Journal of Engineering and Thermal Sciences
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3-D finite element analysis on shear lag effect of curved box girder under multi-dimensional seismic excitation
Get PDFShear lag effect of curved box girder under multi-dimensional seismic excitation is studied in this paper. Firstly, spatial finite element model is established based on ANSYS, and a seismic wave, which is recorded in second site, is chosen as ground acceleration time history. Secondly, elastic dynamic time-history analysis focused on shear lag effect is carried out, where 4 working conditions, 3-D seismic, longitudinal-vertical seismic, vertical seismic and transverse seismic only, are considered. Thirdly, critical angle of seismic waves is investigated, it is seen that under seismic excitation, there is a prominent shear lag effect on upper flange at mid-span of the curved box girder, and there are also various shear lag effect modes under the different working conditions of seismic excitation. The shear lag under 3-D seismic is severest, normal stress is concentrated on inside upper flange, then that under longitudinal-vertical seismic is less serious, in which case, the stress is appearing within a regional proximity to the junction between webs and flange, the next is under vertical seismic, and the shear lag effect under transverse seismic is most non-prominent. Finally, the numeric results are compared with the experimental results from a vibration table testing, which shows great consistencies
Nonlinear dynamic analysis of a coupled lateral-torsional spur gear with eccentricity
Get PDFIn this study, the dynamic behaviors of gear system are systematically analyzed with coupled lateral-torsional vibration caused by the gear meshing. A 4-degree-of-freedom (DOF) lumped parameter dynamic model for a spur gear, considering gravity, backlash, eccentricity, transmission errors, external excitation, is proposed. Parametric studies are performed to understand the influence of key parameters such as rotational speed ω, backlash b and error fluctuation er on the nonlinear dynamic behavior. The frequency response characteristics of spur gear system show that lateral resonance frequency and torsional resonance frequency simultaneously exhibit in lateral direction. In addition, other nonlinear phenomena including various forms of periodic, quasi-periodic and chaotic vibrations are analyzed. The results show that the nonlinear dynamical behaviors such jump discontinuous phenomena, single-sided impact and double-sided impact are strongly attributed to interaction between backlash, eccentricity and error fluctuant amplitude. Significantly, the appropriate rotational speed and decrease error fluctuant amplitude could effectively control the nonlinear vibration. Whereas the backlash has a complicated effect on the nonlinear dynamical characteristics. The results presented in this paper show that an analysis of the coupled lateral-torsional vibration (CLTV) of the spur transmission gear system. Some research results presented in this paper are useful to dynamic design and vibration control of spur gear transmission system
Study on the diagnosis of rub-impact fault based on finite element method and envelope demodulation
Get PDFIn this paper, the vibration characteristic of the casing under rub-impact condition is analyzed by using finite element method, envelope demodulation and empirical mode decomposition. Firstly, aiming at the structure characteristics of the casing of the rotor system, the finite element model is established by ANSYS software. Modal analysis and transient analysis are carried out in detail. The first six order natural frequencies and corresponding vibration modes are acquired in the mode analysis. The transient response history and time-amplitude curves are obtained in the harmonic response analysis. The vibration characteristics and rule of the casing under rub-impact condition are also presented in the transient dynamic analysis. Secondly, the vibration mechanism analysis of the casing is performed. Since the pulse force due to rubbing fault may lead to casing’s resonance, the envelope demodulation method and empirical mode decomposition (EMD) are utilized to diagnose the rubbing fault. By means of the envelope demodulation and EMD, the stator’s vibration signal is analyzed, and the rub-impact fault diagnosis is fulfilled. Finally, as for the aero-engine, the vibration signal obtained is just the acceleration on casing, and it is of great difficulty to obtain the vibration displacement. Hence, experiment of one-point rub-impact is conducted, and the validity and feasibility of the method adopted are verified by the testing response data. Besides, the casing vibration acceleration signals are analyzed in order to extract the rubbing fault’s features. Results demonstrate that the casing resonance envelope signal is very suitable for detecting the rub-impact fault. It is worth relying that envelope demodulation method and EMD would have a promising application for the rubbing fault diagnosis between the rotor and the casing
A method for modal loss factor estimation based on Gauss-Newton iteration
