A joint method to retrieve directional ocean wave spectra from SAR and wave spectrometer data

This paper proposes a joint method to simultaneously retrieve wave spectra at dif ferent scales from spaceborne Synthetic Aperture Radar(SAR) and wave spectrometer data. The method combines the output from the two dif ferent sensors to overcome retrieval limitations that occur in some sea states. The wave spectrometer sensitivity coeffi cient is estimated using an ef fective signifi cant wave height(SWH), which is an average of SAR-derived and wave spectrometer-derived SWH. This averaging extends the area of the sea surface sampled by the nadir beam of the wave spectrometer to improve the accuracy of the estimated sensitivity coeffi cient in inhomogeneous sea states. Wave spectra are then retrieved from SAR data using wave spectrometer-derived spectra as fi rst guess spectra to complement the short waves lost in SAR data retrieval. In addition, the problem of 180° ambiguity in retrieved spectra is overcome using SAR imaginary cross spectra. Simulated data were used to validate the joint method. The simulations demonstrated that retrieved wave parameters, including SWH, peak wave length(PWL), and peak wave direction(PWD), agree well with reference parameters. Collocated data from ENVISAT advanced SAR(ASAR), the airborne wave spectrometer STORM, the PHAROS buoy, and the European Centre for Medium-Range Weather Forecasting(ECMWF) were then used to verify the proposed method. Wave parameters retrieved from STORM and two ASAR images were compared to buoy and ECMWF wave data. Most of the retrieved parameters were comparable to reference parameters. The results of this study show that the proposed joint retrieval method could be a valuable complement to traditional methods used to retrieve directional ocean wave spectra, particularly in inhomogeneous sea states.

An empirical method for joint inversion of wave and wind parameters based on SAR and wave spectrometer data

Synthetic aperture radar(SAR)and wave spectrometers,crucial in microwave remote sensing,play an essential role in monitoring sea surface wind and wave conditions.However,they face inherent limitations in observing sea surface phenomena.SAR systems,for instance,are hindered by an azimuth cut-off phenomenon in sea surface wind field observation.Wave spectrometers,while unaffected by the azimuth cutoff phenomenon,struggle with low azimuth resolution,impacting the capture of detailed wave and wind field data.This study utilizes SAR and surface wave investigation and monitoring(SWIM)data to initially extract key feature parameters,which are then prioritized using the extreme gradient boosting(XGBoost)algorithm.The research further addresses feature collinearity through a combined analysis of feature importance and correlation,leading to the development of an inversion model for wave and wind parameters based on XGBoost.A comparative analysis of this model with ERA5 reanalysis and buoy data for of significant wave height,mean wave period,wind direction,and wind speed reveals root mean square errors of 0.212 m,0.525 s,27.446°,and 1.092 m/s,compared to 0.314 m,0.888 s,27.698°,and 1.315 m/s from buoy data,respectively.These results demonstrate the model’s effective retrieval of wave and wind parameters.Finally,the model,incorporating altimeter and scatterometer data,is evaluated against SAR/SWIM single and dual payload inversion methods across different wind speeds.This comparison highlights the model’s superior inversion accuracy over other methods.

A SPARSITY AND COMPRESSION RATIO JOINT ADJUSTMENT METHOD FOR COLLABORATIVE SPECTRUM SENSING

Spectrum sensing is the fundamental task for Cognitive Radio (CR). To overcome the challenge of high sampling rate in traditional spectral estimation methods, Compressed Sensing (CS) theory is developed. A sparsity and compression ratio joint adjustment algorithm for compressed spectrum sensing in CR network is investigated, with the hypothesis that the sparsity level is unknown as priori knowledge at CR terminals. As perfect spectrum reconstruction is not necessarily required during spectrum detection process, the proposed algorithm only performs a rough estimate of sparsity level. Meanwhile, in order to further reduce the sensing measurement, different compression ratios for CR terminals with varying Signal-to-Noise Ratio (SNR) are considered. The proposed algorithm, which optimizes the compression ratio as well as the estimated sparsity level, can greatly reduce the sensing measurement without degrading the detection performance. It also requires less steps of iteration for convergence. Corroborating simulation results are presented to testify the effectiveness of the proposed algorithm for collaborative spectrum sensing.

