SOLID278 Element Description

SOLID278 has a 3D thermal conduction capability. The element has eight nodes with a single degree of freedom, temperature, at each node. The element is applicable to a 3D, steady-state or transient thermal analysis. The element can also account for heat transfer by a mass flow with a prescribed velocity field (see Mass Transport (Advection) in the Theory Reference). If the model containing the conducting solid element is also to be analyzed structurally, the element should be replaced by an equivalent structural element (such as SOLID185). See SOLID279 for a similar thermal element, with mid-edge node capability. For more details about this element, see SOLID278 - 3D 8-Node Homogeneous/Layered Thermal Solid in the Theory Reference.

SOLID278 is available in these forms:

See SOLID278 in the Mechanical APDL Theory Reference for more details about this element.

A higher-order version of the SOLID278 element is SOLID279.

SOLID278 Homogeneous Thermal Solid Element Description

SOLID278 Thermal Solid is suitable for modeling general 3D solid heat conduction. It allows for prism and tetrahedral degenerations when used in irregular regions. SOLID278 is designed to be a companion element for SOLID185.

Figure 278.1: SOLID278 Homogeneous Thermal Solid Geometry

SOLID278 Homogeneous Thermal Solid Input Data

The geometry and node locations for this element are shown in Figure 278.1: SOLID278 Homogeneous Thermal Solid Geometry. The element is defined by eight nodes and the orthotropic material properties. The default element coordinate system is along global directions. You may define an element coordinate system using ESYS, which forms the basis for orthotropic material directions (namely, for thermal conductivity). Specific heat and density are ignored for steady-state solutions. Properties not input default as described in the Material Reference.

As described in Coordinate Systems, you can use ESYS to orient the material properties and the temperature gradient and heat flux output. Use RSYS to choose output that follows the material coordinate system or the global coordinate system.

Element loads are described in Element Loading. Convection or heat flux (but not both) and radiation may be input as surface loads at the element faces as shown by the circled numbers on Figure 278.1: SOLID278 Homogeneous Thermal Solid Geometry. 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).

A mass transport option is available with KEYOPT(11). With this option, you specify the velocity components VX, VY, and VZ by issuing BF,,VELO,VX,VY, VZ. There is no restriction on the element Peclet number (Pe) for this element, and it offers the Streamline Upwind Petrov-Galerkin (SUPG) formulation and Discontinuity Capturing (DC) terms that enable convergence for high Pe conditions (see Galerkin or Streamline Upwind Petrov-Galerkin (SUPG) Formulation in the Thermal Analysis Guide). You can control the settings that activate the SUPG formulation and include one of three DC terms to smooth spurious oscillations if they arise in your solution by setting real constants with the R and RMORE commands as detailed in the table below. With mass transport, temperatures should be specified along the entire inlet boundary to assure a stable solution, and you should use specific heat (C) and density (DENS) material properties instead of enthalpy (ENTH). For more detais, see Mass Transport (Advection) in the Theory Reference and Mass Transport (Advection) in the Thermal Analysis Guide.

"SOLID278 Homogeneous Thermal Solid Input Summary" contains a summary of element input. For a general description of element input, see Element Input.

SOLID278 Homogeneous Thermal Solid Output Data

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

Output temperatures may be read by structural solid elements (such as SOLID185 and SOLSH190) via the LDREAD,TEMP command.

Convection heat flux is positive out of the element; applied heat flux is positive into the element.

The element output directions are parallel to the element coordinate system.

A general description of solution output is given in Solution Output. See the Basic Analysis Guide for ways to view results.

The Element Output Definitions table uses the following notation:

A colon (:) in the Name column indicates that the item can be accessed by the Component Name method (ETABLE, ESOL). The O column indicates the availability of the items in the file jobname.out. The R column indicates the availability of the items in the results file.

In either the O or R columns, “Y” indicates that the item is always available, a letter or number refers to a table footnote that describes when the item is conditionally available, and “-” indicates that the item is not available.

Table 278.2: SOLID278 homogeneous Thermal Solid Item and Sequence Numbers lists output available via ETABLE using the Sequence Number method. See Element Table for Variables Identified By Sequence Number in the Basic Analysis Guide and The Item and Sequence Number Table in this reference for more information. The following notation is used in Table 278.2: SOLID278 homogeneous Thermal Solid Item and Sequence Numbers:

SOLID278 Homogeneous Thermal Solid Assumptions and Restrictions

This element is available in layered form. See "SOLID278 Layered Thermal Solid Assumptions and Restrictions".

SOLID278 Layered Thermal Solid Element Description

Use SOLID278 Layered Thermal Solid to model heat conduction in layered thick shells or solids. The layered section definition is given by section (SECxxx) commands. A prism degeneration option is also available.

Figure 278.2: SOLID278 Layered Thermal Solid Geometry

x_o = Element x-axis if ESYS is not specified.

x = Element x-axis if ESYS is specified.

SOLID278 Layered Thermal Solid Input Data

The geometry and node locations for this element are shown in Figure 278.2: SOLID278 Layered Thermal Solid Geometry. The element is defined by eight nodes. A prism-shaped element may be formed by defining the same node numbers for nodes K and L, and O and P.

