Transfer matrix method for free and forced vibrations of multi-level functionally graded material stepped beams with different boundary conditions

Functionally graded materials(FGMs)are a novel class of composite materials that have attracted significant attention in the field of engineering due to their unique mechanical properties.This study aims to explore the dynamic behaviors of an FGM stepped beam with different boundary conditions based on an efficient solving method.Under the assumptions of the Euler-Bernoulli beam theory,the governing differential equations of an individual FGM beam are derived with Hamilton’s principle and decoupled via the separation-of-variable approach.Then,the free and forced vibrations of the FGM stepped beam are solved with the transfer matrix method(TMM).Two models,i.e.,a three-level FGM stepped beam and a five-level FGM stepped beam,are considered,and their natural frequencies and mode shapes are presented.To demonstrate the validity of the method in this paper,the simulation results by ABAQUS are also given.On this basis,the detailed parametric analyses on the frequencies and dynamic responses of the three-level FGM stepped beam are carried out.The results show the accuracy and efficiency of the TMM.

Effective transmittance of Fabry–Perot cavity under non-parallel beam incidence

The Fabry–Perot(FP) resonant cavity is widely used in laser and spectroscopic measurements due to its unique interference transfer function(ITF). In the ideal case of parallel incident light, the ITF of the FP resonant cavity can be expressed by the Airy function. However, in reality, it is difficult to achieve perfect parallelism with collimated beams. In this article, a theoretical model is established for non-parallel light incidence, which assumes that the non-parallel incident light is a cone-shaped beam, and the cone angle is used to quantify the non-parallelism of the beam. The transmittance function of the FP resonant cavity under non-parallel light incidence is derived. The accuracy of the model is experimentally verified. Based on this model, the effects of divergence angle, tilt angle and FP cavity parameters(reflectivity, cavity length)on the ITF are studied. The reasons for the decrease in peak value, broadening and asymmetry of the interference peak under non-parallel light incidence are explained. It is suggested that a fine balance between the interference peak and the collimation effect of the incident light should be considered in the design and application of FP resonant cavities, especially for tilted applications such as angle-scanned spectroscopy. The research results of this article have certain significance for the design and application of FP resonant cavities.

Experimental Study on Force Behavior of Steel Rein forced Concrete Transfer Beam Structure with Basement of Large Space

Based on comparative test of two transfer story models, in one of which the transfer beam and basement column is constructed of steel reinforced concrete, and the other is constructed of ordinary reinforced concrete, its force behavior, ductility and failure mechanism under vertical and horizontal loads are studied. The results show that loading bearing and seismic behavior of transfer story structure with steel reinforced concrete beam and basement column is good. The relative design suggestion is put forward.

Analysis of metal transfer during electron beam welding with filler wire

The metal transfer mode of electron beam welding （EBW） with filler wire was studied experimentally. The spatial position between the electron beam and the filler wire was defined. Basing on the charge coupled device （CCD） visual sensing system, the metal transfer mode of filler wire was investigated. The results showed that there were five transfer modes during EBW process due to different wire feed rates and spatial positions between beam and filler wire, such as short-circuiting mode, molten metal bridge mode, small droplet mode, big droplet mode and mixed mode. By comparing the weld appearance of different transfer modes, the molten metal bridge transfer was proved to be the best transfer mode.

Magnet lattice design of the SSRF electron-beam transfer lines

Under three-dimensional plane geometrical constraints ( X,Y,θ ), with two asymmetric achromatic sections, the combined three-section structural FODO-like magnet lattice design is adopted and finely optimized in the SSRF electron-beam transfer lines. The magnet lattice has high flexibility and robustness, and the Courant–Snyder parameters can be easily adjusted within a wide range to meet the requirements of transmission and injection for different operation modes of the linear accelerator, booster synchrotron, and storage ring. In this article, the main parameters of the linear optics design of the SSRF electron-beam transfer lines are described, involving the physical design criteria, the total geometrical layout, the magnet lattice, and the beam Courant–Snyder parameters matching. The studies of the variant beam dynamic simulation program calculations show that the design purpose of the efficient beam transmission and injection will be basically achieved.

