Irregular surface seismic forward modeling by a body-fitted rotated–staggered-grid finite-difference method

Finite-difference(FD) methods are widely used in seismic forward modeling owing to their computational efficiency but are not readily applicable to irregular topographies. Thus, several FD methods based on the transformation to curvilinear coordinates using body-fitted grids have been proposed, e.g., stand staggered grid(SSG) with interpolation, nonstaggered grid, rotated staggered grid(RSG), and fully staggered. The FD based on the RSG is somewhat superior to others because it satisfies the spatial distribution of the wave equation without additional memory and computational requirements; furthermore, it is simpler to implement. We use the RSG FD method to transform the firstorder stress–velocity equation in the curvilinear coordinates system and introduce the highprecision adaptive, unilateral mimetic finite-difference(UMFD) method to process the freeboundary conditions of an irregular surface. The numerical results suggest that the precision of the solution is higher than that of the vacuum formalism. When the minimum wavelength is low, UMFD avoids the surface wave dispersion. We compare FD methods based on RSG, SEM, and nonstaggered grid and infer that all simulation results are consistent but the computational efficiency of the RSG FD method is higher than the rest.

Rotational Friction Damper’s Performance for Controlling Seismic Response of High Speed Railway Bridge-Track System

CRTS-II slab ballastless track on bridge is a unique system in China high speed railway.The application of longitudinal continuous track system has obviously changed dynamic characteristics of bridge structure.The bridge system and CRTS-II track system form a complex nonlinear system.To investigate the seismic response of high speed railway(HSR)simply supported bridge-track system,nonlinear models of three-span simply supported bridge with piers of different height and CRTS-II slab ballastless track system are established.By seismic analysis,it is found that shear alveolar in CRTS-II track system is more prone to be damaged than bridge components,such as piers,girders and bearings.The result shows that the inconsistent displacement of bridge girders is the main cause of the CRTS-II track system’s damage.Then the rotational friction damper(RFD)is adopted,which utilizes the device’s rotation and friction to dissipate seismic energy.The hysteretic behavior of RFD is studied by numerical and experimental methods.Results prove that RFD can provide good hysteretic energy dissipation ability with stable performance.Furthermore,the analysis of RFD’s influence on seismic response of HSR bridge-track system shows that RFD with larger sliding force is more effective in controlling excessive inconsistent displacement where RFD is installed,though response of other bridge spans could slightly deteriorated.

Methods for estimating rotational components of seismic ground motion and their numerical comparisons

Rotational components play an important role in natural earthquake research,engineering seismic investigation,building monitoring,seismic exploration and other fields.Traditional researches mainly focus on three translational components,but less on rotational ones.As the precision of rotational sensing techniques has increased,many scholars have paid more attention to the seismic rotational motions.Because the rotational observations are not very popular before and now,approximately converting the translational components into rotational components is utilized in rotation analysis.Based on numerical six-component seismic data with the finite difference method,we compare three different conversion methods,the travelling-wave,frequency-domain and the difference method,to analyze their characteristics and feasibilities when they are applied to estimate rotational components with translational observations.

Numerical simulation of seismic wavefields in TTI media using the rotated staggered-grid compact finite-difference scheme

Numerical simulation in transverse isotropic media with tilted symmetry axis（TTI） using the standard staggered-grid finite-difference scheme（SSG）results in errors caused by averaging or interpolation. In order to eliminate the errors, a method of rotated staggered-grid finite-difference scheme（RSG） is proposed. However, the RSG brings serious numerical dispersion. The compact staggered-grid finite-difference scheme（CSG） is an implicit difference scheme, which use fewer grid points to suppress dispersion more effectively than the SSG. This paper combines the CSG with the RSG to derive a rotated staggered-grid compact finite-difference scheme（RSGC）. The numerical experiments indicate that the RSGC has weaker numerical dispersion and better accuracy than the RSG.

Analysis of flow response to fluctuation of rotational speed in a radial impeller

By discretizing the convection terms with AUSM+-up scheme in the rotating coordinate system,a finite volume analysis code based on multi-block structured grids was developed independently so as to realize the numerical solving of internal flow fields of turbomachineries.Taking an unshrouded radial impeller with the working fluid of water vapour as the research object,the flow response to the fluctuation of rotational speed was calculated.By comparing the surface pressure profiles and velocity contours calculated by the code and commercial software respectively,the accuracy of flow solver was verified.The analysis of flow response data indicates that,as the working condition shifts closer towards the surge boundary,the response of flow parameters such as mass flow and aerodynamic torque will be more nonsynchronous with the fluctuation of rotational speed,and also the influence of density variation on mass flow variation will be smaller.Moreover,the transient variation region of working condition performance will deviate farther away from the steady performance curve as the working condition approaches the surge boundary.Compared to the working conditions with small mass flows,the distribution characteristics of pressure difference load on the blade surface vary little under large mass flow conditions.The reduction of fluctuation amplitude of rotational speed exerts no influence on abating the hysteresis of flow response.

