管式预粘合纸箱结构参数与抗压强度的相关关系

目的研究管式预粘合纸箱结构参数与抗压强度的相关关系,为优化纸箱结构设计以及提高其抗压强度提供依据。方法首先设计普通、四棱台、花形锁等3种代表性管式预粘合纸箱,进而确定3种纸箱影响抗压强度的关键结构参数。其次将各结构参数依次作为自变量,其余结构参数作为常量,利用纸箱抗压试验机进行空箱抗压试验,记录各自的最大压溃力。最后对实验数据进行分析,明确抗压强度与结构参数间的相关关系。结果 3种纸箱的抗压强度均随着周长的增大而增大,其抗压强度并非全部随高度的增大而降低。考虑周长因素时,普通箱的抗压强度最佳;考虑高度因素时,花形锁箱的抗压强度最佳;考虑箱型因素时,当普通箱长宽比接近1.0,四棱台箱下上底比在1.2~1.4范围内,花形锁箱的啮合点和花形锁圆心的连线与水平线所成夹角接近30°时,抗压强度最佳。因结构参数的影响,管式预粘合纸箱的抗压强度整体上显著优于标准开槽纸箱。结论预粘合纸箱的关键结构参数对其抗压强度有显著影响,在设计时应给予足够的重视。     

对广电数字化运动的几点看法——兼谈对信息时代的数字技术标准化意义的反思

从信息革命的角度对于当前这场广电数字化运动做定位分析。对当前数字电视领域中的一些有争议的问题提出了看法。如,公共平台与收费平台的关系,服务平台的统一,整体平移,外来标准和自主标准,数字标准的统一等。提出了对标准化意义的反思。指出,在信息时代,给社会和技术带来进步的往往是追求标准化的过程,而不是标准建立的事实本身。近几年来,许多人已经开始意识到工业时代标准化的“旧瓶”,已经很难装下信息时代数字技术的“新酒”。标准化的工作要有一种新思维来适应信息社会的变化和特点。     

三叉杆式万向联轴器的平均传动效率分析

为获得三叉杆式万向联轴器的平均传动效率，分析了三叉杆式万向联轴器输入轴上滑块的运动规律。首先，在滑块中心建立辅助坐标系，求出滑块在它与导向槽接触面中心相对导向槽的滑动速度以及滑块中心相对导向槽的滑动速度；其次，利用摩擦功率损失与速度的关系式，推导出三叉杆式万向联轴器的瞬时传动效率；最后，通过积分得出三叉杆式万向联轴器平均传动效率的表达式。通过分析发现：三叉杆式万向联轴器的平均传动效率与摩擦系数、输入轴与输出轴偏转角、叉杆半径和回转半径有关，平均传动效率随着摩擦系数、偏转角、叉杆半径的增大而减小，随着回转半径的增大而增大。该结果可为三叉杆式万向联轴器的设计和应用提供重要理论依据。     

Generalized RayleighWave Dispersion Analysis in a Pre-stressed Elastic Stratified Half-space with Imperfectly Bonded Interfaces

Within the framework of the piecewise homogeneous body model the influence of the shear-spring type imperfect contact conditions on the dispersion relation of the generalized Rayleigh waves in the system consisting of the initially stressed covering layer and initially stressed half plane is investigated. The second version of the small initial deformation theory of the three-dimensional linearized theory of elastic waves in initially stressed bodies is applied and the elasticity relations of the materials of the constituents are described by the Murnaghan potential. The magnitude of the imperfectness of the contact conditions is estimated through the shear-spring type parameter. Consequently, the influence of the imperfectness of the contact conditions on the generalized Rayleigh wave propagation velocity is studied through the influence of the values of this parameter. Numerical results on the action of the imperfectness of the contact conditions and the influence of the initial stresses in the constituents on the wave dispersion curves are presented and discussed. In particular, it is established that the magnitude of action of the imperfectness of the contact conditions under the influence of the initial stresses on the wave propagation velocity cannot be limited with corresponding ones obtained in the case where the contact between the constituents is complete and in the case where this contact is full slipping one. The possible application of the obtained results on the geophysical and geotechnical engineering is also discussed.     

放疗床多目标协调机构参数优化研究

随着精确放疗技术在肿瘤治疗中的广泛应用,放疗床的研发也受到人们越来越多的关注.为了达到使放疗床的工作空间和结构尺寸能够满足实际使用要求的目的,提出针对6-HTRT并联构型放疗床的一种多目标协调的机构参数优化方法.研究过程中首先对放疗床进行了运动学分析,结合运动学逆解约束条件,对双端虎克铰形式的并联放疗床进行工作空间的精确分析,并得到工作空间随各结构参数的变化规律,为放疗床的参数优化提供依据.其次,针对提高虎克铰强度及刚度问题,提出了一种虎克铰初始安装角度优化方法.之后考虑工作空间、放疗床受力、雅可比矩阵条件数,同时构建关于条件数全域均值、条件数波动情况的目标函数,对放疗床进行参数的具体优化.最终得到了放疗床各结构参数,经验证使得放疗床的雅可比矩阵条件数在工作空间内较小且分布均匀.由上述可知,所研究的放疗床多目标协调机构参数优化方法在一定范围内可以减小雅克比矩阵条件数,使经过参数优化后的放疗床得到合理的工作空间和结构尺寸,满足实际使用的要求.     

