Browsing by Subject "Simulation methods"
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Item A comparison of simulation methods with finite-difference and finite element methods for solving Vlasov-Poisson systems(Texas Tech University, 1986-08) Ho, Wai HungWe consider the one dimensional periodic Vlasov-Poisson equation and discuss various approximations. These include the particle-in-cell method, the upstream-downstream method (a finite element method) and the Lax-Wendroff method (a finite-difference method). The model considered as a test problem numerically simulates electrons moving over a fixed, uniform positive background when, as an initial condition for the electron distribution, a Maxwellian beam is imposed. Landau damping phenomena are observed for all approximation methods. Good agreements on charge conservation have been observed for both finite element and finite-difference methods for up to 12.5 plasma periods. Numerical experiments show that for very short plasma periods (e.g., 2 plasma periods) the total energy of a Vlasov plasma system is conserved with finite element methods; however, it is not well conserved at all for longer plasma periods. Nevertheless, with finite - difference methods energy conservation of the system satisfactorily holds for up to 10 plasma periods. Modification of mesh sizes and time steps shows that fine mesh sizes and small time steps can be used for reducing numerical diffusion effects. Based on different numerical results, we make a comparative study of finite element and finite-difference methods with particle - in - cell methods.Item A decision simulation exercise in business cycles and forecasting(1964-08) Slayback, Harry BakerNot AvailableItem A simulation approach to stochastic linear programming(Texas Tech University, 1973-05) Armstrong, Walter PatrickNot availableItem Advanced tabulation techniques for faster dynamic simulation, state estimation and flowsheet optimization(2009-08) Abrol, Sidharth; Edgar, Thomas F.Large-scale processes that are modeled using differential algebraic equations based on mass and energy balance calculations at times require excessive computation time to simulate. Depending on the complexity of the model, these simulations may require many iterations to converge and in some cases they may not converge at all. Application of a storage and retrieval technique, named in situ adaptive tabulation or ISAT is proposed for faster convergence of process simulation models. Comparison with neural networks is performed, and better performance using ISAT for extrapolation is shown. In particular, the requirement of real-time dynamic simulation is discussed for operating training simulators (OTS). Integration of ISAT to a process simulator (CHEMCAD®) using the input-output data only is shown. A regression technique based on partial least squares (PLS) is suggested to approximate the sensitivity without accessing the first-principles model. Different record distribution strategies to build an ISAT database are proposed and better performance using the suggested techniques is shown for different case studies. A modified ISAT algorithm (mISAT) is described to improve the retrieval rate, and its performance is compared with the original approach in a case study. State estimation is a key requirement of many process control and monitoring strategies. Different nonlinear state estimation techniques studied in the past are discussed with their relative advantages/disadvantages. A robust state estimation technique like moving horizon estimation (MHE) has a trade-off between accuracy of state estimates and the computational cost. Implementation of MHE based ISAT is shown for faster state estimation, with an accuracy same as that of MHE. Flowsheet optimization aims to optimize an objective or cost function by changing various independent process variables, subject to design and model constraints. Depending on the nonlinearity of the process units, an optimization routine can make a number of calls for flowsheet (simulation) convergence, thereby making the computation time prohibitive. Storage and retrieval of the simulation trajectories can speed-up process optimization, which is shown using a CHEMCAD® flowsheet. Online integration of an ISAT database to solve the simulation problem along with an outer-loop consisting of the optimization routine is shown using the sequential-modular approach.Item An integration of systems, simulation, and EDP in the design of an information model(Texas Tech University, 1967-08) Lokey, Kenneth RayNot availableItem An investigation of the effects of simulation on attitudes of home economics education majors(Texas Tech University, 1970-08) Fry, Martha VirginiaNot availableItem Dynamic response of laterally-loaded piles(2009-05) Thammarak, Punchet; Tassoulas, John LambrosThe laterally-loaded pile has long been a topic of research interest. Several models of the soil surrounding a pile have been developed for simulation of lateral pile behavior, ranging from simple spring and dashpot models to sophisticated three-dimensional finite-element models. However, results from the available pile-soil models are not accurate due to inherent approximations or constraints. For the springs and dashpots representation, the real and imaginary stiffness are calculated by idealizing the soil domain as a series of plane-strain slices leading to unrealistic pile behavior at low frequencies while the three-dimensional finite-element analysis is very computationally demanding. Therefore, this dissertation research seeks to contribute toward procedures that are computationally cost-effective while accuracy of the computed response is maintained identical or close to that of the three-dimensional finite-element solution. Based on the fact that purely-elastic soil displacement variations in azimuthal direction