add tangential projection

models/loadbone.py

@@ -188,8 +188,19 @@ def scale_loads(loads, total_force):
 
 
 def create_uniform_loads(nodes, tris, total_force, target=None):
-    """create uniform tensile loads, normal to the facets
+    """ Ad Hoc Uniform Traction Model (Grosse et al. 2007)
+
+    "In this model, we applied uniform traction to the surfaces
+    of finite elements that represent the muscle attachment
+    areas. The direction of the traction load is not normal
+    to the surface of the element. Rather, the direction
+    of traction varied from element to element such that the
+    traction load is always directed toward the force focal
+    node of each muscle attachment group."
+
+    note: if target==None: the traction is normal to the facet
     """
+    project=True
     loads = [Pt([0,0,0]) for n in nodes ]
 
     if target:
@@ -215,6 +226,12 @@ def create_uniform_loads(nodes, tris, total_force, target=None):
         
         force = (area/3)*direct      # compute nodal force
 
+        if project:
+            ps = force*nunit
+            print(f'ps={ps}')
+            if ps<0.0: # no line of sight => projection onto the element plane
+                force = force - ps*nunit
+
         for i in range(3):          # 3 nodes per triangle
             loads[tri[i]]+=force    # assembly