INFLUENCE OF INERTIA AND ASPECT RATIO ON THE TORSIONAL GALLOPING OF SINGLE-AXIS SOLAR TRACKERS
engineering structures, VOL. 243 (2021) 112682.
Eva Martínez-García, Eduardo Blanco Marigorta, Jorge Parrondo Gayo and Antonio Navarro- Manso.
Single-axis solar trackers are currently one of the cheapest systems for electricity generation. However, they may have to face significant maintenance costs depending on environmental and climatic factors. Weather is believed to provoke approximately half of the damages registered in solar tracker systems, and a large part of them are due to dynamic wind load. Torsional galloping – or, more precisely, flutter with one degree of freedom – is a phenomenon that arises when the wind speed exceeds a certain critical value. It causes the tracker to undergo angular oscillations with increasing amplitude until the structure collapses. The phenomenon is intrinsically linked to geometric and structural parameters, some of which exhibit a wide range of variation in the current market, depending on the configuration and design of the trackers. This article presents an analytical and experimental study on how the onset of torsional galloping is influenced by the inertia of the modules and the aspect ratio of the panel; it also includes the effect of the torque tube stiffness. The analytical study starts from the equation of motion involving the aeroelastic derivatives and the torque equation in differential form. Tests have been conducted on aeroelastic models of the structures of interest. It has been found that the critical reduced velocity of galloping changes with tilt angle, but it is essentially independent of the main structural parameters: torsional stiffness, inertia and aspect ratio. The results are finally presented in a Stability Diagram for the correct and optimal dimensioning of these structures against torsional galloping.
(Extended Stability Diagram, "Diagrama de Estabilidad del Tracker").
(Extended Stability Diagram, "Diagrama de Estabilidad del Tracker").
Experimental determination of the resistance of a single-axis solar tracker to torsional galloping
JOURNAL OF STRUCTURAL AND ENGINEERING MECHANICS, Vol. 78, No. 5 (2021) 519-528.
Eva Martínez-García, Eduardo Blanco Marigorta, Jorge Parrondo Gayo and Antonio Navarro- Manso.
One of the most efficient designs of solar trackers for photovoltaic panels is the single-axis tracker, which holds the panels along a torque tube that is driven by a motor at the central section. These trackers have evolved to become extremely slender structures due to mechanical optimization against static load and the need of cost reduction in a very competitive market. Owing to the corresponding decrease in mechanical resistance, some of these trackers have suffered aeroelastic instability even at moderate wind speeds, leading to catastrophic failures. In the present work, an analytical and experimental approach has been developed to study that phenomenon. The analytical study has led to identify the dimensionless parameters that govern the motion of the panel-tracker structure. Also, systematic wind tunnel experiments have been carried out on a 3D aeroelastic scale model. The tests have been successful in reproducing the aeroelastic phenomena arising in real-scale cases and have allowed the identification and a close characterization of the phenomenon. The main results have been the determination of the critical velocity for torsional galloping as a function of tilt angle and a calculation methodology for the optimal sizing of solar tracker shafts.
(Extended Stability Diagram, "Diagrama de Estabilidad del Tracker").
(Extended Stability Diagram, "Diagrama de Estabilidad del Tracker").
A new steel bridge launching system based on self-supporting double deck: structural numerical simulation and wind tunnel tests
PhD. Author: Antonio Navarro-Manso. Directors: Prof. Dr. Daniel Castro-Fresno & Prof. Dr. Juan José del Coz Díaz. E.T.S.I.C.C. y P., Santander, University of Cantabria. June 2013. Cum Laude and Distinct (2015).
During the bridge launching stage, the structure must resist different and bigger efforts (higher than those of its lifespan) as the process goes forward. Nowadays this efficient building system is limited by the maximum long span of the bridge and the patch loading phenomenon in slender steel webs.
This Thesis designs and optimizes a new steel bridge launching method and a continuous pushing system. The challenge is to get a length of about 150 m, therefore the lateral span of the structure is used on the weakest cross sections during the launching.
In this way, auxiliary means will not be needed and wasted time can be reduced. The new system allows to compete against another construction systems when a bridge has to be erected (basically cantilever or movable scaffolding for prestressed concrete bridges).
