Francisco Garcia Benitez - Academia.edu (original) (raw)

Papers by Francisco Garcia Benitez

Computational Mechanics ’95, 1995

The fundamental solution of an infinite three-dimensional, linear, elastic, orthotropic, homogene... more The fundamental solution of an infinite three-dimensional, linear, elastic, orthotropic, homogeneous layer subjected to an arbitrary buried source is presented. The results are subsequently utilized to formulate the multilayered orthotropic medium problem by means of transfer matrices.

This paper describes the tests performed for the optical evaluation of the stress field surroundi... more This paper describes the tests performed for the optical evaluation of the stress field surrounding crack growth under impact loading. The specimens are graphite-epoxy laminates. A description of the equipment used (split-Hopkinson-pressure-bar rig, high-speed photograph camera, flash and laser illumination) is covered. The specially manufactured interface, trigger and timing electronics are also described. The described set-up can be used with the optical techniques of caustics and CGS to evaluate the strain field around a dynamically propagating crack. By employing a flash light rather than the laser light source, the crack propagation can be studied visually. The test-rig is used for testing polymers and laminated composites under in-plane impact loads. The exposed surface of the specimens which were used for crack speed measurements and stress field evaluations was covered by matte white paint and vapour deposited aluminium for light reflection. Results obtained for laminates wi...

Advances in Intelligent Systems and Computing, 2014

The Frank-Wolfe algorithm has been for years the most widely used method for solving the traffic ... more The Frank-Wolfe algorithm has been for years the most widely used method for solving the traffic assignment problem (TAP). In the last decade there have been new proposals for the resolution of the TAP. It has been shown that these algorithms are feasible for large scale problems with very high convergence, much higher than the achieved by the Frank-Wolfe algorithm. The O/D matrix adjustment problem based upon traffic counts can be formulated as a bilevel optimization problem in which the TAP is the lower level. The convergence of the TAP and the computational cost can be critical because the number of TAPs to be solved during each step of the process is very high. This paper exploits the possibilities offered by new TAP methods in the O/D matrix adjustment problem. Numerical examples on medium-sized networks using the new proposed methods are presented.

Application of Fracture Mechanics to Materials and Structures, 1984

A dynamic fracture initiation test, based on a compact tension specimen loaded in a split Hopkins... more A dynamic fracture initiation test, based on a compact tension specimen loaded in a split Hopkinson bar apparatus is described. The problems presented by frictional effects are discussed. It is shown that equilibrium is achieved within 60 µs, with an upper limit to the loading rate corresponding to 106 MPam1/2s-1.

Boundary Element Methods in Engineering, 1982

The conventional boundary element method solving for the problems of two-dimensional anisotropic ... more The conventional boundary element method solving for the problems of two-dimensional anisotropic elastic solids with prescribed traction and/or prescribed displacement boundary conditions is extended to the frictional contact problems. A complete system of linear equations is constructed by boundary integral equations and contact constraint relations. The contact solutions are obtained by using an efficient, iterative and fully incremental loading technique. By using this technique, the nonlinearity raised by unknown contact region and unknown slip direction of frictional contact can be approximated by the accumulation of linear increments. The incremental load is determined by using the load extrapolation technique that allows only one or two node pairs come into contact in each iteration. The slip direction of frictional contact is decided by referring to the relative tangential slip in the frictionless state. To avoid reassembling the whole system equations in each iteration, a suitable arrangement of the equation system is made and a fast solver is adopted to get the solution without resolving the entire system of equations. When the contact bodies contain holes, cracks or inclusions, we use a special boundary element whose fundamental solution satisfies the boundary condition along the hole/crack/inclusion boundary. The validation of the proposed method is demonstrated through several numerical examples, which further lead to the discussion of the effects of friction coefficient, material anisotropy, holes, cracks and inclusions on contact.

Vehicle System Dynamics, 1990

The objective of this study is optimizing the components design of a vehicle suspension system un... more The objective of this study is optimizing the components design of a vehicle suspension system under excitation due to road roughness. The vehicle is modelled as a dynamic system made of masses interconnected by, linear, springs and dampers. The optimizing code provides values corresponding to the caracteristics of masses, dampers and springs which, within a range, minimize the objective function for a defined excitation. This objective function auantifies the vehicle comfort level. The optimization method used is thesequential ~i n e &~r o~r a m m i n~ by iteratively applying the Simplex algorithm. The model response is obtained in frequency domain and the vehicle excitation can be either random or deterministic. The exact nature of the optimization problem, objective function and restrictions, depend on the type of excitation considered. In succeeding paragraphs, the problem formulation together with a comparison with other authors is presented.

