Search

[Abstract:] In this paper, a new method for structural topology optimization considering minimum weight and local stress constraints is proposed. For this purpose, the Overweight Approach, an improvement of the so-called Damage Approach, is used. In this method, a virtual relative density is defined as a function of the violation of the local stress constraints. The virtual relative density is increased as stresses exceed the maximum allowable value. The optimization algorithm will provide a design with a minimal variation of the relative density. The structural analysis is performed by means of the Finite Element Method (FEM) and the distribution of material is modelled in terms of a uniform relative density within each element. Moreover, the optimization is addressed by means of the Sequential Linear Programming algorithm (SLP). Finally, the proposed methodology is tested by means of some benchmark problems, and the results show that the Overweight Approach is a feasible alternative for the Damage Approach and the stress constraint aggregation techniques.

[Abstract] This paper presents a mathematical and numerical formulation to design and analyze grounding systems in underground electrical substations. The developed approach is based on the well known Maxwell’s Equations. The proposed problem is solved by means of the Boundary Element Method (BEM). The utilization of BEM allows to introduce the geometry and electrical characteristics of the enclosure in a uniform soil. Therefore, a more realistic approximation of the soil structure is achieved. This formulation allows to obtain the main parameters of these protection systems (the grid resistance, the Ground Potential Rise, and the step and mesh voltage). It also allows to compute the surface and step voltage distributions. In addition, as a secondary result, the voltage and current density distributions over the enclosure are obtained. Finally, two grounding system analyses of real underground electrical substations are presented to demonstrate the industrial application and the modelization capabilities of the proposed formulation.

[Abstract:] This paper presents a computer software for the optimization of power transmission structures. The software employs a modified version of the Simulated Annealing algorithm that has been proven effective in large engineering problems. The target structures are three-dimensional steel trusses to be used as supporting towers of electrical lines. A mixed formulation merging continuous and discrete design variables is proposed for optimizing the size and shape of the trusses, including a first-order sensitivity analysis that reduces the computational cost. The implementation can be adapted to any kind of transmission tower and allows to quickly create a model to be analyzed and optimized in a few sequential steps. Despite its simplicity of use, the tools provided by the proposed framework allow to perform a full analysis of the design and provide an entire comprehension of its structural behavior. The software also includes a post-process and visualization tool set in a user-friendly graphical interface.

[Abstract] In this work, a new discretization of the source term of the shallow water equations with non-flat bottom geometry is proposed to obtain a well-balanced scheme. A Smoothed Particle Hydrodynamics Arbitrary Lagrangian-Eulerian formulation based on Riemann solvers is presented to solve the SWE. Moving-Least Squares approximations are used to compute high-order reconstructions of the numerical fluxes and, stability is achieved using the a posteriori MOOD paradigm. Several benchmark 1D and 2D numerical problems are considered to test and validate the properties and behavior of the presented schemes.

[Abstract] A highly accurate SPH method with a new stabilization paradigm has been introduced by the authors in a recent paper aimed to solve Euler equations for ideal gases. We present here the extension of the method to viscous incompressible flow. Incompressibility is tackled assuming a weakly compressible approach. The method adopts the SPH-ALE framework and improves accuracy by taking high-order variable reconstruction of the Riemann states at the midpoints between interacting particles. The moving least squares technique is used to estimate the derivatives required for the Taylor approximations for convective fluxes, and also provides the derivatives needed to discretize the viscous flux terms. Stability is preserved by implementing the a posteriori Multi-dimensional Optimal Order Detection (MOOD) method procedure thus avoiding the utilization of any slope/flux limiter or artificial viscosity. The capabilities of the method are illustrated by solving one- and two-dimensional Riemann problems and benchmark cases. The proposed methodology shows improvements in accuracy in the Riemann problems and does not require any parameter calibration. In addition, the method is extended to the solution of viscous flow and results are validated with the analytical Taylor–Green, Couette and Poiseuille flows, and lid-driven cavity test cases.

