Dynamic Design Analysis Method

Since the DDAM analysis uses the results from a modal analysis, specify which design scenario in the current model has the modal results with the Use modal results from design scenario field.

Note: The Model Units of the DDAM analysis must be identical to the Model Units of the modal results.

Define Parameters

The first parameter that must be specified for a DDAM analysis is the type of ship on which the model is located. This is done in the Type of ship drop-down menu on the General tab of the Analysis Parameters dialog box. If the ship is on the surface of the water, select the Surface option. If the ship is below the surface, select the Submarine option.

The next parameters that must be specified is where the model is mounted on the ship. This is done in the Mounting locations drop-down menu. For surface ships, the Attached to hull option should be used for the main structural members of the ship including structural bulkheads, structural bulkhead stiffeners below the main deck, and shell plating above the waterline. The Attached to deck option should be used for the main deck and above, decks, platforms, and non-structural bulkheads below the main deck. The Attached to shell plating should be used for shell plating below the waterline. For submarines, the Attached to hull option should be used for the main structural members of the ship including hull frames, structural bulkheads, and structural bulkhead stiffeners. The Attached to deck option should be used for the decks, platforms, and non-structural bulkheads. The Attached to shell plating should be used for shell plating.

The next parameter that must be specified is which spectra are considered in the DDAM analysis. This is done in the Shock uses drop-down menu. The direction of each spectra can be specified using controls in the Advanced tab. The default directions for the fore and aft, athwartship and vertical shock spectra are the X, Y and Z Directions respectively. The case in which all three spectra are considered generally results in the worst case scenario.

The last parameter that must be specified is the type of materials that are being used. You can choose between elastic, elastic-plastic and reduced elastic materials in the Type of material drop-down menu.

Solution Options

You can choose between using the velocity or acceleration spectrum as the input spectrum using the Input spectrum type based on drop-down menu in the Solution tab of the Analysis Parameters dialog box. If the input spectrum is set to Velocity or acceleration, both the velocity and acceleration multipliers are calculated, and the smaller of the two values is used. However, the multiplier is never smaller than 2316.

By default, all the calculated modes is used during the analysis. If the Include all modes check box is deactivated, you can control which modes are included and excluded based on the frequency or modal mass in the Mode Inclusion Options and Mode Exclusion Options sections.

The Percent memory allocation on the Analysis Parameters dialog box controls how much of the available RAM is used to read the element data and to assemble the matrices. (When the value is less than or equal to 100%, the available physical memory is used. When the value of this input is greater than 100%, the memory allocation uses available physical and virtual memory.)

Control Data in Output Files

Before performing the analysis, you can select additional output to be created. The Output tab of the Analysis Parameters dialog box can be used to control the data that is output. Except as noted, this additional output is text based, so these options will not affect the results that can be viewed in the Results Environment.

Activating the Displacement data option will write the displacement results to the text summary file. Depending on the model size and the number of output time steps, this could make the file very large.
Activating the Stress data option will write the stress results to a text file. Depending on the model size and number of output time steps, this file could be very large.
Activating the Stress/strain at midside nodes (binary) check box will output the stress and strain at midside nodes to the binary result files. These results can then be displayed in the Results environment. (Midside nodes are an option that can be activated for certain element types using the Element Definition dialog box.)

User-Specified Coefficients

By activating the Use user-specified coefficients check box in the Optional tab of the Analysis Parameters dialog box, user-specified coefficients is used in place of the coefficients given in unclassified DDAM documentation. These coefficients, in conjunction with the general functional form, allow users to perform a custom DDAM analysis. The coefficients are input using an ASCII text file. Specify the location must in the Filename field. For details on the format of this file, go to User-Specified Coefficients in DDAM Analyses.

Perform Secured Analyses

Often, models are created on an unclassified or non-secured computer. When using the user-specified coefficients, those values are often classified. You may not want to enter them on the non-secured computer. In this situation, use the Security Feature section of the Optional tab. When Secured run is activated, it permits DDAM to calculate design values on an isolated secured machine (called laptop in this write-up) and then finish the analysis back on the non-secured machine (called desktop in this write-up). The communication between two machines can be carried out by a 1.44MB capacity floppy disk or other storage media. The procedure is as follows:

Run the modal analysis as usual on the non-secured desktop and set up the DDAM analysis as usual, except for the following (located under the Analysis Parameters Optional tab):
1. To use secured coefficients, the setup and run is easier if one clicks the Use user-specified coefficients check box and then Browse or type the Filename. The Filename and location of the file specified in this step must be the same on both computers. However, the coefficient file on the non-secured desktop does not need to contain anything; the file only needs to exist.
2. Check the box for Secured run.
3. Set the Running phase to Prepare data.
4. Use the Browse button to specify a file to be created (Data filename for/from secured run). This file is transferred to the secured laptop in a later step. (It may be best to avoid spaces in the name of this transfer file.)
Run the DDAM analysis on the desktop. This will generate the transfer files.
Follow the instructions given on the pop-up dialog box when the analysis completes. Namely,
1. Copy the .S40 file and .BAT file to a disk.
2. Take the disk to the secured laptop.
After clicking OK on the pop-up, the DDAM analysis will indicate that the analysis did not finish. This occurs because no results have been created yet.
On the secured laptop, make sure that the Autodesk Simulation installation folder is listed in the Path environment variable. (Go to the Windows StartSettingsControl Panel System Advanced Environment Variables.)
Edit the coefficient file specified in step 1a on the laptop and put in the classified DDAM coefficients, as follows:
1. Copy the default file DDAM.DEF located in the Autodesk Simulation installation folder to the appropriate folder location and filename on the laptop.
2. Follow corporate policy to obtain the classified coefficients and edit them into the secured DDAM coefficient file.
To run the DDAM on the secured laptop, it is best to do the following:
1. Open a DOS or Command window.
2. Set the prompt to the drive and folder containing the .S40 and .BAT files copied from the desktop.
3. Type the name of the .BAT file
4. Press Enter to run the analysis. This will create a .DAM file.
5. Alternatively, you can use Windows Explorer to double-click the .BAT file, but any errors that may occur are not displayed.
Now that the use of the classified coefficients is complete, follow corporate policy to secure the values. Delete the coefficient file if necessary, and return any documents.
Copy the .DAM file from the secured laptop to the non-secured desktop where the .S40 file was created during the first part of the analysis.
On the non-secured desktop, set the Analysis Parameters Optional Running Phase to Continue with secured data and Browse for the .DAM file.
Run the DDAM analysis. The deflections and stresses is calculated as normal.

Advanced Solution Options

The Advanced tab of the Analysis Parameters dialog box can be used to customize the spectrum factors and directions. In the Advanced Settings and Controls section you can specify the scale factors for each direction and select the global direction for each spectrum direction.