西北干旱区局部暴雨洪水面频率分析

在全面收集中国西北三省(区)历史洪水、定点洪水、动点洪水调查结果的基础上,分内陆河、黄河、长江流域进行了洪水的面频率分析,得出了西北干旱区局部暴雨洪水面频率曲线,应用条件概率理论将面频率与点频率叠加,处理工程水文设计中的历史洪水和特大洪水。实例应用结果表明:该方法有效地提高了适线精度,更加符合实际且节约工程造价。

侵蚀基准面下降对弯道河床演变的影响

概化设计了一在出口处布设有高度可变的拦沙坎的弯曲河道模型,利用声学多普勒流速仪和数字波高仪测得13个特征断面的瞬时流速与瞬时水位数据,依托激光扫描技术获得试验床面的精确数字高程,以此来探讨侵蚀基准面下降对弯道河床演变的影响。结果发现:粗化层对河床有一定的保护作用,当侵蚀基准面小幅下降而导致流速小幅增大时,粗化层的保护作用可一定程度地抵减流速的增量,减弱甚至避免水流对河床的冲蚀;当侵蚀基准面下降幅度较大时,河床会被全局冲蚀,但各局部的被冲蚀程度并不相同,其中过渡段主流带的被冲蚀程度较小,弯段凹侧主流顶冲区的被冲蚀程度较大;越靠近侵蚀基准面的区域,侵蚀基准面的下降越易增强该区域的水流强度,越易使该区域的河床被冲蚀;在侵蚀基准面下降幅度较小且槽底未见裸露的情况下,连续弯道完整周期的床面高程频率分布总体上接近于正态分布,但若从细节上看其分布具有双峰特征;双峰特征为半周期床面高程频率分布所特有,完整周期床面高程频率分布的双峰特征只是半周期床面高程频率分布双峰特征叠加的结果;当侵蚀基准面下降至槽底时,主流顶冲区的槽底会严重裸露,连续弯道完整周期的床面高程频率分布仍具有双峰特征,但其总体形态已明显偏离正态分布。

多频段共口径遥感信号接收天伺馈系统设计

针对多频段遥感信号接收系统对S/C/X/Ku/Ka五频段信号共口径接收、高精度指向和全空域过顶稳定跟踪需求,研制了一种多频段遥感信号接收天伺馈系统,解决了天线多频段共口径接收和波束窄、信号难捕获跟踪的技术难题。提出并采用“频率选择副面+旋转”换馈方式、高精度筋开槽微应力胶粘面板、时间最优的非线性多模自适应跟踪控制技术,实现了多频段信号高可靠共口径接收和高精度指向及稳定过顶跟踪。对塔测试结果表明,所设计的多频段共口径接收天伺馈系统具有优良的性能,天线增益、第一旁瓣电平、差波束零深、跟踪精度和指向精度等各项指标均满足指标要求;对星动态跟踪测试表明,Ka频段指向均方根误差优于0.0136°,Ka频段跟踪方位均方根误差优于0.0056°,俯仰均方根误差优于0.0045°。验证了所提天伺馈系统设计的有效性,可用于指导多频段大口径遥感接收天伺馈系统设计。

用高阶单元分析平面应力结构的自由振动

基于YKCheung带面内转角的平面应力单元 ,提出了一种用于剪力墙结构自由振动分析的 32～ 5 6自由度的高阶单元 ,单元的每个节点采用u ,u/x和v ,v/x为自由度 ,在墙体水平方向采用 3次Hermite函数 ,铅垂方向采用了 3～ 6次Lagrange多项式 ,对开孔墙体则提出了按剪切刚度等效和质量密度等效的连续化方法 .为了克服高阶元列式复杂的困难 ,采用下标求和形式的表达式通过标准有限元过程获得了单元刚度矩阵和质量矩阵 ,再用迭代法计算结构自振频率 给出了 5个算例 ,验证了高阶元所具有的高精度 ,并发现了剪力墙结构前3阶振型中当高宽比H/B≤ 10时 ,第 3阶振型为竖向振动 ,而当H/B≤ 2时 ,第 2 。

