Experimental Study of the Motion Modes of a Planar Mechanical System with Multi-Clearance Revolute Joints

Clearances in joints of a mechanical multibody system can induce impulsive forces, leading to vibrations that compromise the system’s reliability, stability, and lifespan. Through dynamic analysis, designers can investigate the effects of the clearances on the dynamics of the multibody system. A revolute joint with clearance exhibits three motions which are;free-flight, impact and continuous contact motion modes. Therefore, a multibody system with n-number of revolute clearance joints will exhibit 3n motion modes which are a combination of the three motions in each joint. This study investigates experimentally the nine motion modes in a mechanical system with two revolute clearance joints. A slider crank mechanism has been used as the demonstrative example. We observed that the experimental curve exhibits a greater impact compared to the simulation curve. In conclusion, this experimental investigation offers valuable insights into the dynamics of planar mechanical systems with multiple clearance revolute joints. Utilizing a slider-crank mechanism for data acquisition, the study successfully confirmed seven out of nine motion modes previously identified in numerical research. The missing modes are attributed to inherent complexities in real-world systems, such as journal-bearing misalignment.

Shear mechanical properties and fracturing responses of layered rough jointed rock-like materials

This study aims to investigate mechanical properties and failure mechanisms of layered rock with rough joint surfaces under direct shear loading.Cubic layered samples with dimensions of 100 mm×100 mm×100 mm were casted using rock-like materials,with anisotropic angle(α)and joint roughness coefficient(JRC)ranging from 15°to 75°and 2-20,respectively.The direct shear tests were conducted under the application of initial normal stress(σ_(n)) ranging from 1-4 MPa.The test results indicate significant differences in mechanical properties,acoustic emission(AE)responses,maximum principal strain fields,and ultimate failure modes of layered samples under different test conditions.The peak stress increases with the increasingαand achieves a maximum value atα=60°or 75°.As σ_(n) increases,the peak stress shows an increasing trend,with correlation coefficients R² ranging from 0.918 to 0.995 for the linear least squares fitting.As JRC increases from 2-4 to 18-20,the cohesion increases by 86.32%whenα=15°,while the cohesion decreases by 27.93%whenα=75°.The differences in roughness characteristics of shear failure surface induced byαresult in anisotropic post-peak AE responses,which is characterized by active AE signals whenαis small and quiet AE signals for a largeα.For a given JRC=6-8 andσ_(n)=1 MPa,asαincreases,the accumulative AE counts increase by 224.31%(αincreased from 15°to 60°),and then decrease by 14.68%(αincreased from 60°to 75°).The shear failure surface is formed along the weak interlayer whenα=15°and penetrates the layered matrix whenα=60°.Whenα=15°,as σ_(n) increases,the adjacent weak interlayer induces a change in the direction of tensile cracks propagation,resulting in a stepped pattern of cracks distribution.The increase in JRC intensifies roughness characteristics of shear failure surface for a smallα,however,it is not pronounced for a largeα.The findings will contribute to a better understanding of the mechanical responses and failure mechanisms of the layered rocks subjected to shear loads.

Drop failure modes of Sn-3.0Ag-0.5Cu solder joints in wafer level chip scale package

To reveal the drop failure modes of the wafer level chip scale packages （WLCSPs） with Sn-3.0Ag-0.5Cu solder joints, board level drop tests were performed according to the JEDEC standard. Six failure modes were identified, i.e., short FR-4 cracks and complete FR-4 cracks at the printing circuit board （PCB） side, split between redistribution layer （RDL） and Cu under bump metallization （UBM）, RDL fracture, bulk cracks and partial bulk and intermetallic compound （IMC） cracks at the chip side. For the outmost solder joints, complete FR-4 cracks tended to occur, due to large deformation of PCB and low strength of FR-4 dielectric layer. The formation of complete FR-4 cracks largely absorbed the impact energy, resulting in the absence of other failure modes. For the inner solder joints, the absorption of impact energy by the short FR-4 cracks was limited, resulting in other failure modes at the chip side.

