G. V. Loganathan

Decision tool for optimal replacement of plumbing systems

There is a noticeable increase in pinhole corrosion in copper plumbing pipes. Home is the most valuable asset for the majority of homeowners. The possibility of falling home value and health concerns have caused considerable anxiety among affected homeowners. There is a need for a decision tool that can determine whether to continue repair or to replace the system. In this article, a model capable of replicating time-dependent failure rate is proposed to generate synthetic sequences of leak arrivals. An economically sustainable optimality criterion is exploited to designate optimal replacement time of the plumbing system. The analysis is applied to a real system.

Work in progress - spiral curriculum approach to reformulate engineering curriculum

A theme-based spiral curriculum approach is being adopted to initiate the department-level reform (DLR) of the freshman engineering and the bioprocess engineering curricula at Virginia Tech. A large number of engineering faculty members are collaborating with experts in educational psychology and academic assessment to accomplish the objectives of this 3-year NSF supported project that began in September 2004. Successful implementation of the spiral approach will be used as a model for incorporating similar reforms in other engineering departments and elsewhere

CONSUMER CONCERNS AND PREFERENCE-TRADEOFFS IN HOME PLUMBING SYSTEMS

In the USA, about 90% of drinking water home plumbing systems use copper pipes. Pinhole leaks in copper plumbing pipes have become a concern nationwide. For majority of homeowners, their home is the most valuable asset. The possibility of losing home insurance, falling home value and health concerns have caused considerable anxiety among the affected homeowners. They are seeking a tool that would enable them to decide on whether to continue to repair or replace their plumbing system. They are also looking for advice on what factors are to be considered in a replacement decision. Plastic pipes such as PEX (Cross-linked polyethylene) and CPVC (Chlorinated Polyvinyl Chloride) are used along with the copper. Stainless steel is being considered but does not have a significant market share. In a focus group study, we elicited consumer preferences towards a variety of attributes associated with a plumbing system. We formalized the attribute ranking within the frame work of the Analytic Hierarchy Process (AHP). Multiple attributes including price, corrosion resistance, fire retardance, health effects, longevity, re-sale value of home, and taste and odor are considered. Participants’ overall preference tradeoffs are reported in this paper.

Analyzing Copper Plumbing Pipe Failures

Pinhole leak in home copper plumbing has emerged as a significant issue. In the major water distribution system managed by municipalities and water utilities the costs are distributed among all subscribers. The home plumbing repair/replacement cost and possible water damage cost must be addressed by the home owner. There are also issues of the value of home, insurance rates, health consequences, and taste and odor problems. These issues have become a major concern to home owners. We present a methodology that accounts for random arrivals of leak events in determining the optimal replacement time.

Dynamic Modeling of Droughts

Long term monthly records of Palmer drought index in respect of one climatic division each in Arizona, California, and Virginia are analyzed to explain empirically observed bi-modal distribution. The classical Fokker Planck equation is solved to obtain steady state and time varying probability density functions of the index. An example is presented showing application of computed densities in making forecasts of index values.

A Stochastic Characterization of Palmer Drought Severity Index

The Palmer Drought Severity Index (PDSI) combines a set of key meteorologic and hydrologic variables to assign a numerical value for drought severity which can be used as a unified drought scale for comparison among different geographical regions. The index values are further put in several drought severity classes with highest class being the severest drought. This class assignment is taken advantage of, to formulate a time varying (non-homogeneous) Markov chain approach for characterizing the underlying drought stochastic process. The approach identifies drought prone geographical regions, persisting drought classes, periods of return to a particular drought class, and yields short term predictions for future droughts. A time homogenous Markov chain is also formulated. The average of the statistics taken over all months from the non-homogeneous Markov chain agrees quite well with that of the time homogeneous chain. Monthly statistics from the non-homogeneous chain also compare very well with the empirical results obtained with the aid of 1152 months of data for the years 1895–1990 belonging to two climatic divisions in Virginia, USA, namely the Tidewater Region the Southwest Mountains Regions. The Tidewater Region is short of water as opposed to the Southwest Mountains Regions which is water rich.