Investigating effective factors on risk perception, safety attitude and safety performance of construction workers of Shiraz city, 2012

Background and Aims: Construction sites are one of the most hazardous places in industries because of variety of activities, hazards and harmful agents. Therefore, workers employed in these sites are always exposed to risks of injuries. The aim of this study was to investigate the effective factors of risk perception, safety attitude and performance on construction workers.Materials and Methods: In this cross-sectional study, effective factors on risk perception, safety attitude and performance of 295 construction workers in Shiraz city were investigated. The study was conducted using a validated questionnaire which was completed through interview. Data were analyzed by using SPSS16. The level of significance was considered 0.05.Results: While the risk perception of 77.6 % of the study population was high, only 48.5 % had high safety attitude. However, 93.6% of construction workers had high safety performance. Among studied variables, association of risk perception with age, education and being witness of accident was significant. Moreover, the association of safety attitude with having insurance and safety performance with work experience, marital status and occurrence of accident for relatives was significant (p<0.05).Conclusion: The result of this study showed that by increasing risk perception of construction workers, their attitude and safety performance could be improved.Key words: Construction workers, Risk perception, Safety attitude, Construction sit

A Hierarchal Planning Framework for AUV Mission Management in a Spatio-Temporal Varying Ocean

The purpose of this paper is to provide a hierarchical dynamic mission planning framework for a single autonomous underwater vehicle (AUV) to accomplish task-assign process in a limited time interval while operating in an uncertain undersea environment, where spatio-temporal variability of the operating field is taken into account. To this end, a high level reactive mission planner and a low level motion planning system are constructed. The high level system is responsible for task priority assignment and guiding the vehicle toward a target of interest considering on-time termination of the mission. The lower layer is in charge of generating optimal trajectories based on sequence of tasks and dynamicity of operating terrain. The mission planner is able to reactively re-arrange the tasks based on mission/terrain updates while the low level planner is capable of coping unexpected changes of the terrain by correcting the old path and re-generating a new trajectory. As a result, the vehicle is able to undertake the maximum number of tasks with certain degree of maneuverability having situational awareness of the operating field. The computational engine of the mentioned framework is based on the biogeography based optimization (BBO) algorithm that is capable of providing efficient solutions. To evaluate the performance of the proposed framework, firstly, a realistic model of undersea environment is provided based on realistic map data, and then several scenarios, treated as real experiments, are designed through the simulation study. Additionally, to show the robustness and reliability of the framework, Monte-Carlo simulation is carried out and statistical analysis is performed. The results of simulations indicate the significant potential of the two-level hierarchical mission planning system in mission success and its applicability for real-time implementation

Modelling the fatigue crack growth in friction stir welded joint of 2024-T351 Al alloy

In this work the fatigue crack propagation within the friction stir welded (FSW) joint of 2024-T351 Al alloy is studied as well as fatigue lifetime of the joint using Walker and Nicholls models. The FSW joint is characterised in terms of the residual stress (using the hole drilling technique), material, and cyclic properties. The material surface is polished in order to avoid any surface irregularities. The crack initiation is detected applying scanning electron microscopy (SEM), however plastic replication technique is used to monitor the crack propagation. The concepts of crack closure, residual stress and stress relaxation are incorporated into both models. Finally the results are validated and compared together regarding to the experiments

