Дисертації: "Non-linear dynamic analyses"

1

Varun. "A non-linear dynamic macroelement for soil structure interaction analyses of piles in liquefiable sites." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34718.

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A macroelement is developed for soil-structure interaction analyses of piles in liquefiable soils, which captures efficiently the fundamental mechanisms of saturated granular soil behavior. The mechanical model comprises a nonlinear Winkler-type model that accounts for soil resistance acting along the circumference of the pile, and a coupled viscous damper that simulates changes in radiation damping with increasing material non-linearity. Three-dimensional (3D) finite element (FE) simulations are conducted for a pile in radially homogeneous soil to identify the critical parameters governing the response. The identified parameters, i.e., hydraulic conductivity, loading rate of dynamic loading, dilation angle and liquefaction potential are then expressed in dimensionless form. Next, the macroelement parameters are calibrated as a function of the soil properties and the effective stress. A semi-empirical approach that accounts for the effects of soil-structure interaction on pore pressure generation in the vicinity of pile is used to detect the onset of liquefaction. The predictions are compared with field data obtained using blast induced liquefaction and centrifuge tests and found to be in good agreement. Finally, the macroelement formulation is extended to account for coupling in both lateral directions. FEM simulations indicate that response assuming no coupling between the two horizontal directions for biaxial loading tends to overestimate the soil resistance and fails to capture features like 'apparent negative stiffness', 'strain hardening' and 'rounded corners'.

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2

Hughes, Jonathan L. "Applications of Stability Analysis to Nonlinear Discrete Dynamical Systems Modeling Interactions." VCU Scholars Compass, 2015. http://scholarscompass.vcu.edu/etd/3819.

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Many of the phenomena studied in the natural and social sciences are governed by processes which are discrete and nonlinear in nature, while the most highly developed and commonly used mathematical models are linear and continuous. There are significant differences between the discrete and the continuous, the nonlinear and the linear cases, and the development of mathematical models which exhibit the discrete, nonlinear properties occurring in nature and society is critical to future scientific progress. This thesis presents the basic theory of discrete dynamical systems and stability analysis and explores several applications of this theory to nonlinear systems which model interactions involving economic agents and biological populations. In particular we will explore the stability properties of equilibria associated with inter-species and intergenerational population dynamics in biology and market price and agent composition dynamics in economics.

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3

Kahraman, Ahmet. "Non-linear dynamic analysis of geared systems /." The Ohio State University, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487676847117141.

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4

Latini, Corazzini Valentina. "Non-linear dynamic analysis of offshore structures." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amslaurea.unibo.it/359/.

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5

Wilson, Jonathan P. "Non-linear dynamics and power systems." Thesis, University of Bath, 2000. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341136.

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6

Le, Thanh Nam. "Non-linear Dynamic analysis of corotational beam structures." Thesis, KTH, Bro- och stålbyggnad, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-36799.

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7

Patil, Anupkumar. "Non-linear dynamical analysis of biosignals." Thesis, University of Strathclyde, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.502349.

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Biosignals are physiological signals that are recorded from various parts of the body. Some of the major biosignals are electromyograms (EMG), electroencephalograms (EEG) and electrocardiograms (ECG). These signals are of great clinical and diagnostic importance, and are analysed to understand their behaviour and to extract maximum information from them. However, they tend to be random and unpredictable in nature (non-linear). Conventional linear methods of analysis are insufficient. Hence, analysis using non-linear and dynamical system theory, chaos theory and fractal dimensions, is proving to be very beneficial. In this project, EGG signals are of interest. Changes in the normal rhythm of a human heart may result in different cardiac arrhythmias, which may be fatal or cause irreparable damage to the heart when sustained over long periods of time. Hence the ability to identify arrhythmias from EGG recordings is of importance for clinical diagnosis and treatment and also for understanding the electrophysiological mechanism of arrhythmias.

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8

Richardson, Thomas Stuart. "Continuation methods applied to non linear flight dynamics and control." Thesis, University of Bristol, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268783.

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9

Cheng, Gang. "Analyzing and Solving Non-Linear Stochastic Dynamic Models on Non-Periodic Discrete Time Domains." TopSCHOLAR®, 2013. http://digitalcommons.wku.edu/theses/1236.

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Stochastic dynamic programming is a recursive method for solving sequential or multistage decision problems. It helps economists and mathematicians construct and solve a huge variety of sequential decision making problems in stochastic cases. Research on stochastic dynamic programming is important and meaningful because stochastic dynamic programming reflects the behavior of the decision maker without risk aversion; i.e., decision making under uncertainty. In the solution process, it is extremely difficult to represent the existing or future state precisely since uncertainty is a state of having limited knowledge. Indeed, compared to the deterministic case, which is decision making under certainty, the stochastic case is more realistic and gives more accurate results because the majority of problems in reality inevitably have many unknown parameters. In addition, time scale calculus theory is applicable to any field in which a dynamic process can be described with discrete or continuous models. Many stochastic dynamic models are discrete or continuous, so the results of time scale calculus are directly applicable to them as well. The aim of this thesis is to introduce a general form of a stochastic dynamic sequence problem on complex discrete time domains and to find the optimal sequence which maximizes the sequence problem.

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10

Suliman, Ridhwaan. "A quadratic non-linear elasticity formulation for the dynamic behaviour of fluid-loaded structures." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/277824.

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This work details the development and implementation of a numerical model capable of solving strongly-coupled fluid-structure interaction problems involving long thin structures, which are common multi-physics problems encountered in many applications. In most fluid-structure interaction problems the deformation of the slender elastic bodies is significant and cannot be described by a purely linear analysis. We present a new formulation to model these larger displacements. By extending the standard modal decomposition technique for linear structural analysis, the governing equations and boundary conditions are updated to account for the leading-order non-linear terms and a new modal formulation with quadratic modes is derived. The quadratic modal approach is tested on standard benchmark problems of increasing complexity and compared with analytical and full non-linear numerical solutions. Two computational fluid-structure interaction approaches are then implemented in a partitioned manner: a finite volume method for discretisation of both the fluid and solid domains and the quadratic modal formulation for the structure coupled with a finite volume fluid solver. Strong-coupling is achieved by means of a fixed-point solver with dynamic relaxation. The fluid-structure interaction approaches are validated and compared on benchmark problems of increasing complexity and strength of coupling between the fluid and solid domains. Fluid-structure interaction systems may become unstable due to the interaction between the fluid-induced pressure and structural rigidity. A thorough stability analysis of finite elastic plates in uniform flow is conducted by varying the structural length and flow velocity showing that these are critical parameters. Validation of the results with those from analytical methods is done. An analysis of the dynamic interactions between multiple finite plates in various configurations is also conducted.

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11

Huang, Shiling. "Linear stability analysis of non-reacting and reacting elliptical jets." Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06062008-164706/.

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12

Zangeneh, Kamali Abbas. "Shear Strength of Reinforced Concrete Beams subjected to Blast Loading : Non-linear Dynamic Analysis." Thesis, KTH, Bro- och stålbyggnad, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-104241.

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The experimental investigations performed on the behaviour of reinforce concrete elements subjected to blast loading have revealed that the shear mechanisms and ductility play important roles in the overall response and failure mode of such structures. The main aim of this master thesis is to study the possibility of using finite element method as a tool for predicting the dynamic response of blast loaded reinforced concrete beams and evaluation of their shear strength. In this study, the commercial software, ABAQUS/Explicit has been used by implementing appropriate constitutive material models in order to consider the material nonlinearity, stiffness degradation and strain rate effects. The results of some blast loaded tested beams have been used for verification and calibration of the model. As a secondary objective, the calibrated model used to study the influence of some important factors on the shear strength of reinforced concrete beams and investigate their effects on the failure mode. The results used as a reference and compared with the calculations according to some design codes for blast resistance design. The results of the present research show that the implemented nonlinear finite element model successfully simulates the dynamic responses including displacement/reaction force time histories and induced damage patterns of blast tested beams with reasonable accuracy. The results of performed parametric study confirm that the ductility play important role in the failure behaviour of studied beams. The numerical simulations show that dynamic response of a soft element is more ductile than the stiffer one and the shear forces are thereby limited. Thus, although a soft element fails by large deformations in flexure, a stiff element may experience a brittle shear failure mode for the same load intensity. The comparison between the results of numerical analysis and design codes calculation show that the American approach in shear design of reinforced concrete elements subjected to blast loading is relatively conservative, similar to static design approach and do not consider the effect of ductility in the shear design procedure. On the contrary, the procedure that Swedish guideline implemented somehow considers the effect of ductility on the shear strength of reinforced concrete elements subjected to impulsive loads. Further research should involve the using the developed finite element model as a tool in order to theoretically study the dynamic response of blast loaded reinforced concrete elements and their failure modes. The results of numerical simulations can be used as a reference to derive simplified computational methods for practical design purposes.

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13

Mäkikallio, T. (Timo). "Analysis of heart rate dynamics by methods derived from nonlinear mathematics:clinical applicability and prognostic significance." Doctoral thesis, University of Oulu, 1998. http://urn.fi/urn:isbn:9514250133.

