Stochastic Dynamics of a Nonlinear Misaligned Rotor System Subject to Random Fluid-Induced Forces

In this paper, stochastic responses and behaviors of a nonlinear rotor system with the fault of uncertain parallel misalignment and under random fluid-induced forces are investigated. First, the equations of motion of the rotor system are derived by taking into account the nonlinear journal bearings, the unsymmetrical section of the shaft, and the displacement constraint between the two adjacent rotors. Then, the modeling on uncertainties of misalignment and random fluid-induced forces are developed based on the polynomial chaos expansion (PCE) technique, where the misalignment is modeled as a bounded random variable with parameter g distribution and the fluid-induced force as a random variable with standard white noise process. Finally, examples on the stochastic dynamic behaviors of the nonlinear generator-rotor system are studied, and the influences of the uncertainties on the effects of shaft misalignment, the stochastic behaviors near bifurcation point as well as the distribution of the system responses are well demonstrated

An Active Nonlinear Controller Emulating a Pendulum-Type Auto-parametric Vibration Absorber

Purpose: In this paper, a nonlinear active vibration control method, which is suitable for the vibration mitigation of both linear and nonlinear structures, is proposed. The main idea of this method is to make the controller emulate a pendulum-type auto-parametric vibration absorber, with the purpose of counteracting the different types of nonlinearity in structures. In this way, the difficulty in the passive realization of the pendulum-type vibration absorber due to the physical unsuitable parameters can also be well released. Methods: The idea of introducing an exosystem in Byrnes–Isidori regulator is borrowed to design the nonlinear controller. The steps to choose the parameters of the controller are introduced. The validity and robustness of the controller for the vibration mitigation of both linear and nonlinear oscillators are investigated by numerical examples of application. Results: The simulation results show that the proposed nonlinear controller can effectively mitigate the vibration not only of linear oscillators, but also of nonlinear oscillators with third-, quintic- and seventh-order nonlinearities. The good robustness of the proposed nonlinear controller is also demonstrated.SCOPUS: ar.jDecretOANoAutActifinfo:eu-repo/semantics/publishe

Active tendon control of suspension bridges: Study on the active cables configuration

In a previous study, thepotential of damping suspensionbridges with active stay cables has been evaluated on a numerical modelof a suspension bridge, and demonstrated experimentally on a laboratory mockup. In this paper, we extend our study to explore two different configurations of the active stay-cables: One classical configuration, corresponding to attaching the active stay-cables between the top of the pylons and the deck(configuration I) and, another configuration, consisting of attaching the stay-cables between the base of the pylonsand the catenary (configuration II). The analysis confirmed thatboth configurations are effective with a slight superiority of the second configuration. The study is conducted numerically and experimentally on a suspensionbridge mock-up, by considering two types of active stay-cables. The experimental results confirmed the numerical predictions, and demonstrated the effectiveness of the second configuration.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Passive damping of suspension bridges using multi-degree of freedom tuned mass dampers

Tuned Mass Dampers (TMDs) are a very popular, economical and robust way of mitigating the dynamic response of civil engineering structures. However, their classical implementation involves as many TMDs as there are critical modes. This paper analyzes a TMD with two degrees of freedom targeted at mitigating simultaneously a bending and a torsion mode of a bridge deck. The system parameters can be tuned independently for the bending and the torsion mode. The study is conducted numerically and experimentally on a laboratory mock-up of a suspension bridge.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

S100A9 aggravates early brain injury after subarachnoid hemorrhage via inducing neuroinflammation and inflammasome activation

Summary: Subarachnoid hemorrhage (SAH) is a stroke subtype with high mortality, and its severity is closely related to the short-term prognosis of SAH patients. S100 calcium-binding protein A9 (S100A9) has been shown to be associated with some neurological diseases. In this study, the concentration of S100A9 in clinical cerebrospinal fluid samples was detected by enzyme-linked immunosorbent assay (ELISA), and the relationship between S100A9 and the prognosis of patients was explored. In addition, WT mice and S100A9 knockout mice were used to establish an in vivo SAH model. Neurological scores, brain water content, and histopathological staining were performed after a specified time. A co-culture model of BV2 and HT22 cells was treated with heme chloride to establish an in vitro SAH model. Our study confirmed that the expression of S100A9 protein in the CSF of SAH patients is increased, and it is related to the short-term prognosis of SAH patients. S100A9 protein is highly expressed in microglia in the central nervous system. S100A9 gene knockout significantly improved neurological function scores and reduced neuronal apoptosis. S100A9 protein can activate TLR4 receptor, promote nuclear transcription of NF-κB, increase the activation of inflammatory body, and ultimately aggravate nerve injury

Smoking, acute mountain sickness and altitude acclimatisation: a cohort study

RATIONALE: The relationship between cigarette smoking and acute mountain sickness (AMS) is not clear. OBJECTIVE: To assess AMS risk and altitude acclimatisation in relation to smoking. METHODS: 200 healthy non-smokers and 182 cigarette smokers were recruited from Han lowland workers. These were men without prior altitude exposure, matched for age, health status and occupation, who were transported to an altitude of 4525 masl. MEASUREMENTS: AMS, smoking habits, arterial saturation (SpO2), haemoglobin (Hb), lung function and mean pulmonary artery pressure (PAPm) were assessed upon arrival and after 3 and 6 months. MAIN RESULTS: Compared with non-smokers, smokers had a lower incidence of AMS and lower AMS scores than non-smokers upon arrival; higher Hb and PAPm associated with lower SpO2 at 3 and 6 months at altitude; and lower forced expiratory volume in 1 s and maximal voluntary ventilation at 3 and 6 months. CONCLUSIONS: Smoking slightly decreases the risk of AMS but impairs long-term altitude acclimatisation and lung function during a prolonged stay at high altitude

Reduced incidence and severity of acute mountain sickness in Qinghai-Tibet railroad construction workers after repeated 7-month exposures despite 5-month low altitude periods

The construction of the Qinghai-Tibet railroad provided a unique opportunity to study the relation between intermittent altitude exposure and acute mountain sickness (AMS). For 5 yr, workers spent 7-month periods at altitude interspaced with 5-month periods at sea level; the incidence, severity, and risk factors of AMS were prospectively investigated. Six hundred lowlanders commuted for 5 yr between near sea level and approximately 4500 m and were compared to 600 other lowland workers, recruited each year upon their first ascent to high altitude as newcomers, and to 200 Tibetan workers native to approximately 4500 m. AMS was assessed with the Lake Louise Scoring System. The incidence and severity of AMS in commuters were lower upon each subsequent exposure, whereas they remained similar in newcomers each year. AMS susceptibility was thus lowered by repeated exposure to altitude. Repeated exposure increased resting Sao(2) and decreased resting heart rate. Tibetans had no AMS, higher Sao(2), and lower heart rates. In conclusion, repetitive 7-month exposures increasingly protect lowlanders against AMS, even when interspaced with 5-month periods spent at low altitude, but do not allow attaining the level of adaptation of altitude natives