Date of Award:

5-2016

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Committee Chair(s)

Blake P. Tullis

Committee

Blake P. Tullis

Committee

Michael C. Johnson

Committee

Joseph A. Caliendo

Abstract

Linear weirs are a type of hydraulic structure that have been used for centuries with many different applications. One of the characteristics of weirs that is particularly useful is the head-discharge relationship where the discharge over the weir is directly related to the upstream water depth above the crest. In general, the head-discharge relationship for a weir is determined experimentally using geometrically similar models. Due to space, time, money, and discharge capacity limitations at water laboratories, creating full scale models is not always a feasible option when determining head-discharge relationships for weirs, resulting in the use of smaller scale models. However, as the model size decreases, the accuracy with which the model replicates the behavior of the prototype decreases. This disparity is caused by scale effects such as viscosity and surface tension, which prevent the model from behaving the same as the real world prototype. Over the years, researchers have developed rules of thumb or guidelines in the determining the size of a model in which scale effects can be avoided. These guidelines are often vague and based on previous experience.

The purpose of this research was to evaluate size scale effects for linear weirs to determine how size scale effects affect the head-discharge relationship for different model sizes and crest shapes. Physical models of 12 geometrically similar weirs were tested for three different crest shapes (flat-top, quarter-round, half-round) and weir model heights (24-, 12-, 6-, and 3-in). Head-discharge curves were developed for each model and compared to determine where variations existed between the different model heights. The profile of the flow over the weir or nappe profile was documented using digital photographs to determine if the behavior of the nappe varied for different model sizes. The results of this study will help modelers determine if the size of their linear weir model is sufficient to avoid scale effects.

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