Hao Wu

The elastic stage similarity law constitutes the key basis for developing the full-process similarity law. This study proposes an elastic stage dynamic similarity law for soil–pile shaking table tests, which enables the quantitative prediction of prototype responses, including pile head acceleration, pile head displacement and pile bending moment, from model test results, even when there are errors in the dynamic shear modulus of model soil. Shaking table tests are conducted on soil–pile interaction models with scale ratios of 1:1, 1:2, and 1:4 to validate the proposed similarity law. All back-calculated responses show errors of less than 5%. Numerical simulation comparison with the artificial mass similarity law proves significant advantage of the proposed similarity law.

The large shaking table at Tianjin University's National Facility for Earthquake Engineering Simulation (NFEES) is the largest in the world, featuring a rigid‐flexible foundation differing from the conventional rigid block type. This design meets the structural requirements for large‐scale shaking tables and is suitable for sites without ideal soil conditions. However, the vibration response characteristics and spatial distribution patterns of this foundation under dynamic loading remain insufficiently studied. This paper presents a test investigation into this newly developed foundation's response, employing white noise sweep and sinusoidal excitation tests to obtain actual acceleration response data and its spatial distribution. Furthermore, the key factors influencing the acceleration response distribution are analyzed by considering both the structural properties and the excitation characteristics. The results show that at excitation frequencies below 15 Hz, the foundation exhibits good overall integrity. In contrast, high‐frequency horizontal excitations tend to localize the response in the excitation region, while high‐frequency vertical excitations amplify the response in the flexible area, leading to a clear deviation from rigid‐body motion. This study provides a reliable and authentic data source for future theoretical and numerical research, and the findings offer valuable engineering insights and practical guidance for the design and application of similar large‐scale shaking table foundations.

Abnormal theta band (4–8 Hz) cortical oscillations have been identified as a pathological hallmark in Alzheimer’s disease (AD), which can be suppressed through high-frequency electrical stimulation (ES). However, their neural origins and mechanistic underpinnings remain poorly understood. In this work, we develop a mathematical model to characterize AD-related cortical theta oscillations. Through linear equivalent transformation of the physiological model and describing function analysis, we elucidate the network mechanism underlying these pathological oscillations. The results demonstrate that the reduced synaptic inhibition from fast inhibitory interneurons to pyramidal neuron populations drives the cortical network into a pathological low-frequency (theta band) oscillatory state. The oscillation frequency and amplitude can be directly determined from the intersection points between the Nyquist curve of the model’s linear component and the negative inverse curve of the nonlinear element’s describing function. Conversely, the separation between these curves driven by external stimulation visually represents how stimulation can shift the cortical network away from abnormal theta oscillations. The describing function analysis not only provides a mechanistic explanation for aberrant oscillations but also enables precise prediction of effective stimulation parameters for suppressing pathological theta activity. This work offers a novel framework to reveal the “push-pull” network effects of AD, providing an intuitive understanding of cortical stimulation mechanisms and a quantitative approach for optimizing neuromodulation strategies in AD.

In mountainous regions, the complex interplay between topography and geology significantly influences seismic wave propagation and amplification, posing considerable challenges to engineering seismic design. This study investigated the seismic amplification effects of platform-canyon combined topography through the shaking table tests. A scaled model with symmetrical geometry but distinct geological configurations (loess on the left side versus granite-overlain-by-loess on the right) was subjected to various seismic and sinusoidal excitations with peak accelerations ranging from 0.1g to 1.2g. The horizontal and vertical dynamic responses, characterized by the ground motion amplification factor (GMAF), were systematically analyzed. The main findings were as follows. First, the topography exerted a dominant control on the horizontal response. The less-constrained platform triggered a pronounced "whip effect," resulting in a peak horizontal displacement 20%-50% greater than that of the canyon, with the maximum horizontal GMAF (up to 3.03) occurring at the platform crest. Second, the geological structure significantly modified the surface response. The model side with an underlying granite layer exhibited a 36.3% stronger amplification (coefficient up to 4.13) compared to the side with a single loess layer, highlighting the role of higher elastic modulus. Third, resonant amplification was governed by the coupling between the site's natural frequency and the input wave spectrum. A local GMAF of 6.74 was recorded under specific frequency-matching conditions (10 Hz - Kobe wave). Finally, the vertical response exhibited high-frequency selectivity and spatial heterogeneity, being more pronounced on the granite side and at frequencies exceeding the site's vertical predominant frequency (20 Hz). These results quantitatively elucidate the amplification mechanisms arising from the combined influence of complex topography and variable geology. The findings provide a crucial experimental basis and theoretical reference for the seismic design and risk assessment of engineering structures in mountainous areas.

