Scipedia: Documents published in 2020

Epoch-by-epoch phase difference method to evaluate GNSS single-frequency phase data quality

Xin Liu — Wed, 29 Jan 2020 12:36:11 +0100

The quality of Global Navigation Satellite SystemsGlobal Navigation Satellite Systems Global Navigation Satellite Systems (Global Navigation Satellite Systems Global Navigation Satellite Systems Global Navigation Satellite Systems GNSS) data is one important factor for precise navigation and positioning by using GNSS technique. We proposed a new method to monitor GNSS single-frequency phase data quality by using high-rate epoch-by-epoch phase difference (EEPD). We analyzed the influence of ephemeris, carrier frequency (L1, L2 and L3) and latitude (high latitude, middle latitude and low latitude) on the phase data quality evaluation. It is concluded that the use of broadcast and final orbit has little effect on the phase data quality evaluation with EEPD. The broadcast ephemeris can be used while analyzing GNSS single-frequency data quality in real time. The results obtained by using L1, L2 and L3 observations are almost the same and the GNSS phase quality evaluation can be analyzed by using single-frequency data. The latitudes of stations have a great influence on the quality evaluation of phase data using EEPD. At the same time, Bernese software is used to analyze the feasibility and reliability of EEPD. The results obtained with EEPD are compared with those obtained by Bernese. The results by different methods show good consistency, which shows that EEPD can be reliably used to evaluate the GNSS data quality.

Epoch-by-epoch Phase Difference Method to Evaluate GNSS Single-frequency Phase Data Quality[[#fn-2|²]]

Xin Liu — Wed, 29 Jan 2020 12:26:14 +0100

1 Corresponding author: Xin Liu; E-mail: [mailto:xinliu1969@126.com xinliu1969@126.com]

Epoch-by-epoch Phase Difference Method to Evaluate GNSS Single-frequency Phase Data Quality

Xin Liu — Wed, 29 Jan 2020 12:02:21 +0100

Vulnerability and ductility concepts in the seismic design of buildings

María Jesús Samper — Wed, 29 Jan 2020 11:47:44 +0100

In spite of the every time better understanding and knowledge of the factors that influence in the seismic behaviour of the buildings, there is a great difference at the moment between the theoretical developments that are carried out continually in the field of earthquake engineering and the concepts that are applied in the seismic design codes of many countries. This fact is reflected clearly in the very irregular seismic behaviour of the buildings during the big earthquakes occurred in the world in the last years. The earthquake design codes make exhaustive recommendations concerning the seismic loads, the simplified methods of structural analysis to be applied, to the details that should incorporate in the seismic design and construction of the structural elements and, in lesser measure, to the conceptual design of the buildings. Therefore, special attention is paid in this work to the structural ductility and its influence on the seismic vulnerability of the buildings and on their seismic damage and risk.

A Lagrangian nodal integration method for free-surface fluid flows

María Jesús Samper — Tue, 28 Jan 2020 16:16:17 +0100

We present a Lagrangian nodal integration method for the simulation of Newtonian and non-Newtonian free-surface fluid flows. The proposed nodal Lagrangian method uses a finite element mesh to discretize the computational domain and to define the (linear) shape functions for the unknown nodal variables, as in the standard Particle Finite Element Method (PFEM). In this approach, however, the integrals are performed over nodal patches and not over elements, and strains/stresses are defined at nodes and not at Gauss points. This allows to limit the drawbacks associated with the remeshing and leads to a more accurate stress computation than in the classical elemental PFEM. Several numerical tests, in 2D and in 3D, are presented to validate the proposed nodal PFEM. In all cases, the method has shown a very good agreement with analytical solutions and with experimental and numerical results from the literature. A thorough comparison between nodal and elemental PFEMs is also presented, focusing on crucial issues, such as solution accuracy, convergence, mass conservation and sensitivity to mesh distortion.

Statical and dynamical behaviour of thin fibre reinforced composite laminates with different shapes

María Jesús Samper — Tue, 28 Jan 2020 12:11:28 +0100

Based on the classical laminated plate theory, a variational approach for the study of the statical and dynamical behaviour of arbitrary quadrilateral anisotropic plates with various boundary conditions is developed. The analytical formulation uses the Ritz method in conjunction with natural coordinates to express the geometry of general plates in a simple form. The deflection of the plate is approximated by a set of beam characteristic orthogonal polynomials generated using the Gram–Schmidt procedure. The algorithm developed is quite general and can be used to study fibre reinforced composite laminates with symmetric lay-ups, which may have general anisotropy and any combinations of clamped, simply supported and free edge support conditions. Various numerical applications are presented and some results are compared with existing values in the literature to demonstrate the accuracy and flexibility of the present method. New results were also determined for plates with different geometrical shapes, combinations of boundary conditions, several stacking sequences and various angles of fibre orientation.

Estudio numérico del comportamiento de los hormigones reforzados con fibras cortas

María Jesús Samper — Tue, 28 Jan 2020 11:48:49 +0100

En este trabajo se presenta un acercamiento al estudio del comportamiento de los hormigones reforzados con fibras cortas. Se establece una formulación basada en una modificación de la teoría de mezclas clásica para determinar sus parámetros mecánicos a partir de las características de los materiales componentes (hormigón fibras cortas). También se muestran resultados numéricos obtenidos mediante el método de los elementos finitos y se comentan las posibilidades de un método analítico simplificado para el estudio de su comportamiento. El desarrollo del trabajo trata sobre el comportamiento del hormigón reforzado con fibras y las características que justifican su utilización. Se estudia el equilibrio interno y mecanismo de transmisión de tensiones entre el hormigón y las fibras cortas y la formulación general del problema e inserción dentro de la técnica de los elementos finitos. Se hace un breve comentario sobre el tratamiento simplificado del comportamiento de los hormigones reforzados con fibras cortas y se presenta un ejemplo de comprobación.

Definition of a general implicit orthotropic yield criterion

María Jesús Samper — Tue, 28 Jan 2020 11:01:01 +0100

The definition of an orthotropic yield criterion presents a serious challenge in the formulation of constitutive models based on such theories as elastoplasticity, viscoplasticity, damage, etc. The need to model the behavior of a real orthotropic material requires the formulation of orthotropic yield criteria, and these may be difficult to obtain. For metals, orthotropic yield functions have been formulated by Hill [Proc. Roy. Soc. Lon. Ser. A 193 (1948) 281; J. Mech. Phys. Solids 38(3) (1990) 200], Barlat [Int. J. Plasticity 5 (1989) 51; 7 (1991) 693], Chu [NUMISHEET 93 (1993) 199] and Dutko et al. [Comput. Methods Appl. Mech. Engrg. 109 (1993) 73], but in many cases these functions do not describe the true behavior of the metal. The situation is worse when one attempts to represent a nonmetal such as a polymer, ceramic or composite.

In this paper, we present a general definition of an explicit orthotropic yield criterion together with a general method for defining implicit orthotropic yield functions. The latter formulation is based on the transformed-tensor method, whose principal advantage lies in the possibility of adjusting an arbitrary isotropic yield criterion to the behavior of an anisotropic material. As example we choose the adjustment to the Hill, Hoffman [J. Comp. Materials 1 (1967) 200] and Tsai–Wu [J. Comp. Materials 5 (1971) 58] criteria, but these particular cases serve to establish the methodology for achieving the desired function adjustment for any other well-known criterion or experimental set of data obtained from laboratory.

Life prediction of structures. Numerical study and treatment of structural durability, a brief report

María Jesús Samper — Tue, 28 Jan 2020 10:39:00 +0100

This work is a brief report about the problem of life -or, durability study- of structural materials, undergoing mechanical, thermal and chemical actions. This document is approached from numerical techniques and, it highlights the potential of these types of tools un the study of structures undergoing very complex and coupled phenomena.

