共查询到20条相似文献,搜索用时 93 毫秒
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朱超 《航空精密制造技术》2007,43(6)
"最大限度满足顾客的需求",这一不变的信念伴随着北京凝华实业有限公司走过了13年的风风雨雨,如今,这个观念已经深入到企业经营理念和企业文化的方方面面,并不断通过业务流程的重组和人员区域化的设置,成为公司上下遵从的理念。此外,凝华的"诚信、卓越、责任、中兴"价值观将全体员工的心凝聚在一起,尽展个人才华。而对于公司的常务副总裁李欲超先生来说,思考更多的,则是公司的发展方向。 相似文献
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在虹膜识别系统中,质量较差的虹膜图像可能被系统拒识,导致身份识别或身份认证的失败.因此有必要在虹膜图像的采集端引入质量评价环节,从虹膜图像采集仪输出的视频序列中挑选出符合识别系统要求的虹膜图像.为了减少序列图像质量评价的时间,根据图像的性质,对输入的序列图像进行步进式质量评价,不同的阶段设置不同的门限,只有满足要求的图像才能进入下一阶段的评价,这样将大大减少进行全部步骤评价的图像数量,能有效缩短序列图像评价的时间,保证了选取图像的质量和速度.试验结果表明,该算法能够有效地选择符合质量要求的虹膜图像. 相似文献
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2010年,将开启21世纪第二个十年。回首过去的十年,中国民航经历了一系列未曾预计到的挑战。首先是恐怖主义威胁。2001年的9.11事件,空前地将全世界的目光聚焦在恐怖主义对航空业的威胁上,世界民航业为此付出了惨重代价。对中国民航的影响要小一些, 相似文献
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坐落于南美洲西南端的智利,地域狭长,东倚安第斯山脉,西濒太平洋,南接南极洲。并且日照长,白天酷热,夜间寒冷。得天独厚的地理条件和宜人的地中海气候为智利葡萄的生长提供了有利的条件。智利的气候对葡萄树的光合作用帮助很大,晚上的低温又给予了葡萄树充分的休息,这是促成葡萄成熟、色泽香气宜人的最理想条件。另外,智利天然的环境也使得葡萄很少受到病毒的入侵,如此好的种植环境,全球都很少见。事实上,除了得天独厚的地理环境外,真正值得智利骄傲的是它的葡萄酒文化深受法国的影响,尤其 相似文献
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女人钟爱的名牌手袋品牌说不上无数,也是数之不少。然而专为旅途而设的奢侈品皮具,却是稀少而珍贵。因旅途上实用的需求,使得成就奢侈品般的华贵难上加难。上等的材质、精良的做工是必不可少的,内部的巧妙构造和持久耐 相似文献
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Composite control method for stabilizing spacecraft attitude in terms of Rodrigues parameters 总被引:1,自引:1,他引:0
In this paper, the attitude stabilization problem of a rigid spacecraft described by Rodrigues parameters is investigated via a composite control strategy, which combines a feedback control law designed by a finite time control technique with a feedforward compensator based on a linear disturbance observer (DOB) method. By choosing a suitable coordinate transformation, the spacecraft dynamics can be divided into three second-order subsystems. Each subsystem includes a certain part and an uncertain part. By using the finite time control technique, a continuous finite time controller is designed for the certain part. The uncertain part is considered to be a lumped disturbance, which is estimated by a DOB, and a corresponding feedforward design is then implemented to compensate the disturbance. Simulation results are employed to confirm the effectiveness of the proposed approach. 相似文献
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A comparative study on acoustic damping induced by half-wave, quarter-wave, and Helmholtz resonators 总被引:2,自引:0,他引:2
The damping characteristics of three-type resonators, a half-wave, a quarter-wave, and a Helmholtz resonator are studied experimentally by adopting linear acoustic test. A quantitative acoustic property of sound absorption coefficient in a model enclosure with the resonators is measured and thereby, the acoustic-damping capacity of a resonator is characterized. For a comparative study on acoustic damping, the damping capacity of a half-wave resonator is compared with that of the other resonators. A half-wave and a quarter-wave resonators have the same damping mechanism, but a quarter-wave resonator has much larger damping capacity than a half-wave resonator with the same diameter of a single resonator. It is found that shorter length of a resonator has the advantage of longer one with respect to the damping capacity. The damping capacity of a Helmholtz resonator increases with cavity volume and does as the orifice length decreases. A Helmholtz resonator has the highest damping capacity of three-type resonators and a half-wave resonator has the lowest. Besides, a Helmholtz resonator requires the smallest number of resonators for optimal damping. The design criterion of each resonator on the optimal damping is provided by the normalized parameter of open-area ratio and the similarity behavior for the optimal damping is observed for various enclosure diameters. 相似文献
