基于子结构模型的平置式浮筏隔振系统功率流传递特性分析

针对大型船用浮筏隔振系统的声学优化设计问题,从振动能量传递角度出发,研究浮筏隔振系统各子结构参数变化对系统隔振性能的影响,分析振动能量由设备机脚经浮筏隔振系统传至基础的传递规律。采用子结构导纳综合法,建立基于弹性基础的多激励源多自由度浮筏隔振系统动力学模型,通过仿真分析不同子结构参数条件下浮筏系统振动功率流传递特性和变化规律。仿真结果表明:平置式浮筏系统中隔振器刚度、机组和筏体质量、弹性基础板厚度等结构参数对传入基础的功率流影响较大,减小隔振器刚度、增加机组设备、增加筏体质量、增大基础板厚度均可有效降低传入基础的振动能量。

双半轴轴系结构的功率流传递特性

针对双半轴转台结构在工作中的振动问题,建立了具有典型半轴式结构的转台轴系(轴—轴承—框架)动力学模型.采用传递矩阵和子结构导纳功率流法,分别推导了转台轴系的各部分子结构的功率流表达式,通过实验分析了转台各部分结构的功率流传递特性;并从系统的振动传递路径角度,采用振动功率流法分析了转台各部分结构的能量损耗情况.实验结果表明:具有典型半轴式结构的转台,其闭环式结构特点会导致结构振动产生明显的耦合情况;从振动传递路径角度,以功率流作为评价指标能更有效地分析出各条传递路径上的能量损耗情况,并针对性地采取减振降噪措施.

齿轮箱类结构振动功率流分析

齿轮箱作为机械设备中常见的振动噪声源 ,其振动和噪声问题已日益成为重要的研究课题 .以功率流作为评价手段 ,运用子结构导纳法研究了齿轮箱类结构振动能量的传递特性 ,并以常见的单级齿轮传动齿轮箱为模型进行了计算 .研究结果表明

网结构隔振特性的理论与实验研究

针对航天器微振动高性能隔振的特殊要求,提出一种基于网结构的新型隔振方法,对由振源-网结构-弹性边界构成的耦合系统进行了振动建模与分析。对于网结构,采用子结构导纳综合法建立其模型,获得了垂直于网面的频域振动方程;对于边界梁,采用弦-梁单向耦合,将动态张力沿垂直和水平方向分解,得到振动响应的完整描述。在此模型基础上,分析了耦合系统的振动传递特性。为验证理论的正确性,设计并搭建了网结构微振动实验台。结果表明,网结构平台具有良好的被动隔振效果,在较宽的频段内,可以实现20 d B以上的振动衰减。

带有回转机构系统的功率流传递特性研究

本文将具有回转机构的系统作为复杂柔性耦合系统进行研究,采用子结构导纳法和模态综合法进行分析,并在结构声传递路径方面引入带有耦合项的六自由度多维柔性连接刚度矩阵。以齿轮箱类系统为特例研究了在齿轮边缘平面力的作用下,系统的功率流传递路径中各方向力之间的耦合关系,尤其是引起箱体横向振动的功率流传递特性。为该类系统的噪声振动控制提供了理论分析基础。

主被动联合隔振系统中的功率流传递特性

被动和主动隔振各有优势,主被动联合隔振是隔振研究的方向。针对船舰、高层建筑等柔性基础结构的振动隔离问题,以传递到柔性基础的功率流为目标函数,运用子结构导纳综合法推求主被动隔振的功率流传递控制式,对结构进行优化设计。探讨了两种主被动联合隔振的控制策略,最后通过模拟系统的数值例子得出了几个结论。

