Root Mean Square Velocity Research Articles

Finite-size particles in turbulent channel flow: quadrant analysis and acceleration statistics

ABSTRACTThe interaction between finite-size particles and turbulent channel flow in the absence of gravity is studied by direct numerical simulations (DNS). The study is motivated by DNS observations of a turbulent channel flow with high-density, pointwise particles, that cluster in regions of high streamwise root-mean-square (RMS) acceleration close to the wall, contrary to what is observed in homogeneous isotropic turbulence. The aim of the present study is to explore if this is still the case when size effects are taken into account in the DNS. Based on the analysis of the velocity and acceleration statistics, the present DNS shows that, close to the wall, particles with ρp/ρf ranging from 2 to 4 are surrounded by regions with low streamwise RMS velocity but high streamwise RMS acceleration. According to the normalised particle acceleration probability density functions (PDFs), size effects become important in the near-wall region. As particle inertia increases, the normalised PDFs of particle acceleration tend to a Gaussian distribution. The tails of the normalised PDFs of the fluid conditioned by the presence of particles are higher than that of the unconditioned fluid close to the wall.

Lattice Boltzmann method and RANS approach for simulation of turbulent flows and particle transport and deposition

Using the lattice-Boltzmann computational approach in conjunction with the Reynolds averaged Navier–Stokes (RANS) model, several turbulent flows and the transport and deposition of particles in different passages were studied. The new lattice Boltzmann method (LBM) solved the RANS equations coupled with the standard and renormalization group k−ɛ turbulence models. In particular, the LBM formulation was augmented by the addition of two transport equations for the probability distribution function of populations of k and ɛ. The discrete random walk model was used to generate the instantaneous turbulence fluctuations. For turbulent channel flows, the analytical fits to the root mean-square velocity fluctuations obtained by the direct numerical simulation of the turbulent flow were used in the analysis. Attention was given to the proper evaluation of the wall normal turbulent velocity fluctuations particularly near the wall. The simulation results were compared with the available numerical simulation and experimental data. The new LBM–RANS model is shown to provide a reasonably accurate description of turbulent flows and particle transport and deposition at modest computational cost.

Vibration analysis of a diesel engine using biodiesel fuel blended with nano particles by dual fueling of hydrogen

In pursuit of environmental friendly alternative fuels for diesel engines, biodiesel is a promising alternative. Efforts are on in utilizing the biodiesel with diesel in Internal Combustion (IC) engines, because of its reduced pollution characteristics. Long-term effects of these biofuels in IC engines have not been explored earnestly. Enduring effects of which are high noise & vibration and irregular & erratic combustion leading to knocking. Few researches on vibration analysis of biodiesel blends have been reported. Hence, an effort is made to study the vibration characteristics of biodiesel blends amidst Zinc Oxide (ZnO) nano particles with hydrogen in dual fuel mode. Initially, experimentation is carried out to record vibration signatures with 100 ppm concentration of ZnO particles of 20 & 40 nm sizes suspended in Jatropha Methyl Ester (JME) biodiesel along with hydrogen as secondary fuel. In order to avoid strenuous experimentation Artificial Neural Network (ANN) model was developed to predict Root Mean Square (RMS) of velocity. ANN predictions are found to be scrupulously matching with the experimental values as manifested by the regression values of 0.97185, 0.98574 & 0.96913 for prediction of RMS velocities in horizontal, vertical & axial directions respectively. It is found that the best fuel blend with least vibration is B30 & B20 with nano particle of size 40 nm for hydrogen flow rates of 0.5, 1.0 & 1.5 l/min.

Understanding In-Cylinder Flow Variability Using Large-Eddy Simulations

Multicycle large-eddy simulations (LES) of motored flow in an optical engine housed at the University of Michigan have been performed. The simulated flow field is compared against particle image velocimetry (PIV) data in several cutting planes. Circular statistical methods have been used to isolate the contributions to overall turbulent fluctuations from changes in flow direction or magnitude. High levels of turbulence, as indicated by high velocity root mean square (RMS) values, exist in relatively large regions of the combustion chamber. But the circular standard deviation (CSD), a measure of the variability in flow direction independent of velocity magnitude, is much more limited to specific regions or points, indicating that much of the turbulence is from variable flow magnitude rather than variable flow direction. Using the CSD is also a promising method to identify critical points, such as vortex centers or stagnation points, within the flow, which may prove useful for future engine designers.

