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In order to reduce the drag torque under high speed conditions, the equivalent radius is introduced into the traditional low speed torque model of a wet clutch with track vehicle, and the calculation model of the drag torque with radial groove is derived. An optimization design model is established with 3 working condition parameters of the clutch and 5 structural parameters of the friction plate as design variables, and the minimum drag torque as the optimization objective. The objective function is solved based on the whale optimization algorithm (WOA) , and the drag torque is reduced by 35.6% after optimization. The dynamic response model of the objective function is established by Simulink software, and the optimization results are verified. The results show that the optimization method is effective and can provide some reference for structural design and parameter optimization of wet clutches.

In order to improve the bearing performance and test accuracy of vehicle vibration test benches, a test bench which can simulate vehicle vibration environment in an all-round way is designed based on a 6-UPS parallel mechanism. Through the mechanism analysis and degree of freedom calculation of the 6-UPS parallel mechanism, the pose relationship between components is established, the kinematics equation of the bench is deduced, and the kinematic characteristics of the bench are studied. By establishing the simulation model of vehicle vibration test benches, the kinematic simulation analysis of the bench is carried out using Adams software, and the kinematic parameters of the bench are verified theoretically. The results show that the vehicle vibration test bench can move according to the predetermined trajectory, the simulation curve is smooth without mutation, and the designed bench can meet the expected performance indexes, which verifies the rationality of the bench design. This study lays a foundation for the dynamic analysis, control strategy research and optimization design of vehicle vibration test benches.

In order to obtain the stiffness-damping feature of cross-arm damping seat of special vehicles, the dynamic simulation model of cross-arm seat is established. The time-frequency responses on the level D road and different vehicle speed conditions（5 km/h, 15 km/h, 25 km/h and 35 km/h） are analyzed. With considering the weighted root-mean square（RMS） acceleration in criterion ISO 2631-1:1997 as an evaluation index, the ride comfort of the seat with different matching relationships of stiffness and damp are discussed. Furthermore, the real vehicle validation experiment is conducted. The results show that the seat vertical acceleration under different speeds has the non-stationary random characteristic. The seat vibration intensifies with the increase of the speed. Under different vehicle speed conditions, the first two model frequencies for the seat concentrates in 3 Hz～10 Hz, which includes the human sensitivity frequency ranges, inducing the poor ride comfort performance. Additionally, the simulation results agree with the experimental data, which verifies the correctness of the dynamic simulation model. The research has certain reference for multi-objective matching optimization design about the stiffness-damping parameters for the seat comfort of special all-terrain vehicles and engineering applications.

In order to realize high efficiency and energy saving in surface milling,this paper takes surface milling as an example to study the optimization method milling path of ball milling cutter based on hybrid algorithm. First of all,considering the spindle speed,feed,surface quality and the actual constraints of no repeat tool,a tool path optimization model with the goal of high efficiency and energy saving was established. According to the workpiece processing requirements,the surface is discretized to obtain a reasonable number of knife contact points. The crossover,mutation and reversal operations of genetic algorithm are introduced to improve the particle swarm optimization algorithm. Finally,the effectiveness of the proposed method is verified by two semi-finishing experiments.

Stress concentration caused by holes in a component is always an important research topic in structural safety assessment. Many studies have been carried out on linear elastic materials under static loading,including the effects of hole shape,material anisotropy and loading direction on stress concentration. However,the coupling effect of the nonlinear stressstrain relationship and the strain-rate effect will lead to a great difference between the stress concentration for the plastic material and the existing linear elastic results when the material is under dynamic loading,especially for many kinds of metal materials with plastic deformation. Therefore,based on the Johnson-Cook model,the stress concentration at the hole root of a typical 45 steel plate under dynamic loading is systematically analyzed using finite element method. The results show that the plastic stress concentration factor depends not only on the loading magnitude（ strain） but also on the loading speed（ strain rate）. For the plate at plane stress state under the remote strain of 1%,the stress concentration factor at the circle hole for ε∞= 20/s is around 10%higher than that for ε∞= 0. 1/s,while the stress concentration factor at the elliptic hole with the shape factor（ minor axis/major axis） of 0. 5 for ε∞= 20/s is around 11% higher than that for ε∞= 0. 1/s.

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.

