Time History Research Articles

Theory for plunger-type wavemakers to generate second-order Stokes waves and Smoothed Particle Hydrodynamics verification

Plunger-type wavemakers are used in ocean engineering laboratories globally. However, the wave-making theories remain incomplete due to the complex geometries of the plungers. This work derives the motion equations for an arbitrary-geometry plunger to generate second-order Stokes waves, along with the generic constraints on wave parameters. Taking wedge-shaped and cylinder-shaped plungers as examples, the motion equations and constraints are detailed. Subsequently, a smoothed particle hydrodynamics (SPH) model for the plunger-induced waves is established and validated by accurately reproducing published experimental results. Finally, the SPH model is applied to simulate the wave generation by the two plungers. The computed wave profiles, water pressures, and flow velocities are compared with their analytical solutions in terms of spatial distribution and time history. Additionally, the wave field stability and the wave generation process are evaluated. The results demonstrate that second-order Stokes waves with target waveforms can be precisely generated using an arbitrary-geometry plunger-type wavemaker within a short transition distance and time, thereby verifying the reliability of the proposed wavemaker theory.

Large aperture microphone array measurement at operating airport for sound source model creation of J-FRAIN

In 2022, authors conducted microphone array measurements at an operating airport to create sound source models for commercial aircraft based on the noise prediction framework J-FRAIN. A similar measurement was also performed by our colleagues in 2019, but it was a trial to establish the concept of the framework and was done using a microphone array in which the number of microphones was reduced to about half. In order to improve the accuracy of the sound source models, the microphone array with a 30-meter diameter consisting of 195 microphones mounted on the ground was used in 2022. Recording-based simultaneous noise measurement using sound level meters was also performed around the airport to validate prediction results in terms of time histories of 1/3 octave band sound pressure levels. This paper describes an overview of the microphone array measurements conducted in 2022 and a case study of noise prediction around the airport using sound source models created from the data of microphone array measurements conducted in 2022. Predicted results are compared with 1/3 octave band data measured using sound level meters mounted at a height of 4 m above the ground at sites of noise monitoring stations around the airport.

Uncertainty and Latin Hypercube Sampling in Geotechnical Earthquake Engineering

A soil–foundation–structure system (SFSS) often exhibits different responses compared to a fixed-base structure when subjected to earthquake ground motion. Both kinematic and inertial soil–foundation–structure interactions can significantly influence the structural performance of buildings. Numerous parameters within an SFSS affect its overall response, introducing inherent uncertainty into the solution. Performing time history analyses, even for a linear elastic coupled SFSS, requires considerable computational effort. To reduce the computational cost without compromising accuracy, the use of the Latin Hypercube Sampling (LHS) technique is proposed herein. Sampling techniques are rarely employed in soil–foundation–structure interaction analyses, yet they are highly beneficial. These methodologies allow analyses determined by sampling to be conducted using commercial codes designed for deterministic analyses, without requiring any modifications. The advantage is that the number of analyses determined by the sampling size is significantly reduced as compared to considering all combinations of input parameters. After identifying the important samples, one can evaluate the seismic demand of selected soil–foundation–bridge pier systems using finite element numerical software. This paper indicates that LHS reduces computational effort by 60%, whereas structural response components (translation, rocking) show distinct trends for different systems.

A distributed dynamic load identification approach for thin plates based on inverse Finite Element Method and radial basis function fitting via strain response

Dynamic load identification is crucial for structural design and health monitoring. Traditional methods for distributed dynamic loads (DDLs) typically involve establishing a transfer matrix, which often leads to ill-posed problems. In this paper, a novel method based on the inverse Finite Element Method (iFEM) and radial basis function (RBF) fitting was proposed to identify DDLs from measured strain responses. The method begins with the reconstruction of the displacement field from discrete strain data using iFEM, followed by applying RBF fitting to obtain a continuous displacement field. To enhance the performance of the RBF fitting, a constrained matrix for force boundary conditions is introduced, along with a selection rule for the RBF shape parameter. The identified loads are subsequently determined by incorporating the well-fitted RBFs into the motion equations of thin plates. This approach eliminates the need for a transfer matrix, thereby avoiding ill-posedness, and enables the simultaneous identification of the spatial distribution and time history of the loads. Three numerical examples for the identification of concentrated loads, uniformly distributed loads, and globally distributed loads demonstrate the method's effectiveness, accuracy, and noise resistance, with additional validation provided through a comparison with the classic time-domain method.

