Vision-based modal analysis techniques have gained attention due to their non-contact，full-field measurement capabilities，making them particularly suitable for the dynamic testing of large-scale or thin-walled structures. However，these techniques often require cameras to be fixed to the ground to avoid coupling with the vibrations of the test structure，a requirement that can be too restrictive in real-world applications. This paper proposes a method to compensate for camera motion using homography transformation，followed by the extraction of the test structure’s movement by applying the dense optical flow method to the stabilized video. The procedure involves transforming the video captured by a moving camera using feature matching algorithms，where a homography matrix compensates for six degrees of camera motions. Several "virtual vision sensors" are selected on the edges of the structure，and their vibrations are estimated using optical flow methods. Structural modal parameters are then extracted from the output-only data using stochastic subspace identification algorithms. The proposed procedure was applied to videos recorded using a moving smartphone to conduct an operating modal analysis of a 2 m cantilevered beam. To validate the procedure，the vision-based analysis results were compared with measurements taken with a Scanning Laser Doppler Vibrometer. The results show an average discrepancy of 0.4% and 11.5% for the first five natural frequencies and damping ratios of the beam，respectively. The mode shapes also show strong correlation between the two measurement techniques，as indicated by the diagonal MAC values greater than 98%. Therefore，the proposed procedure effectively cancels out camera motions and achieves accurate estimation of structural modal parameters.

This paper introduces a method of using indicial functions （IFs） to simulate the time-domain expressions of self-excited aerodynamic loads of bridge decks，and studies the precision of this simulation. A modern genetic optimization algorithm is proposed to identify the parameters of IFs based on the tested flutter derivatives. During the simulation process，the equivalent relation between flutter derivatives and IFs parameters is first established. Then，the genetic optimization algorithm is implemented to identify all the IFs parameters using the MATLAB software. Based on the obtained IFs parameters，the fitted flutter derivatives are calculated according to the relation expression between IFs parameters and flutter derivatives. Finally，the simulation precision is evaluated by comparing the fitted and tested flutter derivatives. Numerical results indicate that the genetic optimization algorithm has high computational efficiency and is not affected by the number or range of parameters. The number of IFs parameters greatly influences the fitting precision of the flutter derivative. When the number of IFs parameters is small，the fitting precision is not ideal for complex flutter derivative curves. As the number of IFs parameters increases，the fitting precision significantly improves. The difference in fitting precision directly affects the critical wind speed of flutter obtained by the subsequent time-domain flutter analysis. Therefore，it is necessary to carefully select the number of IFs parameters based on the properties of flutter derivative curves. This allows for the simulation of a high-precision time-domain self-excited aerodynamic loads model，which can accurately evaluate the flutter stability of long-span bridges.

Concrete filled double-skin tubular structures （CFDST） that reuse waste steel slag demonstrate advantages in sustainable resource use. The interaction and coordination between steel tube and concrete make CFDST an effective solution to the stability issues，considering the expansion characteristic of steel slag. The expansion performance of the steel slag concrete can enhance the bond between the steel tube and its sandwich concrete. This paper presents a series of tests on a steel slag CFDST T-Joint under pseudo-static loading conditions to investigate its seismic performance. Five specimens were tested，including one ordinary concrete test specimen and four steel slag concrete test specimens. The variables tested were concrete type，hollow ratio，diameter ratio，and axial compression ratio. The results show that while the bearing capacity of steel slag concrete specimens is slightly lower than that of ordinary concrete，the displacement ductility and energy dissipation capacity significantly increased，by 69.46% and 48.20% respectively. As the hollow ratio increases from 0.3 to 0.5，the displacement ductility coefficient of the specimen increases by 9.69%. When the diameter ratio of branch main increases from 0.40 to 0.68，the displacement ductility coefficient increases by 82.44%. However，when the axial compression ratio increases from 0.1 to 0.2，the displacement ductility coefficient of the specimen decreases by 17.98%. A finite element model was established to simulate the hysteretic properties of the specimen. The simulation results are in agreement with the test results，verifying the validity of the finite element model. Based on the verified finite model，the parameters of influencing factors on the bearing capacity of the specimen were analyzed，and the optimum hollow ratio of the specimen was found to be about 70%. The use of steel slag greatly improves the seismic performance of the CFDST T-joint and can be widely used in concrete-filled steel tube engineering structures.

