摘要：
Internal damage imaging in concrete structures has consistently presented significant challenges as a complex multi-component material. To enhance the accuracy and efficiency of internal damage identification in concrete structures, an improved plane wave imaging technique based on the wavenumber algorithm is proposed in the paper. The introduction of the wavenumber algorithm provides a mathematical solution to the inverse problem for the assumed forward wave propagation model, which is more rigorous than the ray-based theory in mathematics. By comparing with the total focusing method and the conventional plane wave imaging technique, the proposed imaging technique exhibits significant advantages in imaging different types of damage in concrete structures. Subsequently, the 3D damage state of the simulated reinforcement steel debonding in concrete structures was reconstructed employing the proposed imaging technique. The enhanced imaging efficiency and optimized imaging quality settled the proposed imaging technique a promising candidate for future internal damage identification of concrete structures.
Internal damage imaging in concrete structures has consistently presented significant challenges as a complex multi-component material. To enhance the accuracy and efficiency of internal damage identification in concrete structures, an improved plane wave imaging technique based on the wavenumber algorithm is proposed in the paper. The introduction of the wavenumber algorithm provides a mathematical solution to the inverse problem for the assumed forward wave propagation model, which is more rigorous than the ray-based theory in mathematics. By comparing with the total focusing method and the conventional plane wave imaging technique, the proposed imaging technique exhibits significant advantages in imaging different types of damage in concrete structures. Subsequently, the 3D damage state of the simulated reinforcement steel debonding in concrete structures was reconstructed employing the proposed imaging technique. The enhanced imaging efficiency and optimized imaging quality settled the proposed imaging technique a promising candidate for future internal damage identification of concrete structures.
摘要：
The solid propellant is a particle-reinforced material with significant tension-compression asymmetry. Based on the constant-speed tensile test, constant-speed compression test, and cross-sectional SEM scanning test, this study investigated the differences in the mechanical properties of the HTPB propellant under tensile and compressive loading and the underlying mechanisms. The results show that the tensile strength of HTPB propellant is much smaller than compressive strength. According to the SEM test results of the failure surface, the tensile mechanical properties of the propellant are mainly affected by matrix, and the influence of particles on the mechanical properties is more obvious during the compression process. According to test data, a tension-compression integrated nonlinear constitutive model was constructed, and its application in simulation calculation was realized. The results show that the theoretical, simulation calculation and test results are in good agreement. At 15% strain, the maximum error between the theoretical results and the experimental curve is 9.1% and 4.8% respectively in the process of tension and compression. Therefore, the model can accurately describe the stress-strain relationship of HTPB propellant under different strain rates of tensile and compression. This model can provide theoretical support for accurately evaluating the structural integrity of SRMs.
摘要：
In order to investigate the influence of the coexistence of clay and silt on the compression characteristics of sand, one-dimensional compression consolidation tests were carried out on reconstituted saturated sand-silt-clay mixtures with a constant initial void ratio, and the effects of fines content (FC) and clay-silt ratio (CS) on the compression characteristics of mixed soils were studied. The mechanism of the experimental results was additionally explained from a microscopic perspective. The test results show that: the compressibility of mixed soil increased with the increase in FC; the compressibility change rule of mixed soils with different CS is consistent under the same FC; the influence of CS on the e-lgp (the void ratio (e) versus logarithm of the pressure (p)) curve of mixed soil is inconsistent when FC is different: when FC = 3%, the compressibility of mixed soil decreased with the increase in CS; when FC = 7% and 10%, the compressibility of mixed soil gradually increased with the increase in CS; when FC = 5%, the compressibility of mixed soil did not show an obvious changing law with the increase in CS, and the compressibility of the specimen with FC = 5%-CS = 1 (FC = 5%, CS = 1) was the largest; when CS was same, the difference between e-lgp curves of mixed soil with different FC increased with the increase in CS. The compression model of sand-silt-clay mixtures was established, which can consider the effects of FC and CS. The reliability and applicability of the proposed model were verified by combining the experimental results of this paper and the test data of sand-clay mixture and sand-silt mixture in other literature.
