Dynamic Design Analysis Method Data
Description: Defines data needed to perform DDAM analysis.
Format:
Example:
| Field | Definition | Type | Default |
|---|---|---|---|
| SID | Set identification number. | Integer > 0 | Required |
| VFi | Velocity scale factors. See Remark 1. | Real | Required |
| AFi | Acceleration scale factors. See Remark 1. | Real | Required |
| VA, VB, VC | Velocity weighting factors. See Remark 1. | Real | Required |
| AA, AB, AC, AD | Acceleration weighting factors. See Remark 1. | Real | Required, see Remark 2 |
| STYPE | Ship type, one of the following character variables: SURFACE for surface ship or SUBMERG for submerged. | Character | Required |
| LTYPE | Mounting location, one of the following character variables: DECK, HULL, or SHELL. | Character | Required |
| DIRSEQ | Shock direction sequence. (Up to three unique digits may be placed in the field with no embedded blanks.) See Remark 3. | 1 ≤ Integers ≤ 3 | 123 |
| FADIR | Forward-aft component number. See Remark 3. | 1 ≤ Integers ≤ 3 | 1 |
| VDIR | Vertical component number. See Remark 3. | 1 ≤ Integers ≤ 3 | 3 |
| GCF | Mass to weight conversion factor. | Real | 386.4 |
| MINACC | Minimum acceleration. See Remark 4. | Real | See Remark 4 |
| CUTOFF | Modal mass cutoff percentage. See Remark 5. | Real | 80.0 |
| MTYPE | Material type, one of the following character variables: ELASTIC or PLASTIC. See Remark 6. | Character | ELASTIC |
| METHOD | Response spectra generation method, one of the following character variables: DDS-072 or NRL-1396. See Remark 7. | Character | DDS-072 |
| MINMEM | Minimum percent modal effective mass which defines modes that will be included after CUTOFF is achieved. | Real | 1.0 |
Remarks:
- The user supplied velocity, acceleration, and weighting factors are used to compute the velocity and acceleration spectra which serves as the input for response/shock spectrum analysis. The formulas for a SURFACE ship with HULL or SHELL mounted equipment (METHOD = DDS-072) or with DECK, HULL, or SHELL mounted equipment (METHOD = DDS-1396) are given by:
For all other ship types and mounting locations, the formulas are:
Where M is the modal weight in kips calculated internally for that mode. The VFi and AFi coefficients defined in fields 3 through 8 correspond to the shock coefficients in each model direction. For example, VF1 and AF1 correspond to the shock coefficients in the model x-direction, VF2 and AF2 the y-direction, and VF3 and AF3 the z-direction.
- The AD weighting factor is required when STYPE is SURFACE and
- METHOD is DDS-072 and LTYPE is either HULL or SHELL.
- METHOD is NRL-1396 and LTYPE is DECK, HULL or SHELL.
- The DIRSEQ field defines which directions will be analyzed and the order they will be analyzed in. The FADIR and VDIR fields define which direction components in DIRSEQ correspond to the forward-aft and vertical directions, respectively. The athwartship direction is determined using the remaining direction. Each direction (1-3) corresponds to a velocity and acceleration factor defined in fields 3 through 8 on this entry. Direction 1 corresponds to the model x-direction, direction 2 the y-direction, and direction 3 the z-direction.
- If accelerations generated in Remark 1 are less than MINACC, the MINACC value will be used. The default value for MINACC is 1.0 when METHOD is DDS-072 and 6.0 when METHOD is NRL-1396.
- The modal mass cutoff percentage is percentage of total mass at which modal processing ceases. DDAM analysis requires that only a percentage (typically 80%) of the total modal mass needs to be included in the NRL summation.
- The material type specified in the MTYPE field only affects the output labels and is not used in the analysis. The character variable PLASTIC does not indicate or initiate nonlinear analysis.
- METHOD=DDS-072 specifies the equation format described in Design Data Sheet DDS-072 (Classified), 1972. This is the formal specification for the Dynamic Design Analysis Method (DDAM).
- The default units for DDAMDAT data are IN-LBF-SEC. Other units may be used by setting the UNITS model parameter. Note that the GCF field is always in units of in/sec2. (See Section 5, Parameters, for more information on UNITS.)