representing various stages of the tide, the model boundaries generate complex
patterns that include large-scale turbulent-like features such as gyres and 3-D
velocity structures. The flow patterns reveal regions of faster and slower current
velocities, and potential sediment deposition areas can be readily identified.
The purpose of the small-scale physical models was to perform an initial
investigation of the complex flow regime using an economical tool with the hope
of identifying the physical mechanism responsible for shoaling of the Port of
Anchorage. An added benefit of the models was the capability to modify
physical conditions and immediately observe changes brought about in the
system. This allowed potential engineering solutions to be examined rapidly.
For example, impacts caused by structures intended to redirect flows could be
assessed and optimized using the small-scale models.
Turbulent scale effect in geometrically distorted physical models
The second component was to examine potential turbulence scale effects that
might occur in geometrically distorted physical models. The Alaska District is
contemplating construction of a large physical model to simulate tidal flow in
Cook Inlet and at the Port of Anchorage. The proposed model would be
constructed at considerable expense, and it would be the primary tool for
investigating problems and developing solutions for the region centered on the
Port of Anchorage. The area encompassed in this model would require that the
model horizontal length scale would be different than the vertical length scale.
Generally, geometric distortion of tidal flow models is an accepted practice
because vertical velocities and accelerations are considered negligible. However,
flow patterns in Cook Inlet exhibit regions of flow separation and entrainment,
which can produce non-negligible vertical components to the flow. If these
vertical flow structures are thought to be important to the shoaling and scour
processes that are to be examined in the large-scale physical model, it is crucial
to determine potential scale effects that might arise from incorrectly simulating
3-D turbulence in geometrically distorted physical models.
The purpose of this component is to assess the turbulence scale effect that
arises in geometrically distorted physical models of tidal flow, and to determine
whether this scale effect would adversely impact results obtained from the
proposed large-scale model of Cook Inlet.
The original scope of work called for four study tasks. A fifth task was
added based on observations of the physical models during the first site visit by
Alaska District engineers. These tasks are briefly described as follows:
Task 1: Large-area idealized flow model of Cook Inlet
The objective of this task was to identify and examine in a semiquantitative
way the large-scale flow patterns in upper Cook Inlet during maximum ebb and
Chapter 1 Introduction