Abstract:For the contact fatigue failure problem of vehicles'hypoid gears under complex conditions,the rain-flow counting method and Goodman's average stress equation were used to establish a contact statics model.The load-time history of the contact gear surface was extracted.And the load spectrum of hypoid gears was produced.The research focused on predicting the high-cycling fatigue life of hypoid gears based on the load spectrum.The study also utilized the finite element method to simulate gear teeth's meshing or contact behaviour under loading conditions.Moreover,the influence mechanism of fatigue damage criterion on the gear fatigue life prediction was revealed.The proposed method is highly significant in assessing and predicting the high-cycling fatigue life of vehicles'hypoid gears.

Abstract:To solve the stress concentration problem caused by tooth interference and insufficient tooth surface contact during the operation of harmonic reducers,an axial modification method based on the finite element method(FEM)was proposed.Firstly,the profiles of the flexspline and circular spline were designed based on the requirement of tooth contact analysis(TCA),laying a foundation for the accurate simulation of the working state of the harmonic reducer.Subsequently,the flexspline model was reconstructed based on the FEM for TCA.On the premise of maintaining the integrity of the original flexspline profile,axial modification was conducted.Finally,the modification effect was verified through finite element simulation.The results show that after modification,the maximum equivalent stress and meshing pressure on the flexspline tooth surface are significantly reduced,and the tooth surface contact area is obviously expanded.This method effectively solves the problems of tooth interference and stress concentration,significantly improves transmission smoothness,and provides technical reference for the optimization of gear meshing performance of harmonic reducers.

Abstract:Vertical axis wind turbines have gradually become a research hotspot due to their ease of scalability,but the research involving structural aspects is relatively limited.Therefore,a blade and strut composite layup design solution was proposed to meet the structural performance requirements.The computational fluid dynamics method was used to obtain the aerodynamic loads under extreme environments and loaded them onto the wind turbine surface.The finite element method was used to perform the statics and modal analysis.The results show that the proposed wind turbine blade,strut,and tower have sufficient safety under extreme loads.The maximum displacement is located at the top of the blade trailing edge,the maximum stress is located at the connection between the tower and the strut,and the maximum strain is located at the blade web in contact with the strut;the vertical axis wind turbine wind wheel still has strong torsional load characteristics under the windward condition;the wind turbine operating frequency is less than the wind turbine first-order natural frequency,and its relative difference exceeds 10%.The wind turbine will not resonate under rated conditions.

Abstract:Considering the uncertainty associated with structural boundary conditions,a method for modifying the boundary constraint static model of beam structures was proposed based on the homotopy stochastic finite element method.The overall modification of both the beam body elements and boundary elements was achieved using uncertain static measurement data.By employing the static condensation method,computational degrees of freedom were ensured to match measured degrees of freedom.Regularization methods were applied to mitigate ill-conditioned solutions in modification equations for stochastic models.The probabilistic residual minimization method enables optimal selection of homotopy coefficients,ensured accurate identification of boundary constraints and precise overall modification.Finally,simulations on variable-section concrete beams and static loading tests on aluminum alloy beams were conducted to verify the effectiveness of this approach.

Abstract:In order to construct a bone scaffold structure with good biological properties,P-type,FRD-type homogeneous multi-porous scaffolds and P&FRD gradient multi-porous scaffolds with different porosities and unit cell scales were designed based on the triply periodic minimal surface(TPMS).The effects of unit cell types,porosities and unit cell scales on the mechanical and biological properties of TPMS multi-porous scaffolds were investigated by tests and finite element simulation.The results show that the internal pores of homogeneous and gradient multi-porous scaffolds based on TPMS have good connectivity.The mechanical properties of multi-porous scaffolds decrease with the increase of porosity,but the permeability increases with the increase of porosity.Increasing the unit cell scale can significantly improve the permeability of multi-porous scaffolds.The permeability of the gradient multi-porous scaffold is also affected by the seepage direction.The gradient multi-porous scaffolds can synthesize the performance characteristics of each homogeneous unit cell structure,and show different mechanical and biological properties in different regions of the scaffold,which is closer to the structure and biological properties of human bone.

