Frequency Distribution Of Velocities Research Articles

Experimental Study on Ground Vibration Caused by the Blast Loading of an Explosion Vessel

To investigate the ground vibration caused by the internal blast loading of an explosion vessel while evaluating the damage caused by vibration propagation to surrounding buildings, a series of explosion vibration tests were carried out using an explosion vessel. The blasting vibration monitors recorded the vibration parameters, and the vibration velocity frequency distributions were analyzed by the Hilbert–Huang transform (HHT) method. The results show that the explosion vibration velocity is closely related to the explosive charge and propagation distance. The effect of an explosive charge and propagation distance on the vibration amplitude at frequencies of 20–60[Formula: see text]Hz is not apparent, but at frequencies of 5–10[Formula: see text]Hz, low-order frequencies are noticeable. Furthermore, the energy amplitude and vibration action duration increase with increasing explosive charge and decrease with increasing propagation distance. The results provide an essential reference for studying the propagation law and effects on ground vibration waves produced by blast loading in an explosion vessel.

Evaluation of a geomorphic instream flow tool for conducting hydraulic‐habitat modelling

AbstractConventional hydraulic‐habitat modelling methods are time‐consuming to implement. In response to repeated calls for more efficient and practical approaches, researchers have developed a geomorphic instream‐flow tool (GIFT) that combines a method to simulate reach‐averaged hydraulics at flows less than bankfull and depth and velocity frequency distributions to develop streamflow‐fish habitat relationships. This approach requires fewer resources to implement than conventional methods, but it has not been widely adopted because it has been subject to minimal testing and validation. This study evaluates the performance of GIFT by comparing its outputs to empirical measurements and conventional model outputs from eight rivers in western North America. The results of this comparison indicate that the root mean square errors for average depth and velocity were 0.078 m and 0.047 m/s, respectively, and the fit of modelled depth and velocity frequency distributions was satisfactory (index of agreement >0.9) for 11 of 15 surveys for depth and 12 of 15 surveys for velocity. GIFT‐derived fish habitat‐streamflow relationships peaked at lower flows than benchmark relationships in smaller streams (mean annual discharge [MAD] < 0.15 m3/s) and are markedly differed from the benchmark in the largest river (MAD of 87 m3/s). GIFT was also paired with a geomorphic regime model to predict the direction of changes in channel morphology and fish habitat following forest harvesting in one watershed. GIFT provides an alternative to conventional modelling approaches for single‐thread, gravel‐bed rivers with a MAD of around 15 m3/s or less. Application of this technique outside of these bounds, or in other regions should proceed with caution, as these scenarios have not been tested.

Analyzing the turbulent planetary boundary layer by remote sensing systems: the Doppler wind lidar, aerosol elastic lidar and microwave radiometer

Abstract. The planetary boundary layer (PBL) is the lowermost region of troposphere and is endowed with turbulent characteristics, which can have mechanical and/or thermodynamic origins. This behavior gives this layer great importance, mainly in studies about pollutant dispersion and weather forecasting. However, the instruments usually applied in studies of turbulence in the PBL have limitations in spatial resolution (anemometer towers) or temporal resolution (instrumentation aboard an aircraft). Ground-based remote sensing, both active and passive, offers an alternative for studying the PBL. In this study we show the capabilities of combining different remote sensing systems (microwave radiometer – MWR, Doppler lidar – DL – and elastic lidar – EL) for retrieving a detailed picture on the PBL turbulent features. The statistical moments of the high frequency distributions of the vertical wind velocity, derived from DL, and of the backscattered coefficient, derived from EL, are corrected by two methodologies, namely first lag correction and -2/3 law correction. The corrected profiles, obtained from DL data, present small differences when compared with the uncorrected profiles, showing the low influence of noise and the viability of the proposed methodology. Concerning EL, in addition to analyzing the influence of noise, we explore the use of different wavelengths that usually include EL systems operated in extended networks, like the European Aerosol Research Lidar Network (EARLINET), Latin American Lidar Network (LALINET), NASA Micro-Pulse Lidar Network (MPLNET) or Skyradiometer Network (SKYNET). In this way we want to show the feasibility of extending the capability of existing monitoring networks without strong investments or changes in their measurements protocols. Two case studies were analyzed in detail, one corresponding to a well-defined PBL and another corresponding to a situation with presence of a Saharan dust lofted aerosol layer and clouds. In both cases we discuss results provided by the different instruments showing their complementarity and the precautions to be applied in the data interpretation. Our study shows that the use of EL at 532 nm requires a careful correction of the signal using the first lag time correction in order to get reliable turbulence information on the PBL.

