Time History Research Articles

The Politics of French History in Times of Crisis

A roundtable discussion following the Western Society for French History online event, "The Politics of French History in Times of Crisis" that took place on October 21st, 2023, with an introduction from moderator Sarah Horowitz (W & L University). In this written exchange, Jacqueline Couti (Rice University), Corinne Gressang (Slippery Rock University), Terry Peterson (Florida International University), and K. Ringelberg (Elon University) discuss their experiences with external pressures on their teaching and research, and how they have struggled to support students and colleagues of color and/or who belong to the LGBTQ+ community in a time when academia is facing renewed threats of censorship and political interference.

A Quasi Time-Domain Method for Fatigue Analysis of Reactor Pressure Vessels in Floating Nuclear Power Plants in Marine Environments

The reactor pressure vessel (RPV) in onshore nuclear power plants is typically analysed for fatigue life by considering the temperature, internal pressure, and seismic effects using a simplified time-domain fatigue analysis. In contrast, the frequency-domain fatigue analysis method is commonly employed to assess the fatigue life of ship structures. The RPV of a floating nuclear power plant (FNPP) is subjected to a combination of temperature, internal pressure, and wave loads in the marine environment. Consequently, it is essential to effectively integrate the frequency-domain fatigue analysis method used for hull structures with the time-domain fatigue analysis method for RPVs in FNPPs or, alternatively, to develop a suitable method that effectively accounts for the temperature, internal pressure, and wave loads. In this study, a quasi-time-domain method is proposed for the fatigue analysis of RPVs in FNPPs. In this method, secondary components of marine environmental loads are filtered out using principal component analysis. Subsequently, the stress spectrum induced by waves is transformed into a stress time history. Fatigue stress under the combined influence of temperature, internal pressure, and wave loads is then obtained through a stress component superposition method. Finally, the accuracy of the quasi-time-domain method was validated through three numerical examples. The results indicate that the calculated values obtained by the quasi-time-domain method are slightly higher than those obtained by the traditional time-domain method, with a maximum deviation of no more than 24%. Additionally, the computation time of the quasi-time-domain method is reduced by 98.67% compared to the traditional time-domain method.

SOME COMMENTS ON THE NATURE OF GLASSES

ABSTRACT I undertake a brief presentation of the early history of the development of our modern understanding of glass-forming liquids that provides a look at how the scientific and technological communities were viewing the state of the art and how the knowledge in the field developed. I discuss aspects of our understanding from how the Vogel–Fulcher–Tammann (VFT) equation became known to questions about the development of the concept of the “ideal” glass transition. The framework for this history leads us to ask whether some of the cautions that the pioneering researchers provided should have been taken more seriously by the community. I discuss, in particular, the view presented by Tammann and Hesse [Z. Anorg. Allg. Chem. 156, 245 (1926)] cautioning that the apparent singularity of the viscosity at a finite temperature was not physical and how the, now famous, VFT equation is accurate for interpolation rather than for extrapolation. The other point is the strong sense by much of the glass community that the so-called Kauzmann paradox [Chem. Rev. 43, 219 (1948)] is fundamental to glass-formation despite the comment by Kauzmann himself that the extrapolation of the entropy to negative values is “operationally meaningless.” I build on these ideas through a presentation of my own data and that of others that addresses the Tammann and Hesse comment through experiments that show that there is not a viscosity (or relaxation time) divergence near to the Kauzmann or VFT temperatures, and I show that the equilibrium entropy of a polymer that cannot crystallize shows no evidence of an ideal glass transition that is often invoked as a means of avoiding the Kauzmann paradox. In addition to providing some sense of the history of time (or a brief history of time and temperature in glass-forming liquids, with apologies to Stephen Hawking) and viscosity, I think that the data presented lead to the conclusion that much of our understanding of the problem of glass-formation is based on misleading interpretations of the original works as well as being inconsistent with the newer data that have been published over that past 25 yr or so. On an optimistic note, there are newer models that do not rely on the VFT divergence or the Kauzmann paradox to account for glass-formation in supercooled or equilibrium liquids. In addition, the experimental situation clearly leads to the possibility of deeper investigations into the “deep glassy state” through “finessing” the geological timescale issue of creating equilibrium glasses. Such investigations are ultimately important to understanding behavior of glassy materials, especially polymers, that are used deep in the glassy state, but still close enough to the glass temperature that models able to reliably predict their behavior require better representations of glass-formation to engineer their performance.

