Vibration source identification using an energy density method

The localization of shaking forces acting on an operating machine is an important step to identify vibration and noise sources. The forced vibration response of a linearly vibrating structure is assumed to be linear. However, the energy distribution of a linearly vibrating structure contains “coupled terms” in the modal decomposition of the vibration energy density function. These coupled energy terms represent the cross-modal energy density associated with the exciting force of a dynamic structure under forced vibration. In this research, it is proved analytically that the high-order cross-modal energy densities of a linear dynamic structure are highly correlated to the location of the external exciting force. Using this finding, a new force localization index based on the high-order cross-modal energy densities of a dynamic structure is proposed and tested. Numerical tests on uniform and step beam structures under force excitation with different frequencies and locations have been carried out to test the effectiveness of the proposed force localization method. It is found that the proposed force localization method works well on vibrating beam structures. Experiments are carried out to verify the proposed force localization method.

Mechanical systems of precise robots with vibrodrives, the vibrating mass of the exciting force of which performs impacts into deformable support and direction of the exciting force coincides with the line of relative motion of the system

Manipulator consisting from one sided self stopping mechanism and two masses which interact through an elastic – dissipative member is investigated. The drive of the manipulator is the generator of mechanical vibrations. With such elements the system is nonlinear. A separate case is investigated when static positions of equilibrium of both masses are located in one point. Because of this spectrums of eigenfrequencies are linear and infinite. All those facts mean that the operation of the manipulator is optimal. Fast development of robots gives rise to the investigations of increasing intensity creating various types of robots especially in the area of high precision. Mechanical systems of robot must perform laws and trajectories of motion, positioning in space with highest possible precision as well as ensure dynamicity of highest possible stability. Those aims are achieved in the presented paper by creating a structure of the best design, based on vibroimpacts as well as by choosing corresponding nonlinear parameters of the system. The investigation is performed by analytical – numerical method. The obtained results enable to create mechanical systems for precise robots.

Research on Characteristics of Fluid Exciting Force of Reactor Internals

Flow-induced vibration is an important issue related to the safety and reliability of nuclear reactor, which need to be analyzed and evaluated in the design stage. In order to obtain the input loads and key parameters used in the calculation of flow-induced vibration of reactor vessel internals (RVIs) that need to satisfy the engineering requirements. The typical RVIs are selected as the research object, and the fluid exciting force characteristics are studied based on the computational fluid dynamics methods. The results show that the fluid exciting force acting on the RVIs is a wide-band stochastic process. For upper internal, the largest pressure fluctuation occurs at the guide tubes and support columns located near the outlet. Therefore, it is necessary to pay more attention to these guide tubes and support columns in response analysis. As for core barrel, the root mean square value of the pressure fluctuation changes drastically at the inlet and outlet location. For lower internal, the lower flow field of RVIs is relatively disordered, and its pressure fluctuation possesses irregular characteristics. Each component of lower internal need to be considered in analysis and evaluation.

INFLUENCE OF THE MESH SHAPE OF THE FINE LITTER CLEANER FOR RAW COTTON ON THE CLEANING EFFECT

Increasing the efficiency of cleaning raw cotton from weeds will ultimately improve the quality of products in the textile industry. It has been established that when using cylindrical mesh on purifiers with peg drums, the exciting force acting on the strips from the side of the net has a stable frequency, determined mainly by the frequency of rotation of the peg drum. This mode of operation of the cleaner does not effectively remove trash impurities. To improve the efficiency of the cleaner, it is proposed to use a grid in the form of a multifaceted prism. It was found that, by design conditions, the minimum number of mesh faces is four. The dependence of the cleaning effect on the number of faces of the perforated mesh of the cleaner has been experimentally obtained. It was found that with an increase in the number of mesh edges, the cleaning effect and fiber damage decrease. With the number of faces equal to six, it is possible to achieve an increase in the cleaning effect by an average of 16 % with a slight increase in fibre damage.

Study on dynamic characteristics of leaf spring system in vibration screen

By studying dynamic characteristics of the leaf spring system, a new elastic component is designed to reduce the working load and to a certain extent to ensure the linearity as well as increase the amplitude in the vertical and horizontal directions in vibration screen. The modal parameters, amplitudes, and amplification factors of the leaf spring system are studied by simulation and experiment. The modal results show that the leaf spring system vibrates in horizontal and vertical directions in first and second mode shapes, respectively. It is conducive to loosening and moving the particles on the vibration screen. In addition, it is found that the maximum amplitude and amplification factor in the horizontal direction appear at 300 r/min (5 Hz) while those in the vertical direction appear at 480 r/min (8 Hz), which are higher than those in the disc spring system. Moreover, the amplitude of the leaf spring system increases proportionally with the increase of exciting force while the amplification factors are basically the same under different exciting forces, indicating the good linearity of the leaf spring system. Furthermore, the minimum exciting force occurs in the leaf spring system under the same amplitude by comparing the exciting force among different elastic components. The above works can provide guidance for the industrial production in vibration screen.

Multistage Asymmetric Rotors Coaxial Measurement Stacking Method Based on Minimization of Exciting Force

The unbalanced exciting force of high-speed rotary asymmetric rotor equipment is the main factor causing rotor vibration. In order to effectively suppress the vibration of the asymmetric rotor equipment, the paper establishes a multistage asymmetric rotor coaxial measurement stacking method that minimizes the exciting force. By analyzing the propagation process of the centroid of the multistage asymmetric rotor assembly and analyzing the relationship between the geometric center and the centroid of a single asymmetric rotor, a multistage asymmetric unbalanced rotor propagation model based on geometric center stacking is established. The genetic algorithm is used to optimize the unbalance of the multistage asymmetric rotors. Combined with the vibration principle under the exciting force, the vibration amplitude of the left bearing at different rotation speeds under the minimization of the exciting force and the random assembly phase is analyzed. Finally, the experimental asymmetric rotors are dynamically measured, combined with the asymmetric rotors’ geometric error measurement experiment. The experimental results confirm that the vibration amplitude of the assembly phase with the minimum exciting force is smaller than the vibration amplitude under the random assembly phase at three-speed modes, and the optimization rate reached 73.2% at 9000 rpm, which proves the effectiveness of the assembly method in minimizing the exciting force.

STUDY ON STRUCTURAL-ACOUSTIC CHARACTERISTICS OF CYLINDRICAL SHELL BASED ON WAVENUMBER SPECTRUM ANALYSIS METHOD

By the finite element method, the structural vibration response is calculated under the action of the axial exciting force and the moment with different distribution form, and then the transfer function of the mean square normal velocity is analyzed. The wavenumber spectrum analysis method is used to separate and quantify the shell vibration in the wavenumber domain, and then the relation between the structural vibration characteristics and the structural wavelength is summarized. It is concluded that the structural vibration and radiated noise can be reduced under the symmetric action of axial exciting force and the moment. Based on the above conclusion, a symmetrical thrust bearing supporting system is designed and the stiffness of the supporting structure in the axial direction is controlled by selecting suitable size of structural members, therefore, the structural vibration and radiated noise of the submarine is reduced significantly.