行人SMD模型参数对人群-结构耦合动力特性的影响

分析行人单自由度弹簧-质量-阻尼器系统中模型参数的随机特性,建立步行人群-结构耦合自由振动方程,采用复模态法求解得到结构的固有频率和阻尼比。研究行人频率、阻尼比和弹性质量对结构基频和阻尼比变化率的影响;应用Monte-Carlo仿真,得到不同频率结构在不同的人群与结构质量比下的基频和阻尼比的95%及5%分位点。分析表明,当空载结构与行人的频率比约为1.1时,结构基频和阻尼比的变化率最大;空载结构基频离行人频率范围较近时,质量比增大会使结构基频和阻尼比的随机散布增大。     

开放系统悬臂类结构的动力特性计算方法

结构总是修建在一定的场地而形成土-结构相互作用的开放系统。为解决开放体系下悬臂类结构的自振频率、振型和考虑辐射阻尼下模态阻尼比的计算问题,提出了脉冲荷载响应模态分析法。该方法采用直接有限元法建立土-结构相互作用有限元模型,对结构施加脉冲荷载得到结构动力反应后,由模态识别方法计算结构的动力特性。随后,以一个悬臂类五层框架结构为例研究了计算动力特性随土体计算范围变化的规律和脉冲荷载激励点位置对计算结果的影响。在此基础上,讨论了土体材料阻尼对模态阻尼比的影响,并与集总参数模型和直接模态分析法进行对比,说明不同方法的计算精度。计算结果表明,随着土域计算范围的增加,脉冲荷载响应模态分析法所得的动力特性将逐渐收敛到精确解;当土体计算范围大于结构基频所对应的波长的2倍时,结构自振频率的误差小于1%,模态阻尼比的误差小于5%;以非模态节点作为激励点都可以得到比较精确的结果;三参数集总参数模型所得模态阻尼比存在显著误差,直接模态分析法所得模型的基频随土域范围增大而趋向于零;相比于辐射阻尼,土体材料阻尼对结构的各阶模态阻尼比的影响较小。     

人体姿态对人-结构耦合系统竖向动力特性影响试验研究

为明确静态人体与轻柔结构之间的竖向相互作用规律,以自主设计制作的简支人行桥模型(基频3.67 Hz、净跨11.80 m)为试验平台,测试了单人人体静立、下蹲与静坐三种姿态及等重质量块对人-结构耦合系统竖向动力特性的影响规律,并结合典型文献试验结果进行了对比与归纳总结。试验结果表明:人体静立、静坐姿态均会降低结构一阶竖向振动频率,而人体下蹲姿态将提高结构一阶竖向振动频率,其中人体静坐姿态对结构一阶竖向振动频率影响程度最大;三种人体姿态均能提高结构一阶竖向模态阻尼比,其中人体静坐姿态提升效应最为显著;采用等重质量块模拟人体,与人体不同姿态对结构振动频率的影响程度基本相当,但无法有效地模拟结构模态阻尼比的变化。综合比较两种结果可知:导致不同文献中人体姿态对结构竖向振动频率与模态阻尼比的影响结果存在离散性的最主要因素为人-结构质量比,其次为人-结构频率比。     

人行桥阻尼索减振研究EI北大核心CSCD

随着人行桥跨度不断增加,其固有频率受行人质量的影响增大,为提高人行桥的宽频减振效果,提出了一种由阻尼器、复位弹簧并联后再与拉索串联而成的阻尼索减振方法。首先,以简支梁模拟人行桥,建立了阻尼索-人行桥弯曲振动方程,采用解析法获得了阻尼索为人行桥提供的附加阻尼比计算公式。然后,通过模型试验分析了桥梁频率、阻尼器黏性系数等参数变化时阻尼索为桥梁提供的附加阻尼比变化规律。研究结果表明,阻尼索可为人行桥提供非常大的附加阻尼比,附加阻尼比理论计算公式与试验结果吻合。最后,基于附加阻尼比理论计算公式,对阻尼索减振性能进行了参数影响分析。     