主给水调节阀节流窗口周向设计及其对流动特性的影响

安装于核电站二回路的主给水调节阀通过控制给水流量来调节蒸汽发生器内的水位高度,因此主给水调节阀的流动特性影响着核电站的运行安全与效率.首先,提出了无量纲的节流窗口周向布置不平衡度δ,进行主给水调节阀节流窗口周向设计;其次,利用经网格无关性与流量实验验证的数值模拟方法分析了阀内流场的速度和压力分布特性;最后,探讨了节流窗...     

索-曲梁组合结构的面内振动

研究了索-曲梁组合结构的面内动力特性。首先利用Hamilton变分原理得到索-曲梁的线性运动方程以及索-曲梁组合结构的边界条件,然后在给定位移边界条件下通过解析求解得到索、曲梁各自的特征值,进而可以确定组合结构的固有频率。最后讨论了索的倾角和曲梁半径以及曲梁的不同截面对组合结构固有频率的影响,并且与有限元结果进行了对比。结果表明固有频率与索与曲梁的质量比、曲梁半径以及索的倾角有关。     

Diffraction of a one-dimensional phase grating in the deep Fresnel field

We analyze theoretically the diffraction of phase gratings in the deep Fresnel field on the basis of the theory of scalar diffraction and Green's theorem and present the general formula for the diffraction intensity of a one-dimensional sinusoidal phase grating. The numerical calculations show that in the deep Fresnel region the diffraction distribution can be described by designating three characteristic regions that are influenced by the parameters of the grating. The microlensing effect of the interface of the phase grating provides the corresponding explanation. Moreover, according to the viewpoint that the diffraction intensity distribution is the result of the interference of the diffraction orders of the grating, we find that the diffraction patterns, depending on the carved depth of the phase grating, are determined by the contributing diffraction orders, their relative power, and the quasi-Talbot effect of the phase grating, which results from the second meeting of the diffraction orders carrying most of the power of the total field, as in the case of the amplitude grating.     

除尘器壳体双肢组合截面立柱轴压稳定性研究

除尘器壳体围护结构中的立柱因需要支承顶部较宽截面的箱形梁以及承担较大的轴力而设计成双肢H型钢组合截面。利用非线性有限元方法,研究此双肢组合截面柱在考虑初始缺陷情况下承受轴向压力时的稳定性。研究表明,立柱轧制、墙板与立柱焊接产生的残余应力会小幅降低立柱稳定承载力。立柱的失稳形式为柱顶跨段内前翼缘与前腹板组成T形截面整体弯扭失稳与腹板局部失稳同时发生的相关失稳。墙板与两肢间连接墙板作为蒙皮板,为立柱承担部分荷载并约束其侧向变形。连接墙板越靠近前翼缘,立柱的稳定性越好。连接墙板宽度、墙板宽度、墙板角钢加劲肋刚度和节点连接板厚度等因素对立柱稳定性影响较小。仅邻近立柱的墙板和连接墙板增厚可对立柱稳定性有增强作用,远离立柱的墙板壁厚影响较小。立柱稳定系数与H型钢柱翼缘宽厚比的关系不是单调的;立柱绕弱轴弯曲长细比、腹板高厚比的增大会降低立柱稳定性。基于大量非线性有限元计算结果,提出了除尘器壳体中双肢组合截面轴心受压柱稳定承载力的计算建议。     

侧滑角对超空泡航行体转弯运动沾湿区域的影响

为了提高通气超空泡航行体在转弯运动过程中空泡和航行体的运动一致性,基于有限体积法和VOF多相流模型,采用动态网格技术对航行体转弯运动的空泡形态特性进行了非定常数值模拟研究。通过对航行体沾湿区域的分析,揭示了沾湿区域形成的原因,利用空化器对空泡轴线的定向效应,提出了合理改变侧滑角减缓沾湿区域出现的具体方法。通过分析侧滑角和侧滑角速度对航行体沾湿区域的影响,提出了超空泡航行体转弯运动过程中,在给定偏航角条件下避免出现沾湿区域的侧滑角和侧滑角速度的适用范围,为进一步研究超空泡航行体机动运动问题提供参考。     

