Horizontal Normal Force on Buried Rigid Pipelines in Fluctuant Liquefied Silty Soil

The submarine pipelines that are buried in the Yellow River subaqueous delta can be subject to fluctuant local-liquefied soil caused by storm wave action, possibly causing pipeline damage. An experimental investigation was carried out in a wave flume to study the horizontal normal force on buried rigid pipelines in fluctuant liquefied soil. In this experiment, the soil bed was made of silt from the Yellow River Delta, whereas a steel pipe served as pipeline. Under the experimental conditions, the normal force range on the pipeline in fluctuant liquefied soil was several times higher than that in stable soil, specifically on the side of the pipeline exposed to the wave direction. The resultant force of the horizontal normal forces on the buried pipeline grew by about one order of magnitude after soil liquefaction.

Normal reference value of forced vital capacity of Chinese younger women and geographical factors

Objective To supply a scientific basis for standardizing the normal reference value of forced vital capacity(FVC)of Chinese younger women.Methods We studied the relationship between the normal reference value of 21767 samples of FVC of younger women and eight geographical factors in 157 areas in China.Results It was found that the correlation between geographical factors and the normal reference value of FVC of younger women was quite significant(F=5.884,P=0.000).By adopting the method of mathematical regression analysis,one regression equation was inferred:=3.146+0.00006919X1+0.01315X4-0.006966X6+0.09524X8±0.254.In the above equation,is the normal reference value of younger women’ FVC(L);X1 is the altitude(m);X4 is the annual mean air temperature(℃);X6 is the annual mean relative humidity(%);X8 is the annual mean wind speed(m/s);0.254 is the value of the residual standard deviation.Conclusion If geographical values are obtained in a certain area,the normal reference value of FVC of younger women in this area can be obtained by using the regression equation.Furthermore,according to the geographical factors,China can be divided into eight regions:Northeast China Region,North China Region,Shanxi-Shaanxi-Inner Mongolia Region,middle and lower reaches of the Yangzte River Region,Southeast China Region,Northwest China Region,Southwest China Region,and Qinghai-Tibet Plateau Region.

Normal Force and Sag Resistance of Pipe Conveyor

Pipe belt conveyor is a new type of environmentally friendly and efficient bulk conveying equipment.In the design of the roller,the belt and the driving motor of pipe belt conveyor,the sag resistance is a key parameter.Meanwhile,the normal force between the conveyor belt and the roller group is the other important factor need be considered and has a great influence on the sag resistance.This paper analyzes a pipe belt conveyor with a diameter of 150 mm to study the calculation method of normal force.And the relationship between the normal force and the sag resistance is explored.Firstly,the normal force is decomposed into three components related to the forming force of belt,material gravity and belt gravity.So it can be expressed as a linear combination of these three quantities,and the coefficients of each component are obtained based on the dynamic analysis of belt-roller.The results show that the coefficient is mainly affected by the material filling rate,and is almost not affected by the distance between the rollers and the density of the material.The calculation method of the normal force is eventually obtained.Secondly,the normal force in the case of different material filling rates is tested by experiments,and the calculation method of the normal force is verified.Thirdly,the variation law of the sag resistance in the case of different roller group spacing and material filling rate is studied by the dynamic model.It is found that the roller group spacing and material filling rate affects the sag resistance by changing the normal force.There is a power function relationship between the sag resistance and the normal force.In the case of different roller group spacing and material filling rate,the relationship among the sag resistance and the normal force remains unchanged.This study results are of great significance to the design of pipe belt conveyor.

The Work of a Normal Force

It is shown that an impulsive force acting on a particle perpendicular to its velocity vector cannot change its direction of motion without increasing its kinetic energy. If the particle’s kinetic energy is to remain unchanged, the impulsive force must have a component in the direction opposite to the direction of motion. This situation is also realized in the case of a continuous force acting perpendicular to the velocity vector of the particle, when the particle's motion is viewed as a sequence of infinitesimal steps.

A Study of Effect of Various Normal Force Loading Forms on Frictional Stick-Slip Vibration

In this work,a comparative study is performed to investigate the influence of time-varying normal forces on the friction properties and friction-induced stick-slip vibration(FIV)by experimental and theoretical methods.In the experiments,constant and harmonic-varying normal forces are applied,respectively.The measured vibration signals under two loading forms are compared in both time and frequency domains.In addition,mathematical tools such as phase space reconstruction and Fourier spectra are used to reveal the science behind the complicated dynamic behavior.It can be found that the friction system shows steady stick-slip vibration,and the main frequency does not vary with the magnitude of the constant normal force,but the size of limit cycle increases with the magnitude of the constant normal force.In contrast,the friction system under the harmonic normal force shows complicated behavior,for example,higher-frequency larger-amplitude vibration occurs and looks chaotic as the frequency of the normal force increases.The interesting findings offer a new way for controlling FIV in engineering applications.

