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某型轨道车车体与车架焊接与螺栓联接有限元计算对比 认领
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作者 李胜男 《科技创新与应用》 2021年第2期72-75,共4页
随着有限元技术的发展,轨道交通技术也在与时俱进。文章主要通过对轨道车的钢结构车体和底架的焊接和螺栓连接进行了对比,着重在车体强度和刚度方面进行分析。通过相关轨道车标准进行有限元仿真分析,从而得出有说服力的证据。在轨道车... 随着有限元技术的发展,轨道交通技术也在与时俱进。文章主要通过对轨道车的钢结构车体和底架的焊接和螺栓连接进行了对比,着重在车体强度和刚度方面进行分析。通过相关轨道车标准进行有限元仿真分析,从而得出有说服力的证据。在轨道车车体钢结构设计研发方面提供有力依据,为未来模块化研发设计奠定技术基础,从而使工程师在设计相似的轨道车辆车体钢结构方面用作参考。 展开更多
关键词 轨道车 车架 车体 螺栓连接 强度 刚度
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六自由度关节机器人测定套筒型导向生长棒的生物力学特征 认领
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作者 薛静波 朱斌 +3 位作者 李昃鹏 王程 欧阳智华 晏怡果 《中国组织工程研究》 CAS 北大核心 2021年第15期2297-2302,共6页
背景:早发性脊柱侧凸的治疗较为困难,传统的生长棒经系统证实对其有治疗作用,但需要重复多次手术干预,并且自发性融合率、手术部位感染、杆断裂等并发症发生率较高,因此需要一种既能校正脊柱生理曲线又能允许脊柱生长同时避免多次手术... 背景:早发性脊柱侧凸的治疗较为困难,传统的生长棒经系统证实对其有治疗作用,但需要重复多次手术干预,并且自发性融合率、手术部位感染、杆断裂等并发症发生率较高,因此需要一种既能校正脊柱生理曲线又能允许脊柱生长同时避免多次手术干预、降低自发性融合的生长棒系统。目的:采用六自由度关节机器人评估套筒型导向生长棒的生物力学性能。方法:分别依次将套筒型导向生长棒系统及传统椎弓根螺钉内固定系统置于8具幼猪脊柱标本,采用六自由度关节机器人进行幼猪脊柱标本在屈伸位、侧弯位及轴向旋转位的柔韧性测试。结果与结论:①在活动度的测试中,套筒型导向生长棒系统以及传统椎弓根螺钉内固定系统在屈伸位活动度之间的差异无显著性意义(P>0.05);侧弯位活动度分别为(30.50±5.32)°和(28.25±4.24)°,差异有显著性意义(P<0.05);轴向旋转位活动度分别为(67.88±9.55)°和(35.25±5.09)°,差异有显著性意义(P<0.05);②在中性区刚度的测试中,套筒型导向生长棒系统以及传统椎弓根螺钉内固定系统在屈伸位、侧弯位的中性刚度相比差异无显著性意义(P=0.914,0.207);轴向旋转时中性区刚度分别为(0.05±0.01)N•m/(°)和(0.08±0.01)N•m/(°),差异有显著性意义(P=0.003);③提示与传统椎弓根螺钉内固定系统相比,套筒型导向生长棒在轴向旋转及侧弯位活动度增加;同时在旋转位时,套筒型导向生长棒置入后的脊柱标本较传统椎弓根螺钉内固定置入后刚性低。 展开更多
关键词 套筒型导向生长棒 椎弓根螺钉 内固定 生物力学 活动度 刚度
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体外冲击波对脑卒中患者桡侧和尺侧腕屈肌肌肉张力、刚度及弹性的即刻影响 认领
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作者 鲍赛荣 张其明 +1 位作者 杨杏萍 刘春龙 《中国组织工程研究》 CAS 北大核心 2021年第2期228-231,共4页
背景:研究表明,桡侧腕屈肌和尺侧腕屈肌弹性的大小与手握力的大小相关,其张力和刚度直接影响着拇指侧捏力和掌心抓握的能力。体外冲击波对于缓解脑卒中后肢体痉挛有明确的疗效。目的:观察体外冲击波对脑卒中患者桡侧腕屈肌和尺侧腕屈肌... 背景:研究表明,桡侧腕屈肌和尺侧腕屈肌弹性的大小与手握力的大小相关,其张力和刚度直接影响着拇指侧捏力和掌心抓握的能力。体外冲击波对于缓解脑卒中后肢体痉挛有明确的疗效。目的:观察体外冲击波对脑卒中患者桡侧腕屈肌和尺侧腕屈肌的肌肉张力、刚度及弹性的即刻影响。方法:选取20例符合入选标准的脑卒中偏瘫患者,对其桡侧腕屈肌和尺侧腕屈肌进行单次体外冲击波治疗。在治疗前及单次体外冲击波治疗结束后5 min,应用Myonton-3肌肉张力检测仪测得患侧桡侧腕屈肌及尺侧腕屈肌的阻尼振动频率(体现肌肉张力)、对数衰减值(反映肌肉弹性)、动态刚度(体现肌肉刚度),同时结合改良Tardieu量表(MTS)评估腕屈肌肌张力。研究方案的实施符合广东药科大学附属第一医院的相关伦理要求,参与试验的患病个体及其家属对试验过程完全知情同意。结果与结论:①干预后,20例患者桡侧腕屈肌及尺侧腕屈肌的阻尼振动频率、对数衰减值、动态刚度、肌肉反应的质量均较治疗前下降(P<0.01);②患侧腕关节被动背伸角度、最快速度下的腕背伸卡住角度均较治疗前增加(P<0.01);③结果说明,单次体外冲击波能有效降低脑卒中患者桡侧腕屈肌和尺侧腕屈肌的肌张力及刚度,改善其弹性,并可增大腕背伸被动活动范围。 展开更多
关键词 体外冲击波 脑卒中 肌张力 刚度 弹性
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电动深层肌肉刺激对脑卒中患者肱二头肌张力、弹性及硬度的影响 认领
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作者 鲍赛荣 林利华 +2 位作者 单莎瑞 杨杏萍 刘春龙 《中国组织工程研究》 CAS 北大核心 2021年第20期3138-3143,共6页
背景:电动深层肌肉刺激作为一种局部振动疗法可缓解因劳累或牵拉导致的损伤、乳酸堆积,或者筋膜间粘连导致的疼痛与功能受限,但其对抗痉挛作用的研究报道较少。目的:探讨电动深层肌肉刺激对脑卒中患者肱二头肌张力、弹性及硬度的影响。... 背景:电动深层肌肉刺激作为一种局部振动疗法可缓解因劳累或牵拉导致的损伤、乳酸堆积,或者筋膜间粘连导致的疼痛与功能受限,但其对抗痉挛作用的研究报道较少。目的:探讨电动深层肌肉刺激对脑卒中患者肱二头肌张力、弹性及硬度的影响。方法:选择2019年5至12月广东药科大学附属第一医院收治的脑卒中偏瘫患者60例,按随机数字表法分3组治疗,每组20例:对照组接受常规的康复训练和药物治疗;牵伸组在常规康复训练和药物治疗的基础上进行肱二头肌牵伸训练,每次10 min,1次/d,每周5次,连续治疗3周;试验组在常规康复训练和药物治疗的基础上进行牵伸状态下的电动深层肌肉刺激,每次10 min,1次/d,每周5次,连续治疗3周。治疗前、首次治疗后及全部治疗结束后测试肱二头肌阻尼振动频率(F值,反映肌张力)、对数衰减值(D值,反映肌肉弹性)及动态刚度(S值,反映肌肉硬度),并进行改良Tardieu量表(肘关节屈曲起始角度R值、快速牵伸肘关节卡住角度R1值与肌肉反应质量X值)及上肢肩肘部分Fugl-Meyer量表(FMA评分)评定。研究经广东药科大学附属第一医院伦理委员会批准,审批号:医伦审[2019]第(181)号。结果与结论:①首次治疗后,牵伸组和试验组的F、S、D、R1、X值低于治疗前(P<0.05),试验组的R值低于治疗前(P<0.05)、FMA评分高于治疗前(P<0.05);治疗结束后,3组的F、S、D、R、R1、X值均低于治疗前(P<0.05),FMA评分高于治疗前(P<0.05);②牵伸组首次治疗后的F、S值低于对照组(P<0.05),两组治疗结束后的所有参数比较无差异(P>0.05);牵伸组和试验组间首次治疗后的所有参数比较无差异(P﹥0.05),试验组治疗结束后的F、S、D、R1和X值低于牵伸组(P<0.05),FMA评分高于牵伸组(P<0.05);试验组首次治疗后的F、S值低于对照组(P<0.05),治疗结束后的所有参数均优于对照组(P<0.05);③结果表明,电动深层肌肉刺激� 展开更多
