一种准零刚度系统隔振性能的几何参数优化分析

提出了一种采用菱形连杆组件作为负刚度机构的准零刚度隔振器(下文简称菱形准零刚度隔振器).通过静力学分析方法,建立了菱形准零刚度隔振器数学模型,并与其他调节变量较少的隔振器模型进行了对比;以被测量曲线在隔振器平衡位置处的曲率作为评价参数,研究了负刚度机构几何参数对系统刚度、阻尼非线性的影响,推导了利用几何参数进行隔振优化...     

二苯多烯分子的光物理性质与共轭长度的关系

应用无辐射跃迁理论, 结合密度泛函理论, 研究了共轭多烯体系光物理性质随共轭长度变化的规律. 结果表明, 辐射跃迁速率与共轭长度几乎无关, 但无辐射跃迁速率随链长而增加. 这是因为当共轭链增长时, 振子强度增加, 跃迁能减小, 从而对辐射跃迁速率相抵消, 而在无辐射跃迁过程中, 能隙规则起到主导作用.     

长周期光纤光栅弯曲传感特性

基于耦合模理论和微扰近似,研究了长周期光纤光栅(LPFG)弯曲传感特性与弯曲曲率及光栅结构参数(光栅长度和栅格周期)之间的关系.当弯曲曲率增大到某一值时,一个透射峰分裂为两个,两个分裂峰的谐振波长与弯曲曲率的变化关系呈二次曲线关系,与栅格周期成反比变化,而与光栅长度基本无关.利用B-Ge共掺单模光纤制作的LPFG证实了理论的正确性,且具有很好的重复性.     

适合于内窥成像的共路型光学相干层析成像系统

提出了一种采用光纤型迈克耳孙干涉仪进行光程补偿的菲佐型光学相干层析成像(OCT)系统.该系统的传感探头为共路干涉结构,以解决现有内窥光学相干层析成像系统中存在的探头运动导致图像失真、以及更换使用不同探头时需进行色散和偏振态调节等问题.光程补偿和振动干扰实验结果表明,光程补偿方法正确可行,系统对环境干扰不敏感.利用研制的系统对反射镜和近红外卡进行了成像实验,验证了系统的有效性.提出的方法非常适合于内窥成像,并给出了把系统扩展为内窥光学相干层析成像系统的具体实现过程.     

一种利用岩块特征长度估算二维渗吸量的新方法

对于存在大量亲水疏油岩块的天然裂缝性油藏,自发渗吸是基质岩块和裂缝系统油水交换的重要驱动机制.对于一维渗吸问题,前期存在自相似解析解,后期可以用近似解析解描述,从而可以很方便地估算出岩块剩余油饱和度和岩块出油速率.本文研究了二维矩形岩块在不同边界条件下渗吸过程的近似解析解,通过引入特征长度,将二维岩块渗吸问题等效为一维,从而可以有效利用一维近似解析解来估算出二维岩块渗吸过程中剩余油饱和度和岩块出油速率随时间的变化.本文提出了一个新的混合特征长度,在渗吸前期取岩块面积与岩块开放边界长度之比;在渗吸后期,特征长度根据前期特征长度和Ma等提出的特征长度按饱和度插值确定.通过数值检验比较了几种常见的特征长度取法和本文提出的混合特征长度取法,结果表明新的混合特征长度总体性能优于其他已有的特征长度取法,并且适用于本文列举的所有边界条件.     

基于树脂层强度预测分层萌生载荷

轴向拉伸下的层合板在自由边缘附近存在奇异应力场,容易产生分层萌生进而导致结构破坏.而大多数基于材料力学方法的分层萌生研究对强度参数的确定有较强的主观性,缺乏合理解释.本文通过在层间插入一定厚度的树脂层,将分层萌生视为层间树脂层在三维应力状态下的强度破坏,根据有明确试验标准的树脂强度和Mohr判据判断是否发生分层萌生.采用Pipes-Pagano的均匀轴向拉伸模型计算应力场,对层间应力与树脂层面外应力进行了对比.取临界长度为4个单层板厚度对T800/914层合板的分层萌生进行了预测,结果表明预测值与实验值吻合良好.     

