To address the inadequacy of existing models for predicting the flow resistivity of kapok felt，the airflow resistivity of kapok felt with different bulk densities is tested. Initially，the airflow resistivity of kapok felt is calculated using empirical and theoretical models commonly used in fibrous materials. Subsequently，a new empirical model suitable for predicting the flow resistivity of kapok felt is developed by fitting the experimental data. Finally，considering the cross-sectional geometries and arrangement of kapok fibers at different bulk densities，theoretical models for the flow resistivity of kapok felt are derived by determining the average velocity and frictional force within micro-units，for both circular and flattened fiber cross-sections，based on the Tarnow model and the Hagen-Poiseuille flow assumption. The models are further modified using a flattening ratio parameter. Results demonstrate that compared to the measured values，the prediction accuracy of existing models for kapok felt flow resistivity is low. The modified model is applicable to transitional states between the two cross-sectional geometries. Within the bulk density range of 20 to 180 kg/m³，the modified model exhibits high prediction accuracy.

In order to analyze the reliablility of hypersonic flight vehicles，the longitudinal model of the vehicle is simplified as a cantilever beam structure，and a limit state function is formulated. To address the uncertainty of variable parameters within the limit state function，a hybrid reliability analysis method based on a two-stage Kriging model is proposed. For the first stage，initial sample points are selected to construct an initial Kriging model centered on potential failure points meeting specified accuracy requirements，ensuring the model satisfies this accuracy criterion. For the second stage，a hybrid reliability analysis of the flight vehicle is performed using the initial Kriging model and the first-order reliability method. The Kriging model is adaptively updated by incorporating learning functions，thereby enhancing the efficiency and accuracy of reliability calculations. Comparing the results with existing methods under different parameters of ultimate strength，cantilever beam height，and width，it is demonstrated that the proposed method can meet the requirements for real-time and accurate reliability analysis of the hypersonic vehicle.

A parameter identification method is proposed to accurately capture the nonlinear dynamic characteristics of dielectric elastomer actuators （DEAs）. First，the response signal of the actuator is acquired under swept-frequency excitation using the time-frequency analysis capability of the transient-extracting transform （TET）. Then，the harmonic and fundamental frequency components are separated and extracted，and the transfer functions for each component are computed to derive the overall transfer function of the DEA. Finally，the results are compared with experimental data. The proposed method achieves a fitting accuracy of 92.11% for the fundamental frequency transfer function and 90.35% for the second harmonic transfer function. This approach does not require prior knowledge of material properties or free energy density functions，and incorporates the influence of high-order harmonic components，offering a novel solution for parameter identification in electroactive material structures.

To investigate the fault mechanism of blade cracks and to analyze the effects of blade crack on the three-dimensional （3D） tip clearance of the rotor system，while comprehensively considering blade radial deformation，flap-wise bending，and chordwise bending，this paper develops a novel dynamic model of the rotor system based on continuum theory. With the blade breathing crack model under the three-dimensional stress state，a 3D tip clearance dynamic response model of rotor system with blade cracks is further established. The accuracy of the dynamic model is validated by comparing it with the finite element model and experiments. On this basis，the effect of blade crack depth and location on the 3D tip clearance in rotor system is further analyzed. The results show that the amplitudes of the high frequency doubling component of the 3D tip clearance increase with crack depth，while both the fundamental frequency and the high frequency doubling component of the 3D tip clearance show a non-monootonic trend as the relative crack location increases. The research results provide theoretical guidance for research on monitoring and diagnosis method of aero-engine blade crack based on 3D tip clearance.

A novel approach based on electromechanical impedance is proposed to evaluate the corrosion degree for grounding conductors，which are difficult to simply detect and evaluate for traditional methods. Firstly，according to the electrochemical corrosion model of metals，the grounding conductor parametric corrosion model is established by importing the change of grounding conductor radius as corrosion parameter. Secondly，the corrosion model between an electromechanical impedance resonance frequency and corrosion parameter is established with the analysis of system electromechanical impedance and conductor mechanical admittance. Then，the resonance frequency and corrosion parameter signal of grounding conductors are obtained via finite element simulation method，while the coefficient of the corrosion model is obtained by the least square method. The results show that the electromechanical impedance detected by asymmetrical sensor layout can reflect variations of the corrosion parameter more clearly than that by symmetrical sensor layout. Linear model by finite element simulation and the least square method can predict the corrosion parameter. Moreover，the high consistency between the datum predicted by the linear model and the experimental datum，indicates the linear model is very accurate and can be used to detect the conductor corrosion in field applications.

