This paper addresses the extremal problem of the null subcarriers based Doppler scale estimation in underwater acoustic （UWA） orthogonal frequency division multiplexing （OFDM） communication. The cost function cons...This paper addresses the extremal problem of the null subcarriers based Doppler scale estimation in underwater acoustic （UWA） orthogonal frequency division multiplexing （OFDM） communication. The cost function constructed of the total energy of null subcarriers through discrete Fourier transform （DFT） is proposed. The frequencies of null subcarriers are identified from non-uniform Doppler shift at each tentative scaling factor. Then it is proved that the cost function can be fitted as a quadratic polynomial near the global minimum. An accurate Doppler scale estimation is achieved by the location of the global scarifying precision and increasing the computation minimum through polynomial interpolation, without complexity. A shallow water experiment is conducted to demonstrate the performance of the proposed method. Excellent performance results are obtained in ultrawideband UWA channels with a relative bandwidth of 67%, when the transmitter and the receiver are moving at a relative speed of 5 kn, which validates the proposed method.展开更多
Based on the three-term decomposition model for turbulent flows, the fundamental equations for quasi-periodic motions are obtained, and the approximate analytical solutions of these second-order nonlinear partial diff...Based on the three-term decomposition model for turbulent flows, the fundamental equations for quasi-periodic motions are obtained, and the approximate analytical solutions of these second-order nonlinear partial differential equations are derived by using the match method. The effects on the mo- mentum, heat and mass transport processes in the wall turbulent flows can be estimated approximately.展开更多
One of the essential techniques for using underwater robots to fish sea cucumbers is that the robots must track sea cucumbers using computer vision technology.Tracking underwater targets is a challenging task due to s...One of the essential techniques for using underwater robots to fish sea cucumbers is that the robots must track sea cucumbers using computer vision technology.Tracking underwater targets is a challenging task due to suspension,water absorption,and light scattering.This study proposed a simple but effective algorithm for sea cucumber tracking based on Kernelized Correlation Filters(KCF)framework.This method tracked the head and tail of the sea cucumber respectively and calculated the scale change according to the distance between the head and tail.The KCF method was improved on three strategies.First of all,the target was searched at the predicted position to improve accuracy.Secondly,an adaptive learning rate updating method based on the detection score of each frame was proposed.Finally,the adaptive size of the histogram of the oriented gradient(HOG)feature was used to balance the accuracy and efficiency.Experimental results showed that the algorithm had good tracking performance.展开更多
基金supported by the National Natural Science Foundation of China(6120109661471137+4 种基金61501061)the Qing Lan Project of Jiangsu Province,the Science and Technology Program of Changzhou City(CJ20130026CE20135060CE20145055)the State Key Laboratory of Ocean Engineering(Shanghai Jiao Tong University)(1316)
文摘This paper addresses the extremal problem of the null subcarriers based Doppler scale estimation in underwater acoustic （UWA） orthogonal frequency division multiplexing （OFDM） communication. The cost function constructed of the total energy of null subcarriers through discrete Fourier transform （DFT） is proposed. The frequencies of null subcarriers are identified from non-uniform Doppler shift at each tentative scaling factor. Then it is proved that the cost function can be fitted as a quadratic polynomial near the global minimum. An accurate Doppler scale estimation is achieved by the location of the global scarifying precision and increasing the computation minimum through polynomial interpolation, without complexity. A shallow water experiment is conducted to demonstrate the performance of the proposed method. Excellent performance results are obtained in ultrawideband UWA channels with a relative bandwidth of 67%, when the transmitter and the receiver are moving at a relative speed of 5 kn, which validates the proposed method.
文摘Based on the three-term decomposition model for turbulent flows, the fundamental equations for quasi-periodic motions are obtained, and the approximate analytical solutions of these second-order nonlinear partial differential equations are derived by using the match method. The effects on the mo- mentum, heat and mass transport processes in the wall turbulent flows can be estimated approximately.
基金This work was financially supported by the Basic Research Project of Higher Education Institutions of Liaoning Province(Grant No.20210126,No.20210135).
文摘One of the essential techniques for using underwater robots to fish sea cucumbers is that the robots must track sea cucumbers using computer vision technology.Tracking underwater targets is a challenging task due to suspension,water absorption,and light scattering.This study proposed a simple but effective algorithm for sea cucumber tracking based on Kernelized Correlation Filters(KCF)framework.This method tracked the head and tail of the sea cucumber respectively and calculated the scale change according to the distance between the head and tail.The KCF method was improved on three strategies.First of all,the target was searched at the predicted position to improve accuracy.Secondly,an adaptive learning rate updating method based on the detection score of each frame was proposed.Finally,the adaptive size of the histogram of the oriented gradient(HOG)feature was used to balance the accuracy and efficiency.Experimental results showed that the algorithm had good tracking performance.
