Nonlinear Analysis Research Articles

Improved General Relativity Search Algorithm (IGRSA) for Designing Power System Stabilizers

This paper proposes a novel optimization algorithm for designing power system stabilizers (PSSs). The prospect of attaining higher stability motivated the authors to creat a new optimization algorithm for this study. A novel algorithm named the Improved General. Relativity Search Algorithm (IGRSA) was also developed by cloud theory to improve the performance of GRSA. The supremacy of the proposed approach is tested by comparing it with an introduced objective function in a medium multi-machine power system. The nonlinear simulation results and eigenvalues analysis has demonstrated that the proposed approach in this study is highly effective in enhancing the dynamic stability of the power system.

Non-linear causal effects of kidney function on the risk of heart failure: a Mendelian randomization study

Abstract Background Kidney insufficiency is defined as the early stage of heart failure, but Mendelian randomization (MR) analyses based on several large heart failure cohorts suggest no linear causal effect between kidney function and heart failure (HF), inconsistent with observational studies evidence. However, whether there is a non-linear causal relationship between kidney function and HF has not been reported. Methods and Results Observational and non-linear MR analyses were performed using individual-level data from a UK Biobank cohort of white British ancestry subjects (N = 386,304). There were non-linear observational associations of between kidney function as assessed with estimated glomerular filtration rate (eGFR) and HF (P for nonlinear <0.001). Non-linear MR analyses showed a U-shaped association between genetically predicted eGFR values (both creatinine- and cystatin C-based eGFR) and the risk of HF (Quadratic P value < 0.05) and the risk of HF increased with both reduced and supranormal eGFR levels (β1 = -1.70E-05, P1-value = 0.004; β2 = 3.56E-06, P2-value = 0.004). Conclusion This study observed a non-linear U-shaped genetic relationship between eGFR and HF outcomes, indicating that both reduced and supranormal eGFR may be causally linked to a higher risk of HF.Central Illustration

Asymmetric effects of life and non-life insurance on economic growth in Saudi Arabia: A nonlinear analysis

This paper explores the asymmetric effects of life and non-life insurance on economic growth in Saudi Arabia. Quarterly data on insurance penetration rates and GDP growth from 2009 to 2022, obtained from the Global Economy, Saudi Arabian Monetary Authority, and World Bank databases, are utilized. A nonlinear autoregressive distributed lag (NARDL) model is employed to examine the relationships between insurance and growth. The results reveal a significant and asymmetric relationship between life insurance penetration and GDP growth. Specifically, a 1% increase in life insurance penetration is associated with a 0.3% increase in GDP growth in the long run, while a 1% decrease shows no significant effect. For non-life insurance, both increases and decreases demonstrate significant but asymmetric impacts on growth. A 1% increase in non-life insurance penetration corresponds to a 0.2% increase in GDP growth, whereas a 1% decrease is linked to a 0.15% decrease in GDP growth. These findings support the ‘supply-leading’ hypothesis, suggesting that the insurance sector can play a leading role in promoting economic growth. The results provide new quantitative insights into the relationship between insurance and economic growth in Saudi Arabia, offering valuable implications for policymakers. It is suggested that the insurance industry can be leveraged to foster economic growth by promoting life insurance and managing the asymmetric impacts of non-life insurance.

Nonlinear dispersion analysis using dynamic traveling wave model in chemical kinetics

Nonlinear dispersion analysis using dynamic traveling wave model in chemical kinetics

Seismic performance of near-fault girder bridges based on laminated rubber bearings under the impact of sequential earthquakes

Strong aftershocks frequently follow near-fault earthquakes, exacerbating the damage to bridges already impacted by the main shock. However, current seismic design codes worldwide overlook the adverse effects of aftershocks on near-fault bridges. Therefore, it is imperative to conduct research on the seismic performance of near-fault girder bridges under sequential earthquakes. This study proposes a seismic isolation design for near-fault girder bridges subjected to sequential earthquakes, utilizing laminated rubber bearings, sacrificial shear keys, and cable-type unseating prevention devices. Seismic ground motion records from typical stations during the Turkey-Syria earthquakes were collected to assess the seismic safety of bridges. Nonlinear time-history analysis systematically investigated the seismic displacements of the laminated rubber bearings and girder, as well as the seismic damage of shear keys and pier. The results show that the lateral displacement of the girder induced by the sequential earthquake was approximately 1.5 times greater than that caused by a single main shock, while the longitudinal displacement of the girder remained similar. The seismic isolation design proposed in this study not only controlled the relative displacement between the piers and the girder but also effectively protected the pier from severe seismic damage, ensuring the bridge’s functionality after the sequential earthquake.

