Vibration isolation systems with quasi-zero stiffness (QZS) performance have been widely studied because of their characteristics: high static stiffness and low dynamic stiffness. However, the ...effective displacement range of QZS is usually so small that strongly limits its application existing in real engineering. Thus, this study’ main innovation is to attempt to expand the effective displacement range of the QZS system via a semi-active control strategy. We first present a novel quasi-zero stiffness (QZS) vibration isolation system. The QZS characteristic is achieved by combining a mechanism with six oblique springs and a coil spring, which provide negative stiffness and positive stiffness, respectively. The effects of inclination angles of oblique springs on the negative stiffness of the system are first discussed via the static analysis method. The dynamic characteristics under simple harmonic excitation are then analyzed using the harmonic balance method, including the jumping phenomena and force–displacement transmissibility. To further enlarge the effective displacement range of QZS, a feedback displacement strategy is utilized to actively adjust the inclination angles of oblique springs and realize the alteration of the stiffness of the QZS system. Results obtained from theoretical analysis show that, in the aspect of low-frequency vibration isolation performance, different from linear systems, the proposed QZS system has obvious advantages, and the displacement range of quasi-zero stiffness property is significantly expanded from a single equilibrium point to a relatively lager range when the semi-active control strategy is implemented. Furthermore, the virtual prototype simulation results reveal that the proposed QZS system can maintain excellent vibration isolation performance under significant amplitude vibration after adding control.
Porous/multi-cell structures are widely used in practical engineering due to their excellent energy absorption capacity and lightweight. In recent decades, as an important member of porous ...structures, lattice structure is found to have extremely excellent energy absorption capacity per unit mass. It has become a hot spot in the research of porous structures for energy absorption properties. There are more and more studies on energy absorption characteristics of lattice structures in the world. This paper reviews and discusses the research work on the energy absorption characteristics of lattice structures in recent years. Firstly, the performance evaluation indexes and loading conditions for energy absorption of the lattice structures are summarized. Then, the lattice structures in the current research literature are classified, and the lattice structures are divided into 2D lattice structure and 3D lattice structure. The 2D lattice structures are divided into general structure, auxetic structure and hierarchical structure, while the 3D lattice structures are divided into truss-based, plate-based, shell-based and hierarchical 3D lattice structure. Furthermore, the energy absorption properties of different types of 2D and 3D lattice structures are introduced in detail. Then, the fabrication process and the engineering application for energy absorption of the lattice structures are introduced. Finally, the future research direction of energy absorption of lattice structure is predicted. Therefore, this work provides a useful platform for researchers and engineers to design energy absorbed lattice structures, and provides a basis for developing new excellent energy absorbed lattice structures.
Waterjet machining has attracted great attention in the conditions of hard-to-machine materials, microstructures, or complicated industrial components, and it has become well-established in all major ...areas of theoretical researches and already been found across the broad spectrum of technical application areas especially in the specific sectors of scientific frontiers, including the mechanical precision component, advanced functional material, intelligent automotive engineering, aerospace equipment, renewable energy science, leading medical instruments, etc. This paper reviews the historical and latest research developments and integrated applications of waterjet machining in the domains of mechanism and performances, which covers a lot of key aspects such as waterjet machining optimization, dynamic simulation and process monitoring of machining process, and the influence mechanism of waterjet machining as well. Its machining mechanism, performance capability, functional advantages, and inherent disadvantages are characterized and assessed in detail, so that the integrated applications of multifield-assisted waterjet machining can be introduced and focused thereafter. Finally, various future development prospects in all the abovementioned aspects of waterjet machining are discussed systematically and explored subsequently, which contribute to the acquirement of a series of comprehensive conclusions. This review can be used as suitable and effective tools to study and summarize the complicated correlations between waterjet machining mechanism and its actual working performances in different environmental conditions; therefore, this proposed investigation facilitates the precision manufacture or characteristic improvements of industrial product with higher efficiency and better quality in return.