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Abstract The traditional methods of analysing heart rate variability based on means and variance are unable to detect subtle but potentially important changes in interbeat heart rate behaviour. This research was designed to evaluate the clinical applicability and prognostic significance of new dynamical methods of analysing heart rate behaviour derived from nonlinear mathematics. The study covered four different patient populations, their controls and one general population of elderly people. The first patient group consisted of 38 patients with coronary artery disease without previous myocardial infarction, the second of 40 coronary artery disease patients with a prior Q-wave myocardial infarction, and the third of 45 patients with a history of ventricular tachyarrhythmia. The fourth group comprised 10 patients with a previous myocardial infarction who had experienced ventricular fibrillation during electrocardiographic recordings. The fifth group comprised a random sample of 347 community-living elderly people invited for a follow-up of 10 years after electrocardiographic recordings. Heart rate variability was analysed by traditional time and frequency domain methods. The new dynamical measures derived from nonlinear dynamics were: 1) approximate entropy, which reflects the complexity of the data, 2) detrended fluctuation analysis, which describes the presence or absence of fractal correlation properties of time series data, and 3) power-law relationship analysis, which demonstrates the distribution of spectral characteristics of RR intervals, but does not reflect the magnitude of spectral power in different spectral bands. Approximate entropy was higher in postinfarction patients (1.17 ± 0.22), but lower in coronary artery disease patients without myocardial infarction (0.93 ± 0.17) than in healthy controls (1.03 ± 014, p < 0.01, p < 0.05 respectively). It did not differ between patients with and without ventricular arrhythmia. The short term fractal-like scaling exponent of the detrended fluctuation analysis was higher in coronary artery disease patients without myocardial infarction (1.34 ± 0.15, p < 0.001), but not in postinfarction patients without arrhythmia (1.06 ± 0.13) compared with healthy controls (1.09 ± 0.13). The short term exponent was markedly reduced in patients with life-threatening arrhythmia (0.85 ± 0.25 ventricular tachycardia patients, 0.68 ± 0.18 ventricular fibrillation patients, p < 0.001 for both). The long term power-law slope of the power-law scaling analysis was lower in the ventricular fibrillation group than in postinfarction controls without arrhythmia risk (-1.63 ± 0.24 vs. -1.33 ± 0.23, p < 0.01) and predicted mortality in a general elderly population with an adjusted relative risk of 1.74 (95% CI 1.42–2.13). The present observations demonstrate that dynamic analysis of heart rate behaviour gives new insight into analysis of heart rate dynamics in various cardiovascular disorders. The breakdown of the normal fractal-like organising principle of heart rate variability is associated with an increased risk of mortality and vulnerability to life-threatening arrhythmias.

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14

Duan, Chengwu. "Dynamic analysis of dry friction path in a torsional system." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1092672620.

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Thesis (Ph. D.)--Ohio State University, 2004.
Title from first page of PDF file. Document formatted into pages; contains xxiv, 200 p.; also includes graphics (some col.). Includes bibliographical references (p. 196-200). Available online via OhioLINK's ETD Center

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15

Alam, Md Shafiful. "Iterative Methods to Solve Systems of Nonlinear Algebraic Equations." TopSCHOLAR®, 2018. https://digitalcommons.wku.edu/theses/2305.

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Iterative methods have been a very important area of study in numerical analysis since the inception of computational science. Their use ranges from solving algebraic equations to systems of differential equations and many more. In this thesis, we discuss several iterative methods, however our main focus is Newton's method. We present a detailed study of Newton's method, its order of convergence and the asymptotic error constant when solving problems of various types as well as analyze several pitfalls, which can affect convergence. We also pose some necessary and sufficient conditions on the function f for higher order of convergence. Different acceleration techniques are discussed with analysis of the asymptotic behavior of the iterates. Analogies between single variable and multivariable problems are detailed. We also explore some interesting phenomena while analyzing Newton's method for complex variables.

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16

陶冬玲 and Dong-ling Tao. "Modal parameter identification for non-linear systems using the time-domain fourier filter output method." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1997. http://hub.hku.hk/bib/B31236169.

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17

Tao, Dong-ling. "Modal parameter identification for non-linear systems using the time-domain fourier filter output method /." Hong Kong : University of Hong Kong, 1997. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19013310.

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18

Cassidy, Mark Jason. "Non-linear analysis of jack-up structures subjected to random waves." Thesis, University of Oxford, 1999. http://ora.ox.ac.uk/objects/uuid:02b96107-638b-4200-9fd7-fa49635594e3.

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There is a steadily increasing demand for the use of jack-up units in deeper water and harsher environments. Confidence in their use in these environments requires jack-up analysis techniques to reflect accurately the physical processes occurring. This thesis is concerned with the models appropriate for the dynamic assessment of jack-ups, an important issue in long-term reliability considerations. The motivation is to achieve a balanced approach in considering the non-linearities in the structure, foundations and wave loading. A work hardening plasticity model is outlined for the combined vertical, moment and horizontal loading of spudcan footings on dense sand. Empirical expressions for the yield surface in combined load space and a flow rule for prediction of footing displacements during yield are given. Theoretical lower bound bearing capacity factors for conical footings in sand have been derived and are used in a strain-hardening law to define the variation in size of the yield surface with the plastic component of vertical penetration. The complete incremental numerical model has been implemented into a plane frame analysis program named JAKUP. The spectral content of wave loading is considered using NewWave theory, and the importance of random wave histories shown by constraining the deterministic NewWave into a completely random surface elevation. Using this technique, a method for determining short-term extreme response statistics for a sea-state is demonstrated. A numerical experiment on an example jack-up and central North Sea location is shown to emphasise the difference in long-term extreme response according to various footing assumptions. The role of sea-state severity in the variation of short-term extreme response statistics is also highlighted. Finally, probabilistic methods are used to develop further understanding of the response behaviour of jack-ups. A sensitivity study of influential variables (with probabilistic formulations as opposed to deterministic values) has been conducted using the response surface methodology.

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19

Sima, Brum Jose Fernando. "A model for the non linear dynamic analysis of reinforced concrete and masonry framed structures." Doctoral thesis, Universitat Politècnica de Catalunya, 2010. http://hdl.handle.net/10803/6173.

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La evaluación de la respuesta dinámica o sísmica de estructuras complejas a menudo requiere de la integración en el dominio del tiempo de la ecuación de equilibro dinámico de la estructura, en el marco de un análisis no lineal. En el caso de estructuras de fábrica y hormigón armado, el uso de este tipo de métodos cobra especial importancia, debido al complejo comportamiento no lineal que presentan, incluso para niveles bajos de carga. Muchas de estas estructuras pueden idealizarse como entramados espaciales de barras. En las últimas dos décadas, se ha desarrollado en la UPC una generalización de los métodos matriciales convencionales para el análisis de entramados espaciales de barras, la llamada Formulación Matricial Generalizada (FMG). La formulación básica para elementos de directriz curva y sección variable fue presentada inicialmente por Carrascón et al. (1987). Posteriormente, Carol y Murcia (1989) aplicaron esta formulación al análisis non lineal de procesos variables en el tiempo. Esta formulación fue extendida luego al análisis no lineal geométrico y del material de estructuras de obra de fábrica (Molins, 1996; Molins y Roca, 1998). Una extensión de la formulación estática básica al análisis dinámico lineal fue presentada por Molins et al. (1998) a través de la propuesta de una matriz de masa consistente. Esta formulación ha probado ser una herramienta eficiente para el análisis no lineal de estructuras de pórticos espaciales, durante más de quince años de aplicación en el Departamento de Ingeniería de la Construcción de la UPC.
El objetivo fundamental de este trabajo es extender la FMG al análisis dinámico no lineal de estructuras espaciales de barras de hormigón armado y obra de fábrica. Para ello, la formulación básica ha sido complementada con varias nuevas características:

· Se ha desarrollado un modelo constitutivo cíclico uniaxial para el hormigón y la obra de fábrica sometida tanto a cargas cíclicas de compresión como de tracción. Se ha puesto especial énfasis en la descripción de la degradación de la rigidez producida durante los ciclos de carga en tracción y compresión, la forma de las curvas de carga y descarga, y la transición entre abertura y cierre de fisuras. Se consideran dos parámetros independientes de daño, una para tracción y otro para compresión. En el caso de cargas cíclicas de compresión, el modelo se derivó de resultados experimentales obtenidos por otros autores, considerando la dependencia de las diferentes variables con el nivel de daño alcanzado, mientras que en el caso de cargas cíclicas de tracción, se propone un modelo simple basado en observaciones experimentales.

· Se adoptó un modelo constitutivo para el acero de refuerzo sometido a cargas cíclicas, el conocido modelo de Menegotto-Pinto.

· Finalmente, se adoptó un procedimiento para la integración de la ecuación de equilibrio dinámico de la estructura.

Una vez implementado en ordenador, el modelo propuesto a sido aplicado a varios casos de estructuras aporticadas de hormigón armado y obra de fábrica sometidas a cargas de tipo cíclico y dinámico. Los resultados obtenidos demuestran que el modelo propuesto permite predecir adecuadamente la respuesta cíclica/dinámica de este tipo estructuras.
The assessment of the dynamic or seismic performance of complex structures often requires the integration in the time domain of the structural equation of motion in the frame of a non-linear analysis. In the case of masonry and reinforced concrete structures, the use of these methods for the assessment of the structure become of great importance, due to its complex non linear behavior, even for low levels of loading. A great number of these structures may be idealized as spatial frames. A generalization of the conventional matrix methods for the analysis of spatial framed structures has been developed in the UPC during the last two decades, the so-called Generalized Matrix Formulation (GMF). The basic formulation for curved elements with variable cross section was presented by Carrascón et al. (1987). Carol and Murcia (1989) extended this flexibility based formulation to the non linear time dependant analysis. This formulation was later extended to the geometrical and material non linear analysis of masonry framed structures (Molins, 1996; Molins and Roca, 1998). An extension of the basic formulation to the linear dynamic analysis was later proposed by Molins et al. (1998) through the introduction of a consistent mass matrix. The formulation has proved for more than fifteen years of extensive use, to be an efficient tool for the analysis of 3D framed structures.
The aim of this research is to extend the GMF to the non linear dynamic analysis of reinforced concrete and masonry framed structures. Following this main goal, the basic formulation has been complemented with a series of new features:
· A uniaxial constitutive model for concrete and masonry subjected to cyclic loadings in both compression and tension has been proposed. Particular emphasis has been paid to the description of the strength and stiffness degradation produced by the load cycling in both, tension and compression, the shape of unloading and reloading curves and the transition between opening and closing of cracks. Two independent damage parameters in compression and in tension have been introduced to model the concrete degradation due to increasing loads. In the case of cyclic compressive loading, the model has been derived from experimental results obtained by other authors by considering the dependency of the cyclic variables with the damage level attained by the concrete. In the case of cyclic tension a simple model is adopted based on experimental observations.
· A constitutive model for the cyclic behavior of reinforcing steel, the well known Menegotto-Pinto model, has been adopted.
· Finally, a time step procedure for the integration of the dynamic equilibrium equation of the structure has been adopted.
In order to show the capabilities of the proposed formulation, once implemented in a computer program, it has been applied in three examples of structures subjected to cyclic and dynamic loadings. The obtained results show that the model may adequately predict the cyclic/dynamic response of this type of structures.

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20

Dunton, Alec. "Topological Data Analysis for Systems of Coupled Oscillators." Scholarship @ Claremont, 2016. http://scholarship.claremont.edu/hmc_theses/79.

