Narrow-band Process Research Articles

Hierarchical neural processing in γ oscillations for syntactic and semantic operations accounts for first- and second-language epistemology.

We discuss event-related power differences (ERPDs) in low- and broadband-γ oscillations as the embedded-clause edge is processed in wh-dependencies such as Which decision regarding/about him/her did Paul say that Lydie rejected without hesitation? in first (L1) and second language (L2) French speakers. The experimental conditions manipulated whether pronouns appeared in modifiers (Mods; regarding him/her) or in noun complements (Comps; about him/her) and whether they matched or mismatched a matrix-clause subject in gender. Across L1 and L2 speakers, we found that anaphora-linked ERPDs for Mods vs. Comps in evoked power first arose in low γ and then in broadband γ. Referential elements first seem to be retrieved from working memory by narrowband processes in low γ and then referential identification seems to be computed in broadband-γ output. Interactions between discourse- and syntax-based referential processes for the Mods vs. Comps in these ERPDs furthermore suggest that multidomain γ-band processing enables a range of elementary operations for discourse and semantic interpretation. We argue that a multidomain mechanism enabling operations conditioned by the syntactic and semantic nature of the elements processed interacts with local brain microcircuits representing features and feature sets that have been established in L1 or L2 acquisition, accounting for a single language epistemology across learning contexts.

Extreme value analysis of multivariate Gaussian processes with wave-passage effects

Extreme value analysis is a central aspect of random vibration applications. Most studies focus on a univariate process. System reliability necessitates the extreme value across multiple correlated processes, but analytical methods are scarce and confined to low-dimensional problems. Recently, the authors proposed an analytical method for the extreme analysis of multivariate Gaussian processes. The exact upcrossing rate is derived for the maximum process representing the instantaneous maxima over all processes, and the extreme value distribution is obtained from the Poisson approximation. Nevertheless, for applications involving the wave-passage effect that is commonplace in random vibration, the upcrossings manifest in clumps, rendering the Poisson approximation conservative. The clumping from wave-passage is a complex novel phenomenon, differing from the clumping in narrowband processes. This paper extends the prior work by developing an analytical method for predicting the clump size, thereby providing an accurate prediction of the multivariate extreme value while accounting for the wave-passage effect. The method is powerful as it is fast and amenable to high-dimensional problems. Two examples include the propagation of ocean waves and a multi-span bridge subjected to propagating ground motions. The proposed method is shown to accurately predict the clumping factor and the probability of failure, compared to numerical simulations. In contrast, the Poisson approximation using the exact upcrossing rate noticeably overestimates the failure probability.

Effects of size and location of magnetorheological segments on random vibration response of laminated composite beams using an N-layer of layerwise theory

Laminated composite beams are widely used in engineering applications, including wind turbine blades and automobile, where the structures are highly subjected to non-deterministic random loadings, requiring a reliable technique to ensure the stability of the structure during operation. Recently, to mitigate the effects of random loadings on the structural stability of the structure, segments of magnetorheological (MR) fluids have been embedded in the laminated beams (MR-laminated beams). In this work, the effects of the size and location of MR-fluid segments on random vibration characteristics are investigated. A laminated beam is considered in which several layers/segments are filled with MR fluids and are subjected to several random loads. An N-layer model of layerwise theory (LWT) developed by the present authors in previous work is considered for computational purposes. A finite element model based on LWT is developed to study the numerical examples. MR-laminated beams consist of five sections; two MR-fluid sections and three composite sections have been studied using LWT. To justify the numerical results, the first three natural frequencies of a laminated beam without an MR layer are solved using a 3D model in COMSOL software which shows a close match with the results of LWT. An in-house experimental setup has been developed to verify the simulation results. The simulation results are then compared with the first-order shear deformation theory (FSDT) and verified by several experimental tests. The effects of MR fluid segments on the dynamic response of MR-laminated beams for six different configurations have been investigated. In addition, the effects of thicknesses of MR fluid section on the dynamic behavior of structures have been investigated. Effects of magnetic fields on statistical properties, correlation, and autocorrelation on MR-laminated beams made of E-glass and fiber-carbon have been investigated. As a case study, the vibration response of a wind turbine blade made of an MR-laminated beam has been investigated using a narrow band process.

