Search for hidden periodicity in magnetometric measurements performed during auroras

A method for detecting discrete equidistant spectra in high-latitude magnetic observations is proposed. The method finds approximate solutions of the classical Schuster problem, which finds a hidden periodicity in observations with considerable noise. The usage of difference signals makes it possible to increase the latitudinal resolution of the magnetometric diagnostics. The equidistant spectra of two different types have been detected based on the proposed method. The spectra of the first type are interpreted as frequencies of coupled compressional-transverse magnetohydrodyncompressionalamic oscillations in the magnetospheric cavity. The origin of the second type of spectra can be related to a rotating source, i.e., a small-scale vortex of magnetospheric convection. Such an interpretation takes into consideration the Doppler frequency shift caused by entrainment of the ionospheric neutral gas by magnetospheric convection. The results confirm the conclusion that discrete auroral frequencies are stable under disturbed conditions.     

结构振动的模糊状态控制法

本文介绍了一种模糊状态控制法,将结构的状态（即反应）进行模糊化,按照某种经验法则对结构反应进行控制。使用这种方法使得振动控制计算简便、控制直接和控制效果显著。     

自标定法在低频振动传感器参数校准中的应用

介绍了自标定法在低频振动传感器参数校准中的应用,阐述了该方法用于校准的理论依据及适用范围,并将自标定法获得的校准数据和用振动标准装置获得的校准数据进行了比较,通过实测数据证实了自标定法的标定结果在一定的频率范围内是可信的.由于自标定法不需要复杂的标定设备,简单方便,因此具有较好的实用价值.最后,分析了自标定法的误差来源...     

去除交通环境振动观测记录中本底振动的自互功率谱法

去除环境振动观测记录中的本底振动是提高信噪比、揭示交通环境振动特征的一个重要环节.本文在分析现有从交通环境振动观测记录中去除本底振动方法不足的基础上,从考虑本底振动与观测振动互相关性出发,提出了采用自互功率谱法去除本底振动的新方法,推导了计算公式,并通过实际算例论证了方法的可靠性.分析结果表明,本文提出的自互功率谱法能够更有效地去除观测数据中的本底干扰,获得更贴近实际的交通环境振动的功率谱、时程、振动级以及加权振级.在本底振动占优势的低频段,本文提出的方法较现有方法计算精度有明显的提高.     

双排隔振屏障对振动波的阻隔作用及动力响应分析

本文采用模拟试验的方法,对分层土地基中双排隔振屏障对振动波的动力响应进行了探讨,并研究了桩长与土层分界面位置关系、激振频率对其隔振效果的影响作用,得出结论:（1）屏障前振动强度远大于屏障后振动强度,并随着振源距、激振频率、桩长的增加而下降,且屏障前出现明显振动增强现象,在激振频率80 Hz时产生振动峰值,振动强度在高频时基本稳定,继续增加激振频率,振动强度并不会发生明显变化。（2）屏障后中线左右2倍桩长范围内为整个隔振区域的薄弱区,其他区域则由包络线围成一个封闭有效隔振区。（3）屏障对中频和高频有更好的隔振效果,且桩长越大有效隔振面积越大,当桩长超过土层分界面时,有效隔振面积可达到53.25%～69.78%,但此时有效隔振面积增幅由原来的14.29%下降到11.64%,增幅降低了约3%。（4）未设屏障区振动强度较小,随激振频率小范围内浮动,在激振频率为30 Hz和80 Hz时取得振动峰值,且随着屏障布置方向减小,即靠近屏障一侧振动强度较强,远离屏障一侧振动强度较弱。     

Explicit concomitance of implicit method to solve vibration equation

It has been proven that the implicit method used to solve the vibration equation can be transformed into an explicit method,which is called the concomitant explicit method.The constant acceleration met...     