关键词 肌肉 电动深层肌肉刺激 脑卒中 肌张力 弹性 硬度 肱二头肌
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文章速递发动机盖外板刚度研究 认领
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作者 朱百庆 《模具工业》 北大核心 2021年第1期24-27,共4页
为了寻求发动机盖外板刚度不足的原因,从根本上解决该问题,对影响刚度和强度的关键因素进行了理论分析和研究,并运用AutoForm软件对发动机盖外板进行了抗凹刚度模拟试验,用试验结果验证理论分析,验证了影响发动机盖外板刚度的关键因素... 为了寻求发动机盖外板刚度不足的原因,从根本上解决该问题,对影响刚度和强度的关键因素进行了理论分析和研究,并运用AutoForm软件对发动机盖外板进行了抗凹刚度模拟试验,用试验结果验证理论分析,验证了影响发动机盖外板刚度的关键因素是曲率半径,为产品设计时保证零件的刚度提供理论依据,为提升零件刚度提供正确思路。 展开更多
关键词 发动机盖外板 刚度 强度 抗凹性 减薄率 曲率半径
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Analysis of Speeds of Cylinders of Saw Gins and Linters and Determination of Critical Frequencies for them 认领
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作者 Akmal Umarov Kamola Ortikova Akramjon Sarimsakov 《工程(英文)(1947-3931)》 2020年第10期715-722,共8页
With an increase in the density of the seed roll in the roll box of the saw gin, the quality indicators of the fiber and seed are poor, energy consumption increases, machine breakdowns increase, and when the density d... With an increase in the density of the seed roll in the roll box of the saw gin, the quality indicators of the fiber and seed are poor, energy consumption increases, machine breakdowns increase, and when the density decreases, the performance of the saw gin increases. Therefore, the density control of the seed roll is one of the important problems in the ginning process. The paper proposes a change in the rotation speed of the saw cylinder with a decrease in the diameter of its numerical linear speed and machine productivity. The article describes the problem of regulating the density of a seed roll in a saw gin of the DP series, provides an overview of work on regulating the operation of the machine, determines the dependence of the productivity of gins and linters on the state of the saw system in these machines, as well as changes in the linear speed of the saw by changing its diameter. Also, the critical speed of the gin and linter saw cylinder was determined to prevent resonance. In this case, the Simulation package of the SolidWorks computer program was used. The results of the study made it possible to adjust the speed of the cylinders when changing the diameter of the saws, which improved the productivity of the machine while maintaining the quality of the fiber and seed. 展开更多
关键词 Cotton Saw Gin Roll Box Seed Roll Productivity Rotation Frequency Critical Frequency Resonance STIFFNESS Mass Total Effective Mass SolidWorks Simulation
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Non-invasive tests for the prediction of primary hepatocellular carcinoma 认领
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作者 Giovanni Marasco Antonio Colecchia +9 位作者 Giovanni Silva Benedetta Rossini Leonardo Henry Eusebi Federico Ravaioli Elton Dajti Luigina Vanessa Alemanni Luigi Colecchia Matteo Renzulli Rita Golfieri Davide Festi 《世界胃肠病学杂志:英文版》 SCIE CAS 2020年第24期3326-3343,共18页
