Abnormal Head Values in Extended Model Area with Head Line Sink

[ArtemisRo]

I have created a groundwater model using a Head Line Sink in QGIS-Timml, and I have successfully obtained reasonable head values for each layer within the initial model area. However, when I extend the model area and perform calculations, I am encountering excessively high and unrealistic head values.
Attached is a photo illustrating the issue.
Additionally, I've included the Python script used to define and execute the current model.

Model code to reproduce the error:

import numpy as np
import timml

model = timml.ModelMaq(
    kaq=[6.0, 2.5, 65.0],
    z=[-2.0, -2.0, -4.5, -10.0, -18.0, -19.0, -33.0],
    c=[700.0, 500.0, 50.0],
    topboundary="semi",
    npor=[None, None, None, None, None, None],
    hstar=0.0,
)
Riolering2_0 = timml.HeadLineSinkString(
    xy=[
        [81339.22502708525, 436686.6311739245],
        [81350.79144223033, 436681.7205188097],
        [81389.29293477698, 436681.8738948385],
    ],
    hls=-2.7,
    res=0.001,
    wh=4.0,
    order=7,
    layers=0,
    label=None,
    model=model,
)

model.solve()
head = model.headgrid(
    xg=np.arange(80540.0, 82170.0, 20.0), yg=np.arange(437350.0, 436220.0, -20.0)
)


print('max head: ', head.max())

[mbakker7]

I am afraid you found a bug. The line-sink doesn't go nicely to zero at larger distance when the order is large.
Simplified problem:

import timml as tml
ml = tml.ModelMaq(kaq=[6.0], z=[1, 0, -2], c=[700.0], topboundary="semi", hstar=0.0)
ls2 = tml.HeadLineSink(ml, x1=-20, y1=0, x2=20, y2=0, hls=2, order=7)
ml.solve()
ml.contour([-800, 800, -400, 400], ngr=50)

[dbrakenhoff]

Hi @ArtemisRo,

Thanks for posting your issue. I contoured the heads after running your script, and near the element, the solution seems pretty reasonable.

xg = np.arange(81_250, 81_475, 5) 
yg = np.arange(436_800, 436_550, -5)
head = model.headgrid(xg=xg, yg=yg)
plt.contour(xg, yg, head[0])
plt.axis("equal")
model.plot(newfig=False)

The solution "far away" becomes unstable, resulting in the extremely large heads you're seeing.

Lowering the order of the element helps in this case. With order=3:

The reason for this I'm not entirely sure about, but we'll look into it!