During the assembly of aircraft engines, some clearance is left in the rolling bearings mainly to reduce friction. However this clearance might allow the rolling element to vibrate during flight. Indeed, unwanted vibrations called non-synchronous vibrations (NSV) appear on the data recorded by the sensors on some development engines. NSV can be dangerous for the engine so they are closely monitored.  To prevent the appearance of the NSV, they are investigated by the engineers as soon as they appear during tests. The main source of the NSV is most likely to be the rolling bearings in the rotor because they induce a non-linear behaviour. The bearings of development engines were investigated on Finite Element Method (FEM) software for example but other methods could bring a contribution for the understanding of the NSV.  In this study, a multibody modelling software is used to try to model and explain the observed sub-synchronous vibrations considered as NSV. A model of the rotor of a prototype engine on a FEM software is provided and then reduced to be implemented in the new software. The behaviour of this new model is tested through modal analysis and response to imbalance.  Once the model is properly set, a parametric study is performed to see the effect of the thrust, gravity, imbalance weight and clearance on the system. It shows that clearance and gravity are key parameters while thrust and the imbalance weight have a minor impact on the NSV. This study has also helped to fix the parameters used to reproduce the NSV observed in the experiments.  Then, a second study focus on the influence of the clearance of the roller bearings on the NSV. This study defines a range of clearance that can be implemented on the engine to avoid the NSV. It also proved that the vibrations were very sensitive to a small change in the clearance values.  Finally, by studying the previous configurations, a link between the stiffness of the bearing and the occurrence of the NSV was established. In fact, the NSV appear only when the two roller bearings both have no stiffness because the clearance is not filled by the radial load. The rolling element is thus free to vibrate in its ring. It was noticed that the NSV has more chance to occur if it has already come out earlier in the run-up of the engine.  The multibody software is therefore perfectly able to reproduce the vibrations in a rotor. It is now a tool that can be used during the development process. / Vid montering av flygplansmotorer lämnas ett spelrum i rullningslagren främst för att minska friktionen. Detta spelrum kan emellertid tillåta att rullelementet vibrerar under flygning. Faktum är att oönskade vibrationer som kallas non-synchronous vibrations (NSV) visas på data som registreras av sensorerna på utveckling motorerna. NSV kan vara farligt för motorn och övervakas därför noggrant.För att förhindra uppkomsten av NSV utreds de regelbundet av ingenjörerna. Den huvudsakliga källan till NSV är troligen rullager i rotorn eftersom de inducerar ett icke-linjärt beteende. Lagren för utveckling motorer undersöktes till exempel med Finita Element-metoden (FEM) programvara men andra metoder skulle kunna bidra till förståelsen av NSV. I denna studie används en multibody-modelleringsprogramvara för att försöka modellera och förklara de observerade subsynkrona vibrationerna som betraktas som NSV. En modell av rotorn till en utveckling motor tillhandahålls i ett FEM-program och reduceras sedan för att implementeras i den nya mjukvaran. Beteendet hos denna nya modell testas genom modal analys och respons på obalans. När modellen är inställd utförs en parametrisk studie för att se effekten av dragkraften, gravitationen, obalansvikten och frigången i systemet.Den visar att frigång och gravitation är nyckelparametrar medan dragkraft och obalansvikt har en mindre inverkan på NSV. Denna studie har också hjälpt till att bestämma de parametrar som används för att reproducera NSV som observerats i experimenten. Därefter fokuserar en andra studie på inverkan av rullagernas frigång på NSV. Denna studie definierar ett intervall av spelrum som kan implementeras på motorn för att undvika NSV. Det visade sig också att vibrationerna var mycket känsliga för en liten ändring av frigångsvärdena.Slutligen, genom att studera de tidigare konfigurationerna, etablerades en koppling mellan lagrets styvhet och förekomsten av NSV. Faktum är att NSV endast visas när de två rullagren båda inte har någon styvhet eftersom spelet inte fylls av den radiella belastningen. Rullelementet är således fritt att vibrera i sin ring. Det märktes att NSV har större chans att inträffa om den redan sker tidigare i motorns start. Multibody-mjukvaran är därför perfekt för att reproducera vibrationerna i en rotor. Det är nu ett verktyg som kan användas under utvecklingsprocessen.

CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico / FAPEMIG - Fundação de Amparo a Pesquisa do Estado de Minas Gerais / INCT-EIE - Instituto Nacional de Ciência e Tecnologia De Estruturas Inteligentes em Engenharia / Os sistemas de suspensão automotivos são projetados para permitir que o condutor tenha controle total do veículo. Esses sistemas devem garantir com eficiência o isolamento de vibração para o interior do automóvel, a aderência entre os pneus e o solo e a estabilidade do veículo durante a execução de manobras que envolvam mudança de direção. Neste trabalho foi conduzida uma investigação experimental sobre o comportamento dinâmico de um veículo de passeio da categoria hatch compacto premium. Manobras específicas de handling e ride foram consideradas nos testes físicos, a fim de avaliar a resposta do sistema de direção e o conforto dos passageiros. Handling se refere ao modo como o veículo se comporta durante a execução de manobras de mudança de direção e ride se relaciona à forma como a suspensão do veículo responde as irregularidades de pista durante o ato de dirigir. O trabalho de pesquisa contempla a definição de uma metodologia aplicada ao desenvolvimento de um modelo completo de veículo, através do método de multicorpos. Na modelagem matemática, a maioria dos componentes de suspensão foram considerados como rígidos, visto que as deformações elásticas são suficientemente pequenas, podendo assim serem consideradas desprezíveis. No entanto, é considerada a presença de alguns elementos flexíveis, em particular a barra estabilizadora e o eixo de torção, que se revelam essenciais na tentativa de construção de um modelo capaz de reproduzir adequadamente os efeitos não lineares. Nesse sentido, a barra estabilizadora foi representada como um corpo flexível, com o objetivo de incluir a sua não linearidade geométrica no modelo. Já a modelagem do eixo de torção foi baseada em uma técnica de cossimulação que utiliza um solver de multicorpos e um solver externo de elementos finitos para análise não linear. Simulações do comportamento dinâmico foram realizadas a fim de verificar a abrangência do modelo e correlação com os dados experimentais. O estudo de ride é apresentado enfatizando a métrica necessária para quantificar o conforto do veículo, de acordo com a norma ISO 2631-1. Os dados coletados experimentalmente foram processados no domínio da frequência e do tempo utilizando o software LMS Test.Lab. O processo de construção e simulação do modelo virtual foi realizado utilizando o software LMS Virtual.Lab Motion para a simulação de multicorpos e o LMS Samcef MECANO para a simulação de elementos finitos. / Automotive suspension systems are designed to allow the driver full control of the vehicle. These systems must efficiently ensure the vibration insulation of the car cabin, the tire grip on the road and the vehicle’s stability during turning maneuvers. In this study, an experimental investigation of the dynamic behavior of a subcompact premium car was conducted. Typical ride and handling maneuvers were considered in the physical tests in order to evaluate the steering response and passengers comfort. Vehicle handling refers to the way that the vehicle performs during turning maneuvers, and ride to how the vehicle suspension responds to the track irregularities during the act of driving. This work describes the methodology used for the development of a full vehicle model through the multibody method. In mathematical modeling, the majority of vehicle suspension components were included in the model as rigid bodies, due to the fact the elastic deformations are sufficiently small and hence negligible. However, there is the presence of some flexible elements, in particular the stabilizer bar and the twist beam, which are essential in the attempt to build a model capable of properly reproducing the nonlinear effects. Accordingly, the stabilizer bar was represented as a flexible body, in order to include geometric non-linearity into the model. The modeling of the twist beam was based on a co-simulation technique that uses a multibody solver and an external nonlinear solver for finite element method analysis. Dynamic behavior simulations were performed to verify the scope of the model and correlated with the experimental data. The ride comfort study was carried out emphasizing the required metric to quantify the vehicle comfort according to ISO 2631-1. The data collected were processed and analyzed in frequency and time domain using the LMS Test.Lab software. The building and simulation of the virtual model was performed using the LMS Virtual.Lab Motion software for the multibody simulation and LMS Samcef MECANO software for the finite element simulation. / Dissertação (Mestrado)