柔性机构动态可靠性分析的新方法

为了改善柔性机构动态可靠性分析的效率和精度,基于支持向量机SVM(Support Vector Machine)回归理论,提出了一种柔性机构动态可靠性分析高效率高精度的SVM回归极值法SREM(SVM Regression Extremum Method)。首先,介绍了柔性机构可靠性分析的基本理论;其次,融合蒙特卡洛法MC(Monte Carlo)和SVM回归理论,建立了柔性机构动态响应极值的代理模型,并利用代理模型进行柔性机构可靠性分析。最后,利用SREM法对柔性机构实例进行了可靠性分析,并与MC和人工神经网络ANN(Artificial Neural Networks)的分析结果进行比较。结果显示,在小样本情况下,进行柔性机构动态可靠性分析时,SREM的计算效率和计算精度都比ANN高;SREM的计算效率比MC大大提高,计算精度与MC相当。验证了在柔性机构可靠性分析中SREM的高效率和高精度,并证明了SREM在柔性机构可靠性分析中的可行性和有效行性。     

Exact geometric theory for flexible,fluid-conducting tubes

Instability of flexible tubes conducting fluid, or “garden hose instability”, is a phenomenon both familiar from everyday life and important for applications, which has been actively studied. However, previous works did not consider one of the most crucial physical effects — the dynamical change of the cross-section. We show how to consistently address this issue by coupling the geometrically exact rod dynamics with the fluid motion via the use of a constrained Hamilton's variational principle. We find strong effect of this dynamics on stability, and derive a variety of exact nonlinear solutions of traveling-wave type.     

基于近红外光谱的柔性基底紫外臭氧改性效果表征研究

近年来,随着纳米科技、聚合物材料和先进制造技术的发展,以柔性传感器为代表的新兴柔性电子器件在可穿戴、健康医疗、物联网终端等领域发挥着越来越重要的作用。作为柔性电子器件的载体,柔性基底对传感器的机械可靠性和电学传感性能等方面有着重要的意义。但由于其表面非极性键造成的高疏水性限制了功能性材料在其表面的沉积,常常造成柔性基底层与电极层/敏感层之间不稳定的界面结合。因此,利用紫外臭氧处理对柔性基底表面改性受到了广泛的关注。利用近红外光谱技术对柔性基底的紫外臭氧处理效果进行快速精准评估,旨在从基团分子层面探究其改性效果,在实际应用中是对传统依靠接触角测量评估方法的有效补充。具体而言,对四种常见的柔性基底材料聚二甲基硅氧烷(PDMS)、聚萘二甲酸乙二醇酯（PEN）、聚对苯二甲酸乙二醇酯（PET）和聚酰亚胺（PI）进行了1/2/5/10 min不同时长的紫外臭氧（UVO）改性处理,并利用近红外光谱对其改性效果进行表征研究,最后利用接触角测量方法对上述的表征结果进行了验证分析。近红外光谱分析表明：对于柔性PDMS基底,紫外光能量不足以切断其中的甲基（—CH₃）官能团和（—C—Si—）等化学键,无法引入羟基、羧基等亲水性基团。对于柔性PEN和PET基底而言,紫外臭氧处理的效果要优于柔性PDMS基底,且对柔性PET基底的处理效果要优于柔性PEN基底,其原因可能是PEN基底材料中萘环的双环结构具有很强的紫外光吸收能力,阻隔了380 nm以下的大部分紫外线能量。对于柔性PI基底,紫外臭氧处理可以有效引入羟基（—OH）和羧基（—COOH）等活性基团,且这些官能团的强度和数量随着处理时间的增加而增加,从而在短时间内使得PI基底表面能增大、接触角减小、湿润性提高。接触角测试结果验证：紫外臭氧处理对于柔性PDMS基底处理效果不明显（接触角下降幅度为8.4%）;对柔性PET基底处理的效果（接触角下降幅度为39.6%）要优于柔性PEN基底的处理效果（接触角下降幅度为9.4%）;紫外臭氧处理的效果对柔性PI基底处理效果最佳,接触角下降幅度达到了62.7%。     

Numerical simulation of the interaction between flow and flexible nets

A numerical approach is proposed to simulate the interaction between flow and flexible nets in steady current. The numerical approach is based on the joint use of the porous-media model and the lumped-mass model. The configuration of flexible nets can be simulated using the lumped-mass model and the flow field around fishing nets can be simulated using the porous-media model. Using an appropriate iterative scheme, the fluid–structure interaction problem can be solved and the steady flow field around flexible nets can be obtained. In order to validate the numerical models, the numerical results were compared with the data obtained from corresponding physical model tests. The comparisons show that the numerical results are in good agreement with the experimental data. Using the proposed numerical approach, this paper presents the flow field around a single flexible net and two flexible nets with a spacing distance. Both the configuration of the flexible nets and the flow velocity results are in accordance with those of the corresponding physical model tests.     

