三叉式-球笼式双联万向联轴器的扭转振动特性分析

大型旋转机械传动系统的振动特性直接影响其运行平稳性,而万向联轴器是传动系统中必不可少的关键零部件.为此,以三叉式-球笼式双联万向联轴器为研究对象,对其扭转振动特性进行分析.首先,建立三叉式-球笼式双联万向联轴器的扭转振动模型,并基于拉格朗日方程建立其动力学方程.然后,利用Runge-Kutta算法对所建立的动力学方程进...     

SWL550型十字轴万向联轴器结构建模及有限元分析

利用现代设计技术对SWL550型十字轴万向联轴器进行结构设计及强度计算。通过对十字轴万向联轴器的力学分析,得到重要零部件的载荷边界条件。基于CATIA软件建立重要零部件模型,通过CATIA的有限元分析模块对其进行有限元分析,危险截面的Von Mises应力与理论计算值基本吻合。用数字化模型代替传统的实物联轴器实验,简化了联轴器的设计开发过程。     

弹丸定心部-身管接触模型及其应用

研究弹丸定心部与炮膛的接触现象对于理解弹丸膛内运动规律具有重要的意义,为此提出一个弹丸定心部-身管接触模型。假设定心部与阳线间的接触应力只沿阳线长度方向变化,将阳线表面简化成空间曲线;用阳线围成的笼形结构描述内膛的几何,提出了定心部与阳线的接触检测算法。将弹丸和身管沿着圆周方向展开,使用一个二维接触问题的解析解计算接触应力。针对接触应力的方根奇异性,采用Chebyshev-Gauss积分公式计算定心部与阳线的接触载荷。给出了确定模型参数的拟合方法和参数辨识方法。理论分析表明定心部与炮膛的接触刚度随着弹丸膛内行程变化。根据数值算例分析了弹丸质心偏移量对定心部与炮膛接触方式及前定心部磨损刻痕形成的影响。计算结果表明定心部受力的等效接触点并不位于定心部中心或棱线上。     

球面渐开线齿形的螺旋锥齿轮NURBS设计

 为避免传统设计和加工的近似球面渐开线齿形螺旋锥齿轮存在的缺陷,提出了一种新型螺旋锥齿轮设计方案．从齿面精确组成和形状特征出发,将球面渐开线理论应用于齿面基本曲线的方程表达式求导中,实现了齿面曲线的分段参数化．然后,对组成齿面的各区域分别求取齿面离散点数据,并采用三次均匀B样条曲面方法进行初步的拟合与拼接．为了进一步提高齿面精度,借助NURBS方法对拼接后的齿面进行了统一的NURBS精确拟合,并给出了齿面统一参数化的优化方法．最后的算例表明了相关方法的精确性和可行性,为螺旋锥齿轮的数字化设计与NURBS加工提供了新的思路与途径．     

摩托车零部件模糊可靠性设计方法的研究

简述了摩托车零部件进行模糊可靠性设计的必要性,并从模糊可靠性设计的理论基础人手,通过对应力一强度干涉理论的相关方法的分析,并考虑摩托车零部件应力及其组合的随机性和相关强度的模糊性,讨论了适合摩托车零部件的以强度为模糊量同时以应力为随机量的一种模糊可靠性设计方法．举例说明了如何确定一些相关的参数,如何将模糊事件转化为普通事件的技术。     

纳秒脉冲驱动下铝基微沟道等离子体放电特性研究北大核心CSCD

本文设计制作了基于铝基衬底的微沟道阵列器件,并研究了纳秒脉冲微沟道等离子体放电特性。通过调控纳秒脉冲输出波形,获得了脉冲参数对微沟道等离子体放电特性的影响规律。结果表明,相比于传统的正弦波驱动,纳秒脉冲微沟道等离子体放电更集中,耦合效应更明显,且等离子体特性更易于调控。当改变脉冲参数时,6%左右的波形过冲电压会造成微沟道等离子体放电强度~30%的改变。另外,脉冲上升沿时间越短,放电强度越高,当上升沿时间由152 ns缩短至32 ns时,放电强度可提升~30%。     

纳秒脉冲驱动下铝基微沟道等离子体放电特性研究

本文设计制作了基于铝基衬底的微沟道阵列器件,并研究了纳秒脉冲微沟道等离子体放电特性。通过调控纳秒脉冲输出波形,获得了脉冲参数对微沟道等离子体放电特性的影响规律。结果表明,相比于传统的正弦波驱动,纳秒脉冲微沟道等离子体放电更集中,耦合效应更明显,且等离子体特性更易于调控。当改变脉冲参数时,6%左右的波形过冲电压会造成微沟道等离子体放电强度～30%的改变。另外,脉冲上升沿时间越短,放电强度越高,当上升沿时间由152 ns缩短至32 ns时,放电强度可提升～30%。     

