Merge branch 'documentation/aeroanalysis' into 'develop'

Documentation for aerodynamic analysis

See merge request !33

docs/documentation/analysis/aerodynamic_analysis/aerodynamic_principles.md

+
+# Aerodynamic principles {#aerodynamicprinciples}
+
+All methods for calculationg the properties of an aircraft face a trade off between accuracy on one hand and complexity and computing effort on the other hand.
+
+A typical aircraft in UNICADO takes roughly 20 to 30 iterations to converge in the design loop.
+For each iteration, the full aerodynamic properties have to be calculated.
+To enable extensive design space exploration and optimization studies in a reasonable time frame, the whole design process in UNICADO should takes less then an hour.
+The aerodynamic analysis therefore should be finished in under a minute.
+As a consequence of this requirement, the preliminary aircraft design in general, including UNICADO, is limited to lower fidelity methods, ranging from semi-empirical formulas to analytical approaches.
+
+**aerodynamic_analysis** contains a set off different methods and will be expanded in future.
+
+
+## Methods
+
+Currently there are **methods** with differing levels of fidelity implemented. These methods are listed in the table below.
+
+| Aerodynamic value                               | Methods                       | Fidelity level                    | Application                               |
+|-------------------------------------------------|-------------------------------|-----------------------------------|-------------------------------------------|
+|Lift, induced drag and pitching moment           | Lifting Line                  | analytical                        | Lifting surfaces in general               |
+|Lift, induced drag and pitching moment with corrections for TAW   | Lifting Line | analytical/semi-empirical         | Wing and stabilizer for TAW               |
+|Viscous drag                                     | According to Raymer           | semi-empirical                    | Lifting surfaces, fuselages and nacelles  |
+|Wave drag                                        | According to Mason            | semi-empirical                    | Lifting surfaces                          |
+|High lift adaptions                              | According to Raymer and Howe  | semi-empirical                    | TAW configuration                         |
+|Trim function                                    | Linear interpolation          |             -                     | Trimming via all movable horizontal stabilizer |
+
+The aim is to extend the method set with new calculation methods of variing fidelites for conventional TAW and and conventional configurations like the BWB.
+
+## Strategies
+
+The methods shown above have certain limitations:
+- No method can provide all aerodynamic values needed
+- The methods are only valid for certain flight conditions and aircraft configurations
+- Most methods need other aerodynamic values as input for their calculation
+  
+Because of these shortcommings, the engineer has to select a suitable set of methods for their aircraft and bundle them together into a **strategy**.
+Due to the complexitiy in the fields of aerodynamics, the individual methods cannot be pluged in and out of a strategy, rather the strategies are tailor made for a given case.
+For illustration, the default strategy for calculation of the polars for the TAW is explained in the next chapter.
+
+
+## Example strategy for tube and wing
+
+### Lifting Line
+Lifting Line is a method to calculate the lift distribution and the induced drag.
+For this purpose, the potential equations are used, i.e. the flow is simplified and assumed to be frictionless, rotationless and incompressible.
+The wing is reduced to its skeletal lines.
+This simplified geometry is divided into trapezoidal elementary wings, which are covered with free and bound vortices.
+A system of equations is constructed from the vortex system and the boundary conditions, the solution of which is used to calculate the lift distribution.
+For a more in-depth discussion, the  dissertation by Horstmann (Horstmann 1987: Ein Mehrfach-Traglinienverfahren und seine Verwendung für Entwurf und Nachrechnung nichtplanarer Flügelanordnungen) is recommended.
+
+The following picture shows the lifitng surfaces of a typical TAW aircraft discretized into elementary wings according to the lifting line method:
+![A wing and horizontal tailplane broken down into elementary wings](img/ll_geom.png)
+
+The Prandtl-Glauert transformation is applied to the polars from Lifting Line.
+Lift coefficients, induced drag and pitch moment coefficients are thus transformed to include the compressibility effects.
+The lift distribution calculated using lifting line agrees well with CFD results for both the conventional wing and the blended wing body.
