Abstract:In order to improve the kinetic stability of quadrotor unmanned aerial vehicles, the effect of mechanical and structural parameters on the system stability was studied. The process during yawing state is taken as an example for investigation. According to the calculation process of Lyapunov exponents based on the dynamical model, the key mechanical and structural parameters significantly influencing the dynamic stability were obtained. The method of Lyapunov exponents was adopted to establish the relationship between such key parameters and the motion stability, which was utilized to design the mechanical and structural parameters, and then to optimize the stability control system. Finally, the theoretical analysis was validated through experimental tests. Compared with the Lyapunov′s second method, the main advantage of this method is that it is easy to construct the process of calculating exponent, which makes the stability analysis for complicated nonlinear systems possible.

Abstract:As one of the most widely used manufacturing technologies, turning has been a hot topic regarding requirements for high efficiency, high quality and high precision. This paper presents stability analysis of 1 DoF, 3 DoF, and 9 DoF turning models in the parameter plane of cutting width and spindle speed. The obtained stability charts show that when realistic damping is considered, the stability region predicted by 1 DoF model is more conservative than by higher DoF models in relatively low speed range, while in high speed range higher DoF models give much smaller stability region due to the presence of higher order vibrations.

Abstract:The existence of toothside backlash in gear transmission system induces rich nonlinear dynamical behaviors. Considering the nonlinear dynamic model of a two-degrees-of-freedom gear transmission system, the bifurcation and chaos of the system were analyzed by using the simple cell mapping method. Firstly, the global characteristics of the nonlinear gear system were analyzed, and the attractor and attracting domain were obtained. The results show that, with changing excitation frequency, the system exhibits coexistence of multiperiodic solutions and coexistence of periodic and chaotic motions. Furthermore, the phase diagram of the trajectory of the system was compared with that of the Poincaré section. It is shown that, under different initial conditions, the system presents different periodic or chaotic motions. Therefore, based on the numerical results by the simple cell mapping method, ideal system responses, such as periodic motions, can be realized by reasonably selecting the initial conditions, when certain parameters make the system undergoes complicated responses.

Abstract:The global characteristics of transient response of a singledegreeoffreedom shape memory oscillator under rectangular pulse excitation were investigated. The equation of motion was established by using a polynomial constitutive model to describe the restitution force of the oscillator. Here, the response of the oscillator under rectangular pulse excitation was divided into two stages. The first stage was the attenuation vibration under an external constant force excitation, while the second stage was the attenuation vibration without any external force excitation. The number of equilibrium points was discussed, and the phase plane and time history of the shape memory oscillator on different conditions were given. Finally, numerical solutions were presented to validate the theoretical results.

Abstract:For the rocket pressurization system,safety pneumatic valve is a security device which protects the propellant tank from overpressure. On a ground test,the main valve revealed a phenomenon of flutter as the valve opening or closing,which may induces damage to some parts,what′s worse,threatens the product performance. To find out the cause of valve flutter, based on fluidstructure interaction of N-S dynamic grid flow equation of and nonlinear contact rigid body motion control equation,aerodynamic load is computed by Realizable k-ε turbulence model and explicit dynamic algorithm. The mechanism of valve flutter phenomenon is pressure fluctuation coupling with structural frequency and piston rod produces plastic deformation under impact response with position bolt. An improvement measure to improve structural frequency is increasing the size of moving parts. Following with ground test verification,the result shows that the measure being taken can suppress the safety pneumatic valve flutter effectively,which has practical engineering value.

Abstract:A micro piezoelectric energy harvesting is designed based on a bistable plate that is twolayered square plates fixed in the midpoint of the plates and free at four edges. Based on strain gradient theory, considering the size effect, a micropiezoelectric element is defined using Userdefined Finite Element Subroutine (UEL) in ABAQUS. With the thermalforceelectric coupling analysis method, it is found that there are different deformation shapes under different excitation frequencies. The analysis nonlinear dynamic shows that the structure can change more vibration energy to electric energy before its first natural frequency, and there exists snapthrough behavior in its frequency response range. The optimum working frequency and maximum output voltage are concluded for the micro piezoelectric energy harvesting. The research findings have an important guiding significance for design of micro piezoelectric energy harvesting.