Practical imaging algorithms in ultra-wideband radar systems using active aperture synthesis and stochastic probing signals

The subject of the manuscript is the algorithms for radar imaging. This research develops imaging methods and algorithms for wideband and ultrawideband active aperture synthesis systems with antenna arrays and stochastic probing signals. The use of antenna arrays makes it possible to obtain radar images without the need to move radar or antenna system in space. The use of wideband and ultra-wideband stochastic probing signals is justified by their narrow autocorrelation functions. This increased the resolution of the obtained images. The main idea of the proposed algorithms is to filter the original wideband signal into several narrowband processes. Furthermore, only the central frequencies of each narrowband signal were processed. This approach allows us to use the classical widespread methods of aperture synthesis for the case of a wideband signal. Usually, they are applicable only for narrowband signals that satisfy the condition of a quasi-monochromatic approximation. This significantly reduces the overall computational complexity of the imaging algorithm, which simplifies its further practical implementation on the existing radioelement base. Because of the simulation, a primary radar image has been obtained and the overall performance of the proposed approach to processing wideband signals has been confirmed. An increase in the quality of the obtained image when using a multiple of frequency ranges is shown. An experimental study of the effect of processing a wideband signal only at its centre frequency instead of the entire frequency band is conducted. During the experiment, the correlation functions of the signals received by two spaced receivers were obtained. As a result, the Van Cittert-Zernike theorem has been experimentally confirmed. It allows signal processing only at its centre frequency instead of the entire frequency band. Simultaneously, the prospect of expanding the bandwidth of the probing signal is indicated. It, in the presence of a wideband element base and devices for high-speed signal processing, will further increase the imaging resolution of a radar system.

РАСЧЁТНО-ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ ВЛИЯНИЯ ДЕМПФИРОВАНИЯ КОНСТРУКЦИИ НА ЕЁ ДОЛГОВЕЧНОСТЬ ПРИ СЛУЧАЙНОМ НАГРУЖЕНИИ

Mechanical engineering products are often subjected to dynamic impact during operation. The analysis of the durability of structures functioning under random multi-frequency loading requires taking into account their dynamic parameters (natural frequencies and vibration forms, damping, etc.). This paper analyzes the influence of the damping coefficient on the durability of a structurally similar specimen using a method for the narrow-band process and the Dirlik method. A computational scheme based on a finite element model determines the stress spectral density. The study defines the range of the damping coefficient variation by experiment and calculates the durability of the damping coefficient. The influence of damping on durability is analyzed by different methods. The calculations are experimentally verified.

Two-photon spontaneous emission of an atom in a cosmic string background

It is well known that the vicinities of an atomic system may substantially affect its radiative properties. In this work, we consider the influence of a cosmic string background in the spontaneous emission of an excited atom. We start by computing the one-photon spontaneous emission rate of a quantum emitter, which is a narrow band process, and then we analyze the more complex case of the two-photon spontaneous emission, which is a broadband and much richer phenomenon. In the former case, we analyze not only the behavior of the decay rate with the distance from the atom to the string, but also with the deficit angle associated with the cosmic string metric. In the latter case, we show that the spectral distribution of the emitted photons is substantially affected by the cosmic string background.

