Vibration Isolation Of Structures Research Articles

Dynamic stability and vibration isolation property of a foot-leg coupling bio-inspired vibration isolation structure

Dynamic stability and vibration isolation property of a foot-leg coupling bio-inspired vibration isolation structure

Design of low-frequency circular metastructure isolators with high-load-bearing capacity

Traditional vibration isolation structures cannot work effectively for low-frequency vibration under heavy loads, due to the inherent contradiction between the high-static and low-dynamic stiffness of these structures. Although the challenge can be effectively addressed by introducing a negative stiffness mechanism, the existing structures inevitably have complex configurations. Metastructures, a class of man-made structures with both extraordinary mechanical properties and simple configurations, provide a new insight for low-frequency vibration isolation technology. In this paper, circular metastructure isolators consisting of some simple beams are designed for low-frequency vibration, including a single-layer isolator and a double-layer isolator, and their static and dynamic characteristics are studied, respectively. For the static characteristic, the force–displacement and stiffness-displacement curves are obtained by finite element simulation; for the dynamic characteristic, the vibration transmissibility curves are obtained analytically and numerically. The result shows that the circular nonlinear single-layer isolator has excellent low-frequency isolation performance, and the isolation frequency band will decrease about 20 Hz when the isolated mass is fixed at 1.535 kg, compared with a similar circular linear isolator. These static and dynamic properties are well verified through experiments. Our work provides an innovative approach for the low-frequency vibration isolation and has wide potential applications in aeronautics.

Band gap characteristics of new composite multiple locally resonant phononic crystal metamaterial

Locally resonant phononic crystal (LRPC) exhibit elastic wave band gap characteristics within a specific low-frequency range, but their band gap width is relatively narrow, which has certain limitations in practical engineering applications. In order to open a lower frequency band gap and broaden the band gap range, this paper proposes a new composite multiple locally resonant phononic crystal (CMLRPC). Firstly, the band structure of the CMLRPC is calculated by using the finite element method, and then the formation mechanism of the band gap of the CMLRPC is studied by analyzing its vibration mode, and the band gap width is expanded by adjusting the size of the single primitive cell in the supercell model of the CMLRPC. Secondly, an equivalent mass-spring system model for CMLRPC is established to calculate the starting frequency and cut-off frequency of the band gap, and the calculated results are in good agreement with the finite element calculation. Finally, the frequency response function of the CMLRPC is calculated and its attenuation characteristics are analyzed. Within the band gap frequency range, the attenuation values of the CMLRPC are mostly above 20 dB, indicating a good attenuation effect. Compared with traditional LRPC, this new CMLRPC opens multiple band gaps in the frequency range of 200 Hz, with a wider band gap width and better attenuation effect. In addition, considering both the contact between single primitive cell and the adjustment of their spacing in the supercell model of the CMLRPC, lower and wider band gap can be obtained. The research results of this paper provide a new design idea and method for obtaining low-frequency band gap in LRPC, and can provide reference for the design of vibration reduction and isolation structures in the field of low-frequency vibration control.

Study on vibration response and isolation of substation structure under subway load excitation

This study takes the indoor substation adjacent to the elevated bridge subway line as the engineering background, investigates the structural vibration response law of the substation induced by the operation of the subway line through on-site vibration measurement, and proposes a novel nonlinear gas-spring quasi-zero stiffness isolator (NGS-QZSI) is proposed to reduce the structural vertical vibration and further reduce the safety distance. The software ABAQUS is used to establish a structure-equipment coupling numerical analysis model considering soil-structure interaction, and its effectiveness and accuracy are validated based on the measured results. The structural vibration response analysis is carried out under different vibration source distances, and a nonlinear gas-spring quasi-zero stiffness isolator is proposed to be employed for substation structural vibration isolation. The research results show that the substation structure under subway load excitation is dominated by vertical vibration, and its vibration response increases gradually with the increase of floor level. When the substation structure is less than 45 m from the subway line, the structural response exceeds the safety limit (12.5 μm/s) of the VC-C standard. With the vibration isolator attached, the structural vibration response is significantly reduced, with the peak and root mean square response controlled by more than 70 %. Particularly, the safe distance of the substation from the subway line is reduced from 45 m to 20 m. Moreover, the frequency domain result analysis indicates that the proposed nonlinear vibration isolator can effectively control the low-frequency vibration of the structure.

