Median Diameter D50 Research Articles

A new model for the viscosity of highly concentrated multi-sized particulate Bingham slurries

ABSTRACTBench scale tests were carried out to investigate the rheological properties of multi-sized particulate Bingham slurries at high solid concentrations ranging from 50% to 70% by weight. In addition, rheological data from Biswas et al. (2000) and Chandel et al. (2009, 2010) have also been considered. Based on these extensive amount of rheological data, an empirical model is proposed for viscosity as a function of solid volume fraction (ɸ), maximum solid volume fraction (ɸm), median particle diameter (d50), and coefficient of uniformity (Cu) using optimization and nonlinear least-square curve-fitting technique. The proposed model shows good agreement with the experimental data considered in the present study and is found to be much better than the previously developed models in predicting the viscosity of multi-sized particulate Bingham slurries at high solid concentrations.

Sandbar and beach-face evolution on a prototype coarse sandy barrier

On steep beaches, the cross-shore movement of sand in response to ‘erosive’ storm waves and ‘accretive’ swell waves can lead to temporal changes between a barred winter profile and a non-barred summer profile with a pronounced berm in the upper swash zone. Despite recent improvements in predicting berm formation and evolution within process-based morphodynamic models, substantial demand for improvement in understanding swash processes and associated surf–swash sand exchange remains. Here, we analyze bed level data collected on a near-prototype, 4.5-m high and 75-m wide sandy beach (median grain diameter D50=430μm) with a lagoon situated at its landward side. In particular, we distinguish between surf–swash sand exchange (time scale of tens of minutes to hours), the net effect of single and multiple swash events on the entire beach face (time scale of a few seconds to hours), and instantaneous bed variability at 3 cross-shore locations within individual swashes. During ‘erosive’ waves (Hs=0.8m, Tp=8s) sand on the initially 1:15 planar profile was predominantly eroded from the inner surf zone to be deposited in the outer surf zone as a sandbar, indicating minimal surf–swash sand exchange. Subsequent ‘accretive’ waves (Hs=0.6m, Tp=12s) caused substantially larger surf–swash sand exchange: the pre-existing sandbar migrated onshore and decayed, with the sand ending up on the beach face in a prominent (up to 0.7m high), steep (1:6) berm. We found the dynamics of the berm to be governed primarily by wave conditions and the antecedent morphology, with ground water gradients of additional importance when morphodynamic feedback between swash flow and the berm is small. The observed bed level change within a swash and averaged over a swash event could be substantial (several centimeters) during all wave conditions, but the net (i.e., averaged over multiple swash events) bed level change was strongly suppressed because erosive and accretionary swashes nearly balanced. In addition, the local beach face slope could be instantaneously ≈25% steeper or shallower than the median slope, or the initial or final slope. We anticipate that our data will stimulate new model development, as to increase the range of conditions and settings in which morphodynamic models can be applied realistically and reliably.

Properties and application of a novel type of glycidyl azide polymer modified double-base spherical powders

GAP modified double-base powder was prepared by an internal solution method and applied in cross-linked modified double-base propellants. It was found that if GAP content was not more than 30 %, the modified double-base powders had high roundness rate, no bonding between the particles and excellent fluidity. The median diameter (d50) of powders was decreased from 90.24 to 72.41 μm when the amount of GAP increased from 0.0 to 30.0 %. The thermal decomposition peak temperatures of –N3 and GAP’s main chain were found to be lower for the 10.0, 20.0 and 30.0 % GAP modified powders than the corresponding peak temperatures for pure GAP. The drop mass impact sensitivity of the modified powders is reduced as the mass ratio of GAP increases. It was experimentally shown that GAP modified double-base powders can improve the mechanical characteristics of the propellant with a maximum tensile strength (σm) between 0.45 MPa < σm < 1.18 MPa and an elongation at maximum tensile strength (em) between 29.80 % < em < 52.60 % at temperatures of −40, +20 and +50 °C.

Settling Efficiency of Urban Particulate Matter Transported by Stormwater Runoff.

The main purpose of control measures in urban areas is to retain particulate matter washed out by stormwater over impermeable surfaces. In stormwater control measures, particulate matter removal typically occurs via sedimentation. Settling column tests were performed to examine the settling efficiency of such units using monodisperse and heterodisperse particulate matter (for which the particle size distributions were measured and modelled by the cumulative gamma distribution). To investigate the dependence of settling efficiency from the particulate matter, a variant of the evolutionary polynomial regression (EPR), a Microsoft Excel function based on multi-objective EPR technique (EPR-MOGA), called EPR MOGA XL, was used as a data-mining strategy. The results from this study have shown that settling efficiency is a function of the initial total suspended solids (TSS) concentration and of the median diameter (d50 index), obtained from the particle size distributions (PSDs) of the samples.

