Water-filled low-resistance optical fairing for unmanned underwater vehicles

With the increasing demand for navigation, obstacle avoidance and exploration, optical cameras are increasingly installed on unmanned underwater vehicles(UUVs). In order to meet the hydrodynamic performance requirements of UUVs, optical camera needs to be equipped inside optical fairing. However, traditional optical fairing can make optical cameras defocus and distortion, due to the difference in refractive index inside and outside the optical fairing. One of the common solutions is to replace the fairing with optical flat panel, but it will increase water resistance of UUV and affect the hydrodynamic performance. Another solution is to choose an optical camera that matches the additional focal length brought by the curvature of optical fairing, so that the optical fairing becomes a part of the camera lens. But the position of optical camera and optical fairing must be set strictly and precisely. Therefore, it is impossible to flexibly change camera, lens, optical fairing, and their positions. In this paper, a novel underwater low-resistance optical fairing is proposed. The shape of optical fairing is designed streamlined to reduce water resistance, and the water-filled structure eliminates the defocus and distortion effects caused by refractive index difference. Numerical simulations are performed to analyze the aberration and distortion caused by optical fairing. Comparison experiments of the proposed optical fairing and traditional optical fairing are performed. It is shown that the proposed fairing is simple in structure and flexible in implementation, which can enable clear imaging of optical cameras, and can be easily installed to achieve better hydrodynamic performance of UUVs.