DOES RESIN TAPPING AFFECT THE TAPERING AND ACCUMULATION OF MERCHANTABLE TIMBER VOLUME IN PINE TREES?

Form factors and taper functions are used for the quantitative and qualitative description of tree stem shape. In southeastern Mexico, there are plantations of Pinus caribaea var. hondurensis (Sénécl.) W.H. Barrett & Golfari, Pinus elliottii var. elliottii Engelm., and hybrids between these species to simultaneously produce resin and wood. Farmers need to know whether the practice of resin tapping to death has a negative impact on tree shape and volume of the wood produced. To answer these questions, this study compared the shape, taper, and volume of resin-tapped and untapped trees from three P. caribaea origins. A total of 198 trees (99 resin-tapped and 99 untapped) were measured in all diameter categories of the plantation. Total volume models, along with a compatible taper system and variable merchantable timber volume, were fitted using linear and nonlinear regression analyses. To compensate for the lack of initial tree size data prior to tapping, indicator variables (dummies) and an additive structure were used to parameterize volume and taper models. Untapped trees accumulated greater volume than tapped trees. In contrast, the form factor (ff) of resin-tapped trees (ff = 0.51) was greater than that of untapped trees (ff = 0.45). The form factor increased due to tapping between 4 and 7 % depending on the origin, although the hybrid P. caribaea × P. elliottii presented the most desirable stem geometry in tapped and untapped trees. Based on the Demaerschalk model, the variability is estimated at 99 and 97 % of the merchantable and taper volumes, respectively.

LVEF trajectory in HFimpEF and its association with prognosis

Abstract Background The 2021 revised Universal Definition of Heart Failure (HF) introduced the subgroup known as HF with improved ejection fraction (HFimpEF), aiming to establish a standardized definition for left ventricular ejection fraction (LVEF) improvement and emphasize the importance of longitudinally assessment of LVEF. However, there remains an insufficient characterization of the association between serial LVEF trajectory before and after impEF, and outcomes in HFimpEF. Purpose We aim to delineate the LVEF trajectory in patients with impEF and to discern specific LVEF trajectory pattern that portends an unfavorable prognosis. Methods We conducted a retrospective analysis by including hospitalized HF patients with baseline LVEF ≤ 40% and satisfactory serial echocardiographic follow-ups. ImpEF was defined as a follow-up LVEF measurement of > 40% with a ≥10-point increase from baseline. Longitudinal LVEF trajectories for patients with impEF (before and after LVEF improvement) were plotted according to the clinical outcome of all-cause death using Loess curves. LVEF changes over time were analyzed by unconditional non-linear mixed-effects modeling, and compared between the groups of patients who died and those who survived using conditional non-linear mixed-effects modeling. Results Among the initial 923 patients with reduced LVEF, 517 had impEF. According to Loess curves and non-linear mixed-effects analysis, LVEF trajectory of impEF differed according to the clinical outcome of death. For patients who suffered all-cause death, there was a comparatively limited improvement in LVEF followed by a more rapid plateauing and decline, exhibiting an inverted U-shaped pattern with lower LVEF values towards both ends of the distribution. Conclusions In HFimpEF, an inverted U-shaped trajectory of LVEF, characterized by limited initial improvement followed by subsequent decline, is associated with poorer prognosis. Serial LVEF monitoring in patients with HFimpEF could help with early identification of at-risk patients.Graphical Abstract

Nonlinear analysis of three-dimensional hyperelastic problems using radial point interpolation method

