Use Of Nonlinear Analysis Research Articles

The use of nonlinear analysis in understanding postural control: A scoping review

Nonlinear analyses have emerged as an approach to unraveling the intricate dynamics and underlying mechanisms of postural control, offering insights into the complex interplay of physiological and biomechanical factors. However, achieving a comprehensive understanding of the application of nonlinear analysis in postural control studies remains a challenge due to the various nonlinear measurement methods currently available. Thus, this scoping review aimed to identify existing nonlinear analyses used to study postural control in both dynamic and quiet tasks, and to summarize and disseminate the available literature on the use of nonlinear analysis in postural control. For this purpose, a scoping review was conducted and reported following the PRISMA Extension for Scoping Reviews (PRISMA-ScR) Checklist and Explanation. Searches were conducted up to July 2023 on PubMed/Medline, Embase, CINAHL, Web of Science, and Google Scholar databases, resulting in the inclusion of 397 unique studies. The main classes employed among the studies were entropy-based, fractal-based, quantification of recurrence plots, and quantification of stability, with a total of 91 different algorithms distributed among these classes. The most common condition used to study postural control was quiet standing, followed by dynamic standing and gait tasks. Although various algorithms were utilized for this purpose, sample entropy was employed in 43% of studies to explore mechanisms related to postural control. Among them, 28% were in quiet standing, 3.27% were in dynamic standing, and 4.78% to study postural control during the gait. The results also provide insights into nonlinear analysis for future studies, concerning the complexity and interactions within the postural control system across various task demands.

Applied Nonlinear Analysis for Efficient Communication Signal Processing and Network Management

The use of nonlinear analysis in network management and communication signal processing is a revolutionary strategy that is redefining contemporary networking paradigms. The goal of this project is to improve communication systems' resilience, efficiency, and agility by integrating cutting-edge nonlinear techniques. This study investigates the complex relationship between signal processing and network management using nonlinear analysis techniques in order to meet the growing needs of modern networks. Nonlinear approaches provide dynamic signal processing methods, enabling in-the-moment modifications that maximise data transfer under variable network circumstances. Prioritising data streams is made easier by this integration, which also improves network speed and efficiently allocates resources to guarantee Quality of Service (QoS). The study explores the complexities of interdisciplinary ideas, using the concepts of nonlinear analysis to comprehend phase transitions, emergent network architectures, and networks' inherent ability to self-organize. By deciphering the complexity of network behaviours and their evolution, this understanding aids in the creation of more effective management techniques. However, there are difficulties with computing complexity, interoperability, and skill adaption when using nonlinear analysis in network management. To properly utilise nonlinear approaches for network management and communication signal processing optimisation, these obstacles must be overcome. The research is important because it may lead to game-changing advancements in communication systems by introducing cutting-edge ways that go beyond the constraints of conventional, linear methods. The findings show potential for more effective and secure communication systems, which can meet the increasing needs of modern networking.

Effect of mechanical nonlinearity on the electromagnetic response of a microwave tunable metamaterial

Tunable metamaterials functionalities change in response to external stimuli. Mechanical deformation is known to be an efficient approach to tune the electromagnetic response of a deformable metamaterial. However, in the case of large mechanical deformations, which are usually required to fully exploit the potential of the tunable metamaterials, the linear elastic mechanical analysis is no longer suitable. Nevertheless, nonlinear mechanical analysis is missing in the studies of mechanically tunable metamaterials. In this paper, we study the importance of considering nonlinearity in mechanical behavior when analyzing the response of a deformable metamaterial and its effects on electromagnetic behavior. We consider a microwave metamaterial formed by copper four-cut split ring resonators on a Polydimethylsiloxane (PDMS) substrate. Applying both displacement and force stimuli, we show that when the deformation is large, more than 10 percent strain, the use of nonlinear analysis considering the geometrical and material nonlinearities is imperative. We further show that the discrepancies between the linear and nonlinear analyses appear in overestimating the stress, underestimating the tunability of the metamaterial responses, and mispredicting the negative permeability regions.

Hurst exponent as a robust measure of EEG signal: emphasis on slow activity in children

A growing body of literature has investigated the use of nonlinear analysis of electroencephalographic (EEG) signal and particularly the Hurst exponent as a method for studying EEG dynamics. In this paper we make an emphasis on investigation of the Hurst exponent in slow frequency bands in children during the first two years of life.

