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Camouflage is widespread in nature, engineering, and the military. Dynamic surface wrinkles enable a material the on-demand control of the reflected optical signal and may provide an alternative to achieve adaptive camouflage. Here, we demonstrate a feasible strategy for adaptive visible camouflage based on light-driven dynamic surface wrinkles using a bilayer system comprising an anthracene-containing copolymer (PAN) and pigment-containing poly (dimethylsiloxane) (pigment-PDMS). In this system, the photothermal effect–induced thermal expansion of pigment-PDMS could eliminate the wrinkles. The multiwavelength light–driven dynamic surface wrinkles could tune the scattering of light and the visibility of the PAN film interference color. Consequently, the color captured by the observer could switch between the exposure state that is distinguished from the background and the camouflage state that is similar to the surroundings. The bilayer wrinkling system toward adaptive visible camouflage is simple to configure, easy to operate, versatile, and exhibits in situ dynamic characteristics without any external sensors and extra stimuli.

With the increasingly harsh service conditions, higher requirements are put forward for the cage of ceramic bearings. In this study, dynamic model of full ceramic ball bearing, in which the motion characteristics of cage is considered, under condition of non-lubrication is established, and the model accuracy is also verified by experiments. The change of contact angles, influence of ball-pocket clearance and guide clearance on the dynamic characteristics of cage are studied. Dynamic characteristics of the cage under different axial loads and rotation speeds are studied. The results show that the influence of rotation speed, radial load and axial load on contact angles are basically the same, while the increase in axial load helps to reduce the difference between internal and external contact angles. With the increase in ball-pocket clearance and guide clearance, the slip ratio of cage decreases first and then increases, so there is an optimal ball-pocket clearance and guide clearance, which makes the cage stable. Compared with the rotational speed, the axial load has a greater impact on the dynamic characteristics of the cage. The results have certain reference value for the optimal design and manufacture of full ceramic bearing cage under non-lubrication conditions.

This paper researches the stability and multi-frequency dynamic characteristics of nonlinear grid-connected pumped storage-wind power interconnection system (PS-WPIS). Firstly, a nonlinear model of grid-connected PS-WPIS is established. Then, the system stability and multi-frequency characteristics are revealed through stable domain and dynamic response analysis. Furthermore, the coupling mechanism of grid-connected PS-WPIS is explained, and the effect of capacity ratio on system stability is studied. Finally, the effect of hydraulic, mechanical and electrical parameters on grid-connected PS-WPIS is revealed. The results show that the stable domain of grid-connected PS-WPIS consists of two horizontal bifurcation lines and one curving bifurcation line. The former is related to wind power subsystem, and the latter is related to pumped storage subsystem. The grid-connected PS-WPIS contains the phenomenon of multi-frequency oscillations. The multi-frequency oscillations are generated by the coupling effect of pumped storage subsystem and wind power subsystem. The capacity increase of pumped storage or wind power worsens the stability and dynamic response of grid-connected PS-WPIS. The regulation performance of grid-connected PS-WPIS can be significantly improved by selecting smaller values of flow inertia time constant of penstock and time constant of wind turbine shafting.

Flexible multibody system (FMBS) refers to a mechanical system, which consists of flexible components and kinematic pairs, and undergoes both overall motions and deformations. FMBS serves as a useful dynamic model for many advanced industrial products, such as flexible robots, helicopter rotors and deployable space antennas. Traditionally, the design of flexible components in an FMBS mainly relies on the trial-and-error method, which is time-consuming and cannot guarantee the best design. In addition, the optimization design of the flexible components in an FMBS usually uses a component-based approach without accounting for the interaction between a component to be optimized and the FMBS of concern. Yet, when a component gets more and more flexible, the interaction between the component and the FMBS plays a nonnegligible role in optimization and requires the FMBS-based optimization. This feature article presents the basic ideas and methods for the dynamic topology optimization of an FMBS mainly based on the studies of the authors over the past decade. The article focuses on four emerging topology optimization problems of an FMBS as follows, (i) topology optimization of dynamic responses and dynamic characteristics, (ii) fully coupled and weakly coupled optimizations, (iii) topology optimization of time-varying systems, and (iv) optimization designs and prototype tests of flexible robots. Together with concluding remarks, the article addresses some open problems of the dynamic topology optimization of an FMBS for future researches.

This paper presents a novel modeling approach to predict the nonlinear dynamic characteristics of automotive mounts and shock absorbers. Firstly, the concept of the hybrid ANN (artificial neural network)–mechanical modeling approach is presented, which consists of an equivalent mechanical model to characterize the trend of the dynamic characteristic and a neural network model to compensate for the errors introduced by uncaptured nonlinearities. Then experiments are carried out on a rubber mount, a hydraulic mount and a shock absorber to measure their static and dynamic characteristics. Parameters of the equivalent mechanical model are identified, and the neural network model is trained. The hybrid models are validated under harmonic and random excitations with a relative error of less than 8%. Finally, the developed models for the rubber mounts, hydraulic mounts and shock absorbers are integrated into a vehicle model to evaluate the impact of nonlinearity on vehicle ride comfort. The results show that ignoring the nonlinearity of the hydraulic mounts will introduce the largest calculation errors in the analysis of vehicle ride comfort, followed by the shock absorber, and the rubber mount is the smallest.

