Nonlinear Analytical Model Research Articles

Physical parameters identification for full‐scale ten‐story reinforced concrete building with degrading tri‐linear model by modal iterative error correction method

AbstractTo assess the post‐earthquake seismic safety of buildings, it is crucial to predict seismic response, and it is necessary to set the appropriate physical parameters of the response analysis model. Numerous methods have been proposed to identify physical parameters. However, most of them are limited to linear systems, and previous researches on nonlinear systems have difficulties in practical applications. In this paper, a nonlinear response analysis model is identified for a full‐scale ten‐story reinforced concrete building with the degrading tri‐linear stiffness model by the modal iterative error correction (MIEC) method, and the accuracy of this technique is discussed by comparing with the shaking table test.

Stainless steel top-seat angle beam-to-column connection: Full-scale test and analytical modelling

Stainless steel (SS) is increasingly used for structural applications in the construction industry as its beneficial properties outweigh initial material costs when sustainability aspects and the whole life cycle of structures are appropriately accounted for in the structural design. Despite the well-recognised significance of connections in bare metallic construction, experimental research on SS beam-to-column connections, especially full-scale test results, are scarce. This paper presents a full-scale experimental investigation on the semi-rigid behaviour of top-seat bolted connection (also known as ‘flange cleat’ connection) made from austenitic SS. Deformation characteristics of various elements of the connection were carefully investigated and subsequently used to calibrate nonlinear FE models for parametric analysis. Obtained numerical results were used to develop a four-parameter power model that relies on simplified expressions for key input parameters to predict the semi-rigid behaviour of bolted top-seat connections. Results predicted using the proposed model and those obtained using currently available techniques based on carbon steel behaviour were compared. Outcomes of the current research highlighted the significance of appropriate inclusion of stain hardening offered by austenitic grade to capture the semi-rigid response of such connections.

An analytical method for full-range mechanical behavior of continuous slab-deck in multi-span simply supported concrete bridges

Connecting the ends of girders with a continuous slab-deck to make a multiple-span simply supported girder bridge provides many benefits, but there is no suitable nonlinear analysis model which considers continuous slab-deck cracking under tension and bending. In this article, the rotational spring model is further refined to replace the restraining effects at both ends of the girder by the simplified mechanical model associated with axial stiffness, bending stiffness, and shear stiffness. Then, it is introduced into the analysis of continuous slab-deck. The more accurate rotations and displacements of both ends of continuous slab-deck are obtained to investigate the more precise moment and tension of the continuous slab-deck. Furthermore, this article presents an improved nonlinear analysis model of continuous slab-deck based on a detailed boundary rotational spring model. The displacements of important positions and the strain of key components in continuous slab-deck after cracking are investigated by numerical analysis and full-scale model test to verify the accuracy of the proposed nonlinear analysis model. The result shows that the nonlinear analysis model presented in this article could successfully evaluate the depth of cracks and the stress of rebars in continuous slab-deck, and it is instructional in predicting the cracking state of the continuous slab-deck and the reinforcement design.

Short-term effect of meteorological factors on the risk of rheumatoid arthritis hospital admissions: A distributed lag non-linear analysis in Hefei, China

Rheumatoid arthritis (RA) is an autoimmune disease, mainly characterized by erosional arthritis. The proportion of adults suffering from RA is about 0.5%–1%. There have been reports on the association of rainfall and traffic-related air pollutants with RA hospitalization rates. However, there have been no studies on the association of diurnal temperature range (DTR) and relative humidity (RH) with RA hospitalization rates. This study aimed to examine the short-term association of DTR, RH and other meteorological factors with the hospital admission rate of RA patients, while excluding the interference of PM2.5, SO2, NO2, CO and O3 atmospheric pollutants. We collected daily RA occupancy rate and meteorological factor data in Hefei city from 2015 to 2018 and used the generalized additive model (GAM) combined with the distributed lag nonlinear model (DLNM) for time series analysis, and further stratified analysis by gender and age. Single-day and cumulative-day risk estimates of RA admissions were expressed as relative risk (RR) and its 95% confidence interval (95% CI). For the cumulative-day lag model, high RH was statistically significant after cumulative lag 0–8 days, and the effect gradually increases. Stratified analysis shows that females seem to be more susceptible to high or extremely high DTR and RH exposure, and extremely high DTR exposure may increase the risk of RA admission in all populations. In conclusion, this study found that high DTR and high RH exposure increased the risk of hospitalization in RA patients and provided clues to the potential association between other meteorological factors and RA.

