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The adverse effects of flexible structure and wear clearances on dynamic performance of mechanical systems cannot be ignored. At present, scholars have carried out extensive research on mechanism with clearance, but few consider the coupling effect of wear clearance and flexible structure on dynamic performance of mechanism. Therefore, this paper develops a dynamic model of six-link mechanism considering multiple wear clearances and flexible structure through Lagrange method. The influence of clearance size and frictional coefficient on dynamic performance and nonlinear characteristics of mechanism is investigated. In view of the adverse effects of wear clearances and flexible structure on the performance of mechanism, a new optimization method of mechanism based on simulated annealing algorithm (SAA) is proposed. This method takes the mass parameters of each component for mechanism as the design variables and minimizes the maximal wear depth of clearance as the objective function. The results indicate that the optimization method can reduce the vibration and error, and improve the overall dynamic performance of mechanism.

This study concerns dynamic behaviors and vibration reduction of the flexible structure subjected to a moving mass traveling on it. The mathematical model of a simply supported beam carrying a moving particle mass is derived according to the Hamilton’s principle. Dynamic responses of the substrate flexible beam under various traveling profiles are analyzed and implied that the moving mass would induce evident motion-induced dynamic deflection and residual vibration, and such effects highly depend on the motion profiles. The key novelty of this paper is proposing a data-driven, high-efficiency vibration-reduction motion planning approach to the moving mass. Such a motion planning approach is imposed by quintic spline curves and Kriging surrogate model-based optimization algorithm combined with the expected improvement infilling-sampling criterion. The optimization results reveal that a favorable motion profile can be found by using only 2 waypoints and within approximately 100 samplings. In the case of minimization of the transient deflection amplitude, lower transient deflection, which is even lower than the static value, can be obtained using the optimized motion profile. In the case of minimization of residual vibration energy, a smooth deformation history of the substrate beam can be produced, while the vibration energy has also been significantly reduced. Using the minimization of residual vibration energy as the objective function is primarily recommended in the motion planning issue. Improved motion profiles with varied terminal times could also be obtained and proved the robustness of the proposed optimization approach. The proposed data-driven optimization approach could provide a feasible and high-efficiency way to design a favorable traveling profile for a moving mass system from the perspective of structural vibration reduction.

Morphing aircraft can adaptively regulate their aerodynamic layout to meet the demands of varying flight conditions, improve their aerodynamic efficiency, and reduce their energy consumption. The design and fabrication of high-performance, lightweight, and intelligent morphing structures have become a hot topic in advanced aircraft design. This paper discusses morphing aircraft development history, structural characteristics, existing applications, and future prospects. First, some conventional mechanical morphing aircraft are examined with focus on their morphing modes, mechanisms, advantages, and disadvantages. Second, the novel applications of several technologies for morphing unmanned aerial vehicles, including additive manufacturing for fabricating complex morphing structures, lattice technology for reducing structural weight, and multi-mode morphing combined with flexible skins and foldable structures, are summarized and categorized. Moreover, in consideration of the further development of active morphing aircraft, the paper reviews morphing structures driven by smart material actuators, such as shape memory alloy and macro-fiber composites, and analyzes their advantages and limitations. Third, the paper discusses multiple challenges, including flexible structures, flexible skins, and control systems, in the design of future morphing aircraft. Lastly, the development and application of morphing structures in the aerospace field are discussed to provide a reference for future research and engineering applications.

Satellite borne flexible structure is a multi-degree-of-freedom system, which contains complex dynamic characteristics such as time-varying parameters, geometric nonlinearity, gap nonlinearity, and so on. Flexible structure suspension typically results in geometric nonlinearity. The oscillation equation with nonlinear term is established according to the law of motion of a nonlinear pendulum and considering the influence of medium swing angle and lateral force. The perturbation approach is used to get the relationship between vibration frequency and the nonlinear term, and the impact of factors on vibration characteristics is investigated. The satellite borne flexible structure’s active vibration control (AVC) system is then established. Considering proportional differential (PD) or fuzzy control adjustment, variable step size least mean square (VSS-LMS) adaptive filtering algorithm is used to calculate the control signal, and considering the influence of geometric nonlinearity, the actuator is used to suppress the vibration of the satellite borne flexible structure. Finally, the vibration response’s amplitude under steady-state excitation significantly decreases as an outcome of the vibration control simulation.