Pitching stability of diving seabirds during underwater locomotion: a comparison among alcids and a penguin

In animals, recoil motion resulting from underwater propulsion can destabilise trajectory and decrease locomotory performance. The posture of diving seabirds fluctuates simultaneously with their appendage beat, especially in the vertical plane, because of the recoil force of the beat. Seabirds that fly and swim face trade-offs between maximising their locomotory performance in one medium relative to the other, and flightless penguins were hypothesised to have higher underwater pitching stability than alcids that fly and swim. To test this hypothesis, we investigated the in situ pitching stability of three species of diving seabirds, including a penguin, Pygoscelis adeliae, and two species of alcids, Cerorhinca monocerata and Uria lomvia. A high-resolution gyroscope data logger was attached to the back of each bird and recorded the angular velocity of the body during the descent phase of dives. For all three species, the root mean square (RMS) of the angular velocity, which indicated the level of angular fluctuation, was negatively correlated with the depth. Many factors, such as the dorsoventral acceleration resulting from wing beat, dive angle, speed, and current depth, as well as the maximum depth in each dive, significantly affected the angular velocity RMS. The angular velocity RMS at a given depth (e.g. 5 and 10 m) significantly increased with the maximum depth of the dives, suggesting buoyancy regulation relative to the target depth to reduce the destabilising angular momentum in all three species. During entire descent periods, the angular fluctuation was generally lower in P. adeliae than in the two species of alcids, supporting the hypothesis of a higher pitching stability in penguins. Furthermore, the angular fluctuation of U. lomvia was lower than that of C. monocerata at deeper depths, suggesting higher pitching stability and more efficient underwater locomotion in U. lomvia. This study demonstrated a difference in the pitching stability, which is an important component of underwater locomotory efficiency, of a penguin and two alcid species while diving freely in natural conditions. In situ angular fluctuation data obtained by gyroscope would be useful to understand the locomotory strategy of swimming animals.

Determining velocities in high frequency electromagnetic prospecting by phase shift plus interpolation migration

Phase Shift Plus Interpolation (PSPI) Migration is one of the most popular migration methods that is used not only in Seismic Data Processing but also in interpreting high frequency electromagnetic prospecting [Ground Penetrating Radar (GPR) data]. Based on the similarities between the principle of the propagation of electromagnetic wave and the mechanical wave, migration methods could be applied to interpreting GPR data as a particular step to calculate the medium’s velocity, estimate the depth, shape and size of buried objects. Noticeably, there are two kinds of velocities usually used in migration methods: root mean square (RMS) velocity, which is used in F – K, Finite Difference and Kirchhoff Migration, and interval velocity, which is used in PSPI Migration. RMS velocity is the average velocity taken into account by considering the influence of the upper layer’s instantaneous velocity; whereas the interval velocity only reflect the practical velocity of one layer. In this paper, the problem of how to apply PSPI Migration to interpret GPR data will be presented. Some results of model datum and real datum were also examined. Besides, we made a comparison of using RMS velocity and interval velocity, and then explain how these two types of velocity could be combined to receive the best result.

Um estudo numérico da influência da radiação sobre a turbulência em uma chama turbulenta 2D axissimétrica

This paper presents a study of the influence of thermal radiation on turbulence in the simulation of a turbulent, non-premixed methane-air flame. In such a problem, two aspects need to be considered for a precise evaluation of the thermal radiation: the turbulence-radiation interactions (TRI), and the radiative properties of the participating species, which are treated here with the weighted-sum-of-gray-gases (WSGG) model based on recently obtained correlations from HITEMP2010 database. The chemical reactions rates were considered as the minimum values between the Arrhenius and Eddy Break-Up rates. A twostep global reaction mechanism was employed, while the turbulence modeling was considered via standard k–e model. The source terms of the energy equation consisted of the heat generated in the chemical reaction rates as well as in the radiation exchanges. The discrete ordinates method (DOM) was employed to solve the radiative transfer equation (RTE), including the TRI. Comparisons of simulations with/without radiation demonstrated that radiation influenced turbulent-properties (root mean square of velocity and temperature fluctuations, and turbulent kinetic energy of the velocity fluctuations). Radiation smoothed turbulent-properties fields. The influence of radiation was more important on the temperature fluctuations than on the velocity fluctuations. Keywords: thermal radiation, turbulence, TRI, CFD, non-premixed flame.

