• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 368
  • 140
  • 54
  • 33
  • 7
  • 6
  • 5
  • 3
  • 3
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 747
  • 747
  • 520
  • 177
  • 144
  • 141
  • 140
  • 119
  • 91
  • 89
  • 82
  • 75
  • 73
  • 71
  • 71
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
201

Subsurface Flow Management and Real-Time Production Optimization using Model Predictive Control

Lopez, Thomas Jai 2011 December 1900 (has links)
One of the key challenges in the Oil & Gas industry is to best manage reservoirs under different conditions, constrained by production rates based on various economic scenarios, in order to meet energy demands and maximize profit. To address the energy demand challenges, a transformation in the paradigm of the utilization of "real-time" data has to be brought to bear, as one changes from a static decision making to a dynamical and data-driven management of production in conjunction with real-time risk assessment. The use of modern methods of computational modeling and simulation may be the only means to account for the two major tasks involved in this paradigm shift: (1) large-scale computations; and (2) efficient utilization of the deluge of data streams. Recently, history matching and optimization were brought together in the oil industry into an integrated and more structured approach called optimal closed-loop reservoir management. Closed-loop control algorithms have already been applied extensively in other engineering fields, including aerospace, mechanical, electrical and chemical engineering. However, their applications to porous media flow, such as - in the current practices and improvements in oil and gas recovery, in aquifer management, in bio-landfill optimization, and in CO2 sequestration have been minimal due to the large-scale nature of existing problems that generate complex models for controller design and real-time implementation. Their applicability to a realistic field is also an open topic because of the large-scale nature of existing problems that generate complex models for controller design and real-time implementation, hindering its applicability. Basically, three sources of high-dimensionality can be identified from the underlying reservoir models: size of parameter space, size of state space, and the number of scenarios or realizations necessary to account for uncertainty. In this paper we will address type problem of high dimensionality by focusing on the mitigation of the size of the state-space models by means of model-order reduction techniques in a systems framework. We will show how one can obtain accurate reduced order models which are amenable to fast implementations in the closed-loop framework .The research will focus on System Identification (System-ID) (Jansen, 2009) and Model Predictive Control (MPC) (Gildin, 2008) to serve this purpose. A mathematical treatment of System-ID and MPC as applied to reservoir simulation will be presented. Linear MPC would be studied on two specific reservoir models after generating low-order reservoir models using System-ID methods. All the comparisons are provided from a set of realistic simulations using the commercial reservoir simulator called Eclipse. With the improvements in oil recovery and reductions in water production effectively for both the cases that were considered, we could reinforce our stance in proposing the implementation of MPC and System-ID towards the ultimate goal of "real-time" production optimization.
202

Inferential Control Of Boric Acid Production System

Dervisoglu, Ozgecan 01 August 2007 (has links) (PDF)
Inferential control of boric acid production system using the reaction of colemanite with sulfuric acid in four continuously stirred tank reactors (CSTR) connected in series is aimed. In this control scheme, pH of the product is measured on-line instead of boric acid concentration for control purposes. An empirical correlation between pH and boric acid concentration is developed using the collected data in a batch reacting system in laboratory-scale and this correlation is utilized in the control system for estimator design. The transfer function model of the 4-CSTR system previously obtained is used in the MPC controller design. In the experiments done previously for the modelling of 4-CSTR system, it was observed that the reaction goes complete within the first reactor. Therefore, the control is based on the measurements of pH of the second reactor by manipulating the flow rate of sulfuric acid given to the first reactor, while the flow rate of colemanite fed to the system is considered as disturbance. The designed controller&rsquo / s performance is tested for set point tracking, disturbance rejection and robustness issues using a simulation program. It is found that, the designed controller is performing satisfactorily, using the inferential control strategy for this complex reacting system.
203

Adaptive control of real-time media applications in best-effort networks

Khariwal, Vivek 15 November 2004 (has links)
Quality of Service (QoS) in real-time media applications can be defined as the ability to guarantee the delivery of packets from source to destination over best-effort networks within some constraints. These constraints defined as the QoS metrics are end-to-end packet delay, delay jitter, throughtput, and packet losses. Transporting real-time media applications over best-effort networks, e.g. the Internet, is an area of current research. Both the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) have failed to provide the desired QoS. This research aims at developing application-level end-to-end QoS controls to improve the user-perceived quality of real-time media applications over best-effort networks, such as, the public Internet. In this research an end-to-end packet based approach is developed. The end-to- end packet based approach consists of source buffer, network simulator ns-2, destina- tion buffer, and controller. Unconstrained model predictive control (MPC) methods are implemented by the controller at the application layer. The end-to-end packet based approach uses end-to-end network measurements and predictions as feedback signals. Effectiveness of the developed control methods are examined using Matlab and ns-2. The results demonstrate that sender-based control schemes utilizing UDP at transport layer are effective in providing QoS for real-time media applications transported over best-effort networks. Significant improvements in providing QoS are visible by the reduction of packet losses and the elimination of disruptions during the playback of real-time media. This is accompanied by either a decrease or increase in the playback start-time.
204

