大范围运动刚体-柔性梁刚柔耦合动力学分析

对自由大范围运动情况下刚体-柔性梁系统的刚柔耦合动力学特性进行了研究.考虑系统作平面大范围运动及柔性梁的纵向和横向变形,在纵向变形位移中计及横向弯曲引起的轴向缩短,即耦合变形项.采用假设模态法对柔性梁进行离散,运用拉格朗日方程推导出系统刚柔耦合动力学方程.分大范围运动为转动、平动,平面运动进行了动力学仿真,重点探讨了大范围平动下的刚体-柔性梁系统的刚柔耦合动力学特性.首先研究了系统在外界激励作用下的耦合动力学,其次分析了已知大范围平动对柔性梁小变形运动的影响.结果表明:零次近似模型不能反映大范围平动和柔性梁小变形运动之间的耦合作用;在不同的大范围平动加速度下,柔性梁中既可存在动力刚化效应,也可存在动力柔化效应.     

热载荷作用下大变形柔性梁刚柔耦合动力学分析

从非线性应变-位移关系式出发,用虚功原理建立了热载荷作用的柔性梁的热传导方程和旋转刚体-梁系统的刚-柔耦合动力学方程.由于考虑了刚度阵的高次变形项,适用于大变形问题.对温度、弹性变形和刚体运动变量联合求解.研究了热流引起的温度梯度对弹性变形和刚体转动的影响,以及在大变形情况下的几何非线性效应.     

旋转柔性梁的动力学建模及分析

基于一次近似理论，采用弧坐标分量和Cartesian坐标分量共同描述柔性梁的变形场，并采用Green应变张量描述应变能，用Hamilton原理建立系统动力学方程。揭示产生动力刚化现象的力学本质。采用有限元方法进行离散，基于数值实验系统地研究旋转柔性梁的动力刚化现象。计算表明，旋转柔性梁的横向固有频率随旋转角速度和中心刚体半径的增大而增大．从而只存在一阶临界转速，且当中心刚体半径超过临界半径时．不存在临界转速。     

作大范围平动弹性梁的动力学性质

本文利用初始构形，中间构形和现时构形三种构形，给出了作大范围平动弹性结构的运动学描述方法，建立了作大范围平动弹性梁的刚－柔耦合动力学控制方程。利用Melnikov方法和数值仿真技术，讨论了作大范围平动弹性梁的全局分岔和混沌性质，通过分析表明，当大范围平动超过某一临界速度时，它对弹性结构动力学性质的影响有着决定性的作用。本文的研究将有利于柔性多体系统的刚－柔耦合动力学建模理论的发展。     

无网格法在中心刚体-旋转柔性梁系统动力学分析中的应用EI北大核心CSCD

将无网格点插值法、径向基点插值法、光滑节点插值法用于中心刚体-旋转柔性梁的动力学分析。基于浮动坐标系方法,考虑梁的纵向拉伸变形和横向弯曲变形,并计入横向弯曲变形引起的纵向缩短,即非线性耦合项,运用第二类Lagrange方程推导得到作大范围运动的中心刚体-旋转柔性梁系统的动力学方程。将无网格法的仿真结果与有限元法和假设模态法进行比较分析,表明其作为一种柔性体离散方法在中心刚体-旋转柔性梁的刚柔耦合多体系统动力学的研究中具有可推广性。     

大变形刚-柔耦合系统仿真和实验研究

通过气浮台和梁系统的刚-柔耦合动力学实验研究完备的几何非线性模型和一次近似模型在大变形情况下的适用性.首先从Green应变与位移的非线性关系式出发,用绝对节点坐标法建立了弹性梁的完备的几何非线性动力学模型,并考虑结构阻尼建立了气浮台和梁系统的刚-柔耦合动力学方程,然后利用非接触式的运动测量仪和应变仪测量特征点的速度、角速度和应变,通过理论和实验结果的数值对比验证了几何非线性动力学模型的正确性,在此基础上进一步分析基于小变形的一次近似模型的适用性.     

带轴向运动柔性梁附件航天器的刚-柔耦合动力学分析

针对当前航天器面向大型化、复杂化和精密化方向发展,为了提高航天器的使用寿命、运行精度和工作效率,考虑航天器主体和轴向运动柔性梁的刚-柔耦合作用是十分有必要的。基于Euler-Bernoulli梁理论以及刚-柔耦合建模方法,建立了航天器主体-轴向运动柔性梁刚-柔耦合系统的动力学模型。根据Hamilton原理推导出刚-柔耦合系统的动力学方程,采用分离变量法和振型叠加法求解耦合系统的动力学方程。利用四阶Runge-Kutta法进行数值计算。通过数值算例分析航天器主体半径、航天器主体面密度和柔性梁轴向速度对柔性梁横向振动以及对航天器姿态角的影响。     

