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    01 November 2024, Volume 45 Issue 11
    Articles
    Prediction of single cell mechanical properties in microchannels based on deep learning
    Jiajie GONG, Xinyue LIU, Yancong ZHANG, Fengping ZHU, Guohui HU
    2024, 45(11):  1857-1874.  doi:10.1007/s10483-024-3187-6
    Abstract ( 178 )   HTML ( 27)   PDF (2158KB) ( 88 )  
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    Traditional methods for measuring single-cell mechanical characteristics face several challenges, including lengthy measurement times, low throughput, and a requirement for advanced technical skills. To overcome these challenges, a novel machine learning (ML) approach is implemented based on the convolutional neural networks (CNNs), aiming at predicting cells' elastic modulus and constitutive equations from their deformations while passing through micro-constriction channels. In the present study, the computational fluid dynamics technology is used to generate a dataset within the range of the cell elastic modulus, incorporating three widely-used constitutive models that characterize the cellular mechanical behavior, i.e., the Mooney-Rivlin (M-R), Neo-Hookean (N-H), and Kelvin-Voigt (K-V) models. Utilizing this dataset, a multi-input convolutional neural network (MI-CNN) algorithm is developed by incorporating cellular deformation data as well as the time and positional information. This approach accurately predicts the cell elastic modulus, with a coefficient of determination R2 of 0.999, a root mean square error of 0.218, and a mean absolute percentage error of 1.089%. The model consistently achieves high-precision predictions of the cellular elastic modulus with a maximum R2 of 0.99, even when the stochastic noise is added to the simulated data. One significant feature of the present model is that it has the ability to effectively classify the three types of constitutive equations we applied. The model accurately and reliably predicts single-cell mechanical properties, showcasing a robust ability to generalize. We demonstrate that incorporating deformation features at multiple time points can enhance the algorithm's accuracy and generalization. This algorithm presents a possibility for high-throughput, highly automated, real-time, and precise characterization of single-cell mechanical properties.

    Actively tunable sandwich acoustic metamaterials with magnetorheological elastomers
    Jinhui LIU, Yu XUE, Zhihong GAO, A. O. KRUSHYNSKA, Jinqiang LI
    2024, 45(11):  1875-1894.  doi:10.1007/s10483-024-3186-9
    Abstract ( 157 )   HTML ( 4)   PDF (3756KB) ( 127 )  
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    Sandwich structures are widespread in engineering applications because of their advantageous mechanical properties. Recently, their acoustic performance has also been improved to enable attenuation of low-frequency vibrations induced by noisy environments. Here, we propose a new design of sandwich plates (SPs) featuring a metamaterial core with an actively tunable low-frequency bandgap. The core contains magnetorheological elastomer (MRE) resonators which are arranged periodically and enable controlling wave attenuation by an external magnetic field. We analytically estimate the sound transmission loss (STL) of the plate using the space harmonic expansion method. The low frequency sound insulation performance is also analyzed by the equivalent dynamic density method, and the accuracy of the obtained results is verified by finite-element simulations. Our results demonstrate that the STL of the proposed plate is enhanced compared with a typical SP analog, and the induced bandgap can be effectively tuned to desired frequencies. This study further advances the field of actively controlled acoustic metamaterials, and paves the way to their practical applications.

    Unlocking multidirectional and broadband wind energy harvesting with triboelectric nanogenerator and vortex-induced vibration of sphere
    Lanbin ZHANG, Yixiang HE, Bo MENG, Huliang DAI, Lin WANG
    2024, 45(11):  1895-1912.  doi:10.1007/s10483-024-3185-8
    Abstract ( 144 )   HTML ( 6)   PDF (11852KB) ( 87 )  
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    A unique oscillating wind-driven triboelectric nanogenerator (OWTENG) based on the sphere's vortex-induced vibration (VIV) behavior is proposed in this study, which can harvest wind energy across a multitude of horizontal directions. With the Euler-Lagrange method, the coupled governing equations of the OWTENG are established and subsequently validated by experimental tests. The vibrational properties and output performance of the OWTENG for varying wind speeds are analyzed, demonstrating its effectiveness in capturing wind energy across a broad range of wind speeds (from 2.20 m/s to 8.84 m/s), and the OWTENG achieves its peak output power of 106.3 μW at a wind speed of 5.72 m/s. Furthermore, the OWTENG maintains a steady output power across various wind directions within the speed range of 2.20 m/s to 7.63 m/s. Nevertheless, when the wind speed exceeds 7.63 m/s, the vibrational characteristics of the sphere shift based on the wind direction, leading to fluctuations in the OWTENG's output power. This research presents an innovative approach for designing vibrational triboelectric nanogenerators, offering valuable insights into harvesting wind energy from diverse directions and speeds.