Damage equivalent load synthesis and stochastic extrapolation for fatigue life validation

Abstract. Present verification of the fatigue life margins on wind turbine structures utilizes damage equivalent load (DEL) computations over a limited time duration. In this article, a procedure to determine long-term fatigue damage and remaining life is presented as a combination of stochastic extrapolation of the 10 min DEL to determine its probability of exceedance and computationally fast synthesis of DELs using level crossings of a Gaussian process. Both the synthesis of DELs and long-term stochastic extrapolation are validated using measured loads from a wind farm. The extrapolation for the blade root flap and tower base fore–aft damage equivalent moment is presented using a three-parameter Weibull distribution, whereby the long-term damage equivalent load levels are forecast for both simulated and measured values. The damage equivalent load magnitude at a selected target probability of exceedance provides an indicator of the integrity of the structure for the next year. The extrapolated damage equivalent load over a year is validated using measured multi-year damage equivalent loads from a turbine in the Lillgrund wind farm, which is subject to wakes. The simulation of damage equivalent loads using the method of level crossings of a Gaussian process is shown to be able to reconstruct the damage equivalent load for both blade root and tower base moments. The prediction of the tower base fore–aft DEL is demonstrated to be feasible when using the Vanmarcke correction for very narrow band processes. The combined method of fast damage equivalent load computations and stochastic extrapolation to the next year allows a quick and accurate forecasting of structural integrity of operational wind turbines.

Detection of radar signals scattered by acoustic disturbances generated by UAVs

The problem of UAV radar monitoring by its acoustic radiation is considered. It is shown that in a number of practical cases such an approach is preferable to observation by radar methods directly from the UAV airframe. It is noted that the radio signals scattered by acoustic packets from the UAV are characterized by an unknown in advance complex envelope, which does not allow the use of optimal filtering methods for their detection and estimation. It is shown that to solve these problems, it is advisable to use the principle of accumulation over the observation interval of the energy of a narrow-band random process reduced to the noise dispersion, using the statistical differences between noise fluctuations and the additive "signal-plus-noise" mixture. It is shown that the energy estimate reduced to noise has either a central or an off-center "chi-square" distribution with a certain number of degrees of freedom and an off-center parameter greater than or equal to zero. As a result of comparing the current value of the no centrality parameter with the threshold value, a decision is made on the presence or absence of a useful signal in the observation interval with minimal a priori information about its parameters. It is noted that the well-known expressions for the differential probability densities of the central and non-central chi-square distributions allow one to obtain qualitative estimates of the synthesized detector. A practical structural diagram of a detector using processing of received oscillations in quadrature channels is proposed.

Narrowbandness of seismic ground displacement on a broader area of the lithosphere and importance on base motion in isolated structures

Power spectral density of horizontal ground displacement of large and recent events in earthquake-prone Latin America is analyzed. The results confirm -in a larger region of the world- that strong motion horizontal displacement is a narrowband process, which was previously demonstrated solely on a very limited area: the State of California. Nonetheless, those limited and previous results proved to be important in seismic base isolation; particularly, in the solution of the problem of large displacements at the structure base. This is a current problem for which more expensive techniques than passive control are presently being implemented, as active or hybrid control; therefore, it is emphasized that a solution exists within simple base isolation, and it is based on ground displacement narrowbandness.

Influence of the excitation frequency content on the efficiency of a tuned liquid column damper

The current study addresses the influence of the excitation frequency content on the efficiency of a tuned liquid column damper (TLCD) to control the displacement response in structures subjected to seismic excitations. A time-domain stochastic stationary analysis is performed, and an equivalent statistical linearization for the TLCD is obtained. The results show that the TLCD is more efficient in structures subjected to broadband processes. In narrowband processes, the maximum performance of the TLCD occurs when the linear equivalent period of the system TLCD-structure tunes the TLCD period, and the frequency of the structure matches the predominant frequency of the input motion. Results derived from this analysis are validated through two time-history seismic analyses.