Engineering Fracture Mechanics, 1984

Abstract Part I of this report, published in a detached part, the theoretical and numerical funda... more Abstract Part I of this report, published in a detached part, the theoretical and numerical fundamentals of BIEM techniques in dynamic were presented. In Part II, numerical results for input problems obtained by BIEM, through a dynamic program of general applications, are shown.

Engineering Fracture Mechanics, 1984

Abstract In Part I of this report, the theoretical and numerical fundamentals of BIEM techniques ... more Abstract In Part I of this report, the theoretical and numerical fundamentals of BIEM techniques in real transformed dynamic are presented. Interesting remarks on how the numerical integrations have been done, are pointed out in the method. In Part II, to be published in a detailed paper, numerical results for impact problems obtained by BIE Method, through a dynamic program of general application, will be shown.

Vehicle System Dynamics, 1990

ABSTRACT

To represent the behaviour of travellers when they are deciding how they are going to get to thei... more To represent the behaviour of travellers when they are deciding how they are going to get to their destination, discrete choice models, based on the random utility theory, have become one of the most widely used tools. The field in which these models were developed was halfway between econometrics and transport engineering, although the latter now constitutes one of their principal areas of application. In the transport field, they have mainly been applied to mode choice, but also to the choice of destination, route, and other important decisions such as the vehicle ownership.

The need of an urban transport strategy on urban areas which solves the environmental problems de... more The need of an urban transport strategy on urban areas which solves the environmental problems derived from traffic without decreasing the trip attraction of these urban areas is taken for granted. Besides there is also a clear consensus among researchers and institutions in the need for integrated transport strategies (May et al., 2006; Zhang et al., 2006). But there is still a lack of knowledge on the policy measures to be implemented. This research aims to deepen in the understanding of how do different measures interact when implemented together: synergies and complementarities between them. The methodological approach to achieve this objective has been the double analysis ? quantitative and comprehensive ? of the different impacts produced, first of all by each of the measures by itself, and later on combining these measures. For this analysis, we have first defined the objectives to achieve within the transport strategy ? emissions and noise decrease without losing trip attrac...

Libro de Actas CIT2016. XII Congreso de Ingeniería del Transporte, 2016

El análisis de la movilidad en una determinada región es un aspecto esencial en las tareas de pla... more El análisis de la movilidad en una determinada región es un aspecto esencial en las tareas de planificación del transporte, siendo vital manejar información actualizada a fin de que sus resultados sean más dinámicos y realistas. Recientemente se ha producido un gran desarrollo en la sensorización del tráfico, ligado tanto a la propia infraestructura como al vehículo, surgiendo cada vez más fuentes de datos provenientes de otras actividades que pueden enriquecer la información de movilidad existente. En este sentido la telefonía móvil se perfila como alternativa con alto potencial para la recopilación de datos de movilidad. El propio funcionamiento de estos sistemas genera ciertos registros espacio-temporales que, debidamente tratados y encriptados sin revelar información confidencial de sus abonados, permitiría inferir datos relativos a la dinámica de actividad humana de forma transparente. Sin embargo, esta fuente de información procede de una tecnología diseñada con otra finalidad...

El peaje urbano ha demostrado ser una de las medidas más efectivas a la hora de promover un cambi... more El peaje urbano ha demostrado ser una de las medidas más efectivas a la hora de promover un cambio en el reparto modal, como ha quedado demostrado en diversas ciudades como Londres o Estocolmo. Los efectos, no obstante, son muy diferentes según el esquema de peaje implantado, pudiendo incluso provocar efectos adversos en algunas zonas.

Le Journal de Physique IV, 1997

This paper describes the test performed for the optical evaluation of propagating cracks, which a... more This paper describes the test performed for the optical evaluation of propagating cracks, which assess the severity of trougll cracks in composite laminates. The paper begins with the description of the experimental rig designed for dynamically loading the specimens. In particular a modified split-Hopkinson pressure bar for impacts at metlium range (10 to 30 m/s) is covered. The specimens are prepared in order to have a mirror reHrrtive surface, by depositing aluminium, which is used to reflect a laser collimated bram in ortler to visl~nlize optically the dynamic event in the crack neighborhood. RisumC : Ce papier dkcr~t le tesL rtallsk pour I'observation optique de la propagation de fissures dans les composiles. La configuration experimentale esr decrile. en parriculier, une barre de Hopkinson modifike pour obrenir des impacts dans le domaine de 10 A 30 mls. Les kchantillons sont prepares afin de disposer d'une surface dr reflexion de type miroir, en dkposant de I'aluminium. Une melhodr u~ilisant un li~isceau laser collimate esL utilisee pour observer optiquement les phenomPnes dynamiques dans le volslnafe de la fissurc.