Measurements of pressure drop and particle velocity in a pseudo 2-D rectangular bed with Geldart Group D particles

A small scale pseudo 2-D bed of dimension 0.075m×0.23m×1.22m was utilized to measure the pressure drop and velocity statistics of Geldart Group D nylon beads. The pressure drop was measured using a fast-response pressure transducer and the particle velocities were measured with high speed particle image velocimetry, with particle tracking, in a slugging flow regime for three different superficial gas velocities (2, 3 & 4 times the minimum fluidization velocity (Umf)). At superficial gas velocity of 3 Umf, the measured slugging frequency was about 2.5Hz, while at conditions close to 2 Umf and 4 Umf, the slugging frequency was about 1.5 and 1.7Hz. Additionally, at 3 Umf condition, the bed exhibited a much higher root mean square (RMS) of pressure drop fluctuations than those at 2 Umf and 4 Umf. The varying trend suggested an existence of a complicated regime change for these shallow bed measurements that had not been previously explored. The measurement of millions of individual particle velocities at the vicinity of the wall had enabled accurate measurement of higher order statistics including RMS, granular temperature, skewness, and kurtosis of particle velocity. The measured skewness and kurtosis of the velocity distribution indicated that the particle velocity distribution deviated substantially from a normal distribution as the intersection of walls of the rectangular bed was approached.

Relationship of multiscale entropy to task difficulty and sway velocity in healthy young adults

Purpose/background: Multiscale entropy (MSE) is a nonlinear measure of postural control that quantifies how complex the postural sway is by assigning a complexity index to the center of pressure (COP) oscillations. While complexity has been shown to be task dependent, the relationship between sway complexity and level of task challenge is currently unclear. This study tested whether MSE can detect short-term changes in postural control in response to increased standing balance task difficulty in healthy young adults and compared this response to that of a traditional measure of postural steadiness, root mean square of velocity (VRMS).Methods: COP data from 20 s of quiet stance were analyzed when 30 healthy young adults stood on the following surfaces: on floor and foam with eyes open and closed and on the compliant side of a Both Sides Up (BOSU) ball with eyes open. Complexity index (CompI) was derived from MSE curves.Results: Repeated measures analysis of variance across standing conditions showed a statistically significant effect of condition (p < 0.001) in both the anterior–posterior and medio-lateral directions for both CompI and VRMS. In the medio-lateral direction there was a gradual increase in CompI and VRMS with increased standing challenge. In the anterior–posterior direction, VRMS showed a gradual increase whereas CompI showed significant differences between the BOSU and all other conditions. CompI was moderately and significantly correlated with VRMS.Conclusions: Both nonlinear and traditional measures of postural control were sensitive to the task and increased with increasing difficulty of standing balance tasks in healthy young adults.

Exploring the effect of electrical muscle stimulation as a novel treatment of intractable tremor in Parkinson's disease

