Time-domain Approach Research Articles

Calibration of high-fidelity hydrodynamic models utilizing on-site vessel response measurements

With a focus on weather-restricted marine operations, a comprehensive work on numerical model calibration is conducted to improve the vessel response prediction accuracy in real environmental conditions. This framework involves using existing physics-based models in which the metocean and system parameters are entered as inputs to derive vessel responses. The numerical models based on linear potential flow theory resolve only a part of the physics, i.e., it does not account for viscous damping effects. Moreover, significant uncertainties are associated with the system parameters related to the vessel operational conditions that are not known or measured directly. Therefore, the present paper integrates the vessel model with a derivative-free Lipschitz optimization technique to calibrate the vessel system parameters. For efficient optimization, the most influential variables are identified by conducting a sensitivity study for relevant quantities of interest using a cost-effective Polynomial Chaos model. The sensitivity analysis assumes independent uniform distributions for the system parameters with proper lower and upper limits. Subsequently, estimates of the highly influential variables are optimized using on-site vessel measurements, and in turn, utilized for superior response estimation. The response computations based on the numerical wave spectrum produced superior results in comparison with the results based on the parametric wave spectrum. The calibration algorithm is validated with full-scale measurements using frequency and time domain approaches for simulating vessel motions. It has been quantitatively revealed that the Center of Gravity parameters associated with the vessel operational characteristics and sea state-dependent additional damping coefficients govern the Roll response variation to a great extent. The calibration of these parameters resulted in improved Roll spectra estimations that match the measured spectra closely.

Battery Parameter Analysis through Electrochemical Impedance Spectroscopy at Different State of Charge Levels

This paper presents a systematic approach to extract electrical equivalent circuit model (ECM) parameters of the Li-ion battery (LIB) based on electrochemical impedance spectroscopy (EIS). Particularly, the proposed approach is suitable to practical applications where the measurement noise can be significant, resulting in a low signal-to-noise ratio. Given the EIS measurements, the proposed approach can be used to obtain the ECM parameters of a battery. Then, a time domain approach is employed to validate the accuracy of estimated ECM parameters. In order to investigate whether the ECM parameters vary as the battery’s state of charge (SOC) changes, the EIS experiment was repeated at nine different SOCs. The experimental results show that the proposed approach is consistent in estimating the ECM parameters. It is found that the battery parameters, such as internal resistance, capacitance and inductance, remain the same for practical SOC ranges starting from 20% until 90%. The ECM parameters saw a significant change at low SOC levels. Furthermore, the experimental data show that the resistive components estimated in the frequency domain are very close to the internal resistance estimated in the time domain. The proposed approach was applied to eight different battery cells consisting of two different manufacturers and produced consistent results.

Single-shot time-folded fluorescence lifetime imaging

Fluorescence lifetime imaging is an important tool in bioimaging that allows one to detect subtle changes in cell dynamics and their environment. Most time-domain approaches currently involve scanning a single illumination point across the sample, which can make imaging dynamic scenes challenging, while single-shot "rapid lifetime determination" can suffer from large uncertainties when the lifetime is not appropriately sampled. Here, we propose a time-folded fluorescence lifetime imaging microscopy (TFFLIM) approach, whereby a time-folding cavity provides multiple spatially sheared replicas of the lifetime, each shifted temporally with respect to a fixed time gate. This provides a robust, single-shot FLIM approach that we experimentally validate across a broad lifetime range on fluorescent beads and Convallaria samples.

Frequency-Domain Method for Characterization of Upconversion Luminescence Kinetics.

The frequency-domain (FD) method provides an alternative to the commonly used time-domain (TD) approach in characterizing the luminescence kinetics of luminophores, with its own strengths, e.g., the capability to decouple multiple lifetime components with higher reliability and accuracy. While extensively explored for characterizing luminophores with down-shifted emission, this method has not been investigated for studying nonlinear luminescent materials such as lanthanide-doped upconversion nanoparticles (UCNPs), featuring more complicated kinetics. In this work, employing a simplified rate-equation model representing a standard two-photon energy-transfer upconversion process, we thoroughly analyzed the response of the luminescence of UCNPs in the FD method. We found that the FD method can potentially obtain from a single experiment the effective decay rates of three critical energy states of the sensitizer/activator ions involved in the upconversion process. The validity of the FD method is demonstrated by experimental data, agreeing reasonably well with the results obtained by TD methods.

