Dynamic Stress Response Research Articles

Testing and Evaluation on Dynamic Response of a New Modified Soil Subgrade under Freeze-Thaw Cycles

Abstract Dynamic response analysis is an effective method of evaluating the strength, deformation, and stability of subgrade under repeated vehicle traffic loads. It is usually premised on the results of a field test, which not only requires a lot of manpower and money but also can be easily affected by extraneous factors. In this study, a laboratory test was conducted in order to examine the dynamic response of a new type subgrade: silty clay (SC) modified by fly ash and crumb rubber (RFS). A novel tester was adopted in order to simulate and impulse traffic loads with different vehicle speeds/weights on subgrade materials. In addition, the dynamic stress and acceleration responses of RFS and SC were analyzed under varying speeds and axle loads under 0–5 freeze-thaw (F-T) cycles. Thereafter, scanning electron microscope tests were conducted to bring about clarity regarding the effect on the internal structural changes of two test soils in order to elaborate on the reasons for these dynamic response changes. According to the findings of these tests, the dynamic stability of SC is better than the RFS before F-T cycles. However, the RFS provides better resistance to F-T dynamic stability as the F-T cycle goes on. In particular, the RFS is more suitable for subgrade filling in seasonally frozen regions. Against this backdrop, the current article proposes a convenient method to evaluate the dynamic response of subgrade in laboratory, besides providing a reference for the dynamic characteristics of RFS.

Three-dimensional linear seismic analysis of normal concrete gravity dam

The three-dimensional linear finite element model is established for the bottom outlet dam section of concrete gravity dam. Mode-superposition response spectrum method and the massless foundation time history method are adopted to analyze the static and dynamic comprehensive stress response and displacement response of the dam under the action of the standard response spectrum of the design earthquake or the corresponding artificial wave under the action of design earthquake and check earthquake. The results show that the dam works well in seismic condition. In addition, the influence of radiation damping of infinite foundation on the dynamic response of the dam section under different seismic waves is analysed. By comparing the dynamic and static comprehensive stress changes of the dam, it shows that after considering the radiation damping effect of the infinite foundation, the dynamic response of the dam body is significantly reduced.

Fast modification-aimed stress modal analysis of thin plates with holes/notches

Thin plates are widely applied in engineering structures due to their excellent mechanical performance. This paper studies the stress modal analysis (SMA) of thin plates with holes/notches for the purpose of local structural dynamic modification (SDM). Identification of predominant components of stress state at critical locations is theoretically demonstrated. To pursue possible dynamic stress reduction, a fast modification strategy is proposed by using the SMA information, which involves a two-step procedure. First, modal participation factors (MPFs) are validated in SMA and then utilized to determine the predominant modes. Second, components of stress are evaluated for the predominant stress mode shapes (sSMSs11The superscript is to distinguish the stress from the strain in present paper.). Structural dynamic simulations of a representative L-shaped thin plate with hole/notches were implemented. The sSMSs in x-, y-, and xy- directions were compared in details. Together with MPFs, sSMSs can help to identify the dangerous stresses (both the location and the direction), and then to modify the local structure to suppress dynamic stress response. By taking full advantage of numerically-obtained sSMSs along different directions, local structural modification for dynamic stress reduction can be applied in a straightforward way with high efficiency prior to the full dynamic response analysis. This research is aimed to serve as a first step towards the development of SMA-based SDM strategy for real thin-walled structures with more complex geometric details and local changes.

Dynamic Photophysiological Stress Response of a Model Diatom to Ten Environmental Stresses.