A new polar motion prediction method combined with the difference between polar motion series

After the first Earth Orientation Parameters Prediction Comparison Campaign(1 st EOP PCC),the traditional method using least-squares extrapolation and autoregressive(LS+AR)models was considered as one of the polar motion prediction methods with higher accuracy.The traditional method predicts individual polar motion series separately,which has a single input data and limited improvement in prediction accuracy.To address this problem,this paper proposes a new method for predicting polar motion by combining the difference between polar motion series.The X,Y,and Y-X series were predicted separately using LS+AR models.Then,the new forecast value of X series is obtained by combining the forecast value of Y series with that of Y-X series;the new forecast value of Y series is obtained by combining the forecast value of X series with that of Y-X series.The hindcast experimental comparison results from January 1,2011 to April 4,2021 show that the new method achieves a maximum improvement of 12.95%and 14.96%over the traditional method in the X and Y directions,respectively.The new method has obvious advantages compared with the differential method.This study tests the stability and superiority of the new method and provides a new idea for the research of polar motion prediction.

Analytical and Numerical Solutions for a Rotating Annular Disk of Variable Thickness

In this paper, the analytical and numerical solutions for rotating variable-thickness solid disk and numerical solution for rotating variable-thickness annular disk are presented. The outer edge of the solid disk and the inner and outer edges of the annular disk are considered to have clamped boundary conditions. Two different cases for the radially varying thickness of the solid and annular disks are given. The numerical solution as well as the analytical solution is available for the first case of the solid disk while the analytical solution is not available for the second case of the annular disk. Both analytical and numerical results for displacement and stresses will be investigated for the first case of radially varying thickness. The accuracy of the present numerical solution is discussed and its ability of use for the second case of radially varying thickness is investigated. Finally, the distributions of displacement and stresses will be presented and the appropriate comparisons and discussions are made at the same angular velocity.

MILU-CG METHOD AND THE NUMERICAL STUDY ON THE FLOW AROUND A ROTATINGCIRCULAR CYLINDER

A hybrid finite difference method and vortex method (HDV), which is based on domain decomposition and proposed by the authors (1992), is improved by using a modified incomplete LU decomposition conjugate gradient method (MILU-CG), and a high order implicit difference algorithm. The flow around a rotating circular cylinder at Reynolds number R-e = 1000, 200 and the angular to rectilinear speed ratio alpha is an element of (0.5, 3.25) is studied numerically. The long-time full developed features about the variations of the vortex patterns in the wake, and drag, lift forces on the cylinder are given. The calculated streamline contours agreed well with the experimental visualized flow pictures. The existence of critical states and the vortex patterns at the states are given for the first time. The maximum lift to drag force ratio can be obtained nearby the critical states.

Two solutions for the BVP of a rotating variable-thickness solid disk

This paper presents the analytical and numerical solutions for a rotating variable-thickness solid disk. The outer edge of the solid disk is considered to have free boundary conditions. The governing equation is derived from the basic equations of the rotating solid disk and it is solved analytically or numerically using finite difference algorithm. Both analytical and numerical results for the distributions of stress function and stresses of variable-thickness solid disks are obtained. Finally, the distributions of stress function and stresses are presented and the appropriate comparisons and discussions are made at the same angular velocity.

Impulsively Started Horizontal Riga Plate Embedded in Unsteady Casson Fluid Flow with Rotation

This article is based on the impulsively started horizontal Riga plate in two dimensional unsteady Casson fluid flows with rotation. The plate starts abruptly from the rest relative to the rotating fluids moving with uniform acceleration in its plane. Numerical solutions are acquired by using explicit finite difference method and estimated results have been gained for various values of the Rotational parameter, modified Hartmann number, Prandtl number, Radiative parameter, Eckert number, Heat source parameter, Schmidt number, and the Soret number. Both the Compaq visual FORTRAN 6.6a and MATLAB R2015a tools have been used to find the numerical solutions and the graphical presentation. The Skin friction, Nusselt number and Sherwood number have been computed and the effects of some pertinent parameters on various distributions are discussed briefly and presented graphically.

Nonlinear Polarization Rotation Characteristic Phenomenon in a Bulk Semiconductor Optical Amplifier

The phenomena of polarization rotation induced by self-modulation in semiconductor optical amplifier (SOA) are analyzed theoretically. The relationship between polarization parameters and gain as well as phase is obtained by the correlation parameter of ellipse polarization and SOA nonlinearity polarization rotation theory. The experiment employs polarizer drive by walking electromotor and power meter, the light power of 360 degree is measured. The transformation law of output polarization power components is found for obvious polarization rotation in the selected coordinate axes based on connection of polarization state in difference axes. Using this law make the manipulation easily on getting ideal polarization state. It can offer a fine method to realize all-optical switch and other logic elements in experiment. This work is of great significance for the applications of SOA nonlinear polarization rotation at high-speed all-optical signal processing and all-optical logic gate.

