High frequency signal amplitude fluctuations in shallow water

2007 ◽  
Vol 121 (5) ◽  
pp. 3040-3040 ◽  
Author(s):  
Nicholas P. Chotiros ◽  
Marcia J. Isakson ◽  
James N. Piper ◽  
Mario Zampolli
Keyword(s):  
Shallow Water ◽  
High Frequency ◽  
Signal Amplitude ◽  
Frequency Signal ◽  
High Frequency Signal ◽  
Amplitude Fluctuations

scholarly journals Результаты экспериментальных исследований по обнаружению пловцов при развитой структуре интерференционного гидроакустического поля в прибрежной акватории берегового клина

2020 ◽  
Author(s):  
R.V. Viktorov ◽  
A.O. Lipovetskiy
Keyword(s):  
High Frequency ◽  
Experimental Studies ◽  
Water Area ◽  
Frequency Signal ◽  
High Frequency Signal ◽  
Amplitude Fluctuations ◽  
Adaptive Compensator ◽  
Underwater Object ◽  
Interference Canceller ◽  
Principal Possibility

В статье показано, что прилегающая к особо важным объектам акватория берегового клина, остается не освещенной, и при подсветке высокочастотным сигналом, в ней формируется интерференционное гидроакустическое поле, в котором можно регистрировать движущихся пловцов. Рассматривается механизм возникновения амплитудной модуляции при отражении гидроакустического сигнала от взволнованной морской поверхности. Приведены результаты компьютерного моделирования, а также лабораторных исследований, показывающие принципиальную возможность выделения на приемном устройстве амплитудных флуктуаций, вызванных движением подводного объекта в созданном интерференционном поле. Представлена модель адаптивного компенсатора помех, а также приведены результаты натурных экспериментальных исследований, которые показывают, что предлагаемый компенсатор позволяет подавить помеху, вызванную отражением высокочастотного сигнала от взволнованной поверхности на приемном устройстве и выделить амплитудные флуктуации, вызванные движением пловца. Показана эффективность снижения среднеквадратической ошибки помехи на измерительном приемном устройстве после адаптивного компенсатора, а также предложена схема обнаружителя движущегося подводного объекта.The article shows that the water area of the coastal wedge adjacent to particularly important objects remains unlit, and when illuminated by a high-frequency signal, an interference hydroacoustic field is formed in it, in which moving swimmers can be registered. The mechanism of occurrence of amplitude modulation at reflection of a hydroacoustic signal from the agitated sea surface is considered. The results of computer simulation and laboratory studies are presented, showing the principal possibility of isolation on the receiving device amplitude fluctuations caused by the movement of an underwater object in the created interference field. The model of adaptive interference canceller and the results of field experimental studies, which show that the proposed compensator can suppress interference caused by reflection of high-frequency signal from the rough surface on the receiving device and to allocate the amplitude fluctuations caused by the movement of the swimmer. The efficiency of reducing the RMS error of interference on the measuring receiver after the adaptive compensator is shown, and the scheme of the detector of a moving underwater object is proposed.

Optimum Vibrational Resonance in a Time-Delay Bistable System Driven by Biharmonic Signals

2014 ◽  
Vol 651-653 ◽  
pp. 2172-2176
Author(s):  
Yun Liang Meng ◽  
Chang Xing Pei ◽  
Dong Wu Li
Keyword(s):  
Time Delay ◽  
High Frequency ◽  
Low Frequency ◽  
Signal Amplitude ◽  
Resonance Peak ◽  
Response Amplitude ◽  
Bistable System ◽  
Vibrational Resonance ◽  
Frequency Signal ◽  
High Frequency Signal

The optimum vibrational resonance in a time-delay bistable system driven by bihiarmonic signals is discussed in this paper. The theoretically expression for the response amplitude gain of low frequency signal in the time-delay bistable system is deduced, and the effects of time delay parameter on the optimum vibrational resonance peak and the required amplitude of high frequency signal are investigated. It is shown that the optimum vibrational resonance can be achieved by adjusting the high frequency signal amplitude and time delay parameter jointly. Meanwhile, the optimum vibrational resonance appeared periodically with time delay parameter and the period is equal to the period of low-frequency signal. The amplitude of high-frequency signal required for the optimum vibrational resonance can be fixed or varied with different time delay parameter depending on the ratio of the frequencies between biharmonic signals.

Dither in a rolling airframe flight vehicle with a two-position actuator: An amplitude distribution approach

2016 ◽  
Vol 39 (8) ◽  
pp. 1205-1215 ◽  
Author(s):  
Bahram Mohammadi ◽  
Mohammad Reza Arvan ◽  
Yousof Koohmaskan
Keyword(s):  
High Frequency ◽  
Degrees Of Freedom ◽  
Coupling Effect ◽  
Cross Coupling ◽  
Amplitude Distribution ◽  
Feedback System ◽  
Flight Vehicle ◽  
Frequency Signal ◽  
High Frequency Signal ◽  
Minimal Error

Rolling airframe manoeuvring is a type of manoeuvre in which the missile provides continuous roll during flight. Cross-coupling between the angle of attack and sideslip in rolling airframe missiles (RAMs) yields a coning motion around the flight path. As the pitch and yaw cross-coupling effect decreases, the radius of this coning motion decreases and the accuracy of the control system increases. Two-position (on–off) actuators are used in most RAMs. The presence of a two-position actuator in a feedback system makes its characteristics non-linear. A high-frequency signal so-called dither is applied to compensate for the non-linearity effect of the actuator characteristic in the feedback system and to stabilize the coning motion. The amplitude distribution function (ADF) method in dither analysis shows that the smoothed non-linearity characteristic can be computed as the convolution of the original non-linearity and the ADF of the dither signal. According to the four-degrees-of-freedom (4-DOF) equations of RAMs in a non-rolling frame and regarding various dither signals through the ADF approach on a two-position actuator, an analytical condition for dither amplitude in coning motion stability of RAMs is derived. It was shown that the triangular signal with specified amplitude and high enough frequency led to a smoother response of two-position actuators. Finally, by applying beam-riding guidance to a RAM, the performance of dithers for decreasing the distance of the missile from the centre of the beam is validated through simulations. It is illustrated that applying the triangular dither resulted in minimal error.

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