Stressful environmental conditions can induce many different acclimation mechanisms in marine phytoplankton, resulting in a range of changes in their photophysiology. Here we characterize the common photophysiological stress response of the model diatom Thalassiosira pseudonana to ten environmental stressors and identify diagnostic responses to particular stressors. We quantify the magnitude and temporal trajectory of physiological parameters including the functional absorption cross-section of PSII (σPSII ), quantum efficiency of PSII, non-photochemical quenching (NPQ), cell volume, Chl a, and carotenoid (Car) content in response to nutrient starvation (nitrogen (N), phosphorus (P), silicon (Si), and iron (Fe)), changes in temperature, irradiance, pH, and reactive oxygen species (ROS) over 5 time points (0, 2, 6, 24, 72h). We find changes in conditions: temperature, irradiance, and ROS, often result in the most rapid changes in photophysiological parameters (<2h), and in some cases are followed by recovery. In contrast, nutrient starvation (N, P, Si, Fe) often has slower (6-72h) but ultimately larger magnitude effects on many photophysiological parameters. Diagnostic changes include large increases in cell volume under Si-starvation, very large increases in NPQ under P-starvation, and large decreases in the σPSII under high light. The ultimate goal of this analysis is to facilitate and enhance the interpretation of fluorescence data and our understanding of phytoplankton photophysiology from laboratory and field studies.

Experimental Analysis on Dynamic Response of X‐Section Piled Raft Composite Foundation under Cyclic Axial Load for Ballastless Track in Soft Soil

Large‐scale model tests were established at a scale of 1/5 using a 7 m deep model tank with cross‐sectional dimension of 5 m × 4 m, to study the vibration response characteristics of ballastless track, embankment, and X‐section piled raft foundation under cyclic axial load, including the vibration displacement, velocity, dynamic soil, and pile stress. Cyclic dynamic loading can be achieved by controlling the loading frequency and cycles through the vibration servo control loading system. The test results are presented in the variation of dynamic displacement, velocity, and stress of X‐section piled raft composite foundation. The vibration displacement, velocity, and stress of the track, embankment, and pile foundation follow a pattern of vibration characteristics of loading sine wave. The vibration characteristics of loading waves can be identified easily from the peaks and troughs in the dynamic response of displacement, velocity, and stress at many locations of track slab, embankment, cushion, and underlying soil, at which the vibration response presents almost monotonically increasing tendency with the loading frequencies. With the increase of loading frequency, the vibration responses at the track structure and embankment have higher increasing rates than those at substructure (raft, cushion, and subsoil). The piled raft bears more dynamic load than cushion and subsoils, to ensure long‐term dynamic stability and safety of the foundation soils. The model testing results provide a better understanding of the dynamic response characteristics of ballastless track, embankment, and X‐section piled raft foundation under cyclic axial load in soft soil.

Dynamic analysis of elliptical vibrating screen based on disc motor

ABSTRACT According to the requirements of the current drilling fluid vibrating screen for high efficiency, high reliability and low energy consumption, an elliptical vibrating screen based on disk motor is proposed. The dynamic analysis model of the vibrating screen of the three-excited motor is established, and the dynamic characteristics of the whole system and key structures are studied by multi-body dynamics and finite element method. The dynamic stress response characteristics of the rigid flexible coupling system of screen box are mainly analysed. Based on the deformation and stress of the flexible body damage node analysis results, through the fatigue cumulative damage theory and rain-flow counting method against casing load surface fatigue life prediction, verifying the reliability of fatigue life of screen box. The result shows that: Three Eccentric Rotors elliptical vibrating screen can achieve balanced elliptical vibration track, meeting the requirements of high stable amplitude vibration, and its natural frequency, structural strength and fatigue life all meet the engineering requirements, verifying the feasibility and effectiveness of the design scheme.

Sis1 potentiates the stress response to protein aggregation and elevated temperature

Cells adapt to conditions that compromise protein conformational stability by activating various stress response pathways, but the mechanisms used in sensing misfolded proteins remain unclear. Moreover, aggregates of disease proteins often fail to induce a productive stress response. Here, using a yeast model of polyQ protein aggregation, we identified Sis1, an essential Hsp40 co-chaperone of Hsp70, as a critical sensor of proteotoxic stress. At elevated levels, Sis1 prevented the formation of dense polyQ inclusions and directed soluble polyQ oligomers towards the formation of permeable condensates. Hsp70 accumulated in a liquid-like state within this polyQ meshwork, resulting in a potent activation of the HSF1 dependent stress response. Sis1, and the homologous DnaJB6 in mammalian cells, also regulated the magnitude of the cellular heat stress response, suggesting a general role in sensing protein misfolding. Sis1/DnaJB6 functions as a limiting regulator to enable a dynamic stress response and avoid hypersensitivity to environmental changes.

