Object-oriented CAD for Hydraulic Circuits of Pressing Machines

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平面旋涡(中心型奇点)水力特性的探讨

本文讨论了平面旋涡(中心型奇点)的水力特性.说明了这种旋涡的中心被封闭的流线所包围，中心点的流速为零，封闭流线为椭圆曲线；给出了旋涡内流速与压强，旋涡的环量、涡量以及角动量的表达式；建立了旋涡水力参数和主流水力参数的连接条件，包括两个运动连接条件和两个动力连接条件；将得到的理论结果应用于侧墙突扩或跌坎流，得到的旋涡中心压强表明，在一般明渠条件下，主流流速大于20m/s时旋涡区有可能出现空蚀；应用于水跃时发现，跃长与跃高之比和突扩流旋涡的长宽比基本相同，估计了水跃旋滚区的紊流运动粘滞系数；应用于交岔渠道的旋涡时，指出了旋涡宽度与渠宽之比必须小于0.160，给出了一个数例     

Physiological cost of energy-equivalent noise exposures with a rating level of 85 dB(A):: Hearing threshold shifts associated with energetically negligible continuous and impulse noise

In industry continuous or impulse noise does not occur exclusively; rather it is a combination of both. If low-level continuous noise or impulse noise (below 120 dB) is added to an already existing high-level continuous noise this often numerically causes no essential increase in the rating level. Yet, it cannot be expected that also aural strain of these exposures is always negligible. Therefore, in a cross-over test series, ten male subjects (Ss) were exposed to white noise of 94 dB(A) for 1 h (TS I), energy-equivalent to an 8 h-rating level L_Ard of 85 dB(A). In a second test series (TS II) the same exposure was combined with 900 energetically negligible 5-ms impulses with a noise level of 113 dB(A) which increased the rating level by only 0.4 dB. The noise exposure of TS I and TS II was followed by an idealized resting phase in a soundproof cabin. In a third test series (TS III) the continuous noise of 94 dB(A) / 1 h was followed by 3 h of white noise at 70 dB(A). Such an additional load increases the L_Ard by merely 0.1 dB to 85.1 dB(A). In all three test series, the noise-induced temporary threshold shift (TTS₂) and its restitution were measured. The continuous noise exposure of 94 dB(A) for 1 h was associated with a TTS₂ of around 20 dB which disappeared completely after about 2 h. The additional impulse noise caused a small increase in the TTS₂ and a prolongation of the restitution time. The maximum mean temporary threshold shift for the group increased only slightly (from 22.5 to 25.9 dB, which nevertheless can be statistically proven at a significance level of p 0.99). Yet, more importantly, the restitution time increased from 126 to 175 min, i. e. 3 h, which can be statistically proven at a significance level of p0.95. The TTS₂-values of TS III did not differ significantly from those resulting from TS I. That was expected as the conditions up to that point in time were identical. But due to the additional subsequent exposure, the mean restitution time increased considerably from 126 min up to 240 min (4 h). The mean total physiological cost represented by the integrated restitution temporary threshold shift (IRTTS) increased in TS II by approximately 40% and in TS III even by 140%.

Relevance to industry

The results of the study show that levels of noise which have no influence on the rating level which traditionally is calculated according to the energy-equivalence principle are often of great importance, as they can lead to considerably prolonged restitution times. Therefore, the purely energy-equivalent determination of the rating level of both impulse noise and low sound levels can lead to an underestimation of latent problems so that over time a reversible TTS can evolve into a permanent threshold shift. The results are also of importance for the acoustic design of break rooms for noise-exposed workers. There should be conditions that allow an undisturbed restitution of hearing.     

双眼立体感知几何模型的研究

利用普通针孔成象的双摄像模型对双眼立体感知几何模型进行了研究，详细讨论了体视象空间的视觉重构，最后通过实验分析了影响体视的因素。     

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基于电机转矩和功率因数方程研究的基础,提出了一种依据电、磁负荷等参数解释横向磁场高转矩密度和低功率因数性能特点的新观点。该方法清晰、明确地给出了电机转矩密度和功率因数同电、磁负荷,漏磁,结构参数以及矢量控制的关系。结论对于同类电机设计及其性能与控制方式的分析具有一定的指导意义。     

改进的分裂基-2/8 FFT算法

文中介绍改进的频率抽取(DIF)分裂基-2/8 FFT算法.与传统算法相比,没有增加结构和计算量的复杂性,显著地减少旋转因子个数和查表频率.通过计算点数为512、1024和2048的DFT,分析结果表明改进算法有效可行.     

二阶RLC滤波电路品质因数推导中的巧合

给出几种二阶RLC滤波电路在一般文献分析时定义的品质因数,由品质因数的能量定义,分别求出了这几种电路的品质因数,所求结果却与文献在分析时定义的品质因数不相符。若按电源等效定理,将电源进行等效变换,变换后电路的品质因数却与文献分析时定义的相同。但电源等效是外等效,即对电源外部电路等效,对电源本身并不等效,经电源等效变换前后电路并不等效,由变换后电路所得的品质因素不应当为原电路的品质因素,这是1种巧合。     

水轮发电机转子动态接地故障原因分析及处理

介绍了一水轮发电机在运行中出现的“保护装置报警动作”和“转子接地报警动作”的故障现象;详细介绍了故障点的寻找过程,找出了故障的原因是转子磁极部分存在动态接地点。故障点寻找的启示是:对于转子动态接地故障不能单凭经验和用习惯思维方式去分析故障的原因,而应该结合实际情况,提出新的思维方式去分析和处理。     

一种改进的变焦遗传算法

提出一种新的变焦遗传算法,在保持串长不变的条件下,大幅度缩小搜索区间,明显提高了遗传算法的收敛速度和解的精度.本文提出的方法对大范围、高精度情况尤其适合.仿真结果说明了算法的有效 性.􀁽     

用基于相对辐射校正的TM影像监测绍兴土地覆盖变化

基于绍兴市1984年和1997年的两期TM影像，用相对辐射校正方法将1997年的影像校正到1984年的辐射水平上，消除多时相遥感影像问地物的辐射差异，对两期影像分别做最大似然分类，构建覆盖转移矩阵，将分类图分析运算构建覆盖变化分类混淆矩阵，并结合土地覆盖变化的驱动因子，分析得出，绍兴土地覆盖变化主要因素是城镇的扩展及人们饮食结构的变化。