Nonlinear distortion of angle modulation signal in output power amplifiers

The output power amplifier is operated in nonlinear mode to increase its efficiency, at which the signal is distorted more. The goal is to analyze effects of nonlinearity on the modulating signal of angle-modulated signal distortions for single-ended and push-pull output power amplifiers with memory and without it. The amplifier characteristic ic(vBE) is preset by the cubic polynomial. The output voltage of memoryless amplifier uout(t) is found by Ohm's law. And in case with amplifier with memory, the output voltage uout(t) is found by Complex amplitude method with a Fourier series of function ic(t). The output voltage uout(t) is represented as the narrowband process with envelope of the waveform U1(t) and initial phase Ф1(t) to determine the angular modulation law Ф1(t) at the amplifier output. The function U1(t) is defined as combination of in-phase А(t) and quadrature В(t) components. The distortion estimate based on Total Harmonic Distortion (THD). The measurement of THD is defined as the ratio of the RMS amplitude of a set of higher harmonic frequencies to the RMS amplitude of the first harmonic. The spectrum of function Ф1(t) is represented a Fourier series. In single-ended memoryless amplifier and non-cutoff mode, the THD decreases as m increases and THD of modulating signal is {37.6; 18.8; 6.3%} at m {0.5; 1; 3}. In cutoff mode, the smallest THD is {15.18; 5.13%} at m {1; 3} as θ = 140o. In push-pull memoryless amplifier and θ = 90o, the THD is {22.2; 11.1; 3.7%} at m {0.5; 1; 3} which is 1.7 times less than in a single-ended amplifier without cutoff. This is due to compensation even-order harmonic of amplified signal at the output of a pushpull amplifier. In this case of memoryless amplifier, the transistor load is a parallel RLC circuit. The distortion decreases under m increases at first (up m is 1.5), but then rapidly increases (from m is 1.7). This is due to increase of the parasitic harmonics level caused by the nonlinearity of the phase-frequency characteristic of RLC circuit. The calculations show that THD of modulating signal is 3.35, 9.02 and 22.88 % at Q = 10 and m {0.5; 1; 3}, respectively. In cutoff mode, the smallest THD is at θ = 90o and it does not depend on θ at large values of m. In push-pull amplifier with memory, the THD is 2.8, 2.5 and 3.0 times less than for a singleended amplifier without cutoff at Q {2.5; 5; 10}, respectively. The results of this paper can be used for the design of signal processing systems.

Varied approaches to loading assessment in fatigue studies

In this paper, the authors want to draw readers’ attention to one long-standing question: which approach is preferable for estimation longevities in fatigue problem, the time domain approach (Rainflow) or the frequency domain one (Dirlik and others)? This question is important in engineering problems, particularly in problems of prolongation of the guaranteed service life. The discussion here is restricted by the longevity evaluation only at the post-processing stage of unidirectional loaded machine parts. It means the realizations might be recorded.Some experimental and speculative evidence of preferable use the Rainflow method is shown. Taking into account the huge computer's power nowadays, the question of the irrelevance of appellation to the calculation accelerating using the spectral methods is specially discussed.There are areas, where the spectral methods are really necessary. There is only a need to recommend the restriction of their application scope to these special situations. It seems there is no need in inventing new spectral complicated algorithms only to stress out at the end, that their result coincides with the Rainflow outcome. That might be confusing for the practicing engineers.Currently, the main attention among supporters of spectral methods is focused on non-stationary and non-Gaussian random processes. (to estimate the spectral density is impossible for non-stationary processes, according to definition). These researchers seem to have forgotten, that even for these complicated situations the decision has already existed: that is the Rainflow and its analogues.The paper shows extensive laboratory experiment results of random fatigue testing of aluminum flat specimens under regular (to build the fatigue curve) and irregular (random) loading. The fatigue life curve (Gassner curve) has been built. These results allowed to compare the existing computation methods of longevity estimation. In the particular situation of narrow-band process, the methods seem to provide comparative results.Considered are methodological issues related to the assessment of the necessary and sufficient realization length, the influence of RMS, cycle counting methods and some possibilities of computing resources saving when using the Rainflow method. The stability of the Rainflow estimates is confirmed. Some problems with the choice of parameters during the longevity assessment by the Dirlik method were noted.

Application of the polynomial filtering algorithm to identification of the narrowband process parameters

A polynomial filtering algorithm has been implemented to identify the central frequency and correlation interval of a narrowband process. The efficiency of the polynomial filtering algorithm is carried out by comparing it with the potential accuracy calculated using the algorithm based on multi-alternative filtering. Recurrent relations are proposed for determining the lower bound of accuracy for estimating the parameters of a narrowband process. The possibility of using less computationally expensive procedures for calculating the lower bound of accuracy is investigated.

