Snap-through behaviors and nonlinear vibrations of a bistable composite laminated cantilever shell:an experimental and numerical study

The snap-through behaviors and nonlinear vibrations are investigated for a bistable composite laminated cantilever shell subjected to transversal foundation excitation based on experimental and theoretical approaches.An improved experimental specimen is designed in order to satisfy the cantilever support boundary condition,which is composed of an asymmetric region and a symmetric region.The symmetric region of the experimental specimen is entirely clamped,which is rigidly connected to an electromagnetic shaker,while the asymmetric region remains free of constraint.Different motion paths are realized for the bistable cantilever shell by changing the input signal levels of the electromagnetic shaker,and the displacement responses of the shell are collected by the laser displacement sensors.The numerical simulation is conducted based on the established theoretical model of the bistable composite laminated cantilever shell,and an off-axis three-dimensional dynamic snap-through domain is obtained.The numerical solutions are in good agreement with the experimental results.The nonlinear stiffness characteristics,dynamic snap-through domain,and chaos and bifurcation behaviors of the shell are quantitatively analyzed.Due to the asymmetry of the boundary condition and the shell,the upper stable-state of the shell exhibits an obvious soft spring stiffness characteristic,and the lower stable-state shows a linear stiffness characteristic of the shell.

Generative optimization of bistable plates with deep learning

Bistate plates have found extensive applications in the domains of smart structures and energy harvesting devices.Most bistable curved plates are characterized by a constant thickness profile.Regrettably,due to the inherent complexity of this problem,relatively little attention has been devoted to this area.In this study,we demonstrate how deep learning can facilitate the discovery of novel plate profiles that cater to multiple objectives,including maximizing stiffness,forward snapping force,and backward snapping force.Our proposed approach is distinguished by its efficiency in terms of low computational energy consumption and high effectiveness.It holds promise for future applications in the design and optimization of multistable structures with diverse objectives,addressing the requirements of various fields.

Controllable optical bistability in a Fabry-Pérot cavity with a nonlinear three-dimensional Dirac semimetal

Optical bistability(OB)is capable of rapidly and reversibly transforming a parameter of an optical signal from one state to another,and homologous nonlinear optical bistable devices are core components of high-speed all-optical communication and all-optical networks.In this paper,we theoretically investigated the controllable OB from a Fabry-Pérot(FP)cavity with a nonlinear three-dimensional Dirac semimetal(3D DSM)in the terahertz band.The OB stems from the third-order nonlinear bulk conductivity of the 3D DSM and the resonance mode has a positive effect on the generation of OB.This FP cavity structure is able to tune the OB because the transmittance and the reflectance can be modulated by the Fermi energy of the 3D DSM.We believe that this FP cavity configuration could provide a reference concept for realizing tunable bistable devices.

Performance enhancement of a viscoelastic bistable energy harvester using time-delayed feedback control

This paper focuses on the stochastic analysis of a viscoelastic bistable energy harvesting system under colored noise and harmonic excitation, and adopts the time-delayed feedback control to improve its harvesting efficiency. Firstly, to obtain the dimensionless governing equation of the system, the original bistable system is approximated as a system without viscoelastic term by using the stochastic averaging method of energy envelope, and then is further decoupled to derive an equivalent system. The credibility of the proposed method is validated by contrasting the consistency between the numerical and the analytical results of the equivalent system under different noise conditions. The influence of system parameters on average output power is analyzed, and the control effect of the time-delayed feedback control on system performance is compared. The output performance of the system is improved with the occurrence of stochastic resonance(SR). Therefore, the signal-to-noise ratio expression for measuring SR is derived, and the dependence of its SR behavior on different parameters is explored.

Theoretical and experimental investigation of the resonance responses and chaotic dynamics of a bistable laminated composite shell in the dynamic snap-through mode

The dynamic model of a bistable laminated composite shell simply supported by four corners is further developed to investigate the resonance responses and chaotic behaviors.The existence of the 1:1 resonance relationship between two order vibration modes of the system is verified.The resonance response of this class of bistable structures in the dynamic snap-through mode is investigated,and the four-dimensional(4D)nonlinear modulation equations are derived based on the 1:1 internal resonance relationship by means of the multiple scales method.The Hopf bifurcation and instability interval of the amplitude frequency and force amplitude curves are analyzed.The discussion focuses on investigating the effects of key parameters,e.g.,excitation amplitude,damping coefficient,and detuning parameters,on the resonance responses.The numerical simulations show that the foundation excitation and the degree of coupling between the vibration modes exert a substantial effect on the chaotic dynamics of the system.Furthermore,the significant motions under particular excitation conditions are visualized by bifurcation diagrams,time histories,phase portraits,three-dimensional(3D)phase portraits,and Poincare maps.Finally,the vibration experiment is carried out to study the amplitude frequency responses and bifurcation characteristics for the bistable laminated composite shell,yielding results that are qualitatively consistent with the theoretical results.