Museomics reveal origins of East African Pleophylla forest chafers and Miocene forest connectivity

Here we present a nearly complete species-level phylogeny including 23 of the 25 known species of the forest-dwelling herbivorous scarab chafer beetle genus Pleophylla (Coleoptera: Scarabaeidae: Sericinae), based on the analysis of 950 nuclear genes (metazoan-level universal single-copy orthologs; mzl-USCOs). DNA sequences were obtained from freshly collected, ethanol-preserved samples and from dried museum specimens by target enrichment or genome shotgun sequencing. Alignment completeness of mzl-USCOs newly obtained here by target DNA enrichment of ethanol samples were very heterogenous and lower (29–62 %) than in Dietz et al. (2023a), while that of sequences recovered from dried samples was even lower (∼19 %). Alignment completeness of the sequences obtained from low coverage shotgun sequencing was highest (∼92 %), although the average coverage was much lower than for the target enrichment samples. We used the resulting phylogeny to reconstruct the historical biogeography of the group. To estimate a time-calibrated tree, we combined the mzl-USCO data of Pleophylla with a nucleotide alignment from an available transcriptomic dataset of Scarabaeoidea and used two different sets of secondary calibration points. Despite the problems associated with the capture rate of mzl-USCO sequences from museum specimens, we were able to infer a well-resolved phylogeny of the genus Pleophylla that also provided reliable estimates of the phylogenetic position of species for which we had little sequence data. Our study clearly identified South Africa as the geographic origin of Pleophylla. Timing and biogeographic history confirm a persistent fragmentation of forests since the Eocene. The occurrence of only one long-distance dispersal event from southern Africa to the Eastern African Arc even during the Miocene highlights the limited dispersal possibilities for these forest-adapted chafers, which do not seem to have had important northerly range expansions along hypothetical forest corridors during the Pleistocene.

A Novel Method for Aircraft Structural Dynamic Strain Trend Signal Processing via Optimized Parallel Computing

In this study, we investigate the underlying causes of drift in the time history curves of measured parameters obtained through strain electrical measurements and assess their impacts on load measurements. To address the challenge of efficiently processing large volumes of aircraft load data, we propose and analyze a multi-level parallel algorithm specifically designed for the data processing of aircraft load measurements. To achieve this objective, we discuss parallel processing at both medium- and fine-grained levels and develop two distinct parallel processing algorithms: one for coarse- and medium-grained aircraft-type data streams, and another for medium- and fine-grained takeoff and landing data streams. The efficacy of these algorithms is validated through the processing of load data measured on a specific aircraft wing. The results demonstrate that the proposed approach offers a novel technical pathway for large-scale scientific computations and enhances data processing efficiency in the domain of aircraft load spectrum analysis.

Experimental and numerical investigation of low‐velocity impact behavior and failure mode of shear deficient RC beam strengthened with CFRP strips

AbstractIt is well‐known that shear failure is a collapse mechanism that is the riskiest, fastest, and catastrophic and occurs with no visible signs of damage or prior warning for RC beams. Therefore, to prevent brittle shear failure, the RC beams should include sufficient shear reinforcement, such as stirrups, and be designed to have sufficient shear capacity. However, the RC beams' shear capacity becomes inadequate for various reasons. One of these reasons may be the acting of the impulsive impact load, which is uncommon and disregarded in the design phase on the RC beams. An experimental program was conducted to examine the impact behavior and failure mode of shear‐deficient RC beams in the scope of the present study. Besides, it aims to investigate the effectiveness of the strengthening method using CFRP strips in improving the general behavior, failure mode, and performance of shear‐deficient RC beams exposed to impact load. The time histories of the accelerations, displacements, impact loads, and strains in the CFRP strips were measured. They were interpreted how they are affected by experimental variables examined in the experimental study. Furthermore, the finite element model of the specimens was generated in the LS‐DYNA software, and the experimental and numerical results were compared by performing finite element analysis in terms of failure modes and general behavior.

