Effect of welding sequence on residual stress in thin-walled octagonal pipe-plate structure

A three-dimensional finite element approach based on ABAQUS code was developed to investigate the effect of welding sequence on welding residual stress distribution in a thin-walled 6061 aluminum alloy structure. To obtain sound numerical results, the therrno-mechanical behaviour was simulated using a direct-coupled formulation. Nine different simulation sequences were carried out by single-pass TIG welding of an octagonal pipe-plate joint, and the distributions of longitudinal and transverse residual stresses both on the outer and inner surfaces of the pipe were analyzed. The results suggest that the final residual stresses in the weld and its vicinity are not affected by the initial residual stresses of the structure. Selecting a suitable welding sequence can reduce the final residual stress in an octagonal pipe-plate joint.

Effects of welding parameters and welding sequence on residual stress and distortion in Al6061-T6 aluminum alloy for T-shaped welded joint

The distribution of temperature and then the distribution of residual stress and distortion in the stiffened aluminum alloy Al6061-T6 plates under the metal inert gas(MIG)welding process were investigated by three dimensional thermo-mechanical coupled finite element model using Ansys software.The properties of materials were considered temperature-dependent and the filler metal was added to the workpiece by the element birth and death technique.In three modes of current,two different speeds and two various sequences,the distribution of residual stress and distortion were calculated and analyzed.The results showed that increase in welding speed decreased the vertical deflection in the plate,transverse shrinkage and angular distortion of plate and the lateral deflection of stiffener,but increased the maximum longitudinal tensile stress in the plate and stiffener.Furthermore,increase in current increased the residual stress and deformation in the plate and stiffener,and the change in the welding sequence changed the distribution of the distortion in the plate and the stiffener without significant change in the distribution of the longitudinal residual stress.

Approach to blind estimation of the PN sequence in DS-SS signals with residual carrier

This paper presents an approach of singular value de- composition plus digital phase lock loop to solve the difficult problem of blind pseudo-noise （PN） sequence estimation in low signal to noise ratios （SNR） direct sequence spread spectrum （DS-SS） signals with residual carrier. This approach needs some given parameters, such as the period and code rate of PN sequence. The received signal is firstly sampled and divided into non-overlapping signal vectors according to a temporal window, whose duration is two periods of PN sequence. An autocorrelation matrix is then computed and accumulated by those signal vectors one by one. The PN sequence with residual carrier can be estimated by the principal eigenvector of the autocorrelation matrix. Further more, a digital phase lock loop is used to process the estimated PN sequence, it estimates and tracks the residual carrier and removes the residual carrier in the end. Theory analysis and computer simulation results show that this approach can effectively realize the PN sequence blind estimation from the input DS-SS signals with residual carrier in lower SNR.

Effect of welding sequence on residual stress and deformation of 6061-T6 aluminium alloy automobile component

Four different welding sequences of double-pulse MIG welding were conducted for 6061-T6 aluminum alloy automobile bumpers by using nonlinear elastoplasticity finite element method based on ABAQUS software.The post-welding residual stress and deformation were definitely different among the four welding sequences.The results showed that the highest temperature in Solution A was approximately 200℃higher than the melting point of base metal.High residual stress was resulted from this large temperature gradient and mainly concentrated on the welding vicinity between beam and crash box.The welding deformation primarily occurred in both of the contraction of two-ends of the beam and the self-contraction of crash box.Compared with other welding sequences,the residual stress in Solution A was the smallest,whereas the welding deformation was the largest.However,the optimal sequence was Solution B because of the effective reduction of residual stress and good assembly requirements.

Influence of welding sequence on welding residual stress of aluminum alloy flat butt welding

Welding residual stress of 2219 aluminum alloy flat with one groove is analyzed by ellipsoid heat source model. The result shows that the reasonable welding sequence can meliorate the distribution of residual stress and greatly decrease the peak value of welding residual stress if the converse welding method is adopted between adjacent layers in multi-layer weld or between adjacent beads in every layer. The numerical simulation results of the double V-groove thick plate welding model show that the welding sequence influences the value and distribution of the welding residual stress greatly. A more reasonable welding sequence is educed, and the reliability of the numerical simulation results is proved by the experimental results.

