Comparison of delay compensation methods for real-time hybrid simulation using frequency-domain evaluation index

The delay compensation method plays an essential role in maintaining the stability and achieving accurate real-time hybrid simulation results. The effectiveness of various compensation methods in different test scenarios, however, needs to be quantitatively evaluated. In this study, four compensation methods （i.e., the polynomial extrapolation, the linear acceleration extrapolation, the inverse compensation and the adaptive inverse compensation） are selected and compared experimentally using a frequency evaluation index （FEI） method. The effectiveness of the FEI method is first verified through comparison with the discrete transfer fimction approach for compensation methods assuming constant delay. Incomparable advantage is further demonstrated for the FEI method when applied to adaptive compensation methods, where the discrete transfer function approach is difficult to implement. Both numerical simulation and laboratory tests with predefined displacements are conducted using sinusoidal signals and random signals as inputs. Findings from numerical simulation and experimental results demonstrate that the FEI method is an efficient and effective approach to compare the performance of different compensation methods, especially for those requiring adaptation of compensation parameters.

Wideband reverberation suppression in beams domain based on angular distribution index

Based on the properties of wideband source’s spatial spread,an algorithm for reverberation suppression in beams domain is proposed.In an effective observation range,a compact bank of receiving spatial beams is operated to transform the data from element domain to beam domain.Angular Distribution Index(ADI) is obtained by comparing to a reference value which is computed by Monte Carlo Integration.ADI decreases with a stronger target echo.Hence,choosing an appropriate threshold of ADI,the target echo can be separated from reverberation by cutting off the high AD components.The filter is compatible with the procedures of beamforming and detection for the current sonar.The computation complexity of the filter is low.The relationships between ADI and frequency,bandwidth,signal-reverberation ratio,are illustrated by a simulation example.The processing results based on the lake-trial and sea-trial data show that reverberation can be significantly suppressed,and threshold choosing for wideband ADI filter is fault tolerant.