EPS混合土地基-沉箱抗震性能振动台模型试验

采用振动台试验研究了饱和砂土地基(CSS)和EPS混合土地基(CES)两种地基模型下沉箱结构的抗震性能。对比了两种不同地基模型下土体动力响应特征及沉箱结构动力稳定性,探讨了动力作用下沉箱的受力状态及失稳机制,分析了EPS混合土地基对上部沉箱结构地震稳定性的影响。试验结果表明:振动过程中CES工况的超孔压发展速率明显低于CSS,EPS混合土可显著提高模型抗液化性能。墙后填土作用于沉箱的动土压力沿深度方向呈三角形分布,沉箱中部位置动土压力最大。CES工况沉箱动力响应,包括加速度、位移及转动角等均小于CSS,表现出更好的抗震性能。CES沉箱所受动土推力与惯性力存在明显的相位差,有利于提高沉箱结构的稳定性。

大吨位转体桥梁不平衡力矩计算方法优化研究

针对常用的不平衡力矩计算方法无法适应于大吨位转体桥梁而造成较大计算误差的问题,基于常用的球铰转动法和球铰应力差法,以某大吨位转体桥为背景,对2种方法的不平衡力矩计算结果进行对比,以确定适合大吨位转体桥梁不平衡力矩计算方法;建立球铰有限元模型,分析不平衡力矩对球铰应力差分布规律;采用增广拉格朗日方程对基于球铰应力差法的不平衡力矩计算公式进行优化,并以多座桥梁为例验证优化公式的适用性。结果表明:球铰应力差法与球铰转动法的不平衡力矩计算值相对误差较小;球铰两侧应力差值的大小随着与球铰中心距离的增加呈现先增大后减小的变化趋势;不平衡力矩有限元分析值大于实测值,且两者的相对误差随着不平衡力矩的增加显著增大,最大相对误差为33.4%,优化后的球铰应力差法计算得到的不平衡力矩值与实测值的相对误差在15%以内,表明优化效果良好。

基于深度残差收缩迁移网络的复杂工况下滚动轴承故障诊断

针对噪声和不同转速的复杂工况下滚动轴承故障诊断问题,提出一种基于深度残差收缩迁移网络的复杂工况下滚动轴承故障诊断方法。在深度残差收缩网络中加入领域适配层构建出具备降噪与适配能力的深度残差收缩迁移网络,从而减小噪声带来的干扰及转速变化导致的分布差异。首先,利用注意力机制学习经卷积层后各特征通道的重要性自动设定一组阈值,借助软阈值化将阈值范围内的特征置为零,减少噪声带来的干扰;然后,通过边缘分布适配对齐两域特征分布,减小转速变化带来的分布差异;最后,在Softmax分类层下实现端到端的复杂工况下滚动轴承故障诊断。复杂工况下滚动轴承故障诊断试验验证了所提方法的可行性和有效性。

基于异步旋转磁极的TC4薄板双面磁粒研磨工艺研究

目的为提升传统磁粒研磨TC4薄板的加工效率,改善表面形貌,设计了相对磁极产生相对转速差的双面磁粒研磨装置。方法基于两侧相对磁极的异步旋转,使两侧磁极产生相对转速差,进行磁性磨粒的受力和运动分析,对材料去除量进行计算分析。利用Maxwell软件,对不同的相对转速差进行磁场的模拟仿真,进而使用设计的双面磁粒研磨加工装置,对TC4薄板的双面进行研磨。最后,使用粗糙度仪和超景深3D电子显微镜,对研磨前后的工件表面进行观察分析。结果对于磁极的同步旋转,即当两侧磁极转速为500 r/min时,正面表面粗糙度Ra的平均值从0.47μm下降至0.2μm,下降幅度为57%,反面表面粗糙度Ra的平均值从0.46μm下降至0.21μm,下降幅度为54%。对于磁极异步旋转,即磁极Ⅰ转速为500r/min、磁极Ⅱ转速为600 r/min时,正面表面粗糙度Ra的平均值从0.47μm下降至0.1μm,下降幅度为78%,反面表面粗糙度Ra的平均值从0.48μm下降至0.1μm,下降幅度为79%,正面最大高度差的平均值从62.5μm下降至10.4μm,下降幅度为83%,反面最大高度差的平均值从63.2μm下降至10.3μm,下降幅度为84%,材料去除效率最高,表面质量得到有效改善。结论采用异步旋转双面磁粒研磨的方式,可以有效促进磁性磨粒的翻滚运动,加速切削刃的更新。该装置加工时能够产生相对较高的磁感应强度,磁场梯度变化适中,有利于提升表面质量,修复工件表面的缺陷,大幅度提升了研磨的效率。

