Luis Romera - Academia.edu (original) (raw)

Papers by Luis Romera

Structural and Multidisciplinary Optimization, Jul 16, 2019

This research concerns the crashworthiness enhancement of a model of a Boeing 737-200 fuselage se... more This research concerns the crashworthiness enhancement of a model of a Boeing 737-200 fuselage section. Using a validated numerical specimen, four thin-walled crushable hybrid energy absorbers are added to the aircraft to work as vertical struts. The absorbers are composed of a hollow aluminium tube, a star-shaped glass-fibre reinforced polymer inner matrix and foam extrusions. The absorbers-with variable tube edge and thickness, composite thickness and core height-are single-and multi-objectively optimised. Surrogate models and genetic algorithms are used for the minimisation of acceleration loads, injury levels and the strut's weight. Results yield a more efficient frames' collapse evolution with plastic dissipation increased by over 50%. Consequently, acceleration peaks are up to 50% lower at the two measured locations while maintaining low mass values. Injury levels were also reduced from severe to moderate according to an Eiband diagram.

Lecture notes in civil engineering, 2019

This paper describes a research carried out for the design of a wind mill tower reduced-scale mod... more This paper describes a research carried out for the design of a wind mill tower reduced-scale model to be built and tested in the boundary layer wind tunnel at the University of La Coruna. It is well known that one of the many requirement of a reduced-scale model is its capability of reproduce the natural frequencies and vibration modes of the real structure. In this research, this is achieved by using a technique developed by the authors in a previous work and adapted to this particular case. This technique is based on the use of optimization algorithms, allowing the minimization of the error between these dynamic properties of the reduced-scale model and the target values. The numerical results are presented.

WIT Transactions on the Built Environment, 1970

In this paper a comprehensive study of the existing Spanish dam of Bolarque is presented. The dam... more In this paper a comprehensive study of the existing Spanish dam of Bolarque is presented. The dam was composed of two different classes of concrete and also two choices of material characteristic of the rock foundation were considered. The seismic analysis was earned out taking in account the dam-foundation rockimpounded water interaction. Additionally, thermal loadings were included by using an equivalent structural model. Overall 128 structural analyses were carried out to complete consider the necessary combinations of materials, seismic and thermal loadings. Numerical results are presented showing the behaviour of the dam under the worst situations for empty and full reservoir. 1. A BRIEF HISTORY OF BOLARQUE DAM The Bolarque dam was built in 1910 and works to increase its height and therefore to improve the volume of impounded water were carried out in 1954-1955. Figure la shows the cross-section of the dam and Figure Ib the structural model which acommodate quite properly the actual geomeuy.

Structural and Multidisciplinary Optimization, Jun 12, 2015

ABSTRACT In the field of automotive safety, the lightweight design of crash absorbers is an impor... more ABSTRACT In the field of automotive safety, the lightweight design of crash absorbers is an important research topic with a direct effect on the occupant safety levels. The design of these absorbers usually requires an optimization of their crashworthiness, which can include multi-objective and reliability-based optimization techniques. This process is very time-consuming, and in spite of the continuous growing of computational power, the problem needs a reliable solving scheme. The use of surrogate models and parallel computing are suitable alternatives to deal with this issue. However, the strongly non-linear response functions obtained from the finite element simulations need careful treatment. This work contributes with the application of a surrogate-based reliability-based design optimization method to an original design of a crash absorber made of metal and a glass-fiber reinforced polymer which is subjected to a frontal impact. Multi-adaptive regression splines models are employed to emulate the original responses, and three different approaches in the sampling stage of the method are compared. The absorbed energy and the mass of the element are considered as objective functions, while the peak value of the force transmitted to the occupants of the vehicle is the design constraint. A discussion of the employed materials is presented and the proposed approaches are compared. Finally, several Pareto fronts are obtained as a solution to the probabilistic problem. Results show that a combination of aluminum and glass fiber reinforced polymer is optimum for this problem, and some design rules are offered.

This paper presents the computer code MEFLAP which allows a complete structural modeling of concr... more This paper presents the computer code MEFLAP which allows a complete structural modeling of concrete bridges that have voided slab deck, which is a common design for medium span length bridges. The structural model is made with shell and bar elements and the voided part of the cross section is modeled considering orthotropic material. MEFLAP has a user friendly graphical interface and once the input data is completed a link is provided to the commercial code COSMOS/M that carries out the structural analysis. Afterwards a graphical postprocessor allows the user an easy visualization of a wide range of structural responses including stress components, nodal displacements and internal forces. A real example of a three span bridge is included in this presentation with the aim to show the features of the MEFLAP code.

