9.1.4 Continuous Damping

Continuous damping may be specified via spring/dashpot elements with a damping factor: a two-node spring/dashpot for a connection between two nodes [Fig.9.3a], or a one-node spring/dashpot for a discrete dashpot in a specific direction [Fig.9.3b].^9.1

Figure 9.3: Continuous damping

    (syntax)

DAMP c

is the constant damping coefficient C (C $\geq$ 0 ) to simulate continuous damping by dashpot behavior. By default, DIANA assumes `no damping'. [C = 0 ] The damping is applied in the direction of the element axis.

DAMPFR

specifies frequency dependent damping which is only valid in a frequency response analysis. Values f1 to fn are frequencies f₁ to f_n and c1 to cn are the corresponding damping coefficients C₁ to C_n [Fig.9.4]. ( C_i $\geq$ 0 )The number of points that you may specify is virtually unlimited.

Figure 9.4: Frequency dependent damping

DIANA determines the actual damping coefficient for a specific frequency by means of linear interpolation. If the frequency is outside the interval f₁ to f_n , then DIANA assumes no damping: C = 0 .

    (file.dat)

'ELEMEN'
CONNEC
 32  SP2TR 78 95
 33  SP1TR 127
MATERI
 / 32 /  11
 / 33 /  12
GEOMET
 / 33 /  1
'MATERI'
   11  DAMP    0.48
       SPRING  0.0
   12  DAMPFR  0.2 0.48   2.5 0.96  15.0  1.83
       SPRING  0.0
'GEOMET'
   1   AXIS  1.0 1.0 0.0

Note in this example that the specification of the spring stiffness is obligatory. Therefore, a zero spring stiffness must be input if the spring element must act as a dashpot only. Element 33 is a one-node spring SP1TR. The axis direction of such an element must be specified in table 'GEOMET'. In this example, the damping of element 33 depends on the frequency within the range from 0.2 to 15 Hz. Outside that range there is no damping and the element is a dummy.