288 research outputs found
A DMST-based tool to establish the best aspect ratio, solidity and rotational speed for tidal turbines in real sea conditions
No full textA Double Multiple Stream Tube (DMST) routine to predict the performance of cross-flow hydrokinetic turbines in real environments is presented, along with a site assessment application to identify the most efficient turbine aspect ratio, solidity and configuration (single, or paired) for a selected area of the Northern Adriatic Sea. The peculiarity of this DMST tool is its 3D character, since it allows to reproduce the vertical distribution of the torque generated by the turbine. To this end, correlations for fluid dynamic phenomena, based on high-fidelity fully CFD simulations, were implemented. The marine circulation code SHYFEM is adopted to obtain velocity profiles for a half lunar cycle period. The sites with the highest mean kinetic power were identified. The DMST routine is equipped with an iterative process able to establish which rotational speed maximizes the power output. Indeed, a spatially non-uniform velocity profile requires to determine the flow velocity more suitable to obtain the rotational speed via Tip Speed Ratio (TSR) definition. To this end, the section of the blades working at optimal TSR varies from top to bottom, until the maximum power is reached. It works as a virtual Maximum Power Point Tracking system able to adapt the turbine operating conditions for the different turbine geometries, and for changes in flow conditions. The results show that for the case study, the performance curve shape influences the optimal TSR blade section: the latter is often located in the upper part of the turbine for the low solidity, whereas, for high solidity turbines, in the bottom half part
Embedding of a blade-element analytical model into the shyfem marine circulation code to predict the performance of cross-flow turbines /
No full textOur aim was to embed a 2D analytical model of a cross-flow tidal turbine inside the open-source SHYFEM marine circulation code. Other studies on the environmental impact of Tidal Energy Converters use marine circulation codes with simplified approaches: performance coefficients are fixed a priori regardless of the operating conditions and turbine geometrical parameters, and usually, the computational grid is so coarse that the device occupies one or few cells. In this work, a hybrid analytical computational fluid dynamic model based on Blade Element Momentum theory is implemented: since the turbine blades are not present in the grid, the flow is slowed down by means of bottom frictions applied to the seabed corresponding to forces equal and opposite to those that the blades would experience during their rotation. This simplified approach allowed reproducing the turbine behavior for both mechanical power generation and the turbine effect on the surrounding flow field. Moreover, the model was able to predict the interaction between the turbines belonging to a small cluster with hugely shorter calculation time compared to pure Computational Fluid Dynamics
A turbines-module adapted to the marine site for tidal farms layout optimization
No full textThe ocean energy exploitation is arousing growing interest in the renewable energy sector. In the short term, horizontal axis tidal turbines are the most promising technology due to the accumulated know-how in the field of wind energy. In order to maximize the performance of the devices in a cluster, it is essential to optimize the layout. The marine environment offers different conditions than
atmospheric situations, in terms of confinement and turbulence intensity. Moreover, tidal currents exhibit a highly predictable pattern in speed intensity and direction unlike the wind resource, which has a more random behaviour. Nonetheless, most of tidal sites are characterized by the inversion of flow where the two prevailing directions are not perfectly aligned and opposite, hence the angle
between those directions should be a design variable. In this work we will consider as a case study the site proposed in [1], where this angle is ±20°. For those sites with a flow inversion of almost 180°, the staggered configuration is preferable to avoid wakes interference as mentioned in [2]. Furthermore, many studies [3] had analysed positive interaction between neighbouring devices in a cluster, hence it is important to establish the optimal relative position accounting for fluid dynamic positive effects, and not only negative aspects such
as wake interactions. For this reason, in this work we present a novel approach to determine the best configuration of a cluster of few turbines, a ”module”, which will be the optimized ”building block” for the whole farm. The procedure to be followed consist of two phases in which both the characteristics of the site and those of the turbine are taken into consideration. To place the devices in an optimal configuration, we first consider the change of flow direction during the tidal cycle for the site of interest, allowing only those configurations which avoid wake interference for both prevailing flow directions; then, we assess the best layout by exploiting positive interactions between devices in the cluster. The mutual fluid dynamic influence is analysed by means of a 3D Blade Element Momentum model of the turbine [4] implemented in the Open Source SHYFEM code. A series of simulations is performed to outline the power production trend of the module, and consequently find the optimal distancing between the machines. CFD simulations are also used to
extract the module wake characteristics
A Double Multiple Stream Tube (DMST) routine to identify efficient geometries of cross-flow tidal turbines in site assessment analyses: Paper 594
No full textA routine to predict the performance of cross-flow hydrokinetic turbines, based on the Blade Element Momentum theory, for site assessment purposes is here presented. The routine uses as input the flow data obtained with the open-source marine circulation code SHYFEM. The routine consists in a Double Multiple
Stream Tube model making use of 1D flow simplifications for fast analyses. The dynamic stall sub-model and two original sub-models, implemented to include the effects of blade tip losses and the lateral deviation of streamlines approaching the turbine, have been validated versus results of 3D and 2D CFD simulations. As a
