A Concise Method to Predict the Mean Dynamic Pressure on a Plunge Pool Slab

Hydrodynamic pressure exerted on a plunge pool slab by jet impingement is of high interest in high dam projects. The present study experimentally investigated the characteristics of pressure induced by a jet through a constant width flip bucket (CFB) and a slit flip bucket (SFB). A pressurized plane pipe was employed in the flume experiments to control the inlet velocities in the flip buckets. A concise method is proposed to predict the mean dynamic pressure field. Its implementation is summarized as follows: First, the position of the pressure field is determined by the trajectories of free jets, and to calculate its trajectories, an equation based on parabolic trajectory theory is used; second, the maximum mean dynamic pressure is obtained through dimensional analysis, and then the pressure field is established by applying the law of Gaussian distribution. Those steps are integrated into a concise computing procedure by using some easy-to-obtain parameters. Some key parameters, such as takeoff velocity coefficient, takeoff angle coefficient, and the parameter k2, are also investigated in this paper. The formulas of these coefficients are obtained by fitting the experimental data. Using the proposed method, the easy-to-obtain geometric parameters and initial hydraulic conditions can be used to calculate the maximum mean dynamic pressure on the slab. A comparison between experimental data and calculated results confirmed the practicability of this model. These research results provide a reference for hydraulic applications.     

连续梁在周期荷载下的动力稳定性简化分析方法

对于一般任意支撑的连续梁结构动力稳定性问题,已有的计算方法求解过程都很复杂,给工程设计带来极大的不便．本文提出了一个简化的分析方法,利用现有的商业软件,只需求得连续梁的自然频率及静力屈曲（失稳）荷载,就可容易得到结构的动力失稳区域,当考虑结构阻尼对不稳定区域的影响时,可将阻尼矩阵表达为Rayleigh阻尼的形式．研究结果表明：采用本文计算方法与已有的理论计算方法得到的连续梁主参数共振的不稳定边界非常吻合,而本文计算方法更为简单,计算结果可靠,计算精度高,可满足工程设计的需要．     

动态压缩下Zr基非晶合金失效释能机理

为研究Zr 基非晶合金动态压缩条件下的失效释能机理,采用力学试验机、霍普金森杆、高速摄影、差示扫描量热分析(differential scanning calorimetry, DSC)、扫描电镜(scanning electron microscope, SEM)等,得到了材料应力应变曲线、高速摄影图像、失效式样微观形貌及DSC 曲线,根据实验数据计算了材料的晶化激活能,并拟合了材料的JH-2(Johnson-Holmquist Ⅱ)模型,对材料动态失效过程进行有限元数值模拟。实验结果表明,压缩条件下材料为脆性断裂,断口处观察到典型的脉状纹样及液滴状结构,材料失效过程伴随着释能现象;数值模拟结果表明,材料裂纹局部的瞬时内能大于材料晶化激活能。动态压缩下材料的失效释能机理即为材料破碎释放储存的弹性势能,并导致材料局部晶化释能,释能强度与应变率成正相关。     

Triple Self‐Sorting in Constitutional Dynamic Networks: Parallel Generation of Imine‐Based CuI,FeII, and ZnII Complexes

Three imine‐based metal complexes, having no overlap in terms of their compositions, have been simultaneously generated from the self‐sorting of a constitutional dynamic library (CDL) containing three amines, three aldehydes, and three metal salts. The hierarchical ordering of the stability of the three metal complexes assembled and the leveraging of the antagonistic and agonistic relationships existing between the constituents within the constitutional dynamic network corresponding to the CDL were pivotal in achieving the sorting. Examination of the process by NMR spectroscopy showed that the self‐sorting of the Fe^II and Zn^II complexes depended on an interplay between the thermodynamic driving forces and a kinetic trap involved in their assembly. These results also exemplify the concept of “simplexity”—the fact that the output of a self‐assembling system may be simplified by increasing its initial compositional complexity—as the two complexes could self‐sort only in the presence of the third pair of organic components, those of the Cu^I complex.     