Nutritional status of patients with gastrointestinal cancers and analysis of factors for postoperative infections.

Patients with gastrointestinal cancer have a higher risk of malnutrition and postoperative infection. To investigate the nutritional status of patients with gastrointestinal cancers and factors for postoperative infections. Based on the nutritional risk status, 294 patients with gastrointestinal tumours were divided into a nutritional risk group and a non-nutritional risk group, and the differences between the two groups were compared. Among the included patients, 128 were at preoperative nutritional risk (43.54%); there were significant differences between the two groups in terms of age (66.25 ± 11.73 vs. 58.36 ± 10.41 years, P < 0.001), percentage of gastric cancers (39.84% vs. 28.92%, P = 0.049), percentage of stage IV tumours (60.16% vs. 45.18%, P = 0.011), total protein (64.90 ± 6.82 vs. 67.21 ± 7.41g/L, P = 0.007), albumin (38.32 ± 4.74 vs. 41.61 ± 5.10g/L, P < 0.001) and haemoglobin (112.72 ± 22.63 vs. 125.11 ± 22.79g/L, P < 0.001). Multivariate logistic regression analysis showed that risk factors for postoperative infections in patients included age ≥ 60 years (odds ratio [OR] = 2.266 95%CI = 1.357-4.134), Nutrition Risk Screening (NRS)-2002 score ≥ 3 (OR = 2.183, 95%CI = 1.218-4.102), alcohol history (OR = 2.505, 95%CI = 1.370-4.683), comorbid diabetes mellitus (OR = 2.110, 95%CI = 1.381-4.023) and surgical time ≥ 6h (OR = 2.446, 95%CI = 1.359-4.758). Patients with gastrointestinal cancers are at high incidence of preoperative nutritional risk, and those with an NRS-2002 score of > 3, history of alcohol consumption and surgical time of > 6h have a higher risk of postoperative infections.

Modeling the Time-Dependent Variation of Road Salt Concentrations Using Analytical and Machine-Learning Approaches to Advance Service Life Predictions for Concrete Structures

The exposure of concrete structures to environmental and climatic conditions is detrimental to their durability. In northern climates, the key contributor to their degradation is corrosion of the reinforcing steel because of chloride ions originating from de-icing salts applied on roadways during the winter season. In consequence, a key input parameter for predicting the time to the initiation of corrosion for concrete elements is the time history of the concentration of chloride ions at their surfaces. To investigate this issue, a specialized mobile monitoring station was deployed along a roadway over several winter seasons to collect data on salting operations, weather conditions, and the temporal variation of chloride ion levels on the roadway. At first, salting operations were monitored, and then exploratory and machine-learning algorithms were applied to develop relationships between weather conditions, road conditions, and chloride ion concentrations. The first proposed model is based on the simulation modeling approach, while the second is based on the machine-learning XGBoost model. The findings demonstrate that both models can predict the variation of salt concentration on the road surface as a function of time after a salting operation. By accounting for the time dependency of surface chloride in service life models, more accurate predictions of corrosion initiation time are possible, since the rate of penetration of chloride ions is highly dependent on wetting/drying cycles throughout the winter.

Crafting history in real time: The count-duke of Olivares, the Holy Roman Empire and generalissimo Wallenstein on the Spanish stage (1632–1634)

This essay explores the portrayal of Albrecht von Wallenstein’s downfall on the Spanish stage during the Thirty Years’ War. El prodigio de Alemania (1634), a play written by Calderón de la Barca and Antonio Coello, serves as a topic of study for understanding international politics of the time. The death of King Gustavus Adolphus of Sweden at the Battle of Lützen (1632) marked a turning point in the career of Wallenstein, who had played a significant role as the general commander during the conflict. The play itself was a product of Prime Minister Olivares’ domestic and international policies and aimed to legitimize specific ideological interests. The essay focuses on the manipulation of theatre as a means of enhancing the reputation of the Spanish monarchy and examines how the construction of the play allows us to comprehend the strained relations between Spain and the Holy Roman Empire during the war. It also scrutinizes the modifications made to the literary product to align with the changing political realities and illuminates the significance of Spanish theatre in crafting historical narratives and propagating political ideologies during the first half of the seventeenth century.