作者机构：
[Song, Jun; Wang, Xiangjun; Li, Chunguang] School of Civil Engineering, Changsha University of Science & Technology, Changsha 410114, China;Elite Engineering School, Changsha University of Science & Technology, Changsha 410114, China;State Key Laboratory of Disaster Prevention & Reduction for Power Grid, Changsha University of Science & Technology, Changsha 410114, China;[Li, Kai] School of Civil Engineering, Changsha University of Science & Technology, Changsha 410114, China<&wdkj&>Elite Engineering School, Changsha University of Science & Technology, Changsha 410114, China<&wdkj&>State Key Laboratory of Disaster Prevention & Reduction for Power Grid, Changsha University of Science & Technology, Changsha 410114, China;[Han, Yan] School of Civil Engineering, Changsha University of Science & Technology, Changsha 410114, China<&wdkj&>Elite Engineering School, Changsha University of Science & Technology, Changsha 410114, China
通讯机构：
[Kai Li] S;School of Civil Engineering, Changsha University of Science & Technology, Changsha 410114, China<&wdkj&>Elite Engineering School, Changsha University of Science & Technology, Changsha 410114, China<&wdkj&>State Key Laboratory of Disaster Prevention & Reduction for Power Grid, Changsha University of Science & Technology, Changsha 410114, China
摘要：
Nonlinear flutter has attracted wide attention due to the bottleneck caused by linear flutter theory on flutter-resistant design of super-long-span bridges. The longer the span, the more closely spaced the natural modes, which may cause competition among flutter-modes in a nonlinear flutter, but it is rarely reported so far. To this end, this study experimentally investigates the 3D nonlinear flutter characteristics of a long-span suspension bridge with closely spaced natural modes based on full-bridge aeroelastic model wind tunnel tests. Since there are two unstable flutter-modes within the interested post-critical regime and thus various complex but interesting flutter-modes competition processes were observed, such as continuous modes competition where the vibration amplitude evolution exhibits various different types of “sawtooth” shapes during stable vibration stages. Meanwhile, the complex nonlinear bifurcation behaviors caused by modes competition were also observed. The evolutionary characteristics of flutter-modes competition are analyzed in detail and relevant mechanisms are discussed. As the wind speed increases, the flutter of the studied bridge mainly undergoes a transition from being dominated by the symmetric mode to being dominated by the antisymmetric mode, accompanied by a continuous modes competition zone in between as a transitional zone. The results show that the continuous modes competition will result in a decrease in the maximum amplitude RMS of the full-span, which is beneficial for the structure. But it may also lead to a transient increase in the maximum amplitude of the full-span due to the coupling vibration shape formed by the two significant flutter-modes, which may be bad for the structure.
Nonlinear flutter has attracted wide attention due to the bottleneck caused by linear flutter theory on flutter-resistant design of super-long-span bridges. The longer the span, the more closely spaced the natural modes, which may cause competition among flutter-modes in a nonlinear flutter, but it is rarely reported so far. To this end, this study experimentally investigates the 3D nonlinear flutter characteristics of a long-span suspension bridge with closely spaced natural modes based on full-bridge aeroelastic model wind tunnel tests. Since there are two unstable flutter-modes within the interested post-critical regime and thus various complex but interesting flutter-modes competition processes were observed, such as continuous modes competition where the vibration amplitude evolution exhibits various different types of “sawtooth” shapes during stable vibration stages. Meanwhile, the complex nonlinear bifurcation behaviors caused by modes competition were also observed. The evolutionary characteristics of flutter-modes competition are analyzed in detail and relevant mechanisms are discussed. As the wind speed increases, the flutter of the studied bridge mainly undergoes a transition from being dominated by the symmetric mode to being dominated by the antisymmetric mode, accompanied by a continuous modes competition zone in between as a transitional zone. The results show that the continuous modes competition will result in a decrease in the maximum amplitude RMS of the full-span, which is beneficial for the structure. But it may also lead to a transient increase in the maximum amplitude of the full-span due to the coupling vibration shape formed by the two significant flutter-modes, which may be bad for the structure.