Nonlinear Models of Laminar Premixed Slit Flame Responses Subjected to Two-Way Perturbations

Transversal and longitudinal combustion instabilities typically present in gas turbines and rocket engines. It is thus important to investigate the flame responses of the two directional disturbances. When the disturbance level remains weak, the flame response can be considered linear. The flame transfer function (FTF) is typically used, and the global FTF can be easily obtained by superposition of the FTFs at the two-directional forcing. However, when the disturbances arise, the flame response becomes nonlinear due to the nonlinear responses at the two directions and their couplings. The present work thus presents nonlinear analytical models (flame describing function [FDF]) of a two-dimensional laminar premixed slit flame subjected to simultaneously longitudinal and transverse bulk mean flows and disturbances. These nonlinear models are derived based on the asymptotic expansion of the -equation model of the dynamic flame front. A velocity perturbation model is proposed by considering the change of disturbance convection speed with forcing frequency. To analyze the nonlinear coupling effect of the two-directional forcing, a partly FDF is introduced by neglecting the coupling term. By comparing the results from the FDF, partly FDF, and the FTF, the nonlinear effects are investigated. As the flame tip movement plays an important role in the FDFs for the slit flame, the global effects of flame tip movement on the FDFs are also quantified.

Hyperspectral and Full-Waveform LiDAR Improve Mapping of Tropical Dry Forest’s Successional Stages

Accurate estimation of the degree of regeneration in tropical dry forest (TDF) is critical for conservation policymaking and evaluation. Hyperspectral remote sensing and light detection and ranging (LiDAR) have been used to characterize the deterministic successional stages in a TDF. These successional stages, classified as early, intermediate, and late, are considered a proxy for mapping the age since the abandonment of a given forest area. Expanding on the need for more accurate successional forest mapping, our study considers the age attributes of a TDF study area as a continuous expression of relative attribute scores/levels that vary along the process of ecological succession. Specifically, two remote-sensing data sets: HyMap (hyperspectral) and LVIS (waveform LiDAR), were acquired at the Santa Rosa National Park Environmental Monitoring Super Site (SRNP-EMSS) in Costa Rica, were used to generate age-attribute metrics. These metrics were then used as entry-level variables on a randomized nonlinear archetypal analysis (RNAA) model to select the most informative metrics from both data sets. Next, a relative attribute learning (RAL) algorithm was adapted for both independent and fused metrics to comparatively learn the relative attribute levels of the forest ages of the study area. In this study, four HyMap indices and five LVIS metrics were found to have the potential to map the forest ages of the study area, and compared with these results, a significant improvement was found through the fusion of the metrics on the accuracy of the generated forest age maps. By linking the age group mapping and the relative attribute mapping results, a dynamic gradient of the age-attribute transition patterns emerged.

Nonlinear three-dimensional anisotropic material model for failure analysis of timber

In this paper, a constitutive material model is proposed to model the nonlinear mechanical response of timber, as elastoplastic orthotropic material under three-dimensional (3D) stress state. An associated flow rule model based on Hoffmann yield criterion and plastic potential is adopted for describing the plasticity of timber under compression. Isotropic strain hardening during plastic deformation is incorporated into Hoffman yield criterion by assuming that equivalent yield stress is a function of the equivalent plastic strain. A stress-based continuum damage formulation with four independent failure criteria in tension and compression is used. The proposed model is implemented as a user material subroutine UMAT in ABAQUS. The results obtained in numerical simulations are evaluated and compared with experimental results. A good agreement has been found between numerical simulations and the experimental results. Therefore, the proposed constitutive model can be used further in numerical simulations of the anisotropic behavior of timber.