Hepatocellular carcinoma(HCC)is one of the most common malignancies in the world and it is one of the main complications of cirrhosis and portal hypertension.Even in the presence of a well-established follow-up protoc... Hepatocellular carcinoma(HCC)is one of the most common malignancies in the world and it is one of the main complications of cirrhosis and portal hypertension.Even in the presence of a well-established follow-up protocol for cirrhotic patients,to date poor data are available on predictive markers for primary HCC occurrence in the setting of compensated advanced chronic liver disease patients(cACLD).The gold standard method to evaluate the prognosis of patients with cACLD,beyond liver fibrosis assessed with histology,is the measurement of the hepatic venous pressure gradient(HVPG).An HVPG≥10 mmHg has been related to an increased risk of HCC in cACLD patients.However,these methods are burdened by additional costs and risks for patients and are mostly available only in referral centers.In the last decade increasing research has focused on the evaluation of several,simple,non-invasive tests(NITs)as predictors of HCC development.We reviewed the currently available literature on biochemical and ultrasound-based scores developed for the noninvasive evaluation of liver fibrosis and portal hypertension in predicting primary HCC.We found that the most reliable methods to assess HCC risk were the liver stiffness measurement,the aspartate aminotransferase to platelet ratio index score and the fibrosis-4 index.Other promising NITs need further investigations and validation for different liver disease aetiologies. 展开更多
关键词 Non-invasive test Fibrosis-4 index Hepatocellular carcinoma Liver stiffness measurement Spleen stiffness measurement Albi
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Seismic Site Specific Study for Seismic Microzonation: A Way Forward for Risk Resiliency of Vital Infrastructure in Sikkim, India 认领
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作者 O. P. Mishra Priya Singh +7 位作者 B. Ram Sasi Kiran Gera O. P. Singh K. K. Mukherjee G. K. Chakrabortty S. V. N. Chandrasekhar A. Selinraj S. K. Som 《地球科学国际期刊(英文)》 2020年第3期125-144,共20页
Seismic Microzonation comprising study of site specific seismic Microtremor (H/V ratio) is deployed to generate seismological parameters (Peak Frequency, Peak Amplification, Site Vulnerability Index) that may help est... Seismic Microzonation comprising study of site specific seismic Microtremor (H/V ratio) is deployed to generate seismological parameters (Peak Frequency, Peak Amplification, Site Vulnerability Index) that may help estimate requisite factors for sound building design codes that can be used to construct risk resilient infrastructures. In this paper the site of Pakyong, Sikkim, India has been investigated by dividing it into three differed zones (Zone 1, Zone II, Zone III). The study area is associated with site amplification factor varying from 1.47 to 11.49 with corresponding frequency variations from 0.5 Hz - 12.5 Hz in which site vulnerability index found varied from 0.2 to 220.6. The anomalous subsurface