摘要：
Bridge steel, frequently employed in cross-sea bridge construction, exhibits excellent weldability, superior strength, and toughness. The service life and stability of steel structures are influenced by the presence of corrosive ions within marine environments, necessitating an in-depth examination of the corrosion mechanisms affecting bridge steel. In this study, Q370qD bridge steel was subjected to heat treatment to evaluate the influence of microstructural variations on its corrosion behavior. The microstructure of untreated steel (alloy F) predominantly consists of granular ferrite. Subsequent high-temperature heat treatment induces a partial transformation in the steel microstructure (alloy A), yielding lath carbide-free bainite. Post-immersion tests show both alloy surfaces densely covered with gamma-FeOOH, alpha-FeOOH, and a mixture of Fe3O4 and Fe2O3. Over time, gamma-FeOOH undergoes partial conversion into the more stable alpha-FeOOH form, enhancing the protective barrier against the matrix for both alloys. Alloy F exhibits a significant reduction in corrosion rate compared to alloy A. The proportion of alpha-FeOOH in alloy A initially decreases then increases with prolonged exposure, while in alloy F, it consistently rises. The corrosion resistance of alloy A surpasses that of alloy F, which is attributed to the lath-shaped carbide-free bainite's effectiveness in obstructing Cl- penetration and thereby improving corrosion resistance.
摘要：
This study investigates the coupled responses between the alongwind and acrosswind directions of a variable cross-section bridge tower model through wind tunnel experiments. Uniform and two turbulent flows with four different wind directions are designed to study their influences. The results show a significant coupling effect between the alongwind and acrosswind responses, influenced by incoming flow conditions and structure damping. In uniform flow, two distinct vortex-induced vibration (VIV) regions are observed when the structural damping is low, possibly due to the variable cross-section. When coupled VIV occurs, the responses of both alongwind and acrosswind directions show a hardening non-Gaussian distribution, and the kurtosis value is close to 1.5. The increase of structural damping will weaken the coupling effect, but slightly increase the dominant frequency of the coupling. Turbulence intensity reduces the VIV effect and coupling effect but does not eliminate the coupling in galloping. In particular, the critical wind speed of galloping will decrease with the increase of turbulence intensity. The coupling effect is prominent at 0° wind direction, mainly dominated by the acrosswind direction. However, the coupling effect is weak in other wind directions and is primarily dominated by the alongwind direction. The coupling effect makes the energy transfer between the alongwind and acrosswind directions, which is crucial for designing variable cross-section high-rise buildings and tower structures susceptible to wind-induced vibration.
This study investigates the coupled responses between the alongwind and acrosswind directions of a variable cross-section bridge tower model through wind tunnel experiments. Uniform and two turbulent flows with four different wind directions are designed to study their influences. The results show a significant coupling effect between the alongwind and acrosswind responses, influenced by incoming flow conditions and structure damping. In uniform flow, two distinct vortex-induced vibration (VIV) regions are observed when the structural damping is low, possibly due to the variable cross-section. When coupled VIV occurs, the responses of both alongwind and acrosswind directions show a hardening non-Gaussian distribution, and the kurtosis value is close to 1.5. The increase of structural damping will weaken the coupling effect, but slightly increase the dominant frequency of the coupling. Turbulence intensity reduces the VIV effect and coupling effect but does not eliminate the coupling in galloping. In particular, the critical wind speed of galloping will decrease with the increase of turbulence intensity. The coupling effect is prominent at 0° wind direction, mainly dominated by the acrosswind direction. However, the coupling effect is weak in other wind directions and is primarily dominated by the alongwind direction. The coupling effect makes the energy transfer between the alongwind and acrosswind directions, which is crucial for designing variable cross-section high-rise buildings and tower structures susceptible to wind-induced vibration.
摘要：
This study presents a novel method for calculating the stress and bending moment in reinforced concrete (RC) beams strengthened with prestressed near-surface-mounted (NSM) carbon fiber-reinforced polymer (CFRP), focusing specifically on separation failure at the end concrete cover. By characterizing the geometry of the failure body and integrating it with the concrete tooth model, a comprehensive theoretical framework has been developed. This framework utilizes sectional strain distribution characteristics to establish the bending moment-curvature relationship and the load-deflection curve during loading. Comparisons with experimental data confirm the accuracy and applicability of this analytical model. The results demonstrate that the model is capable of accurately predicting the load-deflection behavior of the strengthened beam. Additionally, this study underscores the substantial impact of the CFRP prestress level on the concrete cover separation failure, showing that optimizing prestress settings can effectively enhance the ductility and bearing capacity of the strengthened beam.