压电双杆隔振平台的振动建模和控制仿真

针对微振动控制提出一种主被动混合隔振平台,主被动混合隔振平台主要由梁、杆、刚体质量和弹簧等构成,采用机械导纳和子结构弹性连接综合法进行主被动隔振平台的动力学建模,分别获得干扰力和主动控制力到受控端目标点的频响函数,并和有限元法的计算结果进行对比,验证动力学模型。通过有限元方法,计算得到主被动混合隔振平台的固有频率和振型。在此基础上,采用滤波自适应算法Fx-LMS,分别控制由干扰力引起的平台平动、转动以及平动和转动的耦合。建模分析揭示了主被动隔振平台的振动传递机理与规律,控制仿真表明压电双杆隔振平台具有良好的隔振性能。

冰箱压缩机支承系统的动力学分析与优化

以冰箱压缩机隔振系统为背景,建立柔性基础双层隔振系统力学模型,运用子结构导纳法推导隔振系统传递率公式。以推导出的理论公式为基础,应用遗传算法对隔振系统参数进行优化研究。文中还对理论公式和部分优化结果进行数值仿真和试验验证。试验和优化结果验证理论分析的正确性,研究结果具有工程应用价值。

加工中心主轴系统两点结合RCSA逆算法

研究了加工中心主轴系统动力学特性理论预测方法,采用导纳综合子结构法对加工系统进行动力学建模.在动力学模型中,刀具和刀柄在2个单点结合,每个点具有一个横向位移自由度.两点结合的动力学模型无须考虑节点的转角自由度,因此简单可行.在求解方法上采用RCSA逆算法求解刀柄末端位移导纳矩阵,解决了刀柄结构复杂不易建模的难题和空间位移导纳有限不易测试的问题.然后进行算例研究,对长度为245,147和168 mm的刀具与相同刀柄耦合进行验证.结果表明,该RCSA逆算法能够准确求出刀柄位移导纳矩阵,并可根据刀柄位移导纳准确获得不同长度刀具安装进刀柄的复杂耦合情况下刀具末端的位移导纳.

Polaronic Effects of an Exciton in a Cylindrical Quantum Wire

The effects of exciton-optical phonon interaction on the binding energy and the total and reduced effective masses of an exciton in a cylindrical quantum wire have been investigated. We adopt a perturbative-PLL [T.D. Lee,F. Low, and D. Pines, Phys. Rev. B90 (1953) 297] technique to construct an effective Hamiltonian and then use a variational solution to deal with the exciton-phonon system. The interactions of exciton with the longitudinal-optical phonon and the surface-optical phonon have been taken into consideration. The numerical calculations for GaAs show that the influences of phonon modes on the exciton in a quasi-one-dimensional quantum wire are considerable and should not be neglected. Moreover the numerical results for heavy- and light-hole exciton are obtained, which show that the polaronic effects on two types of excitons are very different but both depend heavily on the sizes of the wire.

Energy Spectra of Excitons Bound to a Neutral Acceptor in Quantum Dots

The energy spectra of the ground state for an exciton (X) trapped by a neutral acceptor (A0) in a quantum dot with a parabolic confinement have been calculated as a function of the electron-to-hole mass ratio σ by using the hyperspherical coordinates. We find that the (A0,X) complex confined in a quantum dot has in general a larger binding energy than those in a two-dimensional quantum well and a three-dimensional bulk semiconductor, and the binding energy decreases with the increase of the electron-to-hole mass ratio.

多点激励下加筋板壳耦合结构的振动特性

该文基于改进的子结构线导纳方法,建立了多点激励下加筋板壳耦合结构的振动模型。首先对理论模型采用ANSYS进行了验证;进而使用该模型分析了多点激励的分布方向和位置对结构振动响应的影响。研究表明:当激励源的总幅值恒定时,多点激励下从铺板传递到壳体的振动响应小于单点激励的情况;将多点激励沿垂直于板壳衔接线方向分布且位于铺板的中心线上,可以有效地降低从铺板传递到壳体的振动响应。实际工程中,对于激励源恒定的机械设备,应采用多点方式将其沿垂直于铺板与壳体衔接线的方向安装在铺板的中心线上,以提高系统的声学性能。

