Wind-induced Flow Research Articles

Verification of the Salt Transport Model Due to Wind-induced Flow Based on Field Data

Verification of the Salt Transport Model Due to Wind-induced Flow Based on Field Data

Salt Transport from Bottom to Surface Layer at the Interface Due to a Wind-Induced Flow

Salt Transport from Bottom to Surface Layer at the Interface Due to a Wind-Induced Flow

Surface Films and Mixing in Two‐Layer Fluid

An experimental investigation of wind-induced flow and mixing processes in a two-layered system influenced by a thin film persisting on the water surface is reported in this study. Detailed documentation and description of the wind-induced flow and mixing processes are given. The entrainment rates and flow pattern depend on two dimensionless numbers, one characterizing the influence of surface films, the other characterizing the response of stratified basins to wind stress in the absence of surface films. The differences between the flow and mixing processes of a two-layered system influenced and not influenced by a surface film are pointed out and discussed.

Numerical simulations of the tidal- and wind-driven circulation in Narragansett Bay

A three-dimensional numerical hydrodynamic model was used to study the tides and certain aspects of the wind-forced flow in Narragansett Bay. The governing equations are solved using the Galerkin-spectral method in the vertical and explicit finite differences in the horizontal and time. A split-mode formulation is used to minimize computational time. Simulations of the M 2 tide gave average errors of less than 2% in amplitude and 2° in phase when compared with observations at 12 tidal-height stations within the Bay. An investigation of the Bay's response to steady, spatially uniform wind forcing indicated that the non-linear interaction between the tidal and wind induced motions strongly affected the predicted steady state current pattern. Calculation of the steady-state wind-induced transports showed that a significant exchange exists between the West Passage, East Passage and Sakonnet River. The dependence of the exchange on the wind magnitude and direction and on the choice of vertical eddy viscosity was investigated. A comparison between modeled results and measurements of current at three locations in the Bay indicated that the model is capable of reproducing some of the features of the wind-induced flow.

Measuring the wind-induced water surface flow by laser Doppler velocimetry

The way to adjust the laser Doppler velocimeter for measuring the water motions near a moving air-water interface is described by specifying the experimental arrangement, the choice of the scattering configuration, the seeding problems and the preliminary tests which were performed. This technique is then used to explore the motions induced by the wind near the water surface. Illustrative results on the instantaneous longitudinal and vertical velocities, the mean profiles and the respective spectra are presented and discussed. It appears that the Eulerian measuring method when applied to such flows and the presence of dropouts on the signals may require significant corrections of the original data before any physical interpretation.

On determining current profiles in oscillatory flows

The time dependency of the linear three-dimensional hydrodynamic equations which describe oscillatory flow, is removed by expressing the horizontal components of current in terms of rotary components at a prescribed frequency. By this means two time independent equations (one for each rotary component) are derived, which can be readily solved using the Galerkin method, in a manner analogous to that developed by the author for steady-state wind-induced flow. The method is used to examine the influence of eddy viscosity on tidal current profiles. Two distinct flow regimes are identified. In one the water depth exceeds the thickness of the bottom stress layer, in the other, water depth is less than the thickness of this layer. The influence of these two depth regimes, and the magnitude and vertical variation of eddy viscosity on tidal current profiles is examined. The possibility of using the method to give tidal profiles from vertically integrated models is discussed.

Application of a sigma coordinate sea model to the calculation of wind-induced currents

A three-dimensional numerical sea model is formulated in terms of sigma coordinates in the vertical. The vertical grid spacing in the model is arbitrary and can be refined to give enhanced resolution in high shear regions (e.g., close to the sea surface in wind-driven flows, and/or across the thermocline in stratified flows). A method of accurately determining surface currents and indicating how fine a grid is required in the surface layer is described. The problem of determining a suitable formulation of vertical eddy viscosity to use in a model of wind-induced flow in a tidal sea is considered in detail. A formulation in which surface eddy viscosity depends upon the roughness of the sea surface and the transfer of momentum to depth by surface waves appears reasonable. Below the surface layer turbulence is related to the current at depth. Idealized calculations are performed to demonstrate the accuracy and stability of the sigma coordinate model. Results of these calculations indicate that the formulation of eddy viscosity developed in this paper can explain the high surface shears reported in lake measurements of wind-induced surface currents, and the lack of shear under strong wind conditions in the open sea ( GORDON, 1982, Journal of Geophysical Research, 87, 1939–1951 ). Surface current to surface wind ratio are also computed.

A Numerical Study of Tunnel Fires

Abstract Abstract—A numerical study of accidental highway tunnel fires is made using a two-dimensional numerical model. The role of ventilation systems on the early phase of the fire is investigated. The effects of the wind-induced flow through the tunnel, the burning rate, and the rate of fuel addition are also studied. The results, although preliminary, show the coupling between combustion and fluid mechanics, and indicate that the flow induced by combustion plays a dominant role in the problem.