跨临界CO2两相流引射制冷系统性能实验研究

对跨临界CO2两相流引射制冷系统性能进行了实验,分析了工况及引射器几何参数对系统性能的影响,结果表明:在实验工况范围内,跨临界CO2两相流引射制冷系统制冷量和COP随气体冷却器压力的升高而升高,随气体冷却器出口温度的升高而降低。对于使用不同喉部直径喷嘴的系统,在相同工况下,引射器喷嘴喉部直径较大的系统的性能较好。对于使用不同直径混合室的系统,随着气体冷却器压力的升高,使用小直径混合室的系统COP变化较大;当气体冷却器压力较低时,使用大直径混合室的系统COP较高,而当气体冷却器压力较高时,使用小混合室直径的系统性能较好。在相同工况下,与传统跨临界CO2循环进行比较,两相流引射制冷循环系统COP最大可提高14%。     

考虑紧固螺栓的三排滚柱式转盘轴承载荷分布计算

螺栓是转盘轴承的关键紧固件。为考察紧固螺栓工作参数对转盘轴承载荷分布的影响,提出了一种针对三排滚柱式转盘轴承的有限元等效建模方法。首先,基于三排滚柱式转盘轴承的结构特点和受力情况,建立考虑紧固螺栓的转盘轴承有限元模型,并从减少计算量和保证计算效率等方面考虑,采用非线性弹簧单元模拟滚子,通过有限元仿真快速获取了该转盘轴承的载荷分布。然后,设计并开展三排滚柱式转盘轴承静态加载试验,通过有限元仿真结果和试验结果的对比验证了所构建有限元模型的准确性。最后,基于构建的有限元模型,分析了螺栓预紧力和螺栓结合面处摩擦系数对三排滚柱式转盘轴承载荷分布的影响。仿真结果表明：螺栓预紧力对三排滚柱式转盘轴承载荷分布的影响显著,而螺栓结合面处摩擦系数的影响微弱,其中上排滚子承受的最大载荷随螺栓预紧力的增大而增大,下排滚子承受的最大载荷随预紧力的增大而减小;在轴向力和倾覆力矩的联合作用下,三排滚柱式转盘轴承下排滚子承受的载荷总体上高于上排滚子,充足的螺栓预紧力可以提高转盘轴承的承载能力,而螺栓预紧力不足则会使下排滚子承受更大的载荷,导致转盘轴承提前失效。研究结果可为转盘轴承的安装和后期维护提供参考。     

部分相干平顶光束的实验研究

本文利用对入射光进行相干度调制的方法,在实验上研究了聚焦光场中的部分相干平顶光束,用CCD记录了光束的产生和演变过程,验证了聚焦光场中部分相干平顶光束的存在.此外,还研究了对于不同的聚焦透镜焦距和环形光阑中心拦截比,不同空间相干度对平顶光束的影响.研究表明,两处平顶光束的大小及两处平顶光束之间的距离随着空间相干长度和环形光阑拦截比的增大而减小,随聚焦透镜焦距的增大而增大.     

螺栓位置与换能器有效机电耦合系数的关系

研究了螺栓在换能器中部或后部(后置)位置时,对有效机电耦合系数的影响。将螺栓等效为T型四端网络,利用换能器的机电等效电路,全面分析了其对应的有效机电耦合系数与螺栓长度之间的变化关系。结果表明,螺栓处于中部时,换能器的机电耦合系数与螺栓长度呈正相关趋势;螺栓位于后端时,换能器的机电耦合系数与螺栓长度先呈正相关变化,随后呈负相关变化;相比于螺栓位于中部,后置螺栓长度的变化对有效机电耦合系数的波动比较大,但有机电耦合效率的系数数值均比中部位置螺栓的值小。这说明螺栓置于中部时机电耦合性能更好。     

科氏质量流量计振幅对零点影响

针对科里奥利质量流量计振幅改变引起零点漂移的问题,首先通过简化模型建立流量管的弯曲振动方程,求解两检测点的位移响应,得到零点相位差与振幅之间的线性关系;然后采集不同振幅下的传感器放大信号,编写过零检测算法,计算零点相位差,建立零点与振幅之间关系的直线,实验验证零点与振幅的线性关系;最后结合检定规程和零点计算结果,定性和定量地分析振幅改变引入的零点漂移导致的测量误差,结果表明,振幅改变越大,引入的测量误差越大,当流量为10 kg/min时,振幅改变10 mV引入的测量误差达0.727%。     

Modelling experimental bond fatigue failures of concrete beams strengthened with NSM CFRP rods

Near surface mounting (NSM) is a promising strengthening technique provided that the full bond between the strengthening material and the existing structure develops. Wahab et al. (2011) reported fatigue bond failures by de-bonding between the CFRP rod and the epoxy that started at mid span. As the load was cycled, the de-bonding propagated towards the support. The model presented here describes the failure of those beams. The de-bonding was modeled as a crack growing at the interface between the CFRP rod and the epoxy where the driving force was the interfacial shear stresses between the CFRP rod and the epoxy. Once the stresses at the crack tip exceeded the allowable fatigue stresses between the CFRP rod and the epoxy, de-bonding occurred and the crack length increased. Ahead of the crack tip, the CFRP rod was fully bonded to the epoxy and the forces decayed exponentially. Behind the crack tip, the rod was partially de-bonded. The experimental and calculated number of cycles until excessive slipping between the CFRP rod and the epoxy occurred and the forces in the CFRP rod at all locations in the shear span at the onset of failure were in good agreement.     

