Spatially Varying Friction Coefficient File (fort.21)

Spatially variable nodal friction coefficients. This file is only read when NWP =1 or 2 in the Model Parameter and Periodic Boundary Condition File.

The basic file structure is shown below. Each line of input data is represented by a line containing the input variable name(s) in bold face type. Blank lines are only to enhance readability. Loops indicate multiple lines of input. Definitions of each variable are provided via hot links.

 

if NWP = 1
AFRIC
for k=1, NP
JN, FRIC(k)
end k loop

if NWP = 2
AFRIC
NBPNODES
for k=1, NBPNODES
NBNNUM(k), BK(k), BALPHA(k), BDELX(k), POAN(k)
end k loop

Notes for NWP = 1

The friction coefficient must be input for all nodes.  If NOLIBF = 0, the friction coefficient is assumed to be the linear friction coefficient (TAU).  If NOLIBF = 1, the friction coefficient is assumed to be the quadratic friction coefficient (CF).  If NOLIBF = 2, the friction coefficient is assumed to be the minimum friction coefficient (CF).

Notes for NWP = 2

Special considerations must be used when designing a grid for an ADCIRC application that includes the effects of bridge pilings.  Specifically, it is necessary to build the grid to provide at least three rows of nodes that parallel the bridge span.  One row of nodes (centerline nodes) should lie along the approximate centerline of the bridge while the second and third rows of nodes (adjacent nodes) should lie on either side of the centerline nodes in the along steam direction.  An initial implementation of obstruction drag in ADCIRC placed this drag entirely at the row of centerline nodes.  However, tests showed that this arrangement led to significant oscillations in the numerical solution.  The oscillations abated when the obstruction drag was distributed in the along stream direction so that 25 percent was located at each row of adjacent nodes and 50 percent was located at the row of centerline nodes.  Node numbers and coefficient values at all nodes on the centerline and two adjacent rows must be entered in this input file.  It is not necessary for centerline nodes to correspond to actual piling positions, (i.e., in the cross stream direction), since the overall effect of the pilings on the large scale circulation is all that is being represented.  It is important, however, to construct a grid that is as uniform as possible in the vicinity of the bridge.