TABDMP1

Bulk Data Entry

TABDMP1 – Modal Damping Table

Description

Defines modal damping as a tabular function of natural frequency.

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
TABDMP1	TID	TYPE
	f1	g1	f2	g2	f3	g3	f4	g4
	f5	g5	…	…	…	…	…	…

Example

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
TABDMP1	2
	2.5	0.01057	2.6	0.1362	ENDT

Field	Contents
TID	Table identification number. No default (Integer > 0)
TYPE	Type of damping units. Default = G (G, CRIT, or Q)
$image\tabdmp11.gif$	Natural frequency value in cycles per unit time. No default (Real > 0.0)
$image\tabdmp12.gif$	Damping value. No default (Real)

Comments

Modal damping tables must be selected in the subcase information section, using the SDAMPING command. This form of damping is used only in the modal method of frequency response analysis.
A METHOD statement must be present in the SUBCASE.
The frequency values, $image\tabdmp11.gif$ , must be specified in either ascending or descending order, but not both.
Discontinuities may be specified between any two points except the two starting points or two end points. For example, in figure 1 discontinuities are allowed only between points f2 through f7. Also, if g is evaluated at a discontinuity, then the average value of g is used. In figure 1, the value of g at f=f3 is g = (g3+g4)/2.
At least one continuation entry must be specified.
Any $image\tabdmp11.gif$ or $image\tabdmp12.gif$ entry may be ignored by placing 'SKIP' in either of the two fields used for that entry.
The end of the table is indicated by the existence of 'ENDT' in either of the two fields following the last entry. An error is detected if any continuations follow the entry containing the end-of-table flag 'ENDT'.
The TABDMP1 uses the algorithm: $image\tabcomment7.gif$

where f is input to the table and g is returned. The table look-up $image\tabcomment72.gif$ is performed using linear interpolation within the table and linear extrapolation outsied the table using the two starting or end points. See figure 1. No warning messages are issued if table data is input incorrectly.

$image\tabdmp1.gif$

Figure 1. Example of Table Extrapolation and Discontinuity

The KDAMP option, on the PARAM card, may be used to switch between viscous and structural damping. Viscous is the default and is used when PARAM, KDAMP is not present.

KDAMP	Result
1 (default)	B matrix
-1	(1+ig)K matrix

If TYPE is 'G' or blank, the damping values $image\tabdmp12.gif$ are in units of equivalent viscous dampers as follows: $image\tab10.gif$

If TYPE is 'CRIT', the damping values $image\tabdmp12.gif$ are in units of fraction of critical damping $image\cco.gif$ If TYPE is 'Q', the damping values $image\tabdmp12.gif$ are in the units of amplification or quality factor, Q. These constants are related by the following equations:

$image\tab102.gif$

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