Energy Transfer among Modes in a Non-Slender Elastic Beam Subject to Vortex-Induced Vibration

The vibration of an elastic beam experiencing vortex-induced vibration is numerically analyzed employing a wake-oscillator model. The influence of the excited mode, the initial velocity, the shedding pulsation and the mass ratio on the energy transfer among modes and the vibration amplitude is determined. Multiple frequencies are detected, and the power spectral density of the beam tip time series is used to calculate the dominant frequency.

纳米隔热材料在板坯加热炉水梁中的应用研究

针对新型纳米绝热保温材料在高温板坯加热炉的应用,开展了传统水梁包扎方式与新型纳米隔热包扎方式的对比研究。通过数值仿真分析对不同方案隔热效果及温度分布进行了预测,并搭建水冷实验系统对采用不同包扎方式的水梁散热量进行测试分析。测试结果表明随着炉温逐步升高,纤维隔热材料的导热系数快速上升,常规纤维隔热水梁散热快速增加,而纳米隔热材料的导热系数增加较小,故此纳米隔热水梁的散热增加较为缓慢,两种方案散热量的差距随着炉温升高而逐渐增大。在此基础上开展了工程应用,应用效果与数值仿真及实验研究数据吻合良好。工程应用对比结果表明,纳米隔热水梁相对传统水梁包扎方案可实现水梁区域能耗降低25%,具有较好的经济和生态效益。

基于DDPG的智能反射面辅助无线携能通信系统性能优化

针对智能反射面(IRS, intelligent reflecting surface)辅助的多输入单输出(MISO, multiple input singleoutput)无线携能通信(SWIPT, simultaneous wireless information and power transfer)系统,考虑基站最大发射功率、IRS反射相移矩阵的单位膜约束和能量接收器的最小能量约束,以最大化信息传输速率为目标,联合优化了基站处的波束成形向量和智能反射面的反射波束成形向量。为解决非凸优化问题,提出了一种基于深度强化学习的深度确定性策略梯度(DDPG, deep deterministic policy gradient)算法。仿真结果表明,DDPG算法的平均奖励与学习率有关,在选取合适的学习率的条件下,DDPG算法能获得与传统优化算法相近的平均互信息,但运行时间明显低于传统的非凸优化算法,即使增加天线数和反射单元数,DDPG算法依然可以在较短的时间内收敛。这说明DDPG算法能有效地提高计算效率,更适合实时性要求较高的通信业务。

脉冲束流下车载加速器中子源靶传热特性

为了研究不同脉冲束流频率下车载加速器中子源靶的传热特性及其热动态响应,通过调整脉冲束流的频率或脉宽对背部冷却微通道靶的传热性能进行模拟,并通过分析靶内部结构的热沉积分布,探究车载加速器中子源靶的热负载上限以及制约束流的因素。选用能量为2.5 MeV、峰值流强为10 mA的束流开展模拟,结果表明:当束流占空比保持在3%不变时,靶的最高温度呈周期波动,且存在上下包络;随着束流频率的上升,每个脉冲周期内靶的上包络温度逐渐下降,这是由于每个脉冲期间的热冲击下降所导致的;频率上升时,每个周期内加热时间与冷却时间同时缩短,导致其下包络温度在最开始增大后基本保持不变;靶的最高温度随着束流频率增加出现从锂层到中间层钽层的转移。该研究对于车载加速器中子源的束流参数选择和靶冷却设计具有一定的参考价值。

