Wei-Jiun Su

The Performance Improvements of Train Suspension Systems with Mechanical Networks Employing Inerters

This paper investigates the performance benefits of train suspension systems employing a new mechanical network element called an inerter. An inerter is a true mechanical two-terminal element with the applied force proportional to the relative acceleration across the terminals. Until now, ideal inerters have been applied to car and motorcycle suspension systems, for which a significant performance improvement was reported. In this paper, we discuss the performance benefits of train suspension systems employing inerters. The study was carried out in three phases. First, fixed suspension structures were applied to train suspension systems, and optimised for two performance measures. Secondly, this optimisation was further carried out using linear matrix inequality approaches to discuss the achievable performance of passive networks. The resulting networks can then be realised by synthesis methods, such as the Brune and Bott–Duffin realisation. Finally, the nonlinear properties of inerter models and their impact on system performance were discussed. From the results, the inerter was deemed effective in improving the performance of train suspension systems.

Impact of inerter nonlinearities on vehicle suspension control

This paper discusses the nonlinear properties of inerters and their impact on vehicle suspension control. The inerter was recently introduced as an ideal mechanical two-terminal element, which is a substitute for the mass element, where the applied force is proportional to the relative acceleration across the terminals. Until now, ideal inerters have been applied to vehicle, motorcycle and train suspension systems, in which significant performance improvement was achieved. However, due to the mechanical construction, some nonlinear properties of the existing mechanical models of inerters are noted. This paper investigates the inerter nonlinearities, including friction, backlash and the elastic effect, and their influence on vehicle suspension performance. A testing platform is also built to verify the nonlinear properties of the inerter model.

Modeling and analyses of a connected multi-car train system employing the inerter:

This article develops the model of a connected multi-car train system and discusses the improvement of stability and performance by the inerter. The inerter is a genuine two-terminal element, whose reacting force is proportional to the relative acceleration across its terminals. First, we build a 31-degree-of-freedom full-train model by a multi-body package, called AutoSim, and show that its stability can be significantly improved by the inerter. Second, we derive a multi-car train model, by another multi-body package, called SimMechanics, and discuss the impacts of the number of connected cars on system stability: connecting cars tends to decrease the critical speed. Furthermore, we extend the discussion to performance and show that the connecting cars will increase the settling time, but has no influence on the passenger comfort. Finally, we apply network synthesis methods to realize a mechatronic network and conduct experimental verification. Based on the results, the inerter is deemed effective in improving the stability and performance of connected multi-car trains.

Design and development of a broadband magnet-induced dual-cantilever piezoelectric energy harvester

In this article, a broadband magnet-induced dual-cantilever piezoelectric energy harvester is designed and developed. The dual-cantilever structure consists of an outer and an inner beams with magnets attached to the tips. The magnets generate nonlinear repulsive force between the two beams and make the structure bistable. In the theoretical model, each beam is considered as a single-degree-of-freedom system with magnetic force applied at the free end. From the simulation results, chaotic motion is observed in a wide frequency range. A prototype of the harvester is built and verified with the simulation results. The simulation and experimental results show good agreement with respect to the power bandwidth and amplitude. The distance between magnets is adjusted to observe its effect on the power response of the harvester. The inner and outer beams are simulated and tested independently first to observe the performance of each beam. Finally, an interface circuit is designed to combine all piezoelectric plates to acquire the overall performance. By comparing with the traditional piezoelectric energy harvester, the new design is shown to provide a significant improvement in bandwidth.

An innovative tri-directional broadband piezoelectric energy harvester

This paper presents a tri-directional piezoelectric energy harvester that is able to harvest vibration energy over a wide bandwidth from three orthogonal directions. The harvester consists of a main beam, an auxiliary beam, and a spring-mass system, with magnets integrated to introduce nonlinear force and couple the three sub-systems. Theoretical analysis and experiments were performed at constant acceleration under frequency sweeps to acquire frequency responses. The experimental results show that the voltage can achieve more than 2 V over more than 5 Hz of bandwidth with 1 MΩ load in the three orthogonal directions.