Fatigue Behavior Analysis and Life Prediction of Overhead Conductors Subject to Narrowband Vibration

This paper aims to present a contribution to the study of the effect of random vibration on the useful life of overhead conductors. This study compares two approaches based on an acquired vibration signal. The first one is the time-domain approach (based on rainflow cycle counting), while the second one is the frequency-domain approach (based on power spectral density moments). Laboratory simulation of aeolian vibration was used in finding the fatigue characteristics of a ACSR 397,5MCM – IBIS conductor. The S-N diagram was generated by performing 9 fatigue tests under constant amplitude conditions and 13 fatigue tests in narrowband excitation conditions. The reported tests were performed to assess the effect of random loading on fatigue life considering the two approaches for estimating fatigue life. A good correlation was found between the estimated fatigue lives using the time-domain and frequency-domain approaches and the experimental data.

An Efficient FDTD Method Based on Subgridding Technique and One-Step Leapfrog ADI-FDTD

In this letter, a 3-D subgridding finite-difference time-domain (FDTD) approach is proposed. The calculation domain is divided into regions with dense meshes and regions with coarse meshes. By applying the proposed subgridding technique to dense grid regions, memory and computation resources can be significantly reduced. Furthermore, the Courant–Friedrich–Levy (CFL) limitation of dense mesh regions is broken by the one-step leapfrog alternately direction-implicit (ADI)-FDTD. Coarse and dense regions can adopt a uniform time step, which is limited only by the standard FDTD CFL condition for coarse meshes. In comparison with the standard FDTD approach and the subgridding FDTD approach, numerical results demonstrate the efficiency and accuracy of the proposed method.

A performance comparison of heterostructure surface plasmon resonance biosensor for the diagnosis of novel coronavirus SARS-CoV-2.

This paper presents a performance comparison of heterostructure surface plasmon resonance (SPR) biosensors for the application of Novel Coronavirus SARS-CoV-2 diagnosis. The comparison is performed and compared with the existing literature based on the performance parameters in terms of several prisms such as BaF2, BK7, CaF2, CsF, SF6, and SiO2, several adhesion layers such as TiO2, Chromium, plasmonic metals such as Ag, Au, and two-dimensional (2D) transition metal dichalcogenides materials such as BP, Graphene, PtSe2 MoS2, MoSe2, WS2, WSe2. To study the performance of the heterostructure SPR sensor, the transfer matrix method is applied, and to analyses, the electric field intensity near the graphene-sensing layer contact, the finite-difference time-domain approach is utilized. Numerical results show that the heterostructure comprised of CaF2/TiO2/Ag/BP/Graphene/Sensing-layer has the best sensitivity and detection accuracy. The proposed sensor has an angle shift sensitivity of 390°/refractive index unit (RIU). Furthermore, the sensor achieved a detection accuracy of 0.464, a quality factor of 92.86/RIU, a figure of merit of 87.95, and a combined sensitive factor of 85.28. Furthermore, varied concentrations (0-1000nM) of biomolecule binding interactions between ligands and analytes have been observed for the prospects of diagnosis of the SARS-CoV-2 virus. Results demonstrate that the proposed sensor is well suited for real-time and label-free detection particularly SARS-CoV-2 virus detection.

Time-Domain Structural Damage and Loss Estimates for Wind Loads: Road to Resilience-Targeted and Smart Buildings Design

A time-domain wind-induced damage evaluation for the risk- and resilience-targeted design of building structures requires nonlinear dynamic analysis (NDA) solvers to handle long duration input loads. Moreover, post-construction damage identification based on real-time vibration monitoring depends on accurate damage simulation from the design stage and available artificial intelligence (AI)-based technology. In this paper, an integrated time-domain approach for the performance-based analysis and design for wind is presented. The nonlinear dynamic analysis (NDA) is performed with the Force Analogy Method (FAM) and the state–space formulation to solve the nonlinear equations of motion. Then, the Incremental Dynamic Analysis (IDA) is used to perform probabilistic fragility analyses for a typical reinforced concrete (RC) frame structure. The analysis also provides estimates of expected losses, gives the building owners business support data to compare, e.g., the final annual building income (FABI), the cost of repair and the function recovery duration for various wind events in an integrated resilience-based building design framework. This provides the basis for mapping structural damage on large urban scales and for straightforward quantification of wind-induced damage from available response acceleration time-series acquired from real-time vibration monitoring.

