Over recent years, wireless communication systems have been experiencing a dramatic and continuous growth in the number of subscribers, thus placing extra demands on system capacity. At the same time, keeping Quality of Service (QoS) at an acceptable level is a critical concern and a challenge to the wireless network designer. In this sense, performance analysis must be the first step in designing or improving a network. Thus, powerful mathematical tools for analysing most of the performance metrics in the network are required. A good modelling and analysis of the wireless cellular networks will lead to a high level of QoS. In this thesis, different analytical models of various handoff schemes and resource re-allocation in homogeneous and heterogeneous wireless cellular networks are developed and investigated. The sustained increase in users and the request for advanced services are some of the key motivations for considering the designing of Hierarchical Cellular Networks (HCN). In this type of system, calls can be blocked in a microcell flow over to an overlay macrocell. Microcells in the HCN can be replaced by WLANs as this can provide high bandwidth and its users have limited mobility features. Efficient sharing of resources between wireless cellular networks and WLANs will improve the capacity as well as QoS metrics. This thesis first presents an analytical model for priority handoff mechanisms, where new calls and handoff calls are captured by two different traffic arrival processes, respectively. Using this analytical model, the optimised number of channels assigned to II handover calls, with the aim of minimising the drop probability under given network scenarios, has been investigated. Also, an analytical model of a network containing two cells has been developed to measure the different performance parameters for each of the cells in the network, as well as altogether as one network system. Secondly, a new solution is proposed to manage the bandwidth and re-allocate it in a proper way to maintain the QoS for all types of calls. Thirdly, performance models for microcells and macrocells in hierarchical cellular networks have been developed by using a combination of different handoff schemes. Finally, the microcell in HCN is replaced by WLANs and a prioritised vertical handoff scheme in an integrated UMTS/WLAN network has been developed. Simulation experiments have been conducted to validate the accuracy of these analytical models. The models have then been used to investigate the performance of the networks under different scenarios.

La congestion routière est le résultat d’un excès de la demande sur l’offre. Sur le réseau autoroutier en particulier, la congestion apparaît soit en section courante, soit au niveau des bretelles d’accès, des bretelles de sortie ou des zones d’entrecroisement qui sont généralement appelées les discontinuités ou nœuds du réseau routier. Les objectif de la thèse sont (i) d'apporter des éclairages sur la phénoménologie du trafic au droit des discontinuités du réseau autoroutier et (ii) de proposer des modèles macroscopiques pour en prédire le fonctionnement et évaluer des stratégies d'optimisation de l'écoulement du flux. Contrairement aux modèles existants, les modèles proposés dans cette thèse prennent en compte les phénomènes physiques du trafic en intégrant explicitement les comportements individuels des usagers. Après avoir présenté les outils méthodologiques et expérimentaux mobilisés, la thèse propose une analyse empirique des changements de voie à partir de données individuelles de trajectoires. Sur la base des résultats empiriques, la thèse présente ensuite les modèles analytiques développés qui sont utilisés dans une dernière partie pour proposer des stratégies d'optimisation de l'écoulement du flux du trafic. / The congestion occurs when the demand is higher than the supply. On the highway network, the congestion forms on the diverges, the merges and the weaving section which are generally named the discontinuities of the network. The thesis aims at (i) investigating the traffic phenomenology at the discontinuities of the highway network and (ii) developing macroscopic traffic flow model to forecast their operation and evaluate traffic regulations. Those models will explicitly integrate the drivers' microscopic behaviors. The thesis presents first the methodological and experimental tools. Then, it proposes an empirical analysis of the lane-changes at two merges and one weaving sections. The thesis describes the analytical models while it ends with operational applications of those models.

