Ingeniería Mecánica y de Fabricación

URI permanente para esta comunidadhttps://hdl.handle.net/11441/11371

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3D contact effects in fretting fatigue tests
(Elsevier, 2022-04) Vázquez Valeo, Jesús; Erena Guardia, Diego; Navarro Pintado, Carlos; Domínguez Abascal, Jaime; Universidad de Sevilla. Departamento de Ingeniería Mecánica y Fabricación; Universidad de Sevilla. TEP111: Ingeniería mecánica
Fretting fatigue is a material damage phenomenon produced in mechanical contacts. This phenomenon mainly produces surface cracking, and depending on the fretting regime, surface wear. In the bibliography many different types of fretting tests, with different geometries have been proposed. This paper numerically analyses, via FEM models, some fretting tests with cylindrical pads and test specimens having different geometries that are frequently used in the literature. In such cases, non-negligible 3D effects are produced. The differences between the contact stress field obtained with different approaches are analysed and discussed.
A bone remodelling model including the effect of damage on the steering of BMUs
(Elsevier, 2014) Martínez Reina, Francisco Javier; Reina, I.; Domínguez Abascal, Jaime; García Aznar, J. M.; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Universidad de Sevilla. TEP111: Ingeniería Mecánica
Bone remodelling in cortical bone is performed by the so-called basic multicellular units (BMUs), which produce osteons after completing the remodelling sequence. Burger et al. (2003) hypothesized that BMUs follow the direction of the prevalent local stress in the bone. More recently, Martin (2007) has shown that BMUs must be somehow guided by microstructural damage as well. The interaction of both variables, strain and damage, in the guidance of BMUs has been incorporated into a bone remodelling model for cortical bone. This model accounts for variations in porosity, anisotropy and damage level. The bone remodelling model has been applied to a finite element model of the diaphysis of a human femur. The trajectories of the BMUs have been analysed throughout the diaphysis and compared with the orientation of osteons measured experimentally. Some interesting observations, like the typical fan arrangement of osteons near the periosteum, can be explained with the proposed remodelling model. Moreover, the efficiency of BMUs in damage repairing has been shown to be greater if BMUs are guided by damage.
A comprehensive methodology to obtain electrical analogues of linear mechanical systems
(Elsevier, 2023) López Martínez, Javier A.; García Vallejo, Daniel; Alcayde García, Alfredo; Sánchez Salinas, Silvia; Montoya, Francisco G.; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Ministerio de Ciencia e Innovación (MICIN). España; Universidad de Sevilla. TEP111: Ingeniería Mecánica
Electrical analogues of linear mechanical systems have traditionally been obtained using a set of rules that can potentially be tedious when applied to complex systems. In addition, such rules do not cover all the possibilities of mechanical systems including rotational and translational generalized coordinates. The present work establishes a comprehensive and systematic methodology for obtaining the electrical analogue of any mechanical system modelled by rigid bodies, springs, and dampers. The method is simple and straightforward. First, the dynamic equations of the mechanical system are derived into matrix form. These equations are then translated to the electrical domain by means of the electromechanical analogy and, finally, the electrical circuit is obtained by direct inspection of the matrices. In addition, the method can deal with a combination of translational and rotational coordinates in the definition of the mechanical model. To support the proposed method, and beyond the planar vehicle models found in the literature, the electrical analogue of a linear 3D 7-DOF full car model is presented in this work.
A fast and non-degenerate scheme for the evaluation of the 3D fundamental solution and its derivatives for fully anisotropic magneto-electro-elastic materials
(Elsevier, 2019-08) Buroni Cuneo, Federico Carlos; Ubessi, Cristiano; Hattori Da Silva, Gabriel; Marczak, Rogério J.; Sáez Pérez, Andrés; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Universidad de Sevilla. Departamento de Mecánica de Medios Continuos y Teoría de Estructuras; Ministerio de Economía y Competitividad (MINECO). España
A new expression for the fundamental solution is introduced, presenting three relevant characteristics: (i) it is explicit in terms of the Stroh's eigenvalues, (ii) it remains well-defined when some Stroh's eigenvalues are repeated, and (iii) it is exact. A fast and robust numerical scheme for the evaluation of the fundamental solution and its derivatives developed from double Fourier series representations is presented. The Fourier series representation is possible due to the periodic nature of the solution. The attractiveness of this series solution is that the information of the material properties is contained only in the Fourier coefficients, while the information of the dependence of the evaluation point is contained in simple trigonometric functions. This implies that any order derivatives can be determined by spatial differentiation of the trigonometric functions. Moreover, Fourier coefficients need to be obtained only once for a given material, leading to an efficient methodology. The robustness of the scheme arises from the properties (i) and (ii) of the new expression for the fundamental solution, which is used to compute the Fourier coefficients. The proposed approach combines the clean structure of the Stroh formalism with the simplicity of Fourier expansions, addressing the old drawbacks of anisotropic fundamental solutions.