Understanding complex dynamics of behavioral, neurochemical and transcriptomic changes induced by prolonged chronic unpredictable stress in zebrafish

Stress-related neuropsychiatric disorders are widespread, debilitating and often treatment-resistant illnesses that represent an urgent unmet biomedical problem. Animal models of these disorders are widely used to study stress pathogenesis. A more recent and historically less utilized model organism, the zebrafish (Danio rerio), is a valuable tool in stress neuroscience research. Utilizing the 5-week chronic unpredictable stress (CUS) model, here we examined brain transcriptomic profiles and complex dynamic behavioral stress responses, as well as neurochemical alterations in adult zebrafish and their correction by chronic antidepressant, fluoxetine, treatment. Overall, CUS induced complex neurochemical and behavioral alterations in zebrafish, including stable anxiety-like behaviors and serotonin metabolism deficits. Chronic fluoxetine (0.1 mg/L for 11 days) rescued most of the observed behavioral and neurochemical responses. Finally, whole-genome brain transcriptomic analyses revealed altered expression of various CNS genes (partially rescued by chronic fluoxetine), including inflammation-, ubiquitin- and arrestin-related genes. Collectively, this supports zebrafish as a valuable translational tool to study stress-related pathogenesis, whose anxiety and serotonergic deficits parallel rodent and clinical studies, and genomic analyses implicate neuroinflammation, structural neuronal remodeling and arrestin/ubiquitin pathways in both stress pathogenesis and its potential therapy.

Modeling and numerical simulation of the dynamic behavior of magneto-electro-elastic multilayer plates based on a Winkler-Pasternak elastic foundation

This work presents the effect of the elastic foundation and the viscoelastic interface on the dynamic behavior of laminated magneto-electro-elastic rectangular plates with simply supported boundary conditions using the state space method in Laplace domain. The Kelvin-Voigt model is used to take into accounted the viscoelastic interface effects in this domain. The final solution is transferred to the time domain by the Fourier inversion method. The dynamic responses of 3D displacements, stresses, and electric and magnetic displacements are analyzed with respect to the thickness direction and the orthotropic behavior under harmonic stress. A variant of the numerical tests shown the effect of the Winkler-Pasternak elastic foundation on a magneto-electro-elastic rectangular plates dynamic behavior and may contribute to optimize the design and the manufacturing of these materials.

A Simplified Analytical Solution of Mechanical Responses of Soil Subjected to Repeated Impact Loading

A simplified dynamic response model is proposed based on the deformation and dynamic stress response characteristics of soil under impact loading. The foundation is divided into two distinct zones: a projection cylinder acting vertically under impact loading and a hollow cylinder outside the projection area. It is assumed that the ramming deformation of the projected cylinder under the vertical impact load is a quasi-static loading process under the maximum contact dynamic stress through the quasi-static method, and the settlement calculation without lateral deformation is given. It is assumed that the inner wall of the hollow cylinder is subjected to horizontal lateral pressure and the analytical solution of the horizontal dynamic stress considering the plastic deformation of soil is given. The simplified dynamic response model can reflect the mechanical response of soil under impulse train load well which can provide reference for similar projects.