Abstract:Experimental results of dynamic features of traveling wave of vortex-induced vibration(VIV) of a long slender cylindrical structure were given. The experiments were carried out in a water tank. In order to observe the occurrence of travelling wave in the tank of limited width, the aluminum pipe of 0.006 m in diameter and 3.31 m in length was used, so the aspect ratio of model is over 500. The structure was dragged by a trailer whose velocity can reach 1.5m/s. The weight of 2.5kg was employed to provide the end tension. A method that was used to assess the contribution of traveling in whole vibration waves was introduced. The traveling wave ellipse was employed to fit the distribution of the amplitudes of vortexinduced vibrations along the length of the model. The experimental results show that, the traveling wave appeared over a given velocity range and when the velocity was 0.9m/s, the traveling wave was notable. Except the velocity is 0.9m/s, the traveling wave ratio is around 0.2. Result showed the travelling wave under low mode was observed, this is beyond the limit defined by travelling wave criterion. Finally based on observation of experimental data and theoretical analysis, a new traveling wave formation phenomenon was given.

Abstract:In order to study the dynamic characteristics of the rotor system under unbalanced-misalignment, a dynamic model of the rotor-roller bearing coupling system was established. Consider the parallel misalignment of the gear coupling, and the center of mass and centroid of the rigid turntable are not concentric. Using the Lagrange method, we deduced the dynamic equations of the system. Moreover, numerical analysis is used to analyze the influence of the different misalignment of the coupling, the quality of the different couplings participating in the vibration and the different supporting conditions on the dynamic characteristics of the rotor system. The calculation results show that due to the misalignment, when the rotational speed of the rotor system reaches onehalf of the critical speed, the lateral vibration displacement of the disk increases significantly. That is, the misalignment will make the system at onehalf critical speed. Produce an unstable area. When the rolling bearing is used, as the degree of misalignment increases, the rotational speed corresponding to the maximum amplitude of the rotor in the unstable region gradually increases, and when linear support is used, such a phenomenon has not occurred. As the quality of the coupling participates in the vibration, the vibration of the system at onehalf of the critical speed becomes more and more severely.

Abstract:The synchronization of biological neural networks plays an important role in the information processing of brain. In this paper, the dendritic-integration effect in Hodgkin-Huxley neuronal network was considered to obtain a modified DHH (Dendritic-integration-rule-based HH) neuronal network model,and the firing and synchronization characteristics of the network were studied. Firstly,taking a coupled system of three inhibitory neurons as an example,it is found that the dendriticintegration effect enhances the firing threshold of neurons. Then a globally coupled inhibitory neuronal network and a globally coupled excitatory neuronal network were established, respectively,which show that large coupling strength not only induce the networks to achieve nearly complete synchronization but also greatly affect the firing amplitudes of the networks. Interestingly,when the integration coefficient is set to be a certain value,the inhibitory neuronal network achieves the highest extent of synchronization,while the excitatory neuronal network achieves the lowest extent of synchronization.

Abstract:Based on the white noise random vibration experiment of an 8story steel shear building model, the structural undamaged and 8 damaged cases were analyzed from the structural acceleration responses′ mean, skewness, kurtosis, probability density function(PDF) and cumulative distribution function(CDF) respectively. The results demonstrated that the difference of skewness and kurtosis is not obvious to structural damage, but the acceleration probability density function could be used for preliminary damage identification to determine whether the damage has happened or not, and the statistical characteristics of variance could locate the damages.

Abstract:An improved Lorenz-like system was constructed for weak harmonic signal recognition in strong noise. Applying the law of large numbers, the thresholds were calculated from the bifurcation diagrams, and the mode of statistical data was taken as the critical value. The influence of the noise on the thresholds was also revealed. The amplitude of the weak harmonic signal was identified by the threshold difference of the change in the number of attractors detected before and after adding the weak harmonic signal to the system. The results showed that the reliability and accuracy was 89.5% and the minimum signal-to-noise ratio(SNR) was -33dB. Compared to the Duffing system and the controlled Lorenz-like system, the improved Lorenz-like system had the advantages of higher threshold reliability, lower SNR and lower detection threshold, which was more suitable for identifying signal parameters in strong noise. Additionally, the theoretical results were validated by the analog circuit of the improved Lorenz-like system created by Multisim software.

Abstract:For the combined spacecraft consisting of the servicing spacecraft and noncooperative target, the measured angular rate signals of the combined spacecraft are often affected by large noises, which will influence the subsequent control accuracy seriously. Due to the unknown inertia tensor of the noncooperative target, the signal cannot be effectively denoised using model information. To solve the abovementioned problem, an angular rate signals denoising method of the combined spacecraft based on the deep learning method is proposed in this paper, which do not require the model information in advance, and is absolutely datadriven. Based on the deep learning, the generative process of the training data which is needed for angular rate denoising is firstly presented, and then a deep network model for angular rate signals denoising of the combined spacecraft is constructed, including the methods of optimization and parameter initialization of the model. Finally, denoising effects are compared between the proposed method and the wavelet denoising method using test data. The result shows that the proposed deep learning method has a better denoising effect than the wavelet method.