Sensitivity study of BARC assembly

This paper will present modal analysis results from a systematic study of the assembly of the Box Assembly with Removable Component (BARC). The paper will present results from testing done with both the cut and un-cut version of the BARC and with the different pieces of the BARC both bolted together and attached with a structural adhesive. The boundary condition will be a fixed base excitation. The results will be presented in terms of both Frequency Response Functions (FRFs) and mode shapes and natural frequencies with a goal of showing how the BARC fixture changes with each assembly modification. Upon completion of this testing it is anticipated that a thorough understanding of how assembly methods change the dynamic response of the fixture. This may lead to a suggested assembly method for anyone testing a BARC fixture

Initial modal results and operating data acquisition of shock/vibration fixture

This paper presents the initial experimental and FEA based modal analysis results obtained on a test assembly developed specifically to study the effects of component boundary conditions and excitation techniques on test damage potential during component qualification testing. This assembly was developed as a platform with a simple “component” and “next assembly” that allows the component to be removed and attached via a fixture to shock or vibration test equipment. All data and results will be made publicly available for other groups wishing to study the test assembly in pursuit of insight into how to define appropriate boundary conditions for component testing

Understanding multi-axis SRS testing results

This paper presents a study done on a round resonant plate fixture used for Shock Response Spectrum (SRS) testing. The goal of this study was to understand the magnitude and character of both on axis and off-axis, with respect to shock input, response of the plate at various locations. The resonant plate was modeled using linear FEA as well as tested experimentally. Tools and approaches based on modal decomposition were developed to understand how the natural frequencies and mode shapes of the structure contribute to the SRS response at a given point and direction on the fixture and/or plate. It is seen that in some instances, the off-axis SRS response can have both a higher amplitude response as well as a different “knee” frequency which can make meeting a designated SRS target very difficult. It is shown that by understanding the modal properties of the plate/fixture assembly, the SRS results can be understood. These results will lead to the capability to predict both the on axis and off-axis SRS response for a given input/output set of locations and eventually the ability to choose the ideal locations to achieve a set of on and off-axis SRS responses to meet a given criteria

Effects of variable thickness circular plates on frequency response functions and shock response spectrum

Resonant plates used for shock testing are typically a constant thickness. Prior research demonstrated that circular plates utilize symmetry to limit the number of contributing modes, although more design control is necessary to achieve target shock response spectra (SRS). Analytical modeling results show that variable thickness plates provide more flexibility to meet a target SRS. The first membrane mode of a circular plate correlates with the knee frequency in the shock response spectrum. Higher order membrane modes can cause the SRS to occur outside of the target band. Concave plates decrease the frequency band between first membrane mode and higher order membrane modes, while convex plates show the opposite effect. Using this theory, resonant plate cross section can be altered to tune resonant plate natural frequencies in order to achieve target SRS

Inverse force estimation for resonant shock plate application

Resonant shock plate testing uses a projectile and programmer material to deliver and tune an impulsive force. Typically, the force level is too high to directly measure with conventional force sensors, so the spectral and temporal characteristics of these forces are not well understood. Non-linear simulations of the projectile, programmer, shock plate, and fixture are currently used to predict the results and design a resonant shock plate. A linear model of the resonant shock plate and fixture could be used if a reasonable representation of the applied force was known. This paper explores the use of inverse force estimation to estimate the spectral content of the force applied from the projectile through the programmer material. The process involves de-convolving the resonant plate response and the impulse response of the resonant plate/fixture system. A spectral representation of the force can be obtained by dividing the linear spectrum of the resonant plate/fixture response and its frequency response function

Results of a multinational study suggest the need for rapid diagnosis and early antiviral treatment at the onset of herpetic meningoencephalitis