Long-term results of intensive care patients with post-intubation tracheal stenosis: 7 years follow-up.

Benign tracheal stenosis (TS) is a potentially life-threatening condition caused by iatrogenic events resulting from endotracheal intubation and tracheostomy. The study aimed to determine the clinical characteristics, management, and long-term outcomes of patients with simple or complex post-intubation tracheal stenosis (PITS) who were admitted to the intensive care unit (ICU). Retrospective analysis of patients admitted to the ICU between June 2016 and June 2022 and diagnosed with PITS were performed until June 2023. 76 patients (mean age 54.9 ± 17.3%, 63.2% male, 61.8% complex stenosis) admitted to the ICU were analysed. The diagnosis of PITS was made by fiberoptic bronchoscopy (FOB) in 53.9% and computed tomography (CT) in 46.1%. The most common location of stenosis was the upper trachea area (57.9%, n = 44). The median stenosis length of the TS was 1.9cm (median 2cm for complex stenosis, 1cm for simple stenosis, p < 0.001). Complex stenosis was associated with longer intubation time and multiple intubation history (p = 0.011, p = 0.028). At the same; complex stenosis was associated with prolonged and high stenosis percentage (p < 0.001). While dilatation and cryotherapy were sufficient for treatment in all patients with simple stenosis, the stent was applied to 34% patients with complex stenosis. Recurrence was higher in complex stenosis after bronchoscopic procedure (complex stenosis 95.7%, simple stenosis 17.2%). 19 (25%) patients required surgical operation, and all of these patients had complex stenosis (p < 0.001). Median follow-up was 33 months for simple stenosis and 34 months for complex stenosis. ICU length of stay (LOS) was longer in patients with complex stenosis. There was no statistically significant difference between TS classes in terms of ICU mortality (p = 0.466), 1-year mortality (p = 0.951), and mortality during follow-up (p = 0.608). PITS is a challenging situation in ICU patients. In patients with a preliminary diagnosis of PITS, bronchoscopy should be performed without delay, and it should be known that interventional bronchoscopy is not only a diagnostic tool but an effective strategy in treatment management after the diagnosis is finalised. The advantage of interventional bronchoscopy is that it alleviates symptoms that necessitate hospitalisation in the ICU and eliminates the need for ICU of patients.

Investigation of the Seismic Performance of a Multi-Story, Multi-Bay Special Truss Moment Steel Frame with X-Diagonal Shape Memory Alloy Bars

In this work, the seismic response of a multi-story, multi-bay special truss moment frame (STMF) with Ni-Ti shape memory alloys (SMAs) incorporated in the form of X-diagonal braces in the special segment is investigated. The diameter of the SMAs per diagonal in each floor was initially determined, considering the expected ultimate strength of the special segment, developed when the frame reaches its target drift and the desirable collapse mechanism, i.e., the formation of plastic hinges, according to the performance-based plastic design procedure. To further investigate the response of the structure with the SMAs incorporated, half the calculated SMA diameters were introduced. Continuing, three more cases were investigated: the mean value of the SMA diameter was introduced at each floor (case DC1), half the SMA diameter of case DC1 (case DC2), and twice the SMA diameter of case DC1 (case CD3). Dynamic time history analyses under seven benchmark earthquakes were conducted using commercial nonlinear Finite Element software (SeismoStruct 2024). Results were presented in the form of top-displacement time histories, the SMAs force–displacement curves, and maximum inter-story drifts, calculating also maximum SMA displacements. The analysis outcomes highlight the potential of the SMAs to be considered as a novel material in the seismic retrofit of steel structures. Both design approaches presented exhibit a certain amount of effectiveness, depending on the distribution, with the placement of the SMA bars and the seismic excitation considered. Further research is suggested to fully understand the capabilities of the use of SMAs as dissipation devices in steel structures.

