Institute for Systems Research Technical Reports
Permanent URI for this collectionhttp://hdl.handle.net/1903/4376
This archive contains a collection of reports generated by the faculty and students of the Institute for Systems Research (ISR), a permanent, interdisciplinary research unit in the A. James Clark School of Engineering at the University of Maryland. ISR-based projects are conducted through partnerships with industry and government, bringing together faculty and students from multiple academic departments and colleges across the university.
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Item Queueing Network Approximations for Mass Dispensing and Vaccination Clinics(2007) Pilehvar, Ali; Herrmann, Jeffrey; ISRTo respond to bioterrorism events or to curb outbreaks of contagious diseases, county health departments must set up and operate clinics to dispense medications or vaccines. Planning these clinics before such an event occurs requires determining clinic capacity and estimating queueing performance.Due to the nature of these facilities, we model a clinic as an open queueing network and estimate the time that county residents will spend at each workstation in such facilities. County residents are the customers, and the servers are the clinic staffs, who are the critical resource. Residents arrive according to an external (not necessarily Poisson) arrival process. When a resident arrives, he goes to the first workstation. Based on his information the resident moves from one workstation to another in the clinic.
We decompose the queueing network by estimating the performance of each workstation using a combination of exact and approximate models. There is a network of nodes and directed arcs. The nodes represent service facilities (workstations) and the arcs represent residentsflows through the clinic. We characterize each workstation by the first two moments of the interarrival time and service time distributions and consider it as a G/G/m queueing system. Congestion measures for the entire network are obtained by assuming as an approximation that the nodes are stochastically independent given the approximate flow parameters.
A key contribution of this thesis is to introduce approximations for workstations with batch arrivals and multiple parallel servers, for workstations with batch service processes and multiple parallel servers, and for self service workstations.
We validated the models for likely scenarios using data collected from emergency preparedness exercises and from simulation experiments. Although this research was motivated by this specific application, it should be applicable also to the design and analysis of manufacturing systems with batch service processes.
Item National Aviation System Congestion Management(2006) Karimi, Sahand; Lovell, David; ISRThis report will mainly talk about three different projects, all of which focus on the theme of improving the operation of the national airspace system in order to make it more efficient. All of these projects contain a common component which is to predict delays and cancellations. In my research, I have performed significant amounts of statistical analysis & modeling with detailed data collected from air carriers nationwide. My part of work (Queuing delays) is a part of predicting delays and cancellations.Item Attack Evolution: Identifying Attack Evolution Characteristics to Predict Future Attacks(2006) Monahan-Pendergast, MaryTheresa; Cukier, Michel; ISRSeveral approaches can be considered to predict the evolution of computer security attacks, such as statistical approaches and ed Teams. This research proposes a third and completely novel approach for predicting the evolution of an attack threat. Our goal is to move from the destructive nature and malicious intent associated with an attack to the root of what an attack creation is: having successfully solved a complex problem. By approaching attacks from the perspective of the creator, we will chart the way in which attacks are developed over time and attempt to extract evolutionary patterns. These patterns will eventually be used for the prediction of future attacks.Item Systems Engineering: Quick Dispensing Clinic and Schroeder Industries(2006) Gaska, Kristen; Gheen, Kirsten; Herrmann, Jeffrey; ISRDuring the course of our ten-week program, we have been working with Dr. Jeffrey Herrmann on projects involving computer simulations. We have had two projects dealing with applied industrial engineering theories, Brooke Grove Clinic and Schroeder Industries.Our first assignment was to read and understand the software Dr. Hermann and his team has created over the past five years. The Clinic Generator Software was created from results of numerous simulated vaccinations to help prepare local authorities in case of bio-terrorism or life-threatening infectious diseases. We used and tested the software after reading the user guide to make sure that there were no errors before the release of the new version. By testing the new version, we were able to help resolve problems such as the ability to open specific files on different computer systems.
