Stability and accuracy of central difference method for real-time dynamic substructure testing considering mass participation coefficient

For real-time dynamic substructure testing(RTDST),the influence of the inertia force of fluid specimens on the stability and accuracy of the integration algorithms has never been investigated.Therefore,this study proposes to investigate the stability and accuracy of the central difference method(CDM)for RTDST considering the specimen mass participation coefficient.First,the theory of the CDM for RTDST is presented.Next,the stability and accuracy of the CDM for RTDST considering the specimen mass participation coefficient are investigated.Finally,numerical simulations and experimental tests are conducted for verifying the effectiveness of the method.The study indicates that the stability of the algorithm is affected by the mass participation coefficient of the specimen,and the stability limit first increases and then decreases as the mass participation coefficient increases.In most cases,the mass participation coefficient will increase the stability limit of the algorithm,but in specific circumstances,the algorithm may lose its stability.The stability and accuracy of the CDM considering the mass participation coefficient are verified by numerical simulations and experimental tests on a three-story frame structure with a tuned liquid damper.

Seismic performance evaluation of water supply pipes installed in a full-scale RC frame structure based on a shaking table test

As an important part of nonstructural components,the seismic response of indoor water supply pipes deserves much attention.This paper presents shaking table test research on water supply pipes installed in a full-scale reinforced concrete(RC)frame structure.Different material pipes and different methods for penetrating the reinforced concrete floors are combined to evaluate the difference in seismic performance.Floor response spectra and pipe acceleration amplification factors based on test data are discussed and compared with code provisions.A seismic fragility study of displacement demand is conducted based on numerical simulation.The acceleration response and displacement response of different combinations are compared.The results show that the combination of different pipe materials and different passing-through methods can cause obvious differences in the seismic response of indoor riser pipes.

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.

Experimental investigation on shear strength deterioration at the interface between different rock types under cyclic loading

The shear strength deterioration of bedding planes between different rock types induced by cyclic loading is vital to reasonably evaluate the stability of soft and hard interbedded bedding rock slopes under earthquake;however,rare work has been devoted to this subject due to lack of attention.In this study,experimental investigations on shear strength weakening of discontinuities with different joint wall material(DDJM)under cyclic loading were conducted by taking the interface between siltstone and mudstone in the Shaba slope of Yunnan Province,China as research objects.A total of 99 pairs of similar material samples of DDJM(81 pairs)and discontinuities with identical joint wall material(DIJM)(18 pairs)were fabricated by inserting plates,engraved with typical surface morphology obtained by performing three-dimensional laser scanning on natural DDJMs sampled from field,into mold boxes.Cyclic shear tests were conducted on these samples to study their shear strength changes with the cyclic number considering the effects of normal stress,joint surface morphology,shear displacement amplitude and shear rate.The results indicate that the shear stress vs.shear displacement curves under each shear cycle and the peak shear strength vs.cyclic number curves of the studied DDJMs are between those of DIJMs with siltstone and mudstone,while closer to those of DIJMs with mudstone.The peak shear strengths of DDJMs exhibit an initial rapid decline followed by a gradual decrease with the cyclic number and the decrease rate varies from 6%to 55.9%for samples with varied surface morphology under different testing conditions.The normal stress,joint surface morphology,shear displacement amplitude and shear rate collectively influence the shear strength deterioration of DDJM under cyclic shear loading,with the degree of influence being greater for larger normal stress,rougher surface morphology,larger shear displacement amplitude and faster shear rate.

A Problem of Testing Homogeneity Against Order Constraints on Risk Differences

Consider I pairs of independent binomial variates x0i and x1i with corresponding parameters P0i and p1i and sample sizes n0i and n1i for i=1, …,I. Let △i = P1i-P0i be the difference of the two binomial parameters, where △i’s are to be of interest and P0i’s are nuisance parameters. The null hypothesis of homogeneity on the risk difference can be written as

A Test of U-type for Goodness-of-fit in Regression Models Through Martingale Difference Divergence

Based on the martingale difference divergence,a recently proposed metric for quantifying conditional mean dependence,we introduce a consistent test of U-type for the goodness-of-fit of linear models under conditional mean restriction.Methodologically,our test allows heteroscedastic regression models without imposing any condition on the distribution of the error,utilizes effectively important information contained in the distance of the vector of covariates,has a simple form,is easy to implement,and is free of the subjective choice of parameters.Theoretically,our mathematical analysis is of own interest since it does not take advantage of the empirical process theory and provides some insights on the asymptotic behavior of U-statistic in the framework of model diagnostics.The asymptotic null distribution of the proposed test statistic is derived and its asymptotic power behavior against fixed alternatives and local alternatives converging to the null at the parametric rate is also presented.In particular,we show that its asymptotic null distribution is very different from that obtained for the true error and their differences are interestingly related to the form expression for the estimated parameter vector embodied in regression function and a martingale difference divergence matrix.Since the asymptotic null distribution of the test statistic depends on data generating process,we propose a wild bootstrap scheme to approximate its null distribution.The consistency of the bootstrap scheme is justified.Numerical studies are undertaken to show the good performance of the new test.

