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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Natural frequency and transient dynamic analysis of vehicle integrated RBS 70 NG system

Kadhim, Ammar January 2018 (has links)
Abstract This study is a master thesis in mechanical engineering at Karlstad’s University that treats operation disturbances that occur during the use of a vehicle integrated air-defense system called Robot-system 70 New Generation (RBS 70 NG) in cooperation with SAAB Dynamics AB. RBS 70 NG is a man-portable air-defense system (MANPADS) which is designed for anti-aircraft warfare and can be used in all climate zones.  The system usually operates on a hard surface such as gravel or hard soil, but for this project the aim is to integrate the system to operate on a vehicle platform. There are two disturbing factors that could affect the system during operation; the first is that the system is displaced due to the external forces that act on the system during use. The second disturbance specification is that the natural frequency of the entire system should be within a range of 3.5-6 Hz for vehicles installed RBS 70 NG [1]. The system is studied by using a simple mathematical model and by the use of computer aided software programs including CATIA V5 R22 and ANSYS R18.1. The modified design of the complete system showed that by adding four external legs to the platform, a natural frequency in-between the given interval is reached. A Transient Response Analysis was done to analyze the MANPADS ground version in order to make have some sort of a reference when studying the vehicle version of the RBS 70 NG and to make both system as similar as possible. The displacement of the system sight was similar for both versions of the system, when operating on the ground and on a vehicle. / Sammanfattning Den här studien är ett examensarbete inom maskinteknik på Karlstads Universitet, som behandlar driftstörningar för ett fordon integrerat ”Robotsystem 70 New Generation” i samarbete med SAAB Dynamics AB. Robotsystem 70 (RBS 70 NG) är ett luftvärnsrobotsystem som tillverkas i Sverige av SAAB Dynamics AB. Systemet används vanligtvis på hårda underlag som till exempel mark och grus, men i den här rapporten studeras integrationen av systemet på ett fordons plattform. Två störningsspecifikationer uppkommer vid användning av RBS 70 NG som tas hänsyn till, den första är att systemets förskjutning som exciteras via de krafter som uppkommer vid utskjutning inte stör systemet under drift. Den andra störningsspecifikationen är att den naturliga frekvensen för hela systemet bör ligga på ett intervall mellan 3,5–6 Hz för fordon installerat RBS 70 NG [1]. Analyserna har gjorts dels genom en förenklad teoretisk modell av systemet och genom användning av datorbaserade program såsom CATIA V5 R22 och ANSYS R18.1. Konstruktions ändringar på plattformen gjordes för att uppnå den minimala gränsen på egenfrekvensen på ca 3,5 Hz. Montering av fyra externa stödben på plattformen gav godkända värden på egenfrekvensen. En så kallad ”Transient Response Analysis” utfördes med hjälp av ANSYS R18.1 som visade att systemet utan konstruktions ändringar förskjuts med mindre än det minimala tillåtna värdet som tidigare beskrivet och att de pålagda krafterna inte var tillräckligt stora för att störa systemets drift.
2

AnÃlise transiente paramÃtrica de sistema poste-defensa devido ao choque de veÃculos

Janiel Silva de Queiroz 28 November 2011 (has links)
Sabe-se que à inevitÃvel a ocorrÃncia de acidentes de trÃnsito em rodovias, onde centenas de milhares de veÃculos transitam a cada dia e que, alÃm de gerarem fatalidades, geram danos materiais, fÃsicos e morais Ãs pessoas envolvidas. Quando os acidentes envolvem colisÃes com um poste de distribuiÃÃo de energia elÃtrica, estes sÃo responsÃveis por deixar, em mÃdia, cinco mil residÃncias sem fornecimento de energia de forma imediata. Nestes casos, essa interrupÃÃo no fornecimento pode durar atà quatro horas para os moradores prÃximos ao local da colisÃo devido ao trabalho de substituiÃÃo, bem como gerar altos custos com a reposiÃÃo dos postes. Portanto, faz-se necessÃrio o estudo de um sistema de defensa de postes visando à proteÃÃo destes, bem como salvaguardar os motoristas de veÃculos em caso de colisÃo. O objetivo deste trabalho consiste em avaliar o comportamento do poste e do sistema poste-defensa devido ao choque de veÃculos. Para tanto, sÃo realizadas duas anÃlises paramÃtricas. A primeira consiste na anÃlise modal numÃrica a fim de se determinar a influÃncia de componentes tais como cabos e defensas nos parÃmetros naturais do poste. A segunda consiste na anÃlise transiente paramÃtrica do poste e do conjunto poste-defensa. Neste caso, sÃo variadas a massa do veÃculo, sua velocidade e o tempo de impacto. Estas anÃlises sÃo realizadas no programa comercial, baseado no MÃtodo dos Elementos Finitos, SAP2000 V.14.0. A histÃria no tempo do deslocamento da extremidade livre do poste à comparada entre os diversos modelos, bem como com os resultados das amplitudes das cargas dinÃmicas aplicadas de forma estÃtica. Dos resultados observa-se que a defensa cumpre seu papel diminuindo a possibilidade de colapso devido aumentar as frequÃncias naturais e afastando-as das frequÃncias de excitaÃÃo das cargas de impacto. Da anÃlise transiente conclui-se que a defensa aumenta a rigidez do sistema reduzindo os deslocamentos. / It is known that is inevitable the incidence of traffic accidents in highways, where hundreds of thousands of vehicles pass daily. These accidents can cause material damages, physical and moral injuries to involved persons, besides fatalities. When collisions are into an electric distribution pole, these are responsible by five thousand residences without electric power immediately. In this case, the stop in supplying can take four hours to residents who live close to accident site due to replacement work, as well as to generating high costs to replace the poles. So, it is necessary to study a system that protects the pole, as well as safeguards the vehicles drivers in case of collision. The objective of this work is to evaluate the behavior of pole and of system pole-defence due to the vehicles shock. Two parametric analyses are carried out. The first one is the numerical modal analysis in order to determine the influence of components like cables and defence in the pole natural parameters. The second one is the transient parametric analysis of pole and of pole-defence system. In this case, the vehicle mass and his impact time are varied. These analyses are executed in the commercial program based on the Finite Elements Method, SAP2000 V.14.0. The displacement history of pole free end is compared between the several models, as well as with the results obtained when the dynamic load maximum value is applied statically. From results it is noticed that defence carries out his paper reducing the possibility of collapse due to increasing the natural frequencies and making away from excitation frequencies of impact loads. From transient analysis it is concluded that defence raises the rigidity of the system by reducing the displacements.
3

