ten highway variables, six of them functioning as both mean speed and speed dispersion factors, were identified as speed factors on tangent segments. Four highway and curve variables, two of them functioning as both mean speed and speed dispersion factors, were identified as speed factors on horizontal curves. The developed free-flow speed models have the same prediction capabilities as traditional ordinary-least-squares models developed for specific percentile speeds. The advantages of the developed models include predicting any user-specified percentile, involving more highway characteristics as speed factors than traditional regression models, and separating the impacts on mean speed from the impacts on speed dispersion.

scholarly journals Comparison of Telbivudine and Entecavir Therapy on Nephritic Function and Drug Resistance in Patients with Hepatitis B Virus-Related Compensated Cirrhosis

2016 ◽  
Vol 40 (1-2) ◽  
pp. 370-378 ◽  
Author(s):  
Huajiang Shen ◽  
Feng Ding ◽  
Zhiwei Wang ◽  
Fang Sun ◽  
Yafeng Yu ◽  
...  
Keyword(s):  
Drug Resistance ◽  
Hepatitis B Virus ◽  
Hepatitis B ◽  
Function Method ◽  
Filtration Rate ◽  
Resistance Rate ◽  
Compensated Cirrhosis ◽  
B Virus ◽  
The Mean ◽  
The Impact

Background: To compare the impact of telbivudine (LDT) and entecavir (ETV) administration on nephritic function. Method: One hundred thirty patients diagnosed with hepatitis B virus (HBV)-related compensated cirrhosis were randomly divided into LDT (600 mg/d) or ETV (0.5 mg/d) groups. Results: The drug resistance rate was higher following LDT treatment compared to ETV treatment (16.9% vs. 1.5%, P=0.0006). The mean creatinine level decreased compared to baseline in the LDT group (0.81 vs. 0.94 mg/dl, P=0.000). The change in median glomerular filtration rate (eGFR) compared to baseline in the LTD and ETV groups was 22.3 and -3.3, respectively, at 2 years (P=0.000). In patients with mild nephritic injury (eGFR< 90 ml/min/1.73m2), the median eGFR increased by 28.0 ml/min/1.73m2 in the LDT group and decreased by 4.3 ml/min/1.73m2 in the ETV group (p=0.000). The eGFR in 88.5% of patients (23/26) from the LDT group increased > 90 ml/min/1.73m2. The percentage of patients with an eGFR > 90 ml/min/1.73m2 increased from 60.0% to 92.3% in the LDT group and from 64.6% to 69.2% in the ETV group. Conclusion: In patients with HBV-related compensated cirrhosis, LDT treatment was more effective in protecting nephritic function and was associated with a higher drug resistance rate, but did not contribute to a better outcome compared with ETV treatment.

Transport equation for the mean turbulent energy dissipation rate on the centreline of a fully developed channel flow

2015 ◽  
Vol 777 ◽  
pp. 151-177 ◽  
Author(s):  
S. L. Tang ◽  
R. A. Antonia ◽  
L. Djenidi ◽  
H. Abe ◽  
T. Zhou ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Transport Equation ◽  
Channel Flow ◽  
Dissipation Rate ◽  
Turbulent Energy ◽  
Energy Dissipation Rate ◽  
Grid Turbulence ◽  
Normal Velocity ◽  
Turbulent Energy Dissipation Rate ◽  
The Mean

The transport equation for the mean turbulent energy dissipation rate $\overline{{\it\epsilon}}$ along the centreline of a fully developed channel flow is derived by applying the limit at small separations to the two-point budget equation. Since the ratio of the isotropic energy dissipation rate to the mean turbulent energy dissipation rate $\overline{{\it\epsilon}}_{iso}/\overline{{\it\epsilon}}$ is sufficiently close to 1 on the centreline, our main focus is on the isotropic form of the transport equation. It is found that the imbalance between the production of $\overline{{\it\epsilon}}$ due to vortex stretching and the destruction of $\overline{{\it\epsilon}}$ caused by the action of viscosity is governed by the diffusion of $\overline{{\it\epsilon}}$ by the wall-normal velocity fluctuation. This imbalance is intrinsically different from the advection-driven imbalance in decaying-type flows, such as grid turbulence, jets and wakes. In effect, the different types of imbalance represent different constraints on the relation between the skewness of the longitudinal velocity derivative $S_{1,1}$ and the destruction coefficient $G$ of enstrophy in different flows, thus resulting in non-universal approaches of $S_{1,1}$ towards a constant value as the Taylor microscale Reynolds number, $R_{{\it\lambda}}$, increases. For example, the approach is slower for the measured values of $S_{1,1}$ along either the channel or pipe centreline than along the axis in the self-preserving region of a round jet. The data for $S_{1,1}$ collected in different flows strongly suggest that, in each flow, the magnitude of $S_{1,1}$ is bounded, the value being slightly larger than 0.5.

