This paper establishes the governing equations of the nonlinear vibration of a functionally graded shell with a crack，based on the extended isogeometric analysis （XIGA） and the first-order shear deformation theory. The study investigates the effects of the crack on the nonlinear vibrational frequency ratio of the model，taking into account large amplitude vibrations. Enriched functions，which represent displacement changes，are used to describe the position and length of the crack. This approach enhances calculation accuracy and avoids mesh refinement at the crack. The nonlinear governing equation is solved using the direct iteration method，and its correctness is validated by comparing the results with existing literature. The study further explores the effects of the pre-twisted angle，crack location，crack length and material variation parameters on the nonlinear vibration characteristics of the pre-twisted shells with cracks.

A segmented damping device is designed using a cam mechanism in this study. Based on the traditional Voigt dynamic vibration absorber，this device is installed between the main system and subsystem of the dynamic vibration absorber，and the dynamic equation of the vibration absorber is established. Using the principle of equivalent damping energy dissipation within one vibration period，the equivalent damping coefficient of the segmented damping device at the same vibration frequency is obtained. The theoretical solution of a dynamic vibration absorber with piecewise damping characteristic is derived and verified by numerical solution. The vibration absorption characteristics of undamped，traditional linear damping，and dynamic absorber with piecewise damping are compared and analyzed. The results show that the amplitude frequency characteristics of the dynamic vibration absorber with piecewise damping characteristics integrate the characteristics of undamped and traditional linear damping dynamic vibration absorbers. This ensures that the amplitude of the main system at the anti-resonance point is very low，and the suppression effect of the resonance amplitude of the main system is close to that of the traditional linear damping dynamic vibration absorber.

An Automatic Ball Balancer （ABB） can entirely eliminate the unknown imbalance of the rotor above the critical speed. However，it has the disadvantage of causing large amplitude resonance response and unstable oscillation near the critical speed. To overcome these shortcomings and improve its vibration suppression performance，this paper proposes the addition of a Dynamic Vibration Absorber （DVA）. Using the Jeffcott eccentric rotor model as the research object，dynamic equations are established to control the unbalanced vibration of the rotor when the DVA and ABB are used either separately or in combination，based on the Lagrange equation. The harmonic balance method is used to solve the amplitude expression of the new coupling system，and the influence laws of each parameter on the steady-state amplitude-frequency curve are analyzed to obtain more suitable parameters. The steady-state amplitude-frequency characteristic diagram and the transient amplitude time-domain change curves are obtained using the Runge-Kutta numerical calculation method. The comparison results show that the new scheme of combining the two methods effectively reduces the vibration level of the rotor when passing through the critical resonance region，and causes the rotor to attenuate to zero amplitude above the critical speed. This new scheme achieves the goal of combining the advantages of the two methods and provides superior vibration suppression.

Ambient environments are rich in rotational energy resources. These can be converted into useful electric energy through energy conversion materials to，powering embedded devices and wireless sensors in the Internet of Things. As such，energy harvesting technology could potentially address the environmental pollution and high maintenance costs associated with traditional chemical batteries. This paper proposes a novel time-varying potential well magnetic-coupled bistable energy harvesting system with low potential barriers to enhance the energy harvesting performance in ultra-low frequency rotating environments （below 3 Hz）. The proposed system comprises a forward steel beam and an inverted piezoelectric beam installed on a rotational plate. Mutually exclusive magnets are attached to the free ends of both beams，creating three equilibrium positions due to the magnetic force，two of which are stable. This gives the system its coupled bistable characteristics. The free end of the forward steel beam is distanced from the center of the rotational plate，making it a centrifugal hardening beam. Conversely，the free end of the inverted piezoelectric beam is closer to the center，making it a centrifugal softening beam. Taking into account the influence of the centrifugal effect，the distributed parameter electromechanical coupling equation of the system is derived in the rotational coordinate system using the energy method，Lagrange equation，piezoelectric theory，and more. A magnetic calculation model is used to analyze the influence of magnetic spacing and the centrifugal effect on the potential energy well and the energy harvesting performance of the system. Finally，numerical simulations and experimental results verify that，compared to the linear energy harvesting system，the proposed magnetic-coupled bistable energy harvesting system has a wider operating frequency range （0~2.67 Hz） and higher output voltage （greater than 2 V）.

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.

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.

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.

Traditional designs of viscous dampers for large-span cable-stayed bridges often suffer from low efficiency and challenges in balancing multiple，mutually constrained damping control objectives. To address these issues，this paper proposes an improved multi-objective particle swarm algorithm for optimal damper parameters design，based on the "variational" method of genetic algorithms. A finite element model of a large span cable-stayed bridge was established，and a seismic response analysis of the entire bridge was conducted. Viscous dampers were installed in the longitudinal direction of the bridge according to the seismic demand. Response surface mathematical models were established to represent the relationships between the seismic responses of the tower bottom bending moment，damping force，beam end displacement，and the damper parameters. Using the seismic response surface model，a global automatic optimization search analysis of the damper parameters was performed using the proposed algorithm，resulting in the determination of the optimal damper parameters. Additionally，a set of damping parameter combinations were determined for comparative analysis using the traditional parameter sensitivity analysis method. The results show that the optimization method offers good computational accuracy，high optimization efficiency，and a better trade-off among multiple，mutually constrained seismic control objectives. The combination of damper parameters obtained by the optimization algorithm，compared to the damping response of the combination of damping parameters obtained by the conventional method，increases the bottom bending moment of the tower by 1.73%，reduces the damping force by 5.97%，and reduces the displacement of the beam end by 1.66%. The optimized parameter combinations of dampers with higher accuracy are determined without the need for multiple finite element trial calculations，resulting in improved damping effect and significant time savings.

This paper proposes a Tuned Negative-stiffness Inerter Mass Damper （TNIMD） to mitigate seismic vibrations in primary structures during earthquake excitation. The equations of motion for the coupled system of the primary structure and TNIMD are obtained using the Lagrange function，and fixed-point theory is applied for optimal design. The impact of negative-stiffness coefficient on control performance is also discussed. Subsequently，a parametric analysis and evaluation of seismic vibration control are conducted. The results indicate that the displacement response of a primary structure equipped with the TNIMD is significantly less than those with a Vibration Tuned Mass Damper with Inerter （VTMDI） without a negative-stiffness spring. Furthermore，the smaller the mass and inertance ratios，the greater the advantages of TNIMD in vibration control，outperforming VTMDI. This confirms the requirement of installation limitations and the selection of a small mass ratio engineering. Additionally，seismic analysis shows the displacement and absolute acceleration of a primary structure equipped with TNIMD are superior to VTMDI under far-field，near field with pulse，and near-field without pulse earthquakes. The theoretical analysis and optimal design presented in this paper are suggested for engineering applications for seismic vibration control using TNIMD.

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.