Q:

Dummy Structure and Delete Joint options in SACS Seastate

 

R:

Let us walk through a simple model to understand how the dummy structure and delete joint options work in SACS.

The geometry is developed in such a way that the base elevation is 0. Corresponding elevations are shown in the below snap.

While defining the dummy element, SACS gives 2 options of joint selection.

1. Boundary joints: the boundary joints refer to the connection of dummy member with the main structural component. This will be designated as “KEEP” in the DUMMY command in datagen.

2. Dummy joints: And the dummy joints refer to the joints which form the dummy element. These joints will be designated as “DELETE” in the DUMMY command in datagen.

 

When the datagen is checked, the following is seen

As we see the modeling of Dummy structure is done now, please note that these elements do not contribute to the overall structural stiffnesses and only used for load generations. Seastate can calculate any loads applied on these structures and transfer them into the main structure. In the post graphical options, these dummy members are not seen as their purpose in the model is limited to load generation.

Let us apply a concentrated load on the edge of the dummy structure as shown below.

 

After the run, when the post view file is checked, the model looks like the following:

The dummy elements along with the dummy joints are no longer seen.

If the applied load is checked, it is found that the applied load is now transferred to the boundary joint, along with the corresponding moments due to eccentricity.