Today's concrete is no longer a simple combination of cement, aggregates and water. With increased use of various types of waste materials as supplementary cementitious materials and chemical admixtures, material incompatibility problems have been observed in concrete construction. As a result, some of the greatest problems in concrete manufacturing occur when concrete does not stiffen or harden on time. To this end, a new innovative type of cementing technique (based on the principles of magnetorheology) is presented that allows for the real-time control over the stiffening or setting behavior of concrete. In traditional magnetorheological (MR) fluids, magnetic particles are mostly submerged in Newtonian carrier fluids using high volumetric contents (40-50%) of magnetic particles. A key interest in this work was to investigate if using a non-Newtonian carrier fluid like cement paste with low dosages of magnetic particles would yield an MR effect. Rheological tests were conducted on paste mixtures containing small dosages of magnetic particles (less than 2% volume fraction) and when a magnetic field was applied, it was determined that the shear resistance of the paste could be altered significantly. The response of the paste was found to be dependent on the magnitude of the applied field, concentration of the magnetic particles and surface chemistry of magnetic particles. Furthermore the magnetic particles used in this research to create the MR cement paste did not have any effect on cement hydration products or on compressive strength results. It was shown that the rheological behavior of cement paste could even be adapted to simulate "setting" behavior when an MR-based approach is used. Thus, the potential to create a cement-based material whose fresh state behavior can be adapted on-demand by the user to achieve a desired behavior may soon be a reality. Such a material can be useful in applications in which controlling the fresh-state behavior is critical, and could transform the way cement-based materials are cast. In addition, possibilities to create a smart cement-based composite from the fresh to the hardened state may be possible if the magnetic particles could later be used for structural health monitoring. / text

Disertační se práce se zabývala vývojem magnetoreologického (MR) tlumiče odpružení pro kosmonautiku. Dle současného stavu poznání jsou důležitými parametry pro semi-aktivně řízený tlumič pro kosmonautiku hermetické oddělení pracovní kapaliny od zbytku nosiče a krátká časová odezva tlumícího elementu. Těmto požadavkům vyhovuje magnetoreologický tlumič s vlnovcovou jednotkou. Magnetický obvod MR tlumiče pro kosmonautiku byl vyroben z feritového materiálu, který umožnil výrazně snížit časovou odezvu. Hermetičnost byla zajištěna použitím vlnovcové jednotky. Konstrukce takového typu tlumiče ovšem přináší celou řadu problémů. Vyvinutý MR tlumič s feritovým magnetickým obvodem dosahoval časové odezvy 4.1 ms a dynamického rozsahu 8. Během konstrukčních prací na MR tlumiči pro kosmonautiku byly hledány nové metody pro konstrukci semi-aktivně řízeného MR tlumiče s krátkou časovou odezvou. Konkrétně se jednalo o metodu eliminace vířivých proudů v magnetickém obvodu MR tlumiče, magnetostatický a transietní magnetický model, CFD model obtokové štěrbiny, hydraulický model MR tlumiče a jejich experimentální verifikace. Tyto nové metody umožní konstrukci MR tlumiče pro kosmonautiku lehčí, s nižší časovou odezvou a vyšším dynamickým rozsahem.

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This thesis deals with the experimental study of magnetorheological shaft seal. The purpose of this diploma thesis is to describe the operating parameters of rotational magnetoreological shaft seal. In thesis, the effects of magnetic field and shaft speed on the pressure resistance and braking torque are described. Operating parameters were measured by an experimental device. Research has shown that the magnetoreological seal is characterized by a high pressure resistant. Disadvantages are the high braking torque and leakage of carrier oil from the magnetorheological fluid. These problems have been solved by a new design of magnetic circuit, that has been identified as a magnetoreological gradient pinch seal (MRGPS).

In this study we introduce an elastic composite, which has been manufactured using a fine carbonyl iron powder coated with a polymeric dielectric shell and dispersed in a silicone elastomer in a way as it is typically done manufacturing magnetorheological elastomers. Due to the used filler such a material possesses the capability of exhibiting magneto- and electrorheological effects. Our experiments have shown that the application of the magnetic field to the composite results in the magnetorheological effect, which becomes stronger in the case of the additional application of an electric field.

Recently, based on the physics of viscosity, we developed a new technology, which utilizes electric or magnetic fields to change the rheology of complex fluids to reduce the viscosity, while keeping the temperature unchanged. The method is universal and applicable to all complex fluids with suspended particles of nano-meter, sub-micrometer, or micrometer size. Completely different from the traditional viscosity reduction method, raising the temperature, this technology is energy-efficient, as it only requires small amount of energy to aggregate the suspended particles. In this thesis, we will first discuss this new technology in detail, both in theory and practice. Then, we will report applications of our technology to energy science research. Presently, 80% of all energy sources are liquid fuels. The viscosity of liquid fuels plays an important role in energy production and energy conservation. With an electric field, we can reduce the viscosity of asphalt-based crude oil. This is important and useful for heavy crude oil and off-shore crude oil production and transportation. Especially, since there is no practical way to raise the temperature of crude oil inside the deepwater pipelines, our technology may play a key role in future off-shore crude oil production. Electrorehology can also be used to reduce the viscosity of refinery fuels, such as diesel fuel and gasoline. When we apply this technology to fuel injection, the fuel droplets in the fuel atomization become smaller, leading to faster combustion in the engine chambers. As the fuel efficiency of internal combustion engines depends on the combustion speed and timing, the fast combustion produces much higher fuel efficiency. Therefore, adding our technology on existing engines improves the engine efficiency significantly. A theoretical model for the engine combustion, which explains how fast combustion improves the engine efficiency, is also presented in the thesis. / Physics

The master thesis deals with design, manufacturing and testing of a prototype magnetorheological damper developed for Formula Student vehicle. The aim was to design and test the damper with similar damping properties to the vehicle as a conventional damper has. Target force-velocity curves were set using quarter car model and evaluated comparing minimal contact force of a tyre for conventional and newly developed damper characteristics. Structural analysis of designed parts, hydraulic and static magnetic analysis were performed. Manufacturing of a specific part magnetorheological damper part was described – piston. Manufactured prototype damper characteristics were evaluated.