Seismic wave input method for three-dimensional soil-structure dynamic interaction analysis based on the substructure of artificial boundaries

The method of inputting the seismic wave determines the accuracy of the simulation of soil-structure dynamic interaction. The wave method is a commonly used approach for seismic wave input, which converts the incident wave into equivalent loads on the cutoff boundaries. The wave method has high precision, but the implementation is complicated, especially for three-dimensional models. By deducing another form of equivalent input seismic loads in the fi nite element model, a new seismic wave input method is proposed. In the new method, by imposing the displacements of the free wave fi eld on the nodes of the substructure composed of elements that contain artifi cial boundaries, the equivalent input seismic loads are obtained through dynamic analysis of the substructure. Subsequently, the equivalent input seismic loads are imposed on the artifi cial boundary nodes to complete the seismic wave input and perform seismic analysis of the soil-structure dynamic interaction model. Compared with the wave method, the new method is simplifi ed by avoiding the complex processes of calculating the equivalent input seismic loads. The validity of the new method is verifi ed by the dynamic analysis numerical examples of the homogeneous and layered half space under vertical and oblique incident seismic waves.

Longitudinal waves in one dimensional non-uniform waveguides

Wave approach is used to analyze the longitudinal wave motion in one dimensional non-uniform waveguides.With assumptions of constant wave velocity and no wave conversion,there exist four types of non-uniform rods and corresponding traveling wave solutions are investigated.The obtained results indicate that the kinetic energy is preserved as a constant and the wave amplitude is inversely proportional to square root of the cross-sectional area of the rod.Under certain condition,there exists a cut-off frequency for the rod with variation in geometric or material properties,below which waves do not propagate along the non-uniform rod.For the rod with arbitrary variable cross-section, the conclusions are similar if the wave frequency is high enough.And a series solution of the wave motion is presented.

Comparison Study on Wind Input and Whitecapping Dissipation Expressions in Numerical Simulation of Typhoon-Generated Waves

In order to investigate the effect of wind input and whitecapping dissipation on the simulation of typhoon-waves, three experiments are conducted with the latest version of SWAN （Simulating WAves Nearshore） model. The three experiments adopt the Komen, Janssens, and Westhuysen expressions for wind input and whitecapping dissipation, respectively. Besides the above-mentioned source tems, other parameterization schemes in these experiments are the same. It shows that the experiment with the Westhuysen expression result in the least simulation errors while that with the Janssens expression has the most. The results from the experiments with Komen and Westhuysen expressions show that the differenees in significant wave height （SWH） have a good correlation with the differences in dissipation energy caused by whiteeapping. This indicates that the whitecapping dissipation source term plays an important role in the resultant differences of the simulated SWH between the two experiments.

An evaluation of input/dissipation terms in WAVEWATCH Ⅲ using in situ and satellite significant wave height data in the South China Sea

A WAVEWATCH III version 3.14（WW3） wave model is used to evaluate input/dissipation source term packages WAM3, WAM4 and TC96 considering the effect of atmospheric instability. The comparisons of a significant wave height acquired from the model with different packages have been performed based on wave observation radar and HY-2 altimetry significant wave height data through five experiments in the South China Sea domain spanning latitudes of 0°–35°N and longitudes of 100°–135°E. The sensitivity of the wind speed correction parameter in the TC96 package also has been analyzed. From the results, the model is unable to dissipate the wave energy efficiently during a swell propagation with either source packages. It is found that TC96 formulation with the ＂effective wind speed＂ strategy performs better than WAM3 and WAM4 formulations. The wind speed correction parameter in the TC96 source package is very sensitive and needs to be calibrated and selected before the WW3 model can be applied to a specific region.

