Flexible multibody formulations allow the dynamic analysis of mechanisms with slender or thin-walled structures that deform during their operation. However, the majority of the existing flexible multibody methodologies are formulated assuming finite element models featuring 6 nodal degrees of freedom, specifically 3 translations and 3 rotations. This work initially revises the existing flexible multibody methodology in which the modeling of the flexibility is independent of the modeling of the baseline multibody system while ensuring the coupling between the rigid and flexible components. The flexible multibody methodology includes the use of suitable reference conditions, the component mode synthesis, and the virtual bodies methodology. Commonly, solid elements found in finite element software exclusively have three nodal translation degrees of freedom, featuring no explicit angular degrees of freedom. In this work, we propose the enhancement of the existing formulation for a rigid-flexible joint to support the use of virtual bodies rigidly connected to the nodes of solid elements. The computational implementation of the methodology is demonstrated using a benchmark case. The methodology developed in this work is further applied to study the dynamics of a locomotive with a flexible bogie frame. Although not influencing the overall vehicle dynamics, the bogie flexible multibody model allows the evaluation of the PSD of the accelerations in different points of the bogie that are sensitive to structural defects. The comparison of the response of healthy and damaged bogie frames supports the development of tools to monitor the condition of bogie frames during the operation. This development will be explored in forthcoming works, thus expanding the use of flexible multibody methodologies to new applications.
The implementation of a condition-based maintenance policy for railway locomotives requires the development of models and methods to monitor the condition of bogie components using computer simulations, focusing on bogie frame damage and degradation of elements of the suspension system. First, the computational models are verified through the comparison of their results against the actual vehicle response, recorded in an experimental measurement campaign. The variability of the operating conditions and the parameter uncertainty are considered in the definition of the simulations using experimental design techniques. These strategies also contribute to solve the problem of the high computational cost associated with simulations of highly non-linear railway dynamics using detailed vehicle models. The post-processing involves a variety of methods including the analysis of signals in the frequency domain using the concept of transmissibility, in addition to the use of regression and statistical tools to model the vehicle response in the time domain. Condition classification methodologies are proposed to detect and locate damage on the bogie frame and the failure of suspension elements. The final result is the successful development of digital twins for the condition monitoring of the locomotive bogie structural heath and for the suspensions. In the process a methodological framework is presented to allow the use of the developments obtained in other applications for which the identification of physically based digital twins are of importance
The condition monitoring of the suspensions of railway vehicles is of utmost importance, allowing the reduction of the maintenance actions and the increase in the operational safety. However, the available methods often require a simplification of the vehicle through linearised models, a high number of sensors, or the use of complex algorithms that disregard the mechanical phenomena that explain the vehicle dynamics. This work suggests the Localized Transmissibility Damage Indicator (LTDI), based on the existing Transmissibility Damage Indicator (TDI), to detect damage in the springs of a locomotive, using pairs of sensors placed in the bogie frame and the axle boxes. For that purpose, multibody simulations are used to simulate the dynamic behaviour of the vehicle in tangent tracks under nominal and damaged conditions. The results from multibody simulations allow the calculation of the LTDI values for different levels of damage and various operation conditions, as well as the study of the effect of the variability inherent to the railway operation. The results show that the LTDI is significantly sensitive to damage. However, depending on the use of the lateral or vertical response, the LTDI is more suitable to detect the stiffness increase or decrease, or even to locate the damage. In conclusion, the LTDI is a promising method for the detection of damage on suspension elements of railway vehicles.
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