Generation of artificial earthquake time histories and power spectral density for seismic analysis of nuclear power plants

Regulatory Guide (RG) 1.60 presents the response spectra for the seismic design of nuclear power plants. New reactor designs necessitate Modified Design Response Spectra (MDRS), extending the high-frequency range from Design Response Spectra (DRS) in RG 1.60. This paper explores the generation procedure of artificial earthquake time histories conforming to acceptable criteria outlined in SRP Section 3.7.1 for MDRS. The process involves defining MDRS, generating artificial time histories, calculating Power Spectral Density (PSD), and producing Artificial Earthquake Ground Motions (AEGMs). Modified spectra broaden the high-frequency range and increase acceleration values at specific frequencies. For AEGM generation, two Approaches are explored using P-CARES and in-house code. Generated AEGMs satisfy the criteria outlined in SRP Section 3.7.1, ensuring compatibility with target response spectra. Additionally, seismic analyses of a nuclear power plant model, both with or without a base isolator, are conducted, and the results of the structural response using the seismic ground motion produced through the two Approaches are compared. The seismic response of the nuclear power plant model based on Approach 1 is somewhat higher than that based on Approach 2. The accelerations of the structure with the base isolator are significantly reduced compared to the structure without the base isolator.

An optimal nonlinear fractional order controller for passive/active base isolation building equipped with friction-tuned mass dampers

This paper presents an optimal nonlinear fractional-order controller (ONFOC) designed to reduce the seismic responses of tall buildings equipped with a base-isolation (BI) system and friction-tuned mass dampers (FTMDs). The parameters for the BI and FTMD systems, as well as their combinations (BI-FTMD and active BI-FTMD or ABI-FTMD), were optimized separately using a multi-objective quantum-inspired seagull optimization algorithm (MOQSOA). The seismic performances of the BI, FTMD, BI-FTMD, and ABI-FTMD systems for a 15-storey building subjected to two far-field (Loma Prieta and Landers) and two near-fields (Tabas and Northridge) earthquakes were evaluated. The results indicated that structures with BI, FTMD, BI-FTMD, and ABI-FTMD systems outperformed the uncontrolled structure in reducing structural responses during the design earthquakes (Loma Prieta and Tabas). However, under validation earthquakes (Landers and Northridge), the peak acceleration of the building with the FTMD system was worse than that of the uncontrolled structure during the near-field Tabas earthquake. To address this issue, we proposed a combination of the active BI system and the FTMD system. Time history analysis results demonstrated that for the building equipped with the ABI-FTMD system, the peak displacement, peak acceleration, and peak inter-storey drift were reduced by approximately 60%, 64%, and 78%, respectively, as compared to the uncontrolled structure.

Soil-structure interaction analysis of nuclear power plant structure using multi-step method in time-domain

Recently, several countries have experienced strong earthquakes, and there has been growing interest in the seismic design of structures. Particularly, consideration of soil-structure interaction (SSI) has become important when performing seismic response analysis for nuclear power plant (NPP) structures. A seismic analysis method that considers SSI in the time domain has been proposed in previous studies. This method is applicable to the seismic response of structures, because it can consider the influence of the SSI effect with the impedance function in the frequency domain and simultaneously considers the structural nonlinearity. However, it has only been applied to the structure comprising a single beam-stick. In this study, a modified method for applying it to more general structures is proposed, and its applicability is validated with an actual reactor containment building (RCB) structure comprising a three beam-sticks. Validation was performed by comparing the seismic responses with those of ACS SASSI. Using the proposed method, SSI analysis was performed with three soil profiles and the results were compared to investigate the effect of SSI on seismic responses, including the in-structure response spectrum (ISRS) and time history acceleration. For more realistic analysis, soil profile and earthquake input motion occurred in South Korea are adopted. Further, a multi-step method considering nonlinear behavior was also performed and compared with the linear case.

The time history of dynamic response of permeable asphalt mixture pavement based on PFC2D

To investigate the dynamic response of permeable asphalt mixture pavements, a discrete element model was developed using PFC2D under the coupling of seepage and stress fields. This study examines the excess pore water pressure and dynamic behavior of permeable asphalt mixture pavements under the coupling of seepage and stress fields. The findings indicate that the excess pore water pressure amplifies compressive strain and stress at the base of the permeable asphalt mixture over time, while exhibiting alternating positive and negative fluctuations as a roller traverses the pavement.