Uma metodologia para desenvolvimento de programas paralelos eficientes deve especificar mecanismos capazes de caracterizar o comportamento das aplicações e permitir estudos sobre o desempenho de diferentes modelos de soluções. Nos ambientes distribuídos, em particular, a eficiência da solução também está relacionada a estratégia utilizada na divisão e distribuição do trabalho entre os processos que cooperam na solução do problema. Para abordar estes aspectos, uma metodologia, denominada PEMPIs-Het (Performance Estimation of MPI Programs in Heterogeneous Systems), é especificada e apresentada nesta tese. A metodologia permite a modelagem, avaliação e predição de desempenho de programas paralelos em ambientes homogêneos e heterogêneos. Técnicas de modelagem analítica são utilizadas para representar o comportamento das aplicações no ambiente distribuído. Um modelo gráfico, denominado DP*Graph++, é proposto para ilustrar as principais estruturas do código da aplicação e facilitar análises sobre a complexidade algorítmica do programa. Algumas aplicações são modeladas e a precisão das predições é verificada através de testes experimentais. Os modelos de desempenho permitem uma estimativa pontual para o tempo de execução da aplicação. Entretanto, uma estratégia alternativa, baseada em intervalos de predição, também é discutida e avaliada. Algumas estratégias para balanceamento de carga de aplicações paralelas distribuídas são implementadas e avaliadas. Estasestratégias utilizam informações de um vetor com índices de desempenho (Vector of Relative Performances - VRP), gerados pelos modelos analíticos, para especificar a divisão e distribuição do trabalho. Estes índices caracterizam a capacidade computacional das máquinas. Uma formalização matemática é apresentada para explicar como os índices são determinados. ) Testes experimentais são realizados para verificar a aplicabilidade das estratégias e a eficiência no balanceamento das cargas. / A methodology for developing efficient parallel programs must specify mechanisms capable of characterizing the behavior of applications and allow studies on the performance of different solution models. In distributed environments, in particular, the solution efficiency is also related to strategy adopted in the division and distribution of work among the processes which cooperate in the solution of the problem. To address these issues, a methodology, called PEMPIs-Het (Performance Estimation of MPI Programs in Heterogeneous Systems), is specified and presented in this thesis. The methodology allows performance modeling, evaluation and prediction of parallel programs in homogeneous and heterogeneous environments. Analytical modeling techniques are used to represent the applications behavior in the distributed environment. A graph model, called DP*Graph++, is proposed to illustrate the main structures of the application code and facilitate some analyses about the program algorithmic complexity. Some applications are modeled and the accuracy of predictions is verified by experimental tests. The models allow estimate a punctual performance to the application execution time. Meanwhile, an alternative strategy, based on prediction intervals, is also discussed and evaluated. Some strategies for load balancing of distributed parallel applications are implemented and evaluated. These strategies use information from a vector with performance indexes (Vector of RelativePerformances - VRP), generated by analytical models to specify the division and distribution of work. These indexes characterize the machines computational capacity. A mathematical formalization is presented to explain how the rates are determined. Experimental tests are conducted to verify the applicability and effectiveness of the strategies in load balancing

Os enrijecedores à flexão ou bending stiffeners contemplados neste trabalho são componentes estruturais auxiliares utilizados em linhas flexíveis em suas conexões com unidades flutuantes em sistemas de produção de petróleo offshore. A configuração destes acessórios deve conferir à instalação uma variação gradual da rigidez à flexão próximo ao ponto de fixação da linha flexível à unidade flutuante, diminuindo sua curvatura e suavizando o campo de tensões, evitando assim que a linha ultrapasse a curvatura máxima estabelecida em projeto. Na análise estrutural destes acessórios, diversas simplificações geométricas são consideradas e, em geral, os modelos propostos partem de uma geometria cônica simples. Na prática, entretanto, é comum a existência de unidades que envolvem até quatro diferentes seções. Este trabalho apresenta uma análise estrutural estática destes componentes complexos por meio de um modelo linear elástico, analiticamente formulado, que resulta em uma equação diferencial não-linear de segunda ordem com coeficientes variáveis. O problema matemático de valor de contorno é então solucionado numericamente com um código desenvolvido em Matlab®, usando uma função interna baseada no método de colocação em oposição ao método de tiros, freqüentemente usado em trabalhos anteriores. Finalmente, soluções previamente obtidas por outros autores com modelos analítico-numéricos e com elementos finitos são utilizadas para validar as soluções aqui obtidas, seguidas de uma análise paramétrica da geometria complexa de novos enrijecedores à flexão, além de breve discussão sobre análise dimensional e questões normativas relacionadas ao projeto destes acessórios. / The bending stiffeners discussed in this work are ancillary structural components installed on flexible lines at their connections with floating units in offshore oil production systems. The configuration of these accessories must provide the installation with a gradual variation of the bending stiffness near the lines attaching point, smoothing the curvature and the stress field of the compliant structure therein fixed, thus avoiding exceeding its designed structural bending limit. In the structural analysis of these accessories, several geometric simplifications are considered and, in general, the proposed models start from a simple conic geometry. In practice, however, bending stiffeners geometries are not so simple. Indeed, units consisting of four different sections are common. This work presents a parametric static structural analysis of these complex components by means of an analytically formulated linear elastic model, which results in a second order non-linear differential equation with variable coefficients. The ensuing mathematical boundary value problem is then solved numerically with a code developed in Matlab®, using an internal function based on the collocation method as opposed to the shooting method, frequently used in previous works. Finally, solutions obtained previously by other authors, with analytical-numerical and finite element models, are used to validate the solutions obtained herein, followed by a parametric analysis of the complex geometry of new bending stiffeners, besides brief related dimensional analysis and normative discussions.