Large Eddy Simulation study on the structure of turbulent flow in a complex city

Large Eddy Simulation (LES) of atmospheric flows has become an increasingly popular modelling approach within the last years, as it has the potential to provide deeper insight into unsteady flow phenomena. LES can be improved and validated using specifically designed and well documented wind tunnel datasets. In this work, we evaluate the performance of LES against a wind tunnel experiment in a semi-idealized city (“Michel-Stadt”; CEDVAL-LES database) and use the LES results to study the structure of the turbulent flow at the particular urban area. The first, second and third order statistics are presented, as well as velocity frequency distributions and energy spectra. The results compare well with the experimental values. Information about special features of the flow field is also provided. A particular focus of this work is put on the influence of grid resolution on the results. Five different grids are examined and the required resolution for turbulent flow within the canopy layer is evaluated. This study reveals the strong potential of LES for urban flow simulations. It is shown that LES can assess highly non-Gaussian flow behaviour in street canyons, which has implications for urban ventilation, wind comfort assessment and urban design.

Convective-stratiform rainfall separation of Typhoon Fitow (2013): A 3D WRF modeling study

Surface precipitation budget equation in a three-dimensional (3D) WRF model framework is derived. By applying the convective-stratiform partition method to the surface precipitation budget equation in the 3D model, this study separated convective and stratiform rainfall of typhoon Fitow (2013). The separations are further verified by examining statistics of vertical velocity, surface precipitation budget, and cloud microphysical budget. Results show that water vapor convergence moistens local atmosphere and offsets hydrometeor divergence, and producing convective rainfall, while hydrometeor convergence primarily supports stratiform rainfall, since water vapor divergence and local atmospheric drying generally cancelled out. Mean ascending motions are prevailing in the entire troposphere in the convective region, whereas mean descending motions occur below 5 km and mean ascending motions occur above in the stratiform region. The frequency distribution of vertical velocity shows vertical velocity has wide distribution with the maximum values up to 13 m s^(-1) in the convective regions, whereas it has narrow distribution with absolute values confined within 7 m s^(-1) in the stratiform region. Liquid cloud microphysics is dominant in convective regions and ice cloud microphysics is dominant in stratiform regions. These indicate that the statistics results are generally consistent with the corresponding physical characteristics of the convective-stratiform rainfall structures generalized by previous studies.

Differences in Reproductive Behavior between Spawning and Non-Spawning Zebrafish Pairs and the Effects of 17α-Ethinylestradiol (EE2).

Reproductive success manifested by spawning and fertilization, in most fish, depends partly on an appropriate courtship behavior by both sexes. The zebrafish reproductive behavior can be resolved in some of its constituent elements by a computerized vision system and described in unbiased quantitative terms. Pairs of adult male and female zebrafish were monitored with automatic video tracking at 16 Hz for 45 min in a tank with a spawning area in one corner. Subsequently, spawning, if any, was registered and the swimming behavior and mutual interactions of the two fish were quantified. Further, temporal and frequency distributions of average velocity and turning rate were produced. It is demonstrated that the courtship behavior in spawning pairs differs markedly from non-spawning pairs with differences in both male and female behavior. EE2 (17α-ethinylestradiol), a contraceptive hormone found in aquatic environments, has only a slight effect on these behavior differences between spawning and non-spawning pairs.