Distinct element modelling of fracture plan control in continuum and jointed rock mass in presplitting method of surface mining

Controlled blasting techniques are used to control overbreak and to aid in the stability of the remaining rock formation. Presplitting is one of the most common methods which is used in many open pit mining and surface blast design. The purpose of presplitting is to form a fracture plane across which the radial cracks from the production blast cannot travel. The purpose of this study is to investigate of effect of presplitting on the generation of a smooth wall in continuum and jointed rock mass. The 2D distinct element code was used to simulate the presplitting in a rock slope. The blast load history as a function of time was applied to the inner wall of each blasthole. Important parameters that were considered in the analysis were stress tensor and fracturing pattern. The blast loading magnitude and blasthole spacing and jointing pattern were found to be very significant in the final results.

Analysis profile of the fully grouted rock bolt in jointed rock using analytical and numerical methods

The purpose of this study was to investigate the effect of bolt profile on load transfer mechanism of fully grouted bolts in jointed rocks using analytical and numerical methods. Based on the analytical method with development of methods, a new model is presented. To validate the analytical model, five different profiles modeled by ANSYS software. The profile of rock bolts T3 and T4with load transfer capacity,respectively 180 and 195 kN in the jointed rocks was selected as the optimum profiles. Finally, the selected profiles were examined in Tabas Coal Mine. FLAC analysis indicates that patterns 6+7 with2 NO flexi bolt 4 m better than other patterns within the faulted zone.

Experimental and Finite Element Method Studies of J-Lead Solder Joint Reliability

A comprehensive experimental and numerical study of solder joints for plastic leaded chip carrier (PLCC) 84-Pin, 1.27 mm pitch was carried out. The reliability of solder joints was assessed through accelerated thermal cycling at the temperature range of - 55℃-125℃. The samples were taken out to observe the evolution in microstructure, such as grain coarsening, initiation and propagation of cracks. It was found that the Pb-rich phases segregated gradually and formed a continuous layer adjacent to the intermetallic compound (IMC) layer with increasing the number of thermal cycles, resulting in cracks near the solder/lead interface. The response of stress and strain was studied using nonlinear finite element method (FEM), and the results agreed well with the experimental data.

关刺针法配合超声波治疗气滞血瘀型髌股关节疼痛综合征的临床观察

【目的】观察关刺针法配合超声波治疗气滞血瘀型髌股关节疼痛综合征的临床疗效。【方法】将86例气滞血瘀型髌股关节疼痛综合征患者随机分为观察组和对照组,每组各43例。对照组给予西医常规治疗联合功能锻炼,观察组在对照组治疗的基础上,给予关刺针法联合超声波治疗。连续治疗2周。治疗2周后,评价2组临床疗效,观察2组患者治疗前后膝关节疼痛视觉模拟量表(VAS)评分的变化情况,以及Kujala量表评分的情况。比较2组患者治疗前后患侧膝关节主动屈膝活动度(AROM)的变化情况。【结果】(1)治疗后,2组患者的VAS评分明显改善(P<0.05),且观察组在改善VAS评分水平方面明显优于对照组,差异有统计学意义(P<0.05)。(2)治疗后,2组患者的Kujala评分明显改善(P<0.05),且观察组在改善Kujala评分水平方面明显优于对照组,差异有统计学意义(P<0.05)。(3)治疗后,2组患者的AROM明显改善(P<0.05),且观察组在改善AROM水平方面明显优于对照组,差异有统计学意义(P<0.05)。(4)观察组总有效率为95.35%(41/43),对照组为81.40%(35/43)。观察组疗效优于对照组,差异有统计学意义(P<0.05)。【结论】关刺针法配合超声波治疗髌股关节疼痛综合征,能明显缓解患者的疼痛症状,促进膝关节功能的恢复,临床疗效显著。

Interfacial microstructure and mechanical properties of Ti-6Al-4V/Al7050 joints fabricated using the insert molding method