formation with its high amplification corresponds to the centre of the Pakyong sites having conspicuous trend in NW-SE direction suggesting the existence of geological formations of Chlorite, Phyllite with intercalations of Quartzite beneath the centre of Pakyong site. The risk associated with vulnerability index for different zones maintains its variability as Zone I > Zone II > Zone III, indicating the low vulnerability index values are attributed to compact parts of the sub-surface materials with less amplifications whilst high vulnerability index of the site corresponds to relatively lower strength of the sub-surface materials and soft sediments underlying the Pakyong site which can be used for constructing risk resilient structure by enhancing the stiffness coefficient of the sub-surface by providing plausible engineering solutions for the purpose. 展开更多
关键词 SEISMIC SITE Specific SEISMIC MICROZONATION RISK Resilient H/V Ratio PEAK Amplification PEAK Frequency SITE Vulnerability Index Stiffness Coefficient
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Assessment of Existing Bridge’s Beam Bending Stiffness Using Crack Characteristics 认领
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作者 Donglian Tan 《工程(英文)(1947-3931)》 2020年第2期82-89,共8页
At present, the bearing capacity evaluation is mainly based on load detection, which requires closed traffic and has certain risks. With the increase of service time, the cracks of reinforced concrete beam bridge will... At present, the bearing capacity evaluation is mainly based on load detection, which requires closed traffic and has certain risks. With the increase of service time, the cracks of reinforced concrete beam bridge will gradually develop and the stiffness will reduce, resulting in the decrease of bearing capacity. Therefore, in this paper, the calculation of stiffness reduction coefficient by using crack characteristic parameters, which provides basic data for bearing capacity evaluation, has been studied. In this paper, using regression analysis through fracture characteristics of four model beam observation and test load-displacement curve characteristic parameters, crack flexural rigidity of the beam bridge relationship has been set up. The qualitative assessment based appearance of cracks in the structure of checks has been converted to quantitative assessment. And compared with the test results of a real bridge, comparative results show that the assessment is objective and reliable. It makes the assessment more objective and scientific. A new way of Quantitative assessment of the structural performance has been provided for a large number of existing reinforced concrete beam bridge. 展开更多
关键词 BEAM Bridge CRACK CHARACTERISTICS BENDING STIFFNESS ASSESSMENT
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Analysis of Vibration of the Euler-Bernoulli Pipe Conveying Fluid by Dynamic Stiffness Method and Transfer Matrix 认领
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作者 Yunfeng Li Yundong Li Naveed Akbar 《应用数学与应用物理(英文)》 2020年第1期172-183,共12页
