Transmission lines galloping is a low frequency, large amplitude vibration phenomenon caused by icing and strong wind, which seriously endanger affects the safety of the power grid. The galloping response and galloping control of 500 kV transmission line arewere studied by using numerical simulation method in this paper. Firstly, taking crescent-shaped, fan-shaped, and D-shaped ice covered split conductors as examples, the influence of wake effect and wind attack angle on the aerodynamic characteristics of the conductors under different ice covered shapes was studied. Based on the obtained aerodynamic coefficients, the aerodynamic load was calculated and the galloping response of the ice covered split conductors was studied. A new galloping control method for anti-galloping line spacing bars and phase spacing bars was proposed. By comparing the galloping displacement response of the central conductor in the span with the installation of ordinary inter line spacers, the results show that the installation of new anti-galloping inter line spacers can reduce the galloping response of single-phase split conductors by 93.18% (vertical direction) and 60.30% (horizontal direction); The installation of new anti-galloping phase and line spacing bars can reduce the galloping response of three-phase split conductors by 90.73% (vertical direction) and 86.05% (horizontal direction), the galloping control effect is significant. The research results of this paper provide a new method for the galloping control of ice covered split conductors.

Application ofSstabilizing piles is the main reinforcement measure of the slope. In research, stabilizing piles are often simplified to elastic or elastic-plastic structuresoften use elastic or elastoplastic models, which do not reflect the failure caused by shear forces and bending moments. To study the instability mechanism of the stabilized pile slope, a correction module based was established, which simulated the fracture by adding the failure stage. Based on the Wenchuan earthquake investigation, the selection principle of failure criterion iwas analyzed. The new model is was applied to the dynamic response analysis. The influence of pile failure on the slope is was explored from the indexes of maximum shear force, acceleration, spectrum, and displacement. Besides, the deformation coordination relationship between piles in the three-dimensional slope is was discussed under the fracture frame. The results show that: 1) the fracture effect can be achieved by constructing and calling the correction module. The modified model has two stages. Once the internal force reaches the limit value, the anti-sliding effect of the pile disappears. The failure will cause a sudden change of acceleration, higher frequency, and greater residual displacement. 3) The fracture sequence is the reflection of the relationship between the stabilizing piles. The neglect of pile interaction may lead to the underestimation of landslide risk

The evaluation indexes of seismic damage state can be used to quickly evaluate the performance state of reinforced soil retaining walls (RSRWs) after the earthquake, and can also be used for seismic fragility analysis and performance-based seismic design methods. In view of the lack of seismic damage assessment indexes for wrap-faced RSRWs, exploring the variation rule of dynamic properties and its relationship with the damage degree through shaking table tests. The results show that the deformation mode of the wrap-faced RSRWs changes with the increase of dynamic load intensity, and the maximum total residual displacement is 27.8 mm (2.78% H) when all loading conditions were over. The dynamic characteristics of the structure can characterize the damage state of the structure. With the increase of the dynamic load intensity, the equivalent shear strain increases from 1×10-4 to 2×10-2, and the structure was in an even more dangerous state. Finally, a method for determining the seismic damage assessment indexes of RSRWs based on the distribution law of dynamic characteristics and displacement index was proposed, by which the seismic damage state of wrap-faced RSRWs was defined as three levels and the corresponding displacement index iwas given.

Aiming at the problems of poor noise immunity and insufficient model training of traditional deep learning models in a small-sample and strong noise environment, a method based on Adaptive Maximum Second -order Cyclostationarity Blind Deconvolution (ACYCBD) combining Markov (ACYCBD) combined with Markov Transition Field (MTF) and MobileViT for rolling bearing fault diagnosis. Firstly, the impact signal of bearing faults under strong noise background is enhanced by parameter-adaptive CYCBD algorithm to reduce the influence of strong background noise, then, MTF is used to transform the preprocessed one-dimensional bearing vibration signal into a two-dimensional feature image with temporal correlation, and finally, the MTF image is inputted into the MobileViT network for training to get the fault diagnosis results, which is applied to the Southeast University Gearbox dataset and Shenyang University of Technology laboratory rolling bearing dataset to verify the fault identification accuracy of the proposed method in small sample strong noise conditions, the results show that, in the small sample strong noise conditions, ACYCBD processed data, the trained model has a higher accuracy, compared to maximum correlated kurtosis deconvolution, variational mode decomposition, ensemble empirical mode decompositionaccuracy increased by 1.73, 1.99, 2.2 After using MTF for modal transformation, the accuracy is 2.59, 3.12 and 2.72 percentage points higher than that of Gramian angular field, continuous wavelet transform and RP, respectively; comparing with other deep learning models, the method proposed in this paper has higher anti-interference ability and generalization performance under the above conditions. 