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Coupled oscillators, such as groups of fireflies or clusters of neurons, are found throughout nature and are frequently modeled in the applied mathematics literature. Earlier work by Kuramoto, Strogatz, and others has led to a deep understanding of the emergent behavior of systems of such oscillators using traditional dynamical systems methods. In this project we outline the application of techniques from topological data analysis to understanding the dynamics of systems of coupled oscillators. This includes the examination of partitions, partial synchronization, and attractors. By looking for clustering in a data space consisting of the phase change of oscillators over a set of time delays we hope to reconstruct attractors and identify members of these clusters.

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21

Blignaut, Caitlyn. "A Non-linear Visco-elastic Model for Dynamic Finite Element Simulation of Bovine Cortical Bone." Master's thesis, Faculty of Engineering and the Built Environment, 2021. http://hdl.handle.net/11427/33433.

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Modelling and simulation of the human body during an impact situation such as a car accident, can lead to better designed safety features on vehicles. In order to achieve this, investigation into the material properties and the creation of a numerical model of cortical bone is needed. One approach to creating a material model of cortical bone suitable for these situations is to describe the material model as visco-elastic, as reported by Shim et al. [1], Bekker et al. [2] and Cloete et al. [3]. The work by Shim et al. and Bekker et al. developed three-dimensional models, but do not accurately capture the transition in behaviour in the intermediate strain rate region, while Cloete et al. developed a phenomenological model which captures the intermediate strain rate behaviour in one dimension. This work aims to verify and extend these models. The intermediate strain rate regime (1 s−1 to 100 s−1 ) is of particular interest because it is a key characteristic of the behaviour of cortical bone and several studies have been conducted to gather experimental data in this region [3, 4, 5, 6]. The behaviour can be captured using non-linear viscoelastic models. This dissertation focuses on the development and implementation of a material model of cortical bone based on non-linear visco-elastic models to capture the intermediate strain rate regime behaviour. The material model was developed using uni-axial test results from cortical bone. The model by Cloete et al. has been improved and extended, and issues of local and global strain rate with regards to the viscosity have been clarified. A hereditary integral approach was taken in the analysis and implementation of discrete models and was found to be consistent with mathematical models. The model developed was extended to three dimensions in a manner similar to that of Shim et al. and Bekker et al. for implementation in commercial finite element software (LS-Dyna and Abaqus).

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22

PHAMAVANH, Kongkeo, 睦. 伊藤, Atsushi ITOH, 光. 中村, Hikaru NAKAMURA, 忠顕田邉 та Tada-aki TANABE. "RC構造の繰り返し及び動的解析における格子等価連続体化法の適応性". 土木学会, 2004. http://hdl.handle.net/2237/8617.

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23

Fung, Chi Fung. "On-line dynamical system modelling using radial basis function networks in adaptive non-linear noise cancellation." Thesis, University of Sheffield, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389790.

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24

Ko, Seung-uk. "Human gait analysis by gait pattern measurement and forward dynamic model combined with non linear feedback control /." Connect to this title online, 2007. http://hdl.handle.net/1957/3754.

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25

KRUTZ, JILL E. "DESIGN OF A HYDRAULIC ACTUATOR TEST STAND FOR NON-LINEAR ANALYSIS OF HYDRAULIC ACTUATOR SYSTEM." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin990813095.

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26

Thompson, Richard Saint George. "Development of non-linear numerical models appropriate for the analysis of jack-up units." Thesis, University of Oxford, 1996. http://ora.ox.ac.uk/objects/uuid:5804719a-8643-49c3-a9f3-105f35dce9ca.

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Jack-up units have considerable economic significance because they are used to carry out a large proportion of the world's oil and gas exploration in water depths less than 90.0m. Due to the increase in use of jack-ups in harsher environments, analysis techniques assuming quasi-static and linear structural behaviour have had to be reassessed. This thesis is concerned with non-linear dynamic analysis methods appropriate for a jack-up assessment. Jack-up modelling requires realistic representation of the structure, the foundations and the environmental loading, together with the implementation of appropriate dynamic analysis algorithms. Techniques for each of these aspects of jack-up analysis are reviewed and the implementation of several of the methods in an advanced plane frame analysis program called JAKUP is described. Geometric non-linearity in the structure and work hardening plasticity at the foundations are accounted for in the program. Test cases are presented to verify the implementation of the methods and then some illustrative plane frame quasi-static and dynamic analyses are described. These simple models highlight the importance of accounting for dynamic motions in a jack-up analysis. For the quasi-static analyses, the assumption of pinned footing behaviour is seen to always result in the most conservative displacement and moment predictions. However, the analyses show that this is not always the case when dynamic amplification is accounted for.

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27

Frazier, William. "Application of Symplectic Integration on a Dynamical System." Digital Commons @ East Tennessee State University, 2017. https://dc.etsu.edu/etd/3213.

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Molecular Dynamics (MD) is the numerical simulation of a large system of interacting molecules, and one of the key components of a MD simulation is the numerical estimation of the solutions to a system of nonlinear differential equations. Such systems are very sensitive to discretization and round-off error, and correspondingly, standard techniques such as Runge-Kutta methods can lead to poor results. However, MD systems are conservative, which means that we can use Hamiltonian mechanics and symplectic transformations (also known as canonical transformations) in analyzing and approximating solutions. This is standard in MD applications, leading to numerical techniques known as symplectic integrators, and often, these techniques are developed for well-understood Hamiltonian systems such as Hill’s lunar equation. In this presentation, we explore how well symplectic techniques developed for well-understood systems (specifically, Hill’s Lunar equation) address discretization errors in MD systems which fail for one or more reasons.

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28

Fathala, Giuma Musbah. "Analysis and implementation of radial basis function neural network for controlling non-linear dynamical systems." Thesis, University of Newcastle upon Tyne, 1998. http://hdl.handle.net/10443/3114.

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Modelling and control of non-linear systems are not easy, which are now being solved by the application of neural networks. Neural networks have been proved to solve these problems as they are described by adjustable parameters which are readily adaptable online. Many types of neural networks have been used and the most common one is the backpropagation algorithm. The algorithm has some disadvantages, such as slow convergence and construction complexity. An alternative neural networks to overcome the limitations associated with the backpropagation algorithm is the Radial Basis Function Network which has been widely used for solving many complex problems. The Radial Basis Function Network is considered in this theses, along with a new adaptive algorithm which has been developed to overcome the problem of the optimum parameter selection. Use of the new algorithm reduces the trial and error of selecting the minimum required number of centres and guarantees the optimum values of the centres, the widths between the centres and the network weights. Computer simulation usmg SimulinklMatlab packages, demonstrated the results of modelling and control of non-linear systems. Moreover, the algorithm is used for selecting the optimum parameters of a non-linear real system 'Brushless DC Motor'. In the laboratory implementation satisfactory results have been achieved, which show that the Radial Basis Function may be used for modelling and on-line control of such real non-linear systems.

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29

Vikman, Noa, and Gustav Romare. "Models of the Universe : An analysis of the asymptotic behaviour of non-linear dynamical systems." Thesis, KTH, Skolan för teknikvetenskap (SCI), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-297891.

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In this thesis we present some relevant theory, and then we rigorously investigate the existence intervals and the asymptotic behaviors of three cosmological models. The first model we investigate is based on the Friedmann-Lemaître-Robertson-Walker (FLRW) metric, which is consistent with the cosmological principle. This is a common assumption which asserts that the universe is spatially homogeneous and isotropic. The second and third models are of Bianchi type I and Bianchi type II respectively, which are both anisotropic, but spatially homogeneous models. For all models we find that the existence interval is (0,∞), meaning that they all predict an origin of the universe for some past time, while guaranteeing the existence of the universe for all future times. Furthermore we prove that in all models the universe expands exponentially for times far in the future and that the non-isotropic solutions tend towards isotropic solutions forward in time. Differences were found in the asymptotic behavior backward in time, as the FLRW-model was shown to behave like the square root for times close to t=0, while the anisotropy in the Bianchi type I and Bianchi type II models became unbounded close to t=0. It was found that there were no differences in the asymptotic behavior between the two anisotropic models. Finally we investigated some interesting aspects specific for each model. For instance the behaviour of light-like curves were analysed in the FLRW-solutions and vacuum solutions were investigated in the Bianchi type I and Bianchi type II models.

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30

Bouchonneau, Déborah. "Analyse du potentiel de développement des ressources d’hydrocarbure non conventionnelles." Thesis, Montpellier 1, 2011. http://www.theses.fr/2011MON10053/document.

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Les perspectives énergétiques globales soulignent une demande croissante d'énergie sur les prochaines décennies. Le pétrole brut devrait représenter environ 35% de l'offre d'énergie primaire à l'horizon 2030 d'après l'AIE. Parmi les sources d'approvisionnement, les hydrocarbures "non conventionnels" devraient contribuer significativement à l'offre de produits pétroliers, puisqu'ils présentent un intérêt stratégique en termes de réserves et d'indépendance énergétique. L'objectif de cette thèse est l'étude du potentiel de développement des ressources d'hydrocarbure non conventionnelles sous différents scénarios liés au contexte économique et environnemental. Les sables asphaltiques, principalement localisés au Canada, constituent notre cas d'application. La première partie de cette thèse a mis en évidence deux phases de développement: la première, de 1980 à 2005, correspondant à l'émergence de la filière grâce à des leviers réglementaires, économiques et géographiques; la seconde, amorcée en 2005 avec la dégradation du contexte économique, pendant laquelle le développement de la filière s'est fortement ralenti. La seconde partie de cette thèse porte sur l'analyse prospective à horizon 2050. L'élaboration d'un premier modèle basé sur la programmation linéaire a permis de quantifier l'offre tendancielle sous différents scénarios déterministes de prix et de réglementations environnementales. En particulier, la décision d'investissement apparaît significativement impactée par l'introduction d'une taxe CO2. Un second modèle basé sur la programmation dynamique a permis d'évaluer l'offre prospective en présence d'incertitudes. Un impact négatif de l'incertitude et de la volatilité des prix sur la décision d'investissement a été mis en évidence, avec ou sans réglementation environnementale. Cet impact négatif est accentué lorsqu'une incertitude supplémentaire sur le cadre réglementaire environnemental est introduite
International energy outlook emphasizes an increasing energy demand over the next decades. Crude oil should represent about 35% of primary energy supply by 2030 according to the IEA. Among supply sources, non conventional crude oil should contribute significantly to the supply of petroleum products, being strategic in terms of reserves and energy independence. This thesis aims to evaluate the development potential of non conventional crude oil using different scenarios regarding the economic and environmental context. Oil sands, essentially located in Canada, constitute our application. The first part of this thesis highlights two development phases: the first one, from 1980 to 2005, corresponding to the emergence of the oil sands sector through regulatory, economic and geographical levers; the second one, started in 2005 with the deterioration of the economic climate, during which oil sands development slowed down significantly. The second part of this thesis focuses on the prospective analysis of the horizon 2050. Firstly, the development of a supply model based on linear programming allowed us to quantify non conventional oil trend supply under deterministic price and environmental regulation scenarios. In particular, investment decision is significantly affected by the establishment of a CO2 tax. Secondly, the development of another supply model based on dynamic programming allowed us to evaluate future non conventional crude oil supply under uncertainties. A negative impact of price uncertainty and volatility on investment decision is highlighted, under or without environmental regulation. This negative impact is strengthened by the introduction of a supplementary uncertainty in environmental legal framework

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31

Sonje, Abhijit Ravindra. "Experimental and finite element investigation into the effects of manufacturing variability on the dynamic response of a bolted interface between a bracket and a thin-walled sheet metal structure." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1546418059243072.

