期刊：
International Journal of Mechanical Engineering Education,2020年48(3):271-283 ISSN：0306-4190
通讯作者：
Zhiliang Huang
作者机构：
School of Mechanical and Electrical Engineering, Hunan City University, PR China;College of Mechanical and Vehicle Engineering, Hunan University, PR China
通讯机构：
School of Mechanical and Electrical Engineering, Hunan City University, China
摘要：
In this paper, a teaching strategy which effectively enhances the students’ ability to solve practical problems is developed, and thus it can provide a potential tool for engineering mechanics teaching. Through organically integrating optimization theory into mechanics modeling, students’ skill of structural optimization modeling is improved, which help them understand basic concepts involved in mechanics and mathematics and master a general method for practical problem solving. The corresponding course unit is designed to instruct students to perform structural optimization modeling for a series of similar but non-identical mechanics problems, which can motivate them to actively explore the essential relationship between mechanics equations and mathematical models. The effectiveness of the proposed strategy is demonstrated by the “six principles” for designing thought-revealing activities and the feedback from all participants in the course.
期刊：
Journal of Materials Research and Technology,2020年9(6):15433-15441 ISSN：2238-7854
通讯作者：
Zhan, Lihua;Xu, Yongqian
作者机构：
[Xu, Yongqian; Zhan, Lihua; Xu, YQ; Chen, Kai] Cent South Univ, Coll Mech & Elect Engn, Changsha 410083, Peoples R China.;[Xu, Yongqian; Zhan, Lihua; Xu, YQ; Chen, Kai] Cent South Univ, State Key Lab High Performance Complex Mfg, Changsha 410083, Peoples R China.;[Liu, Yuzhen] Hunan City Univ, Coll Mech & Elect Engn, Yiyang 413000, Peoples R China.
通讯机构：
[Zhan, LH; Xu, YQ] C;Cent South Univ, Coll Mech & Elect Engn, Changsha 410083, Peoples R China.;Cent South Univ, State Key Lab High Performance Complex Mfg, Changsha 410083, Peoples R China.
关键词：
AA7150 aluminum alloy;Pulsed current density;Creep-aging behavior;Microstructural evolution
摘要：
High pulsed current density has both thermal and athermal effects on the metals, meaning that it can be used to promote the metal forming efficiency. Additionally, it can also be used in the creep-ageing forming of high-strength aluminum alloys. In this present study, the creep-aging behavior, mechanical properties, and microstructural evolution were investigated at various current densities of AA7150 aluminum alloy. The results have shown that the electropulsing treatment (EPT) can increase the dislocation movement and decrease the dislocation density for the coupling of thermal and athermal effects. As such, it could improve both the creep rate and strain by increasing the pulsed current density. Compared with the creep aging at 0 A/mu m(2), the average grain size at 8 A/mu m(2) decreased from 15.3 mm to 11.6 mm. The EPT can increase the atom diffusion rate, leading to the precipitation and growth of eta' phase. Additionally, due to the thermal effect variations at different current densities, the effect of temperature was studied both via simulation and experimentally. (C) 2020 The Authors. Published by Elsevier B.V.
摘要：
To deal with the nonlinear coupling, strong disturbances and parametric uncertainties existing in the multi-motor web-winding system, a robust decentralized $H_\infty $ control method is proposed in this paper. First, the whole web-winding system is considered as a synthetic system composed of several subsystems. Giving that some parameters are time dependent and set points are modified during the winding process, each subsystem can be seen as a dynamic interval system and interval matrix is introduced. Then, a robust decentralized $H_\infty $ controller is designed to attenuate tension fluctuations introduced by the external disturbances and interaction between two consecutive subsystems. Sufficient condition for the existence of robust decentralized $H_\infty $ control law is presented in terms of linear matrix inequality. Finally, some simulations and experiments are conducted with the conventional decentralized controller and the proposed controller. The comparative results show that the proposed control scheme greatly improves the control performance of the web tensions.
