=====================================
Add low fidelity engineering modeling
=====================================

In this section, a few simplified engineering models are added to the `example4 <https://github.com/ORNL-Fusion/tokdesigner-doc/tree/main/examples/example4>`_

Template
--------

`example5 <https://github.com/ORNL-Fusion/tokdesigner-doc/tree/main/examples/example5>`_

Evaulation
----------

**Command line**

.. code-block:: bash

  evaluate.py --input=evaluate.json --output=evaluate.dat --nsample=100000 --quiet

**evaluate.json**

.. code-block:: python

  {
    "scan": {
      "d_blanket" : {"type": "range", "ymin":0.2, "ymax":0.4},
      "d_tf"      : {"type": "range", "ymin":0.4, "ymax":1.2},
      "d_cs"      : {"type": "range", "ymin":0.2, "ymax":0.6},
      "f_wp"      : {"type": "range", "ymin":0.5, "ymax":0.8},
      "f_r_tf_out": {"type": "range", "ymin":2.5, "ymax":4.5}
    },
  
    "const": {
      "aratio"      : 3.0,
      "a"           : 1.3333,
      "kappa"       : 2.0,
      "delta"       : 0.6,
      "bt"          : 7.0,
      "ip"          : 8.1,

      "pinj"        : 38.0,
      "fgw_ped"     : 1.0,
      "nepeak"      : 1.9,
      "h98"         : 1.4,
  
      "eta_cd"      : 0.25,
      "eta_th"      : 0.33,
  
      "d_sol"       : 0.1,
      "d_str"       : 0.1,
      "gap_vv"      : 0.05,
      "d_vv"        : 0.15,
      "gap_shield"  : 0.05, 
      "d_shield"    : 0.225, 
      "gap_tf"      : 0.083,
      "gap_cs"      : 0.08,
  
      "t_helium"    : 4.5,
      "strain_sc"   : -0.005,
      "f_sc_copper" : 0.69,
      "f_sc_helium" : 0.46,
      "f_sc_conductor": 0.28  
    },
  
    "model": {
      "r"         : ["expr", "a * aratio"                 ],
      "betan_ped" : ["base", {}   ],
      "te_ped"    : ["base", {"dependency":"betan_ped"}   ],
      "ti_ped"    : ["expr", "te_ped"                     ],
      "ngw"       : ["base", {}                           ],
      "ne_ped"    : ["expr", "fgw_ped * ngw"              ], 
      "ne_axis"   : ["expr", "nepeak * ne_ped"            ],
      "betan"     : ["file", "fitout.json" ],
      "pfus"      : ["file", "fitout.json" ],
      "fbs"       : ["file", "fitout.json" ],
      "pnet"      : ["base", {}],
  
      "d_wp"      : ["expr", "f_wp * d_tf"], 
      "r_tf"      : ["expr", "r - ( a + d_sol + d_blanket + d_str + gap_vv + gap_shield + d_shield + gap_tf + d_tf )"],
      "r_cs"      : ["expr", "r_tf - ( gap_cs + d_cs )"],
      "r_tf_out"  : ["expr", "r + f_r_tf_out * a"],
  
      "bmax"      : ["base", {}],
      "itf"       : ["base", {}],
      "jtf"       : ["base", {}],
      "tf_stress_axial" : ["base", {}],
      "tf_stress_hoop"  : ["base", {}],
      "tf_stress" : ["expr", "tf_stress_axial + tf_stress_hoop"],
      "jsc_crit"  : ["base", {}], 
      "jtf_crit"  : ["expr", "jsc_crit * f_sc_copper * f_sc_helium * f_sc_conductor" ],
      "f_jtf_crit": ["expr", "jtf / jtf_crit"]
    }
  
  }


For the illustration purpose, one of the simplified radial build models is employed, which is mainly defined by the inboard thicknesses for a set of the tokamak structures including blanket (``d_blanket``), structure ring (``d_str``), vacuum vessel (``d_vv``), thermal shield (``d_shield``), TF coil (``d_tf``), and central solenoid (``d_cs``), along with the gaps between the structures (``gap_vv``, ``gap_shield``, ``gap_tf``, ``gap_cs``). See the :doc:`parametric geometry representation of tokamak<geometry>` and the :doc:`definition of TokDesinger variables<variable>` 

For the CAT-like reference case (``aratio`` = 3,  ``pinj`` = 38 MW, ``fgw_ped`` = 1, ``h98`` = 1.4), this example evaluates:

* TF coil stress (``tf_stress``) = sum of the hoop  (``tf_stress_hoop``) and axial (``tf_stress_axial``) stresses 
* TF coil current density in the winding pack (``jtf``) to produce the target magnetic field (``bt`` = 7 T at the plasma geometry center ``r`` = 4 m) 
* TF coil current density **limit** in the winding pack (``jtf_crit``) imposed by the critical superconductor coil current density (``jsc_crit``).

for a range of the radial build dimensions, in particular to decide a feasible thickness range of TF coil (``d_tf``) and blanket (``d_blanket``).


Filtering
---------

The constraints used in this example are:

* ``tf_stress`` < 500 MPa 
* ``jtf`` < ``jtf_crit``
* ``r_cs`` > 0.2 m 

, where ``r_cs`` is the inner radius of central solenoid.

**Command line**

.. code-block:: bash

    filter.py --input=filter.json --dbfile=evaluate.dat --output=filter.dat


**filter.json**

.. code-block:: python

   {
   "filter": {
     "tf_stress" : ["max", 500.0],
     "f_jtf_crit"  : ["max", 1.0],
     "r_cs" : ["min", 0.2]
   }
   }

.. image:: simple_engineering_aratio_3.png
  :width: 800
  :align: center
  :alt: Evaluation and Filtering

The blue + red points satisfy the radial build (``r_cs`` > 0.2) and the TF coil stress constraint (``tf_stress`` <  500 MPa). The red points satisfy additional superconductor current limit (``jtf`` < ``jtf_crit``).