Applied Mechanics and Materials Vol. 724

Abstract:

The characteristics of quasi-zero stiffness(QZS) system with nonlinear positive and negative stiffness is researched. A modified QZS model with nonlinear spring element is established and the stiffness curves are obtained based on the analysis of relationship between spring force and displacement. A non-dimensional form of QZS is deduced to discover its essential laws, and simulation is presented with different nonlinear springs. Then the force transmissibility of QZS is verified with the experiment, which shows that the QZS isolation performance is better than the linear one in the low frequency band, and there exists no resonant peak in this system.

Abstract: For the prestressed substructure analysis, the existing CMS super-element methods are only suitable for the model that relatively simple structure, less meshing and small number of nodes. Since the complex structure and more mesh division of an arbitrary large model such as a mistuned bladed disk system, it is more time-consuming for the dynamic characteristics analysis. Because of above shortcoming, an approximate analysis method is presented, it is called fixed interface prestressed-free interface CMS super-element method. The accuracy of this method is predicted by the example. The results showed that the dimensionless dynamic frequency maximum relative error of system is 3.072215%, which can be to meet the requirement of accuracy.

Abstract: In order to study the nonlinear vibration problems of cable with a particular constraint, the mathematical model for the object of study should be established firstly with the elastic mechanics method. In order to obtain the mathematical model of differential form, the Galerkin method is used to make the mathematical model discrete and modal truncation, so the infinite dimensional solution space of the mathematical model can be transformed into the finite dimensional one. Main factors influencing the vibration of the cable system are analyzed, and the simulation analysis about the effects of various parameters on frequency is carried out. The analysis results show that the internal resonance modes may exist, and provide a theoretical basis for improving the safety and reliability of laying cables in actual conditions.

Abstract: Multi-Rotor Horizontal Axis Wind Turbine (MR-HAWT) system with three 2kW Horizontal Axis Wind Turbines (HAWTs) is the research object. After some appropriate simplifications, the finite element model is established and verified by experiments. The vibration characteristic of the tower under rotors’ periodic excitations is studied through transient analysis method and compared with 6kW single-rotor HAWT system. The result shows that the maximum stress of the 3-Rotor Horizontal Axis Wind Turbine (3R-HAWT) system is less than the single-rotor HAWT, so the safety of the 3R-HAWT system is superior to the single-rotor HAWT system.

Abstract: This paper studies the roller bearing fault diagnosis method with harmonic wavelet packet and Decision Tree-Support Vector Machine (DT-SVM). The harmonic wavelet packet possesses better performances for its box-shaped spectrum and unlimited subdivision compared with the conventional time-frequency feature exaction method. Firstly, the proposed method decomposes the roller bearing vibration signal with harmonic wavelet packet and extracts the feature energy with coefficients of each spectrum. After the feature energy is normalized, feature vector are available. Based on multi-level binary tree, this paper designs the multi-classification SVM model due to its superior nonlinear mapping capability. Three two-classifications are incorporated to diagnosis the roller bearing faults. Finally, the proposed method is illustrated with the vibration data from the roller bearing stand of electric engineering lab in case western reserve university. Experimental results illustrate the higher accuracy of the proposed method compared with conventional method.

Abstract: The cable structure has been wildly applied to all kind of engineering structures. So, the accurate analysis of the dynamic features of the cable structure is particularly important. In this paper, the finite element model of suspended cable was established by ABAQUS software, cable element and beam element were used respectively to study in-plane and out-of-plane modal variation with sag according to different span and dip angle of suspended cable, the influence of bending rigidity on modal are obtained. Finally, a comparative analysis with the classic linear theory of vibrations of a small sag suspended cable should be done to determine the applicability of this theory. Modal analysis is the basis of model superposition method. It has important theoretical significance to research the impact of sag on modal to vibration control for large-span suspended cable.

Abstract: To get the noise transmission mechanism in the carbody is the precondition for noise control. In order to study the noise transmission mechanism in the carbody of the high-speed trains, the relationship of the sound pressure level (SPL) and the vibration level (VL) was analyzed base on plane sound wave, and then a special test bench in laboratory was built to evaluate the relationship. Concentrated force load and sound load wre used in the experiment. First, the “SPL-VL” formulas in every one-third octaves were found under force load. Then the sound load test was used to evaluate the formulas. The result indicates that the noise radiated by the structure bending vibration accounts for a large proportion of interior noise in the special multilayer thin-wall carbody of high-speed trains. Damping treatment is used for further instructions.

Abstract: Vibroplatform test is an important means of testing the dynamic characteristics of the laboratory sim-ulating structure under seismic action. For structure whose volume and weight exceed the limits of vibroplatfor-m tests is usually carried out through model test according to the similarity theory. So how to deal with the simil-ar relationships among the test model and how to verify thethe rationality of vibration control strategy through testing results become the key and fundamentalproblems. 1:15 scaled models will be made through the dimensional analysis based on a 4 layersL-shaped frame structure as the proto-type , which are made from micro-concrete, aluminum alloyand plexiglass. SFMT sap2000 is used to make a dynamic analysis to get the values of period,acceleration, velocity, etc. Comparing the results of prototype inferred from model through similarrelationship with theoretica-l values of prototype to get the correct formula and confirm the bestscaled model and then provide references f-or model test later.

Abstract: Multi-Agent system (MAS) is used to control the radiation noise in a rectangular enclosure, which is surrounded by two flexible plates and four rigid plates. The noise is generateded by the vibration of the exciting flexible plane. A MAS is established to coordinate the active noise control method, and these agents are controlled by a coordination object which includes compete and cooperative rules. These agents are competitiveness, so the MAS can provide fault-tolerant capabilities for the control mechanism. Meanwhile, these agents are independent and modular, and can be used in “Plug-and-Play” control field. The formula is derivate to calculate the sound pressure in the enclosure when there some point forces applied on the flexible plates, and the simulation shows using MAS to control the noise in the cavity is effective.

Abstract: A self-developed extension configuration of high-temperature ceramic pole was used to transfer the vibration signals to non-high temperature zone, and the vibration signals of composite wing structure under high-temperature environment were identified by the ordinary acceleration sensors. The experimental measurement on the key vibration characteristic parameters of composite wing structure under high temperature thermal vibration environment up to 1100°C (e.g., the natural frequency, mode shape) was realized. The experimental results can provide an important basis for the dynamic performance analysis and safety design of composite wing structure under high-temperature thermal vibration conditions.