Analysis and optimization of composite stringers

The use of the stiffened panels in the aircraft/aeronautical industry has been growing in the last decades. On the other hand, the exponential growth in the use of composite materials in the last years has had a strong 2/2 influence in these structural components and in the industry in general. In consequence, with this new material unknown characteristics appear, for example new failure mechanisms, producing high complexity when simulation, analysis and testing are performed. For this reason, thanks to the increment in the power of the computers, the use of virtual tests with finite element method has become crucial in the simulation of the components with high structural responsibility. In the same way, the general spread of computational resources has made possible the use of optimization methods in the design process of stiffened panels. Optimization methods are able to find the best design according to some criteria, by modifying different parametersL'ús de panells rigiditzats a la indústria aeronàutica i aeroespacial ha anat creixent les darreres dècades. Per altra banda, el creixement exponencial de l'ús dels materials compòsits en els últims anys també ha tingut una forta incidència en aquests components estructurals i en la indústria en general. Aquest nous materials fan aparèixer comportaments desconeguts fins al moment, com per exemple l'aparició de nous mecanismes de fallada. Aquests fets provoquen que el càlcul, anàlisi i assaig d'estructures de material compòsit sigui complex. Per aquest motiu, sumat a l'augment de potència de càlcul dels ordinadors, l'assaig virtual amb el mètode dels elements finits ha anat agafant una importància cabdal en el càlcul de components d'alta responsabilitat estructural. De la mateixa manera, l'intent de millorar els panells rigiditzats ha portat a utilitzar mètodes d'optimització. Modificant diferents paràmetres es busca dissenyar panells rigiditzats per realitzar una tasca desitjada de manera òptim

Anàlisis, gestió de projecte executiu i licitació amb comparatius, previ contracte d'obra: control de despesa directa d'obra

Una gestora d’obres rep un projecte, revisa, licita, contracte, controla i lliure una obra. L’empresa fa un pas més i no només es queda amb la part executiva d’obra sinó que també entra de ple en la fase de projecte, auditant i projectant al costat de l’arquitecte, l’enginyer o de qualsevol altre Direcció Facultativa, amb la finalitat d’obtenir una qualitat excel·lent de projecte i posteriorment de licitació.... De manera inicial, un promotor desconeix que es pugui fer gestió de projecte, però és la clau per poder tenir un bon control de l’obra en una segona fase. L’objectiu d’una gestora és tenir un Projecte Executiu similar a un “manual de muntatge” de qualsevol estri que es pugui arribar a comprar per muntarse’l un mateix

Implementation and Testing of Two Bee-Based Algorithms in Finite Element Model Updating

Finite Element Model Updating has recently arisen as an issue of vast importance on the design, construction and maintenance of structures in civil engineering. Many algorithms have been proposed, developed and enhanced in order to accomplish the demands of the updating process, mainly to achieve computationally efficient programs and greater results.The present Master Thesis proposes two new algorithms to be used in Finite Element Model Updating: the Bees Algorithms (BA) and the Artificial Bee Colony algorithm (ABC). Both were first proposed in 2005, are based on the foraging behaviour of bees and have been proved to be efficient algorithms in other fields. The objective of this Master Thesis is, thus, to implement and to test these two newalgorithms in Finite Element Model Updating for a cantilever beam. The Finite Element Model and the algorithms are programmed, followed by the extraction of the experimental frequencies and the updating process. Results, comparison of these two methods and conclusions are given at the end of this report, as well as suggestions for further work

Frequency effects of pedestrian loads on footbridges

Current Standards suggest for a footbridge dynamic analysis periodic load models which do not consider the imperfection nature of human walking. They not only do not represent pedestrian dynamic loads precisely but also exaggerate a tuned mass damper efficiency. The purpose of this study was to expose this lack of realistic load formulation and the differences obtained between a footbridge response by means of the Standard models and a more realistic loading scenario which considered the existent frequency scatter in walking loads. Another aim was to show the tuned mass damper loss of reduction when a frequency scatter was introduced to pedestrian dynamic loads. The study started with a literature survey which allowed the author to understand and collect what researchers had developed so far regarding footbridge analysis. Next, a dynamic analysis was carried out by applying periodic and near-periodic walking loads to a finite element footbridge, and running a time integration dynamic analysis in order to obtain the structure response under each loading scenario. The results indicated that existing load models underestimate in some cases the levels of vibrations reached by a footbridge, compared to the footbridge response obtained by means of a more realistic loading scenario. Moreover, it was found that indeed a tuned mass damper amplitude reduction becomes overestimated when near-periodic walking loads are used. All the results obtained by the simulations were compared to existing formulation in order to prove its accuracy. The principal conclusion was that actual Standards do not represent human-induced loads in a precise way and, as a consequence, tuned mass dampers designed according to them are expected to provide an amplitude reduction which cannot be reached.Outgoin