基于能值分析的湖北省稻虾综合种养环境影响空间差异研究

基于湖北监利县、公安县、潜江市、洪湖市、石首市5个县(市)的实地调研数据,构建能量流动模型,并运用能值分析方法,计算5个县(市)稻虾综合种养系统的能值投入产出情况以及相关指标,揭示稻虾综合种养系统环境影响的空间差异。结果表明,从整体上看,5个县(市)的稻虾综合种养活动尚未对环境造成显著压力,显示出良好的生态效益。但内部存在明显的空间差异,东南部地区如监利、洪湖等依赖自然资源较多,可持续发展指数较高;西北部地区如潜江等则呈现出高投入高产出的特点,环境负载率相对较高。

Noise-like pulse generation from a thulium-doped fiber laser using nonlinear polarization rotation with different net anomalous dispersion

A mode-locked thulium-doped fiber laser(TDFL) based on nonlinear polarization rotation(NPR) with different net anomalous dispersion is demonstrated. When the cavity dispersion is-1.425 ps^2, the noise-like(NL) pulse with coherence spike width of 406 fs and pulse energy of 12.342 nJ is generated at a center wavelength of 2003.2 nm with 3 dB spectral bandwidth of 23.20 nm. In the experimental period of 400 min, the 3 dB spectral bandwidth variation, the output power fluctuation, and the central wavelength shift are less than 0.06 nm, 0.04 d B, and0.4 nm, respectively, indicating that the NPR-based TDFL operating in the NL regime holds good long-term stability.

Evaluation of the effects of EPS composite soil replacement on the dynamic performance of caisson structure using shaking table tests

The seismic performance of a caisson structure under two types of models with a saturated sandy foundation(CSS)and an expanded polystyrene(EPS)composite soil foundation(CES)are studied using shaking table tests.The macro phenomena of the two different foundation models are described and analyzed.The effects of the replacement of EPS composite soil on seismic-induced liquefaction of backfill and the dynamic performance of a caisson structure are evaluated in detail.The results show that the excess pore water pressure generation in the CES is significantly slower than that in the CSS during the shaking.The dynamic earth pressure acting on the caisson has a triangular shape.The response of horizontal acceleration,displacement,settlement,and rotation angle of the caisson in the CES is smaller than that in the CSS,which means the caisson in the CES has a better seismic performance.Furthermore,the out-of-phase phenomenon between dynamic earth thrust and inertial force in the CES is more obvious than that in the CSS,which is beneficial to reduce the lateral force and improve the stability of the caisson structure.

基于面积差异等效建模的电液比例位置系统FMAPID控制

公路边坡护坡骨架施工车是聚焦于公路边坡土壤开槽和水泥混凝土滑模的工程机械装备。针对公路边坡护坡骨架施工车旋转臂在边坡环境的运动控制问题,设计一种基于模糊多参数自适应比例积分微分(proportional integral derivative,PID)的位置反馈控制策略。考虑到非对称液压缸两腔的差异,采用面积差异等效建模法建立阀控非对称液压缸的线性数学模型。通过定义模糊子集、选取隶属函数、建立模糊规则,使用模糊多参数自适应PID控制算法,实现旋转臂非对称液压缸位置控制。仿真和试验结果表明,基于面积差异等效数学模型的模糊多参数自适应PID能够有效地提高液压缸位置跟踪控制精度,验证了所提控制算法的有效性。

耕地轮作休耕政策对粮食绿色生产的促进作用——基于中国耕地轮作休耕制度试点的准自然实验

基于中国耕地轮作休耕制度试点为准自然实验,根据2000—2019年中国省际面板数据,运用双重差分(DID)、非期望的超效率-Malmquist生产指数(SBM-Malmquist)、系统广义矩估计(SYS-GMM)方法,实证检验耕地轮作休耕对粮食绿色生产的影响效应。结果表明:中国粮食绿色生产以及促进粮食绿色生产的粮食绿色生产技术进步与粮食绿色生产技术效率均具有较大的提升空间;耕地轮作休耕制度试点显著促进了粮食绿色生产,主要表现为粮食生产绿色技术效率的持续改善以推动粮食绿色全要素生产率的增长。从粮食绿色生产视角准确客观评估耕地轮作休耕制度试点的政策绩效,对于当前试点地区调整或完善耕地轮作休耕制度的政策举措,推动耕地轮作休耕制度的常态化、制度化具有重要的政策蕴含,也为当前促进粮食绿色生产提供路径参考。