**3.3 Determination of material properties**

In determining the material properties, this depends on the material used for the ship structure. The material in question is one that has a modulus of elasticity (Young's modulus), a poisson ratio and a certain density.

### **3.4 Finite element making (mesh density)**

Determining the size of the element (mesh density) is very important. If the size of the element (mesh) is too coarse, the result may deviate considerably and may even result in an error. However, if the mesh is too fine then we will only waste computer resources, the time required to run is very long, or even the model is too large to be completed on the computer used [11].

The FPB 42 m fast boat model with a length of 42 m that has been made, has 155,988 degrees of freedom so it is hoped that the model can represent it well. The elements are tried to be the same as the example model above, namely all plate elements are expected to have a square shape, but because of the difficulties faced if all of them have to be squared, then there are elements that are made triangles or rectangles with a ratio of length to maximum width of 2.

The size of the largest element that can be created is limited by the following:


In the current model, it only consists of line and area elements, so only free mesh and mapped mesh are used. For the meshing area, this time, we use more meshing (free mesh) with the element length determined or the line division determined in advance. This is easier and you get the desired results. Meanwhile, for elements with identical shapes, meshing is performed using the mapped mesh, which is one of the elements that has been meshed for the first time as a reference using the free mesh. Then the next element can be meshed using a mapped mesh, with the size of the formed element the

#### *Finite Element Method for Ship Composite-Based on Aluminum DOI: http://dx.doi.org/10.5772/intechopen.94973*

result will be the same as the element that was first meshed. However, not all areas can easily be elemented in this way. This is due to the size of the area that is too small and the various geometric shapes of the model. Thus, in making elements it is not possible to create elements with the size planned above. For that, a smaller element size is determined. If this still cannot be done, the area is redefined, that is, it is made the same area with a smaller line division but still close to the desired element shape.

To make a beam element, a line is needed, because the beam is a LINE element. The way to make it is almost the same as the meshing process on the plate elements, namely by first determining the element attributes, then meshing it using free mesh. It's just that in this meshing beam there is no need to divide the lines or determine the length of the elements, because this has been done during the meshing area. In addition, the meshing beam also has an orientation keypoint. Namely the keypoint that is used to determine the direction of the mesh section. Each line has a normal direction so that in making beam elements, the beam direction (node I and J) is meshed following the normal direction of the line. If after the mesh the beam direction is not as desired, the line must be reversed (reverse normal line). Because on a ship the entire profile faces the midship, whether the profile is on the base, deck, ivory or reinforcement, the orientation of the keypoint placement is attempted to be able to direct the section of the mesh beam (**Figure 3**) to face the midship.

For mass elements only a keypoint is needed. And for the manufacturing process, namely by selecting the keypoint closest to the location of the mass or center of gravity of the mass being modeled, then the keypoint is used as a mass element. The masses being modeled include the main motor, auxiliary motor, gear box, and other equipment which has a relatively large mass.

After the meshing process is complete, it is necessary to check the shell element whether the elements that have been made are in good condition or not. The maximum warping factor for the Shell 93 warning element is "none", the element may curve outward from the plane of the plate. From all existing tests it has been shown that all elements are in good condition, there are no warning elements or error elements. So that the model made, namely the EN AC-4310 (AlSi10Mg (b)) + SiC composite material ship, has represented the ship well, as shown in **Figure 4** is the image of the overall ship model.

The ability of a ship to float is based on Archimedes' law, the buoyancy force obtained is proportional to the weight of the water it displaces (hydrostatic support). Generally these ships are referred to as ships with hull displacement. The displacement weight is the volume weight of water displaced by the hull. So the weight of the volume of water displaced is the weight of the ship (Eq. 1) (Taggart, 1980):

$$
\Delta\_{\text{B}}(\text{Newton}) = \text{LxBxTxCBxgx} \tag{1}
$$

**Figure 3.** *Beam elements (beam and deck supports).*

**Figure 4.** *Draw the whole ship model.*

If it is used as mass displacement (ton) then it is divided by g, so that Eq. (2)

$$
\Delta\_{\mathbf{m}}(\text{ton}) = \text{LxBxTxCBx} \rho \tag{2}
$$

Information:

Δ<sup>B</sup> = weight of displasmen (Newton)

