The vibration suppression performance of the pyramid lattice core sandwich plates is receiving increasing attention and needs further investigation for technical upgrading of potential engineering ...applications. Inspired by the localized resonant mechanism of the acoustic metamaterials and considering the integrity of the lattice sandwich plate, we reshaped a sandwich pyramid lattice core with resonant rings (SPLCRR). Finite element (FE) models are built up for the calculations of the dispersion curves and vibration transmission. The validity of the bandgap of the SPLCRR and remarkable vibration suppression are verified by experimental observations and the numerical methods. Furthermore, the effects of geometric parameters, material parameters and period parameters on the bandgaps of the SPLCRR are systematically investigated, which offers a deeper understanding of the underlying mechanism of bandgap and helps the SPLCRR structure meet the technological update requirements of practical engineering design.
The pyramid-type lattice sandwich panel is known for its exemplary mechanical characteristics. In this study, we draw inspiration from the local resonance mechanisms observed in acoustic ...metamaterials and introduce a resonant ring to enhance the capabilities of the panel for damping low-frequency vibrations. We use the finite element method to develop a model to explore the band structure and the corresponding vibrational responses, with a particular emphasis on the significant influence of the bandgap. A comprehensive comparison between the results of experiments and those of simulations unequivocally validated our proposed model. Crucially, our findings underscore that the damping-related effect can be enhanced and the desired range of frequencies can be fine-tuned by appropriately selecting the geometric and periodic parameters of the lattice sandwich panel. These insights have important implications for tailoring materials to specific engineering applications.
Four-degree-of-freedom (4-DOF) human-chair coupling models are constructed to characterize the different contact modes between the head, chest back, waist back and backrest. The seat-to-head transfer ...ratio (STHT) is used as an evaluation metric for vibration reduction effectiveness. The simulated vibration reduction ratio of the model is close to the experimental results, which proves the validity of the model. The peak STHT is obviously reduced (P < 0.05, T-test) with seat-backrest support. The experiments show that supporting the head (
, P < 0.05, Wilcoxon matched-pairs signed ranks) has the best vibration reduction effect (21%), supporting the chest back (
, P < 0.05) has a reduced effect (11%), and supporting the waist back (
, P < 0.05) has the weakest effect (4%). When the upper torso is in full contact with the backrest, the peak STHT curve and resonance frequency are positively correlated with the contact stiffness of the seat surface and negatively correlated with the contact damping. In order to reduce the seat-to-head transfer ratio, the lowest STHT peak and lowest total energy judgments were proposed as the selection methods for the selection of the contact stiffness and damping of the backrest in two environments (periodic and non-periodic excitation), respectively.
Isotropic magnetorheological elastomers (MREs) with hybrid-size particles are proposed to tailor the zero-field elastic modulus and the relative magnetorheological rate. The hyperelastic ...magneto-mechanical property of MREs with hybrid-size CIPs (carbonyl iron particles) was experimentally investigated under large strain, which showed differential hyperelastic mechanical behavior with different hybrid-size ratios. Quasi-static magneto-mechanical compression tests corresponding to MREs with different hybrid size ratios and mass fractions were performed to analyze the effects of hybrid size ratio, magnetic flux density, and CIP mass fraction on the magneto-mechanical properties. An extended Knowles magneto-mechanical hyperelastic model based on magnetic energy, coupling the magnetic interaction, is proposed to predict the influence of mass fraction, hybrid size ratio, and magnetic flux density on the magneto-mechanical properties of isotropic MRE. Comparing the experimental and predicted results, the proposed model can accurately evaluate the quasi-static compressive magneto-mechanical properties, which show that the predicted mean square deviations of the magneto-mechanical constitutive curves for different mass fractions are all in the range of 0.9-1. The results demonstrate that the proposed hyperelastic magneto-mechanical model, evaluating the magneto-mechanical properties of isotropic MREs with hybrid-size CIPs, has a significant stress-strain relationship. The proposed model is important for the characterization of magneto-mechanical properties of MRE-based smart devices.
