铝蜂窝“Y”形单元准静态压溃有限元模拟研究

目的基于胶接强度对铝蜂窝吸能特性的重要影响,利用铝蜂窝的最小周期结构——"Y"型单元研究铝蜂窝结构的异面压缩变形过程和能量吸收特性,以了解不同胶黏剂对铝蜂窝吸能性能的影响。方法以Von Mises本构模型来表征胶黏剂的力学性能,建立一种含胶层的"Y"型单元有限元模型,模拟铝蜂窝结构的压溃变形过程,并得到胶层的变形和失效现象。结果不同胶黏剂失效情况不同,与之对应"Y"型单元的平均压缩强度和能量吸能值也有区别。该模型能够有效地模拟铝蜂窝结构的压溃变形过程,并准确预报胶层的变形和失效。通过实验验证所建立的"Y"型单元有限元模型计算精度能够满足实际工程需要。结论通过对"Y"形的单元准静态的压溃有限元模拟,选择了合适的胶黏剂制造铝蜂窝,并为后续包装缓冲件深入研究打下了基础。     

机械结构相似度评价及可靠性预计研究

在用传统的相似产品法进行可靠性预计时,所选取的相似产品与评价对象之间差异较大,会造成预计结果的偏差较大。为解决这一问题,提出了一种基于"功能—运动—动作"结构化分解的可靠性预计新方法。通过明确产品的各大运动功能建立功能层,分析完成各功能的机械部件运动建立运动层,确定实现各机械部件运动的元动作运动单元建立元动作层,建立了可靠性预计的"功能—运动—元动作运动单元"层次模型。引入区间层次分析法,确定了"功能—运动—元动作运动单元"层次模型中各子代运动单元对父代运动单元的可靠性影响权重,并构建了由子代运动单元预计父代运动单元可靠性的数学模型。确定影响评价机械结构相似度的因素,构建了区间数综合评判云模型并选取与元动作运动单元相似的参考结构,以区间数综合评价云模型得出的相似度值修正参考结构的可靠性数据来预计元动作运动单元的可靠性。将元动作运动单元的可靠性预计值代入数学模型,层层预计父代运动单元的可靠性,从而得出整个产品的可靠性水平。最后以数控转台为例进行了分析,得出了可靠性预计值,并将该方法与传统方法进行了比较。结果表明,新的可靠性预计方法具有较好的可行性和较高的准确性。     

GFRP复合材料与砖界面粘结性能的数值模拟

纤维复合材料(Fiber Reinforced Polymer,FRP)加固砌体结构剥离破坏是一种常见的破坏形式。对玻璃纤维复合材料(GFRP)和砖粘结界面进行数值模拟,用Solid65单元和Shell41单元分别模拟砖和GFRP,采用接触单元的方法,用"接触对"将砖实体单元和GFRP单元连接在一起,研究粘结界面的应力、应变分布特点和破坏过程。分析结果表明用有限元模拟分析粘结界面应力状态具有一定的可行性。     

三杆类桁架材料模型多工况最小柔度优化

研究了多工况结构柔度最小化方法。提出了3杆类桁架连续体材料模型。推导了该材料的刚度矩阵及其导数。通过优化杆件分布场得到优化的类桁架连续体。克服了目前普遍采用单元的"有"和"无"表示结构拓扑的轮廓粗糙、锯齿状边界问题。结点位置的杆件密度和方向作为设计变量,杆件在单元内的密度和方向通过结点位置的数值插值得到,并且在单元内连续变化。由于没有抑制中间密度,完全不存在数值不稳定问题。类桁架连续体由于与杆系结构有明确的对应关系,可以合理地转化杆系结构。选择杆件分布场中的部分杆件可以形成杆系结构。如果再进一步作尺寸和形状优化就可以得到最终的拓扑优化结构。     

