基于土层振动频响函数预测地铁环境振动的频域解析方法

根据土层振动频响函数反映土层固有特性的原理,提出基于土层振动频响函数预测地铁环境振动的频域解析方法。首先采用车轨解析模型计算得到作用于隧道基底的系列频域力;然后采用土体解析模型计算得到系列频域力作用点处到地面预测点处的系列土层振动频响函数;再根据土层固有特性不随输入荷载大小而改变的性质,将单个频域力与其对应的土层振动频响函数进行复数相乘,得到单个频域力作用下地面预测点处的振动响应;最后将各作用点处振动响应累加得到地面预测点处的振动响应。采用此方法预测北京地铁1号线东单站至建国门站区间由地铁列车运行引起的地面振动响应,并利用现场地面振动测试数据进行验证。结果表明:预测的地面振动加速度时程波形及频谱波形、地面振动1/3倍频程加速度级曲线和Z振级均与现场实测结果基本一致;该预测方法具有计算速度快、预测精度高、预测频带宽等特点,可以有效地预测地铁运行引起的环境振动响应。

INTRASEASONAL OSCILLATIONS IN ASIA TO WESTERN PACIFIC REGION IN BOREAL SUMMER:CONTRASTIVE ANALYSIS FOR ACTIVE AND INACTIVE YEARS OF TROPICAL CYCLONES

Comparative analysis is carried out by using finite-domain power spectrum and lagged regression methods for the propagating characteristics and air-sea interaction processes of intraseasonal oscillations (ISOs) in the Asia to western Pacific (AWP) region during the boreal summer between the active and inactive tropical cyclone (TC) years from 1979 to 2004.The results show as follows.(1) There exist more significant eastward propagating characteristics of the ISO in the active TC years over the whole AWP region.The ISOs of convection propagate zonally with more eastward extension in the years with active tropical cyclone activities,during which the 20-60-day period is strengthened,western Pacific becomes an area with evident characteristics of the propagation that is closely related to TC activities.(2) The air-sea interaction processes are the same in both active and inactive TC years,and the energy exchanges between the air and the sea play a role in maintaining the northwestward propagation of ISOs.(3) The air-sea interaction is more intensive in the active TC years than in the inactive ones.It is particularly true for the latent heat release by condensation as the result of convection,which may be one of the reasons resulting in significant differences in characteristics of ISOs between the active and inactive TC years.

Parameters Analysis of Gastric Motility Signals in Time Domain and Frequency Domain

In order to assess gastric motility, a new noninvasive method was addressed. Firstly, bio-impedance and stomach electric signals were recorded from the healthy control group and the pathologic stomach group. Wavelet transform was used to remove the influence of the heart activity signals. By analyzing and processing the two signals of the time domain and frequency domain, we get the corresponding parameters of the two groups. According to all the parameters, several verification tests have been carried out, from the result of the statistics, we can find that in both time and frequency domains, impedance signal and synchronize EGG （electrogastrogram） have some similar features. However synchronize EGG cannot be totally instead by gastric motility, especially in morbid state, EGG is not correspondence to impedance signal. The gastric contraction or gastric emptying is a complex procedure including electrical and mechanical activity. Electrical impedance （EIP） and the synchronous EGG should be analyzed together. In conclusion, the parameters have the value to evaluate gastric motility.

Hydroelasticity Analysis in Frequency Domain and Time Domain

Hydroelasticity has been introduced in ship seakeeping assessment for more than three decades, and it finally becomes an essential tool in marine industry for design of some types of ship. In the 35 years of evolution, hydroelasticity methods applied in industry of marine and offshore energy grown up from two dimensional to three dimensional and now has analysis models of linear model in frequency domain and nonlinear model in time domain. In this paper, we present the three dimensional hydroelasticity theory model in frequency domain and time domain, show the difference in the approach, and discuss their applications in wave-structure interaction.

Dynamical Consensus Algorithm for Second-Order Multi-Agent Systems Subjected to Communication Delay

To solve the dynamical consensus problem of second-order multi-agent systems with communication delay,delay-dependent compensations are added into the normal asynchronously-coupled consensus algorithm so as to make the agents achieve a dynamical consensus. Based on frequency-domain analysis, sufficient conditions are gained for second-order multi-agent systems with communication delay under leaderless and leader-following consensus algorithms respectively. Simulation illustrates the correctness of the results.

Frequency/time domain modeling of a direct drive point absorber wave energy converter

Two different methods to model a point absorber wave energy converter （WEC） with direct drive linear power take-off （PTO） are proposed in the present study： the frequency domain （FD） method and the time domain （TD） method. In the FD analysis, the frequency response function （FRF） of the WEC device is obtained via the equation of motion, and the expressions of power capture width in regular and random waves are derived as well. In the TD modeling, based on a state space approximation of the convolution term in the motion equation, both regular wave and random wave simulations are carded out. The regular wave simulation results indicate that the state space approximation is sufficiently accurate and the capture width reaches the maximum in the vicinity of the natural frequency. In the random wave simulations, the effects of buoy size, the PTO damping and wave climate on the power capture width are discussed in detail, which leads to the conclusion that the capture widths are influenced by the natural frequency of the WEC device, peak frequency of the wave spectrum, the amplitude of FRF and PTO damping. Furthermore, the increase of the capture width is at the cost of a relatively large buoy size and PTO damping when control is not included.