Dynamic modeling and vibration characteristics analysis of parallel antenna

Step-type compound planetary gear sets are widely applied in vehicle systems. Comprehensive dynamic model of step-type compound planetary gear sets, which includes translational, rotational vibrations and static transmission errors, was established. Natural vibration characteristics of the system, such as natural frequencies and vibration modes, were analyzed. Belt shape distribution characteristics of its natural frequencies was researched. According to vibration characteristics of both central components and planets, natural vibration modes of the system are classified into three types: central components translational vibration and planets random vibration, central components rotational vibration and planets identical vibration, central components static and adjacent planets reverse vibration mode.

The principle of the magnetic levitation cylindrical linear motion guide and the theory of vibration analysis were introduced. By finite element analysis software ANSYS, modal analysis for guide was made to get the natural frequencies and vibration modes, the harmonic response analysis was also made to get the displacement response by the cutting force on the basis of modal analysis, and the influence of displacement on electromagnetic force was analysised.

In order to clarify the influence of water on the natural vibration of bridge with complex piers, based on a continuous beam with 4-column pier, the numerical analysis model is established. Single column circular pier is taken to discuss the range of waters. Then the influences of water on the natural vibration are analyzed. The research shows that waters reduce the natural frequency. When waters area width is less than 10 m, the natural frequency of the pier decreases. And the first-order longitudinal bending frequency is reduced by 3.36%. When waters area width is more than 10 m, the vibration frequencies tend to be stable gradually. Therefore, the waters 10 m can be regarded as an infinite boundary. The natural frequencies of single column pier and 4-column pier decrease with the increase of water depth. When the water depth is less than 10 m, the changes of natural frequency of the first four orders of single column pier are relatively small, and the changes of 5–10 order natural frequency are large. The maximum effect of the first ten orders is 14.84%. The natural vibration frequency of the bridge decreases gradually with the increase of water depth. The maximum effect of the first five orders is 3.33%.

Quadruped animals switch gait patterns with walking frequency for energy-effective walking. This is similar to the phenomenon that excited natural vibration modes are switched with vibration frequency in a MDOFs system. Therefore, in this paper, it is assumed that quadruped animals walk by using the natural vibration of their own musculoskeletal systems. In the simplest rigid-body-link model consisting of a body and four legs, there are the natural vibration modes similar to the gait patterns (trot, pace and gallop) of quadruped animals. However, all the natural frequencies in the model exist near the natural frequency in the free leg, and are accordingly different from the walking frequencies of actual quadruped animals. In the rigid-body-link model added a scapular and a pelvic on observations of quadrupted walking, the natural frequency of the gallop mode corresponding to high speed walking raises greatly and approaches the walking frequency. If the physical characteristics of horses were applied to the rigid-body-link model added the leg's joints, the natural vibration in the model is close to the gait patterns of horses.

When drilling oil wells, drill-pipe strings are the main components that constrain reliability and efficiency of drilling rigs. The highest number of drill-string failures is caused by pipe parting. It is suggested that pipe-parting failures are preceded by the formation of a portion having a through-thickness radial lengthwise cut or a notched portion with a smaller cross-sectional area. Neither lengthwise cut nor crack in the rod can be determined using natural frequencies of longitudinal or flexural vibrations, because in the zone of the cut there is no reduction of the area and axial moments of inertia in the rod’s cross section. Therefore, this article deals with natural torsional vibrations of a drill string having damages as a through-thickness radial lengthwise cut and as a lateral notch. It has been found that in the case of the cut or the notch located within the vibration node, natural frequencies do not depend on the lengths of these damages. As the length of the cut or the notch increases, the lower frequencies of natural torsional vibrations will decrease. For the drill-string lengthwise through-thickness cut, changes in the natural torsional vibration frequencies are considerable as compared to similar frequencies for the drill string having a lateral notch. Using two natural torsional vibration frequencies, we can determine the initial coordinate and length of the through-thickness radial lengthwise cut on the drill string. Using three natural torsional vibration frequencies, we can determine the coordinate, length and parameter of the notch.