Abstract:Under the medium and high speed of spherical hybrid sliding bearings,the dynamic pressure effect causes the fluid in the wedge space to whirl,and the vibration characteristics of the rotor may be affected by the oil whirl,so the rotation accuracy of the main shaft is reduced.The spherical hybrid sliding bearings with the orifice throttle was divided into cylindrical and conical whirl.The lubrication mathematical model and rotor dynamic model were established and solved simultaneously,the journal center trajectory and vibration amplitude were obtained.The influence of the centroid offset distance and initial deflection angle on the vibration characteristics of the rotor system were studied.The results show that,compared with the pure cylindrical whirl,the stability of the journal center trajectory decreases and the vibration amplitude increases after considering the conical whirl.With the increase of the centroid offset distance,the stability and vibration amplitude of the journal center trajectory decrease greatly.With the increase of the initial deflection angle,the stability and vibration amplitude of the journal center trajectory decrease only slightly.It can be concluded that changing the distance of the centroid offset has more influence on the stability of the journal center trajectory and the vibration characteristics of the rotor system than changing the initial deflection angle.

Abstract: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.

Abstract: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.

Abstract: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.

Abstract:In order to gain insight into the stability of the tracking frame structure of shipborne large-aperture telescopes,the stability of typical ground-level telescope tracking frames was studied.According to the external load borne by the equipment in the case of ship,the external load was parameterized and entered into the finite element software.The pre-treatment software and finite element software were used to analyze the structural deformation under static wind load.Then,the natural frequency of the structure was solved,and a simple response spectrum analysis calculation was proposed instead of the tedious random response analysis to analyze the stability of the equipment under dynamic wind load and wave excitation.According to the stress and deformation values obtained from the results,it was ensured that the shipborne telescope tracking frame theoretically meets the strength requirements and design accuracy requirements under shipborne conditions.Under the static wind load,the maximum stress value of the tracking frame structure is about 14.07 MPa,which was less than the yield strength of steel 355 MPa,the maximum deformation variable was about 0.02 mm,which was less than the design accuracy error coaxiality ϕ0.1 mm,and the natural frequency 1st-6th order mode value was 40.15,49.65,66.86,82.93,91.38,115.89 Hz.Under dynamic wind load,the peak value of structural stress was 3.92 MPa and the maximum deformation variable was 0.01 mm,and under the excitation of ocean waves,the peak of structural stress was 5.88 MPa and the maximum deformation variable was 0.02 mm,which was less than the yield strength and design accuracy error coaxiality of steel.The error between the modal value obtained by the modal test and the calculated modal value is within 10%.Combining theoretical simulation and practical tests,the tracker structure can work normally under shipborne conditions.

Abstract:Aiming at the storage life evaluation of photodetectors,a new evaluation method for multi-parameter competitive failure storage life assessment based on Monte-Carlo method was proposed.This method comprehensively considered whether the key performance parameters of the sample have deteriorated or improved trend.Firstly,the optimal degradation model with a single parameter was selected by performance degradation modeling,so that the pseudo-life of the sample with increasing degradation trend was calculated according to the failure threshold,and the pseudo-life was regarded as the right-censored data for the sample with decreasing degradation trend.Furthermore,the optimal distribution of a single performance parameter was selected based on the pseudo-life data combined with the expectation maximization(EM)algorithm,and then the competitive failure evaluation of multi-parameters was carried out by Monte-Carlo sampling method.According to the case analysis of the photodetector storage,the feasibility of this method was verified.

