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.

Current studies on the failure modes and safety evaluation of asphalt concrete core walls and dam bodies under the spatial oblique incidence of seismic waves are significantly lacking. This paper considers the spatial variability of the SH wave incident azimuth，and constructs the non-uniform free field on the foundation boundary based on the wave field superposition principle. It establishes a wave input method for SH waves with three-dimensional space oblique incidence. An empirical formula is then established for the change in the instantaneous tensile strength of asphalt concrete with the strain rate，based on the test results. A new method for core wall safety evaluation，based on instantaneous tensile stress and instantaneous tensile strength，is proposed to judge the tensile failure of elements. The influence of the incident azimuth on the dislocation between the transition material and the core wall，and the stress of the core wall，are analyzed. A shear failure evaluation of the dam body is carried out，and the seismic weak parts of the core wall and the dam body under different incident orientations are clarified. The results show that the seismic wave vibration direction parallel to the water flow direction is the most unfavorable excitation direction for transition material dislocation，core wall tensile stress，and local dynamic shear failure of the dam body. Compared with the vibration direction parallel to the dam axis direction，the horizontal detachment and vertical dislocation of the transition material increased by 19.25 times and 2.19 times respectively when the vibration direction was parallel to the water flow direction. The maximum tensile stress of the core wall increased by 1.8 times，and the dynamic shear failure depth of the upstream dam slope element deepened. Moreover，compared with the core tensile failure judgment method proposed in this paper，the traditional judgment method will lead to an overestimation of the damage degree of the core wall.

To broaden the site selection for nuclear power plants，it is vital to assess the seismic safety of nuclear power structures in non-rock sites with pile foundations. Current pile-soil-structure interaction analysis methods，such as the Winkler foundation model and the p-y method，simplify the interaction problem and struggle to reflect complex foundation situations. While the integral finite element method can consider complex foundation situations，it is computationally intensive and inefficient. This paper introduces an efficient three-dimensional time-domain method，Partitioned Analysis of Soil-Structure Interaction （PASSI），which uses different time steps for pile foundation and soil to avoid unnecessary calculations. A three-dimensional finite element model of the pile-soil-nuclear power structure interaction is established，with the AP1000 nuclear island structure as the research object. The effectiveness of this asynchronous algorithm is verified by inputting pulse waves，and the characteristics of the maximum shear force and bending moment of the pile are analyzed by combining the kinematic and inertial interactions. The response of the pile-soil-nuclear power structure under the seismic wave input is then analyzed. Since the degrees of freedom of the pile are insignificant compared to the soil，the additional computational volume of the pile can be neglected when using the pile-soil asynchronous algorithm. This efficient method is expected to be used in the analysis of the dynamic interaction of large nuclear power structures with pile-soil-structures.

The study investigates the dynamic elastic modulus and damping ratio of sand and gravel under single and bidirectional cyclic loads using a large-scale vibration triaxial test. It also analyzes the effects of confining pressure and radial cyclic stress on the dynamic parameters of sand and gravel. The results show that in the bidirectional vibration triaxial test，the axial dynamic strain of sand and gravel is less influenced by the radial dynamic stress，with the dynamic strain primarily related to the applied axial dynamic stress. Under both unidirectional and bidirectional vibration，the dynamic elastic modulus of sand and gravel gradually decreases with the increase of dynamic strain. Under bidirectional vibration，the decay rate of dynamic elastic modulus of sand and gravel remains essentially unchanged，and the dynamic modulus of bidirectional vibration is lower than that of unidirectional vibration under the same dynamic strain. The damping ratio of sand and gravel under bidirectional vibration is larger than that under unidirectional vibration，and the dynamic strain energy consumed under bidirectional vibration is larger. Based on the analysis of the maximum dynamic elastic modulus and dynamic modulus ratio under the two test conditions，a conversion relation expressing the maximum dynamic elastic modulus under single and double direction test conditions and a correction model of the dynamic modulus ratio and dynamic strain in the bidirectional vibration test were established. The research results can provide a theoretical basis for the seismic design of sand and gravel in high earth-rock dams.

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.

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.

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.

This paper proposes a fault diagnosis method for rolling bearings under variable speed conditions，based on the Adaptive Window Rotation Optimization Short-Time Fourier Transform （AWROSTFT）. This method addresses the issue of low energy concentration caused by the fixed window effect in Short-Time Fourier Transform （STFT）. Variational Mode Decomposition （VMD） is used to reduce the noise of the original vibration signal，and Particle Swarm Optimization （PSO） is employed to solve the complex problem of VMD parameter selection. A series of rotation operators are adaptively matched to the horizontal window in STFT using the tangent idea，aligning the rotation direction of the window with the instantaneous frequency modulation to improve the energy concentration of time-frequency representation. The instantaneous frequency，extracted by the spectral peak detection method，is divided by the frequency transformation curve. The result is matched with the fault characteristic coefficient of the bearing to achieve fault diagnosis of the rolling bearing under variable speed conditions. The results of simulation and experimental signals show that the proposed method effectively combines the advantages of PSO-VMD and AWROSTFT. Through the adaptive rotation window with the idea of tangency，the angle between the signal and the window function is globally reduced to zero，improving energy concentration，sharpening the time-frequency ridge line，and enabling fault diagnosis of rolling bearings under variable speed conditions.

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.

Research on the increasingly significant issue of fatigue failure in pedestrian structures due to crowd-induced vibrations is limited. This paper uses a steel-glass footbridge as a test platform to study the fatigue performance of the footbridge before and after the installation of a Tuned Mass Damper （TMD）. The APS400 electronic shaker is used to simulate pedestrian load，and long-term strain monitoring data is analyzed to determine the fatigue stress spectrum and daily average damage degree of the structure，which is then used to estimate its fatigue life. The results show that the installation of the TMD reduced the peak acceleration at half of the structure from 0.15 m/s² to 0.084 m/s²，a vibration reduction rate of 44.0%. The peak displacement was reduced from 2.98 mm to 0.92 mm，a vibration reduction rate of 69.1%； and the strain amplitude was reduced from 40 to 13，a vibration reduction rate of 67.5%. The amplitude of the equivalent effect force across the middle of the structure is the largest，and the fatigue life is the shortest，at 74 years. After the installation of the TMD，the fatigue life of the structure span increased to 2880 years，nearly 39 times longer，and the fatigue life at other measurement points extended by 3.95 times and 7.41 times.