Stress Uniformity Process of Specimens in SHPB Test Under Different Loading Conditions of Rectangular and Half-Sine Input Waves

Based on the characteristics of 1D waves,the stress uniformity process in specimens under different loading conditions of rectangular and half-sine input waves was analyzed in split Hopkinson pressure bar (SHPB) test.The results show that the times of an elastic wave propa-gating from one end to the other in a specimen to attain stress equilibrium,is related to input wave-forms and relative mechanical impedance between the specimen and the input/output bars.Here-into,with the increae of the relative impedance,the times decreases under rectangular input waves loading,while it increases under half-sine input wave loading.The dimensionless stress value of specimen corresponding to the status of stress equilibrium increases with the increase of the rela-tive mechanical impedance.However,the dimensionless stress value under half-sine input wave loading is significantly lower than the value under rectangular input wave loading for specimen with low mechanical impedance,and the relative differentia of the dimensionless stress values under two loading conditions decreases with the increase of the relative mechanical impedance.In gen-eral,the forced state of specimen with relatively low mechanical impedance under half-sine input wave loading is evidently superior to the state under rectangular input wave loading in SHPB test,and the advantages of forced state under half-sine input wave loading turns weak with the increase of the relative mechanical impedance.

Influence of Axial Loads to Propagation Characteristics of the Elastic Wave in a Non-Uniform Shaft

The vibration propagates through the shaft in the form of elastic waves. The propagation characteristics of the elastic waves are a ected by the axial loads. The influence of the axial loads to the propagation characteristics of the elastic waves is studied in this paper. Firstly, the transfer matrix of the elastic waves for the non-uniform shaft with axial loads is deduced by combining the transfer matrix without axial load and the additional equation caused by the axial load. And then, a numerical method is used to study the influence of the axial load, non-uniformity and the rotating speed to the propagation characteristics of the elastic waves. It’s found that a new Stop Band will appear due to the axial force, and the central frequency of which will decrease as the increase of the force, while the band width of which remains the same. The central frequency of the new Stop Band will also increase as the increase of the cross-section area ratio;however, the rotating speed of the shaft doesn’t a ect the propagation characteristics of the elastic waves obviously. Finally, an experimental rig is built up for further study, even though there are some small local errors, the results of experiments match well with the numerical ones, which indicates the validation of the theoretical results. The result can help to study the influence of the axial load to the dynamics of a non-uniform shaft and help to reveal the vibration propagating mechanism in such a shaft.

Characteristics of Mesh Wave Impedance in FDTD Non-Uniform Mesh

In order to increase the evaluating precision of mesh reflection wave, the mesh wave impedance (MWI) is extended to the non-uniform mesh in 1-D and 2-D cases for the first time on the basis of the Yee's positional relation for electromagnetic field components. Lots of characteristics are obtained for different mesh sizes and frequencies. Then the reflection coefficient caused by the non-uniform mesh can be calculated according to the theory of equivalent transmission line. By comparing it with that calculated by MWI in the uniform mesh, it is found that the evaluating error can be largely reduced and is in good agreement with that directly computed by FDTD method. And this extension of MWI can be used in the error analysis of complex mesh.

Effects of wind input and wave dissipation formulations on the steady Ekman current solution

The effects of different wind input and wave dissipation formulations on the steady Ekman current solution are described. Two formulations are considered: one from the wave modeling(WAM) program proposed by Hasselmann and Komen and the other provided by Tsagareli and Babanin. The solution adopted for our study was presented by Song for the wave-modifi ed Ekman current model that included the Stokes drift, wind input, and wave dissipation with eddy viscosity increasing linearly with depth. Using the Combi spectrum with tail effects, the solutions are calculated using two formulations for wind input and wave dissipation, and compared. Differences in the results are not negligible. Furthermore, the solution presented by Song and Xu for the eddy viscosity formulated using the K-Profi le Parameterization scheme under wind input and wave dissipation given by Tsagareli and Babanin is compared with that obtained for a depth-dependent eddy viscosity. The solutions are further compared with the available well-known observational data. The result indicates that the Tsagareli and Babanin scheme is more suitable for use in the model when capillary waves are included, and the solution calculated using the K-Profi le Parameterization scheme agrees best with observations.