Ti-6Al-4V/Al7050 joints were fabricated by a method of insert molding and corresponding interfacial microstructure and mechanical properties were investigated. The interfacial thickness was sensitive to holding temperature during the first stage, and a good metallurgical bonding interface with a thickness of about 90 μm can be obtained at 750°C. X-ray diffraction, transmission electron microscopy, and thermodynamic analyses showed that the interface mainly contained intermetallic compound TiAl_3 and Al matrix. The joints featured good mechanical properties, i.e., shear strength of 154 MPa, tensile strength of 215 MPa, and compressive strength of 283 MPa, which are superior to those of joints fabricated by other methods. Coherent boundaries between Al/TiAl_3 and TiAl_3/Ti were confirmed to contribute to outstanding interfacial mechanical properties and also explained constant fracture occurrence in the Al matrix. Follow-up studies should focus on improving mechanical properties of the Al matrix by deformation and heat treatment.

Research on Simulation Methods of Electric Field Intensity on Surface of 10 kV Cable Joint

The electric field intensity (EFI) is important characteristic quantity for evaluating the internal insulation state of cable joints. Based on finite element method, this paper proposes two EFI research methods, field-circuit coupling method and equivalent circuit method. The average EFI of the inner surface of the outer semi-conducting shield can be calculated from the current in the measuring circuit. The relative error between these two methods is about 15%, which roughly proves the consistency of the two methods. Further practical application research enables online monitoring of cable joints.

APPLICATION OF THE PROBABILISTIC FRACTURE MECHANICS METHOD OF PREDICTING THE FATIGUE LIFE OF TUBULAR JOINTS

In this paper .fatigue strength of T-type tubularjoints subjected to in-planebending or out-of-plane bending load is investigated By, considering material constantsand initial crack sizes as random variables and applying Monte Carlo simulation method, we have giyen a statistical analvsis on fatigue life. Simultaneously, linearregression analyses of computed resuldts are performed and compared with that of theknown experimental data.

中国家庭联合收入财富不平等测度研究

使用年金法构建同时包含收入和财富的一维指标,即联合收入财富,基于该指标全面测度中国经济不平等程度并进行分解。结果发现:与收入不平等相比,联合收入财富基尼系数提高了13.36个百分点,其中房屋是影响家庭经济不平等的最重要财富形式;联合收入财富不平等程度在各年龄分组、城乡和地区之间存在较大的异质性;联合收入财富不平等主要由收入和财富年金值的边际分布本身所导致,而两大边际分布之间的关系对总体不平等的影响相对较小。

基于TOPSIS-Shapley值法的梯级水电站补偿效益分摊研究

针对流域内联合电站数目众多但利益分配存在纠纷的情况,旨在提出一种更为合理的梯级电站利益分配方法。基于Shapley值法和TOPSIS法,综合考虑电站贡献及电站对不同客观分摊方法的相对满意程度,建立TOPSIS-Shapley值法梯级电站补偿效益分摊模型,同时为解决Shapley值法在求解多利益主体梯级电站联合调度增益分配问题中的局限性,引入聚合降维思想。模型思路如下:将上游电站联合调度前后梯级发电效益的增量作为补偿效益,首先采取四种不同的客观分摊方法对电站特性参数指标进行计算,构成TOPSIS的基础决策矩阵,利用TOPSIS原理得出电站对各个分摊方法的相对满意度,同时采用联盟博弈理论,计算电站所有可能联盟方式下的发电效益,得到基于Shapley值的补偿效益分摊结果,最后将TOPSIS原理得出的分摊系数与由Shapley值法所得的分摊系数结合形成综合分摊权重,应用于黑河上游的八级电站补偿效益分摊中。工程应用实例表明:该方法不仅考虑了联盟电站对整体的边际贡献和各电站的分摊满意程度,且兼顾了电站的特性指标差异,合理量化和分配了各电站间的发电补偿效益,分摊结果公平合理、易被各方接受,可促进流域各级电站参与联合调度从而达到整体效益最大的目标,对于数量较多的梯级水电站补偿效益分配问题具有重要参考意义。