A fast feedback controlled magnetic drive for the ASDEX Upgrade fast-ion loss detectors
(AIP Publishing, 2016-11) Ayllón Guerola, Juan Manuel; Gonzalez Martin, Javier; García Muñoz, Manuel; Rivero Rodriguez, Juan Francisco; Herrmann, A.; Galdón Quiroga, Joaquín; García López, Francisco Javier; Rodríguez Ramos, Mauricio; Sanchís Sánchez, Lucía; Domínguez, A. D.; García Vallejo, Daniel; Domínguez Abascal, Jaime; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Universidad de Sevilla. Departamento de Ingeniería Mecánica y Fabricación; Universidad de Sevilla. RNM138: Física Nuclear Aplicada; Universidad de Sevilla. TEP111: Ingeniería Mecánica; Universidad de Sevilla. TEP956: Flujos Multifásicos
A magnetically driven fast-ion loss detector system for the ASDEX Upgrade tokamak has been designed and will be presented here. The device is feedback controlled to adapt the detector head position to the heat load and physics requirements. Dynamic simulations have been performed taking into account effects such as friction, coil self-induction, and eddy currents. A real time positioning control algorithm to maximize the detector operational window has been developed. This algorithm considers dynamical behavior and mechanical resistance as well as measured and predicted thermal loads. The mechanical design and real time predictive algorithm presented here may be used for other reciprocating systems.
A fast model to resolve the velocity-space of fast-ion losses detected in ASDEX Upgrade and MAST Upgrade
(Institute of Physics Publishing, 2019) Rivero Rodríguez, Juan Francisco; García Muñoz, Manuel; Galdón Quiroga, Joaquín; González Martín, Javier; Ayllón Guerola, Juan Manuel; García Vallejo, Daniel; Martin, R.; McClements, K. G.; Sanchís Sánchez, Lucía; Zoletnik, S.; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Universidad de Sevilla; Comunidad Europea de Energía Atómica (EURATOM)
A forward model to resolve the fast-ion loss velocity-space on a fast-ion loss detector (FILD) probe head (FILDSIM) has been extended, making it possible to perform real-time analysis of the FILD data ("real-time FILDSIM"). Parametric pre-processing with FILDSIM enables real-time mapping of the raw FILD measurements to the velocity-space of the fast-ion distribution reaching the FILD probe, which depends on the local magnetic field at the probe head. Such parametric pre-processing facilitates the study of fast-ion losses in stages of the discharge other than the flat-top, such as the ramp-up phase when changes in the local magnetic field at the probe head cannot be neglected. Real-time FILDSIM has been applied to the existing and newly installed FILDs in ASDEX Upgrade and will be used for the forthcoming FILD in MAST-Upgrade. Due to the larger size of the MAST-U FILD probe, the approximation used in FILDSIM of a uniform magnetic field in the FILD region has been generalised to the case of a non-uniform field, with gyro-orbits calculated numerically in this field.
A fretting fatigue model based on self-steered cracks
(Elsevier B.V., 2022-02) Erena Guardia, Diego; Vázquez Valeo, Jesús; Navarro Pintado, Carlos; Domínguez Abascal, Jaime; Universidad de Sevilla. Departamento de Ingeniería Mecánica y Fabricación; Universidad de Sevilla. TEP111: Ingeniería Mecánica
In this article a new fretting fatigue life prediction model is presented. The model can be classified as a variable crack initiation length: the crack initiation and crack propagation phases are calculated as a function of the crack initiation length, and among all the feasible crack initiation lengths and orientations, that producing the minimum fatigue life is considered. In this new proposal the crack direction is automatically determined as a function of fatigue parameters in both phases: initiation and propagation. The model is applied to a wide experimental campaign of fretting fatigue tests, and excellent correlation is obtained between experimental and predicted fretting fatigue lives and crack paths.
