A vibration harvester is usually designed to work in resonance responding to source vibration. However, in many cases, this source vibration may occur at a wide range of frequencies. If the harvester has very narrow tuning range, it becomes ineffective when there is a mismatch in the frequencies between source excitation and device resonance. Increasing the bandwidth of vibration harvesters has been an important design objective. We propose a two-stage design to improve of a harvester's performance. In a previous work [J. S. Fernando and Q. Sun, Rev. Sci. Instrum. 84(11), 114704 (2013)], we have demonstrated that use of a two-stage design can increase the power production at a single frequency excitation. In this paper, we will show that a two-stage design can also increase the width of the usable frequency band of the harvester. An optimization routine was used to determine the optimal choice of harvester design parameters with respect to the maximization of an objective function. Experiments were used to verify the electromechanical model as well as the trends predicted by the optimization. Performance comparisons between single- and two-stage harvesters are made through numerical simulation and experiments.
Clutch judder causes discomfort in a car. This undesirable event not only creates noise and vibrations, it also disturbs the normal functionality of other components in the driveline, especially the gearbox, which is prone to oscillating inputs. Although there are numerous separate studies on clutch judder and gearbox vibrations, a combined study is necessary in order to investigate the coupled dynamics, especially the effect of vibrations in a clutch on gearbox vibrations. In this paper, a dynamic model is presented for the driveline, including the details of a gearbox and a dry clutch. It allows us to investigate the effect of clutch parameters and to simulate conditions with and without judder. The obtained dynamical equations are then solved numerically. The influence of judder on gear dynamics and passenger comfort is investigated. The results show that judder causes loss of contact in the gearbox in most cases. In more severe cases of judder, it can cause rattle not only in the unloaded gear, but also in the loaded gears. A modal analysis and a frequency spectrum analysis are conducted as well in order to identify the frequency components of the system vibrations and to verify the obtained results. Parts of the results are compared with the theoretical and experimental data from other research studies, which show agreement and serve to validate the model in this work.
A vibration harvester is usually designed to work in resonance responding to source vibration. Many existing types of harvesters use a single mechanical resonator to amplify the excitation vibrations. However, these harvesters are inherently limited in the amount of power that they can produce, due to their design, particularly in the limited number of design parameters. In our study, we propose a two-stage design to improve a harvester's performance both in power production and in bandwidth widening. In this paper, we demonstrate that a two-stage design can increase the power production when the device is intended to operate under a single frequency excitation. Harvester parameters are optimized to provide maximum power production. Power production comparisons between single-stage and two-stage harvesters are made through numerical simulation and experiments.
This paper is concerned with modeling methodologies using a combined physics-based and data-driven approach. The purpose of such models is to assist machinery fault diagnosis, root cause analysis, and system failure prediction. Particularly, we focus on capturing a class of faults, which, when developed in a physical system, would manifest themselves as "new dynamics". In other words, they are not present in healthy conditions. Examples include joints and connectors in multi-body systems. Under healthy conditions, they are typically represented by ideal boundary conditions. However, when faults have developed, they become entities with dynamic responses to input excitations. We propose a Bayesian inference-based methodology to detect the development of these new dynamics through model parameter uncertainty quantification. We demonstrate the effectiveness of this method through numerical experiments on a rotating mechanical system.
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