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Experimental investigation of closed-loop active control to modulate coherent structures by mu-level method

Chinese Physics B 2024年第7期33卷 408-417页

作者：白建侠范子椰姜楠李秋营郑小波 Department of Mathematics Tianjin Renai CollegeTianjin 301636China Institute of mechanics Department of MechanicsSchool of Mechanical EngineeringTianjin UniversityTianjin 300354China college of Energy and Power engineering Lanzhou University of TechnologyLanzhou 730050China Tianjin Key Laboratory of Modern engineering mechanics Tianjin 300354China

The experimental research on zero-net-mass-flux jet closed-loop active control was conducted in the wind *** mu-level method successfully detected burst events of the coherent structures. The streamwise velocity signals in the turbulent boundary layer were measured by HWA. The drag reduction rate of 16.7% is obtained comparable to that of the open-loop control and saves 75% of the input energy at the asynchronous 100 V/160 Hz control case, which reflects the advantages of the closed-loop control. The experimental findings indicate that the intensity increases in the near-wall *** perturbation of the PZT vibrators on the skewness factor is concentrated in the region y+< 60. The generation of highspeed fluids is depressed and the downward effect of high-speed fluids weakens. The alteration of energy distribution and the discernible impact of modulation between structures of varying scales are observed. The correlation coefficient exhibits a strong positive correlation, which indicates that the large-scale structures produce modulation effect on small-scale *** occurrence of burst events is effectively suppressed. The disturbance has the characteristics of stable periodicity,positive and negative symmetry, low intermittency, and high pulsation strength. The conditional phase waveform shows that the fluctuation amplitude increases, indicating amplitude modulation effects on coherent structures.

关键词： turbulent boundary layer(TBL) burst event coherent structures mu-level method

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Automatic detection and assessment of crack development in ultra-high performance concrete in the spatial and Fourier domains

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Frontiers of Structural and civil engineering 2024年第3期18卷 350-364页

作者： Jixing CAO Yao ZHANG Haijie HE Weibing PENG Weigang ZHAO Zhiguo YAN Hehua ZHU School of Safety engineering and Emergency Management Shijiazhuang Tiedao UniversityShijiazhuang 050043China college of civil engineering and Architecture Zhejiang UniversityHangzhou 310058China college of civil and Architectural engineering Taizhou UniversityTaizhou 318000China college of civil engineering and Architecture Zhejiang University of TechnologyHangzhou 310014China Department of Geotechnical engineering Tongji UniversityShanghai 200092China

Automatic detection and assessment of surface cracks are beneficial for understanding the mechanical performance of ultra-high performance concrete(UHPC).This study detects crack evolution using a novel dynamic mode decomposition(DMD)*** this method,the sparse matrix‘determined’from images is used to reconstruct the foreground that contains cracks,and the global threshold method is adopted to extract the crack *** application of the DMD method to the three-point bending test demonstrates the efficiency in inspecting cracks with high ***,the geometric features,including the area and its projection in two major directions,are evaluated over *** relationship between the geometric properties of cracks and load-displacement curves of UHPC is *** to the irregular shape of cracks in the spatial domain,the cracks are then transformed into the Fourier domain to assess their *** indicate that crack patterns in the Fourier domain exhibit a distinct concentration around a central ***,the power spectral density of cracks exhibits an increasing trend over *** investigation into crack evolution in both the spatial and Fourier domains contributes significantly to elucidating the mechanical behavior of UHPC.