Hyperelastic materials are primarily common in real life as well as in industry applications, and studying this kind of material is still an active research area. Naturally, the characteristic of hyperelastic material will be expressed when it undergoes large deformation, so the geometrical nonlinear effect should be considered. To analyze the behavior of hyperelastic material, the Neo-Hookean model is imposed in this study because of its simplicity. The model shows the nonlinear behavior when the deformation becomes large due to the nonlinear displacement-strain relation. This constitutive relation also gives a good correlation with experimental data. This study performs a meshless method, namely the radial point interpolation method (RPIM), to analyze the nonlinear behavior of Neo-Hookean hyperelastic material under a finite deformation state in three-dimensional space. The standard Newton-Raphson technique is applied to obtain the nonlinear solutions. Unlike mesh-based approaches, the meshless method shows its advantages in large deformation problems due to its mesh independence. In this paper, the numerical results of three-dimensional problems that undergo large deformation will be calculated and validated with solutions derived from previous studies. By investigating the obtained results, the superior ability of RPIM in hyperelastic problems can be proved.

Study on Evaluation and Prediction Model of Long-term Mechanical Properties of Fine-grained Saline Soil Subgrade

In this thorough examination, we dive deep into the long-lasting mechanical characteristics of fine-grained saline soil subgrades, aspiring to establish a precise and reliable collection of predictive models. Our objective is to provide a solid scientific footing for the design and ongoing upkeep of road networks within saline soil environments. Analyzing prolonged monitoring data across diverse highway subgrades within a prototypical saline soil locale, we unveil the intricate temporal fluctuations and environmental sensitivities of the soil’s mechanical properties under continuous load. Precisely, the subgrade’s compressive modulus dwindled by 15%, while shear strength declined by 8% over a five-year period. These trends intensify during rainy and scorching seasons, with drops surpassing 20% and 12% respectively. Leveraging this intricate data, we deploy nonlinear regression analysis and sophisticated machine learning algorithms to construct a predictive model tailored for the long-term mechanical properties of fine-grained saline soil roadbeds. This model integrates a multitude of factors, including load duration, temperature, humidity, and more, delivering accurate forecasts of key subgrade indicators like compressive modulus, shear strength, and beyond. In the verification stage, compared with the measured data, the error rate of the model prediction results is controlled within 5%, showing high prediction accuracy and stability. In addition, we also carried on the sensitivity analysis to the model, found that the load size and the duration of the impact on the mechanical properties of the roadbed is the most significant. Therefore, in the design of road engineering in saline soil areas, the influence of these factors should be fully considered, and reasonable engineering measures should be taken to ensure the safety and durability of roads. This study not only provides effective data support for the long-term mechanical performance evaluation of fine-grained saline soil roadbed, but also provides an important theoretical reference for engineering practice in related fields.

A Novel Two-Lane Lattice Model Considering the Synergistic Effects of Drivers’ Smooth Driving and Aggressive Lane-Changing Behaviors

Most existing two-lane traffic flow lattice models fail to fully consider the interactions between drivers’ aggressive lane-changing behaviors and their desire for smooth driving, as well as their combined effects on traffic dynamics. To fill this research gap, under symmetric lane-changing rules, this paper proposes a novel two-lane lattice model that incorporates these two factors as co-influencers. Based on linear and nonlinear stability analyses, we derive the linear stability conditions of the new model, along with the density wave equation and its solutions describing traffic congestion propagation near critical points. Numerical simulations validate the theoretical findings. The results indicate that in the two-lane framework, enhancing either drivers’ lane-changing aggressiveness or introducing the desire for smooth driving alone can somewhat improve traffic flow stability. However, when considering their synergistic effects, traffic flow stability is enhanced more significantly, and the traffic congestion is suppressed more effectively.

Nonlinear seismic response analysis of long-span railway cable-stayed bridges crossing strike-slip faults

Active faults along railways in the mountainous regions of western China pose significant challenges to bridge safety. To ensure the safe operation of long-span railway bridges under complex geological conditions, this study investigates the synthesis of artificial ground motions for bridges crossing strike-slip faults and analyzes their nonlinear seismic response. First, we develop a theoretical method for simulating high- and low-frequency seismic motions using a finite fault and an equivalent velocity pulse model. Next, using a specific long-span railway cable-stayed bridge as a case study, we construct a nonlinear finite element model with OpenSees software. Finally, we assess the seismic response of key bridge components considering various crossing angles, seismic amplitudes, fault rupture directivity, and fling-step effects. The results show that the crossing angle significantly influences the seismic response, with longitudinal and transverse responses exhibiting opposite patterns. Additionally, the scaling factor of seismic motion significantly affects bridge response. For bridges crossing strike-slip faults, the longitudinal response exhibits a sudden increase in displacement due to instantaneous velocity pulses, while the transverse response shows notable residual displacement influenced by the fling-step effect. However, the critical section curvatures of bridge towers and piers remain within the elastic range across all crossing angles, indicating that controlling large displacement deformations is crucial for the seismic design of bridges crossing strike-slip faults.

