661 research outputs found
Estimation of aquifer lower layer hydraulic conductivity values through base flow hydrograph rising limb analysis
The estimation of catchment-averaged aquifer hydraulic conductivity values is usually performed through a base flow recession analysis. Relationships between the first time derivatives of the base flow and the base flow values themselves, derived for small and large values of time, are used for this purpose. However, in the derivation of the short-time equations, an initially fully saturated aquifer without recharge with sudden drawdown is assumed, which occurs very rarely in reality. It is demonstrated that this approach leads to a nonnegligible error in the parameter estimates. A new relationship is derived, valid for the rising limb of a base flow hydrograph, succeeding a long rainless period. Application of this equation leads to accurate estimates of the aquifer lower layer saturated hydraulic conductivity. Further, it has been shown analytically that, if base flow is modeled using the linearized Boussinesq equation, the base flow depends on the effective aquifer depth and the ratio of the saturated hydraulic conductivity to the drainable porosity, not on these three parameters separately. The results of the new short-time expression are consistent with this finding, as opposed to the use of a traditional base flow recession analysis. When base flow is modeled using the nonlinear Boussinesq equation, the new expression can be used, without a second equation for large values of time, to estimate the aquifer lower layer hydraulic conductivity. Overall, the results in this paper suggest that the new methodology outperforms a traditional recession analysis for the estimation of catchment-averaged aquifer hydraulic conductivities
Towards the numerical simulation of 5 Floating Point Absorber Wave Energy Converters installed in a line array using OpenFOAM
In this paper we use the CFD toolbox OpenFOAM to
perform numerical simulations of multiple floating point
absorber Wave Energy Converters (WECs) in a numerical wave
basin. The two-phase Navier-Stokes fluid solver is coupled with a
motion solver to simulate the wave-induced rigid body heave
motion. The purpose of this paper is twofold. The first objective
is to extend numerical simulations of a single WEC unit to
multiple WECs and to tackle the issues of modelling individual
floating objects close to each other in an array layout. The second
objective aims to include all the physical processes (e.g. friction
forces) observed during experimental model tests in the
numerical simulations. The achievements are verified by
validating the numerical model with laboratory experiments for
free decay and regular wave tests using a line array of two and
five WECs. For all the simulations presented, a good agreement
is found between the numerical and experimental results for the
WECs’ heave motions, the surge forces on the WECs and the
perturbed wave field. As a result, our coupled CFD–motion
solver proves to be a suitable and accurate toolbox for the study
of wave-structure interaction problems of WEC arrays.location: Cork, Irelandstatus: publishe
Numerical simulation of an array of heaving floating point absorber wave energy converters using OpenFOAM
In this paper we use the CFD toolbox OpenFOAM to perform numerical
simulations of multiple floating point absorber Wave Energy Converters (WECs) in a
numerical wave basin. The two-phase Navier-Stokes fluid solver is coupled with a motion
solver to simulate the wave-induced rigid body heave motion. The key of this paper is
to extend numerical simulations of a single WEC unit to multiple WECs and to tackle the issues of
modelling individual floating objects close to each other in an array lay-out. The developed
numerical model is validated with laboratory experiments for free decay tests and for
a regular wave train using two or five WECs in the array. For all the simulations presented, a good
agreement is found between the numerical and experimental results for the WECs’ heave
motions, the surge forces on the WECs and the perturbed wave field. As a result, our coupled
CFD–motion solver proofs to be a suitable and accurate toolbox for the study of
wave-structure interaction problems of multiple floating bodies in an array configuration
The effect of migrating dune forms on the flow field of an alluvial river
The bed of an alluvial river is highly susceptible to changes during the course of its existence. Besides variations of the large scale topography and plan form of the river, smaller scale dune forms can be observed. These recurring dune forms migrate on top of the large scale topography and can yield local yet important variations in the flow field. In order to study the effect of migrating dune forms on the flow characteristics and consequently the erosive capacity of an alluvial river, an experiment with mobile bed has been carried out in a laboratory flume representing a sharp meander bend. In this experiment, changes to an initially flat, slightly sloped river bed under a steady flow and sediment discharge were observed until a recurring pattern of migrating dune forms could be seen on top of the characteristic pool-bar topography of meander bends. Once the dune forms were established, an Acoustic Doppler Velocity Profiler (ADVP) was placed in several positions alongside the river bend and used to measure the flow depth and flow characteristics under the influence of the passing dunes. Several times during the experiment, the topography was mapped using laser altimetry on a grid of large spatial resolution in order to isolate the dune forms from the large scale topography and determine the dune characteristics and the dune celerity. In this paper the large scale topography and dune characteristics will be shown and the effect of the migrating dune forms on the flow field and the erosive capacity will be discussed in detail
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