On the Judgement of Full-Period Sequences and a Novel Congruential Map with Double Modulus on Z(p^n)

This paper studies the judgement problem of full-period maps on Z(p^n) and proposes a novel congruential map with double modulus on Z(p^n). The full-period properties of the sequences generated by the novel map are studied completely. We prove some theorems including full-period judgement theorem on Z(p^n) and validate them by some numerical experiments. In the experiments, full-period sequences are generated by a full-period map on Z(p^n). By the binarization, full-period sequences are transformed into binary sequences. Then, we test the binary sequences with the NIST SP 800-22 software package and make the poker test. The passing rates of the statistical tests are high in NIST test and the sequences pass the poker test. So the randomness and statistic characteristics of the binary sequences are good. The analysis and experiments show that these full-period maps can be applied in the pseudo-random number generation(PRNG), cryptography, spread spectrum communications and so on.

INJECTIVE MAPS ON PRIMITIVE SEQUENCES OVER Z/(p^e)

Let Z/（p^e） be the integer residue ring modulo p^e with p an odd prime and integer e ≥ 3. For a sequence a over Z/（p^e）, there is a unique p-adic decomposition a- = a-0 ＋a-1 .p ＋… ＋ a-e-l .p^e-1 where each a-i can be regarded as a sequence over Z/（p）, 0 ≤ i ≤ e - 1. Let f（x） be a primitive polynomial over Z/（p^e） and G＇（f（x）,p^e） the set of all primitive sequences generated by f（x） over Z/（p^e）. For μ（x） ∈ Z/（p）[x] with deg（μ（x）） ≥ 2 and gad（1 ＋ deg（μ（x））,p- 1） = 1, setφe-1 （x0, x1,… , xe-1） = xe-1. [μ（xe-2） ＋ ηe-3（x0, X1,…, xe-3）] ＋ ηe-2（x0, X1,…, xe-2） which is a function of e variables over Z/（p）. Then the compressing mapφe-1 ： G＇（f（x）,p^e） → （Z/（p））^∞ ,a-→φe-1（a-0,a-1, … ,a-e-1） is injective. That is, for a-,b-∈ G＇（f（x）,p^e）, a- = b- if and only if φe-1 （a-0,a-1, … ,a-e-1） = φe-1（b-0, b-1,… ,b-e-1）. As for the case of e = 2, similar result is also given. Furthermore, if functions φe-1 and ψe-1 over Z/（p） are both of the above form and satisfy φe-1（a-0,a-1,…,a-e-1）=ψe-1（b-0, b-1,… ,b-e-1） for a-,b-∈G＇（f（x）,p^e）, the relations between a- and b-, φe-1 and ψe-1 are discussed

Multi-Value Sequence Generated over Sub Extension Field and Its Properties

Pseudo-random sequences with long period, low correlation, high linear complexity, and uniform distribution of bit patterns are widely used in the field of information security and cryptography. This paper proposes an approach for generating a pseudo-random multi-value sequence (including a binary sequence) by utilizing a primitive polynomial, trace function, and k-th power residue symbol over the sub extension field. All our previous sequences are defined over the prime field, whereas, proposed sequence in this paper is defined over the sub extension field. Thus, it’s a new and innovative perception to consider the sub extension field during the sequence generation procedure. By considering the sub extension field, two notable outcomes are: proposed sequence holds higher linear complexity and more uniform distribution of bit patterns compared to our previous work which defined over the prime field. Additionally, other important properties of the proposed multi-value sequence such as period, autocorrelation, and cross-correlation are theoretically shown along with some experimental results.