Slutfasstyrning av robot : en jämförelse mellan LQ och MPC

Sjögren, Sofia, Wollinger, Nina January 2007 (has links)
<p>Arbetet har utförts på Saab Bofors Dynamics i Karlskoga och dess syfte var att undersöka om det är möjligt att använda modellbaserad prediktionsreglering, MPC, vid slutfasstyrning av en viss typ av robot. Som referensram används linjärkvadratisk reglering, LQ, eftersom denna reglermetod har undersökts tidigare och visat sig fungera bra vid slutfasstyrning, dock för en annan typ av robot. Anledningen till att man vill undersöka om det är möjligt att använda MPC är att styrlagen enkelt tar hand om begränsningar på systemet på ett direkt och intuitivt sätt.</p><p>Styrlagarnas uppgift är att styra en robot i dess slutfas då det finns krav och önskemål på roboten som bör vara uppfyllda. Till exempel finns det begränsningar på styrsignalen samt önskemål om att träff ska ske i en viss träffpunkt och även med en viss träffvinkel. För att utvärdera resultaten undersöks och jämförs de två styrlagarnas prestanda och robusthet.</p><p>För att kunna utvärdera styrlagarnas egenskaper och jämföra dem implementeras de båda i en befintlig detaljerad simuleringsmiljö, som har utvecklats på Saab Bofors Dynamics i Karlskoga.</p><p>De prestanda och robusthetstester som har utförts uppvisar små skillnader på de två styrlagarna och slutsatsen blir därmed att det är möjligt att använda modellbaserad prediktionsreglering vid slutfasstyrning av en viss typ av robot eftersom det sedan tidigare är känt att linjärkvadratisk reglering är en bra styrlag att använda. För att se vilken av de två styrlagarna som är bäst vid slutfasstyrning av en viss typ av robot behöver det göras vissa ändringar och mer detaljerade undersökningar utföras.</p>
205

Thermal modeling, analysis, and control of a space suit

Campbell, Anthony B. January 1999 (has links)
Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves [217]-221). Also available on the Internet.
206

Multivariable predictive control development and application in food extrusion processes /

Hong, Feng, January 1999 (has links)
Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 154-159). Also available on the Internet.
207

Weighting normalization in optimal predictive control /

Wang, Shensheng, January 2001 (has links)
Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 125-133). Also available on the Internet.
208

Multivariable predictive control development and application in food extrusion processes

Hong, Feng, January 1999 (has links)
Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 154-159). Also available on the Internet.
209

Weighting normalization in optimal predictive control

Wang, Shensheng, January 2001 (has links)
Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 125-133). Also available on the Internet.
210

The roles of allocentric representations in autonomous local navigation

Ta Huynh, Duy Nguyen 08 June 2015 (has links)
In this thesis, I study the computational advantages of the allocentric represen- tation as compared to the egocentric representation for autonomous local navigation. Whereas in the allocentric framework, all variables of interest are represented with respect to a coordinate frame attached to an object in the scene, in the egocentric one, they are always represented with respect to the robot frame at each time step. In contrast with well-known results in the Simultaneous Localization and Mapping literature, I show that the amounts of nonlinearity of these two representations, where poses are elements of Lie-group manifolds, do not affect the accuracy of Gaussian- based filtering methods for perception at both the feature level and the object level. Furthermore, although these two representations are equivalent at the object level, the allocentric filtering framework is better than the egocentric one at the feature level due to its advantages in the marginalization process. Moreover, I show that the object- centric perspective, inspired by the allocentric representation, enables novel linear- time filtering algorithms, which significantly outperform state-of-the-art feature-based filtering methods with a small trade-off in accuracy due to a low-rank approximation. Finally, I show that the allocentric representation is also better than the egocentric representation in Model Predictive Control for local trajectory planning and obstacle avoidance tasks.

Page generated in 0.0998 seconds