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Dynamic response prediction of non-obstructive particle damping using principles of gas-solid flows
Get PDFParticle damping is a kind of passive and strongly nonlinear damping for energy dissipation. Many researchers have expended huge amounts of effort and time to study internal mechanism of particle damping. However, there is not a systematic and feasible approach for estimating damping performance of non-obstructive particle damping (NOPD). In this paper, we performed studies to mathematically evaluate the damping effect of particle damping based on principles of gas-solid flows. In consideration of the structural characteristics of NOPD which granular materials should be filled into sealed cavity of vibrating structure and the damping act on lateral and bottom of holes in NOPD technology, the gross damping is divided into lateral damping and bottom damping by Janson's theory of stress change direction. And the damping coefficients are compiled into a plug-in by MATLAB and are invoked in FEM software by enterprise integration kits of COMSOL. Meanwhile the frequency domain and time domain analysis of the experiment are used to verify the prediction accuracy of dynamic vibration response of an aluminium cantilever beam which ONPD is imposed at the free end with different packing rate and granular material, the result indicate that the mathematical model has excellent performance to predict the dynamic vibration response of NOPD. Then, the relationship damping effect with the particle filling ratio, particle density and length-diameter ratio of the hole is also researched using co-simulation, it should be noted that larger packing rate and particle density, smaller length-diameter ratio of the hole can play excellent damping effects in NOPD
Dynamic characteristic analysis of a roller bearing rotor system
Get PDFIn order to study the dynamic characteristics of a rotor system incorporated with roller bearings, a detailed finite element model of the rotor system was established. Both the roller bearings and pedestals were considered. Then investigations on dynamic characteristics of the rotor system were conducted, in which critical speeds and unbalance response of the rotor system were obtained and analyzed. Following conclusions can be reached from the numerical results: 1) the second and third critical speeds of the rotor system are 25260 rpm and 113400 rpm, both of which are outside of the operating speed range 31800 rpm-55320 rpm. 2) Within the operating speed range 31800 rpm-55320 rpm, unbalance response of both the centrifugal impeller and the turbine disk are smaller than the corresponding clearances. However, with increasing rotational speed, amplitude of the unbalance response for the centrifugal impeller increases while that of the turbine disk decreases
Effects of oil film properties on roller bearing with light loads under various slip factors
Get PDFIn this paper, ideal and general kinematics and models of roller bearing were built, and the oil film thickness for a roller bearing under a light load was analyzed with different slip factors. And then a new method to calculate the oil film thickness by considering a double slip ratio was developed, and the effects of different slip factors such as the slip ratio, inner ring speed, and radial load on the oil film thickness were investigated systematically. Under a zero slip ratio, the results showed that the film thickness increases with the inner ring speed. The radial load shows the reverse trend, and different slip factors affect the oil film properties differently. In the case with double slip ratio, the results showed that the film thickness slightly decreases as the roller slip ratio increases, whereas the cage slip ratio shows the reverse trend. The roller and cage slip ratios have different effects on the oil film thickness. The oil film distribution is affected by the combined action of the two slip ratios, the inner ring speed, and the radial load. The cage slip ratio can often be considered to be the main factor for calculating the oil film thickness
Vibration and control research of pipe penetration piece
Get PDFThe concealment capability of submarine is seriously restricted by the vibration of pipe penetration piece which is an important obstacle to the development of ‘quiet submarine’. In this paper, the characteristics and structures of pipe penetration piece are analyzed. Combining with domestic and foreign achievements, the active and passive methods of piping vibration reduction were introduced, and the measures of piping vibration isolation were elaborated. It provides reference for the vibration control of pipe penetration piece
Studying the effects of earthquakes near and far fault region on seismic behavior of dual frame equipped with viscous damper
Get PDFThe effects of strong earthquakes in the past years show that the acceleration of near fault earthquake, for having impact motion with long periods at the beginning of the record, “exerted” have significant differences with far-fault earthquakes. Adverse effects of such earthquakes increases by approaching the main time of period of structures to period of these earthquakes. Nowadays using energy dissipation systems, in order to reduce the vibrations of the structure has been very common. Such these energy dissipation systems can be noted viscose dampers that by having hysteresis loops of fat greatly increase energy loss in buildings. In this study, the number of dual-steel frames equipped with nonlinear viscous dampers and by applying records seismic near and far fault to the frames of 4, 6, 8 and 10 floors, behavior and response of these types of frames by nonlinear analysis and in Perform 3D software is evaluated
