Showing papers on "Impulse (physics) published in 2017"
TL;DR: A novel data-driven fault diagnosis method based on sparse representation and shift-invariant dictionary learning is proposed, which proves the effectiveness and robustness of the proposed method and the comparison with the state-of-the-art method is illustrated.
Abstract: It is always a primary challenge in fault diagnosis of a wind turbine generator to extract fault character information under strong noise and nonstationary condition. As a novel signal processing method, sparse representation shows excellent performance in time–frequency analysis and feature extraction. However, its result is directly influenced by dictionary, whose atoms should be as similar with signal's inner structure as possible. Due to the variability of operation environment and physical structure in industrial systems, the patterns of impulse signals are changing over time, which makes creating a proper dictionary even harder. To solve the problem, a novel data-driven fault diagnosis method based on sparse representation and shift-invariant dictionary learning is proposed. The impulse signals at different locations with the same characteristic can be represented by only one atom through shift operation. Then, the shift-invariant dictionary is generated by taking all the possible shifts of a few short atoms and, consequently, is more applicable to represent long signals that in the same pattern appear periodically. Based on the learnt shift-invariant dictionary, the coefficients obtained can be sparser, with the extracted impulse signal being closer to the real signal. Finally, the time–frequency representation of the impulse component is obtained with consideration of both the Wigner–Ville distribution of every atom and the corresponding sparse coefficient. The excellent performance of different fault diagnoses in a fault simulator and a wind turbine proves the effectiveness and robustness of the proposed method. Meanwhile, the comparison with the state-of-the-art method is illustrated, which highlights the superiority of the proposed method.
159 citations
TL;DR: The impulse signal is an instant change signal in very short time, and since the cost function is highly nonlinear, the nonlinear optimization methods are adopted to derive the parameter estimation algorithms to enhance the estimation accuracy.
Abstract: The impulse signal is an instant change signal in very short time. It is widely used in signal processing, electronic technique, communication and system identification. This paper considers the parameter estimation problems for dynamical systems by means of the impulse response measurement data. Since the cost function is highly nonlinear, the nonlinear optimization methods are adopted to derive the parameter estimation algorithms to enhance the estimation accuracy. By using the iterative scheme, the Newton iterative algorithm and the gradient iterative algorithm are proposed for estimating the parameters of dynamical systems. Also, a damping factor is introduced to improve the algorithm stability. Finally, using simulation examples, this paper analyzes and compares the merit and weakness of the proposed algorithms.
101 citations
TL;DR: In this paper, the structural response of composite panels with triple layered graded honeycomb cores under blast loading was analyzed by using finite element software LS-DYNA after validation against the experiments and the structural deformation modes were classified into three types and the core layer deformation was divided into three regions.
88 citations
TL;DR: The main tool used is the construction of an impulse-time-dependent complete Lyapunov functional, which derives delay-dependent sufficient conditions for exponential stability and L 2 -gain in terms of linear matrix inequalities.
71 citations
TL;DR: In this article, the combined processes of self-sputter (SS)-recycling and process gas recycling in high power impulse magnetron sputtering (HiPIMS) discharges were analyzed using the generalized recycling model.
Abstract: The combined processes of self-sputter (SS)-recycling and process gas recycling in high power impulse magnetron sputtering (HiPIMS) discharges are analyzed using the generalized recycling model (GR ...
68 citations
TL;DR: Some FTS criteria for the nonlinear impulsive sampled-data systems are derived in terms of linear matrix inequalities (LMIs), which can be easily verified via the LMI toolbox.
Abstract: This paper investigates the finite time stability (FTS) for nonlinear impulsive sampled-data systems. By constructing an appropriated Lyapunov function and employing average impulsive interval (AII) method, some FTS criteria for the nonlinear impulsive sampled-data systems are derived in terms of linear matrix inequalities (LMIs), which can be easily verified via the LMI toolbox. The hybrid controller including sampled-data controller and impulsive controller is designed via the established LMIs. Moreover, the impulse effect considered in this paper including stabilizing impulse and destabilizing impulse. Our developed results are less conservative than the recent work in the literature. Finally, two numerical examples are provided to show the applications of the proposed criteria.
65 citations
TL;DR: Simulations show that the best RIR interpolation is obtained when combining the novel time-domain acoustic model with the spatio-temporal sparsity regularization, outperforming the results of the plane wave decomposition model even when far fewer microphone measurements are available.
