Under the action of strong seismic excitations，structures exhibit time-varying dynamic characteristics due to damage. Variational mode decomposition （VMD） can be used to analyze the instantaneous frequency variation of structural seismic responses and reveal the damage condition of structures during earthquake. When VMD is adopted for decomposing the non-stationary responses，there exists the problem of mode aliasing due to the artificially presetting the number of decomposed modes K and the quadratic penalty factor α. Aiming at solving this problem，an improved variational mode decomposition （IVMD） algorithm is proposed in this study，which，combined with Hilbert transform （HT），can more accurately identify the instantaneous frequencies of time-varying structures under non-stationary seismic excitations. The multiple signal classification （MUSIC） algorithm is used to determine the number of decomposition modes K. The comprehensive objective function is constructed based on the overall orthogonal coefficient and energy ratio coefficient，and the slap swarm algorithm （SSA） is used to optimize and determine the optimal quadratic penalty factor α. Based on the optimized parameters K and α，IVMD-HT is used to identify the instantaneous frequency of time-varying structures from the seismic responses. A simulated signal and the seismic responses of a 4-layer time-varying frame structure show that the accuracy of identified instantaneous frequencies by using the IVMD algorithm is higher than the identified ones by using the VMD algorithm. The feasibility of the proposed method is verified by using shaking table test data of a 12-story reinforced concrete frame structure model.

A nonlinear two-degree-of-freedom system is used to construct an aircraft landing gear model. The stochastic excitation of the uneven runway to the system is described by time-domain noise，and the road roughness coefficient is used to describe the roughness of runway. Based on the probability density function and the statistics of system response，the influence of uneven runway on aircraft landing gear system is investigated. The reliability of the landing gear model and the passenger comfort under different road roughness coefficients are analyzed by establishing the relationship between the safety zones，comfort zones and the system response. The results show that the larger the road roughness coefficient is，the more fluctuation of the system state variable will be. The reliability and comfort of the system are negatively correlated with the road roughness coefficient. In addition，when the road roughness coefficient is small，the mean first-passage time and comfort of the system are more significantly affected by random disturbance. The present paper provides a theoretical basis for aircraft riding comfort and landing gear development and design.

Based on the finite element software ANSYS Workbench，the finite element model of the foil gas bearing movement in compressible fluid medium is established，and the fluid-structure coupling numerical simulation of the bearing movement state is carried out by using the 6DOF dynamic grid calculation method. The influence of different speed and wave foil structure parameters （length ratio，height and thickness of wave foil） on dynamic characteristics of bearing is discussed. The simulation results show that with the increase of rotational speed，the bearing capacity increases，but the stability decreases，and the instability phenomenon is more likely to occur. When the length ratio is between 1~1.5 and the thickness is 0.16 mm，it can not only ensure the high stiffness of the bearing，but also obtain large damping. The height of wave foil is inversely proportional to the dynamic characteristics of bearing. The simulation results are compared with the experimental results to verify the correctness and effectiveness of the simulation calculation method. Meanwhile，the research of this paper provides a theoretical basis for optimizing the wave foil structure，improving the dynamic characteristics of bearings and improving the stability.

In order to satisfy both cushioning and fast-extension performances，the carrier aircraft nose landing gear often adopts the dual-chamber buffer design. Based on a certain type nose landing gear，this paper establishes the dynamic model of the cushioning performance analysis and compares the simulation calculation results with the test results to ensure the validity and correctness of the theoretical dynamic model. The parameter sensitivity analysis of cushioning performance is carried out for the initial filling pressure and volume ratio of the high- and low-pressure chambers of the buffer. Results show that the effects of the initial filling pressure and high- and low-pressure chambers volume ratios on the cushioning performance is different from their impacts on the fast-extension performance. Therefore，the design of the nose landing gear buffer of the carrier aircraft needs to be continuously optimized for taking the cushioning and fast-extension performances into account synchronously.

In order to seek a kind of tank structure which can absorb shock and reduce costs，a new structure system of isolation tank is proposed. The restoring force model of rolling isolation is deduced by the principle of balances of forces，and the restoring force model of composite rolling isolation device is obtained. Based on the three-particle model and site soil model，the simplified mechanical model and motion equations of the new isolation tank considering soil-tank-liquid interaction （STLI） are proposed，and the seismic responses of seismic tank and new isolation tank that considered STLI and Non-STLI are studied under different sites. The results show that the new isolation tank can effectively reduce the base shear and overturning moment，but the control of the sloshing wave height is limited. It is suggested that in the high intensity area，under the premise of meeting the shaking wave height，the new isolation tank can be designed to reduce the intensity. After considering the STLI effect，the base shear and overturning moment of seismic tank decrease obviously. The discrepancy rate gradually increases from class Ⅰ site to class Ⅳ site，and the decrease is most significant in soft soil. The seismic responses of the new isolation tank are less affected by the STLI，which can effectively cut off the coupling between the superstructure and the site soil，and weaken the influence of the STLI effect on the superstructure.

