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1.
《International Journal of Hydrogen Energy》2022,47(3):2040-2049
The motion trajectory of hydrogen leakage is an essential safe issue for the application of hydrogen energy. A dimensionless fast-running motion trajectory prediction model is proposed to predict the dispersion characteristics of the buoyant jet of hydrogen leakage for the accident. The impact of different leakage angles, leakage velocity and thermal stratification of ambient air on hydrogen leakage behavior was analyzed. The new developed model was verified by experimental results in literatures. Leakage hydrogen can flow upwards freely in a uniform environment. However, it shows an oscillating trajectory at a certain height in a thermally stratified environment, which is so called “locking phenomenon”. The trajectory of hydrogen leakage is upward and hydrogen gathers at the top of the space to form stratification in a uniform environment, while the hydrogen leakage shows an oscillating trajectory at a certain height in a thermal stratification environment. With the increase of Froude number Fr, it shows that the stable height and maximum height of the leakage airflow have a trend of rising first and then falling in a thermally stratified environment. The findings are expected to give guidance in real-world situations, for example, a larger Fr value and a larger temperature gradient can lead to a decrease in the stable height in the thermally stratified environment. It is found that the fitting of the stable height with different temperature gradients satisfies the power function relationship. This work is expected to be helpful for reducing hydrogen leakage accumulation and explosion risk. 相似文献
2.
This paper introduces the potential feasibility that ELID (electrolytic in-process dressing) grinding replaces superfinishing in bearing manufacturing, but ELID grinding will bring new challenges. Different regions present distinguish surface profile due to the non-uniform contact in ELID groove grinding. However, few reports explaining the non-uniform contact are available. This article explores the mechanisms of the non-uniform contact during ELID groove grinding. Experiments on the non-uniform contact between bearing raceway and grinding wheel have been carried out under different conditions. The results show that non-uniform contact exists in ELID groove grinding process and it exerts influence on the profile of the raceway surface. Non-uniform contact influences the Rsk and Rku value all the time, but it influences the Ra value occasionally. Improvement strategies of eliminating the non-uniform contact are also discussed based on the experimental study. 相似文献
3.
马尔可夫跳变线性系统(MJLS)是一种具有多个模态的随机系统,系统在各个模态之间的跳变转移由一组马尔可夫链来决定。MJLS模型因其在表示过程中可以产生突变而更能精确的描述实际工程应用中的系统。近年来,MJLS的最优控制问题成为了研究的热点,动态规划、极大值原理以及线性矩阵不等式等成为了解决此类问题的主流方法。本文对MJLS最优控制领域的研究现状进行了综述。分别对一般情况下、带有噪声的情况下、带有时滞的情况下以及某些特定情况下的MLJS最优控制问题的国内外研究现状进行论述。最后进行了总结并提出MJLS最优控制领域未来值得关注的研究方向。 相似文献
4.
A Lattice Approach to Image Segmentation 总被引:1,自引:0,他引:1
Jean Serra 《Journal of Mathematical Imaging and Vision》2006,24(1):83-130
After a formal definition of segmentation as the largest partition of the space according to a criterion σ and a function
f, the notion of a morphological connection is reminded. It is used as an input to a central theorem of the paper (Theorem
8), that identifies segmentation with the connections that are based on connective criteria. Just as connections, the segmentations can then
be regrouped by suprema and infima. The generality of the theorem makes it valid for functions from any space to any other
one. Two propositions make precise the AND and OR combinations of connective criteria.
The soundness of the approach is demonstrated by listing a series of segmentation techniques. One considers first the cases
when the segmentation under study does not involve initial seeds. Various modes of regularity are discussed, which all derive
from Lipschitz functions. A second category of examples involves the presence of seeds around which the partition of the space
is organized. An overall proposition shows that these examples are a matter for the central theorem. Watershed and jump connection
based segmentations illustrate this type of situation. The third and last category of examples deals with cases when the segmentation
occurs in an indirect space, such as an histogram, and is then projected back on the actual space under study.
The relationships between filtering and segmentation are then investigated. A theoretical chapter introduces and studies the
two notions of a pulse opening and of a connected operator. The conditions under which a family of pulse openings can yield a connected filter are clarified. The ability of segmentations
to generate pyramids, or hierarchies, is analyzed. A distinction is made between weak hierarchies where the partitions increase
when going up in the pyramid, and the strong hierarchies where the various levels are structured as semi-groups, and particularly
as granulometric semi-groups.
The last section is based on one example, and goes back over the controversy about “lattice” versus “functional” optimization.
The problem is now tackled via a case of colour segmentation, where the saturation serves as a cursor between luminance and
hue. The emphasis is put on the difficulty of grouping the various necessary optimizations into a single one. 相似文献
5.
本文介绍了薄膜隧道发光结的基本结构、发光机理,阐述了其I-V特性中的负阻现象。简单介绍了MIM结构负阻的几种解释,根据热像仪照片和低温测试结果分析,再结合Dearmaley导电模型,我们提出了MIM负阻的物理模型,理论与实验符合较好,最后分析了负阻现象的应用前景。 相似文献
6.
7.
Nucleation Mechanism for Bainite 总被引:4,自引:0,他引:4
Based on the experimental results that solute-depleted zone was observed in Cu-28Zn-4AI (mass fraction) at 523 K, AG is calculated as a positive according to the thermodynamic criteria for the spinodal decomposition of a ternary systems. So, the solute-depleted zone cannot be formed by spinodal decomposition. Dislocation density required by the formation of solute-depleted zone is estimated greater than 7.89×109 cm-2, according to the segregation of solute atoms around dislocations, which is not consistent with the practical situation for the alloy at 523 K. Associated with the internal friction experimental fact that internal friction peaks appear within the incubation for bainitic transformation in Cu-Zn-AI alloy, the equilibrium temperature, TO, is evaluated as 433 K for solute-depleted Cu-25Zn-3.4AI, which is lower than the experimental temperature 523 K. Thus, nucleation by shear mechanism is impossible in this circumstance. Therefore, it is concluded that, like bainite in steels and Ag-Cd, bainite in 相似文献
8.
9.
以山西省河津市小梁乡为代表,研究了因建筑业的发展壮大而产生的社会经济空心化现象,分析了其形成原因,并提出了解决措施,以期引起大家对这一社会经济现象的关注,开展更深层次的研究。 相似文献
10.
在长隧洞的施工中,采用掘进机施工的工程越来越多,特别是国外掘进机的引进,加快了长隧洞工程的开发。而国产掘进机由于其性能和材质方面的原因,存在着一定的技术缺陷.通过国产SJ-45型掘进机在龙门滩工程的施工应用,分析和总结了SJ-45型掘进机的机械性能和存在的技术问题及处理结果,以利于国产掘进机的科研、生产和施工。 相似文献