An empirical expression for on the axis of a slightly heated turbulent round jet

2019 ◽  
Vol 867 ◽  
pp. 392-413 ◽  
Author(s):  
J. Lemay ◽  
L. Djenidi ◽  
R. A. Antonia ◽  
A. Benaïssa
Keyword(s):  
Structure Function ◽  
Dissipation Rate ◽  
Velocity Structure ◽  
Power Laws ◽  
Second Order ◽  
Temperature Structure ◽  
Analytical Expression ◽  
Round Jet ◽  
Mean Temperature ◽  
The Mean

Self-preservation analyses of the equations for the mean temperature and the second-order temperature structure function on the axis of a slightly heated turbulent round jet are exploited in an attempt to develop an analytical expression for$\unicode[STIX]{x1D716}_{\unicode[STIX]{x1D703}}$, the mean dissipation rate of$\overline{\unicode[STIX]{x1D703}^{2}}/2$, where$\overline{\unicode[STIX]{x1D703}^{2}}$is the temperature variance. The analytical approach follows that of Thiessetet al.(J. Fluid Mech., vol. 748, 2014, R2) who developed an expression for$\unicode[STIX]{x1D716}_{k}$, the mean turbulent kinetic energy dissipation rate, using the transport equation for$\overline{(\unicode[STIX]{x1D6FF}u)^{2}}$, the second-order velocity structure function. Experimental data show that complete self-preservation for all scales of motion is very well satisfied along the jet axis for streamwise distances larger than approximately 30 times the nozzle diameter. This validation of the analytical results is of particular interest as it provides justification and confidence in the analytical derivation of power laws representing the streamwise evolution of different physical quantities along the axis, such as:$\unicode[STIX]{x1D702}$,$\unicode[STIX]{x1D706}$,$\unicode[STIX]{x1D706}_{\unicode[STIX]{x1D703}}$,$R_{U}$,$R_{\unicode[STIX]{x1D6E9}}$(all representing characteristic length scales), the mean temperature excess$\unicode[STIX]{x1D6E9}_{0}$, the mixed velocity–temperature moments$\overline{u\unicode[STIX]{x1D703}^{2}}$,$\overline{v\unicode[STIX]{x1D703}^{2}}$and$\overline{\unicode[STIX]{x1D703}^{2}}$and$\unicode[STIX]{x1D716}_{\unicode[STIX]{x1D703}}$. Simple models are proposed for$\overline{u\unicode[STIX]{x1D703}^{2}}$and$\overline{v\unicode[STIX]{x1D703}^{2}}$in order to derive an analytical expression for$A_{\unicode[STIX]{x1D716}_{\unicode[STIX]{x1D703}}}$, the prefactor of the power law describing the streamwise evolution of$\unicode[STIX]{x1D716}_{\unicode[STIX]{x1D703}}$. Further, expressions are also derived for the turbulent Péclet number and the thermal-to-mechanical time scale ratio. These expressions involve global parameters that are most likely to be influenced by the initial and/or boundary conditions and are therefore expected to be flow dependent.