A simplified model for free vibration analysis of functionally graded plates is proposed based on higher-order shear deformation theory，the most significant feature of which is that it applies for the vibration analysis of functionally graded plates without any shear corrections. Compared with other shear deformation theories that contain more unknown variables，this model contains only one control equation，and thus greatly reduces the computational cost. Based on this simplified model，the free vibration of functionally graded rectangular plates with simple support boundary conditions is investigated and compared with other existing literature. The results show that the simplified model proposed in this paper is simple and accurate in solving the free vibration behavior of functional gradient plates. In addition，the effects of different gradient indices，aspect ratios，and length-thickness ratios on the free vibration behavior of functionally gradient plates are analytically discussed in the paper by several numerical arithmetic examples.

Oscillating underwater flexible structure actuated by smart materials are widely used in the fields of robotic fish，autonomous underwater vehicle，precision medical instrument，and so on. In this paper，the nonlinear hydrodynamics of an underwater Macro Fiber Composite （MFC）-actuated flexible cantilever undergoing large amplitude vibration is studied. The fluid-structure coupled dynamic equation of the proposed structure is established. Parametric 2D CFD studies of the proposed structure at different characteristic frequencies and amplitudes are performed. The distribution and evolution of the flow field in the vicinity of the vibrating structure are revealed. CFD results show that the vortex shedding，diffusion and convection phenomena which are responsible for the nonlinear hydrodynamic damping effect appear as the vibration amplitude increases. Then，a manageable expression for the revised hydrodynamic function governed by the interplay of the characteristic frequency and vibration amplitude is presented to model the hydrodynamic load exerted on the flexible structure undergoing finite amplitude vibration. The imaginary part of the revised hydrodynamic function which accounts for the hydrodynamic damping effect decreases with the characteristic frequency for the small amplitude vibration. It first decreases then increases for the finite amplitude vibration，exhibiting a strong nonlinear behavior. Experimental results show that the measured frequency response spectrums of the proposed structure undergoing finite amplitude match well with the predicted results of the developed model. Thus，the validities of the developed hydrodynamic function and fluid-structure coupled dynamic equation are demonstrated.

The additional tuning mass damper is a traditional control technique for the chimney，but it usually requires a large additional tuning mass and auxiliary installation space，which brings inconvenience to the construction and installation. This study proposes utilizing the additional tuned mass inerter system （TMIS） to reduce seismic responses of the chimney. The apparent mass effect of the inerter is employed to achieve the goal of lightweight control. Meanwhile，considering that the influence of high-order modes of the high-rise chimney on its seismic responses cannot be ignored，the distributed TMISs arranged along the height of the chimney are proposed to achieve the multimode control effect. Mechanical models of the TMISs based on two different inerter subsystems are established，and the equations of motion for the chimney with corresponding additional distributed TMISs are established. Taking Kanai-Tajimi’s spectrum as the random seismic excitation input and based on the extended fixed-point theory，the simplified assumptions for part of the design parameters of distributed TMISs are proposed. The demand-oriented multimode optimization design method for the chimney with distributed TMISs is presented. The effectiveness of the proposed design method is verified by a design case. The lightweight and multimode control effects of additional distributed TMISs are examined by comparative analyses. The rationality of the simplification based on the extended fixed-point theory is verified through parameter analysis. The results show that the proposed design method can achieve the expected target performance using the two distributed TMISs. Both the two distributed TMISs behave obvious lightweight control effect.

The fault diagnosis method based on deep learning is widely used in the fault diagnosis of key mechanical components represented by bearings. The premise of achieving ideal results is that there are enough fault samples and the training set and test set meet the same distribution requirements. However，the data distribution will change under the actual working conditions，which makes it difficult to apply the diagnostic model under the original working conditions to the new working conditions. For this reason，the domain adaptation transfer learning method is used to solve the problem of different distribution of training sets and test sets，and its key point is to achieve data distribution adaptation，that is，to measure data distribution differences and use the measurement results to guide model training，which can effectively improve learning efficiency and diagnostic accuracy. On this basis，this paper proposes a new domain adaptation method based on adversarial learning. The core of this method is to combine the proposed exponential adjustment strategy with adversarial network to make the network adapt to different data distribution in source domain and target domain more specifically in the process of fault diagnosis. The network consists of a feature extractor，a classifier，a global domain discriminator，and multiple local domain discriminators，and the model is optimized by using the adversarial strategy and adaptive moment estimation algorithm，and adjusted the importance of marginal distribution and conditional distribution by using the exponential adaptive factor set based on the exponential adjustment strategy，so that the model could diagnose faults stably and efficiently. The proposed method is verified in bearing diagnosis cases of cross-speed，cross-load and simultaneous cross-speed load. The results show that the method in this paper is better than other domain adaptation methods in diagnosis effect and has better stability.

Recursive Least Squares algorithm is widely adopted in the field of micro-vibration adaptive control because of its simplicity and speed. Due to the particularity and complexity of the disturbance environment in the micro-vibration active control application，the robustness of the parameter adaptive algorithm used in the micro-vibration control needs to be considered. For the Multiple-Input Multiple-Output （MIMO） active vibration control system，this paper presents a MIMO robust parameter adaptive algorithm based on an Infinite Impulse Response （IIR） filter. This robust parameter adaptive algorithm takes advantage of the dead zone and normalization. The deducing process and convergence analysis of the robust parameter adaptive algorithm are illustrated in detail. A 3-DOF real time micro-vibration control experimental platform has been constructed. Comparison are provided with sine disturbance，double sine disturbance and broadband disturbance. Experimental results confirm the feasibility and robust of the proposed algorithm.