Aiming at the problem of nonlinear vertical vibration control during the dynamic rolling of strip mills, a nonlinear vibration absorber with the disc spring was designed. Firstly, considering the constraints of dynamic rolling force of the rolling mill in the vertical direction, the mathematical model of the rolling mill under the control of the nonlinear vibration absorber was established, the amplitude-frequency characteristic curve equation of the system was solved by the multi-scale method, and the influence of damping, excitation amplitude and nonlinear stiffness on the vibration suppression effect of nonlinear dynamic vibration absorber was discussed. Secondly, by analyzing the spectrum curve and time domain curve, the vibration absorber device could increase the distance between the resonance frequency and the main resonance frequency, and shorten the time of the rolling mill system from the unstable state to the stable cycle was concluded. The results show that the addition of nonlinear vibration absorber can effectively increase the anti-vibration ability of the system and suppress the vertical vibration of the system.

Limited by the vibrator structure, there are some problems such as low down-going earth energy and shallow down-going depth of shear-wave signals when the shear-wave vibroseis is excited. Therefore, the influence of different combinations of shear-wave vibroseis vibrators on the excitation effect was innovatively studied through the three-dimensional finite element numerical simulation. Firstly, based on three-dimensional nine-component data and two types of combinations,eight modes of vibration excitation of combined shear-wave vibroseis were considered, a vibrator-earth finite element model was established, and an evaluation system of the vibration excitation effect of the combined shear-wave vibroseis was constructed. Secondly, based on this evaluation system, the influence of the various combined excitation modes of the shear-wave vibroseis on the downward energy of the earth, the downward depth of shear-wave signals and the mutual interference between combined excitation waves was analyzed in detail. The results show that, compared with a single shear-wave vibroseis, when two SHY shear-wave vibroseises are arranged side by side for the normal excitation, the incoming earth energy is increased by 86.36%, and the displacement amplitude of earth particles is increased by 73.40% on average. When two SHX shear-wave vibroseises are excited in the normal direction, the incoming earth energy increases by 97.48%, and the displacement amplitude of earth particles increases by 58.61% on average, which greatly improves the excitation effect. The research results can provide the guidance for improving the excitation effect of the shear-wave vibroseis and the reference for the design of combined excitation mode of the shear-wave vibroseis.

The slat of aircraft is subjected to the combined action of thermal load and aerodynamic force during its service, which has an impact on the safety of the structure. The typical aluminum alloy structure widely used in slat structure is taken as the main research object, and the stress distribution and structural strength under the combined action of heat and force were studied by experiment and finite element method. Firstly, in order to explore the influence of temperature on material properties, the linear tensile test of 2024-T62 rectangular thin plate and the high temperature tensile failure test of perforated thin plate were carried out under four different temperature conditions. The test shows that the high temperature environment has a reduction effect on the elastic modulus of the material, and at 190 °C, the bearing strength of the test piece decreased by 15%. Therefore, considering the reduction effect of temperature on material parameters can establish a more accurate model for predicting structural strength. Secondly, aiming at the thermal stress problem of aluminum alloy parts and structures, the test and simulation of aluminum alloy sheet and simplified slat structure under the combined action of heat and force were carried out respectively. A set of modeling method and thermal stress measurement test technology under the combined action of heat and force were established. The maximum error between the simulation and test results of aluminum alloy sheet is 10%. The thermal stress simulation of the simplified slat structure has a good trend compared with the experimental results, and the maximum error is 20%. In addition, through the experiment, it is also found that the thermal stress is particularly sensitive to the setting of boundary conditions. For the model with complex constraints, it is necessary to expand the modeling range to the stable boundary conditions to simulate the actual thermal stress.

Low-cycle fatigue is a typical failure mode of engine pistons. In order to study the influence of multi-source uncertainty factors on the reliability of low-circumference fatigue of pistons and improve the efficiency of the reliability analysis, a new reliability calculation method is constructed based on the polynomial-chaos-based Kriging (PC-Kriging) model and the Monte Carlo simulation (MCS), and the accuracy and efficiency of this method are proved by numerical examples.Taking the piston group structure of a certain diesel engine as the research object, a finite element model of the piston is established based on the thermal-mechanical coupling analysis, and the reliability analysis of the piston for low-cycle fatigue is carried out by using this method, taking into account the critical dimensions, the material properties, and the uncertainty of the load. The results of the reliability analysis show that, compared with the same type of method, this method is more efficient in calculation, requiring only 20+93 finite element calculations, and the probability of fatigue failure is 1.053% when the expected design life of the piston is 1.4×10⁴. The sensitivity analysis shows that, the height of the piston, the piston diameter,the elasticity modulus of the material, and the parameters of the fatigue calculation model have a greater influence on the reliability. The analysis results can provide a guidance for the reliability design of the piston.

In order to reveal the nonlinear dynamics behavior of the marine rotor-bearing system under complex transport motions (heaving, swaying, yawing and pitching), the dynamical model of the rotor-bearing system with the nonlinear oil film force and transport inertial forces was built based on, Lagrange’s equation.The effects of the rotating speed and transport motion parameters on the nonlinear dynamics behaviors of the system were mainly analyzed. The results show that the amplitude and oil film whirl interval of the system are larger when considering the coupling motion of heaving, swaying,yawing and pitching than those when not considering this motion. Affected by the coupled transport motion, the rotor will deflect obviously at a lower speed. At a certain rotational speed, with the increase of heaving amplitude, swaying frequency or swaying amplitude, the amplitude jump phenomenon caused by the oil whirl appears in the vibration response of the system，and the motion state of the system undergoes quasi-periodic and chaos. With the increase of swaying frequency, yawing amplitude, yawing frequency, pitching amplitude or pitching frequency, the system is always in a quasi-periodic vibration state,but the vibration amplitude of the rotor increases in varying degrees.

