Define custom DDAM shock coefficients

If you do not want to use the standard DDS-072-1 shock coefficients, you can define explicit coefficients for reference acceleration and reference velocity as input to the DDAM event.

For more information about the reference acceleration and reference velocity equations, see DDAM reference acceleration and velocity.

You can enter the coefficients in the Input DDAM Coefficients dialog box each time you perform the response evaluation, or you can predefine the coefficients in a text file.

Predefine the shock coefficients in a text file

You can predefine the shock coefficients in a text file for the response evaluation to reference.

1. Open a text editor and create a new text file.

2. Copy the text below and paste it into the text file you created.$  Lines that start with $ are treated as comments $ Format of COEF entry $COEF   SURF    DECK    ELASTIC  $       VF(1)   VF(2)   VF(3)   AF(1)   AF(2)   AF(3)          $       VA      VB      VC      AA      AB      AC      AD         $ COEF    SURF    DECK    ELASTIC          .2      .4      1.0     .2      .4      1.0                  60.     12.     6.      10.     42.0     6.     6.         COEF    SURF    HULL    ELASTIC          .2      .4      1.0     .2      .4      1.0                60.     12.     6.      20.     37.5    12.     6.        COEF    SURF    SHELL   ELASTIC          .2      .4      1.0     .2      .4      1.0                 60.     12.     6.      20.     37.5    12.     6.         COEF    SURF    DECK    ELPL          .2      .4      1.0     .2      .4      1.0                60.     12.     6.      10.     42.0     6.     6.         COEF    SURF    HULL    ELPL          .2      .4      1.0     .2      .4      1.0                60.     12.     6.      20.     37.5    12.     6.        COEF    SUB     DECK    ELASTIC          .4      1.0     1.0     .4      1.0     1.0                   20.     480.    100.    10.4    480.    20.     20.                     COEF    SUB     HULL    ELASTIC          .4      1.0     1.0     .4      1.0     1.0                    20.     480.    100.    10.4    480.    20.     20.                   COEF    SUB     SHELL   ELASTIC          .08     .2      1.0     .08     .2      1.0                       20.     480.    100.    10.4    480.    20.     20.                       COEF    SUB     DECK    ELPL         .4      1.0     .5      .8      2.0     1.0                            20.     480.    100.    10.4    480.    20.     20.                      COEF    SUB     HULL    ELPL         .4      1.0     1.0     .4      1.0     1.0                            20.     480.    100.    10.4    480.    20.     20.

3. Replace the sample coefficients in the text file with your own coefficients, using the format shown in the $ comments. In the $ comments, the numbers in parentheses correspond to directions: (1) — Fore-Aft(2) — Athwartship(3) — Vertical

4. Save the text file with a .dcf extension and make note of its location.

5. Create a new DDAM event.

6. In the New Event dialog box, select the appropriate Ship Type and Mounting type.

7. Under Response Type, select the type of deformation that is permitted due to shock. Elastic does not permit permanent deformation. Elastic-Plastic permits limited deformation.

8. From the Formulation list, select User Defined.

9. In the Minimum G box, accept the default acceleration of 6 or type a different value. For details about how the minimum g is used in the shock spectrum equation, see DDAM reference acceleration and velocity.

10. Under Coefficient Definition Method, click By Coefficient File.

11. In the Coefficient File box, browse to the location where you saved the coefficients text file in the previous steps.

12. Click OK to dismiss the New Event dialog box.

13. In the New Translational DDAM Excitation dialog box, define the DDAM excitation. Under Loading Type, select the direction of the shock (Vertical, Athwart Ship, or Fore and Aft). This determines the coefficients the software will use from your coefficients file.From the Components list, select the component direction for the excitation. The available components depend on the directions that were solved for when you solved the model. For example, if the enforced motion location was defined in the X and Y directions, only X and Y will be available for selection as the component. The direction component you select should correspond to the Loading Type direction.

14. Perform the response evaluation.

15. Click OK. The response evaluation completes using the coefficients defined in the coefficients text file.

Define the shock coefficients during response evaluation

Alternatively, you can enter the coefficients each time you perform the response evaluation. The values are not stored after the software completes the evaluation calculation.

1. Create a new DDAM event.

2. In the New Event dialog box, under Coefficient Definition Method, click Input Manually.

3. Follow steps 6-9 from the above procedure.

4. Click OK to dismiss the New Event dialog box.

5. In the New Translational DDAM Excitation dialog box, define the DDAM excitation. Under Loading Type, select the direction of the shock (Vertical, Athwart Ship, or Fore and Aft). This determines the coefficients the software will use from your coefficients file.From the Components list, select the component direction for the excitation. The available components depend on the directions that were solved for when you solved the model. For example, if the enforced motion location was defined in the X and Y directions, only X and Y will be available for selection as the component. The direction component you select should correspond to the Loading Type direction.

6. Perform the response evaluation.

7. Click OK. The Input DDAM Coefficients dialog box appears.

8. Type the custom coefficients and click OK.

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