求解混合边值振动问题的辅助函数法

提出辅助函数方法,为混合边值振动问题求解提供一种手段。以圆柱第2类边值出平面简谐振动问题为例阐述辅助函数的基本思想和定义;以半空间凹陷地形出平面散射问题为例讨论辅助函数的构造原则和正确方式;利用辅助函数法给出圆柱一般混合边值出平面简谐振动问题解答;讨论采用辅助函数法在位移和应力边界交接处级数解答的收敛情况;给出若干算例,说明辅助函数法的可行性和有效性。     

大型斜拉桥风致振动可靠性分析方法

本文研究了大型柔性结构的非线性动力学行为及其引起的异频共振，提出了大型柔性结构的可靠性分析方法，并以大型斜拉桥的风致振动为例，通过对系统失效形式的分析，利用可靠性理论对其进行可靠指标计算。这种方法应用于大跨度悬索斜拉桥的方案优选及可靠笥分析中，在处理几何非线性及动力问题时有较好效果。     

井下振动环境分析与模拟

智能导钻井下工具及仪器在钻进过程中产生复杂的振动, 剧烈或长时间振动会造成井下仪器的电路故障与钻具机械疲劳破坏, 引发钻井事故, 增加钻井成本.为了验证井下仪器的振动环境适应性与可靠性, 需要开展破坏机理、井下工况数据采集与分析、测试与试验的体系化研究, 在实验室充分发现仪器潜在的故障, 不断迭代升级, 提升仪器可靠性.本文通过自主研制的井下振动冲击记录仪器在实钻井中采集真实的振动环境数据, 对数据进行处理分析后, 制定了三个方向的振动试验条件; 定制研制了国内首台专门用于井下仪器测试的双台并激振动试验系统, 研究了基于双台振动设备的并激振动试验与测试方法, 实现了实验室条件下真实模拟井下振动环境, 构建的系统化井下振动试验平台有效支撑了井下工具及仪器的高质量研发.

     

基于水文-地球物理模型的地下水污染磁电阻率异常动态监测仿真

We present a forward-modeling investigation of time-dependent ground magnetometric resistivity （MMR） anomalies associated with transient leachate transport in groundwater systems. Numerical geo-electrical models are constructed based on the hydrological simulation results of leachate plumes from a highly conceptualized landfill system and the resultant MMR responses are computed using a modified finite difference software MMR2DFD. Three transmitter configurations （i.e., single source, MMR-TE, and MMR-TM modes） and two hydrological models （i.e., uniform and faulted porous media） are considered. Our forward modeling results for the uniform porous medium indicates that the magnetic field components perpendicular to the dominant current flow contain the most information of the underground targets and the MMR-TE mode is an appropriate configuration for detecting contaminant plumes. The modeling experiments for the faulted porous medium also confirm that the MMR method is capable of mapping and monitoring the extent of contaminant plumes in aroundwater systems.     

典型振动信号时-频分析方法研究

首先对比较简单的单分量信号和多分量信号进行时-频分析,对比了不同时-频分析方法(STFT、WD、Hilbert时-频谱分析、连续小波分析)的分析精度。结果表明对单分量信号和可以分解为若干单分量信号叠加的多分量信号,Hilbert时-频谱分析精度最好,WD和STFT次之,连续小波变换的精度最差;由于Hilbert时-频谱分析和WD方法要求信号为单分量信号或可以分解为若干单分量的信号,故其不适用于复杂信号的时-频分析;对多分量信号,STFT时-频谱较连续小波时-频谱精度高些。需要指出的是,当使用STFT方法时,取不同的窗参数,STFT的时-频分析精度相差很大,必须使用合适的窗参数,以取得较好的分析效果。此外还对El Centro波的两水平分量和人工合成的地震动进行了时-频分析,虽然STFT的时间分辨率和频率分辨率存在矛盾,但它对信号的适应性最强,对复杂信号的时-频分析精度一般可以满足需要,而连续小波变换进行信号的时-频分析时,时-频分辨精度最差,且对于大于30Hz的频率分量,随频率的增加,时-频分析的效果和精度迅速变差,说明小波变换并不适合于做时-频分析,尤其对于高频信号,用连续小波变换得到的时-频谱图看起来很粗糙,而且很难准确解释。进一步对比了真实地震动和人工地震动的时-频分布,认为用胡聿贤教授合成人工地震动的方法合成的地震动在时-频域上的分布和真实地震动相似。     

Damped vibration mode superposition method for dynamic response analysis

In the dynamic response analysis of extremely complex structural systems in which the damping characteristics of each element are independent, the damping matrix is not always diagonalized by the use of undamped free vibration mode shapes. In the present paper, a mode-superposition method by the use of damped free vibration mode shapes is developed for such structural systems. It is also shown that the Fast Fourier Transform (FFT) procedures, that are available for the dynamic response analysis of linear structural systems, are used effectively in this mode-superposition method with good accuracy.     

