No description available.

No description available.

Magnetorheological dampers, or as they are more commonly called, MR dampers, are being developed for a wide variety of applications where controllable damping is desired. These applications include dampers for automobiles, heavy trucks, bicycles, prosthetic limbs, gun recoil systems, and possibly others. This thesis first introduces MR technology through a discussion of MR fluid and then by giving a broad overview of MR devices that are being developed. After giving the reader an understanding of MR technology and devices, MR damper basics are presented. This section includes a discussion of MR damper types, mathematical fundamentals, and an approach to magnetic circuit design. With the necessary background information covered, MR dampers for automotive use are then discussed. Specifically, designs for MR dampers that were built for a Mercedes ML-430 and for a Ford Expedition are presented along with their respective test results. These test results are presented and compared with the original equipment hydraulic dampers. After discussing automotive MR dampers, designs for gun recoil applications are presented. Specifically, two different MR damper designs are discussed along with live-fire test results for the first damper. Finally, two hybrid dampers that were based on a modified adjustable hydraulic damper are presented. These hybrid dampers, if pursued further, may develop into controllable replacements for large hydraulic dampers such as those installed on large vehicles and field Howitzers. In conclusion, recommendations are made for materials as well as for seal selection and other design aspects. / Master of Science

No description available.

Abstract This thesis deals with the analysis of the rheological structure and tectonic modelling of the Fennoscandian Shield. First, a short introduction to the geology and geophysics of the Fennoscandian Shield is presented followed by a description of rheological concepts. Second, the applied modelling procedures, together with the sources of error are explained. Last a brief summary of each original paper including conclusions is given. Understanding rheological conditions through the entire lithosphere and even deeper is the key for understanding the deformation of the earth's interior. Thus, investigating the rheological structure and possible consequences resulting from tectonic loading are required to some extent when interpreting geophysical data into tectonic models. In this thesis rheological structure is obtained by calculating rheological strength in different locations of the central Fennoscandian Shield. These locations are mainly situated along different deep seismic sounding (DSS) profiles as they provide necessary geophysical information required for model construction. Modelling begins by solving the thermal structure in the lithosphere, as rheological behaviour, mainly ductile flow is strongly controlled by temperature. Results from these calculations show that the rheological structure of the lithosphere depends on the thermal conditions resulting in significant areal variations. Generally, the central Fennoscandian Shield can be considered to be rheologically rather strong. Rheologically weak layers are however usually found in the lower crust. Correlation of the rheological structure with earthquake focal depth data shows that brittle fracture is the relevant mechanism in the earthquake generation and that non-occurrence of deep earthquakes implies low stress or high strength conditions deeper in the crust. Calculated rheological structure is furthermore used as a material parameter in the structural models which are solved next. These results suggest that it is highly unlikely that any considerable ductile deformation in the crust of the central Fennoscandian Shield exists and it seems that the present-day thermal and mechanical conditions in the investigated area do not favour such processes in significant amounts.

