i | = | Waveband index |
s | = | Stefan-Boltsmann constant |
nbands | = | Number of wavebands |
F | = | Black body function from at temperature T |
T1,T2 | = | Temperatures of surfaces 1 and 2, respectively |
R | = | Effective radiative resistance between surfaces 1 and 2, taking into account possibly time, temperature, and waveband |
t | = | Time |
l | = | Wave length |
RESTYP, SUBTYP, NODE1, NODE2, NODE3, MPID, DATA1, DATA2, DATA3, LAMBDA1, LAMBDA2
Input Data | Description |
RESTYP | Resistor type, character, R or W. |
SUBTYP | Resistor subtype, integer, 1 through 12. |
NODE1 | First node in the resistor record, integer. |
NODE2 | Second node in the resistor record, integer. |
NODE3 | Third node in the resistor record, integer (not always used, but must be present as a place holder). |
MPID | Material property ID for Patran Thermal, integer. |
DATA1 | Data for use in calculating the resistor value, real. |
DATA2 | Data for use in calculating the resistor value, real (not always used, but must be present as a place holder). |
DATA3 | Data for use in calculating the resistor value, real (not always used, but must be present as a place holder). |
LAMBDA1 | Beginning wavelength of waveband, real (not used for type R resistors, but must be present as a place holder). |
LAMBDA2 | Ending wavelength of waveband, real (not used for type R resistors, but must be present as a place holder). |
Subtype 1 | R = (1.0 - EPSILON) / (EPSILON * AREA) |
This resistor is used between a gray surface and a radiosity node, with an emissivity, EPSILON, which is evaluated from a material property, MPID. If the material property is temperature dependent, it will be evaluated at the temperature of NODE1. Typically, NODE1 is the surface node and NODE2 is the radiosity node. The variable, AREA, is the area (nodal subarea) associated with NODE1. NODE3 is not used for this resistor. | |
Subtype 2 | R = 1.0 / ( FF * AREA * TAU ) |
This resistor is used between radiosity nodes and has a participating media transmissivity, TAU, evaluated directly from a material property, MPID. If the transmissivity material property is temperature dependent, it will be evaluated at the temperature of NODE3. Typically, NODE1 and NODE2 represent the radiosity nodes and NODE3 the participating media node. DATA1 contains the area, AREA, associated with NODE2. DATA2 contains the viewfactor, FF, from NODE2 to NODE1. If one of the radiosity nodes is an AMBNOD, then it will typically be NODE1. Currently, this subtype is not created by Viewfactor since subtype 9 is adequate for the present requirements and requires less computational time. | |
Subtype 3 | R = 1.0 / ( FF * AREA * ( 1.0 - TAU ) ) |
This resistor is similar to subtype 2, except this subtype is used to represent the radiant interchange between a radiosity node, NODE2, and a participating media node, NODE1. Typically, NODE3 and NODE1 are the same, but this is not required. Currently, this subtype is not created by Viewfactor since subtype 10 is adequate for the present requirements and requires less computational time. | |
Subtype 4 | R = 1.0 / ( DATA1 * DATA2 ) |
This is a general purpose resistor between NODE1 and NODE2 whose value is determined by multiplying two constants, for example the viewfactor and the area for a case with no participating media. NODE3 is not used for this resistor. Currently, this subtype is not created by Viewfactor since subtype 5 is adequate for the present requirements and requires less computational time. | |
Subtype 5 | R = 1 / DATA1 |
This is another general purpose resistor between NODE1 and NODE2 and is the simplest and computationally fastest resistor. It is useful whenever material properties are known constants and do not require access to the Patran Thermal material property data. Two typical uses are (1) between two radiosity nodes with DATA1 = FF * AREA * TAU, or (2) as an emissivity resistor between a non-black surface node and a radiosity node with DATA 1 = (EPSILON * AREA ) / ( 1.0 - EPSILON ). NODE3 is not used for this resistor. | |
Subtype 6 | R = ( 1.0 - DATA2 ) / ( DATA2 * DATA1 ) |