A general framework for continuum damage models. II. Integration algorithms, with applications to the numerical simulation of porous metals

María Jesús Samper — Tue, 28 Jan 2020 10:19:40 +0100

In this paper, we develop numerical algorithms for the integration of the continuum plastic damage models formulated in the general framework identified in Part I of this work. More specifically, we focus our attention on a particular plastic damage model of porous metals, involving a classical von Mises yield criterion coupled with a pressure dependent damage surface to model the nucleation and growth of voids in the metallic matrix. Unilateral damage leading to a sudden change of stiffness in the material's response due to the closing/opening of these voids is also incorporated through the imposition of the unilateral constraint of a positive void fraction, thus, illustrating the clear physical significance added by this framework in the resulting constitutive models. The proposed integration algorithms fully use the modularity of the identified framework, leading in this way to independent integration algorithms for the elastoplastic part and each damage mechanism. Remarkably, all these individual integration schemes share the same formal structure as the classical return mapping algorithms employed in the numerical integration of elastoplastic models, namely an operator split structure consisting of a trial state and the return map imposing the plastic and damage consistency, respectively. A Newton iterative scheme imposes the equilibrium (equal stresses) among the different mechanisms of the response of the material. This modular structure allows to obtain the closed-form consistent linearization, involving in a simple form the algorithmic consistent tangents corresponding to each independent mechanism, thus resulting in a very modular and efficient computational implementation. The performance of the proposed algorithms is illustrated in several representative numerical simulations.

A general framework for continuum damage models. I. Infinitesimal plastic damage models in stress space

María Jesús Samper — Tue, 28 Jan 2020 10:12:39 +0100

We identify in this paper a general framework for the development of continuum damage models in their fully coupled plastic damage form. The focus of this paper is directed to the general formulation of infinitesimal models defined by yield and damage surfaces in stress space. The main feature of the proposed formulation is the direct and independent consideration of the damage mechanisms (isotropic damage, cracking, etc.) degrading the stiffness of the material, thus allowing for a complete physical characterization of these effects. This modular structure is accomplished by a kinematic decomposition of the strains in an elastic, plastic and multiple damage parts, as belonging to each activated damage mechanism. An additive decomposition in the infinitesimal range of interest is considered. Based on this decomposition, the constitutive characterization alluded to above for each damage mechanism is carried out in a complete thermodynamically consistent framework. One of the virtues of the considered framework is the fact that it includes many of the diverse damage models existing in the literature as particular cases. In this way, the developments presented herein furnish a unified framework for the formulation of continuum damage models, including isotropic damage, compliance based formulations, effective stress anisotropic models, smeared crack models and the related formulations of cracking and damage based on strong discontinuities. Besides the clear physical significance added to these existing formulations, the proposed framework also defines a very convenient context for the efficient numerical integration of the resulting models. This aspect is explored in Part II of this work, as it is the application of the framework proposed herein to the numerical simulation of porous metals.

The use of particle methods for the simulations of additive manufacturing processes

María Jesús Samper — Mon, 27 Jan 2020 16:56:02 +0100

Massively parallel methods for immersed boundary simulations of particles in viscoelastic fluids

María Jesús Samper — Mon, 27 Jan 2020 16:53:50 +0100

Particle scale modelling in soil mechanics: Stiffness, strength, and seepage

María Jesús Samper — Mon, 27 Jan 2020 16:48:26 +0100

Coupled plastic-damaged model

María Jesús Samper — Mon, 27 Jan 2020 16:42:03 +0100

A constitutive model that couples plasticity and damage is presented. The model is thermodynamically consistent and comes from a generalization of classical plasticity theory and isotropic damage theory of Kachanov. Coupling between plasticity and damage is achieved through a simultaneous solution of the plastic and the damage problem. After a description of the model, a numerical algorithm for the integration of the resulting constitutive equations is presented. It is an Euler Backward type of algorithm that is particularly suitable to solve plain stress non-linear problems with a 2D finite element program. The consistent stiffness matrix is also derived. The paper is completed with some application examples that show that the model presented accurately reproduces the behaviour of elastic-plastic-damaged materials.

Is particle and mesh a promissory combination for stable and high order schemes

María Jesús Samper — Mon, 27 Jan 2020 16:40:34 +0100

Discrete element modelling in granular mechanics, Recent breakthroughs

María Jesús Samper — Mon, 27 Jan 2020 16:29:32 +0100

The bonded DEM. Strength and weakness

María Jesús Samper — Mon, 27 Jan 2020 16:25:21 +0100

A plasticity model for simulation of industrial powder compaction processes

María Jesús Samper — Mon, 27 Jan 2020 16:22:53 +0100

A constitutive model, based on large strain plasticity, for simulation of industrial powder compaction processes is presented. The elastic response is stated in terms of a hyperelastic model based on a hookean elastic free energy. Plastic response is defined in terms of a two parameter yield surface that evolves in terms of the relative density. Two different flow rules are considered and tested in front of some available experimental results. Application to the simulation of an actual powder-metallurgy compaction process is also shown.

Granular flows and particle-laden fluids interacting with thin flexible structures

María Jesús Samper — Mon, 27 Jan 2020 16:17:41 +0100

Evaluation of the damage degree in buildings structures subjected to earthquakes

María Jesús Samper — Mon, 27 Jan 2020 14:48:32 +0100

This paper represents an overview of the investigation pursued by the authors in the field of damage evaluation of concrete structures. A procedure to evaluate the damage of reinforced concrete structures subjected to static and dynamic actions has been developed, which is based on a local damage constitutive model using Kachanov’s theory. The constitutive model is used within a finite element frame, a non-linear Newmark-type tangent incremental time integration scheme is employed and finally, an overall global damage index, based on potential energy criteria, is developed and justified.

Analysis of MFS-DRM formulations for nonhomogeneous diffusion problems

DANIELA SANTURIO — Wed, 22 Jan 2020 00:32:08 +0100

This paper presents tests and applications related to the Method of the Fundamental Solutions (MFS) for nonhomogeneous diffusion equations. The dual reciprocity method was applied to approximate the particular solution and different MSF were applied to solve the homogeneous equation. The computational accuracy for three different versions submitted to diverse geometries, initial, boundary and nonhomogeneous conditions is compared. The first version is the MFS, based on the fundamental solutions to the modified Helmholtz operator; the second and third versions are based on transient fundamental solutions proposed directly for the diffusion governing equation. This paper evaluates particularities for all methods proposed as the solution advances in time until steady-state solutions are reached. The developed computer codes are applied to several examples with the intention of demonstrating the methods’ effectiveness and applicability.

Optimización geométrica de aliviaderos en tecla de piano para la mejora de su capacidad hidráulica

Fernando Salazar — Tue, 21 Jan 2020 09:04:02 +0100

En esta comunicación se expone el estudio realizado para la mejora de la capacidad de desagüe de aliviaderos en tecla de piano mediante la optimización de su diseño geométrico en base a modelación numérica validada físicamente. Se muestra para un cierto diseño base de aliviadero en tecla de piano, el patrón de flujo que induce la geometría y su influencia en la capacidad de desagüe. Se observó una reconducción del flujo por los voladizos del aliviadero, lo que provoca zonas de baja velocidad y concentración de líneas de corriente, dificultando el desagüe. Una vez estudiado el patrón flujo se procedió al rediseño de la geometría del aliviadero, en base a la detección en el modelo numérico de las zonas de baja velocidad inducidas por el contorno geométrico. La nueva geometría de aliviadero optimizada se modeló numéricamente, observándose un aumento de la
capacidad de desagüe respecto a la geometría base.

Algoritmo adaptativo para la estimación de pérdidas de agua en redes basado en análisis avanzado de Caudales Mínimos Nocturnos (CMN)

Fernando Salazar — Tue, 21 Jan 2020 08:50:03 +0100

El método del Caudal Mínimo Nocturno (CMN) es un concepto ampliamente utilizado para la estimación de fugas y otros objetivos estratégicos en empresas operadoras de agua. Si bien es un procedimiento de fácil aplicabilidad, existe un gran abanico de submétodos de aplicación, pudiendo introducirse una gran incertidumbre en los cálculos si no se seleccionan correctamente los criterios a utilizar. En este estudio se presenta un algoritmo capaz de asistir en la elección del mejor enfoque para el cálculo de CMN en función de los datos disponibles, las características de cada caso y el objetivo perseguido. Para elaborar dicho algoritmo se han ejecutado tres acciones: (i) revisión exhaustiva de literatura especializada y recopilación de submétodos utilizados en casos reales a nivel global, (ii) elaboración de un algoritmo multi-criterio capaz de seleccionar la mejor opción en cada fase del cálculo y (iii) presentación de una plataforma informática, llamada WatEner, en la que se integrará progresivamente el algoritmo propuesto.

