Flow Front Velocity Research Articles

Measurement of dynamic capillary pressure and viscosity via the multi-sample micro-slit rheometer

Abstract We develop two direct methods to simultaneously measure the dynamic capillary pressure and the viscosity of fluids by application of differential forces during flow into micro-channels. In the first method, a series of external pressures is applied in conjunction with the dynamic capillary pressure and a “Bagley analysis” is applied to the flow front velocity, and in the second, we utilize differential gravitational forces. By explicitly measuring the dynamic capillary pressure, the measurement window of the recently developed multi-sample micro-slit rheometer is extended to the regime where capillary forces are significant. These measurement methods will be useful in understanding filling flows encountered in diverse areas such as microfluidics, oil recovery and biological transport.

Ground vibrations produced by rock motions and debris flows

In this study we compare ground vibrations generated by various rocks and debris flows at the same channel to explore the origin of ground vibrations caused by debris flows. In field experiments we identified the ground vibrations caused by motions of individual rocks. Ground vibrations were detected by geophones and analyzed in the time‐frequency domains. We found that ground vibrations caused by individual rocks were 10–150 Hz and that larger stones generate ground vibrations with lower peak frequencies. A sphere‐packing model of granular rocks was used to estimate the propagation speed of ground vibrations. This was found to be underestimated when compared with our experimental data. The signal decay rate was obtained under the assumption that ground vibrations propagate as exponentially attenuating cylindrical waves. Ground vibrations produced by a debris flow at Ai‐Yu‐Zi Creek, Nan‐Tou, Taiwan, on 2 July 2004 revealed that the debris flow forefront produced vibrations lower than 50 Hz and ranged between 50 and 100 Hz after the front had passed. When the main front was closest to the sensor, the frequency spectrum covered a wide range, from 10 to 250 Hz. The mean velocity of the debris flow front was 13.3 m/s. Frequencies of ground vibrations caused by individual rocks are within the frequency range of ground vibrations captured during the debris flow, confirming that one of the main sources of ground vibration caused by debris flows is the interaction of rocks or boulders with the channel bed.

Measurement of Ultra High-Speed Injection Molding Process Using Thin Bar-Flow Cavity

In this study, we investigated the correlation between the flow-front velocity and gas pressure inside the cavity during ultra high-speed filling under different gas-vent conditions and sprue volumes using polypropylene and a thin bar-flow cavity mold with a thickness of 0.5mm. The results are summarized as below.(1) In the case of normal exhaust (with gas-vent) and forced exhaust (with vacuum-pumping), the resin completely filled the cavity, but without gas-vents, the flow front velocity dropped and led to incomplete filling. In addition, the gas pressure in the cavity exceeded 4MPa.(2) With a reduced volume sprue of about 40% the normal volume, the peak gas pressure inside the cavity dropped, the speed of the resin in the runner increased (about 30%), and the flow front advance velocity in the cavity also increased (about 35%). It was also found that the flow length increased by about 10%, indicating that a decrease in the sprue volume contributed to increasing flow length.

Examining flow emplacement through the surface morphology of three rapidly emplaced, solidified lava flows, K?lauea Volcano, Hawai'i

