Two Alternative System Reliability Approaches to the Serviceability Condition Assessment of Spillway Gate Systems on Dams
The U.S. Army Corps of Engineers is one of the Nation’s largest managers of infrastructure. It is responsible for maintaining and operating the Nation’s navigable waterways and is the primary agency for maintaining federal flood control dams. This includes a vast amount of infrastructure that includes roughly 270 navigation dams, 350 reservoir dams, and 238 lock chambers (Bullock and Foltz 1995). The navigable inland waterways carry roughly 17% of the Nation’s intercity cargo – an important economic role (USACE 2004). Over half of the locks and dams are over 50 years old. The entire inventory is deteriorating over time and requires billions of dollars to upgrade, maintain, and repair. The Corps of Engineers requires that a strength-based reliability analysis be completed to justify major rehabilitation projects. Reliability methods are preferred for cost-benefits analyses and for quantifying risk. More often, however, it is the general serviceability of a structure that dictates the requirements for maintenance and repair. The Corps of Engineers has developed a Condition Index (CI) rating system for a variety of structures that assesses the general serviceability condition of a structure based on periodic visual inspections. A Condition Index (CI) is a rating between 0 and 100 that describes the condition of a structure at a point in time. The CI is based on a series of observations by an inspector. At the component level, the inspector classifies what he or she sees into the predefined descriptive category that best matches the observation. Some CIs also include measurements. More often, the condition scores are based on descriptive word pictures that are often vague and difficult to quantify. Chouinard et.al. (2003) developed a deterministic CI rating system for spillway gate systems on dams. The gate system contained 122 separate inspectable components, each with its own condition rating table. The structure was decomposed into a seven-level structural hierarchy of systems, sub-systems, and components. The highest levels are shown in Figure 1. Estes et.al. (2005) developed a reliability-based approach that assigns probabilistic CI ratings for groups of components, systems, and projects. The approach accounts for the considerable uncertainty associated with the CI process which includes: • Uncertainty in the ability of different inspectors to reliably choose the correct condition state and to a greater degree, the appropriate score within a condition state 17 ANALYSIS AND COMPUTATION SPECIALTY CONFERENCE th
Reliability analysis of spillway gate systems
The goal of this research is to develop a methodology to accurately determine the reliability of spillway gate systems particularly for spillways that experience harsh environmental conditions and prolonged periods of dormancy. The significance of this study lies in the fact that spillways are rarely in use and remain inactive for most of their service life. Components of emergency spillway gate systems spend the majority of their service life in a dormant state and are activated only during emergencies such as floods or load rejection or on a regular basis for inspection and testing. Also, most spillways are located in remote areas and are subjected to severe environmental conditions which can cause early degradation of components. Furthermore, components of old spillway gate systems are often custom made with no readily available spare parts and little information on the reliability of existing components. These characteristics are very different from those of the equipment used in an industrial setting making it difficult for traditional methods to deliver accurate estimates on the reliability of such systems. Therefore, the development of a methodology that is customized to such conditions and incorporates unique parameters and state-of-the-art reliability techniques can contribute greatly to the dam industry by ensuring the safe operation of spillway systems on demand. The first step in this approach is geared towards system modeling in which a reliability model is developed for the spillway gate system taking into account all components, their relative interactions, latent failures due to dormancy, environmental conditions and type and frequency of inspections and tests. The next step is to develop a quantitative approach to update the availability of the spillway gate system based on real time conditions after each inspection. In this step, a Condition Indexing (CI) approach is combined with dormant availability analysis to evaluate the changes in the state of the system in real time using CI data obtained at each inspection. This approach provides a tool for dam owners to convert qualitative and descriptive results obtained from inspections to an index used as a comparative measure to detect real time changes in the availability of spillway gate systems. Next, inspection and testing procedures of spillway gate systems are investigated to evaluate the effect of different types and frequencies on the reliability of various types of components and the entire system. Lastly, the optimum inspection and testing strategy is determined, minimizing system costs including costs related to inspection and testing and the consequences of failure while at the same time maintaining the availability of the spillway gate system above a predefined limit. Genetic algorithm and Creeping Random Search are used to solve this optimization problem. Using these methods the optimum interval for each type of test is determined and the minimum system cost is calculated based on the optimum intervals.This methodology is used to develop…
HYPERGOLIC REACTION MECHANISMS OF CATALYTICALLY PROMOTED FUELS WITH ROCKET GRADE HYDROGEN PEROXIDE
Abstract The coupling of the physical and chemical processes controlling the ignition delays (τ ign ) of hypergolic propellants complicates the direct analysis of the transient ignition processes. The transport properties of both the propellants and the ambient gas, and the heat of vaporization and reaction affect τ ign and must be considered experimentally. Furthermore, since hypergolic ignition occurs, by definition, on contact, the mechanics of initial contact and subsequent mixing can affect τ ign and must also be considered. Experimental results from a study of the hypergolic ignition of a catalytically promoted fuel with rocket grade hydrogen peroxide (RGHP) are presented. Statistical analysis of the experimental data was conducted to evaluate the relative effects of RGHP concentration, initial ambient pressure, and the ambient gas on τ ign . At RGHP concentrations of less than 92% in water, stable ignition was difficult to achieve. At sufficiently high Lewis number, an oscillatory ignition process is observed. A phenomenological model comprising mixing, RGHP decomposition, fuel heating and vaporization, and auto-ignition is presented and compared to the experimental results.