Mejora de la seguridad hidrológica e incremento de la capacidad de embalse de presas de fábrica mediante aliviaderos con cajeros altamente convergentes

Fernando Salazar — Tue, 21 Jan 2020 08:46:04 +0100

El empleo en aliviaderos de presas de fábrica de canales laterales para la recogida de los vertidos en la zona de estribos ha sido una solución utilizada con relativa frecuencia lo largo de la historia en casos en los que la longitud de vertido era sensiblemente superior a la anchura del valle aguas abajo de la presa. Este tipo de aliviaderos en presas existentes puede tener como objetivo el aumento de capacidad de su aliviadero o bien el aumento de los niveles máximos de explotación del embalse manteniendo la capacidad de desagüe con los resguardos exigidos. A pesar de estos antecedentes, no existen estudios metodológicos que proporcionen criterios para su diseño, ni conclusiones sobre el efecto que producen este tipo de aliviaderos en la disipación de energía en cuencos de pie de presa. Ante esta situación, se está desarrollando el proyecto de investigación aplicada CALA, cuyo objeto principal es definir criterios para el diseño de ese tipo de aliviaderos y el desarrollo de un software de cálculo que permita su predimensionamiento y optimización.

Tratamiento y análisis inteligente de datos del comportamiento de estructuras hidráulicas

Fernando Salazar — Tue, 21 Jan 2020 08:35:02 +0100

El rendimiento de los dispositivos de monitorización ha experimentado mejoras permitiendo disponer de más información sobre el comportamiento de las estructuras. Sin embargo, las inversiones realizadas en modernización de sistemas de medida no se recuperan a menos que se complementen con aplicaciones capaces de manejar una información tan amplia y diversa.

En esta contribución, se presenta una herramienta de software para importar, explorar, limpiar y analizar datos de monitorización. Además, permite la generación de modelos de predicción basados en machine learning, así como la interpretación de la respuesta del sistema a las acciones o cargas en funcionamiento.

La metodología y la estructura general se dividen en dos fases: i) carga, depuración, completado y análisis datos, y ii) generación e interpretación de modelos predictivos basados en machine learning. El mismo modelo puede utilizarse para la detección de anomalías comparando las predicciones con el comportamiento registrado.

Teaching structural engineering concepts in a civil engineering course based on a didactic game

Eric Forcael — Wed, 15 Jan 2020 18:23:03 +0100

This research analyzes a methodology of non-traditional teaching, based on a didactic game applied into teaching structural engineering concepts within a Statics course —part of a Civil Engineering program—, in which students performed structural analyses in trusses and their respective support systems, by constructing small structures, to later compare results with structural analyses based on theory. Two groups were conformed, where the control group was taught based on traditional teaching lectures, and the test group, to which a didactic teaching methodology based on the structural game developed in this research was applied. For the analysis of both groups, non-parametrical statistical analyses were conducted, along with a qualitative analysis. The statistical analyses evidenced that the didactic methodology proposed here showed to be more efficient for teaching structural concepts, obtaining a high degree of acceptance from students, according to the qualitative analysis carried out, which would motivate its use in other engineering courses.

Análisis de la percepción de las condiciones ergoambientales de una sala de aprendizaje activo

Diego Yáñez — Wed, 08 Jan 2020 18:16:02 +0100

Contexto: Las Aulas de Aprendizaje Activo son entornos de aprendizaje centrados en el estudiante en los que abunda la tecnología, los cuales favorecen un aprendizaje dinámico y colaborativo. En este sentido, la ergonomía ambiental de estas Aulas, la cual considera factores como el ruido, la iluminación y la temperatura, es fundamental para el logro del bienestar de los individuos en el contexto educativo.

Objetivo: Este estudio busca conocer la percepción que tienen los estudiantes respecto de las condiciones de una Sala de Aprendizaje Activo.

Metodología: Para esto se aplicó una encuesta a 85 estudiantes de Ingeniería Civil Industrial que utilizaron esta sala durante el primer semestre de 2019.

Resultados: Los resultados evidencian una valoración positiva a la iluminación artificial, pero declaran cierta insatisfacción respecto de iluminación natural, asimismo, muestran satisfacción respecto del ruido que afecta a la sala aun cuando manifiestan que la sala carece de un buen sistema de aislación respecto de salas adyacentes. Además, consideran que las condiciones de temperatura y ventilación no son adecuadas. Lo anterior plantea desafíos a futuro en torno a mejorar las condiciones ergoambientales de la sala, además de evaluar el impacto de estas condiciones en el rendimiento del aprendizaje de los estudiantes.

Experiments on reinforced brick masonry vaulted light roofs

María Jesús Samper — Wed, 08 Jan 2020 10:32:44 +0100

This paper describes structural tests of thin vaults made of reinforced brick masonry. The experiments consist of concentrated loading tests of 14 full-scale laboratory vaults. These vaults are designed to include common situations such as short- to midspan length, low-mid-high rise, rigid-flexible-sliding supports, instantaneous-sustained loading, low-high strength mortar, point-line loading, central-eccentric loading, point-line supports, hinged-clamped supports, symmetric-asymmetric shape, double layer versus single layer reinforcement, and uniaxial-biaxial bending, among others. The tests mainly aim to obtain the collapse loads and to characterize the pre- and post-peak response. The results show satisfactory structural performance, both in terms of ductility and strength. Moreover, it is possible to predict the structural response with numerical models developed specifically for this purpose. Flat specimens were also tested to determine the punching shear strength of the vaults. This work is part of a larger research project aimed at promoting innovative semi-prefabrication techniques for reinforced brick masonry vaulted light roofs.

A numerical-experimental method for characterizing recycled asphalt mixtures

María Jesús Samper — Wed, 08 Jan 2020 09:46:02 +0100

Experimental techniques usually employed in the characterization of conventional mixes are not able to clearly describe some specific properties of the recycled mixes, which are determinant in the material's mechanical response like cracking strength or tenacity. These new specific properties demands new methods of testing to know the really conditioning mechanical variables taking part in the process, so that being able to characterize and design new recycled mixes in an optimum way. In this paper, the direct tensile test is analyzed as a suitable method for evaluating the properties of recycled asphalt mixtures for different percentages of reclaimed asphalt pavement. A constitutive formulation has been developed to simulate the experimental results and can be used in conjunction with the experimental analysis of the recycled asphalt properties to provide an accurate characterization of the material.

Limit analysis of reinforced masonry vaults

María Jesús Samper — Tue, 07 Jan 2020 16:47:09 +0100

Reinforced brick masonry has experienced only scarce use as a fully structural material due to, among other reasons, the lack of design criteria and calculation tools allowing a scientific, but also practical, engineering approach to design and assessment. Aiming at contributing to a more widespread use of this material, a simplified method for the ultimate analysis of reinforced masonry arches and cylindrical vaults, based on the lower-bound theorem (or static approach) of plasticity, has been developed. This approach has been satisfactorily validated by comparison with experimental and numerical results obtained by more accurate numerical models.

A viscoplastic constitutive model with strain rate variables for asphalt mixtures—numerical simulation

María Jesús Samper — Tue, 07 Jan 2020 15:36:39 +0100

The study and development of recycling techniques for pavements is an increasing activity in engineering nowadays. This research line demands a more realistic characterization of the material properties with the aim of simulate the asphalt mixture’s response placed into a multilayered system over granular bases, under dynamic loads, considering also temperature variation or strength reduction for cyclic loads.

In order to improve the current formulations, a new viscoplastic model has been developed assuming the strain rate dependency of the material’s response observed in the experimental tests. The strain rate variable affects in a significant way the Young modulus and the viscosity parameter of the model. According to this hypothesis a constitutive equations have been formulated. The mechanical variables involved have been calibrated according to experimental results, developing new expressions for the strain rate dependent parameters. The new viscoplastic model permits us to characterize the material’s response with a few mechanical values, easily obtained from standard laboratory tests. The results obtained show a good approximation to experimental laboratory curves for different rates of loading and temperatures.

The model has been applied to simulate the response of a real flexible pavement structure conformed by two asphalt layers over two granular bases, that’s materials with different constitutive behaviors. Experimental tests in the recycled track have been made obtaining the horizontal strain evolution under dynamic load. Different loading rates and temperatures, as well as cracked and continuum pavement responses have been considered in the study. Strains were measured in the interface between the two asphalt layers and simulated using the here proposed model offering a fairly good approximation of the real response observed in the track, although the degree of variation even in the experimental curves is quite high.

The results of this study represent a proper base for further developments in structural analysis of pavement layers, considering more complex phenomena, determinant in the long term material’s response, to develop a numerical tool for pavements’ design and lifetime prediction.

