For a numerical simulation paper, is it necessary to include boundary conditions and initial conditions in the paper? I am writing a paper on an engineering topic. We have an experimentally validated simpler model.

Questions:


The current paper extends the previous model for a more complex problem and explores the area numerically. Is it necessary to always include experimental validation for a numerical model, especially since we have already validated it for a simpler case? Is this enough for publication?
Since the primary domain equation, boundary condition and initial condition is the same (what varies between the simpler model and the more complex model is the parameters in the domain equation are more complex), is it necessary to include the boundary condition and initial condition in the paper as well, or can I just refer to the previous paper/include in the appendix? I am trying to reduce the size of the paper, and make it more readable.
The simulation methodology is more complex, because of the increased complexity of the domain equation. Does it help if I include the simulation methodology in the paper? Or should I just put it in the appendix?
Is it necessary to always include experimental validation for a numerical model?


Typically, yes, this is necessary. When you are going to publish an altered model (e.g., a more complex one), you need to demonstrate how the modifications play out in an experimental setup.


  Is it necessary to include the boundary condition and initial condition in the paper as well, or can I just refer to the previous paper/include in the appendix?


You may choose to either refer to your previous paper, or include them in your new paper (or do both). It is perfectly fine to refer to your previous publication, e.g., when you are trying to reduce the paper length, as long as the conditions are identical. However, when you want your new paper to be self-contained, or your previous paper was at a more obscure venue, it might be wise to include them in the new paper.


  Does it help if I include the simulation methodology in the paper? Or should I just put it in the appendix?


It is impossible to decide that without knowing the specifics, the journal's policy, and what is usual within your field.