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Large-scale morphodynamic experiments on a beach drainage system
No full textThis research describes a unique set of experiments undertaken at the Large Wave Channel (Hannover) aimed to study the morphodynamic behaviour of a beach face containing a buried drainage system. The advantage of using a large wave flume is that scale effects that affected previous laboratory experiments are minimized. This compares the response of the undrained beach under controlled wave forcing with the response of the drained one with the same wave action. Low, medium and high levels of wave energy were used for the experiments, with significant wave heights of 0.39–0.83 m and wave steepnesses between 0.004 and 0.013. Any positive effect of the drains on the beach face was confined by the position of the cone of depression in the aquifer surface. The best performance of the system was observed with two drains operating at the same time under low to moderate wave energy
Beach sediment mixing under drained and undrained conditions
No full textThe paper describes a set of experiments undertaken at the Grosser Wellen Kanal (GWK) in Hannover on sediment
mixing on a beachface exposed to the action of a buried drainage system. Experiments were performed using a set of
drains (up to three working simultaneously), located at variable distance from the shoreline. Wave energy during the
tests ranged from medium (0.59 m < Hs < 0.61 m) to high (0.76 m < Hs < 0.83 m). Beach profiles were measured at the
end of each test. Further validation came from measurements using a grid of rods that were monitored at the same time
as the beach profiles were surveyed. While some beach stabilization was observed for low energy conditions, for
medium and high energy conditions the benefit of having the drains operative was not so clear. The comparison
between beach profiler and rods showed good agreement regarding relative vertical accretion and erosion events. In any
case, it was evident that the sedimentary effect on the beachface was confined to a narrow area above the drains. The
drained area showed slightly lower values of sediment mixing under drained conditions, but evidently this factor was
not important enough to trigger a widespread beach stabilization. Values of sediment mixing averaged across the whole
beachface ranged between 2-4 % and 4-6 % of the breaking wave height respectively for high and medium energy wave
conditions. Grain size, beach slope and drain configurations used here are fully comparable to field installations present
in the literature
Laboratory study on a beach drainage system
No full textIn recent years Beach Drainage Systems (BDS) have been considered as an innovative approach to stabilize the
beachface even if it still has to be proven to what extent they are effective in stabilizing the beach or causing accretion.
This paper describes tests carried out at the “GrosserWellenKanal” in Hannover aimed at improving the knowledge
of the hydrodynamic and morphodynamic behaviour of a beach containing a buried drainage system. Scale
effects that affected previous BDS laboratory experiments are minimized by the large scale. The morphodynamic response
of the undrained beach compared to a beach drained under the same type of wave action is reported. Experiments
were undertaken using a set of multiple drains, up to three working simultaneously, located below the beach
and at variable distances from the shoreline. The experimental program was organized in a series of tests with variable wave
energy.While a positive effect was observed under low energy conditions, for medium and high energy
conditions, the benefit of having the drains operative was not always clear. In any case, it was evident that any positive
effect of the drains on the beachface was limited to the position of the cone of depression represented by the
lowering of the hydraulic head
The influence of a Beach Drainage System on wave reflection and surf beat processes
No full textBeach Drainage Systems (BDS) have been installed at many sites around the world as a soft-engineering method able to stabilize the shoreline. The present work pays attention to hydrodynamic aspects concerning wave reflection and surf beat oscillations influenced by an artificial element acting in the nearshore such as a BDS. Full scale experiments on a BDS were carried out at the GWK flume in Hannover, in order to obtain useful information for defining correct design guidelines for such a system. Experiments were performed with different configurations, having one or more drains active. The BDS consisted of 4 PVC pipes located below the beach and at variable distance from the shoreline. The wave reflection on the beach was evaluated through the nearshore wave gauges using two different methods and the pressure transducers located inside the beach near the drains were used to evaluate surf beat oscillations. The main results show an increasing trend of the reflection coefficient during each test due to the progressive beach saturation and a stabilization of the reflection process induced by the lowering of the water table inside the beach due to the drainage. Moreover the presence of the BDS tends to back shift the wave frequencies towards the frequency range of long period infragravity waves. The presence of a larger infragravity energy induced by the drainage tends to enhance the onshore sediment flux. The analyses give useful hydrodynamic information on what influences the morphodynamic behaviour of a beach equipped with BDS
Smoothing of Slug Tests for Laboratory Scale Aquifer Assessment—A Comparison among Different Porous Media
No full textA filtering analysis of hydraulic head data deduced from slug tests injected in a confined aquifer with different porous media is proposed. Experimental laboratory tests were conducted in a large-scale physical model developed at the University of Calabria. The hydraulic head data were deduced from the records of a pressure sensor arranged in the injection well and subjected to a processing operation to filter the high-frequency noise. The involved smoothing techniques are the Fourier transform and two types of wavelet transform. The performances of the filtered hydraulic heads were examined for different slug volumes and four model layouts in terms of optimal fitting of the Cooper's analytical solution. The hydraulic head variations in the confined aquifer were analyzed using wavelet transform in order to discover their energy contributions and frequency oscillations. Finally, the raw and smoothed hydraulic heads were adopted to calculate the hydraulic conductivity of the aquifer
