Single wall carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) were dispersed in mineral oil and epoxy resin. The magnetorheological properties of these dispersions were studied using a parallel plate rheometer. Strain sweeps, frequency sweeps, magneto sweeps and steady shear tests were conducted in various magnetic fields. G', G", h* and ty increased with increasing magnetic field, which was partially attributed to the increasing degree of the alignment of nanotubes in a stronger magnetic field. The SWNT/mo dispersions exhibited more pronounced magnetic field dependence than SWNT/ep and MWNT/mo counterparts due to their much lower viscosity. The alignment of SWNTs in mineral oil increased with rising nanotube concentration up to 2.5vol% but were significantly restricted at 6.41vol% due to nanotube flocculation.

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Combining shock and vibration isolation into a single isolation system package is explored through the use of an air spring in parallel with a controlled magnetorheological fluid damper. The benefits of combining shock and vibration isolation into a single package is discussed. Modeling and control issues are investigated and test and simulation results are discussed. It is shown that this hybrid isolation system provides significantly increased performance over current state-of-the-art passive systems. Also explored is the feasibility of scavenging and storing ambient shipboard vibration energy for use in powering the isolation system. To date the literature has not adequately explored the direct design of a combined shock and vibration isolation system. As shock and vibration isolation are typically conflicting goals, the traditional approach has been to design separate shock and vibration isolation systems and operate them in parallel. This approach invariably leads to compromises in terms of the performance of both systems. Additionally, while considerable research has been performed on magnetorheological fluids and devices based on these fluids, there has been little research performed on the use of these fluids in devices that are subjected to high velocities such as the velocity seen by a ship exposed to underwater near-miss explosive events. Also missing from the literature is any research involving the scavenging and storage of ambient shipboard vibration energy. While the focus of this work is on the use of this scavenged energy to power the subject isolation system, many other uses for this energy can be envisioned. Experimental and analytical results from this research clearly show the advantages of this hybrid isolation system. Drop tests show that inputs as great as 167 g's were reduced to 3.42 g's above mount at 1.11 inches of deflection using a Velocity Feedback controller suggested by the author. When contrasted with typical test results with similar inputs, the subject isolation system achieved reductions in above mount accelerations of 300% and reductions in mount deflections of 200% over current state-of-the-art passive shipboard isolation systems. Furthermore, simulations using a validated model of the isolation system suggest that this performance improvement can be achieved in multi-degree-of-freedom isolation systems as well. It was shown that above mount accelerations in the vertical and athwartship directions could be effectively limited to a predefined value, while achieving the absolute minimum mount defections, using an Acceleration Limiting Bang-Bang controller suggested by the author. Further experimentation suggests that the subject isolation system could be entirely self-powered from scavenged ambient shipboard vibration energy. An experiment using an energy scavenging and storage system consisting of a Piezoelectric Stack Generator and a bank of ultracapacitors showed that enough energy could be harvested to power the isolation system though several shock events. / Ph. D.

Magnetorheolgical (MR) fluid dampers have the capability of changing their effective damping force depending on the current input to the damper. A number of factors in the construction of the damper, as well as the properties of the fluid and the electromagnet, create a dynamic response of the damper that cannot be fully described with a static model dependent on current and velocity. This study will compare different techniques for modeling the force response of the damper in the current-velocity space. To ensure that all the dynamic response characteristics of the damper are captured in data collection, random input signals were used for velocity and current inputs. By providing a normally distributed random signal for velocity to a shock dynamometer and a uniformly distributed random signal for current to a Lord rheonetic seat damper, the force response could be measured. The data from this test is analyzed as a two dimensional signal, a three dimensional force plot in the current velocity plane, and as a probability density function. Four models are created to fit the data. The first is a linear model dependent solely on current. The second is a nonlinear model dependent on both current and velocity. The third model takes the nonlinear model and includes a filter that affects the force response of the model with time. Each of these three approaches are compared based on the total error in the force response and the models? ability to match the PDF of the data. Finally, a fourth model is created for the damper that improves the nonlinear model by making one parameter a probability parameter defined by a PDF calculated from the data. However, because it is a probability model, the error cannot be found through comparison to the data. / Master of Science