Uma metodologia para desenvolvimento de programas paralelos eficientes deve especificar mecanismos capazes de caracterizar o comportamento das aplicações e permitir estudos sobre o desempenho de diferentes modelos de soluções. Nos ambientes distribuídos, em particular, a eficiência da solução também está relacionada a estratégia utilizada na divisão e distribuição do trabalho entre os processos que cooperam na solução do problema. Para abordar estes aspectos, uma metodologia, denominada PEMPIs-Het (Performance Estimation of MPI Programs in Heterogeneous Systems), é especificada e apresentada nesta tese. A metodologia permite a modelagem, avaliação e predição de desempenho de programas paralelos em ambientes homogêneos e heterogêneos. Técnicas de modelagem analítica são utilizadas para representar o comportamento das aplicações no ambiente distribuído. Um modelo gráfico, denominado DP*Graph++, é proposto para ilustrar as principais estruturas do código da aplicação e facilitar análises sobre a complexidade algorítmica do programa. Algumas aplicações são modeladas e a precisão das predições é verificada através de testes experimentais. Os modelos de desempenho permitem uma estimativa pontual para o tempo de execução da aplicação. Entretanto, uma estratégia alternativa, baseada em intervalos de predição, também é discutida e avaliada. Algumas estratégias para balanceamento de carga de aplicações paralelas distribuídas são implementadas e avaliadas. Estasestratégias utilizam informações de um vetor com índices de desempenho (Vector of Relative Performances - VRP), gerados pelos modelos analíticos, para especificar a divisão e distribuição do trabalho. Estes índices caracterizam a capacidade computacional das máquinas. Uma formalização matemática é apresentada para explicar como os índices são determinados. ) Testes experimentais são realizados para verificar a aplicabilidade das estratégias e a eficiência no balanceamento das cargas. / A methodology for developing efficient parallel programs must specify mechanisms capable of characterizing the behavior of applications and allow studies on the performance of different solution models. In distributed environments, in particular, the solution efficiency is also related to strategy adopted in the division and distribution of work among the processes which cooperate in the solution of the problem. To address these issues, a methodology, called PEMPIs-Het (Performance Estimation of MPI Programs in Heterogeneous Systems), is specified and presented in this thesis. The methodology allows performance modeling, evaluation and prediction of parallel programs in homogeneous and heterogeneous environments. Analytical modeling techniques are used to represent the applications behavior in the distributed environment. A graph model, called DP*Graph++, is proposed to illustrate the main structures of the application code and facilitate some analyses about the program algorithmic complexity. Some applications are modeled and the accuracy of predictions is verified by experimental tests. The models allow estimate a punctual performance to the application execution time. Meanwhile, an alternative strategy, based on prediction intervals, is also discussed and evaluated. Some strategies for load balancing of distributed parallel applications are implemented and evaluated. These strategies use information from a vector with performance indexes (Vector of RelativePerformances - VRP), generated by analytical models to specify the division and distribution of work. These indexes characterize the machines computational capacity. A mathematical formalization is presented to explain how the rates are determined. Experimental tests are conducted to verify the applicability and effectiveness of the strategies in load balancing

The recovery characteristics of Bolu-Himmetoglu, Bolu-Hatildag, K&uuml / tahya- Seyit&ouml / mer, and Nigde-Ulukisla oil shale samples and Bati Raman, &Ccedil / amurlu, and Garzan crude oil samples were tested experimentally using retort and microwave heating techniques. Many parameters like heating time, porosity, water saturation were studied. To enhance the efficiency of the processes three different iron powders (i.e. / Fe, Fe2O3, and FeCl3) were added to the samples and the doses of the iron powders were optimized. While crude oil viscosities were measured to explain the fluid rheologies, since it is impossible to measure the shale oil viscosity at the laboratory conditions due to its very high viscosity, shale oil viscosities were obtained numerically by using the electrical heating option of a reservoir simulator (CMG, STARS 2007) by matching between the laboratory and numerical oil production and temperature distribution results. Then the field scale simulations for retorting of oil shale and crude oil fields were conducted. Since the microwave heating cannot be simulated by CMG, STARS, microwave heating was modeled analytically. In order to explain the feasibility of heating processes, an economic evaluation was carried out. The experimental, numerical, and analytical results show that field scale oil recovery from oil shales and heavy crude oils by electrical and electromagnetic heating could be economically viable. While microwave heating is advantageous from an operational point of view, retorting is advantageous if the technically feasibility of the study is considered.