Balance dynamics are related to age and levels of expertise. Application in young and adult tennis players.

In tennis, coaches consider balance fundamental for the acquisition of skilled motor performance. However, the potential relationship between balance and tennis expertise and performance has not been explored yet. Therefore, this study assessed the relationship between balance and tennis performance using linear and non-linear parameters through 1) the comparison of tennis players of different ages and levels of expertise, and 2) analyzing the relationship between balance and tennis serving speed and accuracy. One hundred and six recreational and expert male tennis players took part in the study (age range 10-35 years old). Temporal dynamics of postural control during a balance task on an unstable surface were analyzed through the mean velocity and the detrended fluctuation analysis (DFAV) of center of pressure (COP). Tennis serve performance was quantified by measuring accuracy and speed. Traditional variables measuring balance performance only showed differences according to age but not to sport performance. COP showed a reduction of auto-correlated variability (reflected by DFAV) with age but mainly in expert players. COP dynamics was the only balance parameter discriminating sport expertise and it was related to age. Balance dynamics exhibited by expert tennis players DFAV results support the idea that, along the years, sport experience induces balance adaptations characterized by a higher ability to perform postural adjustments. These results also reinforce the use of non-linear analysis to reveal subtle balance adaptations produced by sport practice. Finally, the lack of correlations suggests that balance, measured with scattering variables, in a non-specific task is not a main determinant of sport performance in tennis serve.

Identification of Fracture Mechanic Properties of Concrete and Analysis of Shear Capacity of Reinforced Concrete Beams without Transverse Reinforcement.

The study of new and innovative quasi-brittle materials offers new possibilities for use in construction, but detailed knowledge of their behavior and mechanical properties is required. The use of new materials in the design solution of a structure is usually associated with numerical methods, which has a number of both advantages and disadvantages. Sophisticated numerical methods, without a sufficiently detailed input knowledge, can provide highly variable results with little informative value. The main goal of this article is to present the procedure for the identification of fracture mechanical parameters for a specific concrete with the use of developed inverse analysis combining multi-criteria decision analysis, stochastic modelling and nonlinear analysis. Subsequently, the identified mechanical parameters of concrete are used for the parametric study of shear resistance of structural beams without shear reinforcement, as an alternative or generalized approach to the study of damage to concrete and concrete structures. This research includes an experimental program using 24 reinforced concrete beams and a detailed determination of basic and specific mechanical properties during laboratory tests. The process of inverse analysis is illustrated in detail for the solved task. The use of nonlinear analysis for detailed failure modelling is based on a 3D computational model and a fracture plastic material model for concrete. Finally, the results of the experimental program and numerical modelling are discussed, leading to a number of conclusions.

Diagnosing Intermittent Faults through Non-linear Analysis

To cope with certain exogenous stimuli, there have been inexorable advances of technology, with an increased focus and fascination with the accuracy of diagnostic equipment. This can become a difficult problem to solve as it warrants real-time monitoring whilst taking up unnecessary measures to improve overall system reliability and maintainability. Intermittent faults may be benign or malignant in nature and their overall impact on a system varies with mission objectives and operating conditions. Major failures can often be averted if these problems can be detected sufficiently in advance by observing them in dynamical behaviour. The phase space trajectory reconstructed from a time series is known to elucidate such behaviours however it is seldom applied for fault analysis. This article makes use of dynamic system theory and investigates its application for fault estimation by analysing non-stationarities which arise due to the changing dynamics under intermittent conditions. Intermittent fault detection presents a challenge for traditional fault diagnostic equipment as they do not manifest themselves all the time. The idea is to move away from the traditional approaches and investigate the use of non-linear analysis by building a reference trajectory using the phase space reconstruction. This is used as an objective measure for any deviations caused by intermittent phenomena. The method is validated using simulated data and shows promise. The implications of the study are to identify new fault isolation bounds necessary to improve diagnostic success rates and potentially lead to early diagnosis of intermittent faults in electrical equipment.