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32

Tran, Tuan H. "Landing-Gear Impact Response: A Non-linear Finite Element Approach." UNF Digital Commons, 2019. https://digitalcommons.unf.edu/etd/896.

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The primary objective of this research is to formulate a methodology of assessing the maximum impact loading condition that will incur onto an aircraft’s landing gear system via Finite Element Analysis (FEA) and appropriately determining its corresponding structural and impact responses to minimize potential design failures during hard landing (abnormal impact) and shock absorption testing. Both static and dynamic loading condition were closely analyzed, compared, and derived through the Federal Aviation Administration’s (FAA) airworthiness regulations and empirical testing data. In this research, a nonlinear transient dynamic analysis is developed and established via NASTRAN advanced nonlinear finite element model (FEM) to simulate the worst-case loading condition. Under the appropriate loading analysis, the eye-bar and contact patch region theory were then utilized to simulate the tire and nose wheel interface more accurately. The open geometry of the nose landing gear was also optimized to minimize the effect of stress concentration. The result of this research is conformed to the FAA’s regulations and bound to have an impact on the design and development of small and large aircraft’s landing gear for both near and distant future.

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33

OHU, IKECHUKWU POLYCARP NNAMDI. "Analysis of Ergonomics and Highly Non-linear Dynamics of Surgical Motions and Muscle Activations in Minimally Invasive Surgery." OpenSIUC, 2015. https://opensiuc.lib.siu.edu/dissertations/1063.

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Minimally invasive surgery (MIS) is becoming increasing popular and widely adopted on account of relative post-operative advantages (shorter hospital stays, less scarification, trauma and post-operative pain) it offers patients when compared to open surgery. Nonetheless, the surge in demand for MIS procedures are not met with commensurate availability of experts in the field, thus leading to excessive stress attributable to increased case load, and an increase in the number of surgery interns requiring training with far less MIS experts to provide it. Also, musculoskeletal discomforts experienced by MIS surgeons have been attributed to ergonomic factors among other causes, and a required verification of the viability of fundamentals of laparoscopic surgery (FLS) as a valid ergonomic discriminator between traditional MIS and robot-assisted MIS was tested and validated. Real-time, subject-centered, and objective quantification of surgical skills has long been a challenge. A proposed solution is presented here involving the application of complexity theory (time delay and Hurst exponent principles) to the analysis of phase space reconstructions of time series data, generated by periodic changes in Euler coordinates of surgical graspers while being used by MIS novices and experts. A comparison of Hurst exponent and time delay values over multiple iterations of the same task provides quantitative insight on MIS skills improvement and experience.

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34

PISANO, FABIO. "Analysis and synthesis techniques of nonlinear dynamical systems with applications to diagnostic of controlled thermonuclear fusion reactors." Doctoral thesis, Università degli Studi di Cagliari, 2013. http://hdl.handle.net/11584/266202.

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Nonlinear dynamical systems are of wide interest to engineers, physicists and mathematicians, and this is due to the fact that most of physical systems in nature are inherently non-linear. The nonlinearity of these systems has consequences on their time-evolution, which in some cases can be completely unpredictable, apparently random, although fundamentally deterministic. Chaotic systems are striking examples of this. In most cases, there are no hard and fast rules to analyse these systems. Often, their solutions cannot be obtained in closed form, and it is necessary to resort to numerical integration techniques, which, in case of high sensitivity to initial conditions, lead to ill-conditioning problems and high computational costs. The dynamical system theory, the branch of mathematics used to describe the behaviour of these systems, focuses not on finding exact solutions to the equations describing the dynamical system, but rather on knowing if the system stabilises to a steady state in the long term, and what are the possible attractors, e.g. a quasi-periodic or chaotic attractors. Regarding the synthesis, from both a practical and a theoretical standpoint, it is very desirable to develop methods of synthesizing these systems. Although extensive theory has been developed for linear systems, no complete formulation for nonlinear systems synthesis is present today. The main topic of this thesis is the solution of engineering problems related to the analysis and synthesis of nonlinear and chaotic systems. In particular, a new algorithm which optimizes Lyapunov exponents estimation in piecewise linear systems has been applied to PWL and polynomial chaotic systems. In the field of complex systems synthesis, a systematic method to project systems of order 2n characterized by two positive Lyapunov exponents, has been proposed. This procedure couples nth-order chaotic systems with a suitable nonlinear coupling function. Furthermore, a method for the fault detection has been developed. In the field of time series analysis, a new denoising method, based on the wavelet transform of the noisy signal, has been described. The method implements a variable thresholding, whose optimal value is determined by analysing the cross-correlation between the denoised signal and the residuals and by applying different criteria depending on the particular decomposition level. Finally, a study of dynamical behaviour of Type I ELMs has been performed for a future modelization of the phenomenon. In this context, a statistical analysis of time intervals between successive Type I ELMs has been proposed.---------------------------------- Il tema principale di questa tesi è la soluzione di problemi ingegneristici legati all’analisi e alla sintesi di sistemi dinamici non lineari. I sistemi dinamici non lineari sono di largo interesse per ingegneri, fisici e matematici, e questo è dovuto al fatto che la maggior parte dei sistemi fisici in natura è intrinsecamente non lineare. La non linearità di questi sistemi ha conseguenze sulla loro evoluzione temporale, che in certi casi può rivelarsi del tutto imprevedibile, apparentemente casuale, seppure fondamentalmente deterministica. I sistemi caotici sono un esempio lampante di questo comportamento. Nella maggior parte dei casi non esistono delle regole standard per l’analisi di questi sistemi. Spesso, le soluzioni non possono essere ottenute in forma chiusa, ed è necessario ricorrere a tecniche di integrazione numerica, che, in caso di elevata sensibilità alle condizioni iniziali, portano a problemi di mal condizionamento e di elevato costo computazionale. La teoria dei sistemi dinamici, la branca della matematica usata per descrivere il comportamento di questi sistemi, non si concentra sulla ricerca di soluzioni esatte per le equazioni che descrivono il sistema dinamico, ma piuttosto sull’analisi del comportamento a lungo termine del sistema, per sapere se questo si stabilizzi in uno stato stabile e per sapere quali siano i possibili attrattori, ad esempio, attrattori quasi-periodici o caotici. Per quanto riguarda la sintesi, sia da un punto di vista pratico che teorico, è molto importante lo sviluppo di metodi in grado di sintetizzare questi sistemi. Sebbene per i sistemi lineari sia stata sviluppata una teoria ampia e esaustiva, al momento non esiste alcuna formulazione completa per la sintesi di sistemi non lineari. In questa tesi saranno affrontati problemi di caratterizzazione, analisi e sintesi, legati allo studio di sistemi non lineari e caotici. La caratterizzazione dinamica di un sistema non lineare permette di individuarne il comportamento qualitativo a lungo termine. Gli esponenti di Lyapunov sono degli strumenti che permettono di determinare il comportamento asintotico di un sistema dinamico. Essi danno informazioni circa il tasso di divergenza di traiettorie vicine, caratteristica chiave delle dinamiche caotiche. Le tecniche esistenti per il calcolo degli esponenti di Lyapunov sono computazionalmente costose, e questo fatto ha in qualche modo precluso l’uso estensivo di questi strumenti in problemi di grandi dimensioni. Inoltre, durante il calcolo degli esponenti sorgono dei problemi di tipo numerico, per ciò il calcolo deve essere affrontato con cautela. L’implementazione di algoritmi veloci e accurati per il calcolo degli esponenti di Lyapunov è un problema di interesse attuale. In molti casi pratici il vettore di stato del sistema non è disponibile, e una serie temporale rappresenta l’unica informazione a disposizione. L’analisi di serie storiche è un metodo di analisi dei dati provenienti da serie temporali che ha lo scopo di estrarre delle statistiche significative e altre caratteristiche dei dati, e di ottenere una comprensione della struttura e dei fattori fondamentali che hanno prodotto i dati osservati. Per esempio, un problema dei reattori a fusione termonucleare controllata è l’analisi di serie storiche della radiazione Dα, caratteristica del fenomeno chiamato Edge Localized Modes (ELMs). La comprensione e il 16 controllo degli ELMs sono problemi cruciali per il funzionamento di ITER, in cui il type-I ELMy H-mode è stato scelto come scenario di funzionamento standard. Determinare se la dinamica degli ELM sia caotica o casuale è cruciale per la corretta descrizione dell’ELM cycle. La caratterizzazione dinamica effettuata sulle serie temporali ricorrendo al cosiddetto spazio di embedding, può essere utilizzata per distinguere serie random da serie caotiche. Uno dei problemi più frequenti che si incontra nell’analisi di serie storiche sperimentali è la presenza di rumore, che in alcuni casi può raggiungere anche il 10% o il 20% del segnale. È quindi essenziale , prima di ogni analisi, sviluppare una tecnica appropriata e robusta per il denosing. Quando il modello del sistema è noto, l’analisi di serie storiche può essere applicata al rilevamento di guasti. Questo problema può essere formalizzato come un problema di identificazione dei parametri. In questi casi, la teorie dell’algebra differenziale fornisce utili informazioni circa la natura dei rapporti fra l’osservabile scalare, le variabili di stato e gli altri parametri del sistema. La sintesi di sistemi caotici è un problema fondamentale e interessante. Questi sistemi non implicano soltanto un metodo di realizzazione di modelli matematici esistenti ma anche di importanti sistemi fisici reali. La maggior parte dei metodi presentati in letteratura dimostra numericamente la presenza di dinamiche caotiche, per mezzo del calcolo degli esponenti di Lyapunov. In particolare, le dinamiche ipercaotiche sono identificate dalla presenza di due esponenti di Lyapunov positivi.