FREE VIBRATION ANALYSIS AND PHYSICAL PARAMETER IDENTIFICATION OF NON-UNIFORM BEAM CARRYING SPRING-MASS SYSTEMS

To analyze a multibody system composed of non-uniform beam and spring-mass subsystems, the model discretization is carried on by utilizing the finite element method（FEM）, the dynamic model of non-uniform beam is developed by using the transfer matrix method of multibody system（MS-TMM）, the transfer matrix of non-u- niform beam is derived, and the natural frequencies are computed. Compared with the numerical assembly method （NAM）, the results by MS-TMM have good agreement with the results by FEM, and are better than the results by NAM. When using the high precision method, the global dynamic equations of the complex multibody system are not needed and the orders of involved system matrices are decreased greatly. For the investigation on the re- verse problem of the physical parameter identification of multibody system, MS-TMM and the optimization tech- nology based on genetic algorithms（GAs） are combined and extended. The identification problem is exchanged for an optimization problem, and it is formulated as a global minimum solution of the objective function with respect to natural frequencies of multibody system. At last, the numerical example of non-uniform beam with attach- ments is discussed, and the identification results indicate the feasibility and the effectivity of the proposed aop- proach.

基于迁移学习的室内波束选择优化方法

使用基于深度学习的室内波束选择方法可以显著提高波束匹配概率和搜索效率,但该方法需要大型数据集来调整其大量可训练参数,导致了额外的系统开销。针对这一不足,结合一种迁移学习技术,使得目标场景神经网络以小数据集方式获得与大数据集相近的匹配精度,从而减小基于深度学习的波束选择方法中数据集大小对匹配结果产生的影响。首先使用大型数据集在一个源场景中对源神经网络进行充分训练,使得网络参数能够充分包含信道状态信息以及环境信息;而后利用源神经网络参数对目标场景中的神经网络进行不同程度初始化,使该神经网络在经过小数据集训练后依然可以获得较好的波束匹配性能。仿真结果表明,针对室内波束选择场景,在数据集有限的情况下,使用迁移学习方法进行波束选择,同样可以获得较高的匹配精度。

大跨度悬挂式单轨钢箱组合梁总体设计及关键技术研究

悬挂式单轨是一种轻型、中速、低成本的新型轨道交通方式,结构轻盈、美观,但是当跨越河流、沟壑等障碍时,存在明显短板。从结构受力、运行安全角度出发,提出一种在斜拉桥的主梁上架设轨道墩柱和轨道梁的新型组合梁结构方案,突破常规悬挂式单轨跨越能力受限的壁垒。为研究斜拉桥主梁与轨道梁墩柱结合部位复杂的受力情况和传力路径,采用ANSYS软件分别建立钢箱梁区段和混凝土箱梁区段有限元模型。结果表明:钢箱梁区段,墩柱荷载主要传递给与之直接相连的横隔板以及中腹板,其中,横隔板受力比较均匀,中腹板受力主要集中在以墩柱为中心,半径约2 m的范围内,基本可以传递至钢梁底板。墩柱轴力的58%传递给与之直接相连的横隔板;墩柱横桥向弯矩的传递过程中,58.8%的剪力传递给与之直接相连的横隔板;墩柱顺桥向弯矩的传递过程中,53.4%的剪力传递给中腹板;混凝土箱梁区段,墩柱荷载主要传递给与之直接相连的混凝土腹板、横隔板。混凝土受力主要集中在以结合面为中心,半径约2 m的范围内,墩柱荷载在结合面以下约0.5 m的范围内基本完成传递,墩柱轴力的68.8%传递给与之直接相连的横隔板;墩柱横桥向弯矩的传递过程中,86.4%的剪力传递给与之直接相连的横隔板;墩柱顺桥向弯矩的传递过程中,44.6%的剪力传递给中腹板。

襄阳大厦超限高层结构设计

襄阳大厦结构高度249.6m,地上共58层,塔楼采用框架-核心筒结构体系,存在分段折柱、核心筒单侧收进、高位转换、连梁支承楼盖梁等特点。针对结构设计过程中的重难点,通过合理的计算分析与加强措施,确保与分段折柱相连的水平构件、核心筒墙体、转换构件的安全问题,并采用新型分段式连梁解决楼盖梁支承在连梁上的设计问题。弹性及弹塑性验算结果表明,结构满足预期抗震性能目标,各项结构措施合理可靠,结构设计安全合理。

