Flow and tide boundaries¶

What this shows: the boundary settings for the flow and water level, on each side of the grid.

Prerequisites: Tutorial 2: Defining the model grid (for the names of the grid sides) and Tutorial 5: Choosing model settings.

You will learn:

• which flow boundary types exist for the offshore, back and lateral boundaries
• how lateral wave boundaries avoid shadow zones
• how water levels are applied with tideloc, and how this interacts with tide forcing

Data used: none.

Setup¶

In [1]:

from rompy.logging import config as logging_config
from rompy_xbeach.components.boundary.parameters import (
    FlowBoundaryConditions,
    TideBoundaryConditions,
)

logging_config.update(level="WARNING")  # rompy logs every step, show warnings only


def show(component):
    """Print the XBeach parameters a component writes to params.txt."""
    params = component.get(destdir=None)
    for key, value in params.items():
        print(f"{key} = {value}")
    if not params:
        print("(nothing written, XBeach defaults apply)")

from rompy.logging import config as logging_config from rompy_xbeach.components.boundary.parameters import ( FlowBoundaryConditions, TideBoundaryConditions, ) logging_config.update(level="WARNING") # rompy logs every step, show warnings only def show(component): """Print the XBeach parameters a component writes to params.txt.""" params = component.get(destdir=None) for key, value in params.items(): print(f"{key} = {value}") if not params: print("(nothing written, XBeach defaults apply)")

1. Flow boundaries¶

The four sides of the grid are front (offshore), back (landward), and left and right (lateral):

Side	Options	XBeach default
front	abs_2d, abs_1d, wall, wlevel, nonh_1d, waveflume	abs_2d
back	abs_2d, abs_1d, wall, wlevel	abs_2d
left, right	neumann, wall, no_advec, neumann_v, abs_1d	neumann

abs_2d and abs_1d are absorbing-generating boundaries that let waves leave the domain, wall blocks all flow, wlevel imposes a water level, and neumann assumes no alongshore gradient.

In [2]:

show(FlowBoundaryConditions())

show(FlowBoundaryConditions())

(nothing written, XBeach defaults apply)

A beach backed by a dune or seawall, with a closed landward boundary:

In [3]:

show(
    FlowBoundaryConditions(front="abs_2d", back="wall", left="neumann", right="neumann")
)

show( FlowBoundaryConditions(front="abs_2d", back="wall", left="neumann", right="neumann") )

front = abs_2d
back = wall
left = neumann
right = neumann

For a laboratory flume, the offshore boundary acts as a wave maker and the sides are walls:

In [4]:

show(
    FlowBoundaryConditions(front="waveflume", back="abs_1d", left="wall", right="wall")
)

show( FlowBoundaryConditions(front="waveflume", back="abs_1d", left="wall", right="wall") )

front = waveflume
back = abs_1d
left = wall
right = wall

2. Lateral wave boundaries¶

With the default neumann, oblique waves can leave a shadow zone near the lateral boundaries. wavecrest assumes no gradient along the wave crests, which reduces this. cyclic connects the two sides for alongshore-uniform tests.

In [5]:

show(FlowBoundaryConditions(lateralwave="wavecrest"))

show(FlowBoundaryConditions(lateralwave="wavecrest"))

lateralwave = wavecrest

3. Water level boundaries¶

tideloc sets how many water level signals are applied:

tideloc	Water level
0	Constant level zs0 everywhere, no tide file
1	One signal along the offshore boundary
2	Two signals, offshore and landward (paulrevere="land") or at the two offshore corners ("sea")
4	One signal at each corner

XBeach defaults to tideloc=2, which needs a tide file. Without tide forcing, set tideloc=0:

In [6]:

show(TideBoundaryConditions(tideloc=0, zs0=0.3))

show(TideBoundaryConditions(tideloc=0, zs0=0.3))

tideloc = 0
zs0 = 0.3

tidetype controls how the water level is imposed: velocity (default) through the flow velocities, instant directly on the water level, or hybrid.

In [7]:

show(TideBoundaryConditions(tidetype="instant"))

show(TideBoundaryConditions(tidetype="instant"))

tidetype = instant

Interaction with water level forcing¶

The water level forcing classes in input.tide write a single timeseries and set tideloc=1 themselves (see water levels). The tide_boundary parameters are applied after the forcing, so a tideloc set there overrides the forcing. When you use water level forcing, leave tideloc unset and use tide_boundary only for settings such as tidetype.

Summary¶

• FlowBoundaryConditions sets the flow boundary on each side, plus the lateral wave boundary.
• TideBoundaryConditions sets how water levels are applied. Use tideloc=0 without tide forcing, and leave it unset with tide forcing.
• Wave boundaries are set separately, through input.wave.