During the rice-threshing process, straws always attached to a threshing cylinder and induced vibration and modal variation. In this paper, the constraint and threshing modals of the threshing cylinder were tested under idling and load conditions, and the causes of vibration and modal variation were explained. Based on the constraint and modal of the threshing cylinder, the vibration amplitudes and frequencies undergoing rice threshing were tested and analyzed. Results showed that mass of straws decreased gradually with the separation of rice grains and straws. And there was a nonuniform change in the circumferential resistance of the threshing cylinder. The fluctuating torque, speed, and frequencies during threshing process would cause vibration of the threshing cylinder. During rice-threshing process, the other natural frequencies were greater than the excitation frequency. With the accumulation of a large amount of straws, the threshing modal frequencies of the tangential threshing cylinder increased. The threshing bars caused vibration of the tangential threshing cylinder in the left and right direction mainly at two frequencies. At idling state of no-load, the vibration frequency 42.97 Hz of the tangential threshing cylinder in X direction was close to the constraint modal frequency 41.58 Hz. The eccentric load caused the excitation frequency to increase during the rice-threshing process. The vibration frequency was also closely related to the threshing modal. The tangential threshing cylinder with low vibration characteristics could be designed by using the eccentric vibration characteristics during the threshing process.

In modern aerospace technology, strapdown inertial navigation systems (SINS) are widely used, using fiber-optic (FOG) or ring laser (CLG) gyroscopes. During the operation of such systems, the sensitivity axes are rotated relative to the basic coordinate system. The resulting angles between the axes of the base coordinate system and the axes of sensitivity of the navigation system (non-orthogonality) are one of the factors leading to an increase in the measurement errors of the device, which affects the measurement accuracy. During operation, the system is affected by vibrations of various nature, the impact of which can contribute to the appearance of non-orthogonality. The purpose of this work is to determine the maximum permissible vibration amplitudes affecting the SINS body according to the permissible values ​​of the deviation of the FOG sensitivity axes for two variants of the SINS layout. An approach to determining the permissible amplitudes of an external harmonic impact on the unit of a strapdown inertial navigation system based on fiber-optic or ring laser gyroscopes is considered. A design scheme, mathematical and finite element models for calculating natural frequencies and forced oscillations of a strapdown inertial navigation system unit have been developed. In various frequency ranges, numerical calculations have determined the boundary values ​​of the amplitudes of the external harmonic impact on the base of specific configurations of the SINS assembly. It has been established that dangerous states take place in the region of the 1st natural frequency of the system, as well as near higher frequencies. Comparison of the results for design options 1 and 2 allows us to conclude that in order to weaken the effect of vibrations on the accuracy of the SINS unit, it is advisable that the lowest natural vibration frequencies for the SINS assembly be as high as possible (more than 1000 Hz).
 Key words: vibration; fiber optic gyroscope; strapdown inertial navigation system; finite element method; natural frequencies and modes of vibration.

Modal and Harmonic Response Analysis of Key Components of Ditch Device Based on ANSYS

The article considers the problem of assessing the stability of the continuously welded track at its temperature elongation and proposes a method for this assessment by comparing the actual temperature of fastening the rail strings with the standard one. A method for determining the actual temperature of rail fastening is presented, which consists in measuring its temperature and natural vibration frequencies, followed by an analysis of the dependence of the change in the natural frequency of the rail head in the transverse direction on the magnitude of the longitudinal force applied to the rail. The methodology of the tests performed at the bench and section of the continuously welded track of the Ozerskaya branch of the Moscow railway is described. The essence of the technique is to determine the values of natural vibrations using various measuring instruments (strain gauges, vibration transducers, sound level meters) at different values of the longitudinal force applied to the rail. Natural vibrations were excited by hitting the rail head in the transverse direction. A comparative analysis of the forms and frequencies of natural vibrations of the rail head is carried out according to the test results in bench and operational area conditions. It was found that the closest convergence of the vibration frequencies of the rail head in the transverse direction corresponds to the first mode of vibration. During bench tests, the dependence of the frequency change of the first form of natural vibrations of the rail head in the transverse direction on the magnitude of the longitudinal force applied to the rail was determined. According to the results of a comparative analysis of the results of measurements of the natural frequencies of rail oscillations, the possibility of using a sound level meter or similar measuring instruments for their registration was established. The calculation of the actual temperature of the rail fastening is also given on the example of the section of the continuously welded track of the Ozerskaya branch of the Moscow railway and its compliance with the normative for this region is established.