This is the constant known property version of subtype 1 where DATA2 is typically EPSILON and DATA1 is AREA. NODE3 is not used for this resistor. Presently, this subtype is not created by Viewfactor since subtype 5 is adequate for the present requirements and requires less computational time. | |
Subtype 7 | R = 1.0 / ( FF * AREA * TAU ) |
This resistor is used between radiosity nodes and has a participating media transmissivity, TAU, evaluated using Beer's law ( TAU = EXP( - KAPPA * DISTANCE ) ) and an extinction coefficient from a material property, MPID. If the extinction coefficient material property is temperature dependent, it will be evaluated at the temperature of NODE3. Typically, NODE1 and NODE2 represent the radiosity nodes and NODE3 the participating media node. DATA1 contains the area, AREA, associated with NODE2. DATA2 contains the viewfactor, FF, from NODE2 to NODE1. DATA3 contains the mean beam length from the surface associated with NODE2 to the surface associated with NODE1. If one of the radiosity nodes is an AMBNOD, then it will typically be NODE1. Currently, this subtype is not created by Viewfactor since subtype 11 is adequate for the present requirements and requires less computational time. | |
Subtype 8 | R = 1.0 / ( FF * AREA * ( 1.0 - TAU ) ) |
This resistor is similar to subtype 7, except this subtype is used to represent the radiant interchange between a radiosity node, NODE2, and a participating media node, NODE1. Typically, NODE3 and NODE1 are the same, but this is not required. Currently, this subtype is not created by Viewfactor since subtype 12 is adequate for the present requirements and requires less computational time. | |
Subtype 9 | R = 1.0 / ( FA * TAU ) |
This resistor is similar to subtype 2, but the FF and AREA have been combined by multiplication into FA and stored in DATA1. DATA2 is not used. | |
Subtype 10 | R = 1.0 / ( FA * ( 1.0 - TAU ) ) |
This resistor is similar to subtype 3. It is to subtype 3 what subtype 9 is to subtype 2. | |
Subtype 11 | R = 1.0 / ( FA * TAU ) |
This resistor is similar to subtype 7, but the FF and AREA have been combined by multiplication into FA and stored in DATA1. DATA2 in not used. | |
Subtype 12 | R = 1.0 / ( FA * ( 1.0 - TAU ) ) |
This resistor is similar to subtype 8. It is to subtype 8 what subtype 11 is to subtype 7. |
Finite Element | |
Action: | Create |
Object: | Material Property |
Method: | General |
Note: | Make sure you have selected Patran Thermal as the analysis preference. |
KEYWORD TID nbands
TID | Valid TIDs are positive integers. TIDs will be associated with UIDs from the Patran Viewfactor LBC form. |
nbands | Valid values of nbands are non-negative integers. If nbands is zero (the default), then this template will cause R-type resistors to be created; otherwise, W-type resistors will be created when this template is referenced. |
VFAC | 99 |
VFAC | 1001 | 6 |
CONSTANT_EPSILON, CONSTANT_TAU, EMPID, TMPID, LAMBDA1, LAMBDA2, KFLAG, COLLAPSE
Input Data | Description |
CONSTANT_EPSILON | This field is required and must be a real number. It is the value of the surface’s constant emissivity, or if the emissivity is not constant, then it must have the value 0.0. Valid values of emissivity are greater than 0.0 and less than or equal to 1.0. If the emissivity is not constant, then the material property ID which describes the property must be given in the EMPID field. |
CONSTANT_TAU | This field is optional and defaults to 1.0. It is the value of the constant transmissivity of the participating media if any (the transmissivity of a vacuum is 1.0, hence the default value). If this value is not constant, then it must be given the value 0.0 here. Valid values of constant transmissivity are greater than 0.0 and less than or equal to 1.0. If the KFLAG is set to 1, then this value will represent the extinction coefficient for absorption according to Beer's Law and valid values are greater than 0.0. If the extinction coefficient is not constant, then this value must be set to zero. If this property, either transmissivity or extinction coefficient, is not constant, the material property ID which describes the property must be given in TMPID field. |
