How to get Internal Force value in Tetrahedral elements?

[ozupiece]

Hi,

Please tell me how to get Internal Force value in Tetrahedral elements. Developer told me about getting displacement. I try to change the code to get Internal Force value but I can't do because I'm beginner at C#. I guess that I should use 'GetInternalForce' method... The code is as follows.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using BriefFiniteElementNet;
using BriefFiniteElementNet.Elements;

namespace BfeTestApplication
{
    class Program
    {
        static void Main(string[] args)
        {
            var model = new BriefFiniteElementNet.Model();

            var p = new Point[20];
            var ns = new Node[20];

            p[0] = new Point(x: 0, y: 1, z: 0);
            p[1] = new Point(x: 0, y: 0, z: 0);
            p[2] = new Point(x: 0.20, y: 0, z: 0);
            p[3] = new Point(x: 0.20, y: 0, z: 0.20);
            p[4] = new Point(x: 0.20, y: 1, z: 0);
            p[5] = new Point(x: 0.20, y: 1, z: 0.20);
            p[6] = new Point(x: 0, y: 1, z: 0.20);
            p[7] = new Point(x: 0, y: 0, z: 0.20);
            p[8] = new Point(x: 0, y: 0.50, z: 0);
            p[9] = new Point(x: 0.20, y: 0.50, z: 0);
            p[10] = new Point(x: 0, y: 0.50, z: 0.20);
            p[11] = new Point(x: 0.20, y: 0.50, z: 0.20);
            p[12] = new Point(x: 0.20, y: 0.25, z: 0.20);
            p[13] = new Point(x: 0, y: 0.25, z: 0.20);
            p[14] = new Point(x: 0, y: 0.25, z: 0);
            p[15] = new Point(x: 0.20, y: 0.25, z: 0);
            p[16] = new Point(x: 0.20, y: 0.75, z: 0.20);
            p[17] = new Point(x: 0.20, y: 0.75, z: 0);
            p[18] = new Point(x: 0, y: 0.75, z: 0);
            p[19] = new Point(x: 0, y: 0.75, z: 0.20);

            for (var i = 0; i < 20; i++)
            {
                model.Nodes.Add(ns[i] = new Node(p[i]));
                ns[i].Label = "n" + i.ToString();
                ns[i].Constraints = Constraints.RotationFixed;
            }

            var mesh = new int[24][];

            mesh[0] = new int[] { 0, 4, 16, 17 };
            mesh[1] = new int[] { 8, 15, 12, 14 };
            mesh[2] = new int[] { 8, 16, 17, 18 };
            mesh[3] = new int[] { 10, 8, 11, 12 };
            mesh[4] = new int[] { 5, 19, 0, 16 };
            mesh[5] = new int[] { 1, 15, 14, 12 };
            mesh[6] = new int[] { 8, 10, 11, 16 };
            mesh[7] = new int[] { 3, 13, 1, 7 };
            mesh[8] = new int[] { 3, 13, 12, 1 };
            mesh[9] = new int[] { 8, 12, 13, 14 };
            mesh[10] = new int[] { 1, 15, 12, 2 };
            mesh[11] = new int[] { 9, 8, 11, 16 };
            mesh[12] = new int[] { 10, 8, 12, 13 };
            mesh[13] = new int[] { 5, 0, 4, 16 };
            mesh[14] = new int[] { 5, 19, 6, 0 };
            mesh[15] = new int[] { 8, 19, 16, 18 };
            mesh[16] = new int[] { 8, 19, 10, 16 };
            mesh[17] = new int[] { 0, 19, 18, 16 };
            mesh[18] = new int[] { 1, 3, 2, 12 };
            mesh[19] = new int[] { 8, 15, 9, 12 };
            mesh[20] = new int[] { 13, 12, 1, 14 };
            mesh[21] = new int[] { 8, 9, 11, 12 };
            mesh[22] = new int[] { 9, 8, 16, 17 };
            mesh[23] = new int[] { 16, 0, 17, 18 };

            foreach (var elm in mesh)
            {
                var felm = new Tetrahedral();

                felm.Nodes[0] = ns[elm[0]];
                felm.Nodes[1] = ns[elm[1]];
                felm.Nodes[2] = ns[elm[2]];
                felm.Nodes[3] = ns[elm[3]];

                felm.E = 210e9;
                felm.Nu = 0.33;
                model.Elements.Add(felm);
            }

            var relm = new BriefFiniteElementNet.MpcElements.RigidElement_MPC();
            relm.Nodes = new NodeList() { ns[0], ns[4], ns[5], ns[6] };
            relm.UseForAllLoads = true;
            //model.MpcElements.Add(relm);

            ns[1].Constraints = ns[2].Constraints = ns[3].Constraints = ns[7].Constraints = Constraints.Fixed;

            var load = new BriefFiniteElementNet.NodalLoad();
            var frc = new Force();
            frc.Fz = 1000;// 1kN force in Z direction
            load.Force = frc;

            ns[5].Loads.Add(load);
            ns[6].Loads.Add(load);

            model.Solve_MPC();

            var d5 = ns[5].GetNodalDisplacement();
            var d6 = ns[6].GetNodalDisplacement();

            Console.WriteLine("Nodal displacement in Z direction is {0} meters (thus {1} mm)", d5.DZ, d5.DZ * 1000);
            Console.WriteLine("Nodal displacement in Z direction is {0} meters (thus {1} mm)", d6.DZ, d6.DZ * 1000);
        }
    }
}

[epsi1on]

Hi, Yes, you should use GetInternalForce() method on Tetrahedron element:

var tetra = model.Elements[0] as Tetrahedral;

var stress = tetra.GetInternalForce(LoadCombination.DefaultLoadCombination);

but please keep in mind that the result of code of Tetrahedral element is not validated yet. i mean we should first make sure that the tetrahedral code works properly and exactly like other implementations of Tetrahedral, then use it. So there is not warranty that result are even usable, maybe you get a very wrong result...

Regards

[ozupiece]

Thank you for your reply and warning. I will try to make comparison between the result and beam element's result.

Kind Regards

[epsi1on]

Hello @ozupiece , Do you know any formulation for interna force of tetrahedron element?