Oscar Lopez-Garcia

Wind tunnel analysis of the aerodynamic loads on rolling stock over railway embankments: the effect of shelter windbreaks.

Wind-flow pattern over embankments involves an overexposure of the rolling stock travelling on them to wind loads. Windbreaks are a common solution for changing the flow characteristic in order to decrease unwanted effects induced by the presence of cross-wind. The shelter effectiveness of a set of windbreaks placed over a railway twin-track embankment is experimentally analysed. A set of two-dimensional wind tunnel tests are undertaken and results corresponding to pressure tap measurements over a section of a typical high-speed train are herein presented. The results indicate that even small-height windbreaks provide sheltering effects to the vehicles. Also, eaves located at the windbreak tips seem to improve their sheltering effect.

On Roof Geometry for Urban Wind Energy Exploitation in High-Rise Buildings

The European program HORIZON2020 aims to have 20% of electricity produced by renewable sources. The building sector represents 40% of the European Union energy consumption. Reducing energy consumption in buildings is therefore a priority for energy efficiency. The present investigation explores the most adequate roof shapes compatible with the placement of different types of small wind energy generators on high-rise buildings for urban wind energy exploitation. The wind flow around traditional state-of-the-art roof shapes is considered. In addition, the influence of the roof edge on the wind flow on high-rise buildings is analyzed. These geometries are investigated, both qualitatively and quantitatively, and the turbulence intensity threshold for horizontal axis wind turbines is considered. The most adequate shapes for wind energy exploitation are identified, studying vertical profiles of velocity, turbulent kinetic energy and turbulence intensity. Curved shapes are the most interesting building roof shapes from the wind energy exploitation point of view, leading to the highest speed-up and the lowest turbulence intensity.

Development of a current sensor based on active materials for high-voltage transmission systems

This paper presents the development of a new class of current sensor based on active materials for high-voltage transmission systems. This current sensor is an innovative design with respect to conventional current measurement transformers. The alternating current signal to be measured induces a magnetic field in an emitter which consists of a magnetostrictive material. The emitter transforms the current magnetic energy into mechanical energy in the form of mechanical waves due to the alternating nature of the induced magnetic field. These waves are transmitted through a dielectric structure until a piezoelectric stack, the receiver, is reached which converts the mechanical energy back into electrical energy. An electronic signal module processes this low electrical current and estimates the primary current to be measured. A numerical model has been developed to evaluate the preliminary design. A small scale prototype has been built and tested to demonstrate the feasibility of the current sensor. Experimental data have been used to fit the damping parameters of the model.

Effects of the water level on the flow topology over the Bolund island

We have analyzed the influence of the actual height of Bolund island above water level on different full-scale statistics of the velocity field over the peninsula. Our analysis is focused on the database of 10-minute statistics provided by Riso-DTU for the Bolund Blind Experiment. We have considered 10-minut.e periods with near-neutral atmospheric conditions, mean wind speed values in the interval [5,20] m/s, and westerly wind directions. As expected, statistics such as speed-up, normalized increase of turbulent kinetic energy and probability of recirculating flow show a large dependence on the emerged height of the island for the locations close to the escarpment. For the published ensemble mean values of speed-up and normalized increase of turbulent kinetic energy in these locations, we propose that some ammount of uncertainty could be explained as a deterministic dependence of the flow field statistics upon the actual height of the Bolund island above the sea level.

Influence of Embankments With Parapets on the Cross-Wind Turbulence Intensity at the Contact Wire of Railway Overheads

Winds as an environmental factor can cause significant difficulties for the railway system operation. The railway overhead has been particularly vulnerable to cross-winds related problems, such as development of undamped oscillations due to galloping phenomenon. The installation of windbreaks to decrease the aerodynamic loads on the train can affect the loads on railway overheads triggering cable galloping. One essential parameter to indicate the influence of the parapet wake on the catenary contact wire is the turbulence intensity. In this paper the results of an experimental analysis of the turbulence intensity due to the presence of parapets carried out in a wind tunnel are reported. Embankments equipped with different parapets have been tested and turbulence intensity has been measured at both contact wire locations, windward and leeward. The relative influence of the parapets is measured through a reduced turbulence intensity, defined as the ratio between the turbulence intensity measured with parapet and the turbulence intensity in the case without any parapet on the embankment. In general the reduced turbulence intensity increases as the height of the parapet increases.Copyright

Consideration of tip speed limitations in preliminary analysis of minimum COE wind turbines

A relation between Cost Of Energy, COE, maximum allowed tip speed, and rated wind speed, is obtained for wind turbines with a given goal rated power. The wind regime is characterised by the corresponding parameters of the probability density function of wind speed. The non-dimensional characteristics of the rotor: number of blades, the blade radial distributions of local solidity, twist, angle, and airfoil type, play the role of parameters in the mentioned relation. The COE is estimated using a cost model commonly used by the designers. This cost model requires basic design data such as the rotor radius and the ratio between the hub height and the rotor radius. Certain design options, DO, related to the technology of the power plant, tower and blades are also required as inputs. The function obtained for the COE can be explored to find those values of rotor radius that give rise to minimum cost of energy for a given wind regime as the tip speed limitation changes. The analysis reveals that iso-COE lines evolve parallel to iso-radius lines for large values of limit tip speed but that this is not the case for small values of the tip speed limits. It is concluded that., as the tip speed limit decreases, the optimum decision for keeping minimum COE values can be: a) reducing the rotor radius for places with high weibull scale parameter or b) increasing the rotor radius for places with low weibull scale parameter.

Coupled Electromechanical Optimization of Power Transmission Lines

This paper presents a multidisciplinary design and optimization method of power transmission lines. This optimization method solves both mechanical and electrical problems by a new strongly coupled method that also optimizes the potential designs using a genetic algorithm. A multi-objective function is formulated to simplify a constrained typical optimization problem into an unconstrained one. The scope of this work is the sizing and configuration optimization problem with fixed topology. The method is applied to a railway overhead transmission line. The genetic algorithm is applied to mechanical, electrical and electromechanical optimization problems obtaining good results. Finally, the solution of the electromechanical optimization problem is a trade-off between the multidisciplinary nature of the problem and the sort of optimization, sizing and configuration.

Coupled electromechanical cost optimization of high speed railway overheads

This paper presents a coupled electromechanical optimization of the cost of high speed railway overheads. The proposed electromechanical optimization solves the coupled mechanical and electrical problems by obtaining the railway overhead with minimum cost. A simple model cost of the railway overhead is proposed. This model cost defines the global cost per kilometer, which is mainly composed by the costs of material used in the construction of the overhead supports and the electric lines respectively. Using a standard genetic algorithm the optimized railway overhead is obtained. The parameters which describe the railway overhead are defined by: (i) sizing and (ii) configuration of the overhead supports; (iii) geometric location and (iv) type of electric conductors. The constraints considered are: (i) maximum allowable stress, and (ii) structural static stability; (iii) structure gauge to limit the position of physical conductors, (iv) minimum distance between conductors or between conductor and earth and (v) maximum allowable current of each conductor. In addition, the fitness function also considers the minimization of the equivalent electrical system impedance as a secondary optimization criterion. This optimization method has been successfully applied to the design of the high speed railway overhead C-350, used in the new line Madrid-Barcelona-French Border. The optimized railway overhead shows an overall improvement at two levels. Firstly, the performance is enhanced, and secondly, the global cost is reduced. The obtained results are compared with the non-optimized configuration in order to demonstrate the obtained improvements