基于宏基因组分析菌渣微生物群落组成和功能多样性

为探究双孢菇菌渣发酵过程中微生物菌群组成变化和功能多样性,对双孢菇菌渣加猪粪混合堆肥的0、8、16和20d样品进行宏基因组测序,分析菌渣堆肥过程中微生物群落组成的变化并挖掘其功能基因。结果表明:(1)双孢菇菌渣有机肥发酵初期0d时与发酵8、16和20d时的微生物群落组成变化较大,同时在KEGG数据库中进行功能多样性分析和聚类分析发现0d、8d样本距离相对较近,16d和20d样本距离相对较近。(2)从不同时间段的菌渣有机肥中一共鉴定出28257个种,其中发酵0、8、16和20d样本物种分别占物种总数的61.04%、85.35%、86.08%和85.40%。(3)自然发酵0d时优势菌门为厚壁菌门,随着发酵时间的增加优势菌门逐渐变为变形菌门、拟杆菌门和放线菌门等;芽孢杆菌科及类芽孢杆菌科在发酵过程中一直为关键菌科;优势菌种为热噬淀粉芽胞杆菌和嗜热芽孢杆菌。(4)菌渣发酵过程中功能基因主要位于碳水化合物代谢、氨基酸代谢、核苷酸代谢和辅因子和维生素的代谢途径;碳水化合物酶占比较多的为糖基转移酶和糖苷水解酶,最低为多糖裂解酶,分别占比为38.8%、38.1%和1.2%;丰度最高的3个抗性基因分别为多耐药性抗性基因、大环内酯抗性基因和四环素抗性基因。

基于16S rDNA测序分析不同剩余采食量皖南黄兔盲肠中微生物菌落多样性

[目的]本研究旨在探究皖南黄兔个体间剩余采食量水平差异与盲肠菌群多样性的关系。[方法]选取体重、年龄相近的110只皖南黄兔仔兔进行60 d的饲养试验,试验结束后测定个体剩余采食量(residual feed intake, RFI),根据RFI值选出5只高RFI和5只低RFI皖南黄兔母兔,分别为H组(高RFI值)和L组(低RFI值)。利用16S rDNA扩增子测序技术对H组和L组母兔盲肠内容物进行比较分析。[结果]不同剩余采食量水平的家兔盲肠菌群组成丰富度无显著差异(P>0.05),而菌落多样性存在一定差异。L组黄兔盲肠微生物中纺锤链杆属(Fusicatenibacter)、经黏液真杆菌属(Blautia)、毛螺菌属(Lachnospira)、草酸杆菌属(Oxalobacter)、肠杆菌属(Intestinibacter)的相对丰度显著高于H组(P<0.05);Paludicola、Mailhella、螺杆菌属(Helicobacter)、假单胞菌属(Pseudomonas)的相对丰度显著低于H组(P<0.05)。[结论]不同RFI水平的皖南黄兔群体盲肠菌群多样性和结构组成存在一定差异,包括毛螺菌属、纺锤链杆菌属、结肠杆菌等与血脂代谢、血糖调节过程相关的菌群在两组间的丰度存在显著差异。调节肠道菌群的结构及丰度可能是改善家兔饲料利用效率的有效途径。

变分资格迹元强化循环网络用于空间滚动轴承剩余寿命预测

针对经典时间循环神经网络(SRNNs)在预测时间序列中存在长时依赖的缺陷,同时由于遍历整个训练数据集进行现有监督式学习增加了时间复杂度,造成SRNNs在预测空间滚动轴承剩余寿命中存在预测精度和计算效率较低的问题,提出一种变分资格迹元强化循环网络(VETMRRN)。在VETMRRN中,构建新型时间循环网络结构以增大历史信息记忆量,并设计基于神谕门机制的元学习超参数自初始化网络来加速搜索VETMRRN的最优回顾序列长度;设计含有资格迹算子的变分自编码元策略梯度学习算法,以提高对VETMRRN参数的训练速度和全局优化效果。在此基础上提出基于VETMRRN的空间滚动轴承剩余寿命预测方法。首先采用Shapely值特征融合提取空间滚动轴承的性能退化特征;然后将性能退化特征输入VETMRRN中预测性能退化特征趋势;最后建立威布尔分布可靠度模型来预测空间滚动轴承的剩余寿命。该方法具有较高的预测精度、较好的泛化性能和较高的计算效率。最后通过空间滚动轴承剩余寿命预测实例证明了该方法的有效性。

