共查询到20条相似文献，搜索用时 203 毫秒
1.
研究了标准k ε模式 ,双尺度湍流模式 ,并对其在壁面附近作出长度尺度修正 在此基础上 ,选择了几个基准流动 :二维可压缩拐角、锥柱裙组合体绕流和斜激波 /平板湍流边界层干扰 ,进行数值计算 .通过数值计算和实验结果的比较 ,发现修正湍流模式对流动分离、摩阻和热流的计算具有更好的效果 . 相似文献
2.
高超声速边界层工程转捩模式研究 总被引：4，自引：0，他引：4
在流动从层流过渡到湍流的转捩区域,传统的湍流模式由于没有考虑到脉动的间歇性,因此不能很好给出转捩区域流动的发展过程。考虑湍流脉动的间歇性,引入间歇因子,根据Hassan构造湍流转捩模式的思想来建立基于SST湍流模式的湍流工程转捩模式。应用该工程转捩模式,数值模拟了轴对称高超音速尖锥绕流,计算结果与实验符合良好,表明作者发展的工程转捩模式可以成功应用于高超声速飞行器工程转捩问题的计算。 相似文献
3.
湍流的多重尺度理论可以根据几类典型的失稳机理产生不同的大尺度运动计算湍流流场,从而使湍流流场的实际计算找到可信的理论依据,改进目前已有的过于偏重经验关系或经验常数的计算模式,使其能比较普适地解决一些湍流问题。 相似文献
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张家麟 《中国科学院研究生院学报》1988,(2)
本文使用张量分析方法系统推导并给出了用于描述叶轮机械内跨声速位流的使用非正交曲线坐标非正交速度分量的散度形式的二维及三维势函数方程。这一整套势函数方程可应用于叶轮机械内任意形状的S_1、S_2流面上跨声速流动及准三元、全三元跨声速流动的分析及设计问题的求解计算。文中还给出了这些方程的求解步序。 相似文献
6.
混沌、湍流和非平衡统计力学 总被引：1，自引：0，他引：1
为了探索填补非线性系统混沌研究和完全发展湍流研究间的“空白”,笔者提出一个低阶的混沌动力学模型,虽然其相空间维度仅20,但能模拟完全发展湍流的主要特征。湍流是个复杂的大系统,其相空间维度大于10~(10),精细地研究它的奇异吸引子的几何结构和动力学行为是不可能和没有意义的,必须进行统计研究。湍流统计理论的核心是封闭性问题,根源于N—S方程的非线性。笔者应用非平衡统计力学解决封闭性问题,能成功地处理很多小尺度统计特性问题。 相似文献
7.
激波诱导的湍流边界层分离,由于其流场结构复杂并具有高度不稳定性,目前理论计算还无法准确模拟,因而一直是航空、航天和其它许多应用流体力学领域的一个难题。航天飞机和其它高速再入飞行器的表面翼、襟、进气道入口等处,由于激波与湍流边界层相互作用,使物面边界层产生分离一再附,引起严重的局部气动加热,而分离激波出现的大尺度低频振荡,不仅产生严重的气动噪声,还会引起振动疲劳,直接影响飞行器的性能和安全。因此,选择飞行器表面若干典型有实际意义的局部激波干扰流场,研究它们的流动特性,并在一定认识的基础上建立近似的预测模式和开发实用的控制方法,已成为当今航天高技术领域空气动力学研究的一个热点。 相似文献
8.
旋一个水龙头至全开，然后可见起初均匀、清澈的水流出现变化，接着突然变得混浊。在这个领域进行第一次实验后的一个多世纪里，引起和维持这种管内湍流的机制仍然不十分清楚。模拟实验暗示向前流动周期变化的旋涡也许是湍流形成的基础，但没有人曾经观察到这种飞逝的涡流。荷兰Delft理工大学的研究人员领导的一个研究小组，通过发射激光穿过湍流， 相似文献
9.
现结合逢石河特大桥主桥,对该连续刚构桥高墩进行了线性稳定分析、考虑几何非线性的第二类稳定分析和考虑双重非线性的第二类稳定分析。结果表明:线性稳定分析与能量法推导的理论值符合较好,几何非线性的临界荷载比线性的临界荷载有所减小;考虑几何和材料双重非线性的高墩承载能力计算值下降较大,在高墩大跨连续刚构桥稳定性分析中应考虑双重非线性的影响。 相似文献
10.
