Time-domain Procedure Research Articles

Time series clustering using fragmented autocorrelations

We propose and study an autocorrelation procedure designed to characterize and compare large sets of long time series. This time-domain procedure is contrasted with a frequency-domain approach that has recently been introduced and discussed in the literature. In both cases, instead of using all the information available from data, which would be computationally very expensive, adequate regularization rules select and summarize the most relevant information suitable for clustering purposes. Essentially, we suggest to use the autocorrelation coefficients of the time series that are only computed around the lags of greatest interest. Then, we study this method in several ways. We argue theoretically that fragmenting the autocorrelation function can have efficiency advantages when comparing time series. By means of a large simulation study, we show that the suggested procedure can condense the relevant information of the time series. We compare its results with those from the frequency domain counterpart. We further illustrate this procedure in a study of the evolution of several stock markets indices and show the effect of recent financial crises on the behaviour of these indices.

Ultra-fast and compact optical Galois field adder based on the LPhC structure and phase shift keying.

In this study, we propose a novel, to the best of our knowledge, all-optical Galois field (AOGF) adder that utilizes logic all-optical XOR gates. The design is founded on optical beams' constructive and destructive interference phenomenon and incorporates the phase shift keying technique within a two-dimensional linear photonic crystal (2D-LPhC) structure. The suggested AOGF adder comprises eight input ports and four output ports. We employ the finite difference time domain (FDTD) procedure to obtain the electric field distribution in this structure. The FDTD simulation results of the proposed AOGF adder demonstrate that the minimum and maximum values of the normalized power at ON and OFF states (P 1,min, P 0,max) for the output ports are 95% and 1.7%, respectively. Additionally, we obtain different functional parameters, including the ON-OFF contrast ratio, rise time, fall time, and total footprint, which are measured at 17.47dB, 0.1ps, 0.05ps, and 147µm 2, respectively.

A time domain procedure for the identification of periodic structures

A procedure for the identification of dispersion curves and mechanical characteristics of linear and nonlinear one-dimensional (1D) periodic structures is proposed herein. The procedure exploits the application of Floquet–Bloch (F–B) boundary conditions to a reference subsystem (RS) extracted from a mechanical metastructure. The dispersion curves (frequency vs.wavenumbers) are estimated from the computation of the frequency response functions (FRFs) of the RS for different wavenumbers in input. The proposed procedure is applied and validated on various models, including a 1D mass-in-mass system characterized by cubic nonlinear springs. As expected, the nonlinear system exhibits a distinct dependence on the amplitude of the excitation. In addition, a revised application of the subspace identification (SI) method is exploited for the identification of hardening-type nonlinear mechanical characteristics. For the sake of completeness, the identification procedure is also tested on a waveguide in axial and flexural vibrations. Due to its single output from a measuring cell, and two inputs, the proposed method is particularly suitable for the experimental characterization of periodic structures.

On silicon nanobubbles in space for scattering and interception of solar radiation to ease high-temperature induced climate change

A thin film of silicon-based nanobubbles was recently suggested that could block a fraction of the sun’s radiation to alleviate the present climate crisis. But detailed information is limited to the composition, architecture, fabrication, and optical properties of the film. We examine here the optical response of Si nanobubbles in the range of 300–1000 nm to evaluate the feasibility using semi numerical solution of Maxwell’s equations, following the Mie and finite-difference time-domain procedures. We analyzed a variety of bubble sizes, thicknesses, and configurations. The calculations yield resonance scattering spectra, intensities, and field distributions. We also analyzed some many-body effects using doublets of bubbles. We show, due to high valence electron density, silicon exhibits strong polarization/plasmonic resonance scattering and absorption enhancements over the geometrical factor, which afford lighter but more efficient interception with a wide band neutral density filtering across the relevant solar light spectrum. We show that it is sufficient to use a sub monolayer raft with ∼0.75% coverage, consisting of thin (∼15 nm) but large silicon nanobubbles (∼550 nm diameter), to achieve 1.8% blockage of solar light with neutral density filtering, and ∼0.78 mg/m2 silicon, much less than the mass effective limit set earlier at 1.5 g/m2. We evaluated solid counterpart nanoparticles, which may be produced in blowing/inflation procedures of molten silicon, as well as aging by including silicon oxide capping. The studies confirm the feasibility of a space bubble filtering raft, with insignificant imbalance of the correlated color temperature (CCT) and color rendering index characteristics of sunlight.