+Since the concept of the induced drag is based on the lifting line theory, it cannot be validated by CFD methods, which are based on the Navier-Stokes-Equations.
+Several semi-empirical corrections are integrated into the lifting line methodology in UNICADO.
+Based on Roskam, induced drag is calculated for the fuselage and nacelles.
+The pitching moment is corrected for fuselage and nacelle influences based on Torenbeek (Torenbeek, E. - Advanced Aircraft Design, 2013, ISBN: 9781119969303).
+
+### Viscous drag according to Raymer
+The frictional drag/viscous drag/zero lift drag is calculated based on the method of Raymer (Raymer 1992: Aircraft Design: A Conceptual Approach, page 280 ff).
+Contrary to what the name suggests, the viscous drag also regards influences of the boundary layer, which makes validation by CFD calculations difficult.
+
+For this purpose, the aircraft is broken down into its individual components, whose drag is calculated from a form factor, interference factor, friction coefficient and the wetted area:
+
+$
+    C_{D0} = \frac{\sum(C_{fc}FF_{c}Q_{c}S_{wet,c})}{S_{ref}}+C_{Dmisc}+C_{DLP}
+$
+
+The form factors are calculated using semi-empirical formulas, the interference factors are derived from the recommendations in the text (page 284 f).
+The friction coefficient is derived from the flow around a flat plate and depends on the Reynolds number and the surface roughness.
+
+In addition to the drags for the individual components, a 'miscellaneous drag' is calculated.
+This includes resistance caused by gas entering and leaving the hull through leaks and resistance caused by antennas, protrusions and the like.
+In total, the viscous drag depends only on the geometry, Reynolds number and Mach number and is thus constant over an entire aircraft polar.
+A calibration method is built in which the viscous drag is calibrated using an exponential function based on the lift coefficient.
+Thus, the viscous drag slightly increases with increasing lift.
+
+### Wave drag according to Mason
+The wave drag is the pressure drag generated by the occurrence of a shock wave.
+A compression shock reduces the static pressure of the fluid, which results in the surface pressure at the trailing edge of the profile being weaker than at the leading edge.
+The wave drag therefore only occurs when a compression shock occurs.
+From flight data it could be deduced that with increasing Mach number the wave drag is only between 0 and 10 drag counts and increases slightly linearly up to a Mach divergence number, above which the wave drag increases exponentially.
+This behavior of the wave drag is approximated by a fourth degree polynomial.
+
+The following picture shows the drag creep in the flight test data of a DC-9-30, according to Gur, Full-COnfiguration Drag Estimation, 2010:
+![The rise of the wave drag for a typical aircraft](img/Drag_creep.png)
+
+To calculate the wave drag, the critical Mach number is required, which is calculated according to the Korn-Mason equation (Mason 1990: Analytic Models for Technology Integration in Arcraft Design).
+To calculate the critical Mach number, the wing sweep, the profile thickness ratio, the local lift coefficient and the "profile technology factor" are required.
+Two values ​​are given for the profile technology factor, 0.87 for conventional and 0.95 for transonic profiles.
+Since the local lift coefficient is included in the formula for the critical Mach number, the wing is divided into individual strips for the drag calculation.
+
+For each strip, the local critical Mach number and the local wave drag are calculated and then summed up.
+In Gur 2010: Full-Configuration Drag Estimation a simple, area-weighted summation over all wing strips is proposed.
+The wave drag is then calibrated like the viscous drag using an exponential function based on the lift coefficient.
+
+### High lift polars
+Analysis of the aircraft in high lift configurations, with extended leading and trailing edge high lift devices, poses difficulties, even in numerical or experimental setups.
+In the interest of saving computing time and ressources in the aerodynamic analysis, the only valid option is to rely on semi-empirical calculations.
+
+The high lift polars are calculated for the following cases:
+
+- Take Off
+
+- Take Off landing gear retracted
+
+- Climb
+
+- Approach
+
+- Approach with landing gear
+
+- Landing
+
+For this, the number, type, postions and areas of all leading and trailing edge devices are read in.
+The geometric parameters of the high lift devices are used to calculate a maximum lift coefficient and shifts of the drag and moment coefficients, based on a set of semi-empirical formulas.
+
+The following picture shows the shifts in lift and drag in the high lift polars for a typical short medium range passernger aircraft according to the method:
+![An example of a clean polar and transformed high lift polars at Mach 0.2](img/high_lift_shift.png)
\ No newline at end of file