A Market-Based Analysis on the Main Characteristics of Gearboxes Used in Onshore Wind Turbines
(MDPI, 2017-10-25) Vázquez-Hernández, Cristina; Serrano-González, Javier; Centeno Báez, Gabriel; Universidad de Sevilla. Departamento de Ingeniería Eléctrica; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
Even though wind energy is one of the most mature renewable technologies, it is in continuous development not only because of the trend towards larger wind turbines but also because of the development of new technological solutions. The gearbox is one of the components of the drive train in which the industry is concentrating more effort on research and development. Larger rotor blades lead to more demanding requirements for this component as a consequence of a higher mechanical torque and multiplication ratio (due to lower rotational speed of blades while the rotational speed on the generator side remains at similar values). In addition, operating conditions become increasingly demanding in terms of reliability, performance, and compactness. This paper analyses the different gearbox arrangements that are implemented by manufacturers of onshore wind turbines, as well as their market penetration (including different aspects that affect the design of the gearbox, such as drive train configuration and turbine size). The analysis carried out shows a clear convergence towards gearboxes with three stages. However, there is a noticeable diversity in the types of gears used, depending to a large extent on the preferences of each manufacturer but also on the nominal power of the wind turbine and drive train configuration.
A New Algorithm for the Evaluation of the Elastic Forces in the Absolute Nodal Coordinate Formulation
(Eccomas Proceedia, 2004) García Vallejo, Daniel; Mayo Núñez, Juana María; Escalona Franco, José Luis; Domínguez Abascal, Jaime; Universidad de Sevilla. Departamento de Mecánica de Medios Continuos y Teoría de Estructuras
The use of the Absolute Nodal Coordinate Formulation (ANCF) to model flexible multibody systems leads to a system of equations in which the mass matrix is constant. Among other advantages of the ANCF, as the simplicity of the formulation of joint constraint, the constancy of the mass matrix is specially useful since it implies that the mass matrix is calculated once before the analysis and stored as a invariant quantity. On the other hand, the evaluation of the elastic forces has been considered as a difficult task since they result in large nonlinear functions. Both linear and nonlinear formulations based on either Continuum Mechanics or Timoshenko/Euler-Bernoulli approaches have been supposed to lead to the same level of complexity of the elastic force function. The evaluation of the elastic forces when using a nonlinear Continuum Mechanics approach requires, as presented in the literature, the integration over the volume of the element. However, it can be shown that this integration can be avoided for every evaluation since there is a closed form of the elastic force function that can be obtained before the simulation. Finite elements based on ANCF have such a large number of nodal coordinate (24 and 48 for three-dimensional beams and plates, respectively) that the search for a closed form of the elastic force function becomes difficult and costly. This paper presents a set of constant matrices that are integrated in advance (before simulation) and allows the evaluation of the elastic forces without the integration over the volume of the element suggested in the literature. In addition, the amount of data that has to be stored in order to evaluate the function is reduced. These constant matrices together with the mass matrix complete the set of invariants of the ANCF that allows an acceleration of simulations. Numerical simulations comparing CPU time and number of arithmetic operations carried out when these invariant matrices are used with those carried out when they are not used, support the convenience of their use.
A New Electromechanical Analogy Approach Based on Electrostatic Coupling for Vertical Dynamic Analysis of Planar Vehicle Models
(Institute of Electrical and Electronics Engineers Inc., 2021) López Martínez, Javier; Castillo Martínez, Javier; García Vallejo, Daniel; Alcayde, Alfredo; Gil Montoya, Francisco; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
Analogies between mechanical and electrical systems have been developed and applied for almost a century, and they have proved their usefulness in the study of mechanical and electrical systems. The development of new elements such as the inerter or the memristor is a clear example. However, new applications and possibilities of using these analogues remain to be explored. In this work, the electrical analogues of different vehicle models are presented. A new and not previously reported analogy between inertial coupling and electrostatic capacitive coupling is found and described. Several examples are provided to highlight the benefits of this analogy. Well-known mechanical systems like the half-car or three three-axle vehicle models are discussed and some numerical results are presented. To the best of the author’s knowledge, such systems were never dealt with by using a full electromechanical analogy. The mechanical equations are also derived and compared with those of the electrical domain for harmonic steady-state analysis.