Étude thermo-hydraulique de l'écoulement du modérateur dans le réacteur CANDU-6

Étant donné la taille (6,0 m×7,6 m) ainsi que le domaine multiplement connexe qui caractérisent la cuve des réacteurs CANDU-6 (380 canaux dans la cuve), la physique qui gouverne le comportement du fluide modérateur est encore mal connue de nos jours. L’échantillonnage de données dans un réacteur en fonction nécessite d’apporter des changements à la configuration de la cuve du réacteur afin d’y insérer des sondes. De plus, la présence d’une zone intense de radiations empêche l’utilisation des capteurs courants d’échantillonnage. En conséquence, l’écoulement du modérateur doit nécessairement être étudié à l’aide d’un modèle expérimental ou d’un modèle numérique. Pour ce qui est du modèle expérimental, la fabrication et la mise en fonction de telles installations coûtent très cher. De plus, les paramètres de la mise à l’échelle du système pour fabriquer un modèle expérimental à l’échelle réduite sont en contradiction. En conséquence, la modélisation numérique reste une alternative importante. Actuellement, l’industrie nucléaire utilise une approche numérique, dite de milieu poreux, qui approxime le domaine par un milieu continu où le réseau des tubes est remplacé par des résistances hydrauliques distribuées. Ce modèle est capable de décrire les phénomènes macroscopiques de l’écoulement, mais ne tient pas compte des effets locaux ayant un impact sur l’écoulement global, tel que les distributions de températures et de vitesses à proximité des tubes ainsi que des instabilités hydrodynamiques. Dans le contexte de la sûreté nucléaire, on s’intéresse aux effets locaux autour des tubes de calandre. En effet, des simulations faites par cette approche prédisent que l’écoulement peut prendre plusieurs configurations hydrodynamiques dont, pour certaines, l’écoulement montre un comportement asymétrique au sein de la cuve. Ceci peut provoquer une ébullition du modérateur sur la paroi des canaux. Dans de telles conditions, le coefficient de réactivité peut varier de manière importante, se traduisant par l’accroissement de la puissance du réacteur. Ceci peut avoir des conséquences majeures pour la sûreté nucléaire. Une modélisation CFD (Computational Fluid Dynamics) détaillée tenant compte des effets locaux s’avère donc nécessaire. Le but de ce travail de recherche est de modéliser le comportement complexe de l’écoulement du modérateur au sein de la cuve d’un réacteur nucléaire CANDU-6, notamment à proximité des tubes de calandre. Ces simulations servent à identifier les configurations possibles de l’écoulement dans la calandre. Cette étude consiste ainsi à formuler des bases théoriques à l’origine des instabilités macroscopiques du modérateur, c.-à-d. des mouvements asymétriques qui peuvent provoquer l’ébullition du modérateur. Le défi du projet est de déterminer l’impact de ces configurations de l’écoulement sur la réactivité du réacteur CANDU-6.----------Abstract Considering the size (6m×7.6 m) and the quite complex hydrodynamic domain of CANDU reactors (i.e. 380 fuel channels embded in the vessel), the motion of the the moderator flow in the calandria is still not perfectly understood until today. Data sampling process from a reactor in operation necessitates several modifications on the calandria vessel to get access to the core. Furthermore, the intense radiation area in the reactor core requires the use of quite particular measurement instruments. Consequently, the moderator flow must necessarily be studied through experimental and/or numerical models. Concerning experimental tests, fabrication and operation of such a huge facility is very expensive. Moreover, the scaling groups of CANDU reactors are in contradiction. Consequently, numerical simulations constitute an appealing. Because of the aforementioned constraints (i.e. complexity of the domain), the porous medium method has been used to study the moderator flow by the nuclear industry. This approach approximates the hydraulic domain as a continuous medium where, the tube bundle is replaced by hydraulic resistances. This model has the ability to predict macroscopic characteristics of the flow motion. However, it can not simulate the local effects such as temperature and velocity distributions near the calandria tubes. In the framework of nuclear safety, local effects around the calandria tubes are a point of high interest. Predictions of porous medium method previously showed that the moderator flow can develop several hydrodynamic configurations. For some, an asymmetric behaviour in calandria vessel was observed. This can result in boiling of the moderator flow at proximity of fuel channels. In such conditions, the reactivity coefficient can change significantly, resulting in variation of the reactor power. For this reason, a CFD model that takes into account the local effects is therefore necessary to study the motion of the moderator in the calandria. The purpose of this research is to model the complex behaviour of the flow moderator in CANDU-6 calandria, especially at proximity of calandria tubes. These simulations are used to identify possible flow configurations. This study is thus to formulate theoretical bases on behalf of macroscopic instabilities in the moderator, i.e. asymmetric motions which may cause boiling. The project’s challenge was to determine the impact of these flow configurations on the reactivity of CANDU reactor

Atomistic modeling of energetics and dynamics of diffusive and frictional phenomena in C60/graphene-based systems

Ph.DDOCTOR OF PHILOSOPH

Amélioration de la condition frontière de face de soufflante pour la conception de l'admission d'air sous distorsion

