MECHANISM RESEARCH FOR 3D NON-AXISYMMETRIC THIN-WALL TUBE OFFSET SPINNING

Difference of offset spinning with conventional symmetric spinning is analyzed. A 3D FEM model for offset tube neck-spinning is established and the spinning process is simulated by means of ANSYS software. Dynamic boundary and contact problems in simulation are solved. Transient stress distribution of contact area, transient strain distribution of nodes in typical section and strain distribution of the workpiece at last are attained, the place and the cause of crack are analyzed. Strain variation curves with time of offset spinning and conventional spinning are compared. It shows the mechanism difference between offset spinning and conventional spinning. In addition, simulation results show how strain distribution of typical section, thickness of some typical nodes, axial extension in left section and force of three rollers change with time. According to the study of the variation curve, material flow law along radial, tangential and axial direction is attained and the whole spinning process is studied. The simulation results discover that offset distance is the key to manufacture offset non-symmetric tube, and process parameters change with spinning angle. Experiment data really reflect different process parameters＇ influence on conventional symmetric and offset spinning force. Experiments accord well with simulation.

Comparison and analysis of two Coulomb friction models on the dynamic behavior of slider-crank mechanism with a revolute clearance joint

The objective of this study is to investigate the effects of the Coulomb dry friction model versus the modified Coulomb friction model on the dynamic behavior of the slider-crank mechanism with a revolute clearance joint. The normal and tangential forces acting on the contact points between the journal and the bearing are described by using a Hertzian-based contact force model and the Coulomb friction models, respectively.The dynamic equations of the mechanism are derived based on the Lagrange equations of the first kind and the Baumgarte stabilization method. The frictional force is solved via the linear complementarity problem(LCP) algorithm and the trial-and-error algorithm.Finally, three numerical examples are given to show the influence of the two Coulomb friction models on the dynamic behavior of the mechanism. Numerical results show that due to the stick friction, the slider-crank mechanism may exhibit stick-slip motion and can balance at some special positions, while the mechanism with ideal joints cannot.

Kinematic Analysis of Elliptic-Gear & Eccentric Slider-Crank & Uniform-Pitch Screw Weft-Insertion Mechanism

In order to analyze the kinematic performances of elliptic-gear & eccentric slider-crank & uniform-pitch screw weft-insertion mechanism proposed by us,kinematic mathematic models of the mechanism were established,and an aided analytic software was compiled.Influences of some important parameters on the kinematic characteristics of the mechanism were analyzed.A group of preferable parameters were obtained according to the software and some requirements.Comparisons of kinematic performances were made between the proposed mechanism and the variable-pitch screw insertion mechanism of C401 rapier loom manufactured by Vamatex Corp in Italy.The results show that the proposed mechanism can meet the requirements of inserting wefts.

A method to calculate and counterbalance the inertia force of slider-crank mechanisms in high-speed presses

A new method to calculate and counterbalance the inertia force of slider-crank mechanisms in high-speed mechanical presses was put forward. By analyzing the kinematic characteristics of a center-located slider-crank mechanism whose crank rotates at a constant angular velocity,the kinematic parameters of the slide,connecting rod and crank were formulated approximately. On the basis of the results above,three inertia forces and the input moment in the mechanism during its idle running were investigated and formulated by dynamic analysis. A verification experiment was performed on a slider-crank mechanism at a high-speed press machine. The forces derived from the established formulas were compared respectively with those obtained by the ADAMS software and the classical method of connecting rod mass substitution. It was experimentally found that the proposed formulas have an improved performance over related earlier techniques. By use of these results,a 1 000 kN 1 250 rpm four-point high-speed press machine was designed and manufactured. The slide of this press is driven by four sets of slider-crank mechanisms with symmetrical layout and opposite rotation directions to counterbalance the horizontal inertia forces. Four eccentric counterbalance blocks were designed to counterbalance the vertical force after their mass and equivalent eccentric radius were formulated. The high-speed press machine designed by the proposed counterbalance method has worked with satisfactory performance and good dynamic balance for more than four years in practical production.