Variation in joint mode of the tropical Indian-Pacific Ocean thermodynamic anomaly

Previous research has defined the index of the Indian-Pacific thermodynamic anomaly joint mode (IPTAJM) and suggested that the winter IPTAJM has an important impact on summer rainfall over China. However, the possible causes for the interannual and decadal variability of the IPTAJM are still unclear. Therefore, this work investigates zonal displacements of both the western Pacific warm pool (WPWP) and the eastern Indian Ocean warm pool (EIOWP). The relationships between the WPWP and the EIOWP and the IPTAJM are each examined, and then the impacts of the zonal wind anomalies over the equatorial Pacific and Indian Oceans on the IPTAJM are studied. The WPWP eastern edge anomaly displays significant interannual and decadal variability and experienced a regime shift in about 1976 and 1998, whereas the EIOWP western edge exhibits only distinct interannual variability. The decadal variability of the IPTAJM may be mainly caused by both the zonal migration of the WPWP and the 850 hPa zonal wind anomaly over the central equatorial Pacific. On the other hand, the zonal migrations of both the WPWP and the EIOWP and the zonal wind anomalies over the central equatorial Pacific and the eastern equatorial Indian Ocean may be all responsible for the interannual variability of the IPTAJM.

Joint analysis of urban shopping destination and travel mode choice accounting for potential spatial correlation between alternatives

In recent years,there have been important developments in the joint analysis of the travel behavior based on discrete choice models as well as in the formulation of increasingly flexible closed-form models belonging to the generalized extreme value class.The objective of this work is to describe the simultaneous choice of shopping destination and travel-to-shop mode in downtown area by making use of the cross-nested logit(CNL) structure that allows for potential spatial correlation.The analysis uses data collected in the downtown areas of Maryland-Washington,D.C.region for shopping trips,considering household,individual,land use,and travel-related characteristics.The estimation results show that the dissimilarity parameter in the CNL model is 0.37 and significant at the 95% level,indicating that the alternatives have high spatial correlation for the short shopping distance.The results of analysis reveal detailed significant influences on travel behavior of joint choice shopping destination and travel mode.Moreover,a Monte Carlo simulation for a group of scenarios arising from transportation policies and parking fees in downtown area,was undertaken to examine the impact of a change in car travel cost on the shopping destination and travel mode switching.These findings have important implications for transportation demand management and urban planning.

MODELING AND CONTROLLING OF PARALLEL MANIPULATOR JOINT DRIVEN BY PNEUMATIC MUSCLES

A parallel manipulator joint driven by three pneumatic muscles and its posture control strategy are presented. Based on geometric constraints and dynamics, a system model is developed through which some influences on dynamic response and open-loop gain are analyzed including the supply pressure, the initial pressure and the volume of pneumatic muscle. A sliding-mode controller with a nonlinear switching function is applied to control posture, which adopts the combination of a main method that separates control of each muscle and an auxiliary method that postures error evaluation of multiple muscles, especially adopting the segmented and intelligent adjustments of sliding-mode parameters to fit different expected postures and initial states. Experimental results show that this control strategy not only amounts to the steady-state error of 0. 1° without overshoot, but also achieves good trajectory tracking.

Influence of Non-uniform Parameter of Bolt Joint on Complexity of Frequency Characteristics of Cylindrical Shell

Bolt connection is one of the main fixing methods of cylindrical shell structures.A typical bolted connection model is considered as a tuned system.However,in the actual working conditions,due to the manufacturing error,installation error and uneven materials of bolts,there are always random errors between different bolts.To investigate the influence of non-uniform parameters of bolt joint,including the stiffness and the distribution position,on frequency complexity characteristics of cylindrical shell through a statistical method is the main aim of this paper.The bolted joints considered here were simplified as a series of springs with random features.The vibration equation of the bolted joined cylindrical shell was derived based on Sanders’thin shell theory.The Monte Carlo simulation and statistical theory were applied to the statistical analysis of mode characteristics of the system.First,the frequency and mode shape of the tuned system were investigated and compared with FEM.Then,the effect of the random distribution and the random constraint stiffness of the bolts on the frequency and mode shape were studied.And the statistical analysis on the natural frequencies was evaluated for different mistuned levels.And some special cases were presented to help understand the effect of random mistuning.This research introduces random theory into the modeling of bolted joints and proposes a reference result to interpret the complexity of the modal characteristics of cylindrical shells with non-uniform parameters of bolt joints.

