Suppression of axial-torsional vibrations in drilling system described by neutral-type delay differential equations

Vibrations in deep drilling systems lead to efficiency deterioration and may even cause the system failure. In this paper, a controller is designed aiming at mitigation of these vibrations, which is based on a neutral-type time delay model that represents distributed axial and torsional dynamics. First, the stability of the associated linearized dynamics is analyzed using a spectral approach. Furthermore, the open-loop system is shown to be stabilizable by state feedback which supports subsequent controller design. An optimization-based continuous pole placement technique has been employed to design a stabilizing controller, which mitigates steady-state drill-string vibrations. The effectiveness of the controller is shown in a representative case study

Suppression of axial-torsional vibrations in drilling system described by neutral-type delay differential equations

Vibrations in deep drilling systems lead to efficiency deterioration and may even cause the system failure. In this paper, a controller is designed aiming at mitigation of these vibrations, which is based on a neutral-type time delay model that represents distributed axial and torsional dynamics. First, the stability of the associated linearized dynamics is analyzed using a spectral approach. Furthermore, the open-loop system is shown to be stabilizable by state feedback which supports subsequent controller design. An optimization-based continuous pole placement technique has been employed to design a stabilizing controller, which mitigates steady-state drill-string vibrations. The effectiveness of the controller is shown in a representative case study

Removal of Phenols from Wastewater with Encapsulated Horseradish Peroxidase in Calcium Alginate

Abstract -Horseradish peroxidase was encapsulated in calcium alginate for the purpose of phenol removal. Upon immobilization, pH profile of enzyme activity changes as it shows higher value at basic and acidic solution. Investigation into time course of phenol removal for both encapsulated and free enzyme showed that encapsulated enzyme had nearly similar efficiency in comparison with the same concentration of free enzyme; however the capsules were reusable up to four cycles without any changes in their retention activity

Pilot Study of the Effects of Tai Chi on Elderly Fall Risks

Introduction. Falls in the elderly are a significant public health concern. Tai Chi has been shown to reduce falls in this population and increase muscle strength, balance, mood, confidence and sleep.https://scholarworks.uvm.edu/comphp_gallery/1087/thumbnail.jp

Improving reservoir conformance using gelled polymer systems. Final report, September 25, 1992--July 31, 1996

The objectives of the research program were to (1) identify and develop polymer systems which have potential to improve reservoir conformance of fluid displacement processes, (2) determine the performance of these systems in bulk and in porous media, and (3) develop methods to predict their performance in field applications. The research focused on four types of gel systems--KUSP1 systems that contain an aqueous polysaccharide designated KUSP1, phenolic-aldehyde systems composed of resorcinol and formaldehyde, colloidal-dispersion systems composed of polyacrylamide and aluminum citrate, and a chromium-based system where polyacrylamide is crosslinked by chromium(III). Gelation behavior of the resorcinol-formaldehyde systems and the KUSP1-borate system was examined. Size distributions of aggregates that form in the polyacrylamide-aluminum colloidal-dispersion gel system were determined. Permeabilities to brine of several rock materials were significantly reduced by gel treatments using the KUSP1 polymer-ester (monoethyl phthalate) system, the KUSP1 polymer-boric acid system, and the sulfomethylated resorcinol-formaldehyde system were also shown to significantly reduce the permeability to supercritical carbon dioxide. A mathematical model was developed to simulate the behavior of a chromium redox-polyacrylamide gel system that is injected through a wellbore into a multi-layer reservoir in which crossflow between layers is allowed. The model describes gelation kinetics and filtration of pre-gel aggregates in the reservoir. Studies using the model demonstrated the effect filtration of gel aggregates has on the placement of gel systems in layered reservoirs

In situ permeability modification using gelled polymer systems. Topical report, June 10, 1996--April 10, 1997