非刚性管中换能器灵敏度的测量方法研究

为实现非刚性管中的换能器低频灵敏度校准,提出了基于互易常数修正的管中灵敏度校准方法。首先,基于管中非刚性边界条件和声压的方程进行了互易常数的推导及修正,并围绕管中互易常数的修正开展了仿真分析,得到测量频率段互易常数的修正值;其次,搭建实验系统开展了基于互易法的管中换能器的灵敏度测量研究。研究表明,管中互易常数的修正使互易换能器灵敏度值更加接近自由场互易法测得的灵敏度值。在0.5~4kHz 频率范围,补偿后的互易换能器灵敏度级最大起伏为-1.41dB,极大改善了未修正的测量情况,与自由场测量值的误差较小,符合声学计量要求。通过对实验与仿真进行对比分析,验证了该方法的有效性和准确性。     

CFRP感应加热线圈中心区域温度场

感应加热技术是实现碳纤维增强树脂复合材料(CFRP)低能耗高效固化成型的有效方法,提高CFRP感应加热温度场均匀性是保证成型质量的关键,而线圈中心区域温度场均匀性是保证材料整体温度均匀性的关键。根据电磁加热原理建立了CFRP有限元多场耦合的分析模型,通过对模拟计算和实验过程的温度场升温及分布情况的对比分析,证明了本仿真可以准确模拟CFRP感应加热温度场分布。根据图像的熵值理论将温度场均匀性通过熵值大小进行表示,实现了CFRP感应加热温度场均匀性的量化分析,并通过有限元模型计算研究了线圈直径及线圈与材料间距对线圈中心区域温度场均匀性的影响,得到了中心区域温度场均匀性与线圈直径及材料间距之间的关系曲线,为组合式线圈均匀加热CFRP提供了线圈直径及材料间距大小选择的理论依据。      

考虑扭矩影响的四边简支矩形板内力分析及配筋修正

混凝土四边简支矩形板一般是基于弹性薄板小挠度理论求出跨中弯矩布置板底钢筋,支座设置构造钢筋.该文基于弹性薄板小挠度理论,求解了板内扭矩分布.由分析可知,四边简支矩形板内具有复杂的扭矩分布,特别在角部部位其扭矩值将接近板的跨中正弯矩,由扭矩合成的主弯矩将使板角开裂.按照现行规范,仅在四边简支矩形板支座设置构造配筋是不合理的,无法满足抗扭需要,必须在角部配置受力钢筋.通过对比四边简支板与固支板沿对角线方向主弯矩的差异,指出边梁约束对板角混凝土开裂的缓解作用;该文揭示了目前混凝土简支楼板设计存在的不足,并对双向板、单向板合理设计提出了不同建议.     

Numerical simulations of the void distribution characteristics of crushed rock masses in mine gobs

The internal stress levels of the crushed rock masses will change the movement states of the rock masses in the gob, and then affect the void distributions of crushed rock mass, and finally change the flow of gas in the gob. In this study, under the Lagrange framework, based on a discrete element method and a Hertz-Mindlin contact model, self-programming was used to simulate the compaction processes of a rock mass in mining gobs. The compression amounts were set as 0%, 5%, 10%, 15%, 20%, and 25%, respectively. The effects on the void distributions of the crushed rock masses of the internal stress levels of the crushed rock masses under the external load conditions were examined by changing the motion state of the rock blocks within in the gobs. The results showed that during the compression processes, the external loads could not be uniformly transmitted from the top of the crushed rock masses to the lower sections. Therefore the stress levels in the upper sections of the crashed rock masses were significantly higher than those of the lower sections. In addition, due to the rock blocks in the upper section of the crushed rock masses experiencing higher degrees of interference from the external forces, the sliding speeds of the upper rock blocks were also larger. At the same time, the rock blocks in the upper sections of the crushed rock masses tended to slide downward down longer. The migration of the rock blocks caused the upper rock blocks to become densely packed, and the coordination numbers of the rock blocks were large. However, the lower rock blocks were loosely distributed, and the coordination numbers of the rock blocks were small. This resulted in the void ratios in the lower sections of the crushed rock masses being higher than the void ratios in other layers of the crushed rock masses, with the void ratios of the lower sections of the rock masses determined to be 1.1–1.4 times that of the upper sections.