Study on Plasticity Modification for Measuring High Residual Stress by Hole-Drilling Method

Hole-drilling method is a commonly used method for measuring residual stress. The calibration coefficients in ASTM E837-13 a would cause large errors due to the plasticity deformation of materials. In the study, calibration coefficients were modified in the plasticity deformation stage based on the distortion energy theory. The calibration experiment of calibration coefficients was simulated by the finite element model, and the plasticity modification formulas of 7075 aluminum alloy were obtained. From the results of uniaxial tensile loading test, the measuring errors of high residual stress are significantly reduced from-4.071%～53.440% to-5.140% ～ 0.609% after the plasticity modification. This work provides an effective way to expand the application of hole-drilling method.

Discussion on the application prospect of the transient electromagnetic method based on the dual launcher and mine advanced detection

The dual transmitter implements the equivalent anti-magnetic flux transient electromagnetic method, which can effectively reduce the scope of the transient electromagnetic detection blind area. However, this method is rarely reported in the detection of pipelines in urban geophysical exploration and the application of coal mines. Based on this, this paper realizes the equivalent anti-magnetic flux transient electromagnetic method based on the dual launcher. The suppression effect of this method on the blind area is analyzed by physical simulation. And the detection experiment of underground pipelines is carried out outdoors. The results show that the dual launcher can significantly reduce the turn-off time, thereby effectively reducing the impact of the blind area on the detection results, and the pipeline detection results verify the device’s effectiveness. Finally, based on the ground experimental results, the application prospect of mine advanced detection is discussed. Compared with other detection fields, the formation of blind areas is mainly caused by the equipment. If the dual launcher can be used to reduce the blind area, the accuracy of advanced detection can be improved more effectively. The above research results are of great significance for improving the detection accuracy of the underground transient electromagnetic method.

Blind detection of liquefaction by existing methods for New Zealand M_L6.3 earthquake on Feb. 22,2011

Real-time liquefaction monitoring and warning techniques are new ways to mitigate liquefaction hazard. A key point is to establish a reverse liquefaction detection method based on seismic records. However, the existing methods are quite limited and the reliability requires verification. On Feb. 22, 2011 an earthquake of magnitude 6.3 struck at New Zealand＇s South Island. Remarkable liquefaction phenomena were reported, which provide an opportunity to verify the existing liquefaction detection methods. 27 acceleration records within 50 km to the epicenter were selected to perform a blind detection by using the existing methods, including Miyajima method, Suzuki method, Kostadinov-Yamazaki method and Yuan-Sun method. The blind detection results indicate that Yuan-Sun method gives correct results for seven confirmed sites, and Suzuki method and Yuan-Sun method yield correct detection for a reported non-liquefied site. Four methods including the Yuan-Sun method give identical detection for four sites and three methods also including the Yuan-Sun method give identical detection for ten sites. Besides, there are five sites, for which the four methods give opposite detection.

ROBUSTNESS OF THE SUBSPACE METHOD FOR BLIND SIGNATURE WAVEFORM ESTIMATION WITH RESPECT TO CHANNEL ORDER IN ASYNCHRONOUS DS-CDMA SYSTEMS

The robustness of the subspace method for blind signature waveform estimation with respect to channel order is analyzed in asynchronous DS-CDMA systems theoretically. Theoretical analysis and simulation results show that the overestimating of the channel order will lead to the degradation of the quality of the estimated signature waveform. So we should adopt the channel order as small as possible.

Neutron-gamma discrimination method based on blind source separation and machine learning

The discrimination of neutrons from gamma rays in a mixed radiation field is crucial in neutron detection tasks.Several approaches have been proposed to enhance the performance and accuracy of neutron-gamma discrimination.However,their performances are often associated with certain factors,such as experimental requirements and resulting mixed signals.The main purpose of this study is to achieve fast and accurate neutron-gamma discrimination without a priori information on the signal to be analyzed,as well as the experimental setup.Here,a novel method is proposed based on two concepts.The first method exploits the power of nonnegative tensor factorization(NTF)as a blind source separation method to extract the original components from the mixture signals recorded at the output of the stilbene scintillator detector.The second one is based on the principles of support vector machine(SVM)to identify and discriminate these components.In addition to these two main methods,we adopted the Mexican-hat function as a continuous wavelet transform to characterize the components extracted using the NTF model.The resulting scalograms are processed as colored images,which are segmented into two distinct classes using the Otsu thresholding method to extract the features of interest of the neutrons and gamma-ray components from the background noise.We subsequently used principal component analysis to select the most significant of these features wich are used in the training and testing datasets for SVM.Bias-variance analysis is used to optimize the SVM model by finding the optimal level of model complexity with the highest possible generalization performance.In this framework,the obtained results have verified a suitable bias–variance trade-off value.We achieved an operational SVM prediction model for neutron-gamma classification with a high true-positive rate.The accuracy and performance of the SVM based on the NTF was evaluated and validated by comparing it to the charge comparison method via figure of merit.The results indicate that the proposed approach has a superior discrimination quality(figure of merit of 2.20).

