微孔节流气体静压止推轴承跨缝过程时变特性研究

目前,大型气浮平台均采用花岗岩平台拼接而成,平台拼缝会对实验效果产生一定影响。针对上述问题,以微孔节流气体静压轴承运动中经过平台拼缝时的时变特性为研究对象,建立微孔节流止推轴承物理模型,并使用CFD软件与UDF相结合的动网格技术实现轴承跨越平台拼缝的动态过程仿真,研究不同气膜厚度、进气口压力、平台拼缝位置对轴承承载力和压力分布的影响。结果表明：当平台拼缝到达微孔分布圆附近时承载力急速下降,且平台拼缝到达轴承中心时承载力下降到最小值;随着气膜厚度的增加,轴承承载力的最大损失比例随之增加,并最终稳定到0.6;平台拼缝位于供气孔分布圆之外时,轴承边缘与平台拼缝之间的承载面将失效;通过增加进气口压力,轴承承载力整体有明显提升,但承载力损失速度也明显加快。     

4～5 MW风力发电机组增速箱轴承试验机研制

为验证4～5 MW风电增速箱轴承性能,研制一台轴承试验机。该试验机可以通过载荷谱控制轴承旋转方向、转速、承受的轴向和径向载荷以及润滑油流量来模拟轴承实际工况,并使用测量轴承振动和温度的方法来侧面反映轴承的实时状态。使用变频器控制变频调速电机使轴承变速变向,液压比例伺服阀可变精准加载,润滑比例流量阀调整润滑油流量,铂热电阻温度传感器测量轴承温度,加速度传感器配合振动采集模块测量轴承振动。试验机可以通过加快轴承转速和增大轴承载荷的方法,只需要普通寿命试验几十分之一的时间就足以完成强化寿命试验。通过50 000 min的测试,试验机运行平稳、可靠性良好,数据正常,达到了设计目的。     

基于多重移位复用的轴承健康监测报警存储方法研究

旋转机械正朝着高速化、智能化、高性能方向发展,为及时发现早期故障,需要研发健康监测系统。报警存储用于分析故障原因,是系统核心。针对大多系统报警存储存在缓存时间长度随采样率变化、缓存数据丢失、单次报警等问题,提出一种基于多重移位复用的方法,将多个移位寄存器、队列和循环索引相结合并利用LabVIEW平台实现该方法。实验结果表明,该方法可以自动存储报警前后10 s内所有数据,解决了数据丢失、单次报警等问题。     

GCr15SiMn贝氏体轴承钢超声滚压表层组织与性能

目的 研究超声滚压加工对贝氏体轴承钢的影响,并分析超声滚压工艺参数对贝氏体轴承钢试样表层组织及性能的影响规律,为提升贝氏体轴承表面性能提供理论及试验依据。方法 通过超声滚压加工前后试样对比分析,确定超声滚压处理技术对贝氏体轴承钢组织性能的提升;通过单因素试验法,研究超声滚压工艺试样组织、性能的影响规律;通过表面与截面组织相结合的方法,分析贝氏体轴承钢组织的类别特征。结果 根据试样表面状态可将原始试样分为3类:细晶层存在表面微裂纹的截面组织、细晶层无裂纹的截面组织及无细晶层截面组织。超声滚压后,3类截面组织均产生塑性变形层,无细晶层截面组织形成的塑性变形层最厚。超声滚压处理后,存在于原始试样表面的机加工纹理变细,犁沟变浅;试样表面粗糙度降幅可达75%,试样表面硬度增幅为4%,且试样表面产生了约90 μm硬化层。结论 相同静压力下,随电流增加,试样表面粗糙度显著降低,塑性变形层显著增加,硬度、硬化层深度增加但增幅较小;相同电流下,随静压力增加,试样表面硬度、塑性变形层深度、硬化层深度及表面硬度增加,粗糙度变化不大。     

航空轴承内圈滚道磨削残余应力的工艺优化及试验研究

对国内外8Cr4Mo4V钢制航空轴承套圈滚道磨削残余应力进行了对比试验,根据航空轴承内套圈滚道磨削工艺特点,基于ABAQUS建立轴承内套圈滚道磨削残余应力的有限元分析模型并进行了数值计算,对内套圈滚道的残余应力进行了检测、分析及验证,进而优化了轴承内套圈滚道磨削工艺。结果表明：通过增加喷丸工序、适当提高进给速度和终磨采用220目白刚玉砂轮替代石墨砂轮可有效提高轴承内圈滚道残余压应力。     

基于MRSVD与LMD的工业机器人交叉滚子轴承故障特征提取

针对奇异值分解(SVD)优化局部均值分解(LMD)方法提取工业机器人交叉滚子轴承振动信号微弱故障特征分量时出现的模态混淆现象,提出一种基于最大分辨率SVD与LMD的工业机器人交叉滚子轴承故障特征提取方法。以最大奇异值分辨率原则将一维振动信号构造成Hankel矩阵,采用SVD对Hankel矩阵进行分解得到奇异值序列;按照奇异值曲率谱原则及非目标值抑制原则对奇异值序列进行重构,将包含故障突变信息的重构奇异值序列进行SVD逆运算得到重构振动信号;最后利用LMD方法对重构振动信号进行故障特征提取,得到能够表征原始振动信号振动特征的故障特征分量。通过与SVD优化LMD方法对比可知,该方法完整地提取了工业机器人交叉滚子轴承振动信号的微弱故障特征分量,改善了模态混淆现象。     