The Method of Finite Difference Regression

In this paper I present a novel polynomial regression method called Finite Difference Regression for a uniformly sampled sequence of noisy data points that determines the order of the best fitting polynomial and provides estimates of its coefficients. Unlike classical least-squares polynomial regression methods in the case where the order of the best fitting polynomial is unknown and must be determined from the R2 value of the fit, I show how the t-test from statistics can be combined with the method of finite differences to yield a more sensitive and objective measure of the order of the best fitting polynomial. Furthermore, it is shown how these finite differences used in the determination of the order, can be reemployed to produce excellent estimates of the coefficients of the best fitting polynomial. I show that not only are these coefficients unbiased and consistent, but also that the asymptotic properties of the fit get better with increasing degrees of the fitting polynomial.

Research on damage failure mechanism and dynamic mechanical behavior of layered shale with different angles under confining pressure

The hydrostatic or confining pressure of deep rocks has a significant impact on the mechanical behavior of brittle materials.Especially when confining pressure is applied,the mechanical properties of rock materials will undergo significant changes.Considering that the process of shale sample subjected to impact load is in a closed container in the dynamic triaxial SHPB test,the failure process of the sample cannot be observed.Meanwhile,the activation volume of the shale sample would be large and local failure would occur in the test under the high strain rate loading.Therefore,thefinite element model of shale considering the bedding effect under confining pressure was established in this study.Taking shale materials with different bedding dip angles as simulation objects,the dynamic failure characteristics of shale were studied using the dynamic analysis software ANSYS/LS‐DYNA from three aspects:stress‐strain curve,failure growth process,and failure morphology.The research results obtained can serve as the key technical parameters for deep resource extraction.

基于近红外光谱技术苹果尺寸差异对糖度模型适用性的影响

为消除水果自身尺寸差异对其糖度预测模型的不利影响,进一步提高水果分选模型精度,应用近红外光谱在线检测装置采集不同果径苹果的近红外光谱,对光谱进行多种预处理后,分别建立苹果可溶性固形物的偏最小二乘法模型,再用苹果果径75~85mm组中的建模集预测苹果果径分别为65~75、85~95mm组中的预测集样品,最后用果径组65~75、75~85、85~95 mm中的建模集和预测集,分别作为混合苹果尺寸糖度预测模型的建模集和预测集,并利用特征光谱选择算法对模型进行简化,建立苹果糖度通用预测模型。结果显示:与建模集和预测集果径不同时所建立的苹果糖度预测模型最优组相比,其相关系数Rp由0.805提高至0.943,预测集均方根误差值RMSEP由0.778减小至0.480,RPD由0.96增加至3.05,再对建立的通用模型进行简化,可以降低苹果尺寸对苹果糖度模型的影响,提高模型预测性能。

3种最大摄氧量实验室直接测试方法结果比较、回归分析与应用

目的:通过实验研究比较3种常用最大摄氧量(VO2max)实验室直接测试法测试结果间差异,探讨不同方法测试结果间线性回归关系,便于不同方法测试结果间的互相预测与实现可比性。方法:采用整群抽样、组内交互设计的准实验研究,对20名越野滑雪男运动员分别采用Bruce法(方法1)、功率自行车90秒递增负荷法(方法2)、跑台1分钟递增负荷法(方法3)3种方法进行最大摄氧量直接测试,每两种方法测试间歇期为1周。自变量为3种最大摄氧量测试方法,因变量为最大摄氧量。结果:(1)3种测试方法最大摄氧量的组间均值方差分析结果显示组间差异具有统计学意义(P<0.01),多重比较结果显示方法1的最大摄氧量>方法3>方法2,差异均具有统计学意义(P<0.05);(2)3种方法测试结果个体差值的频数统计显示,测试方法1的最大摄氧量高于方法2约6 ml/min·kg,高于方法3约3 ml/min·kg;(3)同等跑台跑速下,方法3的平均血乳酸高于方法1,且方法3达有氧阈、无氧阈的跑速均低于方法1约一个速度单位(1 km/h);(4)方法1与方法2、方法1与方法3测试结果的线性回归分析显示,回归模型与回归系数均具有统计学意义(P<0.001),线性模型检验拟合度R2分别为9.25、9.05。结论:(1)Bruce法在评价运动员阶段最大摄氧量的最大值方面效果最好,其它两种方法与其存在线性回归关系,可用于不同测试方法结果间的互相预测;(2)不同项目、不同水平的运动员可分别采用适合其能力特点的方法进行最大摄氧量测试;(3)有氧阈、无氧阈对应的跑速、心率变化区间可作为把控有氧阈、无氧阈训练强度的有效、便捷方法。