Nonlinear effects of bolted flange connections in aeroengine casing assemblies

Aeroengine manufacturers face fundamental limitations when correlating experimental dynamic analysis with finite element method models. The source of inconsistency between model predictions and experimental test data can be attributed to nonlinear behaviour at the bolted flange interface. The two main sources of nonlinearities in aeroengine casing assemblies are damping dissipation and the nonlinear effects of boundary conditions. In this research, a novel and robust analytical formulation is proposed for implementation in FE analysis that accurately captures and represents the nonlinear dynamic characteristics of bolted flange connections. The proposed nonlinear analytical lump model has demonstrated significant accuracy and precision in capturing the nonlinear dynamic characteristics of bolted flange connections with spigots under various loading conditions. The proposed model clearly represents and characterizes the nonlinear phenomena of peak amplitude damping and frequency shift. It is also computationally efficient, making the model feasible for implementation when performing nonlinear analyses of large structural assemblies such as full aeroengine models. Moreover, the proposed analytical lump model is universal, permitting its implementation in various structures with different material properties and geometries. The validity and accuracy of the proposed model has been verified using nonlinear experimental test data for an aeroengine casing assembly.

Structural behaviour of folded timber sandwich structures

This paper aims to characterise the mechanical behaviour of folded timber sandwich structures developed using integral rotational press-fit (RPF) joints. Six folded arches are tested to failure, under three load cases designed to induce different sagging and hogging conditions at internal joints. Experimental testing showed failures occurring at joint locations with maximum hogging moment, with two failure types observed as FRP tensile fracture and core compressive rupture. A nonlinear static analysis and simplified 2D frame model is proposed to predict moment distribution and failure load for FRP fracture modes. This model characterises the RPF joint as a nonlinear semi-rigid hinge, with assigned bilinear moment–curvature relation obtained from analysis of joint strain data collected during arch testing. Core compressive failures are shown to occur as an inelastic core buckling behaviour when there is misalignment between assembled core segments.

Analytical model building for Type-3 wind farm subsynchronous oscillation analysis

Many real-world scenarios confirmed insights developed based on the dq-frame nonlinear analytical model for doubly-fed induction generator (DFIG)-based type-3 wind subsynchronous resonance (SSR) study by the authors in 2010. A few real-world observations do not align with the simulation results from that model. In real-world scenarios, when a type-3 wind farm is radially connected to a series compensated line, even at a low compensation level, SSR occurs. This phenomenon has not been replicated by the nonlinear analytical model. In this paper, we revisited the analytical model by including phase-locked-loop (PLL). A modular modeling approach is presented in this paper. The inputs and outputs of each subsystem and the interconnections among subsystems are identified first. The overall system is then developed with all blocks integrated. The analytical model is capable of dealing with various transmission topologies, providing both large-signal time-domain simulation results and small-signal analysis. The new analytical model can successfully replicate the aforementioned phenomena and provide insights of type-3 wind SSR phenomena. The accompanying software package will be posted in the public domain.

Nonlinear analytical modelling of flat and hyperbolic paraboloidal panels under shear

The hyperbolic paraboloid (hypar) form has been widely used in long-span roof structures and is the subject of much research under out-of-plane loading. However, the behaviour of hypars under in-plane loading has been less keenly studied, and there is no suitable guidance for their design in current codes of practice. A nonlinear analytical model treating the hypar as a deliberate imperfection applied to a flat plate is presented. A Rayleigh–Ritz formulation using appropriate shape functions is developed and the resulting equations are solved using numerical continuation techniques. The results are verified with nonlinear finite-element models, showing good correlation across a range of thicknesses and degrees of initial curvature. Key modal contributions that influence the behaviour of the hypar are identified, providing insight into the nonlinear behaviour of hypars subject to in-plane shear. The main differences in behaviour between the flat plate and the hypar panel are shown to be most prevalent in the early stages of loading, where the influence of the initial geometry is at its greatest.