Design and Analysis on Compression Mechanism of Small Square Bales of Sugarcane Leaf Baler

With more and more attention paid to comprehensive utilization of agricul-tural biomass resources, environment pol ution caused by large-scale burning of sug-arcane leaves can be effectively avoided, and it is urgent to resolve storage issue of sugarcane leaf. Through referring to the relevant domestic baler models and re-search findings, preliminary design and analysis were conducted on key components compression mechanism of smal sugarcane leaf baler, involving the open compres-sion principle for sugarcane leaf square baler, determination of the crank slider-type compression mechanism and the main parameters such as crank length, compres-sion frequency, feed rate and feed inlet length. Based on SolidWorks software, this paper established the 3-dimensional models of slider-crank type compression mech-anism, and imported it into ADMAMS software for the motion simulation analysis, to establish the foundation for the design and manufacture of subsequent smal sugar-cane leaf square baler prototype.

Mechanical Properties of New Type Negative Offset Structure During Shearing Process of Heavy Steel Plate

According to the revised Cailikefu＇s rolling shear force formula, motion path equation of spatial seven-bar path was built, and a mechanical model, with the new structural feature of negative offset, was thus successfully established for 2 800 mm heavy shear of some iron and steel company. Shear and bar forces of steel plate, before and after the adoption of negative offset structure, were analyzed, as well as horizontal force component of mechanism that influences pure rolling shear and back-wall push force that keeps blade clearance. It was found that the back-wall push force keeps large even at the time that the maximum rolling shear was obtained; meanwhile, back-wall push force is the most approximate to side forces when 60--100 mm of offset was adopted. Both theoretical results and onsite shear quality show that the negative offset plays an important role in ensuring the stability of pure rolling shear and keeping blade clearance constant.

Research on Mechanical Model and Properties of New-type Negative Offset Structure in Spatial Seven-bar Heavy Shear

According to revised Cailikefu’s rolling shear force formula,motion path equation of spatial seven-bar path is built,and mechanical model,with such new structural features as negative offset,is thus successfully established for 2 800 mm heavy shear of some Iron&Steel Company. Shear force and bar force of steel plate,before and after adoption of negative offset structure,are analyzed,as well as horizontal force component of mechanism that influences pure rolling shear and back-wall push force that keeps blade clearance. The discovery is that back-wall push force could be kept large enough at rolling start-up (i.e. the time that the maximum rolling shear produces),meanwhile,back-wall push force is the most approximate to side forces with adoption of 60 mm-100 mm offset. Theoretical results and on-site shear quality both indicate that new structural features such as negative offset plays an important role in ensuring pure rolling shear and keeping blade clearance constant,which provide an effective means to improve quality of steel plate.

取秧侧向零偏移的空间轨迹再生稻分插机构设计与试验

为了解决现有空间行星轮系式分插机构在再生稻宽窄行机械化种植取秧过程中出现侧向偏移量和侧向偏转角的技术难题,本文提出一种具有局部平面轨迹特性的空间轨迹不等速行星轮系机构,并开展基于取秧口和机构回转中心位置约束下的宽窄行分插机构综合研究。构建了基于关键位姿点(取秧起始点、取秧结束点、推秧点)的空间轮系机构运动综合模型,利用关键位姿点求解机构杆长参数与空间交错轴信息,并通过优选二杆相对角位移参数实现机构传动比分配。将不完全非圆齿轮副引入空间行星轮系机构,利用间歇机构锁止弧约束行星轴,实现机构取秧过程侧向零偏移量、侧向零偏转角的平面轨迹段。通过仿真分析与机构样机试验验证了机构实际作业性能与理论设计相一致,结果表明:分插机构取秧侧向零偏移量,取秧侧向零偏转角,推秧侧向总偏移量为50.24 mm、取秧角为5.18°、推秧角为71.56°、推秧侧向角为16.26°、插秧穴口宽度为22.43 mm、轨迹高度为289.76 mm,满足预期设计要求。最后通过田间试验验证,分插机构可实现等行距取秧口和既定机构回转中心下宽行(40 cm)与窄行(20 cm)间隔机插,满足再生稻宽窄行种植要求。

