最新刊期
期 6 ， 2020
- 摘要：For the faults of hydropower unit with strong coupling and uncertainty,the traditional fault expression method based on the uniform feature vector is easy to submerge the effect of fault expression and limit the fault diagnosis accuracy and timeliness directly.Given this,we presented a bionic fault diagnosis method,which imitates the human brain thinking and proposes the concept of dependent feature vector（DFV）,which logical structure is described by feature selection tree and extracted by feature extraction tree.DFV deeply excavates the intricate relationship between faults by using its nested structure,and realizes the comprehensive mining of the quantity and quality differences between faults of hydroelectric units.It deeply reveals the intrinsic relationship between different faults and faults and features,effectively extracts the essential differences of different faults,and improves the validity of fault expression.Furthermore,the intelligent classification method is realized by combining DFV and probabilistic neural network,the experimental results show that the method can complete the fault diagnosis of hydropower units and achieve excellent diagnostic validity and timeliness.关键词：Hydroelectric generating set;Dependent feature vector;Comprehensive differences mining;Bionic fault diagnosis;Feature selection
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发布时间：2022-09-22 - 摘要：In order to study the variation law of gear crack fault vibration signal under different conditions,the gear crack fault was simulated based on the characteristic of flexible body in ADAMS,and the fully flexible gearbox models with different degrees of gear crack fault were established.Crack depth,position of measuring points,input speed and load torque were analyzed on their effects to vibration signal of the gearbox.The results show that the deeper the crack,the closer the position of the measuring point to the crack failure source,the larger the input speed and load torque,the greater the impact and amplitude of the vibration signal,and the amplitude of the vertical acceleration signal is larger than that of the axial acceleration signal.The analysis results of the transmission characteristics of the system show that the transmission law and frequency distribution of the vibration signal are basically consistent with the results of the variation law of vibration signal of different measuring points,and the simulation results are verified by hammering experiments.The research results have a certain reference value for the simulation and experimental research of gear crack fault.关键词：Gear crack;ADAMS;Fully flexible model;Transfer characteristic;Hammering experiment
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发布时间：2022-09-22 - 摘要：The problem in the processing of mechanical fault vibration signal by variational nonlinear chirp mode decomposition（VNCMD）,the noise leads to time-frequency surface blurring,which reduces the accuracy of time-frequency ridges extracted,and then affects the decomposition effect of VNCMD,is aimed at,so a joint fault diagnosis of convex optimization and VNCMD is proposed.The noise can be eliminated by solving the sparse approximate solution of signal via the convex optimization algorithm,which can improve the readability of the time-frequency surface,so as to obtain accurate timefrequency ridges.Then,by using these ridges,the fault features of the signal can be extracted effectively via VNCMD.Through the analysis of simulated signal and the measured bearing outer ring fault data,the results demonstrate that the proposed method can realize the accurate extraction of rolling bearing fault feature.关键词：Convex optimization;VNCMD;Time-frequency ridge curves;Fault feature extraction
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发布时间：2022-09-22 - 摘要：Considering the shortcomings of the maximum correlated kurtosis deconvolution（MCKD） method that cannot automatically identify the period of bearing fault impulses,exists the resampling process and the multiple input parameters,an adaptive maximum correlated kurtosis deconvolution（AMCKD） method is proposed.The periodic modulation intensity（PMI） of envelope signal is used to identify the period of bearing fault impulses adaptively.Moreover,the period is constantly updated during searching for the optimal deconvolution filter iteratively,so that the real fault period is gradually approximated.Finally,the filtered signal with the largest correlated kurtosis is selected as the optimal deconvolution signal.Compared with MCKD method,AMCKD method can identify fault impulse period adaptively,avoid signal resampling process,and reduce the input parameters of the algorithm.Simulated and experimental results verify the effectiveness of this method in early fault feature extraction of rolling bearings,and the comparison with fast kurtogram method shows the superiority of AMCKD method in enhancing periodic impulse characteristics.关键词：Feature extraction;Incipient fault;Rolling element bearings;Adaptive maximum correlated kurtosis deconvolution;Periodic modulation intensity