圆筒混合机滚圈与托辊强度计算

大型混料设备滚圈与托辊间接触应力很大,校核钢制托辊与滚圈的接触应力是大型混合机设计成功与否的重要因素之一。本文就接触应力进行详细计算,验证设计参数是合理的。     

数字前馈跟踪控制器的频域迭代设计方法

 数字前馈控制器用于提高伺服系统跟踪性能,在工程应用中通常包含如下设计环节：闭环对象参数辨识、闭环离散化和设计前馈控制器,上述各环节都会引入设计误差,最终导致所设计的前馈控制器跟踪性能变差.针对上述问题,利用闭环对象的实测频率特性数据,提出一种新型的频域迭代设计方法,能有效消除各环节误差.通过对设计过程的频率特性差值的变化分析,给出了迭代算法的步骤.该方法将反馈控制思想引入前馈控制器设计过程,根据频率特性差值,不断修正对象频率特性数据,通过设计过程的迭代,使跟踪误差显著减小.以某飞行转台伺服系统为例,进行数值仿真和应用研究,结果表明了该方法的有效性,能显著拓宽伺服系统的跟踪频带,减小对低频信号的跟踪误差．     

基于改进形态滤波与TLS-ESPRIT算法的电力系统低频振荡模态辨识

针对广域测量低频振荡辨识过程中的噪声干扰和定阶问题,提出一种高精度低频振荡模态辨识方法。该方法基于粒子群优化算法(PSO-GA)设计广义形态滤波器的加权参数,改进后的滤波器可以较好去除噪声;将低频振荡信号通过该滤波器滤波后再使用改进总体最小二乘法-旋转不变技术(TLS-ESPRIT)算法进行模态辨识,可以准确获得各个模态参数。对于辨识算法的定阶问题,把奇异值差值与最大奇异值比值引入到TLS-ESPRIT算法中,采用该方式进行系统定阶,不仅计算量和受主观因素影响小,而且还可以提高辨识效率以及辨识的准确性。通过系统模型仿真以及电网实际案例证明提出的方法能够较快速准确地辨识低频振荡参数,且在抗噪性及辨识精度方面有较大的优势。     

Failure assessment on offshore girth welded pipelines due to corrosion defects

Corrosion is an electrochemical process in offshore pipelines where the material strength begins to decrease as corrosion advances. Numerous studies have been performed to determine the remaining strengths (failure pressure) of corroded pipelines. Currently the axial corrosions of the girth welded pipelines still leave much to be understood. This study attempted to simulate girth welded pipeline with various corroded depths and lengths in order to compare with offshore pipeline design manuals. Based on the numerical results, the influence of corrosion defects parameters on remaining strengths were investigated for girth welded pipelines. The investigation on the effect of strength mismatch revealed that in the cases of under‐matched, higher failure pressures are obtained. Comparisons of current results with B31G‐2012 and DNV‐RP‐F101 demonstrated that both codes may produce somewhat conservative predictions on the failure pressure. Furthermore, an equation was proposed to evaluate the corrosion progress across girth welded pipelines.     

Constitutive equations optimized for determining strengths of metallic alloys

We investigate compatibilities of three constitutive equations, the Hollomon, the Swift, and the Voce equations for determination of yield and ultimate tensile strengths based on tensile true stress–strain curves of 27 metal alloys including those with power-law type and linear-type strain-hardening. We analyze each constitutive equation in terms of yield strength determined by the intercept of the linear elastic loading curve and plastic flow curve and ultimate tensile strength evaluated by the concept of instability in tension. We found that the describing plastic flow is very sensitive in determination of the yield strength and tensile strength from parameters of constitutive equation. Voce equation gives estimate yield strength and tensile strength better than Hollomon and Swift equations.     

复合材料层板冲击后压缩强度经验预测公式

复合材料被广泛应用于飞机结构中,其损伤容限性能是飞行器设计的重要指标。提出了一种基于冲击能量预测复合材料层板受冲击后剩余压缩强度的经验预测公式,并通过试验方法分析了剩余强度的影响因素,确定了经验公式形式与参数,对经验公式预测结果进行了验证。经过一定量的试验验证,本文所提出的经验预测方法的预测结果与试验结果吻合良好,研究结果表明,该方法是一种简便迅速的剩余强度工程预测方法。试验结果表明：剩余强度与冲击能量的关系适合采用分段幂函数进行拟合;冲击能量、层板厚度、铺层比例和韧性对复合材料层板冲击后压缩强度有较明显的影响,而冲头直径对剩余强度的影响不显著。     

An empirical evaluation of structure-property relationships in natural fibres and their fracture behaviour

An attempt is made in this paper to arrive at an empirical relationship between the structure and properties of lignocellulosic fibres through computer analysis. Significant regression equations for ultimate tensile strength (UTS) and percentage elongation of these fibres with structural parameters such as chemical composition, microfibril angle etc., have been arrived at using best fit. The results clearly indicate a narrowing down of the deviations between the observed and derived values of mechanical parameters reported earlier. This is attributed to (a) consideration of several structural parameters in the regression equation and (b) the analysis being free from any assumptions. Finally the fracture modes observed in these fibres have been classified and this is explained in terms of structure-property relationships.     

