Card 6n - Heat Flux View Factor Request to Radiative Sources

This optional card calculates heat flux view factors from radiative sources such as light sources.

Parameters: L, N1, N2, POWER, TIME, AFLAG, REVN1, REVN2, POWERIR, THETA, PHI, ARRAYNO, DIRFLAG

L

L is the type of heat flux view factor request.

  • L = SOURCES12 (or 25) calculates a heat flux view factor from source element(s) N1 to element(s) N2 with shadowing. If N1 and N2 are both group names, all the heat flux view factors from the elements of N1 to the elements of N2 will be calculated.
  • L = SOURCEN12 (or 26) is the same as SOURCES12 with no shadowing.
  • L = SOURCESALL (or 27) calculates all the heat flux view factors for source element(s) N1 with shadowing, starting with the heat flux view factor to N2. N2 = 0 calculates all the heat flux view factors for source element(s) N1. If N1 is a group name, all the heat flux view factors for the elements of that group will be calculated.
  • L = SOURCENALL (or 28) is the same as SOURCESALL with no shadowing.

N1

N1 is the radiative source. N1 may be an element number or a group name.

N2

N2 is the element or group name of the element(s) for which the heat flux view factors are calculated. N2 must be set to 0 for the SOURCESALL and SOURCENALL cards.

POWER

POWER is the value of the solar spectrum heat load per unit time emitted by the N1 source elements. POWER may not be negative. To ensure that the specified amount of solar spectrum radiation is emitted by the N1 source elements and none of it is re-absorbed by them due to reflection, their absorptivity value will be set to zero in the POWER module.

If POWER is Tn, where n is a table number (e.g. T10), and n is a table whose dependent variable is QNODE, and TIME is CONSTANT, then the POWER value will be interpolated from the table n by the Analyzer during run time.

For multispectral runs (Card 9 PARAM SPECTRA Card) the values of POWER and POWERIR are multiplied together to yield the heat load per unit time. If the sources are wavelength-dependent, either POWER or POWERIR must reference a table specifying the wavelength dependence.

TIME

TIME specifies the time value when the heat flux view factors are defined. TIME may also be the flag CONSTANT (or –99990). If TIME is blank, it defaults to CONSTANT.

AFLAG

AFLAG determines whether the values specified in the POWER and POWERIR fields are emitted heat loads per unit area, per element, or emitted by all the elements N1.

  • AFLAG = ABSOLUTE (or 0): For this option POWER and POWERIR are the emitted power values for the element N1.
  • AFLAG = AREA (or 1): For this option POWER and POWERIR are the emitted power per unit area values for the element N1.
  • AFLAG = TOTAL (or 2): For this option, if POWER or POWERIR are of the form Tn, and table n has the independent variable EID, or it has the independent variable OPERAT and the dependent variable TABLE, and one of the tables listed in n has the independent variable EID, then the heat load is calculated according to the following formula:

where:

  • H(I) is the heat load emitted per unit time by the radiating source element I, where I is a member of the group N1.
  • Ω(I) is the value interpolated from the table n for element I.
  • AREA(I) is the area of element I.
  • F is a multiplying factor, which is obtained by interpolation from the non-EID table if the independent variable is OPERAT. If the independent variable is EID, then F=1.

For the TOTAL option N1 must be a group name.

AFLAG = blank, which defaults to AREA.

AFLAG = INCABSOLUTE (or 3), INCAREA (or 4), or INCTOTAL (or 5): INCABSOLUTE, INCAREA, and INCTOTAL behave the same way as the ABSOLUTE, AREA, and TOTAL options, except that instead of view factors being calculated and written on VUFF, heat loads are written on MODLF. The magnitude of the heat loads is equal to what the elements would have absorbed had they all been perfectly black.

REVN1

REVN1 may be 0, blank, an element ID, or a group name. The reverse sides of the REVN1 element(s) are added to the N1 source elements.

REVN2

REVN2 is applicable for L = SOURCES12 or SOURCEN12, otherwise it must be blank or 0. REVN2 may be 0 or an element or a group name, and the reverse sides of the REVN2 element(s) are added to the N2 elements.

POWERIR

POWERIR is the IR spectrum heat load per unit time emitted by the source element(s). To ensure that the specified amount of IR spectrum radiation is emitted by the N1 source elements and none of it is re-absorbed by them due to reflection, their emissivity value will be set to zero in the POWER module.

