由于棉花秸秆在机械化收获和粉碎加工过程中缺乏准确的仿真模型参数,从而造成在机具设计中仿真效果和实际作业存在较大的差异,在一定程度上限制了棉花秸秆收获以及粉碎装置的设计研究。本文以新疆棉花秸秆作为试验材料,开展仿真分析研究...由于棉花秸秆在机械化收获和粉碎加工过程中缺乏准确的仿真模型参数,从而造成在机具设计中仿真效果和实际作业存在较大的差异,在一定程度上限制了棉花秸秆收获以及粉碎装置的设计研究。本文以新疆棉花秸秆作为试验材料,开展仿真分析研究,通过物理试验测定棉花秸秆的本征参数后,利用EDEM软件进行试验仿真,对棉花秸秆进行参数标定。采用堆积角试验和弯曲试验方法,测量出棉花秸秆堆积角和最大破坏载荷分别为28.62°和143.21 N。应用Hertz-Mindlin no slip模型和Hertz-Mindlin with bonding模型进行棉花秸秆的堆积角仿真试验和弯曲仿真试验,得到棉花秸秆之间碰撞恢复系数、静摩擦因数、滚动摩擦因数和棉花秸秆-钢之间碰撞恢复系数、静摩擦因数、滚动摩擦因数分别为0.5、0.41、0.06、0.5、0.37、0.08,以及棉花秸秆法向接触刚度、切向接触刚度、临界法向应力与临界切向应力分别为4.15×1010N/m、5.60×1010N/m、40 MPa、50 MPa。将以上结果进行粉碎试验验证,棉花秸秆粉碎后依据长度和宽度不同,分为粉末型物料、破碎型物料、未破碎型物料,仿真试验质量和实际试验质量之间偏差为6.84%、8.29%、7.37%,证明了参数的可行性,可用于棉花秸秆参数标定。展开更多
Concerning the issue of high-dimensions and low-failure probabilities including implicit and highly nonlinear limit state function, reliability analysis based on the directional importance sampling in combination with...Concerning the issue of high-dimensions and low-failure probabilities including implicit and highly nonlinear limit state function, reliability analysis based on the directional importance sampling in combination with the radial basis function （RBF） neural network is used, and the RBF neural network based on first-order reliability method （FORM） is to approximate the unknown implicit limit state functions and calculate the most probable point （MPP） with iterative algorithm. For good efficiency, based on the ideas that directional sampling reduces dimensionality and importance sampling focuses on the domain contributing to failure probability, the joint probability density function of importance sampling is constructed, and the sampling center is moved to MPP to ensure that more random sample points draw belong to the failure domain and the simulation efficiency is improved. Then the numerical example of initiating explosive devices for rocket booster explosive bolts demonstrates the applicability, versatility and accuracy of the approach compared with other reliability simulation algorithm.展开更多
【目的】调查我国学术期刊在重大突发事件中的反应速度、应变能力、数字化出版、研究内容和传播效果等。【方法】以中国知网(China National Knowledge Infrastructure,CNKI)网络首发的新型冠状病毒肺炎(COVID-19)相关论文为对象,通过Ph...【目的】调查我国学术期刊在重大突发事件中的反应速度、应变能力、数字化出版、研究内容和传播效果等。【方法】以中国知网(China National Knowledge Infrastructure,CNKI)网络首发的新型冠状病毒肺炎(COVID-19)相关论文为对象,通过Phyth 3.6软件编写数据挖掘程序来获取发表论文及其期刊信息,应用Excel软件对数据进行统计分析。【结果】2020年1月21日至2020年2月26日,共有146种中国学术期刊在CNKI平台以开放获取(Open Access,OA)形式出版COVID-19研究论文565篇,内容涉及疫情预测、疫情防控、临床诊治、病毒病理等;CNKI平台在整合传播过程中,影响力较大,效果显著,截至2020年2月27日,已有公开显示网络下载数据的460篇论文的总下载量为719485次,篇均下载量为1571次,下载超过5000次的论文有18篇,超过1000次的论文有228篇,占49.6%。【结论】我国学术期刊在疫情防控期间主要存在整体上反应不够迅速、数字化出版能力不强、网络首发平台应用不充分、行动力区域性不平衡等问题,应加快推进期刊出版的数字化、集约化和整合传播。展开更多
Deformation of the bulk metallic glasses (BMGs) and the creation and propagation of the shear bands are closely interconnected.Shearing force was loaded on Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 (Vit.1) BMGs by cutti...Deformation of the bulk metallic glasses (BMGs) and the creation and propagation of the shear bands are closely interconnected.Shearing force was loaded on Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 (Vit.1) BMGs by cutting during the turning of the BMG rod.The temperature rise of alloy on the shear bands was calculated and the result showed that it could reach the temperature of the super-cooled liquid zone or exceed the melting point.The temperature rise caused viscous fluid flow and brought about the deformation of BMGs.This suggested that the deformation of BMGs was derived,at least to some extent,from the adiabatic shear temperature rise.展开更多
The thermal stability and glass forming ability (GFA) of Zr35-xTi30Cu7.5Be27.5Agx (x = 0-10) alloys were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and ultrasonic techniques. We found ...The thermal stability and glass forming ability (GFA) of Zr35-xTi30Cu7.5Be27.5Agx (x = 0-10) alloys were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and ultrasonic techniques. We found that the addition of 1 at.% Ag can considerably enhance the GFA as indicated by an increase in the critical glass dimension from 15 mm in the Zr35Ti30Cu7.5Be27.5 alloy to 20 mm in the Zr34Ti30Cu7.5Be27.5Ag1 alloy. However, with the addition of more Ag the supercooled liquid region (△Tx) and y parameter (defined as Tx/(Tg+Tl)) drastically decreased from 155 K and 0.436 to 76 K and 0.363, respectively, resulting in a decrease in the GFA. Additionally, the elastic constant (the ratio of shear modulus to bulk modulus or Poisson's ratio) was also used as a gauge to evaluate the GFA in Zr35-xTi30Cu7.5Be27.5Agx alloys.展开更多