Elastoplastic plate shakes down under repeated impulsive loadings

When subjected to repeated dynamic impacts at identical load level, a metallic monolithic beam/plate may reach a stable state wherein measurable deformation ceases (i.e., shakedown in elastic state) after undergoing a sequence of elastoplastic deformations, which has been termed as “pseudo-shakedown” (P-S) (Jones, 1973, Shen and Jones, 1992). While the response of a single beam/plate under repeated low-velocity impacts has been thoroughly studied, its dynamic behavior under high-velocity impacts, such as explosive or alternating impulsive loads, is difficult to measure experimentally, due mainly to high costs and setup challenges. In the current study, the method of metallic foam projectile impact was employed to produce repeated impulsive loadings on a fully-clamped elastoplastic monolithic plate made of L907A (a Chinese standard shipbuilding steel). Its dynamic responses, including mid-point deflection versus time histories, final deflections, and deformation modes after each impact, were systematically measured. The phenomenon of dynamic shakedown was observed. To further explore this phenomenon, the method of finite elements (FE) was employed to simulate the repeated impulsive impact test, and its prediction accuracy was validated against experimental results. Unlike an elastoplastic (e.g., steel) monolithic plate subjected to repeated low-velocity impacts, which exhibits zero plastic energy dissipation in the P-S (pseudo-shakedown) state, the same plate under repeated high-velocity impacts shows a small level of plastic energy dissipation in the P-S state, mainly due to more extreme loading conditions. The initial impact momentum, yield strength, and tangent modulus of the material the plate is made of significantly affect both the stable deflection in the P-S state and the number of impacts needed to reach it, while the elastic modulus has limited influence. A modified dimensionless impulse loading number, accounting for the strain-hardening effect, is proposed. An approximately linear relationship between stable deflection in the P-S state and impulsive loading is found in dimensionless form.

Study on shock wave load characteristics from condensed phase explosive detonations in deep-water explosions

This study investigates shock wave load characteristics from condensed phase explosive detonations in deep-water environments using a high-order compressible multiphase solver. Spatial terms of the solver are discretized by fifth-order weighted essentially non-oscillatory reconstruction in characteristic space, while a third-order total variation diminishing Runge–Kutta method is adopted to deal with the temporal terms. The level-set method captures multiphase interfaces, while a programed burn model describes detonation wave generation. Numerical and experimental validations focus on shock waves in explosives interacting with water. Validations across shallow and deep-water conditions align numerical results with theoretical and experimental values. The solver examines shock wave characteristics across varied charge masses and water depths, revealing peak pressure deviations under identical conditions. The numerical simulation results indicate that the similarity of shock wave loads in underwater explosions is evident not only in peak pressures but also in the pressure–time history curves. Through extensive comparative analysis of results, it has been found that existing formulas for calculating shock wave positive pressure durations are not applicable to deep-water explosions. The research findings and analytical methods presented in this paper can serve as crucial references for further studies on the characteristics of shock wave loads in deep-water explosions.

Examining a Conservative Phase-Field Lattice Boltzmann Model for Two-Phase Flows

In this study, a conservative phase-field lattice Boltzmann model is examined for simulating immiscible two-phase flows with large density and viscosity ratios. This model is built upon the Allen–Cahn equation, incorporating a filtered collision operator and high-order corrections in the equilibrium distribution functions. The numerical model is also integrated with the volumetric boundary scheme and the immersed boundary method to achieve various stationary and moving boundary conditions on arbitrary geometries for different application scenarios. A comprehensive evaluation of this phase-field solver is conducted through a range of academic and industrial cases. First, droplet splashing cases at different Reynolds numbers are studied. The phase-field LB model effectively captures the surface wave motion and splashing of the droplet, although some smearing of small structures is observed due to the diffused interface property of the numerical model. Second, a tuned liquid damper is simulated, accurately capturing sloshing forces on solid walls. In the simulation of a dam-breaking case, predicted gauge pressure and free-surface elevation time histories compare well with experimental data. Lastly, a gearbox case under dip lubrication is simulated, with both the gearbox churning loss and oil distribution being well predicted across a range of rotating speeds. The validation studies demonstrate the effectiveness of the present phase-field lattice Boltzmann model in simulating immiscible two-phase flows with large and realistic density and viscosity ratios. The strengths, limitations, and weaknesses of the conservative phase-field LB model are discussed, and suggestions for the development and application of this numerical model are provided.