本文介绍过去十年我们在湍流实验研究中取得的某些进展。如边界层湍流中的高阶共振干涉,二维混合层中的转捩过程,拟序结构和近声场的相互作用,不稳定波辐射噪声,自由气流中的湍流对湍流分离的影响等。某些关于湍流模式理论以及粒子群和湍流相互作用的实验研究将在不久可得到某些有意义的结果。 相似文献
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The Hammerstein–Wiener model is a nonlinear system with three blocks where a dynamic linear block is sandwiched between two static nonlinear blocks. For parameter learning of the Hammerstein–Wiener model, the synchronous parameter learning methods are proposed to learn the model parameters by constructing hybrid model of the three series block, such as over parameterization method, subspace method and maximum likelihood method. It should be pointed out that the aforementioned methods appeared the product term of model parameters in the process of parameter learning, and parameter separation method is further adopted to separate hybrid parameters, which increases the complexity of parameter learning. To address this issue, a novel three-stage parameter learning method of the neuro-fuzzy based Hammerstein–Wiener model corrupted by process noise using combined signals is developed in this paper. The combined signals are designed to completely separate the parameter learning issues of the static input nonlinear block, the linear dynamic block and the static output nonlinear block, which effectively simplifies the process of parameter learning of the Hammerstein–Wiener model. Parameter learning of the Hammerstein–Wiener model are summarized into the following three aspects: The first one is to learn the output static nonlinear block parameters using two sets of separable signals with different sizes. The second one is to estimate the linear dynamic block parameters by means of the correlation analysis method, the unmeasurable intermediate variable information problem is effectively handled. The final one is to determine the parameters of the static input nonlinear block and the moving average noise model using recursive extended least square scheme. The simulation results are presented to illustrate that the proposed learning approach yields high learning accuracy and good robustness for the Hammerstein–Wiener model corrupted by process noise. 相似文献
13.
石铸 《中国科学院研究生院学报》1993,31(5):432-450
The Present paper is a preliminary result of study on three genera,
Dubyaea, Syncalathium and Soroseris of the tribe Lactuceae (Compositae) in China.
The genus Dubyaea in China so far known consists of 14 species, of which
six are described here as new: D. pteroponda Shih, D. lanceolate Shih, D.
muliensis Shih, D. panduriformis Shih, D. cymiformis Shih and D. jinyangensis
Shih. In addition, one new combination, i.e.D. bhotanica (Hutch.) Shih, is
made.
There are six species in the genus Syncalathium in Chinese flora, of which one
species is described here as new. This is S. orbiculariforme Shih. A new combina-
tion, S. pilosum (Hand.-Mazz.) Shih, is made in the paper.
The genus Soroseris comprises nine species, of which three are described here
as new, S. teres Shih, S. chrysocephala Shih and S. qinghaiensis Shih. Three new
combinations, i.e.S. trichocarpa (Franch.) Shih, S. hirsuta (Anth.) Shih, and S.erysimoides (Hand.-Mazz.) Shih are made in the present paper. 相似文献
14.
J. Louis Tylee 《Journal of The Franklin Institute》1983,315(3):165-178
Bond graph methods are used to derive a nonlinear model of a U-tube steam generator like those used in pressurized water reactor (PWR) power plants. A major advantage of bond graph modeling is the ease with which different subsystem models can be interconnected; this feature is demonstrated in the steam generator modeling. Individual models of primary water cooling, generator tube heat capacity, secondary and downcomer fluid mass and energy flows, the feedwater supply system, and the main steam control valve are developed. The complete bond graph model is validated using data from a test reactor steam generator. 相似文献
15.
石铸 《中国科学院研究生院学报》1986,24(4):292-296
Almost no differences are seen in habit and infrescence between the gene-
ra Vladimiria and Dolomiaea; the former that was founded on the basis of Jurinea sal-
winensis Hand.-Mazz. by Iljin should be transferred to the later that was earlier found-
ed on the basis of D. macrocephala DC. by De Candolle. But considering the style which
has fine, spreading and apex-acute branches in the group Vladimiria, it is reasonable
to treat the group Vladimiria as a section in the genus Dolomiaea, i.e. Dolomiaea sect.
