minor feature GetExactDisplacement

Sources/BriefFiniteElementNet/Elements/BarElement.cs

@@ -1042,10 +1042,46 @@ public Displacement GetInternalDisplacementAt(double xi, LoadCase loadCase)
             return buf;
         }
 
-        
+
         public Displacement GetExactInternalDisplacementAt(double xi, LoadCase loadCase)
         {
-            throw new NotImplementedException();
+            {
+                //check to see if xi is exactly on any discrete points, for example shear exactly under a a concentrated force point is not a single value so exception must thrown
+
+                var discretePoints = new List<IsoPoint>();
+
+                discretePoints.AddRange(this.GetInternalForceDiscretationPoints());
+
+
+                foreach (var load in Loads)
+                {
+                    if (load.Case == loadCase)
+                        discretePoints.AddRange(load.GetInternalForceDiscretationPoints());
+                }
+
+                foreach (var point in discretePoints)
+                {
+                    if (xi == point.Xi)
+                        throw new InvalidInternalForceLocationException(string.Format(CultureInfo.CurrentCulture, "Internal force diagram and value is descrete at xi = {0}, thus have no value in this location. try to find internal force a little bit after or before this point", xi));
+                }
+            }
+
+            var approx = GetInternalDisplacementAt(xi, loadCase);
+
+            var helpers = GetHelpers();
+
+            var buf = approx;
+
+
+            foreach (var load in this.Loads)
+                if (load.Case == loadCase)
+                    foreach (var helper in helpers)
+                    {
+                        var d = helper.GetLoadDisplacementAt(this, load, new[] { xi });
+                        buf += d;
+                    }
+
+            return buf;
         }
 
 
@@ -1057,7 +1093,7 @@ public Displacement GetInternalDisplacementAt(double xi)
 
         public Displacement GetExactInternalDisplacementAt(double xi)
         {
-            throw new NotImplementedException();
+            return GetExactInternalDisplacementAt(xi, LoadCase.DefaultLoadCase);
         }
         #endregion
 

UnitTests/Tests/BarElementExactInternalDisplacement.cs

@@ -56,7 +56,66 @@ public void TestEulerBernouly_Distributed_dirz()
                 //https://mechanicalc.com/reference/beam-deflection-tables
                 var expected = (w * x * x) / (24 * E * I) * (L - x) * (L - x);
 
-                Assert.IsTrue(Math.Abs(current-expected) < epsilon, "invalid value");
+                Assert.IsTrue(Math.Abs(current - expected) < epsilon, "invalid value");
+
+                if (x != 0 && x != L)
+                {
+                    Assert.IsTrue(Math.Sign(current) == Math.Sign(w), "invalid sign");
+                }
+            }
+
+        }
+
+
+        [Test]
+        public void TestEulerBernouly_Distributed_diry()
+        {
+            //internal force of 2 node beam beam with uniform load and both ends fixed
+
+            var dir = BeamDirection.Y;
+            var w = 2.0;
+            var L = 4;//[m]
+            var I = 1;
+            var E = 1;
+
+            var nodes = new Node[2];
+
+            nodes[0] = (new Node(0, 0, 0));
+            nodes[1] = (new Node(L, 0, 0));
+
+            var elm = new BarElement(nodes[0], nodes[1]);
+            elm.Section = new UniformParametric1DSection(0, I, 0);
+            elm.Material = UniformIsotropicMaterial.CreateFromYoungPoisson(E, 0.25);
+
+            var u1 = new Loads.UniformLoad();
+
+            u1.Case = LoadCase.DefaultLoadCase;
+            u1.Direction = Vector.K;
+            u1.CoordinationSystem = CoordinationSystem.Local;
+            u1.Magnitude = w;
+
+            //u1.ForceIsoLocation = new IsoPoint(elm.LocalCoordsToIsoCoords(forceLocation)[0]);
+
+            var hlpr = new EulerBernoulliBeamHelper2Node(dir, elm);
+
+            var epsilon = 1e-6;
+
+
+            foreach (var x in CalcUtil.Divide(L, 10))
+            {
+                var xi = elm.LocalCoordsToIsoCoords(x);
+
+                var current = hlpr.GetLoadDisplacementAt(elm, u1, xi).DZ;
+
+                //https://mechanicalc.com/reference/beam-deflection-tables
+                var expected = (w * x * x) / (24 * E * I) * (L - x) * (L - x);
+
+                Assert.IsTrue(Math.Abs(current - expected) < epsilon, "invalid value");
+
+                if (x != 0 && x != L)
+                {
+                    Assert.IsTrue(Math.Sign(current) == Math.Sign(w), "invalid sign");
+                }
             }
 
         }