Item Synthesis and Validation of High-Level Behavior Models for Narrow Waterway Management Systems(2005) Kaisar, Evangelos; Austin, Mark; ISR; SEILThis report formulates a new methodology for the incremental transformation of informal operations concepts for a waterway management system into system-level designs, the latter being formal enough to support automated validation of anticipated component- and system-level behaviors. Scenario specifications and models of behavior are formally modeled as labeled transition systems (LTSs). Each object is the management system is assumed to have behavior that can be defined by a finite state machine; thus, the waterway management system architecture is modeled as a network of communicating finite state machines. Architecture-level behaviors are validated using the Labeled Transition System Analyzer (LTSA). We exercise the methodology by working step by step through the synthesis and validation of a high-level behavior model for a ship passing through a waterway network.Item Phase Analysis of Actuator Response for Sub-Optimal Bang-Bang and Velocity Cancellation Control of Base Isolated Structures(2005) Austin, Mark; Sebastianelli, Robert; ISR; SEILStarting with simplified models of displacement response for a base isolated structure supplemented with sub-optimal bang-bang control, we formulate models of phase analysis of actuator force direction in relation to system displacements and velocities. For the case of steady state displacement response, we prove that the direction of actuator application can neither be perfectly in phase with displacements, nor perfectly in phase with velocities. In practice, however, the actuator force direction is ``almost in phase' with velocities and ``almost orthogonal' to sign changes in displacements. This observation suggests that a very simple velocity cancellation control might be effective in adding value to base isolation system responses. Numerical experiments are conducted to assess improvements in performance due to sub-optimal bang-bang control and velocity cancellation control, and to validate the extent to which the phase analysis predictions hold in linearly elastic and nonlinear time-domain settings.Item Using Categorical Information in Multidimensional Data Sets: Interactive Partition and Cluster Comparison(2005) Seo, Jinwook; Shneiderman, Ben; ISRMultidimensional data sets often include categorical information. When most columns have categorical information, clustering the data set by similarity of categorical values can reveal interesting patterns in the data set. However, when the data set includes only a small number (one or two) of categorical columns, the categorical information is probably more useful as a way to partition the data set. For example, researchers might be interested in gene expression data for healthy vs. diseased patients or stock performance for common, preferred, or convertible shares. For these cases, we present a novel way to utilize the categorical information together with clustering algorithms. Instead of incorporating categorical information into the clustering process, we can partition the data set according to categorical information. Clustering is then performed with each subset to generate two or more clustering results, each of which is homogeneous (i.e. only includes the same categorical value for the categorical column). By comparing the partitioned clustering results, users can get meaningful insights into the data set: users can identify an interesting group of items that are differentially/similarly expressed in two different homogeneous partitions. The partition can be done in two different directions: (1) by rows if categorical information is available for each column (e.g. some columns are from disease samples and other columns are from healthy samples) or (2) by a column if a column contains categorical information (e.g. a column represents a categorical attribute such as colors or sex). We designed and implemented an interface to facilitate this interactive partition-based clustering results comparison. Coordination between clustering results displays and comparison results overview enables users to identify interesting clusters, and a simple grid display clearly reveals correspondence between two clusters.Item Bi-Level Hierarchical Layouts for Photo Libraries: Algorithms for Design Optimization with Quantum Content(2005) Kustanowitz, Jack; Shneiderman, Ben; ISRA frequently-used layout for a collection of two-dimensional, fixed aspect-ratio objects, such as photo thumbnails, is the grid, in which rows and columns are configured to match the allowed space. However, in cases where these objects have some group relationship among them, it can be advantageous to show this relationship in the layout, rather than in textual captions. We use an annotated digital photo collection as a case study of an auto-layout technique in which a two-level hierarchy is generated, consisting of a primary, central region with secondary regions (typically 2-12 regions) surrounding it. We show that given specific requirements, this technique is also optimal, in the sense that it will generate the largest size for the objects. Since all objects are the same size we refer to them as quantum content. These algorithms are designed to be real-time, enabling a compelling interactive display as users resize the canvas, or move and resize the primary region. The interactive redisplay also occurs as users add regions or objects to a secondary region.Item Energy- and Power-Balance Assessment of Base Isolated Structures Supplemented with Modified Bang-Bang Control(2005) Sebastianelli, Robert; Austin, Mark; ISR; SEILThis report is the second in series investigating the feasibility of supplementing base isolation with active bang-bang control mechanisms. We formulate discrete approximations to energy- and power-balance equations for a base isolated structure supplemented with constant stiffness bang-bang (CKBB) control. Numerical experiments are conducted to: (1) Identify situations when constant stiffness bang-bang control is most likely to ``add value' to system responses due to base isolation alone, and (2) Quantitatively determine the work done and power required by the actuators. A key observation from the numerical experiments is that ``overall performance' of the actuators is coupled to ``input energy per unit time.'Item Computational Assessment of Suboptimal Bang-Bang Control Strategies for Performance-Based Design of Base Isolated Structures(2005) Sebastianelli, Robert; Austin, Mark; ISR; SEILThis report explores the symbolic solution of the Lyapunov matrix equation as it applies to modified bang-bang control of base isolated structures. We present the Modified Bang-Bang Control strategy for active control of structures. Based on energy concepts, we formulate a rational choice of the ``${ f Q}$" matrix that partitions the amount of potential energy in a base isolated system into two parts: (1) potential energy directed to the main structural system, and (2) potential energy directed to the isolation devices. This symbolic analysis of a 2-DOF system leads to investigating a choice of the ${ f Q}$ matrix that minimizes the entire potential and/or kinetic energy of a emph{n}-DOF structure during an earthquake ground event. Using symbolic analyis procedures, We show that when the entire potential and/or kinetic energy of a emph{n}-DOF structure with uniform mass is minimized, solutions to the Lyapunov matrix equation assume a greatly simplified form. Moreover, this solution to the modified bang-bang control problem is easily calculated without needing to solve the Lyapunov matrix equation. Modified bang-bang control can be easily incorporated into the second-order differential equation of motion for the structure giving intuitive insight as to the effect of active control on the response of the structure. We show that this control strategy is insensititive to localized, nonlinear stiffness changes in the base isolators and therefore is well-suited for this problem area.