Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Two-scale momentum theory for time-dependent modelling of large wind
  farms   This paper presents a theory based on the law of momentum conservation to
define and help analyse the problem of large wind farm aerodynamics. The theory
splits the problem into two sub-problems; namely an 'external' (or farm-scale)
problem, which is a time-dependent problem considering large-scale motions of
the atmospheric boundary layer (ABL) to assess the amount of momentum available
to the ABL's bottom resistance at a certain time; and an 'internal' (or
turbine-scale) problem, which is a quasi-steady (in terms of large-scale
motions of the ABL) problem describing the breakdown of the ABL's bottom
resistance into wind turbine drag and land/sea surface friction. The two
sub-problems are coupled to each other through a non-dimensional parameter
called 'farm wind-speed reduction factor' or 'farm induction factor,' for which
a simple analytic equation is derived that can be solved iteratively using
information obtained from both sub-problems. This general form of coupling
allows us to use the present theory with various types of flow models for each
scale, such as a numerical weather prediction (NWP) model for the external
problem and a computational fluid dynamics (CFD) model for the internal
problem. The theory is presented for a simplified wind farm situation first,
followed by a discussion on how the theory can be applied (in an approximate
manner) to real-world problems; for example, how to estimate the power loss due
to the so-called 'wind farm blockage effect' for a given large wind farm under
given environmental conditions.

33
The categories of this paper are: plasm-ph
9
The categories of this paper are: nlin
1
The categories of this paper are: cs
2
The categories of this paper are: math
15
The categories of this paper are: nucl-ex
18
The categories of this paper are: econ
0
The categories of this paper are: hep-ph
13
The categories of this paper are: quant-ph
16
The categories of this paper are: stat
23
The categories of this paper are: solv-int
8
The categories of this paper are: hep-ex
6
The categories of this paper are: astro-ph
11
The categories of this paper are: hep-lat
37
The categories of this paper are: supr-con
5
The categories of this paper are: gr-qc
34
The categories of this paper are: chem-ph