Modeling the dynamics of flow in gas pipelines
The description of nonstationary one-dimensional flow of a nonideal gas in a pipe is treated with the goal of developing a mathematical description of flow and pressure (density) dynamics adequate for creating a simulation model of large pipeline networks, the analysis starts from Newton's equation of motion. The continuity equation, and the energy equation. The authors determine the relationships among: space discretization, terms of Newton's equation, and frequency of the dynamic processes occurring in the system. The resulting dynamic description of a pipe is discussed for two different modes of space discretization, and quantitative rules for space discretization are given.
Simulation and State Estimation of Transient Flow in Gas Pipeline Networks Using a Transfer Function Model
Dynamic simulation models of gas pipeline networks can be used for on-line applications such as state estimation, leak detection, etc. A prime requirement for such models is computational efficiency. In this paper, a transfer function model of a gas pipeline is used as a basis for developing a dynamic simulator for gas pipeline networks. The simulator is incorporated in a data reconciliation framework, which is ideally suited for on-line state estimation based on all available measurements of pressures and flow rates. The American Gas Association (AGA) model is used for making realistic computations of the gas compressibility. Accuracy and computational efficiency of the proposed method are evaluated by comparing our results with those obtained using a fully nonlinear second-order accurate finite difference method. The ability of the proposed approach for obtaining accurate state estimation from noisy measurements is demonstrated through simulations on an example network. We also demonstrate the use of the proposed approach for estimating an unknown demand at any node by exploiting the redundancy in measurements.
Code switching in Ahdaf Soueif's The Map of Love
This article examines the phenomenon of code switching in The Map of Love (1999) by the Egyptian—British writer Ahdaf Soueif. Though she chooses English as a medium for her creative expression, Soueif deploys Arabic in her narrative to represent different aspects of the linguistic and cultural norms of Egyptian society. The article's methodology is informed by Kachru's framework on contact literature and his categorization of the occurrence of literary code switching or bilingual creativity into different strategies that encompass cultural and linguistic processes. The results indicate the predominance in The Map of Love of the discourse strategies of employing lexical borrowing, culture-bound references and translational transfer. Finally, the article analyzes the functional motivation of code switching in the postcolonial context of the novel and how the use of certain creative strategies might enhance or diminish the narrative's effectiveness and readability.