case study, the tool is applied to an area of the northern Adriatic Sea in order to quickly identify locations with the highest hydrokinetic potential and, at the same time, to find the most efficient turbine aspect ratio and configuration (single or paired turbines) taking into account the bathymetric constraints. The results show that turbines, with short aspect ratio, and paired turbines (with the same overall frontal area of a single rotor) can give the best power outputs thanks to higher flow speeds available at the top of the water column and more favorable Reynolds number and distribution of tip speed ratios along the blade
A Double Multiple Stream Tube (DMST) routine for site assessment to select efficient turbine aspect ratios and solidities in real marine environments
No full textA MATLAB routine, based on a Double Multiple Stream Tube model, developed to quickly predict the performance of cross-flow hydrokinetic turbine, here is presented. The routine evaluate flow data obtained with the open-source marine circulation code SHYFEM. The tool can establish the best locations to place tidal devices taking into account bathymetric constraints and the hydrokinetic potential. Hence, it can be used to decide the best set of geometrical parameters. The geometrical variables of our analysis are turbine frontal area, aspect ratio and solidity. Several sub-models, validated with 3D and 2D CFD simulations, reproduce phenomena such as dynamic stall, fluid dynamic tips losses and the lateral deviation of streamlines approaching the turbine. As a case study, the tool is applied to an area of the northern Adriatic Sea. After having identified some suitable sites to exploit the energy resource, we have compared behaviours of different turbines. The set of geometrical parameters that gives the best performance in terms of power coefficient can vary considering several locations. Conversely, the power production is always greater for turbine with low aspect ratio (for a fixed solidity and area). Indeed, shorter devices benefit from higher hydrokinetic potentials at the top of the water column
A model chain approach for coastal inundation: Application to the bay of Alghero
No full textCoastal inundation is an important threat for many nearshore regions worldwide, and has significantly increased
in the last years also due to sea-level rise and augmented impact of extreme events, like sea storms. Many
countries and regions have recently invested to overcome such problems, which commonly lead to structure
damages, beach erosion and many other consequences. Numerical modeling is an important tool for coastal
inundation prediction, being a valuable support for management issues to mitigate the inundation risk or suggest
resilient solutions. The present work illustrates a novel approach, based on a numerical model chain that exploits
a tide-surge-wave operational modeling system (Kassandra), a phase-averaged model (ROMS-SWAN) for the
wave propagation towards the shore, and a phase-resolving solver (NSWE) for the prediction of runup and
coastal inundation. Such a chain is applied to the bay of Alghero (Sardinia, Italy), where the results of the
mentioned chain are compared to those obtained using, in place of the phase-averaged model, an analytical
model for the wave propagation. Results confirm that both chain approaches provide comparable inundations,
though the use of the analytical, more approximate (e.g., less accurate and reliable description of wave breaking
dissipation), model suggests more severe conditions and larger flooded areas. Our contribution provides a
methodological approach for an accurate and reliable estimate of coastal flooding
A BEM-Based Model of a Horizontal Axis Tidal Turbine in the 3D Shallow Water Code SHYFEM
No full textWe present a novel 3D implementation of a horizontal axis tidal turbine (HATT) in the shallow water hydrostatic code SHYFEM. The uniqueness of this work involves the blade element momentum (BEM) approach: the turbine is parameterized by applying momentum sink terms in the x and y momentum equations. In this way, the turbine performance is the result of both the flow conditions and the turbine’s geometric characteristics. For these reasons, the model is suitable for farm-layout studies, since it is able to predict the realistic behavior of every turbine in a farm, considering the surrounding flow field. Moreover, the use of a shallow water code, able to reproduce coastal morphology, bathymetry wind, and tide effects, allows for studying turbine farms in realistic environments
DEBORA: Developing an Interface to Support Collaboration in a Digital Library
No full textInterfaces to library systems have largely failed to represent the in-herently collaborative nature of information work. This paper describes how collaborative functionality is being implemented as part of the DEBORA project to provide access to digitised Renaissance documents. Work practices of users of Renaissance documents are described and the collaborative features of the client software are outlined. Functionalities discussed include annotation, the creation of virtual books and the inclusion of user-supplied metadata
The summer 2022 drought: a taste of future climate for the Po valley (Italy)?
No full textThe severe drought that affected large areas of Europe in Spring and Summer 2022 hit the Po valley (northern Italy) with an intense water scarcity crisis. Productive activities, particularly agriculture, suffered the consequences of water shortage, and the coastal regions of the Po Delta underwent extensive saltwater intrusion. By relying on observed discharge records and on precipitation data from reanalysis and climate models, we analyse the 2022 event in the framework of the recent past statistics and in future scenarios. Alongside with a projection of future rainfall regimes on the Po River basin in two climate change scenarios, our analysis shows that persistent negative rainfall anomalies like the ones that characterised the 2022 event, though unlikely to become a typical feature of future climate, could remarkably increase their frequency, particularly in a severe climate change condition. Moreover, their impacts will be magnified by rising temperatures and, in coastal areas, by rising sea level, enhancing the salinisation of agricultural lands and altering the dynamics of transitional ecosystems. While providing a first quantitative assessment of an event that struck a strategic productive and environmental region of the Italian territory, this brief communication points out the importance of a multi-disciplinary, basin-scale approach to climate change adaptation
- …
