Theoretical and numerical investigation of HF elastic wave propagation in two-dimensional periodic beam lattices

The elastic wave propagation phenomena in two-dimensional periodic beam lattices are studied by using the Bloch wave transform. The numerical modeling is applied to the hexagonal and the rectangular beam lattices, in which, both the in-plane （with respect to the lattice plane） and out-of-plane waves are considered. The dispersion relations are obtained by calculating the Bloch eigenfrequencies and eigenmodes. The frequency bandgaps are observed and the influence of the elastic and geometric properties of the primitive cell on the bandgaps is studied. By analyzing the phase and the group velocities of the Bloch wave modes, the anisotropic behaviors and the dispersive characteristics of the hexagonal beam lattice with respect to the wave prop- agation are highlighted in high frequency domains. One im- portant result presented herein is the comparison between the first Bloch wave modes to the membrane and bend- ing/transverse shear wave modes of the classical equivalent homogenized orthotropic plate model of the hexagonal beam lattice. It is shown that, in low frequency ranges, the homog- enized plate model can correctly represent both the in-plane and out-of-plane dynamic behaviors of the beam lattice, its frequency validity domain can be precisely evaluated thanks to the Bloch modal analysis. As another important and original result, we have highlighted the existence of the retro- propagating Bloch wave modes with a negative group veloc- ity, and of the corresponding ＂retro-propagating＂ frequency bands.

Elastic Wave Scattering by Two-Dimensional Periodical Array of Cylinders

We extend the multiple-scattering theory (MST) for elastic wave scattering and propagating in two-dimensional composite. The formalism for the band structure calculation is presented by taking into account the full vector character of the elastic wave. As a demonstration of application of the formalism we calculate the band structure of elastic wave propagating in a two-dimensional periodic arrangement of cylinders. The results manifest that the MST shows great promise in complementing the plane-wave (PW) approach for the study of elastic wave.

Dynamical response of hyper-elastic cylindrical shells under periodic load

Dynamical responses, such as motion and destruction of hyper-elastic cylindrical shells subject to periodic or suddenly applied constant load on the inner surface, are studied within a framework of finite elasto-dynamics. By numerical computation and dynamic qualitative analysis of the nonlinear differential equation, it is shown that there exists a certain critical value for the internal load describing motion of the inner surface of the shell. Motion of the shell is nonlinear periodic or quasi-periodic oscillation when the average load of the periodic load or the constant load is less than its critical value. However, the shell will be destroyed when the load exceeds the critical value. Solution to the static equilibrium problem is a fixed point for the dynamical response of the corresponding system under a suddenly applied constant load. The property of fixed point is related to the property of the dynamical solution and motion of the shell. The effects of thickness and load parameters on the critical value and oscillation of the shell are discussed.

Band structures of elastic waves in two-dimensional eight-fold solid–solid quasi-periodic phononic crystals

Combined with the supercell method, band structures of the anti-plane and in-plane modes of two-dimensional （2D） eight-fold solid-solid quasi-periodic phononic crystals （QPNCs） are calculated by using the finite element method. The influences of the supercell on the band structure and the wave localization phenomenon are discussed based on the modal distributions. The reason for the appearance of unphysical bands is analyzed. The influence of the incidence angle on the transmission spectrum is also discussed.

A CLOSED-FORM ALGORITHM FOR THE STEADY-STATE RESPONSE OF ELASTIC MECHANISMS

This paper presents a closed-form algorithm for the steady-state response of elastic mecha-nisms. Based on an analytic expression of the initial conditions, the steady-state response can beobtained by just one cycle of integration, thus the algorithm is of high efficiency. The algorithm isthen verified by comparing the computational results with the previously published experimental re-sults.

DYNAMICAL FORMATION OF CAVITY IN A COMPOSED HYPER-ELASTIC SPHERE

The dynamical formation of cavity in a hyper_elastic sphere composed of two materials with the incompressible strain energy function, subjected to a suddenly applied uniform radial tensile boundary dead_load, was studied following the theory of finite deformation dynamics. Besides a trivial solution corresponding to the homogeneous static state, a cavity forms at the center of the sphere when the tensile load is larger than its critical value. An exact differential relation between the cavity radius and the tensile land was obtained. It is proved that the evolution of cavity radius with time displays nonlinear periodic oscillations. The phase diagram for oscillation, the maximum amplitude, the approximate period and the critical load were all discussed.

