Applied Mechanics and Materials Vols. 105-107

Abstract: In order to improve the driver confortness, the 5-DOF analysis mathematical car model with the active seat air-spring suspension system was built. Based on the linear stochastic optimal control theory (LQG), the signal of road’s input as excitation source was used to design the optimal law of this seat active control system. MATLAB simulation programming language was applicated for the response simulation. The results show that the control strategy on the road excitation system has a good applicability on controlling the vibration of the driver’s seat and active seat suspension can more effectively reduce the driver’s vertical vibration acceleration than passive seat suspension.

Abstract: This paper presents a guide to identify optimal damper location to reduce vibration on built-up structures. The guide is derived from simulation studies carried out on a set of benchmark models. Optimization is carried out using genetic algorithm. Optimal location is found using found using Generic algorithm and the hybrid method. The hybrid modelling method combines the finite element method (FEM) and Statistical energy analysis (SEA) to provide an efficient response predication for mid-high frequencies. The guide to find optimal damper location is tested on a fuselage model of Boeing 737. The fuselage model is developed using VA One software. Good agreement is seen for the optimal locations using the simple guide and result from VA One.

Abstract: Crack detection, Hilbert–Huang transform, Wavelet analysis Abstract. This paper illustrates the feasibility of the Hilbert–Huang transform (HHT) as a signal processing tool for detecting structural cracks. HHT is a promising method to extract the properties of nonlinear signals. However the HHT has some shortcomings, for example some undesirable pseudo-IMFs and multi-component IMF. The crack detection method based on the wavelet analysis and HHT is proposed to analyze response signals: the wavelet analysis is used to decompose the signal into a set of narrow band signals prior to the HHT. Then, a screening process is conducted to remove unrelated IMFs. By comparing the IMFs’ instantaneous amplitudes, the existence of structural crack is detected. Finally, the experiment results of the cantilever beams prove the reliability of this method.

Abstract: Nowadays, bridge cranes have a tendency to be designed for big lifting capacity, wide span with high operating speed. Several long horizontal cracks have been found in web plates of the rail girder, which is terrible threat to crane’s safety. Firstly, the local stress distribution of web plates is illustrated in a semicircle form based on the elastic-plastic contact theory. Then the cyclical variation of shear stress is analyzed due to high frequency and impulsive moving wheel loads. Finally, a fatigue crack propagation model is proposed according to the strain energy density law. It is found that the shear stress and welding residual stress give rise to the fatigue horizontal crack near welding seam.

Abstract: About tyre vibration sound issues, domestic and foreign scholars have conducted a lot of researches. Existing research results show that: the road texture and tyre tread have a significant effect on the tyre/road noise. Since the road surface texture and tyre tread pattern have impact on the tyre noise, whether the coupling relationship of road surface texture and tyre tread pattern has influence on noise In this paper, from coupling viewpoint of road surface texture and tyre tread pattern, road surface texture and tread pattern of geometric morphology were calculated by digital gray level images fractal dimension and discretized into finite element model, then the vertical contact force within contact surface of tyre and pavement, which is exciting force in tyre vibration model, last numerical calculation of evaluating noise from vibrating tyre was completed by tyres vibration model and basic principle of boundary element method for calculating sound field.

Abstract: In order to identify noise sources of an excavator in non-library environment, a complex-valued algorithm in frequency domain was applied. Firstly, an acoustic camera was used to acquire excavator’s noise signals, which were convolutive mixtures in time domain interfered by echo. Secondly, signals in time domain transformed into frequency domain by FT, turned to be complex-valued mixtures. Then, independent components of noise signals were obtained through separation of complex-valued mixtures using complex-valued algorithm based on independent component analysis. Finally, according to noise of diesel with muffler was mainly consist of surface noise, the relationship between principal frequencies and structrual parts was founded by comparing frequency-amplitude spectra and modal analysis in Ansys. Research shows that complex-valued algorithm based on fast fixed-point independent component analysis can effectively separate noise signals from an excavator in time domain, and noise sources can be well ascertained by comparing the modal analysis with blind separation components.

Abstract: Intermittent fault is an important factor causing built-in test(BIT) false alarm. Diagnosing intermittent fault is an important approach to restrain BIT false alarms. This paper proposes a intermittent faults diagnostic methods based on empirical mode decomposition (EMD) and multiple support vector machine (MSVM). Firstly, the EMD method is used to decompose the original signal into a number of intrinsic mode function (IMF), the auto-regressive (AR) model of each IMF component is established. The AR model parameters and the variance of remnant are regarded as the feature vectors, are input to MSVM classifier, so the working conditions and faults are classified. The experimental results show that the BIT false alarm caused by intermittent fault can be effectively reduced by this proposed method.

Abstract: In Free Space Optic (FSO) communication, the alignment between transmitter and receiver telescope is very important. The line of sight of their optics must be aligned during the entire communication time; this is crutial in large distance data transmission. One of the factors that causes misalignment is vibration, either at the transmitter or the receiver. In this work, active vibration isolation (AVI) system is designed and developed to tackle this issue. An AVI system isolates FSO devices from direct disturbances or ground vibrations. The LQR controller is proposed and implimented with LabVIEW. A mathematical model of the isolator is derived and the prototype model of the AVI system is designed in SolidWorks. This prototype model is integrated with LabVIEW software to perform virtual prototyping.

Abstract: Structural health monitoring provides accurate information about structure’s safety and integrity. The vibration-based structural health monitoring involves extracting a feature which robustly quantifies damage induced change to the structure. Recent work has focused on damage features extracted from the state space attractor of the structural response. Some of these features involve prediction error and local variance ratio. In the present paper, a five degree of freedom spring damper system forced by a Lorenz excitation is used to evaluate these two typical damage features. Their ability of identification damage level and location is characterized and compared.

Abstract: According to the generating process and propagation characteristics of earth-fault transient signal, an earth-fault location method for distribution network based on transient signal is presented. In the method, in order to change line characteristic impedance, a resonant filter circuit is paralleled in line segment border, so that it could cause transient current energy differences in feature frequency band on both sides of detection device. The location method achieves earth-fault area location through comparing transient current energy and energy attenuation coefficient in feature frequency band. The simulation test result shows that the method isn't influenced by distribution system grounded style, operation style and other factors and which could detect the earth-fault area rapidly and reliably in distribution network and has a high project application value.