文摘由于棉花秸秆在机械化收获和粉碎加工过程中缺乏准确的仿真模型参数,从而造成在机具设计中仿真效果和实际作业存在较大的差异,在一定程度上限制了棉花秸秆收获以及粉碎装置的设计研究。本文以新疆棉花秸秆作为试验材料,开展仿真分析研究,通过物理试验测定棉花秸秆的本征参数后,利用EDEM软件进行试验仿真,对棉花秸秆进行参数标定。采用堆积角试验和弯曲试验方法,测量出棉花秸秆堆积角和最大破坏载荷分别为28.62°和143.21 N。应用Hertz-Mindlin no slip模型和Hertz-Mindlin with bonding模型进行棉花秸秆的堆积角仿真试验和弯曲仿真试验,得到棉花秸秆之间碰撞恢复系数、静摩擦因数、滚动摩擦因数和棉花秸秆-钢之间碰撞恢复系数、静摩擦因数、滚动摩擦因数分别为0.5、0.41、0.06、0.5、0.37、0.08,以及棉花秸秆法向接触刚度、切向接触刚度、临界法向应力与临界切向应力分别为4.15×1010N/m、5.60×1010N/m、40 MPa、50 MPa。将以上结果进行粉碎试验验证,棉花秸秆粉碎后依据长度和宽度不同,分为粉末型物料、破碎型物料、未破碎型物料,仿真试验质量和实际试验质量之间偏差为6.84%、8.29%、7.37%,证明了参数的可行性,可用于棉花秸秆参数标定。
文摘Concerning the issue of high-dimensions and low-failure probabilities including implicit and highly nonlinear limit state function, reliability analysis based on the directional importance sampling in combination with the radial basis function （RBF） neural network is used, and the RBF neural network based on first-order reliability method （FORM） is to approximate the unknown implicit limit state functions and calculate the most probable point （MPP） with iterative algorithm. For good efficiency, based on the ideas that directional sampling reduces dimensionality and importance sampling focuses on the domain contributing to failure probability, the joint probability density function of importance sampling is constructed, and the sampling center is moved to MPP to ensure that more random sample points draw belong to the failure domain and the simulation efficiency is improved. Then the numerical example of initiating explosive devices for rocket booster explosive bolts demonstrates the applicability, versatility and accuracy of the approach compared with other reliability simulation algorithm.
基金supported by the National Basic Research Program of China (Grant No. 2010CB731600)the National Natural Science Foundation of China (Grant Nos. 50731005,50821001 and 51171163)+1 种基金the Doctoral Fund of Ministry of Education of China (Grant No. 20101333110004)the Nature Science Foundation of Hebei (Grant No. E2010001176)
文摘Deformation of the bulk metallic glasses (BMGs) and the creation and propagation of the shear bands are closely interconnected.Shearing force was loaded on Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 (Vit.1) BMGs by cutting during the turning of the BMG rod.The temperature rise of alloy on the shear bands was calculated and the result showed that it could reach the temperature of the super-cooled liquid zone or exceed the melting point.The temperature rise caused viscous fluid flow and brought about the deformation of BMGs.This suggested that the deformation of BMGs was derived,at least to some extent,from the adiabatic shear temperature rise.
基金supported by the National Natural Science Foundation of China (50731005, 50821001 and 51171163)the National Basic Research Program of China (2010CB731600)+1 种基金the Hebei Natural Science Foundation (E2010001176)the Doctoral Fund of Ministry of Education of China (20101333110004)
文摘The thermal stability and glass forming ability (GFA) of Zr35-xTi30Cu7.5Be27.5Agx (x = 0-10) alloys were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and ultrasonic techniques. We found that the addition of 1 at.% Ag can considerably enhance the GFA as indicated by an increase in the critical glass dimension from 15 mm in the Zr35Ti30Cu7.5Be27.5 alloy to 20 mm in the Zr34Ti30Cu7.5Be27.5Ag1 alloy. However, with the addition of more Ag the supercooled liquid region (△Tx) and y parameter (defined as Tx/(Tg+Tl)) drastically decreased from 155 K and 0.436 to 76 K and 0.363, respectively, resulting in a decrease in the GFA. Additionally, the elastic constant (the ratio of shear modulus to bulk modulus or Poisson's ratio) was also used as a gauge to evaluate the GFA in Zr35-xTi30Cu7.5Be27.5Agx alloys.