Frequency effects of pedestrian loads on footbridges

Current Standards suggest for a footbridge dynamic analysis periodic load models which do not consider the imperfection nature of human walking. They not only do not represent pedestrian dynamic loads precisely but also exaggerate a tuned mass damper efficiency. The purpose of this study was to expose this lack of realistic load formulation and the differences obtained between a footbridge response by means of the Standard models and a more realistic loading scenario which considered the existent frequency scatter in walking loads. Another aim was to show the tuned mass damper loss of reduction when a frequency scatter was introduced to pedestrian dynamic loads. The study started with a literature survey which allowed the author to understand and collect what researchers had developed so far regarding footbridge analysis. Next, a dynamic analysis was carried out by applying periodic and near-periodic walking loads to a finite element footbridge, and running a time integration dynamic analysis in order to obtain the structure response under each loading scenario. The results indicated that existing load models underestimate in some cases the levels of vibrations reached by a footbridge, compared to the footbridge response obtained by means of a more realistic loading scenario. Moreover, it was found that indeed a tuned mass damper amplitude reduction becomes overestimated when near-periodic walking loads are used. All the results obtained by the simulations were compared to existing formulation in order to prove its accuracy. The principal conclusion was that actual Standards do not represent human-induced loads in a precise way and, as a consequence, tuned mass dampers designed according to them are expected to provide an amplitude reduction which cannot be reached.Outgoin

Virtual test of stiffened panels of composite materials under compression load

Tese de mestrado integrado. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto, Escola Politècnica Superior. Universitat de Girona. 200

Anàlisi del creixement del coxal a partir de material ossi i les seves aplicacions en la Medicina Forense i l'Antropologia