摘要：
With the increase of the density of subway line in big cities, it is common for newly built shield tunnels to cross beneath the existing pile foundations at short distances. When the disturbance generated during the construction of the shield tunnels is transmitted to the bearing stratum of the existing pile tip, a punching shear failure may occur in the bearing stratum. To study the evolution process and final form of the punching shear failure of the bearing stratum, a scaled model test based on the Particle Image Velocimetry (PIV) technology is designed. By using PIV technology to analyze deformation images of the bearing stratum, the failure range and shape of the bearing stratum between the pile tip and tunnel induced by excavation are obtained. Using the failure shape of the bearing stratum provided by the model test, a theoretical failure mechanism based on the spatial discretization technique is constructed. The limit analysis theorem is employed here to calculate the theoretical solution of the punching shear failure surface of the bearing stratum. The good agreement of the failure range for the bearing stratum between the model test and theoretical result indicates that the model test presented here is effective.
With the increase of the density of subway line in big cities, it is common for newly built shield tunnels to cross beneath the existing pile foundations at short distances. When the disturbance generated during the construction of the shield tunnels is transmitted to the bearing stratum of the existing pile tip, a punching shear failure may occur in the bearing stratum. To study the evolution process and final form of the punching shear failure of the bearing stratum, a scaled model test based on the Particle Image Velocimetry (PIV) technology is designed. By using PIV technology to analyze deformation images of the bearing stratum, the failure range and shape of the bearing stratum between the pile tip and tunnel induced by excavation are obtained. Using the failure shape of the bearing stratum provided by the model test, a theoretical failure mechanism based on the spatial discretization technique is constructed. The limit analysis theorem is employed here to calculate the theoretical solution of the punching shear failure surface of the bearing stratum. The good agreement of the failure range for the bearing stratum between the model test and theoretical result indicates that the model test presented here is effective.
摘要：
In order to enhance the efficiency of stochastic vibration analysis for train–bridge coupling systems, this paper proposes a novel approach based on the parallel adaptive enhanced (PAE)-surrogate model. First, an initial surrogate model is established to predict the extreme values of dynamic responses in the train–bridge coupling system using a small number of training samples. Second, a multipoint adaptive sampling method is employed to determine a set of new samples that provide more information. The theoretical extreme values of the dynamic responses corresponding to the new samples are calculated using parallel computing technology. Third, the surrogate model is optimized by incorporating the set of new samples and their corresponding theoretical extreme values. Finally, new samples are continuously added, and the surrogate model is enhanced until the number of training samples reaches the preset requirement. To validate the effectiveness of the proposed method, two examples are examined, encompassing analytical functions and the analysis of the wheel load reduction rate (WLRR) for trains on the bridge. The results show that the proposed PAE-surrogate model can select samples containing valuable information, significantly improving the prediction accuracy of the surrogate model without increasing the number of training samples. Additionally, the proposed method can fully exploit computational resources, thereby decreasing the number of iterations needed and increasing training efficiency. By considering a four-car CHR2 train passing through a three-span simply supported girder bridge as an example, the proposed method achieves 2.62[Formula: see text]times higher training efficiency compared to the nonparallel method.
摘要：
Critical shear stress and erosion rate are two key factors for the prediction of the incipient motion of sediment and the transport of sediment. Seabed seepage can significantly alter the pore pressure gradient within the soil and the hydrodynamics around the surface of the seabed, further affecting erosion processes. Previous studies attempted to theoretically clarify the effect of the seepage force on sediment incipient motion. In this study, a newly designed erosion–seepage system (ESS) that considers the effect of seepage under steady or oscillatory flow is used to simulate the erosion process. Through the designed ESS, the erosion height per unit time was measured directly on the Yellow River sand, and the upward seepage force was applied at the bottom of the soil sample in the process. Then, the relationship between the erosion rate and seepage was established.The experimental results show that upward seepage reduces the critical shear stress of the sand bed and increases the erosion rate of the soils under both steady flow and oscillatory flow conditions. The erosion coefficients in the erosion models decrease with increasing seepage gradient. The effect of seepage on erosion is more obvious when the flow velocity of the steady stream is large, while the effect of seepage on erosion is relatively small under the oscillatory state with a shorter period. However, when violent erosion of soil samples occurs, seepage under both flow conditions greatly increases the erosion rate.