Bayesian monitoring of substructures under unknown interface assumption

Structural Health Monitoring (SHM) enables assessing in-service structures’ performance by localizing structural anomaly instances immediately after their occurrence. Typical SHM approaches monitor the entire structural spatial domain aggravating the required density and cost of instrumentation. Further, with model-based approaches, the entire structural domain is needed to be defined with high dimensional, compute-intensive models rendering the SHM approaches ill-posed and slow especially when the instrumentation is limited and system observability is compromised. Moreover, in absence of high-fidelity models, oversimplification and subsequent model inaccuracies may lead to inaccurate estimation and possibly false alarms even if a subdomain is modeled inaccurately, e.g. support boundaries. To mitigate such issues, stand-alone monitoring focusing only on a subdomain of interest may be a computationally cheaper and prompt approach while being substantially robust to false alarms. Typically, such stand-alone substructure monitoring approaches demand extensive measurement of the interface, which can be a challenge in real-life applications. This paper presents a novel filtering-based online time domain approach for estimating substructure parameters without the need to measure or estimate the substructure interfaces. The proposed component-wise estimation is stand-alone so that the health estimation of the complete structural domain can be undertaken in parallel and later coupled through post-processing. The requirement of the interface measurement has been alleviated by employing an output injection approach. The proposal has been validated on a numerical beam structure subjected to arbitrary forces and subsequently, the sensitivity against noise and damage severity of the proposal has been investigated. Finally, the proposal is validated on a real beam to illustrate its real-life applicability and significance.

Motions Assessment Using a Time Domain Approach for a Research Ship in Antarctic Waters

An approach combining frequency and time domain analysis is introduced in this study for ship motions assessment. The open-source NEMOH code is utilized to compute the excitation forces and the hydrodynamic coefficients, while heave and pitch motions time histories are determined by solving the Cummins equations in the time domain. The study compares the numerical outcomes for the heave, pitch, and vertical acceleration at the center of gravity with data obtained from a smartphone onboard during an oceanographic expedition in the Antarctic Ocean in early 2020 on the “Laura Bassi” research vessel. In order to validate the proposed method, weather forecast data from the global-WAM (GWAM) model are utilized. The comparison reveals a good agreement between numerical results and onboard measurements, with differences in motion values remaining below 10% and accelerations below 15%. Therefore, the developed code, taking into account its future improvements, represents an initial step towards creating a promising tool for an accurate estimation of ship motions and accelerations.

Efficient time-domain approach for hydroelastic-structural analysis including hydrodynamic pressure distribution on a moored SFT

This study investigates the hydroelastic analysis of a moored SFT (submerged floating tunnel) and the corresponding hydrodynamic pressure distribution under wave excitations. Time-domain discrete-module-beam (DMB) method, in which an elastic structure is modeled by multiple sub-bodies with beam elements, is employed to express the deformable tunnel with multiple mooring lines. Moreover, the top-down scheme is also adopted for detailed structure analyses with less computational cost, which applies the calculated hydrodynamic pressure distribution over SFT's surface to the three-dimensional finite element model. The hydrodynamic pressure includes both wave-induced diffraction pressure and motion-induced radiation pressure. For the validation of the developed numerical approach, comparisons are made with computationally intensive hydroelastic-structural direct-coupled method, two-dimensional wave flume experiment, and independently developed inhouse moored-SFT-simulation program. Furthermore, the influences of flexural motions with buoyancy-weight ratio (BWR) (or bending stiffness) and regular/irregular wave conditions on the dynamic pressure distribution and the resulting local stresses are investigated.

A Time-Domain Approach for Accurate Spectral Source Estimation with Application to Ridgecrest, California, Earthquakes

ABSTRACTWe determine the seismic moment and corner frequency of earthquakes using narrowband, time-domain measurements of the maximum shear-wave displacement amplitude. Each S wave is passed through a set of one-octave band-pass filters between 0.25 and 32 Hz to measure the peak amplitude on the horizontal components. Following the development of Richter (1935) local magnitude scale, we derive a functional form of maximum amplitude versus distance, but separately for each frequency band, and use them to estimate wave attenuation as a function of frequency and distance. Attenuation is a strong function of frequency, approximately proportional to 1/f, with path averaged Q increasing (attenuation decreasing) with propagation distance. We use these empirical attenuation curves to correct the time-domain peak amplitudes to a reference distance of 10 km to recover the source spectrum. We find that the spectral shape is consistent with the Brune model, showing a well-defined plateau at low frequency and a decay at high frequency proportional to ω−2. We use the median spectrum for stations at distances up to 120 km for each event to measure the moment and corner frequency. This time-domain method provides a reliable and efficient way to accurately measure earthquake source parameters.

