# Undertow modelling - Forum - XBeach

## bug message reminder

**crash or bug**, please remember to

**include**an entire

**model setup**in your post that reproduces the crash or exposes the bug. Also add the

**XBlog.txt**file. This is necessary information for people that are trying to help you. Including your model setup can be achieved by adding the zipped run directory (excluding output) as an attachment to the post.

## Forum

### Undertow modelling

JS

##### Jan Schönhofer, modified 3 Years ago.

#### Undertow modelling

Capillary Posts: 1 Join Date: 10/22/14 Recent Posts 10

I need to model wave driven nearshore currents. I’m interested in the undertow generated by shore-normal wave approach. For this purpose I used a real beach profile configuration and applied a shore-normal wave at offshore boundary of the domain. I focus on stationary analysis (

For this situation the computations yield a nil Lagrangian current

The same conclusion can be drawn by theoretical analysis of the governing equations. Let us consider the continuity equation (GLM):

d_eta/d_t + d_hu/d_x + d_hv/dy = 0

The first left hand term is nil, because the studied case is stationary. Also, the third left hand term is nil, because there is no alongshore variability. Thus, the following term remains:

d_hu/dx = 0

which is true for variable bathymetry only in case when

Does this mean I make a mistake in my settings (params file)?

Does it mean XBeach is unable to model the undertow containing the effects of Stokes drift and wave breaking driven flows?

How should the undertow be modeled?

*instat = 0*).For this situation the computations yield a nil Lagrangian current

*u = 0*. A current that possesses some undertow characteristics is an Eulerian current*ue*, which is a mirror reflection of Stokes drift*uwf*. In my view though, it is not a genuine undertow, because it has no component resulting from wave breaking (that is a current resulting from radiation stress gradient).The same conclusion can be drawn by theoretical analysis of the governing equations. Let us consider the continuity equation (GLM):

d_eta/d_t + d_hu/d_x + d_hv/dy = 0

The first left hand term is nil, because the studied case is stationary. Also, the third left hand term is nil, because there is no alongshore variability. Thus, the following term remains:

d_hu/dx = 0

which is true for variable bathymetry only in case when

*u*is nil. This confirms results of computations, where the Lagrangian current*u*was equal to zero.**Questions:**Does this mean I make a mistake in my settings (params file)?

Does it mean XBeach is unable to model the undertow containing the effects of Stokes drift and wave breaking driven flows?

How should the undertow be modeled?

### Attachments:

MA

##### morgan alice, modified 6 Days ago.

#### RE: Undertow modelling

Capillary Posts: 1 Join Date: 1/20/20 Recent Posts 00

here i am talking about the global waves that is driven from the solar model, as we describe and analyze the recently and made some changes with the 3D global model. this model contains two temperature magnetohydrodynamics that an equation coupled, so far also closed to a magnetic field, we cipd assignments received the research paper on the same topic, where i also discuss the Poynting flux of chromospheric.