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.

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.

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.

A comparative analysis of seismic response of shallow buried underground structure under incident P,SV and Rayleigh waves

In this study,A time-domain seismic response analysis method and a calculation model of the underground structure that can realize the input of seismic P,SV and Rayleigh waves are established,based on the viscoelastic artificial boundary elements and the boundary substructure method for seismic wave input.After verifying the calculation accuracy,a comparative study on seismic response of a shallow-buried,double-deck,double-span subway station structure under incident P,SV and Rayleigh waves is conducted.The research results show that there are certain differences in the cross-sectional internal force distribution characteristics of underground structures under different types of seismic waves.The research results show that there are certain differences in the internal force distribution characteristics of underground structures under different types of seismic waves.At the bottom of the side wall,the top and bottom of the center pillar of the underground structure,the section bending moments of the underground structure under the incidences of SV wave and Rayleigh wave are relatively close,and are significantly larger than the calculation result under the incidence of P wave.At the center of the side wall and the top floor of the structure,the peak value of the cross-sectional internal force under the incident Rayleigh wave is larger than the calculation result under SV wave.In addition,the floor of the underground structure under Rayleigh waves vibrates in both the horizontal and vertical directions,and the magnification effect in the vertical direction is more significant.Considering that the current seismic research of underground structures mainly considers the effect of body waves such as the shear waves,sufficient attention should be paid to the incidence of Rayleigh waves in the future seismic design of shallow underground structures.

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。

Hybrid Precoder and Combiner Design with Finite Resolution PSs for mmWave MIMO Systems

Hybrid precoding and combining have been considered as a promising technology, which can provide a compromise between hardware complexity and system performance in millimeter wave multiple-input multiple-output systems. However, most existing hybrid precoder and combiner designs generally assume that infinite resolution phase shifters(PSs) are used to produce the analog beamformers. In a practical scene, the design with accurate PSs can lead to high hardware cost and power consumption. In this paper, we investigate the hybrid precoder and combiner design with finite resolution PSs in millimeter wave systems. We employ alternate optimization as the main strategy to jointly design analog precoder and combiner. In addition, we propose a low complexity algorithm, where the analog beamformers are implemented only by finite resolution PSs to maximize spectral efficiency. Then, the digital precoder and combiner are designed based on the obtained analog beamformers to improve the spectral efficiency. Finally, simulation results and mathematical analysis show that the proposed algorithm with low-resolution PSs can achieve near-optimal performance and have low complexity.

Energy budget of surface waves in the global ocean

Mechanical energy input from atmosphere and losses from wave-breaking dissipation of sea surface waves are estimated by a direct scheme. This scheme is based on the integration in the wavenumber space of the wind input and breaking dissipation source functions of the MASNUM wave model. The global amount of wind energy input, averaged in 2005, is about 57 TW, and the wave-breaking dissipation summed in deep-water is about 33 TW, over a half of the wind energy input. The residual may be dissipated by beach processes. Global distributions of the energy input and breaking dissipation concentrate in the westerlies of the Southern Hemisphere.

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.

Similarities of Some Wind Input and Dissipation Source Terms

Wind input parameterizations proposed by Jeffreys, Sverdrup and Munk, and Plant are analyzed. It is found by analogy that the similarity of integrals of the three wind input parameterizations exists. Wave breaking dissipation parameterizations proposed by Tsikunov, Hasselmann, and Phillips are also analyzed. Likewise it is found by analogy that the similarity of integrals of the three dissipation parameterizations exists. The similarities of wind input and dissipation are applied to the investigation of the fetch-limited growth of wind waves, together with the 3/2 power law presented by Toba. Some semi-empirical formulas concerning the growth of wave height and period with fetch are presented. The results from the formulas are in good agreement with previous field observations.

Increasing the Transmission Power by Use of an Antireflecting Dielectric Layer in Microwave Therapy

Reflection and transmission of the plane electromagnetic waves at a frequencyof 2450 MHz at normal incidence on the body surface are studied according to electro-magnetic theory.Our results showed that only 43% electromagnetic energy can penetrateinto the body tissues and 57% electromagnetic energy is reflected back to the air.Thenthe concept of input wave impedance is introduced to study how to decrease the energy re-flection coefficient of the plane electromagnetic waves incident vertically upon the three-layer model of the tissues (skin-fat-muscle).Our results showed that provided the thick-nesses of the skin and fat layers are given,we can evaluate theoretically the thickness andrelative permittivity of the dielectric layer which could raise the energy transmission coef-ficient of the incident waves to 99.99%.

