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991.
为了获得压力不匹配对超/亚声速混合层空间分布与增长、压力分布和相似性等特征的影响规律,开展试验和数值模拟研究。通过粒子图像测速技术PIV测量混合层空间分布,标准k-ω模型模拟稳态流场特征。超声速气流马赫数为1.32,亚声速气流马赫数为0.11,五组不同压比分别为0.82,0.95,1.11,1.22和1.47。研究结果表明:压力不匹配对混合层增长的影响较弱;当压比>1时,混合层沿流向呈现波纹分布,静压呈现高、低压交替分布;压比增加,混合层内无量纲速度分布不变,无量纲总压减小,而湍流强度增加。基于无粘假设的预测模型捕捉了波节的基本结构与分布。 相似文献
992.
A new method to predict fatigue crack growth rate of materials based on average cyclic plasticity strain damage accumulation 总被引:3,自引:3,他引:0
By introducing a fatigue blunting factor, the cyclic elasto-plastic Hutchinson-Rice-Rosengren (HRR) field near the crack tip under the cyclic loading is modified. And, an average damage per loading-cycle in the cyclic plastic deformation region is defined due to Manson-Coffin law. Then, according to the linear damage accumulation theory-Miner law, a new model for predicting the fatigue crack growth (FCG) of the opening mode crack based on the low cycle fatigue (LCF) damage is set up. The step length of crack propagation is assumed to be the size of cyclic plastic zone. It is clear that every parameter of the new model has clearly physical meaning which does not need any human debugging. Based on the LCF test data, the FCG predictions given by the new model are consistent with the FCG test results of Cr2Ni2MoV and X12CrMoWVNbN 10-1-1. What’s more, referring to the relative researches, the good predictability of the new model is also proved on six kinds of materials. 相似文献
993.
霍西恒王大伟李革萍李志茂 《民用飞机设计与研究》2013,(4):13-16,45
介绍了某型支线客机机翼防冰系统的性能验证思路,即通过采用2.5D试验模型验证三维防冰系统的性能j选取一个典型状态点分别进行了2.5D及三维模型的性能汁算分析,同时进行了相同状态点时2.5D模型的冰风洞试验结果分析,最后将2.5D模型计算结果与试验结果进行对比分析,修正3D模型的汁算结果,从而达到验证整个防冰系统性能的目的。 相似文献
994.
Because of its chemical and radiative properties, atmospheric ozone constitutes a key element of the Earth’s climate system.
Absorption of sunlight by ozone in the ultraviolet wavelength range is responsible for stratospheric heating, and determines
the temperature structure of the middle atmosphere. Changes in middle atmospheric ozone concentrations result in an altered
radiative input to the troposphere and to the Earth’s surface, with implications on the energy balance and the chemical composition
of the lower atmosphere. Although a wide range of ground- and satellite-based measurements of its integrated content and of
its vertical distribution have been performed since several decades, a number of uncertainties still remain as to the response
of middle atmospheric ozone to changes in solar irradiance over decadal time scales. This paper presents an overview of achieved
findings, including a discussion of commonly applied data analysis methods and of their implication for the obtained results.
We suggest that because it does not imply least-squares fitting of prescribed periodic or proxy data functions into the considered
times series, time-domain analysis provides a more reliable method than multiple regression analysis for extracting decadal-scale
signals from observational ozone datasets. Applied to decadal ground-based observations, time-domain analysis indicates an
average middle atmospheric ozone increase of the order of 2% from solar minimum to solar maximum, which is in reasonable agreement
with model results. 相似文献
995.
This paper studies the response of the middle atmosphere to the 11-year solar cycle. The study is based on numerical simulations
with the Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA), a chemistry climate model that resolves the atmosphere
from the Earth’s surface up to about 250 km. Results presented here are obtained in two multi-year time-slice runs for solar
maximum and minimum conditions, respectively. The magnitude of the simulated annual and zonal mean stratospheric response
in temperature and ozone corresponds well to observations. The dynamical model response is studied for northern hemisphere
winter. Here, the zonal mean wind change differs substantially from observations. The statistical significance of the model’s
dynamical response is, however, poor for most regions of the atmosphere. Finally, we discuss several issues that render the
evaluation of model results with available analyses of observational data of the stratosphere and mesosphere difficult. This
includes the possibility that the atmospheric response to solar variability may depend strongly on longitude. 相似文献
996.
玉米空间飞行处理细胞超微结构变异的研究 总被引:1,自引:0,他引:1
玉米干种子搭载于返回式卫星上,经离海平面176km至354km的空间条件处理,发现处理后的玉米叶片超微结构发生各种变异。主要变异包括:细胞质壁分离,液泡增大,细胞壁加厚、扭曲,胞间连丝增多,出现叶绿体基粒盘和基质类囊体的变异,细胞核和叶绿体变形,内质网的数量增多、体积增大,以及其它细胞内膜系统与其它超微结构的变化。 相似文献
997.
童成意 《长沙航空职业技术学院学报》2003,3(4):47-48
本文主要阐述了基于并口EPP协议的软件加密卡的硬件设计。根据实践经验,重点介绍了器件选型与EPP并口时序关键点等注意事项。具有较强的实践意义。 相似文献
998.
根据动态规划原理,提出以控制成本为前提、利用计算机软件辅助计算对复杂测试系统的相对不确定度进行合理分配的方法。这种方法既能满足成本控制又能保证系统的相对不确定度指标的要求。 相似文献
999.
H.M. Cathey Jr. 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
The desire for longer duration stratospheric flights at constant float altitudes for heavy payloads has been the focus of the development of the National Aeronautics and Space Administration’s (NASA) Ultra Long Duration Balloon (ULDB) effort. Recent efforts have focused on ground testing and analysis to understand the previously observed issue of balloon deployment. A revised approach to the pumpkin balloon design has been tested through ground testing of model balloons and through two test flights. The design approach does not require foreshortening, and will significantly reduce the balloon handling during manufacture reducing the chances of inducing damage to the envelope. Successful ground testing of model balloons lead to the fabrication and test flight of a ∼176,000 m3 (∼6.2 MCF – Million Cubic Foot) balloon. Pre-flight analytical predictions predicted that the proposed flight balloon design to be stable and should fully deploy. This paper provides an overview of this first test flight of the revised Ultra Long Duration Balloon design which was a short domestic test flight from Ft. Sumner, NM, USA. This balloon fully deployed, but developed a leak under pressurization. After an extensive investigation to the cause of the leak, a second test flight balloon was fabricated. This ∼176,000 m3 (∼6.2 MCF) balloon was flown from Kiruna, Sweden in June of 2006. Flight results for both test flights, including flight performance are presented. 相似文献
1000.