# 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

## Definitions

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)

1. HYBDAMP/SID can be set by the HYBDAMP I/O Options Entry in the I/O section of the input data.
2. Hybrid damping can be defined as:
If KDAMP is set to 1/NO (Default), then:(1)
$BH=\left[M\right]\left[{\varphi }_{1}{\varphi }_{2}\cdots {\varphi }_{n}\right]\left[\begin{array}{cccc}b\left({\omega }_{1}\right)& & & \\ & b\left({\omega }_{2}\right)& & \\ & & \cdots & \\ & & & b\left({\omega }_{n}\right)\end{array}\right]\left[\begin{array}{c}{\varphi }_{1}^{T}\\ {\varphi }_{2}^{T}\\ \cdots \\ {\varphi }_{n}^{T}\end{array}\right]\left[M\right]$
If KDAMP is set to -1/YES, then:(2)
$KH=\left[M\right]\left[{\varphi }_{1}{\varphi }_{2}\cdots {\varphi }_{n}\right]\left[\begin{array}{cccc}g\left({\omega }_{1}\right)& & & \\ & g\left({\omega }_{2}\right)& & \\ & & \cdots & \\ & & & g\left({\omega }_{n}\right)\end{array}\right]\left[\begin{array}{c}{\varphi }_{1}^{T}\\ {\varphi }_{2}^{T}\\ \cdots \\ {\varphi }_{n}^{T}\end{array}\right]\left[M\right]$
Where,
$\varphi$ i
Modes of the structure
[M]
Structural mass matrix
b( $\omega$ i)
Modal damping values (b( $\omega$ i) = g( $\omega$ i) $\omega$ imi)
g( $\omega$ i)
Are equal to twice the critical damping ratios calculated from the TABDMP1 entry
$\omega$ i
Natural frequency of mode $\varphi$ i
mi
Generalized mass of mode $\varphi$ i