关键词：
Most probable point (MPP);performance measure approach (PMA);reliability-based design optimization (RBDO);time-variant reliability;stochastic process
摘要：
Although a series of decoupled or single loop methods have been developed for reliability-based design optimization (RBDO) problems to improve the computational efficiency, it seems hard to extend these strategies to time-variant RBDO due to the complexity of the problems brought by the involvement of time. This paper proposes a new approach for time-variant reliability-based design optimization, expecting to provide an efficient tool for design of some complex structure under time-variant uncertainties. The main idea of the proposed method is the definition of the equivalent most probable point (EMPP). With the EMPP, the original time-variant RBDO problem can be transformed into an equivalent time-invariant RBDO problem formulated by performance measure approach (PMA). Hence, the existing PMA-based time-invariant RBDO methods can be applied to solve the equivalent problem. Therefore, those RBDO methods can be easily extended to time-variant RBDO problems, and hence the computational cost can be effectively reduced. Finally, two numerical examples and an engineering application are used to demonstrate the effectiveness of the proposed method.
摘要：
This paper develops an uncertainty propagation analysis method to analyze transmit/receive (T/R) modules with uncertain parameters, such as variability and tolerances in the physical parameters and geometry produced in the manufacturing processes. The method is a combination of the variance decomposition-based sensitivity analysis and the moment-based arbitrary polynomial chaos (MBaPC). First, the electromagnetic simulation model of a practical T/R module is created. Secondly, based on the model, the sensitivity analysis is carried out to determine the sensitive parameters to the amplitude difference and the phase difference between the input and output electromagnetic signal. Thirdly, their four order statistical moments are calculated using the MBaPC. At last, according to the maximum entropy principle, the statistical moments are used to fit the probability distribution functions of the amplitude difference and the phase difference of the T/R module. The results computed by MBaPC have been validated accurate and efficient compared with Monte Carlo simulation approach.
摘要：
目的观察经口鼻面罩实施压力支持通气(PSV)时不同压力支持(PS)水平对肺力学模型呼吸力学特性参数测算准确性的影响。方法使用ASL5000肺模拟器模拟慢性阻塞性肺疾病患者,设置系统顺应性(C_(rs))为50 mL/cm H_2O,气道阻力(R_(aw))为20 cm H_2O/(L·s),吸气时间为1.6 s,呼吸频率为15次/min。Respironics V60呼吸机以S/T模式运行,呼气末正压为5 cm H_2O,PS水平分别为5、10、15、20和25 cm H_2O,后备通气频率为10次/min。收集在系统泄漏量为25~28 L/min时的通气参数变化并采用新型动态法测算C_(rs)以及吸气和呼气阻力(R_(insp)和R_(exp))。结果PS为5、10和20 cm H_2O时,潮气量(V_T)分别为(281.45±4.26)、(456.81±1.91)和(747.45±3.22)mL(P<0.01);PS为25 cm H_2O时出现明显人机不同步现象,呼吸机无法提供同步通气。PS为5 cm H_2O时吸呼切换流量比(CC)仅为(15.62±3.11)%,PS增至20 cm H_2O时CC增高至(24.50±0.77)%(P<0.01)。 PS<20 cm H_2O时始终存在吸呼过早切换,但随着PS水平的增高过早切换逐渐减轻,PS为20 cm H_2O时出现延迟切换,切换延迟时间为(33.60±15.91)ms(P<0.01)。PS为10 cm H_2O时C_(rs)的测算值为(46.19±1.57)mL/cm H_2O,与模拟肺设置值接近;高水平PS时C_(rs)测算值逐渐减小。PS≥15 cm H_2O后,R_(insp)和R_(exp)的测算值接近模拟肺设置值。结论新型动态法技术可在无创通气状态、不阻断患者自主呼吸条件下持续测算其呼吸力学特性参数。高水平PS通气时高吸气流量对测算R_(aw)有利,而C_(rs)的测算受实际V_T的影响。
