Optimal electromagnetic energy extraction from transverse galloping

A fully coupled electro-fluid-elastic model for electromagnetic energy harvesting from Transverse Galloping is presented here. The model considers a one degree-of-freedom galloping oscillator where fluid forces are described resorting to quasi-steady conditions; the electromagnetic generator is modelled by an equivalent electrical circuit where power is dissipated at an electrical load resistance; the galloping oscillator and the electromagnetic model are coupled appropriately. Two different levels of simplification have been made depending on the comparison between the characteristic electrical and mechanical timescales. The effect of the electrical resistance load on the energy harvested is studied theoretically. For fixed geometry and mechanical parameters, it has been found that there exists an optimal electrical resistance load for each reduced velocity. On the practical side, this result can be helpful to design tracking-point strategies to maximize energy harvesting for variable flow velocity conditions

Enhanced mechanical energy extraction from transverse galloping using a dual mass system

This paper offers a theoretical study of energy extraction through transverse galloping using a dual-mass system. To this end, a two-degree-of-freedom model is developed where fluid forces on the galloping body are described resorting to quasi-steady hypothesis; the model is solved approximately by using the Harmonic Balance Method. Three possible configurations of the dual-mass system have been analyzed. Two of them show an improvement in the efficiency of energy extraction with respect to that of the single mass configuration when the mechanical properties of the dual-mass system are appropriately chosen. In addition, the dual-mass system promotes a broadening of the values of the incident flow velocities at which the efficiency is kept high

Optimal energy harvesting from vortex-induced and transverse galloping vibrations