Ultrasonic guided wave detection technology has the advantages of high efficiency, low cost and convenient detection, and is widely used in pipeline damage detection. However, the propagation of ultrasonic guided wave in the pipeline is affected by the environment such as temperature and load, which seriously interferes with the extraction and recognition of damage information. Therefore, a machine learning pipeline damage identification method based on particle swarm optimization - bidirectional gated recurrent unit - attention mechanism (PSO-BiGRU-Attention) model is proposed in this paper. The model effectively establishes a mapping between raw ultrasonic guided wave data and the state of the pipeline, thereby enhancing the capability of the feature extraction layer to discern damage characteristics, mitigating environmental interferences, and accurately detecting authentic damage signals. Taking the test bench of circulating water cooling pipeline in nuclear industry as the experimental object, the pipeline damage identification experiment under the condition of temperature and load changes was carried out. Through the experimental analysis, it is verified that the model can effectively realize the pipeline damage identification, and the recognition accuracy is better than other models such as recurrent neural network, long short-term memory, bidirectional gated recurrent unit, etc., which proves the effectiveness and superiority of the proposed method in this paper.

Images can be converted into feature vectors by multi-graph convolutional network (M-GCN), and the aggregation of similar nodes can be enhanced by graph convolution operation. Due to the limitation of field space and economic conditions, it is impossible to collect sufficient fault samples of hydraulic pump, resulting the problem of small sample. When M-GCN is introduced to diagnose fault of hydraulic pump, there are problems such as insufficient discrimination and single information in the feature expression. Therefore, an improved multi-graph convolutional network, namely MMH-GCN, was proposed in this paper. In order to solve the problem of insufficient discrimination of model feature extraction, masked autoencoder (MAE) was introduced to reduce the encoding dimension and extract key image features, so as to improve diagnostic accuracy based on small sample size. For solving the problem of single feature information, the heterogeneous graph attention network (HAN) was introduced to extract much abundant and comprehensive features of graph structure data, so as to improve diagnostic accuracy and efficiency based on small sample size. Through the measured fault experimental verification and analysis of hydraulic pump, it can be seen that the MMH-GCN proposed in this paper has obvious efficiency and superiority compared with the original M-GCN, and the diagnostic accuracy and efficiency are increased by 12.14% and 14.63% respectively.

In order to improve the measurement accuracy of embedded integrated optoelectronic aiming system, I have studied the error compensation method of the key component digital magnetic compass in the system. On the basis of in-depth analysis of the principle of full attitude error compensation, a method of error optimization compensation based on geomagnetic components is proposed to address its compensation limitations. A new error compensation framework has been constructed to estimate nonlinear factors through particle swarm search algorithm. I designed a magnetic compass error compensation experiment. Experimental results have shown that the error optimization compensation method based on geomagnetic components effectively improves the accuracy of heading measurement, with an improvement range of 10% to 20%. This method has significant application value in on-site calibration of digital magnetic compasses.

This paper proposes a method to mitigate the local scour protection of offshore wind turbine pile foundations by adopting a tidal current energy turbine wake stream, and conducts a study on the mutual interference between the wake stream of a horizontal axis tidal current energy turbine and the seabed bed. Taking the horizontal-axis tidal current energy turbine as the research object, the effects of the turbine installation heights of 0.75D, 1D and 1.25D on the wake velocity loss, wake vortex structure, and its effect on the bed shear stress are analysed. The results show that: in the x/D<3 near wake zone, the distribution of wake velocity deficit is similar under the installation height, and the larger the installation height is, the smaller the accelerated flow velocity above the bed is; in the far wake zone, the wake velocity deficit increases with the installation height, and the larger the flow velocity is at the surface of the seabed, which destroys the symmetry of the wake zone; in the case of the installation height H=0.75D, the tip vortex is dissipated in the collision with the bed surface in the far wake zone, and the vortex structure Meandering occurs; the bed shear stress in the wake area shows a tendency of decreasing and then increasing, and the installation heights are less than 1 between x/D=6-9, and all of them reach the minimum at x/D=8. In order to mitigate the scouring of the wind power pile foundation, the installation height of the turbine, H=1D, and the spacing of installation is the most suitable for the downstream, x/D=6-9.

The temperature, stress, vibration, and other signals serve as crucial parameters assessing and evaluating the operational status and performance of gears. Real-time multidimensional signal monitoring is crucial to ensuring the safe operation of gear equipment. A gear multi-dimensional signal testing system was developed based on wireless relay Wi-Fi network, enabling real-time signal transmission without modifying the gearbox structure. The integrated design allows real-time acquisition of gear temperature, stress, and vibration signals. This system has been validated through gear performance experiments. The temperature, stress, and vibration test range of the testing device are 0 to 150 °C, 0 to 20000 με (microstrain), and ±40 g, respectively. The testing system on the FZG gear test rig effectively captures changes in multi-dimensional gear signals under different load stages, revealing patterns in signal characteristics and eventual failure throughout service. Compared to traditional disassembly-based adhesive judgment methods, testing efficiency has increased by 50%.