Harnessing chiral buckling structure to design tunable local resonance metamaterial for low-frequency vibration isolation

This paper proposes a tunable local resonance metamaterial with chiral buckling structures for low-frequency vibration isolation. The unit cell consists of the inner and outer buckling stiffness structure, basic structure, and local resonator. The bistability of three kinds of unit cells with different initial shapes of beams is investigated and compared via the elliptic integral method and finite element analysis. Then, their axial stiffness in different states is studied. The dynamic responses of the metamaterial with simple unit cells and hybrid supercells are theoretically derived and analyzed by Bloch's theorem and transfer coefficient method. Theoretical, numerical, and experimental results demonstrate that the unit cell with initially convex downward beams has strong bistability and determinate deformation modes. The axial stiffness of the unit cell in two stable states differs by an order of magnitude. Changing some specific parameters broadens the gap in the axial stiffness between the two stable states. The axial negative stiffness characteristics and rotation effect of the unit cell have the potential for energy dissipation and tensile-torsion material. The metamaterial with simple unit cells has tunable and wide band gap and low-frequency vibration isolation via the stable states switching of the inner and outer buckling stiffness structures. The metamaterial with hybrid supercells can further broaden the band gap width and lower the band gap frequency, which has up to 16 different band gap characteristics.

A New Type of Inerter with Easily Adjustable Inertance and Superior Adaptability: Crank Train Inerter

A new type of inerter, called a crank train inerter (CTI), is investigated for structural vibration isolation. The CTI consists of a crank, a linking rod, a gear-pinion box, and a flywheel that generates inertance. It has advantages of quick adjustment of inertance and strong adaptability to other disturbances. First, the inertial force provided by the CTI is linearized and expressed in a simple format; the minimum length of linking rod and crank are obtained for a CTI operating linearly under various deformed configurations. Then, the motion equation of the coupled structure-CTI system is formulated, and transmissibility is analyzed. Laboratory experiments are next carried out to verify the CTI’s mechanical property and vibration isolation performance. It is shown that the inertance of the CTI obtained in the tests agrees well with the analytical result. CTIs can significantly decrease the amplitude-frequency responses at the fundamental frequency but cannot achieve vibration isolation in a full frequency range. Finally, the seismic control effect of base-isolated buildings with and without CTI is numerically studied. An optimal design method of the CTI is proposed, and the story drift ratio and deformation of the isolation layer can be reduced simultaneously with the optimal inertance. The installation methods of CTIs for buildings are also presented.

Development of vibration isolation models in vibratory roller’s seat and cabin: A survey

Under the impaction of excitation forces of the elastic tire/rigid drum and off-road soil ground interactions, the vibratory roller’s ride quality had been strongly influenced. Thus, the vibration isolation models and structures of the vehicle’s cabin and seat are studied and improved for enhancing the vehicle’s ride quality. To have an overview of the study and development process of the seat suspensions and cabin isolations, this research provides the overall view of the seat and cabin’s vibration isolation models developed and applied to the vibratory rollers based on the results of the existing studies. The study shows that with the semiactive hydraulic isolations (HIs) or semiactive pneumatic-hydraulic isolations (PHIs) applied to the cabin’s vibration isolations, the cabin shaking and driver’s ride quality have been remarkably ameliorated, while, with quasi-zero stiffness elements (QSE) added into the seat suspension, the driver’s ride quality has been greatly ameliorated. Based on the studied results, to control the cabin shaking and enhance the driver’s ride quality, a combination between the cabin’s semiactive HIs and the seat’s QSE should be developed in further studies.