[Abstract:] Typical industry models for Offshore Wind Turbines with fixed substructures are based on decoupled models between the wind turbine and the substructure. It is proved that the complete dynamic response of the structure can only be captured with coupled models. In this paper a fully-coupled model for Offshore Wind Turbines with jacket support is presented. The computational model allows to obtain an accurate response of the whole structure and the dynamic interaction between all the elements. It also allows to reproduce particular effects such as the aerodynamic damping without the need for artificial damping ratios which would be needed in decoupled models. Typical environmental offshore conditions are integrated in the model and the response of the structure is obtained by means of a non-linear time integration algorithm in order to include the effect of the continuous rotation of the blades. A cost-efficient approach for the determination of fatigue-damage in the joints of the jackets is proposed. It is based on short-time simulations which allow to accurately estimate the long-term damage in general. The estimation shows a good agreement when compared to the damage values obtained by performing the whole time-interval simulation.

[Abstract] It takes time for society to digest changes, but we are changing. We can not deny climate change anymore and, as a species, we have come to realize there is an urgent need to change our energy generation habits. They have changed indeed and, in the last decades, renewable energies have clearly colored the picture of energy sources. Particularly, wind energy is called to be one of the most valuable cards in the hand of renewable energies in the near future. However, the current trend, and target of this thesis, are not the typical wind turbines installed inland. In the last years, the preferred location for the placement of wind farms has traveled, or we better say sailed from land to the seas, seeking for higher efficiency and exploitation of wind’s potential. Even though there are reasons to carry wind turbines offshore, the trip is neither easy nor low-cost and implies the analysis and design of new substructures to bear the weight of the turbines. Those substructures are called jackets. This thesis defines a procedure of analysis of the dynamic behavior of offshore wind turbines supported by jackets. Upon that analysis, a structural optimization problem is defined and solved using mathematical and numerical optimization techniques. The goal is to reduce the amount of material needed to manufacture the jackets and therefore reduce the investment of offshore wind turbine structures and consequently the indirect cost of energy production. The structural model is based on a non-linear dynamic analysis of three dimensional framed structures for fully coupled offshore wind turbines considering the rotation of the blades. Special care is taken in the description of the environmental loading conditions. Wind and wave actions and forces on the elements of the structure are thoroughly modeled. One of the most decisive aspects in the design of offshore structures is fatigue in steel elements arising from cyclic loads. In this thesis fatigue damage is assessed in

[Abstract] It takes time for society to digest changes, but we are changing. We can not deny climate change anymore and, as a species, we have come to realize there is an urgent need to change our energy generation habits. They have changed indeed and, in the last decades, renewable energies have clearly colored the picture of energy sources. Particularly, wind energy is called to be one of the most valuable cards in the hand of renewable energies in the near future. However, the current trend, and target of this thesis, are not the typical wind turbines installed inland. In the last years, the preferred location for the placement of wind farms has traveled, or we better say sailed from land to the seas, seeking for higher efficiency and exploitation of wind’s potential. Even though there are reasons to carry wind turbines offshore, the trip is neither easy nor low-cost and implies the analysis and design of new substructures to bear the weight of the turbines. Those substructures are called jackets. This thesis defines a procedure of analysis of the dynamic behavior of offshore wind turbines supported by jackets. Upon that analysis, a structural optimization problem is defined and solved using mathematical and numerical optimization techniques. The goal is to reduce the amount of material needed to manufacture the jackets and therefore reduce the investment of offshore wind turbine structures and consequently the indirect cost of energy production. The structural model is based on a non-linear dynamic analysis of three dimensional framed structures for fully coupled offshore wind turbines considering the rotation of the blades. Special care is taken in the description of the environmental loading conditions. Wind and wave actions and forces on the elements of the structure are thoroughly modeled. One of the most decisive aspects in the design of offshore structures is fatigue in steel elements arising from cyclic loads. In this thesis fatigue damage is assessed in