Experimental and numerical investigation of failure modes in RC frame structures designed using the equivalent linearization method

The codes of many countries currently employ the column-to-beam flexural strength ratio (CBFSR) based on frequent earthquake internal forces to achieve the expected strong-column-weak-beam (SCWB) ductile failure mode. However, real earthquake damage indicates a general failure to achieve SCWB. The design method based on frequent earthquake internal forces struggles to consider factors such as internal force redistribution and variable axial forces under rare earthquakes. Therefore, developing a seismic design method directly based on rare earthquake internal forces is crucial. The equivalent linearization method is a practical approach for obtaining the internal forces of RC frame structures under strong earthquakes without extensive nonlinear computations. In this paper, nonlinear finite element analyses of RC frame structures with expected SCWB failure modes under various structural parameters were conducted to obtain ductility coefficients under rare earthquakes. Using the equivalent linearization method based on secant stiffness, the equivalent stiffness and damping of beams and columns were calculated. Simplified parameters were determined for engineering applications to facilitate seismic design based on rare earthquake internal forces. Two RC frame structures were designed using both the equivalent linearization method and the CBFSR code method, and then subjected to pseudo-static low-cycle reciprocating loading tests. The study investigated failure modes and hysteretic energy dissipation, as well as overall stiffness and bearing capacity under earthquake conditions. Results showed that the equivalent linearization method can effectively direct RC frame structures to achieve the expected strong earthquake failure mode.The dynamic time history analysis was performed on finite element models of different heights, and the results indicated that the equivalent linearization method significantly reduced plastic hinge occurrences and ductility coefficients of column ends, resulting in improved seismic performance compared to the CBFSR code method.

An Evaluation of the Structural Behaviour of Historic Buildings Under Seismic Action: A Multidisciplinary Approach Using Two Case Studies

The evaluation of the structural behaviour of iconic historic buildings represents one of the most current structural engineering research topics. However, despite the various research works carried out during recent decades, several issues still remain open. One of the most important aspects is related to the correct reconstruction of the complex geometries that characterise this type of construction and that influence structural behaviour, especially in the presence of the horizontal loads caused by seismic action. For these reasons, different techniques have been proposed based on the use of laser scanners, Unmanned Aerial Vehicles (UAVs), and terrestrial photogrammetry. At the same time, several analysis methods have been developed that include the use of linear and non-linear approaches. In this present paper, the seismic performance of the Santa Maria Novella basilica and Santa Maria di Collemaggio basilica (before the partial collapse due to the 2009 L’Aquila earthquake) were investigated in detail by means of several numerical analyses. In particular, a series of non-linear time history analyses (NTHAs) were carried out, as reported in the Italian Building Code. To represent the non-linear behaviour of the main structural elements, smeared cracking (CSC) constitutive law was adopted. The geometry of the structures was reconstructed from a complete laser scanner survey of the churches, in order to consider all the intrinsic irregularities that characterise the heritage buildings. Finally, a comparison between the structural behaviour of the two case studies was carried out, highlighting the differences and similar aspects, focusing on possible collapse mechanisms and the identification of the most critical structural elements represented, in both cases analysed, by the main pillars of the transept.

A centrifuge modelling setup for dewatering, rewetting, and characterizing soil deposits

Dewatering in soils serves various purposes in the field of geotechnical engineering as well as other disciplines. In geotechnical engineering, dewatering is effective for improving stability, reducing settlements, and limiting seepage of contaminated pore fluid. This study details the development of an experimental setup that enables dewatering and rewetting soil deposits in-flight in a geotechnical centrifuge while the pore pressures/suctions and moisture contents are measured. Cone penetration tests and shear wave velocity measurements are also used to characterize the material in-flight. Detailed discussion is provided regarding the construction of the tensiometers and calibration of the moisture content probes. Tests are performed on two coal combustion products (CCPs) to exemplify the capabilities of the equipment. Illustrative test results provide time histories and profiles of soil suction and water content at different depths, agreeing well with measurements from laboratory soil-water retention curves. The results also show that dewatering of the CCP deposits leads to significant increases in strength and stiffness, and that after subsequent rewetting, the material maintains a permanent increase in stiffness. The developed system enables an economical and reliable study of the impacts related to dewatering and rewetting cycles to fulfill research purposes in a broad range of engineering disciplines.