Composite material behavior using a homogenization double scale method

María Jesús Samper — Tue, 07 Jan 2020 15:06:31 +0100

In this paper, we present a two-scale numerical method in which structures made up of composite materials are simulated. The method proposed lies within the context of homogenization theory and assumes the periodicity of the internal structure of the material. The problem is divided into two scales of different orders of magnitude: A macroscopic scale in which the body and structure of the composite material is simulated, and a microscopic scale in which an elemental volume called a “cell” simulates the material. In this work, the homogenized strain tensor is related to the transformation of the periodicity vectors. The problem of composite materials is posed as a coupled, two-scale problem, in which the constitutive equation of the composite material becomes the solution of the boundary-value problem in the cell domain. Solving various examples found in the bibliography on this subject demonstrates the validity of the method.

Numerical study of the behaviour of concrete reinforced with short fibers

María Jesús Samper — Tue, 07 Jan 2020 14:58:31 +0100

An approach for the short fibers reinforced concrete behavior is presented in this work. A formulation based on a modification of the classical mixing theory to obtain the composite mechanical properties starting from the single compounding characteristics (concrete−short fibers) is developed.

Numerical results obtained by means of the finite element method are also shown and the possibilities of using a simplified analytical method in the study of the short fibers reinforced concrete are commented.

The development of the work studies the behavior of the concrete reinforced with short fibers and the characteristics that justify its use. It studies the internal balance and the stress transmission mechanism between the concrete and the short fibers as well as the general formulation of the problem and its insertion within the frame of the finite element technique.

A brief comment is made on the simplified treatment of the behavior of the concrete reinforced with short fibers and a validation example is presented.

Use of dampers and seismic connectors in bridges

María Jesús Samper — Tue, 07 Jan 2020 14:16:29 +0100

The earthquakes have always represented on of the most dread destructive phenomena, for they affect the last stability of the structures. The modern societies are not prepared any more to accept then as a fatility, and the trend is now to provide, for structures situated in critical seismic zones, specific devices which nullify, or at least reduce the effect of the earthquakes.

In this paper we are going to present the effects that the establishment of two similar seismic devices - the dampers and the seismic connectors - produces in different kinds of bridges.

Plataforma computacional para el análisis y simulación de sistemas rotor-cojinete de múltiples grados de libertad

José Mendoza — Thu, 02 Jan 2020 23:19:05 +0100

En este artículo, se presenta el desarrollo de una plataforma computacional para el análisis y simulación de sistemas rotor-cojinete de múltiples grados de libertad. La plataforma computacional se programó utilizando el software comercial Matlab, y está soportada por la formulación matemática basada en el método del elemento finito para el modelado de sistemas rotodinámicos. Para lo anterior, se consideró un elemento finito tipo viga con cuatro grados de libertad por nodo, efectos de inercia rotacional, momentos giroscópicos, deformaciones por cortante y amortiguamiento externo. El objetivo de la plataforma computacional es resolver la ecuación general de movimiento del sistema rotor-cojinete mediante los métodos de solución: directo y Newmark. La solución mediante el método directo permite conocer información del sistema tal como: frecuencias naturales, diagrama de Campbell, formas modales y la respuesta de vibración del sistema en estado estable. Por otro lado, la respuesta vibratoria en función del tiempo se obtiene de forma numérica mediante el método de Newmark. La validación de la plataforma computacional se realizó comparando los resultados obtenidos con resultados reportados en la literatura, así como con datos experimentales.

¿Descanso para hoy o estrés para mañana?: Beneficios y costos de los paros estudiantiles en ingeniería y ciencias

Juan P, Ross — Thu, 02 Jan 2020 22:33:03 +0100

El objetivo de este trabajo es analizar los beneficios y costos de los paros estudiantiles según la percepción de los estudiantes de la Facultad de Ciencias Físicas y Matemáticas de la Universidad de Chile. Para esto, se realizó un cuestionario sobre el último paro mayor a cinco semanas vivenciado por los estudiantes. La muestra final consistió en 875 estudiantes, representativos de la Facultad. En particular, este trabajo presenta una categorización a las respuestas de texto libre a la pregunta: ¿Qué impactos positivos y negativos en tu rendimiento y en otros aspectos de tu vida académica y/o personal tuvo la paralización? Mediante un análisis cualitativo, se definieron ocho categorías para los impactos positivos y negativos. Entre las categorías se encuentran aspectos académicos, tales como “Rendimiento académico” y “Ritmo de estudio”, y otros aspectos personales como “Estrés”, “Tiempo para compartir con cercanos” y “Actividades recreativas”. Los estudiantes reportan como mayor beneficio que el paro les da tiempo para descansar y reducir significativamente los niveles de estrés. Por otro lado, el principal impacto negativo es el cambio de ritmo asociado a las paralizaciones y la posterior vuelta a clases. Este estudio muestra un pionero acercamiento a uno de los fenómenos que con recurrencia afectan a los estudiantes de la educación superior chilena.

Analytical formulation of the stiffness method for 2D reticular structures using Green functions

Juan Camilo Molina-Villegas — Thu, 02 Jan 2020 16:15:20 +0100

Green functions (F.G.) are defined as the response of a medium to a unit point load and are widely used to solve boundary value problems. Unfortunately, in structural analysis, its use is limited and they are only used indirectly and with another name in the calculation of influence lines and in the formulation of the virtual work method. This article presents the Green functions stiffness method, which is a novel methodology to obtain the analytical or exact response of two dimensional frames, which mixes the stiffnes method and the Green functions, the latter used for the calculation of displacement fields. In particular, the formulation will be carried out for bar elements (subjected to axial force), beam elements (subjected to shear force and bending moment), beam over flexible foundation elements (subjected to shear force and bending moment) and two dimensional frames (subjected to axial force, cutting force and bending moment). This formulation has as its main property that it can be used to compute the analytic reponse for any external load distribution and minimizes the number of elements to be used in discretizations. In addition, the equivalence of this formulation with that obtained by an “exact” implementation of the finite element method is presented.

Survey research on dynamic CTA data analysis for peripheral artery occlusive disease

Zehong LIN — Wed, 25 Dec 2019 01:04:14 +0100

The purpose of this study is to review the research which was mainly about the evaluation the vascular stenosis or muscle ischemia to assist in the diagnosis of peripheral arterial occlusive disease using dynamic CTA data. With the recent rapid evolution of multislice computed tomography scanners, runoff CTA of the peripheral artery has become a widely used diagnostic option in patients with PAOD. Furthermore the dynamic CTA of the lower extremity provides improved arterial contrast enhancement and a higher diagnostic confidence for assessment of stenosis and occlusion than runoff CTA. The method, the data characteristic and the conclusion of all the qualitative and quantitative research were covered in this study. Finally, the future research direction of the dynamic CTA analysis to assist diagnosis was given.

Cálculo de daño en pavimentos mediante un análisis hidro-mecánico de pavimentos flexibles

Carlos Chávez — Fri, 20 Dec 2019 15:24:03 +0100

A hydro-mechanical analysis of a pavement is presented in which the variation of the water content is considered for the estimation of modulus of elasticity of the layers of soil in the pavement. To do this, the Richards differential equation and equilibrium in the axi-symmetric condition are solved simultaneously, considering a non-linear elasticity that depends on the suction and stress state in the soil. With this type of analysis, it is possible to quantify the variation of the damage with respect to time and visualize the deterioration of the pavement structures. It is considered a practical case in which the increase in damage is quantified in function of the variation of environmental conditions and conclusions are obtained.

Design and implementation of prototype for XLPE cable aging test

Sergio Rivera — Thu, 19 Dec 2019 05:49:13 +0100

The current increase in the demand for electric power and the obligation to comply with the regulations associated with reliability and continuity in the supply, have prompted the manufacturers of electrical conductors to focus on designing their products with special care when considering the electrical properties of the materials. The use of XLPE insulated cables in underground transmission lines in 115 kV systems has increased in cities due to urban, environmental and reliability requirements. This is also related to the fact that air networks are exposed to external factors such as lightning, comets, vegetation, animals, etc., which can affect their functioning failures. The fact of using transmission technology with insulated cables gives rise to the need to evaluate the behavior of its components when operating in the long term. To achieve this, it is necessary to implement a procedure that allows analyzing the aging of these elements when operating in load cycles for a certain period of time. Thus, this document presents the development of a prototype that allows conducting the aging test to conductors isolated by XLPE.

