ABSTRACT
Disk springs are widely used as preload and isolation due to their unique mechanical properties. In the prior research, the effect of linear friction on the disk spring was considered, but contact stiffness, another nonlinear contact factor, is ignored. Accordingly, in this paper, the asymmetric displacements of the contact edges are first derived, and the accurate friction dissipations are obtained, as a way to evaluate the effect of friction on the system. Then the velocity of the edges was obtained to establish a dynamic friction model. Meanwhile, the contact displacement and contact stiffness of the edge are obtained by fractal contact theory. Then the nonlinear static and dynamic models of disk spring with friction and contact stiffness are established by the energy method. The load-deflection relationship, stiffness, and hysteresis of disk spring are studied with different contact states. The results show that the model considering contact stiffness and asymmetric friction dissipation can effectively evaluate the static properties of the disk spring. Friction reinforces the nonlinear behavior of the system, while contact stiffness weakens the nonlinearity of the system. And due to the influence of nonlinear contact factors, the transmissibility curves produce multiple resonance peaks.
ABSTRACT
According to the working characteristics of a 1.5 MW wind turbine planetary gear system under complex and random wind load, a two-parameter Weibull distribution model is used to describe the distribution of random wind speed, and the time-varying load caused by random wind speed is obtained. The nonlinear dynamic model of planetary gear transmission system is established by using the lumped parameter method, and the relative relations among various components are derived by using Lagrange method. Then, the relative relationship between the components is solved by Runge Kutta method. Considering the influence of random load and stiffness ratio on the planetary gear transmission system, the nonlinear dynamic response of cyclic load and random wind load on the transmission system is analyzed. The analysis results show that the variation of the stiffness ratio makes the planetary gear have abundant nonlinear dynamics behavior and the planetary gear can get rid of chaos and enter into stable periodic motion by changing the stiffness ratio properly on the premise of ensuring transmission efficiency. For the variable pitch wind turbine, the random change of external load increases the instability of the system.
ABSTRACT
BACKGROUND AND OBJECTIVES: Administration of a loading dose of a statin (HMG-CoA reductase inhibitor) prior to percutaneous coronary intervention (PCI) contributes to protection from myocardial ischemic-reperfusion injury. This trial was designed to investigate the effect and mechanism of loading-dose rosuvastatin therapy before PCI in patients with acute coronary syndrome. METHODS: One hundred and forty-three patients with acute coronary syndrome were randomized to either the loading-dose (rosuvastatin 40 mg given 4 h before PCI) or conventional-dose (rosuvastatin 10 mg given 4 h before PCI) group. Blood samples were collected before and 0, 24, and 72 h post-PCI for measurement of serum cardiac troponin-I (cTn I), creatine kinase-MB (CK-MB), superoxide dismutase (SOD), reactive oxygen species (ROS), and malondialdehyde (MDA). Echocardiography and the major adverse cardiac/cerebrovascular events (MACCE) rate were followed up for 6 months post-PCI. RESULTS: Blood serum CK-MB and cTn I were significantly lower in the loading-dose group than in the conventional-dose group at 24 and 72 h post-PCI [CK-MB: 26.90 ± 3.22 vs. 32.96 ± 2.65 IU/L, P = 0.024; 10.79 ± 4.65 vs. 15.18 ± 5.39 IU/L, P = 0.021. cTn I: 0.046 ± 0.007 vs. 0.055 ± 0.002 ng/mL, P = 0.015; 0.027 ± 0.006 vs. 0.041 ± 0.006 ng/mL, P = 0.026]. Echocardiography at 6 months after PCI revealed significant improvement in cardiac function in the loading-dose group compared with the conventional-dose group (P < 0.05). The MACCE rate at 6 months after PCI in the loading-dose group was lower than in the conventional-dose group (P = 0.0428). The levels of MDA and ROS were decreased and the SOD level was significantly higher in the loading-dose group than in the conventional-dose group at 0, 24, and 72 h post-PCI (P < 0.05). CONCLUSION: Administration of loading-dose rosuvastatin in patients with acute coronary syndrome prior to PCI exerts myocardial protection by inhibition of oxidative stress.