another-take…

hertz_3D.geo
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			cl1 = 0.005;
			cl2 = 0.1;
			cl3 = 0.4;
			Dy = 0.099;
			Dz = 1;
			Point(1) = {0, 0.1-Dy, 0, cl1};
			Point(2) = {0.5, 0.6-Dy, 0, cl2};
			Point(3) = {-0.5, 0.6-Dy, 0, cl2};
			Point(4) = {0, 0.6-Dy, 0, cl2};
			Point(5) = {0, 0.6-Dy, -0.5, cl2};
			Point(6) = {0, 0.6-Dy, 0.5, cl2};

			Point(7) = {0, 0, 0, cl3};
			Point(8) = {0.5, 0, 0, cl3};
			Point(9) = {-0.5, 0, 0, cl3};
			Point(10) = {0, 0, -0.5, cl3};
			Point(11) = {0, 0, 0.5, cl3};

			Circle(1) = {3, 4, 1};
			Circle(2) = {1, 4, 2};
			Circle(3) = {6, 4, 1};
			Circle(4) = {1, 4, 5};
			Circle(5) = {3, 4, 6};
			Circle(6) = {6, 4, 2};
			Circle(7) = {2, 4, 5};
			Circle(8) = {5, 4, 3};
			Line Loop(1) = {3, 2, -6};
			Ruled Surface(1) = {1};
			Line Loop(2) = {-2, -7, 4};
			Ruled Surface(2) = {2};
			Line Loop(3) = {-4, -8, -1};
			Ruled Surface(3) = {3};
			Line Loop(4) = {1, -3, -5};
			Ruled Surface(4) = {4};
			Line Loop(5) = {6, 7, 8, 5};
			Plane Surface(5) = {5};
			Surface Loop(1) = {3, 2, 1, 4, 5};
			Volume(1) = {1};

			Circle(9) = {9, 7, 11};
			Circle(10) = {11, 7, 8};
			Circle(11) = {8, 7, 10};
			Circle(12) = {10, 7, 9};
			Line Loop(6) = {10, 11, 12, 9};
			Plane Surface(6) = {6};
			Extrude {0, -cl3, 0} {
			Surface{6};
			}

			Physical Surface("top_surface") = {5};
			Physical Surface("rigid_surface") = {6};
			Physical Volume("top_body") = {1};
			Physical Volume("bottom_body") = {2};
			Physical Surface("contact_surface") = {1, 2, 4, 3};