#!/usr/bin/env python
# coding: utf-8

# # Minimal Example pandapipes
# 
# ## Creating a low pressure gas network
# 
# We consider the following simple 3-junction example network with an ideal valve as a minimal example:
# 
# <img src="pics/minimal_example.png">
# 
# The above network can be created in pandapipes as follows:

# In[ ]:


import pandapipes as pp

#create empty net
net = pp.create_empty_network(fluid="lgas")

# create junction
j1 = pp.create_junction(net, pn_bar=1.05, tfluid_k=293.15, name="Junction 1")
j2 = pp.create_junction(net, pn_bar=1.05, tfluid_k=293.15, name="Junction 2")    
j3 = pp.create_junction(net, pn_bar=1.05, tfluid_k=293.15, name="Junction 3")    

# create junction elements
ext_grid = pp.create_ext_grid(net, junction=j1, p_bar=1.1, t_k=293.15, name="Grid Connection")
sink = pp.create_sink(net, junction=j3, mdot_kg_per_s=0.045, name="Sink")

# create branch element
pipe = pp.create_pipe_from_parameters(net, from_junction=j1, to_junction=j2, length_km=0.1, diameter_m=0.05, name="Pipe 1")
valve = pp.create_valve(net, from_junction=j2, to_junction=j3, diameter_m=0.05, opened=True, name="Valve 1")


# Note that the fluid used here is ``lgas`` (low-calorific natural gas). You can find 7 predefined fluids in pandapipes:
# - ``lgas`` (low-calorific natural gas)
# - ``hgas`` (high-calorific natural gas)
# - ``hydrogen``
# - ``water``
# - ``biomethane_pure``
# - ``biomethane_treated`` (see [here](https://pandapipes.readthedocs.io/en/latest/fluid_properties/fluids.html) for the composition)
# - ``air``
# 
# And that the predefined valve element is an ideal valve. 

# ## Data Structure
# 
# Each dataframe in a pandapipes net object contains the information about one pandapipes element, such as pipe, sink, valve etc.

# In[ ]:


net.junction


# In[ ]:


net.pipe


# In[ ]:


net.ext_grid


# ## Pipe Flow
# 
# We now run a pipe flow:
# 

# In[ ]:


pp.pipeflow(net)


# And check out at the results for junctions and pipes:

# In[ ]:


net.res_junction


# They're is no pressure loss between junction 2 and junction 3 because of the ideal valve.

# In[ ]:


net.res_pipe


# ### Closed valve
# 
# We now close the valve between junction 2 and junction 3:

# In[ ]:


# Problem can not run pipeflow if valve closed
net.valve.opened = False


# The closed valve cuts the sink from the external grid:
# 
# <img src="pics/minimal_example_closed_valve.png">

# This can be verified by running a power flow and inspecting the results. The pressure and temperature at junction 2 is given as NaN:

# In[ ]:


pp.pipeflow(net)
net.res_junction


# Also the results from the pipe show that the mass flow is almost zero and the speed of the mass flow is zero. 

# In[ ]:


net.res_pipe