Non‐linear time history analyses of a rigid block isolated with unbonded fiber‐reinforced elastomeric isolators (UFREIs): A comparison between 3D finite element and phenomenological models

AbstractNumerical modeling represents a pivotal tool in the seismic analysis and design of structural systems, enabling the detailed prediction and examination of structural responses under seismic loading. This research conducts a comparative analysis of two numerical modeling approaches aimed at simulating the seismic response of unbonded fiber‐reinforced elastomeric isolators (UFREIs). The research focuses on a finite element (FE) model developed using Abaqus and a developed phenomenological model implemented in OpenSees, outlining the development and calibration processes for each. The FE model is developed based on simple rubber material testing data, while the phenomenological model is calibrated using experimental results from cyclic shear tests conducted on the UFREI device and the FE model. The primary objective of this study is to assess the effectiveness of these modeling approaches in predicting UFREI behavior under seismic conditions. This evaluation entails comparing model predictions with experimental data obtained from unidirectional shake table tests performed on a rigid block isolated by two UFREIs. This paper highlights the distinct advantages and limitations of each model in simulating UFREI dynamic responses during seismic events. Furthermore, it provides insights into the modeling techniques and discusses the computational demands and data requirements of each model, thereby aiding in their application to various aspects of seismic analysis and design.

Collapse-based seismic design method

Continuing the structural analysis until the model reaches its ultimate capacity using an incremental nonlinear time history analysis can incorporate all the behavioral complexities of the structure. This approach ensures that all factors influencing the seismic behavior of structures, which can be simulated in numerical modeling, are fully considered in the analysis. This technique addresses many shortcomings in seismic analysis and structural design, using simple criteria for the accurate design of members. With this perspective, this paper explores the collapse-based seismic design method and provides an approach to determine the ultimate tolerable seismic intensity for a structure, or an appropriate collapse seismic intensity. It also establishes design criteria based on the maximum capacity of structural members under maximum loading and utilizes the endurance time method to perform incremental nonlinear time history analysis quickly and easily. Evaluations show that models designed using this method achieve the desired performance level at different seismic hazard levels, provide sufficient seismic capacity, meet all minimum requirements of the seismic code and standards, and are optimized. Therefore, the procedure presented in this paper is introduced for the analysis, design, evaluation, and retrofitting of structures with simple, accurate, and uniform principles.

Application of one-dimensional periodic layers with elastomeric seismic isolators for three-dimensional isolation

Three-dimensional (3D) seismic isolation is an appealing idea to protect structures and their components from earthquake-induced horizontal and vertical ground motions. Past attempts to develop 3D isolation systems were ineffective due to their complexity and reliability issues. One-dimensional periodic material-based isolation systems (1D-PIS) have been extensively researched for applications as raft foundations due to their simple and construction-friendly unit cell designs. These systems aim to attenuate seismic excitations in both horizontal and vertical directions. However, the effectiveness of 1D-PIS in mitigating 3D excitations may be limited due to the potential mismatch between the frequency content of horizontal and vertical vibrations. The present study proposes to combine a conventional horizontal isolation system with a 1D-PIS in the vertical direction to achieve a simple, passive, and efficient three-dimensional isolation system for structures and components. The 1D-PIS is strengthened by incorporating steel shims within the rubber layers and implementing steel casings at its periphery, enabling its utilization as an isolated system. Small-scale experimental and numerical investigations were conducted on strengthened 1D-PIS to study its isolation characteristics in the vertical directions. The study reveals that infinite boundary conditions required for the efficacy of 1D-PIS were achieved through lateral restraint provided by steel shims and steel casings. Notably, the individual isolation characteristics of the conventional and the 1D-PIS are not compromised in the combined isolation system. Nonlinear time history analysis on a prototype combined isolation system confirms its effectiveness in attenuating the seismic response under simultaneous horizontal and vertical ground motions.