Experimental numerical comparision of the pressure drop through an hydrocyclone

Emmanuel Alcocer De Agüero — Wed, 18 Dec 2019 19:57:05 +0100

This paper shows the comparative results of an experimental and numerical study. The numerical simulations were performed with the ANSYS/Fluent software by means of CFD applying RNG k-ε and standard k-ω turbulence models.

Experimental data were recorded of a hydrocyclone mounted on a test bench which operates with a water flow. The values extracted are the inlet pressure, outlet pressure, inlet velocity and outlet velocity. In order to investigate the pressure drop underwent by a hydrocyclone, a pressure assessment was carried out in different areas of the divice geometry.

The results of the numerical study were compared and correlated with the experimental data. The numerical values report a percentage difference of 10.45% for the RNG k-ε model and 1.57% for the standard k-ω model, with respect to the experimentally obtained output pressure. The percentage difference between experimental and numerical pressure drop is 0.04% for standard k-ω model and 0.24% for RNG k-ε model.

By studying finite volumes, the components of axial velocity, tangential velocity and turbulence intensity are calculated. These phenomena are studied simultaneously in this work. The turbulence models used to generate the corresponding analyzes in this work show similarity between both results and flow behavior. The concordance between the computational results and the experimental data is acceptable, so that the numerical simulations applied reach the purpose of this investigation.

Structural optimization of forklift fork based on numerical simulation and mathematical modeling of stress and fatigue

Enlai Zhang — Tue, 17 Dec 2019 04:12:54 +0100

Fork’s related structural design and detail have a significant impact on the overall performance of a forklift. In this paper, the structural stress analysis and strength calculation of the fork were carried out firstly, and the rated load calculations considering dynamic and unbalanced conditions were performed. Also, the restraint conditions were analyzed. Then, a finite element model was established using ANSYS software. In particular, the fork’s structure was optimized by increasing the fillet radius of the fork root and the variation rules between the fillet radius and the maximum structural stress and minimum fatigue life were numerically studied, which was in accordance with the mathematical models of ExpAssoc and Logistic regression, and the corresponding fitting coefficients of R2 was respectively equal to 0.99 and 0.96. Overall, the stress concentration issue of the fork root was improved and the structural strength perquisite was satisfied when using a fillet radius of 75 mm. Both the numerical calculations and theorized mechanical analysis show consistency, where the stress concentration was observed in the fork root’s fillet area, testifying the accuracy of the established finite element model. The numerous methods employed in this work lay an important theoretical basis for the structural optimization of the target fork.

Effect of elbow implant design parameters on loosening: A finite element analysis

Milad Heidari — Fri, 13 Dec 2019 13:35:03 +0100

Loosening of an implant is the main complication after total elbow arthroplasty. The design parameters of the implant are a factor that contributes to the loosening of the implant. In this study, the correlation of loosening and geometry of the elbow implant component was investigated using the finite element method. Image processing software was used to construct elbow bones. Humeral and ulnar components were modeled with various cross-sections and flanges using modeling computer-aided design software. Modeling of all stems was based on conventional cemented fixation. Axial torsion and Anterior-posterior force were applied to the articular surface. Zero-displacement was applied to the proximal humerus and distal ulna. Bone graft was used between the flange and distal humerus bone. The stress shielding of bones and micro-motion were obtained in cement-implant-bone interfaces. Results showed that humeral and ulnar stems with modified diamond cross-section observed less micro-motion in the cement-bone-implant interfaces and as well as the least stress shielding in the distal humerus and proximal ulna compared to others. Furthermore, the modified flange, concave, transferred the least micro-motion to the bone-cement-implant interface and less stress shielding in distal humerus in comparison with trapezium and rectangular ones. This computational analysis represented a step in quantifying the role of interface micro-motion stress shielding of bone in initiating elbow implant loosening. A reduction of micro-motion and stress shielding through design modifications may improve the clinical outcomes.

Numerical implementation for conception of strut and tie models in reinforced concrete structures

Artur Ladeira — Fri, 06 Dec 2019 18:18:54 +0100

O Modelo de Bielas e Tirantes pode ser uma excelente alternativa para o dimensionamento de elementos estruturais em concreto armado submetidos a estado plano de tensão e para regiões que apresentem descontinuidade de ordem geométrica ou estática, substituindo procedimentos empíricos por uma metodologia racional de projeto. Para tornar a concepção do modelo menos dependente da experiência do projetista, o presente artigo tem como objetivo aliar a técnica de otimização topológica ESO (Evolutionary Structural Optimization) ao Método dos Elementos Finitos para geração automática dos modelos de bielas e tirantes. O critério de evolução do método de otimização topológica adotado considera a eliminação de elementos menos solicitados em termos de tensão, a partir de uma análise elástico-linear. Nesse contexto, é possível obter soluções otimizadas de problemas complexos envolvendo o concreto estrutural. São apresentados três exemplos numéricos para comprovação e validação das formulações e técnicas implementadas, cujos modelos de bielas e tirantes obtidos apresentam boa concordância em relação às respostas encontradas em trabalhos científicos precursores sobre o tema.

Guide to multi-objective optimization for the green vehicle routing problem

Júlio César Ferreira — Mon, 02 Dec 2019 20:58:04 +0100

This article aims to present research conducted on the literature regarding Multi-objective Optimization (MOO) for routing problems with environmental considerations (EC), referred to here as Multi-objective Optimization for the Green Vehicle Routing Problem (MOOGVRP). A Brazilian database, CAPES (Coordination for the Improvement of Higher Education Personnel), was used to collect articles of general application, case studies and reviews in English starting from, since 2012. The terms “green vehicle routing problem” (GVRP), “pollution routing problem” (PRP), “vehicle routing problem in reverse logistics” (VRPRL) and “multi-objective” were used in the research protocol. Consequently, this study obtained 1,744 research results that, following the application of the filtering criterion, resulted in a sample of 76 articles from 38 journals, for which a bibliometric data (bibliometric review) survey was conducted. When dealing with the bibliometric data of the sample, it was possible to identify information such as the number of publications per year and types of published works. Information was also identified regarding the most frequently used journals and the countries and institutions that published the most articles on the proposed theme. It was also possible to analyze the frequency of the protocol terms in the title, abstracts and keywords, the relationship between taxonomies, vehicle fleet types, multi-objective procedures, and VRP procedures. Information was also found regarding solution procedures, number of objectives, and programming languages for computational implementation, the frequency of the most used objectives, and the most cited articles in the sample. The originality of this article lies in how the research is presented, highlighting the results and particular details obtained through the survey, which may be considered of great academic importance in the sense of guiding the trends for future research.

Graphical solutions of the two-dimensional Saint-Venant equations by means of channels reticles

Justino Alavez-Ramírez — Wed, 27 Nov 2019 17:38:04 +0100

The knowledge of ancestral peoples is retaken as an important knowledge in their relationship with nature and to face climate change; culture that must be confirmed by science. To give the reason for the mentioned knowledge, when using channel lattices for their plots, it is necessary to model them using flow equations. Applying the equations of shallow water can simulate the hydrodynamic behavior and dissipation of energy by passing a flow in a lattice of channels. To model the grid the geometry of the flow networks used in geotechnics was drawn, the networks are an engineering solution to the Laplace equation. When passing the water through the reticle it was observed, in a 2D simulation with the Iber v2.5 software, that the draft remains constant. It was also noted that the reticle is an efficient way to dissipate energy. In this way it was discovered that the channel lattice is a solution to the equations of a shallow water joint. Through the results obtained, a field of research is intuited when modeling reticles of channels for the use and management of water.

On the vibration behavior of rotatory blades: a numerical approach using the finite element method and the singular value decomposition

María Jesús Samper — Wed, 27 Nov 2019 15:42:39 +0100

The physics lying behind rotordynamics is complex tomodel, so that in many cases numerical
processing is the only feasible approach. Being rotordynamics a field of great interest
in the aerospace industry, the efforts devoted to its understanding are increasing day by
day. Following this tendency, the aim of the present study is to develop a simplified elastodynamic
model for the case of rotating structures such that can be addressed through
numerical tools, built using the finite element method. For the purpose of analysing the
vibration phenomena, modal decomposition and numerical integration have been taken
advantage from. In this context, it has been found that the singular value decomposition
could be applied in structural analysis to extract dominant displacement fluctuations, allowing
the unfolding of global properties of the dynamic response. In the present report,
the singular value decomposition has been applied to cantilever beams undergoing a single
rotation, giving rise to reasonably satisfactory results.