Vladimiria (Iljin) Shih. Therefore, the genus Dolomiaea is expanded in the circums-
cription in the present paper, not only including the primary group with short, com-
pact and apex-rounded style branches, i.e. Dolomiaea sect. Dolomiaea, but also sect. Vla-
dimiria (Iljin) shih with different characters of style-arms.
Nine species and 1 variety as new combinations are listed in the sect. Vladimiria
(Iljin) Shih as following: D. denticulata (Ling) Shih, D. forrestii (Diels) Shih, D.
scabrida (Shih et S. Y. Jin) Shih, D. souliei(Franch.) Shih, D. souliei (Franch) Shih
var. mirabilis (Anth.) Shih, D. berardioidea (Franch.) Shih, D. georgii (Anth.) Shih,
D. edulis (Franch.) Shih, D. salwinensis (Hand.-Mazz.) Shih and D. platylepis (Hand.
-Mazz.) Shih. 相似文献
16.
Ｈａｍｍｅｒｓｔｅｉｎ模型基于神经网络的预测控制方法 总被引：1，自引：0，他引：1
Ｈａｍｍｅｒｓｔｅｉｎ模型是化工过程中最常用的模型之一,它由非线性静态环节和线性动态环节串连 组成,适合描述ｐＨ过程和具有幂函数、死区、开关等非线性特性的过程．这类模型的控制问题可以分解 为：线性模型的控制问题和非线性模型的求根问题．针对Ｈａｍｍｅｒｓｔｅｉｎ模型提出了一种基于神经网络的 模型预测控制策略,采用一组神经网络拟合非线性部分的逆映射．这种方法不需要假设Ｈａｍｍｅｒｓｔｅｉｎ模 型的非线性部分由多项式构成,并且避免已有研究在无根和重根情况下存在的问题．最后通过仿真试验证明了以上结论． 相似文献
17.
石铸 《中国科学院研究生院学报》1984,22(6):445-455
Since the 19th century many botanists have studied the Chinese Cirsium
and a great number of taxa or names has been reported, of which many still need to be
reviewed critically
This work is a preliminaxy result of study on Chinese species of Cirsium. As many
as 65 taxan or names in the literature are reduced to synonym in this paper. The Cir-
sium in China so far known comprises 49 species, of which 9 are described as new, 1 is
a new combination and 4 are new records in Chinese flora. These new species are: C.
subulariforme Shih, S. muliense Shih, C. fanjingshanense Shih, C. periacanthaceum Shih,
C. racemiforme Ling et Shih, C. vernonioides Shih, C. chrysolepis Shih, C. tenuifolium
Shih and the new combination is C. viridifolium (Hand. -Mazz.) Shih. The new records
in China are C. serratuloides (L.) Hill., C. incanum (S. G. Gmel.) Fisch. ex MB., C. la-
natum (Roxb. ex Willd.) Spreng and C. alatum (S. G. Gmel) Bobr.
The Chinese Cirsium is divided into 8 sections in the present paper, of which 3 are
new, namely, Sect. Isolepis Shih, Sect. Tricholepis Shilh and Sect. Hymenolepis Shih,
and I is a new combination, namely, Sect. Spanioptilon (Cass.) Shih. In addition, a new species of the genus Alfredia, A. aspera Slih, is described. 相似文献
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中国后发企业能力积累机制研究———基于联想与华为国际化的案例对比分析 《科学学研究》2021,39(6):1084-1093
国际化是后发企业获取知识、能力积累的重要途径。基于此,本文以联想与华为为研究对象,通过运用案例研究法解析其国际化中能力积累机制。研究结果显示：（1）利用式学习与开发式学习是后发企业国际化中主要的学习策略,前者是企业在海外并购和海外子公司等国际化模式中采纳的主要学习策略,后者是企业在设立海外研发中心的国际化模式中采纳的主要学习策略;（2）基于利用与开发的双元学习机制是后发企业国际化中能力积累的关键机制;（3）后发企业国际化中能力积累的过程分为两个阶段：创新要素获取阶段和能力升级阶段。 相似文献