Developing Programs for Converting MIDAS GEN to ANSYS Models Based on Python

The reasonableness and accuracy of engineering design are often assessed through the use of a variety of structural design analysis software, which are then compared and verified. However, it is challenging for a single analysis software to meet the diverse and complex design requirements. In order to meet the specific engineering requirements, it is necessary to convert the MIDAS result model into an ANSYS structural model and conduct a nonlinear analysis and simulation in ANSYS. Nevertheless, the existing interface is unable to facilitate direct conversion of the model. Accordingly, this paper presents a Python-based ANSYS APDL program that enables the complete conversion of MIDAS GEN structural models to ANSYS finite element models. The program is capable of converting a range of data, including material, section, element, connection, load, node mass, constraint, time history function, and so forth. The program is capable of converting specific connection units, including elastic and general connection units. Additionally, the beam-column section direction, beam end freedom release, rigid element, and special anti-rocking structure of the structure can be considered. Ultimately, the theatre model is transformed. Following a comparison of the analysis results, it was found that the mass and mode of the model before and after the transformation were essentially identical. The maximum error of the first six orders of the structure is 2.95%, with the structural displacement under gravity load remaining essentially unchanged. The research and analysis demonstrate the accuracy and reliability of the MIDAS GEN conversion ANSYS program. The conversion program significantly reduces the time required for direct modeling in ANSYS, enhancing work efficiency. The study has considerable practical significance for the seismic sway design and analysis of buildings based on vibration isolation design.

Expeditious numerical capacity assessment in precast structures via inelastic performance-based spectra

The seismic design of precast structures hinges on unique characteristics intrinsic to precast technology. Emphasis is placed on lightweight structural elements for efficient on-site assembly and cost reduction. This leads to increased slenderness in beams and columns compared to traditional cast-in-situ constructions, accentuating the role of second-order effects. Dry pinned joints, favoured for connecting beams and columns, contribute to the overall efficiency in assemblage. Cast-in-situ concrete is typically reserved for connection to foundations and topping precast floor elements. Pinned joints transform the structure into an ideal isostatic system, with cantilevered columns anchored securely at the base, in designers' mind. However, this transformation reduces the energy dissipation capacity, preventing plastic hinge formation in beams and amplifying P-Delta effects in columns. The simplified approach proposed herein assesses dynamic instability in single and multi-storey precast hinged frames, providing a tool for expeditious numerical capacity assessment, useful at the initial design stage. The goal is to predict dynamic collapse and/or the attainment of specific seismic-oriented limit states based on fundamental structural parameters. Incremental nonlinear dynamic analysis, utilising far-field ground motion records, is employed to evaluate performance of a variety of precast structures modelled as equivalent single-degree-of-freedom systems. The outcomes yield inelastic spectra that provide insights into the structural capacity in terms of response modification factor and could help analysts/designers towards seismic performance-based design as well as the assessment problem. These spectra, which can themselves be taken as metrics for structural performance evaluation (in addition to as a reliable tool/means for design), are generated based on various structural parameters, including building height, column aspect ratios, and floor mass configurations, in relation to different limit states typically deemed crucial in the design of these structures for earthquake-induced actions. Regression analyses of median spectra show that polynomial expressions could fit them with good accuracy, as testified by a coefficient of determination in the 0.76–0.98 range for most of the cases.