WIT Transactions on the Built Environment, 2007

In this paper some of the studies developed by the authors in the last twenty years in the field ... more In this paper some of the studies developed by the authors in the last twenty years in the field of numerical analysis and restoration of historical constructions are presented, with the objective of having a temporal perspective. In all cases the origin of every work was the appearance of several pathologies, that led to structural studies in order to find out the causes of these pathologies and once the way the structure worked and the origin of its problems was understood, the consideration of the necessary restoration. According to our experience, the best way to take into account this difficult and complex process, complementing the engineer’s knowledge, is the use of numerical tools like the finite element method. In each of the cases presented, a set of structural models was developed and validated with the aim of simulating the current structural state, their security level and the relationship between the structural behaviour and the damage observed. Comparison of the cases...

Aerospace Science and Technology, 2017

Ground Vibration Test (GVT) is a crucial step in the design process of a new aircraft. The test i... more Ground Vibration Test (GVT) is a crucial step in the design process of a new aircraft. The test involves the analysis of different load configurations that helps to understand the real structural behaviour, to certificate some extreme load cases and also to validate and improve the Finite Element (FE) model used in the design. The validation of the FE model is done by making a comparison between Frequency Response Functions (FRF) from the GVT and the FE model at some response points. Ideally, numerical and experimental results should be in agreement. This is certainly true in the case of single components but in the case of assemblies it is common that numerical and experimental results show discrepancies, especially in the case of dynamic analysis. These differences increase as the number of components in the assembly grows, because connections are usually not represented sufficiently well in the FE model. The components of these assembled structures are usually connected at a small number of points, and they can be seen as local sources of stiffness and damping. In the FE model these joints can be represented as lumped spring/damper elements in a simplified way. In this paper a formulation of the dynamic equilibrium equation employing a decoupled approach for the joint mechanical properties of an assembly is presented. Later, an optimization process based on this formulation that involves the joint properties as design variables has been developed in order to identify the joint parameters that improve the adjustment between numerical and experimental FRF in the case of harmonic excitations. The approach has been applied to a FE model that represents the connection between a segment of fuselage and the tail cone and to a real aircraft system where experimental data is available. The results achieved with this procedure are very efficient and promising.

International Journal of Adhesion and Adhesives, 2012

Single-lap bonded joints are a common typology, frequently used when designing structural systems... more Single-lap bonded joints are a common typology, frequently used when designing structural systems. Several authors have studied their behaviour in different situations, involving both failure of the adhesive and also of the adherends. So far, the design of such joints has been based on deterministic postulates. In this work, a non-deterministic approach is followed. The reliability of the joint is assessed with several limit state approximation methods. Furthermore, sampling methods and a global reliability approach are considered. The algorithms are applied to the reliability analysis of a generic single-lap bonded joint, where the specific uncertainties related with this typology are taken into account, including mechanical properties and geometrical parameters of adherends and adhesive. All of them are defined as random variables and different cases are studied. Results show that first-and second-order second-moment and advanced mean value methods give an estimation to calculate the probability of failure at early stages of design, when precise values are not required. However, methods based on approximations of limit state surface around the most probable point of failure present a better response in terms of accuracy. Global reliability methods offer a good alternative to limit state approximations, as they present similar accuracy and usually require fewer iterations. Sampling methods often need extensive use of computational resources and are suitable for those cases with a large number of random variables, where computational cost is comparable with that required by other methods.

DYNA INGENIERIA E INDUSTRIA, 2013

Since the signature of the Kyoto Protocol, efforts in the search of processes to slow climate cha... more Since the signature of the Kyoto Protocol, efforts in the search of processes to slow climate change down have been increased. In the case of the manufacture of bituminous mixtures, new products and procedures that allow a significant reduction of greenhouse fumes emissions and of consumption of energy resources, keeping the demanded benefits, have been developed. However, there is still some reluctance to use them, due to the ignorance of manufacturers about the changes needed in asphalt plants to adapt their technology, as well as about the economic consequences of their use. Therefore, this paper shows an analysis of the key technologies used to manufacture mixtures at low temperature that exist nowadays. Changes in plants to incorporate these new technologies are detailed, and an economical and environmental balance that compares the manufacture of these mixes with the traditional hot mixes is carried out. Everything with the aim of encouraging producers and Authorities to employ these new products, both effective, environmentally sustainable and profitable.