钢结构施工力学状态非线性分析方法

施工力学问题分析的难点在于结构时变、材料时变和边界时变的模拟。该文剖析了单元生死技术模拟施工过程的基本原理,从数学和物理上揭示了单元"杀死"、"漂移"和"激活"的机理。探讨了施工过程模拟的分步建模技术。对单元生死技术和分步建模技术的计算模型和精度进行了对比研究。基于经典梁单元,采用FORTRAN语言编制了这两种算法下的分析程序。算例分析表明:两种方法的理论及所编制程序正确,是施工力学问题求解的有效方法。     

基于频率和振型摄动的结构损伤识别方法研究

根据矩阵摄动理论,将结构的质量矩阵和刚度矩阵表示为单元损伤参数的函数,提出了根据频率和振型摄动进行结构损伤识别的方法。首先根据结构损伤前后振型变化建立损伤初定方程和损伤确定方程,利用振型摄动求解单元损伤参数,当两次求解得到的同一单元损伤程度基本一致时,可判定该单元损伤;再将损伤识别结果代入基于频率变化的损伤校核方程,用于检验识别结果的准确性。该方法建立的损伤识别方程为超静定方程,可以保证识别结果的唯一性,避免出现"伪损伤"现象。数值算例表明,即使结构出现损伤程度较小的多个单元损伤,只需测试其一阶振型,也可识别。此外,当结构损伤程度较小时,只需采用一阶摄动方程;当结构损伤程度较大时,可采用二阶摄动方程,以提高识别结果的精度。     

基于Layerwise理论的共固化粘弹阻尼复合材料动特性分析

共固化粘弹性复合材料兼具结构承载和阻尼减振功能。针对传统的混合单元法在应用于粘弹性夹层复合材料结构阻尼性能分析时存在着前处理困难、计算规模大、精度低以及难以考虑正交各向异性铺层自身损耗能力的缺点,推导了一种基于Layerwise离散层理论的四节点四边形复合材料层合板单元,并利用直接复特征值解法建立了共固化粘弹性复合材料结构的阻尼性能分析方法。将该方法应用于不同的阻尼结构,分析结果与文献中已公开结果和混合单元法的计算结果进行了对比验证。结果表明,基于离散层理论的层合板单元具有计算精度高、前处理建模简单和计算规模小的优点,可有效应用于复杂共固化粘弹性复合材料结构的阻尼性能分析和设计。     

基于放大单元的新型荫罩式PDP放电特性的研究

本文采用放大单元的实验方法,设计、制作了新型横直结构及电极结构改进的横直结构放大单元,建立了放大单元光辐射测试系统.在相同条件下比较了不同结构放电单元的红外强度、放电效率,并采用高速ICCD拍摄了相应结构的放电过程.实验结果表明,综合单元结构及电极结构优化的放电单元,其红外强度和放电效率得到了有效提高,有望成为一种较优的荫罩式PDP结构.     

胶粘剂对光机结构动力学特性的影响

胶粘剂广泛应用于光机结构中,其对光机结构的动力学特性有不可忽视的影响。本文采用有限元建模的方法对含胶粘剂的透镜镜组进行动力学特性分析。建立忽略胶层、节点耦合以及"粘合单元"连接胶合面三种有限元模型,并分别对两种胶粘剂粘接的透镜镜组进行模态分析。为了验证三种建模方法的有效性,对不同透镜镜组进行模态测试,获取一阶模态频率与振型。仿真计算与测试结果对比表明:忽略胶层影响的模型计算结果存在较大误差,节点耦合以及"粘合单元"连接胶合面所建立的模型的一阶模态频率与实验测试误差小于5%,振型也与测试结果一致。这表明节点耦合以及"粘合单元"连接胶合面两种有限元模型是有效的。进一步分析胶粘剂材料属性对透镜模态频率的影响,胶粘剂的杨氏模量对模态频率影响明显,泊松比与密度影响较小,对光机结构中胶粘剂的选用具有参考意义。     