Interaction of Methane with Single-Walled Carbon Nanotubes: Role of Defects,Curvature and Nanotubes Type

We investigate the interaction of single-walled carbon nanotubes （SWCNTs） and methane molecule from the first principles. Adsorption energies are calculated, and methane affinities for the typical semiconducting and metallic nanotubes are compared. We also discuss role of the structural defects and nanotube curvature on the adsorption capability of the SWCNTs. We could observe larger adsorption energies for the metallic CNTs in comparison with the semiconducting CNTs. The obtained results for the zig zag nanotubes with various diameters reveal that the adsorption energy is higher for nanotubes with larger diameters. For defected tubes the adsorption energies are calculated for various configurations such as methane molecule approaching to the defect sites pentagon, hexagon, and heptagon in the tube surface. The results show that the introduce defects have an important contribution to the adsorption mechanism of the methane on SWNTs.

Electronic structure and optical property of boron doped semiconducting graphene nanoribbons

We present a system study on the electronic structure and optical property of boron doped semiconducting graphene nanoribbons using the density functional theory. Energy band structure, density of states, deformation density, Mulliken popular and optical spectra are considered to show the special electronic structure of boron doped semiconducting graphene nanoribbons. The C-B bond form is discussed in detail. From our analysis it is concluded that the Fermi energy of boron doped semiconducting graphene nanoribbons gets lower than that of intrinsic semiconducting graphene nanoribbons. Our results also show that the boron doped semiconducting graphene nanoribbons behave as p-type semiconducting and that the absorption coefficient of boron doped armchair graphene nanoribbons is generally enhanced between 2.0 eV and 3.3 eV. Therefore, our results have a great significance in developing nano-material for fabricating the nano-photovoltaic devices.

Large work function shift of organic semiconductors inducing enhanced interracial electron transfer in organic optoelectronics enabled by porphyrin aggregated nanostructures

We report on large work function shifts induced by the coverage of several organic semiconducting （OSC） films commonly used in organic light emitting diodes （OLEDs） and organic photovoltaics （OPVs） with a porphyrin aggregated layer. The insertion between the organic film and the aluminum cathode of an aggregated layer based on the meso-tetrakis（1-methylpyridinium-4-yl） porphyrin chloride （porphyrin 1）, with its molecules adopting a face-to-face orientation parallel to the organic substrate, results in a significant shift of the OSC work function towards lower values due to the formation of a large interfacial dipole and induces large enhancement of either the OLED or OPV device efficiency. OLEDs based on poly[（9,9-dioctylfluorenyl-2,7-diyl）-co-（1,4-benzo-2,1＇,3-thiadiazole）J （F8BT） and incorporating the porphyrin 1 at the cathode interface exhibited current efficiency values up to 13.8 cd/A, an almost three-fold improvement over the efficiency of 4.5 cd/A of the reference device. Accordingly, OPVs based on poly（3- hexylthiophene） （P3HT）, [6,6]-phenyl-C61 butyric acid methyl ester （PC61BM） and porphyrin 1 increased their external quantum efficiencies to 4.4% relative to 2.7% for the reference device without the porphyrin layer. The incorporation of a layer based on the zinc meso-tetrakis （1-methylpyridinium-4-yl）porphyrin chloride （porphyrin 2）, with its molecules adopting an edge-to-edge orientation, also introduced improvements, albeit more modest in all cases, highlighting the impact of molecular orientation.