关键词： dynamic mode decomposition ultra-high performance concrete crack detection geometric features Fourier domain

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Dynamics and vibration reduction performance of asymmetric tristable nonlinear energy sink

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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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Anisotropic swelling pressures of compacted GMZ bentonite infiltrated with salt solutions

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Journal of Rock mechanics and Geotechnical engineering 2024年第9期16卷 3772-3785页

作者： Jing Ma Yong-Gui Chen Ling-Yan Jia Wei-Min Ye Dong-Bei Wu Qiong Wang Department of Geotechnical engineering College of Civil EngineeringTongji UniversityShanghai200092China State Key Laboratory of Disaster Reduction in civil engineering College of Civil EngineeringTongji UniversityShanghai200092China School of Chemical Science and engineering Tongji UniversityShanghai200092China

In the high-level radioactive waste(HLW)deep geological repository,bentonite is compacted uniaxially,and then arranged vertically in engineered *** assembly scheme induces the initial anisotropy,and with hydration,it develops more evidently under chemical *** investigate the anisotropic swelling of compacted Gaomiaozi(GMZ)bentonite and the further response to saline effects,a series of constant-volume swelling pressure tests were *** showed that dry density enhanced the bentonite swelling and raised the final anisotropy,whereas saline inhibited the bentonite swelling but still promoted the final *** final anisotropy coefficient(ratio of radial to axial pressure)obeyed the Boltzmann sigmoid attenuation function,decreasing with concentration and dry density,converging to a minimum value of *** staged evolution of anisotropy coefficient was discovered,that saline inhibited the rise of the anisotropy coefficient(Dd)in the isotropic process greater than the valley(d1)in the anisotropic process,leading to the final anisotropy *** isotropic stage amplified the impact of soil structure rearrangement on the macro-swelling pressure ***,a new method for predicting swelling pressures of compacted bentonite was proposed,by expanding the equations of Gouy-Chapman theory with a dissipative wedge *** evolutionary function was constructed,revealing the correlation between the occurrence time and the pressure value due to the structure rearrangement and the former crystalline ***,a design reference for dry density was given,based on the chemical conditions around the pre-site in Beishan,*** anisotropy promoted by saline would cause a greater drop of radial pressure,making the previous threshold on axial swelling fail.

关键词： HLW deep geological repository Compacted GMZ bentonite Anisotropic swelling pressure Multi-scale structure Saline effect

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Customizable multifunctional metasurface absorber based on bidirectional deep neural networks covering the quasi-entire terahertz band

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Chinese Optics Letters 2024年第6期22卷 182-190页

作者： Zhipeng Ding Wei Su Lipeng’an Ye Yuanhang Zhou Wenlong Li Riaz Ali Bin Tang Hongbing Yao college of mechanics and engineering Science Hohai UniversityNanjing 211100China School of Microelectronics and Control engineering Changzhou UniversityChangzhou 213164China

In this work, we propose a novel approach that combines a bidirectional deep neural network(BDNN) with a multifunctional metasurface absorber(MMA) for inverse design, which can effectively address the challenge of on-demand customization for absorbers. The inverse design of absorption peak frequencies can be achieved from 0.5 to 10 terahertz(THz), covering the quasi-entire THz band. Based on this, the BDNN is extended to broadband absorption, and the inverse design yields an MMA at the desired frequency. This work provides a broadly applicable approach to the custom design of multifunctional devices that can facilitate the evaluation and design of metasurfaces in electromagnetic absorption.

关键词： terahertz inverse design bidirectional deep neural network metasurface

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Determination method of mesh size for numerical simulation of blast load in near-ground detonation

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Defence Technology（防务技术） 2024年第8期38卷 111-125页

作者： Doudou Si Zuanfeng Pan Haipeng Zhang college of civil engineering Tongji UniversityShanghai 200092China State Key Lab of Disaster Reduction in civil engineering Tongji UniversityShanghai 200092China

In order to improve the overall resilience of the urban infrastructures, it is required to conduct blast resistant design for important building structures in the city. For complex terrain in the city, it is recommended to determine the blast load on the structures via numerical simulation. Since the mesh size of the numerical model highly depends on the explosion scenario, there is no generally applicable approach for the mesh size selection. An efficient method to determine the mesh size of the numerical model of near-ground detonation based on explosion scenarios is proposed in this study. The effect of mesh size on the propagation of blast wave under different explosive weights was studied, and the correlations between the mesh size effect and the charge weight or the scaled distance was described. Based on the principle of the finite element method and Hopkinson-Cranz scaling law, a mesh size measurement unit related to the explosive weight was proposed as the criterion for determining the mesh size in the numerical simulation. Finally, the applicability of the method proposed in this paper was verified by comparing the results from numerical simulation and the explosion tests and was verified in AUTODYN.