Evaluation of alternatives for parameterization of momentum and water vapor roughness lengths in lakes

Fernando Armani — Tue, 19 Nov 2019 20:13:07 +0100

An assessment of the performance of various parameterization alternatives for roughness lengths of momentum and water vapour was performed. The micrometereological data used in this work was measured in the Itaipu reservoir, Brazil. Four models was tested for momentum roughness length, and four for water vapour. The parameterization for horizontal momentum flux are based on the Charnock equation and generalizations while the water vapour model are based on equations proposed by Brutsaert. The four models for momentum flux produced very similar results, in terms of goodness of fit and errors, and turned out only weakly dependent on friction velocity. Already the parameterizations for water vapor produced more dispersed results, and the best parameterizations found very poorly depend on the Reynolds roughness number, or are independent of it. Both in the case of momentum and water vapour, the optimal parameter values? of each parameterization found for Itaipu are significantly larger than those reported in the literature.

Matching user accounts based on location verification across social networks

Xueyan Zhou — Thu, 31 Oct 2019 11:43:20 +0100

Social network has become the main platform for people to obtain information and connect with each other. Matching user accounts can help us build better users’ profiles and benefit many applications. It has attracted much attention from both industry and academia. At present, cross-platform user identification can be divided into three categories: based on user basic attribute information, user online social structure relationship and user behavior. Research on mobile social networks is a kind of dynamic mixed data analysis. Due to the remarkable heterogeneity of its data across platforms and the incomplete and untrue information caused by users’ concealment behavior, the recognition rate of the algorithm is relatively low. The paper provides a new matching user accounts method based on location verification. First, the self-centered network algorithm is applied to find cross-network edges in the respective networks of the two users to be matched, which is taken as the initial similarity value of the two users. Secondly, the longitude, latitude and time coordinates of a single platform node were used to modify the similarity. Specific 5 time points were selected within 24 hours and the error range of 10min was taken as the calculation method of great circle distance. Thirdly, since the user did not log in a certain social platform in a certain period of time, the convolutional neural network algorithm was adopted to mark the trajectory. Finally, all users in the whole network are identified by iterative operation. Experimental results on artificial random networks and real social networks show that the proposed algorithm has a high readiness rate and recall rate.

Non-linear analyses to assess the seismic performance of RC buildings retrofitted with FRP

Juan-Carlos Vielma-Perez — Sat, 26 Oct 2019 14:07:04 +0200

Post-seismic reinforcement is extensively used to repair structural elements of buildings hit by strong earthquakes, while pre-seismic reinforcement can be very convenient to improve the seismic performance of buildings designed according to less stringent standards than current. One of the most commonly used techniques for both pre and post-seismic retrofit of structures is that of wrapping elements previously identified as weak or damaged with sheets of fiber-reinforced polymers (FRP). This technique may be in fact more advantageous than other strengthening approaches, due to speed of placement, low environmental impact and small load increase. Non-linear methods of analysis can be very helpful for planning the retrofit strategy and assessing in advance its effectiveness. Based on non-linear static and dynamic numerical analyses, the effectiveness of the FRP pre-seismic reinforcement on the global performance of buildings was investigated in this paper with reference to a residential Italian building designed according to obsolete standards. The seismic capacity of the building, before and after the FRP retrofit, was assessed and the efficacy of the seismic rehabilitation was evaluated. The results show that, by improving the local resistance of the most vulnerable elements and the global ductility of the building, the FRP wrapping of the ground-floor columns of the considered building has an important impact on the overall seismic response of the structure, although it cannot entirely avoid undesirable global collapse mechanisms.

Determination of independent damping frequency in civil structures even under very close modes of vibration by applying optimization techniques

LUIS MANUEL VILLA GARCIA — Fri, 18 Oct 2019 18:15:43 +0200

Specific computer programs for identification in modal analysis of structures are not economical, and they may not always be available. This paper presents a technique for simple optimization, getting fast and quality results, in the estimation of the damping ratios for each separate mode, and that can be resolved with a demo version (downloadable for free from the internet) of commercial optimization software. It is suitable for low levels of structural damping (or non-frequency-dependent damping), which are those that appear in large structures. Likewise, it is not necessary for the modes to be separate, or even that the magnitude of the near modes be less than that of those with which we are working; within the algorithm movable residual complements optimize their position according to the frequency and vertical axes (the response magnitude), to take into account the influence of the modes outside the considered range. In addition, it is not very sensitive to the presence of noise in the signal.

Assessment of one equation model for natural convection and the prediction of impingement heat transfer

Mohamed Omri — Sun, 29 Sep 2019 16:07:09 +0200

Spallart and Allmaras [1] is a one-equation turbulence model developed for predicting complex aerodynamic flows. It will be of great interest to extend its application to predict other kind of flows in presence of heat and mass transfer. Specifically we will demonstrate, by considering two applications, that this one equation model may replace the two equation models in several heat transfer applications such as HVAC, electronics cooling and fire propagation in buildings. This will reduce computing time and numerical stiffness in CFD calculations. The first application is the 2D natural turbulent convection in a cavity differentially heated; which was considered as a benchmark case before applying CFD in any HVAC configuration. The exact configuration proposed by Ampofo [2], was then modeled and the radiation effect was studied. The second application proposed by Riera [4] was the numerical prediction of a heat exchanger based on hybrid jet impingement/micro-channel; it was used for managing high heat-flux thermal of power electronics devices. Those applications deal with low and high fluxes transfer respectively and allow demonstrating clearly the capacity of the one equation model to predict confined turbulent natural/ forced convection and jet-impingement heat transfer.

Study of the aerodynamic forces on a simplified shape X-43 aircraft under supersonic conditions, design optimization

Jordi Pons Prats — Fri, 20 Sep 2019 20:19:02 +0200

The paper focuses on the shape optimization, based on the resultant aerodynamic forces, of a simplified X-43 aircraft. The equations of oblique shock waves and Prandtl-Meyer expansion waves, along with the improvement of the aircraft geometry using a genetic algorithm optimisation, will allow to shape and optimize the external dimensions of the bi-dimensional simplified aircraft design. The main purpose of the optimisation is the reduction of the drag force while maintaining a sufficient lift to hold the weight of the aircraft. The optimization is undertaken at four different altitudes, obtaining for each altitude the most favourable aircraft shape to maximize the aircraft efficiency. The study can be extended to various possible aircraft weight configurations.

Pipeline Information Modeling: A New Tool for Pipeline Engineering

Bao Tian — Tue, 27 Aug 2019 09:50:57 +0200

Pipeline Engineering is a comprehensive system project with huge investment, high complexity, strong technical and strict security requirements. The conventional construction and management mode for pipeline project has encountered a variety of bottlenecks in the development, and digital informatization of pipeline is the inevitable trend for the future pipeline industry development. Therefore, combining with the existing technical achievements, this paper puts forward and defines a new concept- “Pipeline Information Modeling (PIM)”, which can use digital model for the whole life-cycle of pipeline management. Its characteristics and architecture are expounded, and the relationship and difference are summarized between PIM and other related theories such as BIM, pipeline integrity management, and digital pipeline. Meanwhile, a case study of several applications in long-distance oil & gas transmission pipeline engineering is analyzed. Finally, the challenges PIM will face in the future development are discussed. PIM is still in its infancy, and theoretical system and technical method still need to be constantly perfected. But its emergence has important significance for improving pipeline engineering scientific and technological level and accelerating transformation of industry informatization, which will have great application foreground. '''Key words:''' Pipeline engineering; Life-cycle; Digital model; Long-distance pipeline;

Time-scale analysis based modal identification using mobile sensors

Mario Marmolejo — Wed, 21 Aug 2019 21:05:08 +0200

'Civil structures, once built and released for use, are expected to fulfil operational standards for extended periods. The fact, a civil structure´s life, is determined by temporary deterioration, harsh ambient, misuse, destruction, and, eventual rehabilitation for current use or conservation for historical reasons. Initially, vibrational analysis with stationary sensors, broad logistics and a large array of sensors to provide densely detailed data were required. The next evolutionary step; the simplification of the while-under-use data-acquisition stage; better, faster, more detailed parameters for diagnosis. With the structure under normal operation, a stationary reference sensor, a mobile sensor able to travel through specific trajectories over the structure, deep computational data analysis provides better, deeper, clearer frequencies, mode shapes and damping ratios. A structural health monitoring system should be able to reliably assess structural wellness under operational conditions. Such are the benefits of a mobile sensor monitoring and diagnosis system. This paper utilizes the time–scale analysis method and the Continuous Wavelet Transform (CWT) through a complex Morlet wavelet to extract modal parameters from the signal responses. The theoretical development is validated by numeric simulations on a simply supported beam and by double experimental confirmation on a pedestrian bridge at Universidad del Valle, in Cali (Colombia), by the technique herein, and by a stationary sensor scheme.

