Many methods and equations have been developed to predict bed load transport rates, most of which use some comparison between shear stress and critical shear stress. The critical shear stress is determined by the point of incipient motion. Researchers have attempted to predict bed load transport both deterministically with mean parameters and stochastically attempting to take into account the fluctuations of velocity at points near threshold. This work attempts to show that more than simple force balances are needed to determine the point at which a particle will move. Turbulent fluctuations in velocity seem to have an effect of particle entrainment. The fluctuations in velocity can be several times greater than their time averaged counterparts. These short durations of high velocity often result in particle movement even though the mean flow may be less than or very near critical conditions. Through experiments of a single spherical particle on a simple bed geometry in air without the effects of water, it is shown that time duration of force has an effect on entrainment. This shows that there may be a constant force-time combination, or impulse, required to entrain sediment. / Master of Science

Content of this thesis deals with electromagnets as operating elements in electric machines. Thesis is divided in two main parts, theoretical and practical. The theoretical part describes electromagnets as electric machine , usage of electromagnets in electrical devices as operating element. Electromagnets are further divided in groups on basis of different criteria. Next, the theory of electromagnetic fields and methods of assesment of static pull and dynamic characteristics is described. Construction and function analysis of researched electromagnet with permanent magnets, which serves as trigger in compact circuit breaker, is also included in this part. Practical part includes measurement of force quantities of researched electromagnet in different operating states an its evaluation. For analysis of dynamic quantities with finite element method were created two-dimensional and three-dimensional models. Evaluation of analysis follows. After that is described simplified design of electromagnet, based onoperating states of researched electromagnet. This part is closed with comparation between results of analysis and designed values of electromagnets.

Content of this thesis deals with electromagnets as operating elements in electric machines. Thesis is divided in two main parts, theoretical and practical. The theoretical part describes electromagnets as an electric machine, usage of electromagnets in electrical devices as operating element. Electromagnets are further divided in groups on the basis of different criteria. Next, the theory of electromagnetic fields and methods of assesment of static pull and dynamic characteristics are described. Construction and function analysis of researched type of electromagnet from OEZ company with permanent magnets, which serves as trigger in compact circuit breaker, is also included in this part. Practical part includes measurement of force quantities of an electromagnet in different operating states and its evaluation. For analysis of dynamic quantities with finite element method was created suitable three-dimensional model of electromgnet. Model is used for simulation ofdifferent operating states.The last part describes measurement of dynamic characteristics of the electromganetic system. This part is closed with comparation of results.

As a solution to mid-air haptic actuation with strong and continuous tactile force, Magnetic Rendering is presented as an intuitive haptic display method applying an electromagnet array to produce a magnetic field in mid-air where the force field can be felt as magnetic repulsive force exerted on the hand through the attached magnet discs. The magnetic field is generated by a specifically designed electromagnet array driven by direct current. By attaching small magnet discs on the hand, the tactile sensation can be perceived by the user. This method can provide a strong tactile force on multiple points covering user’s hand and avoid cumbersome attachments with wires, thus it is suitable for a co-located visual and haptic display. In my work, the detailed design of the electromagnet array for haptic rendering purposes is introduced, which is modelled and tested using Finite Element Method simulations. The model is characterized mathematically, and three methods for controlling the magnetic field are applied accordingly: direct control, system identification and adaptive control. The performance of the simulated model is evaluated in terms of magnetic field distribution, force strength, operation distance and force stiffness. The control algorithms are implemented and tested on a 3-by-3 and a 15-by-15 model, respectively. Simulations are performed on a 15-by-15 model to generate a haptic human face, which results in a smooth force field and accurate force exertion on the control points.

This thesis deals with inductive flowmeters, specifically insertion inductive flowmeters. It examines in detail a blueprint of such flowmeter, consisting of probe, electromagnet, electrodes, exciting module and evaluation of signal. Gauging of a flowmeter designed this way, measuring data, charts, evaluation and interpretation. Consequent measurement in a calibration laboratory to elaborate, evaluate and interpret the results.

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No description available.

La réfrigération magnétique est une technologie émergente grâce à des avantages considérables par rapport aux technologies de réfrigération classiques. Cette technologie basée sur l’effet magnétocalorique offre d’importants avantages environnementaux car d’une part l’efficacité théorique des cycles utilisés est supérieure à celle des technologies classiques et d’autre part son fonctionnement ne nécessite pas une utilisation de gaz/vapeur `a fort effet de serre. En revanche des verrous scientifiques restent à lever, Le modèle multi-physique proposé dans cette thèse à pour but d’améliorer la précision de calcul. Il consiste à coupler un modèle 3D magnétostatique résolu par la méthode des éléments finis, un modèle magnétocalorique analytique et un modèle thermo-fluidique résolu par méthode des différences finies. Parallèlement, un banc d’essais a été conçu, optimisé et réalisé, ce banc permettra de faire des mesures fines des différents phénomènes qui interagissent dans la réfrigération magnétique. / The magnetic refrigeration technology is a promising alternative technology to the production of cold. The work of this thesis deals with studying and designing a magnetic refrigeration prototype. A multiphysic model is developed, this model taking into account several magnetic and magnetocaloric aspect that never dealt in the literature. It is used to investigate the influence of a range of parameters on the performance of the AMR. A new test bench of magnetic refrigeration is also designed, it is based on a particular electromagnet that was optimally realized. The magnetic performances are showed and concord with design prevision. Finally, suggestions for future works are provided based on the knowledge presented here.

The aim of the work was design and realization of device to simplify and speed up the testing of AWS / TPWS train protection system. The first chapter is addressed to description and division of train protection systems. The next chapter describes the process of commissioning the AWS / TPWS system and possible applycation of the device to this process. The final chapters deal with design, specification of components, realization of device and verification of its functionality.

The master thesis is focused on a remanent magnetism of electromagnets of DC contactors. In the first part of the thesis deals with the formation of a magnetic field in different kinds of materials, description of their magnetization and sorting. The next part is focused on the principle and history of an electromagnet. Negative effects and remanent induction of the contactor are described in the end of the theoretical part. The second part is a practical part. First, the reaction times were measured on a pair of DC contactors. Using the obtained data, an electronic circuit was designed to minimize the difference in switching times of the given DC contactors.