The surface morphologies (pāhoehoe and ‘a‘ā) of three short-duration, high effusion rate Kīlauean lava flows record important information about basaltic lava flow emplacement. Variations in the distributions of surface morphology with distance from the vent indicate the cumulative effects of both intrinsic (i.e. composition, temperature, crystallinity) and extrinsic (i.e. topography, effusion rate, flow velocity) parameters of emplacement. Detailed surface mapping with aerial photos and radar imagery reveal that all three flows exhibit a flow facies evolution common to Hawaiian ‘a‘ā flows of (1) pāhoehoe sheet flows, (2) ‘a‘ā-filled channels within pāhoehoe sheets, and (3) channelized ‘a‘ā. The resulting surface morphology distribution is similar among flows, although differences in the length scale of the distribution exist. We characterize the surface morphology distribution by the distance from the vent to the onset of the surface morphology transition (0.5–4 km) and the length of the transition from onset to completion (1.5–7 km). The parameters that affect surface morphology changes are investigated by comparison of two recent flows (July and December 1974). There is no correlation between the location of the surface morphology transition and local changes in slope; instead, ‘a‘ā formation initiates when flows reach a critical groundmass crystallinity of ϕ~0.18. This critical crystallinity, composed primarily of plagioclase and pyroxene microlites, does not appear to be affected by the presence or absence of olivine phenocrsyts. This crystallinity also correlates with theoretical and experimental predictions for the onset of a yield strength and supports the idea that crystal-crystal interactions are controlled primarily by the content of prismatic crystals (e.g. plagioclase). The dependence of the morphologic transition on post-eruptive crystallization requires that the down-flow location of the surface morphology transition is determined by both eruption temperature and effusion rate, with hotter, faster flows traveling greater distances before crystallizing enough to form ‘a‘ā. The length of the transition zone is proportional to the rate of flow cooling, which is dramatically influenced by topographic confinement. A comparison of the surface morphology distributions of these flows to the 1823 Keaiwa flow, which has a similar composition, pre-eruptive topography, and eruption temperature suggests that it was emplaced at effusion and flow advance rates, 300 m3/s and 1–3 m/s, respectively, typical of observed Hawaiian eruptions and much lower than previous estimates from the run-up height of lava. Evaluation of independent methods to determine flow-front velocities indicates that run-up height estimates consistently exceed estimates from tree-mold measurements and observation of active flows of <2 m/s. Channel velocities of 1–3 m/s, inferred through analysis of ‘a‘ā clinker size as a function of distance from the vent, are higher than those inferred at the flow-front.

Control of flow in resin transfer molding with real‐time preform permeability estimation

AbstractVariabilities in the preform structure in situ in the mold are an acknowledged challenge to achieving reliable preform saturation in liquid molding processes. Physical models offer an effective means of deriving real‐time process control decisions so as to steer the resin flow in a desired manner, which ensures complete preform saturation. An important parameter influencing the fidelity of the simulations is the preform permeability, which is a strong function of the preform microstructure. A model‐based control strategy that incorporates the ability to determine and utilize local permeability information in real‐time is of much value, and forms the focus of the paper. An intelligent model‐based controller is developed that uses virtual sensing of permeability to derive optimal decisions on controlling the injection pressures at the mold inlet ports in a resin transfer molding (RTM) process. The controller employs an artificial neural network, trained using process simulation data, as an on‐line flow simulator, and a simulated annealing algorithm to optimize the injection pressures on‐the‐fly during the process. Preform permeability is virtually sensed during the process, based on the flow front velocities and the local pressure gradient along the flow front, estimated using a fuzzy logic model. The controller, implemented on an RTM process, is shown to be able to accurately steer the flow fronts through various preform configurations.

Visualization analysis of flow front behavior during filling process of injection mold cavity by two-axis tracking system

The objective of this research is to develop a system that measures the flow front position dynamically, expands the observing flow front area, and tracks the flow automatically. The development of such a system for the observation of defects of injection moldings and the validation of the developed system are reported here. The developed in-process two-axis tracking system allows observation of the flow front behavior at flow front velocities up to 350 mm/s. In addition to flow marks, we were able to capture pictures of the formation of silver streaks for the first time. The results and developed system validated the postulations of the injection molding defects and also provided a new tool for exploring new frontiers in the analysis of fountain flow.

Experimental quasi-steady density currents

Hyperpycnal flows may be important mechanisms for transporting particles from continents to oceans given their frequency of generation at many modern river mouths. Their deposits are probably very common in the rock record, although they are not frequently recorded in the literature. These currents may last longer and be steadier than surge-like turbidity flows and consequently their deposits are likely to be significantly different. In this paper simple laboratory experiments are used to investigate how flows and deposits may vary. The thickness of the experimental flows near the flow front varies with distance from the source depending on slope, effluent discharge, grain size and sorting. Runout distance varies with the proportion of fine-grained sediment rather than with mean grain size. Flow front velocity varies with effluent discharge and sediment concentration and in a complex manner with mean grain size and sorting. The variation of deposit mass with runout distance depends on proximal slope angle and the maximum mass per unit area (approximating to bed thickness) is inversely dependent on slope angle. Variation in initial suspended particle concentration results in deposits of similar shape but different volume. Although the total mass of the deposit depends on the discharge the maximum mass per unit area (approximating to maximum bed thickness) does not. The distance over which particles are deposited increases and the deposit flattens as particles are deposited progressively further downstream at higher discharges, perhaps relating to more efficient turbulent suspension at higher Re (more complete energy cascade), in addition to longer horizontal component of settling trajectory at higher velocity. The amplitude of mass variation depends on the grain size. As with laboratory surges [Gladstone et al., Sedimentology (1998) 833–844], the finer the sediment the more efficient is the sediment transport.