Magnitude of Air Pollution by Heavy Metals Associated with Aerosols Particles in Algiers

This study evaluated for the first time in Algeria the pollution levels reached by different size distribution of aerosol particles and heavy metals associated with them in a site influenced by the emissions of the road traffic in Algiers. The analysis of heavy metals Fe, Pb, Cu, Mn, Ni, Co and Cd transported by the aerosol particles shows that heavy metals are enriched in varying degrees in the different size distributions. The Pb and Cd and to a lesser degree the Ni and Co are more abundant in the PM-1. The Pb, for example shows a mass fraction of 0.58% in the PM-1, whereas this is only up to 0.40% in the PM-10. Conversely, Fe, Mn and Cu are enriched in the PM-10 than in the PM-1. In order to check in which extent some heavy metals present correlations between them, we compared the levels of heavy metals in pairs in size distribution PM-10, PM-3 and PM-1. These results confirm the data on the enrichment of Pb and Cd in the fraction of very fine particles and the predominant presence of Fe and Mn in coarse particles. Similar to the case of PM-10, we determined the median aerodynamic diameter d50 of both heavy metals Fe and Pb, respectively representative of natural sources and entropy sources (road traffic). The differences in the sizes of metal particles and differences of origin or source can also be visualized by the curves of modal distribution. Distribution curves obtained both for Fe than for Pb are of the mono-modal type.

Experimental study of flow intensity influence on 2-D sand ripple geometry characteristics

Sand ripples are common bedforms. The formation of sand ripples is related to flow conditions; different flow conditions cause different ripple geometries. The main aim of this study was to assess the relationship between flow intensity and two-dimensional ripple geometry characteristics. The experiments were carried out in a laboratory flume with natural sand whose bulk density ρs was 2 650 kg/m3 and median diameter D50 was 0.41 mm. The Froude number (Fr), a flow intensity parameter, varied from 0.16 to 0.53, entirely within the subcritical range. Two-dimensional sand ripple geometry was measured and processed via statistical methods. The probability distributions of ripple length and height were obtained with different flow conditions. Through dimensionless analysis, the relationship between the flow intensity parameter (grain size Reynolds number Re*) and the sand ripple geometry characteristic length (Λ) and height (Δ) was analyzed, and two formulas were obtained: Λ/D50 = 191.76Re*03 and Δ/D50 = 1.97Re*13, which are consistent with previous research results.

Measurement of Stiffness Anisotropy in Kaolinite Using Bender Element Tests in A Floating Wall Consolidometer

Abstract A new floating wall consolidometer-type bender element testing system was developed to study the stiffness anisotropy of clays at applied vertical stresses up to 800 kPa. One-dimensional slurry-consolidated Georgia RP-2 kaolinite samples, prepared with 0.005 and 1 mol/l NaCl solutions, were tested in this system. A floating wall design eliminated the detrimental bending moment that acts upon the horizontally installed benders as a result of soil settlement in a traditional fixed wall setup, which significantly improved the signal quality and bender reuse. Floating wall–soil interface resistance was quantified with pulling tests. Analytical equations were then derived to calculate the wall resistance-corrected vertical effective stress. As a result, stresses applied to the soil were more accurately determined. The bender element (BE) test was used to measure kaolinite's shear wave velocity (Vs), thereby quantifying the small strain stiffness of soils. Average Vs results for RP-2 kaolinite were lower than those for other kaolinites reported in the literature. This was postulated to be primarily due to the longer and more tortuous chains of particle contacts associated with the smaller median diameter (d50 = 0.36 μm) of RP-2 kaolinite samples. BE test results indicated that Vs increased with stress, density, and concentration. The hierarchy of Vs in three orthogonal directions (i.e., hh &amp;gt; hv &amp;gt; vh) agreed with results in the literature. It was also illustrated that Vs anisotropy increased with applied stress and decreased during unloading. In addition, a comparison was made between the BE test in the new floating wall consolidometer and the BE test in a triaxial testing setup.