Myopia Progression in Children: A Comparative Analysis of Pre-Pandemic and Pandemic Periods

Background: The COVID-19 pandemic brought about significant changes in children's lifestyles, including increased screen time and reduced outdoor activities due to school closures and lockdowns. These changes raised concerns about potential myopia progression in children. Methods: This study compared the spherical equivalent (SE) measurements of children aged 8-17 years from two time visits: one before the pandemic (September 2019 - February 2020) and one during the pandemic (March 2020 - February 2022). Data on family history of myopia, screen time, and outdoor activities were also collected. Paired t-tests were used to analyze the differences in SE between the two visits. Results: A total of 11 children participated in the study. The mean change in SE was -1.55 D, indicating a significant increase in myopia during the pandemic (p = 0.046). The average daily screen time was 201 minutes, while outdoor activity time was 42 minutes. Conclusion: The findings suggest a potential corelation between increased screen time, reduced outdoor activities, and myopia progression in children during the pandemic. It is crucial to encourage healthy visual habits, including limiting screen time and promoting outdoor activities, to mitigate the impact of the pandemic on children's vision.

Optimization of the integro-differential hyperbolic model

We consider a model of processes in viscoelastic media. The force arising inside the body may depend not only on the current values but also on the entire time history of the motion (for example, polymers, emulsions, and suspensions exhibit memory properties). Such processes often lead to the necessity of studying hyperbolic integro-differential equations with Volterra integral term. The main goal is to prove the existence and uniqueness of generalized solutions to the corresponding initial-boundary value problem, as well as to investigate the existence of optimal control for systems described by these models. The main results are obtained using the method of a priori inequalities in negative norms. In particular, we justify inequalities in negative norms for the integro-differential operator in certain functional spaces. The work begins with a short description of relevant results with similar formulations and referencing works with physical justification of the model. Afterwards, we describe the problem statement, constraints on equation parameters, and functional spaces used for the investigation. Below are the main results, in particular definitions of generalized solutions and properties on the well-posed of the initial-boundary value problem as well as the existence of optimal control. Control is carried out through the right-hand side of the equation using a certain special operator. It is possible to examine specific examples of such control operators (illustrating various control mechanisms) and the corresponding control spaces. By utilizing proven inequalities and relying on general results of S.I. Lyashko from the theory of a priori inequalities in negative norms, we establish sufficient conditions for the existence of optimal control. In particular, we impose the restrictions on the admissible set of controls and the quality criterion.

Deep learning-based ground motion inversion through recursive structural acceleration response using DRA-LSTM Net

Known ground motion time history is crucial for the precise numerical analysis of structural response and evaluation of its safety. This study introduces the Deep Recursive Attentive Long Short-Term Memory Network (DRA-LSTM Net), a framework designed for the inversion of ground motion (GM) from recorded structural response (SR) during an earthquake. By integrating an attention mechanism in network along with a strategic recursive approach for dataset management, the DRA-LSTM Net achieves high precision in GM inversion. The method incorporates a novel pre-processed matrix format to capture unique recursive behaviour patterns in GM data, enhancing the model’s training, validation efficiency, and prediction accuracy on unseen test datasets. Case studies on single-degree-of-freedom (SDOF) and multi-degree-of-freedom (MDOF) structures highlight the method’s potential for real-time and high-precision GM inversion. Additionally, transfer learning was implemented to fine-tune the pre-trained model with real-world sensor data and structural responses from different floors, demonstrating the model’s adaptability and ability to retain high prediction accuracy across diverse datasets. This approach is particularly useful for regions with limited seismic instrumentation but equipped with structural response sensors.

Laminar burning velocity of ethanol-ethyl acetate mixtures in air

Alcohols, esters, and their mixtures are ubiquitous in the process industry. However, safety data remain limited, especially for mixtures. In this work, the laminar burning velocity, Sl, of ethanol-ethyl acetate mixtures in air was investigated (at 90 °C and atmospheric pressure) through computations performed using three different detailed chemical kinetic mechanisms, and measurements obtained from pressure time histories recorded during closed vessel explosion experiments. Computations were run varying the equivalence ratio, φ, from 0.6 to 1.7, and the mole fraction of ethanol in the fuel mixture from 0 (only ethyl acetate) to 1 (only ethanol). For all systems, explosion experiments were carried out at φ = 1.1, i.e., the composition at which, according to calculations, Sl achieves its maximum value. Regardless of the kinetic mechanism, reasonable agreement is found between computed and experimental data, including experimental data retrieved from the literature for ethanol and ethyl acetate. Results show that the behavior of ethanol-ethyl acetate is bounded between the behaviors of ethanol and ethyl acetate, approaching the former/latter as the mixture is enriched in ethanol/ethyl acetate. Over the whole range of equivalence ratios explored, the values of Sl for ethanol-ethyl acetate are smaller than those obtained by averaging the corresponding values of ethanol and ethyl acetate according to their mole proportions in the fuel mixture. This is also confirmed experimentally. A simple Le Chatelier’s mixing rule-like formula is proved to predict values of Sl that closely match both computed and experimental data, suggesting that the nature of the interaction between ethanol and ethyl acetate is predominantly thermal rather than chemical.

