Journal of Vibroengineering
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Investigation of armature-rail interaction in linear electromagnetic launcher
Get PDFThe behavior of the electromagnetic (EM) launcher depends on the structure of the construction. The dynamics of the EM construction and the local effects of the EM forces are topical issue in exploring and designing EM launcher device. This paper is aimed to refine mechanical behavior of the open barrel design EM launcher structure due to EM force evaluated by EM analysis based on three different shapes of armatures. The 3D finite element EM model was generated and the J×B force density distribution in the rail volume was calculated. The results of EM model calculations were applied further as input for structural mechanics model. The results of the finite element EM and mechanical analysis of the armatures influence are presented
Non-probabilistic analysis of a double-disk rotor system with uncertain parameters
Get PDFVibration is a major issue in rotor systems. Due to the presence of material property dispersions, manufacture or assembling errors and time-varying working status, rotor systems are always subject to uncertainties. The uncertainties should be taken into consideration to understand the dynamic characteristics of rotors more thoroughly. In this study, interval analysis is carried out to investigate the non-probabilistic characteristics of a double-disk rotor with uncertain parameters. The uncertainties are modeled as uncertain-but-bounded variables due to insufficient essential information to define their precise probabilistic distributions. The deterministic analysis model is derived by the finite element method (FEM). The accuracy and effectiveness of the proposed method in solving uncertain rotor problems are validated by comparative study with the Monte Carlo simulation (MCS). Several cases where different physical parameters are regarded as uncertain are investigated and the dynamic response bounds are obtained. Simulations suggest that uncertainties have significant influence on the dynamic characteristics of the rotor system. Multi-source uncertainties propagation can cause heavy vibrations in mechanical systems
Bearing incipient fault diagnosis based upon maximal spectral kurtosis TQWT and group sparsity total variation denoising approach
Get PDFLocalized faults in rolling bearing tend to result in periodic shocks and thus arouse periodic responses in the vibration signal. In this paper, a novel fault diagnosis method based on maximal spectral kurtosis tunable Q-factor wavelet transformation (TQWT) and group sparsity total variation denoising (GS-TVD) is proposed to address the issue of bearing incipient failure. Firstly, the range of Q-factor was pre-selected according to the spectral distribution of impulse component, and bearing vibration signal was transformed by the TQWT method. Then, the spectral kurtosis of each scale transform coefficients was calculated, and the optimal Q-factor and decomposition scale can be selected according to the kurtosis maximum principle. In order to remove the interference components and high-frequency noise from the reconstructed vibration signal generated by inverse TQWT, the GS-TVD approach is employed, thus the cyclic periodicity characteristic and transient impulses can be detected obviously. The two cases experimental results indicate that the proposed technique is more effective and applicable for bearing incipient fault diagnosis compared with traditional method
Dynamics analysis on barrel considering the temporal and spatial distribution of propellant gas by numerical simulation
Get PDFIn terms of the excitation of barrel vibration on the motion modality of projectile during interior ballistic period, a finite element model considering the mutual coupling between projectile and barrel was established to study the dynamics. In consideration of the effects of propellant gas on dynamics response based on vibration theory, the real loading condition of propellant gas acting on barrel was defined by user-defined VDLOAD subroutine, which solved the problem of inaccurate loading and even the failure of loading of gases pressure in previous simulations. Simultaneously, the loading boundary condition was directed by the coupling process of powder combustion and projectile motion, modeled by the user-defined VUAMP subroutine. The dynamics responses of barrel with and without the radial effect of gas pressure were obtained. Moreover, with the aid of realization of radial loading of barrel, the influence of the deviation of mass center of barrel on its dynamics response was also investigated. The obtained results showed that the radial effect of gas pressure causes more violent dynamics responses and plays a non-negligible role in simulating artillery firing process. The dynamics response of barrel is sensitive to the deviation of mass center and the response increases with the increasing value of deviation
Remaining useful life prediction of the ball screw system based on weighted Mahalanobis distance and an exponential model
Get PDFThe ball screw system is one of the crucial components of machine tools and predicting its remaining useful life (RUL) can enhance the reliability and safety of the entire machine tool and reduce maintenance costs. Although quite a few techniques have been developed for the fault diagnosis of the ball screw system, forecasting the RUL of the ball screw system is a remaining challenge. To make up for this deficiency, we present a model-based method to predict the RUL of the ball screw system, which consists of two parts: health indicator (HI) construction and RUL prediction. First, we develop a novel HI, weighted Mahalanobis distance (WDMD). Unlike the Mahalanobis distance (MD), which is constructed by fusing original features directly, the WDMD is formed with some selected features only, and the features are weighted before integration. Second, an exponential model is developed to describe the degradation path of the ball screw system. Then, the particle filtering algorithm is employed to combine the WDMD and the degradation model for state estimation and RUL prediction. The proposed approach is verified by a dataset obtained from an experimental system designed for accelerated life tests of the ball screw system. The results show that the WDMD has a more apparent deterioration trend than the MD and the proposed exponential model performs better than both the linear model and the nonlinear model in RUL prediction
Multi-mode soft switching control for variable pitch of wind turbines based on T-S fuzzy weighted