SUBSPACE METHOD FOR BLIND IDENTIFICATION OF CDMA TIME-VARYING CHANNELS

A new blind method is proposed for identification of CDMA Time-Varying (TV)channels in this paper. By representing the TV channel's impulse responses in the delay-Doppler spread domain, the discrete-time canonical model of CDMA-TV systems is developed and a subspace method to identify blindly the Time-Invariant (TI) coordinates is proposed. Unlike existing basis expansion methods, this new algorithm does not require .estimation of the base frequencies, neither need the assumption of linearly varying delays across symbols. The algorithm offers definite explanation of the expansion coordinates. Simulation demonstrates the effectiveness of the algorithm.

RLS and LMS blind adaptive multi-user detection method and comparison in acoustic communication

RLS and LMS blind adaptive multi-user detection algorithm and multi-user detector was proposed to solve the problem of multi-user signal detection problem encountered in underwater acoustic communication networks.In simulation analysis,RLS and the LMS blind adaptive multi-user detector were designed and tested for synchronous and asynchronous multi-user communication process.The results of SIR comparison and MMSE comparison show that,both of the two methods can realize blind adaptive detection when any user change in multi-user communication,during this process,the training communication sequences are not needed.The RLS algorithm has about 5 dB higher in SIR compared with LMS algorithm,and the convergence velocity of RLS algorithm is also higher than LMS algorithm when the communication users change.RLS algorithm has better ability in multi-user detection than that of LMS algorithm,and it has great attraction and guiding significance for solving the problem of multiple access interference(MAI) in multi-user communication.

Use of Plastic Correction Formula to Improve Accuracy of Welding Residual Stress Test with Blind-Hole Method

The blind-hole method is the most widely used approach to experimentally determine the distribution of residual stress. This paper aims to improve test accuracy of welding residual stress and conducts an experimental study on the strain release factors involved when using the blind-hole method for Q235 and Q345, two steels commonly used in building structures. The ranges of strain release factors A and B in the elastic stage, the effects of strain release factors on residual stress calculated values, and the plastic corrected strain release factors are analyzed considering of the effect of plastic deformation around the blind hole on measurement accuracy. Finally, a simplified calculation formula to determine strain release factors is proposed for use with the blind-hole method. Results show that in the elastic stage, strain release factor A for Q235 and Q345 ranges from-0.399 to-0.525 and strain release factor B from-0.791 to-0.960. Changing the strain release factors A and B shows that calculated residual tensile stress varies in relation to a decrease in both factor values. However, there is a increase in calculated residual compressive stress with a decrease in the strain release factor A value, but there is an decrease with a decrease in strain release factor B value. Calculated residual stress applied to elastic strain release factors is compared with that applied to amended plastic strain release factors for Q235 steel. The maximum deviation between calculated residual stress and test stress is reduced from 21.1 to 1.0%,and for Q345 steel from 26.5 to 1.2%. It is thus evident that the plastic correction formula proposed in this paper can be used in calculations when conducting a residual stress test.

Subspace-Based Blind Channel Estimation Method for MIMO-OFDM Systems

A subspace-based blind channel estination algo rithm for MIMO-OFDM systems is proposed. This algorithm exploits the cyclostationarity introduced by cyclic prefix of OFDM to estimate the channel parameters. The proposed new algorithm is found to be outperforming the other algorithm with respect to convergence rate and achievable mean square error and robustness to channel order over determination.

A Modified Eigenvector Method for Blind Deconvolution of MIMO Systems Using the Matrix Pseudo-Inversion Lemma

Recently we have developed an eigenvector method (EVM) which can achieve the blind deconvolution (BD) for MIMO systems. One of attractive features of the proposed algorithm is that the BD can be achieved by calculating the eigenvectors of a matrix relevant to it. However, the performance accuracy of the EVM depends highly on computational results of the eigenvectors. In this paper, by modifying the EVM, we propose an algorithm which can achieve the BD without calculating the eigenvectors. Then the pseudo-inverse which is needed to carry out the BD is calculated by our proposed matrix pseudo-inversion lemma. Moreover, using a combination of the conventional EVM and the modified EVM, we will show its performances comparing with each EVM. Simulation results will be presented for showing the effectiveness of the proposed methods.