In recent years, many investigators have predicted that with a semiactive suspension it is possible to attain performance gains comparable to those possible with a fully active suspension. In achieving this, the method by which the damper is controlled is one of the crucial factors that ultimately determines the success or failure of a particular semiactive suspension. This study is an investigation into the effectiveness of a number of basic control strategies at controlling vehicle dynamics, particularly vehicle roll. The test vehicle is a Sport Utility Vehicle (SUV), a class of vehicle that regularly sees widely varying vehicle weight (as a result of passengers and load) and can exhibit undesirable levels of vehicle roll. This study includes a suspension system comprised of four controllable magneto-rheological dampers, associated sensors, and controller. There are three distinct phases in this investigation, the first of which is a numerical investigation performed on a four-degree-of-freedom vehicle roll-plane model. The model is subjected to a variety of road and driver induced inputs, and the vehicle response is characterized, with each semiactive control policy. The second phase of this study consists of laboratory testing performed on a Ford Expedition, with the front axle of the vehicle placed on a two-post dynamic rig (tire coupled), and a variety of road inputs applied. The third phase of this testing involves road testing the test vehicle to further evaluate the effectiveness of each of the semiactive control policies at controlling both vehicle comfort (vibration) and stability (roll). In each phase, the semiactive control policies that are investigated are tuned and modified such that the best possible performance is attained. The performance of each of these optimal semiactive systems is then compared. In the first phase of this investigation, two basic skyhook control strategies are investigated and two modified strategies are proposed. Upon numerically investigating the effectiveness of the four control strategies, it is found that the performance achievable with each of the control strategies is heavily dependent on the properties of the controllable damper. The properties of the controllable damper that were particularly important were the upper and lower levels of force that the controllable damper was able to apply. Based on numerical results, the controllable dampers were tuned for each control system. The results indicate that a velocity-based skyhook control policy, in conjunction with force control, is most effective at controlling both road-induced vibration and driver-induced roll. In the second phase of this investigation, the effects of the two skyhook control strategies were again examined. Multiple system inputs including step inputs, chirp inputs, and multi-sine inputs were used, and the results indicate that significant performance gains using the basic skyhook policies are unlikely. The third phase involved road testing the vehicle through specific maneuvers modeling a wide variety of common driving situations. In addition to the two basic skyhook policies, two additional policies augmented with steering wheel position feedback were also examined. It was found that the velocity based skyhook control policy augmented with steering wheel position feedback achieved performance superior to both the stock passive dampers and other control policies tested here. / Ph. D.

A cost-effective, faster and efficient way of screening wheat samples suitable for tortilla production is needed. Hence, we developed prediction models for tortilla quality (diameter, specific volume, color and texture parameters) using grain, flour and dough properties of 16 wheat flours. The prediction models were developed using stepwise multiple regression. Dough rheological tests had higher correlations with tortilla quality than grain and flour chemical tests. Dough resistance to extension was correlated best with tortilla quality, particularly tortilla diameter (r= -0.87, P<0.01). Gluten index was significantly correlated with tortilla diameter (r = -0.67, P less than 0.01) and specific volume (r = -0.73, P less than 0.01). Tortilla diameter was the parameter best predicted. An r2 of 0.87 was obtained when mix-time and dough resistance to extension were entered into the model. This model was validated using another sample set, and an r^2 of 0.91 was obtained. Refined and whole wheat flours, dough and tortillas were compared using five wheat samples. Refined flour doughs were more extensible and softer than whole wheat flour doughs. Whole wheat flour tortillas were larger, thinner and less opaque than refined flour tortillas. Refined wheat flour had much smaller particle size and less fiber than whole wheat flour. These are the major factors that contributed to the observed differences. In general, refined wheat tortillas were more shelf-stable than whole wheat tortillas. However, whole wheat tortillas from strong flours had excellent shelf-stability which must be considered when whole wheat tortillas are processed. . Different objective rheological techniques were used to characterize the texture of refined and whole flour tortillas during storage. Differences in texture between 0, 1 and 4 day-old tortillas were detected by rupture distance from one and two-dimension extensibility techniques. In general, the deformation modulus was not a good parameter to differentiate tortilla texture at the beginning of storage. It detected textural changes of 8 and 14 day-old tortillas. The subjective rollability method detected textural changes after 4 days storage.

The purpose of this study is to identify and quantify factors governing extrudate swell and melt fracture. In the first part, the factors which control the extrudate swell of carbon black (N330) filled styrene-butadiene rubber (SBR) compounds at various states-of-mix were investigated. State-of-mix is quantified by effective filler volume fraction (EFVF), based on an estimate of the amount of rubber immobilised in the carbon black agglomerates. Extrudate swell was found to be dominated by recoverable strain and relaxation time, which are controlled by EFVF. In contrast, shear rate and the rubber-carbon black tridimensional transient network were not found to influence extrudate swell significantly. In the second part, melt fracture of the rubber compounds was investigated in terms of surface texture wavelength. The longer the wavelength, the greater the severity of the surface disruption. It was found that wavelength was controlled strongly by state-of mix (or by EFVF). In addition, a mechanism for melt fracture of the compounds studied has been proposed, based on average energy at the extrudate surface (t.E). Lastly, the influences of additives; paraffinic processing oil, stearic acid or a mixture of predominantly calcium fatty acid soaps on extrudate swell and melt fracture were investigated. For the rubber compounds with paraffinic processing oil or stearic acid, EFVF was found to play an important role in extrudate swell. The mixture of fatty acid soaps was shown to reduce significantly extrudate swell due to the presence of wall slip. The influence of the fatty acid soaps on extrudate swell is more noticeable for extrudates obtained from long dies, in which flow is dominated by shear. The major factors shown to exert a significant influence on melt fracture for the compounds with paraffinic processing oil or stearic acid are EFVF and green strength of the extrudate. Wall slip, promoted by a mixture of fatty acid soaps, was also found to decrease the melt fracture severity, particularly for long dies in which shear stresses are dominant.