Informes de la Construcción, 2021

Se ha desarrollado y aplicado un método simplificado para reevaluar de forma más precisa la segur... more Se ha desarrollado y aplicado un método simplificado para reevaluar de forma más precisa la seguridad al deslizamiento en seis presas de gravedad y contrafuertes en base a los resultados de modelos lineales numéricos, verificando su validez mediante análisis no lineales y medidas experimentales. Se han llevado a cabo sondeos con recuperación de testigo cercanos al tacón aguas arriba para inspeccionar posibles agrietamientos en las interfases hormigón-roca y se han instrumentado con extensómetros para analizar los datos de aperturas. Los resultados obtenidos, demuestran que los criterios de diseño utilizados en los años 50, en algunos casos no cubren el margen de incertidumbre esperado, respaldando así la necesidad de revisar las grandes presas españolas actualizando los análisis tal como rezan las Normas Técnicas de Seguridad de Presas que recientemente ha aprobado el Gobierno.

Journal of Aircraft, 2019

This research focuses on the crashworthiness study and enhancement of commercial aircraft structu... more This research focuses on the crashworthiness study and enhancement of commercial aircraft structures by developing crushable energy absorbers to work as vertical struts. To assess their contribution on a representative crash scenario, a numerical simulation of a Boeing 737-200 drop test developed and verified with experimental data is used as a benchmark. The numerical model is then enhanced with four hybrid energy absorbers designed for programmed and progressive collapse, added in the cargo compartment connecting the underfloor beams and the frames. These devices are composed of a square aluminum tube filled with a composite skeleton and foam extrusions for maximized energy absorption. The enhanced aircraft is later

Composite Structures, 2015

Crashworthiness optimization of aircraft and automotive structures has become one the main resear... more Crashworthiness optimization of aircraft and automotive structures has become one the main research targets for their respective leading industries. The following research proposes a new design of an aircraft's vertical strut. The design consists of a hollow aluminum square tube with a glass-fiber reinforced polymer honeycomb-shaped inner structure. Size and shape surrogate-based optimization techniques are used, with the thicknesses of both materials, cell size and cell shape as design variables. The objective function chosen for the single-objective optimization is the specific energy absorption, while the metrics for the multi-objective optimization are the peak force, mass, absorbed energy and the specific energy absorption. An improvement of 22% of the specific energy absorption with low peak force values is obtained from the singleobjective optimization by significantly changing all design variables. Two Pareto fronts have been obtained from the multi-objective optimization confronting, the specific energy absorption against the peak force and the mass against the energy absorbed. When compared to the baseline model, the optimized models show substantial improvement, increasing the specific energy absorption by 65% or reducing the peak force by over 55%. It has been observed an important effect of the cell shape on the model's performance.

International Journal of Adhesion and Adhesives, 2010

One of the challenges in the analysis and design of bonded joints is the evaluation of the stress... more One of the challenges in the analysis and design of bonded joints is the evaluation of the stress and strain fields at the adhesive layer. Experimental work can be carried out in the laboratory in order to identify the ultimate load value, but numerical methods based on finite element models can be very useful in describing the stress and strain responses for each load step. In this work, the consideration of the accuracy of finite element discretizations used to simulate the joint is under debate. A parametric study aimed to compare the performance of several modelizations of a joint made of two CFRP adherends bonded by a layer of epoxy film adhesive will be presented, in order to help in the development of modelling guidelines. All the simulations were conducted with three-dimensional meshes and geometrical nonlinearity was considered, requiring extensive computation time. Results obtained with different mesh sizes and element types are compared with the available experimental data and all the information is related with the computational cost, allowing decision making about which model to use in every design situation.

Engineering Geology, 2008

This paper presents an analysis of the mobilization of the dolmen of Dombate, a megalithic monume... more This paper presents an analysis of the mobilization of the dolmen of Dombate, a megalithic monument situated in the Northwest of Spain. The study is founded on simple static principles, with the application of basic concepts of soil mechanics (soil reactions were computed by the reaction modulus method) and rock mechanics (a simple secant approach was adopted to model the contact between orthostats). In addition, a simplified geometric model for dolmens was adopted. On the basis of these concepts, a numerical solver able to provide quick estimations of the system's mobilization was developed. Using this tool, a number of sensitivity analyses were conducted to estimate the mobilization that could be caused by a conservation project currently under consideration. It was found that mobilization might be excessive, and therefore, a safer procedure is proposed. In short, this paper puts forth a new rational approach for archaeological practices which may help to estimate the possible consequences of excavations and rehabilitations on megalithic structures.

