In order to forecast the distribution of crest amplitudes and the occurrence of freak waves in a short crested coastal sea,a novel transformed linear simulation method is initially proposed in this paper.A Hermite tra...In order to forecast the distribution of crest amplitudes and the occurrence of freak waves in a short crested coastal sea,a novel transformed linear simulation method is initially proposed in this paper.A Hermite transformation model expressed as a monotonic cubic polynomial serves as the foundation for the novel simulation technique.The wave crest amplitude exceedance probabilities of two sea states-one with a directional wave spectrum based on the measured wave elevation data at the Yura coast and the other with a typical directional JONSWAP wave spectrum-have been predicted using the novel simulation method that has been proposed.The likelihood that a particular critical wave crest amplitude will be exceeded is directly correlated with the probability that freak waves will occur.It is shown that the novel simulation approach suggested can provide predictions that are more precise than those obtained from the Rayleigh crest amplitude distribution model,the Jahns and Wheeler crest amplitude distribution model,or the conventional linear simulation method.This study also demonstrated that the nonlinear simulation method is less effective than the novel simulation method in terms of efficiency.展开更多
VOF （volume of fluid） method has been used to make the numerical simulation of freak wave come true. The comparisons between the numerical results and linear theoretical results corresponding to Eq.（5） have been c...VOF （volume of fluid） method has been used to make the numerical simulation of freak wave come true. The comparisons between the numerical results and linear theoretical results corresponding to Eq.（5） have been carried out to show that the numerical results have a better exhibition of nonlinear characteristics. Wavelet analysis method has been adopted to investigate the time-frequency energy spectrum of simulation freak waves and the results reveal strong nonlinear interaction enables energy to be transferred to high harmonics during the progress of its formation. Varying water depth can enhance the nonlinear interaction, making much more energy be transferred to high harmonics and freak waves with higher asymmetry be generated.展开更多
由于FREAK算法存在不具备尺度不变性的缺陷,特征点匹配策略单一容易出现匹配效果不理想的问题,鉴于SIFT和RANSAC算法思想,本文提出一种改进的FREAK算法:SFREAK(SIFT and FREAK).首先,生成高斯差分金字塔图像,使检测出来的特征点具有尺...由于FREAK算法存在不具备尺度不变性的缺陷,特征点匹配策略单一容易出现匹配效果不理想的问题,鉴于SIFT和RANSAC算法思想,本文提出一种改进的FREAK算法:SFREAK(SIFT and FREAK).首先,生成高斯差分金字塔图像,使检测出来的特征点具有尺度不变性;然后采用FREAK描述符对特征点进行描述,获得二进制描述子;最后,在特征点匹配过程中通过Hamming距离匹配进行粗匹配,并结合RANSAC算法对匹配点对进行提纯,实现两幅图像的特征点匹配.实验结果表明,本文提出的改进算法有效解决了FREAK不具备尺度不变性的缺陷,在图像发生尺度变化时,SFREAK算法特征点匹配准确率达到95.7%,相比于FREAK提高了61.9%.另外,本文改进的算法与传统SIFT、FREAK算法相比,表现出更好的鲁棒性.展开更多
基金financially supported by the Chinese State Key Laboratory of Ocean Engineering(Grant No.GKZD010068/084).
文摘In order to forecast the distribution of crest amplitudes and the occurrence of freak waves in a short crested coastal sea,a novel transformed linear simulation method is initially proposed in this paper.A Hermite transformation model expressed as a monotonic cubic polynomial serves as the foundation for the novel simulation technique.The wave crest amplitude exceedance probabilities of two sea states-one with a directional wave spectrum based on the measured wave elevation data at the Yura coast and the other with a typical directional JONSWAP wave spectrum-have been predicted using the novel simulation method that has been proposed.The likelihood that a particular critical wave crest amplitude will be exceeded is directly correlated with the probability that freak waves will occur.It is shown that the novel simulation approach suggested can provide predictions that are more precise than those obtained from the Rayleigh crest amplitude distribution model,the Jahns and Wheeler crest amplitude distribution model,or the conventional linear simulation method.This study also demonstrated that the nonlinear simulation method is less effective than the novel simulation method in terms of efficiency.
文摘VOF （volume of fluid） method has been used to make the numerical simulation of freak wave come true. The comparisons between the numerical results and linear theoretical results corresponding to Eq.（5） have been carried out to show that the numerical results have a better exhibition of nonlinear characteristics. Wavelet analysis method has been adopted to investigate the time-frequency energy spectrum of simulation freak waves and the results reveal strong nonlinear interaction enables energy to be transferred to high harmonics during the progress of its formation. Varying water depth can enhance the nonlinear interaction, making much more energy be transferred to high harmonics and freak waves with higher asymmetry be generated.
文摘由于FREAK算法存在不具备尺度不变性的缺陷,特征点匹配策略单一容易出现匹配效果不理想的问题,鉴于SIFT和RANSAC算法思想,本文提出一种改进的FREAK算法:SFREAK(SIFT and FREAK).首先,生成高斯差分金字塔图像,使检测出来的特征点具有尺度不变性;然后采用FREAK描述符对特征点进行描述,获得二进制描述子;最后,在特征点匹配过程中通过Hamming距离匹配进行粗匹配,并结合RANSAC算法对匹配点对进行提纯,实现两幅图像的特征点匹配.实验结果表明,本文提出的改进算法有效解决了FREAK不具备尺度不变性的缺陷,在图像发生尺度变化时,SFREAK算法特征点匹配准确率达到95.7%,相比于FREAK提高了61.9%.另外,本文改进的算法与传统SIFT、FREAK算法相比,表现出更好的鲁棒性.