利用计算机视觉识别人行桥时变模态参数

人行桥健康监测及状态评估需解决的关键性问题是如何根据实测响应信号准确估计桥梁阻尼比及自振频率等时变模态参数。为此提出了一套方案,采用基于HS光流法的分段光流法获取桥梁振动全场位移响应,通过重新定义目标函数,利用自适应遗传算法优化变分模态分解（VMD）,对各个位移时程进行分解,结合希尔伯特变换（HT）曲线拟合VMD分解得到的单模态信号求出瞬时频率和阻尼比。在人行桥模型上利用此方案测试不同行人在控制步频、自由行走下的结构响应,得到多组有效的结构位移响应并与激光位移计作对比验证,VMD-HT分解得到的行人-结构相互作用下的瞬时频率和阻尼比与941B传感器作对比验证。结果表明：采用分段光流法的视觉非接触式测量方法对结构响应具有较高的测量精度,与激光位移计的对比误差为0.85%。根据实测信号,利用VMDHT可有效估计结构的时变模态参数。在行人-结构相互作用下,结构自振频率随人数和位移的增加而减小,最大减幅为14.12%,阻尼比随人数和位移的增加而增大,最大增幅为398.33%,控制步频行走相比于自由行走对时变模态参数的影响更大。     

考虑热效应复合材料典型壁板结构模态演变规律

以复合材料加筋板和连接板为研究对象,进行了考虑材料物性变化、热应力及热变形影响因素的跨越屈曲温度热模态分析,研究了壁板结构的模态演变规律。结果表明：热屈曲前,结构各阶频率因受材料物性变化和热应力的影响逐渐减小,而热屈曲后引起的大变形起到增加结构刚度的作用,频率转而增大。热效应会导致结构模态发生相互演变的现象,且高温阶段具有模态密集特征;加筋板的初始挠度、加筋尺寸和方式不仅改变结构热屈曲温度,也会使模态形式发生变化并呈现局部化特点;连接板结构均匀受热后产生的热变形,会"刚化"与其相似的模态,使该阶模态随着温升跃迁至高阶位置。     

带内置可旋转隔板的调谐液体阻尼器减振性能试验研究EI北大核心CSCD

对带内置可旋转隔板调谐液体阻尼器(tuned liquid damper,TLD)进行了振动台试验,首先对波高响应信号进行解耦分离,再采用不同方法识别液体晃动的模态频率和阻尼比,研究了隔板安装位置、隔板和晃动方向夹角(θ)对TLD减振性能的影响。结果表明,受隔板附加质量和耗能作用的影响,TLD的1阶模态频率和相应的模态响应随θ的增大而减小,但隔板附加模态质量对频率的影响还不足以达到导致系统失谐的程度。当θ小于60°时,TLD的1阶模态阻尼比随θ的变化而单调递增,最大可达到8%左右;当θ大于60°时,隔板所产生的阻尼作用弱化了1阶模态响应使晃动呈高阶模态形式,从而导致晃动频率大幅增大,这个结果和已有研究认为TLD晃动模态频率随着角度增加而逐步增大的结论有本质差别,意味着不能通过改变θ大小的方式来实现TLD的调谐,但改变θ可比较容易调节TLD的阻尼比使其达到振动控制所需要的最佳值。     

基于连续碳纤维/树脂智能材料的梁结构应变模态表征

研制了一种具有动态传感功能的碳纤维/树脂智能层, 可用于结构的应变模态诊断。通过不同加载频率下的单向拉伸实验揭示了这种智能材料对低频动态载荷的响应能力, 并理论分析了动态响应误差的影响因素。在此基础上将碳纤维/环氧树脂智能层连续敷设于悬臂梁结构表面代替传统的点式应变片, 进行应变模态测试。测试结果表明, 碳纤维/环氧树脂智能层可以较精确地反映结构的前三阶固有频率, 并较好地表征结构的前三阶应变模态振型。对悬臂梁局部附加质量后重新进行了模态试验, 结果表明: 附加质量后, 智能层反映的结构固有频率显著下降; 同时, 在附加质量所在的节点位置, 智能层反映的应变模态振型有突变产生, 说明智能层所表征的应变模态对结构物性参数变化具有识别能力, 采用智能层与采用应变片的实验结果一致。此外, 基于碳纤维/树脂智能层的可覆盖性, 采用有限的测点全面捕捉了结构的应变模态信息, 并在测试中通过在可疑区域内逐步增加测点, 实现了结构物性参数变化的定位。     