Os enrijecedores à flexão ou bending stiffeners contemplados neste trabalho são componentes estruturais auxiliares utilizados em linhas flexíveis em suas conexões com unidades flutuantes em sistemas de produção de petróleo offshore. A configuração destes acessórios deve conferir à instalação uma variação gradual da rigidez à flexão próximo ao ponto de fixação da linha flexível à unidade flutuante, diminuindo sua curvatura e suavizando o campo de tensões, evitando assim que a linha ultrapasse a curvatura máxima estabelecida em projeto. Na análise estrutural destes acessórios, diversas simplificações geométricas são consideradas e, em geral, os modelos propostos partem de uma geometria cônica simples. Na prática, entretanto, é comum a existência de unidades que envolvem até quatro diferentes seções. Este trabalho apresenta uma análise estrutural estática destes componentes complexos por meio de um modelo linear elástico, analiticamente formulado, que resulta em uma equação diferencial não-linear de segunda ordem com coeficientes variáveis. O problema matemático de valor de contorno é então solucionado numericamente com um código desenvolvido em Matlab®, usando uma função interna baseada no método de colocação em oposição ao método de tiros, freqüentemente usado em trabalhos anteriores. Finalmente, soluções previamente obtidas por outros autores com modelos analítico-numéricos e com elementos finitos são utilizadas para validar as soluções aqui obtidas, seguidas de uma análise paramétrica da geometria complexa de novos enrijecedores à flexão, além de breve discussão sobre análise dimensional e questões normativas relacionadas ao projeto destes acessórios. / The bending stiffeners discussed in this work are ancillary structural components installed on flexible lines at their connections with floating units in offshore oil production systems. The configuration of these accessories must provide the installation with a gradual variation of the bending stiffness near the lines attaching point, smoothing the curvature and the stress field of the compliant structure therein fixed, thus avoiding exceeding its designed structural bending limit. In the structural analysis of these accessories, several geometric simplifications are considered and, in general, the proposed models start from a simple conic geometry. In practice, however, bending stiffeners geometries are not so simple. Indeed, units consisting of four different sections are common. This work presents a parametric static structural analysis of these complex components by means of an analytically formulated linear elastic model, which results in a second order non-linear differential equation with variable coefficients. The ensuing mathematical boundary value problem is then solved numerically with a code developed in Matlab®, using an internal function based on the collocation method as opposed to the shooting method, frequently used in previous works. Finally, solutions obtained previously by other authors, with analytical-numerical and finite element models, are used to validate the solutions obtained herein, followed by a parametric analysis of the complex geometry of new bending stiffeners, besides brief related dimensional analysis and normative discussions.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-07-11T12:45:47Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) AVALIAÇÃO DA DISPONIBILIDADE DE VIDEO SURVEILLANCE AS A SERVICE (VSAAS) - CarlosMagno_vFinal_.pdf: 9082644 bytes, checksum: c59974ef3892ac2c00ead6db128cf7f6 (MD5) / Made available in DSpace on 2016-07-11T12:45:47Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) AVALIAÇÃO DA DISPONIBILIDADE DE VIDEO SURVEILLANCE AS A SERVICE (VSAAS) - CarlosMagno_vFinal_.pdf: 9082644 bytes, checksum: c59974ef3892ac2c00ead6db128cf7f6 (MD5) Previous issue date: 2015-09-04 / CNPq / Nos últimos anos, sistemas de Video Surveillance as a Service (VSaaS) apresentam um aumento significativo na demanda por técnicas de segurança que elevem os níveis de confiabilidade do serviço. Em paralelo, o paradigma de