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Dynamics and vibration reduction performance of asymmetric tristable nonlinear energy sink

Applied Mathematics and mechanics(English Edition) 2024年第3期45卷 389-406页

作者： Hongyan CHEN Youcheng ZENG Hu DING Siukai LAI Liqun CHEN School of Mechanical Engineering University of Science and Technology BeijingBeijing 100083China Shanghai Key Laboratory of mechanics in Energy Engineering Shanghai Frontier Science Center of MechanoinformaticsShanghai Institute of Applied Mathematics and MechanicsSchool of Mechanics and Engineering ScienceShanghai UniversityShanghai 200444China department of Civil and Environmental Engineering The Hong Kong Polytechnic UniversityKowloonHong KongChina

With its complex nonlinear dynamic behavior,the tristable system has shown excellent performance in areas such as energy harvesting and vibration suppression,and has attracted a lot of *** this paper,an asymmetric tristable design is proposed to improve the vibration suppression efficiency of nonlinear energy sinks(NESs)for the first *** proposed asymmetric tristable NES(ATNES)is composed of a pair of oblique springs and a vertical ***,the three stable states,symmetric and asymmetric,can be achieved by the adjustment of the distance and stiffness asymmetry of the oblique *** governing equations of a linear oscillator(LO)coupled with the ATNES are *** approximate analytical solution to the coupled system is obtained by the harmonic balance method(HBM)and verified *** vibration suppression efficiency of three types of ATNES is *** results show that the asymmetric design can improve the efficiency of vibration reduction through comparing the chaotic motion of the NES oscillator between asymmetric steady *** addition,compared with the symmetrical tristable NES(TNES),the ATNES can effectively control smaller structural *** other words,the ATNES can effectively solve the threshold problem of TNES failure to weak ***,this paper reveals the vibration reduction mechanism of the ATNES,and provides a pathway to expand the effective excitation amplitude range of the NES.

关键词： asymmetric nonlinear energy sink(NES) tristable vibration control po-tential barrier

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多重节点法并行求解大规模稀疏线性方程组

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Acta Mechanica Sinica 2024年第4期40卷 159-171页

作者：王永庆刘彬 Applied mechanics Laboratory Department of Engineering MechanicsTsinghua UniversityBeijing100084China

本文以弹性力学为例,提出了多重节点法用于求解大规模稀疏线性方程组.多重节点法利用叠加性将复杂问题分解为简单的子问题,并利用局部性减少计算量.粗节点刚度阵和子区域刚度阵在迭代时不变,使得多重节点法适合求解多工况问题.粗节点和... 详细信息

本文以弹性力学为例,提出了多重节点法用于求解大规模稀疏线性方程组.多重节点法利用叠加性将复杂问题分解为简单的子问题,并利用局部性减少计算量.粗节点刚度阵和子区域刚度阵在迭代时不变,使得多重节点法适合求解多工况问题.粗节点和细节点之间的映射关系通过求解局部有限元模型得到而非插值法,使得多重节点法能够快速求解复杂拓扑问题.为了加快收敛速度,提出了最优粗节点刚度阵,并基于正则化最小二乘法给出了其计算方法.大规模数值实验表明,多重节点法具有很好的可扩展性以及近似线性加速比.与主流算法如多重网格法相比,多重节点法在求解多工况问题时收敛速度更快.

关键词：正则化最小二乘法节点法细节点局部性多重网格法叠加性并行求解插值法

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Effects of surface energy and substrate on modulus determination of biological films by conical indentation

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Science China(Technological Sciences) 2024年第6期67卷 1757-1764页

作者： DING Yue LI Cheng-Ya NIU XinRui WANG Gang-Feng department of Engineering mechanics SVLXi’an Jiaotong UniversityXi’an710049China department of Mechanical Engineering City University of Hong KongHong Kong SAR999077China