Effect of yaw on wake and load characteristics of two tandem offshore wind turbines under neutral atmospheric boundary layer conditions

In this work, we numerically investigated the effects of yaw angle on the wake and power characteristics of two National Renewable Energy Laboratory (NREL) 5 MW wind turbines based on actuator line method (ALM) and large eddy simulation (LES) under a neutral atmospheric boundary layer (ABL) with specified offshore surface roughness. The turbines are placed in tandem, with a spacing of seven rotor diameters, and the yaw angles range from 0° to 30°. The results indicate that under coordinated yaw conditions, the wakes of the two turbines significantly shift with increasing yaw angles, encroaching on the trailing edge of the turbines. The expansion of the wakes also gradually weakens, leading to a reduction in width. The superposition of the wake generated by the downstream turbine diminishes, leading to both turbines exhibiting approximately comparable physical characteristics within their respective wakes. As the wake of the upstream turbine propagates downstream, a secondary low-speed region emerges between the primary low-speed zone of the wake of downstream turbine and the surrounding atmosphere. With the increase in yaw angle, this secondary low-speed region significantly enhances the rate of wake recovery while also inducing a more pronounced deflection of the wake, thereby demonstrating a stronger entrainment effect. Regarding load characteristics, the time history of power characteristics and the power spectral density (PSD) spectra indicate a good turbine response to the inflow. The power characteristics of the upstream turbine exhibit a scaling law is closely related to the yaw angle. The quantitative relationship is established between yaw angle and the power distribution of the turbines, alongside a proposed correlation between the yaw angle and the cos 2(γ) scaled power curve. The power of upstream turbine decreases and the power of downstream turbine gradually increases with the increase in yaw angle. It is further found that the downstream turbine demonstrates optimal performance at a yaw angle of 20°due to the influence of the yawed upstream turbine. These analyses provide insights into the characteristics of wind turbine arrays under yaw conditions from the perspective of unsteady wake features, interactions, and aerodynamic performance, which can aid in wind farm unit planning and control strategies.

Temporal Evolution of Electron Accelerations behind the Dipolarization Front in the Earth's Magnetotail

We report the temporal evolution of electron pitch angle distributions behind the dipolarization front (DF) in the Earth's magnetotail with observations of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft. Taking advantage of multipoint observations from the THEMIS mission lined up in space, we study pitch angle distributions of energetic electrons behind the DF during two typical events. Pancake, rolling-pin, and cigar distributions are observed sequentially during the acceleration process. Based on Liouville's theorem, it is revealed that pancake distribution is dominantly formed by betatron acceleration in the early stage, and rolling-pin distribution is generated by both dominant Fermi and weak betatron acceleration in the transition stage, while cigar distribution is formed by Fermi acceleration finally. Our results provide comprehensive in situ observational evidence of the temporal evolution of electron acceleration behind the DF during propagation.

Chaotic dynamics of flexible graphene electronic membranes with variable density in motion

With advancements in artificial intelligence and wearable technology, flexible electronic devices characterized by their flexibility and extensibility have found widespread applications in fields such as information technology, healthcare, and military. Printing technology can accurately print a circuit diagram onto a flexible membrane substrate by the pressure transfer of a conductive ink, which makes the large-scale printing of flexible graphene electronic membranes possible. However, during the roll-to-roll printing process used to prepare flexible graphene electron membranes, the density of electron membranes is variable due to the uneven distribution of inkjet-printed circuits, which limits the printing speed of flexible graphene electron membranes. Hence, investigating the dynamic properties of flexible graphene electron materials with different densities is of paramount importance to improve the production efficiency and quality of flexible graphene electron membranes. This paper takes roll-to-roll intelligent graphene electronic membranes as the research object. According to Hamilton’s principle, nonlinear vibration partial differential equations for the motion of flexible graphene electron membranes with varying densities were established and subsequently discretized using the assumed displacement function and the Bubnov–Galerkin method. Through numerical calculations, the simulation results obtained based on the fourth-order Runge–Kutta method and the multiscale algorithm were compared, and the multiscale algorithm was verified to be more correct and effective. The primary resonance amplitude–parameter characteristic curve, along with phase-plane portraits, Poincaré maps, power spectrum, time history plots, and bifurcation diagrams, for the nonlinear behavior of the membrane was obtained. The impacts of the density coefficient, velocity, damping ratio, excitation force, and detuning parameters on the nonlinear primary resonance and chaotic behavior of the moving graphene electron membrane were determined, and the stable operational region was identified, laying a theoretical foundation for the development of flexible graphene electronic membranes.

