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排序方式: 共有553条查询结果,搜索用时 203 毫秒
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为快速准确排除飞机引气系统故障,引入CBR方法进行故障诊断。将来自运营方的历史故障经验与生产方的专家知识相结合而构造案例库。首先设计了不同类型知识的表示方法,然后重点研究了案例检索中的相似度,针对A—NN算法相似度作为参考的不足,提出了动态失效比的概念,并以此形成参考度,给出了计算模型。应用示例表明该案例库构造可准确定位故障,为高效的案例推理算法提供基础。 相似文献
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在设计点落压比25和非设计点落压比15条件下,对单边膨胀喷管(SERN)不同尾缘切角模型进行了三维数值模拟,并采用Kriging代理模型以SERN轴向推力系数为目标,对尾缘切角进行多目标优化。研究结果表明:尾缘切角会影响SERN后气体的膨胀,增强流动的三维效应,恰当的尾缘切角会使SERN后气体更充分膨胀,有利于提高SERN的轴向推力系数,改善SERN的性能;通过优化,SERN的轴向推力系数由0.94达到了0.975以上,比优化之前提高了约5%,基于Kriging代理模型的SERN优化方法是有效的。 相似文献
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《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(3):1806-1817
The Earth’s ionosphere can be described by a spherical harmonic (SH) expansion up to a specific degree. However, there exist negative vertical total electron content (VTEC) values in the global ionosphere map (GIM) with the SH expansion model. In this contribution, we specifically investigated the negative VTEC values that are induced by the SH expansion model and validated the performance of the inequality-constrained least squares (ICLS) method in eliminating the negative VTEC values. The GPS data from 2004 to 2017 was selected to cover one solar cycle and the experiments under different solar activity conditions were analyzed. The results in our work show that the occurrence of the negative VTEC values is attributed to the deficiency of the SH expansion model when the VTEC itself is small instead of the unevenly distribution of the GNSS stations. The negative VTEC values appear periodically in the temporal domain, showing apparently one year and half year periods. During one year, two peaks in June and December can be observed in the time series of the negative VTEC values. The number of negative VTEC values in June is obvious larger than that in December. During one solar cycle, the number of negative VTEC values under quiet solar activity condition is obvious larger than that under strong solar activity condition. In the spatial domain, the appearance of the negative VTEC values is strongly related with the movement of the subsolar point. In the latitude of the subsolar point has the largest magnitude, the negative values will appear on the opposite hemisphere and the further from the subsolar point the more negative values. The maximum number of the negative VTEC values in the southern hemisphere appears in June, while the peak value in the northern hemisphere appears in December. The maximum number of negative VTEC values in the southern hemisphere is generally larger than that in the northern hemisphere. In addition, the negative VTEC values are distributed both at middle latitude and high latitude in the southern hemisphere, while they are mainly distributed at high latitude in the northern hemisphere. When the ICLS method is used, the negative VTEC values can be eliminated efficiently and it has nearly no influence on the positive VTEC values. The ICLS method can also improve the receiver’s differential code bias (DCB) and significantly decrease the unreasonable negative slant TEC (STEC) values along the lines of sight. Using the final GIM product of the Jet Propulsion Laboratory (JPLG) as a reference, the root mean square (RMS) of the ICLS solution shows maximum 25%, 20% and 45% improvement relative to the least squares (LS) solution at northern high latitude, southern middle latitude and southern high latitude, respectively. 相似文献
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《中国航空学报》2023,36(3):449-470
The digital twin-driven performance model provides an attractive option for the warn gas-path faults of the gas turbines. However, three technical difficulties need to be solved: (1) low modeling precision caused by individual differences between gas turbines, (2) poor solution efficiency due to excessive iterations, and (3) the false alarm and missing alarm brought by the traditional fixed threshold method. This paper proposes a digital twin model-based early warning method for gas-path faults that breaks through the above obstacles from three aspects. Firstly, a novel performance modeling strategy is proposed to make the simulation effect close to the actual gas turbine by fusing the mechanism model and measurement data. Secondly, the idea of controlling the relative accuracy of model parameters is developed. The introduction of an error module to the existing model can greatly shorten the modeling cycle. The third solution focuses on the early warning based on the digital twin model, which self-learns the alarm threshold of the warning feature of gas-path parameters using the kernel density estimation. The proposed method is utilized to analyze actual measured data of LM2500 +, and the results verify that the new-built digital model has higher accuracy and better efficiency. The comparisons show that the proposed method shows evident superiority in early warning of performance faults for gas turbines over other methods. 相似文献
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