Abstract:The fracturing pump plunger seal pair is one of the components most prone to failure at the hydraulic end of the fracturing pump due to its long-term operation under variable load,reciprocal friction and high pressure,and acidic fracturing fluid.To study the influence of interference magnitude,medium pressure,etc.on the sealing performance of V-shaped sealing ring,the assembly process of V-shaped sealing ring was simulated by using automatic shrinkage fit,the actual fluid pressure action condition of the V-shaped sealing ring was simulated based on fluid pressure penetration,and the finite element model of V-shaped sealing ring was established.Under quasi-static and dynamic sealing,the maximum Mises stress and the variation law of contact pressure of the V-shaped sealing ring were analyzed.A two-stage differential pressure plunger seal structure was proposed,and the sealing performance analysis of the structure was carried out.The results show that the maximum contact pressure of the seals all appear in the V-shaped sealing ring near the high-pressure fluid side,and the maximum stress is mainly in the lip and shoulder of the V-shaped sealing ring in contact with the support ring and press ring,the V-shaped sealing ring is more likely to fail on the side in contact with the plunger.The use of two-stage differential pressure plunger seal can effectively reduce the Mises stress,shear stress,and friction between the V-shaped sealing ring and the plunger,which can extend the working life of the fracturing pump plunger seal and improve the reliability and economy of the fracturing operation.

Abstract:Sandwich structures composed of PET foam core and aluminium alloy panel were taken as reserch object.In the process of fabricating sandwich structures,four types of core materials were employed.Firstly,untreated PET foam core and PET foam cores subjected to subtractive process treatment(unidirectional slotting,bidirectional slotting,and punching).Secondly,the peel resistance performance between the aluminium alloy panel and PET foam core was tested through the drum peel test,while the influence of material subtractive process on shear performance of the sandwich structures was evaluated through the pure shear test.Finally,the peel and shear failure modes,load-displacement responses,and peel and shear strengths of the structures were analysed.The results show that the peel strength between the panel and PET foam core is improved by 48.31%,32.29%,and 16.67%respectively,compared with the untreated structure,by using bidirectional slotting,unidirectional slotting and punching processes.Although the three processing techniques cause damage to the PET foam core,they actually increase respectively the shear yield strength of the sandwich structures by 3.12%,3.90%,and 2.92%,compared to the untreated structure.

Abstract:The creep behavior of 7050-T7451 aluminum alloy under different temperatures and stresses was studied by the uniaxial tensile creep test.Based on continuum damage mechanics,a constitutive model describing the creep behavior of aluminum alloy at high temperature was established.The model took into account the precipitation coarsening,dislocation multiplication/annihilation and microvoid formation during the creep process,and introduced the corresponding damage factor evolution formula to reflect these three damage processes.In addition,the model took into account the additional damage caused by stress increase to reveal the effect of stress on the creep damage.Based on the comparative analysis of the test results and the predicted results,it was verified that the established physical constitutive model can accurately describe the creep behavior of 7050 aluminum alloy under different temperatures and stresses.

Abstract:The disc spring will bear the cyclic displacement load during using,resulting in the fatigue damage and the stiffness degradation of the disc spring,which causes irreversible influence on the compensation function when accumulated sufficiently to cause fracture.Therefore,the disc spring material which occurred internal fatigue and structural stiffness degradation was studied under the cyclic load.By considering characteristics of the geometric nonlinearity and the action of the cyclic load,based on the traditional stiffness degradation model,a stiffness degradation model fitting for disc springs was established.The force change of the structural system,the law of stiffness degradation of the disc spring,and the stiffness degradation model were analyzed and verified with the finite element software.The model was modified based on the test data to obtain the model that can be used to calculate the degradation of the disc spring stiffness.This model can predict the deformation of disc springs'structure in service,and determine the fatigue damage and performance degradation degree,which can provide some basis and reference for the application of disc springs.

Abstract:The fatigue limit of 7085 aluminum alloy was tested by four-point bending fatigue test for samples of different sizes and roughness.The results show that the greater the thickness of the specimen,the greater the ultimate fatigue strength of the material.The higher the surface roughness of the sample,the lower the ultimate fatigue strength of the material.The stress analysis and calculation of the specimen show that the dangerous cross section occurs at the position where the indenter contacts the specimen,where the specimen is subjected to the combined action of bending normal stress and shear force.With the increase of the thickness of the specimen,the shear force on the specimen decreases,and the bending normal stress on the specimen increases under the same fatigue limit.And vice versa.The relation between the surface roughness and the radius of curvature of the sample is shown by establishing a simplified model,and then the relationship between the surface roughness and the fatigue ultimate strength of the material is obtained.