A novel algorithm to resolve lack of convergence and checkerboard instability in bone adaptation simulations using non-local averaging
(Wiley-Blackwell, 2021) Calvo Gallego, José Luis; Pivonka, Peter; García Aznar, José Manuel; Martínez Reina, Francisco Javier; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Consejería de Economía, Conocimiento, Empresas y Universidad (Junta de Andalucía)
Checkerboard is a typical instability in finite element (FE) simulations of bone adaptation and topology optimization in general. It consists in a patchwork pattern with elements of alternating stiffness, producing lack of convergence and instabilities in the predicted bone density. Averaging techniques have been proposed to solve this problem. One of the most acknowledged techniques (node based formulation) has severe drawbacks such as: high sensitivity to mesh density and type of element integration (full vs reduced) and, more importantly, oscillatory solutions also leading to lack of convergence. We propose a new solution consisting in a non-local smoothing technique. It defines, as the mechanical stimulus governing bone adaptation in a certain integration point of the mesh, the average of the stimuli obtained in the neighbour integration points. That average is weighted with a decay function of the distance to the centre of the neighbourhood. The new technique has been shown to overcome all the referred problems and perform in a robust way. It was tested on a hollow cylinder, resembling the diaphysis of a long bone, subjected to bending or torsion. Checkerboard instability was eliminated and local convergence of bone adaptation was achieved rapidly, in contrast to the other averaging technique and to the model without control of checkerboard instability. The new algorithm was also tested with good results on the same geometry but in a model containing a void, which produces a stress concentration that usually leads to checkerboard instability, like in other applications such as simulations of bone-implant interfaces.
A Novel Synergy-Based Approach for the Design of Cable-Driven Exosuits for Walking Assistance
(2022-11-02) Rodríguez Jorge, Daniel; Alonso Sánchez, Francisco Javier; Herrera Navarro, Ignacio; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
The growing tendency of worldwide societies, but particularly in the West, to aging leads to a growing number of individuals that might require any kind of walking assistance. Life expectancy in Spain, for instance, has doubled in barely four generations. As such, there exist numerous solutions, among which exoskeletons must be highlighted as wearable devices with rigid elements that assist, generally driven by motors, human gait in any way. As an alternative to these devices, a new variant, much lighter and cheaper for the user has been proposed: wearable exoskeletons, or exosuits. They, made only of textile elements aside from the actuation system, offer a more comfortable and economic solution to those who can walk, but need an assistive device or, alternatively, wish to increase their motion capabilities: the lack of rigid elements forces the subject to sustain themselves, yet at the same time does not restrict or impede their natural gait in any way. A common variety of exosuits consists of an actuation system, including the motors and the power transmission system, generally included in a backpack and transmitting force via cables anchored to the joints in the so-called anchor points, in most cases textile elements located at the joints that will be actuated. A motor might be required for each target joint and leg: if all hip, knee, and ankle are to be actuated, six motors will be required, which will be the main contributors to the overall system weight and price. This work arises from the need of reducing such weight and price, as well as increasing the wearability of walking-assistance exosuits. The document focuses on the development of a new design approach for exosuits that allows a heavy reduction in the number of actuators required to provide the desired assistance and, thus, offers a much more affordable solution, at the reach of many more potential users. The thesis is, thus, supported by two main cornerstones. On one side, the development of an inverse-dynamics model capable of predicting the forces and torques to be produced by the system to assist human gait, establishing a base for the system design and for its control. On the other side, stands the detailed description of the novel design approach that provides the desired improvements, serving as a guide for future exosuit designs for the lower limb. The latter is where lies the main contribution of this work, which will try to improve current technology with regards to cost and weight: the mechanical design based on synergies. Statistical analysis of human gait demonstrates a rather evident fact: as opposed to other movements, such as grasping an object or holding it, walking has a cyclic nature and presents clear similarities between several of its parameters. A kinematic study performed on the joint flexion-extension angles for hip, knee, and ankle, among others, yields a notable degree of similarity between them. The same happens in the cable forces during gait required to provide a certain fraction of the total joint torque, or in the cable extensions themselves. These similarities make it possible to approach, by statistical means, a dimensionality reduction problem while keeping a high degree of correspondence with the original variables. In other words, the number of required actuation curves, thus the number of required motors, can be significantly reduced, as much as the problem's dimensions. Therefore, a design allowing the actuation of six simultaneous degrees of freedom (up to three joints per leg) has been proposed with only one motor. All of it leads to the main contribution of the work to the current walking-assistance exosuits design: the detailed, rigorous, and mathematical description of a novel method of design targeting the significant reduction in the weight and price of these devices, while also improving their wearability and making them more accessible.