基于偏移注意力机制和多特征融合的点云分类

三维点云由于受到雾、雨和雪等自然天气条件的影响较小而受到了广泛的关注,在交通、能源和医疗等多个领域得到了广泛的应用,其中点云分类旨在划分三维点云数据的类别,为不同领域决策者提供信息,实现解决方案的制订,对自动驾驶、故障诊断和医学影像分析等具有重要意义。点云分类的应用前景广阔,但目前仍面临着诸多挑战。由于点云的无序性、稀疏性和有限性等特点,传统的图像处理和计算机视觉方法难以直接应用于点云数据分析,直接利用卷积神经网络不能有效提取点云特征,部分模型的特征提取不够充分,局部和全局的信息未能有效的利用,可能丢失重要特征信息。针对上述问题,提出一种实现点云的局部和全局特征相结合的多特征融合模块,并结合偏移注意力机制嵌入多特征融合模块实现较深层次点云特征的提取,同时引入残差结构充分利用浅层提取的特征,防止网络过深导致浅层特征丢失。在ModelNet40和ScanObjectNN分类数据集上进行训练和测试,并对实验进行了消融研究和部分数据可视化。实验结果发现该模型在ModelNet40上的分类总体准确率为93.6%,与PointNet、LDGCNN和PCT等模型相比,分类总体准确率分别提高了4.4、0.7和0.4个百分点;在ScanObjectNN上的分类总体准确率为83.7%,与PointNet++和DGCNN相比,分类总体准确率分别提高了5.8和5.6个百分点,具有较高的准确率和鲁棒性。

森林碳汇发展的实践、挑战与展望

森林碳汇被公认为是当前二氧化碳减排乃至应对气候变化,最经济、最现实、综合效益最好的手段,无论在国内还是国际自愿减排碳市场中需求量巨大,势必成为助力实现净零目标的主流选择。为此,论文在生态补偿理论的基础上,首先概述了森林碳汇的多重效益与在自愿减排碳市场中的发展潜力;然后结合已有文献归纳梳理了森林碳汇在当前国际主流碳抵消机制中的发展与实践;在此基础上对中国在未来发展森林碳汇的挑战与展望进行探讨。

特深井井下等效冲击扭矩作用下钻铤接头三维力学特征分析

特深井钻井时钻柱在井下受到强烈的冲击扭矩作用,严重威胁着钻井施工安全,需要进行特深井钻柱井下冲击扭矩的测量和分析。首先,采用三维力学分析方法得到了不同扭矩作用下钻铤螺纹接头的受力特征,建立了内、外螺纹之间相对偏移量与井下等效冲击扭矩之间的对应关系;然后,以西部油田某特深井上部井段ϕ203.2 mm钻铤NC56接头为例,利用刻痕法测量内、外螺纹台肩的相对偏移量,反演得到与偏移量相对应的井下等效冲击扭矩,并用实际测得的钻铤接头卸扣扭矩进行了验证。实测数据表明,钻井过程中井下存在很大的冲击扭矩,使钻铤接头在井下发生二次上扣。根据实测偏移量反演计算的井下等效冲击扭矩与卸扣扭矩吻合程度高,表明该方法具有较好的可靠性。分析表明,上扣预紧状态对钻铤接头的井下二次上扣特性有很大影响,避免欠扭矩上扣是防止钻铤接头井下二次上扣的有效手段。

近距离煤层采空区下综放工作面巷道合理位置研究

近距离煤层综放工作面开采空间大,采动强度高,下位煤层回采巷道受上煤层采动影响存在应力集中、巷道支护困难等问题,因此近距离煤层综放工作面巷道合理位置的选取对后期支护控制起到关键性作用。以西露天煤矿2煤层和1煤层1分层为研究对象,综合考虑了上煤层开采时的底板应力降低区域和下煤层开采时的极限平衡区域,确定了下煤层巷道的合理位置应在距离实体煤柱内错22.79 m以上的区域。基于上述理论计算结果,分析了上煤层开采后底板应力分布规律及不同内错距下巷道围岩变形破坏特征及规律,结果表明:①距离采空区底板越近,应力最大值与最小值相差越明显;②随着内错距不断增大,围岩应力和应力集中系数呈现急剧降低-缓慢增大-稳定的趋势,在内错距20~25 m内应力及应力集中系数相对较小;③巷道围岩塑性区范围呈现先减小后增大的趋势,当巷道处于内错20,25 m时巷道围岩破坏相对较小;④巷道变形量随着内错距增大而逐渐减小,当内错距增加至25 m时,巷道围岩移进量基本保持不变;⑤确定巷道合理内错距为20~25 m。工程应用结果表明:巷道采用内错距24 m布置时,巷道围岩松动破坏深度及变形量均在可控范围内,进一步证明了该内错距的合理性。

