Estimating the cost of new technology insertion into an existing (or new) operating environment is of great concern and interest for those entities that own and operate that technology. New technology has many cost requirements associated with it, for instance; design, manufacturing, operation, maintenance and disposal all add to the life-cycle cost of a technology. Estimation and planning methods are needed to better match the costs associated with technology life-cycle requirements (design, manufacturing, etc.) in order to optimize the spending of funds. By optimizing (or closely matching) predicted technology life-cycle costs to a budget the new technology system will have a high probability of operating more efficiently and will minimize costs. System Dynamics has been used to understand and simulate how complex systems of people and technologies operate over time. Decisions (such as how much funding is allocated when in a technology life-cycle) that occur temporally or in a complex environment (i.e., many causes and effects) can be simulated to evaluate the impact the decision may have. Currently, the majority of decision theories and tools are focused on one moment in time (event-focused) rather than including the dynamic nature that decisions can have over time. Evaluating decisions at one instant versus taking into account the life-cycle impact a decision can have, is especially important to the US Government, where investment decisions can involve billions of dollars today, but potentially hundreds of billions later for technology life-cycle requirements. The Navy has experienced large cost overruns in the implementation of new technologies especially in the operations, support and disposal life-cycle phases. There is a lack of detailed knowledge of the dynamic nature of the technology operations, support and disposal (OS&D) processes undertaken by aircraft-carrier builders and planners. This research effort is to better understand and simulate the dynamics prevalent in the new technology implementation process and use a dynamic modeling technique, namely, System Dynamics in our study. A System Dynamics model based on the information and data obtained from experts including; General Dynamics - Newport News Shipbuilding, the Naval Sea Command Cost Estimating Group, and Virginia Polytechnic and State University - System Performance Laboratory. The model was constructed to simulate and predict the cost of operating, maintaining and disposing of a new technology. The investigation of the dynamics yields four dominant behaviors that characterize the technology OS&D process. These four dynamic behaviors are; exponential growth, goal seeking, overshoot & collapse and S-shaped growth with overshoot. Furthermore, seven dynamic hypotheses in the system are investigated. The model predicts an increase in the risk and degradation of new technologies leads to an increase in the total costs in the technology OS&D process. Three interesting insights that lead to increased total OS&D costs were; an inequality between the requirements for OS&D and provided budget, any delay in additional funding being provided and that as the new technology system grew older, it became less costly to maintain. / Master of Science

Apesar dos sistemas hidráulicos estarem entre os mais antigos meios de transmissão de energia usados pelo homem, atualmente vem recebendo muita atenção nas pesquisas científicas. A busca por maios controle da energia gerada impulsionou um aumento da utilização e aplicação e novas investigações tecnológicas de tais sistemas. Além da alta capacidade de controle e precisão, a sensibilidade, rigidez, força e potência conferem aos sistemas hidráulicos um conjunto completo de propriedades, permitindo sua ampla aplicação nos mais diferentes ramos. Porém a não linearidade da dinâmica de suas partes faz a modelagem dos sistemas hidráulicos ser complexa. Sabendo que a bomba é a parte mais importante do circuito hidráulico, este estudo apresenta um modelo matemático e a simulação computacional de uma bomba de palhetas auto-compensada por pressão com controle tipo integral. O modelo teórico está baseado na aplicação leis da física em quatro partes das bomba: Lei de Newton no carretel de válvulas e no conjunto dos pistões e o anel, e, Lei da Conservação da Massa nos volume de controle sob a pressão de operação Po e no volume sob a pressão interna da carcaça (pressão no servo cilindro), Pcc. O comportamento do sistema foi verificado com a aplicação de uma carga hidráulica proporcionada por um orifício com abertura instantânea (entrada tipo degrau). Dessa maneira a pressão de operação, saída do sistema, apresenta um pequeno transiente no início da simulação e rapidamente entra em regime. No momento no qual a carga hidráulica atua o transiente volta e em seguida entra em regime com o mesmo valor que apresentava antes da entrada degrau, comportamento específico de sistemas com controle tipo PI, proporcional e integral. / Despite the hydraulic systems are among the oldest means of energy transmission used by man, currently they are receiving special attention in scientific researchs. The search for greater control of energy generated spurred an increase in the use and application of technology and new research such systems. Besides high capacity of control and precision, sensitivity, stiffness, speed, strength, power hydraulic systems give a complete set of properties allowing their wide applications in many different areas. But the non-linearity of the dynamics of its parts is the modeling of hydraulic system is complex. Knowing that pumb is the most important part of the hydraulic circuits, this study presents a mathematical model and computer stimulation of a vane-type pump offset by pressure with integral control type. The theoretical model is based on the application laws of physics in four parts of the pumb: Newton\'s law of the spool valves and the coupling of the piston ring and with the Law of Conservation of Mass in volumes of controlling the pressure, and the Po inside if the carcass (pressure in the slave cylinder), Pcc. The behavior of the system was checked with the application of a hydraulic load (request) type entry step. Thus the pressure, leaving the system, presents a transient at the beginning of the simulation and quickly enter into arrangements. At the moment in which the hydraulic load transient operates the back and then enter into arrangements with the same value as presented before the step, specific behavior of systems with full control type.

