Influence of earthquake ground motion incoherency on multi-support structures

A linear response history analysis method is used to determine the influence of three factors:geometric incoherency,wave-passage,and local site characteristics on the response of lnulti-support structures subjected to differential ground motions.A one-span frame and a reduced model of a 24-span bridge,located in Las Vegas,Nevada are studied,in which the influence of each of the three factors and their combinations are analyzed.It is revealed that the incoherency of earthquake ground motion can have a dramatic influence on structural response by modifying the dynamics response to uniform excitation and inducing pseudo-static response,which does not exist in structures subjected to uniform excitation.The total response when all three sources of ground motion incoherency are included is generally larger than that of uniform excitation.

Experimental Investigation and Optimization Design of Multi-Support Pipeline System

The design of aircraft hydraulic pipeline system is limited by many factors,such as the integrity of aviation structure or narrow installation space,so the limited clamp support position should be considered.This paper studied the frequency adjustment and dynamic responses reduction of the multi-support pipeline system through experiment and numerical simulation.To avoid the resonance of pipeline system,we proposed two different optimization programs,one was to avoid aero-engine working range,and another was to avoid aircraft hydraulic pump pulsation range.An optimization method was introduced in this paper to obtain the optimal clamp position.The experiments were introduced to validate the optimization results,and the theoretical optimization results can agree well with the test.With regard to avoiding the aero-engine vibration frequency,the test results revealed that the first natural frequency was far from the aero-engine vibration frequency.And the dynamic frequency sweep results showed that no resonance occurred on the pipeline in the engine vibration frequency range after optimization.Additionally,with regard to avoiding the pump vibration frequency,the test results revealed that natural frequencies have been adjusted and far from the pump vibration frequency.And the dynamic frequency sweep results showed that pipeline under optimal clamp position cannot lead to resonance.The sensitivity analysis results revealed the changing relationships between different clamp position and natural frequency.This study can provide helpful guidance on the analysis and design of practical aircraft pipeline.

A new spatial coherence model and analytical coeffi cients for multi-support response spectrum combination

In this paper, a new spatial coherence model of seismic ground motions is proposed by a fitting procedure. The analytical expressions of modal combination （correlation） coefficients of structural response are developed for multi-support seismic excitations. The coefficients from both the numerical integration and analytical solutions are compared to verify the accuracy of the solutions. It is shown that the analytical expressions of numerical modal combination coefficients are of high accuracy. The results of random responses of an example bridge show that the analytical modal combination coefficients developed in this paper are accurate enough to meet the requirements needed in practice. In addition, the computational efficiency of the analytical solutions of the modal combination coefficients is demonstrated by the response computation of the example bridge. It is found that the time required for the structural response analysis by using the analytical modal combination coefficients is less than 1/20 of that using numerical integral methods.

Research on the random seismic response analysis for multi- and large-span structures to multi-support excitations

The pseudo excitation method(PEM) has been improved into a more practical form,on which the analytic formulae of seismic response power spectral density(PSD) of simplified large-span structural models have been derived.The analytic formulae and numerical computing results of seismic response PSD have been derived to study the mechanism of multi-support excitation effects,such as the wave-passage effect and incoherence effect,for the seismic response of multiand large-span structures.By using a multi-span truss as an example,the influence of multi-support excitation effects on the seismic response of such structures is studied.

Seismic Response Analysis of Long-Span Suspen-Dome under Multi-Support Excitations

A practical suspen-dome project, Changzhou Gym roof, is adopted as an example and its transient analysis based on the multi-support excitations of the earthquake wave is carried out. Compared with the single support excitation, the position and value of the maximum stress under multi-support excitations both change and the amount of elements with obvious changes is large and more than 70% of the total. Moreover, when other terms are not changed, this influence will decrease as the span decreases, but increa...

Seismic response of large-span spatial structures under multi-support and multidimensional excitations including rotational components

To achieve rational and precise seismic response predictions of large span spatial structures(LSSSs),the inherent non-uniformity and multidimensionality characteristics of earthquake ground motions should be properly taken into consideration.However,due to the limitations of available earthquake stations to record seismic rotational components,the effects of rocking and torsional earthquake components are commonly neglected in the seismic analyses of LSSSs.In this study,a newly developed method to extract the rocking and torsion components at any point along the area of a deployed dense array from the translational earthquake recordings is applied to obtain the rotational seismic inputs for a LSSS.The numerical model of an actual LSSS,the Dalian International Conference Center(DICC),is developed to study the influences of multi-support and multidimensional excitations on the seismic responses of LSSSs.The numerical results reveal that the non-uniformity and multidimensionality of ground motion input can considerably affect the dynamic response of the DICC.The specific degree of influence on the overall and local structural displacements,deformations and forces are comprehensively investigated and discussed.