Respirometric measurement of kinetic parameters: effect of activated sludge floc size

2003 ◽  
Vol 48 (8) ◽  
pp. 61-68 ◽  
Author(s):  
K.H. Chu ◽  
H.M. van Veldhuizen ◽  
M.C.M. van Loosdrecht
Keyword(s):  
Energy Dissipation ◽  
Activated Sludge ◽  
Oxygen Saturation ◽  
Dissipation Rate ◽  
Energy Dissipation Rate ◽  
Floc Size ◽  
Saturation Coefficient ◽  
Mixing Intensity ◽  
The Mean ◽  
Photometric Dispersion

The variation of activated sludge floc size with the mixing intensity of a mechanically stirred respirometer, expressed in terms of the mean energy dissipation rate, was characterized using a photometric dispersion analyzer. The floc size decreased rapidly when the energy dissipation rate was increased from 1.33 × 10-3 to 2.68 × 10-3 W/kg. Experiments were performed to investigate the effect of floc size on the oxygen saturation coefficient measured under the condition of acetate oxidation. The respirometric data were interpreted by considering only the kinetics of biochemical reactions. The variation of the oxygen saturation coefficient with mixing intensity was found to correlate with the variation of floc size with mixing intensity. The oxygen saturation coefficient was found to decrease from 0.23 to 0.08 mg/L when the mean energy dissipation rate was increased from 1.33 × 10-3 to 2.68 × 10-3 W/kg. The dependence of the oxygen saturation coefficient on floc size or mixing intensity suggests the presence of mass transfer resistances in large flocs.

scholarly journals Spectral and Structure Function Estimates of Turbulence Dissipation Rates in a High-Flow Tidal Channel Using Broadband ADCPs

2017 ◽  
Vol 34 (1) ◽  
pp. 5-20 ◽  
Author(s):  
Justine M. McMillan ◽  
Alex E. Hay
Keyword(s):  
Structure Function ◽  
Dissipation Rate ◽  
Acoustic Doppler Current Profiler ◽  
Universal Constant ◽  
Flow Speed ◽  
High Flow ◽  
Small Scale ◽  
Order Structure ◽  
Tidal Channel ◽  
Current Profiler

AbstractSpectral and structure function methods are implemented to compute the dissipation rate ε from broadband, diverging-beam acoustic Doppler current profiler (ADCP) data collected at four sites in a high-flow tidal channel. This paper shows that middepth estimates of ε obtained from spectral and second-order structure function (SF2) methods are both lognormally distributed with comparable means and variances. Speed bin–averaged ε values agree to within 16%, depending on the site and tidal phase (ebb/flood). The close agreement between the two independent methods provides further support for the argument put forward by McMillan et al.: that is, that the factor-of-2 difference between shear probe and (spectral) ADCP estimates of ε was likely caused by spatial differences in turbulence levels. The agreement between the spectral and both second- and third-order structure function methods also supports the use of for the SF2 universal constant. Notably, however, the SF3 method was less robust for these data. Two additional aspects of the SF2 approach are examined in some detail: 1) the differences from upstream- and downstream-facing beams are shown to arise from the Reynolds stress and 2) the inability of the ADCP to resolve small-scale motions does not affect the estimates of ε but yields apparent Doppler noise levels that—counterintuitively—decrease with increasing flow speed and increasing dissipation rate. A modified SF2 method that accounts for the variance associated with the unresolved scales removes the flow speed dependence and yields noise level estimates that agree with the spectral values.

Three-component vorticity measurements in a turbulent grid flow

1998 ◽  
Vol 374 ◽  
pp. 29-57 ◽  
Author(s):  
R. A. ANTONIA ◽  
T. ZHOU ◽  
Y. ZHU
Keyword(s):  
Energy Dissipation ◽  
Dissipation Rate ◽  
Velocity Structure ◽  
Transverse Velocity ◽  
Longitudinal Velocity ◽  
Energy Dissipation Rate ◽  
Grid Turbulence ◽  
Local Isotropy ◽  
Velocity Increments ◽  
The Mean

All components of the fluctuating vorticity vector have been measured in decaying grid turbulence using a vorticity probe of relatively simple geometry (four X-probes, i.e. a total of eight hot wires). The data indicate that local isotropy is more closely satisfied than global isotropy, the r.m.s. vorticities being more nearly equal than the r.m.s. velocities. Two checks indicate that the performance of the probe is satisfactory. Firstly, the fully measured mean energy dissipation rate 〈ε〉 is in good agreement with the value inferred from the rate of decay of the mean turbulent energy 〈q2〉 in the quasi-homogeneous region; the isotropic mean energy dissipation rate 〈εiso〉 agrees closely with this value even though individual elements of 〈ε〉 indicate departures from isotropy. Secondly, the measured decay rate of the mean-square vorticity 〈ω2〉 is consistent with that of 〈q2〉 and in reasonable agreement with the isotropic form of the transport equation for 〈ω2〉. Although 〈ε〉≃〈εiso〉, there are discernible differences between the statistics of ε and εiso; in particular, εiso is poorly correlated with either ε or ω2. The behaviour of velocity increments has been examined over a narrow range of separations for which the third-order longitudinal velocity structure function is approximately linear. In this range, transverse velocity increments show larger departures than longitudinal increments from predictions of Kolmogorov (1941). The data indicate that this discrepancy is only partly associated with differences between statistics of locally averaged ε and ω2, the latter remaining more intermittent than the former across this range. It is more likely caused by a departure from isotropy due to the small value of Rλ, the Taylor microscale Reynolds number, in this experiment.

