Analyzing the characteristics of the wave field caused by ships sailing on water is of great significance in the fields of ship engineering, hydrodynamics, and marine environmental protection. This study simulates the...
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Analyzing the characteristics of the wave field caused by ships sailing on water is of great significance in the fields of ship engineering, hydrodynamics, and marine environmental protection. This study simulates the ship wave field of the hull with different speeds in still water and conducts the comparisons between numerical simulations and experimental results. Then a feature capture method based on intelligent search algorithm is developed to extract the environmental field characteristics of ship waves, including the total longitudinal length, peak-trough position, corresponding wave height value, spacing between peaks and troughs, tangent angle at peak-trough position, and ship wave contour angle. Our method can provide good accuracy in feature capture in both symmetric and asymmetric ship wave environmental fields. This work provides technical support for the research on understanding the regularity of ship motion and implanting characteristic parameters into visual software to achieve realistic reconstruction of ship wave environment fields. The extraction technology of this work lays the foundation for extracting environmental field features of two or more ships interacting with each other.
This study addressed the problems of difficult parameter selection of ground point filtering algorithm, slow speed, and susceptibility to wrong classification points of the traditional interpolation algorithm in extra...
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This study addressed the problems of difficult parameter selection of ground point filtering algorithm, slow speed, and susceptibility to wrong classification points of the traditional interpolation algorithm in extracting canopy height model from dense point cloud produced by structure from motion. Finding the true ground is vital for canopy height estimation using unmanned aerial vehicle red, green, and blue point cloud, especially for semiarid area where cloud points of short vegetation like shrubs and dwarf trees generally mixed up with the ground points. This article proposes a ground point extraction strategy that combines the advantages of structural and spectral filtering. Specifically, spectral filtering simplifies the threshold selection for structural filtering, whereas structural filtering removes the outliers from spectral filtering. Considering the misclassified points in the ground filtering algorithm, a fast, nonparametric ground point interpolation algorithm was used to suppress the wrong classification points. This novel algorithm is based on the basic idea of least square quadratic fitting and prediction of terrain profile (PF). The quantitative results show that compared to inverse distance weighting (IDW), radial basis function (RBF), and ordinary kriging (OK), it takes less time (PF: 122 s, IDW: 518 s, RBF: 1374 s, OK: 1129 s), and has lower RMSE (PF: 0.301 m, IDW: 0.549 m, RBF: 0.903 m, OK: 0.427 m).
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