冻融作用下断续节理岩体损伤与力学特性研究

寒区断续节理岩体受冻融作用影响易发生失稳破坏。为探究冻融作用下节理特征对岩体损伤与力学特性的影响,使用相似材料制备不同节理倾角、岩桥长度的断续节理试样,并开展冻融循环试验。通过对冻融试样进行损伤分析与单轴压缩试验,得到了各类试样的劣化损伤特性及其对抗压强度与破坏模式的影响规律。研究表明:冻融作用下,断续节理类岩石试样的劣化模式以片落模式为主,裂纹模式为辅,且不同节理特征试样间存在冻融损伤差异;节理特征与片落损伤的关联较小,但对裂纹扩展的影响显著,节理倾角越大,裂纹发育越不明显,岩桥长度越短,裂纹贯通越迅速,裂纹扩展程度不同是造成试样间冻融损伤差异的主要原因;在差异性冻融损伤的影响下,各类试样的抗压强度普遍降低,并随节理特征的变化表现出不同的强度损失规律;试样破坏过程中延性增强,节理尖端的拉伸裂纹减少、剪切裂纹增多,部分类型试样的破坏模式与岩桥贯通模式发生改变。

考虑碳排放流的电-气互联系统源荷互动低碳经济调度

为应对电力系统存在的弃风、碳排放较高等问题,基于碳排放流理论提出了一种电-气互联系统源荷互动低碳经济调度模型。基于电力系统碳排放流计算方法,推导得到考虑气网动态特性的天然气系统碳排放流计算方法;构建以储液罐装置为主的储碳系统(CSS),CSS与火电机组(TU)、风电机组(WT)、电转气(P2G)设备组成TU-CSS-P2G-WT的联合运行方式;源侧以系统日运行总成本最小计算得到能源网络的碳势时空分布,荷侧根据源侧的碳势信号,基于低碳响应机制建立激励型低碳需求响应模型,合理调整用能行为最小化用户购能总成本;建立源荷互动两阶段低碳经济调度模型,并利用GUROBI进行求解。通过改进由IEEE 39节点和比利时20节点构成的电-气互联系统进行算例分析,验证了所提模型的低碳经济性和灵活性。

基于数值模拟的带C形悬臂段装配式梁柱节点抗震性能研究

对C形悬臂梁柱节点在参数变化情况下的力学性能表现及破坏模式的发展状况进行了分析,按节点拼接部位分别从C形悬臂段、下翼缘盖板、端板3个方向进行扩展研究,共包含C形悬臂段宽度le、C形悬臂段翼缘板厚度dc、盖板长度lp、端板螺栓个数Ne,共4个参数。研究结果表明,C形悬臂段宽度le的变化可以显著影响节点承载力,当悬臂段宽度由350 mm下降至200 mm时,节点屈服承载力下降了20.73%,极限承载力下降了13.10%,同时塑性铰位置发生明显偏移,深刻影响节点焊缝区的应力大小;剩余参数对节点承载力影响不太明显,但却可以显著影响节点破坏模式与应力分布状态,翼缘板厚度dc的增加可以显著改善悬臂段根部的高应力状态,而随着端板螺栓个数Ne的增加,在降低梁上翼缘最外排螺栓孔附近应力的同时,也造成了梁腹板发生鼓曲现象。