Processing and Microstructure Properties of 7055-Al Alloy Prepared by Low-Pressure Spray Forming

Spray forming is a new developed advanced metal-forming process, of which the property benefits from rapid solidification. The porosity produced during the atomization progress can obviously decrease the material performance. In this paper, a self-designed Laval-type atomizer is used to improve atomization efficiency. The atomization results show that the atomizer can obtain well atomization effect at a relative lower atomization pressure, and the mass median diameter d50 is 63.5μm and 43.4μm when the atomization gas pressure P0=0.4 and 0.8MPa separately. The technological parameters are optimized by overall considering the atomized droplet size, gas consumption, deposition property, and the metal yield. By the designed atomizer, the as-deposited billet with lower porosity content can be obtained with the technological parameters of the melting temperature T=800°C, atomization pressure P0=0.6MPa, and spray distance h=500mm. Further test with the deposited billet show that the grain size of the spray formed 7055-Al alloy is mainly ranging 10~30μm, which is about one third of that of as-cast billet.

Properties and Application of a Novel Type of Glycidyl Azide Polymer (GAP)‐Modified Nitrocellulose Powders

AbstractGAP‐modified nitrocellulose powders were prepared by an internal solution method and applied in cross‐linked modified double base (XLDB) propellants. It was found that GAP‐modified nitrocellulose powders exhibit high round, no bonding between the particles and excellent fluidity. When the amount of GAP increased from 10.0 % to 30.0 %, the median diameter (d50) of powders decreased from 134.53 μm to 94.54 μm. The thermal decomposition process of GAP appeared also in the GAP‐modified nitrocellulose powders, but the thermal decomposition peak temperatures of N3 and the GAP main chain were found to be lower for the 10.0 % and 20.0 % GAP‐modified samples than the corresponding peak temperatures for pure GAP, respectively. The plasticizing properties of GAP‐modified nitrocellulose powders are better than that of pure nitrocellulose powders, and the drop weight impact sensitivity of the modified powders is reduced as the mass ratio of GAP increases. It was experimentally shown that GAP‐modified nitrocellulose powders can improve the mechanical characteristics of the propellant with a maximum tensile strength (σm) between 0.36 MPa&lt;σm&lt; 1.10 MPa and an elongation at maximum tensile strength (εm) between 28.8 %&lt;εm&lt;51.8 % at temperatures of −40, +20 and +50 °C.

Determining factor of median diameter in intermetallic compound nanoparticles prepared by pulsed wire discharge

The preparation of NiAl intermetallic compound nanoparticles was carried out by pulsed wire discharge (PWD) using twisted pure Ni and Al wires in N2 ambient gas with varying number of turns of the wire (Nt), energy ratio (K), and ambient gas pressure (P). From the voltage and current waveforms during the wire heating, the energy deposition ratio up to the voltage peak (Kp) was calculated. It increased with an increase in Nt to 0.4 turns/mm and with increases in K and P. Under all the conditions, with an increase in Kp, the Ni composition ratio of the prepared particles (CNi) became closer to that of the wire (= 51.2 mol %). Furthermore, the collection rate (Rc) increased and the median particle diameter (d50) decreased. In particular, the change in d50 due to the change in Nt was not predicted by the relationship of d50 and Dth in our previous report. Single-phase NiAl intermetallic compound nanoparticles were successfully prepared under the condition in which Nt is 0.4 turns/mm, K is 3.4, and P is 100 kPa, where relatively high value of Kp was obtained. From these results, Kp was determined to be an important factor that determines the composition, collection rate, and median diameter of intermetallic compound nanoparticles synthesized by PWD using different kinds of twisted wires under various experimental conditions. This may be because of the selective wire heating in high-resistance parts that are associated with the introduction of lattice defects and/or necks by overwinding.

Synthesis and characterization of the NiFe2O4/Ni3Fe nanocomposite powder and compacts obtained by mechanical milling and spark plasma sintering

Nanocomposite powder and compacts of NiFe2O4/Ni3Fe type were synthesized using mechanical milling and spark plasma sintering (SPS) techniques. The samples have been investigated by X-ray diffraction (XRD), laser particles size analysis, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX). The nanocomposite powder was obtained by mechanical milling in a high planetary ball mill of nanocrystalline NiFe2O4 and nanocrystalline Ni3Fe powders. The nanocomposite powder consists from Ni3Fe particles covered at the surface with a layer of NiFe2O4 fine particles and NiFe2O4 particles. The nanocomposite particles have the median diameter d50 of 1.6μm. The sintering in 400–600°C temperature range preserve the nanocomposite phases but lead to a high porosity. The nanocomposite compacts consist in Ni3Fe clusters surrounded by NiFe2O4. A sintering temperature of 800°C leads to a good density for the nanocomposite compacts and to the new phase formation. The new phase is a wustite type (Fe1−xNixO) and is formed at the metal/ceramic interface. A change in the Ni/Fe ratio, in the spinel structure, was evidenced during sintering. Sintering at a temperature of 800°C, leads to the formation of a mixed iron–nickel ferrite with a very small amount of nickel, Ni1−xFexFe2O4.