Advantages of Spike and Slab Priors for Detecting Differential Item Functioning Relative to Other Bayesian Regularizing Priors and Frequentist Lasso

ABSTRACT An important step in scale development and assessment is to evaluate differential item functioning (DIF) across segments of the population. Recent approaches use lasso regularization to simultaneously detect DIF in all items and avoid incorrect anchor item assumptions that incur inflated error rates for classical DIF evaluation methods. Although promising, lasso methods cause underestimated standard errors and incorrect p-values. An alternative is Bayesian regularization that provides empirical standard errors. However, we point out that using empirical criteria such as credible intervals for selecting DIF parameters has limited validity. We argue that using a spike-and-slab prior with an inclusion probability criterion provides more theoretically coherent DIF selection and inference over Bayesian regularizing priors with empirical selection rules or frequentist lasso. We demonstrate this by simulation studies with Multi-group Item Response Theory and Moderated Nonlinear Factor Analysis models. Practical utility of the spike-and-slab prior selection criterion is discussed.

Correlation Analysis of Ground Motion Duration Indexes and Nonlinear Seismic Responses of a Long-span Continuous Rigid-Frame Bridge with High-Rise Piers

ABSTRACT To investigate the correlations of duration indexes and the nonlinear seismic responses of long-span continuous rigid-frame bridges with high-rise piers (CRFB-LH), an irregular CRFB-LH was selected as the prototype bridge. A construction stage analysis model was simulated in MIDAS/Civil, where the actual construction process was considered and the internal force state was extracted. After that, a nonlinear dynamic analysis model of the CRFB-LH with the equivalent internal force state was simulated via OpenSees. A bracketed duration and significant duration with a continuous-time interval were selected as the duration indexes. Sixty ground motion records with total duration values ranging from 9.91 s to 300 s were used in the nonlinear dynamic analysis. The correlation between the two duration indexes and the nonlinear seismic responses of the CRFB-LH under total-duration ground motions were analyzed. Finally, the effect of different duration indexes on the nonlinear seismic responses of the CRFB-LH was discussed under 30 long-duration ground motions intercepted according to D b0.1g , D s5-75% and D s5-95%. The numerical results show that the correlations of D s with nonlinear seismic responses are better than those of D b, and the latter heavily depends on the absolute acceleration threshold. D s5-95% is preferred for calculating the total hysteretic energy dissipated (HED) from the CRFB-LH. Additionally, while the amount of total HED is not determined by the total duration, the effective time interval of the ground motion duration under different duration indexes has a significant influence on the total HED.

Effect of Different Types of Middle Columns on the Seismic Performance of Single-Story Subway Station Structure

In view of the seismic weak component of the single-frame-type subway station structure, the three-dimensional (3D) time-domain nonlinear finite element static-dynamic coupling analysis model of interaction between soil and subway station structure is established by, respectively, using rectangular reinforced concrete (RRC) columns, circular reinforced concrete (CRC) columns, and prefabricated concrete-filled steel tube (CFST) columns with a quick-connection device proposed in this article. This analysis model is further used to investigate the influence of different types of middle columns on the seismic response characteristics of the underground structure, such as the interstory displacement angle, seismic damage, and dynamic response. The results show that, compared with the rectangular columns, the circular columns with the equal moment of inertia suffer less damage in the earthquake and have better seismic performance. The prefabricated CFST columns can effectively ensure that the middle columns of the station structure are not severely damaged and can be replaced quickly after the earthquake, which improves the overall seismic performance of the subway station structure and the rapid recovery ability of the structural function after the earthquake.

Variation in vibro-acoustic noise due to the defects in an automotive drum brake

Drum brakes are significant contributors to noise and vibration in automobiles causing discomfort to the passengers. The vibration and hence the resulting noise increase due to various inherent defects in the drum brake, such as asymmetry. This work aims to quantify the variation in the vibro-acoustic noise due to several common defects in the drum brake using an integrated non-linear vibration analytical model and a numerical acoustic model. The sources of vibro-acoustic noise sources such as contact and reaction forces are predicted using a four-degree-of-freedom non-linear contact mechanics based analytical model. A finite element based acoustic model of the drum brake is utilized to predict the force to the sound pressure transfer function in the drum brake. Product of the transfer functions and the forces gives the corresponding sound pressure level from which the overall sound pressure levels are estimated. The variation in the overall sound pressure levels due to different drum brake defects is evaluated by introducing defects to the analytical model. The results show that the overall sound pressure level is a strong function of the defects. It is envisioned that the current work will help in the development of effective health monitoring systems.