OSINT as a part of cyber defense system

The paper presents the results of research on the development of fundamental and applied principles for analyzing information flows in global computer networks while conducting open source intelligence (OSINT). The relevance of this task, in particular, concerning the provision of cyber security, the parameters of the modern information space, the existing theoretical and technological solutions are substantiated. The description of methodological and instrumental means of analysis and modeling of information flows, distributed content monitoring of global networks, the creation of multilingual full-text databases, analysis of the dynamics of thematic information flows with the use of nonlinear analysis, automatic formation of models of subject areas in the field of cyber security are presented.

Base Isolation of Buildings with Curved Surface Sliders: Basic Design Criteria and Critical Issues

Curved surface sliders are being used more and more in the seismic isolation of buildings. They are preferred not only because of their lower cost with respect to elastomeric isolators but also of their technical characteristics, such as the fact that the value of the period of vibration is independent of the mass and the automatic coincidence between the gravity mass center of the superstructure and the stiffness center of the isolation system. In this paper, these features are analysed with reference to simple structures, pointing out the possibility of rotations of the superstructure and the loss of contact in some devices. Finally, the importance of the static friction is also emphasized showing the experimental seismic response of an isolation system under a low‐energy earthquake. For all these reasons, the use of nonlinear analysis, revised and detailed in this paper, is advisable for the isolation system made of curved surface sliders.

Urban growth, population, and recession: Unveiling multiple spatial patterns of demographic indicators in a Mediterranean City

AbstractRecessions have traditionally influenced population dynamics, leading to increasing social disparities and a polarised distribution of economic activities. This study identifies differences in short‐term demographic trends before and during the 2007 recession in a metropolitan area of southern Europe. Using vital statistics, indicators were calculated over two distinct time intervals representative of expansion (2000–2007) and recession (2008–2014) waves in Athens, Greece, at the spatial scale of municipalities. Local‐scale changes in population dynamics were considered key indicators to evaluate the crisis' impact on recent urban transformations. Demographic polarisations in urban and rural areas have progressively increased the gap between wealthy and economically disadvantaged districts. In Athens, short‐term population dynamics were influenced by a combination of socioeconomic factors and processes acting at different spatial scales due to suburbanisation, recession, and demographic transition. As a result, the use of nonlinear analysis proves to be a useful tool to investigate urban systems in their complexity and supports the debate over the future development of contemporary cities.

Вплив значних нерівномірних деформацій основи на рівень сейсмостійкості конструктивних систем

Вступ: У статті розглянуте актуальне питання впливу значних нерівномірних деформацій основи різного походження на сейсмостійкість конструктивних систем будівель. Метою дослідження є чисельна оцінка ступеню такого впливу. Вибір методу розрахунків: Для розрахунків запропоновано використання нелінійного статичного розрахунку методом спектру несучої здатності, використаного у подальшому. Чисельна оцінка впливу нерівномірних деформацій основи на сейсмостійкість: Представлений чисельний експеримент, що демонструє ступінь зниження сейсмостійкості системи в залежності від рівня розвитку нерівномірних деформацій основи. Експеримент виконаний на основі моделей стінових систем кам’яної комплексної, а також залізобетонної монолітної конструкцій. Нелінійний розрахунок проводився на послідовний вплив нерівномірного просідання основи та горизонтальних сейсмічних навантажень. Аналіз результатів розрахунків та висновки: В результаті виявлено, що силовий вплив значних нерівномірних деформацій основи здатен суттєво знизити сейсмостійкість конструктивних систем (від одного бала до майже повної втрати при наближенні до граничних значень деформацій). Даний факт визначає необхідність врахування сумісного силового впливу значних нерівномірних деформацій основи та сейсміки, при можливості виникнення обох. При цьому слід враховувати послідовний вплив навантажень, а також рекомендується використання нелінійного статичного розрахунку за принципами методу спектру несучої здатності. При побудові графіків спектру несучої здатності на основі розрахунків в програмних комплексах слід уточнювати рівень розвитку непружних деформацій на основі експериментально підтверджених значень.

Muscle fatigue detection during dynamic contraction under blood flow restriction: Improvement of detection sensitivity using multivariable fatigue indices.

