The classical theory of centralized dynamic characteristics with eight coefficients is adopted for traditional journal bearings. However, under cantilevered load, distributed dynamic characteristics along the axial direction will be generated for the journal bearing with a large aspect ratio (L/D). A double-section loading method simulating shaft bending and excitation was developed, a dynamic characteristic test-rig of a large-aspect-ratio bearing was set-up, the novel four-time vertical excitation method and eight-time cross excitation method were put forward, and the equations of 16 dynamic characteristic coefficients of the bearing were deduced. The dynamic characteristic test was carried out. The results showed that the four-time vertical excitation method had a small response amplitude in the horizontal direction, and was vulnerable to interference by the vibration of the test-rig. The eight-time cross excitation method had a higher SNR with more accurate identification results. When the cantilevered load was not applied, the dynamic characteristic coefficients were evenly distributed along the axial direction, the stiffness coefficients fluctuated slightly as the rotation rate increased, while the main damping coefficients decreased significantly. Shaft bending resulted in a significant increase in local dynamic characteristic coefficients, in which the relative increase in the stiffness coefficients was greater than that of the damping coefficients. Increasing the rotational speed can weaken the effect of shaft bending, and key factors that cause the axially nonuniform distribution of dynamic characteristic coefficients of the bearing are shaft bending and large aspect ratio under low speed and cantilevered load.

The lateral vibration of propulsion shafting is a critical factor affecting the acoustic stealth performance of underwater vehicles. As the main vibration isolation component in transmitting vibrational energy, the damping efficiency of the propulsion shafting support system (PSSS) holds particular significance. This study investigates the dynamic characteristics of the PSSS with the integral squeeze film damper (ISFD). A dynamic model of ISFD–PSSS is developed to systematically analyze the effects of shaft speed and external load on its dynamic behavior. Three test bearings (conventional, 1S, and 3S structure) are designed and manufactured to study the influence of damping structure layout scheme, damping fluid viscosity, unbalanced load, and shaft speed on the vibration reduction ability of ISFD–PSSS through axis orbit and vibration velocity. The results show that the damping effects of ISFD–PSSS are observed across all test conditions, presenting distinct nonlinear patterns. Suppression effectiveness is more pronounced in the vertical direction compared to the horizontal direction. The 3S structure bearing has better vibration reduction and structural stability than other schemes. The research results provide a reference for the vibration control method of rotating machinery.

Cold starting is the biggest challenge for mechanical equipment in polar environments. Selecting suitable friction pair materials and exploring the wear mechanism are keys to improving the reliability in a low-temperature environment. This study analyzed the tribological properties of the two typical materials of hydraulic motor’s rotor at different ambient temperatures, especially at low temperature. Finally, it explored the wear process and mechanism of two sets of friction pairs. The results showed that the low temperature environment not only affects the viscosity of the hydraulic medium in the hydraulic system and changes the lubrication state between the friction pairs, but also enhances the cold brittleness of metal materials and affects the wear characteristics between the friction pairs. There is a maximum difference of around −20 °C. The wear volume of material QT500-7 sharply increases and reaches a maximum of 0.107 mm³ when the normal force is 20 N, which is 3.65 times as much as the wear volume of the LC2-1. When the normal force is 30 N, the wear volume of materials QT500-7 and LC2-1 are 0.125 and 0.036 mm³, respectively. The wear volume of the former is 3.4 times that of the latter. In addition, it indicates that the impact energy of the material affects its tribological properties since the impact energy of the material QT500-7 decreases sharply, including two consecutive subintervals of sharp decreases from 97.3 J to 42.2 J and then to 18.0 J at the temperature of −10 to −30 °C. The material LC2-1 with stable wear performance is more applicable for being processed and manufactured into parts for low-temperature environmental conditions, as there is no serious fluctuation in the temperature range from −40 °C to room temperature. The research findings are expected to provide a theoretical support for hydraulic motors design, material selection and the maintenance of polar deck machinery. They are of great significance for improving the operational reliability of hydraulic motors for polar ships.

Wheeled inverted-pendulum robots with movable upper structures and variable payloads exhibit configuration-dependent equilibrium drift and payload-dependent dynamic variation, which complicate balancing control. This paper proposes a gain-scheduled controller–observer framework for payload-adaptive balancing of such a robot. First, the multi-body system is reduced to a control-oriented equivalent inverted-pendulum model through center-of-mass lumping, from which a parameter-varying linearized model is established. On this basis, an H∞ state-feedback controller with input constraints is synthesized in a linear matrix inequality (LMI) framework, and an augmented-state observer is designed to estimate the residual equilibrium offset induced by payload variation. To improve robustness over the operating range, the frozen-point design is extended to a sampled-model multi-model synthesis framework, and gain scheduling is implemented with respect to the measurable arm angle. Nonlinear Simscape simulations show that the proposed method can recover balance at representative fixed operating points, compensate effectively for load-induced equilibrium drifts, and preserve stable balancing performance under slow arm-angle variation. Quantitative comparisons with an LQR baseline further support the effectiveness of the proposed framework for payload-adaptive balancing control.

Under long-term service conditions, vibration signals of water-lubricated stern bearings exhibit strong nonlinearity, nonstationarity, and multicomponent coupling, which makes accurate feature extraction challenging. To address this issue, this study proposes a progressive EEMD-TFMST-based analysis framework that combines spectral localization, adaptive signal decomposition, noise suppression, and high-resolution time–frequency characterization. Rotational-speed tests and long-duration wear tests were conducted using an SSB-100 test rig, and the lubrication regimes were identified based on friction coefficient variations. The results show that the dominant vibration features are strongly dependent on the lubrication regime and wear stage. With increasing rotational speed, the vibration response evolves from isolated peaks near 400 and 600 Hz under boundary lubrication to enhanced 300–400 Hz components under mixed lubrication, and further to broadband responses within 0–1000 Hz under hydrodynamic lubrication, with dominant peaks mainly concentrated in the 300–500 Hz range. With increasing rotational speed, the lubrication regime gradually changes from boundary lubrication to hydrodynamic lubrication, accompanied by a transition of vibration energy from single-IMF concentration to broadband distribution across multiple IMF components. Long-term operation induces stage-dependent changes in lubrication and vibration behavior: moderate wear improves vibration stability, whereas excessive wear deteriorates lubrication, increases the proportion of mixed lubrication, and promotes energy migration toward lower frequencies with additional high-frequency excitation. Under prolonged high-speed operation, lubrication degradation further induces broadband vibration. The proposed method enables accurate quantification of vibration features and provides a useful basis for service-performance evaluation and early fault warning of water-lubricated stern bearings.