Computação em Nuvem tornou-se uma importante ferramenta para serviços remotos da computação. O VSaaS entrega armazenamento de grande quantidade de dados. Em 2012, 50% do armazenamento em big data que necessitou serem analisados foram de vídeo de vigilância. Em geral, os vídeos têm um alto significado para seus proprietários, não permitindo longos períodos de interrupção. Com o objetivo de evitar baixos desempenhos e ampliar a qualidade dos serviços de vídeo são necessários mecanismos para garantir alta disponibilidade em VSaaS. Entretanto, esta tarefa é difícil sem gerar impacto no custo. O presente trabalho propõe dois sistemas de VSaaS que foram submetidos a análise de disponibilidade, por meio de modelos analíticos (RBD, CTMC e SPN). O primeiro sistema, denominado doméstico, foi caracterizado pelos elementos essenciais para uma estrutura básica do VSaaS para ser utilizado em casas e pequenos comércios. Estes sistemas geraram três arquiteturas que foram modeladas para a obtenção de fórmulas fechadas, elas são importantes para realização de análises. O modelo da arquitetura 1 foi validado e as outras arquiteturas variaram dessas. A arquitetura 3 teve a maior disponibilidade entre as outras arquiteturas, por possuir a quantidade maior de componentes replicados. O downtime (em horas) desta arquitetura comparada com a sem replicações foi em 36,89%. Por ela ter a maior disponibilidade, foi realizada uma análise de sensibilidade que mostrou o componente “Node” como o de maior impacto. No segundo sistema, foi apresentado um VSaaS de uma empresa, chamado empresarial, gerando 18 (dezoito) arquiteturas, uma delas comparada a arquitetura A1 (sem redundância), obteve uma redução significativa do downtime de 30% com um pequeno aumento no custo na ordem de 7%. Caso um determinado serviço exija um downtime menor, outra análise apontou uma arquitetura com redução de 80% ao aumentar 30% do custo. Diante desse panorama foram propostas e analisadas arquiteturas que podem auxiliar administradores a tomar importantes decisões na implementação de VSaaS. / In the last few years, Video Surveillance as a Service VSaaS has shown the significant increase in demand for security mechanisms to ensure reliability higher levels. In parallel, the Cloud Computing paradigm has become an important tool for remote computing services. VSaaS, for example, allows for storage large amounts of data. In 2012, 50% of big data storage were surveillance video and in general, videos have a high significance for their owners, not allowing long periods interruption. To avoid video services with low performance and increase the quality, mechanisms to ensure high availability in VSaaS are required. However, this task is difficult without generating a major impact on cost, so this paper proposes two VSaaS systems who underwent an availability analysis, using analytical models (RBD, CTMC, and SPN). The first system, entitled domestic, was characterized by essential elements of a basic structure VSaaS, for use in homes and small businesses. This system generated three architectures that were modeled to obtain closed formulas; they are important to performing analyzes. The model architecture one was validated, and other architectures vary these. The architecture three had the highest availability of the other architectures, by owning the largest number of replicated components. The downtime (in hours) this architecture compared to a without replication was 36.89%. For having the highest availability, a sensitivity analysis showed the "Node"component as the most relevant. In the second system, was showed a VSaaS in a company and has generated eighteen architectures. One of them compared to a baseline, we obtained a significant reduction in downtime (30%) and a small increase in cost (on the order of 7%). In case, of the service requires less downtime, another analysis pointed an architecture with a reduction 80% of downtime and increased 30% in the cost. We propose and analyze architectures that can help administrators make important decisions in the VSaaS implementation.

