Advanced Materials Research Vols. 199-200

Abstract: The composite element method is utilized to discretise a stepped Euler-Bernoulli beam with a crack. The local stiffness reduction due to the crack is introduced by using a simplified crack model. The finite element equation for the forced vibration analysis is obtained using the composite element method (CEM). The forced vibration response of the cracked stepped beam is numerically calculated using Newmark integration method. Numerical results indicate that the position and depth of a crack affects the low and high natural frequencies and modes of a cantilever beam, respectively. And the position of the crack has significant effects on the dynamic responses of the beam.

Abstract: The mathematical vibration model of travel stabilizing system of wheel loader which was added to reduce spillage of material was built firstly. The equivalent stiffness and damping of travel stabilizing system were deduced, and influence factor was analyzed. In order to solver the characteristic parameter of the mathematical vibration model, the simulation method based on Pro/E and ADAMS was adopted. The result indicates selecting the appropriate parameter of accumulator is the important factor of the effect of travel stabilizing system. This paper is basic of further research on travel stabilizing system.

Abstract: Rotor Complex Fault Vibration signals are very hard to analysis since there are many frequencies lies in them. It needs new signal processing methods to deal with these problems. Empirical Mode Decomposition (EMD) is a non-stationary signal processing method developed recently. The frequency heterodyne EMD method can improve the frequency resolution of EMD by shifting the original frequencies to enlarge the frequencies ratio between components. It proves that the method can enhance the performance of EMD easily and effectively. The paper discusses the principle and steps of this method in detail and uses it to analyse rotor complex fault signals. The result shows that frequency heterodyne EMD method can separate different faults and detect the weaker faults in complex fault more effectively than that of normal EMD method.

Abstract: Principal component analysis (PCA), serving as one of the basic blind signal processing techniques, is extensively employed in all forms of analysis for extracting relevant information from confusing data sets. The principle of PCA is explained in this paper firstly, then the simulation and experiment are carried out to a simply supported beam rig, and PCA is used in frequency domain to identify sources number of several cases. Meanwhile principal components (PCs) contribution coefficient and signal to noise ratio between neighboring PCs (neighboring SNR) are introduced to cutoff minor components quantificationally. The results show that when observation number is equal to or larger than source number and additive noise is feebleness, accurate prediction of the number of uncorrelated excitation sources in a multiple input multiple output system could be obtained by principal component analysis.

Abstract: A large flexible vibration isolation structure is presented in this thesis, and experimental modal test based on the finite element analysis is carried out in order to find out the vibration characteristics of it. Results show that the natural frequencies and mode shapes calculated by finite element method basically conform to those measured from experimental modal test. Some suggestion to vibration active control in further research is also provided.

Abstract: To effectively model and analyze the vibro-impact system with time-varying mass, we considered the discontinuous impacts as a continuous effect of stiffness and viscous damping acting on the system and studied the dynamic performance based on the theory of bifurcation and chaos. It is demonstrated that the system will experience a process of from period-one motion to chaos and again back to period-one motion when the system transit the resonance. Our results may find applications in impact vibrations coupled with dispersive matter.

Abstract: According to the tunnel blasting vibration test at Kiaochow bay Cross-harbor Tunnel Guide Line Project, the regulation of the tunnel vibration velocity has been studied. Based on the analytical results, this paper finds that the change regulation of vertical, horizontal radial and tangential vibration velocity as the different distances from the work face. The tunnel vibration velocity of the rear work face is greater than the unexcavated area. The peak value of the rear work face is 2-2.5 times as large as that of the front work face, vibration velocity of the front work face attenuates gently. The paper figures out the relationship between vibration velocity and distance from sensor to the work face, which can offer a reference to similar studies.

Abstract: According to the 20 layers reinforced concrete frame-shear wall structure building, we carried on blasting vibration monitoring in Qingdao Cross-harbor Tunnel Guide Line Project. The monitoring data of vertical vibration velocity and vertical vibration frequency had been analyzed. The results show vertical vibration velocity and vertical vibration frequency had part of intrinsic association. Vertical vibration velocity was enlarged on the top of the building. Vertical vibration frequency was in the range of 10¹-10² order of magnitude.

Abstract: The article was based upon analysis of the front-and-back surface vibration velocity of the working surface by monitoring the blasting operation at hidden digging section of Jiaozhou Bay cross-harbour tunnel in Tuandao road exit ramp. Research shows that the maxim-um value of the surface blasting vibration velocity appears on the front and back of the ground ,raging from 2 m to 7 m ,just above the working surface instead of the ground just above of the working surface. However, the surface vibration velocity generates behind the working surface was 1.2 to 1.4 times greater than the one generates at the front of the working surface. The front-and-back surface vibration velocity tends to be flattening on the ground which was more than 20 m away from the working surface, just above it.

Abstract: The blasting vibration in Qingdao Cross-harbor Tunnel Guide Line Project is monitored and analyzed. We discover that the surface particle vibration velocity in the range of 5metres around the working face reduces fast, and that does not conform to Sadaovsk formula. This inquiry adopts the hypothesis-fitting-testing method to modify Sadaovsk formula. The empirical formula of the ground vibration velocity caused by blasting in tunnel is obtained.