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发布时间：2022-09-22 - 摘要：According to characteristics of the bearing signal,the second-order cyclic demodulation information was introduced into machine learning,and a multi-domain kernel extreme learning machine（MKELM） based on the combination of cyclic autocorrelation（CAF） frequency domain features and time domain features（TD） was proposed to accurately identify the bearing status.The algorithm constructed a CAF function based on the second-order cyclic characteristics of the bearing signal to extract the cyclic frequency domain features of the samples,then combined them with the time domain feature quantities of the samples.The matching factors of multi-domain feature vectors was designed to fuse TD and CAF feature vectors; finally,the fused CAF-TD sample features was input into the kernel extreme learning machine for cluster regression.The spindle bearing experimental results show that the cyclic frequency domain statistics extracted based on CAF can sensitively reflect the signal characteristics.Compared with the classic classifier,the CAF-TD multi-domain kernel extreme learning machine can extract more feature information from limited samples and obtain more accurate diagnostic result.关键词：Bearing;Cyclic autocorrelation;Kernel extreme learning machine;Pattern recognition
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发布时间：2022-09-22 - 摘要：In order to describe rotor-bearing system more accurately and to consider the influence of nonlinear oil film force and rubbing force,this paper establishes a single disk rubbing rotor-bearing system model with nonlinear support,and deduces the dimensionless motion equation of the system.The four-order runge-kutta method was used to numerically calculate the equation.The bifurcation diagram,axis trajectory diagram,Poincare cross section diagram and maximum rubbing force diagram were comprehensively used to study the dynamic behavior of the system,and the influence of eccentricity and rotation speed on the nonlinear dynamic characteristics of the system was analyzed.The analysis results show that with the decrease of eccentricity and the increase of rotating speed ratio,the rubbing force between rotating stator will also decrease,the chaotic region of the system will also decrease,and the system is in periodic motion,thus the stability of the system can be improved.关键词：Rotor-to-stator contract;Rotor-bearing system;Oil-film force;Bifurcation
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发布时间：2022-09-22 - 摘要：In ultrasonic tests,the redundant signal and random noise are easily to be generated when the sensor collects data.Compressing and reconstructing the signal or noise always get the researchers’ attention.Based on the theory of compressive sensing and ultrasonic testing method,an improved CoSaMP for tube fouling ultrasonic testing compression and reconstruction was proposed:The K-SVD algorithm was used to sparsely represent the ultrasonic testing signal.The relationship between the peak signal to noise ratio and the number of iterations was derived to determine the sparse degree adaptively.Finally,the sparsity differences of the echo signal and random noise in the transform domain was used to pick up effective information.The results showed that the improved CoSaMP algorithm can accurately locate signal sparsity.The reconstructed signal reflects that the characteristics of the original signal and the operation time are shorter.That proves the feasibility of the improved CoSaMP algorithm.关键词：Heat exchange tube;Ultrasonic testing signal;Compressive sensing;Noise suppression;Compressive sampling matching pursuit;Peak signal to noise ratio
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发布时间：2022-09-22 - 摘要：The load spectrum of automotive chassis components is the key factor to analyze the fatigue,reliability and durability of components.However,it still needs further practice and direct verification in the process of extracting road load spectrum and the key link processing,as well as error evaluation,etc.Based on this,this paper takes a certain type of automobile steering knuckle as the research object,established rigid-flexible coupling multi-body dynamic simulation model of the whole vehicle,and calibrated it through the test site reinforced the road test,the error between the monitoring signal of the measured key points and the iterative simulation is less than 30%,which verifies the response accuracy of the vehicle multi-body model; The load spectrum of road surface strengthened by endurance test of real vehicle was collected,and the load spectrum of steering knuckle connection points was obtained by simulation decomposition using virtual iteration method; Take typical working conditions of stone road Cand washboard road as examples,the inertia release method was used to solve the time-domain strain field of steering knuckle by using the load spectrum of connection points as input excitation,and time-domain strain curves of monitoring points are obtained,the relative error of the analysis of measured signals is less than 20%,which meets the accuracy requirements of the subsequent use of the load spectrum.The results show that strain calibration method is a direct verification of the effect of virtual iteration load spectrum extraction,which proves the feasibility and accuracy of the load spectrum extraction technical route,and provides a reference for the development of automobile chassis parts and fatigue durability analysis and verification.关键词：Load spectrum;Rigid-flexible coupled multi-body model;Virtual iteration method;Steering knuckle
