I want to perform an AC electromagnetic analysis in which a transmitting ("TX") coil producing harmonically varying source field is physically very small compared to the extent of the surrounding domain. To keep element count down, I wish the mesh at the field source to be as coarse as possible.
I found that SOURC36 used in a coarse SOLID117 mesh resulted in an inaccurate representation of the field source. Explicit modeling of the geometry of the TX coil leads to undesirably high element count. What would you suggest as an alternative?
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Two options to consider are: 1) SOLID97 model using F,,CSGx/y/z excitation (see attached model02.inp). This is acceptable when highly permeable regions do not exist in the modeled domain. 2) SOLID117 model using D,,AZ excitation (see attached model13.inp). This is acceptable even when highly permeable regions DO exist in the modeled domain. The models are of a circular AC energized coil positioned over an electrically conductive disk. The second option is undocumented at release 10. Please use with caution for reasons stated below: The direction in which AZ (and therefore that of the coil current it represents) acts is governed by the following (see below). Please, PLEASE review section 12.10 in the Theory reference and Chapter 6 in the Low frequency Guide. From the Theory Guide: 12.10. Electromagnetic Edge Elements The side nodes, M, N, O, and P are used to: ` support the edge-flux DOFs, labeled as AZ. The positive orientation of an edge is defined to point from the adjacent (to the edge) corner node with lower node number to the other adjacent node with higher node number. For example, edge, M, is oriented from node I to J if I has a smaller node number than J; otherwise it is oriented from J to I. A few excerpts from the Low Frequency Guide: Chapter 6. 3-D Magnetostatics and Fundamentals of Edge-Based Analysis The edge method is a version of the magnetic vector potential where the magnetic degrees of freedom are located on element edge nodes, rather than corner nodes. For SOLID117, the ANSYS edge element, the degree of freedom is the integral of the tangential component of the vector potential A along the element edge. A physical interpretation: if you sum the values of the edge DOF (flux) around a closed loop formed by the edges, you obtain the flux passing through the closed loop. A positive flux value along an element edge indicates that the edge vector is oriented from the lower corner node number to the high corner node number (shared by the element edge). The closed loop orientation and the flux direction is related by the right hand rule. In ANSYS, the label AZ represents the edge-flux degree of freedom. AZ is expressed in units of Weber (Volt-secs) in the MKS system. SOLID117 is a 20-node brick shape. Its 12 side nodes carry the edge-flux DOF, AZ. The edge is oriented to point from the lower corner node number to the higher node number. |
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