Seakeeping criteria of a moored and articulated multibody floating platform in head seas

Within the Space@Sea project, a multi-use floating concept was proposed by following the analogy of standardization to enlarge a floating platform using a multitude of smaller structures. An operability analysis must be performed to identify its seakeeping criteria and how the criteria limit its functionality. A two-step strategy is proposed to calculate the responses of the target floating concept in head waves, where nonlinearities of the mooring lines and mechanical joints are taken into account. The weakly nonlinear time-domain procedure relies on a diffraction-radiation model in the frequency domain. The motions of floating bodies are solved in the time domain, in which nonlinear Froude-Krylov and hydrostatic forces are estimated under instantaneous incident wave surface. Multibody interactions are resolved under consideration of catenary mooring lines and hinged joints. Wave-induced motions and loads are expressed in terms of transfer function for determining the limiting criteria, including the translational and rotational motions velocities and accelerations; relative motions, velocities and accelerations between module floaters; mooring tensions; as well as hinge forces. Assessments are carried out for various sea conditions against the prescribed values, for the chosen criteria, to address safety issues due to sever platform responses. Different operational requirements for trained workers and untrained passengers of motions and accelerations are taken into consideration. Results show that rotational motions have a significant influence on the platform’s seakeeping performance. Nevertheless, the root mean square (RMS) value of vertical acceleration dominates the comfort of persons onboard, defining the final limiting criterion of the entire platform.

A stepwise artificial boundary condition for wave propagation in elasto-plastic media

Wave propagation in elasto-plastic media is often encountered in earthquake geotechnical engineering. However, dynamic boundary conditions in the numerical simulation of wave propagation problems are often developed based on linear elastic assumptions. In this study, the method of characteristics is utilized to propose a novel stepwise artificial boundary condition (S-ABC) for wave propagation in elasto-plastic media. The numerical implementation of S-ABC within a finite element procedure in time domain is developed. Typical numerical examples are chosen to verify the efficiency of this ABC, including: 1) a semi-infinite soil column model subjected to impulse load, where the influence of unloading wave front in elasto-plastic media is discussed; 2) an infinite and a finite soil column model under cyclic seismic wave input, where the proposed S-ABC is compared with the traditional viscoelastic artificial boundary condition (V-ABC). Numerical results demonstrate the significantly higher accuracy and robustness of the proposed S-ABC for nonlinear and elasto-plastic media compared to traditional V-ABC. The influence of unloading wave front on artificial boundary condition for elasto-plastic media is also revealed, which has not been reported previously.

Comparison of some selected time-domain fatigue failure criteria dedicated for multi input random non-proportional loading conditions in industrial components

This paper presents time-domain procedure to evaluate High-Cycle Fatigue (HCF) life of industrial components with complicated geometries and subjected to multi-input random loading conditions. To this end, the authors discuss some well-known equivalent stress criteria which can consider the orientation of critical plane changes with the time in non-proportional loading conditions to estimate the time history of equivalent stress. This task is successfully accomplished by knowing time histories of local stress tensor components in a critical area of the part that is prone to failure. Next, two different categories were used to predict fatigue life of component: 1- Linear Damage Accumulation (LDA) rule by employing Rain-flow cycle counting and 2- probabilistic approach by utilizing level crossing counting method. To apply these methodologies and awareness of their challenges, a case study was performed on the automotive steering knuckle. Finally, the predicted lives were compared to experimental results, and the accuracies of different fatigue life assessment techniques were reported. The obtained results show that combination of Rain-flow cycle counting with the Liu-Zenner criterion and especially, with the Energy-based instant fatigue damage tracing proposed by Shariyat lead to the highest accuracies. However, using the probabilistic approach, we will get the response in a much shorter time compared to another category. Therefore, the choice which method to use also depends on the parameters of the research situation, and the interaction of the two factors of prediction accuracy and prediction time in the industry.

A novel proposal for all optical 1-bit comparator based on 2D linear photonic crystal

We employ seven optical waveguides based on two-dimensional linear photonic crystal (LPhC) to realize an all optical comparator (AOCMP). The proposed 1-bit AOCMP has a very simple structure with a footprint of 356 μm2 which is composed of 31 × 33 cubic lattice of silicon rods immersed in air. This LPhC comparator comprises two input ports and two output ports. The functionality of the proposed 1-bit AOCMP is based on constructive and destructive interference phenomenon of optical beams and phase shift keying technique. The finite difference time domain (FDTD) procedure based on Yee’s Algorithm is used to compute the propagation of optical waves in this structure. The FDTD simulation results of suggested 1-bit AOCMP indicate that the minimum and maximum values of the normalized power at ON and OFF states for output ports are 62% and 10%, respectively. Also, the ON–OFF contrast ratio, bit rate, rise and fall times (Tr and Tf) of the suggested design are about 7.92 dB, 2.22 Tb/S, 0.15 ps and 0.05 ps, respectively.