Experimental Study of the Grain‐Flow, Fluid‐Mud Transition in Debris Flows

We have performed a series of laboratory experiments that clarify the nature of the transition between fluid‐mud and grain‐flow behavior. The surface velocity structure and the speed of the nose of debris flows in channels with semicircular cross sections were measured with several cameras and visual tracers, while the mass flow rate was recorded using a load cell at the exit chamber. Other rheological tests were used to calculate independently the yield strength and matrix viscosity of the debris‐flow mixture. Shear rates were varied by nearly an order of magnitude for each mixture by changing the channel radius and slope. Shear rates were significantly higher than expected (6–55 s−1), given the modest slopes examined (10.7°–15.2°). The large values were primarily a result of the concentration of shear into narrow bands between a central nondeforming plug and the sidewall. As a result, the shear rate of interest was calculated by using the width of the shear band and the plug velocity, as opposed to the flow depth and front velocity. The slurries exhibited predominantly fluid‐mud behavior with finite yield strength and shear‐thinning rheologies in the debris‐flow body, while frictional behavior was often observed at the front, or snout. The addition of sand or small amounts of clay tended to make the body of the flows behave in a more Bingham‐like fashion (i.e., closer to a linear viscous flow for shear stresses exceeding the yield stress). The addition of sand also tended to accentuate the frictional behavior at the snout. Transition to frictional grain‐flow behavior occurred first at the front, for body friction numbers on the order of 100. Similar behavior has been observed in an allied field site in the Italian Alps. In the experiments, it was hypothesized that the snout‐grain‐flow transition was a result of concentration of the coarsest material at the flow front, reduced shear near the snout, and loss of matrix from the snout to the bed. Regardless of the frictional effects at the snout, flow resistance in the body was nearly always regulated by yield‐stress and shear‐thinning properties, with no discernible boundary slip, despite volumetric sand contents in excess of 50%.

FIELD CHARACTERISTICS AND EROSIONAL PROCESSES ASSOCIATED WITH KOMATIITIC LAVAS: IMPLICATIONS FOR FLOW BEHAVIOR

Although komatiitic lavas have long been depicted as turbulent flows, especially near the vent, field characteristics indicate that many komatiitic lavas did not flow turbulently, or only initially so. The bases of komatiites are commonly conformable wit h their substrate, including fine pelitic sediments, and the margins of komatiites are overwhelmingly coherent, or marked by loca l quench-fragmented hyaloclastite breccia. Autobreccias are notably missing. These characteristics are not consistent with turbulent flow, but clearly indicate conditions of laminar flow. If komatiitic flows were turbulent, they should commonly have scour ed into substrate sediments through a variety of physical erosion processes, including foundering into underlying seafloor sedimen ts, because of density inversion, and turbulence-induced scouring of sediments. These features are not commonly developed, also indicating that generally komatiites were emplaced under tranquil, laminar-flow conditions. Trough-like structures that commonly host nickel sulfide mineralization have commonly been interpreted to originate by thermal erosion of substrate by the komatiitic lava. The evidence supporting thermal erosion is not strong, and commonly ambiguous. Trough structures at Kambalda, Western Australia, are fault bounded, as noted by several previous investigators. However, there is a common, but not universal , antithetic relationship between trough presence and sediment absence. Removal of sediment from troughs could be explained by physical erosion, with an initial narrow, turbulent flow-head scouring a channel in the underlying sediments. As the lava flows spread laterally, their flow-front velocity decreased, and flow became laminar, so explaining the conformable contacts with substrate and the presence of coherent crusts represented by the random spinifex textural zone. Thermal erosion was rare, and could only have resulted beneath sustained lava tubes, within the flow interior, not from the flow head.