The noise of automotive electronic water pump (EWP) is an important indicator of the performance of EWP,and its active control is conducive to improve the sound quality of the car. In order to achieve the active control of the noise of EWP, a hybrid random carrier space vector pulse width modulation (HRCSVPWM) strategy was proposed. Firstly, the Xorshift algorithm was used to design a random sequence generator to generate random numbers with good randomness to disperse a large number of harmonics concentrated in the carrier frequency and its integer multiples. Secondly, the sawtooth wave period function was combined to increase the weakening effect on the pulse width modulation (PWM) harmonic amplitude. Then, the simulation model of the EWP was constructed to investigate the harmonic suppression effects of control strategies of space vector pulse width modulation (SVPWM), random carrier space vector pulse width modulation (RCSVPWM) and HRCSVPWM, to verify the ability of HRCSVPWM to suppress PWM harmonics. Finally, EWP noise test platform was constructed to analyses the noise of EWP under three types of control strategies.The results show that the noise suppression effect of HRCSVPWM is remarkable, which can make the noise’s sound pressure level of EWP decrease significantly, with an average decrease of about 3 dB.

Aiming at the noise problem of the automobile electric seat adjuster, a pair of modified worm and modified helical gear was adopted for its main transmission system to reduce the meshing impact. The mathematical model was established, and several worms and helical gears with different modifications were processed. The noise test bench was built,and the acceleration spectrum of the automobile seat adjuster under the original models and different modifications were tested. Then the whole device’s noise reduction test was conducted with the optimized combination of tooth profile modification. The analysis results show that the appropriate profile modification of the worm and helical gear can effectively reduce the acceleration spectrum peak. With 0.04 mm and 0.02 mm modification respectively for the helical gear and the worm, the acceleration peak value of seat adjuster is significantly lower than that of the original product. The difference between the 6 sets of test products maximum noise and the standard products is within 1.6 dB, and the acceleration spectrum and acceleration peak of the experimental products are significantly reduced compared to the original product, which can verify noise reduction by the tooth profile modification of worm and helical gear pair is feasible.

An improved northern goshawk optimization (INGO) algorithm was proposed to address the local optimization problem that swarm intelligence algorithms often encounter when optimizing support vector machine (SVM) models, and it was applied to fault diagnosis of rolling bearings. By introducing an adaptive inertia weight factor based on the cosine variation and a Cauchy mutation strategy, the northern goshawk optimization (NGO) algorithm was improved, and an INGO-SVM fault diagnosis model was constructed using SVM. In order to evaluate the performance of the improved algorithm,firstly, benchmark testing functions were used for experiments, and the improved algorithm was compared with existing optimization algorithms such as NGO, particle swarm optimization (PSO), sparrow search algorithm (SSA), etc. The results show that the performance of the improved algorithm is improved to a certain extent. At the same time, the original diagnostic signals were feature extracted through wavelet packet decomposition and divided into 10 categories. The energy of each frequency band in the 3rd layer was used as the feature vector and input into the fault diagnosis model. Finally, the performance of the improved algorithm was compared with the other three algorithms in optimizing SVM parameters for fault classification. The results show that the improved algorithm can effectively and accurately achieve different fault classifications, with an accuracy rate of 99.39%, verifying the effectiveness and feasibility of this method.

Abnormal vibration in the pipeline associated with large synchronous condensers not only reduces the lifespan of the pipeline but also affects the supply of the lubricating oil and coolant for the synchronous condenser, posing a serious risk of major safety accidents and jeopardizing the stability of the power system. The lubricating oil supply pipeline of a specific ultra-high voltage converter station synchronous condenser was taken as the research object. Multiple methods, including field measurements, fluid-structure coupling, and harmonic response analysis, were used to investigate the causes and mechanisms of the pipeline vibration. The results indicate that the periodic excitation force generated by the synchronous condenser itself is the main cause of pipeline vibration. Furthermore, a pipeline vibration reduction measure based on a tuned mass damper(TMD) was proposed. Experimental and simulation data shows that installing a TMD at the intermediate positions between suspension supports 4 and 5, as well as 6 and 7 in the lubricating oil supply pipeline system, yields the best vibration reduction effect. This approach can reduce the vibration acceleration of the pipeline system by over 90% and exhibits the excellent vibration reduction performance.

In order to clarify the dynamic response, damage situation, and failure mode of titanium/steel corrugated composite plates and interfaces under impact loads, small energy (53 J）impact experiments were conducted on titanium/steel corrugated composite plates using a light air cannon. On the basis of verifying the effectiveness of the numerical calculation model, numerical simulations were conducted on composite plates under various velocities to study the impact mechanical response of composite plates and their interfaces under various energies. The results show that, under low energy impact conditions, the front of the corrugated composite plate shows plastic expansion damage, and the back plate has protrusions with cracks at the raised areas. The corrugated interface layer is tightly bonded and overall concave; cut the target plate along the impact center and observe that there are no cracks, delamination, or other damages on the cross-section. This is different from fiber reinforced composite laminates. There will generally be obvious delamination inside when there is barely visible damage on the impact surface. In numerical simulation, the cohesive force interface damage area of the corrugated composite plate under impact is less than that of the planar interface composite plate. When subjected to low energy impact, the absorption of bullet kinetic energy by the corrugated plate is mainly dominated by overall deformation energy absorption, and the damage to the titanium/steel composite plate at the corrugated interface is relatively small. Under various energy impacts,corrugated interface composite plates have tighter interface bonding, better structural integrity, and are less prone to damage compared to planar interface composite plates.