分数阶粘弹性地基上裂纹梁的自由振动

本文研究了分数阶粘弹性Pasternak地基上含多裂纹Euler梁的自由振动问题.首先,引入分数阶导数概念,建立粘弹性Pasternak地基模型,推导出地基应力-应变本构的复模量以及地基反力.其次,将裂纹等效成无质量扭转弹簧,借助于裂纹能量释放率和应力强度因子的关系,推导出梁的局部柔度.然后,基于传递矩阵方法,建立含多裂纹梁的分段传递矩阵进而得到总体传递矩阵.最后,基于梁的边界条件,建立求解裂纹梁的复固有频率及振型的线性代数方程组,数值求解得到含多裂纹梁的固有频率及振型.以含双裂纹的两端简支Euler梁为例,数值计算了复固有频率和振型.并基于曲率模态分析裂纹位置对复固有频率和振型的影响.数值结果揭示了粘弹性地基的分数阶系数、粘性系数以及裂纹位置和裂纹深度对复固频率和振型的影响规律.

防磨梁与防磨格栅对循环流化床锅炉炉内传热的影响

循环流化床(circulating fluidized bed,CFB)锅炉普遍存在炉膛水冷壁磨损严重的问题。为提高运行可靠性,目前一般通过加装防磨梁或防磨格栅实现主动防磨,但该方式会引起流场变化,并对锅炉运行参数以及炉内传热造成影响。因此,建立循环流化床锅炉全炉膛水冷壁传热计算模型,提出加装防磨梁、防磨格栅后的边壁区颗粒浓度及传热面积修正系数计算方法,利用该模型对某440 t/h CFB锅炉炉内传热特性进行计算。结果显示:水冷壁加装防磨梁后,传热系数和传热能力有所下降,下降幅度和防磨梁数量有关,采用6道和12道防磨梁时,传热系数分别下降0.32%和2.89%,传热量分别下降3.28%和8.68%;比较而言,防磨格栅对炉内传热系数和传热能力影响较小,加装与防磨梁相同数量的防磨格栅时,表现出了一定的传热强化效果,传热量略有上升,当防磨格栅加装数量增加至30道时,传热系数下降5.76%,传热量上升1.59%。防磨格栅在降低水冷壁磨损的同时,对锅炉运行造成的影响较小,优于防磨梁。该模型可对CFB锅炉防磨技术的选用以及设计方案优化提供理论参考。

基于传递矩阵法的Timoshenko裂纹梁自振特性分析

首先基于传递矩阵法,将裂纹截面假定一无质量扭转弹簧,通过扭转弹簧建立起各段子梁在裂纹截面处的矩阵传递关系,推导出含任意裂纹Timoshenko梁及无裂纹Timoshenko梁的传递矩阵,引入边界条件简化矩阵方程,并利用Matlab对方程进行求解。其次讨论了裂纹位置和相对深度对单裂纹简支梁自振频率的影响,与文献结果进行对比,误差最多不超过1%;然后通过ABAQUS建立悬臂梁及两端固支梁有限元模型,分析相对裂纹深度对自振频率的影响,计算结果与有限元结果进行对比,误差不超过3.86%;最后研究了不同跨高比下相对裂纹深度对Timoshenko简支梁自振频率的影响,计算结果与文献最大误差为4.56%,验证了本文方法的有效性及适用性。

