科创中国

Longitudinal vibration,torsional vibration and their coupled vibration are the main vibration modes of the crankshaft-sliding bearing system.However,these vibrations of the propeller-crankshaft-sliding bearing system generated by the fluid exciting force on the propeller are much more complex.Currently,the torsional and longitudinal vibrations have been studied separately while the research on their coupled vibration is few,and the influence of the propeller structure to dynamic characteristics of a crankshaft has not been studied yet.In order to describe the dynamic properties of a crankshaft accurately,a nonlinear dynamic model is proposed taking the effect of torsional-longitudinal coupling and the variable inertia of propeller,connecting rod and piston into account.Numerical simulation cases are carried out to calculate the response data of the system in time and frequency domains under the working speed and over-speed,respectively.Results of vibration analysis of the propeller and crankshaft system coupled in torsional and longitudinal direction indicate that the system dynamic behaviors are relatively complicated especially in the components of the frequency response.For example,the 4 times of an exciting frequency acting on the propeller by fluid appears at 130 r/min,while not yield at 105 r/min.While the possible abnormal vibration at over-speed just needs to be vigilant.So when designing the propeller shafting used in marine diesel engines,strength calculation and vibration analysis based only on linear model may cause great errors and the proposed research provides some references to design diesel engine propeller shafting used in large marines.

The major methods to investigate the airbags cushion system are experimental method,thermodynamic method and finite element method(FEM).Airbags cushion systems are very complicated and very difficult to be investigated thoroughly by such methods.For experimental method,it is nearly impossible to completely analyze and optimize the cushion characteristics of airbags of airborne vehicle because of charge issue,safety concern and time constraint.Thermodynamic method fails to take the non-linear effects of large airbag deformation and varied contact conditions into consideration.For finite element method,the FE model is usually complicated and the calculation takes tens of hours of CPU time.As a result,the optimization of the design based on a nonlinear model is very difficult by traditional iterative approach method.In this paper,a model based on FEM and control volume method is proposed to simulate landing cushion process of airborne vehicle with airbags cushion system in order to analyze and optimize the parameters in airbags cushion system.At first,the performance of airbags cushion system model is verified experimentally.In airdrop test,accelerometers are fixed in 4 test points distributed over engine mount,top,bottom and side armor plate of hull to obtain acceleration curves with time.The simulation results are obtained under the same conditions of the airdrop test and the simulation results agree very well with the experimental results,which indicate the established model is valid for further optimization.To optimize the parameters of airbags,equivalent response model based on Latin Hypercube DOE and radial basis function is employed instead of the complex finite element model.Then the optimal results based on equivalent response model are obtained using simulated annealing algorithm.After optimization,the maximal acceleration of airborne vehicle landing reduces 19.83%,while the energy absorption by airbags increases7.85%.The performance of the airbags cushion system thus is largely improved through optimization,which indicates the proposed method has the capability of solving the parameter optimization problem of airbags cushion system for airborne vehicle.

Axial-grooved gas-lubricated journal bearings have been widely applied to precision instrument due to their high accuracy, low friction, low noise and high stability. The rotor system with axial-grooved gas-lubricated journal bearing support is a typical nonlinear dynamic system. The nonlinear analysis measures have to be adopted to analyze the behaviors of the axial-grooved gas-lubricated journal bearing-rotor nonlinear system as the linear analysis measures fail. The bifurcation and chaos of nonlinear rotor system with three axial-grooved gas-lubricated journal bearing support are investigated by nonlinear dynamics theory. A time-dependent mathematical model is established to describe the pressure distribution in the axial-grooved compressible gas-lubricated journal bearing. The time-dependent compressible gas-lubricated Reynolds equation is solved by the differential transformation method. The gyroscopic effect of the rotor supported by gas-lubricated journal bearing with three axial grooves is taken into consideration in the model of the system, and the dynamic equation of motion is calculated by the modified Wilson-θ-based method. To analyze the unbalanced responses of the rotor system supported by finite length gas-lubricated journal bearings, such as bifurcation and chaos, the bifurcation diagram, the orbit diagram, the Poincaré map, the time series and the frequency spectrum are employed. The numerical results reveal that the nonlinear gas film forces have a significant influence on the stability of rotor system and there are the rich nonlinear phenomena, such as the periodic, period-doubling, quasi-periodic, period-4 and chaotic motion, and so on. The proposed models and numerical results can provide a theoretical direction to the design of axial-grooved gas-lubricated journal bearing-rotor system.

溶液表面张力和浓度关系模型的正确选择对提高表面张力测定实验数据的计算结果的准确度具有重要的意义.本文首先介绍了非线性模型参数确定的计算原理,然后介绍了表面张力测定实验数据处理中饱和吸附量和分子横截面积的计算方法,通过VB研制的软件对一组实验数据进行了计算,从理论分析和实例验证2个角度对4种比较典型的模型进行了研究,研究表明:在低浓度区域,适合采用对数模型,在当溶液浓度较高时,适合采用指数模型.本文研制的表面张力计算软件不仅可用于物化实验教学,也可作为研究表面张力和溶液浓度关系的一个计算工具.