Results from a research program on the application of gelled polymer technology for in situ permeability modification are presented in this report. The objective of this technology when used with displacement processes such as waterflooding is to reduce the permeability in fractures and/or high permeability matrix zones to improve volumetric sweep efficiency of the displacement process. In production wells, the objective is to reduce water influx. The research program is focused on five areas: gel treatment in fractured systems; gel treatment in carbonate rocks; in-depth placement of gels; gel systems for application in carbon dioxide flooding; and gel treatment in production wells. The research program is primarily an experimental program directed at improving the understanding of gelled polymer systems and how these systems can be used to increase oil recovery from petroleum reservoirs. A summary of progress for research conducted in the first 10 months of a 28 month program is described in the following sections

Assessment of Chemical Inhibitor Addition to Improve the Gas Production from Biowaste

The coexistence of sulphate-reducing bacteria and methanogenic archaea in the reactors during the anaerobic digestion from sulphate-containing waste could favor the accumulation of sulfide on the biogas, and therefore reduce its quality. In this study, the effect of sulphate-reducing bacteria inhibitor (MoO−2 4 ) addition in a two phase system from sulphate-containing municipal solid waste to improve the quality of the biogas has been investigated. The results showed that although SRB and sulphide production decreased, the use of inhibitor was not effective to improve the anaerobic digestion in a two phase system from sulphate-containing waste, since a significant decrease on biogas and organic matter removal were observed. Before MoO−2 4 addition the average values of volatile solid were around 12 g/kg, after 5 days of inhibitor use, those values did exceed to 28 g/kg. Molybdate caused acidification in the reactor and it was according to decrease in the pH values. In relation to microbial consortia, the effect of inhibitor was a decrease in Bacteria (44%; 60% in sulphate-reducing bacteria) and Archaea (38%) population

Culture, technology and local networks: towards a sociology of ‘making’ in education

This article is about ‘making’ in education. Often associated with software programming (as in ‘digital making’), making can also involve creating or modifying physical technological artefacts. In this paper, making is examined as a phenomenon that occurs at the intersection of culture, the economy, technology and education. The focus is not on the effects on cognitive gains or motivations, but on locating making in a social, historical and economic context. Making is also described as a form of ‘material connotation’, where connotation refers to the process through which the technical structure of artefacts is altered by culture and society. In the second part of the paper, the theoretical discussion is complemented by a case study in which making is described as a networked phenomenon where technology companies, consultants, volunteers, schools, and students were all implicated in turning a nebulous set of practices and discourses into an educational reality

Permeability reduction in porous materials by in situ

The effect of in situ formed silica gel on the permeability of a porous material was investigated experimentally. Gelling solutions of tetra-methyl-ortho-silicate (TMOS) and methanol in water were imbibed into dry sandstone plates and cured for several days. The permeability of the untreated sandstone is on the order of 1 µm^2, whereas the intrinsic permeability of the silica alcogel is 5–6 orders of magnitude lower. The method of beam bending was employed to measure concurrently the permeability D and Young’s modulus Ep of cylindrical gel rods, prepared from the TMOS-based sol-gel solutions. Second, the permeabilities and moduli of the treated sandstones were measured. For both types of samples the gel structure was varied by varying the concentration of the TMOS in a solution and the pH of the water used. The parameters D and Ep follow from a detailed analysis of the measured relaxation of the load that is applied to the sample under constant deflection. In case of the gels, the relaxation was interpreted using common expressions for hydrodynamic relaxation and viscoelastic (VE) relaxation. It was found that the permeability of the gels decreases with increasing silica content and that acid-catalyzed gels exhibit a significantly lower permeability than base-catalyzed gels. The modulus Ep increases with increasing silica content and aging time. The relaxation data of the sandstone—treated with gel—exhibited a more complex behavior. The normalized load curves showed hydrodynamic relaxation as well as strong and fast VE relaxation. The relaxation data for the rock samples treated with the lowest concentration gel was fitted successfully with the predictions. For higher concentrations the fit was less accurate, but the permeability estimates were within an order of magnitude. The overall permeability of the treated rock is higher than the intrinsic permeability of the gels; this indicates that the gel does not completely fill the pore space. Nevertheless, the permeability is reduced by a factor 10^4 with respect to untreated sandstone, and therefore the gel adequately blocks the pores