Electromotive Force Calculation of Fifteen-phase Induction Motors With Non-sinusoidal Supply

非正弦供电十五相感应电机基波磁动势正幅值与3次谐波磁动势负幅值不在同一位置时的叠加磁动势波形称为常规磁动势波形,此种情况下感应电动势的计算是该种电机电磁性能分析与优化设计的前提。与正弦磁动势或理想叠加磁动势不同,常规磁动势下电机的感应电动势与激磁电流相位因磁路饱和不再相差/2,为此提出把感应电动势作为激磁电流流控电压源的处理方法。鉴于电机每半个极下气隙磁密波形不再相同的情况,提出基于电机1个极距区域的拓展分布磁路法计算气隙磁密,进而求出基波感应电动势与3次谐波感应电动势。非正弦供电十五相感应电机样机的感应电动势计算值与实测值相互吻合,说明了拓展分布磁路法计算感应电动势有效且具有较高的准确度。

Analysis of the Force Acting on the Sucker Rod by Polymer Solution

With selecting lower-convected Maxwell constitutive equation, polymer solution flow equation in eccentric annulus is established. And the distribution rule of the force acting on the sucker rod by polymer solution has been gained. The result shows the eccentric ratio and the movement velocity of the sucker rod are major influence factors on the radial force. The greater the ratio is, the greater the force of sucker rod is. Then the eccentric wear is easier to appear.

Seismic Theory of Tides; Theory of Forced Seismic Waves

Proceeding from the statement about presence of the normal resilient medium in the cosmic space, the author concludes seismic nature of tides and a number of other aspects of this phenomenon. The analysis of contradiction of the theory of tsunami to empiric facts led the author to conclude that the tsunami are forced and not free waves, and that the key moment in their distribution is the seismic compression of water.

考虑弯曲空间效应影响的箱梁强迫振动分析

选取附加挠度为剪力滞广义位移,箱梁体系总动能中计入剪力滞附加变形的影响,综合运用薄壁结构弹性理论和Hamilton原理,建立考虑弯曲空间效应影响的箱梁强迫振动控制微分方程及边界条件,并给出任意简谐荷载作用下简支和连续箱梁的强迫振动解析解。引入振动频率影响的应力和挠度放大系数,详细分析简支、连续箱梁剪切剪力滞效应在初等梁结果中的占比及放大系数分布规律。算例分析表明:考虑弯曲空间效应影响的箱梁截面纵向动应力与有限元结果吻合良好;振动频率越大,应力和挠度放大系数、剪切效应占比越大,剪力滞效应占比越小;同频率振动时,简支箱梁放大系数远大于两跨连续箱梁(单跨长等于简支跨长),且频率越高,差值比越大;基频内振动时,箱梁纵向应力计算可忽略剪力滞效应,挠度计算需考虑剪切变形的影响。

轨道不平顺激励对高温超导磁浮列车电机悬挂的影响

高温超导磁浮列车在运行过程中受到轨道随机不平顺激励的影响,车体和磁浮架的振动会传递至直线电机动子而导致气隙变化,变化后的电磁力反作用于电机悬挂系统,进而影响磁浮架和车体振动。二者的耦合振动一定程度上会影响高温超导磁浮列车的安全运行。为了减少轨道随机不平顺激励对电机悬挂系统的影响,文章建立了多刚体动力学理论模型,并在周期性激励的作用下,对理论模型进行了动力学响应的仿真验证,证明了动力学理论模型的正确性。进一步地,在UM软件中以电机法向力和轨道随机不平顺作为外部激励,对高温超导磁浮列车动力学模型进行仿真,研究了电机悬挂系统的垂向刚度对直线电机气隙、车体和悬浮架振动、列车运行平稳性等参数的影响并对该刚度值进行了合理优化。结果表明:增大直线电机悬挂系统的垂向刚度能一定程度提高车体平稳性;同时增大垂向刚度能一定程度上减小气隙的变化和电机的振动,从而降低和悬浮架的耦合作用。研究结果是在特定的结构参数、负载条件下的仿真分析结果,可为高温超导磁浮列车动力学分析提供一定参考作用。

