Unlike uniform motion, when an object moves underwater with variable speed, it experiences additional resistance from the water, commonly referred to as added mass force. At present, several methods exist to solve this force, including theoretical, experimental, and simulation approaches. This paper addresses the challenge of determining the added mass force for irregularly shaped small objects undergoing variable speed motion underwater, proposing a method to obtain the added mass force through numerical simulation. It employs regression analysis and parameter separation analysis to solve the added mass force, added mass, viscous drag coefficient, and pressure drag coefficient. The results indicate that an added mass force exists during both the acceleration and deceleration of the object, with little difference between them. Under the same velocity conditions, significant differences exist in pressure drag forces, while differences in viscous drag forces are not significant. This suggests that the primary source of added mass force is pressure drag, with viscous drag having little effect on it. During acceleration, the surrounding fluid accelerates with the object, increasing the pressure drag with a high-pressure area concentrating at the object’s front, forming an added mass force that is directed backward. By contrast, during deceleration, the fluid at the object’s front tends to detach, and the fluid at the rear rushes forward, leading to a smaller high-pressure area at the front and a larger one at the rear, reducing the pressure drag and forming an added mass force that is directed forward. By comparing the added mass of a standard ellipsoid obtained from numerical simulation with theoretical values, the regression analysis method is proven to be highly accurate and entirely applicable for solving the added mass of underwater vehicles.

The traditional method is capable of detecting and tracking stationary and slow-moving targets in a sea surface environment. However, the signal focusing capability of such a method could be greatly reduced especially for those variable-speed targets. To solve this problem, a novel tracking algorithm combining range envelope alignment and azimuth phase filtering is proposed. In this method, the motion of the airborne maritime surveillance radar platform is firstly compensated for target echoes. Secondly, range envelope alignment is performed to correct the unpredictable range migration of the target after pulse compression. The higher-order phase difference between the adjacent pulses is estimated and compensated. Ultimately, such pulse series are accumulated through azimuth Fourier transform. Traditional methods compensate only for platform motion, limiting their ability to handle variable-speed targets. The proposed algorithm addresses this limitation by compensating for both platform and target motion, significantly improving signal focusing and tracking accuracy. A detailed analysis shows that our algorithm can significantly increase the signal accumulating gain and improve the focusing effect. The simulation results are provided to demonstrate the effectiveness of the proposed algorithm.

Most gun-launched guided projectiles adopt a spinning airframe to simplify the control structure and improve stability. However, the cross-coupling effects of inertia, aerodynamics, and control caused by spinning increase the difficulty of the autopilot design. This paper proposes an adaptive attitude autopilot design method for a class of spinning projectiles with time-varying aerodynamic uncertainties. First, a fully actuated attitude dynamic model of the pitch/yaw channel for a spinning projectile is established, in which the aerodynamic force/moment are regarded as time-varying uncertainties. Second, an adaptive attitude autopilot is proposed by combining fully actuated system theory and adaptive control theory to restore the linear characteristics of the closed-loop system. Then, a parameter-safe adaptive law is presented using control barrier functions to ensure the boundedness of estimation parameters and improve the robustness of the closed-loop system. Finally, comparative numerical simulations are performed to demonstrate that the proposed attitude control method can guarantee the boundedness of both the tracking error and estimation error.

The dual-channel control of roll missiles offers advantages such as simplified control systems and improved thrust eccentricity. However, it also faces challenges related to the interlinked coupling of aerodynamics, inertia, and control. To achieve decoupling control between channels, a simplified dynamic model of roll missiles that incorporates rudder dynamics was established. Based on this model, a decoupling controller using Active Disturbance Rejection Control (ADRC) was designed. This controller does not require precise input-output relationships of the model, but only needs to perform static decoupling on the coupling matrix of control actions to construct separate control channels. The dynamic coupling between channels, as well as the effects of model perturbations and external disturbances, are estimated and compensated in real time by an Extended State Observer (ESO). Simulation results indicate that the designed ADRC controller exhibits good dynamic performance, high stability accuracy, robustness, and interference resistance.

Stable and precise force contact is critical in human-robot interaction, typically requiring precise sensors and advanced algorithms. This paper presents a novel adjustable constant-force mechanism (CFM) serving as a force generator for massage robotic systems, aiming to reduce hardware costs and system development complexity. The passive CFM, comprising gears and springs, is further integrated with an active motor to enable online adjustment and continuous operation. As the primary innovation, the harmonic principle is employed for force regulation in the CFM, replacing traditional methods such as altering the number or assembly position of springs, which provides a more convenient integration with automated systems. This involves the superposition of two elastic systems with identical configurations, where only the phase angle is extracted as the sole control variable for force modulation. A prototype was constructed to experimentally validate its performance. Results demonstrate that the proposed solution achieves a maximum constant output force of 18.34 N over a 55 mm range, and it can be adjusted online to the appropriate level as required by the task.