•A type of parallel non-concentricity is defined.•The dual-rotor system model with non-concentricity is established.•The envelope curve of the orbit and polar angle difference are discussed.•The ...relation between the polar angle difference and the phase angles is calculated.•The effects of the non-concentricity phase angle and the offset are discussed.
The machining deviation of the positioning hole of the inter-shaft bearing can cause the fault of the non-concentricity of the dual-rotor system. Aiming at the above problem, a type of parallel non-concentricity is defined, the phase angle and the offset of which are utilized to modify the contact force model of the inter-shaft bearing. The results obtained by the Newmark-β method show that the non-concentricity phase angle and the non-concentricity offset will change the amplitude when the dual-rotor system passes the first critical speed. It is observed that there are 2X and 3X frequencies of the rotational speeds of high- and low-pressure rotors and several combination frequencies of the two rotational speeds, in which the subtraction frequency of high- and low-pressure rotors is dominant. With the non-concentricity phase angle changes, the shape of the orbit and the envelope curve of the orbit of high- and low-pressure rotors will shift. The quantitative correspondence between the polar angle difference and the non-concentricity phase angles is discovered, which can be used to diagnose the fault of the non-concentricity of the dual-rotor system.
This paper aims to investigate the nonlinear vibration characteristics and stability of a dual-disk rotor-bearing system under multi-frequency excitations. A 4-degree-of-freedom dynamic model is ...established using the assumed mode method, considering the bearing’s cubic nonlinearity. The system is solved using the multiple scale method combined with arc-length continuation. The stability of the system’s solutions is determined by solving the eigenvalues of the Jacobian matrix of the averaged equations. The nonlinear vibration characteristics and stability of the dual-disk rotor system under simultaneous resonance conditions are obtained. The results show that changes in system parameters can lead to Saddle-Node and Hopf bifurcations, as well as the occurrence of multi-valued solutions and symmetry-breaking phenomena. Additionally, simultaneous resonance leads to interaction between the two modes, where the relative positions of the resonance peaks of these modes influence the system’s dynamic behavior. Variations in system parameters can alter the relative positions of resonance peaks, leading to more complex effects on nonlinear responses. This research provides significant insights into the dynamic behavior of the dual-disk rotor-bearing system under multi-frequency excitations, which is meaningful for designing and optimizing rotor systems.
Carbon nanotubes have been widely used as test channels to study nanofluidic transport, which has been found to have distinctive properties compared to transport of fluids in macroscopic channels. A ...long-standing challenge in the study of mass transport through carbon nanotubes (CNTs) is the determination of flow enhancement. Various experimental investigations have been conducted to measure the flow rate through CNTs, mainly based on either vertically aligned CNT membranes or individual CNTs. Here, we proposed an alternative approach that can be used to quantify the mass transport through CNTs. This is a simple method relying on the use of carbon nanotube–polystyrene bundles, which are made of CNTs pulled out from a vertically aligned CNT array and glued together by polystyrene. We experimentally showed by using fluorescent tagging that the composite bundles allowed measureable and selective mass transport through CNTs. This type of composite bundle may be useful in various CNT research areas as they are simple to fabricate, less likely to form macroscopic cracks, and offer a high density of CNT pores while maintaining the aligned morphology of CNTs.
Utilization of carbon nanotubes (CNTs) in fabrication of electrodes for electrochemical detection often faces a conflicting goal: achieving both high response current and high mass transfer ...coefficient. Typically, electrodes made in a form of CNT ensembles offer high response current as a result of the large number of CNTs. However, these electrodes have substantially low mass transfer coefficients due to overlapping of diffusion fields between neighboring CNTs. To resolve this conflict, we design band electrodes made of vertically-aligned CNT (CNBEs), which are macro-sized in length and submicro-sized in width. We show that the distinct dimensions of the CNBEs allow both high response currents and mass transfer coefficients. We also demonstrate that CNBEs offer excellent detection performances including wide linear range, high sensitivity, and low limit of detection in channel flow voltammetry.
•Carbon nanotube band electrodes (CNBEs) are fabricated and embedded in microfluidics systems.•CNBEs are capable of achieve both high response current and high mass transfer coefficient.•Mass transfer coefficient at CNBEs is enhanced ~32-fold compared to that of vertically-aligned CNT nanoelectrode arrays.•Utilization of CNBEs in channel flow voltammetry for detecting K3Fe(CN)6 and dopamine demonstrates excellent performance.
In this paper, the combination resonance characteristics of a high-dimensional dual-rotor-bearing-casing system with bearing nonlinearities are presented. All the periodic solution branches, ...including the unstable solutions of the system, are obtained by the semi-analytical harmonic balance method. Two primary and two combination resonance regions are found in the amplitude–frequency responses, with the vibration jump and multiple solutions phenomena being observed. Furthermore, the amplitude–frequency responses with separated frequencies are analyzed; it is shown that the vibration responses of the combination resonance regions are dominated by the combination frequencies of the rotating speeds of the high- and low-pressure rotors. Moreover, parametric analysis shows that the combination resonances are sensitive to the change in the inter-shaft bearing clearance. With the increase in clearance, the combination resonance regions are widened. The results in this paper provide a better understanding of the combination resonances in high-dimensional dual-rotor-bearing-casing systems.
•A general and efficient harmonic balance method for nonlinear dynamic simulation is proposed.•By employing the FFT technique, the Jacobian matrix is obtained in a general and efficient manner.•The ...constant tensor matrices devoid of reliance on the equation's specific formulation facilitates obtaining the Jacobian matrix in a general manner.•Loop computations are no longer requisite facilitates obtaining the Jacobian matrix in an efficient manner.•Computational findings across two distinct scenarios unequivocally demonstrate the superior computational efficiency of the GE-HB method.
