Wave Radiation from Bottom Vibrations in Open-Channel Flow with Uniform Vorticity

A comparison is made of results for barotropic, surface and abyssal flows during the formation and passage of a warm-core ring in the East Australian Current. The barotropic velocities are estimated from sea-floor measurements of the horizontal electric field, which is induced by water motion. Values for the surface and near-bottom velocities are obtained generally by more traditional methods. A strong similarity is observed between the directions of the barotropic and surface flows. At a site close to the foot of the continental slope, the barotropic and near-bottom velocities are also similar, both in direction and magnitude. A possible explanation for this effect is that proximity to the coast constrains flow directions and causes the streamlines at depth to converge on the western (or near-shore) side of the warm-core ring. The determination of barotropic velocities enables barotropic volume transports to be estimated and compared with traditional geostrophic volume transports calculated for water motion between the surface and a depth of 1300 m. The barotropic transports are found to be greater than the geostrophic transports by a factor of approximately 1.6, indicating the significance of deep-water flow in the East Australian Current.

The hydrodynamics of surface tidal flow exchange in saltmarshes

Oscillatory line source for water waves in shear flow

An alternative linear flow model and boundary integral flow representation for ship motions in regular waves

A similarity transform is used to analyse the flow of an upper-convected Maxwell fluid in an infinitely long cylinder whose surface has a velocity that increases in magnitude linearly with axial coordinate. Two types of problem are considered, the accelerated surface flow - when the surface velocity is outward towards the tube ends, and the decelerated surface flow - when it is inward. For the accelerated surface flow, the introduction of elasticity prevents the loss of similarity solution that occurs without elasticity at a Reynolds number (Re) of 10.25: with elasticity, solutions up to a Reynolds number of 95 were computed. As elasticity is introduced, normal stress gradients in an elastic boundary layer near the accelerated surface help offset inertially generated negative axial pressure gradients; with sufficient elasticity the turning point in the non-elastic solution family at Re = 10.25 disappears. For the decelerated surface flow, solutions could not be computed beyond a critical Re that depends on the level of elasticity considered, because at this critical Re, the axial velocity profile at the centreline becomes infinitely blunt.

An integrated model of fully coupled two-phase surface and subsurface flow was built by using GETFLOWS (GEneral purpose Terrestrial fluid-FLOW Simulator), a finite difference fluid-flow numerical simulator, to perform quantitative evaluation of exchange of overland water and groundwater, subsurface seepage and surface water runoff on the hillside slope surface. Surface water on hillside slope was modeled as open-channel flows and coupled with air-water two phase Darcy flow for underground permeation by using a generalized flow formula. In this study, a simple verification model was firstly built and validated by the extensively used Abdul and Gillham example with simulating the coupled surface and subsurface flow. Then a three-dimensional integrated model of surface and subsurface flow was built by using the DEM (Digital Elevation Model) of a natural mountain slope in Hokkaido, Japan, where runoff induced several debris flows and slope failures occurred during Typhoon 10 hit Hokkaido in 2016. Finally the results of integrated simulation was compared with the results from two-dimensional (2D) impermeable plane flow simulation using Nays2D Flood solver of the iRIC software in the same region. The results suggest that on the hillside slope upstream of embankment, the infiltration rate is equals to the rainfall intensity at the beginning of the rainfall event. After the rainfall intensity is greater than the soil infiltration capacity, runoff is generated. The runoff from upstream allows more water to infiltrate into the embankment causing the possibility of slope failure at the exit of the valley to be much greater than other locations along the highway.KeywordsIntegrated modelingSurface flowSubsurface flowGETFLOWSInfiltration excess runoff

Open channels can range from small irrigation furrows to huge irrigation canals that are hundreds of kilometers long and supply billions of cubic meters per year for irrigation, industry, and domestic purposes. Agricultural canal categories include the irrigation district main, secondary and tertiary canals, laterals, on-farm irrigation ditches, and drainage channels. This chapter covers the structures and principles that are related to open channel delivery of water to agriculture: water diversion structures, conveyance efficiency, siphons, canal hydraulics (uniform flow, energy drop structures, and gradually varied flow), and flow measurement. The government has encouraged farmers to conserve water by lining irrigation ditches with concrete (Fig. 11.1); however, concrete channels can develop cracks and gaps that have excessive water loss. Economic analysis can determine whether lining a canal is worth the cost. Manning’s equation calculates the head loss along a canal based on slope, roughness, and channel geometry. Energy dissipation structures use supercritical flow and hydraulic jumps to dissipate energy. The Froude number determines the relationship between subcritical and supercritical flow. A finite difference solution calculates water depth changes along a canal with gradually varied flow.