This thesis dealt with the techniques that could be used for the pre-assessment of contaminated sites. The goals of the thesis were based on a simple fact that every contaminated site possesses certain potential to degrade natural resources, specifically groundwater and land resources. The thesis focused on using mathematical and statistical techniques to predict the maximum length of contaminated plumes or Lmax, which it considered as a key parameter that could be used for the site assessment. As the first thesis work, data from KORA sites were compiled and analysed. From the analyses, it was found that the Lmax for BTEX plumes are in average under 150 m long. Further, for this work, Analytical Models that can be used to estimate Lmax were reviewed and, examples comparing model and fifield Lmax were presented. The second work for the thesis focused on a development and analysis of a new 3D-analytical model for a fifinite planar and fully penetrating source. An implicit expression for predicting Lmax was obtained. The analysis of the developed model suggested that the longest Lmax will result if the source takes an approximately square shape. The last part of the thesis improved the 3D-analytical model obtained in the second work by presenting an expression for a fifinite planar source that only partially penetrates the aquifer. For this work, a very simple numerical technique was developed that not only simplififies numerical analysis of the scenarios considered in this thesis but it also bears potentials to be used for very complex subsurface reaction transport scenarios. This thesis has been successful in narrowing research-gaps on problems related to contaminated sites management. / Diese Doktorarbeit befasste sich mit Methoden, welche für eine Vorabbewertung von kontaminierten Standorten genutzt werden können. Die Ziele der Arbeit basierten auf dem einfachen Fakt, dass jeder kontaminierte Standort ein bestimmtes Potential besitzt, natürliche Ressourcen, speziell Grundwasser- und Bodenressourcen, in ihrer Qualität negativ zu beeinträchtigen. Die Arbeit war auf die Nutzung mathematischer und statistischer Techniken zur Abschätzung der maximalen Schadstofffahnenlänge, auch Lmax, fokussiert, welche als entscheidender Parameter für die Standortbewertung genutzt werden kann. Der erste Teil der Doktorarbeit beinhaltete die Zusammenstellung und Analyse von Daten einer Vielzahl von KORA-Standorten. Anhand dieser Untersuchungen konnte festgestellt werden, dass Lmax von BTEX-Fahnen im Mittel unterhalb von 150 m liegt. Des Weiteren wurden für diese Arbeit analytische Modelle, welche für die Abschätzung von Lmax genutzt werden können, kritisch bewertet und vergleichende Beispiele zwischen mit Modellierung bestimmter und im Feld ermittelter Lmax präsentiert. Der zweite Teil der Doktorarbeit zielte auf die Entwicklung und Analyse eines neuen dreidimensionalen, analytischen Models für eine finite, planare und über die komplette Mächtigkeit vorherrschende Quelle ab. Es konnte ein impliziter mathematischer Ausdruck zur Vorhersage von Lmax gewonnen werden. Die Analyse des Models wies darauf hin, dass maximale Lmax erreicht werden, wenn die Quelle eine annähernd quadratische Form aufweist. Der letzte Teil der Doktorarbeit diente der Weiterentwicklung des dreidimensionalen, analytischen Modells aus dem zweiten Teil durch die Entwicklung eines Ausdrucks für eine finite, planare Quelle, welche jedoch nur teilweise die Mächtigkeit des Grundwasserleiters kontaminiert. Für diese Arbeit wurde ein sehr einfacher numerischer Ansatz entwickelt, welcher die numerische Analyse der in dieser Arbeit berücksichtigten Szenarien nicht einfach nur erleichtert, sondern auch das Potential beinhaltet diesen auf komplexe, reaktive Transportszenarien im Untergrund anzuwenden. Abschließend kann gesagt werden, dass diese Arbeit erfolgreich zur Verringerung von Forschungslücken in der Problematik des Managements kontaminierter Standorte beigetragen hat.

No / Trust management in mobile ad hoc networks (MANETs) has become a significant issue in securing routing protocols to choose reliable and trusted paths. Trust is used to cope with defection problems of nodes and stimulate them to cooperate. However, trust is a highly complex concept because of the subjective nature of trustworthiness, and has several social properties, due to its social origins. In this paper, a friendship-based trust model is proposed for MANETs to secure routing protocol from source to destination, in which multiple social degrees of friendships are introduced to represent the degree of nodes' trustworthiness. The model considers the behaviour of nodes as a human pattern to reflect the complexity of trust subjectivity and different views. More importantly, the model considers the dynamic differentiation of friendship degree over time, and utilises both direct and indirect friendship-based trust information. The model overcomes the limitation of neglecting the social behaviours of nodes when evaluating trustworthiness. The empirical analysis shows the greater robustness and accuracy of the trust model in a dynamic MANET environment.