A general formula for non-cohesive bed load sediment transport

Vortex-induced vibration (VIV) of a circular cylinder in combined steady and oscillatory flow

Theory and simulation of steady, small-amplitude, and large-amplitude oscillatory capillary Poiseuille flow of discotic mesophases are presented, discussed, and used to provide an integrated framework to characterize the rheology of precursors used in the manufacturing of carbon super-fibers. The underlying microstructural changes responsible for the non-Newtonian rheology are presented and discussed, taking into account dynamic couplings between orientation and velocity fields. Proper scaling of viscoelastic material functions leads to superposition and hence provides a better fundamental understanding of flow processes in steady and oscillatory flows. The relations between shear-thinning behavior in steady flow, elastic storage in small-amplitude oscillatory shear, and flow enhancement in pulsatile flow are established.

Bed load transport under different streambed conditions – a field experimental study in a mountain stream

Incipient conditions of cohesive sediments in oscillatory flows

Present study examines responses of the longitudinal bed profiles to bed shear stress changes and associated changes of the bed load transport rates which are caused in straight open channels with different flow widths where the channel is connected by an abruptly widened approach or a narrowed one. To investigate the response of bed slope ratio to the change of bed-load transport rate, we employ two bed load formulas for discussions; one is the bed- load formula characterized by τ∗3/2 with τ∗c, and the other is the bed load formula expressed by τ∗5/2. Besides, to see role of the bed load formula explicitly in the regime relation, the regime formulas for describing the bed slope ratio, specific bed elevation etc. were obtained, assuming that an equilibrium sediment transportation accomplished. The regime formula shows that the bed slope ratio, i2/i1 increases monotonically with the increase of the flow width ratio when τ∗5/2 type of the bed load formula is employed in the regime equation, where suffixes 1 and 2 show the quantities upstream and downstream. However, the regime formula shows that the bed slope ratio depends on the bed shear stress change when τ∗3/2 type bed load formula is employed. The present study topics are classic, and not new, but it is very important to study the response of the longitudinal bed profile to the bed load transport rate to look for a suitable form of the bed load equation.

Subsurface contamination by volatile organic contaminants (VOC`s) in the vadose zone and groundwater is primarily due to leaking underground storage tanks and industrial spills. Soil vapor extraction is a technique that is being used successfully to remove VOC`s from the subsurface. A flow of air is established through the soil to remove the vapor phase component of the contaminant. Soil vapor extraction will initially remove high levels of contaminant that is already present in the macropores. The concentration will start to decline as the removal from the soil matrix becomes limited by diffusion of contaminant from regions away from the air flow paths. This study examines potential methods of overcoming the diffusion limitation by adding an oscillatory component to the steady air flow and by pulsed flow, which involves turning air flow on and off at predetermined intervals. The study considered only the removal of water from the soil to try to establish general vapor behavior in the soil under the imposed conditions. Based on a statistical analysis, both the oscillatory and pulsed flow showed an improved water removal rate over the steady state flow. The effect of oscillatory flow was only examined at higher frequencies. The literature indicates that oscillations at lower frequencies may be more effective. Pulsed flow showed the most efficient removal of water compared to steady state conditions. The pulsed flow was most efficient because rather than reducing the diffusion limitation, the system would shut down and wait for diffusion to occur. This optimizes energy consumption, but does not reduce treatment time. The oscillatory flow actually reduced the diffusion limitation within the column which could result in a shorter treatment time.

A prototype experimental setup is designed to convert steady air flow into an oscillatory anharmonic acoustic pulsed flow, under special experimental conditions. The steady flow in a cylindrical reactor column of 3 m height and 15 cm in diameter with a porous layer, transforms itself abruptly into an oscillatory acoustic pulsed flow. Experimental results show the existence of a threshold for flow-rate, beyond which this transformation into anharmonic oscillatory flow takes place. This change in flow regime is analogous to the phenomenon of bifurcation in a chaotic system, with abrupt change from one energy state into another. Experimental results show that the acoustic oscillations amplitude depends on system size. Preliminary mathematical model will be presented that includes; relaxation oscillations, non-equilibrium thermodynamics, and Joule-Thomson effect. The frequencies at peak amplitude for the acoustic vibrations in the reactor column are expressed in terms of flow-rate, pressure-drop, viscosity, and dimensionless characteristic numbers of the air flow in the system.

Theories of flow birefringence in steady and oscillatory shear flow for spheroidal particles are compared. It is shown, that proper normalization of birefringence functions make them identical for both flows at low gradients and frequencies. The deviations at high gradients and frequencies increase with increasing particle axial ratio. The theory for polydisperse particles is developed. From the limiting behavior at low and high gradients and frequencies it is possible to find various averages of the relaxation times of the particles and hence some description of the polydispersity. The differences between steady and oscillatory flow behavior for a monodisperse system persist even for the polydisperse case thus giving the possibility of indirectly checking some aspects of the monodisperse theory. Experiments on microcrystalline alumina (Baymal), tobacco mosaic virus, and bentonite are in essential agreement with theoretical predictions.