Data in the literature regarding the factors that predict unfavorable outcomes in adult herpetic meningoencephalitis (HME) cases are scarce. We conducted a multicenter study in order to provide insights into the predictors of HME outcomes, with special emphasis on the use and timing of antiviral treatment. Samples from 501 patients with molecular confirmation from cerebrospinal fluid were included from 35 referral centers in 10 countries. Four hundred thirty-eight patients were found to be eligible for the analysis. Overall, 232 (52.9%) patients experienced unfavorable outcomes, 44 died, and 188 survived, with sequelae. Age (odds ratio [OR], 1.04; 95% confidence interval [CI], 1.02 to 1.05), Glasgow Coma Scale score (OR, 0.84; 95% CI, 0.77 to 0.93), and symptomatic periods of 2 to 7 days (OR, 1.80; 95% CI, 1.16 to 2.79) and >7 days (OR, 3.75; 95% CI, 1.72 to 8.15) until the commencement of treatment predicted unfavorable outcomes. The outcome in HME patients is related to a combination of therapeutic and host factors. This study suggests that rapid diagnosis and early administration of antiviral treatment in HME patients are keys to a favorable outcome

Managing atypical and typical herpetic central nervous system infections: results of a multinational study

There have been many studies pertaining to the management of herpetic meningoencephalitis (HME), but the majority of them have focussed on virologically unconfirmed cases or included only small sample sizes. We have conducted a multicentre study aimed at providing management strategies for HME. Overall, 501 adult patients with PCR-proven HME were included retrospectively from 35 referral centres in 10 countries; 496 patients were found to be eligible for the analysis. Cerebrospinal fluid (CSF) analysis using a PCR assay yielded herpes simplex virus (HSV)-1 DNA in 351 patients (70.8%), HSV-2 DNA in 83 patients (16.7%) and undefined HSV DNA type in 62 patients (12.5%). A total of 379 patients (76.4%) had at least one of the specified characteristics of encephalitis, and we placed these patients into the encephalitis presentation group. The remaining 117 patients (23.6%) had none of these findings, and these patients were placed in the nonencephalitis presentation group. Abnormalities suggestive of encephalitis were detected in magnetic resonance imaging (MRI) in 83.9% of the patients and in electroencephalography (EEG) in 91.0% of patients in the encephalitis presentation group. In the nonencephalitis presentation group, MRI and EEG data were suggestive of encephalitis in 33.3 and 61.9% of patients, respectively. However, the concomitant use of MRI and EEG indicated encephalitis in 96.3 and 87.5% of the cases with and without encephalitic clinical presentation, respectively. Considering the subtle nature of HME, CSF HSV PCR, EEG and MRI data should be collected for all patients with a central nervous system infection

Managing Atypical and Typical herpetic central nervous system infections: results of A Multinational study

International audienceThere have been many studies pertaining to the management of herpetic meningoencephalitis (HME), but the majority of them have focused on virologically unconfirmed cases or included only small sample sizes. We have conducted a multicentre study aimed at providing management strategies for HME. Overall, 501 adult patients with PCR-proven HME were included retrospectively from 35 referral centres in 10 countries; 496 patients were found to be eligible for the analysis. Cerebrospinal fluid (CSF) analysis using a PCR assay yielded herpes simplex virus (HSV)-1 DNA in 351 patients (70.8%), HSV-2 DNA in 83 patients (16.7%) and undefined HSV-DNA type in 62 patients (12.5%). A total of 379 patients (76.4%) had at least one of the specified characteristics of encephalitis, and we placed these patients into the encephalitis presentation group. The remaining 117 patients (23.6%) had none of these findings, and these patients were placed in the non-encephalitis presentation group. Abnormalities suggestive of encephalitis were detected in magnetic resonance imaging (MRI) in 83.9% of the patients and in electroencephalography (EEG) in 91.0% of patients in the encephalitis presentation group. In the non-encephalitis presentation group, MRI and EEG data were suggestive of encephalitis in 33.3% and 61.9% of patients, respectively. However, the concomitant use of MRI and EEG indicated encephalitis in 96.3% and 87.5% of the cases with and without encephalitic clinical presentation, respectively. CSF HSV-PCR, EEG and MRI data should be collected for all patients with a central nervous system infection considering the subtle nature of HM