基于功率流法梯式轨枕轨道减振性能研究

为研究梯式轨枕轨道的减振性能,将梯式轨枕轨道系统简化为四端网络。利用功率流法,分析纵向轨枕截面宽、高以及枕下弹性垫板动刚度、材料损耗因子对梯式轨枕轨道系统减振性能的影响。分析表明:枕下弹性垫板动刚度增大,使得传递到整体道床的总功率流增大,同时纵向轨枕的自振频率也增大;枕下弹性垫板材料损耗因子、纵向轨枕横截面宽、高的增大,都能使传递到整体道床的总功率流减少,同时纵向轨枕截面宽、高的增大降低了纵向轨枕自振频率。因此,应尽量增大纵向轨枕截面面积和枕下弹性垫板材料损耗因子以及减小枕下弹性垫板动刚度,从而获得更好的减振效果。     

Analysis of train-induced vibrations and vibration reduction schemes above and below critical Rayleigh speeds by finite element method

This paper simulates soil vibration under the train speed below and over the soil Rayleigh speed using the three-dimensional finite element method. Two vibration isolation schemes were studied including the soil improvement around the railway and the concrete slab constructed between the rail and soil. Numerical results indicate that the vibration increases considerably and decays slowly when the train speed exceeds the soil Rayleigh speed. The wave direction and dominant frequencies are the simple functions of the train speed, the soil Rayleigh speed and the train compartment length. When the train speed exceeds the shear wave speed, the vibration magnitude is critical and not sensitive to the train speed. To reduce this vibration, the two isolation schemes investigated in this study are useful for the train speed over the soil Rayleigh speed, but they are not efficient for the train speed below the soil Rayleigh speed.     

抗震结构的阻尼减振效果分析

研究了抗震结构的阻尼减振效果。首先，考虑了单自由度体系在不同频率简谐干扰作用下阻尼比对结构反应的减小效果；然后，考虑了阻尼比对结构地震反应谱的影响，分析了我国现行建筑抗震设计规范反应谱，并讨论了不同阻尼比对水平地震影响系数的修正公式。     

A response spectrum method for random vibration analysis of mdf systems

A response spectrum method for stationary random vibration analysis of linear, multi-degree-of-freedom systems is developed. The method is based on the assumption that the input excitation is a wide-band, stationary Gaussian process and the response is stationary. However, it can also be used as a good approximation for the response to a transient stationary Gaussian input with a duration several times longer than the fundamental period of the system. Various response quantities, including the mean-squares of the response and its time derivative, the response mean frequency, and the cumulative distribution and the mean and variance of the peak response are obtained in terms of the ordinates of the mean response spectrum of the input excitation and the modal properties of the system. The formulation includes the cross-correlation between modal responses, which is shown to be significant for modes with closely spaced natural frequencies. The proposed procedure is demonstrated for an example structure that is subjected to an ensemble of earthquake-induced base excitations. Computed results based on the response spectrum method are in close agreement with simulation results obtained from time-history dynamic analysis. The significance of closely spaced modes and the error associated with a conventional method that neglects the modal correlations are also demonstrated.     

打桩引起的地面振动的研究

为了对打桩引起的地面振动进行研究,应用一维应力波理论建立了粘弹性成层土中等截面弹性桩的力学模型,得到了桩中任意一点处位移的半解析解。利用桩与土的相互作用将桩对土的作用力简化到各土层面上。在复阻尼理论和纳维方程的基础上,利用分层法得到了任意荷载作用下土的位移、速度和加速度的解。从而得到了打桩引起的地面振动的衰减特性。通过实测结果和计算结果的比较说明了该方法的可行性。     

利用振动法测量预应力体外索的索力

为了能够利用振动法测量316国道洪塘大桥预应力体外索的索力,本文根据理想弦的振动方程以及梁的横向振动方程,建立起有灌浆预应力体外索索力的计算模型,该计算模型中含有两个权重系数λ1、λ2。利用该桥体外预应力索的模型实验数据,通过最小二乘法拟合出系数λ1、λ2并得到体外索索力的计算公式。误差分析表明该体外索索力计算公式误差小,可以用于洪塘大桥体外索索力计算以及该桥体外索长期健康监测。     

Free vibration and transient response of thick and thin plates using the finite element method

An isoparametric quadrilateral plate bending element is used for the free and forced vibration analysis of both thick and thin plates. Plates of rectangular, circular and triangular planform are analysed and excellent results are obtained. The element performance is assessed by comparison with analytical solutions based on Mindlin's thick plate theory, three-dimensional elasticity solutions and solutions based on thin plate theory.