岩体节理体积频率的计算方法及工程应用

利用Monte-Carlo原理进行三维结构面网络模拟是研究岩体内节理面发育规律最常用的技术手段,节理体积频率(λv)则是影响结构面网络模拟正确与否的关键参数之一,需要根据野外实测节理线频率(λ)进行换算。利用三维结构面网络模拟程序,提出了基于线频率反演节理体积频率的新思路。首先赋给某组节理一个初始体积频率,利用三维结构面网络模拟程序,生成只包含该组节理的三维网络模型样本,计算此模型中该组节理在测线方向上的线频率,不同体积频率(λv)对应不同线频率(λ),进而可建立两者的函数关系,最后将测线方向上该组节理的线频率带入该函数即可确定其体积频率。以贵州省息烽县鱼简河水库坝址区岩体为例,按照上述思路根据测线法统计数据计算了节理体积频率,结果表明λv与λ之间呈现出高度的线性关系。当节理圆盘半径服从对数正态分布时,λv与λmax的比值约为0.4～1.0,而当节理圆盘半径服从负指数分布时,λv与λmax的比值约为1.3～3.5。最后依据《工程岩体分级标准(GB50218-94)》表3.3.1、表3.4.3和表3.4.4,分别基于线频率和体积频率对鱼简河水库坝肩岩体完整性进行了评价,结果表明,后者评价结果的可信度比前者高。

基于小型化单元的L/X双频共用FSS副反射面设计

频率选择表面(FSS)可用于反射面天线的副反射面,为反射面天线系统实现多频段工作提供一种有效方法。提出一种基于卷曲圆环结构的小型化频率选择结构,对L频段的电磁呈透射特性,对X频段电磁波呈反射特性,其阻带带宽高达40%。文中对FSS副面进行了加工和测试,测试结果显示,在L和X频段,FSS副面的插入损耗分别小于0.63 dB和0.5 dB,基于该副面的5.2 m L/X双频共用卡式天线的效率大于51.3%,第一旁瓣低于-18.08 dB。文中设计的FSS具有小型化、宽带低损耗、角度稳定性高的优点,可用于多频共用反射面天线的工程设计。

二维光子晶体负折射现象条件及特性研究

结合光子晶体带隙图和等频率线图分析了二维光子晶体中出现负折射现象的条件,得出了负折射现象出现的频率范围.采用有限时域差分法模拟了光在光子晶体界面和内部的传输行为,验证了以上理论所给出的负折射出现的频段,观察到了明显的负折射现象.比较了不同介质、不同晶格结构光子晶体中不同频率的负折射行为.提出一种新结构的六角型二维三角晶格光子晶体分光镜的模型.

FREE VIBRATION ANALYSIS AND PHYSICAL PARAMETER IDENTIFICATION OF NON-UNIFORM BEAM CARRYING SPRING-MASS SYSTEMS

To analyze a multibody system composed of non-uniform beam and spring-mass subsystems, the model discretization is carried on by utilizing the finite element method（FEM）, the dynamic model of non-uniform beam is developed by using the transfer matrix method of multibody system（MS-TMM）, the transfer matrix of non-u- niform beam is derived, and the natural frequencies are computed. Compared with the numerical assembly method （NAM）, the results by MS-TMM have good agreement with the results by FEM, and are better than the results by NAM. When using the high precision method, the global dynamic equations of the complex multibody system are not needed and the orders of involved system matrices are decreased greatly. For the investigation on the re- verse problem of the physical parameter identification of multibody system, MS-TMM and the optimization tech- nology based on genetic algorithms（GAs） are combined and extended. The identification problem is exchanged for an optimization problem, and it is formulated as a global minimum solution of the objective function with respect to natural frequencies of multibody system. At last, the numerical example of non-uniform beam with attach- ments is discussed, and the identification results indicate the feasibility and the effectivity of the proposed aop- proach.