计及变形耦合项的平面柔性梁动力学建模及频率分析

考虑了变形产生的几何非线性效应对作大范围运动的平面柔性梁的影响，在其纵向、横向的变形位移中均考虑了变形的二次耦合变量，从非线性应变-变形位移的原理出发，说明增加耦合变量后。使得剪应变近似为零，由此得出的变形模式更符合工程实际和简化需要。考虑两个方向的变形耦合后，采用有限元离散，通过Lagrange方程导出系统的动力学方程。最后对一作旋转运动的平面柔性梁进行仿真计算，并对其固有频率进行分析研究。将本文模型所得的结论。与一次耦合动力学模型、零次近似模型进行比较，说明了三种模型的差异。得到了作旋转运动的平面柔性梁的一些新特点。     

改进EFG法用于旋转梁的刚柔耦合动力学研究

采用全域插值广义移动最小二乘(IGMLS)的改进无网格伽辽金(EFG)法,对旋转中心刚体-柔性梁系统的刚柔耦合动力学特性进行研究。利用考虑了柔性梁横向变形引起的非线性耦合项的一次近似耦合模型,根据Hamilton原理和EFG离散方法得到刚柔耦合系统的无网格动力学离散方程。在大范围运动未知的情况下,采用数值方法对刚柔耦合系统进行动力响应的仿真计算,并对EFG法的主要影响因素进行了讨论分析。通过与有限元法的数值计算结果对比,验证EFG法用于刚柔耦合系统动力学研究的有效性及可行性,并为无网格法用于更复杂的柔性多体动力学的研究提供了理论依据。     

一种基于应变插值大变形梁单元的刚-柔耦合动力学分析

柔性多体系统动力学中的“动力刚化”现象起因于变形间的耦合。一次近似模型成功地解决了小变形情况下的刚柔耦合建模问题,但在大变形情况下则需要考虑更多的耦合效应。本文选取表征梁弯曲应变的曲率和轴向应变作为单元参数进行离散;在大变形大转动基础上得到了单元两端节点运动学参数的递推关系,构造出了能够自动计及“动力刚化项”且适用于大变形刚柔耦合动力学分析的平面梁单元。最后采用本文所提应变插值单元求解了包含大变形和刚柔耦合动力学柔性梁的数值算例,验证了文中算法的正确性和有效性。     

全悬挂多点啮合柔性支承传动系统频率响应分析

本文对全悬挂多点啮合柔性支承传动系统在简谐激励下的响应进行了研究。通过拉氏变换和频率响应法获得了该系统的稳态解,发现了在简谐激励下,当结构参数满足一定条件时,主轴动应力将变为零这一特性。     

绕弹性水翼非定常空化流激振动特性研究

该文通过实验和数值计算相结合的方法,对弹性水翼非定常空化流激振动特性进行了研究。实验中,采用高速摄像机获取云状空化不同发展阶段的流动发展规律,应用激光测振仪测量弹性水翼的流激振动特性,通过同步测量技术获取水翼振动特性数据并结合空穴形态图对其进行分析,同时在实验结果基础上加入数值计算部分对流激振动特性进行进一步的说明。研究结果表明：云状空穴的发展为一个准周期过程,包括附着型空穴的生长、空穴的脉动以及空穴的脱落三个阶段;弹性水翼的振动主要受空穴发展过程的影响,因此流激振动特性呈现出周期性的变化过程,且弹性水翼振动主导频率为空穴脱落频率;在不同的空穴发展阶段,表现出不同流激振动特性,并且在空穴脉动和空泡脱落阶段水翼振动较为剧烈。     

A Voltage‐Boosting Strategy Enabling a Low‐Frequency,Flexible Electromagnetic Wave Absorption Device

Nowadays, low‐frequency electromagnetic interference (<2.0 GHz) remains a key core issue that plagues the effective attenuation performance of conventional absorption devices prepared via the component‐morphology method (Strategy I). According to theoretical calculations, one fundamental solution is to develop a material that possesses a high ε′ but lower ε″. Thus, it is attempted to control the dielectric values via applying an external electrical field, which inducts changes in the macrostructure toward a performance improvement (Strategy II). A sandwich‐structured flexible electronic absorption device is designed using a carbon film electrode to conduct an external current. Simultaneously, an absorption layer that is highly responsive to an external voltage is selected via Strategy I. Relying on the synergistic effects from Strategies I and II, this device demonstrates an absorption value of more than 85% at 1.5–2.0 GHz with an applied voltage of 16 V while reducing the thickness to ≈5 mm. In addition, the device also shows a good absorption property at 25–150 °C. The method of utilizing an external voltage to break the intrinsic dielectric feature by modifying a traditional electronic absorption device is demonstrated for the first time and has great significance in solving the low‐frequency electromagnetic interference issue.     