Position control of the mechanical structure with naturally limited stiffness is a common problem. Moreover, the system is usually exposed to random exciting by the external force effects and yet it is needed to hold the system in the desired position. Such an example in engineering practice can be the machine tool quill slim structure, which determines the machining accuracy and the machined surface quality. The limited structure stiffness can be overcome by suitable support structure solution. In principle, it is a matter of introducing the necessary force effect in the place where it is necessary to ensure the required position. A promising means how to apply control force to the flexible structure tip can be a thin cable structure with the force actuation and proper force control. The resulting system is characterized by increased stiffness achieved in a mechatronic manner. Therefore, the introduced concept is called mechatronic stiffness. The article describes selected mechanical arrangement of the mechatronic stiffness concept, its features, behaviour and control results. The proposed approach offers a solution for precise position control of the flexible structure. An experimental device was created in parallel with the simulation experiment and preliminary simulation results are obtained. The described concept is transferable to other flexible structures such as various manipulators.

This paper investigates the dynamic response of space flexible structures with control moment gyroscopics (CMGs) in which uncertain-but-bounded parameters are considered. The uncertainties in the dynamic modeling of flexible structure are treated as interval parameters and an interval gyroscopic model is established. Afterwards, a rational series expansion-interval perturbation finite element method (RSE-IPFEM) is proposed to estimate the upper and lower bounds of the interval dynamic response of the gyroscopic flexible structure. Meanwhile, the Monte Carlo method is presented to provide a reference solution. Two numerical cases are given to demonstrate the effectiveness and feasibility of the RSE-IPFEM. The results show that the uncertainties of Young’s modulus and rotor speed have a great impact on the dynamic response of the gyroscopic flexible structure.

Highlights Highly crystalline 2D metal hydrogen-bonded organic frameworks (2D-M-HOFs) including 2D-Cu-HOF and 2D-Ni-HOF were designed and synthesized. The 2D-M-HOF with flexible ligands leads to the formation of the self-adaption interlayered sites, which facilitate the C–C couple and overcome the limitations of the coadsorption of multiple intermediates in the electrocatalytic CO 2 reduction reaction. The undulated 2D-Cu-HOF exhibits outstanding activity and selectivity for electrocatalytic reduction of CO 2 to C 2 products with a total Faradaic efficiency of 82.1% (48.2% for C 2 H 5 OH and 33.9% for C 2 H 4 ) at −1.2 V vs. RHE. The hydrogen-bonded organic frameworks (HOFs) as a new type of porous framework materials have been widely studied in various areas. However, the lack of appropriate active sites, low intrinsic conductivity, and poor stability limited their performance in the field of electrocatalysis. Herein, we designed two 2D metal hydrogen-bonded organic frameworks (2D–M–HOF, M = Cu 2+ or Ni 2+ ) with coordination compounds based on 2,3,6,7,14,15-hexahydroxyl cyclotricatechylene and transition metal ions (Cu 2+ and Ni 2+ ), respectively. The crystal structure of 2D–Cu–HOF is determined by continuous rotation electron diffraction, indicating an undulated 2D hydrogen-bond network with interlayered π-π stacking. The flexible structure of 2D–M–HOF leads to the formation of self-adaption interlayered sites, resulting in superior activity and selectivity in the electrocatalytic conversion of CO 2 to C 2 products, achieving a total Faradaic efficiency exceeding 80% due to the high-efficiency C–C coupling. The experimental results and density functional calculations verify that the undulated 2D–M–HOF enables the energetically favorable formation of *OCCHO intermediate. This work provides a promising strategy for designing HOF catalysts in electrocatalysis and related processes.