Broadband energy harvesting through a piezoelectric beam subjected to dynamic compressive loading

This paper investigates the design and analysis of a broadband piezoelectric energy harvester that uses a simply supported piezoelectric beam compressed by dynamic loading. The beam is restrained at one end and carries a moving mass at the other end where a magnetic force is applied axially. Taking advantage of the flexibility of the slender beam and the nonlinearity of the magnetic force, the design aims to enhance the harvesters functionality with a broad frequency bandwidth. Both theoretical and experimental investigations are performed in this study over a range of excitation frequencies. Specifically, the electromechanical model of the harvester is analytically developed by means of the energy-based method and the extended Hamiltons principle. Using the derived model, a parametric study is carried out to obtain the harvesters voltage response under parametric excitations. Furthermore, the effects of various parameters on the harvesters voltage response are examined. A prototype harvester is fabricated and experimentally tested. The theoretical model is validated against experimental data to confirm the harvesters nonlinear response behaviors and enhanced capabilities. Both simulation and experiment illustrate that the harvester exhibits a softening nonlinearity and hence a broad frequency bandwidth with large-amplitude voltage response. It is also shown from numerical simulations that the harvesters performance can be further improved by properly selecting the end mass and reducing the mechanical damping. The present findings demonstrate that dynamic compressive loadings can be successfully utilized to increase the harvesters voltage output and frequency bandwidth.

Design and development of a novel bi-directional piezoelectric energy harvester

In this paper, a novel bi-directional piezoelectric energy harvester which can harvest vibration energy bi-directionally is introduced and investigated theoretically and experimentally. The proposed harvester is composed of two sub-systems: a main beam to generate electricity and a spring–mass oscillator to trigger the vibration of the main beam from an additional direction by using magnets to couple the two sub-systems. The theoretical model is built on the basis of the Euler–Bernoulli beam theory and the magnetic charge model. A prototype is fabricated to test the performance of the harvester experimentally. Linear upward and downward frequency sweeps are used to obtain the frequency responses. The experimental results show good agreement with the theoretical model under frequency sweeps. A comparison with a beam–beam bi-directional piezoelectric energy harvester is also performed experimentally. Although both bi-directional piezoelectric energy harvesters exhibit the capability of harvesting vibration energy in two orthogonal directions, the beam–spring energy harvester shows a more consistent performance in both directions as regards the bandwidth and amplitude of the frequency responses.

Inerter Nonlinearities and the Impact on Suspension Control

This paper discusses the nonlinear properties of Inerters and their impact on vehicle suspension control. The Inerter was recently introduced as an ideal mechanical two-terminal element which is a substitute for the mass element with the applied force proportional to the relative acceleration across the terminals. Until now, ideal Inerters have been applied to car, motorcycle and train suspension systems, in which significant performance improvement was achieved. However, due to the mechanical construction, some nonlinear properties of the existing mechanical Inerter models are noted. This paper investigates the Inerter nonlinearities, including friction, backlash and the elastic effect, and their influence on vehicle suspension performance. A testing platform is also built to verify the nonlinear properties of the Inerter model. It is shown from the results that the suspension performance is in general degraded by Inerter nonlinearities. However, the overall suspension performance with Inerters is still better than the traditional suspensions.

Modeling of V-Shaped Beam-Mass Piezoelectric Energy Harvester: Impact of the Angle Between the Beams

Piezoelectric material has been widely utilized in vibration-based energy harvesters (VEH). The most common configuration of piezoelectric energy harvester is a cantilevered beam with unimorph or bimorph piezoelectric layers. In this paper, a new configuration of PEH is proposed. Two beams are assembled as V shape with tip masses attached. The first beam is a cantilevered beam with tip mass while the second beam is attached to the end of the first beam with a certain angle. Piezoelectric layers are attached to both beams in unimorph configuration for power generation. The analytical solution is derived based on Euler-Bernoulli beam theory. In this analysis, the angle varies from 0 to 135 degree to see the influence of angle on voltage and power frequency response. The V-shaped VEH is proven to have the second resonant frequency relatively close to the first resonant frequency when compared with conventional cantilevered VEH. Furthermore, the angle between the two beams will influence the ratio of the second to the first resonant frequency. By choosing a suitable angle, the V-shaped structure can effectively broaden the bandwidth.© 2012 ASME

Wrinkle localization in membrane structures patched with macro-fiber composite actuators: Inflatable space antenna applications

Kapton membranes have received much attention in the fabrication of space inflatable antenna technology in the recent years. While prized for their light designs, their delicate nature makes them susceptible to various kinds of disturbances in space environments that result in structural vibrations or wrinkle formation. In this regard, macro-fiber composite actuators have been commonly used for vibration control of these membrane structures. However, wrinkle control remains one of the major challenges in their designs. Some of the research in the previous literature has attempted to quantify the wrinkle behavior of these membranes when subject to boundary forces. Yet, in all the previous study, the effects of macro-fiber composite patches, a major compartment of these structures, on their wrinkle formation have been ignored. The presented article studies the effects of these patches on localization of wrinkles and their patterns in Kapton membranes. The numerical results are validated experimentally using photogrammetry techniques. Two membrane configurations are studied: one considers rectangular membranes with clamped-sliding boundary conditions and the other pertains to square membranes with symmetric corner loadings.