Trans RINA, Vol 161, Part A4, Intl J Maritime Eng, Oct-Dec 2019
Example 4: Perforated composite skew plates at different skew angles.
In the next example, a simply supported skew laminate (0/90/0) with a skew cut-out (0.2a × 0.2b) at the center is analysed considering thickness ratio h/a=0.1. An analysis is performed considering various skew angles (α=15°, 30°, 45°, 60° and 75°) as shown in Figure. 1b. The results are presented in Table 5. As expected, as the skew angle increases, frequency also increases since the mass of the plate decreases.
Example 5: Perforated composite skew plates with different cut-out sizes.
Cross-ply (0/90) skew laminate having simply supported (Figure. 1b) and fixed supported (Figure. 1c) along all the four edges with skew laminate (α=30°), thickness
ratio h/a=0.01 and different cut-out sizes at the plate center are analysed. The results are reported in Table 6. It is seen that as cut out size increases, frequency decreases due to decrease of the stiffness of the plate in case of simply supported but it is reversed in case of the fixed supported plate.
Example 6: Perforated composite skew plates with different aspect ratios.
Next, a four-layer anti-symmetric (0/90/0/90) skew laminate with two inclined edges fixed and other two straight edges are free having central skew cut out (0.2a × 0.2b) is investigated (Figure. 1d). The analysis is performed considering different aspect ratio (a/b=1.0, 1.5, 2.0, 2.5, 3.0). Results are presented in Table 7. It is seen that as the aspect ratio increases frequency decreases, since the mass of the plate increases.
Table 5. Frequencies = 2√ 2⁄ /ℎ of a simply supported, cross-ply (0/90/0) skew laminate having skew cut-out (0.2a × 0.2b) at the plate center (a=b, h/a=0.1)
Skew angle 15° 12.59 30° 15.50 45° 22.23 60° 23.97 75° 29.70 40.14 49.31 50.70 26.87 36.31 38.58 42.58 26.47 27.23 30.99 40.48 21.23 25.31 27.22 34.69 1 11.41 2 18.67
First five natural frequencies 3
22.88 4 25.57 5 27.94
A-368
©2019: The Royal Institution of Naval Architects
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