含Y型组合节理花岗岩单轴压缩破坏机理及声发射特征

利用劈裂法在花岗岩试件中预制不同倾角的Y型组合节理,进行单轴压缩实验,分析组合节理倾角对破坏模式、峰值强度、表面变形场、声发射能量释放特征的影响,探究不同破坏模式下的破坏机理.实验结果表明:1)含Y型组合节理岩石随节理倾角变化呈现整体破坏、楔形体弹射破坏和沿主节理面破坏三种主要模式;2)组合节理夹角、主节理倾角均与岩石强度具有负相关关系;3)破坏模式从整体破坏转变到弹射破坏、沿主节理破坏时,滑移变形集中区域由次节理向主节理转变,AE高能级事件诱发原因由主、次节理压密及滑移错动向主节理压密及滑移错动转变;4)随主节理倾角的不断增大,主节理面上释放的能量更高、能量的分布更加不均匀.

JCI理念为框架的模式在消毒供应室医用器械管理中的应用效果

目的 探讨国际医疗卫生机构认证联合委员会(JCI)理念为框架管理模式在消毒供应室医用器械管理中的应用效果。方法 采用随机数字表法将2019年1月至2020年1月在消毒供应室工作的30例医护人员,随机分为对照组和试验组,每组15例。对照组采用常规管理模式,试验组采用以JCI理念为框架的管理模式。观察2组护理服务质量、综合素质、医护人员满意度和器械管理效果进行评价。结果 2组护理质量比较,试验组护理流程、质量监管、安全意识、感染风险评分显著高于对照组(P<0.05)。2组管理前综合素质评分比较,差异无统计学意义(P>0.05)。2组管理后安全知识掌握、主动服务意识、风险防控能力和专业素养均高于管理前,差异均有统计学意义(P<0.05)。试验组管理后安全知识掌握、主动服务意识、风险防控能力和专业素养均高于对照组,差异均有统计学意义(P<0.05)。试验组医务人员满意率,灭菌、清洗、检查、包装、发放和回收合格率明显高于对照组,差异均有统计学意义(P<0.05)。结论 JCI理念为框架管理模式在消毒供应室医用器械管理中的应用效果良好,能有效提高护理质量与护理安全性,增加医护人员满意度,可用于医疗管理之中。

湿热老化对FRP-钢胶接节点力学性能的影响

为进一步研究湿热老化对纤维增强复合材料(FRP)-钢胶接节点力学性能的影响,在现有试验的基础上,采用轮盘加载装置,分别从6个加载条件对湿热老化处理后的FRP-钢胶接节点进行一系列加载测试,研究了湿热老化对FRP-钢胶接节点的极限破坏荷载、破坏模式、刚度以及强度破坏准则的影响,并将结果与未老化胶接节点进行比较。试验结果表明:在剪切和拉伸荷载作用下,湿热老化显著降低了FRP-钢胶接节点的极限破坏荷载,分别降至11.0 kN和41.9 kN;在组合荷载作用下,湿热老化对极限破坏荷载的影响较小;老化与未老化FRP-钢胶接节点的强度破坏准则曲线彼此接近;对于拉伸和拉伸/剪切组合荷载条件,湿热老化改变了FRP-钢胶接节点的破坏模式,即从FRP夹芯板和结构胶粘贴层之间的部分界面破坏到覆盖整个结构胶粘结区域的FRP分层破坏和纤维断裂破坏的组合;在6个加载条件下,湿热老化均明显降低了FRP-钢胶接节点的刚度。因此,在设计及使用FRP-钢胶接节点时,应该充分考虑湿热老化对FRP-钢胶接节点力学性能的影响,避免其发生结构破坏。

“校企联培制”模式下应用型卓越人才培养路径探究——以湖北大学知行学院为例

近年来地方应用型本科高校以服务地方经济和产业需求为己任,着重培养学生的工程和创新技术应用能力,高校与企业合作,发挥各自优势,实现生产、教学、科研的深度合作,共同完成人才培养。介绍机械类专业在新工科背景下,以培养应用型卓越人才为目标,基于“校企联培制”的总体思路,实施学校专业教学计划与企业工程师培养计划“双计划”,在人才培养体系设计、校企资源整合、就业平台搭建和师资力量提升等方面进行改革,实施产教融合,提升就业能力,最终实现人才的高质量培养和就业。