L ’intégration de systèmes mécaniques complexes soumis à des environnements vibratoirescontraignants nécessite de tenir compte, dès la conception, des sollicitations réelles d’usage.La thèse montre que l’environnement vibratoire ainsi que la durée d’exposition dépendent del’utilisation qui sera faite d’un système tout au long de son cycle de vie. L’ évaluation de sonl’utilisation repose sur l’ évolution conjointe du comportement des utilisateurs et du développementde la technologie du système.L’analyse de la sûreté de fonctionnement d’un système mécanique complexe a permis de considérerle système dans son ensemble et d’investiguer ainsi de fac¸on approfondie le comportementdynamique de composants critiques. La modélisation simple de systèmes mécaniques précisequalitativement et quantitativement les comportements dynamiques principaux et simule lessollicitations vibratoires auxquelles un composant critique identifié est soumis. Sur cette base, lamodélisation du comportement d’un composant mécanique permet d’ évaluer le dommage par fatiguequ’il subira. Cet indicateur apporte au concepteur une aide aux choix de la géométrie du composant.Enfin, l’environnement climatique ainsi que des impacts li ´es au fonctionnement interne du système,ont ´ et ´e pris en compte par la réalisation d’essais vibro-climatiques en fonctionnement. Ces étudesont été menées sur un système à pile à combustible intégré à un véhicule électrique à hydrogène.Elles ont permis de mettre au point un cheminement comme appui `a la conception des systèmesmécaniques complexes.Le cheminement pluridisciplinaire propos´e dans cette thèse repose donc sur l’interaction de travauxde recherche issus principalement des domaines de la sociologie, de la sûreté de fonctionnement etde la mécanique. / The integration of complex mechanical systems subject to stringent vibration environments requiresconsideration of the real conditions of use from the beginning of the design phase.The thesis shows that the vibration environment and the duration of exposure to this environmentdepend on the use of the system throughout its life cycle. The evaluation of its use is based on thejoint evolution of both the user behavior and the system technology development.The dependability analysis of a complex mechanical system leads to consider the system as a wholeand thus to investigate in depth the dynamic behavior of critical components. A basic modeling ofthe mechanical system allows to qualitatively and quantitatively identify key dynamic behaviors anddetermines the vibration loads to which selected critical components are subjected. On this basis,modeling the behavior of a mechanical component leads to assess its fatigue damage. This indicatorhelps the designer in his choice of component geometry.Finally, the climatic environment as well as effects related to the internal functioning of the system,have been taken into account by performing vibro-climatic tests of on an operating systems, i.e. a fuelcell system integrated into a hydrogen electric vehicle. This helped to develop a procedure to supportthe design of complex mechanical systems.