基于分层壳单元的现浇混凝土空心楼板数值模拟

现浇混凝土空心楼板中由于存在不连续的孔洞,目前常采用的实体单元分析既复杂且计算效率低。分层壳单元根据组成材料的不同将壳分成多层,可考虑面内弯曲-面内剪切-面外弯曲之间的耦合作用,能够较全面地反映壳体结构的空间力学性能。该文在分层壳单元的基础上,通过设置2条对称的连续"空心层",根据面积和刚度相等原则,经计算得到"空心层"厚度和距截面中性轴的距离,并以此对分层壳单元各组成材料进行划分。通过与试验进行对比,数值模拟结果与试验结果吻合良好,表明该文提出的"空心层"分层壳单元具有较高的精度,能较准确的模拟混凝土空心楼板各项非线性力学性能,且建模方便具有很好的实用性,可运用于实际工程。     

High fluorescence of carbazole derivatives for bioimaging of endoplasmic reticulum and lysosome: the influence of molecular structure on optical properties and cell uptake

Three new carbazole derivatives (L1–L3) with different functional groups have been synthesized and characterized. L1 and L2 are connected through methylene unit to construct L3 with enhanced molecular distortion configuration. The compounds exhibit dependent aggregation-induced enhanced emission (AIEE) properties and cellar uptake region in HepG2 cells. It is demonstrated that L1 and L2 exhibit modest AIEE properties in THF–H₂O mixtures, while L3 shows superior AIEE character with 13 times enhancement. This is because of the enhanced molecular distortion configuration of L3 and the related restriction of π–π stacking interactions between adjacent L3 molecules resulted from the introduction of methylene unit. Due to the unique structure of the compounds, the superior fluorescence emission of L1–L3 in aqueous media, further imaging studies demonstrated the suitability of probes L1–L3 for the biological applications in both human liver hepatocellular carcinoma cells (HepG2) and plant tissues of Arabidopsis seedlings. The imidazole unit in L2 leads selective target to lysosome of HepG2 cells through acid–base interactions, while L1 and L3 are inclined to act with endoplasmic reticulum.     

Long Periodic Structure in ZrO2-Y2O3 Ceramics

A new type of long periodic structure has been found in Zr02-Y2O3 ceramics in annealed states. High resolution electron microscopy (HREM), selected area electron diffraction, and computer simulation have been used to reveal the presence of the long periodic structure. The unit-cell of the long periodic structure consists of a cubic ZrO2 unit cell and L10- like phase one.     

Metamaterial-Based Compact Antenna with Defected Ground Structure for 5G and Beyond

In this paper, a unit cell of a single-negative metamaterial structure loaded with a meander line and defected ground structure (DGS) is investigated as the principle radiating element of an antenna. The unit cell antenna causes even or odd mode resonances similar to the unit cell structure depending on the orientation of the microstrip feed used to excite the unit cell. However, the orientation which gives low-frequency resonance is considered here. The unit cell antenna is then loaded with a meander line which is parallel to the split bearing side and connects the other two sides orthogonal to the split bearing side. This modified structure excites another mode of resonance at high frequency when a meander line defect is loaded on the metallic ground plane. Specific parameters of the meander line structure, the DGS shape, and the unit cell are optimized to place these two resonances at different frequencies with proper frequency intervals to enhance the bandwidth. Finally, the feed is placed in an offset position for better impedance matching without affecting the bandwidth The compact dimension of the antenna is 0.25 λL × 0.23 λL × 0.02 λL, where λL is the free space wavelength with respect to the center frequency of the impedance bandwidth. The proposed antenna is fabricated and measured. Experimental results reveal that the modified design gives monopole like radiation patterns which achieves a fractional operating bandwidth of 26.6%, from 3.26 to 4.26 GHz for |S11|<−10 dB and a pick gain of 1.26 dBi is realized. In addition, the simulated and measured cross-polarization levels are both less than −15 dB in the horizontal plane.     