Some news sufficient conditions for oscillation of all solutions of a class of second order differential equations with several sub-linear neutral terms are given. Our results not only extend several classical oscillation theorems but also improve and generalize those reported in the literature, recently. Examples are included to illustrate the importance of the results obtained.

To explore the influence of structural damage on the dynamic behavior of folded graphene-modified materials, this study employed finite element methods to calculate the stress intensity factor at the crack tip of Graphene Origami (GOri) enabled gradient beams with a negative Poisson's ratio function. Combining the rotational spring model with the first-order shear deformation theory, the free vibration equation of the beam was derived using the Ritz method and Hamilton's principle, and the natural frequencies of the beam were solved. The results indicate that, due to its gradient distribution, the folded degree of graphene origami affects the stress intensity factor at the crack tip, which correlates with the crack length. Moreover, when GOris are distributed closer to the surface of the beam, the natural frequency of the beam increases. The natural frequency of the beam also increases with the increase of GOri mass fraction. For instance, with a hydrogen coverage rate of 20% for GOri, increasing GOri by only 0.15% can lead to a 3.9% increase in the natural frequency of the beam. However, as the folded degree of GOri increases, the natural frequency of the beam decreases. Further research reveals that changing the folded degree, distribution gradient, and concentration of GOri to enhance the stiffness of the beam also makes the beam more sensitive to the crack in its vibration behavior.

Circular curved beam pedestrian bridges have been applied in urban bridge construction, and curved bridges are more prone to large vibrations under pedestrian excitation due to bending and torsional coupling. In order to reduce the human-induced excitation response of the pedestrian bridge, this paper proposes a damping cable device composed of a damper and a return spring connected in parallel with the main cable, and carries out theoretical analysis and experimental research on the vibration reduction of the circular curved beam pedestrian bridge and the damping cable. Firstly, the differential equation of vibration of the fixed circular curved beam at both ends is established, the mode shape and eigenfrequency of the out-of-plane vibration of the curved beam are obtained by the differential transformation method (DTM), and then the additional damping ratio provided by the damping cable for the curved beam is obtained by the modal analysis method. The model of the curved beam with fixed support at both ends was made, and the additional damping ratio of the curved beam under different installation positions and different viscous coefficients of the damper cable was measured. The results show that the theoretical analysis results of the additional damping ratio of the circular curved beam provided by the damping cable are consistent with the experimental results. The damping cable can greatly increase the additional damping ratio of the circular curved beam, and suppress the vibration of the curved beam well.

Aiming at the shortcoming of the current closed-loop servo control system based on ON-OFF control strategy in the light-induced strain displacement of PLZT actuator, a dynamic model and predictive control method of strain displacement of PLZT actuator based on T-S fuzzy model is proposed. Firstly, the T-S fuzzy model of photo-induced strain displacement of PLZT actuator is established. The fuzzy C-means clustering algorithm based on subtractive clustering is used to identify the antecedent and the SVD(singular value decomposition) algorithm is used to identify the consequent. The validity of the established model is verified by fitting degree simulation. Then, based on the established T-S fuzzy model, the closed-loop control of the photo-induced strain displacement of the PLZT actuator is carried out by combining the predictive control method, and the algorithm is verified by simulation. The simulation results show that for the control of PLZT driver micro-displacement, the control algorithm in this paper reduces the buffeting based on the ON-OFF control strategy and has better control effect.

In the long-term health monitoring process of civil engineering structures, the influence of changing environments on the dynamic characteristics of the structure may even mask the changes in dynamic characteristics caused by damage, which renders traditional vibration-based damage identification methods ineffective. The independent component analysis (ICA) method can be used to separate the effects of environmental factors, however its effectiveness is limited by the need for highly linear correlation between data. To address this issue, this paper introduces switching temperature into the ICA method, and proposes a switching ICA damage identification method considering the influence of nonlinear environmental factors. This method combines principal component analysis (PCA) and Gaussian mixture model (GMM) to determine the temperature switching point, and uses the switching temperature to piecewise linearize the nonlinearly related frequency data; then, for the piecewise linearized frequency data, the ICA method is used to calculate the environmental source of the data and damage source; finally, based on the ICA damage source, the SPE statistic is calculated as the damage index, and early damage is detected through the X⁃bar control chart. A 7-degree-of-freedom numerical example and monitoring data of the Z24 bridge verify the effectiveness of the proposed method.

In the process of grasping workpieces, industrial robots often face the contradiction of excessive gripping force causing damage to the workpiece, and too little gripping force leading to slippage. To address this issue, a rapid sliding detection method is proposed using polyvinylidene fluoride (PVDF) piezoelectric sensors as tactile perception elements. First, the sensor signal is decomposed and reconstructed using the Variational Mode Decomposition (VMD) optimized by the Archimedes Optimization Algorithm (AOA) to reduce noise interference. Next, extract the time-frequency domain features of the signal to construct the signal feature set. Finally, use the Dung Beetle Optimization (DBO) algorithm to optimize the selection of parameters for Long Short-term Memory Networks (LSTM). Apply the optimized parameters obtained from DBO along with the signal feature set to construct the sliding detection recognition model. The proposed sliding detection method was applied to an experiment involving electric gripper grasping. The results demonstrate precise and rapid recognition of contact status, achieving 100% accuracy with recognition times under 20ms. Based on the recognition results, the gripping force of the electric gripper can be adjusted in real-time. 