BackgroundAs the pathophysiology of tremor in Parkinson disease (PD) involves a complex interaction between central and peripheral mechanisms, we propose that modulation of peripheral reflex mechanism by electrical muscle stimulation (EMS) may improve tremor temporarily. ObjectivesTo determine the efficacy of EMS as a treatment for drug resistant tremor in PD patients. MethodsThis study was a single-blinded, quasi-experimental study involving 34 PD patients with classic resting tremor as confirmed by tremor analysis. The EMS was given at 50Hz over the abductor pollicis brevis and interrosseus muscles for 10s with identified tremor parameters before and during stimulation as primary outcomes. ResultsCompared to before stimulation, we observed a significant reduction in the root mean square (RMS) of the angular velocity (p<0.001) and peak magnitude (p<0.001) of resting tremor while tremor frequency (p=0.126) and dispersion (p=0.284) remained unchanged during stimulation. The UPDRS tremor score decreased from 10.59 (SD=1.74) before stimulation to 8.85 (SD=2.19) during stimulation (p<0.001). The average percentage of improvement of the peak magnitude and RMS angular velocity was 49.57% (SD=38.89) and 43.81% (SD=33.15) respectively. 70.6% and 61.8% of patients experienced at least 30% tremor attenuation as calculated from the peak magnitude and RMS angular velocity respectively. ConclusionsOur study demonstrated the efficacy of EMS in temporarily improving resting tremor in medically intractable PD patients. Although tremor severity decreased, they were not completely eliminated and continued with a similar frequency, thus demonstrating the role of peripheral reflex mechanism in the modulation of tremor, but not as a generator. EMS should be further explored as a possible therapeutic intervention for tremor in PD.

An artificial neural network approach to investigate surface roughness and vibration of workpiece in boring of AISI1040 steels

In metal cutting, tool failure and surface roughness are the important aspects that affect product quality and production cost, and these are affected mainly by vibration of workpiece. Current techniques do not have a proper method to measure vibration of a rotating workpiece so as to use it as a parameter to replace a cutting tool at an appropriate time. The purpose of the present work is therefore to use of laser Doppler vibrometer (LDV) to measure the vibration of workpiece without interfering the machining. Subsequent to obtaining the workpiece vibration data, artificial neural network (ANN) method was adopted to predict surface roughness and root mean square (RMS) velocity of workpiece vibration. According to Taguchi design of experiments, 18 experiments were prepared with two levels of nose radius and three levels of cutting speed and feed rate. Experiments were conducted on CNC lathe to obtain data of surface roughness and RMS of workpiece vibration velocity in boring of AISI 1040. A multilayer feedforward ANN model was developed and trained with the experimental data using back propagation algorithm. Further, the ANN was used to predict surface roughness and RMS velocity of workpiece vibration. The predicted values were compared with the collected experimental data and percentage error was computed. Less percentage of error was found between the experimental and predicted values.

Large Eddy Simulation of piloted pulverized coal combustion using the velocity-scalar joint filtered density function model

Abstract A piloted pulverized coal jet flame was simulated by Large Eddy Simulation (LES). For the sub-grid scale (SGS) effects of the turbulence velocity and the scalar fluctuation of the gas flow on the coal particles, the velocity-scalar joint filtered density function (VSJFDF) model was used. Other models such as the governing equations for particles and coal combustion sub-models were also presented. Simulation results with the VSJFDF model, non-VSJFDF model and those by Franchetti et al. [7] were compared with the experimental data, including the mean and RMS (root mean square) velocity, temperature and species concentrations. The results showed that VSJFDF can distinctly improve the predictions, both in quantity and quality. The location where coal particles start burning could be roughly predicted along the centerline of the flame by VSJFDF model.

Application of Mixture of Gaussian Clustering on Joint Facies Interpretation of Seismic and Magnetotelluric Sections

Seismic and magnetotelluric (MT) methods are the most applicable geophysical methods in exploration of hydrocarbon resources. In this paper, mixture of Gaussian clustering is used to combine seismic and MT images under the scheme of Expectation/Maximization (EM) algorithm. Pre-Stack Depth Migration (PSDM) velocity, Root Mean Square (RMS) velocity and vertical gradient of RMS velocity of seismic and resistivity model of MT along 19.3 km MUN-21 profile in Munir Block that has been located in Southwest of Iran in Dezful embayment over the Seh-Qanat anticline are applied. The anticline is the most important oil trap of this area. The Expectation/Maximization (EM) method that has been applied includes: (1) creation of data vectors from the seismic and MT images using image processing techniques, (2) normalizing and mapping using Principal Component Analysis (PCA) procedure (3) unsupervised learning of dataset matrix, (4) setting the matrix in Expectation/Maximization (EM) iteration algorithm (5) remapping to physical space. The final model consists fof six classes which could be given to eight formations that belong to Eocene to Neocomian geological age. Pre-Stack Depth Migration (PSDM) velocity model obtained from seismic study on Seh-Qanat anticline only detected 2 horizons of formations, Asmari and Sarvak Formations; however, the current methodology introduces subdivision anticline into six classes by matching it to the log information of Seh-Qanat Deep-1 (SQD-1) borehole where it was excavated over the anticline with total depth of 2876 m.