Is a Cooling-Off Period Necessary in Divorce Proceedings?

Six draft sections （m specific areas of the Civil Code were submitted to the Standing Committee of the National People＇s Congress. China＇s top legislature, on August 27. One of them, the controversial draft on marriage and family, has aroused much debate among Internet users. It proposes a one-month cooling-off period for couples who wish to part ways and apply to divorce registration agencies. During the cooling-off month after a divorce registration agency receives a divorce application, either the husband or the wife can stop the application. After the cooling-off month, both sides are required to go to the agency for the divorce certificates. Failing to do so will mean the divorce application is canceled automatically.

恒频声学二极管的设计及特性研究

声学二极管能控制声波仅在一个方向有效传输在反方向无法传播,在通信技术中具有广泛的应用,然而目前大多数的声学二极管设计是基于非线性效应使系统只通过新的高次频率并阻止原频率的传输.本文利用不对称结构与弱非线性声子晶体的组合,提出了一种一维声二极管模型,实现弹性波的不对称传输,并保持频率不变.该模型由左端的变幅杆和右端的非线性弹簧质量链组成,理论分析表明,该声学二极管具有与电子二极管相同的正向和反向特性,并通过有限元仿真验证了该模型的有效性.

考虑周期折减的结构弹性时程分析调整方法

针对结构弹性时程分析时无法考虑周期折减的问题展开研究,通过对比结构时程分析的过程中,地震波的选取是否考虑周期折减的差异,提出采用增大系数放大时程分析法输入地震波有效峰值加速度以及地震响应;考虑弹性时程分析过程中,周期折减对结构地震作用的增大效应。理论分析增大系数取值的影响因素,并基于单自由度体系对比两种调整方法的效果及差异,采用实际算例以验证所提出弹性时程分析中考虑周期折减调整方法的有效性。结果表明:增大系数的取值与周期折减系数、结构自振周期及场地特征周期等因素有关;对于单自由度体系,两种调整方法具有完全相同的调整效果;按文章提出方法考虑周期折减的算例结构,弹性时程分析所得各楼层地震剪力及层间位移角与考虑周期折减的反应谱(CQC)计算结果均较为接近。

离婚冷静期制度实施的困境与出路

随着经济社会的发展,我国离婚率呈上升趋势,并出现闪婚闪离、冲动离婚等现象。对此,2020年《中华人民共和国民法典》首次增设离婚冷静期,旨在通过立法约束减少冲动离婚和轻率离婚,挽救可维系的婚姻。目前,离婚冷静期制度实施已经初显成效,部分夫妇在冷静期结束后选择放弃离婚。但在法律实践中也出现了适用期限缺乏弹性、协议离婚与诉讼离婚同步申请导致冷静期虚化、配套措施不完善等问题。因此,应通过设立灵活且有弹性的离婚冷静期期限、设置排除适用离婚冷静期的情形和离婚申请前置审查程序、完善调解措施等举措,逐步健全离婚冷静期制度,使之更加符合当前婚姻法律改革的发展和需要。

浅谈干挂石材用胶粘剂的性能和使用

本文简述了目前干挂石材用胶粘剂的行业现状,通过检测数据分析了干挂胶各项检测参数反映的产品特性及使用过程中的注意事项,强调了在新材料、新工艺、新配方不断发展的时代背景下工程检测的必要性和重要性。

Symplectic analysis for wave propagation in one-dimensional nonlinear periodic structures

The wave propagation problem in the nonlinear periodic mass-spring structure chain is analyzed using the symplectic mathematical method. The energy method is used to construct the dynamic equation, and the nonlinear dynamic equation is linearized using the small parameter perturbation method. Eigen-solutions of the symplectic matrix are used to analyze the wave propagation problem in nonlinear periodic lattices. Nonlinearity in the mass-spring chain, arising from the nonlinear spring stiffness effect, has profound effects on the overall transmission of the chain. The wave propagation characteristics are altered due to nonlinearity, and related to the incident wave intensity, which is a genuine nonlinear effect not present in the corresponding linear model. Numerical results show how the increase of nonlinearity or incident wave amplitude leads to closing of transmitting gaps. Comparison with the normal recursive approach shows effectiveness and superiority of the symplectic method for the wave propagation problem in nonlinear periodic structures.