主余震序列作用对剪力墙结构动力响应影响分析

为了研究主余震序列作用对高层剪力墙结构动力响应的影响,以某超高层作为研究基础建立了其动力弹塑性分析模型,开展了相关研究工作。选取10个真实主余震序列作用事件,构造了14条主余震序列作用作为输入的地震荷载;以PGA、PGV、PGA/PGV等作为表征地震动强度的指标,计算了结构在主余震序列作用及仅主震作用下的结构塑性耗能、最大残余层间位移角的增量损伤比及Karl Pearson相关系数;分析了主余震序列作用下结构塑性耗能及最大残余层间位移角的特点和地震动强度指标与增量损伤比的相关性。结果表明,主余震序列作用加剧了结构损伤,其塑性耗能增量平均达24%~28%;主余震序列作用下结构最大残余层间位移角有可能增大,也有可能减少。基于塑性耗能的结构主余震增量损伤比与PGV、SED、SI等速度相关的地震动强度表征指标均表现出了较强的相关性,可考虑作为选择和调整主余震序列作用地震波的指标;基于最大残余层间位移角的结构主余震增量损伤比则与地震动强度指标相关性较弱。

Asymptotic normality of error density estimator in stationary and explosive autoregressive models

In this paper,we consider the limit distribution of the error density function estima-tor in the rst-order autoregressive models with negatively associated and positively associated random errors.Under mild regularity assumptions,some asymptotic normality results of the residual density estimator are obtained when the autoregressive models are stationary process and explosive process.In order to illustrate these results,some simulations such as con dence intervals and mean integrated square errors are provided in this paper.It shows that the residual density estimator can replace the density\estimator"which contains errors.

基于层次交互动态注意力与序列学习的图像超分辨率重建

针对图像超分辨率中网络关注度不足、模块间协同性弱和深层特征表征消失等问题,提出了一种结合层次交互动态注意力与序列学习单元的多级残差聚合超分辨率重建模型。模型采用多层次特征融合与跳跃连接的网络结构,结合不同层次的特征,捕获从低到高的不同级别的信息,生成更丰富和准确的表征。模块里通过残差连接避免梯度消失,实现深度网络的平滑损失空间和灵活增加。提出动态层次融合注意力模块动态计算各个特征的重要性权重,进行有选择性的特征融合,并通过序列学习单元捕获更长范围的上下文信息。提出多尺度特征融合模块将不同感受野的特征信息提取融合,以挖掘更深层的特征表示。模块尾部引入轻量化无参注意力机制自适应加权特征图,恢复图像高频细节。实验结果表明,相较于主流算法,提出的算法在各种公开测试集(Set5、Set14、BSD100、Urban100、Manga109)上进行3倍超分辨率重建评估,平均峰值信噪比提升约0.47dB,平均结构相似性提升约0.0068。且在遥感图像超分辨率重建方面展示出实际应用潜力。证明其在图像超分辨率重建方面的优越性。

塔式起重机顶升架焊接顺序优化仿真

顶升架是为适应不同的施工需求利用套架和液压系统对塔式起重机的高度进行调整的顶升结构。其作为一种典型的焊接结构,焊接时产生的残余变形会对塔机的安全应用产生重要影响。利用固有应变法,首先建立以二维网格为主的有限元模型,利用双椭球热源模型,并根据实际生产工艺,通过焊接软件对不同焊接顺序塔式起重机的顶升架进行焊接数值模拟对比,并确定最优焊接顺序。结果表明:经过对焊接顺序进行优化,能有效控制焊接产生的残余应力与变形,该研究具有一定的现实指导意义。

关于不定方程x^(3)-1=114y^(2)