Effects of surface finish and treatment on the fatigue behaviour of vibrating cylinder block using frequency response approach

This paper presents the effects of surface finish and treatment on the high cycle fatigue behaviour of vibrating cylinder block of a new two-stroke free piston engine at complex variable amplitude loading conditions using frequency response approach. Finite element modelling and frequency response analysis was conducted using finite element analysis software Package MSC.PATRAN/MSC.NASTRAN and fatigue life prediction was carded out using MSC.FATIGUE software. Based on the finite element results, different frequency response approach was applied to predict the cylinder block fatigue life. Results for different load histories and material combinations are also discussed. Results indicated great effects for all surface finish and treatment. It is concluded that polished and cast surface finish conditions give the highest and lowest cylinder block lives, respectively; and that Nitrided treatment leads to longest cylinder block life. The results were used to draw contour plots of fatigue life and damage in the worst or most damaging case.

Imposing Active Sources during High-Frequency Passive Surface-Wave Measurement

Passive surface-wave utilization has been intensively studied as a means of compensating for the short-age of low-frequency information in active surface-wave measurement, In general, passive surface-wave methods cannot provide phase velocities up to several tens of hertz; thus, active surface-wave methods are often required in order to increase the frequency range, To reduce the amount of field work, we pro-pose a strategy for a high-frequency passive surface-wave survey that imposes active sources during con-tinuous passive surface-wave observation; we call our strategy ＂mixed-source surface-wave （MSW） measurement,＂ Short-duration （within 10 min） passive surface waves and mixed-source surface waves were recorded at three sites with different noise levels： namely, inside a school, along a road, and along a railway, Spectral analysis indicates that the high-frequency energy is improved by imposing active sources during continuous passive surface-wave observation, The spatial autocorrelation （SPAC） method and the multichannel analysis of passive surface waves （MAPS） method based on cross-correlations were performed on the recorded time sequences, The results demonstrate the flexibility and applicability of the proposed method for high-frequency phase velocity analysis, We suggest that it will be constructive to perform MSW measurement in a seismic investigation, rather than exclusively performing either active surface-wave measurement or passive surface-wave measurement,

Closure behavior of rock joint under dynamic loading

The normal compression tests on intact samples and artificial joints with different saw-tooth shape under cyclic loading and half-sine waves of different frequencies were performed by using Instron1342 servo-controlled material testing machine. The specimens were made artificially with mortar. The loading frequency ranged from 0.005 Hz to 0.1 Hz. The experimental results show that joint closure curves are non-linear and concave up. The stress-deformation curves under cyclic loading exhibit hysteresis and permanent set that diminish rapidly and keep constant finally on successive cycles. Normal displacement successively decreases from the joint J1 to J2, to J3 under the same normal loads regardless of frequency. Considering the loading frequency effect, normal displacement of joint J1 decreases with increasing the loading frequency except that the loading frequency is 0.05 Hz. Normal displacement of joint J2 increases with increasing the loading frequency. Normal displacement of joint J3 increases with increasing the loading frequency when the frequency ranges from 0.005 Hz to 0.05 Hz. Its normal displacement, however, becomes least when the loading frequency is 0.1 Hz.

Photodetachment of H^- Near a Dielectric Surface

Using the closed orbit theory, the photodetachment cross section of H- near a dielectric surface has been derived and calculated. The results show that the dielectric surface has great influence on the photodetachment process of negative ion near the ionization threshold. Above the ionization threshold, the photodetachment cross section starts to oscillate. With the increase of the energy, the oscillating amplitude decreases and the oscillating frequency increases. The oscillation in the photodetachment cross section of H- in the presence of a dielectric surface is either larger or smaller than the photodetachment of H- without the surface. As the photon energy is larger than the critical value Epc, the oscillatory structure disappeared and the cross section approaches to the case of the photodetachment of H- without any external fields. For a given detached-electron energy, the photodetachment cross section becomes decreased with the increase of the ion-surface distance. Besides, the dielectric constant has great influence on the photodetachment of H-. With the increase of the dielectric constant, the oscillation in the cross section becomes increased. As the dielectric constant increases to infinity, the cross section is the same as the photodetachment of H- near a metal surface. This study provides a new understanding on the photodetachment process of H- in the presence of a dielectric surface.