Dynamic characteristics analysis of bilayer bio-inspired X-shaped vibration isolation structure

Based on the vibration isolation properties of the coupled toe-leg structure of the biped bird, a bilayer bio-inspired X-shaped vibration isolation structure (BBXVI) considering the coordination function between skeleton type and muscle/tendon is proposed in this research. The mapping relationships of equivalent restoring force–displacement and equivalent stiffness–displacement with various parameters are analyzed by statics, the parameter condition and the modulation of nonlinear behavior of the BBXVI to achieve quasi-zero stiffness (QZS) are investigated. Based on establishing dynamic model of the bilayer X-shaped structure, the effects of initial angle, rod-length ratio and rod length on dynamic characteristics and vibration transmissibility of the BBXVI subjected to displacement excitation are studied by incremental harmonic balance method (IHBM). The study found that the BBXVI presents excellent low frequency vibration isolation performance. With increasing α1, the QZS characteristic, vibration isolation bandwidth and response amplitude of the BBXVI increase first and then decrease. The larger rod-length ratio and longer rod length can increase the vibration isolation bandwidth and improve the vibration isolation performance. In addition, longer rod length could make the equivalent stiffness of the BBXVI gradually evolve from hardening spring to softening spring properties, and the vibration transmission property of the vibration isolation system is changed.

Identification of Asymmetric Bouc–Wen Hysteresis Under Intense Noise by Only Measuring Acceleration

Abstract Parameter identification of hysteretic models is significant for predicting structural dynamic response in vibration isolation structures. However, quasi-static testing and displacement measurement methods are not convenient for assembly structures and sensor layouts. Moreover, the methods based on evolutionary optimization need to provide appropriate boundary conditions for convergence and efficiency. Therefore, a novel hybrid identification method that takes the advantage of physics-informed parameter constraints and only acceleration measurement is proposed to identify the asymmetric Bouc–Wen hysteresis model. The restoring force surface is constructed for hysteretic force extraction based on the measurement of base excitation and isolated mass acceleration. The polynomial fitting and limit cycle approach are utilized for physical information given of an improved Bouc–Wen model. Furthermore, the evolutionary algorithm based on parameter constraints is implemented for final parameter estimation. A numerical simulation of an asymmetric Bouc–Wen model shows that the proposed method can keep an normalized mean square error (NMSE) of 0.19% under the noise level of 30 dB. The reconstructed hysteresis loop keeps in good agreement with the theoretical one.

Vibration isolation performance analysis of a bilateral supported bio-inspired anti-vibration control system

To achieve better anti-vibration performance in a low frequency region and expand the range of vibration isolation, a bilateral supported bio-inspired anti-vibration (BBAV) structure composed of purely linear elements is proposed, inspired by the motion form of bird legs and the nonlinear extension and compression of muscles and tendons. The kinematic relations and nonlinear dynamic model considering vertical and rotational vibrations are established. The loading capacity and equivalent stiffness are investigated with key parameters. The amplitude-frequency characteristics and force transmissibility are used to evaluate the stability and anti-vibration performance with the effects of the excitation amplitude, rod length, installation angle, and spring stiffness. The results show that the loading requirements and resonant characteristics of the BBAV structure are adjustable, and superior vibration isolation performance can be achieved readily by tuning the parameters. The X-shaped vibration structure is sensitive to the spring stiffness, which exhibits a wider vibration isolation bandwidth with smaller spring stiffness. Besides, depending on the parameters, the nonlinear behavior of the BBAV system can be interconverted between the softening type and the hardening type. The theoretical analysis in this study demonstrates the advantages and effectiveness of the vibration isolation structure.

Hierarchical re-entrant honeycomb metamaterial for energy absorption and vibration insulation

