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61.
本文给出一种将常规电阻应变片贴在距裂纹尖端较远处测量Ⅰ型裂纹应力强度因子K_1的方法。此法实际上是一种实验法与数值法相结合的方法。用实验法测出应变,应变又可以用含待定系数的Williams级数表示,它们组成一组线性代数方程组。解此方程组,可获得待定系数,由待定系数与应力强度因子的已知关系,可求出K_1。 远场应变测量法,避开了裂纹尖端邻域应变梯度很大的区域和可能的塑性区,因而应变测量比较准确。 测出的应变输入数据处理设备及计算机就可以快速实时地知道含裂纹结构在承载情况的K_1,便于进行破坏控制,使设备安全而可靠的工作。 相似文献
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用计算流体力学和风洞试验的方法对以锥导乘波体为基础生成的高超声速乘波飞行器的气动性能进行了研究。结果表明,以马赫数6,攻角4度为设计状态的乘波体,在马赫数5~7,攻角4~6度的范围内,都具有良好的气动特性,升阻比接近4。最后,提出了一个简单的以参考温度方法为基础的粘性阻力分析方法。该方法配合使用风洞试验和计算流体的结果,可以用来验证计算流体中难以计算准确的粘性阻力,也可以用来分析在风洞试验难以直接得到的粘性阻力。对于工程上的粘性阻力分析是一个有用的办法。 相似文献
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Stephen Malys Russell Solomon Jason Drotar Todd Kawakami Thomas Johnson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(2):834-844
The operational Terrestrial Reference Frames (TRFs) realized through the evaluation of broadcast ephemerides for GPS, GLONASS, Galileo, BeiDou-2 and BeiDou-3 have been compared to IGS14, the TRF realized by the International GNSS Service (IGS). The TRFs realized by the GPS, GLONASS, Galileo, and BeiDou-2 and BeiDou-3 broadcast ephemerides are the orbital realizations of WGS 84 (G1762′), PZ90.11, GTRF19v01, and BDCS respectively. These TRFs are compared using up to 56 days of data (21 July-14 Sept 2019) at a 5 or 15-min rate. The operational TRFs are compared to IGS14 in a 7-parameter similarity (Helmert) transformation. Numerical results show that the operational GNSS TRFs differ from IGS14 at a level no greater than 4 cm for Galileo, 6 cm for GPS and BeiDou-3, 13 cm for GLONASS, and 48 cm for a limited set of BeiDou-2 Medium Earth Orbit (MEO) vehicles. 相似文献
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P. Hartogh G.R. Sonnemann M. Grygalashvyly Ch. Jarchow 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
We compared 8 years of ozone measurements taken at Lindau (51.66° N, 10.13° E) at altitudes between 40 and 60 km using the microwave technique with the CIRA ozone reference model that was established 20 years ago (Keating et al., 1990). We observed a remarkable decrease in ozone density in the stratopause region (i.e., an altitude of 50 km), but the decrease in ozone density in the middle mesosphere (i.e., up to 60 km in altitude) is slight. Likewise, we observed only a moderate decrease in the atmospheric region below the stratopause. Other studies have found the strongest ozone decrease at 40 km and a more moderate decrease at 50 km, which is somewhat in contradiction to our results. This decrease in ozone density also strongly depends on the season. Similar results showed model calculations using the GCM COMMA-IAP when considering the increase in methane. In the lower mesosphere/stratopause region, the strongest impact on the concentration of odd oxygen (i.e., O3 and O) was observed due to a catalytic cycle that destroys odd oxygen, including atomic oxygen and hydrogen radicals. The hydrogen radicals mainly result from an increase in water vapor with the growing anthropogenic release of methane. The finding suggesting that the stratopause region is apparently attacked more strongly by the water vapor increase has been interpreted in terms of the action of this catalytic cycle, which is most effective near the stratopause and amplified by a positive feedback between the ozone column density and the ozone dissociation rate, thereby chemically influencing the ozone density. However, the rising carbon dioxide concentration cools the middle atmosphere, thereby damping the ozone decline by hydrogen radicals. 相似文献
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Daniel Okoh Lee-Anne McKinnell Pierre Cilliers Pius Okeke 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
This paper presents the development of a Total Electron Content (TEC) map for the Nigerian ionosphere. In this work, TEC measurements obtained from the AFRL-SCINDA GPS (Air Force Research Laboratory-Scintillation Network Decision Aid, Global Positioning System) equipment installed at Nsukka (6.87°N, 7.38°E) are used to adapt the International Reference Ionosphere (IRI) model for the Nigerian Ionosphere. The map is being developed as a computer program (implemented in the MATLAB programming language) that shows spatial and temporal representations of TEC for the Nigerian ionosphere. The method is aimed at showing how the IRI model can be used to estimate VTEC over wide areas by incorporating GPS measurements. This method is validated by using GPS VTEC data collected from a station in Ilorin (8.50°N, 4.55°E). 相似文献
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