RÉSUMÉ La conception d'une prise d’air pour une turbine à gaz implique des calculs de dynamique des fluides (CFD) suivis d’évaluations expérimentales sur banc d’essai. Dans les deux cas, le moteur est pris en compte comme un puits de masse imposé à quelques rayons de pales de distance après le plan de la soufflante réelle. En général, cette approche est suffisante pour concevoir la géométrie d'admission d’air pour une faible distorsion de l’écoulement au niveau de la face de la soufflante. En réalisant ce type de modélisation, on ne prend pas en compte l’effet de l’interaction entre l’aube et l’écoulement sous distorsion. En réalité, la soufflante fait l’effort de compenser la distorsion de l’écoulement et le rendement de compresseur est influencé par la distorsion. Ces phénomènes ne sont pas considérés par l’imposition d’une condition frontière uniforme à la sortie de la prise d’air. À l’avenir, le positionnement des moteurs d’avion à réaction engendrera de nombreuses situations avec des niveaux de distorsion plus élevés en entrée de la soufflante. Dans ces cas, ne pas prendre en compte les pales de la soufflante conduit à des solutions CFD inexactes dans la prise d’air. Cette prise en compte lors de la phase conception de la prise d’air exigerait des calculs intensifs et coûteux, par exemple une modélisation 3-D instationnaire de l’aube. La solution proposée dans ce document pour le calcul CFD est la conception d’une nouvelle condition frontière appliquée sur le plan de la soufflante qui pourrait mieux représenter l’effet des pales de la soufflante sur l’écoulement dans la prise d’air en présence de distorsion. Cette nouvelle condition aux limites est une composition de plusieurs compresseurs en parallèle dont chacun influence l’écoulement d’une manière à atténuer la distorsion. La méthode est définie et validée selon le fonctionnement de soufflantes existantes.----------ABSTRACT The design of an intake for a gas turbine engine involves CFD-based investigations and experimental assessment in the intake test rig. In both cases, the engine is represented by a mass flux sink, usually imposed a few fan radius aft of the real fan face. In general, this approach is sufficient to design intake geometry for low distortion at the fan face. When considering future installations, many situations could arise when distortion level will be higher at the fan face. In these cases, the effect of the fan and its reaction on the distortion is expected to be more important. Situations could arise where flow separation in the intake could be triggered or suppressed when considering or not the coupling between the fan and the intake. An expensive solution would be to include the fan analysis during the intake design, but this solution is too computationally intensive to be useful in design mode. The solution proposed in this paper for the CFD is to design a new boundary condition applied to the plane of the fan that could better represent the effect of the fan blades on the flow in the intake air in the presence of distortion. This new boundary condition is defined as the operation of some existing fans. This new boundary condition is a composition of several compressors in parallel. Each of these compressors influences the flow in a manner to attenuate the flow distortion. The proposed method is defined and validated according to the operation of existing fans

A multi‐layer framework for energy efficiency assessment of shore‐to‐ship fast charging systems including onshore batteries

This paper proposes a three-layer framework for energy efficiency evaluation of Shore-to-Ship Charging (S2SC) systems using load-dependent loss models of the components. The considered S2SC system is supplied by the grid but is also supported by On-Shore Batteries (OSB). The presented approach is then used to investigate the impact of the specific design and operational parameters on energy efficiency. Power system architectures for three general S2SC solutions for ac, dc, and inductive charging are defined and compared in terms of energy efficiency. Operational parameters are also considered in the analysis, namely, the grid power ratio, determining the load sharing between the grid and the OSB, as well as the OSB charging profile. A case study is performed with peak charging power of 1 MW, and the most efficient S2SC solutions are identified for both ac- and dc-based onboard power systems. Moreover, it is shown that charging OSB with the highest available power from the grid between the charging breaks would often lead to higher energy efficiency than the maximum utilization of the available charging time. Field data from a real S2SC system is used to verify the estimated energy efficiency by the proposed framework. The analysis of the real case S2SC is then extended to include and verify a projected OSB. © 2022 The Authors. IET Electrical Systems in Transportation published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology.A multi‐layer framework for energy efficiency assessment of shore‐to‐ship fast charging systems including onshore batteriespublishedVersio