The dynamic stiffness method and Transfer method is applied to study the vibration characteristics of the Euler-Bernoulli pipe conveying fluid in this paper. According to the dynamics equation of the pipe conveying fl... The dynamic stiffness method and Transfer method is applied to study the vibration characteristics of the Euler-Bernoulli pipe conveying fluid in this paper. According to the dynamics equation of the pipe conveying fluid, the element dynamic stiffness is established. The vibration characteristic of the single-span pipe is analyzed under two kinds of boundary conditions. The results compared with the literature, which has a good consistency. Based on this method, natural frequency and the critical speed of the two types of multi-span pipe are deserved. This paper shows that the dynamic stiffness method and transfer matrix is an effective method to deal with the vibration problem of pipe conveying fluid. 展开更多
关键词 DYNAMIC STIFFNESS Transfer Matrix Euler-Bernoulli Pipe
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有砟轨道结构刚度变化对既有线的影响研究 认领
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作者 鹿瑶 《江苏科技信息》 2020年第5期36-40,共5页
我国高速铁路迅猛发展,列车速度的增加会使得运营过程中的舒适性和平稳性受到影响。轨道刚度在铁路系统中拥有重要地位,它是车轮与轨道之间响应分布的影响成分,会使得轨道的应力分布和结构振动产生不同的变化,还会关系到铁路火车的行驶... 我国高速铁路迅猛发展,列车速度的增加会使得运营过程中的舒适性和平稳性受到影响。轨道刚度在铁路系统中拥有重要地位,它是车轮与轨道之间响应分布的影响成分,会使得轨道的应力分布和结构振动产生不同的变化,还会关系到铁路火车的行驶速度。文章考虑轨道各部分应力以及每个部位在轨道中承担的作用,从有砟轨道结构的实际形式出发,使用准静态研究方法中常用的3层弹簧轨道结构垂直震动系统为基本系统,利用软件构建将钢轨视为连续弹性离散点支承上的有限长梁的3层弹性点支承梁模型模拟轨道结构。仿真14个不同情况,每个情况都采用不同的钢轨抗弯刚度以及扣件、道床和路基刚度模拟既有线中刚度的改变,施加静态荷载和周期性的动态荷载后,分析静态及动态响应的变化规律。以扣件刚度和道床刚度的比例值作为横坐标,模拟轨道结构响应的变化曲线,以曲线最低点对应的横坐标值0.5作为结构的最优刚度比。文章通过动力学优化求得有砟轨道结构总刚度控制范围。 展开更多
关键词 有砟轨道 刚度 最优刚度比 动力学优化
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Improving the performance of conventional base isolation systems by an external variable negative stiffness device under near-fault and long-period ground motions 认领
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作者 Sandhya Nepal Masato Saitoh 《地震工程与工程振动:英文版》 SCIE EI CSCD 2020年第4期985-1003,共19页
Recent studies have shown that base-isolated objects with long fundamental natural periods are highly influenced by long-period earthquakes. These long-period waves result in large displacements for isolators, possibl... Recent studies have shown that base-isolated objects with long fundamental natural periods are highly influenced by long-period earthquakes. These long-period waves result in large displacements for isolators, possibly leading to exceedance of the allowable displacement limits. Conventional isolation systems, in general, fail to resist such large displacements. This has prompted the need to modify conventional base isolation systems. The current work focuses on the development of an external device, comprising a unit of negative and positive springs, for improving the performance of conventional base isolation systems. This unit accelerates the change in the stiffness of the isolation system where the stiffness of the positive spring varies linearly in terms of the displacement response of the isolated objects. The target objects of the present study are small structures such as computer servers, sensitive instruments and machinery. Numerical studies show that the increase in the damping of the system and the slope of the linear function is effective in reducing the displacement response. An optimal range of damping values and slope, satisfying the stability condition and the allowable limits of both displacement and acceleration responses when the system is subjected to near-fault and long-period ground motions simultaneously, is proposed. 展开更多
