Time decay for porosity problems

In this paper, we numerically study porosity problems with three different dissipa- tion mechanisms. The root behavior is analyzed for each case. Then, by using the finite element method and the Newmark- scheme, fully discrete approximations are introduced and some numerical results are described to show the energy evolution depending on the viscosity coefficient.Peer ReviewedPostprint (published version

On the time decay for the MGT-type porosity problems

In this work we study three different dissipation mechanisms arising in the so-called Moore-Gibson-Thompson porosity. The three cases correspond to the MGT-porous hyperviscosity (fourth-order term), the MGT-porous viscosity (second-order term) and the MGT-porous weak viscosity (zerothorder term). For all the cases, we prove that there exists a unique solution to the problem and we analyze the resulting point spectrum. We also show that there is an exponential energy decay for the first case, meanwhile for the second and third case only a polynomial decay is found. Finally, we present some one-dimensional numerical simulations to illustrate the behaviour of the discrete energy for each caseThis paper is part of the projects PGC2018-096696-B-I00 and PID2019-105118GB-I00, funded by the Spanish Ministry of Science, Innovation and Universities and FEDER "A way to make Europe".Peer ReviewedPostprint (author's final draft

Finite element error analysis of a viscoelastic Timoshenko beam with thermodiffusion effects

In this paper, a thermomechanical problem involving a viscoelastic Timoshenko beam is analyzed from a numerical point of view. The so-called thermodiffusion effects are also included in the model. The problem is written as a linear system composed of two second-order-in-time partial differential equations for the transverse displacement and the rotational movement, and two first-order-in-time partial differential equations for the temperature and the chemical potential. The corresponding variational formulation leads to a coupled system of first-order linear variational equations written in terms of the transverse velocity, the rotation speed, the temperature and the chemical potential. The existence and uniqueness of solutions, as well as the energy decay property, are stated. Then, we focus on the numerical approximation of this weak problem by using the implicit Euler scheme to discretize the time derivatives and the classical finite element method to approximate the spatial variable. A discrete stability property and some a priori error estimates are shown, from which we can conclude the linear convergence of the approximations under suitable additional regularity conditions. Finally, some numerical simulations are performed to demonstrate the accuracy of the scheme, the behavior of the discrete energy decay and the dependence of the solution with respect to some parameters

On the fully discrete approximations of the MGT two-temperatures thermoelastic problem

We consider a one-dimensional two-temperatures thermoelastic model. The corresponding variational problem leads to a coupled system which is written in terms of the mechanical velocity, the temperature speed and the inductive tempera- ture. An existence and uniqueness result is recalled. Then, fully discrete approxima- tions are introduced by using the finite element method and the implicit Euler scheme. A priori error estimates are proved and the linear convergence of the approximations is deduced under suitable additional regularity conditions. Finally, some numerical simulations are shown to demonstrate the accuracy of the proposed algorithm and the behavior of the discrete energy.Peer ReviewedPostprint (published version

Analysis of Damage Models for Cortical Bone

Bone tissue is a material with a complex structure and mechanical properties. Diseases or even normal repetitive loads may cause microfractures to appear in the bone structure, leading to a deterioration of its properties. A better understanding of this phenomenon will lead to better predictions of bone fracture or bone-implant performance. In this work, the model proposed by Frémond and Nedjar in 1996 (initially for concrete structures) is numerically analyzed and compared against a bone specific mechanical model proposed by García et al. in 2009. The objective is to evaluate both models implemented with a finite element method. This will allow us to determine if the modified Frémond–Nedjar model is adequate for this purpose. We show that, in one dimension, both models show similar results, reproducing the qualitative behaviour of bone subjected to typical engineering tests. In particular, the Frémond–Nedjar model with the introduced modifications shows good agreement with experimental data. Finally, some two-dimensional results are also provided for the Frémond–Nedjar model to show its behaviour in the simulation of a real tensile test

Optimization of the Auxiliary-Beam System in Railway Bridge Vibration Mitigation Using FEM Simulation and Genetic Algorithms

In this paper, we present the optimization of a vibration mitigation system for railway bridges. These structures are subjected to significant moving loads, whose dynamic characteristics may produce resonance effects, compromising the integrity of the bridge and the security of the passengers if the speed or the load of the train is not controlled. The study focuses on the Auxiliary Beam system. It consists of a beam located under the bridge and connected to the slab by viscous dampers. The symmetry of the problem allowed for the use of a 2D Finite Element model of the system. This model was used together with a genetic algorithm in order to evaluate the behaviour of different candidates and to optimize the design parameters: the inertia of the beam and the damper coefficient. The goal of the optimization process is to minimize the acceleration of the bridge while adding the lightest mitigation system possible. The combination of a Finite Element Model and Genetic Algorithm helps to address the complex problem and to find an optimized set of structural parameters. The system finally shows good behaviour for optimal parameters

Fabrication and magnetic functionalization of cylindrical porous anodic alumina

The fabrication and magnetic functionalization of cylindrical porous anodic alumna (CPAA) was examined. The process are engineered onto aluminum wires with milli- and micrometric diameter so that the grown nanopores are disposed in a radial configuration. The structural study revealed the possibility to make these CPAA permeable to obtain micronucleus with engineering manrope surfaces. CPAAs had been employed as templates for the preparation of highly ordered arrays of radical metallic nannies filling the pores by electroplating techniques. The final radial manrope diameter can be more accurately prepared by suitable wet etching in a phosphoric acid solution at varying concentrations. A progressive, exponentially decaying, modulating stairway reduction of voltage was applied from the corresponding anodizing voltage to decrease the oxide layer between the aluminum foil and the bottom of the pores.Peer Reviewe