New Periodic Wave Solutions and Their Interaction for （2＋1）-dimensional KdV Equation

A class of new doubly periodic wave solutions for （2＋1）-dimensional KdV equation are obtained by introducing appropriate Jacobi elliptic functions and Weierstrass elliptic functions in the general solution（contains two arbitrary functions） got by means of multilinear variable separation approach for （2＋1）-dimensional KdV equation. Limiting cases are considered and some localized excitations are derived, such as dromion, multidromions, dromion-antidromion, multidromions-antidromions, and so on. Some solutions of the dromion-antidromion and multidromions-antidromions are periodic in one direction but localized in the other direction. The interaction properties of these solutions, which are numerically studied, reveal that some of them are nonelastic and some are completely elastic. Furthermore, these results are visualized.

基于大小交路的城轨列车开行频率与票价综合优化方法

针对城市轨道交通线路客流时空分布不均衡问题,为缓解高峰时段客流压力,均衡时段客流,提升列车运输能力利用率,提出基于大小交路的城轨列车开行频率与票价综合优化方法。构建双层优化模型,其中上层模型为多时段大小交路列车开行频率及票价综合优化模型,模型以不同运营时段内大小交路列车开行数量、不同运营时段内票价率为决策变量,以企业运营效益最大为优化目标。下层模型为基于弹性需求的多时段随机客流分配模型,考虑票价优化对旅客出行需求的影响,在分析旅客广义出行费用的基础上,建立旅客出行弹性需求函数。设计嵌套Logit随机用户客流分配方法的遗传算法对双层模型进行求解,并进行算例分析,验证优化模型可行性。算例结果表明:1)通过对各运营时段票价和大小交路列车开行频率综合优化能够满足城轨线路各区段的旅客出行需求,降低高峰运营时段内客流量,均衡同一OD对在不同运营时段内的出行需求,充分缓解线路客流的时空分布不均衡的现状;2)城轨票价优化能够在一定程度上吸引更多潜在客流,有效提升企业票价收益,提高旅客人车公里数,同时开行大小交路列车能避免列车运输能力浪费,从而降低企业运营成本。所提出的方法能够为城轨列车开行方案和票价制定提供理论基础。

心理弹性、社会支持对维持性血液透析诱导期病人恐惧疾病进展的影响

目的:探讨心理弹性、社会支持对维持性血液透析(MHD)诱导期病人恐惧疾病进展的影响。方法:选取MHD诱导期病人152例,采用一般资料量表、心理弹性量表、社会支持量表和恐惧疾病进展量表进行问卷调查。结果:143例病人最终纳入调查。心理弹性问卷总得分(58.73±10.37)分、社会支持总分(38.15±5.59)分、恐惧疾病进展总得分为(46.53±7.02)分。不同年龄、婚姻、学历、家庭月收入、并发症、血液透析知识的MHD诱导期病人的心理弹性得分差异有统计学意义(P<0.01);不同年龄、婚姻、学历、家庭月收入的病人社会支持差异有统计学意义(P<0.01);不同年龄、婚姻、家庭月收入、并发症、血液透析知识的病人恐惧疾病进展差异有统计学意义(P<0.01)。心理弹性及其维度与恐惧疾病进展呈负相关性(P<0.05~P<0.01);社会支持维度中,除支持的利用度(P>0.05)外,其余各维度均与恐惧疾病进展呈负相关性(P<0.05~P<0.01)。经多重线性回归分析显示,年龄大和并发症≥3个的MHD诱导期病人恐惧疾病进展评分高(P<0.05和P<0.01)),已婚、家庭月收入>10 000元、血液透析知识较多、心理弹性和社会支持得分高的病人恐惧疾病进展评分低(P<0.05~P<0.01),7个变量对病人恐惧疾病进展评分的影响为79.3%(P<0.05)。结论:MHD病人的恐惧疾病是一个复杂的、受多种因素影响的心理感受。临床上医护人员应采取针对性的干预措施,帮助病人建立正确的应对方式,从而缓解疾病进展恐惧心理。