关键词 base isolation near-fault earthquakes long-period earthquakes negative stiffness variable stiffness
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Improved Stiffness Modeling for An Exechon‑Like Parallel Kinematic Machine(PKM)and Its Application 认领
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作者 Nanyan Shen Liang Geng +3 位作者 Jing Li Fei Ye Zhuang Yu Zirui Wang 《中国机械工程学报:英文版》 SCIE EI CAS CSCD 2020年第3期130-141,共12页
Hole drilling or contour milling for the large and complex workpieces such as automobile panels and aircraft fuselages makes a high combined demand on machining accuracy,stiffness and workspace of machining equipment.... Hole drilling or contour milling for the large and complex workpieces such as automobile panels and aircraft fuselages makes a high combined demand on machining accuracy,stiffness and workspace of machining equipment.Therefore,a 5-DOF(degrees of freedom)parallel kinematic machine(PKM)with redundant constraints is proposed.Based on the kinematics analysis of the parallel mechanism using intermediate variables,the kinematics problems of the PKM are solved through equivalent kinematics model.The structural stiffness matrix method is adopted to model the stiffness of the parallel mechanism of the PKM,where the stiffness of each joint and branch component is obtained by stiffness formula and finite element analysis.And the stiffness model of the parallel mechanism is improved by correction coefficient matrix,each element of which is constructed as a polynomial function of three independent end variables of the parallel mechanism.The terminal stiffness matrices obtained by simulation result are used to determine the coefficients of polynomial function by least square fitting to describe the correction coefficient over the workspace of the parallel mechanism quantitatively.The experiment results prove that the modification method can greatly improve the stiffness model of the parallel mechanism.To enhance the machining accuracy of the PKM,the proposed kinematics model and the improved stiffness model are utilized to optimize the working stiffness of parallel machine by searching the best relative position of parallel machine and workpiece.A plate workpiece taken as example is examined in the case study section,which demonstrates the effectiveness of optimization method. 展开更多
关键词 PKM 5-DOF Equivalent kinematics model Intermediate variables Stiffness correction coefficient Optimal working stiffness
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A semi-analytical approach to the elastic loading behaviour of rough surfaces 认领
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作者 Xiaogang ZHANG Yali ZHANG Zhongmin JIN 《摩擦:英文版》 SCIE CSCD 2020年第5期970-981,共12页