高等教育综合改革与师范大学转型发展

建设新质师范大学是师范大学开展高等教育综合改革的时代选择,也是以教学与研究为基础、服务社会高质量发展为中心的新型师范大学的改革方向。这种新质师范大学展现出办学赛道新、教育模式新、育人能力新、结构要素新、办学使命新、科教融合新等若干新质属性。建设好新质师范大学,坚守人才培养职能、完善立德树人机制是“人才提质”之路,强化科学研究职能、完善高校科技创新机制是“创新提质”之路,提升社会服务职能、完善高校学科与产业衔接机制是“改革提质”之路,夯实文化传承创新职能、完善教师教育体制是“强师提质”之路,深化国际交流合作职能、完善高水平对外开放体制机制是“开放提质”之路。

基于变桨与襟翼协同的降载特性研究及机理分析

研究了尾缘襟翼长度、偏转角和攻角对翼型降载特性的影响,并分析其影响机理。结果表明:变桨与尾缘襟翼的协同控制可有效实现挥舞方向上的降载;尾缘襟翼长度越大,尾缘偏转角越小,攻角越远离临界值,降载性能越佳;偏转角增大会导致临界攻角位置前移;为实现快速降载,在正偏转角、大攻角下优先选择尾缘控制,其他情况下均优先选择变桨控制;降载特性与翼型及翼缝流体分布密切相关,压差越小,降载性能越好。

常开燃油电磁阀高低温流场特性

常开燃油电磁阀作为共轨燃油喷射系统的关键控制部件,研究启闭两种工作过程中,温度的高低变化对电磁阀流场特性的影响规律,在燃油阀材料的选择和结构优化设计上具有重要意义。首先,对常开燃油电磁阀的工作原理进行分析,并且利用Workbench建立热固耦合有限元仿真模型。其次,深入研究该燃油阀受高低温影响的形变规律,以及阀芯在开启和关闭过程中所受液压力的变化规律。最后,采用Fluent流场仿真软件,研究阀口不同开度下,温度对燃油阀流量-压差特性的影响规律。结果表明,温度对阀口形变影响较小;在启闭两种工作过程中,阀芯所受液压力均呈先增加再减小的变化规律;在同一条件下,燃油介质温度越低压差越大。对燃油电磁阀高低温的仿真分析,在常开燃油电磁阀的初始设计阶段,具有重要实践意义。

不同攻击角下镐型截齿线性切削破岩特性

深入探讨不同攻击角下镐型截齿线性切削破岩特性,以期优化截齿参数设计,提升破岩效率,降低能耗。构建镐型截齿破岩MatDEM数值模型,开展不同攻击角下线性切削破岩数值模拟,获得截齿力、裂纹扩展模式以及破岩效率等关键参数。结果显示,截齿平均切削力、法向力均表现出随着截齿攻击角度增加而增大;岩石破坏模式随着截齿攻击角的增加由张拉破坏为主转变为压剪破坏为主;在切削深度为12 mm时,岩石破碎效率的最优攻角为40°,在切削深度为15 mm时,岩石破碎效率的最优攻角在55°~60°。不同的攻击角会导致截齿与岩石之间产生不同的破坏模式,进而影响破岩过程中的能量转换与效率。本文研究结论可为镐型截齿的结构参数优化设计提供参考依据,提高悬臂式掘进机的采掘效率。

基于无网格方法的机械结合面接触分析

典型的无网格方法采用移动最小二乘函数(moving least squares,MLS)作为近似函数,但由于MLS不具备Kronecker delta函数性质,本质边界施加困难。LRPIM是采用径向基点插值形函数的无网格方法,本质边界条件无需特殊处理,可以直接施加,在保持高精度的前提下提高计算效率。将LRPIM应用于机械结合面接触问题的计算。根据位移连续条件推导了含接触特性的线性互补方程,建立了基于LRPIM的计算模型,采用线性互补算法利用数值积分计算了几种典型的接触问题,得到了接触面压力分布和接触变形,分析了插值函数形状参数和积分域尺寸对计算结果的影响。研究结果表明,插值函数形状参数α_(c)对接触力的影响较小,而形状参数q取-0.5~1.2时有较好的收敛效果;积分域无量纲尺寸a_(qx)、a_(qy)大于1.5时计算结果开始收敛,大于2.5时出现发散现象,取值2.1时收敛效果最佳。将计算结果与已有结果进行比较,表明本研究方法有较高的求解精度。