Advanced Signal Processing Methods for Inspection of Aircraft Structural Materials

Abstract Aircraft, their assemblies, and units must provide high durability and reliability, and maintain mechanical and technological characteristics throughout the life span of the aircraft. Different elements of aircraft structures work under mechanical loads, over a wide temperature range, with varying degrees of exposure to corrosive environments. Aircraft structural materials have a variation in the characteristics values and require the various testing methods for their inspection. In many NDT methods applied in aviation materials testing, signals that could be represented by a narrowband processes model are used. Known methods of their processing are focused on determining and analyzing the signals amplitude characteristics, but the information resource contained in phase characteristics is not used. In the article, the methodology for signal processing and determining phase characteristics in the time domain are discussed. It is based on the combination of the discrete Hilbert transform and the deterministic and statistical methods of the phase measurement. There are given examples of the application of the methodology for pulsed eddy current testing of electrically conductive materials and products, ultrasonic thickness measurement of products made of materials have significant ultrasonic attenuation, the realization impulse variant of acoustic impedance flaw detection of products made of composite materials. The examples have shown that the proposed signal processing methodology enables to determine new information parameters and signal characteristics for the industry, and extend the scope of known NDT methods.

Non-linear dynamic response of a cable system with a tuned mass damper to stochastic base excitation via equivalent linearization technique

Non-linear dynamic model of a cable–mass system with a transverse tuned mass damper is considered. The system is moving in a vertical host structure therefore the cable length varies slowly over time. Under the time-dependent external loads the sway of host structure with low frequencies and high amplitudes can be observed. That yields the base excitation which in turn results in the excitation of a cable system. The original model is governed by a system of non-linear partial differential equations with corresponding boundary conditions defined in a slowly time-variant space domain. To discretise the continuous model the Galerkin method is used. The assumption of the analysis is that the lateral displacements of the cable are coupled with its longitudinal elastic stretching. This brings the quadratic couplings between the longitudinal and transverse modes and cubic nonlinear terms due to the couplings between the transverse modes. To mitigate the dynamic response of the cable in the resonance region the tuned mass damper is applied. The stochastic base excitation, assumed as a narrow-band process mean-square equivalent to the harmonic process, is idealized with the aid of two linear filters: one second-order and one first-order. To determine the stochastic response the equivalent linearization technique is used. Mean values and variances of particular random state variable have been calculated numerically under various operational conditions. The stochastic results have been compared with the deterministic response to a harmonic process base excitation.

Fatigue of offshore structures: A review of statistical fatigue damage assessment for stochastic loadings

Structural offshore fatigue can be accelerated way to reduce the time required for testing. In this regard, a statistical analysis of the loads must be performed to reduce loads with low damage contribution, while the uncertainties from external sources are retained. This process generates the spectrum required to perform the accelerated tests. Subsequently, the spectrum can be extrapolated, which increases the damage and reduces the testing time. In this work, a review of the main types of offshore structures is presented, including a description of the main statistical signal process analysis. In addition, a review of the damage model used in offshore analysis is presented. This can be modelled as a Gaussian or narrow-band process, depending on the variable amplitude loading which generates a random process due to waves.

Nonlinear Stochastic Analysis of Footbridge Lateral Vibration Based on Probability Density Evolution Method

Footbridge lateral vibration remains an unsolved problem and is characterized by the following: (1) pedestrians are sensitive to bridge vibration, which causes the pedestrian’s excitation being dependent on the bridge vibration; (2) pedestrian lateral excitation is a stochastic process rather than a perfect periodic load. Therefore, footbridge lateral vibration is essentially a complex nonlinear stochastic vibration system. Thus far, an effective method of dealing with such nonlinear stochastic vibration of footbridges remains lacking. A framework based on the probability density evolution (PDE) method is presented. For the mathematical model, the parameter resonance model is used to describe the pedestrian‐bridge interaction while treating the pedestrian lateral excitation as a narrow‐band process. For the analysis method, PDE is used to solve the nonlinear stochastic equations in combination with the number theoretical and finite difference methods. The proposed method establishes a new approach in studying footbridge lateral vibration. First, PDE based on the small sample strategy avoids the large amount of computation. Second, the randomness of both structural parameters and pedestrian lateral excitation could be taken into consideration by the proposed method. Third, based on the probability results with rich information, the serviceability, dynamic reliability, and random stability analyses are realized in a convenient manner.