are known, the surrounding soil can be formulated in terms of an equivalent one-dimensional model leading to a significant reduction of computational cost. The pile with conventional soil-slice model will be explored first. Next, models with shear stresses between soil slices, including and neglecting the soil vertical displacement, are investigated. Excellent agreement of results from the proposed models with three-dimensional finite-element solutions can be achieved with only small additional computational cost.Item Parallel processing for system simulation(Texas Tech University, 1982-05) Tai, Heng-mingIn this thesis, a relaxation algorithm is proposed for solving large scale system simulation problems in parallel. This algorithm is composed of both a time-step parallel algorithm and a component-wise parallel algorithm and fully exploits the interconnected nature of the system which is characterized by a component connection model. Furthermore, the possibility of this algorithm being implemented with the structures suggested by Pottle [6] and Van Ness [2] is discussed. In chapter 2, the component connection model of a dynamical system and the classical (sequential) relaxation algorithm are reviewed. In chapter 3, we describe not only the time-step parallel algorithm and the component is parallel algorithm, but also the combination of these two algorithms to formulate a "highly parallel" system simulation algorithm. Chapter 4 illustrates a number of examples in which the possible trade offs between efficiency, speed-up ratio, and waiting time are analyzed. Finally, some concluding remarks are made in chapter 5.Item Scheduling of Generalized Cambridge Rings(2009-08) Bauer, Daniel Howard; Hasenbein, John J.A Generalized Cambridge Ring is a queueing system that can be used as an approximate model of some material handling systems used in modern factories. It consists of one or more vehicles that carry cargo from origins to destinations around a loop, with queues forming when cargo temporarily exceeds the capacity of the system. For some Generalized Cambridge Rings that satisfy the usual traffic conditions for stability, it is demonstrated that some nonidling scheduling polices are unstable. A good scheduling policy will increase the efficiency of these systems by reducing waiting times and by therefore also reducing work in process (WIP). Simple heuristic policies are developed which provide substantial improvements over the commonly used first-in-first-out (FIFO) policy. Variances are incorporated into previously developed fluid models that used only means to produce a more accurate partially discrete fluid mean-variance model, which is used to further reduce waiting times. Optimal policies are obtained for some simple special cases, and simulations are used to compare policies in more general cases. The methods developed may be applicable to other queueing systems.Item Simulation models for production scheduling(Texas Tech University, 1972-08) Vogel, WolfgangNot availableItem Simulation of dynamic systems with uncertain parameters(2004) Zhang, Fu; Longoria, Raul G.Item Techniques for Simulating a Bivariate Uniform(Texas Tech University, 1984-05) Chan, Ka-lingNot Available.Item The Use of Simulation Games to Change Attitudes in Home and Family Living Classes(Texas Tech University, 1971-12) Harbin, DorineNot Available.Item Virtual pterosaurs: the use of surface laser scanning and three-dimensional computer modeling to create digital animation for museum research and exhibit(Texas Tech University, 2003-12) MacDonald, KathrynIn the growing age of technology, museums and other research institutions are investigating the uses of virtual images for the study and preservation of their objects. In the realm of museum research, digitized images are easier to manipulate than the large or fixed items they may represent and their use reduces the need to handle and potentially harm valuable originals. Alternately, in the area of museum education, animation is a good way to inform the public by helping them visualize things that have no parallel in nature, such as extinct creatures. Further, the digitized skeletal detail is more accurate than that rendered by hand. However, is it possible for smaller museums to produce accurate virtual images for their own use within their limited budgets and time frames? This project sought to produce a cost-effective, time saving model that would be within the realm of that attainable by smaller museums by utilizing available hardware and software that promised to enhance output while shortening production time. Cast skeletons of Quetzalcoatlus and Anhanguera were scanned using a surface laser scanner to capture a point cloud. This data was registered together to form three-dimensional point models which were converted into three-dimensional polygonal meshes for modeling and animation. Creation of inverse kinematic (IK) chains allowed for range of motion limitations to be applied thereby facilitating manipulation for detailed study. While the technique offers a promising alternative to expensive CT scans and potentially damaging stylus digitizers, one must consider the size-limitations of the equipment, access to hardware and software, time constraints on the project and the learning curve of the design team before selecting the method appropriate to the project. While the results were satisfactory for exhibit purposes and scanners are capable of capturing minute detail, until computer hardware power increases, the level of detail that can be stored and shared by institutions will remain limited. In the end, this technology offers a promising alternative to traditional methods of biomechanical research and data storage and affords the opportunity for attractive in-house exhibits, saved in the format of choice and specific to institutional research