This paper presents a general and efficient harmonic balance (GE-HB) method to expeditiously evaluate the periodic responses of nonlinear systems. By employing the fast Fourier transform (FFT) technique, it rapidly computes harmonic expansion coefficients of the nonlinear terms and their corresponding constant tensor matrices. Notably, the nonlinear part of the Jacobian matrix is just the product of the coefficients and the constant tensor matrices, loop computations are no longer requisite for calculating the Jacobian matrix. This, facilitates accelerated determination of the nonlinear portion of the Jacobian matrix, thus obtaining the periodic responses of the system in an efficient manner. Furthermore, the constant tensor matrices are exclusively contingent upon the harmonic bases of the system's periodic response, devoid of reliance on the equation's specific formulation, facilitates obtaining the Jacobian matrix in a general manner. Simulation results on a 20-degree-of-freedom nonlinear oscillator chain system demonstrate that the efficiency of the GE-HB method is about tenfold that of the harmonic balance-alternating frequency/time domain (HB-AFT) method and twenty-fivefold that of the fourth-order Runge-Kutta (RK4) method. Further, the simulation of a 284-degree-of-freedom nonlinear rotor system exhibits the GE-HB method's computational efficiency surpassing HB-AFT method by over 500 times and Newmark method by over 3000 times. Moreover, in these two examples, the GE-HB method captures all solution branches, including unstable periodic solutions, providing comprehensive insights into periodic responses of the systems. The GE-HB method proposed here has the potential to explore dynamic characteristics for high-dimensional complex nonlinear systems in engineering.
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Quasi-zero-stiffness (QZS) vibration isolator is widely used in low-frequency vibration isolation due to its high-static-low-dynamic-stiffness (HSLDS) characteristics. The complex nonlinear force of ...the QZS vibration isolator increases the difficulty of solving it while realizing the HSLDS characteristics. The typical analysis method is to use Taylor expansion to simplify the nonlinear force and make it approximate to polynomial form, which leads to inaccurate analysis results in the case of large excitation and small damping. Therefore, the modified incremental harmonic balance (IHB) method is used to directly analyze the dynamic characteristics of the QZS vibration isolator without simplification in this paper. The classical three-spring QZS vibration isolation model is used as the calculation example. The results are different from the previous approximate equation analysis results in three aspects: (1) There is no unbounded response of the system under displacement excitation; (2) Even harmonics and constant terms also exist in the response of the system and can lead to multiple solution intervals; (3) In the case of small damping and large excitation, both displacement excitation and force excitation have subharmonic resonance, reducing the vibration isolation performance of the system. In addition, the accuracy of the solution obtained by the IHB method is verified by the Runge–Kutta method. The accurate analysis method in this paper provides favorable theoretical support for the design and optimization of vibration isolators.
For biological triboelectric nanogenerator (bio-TENG), its inherent deficiencies such as low output power density, monotonous triboelectric behavior, and limited choice of triboelectric materials ...greatly restrict its wide-scale application. For remedy this, a typical plant protein of rice glutelin (RG) recycled from by-product of starch industry was utilized as a model to investigate the mechanism of triboelectric charging behavior related to protein structure. Using a facile interface-engineering technology of pH-cycle as the research method, the secondary structure of RG strongly influenced its triboelectric property is discovered and the possible mechanism was proposed and verified. Based on this, we achieved ~16 times promotion of output and enabled manipulation of the triboelectric performance of the protein. In this way, not only can we recycle wasted resources back to more valuable areas, but the adjustable properties of proteins as soft matter also highlight their potential as biomaterials in sustainable triboelectric electronic applications such as next-generation intelligent packaging, wearable, and implantable medical devices.
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•Tunable properties of proteins in sustainable triboelectric electronic are explored.•The mechanism of triboelectric behavior related to protein structure is revealed.•~16 times promotion of output performance for bio-TENG can be achieved.•A by-product of plant protein is recycled as eco-friendly triboelectric films.
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•CNT nanoelectrode arrays were fabricated and embedded in microfluidic systems.•Effect of array diameter on mass transfer coefficient was investigated.•Effect of forced convection on ...mass transfer coefficient was investigated.
The mass transfer of analytes is a major limiting factor of electrochemical response at vertically-aligned carbon nanotube nanoelectrode arrays (VCNs). In this study, the dependence of the mass transfer coefficient on the array diameter and force convection is studied experimentally. The mass transfer coefficient is shown to increase 2 folds by reducing the array diameter from 2 mm to 50 μm, while it increases 20 folds by introducing force convection at the flow rate 2000 μL min−1. The VCNs used with channel flow voltammetry exhibit low limit of detection (5 nM), high sensitivity, and wide linear range for detecting both K3Fe(CN)6 and dopamine. The VCNs can be used on lab-on-a-chip systems for analytical applications. It is anticipated a combined approach of reducing array diameter and introducing forced convection can be used to significantly improve electrochemical responses of other nanoelectrode arrays.
Noise is a fundamental challenge for sensors deployed in daily environments for ambient sensing, health monitoring, and wireless networking. Current strategies for noise mitigation rely primarily on ...reducing or removing noise. Here, we introduce stochastic exceptional points and show the utility to reverse the detrimental effect of noise. The stochastic process theory illustrates that the stochastic exceptional points manifest as fluctuating sensory thresholds that give rise to stochastic resonance, a counterintuitive phenomenon in which the added noise increases the system's ability to detect weak signals. Demonstrations using a wearable wireless sensor show that the stochastic exceptional points lead to more accurate tracking of a person's vital signs during exercise. Our results may lead to a distinct class of sensors that overcome and are enhanced by ambient noise for applications ranging from healthcare to the internet of things.