En l'estudi de restes osteològiques, l'os coxal és un element important tant per a la determinació sexual com per a l'estimació de l'edat. Malgrat l'existència d'una extensa bibliografia no sempre els problemes metodològics han estat ben resolts, sobretot en els coxals infantils. El problema rau principalment en la manca d'un estudi dels canvis que tenen lloc en els elements del coxal durant el creixement. Els estudis de creixement a partir de material osteològic resulten difícils de realitzar a causa de la dificultat de comparació de les mesures infantils amb les adultes. No obstant, aquest problema és de fàcil solució si és té la localització precisa del punt acetabular com a punt de referència a totes les edats. A partir de 327 individus d'edats compreses entre el naixement i els 97 anys, pertanyents a quatre col·leccions europees, es planteja la localització exacta del punt acetabular mitjançant una anàlisi morfològica, i l'estudi del comportament del creixement de 25 variables mètriques, comparables entre adults i subadults, mitjançant la regressió polinòmica. El punt acetabular en els coxals immadurs està clarament representat pel punt d'unió en la fossa acetabular i per les línies de fusió de cada element del coxal. En els ossos coxals adults s'observa que la fossa acetabular té forma de trèvol. La comparació de la morfologia acetabular dels coxals immadurs amb els coxals madurs suggereix que el punt acetabular dels coxals adults està sempre representat per la indentació entre el lòbul superior i l'anterior de la fossa acetabular. Malgrat l'ampli espectre de temps i la diversitat genètica de la mostra, sempre ha estat possible la localització del punt acetabular, no observant-se variabilitat ni intra ni inter observador. A diferència dels mètodes clàssics la variabilitat observada en la fossa acetabular és causada per la variabilitat del mateix punt acetabular. Aquest mètode resulta d'aplicació simple i permet realitzar estudis del coxal amb variables amb major sentit anatòmic i comparables tant entre els individus infantils i adults d'una mateixa població com entre poblacions diferents. Per aquesta raó aquest punt, el punt acetabular anatòmic és el punt que s'utilitza en el nostre estudi mètric. En l'estudi mètric s'observa que les quatre sèries estudiades tenen unes dimensions corporals semblants i les diferències principals no estan en la robustesa sinó en les proporcions pèlviques de la sèrie britànica respecte a les ibèriques. La mostra presenta un desenvolupament semblant al de la població actual d'Europa occidental. Les edats d'inici del brot puberal i de maduresa acetabular (edat d'unió dels elements acetabulars) entren dins els intervals d'edat que es consideren normals per a la població actual. Per altra banda, el comportament de les corbes de creixement de les mesures analitzades és molt igual al trobat en mesures semblants o relacionades a les d'aquest estudi en població actual. Les variables verticals presenten un comportament lineal amb una taxa de creixement constant i les variables horitzontals presenten un alentiment del creixement abans del brot puberal. S'ha evidenciat creixement en el coxal fins als 25 anys aproximadament, en la longitud del pubis, l'amplada de l'escotadura ciàtica, l'índex isquiopúbic i l'índex de l'escotadura ciàtica en els dos sexes, i en la longitud de l'isqui en el sexe masculí. Aquest creixement és difícil atribuir-lo a una maduració retardada de les sèries analitzades perquè, com s'ha vist anteriorment, el desenvolupament d'aquestes sèries és comparable al de la població actual. Aquest fet permet afirmar que el creixement de la longitud del pubis i l'amplada escotadura cotilociàtica en els dos sexes i la longitud de l'isqui en la sèrie masculina dura fins al voltant dels 25 anys. Per altra banda, també s'ha observat l'increment amb l'edat, en els dos sexes, de l'amplada cotilociàtica, l'altura del coxal, l'amplada de l'ili i la disminució de l'amplada de l'escotadura ciàtica i l'índex cotilociàtic. Aquestes variacions són causades pel creixement en gruix de l'os a causa de l'aposició en el periosti. En l'anàlisi de les diferències sexuals no s'observa dimorfisme sexual durant els 9 primers anys de vida, excepte en l'índex isquiopúbic que ha resultat significatiu entre els 0 i 5 anys. Malgrat només es trobin diferències sexuals en l'índex isquiopúbic, també resulten interessants durant els primers 9 anys de vida la resta d'índexs analitzats. També semblen tenir possibilitats les variables absolutes relacionades amb el diàmetre acetabular, però fan falta més dades per a poder-ho confirmar. Les variables més significatives en la discriminació sexual del coxal adult: longitud de l'isqui, amplada cotilociàtica, altura del coxal, índex del coxal, diàmetre acetabular, i les variables relacionades amb el diàmetre acetabular proposades en aquest treball. L'amplada cotilociàtica i l'altura del coxal i els índexs analitzats no són recomanables per a l'estudi del creixement del coxal ni per a la determinació de l'edat a causa de la gran dispersió. Les variables recomanables per l'estimació de l'edat són la longitud de l'isqui, l'amplada de l'ili, la longitud de l'ili. De totes elles la més interessant és la longitud de l'isqui, pel fet de tenir l'expressió matemàtica més senzilla, una funció de primer grau. La relació de l'edat i la longitud de l'isqui es manté en la funció inversa, cosa que fa molt fàcil el càlcul de l'edat. També és interessant per la manca de diferències sexuals durant tota l'etapa de creixement.In the analysis of osteological remains, the coxal bone is an important element for both sexual determination and age at death estimation. In spite of the extensive bibliography about these topics, there are some methodological problems specifically in the subadult coxal. This is due to the lack of a study about the coxal changes during growth from osteological material. This kind of studies are difficult because the subadult measures are not comparable with adult measures. However, this problem will be easy resolved using the acetabular point as a reference point between adults and subadults. For this reason the aim of this work is to provide the location of the acetabular point based on a morphological study, and to analyse the growth of 25 metrical variables which are comparable between adults and subadults based on polynomial regression. The material used was 327 individuals age ranging from new-borns to 97 years and belonging to four European collections with sex and age known.The acetabular point in immature coxal bones is clearly represented by the point of fusion lines for each bony element of the coxal bone at the acetabular fossa level. In the adult coxal bones, the acetabular fossa has an irregular clover-leaf shape and, the superior lobe is smaller than the anterior and posterior lobes. The cross-sectional analysis of the acetabular morphology suggests that the acetabular point in adult coxal bones is always represented by the indentation between the superior and the anterior lobe of the acetabular fossa. In the metrical study of the present work, in spite of some differences in the pelvic proportions between the Britannic population respect Iberian ones No differences statistically significant in corporal size are found. The development of the analysed sample is like the contemporary European population. The start of the puberal growth spurt and the acetabular maturity (age of fusion of the three acetabular elements) are into the normal ranges for the contemporary population. On the other hand, the behaviour of the growth curves from the analysed variables in the present study is similar to the curves obtained for similar or relating measures in the actual population. The vertical variables have a lineal behaviour with a constant growth tax. The horizontal variables have a no constant growth tax, they present a decreasing tax before the start of the puberal growth spurt. The present study shows growth into the coxal until 25 years of age approximately, specifically in the pubic length, sciatic notch width, ischium-pubic index, sciatic notch index in both sexes, and the ischium length in the masculine sex. We can not attribute this growth to the delay in the maturation of the analysed series because, as previously previously, the development of the series are similar to the contemporary European population. This permits us to affirm that the growth into the pubic length, the sciatic notch width in both sexes and the ischium length in masculine sexe is until 25 years approximately. In the other hand, we can also observe increase of the cotylosciatic width, coxal height and ilium width and the decrease of the sciatic notch in both sexes related with ages. This variations are caused for the apposition on the periostium. With respect the sexual differences we did not observe significative differences after 10 years old, with the exception at the ischium-pubic index between 0 to 5 years. The ischium-pubic index is the only variable with significative differences, however also seems interesting for the sexual discrimination the absolute variables relating with the diameter of acetabulm; but it would be necessary more data to confirm this observation. The variables more significatives in the sexual discrimination of the adult coxal are: ischium length, cotylosciatic index, coxal height, coxal index, acetabular diameter and the variables relating with de acetabular diameters described in this study. The cotylosciatic width, coxal height and the analysed index are not recommendable either for the growth analysis nor for age estimation due to his big dispersion. The recommended variables for age estimation are the ischium length, ilium width and ilium length. The most interesting is the ischium length due to the lack of sexual differences into this variable during growth. This is important in archaeological material where the sex is unknown