Abstract: Room Impulse Responses (RIRs) are typically measured using a set of microphones and a loudspeaker. When RIRs spanning a large volume are needed, many microphone measurements must be used to spatially sample the sound field. In order to reduce the number of microphone measurements, RIRs can be spatially interpolated. In the present study, RIR interpolation is formulated as an inverse problem. This inverse problem relies on a particular acoustic model capable of representing the measurements. Two different acoustic models are compared: the plane wave decomposition model and a novel time-domain model, which consists of a collection of equivalent sources creating spherical waves. These acoustic models can both approximate any reverberant sound field created by a far-field sound source. In order to produce an accurate RIR interpolation, sparsity regularization is employed when solving the inverse problem. In particular, by combining different acoustic models with different sparsity promoting regularizations, spatial sparsity, spatio-spectral sparsity, and spatio-temporal sparsity are compared. The inverse problem is solved using a matrix-free large-scale optimization algorithm. Simulations show that the best RIR interpolation is obtained when combining the novel time-domain acoustic model with the spatio-temporal sparsity regularization, outperforming the results of the plane wave decomposition model even when far fewer microphone measurements are available.
46 citations
01 Sep 2017
TL;DR: In this article, the authors investigated the effect of dichlorodifluoromethane (R12) gas and mixtures with nitrogen (N2) and air at different pressures and mixing ratios and showed good alternative to S F 6 gas in terms of highvoltage application.
Abstract: In this study, dichlorodifluoromethane (R12) gas and mixtures with nitrogen (N2) and air at different pressures and mixing ratios have been investigated and showed good alternative to S F 6 gas in terms of high-voltage application. Mixed gases contain R12 gas, they offer good dielectric properties and possibility to be used in low-temperature environment. Synergistic effects and self-recoverability test have been performed. Dielectric strength under quasi-uniform field showed in the order of S F 6 > R 12 > N 2 > air in alternating current (AC), direct current (DC) and impulse was examined. Mixture R12/N2 (80/20%) could reach over 0.90–0.95 times to that of S F 6 gas at 50 lb/in2 at AC and R12/air (70/30%) gives 0.80–0.90 to S F 6 gas. R12 gas presents brilliant self-recoverability. The optimal ratio to switch S F 6 gas is R12/N2 (80/20%) and R12/air (70/30%) is based on the authors’ experimental condition and setup.
43 citations
TL;DR: In this paper, a voltage impulse perturbation approach based on negative resistance is applied to trigger high-energy-orbit responses of piezoelectric nonlinear energy harvesters.
Abstract: Nonlinear energy harvesters have attracted wide research attentions to achieve broadband performances in recent years. Nonlinear structures have multiple solutions in certain frequency region that contains high-energy and low-energy orbits. It is effectively the frequency region of capturing a high-energy orbit that determines the broadband performance. Thus, maintaining large-amplitude high-energy-orbit oscillations is highly desired. In this paper, a voltage impulse perturbation approach based on negative resistance is applied to trigger high-energy-orbit responses of piezoelectric nonlinear energy harvesters. First, the mechanism of the voltage impulse perturbation and the implementation of the synthetic negative resistance circuit are discussed in detail. Subsequently, numerical simulation and experiment are conducted and the results demonstrate that the high-energy-orbit oscillations can be triggered by the voltage impulse perturbation method for both monostable and bistable configurations given various scenarios. It is revealed that the perturbation levels required to trigger and maintain high-energy-orbit oscillations are different for various excitation frequencies in the region where multiple solutions exist. The higher gain in voltage output when high-energy-orbit oscillations are captured is accompanied with the demand of a higher voltage impulse perturbation level.
43 citations
TL;DR: In this article, a predator-prey model with Holling type-I functional response and multi state impulsive feedback control is established, where the intensity of pesticide spraying and the release amount of natural enemies are linearly dependent on the given threshold in the second impulse.