Applied Mathematical Modelling, 1981

This paper presents the application of BIE techniques to elastoplastic three-dimensional problems... more This paper presents the application of BIE techniques to elastoplastic three-dimensional problems. Along with the general procedures the needed ¡ntegrations are described ¡n detail and so is the flow chart of the written program.

Libro de Actas CIT2016. XII Congreso de Ingeniería del Transporte, 2016

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 Intern... more This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0).

WIT Transactions on the Built Environment, 2002

This paper considers a new approach for modelling the tratlic flow in dense urban areas by using ... more This paper considers a new approach for modelling the tratlic flow in dense urban areas by using a mathematical continuum model, which needs information data from a very limited number of points from the network. T’he purpose of this communication is to provide a mathematical foundation for the study of this approach. This methodolo~ can SPA up the computation of relevant values concerning the time evolution of traffic on a city network.

A functional form for the speed-density relationship is presented in this paper. The functional f... more A functional form for the speed-density relationship is presented in this paper. The functional form is characterized by a dimensionless function, the generating function, whose argument is a dimensionless headway, the equivalent headway. The functional form is derived by means of two arguments. The first one arises from the set of properties that the speed-density relationship should satisfy and the second from the driver’s behavior.

This paper addresses the problem of estimating and updating observed origin and destination (OD) ... more This paper addresses the problem of estimating and updating observed origin and destination (OD) matrices based on available link flow information by means of the non-linear programming formulation corresponding to the Augmented Lagrangian Function. Therefore, the paper estimates larger OD matrices in a faster way following an efficient algorithm that minimizes the amount of stored information required for solving large-size problems. A solution algorithm is provided, which has been completely developed and designed to be used within assignment commercial codes. The case of updating a trip matrix, from a home-based survey, of a real problem corresponding to an existing city is analyzed. For this application case two methodologies are reviewed, the first one does not incorporate either constraints related to the total number of trips, the zonal productions and attractions, or individual OD pairs; the second one takes them into account. The results obtained by the application of the m...

Computational Mechanics ’95, 1995

The fundamental solution of an infinite three-dimensional, linear, elastic, orthotropic, homogene... more The fundamental solution of an infinite three-dimensional, linear, elastic, orthotropic, homogeneous layer subjected to an arbitrary buried source is presented. The results are subsequently utilized to formulate the multilayered orthotropic medium problem by means of transfer matrices.

This paper describes the tests performed for the optical evaluation of the stress field surroundi... more This paper describes the tests performed for the optical evaluation of the stress field surrounding crack growth under impact loading. The specimens are graphite-epoxy laminates. A description of the equipment used (split-Hopkinson-pressure-bar rig, high-speed photograph camera, flash and laser illumination) is covered. The specially manufactured interface, trigger and timing electronics are also described. The described set-up can be used with the optical techniques of caustics and CGS to evaluate the strain field around a dynamically propagating crack. By employing a flash light rather than the laser light source, the crack propagation can be studied visually. The test-rig is used for testing polymers and laminated composites under in-plane impact loads. The exposed surface of the specimens which were used for crack speed measurements and stress field evaluations was covered by matte white paint and vapour deposited aluminium for light reflection. Results obtained for laminates wi...

Advances in Intelligent Systems and Computing, 2014

The Frank-Wolfe algorithm has been for years the most widely used method for solving the traffic ... more The Frank-Wolfe algorithm has been for years the most widely used method for solving the traffic assignment problem (TAP). In the last decade there have been new proposals for the resolution of the TAP. It has been shown that these algorithms are feasible for large scale problems with very high convergence, much higher than the achieved by the Frank-Wolfe algorithm. The O/D matrix adjustment problem based upon traffic counts can be formulated as a bilevel optimization problem in which the TAP is the lower level. The convergence of the TAP and the computational cost can be critical because the number of TAPs to be solved during each step of the process is very high. This paper exploits the possibilities offered by new TAP methods in the O/D matrix adjustment problem. Numerical examples on medium-sized networks using the new proposed methods are presented.