A polynomial hyperelastic model for the mixture of fat and glandular tissue in female breast
(Wiley, 2015-09) Calvo Gallego, José Luis; Martínez Reina, Francisco Javier; Domínguez Abascal, Jaime; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Ministerio de Economia, Industria y Competitividad (MINECO). España; Universidad de Sevilla. TEP111: Ingeniería Mecánica
In the breast of adult women, glandular and fat tissues are intermingled and cannot be clearly distinguished. This work studies if this mixture can be treated as a homogenized tissue. A mechanical model is proposed for the mixture of tissues as a function of the fat content. Different distributions of individual tissues and geometries have been tried to verify the validity of the mixture model. A multiscale modelling approach was applied in a finite element model of a representative volume element (RVE) of tissue, formed by randomly assigning fat or glandular elements to the mesh. Both types of tissues have been assumed as isotropic, quasi-incompressible hyperelastic materials, modelled with a polynomial strain energy function, like the homogenized model. The RVE was subjected to several load cases from which the constants of the polynomial function of the homogenized tissue were fitted in the least squares sense. The results confirm that the fat volume ratio is a key factor in determining the properties of the homogenized tissue, but the spatial distribution of fat is not so important. Finally, a simplified model of a breast was developed to check the validity of the homogenized model in a geometry similar to the actual one.
A study of the temporomandibular joint during bruxism
(Nature Publishing Group, 2014) Commisso Cuñarro, María Soledad; Martínez Reina, Francisco Javier; Mayo Núñez, Juana María; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
A finite element model of the temporomandibular joint (TMJ) and the human mandible was fabricated to study the effect of abnormal loading, such as awake and asleep bruxism, on the articular disc. A quasilinear viscoelastic model was used to simulate the behaviour of the disc. The viscoelastic nature of this tissue is shown to be an important factor when sustained (awake bruxism) or cyclic loading (sleep bruxism) is simulated. From the comparison of the two types of bruxism, it was seen that sustained clenching is the most detrimental activity for the TMJ disc, producing an overload that could lead to severe damage of this tissue.
A Track Geometry Measuring System Based on Multibody Kinematics, Inertial Sensors and Computer Vision
(MDPI, 2020-01) Escalona Franco, José Luis; Urda Gómez, Pedro; Muñoz Moreno, Sergio; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Universidad de Sevilla. TEP -111: Ingeniería Mecánica; Universidad de Sevilla. TEP-123: Metalurgia e Ingeniería de los Materiales
This paper describes the kinematics used for the calculation of track geometric irregularities of a new Track Geometry Measuring System (TGMS) to be installed in railway vehicles. The TGMS includes a computer for data acquisition and process, a set of sensors including an inertial measuring unit (IMU, 3D gyroscope and 3D accelerometer), two video cameras and an encoder. The kinematic description, that is borrowed from the multibody dynamics analysis of railway vehicles used in computer simulation codes, is used to calculate the relative motion between the vehicle and the track, and also for the computer vision system and its calibration. The multibody framework is thus used to find the formulas that are needed to calculate the track irregularities (gauge, cross-level, alignment and vertical profile) as a function of sensor data. The TGMS has been experimentally tested in a 1:10 scaled vehicle and track specifically designed for this investigation. The geometric irregularities of a 90 m-scale track have been measured with an alternative and accurate method and the results are compared with the results of the TGMS. Results show a good agreement between both methods of calculation of the geometric irregularities.