At present, in order to detect peripheral muscle fatigue, it is customary to perform a frequency domain analysis using surface electromyography data measured with bipolar leads, and extract characteristic quantities like mean power frequency and median frequency. However, there are times when muscle fatigue variables, typically represented by decreasing wave frequencies, do not occur under certain conditions such as dynamic contraction causing a blood flow restriction. This study has tried to improve muscle fatigue detection sensitivity by utilizing two approaches: alteration of electrode arrangements to monopolar leads and use of nonlinear analysis in addition to frequency domain analysis and time domain analysis. The multivariable fatigue indices calculated by using each analysis method are combined into one synthetic variable using the method named "end to end projection" proposed by Rogers and Macisaac. After the effective indices and combination patterns have been investigated, it was showed that the optimum number of combinations is around four. The results also indicate that the combination method has a potential to improve the detection accuracy and monopolar leads can detect muscle fatigue change more clearly than bipolar ones.

MODELLED PHENOMENON OF BURR FORMATION DURING MACHINING

A model of burr formation on the edge of the workpiece in the course of machining is presented. The material being machined, the cutting tool and the machining parameters were modelled. Material properties and type of its deformations have been modelled with the use of a constitutive Johnson - Cook model. Material damage initiation criteria and associated damage evolution have been modelled with the use of the ductile damage and the JohnsonCook damage initiation criterion. Simulations of the machining process for different depths of cut were carried out. The real burr formation presented by Hashimura was compared with the modelled one. The influence of the cutting parameters on the form and size of burr has been analysed. Calculations have been realised utilising finite element method with the use of nonlinear analysis in ABAQUS/Explicit environment. Based on simulation results, the assessment of the form and size of burr has been made. Burr height was used to evaluate its size, which was derived according to ISO 13715 standard. The goal was to obtain a model that reliably reflects the behaviour of material during machining, with particular emphasis on supporting the creation of cutting phenomenon of burr formation. The results of simulation and computational analysis confirmed that the model reflects the real behaviour of the material.

An efficient geometrically exact beam element for composite columns and its application to concrete encased steel I-sections

In this paper, a computationally efficient geometrically exact and materially non-linear 2D Euler–Bernoulli beam finite element is proposed, which is capable of accurately capturing the buckling behaviour of steel–concrete composite columns and complies with the principles of the general method of Eurocode 4 (EC4) (EN 1994-1-1:2004, 2004). The element is easy to implement and, due to the Euler–Bernoulli constraint, only requires uniaxial material laws for both steel and concrete. The element is subsequently employed to investigate the buckling behaviour of partially and fully concrete encased steel I-section uniformly compressed columns. In particular, the results of a parametric study are presented and discussed, aiming at assessing the influence of the equivalent member imperfections and the concrete material law, in order to provide recommendations concerning their use in non-linear analysis according to the general method of EC4.

Performance-based seismic rehabilitation of existing steel eccentric braced buildings in near fault ground motions

SUMMARY The devastating effects observed in the recent earthquakes, in terms of loss of lives as well as immediate and long-term economic losses, have prompted the need to provide documents concerning the assessment and improvement of the structural performance of existing buildings at the time of an earthquake. In this regard, performance engineering is defined as performance-based seismic design and rehabilitation. There are many reasons for rehabilitation of existing buildings. Changing the building's usage is one of the most common reasons. In the present study, the residential steel buildings were subject to performance-based rehabilitation, converting to educational use. Several steel frames with dual lateral-resistant systems (MRF–EBF) and different numbers of stories were initially designed as residential buildings. The frames were rehabilitated according to the current seismic rehabilitation codes and regulations. Cover plates were used to strengthen structural elements. Variations in structural responses were evaluated before and after retrofitting by the use of nonlinear analysis. Moreover, the performance of rehabilitated structures was evaluated, considering the gross features observed in near-field records. Copyright © 2013 John Wiley & Sons, Ltd.

Performance-based fire design of complex structures

The problem of structural fire safety in the recent years has gained a predominant position within the engineering design, with the affirmation of performance-based structural codes and standards, replacing more and more the traditional prescriptive ones. This is because nowadays, structures always bigger and more complex are designed and built. In modelling such complex structures, there are important aspects and relevant uncertainties that need to be taken into account. This paper focuses on the application of the performance-based fire design to this kind of structures; the systemic approach is identified as the proper tool to manage all the aspect related with the problem. A general framework is presented for this purpose and it is applied to a facility made of steel for the storage of helicopters, with a relatively complex geometry subject to fire. The structure is of interest since, due to its occupancy, it is prone to elevate fire risk. The modelling of the problem proposes the use of non-linear analysis that includes thermo-plastic material, geometric non-linearity and the representation of fire action are done according to a standard parametric curve.