Get PDFA new approach based on Gauss-Newton iteration is proposed to estimate modal damping. Noise resistance of the proposed method and half-power bandwidth method are analyzed and compared by plenty of simulations with different signal-to-noise ratios (SNR). The proposed method is more accurate and stable than half-power bandwidth method in all SNRs, especially when the noise level is high. If SNR ≤ 30 dB, the proposed method should be used for damping estimation instead of half-power bandwidth method. A damping estimation experiment is carried out with both methods, and the results indicate and verify that there is smaller variability for the proposed method
Dynamic characteristic analysis of two-stage quasi-zero stiffness vibration isolation system
Get PDFA novel two-stage quasi-zero stiffness (QZS) vibration isolator was proposed for the purpose of low-frequency vibration isolation. Firstly, the dynamic model of the vibration isolation system was established; furthermore, the force transmissibility of the system under harmonic force excitation was derived by the averaging method; finally, the effects on the vibration isolation performance caused by excitation amplitude, mass ratio and damping ratio were discussed. Results show that, compared with the corresponding two-stage linear system, two-stage QZS system not only has better isolation performance, but also possesses a wider range of isolation frequency provided that the excitation amplitude, mass ratio and damping ratio is appropriate
Thermal characteristics analysis of the slide carriage system of the X axis based on the thermal contact resistance and the environment temperature change
Get PDFIn the electrical discharge machine (EDM), the slide carriage system of the X axis connects the lathe bed and the ram of the Y axis, its thermal-deformation has a directly effect on machining precision. Based on Solid-works and ANSYS Workbench software to build the finite element model (FEM) of the slide carriage system, the heat generation of the motor on the Y axis, and the frictional heat of the bearing and guide as the main thermal source, there are two cases: applied and no contact thermal resistance (TCR) as the thermal-structure coupling deformation analysis. Established a model of the natural convection heat transfer coefficient with the temperature-change according to the actual measured the temperature curve of workshop and mathematical logarithm principle. The analysis told us that: in the thermal analysis of precision mechanical equipment, heat source comes from the external environment temperature and motor heat production, at the same time, the contact thermal resistance and the natural convection heat transfer coefficient with the temperature-change for the thermal characteristics of the equipment will make an important influence
Reanalysis of the structural dynamic characteristics based on double coordinate free-interface mode synthesis and matrix perturbation method
Get PDFThe design of key parts of civil engineering structures often undergo several modifications to ensure that the usability of entire structure meets the requirements. Dynamic characteristics are important parameters to evaluate the performance of structure, so it is necessary to calculate dynamic characteristics after each modification. This paper proposes a new method to calculate the dynamic characteristics of the structures rapidly after each modification. According to this method, the structure is decomposed into relatively simple substructures, and the dynamic characteristics of the whole structure can be obtained by the modal synthesis method (MSM). When a substructure has been modified, its dynamic characteristics can be calculated by using the matrix perturbation method (MPM). The proposed method is applied to the numerical calculation of a Y-shape continuous beam bridge, and the results show that the method is correct and efficient
A concept of technology for non-destructive testing of modernized freight cars based on analysis of their vibration
Get PDFPaper presents a part of research concerning freight cars modernization. The main causes of damage of freight cars plating are chemical interactions of the carried material and the car body as well as mechanical damages. The introduced structural change consists in the use of composite panels to protect the steel plating of a car body. Therefore, it is necessary to carry out a series of studies. In this paper results of virtual simulations of the freight car vibration during its motion as well as verification of a possibility to create a method to verify technical condition of the freight car during its exploitation based on excited vibrations are presented
Dynamics of tripod drive with elastic self-sustaining transmission
Get PDFThe article describes a mathematical model of dynamics of electromechanical drive with elastic transmission gear. A motor is connected to the tripod actuating links by self-sustaining transmission. The analytical conditions of drive dynamic seizure absence have been obtained
Investigation of the quality of arrayed data transmission through wireless networks
Get PDFThis paper investigates the quality of communication in wireless networks and connection quality evaluation on the basic parameters of indoor and outdoor applications with produced experimental data. The analysis of the influence of radio waves propagation conditions of in the wireless communication networks were performed at the different types of medium. Comparison of the radio waves propagation indoors and outdoors has been done. Also, the effect of the obstacles of various materials on radio propagation was performed