Influence of flow-induced bend–twist coupling on the natural vibration responses of flexible hydrofoils

Free vibration of a spherical liquid drop attached to a conical base in zero gravity

Nonlinear vibration isolation for fluid-conveying pipes using quasi-zero stiffness characteristics

In this study, a 3D model of a two‐step sine movable tooth drive is developed in the UG software. The finite element model (FEM) analysis package, ANSYS, is used to calculate the natural frequencies and vibration modes of the drive system. The results show that the first twenty natural frequencies can be classified into five families, including the total system vibration mode, single‐element vibration mode, two‐element vibration mode, three‐element vibration mode, and four‐element vibration mode. The effects of the system parameters on the natural frequencies and the vibration modes are investigated. The track amplitude, the movable tooth radius, the radius of the movable tooth rotation, and the number of movable teeth affect the natural frequencies and vibration modes of the drive system.

The mode characteristics and the parameter sensitivity for a two-stage NGW spur planetary gear system are studied based on the principles of structure natural dynamical characteristics. Considering the influence of flexible structure including shaft, the planet carrier, and the ring-gear, the coupled lateral-torsional-axial vibration dynamical model of the planetary gear system is established under the generalized coordinate system using the shafting element method. With the model, the natural frequency and vibration mode are solved, and the results indicate that the flexibility of ring-gear has a greater effect on natural frequency. Several distinct types of vibration mode are summarized, such as planet torsional mode, sun-gear shaft axial mode, ring-gear axial mode and so on. However, the translational mode which is one of the modes in the coupled lateral-torsional lumped mass model is not found in this study. Within the scope of the time-varying, mesh stiffness mainly affects the planet torsional mode of corresponding stage. Furthermore, the variation of radial bearing stiffness will also do effect on axial vibration mode, and the variation of bearing stiffness not only affects the vibration modes of adjacent stage of planetary gear train, but also affects the nonadjacent stage. The results demonstrate the coupling characteristics of the system under the free vibration condition.

According to the recent Russian norms, when designing building structures, it is necessary to conduct a dynamic analysis of wind loads, which previously was required not in all cases. In arched vaults of profiled arched self-supporting flooring, it was not always necessary to determine the frequencies and forms of natural vibrations. These parameters can be established using the finite element method. Taking into consideration the complex and lengthy modeling process of arched vaults, in particular the contact areas in regular transverse joints, a large number of finite elements in the models and, as a consequence, considerable time for their calculation, it was necessary to identify a sufficient level of detailing of a finite element model for correct calculations of frequencies and forms of vibrations considered in the operation of structures. The influence of the detailing of the finite element model of arched vaults made of profiled flooring on the determination of their natural frequency is revealed. To substantiate the parameters of the finite element model, it was studied how the results of the calculation was influenced by edge effects, the presence of friction in the joints of corrugations of the profiled flooring, the influence of rubber gaskets in the joints on the work of the arched vault. Much attention is paid to the features of the design scheme associated with the choice of the number of sheets of profiled flooring, taking into account the contact nodes, friction forces, etc. It is established that the first vibration frequency is little dependent on the number of sheets of corrugated flooring and the presence of rubber gaskets in the joints. For subsequent frequencies, the difference can be significant.