薄壁件加工系统动态响应分析

薄壁件在铣削加工中容易产生共振或变形,直接影响加工稳定性及加工精度。采用主轴-刀具-工件整体铣削系统连续梁模型,系统研究在动态铣削力作用下,刀具端部与工件端部的动态响应之间的相互影响关系以及对整体系统动态响应影响较大的薄壁件尺寸。结果表明,工件横截面高度对系统共振的影响较为明显,当高度尺寸较小时,工件的低频共振会通过动态铣削力直接反映到刀具端部的振动频响上。工件横截面底边宽度尺寸的增大虽然对共振频率的改变不太明显,但会导致激发出来的刀具共振幅度出现明显降低。研究成果可以为薄壁件铣削加工系统的稳定性控制提供理论基础。     

山地输电线动刚度计算及模态分析

为了揭示地形变化对连续档输电线动态特性的影响，本文提出了基于任意高差角的动刚度理论．首先将单档导线视为连续档导线的子结构，构建了两悬挂点不等高的单档导线振动方程，并在该理论方程中引入了二次项，能够考虑重力沿弦向分量的影响，推导出绝缘子串绕其悬挂点转动的动刚度计算方法，通过动刚度理论研究连续档导线横向振动模态和频率，并应用有限元软件ABAQUS 验证理论模态和频率公式的准确性．所得结果表明，动刚度的计算方法具有较高的精度，理论模态与有限元输出结果吻合较好，同时获得的频率和模态可为山地高压输电线路防舞技术的研究提供依据．     

应力波和动光弹等差条纹的分析与判读

介绍了动光弹的基本原理，并从理论上回答了动光弹应用中的一些问题，如惯性力可否忽略等．并在总结回顾动光弹等差条纹级次判读方法的基础上，提出了把应力波理论与等差条纹分析判读相结合的方法，这样不仅使条纹判读的概念更清晰，而且可提高条纹分析和级次判读的准确性．     

高效耗能黏弹性阻尼框架结构减震性能研究

提出了高效耗能黏弹性阻尼器,研究了该阻尼器对框架结构的减震机理。首先给出了高效耗能黏弹性阻尼器的结构构造,推导了小震、大震与巨震作用下的阻尼放大系数计算公式,由此分析了该放大系数的变化规律。此外,还推导了设置高效耗能黏弹性阻尼框架结构的等效阻尼比。分析表明,框架结构设置高效耗能黏弹性阻尼器在阻尼等效前后顶部位移反应时程曲线相差不超过10%。     

On the numerical determination of optimal inputs

The design of optimal inputs for linear and nonlinear system identification involves the maximization of a quadratic performance index subject to an input energy constraint. In the classical approach, a Lagrange multiplier is introduced whose value is an unknown constant. In recent papers, the Lagrange multiplier has been determined by plotting a curve of the Lagrange multiplier as a function of the critical interval length or a curve of input energy versus the interval length. A new approach is presented in this paper in which the Lagrange multiplier is introduced as a state variable and evaluated simultaneously with the optimal input. Numerical results are given for both a linear and a nonlinear dynamic system.     

Influence of radiation damage on lattice vibration parameters in crystalline and vitreous SiO2

The influence of radiation damage on a number of lattice vibration parameters in two SiO₂ modifications was investigated using IR reflectance spectroscopy. The radiation kinetics of changes in spectral characteristics of SiO₂ fundamental vibrations in crystalline and glassy states were determined. The reflectivity coefficient and the frequency of degenerate vibrations as functions of dose showed minima, the locations of which were governed by the type of sample. At high neutron irradiation doses (10²¹ cm⁻²), certain characteristics of the bands had the same values for both modified materials. Features of the radiation kinetics of sample dynamic parameters were determined. It was deduced that the specific character of the observed radiation-induced changes in spectral and dynamic parameters of vibrations near degenerate modes was due to both the accumulation of radiation damage and a change in the force field surrounding bridging bonds, which is related to a change in the SiO₂ structure. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 354–358, May–June, 2008.