The bolted rotor is a typical rotor structure with light weight, high strength, good rigidity, flexible selection of all kinds of wheel materials, etc., which is formed by pressing and combining several sections of rotors or discs and is widely used in aero-engines and gas turbines. Aiming at blind assembly, trail assembly and inconsistent assembly tightness of bolted rotor, and the degradation and loosening of bolt tightness in service, a quantitative detection method of bolt assembly quality based on GHM multiwavelet was proposed. Using the GHM multiwavelet with excellent characteristics such as symmetry, compactness, orthogonality, vanishing moment and high order vanishing moment, feature extraction of the bolted rotor assembly tightness states was performed. The quantitative detection index of assembly quality was defined by the relative energy band distribution based on multiwavelet. The experimental verification shows that the proposed method can accurately identify six kinds of bolt states from tightness to looseness.

A finite element model of the dynamic fracture in a full size gas pipeline is established based on the cohesive zone model. The dynamic crack growth of X80 pipeline steel was simulated using this model and the quantitative relationship between the crack growth rate and the internal pressure predicted is in agreement with the existing semi-empirical formula. Based on this model, some key parameters which are difficult to be directly measured in pipe blasting test（such as the crack tip opening angle, the stress and strain field surrounding the crack tip, energy dissipation, etc） could be quantitatively studied especially when the crack speed is very high. Accordingly, the proposed model would be a supplementary mean for the full-scale test. Moreover, the crack arrest design of the full-scale pipeline is also discussed based on this model.

The high power transfer case as a key component of a multi-axis super-heavy chassis transmission system,with the characteristics of large torque,high speed,and large temperature difference,rely on splash lubrication and natural air cooling has been unable to meet the need of the chassis for high mobility,high through off-road and extreme ambient temperature. It is necessary to use the forced lubrication system to lubricate the internal hot spots of the transfer case,especially the bearing position. Therefore,the power thermal energy model of the hotspots of the transmission parts is built first,through the heat balance conditions,the flow demand of the lubrication point and the overall are estimated,and then a hydraulic simulation analysis model is established,the matching lubrication system piping is designed. Aiming at the problem of the natural air cooling can’t achieve the system thermal balance requirements in the great power of the transmission system,by calculating the surface wind speed and heat dissipation surface,the heat dissipation capacity of the transfer case itself is evaluated,the external air-cooled radiator and fan are matched according to the heat dissipation requirement.Finally,through the bench and running vehicle test,the design of the high power transfer case forced lubrication system to meet a multi-axis super-heavy chassis of the use of the requirements is verified.

In fault tree analysis of aircraft hydraulic brake system,the probability statistical information of failure rate for bottom event is usually not sufficient.To solve this problem,a fault tree analysis method based on hyper-ellipsoidal model was given.Firstly,according to hydraulic brake system principle and the failure mechanism,the system fault tree model was established.Then the hyper-ellipsoidal model was introduced to describe the uncertainty of bottom event.Finally,the simulation process of system top event failure probability as well as the importance of bottom events was deduced based on double Monte Carlo method,and comparison was made with fault tree analysis under interval model.Results show that the fault tree analysis method under hyper-ellipsoidal model just needs the value range of bottom event failure probability,without requiring the detailed probability statistical information of bottom event.Compared with the interval model,the hyper-ellipsoidal model exhibits stronger robustness,and its results meet the engineering practice better.At the same time,the importance measurement analysis of bottom events was conducted to identify key failure events,which provides guidance for the brake system in design and maintenance.

The dynamic load simulation is a key technology of indoor bench test and an important assessment of automatic transmission performances. In order to achieve EM-CVT dynamic load simulation,the dynamic load simulation method is researched by using MATLAB/Simulink to establish the mathematical model of automatic transmission dynamic load simulation system and combining with the speed tracking control algorithm.The virtual test is carried out,which refers to a section of the NEDC city cycle,the EPA performance index is introduced to evaluate the system performance. The results show that the motors can response to speed and torque instruction of model rapidly,the system can run smoothly,the maximum relative errors of rotational speed and torque are 1% and 8%,the standard errors of estimate（ SE） and the coefficients of determination（ r2） of speed and torque are 4. 3 r/min,17. 7 N·m and 0. 99,0. 91,it has a better performance than EPA performance index.