Study of broad bandwidth vibrational energy harvesting system with optimum thickness of PET substrate

In this paper, we present the development of a flexible PET-based (polyethylene terephthalate; PET) vibrational energy harvesting system with broad bandwidth. This broad bandwidth harvesting system comprises of four units of individual ZnO (zinc oxide) piezoelectric harvester in the form of a cantilever structure connected in parallel, and rectifying circuit with storage module. This system has ability to convert mechanical energy into electrical energy from the varying ambient vibration. The design and simulation of a piezoelectric cantilever plate was described by using commercial software ANSYS FEA (Finite Element Analysis) to determine the optimum thickness of PET substrate, internal stress distribution, operation frequency and electric potential. With the optimum thickness predicted by developed accurate analytical formula analysis, the one-way mechanical strain that is efficient to enhance the induced electric potential can be controlled within the piezoelectric ZnO layer. In addition, the relationship among the model solution of piezoelectric cantilever plate equation, vibration-induced electric potential and electric power was realized. An individual piezoelectric harvester consists of flexible PET substrate, piezoelectric ZnO thin film with (002) c-axis preferred orientation, and selectively deposited UV-curable resin lump structure which is used to change the resonant frequency of the harvester. In combination with multi-harvesters and rectifying with storage module together, an energy harvesting system with broad bandwidth can be fabricated. One individual harvester achieves a maximum OCV (open-circuit voltage) up to 4 V with power density of 1.247 μW/cm³. So far, we succeeded in accomplishing a broad bandwidth system with operating frequency range within 100 Hz-450 Hz to enhance powering efficiency. When the DC voltage (direct current voltage) across a storage module is charged up to 1.55 V after rectification, a flash LED (light emitting diode) is driven.     

Assembly of a new circle connecting circle chain through exerting the template role of a Keggin polyoxometalate

By using the flexible bis(triazole) ligand 1,2-bis(1,2,4-triazol-1-yl)ethane (bte), a polyoxometalate-templated compound, [Zn₂(bte)₄(SiW₁₂O₄₀)]·2H₂O (1), was synthesized under hydrothermal conditions. The compound was characterized by single-crystal X-ray diffraction, elemental analyses, IR spectroscopy, photoluminescence spectroscopy, and cyclic voltammetry. Compound 1 is constructed from two motifs: the [SiW₁₂O₄₀]^4? polyanion and a bi-nuclear metal-organic circle [Zn₂(bte)₂]⁴⁺. The polyanion exerts a template role, inducing the formation of the bi-nuclear circle. The circles build a 1-D circle connecting circle chain through sharing the same Zn ions. Adjacent circles in the chain are vertical with each other. The template polyanion is surrounded by four circles from four different 1-D chains, forming a 3-D supramolecular structure.     

Construction of three 2-D silver(I) coordination architectures with a flexible pyrazine-based ligand

To investigate the impact of weak intermolecular interactions in construction of metal–organic frameworks, three silver(I) coordination complexes with the flexible N-heterocyclic ligand 1-((2-pyrazinyl)-1H-benzoimidazol-1-yl)methyl)-1H-benzotriazole (PBMBT), {Ag(C₁₈H₁₃N₇)NO₃} _n (1), {Ag(C₁₈H₁₃N₇)ClO₄} _n (2), and {Ag(C₁₈H₁₃N₇)SO₃CF₃} _n (3), were prepared under solvothermal conditions and structurally characterized by single-crystal X-ray diffraction, IR spectrum, and elemental analyses. Complexes 1–3 exhibit 2-D reticulate structures, and these 2-D layers are further connected into 3-D supramolecular motifs by π···π interactions and hydrogen bonds. Luminescence indicates that 1–3 show analogous fluorescent emissions compared with the PBMBT in the solid state at room temperature.     

Syntheses,structures, and photoluminescence of three cadmium(II) coordination polymers with flexible bis(benzimidazole) ligands

Three cadmium(II) coordination polymers, [CdBr₂(L₁)] _n (1), [CdI₂(L₂)] _n (2), and Cd₂Br₄(L₃)₂ (3), where L₁?=?1,3-bis(5,6-dimethylbenzimidazole)propane, L₂?=?1,4-bis(5,6-dimethylbenzimidazole)butane, and L₃?=?1,6-bis(5,6-dimethylbenzimidazole)hexane, have been synthesized by hydrothermal methods and characterized by elemental analyses, IR spectra, TGA, PXRD, and X-ray crystallographic diffraction. Complex 1 contains a 1-D helical chain in which CdBr₂ units are linked by L₁. For 2, each CdI₂ is connected by two different conformations of L₂ to form a 1-D zigzag chain. For 3, each CdBr₂ is linked by L₃ bridges to afford a binuclear structure. These results indicate that the spacer length of the ligands play important roles in assembly of Cd(II) coordination polymers. Thermogravimetric analyses and solid-state luminescent properties of the complexes have also been investigated.     

Preparation of chemically sintered ZnO films and their application in dye sensitized solar cells formed on plastic substrates

Meso-porous zinc oxide films were prepared on tin-doped indium oxide-coated, polyethelene naphthalate substrates from binder-free ZnO slurry. The reaction with ammonium hydroxide was found to increase connection between ZnO grains by forming a nano-rod like structure followed by heating at 150 °C. The enhancement of adhesion among ZnO grains was evaluated using a nano-scratch technique. Two different xanthene dyes were used to sensitize ZnO electrodes, with a photo-voltage of 657 mV, fill-factor of 73% and photo-current of 4.1 mA cm⁻² with a maximum light to-electrical energy conversion efficiency of 2.0% being obtained for the plastic based ZnO|mercurochrome|electrolyte solar cell under 1 sun.     

Heteroclinic bifurcations in completely liquid-filled spacecraft with flexible appendage

In this paper, the chaotic dynamics in an attitude transition maneuver of a rigid body with a completely liquid-filled cavity in going from minor axis to major axis spin under the influence of viscous damping and a small flexible appendage constrained to undergo only torsional vibration is investigated. The focus in this paper is on the way in which the dynamics of the liquid and flexible appendage vibration are coupled. The equations of motion are derived and then transformed into a form suitable for the application of Melnikov's method. Melnikov's integral is used to predict the transversal intersections of the stable and unstable manifolds for the perturbed system. An analytical criterion for chaotic motion is derived in terms of the system parameters. This criterion is evaluated for its significance to the design of spacecraft. The dependence of the onset of chaos on quantities such as body shape and magnitude of damping values, fuel fraction and frequency of flexible appendage vibration are investigated.