Implementation and testing of two bee-based algorithms in finite element model updating

Finite Element Model Updating has recently arisen as an issue of vast importance on the design, construction and maintenance of structures in civil engineering. Many algorithms have been proposed, developed and enhanced in order to accomplish the demands of the updating process, mainly to achieve computationally efficient programs and greater results. The present Master Thesis proposes two new algorithms to be used in Finite Element Model Updating: the Bees Algorithms (BA) and the Artificial Bee Colony algorithm (ABC). Both were first proposed in 2005, are based on the foraging behaviour of bees and have been proved to be efficient algorithms in other fields. The objective of this Master Thesis is, thus, to implement and to test these two new algorithms in Finite Element Model Updating for a cantilever beam. The Finite Element Model and the algorithms are programmed, followed by the extraction of the experimental frequencies and the updating process. Results, comparison of these two methods and conclusions are given at the end of this report, as well as suggestions for further work

Frequency effects of pedestrian loads on footbridges

Current Standards suggest for a footbridge dynamic analysis periodic load models which do not consider the imperfection nature of human walking. They not only do not represent pedestrian dynamic loads precisely but also exaggerate a tuned mass damper efficiency. The purpose of this study was to expose this lack of realistic load formulation and the differences obtained between a footbridge response by means of the Standard models and a more realistic loading scenario which considered the existent frequency scatter in walking loads. Another aim was to show the tuned mass damper loss of reduction when a frequency scatter was introduced to pedestrian dynamic loads. The study started with a literature survey which allowed the author to understand and collect what researchers had developed so far regarding footbridge analysis. Next, a dynamic analysis was carried out by applying periodic and near-periodic walking loads to a finite element footbridge, and running a time integration dynamic analysis in order to obtain the structure response under each loading scenario. The results indicated that existing load models underestimate in some cases the levels of vibrations reached by a footbridge, compared to the footbridge response obtained by means of a more realistic loading scenario. Moreover, it was found that indeed a tuned mass damper amplitude reduction becomes overestimated when near-periodic walking loads are used. All the results obtained by the simulations were compared to existing formulation in order to prove its accuracy. The principal conclusion was that actual Standards do not represent human-induced loads in a precise way and, as a consequence, tuned mass dampers designed according to them are expected to provide an amplitude reduction which cannot be reached.Outgoin

Damage tolerance optimization of composite stringer run-out under tensile load

Stringer run-outs are a common solution to achieve the necessary strength, stiffness and geometric requirements of some structural solutions. The mechanical behavior and complexity of such design details requires careful and thorough studies to ensure the structural integrity of the structure. The influence of some geometric variables of the run-out in the interface of the set stringer-panel is crucial to avoid the onset and growth of delamination cracks. In this study, a damage tolerant design of a stringer run-out is achieved by a process of design optimization and surrogate modeling techniques. A parametric finite element model created with python was used to generate a number of different geometrical designs of the stringer run-out. The relevant information of these models was adjusted using Radial Basis Functions (RBF). Finally, the optimization problem was solved using Quasi-Newton method and Genetic Algorithms. In the solution process, the RBF were used to compute the objective function: ratio between the energy release rate and the critical energy release rate according to the Benzeggagh–Kenane mixed mode criterion. Some design guidelines to obtain a damage tolerant stringer-panel interface have been derived from the resultsThe authors wish to acknowledge the Ministerio de Economía y Competitividad for the funding of the project MAT2013-46749-R and particularly to Universitat de Girona for the research Grant coded as BR2011/0