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Statics, linear, and nonlinear dynamics of entangled polystyrene melts simulated through the primitive chain network model A thermodynamically admissible reptation model for fast flows of entangled polymers. II. Model predictions for shear and extensional flowsIn an earlier paper, a nonaffine network model of polymer melts was presented in which the rotation caused by shearing as well as the extension of the test strand are hindered by interactions with the network itself. In that work, it was shown that such a strand motion leads to qualitatively correct steady shear and elongational material properties, even though the strand disentanglement rate was constant and the strand force law was linear. These simplifications were accepted in order to emphasize the effects of the strand motion on material properties. In this paper, however, we show that these idealizations cause the model to fail in the start-up of shearing flow because no overshoot is seen in the shear stress growth function. To address this failure, the finitely extensible nonlinear elastic ͑FENE͒ network model is introduced in which the FENE force law replaces the Hookean force law used in the earlier finitely extensible network strand ͑FENS͒ model. Also, a nonlinear expression for the kinetics of strand disentanglement replaces the assumption of a constant rate of disentanglement. Material properties for the FENE network model are generated by stochastic simulation. The simulation results show that these modifications produce overshoot in the shear stress growth function and result in a more consistent description of finite network strand extensibility.

TX 75083-3836, U.S.A., fax +1-972-952-9435. AbstractThis paper describes an integrated approach, based on corrosion modeling and laboratory testing, to optimize the use of carbon steel in corrosive service for applications such as downhole tubulars, pipelines, and facilities. This approach presents economic advantages, such as reducing the use of expensive corrosion resistant alloys, while ensuring the operational integrity of equipment and facilities. A key part of this integrated approach is to apply reliable corrosion models underpinned with laboratory data. To be most effective, the models should account for the relevant chemistry and physics of the corrosion process, including the effects of detailed water chemistry, liquid hydrocarbons, and the degree of protection from iron carbonate or iron sulfide scales. Ideally, models should account for variations in conditions and flow characteristics along the length of a wellbore or pipeline. Case studies are presented that demonstrate how corrosion modeling in conjunction with laboratory testing may be used to the selection of validate carbon steel for challenging applications.