In situ gelled acids that are based on polymers have been used in the field for several years as an acid diversion agent. These acids should not cause permanent formation damage, and should clean-up rapidly and completely when the well is put back on production. However, recent lab studies indicated that a significant amount of gel was retained inside the core even when the recommended breaker concentration was used. This gel significantly reduced the core permeability. Therefore, the objective of this study is to examine the working mechanisms of the solid breaker and the factors that affect the breaking time. The flowback of the spent acid and the core damage induced by it will also be assessed in detail. Viscosity and rheological experimental studies were conducted using polymer-based in situ gelled acids that used Zr as a crosslinker agent. To form the gel, this acid was neutralized using Pink Desert limestone to pH 3.5-4.The rheological properties of the gel were measured under different breaking conditions for 2 hr using HPHT rotational and oscillatory rheometers. Temperature (150 to 250 degrees F), shear rate (0.1 to 1000 s^-1), and breaker concentrations (0 to 32 lb/Mgal) were the main parameters that were investigated in this study. Experimental results showed that there is no need to add more than 16-ppg breaker concentration at 150 degrees F, while 4-ppg breaker concentration is enough at temperatures higher than 200 degrees F. A full breaking of these acids was obtained when the values of elastic modulus (G') were equalized with the viscose modules (G"). An HPHT filter press was used to simulate the flowback of the spent acid. Viscosity measurements of filtered fluids were used to determine the degree of gel degradation. Carbonate cores that had a 2.5 in. diameter and 0.25 in.thickness were used. Temperature (75 to 250 degrees F) and breaker concentrations (0 to 16 lb/Mgal) were the main parameters that were investigated in this study. Experimental results showed that there was always a gel left inside the rock, and such caused permeability reduction. Time needed to flowback the solution decreased by 50% when the temperature was increased from 150 to 200 degrees F, while it decreased by only 30% when the breaker concentration was doubled. At 150 degrees F, 16-ppg breaker concentration was recommended for breaking the gel. At higher temperatures (>150 degrees F), 8-ppg breaker concentration was enough to help degrade the gel.