Vertical distribution of buoyant Microcystis blooms in a Lagrangian particle tracking model for short‐term forecasts in Lake Erie

AbstractCyanobacterial harmful algal blooms (CHABs) are a problem in western Lake Erie, and in eutrophic fresh waters worldwide. Western Lake Erie is a large (3000 km2), shallow (8 m mean depth), freshwater system. CHABs occur from July to October, when stratification is intermittent in response to wind and surface heating or cooling (polymictic). Existing forecast models give the present location and extent of CHABs from satellite imagery, then predict two‐dimensional (surface) CHAB movement in response to meteorology. In this study, we simulated vertical distribution of buoyant Microcystis colonies, and 3‐D advection, using a Lagrangian particle model forced by currents and turbulent diffusivity from the Finite Volume Community Ocean Model (FVCOM). We estimated the frequency distribution of Microcystis colony buoyant velocity from measured size distributions and buoyant velocities. We evaluated several random‐walk numerical schemes to efficiently minimize particle accumulation artifacts. We selected the Milstein scheme, with linear interpolation of the diffusivity profile in place of cubic splines, and varied the time step at each particle and step based on the curvature of the local diffusivity profile to ensure that the Visser time step criterion was satisfied. Inclusion of vertical mixing with buoyancy significantly improved model skill statistics compared to an advection‐only model, and showed greater skill than a persistence forecast through simulation day 6, in a series of 26 hindcast simulations from 2011. The simulations and in situ observations show the importance of subtle thermal structure, typical of a polymictic lake, along with buoyancy in determining vertical and horizontal distribution of Microcystis.

Study on the flow instability of a spray granulation tower

Abstract The hydrodynamics of a jet-driven swirling flow has a dramatic influence on the separation performance of a spray granulation tower. To understand the macro-instabilities of the flow patterns, this work performs a detailed study on the gas flow field in a spray granulation tower with an array of nozzles. The experimental results attained by a phase Doppler particle analyzer (PDPA) indicate that the flow field is in a fully turbulent state and that a low-frequency oscillation exists in the spray granulation tower. The velocity profiles and frequency distributions obtained using the full-scaled grid system and the Reynolds stress model are in good agreement with experimental data. Based on the observed flow field, a general flow pattern is summarized. Both the experimental and numerical results indicate that a quasi-periodic unsteady velocity flow is observed in the spray granulation tower. Compared with the original spray granulation tower, it is beneficial for reducing the flow oscillation and velocity fluctuation when the baffle is added. The flow stability criterion proposed in this study can characterize the flow state in the spray granulation tower.

Temporal variation in biodeposit organic content and sinking velocity in long-line shellfish culture

We measured the organic content and sinking velocities of biodeposits from two scallop species (Chlamys farreri, Patinopecten yessoensis) and abalone (Haliotis discus hannai) that were cultured on suspended long-lines. Measurements were conducted every two months from April 2010 to February 2011. The shellfish were divided into three size groups (small, middle, and big sizes). At each sample point, we assessed biodeposit organic content, average sinking velocity, the frequency distribution of sinking velocities, and the correlation between organic content and sinking velocity. The organic content of biodeposits varied significantly among months (P 1.9 cm/s. The sinking velocities of biodeposits from C. farreri and P. yessoensis were 0.5–1.5 cm/s and from H. discus hannai were <0.7 cm/s. The organic content was significantly negatively correlated to the sinking velocity of biodeposits in C. farreri (P<0.001) and P. yessoensis (P<0.05).

A CPFD model for a bubbly biomass–sand fluidized bed

This study reports a computational particle fluid dynamics model for the numerical simulation of a sand fluidized bed with 8wt.% and 16wt.% biomass loadings. The proposed CPFD model, based on a Barracuda framework, is validated using experimental data obtained in a 15.2cm diameter bed with a 22.5cm static height. This fluidized bed unit is equipped with a pair of fiber optic sensors allowing one to obtain both the bubble size and bubble velocity frequency distributions in an ample range of experimental conditions. In addition to this, the first-, second-, and third-order statistical moments of the bubble size and the bubble velocity distributions are calculated for each one of the operating conditions studied. On this basis, the present study demonstrates that the proposed CPFD model reproduces the asymmetric character of both bubble size and bubble velocity distributions. In addition, the simulated and experimental bubble size and bubble velocity distributions yield close first-, second-, and third-order statistical moments. Accordingly, one can ascertain that the proposed CPFD model is quite satisfactory for establishing fluid flow patterns in sand–biomass fluidized bed gasifiers.