变压吸附制氧机微型化研究

探讨了变压吸附制氧机微型化的一般途径:使用分离性能好的分子筛,以减小制氧机的体积与重量;在工艺流程中增加均压步骤,以降低能耗,减小体积;优化吸附塔结构,以降低其高度;将双塔结构改为多塔结构,可以很大程度地降低制氧机的高度;把制氧机做成分体式,将其从室内移到室外,以达到室内“零”体积。降低产品气纯度标准,使其仅用于氧保健领域,也是微型化研究的方向。     

Superconductivity in a multi-layered non-fermi liquid

A model of high-T_c superconductivity based on an inter-layer tunneling mechanism is solved in mean-field theory with an arbitrary number of identical layers per unit cell. The nodal structure of the gap function is determined by the nodal structure of the intra-layer contribution to the pairing kernel. The gap-anisotropy in internal layers of each unit cell is enhanced compared to the gap-anisotropy of edge layers. The critical temperature T_c is calculated as a function of number of layers per unit cell, and is found to increase monotonically with increasing number of layers. A possible extension of the model to compounds that nominally have a single CuO₂ layer per unit cell, but where the bare interlayer tunneling matrix element may nevertheless be appreciable is discussed. Such compounds are suggested to have a T_c reminiscent of -layered compounds.     

三维四向复合材料微观模型的研究现状及展望

三雏四向复合材料是一种新结构形式的复合材料,具有优良的力学性能、抗冲击损伤性能及耐烧蚀性能,受到各国学者的重视.在讨论目前较为成功的"米"字型、"六面体截面"交织型、"双扭线"型等单胞微观模型的基础上,提出了"贝塞尔"单胞模型.该模型较好地模拟了三维四向复合材料纤维的走向与微观结构,为下一步深入研究打下了基础.     

Experimental investigation of longitudinal mass transfer in the flow of polyoxyethylene solutions in a round pipe

A method is described for studying longitudinal mass transfer in the turbulent flow of polyoxyethylene solutions in a pipe using nuclear magnetic resonance effects.Notation L length of investigated section of tube - T time of flow over section L - modulation period - modulation frequency - v_av mean velocity - w longitudinal velocity pulsation - l marker length - M magnetization of a unit volume of the liquid - I intensity of NMR signal - q flow rate - c solution concentration Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 41, No. 3, pp. 402–406, September, 1981.     

关于修改“物质的量”,“摩尔”及阿伏伽德罗常数的定义和符号的建议

建议在ＳＩ中,将“物质的量”改为“物质微粒量”,它的符号仍用ｎ,量纲仍为Ｎ。将“摩尔”改为“阿伏伽德罗”,它的符号用Ａｖ。阿伏伽德罗常数的定义修改为“０．０１２ｋｇ碳—１２的原子数目,或１Ａｖ物质微粒的数目”,它的符号采用ＮＡ,而不用Ｌ。     

The state primary standard for the unit of refractive index

The structure, working principle, and basic metrological characteristics are given for the State primary standard for a unit of refractive index GÉT 138-2003.Translated from Izmeritelnaya Tekhnika, No. 11, pp. 3–6, November, 2004.     

Unit fracture energy of certain metals and alloys in thermal shock

An energy-based approach is used to examine the problem of cleavage fracture. The approach is based on a comparison of the store of energy in the specimen and the work done in its fracture. A series of approximate calculations is performed with the use of the program UP-OK to determine the critical unit fracture energy _* necessary to complete the fracture work and fragment the specimen over a period within the submicrosecond range. The specimens were made of titanium (VT1-0), brass (L62, L63), bronze (BrB2, BrB2M), and molybdenum (MCh-1) and had a thickness within the range 0.01–1 mm. They were subjected to a brief pulse of x radiation from a nuclear explosion. The estimates that were obtained showed that the critical unit fracture energy _* is not a material constant but instead depends on the loading conditions. It increases with an increase in the time of action of the tensile stresses in the cleaved cross section.Translated from Problemy Prochnosti, No. 6, pp. 27–32, November–December, 1996.