后疫情时期高职学生心理弹性的教育对策

后疫情时期,心理弹性作为个体在压力事件中适应良好的过程,是高职学生对抗疫情后产物的一种重要心理能力。部分高职学生出现不同程度的心理应激反应,家庭教育的情感功能不能发挥作用。基于此,通过网络平台,建立后疫情时期高职学生心理健康状况教育机制;激发与培养高职学生心理弹性所涵盖的积极个性品质;强化高职学生积极情绪,使他们获得更高层次的价值实现感及主观幸福感;发挥高职学生重要外部力量的作用,提供更多维度的社会支持等方面提出后疫情时期高职学生心理弹性的教育对策。

周期性浮置板轨道弹性波传播行为及波动效应

为探究复杂周期性浮置板轨道结构中的弹性波传播行为及波动效应的内在机理,基于无限周期结构的弹性波理论建立浮置板轨道结构模型,计算并分析结构带隙特征、弹性波传播机制以及移动荷载激励下的波动效应。结果表明:复杂周期性浮置板轨道结构在0~300 Hz范围内存在8个带隙,且带隙可阻碍弹性波在结构中的传播;带隙特征主要受结构刚度影响,可通过改变钢弹簧刚度、剪力铰剪切刚度和基础分布刚度来调节带隙范围;由于浮置板、轨道和隧道衬砌结构的弹性波局域共振作用,浮置板轨道结构减振效果在0-√2倍共振频率范围内劣于整体道床轨道结构,而在大于√2倍共振频率时才优于整体道床轨道结构;结构加速度响应峰值由荷载速度线与频散曲线的交点所产生,带隙和通带范围内弹性波存在不同的波动效应,且带隙对弹性波正向多普勒效应具有抑制作用。

PW-CFRP弹性性能预测及三维钻削仿真

平纹编织结构碳纤维增强树脂基复合材料(plain-woven carbon fiber-reinforced plastic,PW-CFRP)展现出高损伤容限特性,在航空航天领域应用广泛。针对PW-CFRP钻削仿真中由于其材料弹性性能变化导致单一尺度钻削仿真难以体现实际钻削力的问题,研究其弹性性能预测及多尺度三维钻削仿真。基于周期性边界条件的弹性性能参数预测模型,利用预测的材料弹性性能参数,采用多尺度有限元方法,仿真PWCFRP的三维钻削并开展试验验证。研究结果表明:基于周期边界条件的有限元法能准确预测编织复合材料的弹性常数;在剪切载荷下,其编织单胞的边界面均由平面变成曲面,发生凸凹翘曲变形;基于刚度预测模型基础的PW-CFRP三维钻削仿真模型能够准确预测制孔过程中的轴向力、扭矩;在相同工艺参数下,制孔轴向力和扭矩的仿真预测与试验结果相对误差分别为14.2%和8.5%。

超声弹性成像在早产预测中的应用研究进展

早产是导致围生儿发病和死亡的主要原因之一,而宫颈功能不全是导致孕中晚期反复流产和早产的一个重要原因。准确评估孕妇宫颈功能,早期识别早产高风险人群,对预测并及时预防早产、改善不良妊娠结局至关重要。超声弹性成像是近年来迅速发展的一种现代成像技术,其可以客观评估组织软硬程度和均质性,实现宫颈组织软硬度量化,获得多个弹性定量指标,逐渐被用于早产风险的评估。该文就超声弹性成像在早产预测中的应用研究进行了综述。

基于能量法的橡胶浮置板轨道结构弹性波分析

针对城市轨道交通日益严重的环境振动问题,以橡胶浮置板这一城市轨道交通中常用隔振措施为研究对象,从弹性波的角度研究并提升其低频调控的性能。采用平面波级数模拟钢轨的周期性边界条件,用能量法计算了满铺式、条铺式和点铺式橡胶浮置板轨道结构的能量泛函,扫描波数变分得到橡胶浮置板的带隙特性,采用有限元法验证了提出方法的准确性。结果表明:满铺式第一阶带隙截止频率最大;条铺式与点铺式具有更低的截止频率和更宽的通带带宽,且第一阶带隙截止频率随着橡胶垫刚度的增大而提高;浮置板动力吸振器对弹性波的精准调控,为橡胶浮置板轨道低频振动控制的应用提供新的思路和方法。