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大小叶片轴流级反问题设计及数值模拟 总被引:1,自引:0,他引:1
在常规轴流级流线曲率法通流设计和任意中弧线叶型造型方法的基础上,引入了适合于大小叶片的当量扩散因子叶型损失模型,发展了用Miller-Lewis-Hartmann(M-L-H)模型分别计算大叶片和小叶片激波损失的复合激波模型,制定了大小叶片装配方法,建立了大小叶片通流反问题设计系统。用该系统对某级增压比为2.20的单级高负荷后掠风扇进行了后掠和前掠大小叶片改型设计。经计算流体力学(CFD)检验,维持后掠造型的改型,在不提高设计点增压比的条件下,级绝热效率相当,流量和失速裕度都得到了提高;而大小叶片结合前掠的改型,当考虑单排静子的最大载荷将设计级增压比提高至2.31时,级绝热效率略微降低约0.3%,流量略减,失速裕度则显著提高。算例也表明通流反问题设计系统适合于大小叶片轴流级的设计。 相似文献
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非线性刚性转子系统振动的主动控制 总被引:1,自引:0,他引:1
基于转子系统的非线性振动理论,提出了一种通过控制支承刚性的非线性“软”、“硬”特性减少转子通过临界转速时振动的方法。计算和实验结果均表明该方法可大大地减少转子通过临界转速时的振动。 相似文献
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Elkin I.GUTIRREZ VELSQUEZ 《中国航空学报》2017,30(5)
Performance prediction in preliminary design stages of several turbomachinery components is a critical task in order to bring the design processes of these devices to a successful conclusion.In this paper,a review and analysis of the major loss mechanisms and loss models,used to determine the efficiency of a single stage centrifugal compressor,and a subsequent examination to determine an appropriate loss correlation set for estimating the isentropic efficiency in preliminary design stages of centrifugal compressors,were developed.Several semi-empirical correlations,commonly used to predict the efficiency of centrifugal compressors,were implemented in FORTRAN code and then were compared with experimental results in order to establish a loss correlation set to determine,with good approximation,the isentropic efficiency of single stage compressor.The aim of this study is to provide a suitable loss correlation set for determining the isentropic efficiency of a single stage centrifugal compressor,because,with a large amount of loss mechanisms and correlations available in the literature,it is difficult to ascertain how many and which correlations to employ for the correct prediction of the efficiency in the preliminary stage design of a centrifugal compressor.As a result of this study,a set of correlations composed by nine loss mechanisms for single stage centrifugal compressors,conformed by a rotor and a diffuser,are specified. 相似文献
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采用直接数值模拟方法研究了局部矩形凹槽对来流马赫数为6.0的高超声速平板边界层中第二模态扰动演化的影响。引入了透射系数(定义为凹槽下游与上游扰动渐近幅值的比率)来量化凹槽的局部散射效应。数值结果表明:对于较浅的凹槽,频率较低的第二模态扰动被促进,而高频扰动的规律相反。对于大多数情况,凹槽深度的增加使得透射系数减小,这表明凹槽对扰动的促进作用减弱或抑制作用增强。当凹槽的深度超过某一临界值时,透射系数与凹槽深度的关系变为正相关,这表明了另一机制的出现。临界深度受扰动的频率影响:频率越低,临界深度越大。 相似文献
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采用新的构造方法,把不规则分布的素数进行分类,即把单个素数a都同时表示成等距的区间[a,a+h](a为任意素数),在[a,a+h]中的元素为自然数,将[a,a+h]中对应位置有相同情况,或都是素数,或都不是素数的为同一等价类,其中每个[a,a+h]中至少有一个素数a,h取不同自然数时,分类方法不同,显然[a,a+h]的等价类的个数在h有限时是有限的,小于2h/2。 相似文献
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In this paper, a new mission model, called a multi-debris active removal mission with partial debris capture strategy, is proposed. The model assumes that a platform only captures part of the scheduled debris at a time and then releases these debris pieces to a disposal orbit. This process is then repeated until all of the scheduled debris is removed. A genetic algorithm with a multiparameter concatenated coding method is designed to optimize the plan of a multi-debris active removal mission wit... 相似文献