The constituent parts of a magnetorheological (MR) sandwich beam combine to create a powerful damping device. The apparent viscosity of an MR fluid can change with the application of an adjacent magnetic field. Typically, this apparent viscosity rises as the field gets stronger. The resulting resistance to motion makes MR fluids a great choice for damping applications. The sandwich beam is a composite structure with two elastic outer layers and a damping material in between that forms the core layer. Using MR fluid as the damping agent produces good and tunable damping performance while possessing the benefits of a sandwich beam, such as its ease of construction and its form factor. This dissertation pursues two goals. The first goal is related to modeling a beam's dynamics. In addition to creating a new beam model, this research tests the limitations of the DiTaranto model, a popular model in the literature. The second goal is to apply time-varying magnetic fields to the beam to balance damping performance and electromagnet power consumption when the beam undergoes free-decay vibration. The model findings showed that while the DiTaranto model works better than the proposed models, this beam model tends to work best for stiffer outer layers and for electromagnets (assuming they do not span the beam's entire length) placed at the beam's middle or free end, while softer outer layers lead to improved damping performance. With respect to the free-decay analysis, time-varying magnetic fields can possess comparable or faster decay when compared to a constant magnetic field; turning the field on or off during free decay leads to slightly decreased damping performance but with less power consumption for stiffer beams, while softer beams can enjoy both reduced consumption and increased damping when using a damping method like synchronous switch damping.

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.

This thesis deals with design of testing stand for operating parameters magnetic seal. In this thesis was done analysis of construction magnetic circuit and analysis of operating parameters. This work contains FEM analysis of magnetic circuit and experimental tune up. The results of this analysis will be used for design magnetic circuit and geometric sensitivity analysis in test stand.

The better understanding of the behavior of emulsions and suspensions is important in many applications. In general, emulsions allow the delivery of insoluble agents to be uniformly distributed in a more efficient way. At the same time suspensions of rigid particles are used as “smart materialsâ€� as their properties can be changed by the interaction with a magnetic or electric field. In the first part of the talk we consider a periodic emulsion formed by two Newtonian fluids in which one fluid is dispersed under the form of droplets of arbitrary shape, in the presence of surface tension. We assume the droplets have fixed centers of mass and are only allowed to rotate. We are interested in the time-dependent, dilute case when the characteristic size of the droplets aε, of arbitrary shape, is much smaller than the period length ε. We obtain a Brinkman type of fluid flow for the critical size aε = O(ε3) as a replacement of the Stokes flow of the emulsion. Additionally, using Mosco convergence and semigroup theory we extend the convergence to the parabolic case. For the case when the droplets convect with the flow, it can be shown again using Mosco-convergence that, as the size of the droplets converges to zero faster than the distance between the droplets, the emulsion behaves in the limit like the continuous phase and no “strangeâ€� term appears. Moreover, we determine the rate of convergence of the velocity field for the emulsion to that of the velocity for the one fluid problem in both the H1 and L2 norms. Additionally, a second order approximation is determined in terms of the bulk and surface polarization tensors for the cases of uniform and non-uniform surface tension. The second part of the talk is devoted to the study of MR fluids. We consider a suspension of rigid magnetizable particles in a non-conducting, viscous fluid with an applied external magnetic field. Thus, we use the quasi-static Maxwell equations coupled with the Stokes equations to capture the magnetorheological effect. We upscale using two scale asymptotic expansions to obtain the effective equations consisting of a coupled nonlinear system in a connected phase domain as well as the new constitutive laws. The proposed model generalizes the model of Rosenweig by coupling the velocity of the fluid and the magnetic field intensity. Using the finite element method we compute the effective coefficients for the MR fluid. We analyze the resulting MR model for Poiseuille and Couette flows and compare with experimental data for validation.