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发布时间：2022-09-22 - 摘要：Fatigue crack growth tests of 25 Cr2 Ni2 MoV steel with two different heat treatments（550℃× 20 h,580℃× 20 h） were conducted at stress ratios R of 0.1,0.3,0.5 and 0.7,and the fatigue threshold,△Kth,and microscopic mechanism were investigated.Results showed that △Kth increased with the decrease of R,and the heat treatment had varied effects on △Kthunder lower R,while it had less effect under higher R.Fracture morphology observation showed that there existed a large number of facet morphology under lower R,while the facet morphology was gradually reduced with the increase of R.Additionally,the percentage of facet morphology followed a parabolic pattern with △K.It is indicated that R and heat treatment are important influencing factors on △Kth.The crack growth at higher R has weak effect of crack closure,representing the fatigue resistance of the material,and thus can be regarded as the intrinsic property of the material which can be estimated by the proposed model.关键词：25Cr2Ni2MoV steel;Fatigue threshold;Stress ratio;Crack closure;Physical essence
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发布时间：2022-09-22 - 摘要：In order to obtain the ideal surface residual stress of GH4169 milling surface,the optimal interval division method of milling process parameters was proposed,and the orthogonal test of GH4169 milling was designed.The order of the influence of the process parameters on the residual stress was determined by the experiment results and the change trend of the residual stress with the increasing of the process parameters was analyzed.The optimal intervals of process parameters were determined according to the proposed method,and the reliability of the optimized interval was verified by experiments.关键词：Milling;GH4169;Surface residual stress;Process parameters;Optimal range
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发布时间：2022-09-22 - 摘要：Aiming at the problem of introducing large residual compressive stress on the surface of the material due to the quenching process,the high energy density electric current pulse（ECP） technology was introduced to reduce the residual stress in Cr12 MoV steel.The samples were treated with different density ECP and the residual stress and surface hardness of the materials before and after ECP were analyzed by the hole-drilling method and hardness test method.Based on this,an electroplastic model framework was established to explain the mechanism of ECP on residual stress and surface hardness.The results show that high energy density ECP can effectively eliminate the residual stress of quenched Cr12 MoV steel,and increasing the density of the ECP within a certain range can improve the residual stress reduction effect; Surface hardness of quenched Cr12 MoV steel decreased from 61 HRC～64 HRCto 56 HRC～59 HRC;The reduction in dislocation density is an essential cause of residual stress release and surface hardness reduction.The high energy density ECP can be used to reduce the residual stress caused by the quenching process and improve the service life of the parts,which has certain engineering application value.关键词：Pulse current;Cr12MoV steel;Residual stress;Surface Hardness;Electroplasticity
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发布时间：2022-09-22 - 摘要：Machining the micro/nano texture on the surface of the workpiece can effectively improve the surface bearing capacity of the friction pair,while reducing the friction coefficient,friction and wear.Through the research and development status of micro/nano texture,the key design parameters,processing methods,friction reduction mechanism and micro/nano texture combined with coating technology are comprehensively expounded.Among them,the shape,depth,aspect ratio and area ratio of the texture are important parameters which have an impact on the friction and wear; pulsed laser processing technology has the most development prospect in micro/nano texture processing technology;according to the different anti-friction mechanisms of texture under different lubrication conditions,it can be applied to many fields such as machining,biomedicine,etc;the combination of micro/nano texture and coating can improve the bonding force between the coating and the tool surface,thereby improving the cutting performance and anti-bonding wear performance of the tool.Finally,the problems and research prospects in the study of the texture of the friction pair surface and its influence on the tribological properties are pointed out.关键词：Surface texture;Composite micro/nano texture;Processing methods;Friction reduction mechanism