If POWERIR is Tn or -n, where n is a table number (e.g. T10 or -10), and n is a table whose dependent variable is QNODE, and TIME is CONSTANT, then the POWERIR value will be interpolated from the table n by the Analyzer during run time.

For multispectral runs (Card 9 PARAM SPECTRA) the values of POWER and POWERIR are multiplied together to yield the heat load per unit time. If the sources are wavelength-dependent, either POWER or POWERIR must reference a table specifying the wavelength dependence.

THETA

THETA is optional. If THETA is present, the sources send out only collimated rays. If THETA is not present, they send out rays in all directions.

THETA is the angle in degrees between the direction of the collimated rays and the element surface normal. If THETA is not zero, then the elemental material coordinate system must be defined with Card 9 MATVEC.

If the source element N1 is a 1-node element, or DIRFLAG is 1, then THETA is interpreted to be in the global coordinate system.

PHI

PHI is the angle in degrees between the projection of the collimated rays’ direction vector onto the material coordinate system’s XY plane and the X-vector of the material coordinate system, measured positive in the counterclockwise direction.

If THETA is not zero, then the elemental material coordinate system must be defined with Card 9 MATVEC.

If the source element N1 is a 1-node element, or DIRFLAG is 1, PHI is interpreted to be in the global coordinate system.

ARRAYNO

ARRAYNO is optional, and if specified, is the number of an array that contains a distribution vs angle data.

If ARRAYNO is specified, the source N1 is considered to be direction-dependent. The angular distribution in the table is normalized over all solid angle such that the total power specified in the POWER and POWERIR fields is respected. Without the ARRAYNO table referenced, the diffuse source will provide a Lambertian power distribution.

By specifying angular dependence in the table, other distributions can be defined. The intensity emitted by the radiative heat source in a given direction is calculated by multiplying the POWER and POWERIR values by the normalized value interpreted from the array, times the multiplier specified by AFLAG.

The array must be specified with Card 9 ARRAYTYPE and ARRAYDATA. The first independent variable must be DIR_INC, the second independent variable must be ANG_INC, and the dependent variable must be MULTIPLIER.

A MATVEC Card must also be specified for each N1 source element to specify the material directional properties. DIR_INC is the angle in degrees of the emitted ray with respect to the material X axis, and ANG_INC is the angle in degrees of the emitted ray with respect to the material Z axis.

If ARRAYNO is specified, the values of THETA and PHI are ignored.

DIRFLAG

If DIRFLAG is blank or zero, then THETA and PHI are interpreted to be defined in the N1 elements’ material coordinate system. If DIRFLAG is 1, then THETA and PHI are interpreted to be in the global coordinate system.

Code example


 SOURCES1ALL SOURCES 0 1.6
 $ RADIATIVE HEAT FLUX VIEW FACTORS ARE
 $ CALCULATED TO ALL THE ELEMENTS FROM
 $ SOURCE ELEMENTS CALLED SOURCES. THE
 $ EMITTED HEAT LOAD HAS A VALUE OF 1.6
 $ PER UNIT AREA.
 
 SOURCES12 SOURCA 2 2.5 10 ABSOLUTE
 $ RADIATIVE HEAT LOADS ARE CALCULATED FROM
 $ SOURCE SOURCA TO ELEMENT 2 TO AT TIME = 10.
 $ THE EMITTED HEAT LOAD FROM THE ELEMENTS OF
 $ SOURCA HAS A VALUE OF 2.5 PER ELEMENT.

Notes

This card calculates heat flux view factors from radiative sources such as light sources. The calculation procedure is analogous to that of solar loads, with the heat flux view factors replacing the solar view factors. The following procedure should be used to calculate radiative heat loads from source elements.

  1. Define the radiative source elements geometrically. Assign them a group name (e.g. SOURCES) with a Card 9 NAME.
  2. Request all the view factors with a Card 6a VFSALL.
  3. Request the heat flux view factors with a Card 6n SOURCES. Set N1 to the source group name, and specify the POWER and POWERIR parameters. Optionally, you may wish to specify the TIME and AFLAG parameters.
  4. Set the Card 2a M parameter to 194 (= 2+64+128), plus whatever other options you wish to run. These options request that the VUFAC should be run to calculate the view factors and the heat flux view factors and that the