*3.2.2 3D* Shell

The ANSYS element library contains many types of shell elements. As with line elements, these types of shell elements can be used according to needs and analysis to be carried out. For modeling composite ship plate, Shell 93\_8node Structural Shell is used. Shell 93 is particularly good for modeling curved plates. This element has six degrees of freedom at each node: translation in the x, y and z directions and rotation in the x, y and z axes. The deformed form is quadratic in the plane of the element.

Shell 93 is used in ship plate modeling mainly because of its ability to model mostly curved ship plates. Also the deformed quadratic shape allows calculations in the middle of the element (mid-side node) to be more accurate. Element is formed by 8 nodes, 4 thicknesses and orthotropic material. Mid-side nodes on elements cannot be removed and thus these elements are only compatible with quadratic form elements. The orthotropic direction of the material corresponds to the direction of the element's coordinate system. All ship plates are modeled using shell 93, including flat parts such as on the superstructure or on the deck.

#### *3.2.3 Structural mass*

Mass modeling is carried out on the main engine, auxiliary engines, gear boxes, pumps, bollards, windlass, windlass foundations, hydraulic steering engines, anchors, anchor chains, and equipment with a large enough mass. These masses need to be modeled because they are part of the ship structure that must be included in the calculation. Mass modeling uses Mass 21, a point element that has six degrees of freedom and is a centered mass element.

#### *3.2.4 Real constant and section determination*

In determining the constants, the Real Constant set is used in accordance with the selection of elements used in modeling. The Real Constant set for Shell 93 is used to determine the plate thickness. Meanwhile, to determine the mass of each element, the Real Constant set for mass 21 is used. In addition to determining the constants, the beam and shell elements need to be defined sections.

In determining this section, the element size is determined in the cross section of the profile (beam) and plate (shell). For profiles, the thickness and size of the profiles are defined using the beam tool, while for plates the thickness is only defined using the real constant set for shell 93. The Real Constant set for shell 93 is used to determine the thickness of the plate. The Real Constant set for mass 21 is used to determine the mass of each element. **Figure 2** shows the beam section for the T profile.

**Figure 2.** *Beam section for T profile.*