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发布时间：2022-09-22 - 摘要：An improved RSM was proposed to improve the computational efficiency and accuracy of contact fatigue fuzzy reliability analysis of double shock sleeve movable teeth transmission.Based on fuzzy theory,an improved RSM model is established by combining intelligent algorithm and reliability analysis method.Based on the theory of stress-strength interference,the interference reliability model is established with moment,elastic modulus,Poisson’s ratio and working tooth length are taken as input random variables and contact strength of meshing pair is taken as input fuzzy variables.Fuzzy reliability is calculated by different methods,and the distribution characteristics and fuzzy reliability of each response result are obtained.The comparison shows that the improved RSM improves the speed and accuracy of the calculation.关键词：Dual shock wave;Sleeve movable teeth transmission;Fuzzy reliability;Intelligent algorithm;Response surface method
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发布时间：2022-09-22 -
VALVE FUZZY RELIABILITY EVALUATION METHOD BASED ON THE INFLUENCE OF NON-CRITICAL STATE OF THE SYSTEM
摘要：At present,the reliability of a single indicator is evaluated by a conventional reliability model.The results have only two states:the system is completely normal and the system is completely faulty.It is difficult to determine what state the valve system is between "good" and "failed".At the same time,ignoring the impact of non-critical state of the system on system reliability and evaluating method with a single indicator will result in insufficient evaluation results.Therefore,a fuzzy evaluation method based on triple index was proposed.The valve system failure probability PF,the failure probability considering the influence of non-critical states of the system PEF and the mean time between failures MTBF as the indicators to evaluate the reliability gray number clustering were considered.The failure probability considering the influence of the non-critical state of the system was obtained by the cumulative failure probability of the system and the number of expected state transitions.The experimental results indicated that the method can well describe the influence of the non-critical state of the system on the reliability and can determine the reliable level of the system.关键词：Failure probability;Reliability assessment;Fuzzy theory;MTBF- 4
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发布时间：2022-09-22 - 摘要：The research on crashworthiness of thin-walled tubular structures is one of the important researches in the fields of automotive engineering,aerospace and so on.Based on the analysis of material characteristics,structural characteristics and mathematical optimization models of thin-walled tubular structures,this paper expounds the internal relations of loading conditions,deformation modes,energy absorption characteristics and crashworthiness of different types of thin-walled tubular structures.It is proposed that the research on the crashworthiness of thin-walled tubular structures based on structural bionics is an important direction and research idea for future safety and energy-saving research.It provides reference for solving the challenge and the direction of future development in the current research stage.关键词：Thin-walled tubular sturcture;Lightweight;Crashworthiness;Structural bionics
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发布时间：2022-09-22 - 摘要：Aiming at the problem that the contact stiffness analysis method of curvic couplings can not consider the contact interface microscopic morphology,an analytical model of the contact interface stiffness was proposed.Through the stress analysis and stiffness transformation,the general model of curvic couplings contact interface stiffness was obtained,and the GW rough surface model was brought into it to obtain the specific curvic couplings contact interface stiffness formula based on the GW rough surface model.Finally,the analytical model results were compared with finite element results.The effect of surface topography on the contact stiffness of curvic couplings was obtained,and the relationship between the normal contact stiffness and the tangential contact stiffness with the preload and tangential force were obtained.The research shows that the analytical model matches well with the finite element results,which proves the rationality of the analytical model and provides a theoretical reference for the preload force and torque design of the rotors with curvic couplings.关键词：Curvic couplings;Contact stiffness;GW model;Analytical model;Digital modeling
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发布时间：2022-09-22 - 摘要：the formation mechanism of micro-pitting had been described in this paper,the action relationships of various influencing factors had also been analyzed,and the three main action mechanisms of local contact stress,film thickness ratio of lubricating oil and micro mechanical properties for materials had been regularized.Based on elastohydrodynamic lubrication theory and previous test results for Newtonian fluids,the reasonable calculation method of film thickness for lubricating oils had been determined.Through comparative calculations,the specific effects of oil types,lubricating oil temperatures,transmission torques and gear speeds on the oil film thickness had been analyzed.Combined with the micro-pitting design of gear transmission,feasible ideas and operational methods for lubrication improvements and optimizations had also been given.Finally,through the experimental designs,the correctness of the theoretical analysis had been verified,and the basic data for the anti micro-pitting design of the combination for gears of 18 CrNiMo7-6（material）+ISO-VG220（Lubricating oil） had been goted.关键词：Gear transmission;Micro-pitting;Damage mechanism;Fatigue analysis;Lubrication design