Inter-well internal resonance analysis of rectangular asymmetric cross-ply bistable composite laminated cantilever shell under transverse foundation excitation

The chaotic dynamic snap-through and complex nonlinear vibrations are investigated in a rectangular asymmetric cross-ply bistable composite laminated cantilever shell,in cases of 1:2 inter-well internal resonance and primary resonance.The transverse foundation excitation is applied to the fixed end of the structure,and the other end is in a free state.The first-order approximate multiple scales method is employed to perform the perturbation analysis on the dimensionless two-degree-of-freedom ordinary differential motion control equation.The four-dimensional averaged equations are derived in both polar and rectangular coordinate forms.Deriving from the obtained frequency-amplitude and force-amplitude response curves,a detailed analysis is conducted to examine the impacts of excitation amplitude,damping coefficient,and tuning parameter on the nonlinear internal resonance characteristics of the system.The nonlinear softening characteristic is exhibited in the upper stable-state,while the lower stable-state demonstrates the softening and linearity characteristics.Numerical simulation is carried out using the fourth-order Runge-Kutta method,and a series of nonlinear response curves are plotted.Increasing the excitation amplitude further elucidates the global bifurcation and chaotic dynamic snap-through characteristics of the bistable cantilever shell.

Adaptive Bistable Stochastic Resonance Based Weak Signal Reception in Additive Laplacian Noise

Weak signal reception is a very important and challenging problem for communication systems especially in the presence of non-Gaussian noise,and in which case the performance of optimal linear correlated receiver degrades dramatically.Aiming at this,a novel uncorrelated reception scheme based on adaptive bistable stochastic resonance(ABSR)for a weak signal in additive Laplacian noise is investigated.By analyzing the key issue that the quantitative cooperative resonance matching relationship between the characteristics of the noisy signal and the nonlinear bistable system,an analytical expression of the bistable system parameters is derived.On this basis,by means of bistable system parameters self-adaptive adjustment,the counterintuitive stochastic resonance(SR)phenomenon can be easily generated at which the random noise is changed into a benefit to assist signal transmission.Finally,it is demonstrated that approximately 8dB bit error ratio(BER)performance improvement for the ABSR-based uncorrelated receiver when compared with the traditional uncorrelated receiver at low signal to noise ratio(SNR)conditions varying from-30dB to-5dB.

Vibrational resonance in globally coupled bistable systems under the noise background

Effects of system size,coupling strength,and noise on vibrational resonance(VR)of globally coupled bistable systems are investigated.The power spectral amplifications obtained by the three methods all show that the VR exists over a wide range of parameter values.The increase in system size induces and enhances the VR,while the increase in noise intensity suppresses and eventually eliminates the VR.Both the stochastic resonance and the system size resonance can coexist with the VR in different parameter regions.This research has potential applications to the weak signal detection process in stochastic multi-body systems.

自适应双稳态浮子式波浪能发电装置在不规则波中的能量捕获性能研究

传统双稳态波能装置已被证实在规则波中可以通过添加“自适应”特性,来解决由阱内振荡引起的低能量吸收问题。本文以自适应双稳态浮子式波浪能发电装置为研究对象,探讨装置在不规则波中的能量捕获性能情况。通过四阶龙格库塔法数值求解装置的运动控制方程,探究在不同装置参数下,自适应双稳态浮子式波浪能发电装置和传统双稳态浮子式波浪能发电装置以及线性浮子式波浪能发电装置的能量捕获性能表现。结果表明,选取适当的装置参数可以使自适应双稳态浮子式波浪能发电装置显著提升能量捕获性能,而且与线性和常规双稳装置相比,更适应于实际海况中波浪能量捕获。

高速自适应双稳态折纸软体夹持器设计与分析

提出了一种单顶点多折痕(single-vertex and multi-crease,SVMC)的双稳态折纸软体夹持器,具有结构简单、成本低、变形速度快、承载能力强等优点,有效改善了传统模型响应速度慢、夹持效率低等缺陷。该模型基于水弹结构建立,利用球面三角形余弦定理分析了折痕角度之间的关系并建立运动学方程;同时借助扭簧模型探究变形过程中的势能转化规律。分析了折痕长度与初始角度对能力存储和释放过程的影响,并以此为基础优化了模型结构参数。实验结果表明,当受到2.6 N的外部触发力时,软体夹持器可在61 ms内完成从外展姿态到内缩状态的变化,实现对目标表面的快速包络;同时,借助线绳驱动提供更大的夹紧力,完成对目标的高效稳定抓取。此模型可广泛应用于复杂轮廓目标抓取和快速食品分拣领域。