A novel hierarchical re-entrant honeycomb metamaterial is proposed by integrating the re-entrant honeycomb (RH) with square unit cell and named as square re-entrant honeycomb (SRH). The novel hierarchical re-entrant honeycomb can not only improve energy absorption capacity but also present better vibration insulation compared with traditional RH structure. Dynamic crushing behaviors of the SRH structures are investigated theoretically and numerically. The theoretical plateau stress is in good agreement with the numerical plateau stress. Meanwhile, the deformation modes and energy absorption capacity of RH and square re-entrant honeycombs (SRHs) are compared under different impact velocities. The results show that the plateau stress and the specific energy absorption (SEA) of SRHs is higher than RH. Moreover, the vibration isolation capability of the SRHs is studied using finite element analysis. In particular, the introduction of square unit cells expand the band gap, especially in the low frequency range. By adjusting the size of oscillators, the starting and stopping frequencies of band gaps are lower effectively and the number of band gaps is increased. The results indicate that the introduction of the mass inclusions can improve the band gap characteristics of the SRH, which produce local resonance effect and the local resonance type band gap. It also appears multiple band gaps at the same time. In addition, the introduction of the mass inclusions also improves the SEA of the SRH under high-velocity crushing. This work may benefit structural vibration isolation and protection design, which provides a new thought for design and development of advanced multi-functional composite structures and materials in the engineering.

Optimal design of negative-stiffness dampers for improved efficiency of structural seismic isolation

Over the past two decades, negative-stiffness devices have attracted increasing interest in the community of structural vibration isolation and control. They are typically used in combination with supplemental damping devices, and the combined systems are often referred to as negative-stiffness dampers (NSDs). Different types of NSDs have been developed and studied using both theoretical and experimental methods. However, comprehensive comparative studies between optimally designed NSDs for improving the efficiency of structural seismic isolation are inadequate. In this paper, three types of NSDs, i.e., the negative-stiffness viscous damper (NSVD), negative-stiffness viscoelastic damper (NSVeD), and negative-stiffness inertoviscous damper (NSiVD) are considered and compared in terms of their efficiencies for structural seismic isolation. Analytical formulas are derived to calculate the optimal damping coefficients of the NSVeD and NSiVD to maximize the modal damping ratio, thus minimizing the peak transmissibility. Frequency- and time-domain responses of low-frequency structures separately equipped with the three types of NSDs are compared when they are designed to achieve equal modal damping ratios. Moreover, based on the derived analytical optimal formulas, a multi-objective minimization design method is presented to determine the optimal characteristic parameters of NSDs, and simultaneous reduction of isolator displacement and floor response acceleration of a benchmark base-isolated building structures under a suit of design-level ground motions is achieved. The results indicate that the three types of NSDs can be more effective than conventional viscous dampers in reducing floor response accelerations of base-isolated structures without compromising the isolator displacement, and the NSVeD has superior performance over the NSVD and NSiVD in terms of improved efficiency of structural seismic isolation.

Meta-Kagome lattice structures for broadband vibration isolation

One-dimensional (1D) phononic crystal (PC) beams have been extensively studied due to their bandgap properties, but the idea of using this functional beam components to form three-dimensional (3D) periodic structures has rarely been mentioned. In this paper, the PC beam element is used to replace the ordinary member of the conventional Kagome lattice structures, thus, a meta-Kagome lattice (MKL) structure is innovatively constructed with broadband vibration isolation performance. The dispersion analysis is performed to reveal the mechanism of bandgap formation and the reason of getting broad bandgaps. Three kinds of MKL structures, namely, with triangular, rectangular and hexagonal pyramids are designed. The vibration transmission properties of the MKL columns with or without interfaces are studied to illustrate the isolation effect. Moreover, the vibration isolation performance of the sandwich structures composed of MKL cores is also studied, and the influence of the skin characteristics on the properties is discussed. Vibration transmission tests were conducted to verify the results. This work provides a new method to develop 3D multi-functional lattice structures, especially for load-bearing and vibration reduction.

Experimental Analysis of Constrained Layer Damping Structures for Vibration Isolation in Lightweight Railway Vehicles

