Nonlinear Response and Fatigue Estimation of Surface Panels to White and Non-White Gaussian Random Excitations

In stochastic structural dynamics, the majority of analyses have dealt with linear structures under stationary, Gaussian, and band-limited white noise excitations. Although these simplifying assumptions may be justified, in many processes experimental data have shown quite frequently the non-stationary and non-Gaussian characteristics of the loads. An efficient finite element modal formulation has recently been developed to extend the analysis to nonlinear structural responses. Laminated plate theory and von Karman large displacement relations are used to derive the nonlinear equations of motion for an arbitrarily laminated composite panel subjected to combined acoustic and thermal loads. The nonlinear equations of motion in structural node degrees of freedom are then transformed to a set of coupled nonlinear equations in truncated modal coordinates with rather small degrees of freedom. Recorded B-1B flight acoustic pressure fluctuations have shown the non-white power spectral density (PSD) characteristics. This work presents for the first time the nonlinear large amplitude response and fatigue life estimation of arbitrary laminated composite panels subjected to non-white pressure fluctuations with or without a high thermal environment. The Palmgrem-Miner theory is combined with the rainflow counting cycles method in time domain, and with transformed Gaussian models in the frequency domain, to estimate the panel fatigue life. Equivalent band-limited White Noise Sound Pressure Level excitations (EWSPL), which have the same acoustic power within the bandwidth as the B-1B flight data, are generated. Nonlinear response and fatigue life are predicted for the identical panels subjected to EWSPL. Monte Carlo numerical simulation is used for the analysis of the EWSPL. Results show that the flight data with non-white PSD give higher stress characteristics and shorter fatigue life than the corresponding EWSPL

Comparison of Fatigue Life Estimation Using Equivalent Linearization and Time Domain Simulation Methods

The Monte Carlo simulation method in conjunction with the finite element large deflection modal formulation are used to estimate fatigue life of aircraft panels subjected to stationary Gaussian band-limited white-noise excitations. Ten loading cases varying from 106 dB to 160 dB OASPL with bandwidth 1024 Hz are considered. For each load case, response statistics are obtained from an ensemble of 10 response time histories. The finite element nonlinear modal procedure yields time histories, probability density functions (PDF), power spectral densities and higher statistical moments of the maximum deflection and stress/strain. The method of moments of PSD with Dirlik's approach is employed to estimate the panel fatigue life

Study of the formation of ammonia during the purge of a lean NOx Trap

Communication orale par A. KouakouInternational audienc

Hybrid control system for spacecraft antenna boom

Sensitive equipment utilized in aerospace applications experience vibrations from mechanical and thermal disturbances. Without proper vibration suppression systems, the delicate equipment can be severely damaged. A comparison between passive, active and hybrid control of light weight boom structure for space vehicles is carried out. Numerical and experimental analyses using NASTRAN finite element software are performed. Different control methods are applied, and a PID controller is implemented in the experiment. The main target of this research is to study the dynamic response of sensitive and light spacecraft structure like a boom antenna. In this experiment, the source of vibration disturbance is the force applied to one end of the structure and the response signal is captured by an accelerometer sensor at the free end of the beam. Piezoelectric Translator (PTS30 nanopositioning stage) (which is a linear actuator suitable for static and dynamic applications) is used for the reducing the vibration characteristics and thus damping out the vibrations. The maximum displacement provided by this actuator is +/- 15 mm and they provide pushing or pulling force of up to 30 N. The linear speed range of the PTS30 is 0 to 500 micrometer per second. The input to the actuator is provided by the accelerometer sensor through a power amplifier which is connected through a computer. The measured acceleration is integrated to obtain the corresponding velocities. Effectiveness of the control system highly depends on the position of the actuators. The average energy level taken over a frequency bandwidth of 4 Hz to 8 Hz will be considered as a parameter to be minimized. This research focuses on the reduction of vibration behavior of satellite boom structures over a wide frequency bandwidth using hybrid vibration control system. Here we present the results of damping effectiveness for different excitation amplitudes. Copyright © 2010 by ASME

How emergency departments might alert for prehospital heat-related excess mortality?