    Floating periodic pontoons for broad bandgaps of water waves
    Huaqing JIN, Haicheng ZHANG, Ye LU, Daolin XU
    2024, 45(11):  1913-1928.  doi:10.1007/s10483-024-3184-7
    Abstract ( 119 )   HTML ( 2)   PDF (7453KB) ( 95 )  
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    The narrow attenuation bands of traditional marine structures have long been a challenge in mitigating water waves. In this paper, a metastructure (MS) composed of floating periodic pontoons is proposed for broadband water wave attenuation. The interaction of surface gravity waves with the MS is investigated using linear wave theory. The potential solutions of water waves by the MS with a finite array are developed by using the eigenfunction expansion matching method (EEMM), and the band structure of the MS is calculated by the transfer matrix method (TMM), in which the evanescent modes of waves are considered. The solution is verified against the existing numerical result for a special case. Based on the present solution, the association between Bragg resonance reflection and Bloch bandgaps is examined, the effects of pontoon geometry are analyzed, and the comparison between floating MS and bottom-mounted periodic structures is conducted. A computational fluid dynamics (CFD) model is further developed to assess the structures in practical fluid environments, and the floating MS presents excellent wave attenuation performance. The study presented here may provide a promising solution for protecting the coast and offshore structures.

    A thermodynamics-consistent spatiotemporally-nonlocal model for microstructure-dependent heat conduction
    Yu ZHANG, Daming NIE, Xuyao MAO, Li LI
    2024, 45(11):  1929-1948.  doi:10.1007/s10483-024-3180-7
    Abstract ( 125 )   HTML ( 1)   PDF (1116KB) ( 24 )  
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    The spatiotemporally-nonlocal phenomena in heat conduction become significant but challenging for metamaterials with artificial microstructures. However, the microstructure-dependent heat conduction phenomena are captured under the hypothesis of spatiotemporally local equilibrium. To capture the microstructure-dependent heat conduction phenomena, a generalized nonlocal irreversible thermodynamics is proposed by removing both the temporally-local and spatially-local equilibrium hypotheses from the classical irreversible thermodynamics. The generalized nonlocal irreversible thermodynamics has intrinsic length and time parameters and thus can provide a thermodynamics basis for the spatiotemporally-nonlocal law of heat conduction. To remove the temporally-local equilibrium hypothesis, the generalized entropy is assumed to depend not only on the internal energy but also on its first-order and high-order time derivatives. To remove the spatially local equilibrium hypothesis, the thermodynamics flux field in the dissipation function is assumed to relate not only to the thermodynamics force at the reference point but also to the thermodynamics force of the neighboring points. With the developed theoretical framework, the thermodynamics-consistent spatiotemporally-nonlocal models can then be developed for heat transfer problems. Two examples are provided to illustrate the applications of steady-state and transient heat conduction problems.

    Natural frequency analysis of laminated piezoelectric beams with arbitrary polarization directions
    Zhi LI, Cuiying FAN, Mingkai GUO, Guoshuai QIN, Chunsheng LU, Dongying LIU, Minghao ZHAO
    2024, 45(11):  1949-1964.  doi:10.1007/s10483-024-3182-9
    Abstract ( 133 )   HTML ( 0)   PDF (1171KB) ( 80 )  
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    Piezoelectric devices exhibit unique properties that vary with different vibration modes, closely influenced by their polarization direction. This paper presents an analysis on the free vibration of laminated piezoelectric beams with varying polarization directions, using a state-space-based differential quadrature method. First, based on the electro-elasticity theory, the state-space method is extended to anisotropic piezoelectric materials, establishing state-space equations for arbitrary polarized piezoelectric beams. A semi-analytical solution for the natural frequency is then obtained via the differential quadrature method. The study commences by examining the impact of a uniform polarization direction, and then proceeds to analyze six polarization schemes relevant to the current research and applications. Additionally, the effects of geometric dimensions and gradient index on the natural frequencies are explored. The numerical results demonstrate that varying the polarization direction can significantly influence the natural frequencies, offering distinct advantages for piezoelectric elements with different polarizations. This research provides both theoretical insights and numerical methods for the structural design of piezoelectric devices.

    Establishment of the thermo-mechanical coupling model of axle box bearings with track irregularity excitation and analysis of its temperature characteristics
    Min WANG, Shaopu YANG, Yongqiang LIU, Yanhong CHEN, Kai ZHANG
    2024, 45(11):  1965-1986.  doi:10.1007/s10483-024-3188-7
    Abstract ( 128 )   HTML ( 2)   PDF (5876KB) ( 47 )  
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    As an important component of the running gear of high-speed trains, axle box bearings can cause lubricating grease failure and damage to bearing components under continuous high-temperature operation, which will affect the normal operation of high-speed trains. Therefore, bearing temperature is one of the key parameters to be monitored in the online monitoring system for trains. Based on the thermal network method, this paper establishes a thermal network model for the axle box bearing, considering the radial thermal deformation of the double-row tapered roller bearing components caused by the oil film characteristics and the temperature variations of the lubricating grease. A thermo-mechanical coupling model for the grease-lubricated double-row tapered roller axle box bearing of high-speed trains with track irregularity excitation is established. The correctness of the model is verified using the test bench data, and the temperature of the bearing at different rotational speeds, loads, fault sizes, and ambient temperatures are investigated.