Application of Fracture Mechanics to Materials and Structures, 1984

A dynamic fracture initiation test, based on a compact tension specimen loaded in a split Hopkins... more A dynamic fracture initiation test, based on a compact tension specimen loaded in a split Hopkinson bar apparatus is described. The problems presented by frictional effects are discussed. It is shown that equilibrium is achieved within 60 µs, with an upper limit to the loading rate corresponding to 106 MPam1/2s-1.

Boundary Element Methods in Engineering, 1982

The conventional boundary element method solving for the problems of two-dimensional anisotropic ... more The conventional boundary element method solving for the problems of two-dimensional anisotropic elastic solids with prescribed traction and/or prescribed displacement boundary conditions is extended to the frictional contact problems. A complete system of linear equations is constructed by boundary integral equations and contact constraint relations. The contact solutions are obtained by using an efficient, iterative and fully incremental loading technique. By using this technique, the nonlinearity raised by unknown contact region and unknown slip direction of frictional contact can be approximated by the accumulation of linear increments. The incremental load is determined by using the load extrapolation technique that allows only one or two node pairs come into contact in each iteration. The slip direction of frictional contact is decided by referring to the relative tangential slip in the frictionless state. To avoid reassembling the whole system equations in each iteration, a suitable arrangement of the equation system is made and a fast solver is adopted to get the solution without resolving the entire system of equations. When the contact bodies contain holes, cracks or inclusions, we use a special boundary element whose fundamental solution satisfies the boundary condition along the hole/crack/inclusion boundary. The validation of the proposed method is demonstrated through several numerical examples, which further lead to the discussion of the effects of friction coefficient, material anisotropy, holes, cracks and inclusions on contact.

Vehicle System Dynamics, 1990

The objective of this study is optimizing the components design of a vehicle suspension system un... more The objective of this study is optimizing the components design of a vehicle suspension system under excitation due to road roughness. The vehicle is modelled as a dynamic system made of masses interconnected by, linear, springs and dampers. The optimizing code provides values corresponding to the caracteristics of masses, dampers and springs which, within a range, minimize the objective function for a defined excitation. This objective function auantifies the vehicle comfort level. The optimization method used is thesequential ~i n e &~r o~r a m m i n~ by iteratively applying the Simplex algorithm. The model response is obtained in frequency domain and the vehicle excitation can be either random or deterministic. The exact nature of the optimization problem, objective function and restrictions, depend on the type of excitation considered. In succeeding paragraphs, the problem formulation together with a comparison with other authors is presented.

Engineering Fracture Mechanics, 1984

Abstract Part I of this report, published in a detached part, the theoretical and numerical funda... more Abstract Part I of this report, published in a detached part, the theoretical and numerical fundamentals of BIEM techniques in dynamic were presented. In Part II, numerical results for input problems obtained by BIEM, through a dynamic program of general applications, are shown.

Engineering Fracture Mechanics, 1984

Abstract In Part I of this report, the theoretical and numerical fundamentals of BIEM techniques ... more Abstract In Part I of this report, the theoretical and numerical fundamentals of BIEM techniques in real transformed dynamic are presented. Interesting remarks on how the numerical integrations have been done, are pointed out in the method. In Part II, to be published in a detailed paper, numerical results for impact problems obtained by BIE Method, through a dynamic program of general application, will be shown.

Vehicle System Dynamics, 1990

ABSTRACT

To represent the behaviour of travellers when they are deciding how they are going to get to thei... more To represent the behaviour of travellers when they are deciding how they are going to get to their destination, discrete choice models, based on the random utility theory, have become one of the most widely used tools. The field in which these models were developed was halfway between econometrics and transport engineering, although the latter now constitutes one of their principal areas of application. In the transport field, they have mainly been applied to mode choice, but also to the choice of destination, route, and other important decisions such as the vehicle ownership.

The need of an urban transport strategy on urban areas which solves the environmental problems de... more The need of an urban transport strategy on urban areas which solves the environmental problems derived from traffic without decreasing the trip attraction of these urban areas is taken for granted. Besides there is also a clear consensus among researchers and institutions in the need for integrated transport strategies (May et al., 2006; Zhang et al., 2006). But there is still a lack of knowledge on the policy measures to be implemented. This research aims to deepen in the understanding of how do different measures interact when implemented together: synergies and complementarities between them. The methodological approach to achieve this objective has been the double analysis ? quantitative and comprehensive ? of the different impacts produced, first of all by each of the measures by itself, and later on combining these measures. For this analysis, we have first defined the objectives to achieve within the transport strategy ? emissions and noise decrease without losing trip attrac...