Performance analysis of all optical 2 × 1 multiplexer in 2D photonic crystal structure

Abstract In optical processing systems, multiplexer is used to design optical devices such as arithmetic logic unit (ALU) and shift register (SR). Through this paper, we investigate the application of nonlinear photonic crystal ring resonator (PhCRR) based on nonlinear Kerr effect for realizing an all optical 2 × 1 multiplexer. The structure consists of two PhCRRs and five optical waveguides using hexagonal lattice silicon (Si) rods with a background of air. Performance of all optical 2 × 1 multiplexer is replicated with the help of finite difference time domain (FDTD) procedure at a wavelength of 1571 nm, and simulations presented an ultra-compact optical structure with ultra-fast switching speed.

Nonlinear Behaviour of Concrete Buttress Dams under High-Frequency Excitations Taking into Account Topographical Amplifications

Concrete buttress dams could potentially be susceptible to high-frequency vibrations, especially in the cross-stream direction, due to their slender design. Previous studies have mainly focused on low-frequency vibrations in stream direction using a simplified foundation model with the massless method, which does not consider topographic amplifications. This paper therefore investigates the nonlinear behaviour of concrete buttress dams subjected to high-frequency excitations, considering cross-stream vibrations. For comparison, the effect of low-frequency excitations is also investigated. The influence of the irregular topography of the foundation surface on the amplification of seismic waves at the foundation surface and thus in the dam is considered by a rigorous method based on the domain-reduction method using the direct finite element method. The sensitivity of the calculated response of the dam to the free-field modelling approach is investigated by comparing the result with analyses using an analytical method based on one-dimensional wave propagation theory and a massless approach. Available deconvolution software is based on the one-dimensional shear wave propagation to transform the earthquake motion from the foundation surface to the corresponding input motion at depth. Here, a new deconvolution method for both shear and pressure wave propagation is developed based on an iterative time-domain procedure using a one-dimensional finite element column. The examples presented showed that topographic amplifications of high-frequency excitations have a significant impact on the response of this type of dam. Cross-stream vibrations reduced the safety of the dam due to the opening of the joints and the increasing stresses. The foundation modelling approach had a significant impact on the calculated response of the dam. The massless method produced unreliable results, especially for high-frequency excitations. The free-field modelling with the analytical method led to unreliable joint openings. It is therefore recommended to use an accurate approach for foundation modelling, especially in cases where nonlinearity is considered.

A direct time-domain procedure for the seismic analysis of dam–foundation–reservoir systems using the scaled boundary finite element method

In this paper, a direct time-domain procedure for the seismic analysis of dam–reservoir–foundation interactions is presented based on the scaled boundary finite element method (SBFEM). The SBFEM is a semi-analytical method and requires the discretization of boundary only. The geometric complexity in the bounded dam–reservoir–foundation system is easily handled in the SBFEM using quadtree meshes where each structural component can be discretized independently. The elastic wave fields in the unbounded foundation are rigorously captured through SBFE solutions in terms of displacement unit-impulse response functions, while the acoustic wave propagation in the semi-infinite reservoir is modelled by the SBFE-based doubly asymptotic open boundary. The input of seismic excitations is addressed by incorporating the Domain Reduction Method (DRM) into the SBFEM. Cracks are modelled efficiently and accurately by combining the SBFEM and quadtree meshes. The accuracy and efficiency of the proposed methodology is investigated by studying several benchmarks, Pine Flat dam and Jin’anqiao dam.

Vibration signature analysis of coffee beans processing Machineries

It is practical that Major research in the analysis of rolling elements was carried out in the case of one-point defects. For multiple and generalized defect diagnosis, there is a lot of flexibility. The vibration signals for various machines with faulty rolling component bearings are composed & analyzed using vibration signature analysis techniques in this study. Multiple defects on bearing components are used to test the test bearings. The use of vibration signature analysis methods to identify faults in rolling aspect bearings by means of time & frequency domain procedures is investigated in order to determine the best method for fault discovery in the case of several faults in bearing machinery. The feature extracted in this study is expected to be useful in the development of automated fault diagnostics systems for bearing components with multiple defects. In This work we have applied vibration signature analyses on the ball bearings of coffee processing machines and evaluated the results.

