4.78 PLANE78 8-Node Axisymmetric-Harmonic Thermal Solid

The 8-node elements have compatible temperature shapes and are well suited to model curved boundaries.

The element is applicable to a two-dimensional, axisymmetric, steady-state or transient thermal analysis. See Section 14.78 of the ANSYS Theory Reference for more details about this element. If the model containing the element is also to be analyzed structurally, the element should be replaced by the equivalent structural element (such as PLANE83).

Figure 4.78-1 PLANE78 8-Node Axisymmetric-Harmonic Thermal Solid

4.78.1 Input Data

Element loads are described in Section 2.7. Harmonically varying convections or heat fluxes (but not both) may be input as surface loads on the element faces as shown by the circled numbers on Figure 4.78-1. Harmonically varying heat generation rates may be input as element body loads at the nodes. If the node I heat generation rate HG(I) is input and all others are unspecified, they default to HG(I). If all corner node heat generation rates are specified, each midside node heat generation rate defaults to the average heat generation rate of its adjacent corner nodes.

A summary of the element input is given in Table 4.78-1. A general description of element input is given in Section 2.1.

Table 4.78-1 PLANE78 Input Summary

Element Name	PLANE78
Nodes	I, J, K, L, M, N, O, P
Degrees of Freedom	TEMP
Real Constants	None
Material Properties	KXX, KYY, KZZ, DENS, C, ENTH
Surface Loads	Convections: face 1 (J-I), face 2 (K-J), face 3 (L-K), face 4 (I-L) Heat Fluxes: face 1 (J-I), face 2 (K-J), face 3 (L-K), face 4 (I-L)
Body Loads	Heat Generations: HG (I), HG (J), HG (K), HG (L), HG (M), HG (N), HG (O), HG (P)
Mode Number	Input mode number on MODE command
Special Features	Birth and death
Loading Conditions	Input for ISYM on MODE command 1 Symmetric loading -1 Antisymmetric loading
KEYOPT(1)	0 - Consistent specific heat matrix 1 - Diagonalized specific heat matrix

4.78.2 Output Data

• nodal temperatures included in the overall nodal solution
• additional element output as shown in Table 4.78-2

The following notation is used in Table 4.78-2:

A colon (:) in the Name column indicates the item can be accessed by the Component Name method [ETABLE, ESOL] (see Section 2.2.2). The O and R columns indicate the availability of the items in the file Jobname.OUT (O) or in the results file (R), a Y indicates that the item is always available, a number refers to a table footnote which describes when the item is conditionally available, and a - indicates that the item is not available.

Table 4.78-2 PLANE78 Element Output Definitions

Name	Definition	O	R
EL	Element number	Y	Y
NODES	Nodes - I, J, K, L, M, N, O, P	Y	Y
MAT	Material number	Y	Y
MODE	Number of waves in loading	Y	Y
VOLU:	Volume	Y	Y
CENT: X, Y	Center location XC, YC	-	Y
HGEN	Heat generations HG(I), HG(J), HG(K), HG(L), HG(M), HG(N), HG(O), HG(P)	Y	-
TG: X, Y, SUM, Z	Thermal gradient components and vector sum (X and Y) at centroid	1	1
TF: X, Y, SUM, Z	Thermal flux (heat flow rate/cross-sectional area) components and vector sum (X and Y) at centroid	1	1
FACE	Face label	2	2
NODES	Face nodes	2	2
AREA	Face area	2	2
HFILM	Film coefficient	2	2
TAVG, TBULK	Average of the two end nodal temperatures evaluated at peak value, fluid bulk temperature at peak value	2	2
HEAT RATE	Heat flow rate across face by convection	2	2
HEAT RATE/AREA	Heat flow rate per unit area across face by convection	2	2
HFAVG	Average film coefficient of the face	-	2
TBAVG	Average face bulk temperature	-	2
HFLXAVG	Heat flow rate per unit area across face caused by input heat flux	-	2
HFLUX	Heat flux at each node of face	2	2

1. Gradient and flux peak at THETA = 0 and THETA = 90Mode degrees

2. Output only if a surface load is input

Table 4.78-3 lists output available through the ETABLE command using the Sequence Number method. See Chapter 5 of the ANSYS Basic Analysis Procedures Guide and Section 2.2.2.2 of this manual for more information. The following notation is used in Table 4.78-3:

Name - output quantity as defined in the Table 4.78-2

Item - predetermined Item label for ETABLE command

FCn - sequence number for solution items for element Face n

Name	Item	FC1	FC2	FC3	FC4
AREA	NMISC	1	7	13	19
HFAVG	NMISC	2	8	14	20
TAVG	NMISC	3	9	15	21
TBAVG	NMISC	4	10	16	22
HEAT RATE	NMISC	5	11	17	23
HFLXAVG	NMISC	6	12	18	24

4.78.3 Assumptions and Restrictions

If the thermal element is to be replaced by the analogous structural element (PLANE83) with surface stresses requested, the thermal element should be oriented so that face IJ (and also face KL, if applicable) is a free surface. A free surface of the element (i.e., not adjacent to another element and not subjected to a boundary constraint) is assumed to be adiabatic. Thermal transients having a fine integration time step and a severe thermal gradient at the surface will also require a fine mesh at the surface.

Temperature dependent material properties (including the film coefficient) are assumed to be axisymmetric even if the temperature varies harmonically. If MODE=0, properties are evaluated at the temperatures calculated in the previous substep (or at TUNIF if for the first substep). If MODE>0, properties are evaluated at temperatures calculated from the previous MODE=0 substep; if no MODE=0 substep exists, then evaluation is done at 0.0 degrees.

4.78.4 Product Restrictions