The multi‐jointed autonomous underwater vehicle (AUV) has higher manoeuvrability and a smaller turning radius in comparison with an AUV with a rigid body. It is able to implement spatially denser sample collection in three‐dimensional space in the deep ocean for scientific expeditions. As conventional positioning approaches, such as ultra‐short‐baseline and long‐baseline, cannot be employed to obtain the coordinates of a multi‐jointed AUV, because they only work with constant baselines, a novel underwater acoustic positioning system with a single beacon and a varied baseline is proposed. The coordinate transformation based on the angles of rotating joints and the geometry of the multi‐jointed AUV is mathematically modelled. Generalised cross‐correlation is applied to measure the time delays of sound signals between the beacon and the hydrophones on the AUV. Numerical simulations and experiments in an anechoic water tank were carried out, and the impacts of parameters on the accuracy of the estimated coordinates of the multi‐jointed AUV are examined. Accuracies of 0.86% in simulation and 0.2 m (at a range of 30 m) in experiments are demonstrated.

In this paper, we study the phenomenon of separation of traveling and standing waves in a one-dimensional rigid-walled circular duct. The underlying mechanism for separation, mode complexity, is linear and introduced here by a damped side branch representing an impedance discontinuity. The left end of the duct is driven at a single frequency by a harmonic acoustic source, and the right end is a rigid termination. The position and impedance of the side branch are independent parameters in the analysis. Sufficient conditions for acoustic wave separation in the duct are derived analytically and employed in a three-dimensional finite element analysis to verify the theoretical result. A physical experiment, consisting of a circular duct with a damped side branch, was constructed based on analytical predictions, the physical parameters were measured or identified, and its performance was documented. These experimental parameters were employed in a second three-dimensional finite element analysis to obtain a direct comparison with experimental results. The comparison reveals the extent to which higher-order (unmodeled) effects degrade the separation phenomenon. It is demonstrated that an intermediate damped side branch used as a nonresonant device can be predictively designed to achieve nearly ideal separation of traveling and standing waves in a rigid-walled circular duct in order to direct and control acoustic energy transmission through the duct system.