Santiago Hernandez | FUNDACIÓN FILARMONICA DE LA CIUDAD (original) (raw)

Papers by Santiago Hernandez

It is well known that long span suspension bridges are wind prone structures. For decades guarant... more It is well known that long span suspension bridges are wind prone structures. For decades guaranteeing the safe performance of bridges against flutter has been one of the main concerns of designers as that aeroelastic instability can be responsible for the bridge destruction. To date, the project of cable supported bridges has been essentially a trial and error procedure. Nevertheless,

Wind Engineers, JAWE, 2006

Structures 2001, 2001

Conceptual Design of Suspension Bridges Based in Sensitivity Analysis of Flutter Speed. [ASCE Con... more Conceptual Design of Suspension Bridges Based in Sensitivity Analysis of Flutter Speed. [ASCE Conference Proceedings 109, 152 (2001)]. J. Ángel Jurado, Santiago Hernández. Abstract. Stability of long span suspension bridges under wind forces is a very important concern. ...

IEEE Latin America Transactions, 2007

We study the problem of reducing the latency introduced by authentication and network access cont... more We study the problem of reducing the latency introduced by authentication and network access control processes required in heterogeneous wireless networks and based on the Extensible Authentication Protocol. We aim to reduce the time spent on providing access and smooth transition between different technologies which require to perform authentication in order to allow network access. We propose a secure protocol

Proceedings of first ACM/IEEE international workshop on Mobility in the evolving internet architecture - MobiArch '06, 2006

Page 1. GSABA: A Generic Service Authorization Architecture Florian Kohlmayer, Hannes Tschofenig,... more Page 1. GSABA: A Generic Service Authorization Architecture Florian Kohlmayer, Hannes Tschofenig, Rainer Falk Corporate Technology, Siemens AG Otto-Hahn-Ring 6 81739 Munich +49 (89) 636-00 {florian.kohlmayer, hannes.tschofenig, rainer.falk}@siemens.com ...

Proceedings of the 2006 International Conference on Privacy, Security and Trust Bridge the Gap Between PST Technologies and Business Services - PST '06, 2006

Users accessing to the Internet from everywhere will require to have access to the services in wh... more Users accessing to the Internet from everywhere will require to have access to the services in which they have a signed contract. This is the most important feature for roaming users: a way to access to all their services without having in mind where are they connected. For this request, it is required a solution for managing the use of

2007 16th IST Mobile and Wireless Communications Summit, 2007

In this paper we study the issue of providing an efficient and heterogeneous handover in mobile n... more In this paper we study the issue of providing an efficient and heterogeneous handover in mobile networks which involve network access control based on the extensible authentication protocol. The goal is to provide a smooth transition between different technologies without jeopardizing the overall performance during handover process. We propose and analyze a simple but efficient security-oriented architecture that allows a smooth transition between different technologies with different security requirements.

SAE Technical Paper Series, 2013

In this paper, the effect of welded joints on the crashworthiness response of a hybrid system is ... more In this paper, the effect of welded joints on the crashworthiness response of a hybrid system is presented. This hybrid system consists of a steel enclosure filled with different core materials: carbon-fiber reinforced polymer, glass-fiber reinforced polyamide, polyethylene terephthalate foam and natural cork conglomerate. The metallic enclosure is a cold-formed tube which has to be spot-welded to assemble the final design. The focus is set on the assessment of the effect of the pattern and the number of spot welds on the crashworthiness results in terms of absorbed energy. Results show that variations in the number or the geometric distribution of the spot welds have a direct and noticeable effect on the final amount of energy that the part can dissipate. This is due to the crushing mechanism of the metallic column which is highly sensitive to the way that cold-formed sections are joined. From these results, several design recommendations can be proposed for the design of hybrid elements with welded joints, depending on the geometrical and material properties of the system.

Structural and Multidisciplinary Optimization, 2008

This paper focuses on the design of long-span suspension bridges under aeroelastic constraints. S... more This paper focuses on the design of long-span suspension bridges under aeroelastic constraints. Such challenging structures need to be protected against wind-induced instabilities as flutter. The authors envision that a set of scientific disciplines not currently used in bridge engineering may help along the design process and constitute a useful tool. First, the formulation of sensitivity analysis of flutter speed

Structural and Multidisciplinary Optimization, 2009

Cable supported bridges are wind prone structures. Therefore, their aerodynamic behaviour must be... more Cable supported bridges are wind prone structures. Therefore, their aerodynamic behaviour must be studied in depth in order to guarantee their safe performance. In the last decades important achievements have been reached in the study of bridges under wind-induced actions. On the other hand, non-conventional design techniques such as sensitivity analysis or optimum design have not been applied although they

Structural and Multidisciplinary Optimization, 2011

Often the parameters considered as constants in an optimization problem have some uncertainty and... more Often the parameters considered as constants in an optimization problem have some uncertainty and it is interesting to know how the optimum solution is modified when these values are changed. The only way to continue having the optimal solution is to perform a new optimization loop, but this may require a high computational effort if the optimization problem is large. However, there are several procedures to obtain the new optimal design, based on getting the sensitivities of design variables and objective function with respect to a fixed parameter. Most of these methods require obtaining second derivatives which has a significant computational cost. This paper uses the feasible direction-based technique updating the active constraints to obtain the approximate optimum design. This procedure only requires the first derivatives and it is noted that the updating set of active constraints improves the result, making possible a greater fixed parameter variation. This methodology is applied to an example of very common structural optimization problems in technical literature and to a real aircraft structure.