利用扫描隧道显微术对SrTiO_(3)(001)上生长CoSe/FeSe异质界面结构和谱学研究

硒化铁/钛酸锶(001)(FeSe/SrTiO_(3)(001),FeSe/STO)中界面增强的超导电性一直是近些年凝聚态物理领域的热点问题之一,基于FeSe薄膜构筑异质界面是调控其超导电性和构筑新奇量子物态的重要手段。本文报道了利用分子束外延在SrTiO_(3)(001)衬底上制备了高质量硒化钴-硒化铁(CoSe/FeSe)纵向异质结的方法,利用扫描隧道显微镜和扫描隧道谱详细研究了该异质界面的电子性质和电子态密度的实空间分布。由于CoSe/FeSe界面存在强烈的电荷转移,FeSe处于过掺杂状态,导致FeSe/STO界面相互作用已不满足非绝热近似,以及FeSe中超导电性的消失。空间依赖的扫描隧道谱显示,CoSe/FeSe的异质界面边缘处出现了晶向依赖的边缘电子态和边角电子态,这些边界上的电子态受到CoSe/FeSe界面电荷转移效应的调制。该研究为基于单层FeSe/STO界面超导电性的调控及量子结构的构筑提供了借鉴。

基于幅相解耦调制的透射型声超表面的声波调控

文章构造了一种复合型无源结构,利用该结构设计的声学超表面能够实现透射相位和幅度的解耦调控。研究表明,当声波入射至该复合结构后,多腔体结构具有接近于1的透射率和接近于2π的全相位变化,而开孔结构单元可以提供恒定不变的相位和0~1范围内变化的透射率。此外,根据Airy函数的波曲线,选择合适的结构参数,构造出的超表面可以在空气中生成Airy波束,同时利用两个对称的超表面可以实现具有自愈性声聚焦特性的透镜,通过与纯相位调控方法生成的波束现象进行对比,进一步说明幅相解耦方法对于声波精确调控的重要性。文章对于幅相解耦超表面的研究在声波定向传输、全息图像、医学超声成像等方面具有潜在的应用前景。

局域共振夹芯超结构梁带隙特性及实验研究

本文提出了一种新型局域共振夹芯超结构梁,该结构由夹芯梁基体和由软材料包裹质量块组成的局域共振单元构成。分别采用传递矩阵法和有限元法计算了该结构的带隙分布和振动传输特性,搭建了局域共振夹芯超结构梁的振动传输测试实验平台,并与数值计算结果进行对比验证,最后分析了结构参数对结构带隙分布特性的调控规律。研究结果表明,该结构在低频范围内共出现两条弯曲波带隙,带隙频率分别为196.1~339.0 Hz和377.2~655.6 Hz。而完全带隙位于弯曲波带隙内,频率范围为380.0~423.6 Hz。且在这两条弯曲波带隙范围内,弯曲振动传输会发生明显的减弱现象。另外,局域共振夹芯超结构梁的结构参数会对带隙分布特性产生较大影响,通过合理选择结构参数,可以实现局域共振夹芯超结构梁低频率和高带宽的减振要求。

Enabling the transfer matrix method to model serial-parallel compliant mechanisms including curved flexure beams

Compliant mechanisms with curved flexure hinges/beams have potential advantages of small spaces,low stress levels,and flexible design parameters,which have attracted considerable attention in precision engineering,metamaterials,robotics,and so forth.However,serial-parallel configurations with curved flexure hinges/beams often lead to a complicated parametric design.Here,the transfer matrix method is enabled for analysis of both the kinetostatics and dynamics of general serial-parallel compliant mechanisms without deriving laborious formulas or combining other modeling methods.Consequently,serial-parallel compliant mechanisms with curved flexure hinges/beams can be modeled in a straightforward manner based on a single transfer matrix of Timoshenko straight beams using a step-by-step procedure.Theoretical and numerical validations on two customized XY nanopositioners comprised of straight and corrugated flexure units confirm the concise modeling process and high prediction accuracy of the presented approach.In conclusion,the present study provides an enhanced transfer matrix modeling approach to streamline the kinetostatic and dynamic analyses of general serial-parallel compliant mechanisms and beam structures,including curved flexure hinges and irregular-shaped rigid bodies.