Boundary conditions determined by experimentally measured surface properties for wave-based time-domain simulations

Boundary conditions are essential and necessary when simulating sound wave propagation inside an enclosed space. In this work, complex-valued surface acoustical properties for the actual materials are obtained from impedance tube measurements. This work applies model-based Bayesian inference to estimate the exact parameters for arbitrary boundary conditions. The Bayesian approach presented in this work demonstrates the capability to predict the complex-valued surface boundary function of frequency in broadband ranges. This approach is equivalently applicable in different boundary models in time domain depending on wave-based numerical methods used for acoustic modelings, such as the spectral element method or finite-difference time-domain method. With the accurately estimated boundary models, the efficacy of the boundary conditions is explored within the time-domain approaches.

Nonlinear least-squares estimation of shear modulus and shear viscosity in viscoelastic media

Time-domain estimates of the shear wave speed are obtained by performing cross-correlations or by evaluating the time-to-peak for two laterally separated shear wave particle velocity waveforms, where the distance divided by the propagation time yields an approximate value for the shear wave speed. Challenges associated with these time-domain estimation approaches include increasing errors as the shear viscosity increases and the absence of an estimated value for the shear viscosity parameter which is responsible for the rapid attenuation of shear waves in soft tissue. To obtain a time-domain estimate of the shear viscosity that also provides an estimate for the shear wave speed, a nonlinear least squares estimation approach is applied to three-dimensional (3D) shear wave particle velocities computed for a shear elasticity of 1.5 kPa, shear viscosities of 1, 2, 3, and 4 Pa.s, and a realistic simulated 3D acoustic radiation force excitation. The results show cross-correlations tend to over-estimate the value of the shear wave speed, the nonlinear least squares approach tends to under-estimate the value of the shear wave speed, and the nonlinear least square approach produces more accurate estimates as the shear viscosity increases. Two-dimensional maps of each estimated parameter are also shown.

Comparison of thermal effects induced by transcranial focused ultrasound and transcranial pulse stimulation

Abstract The objective of the study was to investigate thermal effects induced through two low-intensity focused ultrasound (LIFU)–based brain stimulation techniques—transcranial focused ultrasound stimulation (tFUS) and transcranial pulse stimulation (TPS). Long trains of acoustic pulses are delivered using tFUS, whereas, the newly introduced TPS delivers ultrashort (∼3 μs) pulses repeated at 4 Hz. It is presumed that TPS by virtue of delivering ultrashort ultrasound pulses reduces the risk for brain heating, but this has not been quantified in the literature. While overall temperature increase depends on the exact combination of stimulation parameters, simulations for tFUS have predicted ∼3°C and ∼<0.2 °C rises in a monkey skull and brain respectively. To our knowledge, the maximum rise ever reported is ∼3°C in rat brain but via a combination of longer duration and higher Ispta than typically used in tFUS. Following our previous work developing an image-derived model for TPS, we extended the models to assess transient heating in TPS as compared to tFUS. A finite difference time domain approach was used to solve the Westervelt-Lighthill equation for the pressure distribution in the head. Average intensity was calculated from the pressure distribution, which was then coupled to Pennes bioheat equation as a heat source. Initial results using certain assumptions indicate brain temperature rises in TPS to be <0.01°C. This indicates temperature rise at least an order of magnitude lower than some common tFUS parameters. While the absolute heating induced by either modality can be modulated by adjusting Ispta (through transducer intensity, duration, or duty cycle), typical tFUS and TPS protocols produce inherently different proportions of temperature versus pressure changes. In addition to risk, knowing the relative differences in temperature versus pressure generated could lend to a deeper understanding of the thermal versus mechanical mechanisms underlying the two techniques. Research Category and Technology and Methods Translational Research: 19. Modeling and computational methods Keywords: Ultrasound, tFUS, TPS, Thermal

The impact of plasmonic electrodes on the photocarrier extraction of inverted organic bulk heterojunction solar cells

Nano-patterning the semiconducting photoactive layer/back electrode interface of organic photovoltaic devices is a widely accepted approach to enhance the power conversion efficiency through the exploitation of numerous photonic and plasmonic effects. Yet, nano-patterning the semiconductor/metal interface leads to intertwined effects that impact the optical as well as the electrical characteristic of solar cells. In this work we aim to disentangle the optical and electrical effects of a nano-structured semiconductor/metal interface on the device performance. For this, we use an inverted bulk heterojunction P3HT:PCBM solar cell structure, where the nano-patterned photoactive layer/back electrode interface is realized by patterning the active layer with sinusoidal grating profiles bearing a periodicity of 300 nm or 400 nm through imprint lithography while varying the photoactive layer thickness (LPAL) between 90 and 400 nm. The optical and electrical device characteristics of nano-patterned solar cells are compared to the characteristics of control devices, featuring a planar photoactive layer/back electrode interface. We find that patterned solar cells show for an enhanced photocurrent generation for a LPAL above 284 nm, which is not observed when using thinner active layer thicknesses. Simulating the optical characteristic of planar and patterned devices through a finite-difference time-domain approach proves for an increased light absorption in presence of a patterned electrode interface, originating from the excitation of propagating surface plasmon and dielectric waveguide modes. Evaluation of the external quantum efficiency characteristic and the voltage dependent charge extraction characteristics of fabricated planar and patterned solar cells reveals, however, that the increased photocurrents of patterned devices do not stem from an optical enhancement but from an improved charge carrier extraction efficiency in the space charge limited extraction regime. Presented findings clearly demonstrate that the improved charge extraction efficiency of patterned solar cells is linked to the periodic surface corrugation of the (back) electrode interface.