Space-confined and substrate-directed synthesis of transition-metal dichalcogenide nanostructures with tunable dimensionality

Atomically thin transition-metal dichalcogenide(TMDC) nanostructures are predicted to exhibit novel physical properties that make them attractive candidates for the fabrication of electronic and optoelectronic devices. However, TMDCs tend to grow in the form of two-dimensional nanoplates(NPs) rather than one-dimensional nanoribbons(NRs) due to their native layered structure. Herein, we have developed a space-confined and substrate-directed chemical vapor deposition strategy for the controllable synthesis of WS2, WSe2, MoSe2, MoS2, WS2(1-x)Se2x NPs and NRs. TMDC NRs with lengths ranging from several micrometers to 100 μm have been obtained and the widths of TMDC NRs can be effectively tuned.Moreover, we found that TMDC NRs show different growth behaviors on van der Waals(vdW) and nonvd W substrates. The micro-nano structures, optical and electronic properties of synthesized TMDC NRs have been systematically investigated. This approach provides a general strategy for controllable synthesis of TMDC NRs, which makes these materials easily accessible as functional building blocks for novel optoelectronic devices.

Electronics and Structural Properties of Single-Walled Carbon Nanotubes Interacting with a Glucose Molecule: ab initio Calculations

The adsorption of glucose molecule on single-walled carbon nanotubes(SWCNTs)is investigated by density functional theory calculations.Adsorption energies and equilibrium distances are evaluated,and glucose binding to the typical semiconducting and metallic nanotubes with various diameters and chirality are compared.We also investigated the role of the structural defects on the adsorption capability of the SWCNTs.We could observe larger adsorption energies for the larger diameters semiconducting CNTs,while the story is paradoxical for the metallic CNTs.The obtained results reveal that the adsorption energy is significantly higher for nanotubes with higher chiral angles.Finally,the adsorption energies are calculated for defected nanotubes for various configurations such as glucose molecule approaching to the pentagon,hexagon,and heptagon sites in the tube surface.We find that the respected defects have a minor contribution to the adsorption mechanism of the glucose on SWNTs.The calculation of electron transfers and the density of states supports that the electronic properties of SWCNTs do not change significantly after the gluycose molecular adsorption.Consequently,one can predict that presence of glucose would neither modify the electronic structure of the SWCNTs nor direct to a change in the conductivity of the intrinsic nanotubes.

Biomimetic brain-like nanostructures for solid polymer electrolytes with fast ion transport

The intrinsic drawbacks of electrolytes and the growth of lithium dendrites limit the development of commercial lithium batteries.To address the aforementioned challenges,a novel biomimetic brain-like nanostructure(BBLN)solid polymer electrolyte was created by manipulating the shape of the incorporated nanoparticles.Our designed BBLN solid polymer electrolyte was created by incorporating spherical core-shell(UIO-66@67)fillers into polymer electrolyte,which is significantly different from traditional polymer-based composite electrolytes.UIO-66@67 spherical nanoparticles are highly favorable to eliminating polymer electrolyte stress and deformation during solidification,indicating a great potential for fabricating highly uniform BBLN solid polymer electrolytes with a substantial number of continuous convolutions.Furthermore,spherical nanoparticles can significantly reduce the crystalline structure of polymer electrolytes,improving polymer chain segmental movement and providing continuous pathways for rapid ion transfer.As a result,BBLN solid polymer electrolyte shows excellent ionic conductivity(9.2×10^(−4)S cm^(−1)),a high lithium transference number(0.74),and outstanding cycle stability against lithium electrodes over 6500 h at room temperature.The concept of biomimetic brain-like nanostructures in this work demonstrates a novel strategy to enhance ion transport in polymerbased electrolytes for solid-state batteries.

E-beam-induced in situ structural transformation in one-dimensional nanomaterials

Electron beam （e-beam） irradiation is an inev- itable, but crucial issue for electron microscopy. Our investigation results show the e-beam-induced in situ structural transformations in silicon （Si） nanowires and zinc oxide （ZnO） nanowires （NWs）, respectively. Crystal to amorphous structure transition was revealed in Si NWs utilizing high resolution electron microscopy and electron energy loss spectroscopy. Reconstruction at the （1010） surface of ZnO NWs was also observed in the transmission electron microscope （TEM） using aberration-corrected electron microscopy. These e-beam-induced in situ struc- tural transformations prove that the electron beam irradi- ation effect is able to be used for the local modification of one-dimensional nanomaterials.