The effect of facing direction on static balance of children while standing on stairs

Background: Balance control is essential to all upright activities, and can be influenced by environmental conditions and tasks. While standing on higher surface, the perception of height was changes in the adults that they might overestimate the height and adopt different strategies, such as stiffness strategy.Children need to stand and engage activities on higher surfaces occasionally, such as playing at playground or walking up/down stairs, but the immature sensory, motor and cognitive development, and insufficient experiences make them unable to balance or react as appropriate as adults. It is hypothesized that facing direction (ascending or descending) while standing on stairs would affect the height perception of children, and thus change their balance control in static stance. Purpose: To investigate the effect of facing direction on the center of pressure (COP) parameters in typically developing children aged 6–9 years while standing on a staircase. Methods: Thirteen children aged 6–9 years (6 girls, 7 boys) were recruited for the study. The average body height was 129.23 cm (SD 11.11), and body weight was 31.15 kg (SD 11.24). Foot length (FL) was measured from the heel to the tip of the big toe, and was used for normalizing the differences of body statue. Ground reaction forces were measured by a portable force plate (9286BA, Kistler Instruments Ltd, Switzerland). The data was collected when the participants maintained static standing for 20 seconds on a staircase with 90 cm in height under two conditions, facing ascending (AscD) and descending direction (DesD). BioWare 4.1 was used to calculate the center of pressure (COP). Twoway ANOVA with repeated measure (height x direction) and pairwise comparisons were employed to verify differences in total path length, sway area, root mean square (RMS) of COP displacement, RMS of COP velocity, and mean power frequency (MPF) of COP. Results:The results indicated there is no interaction effect of height and facing direction on all COP parameters. Height had significant main effect on COP displacement and mean power frequency in antero-posterior (AP) direction. Facing direction had significant main effect on total path length, and RMS of COP velocity in AP direction. While facing AscD, the normalized total path length (112.76± 7.08% of foot length) was significantly larger than DesD (107.23± 6.70% of FL); the RMS of COP velocity in AP direction was significantly larger in AsD (6.34± 0.34% of FL•sec) than that in DesD (5.99± 0.31% of FL•sec). Conclusion(s): It is expected that facing DesD should put more threats on the children than AscD, and thus the children might show increases in COP velocity when facing DesD. However, the results demonstrate that sway velocity in AP direction and total path length of COP is greater when facing AsD than facing DesD, which were not consistent with the adults’ findings. Future studies should increase age range of the participants, so at what age the children adopt the adults’ like strategies can be determined. Implications: This study may help in understanding the development of balance control in children. This matter should be taken into consideration when planning the environment for children at different age.