The Influence of the Motor Traction Vibration on Fatigue Life of the Bogie Frame of the Metro Vehicle

During the service life of metro vehicles, the cracks frequently appear at the root of motor seats. This indicates the previous antifatigue designs are unable to cover the actual operating environment. Some individual loads, such as motor vibration, have been ignored or wrongly understood, which leads to the occurrence of local insufficient fatigue life of the frame. To illustrate the influence of the motor vibration on the fatigue life of the bogie frame, a metro vehicle was taken as an example: first, the precise finite element model of the frame was established, and its correctness was verified; then, the vibration characteristics of the frame were analyzed by sweep frequency calculation; and finally, considering the vibration acceleration signal of the motor measured on a metro line as the excitation, the influence of the random vibration on the fatigue life of the frame under traction and idle running conditions was compared and analyzed by solving the power spectral density of the dynamic stress response at the weak fatigue nodes of the structure. The results show that the energy of the vibration in the frame is mainly concentrated in modes 6 and 7, which are excited by the motor transverse and vertical vibration, respectively, and contribute a lot to the fatigue damage of the frame; the fatigue life of the vital positions of the frame under the traction condition significantly reduces compared to the idle running condition; and the contribution of the low-amplitude vibration above 300 Hz to the fatigue damage can be ignored. At last, the importance of the influence of the motor traction vibration on the fatigue life should be fully considered in the metro vehicle design was proposed.

Concurrent design of composite macrostructure and cellular microstructure with respect to dynamic stress response under random excitations

This paper proposes a concurrent topology optimization method of macrostructural material distribution and periodic microstructure considering dynamic stress response under random excitations. The optimization problem is the minimization of the dynamic stress response of the macrostructure subject to volume constraints in both macrostructure and microstructure. To ensure the safety of the macrostructure, a new relaxation method is put forward to establish a relationship between the dynamic stress limit and the mechanical properties of microstructure. The sensitivities of the dynamic stress response with respect to the design variables in two scales, i.e., macro and micro scales, are derived. Then, the aforementioned optimization problem is solved by the bi-directional evolutionary structural optimization (BESO) method. Finally, several numerical examples are presented to demonstrate the feasibility and effectiveness of the proposed method.

Propagation of shock wave and structure dynamic response of explosion in a subway station: a case study of Wuhan subway station

With the development of urbanization, the construction of the subway has been greatly developed. Meanwhile, the public concern of terrorist attacks on subway stations keeps driving the related research. In this paper, the representative subway station of Wuhan Metro Line 8, Mafangshan station, which is now under construction, is taken as a case, the dynamic finite element numerical simulation software ANSYS/LS-DYNA is employed to establish finite element model. The propagation law transmitting through the station structure and the dynamic response of the station under different TNT charges are analyzed. It is indicated that the propagation of shock wave is complicated due to the semi-closed environment of the station as well as the reflection and transmission of the stress wave in the structure. Specifically, in the station structure, the displacement of the platform plate was the largest, under the explosive action of different TNT charge, the displacement of platform plate is 13.6 mm (5 kg), 22. 8mm (10 kg), 35.2 mm (20 kg), 45.6 cm (30 kg), 68.8 cm (40 kg), respectively. The middle part of the pillar was the largest displacement on the pillar. Based on the dynamic stress response analysis of the station pillar, it shows that the maximum value of the stress value in the pillar is located at the junction of the pillar and the plate. Under the explosive action of 40 kg TNT charge, the maximum tensile stress of the junction of the pillar and the plate reached 45.1 MPa. Therefore, more attention should be paid to anti-explosion measures herein. Besides, through the analysis of the tensile stress value at the bottom of the pillar under different charge quantity, the TNT charge quantity for the crack at the bottom of the pillar is determined to be 6.77 kg by the formula fitting.

Dynamic Stress Responses and Real-Time Symptoms in Binge-Eating Disorder.