Advances in Engineering Software, 2010

... and post-processing, linked to a commercial finite element package. A description of the code... more ... and post-processing, linked to a commercial finite element package. A description of the code is presented, along with the formulation of the orthotropic plate. Verification and comparison examples demonstrate the performance and features of the software and also the ...

Advances in Engineering Software, 2008

The Basilica of Pilar, located in the city of Zaragoza, is one of the most famous Spanish temples... more The Basilica of Pilar, located in the city of Zaragoza, is one of the most famous Spanish temples. Several domes of this church contain frescoes painted by Francisco de Goya, which have suffered damages in the past decades due to various pathologies. The frescoes of the Regina Martirum dome are being restored at the present time. In this paper, we present a set of structural models of the entire temple and local models of the Regina Martirum dome by discussing and comparing the obtained results. The main objective of the research was to identify the current structural state of the church, its safety level and the relationship between the structural behaviour and the damages observed. The behaviour of the main material used in the construction, brick masonry, was simulated first with linear elastic isotropic models and later with several non-linear isotropic models including brittle behaviour in tension and plastic behaviour in compression. In addition, we consider the historical construction and the reinforcement works added to the structure in its history, with the purpose of testing the finite element models by reproducing the pathologies described from the beginning of the current Baroque construction.

Thin-Walled Structures, 2016

This research work investigated the axial crushing behavior of a circular aluminum extrusion in a... more This research work investigated the axial crushing behavior of a circular aluminum extrusion in alloy AA6063-T5 filled with polymeric foam and a glass-fiber structure. The components were experimentally tested under quasi-static and impact loading conditions supported by a material testing campaign. Energy absorption, crush force efficiency and specific energy absorption were experimentally measured in order to assess the performance of a design proposal. Besides, the interaction effects between the different materials has been analyzed in depth and compared to the results for aluminum foam filled extrusions available in the literature. The confinement effect of the foam on the glass fiber plates has been found to have a very remarkable contribution to the energy absorption levels of the component, whereas a negligible foam-extrusion interaction was observed due to the gaps in the initial geometry of the specimen. The investigated component show an overall good performance, specially in terms of crush force efficiency. However, the specific energy absorption of the component was reduced by approximately 10 % compared to the aluminum extrusion alone.

WIT Transactions on The Built Environment

In this paper, the determination of the collapse load of an historical stone arch bridge situated... more In this paper, the determination of the collapse load of an historical stone arch bridge situated in the Northwest of Spain is accomplished. The arch presents damage and its load bearing capacity is reduced, so repair works and restoration are needed. In such circumstances, the assessment of the ultimate load that the bridge can support is very important and so the limit analysis method is applied, which delivers the collapse load and the failure mechanism considering the hypothesis of plastic collapse of the structure. On the other hand, and taking into account that one of the major drawbacks in the analysis of this type of bridge is the lack of accurate data about material properties, a parametric study is performed selecting from all the mechanical parameters governing the bridge response, those with a wider range of variation or those having a more difficult characterization: masonry and backfill unit weight, compressive strength of the masonry, coefficient of radial friction between voussoirs, height of backing, earth pressure coefficient and load dispersion model. For each one of the properties considered, five values are selected, based upon recommendations found in technical literature or in previous experiences with similar bridges, and a series of analyses are performed, obtaining the influence line of kinematic safety factor, with respect to live load, and the critical failure load variation, with respect to each one of the material properties. Results show that the most significant properties having influence in the collapse load are the compressive strength of the masonry, the earth pressure coefficient and the unit weights of materials.

... 1 Santiago Hernández, Professor, School of Civil Engineering, University of La Coruña 2 Luis ... more ... 1 Santiago Hernández, Professor, School of Civil Engineering, University of La Coruña 2 Luis E. Romera, Assistant Professor, School of Civil ... Evaluation of settlements produced by tunnelling was based for many years on empirical or analytical formulae (eg Peck, 1969) and it ...

Concrete international, 2002