Micro-/nano-indentation has become prevalent in evaluating the mechanical characteristics of biological samples,such as cells and ***,the existing contact models describing conical indentation ignore the joint effects of surface energy and substrate,and consequently cannot accurately extract the Young's modulus of biological samples deposited on *** finite element methods,we examine the conical indentation of biological films on substrates while taking surface energy into *** on the dimensional analysis,the explicit relationship between load and indentation depth is achieved for films with their moduli varying from 0.001 to 100 times that of the *** the classical Sneddon's model was employed to analyze the load-depth data,the measured modulus could reach 18 times the real modulus for films on harder substrates,but only 4%of the real modulus for films on softer ***,in micro-/nano-indentations,neglecting the contribution of surface energy would result in an overestimation of the Young's modulus of films depending on the contact *** analytical expression provided here can be utilized to precisely deduce the mechanical characteristics of biological films deposited on substrate from the load and indentation depth data of a conical indentation.

关键词： biological film surface effect substrate effect indentation

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Bending Analysis of Circular Piezoelectric Semiconductor Plates Incorporating Flexoelectricity

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Acta Mechanica Solida Sinica 2024年第4期37卷 613-621页

作者： Liang Sun Zhengguang Xiao Chunli Zhang Weiqiu Chen department of Engineering mechanics Zhejiang UniversityHangzhou310027China department of Basic Courses Naval University of EngineeringWuhan430033China Huanjiang Laboratory Zhuji311816China

Based on the three-dimensional(3D)basic equations of piezoelectric semiconductors(PSs),we establish a two-dimensional(2D)deformation-polarization-carrier coupling bending model for PS structures,taking flexoelectricity into *** analytical solutions to classical flexure of a clamped circular PS thin plate are *** the derived analytical model,we numerically investigate the distributions of electromechanical fields and the concentration of electrons in the circular PS thin plate under an upward concentrated *** effect of flexoelectricity on the multi-field coupling responses of the circular PS plate is *** obtained results provide theoretical guidance for the design of novel PS devices.

关键词： Piezoelectric semiconductor Plate model Flexoelectricity Multi-field coupling

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Velocity transformation for compressible wall-bounded turbulence——An approach through the mixing length hypothesis

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Science China(Physics,mechanics & Astronomy) 2024年第9期67卷 108-125页

作者： Xuke Zhu Yubin Song Xiaoshuo Yang Zhenhua Xia State Key Laboratory of Fluid Power and Mechatronic Systems and department of Engineering mechanics Zhejiang UniversityHangzhou 310027China

In an endeavor to establish a connection between the mean velocity profile in compressible wall-bounded turbulence and its incompressible analogue,a refined version of the Trettel and Larsson's(TL)transformation is systematically derived and rigorously assessed across diverse flow *** the recently proposed intrinsic compressibility effects and modeling the multi-layer structure of mixing lengths,the proposed transformation demonstrates exceptional performance in collapsing 57canonical flow cases,including cooled channel and pipe flows,channel flows with pseudo heat sources,as well as adiabatic and diabatic boundary layer ***,the transformation seamlessly extends to low Reynolds number cooled channel and pipe flows,achieving a level of accuracy unparalleled by other transformations in the current state-of-the-art.

关键词： mixing length hypothesis compressible wall-bounded turbulence velocity transformation law of the wall

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Generative deep-learning-embedded asynchronous structured light for three-dimensional imaging

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Advanced Photonics 2024年第4期6卷 45-58页

作者： Lei Lu Chenhao Bu Zhilong Su Banglei Guan Qifeng Yu Wei Pan Qinghui Zhang Henan University of Technology College of Information Science and Engineering Shanghai University Shanghai Institute of Applied Mathematics and Mechanics School of Mechanics and Engineering ScienceShanghai Key Laboratory of Mechanics in Energy Engineering Shaoxing Research Institute of Shanghai University National University of Defense Technology College of Aerospace Science and Engineering OPT Machine Vision Tech Co. Ltd. Department of Research and Development

