scaling 0.2.3
convert units using Froude and Reynolds similitude

# scaling

Convert quantities between model and prototype scale using Froude and Reynolds similitude.

## Installation

```
pip install scaling
```

## Usage

```python
>>> from scaling import FroudeConverter
>>> froude = FroudeConverter()

>>> # Convert model value of 200 mm to prototype value (m) with scale of 10
>>> froude.model_to_proto(200,Â length_scale=10,Â input_unit='mm',Â target_unit='m')
2.0

>>> # Get Froude scaling exponent for quantities of time
>>>Â froude.scaling_exponent('s')
0.5

>>> # Get length, mass and time dimensions for quantities of energy
>>>Â froude.dimensions('kJ')
'L^2Â M^1Â T^-2'
```

Dataframes are also accepted, and specific units can be specified for the values in the index.

```python
>>> T = 2
>>> H = 100

>>> # Generate regular waves with height=100mm, and period=2s
>>> t = np.arange(0, 10.1, 0.1)
>>> eta = 0.5 * H * np.sin(t * 2 * np.pi / T)

>>> df_model = pd.DataFrame(index=t, data=eta)
>>> df_model.columns = ['$\eta$ (mm)']
>>> df_model.index.name = 'Time (s)'

>>> df_model.plot()
```

![model](https://user-images.githubusercontent.com/11261876/45915234-575e4300-be95-11e8-9edd-30338bd6db2d.png)

```python
>>> # Convert to prototype dimensions, with length scale=25
>>> df_proto = froude.model_to_proto(
        df_model,
        length_scale=25,
        input_unit='mm',
        target_unit='m',
        index_input_unit='s',
        index_target_unit='s')

>>> df_proto.columns = ['$\eta$ (m)']
>>> df_proto.plot()
```
![proto](https://user-images.githubusercontent.com/11261876/45915245-6c3ad680-be95-11e8-9912-2dc2afc16b9a.png)

`scaling` uses `pint` for unit and dimension conversions. `pint` is able to interpret a wide range of different input units.

```python
>>> # Convert water head model value (mm) to prototype pressure value (kPa)
>>> froude.model_to_proto(10,Â length_scale=100, 'mm.H20',Â 'kPa')
9.80665

>>> # Demonstrate different ways of specifying units of newtons
>>>Â froude.dimensions('N')
'L^1Â M^1Â T^-2'
>>>Â froude.dimensions('newton')
'L^1Â M^1Â T^-2'
>>>Â froude.dimensions('kg.m/s/s')
'L^1Â M^1Â T^-2'
>>>Â froude.dimensions('kilogram.metre/second^2')
'L^1Â M^1Â T^-2'
```

## Froude scaling reference

| Quantity     | Dimensions    | Scaling exponent |
|--------------|---------------|------------------|
| Length       | L^1           | Î»^1              |
| Mass         | M^1           | Î»^3              |
| Time         | T^1           | Î»^0.5            |
| Velocity     | L^1 T^-1      | Î»^0.5            |
| Acceleration | L^1 T^-2      | Î»^0              |
| Force        | L^1 M^1 T^-2  | Î»^3              |
| Pressure     | L^-1 M^1 T^-2 | Î»^1              |
| Overtopping  | L^2 T^-1      | Î»^1.5            |


## Reynolds scaling reference

| Quantity     | Dimensions    | Scaling exponent |
|--------------|---------------|------------------|
| Length       | L^1           | Î»^1              |
| Mass         | M^1           | Î»^3              |
| Time         | T^1           | Î»^2              |
| Velocity     | L^1 T^-1      | Î»^-1             |
| Acceleration | L^1 T^-2      | Î»^-3             |
| Force        | L^1 M^1 T^-2  | Î»^0              |
| Pressure     | L^-1 M^1 T^-2 | Î»^-2             |
| Overtopping  | L^2 T^-1      | Î»^0              |