基于等效裂纹法的铝合金T形焊接接头疲劳寿命评估

针对焊接缺陷的多样性、复杂性及随机分散性等特征,提出一种以一组高应力疲劳试验结果作为参考点的等效裂纹法开展焊接结构的疲劳寿命研究。以疲劳试验结果作为参考,假设一个完整板中的初始裂纹等效焊接结构中的缺陷及应力集中效应,基于线弹性断裂力学和Paris公式计算等效裂纹扩展寿命作为焊接结构的疲劳失效寿命。提出基于等效裂纹法的结构疲劳寿命计算流程;开展铝合金T形焊接接头的疲劳试验以及拟合P-S-N曲线;基于T形焊接接头的焊根失效模式采用等效裂纹方法预测T形接头的计算P-S-N曲线,并与试验拟合曲线进行对比,相对误差为10%,验证了该方法的可行性与有效性;最后,通过一组变幅载荷谱疲劳试验与预测P-S-N曲线对比,相对误差均小于15%,同时也验证了该方法对于变幅载荷的适用性,实现了基于一组疲劳试验结果预测全范围T形焊接接头疲劳寿命的评估。以较少的测试和成本实现确定的疲劳寿命,简化了概率疲劳寿命的评估过程,该方法可以推广于其他焊接接头寿命评估中。

Q690厚板对接焊残余应力评估及其对焊接接头断裂性能的影响

[目的]旨在研究高强钢厚板多层多道焊的复杂焊接残余应力,评估其对焊接接头断裂性能的影响。[方法]以75 mm厚Q690高强钢板为研究对象,制定多层多道对接焊工艺,完成对接接头的焊接,使用轮廓法获得中剖面的纵向残余应力,基于自主开发的高效热−弹−塑性有限元计算方法,再现厚板多层多道焊的热循环、微观组织演变等现象,将单轴拉伸试验与GTN损伤模型相结合,提出Q690高强钢板的GTN模型参数,分析金属母材及焊接接头试样的断裂特性和应力−应变曲线。[结果]采用所提方法预测的厚板对接接头熔池形状、金相体积分数都与试验测量基本吻合;考虑焊接固态相变和高强钢轧制初始应力的力学分析,得到的焊接残余应力与试验结果高度一致,并得到了横向残余应力分布;考虑焊接微观缺陷及横向残余应力,阐明了残余应力影响焊接接头断裂性能的力学机理。[结论]相关研究可为高强钢厚板焊接结构残余应力及断裂性能评估提供借鉴和指导。

联合比估计法在敏感性问题调查中的应用

文章基于定性特征敏感性随机化模型——分层抽样下的Warner模型,运用联合比估计法对敏感性问题调查比例的估计量及估计误差进行了理论推导。通过效率比较得出:当各层样本量较大、比估计有效时,联合比估计法的精度优于分层估计法的精度。经调查实例验证,上述结论正确。

城市轨道交通轨面短波不平顺谱实测研究

针对城市轨道交通诱发的振动噪声问题,对轨面短波不平顺进行研究.首先,对上海市轨道交通线路轨面短波不平顺实测数据进行零均值化、剔除异常值、消除趋势项等预处理.其次,利用改进的协方差法计算得到轨面短波不平顺功率谱,分析轨道类型、曲线半径及钢轨接头对轨面短波不平顺功率谱分布规律的影响.然后,基于非线性最小二乘法对轨面短波不平顺谱进行拟合.最后,提出我国城市轨道交通轨面短波不平顺统计谱表达式.研究结果表明:直线段接头区轨面短波不平顺功率谱密度曲线在整个分析波长范围内具有较多特征峰值;直线段接头区上、下行短波不平顺功率谱密度值随波长的分布特征和数值相差不大,说明上、下行的轨面不平顺状态基本相同;钢轨的磨耗程度与曲线半径呈负相关,内、外轨面不平顺功率谱密度的差异随曲线半径的增大而减小,曲线半径是影响轨面不平顺状态的主要因素之一;线路类型对轨面短波不平顺功率谱的影响不大,不同曲线半径、焊接接头影响明显,在对轨道进行维护和养护时需关注小曲线半径区段以及焊接接头区段的不平顺状态.