Response to “Comments on ‘Hydrodynamic and dispersion behavior in a non-porous silica monolith through fluid dynamic study of a computational mimic reconstructed from sub-micro-tomographic scans”’

We respond to the comments made by Hlushkou et al. (2013) [1] (JCA-13-207) to our earlier work [J. Chromatogr. A 1274 (2013) 65], wherein the authors have questioned the validity of our reconstruction of the bulk macropore space in a silica monolith and challenged the interpretations from subsequent computational fluid dynamic simulations. We provide an explanation as to why a monotonic trend in external porosity values cannot be expected with decreasing scanning resolutions. The observed deviations of the pore and skeleton size distributions from those in literature are explained based on the differences in methods used to calculate these distributions. The difference in the scaled axial velocity frequency distributions is explained based on the assumptions made and the distributions are redrawn to reflect the said assumptions. The normalized transient diffusion (peak parking) and dispersion simulations are repeated with a higher resolution of detection planes to measure the variance of spreading pulse, thereby providing an explanation for the anomalies pointed out in our earlier work. Finally, we explain our comparison of the computational expenses with previous work as a study of the trade-off in accuracy that results from the lower resolution scan and use of commercial CFD packages.

Velocity and Depth Distributions in Stream Reaches: Testing European Models in Ecuador

AbstractEuropean statistical hydraulic models developed in France and Germany were tested on how they predicted the frequency distributions of water depth and point velocity measured in 14 reaches in Ecuador during 25 surveys. First, the observed frequency distributions were fitted to parametric functions defined in Europe and the parameters were predicted from the average characteristics of reaches (e.g., discharge rate and mean depth and width) using European regressions. When explaining the frequency of three classes of velocity and three classes of depth among reach surveys, the fitted and predicted distributions had a low absolute bias (<3%). The residual variance of fits relative to the mean class variance was <18%. The residual variance of predicted frequencies was 30–61% for velocity classes and 20–36% for depth classes. Overall, the European models appeared appropriate for Ecuadorian stream reaches but could be improved. This study demonstrates the transferability of statistical hydraulic models ...

Atypical signatures of motor variability found in an individual with ASD

We provide objective metrics of sequential movements and study a young adolescent with Autism Spectrum Disorders (ASD) in relation to novice typical controls (TC) as they learned to perform beginners' martial–arts routines. We studied segments staged to hit an opponent simultaneously performed with supplemental segments. In TC instructed changes in speed had profound differential effects on the intended vs. supplemental segments that were absent in the ASD case. Moreover, the frequency-distribution of velocity and acceleration maxima in TC was well fitted by a Gamma distribution but in the ASD case the fit was exponential yielding uncannily precise motions with atypically low-range of spatio-temporal variability.

Sustained Decrease and Remarkable Increase in Red Blood Cell Velocity in Intraparenchymal Capillaries Associated With Potassium‐Induced Cortical Spreading Depression

To examine changes in red blood cell (RBC) velocity in intraparenchymal capillaries of rat cerebral cortex in response to KCl-induced cortical spreading depression (CSD). In isoflurane-anesthetized rats, the velocity of fluorescently labeled RBCs flowing in capillaries in layer I was measured with a high-speed camera laser-scanning confocal fluorescence microscope, with simultaneous monitoring of DC potential, the electroencephalogram (EEG), partial pressure of oxygen (PO(2) ), and cerebral blood flow (CBF). After KCl application, a transient deflection of DC potential (i.e., CSD) repeatedly appeared concomitantly with depression of EEG, and was propagated in the distal direction. PO(2) transiently decreased and CBF was slowly elevated. The frequency distribution of RBC velocity was shifted downward during CSD and was still low after the passage of CSD. When we observed RBC velocity in 38 individual capillaries, 10 capillaries exhibited slowed-down RBC during CSD and RBC velocity remained low in 2 even after the passage of CSD. On the other hand, RBCs with moderately (<3 mm/sec) or remarkably (>3 mm/sec) increased velocities were seen in 10 and 5 capillaries, respectively. CSD-induced excitation of neurons may sustainably decrease or greatly increase RBC velocity in capillaries.