Tectonic speed limits from plate kinematic reconstructions

The motion of plates and continents on the planet's surface are a manifestation of long-term mantle convection and plate tectonics. Present-day plate velocities provide a snapshot of this ongoing process, and have been used to infer controlling factors on the speeds of plates and continents. However, present-day velocities do not capture plate behaviour over geologically representative periods of time. To address this shortcoming, we use a plate tectonic reconstruction approach to extract time-dependent plate velocities and geometries from which root mean square (RMS) velocities are computed, resulting in a median RMS plate speed of ∼4 cm/yr over 200 Myr. Linking tectonothermal ages of continental lithosphere to the RMS plate velocity analysis, we find that the increasing portions of plate area composed of continental and/or cratonic lithosphere significantly reduces plate speeds. Plates with any cratonic portion have a median RMS velocity of ∼5.8 cm/yr, while plates with more than 25% of cratonic area have a median RMS speed of ∼2.8 cm/yr. The fastest plates (∼8.5 cm/yr RMS speed) have little continental fraction and tend to be bounded by subduction zones, while the slowest plates (∼2.6–2.8 cm/yr RMS speed) have large continental fractions and usually have little to no subducting part of plate perimeter. More generally, oceanic plates tend to move 2–3 times faster than continental plates, consistent with predictions of numerical models of mantle convection. The slower motion of continental plates is compatible with deep keels impinging on asthenospheric flow and increasing shear traction, thus anchoring the plate in the more viscous mantle transition zone. We also find that short-lived (up to ∼10 Myr) rapid accelerations of Africa (∼100 and 65 Ma), North America (∼100 and 55 Ma) and India (∼130,80 and 65 Ma) appear to be correlated with plume head arrivals as recorded by large igneous province (LIPs) emplacement. By evaluating factors influencing plate speeds over the Mesozoic and Cenozoic, our temporal analysis reveals simple principles that can guide the construction and evaluation of absolute plate motion models for times before the Cretaceous in the absence of hotspot tracks and seafloor spreading histories. Based on the post-Pangea plate motions, one principle that can be applied to pre-Pangea times is that plates with less than ∼50% continental area can reach RMS velocities of ∼20 cm/yr, while plates with more than 50% continental fraction do not exceed RMS velocities of ∼10 cm/yr. Similarly, plates with large portions of continental or cratonic area with RMS velocities exceeding ∼15 cm/yr for more than ∼10 Myr should be considered as potential artefacts requiring further justification of plate driving forces in such scenarios.

Characterizing turbulent flow over 3-D idealized and irregular rough surfaces at low Reynolds number

The focus of this work is to demonstrate that the response of flow over a rough wall is significantly different for idealized and irregular roughness when the spacing between the roughness elements (λ) is changed for a given height of the roughness (h). For this purpose, turbulence flow in a channel with walls covered with idealized and irregular roughness has been simulated where the λ/h has been systematically varied in the range of 3–35. A detailed study of the flow statistics such as mean flow, root mean square of velocity and vorticity fluctuations was performed. For the idealized roughness both the inner and outer layer of the turbulent boundary layer are altered due to surface roughness, whereas, only the inner layer is altered due to an irregular roughness with similar geometrical parameters. Two distinct regimes that are evident for flow over idealized roughness based on streamwise spacing (λ/h) can be unified using solidity ratio (measure of degree of sparseness) parameter. Irregular roughness exhibits no sensitivity to λ/h parameter, suggesting that instead of solidity ratio, statistical parameters such as skewness and kurtosis of roughness distribution are more important to classify flow over irregular roughness.

사이클론 청소기 내부 유동에 관한 수치해석적 연구

가정용 진공청소기는 기본적으로 집진장치(dust collector), 프리 필터(pre filter), 모터(motor), 배기 필터(exhaust filter)의 구조를 가지며, 흡입된 먼지가 포함된 공기는 이러한 구조를 지나 깨끗한 공기가 되어 대기로 방출된다. 본 연구에서는 실생활에 사용되고 있는 구조가 다른 2개의 사이클론 청소기를 선정하여 사이클론 청소기 내 집진장치의 내부 공기 유동에 대해 전산유체역학을 적용하여 집진성능을 평가하고자 하였다. 사이클론 콘(cyclone cone) 영역에서 공기의 유선(streamline)을 해석한 결과, 사이클론 콘 영역에서 상당한 선회수를 가지는 것을 확인하였다. 특정 형상의 청소기에 대한 전산해석 결과에서 출구에서의 속도 분포가 매우 불균일한 결과를 나타내었고 이로 인해 집진성능에 악영향이 나타남이 파악되었다. 이 문제를 해결하기 위해 집진장치 형상에 추가적으로 배플을 설치하여, 달라진 속도 분포에 의한 속도 RMS (Root Mean Square) 값의 개선을 평가하였다. General household vacuum cleaners consist of dust collector, pre filter, motor and exhaust filter, and the filtered clean air is discharged to the atmosphere. By using the CFD methods, we estimated the internal flow in two types of commercial cyclone vacuum cleaners to evaluate the dust collection performance. From the analysis, it was known that the number of revolution had higher values in cyclone cone region. CFD analysis in a specific showed non-uniform velocity distribution at outlet, which results in the deterioration of particle collection performance. In order to improve flow condition, the installation of baffle was proposed and the values of velocity RMS were estimated.

