Journal of Vibroengineering
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A CFD study of IGV vane number on hydraulic characteristics and pressure pulsation of an is centrifugal pump
Get PDFVane number is an important parameter of IGV device, which indirectly affects hydraulic performance and pressure pulsation characteristics of the attached pump. In this study, based on an IS pump, the influences of vane number on hydraulic performance and pressure pulsation characteristics were considered. Four set of IGV devices were generated to assemble to the pump with 5, 6, 7 and 9 vanes, respectively. Then the three-dimensional unsteady flow fields were simulated using RNG k-ε turbulence model and sliding mesh by Fluent-16.0. The numerical results showed good agreement with the experimental data, which validated the numerical models. The effects of vane number on pump head and efficiency are different. 6 vanes IGV device can produce higher head while 7 or 9 vanes can bring about higher efficiency. Similarly, the influences of vane number on pressure pulsation in time domain and frequency domain are also complex. 6 vanes IGV device can remarkably decrease power spectral density at all flow rate conditions, but 7 vanes IGV device can improve pump pressure pulsation characteristics and realize better hydraulic stability. Therefore, it is hard to determine the best vane number, but 6 vanes IGV device is suggested for engineering application to obtain better hydraulic performance
Stability and nonlinear self-excited friction-induced vibrations for a minimal model subjected to multiple coalescence patterns
Get PDFIn certain industrial applications with frictional interfaces such as brake systems, the friction-induced vibrations created by coupled modes can lead to a dynamic instability and thus to an important deterioration in the operating condition. As a result, they are considered as a source of critical engineering problem. In addition, the presence of the nonlinearity makes necessary the consideration of the nonlinear dynamic analysis in order to explain clearly the complexity of the contribution of different frequency components due to unstable modes in the self-excited friction-induced vibrations, to get a design as reliable as possible and to avoid catastrophic failure during the operation phase of the mechanism. The present paper is based on previous works of Sinou and Jézéquel and extends them to include a developed damped four-degree-of-freedom system with frictional contact and spring cubic nonlinearities. Its essential goals are to analyze numerically the mode-coupling instability of the four-degree-of-freedom system owing to the friction between the surfaces of contact and to predict its nonlinear dynamic behavior. The numerical study of stability for the static solution of the mechanical system is performed by applying the complex eigenvalue analysis of the linearized differential equations of motion and by identifying the Hopf bifurcation points as a function of the coefficient of kinetic friction. Depending on the Runge-Kutta time-step integration scheme and the fast Fourier transforms, quantitative and qualitative nonlinear phenomena related to self-excited friction-induced oscillations and limit cycle evolutions are observed and discussed for various friction coefficients
Vibroacoustic technique for the fault diagnosis in a gear transmission of a military helicopter
Get PDFThis article presents the results of laboratory studies of a two-stage gear transmission regarding the process of intentionally increasing damage of its tooth. Also, this study discusses the construction of a gear transmission of a military helicopter on the basis of basic kinematic results of its vibroacoustic signals. What is important, the article describes the aim of laboratory stand, which was to authenticate the applied algorithms of technical condition evaluation of combat helicopter. Also, the process of deepening the damage to the tooth of the gear transmission was described. It was made with the use of stable ranges of rotational speed of measurements of transmission casing in three mutually perpendicular directions and have been referred to the condition without damage. In the article, diagnostic criteria are also determined for the assessment of technical conditions of military helicopter equipped with a gear transmission
A fuzzy logic controller for optimal structural control using MR dampers and particle swarm optimization
Get PDFControl devices can be used to dissipate the energy and attenuate undesirable vibration on engineering structures. Recently, to mitigate the response of structures during the earthquakes and high intensity winds, semi active control has been widely used. MR dampers are semi active control devices that are managed by sending external voltage supply. A new adaptive fuzzy logic controller (FLC) is introduced to manage MR damper intelligently. Furthermore, a novel evolutionary algorithm of particle swarm optimization (PSO) was used to optimize the placement and the number of MR dampers and sensors in the sense of minimum resultant vibration magnitude. Numerical efforts were considered to validate the efficiency of proposed FLC. In designer’s point of view, the proposed PSO-FLC controller can find the optimal solutions during a reasonable number of iterations. Finally, results demonstrate that proposed PSO-FLC controller could find the appropriate control force and attenuates the excessive responses in several buildings
Modeling and active disturbance rejection control for sequential airdrop operations
Get PDFWith the assumption t at the motion acceleration of the cargo is unknown, the dynamic model that accords with the engineering practice of sequential cargo airdrop operations is derived by using the separation body method, which can describe the impact of the sequential moving cargos on the flight safety and airdrop-mission capacity. On this basis, a novel flight control method is designed based on the active disturbance rejection control (ADRC) theory. the system is decoupled and linearized through the nonlinear state error feedback; the total unknown disturbances, including unmolded dynamics and uncertainty, are estimated and compensated real-timely by the extended state observer. Moreover, with the consideration of the time-delay system, the ADRC is improved to enhance the accuracy and rapidity of the control system. Simulations are carried out under the condition that one transport aircraft performs sequential airdrop operations. The results verify that the desirable performance and robustness have been achieved and the proposed control method is quite competent for the sequential airdrop operations
Influence of different materials for artificial auditory ossicle on the dynamic characteristics of human ear and research on hearing recovery
