Dynamic Characteristics Analysis of Flexible Rotor System With Pedestal Looseness

Due to the limitation of assembly conditions and working load environment, the design of pedestal looseness is often used in the structural design of aeroengine multi support flexible rotor, which affects the vibration response and stability of the rotor system. In this paper, a dynamic model of a flexible rotor system with pedestal looseness is established for a practical aeroengine flexible rotor system. Next, a nonlinear modal analysis process for the multi degree of freedom nonlinear rotor system is proposed. Based on this, the nonlinear modal characteristics of the flexible rotor system with pedestal looseness are analyzed. An interval prediction method of modal damping interval for stability analysis of rotor system is presented, and the influence of key characteristic parameters on modal damping and vibration stability of rotor system is explored. Finally, the vibration characteristics of the rotor system are obtained by numerical integration method. The results show that the modal characteristics of the rotor vary with the amplitude of the rotor, and have the feature of interval distribution; vibration stability mainly depends on tangential friction and additional lateral constraint; when the amplitude of the rotor is large, the backward whirling motion may occur and the vibration may be unstable. This paper will provide a theoretical method for dynamic optimization of multi support flexible rotor system, which is helpful to ensure the reliability and safety design of aeroengine.

Features of interlaboratory comparison methods when measuring vibroacoustic parameters

External quality control in the form of interlaboratory comparisons (ILCs) is an important criterion of the testing laboratory competence. The study was aimed to summarize the approaches to developing objects for proficiency testing (OPT) based on physical simulation of acoustic noise sources, airborne ultrasound, vibration, and the practice of their use for ILC. Analysis of the OPT effectiveness based on physical simulation of factors, the test benches (TBs), was performed based on their testing and certification results, as well as on the results of appropriate ILCs. The results of using TB as OPT are considered for the following factors: acoustic noise, airborne ultrasound, and vibration. When measuring acoustic noise, TB played back the acoustic noise record with high stability. ILC involving measurement of airborne ultrasound was performed the same way, however, the frequency of the acoustic signal being reproduced was in the range of 11–22 kHz. TBs, based on a manual mechanized tool and a platform equipped with electromechanical agitator, were developed for ILC involving the measurement of local and general vibration. Stability of vibration generated was provided by means of the automated system for maintaining the set level with feedback and proportional integral derivative (PID) controller. When arranging and performing ILCs involving measurement of noise and vibration, a crucial role is played by the methods developed specifically for ILCs, allowing one to take into account all the conditions that affect the measurement results.

Vibration stability analysis of cantilever structure based on symbolic regression algorithm and modal analysis method

The vibration stability of cantilever mechanism under high-speed rotation directly affects the positioning accuracy. Modal analysis method is usually used to study the vibration stability. However, the traditional experimental modal analysis (EMA) method needs to measure the impulse excitation, while the operational modal analysis (OMA) method needs to satisfy the assumption of white noise. Therefore, the existing modal analysis methods cannot be applied to the study of vibration stability of high-frequency cantilever mechanism. In this paper, the symbolic regression (SR) algorithm is combined with the EMA method, and the robustness analysis and feasibility verification are carried out under the condition of adding noise. The validation of the new method is divided into two parts. In the first part, a three degree of freedom (DOF) linear model is constructed, and the modal parameters identified by SR method and state space method are compared. In the second part, the method is applied to identify the modal parameters of stepped bar. The results are compared with the results of LMS (Siemens’ Testlab). Based on the time-domain response signal only, the modal parameters are extracted by SR, and the main vibration frequency is extracted from the response signal. The system simulation and experimental results show the method provides a possibility to analyze the vibration stability of cantilever structure.

Improving the Performance of Wood-Metal Slide Bearings for Forestry Machinery

The performance of slide bearings in forestry machines and equipment is largely determined by the load-carrying capacity and antifriction qualities that depend on the bearing capacity of the sleeve (insert) material, the design rigidity and the nature of the forces during operation. As a result, the bearing materials undergo cyclic changes in the state of the sleeve material, as well as the elements that provide reinforcing, heat-conducting and anti-wear functions. The paper shows the results of research on the stress-strain behavior of anisotropic composite materials in the structures of wood-metal slide bearings. A method for ensuring vibration stability is proposed. It is based on maintaining the damping properties of the support that change in the course of wearing. The functionality of the developed program, which is used to solve the contact and thermal issues in the design of slide bearings, is described. A wood-metal material for making bearing sleeves and inserts from laminated compositions was created and studied. The compositions include a vibration-absorbing and fine-fractional component in a vibration-weighted state and a layered structure heterogeneous in thickness of the sleeve, characterized by a variable elastic modulus, that provides damping properties. The proposed design of a slide bearing using this material is focused on its use mainly in the conditions of shock-cyclic loading, which is typical for operation of most forestry machines and equipment.

Characterization of the vibration, stability and static responses of graphene-reinforced sandwich plates under mechanical and thermal loadings using the refined shear deformation plate theory

An analytical investigation was carried out to assess the free vibration, buckling and deformation responses of simply-supported sandwich plates. The plates constructed with graphene-reinforced polymer composite (GRPC) face sheets and are subjected to mechanical and thermal loadings while being simply-supported or resting on different types of elastic foundation. The temperature-dependent material properties of the face sheets are estimated by employing the modified Halpin-Tsai micromechanical model. The governing differential equations of the system are established based on the refined shear deformation plate theory and solved analytically using the Navier method. The validation of the formulation is carried out through comparisons of the calculated natural frequencies, thermal buckling capacities and maximum deflections of the sandwich plates with those evaluated by the available solutions in the literature. Numerical case studies are considered to examine the influences of the core to face sheet thickness ratio, temperature variation, Winkler- and Pasternak-types foundation, as well as the volume fraction of graphene on the response of the plates. It will be explicitly demonstrated that the vibration, stability and deflection responses of the sandwich plates become significantly affected by the aforementioned parameters.