Defected Ground Structure Multiple Input-Output Antenna For Wireless Applications

In this paper,the investigation of a novel compact 2×2,2×1,and 1×1 Ultra-Wide Band(UWB)based Multiple-Input Multiple-Output(MIMO)antenna with Defected Ground Structure(DGS)is employed.The proposed Electromagnetic Radiation Structures(ERS)is composed of multiple radiating elements.These MIMO antennas are designed and analyzed with and without DGS.The feeding is introduced by a microstrip-fed line to significantly moderate the radiating structure’s overall size,which is 60×40×1 mm.The high directivity and divergence characteristics are attained by introducing the microstripfed lines perpendicular to each other.And the projected MIMO antenna structures are compared with others by using parameters like Return Loss(RL),Voltage Standing Wave Ratio(VSWR),Radiation Pattern(RP),radiation efficiency,and directivity.The same MIMO set-up is redesigned with DGS,and the resultant parameters are compared.Finally,the Multiple Input and Multiple Output Radiating Structures with and without DGS are compared for result considerations like RL,VSWR,RP,radiation efficiency,and directivity.This projected antenna displays an omnidirectional RP with moderate gain,which is highly recommended for human healthcare applications.By introducing the defected ground structure in bottom layer the lower cut-off frequencies of 2.3,4.5 and 6.0 GHz are achieved with few biological effects on radio propagation in human body communications.The proposed design covers numerous well-known wireless standards,along with dual-function DGS slots,and it can be easily integrated into Wireless Body Area Networks(WBAN)in medical applications.This WBAN links the autonomous nodes that may be situated either in the clothes,on-body or beneath the skin of a person.This system typically advances the complete human body and the inter-connected nodes through a wireless communication channel.

基于延迟线组合调相的高能效自适应混合预编码方案

针对毫米波大规模多输入多输出系统采用混合预编码技术所带来的高功耗影响,基于延迟线组合调相器件设计了一种间接全连接型混合预编码系统结构,并提出一种自适应连接的混合预编码方案,可大幅减少与天线直连的调相器数量从而降低硬件造成的功耗损失。方案将编码矩阵的求解分为数字编码矩阵、模拟编码矩阵和开关组成的连接交换矩阵3个部分进行交替优化;提出一种基于互补正交投影矩阵的算法来解决模拟编码矩阵的优化;利用功率约束条件和最小二乘算法简化数字编码矩阵的求解;针对连接交换矩阵的离散组合优化问题,利用低复杂度的交叉熵算法进行优化。仿真结果表明,所提方案可以保证系统性能在接近纯数字预编码方案的同时有效提高系统的能量效率。

地震波斜入射下水平成层覆盖层地基波动输入研究

覆盖层具有土体动力非线性和结构成层特征,地震波斜入射下覆盖层地基自由场计算难度增大、人工边界吸能能力受到限制,制约了地震波动输入精度和应用。以水平成层覆盖层为研究对象,引入势函数理论,构建了地震波斜入射下顶层幅值矩阵与任意层幅值矩阵之间的动态传递关系,获得土体时域应变;基于二维应变状态理论,采用等效线性化法反映土体动力非线性,建立了地震波斜入射下非线性水平成层覆盖层地基自由场解析计算方法。利用作者发展的非线性黏弹性人工边界单元模拟远域辐射阻尼效应,近场波动分析中边界单元参数随内层土体单元动剪应变变化,边界单元吸能能力达到最优。结合解析自由场转换得到的等效输入荷载,建立了适用于地震波斜入射下非线性水平成层覆盖层地基地震波动输入方法。该方法能够依据深部斜入射波和地表地震动实现覆盖层地基波动输入,依据地表地震动实现波动输入是避免了通过基底地震动正演自由场等过程。研究了弹性水平双层和非线性水平多层覆盖层地基地震响应,结果表明,波动输入计算获得位移和应力均与解析解有较高拟合度,计算精度高,可为水平成层覆盖层地基上土石坝地震响应研究提供基础。