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发布时间：2022-09-22 - 摘要：In order to improve the tooth surface contact state of the swinging rod,the elastic deformation of the center and the movable tooth meshing pair during the transmission process is analyzed.With minimum contact force as the target,the ring profile has medicated by combinion of equidistant and displacement modification,the influence of the modification on the contact force of meshing pair as well.Taking the ring-movable tooth engagement pair as an example,it is found that the tooth profile modification method based on the elastic deformation of the meshing pair reduces the maximum contact force and contact stress of the ring-movable tooth meshing pair by 10%,compared with the change of the meshing force in one push cycle before the trimming.By calculating the stiffness of the meshing pair,the average meshing stiffness after trimming is increased by 3%.The simulation of the virtual prototype was performed by Adams.The results show that the output speed is more stable after modification.The correctness of theoretical calculation is verified compared with Workbench finite element simulation.关键词：Swing-rod movable tooth;Modification;State of tooth contact;Adams Simulation;Finite element simulation
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发布时间：2022-09-22 - 摘要：The properties of energy absorption can be effectively improved by different induced structures for thin-walled straight tube.Finite element software（LS-DYNA） was used to simulate the transient response of thin-walled circular tube with internal and outer staggered grooves under axial impact.Axial shock characteristics of force for thin-walled circular tubes with different grooves were compared.The mean load formula considering strain rate effect was derived based on Hosseinipour ’s deformation model.Geometric parameter was introduced to predict peak load.The results show that the thin-walled circular tube with internal and outer staggered grooves can reduce 62.24% peak load and 56.26% mean load compared with thin-walled straight tube.The fold deformation is symmetrical and consistent with Hosseinipour’s deformation model.The prediction results of mean load and peak load are consistent with the finite element results.关键词：Thin-walled circular tube;Groove;Mean load;Peak load;Prediction
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发布时间：2022-09-22 - 摘要：The full-rotation built-in steerable drilling tool is one of the important components of the rotary steerable drilling system.It is a new type of dynamic directional downhole closed-loop rotary steerable drilling tool.In order to study the motion condition of the full-rotation built-in rotary steerable drilling tool,based on the principle of space mechanism,The dynamics concentration parameter model of the full-rotation built-in directional drilling tool was established,and the system dynamics analysis was carried out.The correctness of the model was verified by ADAMS simulation.The results show that the basic parameters of velocity and attitude of the eccentric ring and the guide shaft of the key components are theoretically obtained,and the motion characteristics of the attitude mechanism are revealed.The rotational speed,eccentricity and bit motion of the eccentric ring and the guide shaft are studied.The relationship is obtained,and the variation of each parameter in the guiding system with time is obtained.It lays a theoretical foundation for the research of the full-rotation built-in directional drilling tool and the realization of the optimal design of the drilling system.关键词：Full rotation built-in type;Steering drilling tool;Dynamics;Concentrated paramete;Adams Simulation
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发布时间：2022-09-22 - 摘要：The change of meshing stiffness of gears is caused by the change of meshing position and meshing number between gears when the gears are running.The change of meshing stiffness reflects the change of meshing process of gears.When pitting occurs,the meshing stiffness of gears will change,which will lead to the change of vibration law of gearbox.This change can be used to judge whether the internal fault of gearbox is serious or not.According to the actual situation of pitting,pitting pits are set as elliptical sections.The meshing stiffness under pitting failure is calculated by potential energy method,and the influence of pitting location,size and depth on meshing stiffness is analyzed.The results show that pitting has no effect on the meshing stiffness of the non-pitting area under the gear teeth during the meshing process.The closer the pitting position is to the top of the gear teeth,the greater the impact on the meshing stiffness above the pitting gear teeth.The deeper the pitting pit is,the larger the area is,the more the meshing stiffness decreases,and the more obvious the influence of the area change on the meshing stiffness changes.关键词：Pitting failure;Meshing stiffness;Potential method