This paper presents a computationally efficient multi-resolution topology optimization framework by establishing a novel bi-directional evolutionary structure optimization (BESO) method based on ...extended finite element method (XFEM). In the proposed framework, the high-resolution designs preserving the topological complexity can be obtained with low degree of freedoms (DOFs). The implementation of the presented multi-resolution optimization framework takes good use of the ability of XFEM at accurately modeling material discontinuities within one element. On the basis of XFEM, a strategy of triangulated partition and a new material interpolation model are introduced to represent the finer material distribution. We employ the coarser finite element (FE) mesh to perform the finite element analysis, the sub-parts partitioned from finite elements to describe material properties and the nodal design variables to perform the optimization. To circumvent artificially stiff patterns, a modified sensitivity filter is applied to regularize the solution. The effectiveness and high efficiency of the presented approach are highlighted by typical 2D and 3D examples.
Quasi-zero-stiffness (QZS) vibration isolators have been widely studied, because they show excellent high static and low dynamic stiffnesses and can effectively solve low-frequency and ...ultralow-frequency vibration. However, traditional QZS (T-QZS) vibration isolators usually adopt linear damping, owing to which achieving good isolation performance at both low and high frequencies is difficult. T-QZS isolators exhibit hardening stiffness characteristics, and their vibration isolation performance is even worse than that of linear vibration isolators under a large excitation amplitude. Therefore, this study proposes a QZS isolator with a shear-thinning viscous damper (SVD) to improve the vibration isolation performance of the T-QZS isolators. The force-velocity relation of the SVD is obtained, and a dynamic model is established for the isolator. The dynamic responses of the system are solved using the harmonic balance method (HBM) and the Runge-Kutta method. The vibration isolation performance of the system is evaluated using force transmissibility, and the isolator parameters are analyzed. The results show that compared with the T-QZS isolators, the proposed QZS-SVD isolator achieves the lower initial vibration isolation frequency and peak value, and exhibits better vibration isolation performance at medium and high frequencies. Moreover, the proposed isolator can withstand a large excitation amplitude in the effective vibration isolation range.
Vibration reduction has always been one of hot and important topics in mechanical engineering, especially for the special measurement instrument. In this paper, a novel limb-inspired bionic structure ...is proposed to generate negative stiffness and design a new quasi-zero stiffness isolator via torsion springs, distinguishing from the existing tension spring structures in the literature. The nonlinear mathematical model of the proposed structure is developed and the corresponding dynamic properties are further investigated by using the Harmonic Balance method and ADAMS verification. To evaluate the vibration isolation performance, typical three-springs quasi-zero stiffness (TS QZS) system is selected to compare with the proposed bionic structure. And the graphical processing unit (GPU) parallel technology is applied to perform necessary two-parameter analyses, providing more insights into the effects of parameters on the transmissibility. It is shown that the proposed structure can show advantages over the typical TS QZS system in a wider vibration isolation range for harmonic excitation case and shorter decay time for the impact excitation case.
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A novel limb-inspired bionic structure is proposed to generate negative stiffness and design a new quasi-zero stiffness isolator via torsion springs. To evaluate the vibration isolation performance, typical three-springs quasi-zero stiffness (TS QZS) system is selected to compare with the proposed bionic structure. It is shown that the proposed structure can show advantages over the typical TS QZS system in a wider vibration isolation range for harmonic excitation case and shorter decay time for the impact excitation case.
Some birds’ necks show excellent flexible bending ability, which can be mimicked to design bionic robot. The main challenge is how to deal with the bird neck’s inherent flexibility and redundant ...degrees of freedom. In this study, a design method of a class of bionic hyper-redundant robots mimicking the neck of birds is proposed, taking the chicken as an example. In our design, a bionic vertebrae unit (BVU) with the combination of springs and universal joint is first defined to simulate chicken cervical vertebrae, which is further employed to investigate the connection and motion characteristics. Then, three BVUs in parallel driven by three steel wires form a single cervical segment. Finally, connecting four identical cervical segments constitutes the proposed bionic hyper-redundant robot. The kinematics of the driving space, joint space and task space of the proposed bionic hyper-redundant robot are investigated by combing the geometric analysis method and Denavit-Hartemberg (D-H) parameter method. The reachable workspace is further computed by the Monte Carlo method. Furthermore, the maximum position deviation of the single plane motion experiment on the prototype is about 5.8% of the total length of the four cervical segments. A series of displays of space shape, including
S
-shaped bionic bending configuration and the successful winding and lifting of the object of interest, proves that the proposed robot has excellent flexibility and application potential and that the proposed design method is effective.