An Improved Time-Domain Damage Detection Method for Railway Bridges Subjected to Unknown Moving Loads

There is considerable interest in structural health monitoring (SHM) and damage detection of bridges and considerable progress has been made in this field in recent years. However, several challenges such as sensitivity to low levels of damage and identification without the knowledge of the moving load remain and need to be precisely investigated by researchers. The current work addresses such challenges and proposes an efficient response sensitivity-based model updating procedure in time-domain for damage identification of railway bridges subjected to unknown moving loads. The bridge is modelled as an Euler-Bernoulli beam and the train is modelled as a set of sprung masses passing over the beam. Structural damage is considered as a reduction in the modulus of elasticity of the elements. Sensitivity analysis and Tikhonov regularization methods are adopted and used to solve the inverse problem of the model updating. To verify the efficiency of the model, two numerical models with multiple damage scenarios subjected to unknown moving loads are analyzed. In addition, the efficiency of the proposed method in the presence of measurement noise is also verified. Numerical results reveal that the proposed model-updating procedure simultaneously identifies structural damages as well as the unknown moving loads with an acceptable accuracy. The effect of critical parameters such as mass and speed of the moving vehicle on the accuracy of identification results is investigated as well. Based on the findings of this research, the proposed method can be adopted and applied to online and long-term health monitoring of real bridge structures.

Time-Domain Procedures for Lightning-Induced Voltage Calculation in Electromagnetic Transient Simulators

In this paper, two time-domain procedures are proposed for the calculation of lightning-induced voltages using lossy transmission line models available in electromagnetic transient simulators. In both procedures, the influence of the incident electromagnetic field is represented in the form of current sources that are connected externally at the ends of the illuminated line. One of the procedures is formulated directly in the phase-domain and is compatible with the universal line model (ULM). The second procedure is formulated in the modal domain and is compatible with the transmission line model proposed by Marti. Both procedures are validated taking as reference a first order FDTD solution of telegrapher's equations considering the presence of external electromagnetic fields. It is shown that the proposed procedures can be efficiently and accurately used for the calculation of lightning-induced voltages on overhead lines.

A time-domain procedure for non-Gaussian stationary environmental testing using zero-memory nonlinear transformation

This article proposes a time-domain procedure for a non-Gaussian stationary random vibration test with prescribed power spectral densities. Previous procedures for generating non-Gaussianity suffered from certain defects. For example, zero-memory nonlinear transformation, an algorithm frequently applied to transform Gaussian signals into non-Gaussian signals, often produces changes in both auto-power spectral densities and cross-power spectral densities, which might result in control instability under certain circumstances. In this article, the authors propose a different approach for the zero-memory nonlinear function. First, a time-domain procedure for a non-Gaussian random test is introduced. Second, a rescaling method is applied to correct the magnitude amplification on the auto-power spectral density because of zero-memory nonlinear transformation. We offer experience formulas in this method to adjust the auto-power spectral density of both super-Gaussian and sub-Gaussian responses. Third, a control strategy using a finite impulse response filter is proposed to further improve the auto-power spectral density if the shape of the auto-power spectral density is distorted. The kurtosis loss induced by the filtering process is also analysed and a corresponding solution is put forward to ease the reduction. Numerical test and a biaxial shaker table test are conducted to validate the availability and superiority of the proposed procedure.

Exploring the Connected Brain by fNIRS: Human-to-Human Interactions Engineering

Functional Near Infrared Spectroscopy (fNIRS) is a relatively new neuroimagingtechnique adequate and useful for exploring neural activity in social contexts involving humaninteractions. Compared to functional Magnetic Resonance Imaging (fMRI), fNIRS is easy-to-usesafe, noninvasive, silent, relatively low cost and portable, and applicable to subjects of all ages, thusresulting in a good option for ecological studies involving humans in their real-life context.Moreover, by using hyperscanning technique, fNIRS allows recording the hemodynamic cerebralactivity of two interacting subjects in an ecological context or during a shared performance. Thus,moving from a simple analysis about each subject’s neural response during joint actions towardsmore complex computations makes possible to investigate brain synchrony, that is the if and howone’s brain activity is related to that of another interacting partner simultaneously recorded. Here,we discuss how connectivity analyses, with respect to both time and frequency domain procedures,permitted to deepen some aspects of inter-brain synchrony in relation to emotional closeness, and tohighlight how concurrent, cooperative actions can lead to interpersonal synchrony and bondconstruction.