关键词： Blast load Mesh size effect Numerical simulation Scaled mesh size Verification

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Prediction of damage potential in mainshock–aftershock sequences using machine learning algorithms

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Earthquake engineering and engineering Vibration 2024年第4期23卷 919-938页

作者： Zhou Zhou Wang Meng Han Miao Yu Xiaohui Lu Dagang School of civil and Transportation engineering Beijing University of Civil Engineering and ArchitectureBeijing 100044China Multi-Functional Shaking Tables Laboratory Beijing University of Civil Engineering and ArchitectureBeijing 100044China college of civil engineering Tongji UniversityShanghai 200092China college of civil engineering and Architecture Guilin University of TechnologyGuilin 541004China School of civil engineering Harbin Institute of TechnologyHarbin 150090China

Assessing the potential damage caused by earthquakes is crucial for a community’s emergency *** this study,four machine learning(ML)methods—random forest,extremely randomized trees,AdaBoost(AB),and gradient boosting(GB)—were employed to develop prediction models for the damage potential of the mainshock(DIMS)and mainshock–aftershock sequences(DIMA).Building structures were modeled using eight single-degree-of-freedom(SDOF)systems with different hysteretic rules.A set of 662 recorded mainshock–aftershock(MS-AS)ground motions was selected from the PEER *** intensity measures(IMs)were chosen to represent the characteristics of the mainshock and *** results revealed that the selected ML methods can well predict the structural damage potential of the SDOF systems,except for the AB *** GB model exhibited the best performance,making it the recommended choice for predicting DIMS and DIMA among the four ML ***,the impact of input variables in the prediction was investigated using the shapley additive explanations(SHAP)*** high-correlation variables were sensitive to the structural period(T).At T=1.0 s,the mainshock peak ground velocity(PGVM)and aftershock peak ground displacement(PGDA)significantly influenced the prediction of *** T increased to 5.0 s,the primary high-correlation factor of the mainshock IMs changed from PGVM to the mainshock peak ground displacement(PGDM);however,the highcorrelation variable of the aftershock IMs remained *** high-correlation factors for DIMS showed trends similar to those of ***,a table summarizing the first and second high-correlation variables for predicting DIMS and DIMA were provided,offering a valuable reference for parameter selection in seismic damage prediction for mainshock–aftershock sequences.

关键词： machine learning mainshock-aftershock damage potential prediction the high-correlation variables SDOF systems

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Experimental Study on the Axial Compression Performance of Bamboo Scrimber Columns Embedded with Steel Reinforcing Bars

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Structural Durability & Health Monitoring 2024年第6期18卷 805-833页

作者： Xueyan Lin Mingtao Wu Guodong Li Nan Guo Lidan Mei college of civil engineering and Transportation Northeast Forestry UniversityHarbin150000China Department of Building engineering College of Civil EngineeringTongji UniversityShanghai200092China college of Transportation and civil engineering Fujian Agriculture and Forestry UniversityFuzhou350002China

In this paper,a new type of bamboo scrimber column embedded with steel bars(rebars)was proposed,and the compression performance was improved by pre-embedding rebars during the preparation of the *** effects of the slenderness ratio and the reinforcement ratio on the axial compression performance of reinforced bamboo scrimber columns were studied by axial compression tests on 28 *** results showed that the increase in the slenderness ratio had a significant negative effect on the axial compression performance of the *** the slenderness ratio increased from 19.63 to 51.96,the failure mode changed from strength failure to buckling failure,and the maximum bearing capacity decreased by 43.03%.The axial compression performance of the reinforced bamboo scrimber columns did not significantly improve at a slenderness ratio of 19.63,but the opposite was true at slenderness ratios of 36.95 and *** the reinforcement ratio increased from 0%to 4.52%,the bearing capacity of those with a slenderness ratio of 51.96 increased by up to 16.99%,and the stiffness and ductility were also ***,based on existing specifications,two modification parameters,the overall elastic modulus Ec and the combined strength fcc,were introduced to establish a calculation method for the bearing capacity of the reinforced bamboo scrimber *** calculation results were compared with the test results,and the results showed that the proposed calculation models can more accurately predict the bearing capacity.

