Release 11.0 Documentation for ANSYS
www.kxcad.net Home > CAE Index > ANSYS Index > Release 11.0 Documentation for ANSYS
The following is an example of how to perform a capacitance matrix calculation by issuing ANSYS commands. You can also perform the analysis through the ANSYS GUI menus.
For details on extracting capacitance from multi-conductor systems, see Extracting Capacitance from Multi-conductor Systems in this manual.
In this example, two long cylinders sit above an infinite ground plane. The objective is to compute the self and mutual capacitance coefficients between the conductors and ground.
The ground plane and the Infinite elements share a common boundary at the outer radius of the model. The Infinite elements by nature can only represent a zero potential at the infinite location. Since the ground plane shares a common boundary with the infinite elements, they together represent the ground conductor. The nodes of the ground plane are sufficient to represent the ground conductor since the infinite element nodes are internally grounded by the program. By grouping the other two cylindrical conductor node sets into node components as well, you arrive at a 3-conductor system.
Figure 13.6: "Model Areas of Capacitance Example Problem" displays the model areas and Figure 13.7: "Elements of Capacitance Example Problem" displays the finite elements.
The computed ground and lumped capacitance results for this example problem are as follows:
| (Cg)11 = 0.454E-4 pF | (Cl)11 = 0.354E-4 pF |
| (Cg)12 = -0.998E-5 pF | (Cl)12 = 0.998E-5 pF |
| (Cg)22 = 0.454E-4 pF | (Cl)22 = 0.354E-4 pF |
You can perform this example capacitance matrix calculation using the ANSYS commands shown below. Text prefaced by an exclamation point (!) is a comment.
/batch,list /prep7 /title, Capacitance of two long cylinders above a ground plane a=100 ! Cylinder inside radius (μm) d=400 ! Outer radius of air region ro=800 ! Outer radius of infinite elements et,1,121 ! 8-node 2-D electrostatic element et,2,110,1,1 ! 8-node 2-D Infinite element emunit,epzro,8.854e-6 ! Set free-space permittivity for μMKSV units mp,perx,1,1 cyl4,d/2,d/2,a,0 ! Create mode in first quadrant cyl4,0,0,ro,0,,90 cyl4,0,0,2*ro,0,,90 aovlap,all numcmp,area smrtsiz,4 mshape,1 ! Mesh air region amesh,3 lsel,s,loc,x,1.5*ro lsel,a,loc,y,1.5*ro lesize,all,,,1 type,2 mshape,0 mshkey,1 amesh,2 ! Mesh infinite region arsymm,x,all ! Reflect model about y axis nummrg,node nummrg,kpoi csys,1 nsel,s,loc,x,2*ro sf,all,inf ! Set infinite flag in Infinite elements local,11,1,d/2,d/2 nsel,s,loc,x,a cm,cond1,node ! Assign node component to 1st conductor local,12,1,-d/2,d/2 nsel,s,loc,x,a cm,cond2,node ! Assign node component to 2nd conductor csys,0 nsel,s,loc,y,0 cm,cond3,node ! Assign node component to ground conductor allsel,all finish /solu cmatrix,1,'cond',3,0 ! Compute capacitance matrix coefficients finish