电驱动偏摆式天然橡胶割胶装置设计及运动特性分析

天然橡胶是我国重要的战略物资,针对当前胶工流失严重、割胶作业难以实现机械化等问题,设计一种电驱动偏摆式割胶装置。以理论分析结合数学建模为基础进行,通过Adams与ANSYS建立传动结构的有限元模型,并阐述运动特征规律,来验证模型的构建准确性,分析传动部件在运动情况过程下的应力分布、动态特性及振动机理,为便携式割胶装置的设计以及后期改进提供参照途径。通过运动学分析,刀片摆幅、传动结构受力与理论计算值误差分别为4%和3%;在数值模拟中传动结构的最大应力出现在Y型驱动叉与刀座的连接处,XYZ三个方向面的等效应力均小于材料屈服极限,故不会发生失效与出现共振;通过试验分析,偏摆式割胶装置样机相较于传统人工割胶刀,在割胶速度、耗皮厚度以及割胶深度上的平均值相差分别为42.3%、4.3%、0.6%,其中割胶速度差异较为显著。割胶装置的理论模型分析结果与实际样机加工制造的试验情况基本符合。

CCER重启视角下林业碳汇参与碳市场研究

碳排放权交易市场(碳市场)是中国积极实施应对气候变化战略、落实“双碳”目标的重要载体和动力机制。从重启国家核证自愿减排(CCER)机制重启视角出发,系统回顾国内外学者对中国碳市场与林业碳汇的研究,对CCER重启对碳市场的影响进行深入探讨。作为CCER的主要组成部分,针对林业碳汇进入碳市场面临的问题进行重点研究。研究表明:①国内林业碳汇项目与市场机制具有多样性,包括林业碳汇CDM国际项目、CCER国家项目、地方林业碳汇项目。CCER是各碳排放权交易试点与全国碳市场重要的交易品种;②CCER进入全国碳市场,对于多元化发展碳金融市场有一定帮助,可以丰富碳金融产品种类,增加碳市场活跃度;③林业碳汇参与碳市场交易仍然存在方法学不成熟、制度约束、产权不明晰、交易风险等问题。针对上述问题,本文提出了完善碳汇交易制度的政策体系、明晰林业碳汇产权等建议。

基于Simmechanics的偏置曲柄滑块机构运动学建模及仿真研究

为了提高偏置曲柄滑块机构的设计水平和效率,以MATLAB的动态仿真工具Simulink、Smmchanics为平台,建立了偏置曲柄滑块机构运动分析的仿真模型,具体阐明了这种建模方法与仿真的实现过程,结果表明该仿真方法能方便、准确地得到机构的运动数据,能为机构的选型、优化设计提供参考依据,并对其他类似机构的建模与仿真具有一定的参考价值。

基于DSCI-YOLOv8的纺织品材质分类方法

为了实现工厂的无人化生产,需要高效地对纺织品进行分类。针对传统纺织品生产厂的人工分类方法存在着效率低下、难以满足大规模生产需求的问题。将人工智能和计算机视觉先进技术应用到纺织品材质分类中,提出了一种基于DSCI-YOLOv8的纺织材质分类算法。在YOLOv8模型原有分类网络的基础上添加坐标信息注意力模块,增强模型对不同尺度纺织品材质特征的提取能力,提高了网络分类的准确率,同时减少了计算所需的一部分计算量和参数量;其次将分布偏移卷积加入到C2f网络模块,改进了分类神经部分的网络结构,从而存储器的使用得到降低,计算速度也得到提高。实验结果表明,在自制的纺织品材质分类数据集FMCD上进行测试,改进后的模型相较于YOLOv8模型准确率提高了2.09个百分点,每秒处理图片数提高13.5%。大幅减少计算成本的同时,有效提高了纺织品材质分类的精度和速度。可以满足纺织工业对产品类别分类和质量的检测需求。