Particle Size Determining Equation in Metallic Nanopowder Preparation by Pulsed Wire Discharge

Copper nanopowders are prepared by pulsed wire discharge (PWD) using copper wires in nitrogen gas. From experimental results obtained in the present study and published literature, a relationship to predict the particle size of powders prepared by PWD is proposed. A theoretical plasma/vapor density (Dth), which is the most important factor for controlling the particle size is defined as mPEc-1, where m, P, and Ec are the weight of the wire, pressure of nitrogen gas, and charged energy in the capacitor, respectively. From high-speed photographs obtained during PWD, the relationship between the measured Dexp and Dth is shown by Dexp∝Dth0.6. The relationship between the median particle diameter d50 and Dth is found to be d50∝Dexp∝(Dth0.6)0.4 by transmission electron microscopy observations. This empirical relationship is in agreement with that expected from the formation and growth of particles via Brownian coagulation of free molecules. From the above relationship, it is possible to predict and control the particle size of powders prepared by PWD.

FIELD INVESTIGATION OF SIZE DISTRIBUTION OF SUSPENDED SEDIMENT USING LISST-100

To investigate size distributions of suspended sediments in the surf zone, a field measurement using LISST (Laser In-Situ Scatter and Transmissometer) was conducted at Hasaki, Japan. The time series of suspended sediment concentration (SSC) for a grain size in the sand range (63 to 500 ï­m) had strong correlations with those for other sand grain sizes, and the strong correlations were also observed in the silt range (2.5 to 28 ï­m). However, at zero time lag, the time series of SSC for sand grain sizes had little correlations with those for silt sizes. With considering time lag, the time series of SSC for sand sizes had weak correlations with those for silt sizes, but which time series lagged behind the others, sand particles or silt particles, was not clear. When the total SSC CLISST was larger than 0.2 g/l, the median sediment diameter d50 was scattered around 185 ï­m. However, at CLISST &lt; 0.2 g/l, d50 increased as CLISST increased. With the increase in d50 from 150 to 200 ï­m, the sorting coefficient decreased from 2.4 to 1.2 and the skewness increased from 0.7 to 1.0.

Biocomposites from wheat proteins and fibers: Structure/mechanical properties relationships

For the first time, biocomposites from wheat by-products, i.e. wheat gluten and wheat straw fibers, were prepared using a thermomechanical process. Three types of wheat straw fibers displaying contrasted sizes (median diameter d50=1.1mm, 62μm and 8μm), morphologies and surface reactivities were prepared by successive grinding processes (cut milling (CM), impact milling (IM) and ball milling (BM), respectively). The main objectives of the present study were (i) to gain further scientific knowledge about the impact of fibers characteristics on the mechanical properties of these composite materials, and (ii) to evaluate in which extent the addition of wheat straw fibers could decrease the final cost of materials without altering their mechanical properties. Mechanical properties were assessed through tensile tests and discussed in relation to the structure of materials, especially to the interfacial adhesion between the fiber and the matrix. Globally, an increasing fiber content up to 11.1vol% led to an increase in both the Young's modulus and the stress at break, and to a reduction in the strain at break. Experimental Young's moduli were well predicted by the Tsai–Pagano model for the three types of fibers. Data of specific mechanical energy consumed upon processing, contact angle measurements and observations of cryo-fractured surfaces allowed to demonstrate that the adhesion at the interface wheat straw fiber/wheat gluten was improved by (i) an increased hydrophobicity of wheat straw fibers, which was induced by successive grinding, and (ii) a higher specific surface of fibers which was favoured in the case of small fibers. The interfacial adhesion was improved in the order BM>IM>CM whereas the fiber aspect ratio decreased in the order CM>IM>BM. Thus, a competition between these parameters could occur, explaining why no significant difference in reinforcing effect was achieved between the three types of fibers. Finally, the reinforcing effect of wheat straw fibers was also ascribed to a deplasticizing effect, which was particularly pronounced for BM wheat straw fibers.

