For the chaotic motion of a single-stage gear system with tooth backlash and bearing clearance in some parameter region, the unstable periodic orbit of chaotic attractor was stabilized by improved OGY chaotic control principle. The OGY control for a smooth dynamic system was transformed to a non-smooth multi-dimensional dynamic system by the finite difference method instead of the Jacobi matrix under non-smooth point. And PNF method is used to search the pseudo-fixed points of unstable periodic in chaotic region. The Jacobi matrix and sensitivity column vectors in the improved OGY algorithm were solved according to the dynamic equation and variation form, the periodic orbital interval and transfer characteristics of chaotic attractor were analyzed combined with Poincaré mapping. The simulation results show that the improved OGY control method is also effective for chaos control of multi-dimensional non-smooth gear systems. When the multi-period orbit was continuously controlled, the difficulty of chaos control increases with the increase of the target periodic orbit, and the required parameter perturbation increases correspondingly.

 

The space station solar array is usually flexible cable/membrane structure with large developement area and plenty of mechanism links. It is necessary to establish a fine finite element model, and analyze the transient deformation and stress under high strength on-orbit load conditions. By using the mechanical properties of the Gap element, the inverted Gap elements is used as the connecting unit between the flexible substrate and the storage boxe. Several problems such as pretigthening force on flexible substrate, simulation of discontinuous tension and compression stiffness of the cable, elastic deformation offset of the storage boxe are solved in one stroke. The results of transient shear force and bending moment of improtant companents of solar array are obtained successfully, which provides important decision basis for product design. The results also show that there are significant shortcomings in the application of linear model to this promlem.

 

A method for identifying nonlinear modal parameters of the tail drive shaft system of a helicopter based on the tested frequency response functions was proposed.Using the linear modal analysis and in accordance with the response amplitude linearization theory, the nonlinear modal parameters of the tail drive shaft system were identified by the stepped sine sweep test in order to obtain the frequency response functions at different excitation levels.The results show that the first-order natural frequency of the tail drive shaft system decreases by about 2%, while the damping ratio increases by about 1.5 times, as the amplitude of the excitation force increases.Multiple sets of test analyses were performed under the same state and the results are consistent.The approach for identifying the modal parameters of the nonlinearity of the tail drive shaft system lays a foundation for further research on the dynamic characteristics of the helicopter tail drive shaft system.

For a rectangular cylinder with the width/height ratio of 10, a series of wind tunnel tests with synchronous surface pressure measurement were carried out to investigate the mean, standard deviation, skewness, kurtosis, and correlation coefficient of pressure coefficients under different wind speeds, different initial angles of attack, and different torsional amplitudes.The nonlinear and non-Gaussian distribution characteristics of self-excited forces under large torsional vibration were analyzed.The results indicate that, the mean and standard deviation of pressure coefficients are mainly determined by the initial angle of attack and vibration amplitude, and the influence of wind speed can be neglected.With the increase of vibration amplitude, the separation of airflow is enhanced and the positions of airflow reattachment move to downstream.The pressure correlations enhance with the increasing of torsional amplitude and wind speed.The higher-order harmonic components of the self-excited torsional moment are mainly caused by airflow separation and reattachment.The ratios of higher-order harmonic components increase with the increasing of torsional amplitude.

The high noise that occurs during the operation process of high-parameter control valves in special working conditions is one of the important issues that must be considered in the valve’s parametric design and optimization design.Based on the flow-induced theory, the RNG k-ε  method and BEM were jointly used to simulate and study the influences of elements parameters of a multi-stage steam trap on the sound pressure, distribution and spectrum characteristics of flow induced noises.The results show that the throttling zones, where the pressure pulsation is the strongest, are the main sound source of flow-induced noise; the flow induced noises in the control valves with different sleeve structure parameters; are all of distinct broad spcetrum characteristics; the sound pressure level (SPL) of the noise rises as the sleeve diameter increases, which means that the sleeve with smaller diameter could curb the flow-induced noise better; the SPL decreases first and then  increase as the sleeve clearance increases, when the sleeve clearance is 8 mm, the SPL reaches its minimum 51.02 dB(A).

The prediction of blasting vibration speed and vibration safety control are always the focus of attention in blasting construction.A basic formula was selected as the blasting vibration velocity prediction model, and the parameters K,a,b  were solved based on the principle of least square method.Considering the randomness of blasting vibration, the relative error of blasting vibration velocity (REBVV) was defined.Assuming that the REBVV obeys the normal distribution with the mean value of 0, the distribution model of blasting vibration velocity was deduced by virtue of the transferability of the normal distribution.To improve the utilization ratie of measured data, the relative error variance of generalized blasting vibration velocity was proposed to replace the relative error variance of blasting vibration velocity.By introducing the concept of confidence level in the probability theory, a safety control and evaluation model of blasting vibration was established.Taking the confidence level as 95%, based on the established safety control and evaluation model, suggestions about the blasting construction safety for key controlled sections of the project were provided.

The dynamic vibration absorber (DVA) was proposed to suppress the instability vibration of a rotor/seal system.A model for the rotor/seal system with DVA was established.A numerical method was utilized to obtain the nonlinear characteristics of the rotor/seal system without and with DVA.The critical stability condition was obtained by the Routh-Hurwitz criterion.Then the genetic algorithm was applied to optimize the DVA parameters, and the stability was discussed.The results show that the DVA is effective to change the instability vibration frequency and threshold of the rotor/seal system.The instability vibration can be completely suppressed within a certain range of rotating speed.The DVA can reduce the amplitude of the instability vibration in some range of rotating speed, at which the instability vibration is partially suppressed.