MXenes for Plasmonic Photodetection

MXenes have recently shown impressive optical and plasmonic properties associated with their ultrathin‐atomic‐layer structure. However, their potential use in photonic and plasmonic devices has been only marginally explored. Photodetectors made of five different MXenes are fabricated, among which molybdenum carbide MXene (Mo₂CT_x) exhibits the best performance. Mo₂CT_x MXene thin films deposited on paper substrates exhibit broad photoresponse in the range of 400–800 nm with high responsivity (up to 9 A W^?1), detectivity (≈5 × 10¹¹ Jones), and reliable photoswitching characteristics at a wavelength of 660 nm. Spatially resolved electron energy‐loss spectroscopy and ultrafast femtosecond transient absorption spectroscopy of the MXene nanosheets reveal that the photoresponse of Mo₂CT_x is strongly dependent on its surface plasmon‐assisted hot carriers. Additionally, Mo₂CT_x thin‐film devices are shown to be relatively stable under ambient conditions, continuous illumination and mechanical stresses, illustrating their durable photodetection operation in the visible spectral range. Micro‐Raman spectroscopy conducted on bare Mo₂CT_x film and on gold electrodes allowing for surface‐enhanced Raman scattering demonstrates surface chemistry and a specific low‐frequency band that is related to the vibrational modes of the single nanosheets. The specific ability to detect and excite individual surface plasmon modes provides a viable platform for various MXene‐based optoelectronic applications.     

All-MXene-Printed RF Resonators as Wireless Plant Wearable Sensors for In Situ Ethylene Detection

Printed flexible electronics have emerged as versatile functional components of wearable intelligent devices that bridge the digital information networks with biointerfaces. Recent endeavors in plant wearable sensors provide real-time and in situ insights to study phenotyping traits of crops, whereas monitoring of ethylene, the fundamental phytohormone, remains challenging due to the lack of flexible and scalable manufacturing of plant wearable ethylene sensors. Here the all-MXene-printed flexible radio frequency (RF) resonators are presented as plant wearable sensors for wireless ethylene detection. The facile formation of additive-free MXene ink enables rapid, scalable manufacturing of printed electronics, demonstrating decent printing resolution (2.5% variation), ≈30000 S m⁻¹ conductivity and mechanical robustness. Incorporation of MXene-reduced palladium nanoparticles (MXene@PdNPs) facilitates 1.16% ethylene response at 1 ppm with 0.084 ppm limit of detection. The wireless sensor tags are attached on plant organ surfaces for in situ and continuously profiling of plant ethylene emission to inform the key transition of plant biochemistry, potentially extending the application of printed MXene electronics to enable real-time plant hormone monitoring for precision agriculture and food industrial management.     

Flexible Gallium Nitride for High‐Performance,Strainable Radio‐Frequency Devices

Flexible gallium nitride (GaN) thin films can enable future strainable and conformal devices for transmission of radio‐frequency (RF) signals over large distances for more efficient wireless communication. For the first time, strainable high‐frequency RF GaN devices are demonstrated, whose exceptional performance is enabled by epitaxial growth on 2D boron nitride for chemical‐free transfer to a soft, flexible substrate. The AlGaN/GaN heterostructures transferred to flexible substrates are uniaxially strained up to 0.85% and reveal near state‐of‐the‐art values for electrical performance, with electron mobility exceeding 2000 cm² V^?1 s^?1 and sheet carrier density above 1.07 × 10¹³ cm^?2. The influence of strain on the RF performance of flexible GaN high‐electron‐mobility transistor (HEMT) devices is evaluated, demonstrating cutoff frequencies and maximum oscillation frequencies greater than 42 and 74 GHz, respectively, at up to 0.43% strain, representing a significant advancement toward conformal, highly integrated electronic materials for RF applications.     

12-GHz thin-film transistors on transferrable silicon nanomembranes for high-performance flexible electronics

Multigigahertz flexible electronics are attractive and have broad applications. A gate-after-source/drain fabrication process using preselectively doped single-crystal silicon nanomembranes (SiNM) is an effective approach to realizing high device speed. However, further downscaling this approach has become difficult in lithography alignment. In this full paper, a local alignment scheme in combination with more accurate SiNM transfer measures for minimizing alignment errors is reported. By realizing 1 μm channel alignment for the SiNMs on a soft plastic substrate, thin-film transistors with a record speed of 12 GHz maximum oscillation frequency are demonstrated. These results indicate the great potential of properly processed SiNMs for high-performance flexible electronics.     

Flexible electronics: 12‐GHz Thin‐Film Transistors on Transferrable Silicon Nanomembranes for High‐Performance Flexible Electronics (Small 22/2010)

Multigigahertz flexible electronics are attractive and have broad applications. A gate‐after‐source/drain fabrication process using preselectively doped single‐crystal silicon nanomembranes (SiNM) is an effective approach to realizing high device speed. However, further downscaling this approach has become difficult in lithography alignment. In this full paper, a local alignment scheme in combination with more accurate SiNM transfer measures for minimizing alignment errors is reported. By realizing 1 μm channel alignment for the SiNMs on a soft plastic substrate, thin‐film transistors with a record speed of 12 GHz maximum oscillation frequency are demonstrated. These results indicate the great potential of properly processed SiNMs for high‐performance flexible electronics.