    Torsional vibration suppression and electromechanical coupling characteristics of electric drive system considering misalignment
    Jinxin DOU, Zhenping LI, Hongliang YAO, Muchuan DING, Guochong WEI
    2024, 45(11):  1987-2010.  doi:10.1007/s10483-024-3179-6
    Abstract ( 139 )   HTML ( 4)   PDF (8430KB) ( 55 )  
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    The torque ripples resulting from external electromagnetic excitation and mechanical internal excitation contribute to significant torsional vibration issues within electromechanical coupling systems. To mitigate these fluctuations, a passive control strategy centered around a multi-stable nonlinear energy sink (MNES) is proposed. First, models for electromagnetic torque, gear nonlinear meshing torque, and misalignment torque are established. Building upon this foundation, an electromechanical coupling dynamic model of the electric drive system is formulated. Sensitivity analysis is conducted to determine the sensitive nodes of each mode and to provide guidance for the installation of the MNES. The structure of the MNES is introduced, and an electromechanical coupling dynamic model with the MNES is established. Based on this model, the influence of the misaligned angle on the electromechanical coupling characteristics is analyzed. In addition, the vibration suppression performance of the MNES is studied under both speed and uniform speed conditions. Finally, experimental testing is conducted to verify the vibration suppression performance of the MNES. The results indicate that misalignment triggers the emergence of its characteristic frequencies and associated sidebands. Meanwhile, the MNES effectively mitigates the torsional vibrations in the coupled system, demonstrating suppression rates of 52.69% in simulations and 63.3% in experiments.

    Sufficient variable selection of high dimensional nonparametric nonlinear systems based on Fourier spectrum of density-weighted derivative
    Bing SUN, Changming CHENG, Qiaoyan CAI, Zhike PENG
    2024, 45(11):  2011-2022.  doi:10.1007/s10483-024-3183-6
    Abstract ( 120 )   HTML ( 1)   PDF (383KB) ( 29 )  
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    The variable selection of high dimensional nonparametric nonlinear systems aims to select the contributing variables or to eliminate the redundant variables. For a high dimensional nonparametric nonlinear system, however, identifying whether a variable contributes or not is not easy. Therefore, based on the Fourier spectrum of density-weighted derivative, one novel variable selection approach is developed, which does not suffer from the dimensionality curse and improves the identification accuracy. Furthermore, a necessary and sufficient condition for testing a variable whether it contributes or not is provided. The proposed approach does not require strong assumptions on the distribution, such as elliptical distribution. The simulation study verifies the effectiveness of the novel variable selection algorithm.

    A neural network solution of first-passage problems
    Jiamin QIAN, Lincong CHEN, J. Q. SUN
    2024, 45(11):  2023-2036.  doi:10.1007/s10483-024-3189-8
    Abstract ( 148 )   HTML ( 3)   PDF (1912KB) ( 51 )  
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    This paper proposes a novel method for solving the first-passage time probability problem of nonlinear stochastic dynamic systems. The safe domain boundary is exactly imposed into the radial basis function neural network (RBF-NN) architecture such that the solution is an admissible function of the boundary-value problem. In this way, the neural network solution can automatically satisfy the safe domain boundaries and no longer requires adding the corresponding loss terms, thus efficiently handling structure failure problems defined by various safe domain boundaries. The effectiveness of the proposed method is demonstrated through three nonlinear stochastic examples defined by different safe domains, and the results are validated against the extensive Monte Carlo simulations (MCSs).

    Oscillatory squeeze flow through an Oldroyd-B fluid-saturated porous layer
    Yongjun JIAN
    2024, 45(11):  2037-2054.  doi:10.1007/s10483-024-3181-8
    Abstract ( 141 )   HTML ( 3)   PDF (6639KB) ( 21 )  
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    This study deals with the analytical investigation of oscillatory squeeze film flow through a Brinkman viscoelastic Oldroyd-B fluid-saturated porous layer subject to two vertically harmonically oscillatory disks. The validity of the present proposed analytical solutions is first demonstrated for the Newtonian fluids when both Λ1 and Λ2 tend to zero by comparison with the previous literature. Results demonstrate that an increase in the elasticity parameter Λ1 correlates with a rise in axial velocities, indicating that the relaxation time Λ1 facilitates enhanced squeeze flow. In the case of squeeze film flow in porous layers, low oscillating frequencies exert minimal effects on axial velocities, independent of variations in the viscoelasticity parameter Λ1. However, at higher oscillating frequencies, axial velocities escalate with increasing the viscoelasticity parameter Λ1. Furthermore, the retardation time Λ2 of the viscoelastic fluid shows no significant effect on the axial velocity, regardless of oscillating frequency changes in both pure fluids and porous layers.

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