Nonlinear analysis of pounding between decks of multi-span bridge subjected to multi-support and multi-dimensional earthquake excitation

The nonlinear analysis of pounding between bridge deck segments subjected to multi-support excitations and multi-dimensional earthquake motion was performed.A novel bottom rigid element(BRE)method of the current displacement input model for structural seismic analysis under the multi-support excitations was used to calculate structural dynamic response.In the analysis,pounding between adjacent deck segments was considered.The seismic response of a multi-span bridge subjected to the multi-support excitation,considering not only the traveling-wave effect and partial coherence effect,but also the seismic non-stationary characteristics of multi-support earthquake motion,was simulated using finite element method(FEM).Meanwhile,the seismic response of the bridge under uniform earthquake was also analyzed.Finally,comparative analysis was conducted and some calculation results were shown for pounding effect,under multi-dimensional and multi-support earthquake motion,when performing seismic response analysis of multi-span bridge.Compared with the case of uniform/multi-support/multi-support and multi-dimensional earthquake input,the maximum values of pounding force in the case of multi-support and multi-dimensional earthquake input increase by about 5 8 times;the absolute value of bottom moment and shear force of piers increase by about50%600%and 23.1%900%,respectively.A conclusion can be given that it is very necessary to consider the pounding effect under multi-dimensional and multi-support earthquake motion while performing seismic response analysis of multi-span bridge.

The Liner Formulas between the Supporting Force and Axis Warp of Large-scale Rotary Kiln with Multi-support

Kilns are the key equipment in the metallurgy,architectural and chemistry industry. It is the statically indeterminate system with over load, large torque and multi-support. The kiln move axis warp resulting in that the load distribution is asymmetry, cause many mechanical failure and safe accidents and the interruption of the produce, which bring a great losses. Treating the distribution of the kiln load and the complexity of the stiffness change, the all-purpose model and matrix, used to solve the variable-stiffness beam upon complex load, are established in this paper. The resultant force of kiln in vertical and horizontal direction is calculated. Accordingly, the liner formulas for calculating the supporting force of the support wheels are obtained, and the wheel supporting force also can be easily obtained based on each shell warp. This will provide theory conference for safety management and rational maintenance.

复杂地质条件下多级高边坡组合支护方案与稳定性预测研究

以镇赫高速陈贝屯至煤灰堡段为例,根据工程地质、边坡等级和边坡特性等因素对边坡不同剖面采用衡重式挡墙、俯斜式挡墙、桩+锚索、锚杆+面板等支护形式。从病害原因分析和处治手段出发,研究了多级高边坡支护的质量保证措施。基于LightGBM算法建立边坡稳定性预测模型,验证模型精确性后给出预测模型的特征相对重要性结果和预测结果。结果表明:建立预测模型可较好地预测边坡稳定性;影响边坡稳定性最关键的因素为中土体粘聚力,其次为边坡角β,孔隙压力比和土体重度对边坡稳定性影响不大;镇赫高速K2+051~K2+340段边坡稳定概率为0.9,失稳概率为0.1。本项目运营经验表明,组合支护方案及质量保障措施有效提高了项目施工质量、减少了返工现象,保证了项目的经济效益。

基于LSTM-Informer模型的液压支架压力时空多步长预测

目前多步液压支架压力预测大多为单步液压支架压力的累计预测,单步累计次数越多,累计误差就越大,影响预测精度。针对该问题,提出了一种基于长短时记忆(LSTM)-Informer模型的液压支架压力时空多步长预测方法。采用卡尔曼滤波消除液压支架压力数据中的振动噪声后,在工作面端部和中部各选取相邻的5台液压支架压力数据建立2个时空数据集(数据集1和数据集2),并对时空数据进行标准化预处理。将时空数据输入LSTM模型提取时空特征,并将提取的时空特征输入Informer模型的编码器,经过位置编码后利用多头概率稀疏自注意力来关注压力序列的变化特征,经过最大池化和一维卷积消除最终输出特征图的冗余组合。利用多头概率稀疏自注意力来关注压力序列的变化特征,将Informer模型的解码器改为全连接层,得到液压支架压力的预测结果。实验结果表明:与基于门控循环单元(GRU)、LSTM和Informer模型的预测方法相比,基于LSTM-Informer模型的预测方法在预测6,12,24步长液压支架压力时的均方根误差(RMSE)和平均绝对误差(MAE)均最小;其中基于数据集1预测的6步长液压支架压力的RMSE分别降低了41.63%,49.74%,11.85%,MAE分别降低了41.75%,50.00%,12.00%;基于数据集2预测的6步长液压支架压力的RMSE分别降低了48.15%,59.86%,19.88%,MAE分别降低了49.87%,54.90%,13.16%。