关键词： Bamboo scrimber column steel bar axial compression performance theoretical model

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Theoretical optimization of micropillar arrays for structurally stable bioinspired dry adhesives

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Theoretical & Applied mechanics Letters 2024年第2期14卷 124-129页

作者： Ke Ni Zhengzhi Wang Department of engineering mechanics School of Civil EngineeringWuhan UniversityWuhan 430072China Wuhan University Shenzhen Research Institute Shenzhen 518108China

Inspired by the excellent adhesion performances of setae structure from organisms,micro/nano-pillar array has become one of the paradigms for adhesive *** micropillar arrays are composed of the resin pillars for adhesion and the substrate with different elastic modulus for *** stress singularity at the bi-material corner between the pillars and the substrate can induce the failure of the micropillar-substrate corner and further hinder the fabrication and application of micropillar arrays,yet the design for the stability of the micropillar array lacks systematical and quantitative *** this work,we develop a semi-analytical method to provide the full expressions for the stress distribution within the bi-material corner combining analytical derivations and numerical *** predictions for the stress within the singularity field can be obtained based on the full expressions of the *** good agreement between the predictions and the FEM results demonstrates the high reliability of our *** adopting the strain energy density factor approach,the stability of the pillar-substrate corner is assessed by predicting the failure at the *** the elastic mismatch between the pillar and substrate given in this paper,the stability can be improved by increasing the ratio of the shear modulus of the substrate to that of the *** study provides accurate predictions for the stress distribution at the bi-material corner and can guide the optimization of material combinations of the pillars and the substrate for more stable bioinspired dry adhesives.

关键词： Micropillar array Stability Bi-material corner Dry adhesive

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Friction of graphene on a substrate with a cavity defect

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Science China(Technological Sciences) 2024年第9期67卷 2834-2841页

作者： ZHOU Peng HUO ZhanLei CHANG TienChong Shanghai Institute of Applied Mathematics and mechanics Shanghai Key Laboratory of Mechanics in Energy EngineeringShanghai Frontier Science Center of MechanoinformaticsSchool of Mechanics and Engineering ScienceShanghai UniversityShanghai 200072China The Center for Computational mechanics and engineering Applications Provincial Mechanics Experimental Teaching Demonstration CenterSchool of Civil EngineeringHebei University of EngineeringHandan 056038China Shanghai Institute of Aircraft mechanics and Control Tongji UniversityShanghai 200092China Joint-Research Center for Computational Materials Zhejiang LaboratoryHangzhou 311100China

The frictional behavior of supported graphene is known to be influenced by the physical properties and surface morphologies of the underlying substrate. However, it is unclear how a surface defect on the substrate affects the friction of supported graphene,and it is even unknown how to define the defect-induced friction force in this context. Here we conduct molecular dynamics(MD) simulations to investigate the friction between a square diamond slider and a graphene sheet supported by a copper substrate with a surface cavity defect. Our results demonstrate that the defect-induced friction exhibits a nonlinear increase with cavity size, while it decreases nonlinearly with slider size. We propose that the definition of defect-induced friction can be linked to the increase in friction work over the length of the slider, and is closely correlated to the defect-induced relative change in indentation depth and the ratio of the cavity area to the contact area. These findings provide a comprehensive evaluation of the impact of a substrate cavity defect on the friction of supported graphene and offer insights that may have broader implications for understanding defect-induced friction in other two-dimensional materials.

关键词： friction graphene underneath substrate cavity defect

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