Numerical simulation research on response characteristics of surrounding rock for deep super-large section chamber under dynamic and static combined loading condition

The stability control of surrounding rock for large or super-large section chamber is a difficult technical problem in deep mining condition.Based on the in-site geological conditions of Longgu coal mine,this paper used the dynamic module of FLAC3D to study the response characteristics of deep super-large section chamber under dynamic and static combined loading condition.Results showed that under the static loading condition,the maximum vertical stress,deformation and failure range are large,where the stress concentration coefficient is 1.64.The maximum roof-to-floor and two-sides deformations are 54.6 mm and 53.1 mm,respectively.Then,under the dynamic and static combined loading condition:(1)The influence of dynamic load frequency on the two-sides is more obvious;(2)The dynamic load amplitude has the greatest influence on the stress concentration degree,and the plastic failure tends to develop to the deeper;(3)With the dynamic load source distance increase,the response of surrounding rock is gradually attenuated.On this basis,empirical equations for each dynamic load conditions were obtained by using regression analysis method,and all correlation coefficients are greater than 0.99.This research provided reference for the supporting design of deep super-large section chamber under same or similar conditions.

Vibrational Spectra and Adsorption of Trisiloxane Superspreading Surfactant at Air/Water Interface Studied with Sum Frequency Generation Vibrational Spectroscopy

The C-H stretch vibrational spectra of the trisiloxane superspreading surfactant Silwet L-77 （（CH3）3Si- O-Si（CH3）（C3H6）（OCH2CH2）7-8OCH3）-O-Si（CH3）3） at the air/water interface are measured with the surface Sum Frequency Generation Vibrational Spectroscopy （SFG-VS）. The spectra are dominated with the features from the -Si-CH3 groups around 2905 cm^-1 （symmetric stretch or SS mode） and 2957 ^-1 （mostly the asymmetric stretch or AS mode）, and with the weak but apparent contribution from the -O-CH2- groups around 2880 ^-1 （symmetric stretch or SS mode）. Comparison of the polarization dependent SFG spectra below and above the critical aggregate or micelle concentration （CAC） indicates that the molecular orientation of the C-H related molecular groups remained unchanged at different surface densities of the Silwet L-77 surfactant. The SFG-VS adsorption isotherm suggested that there was no sign of Silwet L-77 bilayer structure formation at the air/water interface. The Gibbs adsorption free energy of the Silwet surfactant to the air/water interface is -42.2±0.8kcal/mol, indicating the unusually strong adsorption ability of the Silwet L-77 superspreading surfactant.

Bar in SILL Questionnaire for Multiple Results Processing： Users＇ Frequency and Confidence

One hundred and fifteen first-year students of Greek took the SILL （Strategy Inventory for Language Learning） questionnaire in an attempt to reveal and activate potential a successful and widely used questionnaire like SILL might have but not identified and investigated so far. The first original point to be investigated, tackled in a previous experiment （Kambakis-Vougiouklis, 2012）, concerns users＇ confidence whether their choice of a specific strategy is effective while the second point concerns the use of the bar as an alternative statistical tool. More specifically, in this particular experiment the bar is not divided only into five equal length spaces as in the first experiment but also into five equal area spaces according to Gauss distribution, giving the researcher the chance to investigate possible differences between two ways of data processing--an advantage only the use of the bar could provide in the analysis stage. Additionally, there are advantages concerning results collection, as subjects and researcher will have a completely free choice among infinite points on a line rather than a limited 3, 4, 5, and 6 of a Likert scale, avoiding at the same time fine verbal differences between different subdivisions. Although the two different methods of processing performed homogeneous behaviour with not statistically considerable differences, it needs further applications in order to reach safe conclusions

Prediction of blast-induced ground vibrations via genetic programming

Excessive ground vibrations, due to blasting, can cause severe damages to the nearby area. Hence, the blast-induced ground vibration prediction is an essential tool for both evaluating and controlling the adverse consequences of blasting. Since there are several effective variables on ground vibrations that have highly nonlinear interactions, no comprehensive model of the blast-induced vibrations are available. In this study, the genetic expression programming technique was employed for prediction of the frequency of the adjacent ground vibrations. Nine input variables were used for prediction of the vibration frequencies at different distances from the blasting face. A high coefficient of determination with low mean absolute percentage error(MAPE) was achieved that demonstrated the suitability of the algorithm in this case. The proposed model outperformed an artificial neural network model that was proposed by other authors for the same dataset.