多源视频数据驱动的舰面保障作业三维重建

针对现有公开的航母舰面保障作业视频数据碎片化、相机角度多变、像素质量低下等问题,提出一种多源视频数据驱动的舰面保障作业三维重建方法.该方法首先对视频中对象轨迹方向进行预测,并采用联合外观和方向相似度的跟踪方法实现视频数据的多目标轨迹跟踪;然后基于跟踪结果,依次采用相似度关联、特征轨迹分割、轨迹聚类提取多源数据中的保障作业对象并进行关联与融合;最后对融合得到的轨迹进行逼真三维重建.在MOT20数据集和舰面保障作业公开视频数据上,实验和用户调研数据的t检验结果表明,采用所提方法有99.5%的把握得到可信的舰面保障作业三维重建效果.

基于电压跌落安全需求的直流微电网多端协同支撑技术

量化直流电压稳定判据,在多端换流器协同下完成暂态电压支撑是直流微电网稳定运行的关键。根据直流微电网运行特性,分析功率波动、直流故障下系统运行点变化轨迹,获得系统具备暂态恢复能力下的直流电压跌落安全区间。基于直流微电网须遵循的等电量原则,根据电压跌落安全区间,计算系统允许放电电量,从而得到直流微电网量化稳定判据。在此基础上,利用交流主网、蓄电池、风机侧换流器的控制潜力,提出直流微电网的多端协同支撑技术,通过释放附加电量满足直流微电网在不同扰动下差异化的电压跌落安全需求,提升系统的暂态稳定裕度。搭建5端直流微电网仿真系统,验证所提控制策略对于直流电压的暂态支撑效果。

矿用单元式液压支架立柱“井”形防冲吸能构件特性分析

为了解决目前煤矿井下巷道支护设备和支护材料在冲击地压作用下发生损坏破坏和失效的问题,设计研发了一种新型多肋板吸能构件。首先,根据防冲支架吸能构件的作用原理,明确了吸能构件的设计要求,提出了一种多肋板型吸能构件,对吸能构件的构型和截面形状展开了结构设计,给出了多肋板型吸能构件尺寸图与三维模型图;基于简化的超折叠单元理论剖析了“井”形管的能量耗散途径,推导出了“井”形管的平均支反力预测公式;其次,采用数值模拟方法对多肋板型吸能构件吸能特性展开了仿真研究,并探究了肋板厚度和不同材料对多肋板型吸能构件的吸能性能的影响,得出了肋板厚度和材料显著影响吸能性能的结论。最后,利用MATLAB的遗传算法进行了优化,利用参数优化结果,重新设计了多肋板型吸能构件,并进行了仿真试验,将仿真试验与压溃试验的结果进行对比分析。分析表明,遗传算法迭代的多肋板型吸能构件具有较好的能量吸收参数,在平台阶段支撑反力的波动较小,能量吸收过程相对稳定,能有效达到能量吸收的效果。

美国融合教育多层级支持系统的实践:框架、成效与启示

推进融合教育高质量发展是全球教育治理的政策焦点与实践主题。近年来,美国将多层级支持系统作为学校教育支持系统改革的抓手,认为这样可以解决专业支持有限、课堂融入困难与系统排斥等问题。多层级支持系统以生态系统理论为指引,以科学循证实践为基石,以多元赋权文化为标尺,澄清了高质量融合教育发展的逻辑架构、运行机制和组织保障,但受制于美国的政治制度体系和社会文化背景,并未充分发挥其应有的效力。我国应批判性地吸收其经验教训,坚持道路自信与实践创新,完善面向全体学生的适宜融合资源保障机制,构筑数据驱动的个性学习资源支持体系,形成多元主体协作参与的资源整合格局。

跨走滑断层多跨简支梁桥地震反应特征与参数分析

为揭示跨走滑断层多跨简支梁桥的地震响应规律,以1座4跨简支梁桥为研究对象,基于OpenSees建立了3维动力弹塑性分析模型;采用“分解-叠加”法合成40组跨断层地震动,以多点激励的方式输入到建立的动力分析模型,进行非线性动力时程分析,研究了跨走滑断层多跨简支梁桥在地震动作用下的地震反应特征,分析了断层的穿越角度和穿越位置对跨走滑断层多跨简支梁桥地震响应的影响。结果表明:地震动作用下跨走滑断层桥梁结构会发生剧烈的位移反应;断层穿越角度和穿越位置对桥梁地震反应有显著的影响;地震动作用下跨断层简支梁桥的扭转效应不可忽视。