Comparison of flow microdynamics for a continuous granular mixer with predictions from periodic slice DEM simulations

Using periodic slice discrete element method (DEM) simulations to model sections of a full continuous blender offers significant savings in computation cost. Before development of a periodic slice based continuous mixer model, the accuracy of periodic slice models for predicting full blender behavior needs to be examined. Flow microdynamics obtained from periodic slice simulations are compared against full blender results by examining speed and velocity frequency distributions. The periodic slice models are found to replicate full blender flow microdynamics well for central sections of the full blender. Reasonably good agreement is obtained for the inlet and outlet regions where the periodic boundary assumption is less valid. Results suggest that the use of periodic slice simulations to represent full blender behavior is a feasible approach which may be extended in the future to develop a full blender model. A small change in particle size is observed to have a negligible effect on the fill level of the continuous mixer, suggesting that larger particles may be used in DEM simulations to predict bulk flow quantities.

Habitat effects on depth and velocity frequency distributions: Implications for modeling hydraulic variation and fish habitat suitability in streams

Describing the velocity and depth attributes of stream channels is a basic goal of theoretical and applied hydrology and is also essential for modeling biological processes in streams. We applied frequency distributions (gamma probability functions fit to point velocity and depth data) to evaluate their ability to describe variation in hydraulic conditions at the channel unit scale among contrasting habitat types (pools, glides, riffles, and runs) at different flows in a small trout stream. Velocity and depth distributions differed systematically between habitat types, with linear regression explaining 65 and 72%, respectively, of variation in gamma distribution parameters related to skewness and kurtosis; however, distribution parameters were not significantly related to discharge. Relative depth explained 68–79% of the variation in slopes of at-a-station hydraulic geometry relationships between different habitat types. Differentiation of habitat types in a velocity–depth phase space was reduced at high flows, and differences in hydraulic geometry exponents were consistent with flow convergence at high discharge. Modeling variance in velocity and depth using locally derived gamma distributions, in conjunction with simple hydraulic geometry, provided accurate estimates of reach average habitat suitability for trout. Frequency distributions derived from a set of New Zealand streams provided much poorer estimates of habitat suitability. Frequency distributions are useful as an heuristic tool for understanding and modeling drivers of spatial variation in hydraulics, and provide a simple method to model hydraulic conditions in streams. However, general transferability of frequency distributions between streams would be improved by validating and refining existing relationships between distribution parameters and easily measured stream characteristics, like habitat type, channel size, gradient, and substrate caliber.

Prediction of fisheries physical habitat values based on hydraulic geometry and frequency distributions of depth and velocity

We propose a technique that allows the estimation of available physical fish habitat in small sized stream reaches (mean annual flow less than 3.5 m3/s) without the need to acquire and analyze extensive site‐specific data commonly used in many instream flow studies. The technique utilizes a modified form of previously published equations that estimate velocity and depth frequency distributions based on reach average velocity and depth which in turn can be calculated using widely known at‐a‐station hydraulic geometry equations. Velocity and depth frequency distributions are then combined with fish preferences for velocity and depth to produce habitat versus discharge relationships for a desired range of flows. When the resulting physical habitat versus discharge relationships for target fish species and life stages are compared to weighted usable area relationships (habitat versus discharge relationships derived using hydraulic and habitat models) developed from site‐specific studies, the prediction error was shown to be less than 15%.

Fall velocities of saltating sand grains in air and their distribution laws

In a cloud of blowing sand, collisions between falling sand grains and the sand bed are an important process that is the main source of additional saltating sand grains, because the collision process transfers momentum to the sand bed and initiates the liftoff of new sand grains. The initial liftoff and fall velocities of saltating sand grains are key parameters in the collision process, but little information exists on the subsequent fall velocities of the saltating sand grains. One important reason for this lack is that the collision process is unclear. Based on experimental data from high-speed multi-flash photographic images obtained in a wind tunnel and on a motion model of saltating sand grains, this paper discusses the fall velocities of saltating sand grains and the corresponding velocity frequency distributions. The results demonstrate that fall angles are small (less than 20°), and decrease with increasing frictional wind velocity. The vertical component of fall velocity increases with increasing frictional wind velocity, and is consistent with the initial vertical liftoff velocity. The fall angle and vertical velocity both follow a gamma distribution. The horizontal fall velocity mainly determines the resultant fall velocity, and both increase with increasing frictional wind velocity. The horizontal and resultant fall velocities follow a Pearson IV distribution. These results improve our understanding of the collision process between falling sand grains and sand beds and will also help us to modify the splash function that connects the parameters of falling saltating sand grains and their initial liftoff parameters.