Experimental investigation on wave set up and nearshore velocity field in presence of a BDS
No full textAn extensive full scale laboratory investigation on a 2D physical model of a Beach Drainage System (BDS) was performed at the GWK in Hannover, Germany. The experiments aimed at improving the knowledge of the hydrodynamic and morphodynamic behaviour of a drained beach in order to allow the definition of the main design criteria. The present paper deals with the nearshore hydrodynamic aspects of a beach equipped with BDS. The adopted BDS consisted by 4 pipes installed below the swash zone and at a variable distance from the shoreline. Several drain configurations were considered under three wave energy conditions, paying attention to water table oscillations, wave set up, undertow currents and high-order velocity moments influenced by the system start up. The results show that the drains lead to a reduction in the water table level and, as a consequence, a lowering of wave set up on the beach. This effect induced a decrease in undertow currents and high-order velocity moments in the surf and swash zones. The observed flow characteristics can be used for energetic-based transport models able to predict erosional/accretionary trends in the nearshore morphodynamic changes under the influence of a BDS. The analyses yield useful hydrodynamic information on the general efficiency of a BDS in different wave conditions
Large eddy simulation within the smoothed particle hydrodynamics: Applications to multiphase flows
No full textIn this paper, the large eddy simulation (LES) model introduced in the smoothed particle hydrodynamics (SPH) by Di Mascio et al. [Phys. Fluids 29, 035102 (2017)] and called d-LES-SPH, is extended to treat multiphase flows. This is achieved by modifying the multiphase d-SPH by Hammani et al. [Comput. Methods Appl. Mech. Eng. 368, 113189 (2020)] by switching the viscous and density diffusion constants to dynamic variables evaluated as turbulence closure terms. The equation for energy conservation is also written for the presented model. The validation is performed for two-dimensional problems, by comparison with other established SPH solvers, with a finite volume method solver based on the turbulence closure corresponding to that adopted for the Lagrangian scheme, and with experimental data. The first test case investigated is a modified Taylor-Green vortex in which the introduction of macro-bubbles of a lighter fluid phase inside the domain is considered. In the second test case, a more violent problem involving wave breaking and splashing dynamics is analyzed. In the final test, the dynamic of a sloshing problem is reproduced. An analysis of turbulence resolution is conducted by considering modeled and resolved turbulent kinetic energies, as well as viscous dissipation and turbulent viscosity dissipation
Experimental investigation on wave set-up and nearshore velocity field in presence of a BDS
No full textExperimental investigation on wave set up and nearshore velocity field in presence of a BDS
No full textAn extensive full scale laboratory investigation on a 2D physical model of a Beach Drainage System (BDS) was performed at the GWK in Hannover, Germany. The experiments aimed at improving the knowledge of the hydrodynamic and morphodynamic behaviour of a drained beach in order to allow the definition of the main design criteria. The present paper deals with the nearshore hydrodynamic aspects of a beach equipped with BDS. The adopted BDS consisted by 4 pipes installed below the swash zone and at a variable distance from the shoreline. Several drain configurations were considered under three wave energy conditions, paying attention to water table oscillations, wave set up, undertow currents and high-order velocity moments influenced by the system start up. The results show that the drains lead to a reduction in the water table level and, as a consequence, a lowering of wave set up on the beach. This effect induced a decrease in undertow currents and high-order velocity moments in the surf and swash zones. The observed flow characteristics can be used for energetic-based transport models able to predict erosional/accretionary trends in the nearshore morphodynamic changes under the influence of a BDS. The analyses yield useful hydrodynamic information on the general efficiency of a BDS in different wave conditions
Experimental investigation on wave set up and nearshore velocity field in presence of a BDS
No full textAn extensive full scale laboratory investigation on a 2D physical model of a Beach Drainage System (BDS) was performed at the GWK in Hannover, Germany. The experiments aimed at improving the knowledge of the hydrodynamic and morphodynamic behaviour of a drained beach in order to allow the definition of the main design criteria. The present paper deals with the nearshore hydrodynamic aspects of a beach equipped with BDS. The adopted BDS consisted by 4 pipes installed below the wash zone and at a variable distance from the shoreline. Several drain configurations were considered under three wave energy conditions, paying attention to water table oscillations, wave set up, undertow currents and high-order velocity moments influenced by the system start up. The results show that the drains lead to a reduction in the water table level and, as a consequence, a lowering of wave set up on the beach. This effect induced a decrease in undertow currents and high-order velocity moments in the surf and swash zones. The observed flow characteristics can be used for energetic-based transport models able to predict erosional/accretionary trends in the nearshore morphodynamic changes under the influence of a BDS. The analyses yield useful hydrodynamic information on the general efficiency of a BDS in different wave conditions
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