Enhancing vibration isolation performance by exploiting novel spring-bar mechanism

This study investigates the use of a spring-bar mechanism (SBM) in a vibration suppression system to improve its performance. The SBM, comprising bars and springs, is configured with a conventional linear spring-damper isolator unit. The dynamic response, force transmissibility, and vibration energy flow behaviour are studied to evaluate the vibration suppression performance of the integrated system. It is found that the SBM can introduce hardening, softening stiffness, or double-well potential characteristics to the system. By tuning the SBM parameters, constant negative stiffness is achieved so that the natural frequency of the overall system is reduced for enhanced low-frequency vibration isolation. It is also found that the proposed design yields a wider effective isolation range compared to the conventional spring-damper isolator and a previously proposed isolator with a negative stiffness mechanism. The frequency response relation of the force-excited system is derived using the averaging method and elliptical functions. It is also found that the system can exhibit chaotic motions, for which the associated time-averaged power is found to tend to an asymptotic value as the averaging time increases. It is shown that the time-averaged power flow variables can be used as uniform performance indices of nonlinear vibration isolators exhibiting periodic or chaotic motions. It is shown that the SBM can assist in reducing force transmission and input power, thereby expanding the frequency range of vibration attenuations

Spectrographic Microfluidic Memory

Recent advancements in micro- and nanoscale fluidic manipulation have enabled the development of a new class of tunable optical structures which are collectively referred to as optofluidic devices. In this paper we will introduce our recent work directed towards the development of a spectrographic optofluidic memory. Data encoding for the memory is based on creating spectrographic codes consisting of multiple species of photoluminescent nanoparticles at discrete intensity levels which are suspended in liquids. The data cocktails are mixed, delivered and stored using a series of soft and hard-lithography microfluidic structures. Semiconductor quantum dots are ideally suited for this application due to their narrow and size tunable emission spectra and consistent excitation wavelength. Both pressure driven and electrokinetic approaches to spectral code writing have been developed and will be experimentally demonstrated here. Novel techniques for data storage and readout are also discussed and demonstrated

Multi-classification method of arrhythmia based on multi-scale residual neural network and multi-channel data fusion

Since ECG contains key characteristic information of arrhythmias, extracting this information is crucial for identifying arrhythmias. Based on this, in order to effectively extract ECG data features and realize automatic detection of arrhythmia, a multi-classification method of arrhythmia based on multi-scale residual neural network and multi-channel data fusion is proposed. First, the features of single-lead ECG signals are extracted and converted into two-dimensional images, and the feature data sets are labeled and divided according to different types of arrhythmias. The improved residual neural network is trained on the training set to obtain the classification model of the neural network. Finally, the classification model is applied to the automatic detection of arrhythmias during exercise. The accuracy of the classification model of this method is as high as 99.60%, and it has high accuracy and generalization ability. The automatic identification of arrhythmia also contributes to the research and development of future wearable devices

Suppression of vibration transmission in coupled systems with an inerter-based nonlinear joint

This study proposes an inerter-based nonlinear passive joint device and investigates its performance in suppression of vibration transmission in coupled systems. The joint device comprises an axial inerter and a pair of lateral inerters creating geometric nonlinearity, with the nonlinear inertance force being a function of the relative displacement, velocity, and acceleration of the two terminals. Both analytical approximations based on the harmonic balance method and numerical integration are used to obtain the steady-state response amplitude. Force transmissibility and time-averaged energy flow variables are used as performance indices to evaluate the vibration transmission in the coupled system, with subsystems representing the dominant modes of interactive engineering structures. The effects of adding the proposed joint to the force-excited subsystem or to the coupling interface of subsystems on suppression performance are examined. It is found that the insertion of the inerter-based nonlinear joint can shift and bend response peaks to lower frequencies, substantially reducing the vibration of the subsystems at prescribed frequencies. By adding the joint device, the level of vibration force and energy transmission between the subsystems can be attenuated in the range of excitation frequencies of interest. It is shown that the inerter-based nonlinear joint can be used to introduce an anti-peak in the response curve and achieve substantially lower levels of force transmission and a reduced amount of energy transmission between subsystems. This work provides an in-depth understanding of the effects of inerter-based nonlinear devices on vibration attenuation and benefits enhanced designs of coupled systems for better dynamic performance

Model-free robust decentralised control of multi-input-multi-output nonlinear interconnected dynamic systems

This study presents a generalised framework for model-free robust decentralised control (MFRDC) of interconnected MIMO dynamic systems, with the goal of significantly reducing complexity in model-based design. A model-free robust sliding mode control, by Lyapunov differential inequality, is presented to achieve simultaneous nonlinear, dynamic, interaction/coupling inversion/cancellation (NDII) for such MIMO systems, which treats the plant/process as a total uncertainty from input to output. The U-control platform is presented, to integrate separately independently designed NDII and an invariant controller (IC) into a complete double loop control system. The associated robust stability and other properties are analysed to provide reference for applications. Two simulated tracking control tests are presented for functionally numerical demonstration, validation of the analytical results and illustration of the transparent procedure for general expansion/applications. These are: a coupled inverted pendulum and a two-input and two-output (TITO) non-affine nonlinear dynamic plant

Enhanced suppression of longitudinal vibration transmission in propulsion shaft system using nonlinear tuned mass damper inerter

This study proposes the use of a novel nonlinear tuned mass damper inerter device in vibration suppression of the ship propulsion shafting system and evaluates its performance. The device consists of an axial inerter and a pair of lateral inerters to create geometric nonlinearity. The system response subjected to propeller forces is determined by using the harmonic balance method with alternating-frequency-time technique and a numerical time-marching method. The force transmissibility and energy flow variables are employed to assess the performance of the device. The results show that the proposed device can reduce the peak force and energy transmission to the foundation while increase the energy dissipation within the device. Its use can lead to an improved vibration attenuation effect than the traditional mass-spring-damper device for low-frequency vibration. The configurations of the nonlinear inerter-based device can be adjusted to obtain an anti-peak at a resonance frequency of the original system, providing superior vibration suppression performance

FDTD analysis of transient fault induced travelling-wave propagation for multi-branch distribution networks

Many methods are available to analyze the process of the travelling-wave propagation. Among these methods, the Finite Difference Time Domain (FDTD) method has a distinct advantage in calculating dynamic process of the travelling wave propagation in the time domain and is thus applied to the field of power system protection for researching transient fault induced travelling-wave propagation. The novelty of this paper is that the attenuation law of the traveling wave signal affected by the fork junction in the multi-branch distribution network is summarized and the cause of failure in the fault location based on the incipient travelling wave front method in distribution networks is found

Adaptive sliding mode attitude control of 2-degrees-of-freedom helicopter system with actuator saturation and disturbances

The modelling uncertainties, external disturbance and actuator saturation issues will degrade the performance and even the safety of flight. To improve control performance, this study proposes an adaptive U-model based double sliding control (UDSMC) algorithm combined with a radial basis function neural network (RBFNN) for a nonlinear two-degrees-of-freedom (2-DOF) helicopter system. Firstly, the adaptive RBFNN is designed to approximate the system dynamics with unknown uncertainties. Furthermore, two adaptive laws are designed to deal with unknown external disturbances and actuator saturation errors. The global stability of the proposed helicopter control system is rigorously guaranteed by the Lyapunov stability analysis, realizing precise attitude tracking control. Finally, the comparative experiments with conventional SMC and adaptive SMC algorithms conducted on the Quanser Aero2 platform demonstrate the effectiveness and feasibility of the proposed 2-DOF helicopter control algorithm