松动及加固后木结构燕尾榫节点抗震性能对比试验

古建筑木结构燕尾榫节点松动是一种常见的残损模式,为研究节点松动对抗震性能的影响,参照宋《营造法式》殿堂二等材的尺度要求,考虑不同松动程度、不同松动程度补强加固和不同松动程度震损后加固的节点,共制作了3组12个节点试件,对其进行低周反复荷载作用下的抗震性能试验.结果表明:不同松动程度补强加固节点及不同松动程度且有损伤加固节点的破坏模式,与不同松动程度节点的破坏模式相似,榫头和卯口挤压变形明显,榫头被拔出,普拍枋与柱顶接触处出现剪切破坏,补强加固节点榫头拔出量明显减小;各节点滞回曲线均有明显“捏缩”效应,整体呈反“Z”型,补强加固节点的滞回环饱满程度略好;随节点松动程度增加,刚度及承载力均降低,随拔榫量的增大,其减小幅度降低;随节点转角增大,耗能能力逐渐减弱,补强加固节点的耗能及防脱榫能力明显高于未加固节点.节点在松动后仍具有较好的变形能力.

Numerical Simulation of Non-linear Joint Using Displacement Discontinuity Method

An iterative algorithm for modeling of non-linear joint by the displacement discontinuity method (DDM) was described, and the effect of the non-linear joint on the in-situ stress field was investigated in this paper. The Barton-Bandis (BB) non-linear joint model and failure criterion were adopted in the new DDM program. Using this program, the stress field around the non-linear joint was obtained, the parameters analysis of the joint was carried out, and the deformation and stress distribution of the joint were studied. The simulation results show that: (1)the in-situ stress is significantly affected by the joint; (2)the increase of stiffness, friction angle, and thickness of the joint affect the stress concentration in different ways; (3)the influence distance of the joint changes with the angle of the joint; (4)the deformation and stress of the joint change with the point position.

智能网联汽车超车路径规划方法

针对自动驾驶车辆超车路径规划的问题,本文提出改进的人工势场法并引入相对速度构建新的引力势场和斥力势场.建立道路边界势场规范行车区域,对障碍物的影响距离进行分段解决局部极值问题,将自动驾驶车辆动力学相关约束融入人工势场法建立超车路径行驶势场模型.选取重庆市内环快速路为试验路网原型,利用无人机以及定点摄像等数据采集方法进行实地调查,并采用MATLAB/Simulink,CarSim和PreScan进行联合仿真分析.实验结果表明:相比传统的人工势场法,在前车静止、前车匀速、前车减速这3种条件下的超车路径曲率分别降低了85.07%,62.69%和83.86%,横向加速度均小于0.13m/s^(2),改进后的路径规划算法可成功实现平稳超车,驾乘人员的舒适性上有显著提升.

CFRP层合板单搭胶接接头胶板界面剥离强度仿真分析

基于异材界面奇异应力场理论,以CFRP层合板单搭胶接结构为对象,通过有限元和实验的方法分析了结构承载时板胶结合界面上出现的应力分布,锁定界面剥离强度关键区域,通过网格无关的有限元应力比值法提升仿真求解精度,最大限度还原板胶界面应力分布,着重探讨了多层各向异性CFRP板与传统均质材料在仿真过程和结果的差异,及搭接长度、胶层厚度、结构胶参数等对板胶界面应力分布及起裂点位置的影响,为板胶界面剥离应力的优化、胶接工艺的改进和单搭胶接接头强度的提升提供理论支撑。结果表明:各层参数不同的CFRP板胶界面承载时,剥离应力的最大处需由三个维度共同约束,其中两个维度的约束结果与均质材料相同,极值位于板胶界面垂直于拉伸方向的边缘,实际结构中失效的起始亦常见于此处,第三维度受层合板多层异性影响,该边缘上应力最大的点既不位于该边缘的中点也不位于界面角部,具体位置由材料参数和胶接结构共同影响。