The increase in awareness of the negative impact of fossil fuels on the environment has been the main driver behind the development of renewable energy technologies in the last few years. Renewable energy sources are well suited for a distributed generation concept, in which generation and storage of energy is located close to the final load with low power capacities (usually 10 MW or less), which enables the use of different sources leading to lower environmental impact. Some of the main renewable sources typically used include biomass, biogas, solar power, geothermal power and geophysical flows power. In particular, geophysical flows constitute an immense natural reservoir of energy present worldwide, being present as wind, river, oceanic or tidal flows among others. Most of the concepts operating nowadays that take advantage of fluid flows to harness energy rely on horizontal-axis turbines. However, conventional wind or water turbines cannot provide efficient power conversion to low-power applications, thus encouraging to seek new technologies to extract energy from fluid flows which can present big differences in their characteristics (namely density, mean velocity, turbulence intensity, etc.) efficiently. Flow-Induced Vibrations (FIV) arise as a promising way of harvesting energy from such geophysical flows efficiently. Coupling phenomena between the dynamics of flexibly-mounted structures and the surrounding flows can lead to self-sustained oscillations of a solid body which correspondingly can be transformed into electrical energy by means of a transducer. Many fluid-solid interactions have been considered recently as a mean to extract energy from current flows including Vortex-Induced Vibrations (VIV), transverse or torsional galloping, flutter or wake-induced vibrations among others. In the present thesis, VIV and transverse galloping oscillations are investigated and optimal configurations will be sought so as to maximize energy production. In first place, VIV of a circular cylinder is investigated. VIV is a resonant type of FIV where large-scale vortices are shed periodically from the body surface which leads to an alternating fluid force on the body. As such, oscillations only occur for a given range of inflow velocities where vortex emission frequency coincides with the natural frequency of oscillation of the body. In particular, it is investigated if through an active rotation of the circular cylinder along its axis proportional to the dynamics of the cylinder (namely, proportional to its transverse displacement or its transverse velocity) it is possible to increase the maximum amplitude of oscillation of the cylinder as well as increasing the range of velocities of the incident flow that yield large amplitude oscillations (broadband character) with the purpose of enhancing energy extraction. Also, as a side result the possibility of reducing oscillations in order to protect structures not meant to suffer from oscillations is evaluated. The effect of rotating the circular cylinder undergoing FIV oscillations is investigated both numerically for the low end Reynolds regime (through a Lattice Boltzmann Method) and experimentally at the “Antonio Barrero Ripoll” free-surface recirculating water channel for the medium range of Reynolds number. Additionally, Particle Image Velocimetry (PIV) technique has been used to visualize the main wake structures appearing behind the rotating cylinder in order to qualitatively determine the effect such rotation has on the vortical structures appearing. Secondly, energy harvesting from transverse galloping is studied. Transverse galloping is a selfinduced instability, in which a small displacement of the body immersed in a cross-flow leads to an oscillatory motion with increasing amplitude once a critical velocity is surpassed. Differently from VIV, transverse galloping is not a resonant type of FIV, thus, once transverse galloping shoots, amplitude continues growing with the incident velocity. Generally speaking, it has been proven that transverse galloping can be correctly described through a non-linear quasi-steady description of the fluid forces as a result of the disparity between the characteristic timescale of motion of the body and the convective timescale. This allows to analytically treat the problem. Here, an integral analytical treatment of the energy harvesting problem through transverse galloping is investigated. In particular, two types of transducers are considered (electromagnetic/piezoelectric) in order to obtain optimal configurations. Also a dual-mass system is investigated. A secondary (out of the flow) mass is elastically mounted to the galloping prism to determine if efficiency can be enhanced. Finally, the possibility of rotating the galloping body is considered to increase energy extraction through a quasi-steady model and compared to numerical simulations of a D-section cross-section at Reynolds 100. RESUMEN La creciente conciencia sobre los efectos negativos de los combustibles fósiles en el medio ambiente se ha convertido en el principal motor de desarrollo de tecnologías asociadas a la generación de energías renovables en los últimos años. Así mismo, dichas fuentes se han adecuado paulatinamente al concepto de generación distribuida, en el que la generación y almacenamiento de dicha energía se ubica cerca del destinatario final con capacidades de baja potencia (usualmente 10 MW o menos), lo que permite utilizar diferentes fuentes que conduzcan a un menor impacto ambiental. Algunas de las principales fuentes renovables que se usan típicamente incluyen la biomasa, biogás, energía solar, energía geotérmica y energía a partir de corrientes geofísicas. Estas corrientes constituyen un inmenso reservorio natural de energía que se encuentra presente en todo el planeta, pudiendo aparecer como corrientes de viento, ríos, corrientes en el océano o de marea entre otros. La mayoría de los conceptos que operan hoy en día y que usan las corrientes geofísicas para extraer energía, se basan en turbinas de eje horizontal. Sin embargo, los aerogeneradores o turbinas de agua convencionales no pueden proporcionar una conversión de energía eficiente para aplicaciones de baja potencia. Esta limitación ha fomentado la búsqueda de nuevas tecnologías que puedan extraer energía de corrientes con grandes diferencias en sus características (densidad, velocidad media, intensidad de turbulencia, etc.) de manera eficiente. Las vibraciones inducidas por flujo (FIV por sus siglas en inglés) surgen como un método prometedor para extraer energía de dichas corrientes geofísicos eficientemente. Los fenómenos de acoplamiento entre las estructuras elásticas y las corrientes circundantes pueden conducir a oscilaciones autosostenidas del cuerpo, que a su vez y de manera apropiada, se pueden transformar en energía eléctrica mediante el empleo de un transductor. Recientemente se ha considerado la posibilidad de utilizar diversos fenómenos de interacción fluido-sólida para extraer energía a partir de corrientes geofísicas, incluyendo entre otros fenómenos las vibraciones inducidas por vórtices (VIV por sus siglas en inglés), galope transversal o torsional, flameo o vibraciones inducidas por la estela. En la presente tesis se analizan las oscilaciones a partir de VIV y galope transversal para la búsqueda de configuraciones óptimas con el objetivo de maximizar la producción de energía. En primer lugar, se explora el fenómeno de VIV de un cilindro circular. VIV es un tipo de resonancia dentro de los FIV, donde los vórtices de gran escala se desprenden periódicamente de la superficie del cuerpo que conduce a la aparición de una fuerza fluida alterna sobre el cuerpo. Como tal, las oscilaciones sólo ocurren para un rango dado de velocidades incidente de la corriente, en donde la frecuencia de emisión de vórtices coincide con la frecuencia natural de oscilación del cuerpo. En particular, se busca evidenciar si mediante una rotación activa del cilindro circular a lo largo de su eje, proporcional a la dinámica de dicho cilindro (es decir, proporcional a su desplazamiento transversal o a su velocidad transversal) es posible aumentar tanto la amplitud máxima de oscilación del cilindro, así como el rango de velocidades incidente de la corriente donde ocurre dicha resonancia, con el objeto de mejorar al máximo posible la extracción de energía. Además, como resultado secundario, se evalúa la posibilidad de reducir las oscilaciones para proteger posibles estructuras que no estén destinadas a oscilar. El efecto de la rotación del cilindro circular sometido a oscilaciones de FIV se investiga tanto numéricamente para el régimen de bajo número de Reynolds (mediante un esquema de Lattice Boltzmann Method), como experimentalmente en el canal de agua de recirculación de superficie libre ”Antonio Barrero Ripoll” para el rango medio del número de Reynolds. Adicionalmente, se ha utilizado la técnica de Velocimetría de Imagen de Partículas (PIV) para visualizar las estructuras principales de la estela que aparecen tras el cilindro y determinar cualitativamente el efecto que tiene dicha rotación sobre los vórtices que aparecen. En segundo lugar, se examina la generación de energía a partir del galope transversal. El galope transversal es una inestabilidad autoinducida, en la que un pequeño desplazamiento del cuerpo inmerso en un flujo transversal conduce a un movimiento oscilatorio con amplitud creciente, una vez superada una velocidad crítica. A diferencia de VIV, el galope transversal no es un tipo de resonancia dentro de los FIV, por lo tanto, una vez que aparece el galope transversal, la amplitud continúa aumentando con la velocidad incidente. En general, se ha demostrado que el galope transversal se puede describir correctamente a través de una descripción cuasi-estática no lineal de las fuerzas fluidas, como resultado de la disparidad entre la escala del tiempo característico de oscilación del cuerpo y la escala de tiempo de residencia fluida. Esto permite tratar analíticamente el problema. En la presente tesis se estudia un tratamiento analítico integral del problema de extracción de energía a partir del fenómeno de galope transversal. En un primer momento, se han considerado dos tipos de transductores (electromagnéticos / piezoeléctricos) para la obtención de configuraciones óptimas que maximicen la extracción energética. También se analiza un sistema de doble masa. Una masa secundaria (fuera del flujo) se monta elásticamente en el prisma galopante para determinar si se puede mejorar la eficiencia. Finalmente, se considera la posibilidad de girar el cuerpo galopante con el objeto de aumentar la extracción de energía analizándose a través de un modelo cuasi-estático y comparándolo con simulaciones numéricas a Reynolds 100