•The first order shear deformation theory and Reissner plate theory are used for analysis of thermal buckling and sound radiation behavior analyses of truss core sandwich structure resting on elastic ...foundation.•The excellent accuracy of the established analytical model is demonstrated by comparisons with numerical simulation results calculated by commercial finite element software (LMS Virtual.Lab).•Effects of the truss core radius, inclination angle and height, temperature field and elastic foundation stiffness coefficient on thermal buckling and sound radiation behavior are also investigated.•A further comprehension was given on the underlying mechanism of sound radiation through lattice truss core sandwich plate structure under thermal environment.
Due to high stiffness and other potential multifunctional application characteristics, truss core sandwich structure offers a promising alternative to traditional stiffened or corrugated sandwich plates used in aerospace and marine industry. And sound radiation from plate structures is a design factor indicating the power reduction, which can help the lattice truss core sandwich structure meet the acoustic requirements for practical engineering design, but the sound radiation performance of this sandwich structure remains unclear. Based on that, the thermal buckling and sound radiation behavior analyses of truss core sandwich structure resting on elastic foundation in thermal environment are presented in this paper. The mechanical behavior of structure–foundation interaction is modeled as two-parameter model including Winkler and shear foundation. The sound radiation due to a concentrated harmonic force in thermal environment is computed by solving the Rayleigh integral. By comparing with numerical simulation results calculated by commercial finite element software, the accuracy and feasibility of theoretical model developed in this paper are validated. The effects of several key parameters including the truss core radius, inclination angle and height, temperature field and elastic foundation stiffness coefficient on thermal buckling and sound radiation behavior have been subsequently investigated.
As a class of newly developed sandwich structures, lattice sandwich structures has attracted more and more researchers attention due to its potential multifunctional application characteristics. Through numerical results, we try to give a further comprehension of the underlying mechanism of acoustic response and to help the lattice truss core sandwich structure meet the acoustic requirements for practical engineering design Display omitted .
This paper introduces an electromagnetic structure utilizing the controllable mechanical properties of magnetorheological elastomer (MRE) materials through magnetic flux. An adaptive elastic ...foundation composed of these materials is explored for vibration reduction and frequency modulation. This study investigates these effects using both a single-mass model and a coupled human–seat model. For objects supported by the adaptive elastic foundation, increasing the magnetic flux enhances the stiffness and damping, thereby significantly reducing the peak response while slightly increasing the resonance frequency. Strategies such as increasing the magnetic flux, reducing the object mass, and minimizing the system’s degrees of freedom and internal damping contribute to enhancing the vibration reduction and frequency modulation in the adaptive elastic foundation. The simulation results indicate that for a seated human (weighing between 72.4 kg and 88.4 kg), the adaptive elastic foundation reduces the head peak response by approximately 15.7% and increases the resonance frequency by approximately 3.4% at a magnetic flux of 138 mT.
In this paper, the nonlinear dynamic system of a brushless DC motor with voltage disturbance is studied analytically via a generalized harmonic balance method. A truncated Fourier series with ...time-varying coefficients is utilized to represent the analytical variations of nonlinear currents and voltages within this dynamic system. Bifurcations of periodic currents and voltages are obtained, and their stability is discussed through eigenvalue analysis. The frequency–amplitude characteristics of periodic currents and voltages exhibit complexity in the frequency domain. Comparative illustrations are provided to contrast the analytical solutions with numerical outcomes for periodic currents and voltages. These analytical findings can be effectively employed for controlling the brushless DC motors experiencing voltage disturbances.