The paper proposes a time-frequency ridge index algorithm for gearboxes under variable speed conditions，based on Dynamic Path Planning of Barycenter （DPPB）. This algorithm addresses the challenge of estimating the instantaneous frequency of signals in a high-noise environment. The algorithm builds upon the analysis of the Multi-Path Matching Pursuit （MMP） ridge index algorithm and its limitations under high noise. By adding windows to the ridge set obtained by the MMP algorithm，a ridge barycenter sparse matrix of the signal is constructed. A dynamic path planning function is then designed for the barycenter sparse matrix to index the barycenters on the ridge line. The optimal time-frequency ridge line is calculated based on the values of the ridge line cost function. The similarity coefficient Ra and confidence σRa are used as measures of the ridge extraction effect. Simulations and experiments indicate that the DPPB algorithm can effectively extract the time-frequency ridge of signals in high-noise environments，and it is more reliable and robust than the peak index algorithm and the MMP algorithm under various noise intensities.

Most wind turbine blade pre-bending designs use the static aeroelastic analysis method. This approach often overlooks the aeroelastic coupling instability caused by the interaction of blade aerodynamic force，inertial force and elastic force. This oversight is particularly significant when considering flutter performance of ultra-long flexible blades of around 100 meters. To analyze the influence of different pre-bending sizes on flutter critical state of blade， aeroelastic model of the blade was designed based on the stiffness equivalence principle of the main beam. Wind tunnel tests revealed differences between the flutter interval and the critical wind speed of two pre-bending blades of a 15 MW wind turbine. Further analysis was conducted on four pre-bending blades using the corrected Blade Element Momentum Theory-Geometrically Exact Beam Theory （BEM-GEBT） coupling calculation method. This analysis compared and analyzed the flutter critical wind speed，aerodynamic force distribution and displacement spectrum characteristics of blades with different pre-bending sizes，revealing the flutter coupling modal mechanism. The research shows that the results of BEM-GEBT coupling calculation method align well with those of wind tunnel test. As the pre-bending size increases，the flutter critical wind speed of flap-edge coupling increases，and the flutter interval range remains essentially the same. The divergence rates of lift coefficient and pitching moment coefficient of different pre-bending blades are positively correlated with the displacement divergence rate. The average wind pressure curve shows significant changes in the pre-bending range of 3~4 m. The flap-edge coupling effect is larger than the flap-torsion coupling effect，and the flutter coupling frequency is dominated by the first-order flapwise frequency.

In this paper，a two-dimensional analytical model for composite beams is first proposed through the equivalent transformation of the cross-section. Based on the mixed variational principle，the dynamic state equations are derived through finite element meshing and interpolation along the length of the beam，with frequency contained nodal displacements and their energy-conjugated stresses as element nodal variables. The differential quadrature method （DQM） is introduced to discretize the equations along the height of the beam，and natural frequencies of composite beams under different axial forces and boundary conditions are obtained. This method was verified by numerical examples about natural frequencies of three beams，i.e. a concrete-wood composite beam，a concrete beam with a corrugated steel web and steel-concrete composite beam. Since the proposed method is based on the two-dimensional theory，it can provide benchmarks for beam theories and error analyses.

The longitudinal linkage of the floating slab track （FST） has weakness due to the dynamic effects of FST longitudinal linkage，which are not adequately considered in the track design. By introducing the method of equivalent density and equivalent foundation coefficient to simplify the model of the base of a steel-spring-FST system，a three-dimensional finite element model of vibration characteristics analysis of prefabricated short and cast-in-situ FST system is established. In the proposed model，the influence of the rail，shear hinge，and foundation under the slab on the vibration characteristics of the floating slab structure is fully considered. The modal analysis and harmonic response analysis are analyzed with a focus on the dynamic effect characteristics of the longitudinal connecting slab of the FST system. The results show that： The modal shape of the FST in the low frequency band of 1~200 Hz mainly shows four types of motion： rigid body motion，bending，bending-torsion combination and torsion； For the prefabricated slab track system，the frequency band in which the floating slab dominates the vibration characteristics of the system conforms the system modal analysis and harmonious response analysis； For the cast-in-situ slab track system，when the frequency is within 32.6~57.8 Hz，the frequency band is the transition band，where the dominant role of the FST in the vibration characteristics of the system is weakened； The lower-order bending modes generated by the coupled slab dynamic effect are expressed as rigid body motion modes in the prefabricated slab system； for the FST composed of N_s slabs，the number of additional modes around each order of bending mode frequency of a single slab caused by the coupled slab effect is N_s/2‒1.