水位差法模拟波浪荷载作用下大直径圆筒稳定性离心模型试验研究

某人工岛护岸工程采用大直径圆筒结构,结构直径和高度尺寸较大,工程所处位置波浪条件恶劣。采用水位差法等效模拟波浪荷载,开展波浪荷载作用下大圆筒施工期稳定特性离心模型试验研究,结果表明,在25 a一遇波吸力荷载作用下,筒体位移模式近似平移,侧向位移量约353 mm,筒顶沉降约为187 mm,施工阶段钢圆筒整体稳定;筒壁环向拉应力均值约为90 MPa,处于钢圆筒材料允许应力范围内;筒壁海侧土压力值随水位差增大至峰值后趋于稳定,表明筒体与周围邻近土体之间没有新的相对位移趋势,大直径钢圆筒护岸结构在波浪荷载作用下是稳定安全的。

刚度差异桩组合桩网结构路基承载特性

刚度差异桩组合桩网结构路基因具有工后沉降小、经济效益好的优点而被广泛应用于铁道工程。与传统桩承结构路基相比,该结构桩土协同工作规律更为复杂,为研究其承载特性和土体沉降变化规律,通过室内模型试验和数值计算分析刚度差异桩组合桩网结构路基在静力荷载下的桩身应力、桩土应力比、格栅应力、桩侧摩阻力和土体沉降变化特点。结果表明:刚、柔性桩的承载力主要由侧摩阻力提供;刚性桩的桩土应力比随上部荷载增加呈先增长后稳定趋势,荷载在路基中沿中心桩体向边缘桩体传递,并沿路堤行车方向朝路堤横断面方向扩散;土工格栅和碎石加筋垫层共同工作,协调荷载进行再分配,均衡路基应力分布;路基中心排桩沿横断面方向的土体沉降近似呈盆状分布,刚性桩控制路基土体变形和沉降的性状明显优于柔性桩;选择性布置刚度较大长桩可减小路基沉降量。

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。

高应变率冲击荷载下节理花岗岩损伤机制研究

针对冲击荷载作用下贯通节理花岗岩动力响应特征和能量演化规律这一研究目标,以含不同倾角节理花岗岩为研究对象,基于不同倾角节理岩体损伤力学理论模型,开展了高应变率下不同节理倾角花岗岩的分离式霍普金森压杆(split Hopkinson pressure bar,简称SHPB)冲击试验,完成了高应变率下花岗岩的损伤特征研究,获取了岩体动态力学性质和能量耗散特征。研究结果表明:(1)基于Druck-Prager准则和Weibull强度分布准则,结合弹性波理论,建立了不同倾角节理岩体的应力-应变理论模型,该模型能够较好地反映花岗岩的抗压强度、弹性模量随节理倾角变化的动态力学特性,具有较强的倾角效应;(2)相同冲击荷载下,随节理倾角的增大,能量反射系数呈线性上升趋势,能量传递系数呈线性下降趋势,岩样的峰值应力逐渐而减小;相同节理倾角下,随冲击荷载增大,能量反射系数先增大后减小,能量传递系数先减小再增大,能量吸收率随节理倾角的增大而减小;(3)当冲击荷载相同时,完整岩样、节理倾角θ=0°和θ=15°岩样的破碎程度较大,而节理倾角θ=30°和θ=45°岩样的破碎程度较小;当节理倾角相同时,随冲击荷载增大,超过岩样最大抗压强度时,岩样由剪切和拉伸破坏逐渐转化成压碎破坏,且破碎程度也随之增大。