The elastic loading behaviour of rough surfaces is derived based on the physical understanding of the contact phenomena, where the pressure distribution is analytically obtained without any negative values or converge... The elastic loading behaviour of rough surfaces is derived based on the physical understanding of the contact phenomena, where the pressure distribution is analytically obtained without any negative values or convergence problems, thus the evolution of the contact behaviour is obtained in a semi-analytical manner. Numerical results obtained by the proposed approach facilitate the understanding of the contact behaviour in the following aspects: 1) the ratio of contact area to load decreases with an increase in real contact area;2) normal approach-load relationship is approximated by an exponential decay under relatively small loads and a linear decay under relatively large loads;and 3) average gap shows an exponential relationship with load only in moderate load range. 展开更多
关键词 surface roughness real contact area interfacial stiffness normal contact stiffness
浅议梁的强度与刚度的关系 认领
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作者 马杭 马永其 +1 位作者 丁伟东 丁超 《力学与实践》 北大核心 2020年第5期617-621,共5页
本文提出了梁的强刚比的定义,用无量纲的形式定量地表达了梁的强度与刚度之间的关系,以期充分发挥材料的潜力并促进材料力学的课堂教学。强刚比与载荷大小无关,其数值可以通过有限元方法或者通过梁的载荷试验来获得。结合工程实际,从设... 本文提出了梁的强刚比的定义,用无量纲的形式定量地表达了梁的强度与刚度之间的关系,以期充分发挥材料的潜力并促进材料力学的课堂教学。强刚比与载荷大小无关,其数值可以通过有限元方法或者通过梁的载荷试验来获得。结合工程实际,从设计和试验两个方面对梁的强刚比及其影响因素进行了简要地探讨和分析。 展开更多
关键词 强度 刚度 强刚比 安全系数
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Gershgorin and Rayleigh Bounds on the Eigenvalues of the Finite-Element Global Matrices via Optimal Similarity Transformations 认领
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作者 Isaac Fried Roberto Riganti Chen Yu 《应用数学(英文)》 2020年第9期922-941,共20页
The large finite element global stiffness matrix is an algebraic, discreet, even-order, differential operator of zero row sums. Direct application of the, practically convenient, readily applied, Gershgorin’s eigenva... The large finite element global stiffness matrix is an algebraic, discreet, even-order, differential operator of zero row sums. Direct application of the, practically convenient, readily applied, Gershgorin’s eigenvalue bounding theorem to this matrix inherently fails to foresee its positive definiteness, predictably, and routinely failing to produce a nontrivial lower bound on the least eigenvalue of this, theoretically assured to be positive definite, matrix. Considered here are practical methods for producing an optimal similarity transformation for the finite-elements global stiffness matrix, following which non trivial, realistic, lower bounds on the least eigenvalue can be located, then further improved. The technique is restricted here to the common case of a global stiffness matrix having only non-positive off-diagonal entries. For such a matrix application of the Gershgorin bounding method may be carried out by a mere matrix vector multiplication. 展开更多
关键词 Finite Elements Global Stiffness Matrix Gershgorin and Rayleigh Computed Upper and Lower Bounds on the Extremal Eigenvalues Similarity Transformations
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基于GA-BP神经网络的机床主轴刚度预测研究 认领
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作者 田祎轩 杨庆东 《机械工程师》 2020年第5期11-13,共3页