基于多阶段递推数据分析的低压台区窃电检测方法

窃电行为不仅会扰乱正常用电秩序,更会影响电网的供电质量和安全运行。针对窃电检测工作中所面临的用户正常用电行为与窃电行为多样化问题,该文提出一种基于多阶段递推数据分析的低压台区窃电检测方法。该方法第1阶段对嫌疑窃电台区进行判定,针对当日线损不是明显激增的情况,提出基于台区线损综合波动率、总分表电流差异率、线损和电流曲线的突变点时间重合度的三步分析法,为窃电嫌疑用户的检测提供了良好的条件;第2阶段提出基于最优特征集的时间序列相似性度量方法,基于欧氏距离度量曲线间数值特征,同时基于动态时间规整(dynamic time warping,DTW)算法度量曲线间的形态特征,实现窃电嫌疑用户的初步筛选;第3阶段提出基于核函数和惩罚参数优化的支持向量机二次深度检测模型(optimize kernel-function and penalty-parameters support vector machine,OKPSVM),其中惩罚参数采用综合改进的粒子群(improved particle swarm optimization,IPSO)算法。通过算例仿真和实际工程应用,整体优化后的支持向量机模型(IPSO-OKPSVM)能够提高深度窃电检测的精准性和适用性。

三层正放四角锥预应力网架稳定性分析

网架以其优良的工程性能成为大跨度结构的首选结构类型之一。为改善传统网架结构在大跨度条件下变形大、用钢量大的缺陷,文中通过对网架施加预应力的方式,达到增强结构整体刚度和承载能力的目的。预应力的施加必然会对网架的稳定性能造成影响,其中支承形式对网架结构的稳定性影响较大。并通过对网架施加不同预应力后进行稳定性分析,得到不同预应力布索方式对网架稳定性影响,为网架的实际工程建设提供参考。

基于UG NX的数控多轴加工工艺改良和配套夹具设计

首先,简要介绍了UG NX编程软件的相关知识;其次,以金属半环和电机外壳为研究对象,分析了其原有的数控加工工艺并提出了优化改进措施;再次,利用UG对研究对象进行了配套工装的仿真设计;最后,利用UG编制研究对象的目标零件多轴数控加工程序,有效保障了产品的加工质量,节省了人力、物力成本,提高了生产效率。

大口径反射镜Bipod支撑结构的装调与检测方法

随着我国遥感卫星对地观测分辨率的不断提升,空间遥感相机的有效口径逐步增大,为有效应对相机在地表装调时的重力误差干扰,大口径遥感相机的装调方式逐步从光轴水平形式转变为光轴竖直形式,与之对应的,相机主反射镜支撑结构与装配需求也在不断革新。为满足反射镜支撑与减重需求,在1 m及以上口径的反射镜支撑形式中,Bipod结构是较为常见的一种结构形式,不同于传统的框式支撑形式,它在光机结构粘接与结构位置标定需求上都有了巨大变革。为保证Bipod支撑结构下反射镜的装配定位精度和面形变化满足系统指标要求,提出了一种结合多目标空间位置转换和Stewart结构运动反演的大口径反射镜组件装调方法,该方法可在有效保证光机结构粘接点精度的同时,仅依靠反射镜自身支撑结构,实现反射镜与主承力板之间的高精度六维调节,系统装调误差可控制在0.04 mm左右。在遥感相机的实际装调过程中,通过分析主反射镜在系统中的装调误差区间,并以此为标准制定了反射镜Bipod结构的定位、粘接、调整和检测方案,实践结果表明该方法可有效控制反射镜的装配定位精度和面形误差,装调结果能够满足大口径遥感相机的系统成像需求。

基于多层全连接神经网络的6C地震波极化向量识别研究

利用机器学习原理,提出一种基于多层全连接(multi-layer fully connected, MFC)神经网络的六分量(six-component, 6C)地震波极化向量识别方法。首先利用6C地震波各波型极化向量数学模型和一系列仿真参数得到5种波型和噪声波型各5 000个极化向量数据集,然后随机选取其中5 000个作为测试集,其余划分为训练集,进行MFC神经网络与支持向量机(support vector machine, SVM)的综合辨识性能对比实验。结果表明,MFC神经网络模型识别5种极化向量类型(SH波和Love波视为一类)和6种极化向量类型的效果均显著优于SVM模型,平均识别率分别达到99.786%和87.940%。