Failure analysis of multi-span masonry arch bridges using combination of point cloud data and three-dimensional numerical modeling

Historical structures, including historical bridges, are part of cultural heritage, conveying the traces and characteristic features of past civilizations. To protect historical structures, it is necessary to prepare their 3D photogrammetric documentation, determine detailed geometric and material properties and perform computer-aided structural analysis using appropriate modeling techniques. The aim of this study is to present an effective, reliable and fast multidisciplinary approach for the analysis of historical masonry bridges. The aforementioned approach was illustrated with an example of the historical Halilviran masonry arch bridge and its behavior under possible loadings. Terrestrial laser scanning (TLS) was used to determine the bridge geometry with high accuracy. Point cloud data obtained from TLS was simplified and a three-dimensional CAD-based solid model of the structure was created. The Halilviran Bridge case study summarized in this report was conducted to examine the technical feasibility of using la¬ser scanning technologies for obtaining as-built records for similar historic bridges. A secondary objective was to identify other applications of this technology, notably for other transportation structures, and use numerical methods to assess the seismic behavior and failure model of the bridge. The seismic behavior of the bridge was examined using a finite-element- based macromodeling technique. Nonlinear dynamic analyses were carried out subsequently to identify the most susceptible regions of the bridge. Interpretation of the results, presented in the form of contour plots illustrating tensile damage and maximum displacements, offered a comprehensive depiction of the seismic response across the entire bridge. The methodology employed in this investigation can be viewed as a robust framework for evaluating the seismic response and potential failure of historical structures.

Impact of Various High Intensity Earthquake Characteristics on the Inelastic Seismic Response of Irregular Medium-Rise Buildings

In the twenty-first century, the seismic design of buildings seems to have become a fully recognized topic. There are guidelines and standards which should be taken into account by designers in seismic areas. Designers using modern international guidelines have ascertained that the behavior of structures is not as expected. New challenges in the construction industry result in the construction of structures with new, unusual shapes. These are structures that do not meet the assumptions of safe construction in seismic areas. Contemporary buildings are also characterized by their irregular distribution of structural elements. Such solutions are not beneficial from the point of view of seismic engineering and can lead to reduced dynamic resistance and damage in such structures. In this paper, a five-storey, irregular-shaped reinforced concrete (RC) building model was subjected to different earthquakes with varying magnitudes, PGA (peak ground acceleration) and PGV (peak ground velocity) values, and durations of the intense shock phase. Once the model was verified using previous in situ measurements, the building model was subjected to five earthquakes. A numerical nonlinear analysis of the building was performed using a verified FEA (finite element analysis) model in the time domain through non-linear time history analysis with the Broyden–Fletcher–Goldfarb–Shanno (BFGS) method. The building’s dynamic properties were measured using various methods of excitation. The model was influenced, among others, by two far-field representative events caused by the last earthquake in Turkey, which resulted in strong ground motion. The analysis results identified the locations of structural damage and allowed for the assessment of the structure’s dynamic resistance. The results of the calculations prove that the duration of the intensive phase of extortion is one of the reasons for building damage in earthquake-prone areas. Building damage occurs with earthquakes that are characterized by an intensive phase of excitation with a long duration and high values of velocity in the earthquake components. The article highlights the inadequate dynamic resistance of the building, leading to excessive displacements and unfavorable structural solutions. Damage to buildings at this earthquake intensity caused damage to the load-bearing structure, which was not designed for such intensities. This paper is a research report with a specific case study of medium-rise irregular RC buildings.

Harvesting both wind energy and vibration energy by a zigzag structure with hybrid magnetic and piezoelectric effects

In practical environments, wind energy and vibration energy often coexist. Considering this, we introduce a new energy harvester designed to concurrently harness wind energy and vibration energy by integrating magnetic and piezoelectric effects. This harvester is composed of a zigzag structure and a bluff body. The bluff body is designed to execute galloping under incoming fluid flow and produce outputs, while the zigzag bi-stable structure can harness the energy of base excitation effectively. The introduction of magnetic interaction leads tothe softening-spring characteristic, which is verified by the nonlinear analysis. This softening-spring nonlinearity canenhance the working frequency range of the harvester. The results obtained from the numerical simulations indicate that the interaction of base excitation and wind flow can significantly improve the non-resonance region output. Corresponding validation experiments are carried out. The results are in good agreement with the numerical ones. Under stochastic excitations, the output power obtained from the hybrid scenario can reach 73.04 μW, representing a 16 % increase compared to the pure base excitation scenario.