Deriving operating characteristic equations for overcurrent protection devices based on eigensystem realization algorithm

Accurate representation of the operating characteristics of conventional inverse-time overcurrent (OC) protection devices plays an important role in protection coordination schemes. Based on the singular value decomposition of the Hankel matrix, this study uses the eigensystem realization algorithm to curve-fit the characteristic curves of OC protection devices under the digital state-space model and obtain the equations of their operating characteristics. This study applies the proposed method to four types of OC protection devices, including two electromechanical OC relays, one digital OC relay, and one power fuse. One characteristic curve from each protection device is selected for curve-fitting. For all four OC protection devices, the absolute error values for the hundreds of sample points between the actual characteristic curves and the corresponding curve-fitting equations are all less than 10 ms. The numbers of fitting components required are determined by the desired maximum absolute values of errors for the fitting equation. Finally, this study uses the derived equation to construct the characteristic curve of customized OC relay to solve the coordination problem of power system protection.     

基于二次回归正交试验的汽轮机排汽缸加装导流板的研究

以某600 MW汽轮机为研究对象,应用计算流体力学软件CFX对低压缸末级和排汽缸的耦合模型进行了数值模拟,基于二次回归正交试验,在排汽缸上端安装导流板来削弱通道涡对排汽缸气动性能的影响,得到了导流板安装参数与静压恢复系数之间的回归方程。方程呈现非线性关系,显著不失拟,且三因素之间互不影响。求解回归方程的最优解,得出最佳的导流板安装方案。安装导流板后,通道涡被破碎,排汽缸的气动性能得到了明显的改善。排汽缸出口的静压恢复系数提高3.008%,总压损失系数降低5.789%,出口截面标准偏差降低了3.043。并且,不同负荷下优化后排汽缸出口的静压恢复系数均大于优化前。     

Effect of carbonation on the rebound number and compressive strength of concrete

Experimental research was performed to clarify the influence of carbonation on the rebound number and the strength evolution of concrete for three strength levels. The results reveal that the strength level dependent influence of carbonation is a source of errors in the existing equations for the strength reduction coefficient; these equations are used to compensate for the influence of surface carbonation in the rebound number method. A new equation for the strength reduction coefficient that can consider the influence of strength level was developed based on field test data extracted from technical reports of the Korea Research Institute of Standards and Science and of four universities. Over a wide range of strength levels, the equation shows good agreement with strength reduction coefficients established experimentally.     

The texture and strength of metallurgical coke

Attempts to relate the tensile strength of pilot-oven cokes, of blast-furnace quality, to their textural compositions, i.e. the proportions present of the various textural components identifiable in polished coke surfaces under polarized light are described. Of the various equations used, a relationship obtained by multi-linear regression (MLR) analysis permitted the strengths of the cokes from 44 blended coal charges to be calculated with the highest precision but gave no insight into coke breakage behaviour. Equations were therefore derived from consideration of a simple structural model of coke failing in tension by intergranular and transgranular mechanisms. Although predicting coke strengths from textural data with lower precision than the MLR equation, these equations permitted the ready identification of those textural components associated with high strength. Transgranular fracture was indicated as the more probable failure mechanism. A small improvement in precision was obtained by taking the porosity of the coke into account.     

Elastic transverse impact on an orthotropic plate

The impact of a solid projectile via an elastic buffer on an orthotropic elastic plate possessing a cylindrical anisotropy has been numerically simulated. The dynamical behavior of the plate is described in terms of the Uflyand-Mindlin wave equations taking into account the rotary inertia and the transverse shear deformations. The wave equations are solved using the ray method and the matching of asymptotic expansions obtained for short times inside and outside the contact zone. The influence of the anisotropy of the plate material on the dynamic contact force and the plate inflection at the impact site has been studied.     

Robustness Testing of a Tablet Formulation Using Multivariate Design

ABSTRACT

A total of 45 experiments were carried out to evaluate the robustness of two similar tablet formulations—a product of two strengths—with respect to normal batch-to-batch variation of the excipients and the active pharmaceutical ingredient. The formulations consist of 10 ingredients. Because of the differing amounts of active pharmaceutical ingredients, the two formulations also differ in the amounts of two of the diluents and one of the binders. The excipients and active pharmaceutical ingredient were characterized in terms of multiple variables, and principal properties were calculated with principal component analysis. A Plackett and Burman design was applied to the principal properties. The relationships between the design factors and two responses, mean disintegration time and mean crushing strength, were evaluated by using regression methods. Both formulations were found to be robust under controlled conditions.