Get PDFThis paper used PATRAN/NASTRAN software to establish a three-dimensional finite element model of human ear and conduct dynamic simulation of hearing system. The correctness of the finite element model was verified through analyzing the tympanic membrane displacement of normal human ear under the sound pressure of 80 dB and comparing with the experimental data. Based on the verified model, this paper qualitatively and quantitatively studied and compared the influence of artificial auditory ossicle with 7 kinds of common materials (titanium, stainless steel, teflon, porous polyethylene, alumina ceramic, EH composites and hydroxylapatite ceramics) on the sound conduction of human ear and the effect of postoperative hearing recovery under different sound pressures (50 dB, 80 dB, 105 dB and 120 dB) at 100-10000 Hz. Results showed that the hearing recovery of human ear had the same effect after replacing artificial auditory ossicle under different sound pressures with different frequency. At different frequencies with the same sound pressure, the postoperative hearing of human ear had different effects after replacing different materials of artificial auditory ossicle. Artificial auditory ossicle of hydroxylapatite ceramics, stainless steel and alumina ceramic had better effect on sound conduction at low frequencies, while artificial auditory ossicle of porous polyethylene and teflon had better effect on sound conduction at high frequencies. Under different sound pressures, replacing artificial auditory ossicle with 7 kinds of common materials showed little difference in the hearing recovery of human ear at each frequency band and had a stable influence on the sound conduction of human ear
Bending fault evaluation for the HP-IP rotor system of the nuclear steam turbine based on the dynamic model
Get PDFWith considering the unbalance mass-fluid film bearings-rotor elements, a dynamics model for the nuclear half-speed 1000 MW saturated steam turbine with No. Dongfang HN1089 is constructed. By solving of the Reynolds Equation and the dynamics model, the oil pressure distribution and dynamic coefficients of the fluid film bearings, and the unbalance response of the rotor, are obtained. The method for evaluating the bending fault based on the dynamics model is proposed, in which the bending parameter is transformed as the unbalance mass. A case on the bending fault evaluation for HN1089 is carried out. The results show that the response sensitivity of HN1089 on the unbalance mass is about 1/6 that of the thermal power units with the same capacity (1000 MW); and it is difficult to decrease the excited response from the bending fault even to add the maximum unbalance mass. In actual, the removing stress in the partial zone and turning method are applied to deal with the HP-IP rotor bending fault, and the response of the repaired rotor is 0.033 m by the actual field test. The results show the model and the method for evaluating the bending fault are accurate and reasonable, which will provide the important theoretical guide for fast and accurately dealing with such bending fault in the steam turbine rotor system
A new improved Kurtogram and its application to planetary gearbox degradation feature analysis
Get PDFBecause of various advantages of planetary transmission system, it has been widely used in modern industry. And study on planetary gearbox degradation feature analysis method has important significance for mechanical system prognostics and health management (PHM). In order to analysis the degradation characteristic of planetary gearbox, Energram is proposed in this paper based on Kurtogram. Kurtogram is used for finding the optimal frequency band to rotating machinery fault diagnosis by calculating kurtosis. Similarly, Energram is used to show the energy trend of each frequency band by calculating energy, and arithmetic Energram is used to show the change of frequency band energy. The principle and application of Energram and arithmetic Energram are described by experimental data examples in this paper. A detailed study of planetary gearbox degradation characteristics is expressed in case study, which including Energram, arithmetic Energram and four particular comparative analyses. And the conclusions of each comparative analysis are given
Research on the characteristics of dynamic behavior of basilar membrane in spiral cochlea
Get PDFThis paper used PATRAN software to establish a three-dimensional spiral cochlear model according to the actual human ears, combined with NASTRAN software to conduct a harmonic response analysis on it and studied the impact of curvature on the amplitude of basilar membrane when spiral basilar membrane was excited. The computational result of the model was consistent with the experimental result reported by previous researchers, which verified the correctness of the model established by this paper. Research found the change rule of ratio of outer radius amplitude to inner radius amplitude in the longitudinal direction of basilar membrane and the change trend of the horizontal amplitude with frequency along the basilar membrane. At high frequencies, it was found that curvature had a great influence on the horizontal amplitude of basilar membrane. In the meanwhile, the structural form of spiral basilar membrane and its change trend with frequency at the position of 12 mm reflected the basilar membrane’s amplification for sound intensity. Regarding the controversial issue in the academic at present, does travelling wave exist in basilar membrane? The theory of travelling wave in basilar membrane was supported by a lot of phase accumulation and delay as shown in phase diagram
A new method for optimizing the parameters of torsional vibration dampers
Get PDFTorsional vibration dampers (TVDs) are essential components for reducing the torsional vibration of a vehicle power transmission system (VPTS). This paper presents a new parameter optimization method for designing TVDs. The method combines the modal inertia and energy methods by adjusting the modal inertia method using an adjustment factor that is optimized using the energy method. The optimization of TVD parameters seeks to minimize the maximum torsional elastic potential energy of the rear axle near the resonance speed, so that the design variables can be optimized by a manual search process. The proposed method is employed to optimize the parameters of single-stage, two-stage parallel, and two-stage series TVDs coupled to a model VPTS. The damping effects of TVDs optimized by the modal inertia method, the energy method, and the proposed method were compared and analyzed, and the calculation efficiencies of the methods were evaluated. Results show that the proposed method provides better damping effects than the modal inertia method, and also provides far better computing efficiency than the energy method