During the operation of transmission lines, the vortex-induced vibration of steel pipe tower is one of the main causes of fatigue cracks in joint parts. In order to reveal the fatigue failure mechanism of typical joints of steel tube tower, the S-N curves of the joints were obtained, and the fatigue tests of two typical joints of steel tube tower were carried out. The section model specimens were designed, and their equivalence was verified by numerical calculation. The loading device and loading system were designed, and fatigue tests were carried out for C-type nodes and X-type nodes. The results show that the fatigue hot spot of typical joints is located at the toe of the welded joint of the structure. After repeated action of fatigue load, fatigue cracks are formed at the fatigue hot spot, and when the cracks reach the critical size, the specimens break rapidly. According to the change curve of strain amplitude at the first extrapolation point, the fatigue failure process of the node can be roughly divided into elastic stage, plastic stage and failure stage, and the loading times corresponding to the turning point of strain amplitude can be used as the fatigue life of the node. The hot spot stress amplitude-fatigue life curves of C-type and X-type joints with 95% survival rate are obtained, which can provide reference for engineering design of UHV transmission lines.

In order to study the acoustic transfer characteristics inside a liquid filled pipeline, this paper proposes a comprehensive method for calculating the acoustic transfer characteristics inside the pipeline based on the transfer matrix method and the four terminal network model. Three methods are proposed to handle the connection between complex pipeline components and other pipeline components. Effectively combining the acoustic impedance characteristic parameters of pipeline components obtained through theoretical analysis and numerical experiments or experimental methods. Theoretical analysis and numerical experimental methods were used to compare and analyze the acoustic impedance parameters and acoustic transmission response of individual pipeline components, and the calculation results of the two methods are in good agreement. The analysis of the sound transmission characteristics of multiple straight pipe components shows that the method 1 proposed in this paper is more accurate in calculating the sound transmission characteristics inside the pipe. On this basis, the sound transmission characteristics of a multi-component system composed of complex valve components were further analyzed, and the calculation results are in good agreement with the numerical method, verifying the correctness of the acoustic characteristics analysis of the multi-component liquid filled pipeline system in this paper.

The airflow generated noise inside a simple expansion chamber muffler is predicted by combining Large Eddy Simulation (LES) and Morhing acoustic analogy in the present work, and the good agreement is observed between the predictions and measurements. Research indicates that wall pressure fluctuations are dominated by hydrodynamic pressure fluctuations within the distance of three pipe diameters in the outlet pipe, and wall pressure fluctuations beyond the distance of six pipe diameters downstream are dominated by sound pressure fluctuations. The airflow generated noise is mainly attributed to the vortex generated by structural change in the muffler. The strong influences at the longitudinal resonance frequency and antiresonance frequency of the expansion chamber are observed.

In order to study the failure characteristics and deformation calculation of steel plate-reinforced concrete shaft structure in soil under secondary explosion, finite element calculation and theoretical analysis were carried out based on the anti-primary explosion test of shaft structure. The failure characteristics of the shaft structure under different primary and secondary explosion proportional explosion distances and the influence of the primary explosion condition on the structural deformation after the secondary explosion were discussed. The evaluation index of the resistance attenuation of the shaft structure after the primary explosion was proposed. The influence of the strength of the shaft concrete and the thickness of the steel plate on the attenuation degree of the resistance were analyzed, and the calculation method of the elastoplastic deformation of the shaft structure under the secondary explosion was constructed. The following conclusions are obtained: ① The failure mode and failure characteristics of the shaft structure under the secondary explosion are same as those under the primary explosion. However, the primary explosion will lead to plastic deformation and resistance attenuation of the structure, which will increase the deformation and damage degree of the shaft structure under the secondary explosion; ② The attenuation degree I of the generalized stiffness Kstru can be used to characterize the resistance change of the shaft structure after primary explosion. And the attenuation degree I is related to the dimensionless circumferential relative displacement α1 of the shaft structure after an explosion; ③ The strength of concrete has little effect on the attenuation of structural resistance. But the increase of the thickness ratio of steel plate to concrete can slow down the attenuation rate of structural resistance. According to the analysis results, the empirical formula of I was obtained by fitting; ④ The semi-empirical calculation method of elastic-plastic deformation of shaft structure under secondary explosion combined with the calculation method of elastic-plastic deformation of shaft structure under primary explosion and the calculation method of structural resistance attenuation is obtained. The error between the semi-empirical calculation method and the numerical simulation calculation result is less than 8.1 %, which can provide the basis for the anti-explosion design calculation and damage assessment of shaft structure.