The disturbances and abnormalities occurring in the components of the Acetylcholine (ACh) neurocycle are considered one of the main features of cholinergic sicknesses like Parkinson’s and Alzheimer’s diseases. A fundamental understanding of the ACh neurocycle is therefore very critical in order to design drugs that keep the ACh concentrations in the normal physiological range. In this dissertation, a novel two-enzyme-two-compartment model is proposed in order to explore the bifurcation, dynamics, and chaotic characteristics of the ACh neurocycle. The model takes into consideration the physiological events of the choline uptake into the presynaptic neuron and the ACh release in the postsynaptic neuron. In order to approach more realistic behavior, two complete kinetic mechanisms for enzymatic processes pH-dependent are built: the first mechanism is for the hydrolysis reaction catalyzed by the acetylcholinesterase (AChE) and the other is for the synthesis reaction catalyzed by the cholineacetyltransferase (ChAT). The effects of hydrogen ion feed concentrations, AChE activity, ChAT activity, feed ACh concentrations, feed choline concentrations, and feed acetate concentrations as bifurcation parameters, on the system performance are studied. It was found that hydrogen ions play an important role, where they create potential differences through the plasma membranes. The concentrations of ACh, choline and acetate in compartments 1 and 2 are affected by the activity of AChE through a certain range of their concentrations, where the activity of AChE is inhibited completely after reaching certain values. A detailed bifurcation analysis over a wide range of parameters is carried out in order to uncover some important features of the system, such as hysteresis, multiplicity, Hopf bifurcation, period doubling, chaotic characteristics, and other complex dynamics. The effects of the feed choline concentrations and the feed acetate concentrations as bifurcation parameters are studied in this dissertation. It is found that the feed choline concentrations play an important role and have a direct effect on the ACh neurocycle through a certain important range of the parameters. However, the feed acetate concentrations have less effect. It is concluded from the results that the feed choline is a more important factor than the feed acetate in ACh processes. The effects of ChAT activity and the choline recycle ratio as bifurcation parameters, on the system performance are investigated. It was found that as the ChAT activity increases, ACh concentrations in compartments 1 and 2 increase continuously. The effect of the choline recycle ratio shows that choline reuptake plays a very critical role in the synthesis of ACh in compartment 1, where it supplies the choline as a substrate for the synthesis reaction by ChAT. The concentrations of ACh, choline and acetate in compartments 1 and 2 are affected by the choline recycle ratio through a certain range of the choline recycle ratio; then, they become constant as the choline recycle ratio increases further. It is concluded from our results that choline uptake is the rate limiting step in the ACh processes in both compartments in comparison to ChAT activity. Based on partial dissociation of the acetic acid in compartments 1, and 2 of the ACh cholinergic system, the two-parameter continuation technique has been applied to investigate the pH range to be closer to physiological ranges of pH values. In addition, static/dynamic solutions of the ACh cholinergic neurocycle system based on feed choline concentration as the main bifurcation parameter in both compartments have been investigated. The findings of the above studies are related to the real phenomena occurring in the neurons, like periodic stimulation of neural cells and non-regular functioning of ACh receptors. It was found that ACh, choline, acetate, and pH exist inside the physiological range associated with taking into consideration the partial dissociation of the acetic acid. The disturbances and irregularities (chaotic attractors) occurring in the ACh cholinergic system may be good indications of cholinergic diseases such as Alzheimer’s and Parkinson’s diseases. The results have been compared to the results of physiological experiments and other published models. As there is strong evidence that cholinergic brain diseases like Alzheimer’s disease and Parkinson’s disease are related to the concentration of ACh, the present findings are useful for uncovering some of the characteristics of these diseases and encouraging more physiological research.

The disturbances and abnormalities occurring in the components of the Acetylcholine (ACh) neurocycle are considered one of the main features of cholinergic sicknesses like Parkinson’s and Alzheimer’s diseases. A fundamental understanding of the ACh neurocycle is therefore very critical in order to design drugs that keep the ACh concentrations in the normal physiological range. In this dissertation, a novel two-enzyme-two-compartment model is proposed in order to explore the bifurcation, dynamics, and chaotic characteristics of the ACh neurocycle. The model takes into consideration the physiological events of the choline uptake into the presynaptic neuron and the ACh release in the postsynaptic neuron. In order to approach more realistic behavior, two complete kinetic mechanisms for enzymatic processes pH-dependent are built: the first mechanism is for the hydrolysis reaction catalyzed by the acetylcholinesterase (AChE) and the other is for the synthesis reaction catalyzed by the cholineacetyltransferase (ChAT). The effects of hydrogen ion feed concentrations, AChE activity, ChAT activity, feed ACh concentrations, feed choline concentrations, and