震陷土层变化下变截面单、群桩动力响应差异

为研究地震动作用下震陷土层厚度不同时大直径变截面单桩与群桩基础的动力响应差异,依托厦门第二东通道翔安大桥,通过振动台模型试验,开展震陷土层厚度30、40、50 cm时,单桩与群桩基础桩周土震陷量、桩顶水平位移、桩身加速度及弯矩动力响应差异研究.结果表明:随着震陷层厚度增大,单桩与群桩基础桩周土震陷量、桩顶水平位移、桩身加速度及弯矩均逐渐增大,且加速度及弯矩在变截面处突变;同一震陷层厚度下,群桩基础桩周土震陷量较单桩大,但群桩基础加速度、桩顶水平位移及桩身弯矩均小于单桩.震陷场地桩基础设计时,应着重考虑变截面单桩与群桩动力响应差异,保证桩基础抗震性能.

充气式橡胶坝的模型试验及有限差分研究

橡胶坝的挡水性能优越,兼具实用性与景观性,被广泛用在城市河流挡水闸坝和溢流坝等领域。充气式橡胶坝相比充水橡胶坝,安装和拆卸更为方便,但目前充气式橡胶坝采用查表法进行粗略设计,过程复杂且存在误差。鉴于此,设计大比尺模型试验测试充气式橡胶坝在充气、挡水条件下的坝袋截面形状和袋体张拉力分布特点。基于有限差分软件建立充气式橡胶坝的力学模型,通过大比尺模型试验和现行设计规范验证了该模型的准确性。分析充气式橡胶坝在挡水过程中横截面几何形状及尺寸、张拉力与上游水位及内部气压之间的关系。结果表明:坝袋宽度B、接地宽度b随上游水位增大呈非线性增加;坝袋高度H、横截面面积A随上游水位增大呈非线性减小。设计工况下,坝袋高度H、横截面面积A随气压增加呈非线性增大,坝袋宽度B、接地宽度b随气压增大呈非线性减小;坝袋张拉力与气压呈正比关系。基于Chapman-Richard曲线模型对设计工况下的几何尺寸、张拉力与内部气压间的关系进行拟合,提出橡胶坝简化设计计算公式,可用于充气式橡胶坝的设计计算。

气温多传感器观测数据差异分析

文章中通过模拟观测场条件和利用计量检定设备进行观测试验,对不同安装方式的温度观测数据对比差值进行统计分析,结果表明:温湿度支架上的保护套管会使传感器测量值滞后于环境温度变化,当观测场环境下的温度传感器露出长度小于4 cm时,气温上升时温度数据低于环境温度,气温下降时温度数据高于环境温度。建议规范传感器安装、温度传感器探头长度应至少较保护套多4 cm。

盾构壁后注浆窜浆模型试验及发生条件研究

全断面围岩管片壁后注浆因向开挖面方向的窜浆现象会引起盾尾空隙注浆不饱满,管片上浮、错台及开裂,螺机喷涌等事故常有发生,已经引起广泛重视。通过设计自制壁后注浆液窜浆模型装置进行试验,分析浆液性质、缝隙厚度、注浆压力差对是否发生窜浆及窜浆量的影响,并探讨了不发生窜浆的临界条件。结果表明:(1)浆液压力与窜浆距离呈线性衰减,当浆液稠度较低时,窜浆量与缝隙厚度、浆液稠度呈近似线性正相关、与浆液的剪切屈服应力呈近似线性负相关,窜浆距离与注浆压力差呈近似线性正相关;当浆液稠度增大时,以上关系将逐渐转化为非线性关系;(2)通过极差分析表明浆液的窜浆量受盾壳与岩层间缝隙厚度影响最大,注浆压力与开挖面压力差影响其次,最后是浆液本身的性质;(3)建立了窜浆临界分析模型和计算公式,得到了窜浆发生条件和判别方法,可用于指导稳定围岩地层中盾构掘进时浆液的配制。

现代服务业综合试点是否促进绿色创新

现代服务业综合试点是推动绿色创新的重要抓手。不但现代服务业综合试点对绿色创新的促进作用在科技服务业占比较高的地区相对更大,而且现代服务业综合试点能促进绿色金融改革创新试验区和“碳排放权”交易试点地区的绿色创新效率快速提升。现代服务业综合试点政策能直接提升一地区的绿色创新能力,而且还能提升周边地区绿色创新能力,各地区综合试点政策对周边地区绿色创新能力具有显著的促进作用。虽然现代服务业综合试点能促进一线城市和二线城市绿色发明专利申请量增长,但现代服务业综合试点不能促进四线城市和五线城市绿色发明专利申请量增长。

核电站用1E级干式变压器应用与鉴定研究

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