Simulation and Measurements of Small Arms Blast Wave Overpressure in the Process of Designing a Silencer
Abstract Simulation and measurements of muzzle blast overpressure and its physical manifestations are studied in this paper. The use of a silencer can have a great influence on the overpressure intensity. A silencer is regarded as an acoustic transducer and a waveguide. Wave equations for an acoustic dotted source of directed effect are used for physical interpretation of overpressure as an acoustic phenomenon. Decomposition approach has proven to be suitable to describe the formation of the output wave of the wave transducer. Electroacoustic analogies are used for simulations. A measurement chain was used to compare the simulation results with the experimental ones.
Dependence of Free-Field Impulse on the Decay Time of Energy Efflux for a Jet Flow.
Abstract : Until now, the peak energy efflux at the jet exit was considered the significant parameter in a scaling approach to estimate the peak overpressure, time of arrival, and positive phase duration from guns and shock tubes. The resulting predictions for the peak overpressure, time of arrival were satisfactory but the positive phase duration prediction was poor. This predicted value of the positive phase duration is used with the peak overpressue prediction to obtain an estimate of an important quantity: the impulse. Here we investigate the characteristic exhaust decay time for the energy efflux at the jet exit as a possible additional significant parameter that might be used to improve predictions for the impulse. Numerical simulation was used to establish that the impulse value depends upon this parameter. Comparison between simulation and experiment is satisfactory. This additional parameter wa sused to correlate the available impulse data. It was determined that the additional parameter significantly improves the prediction capability of the scaling method for predicting impulse. An idealized wave form together with the predicted peak overpressure can be used to obtain an estimate of the positive phase duration. This approach yields less satisfactory agreement with the duration data but this fact is relatively unimportant since the impulse is the quantity of importance. Keywords: Gun muzzle blast; Shock waves; Blast wave scaling; Dimensional analysis.
Wavelet Denoising for Multi-lead High Resolution ECG Signals
The aim of this study was to investigate the application of wavelet denoising in noise reduction of multichannel high resolution ECG signals. In particular, the influence of the selection of wavelet function and the choice of decomposition level on efficiency of denoising process were considered and whole procedures of noise reduction were implemented in MatLab environment. The Fast Wavelet Transform was use. The advantage of used denoising method is noise level decreasing in ECG signals, in which noise reduction by averaging has limited application, i.e. in case of arrhythmia, or in presence of extrasystols.