The vibration signals in the near zone of deep-hole bench blasting often contain trend terms and noise components, causing signal distortion and affecting the analysis of time-frequency characteristics. To address this issue, a joint preprocessing method combining ICEEMDAN algorithm, GMC-penalized sparse denoising, and BEADS algorithm is proposed. The feasibility of this method is validated through simulation signals and applied to the processing of actual near-zone vibration signals from deep-hole bench blasting. The time-frequency characteristics of the reconstructed signal are extracted, and the results indicate that the proposed preprocessing method can eliminate the effects of high-frequency noise and low-frequency trend terms while effectively retaining the true components of the signal, achieving a higher signal-to-noise ratio and lower root mean square error compared to five other methods. In the analysis of actual signals, the preprocessed signal waveform is normalized, high-frequency noise is suppressed, and the low-frequency spectrum is clearer. Time-frequency characteristic analysis reveals that the main frequency of near-zone vibration signals from deep-hole bench blasting is low, with energy mainly concentrated in the 25~150 Hz range, and very low and high frequencies having a lesser energy proportion. Recommendations for blast design parameters are made based on the results of time-frequency characteristics analysis and in accordance with blasting safety regulations. This research is significant for precise analysis of blasting vibration signals and for developing vibration control measures.

Horizontal non-homogeneous site will adversely affect the seismic resistance of the utility tunnel, and the damage of obliquely incident seismic waves to the underground structure is more serious. In order to solve these problems, this paper derives and verifies the horizontal non-homogeneous site equivalent node formula based on the viscous-spring artificial boundary. Then, a three-dimensional finite element model of the utility tunnel and the surrounding soil body is established, and the acceleration, soil pressure increment, displacement and strain responses of the utility tunnel under seismic action are obtained. The influence laws of different incident angles on the response of the utility tunnel under the action of horizontal non-homogeneous site vertical shear wave (SV wave), including acceleration, soil pressure increment, relative slip of the utility tunnel-soil body, and strain of the utility tunnel, are investigated. It is found that the PGA ranges from 0.1g to 0.4g, and the difference between the maximum acceleration response of the utility tunnel with a PGA of 0.1g and 0.4g under the same incidence angle is close to 50%, which indicates that the incidence angle is sensitive to the larger PGA; the relationship between the maximum utility tunnel-soil relative displacement and the incidence angle is not affected by the PGA; the relative displacement and strain enclosing the clay zone is larger, and the overall average energy dissipation is larger than that of the sand zone by 63.2%. The results of this paper can provide a reference for the seismic design of horizontal non-homogeneous site utility tunnels.

In order to study the effects of dry-wet cycles and stress rate on the dynamic tensile properties of limestone, the dynamic splitting tests of limestone samples with different dry-wet cycles grades were carried out by using the split Hopkinson pressure bar (SHPB) test system. Combined with the ultra-high-speed camera, digital image correlation method (DIC) and crack analysis tool FracPaQ, the effects of stress rate and dry-wet cycles on the strain field evolution, crack propagation, energy dissipation and fractal dimension of the samples were investigated. The results show that under the impact load, the main strain concentration domain and the main crack of the specimen first appear in the center of the specimen and develop along its radial direction. The secondary cracks are generated at the contact end of the specimen and the compression bar. The cracks are fully developed and intersected, and the broken surface is formed through, and the specimen is finally destroyed.During the observation period, the main crack opening speeds of the samples with 0 times of dry-wet cycles under the stress rates of 133.48, 149.79, 174.36 and 234.91 GPa•s-1 were 84.67, 94.83, 101.50 and 105.67 m/s, The maximum main crack opening velocity increases with the increase of stress rate. Based on FracPaQ software, it is found that in the early stage of the main crack opening, the normalized length corresponding to the main crack in the horizontal direction of the sample is dominant, and the normalized length corresponding to the crack in the vertical direction increases with the increase of the opening width of the main crack and the expansion of the secondary crack. With the increase of the number of dry-wet cycles, the secondary cracks of the sample gradually develop, which leads to the increase of the normalized length corresponding to the cracks in the vertical direction. The relationship between the length and angle of the fracture trajectory of the specimen during the tensile failure of the limestone conforms to the Gaussian function ; as the stress rate increases, the tensile strength of the sample increases, resulting in an increase in the absorption energy required for failure, accompanied by an increase in the fractal dimension. With the increase of the number of dry-wet cycles, the bearing capacity of the rock sample decreases, the absorption energy required for its failure decreases, and the fractal dimension increases significantly.