Analyse isogéométrique multiéchelle à précision contrôlée en mécanique des structures / Multiscale isogeometric analysis with controlled accuracy appiled to structural mechanics

Chemin, Alexandre 09 November 2015 (has links)
L’analyse isogéométrique pour la résolution de problèmes de la mécanique du solide suscite de vifs intérêts depuis une dizaine d’année. En effet, cette méthode de discrétisation autorise la description exacte des géométries étudiées permettant ainsi de supprimer les erreurs dues à une mauvaise description du domaine spatial étudié. Cependant elle pose un problème théorique de propagation de raffinement lors de la localisation de maillage. Des méthodes pour contourner ce problème ont été proposée dans la littérature mais complexifient grandement la mise en œuvre de cette stratégie de résolution. Cette thèse propose une stratégie de raffinement localisé adaptatif en espace pour les problèmes de statique et en espace temps pour les problèmes de dynamique transitoire dans le cadre de l’analyse isogéométrique. Pour cela une méthode de localisation pour l’analyse isogéométrique en statique basée sur une résolution multigrille est tout d’abord développée pour des problèmes en deux dimensions. Elle présente l’avantage de contourner la problématique de propagation de raffinement de maillage due à l’analyse isogéométrique tout en étant plus simple à mettre en œuvre que les méthodes déjà existantes. De plus, l’utilisation de l’analyse isogéométrique permet de simplifier les procédures de raffinement lors de l’adaptation de maillage qui peuvent être complexes lors de l’utilisationd’éléments finis classiques. Une méthode de raffinement adaptatif espace temps basée sur une résolution multigrille est ensuite développée pour des problèmes en une dimension. Une étude sur la structure des opérateurs est proposée afin de choisir un intégrateur temporel adapté. Les performances de cette stratégies sont mises en évidence, puis une modification de la méthode de résolution est proposée afin de diminuer significativement les coûts de calculs associées à cette résolution. La méthode de raffinement adaptatif espace temps est appliquée à quelques exemples académiques afin de valider son bon comportement lors de la localisation. / Isogeometric analysis applied to structural mechanics problems is a topic of intense concerns for a decade. Indeed, an exact description of geometries studied is allowed by this discretization method suppressing errors due to a bad description of the spatial domain considered. However, a theoretical problem of refinement propagation appears during mesh localization. Local refinement methods for isogeometric analysis has been developed and implied a complexification of the implementation of such a resolution strategy. This PhD thesis expose a space adaptative refinement strategy for linear elastic problems and a space-time one for transient dynamic using isogeometric analysis. For this purpose, a localization method for isogeometric analysis based on a multigrid resolution is developed for 2D linear elastic problems. This method allow to circumvent mesh refinement propagation inherent to isogeometric analysis, and is easier to implement than existing methods. Moreover, the use of isogeometric analysis simplifies refinement procedures occuring during mesh adaptation and which can be really complex using classical finite element analysis. Then, a space-time adaptative refinement based on a multigrid resolution is developed for one dimensional in space problems. A study on operators structure is exposed in order to choose a well suited time integrator. This strategy's performances are highlighted, then an evolution of this method is set up in order to lower computational costs. The space-time adaptaptive refinement is applied to some academical examples to show it good behavior during localization.

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