存在幅相误差时二维稳健超分辨测角算法

针对4D车载毫米波雷达在俯仰与方位维角度分辨力较低、阵列存在幅相误差时测角有偏的问题,提出一种基于快速稀疏贝叶斯学习的稳健二维超分辨测角方法。首先,利用空域稀疏性特点,对角度域空间进行栅格划分,构建了存在幅相误差时的二维超分辨测角信号模型;然后,通过固定点更新的MacKay SBL重构算法实现了多个邻近目标二维角度估计,并利用基于向量点乘的自校正算法对相位误差进行估计,以对有偏的角度估计进行修正;最后,给出了多输入多输出虚拟阵列下的二维角度估计的克拉美-罗界,并分析了所提算法的计算复杂度。仿真结果表明,在大陆ARS548雷达实际12发16收天线布局下,通过对比6种超分辨测角算法,所提方法在低信噪比、少量快拍下和幅相误差较小时,具有较高的角度分辨力与较低的均方根误差。

基于级联角度的AIRS辅助大规模MIMO系统波束跟踪方案

智能反射表面(intelligent reflecting surface,IRS)可以通过提供额外的视线(line of sight,LoS)路径补偿传播损耗或解决阻塞问题,有效地提高毫米波(millimeter wave,mmWave)通信系统的性能,被认为是下一代移动通信的核心技术。与传统的地面IRS相比,部署在无人机、热气球等空中平台上的空中IRS(aerial IRS,AIRS)结合了空中平台的高移动特性/旋转特性和IRS提供的优质链路特性,可以提供更广阔的信号覆盖范围。考虑到现实场景中用户的移动性,通信系统有必要实时调整波束成形以使波束对准移动用户。然而,AIRS不具备有源射频链,难以在AIRS处获取离开角和到达角,增加了波束跟踪的复杂性。针对这一问题,建立了具有时变信道的AIRS辅助mmWave大规模多输入多输出(multiple input multiple output,MIMO)系统模型,结合基站端有源波束成形、AIRS的旋转角度和无源波束成形设计,提出了一种基于级联角度的无迹卡尔曼滤波波束跟踪方案。仿真结果表明,提出的方案具有较高的跟踪精度,同时AIRS的旋转特性对提升系统可达速率起着重要作用。

考虑衬砌减薄及脱空的公路隧道地震易损性研究

衬砌背后脱空、衬砌厚度不足是我国运营隧道的典型质量缺陷,这些缺陷的存在会直接影响隧道结构的抗震性能,加剧隧道的地震损伤。近年来,基于质量缺陷对隧道抗震性能影响的研究多采用确定性方法,缺少考虑地震波随机性的定量评估。依托云南某两车道运营公路隧道,采用增量动力分析(increment dynamic analysis,IDA)方法开展了考虑衬砌减薄及脱空组合缺陷的一系列隧道地震响应时程分析。根据隧道地震易损性分析理论,建立了组合缺陷影响下的公路隧道地震易损性曲线,分析了组合缺陷程度、缺陷位置、围岩等级和地震波入射方向等因素对隧道地震易损性的影响。结果表明:衬砌减薄及脱空组合缺陷程度、缺陷位置、围岩级别和地震波入射方向均对隧道地震易损性有重要影响。组合缺陷的存在增大了隧道结构的易损性,随组合缺陷程度的增大,衬砌地震损伤概率呈非线性增加。质量缺陷对隧道易损性的影响程度随发生部位不同而异,拱肩缺陷对隧道易损性的影响大于拱顶缺陷。围岩等级越差,隧道易损性受组合缺陷的影响就越大。隧道在横向地震作用下的易损性大于竖向地震作用下的易损性,且易损性受地震波方向的影响随缺陷位置的不同而异。缺陷位于拱肩部位时,隧道结构易损性受竖向地震动的影响更大,而缺陷位于拱顶时受横向地震动的影响更大。

近场波动对钢筋混凝土框架结构地震响应的影响

采用一维化时域方法将地震波动转化为等效节点荷载,通过三维黏弹性人工边界单元模拟远场地基辐射阻尼,建立基于刚性地基假定和考虑近场波动的三维钢筋混凝土框架结构有限元模型,对比内力和位移动力时程响应。研究表明:考虑近场波动使钢筋混凝土框架结构自振周期变长;与刚性地基假定相比,在观测点处,梁端弯矩幅值增大,轴力幅值减小,剪力幅值改变;柱端弯矩幅值减小,轴力幅值增大,剪力幅值也存在差异;顶点位移和层间位移均衰减。