摘要：
Images captured under improper exposure conditions lose their brightness information and texture details. Therefore, the enhancement of low-light images has received widespread attention. In recent years, most methods are based on deep convolutional neural networks to enhance low-light images in the spatial domain, which tends to introduce a huge number of parameters, thus limiting their practical applicability. In this paper, we propose a Fourier-based two-stage low-light image enhancement method via mutual learning (FT-LLIE), which sequentially enhance the amplitude and phase components. Specifically, we design the amplitude enhancement module (AEM) and phase enhancement module (PEM). In these two enhancement stages, we design the amplitude enhancement block (AEB) and phase enhancement block (PEB) based on the Fast Fourier Transform (FFT) to deal with the amplitude component and the phase component, respectively. In AEB and PEB, we design spatial unit (SU) and frequency unit (FU) to process spatial and frequency domain information, and adopt a mutual learning strategy so that the local features extracted from the spatial domain and global features extracted from the frequency domain can learn from each other to obtain complementary information to enhance the image. Through extensive experiments, it has been shown that our network requires only a small number of parameters to effectively enhance image details, outperforming existing low-light image enhancement algorithms in both qualitative and quantitative results.
Images captured under improper exposure conditions lose their brightness information and texture details. Therefore, the enhancement of low-light images has received widespread attention. In recent years, most methods are based on deep convolutional neural networks to enhance low-light images in the spatial domain, which tends to introduce a huge number of parameters, thus limiting their practical applicability. In this paper, we propose a Fourier-based two-stage low-light image enhancement method via mutual learning (FT-LLIE), which sequentially enhance the amplitude and phase components. Specifically, we design the amplitude enhancement module (AEM) and phase enhancement module (PEM). In these two enhancement stages, we design the amplitude enhancement block (AEB) and phase enhancement block (PEB) based on the Fast Fourier Transform (FFT) to deal with the amplitude component and the phase component, respectively. In AEB and PEB, we design spatial unit (SU) and frequency unit (FU) to process spatial and frequency domain information, and adopt a mutual learning strategy so that the local features extracted from the spatial domain and global features extracted from the frequency domain can learn from each other to obtain complementary information to enhance the image. Through extensive experiments, it has been shown that our network requires only a small number of parameters to effectively enhance image details, outperforming existing low-light image enhancement algorithms in both qualitative and quantitative results.
摘要：
A new method was proposed for predicting residual stress in light alloys using truncated conical indentation. In this method, a truncated conical indenter with a cone angle of 120°, insensitive to edge-chamfer and friction effects, was used to test the residual stress of light alloys. Selecting the ratio of indentation work between stressed and unstressed specimens as an analytical parameter, a dimensionless truncated conical indentation (TCI) model related to the ratio of indentation work between stressed and unstressed, material properties, and normalized residual stress was established via dimensional analysis and numerical calculations. The TCI model could predict equi-biaxial residual stress and uniaxial residual stress, and its accuracy was verified in a wide range of light alloys with varying residual stress by numerical simulation. The stability of the TCI model is verified numerically by introducing errors in material parameters. Truncated conical indentation tests were conducted on cruciform specimens and rectangular specimens respectively made of three aluminum alloys. The results exhibited the residual stress predicted by proposed method agrees well with the applied stress, and the relative errors between them were within ±10 % in most cases.
A new method was proposed for predicting residual stress in light alloys using truncated conical indentation. In this method, a truncated conical indenter with a cone angle of 120°, insensitive to edge-chamfer and friction effects, was used to test the residual stress of light alloys. Selecting the ratio of indentation work between stressed and unstressed specimens as an analytical parameter, a dimensionless truncated conical indentation (TCI) model related to the ratio of indentation work between stressed and unstressed, material properties, and normalized residual stress was established via dimensional analysis and numerical calculations. The TCI model could predict equi-biaxial residual stress and uniaxial residual stress, and its accuracy was verified in a wide range of light alloys with varying residual stress by numerical simulation. The stability of the TCI model is verified numerically by introducing errors in material parameters. Truncated conical indentation tests were conducted on cruciform specimens and rectangular specimens respectively made of three aluminum alloys. The results exhibited the residual stress predicted by proposed method agrees well with the applied stress, and the relative errors between them were within ±10 % in most cases.
作者机构：
[Long, Chengyun; Long, CY] South China Univ Technol, Shien Ming Wu Sch Intelligent Engn, Guangzhou 511442, Peoples R China.;[Cai, Zizheng; Zhao, Bing; Zhou, Weichao; He, Daji] Changsha Univ Sci & Technol, Sch Civil Engn, Dept Mech, Changsha 410114, Peoples R China.