In fields such as on-orbit maintenance robotic arms and electric driving systems, the two-inertia rotating system with flexible structure (TIRS-FS) has received increasing attention due to its lightweight and flexibility. Flexible structures are prone to elastic deformation during motion, which poses a significant challenge to the dynamic modeling and high-precision control of the TIRS-FS. This paper presents a comparative analysis of three simplified TIRS-FS dynamics models. Based on the more accurate dynamics model obtained, the fuzzy compensated sliding mode control method is proposed to achieve accurate control of the TIRS-FS. Firstly, the TIRS-FS is discretized using the assumed modal method. Then, using the Lagrange equation, the dynamical equations considering the two-dimensional (2D) deformation of the flexible structure and the joint-driven friction are established. Additionally, fuzzy rules are utilized to approximate and compensate for the uncertainty terms present in the TIRS-FS dynamical equations. These fuzzy systems are then combined into a control law. Finally, through simulation analysis and control experiments, it is demonstrated that the proposed control method can effectively achieve accurate control of the TIRS-FS.

Maleic acid (MA) has been studied to replace formaldehyde-based crosslinking agents for antiwrinkle treatment of cotton fabrics for many years. However, the resilience of cotton fabrics treated by MA is not acceptable. In this study, a novel poly-carboxylic acid of ethyldimercaptan disuccinic acid (EDMDSA) was synthesized by MA and 1,2-Dimercaptoethane (DME) via click reaction and then applied on antiwrinkle finishing of cotton fabrics. The chemical structure of EDMDSA was confirmed by nuclear magnetic resonance, Fourier transform infrared spectroscopy, and mass spectra. The results indicated that the recommended antiwrinkle finishing conditions were 0.3 mol L −1 EDMDSA with equal molar ratio of sodium hypophosphite, curing temperature of 170 °C and curing time of 90 s. After treating, the wrinkle recovery angle of cotton fabrics finished by EDMDSA increased from 137.2° of untreated fabrics to 251.3°, which was significantly higher than 216° of those treated by MA. Besides, due to more flexible structure of EDMDSA, the finished cotton fabrics have slightly weaker antiwrinkle performance but higher strength retention than those treated by 1,2,3,4-butanetetracarboxylic acid. Facile synthesis and purification of EDMDSA as well as their excellent crosslinking and durability performance indicate they have a potential industrial-scale application in the field of non-formaldehyde anti-wrinkle treatment. Graphical abstract

In this paper, a novel self-adaptive underactuated robot hand with rigid-flexible coupling fingers (SAU-RFC hand) is proposed. The seven degrees of freedom (DOFs) SAU-RFC hand is driven by four servomotors, consists of three fingers, including two side-turning (ST) fingers and one non-side-turning finger. Specially, the ST fingers can perform synchronous reverse rotation laterally with each other. Each finger with three joints and two DOFs introduces a flexible structure, and the inner part of the proximal phalanx that makes most of the contact with the object is replaced by a flexible belt. The fingers can generate flexion/extension under the pull of the flexible belt, and the middle and distal phalanxes are mechanically coupled through a four-bar linkage. In particular, the flexible belt in the inner direction of the finger will deform, while it will not deform in the outer direction since the outer is a rigid structure. The flexible belt not only plays the role of transmitting power but also has the effect of uniformizing the contact force. Due to the rigid-flexible finger structure, the developed robot hand has a higher self-adaptive grasping ability for objects with different shapes, sizes, and hardness. In addition, the kinematic and kinetic analyses of SAU-RFC hand are performed. A contact force distribution model is established for the flexible belt, which demonstrates its effect of promoting uniform force distribution theoretically. In the end, experiments are conducted on different objects to verify the performance of SAU-RFC hand.