Finite Element Validation of an Energy Attenuator for the Design of a Formula Student Car

Passive safety systems of cars include parts on the structure that, in the event of an impact, can absorb a large amount of the kinetic energy by deforming and crushing in a design-controlled way. One such energy absorber part, located in the front structure of a Formula Student car, was measured under impact in a test bench. The test is modeled within the Finite Element (FE) framework including the weld characteristics and weld failure description. The continuous welding feature is almost always disregarded in parts included in impact test models. In this work, the FE model is fully defined to reproduce the observed results. The test is used for the qualitative and quantitative validation of the crushing model. On the one hand, the acceleration against time curve is reproduced, and on the other hand, the plying shapes and welding failure observed in the test are also correctly described. Finally, a model that includes additional elements of the car structure is also simulated to verify that the energy absorption system is adequate according to the safety regulations

Hiperinsulinemia y sensibilidad a la Sal

La enfermedad coronaria es una de las primeras causas de morbilidad y mortalidad cardiovascular. Para su prevención es necesario diagnosticar y corregir con medidas farmacológicas y no farmacológicas los factores de riesgo cardiovascular modificables. Nosotros hemos desarrollado un programa de diagnostico precoz y tratamiento de factores que incrementan el riesgo a desarrollar enfermedades cardiovasculares y metabólicas, en sujetos "sanos", asintomáticos. Hasta el presente hemos evaluado 153 sujetos. En este trabajo evaluamos la asociación de la sensibilidad a la sal con otros factores de riesgo cardiovascular silente e investigamos los posibles factores predictores de sensibilidad a la sal. La comparación de los sujetos sensibles a la sal (SS), con los sujetos sal resistentes (SR) demostró que los sujetos SS tienen mayor edad, peso corporal, cifras tensionales, niveles elevados de triglicéridos, niveles bajos de HDL-colesterol y de actividad física. Adicionalmente estudiamos el papel de la hiperinsulinemia y de la hiperglicemia en la sensibilidad a la sal, a través de la medición de la incidencia (porcentaje de individuos SS y SR) y severidad de la sensibilidad a la sal en sujetos hiperinsulinémicos e intolerantes glucosados y/o diabéticos comparándolos con sus respectivos controles. No hubo diferencias en la distribución de sensibilidad a la sal entre los diferentes grupos (hiper y normo insulinemicos (insulina en ayunas < 15 uUI/ml), glucotolerantes (glicemia en ayunas <110; 2 horas post carga <140 mg/d) y en los intolerantes glucosados y/o diabéticos. La severidad de la sensibilidad a la sal también fue similar entre los grupos, de hecho, la reducción de la ingesta de sal de 316 ± 13 a 26 ± 3 mmol/día, produjo cambios similares en la presión arterial en sujetos hiperinsulinémicos o en sujetos con niveles normoinsulinémicos y en sujetos tolerantes e intolerantes glucosados y/o diabéticos. Adicionalmente no se encontró correlación entre la magnitud de los cambios de la presión arterial inducidos por la sal y los niveles de insulina y glucosa en ayunas, 2 horas después de la carga oral de glucosa o el área bajo la curva de insulina. En conclusión, nuestros resultados sugieren los niveles de glicemia y de insulina del paciente, no determinan su reactividad vascular a los cambios en ingesta de sal.AbstractCoronary artery disease is one of the leading causes of cardiovascular morbidity and mortality. Early detection and correction of modifiable cardiovascular risk factors is mandatory for disease prevention. A program was develop for the early diagnosis and treatment of factors known to increment the risk of developing cardiovascular and metabolic disease in apparently healthy subjects. Ion this report, we present data for the first 153 individuals evaluated. We investigated the association of salt sensitivity with other cardiovascular risk factors, and in addition, determined which factors predicted salt sensitivity. The comparison of salt sensitive subjects (SS) with salt resistant subjects (SR) demonstrated that SS are older, heavier, have higher blood pressure and triglyceride levels and lower HDL-cholesterol, as well as a lesser level of physical activity. The prevalence and severity of salt sensitivity in hyperinsulinaemic and in glucose intolerant individuals was also investigated. There was no difference in the distribution of salt sensitivity among groups (hyper and normo insulinaemic), glucose tolerant (fasting glucose < 110 mg/dl; 2 hours post oral load < 140 mg/dl) and glucose intolerant and/or diabetic subjects. Reducing salt intake from 316 ± 13 to 26 ± 3 mmol/day, produced similar decreases in blood pressure in hyper- and normoinsulinaemic and in glucose tolerant and glucose intolerant and/or diabetic subjects. In addition, no correlation was found between the magnitude of blood pressure increase induced by high salt and insulin or glucose levels, either fasting, 2 hours post glucose load or calculated as the area under the curve following a 75 gr. glucose load. In conclusion, our results suggest that insulin and glucose levels do not determine the increase in vascular reactivity induced by increases in salt intake