This paper investigates the coordinated behaviour of the multiple Euler–Lagrange systems under diverse interactions with time delays. Specially, in the case of undirected interconnection, the ...proportional plus damping control strategy is proposed and the sufficient conditions of bipartite consensus are derived via energy function based approach. Subsequently, a velocity‐free controller is further developed by introducing a novel second‐order auxiliary system to each agent. In the case of directed network, by fully investigating the property of the Laplacian matrix associated with the cooperative–competitive interactions, a bipartite consensus controller is devised and the input–output property analysis of the system transfer function in frequency domain is presented. Simulation results are provided to demonstrate the effectiveness of the presented algorithms.
Bipartite consensus for multiple Euler–Lagrange systems under signed graphs is investigated, including undirected and directed graphs. A velocity‐free controller is developed to overcome the absence of velocity signal. The input–output property analysis of the system transfer function in frequency domain is studied to deal with the communication time delays.
This paper focuses on the stability analysis for uncertain Takagi–Sugeno (T–S) fuzzy systems with interval time-varying delay. The uncertainties of system parameter matrices are assumed to be ...time-varying and norm-bounded. Some new Lyapunov–Krasovskii functionals (LKFs) are constructed by nonuniformly dividing the whole delay interval into multiple segments and choosing different Lyapunov functionals to different segments in the LKFs. By employing these LKFs, some new delay-derivative-dependent stability criteria are established for the nominal and uncertain T–S fuzzy systems in a convex way. These stability criteria are derived that depend on both the upper and lower bounds of the time derivative of the delay. By employing the new delay partitioning approach, the obtained stability criteria are stated in terms of linear matrix inequality (LMI). They are equivalent or less conservative while involving less decision variables than the existing results. Finally, numerical examples are given to illustrate the effectiveness and reduced conservatism of the proposed results.
► These stability criteria depend on both the upper and lower bounds of the time derivative of the delay. ► Employ some new Lyapunov–Krasovskii functionals (LKFs) to further reduce the conservatism than some existing ones. ► Estimate a tighter upper bound of the derivative of the LKFs by an integral inequality.
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•Developed a ZBSO metamaterial with tailored multistage stiffness.•Experimentally and numerically revealed the tailored multistage stiffness property.•Identified the underlying ...mechanism as both the self-locking and the asymmetrical stiffness.•Demonstrated the merits, e.g. material independent, excellent energy absorption capacity.
Origami-based metamaterial has shown remarkable mechanical properties rarely found in natural materials, but achieving tailored multistage stiffness is still challenging. We propose a novel zigzag-base stacked-origami (ZBSO) metamaterial with tailored multistage stiffness based on crease customization and stacking strategies. A high precision finite element (FE) model to identify the stiffness characteristics of the ZBSO metamaterial has been established, and its accuracy is validated by quasi-static compression experiments. Using the verified FE model, we demonstrate that the multistage stiffness of the ZBSO metamaterial can be effectively tailored through two manners, i.e. varying the microstructures (through introducing new creases to the classical Miura origami unit cell) and altering the stacking way. Three strategies are utilized to vary the microstructure, i.e. adding new creases to the right, left, or both sides of the unit cell. We demonstrate that the multistage stiffness is caused by both the self-locking and asymmetrical stiffness distribution of the ZBSO metamaterial. We further reveal that the proposed ZBSO metamaterial has several outstanding advantages compared with traditional mechanical metamaterials, e.g. material independent, scale-invariant, lightweight, and excellent energy absorption capacity. The unraveled superior mechanical properties of the ZBSO metamaterials pave the way for designing the next-generation cellular metamaterials with tailored stiffness properties.
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