Title page, summary and table of contents only. The complete thesis in print form is available from the University of Adelaide Library. / Ash deposition is a problem in power generation when coal with high ash and alkali contents are utilised. The problem is more severe in fluidised bed combustion where the ash deposition can causes agglomeration of the bed material, may lead to defluidisation of the unit. The successful operation of fluid bed combustion with coal high in ash and alkali content will depend on the ability to control ash deposition. The rheological properties of coal ash under furnace conditions are important in controlling the stickiness and mobility of the molten ash deposition. Therefore, a good knowledge of the rheological properties of coal will improve the understanding of the mechanisms associated with ash deposition, and may assist in controlling the deposition and agglomeration of fluid bed material. At present, a good deal of information about coal ash rheology under conditions similar to those found in fluidised bed combustion is not known, and greater understanding is required. This is primarily due to a lack of reliable instruments and measurement techniques. In this work, a new high temperature rheometer has been developed based on the principle concepts of visco metric flow. The developed rheometer allows fundamental rheological properties, such as shear stress and shear rate, to be obtained without relying on calibrations with materials of known properties. With this instrument the flow characteristics of the tested samples can be determined directly, without assuming a particular fluid model. The new rheometer has the capability to measure the rheological properties of materials at temperatures ranging from 500°C to 1300°C and under different processing conditions. Rheological characteristics and properties of a range of low rank Australian coal ashes have been carried out using the newly developed high temperature rheometer, equipped with a cone and plate measuring geometry. It has been found that coal ash samples exhibit thixotropic and visco plastic flow behaviours. SEM and XRD analyses have revealed that during high temperature rheological measurements the coal ash sample is basically a suspension of colloidal mineral solids in a molten eutectic liquid. The solid phase is mainly silica (SiO₂,), and the liquid phase is a mixture of alkali sulphates mainly CaS0₄, MgS0₄ and Na₂S0₄ compounds. The equilibrium visco metric data of coal ash samples is found to be satisfactorily described using the Herschel-Bulkley model. The equilibrium rheological properties are strongly affected by the concentration levels of CaS0₄, MgS0₄ and Na₂S0₄ . The operating temperature and chemical composition of the surrounding gas phase were also found to affect the rheological properties of the coal ash samples. In order to obtain a better understanding and to model the rheological properties of the coal ashes, a series of synthetic ash mixtures were examined. The synthetic mixtures contained the key chemical components that represent the solid and the liquid phases. The solid phase is represented by silica (SiO₂), while a mixture of CaS0₄, MgS0₄ and Na₂S0₄ compounds represented the liquid phase. In this work, the rheological characteristics of mixtures of synthetic ash were investigated using a factorial experimental design. Using the synthetic ash mixtures together with the statistical design experiment, the effect of key chemical compounds on the rheological properties could be systematically investigated. The rheological results showed that the synthetic mixtures exhibited thixotropic and viscoplastic behaviours. It was also found that mixtures predominantly high in CaS0₄and MgS0₄ had a high degree of thixotropy behaviour, while those mixtures predominantly high in Na₂S0₄ showed a lower degree of thixotropy behaviour. The statistical analysis also showed that Na₂S0₄ is the most significant chemical compound causes a high yield stress and high viscosity. In contrast, CaS0₄and MgS0₄ were found to decrease the value of the yield stress and the viscosity. The rheological behaviour of the synthetic ash mixtures can be used to describe rheological behaviour of the coal ash samples. Relationships between equilibrium flow properties and chemical compounds, and temperatures are developed using a linear regression method. The statistical analysis has shown that CaS0₄, MgS0₄ and Na₂S0₄ , and their interactions are all significant compounds that have effects on the yield stress and viscosity of the synthetic mixtures. It was also found that the yield stress and viscosity decreased with increasing concentration level of either CaS0₄or MgS0₄ . Yield stress and viscosity are increased with increases in the concentration of Na₂S0₄ . The statistical models can successfully predict rheological properties of ash with high concentrations of CaS0₄, MgS0₄ and Na₂S0₄ , but it fails to predict the rheological properties of ashes that also high concentrations of either Fe₂0₃ or Al₂0₃, or a combination of both. The relationship between ash rheology and fluidised bed agglomeration has been established. The yield stress of a coal ash may be used to describe the tendency of the molten ash to deposit on surface of the fluid bed particles. Yield stress also determines the tendency of stickiness of the molten ash deposit to adhere the fluid bed particles during fluidised bed combustion process. The viscosity of the molten ash describes the ability of the molten ash layer to adhere the fluid bed particles after a collision. High viscosity ash tend to hold the colliding particles together longer than a low viscosity ash. Shear thinning behaviour of the ash samples (decreasing viscosity with increasing shear rate) suggests that the operating conditions could be arranged so as to minimise the chance of agglomeration. For example, in order to avoid agglomeration a high viscosity coal ash would benefit from operating the fluidised bed combustion at a high velocity, this is because a high velocity means a higher shear rate and this causes a reduction in the viscosity of the molten ash. Thus, particles agglomerated by a low viscosity ash would be easily broken by the hydrodynamic forces present during the fluidised bed process. Finally, information about ash rheology has formed a basic knowledge for estimating tendency of fluid bed agglomeration when coal obtained from different source is being used. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1141958 / Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 2004