Development of Computational Methodology to Assess Structural Damage in Spillway Sections of Dams, 20-R8131Printer Friendly Version
Inclusive Dates: 01/01/10 Current
Background - Spillways, an integral part of dams, are designed to discharge floodwater and maintain a safe reservoir level to prevent overtopping of dams. However, high flow velocity in spillways during floods results in cavitation that damages the spillway structure and underlying foundation. Cavitation erosion and headcutting with scouring of foundation material are major contributors to dam failure. Most of the dams in the United States and elsewhere in the world were developed with limited hydrological information. Climate change may affect probable maximum flood (PMF) and flood patterns, and may increase the discharge above the design capacity of a spillway in a particular dam. As a result, many spillway structures will need either modifications or new spillway paths to prevent dam overtopping, which could compromise dam integrity. Currently, the dam industry relies primarily on physical model testing and empirical methodologies to predict cavitation potential and guide the hydraulic design of the spillways. These approaches, however, cannot accurately predict scour location, extent, and depth in the prototype structure or help explain erosion dynamics as a result of cavitation. Physical models are generally not amenable to prediction of erosion or other potential spillway damage and failure.
Approach - Advances in computational fluid dynamics and parallel computing have led to the application of full three-dimensional Navier-Stokes equations for simulations in hydraulic structures. In the ongoing project, advanced techniques, such as computational fluid dynamics and mechanistic modeling tools, are combined to simulate the flow and the damage mechanism in an overflow spillway of a concrete dam. The complex flow features, such as turbulence, vortex breakup, and cavitation, are being modeled using commercially available CFD packages. Damage of the spillway structure, such as scour, erosion, and headcutting, are modeled using continuum and discontinuum mechanistic modeling codes. The fluid pressure and forces obtained from simulation of the flow processes using CFD packages are applied to mechanical models as boundary conditions on the spillway surface. The combined approach provides a significant advantage over existing physical and empirical models because a multiple full-scale numerical model analyses can be performed to study the changes in the flow characteristics, geometry, and material properties at a significantly lower cost and turnaround time and with greater certainty and accuracy. The emphasis of the present investigations is to develop a new integrated computational methodology for rehabilitating existing spillways and designing new spillways by significantly reducing the dependence on the hydraulic physical models and empirical relationships.
Accomplishments - Extensive simulations of flow over spillway were carried out to evaluate the role of geometry, turbulence and flow parameters on the characteristics of the unsteady flow and pressure field. These simulations highlighted the importance of spillway height, mass flow rate, and turbulence to flow characteristics and unsteadiness. The simulation results matched well with experimental data. Numerical flow analysis of the Glenn Canyon spillway is in progress to simulate the cavitation erosion observed at the spillway bend. Time-dependent spillway-wall shear stress will be implemented in the geomechanical model to simulate the structural damage.