Hybrid numerical scheme for simulation of transient flow in a pluvial water reservoir

Sara Coelho da Silva — Wed, 21 Aug 2019 16:25:29 +0200

This work presents the numeric simulation of flow in a reservoir, using the finite volume method for solver the system of equations that model the two-dimensional flow in shallow water, neglecting the tangential tensions. The solution of the system of linearized equations was obtained by computational implementation of the Gauss-Seidel iterative method. To illustrate the application of the numerical scheme in hydraulic engineering, it was considered the study of flow in an underground reservoir with internal pillars, whose flow is generated by the opening of two outlet gates. The employed code allowed the temporal analysis of the volume and the flow in the reservoir, the graphical interpretation of the investigated physical phenomenon as well as, the calculation of the precision of the model. The results obtained show the expected physical interpretation, good agreement with literature data, good precision,stability and low computational cost.

Evaluation of the optical contamination of open path CO2 gas analyzers in measurements on a freshwater surface

Fernando Armani — Sun, 14 Jul 2019 15:51:56 +0200

Measurements of air-sea CO₂ fluxes with Eddy Covariance (EC) are generally affected by the optical contamination of open path gas analyzers. Since the conditions of saltwater environments may be similar to those of freshwater environments, in this work we evaluate whether this contamination is occurring in the LI-7500 open path CO₂ gas analyzer (''LI-COR Biosciences Ltd''), used in an experiment to measure greenhouse gas fluxes over the reservoir of the Itaipu Hydroelectric Power Plant. We evaluated the optical contamination indicators in the CO₂ measurements and two corrections for this: the numerical method called PKT method, proposed for CO₂ flux correction over ocean, and a multiple linear regression model. We find that the PKT method does not produce physically plausible results and that, contrary to what has been reported in ocean measurements, the measurements of the Itaipu experiment suffer less interference in more humid conditions. CO₂ correction by the regression model preserved the pattern of CO₂ flux daily variation, but it attenuated the magnitude of the fluxes: the average of the uncorrected fluxes was $-24.35$ μgm^-2s^-1, while the average of the fluxes corrected by the statistical model was $-11.73$ μgm^-2s^-1.

A matheuristic approach to solve the fixed charge transportation problem

Crisiane Oliveira — Thu, 11 Jul 2019 19:49:03 +0200

The Fixed Charge Transportation Problem (FCTP) is a Linear Programming (LP) class, whereby the total shipping cost of a product, from a source to a destination, consists of a unit transportation cost, proportional to the amount of sent items and a fixed charge associated with the opening of the route. The FCTP is NP-hard and has a characteristic in which, as far as the difference between the value of the unit cost and the fixed charge increases, the computational time changes, worsening the performance. This paper purpose a matheuristic approach to the FCTP which results were good when compared to other methods available in the Literature.

Numerical approach to determine the capacity curves of clay masonry walls with openings

Jaime Campbell — Mon, 01 Jul 2019 23:49:11 +0200

In this work a numerical model to obtain the pushover curves of clay masonry walls with openings is presented. These curves represent the non-linear structural behavior of masonry walls with openings subjected to loads in their own plane. The openings represent non-structural elements like doors, windows, among others. These walls can be considered as reinforced or confined masonry and the opening must be rectangular and may have different dimensions and a variable position inside the wall. The main result of the model was a pushover curve, which is compared with the curves obtained from laboratory tests (for walls with and without openings). The model was developed using the software ANSYS [1] version 14.5, based on the model proposed by Campbell and Durán [2].

Hybrid analysis of the crimping process of electrical terminals

Frederico de Oliveira Simões — Sat, 29 Jun 2019 00:50:04 +0200

The crimping of electrical terminals is a forming mechanical process that allow joining connectors to the end of electrical conductors. This process is largely used in the connectors industry, however the knowledge of its mechanical principles still be much discuss. This theory gap is due, probably, to the complexity of the problem. In this work, was looked for advance in the comprehension of this process by means of the development of a General Predictive Equation, that calculates the punch force in the crimping final moment. The methodology used consisted in the development and calibration the model of the crimping process in a Finite Element software, selection of the more influents parameters in the punch force, and development and validation of the General Predictive Equation. The results showed that Plain Stress configuration is the best representation of two dimensions model of crimping process and that only 9 (nine) variables of this model showed relevant to compose the equation. It is concluded also that the development of the General Predictive Equation to calculate punch force is viable, but, it is necessary increases the accuracy of the calculus yet. It is desired that the knowledge generated in this study already allow reduce costs of development and of production of crimped terminals.

Thermal-conductive model algorithm for the accurate calculation of temperatures in electrical power conductors

Dorindo Cardenas — Fri, 21 Jun 2019 03:18:43 +0200

The thermal-conductive models for the calculation of the electrical conductors and their energy dissipations have been able to solve doubts about the power conductors, which has been permanently unsuspected. Before thinking about thermally characterizing an electrical conductor, it was enough with the application of simple Joule-type equations, with constant resistive intrinsic properties in the conductor, as well as invariable considerations in the conditions that surround the conductor. In fact, just as is exposed, this has been published on the top of the best known electrical standards, such as those issued by the National Fire Protection Association (NFPA), as well as those edited by the International Electrotechnical Commission (IEC). It has been demonstrated that electric cables with higher electrical intensities, move away from the behavior predicted by the Joule type models, sometimes with energy dissipations 50% higher than those predicted by Joule. This is due to the non-linearities of the intrinsic properties of the cable, and the inconsistency of the environmental conditions surrounding the cable at the time it is going to heat. The novel thermal-conductive models with just ten years of development, are today a very complete solution with unparalleled accuracy (errors less than 0.01% in energy and temperature) in the thermal predictions of conductors; but due to its high degree of mathematical complexity requires in the most of cases to use numerical methods to obtain practical solutions. In this paper a new general algorithm is shown, which stands out for its simplicity compared to the first thermoconductive models, solving the models in thermal predictions of power electrical cables, without the need of huge databases, with simplicity, maneuverability and excellent practical results.

Solution of the Navier-Stokes equations using projection method and preconditioned conjugated gradient with multigrid and ILU solver

Márcio Anunciação — Wed, 12 Jun 2019 15:56:43 +0200

Among the main problems in the field of Computational Fluid Dynamics (CFD), there is the two-dimensional laminar flow in a transient regime of an incompressible fluid modeled by Navier-Stokes equations. Among the decoupled solutions for this equation system, that is, solutions for velocity regardless to pressure, there are the Projection methods, which separate the solution in three parts, solved in each time steps applying an iterative process regardless to the iterative process for the other variables. It may result, according to the Projection method applied, in two Reaction-Diffusion equations and one Poisson equation to be solved in each time step. This paper sought to develop an algorithm to solve the Navier-Stokes equation, applying the Finite Volume Method (FVM) with second order approximation scheme (CDS), beside a Projection method with incremental pressure-correction scheme, so that each Reaction-Diffusion and the Poisson equation are solved efficiently. Therefore, several solvers were tested for each equation, resulting in an algorithm with the combination that achieved the best result for each equation, with the preconditioned Conjugate Gradient method (PCG) with the Multigrid method (MG) and ILU solver (Incomplete LU factorization) being the methodology used in the whole problem solving process. The geometric Multigrid with V cycle, the correction scheme (CS), the full weighting restriction, the prolongation through bilinear interpolation and the maximum number of levels for the studied cases were utilized. The results achieved were satisfactory, since the proposed methodology accelerated the iterative process considerably in relation to the classical methods available in the literature.