scholarly journals Dynamics of a Simulated Demonstration March: An Efficient Sensitivity Analysis

2021 ◽  
Vol 13 (6) ◽  
pp. 3455
Author(s):  
Simon Rahn ◽  
Marion Gödel ◽  
Rainer Fischer ◽  
Gerta Köster
Keyword(s):  
Sensitivity Analysis ◽  
Monte Carlo ◽  
Standard Deviation ◽  
Management Strategies ◽  
Flow Speed ◽  
Fundamental Rights ◽  
Free Flow ◽  
Governing Parameter ◽  
Flow Speeds ◽  
The Impact

Protest demonstrations are a manifestation of fundamental rights. Authorities are responsible for guiding protesters safely along predefined routes, typically set in an urban built environment. Microscopic crowd simulations support decision-makers in finding sustainable crowd management strategies. Planning routes usually requires knowledge about the length of the demonstration march. This case study quantifies the impact of two uncertain parameters, the number of protesters and the standard deviation of their free-flow speeds, on the length of a protest march through Kaiserslautern, Germany. Over 1000 participants walking through more than 100,000 m2 lead to a computationally demanding model that cannot be analyzed with a standard Monte Carlo ansatz. We select and apply analysis methods that are efficient for large topographies. This combination constitutes the main novelty of this paper: We compute Sobol’ indices with two different methods, based on polynomial chaos expansions, for a down-scaled version of the original set-up and compare them to Monte Carlo computations. We employ the more accurate of the approaches for the full-scale scenario. The global sensitivity analysis reveals a shift in the governing parameter from the number of protesters to the standard deviation of their free-flow speeds over time, stressing the benefits of a time-dependent analysis. We discuss typical actions, for example floats that reduce the variation of the free-flow speed, and their effectiveness in view of the findings.

scholarly journals Process Intensification of Photochemical Oxidations using a High Throughput Rotor-Stator Spinning Disk Reactor: A Strategy for Scale Up

2020 ◽  
Author(s):  
Arnab Chaudhuri ◽  
Koen P. L. Kuijpers ◽  
Raoul Hendrix ◽  
Jasper Hacking ◽  
Parimala Shivaprasad ◽  
...  
Keyword(s):  
High Throughput ◽  
Dissipation Rate ◽  
Catalyst Concentration ◽  
Rotation Speed ◽  
Batch Reactor ◽  
Scale Up ◽  
Process Intensification ◽  
Energy Dissipation Rate ◽  
Spinning Disk ◽  
The Impact

<div>This paper presents a novel high-throughput reactor for intensification of photochemical conversion processes. The photocatalyzed gas-liquid oxidation of α-terpinene to the drug ascaridole with rose-bengal was achieved with throughputs of over 1 kg∙day-1 (71 kg∙day-1∙m-2) under visible light irradiation. The performance of the reactor is correlated to rotation speed, liquid flowrate, gas flowrate, catalyst concentration, substrate concentration, gas holdup, gas bubble size, and energy dissipation rate. The conversion and selectivity increase from 37% to 97% and 75% to 90% respectively with an increase of rotation speed from 100 to 2000 RPM. Compared to conventional photochemical reactors such as the batch reactor or the microreactor, the photo-rotor-stator spinning disk reactor has much higher productivity (270 mmol∙h-1 or 19.2 mol∙h-1∙m-2) and higher selectivity (> 90%), with the latter illustrating the impact of mixing on selectivity. The findings of this study can be used to study, design, optimize and scale photochemical processes using the rotor-stator spinning disk reactor.</div>

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