永磁同步电磁原理的冲击式按压发电机研究

按键开关用的发电机可将按键动作转为电能,为无线按键开关提供电能,在绿色智能家居中有重要的应用价值。本文提出了一种利用电磁原理的冲击式发电机,设计了一种双稳态转换的结构,在两个稳态转换的过程中,线圈中磁力线反向突变,产生电动势脉冲。采用有限元软件对双稳态结构的磁场分布情况进行了分析,对线圈和铁芯尺寸进行了优化设计,结果表明两个稳定状态的线圈中磁力线方向相反,感应电动势基本上随尺寸线性增加。加工组装了发电机样机,通过实验研究发现,按压一次,发电机输出电压可以达到30 V,产生电能达到1469μJ。利用电磁转换原理将按压动作转化为电能,其紧凑的设计、小巧的体积和高输出功率使其具有显著的优势,有望为无线传感网络节点和无线开关提供充足的能源,实现绿色自给运行。

异质微环谐振腔双稳态及全光存储器应用

提出了一种基于异质集成波导的微环谐振腔,对其双稳态现象进行了研究分析,并将其应用于全光存储功能的实现。异质集成波导具有超高的克尔非线性效应,不受热光效应和载流子响应的限制,在超快克尔非线性效应的支持下,该结构具有快速全光切换的能力。设计了一个高品质因子Q=77565的微环谐振腔,用耦合模式理论模拟了其双稳态现象。在峰值功率为474 fJ,宽度为20 ps的脉冲激励下,该微环谐振腔很好地实现了全光存储功能,并通过波分复用的串联微环结构展示了波长可寻址的四位光存储器。研究了基于超高克尔非线性效应的双稳态现象,为实现超快切换速度提供了可能性,在光存储、光开关、人工智能研究等方面具有一定的参考价值。

基于YOLOv5s和双稳随机共振的夜间车辆检测算法

针对夜间车辆检测过程中光照不强导致漏检误检的问题,基于YOLOv5s和双稳随机共振提出一种改进的夜间车辆检测算法。YOLOv5s从4方面进行改进:1)在Backbone和Neck中更换细小结构,提高网络对小目标的检测能力;2)加入由坐标注意力CA和能量注意力SimAM构成的双注意力机制,提高网络对目标的特征提取能力;3)采用轻量化骨干Fasternet,减少模型参数量;4)在Head中采用WIoU损失函数,加快边界框回归损失的收敛速度。利用经典的双稳随机共振对夜间车辆数据集进行低照度图像增强,分析其有效性,并将增强后的夜间车辆图像传入改进的YOLOv5s网络进行训练。实验结果表明,相较于原始YOLOv5s,融合改进的YOLOv5s和双稳随机共振的夜间车辆检测算法在执行远景小目标以及密集遮挡的夜间车辆检测任务时具有更高的准确率和更低的漏检率。

双环境背景稳态变色织物的制备及变色性能

针对常规温致变色纺织品因仅有一个变色点而在某些特殊领域应用时无法实现自主控制颜色的问题,利用分散染料不变色,以及变色微胶囊在高温条件下呈无色态和低温条件下呈有色态的性能特点,将双稳态温致变色微胶囊与分散染料复配,配制出高温浅棕-低温深灰、高温深绿-低温红棕和高温黄绿-低温中灰三种稳态互变的温致变色色浆,并采用筛网印花法将印花色浆施加到纺织品上,制备具有双环境背景稳态互变的迷彩织物。印制的迷彩织物高温和低温变色响应时间分别约为20 s和120 s,变色循环可达200次,耐摩擦色牢度为4~5级,耐水洗色牢度为4级,耐日晒色牢度为3级,且手感较好。此外,分别通过高温和低温刺激,印制的迷彩织物在-5~60℃的环境温度范围内可以稳态呈现两种不同的颜色效果,从而实现对迷彩织物的自主呈色控制。

可调轴向力的振动压电俘能器建模与实验

针对传统能量收集器的工作带宽窄和输出功率低等问题,对一种可调轴向力的双稳态振动压电俘能器进行研究。该俘能器将两个压电悬臂梁自由端通过附加质量连接为一个梁,通过测微调节器控制轴向压力使系统变为双稳态结构。利用非保守力的拉格朗日方程对压电俘能器进行发电分析,建立了机电耦合模型。利用PZT5H压电材料搭建实验样机和平台,进行了系统俘能特性的调查研究。实验研究结果表明,仿真值预测的结构特性与实验结果一致性较好,该结构能有效拓展低频发电带宽,压电扫频输出具有两个明显低频峰值。利用实验对系统的负载参数进行优化,双稳态系统的电压输出峰值能达到17V。