通讯机构：
[Long, CY ] S;[Zhao, B ] C;South China Univ Technol, Shien Ming Wu Sch Intelligent Engn, Guangzhou 511442, Peoples R China.;Changsha Univ Sci & Technol, Sch Civil Engn, Dept Mech, Changsha 410114, Peoples R China.
摘要：
Accurate assessment of the thermal buckling behavior of microdevices is critical for the safe and secure operation of MEMS. However, the coupling of shearing and size effects on the thermal buckling of microbeams remains elusive and needs to be clarified. Here, we propose a theoretical model for the thermal buckling of microbeams that considers both the shearing and size effects, based on the modified gradient elasticity theory combined with the Timoshenko beam model. The explicit analytical forms of the deflection, the bending angle, the shearing angle and the critical buckling temperature rise are presented. The results show that the bending angle increases with the length/thickness ratio while the shearing angle decreases. It is confirmed that the shearing effect cannot be ignored in the thermal buckling of the doubly clamped microbeams with low aspect ratio. The size effect is captured in the thermal buckling of microbeams, which shows an increase in thermoelastic strength with the size reduction. The coupling effect on thermal buckling shows a weakening of the shearing effect by the size effect as the microbeam size decreases. This work could provide a theoretical reference for the design and monitoring of microdevices operating in high temperature environments.
作者：
Zhang, Liang;Jiang, Hao;Zhang, Sheng;Bei, Zhenghao;Huang, Ning
期刊：
Measurement,2025年253:117561 ISSN：0263-2241
通讯作者：
Jiang, H
作者机构：
[Zhang, Liang; Huang, Ning; Zhang, Sheng] Hunan City Univ, Coll Civil Engn, 518 Yingbin East Rd, Yiyang 413000, Hunan, Peoples R China.;[Bei, Zhenghao; Jiang, Hao] Changsha Univ Sci & Technol, Sch Civil Engn, 960 Wanjiali South RD, Changsha 410114, Hunan, Peoples R China.
通讯机构：
[Jiang, H ] C;Changsha Univ Sci & Technol, Sch Civil Engn, 960 Wanjiali South RD, Changsha 410114, Hunan, Peoples R China.
关键词：
Tunnel lining detection;Cavity filler;Forward simulation;Generalized S -transform;Wavelet packet analysis
摘要：
Tunnel lining cavities and other defects can cause cracks in tunnel structures and damage to concrete, seriously affecting the safety of driving in tunnels. Due to varying geological conditions, the materials filling different cavity areas in tunnels differ. By formulating corresponding repair measures for different fillers in cavity areas, many unnecessary losses can be avoided. Therefore, this paper proposes a method based on multi-parameter information for identifying and extracting the characteristics of different fillers in tunnel cavity areas through forward simulation using gprMax software and field test analysis. Ground penetrating radar (GPR) is used to detect cavities of different shapes filled with various media, focusing on cavity signals while reducing interference from I-beams, and reconstructing radar signals through migration. Statistical parameters are introduced for analysis, and techniques such as Fast Fourier Transform, generalized S-transform, and wavelet packet transform are employed to extract features from the processed radar signals. The characteristics of the filling medium in the cavity area are extracted from three aspects: frequency, time–frequency, and energy. This method can provide a reference for interpreting the GPR data of tunnel lining cavity filling media in actual engineering applications.
Tunnel lining cavities and other defects can cause cracks in tunnel structures and damage to concrete, seriously affecting the safety of driving in tunnels. Due to varying geological conditions, the materials filling different cavity areas in tunnels differ. By formulating corresponding repair measures for different fillers in cavity areas, many unnecessary losses can be avoided. Therefore, this paper proposes a method based on multi-parameter information for identifying and extracting the characteristics of different fillers in tunnel cavity areas through forward simulation using gprMax software and field test analysis. Ground penetrating radar (GPR) is used to detect cavities of different shapes filled with various media, focusing on cavity signals while reducing interference from I-beams, and reconstructing radar signals through migration. Statistical parameters are introduced for analysis, and techniques such as Fast Fourier Transform, generalized S-transform, and wavelet packet transform are employed to extract features from the processed radar signals. The characteristics of the filling medium in the cavity area are extracted from three aspects: frequency, time–frequency, and energy. This method can provide a reference for interpreting the GPR data of tunnel lining cavity filling media in actual engineering applications.