Rolling stock manufacturers face the challenge of manufacturing lightweight high-speed trains without deteriorating comfort. One of the difficulties is to mantain or increase structural stiffness and damping as the car bodies become lighter. Leaving aside active solutions, which are expensive and generally complex to implement, increasing structural damping by means of viscoelastic patches (via Constrained Layer Damping) seems to be a viable solution which is in fact already used for acoustic insulation in automotive, aerospace and even railway applications. Although there are works in the literature that try to optimise viscoelastic panels, this work presents an experimental study with two essential contributions: (i) to analyse the influence of a broad set of design parameters such as type of the constraining layer (uniform or honeycomb), thickness of the viscoelastic layer, location, covered area and continuity between patches; and (ii) to consider absolute and specific (per unit mass) damping depending on the design scenario. To locally increase the structural damping of an existing lightweight structure without compromising its weight, partial application of thin viscoelastic and constraining layers turned out to be the best solution. To enhance structural damping from the design stages, disregarding constraining layer mass by incorporating its stiffness into the overall stiffness of the structure, full coverage with thick viscoelastic layer and a honeycomb constraining layer with a high cross-section moment of inertia turned out to be the best option, reaching modal damping ratios up to 22 times higher than structures without viscoelastic materials.

Novel periodic pile barriers in saturated soil and applications to propagation attenuation of shear plane waves

The frequency attenuation zones (AZs) of periodic pile barriers have attracted extensive attention in recent years due to their superior performance in ambient vibration reduction. However, the research on vibration isolation of pile barriers in saturated soil is very limited. Also, the configuration of the traditional pile barrier is simple and the AZ width is narrow, which limits its application in engineering practice. In this paper, to develop novel periodic pile barriers with the maximum relative attenuation zone width (RWAZ) in saturated soil, the topology optimization on the periodic pile unit is carried out with the genetic algorithm (GA) and FEM. For different site conditions, the effects of the saturated soil porosity, the drained elastic modulus, the drained density and the tortuosity coefficient of soil on the optimization results are analyzed, and the corresponding optimized pile structures are proposed, respectively. Thus, the effect of material distribution on the RWAZ is disclosed, and novel periodic pile structures for ambient vibration isolation in saturated soil are developed. Furthermore, the superior shear plane wave attenuation performances of the optimized pile structure in saturated soil are both demonstrated by the established 2D and 3D numerical models.

A three million Q factor tuning fork resonator based on a vibration isolation structure

The quality factor (Q factor) is one of the most important parameters for a resonant sensor since it determines the performance of the resonant system. The mass distribution imbalance caused by the fabrication error has a great impact on the anchor loss, and the Q factor will, thus, decrease drastically. In this work, a vibration isolation structure of the tuning fork is proposed to eliminate the influence of weight imbalance so that an ultrahigh Q factor can be obtained. With this designed vibration isolation structure, we prove that the anchor loss can be reduced significantly via numerical simulations, and we experimentally demonstrate that Qanchor increases by at least 78.6%. Moreover, the surface loss of the fused quartz tuning fork is also reduced after chemical etching, and we use interdigital electrodes for electrostatic excitation to avoid loss caused by the metal film employed in the conventional excitation method. Finally, the Q factor increases to 3 × 106, which is one of the highest test values known at present, and it is 127% larger than that of the tuning fork that uses a coated metal film for electrostatic excitation.

Novel low frequency bionic vibration isolation structure

Inspired by the hind limbs of goats, a bio-inspired polygon vibration isolation structure with nonlinear stiffness and damping is proposed. The bionic mechanism consists of four bionic legs with different rods (as skeleton), 12 inclined tension springs (as muscle or tendon), a bearing platform, a base, and so on. A theoretical model is developed to characterize its stiffness nonlinearity through geometrical and mechanical analysis. Theoretical analysis shows that the bionic structure has nonlinear positive stiffness and large working range. The dynamic model of the structure is established based on the Lagrange principle, and the influence of various structural parameters on the vibration isolation performance of the structure was analyzed combined with ADAMS. Thanks to the unique bionic design, the device allows the stiffness and damping characteristics of the system to be adjusted by varying the structural parameters, resulting in excellent stability, high static and low dynamic stiffness, excellent vibration isolation performance, and good load carrying capacity without active control.