feed acetate concentrations as bifurcation parameters, on the system performance are studied. It was found that hydrogen ions play an important role, where they create potential differences through the plasma membranes. The concentrations of ACh, choline and acetate in compartments 1 and 2 are affected by the activity of AChE through a certain range of their concentrations, where the activity of AChE is inhibited completely after reaching certain values. A detailed bifurcation analysis over a wide range of parameters is carried out in order to uncover some important features of the system, such as hysteresis, multiplicity, Hopf bifurcation, period doubling, chaotic characteristics, and other complex dynamics. The effects of the feed choline concentrations and the feed acetate concentrations as bifurcation parameters are studied in this dissertation. It is found that the feed choline concentrations play an important role and have a direct effect on the ACh neurocycle through a certain important range of the parameters. However, the feed acetate concentrations have less effect. It is concluded from the results that the feed choline is a more important factor than the feed acetate in ACh processes. The effects of ChAT activity and the choline recycle ratio as bifurcation parameters, on the system performance are investigated. It was found that as the ChAT activity increases, ACh concentrations in compartments 1 and 2 increase continuously. The effect of the choline recycle ratio shows that choline reuptake plays a very critical role in the synthesis of ACh in compartment 1, where it supplies the choline as a substrate for the synthesis reaction by ChAT. The concentrations of ACh, choline and acetate in compartments 1 and 2 are affected by the choline recycle ratio through a certain range of the choline recycle ratio; then, they become constant as the choline recycle ratio increases further. It is concluded from our results that choline uptake is the rate limiting step in the ACh processes in both compartments in comparison to ChAT activity. Based on partial dissociation of the acetic acid in compartments 1, and 2 of the ACh cholinergic system, the two-parameter continuation technique has been applied to investigate the pH range to be closer to physiological ranges of pH values. In addition, static/dynamic solutions of the ACh cholinergic neurocycle system based on feed choline concentration as the main bifurcation parameter in both compartments have been investigated. The findings of the above studies are related to the real phenomena occurring in the neurons, like periodic stimulation of neural cells and non-regular functioning of ACh receptors. It was found that ACh, choline, acetate, and pH exist inside the physiological range associated with taking into consideration the partial dissociation of the acetic acid. The disturbances and irregularities (chaotic attractors) occurring in the ACh cholinergic system may be good indications of cholinergic diseases such as Alzheimer’s and Parkinson’s diseases. The results have been compared to the results of physiological experiments and other published models. As there is strong evidence that cholinergic brain diseases like Alzheimer’s disease and Parkinson’s disease are related to the concentration of ACh, the present findings are useful for uncovering some of the characteristics of these diseases and encouraging more physiological research.

For roughly fifteen years the military has sought to use the properties of ceramics for armor applications. Current high-performance ceramics have extremely high compressive strengths and low densities. One ceramic that has been shown to be highly resistant under ballistic impact is silicon carbide (SiC). It has been found that even within the silicon carbides, those manufactured by certain methods and those with certain microstructural properties have advantages over others. In order to understand the microstructural reasons behind variations in ballistic properties, plate impact tests were conducted on two sintered silicon carbides with slightly different microstructures. Two variations of a silicon carbide with the trade name Hexoloy SA were obtained through Saint Gobain. Regular Hexoloy (RH) and Enhanced Hexoloy (EH) are pressureless sintered products having exactly the same chemistries. EH went through additional powder processing prior to sintering, producing a final product with a slightly different morphology than RH. Samples of each were characterized microstructurally including morphology, density, elastic wavespeeds, microhardness, fracture toughness, and flexure strength. The characterization revealed differences in porosity distribution and flexure strength. It was determined that the porosity distribution in EH had fewer large pores leading to an 18% increase in flexural strength over that for RH. The focus of the mechanics of materials community concerning dynamic material behavior is to pin down what exactly is happening microstructurally during ballistic events. Several studies have been conducted where material properties of one ceramic type are varied and the dynamic behavior is tested and analyzed. Usually, from one variation to the next, several properties are different making it hard to isolate the effect of each. For this study, the only difference in the materials was porosity distribution. Plate impact experiments were conducted at the Army Research Laboratory (ARL) using the gas gun facilities within the Impact Physics Branch. A VISAR was utilized to measure free surface velocities. Tests were performed on each material to determine the Hugoniot Elastic Limit (HEL) and spall strength. Spall strength was measured as a function of impact stress, and pulse duration.