Multichannel Blind CT Image Restoration via Variable Splitting and Alternating Direction Method

Computed tomography(CT) blurring caused by point spread function leads to errors in quantification and visualization. In this paper, multichannel blind CT image restoration is proposed to overcome the effect of point spread function. The main advantage from multichannel blind CT image restoration is to exploit the diversity and redundancy of information in different acquisitions. The proposed approach is based on a variable splitting to obtain an equivalent constrained optimization formulation, which is addressed with the alternating direction method of multipliers and simply implemented in the Fourier domain. Numerical experiments illustrate that our method obtains a higher average gain value of at least 1.21 d B in terms of Q metric than the other methods, and it requires only 7 iterations of alternating minimization to obtain a fast convergence.

重氮试验在盲插鼻肠管时末端位置判断中的应用效果研究

目的探讨重氮试验在盲插鼻肠管后末端位置判断的应用效果。方法采用便利抽样法,选取2021年9月至2022年1月山东省某三级甲等医院重症监护病房(intensive care unit,ICU)进行盲插鼻肠管术的216名患者为研究对象。采用重氮试验、测pH值、观察回抽液性质三种方式预测鼻肠管末端位置,以X线摄片为判定的金标准,确认鼻肠管末端位置。比较重氮试验及其他两种方式预测的准确率、敏感度、特异度、阳性结果预测值(positive predictive value,PPV)、阴性结果预测值(negative predictive value,NPV)、阳性似然比(positive likelihood ratio,PLR)、阴性似然比(negative likelihood ratio,NLR)等指标。结果pH值判断的敏感度为97.7%、NPV为84.0%、NLR为0.045;回抽液性质判断的特异度为82.9%、PPV为95.5%、PLR为4.912;重氮试验方式的准确率为92.6%、Kappa系数为0.755;受试者操作特征曲线下面积最大为0.870,95%CI(0.793,0.947)。结论重氮试验判断盲插鼻肠管末端位置的准确率、一致性较好,具有较高的临床预测价值。

自攻螺钉与拉铆钉混合连接受剪承载性能试验

为改善自攻螺钉连接的构件在地震作用下易发生拉脱导致结构严重破坏的缺点,提升冷弯薄壁型钢组合墙体抗破坏能力,分析了组合墙体层间连接处的传力机理,针对自攻螺钉的破坏模式,提出拉铆钉与自攻螺钉混合连接。为研究混合连接的抗剪性能,共进行了48组连接接头抗剪性能试验,包含冷弯薄壁型钢结构常用的5种连接板厚度,不同搭接板厚比(变化范围1.0~2.0),包含纯自攻螺钉连接、纯拉铆钉连接及混合连接的连接方式。观察混合连接的破坏模式,自攻螺钉未发现拉脱破坏,其破坏模式主要表现为:板承压破坏与螺钉倾斜组合破坏、铆钉剪断破坏及板承压与铆钉部分剪断组合破坏3种;相较单一连接方式,混合连接荷载–位移曲线表现出更长的塑性阶段;当板厚比大于1.5且组合板厚小于3.0mm,混合连接的承载力及延性较单一连接增长明显;利用现有计算方法对混合连接的承载力进行累加计算,与试验结果对比,计算结果偏保守。研究发现:混合连接能较好地弥补拉铆钉和自攻螺钉受剪过程中的缺陷,有效改善自攻螺钉拉脱破坏,从而提升连接的承载力及延性;板厚和板厚比是影响混合连接破坏模式及承载力的重要因素,与单一连接相比,板厚比越大,承载力提升越大;排布方式对混合连接的力学性能及破坏机理影响有限;在本文试验工况下,结合混合连接的破坏模式,在现有计算方法的基础上,提出改善后的计算方法,其计算结果更合理。

等值反磁通瞬变电磁法在浅部岩溶探测中的应用研究——以惠州市龙门县某地区为例

传统瞬变电磁法受关断时间和互感的过渡过程影响,存在较大浅部盲区;新近发展迅速的等值反磁通瞬变电磁法从理论和仪器上实现了纯二次场的观测,大大提高了浅部区域的探测精度。为研究等值反磁通瞬变电磁法在100 m以浅岩溶探测的应用效果,以惠州市龙门县某岩溶发育区为靶区,开展了方法有效性研究,取得主要成果与结论:(1)界定的土石界面和圈定的岩溶发育区与已知钻孔揭露情况吻合较好,验证了基于等磁反磁通瞬变电磁法在100 m以浅岩溶探测的有效性;(2)反映区内岩溶具有一定连通性,岩溶大小约1~20 m,岩溶主要发育于20~40 m及60 m以下埋深。研究结果一方面有效圈定了研究区100 m以浅岩溶发育区,对后续桥梁工程的安全建设具有重要意义;另一方面等值反磁通瞬变电磁法具有施工便捷、采集高效、抗干扰强等优势,未来有望在城市浅部空间探测领域实现更大作为。