About kinematic consistency in the inverse dynamics problem in biomechanics
(2015) Ojeda Granja, Joaquín; Martínez Reina, Francisco Javier; Mayo Núñez, Juana María; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Ministerio de Economia, Industria y Competitividad (MINECO). España; Universidad de Sevilla. TEP111: Ingeniería Mecánica
The inverse dynamic analysis is used in the study of the human gait to evaluate the reaction forces transmitted between anatomical segments and to calculate the net joint moments resulting from the muscle activity in each joint. There are two approaches well defined. In the clinical field reconstruction techniques are often applied. The errors caused, mainly, by the relative movement of the skin over the bones make that the joint centres localized in two adjacent segments do not place the same position in the space. Velocities and accelerations are obtained through numerical derivation of the position. Finally, joint moment are calculated to balance the equilibrium equations. On the other hand, the engineers employ multibody models. They apply techniques to reduce the measurement errors and to obtain kinematically consistent data up to the acceleration level and calculate reaction and driving actions by means of the Lagrange multipliers. There is no agreement about which approach provides better results. The first procedure presents errors due to the skin motion which are avoid in the second method introducing errors inherent to the model. In this work, the two approaches were compared. Dynamic residuals defined to balance the Newton's equations were used as a measure of the model goodness. A discussion about the effect of the kinematically inconsistent data on the second approach was carried out. Results highlighted that the addition to the recorded motion of kinematic constrains according to a multibody model could lead to worse results in the inverse dynamic problem.
Active control of Alfvén eigenmodes by external magnetic perturbations with different spatial spectra
(Institute of Physics (IOP), 2024-07) González Martín, Javier; García Muñoz, Manuel; Galdón Quiroga, Joaquín; Todo, Y.; Domínguez Palacios Durán, Jesús José; Dunne, M.; Van Vuuren, Anton Jansen; Liu, Y. Q.; Sanchis Sánchez, Lucía; Spong, D.; Suttrop, W.; Wang, X.; Willensdorfer, M.; Universidad de Sevilla. Departamento de Física Atómica, Molecular y Nuclear; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; European Union (UE). H2020; Ministerio de Ciencia e Innovación (MICIN). España; ; Universidad de Sevilla. FQM402: Ciencias y Tecnologías del Plasma y el Espacio.
Alfvén eigenmodes have been suppressed and excited in tokamak plasmas by (just) modifying the poloidal spectra of externally applied static magnetic perturbations. This effect is observed experimentally when toroidal spectra of n = 2, n = 4 as well as a mixed spectrum of n = 2 and n = 4 is applied. Under the n = 2 magnetic perturbations, the modes are excited or suppressed by modifying the coil phasing between the upper and the lower set of coils. Regardless of the absolute rotation, an even parity for the n = 4 perturbation is observed to reduce the amplitude of the Alfvénic instabilities, while an odd parity amplifies it. To combine the stabilizing (and destabilizing) effect of n = 2 and n = 4, a mixed spectrum is applied, finding similar reduction (and amplification) trends. However, the impact on the mode amplitude is more subtle, due to the reduced coil current required for a mixed spectrum. The signal level on the fast-ion loss detector is sensitive to the applied poloidal spectrum, which is consistent with Hamiltonian full-orbit modelling of an edge resonant transport layer activated by the 3D perturbative fields. An internal redistribution of the fast-ion population is induced, modifying the phase-space gradients driving the Alfvénic instabilities, and ultimately determining their existence. The calculated edge resonant layers for both n = 2 and n = 4 toroidal spectra are consistent with the observed suppressed and excited phases. Moreover, hybrid kinetic-magnetohydrodynamic (MHD) simulations reveal that this edge resonant transport layer overlaps in phase-space with the population responsible for the fast-ion drive. The results presented here may help to control fast-ion driven Alfvénic instabilities in future burning plasmas with a significant fusion born alpha particle population.
Advances in the modeling and dynamic simulation of reeving systems using the arbitrary Lagrangian–Eulerian modal method
(Springer, 2022) Escalona Franco, José Luis; Mohammadi, Narges; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación; Universidad de Sevilla. TEP111: Ingeniería Mecánica
This paper presents new advances in the arbitrary Lagrangian–Eulerian modal method (ALEM) recently developed for the systematic simulation of the dynamics of general reeving systems. These advances are related to a more convenient model of the sheaves dynamics and the use of axial deformation modes to account for non-constant axial forces within the finite elements. Regarding the sheaves dynamics, the original formulation uses kinematic constraints to account for the torque transmission at the sheaves by neglecting the rotary inertia. One of the advances described in this paper is the use of the rotation angles of the sheaves as generalized coordinates together with the rope-to-sheave no-slip assumption as linear constraint equations. This modeling option guarantees the exact torque balance at the sheave without including any nonlinear kinematic constraint. Numerical results show the influence in the system dynamics of the sheave rotary inertia. Regarding the axial forces within the finite elements, the original formulation uses a combination of absolute position coordinates and transverse local modal coordinates to account for the rope absolute position and deformation shape. The axial force, which only depends on the absolute position coordinates, is constant along the element because linear shape functions are assumed to describe the axial displacements. For reeving systems with very long rope spans, as the elevators of high buildings, the constant axial force is inaccurate because the weight of the ropes becomes important and the axial force varies approximately linearly within the rope free span. To account for space-varying axial forces, this paper also introduces modal coordinates in the axial direction. Numerical results show that a set of three modal coordinates in the axial direction is enough to simulate linearly varying axial forces.