摘要：
Traditional physical-driven modal methods are inappropriate for damage diagnosis of long-span flexible structures with complex mechanical behaviour. This study develops a deep Convolutional Neural Network-based damage diagnosis method for in-service bridges by using dynamic responses under moving loads. The dynamic responses were collected from the critical points on the girders of a cable-stayed bridge specimen under vehicle loading. These collected data was transformed into images based on Gramian Angular Field and Markov Transition Field (MTF). A deep learning algorithm based on VGG-19 was used to extract the damage feature from the data images associated with the structural responses. Finally, the unlabelled vibration data were input into the VGG-19 model for structural damage diagnosis. An experimental study was conducted for the damage diagnosis of a scale specimen of a cable-stayed bridge under moving loads. The acceleration signals of the main girder of the cable-stayed bridge under several damage conditions were monitored. The numerical results show the training accuracy of the deep learning method based on VGG-19 with MTF is up to 88%, and the average accuracy of the test dataset is 86.46% for each classification label. The transfer learning method can increase the classification accuracy up to 97.89%, indicating the advantage of intergrating transfer learning and VGG-19 network for structural damage diagnosis. The combination of VGG-19 and MTF algorithm provides a better solution for structural damage diagnosis of in-service infrastructures with long-term monitoring data.
摘要：
Our study employs panel data from 272 Chinese prefecture-level cities (2003-2020), leveraging the "Civilized City" selection campaign as a quasi-natural experiment. Using a Spatial Durbin Difference-in-Differences model, we systematically analyze the policy's impact on local environmental governance performance and its spatial spillover effects, with rigorous robustness checks. Results reveal a significant positive spatial correlation in China's environmental governance performance, indicating interdependence among cities rather than isolated decision-making. The "Civilized City" initiative not only improves local environmental governance but also generates spillover benefits for neighboring regions, thereby enhancing coordinated regional sustainability. Finally, we propose policy recommendations grounded in empirical findings and China's governance context.
摘要：
Stress-constrained topology optimization under geometrical nonlinear conditions is still an open topic as it often encounter difficulties such as mesh distortion, inaccurate stress evaluation and low computational efficiency. For this purpose, this paper develops a novel parallel-computing based topology optimization methodology for geometrically nonlinear continuum structures with stress constraints. To alleviate the mesh distortions in the low-density regions, a smooth material interpolation scheme from with different penalization for the elastic and nonlinear stiffness is proposed. Moreover, a new hybrid stress finite element formulation is included into the geometrically nonlinear topology optimization to capture a more accurate stress distribution that is less sensitive to mesh distortions. Then, to improve the computational efficiency of geometrically nonlinear and sensitivity analysis, a parallel computing framework based on the assembly free iterative solution is established. Meanwhile, an efficient sparse matrix-vector multiplication strategy, which is applicable to solve the geometrically nonlinear problems, is proposed to exploit the computing power of GPU effectively. Finally, several numerical examples are given to illustrate the efficiency and feasibility of the proposed method.
Stress-constrained topology optimization under geometrical nonlinear conditions is still an open topic as it often encounter difficulties such as mesh distortion, inaccurate stress evaluation and low computational efficiency. For this purpose, this paper develops a novel parallel-computing based topology optimization methodology for geometrically nonlinear continuum structures with stress constraints. To alleviate the mesh distortions in the low-density regions, a smooth material interpolation scheme from with different penalization for the elastic and nonlinear stiffness is proposed. Moreover, a new hybrid stress finite element formulation is included into the geometrically nonlinear topology optimization to capture a more accurate stress distribution that is less sensitive to mesh distortions. Then, to improve the computational efficiency of geometrically nonlinear and sensitivity analysis, a parallel computing framework based on the assembly free iterative solution is established. Meanwhile, an efficient sparse matrix-vector multiplication strategy, which is applicable to solve the geometrically nonlinear problems, is proposed to exploit the computing power of GPU effectively. Finally, several numerical examples are given to illustrate the efficiency and feasibility of the proposed method.