The behaviour of the fronts of komatiite lavas in medial to distal settings

Field characteristics of komatiites and observations of flow behaviour and propagation processes for subaerial basalt lavas are used to reconsider the flow behaviour of Archean komatiite lavas. Planar, conformable bases at contacts with pelitic sedimentary strata, the existence of coherent to quench fragmented tops, but the absence of autobreccias, indicate that many komatiite lavas were emplaced passively under laminar flow conditions. To determine how widely this may apply to active komatiite lavas, we model flow front thicknesses. Noting that the preserved flow thickness is thus significantly greater than the thickness of the propagating flow front, we apply the concept of inflation of basalt lava flows to komatiites. Application of the Jeffreys equation allows lava thickness to be determined as a function of flow velocity, viscosity, density and slope of the terrain. Using the results together with estimates of flow front velocities and viscosity in the Reynolds number equation indicates that at expected low flow front velocities in medial to distal settings, most komatiites would have propagated in a laminar flow state. We therefore envisage that komatiites were turbulent in near vent settings and capable of physical erosion, and at times, as previously proposed, channel-forming thermal erosion. As flow area increased downstream, and magma supply rate to the flow front and the flow front velocity decreased significantly, the flow state would have transformed to laminar flow. Preserved flow thicknesses are often considerably greater than the calculated flow front thicknesses for such low viscosity lavas indicating that the final preserved thicknesses are either due to flow inflation, ponding in topography, or that some komatiites were intrusions.

A Closed Form Solution for Flow During the Vacuum Assisted Resin Transfer Molding Process

A closed form solution to the flow of resin in vacuum assisted resin transfer molding process (VARTM) has been derived. VARTM is used extensively for affordable manufacturing of large composite structures. During the VARTM process, a highly permeable distribution medium is incorporated into the preform as a surface layer. During infusion, the resin flows preferentially across the surface and simultaneously through the preform giving rise to a complex flow front. The analytical solution presented here provides insight into the scaling laws governing fill times and resin inlet placement as a function of the properties of the preform, distribution media and resin. The formulation assumes that the flow is fully developed and is divided into two regimes: a saturated region with no crossflow and a flow front region where the resin is infiltrating into the preform from the distribution medium. The flow front region moves with a uniform velocity. The law of conservation of mass and Darcy’s Law for flow through porous media are applied in each region. The resulting equations are nondimensionalized and are solved to yield the flow front shape and the development of the saturated region. It is found that the flow front is parabolic in shape and the length of the saturated region is proportional to the square root of the time elapsed. The results thus obtained are compared to data from full scale simulations and an error analysis of the solution was carried out. It was found that the time to fill is determined with a high degree of accuracy while the error in estimating the flow front length, d, increases with a dimensionless parameter ε=K2xxh22/K2yyd2. The solution allows greater insight into the process physics, enables parametric and optimization studies and can reduce the computational cost of full-scale 3-dimensional simulations. A parametric study is conducted to establish the sensitivity of flow front velocity to the distribution media/preform thickness ratio and permeabilities and preform porosity. The results provide insight into the scaling laws for manufacturing of large scale structures by VARTM. [S1087-1357(00)02002-5]

Pyroclastic flows generated by gravitational instability of the 1996–97 Lava Dome of Soufriere Hills Volcano, Montserrat

Numerous pyroclastic flows were produced during 1996–97 by collapse of the growing andesitic lava dome at Soufriere Hills Volcano, Montserrat. Measured deposit volumes from these flows range from 0.2 to 9 × 106 m³. Flows range from discrete, single pulse events to sustained large scale dome collapse events. Flows entered the sea on the eastern and southern coasts, depositing large fans of material at the coast. Small runout distance (&lt;1 km) flows had average flow front velocities in the order of 3–10 m/s while flow fronts of the larger runout distance flows (up to 6.5 km) advanced in the order of 15–30 m/s. Many flows were locally highly erosive. Field relations show that development of the fine grained ash cloud surge component was enhanced during the larger sustained events. Periods of elevated pyroclastic flow productivity and sustained dome collapse events are linked to pulses of high magma extrusion rates.