Erratum for “Modeling Three-Dimensional Wind-Induced Flows”

Erratum for “Modeling Three-Dimensional Wind-Induced Flows”

Modeling Three-Dimensional Wind-Induced Flows

A three-dimensional numerical model has been developed to study hydrodynamic circulations produced in coastal zones due to tide and wind action. The model consists of a mixed finite-difference/finite element solution of the simplified fluid momentum and continuity equations. A numerical splitting technique is used to reduce the size of model solution matrices while the finite element approach is used over the flow depth to enable irregular sea beds to be tackled easily. Model errors arising from the numerical method are minimized by the use of a Galerkin weighted-residual procedure. The problems associated with modeling the turbulence closure of the basic momentum equations are also investigated with a simplified form of the model and the need for high levels of closure is demonstrated. The potential use of the three-dimensional model is illustrated by prediction of wind-induced flows in Thessaloniki Bay in the Aegean Sea.

On formulating a three-dimensional hydrodynamic sea model with an arbitrary variation of vertical eddy viscosity

A method is presented here for solving the linear hydrodynamic equations for the sea, using an expansion of the horizontal component of current in terms of depth-varying functions (the basis functions) with coefficients that vary with time and horizontal position. The coefficients in this expansion are determined using a finite difference method in the horizontal and the Galerkin technique in the vertical. Initially the method is presented using an expansion of B-splines in the vertical (a finite element representation in the vertical). The ease with which arbitrary surface and bottom boundary conditions can be satisfied with these basis functions is demonstrated. The paper describes in detail the conditions under which a basis set can be used which does not explicitly satisfy bottom or surface boundary conditions. In such circumstances the boundary conditions are of course incorporated into the differential equations of the problem using the Galerkin method. The effect upon accuracy of using a basis set of cosine functions (a spectral representation in the vertical) which do not satisfy a slip bottom boundary condition, compared with using a similar set of functions which do satisfy this condition, is examined. The error in the surface current (which occurs when a basis set which does not satisfy a nonzero stress surface condition is used) is also considered in detail. The paper shows that by using a basis set of cosine functions a computationally economic method can be derived for solving the three-dimensional linear hydrodynamic equations. The method is sufficiently general to allow for an arbitrary vertical eddy viscosity that varies with space and time though a continuous depth variation of current is still retained. In problems involving a wind-induced flow this viscosity can be related to the wind stress acting on the sea surface. An arbitrary depth variation of sea-bed topography is used throughout.

Erratum for “Wind Induced Flow of Water in Network”

Erratum for “Wind Induced Flow of Water in Network”

WIND-INDUCED WATER SURFACE SET-UP AND DRIFT CURRENTS

A systematic experiment to study the wind-induced flow phenomena was conducted in a laboratory tank. The results are related to the wind friction velocity and subsequently scaled for applications at various fetches under different wind velocities. The wind-stress coefficients are found to be well scaled by the Froude number. The bottom friction is measured with an effective shear gauge. The ratios between the bottom stress and the wind stress are obtained. The complete profiles of wind drift current are measured under various wind velocities. A tentative distribution of drift currents in the whole water depth is proposed. The results from the experiment are used to examine the wind-induced flow phenomena in a closed basin.

Wind-induced Flow through the North Channel of the Irish Sea

Summary Potential gradients generated by the flow of water through the North Channel of the Irish Sea were recorded by means of the Portpatrick-Donaghadee submarine cable during the period January to April 1974. The results from a tidal analysis of these recordings were found to be in good agreement with earlier values found by Bowden & Hughes. As in the earlier work, the residual component of voltage, obtained after removal of the tidal component from the recorded signal, was shown to have a significant correlation with the wind field over the Irish Sea. A relationship between residual voltage and wind speed has been developed from the observational data using a technique of numerical fitting and correlation optimization. Using this relationship, estimates of wind-induced flow through the North Channel have been derived for the period of the measurements. The results suggest that the onset of residual flow through the Channel may sometimes precede the associated wind forcing, a phenomena which might be attributed to the effects of atmospheric pressure.

On Wind-induced Flows in Closed Channels

The mean velocity and shear-stress profiles for a wind-induced flow in a closed channel with constant surface slope are first derived using a turbulent viscosity constructed by dimensional arguments. Using a perturbation analysis based on the fact that the surface slope is small, these results are extended to the case where the surface slope, and hence flow conditions generally, are allowed to vary in a downwind direction. Explicit results are obtained for the velocity and shear-stress profiles and also for the surface slope as a function of distance downwind. The results agree quite well with experiment, although better agreement would probably be obtained by using a more elaborate turbulent iscosity_