Get PDFVariable pitch control is an effective way to ensure the constant power operation of the wind turbines over rated wind speed. The pitch actuator acts frequently with larger amplitude and the increasing mechanical fatigue load of parts of wind turbines affects the output quality of generator and damages the service life of wind turbines. The existing switching control methods only switch at a certain threshold, which can result in switch oscillation. In order to deal with these problems, a multi-mode soft switching variable pitch control strategy was put forward based on Takagi-Sugeno (T-S) fuzzy weighted to accomplish soft switch, which combined intelligent control with classical control. The T-S fuzzy inference was carried out according to the error and its change rate, which was used to smooth the modal outputs of fuzzy control, radial basis function neuron network proportion integration differentiation (RBFNN PID) control and proportion integration (PI) control. This method takes the advantages of the three controllers into consideration. A multi-mode soft switch control model for variable pitch of permanent magnet direct drive wind turbines was built in the paper. The simulation results show that this method has the advantages of three control modes, switch oscillation is overcome. The integrated control performance is superior to the others, which can not only stabilize the output power of wind turbines but also reduce the fatigue load
Study on air-cushion isolation control of concrete dam and its anti-cracking effect
Get PDFThe seismic problem of concrete dams has long been a difficult issue facing academic and engineering researchers. Traditional anti-seismic and isolation measures produce unfavorable results in hydraulic structures. However, the air-cushion seismic isolation technique represents a new development orientation for the anti-seismic method of concrete dams. To study the isolation and anti-cracking effects of the air-cushion, the gas-liquid-solid tri-phase coupling numerical model of the air-cushion isolation control of high arch dams is presented in this paper, in which the cracking behavior of concrete is considered. A 300 m level dam was simulated numerically under three different seismic intensities. The results show that the air-cushion reduces the hydrodynamic pressure significantly. The maximum hydrodynamic pressure is reduced by more than 70 %, and the acceleration of the dam crest is reduced by more than 50 % with a 1 m air-cushion. The reduction in hydrodynamic pressure and dam acceleration increases with increasing seismic intensity. In addition, the air-cushion decreases the cracking range of the dam body effectively. Thus, the isolation effects of the air-cushion are remarkable
Experimental and numerical study of the behavior of shallow rectangular tunnels
Get PDFThe behavior of an underground structure under dynamic loading is affected by many factors such as shape, depth and stiffness of the structure as well as the frequency content of the input motion. Scarcity of experimental/field investigations precludes proper understanding of these parameters’ effects on the seismic behavior of aforementioned structures. In this study, the effects of input motion along with structural stiffness properties on seismic behavior of rectangular tunnels are investigated. Three reduced-scale 1 g shaking table models were constructed in 1/48 scale. Tests were carried out in the shaking table facility at the University of Tabriz on model tunnels of the rectangular section of the shallow Tabriz subway tunnel, using input motions of different amplitudes and frequencies. In addition, a numerical study was done using the coupled scaled boundary finite element-finite element (SBFE-FE) method. A good agreement between the numerical model and the results of the experimental test was achieved. Using the shaking table test, the accelerations and bending moments of the tunnel lining were measured. The results show that tunnel lining stiffness affects the acceleration response of the ground. A parametric study by the numerical approach was presented and effects of the variation of elastic modulus and mass density of the soil were evaluated
Analysis on monitoring and controlling techniques about blasting vibration effect of open channel in Taishan nuclear power station
Get PDFThe blasting for bedrock excavation on land for open channel project has a great influence on lock gate in Taishan Nuclear Power Station, therefore, based on blasting vibration monitoring data, the attenuation law of blasting vibration signal has been studied through regression analysis of practical test data by Sadaovsk empirical formula and corresponding time-frequency characteristics was analyzed by Empirical Mode Decomposition based on Hilbert-Huang transform. As for those monitoring data, the results of blast vibration velocity for vertical direction are generally larger than horizontal radial and horizontal tangential direction in the near field of blasting source and the peak particle velocity of vertical direction is usually lower than horizontal radial and horizontal tangential direction in the far field of blasting source; at the same time, their main vibration frequency mostly vary from 10 Hz to 80 Hz which is much higher than natural frequency of lock gate and is beneficial to structural safety and stability of surrounding rock mass for reducing the probability of resonance. To ensure the safety of lock gate, it is of great significance to control maximum explosive weight per delay in advance for different distance from monitoring point to the explosion source according to Safety Regulations for Blasting (GB6722-2014), which shows the excellent effect on blasting damage control of the lock gate and surrounding rock mass. The results from the analysis can be for reference to similar blasting design and blasting construction
Bifurcation and chaos analysis of a gear pair system with multi-clearance
Get PDFIn order to investigate the characteristics of bifurcation and chaos for a spur gear pair system, a three-degree-of-freedom nonlinear dynamic model with multi-clearance is established, in which time-varying meshing stiffness, static transmission error, gear backlash and bearing clearance are comprehensively taken into account. Through introducing a relative generalized coordinate, the dimensionless dynamic equations of motion of system are derived and then solved by using Runge-Kutta numerical integration method. And the bifurcation and chaos features of gear pair are systematically analyzed and discussed from bifurcation diagrams with meshing frequency, gear backlash, bearing clearance and damping ratio as control parameters under different loaded conditions. Meantime, with the help of Poincaré map and phase diagram, the motion forms of system are accurately identified. The analysis results reveal that as meshing frequency increases, the system shows various types of motion states which contain periodic motion, quasi-periodic motion and chaotic motion. Similarly, with the increasing of gear backlash, the system undergoes complex motion forms under lightly loaded condition, whereas it is only in period-one motion state under heavily loaded condition. Furthermore, the system motion state is gradually switched from chaos to periodic or quasi-periodic motion under lightly loaded condition when bearing clearance changes. However, under heavily loaded condition, the bearing clearance has a weak effect on dynamic behavior of the gear system. Apparently, the system tends to be more stable under heavily loaded condition than that under lightly loaded condition. In addition, the growing damping ratio can effectively suppress the chaotic behavior and control nonlinear vibration of gear system. The research results provide useful guidance for dynamic design and vibration control for gear set