HYBDAMP

Bulk Data Entry Defines the application of modal damping to the residual structure in a Direct Transient or Frequency Response analysis.

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
HYBDAMP	`SID`	`METHOD`	`SDAMP`	`KDAMP`

Field	Contents	SI Unit Example
`HYBDAMP`	Keyword for applying modal damping on a direct analysis
`SID`	Unique hybrid damping `SID` (Refer to HYBDAMP I/O Option).
`METHOD`	EIGRL/EIGRA data identification number. Hybrid damping is applied on the modes determined by the eigenvalue analysis. No default (Integer > 0)
`SDAMP`	A TABDMP1 entry identification number for modal damping. No default (Integer > 0)
`KDAMP`	-1/YES Modal damping is entered into the complex stiffness matrix as material damping, instead of viscous damping. 1/NO (Default) Enter the damping as viscous damping. (Integer)

HYBDAMP/SID can be set by the HYBDAMP I/O Options Entry in the I/O section of the input data.
Hybrid damping can be defined as:
If KDAMP is set to 1/NO (Default), then:(1)
$B H = [M] [ϕ_{1} ϕ_{2} \dots ϕ_{n}] [\begin{matrix} b (ω_{1}) \\ b (ω_{2}) \\ \dots \\ b (ω_{n}) \end{matrix}] [\begin{matrix} ϕ_{1}^{T} \\ ϕ_{2}^{T} \\ \dots \\ ϕ_{n}^{T} \end{matrix}] [M]$

If KDAMP is set to -1/YES, then:(2)
$K H = [M] [ϕ_{1} ϕ_{2} \dots ϕ_{n}] [\begin{matrix} g (ω_{1}) \\ g (ω_{2}) \\ \dots \\ g (ω_{n}) \end{matrix}] [\begin{matrix} ϕ_{1}^{T} \\ ϕ_{2}^{T} \\ \dots \\ ϕ_{n}^{T} \end{matrix}] [M]$

Where,

$ϕ$ _i

Modes of the structure

[M]

Structural mass matrix

b( $ω$ _i)

Modal damping values (b( $ω$ _i) = g( $ω$ _i) $ω$ _im_i)

b( $ω$ _i)

Are equal to twice the critical damping ratios calculated from the TABDMP1 entry

$ω$ _i

Natural frequency of mode $ϕ$ _i

m_i

Generalized mass of mode $ϕ$ _i