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发布时间：2022-09-22 - 摘要：The quasi-static radial compression performance of carbon fiber reinforced plastic（CFRP） wound thin-walled aluminum tubes was studied by means of experimental research,theoretical and simulated analysis.Based on the joint action of aluminum and CFRP tubes,the theoretical model of initial failure load and total energy absorption of Al-CFRP hybrid tube under radial compression is established firstly.Then,the quasi-static radial compression experiment of Al-CFRP hybrid tube is carried out and the results show that the experimental results are in good accordance with the theoretical results which verifies the accuracy of the theoretical model that is carried on the supplementary improvement by finite element simulation.Based on the established theoretical model,the effects of winding angle of carbon fiber and the layer thickness ratio of aluminum tube and CFRP tube on initial failure load and total energy absorption of the hybrid tube were studied.The results show that the initial failure load and total energy absorption of the hybrid tube with a stable failure mode and bearing capacity are higher than those of the aluminum tube under quasi-static radial compression;The initial failure load and total energy absorption of the hybrid tube decrease first and then increase with the increase of the winding angle of carbon fiber and the thickness ratio of Al-CFRP layer.关键词：Radial compression;Al-CFRP hybrid tube;Initial failure load;Total energy absorption
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发布时间：2022-09-22 - 摘要：As offshore oil industry moves into ultra-deep water,replacing the steel tensile armors of unbonded flexible pipe with composite is becoming a scheme that can effectively reduce weight and provide better mechanical properties.The anisotropic parameters of composite are obtained by meso-mechanical method,then a model of axisymmetric structure response for composite flexible pipe with composite armored layer is established,which is based on both thick-wall cylinder theory and the differential equation of curved beam,and also the algorithm of cyclic iterative is combined.Failure models of different type of flexible pipes are obtained,and iso-strength method is used for composite armored pipe.A case study shows that composite armors can effectively enhance the tensile strength of unbonded flexible pipe while effectively reduce the overall weight.Results state that volume fraction,elastic modulus and strength of fiber are the important parameters which affect the axial stiffness and tensile strength of unbonded flexible pipe.关键词：Unbonded flexible pipe;Composite armor;Tensile strength
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发布时间：2022-09-22 - 摘要：For the inaccuracy of empirical heat loads for spindle thermal simulations,a thermal simulation analysis method onto motorized spindle unit is proposed.Firstly,the fluid-solid-heat coupling simulation model of the motorized spindle unit is established by Ansys Workbench,with the coolant dynamic heat transfer and thermal resistances of bearing inner-spindle shaft and outer rings-bearing housing being considered.Secondly,based on the simulation model,genetic algorithm is used to optimize and correct the heat generation values of spindle motor/beairngs and ambient heat transfer coefficients.The corrected values above are used as thermal loads for thermal simulation modeling of motorized spindle unit.Based on the model,the dynamic relationship between the heat dissipation power of the coolants and the heat generation power of spindle motor/beairngs is studied.Finally,the model accuracy is verified by the spindle temperature testing experiment.The results show that the optimization correction model can effectively improve the temperature field simulation accuracy of the motorized spindle unit,and the spindle structure and the coolant reach the optimal heat-heating balance when the coolant supply temperature is about 2℃ lower than the ambient temperature.关键词：Motorized spindle unit;Ansys workbench;Fluid-solid-heat coupling;Thermal load;Genetic algorithm
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发布时间：2022-09-22 - 摘要：Taking the working device of a certain type of excavator as the research object,,through the method of market research and the simulation analysis of the validated FEM by static calibration experiment to determine the dangerous position of working device,basing on the experimental data（cylinder displacement,stress etc.）,first take the maximum digging force posture for fatigue test of stress response as "sensitive" posture and loading in the middle of the bucket tip and the level of positive response at-13 DEG direction " sensitive" as direction,solving the multi degree of freedom system actual attitude multiplicity the real danger caused deviation of the object of any other fixed posture and loading direction of the problem.Secondly,the load of the dangerous point spectrum as the driving load spectrum of tip loading force equivalent,finally through the damage consistency test results show that the experimental method is reasonable,which can effectively solve the problem of posture and loading under the laboratory environment working device,to provide reference for similar and Taiwan fatigue experiment of multi degree of freedom system.关键词：Working device;Durability;Bench;Test posture