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
Non-linear dynamic analysis of reinforced concrete bridge columns under vehicle impact loadings
Get PDFA 3D nonlinear impact analysis was performed for reinforced concrete bridge columns under truck impact loadings. Three different boundary conditions were considered to investigate the effect of superstructures on the integral column during impact. Fixed bottom conditions and restraints in the loading direction at the top of the column (Model I) showed the largest damaged area. The dominant failure mode of the column was shear. However, Model II, which is equivalent to Model I with the top released, showed less damage, and the dominant failure modes were flexure rather than shear. In Model III, in which the effect of featured the superstructure was considered, the shear and flexural damage to the column were reduced due to the movement of the superstructures
Nonlinear dynamic characteristic of the spindle-cutter system
Get PDFA nonlinear dynamic model of spindle-cutter coupling system under cutting force, which takes into account the cutter stiffness and the nonlinearity of bearing clearance, is established. Analysis of the cross-section of a two-flute end mill is conducted to determine cutter stiffness. Then, the calculated cutter stiffness is introduced into the nonlinear dynamic model of coupling system. In the modeling of cutting force, the cutting width takes into account the cutter tip displacement. Moreover, nonlinear dynamic characteristics of spindle-cutter coupling system are studied and the effects of bearing clearance on the response of cutter tip are discussed as well, considering unbalanced force. The numerical results show that the bearing clearance strongly affects the equilibrium position. With different values of bearing clearance and rotation speed, the responses of cutter tip exhibit periodic, quasi-periodic and chaotic characteristics. Dynamic characteristics of spindle-cutter system depends on the bearing clearance and rotation speed. The proper bearing clearance and rotation speed should be chosen to ensure a stable cutting and high cutting rate according to the bifurcation diagram. The response of the cutter tip is a quasi-periodic motion when the cutting force is considered. The time-domain response of cutter tip predicted by nonlinear dynamic analysis can provide the basis for machining error prediction
Dynamic response and dangerous point stress analysis of gear transmission system
Get PDFGear transmission is the principal power transmission mode of many machine, the reliability of transmission system has important influence on the accomplishment of daily task. This paper made a gear transmission system as the research object, we build the two-stage gear transmission system model and calculate its dynamic response in theory. Then, we study the mesh stiffness of gear concerning the variation of the mesh position from the gear transmission system. On the basis of these work, we establish the gear system’s finite element simulation model considering the tooth contact of internal gear system. After the simulation, we had get the contact response and the time history of some important area’s equivalent stress. Through these work, we can study the contact stress of the two-stage gear system in theory method and finite element simulation method, which has a guiding significance on the optimum structural design of two-stage transmission gear system
Affection of the technology of multiple-input and multiple-output to the vibratory testing
Get PDFThe model of SIMO or SISO is usually used in the traditional vibration testing while the test item is always excited by multiple excitations in the field. The dynamic characteristics of structure (such as resonant frequency, mode shapes and modal damping) which will provide the basis for further analysis are obtained by vibration testing. Since the shaker needs to be mechanically attached to the structure under test, it is nearly inevitable that some sort of interaction will occur between them. It means that the traditional vibration testing or simulation don't have the ability to completely replicate the environment of test structure in the field which will lead to inaccurate results or even incorrect results. This paper offers differences between traditional SIMO vibration testing and MIMO vibration testing and presents some advantage of MIMO vibration testing which will distinctly improve the situation in laboratory and make boundary in the laboratory more similar to the environment in the field. Compared to traditional SIMO vibration testing, the MIMO vibration testing in the laboratory not only can significantly minimize the phenomenon of drops in the excitation forces close to resonant frequencies but also can replicate the boundary situations of the test item in the field