结合分子动力学验证PBS基共聚物和淀粉复合材料之间的相互作用

将聚乙二醇200(PEG200)或聚乙二醇400(PEG400)作为第四种单体分别和丁二酸(SA)、丁二醇(BDO)、乙二醇(EG)熔融共聚得到不同醚链长度的PEG200-PBES、PEG400-PBES共聚酯,再与改性的热塑性淀粉(TPS)共混,采用溶液混合方法,制备出固体复合材料,并且研究了引入不同醚链长度对复合材料各种性能的影响;结合分子动力学(MD)模拟分析了不同醚链长度(PEG-PBES)/TPS复合体系分子之间的相互作用.研究结果表明,随着醚链的增长,复合材料的相容性显著增加,(PEG400-PBES)/TPS复合体系的χ参数和Emix值更接近于0,内聚能密度及溶度参数值大于(PEG200-PBES)/TPS和PBS/TPS复合体系的相应值,说明PEG400-PBES与TPS有更好的相容性.同时,随着醚链的增长,复合材料拉伸强度由原来的1.86 MPa提高到8.84 MPa,断裂伸长率由25.54%提高到74.75%,热失重50%时的温度由281.68℃提高到310.53℃.     

Incipient electric field determination for bush and streamer stage in dielectric liquid under energy balance condition

This paper introduces a new approach for streamer advance mechanism in dielectric liquid. The existing of bush-like streamer shape early and then a tree structure shape after that has been given an over view and definition by devising a breakdown index for dielectric liquid which reach a value of 25. The deviation of streamer velocity from low values of tens of meter per second, until several kilometer per second from bush-like shape, until complete breakdown has been discussed too. These different stages have been studied on an energy balance concepts. In this paper using energy balance analysis, different critical applied fields have been obtained. These values reach 2.18 MV/cm for one branch channel in bush-like streamer shape and 21.5 MV/cm, for tree streamer. After that, the initial streamer velocities concerning these stages have been introduced. From these analysis the dissociation of dielectric liquids starts when the streamer velocity reach the sound speed in air, 331 m/s. In addition, the dissociation field depends mainly on the physical values of the dielectric medium, such as density, and permittivity have been introduced. In this paper the dissociation starts at an electric field value of 21.5 MV/cm for nearly all dielectric liquids, This result is equal to tree streamer inception value, which can be considered as a new introduced finding. A new energy equation relating injected energy electric field, velocity and new deduced breakdown index in dielectric liquid has been devised. The streamer may stop or continue its advance until complete breakdown. According to many published data for streamer, there is no clear explanation for streamer stopping and continuing it advance. In this paper, the streamer must advance ahead of the bush zone in the gap toward the opposite electrode when the prospective electric field at 66% of the gap achieves a breakdown index of 25. This result can be considered as a new criterion for streamer growth until crossing the gap. These new equations and findings have been applied to several experimental works and achieve good results.     

单模CO2激光器动力学参数的实验研究

给出以失谐量对输出的影响来独立测定单模ＣＯ２激光器有关动力学参数的方法及所得结果。     

Mesoscopic modeling of the polymerization,morphology, and crystallization of stereoblock and stereoregular polypropylenes

Thermoplastic elastomers require domains that act as physical crosslinks, and these can be either glassy regions or crystallites. For crystallites in a polymer such as polypropylene (PP), the challenge is to develop polymerizations that form the long stereoregular chain sequences required to produce crystallites large enough to act as stable temporary crosslinks but not so many of them that the material becomes a significantly crystalline thermoplastic rather than an elastomer. For PP, the requirement is for long isotactic sequences within predominantly elastomeric atactic chains, and catalysts required to achieve such an unusual stereoblock structure are now available. This provided encouragement for the simulations described herein that illustrate some relationships between polymerization mechanisms and distributions of isotactic sequences (particularly those long enough to crystallize). A Windle‐type Monte Carlo algorithm was then applied to arrays of the representative PP chains in searches for matches of crystallizable sequences. This approach provided estimates of degrees of crystallinity, melting points, interfacial free energies, standard free energies of fusion, and Young's moduli at small extensions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 840–853, 2002