基于连续碳纤维/树脂智能材料的梁结构应变模态表征

研制了一种具有动态传感功能的碳纤维/树脂智能层,可用于结构的应变模态诊断.通过不同加载频率下的单向拉伸实验揭示了这种智能材料对低频动态载荷的响应能力,并理论分析了动态响应误差的影响因素.在此基础上将碳纤维/环氧树脂智能层连续敷设于悬臂梁结构表面代替传统的点式应变片,进行应变模态测试.测试结果表明,碳纤维/环氧树脂智能层可以较精确地反映结构的前三阶固有频率,并较好地表征结构的前三阶应变模态振型.对悬臂梁局部附加质量后重新进行了模态试验,结果表明:附加质量后,智能层反映的结构固有频率显著下降;同时,在附加质量所在的节点位置,智能层反映的应变模态振型有突变产生,说明智能层所表征的应变模态对结构物性参数变化具有识别能力,采用智能层与采用应变片的实验结果一致.此外,基于碳纤维/树脂智能层的可覆盖性,采用有限的测点全面捕捉了结构的应变模态信息,并在测试中通过在可疑区域内逐步增加测点,实现了结构物性参数变化的定位.     

利用耦合系统自由振动响应识别结构被控模态和TMD参数

准确从安装TMD后的结构-TMD耦合系统中识别结构被控模态和TMD参数是TMD现场调试的必需条件。针对TMD现场调试中参数识别问题,提出了一种通过结构-TMD耦合系统自由振动试验识别结构被控模态的模态质量、频率和阻尼比以及TMD频率和阻尼比的方法。该方法首先采用随机子空间算法评估耦合系统的离散状态空间模型,然后将其减缩和转化为结构被控模态和TMD耦合的两自由系统连续状态空间模型;最后,利用连续状态矩阵,识别结构被控模态的模态质量、频率和阻尼比以及TMD频率和阻尼比。数值分析研究结果表明:1)该方法抗噪能力强;2)TMD与原结构各模态耦合越强,质量比识别结果误差越大,其他参数识别结果均满足工程要求。通过单层框架结构试验研究,验证了该方法的可行性。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Assessment of intakes of mixtures of radionuclides

Australia has several uranium mines and a large number of mineral sand mines, with associated processing facilities. Exposures resulting from these mining and processing operations usually involve intakes of mixtures of radionuclides. This work describes the development of a suite of first order, linear compartment models, based on the ICRP Publication 66 respiratory tract model, and an analytical solution to the decay equations, for assessing the consequences of such intakes. The computer programs based on these models directly compute excretion, organ retention and organ and whole-body doses for intakes of either single radionuclides or any mixture of radionuclides belonging to the same radioactive decay chain. The intake can be via inhalation, ingestion or injection, and can be acute, chronic or of limited duration. The starting concentration and degree of secular (dis)equilibrium can be specified for each radionuclide. No assumptions need to be made about the relative magnitudes of the radioactive half-lives of the different nuclides.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Analysis of anisotropy of properties on the basis of studies of texture of coarse-grained ingots of thermoelectric materials

An analysis of anisotropy of the properties of a Bi₂Se_0.3Te_2.7 solid solution was carried out using construction of demonstrative surfaces for thermoelectric effectiveness and thermal expansion coefficients. It is shown that the texture is an important factor forming anisotropy of properties and technological fitness of ingots for manufacturing modules. Anisotropy of properties based on the studies of the ingot textures obtained using the float-zone method and Bridgman method (growing thermoelectric plates in a flat cavity) was studied.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Numerical study of methods of linearization of the output characteristics of radio-frequency sensors of the level of dielectric media

Different constructions of the sensing elements of radio-frequency level sensors based on sections of long lines are numerically investigated by means of the Matlab program for the purpose of minimizing the measurement error caused by the nonlinearity of the output characteristic. It is shown that the nonlinearity is lowest for U-shaped designs. The nonlinearity factor KN may be regulated by varying the capacitance of a correcting capacitor connected to the input of the sensing element and (or) the length of one of the sections of the long line. In selecting an optimal capacitance of the correcting capacitor KN ≤ 0.15% for control media with dielectric permittivity in the range 2.2–30.     

Possibilities of Decreasing the Errors of Determination of the Height of the Pole of a Sessile Drop of Melt

We analyze the possibilities of decreasing the errors of measuring the height of the pole of a sessile drop of melt above its equator by determining the position of the equator according to the midpoints of vertical chords of the image of the drop. The optimal distance between these chords and the edge of the image of the drop is chosen within 10–20% of the radius of the equator. The proposed method guarantees the same level of errors of evaluation of the height of the pole and the radius of the equator, which enables one to substantially increase the accuracy of evaluation of the capillary constant and the surface energy of the melt according to the geometric parameters of the sessile drop.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.