SubseaDeep
Mechanical
Hi All,
I had some questions. In our company we provide subsea services and offshore oil & gas engineering. In this we use A-frames and Winches which are placed on vessels/ships/oil platform decks. But we do not place our A-frame and Winches directly on the deck or doubler pads. We use sub-frames (made from beams) between our equipment and the vessel deck. Please see attached file which will make it clear. The A-frame and Winch weigh around 25 and 40 tonnes respectively.
1. Suppose we are designing a Sub-frame (flat horizontal structure with beams only, no columns). Some experienced engineers in our company define/model the "tie-down points of the sub-frame" to the deck as spring connections. As pinned connections will give unrealistic large reactions in the analysis. So we define/model the nodes as springs. Is this correct?
2. The engineers start with modeling the springs with a stiffness of 50 K/in, and then increase it gradually step by step. Sometimes they stop at 100 K/in, or sometimes increase it more. My questions is when do we stop increasing the stiffness of the springs and confirm that a particular stiffness is correct, and the resultant reactions are correct?
3. We specify the same stiffness in all 3 directions. But in practical, the stiffness of the structure underneath is not same in all directions. How do we understand/work with this?
Any advice will be a great help. Please see attached file.
Thanks in advance.
SubseaDeep
I had some questions. In our company we provide subsea services and offshore oil & gas engineering. In this we use A-frames and Winches which are placed on vessels/ships/oil platform decks. But we do not place our A-frame and Winches directly on the deck or doubler pads. We use sub-frames (made from beams) between our equipment and the vessel deck. Please see attached file which will make it clear. The A-frame and Winch weigh around 25 and 40 tonnes respectively.
1. Suppose we are designing a Sub-frame (flat horizontal structure with beams only, no columns). Some experienced engineers in our company define/model the "tie-down points of the sub-frame" to the deck as spring connections. As pinned connections will give unrealistic large reactions in the analysis. So we define/model the nodes as springs. Is this correct?
2. The engineers start with modeling the springs with a stiffness of 50 K/in, and then increase it gradually step by step. Sometimes they stop at 100 K/in, or sometimes increase it more. My questions is when do we stop increasing the stiffness of the springs and confirm that a particular stiffness is correct, and the resultant reactions are correct?
3. We specify the same stiffness in all 3 directions. But in practical, the stiffness of the structure underneath is not same in all directions. How do we understand/work with this?
Any advice will be a great help. Please see attached file.
Thanks in advance.
SubseaDeep