Tragverhalten von geschichteten Deckenelementen aus Normal‐ und Porenleichtbeton

Load bearing behaviour of layered ceiling elements made of regular and porous lightweight concrete Lightweight and efficiently bearing steel reinforced elements may be achieved through the application of regular and porous concrete in a three‐layer cross‐section. While exterior layers of higher strength carry bending moments, a lightweight core layer material holds up to shear stresses. In order to quantify the potential of this construction method, the bearing behaviour of 18 layered ceiling elements with six different geometries was investigated. The goals were both to identify different failure modes, as well as evaluate the suitability of commonly used calculation procedures. The following paper shows that an optimal usage of cross‐sections of ceiling elements can already achieved by using concrete with strengths between 5 MN/m² and 20 MN/m². The efficiently bearing elements are characterized by the fact, that both the concrete, the reinforcing steel and the layer's interface are highly stressed both under pressure and tension. The tested specimens showed both a tensile bending and interface failure with a partly very high utilization of the flexural compressive zone.     

Cone-shaped hollow flexible reinforced concrete foundation (CHFRF) – Innovative for mountain wind turbines

This paper presents an innovative type of mountain wind turbine foundation, namely, the cone-shaped hollow flexible reinforced concrete foundation (CHFRF). It consists of a top plate, a base plate and a side wall that are made of reinforced concrete. The cavity of the CHFRF is filled with rubble and soil directly from the excavation for the CHFRF, which means that it can absorb the spoil. A rubber layer is placed beneath the CHFRF to increase the foundation flexibility to resist cyclic and dynamic loadings and to increase the bearing capacity. The great advantages of the CHFRF are the reduction in the usage of concrete and steel and the protection of the vegetation around the wind turbine, compared with conventional mountain wind turbine foundations that are solid structures. It is verified through model tests and a numerical simulation that the CHFRF can provide higher lateral bearing capacity in comparison to the regular circular gravity-based foundation under the same foundation diameter and height, and that the bearing capacity is increased by approximately 33.5% accordingly. It is also found that the rubber layer can effectively reduce the accumulated rotation of the CHFRF under cyclic loading. The accumulated rotation of the CHFRF with a rubber layer having a thickness of 4 mm is decreased by about 50% compared to that of the CHFRF with a rubber layer having a thickness of 2 mm. In addition, the volume of concrete used for the CHFRF is only one-fifth of that used for the circular gravity-based foundation. Therefore, the CHFRF outperforms regular mountain wind turbine foundations.     

Experimental and theoretical studies on the ultimate bearing capacity of geogrid-reinforced sand

Geosynthetic reinforced soil (GRS) structures have gained popularity in replacing concrete rigid piles as abutments to support medium or small-spanned bridge superstructures in recent years. This study conducted 13 model tests to investigate the ultimate bearing capacity of the GRS mass when sand was used as backfill soil. The GRS mass was constructed and loaded to failure under a plane strain condition. Test results were compared with two analytical solutions available in literature. This study also proposed an analytical model for predicting the ultimate bearing capacity of the GRS mass based on the Mohr-Coulomb failure criterion. The failure surface of the GRS mass was described by the Rankine failure surface. The effects of compaction and reinforcement tension were equivalent to increased confining pressures to account for the reinforcing effects of the geosynthetic reinforcement. The proposed model was verified by the results of the model tests conducted in this study and reported in literature. Results indicated that the proposed model was more capable of predicting the ultimate bearing capacity of the GRS mass than the other two analytical solutions available in literature. The proposed model can be used to predict the ultimate bearing capacity of GRS structures when sand was used as backfill material. In addition, a parametric study was conducted to investigate the effects of friction angle of backfill soil, reinforcement spacing, reinforcement strength, and reinforcement stiffness on the ultimate bearing capacity of the GRS mass calculated with and without compaction effects. Results showed that the ultimate bearing capacity of the GRS mass was significantly affected by the friction angle of backfill soil, reinforcement spacing and strength. Compaction effects resulted in an increase in the ultimate bearing capacity of the GRS mass.     

盾构隧道管片接头抗弯承载力计算模型研究

盾构隧道管片接头承载力的计算是管片设计和服役性能评估的重要部分和关键部分,针对形式相同而细部构造不同的管片接头,提出一套适用于其抗弯承载力计算的理论方法十分重要。鉴于此,文章基于接缝面的不连续特征将接缝面进行适当分区,建立盾构隧道管片接头抗弯承载力计算模型,并给出对应的求解算法。将理论模型的计算结果与接头足尺试验结果进行对比分析,验证理论模型的正确性,然后采用该计算模型对管片接头抗弯承载力进行分析与讨论。结果表明：管片接头抗弯承载力曲线具有明显的非线性特征,随着轴力的增大,接头极限弯矩呈先增大后减小的趋势。混凝土强度对于接头抗弯承载力的影响较为显著,而螺栓强度和螺栓直径对于接头抗弯承载力的影响程度受轴力控制,轴力较小时,上述两参数的增大对于接头抗弯承载力的提升效果明显,轴力较大时效果逐渐减弱,当轴力高于某一阈值后,螺栓对于接头抗弯承载力无影响。文章所提出的抗弯承载力计算模型与研究结果以期为盾构隧道结构设计、试验和性能评估提供重要参考。