A Single Resistor Tunable Grounded Capacitor Dual-Input Differentiator

A new current feedback amplifier (CFA) based dual-input differentiator (DID) design with grounded capacitor is presented;its time constant (τo) is independently tunable by a single resistor. The proposed circuit yields a true DID function with ideal CFA devices. Analysis with nonideal devices having parasitic capacitance (Cp) shows extremely low but finite phase error (θe);suitable design θe could be minimized significantly. The design is practically active-insensitive relative to port mismatch errors (ε) of the active element. An allpass phase shifter circuit implementation is derived with slight modification of the differentiator. Satisfactory experimental results had been verified on typical wave processing and phase-selective filter design applications.

毫米波非正交多址接入的节能资源分配

用户干扰会降低毫米波大规模多输入多输出非正交多址接入(mMIMO-NOMA)系统的能量效率,解决该问题需要采用合理的资源分配方案。基于已知的信道状态信息建立从基站到用户的系统模型,在考虑基站的发射功率和服务质量情况下,提出具有多个约束条件的能效优化问题。该问题受用户分组、预编码、功率分配等多种因素的影响,是一个复杂的非凸问题。首先在假设功率固定的情况下,提出一种用户分组算法对需要提供服务的用户进行匹配分组,在此基础上,最大化全连接架构增益设计模拟预编码,采用迫零法设计数字预编码。其次将能效最大化问题转化为一系列子问题,并采用惩罚函数进行处理。最后设计基于Dinkelbach的迭代算法用于功率分配,根据能效公式计算出能量效率。MATLAB仿真分析结果表明,该方案能够保证用户间公平性,且在能量效率方面优于现有方案。当信噪比为15 dB时,全连接架构的能量效率提升约25.5%,子链接架构的能量效率提升约25.1%。

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。

具有无线携能技术的MIMO-NOMA系统

用户干扰降低了毫米波大规模多输入多输出(MIMO)非正交多址接入(NOMA)系统的频谱效率和能量效率,针对这一问题,提出将无线携能技术(SWIPT)引入基于混合预编码(HP)的MIMO-NOMA系统,并设计了用户分组、混合预编码以及功率分配方案。首先,提出了簇头选择算法,以设计模拟预编码,基于等效信道相关性进行用户分组,并最大化等效信道增益设计数字预编码;其次,为追求用户间的公平性,提出一种基于二分的功率分配方案,以实现最小可达速率最大化。理论分析和仿真结果表明,信噪比(SNR)为5dB时,相较于现有的具有无限携能的正交多址方案,所提方案在全连接架构下频谱效率提升约24.8%,在子连接架构下能量效率提升约24.6%。

基于物理震源模型的跨断层隧道地震响应分析方法

在跨断层隧道的抗震设计和地震响应分析中,目前存在断层错动与地震动耦合加载物理机制不明确和计算理论不完善的问题。基于物理震源模型和简化波动输入法,提出了一种跨断层隧道地震响应分析框架,可在跨断层隧道地震响应分析中实现断层错动和地震动的耦合加载。通过自由场和土-隧道结构相互作用体系两组算例,对该方法和同震变形场法进行了对比,验证了该方法的正确性和先进性。结果表明:在自由场模型的地震响应分析中,该方法计算的加速度响应结果精度显著优于同震变形场法,两种方法的位移响应结果误差均较小;对于土-隧道相互作用模型的地震响应分析,该方法与同震变形场法在隧道衬砌的加速度、位移、等效应力的计算结果分别最大相差19.20%、3.04%、4.48%,隧道衬砌的位移呈现了显著的跨断层分布特性。该方法可以实现模拟断层错动和地震动对隧道结构的共同作用,计算精度较现有方法更高,可用于跨断层工程结构的地震响应分析。

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。

基于场址复杂入射波场的非一致波动输入模型

波动输入模型在表达地面运动非一致特征方面存在局限。为解决该问题,首先通过地震波空间演化分析证实场址入射地震波为复杂波场,进而提出拓展入射波假定至复杂波场的方法发展非一致波动输入模型。该文以确定性波场和粘弹性边界实现非一致波动输入模型,通过数值模拟地面运动与解析解对比验证其可行性。研究结果显示,非一致波动输入模型继承了波动输入模型在模拟地震波传播效应和地基辐射阻尼效应方面的优势,可有效实现场址复杂入射波场的输入。与传统波动输入模型相比,非一致波动输入模型可全面表达地面运动的时间滞后、峰值变化和时程形状差异等非一致特征。

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。

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。