In addition to the nodes, the element input data includes the anisotropic material properties. Anisotropic material directions correspond to the layer coordinate directions which are based on the element coordinate system. The element coordinate system follows the shell convention where the z axis is normal to the surface of the shell. The nodal ordering must follow the convention that I-J-K-L and M-N-O-P element faces represent the bottom and top shell surfaces, respectively. You can change the orientation within the plane of the layers via the SECDATA command in the same way that you would for shell elements (as described in Coordinate Systems). To achieve the correct nodal ordering for a volume mapped (hexahedron) mesh, you can use the VEORIENT command to specify the desired volume orientation before executing the VMESH command. Alternatively, you can use the EORIENT command after automatic meshing to reorient the elements to be in line with the orientation of another element, or to be as parallel as possible to a defined ESYS axis.

Layered Section Definition Using Section Commands

You can associate SOLID278 Layered Solid with a shell section (SECTYPE). The layered composite specifications (including layer thickness, material, orientation, and number of integration points through the thickness of the layer) are specified via shell section (SECxxx) commands. You can use the shell section commands even with a single-layered element. Mechanical APDL obtains the actual layer thicknesses used for element calculations by scaling the input layer thickness so that they are consistent with the thickness between the nodes.

You can designate the number of integration points (1, 3, 5, 7, or 9) located through the thickness of each layer. Two points are located on the top and bottom surfaces respectively and the remaining points are distributed equal distance between the two points. The element requires at least two points through the entire thickness. When no shell section definition is provided, the element is treated as single-layered and uses two integration points through the thickness.

SOLID278 Layered Thermal Solid does not support real constant input for defining layer sections.

SOLID278 Layered Thermal Solid has an option for through-the-thickness degrees of freedom (KEYOPT(3) = 2). As shown in Figure 278.3: Understanding Interpolation Layers, the option works by creating a specified number of material layers (defined via the SECDATA command) per interpolation layer (KEYOPT(6) = n). Each interpolation layer has four internal nodes, one on each face. KEYOPT(3) = 2 offers greater accuracy than KEYOPT(3) = 1 but is more computationally intensive; the more material layers specified per interpolation layer, the greater the accuracy and computational cost.

Figure 278.3: Understanding Interpolation Layers

Other Input

The default orientation for this element has the S1 (shell surface coordinate) axis aligned with the first parametric direction of the element at the center of the element and is shown as x_o in Figure 278.2: SOLID278 Layered Thermal Solid Geometry.

The default first surface direction S1 can be reoriented in the element reference plane (as shown in Figure 278.2: SOLID278 Layered Thermal Solid Geometry) via the ESYS command. You can further rotate S1 by angle THETA (in degrees) for each layer (via the SECDATA command) to create layer-wise coordinate systems. See Coordinate Systems for details.

The geometry, node locations, and the coordinate system for this element are shown in Figure 278.2: SOLID278 Layered Thermal Solid Geometry. The element is defined by eight nodes and the orthotropic material properties. A prism-shaped element may also be formed as shown in Figure 278.2: SOLID278 Layered Thermal Solid Geometry. Orthotropic material directions correspond to the layer coordinate directions. The element coordinate system orientation is as described in Coordinate Systems. Specific heat and density are ignored for steady-state solutions. Properties not input default as described in the Material Reference.

Element loads are described in Element Loading. Convection or heat flux (but not both) and radiation may be input as surface loads at the element faces as shown by the circled numbers on Figure 278.2: SOLID278 Layered Thermal Solid Geometry. Heat generation rates may be input as element body loads on a per layer basis. One heat generation value is applied to the entire layer. If the first layer heat generation rate HG(1) is input, and all others are unspecified, they default to HG(1).

The following table summarizes the element input. Element Input provides a general description of element input.

SOLID278 Layered Thermal Solid Output Data

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

Output temperatures may be read by structural solid elements (such as SOLID185 and SOLSH190) via the LDREAD,TEMP command.

Figure 278.4: SOLID278 Layered Thermal Solid Heat Flux/Temperature Gradient Output

Heat flux directions shown are for global directions.

Convection heat flux is positive out of the element; applied heat flux is positive into the element.

The element output directions are parallel to the layer coordinate system.

A general description of solution output is given in Solution Output. See the Basic Analysis Guide for ways to view results.

To see the temperature distribution through the thickness for this element, enter the POST1 postprocessor (/POST1), then issue /GRAPHICS,POWER and /ESHAPE,1 followed by PLESOL,BFE,TEMP

The Element Output Definitions table uses the following notation:

A colon (:) in the Name column indicates that the item can be accessed by the Component Name method (ETABLE, ESOL). The O column indicates the availability of the items in the file jobname.out. The R column indicates the availability of the items in the results file.

In either the O or R columns, “Y” indicates that the item is always available, a letter or number refers to a table footnote that describes when the item is conditionally available, and “-” indicates that the item is not available.

Table 278.4: SOLID278 Layered Thermal Solid Item and Sequence Numbers lists output available via ETABLE using the Sequence Number method. See Element Table for Variables Identified By Sequence Number in the Basic Analysis Guide and The Item and Sequence Number Table in this reference for more information. The following notation is used in Table 278.4: SOLID278 Layered Thermal Solid Item and Sequence Numbers:

SOLID278 Layered Thermal Solid Assumptions and Restrictions

SOLID278 Product Restrictions

When used in the product(s) listed below, the stated product-specific restrictions apply to this element in addition to the general assumptions and restrictions given in the previous section.

Ansys Mechanical Pro  —