Three-dimensional(3D) imaging with structured light is crucial in diverse scenarios, ranging from intelligent manufacturing and medicine to entertainment. However, current structured light methods rely on projector–camera synchronization, limiting the use of affordable imaging devices and their consumer applications. In this work, we introduce an asynchronous structured light imaging approach based on generative deep neural networks to relax the synchronization constraint, accomplishing the challenges of fringe pattern aliasing, without relying on any a priori constraint of the projection system. To overcome this need, we propose a generative deep neural network with U-Net-like encoder–decoder architecture to learn the underlying fringe features directly by exploring the intrinsic prior principles in the fringe pattern aliasing. We train within an adversarial learning framework and supervise the network training via a statisticsinformed loss function. We demonstrate that by evaluating the performance on fields of intensity, phase, and 3D reconstruction. It is shown that the trained network can separate aliased fringe patterns for producing comparable results with the synchronous one: the absolute error is no greater than 8 μm, and the standard deviation does not exceed 3 μm. Evaluation results on multiple objects and pattern types show it could be generalized for any asynchronous structured light scene.

关键词： asynchrony deep learning fringe pattern projection generative neural networks structured light three-dimensional imaging

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Dynamics of a rotating ring-stiffened sandwich conical shell with an auxetic honeycomb core

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Applied Mathematics and mechanics(English Edition) 2024年第6期45卷 963-982页

作者： S.JAHANGIRI A.GHORBANPOUR ARANI Z.KHODDAMI MARAGHI department of Solid mechanics Faculty of Mechanical EngineeringUniversity of KashanKashan ***Iran Faculty of Engineering Mahallat Institute of Higher EducationMahallat ***Iran

The free vibration analysis of a rotating sandwich conical shell with a reentrant auxetic honeycomb core and homogenous isotropic face layers reinforced with a ring support is *** shell is modeled utilizing the first-order shear deformation theory(FSDT)incorporating the relative,centripetal,and Coriolis accelerations alongside the initial hoop tension created by the *** governing equations,compatibility conditions,and boundary conditions are attained using Hamilton’s *** trigonometric functions,an analytical solution is derived in the circumferential direction,and a numerical one is presented in the meridional direction via the differential quadrature method(DQM).The effects of various factors on the critical rotational speeds and forward and backward frequencies of the shell are *** present work is the first theoretical work regarding the dynamic analysis of a rotating sandwich conical shell with an auxetic honeycomb core strengthened with a ring support.

关键词： free vibration conical shell rotating shell ring support auxetic honeycomb

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Near-field wideband beam training for ELAA with uniform circular array

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Science China(Information Sciences) 2024年第6期67卷 370-383页

作者： Yuhao CHEN Linglong DAI department of electronic Engineering Tsinghua UniversityBeijing National Research Center for Information Science and Technology (BNRist)

Extremely large-scale antenna array(ELAA) at millimeter wave(mmWave) and Terahertz(THz)band has been considered a key technology for combating high attenuation in high-frequency bands in future6G communications. Uniform circular arrays(UCAs) have attracted much attention because of their ability to provide flat beamforming gain at all angles. To realize efficient beamforming, beam training is widely used to acquire channel state information. However, with a large antenna number, the beam training overhead in ELAA systems becomes overwhelming. Moreover, with a large bandwidth, the beam defocus effect severely degrades beam training accuracy. To address these issues, this paper proposes a frequency-dependent focusing(FDF)-based beam training scheme to realize effective beam training in near-field wideband ELAA systems with UCA. Specifically, we first analyze the FDF property of UCA, where signals at different subcarriers can simultaneously focus on different distances. Then, by exploiting the FDF property to search different distances using different subcarriers simultaneously, we design a hierarchical codebook and propose an FDFbased beam training scheme. To reveal the effectiveness of the proposed scheme, we compare its necessary beam training overhead with that of existing schemes. Finally, the simulation results demonstrate that the proposed scheme can achieve accurate beam training in near-field wideband UCA systems with a low beam training overhead.