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35

Goodfellow, Marc. "Spatio-temporal modelling and analysis of epileptiform EEG." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/spatiotemporal-modelling-and-analysis-of-epileptiform-eeg(0f76259a-1a58-44a9-b08b-1402c9b49896).html.

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In this thesis we investigate the mechanisms underlying the generation of abnormal EEG rhythms in epilepsy, which is a crucial step towards better treatment of this disorder in the future. To this end, macroscopic scale mathematical models of the interactions between neuronal populations are examined. In particular, the role of interactions between neural masses that are spatially distributed in cortical networks are explored. In addition, two other important aspects of the modelling process are addressed, namely the conversion of macroscopic model variables into EEG output and the comparison of multivariate, spatio-temporal data. For the latter, we adopt a vectorisation of the correlation matrix of windowed data and subsequent comparison of data by vector distance measures. Our modelling studies indicate that excitatory connectivity between neural masses facilitates self-organised dynamics. In particular, we report for the first time the production of complex rhythmic transients and the generation of intermittent periods of 'abnormal' rhythmic activity in two different models of epileptogenic tissue. These models therefore provide novel accounts of the spontaneous, intermittent transition between normal and pathological rhythms in primarily generalised epilepsies and the evocation of complex, self-terminating, spatio-temporal dynamics by brief stimulation in focal epilepsies. Two key properties of these models are excitability at the macroscopic level and the presence of spatial heterogeneities. The identification of neural mass excitability as an important processes in spatially extended brain networks is a step towards uncovering the multi-scale nature of the pathological mechanisms of epilepsy. A direct consequence of this work is therefore that novel experimental investigations are proposed, which in itself is a validation of our modelling approach. In addition, new considerations regarding the nature of dynamical systems as applied to problems of transitions between rhythmic states are proposed and will prompt future investigations of complex transients in spatio-temporal excitable systems.

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36

Yumer, Mehmet Ersin. "On The Non-linear Vibration And Mistuning Identification Of Bladed Disks." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/3/12611498/index.pdf.

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Forced response analysis of bladed disk assemblies plays a vital role in rotor blade design and has been drawing a great deal of attention both from research community and engine industry for more than half a century. However because of the phenomenon called &lsquo
mistuning&rsquo
, which destroys the cyclic symmetry of a rotor, there have been several difficulties related to forced response analysis ever since, two of which are addressed in this thesis: efficient non-linear forced response analysis of mistuned bladed disks and mistuning identification. On the nonlinear analysis side, a new solution approach is proposed studying the combined effect of non-linearity and mistuning, which is relatively recent in this research area and generally conducted with methods whose convergence and accuracy depend highly on the number of degrees of freedom where non-linear elements are attached. The proposed approach predicts nonlinear forced response of mistuned bladed disk assemblies considering any type of nonlinearity. In this thesis, special attention is given to the friction contact modeling of bladed disks which is the most common type of nonlinearity found in bladed disk assemblies. In the modeling of frictional contact a friction element which enables normal load variation and separation of the contact interface in three-dimensional space is utilized. Moreover, the analysis is carried out in modal domain where the differential equations of motions are converted to a set of non-linear algebraic equations using harmonic balance method and modal superposition technique. Thus, the number of non-linear equations to be solved is independent of the number of non-linear elements used. On the mistuning identification side, a new method is enclosed herein which makes use of neural networks to assess unknown mistuning parameters of a given bladed disk assembly from its assembly modes, thus being suitable for integrally bladed disks. The method assumes that a tuned mathematical model of the rotor under consideration is readily available, which is always the case for today&rsquo
s realistic bladed disk assemblies. A data set of selected mode shapes and natural frequencies is created by a number of simulations performed by mistuning the tuned mathematical model randomly. A neural network created by considering the number of modes, is then trained with this data set for being used to identify mistuning of the rotor from measured data. On top of these, a new adaptive algorithm is developed for harmonic balance method, several intentional mistuning patterns are investigated via excessive Monte-Carlo simulations and a new approach to locate, classify and parametrically identify structural non-linearities is introduced.

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37

Corneli, Marco. "Dynamic stochastic block models, clustering and segmentation in dynamic graphs." Thesis, Paris 1, 2017. http://www.theses.fr/2017PA01E012/document.

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Cette thèse porte sur l’analyse de graphes dynamiques, définis en temps discret ou continu. Nous introduisons une nouvelle extension dynamique du modèle a blocs stochastiques (SBM), appelée dSBM, qui utilise des processus de Poisson non homogènes pour modéliser les interactions parmi les paires de nœuds d’un graphe dynamique. Les fonctions d’intensité des processus ne dépendent que des classes des nœuds comme dans SBM. De plus, ces fonctions d’intensité ont des propriétés de régularité sur des intervalles temporels qui sont à estimer, et à l’intérieur desquels les processus de Poisson redeviennent homogènes. Un récent algorithme d’estimation pour SBM, qui repose sur la maximisation d’un critère exact (ICL exacte) est ici adopté pour estimer les paramètres de dSBM et sélectionner simultanément le modèle optimal. Ensuite, un algorithme exact pour la détection de rupture dans les séries temporelles, la méthode «pruned exact linear time» (PELT), est étendu pour faire de la détection de rupture dans des données de graphe dynamique selon le modèle dSBM. Enfin, le modèle dSBM est étendu ultérieurement pour faire de l’analyse de réseau textuel dynamique. Les réseaux sociaux sont un exemple de réseaux textuels: les acteurs s’échangent des documents (posts, tweets, etc.) dont le contenu textuel peut être utilisé pour faire de la classification et détecter la structure temporelle du graphe dynamique. Le modèle que nous introduisons est appelé «dynamic stochastic topic block model» (dSTBM)
This thesis focuses on the statistical analysis of dynamic graphs, both defined in discrete or continuous time. We introduce a new extension of the stochastic block model (SBM) for dynamic graphs. The proposed approach, called dSBM, adopts non homogeneous Poisson processes to model the interaction times between pairs of nodes in dynamic graphs, either in discrete or continuous time. The intensity functions of the processes only depend on the node clusters, in a block modelling perspective. Moreover, all the intensity functions share some regularity properties on hidden time intervals that need to be estimated. A recent estimation algorithm for SBM, based on the greedy maximization of an exact criterion (exact ICL) is adopted for inference and model selection in dSBM. Moreover, an exact algorithm for change point detection in time series, the "pruned exact linear time" (PELT) method is extended to deal with dynamic graph data modelled via dSBM. The approach we propose can be used for change point analysis in graph data. Finally, a further extension of dSBM is developed to analyse dynamic net- works with textual edges (like social networks, for instance). In this context, the graph edges are associated with documents exchanged between the corresponding vertices. The textual content of the documents can provide additional information about the dynamic graph topological structure. The new model we propose is called "dynamic stochastic topic block model" (dSTBM).Graphs are mathematical structures very suitable to model interactions between objects or actors of interest. Several real networks such as communication networks, financial transaction networks, mobile telephone networks and social networks (Facebook, Linkedin, etc.) can be modelled via graphs. When observing a network, the time variable comes into play in two different ways: we can study the time dates at which the interactions occur and/or the interaction time spans. This thesis only focuses on the first time dimension and each interaction is assumed to be instantaneous, for simplicity. Hence, the network evolution is given by the interaction time dates only. In this framework, graphs can be used in two different ways to model networks. Discrete time […] Continuous time […]. In this thesis both these perspectives are adopted, alternatively. We consider new unsupervised methods to cluster the vertices of a graph into groups of homogeneous connection profiles. In this manuscript, the node groups are assumed to be time invariant to avoid possible identifiability issues. Moreover, the approaches that we propose aim to detect structural changes in the way the node clusters interact with each other. The building block of this thesis is the stochastic block model (SBM), a probabilistic approach initially used in social sciences. The standard SBM assumes that the nodes of a graph belong to hidden (disjoint) clusters and that the probability of observing an edge between two nodes only depends on their clusters. Since no further assumption is made on the connection probabilities, SBM is a very flexible model able to detect different network topologies (hubs, stars, communities, etc.)

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38

Wolf, Frederik Peter Wilhelm. "Complex networks across fields: from climate variability to online dynamics." Doctoral thesis, Humboldt-Universität zu Berlin, 2021. http://dx.doi.org/10.18452/22907.

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Komplexe Netzwerke sind mächtige Werkzeuge, die die Untersuchung komplexer Systeme unterstützen. In vielen Bereichen werden komplexe Netzwerke eingesetzt, um die Dynamik interagierender Entitäten wie Neuronen, Menschen oder sogar Wettersysteme zu verstehen. Darüber hinaus erweitern sich die Anwendungsbereiche mit der stetigen Entwicklung neuer theoretischer Ansätze. In dieser Arbeit wollen wir sowohl den theoretischen Rahmen der Netzwerkwissenschaften weiterentwickeln als auch komplexe Netzwerke in der Klimatologie und der computergestützten Sozialwissenschaft anwenden.
Complex networks are powerful tools enabling the study of complex systems. In many fields, complex networks are used as a tool to gain an understanding of the dynamics of interacting entities such as neurons in a brain, humans on social media, or global weather systems. At the same time, new theoretical frameworks that extend the toolbox of Network Science promote the application of network tools in new research fields. In this thesis, we aim for both, advancing the theoretical framework of Network Science as well as applying complex networks in Climatology and Computational Social Science.

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39

Lekscha, Jaqueline Stefanie. "Complex systems methods for detecting dynamical anomalies in past climate variability." Doctoral thesis, Humboldt-Universität zu Berlin, 2020. http://dx.doi.org/10.18452/21047.