Scattering of Plane P Waves by Circular-arc Canyon Topography:High-frequency Solution

Through the Fourier-Bessel series expansion of wave functions,the analytical solution to the two-dimensional scattering problem of incidental plane P waves by circular-arc canyon topography with different depth-to-width ratio is deduced.Unlike other existing analytical solutions,in order to ensure that the analytical solution is valid for higher frequency incident waves,the asymptotic properties of cylindrical functions are in this paper introduced to directly determine the unknown coefficients of scattering waves,avoiding the solution of linear equation systems and corresponding numerical issues,which in turn expand the frequency band in which the analytical solution is valid.Comparison with other existing analytical solutions demonstrates that the proposed analytical solution is correct.Furthermore,the scattering effects of a circular-arc canyon on the incident plane P wave are analyzed in a comparatively broad frequency band.

Oscillations in Total Photodetachment Cross Sections of a Triatomic Anion

The total photodetachment cross section of a linear triatomic anion is derived for arbitrary laser polarization direction. The cross section is ,shown to be strongly oscillatory when the laser polarization direction is parallel to the axis of the system; the oscillation amplitude decreases and vanishes as the angle between the laser polarization and the anion axis increases and becomes perpendicular to the axis. The average cross section over the orientations of the triatomie system is also obtained. The cross section of the triatomic anion is compared with the cross section of a two-center system. We find there are two oscillation frequencies in the triatomie anion in contrast to only one oscillation frequency in the two-center case. Closed-orbit theory is used to explain the oscillations.

Calculation of hydrodynamics for semi-submersibles based on NURBS

Accurate hydrodynamic calculations for semi-submersibles are critical to support modern rapid exploration and extraction of ocean resources. In order to speed hydrodynamic calculations, lines modeling structures were separated into structural parts and then fitted to Non-uniform Rational B-spline (NURBS). In this way, the bow and stern section lines were generated. Modeling of the intersections of the parts was then done with the universal modeling tool MSC.Patran. Mesh was gererated on the model in order to obtain points of intersection on the joints, and then these points were fitted to NURBS. Next, the patch representation method was adopted to generate the meshes of wetted surfaces and interior free surfaces. Velocity potentials on the surfaces were calculated separately, on basis of which the irregular frequency effect was dealt with in the calculation of hydrodynamic coefficients. Finally, the motion response of the semi-submersible was calculated, and in order to improve calculations of vertical motion, a damping term was affixed in the vertical direction. The results show that the above methods can generate fine mesh accurately representing the wetted surface of a semi-submersible and thus improve the accuracy of hydrodynamic calculations.

On Spatiotemporal Characteristics of Sea Fog Occurrence over the Northern Atlantic from 1909 to 2008

In this paper, the International Comprehensive Ocean and Atmosphere Data Set(ICOADS) is utilized to investigate the horizontal distribution of sea fog occurrence frequency over the Northern Atlantic as well as the meteorological and oceanic conditions for sea fog formation. Sea fog over the Northern Atlantic mainly occurs over middle and high latitudes. Sea fog occurrence frequency over the western region of the Northern Atlantic is higher than that over the eastern region. The season for sea fog occurrence over the Northern Atlantic is generally from April to August. When sea fogs occur, the prevailing wind direction in the study area is from southerly to southwesterly and the favorable wind speed is around 8 m s-1. It is most favorable for the formation of sea fogs when sea surface temperature(SST) is 5℃ to 15℃. When SST is higher than 25℃, it is difficult for the air to get saturated, and there is almost no report of sea fog. When sea fogs form, the difference between sea surface temperature and air temperature is mainly-1 to 3℃, and the difference of 0℃ to 2℃ is the most favorable conditions for fog formation. There are two types of sea fogs prevailing in this region: advection cooling fog and advection evaporating fog.