Stress is a dynamic construct that predicts a range of health behaviors and conditions, including binge eating and excess weight. Thus far, there have been limited and inconsistent findings regarding stress responses in binge-eating disorder (BED) and insufficient consideration of temporal patterns of stress responses across the weight spectrum. The present study used ecological momentary assessment (EMA) to examine stress reactivity (i.e., the magnitude of the initial stress response), recovery (i.e., how long the stress response lasts before returning to baseline), and pileup (i.e., accumulation of repeated experiences of stressors and responses over time) as predictors of binge-eating symptoms (BES) and food craving in BED. Adults with BED (N = 115) completed a 7 day EMA protocol assessing stressful events, perceived stress, binge eating, and food craving prior to being randomized to a behavioral intervention. Generalized estimating equations indicated that moments of greater stress pileup predicted greater subsequent BES (within-person effect). Participants with higher perceived stress and pileup reported greater overall BES and craving, and those with better recovery reported higher overall craving (between-person effects). Findings highlight the importance of considering the dynamic nature of stress responses and, particularly, that the accumulation of stress over the day is an important trigger for BES.

Analysis of failure mechanism of W1-type fastening clip in high speed railway and structure study of damping composite

In this paper, the fastener clip in high-speed railway with the speed of 300–350 km/h is taken as the research object, it studied the relationship among parameters such as high-speed rail wear, dynamic frequency response of clip and dynamic stress of clip, revealed the dynamic failure mechanism of clip damage in high-speed rail caused by high-frequency excitation (580–680 Hz).In order to improve the service life of existing W1-typefastener in high-speed rail on the basis of guaranteeing design requirements and installation interchangeability of clips, taking “keeping away from excitation frequency band and reducing vibration amplitude” as the research objective, the clip geometric parameter optimization based on the correlation theory and the composite damping structure design of clip based on the modal damping theory are mainly promoted. Under the conditions of installation and use of rail clips, high damping clips with different combination of inner and outer diameters are obtained and strength simulation analysis, damping clip samples and dynamic frequency response test of optimized damping clips are carried out. The results show that, (1) with the increase of the equal ratio of outer diameter and damping diameter of high damping clip, the attentive mode frequency of clip increases up to 18.5%;(2) As the ratio of outer diameter and damping diameter of high damping clip increases, the response amplitude of high damping clip significantly decreases, up to 31.6%, (3) As the ratio of outer diameter and damping diameter of high damping clip increases, the overall mass of fastener clip also decreases, up to 9.7%.To a certain extent, the design structure of high damping composite clip is not only far away from the excitation frequency of wheel and rail, but also improves the dynamic fatigue life of clip, saves the cost of fastener system and has more applicability for high-speed railway lines.

Integrating GWAS and Transcriptomics to Identify the Molecular Underpinnings of Thermal Stress Responses in Drosophila melanogaster.

Thermal tolerance of an organism depends on both the ability to dynamically adjust to a thermal stress and preparatory developmental processes that enhance thermal resistance. However, the extent to which standing genetic variation in thermal tolerance alleles influence dynamic stress responses vs. preparatory processes is unknown. Here, using the model species Drosophila melanogaster, we used a combination of Genome Wide Association mapping (GWAS) and transcriptomic profiling to characterize whether genes associated with thermal tolerance are primarily involved in dynamic stress responses or preparatory processes that influence physiological condition at the time of thermal stress. To test our hypotheses, we measured the critical thermal minimum (CTmin) and critical thermal maximum (CTmax) of 100 lines of the Drosophila Genetic Reference Panel (DGRP) and used GWAS to identify loci that explain variation in thermal limits. We observed greater variation in lower thermal limits, with CTmin ranging from 1.81 to 8.60°C, while CTmax ranged from 38.74 to 40.64°C. We identified 151 and 99 distinct genes associated with CTmin and CTmax, respectively, and there was strong support that these genes are involved in both dynamic responses to thermal stress and preparatory processes that increase thermal resistance. Many of the genes identified by GWAS were involved in the direct transcriptional response to thermal stress (72/151 for cold; 59/99 for heat), and overall GWAS candidates were more likely to be differentially expressed than other genes. Further, several GWAS candidates were regulatory genes that may participate in the regulation of stress responses, and gene ontologies related to development and morphogenesis were enriched, suggesting many of these genes influence thermal tolerance through effects on development and physiological status. Overall, our results suggest that thermal tolerance alleles can influence both dynamic plastic responses to thermal stress and preparatory processes that improve thermal resistance. These results also have utility for directly comparing GWAS and transcriptomic approaches for identifying candidate genes associated with thermal tolerance.

