Dear Gmsh community,
I am trying to make a conical tube helix using the Built-In interface. With no
luck. I think I don't quite understand the whole functionality of the Extrude
command. The following is my code to make a tube helix of parametric equation
r(theta)=(Acos(theta),Asin(theta), C*theta).
A=1; C=0.25/Pi;
r=A/10;
nturns=4;
h=1;
Point(1)={A+r,0,0,h};Point(2)={A-r,0,0,h};
Point(3)={A,0,r,h};Point(4)={A,0,-r,h};
//
Circle(2) = {1, 5, 3};Circle(3) = {3, 5, 2};
Circle(4) = {2, 5, 4};Circle(5) = {4, 5, 1};
//+
Curve Loop(1) = {2, 3, 4, 5};Plane Surface(1) = {1};
ext1[] = Extrude {{0,0,C*Pi/2}, {0,0,1}, {0,0,0}, Pi/2} {
Surface{1};
Layers{30};
Recombine;};
For m In {1:4*nturns-1}
ext1[] = Extrude {{0,0,C*Pi/2}, {0,0,1}, {0,0,0}, Pi/2} {
Surface{ext1[0]};
Layers{30};
Recombine;};
EndFor
Transfinite Surface {1};
Recombine Surface{1};
Coherence;
We know that for a conical helix the pitch is constant but radius, curvature
and torsion change. This is possible by making the radius a linear function of
the height. The following is my attempt to make the spiral helix of parametric
equation r(t)=((r+tan(angle)z cos(2pi z), (r+tan(angle) * z sin(2pi z), z ) for
z in [0,max_height].
r = 1/2; //Initial radius
rd = 0.12; //Radius of the cross section
t_final=5;
angle=Pi/4; // Angle in radians;
frec=2*Pi;
layers=100;
Point(1)={r+rd,0,0,h};Point(2)={r-rd,0,0,h};
Point(3)={r,0,rd,h};Point(4)={r,0,-rd,h};
//
Point(5)={r,0,0,h}; //Centro de inicio de superficie extrude
//
Circle(2) = {1, 5, 3};Circle(3) = {3, 5, 2};
Circle(4) = {2, 5, 4};Circle(5) = {4, 5, 1};
Curve Loop(1) = {2, 3, 4, 5};Plane Surface(1) = {1};
z=t_final/layers;
thetha=Tan(angle);
linear_=z+angulo;
ext1[] = Extrude {?} {
Surface{1};
Layers{capas};
Recombine;};
For m In {1:layers}
ext1[] = Extrude {?} {
Surface{ext1[0]};
Layers{capas};
Recombine;};
EndFor
The question marks is because I have no idea how to tell gmsh to make the
appropriate twist. I don't want to use the OpenCASCADE and extrude Using Wire
because I do not have control on the layers of the mesh and cannot use the
recombine and transfinite algorithms successfully, like the code for the
regular helix posted at the beginning.
Thanks in advance!
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