Applied Mechanics and Materials Vols. 128-129

Abstract: Electromagnetic exciting force is the key to generate electromagnetic noise. The characteristics of electromagnetic exciting force and the causing of electromagnetic noise were analyzed after the power was off for cooling fan Permanent Magnet DC (PMDC) motor. Time-stepping finite element method was selected to calculate its several parameters, such as air gap magnetic density harmonics generated by the stator and rotor, torque ripple and unbalanced magnetic pull at its different speed.Experiment on unloading vibration noise was carried out to confirm the validity of electromagnetic exciting force analysis. The results show: electromagnetic force amplitude keeps constant while the motor speed changing. Torque ripple decreases while the motor speed down. A kind of electromagnetic noise called howling noise produced by PMDC motor used in car cooling fan is mainly due to resonance. So the best way to eliminate this motor’s noise is to improve the order of electromagnetic waves and avoid the electromagnetic resonance.

Abstract: Box-Jenkins method of time series in modeling the signal of quartz flex accelerometer is studied in the paper. Firstly, a JSD-I/A quartz flex accelerometer is placed on a level test bench, and the output signal of the JSD-I/A quartz flex accelerometer is acquired. Secondly, the acquired signal of the JSD-I/A quartz flex accelerometer is preprocessed by Db3 wavelet denoising, trend items exacting, and standardized processing. Thirdly, The statistical characteristics of autocorrelation function (ACF) and partial autocorrelation function (PACF) of the processed time series data are analyzed, and the results show that ACF presents tailing characteristic and PACF presents censoring characteristic after 12th order. So AR(12) model is suitable for modeling the processed data of the JSD-I/A quartz flex accelerometer. Fourthly, the AR(12) model’s parameters are estimated by four methods, named least square method (LSM), Yule-Walker method, LUD method and Burg method, respectively. The fitting effects by residuals sum of squares (RSS) of the above estimation methods are compared and the results show that LSM outperforms the other three estimation methods.

Abstract: This paper describes the concept of reverse engineering and the workflow of reverse modeling software — imageware. Using the powerful function of point cloud data processing in imageware, it achieves point cloud data pre-processing, point cloud segmenting, contour curve fitting and surface reconstructing of the human body. Finally, it makes the error evaluation of the surface model. This study may provide original design basis for related research.

Abstract: In this paper, firstly, we discuss the specific processing algorithm of wide-band VLBI signal，which can be used in astronomy and geodesy. We focus on the theory, algorithm, result and by simulation we verified it. When the Chang’E Ⅱ on its orbit, we organize a short baseline interferometer experiment and get correlation fringe successfully, meanwhile, we compare the result with the data of precise theoretical orbit. It proves that the system is successful, and the algorithm is useful and correct.

Abstract: To overcome the flaw of energy efficiency drop in broad band wireless communication with the short time sleep, the energy-saving mechanism of the sleep mode operation was researched in IEEE 802.16e. In this paper we propose a dynamic algorithm to tune the ratio of the sleep windows and receive windows according to the traffic load. Then, a Markov chain model was set up to analyze the energy efficiency and mean access delay. NS2 simulation results show that the proposed algorithm can achieve marked gain in energy efficiency compared to the traditional energy saving mechanism.

Abstract: A study of flow and frequency characteristics of the leading-edge vortices over a delta wing undergoing pitching up-stop motions is presented. The experiments with the dynamic delta wings were conducted in a water channel and a wind tunnel respectively. Among them, the test of the flow visualization was completed in the water channel with the delta wing with pitching up-stop motions. The result shows that in the case of pitching up-stop movement the vortex breakdown position is dependent on the range of incidence at which the wing is subject to pitching up-stop and the reduced frequency k (k=c/2U_∞). Analysis of the pressure signal measured in the wind tunnel shows when the delta wing is subject to pitching-up the nondimensional spiral wave frequency at nominal incidence in post-breakdown is higher than that at corresponding static state and the bigger the k is, the higher the nondimensional spiral wave frequency is. The same conclusion is fitted with different sweep delta wing.

Abstract: This paper studies the detection of weak signal detection using a Duffing Oscillator, which is sensitive to periodic signals but insensitive to noises. The system transits from chaotic to great periodic motion when coupled to the weak periodic signal to be detected. To efficiently determine the phase transition, a novel numerical criterion is proposed based on the sharp increase of variance when phase change happens. Simulation results verified the effectiveness of this method.

Abstract: Based on the time-dependent deformation behavior of solder alloy 63Sn-37Pb at room temperature, a damage-coupled unified visco-plastic multi-axial fatigue model and its failure criterion were proposed. In the evolution equation of damage for the model, the time-dependent effect of damage was taken into account. The model was used to predict the fatigue life under different loading paths. The comparison between the predicted and experimental results demonstrated that the time-dependent failure model can simulate the deformation behavior and predict the fatigue life well under different nonproportional strain paths.

Abstract: Adiabatic shear band (ASB) is a typical response of materials under high strain rate loading. Based on the instability analysis of the thermo-viscoplastic constitutive model, a new rate-dependent failure criteria is proposed, which links dynamical evolution of ASB with macro mechanical critical conditions, and is successfully applied to account for the shear fracture mode of cylindrical structures subjected to explosive loading. Using finite element method, the transient failure procedure and shearing fragments induced by ASB is simulated, and the calculated fracture profile shows a good agreement with the experimental results. The failure analysis indicates that the rate-dependent failure criteria, as well as impulsive loading, govern the shear damage mode of the structures.

Abstract: The in-depth composition of carbon and oxygen in copper beads formed by arc and fire were studied by XPS, respectively. Corresponding to the sputtering depth, the molten product on an arc bead surface layer is with drastic decrease of carbon content and with gentle change of oxygen content which then rapid decreases. While the molten product on a fire bead surface layer is with carbon content decreasing gradually and with oxygen content increasing. As a result, the distributing of C and O and the quantitative results can be used to identify the molten product on a bead induced directly by arc and the molten product on a bead formed by fire, as complementary technique for judgments of fire cause.