半导体量子点分子-腔光机械耦合系统中光学双稳及多稳态的形成及调控

本研究探讨了外部磁场对半导体量子点分子与腔光机械耦合系统中光学双稳态行为的影响.研究结果显示,外部磁场、量子点之间的隧穿耦合以及探测光单光子的失谐可以有效地调控系统的光学双稳态.在弱隧穿和弱磁场条件下,系统的光学双稳态阈值和磁滞回线宽度随着外部磁场和点间隧穿耦合强度的增加而增大.随着磁场强度和隧穿耦合强度的进一步增加,系统的双稳态将演变为多稳态.有趣的是,在强隧穿和强磁场作用下,系统的光学双稳态阈值和磁滞回线宽度随着外部磁场和点间隧穿耦合强度的增加而减小.这种对耦合腔光机械系统中光学双稳态的灵活调控将在可控光开关方面具有潜在的广泛应用前景.

调制信号驱动的时滞非对称双稳系统的随机共振

本文研究了一类同时包含调制信号及加性噪声的时滞非对称双稳系统的随机共振.本文首先基于小时滞近似理论推导了系统的有效势和稳态概率密度,分析了系统参数对有效势阱的影响.然后,本文利用绝热近似理论得到了系统的平均首通时间及信噪比,分析了信号振幅、时滞及时滞强度对平均首通时间和信噪比的影响,结果显示:信号振幅和时滞促进随机共振,时滞强度则先抑制后促进随机共振.从随机共振控制的角度看,调节势函数的对称性较调节时滞或时滞强度更有效.

双稳态压电超结构的超传输滞回效应与非互易编码特性

利用超结构的非线性效应能够实现新颖的振动能量传输调控现象.双稳态超结构存在非线性超传输特性,即在超结构线性化带隙内,当激励幅值超过某个临界值时,传输的振动能量将突变到很大值.文章针对含双稳态分流电路的压电超结构梁,建立了力电耦合非线性动力学数值模型,并采用伽辽金法对数值模型进行降阶处理以提升计算效率.基于上述模型研究了双稳态压电超结构的振动能量非线性传输特性,发现超结构线性局域共振带隙内的超传输特性存在滞回效应,也即向上扫幅激励和向下扫幅激励两种工况下超传输临界值不同.通过改变双稳态电路两个稳定平衡点的间距或者电路在稳定平衡点的共振强度可以移动超传输滞回区间.进一步通过在双稳态压电超结构一侧布置线性共振电路来引入系统非对称性,可使得正方向和反方向的超传输滞回区间发生偏离,利用这种非互易的超传输滞回效应可以在不同激励幅值区间实现不同模式的非互易编码.增强系统非对称性可使得正方向和反方向的超传输滞回区间偏离更加显著,故非互易编码区间具有可调性.文章极大地拓展了超材料的非互易模式,正方向和反方向能量传输性能不再局限于传统超材料固定的“传输”或“非传输”状态,通过合适的非互易编码设计可以实现弹性信息的单向传输功能.

循环噪声作用下周期调制双稳系统的驻留时间分布函数

提出了一种计算循环噪声作用下周期调制双稳系统驻留时间分布函数的理论方法。基于具有分段逃逸速率的两态模型理论,建立粒子逃逸的瞬时速率方程,推导得出驻留时间分布函数的递归表达式。基于此,分别计算信号振幅与循环噪声强度比值较大和较小2种不同情形下驻留时间分布函数的解析表达式。并且,从理论和数值模拟两方面分别阐明了循环噪声对驻留时间分布函数结构的影响。研究结果表明:驻留时间分布函数呈现指数衰减且在循环滞后时间处出现骤然下降趋势,且随着噪声强度和相关强度的增大驻留时间分布函数衰减速度变快,说明循环噪声能够加速粒子在势阱间的跃迁。此外,在周期信号的调制下,驻留时间分布函数在信号半周期的奇数倍处出现一系列峰值,这预示着系统发生了随机共振现象。

具有非平稳参数的二维肿瘤模型的B-tipping分析

本文建立了一个参数是非平稳变化过程的CD8+T细胞与肿瘤细胞相互作用的数学模型.首先对固定参数条件下的系统进行动力学分析,理论结果表明系统存在双稳态现象和鞍结点分岔.其后引入函数s(t)描述CD8+T细胞输入率的非平稳参数变化过程,发现系统在非平稳参数变化下存在B-tipping现象:系统轨迹随着时变参数s(t)的缓慢增加跟踪固定参数系统的轨迹,在分岔点处达到临界状态并经历突变趋向另一个稳定状态.在癌症治疗过程中,通过调节CD8+T细胞的输入率将患者状态移到tipping point可以有效地控制肿瘤生长.