EMPID | This field is an optional integer MPID (material property ID) and defaults to 0. It must assume its default value if a constant emissivity is specified by CONSTANT_EPSILON. If the emissivity is not constant, as indicated by the value 0.0, then EMPID must be nonzero. Positive values of EMPID denote temperature dependence, while negative values of EMPID will be evaluated as functions of time. |
TMPID | This field is an optional integer MPID (material property ID) and defaults to 0. It must assume its default value if a constant transmissivity or extinction coefficient is specified by CONSTANT_TAU. If a constant is not specified, as indicated by its value of 0.0, then the TMPID must be nonzero. Positive values of TMPID denote temperature dependence, while negative values of TMPID will be evaluated as functions of time. The TMPID will evaluate to a transmissivity if the KFLAG is zero and to an extinction coefficient if the KFLAG is one, just as the CONSTANT_TAU does. |
LAMBDA1, LAMBDA2 | These are optional real fields, but either they both must be present or both not present. They are the beginning and ending wavelengths for the present waveband. Note that the wavebands do not necessarily have to be in order of increasing wavelength but must be in the same order for every surface in an enclosure. These fields default to 0.0, the value for the case when nbands is 0. If nbands is greater than 0 (i.e., the properties have spectral dependence), then LAMBDA2 should be greater than LAMBDA1, which should be greater than 0.0. The units used for wavelength are microns or micrometers. |
KFLAG | This optional field signals whether the transmissivity is evaluated directly (KFLAG = 0), either from the constant value or from the MPID referenced in TMPID, or the transmissivity is evaluated using Beer’s Law and an extinction coefficient evaluated from either the constant value or from the MPID referenced by TMPID. The default KFLAG value is 0 and the data must be integer. Beer’s Law may be stated as: Transmissivity = EXP( - Extinction_Coefficient * Distance ) |
COLLAPSE | This optional field signals whether radiosity nodes associated with a given surface node should be collapsed into a single radiosity node. If COLLAPSE is zero (the default value), then the radiosity nodes will not be collapsed. The COLLAPSE_ID associated with a nodal subarea surface is transferred to that nodal subarea’s radiosity node. Then radiosity nodes connected to the same surface node by way of emissivity resistors and having the same nonzero COLLAPSE_ID will be collapsed into one node. The resulting parallel emissivity resistors will be merged if possible. The COLLAPSE_ID must be a non-negative integer. The main advantage of using COLLAPSE to collapse radiosity nodes is that this will result in a much smaller number of radiation resistors in the model. The effect of using COLLAPSE for small resistor networks is shown in Figure 3‑25. The effect is more pronounced for larger networks or for 3-D networks. A smaller number of resistors usually means that the thermal analysis will proceed faster. In the best cases, the number of radiation resistors may be reduced by about a factor of four for 2-D Cartesian or axisymmetric models and by about a factor of 16 for 3-D models. The main advantage of using COLLAPSE to collapse radiosity nodes is that this will result in a much smaller number of radiation resistors in the model. The effect of using COLLAPSE for small resistor networks is shown in Figure 3‑25. The effect is more pronounced for larger networks or for 3-D networks. A smaller number of resistors usually means that the thermal analysis will proceed faster. In the best cases, the number of radiation resistors may be reduced by about a factor of 4 for 2-D Cartesian or axisymmetric models and by about a factor of 16 for 3-D models. Our experience is that the loss of accuracy is quite small for fine meshes and lower temperatures. The user may wish to try the examples in Example Thermal Radiation Problems, 11, using the COLLAPSE field modeling techniques. Other existing models may also be rerun using the new COLLAPSE flag. Then the results can be compared with previous results and provide the user with a basis for deciding when to use or not use the COLLAPSE feature. |