UiS Open Journals (Univ. of Stavanger)
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Overview of how the Calculation of Dynamic Temperature of Drilling Fluids is Closely Linked with Rheology
No full textBased on many years of work with the calculation of dynamic temperature of drilling fluids during operations, a pedagogic overview of how the calculation of heat transfer and temperature is closely linked with fluid flow properties will be given. For example, the onset of vortices and turbulence due to imposed flow and rotation of the drill string / running string has a large impact on heat transfer. Changing from idealized laminar flow with only conduction radially to flow with vortices and turbulence with convective heat transfer also radially, causes a large boost of heat transfer, especially along the outer wall of the drill string. Clearly, the rheological behaviour of the fluid is essential. Different vibrational modes and other disturbances add to the complexity of the picture, such that some effects can be modelled from first principles, while others are too complicated for practical models and must be handled differently
Citizens’ experiences of enablers and barriers to obtaining digital citizenship: E-applications for social assistance
Get PDFThis article focuses on citizens’ experiences of enablers of- and barriers to obtaining digital citizenship. E-applications for social assistance are used as an exemplar. In Sweden, as in many countries, there is political pressure on welfare services to become more digitalized, and to offer different kinds of self-service technology such as e-applications. Even if the goals of implementing these technologies are to increase efficiency and transparency and offer faster services to citizens, there is a risk of expanding the ‘digital divide’. and making it more difficult to obtain one’s digital citizenship and gain access to social rights. This article draws on a qualitative interview study. and explores citizens’ experiences using e-applications in two Swedish municipal social assistance agencies. Results show that most citizens had positive experiences applying for social assistance online, but there were some potential barriers. There were also differences in experiences in the two municipal social assistance agencies. We discuss how the increased digitalization of welfare services seems to push towards a blend of digital and social rights. In this process, social workers play an important role in countering new types of inequalities that emerge in evolving social assistance organizations. The article identifies several areas that merit further research
Additive Manufacturing by Gel-in-Gel Printing
No full textAdditive manufacturing by the 3D-printing processes enables solid free-form fabrication of three-dimensional objects directly from the digital images by melt prepolymers and gels following the post-curing of deposited polymers. Those processes have limitations due to long printing times, low-quality materials, and costs. The gel in gel printing by printing low viscosity materials in a support gel environment addresses those limitations. This process deposits a relatively low viscosity but curable liquids or gels into a medium of support gel. The support gel prevents the collapse or deformity of the printed object under its weight. Once the printing is completed, the object is cured, removed from the support bath, and rinsed off. The support gel can be reused. This sacrificial supporting gel has to be removed easily after 3D printing. There exists a very limited amount of materials suitable for printing and supporting the printed objects in a bath. Some of the support baths studied by different research groups are crosslinked polyacrylic copolymer microgels, granular gels, silica nanoparticle suspensions, and clay suspensions. The design of an appropriate supporting hydrogel bath poses several challenges. The supporting gel has to behave like Bingham plastic, not yielding until a threshold shear force is reached. In the meantime, its yield stress has to be low enough to accommodate nozzle movement. Besides supporting the deposited printing gel, the support bath must exhibit a high plateau shear elastic modulus, G ′. In addition, those viscoelastic properties have been thermo-reversible. Here, we discussed the role of yield stress of printing and support gels on gelling, shape integrity, and interlayer fusion
Controlling Well Leakage: Rheological and Operational Effects
No full textMany hydrocarbon wells leak gas, due to shrinkage and other microannuli that typically form along the cement-casing and cement-formation interfaces. These microannuli are variable due to irregularities in the primary cementing process and other operational anomalies. Repair of such defects is via a process called squeeze cementing, that involves pumping a thin cement slurry into the microannulus under pressure. Trudel & Frigaard1 developed a stochastic model of well leakage able to predict all but extreme (high and low) rates of leakage for a median well in British Columbia (BC), Canada, benchmarked against leakage rates observed in 2010-2019. Izadi et al.2,3 have explored the effects of pumping (yield stress) slurries into these narrow irregular geometries, using a Monte-Carlo approach to account for the extreme variability. This enabled us to give probabilistic predictions of the likely effects of the squeeze cementing operation. Here we extend our analysis to different operational scenarios, showing how rheological effects can influence repair of the microannulus
Effect of Lubricants on the Lubricity of an Intervention Base Oil
