Application of an improved EEMD method in bearing fault diagnosis of induction motors北大核心CSCD

[Objective]In order to overcome the disadvantages of the traditional ensemble empirical mode decomposition (EEMD) method in selecting parameters (integration time and white noise amplitude coefficient) based on experience, and reduce the cost of calculation time, a fast ensemble empirical mode decomposition (FEEMD) method is used to extract the characteristic frequency. [Method]By changing the distribution density of the added white noise, different signal envelopes can be obtained. Furthermore, we can identify the optimal envelope by finding the optimal search window width of the moving mean filter, thereby avoiding the defect of EEMD selecting parameters by experience. At the same time, after the abnormal component in the signal is decomposed, the residual component can be decomposed by EMD to further save the calculation time cost. Finally, the method is combined with Hilbert envelope demodulation technology and applied to the fault characteristic frequency diagnosis of the bearing inner ring of an asynchronous motor. [Results]As the results show, compared with the traditional EEMD method, FEEMD can extract the fault frequency more efficiently. [Conclusion]FEEMD overcomes the disadvantages of the traditional EEMD method in selecting parameters based on experience and shortens the calculation time. As such, it can be effectively applied in bearing fault frequency extraction experiments. © The Author(s) 2022.     

武广高铁路基变形整治施工技术

针对运营中的武广高铁一段路基变形的原因进行了分析,提出了路基变形整治的安全防护方案、监测方法及整治施工工艺,通过工程实践,取得了良好效果,可为类似路基变形整治提供借鉴和参考。     

舰船标准平台模块化设计方法及可制造性研究

针对现代水面舰艇模块化技术发展的需求,以TIRBON系统、CATIA系统为软件平台,提出了基于区域制造标准平台的模块化设计方法,建立了可制造性评价机制,编制了可制造性评价要求。以某护卫舰标准平台典型区段为实例,验证了设计方法和可制造性要求的可行性。研究结论可用于指导水面舰艇的模块化总体设计,提高设计方案的可制造性,为模块化技术的实际应用提供技术支撑。     

我国自行研制的DMUs和EMUs回顾

介绍了我国自行研制的DMUs(内燃动车组)和EMUs(电力动车组)的主要情况及相关技术参数。     

渤海湾客滚船舶应对恶劣天气

低温持续,大风、寒潮侵袭,恶劣天气下的船舶航行困难重重. 1997年5月13日,"鲁渤渡2"与"愉成"轮在雾中相撞,前者沉没;2003年10月12日的寒潮大风使渤海海域多艘船舶遇险,其中"华源顺"船舱进水沉没,仅2名船员获救,15名船员失踪……     

粉煤灰地层大断面连拱隧道开挖进尺研究

粉煤灰地层具有结构松散、强度低、孔隙率大、物理不均匀等特点,隧道穿粉煤灰地层工程地质差因此施工难度大.本文依托盐坪坝隧道研究了开挖进尺对围岩稳定性的影响,利用Rhinoceros建立盐坪坝隧道大断面连拱隧道的网格模型并导入FLAC3D软件中进行数值计算,研究表明:当进行上台阶环形开挖时围岩变形出现突变,开挖进尺对隧道拱顶、拱肩位移影响较大,开挖进尺从2.0 m增加到3.0 m时拱顶变形增加1.09 mm,拱肩变形增加0.9 mm,远大于开挖进尺从1.0 m增加到2.0 m时的变形,考虑开挖安全和施工进度,最终选用2.0 m为施工循环进尺.     

周期函数的几个判定定理

周期函数是数学中比较重要的概念之一,本文给出了几个周期函数的定理并加以证明.     

Flight delays,capacity investment and social welfare under air transport supply-demand equilibrium

This paper analyzes benefits from aviation infrastructure investment under competitive supply-demand equilibrium. The analysis recognizes that, in the air transportation system where economies of density is an inherent characteristic, capacity change would trigger a complicated set of adjustment of and interplay among passenger demand, air fare, flight frequency, aircraft size, and flight delays, leading to an equilibrium shift. An analytical model that incorporates these elements is developed. The results from comparative static analysis show that capacity constraint suppresses demand, reduces flight frequency, and increases passenger generalized cost. Our numerical analysis further reveals that, by switching to larger aircraft size, airlines manage to offset part of the delay effect on unit operating cost, and charge passengers lower fare. With higher capacity, airlines tend to raise both fare and frequency while decreasing aircraft size. More demand emerges in the market, with reduced generalized cost for each traveler. The marginal benefit brought by capacity expansion diminishes as the capacity-demand imbalance becomes less severe. Existing passengers in the market receive most of the benefit, followed by airlines. The welfare gains from induced demand are much smaller. The equilibrium approach yields more plausible investment benefit estimates than does the conventional method. In particular, when forecasting future demand the equilibrium approach is capable of preventing the occurrence of excessive high delays.     

SiC颗粒增强铝基复合材料细观损伤的温度效应

SiC颗粒增强铝基复合材料的宏观力学行为与其微观损伤机理密切相关，随温度的升高，材料力学性能明显下降，SiCD／A356复合材料表现出不同的细观损伤机理．文中对真空双搅拌方法制备的质量分数为20％的SiC颗粒增强铝基复合材料在室温和高温下的细观损伤机制进行了研究，在试样断口上，通过扫描电镜观察到了不同的裂纹萌生和扩展机制，根据不同温度下表现出的不同失效方法，归纳出了复合材料细观损伤的温度效应曲线．研究表明，在室温下复合材料的裂纹萌生以基体撕裂和颗粒断裂为主，高温下其裂纹萌生机制以颗粒脱离和基体撕裂为主．