In response to the challenge of quantitatively diagnosing corrosion damage thickness within pipelines，a quantitative imaging method for pipeline corrosion damage using ultrasonic guided waves is proposed. Firstly，based on the frequency domain finite difference method，a numerical model for multi-path helical propagation of guided waves in pipes is established，enabling rapid calculation of guided wave reception signals when thickness map is known. Secondly，by calculating the received signals in the presence of randomly distributed damage，a database comprising 3 500 samples of damage signals is generated through iteratively running the numerical model. Subsequently，a one-dimensional convolutional neural network imaging model is constructed. The model is trained using the generated database to establish a mapping relationship between thickness maps and reception signals，and inputting the reception signals into the imaging model yields corresponding thickness maps. Finally，the feasibility of the proposed method is experimentally validated. The mean square error between experimental imaging results and actual values is 8.6048×10^-4，the correlation coefficient is 0.711 6，and the imaging model runtime is 0.538 5 seconds. The results indicate that the proposed method can achieve quantitative imaging of corrosion damage thickness within pipelines with high imaging efficiency.

To study the influence of subway wheel polygons on low-frequency vibration of the car body，the polygon wear of wheels of a subway line is investigated，on the basis of grasping the distribution characteristics of wheel polygons of subway lines. A vertical dynamic model of elastic car body considering wheel polygons is established，by the time-domain integral solution method. The relationship between wheel polygon excitation frequency and low frequency vibration of vehicle body is studied. By comparing the low-frequency vibration of wheel polygons of different orders，the effect of changes in the operating speed of metro vehicles under service conditions and changes in the radius of wheel wear on the polygonal action of the wheel body is discussed separately. It is shown that a wheel polygon of order 1—3 at common operating speeds generate a low-frequency excitation frequency of 0—20 Hz，and when the excitation frequency is close to the first-order droop frequency of 10.2 Hz resonance will occur. At the beginning of service，the influence of the second order wheel polygon becomes severe on the low frequency vibration of the car body. With the wear of the wheel radius during service，the influence of the first three order wheel polygon changes on the vibration law of the car body. This paper provides a good reference value for service subway operation and wheel maintenance.

The transient vibration of a vertical axis washing machine is strong in the dehydration process，so a new planar variable damping structure is proposed to reduce the transient vibration. Firstly，the kinetic energy and potential energy of various rigid bodies of the washer are deduced，the generalized forces of the suspension structure are described，the force of the liquid balancer is analyzed，and the vibration model of the vertical axis washing machine is established using Lagrange's equation. The working principle of the planar damping structure is explored，its damping force is described and its suppression effect on transient vibration of the washer is verified. Secondly，the influence of the planar damping structure on dynamic characteristics of the washer is evaluated，the bifurcation theory is employed to analyze stability of the system. Furthermore，the distributions of the stable regions of the system is analyzed，and the appropriate disengaging speed range of the damping structure is obtained. Finally，the effect of the damping structure for suppressing transient suppression of the washer is validated though experiments，and the appropriate disengaging speed of the structure is analyzed. The results show that the planar damping structure can suppress transient vibrations effectively with little influence on other dynamic characteristics of the washer.

In response to unclear mechanisms in compressor fault diagnosis research，this article aims to reveal the variation law of component characteristic changes caused by blade wear，numerical simulation analysis method is used for studying the changes in component characteristics of blades under different degrees of wear. The results show that the degree of compressor performance degradation caused by blade surface wear is more significant than that caused by blade tip wear. With the increased speed，the degree of performance degradation becomes greater. The efficiency decay value caused by the increase of blade tip clearance shows a pattern of first decreasing and then increasing with the increase of pressure ratio. Near the working line of the compressor，the efficiency decay value is relatively stable with the change of pressure ratio，while the flow decay value increases with the increase of pressure ratio. After the increase of blade surface roughness，the decay values of efficiency and flow rate both increase with the increase of pressure ratio. Moreover，there is a decreasing trend in the decay values near stall pressure ratio. Near the working line，varying degrees of blade wear have a greater impact on flow rate than on efficiency. The results can provide a theoretical reference for the research of fault diagnosis methods for aviation engine gas paths.

The friction block of high-speed train brake pads exist in two configurations： holed and non-holed. To investigate the influence of the holed structure on the braking performance，drag braking tests using both types of friction blocks are carried out on a self-developed scaled brake dynamometer for high-speed trains. In addition，finite element simulations are carried out to analyze vibration noise and interface thermal distribution during braking. Experimental and numerical results indicate that the non-holed friction blocks produces continuous self-excited vibration and excites high-intensity squeal noise，whereas the perforated block effectively suppress system instability and reduce squeal noise to some extent. Moreover，the holed structure improves the interfacial thermal distribution，leading to more uniform temperatures on both the friction block surface and the matching brake disc compared to the non-holed blocks.