不定方程是数论中不可或缺的一个分支,它有着悠久的历史与丰富的内容,其理论和方法在各学科和实际生活中都有广泛的应用。运用同余式、递归序列、平方剩余以及Pell方程的解的性质等初等方法对不定方程x^(2)-1=114y^(2)的整数解进行了讨论。首先利用因式分解将原不定方程分解为8种情形,其次运用转化、取模等技巧对8种情形分别分析,最终得出不定方程x^(2)-1=114y^(2)仅有整数解(x,y)=(1,0)。

基于多路卷积聚合的动作识别

为解决视频数据中不同的动作行为时序长短不一,输入的视频帧序列长度固定而导致不同时序特征被忽略的问题,提出了基于多路卷积网络聚合深度学习模型的动作识别方法。网络以不同序列长度和模态的图像作为输入源,构成三条支路,采用多路分支逐层捕捉不同尺度的特征信息,在网路的最后对特征进行聚合并利用softmax分类器对识别结果进行分类。实验结果表明,该模型在UCF101数据集上准确率达到了88.36%,均优于对比实验模型,有效地提高了识别精度,具有一定的竞争力。

基于双分支序列残差注意力的场景文本图像超分辨率重建

针对现有场景文本图像超分辨率重建方法存在的重建文本图像细节信息丢失和边缘模糊的问题,提出一种基于双分支序列残差注意力的重建方法DSRASRN。首先,DSRASRN采用一种新的双分支序列残差注意力模块(DSRAB),该模块采用双分支结构分别专注于水平和垂直方向上的上下文信息提取,并通过高效通道注意力(ECA)机制给予重要信息更高的权重,以增强特征的表达;其次,在DSRASRN内新增文本边缘感知模块(TEAB),增强对文本图像边缘细节和纹理的处理,TEAB采用特定方向的卷积核捕捉特定空间方向上的信息,同时结合具有不同空洞率的空洞卷积来扩大感受野并增强对高频信息的重建能力。在真实场景文本图像数据集TextZoom上的实验结果表明,DSRASRN不仅可以重建出更多的图像细节信息,而且在提高文本识别准确率方面也表现出明显优势。与TSRN、TBSRN、TG、TPGSR方法相比,DSRASRN的峰值信噪比(PSNR)分别提升0.27、0.78、0.59和0.51 dB,且DSRASRN可以使文本识别器ASTER、MORAN和CRNN的平均文本识别精度分别达到65.0%、62.1%和52.0%。此外,真实场景文本识别图像数据集ICDAR2015和SVT上的测试结果表明DSRASRN具有良好的泛化能力。

煤矿短距离供电线路防越级异常机械跳闸自动检测方法

为避免煤矿供电出现重大事故,确保供电线路安全,提出了煤矿短距离供电线路防越级异常机械跳闸自动检测方法。采用迭代法对观察到的时间序列供电线路数据预处理,剔除其噪声点,获得预处理后的供电线路拟合数据。利用余弦相似性,计算2个供电线路矢量在方向上度量特征之间的异常关联性,得到最终的特征子集,实现对机械跳闸的异常特征提取。将提取到的特征值作为变量,输入到建立的防越级机械跳闸自动检测模型中,计算设备状态量集合和目标函数,完成异常跳闸检测。实验结果表明,所提方法能准确检测出煤矿短距离供电线路防越级异常机械跳闸,及时作出应对措施,保证电力安全稳定运行。

Normalized residual displacement spectra for post-mains

Residual displacement,as a significant measure of structural inelasticity,is effectively used in post-earthquake seismic assessment of structures.This demand can be considered for seismic evaluation of structures under multiple earthquakes.This study introduces a simple and novel index to predict the residual displacement of mainshock-damaged structures against subsequent aftershock.The proposed index is defined as a ratio between residual displacement of damaged structures against aftershock and peak inelastic displacement of intact structures under mainshock.In this study,constantstrength spectra based on the index are developed considering the effects of important structural characteristics and also significant seismic parameters.Moreover,analytical equations are presented to predict the proposed index for bi-linear single-degree-of-freedom(SDOF)systems considering both the effects of positive and negative polarities of aftershock.Furthermore,an equation is suggested to estimate the peak inelastic displacement of intact systems under mainshock,which is required to compute the index.