Ajuste de matrices O-D con asignación de alta convergencia
(2013-12-18) Reyes Gutiérrez, Antonio; García Benítez, Francisco; Romero Pérez, Luis Miguel; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
En esta tesis se aborda el problema de la estimación de matrices de viajes en redes de tráfico reales, congestionadas y de grandes dimensiones. Éste es un tema de manifiesta importancia en la planificación del transporte dada la relación existente entre la precisión de las matrices O-D y la calidad de los resultados del proyecto. El objetivo principal ha sido el de encontrar una metodología de ajuste de matrices que sea capaz de afrontar proyectos de grandes redes de tráfico congestionadas, incorporando los últimos modelos de asignación de tráfico de alta convergencia. La información de partida es la matriz de viajes del proyecto desactualizada y datos de aforos de un subconjunto de arcos de la red. El algoritmo de ajuste presentado resuelve iterativamente un problema de asignación de tráfico, cuya solución permite generar la dirección de descenso propuesta, y un problema de estimación, en el que se actualiza la matriz de viajes a través de la dirección de descenso. Se han realizado pruebas numéricas donde se pone en evidencia las mejoras que ofrece el algoritmo: - Se han abordado desde redes de pequeña escala hasta redes de grandes dimensiones como es la red de la comunidad de Madrid. - Se ha comprobado que el cálculo del Jacobiano propuesto genera direcciones de búsqueda más eficientes que las propuestas anteriormente y recogidas en la literatura científica. Esta eficiencia se hace patente en que se alcanzan matrices menos distorsionadas y en un menor número de iteraciones. - Esta nueva formulación tiene en cuenta los efectos de la saturación de vehículos. El Jacobiano considera las influencias de todos los pares O-D, incluso los pares O-D no interceptados por ningún aforo y los que inicialmente no presentan viajes. - Se ha reducido el tiempo de ejecución gracias a la inclusión de nuevos problemas de asignación de tráfico. A su vez, mediante el empleo de estos algoritmos de alta convergencia se ha mejorado la estabilidad, repetitividad y consistencia de las soluciones. Finalmente cabe destacar la utilidad práctica de la herramienta desarrollada, los resultados presentados ponen de manifiesto la amplia variedad de casos que puede tratarse con la formulación propuesta y la flexibilidad de la implementación desarrollada para adaptarse a esta casuística. Esta formulación generalizada presenta además el atractivo de poder ser implementada en el entorno de desarrollo integrado de Matlab con su propio lenguaje de programación. Desde Matlab existe la posibilidad de convertir su propio código de programación en cualquier código de programación como puede ser C, C++, C#, Java, luego en esta tesis se presenta una herramienta que puede ser empleada por todos aquellos profesionales que hayan de enfrentarse a este problema clásico de la Ingeniería del Transporte.
Aletoriedad del crecimiento de grietas por fatiga bajo cargas de amplitud constante
(Grupo español de fractura, 1995) Lapetra, C.; Domínguez Abascal, Jaime; Universidad de Sevilla. Departamento de Ingeniería Mecánica y de Fabricación
El objeto de este trabajo es el análisis de la aleatoriedad de la velocidad de crecimiento de grieta en probetas de aleación de aluminio 2024 teóricamente idénticas, ante las mismas cargas de' amplitud constante. Se presentan los resultados de crecimiento de grieta producidos en una serie de 18 ensayos en probetas tipo "compact". Dichos resultados se analizan estadísticamente, aproximándose distintas leyes de crecimiento considerando aleatorios algunos parámetros de la~ mismas. Entre los resultados obtenidos cabe destacar la influencia del tamaño de grano en los parámetros que defmen la variabilidad de la velocidad de crecimiento entre un instante y otro en una misma probeta, al menos en la superficie y la buena representación del proceso aleatorio de crecimiento que se obtiene empleando un modelo de ley cúbica de crecimiento con dos parámetros aleatorios, a la que se suma un proceso aleatorio determinado.

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