Abstract: In this paper, a predator-prey model with Holling type-I functional response and multi state impulsive feedback control is established, where the intensity of pesticide spraying and the release amount of natural enemies are linearly dependent on the given threshold in the second impulse. Firstly, the existence of order-1 periodic solution of the system is investigated by successor functions and Bendixson theorem of impulsive differential equations, then the stability of periodic solutions is proved by the analogue of the Poincare criterion. Furthermore, in order to reduce the actual total cost and obtain the best economic benefit, the optimal economic threshold is obtained, which provides the optimal strategy for the practical application. Finally, numerical simulations for specific examples are carried out to illustrate the feasibility of the above conclusions.
37 citations
TL;DR: The second author thanks the Engineering and Physical Sciences Research Council (EPSRC) for financial support via its 'Doctoral Training' scheme as mentioned in this paper, which has been used to train hundreds of researchers.
Abstract: The second author thanks the Engineering and Physical Sciences Research Council (EPSRC) for financial support via its 'Doctoral Training' scheme.
TL;DR: It is shown that impulses occurring randomly in impulse time windows can still stabilize and/or synchronize the considered neural networks under certain suitable assumptions.
Abstract: This paper studies the problem of global exponential stabilization and synchronization for impulsive Hopfield-type neural networks with impulse time window. By using the stability theory of impulsive dynamical systems, some sufficient conditions guaranteeing the global exponential stabilization and synchronization of Hopfield-type NNs are derived. The main innovation embodies that the impulsive instants are no longer limited at fixed instants, but suggested to be at some certain time intervals, named by impulse time windows. We shall show that impulses occurring randomly in impulse time windows can still stabilize and/or synchronize the considered neural networks under certain suitable assumptions. Two numerical examples are also given to illustrate the effectiveness of theoretical results.
TL;DR: The results provide a good perspective for using the portable PASCO PS-2142 force plate in sports and clinical biomechanics and reveal good precision and accuracy for the vertical component of the portable force plate.
Abstract: The aim of this study was to determine the precision and accuracy of the vertical and anterior-posterior force components of the portable PASCO PS-2142 force plate. Impulse, peak force, and time to peak force were assessed and compared to a gold standard force plate in three different tasks: vertical jump, forward jump, and sprint start. Two healthy male participants performed ten trials for each task, resulting in 60 trials. Data analyses revealed good precision and accuracy for the vertical component of the portable force plate, with relative bias and root mean square (RMS) error values nearly the same in all tasks for the impulse, time to peak force, and peak force parameters. Precision and accuracy of the anterior-posterior component were lower for the impulse and time to peak force, with relative bias and RMS error values nearly the same between tasks. Despite the lower precision and accuracy of the anterior-posterior component of the portable force plate, these errors were systematic, reflecting a good repeatability of the measure. In addition, all variables presented good agreement between the portable and gold standard platforms. Our results provide a good perspective for using the aforementioned portable force plate in sports and clinical biomechanics.
TL;DR: In this article, the oxygen dynamics in a reactive Ar/O2 high power impulse magnetron sputtering discharge was studied using a new reactive ionization region model and the aim was to identify the dominating phy...
Abstract: The oxygen dynamics in a reactive Ar/O2high power impulse magnetron sputtering discharge hasbeen studied using a new reactive ionization region model. The aim has been to identify thedominating phy ...
TL;DR: It is concluded that the dynamic effects of the reflected pressure pulses should always be considered in structural design, most relevantly when analysing closed structures where the number of reflections can be significant.
TL;DR: In this paper, the minimum impulse of pushing a droplet through a narrow circular constriction is derived and numerically verified, and the existence of this minimum impulse is mathematically derived.
Abstract: Models of a droplet passing through narrow constrictions have wide applications in science and engineering. In this paper, we report our findings on the minimum impulse (momentum change) of pushing a droplet through a narrow circular constriction. The existence of this minimum impulse is mathematically derived and numerically verified. The minimum impulse happens at a critical velocity when the time-averaged Young-Laplace pressure balances the total minor pressure loss in the constriction. Finally, numerical simulations are conducted to verify these concepts. These results could be relevant to problems of energy optimization and studies of chemical and biomedical systems.
TL;DR: In this paper, the authors proposed a new feedback law for the heat equations in a bounded domain with Dirichlet boundary condition, which consists in linking an observation estimate at one time, minimal norm impulse control, approximate inverse source problem and rapid output stabilization.
TL;DR: In this paper, the steady state performance of an axial-flow impulse turbine was studied by carrying out over 140 cases, and the total pressures at the chamber and atmosphere sides and torque output under various incident flow velocities and prescribed rotation speeds were presented.