In addressing the paradigm of acquiring monitoring data in practical engineering for building structures and the limitations of current data-driven algorithms, a building structure damage identification algorithm based on a multi-channel one-dimensional convolutional neural network (1D CNN) is proposed. This method merges feature extraction from vibration data of various building floors, implicitly utilizes multi-channel 1D CNN to extract topological relationships between monitoring points, and extracts high-dimensional damage features from signals to achieve effective identification of building structural damage. Validity of the proposed approach is verified using the IASC-ASCE benchmark model. Comparative analysis with traditional single-channel 1D CNN demonstrates a significant improvement in identification accuracy, with a predictive accuracy reaching 0.989. Furthermore, the introduction of monitoring mechanisms during model training greatly enhances training efficiency. Comparative analysis indicates that the proposed multi-channel model architecture converges faster during training and exhibits more stable extraction of structural damage features.                                                                              

To address the issue of start-up stability in pumped-storage units under low head conditions, this paper introduces a start-up strategy that employs full-size converter variable speed operation in such conditions and simulates the start-up process for pumped-storage units with full-size converter variable speed. It is recognized that the starting speed is a crucial parameter influencing the start-up characteristics of variable speed units with low water head.   However, the specific impact of starting speed on the start-up traits of full-size converter variable speed units under low water head conditions remains uncertain. Consequently, this study delves into the dynamic operating trajectories and the starting characteristics, including volute pressure, draft pipe pressure, and excitation system responses, for a range of starting speeds under low water head conditions. The findings reveal that the variable speed start-up strategy presented herein effectively prevents the unit from entering the inverse "S" characteristic zone. With identical initial settings and governor controls, full-size converter variable speed units that commence start-up at speeds between 82.5% and 87.5% can achieve a stable operating state in a shorter time frame. The initiation of the full-size converter variable speed unit at a variable speed results in a leftward shift of the operational starting area along the characteristic curve, thereby enhancing the stability of the volute pressure within the unit. In addition, the impact on the excitation system is minimal, which is conducive to fundamentally solving the challenges brought by low head start-up and grid connection. The insights gained from this research offer valuable decision-making support for the start-up strategies of both full size converter variable speed unit and fixed speed unit post-modification.

The large-span suspended floor is a flexible structure, which may cause vibration serviceability problems under human-induced vertical loads. In order to study the vertical vibration performances of suspended floors, firstly, vertical vibration of a suspended floor was compared between filed test and finite element simulation. Then, using the single-story equivalent model of the unidirectional ribbed suspended floor system and based on the energy principle, a simplified calculation formula for the vertical fundamental frequency of the floor was derived. Finally, a multi factor impact analysis of the floor fundamental frequency was carried out, and an evaluation process for the serviceability of human-induced vertical vibration of the suspended floor were summarized. Results show that, proposed based on the theory of floor bending vibration, the simplified formula for the vertical fundamental frequency of the suspended floor is accurate, and it is suitable for rapid evaluation of the dynamic performance. The vertical fundamental frequency of the suspended floor can be improved by reducing the spacing between rib beams appropriately, increasing the stiffness of ribs and beams, and arranging hanging pillars reasonably, to avoid excessive vibration when the natural vibration frequency of the suspended floor is close to the frequency of the pedestrian excitation. For the suspended floor under single pedestrian walking, the dynamic response results of theoretical calculation, finite element simulation and field measurement are in good agreement. The research results can provide reference for the vibration performance analysis and the vertical vibration serviceability evaluation of the suspended floor.

The principle of equal limiting penetration velocity is employed to derive an equivalent model applicable to thin target plates of different steel materials, designed to resist the penetration of pointed ovoid bullets. This is achieved through the use of magnitude analysis. The finite element software LS-DYNA was employed to simulate the vertical penetration of the 12.7mm armor-piercing bullet core through the 30CrMnSi target plate and the 45 steel target plate. The resulting equivalent thickness was used to determine the coefficients of the equivalent model for both the 30CrMnSi target plate and the 45 steel target plate. Furthermore, the 30CrMnSi target plate and its equivalent 45 steel target plate were employed in 12.7mm armor-piercing bullet core penetration experiments. The two limit penetration speed error was less than 2.7%. This verifies the correctness of the equivalent model. Additionally, the study can be used to validate the penetration of a bullet through a rocket engine, which is equivalent to the aforementioned experiments. This provides a theoretical basis and data reference.

Vortex induced vibration (VIV) of urban rail transit bridge will not only affect traffic safety, but also cause adverse social impact. Firstly, the coupling vibration analysis model of the wind-vehicle-bridge (WVB) system considering the effect of VIV and track irregularities is established. Take a long-span urban rail transit self-anchored suspension bridge as an example, the effects of track irregularity, the time of train entering the bridge, train speed, amplitude and order of VIV on running performance were analyzed. Then, the train-bridge vertical system under VIV is simplified into a single degree of freedom model. The relationship between vehicle acceleration response and VIV amplitude is derived, and the calculation formula of VIV amplitude limit of the bridge is given. The results show that the train response generally increases with the increase of the train speed, the order of bridge vibration and the amplitude of VIV, and the randomness of track irregularity and the time of train entering the bridge also have a certain influence on the train response. The derived equation takes vehicle performance into account, and the calculated results are in good agreement with the coupled vibration analysis results of WVB system, which can provide reference for the study of VIV amplitude limits of bridges. 