Electronic circular dichroism from real-time propagation in state space.

In this paper, we propose to compute the electronic circular dichroism (ECD) spectra of chiral molecules using a real-time propagation of the time-dependent Schrödinger equation (TDSE) in the space of electronic field-free eigenstates, by coupling TDSE with a given treatment of the electronic structure of the target. The time-dependent induced magnetic moment is used to compute the ECD spectrum from an explicit electric perturbation. The full matrix representing the transition magnetic moment in the space of electronic states is generated from that among pairs of molecular orbitals. In the present work, we show the ECD spectra of methyloxirane, of several conformers of L-alanine, and of the Λ-Co(acac)3 complex, computed from a singly excited ansatz of time-dependent density functional theory eigenstates. The time-domain ECD spectra properly reproduce the frequency-domain ones obtained in the linear-response regime and quantitatively agree with the available experimental data. Moreover, the time-domain approach to ECD allows us to naturally go beyond the ground-state rotationally averaged ECD spectrum, which is the standard outcome of the linear-response theory, e.g., by computing the ECD spectra from electronic excited states.

Fourier Neural Operator Network for Fast Photoacoustic Wave Simulations

Simulation tools for photoacoustic wave propagation have played a key role in advancing photoacoustic imaging by providing quantitative and qualitative insights into parameters affecting image quality. Classical methods for numerically solving the photoacoustic wave equation rely on a fine discretization of space and can become computationally expensive for large computational grids. In this work, we applied Fourier Neural Operator (FNO) networks as a fast data-driven deep learning method for solving the 2D photoacoustic wave equation in a homogeneous medium. Comparisons between the FNO network and pseudo-spectral time domain approach were made for the forward and adjoint simulations. Results demonstrate that the FNO network generated comparable simulations with small errors and was orders of magnitude faster than the pseudo-spectral time domain methods (~26× faster on a 64 × 64 computational grid and ~15× faster on a 128 × 128 computational grid). Moreover, the FNO network was generalizable to the unseen out-of-domain test set with a root-mean-square error of 9.5 × 10−3 in Shepp–Logan, 1.5 × 10−2 in synthetic vasculature, 1.1 × 10−2 in tumor and 1.9 × 10−2 in Mason-M phantoms on a 64 × 64 computational grid and a root mean squared of 6.9 ± 5.5 × 10−3 in the AWA2 dataset on a 128 × 128 computational grid.

Determination of Shielding Effectiveness of a Subnanosecond High-Power EM Interference by an Enclosure with Aperture Using Time Domain Approach

Determination of Shielding Effectiveness of a Subnanosecond High-Power EM Interference by an Enclosure with Aperture Using Time Domain Approach

The Integrated Rescheduling Problem of Berth Allocation and Quay Crane Assignment with Uncertainty

The baseline plan of terminals will be impacted to a certain extent after being affected by uncertain events, such as vessel delay and unscheduled vessel arrival, resulting in disorderly terminal operations, wasted resources, and reduced loading and unloading efficiency, which further aggravates terminal congestion. To effectively cope with the disturbance of terminal operations by the above uncertain events and improve the operational efficiency of container terminals, this paper investigates the integrated rescheduling problem of berth allocation and quay crane assignment with vessel delay and unscheduled vessel arrival. Two steps are designed to deal with uncertainty shocks. The first step is to determine the rescheduling moment by using a rolling time-domain approach. The second step is to establish a rescheduling model and design an improved genetic algorithm(IGA) to obtain a rescheduling solution using various rescheduling strategies at the rescheduling moment. Moreover, through scenario experiments, comparisons with commercial solvers and other algorithms, it can be seen that the solution speed of IGA is better than that of commercial solvers and the average gap does not exceed 6%, which verifies the effectiveness and superiority of this algorithm.