How do I "sink" lines into model so they can become visible for 3D printing?

I am 3D printing models and to give them more detail, I need to show the model’s lines. The problem is those lines are not treated as a gap or other structural component but as another part of the surface so they do not show up in the 3D printed product.

Figure 1

For example, this highlighted line in figure 1 will not show up in the 3D printed model.

Figure 2

It is especially important for those lines to show up on sections like figure 2 since otherwise, it will me smooth and lack detail.

My only ideas for expressing those lines as to somehow “sink” them into a model and convert those lines into trenches. I have crudely drawn what I mean in figure 3.

Figure 3

As you can see, the thin line is the surface from a cross-section perspective and the thick dot is the line. Either I can make that cross section look like a V-shaped trench or a square-shaped one. This is how I intend to express those lines for my 3D printed models but the problem is I do not know how, especially for curved surfaces.

It depends on how you built your surfaces, but you can try this way:

or like this (with Quad Tools)


Thank you! This is exactly what I want!