There are several ways in which a disability can occur. Strokes are a leading cause, affecting older people in particular, with an estimated annual incidence rate of 180, 125, 200, and 280 per 100,000 citizens in the USA, Europe, England, and Scotland, respectively. Muscle strengthening through resistance training has been reported to have a positive effect on the recovery of normal physiological functions after the occurrence of a neurological or traumatic injury. A number of studies have shown that resistance training results in improved mobility, a reduction in pain, and improved stability. Several rehabilitation devices have been developed and introduced for use in the healthcare sector, but a new generation of intelligent therapy-assisted machines is needed if there is to be a significant impact on the numbers of patients that can be treated under current staffing level. In this project, the design and performance of multi-degree-of-freedom smart balland-socket dampers and their application to fully-controllable rehabilitation training systems were investigated. A key feature of these dampers is the use of magnetorheological (MR) fluids which can exhibit dramatic changes in their rheological properties, such as yield stress, when subjected to external magnetic fields. These fast and reversible fluid rheological changes would permit the smart damper to provide the required impedance at orthotic arm joints, which are aimed for upper-limb rehabilitations and in accord with the exercise specifications prescribed by the physiotherapist. An exemplar upper-limb orthotic arm incorporating smart ball-and-socket dampers at its joints was assessed using SolidWorks software and the results confirmed the response of the dampers to variable excitation inputs under an input simulating a wheelchair driving motion. This study also enabled the estimation of the orthotic arm reach envelope, task performance and limitations in which important device design factors such as the angle of rotation of the smart dampers were taken into account. Although, three smart dampers with variable torque resistance capability are required at the shoulder, elbow and wrist joints of upper-limb rehabilitation orthoses, this project was focused on the development of a smart ball-and-socket damper aimed for the shoulder joint only. The target was to produce a compact smart electromagnetic damper that is capable to deliver the required torque resistance with the least power consumption. The efficient excitation of MR fluids requires a magnetic circuit, which consists of a source of magnetic flux and a path to deliver it to the fluid. Electromagnetic finite element analysis using Ansys software were carried out to achieve the optimum design of the damper’s electromagnetic circuit. The effects of the relative permeability of the damper’s materials on the generation of the magnetic field and its delivery to the MR fluid were examined. Other factors such as the coil shape, size, orientation and location in addition to the utilisation of non-magnetic materials in the electromagnetic circuit design were also investigated with the aim to optimise the performance of the smart damper. Furthermore, 3-D electromagnetic analyses were conducted, which confirmed the validity of the 2-D magnetic trials. Accordingly, the size of the MR fluid ball-and-socket damper was estimated with a ball diameter of 100 mm, which was found to produce a braking torque of about 50 N.m when the MR fluid is energised by about 1 Tesla. The performance of the ball-and-socket damper was estimated using theoretical, and numerical approaches. The theoretical model combines the viscous-friction and the controllable field-dependent characteristics of the MR fluid in which a Bingham plastic model was used to simulate the shear stress of the fluid under various input conditions. The numerical approach involved a special procedure to simulate the device performance using computational fluid dynamics techniques, which were performed using Ansys CFX code. Three commercial MR fluids were assessed and it was found that the simulated device torque compared well with the theoretical values. The mechanical design of the optimised ball-and-socket damper was accomplished using SolidWorks software when several important design and manufacturing factors were taken into account. These factors included the assembly of the ball and socket parts, the sealing of the MR fluid inside its designated gap, winding of the coil inside the socket part, maintaining a uniform MR fluid gap, and insertion of the nonmagnetic rings at their predesigned locations. Finally, a dedicated experimental rig was constructed which facilitated the assessment of the smart damper under both static and dynamic testing conditions. It was found that agreement between model predictions and experimental observations was excellent. Furthermore, this device performance was found to meet torque requirements expected in most upper-limb rehabilitation regimes.

Magnetorheological (MR) rubber materials are the solid analogue of magnetorheological fluids; i.e. their rheological properties can be controlled continously, rapidly, and reversibly by an applied magnetic field. They consist of magnetically polarisable particles in an elastomer matrix and they can be made to respond to changes in their environment; hence, they are considered as "smart" materials. Examples of potential applications for these materials are adaptive tuned vibration absorbers, stiffness-tuneable mounts and suspensions, and automotive bushings. The purpose of this work was to increase the knowledge relating to magnetorheological materials for damping applications. The materials should exhibit a large response to an applied magnetic field, and have good mechanical and long-term properties. MR rubber materials were made from nitrile, natural and silicone rubber, with irregularly shaped iron particles several micrometres in size. The particles were not aligned by a magnetic field prior to the vulcanisation; hence, the materials can be considered to be isotropic. These materials show a large MR effect, i.e. an increase in the shear modulus when a magnetic field is applied, although the particles are not aligned within the material. This is explained by the low critical particle volume concentration (CPVC) of such particles. Similar behaviour can be obtained with materials containing carbonyl iron, if the particles are aggregated so that they behave like large irregular particles. The iron particle concentration must be very close to the CPVC in order to obtain a large MR effect without alignment of the particles. The absolute MR effect (MPa) in an isotropic MR rubber material with large irregular iron particles is independent of the matrix material, and the relative MR effect (%) can thus be increased by the addition of plasticisers. However, the obtainable effect is limited by the reinforcement of the particles and by friction between the particles. Therefore, it is very difficult, if not impossible, to achieve an MR effect larger than 60%. Other ways of increasing the MR effect are to increase the strength of the magnetic field, although the materials saturate magnetically at high field strengths, or to use small strain amplitudes. The strong strain amplitude dependence of the MR effect suggests that MR rubber materials are most suitable for low amplitude applications, such as sound and vibration insulation. Measurements at frequencies within the audible frequency range show that this is a promising application for MR rubber materials. The incorporation of large amounts of iron into the rubber matrix decreases the oxidative stability dramatically. This is probably due to iron oxides on the surface of the particles, and to the fact that the oxidation rate is enhanced by iron ions, which are able to diffuse into the matrix. Standard antioxidants do not provide sufficient stabilisation for MR rubbers. Thus, proper stabilisation systems have to be found in order for these materials to be successful in applications.