Movement of and drag force on slender flat plates in an array exposed to combinations of unidirectional and oscillatory flow

The amount of sediment bed load being carried by rivers significantly impacts the inherent development of the riverine systems in terms of hydrodynamic and morphodynamic changes. In this direction, acoustic Doppler current profiler velocity literature data collected at the Óbidos station in the Amazon River were applied to investigate bed-load transport using the Entropy method. First, the cross-sectional velocity distribution was estimated with that model for two scenarios of source data: (a) all surface velocities and (b) single surface velocity as the maximum surface velocity. The latter analysis was conducted with two different assumptions of the surface velocity distribution: parabolic and elliptic. The error percentage for estimation of the mean cross-sectional velocity and discharge was 2.08% based on considering all surface velocities and was 4.08% and 12.5% based on parabolic and elliptic scenarios, respectively. Next, the shear velocity and Shields mobility parameter were calculated for two scenarios. Finally, the dimensionless bed load transport rate was calculated based on a range of particle diameters. Applying the different equations for the dimensionless bed load transport rate based on various scenarios of surface velocity distributions, the results from the entropy method agreed with the experimental data in the literature. Overall, the current study highlighted the potential of the entropy model to estimate river discharge and bed load transport in large rivers relying only on surface velocity.

Vortex-induced vibration of flexible pipe fitted with helical strakes in oscillatory flow

Primary Cilia is appendage that extrudes from cell surface into the extracellular matrix .These organelles play a sensor role for mechanical stimulation in the cell and due to stretch ion channels in its base, play critical role in induce osteogenic differentiation of stem cells. Primary cilia deflected under fluid flow passing through the surface of the cell, which deflection causes tensile ion channels to be opened. In this study, cilia is assumed as linear elastic. The innovative aspect of this research is exerting of oscillatory fluid flow to the primary cilia and evaluating the response of cilia to the fluid flow. The results show that under conditions of exerting the oscillatory fluid flow, maximum strain occur in the base of the cilia which is experienced by tensile ion channels, is 0.5 and in the condition of steady flow is 0.3, Accordingly, mechanical stimuli are sensed by the tensile ionic channels during oscillatory flow higher than steady flow. osteogenic differentiation of stem cells, in addition, the result showed that by using the oscillatory fluid flow the mechanical stimulation better senses by cilia and It is anticipated that exerting oscillatory fluid flow facilitate osteogenic differentiation of stem cell.

Drag forces on aquatic plants in nonlinear random waves plus current

The prediction and calculation of the volume of gravel and/or sand transported down streams and rivers—called bed-load transport is one of the most difficult things for river engineers and designers because, in addition to field measurements, personnel involved in such activities need to be highly experienced. Bed-load transport treated by many engineers marginally or omitted and often receives only minor consideration from engineers or may be entirely disregarded simply because they do not know how to address the issue—in many cases, this is a fundamental problem in river management tasks such as: flood protection works; river bank protection works against erosion; building bridges and culverts; building water reservoirs and dams; checking dams and any other hydraulic structures. Thus, to share our experience in our paper, bed-load transport was calculated in two river/stream mountain catchments, which are different in terms of the characteristics of the catchment area and the level of river engineering works performed along the stream channel—both are tributaries of the Dunajec River and have similar Carpathian flysh geology. The studies were performed in the Mlyne stream and in the Lososina River in Polish Carpathians. Mlynne is one of the streams in the Gorce Mountains—it is prone to flash flooding events and has caused many problems with floods in the past. It flows partially in the natural river channel and partially in a trained river channel lined with concrete revetments. The stream bed load is accumulated in the reservoir upstream of the check dam. The Lososina River is one of the Polish Carpathian mountainous streams which crosses the south of the Beskid Wyspowy Mountains. It mostly has a gravel bed and it is flashy and experiences frequent flooding spring. At the mouth of the Lososina River, there is one of the largest Polish Carpathian artificial lakes—the Czchow lake. The Lososina mostly transports gravel as the bed load to the Czchow water reservoir where the sediment is deposited. In the early seventies, the Lososina was partly canalised, especially in places where passes inhabited areas. The paper compares the situation of bed-load transport in the Lososina River before and after engineering training works showing how much sediment is transported downstream along the river channel to the Czchow artificial lake. Also compared is the Mlynne bed load transport upstream and downstream from the check dam showing how much sediment might be transported and deposited in the reservoir upstream from the check dam and when one could expect this reservoir to be clogged.

Three data-driven techniques, namely artificial neural networks, adaptive-network-based fuzzy inference system, and symbolic regression based on genetic programming, are employed for the prediction of bed load transport rates in gravel-bed steep mountainous streams and rivers in Idaho (U.S.A.), and the potential of several input variables is investigated. The input combinations that were tested are based, mainly, on unit stream power, stream power, and shear stress, and exhibited similarly good performance, with respect to the machine learning technique used, accentuating the importance of the regression model. The derived models are robust, generalize very well in unseen data, and generated results superior to those of some of the widely used bed load formulae, without the need to set a threshold for the initiation of motion, and consequently avoid predicting erroneous zero transport rates.