A series of stiffened panels with different dimensions and types of stiffener are simulated under longitudinal compression in finite element code ANSYS. Two bays/spans model with periodic boundary condition is adopted to consider the influence of neighbouring members. The stiffened panel adopted in the finite element mode is generally cut from the deck or bottom of a ship hull girder, and thus, the constraint on their edges depends to some extent on the relative structural response of the adjacent members. Hence, to understand the effects of constraint condition on the collapse behaviour, an extensive parametric study is carried out, employing a wide geometrical range for bulk carrier and very large crude carrier. Moreover, considering various collapse modes, the load-carrying capacities of the stiffened panels are also investigated for various stiffener types. It is found that the biaxial stress state caused by longitudinal constraint could increase or decrease the load-carrying capacity of the stiffened panel, which depends on the collapse mode and should be noticed. The transverse constraint on the longitudinal edges could cause biaxial stress state, which might increase or decrease the load-carrying capacity of the stiffened panel, which depends on the collapse modes.

This article is intended for proposing a solution to improvement,optimization and lightweight design of the heavy truck’s single-deck frame based on the causes to the fractured traditional double-deck frame assembly produced by SINOTRUCK WANGPAI MOTOR through the optimal design and improvement on the heavy truck‘s frame by finite element analysis of the structural stress and strain,which indicates that the optimized single-deck frame significantly improves in strength and rigidity and is lighter in weight that could satisfy the design requirements. The technology has been successfully applied to mass production of the current product line with good market response and favorable socioeconomic performance brought to the business.

The creeping phenomenon is a common instability phenomenon of chain transmission. Because of the roller conveyor chain often use to transfer power and convey material in the low speed,heavy duty and poor working environment,it more easily happen the creeping phenomenon to affect the normal operation of the conveyor chain. Through analyzing the dynamics characteristic and building the dynamics model of the conveyor chain,the main reasons of why the roller conveyor chain occur the creeping phenomenon are the different friction condition,the system stiffness and dynamic load. Finally,based on the Recurdyn,a simulation model of the roller conveyor chain transmission is built and the relative conclusion is verified.

The wheel gearbox is a key component of Multi-axis super-heavy hybrid test platform,for the special nature of the application,on the one hand to meet the requirements of vehicle wheel power transmission requirements,while also meet lightweight and high reliability requirements.Therefore,in the wheel gearbox design,taking the lightweight for the wheel gearbox as the target,reliability as constraints,the optimization design scheme of the wheel gearbox is proposed.After the high- speed test,full load fatigue test and overload fatigue test verification,the wheel gearbox performance and reliability meet the requirements of super- heavy hybrid multi- axis test platform.

Calculation of gear geometrical center is an important issue in measurement of large gears. On the basis of the establishment of discrete data model of involute gear,a method to calculate the geometrical center of large cylindrical gear is put forward,and the corresponding mathematical model is established. According to the calculated result of gear center,the gear tooth profile error is calculated,and compared with the calculated result with the standard gear geometrical center known. The simulation results show that after adding random noise of the amplitude of 0 318 μm on the grade 8 large gear,the calculated maximum error of gear geometrical center is less than or equal to 1 μm,while the gear tooth profile error between the theoretical value and calculated result is less than or equal to 10 μm,which suggests that the method can be effectively applied to the measurement of large cylindrical gears.

Aiming at the analysis of the position and orientation error on the new 3- PRS parallel mechanism with three adjustable pedestals and variable working space,a geometric analytic method for the forward kinematics analysis of the 3- PRS parallel mechanism is proposed,then the analysis of the working platform end- effector error is derived,and what’s more,the position and orientation of the working platform end- effector is obtained by using software emulation when the three pedestals at different positions. The results show that the end- effector error has obvious changes with the different positions of the three pedestals. This study provides a useful guidance for the error compensation of the new 3- PRS parallel mechanism.

The 3D model of gearbox casing is built in design stage,and the FEA（ Finite Element Analysis） is carried out based on the ANSYS Software,the eight kinds of working conditions of locomotive runs normally are especially analyzed. Comparing with the Goodman curve,the stress of every point of gearbox model is within the Goodman curve. It is indicates that the gearbox casing meets the structural strength requirement,the rationality of structure design for the gearbox is confirmed.