Trichloroethylene (TCE), one of 129 kinds of priority pollutants, is the most common halogenated organic pollutant in the environment. To explore the changes in soil physicochemical properties and ...biological activities then clarify the effects of these factors on bacterial, fungal and actinomycetes communities in Mollisol under TCE stress is the significance of our research. The results indicated that when TCE concentration was greater than 10 mg kg−1, soil quality declined and soil decomposition of organic matter and cycling of mineral nutrients were inhibited through an effect on soil microbial biomass. Operational taxonomic units (OTUs) richness of the bacteria in Mollisol was altered by TCE contamination. The SChao1 and HShannon indices of bacterial communities in Mollisol decreased when 40 mg kg−1 TCE was applied. Meanwhile, the OTU richness of fungi in Mollisol was altered by TCE contamination. The HShannon indices of the fungal communities in Mollisol were inhibited by higher TCE concentrations (20 and 40 mg kg−1 TCE). TCE altered the content of some bacteria, fungi and actinomycetes involved in soil carbon and nitrogen cycling and metabolism, such as Acidobacteria, Proteobacteria, Planctomycetes, Chytridiomycota, Streptomycetales, Pseudonocardiales, Propionibacteriales and Rhizobiales, and thus influenced nutrient cycling and the process of energy metabolism in Mollisol. In addition, redundancy analysis (RDA) results indicated that physicochemical properties and biological activities under TCE contamination significantly affected soil microbial community composition thus confirming that TCE interfered with the carbon and nitrogen cycling and metabolism of soil microorganisms. The results of this study are of great importance for revealing the effects of TCE stress on the microbiological characteristics of Mollisol, and also provide more useful information for determining the potential ecological risk of organic pollutants in Mollisol.
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•TCE above 10 mg kg−1 decreased soil quality and inhibited soil decomposition and cycling.•TCE altered community composition of key microorganism in soil bacteria, fungi and actinomycetes.•The SChao1 and HShannon indices of bacterial communities in Mollisol decreased under 40 mg kg−1 TCE.•Soil physicochemical properties and biological activities under TCE stress affected the microbial community in Mollisol.•TCE interfered with the carbon and nitrogen cycling and metabolism of soil microorganisms.
In order to investigate the noise reduction effect of barrier with multi-well on its top. The effect of the layout of the wells was investigated by the 2D boundary element method (BEM). Results show ...that, the layout of the well would affect the noise reduction effect on receiver which is high from the ground, mainly in the mid frequency range. And the mainly concerned well should better be located close to the source side. Besides, the noise reduction effect relies on the sound diffraction around the top of the barrier, so, the layout of the walls of the wells also plays an important role to improve the performance of the barrier. Different kinds of layouts of the walls of the wells were also calculated and compared. Results show that, the noise reduction effect of the barrier is greatly affected by the layout of the walls of the wells. The performance of barrier which the layout of walls of the wells in ascending order of the heights from the source side to the receiver side is better than that in descending order. Experiments were also carried out in a semi-anechoic chamber, the experimental results agree well with the calculation results.
The performance of a pilot-scale anaerobic membrane bioreactor (AnMBR) for treating antibiotic solvent wastewater under different cross flow velocities (CFV) was investigated. Effects of mixed liquid ...suspended solids (MLSS), colloid total organic carbon (TOC) and CFV on membrane fouling rate (RMF) were also explored in this paper. Throughout 341 days of experiment, the average total removal rate of N, N-Dimethylformamide (DMF) was 98.5% which hardly affected by the variation of CFV, and the compliance rate of DMF was 92% according to the Chinese standard (<25 mg/L). However, the relevant high total removal rate of M-cresol (MC) was achieved as 97.5%, the content of effluent failed to meet the national level emission standard (<0.1 mg/L). The biogas yield and the methane content of the biogas increased gradually with the increase of CFV, and the average methane content were over 70%. There were four kinds of methanogens in AnMBR, Methanosaeta spp was the largest methanogenic community, with an area of 45–70% of the archae. There was a linear relationship between colloid TOC and RMF at different MLSS concentrations. Then a universal mathematical model for the changes of RMF with influence factors was established. The result showed that model well fitted the laboratory data. It is suggested that the model proposed could reflect and manage the membrane fouling of AnMBR treating antibiotic solvent wastewater.
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•The characteristic pollutants DMF and MC were removed effectively under different CFV.•Methanosaeta spp was the largest methanogenic community during four stages in AnMBR.•There was a linear relationship between colloid TOC and RMF at different MLSS.•A universal mathematical model was established and verificated.