Equivalent linearization technique in nonlinear stochastic dynamics of a cable-mass system with time-varying length

In this paper the transverse vibrations of a vertical cable carrying a concentrated mass at its lower end and moving slowly vertically within the host structure are considered. It is assumed that longitudinal inertia of the cable can be neglected, with the longitudinal motion of the concentrated mass coupled with the lateral motion of the cable. An expansion of the lateral displacement of a cable in terms of approximating functions is used. The excitation acting upon the cable-mass system is a base-motion excitation due to the sway motion of a host tall structure. Such a motion of a structure often results due to action of the wind, hence it may be adequately idealized as a narrow-band random process. The narrow-band process is represented as the output of a system of two linear filters to the input in a form of a Gaussian white noise process. The non-linear problem is dealt with by an equivalent linearization technique, where the original non-linear system is replaced with an equivalent linear one, whose coefficients are determined from the condition of minimization of a mean-square error between the non-linear and the linear systems. The mean value and variance of the transverse displacement of the cable as well as those of the longitudinal motion of the lumped mass are determined with the aid of an equivalent linear system and compared with the response of the original non-linear system subjected to the deterministic harmonic excitation.

Refining methods of vibration diagnostics of wear of turbo-prop engine differential speed reduction unit gear teeth

The paper presents results of complex research of vibration behavior of the differential reduction gear unit of a turboprop engine on the basis of statistics of products with repaired reduction gears and those placed under repair. The conducted research made it possible to establish the source of resonant oscillations of the compressor design elements leading to their breakage. It is established that this source is determined by the kinematics of the reduction gear unit and is associated with the wear of its gear teeth. Standards for the intensity of the appropriate discrete component of the reduction gear vibration spectrum and those for the amount of permissible wear are substantiated and established on the basis of the work carried out. A complex of diagnostic parameters of wear based on intensity components of the auto-spectrum and the spectrum of maxima, the depth of amplitude modulation in some narrow-band processes, their characteristics based on the parameters of the current frequency and mutual characteristics was identified. It is shown that for the whole complex of the diagnostic parameters obtained their dependence on the wear value is satisfactorily approximated by a linear characteristic. The obtained results can serve as a basis for the development of a complex of methods of differential reduction gear vibration diagnostics.

Fatigue assessment method of marine structures subjected to two Gaussian random loads

Fatigue assessment is a critical issue for marine structures which usually encounter a combination load of a low frequency and a high frequency component. Furthermore, two components are commonly analyzed separately. In a strict sense, each of two components cannot be considered as narrowband processes. Recently, the authors proposed a combination of fatigue damage method (Han-Ma method) for predicting fatigue damage on the assumption of two well-separated and narrowband Gaussian components. The method is extended to non-narrowband and frequency overlapped cases in this paper. In addition, the application of existing combined spectrum method with dual narrow-banded correction factor (such as Jiao-Moan method, Low's bimodal method, Low-2014 method) and combination of fatigue damage method (such as DNV method, Huang-Moan method) is also investigated. These methods are also compared with some general wide-band spectral methods such as Dirlik method, single-moment method, Benasciutti-Tovo method and Park method. The results show that Jiao-Moan method, Low's bimodal method, Low-2014 method and Han-Ma method can still provide very accurate fatigue damage estimation when two Gaussian processes are separately non-narrowband and have overlapped frequencies. In particular, the accuracy of Low-2014 method and Han-Ma method is very close to that from some general spectral methods in the case that two Gaussian components have overlapped frequencies.