A passive acoustic source localization estimation method based on second-order fractional lower-order covariance is proposed to address the issues of weak anti-interference capability and large localization errors in the presence of strong impulse noise. This method first establishes an optimal four-element array structure with multiple shared points. Then, it employs a bounded non-linear Sigmoid function to process the received signals containing impulse noise. Subsequently, the signals between array elements after processing are subjected to second-order fractional lower-order covariance operation. This involves calculating the self-fractional lower-order covariance of the first element signal and the cross-fractional lower-order covariance between correlated array element signals. The resulting cross-fractional lower-order covariance is then computed once again to further suppress the influence of impulse noise. Finally, source localization calculations are performed based on the obtained delay information. The effectiveness of the proposed method is validated through experiments.

 Downburst is a common extreme wind climate, which is destructive to transmission lines. It is of great significance to study the wind field and wind effect of downburst in order to understand the characteristics of wind field and carry out the design of structure anti-thunder storm reasonably. This study is based on the field measurement project of transmission towers in southern Zhejiang Province. Suspected downburst wind speed data were selected. The measured model of transmission tower is established, and the wind-induced vibration response of transmission tower under the measured wind field is analyzed. The research results show that The measured time-varying average wind speed of downburst can be extracted quickly and accurately by using the moving average method and using the average time distance of 60s. The turbulence intensity of the pulsating wind speed during suspected downburst events, particularly during periods of extreme wind speed, was measured to be approximately 0.2, indicating a close resemblance to a Gaussian distribution. Upon analyzing the temporal variation of turbulence intensity in two wind speed time series, it was observed that the turbulence intensity tends to increase as the measured wind speed becomes larger, especially when the wind field weakens during wind speed reductions. The measured inclination, second and top layer acceleration responses are mainly provided by the first two orders of modes. The foot strain of transmission tower is greatly affected by temperature in a long time range and wind speed in a local short time range. The structural response is mainly provided by the first two orders of modes; Using the nonlinear planning genetic algorithm to record the wind speed timescale through a limited number of measurement points can be a good inverse performance of the wind field parameters, and the reconstructed wind field is better restored to the measured wind field wind speed timescale; The dynamic response of the transmission tower under the effect of the reconstructed wind field is close to the measured data with the same trend and magnitude.

Based on the wave theory of saturated frozen soil medium, the reflection and energy transfer of SH1 with fast propagation speed on the free surface of saturated frozen soil foundation are discussed. In this paper, the free field analysis model of saturated frozen soil is established. Through the Helmholtz vector decomposition theorem and boundary conditions, the theoretical expressions of the amplitude ratio and energy rate of two reflected SH waves are derived. The effects of incident frequency, temperature (ice content), porosity, cementation parameters and contact parameters on the amplitude and energy distribution ratio of the two reflected elastic waves were studied. The results show that as the frequency increases, the amplitude ratio and energy rate of the reflected S1 wave gradually decrease, and the reflected S2 wave increases. When the incident angle is 90°, only the reflected S1 wave exists. When there is no frozen soil (T=0.1 °C), the reflected S2 wave disappears, and the amplitude ratio of S1 wave increases with the increase of temperature. When the temperature is low and the ice content is high, the amplitude ratio of reflected S2 wave is the highest. In addition, the variation of cementation parameters, porosity and contact parameters will significantly affect the amplitude and energy distribution ratio of the two reflected elastic waves.

The safe and stable operation of hydropower units is very important for the safety of power stations and regional power grids. An intelligent early warning method for hydropower units based on Kernel Principal Component Analysis (KPCA) and Long Short-Term Memory (LSTM) is proposed in this paper, which realizes that trend early war function based on multi-channel vibration signal fusion. Firstly, the multi-channel vibration signals of hydropower units are fused, and KPCA is used to compress the data to reduce the amount of information processing in the process of early warning. Furthermore, the early warning threshold is set according to the steady-state operation condition of the unit by the multivariate statistical process control method, and the early warning function based on data fusion is realized. Then, the prediction model of vibration fusion data is constructed based on LSTM, and the prediction function of future operation data is realized. In that end, the effectiveness of the propose method is verified by the given case with a R2 coefficient exceeding 0.97, and realize the state monitoring and alarm prediction. Compared to the KPCA-RNN and KPCA-Informer models, the proposed model demonstrates the best performance on the same experimental data.