关键词： extremely large-scale antenna array (ELAA) uniform circular array (UCA) near-field wideband beam training

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Unknown DDoS Attack Detection with Fuzzy C-Means Clustering and Spatial Location Constraint Prototype Loss

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Computers, Materials & Continua 2024年第2期78卷 2181-2205页

作者： Thanh-Lam Nguyen HaoKao Thanh-Tuan Nguyen Mong-Fong Horng Chin-Shiuh Shieh department of electronic Engineering National Kaohsiung University of Science and TechnologyKaohsiung807618Taiwan department of electronic and Automation Engineering Nha Trang UniversityNha Trang650000Vietnam

Since its inception,the Internet has been rapidly *** the advancement of science and technology and the explosive growth of the population,the demand for the Internet has been on the *** applications in education,healthcare,entertainment,science,and more are being increasingly deployed based on the ***,malicious threats on the internet are on the rise as *** Denial of Service(DDoS)attacks are among the most common and dangerous threats on the internet *** scale and complexity of DDoS attacks are constantly *** Detection Systems(IDS)have been deployed and have demonstrated their effectiveness in defense against those *** addition,the research of Machine Learning(ML)and Deep Learning(DL)in IDS has gained effective results and significant ***,one of the challenges when applying ML and DL techniques in intrusion detection is the identification of unknown *** attacks,which are not encountered during the system’s training,can lead to misclassification with significant *** this research,we focused on addressing the issue of Unknown Attack Detection,combining two methods:Spatial Location Constraint Prototype Loss(SLCPL)and Fuzzy C-Means(FCM).With the proposed method,we achieved promising results compared to traditional *** proposed method demonstrates a very high accuracy of up to 99.8%with a low false positive rate for known attacks on the Intrusion Detection Evaluation Dataset(CICIDS2017)***,the accuracy is also very high,reaching 99.7%,and the precision goes up to 99.9%for unknown DDoS attacks on the DDoS Evaluation Dataset(CICDDoS2019)*** success of the proposed method is due to the combination of SLCPL,an advanced Open-Set Recognition(OSR)technique,and FCM,a traditional yet highly applicable clustering *** has yielded a novel method in the field of unknown attack *** further expands the trend of applying DL and M

关键词： Cybersecurity DDoS unknown attack detection machine learning deep learning incremental learning convolutional neural networks(CNN) open-set recognition(OSR) spatial location constraint prototype loss fuzzy c-means CICIDS2017 CICDDoS2019

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A high aspect ratio surface micromachined accelerometer based on a SiC-CNT composite material

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Microsystems & Nanoengineering 2024年第2期10卷 219-230页

作者： Jiarui Mo Shreyas Shankar Roberto Pezone Guoqi Zhang Sten Vollebregt Laboratory of electronic Components Technology and Materials(ECTM)Department of MicroelectronicsDelft University of TechnologyDelftThe Netherlands

Silicon carbide(SiC)is recognized as an excellent material for microelectromechanical systems(MEMS),especially those operating in challenging environments,such as high temperature,high radiation,and corrosive ***,SiC bulk micromachining is still a challenge,which hinders the development of complex SiC *** address this problem,we present the use of a carbon nanotube(CNT)array coated with amorphous SiC(a-SiC)as an alternative composite material to enable high aspect ratio(HAR)surface *** using a prepatterned catalyst layer,a HAR CNT array can be grown as a structural template and then densified by uniformly filling the CNT bundle with LPCVD *** electrical properties of the resulting SiC-CNT composite were characterized,and the results indicated that the electrical resistivity was dominated by the *** demonstrate the use of this composite in MEMS applications,a capacitive accelerometer was designed,fabricated,and *** fabrication results showed that the composite is fully compatible with the manufacturing of surface micromachining *** Young’s modulus of the composite was extracted from the measured spring constant,and the results show a great improvement in the mechanical properties of the CNTs after coating with *** accelerometer was electrically characterized,and its functionality was confirmed using a mechanical shaker.

关键词： composite surface electrical

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