Continuum structural topological optimization with dynamic stress response constraints

This paper proposes a methodology for the topology optimization of continuum structures subject to dynamic stress response constraints under stochastic loads. The topology optimization model is built, where the objective function is the structural weight, and the dynamic stress constraints are applied. In order to greatly reduce the computational cost of dynamic stress responses and prevent stress concentration phenomenon, the P-norm aggregation function is adopted to replace the dynamic stress response constraints. To solve the defined topology optimization problem, a method with varying dynamic stress response limit is presented, and the sensitivities of the equivalent dynamic stress response constraints with respect to the reciprocal design variables is derived so as to form the explicit approximate functions for structural equivalent dynamic stress response constraints. Then, based on dual theory, an algorithm by using nonlinear programming method with simple trust regions is introduced to solve the optimization problem. Finally, the results of several numerical examples are given to demonstrate the validity and effectiveness of the proposed approach.

Local Finite Element Refinement for Accurate Dynamic Stress via Modal Information Only

Accurate stress responses are the basics for failure analysis of aerospace structures, but they still can be challenging in numerical simulations for dynamic systems. This work exploits the stress mode shapes (SMSs) in local finite element (FE) refinement for the purpose of accurate dynamic stress estimation. Toward structural FE modeling, identification of critical locations via predominant SMSs is theoretically demonstrated. To pursue more accurate dynamic stress, a strategy for local FE refinement is proposed by using the information from stress modal analysis. The strategy involves a two-step procedure. First, modal participation factors (MPFs) are used to extract the predominant modes. Second, retained SMSs are evaluated for the local remeshing. Numerical simulations of a representative thin plate with geometric details were conducted. The SMSs were investigated in detail. Together with MPFs, SMSs can help to localize the dangerous stresses and then refine the local meshes to accurately calculate stress responses. By taking full advantage of numerically obtained SMSs, local structural FE modeling can be applied in a straightforward way with high efficiency. Results indicate that SMSs can reveal the underlying mechanism that governs the overall dynamic stress response.

Investigation of Cortisol Dynamics in Human Sweat Using a Graphene-Based Wireless mHealth System

Understanding and assessing endocrine response to stress is crucial to human performance analysis, stress-related disorder diagnosis, and mental health monitoring. Current approaches for stress monitoring are largely based on questionnaires, which could be very subjective. To avoid stress-inducing blood sampling and to realize continuous, non-invasive, and real-time stress analysis at the molecular levels, we investigate the dynamics of a stress hormone, cortisol, in human sweat using an integrated wireless sensing device. Highly sensitive, selective, and efficient cortisol sensing is enabled by a flexible sensor array that exploits the exceptional performance of laser-induced graphene for electrochemical sensing. Herein, we report the first cortisol diurnal cycle and the dynamic stress response profile constructed from human sweat. Our pilot study demonstrates a strong empirical correlation between serum and sweat cortisol, revealing exciting opportunities offered by sweat analysis toward non-invasive dynamic stress monitoring via wearable and portable sensing platforms.

Nonlinear Response of a Subsea Tunnel Constructed by Two Tunnelling Methods subjected to Strong Seismic Shaking

In this paper, a three-dimensional numerical model is built to study the seismic response of a subsea tunnel constructed by two tunnelling methods, including the TBM tunneling and drill-and-blast tunneling. In the numerical model, the plastic-damage model is used to simulate the elastic and plastic behaviour of concrete under dynamic loadings. To illustrate the seismic response of the tunnel and yet limit the amount of data included in the paper, the work presented is limited to the deformation of tunnel cross sections and dynamic stress responses. Based on the results, the deformation and stressed of different tunnel sections are discussed. Results show that the amplitude of maximal principal stress occurs at sidewall basement of the inner liner. The spandrel and the sidewall basement are the most precarious area.