On closed-form expressions for the approximate electromagnetic response of a sphere interacting with a thin sheet — Part 2: Theory in the moment domain, validation, and examples

Fully analytical formulas are derived for the approximate electromagnetic response of a sphere interacting with a thin sheet in the moment domain. The moment-domain expressions are found to be expressed as simple polynomials of hyperbolic functions. These are significantly simpler to evaluate than the frequency- and time-domain expressions and therefore provide an attractive alternative for modeling. An efficient procedure is outlined for generalizing the moment-domain expression to bipolar-repetitive waveforms. This procedure is validated on a synthetic test example and field data from the Reid-Mahaffy test site, in northern Ontario. Here, results are found in agreement with the work of previous studies. The analytical time-domain procedure is validated through synthetic test examples. The asymptotic formulas for the time-domain expressions are found to significantly reduce the number of required function evaluations, especially for models in which the sphere is not too shallow or not too big or conductive. For example, for a sphere (and overburden) of conductivity (and conductance) of [Formula: see text] (and [Formula: see text]), if the sphere radius is three times smaller than the depth to the top, the amount of required function evaluations is halved; when the ratio is two or less, the asymptotic formulas do not reduce the amount of function evaluations, for the tolerances chosen here. Less-strict tolerances will lead to a further reduction of the required function evaluations.

Time domain predictions of inertial loads on a drifting ship in irregular beam waves

A proper estimation of the ship accelerations, particularly in the transversal direction, is fundamental for predicting the risk of cargo shifts and inherent structural damages in severe irregular seas. A specific situation worth to be considered in this context is the so-called dead ship condition, in which the ship, because of a loss of steering capabilities, is drifting in beam waves at zero speed. Particularly in this situation, a proper modelling of ship dynamics in wave is deemed necessary for a reliable assessment of inertial loads.In this paper three time domain procedures with different accuracy are applied and compared. The aim is to investigate the dependency of inertial loads on the non-linear effects of ship geometry and on the couplings among the 6DOF of the ship.Simulations are carried out with, in input, the same irregular sea realizations in the time domain, obtained from a digitalisation of JONSWAP spectra. A technique allowing for a fine matching of the digitalised spectra to the analytical ones is developed and applied.The investigation indicates that couplings among ship motions trigger larger inertial loads and, accordingly, a larger probability of occurrence for cargo shifting and structural damages.

Foreign direct investment and growth causal-nexus in economic community of West African States: Evidence from spectral causality

The paper examines the causal relationship between FDI and economic growth (GDP) in thirteen ECOWAS countries using both time domain and frequency domain testing procedures using annual data from 1970 to 2015. The results showed that time domain is not adequate in detecting causality. The time domain detected causality in only four out of thirteen countries whilst the frequency domain detected causality at different frequencies and cycles in nine out of thirteen countries. The findings of this study indicate the importance of frequency domain causality, that it decomposes causality at different frequencies and subsequently detects causality at certain cycles lengths. The general observation that economic growth leads FDI calls for ECOWAS leaders to rethink about painful sacrifices they make to attract FDI into the region.

Nonlinear Forced Vibration Analysis of FG-CNTRC Cylindrical Shells Under Thermal Loading Using a Numerical Strategy

Employing an efficient numerical strategy, the nonlinear forced vibration analysis of composite cylindrical shells reinforced with single-walled carbon nanotubes (CNTs) is carried out. It is assumed that the distribution of CNTs along the thickness direction of the shell is uniform or functionally graded and the temperature dependency of the material properties is accounted. The governing equations are presented based on the first-order shear deformation theory along with von-Karman nonlinear strain-displacement relations. The vectorized form of energy functional is derived and directly discretized using numerical differential and integral operators. By the use of variational differential quadrature (VDQ) method, discretized nonlinear governing equations are obtained. Then, the time periodic differential operators are applied to perform the discretization procedure in time domain. Finally, the pseudo-arc length continuation method is employed to solve the nonlinear governing equations and trace the frequency response curve of the nanocomposite cylindrical shell. A comparison study is first presented to verify the efficiency and validity of the proposed numerical method. Comprehensive numerical results are then given to investigate the effects of the involved factors on the nonlinear forced vibration characteristics of the structure. The results show that the changes of fundamental vibrational mode shape have considerable effects on the frequency response curves of composite cylindrical shells reinforced with CNTs.