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Анотація:

Die Analyse von Proxy-Zeitreihen aus Paläoklimaarchiven wie zum Beispiel Baumringen, Seesedimenten, Tropfsteinen und Eisbohrkernen mittels gefensterter Rekurrenznetzwerkanalyse ermöglicht die Identifizierung und Charakterisierung dynamischer Anomalien in der Klimavariabilität der Vergangenheit. Das Ziel der vorliegenden Arbeit ist die Entwicklung einer zuverlässigeren Routine zur gefensterten Rekurrenznetzwerkanalyse. Aufbauend auf dem bestehenden methodischen Rahmen werden die Bereiche der Phasenraumrekonstruktion und des Signifikanztests als verbesserungsfähig identifiziert. Deshalb werden verschiedene Methoden zur Rekonstruktion des Phasenraums aus unregelmäßig abgetasteten, verrauschten Daten verglichen. Außerdem wird ein allgemeiner flächenweiser Signifikanztest eingeführt, der, basierend auf einem ausgewählten Nullmodell, Korrelationen in den Analyseergebnissen numerisch abschätzt, um damit das Problem hoher Raten an falsch positiv signifikanten Ergebnissen zu adressieren. Im zweiten Teil der Arbeit wird die entwickelte Methodik genutzt, um die nichtlineare Variabilität des Klimas der Vergangenheit in Nord- und Südamerika zu untersuchen, indem vier reale Zeitreihen verschiedener Proxys studiert werden. Außerdem werden Proxy-System-Modelle genutzt, um auf die Frage der Eignung von Daten verschiedener Paläoklimaarchive zur Charakterisierung der Klimavariabilität mittels gefensterter Rekurrenznetzwerkanalyse einzugehen. Mit der Arbeit wird der Einsatz nichtlinearer Methoden zur Analyse von Paläoklima-Zeitreihen vorangebracht, das Potential und die Grenzen der gefensterten Rekurrenznetzwerkanalyse aufgezeigt und zukünftige relevante Fragestellungen, die die erhaltenen Ergebnisse und Schlussfolgerungen komplementieren können, identifiziert.
Studying palaeoclimate proxy data from archives such as tree rings, lake sediments, speleothems, and ice cores using windowed recurrence network analysis offers the possibility to characterise dynamical anomalies in past climate variability. This thesis aims at developing a more reliable framework of windowed recurrence network analysis by comparing different phase space reconstruction approaches for non-uniformly sampled noisy data and by tackling the problem of increased numbers of false positive significant points when correlations within the analysis results can not be neglected. For this, different phase space reconstruction approaches are systematically compared and a generalised areawise significance test which implements a numerical estimation of the correlations within the analysis results is introduced. In particular, the test can be used to identify patches of possibly false positive significant points. The developed analysis framework is applied to detect and characterise dynamical anomalies in past climate variability in North and South America by studying four real-world palaeoclimatic time series from different archives. Furthermore, the question whether palaeoclimate proxy time series from different archives are equally well suited for tracking past climate dynamics with windowed recurrence network analysis is approached by using the framework of proxy system modelling. This thesis promotes the use of non-linear methods for analysing palaeoclimate proxy time series, provides a detailed assessment of potentials and limitations of windowed recurrence network analysis and identifies future research directions that can complement the obtained results and conclusions.

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40

May, James E. "Non-Linear Control of Long, Flexible Structures Employing Inter-Modal Energy Transfer [Modal Damping]." University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1247711518.

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41

Kayikci, Duygu y. "The Behavior of Moment Resisting Steel Frames Under Seismic Excitation with Variation of Geometric Dimensions of Architectural Setbacks." Scholarly Repository, 2011. http://scholarlyrepository.miami.edu/oa_dissertations/583.

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This study investigates seismic response of the Moment-Resisting-Steel Frames (MRSF) with the architectural setbacks. The main objective of the study is to understand the variation of the elastic and inelastic, static and dynamic behavior with changes in the geometric dimensions of the tower portion. A second objective of the study is to determine the adequacy of the analysis procedures of various rigors, specified in current seismic design provision, in predicting those behaviors for MRSF with various size of setback. The analytical study is conducted using a regular and 16 irregular models to capture all possible combinations of configuration of setback in five-story, five-bay MRSFs. An irregular model is developed by gradually changing the horizontal and vertical dimensions of the tower portion of the regular base 2D frame-model. All models were designed for (a) equal global displacement and uniform distribution of inter-story drift under First-Mode (FM) lateral force distribution pattern at first significant yield, and (b) equal period of vibration at the first mode, using Nonlinear Static Seismic analysis procedure. Among the conclusions derived from the research is that the variation of (a) the elastic and inelastic inter-story drift, the ductility demand for the top three stories, and (b) the elastic and inelastic global displacement exhibited a pattern similar to the variation of the FM participation factor at the roof, PF1Φr,1. The square-root-of-sum-of-square (SRSS) distribution provided accurate estimates of elastic story shear and inter-story drift demand as well as the story yield strength and drift.

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42

Jagite, George. "Analysis of Slamming Induced Whipping Effects over the Ultimate Strength of Ships." Thesis, Ecole centrale de Nantes, 2020. http://www.theses.fr/2020ECDN0018.

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La première partie de cette thèse est consacrée à l’étude numérique de la résistance ultime dynamique de différentes structures navales. Afin d’évaluer l’influence de l’inertie et de la vitesse de déformation, plusieurs cas de chargement sont considérés, des plus simples, de la forme d’une demie sinusoïde, aux plus réalistes, issus de vagues de design. La résistance ultime dynamique est définie comme le niveau maximal de chargement qui ne conduit pas à la ruine de la structure, et est calculée par un nouvel algorithme itératif. Enfin, la résistance ultime dynamique est comparée à la résistance ultime quasi-statique, ce qui permet de calculer des coefficients de chargements dynamiques, qui évaluent correctement l’influence de la dynamique sur la ruine. La deuxième partie de cette thèse porte sur le développement d’un nouvelle méthode pour le calcul de la réponse au fouettement, en prenant en compte le comportement élastoplastique de la structure. La structure est modélisé avec deux poutres non uniformes, reliées par une rotule non linéaire, dont le comportement est décrit par une relation entre le moment de flexion et la variation d’angle. Le problème hydrodynamique est traité par une méthode à éléments de frontière 3D. Le problème couplé hydro-élastoplastique est ensuite résolu dans le domaine temporel grâce à un logiciel de tenue à la mer. Les calculs sont réalisés sur une large gamme de navires, avec plusieurs cas de chargement réalistes. Ceci permet enfin de calculer un coefficient de résistance dynamique, par comparaison des réponses non-linéaires et linéaires
The first part of this thesis is dedicated to the numerical investigations of dynamic ultimate strength for various ship structures. In order to analyze the influence of the inertia and strain rate effects, different load functions are used, starting from the simplest ones where the loads are defined as half-sine functions, to more realistic ones where the loads are induced by equivalent design waves. The dynamic ultimate strength is defined as the maximum load level that leads to a non-collapse scenario, and it is determined through a newly developed iterative algorithm. Finally, the dynamic ultimate strength is compared with the quasi-static ultimate strength, and the dynamic load factors are derived in order to obtain a proper estimator of the dynamic collapse effect. The second part of the thesis is dedicated to the development of a new method to calculate the non-linear whipping response, where the elastoplastic structural response is considered. The hull girder is modeled as two non-uniform beams, connected with a non-linear hinge, described by the non-linear relation between the internal bending moment and the relative rotation angle. The hydrodynamic problem is solved using the 3D boundary element method. Then, the fully coupled hydro-elastoplastic problem is solved within a partly non-linear time-domain seakeeping program. The calculations are perfomed on a broad range of ships on different realistic loading scenarios Finally, the non-linear and linear whipping resposnes are compared in order to derive the dynamic ultimate capacity factors

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43

Araújo, Francisco Adriano de. "Contribuição ao emprego da mecânica do dano para a análise do comportamento dinâmico não-linear de vigas em concreto armado." Universidade de São Paulo, 2003. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-02052007-093714/.

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O trabalho trata da formulação e implementação numérica de um modelo de dano para o concreto. O objetivo é o de reproduzir laços de histerese observados experimentalmente em diagramas de tensão-deformação uniaxiais quando, a partir de um certo nível de solicitação, e dano correspondente, passam-se a realizar ciclos de descarregamento e recarregamento. O modelo propõe que os laços de histerese resultam da dissipação conjunta decorrente do dano evolutivo e do fenômeno de fricção interna nas faces das fissuras. O fenômeno de fricção interna está relacionado à suposição de que as fissuras não se abrem simplesmente por separação formando faces com superfícies lisas, mas tendem a combinar modos de separação e deslizamento segundo superfícies com uma certa rugosidade. O deslizamento entre as faces das fissuras dá origem a uma deformação por escorregamento, assumida como responsável por um comportamento plástico com encruamento cinemático não-linear. A abordagem termodinâmica considerada no sentido de contemplar a danificação e a fricção interna leva à dedução de que a tensão total num ponto do meio com dano resulta dividida em uma parcela dita tensão elasto-danificada e em uma outra denominada tensão de escorregamento, também dependente do nível de danificação da estrutura. Dois tipos básicos de aplicações são realizadas: as primeiras visam avaliar a influência das variáveis de estado e dos parâmetros do material na forma dos diagramas de tensão-deformação. As outras aplicações são dedicadas à utilização do modelo na análise do comportamento dinâmico de uma viga em concreto armado submetida à vibração forçada. Destaca-se o efeito dos laços de histerese sobre o amortecimento estrutural. Mostra-se que a utilização deste modelo de dano leva à geração de um amortecimento estrutural que com os modelos de dano usuais somente poderia ser obtido a partir da utilização do modelo de amortecimento de Rayleigh, por exemplo, na equação do movimento.
This work deals with numerical formulation and implementation of a damage model to concrete. The aim is to reproduce hysteresis loops observed experimentally in uniaxial stress-strain diagram when cycles of unloading and reloading are produced. The model proposes that the hysteresis loops are due to the coupling between the dissipation of damage process and the internal friction phenomenon between the faces of crack lips. The phenomenon of internal friction is related to the supposition that the crack doesn\'t open itself by separation mode creating plane lips, but there is a tendency to combine opening and sliding modes across irregular surfaces. The sliding between the crack surfaces generates a sliding strain, which is assumed as responsible by a plastic behaviour with non-linear kinematics hardening. The thermodynamic approach considering damage and internal friction leads to the deduction that the total stress at a point is composted by one component named elasto-damage stress and another named sliding stress, both dependent of the structure damage level. Two basic kinds of simulation are performed: the first one aims to evaluate the influence of the state variables and the material parameters over the stress-strain diagrams. The following simulations are dedicated to the use of the model in dynamic analysis of a reinforced concrete beam subjected to vibration. It is emphasized the effect of the structural damping from hysteresis loops. It is showed that the present damage model generates structural damping that could only be obtained with conventional damage model by using the Rayleigh damping approach in the equation of motion.