The large shaking table of the National Facility for Earthquake Engineering Simulation of Tianjin University in China, with the table size of 20 m × 16 m and full load capacity of 1350 t, is the currently existing largest earthquake simulation shaking table in the world. The control room of the shaking table generally experiences excessive vibration during the operation of the shaking table. To protect the control and data recording devices and satisfy the researchers’ comfort in the control room, a three-dimensional isolation platform with semi-active control is proposed and constructed. To deal with the potential resonance problem caused by the wide-band shaking table vibration, a frequency-dependent variable damping semi-active control method is proposed considering the frequency uncertainty. The vibration propagation characteristics from the shaking table to the control room is discussed and the control effect of the isolation platform is studied through site experiment under different vibration conditions. The results show that the designed isolation platform has an average isolation efficiency of 84.6%, 59.4% and 73.2% in the two horizontal and vertical directions, respectively. The average Z-vibration level is reduced from 98.89 dB to 86.20 dB which satisfied the standard for human comfort. The semi-active control function of the isolation platform on vibrations with different frequency characteristics has also been verified.

The frequency bandwidth expansion compound shaking table (FBECST), as a new type of seismic simulation shaking table, offers an effective approach for generating long‐stroke and wide‐band excitation. Nonlinear signal‐based control (NSBC), which enables nonlinear compensation through the linear (transfer function) model of the controlled system, has immense potential for enhancing the performance of the FBECST. This paper proposes a novel NSBC method for the compensation control of a FBECST supporting a nonlinear specimen. The convergence and stability of the proposed method are analyzed by theoretical derivation. The implementation process is described, and the influence of filter configuration on stability and accuracy is discussed. Finally, the effectiveness and advantages of the proposed method are compared and verified with inverse compensation (IC) and offline iterative control (OIC) as baseline methods. A series of numerical and experimental results show that the waveform reproduction ability of the FBECST system with NSBC is better than that with IC. In addition, the accuracy of the proposed NSBC can reach or even exceed the OIC with only a one‐time identification and design process. This work can expand the application scope of the NSBC and provide an effective compensation control method for the FBECST supporting a nonlinear specimen.

The frequency bandwidth expansion compound shaking table (FBECST) provides an effective solution for synchronously achieving large-load, long-stroke, and wide-band excitation. FBECST consists of an upper shaking table (UST) and a lower shaking table (LST) cooperating to realize the compound excitation, which results in a high system complexity compared to the traditional shaking table. However, the coupling mechanism and model-based compensation control method of FBECST have rarely been studied, which greatly limits the ability of FBECST to simulate earthquake excitation. In this paper, a closed-loop transfer function matrix theoretical model of FBECST is developed. Then, the coupling mechanism of FBECST is revealed by theoretical analysis, and the correctness of the mechanism analysis is verified by simulation. Finally, a closed-loop feedforward decoupling compensation control (C-FDCC) method based on the coupling mechanism of FBECST is proposed. A series of numerical analysis results show that even considering the influence of a high natural frequency specimen, the proposed C-FDCC method can achieve good control precision with a time-domain correlation coefficient near 0.98, whereas the three-variable control (TVC) provides insufficient control. This work provides strong support for large-load, long-stroke, and wide-band seismic excitation reproduction through the FBECST.

Ultrasound tomography (UT) is an emerging technique for phase distribution measurement in industrial multiphase flow monitoring. A multimode UT combining the ultrasound transmission and reflection modes is proposed to measure stratified phase distribution and sound speed of liquid–solid mixtures in the horizontal pipe. First, the acoustic attenuation is used to reconstruct the phase distribution with a modified matrix regularization algorithm, and the time-of-flight (TOF) of ultrasound is used to extract the boundary of multiphase layers with the weight Akaike information criterion algorithm. Second, a wavelet fusion method based on the principal component averaging is proposed to fuse the reconstruction images of UT transmission and reflection. Third, numerical investigations are carried out to validate the feasibility of the proposed method. According to the quantitative indexes, the proposed method can effectively reconstruct the phase distribution of multiphase media. Finally, an experimental test pipeline Section is established, and sand–water and oil–water–sand liquid–solid media are investigated. The minimum relative error (RE) and the maximum correlation coefficient (CC) of experimental fusion results can reach 0.33 and 0.94, respectively, and the average measurement error (ME) of the layer height is 3.80%.