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发布时间：2022-09-22 - 摘要：Long-term alternating loads on the connecting bolts of hydro-turbine head cover,which results in fatigue damage causing many serious accidents.Therefore,it is necessary to carry out in-depth study on the calculation method of fatigue life of head cover bolts in order to improve the accuracy of fatigue life calculation.In order to solve the above problems,a method for calculating the fatigue life of Turbine head cover bolts based on combination of power density and short-time Fourier analysis（PD-STFA） is put forward,with emphasis on the influence of coupling action of loading frequency and amplitude load on the fatigue life of head cover bolts.Firstly,the position and stress of dangerous section of connecting bolt are calculated by finite element method;secondly,the average stress of contact surface of bolt head is measured by strain-based hollow pressure sensor,and then the measured average stress of contact surface of bolt head is transformed into the stress of dangerous section according to generalized Hooke’s law;finally,based on linear damage accumulation theory,the fatigue life of the head cover bolts is calculated by PD-STFA method and the traditional rain flow counting method.The calculation results show that the fatigue life of the head cover bolts is 1.966× 10~5 h based on PD-STFA method and 4.113 ×10~5 h based on traditional rain flow counting method.According to the investigation of power plant users,the calculation results based on PD-STFA method are closer to the actual service life of bolts for about 30 years,and can predict the fatigue life of the turbine head cover connecting bolts more accurately,thus providing theoretical guarantee for the safe and stable operation of the hydro-turbine.关键词：Head cover bolt;Short-time fourier analysis;Power density;Rain-flow counting method;Fatigue life
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发布时间：2022-09-22 - 摘要：Taking a low-speed two-stroke marine diesel engine bedplate as the research object.The main bearing seat（material ZG200-400） crack growth rate was tested,and the fatigue crack growth rate and the Paris formula of the stable expansion section were obtained.The three-dimensional crack propagation life analysis model of the main bearing seat was established by the sub-model method.The real boundary conditions of the main bearing seat was obtained by combining with the analysis results of the alternating stress of the bedplate under the actual operating conditions of the engine（360 degree crank angles）.The crack growth life of the main bearing seat with initial crack was calculated.The analysis results show that the crack growth life is less than that of the low-speed two-stroke marine diesel engine overhaul inspection interval.The research results of the thesis provide an reference for the damage tolerance in design engineering application.关键词：Low speed diesel engine;Crack growth;Finite element;Life
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发布时间：2022-09-22 - 摘要：To calculate the fatigue strength of complex handle welded structure under cyclic loading,the stress time history of handle component under cyclic loading was solved using transient modal dynamic analysis method,and the fatigue life of welded structure was calculated using mesh-size insensitive Battlle structural stress approach.It was found that the fatigue strength of original handle welded structure is insufficient because the ear plate connection structure is inconsistent,which results in stress concentration.The transition plate was added to the improved welded structure and the calculation result shows the maximum structural stress near the weld lines is 44.9% lower than that of the original structure,and the stress is relatively uniform.The fatigue life of the improved one was estimated to be 4 years and 5 months.The weld failure of improved welded structure has not occurred for more than 3 years in service in two equipments,which meets the application requirements.For large welded structures which are difficult to conduct physical tests,the numerical calculation based on Battlle structural stress approach can provide a basis for structural design.关键词：Battlle structural stress approach;Electric shovel handle;Welded structure;Fatigue life
