4.90 SOLID90 3-D 20-Node Thermal Solid

4.90 SOLID90 3-D 20-Node Thermal Solid (UP19980821 ) SOLID90 is a higher order version of the 3-D eight node thermal element (SOLID70). The element has 20 nodes with a single degree of freedom, temperature, at each node. The 20-node elements have compatible temperature shapes and are well suited to model curved boundaries.

The 20-node thermal element is applicable to a three-dimensional, steady-state or transient thermal analysis. See Section 14.90 of the ANSYS Theory Reference for more details about this element. If the model containing this element is also to be analyzed structurally, the element should be replaced by the equivalent structural element (such as SOLID95).

Figure 4.90-1 SOLID90 3-D 20-Node Thermal Solid



4.90.1 Input Data

The geometry, node locations, and the coordinate system for this element are shown in Figure 4.90-1. The element is defined by 20 node points and the material properties. A prism-shaped element may be formed by defining duplicate K, L, and S; A and B; and O, P, and W node numbers. A tetrahedral-shaped element and a pyramid-shaped element may also be formed as shown in Figure 4.90-1.

Orthotropic material directions correspond to the element coordinate directions. The element coordinate system orientation is as described in Section 2.3. Specific heat and density are ignored for steady-state solutions. Properties not input default as described in Section 2.4.

Element loads are described in Section 2.7. Convections or heat fluxes (but not both) may be input as surface loads at the element faces as shown by the circled numbers on Figure 4.90-1. 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 4.90-1. A general description of element input is given in Section 2.1.

Table 4.90-1 SOLID90 Input Summary

Element Name

SOLID90

Nodes

I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z, A, B

Degrees of Freedom

TEMP

Real Constants

None

Material Properties

KXX, KYY, KZZ, DENS, C, ENTH

Surface Loads

Convections:
face 1 (J-I-L-K), face 2 (I-J-N-M), face 3 (J-K-O-N),
face 4 (K-L-P-O), face 5 (L-I-M-P), face 6 (M-N-O-P)
Heat Fluxes:
face 1 (J-I-L-K), face 2 (I-J-N-M), face 3 (J-K-O-N),
face 4 (K-L-P-O), face 5 (L-I-M-P), face 6 (M-N-O-P)

Body Loads

Heat Generations:
HG (I), HG (J), HG (K), HG (L), HG (M), HG (N), HG (O),
HG (P), HG (Q), HG (R), HG (S), HG (T), HG (U), HG (V),
HG (W), HG (X), HG (Y), HG (Z), HG (A), HG (B)

Special Features

Birth and death

KEYOPT(1)

0 - Consistent specific heat matrix
1 - Diagonalized specific heat matrix


4.90.2 Output Data

The solution output associated with the element is in two forms:

Heat flowing out of the element is considered to be positive. The element output directions are parallel to the element coordinate system. A general description of solution output is given in Section 2.2. See the ANSYS Basic Analysis Procedures Guide for ways to view results.

The following notation is used in Table 4.90-2:

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 4.90-2 SOLID90 Element Output Definitions

Label

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
VOLU:

Volume

Y Y
CENT: X, Y, Z

Global location of centroid XC, YC, ZC

- Y
HGEN

Heat generations HG(I), HG(J), HG(K), HG(L), HG(M), HG(N), HG(O), HG(P), HG(Q), ..., HG(Z), HG(A), HG(B)

Y -
TG: X, Y, Z, SUM

Thermal gradient components and vector sum at centroid

Y Y
TF: X, Y, Z, SUM

Thermal flux (heat flow rate/cross-sectional area) components and
vector sum at centroid

Y Y
FACE

Face label

1 -
NODES

Corner nodes on this face

1 -
AREA

Face area

1 1
HFILM

Film coefficient

1 -
TAVG

Average face temperature

1 1
TBULK

Fluid bulk temperature

1 -
HEAT RATE

Heat flow rate across face by convection

1 1
HEAT RATE/AREA

Heat flow rate per unit area across face by convection

1 -
HFLUX

Heat flux at each node of face

1 -
HFAVG

Average film coefficient of the face

- 1
TBAVG

Average face bulk temperature

- 1
HFLXAVG

Heat flow rate per unit area across face caused by input heat flux

- 1
1. Output only if a surface load is input

Table 4.90-3 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 4.90-3:

Table 4.90-3 SOLID90 Item and Sequence Numbers for the ETABLE and ESOL Commands

Name

Item

FC1

FC2

FC3

FC4

FC5

FC6

AREA

NMISC

1 7 13 19 25 31
HFAVG

NMISC

2 8 14 20 26 32
TAVG

NMISC

3 9 15 21 27 33
TBAVG

NMISC

4 10 16 22 28 34
HEAT RATE

NMISC

5 11 17 23 29 35
HFLXAVG

NMISC

6 12 18 24 30 36

4.90.3 Assumptions and Restrictions

The element must not have a zero volume. This occurs most frequently when the element is not numbered properly. Elements may be numbered either as shown in Figure 4.90-1 or may have the planes IJKL and MNOP interchanged. The condensed face of a prism-shaped element should not be defined as a convection face. The specific heat and enthalpy are evaluated at each integration point to allow for abrupt changes (such as melting) within a coarse grid of elements.

If the thermal element is to be replaced by a SOLID95 structural element with surface stresses requested, the thermal element should be oriented such that face IJNM and/or face KLPO 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. An edge with a removed midside node implies that the temperature varies linearly, rather than parabolically, along that edge. See Section 2.4.2 of the ANSYS Modeling and Meshing Guide for more information about the use of midside nodes.

Degeneration to the form of pyramid should be used with caution. The element sizes, when degenerated, should be small in order to minimize the field gradients. Pyramid elements are best used as filler elements or in meshing transition zones.

4.90.4 Product Restrictions

ANSYS/Thermal