Tommaso Tamarozzi

STATIC MODES SWITCHING: ON-LINE VARIABLE STATIC AUGMENTATION FOR EFFICIENT FLEXIBLE MULTIBODY SIMULATION

This paper discusses and further investigates a new methodology, “Static Modes Switching” (SMS), improving computational efficiency for elastic multibody (EMBS) systems. This method focuses on mechanisms in which loading is possible in many degrees of freedom, but only few of them are simultaneously loaded at a given moment in time (e.g. sliding elements, gear contact, etc.). The methodology adapts during simulation the mode set used to represent component flexibility, by judiciously choosing only those static modes that are contributing actively to the body deformation. First, the general methodology is presented, then the current work and its original contributions are discussed; namely SMS is tested on a 3D mechanism including multiple flexible bodies on which sliding elements are present. Moreover, as opposed to previous studies, the locations where external excitation is acting is not known a priori. Finally, some limitations of the proposed methodology are treated with focus on the numerical discontinuities introduced by the switching of the modal base and their propagation to neighbouring bodies.Copyright

Integrating Vehicle Body Concept Modelling and Flexible Multi-Body Techniques for Ride and Handling Simulations

This paper deals with the integration of a vehicle body concept modeling methodology, based on reduced models of beams, joints and panels, with flexible Multi-body (MB) representation of the chassis of a passenger car. The aim is to enable ride and handling simulations in the initial phases of the vehicle design process, where the availability of predictive Computer Aided Engineering (CAE) tools is a key factor to steer design choices such that a faster convergence of the vehicle development cycle towards improved products is achieved.The proposed approach is demonstrated on an industrial case study, involving a commercial passenger car, for which a detailed chassis and suspension model for MB simulations is developed in LMS Virtual.Lab Motion. A flexible concept model of the vehicle’s Body In White (BIW) is created as well and included in the MB model to enable fast investigations on how ride and handling performance of the full vehicle are affected by body modifications.To demonstrate the validity of the resulting concept model, a number of standard handling manoeuvres and ride excitations are simulated by using both the flexible MB model described above and a rigid MB model of the vehicle, which is derived from the same FE model. The numerical results are compared to allow assessing the influence of body flexibility on the predicted handling and ride behaviour of the vehicle.Copyright

Dynamic Behavior of Bearings on Offshore Wind Turbine Gearboxes

Gearbox failure is among the highest causes of downtime in a wind turbine, causing a significant loss to the wind energy sector, especially in the complex offshore environment. Quite often, the cause of these gearbox and drivetrain errors, as well as other undesired noise and vibrations issues, is premature bearing failure. Therefore, developing more efficient and reliable bearing models and simulation methods that can accurately predict the nonlinear dynamic loads already in the design phase is still crucial. Without claims of completeness, a few important items to be considered when analyzing bearings and a state-of-the art review for bearing modelling approaches (from analytical lumped parameter models to complex flexible multibody simulations) will be discussed in this chapter. Furthermore, some recent modelling developments and the problem of integrating these bearing models with similar advanced gear models into flexible multibody simulations at full-scale wind turbine drivetrain level will be addressed.

Efficient Transient Analysis of the High-Speed Stage of a Wind Turbine Gearbox by Advanced Model Reduction Techniques and Memory-Effective Discretization

Modern wind turbines are designed to cope with their increased size and capacity. One of the most expensive components of these machines is the gearbox. Its design is more complex than a mere upscaling exercise from predecessors. The stress levels experienced by the different gear stages, the dynamic effects induced by their size and the unparalleled loads transmitted are some of the challenges that design engineers face. Moreover, unexpected events that load the wind turbines such as voltage dips, wind gusts or emergency breaking are expected to be major contributors to the premature failure of these gearboxes. The lack of engineering experience at this scale calls for accurate and efficient simulation tools thereby enabling reliable gearbox design.Standard lumped-parameters models or rigid multibody approaches do not provide a sufficient level of details to study the dynamic effects induced by e.g. gear design modifications (micro-geometry) or to analyze local stress concentrations.More advanced numerical tools are available such as flexible multibody or non-linear FE and allow to model complex contact interactions including all the relevant dynamic effects. Unfortunately the level of mesh refinement needed for an accurate analysis causes these simulations to be computationally expensive with time scales of several weeks to perform a single full rotation of a gear pair.This work introduces a novel efficient simulation tool for dynamic analysis of transmissions. This tool adopts a flexible multibody paradigm but incorporates several advanced features that allows to run simulations up to two orders of magnitudes faster as compared to non-linear FE with the same level of accuracy. A unique non-linear parametric model order reduction technique is used to develop a simulation strategy that is quasi mesh-independent allowing the usage of very fine FE meshes.Finally, in order to limit the memory consumption, a technique is developed to be able to finely mesh only a few of the gears teeth while the remaining gears are coarsely meshed. The main novelty of this approach lies in the possibility to perform full gear rotations without losing spatial resolution as compared to a finely meshed gear.After an accuracy check performed with a sample pair of helical gears, the framework is used to simulate the high speed stage of a three-stage wind turbine gearbox. The combined efficiency and accuracy of the approach is demonstrated by performing a dynamic stress analysis of the high-speed stage with and without a tip-relief modification. Accuracy of the results, simulation time, and memory usage are assessed.Copyright