Diving control of underactuated unmanned undersea vehicle using integral-fast terminal sliding mode control

The problem of diving control for an underactuated unmanned undersea vehicle(UUV) considering the presence of parameters perturbations and wave disturbances was addressesed.The vertical motion of an UUV was divided into two noninteracting subsystems for surge velocity control and diving.To stabilize the vertical motion system,the surge velocity and the depth control controllers were proposed using backstepping technology and an integral-fast terminal sliding mode control(IFTSMC).It is proven that the proposed control scheme can guarantee that all the error signals in the whole closed-loop system globally converge to the sliding surface in finite time and asymptotically converge to the origin along the sliding surface.With a unified control parameters for different motion states,a series of numerical simulation results illustrate the effectiveness of the above designed control scheme,which also shows strong robustness against parameters perturbations and wave disturbances.

Ignition models and simulation of solid propellant of thermodynamic undersea vehicle

The starting characteristics of thermodynamic undersea vehicle systems are determined by the geometry, size and combustion area of solid propellants, which directly effect liquid propellant pipeline design. It is necessary to establish accurate burning models for solid propellants. Based on combustion models using powder rings and two different solid ignition grains, namely star-shaped ignition grains and stuffed ignition grains, a mathematic model of the ignition process of the propulsion system was built. With the help of Matlab, a series of calculations were made to determine the effects of different grains on ignition characteristics. The results show that stuffed ignition grain is best suited to be the ignition grain of a thermodynamic undersea vehicle system.

A simulation method on target strength and circular SAS imaging of Xrudder UUV including multiple acoustic scattering

Target strength(TS)and circular synthetic aperture sonar(CSAS)images provide essential information for active acoustic detection and recognition of non-cooperative unmanned undersea vehicles(UUVs),which pose a significant threat to underwater preset facilities.To access them,we propose an iterative physical acoustics(IPA)-based method to simulate the multiple acoustic scattered fields on rigid surfaces in high-frequency cases.It uses the Helmholtz integral equation with an appropriate Green's function in terms of the Neumann series,and then incorporates the ideas of triangulation and iteration into a numerical implementation.Then two approximate analytic formulae with precise physical meanings are derived to predict the TS and CSAS images of concave targets,respectively.There are no restrictions on the surface's curvature and the order of multiple scattering.The method is validated against the finite element method(FEM)for acoustic scattering from a sphere segment and against an experiment involving an X-rudder UUV's stern.On this basis,we simulate and analyze the TS and CSAS images of an X-rudder UUV.In addition,the influence of the angle of adjacent rudders on the multiple scattering characteristics is discussed.Results show that this method can potentially predict accurate UUV features,especially the multiple scattered features.

Determination of Horizontal Motion through Optical Flow Computations

For intelligent / antonomous subsea vehicles, reliable short-range horizontal positioning is difficult to achieve, particularly over flat bottom topography.A potential solution proposed in this paper utilizes a passive optical sensing method to estimate the vehicle displacement using the bottom surface texture.The suggested optical flow method does not require any feature correspondeuces in images and it is robust in allowing brightness changes between image frames. Fundamentallyt this method is similar to correlation methods attempting to match images and compute the motion disparity. However, in correlation methods, searching a neighbor region blindly for best match is lengthy. Main contributions of this paper come from the analysis showing that optical flow computation based on the general model cannot avoid errors except for null motion although the sign of optical flow keeps correct, and from the development of an iterative shifting method based on the error characteristics to accurately determine motions. Advantages of the proposed method are verified by real image experiments.