基于混合扩张状态观测器的农田平地机液压系统反步滑模控制研究

为解决农田平地机液压系统在复杂地貌平地作业时控制精度低、抗干扰能力差等问题,设计了一种基于混合扩张状态观测器(HESO)的反步滑模控制器。其中,HESO基于输出反馈信号估计系统未知状态和总扰动,并在前馈通道中进行扰动补偿;基于快速趋近律设计的反步滑模控制器输出连续光滑的控制量,增强了系统鲁棒性,克服了系统非线性与参数不确定性问题;通过Lyapunov稳定性理论对所提出的观测器和控制器稳定性进行验证,得到误差一致有界稳定结论;通过AMESim和Matlab/Simulink联合仿真与田间试验对本文控制算法的有效性和优越性进行了验证。在两条地貌情况较为复杂波浪地中单次平地和地貌情况较为相似的两田块进行3次遍历试验表明,使用本文控制方法,平地后高程相较于平地前标高的平均绝对误差、最大绝对误差、绝对误差标准差分别为0.053、0.146、0.037 m和0.02、0.041、0.011 m,较PID算法分别降低36.35%、28.32%、31.37%和62.6%、50%、51.83%。

基于JCI标准的管理模式预防纠纷事件及对患者满意度的影响研究

目的研究基于国际医疗卫生机构认证联合委员会(JCI)标准的管理模式预防纠纷事件及对患者满意度的影响。方法选取2022年3月—2024年3月于医院门诊就诊的102例患者开展研究。将其以电脑编号单双数字法随机分作JCI标准组与常规组各51例。常规组开展常规管理,JCI标准组则开展基于JCI标准的管理。比较两组纠纷事件发生情况、患者满意度、管理质量、就诊前后不良情绪。结果JCI标准组纠纷事件总发生率较常规组更低(1.96%vs 13.73%)(P<0.05)。JCI标准组各项满意度评分较常规组均更高(均P<0.05)。JCI标准组各项管理质量评分较常规组均更高(均P<0.05)。就诊后两组不良情绪评分较就诊前更低,且JCI标准组较常规组更低(均P<0.05)。结论基于JCI标准的管理模式预防纠纷事件的效果较佳,且能明显提升患者满意度以及管理质量,缓解患者不良情绪。

医药联合门诊在老年患者合理用药管理中的工作模式探讨及成效分析

目的介绍南京医科大学第二附属医院老年患者医药联合门诊的工作模式与成效,分析优点与不足,以期为其他药学门诊的建立提供参考。方法选取2019年7月至2022年7月年于该门诊就诊并建立完整随访档案的680例患者,统计分析其一般情况、疾病及用药情况、药物治疗相关问题、药学服务内容等。结果680例患者中53.82%患有高血压,51.91%患者同时患有3种及以上慢性疾病,43.82%患者同时使用4~6种药物。680例患者中有441例存在854个药物治疗问题,平均1.94个/人。其中类型最多的是用药依从性问题,占38.17%。药师干预后患者依从性评分显著提高(P<0.05)。结论药师通过建立医药联合门诊,参与老年患者慢性病药物治疗管理,显著改善患者依从性,提高药物治疗有效性和安全性,进一步促进合理用药。

地方应用型高校拔尖创新人才培养的实践与思考——以延边大学农学院为例

文章以延边大学农学院为例,分析了在新农科背景下地方应用型大学拔尖创新人才培养存在的问题,并以校企联合技术创新实验室为依托阐述了拔尖创新人才培养的经验做法,提出了日常运行管理模式、创新实验项目运行模式、科研项目运行模式等加快拔尖创新人才培养的模式,旨在深化产学研合作,促进拔尖创新人才创新能力和实验、实践能力提升,为地方应用型高校拔尖创新人才培养提供借鉴和参考。

松动及加固后木结构燕尾榫节点抗震性能对比试验

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