Aerodynamic design of bridge deck sections is a key issue in order to guarantee a feasible perfor... more Aerodynamic design of bridge deck sections is a key issue in order to guarantee a feasible performance of wind prone bridges. For years, experimental tests of the proposed Messina Strait Bridge have been carried out in the wind tunnel facilities of the Politecnico di Milano. Those exhaustive and detailing testing campaigns have allowed the identification of potential problems related with the bridge behavior under wind loads. In fact, tender designs of the bridge cross-section had shown risk of one degree of freedom torsional instability due to the negative slope of the moment aerodynamic coefficient for the so-called bare bridge deck section, which is the reference section for this work. The adopted strategy for the mitigation of undesirable wind effects has been in certain occasions the introduction of aerodynamic devices. Experimental test of a certain set of aerodynamic devices are costly, both in terms of time and money, although they give invaluable insight information regardi...

Journal of Constructional Steel Research, 1998

Journal of Bridge Engineering, 2011

ABSTRACT The conventional design process of a launching nose of an incrementally launched bridge ... more ABSTRACT The conventional design process of a launching nose of an incrementally launched bridge is based on trial-and-error methods to reduce bending moment of prestressed concrete deck at the foremost support during launch. With this method, there is no guarantee that the obtained solution is the best among all the possible solutions, since they all depend on the experience and intuition of a designer, and they are also restricted by a limited number of possible iterations. Given that launched bridges constitute an important constructive typology, all the available capacities of design innovation should be incorporated, including numerical optimization. This research work proposes an objective and rigorous formulation to optimize the launching nose of a launched bridge under real constraints that a bridge designer can encounter in practice. Comparing the results obtained by conventional process and those obtained by optimization techniques allows us to verify that some of the assumptions considered in classical design methods of a launching nose are not based on any theoretical foundation. This fact demonstrates the utility of numerical optimization to improve a design. DOI:10.1061/(ASCE)BE.1943-5592.0000169. (C) 2011 American Society of Civil Engineers.

Aerospace Science and Technology, 2010

In this work an uncertainty quantification procedure and a robust design method are applied to th... more In this work an uncertainty quantification procedure and a robust design method are applied to the thermal design of a skin panel and a wing box section. The uncertainty quantification method selected is based on Monte Carlo simulations and a set of common design parameters have been considered and formulated with random values. Numerical results show that the most significant randomness comes from thermal loads and also that the amount of uncertainty decreases from input to output. On the other hand, the Taguchi's method of robust design has been applied to obtain the most appropriate values of a set of control factors in several design situations. In this case, the results show an improvement in the response of the components, maintaining a low dependence on input value variations and producing designs that increase the quality level. (J. Díaz). Fig. 1. Flowchart of uncertainty quantification procedure. 1270-9638/$ -see front matter

Advances in Engineering Software, 2005

A computer code written by the authors at the University of Coruña and aimed to produce optimum d... more A computer code written by the authors at the University of Coruña and aimed to produce optimum design of portal frames is presented in this paper. The PADO software provides the least weight design for the most common types of planar frames. The code incorporates the complete set of constraints considered in the Spanish code of practice for steel structures. The software has a graphical interface to provide a user-friendly communication. Some application examples are presented in this paper to make clear the capabilities of PADO code. q

Advances in Engineering Software, 2011

Design techniques based upon sensitivity analysis are not usual in the current design of suspensi... more Design techniques based upon sensitivity analysis are not usual in the current design of suspension bridges. However, sensitivity analysis has been proved to be a useful tool in the car and aircraft industries. Evaluation of sensitivity analysis is a mandatory step in the way towards an efficient automated optimum design process which would represent a huge jump in the conception of long span bridges. Some of the authors of this paper were pioneers in establishing a methodology for obtaining the sensitivity analysis of flutter speed in suspension bridges a few years ago. That approach was completely analytical and required the evaluation of many matrices related to the phenomenon. In those works the total mass of the deck was considered as constant and such a circumstance supposed a limitation of the method. In the present paper the complete analytical formulation of the sensitivity analysis problem in bridges considering variable deck mass is presented, as well as its application to the design problem of the Great Belt Bridge. Analytical evaluation of sensitivities is a time demanding task, and in order to avoid excessive computation times, distributed computing strategies have been implemented which can be considered as an additional benefit of this approach. For the application example, it has been found that deck cross-section area and torsional inertia are the structural properties with the greatest influence on the flutter performance.

Advances in Engineering Software, 2008

Construction of cable supported bridges has experienced a great impulse in the past decade. Bridg... more Construction of cable supported bridges has experienced a great impulse in the past decade. Bridges having more than 800 m of span length were built in France and Japan and some bridges with span length of more than 1 km are going to be built, such as the Stonecuters bridge in Hong-Kong, and the Chongming in China . Because of the increasing length of this class of bridges, they are becoming prone to phenomena like flutter in a similar way than long span suspension bridges.