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Jokinen, V. (Vesa). "Longitudinal changes and prognostic significance of cardiovascular autonomic regulation assessed by heart rate variability and analysis of non-linear heart rate dynamics." Doctoral thesis, University of Oulu, 2003. http://urn.fi/urn:isbn:9514272005.

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Abstract Several studies have shown that altered cardiovascular autonomic regulation is associated with hypertension, diabetes, aging, angiographic severity of coronary artery disease (CAD), and increased mortality after acute myocardial infarction (AMI). The purpose of this study was to assess the temporal changes and prognostic significance of various measures of heart rate (HR) behaviour and their possible associations to coronary risk variables, and the progression of CAD in different populations. This study comprised five patient populations. The first consisted of 305 patients with recent coronary artery bypass graft surgery (CABG) and lipid abnormalities, the second of 109 male patients with recent CABG, the third of 53 type II diabetic patients with CAD, the fourth of 600 patients with recent AMI, and the fifth of 41 elderly subjects. HR variability and non-linear measures of HR dynamics were analysed. Among the patients with prior CABG, a significant correlation existed between the baseline HR variability (standard deviation of N-N intervals, SDNN) and the progression of CAD (r = 0.26, p < 0.001)). In the longitudinal study of patients with prior CABG, only the fractal indexes of HR dynamics, such as the power law slope (β) and the short-term fractal exponent (α1), decreased significantly. In diabetic patients, SDNN decreased significantly (p < 0.001) during the three-year period. The reduction of SDNN was related to cholesterol, triglyceride, and glucose levels, and also to progression of CAD (r = 0.36, p < 0.01). In the longitudinal follow-up study of patients with recent AMI, reduced fractal indices (α1 and β), and reduced HR turbulence predicted cardiac death when measured at the convalescent phase after AMI. Reduced β and turbulence slope predicted cardiac death when measured at 12 months after AMI. In the elderly population, β (p < 0.001) and α1 (p < 0.01) reduced significantly. Low-frequency power spectra were the only traditional measure of HR variability that decreased significantly during the 16-year period. HR variability is associated with many risk factors of atherosclerosis and with progression of CAD among patients with ischemic heart disease. Fractal HR dynamics are more sensitively able to detect age-related changes in cardiovascular autonomic regulation. Altered fractal HR dynamics and HR turbulence are associated with increased mortality after AMI.

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45

Borra, Chaitanya. "DYNAMICS OF LARGE ARRAY MICRO/NANO RESONATORS." University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron1590758736333883.

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46

LOPES, ELVIS DINATI CHANTRE. "NON-LINEAR DYNAMICAL ANALYSIS OF COMPOSITE FLOORS CONSIDERING THE EFFECTS OF PARTIAL INTERACTION AND BEAM TO COLUMN AND BEAM TO BEAM CONNECTIONS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2012. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=21173@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
O crescimento dos problemas de vibrações excessivas em edificações oriundos de atividades humanas rítmicas tem conduzido à necessidade de desenvolvimento de critérios específicos para projetos estruturais submetidos à ação dessas cargas dinâmicas. Esta foi uma das motivações para o desenvolvimento de uma metodologia de análise para investigação da resposta dinâmica de sistemas estruturais de pisos mistos (aço-concreto). Objetiva-se verificar a influência da interação aço-concreto (interação total e parcial) e, bem como, das ligações estruturais (ligações viga-coluna e viga-viga), sobre a resposta dinâmica não linear de pisos mistos (aço-concreto). Deste modo, são utilizados três modelos de carregamento dinâmico representativos das atividades humanas rítmicas referentes a saltos à vontade e ginástica aeróbica. As cargas dinâmicas são obtidas por meio de testes experimentais e, também, com base em normas e recomendações internacionais de projeto. Com referência a interação aço-concreto, vários tipos de conectores (tipo stud e perfobond) são considerados ao longo da investigação. Mesmo sabendo-se que a análise de vibrações de pisos induzidas por atividades humanas tem sido alvo de inúmeras investigações ao longo dos últimos dois séculos (1828-2012), os autores desconhecem na literatura técnica um trabalho de pesquisa tão abrangente, no que diz respeito à análise dinâmica não linear de pisos mistos (aço-concreto) submetidos à ação de atividades humanas rítmicas, com base na consideração dos efeitos dos conectores (interação aço-concreto) e das ligações (viga-coluna e viga-viga). Diante do exposto, o quadro global investigado neste trabalho de pesquisa demonstra, claramente, um indicativo de que os critérios de projeto devem levar em conta o caráter dinâmico da excitação e, especialmente, a influência da interação aço-concreto e das ligações estruturais, no que tange a verificação dos estados limites de utilização (conforto humano), associados ao comportamento estrutural de pisos mistos de edificações.
The increasing incidence of building vibration problems due to human activities led to a specific design criterion to be addressed in structural design. This was the main motivation for the development of a design methodology centred on the steel-concrete composite floors non-linear dynamic response submitted to loads due to human rhythmic activities. This way, the main objective of this work is to investigate the influence of steel-concrete interaction degree (from total to various levels of partial interaction) and the beam-to-column and beam-to-beam connections effect over the non-linear dynamic behaviour of composite floors. Thus, three dynamic loading models were utilized, in order to simulate human rhythmic activities such as jumping and aerobic gymnastics. The dynamic loads were obtained through experimental tests and based on international design codes and recommendations. Regarding the steel-concrete interaction degree, the stud and perfobond connectors are considered in this investigation. Even though this topic has been studied in the technical literature for nearly two centuries, the steel-concrete composite floors non-linear dynamic analysis submitted to human rhythmic activities has not yet been addressed so comprehensively, as far as the authors are concerned in this investigation, based on the consideration of the connectors (steel-concrete interaction degree) and connections (beam-to-column and beam-to-beam) effects. Considering all aspects mentioned before, the results have demonstrated that the design criteria should include the original nature of the dynamic excitation and, specially, the steel-concrete interaction degree and structural connections effects when the steel-concrete composite floors structural behaviour, related to the serviceability limit states (human comfort) are investigated.

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Maestre, Heredia Jorge. "Towards the application of the isogeometric boundary element analysis to fluid mechanics: non-linear gravity waves and dynamics of deformable capsules in shear flows." Doctoral thesis, Universitat Rovira i Virgili, 2017. http://hdl.handle.net/10803/401587.

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En aquesta tesi es desenvolupa un model numèric eficient i robust per a l’anàlisi de problemes fluid-dinàmics, que posteriorment es valida i s’aplica a dues noves configuracions: (1) les onades generades per una hidroala submergida i (2) la dinàmica d'una càpsula deformable en un flux pulsàtil. El model es basa en el Mètode dels Elements de Contorn (MEC) integrat amb la tecnologia de NURBS i T-spline. Aquesta tècnica es coneguda com Anàlisi Isogeomètric (AIG) i té certs avantatges. El més atractiu és que permet una integració directa entre programes moderns de disseny gràfic (CAD) i eines d’anàlisi numèric, eliminant així laboriosos passos intermedis com la generació de la malla. Aquesta tesi es divideix en dos blocs. El primer bloc tracta sobre la simulació de propagació d’onades no lineals gravitacionals i de la interacció onades-estructures. L’anàlisi d’aquest fenomen és útil per a predir la generació i propagació de tsunamis així com és indispensable per al disseny d’esculleres i estructures flotants. S’assumeix que el fluid és invíscid i irrotacional, resultant una equació de Laplace que es resol mitjançant el MEC. Es resolen diversos exemples en els que es demostra la precisió i estabilitat temporal del model numèric. Addicionalment es simula el front d’onades generat per una hidroala submergida. En el segon bloc s’aplica el AIG a l’estudi del comportament de microcàpsules deformables suspeses en fluxos. La dinàmica de microcàpsules deformables comporta importants implicacions en un ampli rang d’aplicacions biomèdiques i industrials. El AIG-MEC s’utilitza per a resoldre l’equació del fluid mentre que es desenvolupa una formulació basada en el AIG-Mètode dels Elements Finits (MEF) per a l’anàlisi de la mecànica de la membrana. Es resolen diversos exemples en els que es mostra la capacitat del mètode per a la simulació de càpsules sotmeses a grans deformacions. Finalment s’estudia la dinàmica d’una càpsula en un tub amb flux pulsàtil.
En esta tesis se desarrolla un modelo numérico eficiente y robusto para el análisis de problemas fluido-dinámicos, que posteriormente se valida y se aplica a dos nuevas configuraciones: (1) las ondas generadas por un hidroala sumergida y (2) la dinámica de una cápsula deformable en un flujo pulsátil. El modelo se basa en el Método de los Elementos de Contorno (MEC) integrado con la tecnología NURBS and T-spline. Esta técnica es conocida como Análisis Isogeométrico (AIG) y posee ciertas ventajas. La más atractiva es que permite una directa integración entre modernos programas de diseño grafico (CAD) y herramientas de análisis numérico, eliminando así laboriosos pasos intermedios como la generación de la malla. Esta tesis se divide en dos bloques. El primer bloque trata sobre la simulación de propagación la de ondas de gravedad no lineales e la interacción olas-estructuras. El análisis de este fenómeno es útil para predecir la generación y propagación de tsunamis así como es indispensable para el diseño de rompeolas y estructuras flotantes. Se asume que el fluido es inviscido e irrotacional, resultando una ecuación de Laplace que se resuelve mediante el MEC. Se resuelven varios ejemplos en los que se demuestra la precisión y estabilidad temporal del modelo numérico. Adicionalmente se simula el frente de olas generados por una hidroala sumergida. En el Segundo bloque se aplica el AIG al estudio del comportamiento de microcápsulas deformables suspendidas en un flujo. La dinámica de microcápsules deformables conlleva importantes implicaciones en un amplio rango de aplicaciones biomédicas e industriales. El AIG-MEC se usa para resolver la ecuación del fluido mientras que se desarrolla una formulación basada en el AIG-Método de los Elementos Finitos (MEF) para el análisis de la mecánica de la membrana. Se resuelven varios ejemplos en los que se muestra la capacidad del método para la simulación de cápsulas sujetas a grandes deformaciones. Finalmente se estudia la dinámica de una cápsula en un tubo con un flujo pulsátil.
In this Thesis an efficient and robust numerical model for the analysis of fluid dynamic problems has been developed, validated and applied to two novel fluid flow configurations: (1) the waves generated by a submerged foil and (2) the dynamics of microcapsules in pulsating shear flows. The model is based on the Boundary Element Method (BEM) integrated with the NURBS and the T-spline frameworks. This technique is known as Isogeometrical Analysis (IGA) and it offers several advantages. The most attractive is that it allows a direct integration between modern Computer Aid Design geometric systems and numerical engineering analysis tools, removing intermediate steps as the mesh generation. This Thesis is divided into two blocks. The first block deals with the simulation of the propagation of non-linear gravity waves and of the wave-structure interactions. The analysis of this phenomenon is useful to predict the generation and propagation of tsunamis and it is indispensable for the design of breakwaters and floating structures. The flow is assumed to be inviscid and irrotational and the resulting Laplace's equation is solved using BEM. Some benchmark examples are considered to show the temporal accuracy and stability of the method. In addition, the simulation of the waves generated by submerged foils is reported. In the second block the IGA is applied to analyze the behavior of deformable microcapsules in shear flows. The dynamics of deformable capsules have important implications in a wide range of biolomedical and industrial applications. The IGA-BEM is used to solve the Stokes flow equation and an IGA-Finite Element Method (FEM) is developed for the analysis of the capsule mechanics. Some benchmark examples are solved to demonstrate the capability of the present approach for the simulation of capsules subjected to large deformation. Finally, the dynamics of a deformable capsule in a tube under a pulsatile flow is analyzed.