Au cours des dernières quarante années un grand nombre d'études ont analysé les comportements de possession et utilisation des véhicules. Cependant, la plupart de ces études traitent le problème d'un point de vue statique, en omettant les dynamiques qui vraisemblablement guident ces décisions. Le caractère durable des véhicules suggère l'importance de ne pas ignorer l'aspect dynamique des problèmes d'achat, possession et utilisation automobile. Ce travail utilise une approche désagrégée structurelle, basée sur des choix. Le document est composé de trois parties. La première propose une description du problème, par l'analyse de la littérature existante. La seconde présente les opérations préliminaires effectuées sur la base "Parc Auto" pour pouvoir l'utiliser comme panel de véhicules. La dernière partie a pour objectif d'introduire les quatre applications réalisées au cours de ma thèse de doctorat. Une première application propose une approche hédoniste des prix des véhicules. Le deuxième chapitre de cette dernière partie estime un modèle de Rust pour des ménages mono-équipés (c'est à dire une seule voiture à disposition par année) les décisions concernant leur voiture. Un modèle dynamique discret\continu des choix de la durée de possession et d'utilisation des véhicules pour des agents tant myopes que prévoyants. Le dernier chapitre présente un programme dynamique tourné vers le futur pour le problème de la planification des achats. Dans les trois applications, un facteur d'actualisation est utilisé pour tester différents hypothèses de comportement dynamique. Mes résultats indiquent que la préférence temporelle d'un ménage est un élément crucial dans étude de ces décisions. / During the last fort Y years, a large number of studies have analyzed the behaviors related to car holding and use. However, the majority of these studies consider the subject from a static point of view, ignoring the household dynamics and the driver's needs, which are very likely to drive such decisions. The durable character of a vehicle suggests however that such a dynamic cannot be ignored in the study of the vehicle purchase, holding and use decisions. This work employs a disaggregated, structural approach based on real choice to address these dynamics. The document is composed of three parts. In the first part a description of the problem is provided through an analysis of the available literature. The second part includes the description of the operations which are performed on "Parc Auto". This database needs in fact some preliminary treatment if one wants to use it as a vehicle's Panel. In the last part the four applications considered are presented. A first application proposes a hedonic approach to the vehicles' prices. The second chapter of this last part estimates the Rust model for mono-equipped (Le. only one car owned each year) households' decisions concerning their car. A dynamic discrete\continuous choice model of car holding duration and use for both myopic and forward-Iooking agents follow. ln the last chapter a dynamic forward-Iooking program for the purchase planning problem is presented. ln the three dynamic applications, a discount factor tests different effects of dynamic behavior. My findings indicate that a household's time preference is a crucial element in studying these decisions.

Le présent travail de thèse a pour objectif de développer un outil de modélisation par transition d’échelles sous forme de machine d’essais virtuels. Celle-ci, utilisée conjointement aux codes de calculs de structures, permet de déterminer le comportement anisotrope complexe de composites à matrice polypropylène chargés en fibres de verre courtes sous sollicitations dynamiques. La microstructure en cœur-peau induite par le procédé d’injection du matériau est investiguée expérimentalement par μCT. Le comportement dynamique est caractérisé pour des vitesses de déformation allant jusqu’à 200s-1 au moyen d’une une méthodologie expérimentale basée sur l’utilisation d’un joint d’amortissement et d’une optimisation des éprouvettes. Les mécanismes d’endommagement sont analysés expérimentalement par essai in situ. Ils mettent en évidence le phénomène d’endommagent prépondérant qui est la décohésion de l’interface fibre matrice. Basé sur ces résultats expérimentaux, l’approche multi échelles développée consiste en une méthode de Mori Tanaka incrémentale appliquée à une matrice élastoviscoplastique et des renforts enrobés intégrant l’évolution de l’endommagement à l’échelle mésoscopique. L’endommagement introduit dans les enrobages perturbe le transfert de charge entre la matrice et les renforts. De plus, la dépendance à la vitesse de déformation, aux orientations et aux taux de fibre du modèle sont corrélés par des essais. La machine d’essais virtuels est validée par modélisation de structures. L’outil prédictif ainsi développé prend en compte le minimum nécessaire à la description de la microstructure tout en étant fiable et pertinent dans la modélisation de composites sous sollicitations dynamiques modérées. / The current work focuses on the development of a micromechanical modeling tool in the form of a virtual test machine which, used with the structural calculation codes, allows to determine the complex anisotropic behavior of polypropylene matrix composites reinforced with short glass fibers under dynamic loading. The core-skin microstructure induced by the material injection process is investigated experimentally by μCT. The dynamic behavior is characterized for strain rates of up to 200s-1 using an experimental methodology based on the use of a damping joint and specimen optimization. The mechanisms of damage are analyzed experimentally by in situ SEM testing. They highlight the importance of the debonding phenomenon in the damage scenario. Based on these experimental results, the multiscale approach developed consists of an incremental Mori Tanaka method applied to an elastoviscoplastic matrix and coated reinforcements integrating the evolution of damage at the mesoscopic scale. The damage introduced into the coatings disturbs the load transfer between the matrix and the reinforcements. In addition, the strain rate, orientation, and fiber rate dependence of the model are correlated by testing. The virtual testing machine is validated by modeling structures. The developed predictive tool thus takes into account the minimum necessary to describe the microstructure while being reliable and relevant in the modeling of composites under moderate dynamic stress.