Discussion of “Mean Velocity of Mudflows and Debris Flows” by Pierre Y. Julien and Anna Paris

The authors predicted mudflow and debris flow velocities with 350 field and laboratory measurements and obtained a slight trend for V=u to increase with h=d50, and the ratio of V=u is approximately 10 and rarely exceeds 30. The logarithmic relationship of turbulent resistance agrees reasonably well with the measurements. Good results also are obtained with the Manning-Strickler approach. The dispersive stress equation also compares well with the measurements, but only when h=d50 < 50. For individual series data such as Hashimoto and Puerco, there is a trend for V=u to increase with h=d50. But for other individual series data, such as Davies, Rickenmann, Paris, St. Helens, Nevado del Ruiz, Wanglin, Wang, and Wenhai, there is a trend for V=u to decrease with h=d50 (Fig. 1 of the original paper). The discussers have some field data that also show the same phenomena, which are presented in Fig. 1. The database includes a total of 119 flow velocity measurements, in which each point includes flow depth, density (volume concentration), median grain diameter d50, grain size of less than 10% d10, and slope. The data of Jiangjia were obtained from the field measurements in Jiangjia Ravine, Yunnan, China, in 1999; the data of Hunshui were obtained from the field measurements in Hunshui Ravine, Yunnan, China, in 1976–1978; and the data of Liuwan were obtained from the field measurements in Liuwan Ravine, Gansu, China, in 1963–1964. Debris flow is a gravity flow, and the gravity force plays an important role in the movement of debris flow. So debris flow moves on a large slope and deposits on a small slope. Fei and Su (2004) showed that the main driving force of debris flow is provided by particles, not by water. When the volume concentration C 1⁄4 0:27 (or density ρ 1⁄4 1:46 g=cm3), the particle driving force is equal to the water driving force in debris flow. They defined that the minimum density of debris flow is 1:46 g=cm3, and 1:46–1:80 g=cm3 is the range of less viscous debris flow. Therefore, the minimum density of viscous debris flow is 1:80 g=cm3 (C 1⁄4 0:47) (Fei and Su 2004; Yu 2008a). Two types of shear stresses describe these two kinds of debris flows: (1) the viscous stress for viscous debris flow, and (2) the turbulent stress for less viscous debris flow (Fei and Su 2004). As the driving force of debris flow is provided primarily by particles, the coarse particle plays an important role in the movement of debris flow, especially for viscous debris flow with a large volume concentration. So the larger particle diameter, the larger is the velocity. There is a trend for V to increase with d50, and there is a trend for V=u to increase with d50=h. Two empirical equations of mean velocity of viscous debris flow described this relationship (Wu et al. 1993; Yu 2001): V u 1⁄4 27:57 d50 h 0:245 ð1Þ

Closure to “Mean Velocity of Mudflows and Debris Flows” by Pierre Y. Julien and Anna Paris

The authors predicted mudflow and debris flow velocities with 350 field and laboratory measurements and obtained a slight trend for V=u to increase with h=d50, and the ratio of V=u is approximately 10 and rarely exceeds 30. The logarithmic relationship of turbulent resistance agrees reasonably well with the measurements. Good results also are obtained with the Manning-Strickler approach. The dispersive stress equation also compares well with the measurements, but only when h=d50 < 50. For individual series data such as Hashimoto and Puerco, there is a trend for V=u to increase with h=d50. But for other individual series data, such as Davies, Rickenmann, Paris, St. Helens, Nevado del Ruiz, Wanglin, Wang, and Wenhai, there is a trend for V=u to decrease with h=d50 (Fig. 1 of the original paper). The discussers have some field data that also show the same phenomena, which are presented in Fig. 1. The database includes a total of 119 flow velocity measurements, in which each point includes flow depth, density (volume concentration), median grain diameter d50, grain size of less than 10% d10, and slope. The data of Jiangjia were obtained from the field measurements in Jiangjia Ravine, Yunnan, China, in 1999; the data of Hunshui were obtained from the field measurements in Hunshui Ravine, Yunnan, China, in 1976–1978; and the data of Liuwan were obtained from the field measurements in Liuwan Ravine, Gansu, China, in 1963–1964. Debris flow is a gravity flow, and the gravity force plays an important role in the movement of debris flow. So debris flow moves on a large slope and deposits on a small slope. Fei and Su (2004) showed that the main driving force of debris flow is provided by particles, not by water. When the volume concentration C 1⁄4 0:27 (or density ρ 1⁄4 1:46 g=cm3), the particle driving force is equal to the water driving force in debris flow. They defined that the minimum density of debris flow is 1:46 g=cm3, and 1:46–1:80 g=cm3 is the range of less viscous debris flow. Therefore, the minimum density of viscous debris flow is 1:80 g=cm3 (C 1⁄4 0:47) (Fei and Su 2004; Yu 2008a). Two types of shear stresses describe these two kinds of debris flows: (1) the viscous stress for viscous debris flow, and (2) the turbulent stress for less viscous debris flow (Fei and Su 2004). As the driving force of debris flow is provided primarily by particles, the coarse particle plays an important role in the movement of debris flow, especially for viscous debris flow with a large volume concentration. So the larger particle diameter, the larger is the velocity. There is a trend for V to increase with d50, and there is a trend for V=u to increase with d50=h. Two empirical equations of mean velocity of viscous debris flow described this relationship (Wu et al. 1993; Yu 2001): V u 1⁄4 27:57 d50 h 0:245 ð1Þ

