This paper reports on a study of active vibration control of functionally graded beams with upper and lower surface-bonded piezoelectric layers. The model is based on higher-order shear deformation theory and implemen...This paper reports on a study of active vibration control of functionally graded beams with upper and lower surface-bonded piezoelectric layers. The model is based on higher-order shear deformation theory and implemented using the finite element method （FEM）. The proprieties of the functionally graded beam （FGB） are graded along the thickness direction. The piezoelectric actuator provides a damping effect on the FGB by means of a velocity feedback control algorithm. A Matlab program has been developed for the FGB model and compared with ANSYS APDL. Using Newmark＇s method numerical solutions are obtained for the dynamic equations of FGB with piezoelectric layers. Numerical results show the effects of the constituent volume fraction and the influence the feedback control gain on the frequency and dynamic response of FGBs.展开更多
The nonlinear dynamic model of spinning ballistic missiles is established during the first boosting phase of the missile. Based on the conventional backstepping sliding mode control and the assumption of a two time-sc...The nonlinear dynamic model of spinning ballistic missiles is established during the first boosting phase of the missile. Based on the conventional backstepping sliding mode control and the assumption of a two time-scale separation of missile dynamics, a graded sliding mode controller is designed with two sub-sliding surfaces which have invariability to external disturbances and parameter perturbations, and a matrix which comprises three first order low pass filters is introduced to prevent “explosion of terms”. Owing to the upper bounds of the uncertainties are difficult to obtain in advance, adaptive laws are introduced to estimate the values of the uncertainties in real-time. Eventually, the numerical simulation results given to show the proposed controller can ensure the steady flight of missiles.展开更多
目的系统评价稳心颗粒联合西医常规治疗冠心病心绞痛(AP)的疗效及安全性。方法检索PubMed、EMbase、Web of Science、The Cochrane Library、知网、维普、万方、中国生物医学文献数据库,收集稳心颗粒治疗AP的随机对照试验(RCT),检索时...目的系统评价稳心颗粒联合西医常规治疗冠心病心绞痛(AP)的疗效及安全性。方法检索PubMed、EMbase、Web of Science、The Cochrane Library、知网、维普、万方、中国生物医学文献数据库,收集稳心颗粒治疗AP的随机对照试验(RCT),检索时限均为建库至2020年12月,采用Rev Man5.3软件进行Meta分析,GRADEpro软件进行证据质量评价。结果共纳入59个RCT,包括4870名患者,Meta分析结果显示:以西医常规治疗为对照,稳心颗粒联合西医常规治疗组在减少心绞痛发作次数[SMD=-2.41,95%C(I-2.79,-2.02),I^(2)=95%,P<0.0001]、改善心电图疗效[RR=1.29,95%C(I1.20,1.38),I^(2)=0%,P<0.00001]、缩短心绞痛持续时间[SMD=-2.31,95%CI(-2.65,-1.97),I^(2)=94%,P<0.0001]方面,疗效更显著,且心绞痛不同类型的亚组分析提示稳心颗粒联合西医常规治疗组疗效优于对照组;稳心颗粒联合西医常规治疗不稳定型心绞痛(UAP)的不良事件发生率更低[RR=0.77,95%CI(0.62,0.97),I^(2)=0%,P=0.02],对于稳定型心绞痛(SAP),不良反应发生率降低不明显,无明显统计学差异[RR=0.50,95%CI(0.10,2.62),P=0.41]。经漏斗图及egger检验,提示心绞痛发作次数、心电图疗效及不良反应发生率不存在发表偏倚,心绞痛持续时间存在发表偏倚。GRADE系统评估心电图疗效、不良事件发生率为中等质量证据,心绞痛发作次数为低质量证据,心绞痛持续时间为极低质量证据。结论稳心颗粒联合西医常规治疗AP的疗效优于单用西医常规治疗,治疗UAP的不良反应发生率较单用西医常规治疗少。展开更多
文摘This paper reports on a study of active vibration control of functionally graded beams with upper and lower surface-bonded piezoelectric layers. The model is based on higher-order shear deformation theory and implemented using the finite element method （FEM）. The proprieties of the functionally graded beam （FGB） are graded along the thickness direction. The piezoelectric actuator provides a damping effect on the FGB by means of a velocity feedback control algorithm. A Matlab program has been developed for the FGB model and compared with ANSYS APDL. Using Newmark＇s method numerical solutions are obtained for the dynamic equations of FGB with piezoelectric layers. Numerical results show the effects of the constituent volume fraction and the influence the feedback control gain on the frequency and dynamic response of FGBs.
文摘The nonlinear dynamic model of spinning ballistic missiles is established during the first boosting phase of the missile. Based on the conventional backstepping sliding mode control and the assumption of a two time-scale separation of missile dynamics, a graded sliding mode controller is designed with two sub-sliding surfaces which have invariability to external disturbances and parameter perturbations, and a matrix which comprises three first order low pass filters is introduced to prevent “explosion of terms”. Owing to the upper bounds of the uncertainties are difficult to obtain in advance, adaptive laws are introduced to estimate the values of the uncertainties in real-time. Eventually, the numerical simulation results given to show the proposed controller can ensure the steady flight of missiles.