Elastic ring squeeze film dampers (ERSFDs) show superior performances in vibration and noise control in a rotor-bearing system. Currently, the industry of spiral bevel gears is also interested in introducing ERSFDs to improve their dynamic performances. This manuscript develops a new accurate mathematical model of ERSFDs based on the generalized Reynolds equation and proposes a semi-analytical method to calculate the elastic ring deformation of ERSFDs. Moreover, an innovative numerical strategy for calculating the oil-film pressure distribution is presented, and Simpson’s rule is utilized to calculate the oil-film force of ERSFDs. Then the dynamic model of a spiral bevel gear drive supported on ERSFDs is developed by coupling the motion equations of the gear system with the oil-film force, and the dynamic characteristics of the system are studied for the first time. The new mathematical model and oil-film pressure calculation method of ERSFDs proposed in this work can be well applied to the gear system, and the ERSFD has better performance than the classical squeeze film damper in suppressing the nonlinear characteristics of systems in the speed range of 7100–8100 rpm. Besides, the mathematical model and oil-film pressure calculation method of ERSFDs proposed in this paper can be extended to all rotating machinery.

The cage, serving as a pivotal element in rolling bearings, possesses dynamic characteristics that have a direct bearing on the overall performance of the bearing. This paper caters to the requirements of dynamic and strength analysis of the four-point contact ball-bearing cage in high-speed railway traction motors. A rigid-flexible coupling dynamics model of the bearing is established on the ADAMS platform and its dynamic analysis was carried out under variable axial forces and with different guiding clearances. The results show that the variable axial force has little effect on the bearing cage stress, but has a great effect on the bearing cage motion. The guiding clearance has little effect on the stress of the cage, but it affects the displacement and speed of the cage obviously.

Due to various factors, there will inevitably be clearance in the mechanism. The clearance can reduce the accuracy and stability of mechanism, while lubrication effectively improves this situation. Previous researches mainly centered on mechanism with dry friction clearance, but less on complex mechanism with lubrication clearance. Moreover, previous researches mainly centered on dynamic response of mechanism, while less on nonlinear characteristics of mechanism. To research the impact of lubrication clearances of mechanism, nonlinear dynamic characteristics of nine-bar mechanism multi-body system are studied. Lubrication force model is established by modified Pinkus–Sternlicht model. Dynamic model of mechanism with lubrication clearances is established by Lagrange multiplier method. The experimental platform of the mechanism is built, and correctness of theoretical model is verified by experiments. This paper analyzes the influence of dry friction clearances and lubrication clearances on output response of mechanism. The influence of clearance value, lubrication viscosity and driving speed on dynamic response are analyzed. The influence of clearance value and driving speed on nonlinear characteristics of mechanism are analyzed by means of Poincare mapping, phase and bifurcation diagram. The research provides theoretical references for prediction and control of dynamic performance for mechanism with clearance.

Bearing wear is an inevitable and a slowly evolving process. It affects the dynamic response of spindle-bearing systems by changing contact status between ball elements and raceways, causing the machining accuracy of spindle-bearing system to be gradually decreased. The effects of bearing wear evolution on dynamic characteristics of spindle-bearing system are worthy of further investigation, which can provide valuable insights into the wear-induced quantitative diagnosis in spindle-bearing system. In current work, a comprehensive mechanical–thermal–wear coupled model of the spindle-bearing system is proposed to analyze dynamic characteristics of spindle-bearing system considering bearing wear evolution effects. The bearing wear, temperature change and dynamic response under different preload displacements, working loads and spindle speeds conditions are discussed. The results show that both bearing preload and working load significantly affect bearing wear. The magnitude of temperature change of the spindle-bearing system decreases at first and then nearly keeps constant with bearing wear. Bearing wear changes the dominant frequency of the spindle-bearing system and leads to more abundant dynamic response frequency compared with no wear condition. Low- and medium-speed conditions are more valuable than high-speed condition for identifying bearing wear severity. The results of this study could be of significance in decision-making processes that would require identification and quantitative diagnosis of bearing wear evolution and system lifetime prediction.

With the rapid development of aero-engine manufacturing technology, the dual-rotor system has been employed in part of turbofan engine in order to improve the working performance of aircraft more efficiently. In this study, taking the counter-rotation dual-rotor as the research object, the dynamic model of dual rotor-casing coupling system is established by the aid of MATLAB. The dynamic frequency curves are in good agreement with the results in references and calculated by FEM method, that shows the validity and feasibility of the model. The local rub-impact dynamic model of dual rotor-casing coupling system is established, and rubbing analysis is carried out using Newmark-β method. The effects of rotating speed and speed ratio on local rub-impact response are deeply discussed. The results show that with the increase of rotating speed, combined frequencies and frequency multiplication components are more significant. In addition, speed ratio has a great influence on the periodic motion of the system. With the increase of the absolute value of the speed ratio, the whirl radius of the outer rotor and the normal rubbing force increase dramatically.