A novel crank inerter with simple realization: Constitutive model, experimental investigation and effectiveness assessment

The inerter-based device is of increasing interest to scholars in the field of structural vibration control, which is characterized by apparent mass and negative stiffness effects. With this regard, it is potential to develop variable negative stiffness characteristics with the technology of inerter, which is promising to provide improved performance for structural vibration isolation and vibration suppression. In this study, the theoretical analysis and experimental investigation of a novel inerter element, named crank inerter, is performed. The presented crank inerter is proposed to generate a variable negative stiffness effect, which is realized on the basis of a crank mechanism. A constitutive model of crank inerter is developed to predict its mechanical behavior. For an in-depth understanding of the inertial property of the crank inerter, a parametric analysis is conducted on the inertia force calculation of the crank inerter. A prototype crank inerter is fabricated and tested under sinusoidal excitations to verify the proposed constitutive model. A variable negative stiffness of the crank inerter is reflected from the proposed constitutive model. The theoretical results calculated with the proposed constitutive model match well with the experimental data, which verifies that the proposed model can predict the mechanical behavior of the crank inerter. The dynamic analysis of a vibration isolator with a crank inerter is conducted to illustrate its effectiveness using the proposed constitutive model. The analysis results preliminarily show that the isolator with crank inerter can improve the structural performances regarding the peak force transmissibility and frequency band. Based on the presented investigations, a crank inerter with a simple configuration is summarized to be effective for providing an apparent mass effect and variable negative stiffness.

Cockroach-inspired structure for low-frequency vibration isolation

Insects bear huge external loads without injury, for example, cockroaches can withstand forces up to 900 times body weight owing to the shape-changing ability of their jointed exoskeletons and striated muscles, which can absorb huge energy and dissipate by the damping of body-friction. This paper presents a cockroach-inspired structure (CIS) by mimicking the body topology of cockroaches for low-frequency vibration isolation. The exoskeletons, which provide the low-frequency characteristic, are mimicked by a diamond-shape chamber. The striated muscles providing the restoring force are mimicked by springs, and the front legs are mimicked by rods and sliders. The diamond-shape chamber contributes to nonlinear stiffness and the sliders lead to nonlinear damping and inertia effects. The theoretical model was established and the comprehensive parameter studies and optimization efforts were carried out to verify the vibration isolation performance of CIS. The results demonstrate that the nonlinear properties of CIS can dramatically reduce the resonant frequency and peak transmissibility. The spring assembly direction influences the vibration isolation performance. CIS exhibits an anti-resonance phenomenon under a larger inertia. This study creatively provides a type of insect-inspired structures for high-stability and cost-effectiveness low-frequency vibration isolation.

On the nonlinear dynamics of a Kresling-pattern origami under harmonic force excitation

Kresling origami-inspired cylindrical structures have received considerable attention due to their effective deployment characteristics, programmable dual-directional and multifunctional properties, along with their ability to support loads. The Kresling origami investigations to date have focused mostly on their geometry, kinematics, and quasi-static mechanics. While recent works have started to uncover the Kresling origami’s transient deployment dynamics and linear vibration/wave propagation features, the rich nonlinear dynamics of Kresling origami-inspired structures under consistent external excitations have yet to be examined and understood. Given that Kresling origami elements are highly nonlinear so their dynamic responses can be extremely complex under external disturbances, and the fact that in many applications they are embedded in mechanical systems that are continuously excited, such as in robotics, air and ground vehicles, and impact, noise, and vibration isolation structures, this is an important and nontrivial research issue that needs to be addressed.To advance the state of the art, the goal of this research is to explore and uncover the nonlinear dynamics of Kresling origami-inspired tubular structures under consistent forced excitations, in particular harmonic loadings. Time and frequency domain analyses are performed and bifurcation diagrams are developed and analyzed for a range of forcing amplitudes and frequencies. This research reveals the complex responses of Kresling origami-inspired systems, i.e., existence of multiple period-1 attractors, period-n (n>1) attractors, jump from one attractor (limit-cycle) to another attractor, and presence of chaotic attractors for a range of input forcing parameters. The noteworthy result of this study also concerns a synchronization of the origami cylinder’s steady-state axial and rotational (twist) displacements. Without such a forced nonlinear dynamic analysis, these findings have not been and cannot be discovered in previous studies. The insights and knowledge uncovered in this investigation are valuable in raising awareness and providing guidance in the design and control of Kresling origami-based structures for realistic engineering operations, where external dynamic disturbances are often unavoidable.