基于改进YOLOv7-tiny的番茄叶片病虫害检测方法

为解决自然环境中番茄叶片病虫害检测场景复杂、检测精度较低,计算复杂度高等问题,该研究提出一种SLPYOLOv7-tiny的深度学习算法。首先,将主干特征提取网络中部分3×3的卷积Conv2D(2D convolution)改为分布偏移卷积DSConv2D(2D Depthwise Separable Convolution),以减少网络的计算量,并且使计算速度更快,占用内存更少;其次,将无参数注意力机制(parameter-free attention module,SimAM)融合到骨干特征提取网络中,加强模型对病虫害特征的有效提取能力和特征整合能力;最后,将原始YOLOv7-tiny的CIOU损失函数,更替为Focal-EIOU损失函数,加快模型收敛并降低损失值。试验结果表明,SLP-YOLOv7-tiny模型整体识别精准度、召回率、平均精度均值mAP_(0.5)(IOU阈值为0.5时的平均精度)、mAP_(0.5~0.95)(IOU阈值从0.5到0.95之间的平均精度)分别为95.9%、94.6%、98.0%、91.4%,与改进前YOLOv7-tiny相比,分别提升14.7、29.2、20.2、30个百分点,同时,计算量降低了62.6%。与YOLOv5n、YOLOv5s、YOLOv5m、YOLOv7、YOLOv7-tiny、Faster-RCNN、SSD目标检测模型相比,mAP_(0.5)分别提升了2.0、1.6、2.0、2.2、20.2、6.1和5.3个百分点,而计算量大小仅为YOLOv5s、YOLOv5m、YOLOv7、Faster-RCNN、SSD的31.5%、10.6%、4.9%、4.3%、3.8%。结果表明SLP-YOLOv7-tiny可以准确快速地实现番茄叶片病虫害的检测,且模型较小,可为番茄叶片病虫害的快速精准检测的发展提供一定的技术支持。

电动汽车无线充电系统恒流/恒压输出与抗偏移磁能耦合机构研究

在电动汽车无线充电系统中,负载锂电池的充电过程为先恒流再恒压,因此,无线电能传输(wireless power transfer,WPT)系统需要同时具备实现双输出的能力,且在双输出状态之间进行平稳切换。基于此,分析双边LCC(inductor-capacitor-capacitor)拓扑实现与负载无关的恒流/恒压输出条件,给出参数设计方法。针对系统可能会随机在不同方向上出现位移的情况,采用了双向同轴平面线圈的结构,即原边线圈由内外2个沿相反方向绕制的线圈串联组成。通过仿真和实验验证了本文提出的电动汽车无线充电系统具备同时实现恒流/恒压输出的能力,且在多方向偏移工况下实现稳定输出。

关于用能权交易采用节能量抵消机制的探讨

为进一步优化用能权交易体系,本文基于我国现行的用能权交易制度及实践,引入了节能量抵消机制。首先探讨了节能量抵消机制的引入对用能权交易的意义和作用,随后分析了实施该机制应当具备的条件以及现有用能权交易试点地区的具体实施做法。最后,针对引入节能量抵消机制可能引发的“双重核算”问题进行了深入分析与讨论,并对如何有效引入节能量抵消机制提出了具体建议。

基于压电阻抗技术的门式起重机健康监测研究

借助自行搭建的便携式电阻抗测试系统,对额定载重量41 t的龙门起重机进行加载过程监测。采用有限元分析的方法确定起重机加载时的应力分布云图,选择应力集中部位作为监测点。选择4个监测频段,在起重机加载前、加载中和加载后分别对压电传感器进行电阻抗信号测量。结果表明,随着测量频率的增大,压电传感器电阻抗幅值整体上呈现不断减小的趋势。高频段范围内电阻抗峰值和谷值数量更多,对于结构损伤监测的灵敏度更高。当被监测起重机金属结构无裂纹损伤时,整个加载周期内,电阻抗峰值和谷值对应频率不发生偏移。