TL;DR: In this article, the authors examined the oscillatory behavior of complex viscoelastic systems with power-law like relaxation behavior and used the fractional Maxwell model, consisting of a spring and fractional dashpot in series, which produces a power law creep behavior and a relaxation law following the Mittag-Leffler function.
Abstract: This paper examines the oscillatory behavior of complex viscoelastic systems with power law like relaxation behavior. Specifically, we use the fractional Maxwell model, consisting of a spring and fractional dashpot in series, which produces a power-law creep behavior and a relaxation law following the Mittag-Leffler function. The fractional dashpot is characterized by a parameter β, continuously moving from the pure viscous behavior when β = 1 to the purely elastic response when β = 0. In this work, we study the general response function and focus on the oscillatory behavior of a fractional Maxwell system in four regimes: Stress impulse, strain impulse, step stress, and driven oscillations. The solutions are presented in a format analogous to the classical oscillator, showing how the fractional nature of relaxation changes the long-time equilibrium behavior and the short-time transient solutions. We specifically test the critical damping conditions in the fractional regime, since these have a particular r...
TL;DR: In this article, a cylinder-based nonlinear phononic crystal is proposed to achieve nearly complete transmission and strong attenuation under impulse excitation by in-situ control of contact angles between cylinders.
Abstract: We present a novel device that can offer two extremes of elastic wave propagation — nearly complete transmission and strong attenuation under impulse excitation. The mechanism of this highly tunable device relies on intermixing effects of dispersion and nonlinearity. The device consists of identical cylinders arranged in a chain, which interact with each other as per nonlinear Hertz contact law. For a ‘dimer’ configuration, i.e., two different contact angles alternating in the chain, we analytically, numerically, and experimentally show that impulse excitation can either propagate as a localized wave, or it can travel as a highly dispersive wave. Remarkably, these extremes can be achieved in this periodic arrangement simply by in-situ control of contact angles between cylinders. We close the discussion by highlighting the key characteristics of the mechanisms that facilitate strong attenuation of incident impulse. These include low-to-high frequency scattering, and turbulence-like cascading in a periodic system. We thus envision that these adaptive, cylinder-based nonlinear phononic crystals, in conjunction with conventional impact mitigation mechanisms, could be used to design highly tunable and efficient impact manipulation devices.
TL;DR: A new system, named by sandwich control system with impulse time windows, is formed, composed of three parts in a round: the first and last parts are continuous subsystems, while the middle one includes an impulsive operation.
Abstract: In this paper, we formulate a new system, named by sandwich control system with impulse time windows. The present system is a cyclic control system, composed of three parts in a round: the first and last parts are continuous subsystems, while the middle one includes an impulsive operation. Different from the most existing results for impulsive systems, we assume that the impulse moments are unknown but limited to certain intervals (namely, impulse time windows). We then study the stability of the considered systems and obtain an exponential stability criterion in terms of a set of linear matrix inequalities. As a numerical example, Chua oscillator is stabilized by the proposed method.
TL;DR: In this article, an eight-degree-of-freedom (DOF) dynamic model of the gear-shaft bearing-housing system is established and the vertical vibration transmission and energy dissipation characteristics through the multiple transmitting interfaces under the impulse force due to gear fault are studied.
TL;DR: In this paper, the authors conducted twenty-five groups of orthogonal experiments of landslide-induced impulse waves in shallow water where the Froude numbers ranged between 0.6 and 2.0.
TL;DR: The linear impulsive control systems with impulse time windows are formulated and the asymptotic stability of the case of linear systems is studied and several stability criteria are obtained.
Abstract: We formulate the linear impulsive control systems with impulse time windows. Different from the most impulsive systems where the impulses occur at fixed time or when the system states hit a certain hyperplane, the impulse time in the presented systems might be uncertain, but limited to a small time interval, i.e. a time window. Compared with the existing impulsive systems, the systems with impulse time windows is of practical importance. We then study the asymptotic stability of the case of linear systems and obtain several stability criteria. Numerical examples are given to verify the effectiveness of the theoretical results.
TL;DR: This paper proposes, analyzes, and implements a simple and cost-effective impulse commutated modular three-phase circuit to eliminate and solve the associated turn-off spike problem.