Sliding-Window Matrix Pencil Method for Design Optimization with Limit-Cycle Oscillation Constraints

This paper introduces a novel approach to constrain limit-cycle oscillations in design optimization. The approach builds upon a limit-cycle oscillation constraint that bounds the recovery rate to equilibrium, circumventing the need for bifurcation diagrams. Previous work demonstrated the constraint using approximate recovery rates obtained by evaluating the system state velocity for prescribed states. This work proposes a fully nonlinear matrix pencil method that accurately evaluates the recovery rate based on transient simulations. The proposed method captures the amplitude variation in the recovery rate using a short time window that slides along the time history of a quantity of interest. This sliding-window matrix pencil method is first verified for a typical section model. Sensitivity analyses identify guidelines to obtain accurate recovery rates efficiently. The system is then optimized subject to limit-cycle oscillation, flutter, and side constraints, and the results are compared with the ones based on approximate recovery rates. The sliding-window matrix pencil method allows the optimizer to produce a less conservative design while preventing limit-cycle oscillations at desired operating conditions and amplitudes. The approach introduced in this paper can facilitate the inclusion of limit-cycle oscillation considerations in the design phase of a broad class of nonlinear systems.

Nonlinear Dynamic Characteristics of Smart FG-GPLRC Sandwich Varying Thickness Truncated Conical Shell with Internal Resonance for First Three Order Modes

This paper examines the 1:1:1 internal resonant nonlinear dynamic characteristic of the simply supported varying thickness functionally graded graphene platelets reinforced composite (FG-GPLRC) smart truncated sandwich conical shell subject to the combined effects of transverse load and in-plane force. The truncated smart sandwich conical shell is composed of an FG-GPLRC varying thickness core and two magneto-electro-elastic face layers, whose material properties and constitutive relations are individually identified by the rule of mixture, improved Halpin-Tsai approach and generalized Hooke's law. Utilizing the first-order shear deformation theory (FSDT), von Karman's geometrical nonlinearity, Hamilton's principle and Galerkin technique, the 3DOF dimensionless nonlinear dynamic formulations for the truncated smart FG-GPLRC conical shell are established. The multiple-scale technique is applied to developing the averaged equations for the truncated smart FG-GPLRC conical shell under combined resonance. The frequency-response and force-response curves, Poincare maps, phase portraits, time history diagrams, bifurcation and maximum Lyapunov exponent diagrams can be portrayed by the nonlinear equation solver and Runge-Kutta approach. The effects of the damping and tuning parameters, transverse and in-plane forces on the 1:1:1 internal resonant nonlinear dynamic characteristic of truncated smart varying thickness FG-GPLRC sandwich conical shell are examined.

Experiment and kinetics study on OH∗ chemiluminescence up to 3150 K in hydrogen combustion behind reflected shock waves

Chemiluminescence of OH∗ is commonly employed as an optical indicator for the combustion process. It is widely recognized that the generation of OH∗ in hydrogen flames is primarily governed by the reaction H + O + M=>OH∗+M. In this study, the time histories of OH∗ chemiluminescence from the A→X band around 308 nm were recorded behind reflected shock waves for stoichiometric and lean H2/O2 mixtures highly diluted in argon over the temperature range of 1130–3150 K and at the pressure of approximately 0.9 atm. Based on the time histories of OH∗ chemiluminescence, the best-fit reaction rate coefficient for the reaction H + O + M=>OH∗+M was determined as k = 3.17 × 1027exp(-121968 cal mol−1/RT) + 2.25 × 1017exp(-4246 cal mol−1/RT) cm6 mol−2 s−1 over the temperature range studied. Furthermore, by using the current rate coefficient in mechanism predictions, the predicted time histories and relative peak intensities of OH∗ chemiluminescence are in good agreement with experimental results reported in literature.