The displacement of the free liquid surface in geothermal and hydrologic reservoirs is an important capacitance factor. An iterative approach to determining the drawdown of the free liquid surface for a single sink region in a homogeneous, isotropic, Darcy-type porous mediums is discussed. The iterative approach involves a stepwise adjustment of the pressure on the reference surface which replaces the time-dependent free surface condition by a fixed plane Dirichlet type condition so that readily available, standard techniques can be applied. Grouping of producing wells into a single analogous well may be used to treat multiple well cases with the iterative approach. An analytic solution for the infinite half space situation is used to compare solutions with the iterative technique. The analytic solution is derived for a point sink within an infinite, homogeneous, isotropic, Darcy-type porous half space. It is obtained by linearizing the free liquid boundary condition provided that the free surface deviates from its equilibrium reference position by only a small slowly undulating displacement h. The flow pressure at the equilibrium surface is then approximated by the hydrostatic pressure for a column of height h. A standard model is designed to be analogous to the analytic solution. Testing the iterative-procedure calculations for this model against the derived analytic solution produces very satisfactory results provided that the numerical grid spacing is adequately chosen for the problem. Calculations of the linear and quadratic terms of the free surface condition indicate that the neglected quadratic terms are in general small, and the approximation is reasonable. / Graduation date: 1981

In this paper, we introduce a fluid model of dynamic pricing and inventory management for make-to-stock manufacturing systems. Instead of considering a traditional model that is based on how price affects demand, we consider a model that relies on how price and level of inventory affect the time a unit of product remains in inventory. Our motivation is based on the observation that in inventory systems, a unit of product incurs a delay before being sold. This delay depends on the unit price of the product, prices of competitors, and the level of inventory of this product. Moreover, delay data is not hard to acquire and is internally controlled and monitored by the manufacturer. It is interesting to notice that this delay is similar to travel times incurred in a transportation network. The model of this paper includes joint pricing, production and inventory decisions in a competitive, capacitated multi-product dynamic environment. In particular, in this paper we (i) introduce a model for dynamic pricing and inventory control that uses delay rather then demand data and establish connections with traditional demand models, (ii) study analytical properties of this model, (iii) establish conditions under which the model has a solution and finally, (iv) establish an algorithm that solves efficiently a discretized version of the model.

No description available.

No description available.

Quality of Service (QoS) in real-time media applications is an area of current interest because of the increasing demand for audio/video, and generally multimedia applications, over best effort networks, such as the Internet. Media applications are transported using the User Datagram Protocol (UDP) and tend to use a disproportionate amount of network bandwidth as they do not perform congestion or flow control. Methods for application QoS control are desirable to enable users to perceive a consistent media quality. This can be accomplished by either modifying current protocols at the transport layer or by implementing new control algorithms at the application layer irrespective of the protocol used at the transport layer. The objective of this research is to improve the QoS delivered to end-users in real-time applications transported over best-effort packet-switched networks. This is accomplished using UDP at the transport layer, along with adaptive predictive and reactive control at the application layer. An end-to-end fluid model is used, including the source buffer, the network and the destination buffer. Traditional control techniques, along with more advanced adaptive predictive control methods, are considered in order to provide the desirable QoS and make a best-effort network an attractive channel for interactive multimedia applications. The effectiveness of the control methods, is examined using a Simulink-based fluid-level simulator in combination with trace files extracted from the well-known network simulator ns-2. The results show that improvement in real-time applications transported over best-effort networks using unreliable transport protocols, such as UDP, is feasible. The improvement in QoS is reflected in the reduction of flow loss at the expense of flow dead-time increase or playback disruptions or both.

Quality of Service (QoS) in real-time media applications is an area of current interest because of the increasing demand for audio/video, and generally multimedia applications, over best effort networks, such as the Internet. Media applications are transported using the User Datagram Protocol (UDP) and tend to use a disproportionate amount of network bandwidth as they do not perform congestion or flow control. Methods for application QoS control are desirable to enable users to perceive a consistent media quality. This can be accomplished by either modifying current protocols at the transport layer or by implementing new control algorithms at the application layer irrespective of the protocol used at the transport layer. The objective of this research is to improve the QoS delivered to end-users in real-time applications transported over best-effort packet-switched networks. This is accomplished using UDP at the transport layer, along with adaptive predictive and reactive control at the application layer. An end-to-end fluid model is used, including the source buffer, the network and the destination buffer. Traditional control techniques, along with more advanced adaptive predictive control methods, are considered in order to provide the desirable QoS and make a best-effort network an attractive channel for interactive multimedia applications. The effectiveness of the control methods, is examined using a Simulink-based fluid-level simulator in combination with trace files extracted from the well-known network simulator ns-2. The results show that improvement in real-time applications transported over best-effort networks using unreliable transport protocols, such as UDP, is feasible. The improvement in QoS is reflected in the reduction of flow loss at the expense of flow dead-time increase or playback disruptions or both.

In recent years, traffic congestion in transportation networks has grown rapidly and has become an acute problem. The impetus for studying this problem has been further strengthened due to the fast growing field of Intelligent Vehicle Highway Systems (IVHS). Therefore, it is critical to investigate and understand its nature and address questions of the type: how are traffic patterns formed? and how can traffic congestion be alleviated? Understanding drivers' travel times is key behind this problem. In this paper, we present macroscopic models for determining analytical forms for travel times. We take a fluid dynamics approach by noticing that traffic macroscopically behaves like a fluid. Our contributions in this work are the following: (i) We propose two second-order non-separable macroscopic models for analytically estimating travel time functions: the Polynomial Travel Time (PTT) Model and the Exponential Travel Time (ETT) Model. These models generalize the models proposed by Kachani and Perakis as they incorporate second-order effects such as reaction of drivers to upstream and downstream congestion as well as second-order link interaction effects. (ii) Based on piecewise linear and piecewise quadratic approximations of the departure flow rates, we propose different classes of travel time functions for the first-order separable PTT and ETT models, and present the relationship between these functions. (iii) We show how the analysis of the first-order separable PTT Model extends to the second-order model with non-separable velocity functions for acyclic networks. (iv) Finally, we analyze the second-order separable ETT model where the queue propagation term - corresponding to the reaction of drivers to upstream congestion or decongestion - is not neglected. We are able to reduce the analysis to a Burgers equation and then to the more tractable heat equation. / Singapore-MIT Alliance (SMA)

No description available.

No description available.

<p>VehProLib is one of many libraries being developed for the object oriented multi-domain language Modelica. The layout and the current status of the library are shown. The aims of the library are to provide the user with a number of different components with different levels of complexity. The components included range from mean value engine components to in-cylinder models. An efficient way to handle parameters using records is provided. Different bus systems are implemented and discussed. Furthermore are replaceable fluid models introduced in the library. It will be shown that Modelica is a very efficient way to create an advanced modelling library.</p>