An efficient numerical method for subcritical and supercritical open channel flows

Open channel flow or, more appropriately, free surface flow involves flow through a conduit with the liquid surface exposed to a constant pressure (atmosphere). Thus there can be open channel flow through a closed conduit (a pipe) provided the flow is not full bore. Full-bore closed conduit flow is referred to as pressure flow since pressure is the major controlling factor. In contrast, gravity and therefore conduit slope and elevation changes are important factors determining the nature of flow in an open channel. Nevertheless, all the fundamental principles of conservation of momentum, energy and mass (discussed in Chapter 2) are applicable to flow through open channels as they are to closed conduit pressure flows. Figure 4.1 shows the similarity of the energy concepts in both cases. It may be observed from the figure that depth (y) changes in an open channel follow the pattern of pressure (p) changes in a pipe. Comparison between pipe flow and open channel flow

<p>Image-based methods for measuring surface flow velocities in rivers have several advantages, one of them being that the sensor (camera) is not in contact with the water and its mounting position is very flexible hence there is no need of expensive structures to mount it. Additionally, it is possible to measure the whole river width. On the other hand, environmental factors, like wind, can affect the surface velocity and the have an impact on the accuracy of the measurements.</p><p><span>Herein we present an analysis of the wind effect on </span><span>the image based surface velocity at </span><span>Rhine river</span><span>, at the border between Switzerland and Austria. At this location the river width is of approximately 100 meters under low flow conditions, while the width of its floodplain is of about 200 m. </span><span>A</span><span>n</span> <span>ATMOS 22 ultrasonic anemometer </span><span>was installed </span><span>at the site to measure the wind </span><span>intensity</span><span> as well as </span><span>its</span><span> direction. </span></p><p><span>A time series of flow velocities and wind </span><span>from May to October 2019 </span><span>was analyzed. During this period, the </span><span>average disch</span><span>a</span><span>rge </span><span>was </span><span>320 m</span><sup><span>3</span></sup><span>/s and the average </span><span>flow </span><span>velocity 1.7 m/s. While the average wind velocity was of </span><span>2</span><span>.</span><span>3</span><span>m/s which roughly follows the same direction of the river flow.</span></p><p>A rating curve following a power law function was fitted to the image based surface flow measurements. It was found that for maximum wind speeds of 10 m/s, blowing in the opposite direction of the river flow, there was a deviation of 8%. For the average wind speed of 2.3m/s, the deviation was found to be 3%.</p>

A fundamental characteristic of granular flows is that they are typically restricted to thin layers of rapid surface flow. Thus, a complete understanding of surface flows is key for an accurate representation of the dynamics of the entire flow. Experiments were conducted in three-dimensional tumblers: cylindrical tumblers of various diameters, a double-cone tumbler, and a spherical tumbler, the Froude number for the last two being a function of the local geometry and ranging from $2.6\times10^{-5}$ to $7.5\times10^{-4}$. Surface velocity measurements for 1 mm and 2 mm glass particles were obtained using particle tracking velocimetry. Results indicate that the streamwise surface velocity at the midpoint of the flowing layer is a linear function of local flowing layer length, regardless of tumbler shape, particle size, rotation rate, and fill fraction. In addition, the axial velocity of particles at the free surface is negligible. These results are key for the development of three-dimensional models of granular flows.

Modeling spatial and temporal variations in temperature and salinity during stratification and overturn in Dexter Pit Lake, Tuscarora, Nevada, USA

In the past, the solutions to open flow problems were generally found on the basis of experimental data or through the development of theoretical expressions using simplified assumptions. The volume of fluid (VOF) turbulence model can be applied to obtain the flow parameters such as pressure head distributions, velocity distributions, and water surface profiles for flow in open channels. The free overfall in a rectangular open channel that serves as a discharge measuring structure is selected to apply to the VOF model. The predictions of the proposed VOF model are validated using existing experimental data for both subcritical and supercritical flow approach conditions. Based on the path followed by a fluid particle leaving the brink section, the equations for the nappe profiles in supercritical flows are obtained in terms of the end depth. The VOF turbulence model developed is used to predict the characteristics of a free overfall in a rectangular open channel.Key words: turbulence model, VOF model, numerical simulation, overfall characteristics, open channel flow.

Accurate numerical solutions to the problem of finding the location of the interface between two unconfined regions of fluid of different density during the withdrawal process are presented. Supercritical flows are considered, in which the interface is drawn directly into the sink. As the flow rate is reduced, the interface enters the sink more steeply, until the solution method breaks down just before the interface enters the sink vertically from above, and becomes flow from the lower layer only. This lower bound on supercritical flow is compared with the upper bound on single-layer (free surface) flow with good agreement.

Interactions between waves that satisfy uniform potential vorticity are considered. The formal analysis is restricted to a triad of eigenfunctions and the reduced system is constrained to satisfy conservation of total energy and conservation of available potential energy on plane rigid horizontal boundaries. A linear stability analysis is used to establish the properties of unstable waves in two cases: basic flows with anti-symmetry, and basic flows with symmetry in the vertical direction. A necessary condition for instability is that the vertical wavenumber of the basic flow must fall between the vertical wavenumbers associated with the perturbation waves. The properties of unstable waves in both cases are compared and analogies with the stability properties of the two-layer model are pointed out.