Theoretical study of the energy harvesting of a cantilever with attached prism under aeroelastic galloping

The aeroelastic galloping of a cantilever with attached prism has recently attracted the attention of several researchers as a way to harvest energy from an airstream. This arrangement is not entirely analogous to that of classical Transverse Galloping (TG) since the instantaneous attitude of the galloping body (prism) with respect to the incident flow depends both on the velocity of the galloping body and wind speed (like in TG) but also on the rotation angle at the cantilever free end. A new governing parameter emerges, namely the ratio of the cross-section length of the prism to the beam length ?, and its effect on the galloping dynamics and power output needs to be studied. To this end, a theoretical model is here developed where the influence of ? is considered

Enhance of Energy Harvesting from Transverse Galloping by Actively Rotating the Galloping Body

Kinematic rotary control is here proposed conceptually to enhance energy harvesting from Transverse Galloping. The effect of actively orientating the galloping body with respect to the incident flow, by imposing externally a rotation of the body proportional to the motion-induced angle of attack, is studied. To this end, a theoretical model is developed and analyzed, and numerical computations employing the Lattice Boltzmann Method are carried out. Good agreement is found between theoretical model predictions and numerical simulations results. It is found that it is possible to increase significantly the efficiency of energy harvesting with respect to the case without active rotation, which opens the path to consider this idea in practical realizations