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发布时间：2022-09-22 - 摘要：The exhaust pipe of engine is subjected to alternating load of low and high temperatures during operation,which is prone to fatigue damage.For the FSC（Formula Student China） racing engine with the highest speed of 11 000 r/min～13 OOOr/min,the exhaust pipe fatigue problem is more serious.In this paper,the FSC racing exhaust system is taken as the research object to analyze its fatigue strength and optimize the exhaust pipe thickness.Firstly,the Fluent software is used to analyze the conjugate heat transfer of the exhaust system to determine the temperature distribution of the exhaust system.Then the temperature distribution is mapped to the finite element mesh of the exhaust system,and the thermal stress and thermal strain are analyzed by finite element technology.Subsequently,two schemes including exhaust manifold " normal operation-parking cooling" cycle and extreme working condition cycle are designed to carry out the thermal cycle simulation.It is found that the exhaust gas accumulates plastic deformation under the alternating load of each cycle,and the exhaust system will eventually crack and be destroyed.Finally,the fatigue life of the two schemes is studied by using Ansys nCode DesignLife fatigue analysis software.The results show that both schemes effectively reflect the life expectancy of low-cycle fatigue damages under the combined action of exhaust manifold temperature field,thermal stress and strain.Based on the above analysis,the exhaust thickness is optimized by the extreme working condition circulation scheme.and it is verified by experiments that the 1.2 mm thickness steel pipe meets the FSC exhaust requirements.关键词：Exhaust system;Thermal fatigue;"Flow-Thermal-Solid" coupling;Thermal stress;Elastoplastic simulation
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发布时间：2022-09-22 - 摘要：Aiming at the problem that the finite element analysis software can’t deal with the nonlinear characteristics such as elastoplastic element in modal analysis,the static finite element analysis method is used to obtain the variation of the stiffness of the end tooth structure considering the surface contact with the preload force and proposed an equivalent method that can characterize the contact effect on the stiffness of the end tooth joint structure.An equivalent model of the end-toothed rotor considering contact is established.The influence of preload force on the modal and critical speed of the rotor is obtained by the modal analysis of the rotor under different preload conditions.Analysis data indicates that the equivalent method can correctly reflect the influence of contact effect on rotor stiffness in modal analysis,and the accuracy meets the requirements of engineering application.关键词：End-tooth connection;Contact stiffness;Rotor;Preload;Critical speed
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发布时间：2022-09-22 - 摘要：Analyze the force of the agitating mechanism of double shaft vibrating mixer under different working conditions.Combined with the finite element software analysis,the stress,strain and modal shape of the agitating mechanism is obtained.At the same time,the strain pattern is compared with the actual deformation zone to verify the rationality of the finite element analysis.An optimization scheme is proposed aiming at improving the stiffness.After the simulation analysis,the stiffness of the optimized agitating mechanism is obviously enhanced to meet the work requirements.Meanwhile,the strength and natural frequency of the mechanism have also improved.It has an important significance for reducing safety incidents.At the same time,it also lays a theoretical foundation for vertical shaft vibration mixing technology.关键词：Vibratory agitating;Agitating mechanism;Finite element simulation;Modal shape;Structure optimization
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发布时间：2022-09-22 - 摘要：Aiming at checking the performance of a front subframe whether could meet the design requirements.Firstly,the grid model of the front subframe was built by adopting finite element method,and it was modal performance analyzed,the analysis result showed that its first two natural frequency were higher than the engine excitation frequency,so it could meet dynamic performance requirements.Secondly,the front subframe was modal tested,the test result showed that its simulation analysis precision was high.Thirdly,the front suspension dynamic model was built,and it was load based on theoretical forces,so its connection point load of typical working condition were obtained.Fourthly,the front subframe was strength analyzed by adopting inertia release method,the analysis result showed that its stress were lower than material yield value,so it could meet meet the strength characteristics.Lastly,the front subframe was lightweight designed by adopting neighborhood cultivation multiobjective genetic algorithm,the optimal thickness were obtained.Its modal performance and strength performance could meet the requirements after optimization,its weight had been successfully reduced by 9.9%,and it had passed the real vehicle road test verification.The theoretical and scientific reference were provided for obtaining the structural performance and optimization design.关键词：Front subframe;Modal;Frequency;Strength;Lightweight
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发布时间：2022-09-22 -
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