Abstract: Current-fed converters offer enormous potential as power conditioning units for fuel cell applications, owing to precise fuel cell stack current control, short-circuit protection, voltage gain, and stiff fuel cell dc current. Aspects such as low current ripple and smaller input current slope ensure energy efficient operation and better fuel utilization, and enhance the lifetime of the fuel cell stack. However, the demerits of turn-off voltage spike across semiconductor devices limits the operating frequency. This paper proposes, analyzes, and implements a simple and cost-effective impulse commutated modular three-phase circuit to eliminate and solve the associated turn-off spike problem. Impulse commutation permits soft turn-off of devices and clamps the device voltage. The converter efficiently handles the variations in the fuel cell stack voltage and current with variable frequency modulation. Detailed steady-state operation, analysis, and performance of the proposed modular converter with impulse commutation are reported. The proposed impulse commutated three-phase circuit is a potential candidate for high-current applications. The validation of the converter operation on a 1-kW proof-of-concept hardware prototype is performed to substantiate the claims.
TL;DR: By combining the biwindow configuration with weighted median filters, anisotropic morphological directional derivatives (AMDDs) robust to impulse noise are proposed to measure the local grayscale variation around a pixel.
Abstract: Traditional differential-based edge detection suffers from abrupt degradation in performance when images are corrupted by impulse noises. The morphological operators such as the median filters and weighted median filters possess the intrinsic ability to counteract impulse noise. In this paper, by combining the biwindow configuration with weighted median filters, anisotropic morphological directional derivatives (AMDDs) robust to impulse noise are proposed to measure the local grayscale variation around a pixel. For ideal step edges, the AMDD spatial response and directional representation are derived. The characteristics and edge resolution of two kinds of typical biwindows are analyzed thoroughly. In terms of the AMDD spatial response and directional representation of ideal step edges, the spatial matched filter is used to extract the edge strength map (ESM) from the AMDDs of an image. The spatial and directional matched filters are used to extract the edge direction map (EDM). Embedding the extracted ESM and EDM into the standard route of the differential-based edge detection, an anti-impulse-noise AMDD-based edge detector is constructed. It is compared with the existing state-of-the-art detectors on a recognized image dataset for edge detection evaluation. The results show that it attains competitive performance in noise-free and Gaussian noise cases and the best performance in impulse noise cases.
TL;DR: In this article, the authors used UHF and pulse current to detect needle-plane defect under oscillating lightning impulse (OLI) and measured the PD of a needle plane defect under negative OLI.
Abstract: Gas insulated switchgear (GIS) is used in power system more and more widely. With the increased voltage level of power system, field impulse voltage withstand test becomes increasingly important. It would be beneficial for a comprehensive insulation evaluation to carry out the detection of partial discharge (PD) under impulse voltage withstand test in field. Metal protrusions or particles on HV conductor are typical defects in GIS and are critical at lightning impulse voltages. This paper therefore aims at PD characteristics study on needle-plane defect under oscillating lightning impulse (OLI). PD detection system was established based on ultra-high frequency (UHF) and pulse current detection. Then, the PD of a needle-plane defect under negative OLI was measured. The relation between statistical time lag, PD amplitude, PD times and the applied voltage was analyzed respectively based on UHF detection. The results show that UHF detection has high sensitivity and it is suitable in field impulse voltage withstand test. PDs occur around each wave peak of the applied voltage. With the increase of peak voltage, PD magnitude and PD times in each oscillation cycle both increase linearly. Further analysis indicates that the occurrence and development of PD under negative OLI can be interpreted by electron emission from metal surface, field detachment from negative ions and corona stabilization effect. This approach is valuable for PD measurement and analysis in field impulse voltage withstand test for GIS.
TL;DR: In this article, a corrected equation was established by taking a correction factor of impulse per unit area into consideration, in which the relations between the mass of TNT, the stand-off distance and the impulse per units area were determined.
TL;DR: In this paper, a three-phase finite element model based on the finite element method is introduced to simulate the generation and propagation of landslide-generated impulse waves, and this model can be employed to predict and prevent wave-induced hazards.
TL;DR: In this article, the authors investigated the saturated impulse for fully clamped square plates subjected to linearly decaying pressure pulse, which is closer to the pulse produced by explosive loading, and provided an empirical expression for saturated duration based on the elastic-plastic numerical results.