Solitary Density Waves for Improved Traffic Flow Model with Variable Brake Distances

Traffic flow model is improved by introducing variable brake distances with varying slopes. Stability of the traffic flow on a gradient is analyzed and the neutral stability condition is obtained. The KdV (Korteweg-de Vries) equation is derived the use of nonlinear analysis and soliton solution is obtained in the meta-stable region. Solitary density waves are reproduced in the numerical simulations. It is found that as uniform headway is less than the safety distance solitary wave exhibits upward form, otherwise it exhibits downward form. In general the numerical results are in good agreement with the analytical results.

ENGLTHA: An educational tool for earthquake nonlinear and general linear dynamics

AbstractGiven the increasing use of nonlinear analysis in earthquake resistant design via performance‐based design, and ongoing research in simplified nonlinear methods, a software tool was developed for use in the teaching of nonlinear as well as linear structural dynamics. The program caters for single‐degree‐of‐freedom (SDOF) nonlinear systems and emphasizes degrading response as in‐cycle strength degradation, progressive cycle strength degradation, general stiffness degradation, and pinching degradation, or combinations of these, under earthquake ground motions. This is achieved using the smoothly varying endochronic plasticity Da hysteresis model. Utilizing numerical integration, the program also provides approximate solutions for many problems from SDOF linear dynamics such as free undamped or damped vibration, and forced periodic or non‐periodic damped or undamped vibration. As such, the VB6 program is named ENGLTHA—Earthquake Nonlinear and General Linear Time History Analysis, and also calculates elastic and inelastic displacement and acceleration response spectra. This article describes ENGLTHA and how it can be used, via a set of nine experiments, for teaching structural dynamics as a thread trough several courses spanning from the undergraduate to postgraduate levels. © 2009 Wiley Periodicals, Inc. Comput Appl Eng Educ 19: 97–106, 2011

Disproportionate collapse performance of partially restrained steel frames with bolted T-stub connections

Current design and regulatory documents require the assessment of certain buildings with regard to their vulnerability to disproportionate collapse through notional load-bearing element removal followed by an alternative path analysis. While several recent studies have examined the robustness of steel building frames with fully moment-resistant connections and their ability to sustain local damage to load-bearing elements, only limited research is available regarding the robustness of steel frames with partially restrained (PR) connections. This paper investigates the performance of steel frames with partially restrained connections fabricated from bolted T-stubs following damage to load-bearing columns. A macro-model of a bolted T-stub connection for use in nonlinear analysis is presented, verified through experimental data, and incorporated in a nonlinear finite element model to evaluate the performance of PR frames. Two prequalified T-stub connections are considered, one of which is intended to develop the full moment capacity of the beam. The evaluation is conducted for various floor plans of typical office buildings. The analysis indicates that the frames with strong T-stub connections can resist collapse in damage scenarios involving notional removal of one first-story column, while the robustness of the frames with weak T-stub connections is questionable.

Enhanced solid element for modelling of reinforced concrete structures with bond-slip

Since its invention in the <TEX>$19^{th}$</TEX> century, Reinforced Concrete (RC) has been widely used in the construction of a lot of different structures, as buildings, bridges, nuclear central plants, or even ships. The details of the mechanical response for this kind of structures depends directly upon the material behavior of each component: concrete and steel, as well as their interaction through the bond-slip, which makes a rigorous engineering analysis of RC structures quite complicated. Consequently, the practical calculation of RC structures is done by adopting a lot of simplifications and hypotheses validated in the elastic range. Nevertheless, as soon as any RC structural element is working in the inelastic range, it is possible to obtain the numerical prediction of its realistic behavior only through the use of non linear analysis. The aim of this work is to develop a new kind of Finite Element: the "Enhanced Solid Element (ESE)" which takes into account the complex composition of reinforced concrete, being able to handle each dissipative material behavior and their different deformations, and on the other hand, conserving a simplified shape for engineering applications. Based on the recent XFEM developments, we introduce the concept of nodal enrichment to represent kinematics of steel rebars as well as bonding. This enrichment allows to reproduce the strain incompatibility between concrete and steel that occurs because of the bond degradation and slip. This formulation was tested with a couple of simple examples and compared to the results obtained from other standard formulations.