Libro de Actas CIT2016. XII Congreso de Ingeniería del Transporte, 2016

El análisis de la movilidad en una determinada región es un aspecto esencial en las tareas de pla... more El análisis de la movilidad en una determinada región es un aspecto esencial en las tareas de planificación del transporte, siendo vital manejar información actualizada a fin de que sus resultados sean más dinámicos y realistas. Recientemente se ha producido un gran desarrollo en la sensorización del tráfico, ligado tanto a la propia infraestructura como al vehículo, surgiendo cada vez más fuentes de datos provenientes de otras actividades que pueden enriquecer la información de movilidad existente. En este sentido la telefonía móvil se perfila como alternativa con alto potencial para la recopilación de datos de movilidad. El propio funcionamiento de estos sistemas genera ciertos registros espacio-temporales que, debidamente tratados y encriptados sin revelar información confidencial de sus abonados, permitiría inferir datos relativos a la dinámica de actividad humana de forma transparente. Sin embargo, esta fuente de información procede de una tecnología diseñada con otra finalidad...

El peaje urbano ha demostrado ser una de las medidas más efectivas a la hora de promover un cambi... more El peaje urbano ha demostrado ser una de las medidas más efectivas a la hora de promover un cambio en el reparto modal, como ha quedado demostrado en diversas ciudades como Londres o Estocolmo. Los efectos, no obstante, son muy diferentes según el esquema de peaje implantado, pudiendo incluso provocar efectos adversos en algunas zonas.

Le Journal de Physique IV, 1997

This paper describes the test performed for the optical evaluation of propagating cracks, which a... more This paper describes the test performed for the optical evaluation of propagating cracks, which assess the severity of trougll cracks in composite laminates. The paper begins with the description of the experimental rig designed for dynamically loading the specimens. In particular a modified split-Hopkinson pressure bar for impacts at metlium range (10 to 30 m/s) is covered. The specimens are prepared in order to have a mirror reHrrtive surface, by depositing aluminium, which is used to reflect a laser collimated bram in ortler to visl~nlize optically the dynamic event in the crack neighborhood. RisumC : Ce papier dkcr~t le tesL rtallsk pour I'observation optique de la propagation de fissures dans les composiles. La configuration experimentale esr decrile. en parriculier, une barre de Hopkinson modifike pour obrenir des impacts dans le domaine de 10 A 30 mls. Les kchantillons sont prepares afin de disposer d'une surface dr reflexion de type miroir, en dkposant de I'aluminium. Une melhodr u~ilisant un li~isceau laser collimate esL utilisee pour observer optiquement les phenomPnes dynamiques dans le volslnafe de la fissurc.

Applied Mathematical Modelling, 1981

This paper presents the application of BIE techniques to elastoplastic three-dimensional problems... more This paper presents the application of BIE techniques to elastoplastic three-dimensional problems. Along with the general procedures the needed ¡ntegrations are described ¡n detail and so is the flow chart of the written program.

Libro de Actas CIT2016. XII Congreso de Ingeniería del Transporte, 2016

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 Intern... more This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0).

WIT Transactions on the Built Environment, 2002

This paper considers a new approach for modelling the tratlic flow in dense urban areas by using ... more This paper considers a new approach for modelling the tratlic flow in dense urban areas by using a mathematical continuum model, which needs information data from a very limited number of points from the network. T’he purpose of this communication is to provide a mathematical foundation for the study of this approach. This methodolo~ can SPA up the computation of relevant values concerning the time evolution of traffic on a city network.

A functional form for the speed-density relationship is presented in this paper. The functional f... more A functional form for the speed-density relationship is presented in this paper. The functional form is characterized by a dimensionless function, the generating function, whose argument is a dimensionless headway, the equivalent headway. The functional form is derived by means of two arguments. The first one arises from the set of properties that the speed-density relationship should satisfy and the second from the driver’s behavior.

This paper addresses the problem of estimating and updating observed origin and destination (OD) ... more This paper addresses the problem of estimating and updating observed origin and destination (OD) matrices based on available link flow information by means of the non-linear programming formulation corresponding to the Augmented Lagrangian Function. Therefore, the paper estimates larger OD matrices in a faster way following an efficient algorithm that minimizes the amount of stored information required for solving large-size problems. A solution algorithm is provided, which has been completely developed and designed to be used within assignment commercial codes. The case of updating a trip matrix, from a home-based survey, of a real problem corresponding to an existing city is analyzed. For this application case two methodologies are reviewed, the first one does not incorporate either constraints related to the total number of trips, the zonal productions and attractions, or individual OD pairs; the second one takes them into account. The results obtained by the application of the m...