Aiming at the problem of damage accumulation caused by the impact of enemy weapons and the recoil of its own artillery during naval battle, a random multiple impact damage accumulation prediction method combining grey Markov model and Dirlik formula is proposed. Based on GM(1,1) model, a new grey Markov method is given to process and predict random impact load data by introducing Markov state transition matrix. Based on Dirlik formula, a method of damage accumulation and life prediction of parts under random impact is proposed. Taking aluminum alloy 6061 axial samples as the research object, the predicted values of this method are compared with those of Miner method. The results show that the expected damage rate under random impact is positively correlated with kurtosis, and the larger kurtosis has a significant impact on impact fatigue damage. The error between the predicted life value and the real life value obtained by this method is smaller, which is significantly better than the traditional Miner method. This method is reliable and conservative, which can provide data support and theoretical reference for the study of random multiple impact damage accumulation of ship equipment parts.

Multifunctional dredger is an important vessel for inland river dredging. In order to improve its ability to break underwater rocks with uniaxial compressive strength greater than 20 MPa. a saw blade-impact hammer combination cutterhead was designed. The main parameters such as impact head diameter D = 25 mm, notch depth h = 40 mm, notch width w = 4 mm, and free face distance l1 = 30 mm were investigated. Firstly, the experimental investigation of rock breaking characteristics (impact force, specific energy consumption ,and crack length) of single impact head (mass and height) and double impact head (spacing) under free face conditions was carried out. Subsequently, numerical simulations of impact head rock breaking were carried out to elucidate the mechanism. The results show that when the rock has no slotted free face, the form of rock breaking is dominated by compression failure, which is manifested as crater; when the rock has the free face, the form of rock breaking is dominated by tensile failure, and the cracks are more likely to propagate, forming X-shaped main cracks and generating large rock chunks. In the single impact head rock breaking experiments, there exists an optimal impact energy of 250 J, which forms effective rock breaking after the first impact. In dual impact head rock breaking experiments, there exists an optimal spacing of 170 mm, which minimizes the specific energy consumption for cracks penetration.

In autonomous driving, the angle of the passenger seat can be freely adjusted, making the interior space more spacious. In order to improve the safety of passengers in side collisions with different seat back angles, a strategy is proposed to first rotate the passenger seat to a 180 ° angle with the collision direction before colliding. The damage situation of passengers in collisions after rotation under different seat back angles is explored, and the applicability of this strategy is discussed. The influence of factors such as seat back angle and collision time delay on passenger kinematic response and injury risk in different collision scenarios was explored through simulation experiments. The research results show that in side impact simulation tests, there is a risk of secondary collision contact between the upper body of passengers with seat back angles of 100 ° and 120 ° and other passengers or car components. In collision strategies with rotating seats at different backrest angles, adjusting the collision delay time can effectively reduce the risk of head displacement and injury for passengers. Through simulating the collision of the seat after rotating 90 ° within 200ms, it was found that this strategy did not cause additional damage to the occupants, and the strain of the occupants' viscera did not exceed the damage threshold. It also showed a relatively low comprehensive damage risk at different backrest angles. The difference in seat backrest angle has a significant impact on passenger motion response. The strategy of turning the seat to 180 ° first and then crashing can effectively reduce the lateral deviation of the passengers in side impact, reduce the risk of injury in contact with other passengers or other parts in the vehicle, and improve the safety of side impact of autonomous vehicle. 

To promote the development of parachute-free airdrop technology, the impact characteristics of parachute-free airdrop box with composite structure were studied, and the impact response and failure modes were analyzed. Theoretically analyzing the protection mechanism of the parachute-free airdrop box, followed by in-depth simulation using finite element method. The simulation results show that the goods with edge drop and angle drop have large displacement, serious box deformation and long impact duration; the impact energy absorption rate of parachute-free airdrop box is more than 80%, and the efficient energy absorption provides a strong guarantee for goods safety; compared with edge drop and angle drop, the peak acceleration and average impact force of goods are larger for face drop; when the edge drop and the angle drop, the stress and strain level of the parachute-free airdrop box is higher than the face drop. The study shows that the safety of goods is related to the impact area and foam impact thickness, smaller impact area and larger foam thickness can reduce the risk of goods damage; the failure of parachute-free airdrop box is related to their impact area, larger impact area can effectively reduce the degree of impact failure and improve the safety of goods.

The influence of the changing environments on dynamic feature may completely mask the dynamic feature changes caused by damage, making vibration-based methods challenging to effectively detect structural damage. To address this issue, this paper proposes a structural damage detection method based on the Variational Mode Decomposition (VMD), Principal Component Analysis (PCA) and Gaussian Process Regression (GPR). First, the VMD algorithm is used to preprocess the frequency signal to obtain the IMF1 after separating the seasonal environmental patterns; Secondly, the PCA method is used to analyze the IMF1 and calculate the Euclidean distance of the PCA residual; Then, the IMF1 signal and the corresponding PCA residual Euclidean distance are used as input and output, and the GPR model is used to learn the calculation rules between input and output; Finally, the trained GPR model is used to predict the PCA Euclidean distance of the remaining IMF1, the prediction residual between the predicted value and the true value is calculated, and statistical control chart is used for damage warning. Monitoring data from a laboratory wooden bridge and the Z24 bridge are used to verify the effectiveness of this method.