Large-eddy simulation of open channel flow with surface cooling

Results are presented from large-eddy simulations of an unstably stratified open channel flow, driven by a uniform pressure gradient and with zero surface shear stress and a no-slip lower boundary. The unstable stratification is applied by a constant cooling flux at the surface and an adiabatic bottom wall, with a constant source term present to ensure the temperature reaches a statistically steady state. The structure of the turbulence and the turbulence statistics are analyzed with respect to the Rayleigh number (Raτ) representative of the surface buoyancy relative to shear. The impact of the surface cooling-induced buoyancy on mean and root mean square of velocity and temperature, budgets of turbulent kinetic energy (and components), Reynolds shear stress and vertical turbulent heat flux will be investigated. Additionally, colormaps of velocity fluctuations will aid the visualization of turbulent structures on both vertical and horizontal planes in the flow. Under neutrally stratified conditions the flow is characterized by weak, full-depth, streamwise cells similar to but less coherent than Couette cells in plane Couette flow. Increased Raτ and thus increased buoyancy effects due to surface cooling lead to full-depth convection cells of significantly greater spanwise size and coherence, thus termed convective supercells. Full-depth convective cell structures of this magnitude are seen for the first time in this open channel domain, and may have important implications for turbulence analysis in a comparable tidally-driven ocean boundary layer. As such, these results motivate further study of the effect of surface cooling on tidal boundary layers simulated via an oscillating pressure gradient. Such large-scale structures may also have an important impact on RANS-based (Reynolds-averaged Navier–Stokes equations-based) modeling of turbulence within tidal, convective flows.

A sensor fusion method for tracking vertical velocity and height based on inertial and barometric altimeter measurements.

A sensor fusion method was developed for vertical channel stabilization by fusing inertial measurements from an Inertial Measurement Unit (IMU) and pressure altitude measurements from a barometric altimeter integrated in the same device (baro-IMU). An Extended Kalman Filter (EKF) estimated the quaternion from the sensor frame to the navigation frame; the sensed specific force was rotated into the navigation frame and compensated for gravity, yielding the vertical linear acceleration; finally, a complementary filter driven by the vertical linear acceleration and the measured pressure altitude produced estimates of height and vertical velocity. A method was also developed to condition the measured pressure altitude using a whitening filter, which helped to remove the short-term correlation due to environment-dependent pressure changes from raw pressure altitude. The sensor fusion method was implemented to work on-line using data from a wireless baro-IMU and tested for the capability of tracking low-frequency small-amplitude vertical human-like motions that can be critical for stand-alone inertial sensor measurements. Validation tests were performed in different experimental conditions, namely no motion, free-fall motion, forced circular motion and squatting. Accurate on-line tracking of height and vertical velocity was achieved, giving confidence to the use of the sensor fusion method for tracking typical vertical human motions: velocity Root Mean Square Error (RMSE) was in the range 0.04–0.24 m/s; height RMSE was in the range 5–68 cm, with statistically significant performance gains when the whitening filter was used by the sensor fusion method to track relatively high-frequency vertical motions.

Particle-in-cell simulation of two stream instability in the non-extensive statistics

AbstractWe have performed extensive one dimensional particle-in-cell (PIC) simulations to explore generation of electrostatic waves driven by two-stream instability (TSI) that arises due to the interaction between two symmetric counterstreaming electron beams. The electron beams are considered to be cold, collisionless and magnetic-field-free in the presence of neutralizing background of static ions. Here, electrons are described by the non-extensive q-distributions of the Tsallis statistics. Results shows that the electron holes structures are different for various q values such that: (i) for q &gt; 1 cavitation of electron holes are more visible and the excited waves were more strong (ii) for q &lt; 1 the degree of cavitation decreases and for q = 0.5 the holes are not distinguishable. Furthermore, time development of the velocity root-mean-square (VRMS) of electrons for different q-values demonstrate that the maximum energy conversion is increased upon increasing the non-extensivity parameter q up to the values q &gt; 1. The normalized total energy history for a arbitrary entropic index q = 1.5, approves the energy conserving in our PIC simulation.