多线摇摆往复式线锯切割蓝宝石法向力试验研究

多线摇摆往复式线锯切割加工是目前将蓝宝石晶棒切割成晶圆衬底的主要加工方法,加工过程中法向切割力是反映加工过程稳定性的重要指标。测量了多线摇摆往复式线锯切割蓝宝石晶棒过程中产生的法向力F_(n),跟踪了晶棒不同位置和不同切割深度下法向力的变化规律,以法向力变化幅值ΔF_(n)为指标,探究各种工艺参数对加工过程稳定性的影响。试验结果表明:法向力F_(n)与线锯的往复运动、工件的摇摆运动有明确的对应关系,晶棒前端的ΔF_(n)与中后端的有明显的不同。线速度V_(s)、最大摇摆角度θ_(max)、单片耗线量M_(d)、张紧力F_(w)、总切割时间T等工艺参数对ΔF_(n)有着不同的影响。ΔF_(n)的波动程度与线锯磨损有着密切的关系。

机器人恒力干磨削的材料去除深度建模

在机器人末端安装被动柔顺装置进行恒力干磨削加工,材料去除深度较难控制。为确定合适的磨削用量控制材料去除深度,根据磨削理论和磨削力经验公式,建立关于法向压力、进给速度和主轴转速的材料去除深度模型,材料去除深度与磨削用量指数幂的乘积成正比。通过正交实验标定模型的未知参数,建立完整的材料去除深度模型;通过单变量实验分析材料去除深度与磨削用量的关系;通过多变量随机实验对材料去除深度模型进行验证。单变量实验和随机实验表明,材料去除深度与磨削用量指数幂的乘积成正比。在磨削加工精度允许范围内,可以根据材料去除深度模型确定磨削用量控制材料去除深度。

圆环非线性恢复力的梁约束模型建模

圆环隔振器是一种以圆环结构为基础的非线性隔振器,圆环结构在压缩变形过程中会受到压力和环面拉伸的耦合作用,从而产生非线性恢复力,对圆环结构非线性恢复力的精确建模是研究隔振器性能的关键。将圆环结构等分为多段曲梁,利用梁约束模型对每段曲梁建立计及几何非线性的力-位移关系模型,结合曲梁间的力传递关系和几何约束关系,建立了圆环整体在压缩过程中的非线性恢复力模型,并计算了圆环变形过程中所有分段点处的正应力。通过电子伺服疲劳试验机对圆环结构在压缩过程中的恢复力进行了测量,验证了梁约束模型的建模精度。研究结果表明,利用梁约束模型可以表征圆环结构非线性恢复力特性,其建模精度与椭圆积分法相当,而模型表达式和求解过程都比椭圆积分法简洁。圆环在压缩量最大时正应力最大,此时最大正应力在圆环的上下端点。梁约束模型的建模精度随着分段数的增加而提高,当分段数大于12时,梁约束模型的恢复力计算误差小于2%。

边坡稳定性整体分析法中滑面正应力分布研究

边坡稳定性的整体分析法是严格极限平衡法,无严格条分法的不收敛问题,还能实现三维严格极限平衡法。但整体分析法一直居于非主流地位,原因可能是整体分析法无法像Morgenstern-Price法那样产生静力许可力系。针对二维问题,分析了造成这一问题的原因——滑面正应力构造不当,并建议采用双参数滑面应力修正的折线方式和Fourier方式,这2种方式都能满足滑面正应力分布的自然分解和端点条件。对典型边坡案例的分析表明,在产生静力许可力系的能力方面,整体分析法远优于以Morgenstern-Price法为代表的经典条分法。因此建议在边坡稳定性分析中优先采用整体分析法。

基于深度神经网络的船舶系泊受灾预报研究

为避免船舶系泊于码头时遭受恶劣海况而发生的缆绳断裂等问题,通过深度神经网络建立了系泊受灾预测模型,来快速获得系泊船舶所有系泊缆绳的受力。模型输入特征数量为11个,涵盖风、浪、流、涌、船舶吃水及船舶系泊方式等基本参数,输出特征为系泊系统中所有缆绳的受力。对模型的测试结果表明,相比于径向基神经网络,模型具有较高的预测精度,每组测试工况下的平均相对误差不超过10%。可将该模型用于在恶劣海况来临前对系泊系统的安全评估和风险分析,有助于相关人员及时采取应对措施,从而保证系泊系统的稳定性与可靠性。