Applied Mechanics and Materials Vols. 130-134

Abstract: The presence of noise superimposed on a signal limits the receiver’s ability to correctly identify the intended signal. The principal of adaptive noise cancellation is to acquire an estimation of the unwanted interfering signal and subtract it from the corrupted signal. Noise cancellation operation is controlled adaptively with the target of achieving improved signal to noise ratio. This paper describes the Least Mean Squares (LMS) adaptive filtering algorithm. The algorithm was implemented in Matlab and was tested for noise cancellation in speech signals.

Abstract: The spectral subtraction is one of the best methods for elimination of approximate cyclical engine’s noise from degraded speech signal. Here we turn to research about the nonlinear spectral subtraction method and its improved model. After studying the nonlinear method we turn to this method that whether it can improve the quality of enhanced speech signal, propose the short-time spectral subtraction, which needs two inputs. The main input is containing the voice that is corrupted by noise. The other input (noise reference input) contains noise related in some way to that of the main input (background noise). Then use the main input’s frequency spectrum subtract the other input’s frequency spectrum. The results of experiment have proved it’s effective.

Abstract: Performance of the Duffing oscillator to detect weak signals buried in heavy noise is analyzed quantitatively by LCEs. First in the case of noise, differential equations to compute LCE s are derived using RHR algorithm, so the quantitative criteria to identify system states are obtained. Then using LCEs, the threshold value of the forced periodic term is found accurately. Finally the system state and state change are analyzed using LCEs by keeping the threshold value and varying the noise intensity, and the minimum signal to noise ratio is determined. By contrast of phase trajectories and LCEs, it shows that phase trajectories disturbed by strong noise sometimes are ambiguous to our eyes, but through LCEs, the system state can be identified clearly and quantitatively especially in strong noise background. So the minimum signal to noise ratio can be obtained accurately.

Abstract: An improved control strategy for harmonics restraint of doubly fed wind power system is studied in this paper. Considered low order current harmonics (5^th, 7^th and so on) caused by the distortion or unbalanced grid voltage conditions and the variations of generator itself parameters, an improved control strategy is proposed. In this control strategy, a proportional integral (PI) regulator paralleled with a harmonic resonant (R) controller in the synchronous reference frame is proposed for restraining the stator current harmonics. The control strategy presented in this paper has not effect on the control of fundamental current, and need not the harmonic separation filter and the sequence decomposition in multi reference frames. To verify the effectiveness of this control strategy, simulation model of DFIG system is developed in Matlab/Simulink, and experiments are implemented on the doubly fed experiment platform. The results of both simulations and experiments show that the control strategy proposed in this paper could restrain harmonic currents effectively and it is easy to implement digital control.

Abstract: Ultrasonic vibration aided electrical discharge milling in deionized water is proposed and its mechanism is investigated in this paper. The tool electrode is formed to be walled pipe, and high pressure deionized water is supplied through it. Two groups of orthogonal experiments were carried out respectively, one group with ultrasonic vibration on tool electrode and the other without. Research results show that ultrasonic vibration can improve the machining process and surface roughness.

Abstract: This paper introduces a new non-stationary random vibration technique for the analysis of time-dependent random vibration systems. It is based on the pseudo-excitation method (PEM) and precise integration method (PIM), which is extended herein and can improve significantly the analysis efficiency. Based on the random vibration equations with the right-hand side random replaced by a pseudo excitation, the first and second orders of sensitivity formulae are calculated conveniently by differentiating these equations. By use of sensitivity information, the optimization of complicated random vibration can be performed easily. Some numerical examples of vehicle-bridge time-dependent coupled system show the effectiveness and accuracy of present method.

Abstract: A new type of balance drum with grooves was presented, and analyzed the influence of quantity of grooves on performance of centrifugal pump and balance force by the method of numerical simulation and experiment. The liquid flowing situation at the clearance and the differential pressure on both sides of the balance drum under different quantities of grooves were simulated. The efficiency, quantity of flow and axial force were measured by the experiments with different test devices. After comparing and analyzing the results of simulations and experiments, it indicate that with the increase of grooves the resistance in the clearance increase, the leakage losses reduce, the efficiency of pump enhance and the differential pressure between both sides of the balance drum increase, which contributes to balance the axial force.

Abstract: This paper designs the electromagnetic flowmeter in partially filled pipes (EMF-PF), which sensor sets four electrodes. One pair of the electrodes is set on the pipe bottom as the signal injection electrodes that inject the AC pulses used to determine liquid fill height. One pair of long-arc electrodes is set on the pipe wall as the measurement electrodes. The measurement electrodes alternate duties, sensing both the flow and fill height signals. Both the flow and fill height raw signals are disposed in different time period by the same signal processing channels. Experiment result shows that the designed EMF-PF can achieve the flow measurement in partially filled pipes, and the measurement accuracy of this EMF-PF meets the actual requirements.

Abstract: Based on stator-field-orientation control combining with both direct torque control (DTC) and rotor-field-orientation control a speed estimation scheme is presented in this paper. Two key problems are discussed in detail. First is to use phase operation to decide stator-field-orientation angle θs and then the discrete-tracking-differential (DTD) technique is employed to high quality stator current. The experiments show that accurate speed estimation can be obtained by the method.

Abstract: The Simplified sub-entire domain (SSED) basis function method has been introduced and modified to analyze some planar and curved Frequency selective surfaces (FSSs) with finite size. The number of unknowns and memory consumption of the methods are discussed in detail. The reflection coefficients and transmission coefficients are given, which agree well with the reference results.