Interfacial internal wave excitation in the wake of towed ships is studied experimentally in a quasi-two-layer fluid. At a critical ‘resonant’ towing velocity, whose value depends on the structure of ...the vertical density profile, the amplitude of the internal wave train following the ship reaches a maximum, in unison with the development of a drag force acting on the vessel, known in the maritime literature as ‘dead water’. The amplitudes and wavelengths of the emerging internal waves are evaluated for various ship speeds, ship lengths and stratification profiles. The results are compared to linear two- and three-layer theories of freely propagating waves and lee waves. We find that despite the fact that the observed internal waves can have considerable amplitudes, linear theories can still provide a surprisingly adequate description of subcritical-to-supercritical transition and the associated amplification of internal waves. We argue that the latter can be interpreted as a coalescence of frequencies of two fundamental stable wave motions, namely lee waves and propagating interfacial wave modes.
Graphic abstract
In this work we analyze wind speed and solar irradiation data of high spatial and temporal res-olution for an extended area of north-western Africa including the Mediterranean Sea. We ex-ploit the ...ERA5 data bank compiled and maintained by the European Centre for Medium Range Weather Forecast (ECMWF). One of the new products they provide is horizontal wind speed components at a height of 100 m (modern wind turbines have a hub height between 80 and 120 m). We demonstrate that the desert area is an optimal location for wind- and solar electricity production for two peculiar aspects. Firstly, the wind speeds at 100 m over the Sahara are al-most as large as wind speeds over the open sea. Wind speed differences between the standard 10 m altitude and 100 m level are considerably larger over the desert area than over the sea. Secondly, there are utilizable anti-correlations between local wind speeds at 100 m and surface solar radiations over the Sahara. As far as we know, such anti-correlations over our target area are not considered until very recently as an exploitable source of combined solar-wind electricity production. We provide a theoretically optimum combination of the two resources in a simple model framework. The result is that resource combinations between 60-40% and 70-30% wind-solar electricity aggregation (depending on the geographic location) provide and optimally smooth output with a minimal loss of total production achieved by either pure wind or pure photo-voltaic generation.
•Wind speeds at 100 m height over the Sahara are as strong as over open sea.•Spatial correlation lengths for the wind fields are extremely large.•Saharan wind regularly intensifies during nighttime periods, in each season.•Anti-correlations between integrated solar and wind resources improve the smoothness.•The total output power loss at an optimal resource combination is low.
The damping of water surface standing waves (seiche modes) and the associated excitation of baroclinic internal waves are studied experimentally in a quasi-two-layer laboratory setting with a ...topographic obstacle at the bottom representing a seabed sill. We find that topography-induced baroclinic wave drag contributes markedly to seiche damping in such systems. Two major pathways of barotropic–baroclinic energy conversions were observed: the stronger one – involving short-wavelength internal modes of large amplitudes – may occur when the node of the surface seiche is situated above the close vicinity of the sill. The weaker, less significant other pathway is the excitation of long waves or internal seiches along the pycnocline that may resonate with the low-frequency components of the decaying surface forcing.
Interfacial internal wave excitation in the wake of towed ships is studied experimentally in a quasi-two layer fluid. At a critical `resonant' towing velocity, whose value depends on the structure of ...the vertical density profile, the amplitude of the internal wave train following the ship reaches a maximum, in unison with the development of a drag force acting on the vessel, known in the maritime literature as `dead water'. The amplitudes and wavelengths of the emerging internal waves are evaluated for various ship speeds, ship lengths and stratification profiles. The results are compared to linear two- and three-layer theories of freely propagating waves and lee waves. We find that despite the fact that the observed internal waves can have considerable amplitudes, linear theories can still provide a surprisingly adequate description of subcritical-to-supercritical transition and the associated amplification of internal waves.
•mi-analytical model of a new Earth / Water / Air Heat Exchanger EWAHE.•Shallow geothermal auxiliary heating/cooling system.•Case study on the use of the EWAHE heat exchanger for the dual aim of ...cooling thermal water and heating dwelling.
Earth to air heat exchangers are preconditioning systems designed to preheat the new air of buildings in winter. This paper suggests a study of a new horizontal coaxial earth /water/air heat exchanger (EWAHE) where hot water flows in the centre of the exchanger. After an analytical study of the exchanger in steady state regime, its coupling with the surrounding earth modeled in transient regime by spatio-temporal discretization; we obtain a very good correlation of our model under MATLAB with an equivalent three-dimensional CFD model. A parametric study, shows the influence of the ratio of inner diameter/ outer diameter, thermal conductivity of the inner tube and air flow rate/ water flow rate ratio on the energy efficiency of the system. Lastly, a case study of heating a building under Trnsys in south-eastern Algerian climate proves the energy benefits of this coaxial exchanger for cooling drinking water, naturally hot, in the region and to contribute effectively to preheating the air. We ultimately show the possibility of its use in cooling mode.
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