The impact of social media discourse on financial performance of e-commerce companies listed on Borsa Istanbul

This research investigates how changes in public discourse on social media (particularly Twitter, now X) influence financial performance of companies listed on the e-commerce XTCRT index of Borsa Istanbul amid the COVID-19 pandemic. Utilising a unique 4-layer network structure, the study integrates daily closing prices, highest and lowest values, and trading volume data of these companies with Twitter discussions on six categories: culture, economy, health, politics, technology, world affairs. By using advanced computational methods such as multilayer network analysis, long short-term memory architecture, nonlinear autoregressive distributed lag analysis, we find a high responsiveness of the e-commerce index to social media content, particularly in discussions related to health, technology, world affairs. The study underscores that social media discussions significantly shape index composition, resulting in noticeable shifts in market dynamics, including fluctuations in stock prices, trading volumes, and market sentiment. Our study advocates for a more advanced approach to market analysis that incorporates the dynamics of online public discussions.

Seismic evaluation of plan irregular reinforced concrete building equipped with comb teeth metallic passive damper

Active and passive damping devices exhibit significant energy dissipating behavior under seismic loads and are being used to control vibration in buildings worldwide. Comb Teeth Damper (CTD) is one of the most promising recent types of passive dampers which consist of steel plates with multiple teeth designed to dissipate seismic energy by in-plane flexural yielding. In this study, the CTD was modeled and analyzed under lateral cyclic load using the finite element analysis software, ABAQUS. The first phase of this investigation was a comprehensive parametric study on CTD with two different numbers of teeth, namely 4 teeth (4 CTD) and 5 teeth (5 CTD); each model with six different thicknesses, namely 5, 10, 15, 20, 25, and 30 mm. The parametric study showed that by increasing the number of teeth, the load-carrying capacity, initial stiffness, and energy dissipation capacity have increased considerably. A similar trend was observed when the thickness of the damper was increased. From the results of the parametric study, 5CTD with 15 mm thickness damper model was identified as a suitable model for utilizing in Reinforced Concrete (RC) buildings using optimization algorithm. In the second phase, a G + 14 storey plan irregular RC building was modeled in the structural engineering software ETABS and subjected to six different strong earthquake ground motions. The non-linear time history analysis was performed on the building with and without identified CTD and found that the building equipped with dampers reduced 56% top displacement, 60% inter-storey drift, and 33% energy dissipation.

Mechanism analysis of the impact of regional digital transformation on the employment quality in the perspective of labor force structure

Regional digital transformation has revitalized economic development and revolutionized the employment landscape of the labor force. The study employs a dynamic panel system GMM model to investigate the direct and indirect effects of regional digital transformation on the employment quality of China’s labor force using panel data from 31 mainland provinces. The findings suggest that regional digital transformation initially has a negative impact on employment quality, but that it continues to improve continuously as it progresses, showing a “U-shaped” trend. A nonlinear mediation analysis across industry, sector, and skill levels of the labor force structure uncovers a complex, bridging effect on employment quality. This study provides valuable insights for improving employment policies and promoting full employment, highlighting the dynamic interplay between regional digitization and the labor market.

Seismic behavior of base isolated precast frame

The performance of the base-isolated precast frame is examined for both near-field and far-field earthquakes. For comparison, the corresponding base isolated monolithic frame is analyzed. The frames are isolated using a friction pendulum system (FPS), which is appropriately designed to take up the vertical load coming on the frames. The same isolators are provided for the monolithic and precast frames. Two types of precast frames are considered, namely frames with emulated and non-emulated connections. An ensemble of 7 different earthquakes is used for each type of earthquake to obtain the average responses, which include maximum base shear, maximum acceleration, maximum top story displacement, and maximum inter-story drift ratio (MIDR). SAP2000 is used for the non-linear time history analysis of the frames for different earthquakes. The studies are made for three levels of PGA, namely 0.4 g, 0.6 g, and 0.8 g. The study shows that a significant reduction in base shear, top story displacement and MIDR is achieved by base isolating the precast frames. However, the corresponding base isolated monolithic frame offers more reductions in response especially for MIDR. Of the two types of precast frames, the one with emulated connection shows marginally higher reductions of response as compared to the non-emulated connection. Further, the percentage reductions in responses in main shock and after shock remain almost the same for all cases.