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Strand7 from Grasshopper

Strand7 from Grasshopper
This week, we will be talking about a way to incorporate Strand7 (Strand7 — Finite Element Analysis) API into Grasshopper Plugin.
Grasshopper is a visual programming interface & computational design tool for the 3D modeling program Rhinoceros. Strand7 is a great Structural Analysis Software used for wide variety of application is diverse fields of engineering.
What to do if you want to combine the power of Grasshopper (referred to as GH henceforth) & Strand7 (referred to as St7 henceforth) ? Let’s find out.
What to do if you want to combine the power of Grasshopper (referred to as GH henceforth) & Strand7 (referred to as St7 henceforth) ? Let’s find out.
I am assuming you have Rhino & Strand7 installed on your machine.
What’s the use case really? You are working on GH Plugin, and you want to use St7 capabilities (Analysis, Meshing etc.) without leaving the GH environment. This way you can make use of great computational power GH provides & also add St7’s great features in the mix. To achieve this, St7 has thankfully provided St7 API.
For the sake of this blog, let’s assume a simple example. Let’s create a plate in St7 from the co-ordinates taken from GH.
Let’s create a Surface in Grasshopper from 4 Points of the Surface and create a Brep from it.
Grasshopper Image of the Brep
On Rhino side, the plate looks as below.
Rhino Image of the Plate
Strand7 has a rich support for variety of languages, we are choosing C# for our purposes. To add St7 API, we need to add St7API_DotNet.dll as a reference. Also, please copy St7API.cs to your project directory (location of this file in your project is not important. Please add it as per your convention.)
Once you have the relevant dependencies taken care of, Let’s write the actual component to do the export of GH co-ordinates & import the information at Strand7 end. Let’s start with the actual initialization of the API. To do this, you have to call

int iError = St7.St7Init();
          if (iError == St7.ERR7_NoError)
          {
            API_INITIALISED = true;
          }

In all the St7 API calls, you can see consistent use of the integer return type. St7.ERR7_NoError means successful API call. If you open up St7API.cs, you can find all the error codes. For No Error, it is 0.

public const int ERR7_NoError = 0;

Once you have Initialized the API, we can instantiate the new St7 file to do the actual work (create new or open existing).

 //create new
           iErr = St7.St7NewFile(uID, filePath, DirPath);
          
          //open existing
          iErr = St7.St7OpenFile(uID, filePath, DirPath);

Next, for our concerned use case we get the Brep List ( brepList), iterate over it and then create those point on the St7 file by using St7.St7SetNodeXYZ(1, counter, p1);

foreach (Brep brep in brepList)
 {
    BrepSurfaceList faces = brep.Surfaces;
    for (int bfIndex = 0; bfIndex < faces.Count; bfIndex++)
    {
      Surface face = faces[bfIndex];
      NurbsSurface nurbsSurface = face.ToNurbsSurface();
      NurbsSurfacePointList points = nurbsSurface.Points;
   
      List<ControlPoint> controlPointList = points.ToList();
     
      foreach (ControlPoint point in controlPointList)
      {
          double[] p1 = { point.X, point.Y, point.Z };
          //we have got the point, now let’s creat the same point
          // on St7 side.
          St7.St7SetNodeXYZ(1, counter, p1);
         
      }

After creating all the points of the Surface, add the size of the surface and create a Plate from it.

pointList.Insert(0, pointList.Count);

 int[] connection = pointList.ToArray();
 iErr = St7.St7SetElementConnection(1, St7.tyPLATE, plateCounter, plateCounter, connection);
 plateCounter++;

 

After creating a plate, select all the points and create a Face from Plate using St7 API

for (int pc = 1; pc <= plateCounter; pc++)
{
     iErr = St7.St7SetEntitySelectState(1, St7.tyPLATE, pc, 0, St7.btTrue);
}

iErr = St7.St7SetSourceAction(1, St7.saDelete);
iErr = St7.St7SetKeepSelect(1, St7.btFalse);
iErr = St7.St7FaceFromPlate(1, St7.btTrue, St7.btTrue, St7.btFalse);

Once you are done with the processing, let’s save the file and close it.

iErr = St7.St7SaveFile(1);
iErr = St7.St7CloseFile(1);

Complete screenshot of the Grasshopper component indicating all the items in play
GH Component
Lastly, To know for sure if the Plate has indeed been created correctly on the Strand7 side, we can open the St7 and have a look at it.
Strand7 Plate
Beautiful!! Isn’t it!!
Although this was the simple use case; we have seen how to use St7 API and combine GH & St7 in Grasshopper Plugins.
St7 API has lot many methods and it covers various functions ranging from Meshing, Grafting, Analysis & much more. Basically, we can use St7 API for most of the things we can do from Strand7 UI and have immense power in our hands.
References :-
  1. Strand7 — The Strand7 API