基于深度学习的RCF-mmMIMO系统信道估计算法

针对无蜂窝毫米波大规模多输入多输出(CF-mmMIMO)系统信道估计存在的计算复杂度高、导频开销大等问题,提出一种基于深度学习的可重构智能表面(RIS)辅助CF-mmMIMO(RCF-mmMIMO)系统的信道估计算法。该算法引入RIS替代一部分毫米波接入点(AP),增大CF-mmMIMO下的毫米波覆盖范围和信号强度,在一定程度上解决无蜂窝架构下毫米波AP数量众多硬件成本高的问题。对同一AP上不同组天线的RIS级联信道映射关系的存在性进行证明,并通过FCNN神经网络对该信道映射进行建模,显著降低无蜂窝系统中央处理单元处理信道估计时高计算量和高导频开销。仿真实验表明,信道估计算法能够在低计算复杂度、低导频开销下有效提高信道估计的准确性,显著提高系统传输效率。

基于并联加载技术的中波三频共塔天调网络性能优化问题

对于中波三频共塔而言,天调网络在603 kHz频点处的Q值会显著上升,进而引起网络带宽极速降低,直接影响网络运行的安全性。深入研究了中波三频共塔的技术特点和天调网络的运行机理,利用并联加载技术改造铁塔,通过提高发射天线输入阻抗降低603 kHz工作频点处的Q值,可有效提升天调网络运行的安全性和可靠性。

基于MIMO-FMCW雷达的多人生命体征检测

针对多输入多输出(MIMO)体制调频连续波(FMCW)雷达难于对室内环境多人生命体征进行准确检测的问题,本文提出一种基于MIMO-FMCW雷达的多人生命体征检测方法。首先对中频信号做距离维快速傅里叶变换(FFT)和Capon角度估计得到对应的距离角度图,利用二维恒虚警检测技术(2D-CFAR)和基于密度的聚类(DBSCAN)算法确定每个目标的距离角度信息,通过线性约束最小方差(LCMV)准则进行数字波束形成得到目标对应的慢时间维信号,并使用反正切函数完成相位信号的提取,最后利用谐波判别准则实现对呼吸和心跳信号频率的估计继而完成对多目标生命体征检测。实验结果表明,谐波判别准则实现了平均相对误差小于10%的呼吸率和心率检测精度,证明了该方法的有效性。

User Assisted Cooperative Relaying in Beamspace Massive MIMO NOMA Based Systems for Millimeter Wave Communications

A novel scheme‘user assisted cooperative relaying in beamspace massive multiple input multiple output(M-MIMO)non-orthogonal multiple access(NOMA)system’has been proposed to improve coverage area,spectrum and energy efficiency for millimeter wave(mmWave)communications.A downlink system for M users,where base station(BS)is equipped with beamforming lens antenna structure having NRF radio frequency(RF)chains,has been considered.A dynamic cluster of users is formed within a beam and the intermediate users(in that cluster)between beam source and destination(user)act as relaying stations.By the use of successive interference cancellation(SIC)technique of NOMA within a cluster,the relaying stations relay the symbols with improved power to the destination.For maximizing achievable sum rate,transmit precoding and dynamic power allocation for both intra and inter beam power optimization are implemented.Simulations for performance evaluation are carried out to validate that the proposed system outperforms the conventional beamspace M-MIMO NOMA system for mmWave communications in terms of spectrum and energy efficiency.

WAVEWATCHIII模式中风能输入项和耗散项函数对比分析

采用第三代海浪模型WAVEWATCHIII,模拟了中国沿海的台风浪过程,以实测浮标数据作为验证,比较了不同的风能输入项和能量耗散方案对台风浪模拟精度影响,结果表明风能输入项与耗散源项选用Tolman and Chalikov方案计算得到的结果与实测值更加吻合,3种方案中该方案更适合中国沿海台风浪的计算。