Abstract:This article took the folding section cam linkage mechanism of a carton folding machine as an example.Firstly,a preliminary design of the cam was carried out based on actual working conditions.Then,combined with the analytical method designing the cam mechanism based on the allowable pressure angle of the cam,a mathematical model was established with the swing rod angle and the center distance between the cam and the swing rod as design variables.Using the NSGA-Ⅱ optimization algorithm,perform multi-objective optimization design on the cam linkage mechanism and select the optimal solution from the generated Pareto solution set.Based on the optimization results,the preliminary design of the cam linkage combination mechanism was adjusted,and the contour of the cam was obtained through Matlab programming,verifying that the optimized cam pressure angle met the allowable pressure angle.Finally,simulation analysis was conducted on the optimized cam linkage mechanism using Adams software.It is found that the displacement,velocity,and acceleration of the blade movement meet the design requirements,verifying the correctness and feasibility of the optimization results.At the same time,it also provides a reference method for the optimization design of other cam linkage mechanisms.

Abstract:The harsh operational environment of helicopters renders their structures highly susceptible to the initiation and propagation of hole-edge cracks around bolt holes,thereby compromising structural integrity and load-bearing capacity.To monitor hole-edge cracks in helicopter attachment lug structures,piezoelectric guided wave-based structural health monitoring(SHM)techniques are commonly employed.However,due to the difficulty in detecting small cracks at the early stages of propagation and the presence of large through-hole configurations in attachment lug structures,the accuracy of guided wave monitoring remains suboptimal.Therefore,addressing the accuracy issues in crack monitoring of attachment lug structures,this study proposes a piezoelectric guided wave array-based method for hole-edge crack detection.Firstly,damage feature information was extracted from acquired piezoelectric guided wave array signals encompassing the entire sensor network.Subsequently,a damage alarm threshold was established using a mean-value method to facilitate damage detection.Furthermore,an improved delay-and-sum imaging algorithm was developed based on the specific configuration of the attachment lug structure to optimize probability distribution and achieve precise crack localization.Finally,validation was conducted through test monitoring of crack propagation in attachment lug structures.Test outcomes demonstrate that the proposed method enables accurate alarm triggering and localization of hole-edge cracks around bolt holes,with localization errors confined within 2.01 mm,thereby confirming the efficacy and precision of the proposed approach.

Abstract:Aiming at the problems of traditional impact load identification methods,such as the requirement for a large number of sensors,high sampling frequency,and low identification accuracy,a new impact load identification method based on empirical mode decomposition(EMD)technology was proposed.The EMD technology was used to decompose the complete impact response to obtain the modal acceleration response.The impact location was quickly realized by measuring the collinearity between the uncorrected mode shape vector and the column vector of the mode shape matrix in the modal acceleration response.According to the positioning results,an optimization objective function was constructed.The time history of the impact load was fitted by using the Gaussian basis function,and the optimal fitting parameters were quickly solved by using the two-dimensional gradient descent method.Tests conducted on a cantilever plate with dimensions of 600 mm×200 mm×3 mm show that with only one accelerometer,the success rate of 36 impact positioning tests is 91.67%.The peak relative error and relative error index of the reconstruction results are less than 10%and 40%,respectively.

Abstract:To explore the penetration resistance of aluminum alloy tubes under spherical steel projectile impact,focusing on the effects of varying tube radii and wall thicknesses on ballistic limit velocity,providing a foundation for tube protection design.A finite element model of spherical steel projectile penetration into 2024-T42 aluminum alloy targets was established using Ansys/Workbench software and the Johnson-Cook material model,which was then verified.Simulations of the response characteristics of aluminum alloy tubes with different radii and wall thicknesses under normal impact of spherical steel projectiles were conducted,along with an analysis of tube deformation and damage.The study found that the penetration resistance of the upper and lower walls of aluminum alloy tubes differs,with the upper convex structure outperforming the lower concave structure.A smaller tube radius enhances the penetration resistance of the upper wall,while for tubes of the same radius,increasing the wall thickness leads to a roughly linear increase in the ballistic limit velocity of both upper and lower walls.