INTRODUCTION: A major issue raised by the public health consequences of a heat wave is the difficulty of detecting its direct consequences on patient outcome, particularly because of the delay in obtaining definitive mortality results. Since emergency department (ED) activity reflects the global increase of patients' health problems during this period, the profile of patients referred to EDs might be a basis to detect an excess mortality in the catchment area. Our objective was to develop a real-time surveillance model based on ED data to detect excessive heat-related mortality as early as possible. METHODS: A day-to-day composite indicator was built using simple and easily obtainable variables related to patients referred to the ED during the 2003 heat-wave period. The design involved a derivation and validation study based on a real-time surveillance system of two EDs at Cochin Hospital and H?-Dieu Hospital, Paris, France. The participants were 99,976 adult patients registered from 1 May to 30 September during 2001, 2002 and 2003. Among these participants, 3,297, 3,580 and 3,851 patients were referred to the EDs from 3 August to 19 August for 2001, 2002 and 2003, respectively. Variables retained for the indicator were selected using the receiver operating characteristic curve methodology and polynomial regression. RESULTS: The indicator was composed of only three variables: the percentage of patients older than 70 years, the percentage of patients with body temperature above 39 degrees C, and the percentage of patients admitted to or who died in the ED. The curve of the indicator with time appropriately fitted the overall mortality that occurred in the region of interest. CONCLUSION: A composite and simple index based on real-time surveillance was developed according to the profile of patients who visited the ED. It appeared suitable for determining the overall mortality in the corresponding region submitted to the 2003 heat wave. This index should help early warning of excessive mortality and monitoring the efficacy of public health interventions

Recombinant tissue factor pathway inhibitor in severe community-acquired pneumonia : a randomized trial.

RATIONALE: Severe community-acquired pneumonia (sCAP) is a leading cause of death worldwide. Adjunctive therapies for sCAP are needed to further improve outcome. A systemic inhibitor of coagulation, tifacogin (recombinant human tissue factor pathway inhibitor) seemed to provide mortality benefit in the sCAP subgroup of a previous sepsis trial. OBJECTIVES: Evaluate the impact of adjunctive tifacogin on mortality in patients with sCAP. METHODS: A multicenter, randomized, placebo-controlled, double-blind, three-arm study was conducted from July 2005 to June 2008 at 188 centers in North and South America, Europe, South Africa, Asia, Australia, and New Zealand. Adults with sCAP were randomized to receive a continuous intravenous infusion of tifacogin 0.025 mg/kg/h, tifacogin 0.075 mg/kg/h, or matching placebo over 96 hours. MEASUREMENTS AND MAIN RESULTS: Severity-adjusted 28-day all-cause mortality. Of 2,138 randomized patients, 946, 238, and 918 received tifacogin 0.025 mg/kg/h, tifacogin 0.075 mg/kg/h, and placebo, respectively. Tifacogin 0.075 mg/kg/h was discontinued after the first interim analysis according to prespecified futility criterion. The 28-day all-cause mortality rates were similar between the 0.025 mg/kg/h (18%) and placebo groups (17.9%) (P = 0.56). Greater reduction in prothrombin fragment 1+2 and thrombin antithrombin complexes levels relative to baseline throughout the first 96 hours was found with tifacogin 0.025 mg/kg/h than with placebo. The incidence of adverse events and serious adverse events were comparable between the tifacogin 0.025 mg/kg/h and placebo groups. CONCLUSIONS: Tifacogin showed no mortality benefit in patients with sCAP despite evidence of biologic activity

Drotrecogin alfa (Activated) in adults with septic shock

There have been conflicting reports on the efficacy of recombinant human activated protein C, or drotrecogin alfa (activated) (DrotAA), for the treatment of patients with septic shock.In this randomized, double-blind, placebo-controlled, multicenter trial, we assigned 1697 patients with infection, systemic inflammation, and shock who were receiving fluids and vasopressors above a threshold dose for 4 hours to receive either DrotAA (at a dose of 24 μg per kilogram of body weight per hour) or placebo for 96 hours. The primary outcome was death from any cause 28 days after randomization.At 28 days, 223 of 846 patients (26.4%) in the DrotAA group and 202 of 834 (24.2%) in the placebo group had died (relative risk in the DrotAA group, 1.09; 95% confidence interval [CI], 0.92 to 1.28; P=0.31). At 90 days, 287 of 842 patients (34.1%) in the DrotAA group and 269 of 822 (32.7%) in the placebo group had died (relative risk, 1.04; 95% CI, 0.90 to 1.19; P=0.56). Among patients with severe protein C deficiency at baseline, 98 of 342 (28.7%) in the DrotAA group had died at 28 days, as compared with 102 of 331 (30.8%) in the placebo group (risk ratio, 0.93; 95% CI, 0.74 to 1.17; P=0.54). Similarly, rates of death at 28 and 90 days were not significantly different in other predefined subgroups, including patients at increased risk for death. Serious bleeding during the treatment period occurred in 10 patients in the DrotAA group and 8 in the placebo group (P=0.81).DrotAA did not significantly reduce mortality at 28 or 90 days, as compared with placebo, in patients with septic shock. (Funded by Eli Lilly; PROWESS-SHOCK ClinicalTrials.gov number, NCT00604214.)