钢板残余应力检测方法的实验比较

为验证自主研制的透射式励磁感应钢板内应力无损检测系统的测量效果,在工厂生产线上切取了2种材质、不同板形的4块钢板作为残余应力测量试样,分别使用自研系统、X射线衍射法、超声法和盲孔法进行残余应力测量及比较。取样测量实验发现,4种方法的残余应力测量结果相差明显,同一被测点的测量结果也相差较大,在个别被测点出现残余应力测量值符号相反的现象。针对测量结果数据及其存在的差异,从4种方法的检测原理出发,定性分析了产生差异的原因,概括出4种方法的技术特点,并针对每种方法提出若干使用建议。

四种典型球墨铸铁应变释放系数及其塑性修正研究

盲孔法是工程中测量残余应力最普遍的方法,其中材料的应变释放系数是该方法中的关键参数,目前国内外对球墨铸铁的应变释放系数研究相对较少。本文采用盲孔法对四种常用球墨铸铁QT450-10、QT550-6、QT600-3和QT700-4的应变释放系数进行了标定,得到应变释放系数与应力的关系曲线,发现低牌号的球墨铸铁由于铁素体含量多,对应力集中更为敏感,在标定试验中易产生局部的塑性变形。使用基于形状改变比能S的修正方法对四种球墨铸铁的应变释放系数进行修正,发现和其他均质金属材料不同,球墨铸铁应变释放系数与■之间存在良好的线性关系,因此提出了球墨铸铁应变释放系数关于■的修正公式,可直接应用于盲孔法测量球墨铸铁的残余应力。

一种基于Blind Kriging模型和差分进化的电磁结构优化算法

各类电磁结构日趋复杂,设计自由度不断提升.传统优化算法需要对大量的参数组合进行全波仿真试探,设计效率普遍较低。针对这一问题,提出BK(blind Kriging)模型和差分进化相结合的电磁结构优化算法.相比普通Kriging模型,BK模型通过贝叶斯参数选择算法将影响性能的主要因子加入回归模型,提高对响应的预测精度;依据BK模型的预测结果从每代差分进化种群中选择最优个体执行电磁仿真。由于优化过程中大量的电磁计算转移到快速的BK模型,优化效率得到显著提升。通过一个圆波导多螺钉极化转换器的优化设计,表明该方法的求解质量和收敛速度优于现有算法。

结构运营模态参数识别的稀疏分量分析新方法

结合时频掩码技术和模糊C均值聚类,提出一种结构运营模态参数识别新方法。该方法根据结构振动响应的能量信息建立时频掩码,通过时频掩码求解结构模态响应,采用单自由度模态参数识别技术从模态响应中识别模态频率和阻尼比。结构振动响应能量峰值处的时频系数被依次提取,经单源点检测后采用模糊C均值聚类对其聚类,将第一个聚类中心作为模态振型。通过数值案例和框架结构试验验证所提方法的有效性。结果表明,所提方法具有良好的模态参数识别精度和噪声鲁棒性。

基于PRP共轭梯度法求解代价函数的RSC码参数识别算法

Turbo码是一种常用的信道编码方式,正确识别Turbo码首先要正确识别其子递归系统卷积(recursive system convolutional,RSC)码,由于信道噪声与干扰引发误码,这就要求识别算法具有良好的抗误码性能以及识别能力。利用解调软判决序列,通过编码码元约束方程,构建指数形式的代价函数模型,将识别RSC码的生成矩阵问题转化为求解代价函数全域极值的最优化问题,最后在共轭梯度法的基础上,采用新的PRP步长因子来寻找全域极值点。仿真结果表明,所提算法与现有算法相比,收敛速度更快,在低信噪比下也有良好的识别能力。

基于3种方法的福建天气雷达探测环境评估与分析

【目的】我国新一代天气雷达组网探测仍然存在较大盲区,特别是对低层大气的覆盖情况缺少评估。该文旨在研究福建省雷达对低层大气的探测情况,以辅助补盲雷达站址选择。【方法】利用SRTM高分辨率地形数据,采用3种方法,对福建省8部SA天气雷达0.5~3.4°仰角的探测环境,从单站范围、雷达探测重叠度、组网覆盖范围等方面进行分析,其中方法1、方法2、方法3分别基于射线海拔高度不同、射线与地形高度差不同、馈源以上高度不同,对一定高度区间的雷达覆盖情况进行评估。【结果】从业务角度出发评估低层大气探测环境,方法1和方法2的评估效果更优,以方法2为例,分析在盲区新建雷达的补盲效果,结果表明盲区主要位于闽中、闽西南和闽北地区。【结论】补盲雷达若位于靠近福建省界的闽西南区域,能最大程度新增0~2 km高度雷达波束覆盖面积,经计算得出新增面积可达15 000 km2以上。