A Solution to the Inherent List on Nimitz Class Aircraft Carriers

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In accordance with [6], panels of plating shall be proportioned so as not <strong>to</strong> exceed <strong>the</strong> breadth-thickness ratios indicated by: b = short dimension of <strong>the</strong> panel (inches) t = thickness of <strong>the</strong> plate (inches) _b ^ C C = coefficient that is a function of <strong>the</strong> plating material and <strong>the</strong> t ~ K • -V/H location of <strong>the</strong> plating on <strong>the</strong> ship K = coefficient that depends on <strong>the</strong> aspect ratio (AR) of <strong>the</strong> panel H = head of salt water (feet) The coefficients C and K are provided in Table I of Section 100, <strong>the</strong> General Requirements for Hull Structure, in [6]. There are a number of key assumptions that were made following <strong>the</strong>se design criteria for plate panels subjected <strong>to</strong> normal loads. The ship plating is divided up in<strong>to</strong> any number of panels, depending on <strong>the</strong> amount of stiffening that exists. The panel is considered <strong>to</strong> have clamped or fixed ends and is subject <strong>to</strong> cylindrical bending, a plate that is subject <strong>to</strong> bending about one axis only (as usually occurs for long plates). The cross- section of this panel is considered <strong>to</strong> be rectangular in shape with a depth equal <strong>to</strong> <strong>the</strong> plating thickness and a unit width. The K coefficient is important for relatively short panels. The C coefficient is actually derived from standard beam <strong>the</strong>ory for a fixed-fixed beam, by combining allowable stress, specific gravity of salt water, and this K coefficient. An example of a C coefficient derivation starting with beam <strong>the</strong>ory can be seen at <strong>the</strong> end of <strong>the</strong> 2"^* deck sponson shell plating structural calculations shown in Appendix E. Also important <strong>to</strong> consider in <strong>the</strong> structural calculations, particularly for <strong>the</strong> 2"'^ deck sponson shell plating, was <strong>the</strong> maximum shell plating pressure. According <strong>to</strong> CVN 76 specifications, <strong>the</strong> maximum pressure for sponson shell plating is 1000 psf. As a result, <strong>the</strong> limiting weight of Perma Ballast® for <strong>the</strong>se tanks had <strong>to</strong> be calculated based on not exceeding 36
this pressure. This resulted in a reduction of approximately 55 I<strong>to</strong>ns of ballast, for this particular case only. Similarly, <strong>the</strong> only structural analysis performed for <strong>the</strong> 4* deck void was on its deck plating. Once it was determined that deck stiffening would be required, <strong>the</strong> 4* deck tanks were taken out of consideration as a possible location for placing this ballast. Although adding a stiffener down <strong>the</strong> middle of <strong>the</strong> deck plating would alleviate any structural concerns, welding <strong>to</strong> <strong>the</strong> deck plating would have <strong>to</strong> be performed. With welding required on <strong>the</strong> bot<strong>to</strong>m deck plating, a watch would need <strong>to</strong> be stationed on <strong>the</strong> o<strong>the</strong>r side of <strong>the</strong> deck. The tanks below <strong>the</strong>se 4 deck tanks are foam filled and a fire watch cannot be stationed in <strong>the</strong>se tanks. Once a maximum pressure in head of water was calculated, <strong>the</strong> breadth-thickness ratio formula could be used again <strong>to</strong> determine <strong>the</strong> stiffener spacing or limiting short dimension of <strong>the</strong> panel. If <strong>the</strong> calculated maximum distance that <strong>the</strong> stiffeners can be located apart fell less than <strong>the</strong> actual stiffener spacing, <strong>the</strong>n no plastic deformation would occur and stiffening of <strong>the</strong> plating was not required. If stiffening was required, <strong>the</strong>n <strong>the</strong> panel thickness was usually divided in half <strong>to</strong> accommodate <strong>the</strong> calculated pressure. The final calculations involved verifying that <strong>the</strong> calculated maximum allowable stress was less than <strong>the</strong> design allowable stress for <strong>the</strong> particular type of steel, regardless of whe<strong>the</strong>r any modifications were made. The basic equation used <strong>to</strong> calculate <strong>the</strong> maximum stress governing <strong>the</strong> behavior of plating under lateral load, or plate bending, can be seen below. Using small deflection <strong>the</strong>ory, <strong>the</strong> value of <strong>the</strong> coefficient k depends on <strong>the</strong> boundary conditions. For simply supported edges, k=.75 and for clamped edges, k=.5. Simply supported and clamped structural cases are idealizations of structural member support illustrating zero stiffness and infinite stiffness, nei<strong>the</strong>r of which exists in any real-world structural system. On 37
Page 1 and 2: A Solution <strong
Page 3 and 4: A Solution <strong
Page 5 and 6: Table of Contents Abstract 3 Acknow
Page 7 and 8: 1.0 Introduction 1.1 Motivation Air
Page 9 and 10: class. Changes to
Page 11 and 12: classified into fo
Page 13 and 14: o Control the KG g
Page 15 and 16: the intact stabili
Page 17 and 18: for ships propulsion, respectively.
Page 19 and 20: combined with the
Page 21 and 22: 1.3.7 Ballast Addition 1.3.7.1 Wate
Page 23 and 24: 2% entrained air (by volume) in <st
Page 25 and 26: Tank name Tank volume Ballast type
Page 27 and 28: was successfully performed and <str
Page 29 and 30: of each tank's location was added,
Page 31 and 32: 2.3 Preliminary Decision-Making Cos
Page 33 and 34: All further costin
Page 35: 2.4 Structural Analysis One tank on
Page 39 and 40: 2.4.1 Structural Modifications 2.4.
Page 41 and 42: Main Deck Shell FR 165 - FR 180 Tra
Page 43 and 44: 2.4.1.3 Modifications to</s
Page 45 and 46: 3.1 Final POSSE Results The minimum
Page 47 and 48: Table 6: Final Cost, Weight Additio
Page 49 and 50: Corrosion coupons are placed in all
Page 51 and 52: 5.0 Recommendations 1. As can be se
Page 53 and 54: References [I] Design Data Sheet 07
Page 55 and 56: O CO ■*. CM d CVI d CVI d CO d CO
Page 57 and 58: 1
Page 59 and 60: ■ • s*; eo 1 CM ■
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Page 89 and 90:
structural Analysis for Compartment
Page 91 and 92:
Resulting Pressure on Sponson Plati
Page 93 and 94:
Calculations to De
Page 95 and 96:
Stress Calculations: k = coefficien
Page 97 and 98:
Page 99 and 100:
FR 165 - FR 180 Transverse Bulkhead
Page 101 and 102:
Design of Plating for Surface Ships
Page 103 and 104:
Page 105 and 106:
Main Deck Shell FR 165 - FR 180 Tra
Page 107 and 108:
Calculations to De
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
Calculations to De
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Calculations to De
Page 121 and 122:
Stress Calculations: Stiffening k =
Page 123 and 124:
Resulting Pressure on Shell Plating
Page 125 and 126:
Calculations to De
Page 127 and 128:
Stress Calculations for 227 I<stron
Page 129 and 130:
Resulting Pressure on Inner Longitu
Page 131 and 132:
Calculations to De
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Stress Calculations k = coefficient
Page 139 and 140:
Resulting Pressure on Transverse Bu
Page 141 and 142:
Calculations to De
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o ON H 00 ^ ^ o > o -o B u H r^ 00
Page 153 and 154:
MATERIAL WORK SHEET PERMA BALLAST®
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A Solution to the Inherent List on Nimitz Class Aircraft Carriers

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