Appendix C: Structural Damping File Description

The file CHFILE specified in Structural damping specification contains a description of the structural material and slip damping of the cross-section.

1. Material damping

1.1. Unit names, one input line

UT UL UM UF

  • UT: character(6): Unit name for time

  • UL: character(6): Unit name for length

  • UM: character(6): Unit name for mass

  • UF: character(6): Unit name for force

1.2. Estimation of Rayleigh damping, one input line

IEKTYP

  • IEKTYP: real, default: 1: Estimation of Rayleigh damping using geometric and/or material damping stiffness

    • = 1 : both geometric and material damping stiffness are included

    • = 2 : only material stiffness is included

1.3. Material damping control data, one input line

RJ_MTRL  RN_MTRL  FREQREF_MTRL  TEMPREF_MTRL  NTENS_MTRL  NCURV_MTRL  NFREQ_MTRL  NTEMP_MTRL

  • RJ_MTRL: real, default: 0: Material damping constant. Dummy in the present version. \([\mathrm {\frac{FL}{(F/L^2)^nL^3}}]\) where n is the input parameter RN_MTRL. The material damping energy per volume per cycle is \(\mathrm {RJ\_MTRL(\Delta \sigma )^{RN\_MTRL}}\) .

  • RN_MTRL: real, default: 0: Material damping exponent. Used in interpolation of the material damping data given in the table below.

  • FREQREF_MTRL: real, default: 0: Reference frequency for the material damping data given in the table below. Dummy if NFREQ_MTRL = 0. If NFREQ_MTRL > 0 the frequency scaling factor corresponding to FREQREF_MTRL should normally be 1.0. \([\mathrm {Hz}]\)

  • TEMPREF_MTRL: real, default: 0: Reference temperature for the material damping data given in the table below. Dummy if NTEMP_MTRL = 0. If NTEMP_MTRL > 0 the temperature scaling factor corresponding to TEMPREF_MTRL should normally be 1.0.

  • NTENS_MTRL: integer > 0, default: 0: Number of static effective tension levels in the material damping table

  • NCURV_MTRL: integer > 0, default: 0: Number of curvature amplitudes in the material damping table

  • NFREQ_MTRL: integer >= 0, default: 0: Number of frequencies in frequency scaling curve

  • NTEMP_MTRL: integer >= 0, default: 0: Number of temperatures in the temperature scaling curve

1.4. Static effective tension levels, one input line

TEMS_MTRL(1) .... TENS_MTRL(NTENS_MTRL)

  • TENS_MTRL(itens): real, default: 0: Static effective tension level nr. items for material damping \([\mathrm {F}]\)

The static effective tension levels must be given in increasing order.

1.5. Table of material damping data, NCURV_MTRL input lines

CURV_MTRL(icurv) DAMP_MTRL(icurv,1) .... DAMP_MTRL(icurv,NTENS_MTRL)

  • CURV_MTRL(icurv): real, default: 0: Curvature amplitude level nr. icurv for material damping \([\mathrm {1/L}]\)

  • DAMP_MTRL(icurv,itens): real, default: 0: Energy loss per cycle per length for static effective tension TENS_MTRL(itens) and curvature amplitude CURV_MTRL(icurv) \([\mathrm {(FL)/L}]\)

The curvature amplitude levels must be given in increasing order.

Linear interpolation is used on the values \(\mathrm {DAMP\_MTRL(icurv,itens)/(CURV\_MTRL(icurv)^{RN\_MTRL})}\) The first / last values are used for static effective tension or curvature amplitude below / above the range given.

1.6. Frequency scaling of material damping, two input lines

FREQ_SCAL(1) ... FREQ_SCAL(NFREQ_MTRL)

  • FREQ_SCAL(ifreq): real, default: 0: Frequency value nr. ifreq for the frequency scaling of the material damping \([\mathrm {Hz}]\)

SCALE(1) ... SCAL(NFREQ_MTRL)

  • SCALE(ifreq): real, default: 0: Scaling factor corresponding to frequency FREQ_SCAL(ifreq)

Frequency values must be given in increasing order.

Linear interpolation is used for intermediate frequency values. The first / last values are used for frequency values below / above the range given. If the scaling factor corresponding to the reference frequency FREQREF_MTRL is not 1.0, the resulting scaling will be the ratio between the scaling factor for the response frequency and the scaling factor for the reference frequency. Specifying the same scaling factor for all frequencies will thus result in no frequency scaling.

1.7. Temperature scaling of material damping, two input lines

TEMP_SCAL(1) ... TEMP_SCAL(NTEMP_MTRL)

  • TEMP_SCAL(itemp): real, default: 0: Temperature value nr. itemp for the temperature scaling of the material damping

SCALE(1) ... SCAL(NTEMP_MTRL)

  • SCALE(itemp): real, default: 0: Scaling factor corresponding to the temperatire TEMP_SCAL(itemp)

Temperature values must be given in increasing order.

Linear interpolation is used for intermediate temperature values. The first / last values are used for temperature values below / above the range given. If the scaling factor corresponding to the reference temperature TEMPREF_MTRL is not 1.0, the resulting scaling will be the ratio between the scaling factor for the current temperature and the scaling factor for the reference temperature. Specifying the same scaling factor for all temperatures will thus result in no temperature scaling.

2. Slip damping

The slip damping is found as the area enclosed by nonlinear moment-curvature cycles. The Ramberg-Osgood model is used to define the moment-curvature curves.

Specify NTENS_SLIP = 0 below to skip slip damping.

2.1. Slip damping control data, one input line

TEMPREF_SLIP NTENS_SLIP SCALE_SLIP

  • TEMPREF_SLIP: real, default: 0: reference temperature for slip damping, Not used in present version.

  • NTENS_SLIP: integer >= 0, default: 0: Number of static effective tension levels slip damping is given for

    • NTENS_SLIP = 0: Slip damping is not included

  • SCALE_SLIP: real, default: 1.0: Scaling factor for the resulting slip damping.

2.2. Ramberg-Osgood parameters, NTENS_SLIP input lines

TENS_SLIP  CY  MY  ETA  GAMMA  C_SLIP

  • TENS_SLIP: real, default: 0.0: Static effective tension \([\mathrm {F}]\)

  • CY: real, default: 0: Ramberg-Osgood Cy parameter \([\mathrm {1/L}]\)

  • MY: real, default: 0: Ramberg-Osgood My parameter \([\mathrm {FL}]\)

  • ETA: real, default: 0: Ramberg-Osgood eta parameter \([\mathrm {1}]\)

  • GAMMA: real, default: 0: Ramberg-Osgood gamma parameter \([\mathrm {1}]\)

  • C_SLIP: real, default: 0: Curvature for which slip first appears. No energy loss for curvatures below this level. \([\mathrm {1/L}]\)

For a given static tension T and curvature amplitude C, linear interpolation is used between the damping found for curvature C at effective tension values bracketing T. If T is below / above the range given, the damping for C at the first / last tension value is used.