关键词：
Circulation control device;Dual synthetic jets;Lift enhancement;Aerodynamic force;Aerodynamic moment
摘要：
This paper proposes a circulation control device based on dual synthetic jets (DSJs), and its control effect was verified by wind tunnel tests. The experimental pressure and aerodynamic forces were measured to test the control effect of lift enhancement and aerodynamic moment control. After the circulation control is applied, the negative pressure on the suction surface is decreased. Correspondingly, the positive pressure on the pressure surface is increased. The pressure measurement indicated that the pressure distribution trend in a direction favors the lift enhancement. The maximum increment of the lift coefficient was 0.2 when the momentum coefficient was 0.015. The lift–drag ratio was increased by a maximum of 5.4. Applying circulation control before the stall angle of attack can provide stable increments of the roll and pitch moments. In general, the circulation control method based on dual synthetic jets performs well for lift enhancement and aerodynamic moment control.
作者机构：
[Luo, Yuan; Liu, Xiaofan; Zhang, Haiping] College of Civil Engineering, Hunan University of Technology, Zhuzhou 412007, China;[Cui, Jian; Wang, Honghao; Zeng, Weiming] School of Civil Engineering, Changsha University of Science and Technology, Changsha 410114, China;[Huang, Lian] School of Architecture Engineering, Guangxi Minzu Uiniversity, Nanning 530006, China
摘要：
Orthotropic steel decks (OSDs) are welded structures prone to weld defects, increasing the risk of fatigue fracture. It is crucial to clarify the fatigue evolution mechanism of weld defects throughout the entire lifecycle. In this study, the fatigue propagation behavior of weld defects is investigated from the hidden stage to final fracture. Firstly, a full-scale segmental OSD model with prefabricated defects was utilized to investigated fatigue propagation behavior of surface cracks. Secondly, stress intensity factors (SIFs) of welding defects throughout the entire process were simulated using a refined finite element model. Finally, the crack shape evolution and fatigue life were analyzed at different fatigue stages. The research identifies three stages in the fatigue evolution of hidden defects: the hidden defect stage, the initiation stage of surface crack, and the propagation stage of surface crack. Regardless of the initial aspect ratios, hidden defects evolve into a circular, while surface defects evolve into a flattened semi-ellipse. Compared to the propagation life of surface cracks, the hiding life of cracks account for a significantly larger proportion of the total life, and this proportion increases with both the initial aspect ratio and the hidden depth of the defects.
Orthotropic steel decks (OSDs) are welded structures prone to weld defects, increasing the risk of fatigue fracture. It is crucial to clarify the fatigue evolution mechanism of weld defects throughout the entire lifecycle. In this study, the fatigue propagation behavior of weld defects is investigated from the hidden stage to final fracture. Firstly, a full-scale segmental OSD model with prefabricated defects was utilized to investigated fatigue propagation behavior of surface cracks. Secondly, stress intensity factors (SIFs) of welding defects throughout the entire process were simulated using a refined finite element model. Finally, the crack shape evolution and fatigue life were analyzed at different fatigue stages. The research identifies three stages in the fatigue evolution of hidden defects: the hidden defect stage, the initiation stage of surface crack, and the propagation stage of surface crack. Regardless of the initial aspect ratios, hidden defects evolve into a circular, while surface defects evolve into a flattened semi-ellipse. Compared to the propagation life of surface cracks, the hiding life of cracks account for a significantly larger proportion of the total life, and this proportion increases with both the initial aspect ratio and the hidden depth of the defects.
摘要：
Electrical resistivity tomography (ERT) is a key geophysical technique that provides detailed information on subsurface structures by measuring the distribution of electrical resistivity underground. ERT suffers from limitations in electrode arrangement, interference from environmental and instrument noise, and existing data processing algorithms that fail to adequately consider geological heterogeneity and uncertainty, resulting in insufficient inversion resolution. Traditional ERT methods rely on simplified algorithms and a limited number of observation points, which smooths model details and further reduces resolution. To address the resolution issues in ERT, this article proposes a deep learning inversion method that integrates prior physical information. This method uses low-resolution inversion results as prior knowledge to provide the deep learning algorithm with a constrained initial model, thereby combining the physical basis of traditional methods with the data-driven advantages of deep learning. The method not only retains the strengths of traditional inversion but also enhances the resolution and imaging efficiency of the inversion model using deep learning technology. Synthetic data experiments demonstrate that integrating deep learning significantly improves the model’s ability to detail subsurface structures, especially in the transition zones of shallow structures and the recovery of deep anomalies. Results from measured data indicate that the proposed method not only achieves high-resolution inversion but also maintains good consistency with prior information.