Herding and escaping responses of juvenile roundfish to square mesh window in a trawl cod end

The movements of juvenile roundfish, mainly haddock Melanogrammus aeglefinus and whiting Merlangius merlangus, reacting to a square mesh window in the cod end of a bottom trawl were observed during fishing experiments in the North Sea. Two typical behavioral responses of roundfish are described as the herding response and the escaping response, which were analyzed from video recordings by time sequences of the movement parameters. It was found that most of the actively escaping fish approached the square mesh window at right angles by swimming straight ahead with very little change in direction, while most of the herded fish approached the net at obtuse angles and retreated by sharp turning. The herding and escaping responses showed significant difference when characterized by frequency distributions of swimming speed and angular velocity, and both responses showed large and irregular variations in swimming movement parameters like the panic erratic responses. It is concluded that an escaping or herding response to the square mesh window could be decided by an interaction between the predictable parameters that describe the stimuli of net and angular changes of fish response, such as approaching angle, turning angle and angular velocity.

Plume Generation Zones at the margins of Large Low Shear Velocity Provinces on the core–mantle boundary

Large Igneous Province (LIP) eruption sites of the past 300 My lie vertically above 1% slow shear wave velocity ( V s) contours bounding the African and Pacific Large Low Shear Velocity Provinces (LLSVPs) at the core–mantle boundary (CMB), or in the cases of the Siberian and Columbia River LIPs, bounding one or other of two smaller, Low Shear Velocity Provinces (LSVPs). Steep gradients in V s at the CMB coincide with those 1% slow contours. The sites of 24 active hotspot volcanoes project down to the same narrowly defined borders of the LLSVPs at the CMB. Plumes that have generated LIPs and major hotspot volcanoes have risen only from the immediate neighbourhoods of the 1% slow V s contours at the CMB which thus define Plume Generation Zones (PGZs). PGZs projected vertically upward approximately match the + 10 m elevation contour of the geoid showing that the LLSVPs are a dominant control on the positively elevated geoid. Minima in the frequency distribution of shear wave velocities in the lowermost mantle near V s = − 1% indicate that regions with more negative velocities, forming ∼ 2% of total mantle mass, are likely to be of material compositionally different from the rest of the mantle. Because all LIP eruption sites with ages younger than 300 Ma lie above the borders of LLSVPs or LSVPs at the CMB, PGZ footprints are inferred to have remained in the same places for the past 300 My. Because no plumes have risen from the interior of the LLSVPs and because no lithospheric slabs have penetrated those bodies the volumes of the LLSVPs are inferred to have also remained unchanged for the past 300 My. Because the LLSVPs are the dominant control on the positively elevated areas of the geoid those too must have remained as they now are since 300 Ma. The LLSVPs are not rising buoyant objects but stable features of the deep mantle. LIPs have been erupted throughout the past 2.5 Gy indicating that PGZs comparable to those of the past 0.3 Gy and LLSVPs (of which PGZs mark the margins at the CMB) have also existed for at least that long. LLSVPs could thus form the isolated reservoir invoked by some to explain the distinctive isotopic compositions of terrestrial rocks. PGZs lie at places where the boundaries of: (i) The outer core, (ii) one of the LLSVPs or LSVPs, and (iii) the seismically faster part of the deep mantle meet. Horizontal temperature gradients across the steeply inclined margins to the LLSVPs, the interiors of which are hotter than the surrounding mantle, at the CMB are key controls for the generation of plumes. Near the CMB the association of the high temperature of the outer core with an inclined thermal boundary layer at the margins of LLSVPs facilitates the generation of mantle plumes in the PGZs.