Numerical Study on the Capillary Effect of Resin Transfer Molding

A model for the impregnation of resin into a unidirectional packed fiber mats by the dynamics of capillary penetration is developed at a low flow rate where resin flow is parallel to fiber axis. The model takes into account two types of flow, the macroflow around the fiber bundles and the microflow around the fibers in the bundles, occurring simultaneously. Both follows are described by Darcy's law. The large difference in the position of flow front between these two types of flow leads to the potential of void formation in resin transfer molding. The capillary force is considered along the flow front. It can be evaluated as a function of liquid contact angle, interfacial tension, the porosity, and the velocity of flow front. The simulation is based on the body-fitted finite element method. Result shows that the void formation is affected not only by the properties of fiber mats, but also by the injection condition. And the capillary effect is limited as the capillary number is less than 0(10-2).

Petrov-Galerkin finite element analysis for advancing flow front in reaction injection molding

A numerical scheme for computing the advancement of a flow front and related velocity, pressure, conversion and temperature distributions during mold filling in reaction injection molding (RIM) is described in this work. In the RIM process, the convective term in the energy equation is dominant. Therefore, the numerical scheme has incorporated a Petrov-Galerkin finite element method to suppress spurious oscillations and to improve accuracy of the calculations. The other feature of the numerical scheme is that the flow front locations are computed simultaneously with primary variables by using a surface parameterization technique. The numerical results compare well with the reported experimental data. Improved accuracy obtained by this numerical scheme in the flow front region is expected to assist in the predictions of the fiber orientations and the bubble growth in RIM, which are determined primarily by the flow front region.

The 1919?1920 eruption of Mauna Iki, Kilauea: chronology, geologic mapping, and magma transport mechanisms

Utilizing historical accounts, field mapping, and photogeology, this paper presents a chronology of, and an analysis of magma transport during, the December 1919 to August 1920 satellitic shield eruption of Mauna Iki on the SW rift zone of Kilauea Volcano, Hawaii. The eruption can be divided into four stages based on the nature of the eruptive activity. Stage 1 consisted of the shallow injection of a dike from the summit region to the eventual eruption site ∼10 km downrift. During stage 2, a low ridge of pahoehoe formed in the vent area; later a large a'a flow broke out of this ridge and flowed ∼8.5 km SW at an average flow front velocity of 0.5 km/day. The eruption continued until mid-August producing almost exclusively pahoehoe, first as gas-rich overflows from a lava pond (stage 3), and later as denser tube-fed lava (stage 4) that reached almost 8 km from the vent at an average flow-front velocity of 0.1 km/day. Magma transport during the Mauna Iki eruption is examined using three criteria: (1) eruption characteristics and volumetric flow rates; (2) changes in the surface height of the Halemaumau lava lake; and (3) tilt measurements made at the summit of Kilauea. We find good correlation between Halemaumau lake activity and the eruptive stages. Additionally, the E-W component of summit tilt tended to mimic the lake activity. The N-S component, however, did not. Multiple storage zones in the shallow summit region probably accounted for the decoupling of E-W and N-S tilt components. Analysis of these criteria shows that at different times during the eruption, magma was either emplaced into the volcano without eruption, hydraulically drained from Halemaumau to Mauna Iki, or fed at steady-state conditions from summit storage to Mauna Iki. Volume calculations indicate that the supply rate to Kilauea during the eruption was around 3 m3/s, similar to that calculated during the Mauna Ulu and Kupaianaha shield-building eruptions, and consistent with previously determined values of long-term supply to Kilauea.

Boundary integral equations for analyzing the flow of a chopped fiber reinforced polymer compound in compression molding

The flow of a chopped fiber reinforced polymer compound during compression molding is analyzed as a transient moving boundary problem. A special boundary integral formulation is used to calculate flow front velocities. The derivation involves the determination of fundamental solutions for the newly developed equations of motion. A generalized Green's formula is used in conjunction with these solutions to produce the final expressions which incorporate the boundary tractions and velocities directly. The major advantage in adopting a boundary integral approach is that there is no need to solve for interior pressures and velocities. This makes it possible to avoid costly remeshing which can occur with other methods that involve discretization of the entire material region. When required, interior pressures and velocities can be recovered after the solution on the boundary has been determined. The recovery process is relatively straightforward and efficient, since it involves only one-dimensional quadrature. An approximate boundary element representation of the basic integral equations is used to predict flow front progression for elliptical and rectangular charges. Based on a comparison with available analytic solutions for the elliptical charges, we conclude that the method performs well over the entire range of physical and geometric parameters. A furter examination of numerical solutions shows that practical convergence can be obtained for both quadratic and constant boundary elements with moderate mesh spacings.