No full textDuring well intervention operations, the production tubing wall could be worn out due to mechanical interaction with coil tubing. Wear damage is a critical issue in the bend section where the contact force is higher. One of the possible solutions to reduce friction and wear damage is by increasing the lubricity of the intervention and the drilling fluid as well. The improved lubricity also minimizes the torque and drag that allows for reaching longer offset. This paper presents the experimental studies of the impact of six lubricants on industry intervention fluid. Results showed that the lubricants enhance the lubricity of the base oil. The optimized concentration of the lubricant reduced the coefficient of friction by 42-72 %
Gravfeltet i Hålandsmarka, Time kommune, SV-Norge
Get PDFIn 2008, a pre-development excavation examined a grave field on the ridge of Hålandsmarka. The burial ground was in use from the Early Bronze Age to the end of the Iron Age, and the excavation provided an opportunity to gain new insights into the long-term use of a grave field. The Hålandsmarka excavation allowed archaeologists to explore not only reuse of the grave field throughout this period, but also variations in burial form, treatment of the corpse, and grave goods over shorter timespans. The aim of the project has been to challenge the normative approach to graves as containers of a single burial event, and call attention to construction processes and other practices demonstrating the repeated use and transformation of the graves and their surroundings. Graves can be viewed as places of recurring engagement between the living and the dead, and as opportunities to explore the importance, duration and entanglement of material culture. Hålandsmarka should not be considered as a unique site: the results presented here are heavily dependent on our choice of archaeological methods, and we have the responsibility to be aware of the potential for complexity in both past and present practices when planning future excavations. The findings from Hålandsmarka call attention to the multi-temporal and gathered nature of grave fields in particular, as well as the archaeological record in general
High Definition 2-dimensional Numerical Model of Particle Settling on Newtonian and Shear-Thinning Fluids
No full textWell-defined particle sedimentation can provide relevant information in characterizing non-colloidal suspension. Nonetheless, the interaction between phases can become extremely convoluted as agglomerates are formed and broken, dynamically creating regions of high and low shear-rate. Numerical simulations are an alternative to obtain detailed descriptions of said interactions. In this work, the lattice-Boltzmann method is used together with the discrete element method to solve for two-dimensional sedimentation problems for both Newtonian and shear-thinning fluids
A Cost-effective Determination of Pressure - and Temperature-Dependent Viscosity of Polymers by Linking Conventional Viscosity Data to PVT Data
No full textThe viscosity of polymer melts is dependent on various factors such as shear rate, temperature, pressure and molecular structure. High-pressure capillary rheometery (HPCR) can be used to determine viscosity as a function of shear rate and temperature in the shear rate range relevant for injection molding and extrusion processing. Conventional HPCR measurements cannot determine the pressure dependence of viscosity so that it is typically neglected. Particularly at high pressures and low shear rates, the viscosity is therefore underestimated. However, it is possible to determine the pressure dependency using a counter pressure chamber or actively controlled counter pressure viscometer. Nevertheless, these devices are rarely available, and the measuring effort is high compared to conventional measurements. In order to be able to represent the pressure-dependent material behavior and thus improve the accuracy of process simulations in a cost-effective way, the aim of this paper is to use the free volume approach via the coupled equations of state according to Simha and Somcynsky1 to link the temperature and pressure dependence of the melt density to the viscosity. The model was extended according to Utracki and Sedlacek2–4 and applied to true viscosity data at constant shear stresses in the process relevant apparent shear rate range from 1 to 5000 1/s. The necessary viscosity data for the investigated PP and PC at different temperatures in the typical processing range were determined using a conventional HPCR, and a pvT measuring device was used to determine the melt density. The hole fraction as a measure for the free volume is calculated at each shear stress through the coupled equations of state and linked to the true viscosity through error square minimization at the mean pressure in the capillary. This allows for the recalculation of an isobaric viscosity curve at different pressure and temperature levels. For validation of the model viscosities were also measured at various pressure levels using a counter pressure chamber to determine an experimental pressure coefficient. The model results for the investigated materials show a high agreement with the experimentally determined pressure coefficient
Developing Rheological Characterization Methods for Bovine Blood and Hydrogel-Based Artificial Blood
No full textGraphical abstract: Rheological understanding of blood is relevant for the design of cardiovascular medical devices and implants. Erythrocytes are represented by hydrogel beads dispersed in a continuous glycerol phase. The model system is characterized by aims of optical and rheological characterization. The erythrocyte schematic has been taken from 1. The deformable nature of the hydrogel particles can be seen from the pictures taken during the squeezing experiment (see Fig. 4)