In this work, the effect of modified graphene oxide and polytetrafluoroethylene (PTFE) on the tribological and anticorrosion properties of waterborne polyurethane (WPU) was studied. The modified graphene oxide (MGO) was obtained by the surface functionalization modification of graphene oxide (GO) with isophorone diisocyanate (IPDI), and MGO/WPU composite coating and MGO-PTFE/WPU composite coating with different mass fractions of MGO were prepared. The tribological and electrochemical experiment results demonstrated that the tribological properties of the coating and the corrosion resistance of the worn coating were effectively enhanced under the synergistic effect of MGO and PTFE. Finally, a mechanism was proposed to explain the improvement in anticorrosion performance of the worn coating.

In this study, the chemical graft method was used to connect modified graphene oxide (GO) and Fe₃O₄ through covalent bonds. To make full use of the tribological properties of graphene, aligned graphene [email protected]₃O₄/waterborne polyurethane ([email protected]₃O₄/WPU) was prepared in a magnetic field and tribological experiments were carried out on it. The [email protected]₃O₄ was characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and a transmission electron microscopy (TEM). The characterization results show that Fe₃O₄ is successfully loaded on the surface of GO and [email protected]₃O₄ has better dispersibility in WPU. Among the coatings without alignment inducement of [email protected]₃O₄, 0.5 wt % [email protected]₃O₄/WPU has the lowest friction coefficient and wear rate. In addition, the 0.5 wt % aligned [email protected]₃O₄/WPU composite coating has the lowest friction coefficient and wear rate compared with nonaligned and pure WPU coatings. The excellent tribological properties of the aligned composite coating come from its ability to quickly form a uniform and continuous transfer film on the friction counterpair, which avoids direct friction between the friction counterpair and the coating.

Traditional underwater vehicles are limited in speed due to dramatic friction drag on the hull. Supercavitating vehicles exploit supercavitation as a means to reduce drag and increase their underwater speed. Compared with fully wetted vehicles, the non-linearity in the modelling of cavitator, fin and in particular the planing force make the control design of supercavitating vehicles more challenging. Dominant non-linearities associated with planing force are taken into account in the model of supercavitating vehicles in this paper. Two controllers are proposed to realize stable system dynamics and tracking responses, a linear quadratic regulator (LQR) control scheme and a robust backstepping control (RBC) scheme. The proposed backstepping procedure, in association with integral filters technique, exploits the possibility of avoiding the overparameterization problem existing in the classical backstepping process. In particular, the achieved stability is robust to modelling errors in supercavitating vehicles. Compared with the LQR control scheme, the RBC scheme is seen to increase the robustness with saturation compensation algorithm, which can be useful for avoiding actuator saturation in magnitude.

An improved approach is proposed here for searching the global noncircular critical slip surface in a slope with soil variability. To avoid the local minimum, the proposed approach combines a readily available optimization with the simulated annealing algorithm (SAA). The simplified Morgenstern-Price method was used to calculate the factor of safety (Fs) for the generated slip surface. The reliability of the searching strategy was evaluated through the effect of vertices number and the position of the initial slip surface. Subsequently, the proposed method was used to analyze two example problems involving slope profiles with different geometries and strength fields. The results showed that the location of the initial slip surface had a negligible influence on the global critical slip surface as well as the corresponding factor of safety, if the annealing time was sufficient. The location of the global critical slip surface diverged when the segment number was greater than 3. The proposed approach can seek the relative global factor of safety with a calculation accuracy of 1 × 10⁻⁴, which is suitable for engineering use. The noncircular slip surface assumption was superior to the circular slip surface assumption for both the simple multilayered soil slope and the spatially variable soil slope with a low level of strength variation. However, the circular slip surface assumption will also locate more critical slip surfaces if the variation of soil strength reaches a high level. The critical F_s value was determined from the given random strength field other than the assumption of a circular or noncircular slip surface. The noncircular slip surface searching strategy can provide a useful supplement for the limited-equilibrium method (LEM) searching for the critical slip surface in a spatially variable soil slope. Practitioners can select the smaller F_s from these two different assumptions.

Aiming at the time-delay characteristics and nonlinear planing force of supercavitating vehicles in the process of motion, a parameter-dependent robust controller with anti-saturation compensator is proposed. First, the system model with nonlinear planing force is transformed into a parameter dependent linear-parameter-varying model containing time-delay part and non-time-delay part. Then consider the external disturbance input to design a robust controller and use convex polyhedron theory and the parameter dependence characteristics of controller to ensure the stability of the system with cavitation radius perturbation. Finally, the anti-saturation compensation method is used to overcome the input constraints caused by the physical limitations of the control mechanism. The simulation results show that the controller has good control effect and robust performance for supercavitating vehicles with time-delay characteristics.

SiO₂/ZrO₂ and SiO₂/ZrO₂/Al₂O₃ composite organic–inorganic coatings were prepared by the sol-gel technology. The structure of the coating was characterized by IR, particle size analyzer, SEM, and AFM, respectively. The results showed that ZrO₂, SiO₂ (inorganic component), and siloxane had undergone a hydrolytic condensation reaction, and the composite organic–inorganic coatings were formed with -O-M-O- (M is Si, Zr) as molecular skeleton network structure. Adding an appropriate ratio of ZrO₂ sol, no agglomeration and phase separation occurred, which could significantly improve the refractive index, hardness, and light transmittance of the coatings. Al₂O₃ sol could greatly improve the friction resistance of the composite organic–inorganic coatings, and the Bayer ratio of the composite coatings could reach 7.86. By adjusting the proportioning of composite sol solution, the refractive index of the composite transparent coatings could be controlled from 1.52 to 1.65.