The power generation of single-axis PV trackers system is significantly higher than that of the fixed photovoltaic system，making them widely used in recent years. The single-axis PV tracker is prone to torsional aerodynamic instability in the strong wind condition due to its low torsional stiffness，resulting in structural damage. In order to understand the occurrence conditions and mechanism of this vibration further，the present study investigates the influence of structural natural frequency，tilt angle，damping ratio and other parameters on torsional aerodynamic instability through wind tunnel tests with elastic support. The variations of aerodynamic damping and aerodynamic stiffness with wind speed and tilt angle are focused. The result shows torsional aerodynamic instability of single-axis PV trackers shows strong aerodynamic coupling effect. The aerodynamic damping and aerodynamic stiffness are significant parameters that can influence aerodynamic instability，which are sensitive to wind speed and tilt angle with self-excited vibration characteristics. The increase in torsional stiffness can effectively limit the amplitude at certain tilt angles and improve the critical wind speed of the structure at various tilt angles. The unstable tilt angle is approximately located in the range of -15°~20°. It is suggested that a large tilt angle can be used to avoid aerodynamic instability in strong wind. When a small tilt angle is inevitable，higher critical wind speed corresponds to a 0° tilt angle.

Environmental vibration is one of the non-periodic and random broadband excitations. It is of great significance to study the characteristics of vibration energy harvesters under environmental vibrations. In this paper，the modified stochastic averaging method is used to solve the following parameters of piezoelectric beam with a variable cross-section： steady-state probability density function of equivalent amplitude，displacement and velocity，joint probability density function of displacement，and velocity and steady-state mean square output voltage. Then the study investigates the energy acquisition efficiency of a piezoelectric beam with a variable cross-section under Gaussian white noise excitation. The results show that when the load resistance reaches a certain value，the variable section piezoelectric beam with a section coefficient β>0 can produce better steady-state mean square output voltage than the constant section piezoelectric beam with β=0； when the section coefficient β>0，with the increase of the reciprocal of the product of resistance and capacitance，the mean square voltage of the variable-section piezoelectric beam shows a gradually decreasing trend. The trend shows the following rules： when the reciprocal value of the resistance and capacitance reaches a certain value，the larger the β value is，the higher the mean square voltage will become； with the increase of the noise intensity，the mean square voltage of the variable-section piezoelectric beams shows a trend of increasing gradually； when the noise intensity reaches a certain value，the larger the β value is，the higher the mean square voltage will become. The research results in this paper can provide a theoretical basis for the design and application of the variable-section piezoelectric cantilever energy harvesting system.

The supercritical carbon dioxide power cycle system has a very positive effect on the realization of energy saving and emission reduction goals. In this paper，a calculation model is proposed for a foil gas dynamic pressure bearing structure. By fitting the non-ideal state gas supercritical carbon dioxide，the relationship between density and pressure is established. Based on the heat transfer model and the gas lubrication energy equation，the temperature rise of the bearing gas film is analyzed. The Reynolds equation of the lubricating gas is corrected in combination with the turbulent effect in the actual operation process，coupled with the mechanical analysis model，Reynolds equation and energy equations，the static characteristics of foil gas dynamic pressure bearings are analyzed，and compared with air as a medium to analyze the influence of different system parameters and turbulence parameters on the bearing characteristics. The results show that compared with air，the foil gas dynamic pressure bearing using supercritical carbon dioxide as the lubricating gas has a higher bearing capacity，and within a certain range，the bearing capacity can increase with the increase of bearing diameter and width，eccentricity，the rotational speed and the reduction of the bearing clearance. For the turbulent influencing factors，within a certain range，the bearing capacity can increase with the increase of the local Reynolds number and turbulence coefficient，aerodynamic viscosity，density for ambient gas and the decrease of ambient temperature.