Application of Amorphous Boron Granulated With Hydroxyl‐ Terminated Polybutadiene in Fuel‐Rich Solid Propellant

AbstractAmorphous boron powder granulated with HTPB, whose particle diameter could be controlled, was prepared by mechanical mill method. It was found that amorphous boron powder could be granulated with HTPB binder to form B‐HTPB particles, whose median particle diameter (d50) and specific surface area are in the range of 125.0–431.0 µm and 0.02–0.1 m2 g−1, respectively. The B‐HTPB particles could be dispersed in the HTPB binder with relatively low viscosity compared with direct addition of amorphous boron powder to the HTPB binder. The experimental results showed that the content of boron particles in a fuel‐rich propellant could be increased by addition of B‐HTPB particles and the combustion characteristics of the fuel‐rich solid propellant could be improved.

Obtaining solder powders by centrifugal atomization of melt

An experimental installation for obtaining Sn-Pb and Sn-Cu solder powders by the centrifugal atomization of a melt film is described. The effect of various parameters on the median diameter D 50 and the uniformity of the POS-61 powder is studied. It is found that the latter becomes worse with an increase in the disk rotary speed, and the value of D 50 decreases, reaching 36 μm at a speed of 25000 rpm. The optimum height of the film of a melt jet at which the minimum size of powder particles is observed is experimentally determined (15 mm). The effect of oxygen on the oxidation level, fluidity, and bulk density of the powder is studied. At an oxygen content of 0.01 vol % in the atomization medium, the oxygen concentration in the POS-61 powder does not exceed 0.004 wt %, the fluidity of the powder is 11 s, and its bulk density is 4.98 g/m3.

Experimental Study of Sand and Slurry Jets in Water

This paper presents the results of an experimental study of turbulent sand jets and sand-water slurry jets impinging vertically into a stagnant water body. The jets contained silica sand with a median diameter D50 of 206 μm , and with an initial concentration 0.60 by volume for the sand jets, and 0.055–0.124 by volume for the slurry jets. The jets had densimetric Froude numbers between 2.0 and 5.94. The sand concentration and velocity profiles were measured simultaneously using a novel fiber optical probe, up to a distance of 130 do for sand jets, and 65 do for slurry jets, where do is the jet diameter at the water surface. The jets were found to have self-similar Gaussian profiles. The centerline sand concentration within the jets was found to decrease rapidly, following trends similar to single phase plumes. The centerline sand velocity profile decreased significantly before reaching a plateau region. The “terminal” centerline sand velocity within this region varies somewhat depending upon sand mass flu...

Mean Velocity of Mudflows and Debris Flows

Models to predict mudflow and debris flow velocities are tested with 350 field and laboratory measurements. Overall, the turbulent model performs best while the dispersive stress approach only compares well with the measurements when the flow depth h is less than 50 times the median particle diameter d50 . The analysis of field measurements shows that the ratio of mean flow velocity V to shear velocity u∗ is approximately 10, rarely exceeds 30, and increases slightly with relative submergence h/ d50 . The best overall agreement with laboratory and field velocity measurements is obtained with V=5.75 u∗ log h/ d50 .