docs/documentation/analysis/aerodynamic_analysis/getting_started.md

+# Getting started {#getting-started}
+This guide will show you the basic usage of **aerodynamic_analysis**. Following steps are necessary (if you are new to UNICADO check out the [settings and outputs](#settingsandoutputs) first!)
+
+## Step-by-step
+
+It is assumed that you have the `UNICADO Package` installed including the executables. In case you are a developer, you need to build the tool first (see [build instructions on UNICADO website](https://unicado.pages.rwth-aachen.de/unicado.gitlab.io/developer/build/cpp/)).
+
+1. Take an `aircraft_exchange_file` with a fully designed aircraft (fuselage, wing, empennage and nacelles already sized)
+2. Fill out the configuration file - change at least:
+    - in `control_settings` 
+        - `aircraft_exchange_file_name` and `aircraft_exchange_file_directory` to your respective settings
+        - `console_output` at least to `mode_1`
+        - `plot_output` to false (or define `inkscape_path` and `gnuplot_path`)
+    - in `program_settings`
+        - `Trim` enable/disable and tune the trim calculations
+        - `FlightConditions`define your flight conditions with altitude and mach number
+        - The different methods, like `ViscDragRaymer` which are listed can be fine tuned, and customized
+        - Enable/disable and set individual calibration factors in the different methods and for the overall polars in `DragCorrection`
+3. Open terminal and run **aerodynamic_analysis**
+
+
+Following will happen:
+- you see output in the console window
+- csv- files containing the raw lift, drag and moment data for all calculations are created in the `aerodynamic_analysis` folder
+- results are saved via xml-file in the `/aircraft_exchange_file/aero_data` for later use in e.g. **mission_analysis**

docs/documentation/analysis/aerodynamic_analysis/index.md

+# Introduction {#mainpage}
+The tool aerodynamic_analysis is on of the core tools in UNICADO. The overall goal is to calculate the lift and drag for all flight phases ranging from take off to cruise and landing.
+The gool of the tool is to...
+- Enable aerodynamic analysis for conventional and unconventional aircraft configurations
+- calculate the lift to drag polars for all flight phases regarding the aircraft geometry and the altitude and flight speed
+
+
+The [getting started](getting_started.md) gives you a first insight in how to execute the tool and how it generally works. To understand how the aerodynamic analysis works in detail, the documentation is split into a [aerodynamic principles](aerodynamic_principles.md) and a [software architecture](software_architecture.md) section. 
+

docs/documentation/analysis/aerodynamic_analysis/software_architecture.md

+# Software architecture {#softwarearchitecture}
+
+The software architecture is structured into various modules and packages, each handling specific tasks. Below is a description of the main components
+
+- strategies:
+  - **Strategies** define the procedure of calculating the polars by initializing the aircraft geometry, calling methods and copying and processing data.
+  - There are different strategies implemented, stored in the folders corresponding to the aircraft configuration (e.g., `taw`, `bwb`).
+  - Each Strategy has a corresponding `data.cpp` for reading and writing data into the `aircraft.xml` and a `config.cpp`file for reading from the `config.xml`.
+
+- methods:
+  - **Methods** are either derived from literature or rely on external calculation sofwares, data bases or surrogate models.
+  - Methods are structured in a general way, so that they can be accessed by all strategies ranging over different aircraft configurations.
+  - Methods are stored in the `methods` folder and need to be initialized, by **geometry input**, **flight conditions** and **input parameters** from the config file.
\ No newline at end of file

mkdocs.yml

@@ -150,6 +150,14 @@ plugins:
             FILE_PATTERNS: "*.cpp *.h"
             RECURSIVE: True
             EXTRACT_ALL: YES
+        aerodynamic_analysis:
+          src-dirs: ../aircraft-design/aerodynamic_analysis/
+          full-doc: true
+          output: docs/aerodynamic_analysis
+          doxy-cfg:
+            FILE_PATTERNS: "*.cpp *.h"
+            RECURSIVE: True
+            EXTRACT_ALL: YES
         aircraftGeometry2:
           src-dirs: ../aircraft-design/libs/aircraftGeometry2/
           full-doc: true
@@ -321,6 +329,10 @@ nav:                                      # Customizes the main navigation struc
               - ecological_assessment/namespaces.md
               - ecological_assessment/files.md
               - ecological_assessment/functions.md
+          - Aerodynamic Analysis:
+            - Introduction: documentation/analysis/aerodynamic_analysis/getting_started.md
+            - Aerodynamic Principles: documentation/analysis/aerodynamic_analysis/aerodynamic_principles.md
+            - Software Architecture: documentation/analysis/aerodynamic_analysis/software_architecture.md
           - Constraint Analysis:
             - Introduction: documentation/analysis/constraint_analysis/index.md
             - Principles: documentation/analysis/constraint_analysis/principles.md