In this paper a boundary element formulation is developed and used for the analysis of cathodic protection systems of buried slender structures, such as foundations of electric transmission line towers. The foundation...
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In this paper a boundary element formulation is developed and used for the analysis of cathodic protection systems of buried slender structures, such as foundations of electric transmission line towers. The foundation is basically a truss structure and the slenderness of the pieces composing it, brings numerical difficulties into the classical boundary element method. To avoid this problem, the dual boundary element method is implemented: combination of standard and hypersingular integral equations to form a mathematically well-posed system. A simple experiment is carried out where a galvanized metallic sheet is buried alongside two Copper electrodes (anodes) in parallel, with the objective of simulating a two-dimensional problem. The soil resistivity properties are measured along the depth and the non-linear polarization curves describing the relation between the current density and the electrochemical potential at the metallic sheet is investigated. Two situations are analysed: a) current is injected into the ground through both electrodes;b) current is injected through only one of the electrodes. In the numerical implementation, the soil is modeled as a homogeneous layered half-space with a different property for each layer. The validity of the proposed dual approach is discussed and compared with the measurements of potential at the ground surface.
Concrete strength and durability reduction are two of the major consequences of the long-term chemical reaction evolution between the cement alkali and certain minerals from the aggregate. This reaction is known as al...
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Concrete strength and durability reduction are two of the major consequences of the long-term chemical reaction evolution between the cement alkali and certain minerals from the aggregate. This reaction is known as alkali-aggregate reaction. It provokes a heterogeneous expansion of the concrete causing geometry changes and eventually, loss of functionality. In concrete dams these effects can be very costly and the development of numerical tools to diagnose and correct the problem should be welcome. In this work, a parametric model to simulate concrete expansion is proposed, which uses the main AAR influence factors to form its basis. The employed methodology consists on obtaining the spatial distribution of these influence factors, parameters normalization and the use of a constitutive relationship to retrieve the expansive AAR rate of deformation. An optimization technique is also employed to adjust the computed parameters to existing field measurements. The methodology was developed in a commercial finite element package and tested in a for simple three-dimensional finite element model.
One of the most serious problems encountered in Naval steam plants following World War II was the unreliable performance of boiler and main feedpump pneumatic control systems. In addition to control component and syst...
One of the most serious problems encountered in Naval steam plants following World War II was the unreliable performance of boiler and main feedpump pneumatic control systems. In addition to control component and system design deficiencies, these control systems suffered from inadequate methods to measure and adjust system alignment. This paper describes the development of a set of procedures for on-line alignment verification (OLV) of pneumatic main boiler and feedpump control systems. The procedures are designed for use by N avy control system technicians and, in addition to on-line alignment verification, provide guidance for troubleshooting and for performing system alignment. Procedure static checks measure steady state steaming performance and OLV procedure dynamic checks measure the ability of the boiler and control systems to respond to load changes. The paper describes typical control system characteristics that influence OLV procedure content and the supporting analysis that was used to establish alignment criteria ranges that satisfy both steady state and transient performance requirements. Also described is the alignment criteria tolerance analysis along with the steps involved in a typical OLV check procedure development. Descriptions of the various OLV checks, troubleshooting procedures and alignment procedures are provided. Typical shipboard implementation requirements are described and experience to date with the procedures is provided along with a status report on OLV procedure implementations.
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