提出一种基于遗传算法(GA)优化的BP神经网络的机床主轴刚度预测模型,以主轴悬伸量、前后轴承间距、主轴当量外径、前轴承径向刚度、后轴承径向刚度为输入,以主轴末端刚度为输出,训练神经网络,可以预测主轴刚度。研究表明,经过遗传算法... 提出一种基于遗传算法(GA)优化的BP神经网络的机床主轴刚度预测模型,以主轴悬伸量、前后轴承间距、主轴当量外径、前轴承径向刚度、后轴承径向刚度为输入,以主轴末端刚度为输出,训练神经网络,可以预测主轴刚度。研究表明,经过遗传算法优化的BP神经网络模型较未经遗传算法优化的BP神经网络模型而言,拥有较高的预测精度。 展开更多
关键词 机床主轴 刚度 遗传算法 BP神经网络
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湿法水刺可分散材料手感风格评价 认领
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作者 张寅江 占海华 +2 位作者 邹专勇 洪剑寒 孟旭 《毛纺科技》 CAS 北大核心 2020年第6期19-23,共5页
为探究湿法成网水力缠结可分散材料的手感客观参数对其综合手感的影响,利用手感软度分析仪对湿法水刺可分散材料进行手感客观测定,根据主观评价求得的均值作为手感风格综合评价依据,利用逐步回归模型对手感客观参数进行系统筛选。结果表... 为探究湿法成网水力缠结可分散材料的手感客观参数对其综合手感的影响,利用手感软度分析仪对湿法水刺可分散材料进行手感客观测定,根据主观评价求得的均值作为手感风格综合评价依据,利用逐步回归模型对手感客观参数进行系统筛选。结果表明:与材料手感主观评价值关系密切的客观参数为:柔软度、平滑度和硬挺度,且主观评价值与柔软度、平滑度呈负相关,与硬挺度呈正相关。同时主观评价值与柔软度、平滑度和硬挺度的偏相关系数分别为-0.970,-0.854和-0.808。可为开发高品质手感的湿法水刺可分散材料提供参考。 展开更多
关键词 手感风格 湿法水刺 主客观评价 逐步回归 柔软度 平滑度 硬挺度
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含裂纹齿轮传动系统动力学特性研究 认领
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作者 崔守凡 高云 +2 位作者 张振涛 尉朋 周迅 《浙江理工大学学报:自然科学版》 2020年第5期640-646,共7页
为研究齿根裂纹扩展导致的啮合刚度变化对齿轮箱振动的影响,基于含裂纹齿轮系统动力学模型分析了齿轮传动系统的动力学特性。首先建立了渐开线直齿轮两级传动系统的集中参数模型;然后根据该模型,利用数值方法模拟了齿根裂纹的扩展过程,... 为研究齿根裂纹扩展导致的啮合刚度变化对齿轮箱振动的影响,基于含裂纹齿轮系统动力学模型分析了齿轮传动系统的动力学特性。首先建立了渐开线直齿轮两级传动系统的集中参数模型;然后根据该模型,利用数值方法模拟了齿根裂纹的扩展过程,进而采用能量法求解不同裂纹尺寸的齿轮时变啮合刚度;最后将刚度激励作为齿轮系统的激励,代入传动系统集中参数模型,得到传动系统的动力学响应。结果表明:在含裂纹轮齿啮合过程中,齿轮速度级振动时域信号产生周期性冲击变化,而加速度级振动时域信号产生更剧烈的振动冲击;系统负载和转速主要影响动力学响应的幅值、周期和相位;不同故障形式导致齿轮的动力学响应的频率发生变化,主要体现在峰值、频带分布上。该研究结果有助于了解齿轮萌生疲劳裂纹并扩展时齿轮传动系统的动力学特性,为齿轮系统健康状况检测提供理论依据。 展开更多
关键词 渐开线齿轮 刚度 齿根裂纹 动力学响应 频域变换
Regression of liver fibrosis: evidence and challenges 认领
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作者 Ya-Meng Sun Shu-Yan Chen Hong You 《中华医学杂志:英文版》 SCIE CAS CSCD 2020年第14期1696-1702,共7页
It has been reported that liver fibrosis could be reversed after eliminating liver injuries.This article systematically summarizes the evidence of fibrosis regression based on histology,liver stiffness,and serum bioma... It has been reported that liver fibrosis could be reversed after eliminating liver injuries.This article systematically summarizes the evidence of fibrosis regression based on histology,liver stiffness,and serum biomarkers,and discusses several clinically relevant challenges.Evidence from liver biopsy has been regarded as the gold standard in the assessment of fibrosis regression.Semiquantitative staging and grading systems are traditionally and routinely used to define regression.Recently,the predominantly regressive,indeterminate,and predominantly progressive score was proposed,based on the regressive features from“hepatic repair complex”,to provide additional information regarding the quality of fibrosis.For non-invasive assessment,although liver stiffness and serum biomarkers could be applied to reflect the dynamic changes of liver fibrosis,other confounding factors such as liver inflammation have to be considered.In conclusion,both histology and non-invasive methods can provide evidence regarding fibrosis regression.The predictive value of fibrosis regression in long-term prognosis warrants further investigation. 展开更多
关键词 Liver fibrosis Regression REVERSAL Liver biopsy Liver stiffness Serum biomarker
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