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48

Eslick, John. "A Dynamical Study of the Evolution of Pressure Waves Propagating through a Semi-Infinite Region of Homogeneous Gas Combustion Subject to a Time-Harmonic Signal at the Boundary." ScholarWorks@UNO, 2011. http://scholarworks.uno.edu/td/1367.

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In this dissertation, the evolution of a pressure wave driven by a harmonic signal on the boundary during gas combustion is studied. The problem is modeled by a nonlinear, hyperbolic partial differential equation. Steady-state behavior is investigated using the perturbation method to ensure that enough time has passed for any transient effects to have dissipated. The zeroth, first and second-order perturbation solutions are obtained and their moduli are plotted against frequency. It is seen that the first and second-order corrections have unique maxima that shift to the right as the frequency decreases and to the left as the frequency increases. Dispersion relations are determined and their limiting behavior investigated in the low and high frequency regimes. It is seen that for low frequencies, the medium assumes a diffusive-like nature. However, for high frequencies the medium behaves similarly to one exhibiting relaxation. The phase speed is determined and its limiting behavior examined. For low frequencies, the phase speed is approximately equal to sqrt[ω/(n+1)] and for high frequencies, it behaves as 1/(n+1), where n is the mode number. Additionally, a maximum allowable value of the perturbation parameter, ε = 0.8, is determined that ensures boundedness of the solution. The location of the peak of the first-order correction, xmax, as a function of frequency is determined and is seen to approach the limiting value of 0.828/sqrt(ω) as the frequency tends to zero and the constant value of 2 ln 2 as the frequency tends to infinity. Analytic expressions are obtained for the approximate general perturbation solution in the low and high-frequency regimes and are plotted together with the perturbation solution in the corresponding frequency regimes, where the agreement is seen to be excellent. Finally, the solution obtained from the perturbation method is compared with the long-time solution obtained by the finite-difference scheme; again, ensuring that the transient effects have dissipated. Since the finite-difference scheme requires a right boundary, its location is chosen so that the wave dissipates in amplitude enough so that any reflections from the boundary will be negligible. The perturbation solution and the finite-difference solution are found to be in excellent agreement. Thus, the validity of the perturbation method is established.

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49

Garzeri, Flavio José. "Dinâmica não linear de um pórtico plano sob carregamento não ideal: análise numérica e experimental." Universidade de São Paulo, 2001. http://www.teses.usp.br/teses/disponiveis/3/3144/tde-28032017-080049/.

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Анотація:

Nesta tese, apresenta-se a análise numérica e experimental do comportamento dinâmico não linear de um pórtico excitado por uma fonte não ideal - um motor elétrico de corrente contínua desbalanceado - como exemplo dessa classe de problemas. Elabora-se um modelo matemático com quatro graus de liberdade: dois relacionados com o deslocamento horizontal e vertical do ponto de apoio da máquina e dois com os parâmetros de funcionamento do motor elétrico. Adota-se a formulação Lagrangeana para gerar as equações de movimento contendo termos não lineares até ordem cúbica. A solução numérica é obtida através do método de Runge-Kutta com passo adaptativo. Ensaios dinâmicos e estáticos foram realizados com o motor e com o sistema completo, com vistas a validar o modelo matemático. Um sistema de medição digital armazenou todos os dados obtidos em arquivos de fácil leitura pelos programas atualmente disponíveis. Filmagens de alta velocidade e fotografia estroboscópica registraram movimentos típicos relacionados com comportamentos não lineares. Os resultados numéricos e experimentais mostram boa correlação entre si, além de apresentarem alguns dos fenômenos associados ao se forçar uma estrutura a passar por uma de suas ressonâncias excitando-a com um dispositivo com potência limitada, como o efeito Sommerfeld. Outros fenômenos, devido ao comportamento geometricamente não linear da estrutura, são também detectados, tais como saturação modal e transferência de energia.
Numerical and experimental analysis of the nonlinear dynamics of a portal frame excited by a non-ideal source - an unbalanced direct current motor - is presented in this thesis as an example of this class of problems. A four degree of freedom model is elaborated: two of them related to the horizontal and vertical structural displacements and two others to the functioning parameters of the motor. A Lagrangian approach for deducing the equations of motion, up to cubic non-linear terms is followed. The numerical solution is obtained through Runge-Kutta algorithm with adaptive step. Static and dynamic tests were performed with the motor and with the complete system, in order to validate the mathematical model. A digital acquisition system recorded all data in computer files, ready to be read by available commercial programs. High speed filming and stroboscopic photography were used to register typical movements related to nonlinear behavior. Numerical and mathematical results show good correlation, as well as present some phenomena related to passage through resonance with limited power excitation such as the Sommerfeld effect. Some other phenomena, related to the nonlinear behavior of the structure are also detected, as modal saturation and energy transference.

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Huang, Ming-Hui. "Dynamic characteristics of slender suspension footbridges." Thesis, Queensland University of Technology, 2006. https://eprints.qut.edu.au/16450/1/Ming-Hui_Huang_Thesis.pdf.

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Анотація:

Due to the emergence of new materials and advanced engineering technology, slender footbridges are increasingly becoming popular to satisfy the modern transportation needs and the aesthetical requirements of society. These structures however are always "lively" with low stiffness, low mass, low damping and low natural frequencies. As a consequence, they are prone to vibration induced by human activities and can suffer severe vibration serviceability problems, particularly in the lateral direction. This phenomenon has been evidenced by the excessive lateral vibration of many footbridges worldwide such as the Millennium Bridge in London and the T-Bridge in Japan. Unfortunately, present bridge design codes worldwide do not provide sufficient guidelines and information to address such vibrations problems and to ensure safety and serviceability due to the lack of knowledge on the dynamic performance of such slender vibration sensitive bridge structures. A conceptual study has been carried out to comprehensively investigate the dynamic characteristics of slender suspension footbridges under human-induced dynamic loads and a footbridge model in full size with pre-tensioned reverse profiled cables in the vertical and horizontal planes has been proposed for this purpose. A similar physical suspension bridge model was designed and constructed in the laboratory, and experimental testings have been carried out to calibrate the computer simulations. The synchronous excitation induced by walking has been modelled as crowd walking dynamic loads which consist of dynamic vertical force, dynamic lateral force and static vertical force. The dynamic behaviour under synchronous excitation is simulated by resonant vibration at the pacing rate which coincides with a natural frequency of the footbridge structure. Two structural analysis software packages, Microstran and SAP2000 have been employed in the extensive numerical analysis. Research results show that the structural stiffness and vibration properties of suspension footbridges with pre-tensioned reverse profiled cables can be adjusted by choosing different structural parameters such as cable sag, cable section and pretensions in the reverse profiled cables. Slender suspension footbridges always have four main kinds of vibration modes: lateral, torsional, vertical and longitudinal modes. The lateral and torsional modes are often combined together and become two kinds of coupled modes: coupled lateral-torsional modes and coupled torsionallateral modes. Such kind of slender footbridges also have different dynamic performance in the lateral and vertical directions, and damping has only a small effect on the lateral vibration but significant effect on the vertical one. The fundamental coupled lateral-torsional mode and vertical mode are easily excited when crowd walking dynamic loads are distributed on full bridge deck. When the crowd walking dynamic loads are distributed eccentrically on half width of the deck, the fundamental coupled torsional-lateral mode can be excited and large lateral deflection can be induced. Higher order vertical modes and coupled lateral-torsional modes can also be excited by groups of walking pedestrians under certain conditions. It is found that the coupling coefficient introduced in this thesis to describe the coupling of a coupled mode, is an important factor which has significant effect on the lateral dynamic performance of slender suspension footbridges. The coupling coefficient, however, is influenced by many structural parameters such as cable configuration, cable section, cable sag, bridge span and pre-tensions, etc. In general, a large dynamic amplification factor is expected when the fundamental mode of a footbridge structure is the coupled lateral-torsional mode with a small coupling coefficient. The research findings of this thesis are useful in understanding the complex dynamic behaviour of slender and vibration sensitive suspension footbridges under humaninduced dynamic loads. They are also helpful in developing design guidance and techniques to improve the dynamic performance of such slender vibration sensitive footbridges and similar structures and hence to ensure their safety and serviceability.

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Дисертації з теми "Non-linear dynamic analyses"

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