Apesar dos sistemas hidráulicos estarem entre os mais antigos meios de transmissão de energia usados pelo homem, atualmente vem recebendo muita atenção nas pesquisas científicas. A busca por maios controle da energia gerada impulsionou um aumento da utilização e aplicação e novas investigações tecnológicas de tais sistemas. Além da alta capacidade de controle e precisão, a sensibilidade, rigidez, força e potência conferem aos sistemas hidráulicos um conjunto completo de propriedades, permitindo sua ampla aplicação nos mais diferentes ramos. Porém a não linearidade da dinâmica de suas partes faz a modelagem dos sistemas hidráulicos ser complexa. Sabendo que a bomba é a parte mais importante do circuito hidráulico, este estudo apresenta um modelo matemático e a simulação computacional de uma bomba de palhetas auto-compensada por pressão com controle tipo integral. O modelo teórico está baseado na aplicação leis da física em quatro partes das bomba: Lei de Newton no carretel de válvulas e no conjunto dos pistões e o anel, e, Lei da Conservação da Massa nos volume de controle sob a pressão de operação Po e no volume sob a pressão interna da carcaça (pressão no servo cilindro), Pcc. O comportamento do sistema foi verificado com a aplicação de uma carga hidráulica proporcionada por um orifício com abertura instantânea (entrada tipo degrau). Dessa maneira a pressão de operação, saída do sistema, apresenta um pequeno transiente no início da simulação e rapidamente entra em regime. No momento no qual a carga hidráulica atua o transiente volta e em seguida entra em regime com o mesmo valor que apresentava antes da entrada degrau, comportamento específico de sistemas com controle tipo PI, proporcional e integral. / Despite the hydraulic systems are among the oldest means of energy transmission used by man, currently they are receiving special attention in scientific researchs. The search for greater control of energy generated spurred an increase in the use and application of technology and new research such systems. Besides high capacity of control and precision, sensitivity, stiffness, speed, strength, power hydraulic systems give a complete set of properties allowing their wide applications in many different areas. But the non-linearity of the dynamics of its parts is the modeling of hydraulic system is complex. Knowing that pumb is the most important part of the hydraulic circuits, this study presents a mathematical model and computer stimulation of a vane-type pump offset by pressure with integral control type. The theoretical model is based on the application laws of physics in four parts of the pumb: Newton\'s law of the spool valves and the coupling of the piston ring and with the Law of Conservation of Mass in volumes of controlling the pressure, and the Po inside if the carcass (pressure in the slave cylinder), Pcc. The behavior of the system was checked with the application of a hydraulic load (request) type entry step. Thus the pressure, leaving the system, presents a transient at the beginning of the simulation and quickly enter into arrangements. At the moment in which the hydraulic load transient operates the back and then enter into arrangements with the same value as presented before the step, specific behavior of systems with full control type.

Because of property damage and people injuries in, almost, every year in different locations of the earth, unfortunately the topic of understanding trees and their risk assessments under wind forces has not lost its importance since approximately a half of the last century. In contrast to loss its importance, the number of researchers or studies increases with time thanks to inter-disciplinary studies on that topic. In this Thesis, tree dynamics and their risk assessments subjected to wind forces were addressed by two different disciplines (civil engineering and environmental conservation). To mention includes of this inter-disciplinary study, first, a finite element modeling was developed for a real tree in Belchertown, MA. Then this modeling was compared with the experimental tests. After comparing the model and the tests of the real tree, same methodology of the modeling was, again, applied to a different tree in Amherst, MA. Second, a number of wind samples were generated randomly in order to apply to the models of the trees. Then, by comparing the moments at the stem of the trees and calculated maximum moments of the stems, the fragility curves of the failures of these trees was obtained with respect to mean wind-speed of the random wind samples. Third, the decay effects on the fragility curves were investigated by considering decreasing moment capacity of tree cross-sections due to decays. Finally, crown structure effects on tree dynamics were examined by several parametric studies which were applied to the tree in Belchertown, MA. These parametric studies refer to separately changes in several physical (such as stem diameter, branch slenderness ratio etc.) and material property (MOE) of the tree. Thus, thanks to these parametric studies, tree dynamics were understood better and the complex relationship between the stem and branches of the tree was explained better. Those better understandings, off course, produced several important practical outcomes for the life of the trees and as well as human-being.