Nonlinear parametric vibration analysis of radial gates

Siyuan Wu — Thu, 06 Jun 2019 04:57:02 +0200

In this work, based on dynamic characteristics of radial gates, a nonlinear diﬀerential equation of motion for the radial gate arm is established. Excitation conditions of principal parametric resonance and subharmonic parametric resonance are obtained by using multi-scale method and numerical method. The parameter analysis shows that: comparing with traditional calculation method of dynamic instability region division, the presented method is more suitable to analysis of parametric vibration for radial gates as considering the end moment, vibration duration and amplitude. The vibration amplitudes of arm increase with the increase of its length and excitation amplitude, as well as the decrease of arm inclination angle. Moreover, the parametric resonance is easier to be excited and its resonance region become wider with the initial end moment increasing. Since the vibration response of the arm is influenced by the nonlinear term in the equation, the damping effect is limited. Thus, energy transfer method (e.g. tuned mass damper) can be adopted to achieve vibration control.

Uso de analogías eléctricas para entender patologías cardiovasculares

María Jesús Samper — Tue, 28 May 2019 15:44:09 +0200

Through the interconnection of electrical elements such as a resistor, inductor and capacitor, has been developed a reduced-order model of the arterial system capable of describing the behaviour of blood flow. In this modelling, the different differential equations that describe the behaviour of this system are represented implicitly. This allows us to obtain quickly and regulate the performance of the joint model, both in normal physiological conditions and in pathological situations, which makes it a useful tool for teaching or research in cardiovascular physiology. It was implemented two different arterial models, an elastic model and a viscoelastic model, with the aim of analysing the flow and blood pressure that could occur under different physiological conditions. In order to analyse both models, it was contrasted using different orders of elasticity, the pathology of aortic dissection was studied and the results were compared qualitatively with similar solutions observed in the literature. In order to perform these simulations, it was implemented in Matlab a code for solving ordinary differential equations (DAE).

Thermal performance of light blocks in a Mediterranean climate

Hipólito Sousa — Mon, 28 Jan 2019 12:15:04 +0100

The challenge of reducing energy consumption in buildings is fundamental for the near future, considering the impact of buildings in the overall energy demands. Mediterranean regions have a mild heating season and a hot and dry winter. Its climate is characterized by plentiful solar radiation all along the year and large daily range of temperature during the summer. Thermal inertia and insulation material properties can act in a different way along the day and the year, and the better solution for the summer can be the worst solution for the cooling season. Masonry walls that define the boundary between the interior and exterior are one of the most important components of buildings mainly for energy efficiency. Despite being one of the most common and ancient building materials, it is possible to improve its performance working in units, mortars and finishes. This work aims at studying the effect of materials with different thermal insulation and thermal mass on thermal comfort and energy savings of three types of buildings, two single-family houses and one apartment, in a Mediterranean climate. Thermal behavior of traditional and light solutions is compared and it is found that thermal comfort is similar but light solutions present lower energy consumptions for the three studied house topologies. Otherwise, this study shows that housing topology has more influence namely, when comparing energy needs.

Experimental and numerical hydrodynamic analysis of a stepped planing hull

Simone Mancini — Wed, 28 Nov 2018 14:02:04 +0100

This work addresses the experimental and numerical study of a stepped planing hull and the related ﬂuid dynamics phenomena typically occurring in the stepped hull in the unwetted aft body area behind the step. In the last few years, the interest in high-speed planing crafts, with low weight-to-power ratios, has been increasing signiﬁcantly, and, in such context, naval architects have been orienting toward the stepped hull solution. Stepped planing hulls ensure good dynamic stability and seakeeping qualities at high speeds. This is mainly due to the reduction of the wetted area, which is caused by the ﬂow separation occurring at the step. This paper presents the experimental results of towing tank tests in calm water on a single-step hull model, which is the ﬁrst model of a new systematic series. The same ﬂow conditions are analyzed via Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulations (LES), with different moving mesh techniques (overset/chimera and morphing grid), performed at different model speeds. The numerical results are in accordance with experimental data, and overset/chimera grid is found to be the best approach between the analyzed ones. The ﬂow patterns obtained numerically through LES on a reﬁned grid appear similar to the ones observed in towing tank investigations through photographic acquisitions. These ﬂow patterns are dominated by a rather complex 3D arrangement of vortices originating from air spillage at both sides of the step. The understanding of these phenomena is important for the effectiveness of stepped hull designs.

Virtual modelling of stress paths CKoU and CKoD on collapsible porous clayey soils

Juan Carlos Ruge C. — Wed, 07 Nov 2018 02:29:30 +0100

In geotechnical engineering one of the challenges is the soil characterization. Nevertheless, currently it exists computational tools, which permits estimate the soil behaviour from information obtained in the laboratory. This document addresses the numerical modelling of triaxial tests set with Ko consolidation during its shear stage by means of single element test tool. The work methodology was based on the stress paths comparison between lab data and numerical simulations with three different constitutive models: (i) Mohr-Coulomb, (ii) Cam-Clay Modified, (iii) Hypoplastic. Such stress paths were obtained in drained and undrained conditions. The soil material corresponds to a porous collapsible clay from Brasilia (Brazil). Results show the calibration of the parameters for each constitutive model. Besides, presents the stress-strain curves until achieving the critical state condition in the simulations. Finally, it was established the constitutive model that presents the best fitting to the real behaviour of this kind of material, under specific conditions for advanced triaxial tests.

Fragility curves based on the numerical analysis of masonry walls against subsidence, using the Abaqus / CAE software and relying on the pulldown technique

Yaimara Chávez Pérez — Fri, 12 Oct 2018 02:00:05 +0200

The gradual sinking of the surface caused by the subsidence is a geological phenomenon that affects several countries around the world and has been the cause of substantial material damage in elements with low stress strength. Masonry structures have been greatly affected by these differential settlements, due to their low resistance to this solicitation. In order to be able to accurately assess the state of damage present in these structures, during the investigation the behavior of masonry walls of different dimensions is analyzed, under the action of differential settlements. The numerical models were developed through a detailed micro-modeling in the Abaqus / CAE software. The partitions and mortar were considered with Mohr-Coulomb and Drucker-Pragerelastoplastic behavior, joined by interface elements represented in all vertical and horizontal joints. A mesh study was conducted to define the optimum mesh density and its use of a finite first order element. The numerical models were calibrated with experimental results, to then study the influence of the dimensions of the wall in their resistance, obtain the values of angular distortion for which the structure begins to have irreversible deformations, construct the load curves vs. angular distortion and elaborate the fragility curves of the material, through which the damage status of a masonry wall can be assessed, subject to a certain angular distortion value.

Elastic dynamics analysis in steel tubular towers for horizontal axis wind turbines

Douglas Mateus de Lima — Fri, 29 Jun 2018 16:12:45 +0200

This article aims to obtain the dynamic elastic analysis of a steel tube tower for horizontal axis wind turbine using finite elements of bar (own code) and finite elements of bark and solids (modeling in ANSYS). For this, a theoretical foundation is presented that consists in the development of the movement equation from the Lagrange equation. Next, the modal overlay method is presented for solving the matrix motion equation and for obtaining the dynamic response of the tower. In the second part of this article, the development is presented for the assembly of the mass and damping matrices of the tower modeled with its own code in finite elements of the bar. In the part of results, initially, the rigidity, mass and damping matrices are exposed for a certain level of discretization of the modeled tower with finite elements of bar. Then, the results of the modal analysis were done for both the finite element shell model, with and without flexible base, and the finite element model of the bar, in which the modes and the frequencies of vibration of the tower in all the models are presented. Finally, the responses of the tower were analyzed: in the direction of the wind flow, when submitted by a vector of resonant forces to its 1st mode of vibration, representing the floating part of the wind; and, in the transverse direction to the wind flow due to the von Kárman cadenced vortex detachment. The results of the modal analysis made for both the finite element shell model, with and without flexible base, and the finite element model of the bar are similar, especially in the first mode of vibration of the tower. Therefore, the model represented by finite elements (FE) of bar can be used as representative of the dynamic behavior of the tower when it is subjected to the resonant excitations at its fundamental frequency.

Setting of the parameters to capacity spectra of steel buildings

CARLOS ALBERTO BERMUDEZ MEJIA — Mon, 31 Jul 2017 04:58:42 +0200

The first part of this paper provides a theoretical framework on the subject of capacity spectra and its usefulness in studying the seismic vulnerability of buildings. Then, the works of some researchers, which have moved forward in the direction of setting the parameters of those curves, are reported and theirs most important conclusions are highlighted. After that, the models that have been used in this research together with theirs capacity spectra are introduced. Finally, techniques for setting parameters are applied on those curves and the most important results and conclusions are presented.