Comparison of noise generated from simplex and duplex configurations of drum brake using non-linear vibro-acoustic models

The drum brakes used on the rear wheels of automobiles have various configurations. These contribute to the differences in kinematic (geometry) and dynamic (contact, friction) aspects, eventually leading to significantly different vibration and acoustic response. This work attempts to estimate the difference in the vibro-acoustic noise generated by the drum brake's simplex and duplex variants using a combination of non-linear analytical vibration models and a numerical acoustic model. Four degrees-of-freedom lumped parameter models developed for the simplex and the duplex configurations with conformal contact predict the contact and reaction forces during braking. These forces act as the sources for the finite element based acoustic models developed for the two configurations to obtain the sound pressure to force transfer functions. The sound pressure levels are estimated by the product of the predicted forces with the respective transfer functions in the frequency domain. The sound pressure levels of the simplex and duplex drum brakes are quantitatively compared under different braking conditions, and the results are presented. It is expected that this vibro-acoustic analysis will help in designing quieter drum brakes.

RETRACTED: Guided ultrasonic wave-based investigation on the transient response in an axisymmetric viscoelastic cylindrical waveguide

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief, for the unauthorized use of third party research data by the author. The author apologizes for the violation of the journal's code of ethics. One of the conditions of submission of a paper for publication in Ultrasonics is that authors must declare explicitly that their work is original. Use of research outcomes from others without formal permission or without appropriate citation is regarded as an ethical violation. The scientific community takes a very strong view on this matter and apologies are offered to readers of Ultrasonics that this was not detected during the submission process.

Meshfree-based applied mathematical modeling for nonlinear stability analysis of couple stress-based lateral pressurized randomly reinforced microshells

Meshfree-based applied mathematical modeling for nonlinear stability analysis of couple stress-based lateral pressurized randomly reinforced microshells

Nonlinear analytical study of structural laminated glass under hard body impact in the pre-crack stage

Emerging glass structures, which frequently use laminated glass (LG) as load bearing elements, see a significant rise in recent decade. Existing analytical solutions for LG under impact present limitation when introduced into structural LG products, as structural LG having more glass plies and soft polymeric interlayers requires more accurate nonlinear analytical model. In this study, a nonlinear analytical model was proposed for the simply supported square structural LG subjected to hard body impact. The motion equations were established based on a third order shear deformation theory and von Kármán nonlinear strain–displacement relationship. Based on a two-step perturbation method, the solutions of the motion equations were obtained. The fourth-order Runge–Kutta method was used to capture the impact force variation. Drop weight impact tests with increasing impact velocity, were conducted to record the impact force of LG panels before breakage. Eighteen LG panels with PVB or SG interlayers were tested. Through analysing the fracture initiation from high speed photos as well as the impact force variation in the impact attempt causing fracture, certain feature of the experimental impact force response was determined to be validated with analytical prediction. The validation results show that the proposed model can well reproduce the examined feature and achieve satisfactory impact force response. Case study was then designed to investigate the influence due to the safety windows film on reducing the pre-crack impact response. The effective thickness of LG based on the equivalence of indentation was also proposed for the hard body impact.

Nonlinear Dynamic Analysis of Axially Moving Laminated Shape Memory Alloy Beam with 1:3 Internal Resonance.

The remarkable properties of shape memory alloys (SMA) are attracting significant technological interest in many fields of science and engineering. In this paper, a nonlinear dynamic analytical model is developed for a laminated beam with a shape memory alloy layer. The model is derived based on Falk’s polynomial model for SMAs combined with Timoshenko beam theory. In addition, axial velocity, axial pressure, temperature, and complex boundary conditions are also parameters that have been taken into account in the creation of the SMA dynamical equation. The nonlinear vibration characteristics of SMA laminated beams under 1:3 internal resonance are studied. The multi-scale method is used to solve the discretized modal equation system, the characteristic equation of vibration modes coupled to each other in the case of internal resonance, as well as the time-history and phase diagrams of the common resonance amplitude in the system are obtained. The effects of axial velocity and initial conditions on the nonlinear internal resonance characteristics of the system were also studied.