This Thesis designs and optimizes a new steel bridge launching method and a continuous pushing system. The challenge is to get a length of about 150 m, therefore the lateral span of the structure is used on the weakest cross sections during the launching.
In this way, auxiliary means will not be needed and wasted time can be reduced. The new system allows to compete against another construction systems when a bridge has to be erected (basically cantilever or movable scaffolding for prestressed concrete bridges).
Patch loading in slender and high depth steel panels: fem - doe analyses and bridge launching application
Engineering Structures.
This paper studies the optimum way to design both type and position of the stiffeners when a steel bridge is assembled by means of the new protect-patented launching method based on a self-supporting deck system. This procedure is able to launch bridge up to a span of 150 m, in an economical and sustainable way. The main objective of this research paper is to numerically analyze the best stiffener combination and distribution along the length of bridge, both longitudinally and transversally, in order to avoid the patch-loading phenomenon in the slender webs. An optimum design of a triangular cell along the lower plate is also presented. Thus the best stiffener distribution along the deck can be achieved to solve the two most important factors during the launching of a steel bridge: the huge forces on the support section -higher than the serviceability limit state- and buckling instability due to the point loads on the bearings. In this way, a three dimensional finite element model (FEM) is built and the design of experiments technique (DOE) is applied to obtain the best stiffener configuration. The numerical simulation allows the exact definition of the response of the structure to be achieved, covering the gaps and limits which are common in some national and international codes. Very good results have been obtained, in terms of deflection, patch loading resistance and vertical load distribution on the support section. Finally, the most important conclusions of this work are given.
Design and feasibility study of a microgeneration system to obtain renewable energy from tidal currents
Journal of Renewable Sustainable Energy.
Tidal energy to obtain electrical energy is yet an unexploited renewable energy. Existing generator designs and prototypes are not feasible due to the high investment conditioned by their high rated powers and off-shore locations. In addition, these prototypes are not readily available. This investigation presents a design of a microgeneration system with vertical axis microturbines. The design of the microturbines utilizes off-the-shelf electronic components, thus reducing the initial investment. The nominal data for selection of power electronic components and the total energy that can be obtained in a year are calculated. The investigation also studies the feasibility of an 80 kW microgeneration system to be applied in Spain, taking advantage of the actual electricity prices. The feasibility study quantifies the influence of the parameters: initial investment, tidal current speed, operation hours, turbine efficiency, price of electricity, and number of microturbines obtaining the limiting values of the suitable scenarios.
New launching method for steel bridges based on a self-supporting deck system: FEM and DOE analyses
Automation in Construction.
This paper studies a new launching method for steel bridges based on a self-supporting deck system. This new and patent-protected procedure is able to launch bridges of a span length up to 150 m, in an economical and sustainable way. The use of the last span segments to reinforce the critical sections during launching replaces other conventional temporary means applied nowadays. The main objective of this research paper is to numerically analyse the best double deck configuration as well as to define an approach to stiffener distribution in order to avoid the patch loading phenomenon in the slender webs. With this in mind, the pre-design of a triangular cell along the low flange of each web is presented. A three dimensional finite element model (FEM) is built and the design of experiments technique (DOE) is applied to obtain the best bridge configuration. This new construction method can be used together with a continuous launching system in order to increase the velocity of the whole operation and to improve safety during launching. Very good results have been obtained, in terms of deflection, patch loading resistance and vertical load on the pushing device. The comparison with other different construction systems and the application to a real case allows us to ensure the viability of the method described.
New mechanism for continuous and bidirectional displacement of heavy structures: design and analysis.
Automation in Construction.
The aim of this paper is to design and study a new mechanism for moving heavy structures using the force of friction. The mechanism designed is called DCACLM and was patented in 2011. This new device is based on an inverted crawler which is able to displace heavy structures such as large span bridges in a continuous and bidirectional way. Furthermore, the DCACLM design has taken into account other important aspects such as safety and sustainability in order to develop new construction methods. Nonlinear numerical models using the Finite Element Method have been developed to study the complex structural behavior of this new mechanism. The main conclusions provide acceptable results in terms of stresses and strains for the main elements of DCACLM.