Stability and bifurcation analysis of a 2DOF dynamical system with piezoelectric device and feedback control

This study aims to demonstrate the behaviors of a two degree-of-freedom (DOF) dynamical system consisting of attached mass to a nonlinear damped harmonic spring pendulum with a piezoelectric device. Such a system is influenced by a parametric excitation force on the direction of the spring’s elongation and an operating moment at the supported point. A negative-velocity-feedback (NVF) controller is inserted into the main system to reduce the undesired vibrations that affect the system’s efficiency, especially at the resonance state. The equations of motion (EOM) are derived by using Lagrangian equations. Through the use of the multiple-scales-strategy (MSS), approximate solutions (AS) are investigated up to the third order. The accuracy of the AS is verified by comparing them to the obtained numerical solutions (NS) through the fourth-order Runge-Kutta Method (RK-4). The study delves into resonance cases and solvability conditions to provide the modulation equations (ME). Graphical representations showing the time histories of the obtained solutions and frequency responses are presented utilizing Wolfram Mathematica 13.2 in addition to MATLAB software. Additionally, discusses the bifurcation diagrams, Poincaré maps, and Lyapunov exponent spectrums to show the various behavior patterns of the system. To convert vibrating motion into electrical power, a piezoelectric sensor is connected to the dynamical model, which is just one of the energy harvesting (EH) technologies with extensive applications in the commercial, industrial, aerospace, automotive, and medical industries. Moreover, the time histories of the obtained solutions with and without control are analyzed graphically. Finally, resonance curves are used to discuss stability analysis and steady-state solutions.

Self-centering rocking steel frame with column mid-height uplift: Experimental and numerical investigation

This paper proposes a self-centering rocking steel frame with column mid-height uplift (SCRSF-CMU) that exhibits high post-yield stiffness and energy dissipation capacity. The hysteretic performance of the SCRSF-CMU was investigated through cyclic loading tests. A numerical model of the SCRSF-CMU was established and validated against experimental results. Subsequently, the seismic performance of the SCRSF-CMU was compared with that of the self-centering rocking steel frame with column base uplift (SCRSF-CBU) using nonlinear time history analysis. Finally, the seismic responses of the SCRSF-CMU and SCRSF-CBU under varying earthquake intensities were analyzed using the endurance time analysis. The results indicate that the designed SCRSF-CMU demonstrates excellent lateral force resistance, energy dissipation, and self-centering capabilities. The rocking effect and the restoring force of the post-tensioned steel strands effectively controlled the residual lateral displacement of the specimens. The multi-scale numerical model of the SCRSF-CMU accurately captured its hysteretic behavior and deformation patterns. Compared to the SCRSF-CBU, the SCRSF-CMU exhibited superior rocking deformation capacity, post-yield stiffness, and hysteretic energy dissipation. Under MCE excitation, both SCRSF-CMU and SCRSF-CBU showed uniform inter-story drift distribution with minimal residual deformation, creating a satisfactory condition for the post-earthquake repair work if necessary. The high post-yield stiffness of the SCRSF-CMU was more effective in reducing both maximum and residual displacements. Endurance time analysis revealed that SCRSF-CMU and SCRSF-CBU exhibited relatively uniform inter-story drift distribution under SLE, DBE, and MCE earthquakes. Under FE excitation, the inter-story drift ratio of both structures were nearly identical; however, under DBE and MCE excitations, the maximum roof drift ratio and inter-story drift ratio of the SCRSF-CBU were larger, indicating that the SCRSF-CBU had higher deformation demands than the SCRSF-CMU.