STRUCTURE DESIGN AND STRENGTH ASSESSMENT

LIQUEFIED NATURAL GAS (LNG) VESSEL

PREPARED BY :GROUP 9

24 APRIL 2014

EXECUTIVE SUMMARYThis report provides a structural design which consist of amidships scantling and strength assessment for Liquefied Natural Gas (LNG) vessel with the basic overall length (LOA) of 226 meter. Firstly, at the beginning of the project we determine the stiffening size, prepare the midship scantling drawing, prepare scantling list , and lastly calculating the midship section modulus and its strength. The procedure in the scantling design include the calculations of rule dimension, material selection, framing system selection, framing spacing calculations, midship structure drawing, scantling calculations and safety factor analysis. Other calculations including the overall ships dimension and drawing of midship section are attached in the appendices. All the design including plate thickness and section modulus are calculated based on formula provided by the Lloyds Register Rules and Regulations.

TABLE OF CONTENT

CHAPTERTITLE PAGETABLE OF CONTENT

1INTRODUCTION42AIMS OF PROJECT53STRUCTURES DESIGN PROCEDURES5 - 103.1Rule dimension3.2Material Selection Properties3.3Selection of Framing System3.4Plating Thickness3.5Stiffener Scantlings3.6Strength Assessment4MIDSHIP STRUCTURES DRAWING 115 RESULTS12 - 136DISCUSSION137CONCLUSION148REFERENCES149 ACKNOWLEDGEMENT1510APPENDIXES16

LIST OF TABLES

TABLE NO.TITLEPAGETable 3.1Calculation of Midship Section Modulus8Table 3.2Calculation of Actual Section Modulus10Table 3.3Calculation of Safety Factor 10Table 5.1Plate Thickness12Table 5.2Longitudinal Stiffening Members12Table 5.3 Strength Assessment12

1. INTRODUCTION

This project is carried out in order to prepared structural design which consist of amidships scantling and strength assessment for LNG vessel. The ship of interest is a LNG vessel with the basic principles of 226.5 m length, 38 m breadth and 21 m depth. The main purpose of writing this report is to provide clear and detail explanation on the several matters including scantling design procedure where consist of step required in assuring the project is in the schedules. Besides, this report also are prepared to illustrate the final results of this project where consists of actual sectional modulus and the required sectional modulus result by referring to Lloyds Register Rules and Regulations to complete the task. The sectional modulus is basically prepared based on midship scantling drawing.

In order to come out with perfect scantling design result, the calculation process is conducts based on equation taken from ship classification rules and regulation book. For this project, Lloyds Register book is chosen for reference purpose. This project are mainly covers several important part which are started from taking out the particular dimension based on general arrangement drawing, designing the midship section structure for the LNG vessel using longitudinal framing system and at the end prepared the final results of analysis in form of strength assessment referred to lines plan drawing and also midship section drawing.

This report is prepared to briefly explain and discuss with respect to the project finding which involved the calculation and results for midship section thickness and modulus for plating and stiffening member parts. Hence, the midship scantling drawing is prepared to give a graphical view of previous calculation results. Next, followed by discussion part where discuss the suitability of the final result for plating thickness, sectional modulus and finally for the safety factor. At the end of this report, conclusion is prepared to conclude the project.

2. AIM OF REPORTThe aims of the report are as follows:i. To discuss the design procedure in preparing midship scantling design.ii. To present the result of scantling list, moment and strength of 226.5 meter (LOA) of LNG vessel.iii. To determine safety factor of the ship.

3. STRUCTURE DESIGN PROCEDURES

3.1 Rule dimensionsAll dimensions are obtained from previous lines plan and general arrangement plan.Rule dimension calculated are as follows:- Length Rule96% of extreme length of summer load waterline.>> Breadth Rule>> 38.7 m Depth Rule>> 21 m

3.2 Material Selection Properties Material chosen was High Tensile steel Tensile Steel Factor, KL = 0.78 Specified minimum yield stress, O = 315 kg/mm2

3.3Selection of Framing SystemFor LNG vessel, the longitudinal framing was more suitable as it will give extra strength to the ship structure which spans about 226.5m of LOA. It is found that a transverse system only gives approximately a quarter of the strength of a longitudinally framed panel of the same size and thickness. Hence it decided that the ship designed will opting longitudinal framing systems.3.4Plating ThicknessThe proposed LNG vessels plating thickness was calculated using Lloyds Register Guidelines software. Plating that had been calculated are as follows which arranged from top to bottom:- Trunk deck plating Upper deck plating Inner upper deck plating Side plating Inner bulkhead plating Stringer plating Bottom plating Inner bottom plate Upper hopper plating Lower hopper plating Bilge platingSample calculation for plating Upper deck plating calculation (referring to Lloyds rule)

PARTICULAR

L217.95

S2.7

FD0.67

s1700

KL0.78

h40.91

s900

k0.75

tc2

f1.1

L1190

From the rule, it is found that the calculation from (a) produced the greatest result:-t = 0.001s1 (0.059L1 + 7) (FD/kL)t = 0.001(900) (0.059*190 + 7) sqrt(0.67/0.78)t = 11.8 mm note: to achieve production friendly, we taken the value for upper deck plating thickness as 12mmwhere :- t - Thickness of platingL - Length rule (96% of extreme length of summer load waterline)S - Spacing transverselyFD - FD is 0.67 for longitudinal stiffenerkL - tensile steel factor, 0.78 (High Tensile Steel) s1 - s1 = s (spacing at longitudinally)L1 - L1 = L but not taken greater than 190m

3.5 Stiffener ScantlingsSame as plating, the stiffener calculation to determine the section modulus was done by referring to Lloyds Register Guidelines. All stiffener in this project will be standardised using T section to save calculation, cost and to achieve production friendly status. Among the stiffener that has been calculated for this project are as follows:- Deck longitudinal Inner deck longitudinal Side longitudinal Bottom longitudinal Inner bottom longitudinal Bilge longitudinal Hoppers longitudinal Bulkhead longitudinal

Sample calculation for stiffening member is as follows:- Deck longitudinal calculation

PARTICULAR

L217.95

S2.7

FD0.67

s1700

KL0.78

h40.91

s900

k0.78

tc2

f1.1

hT12.7

le2.7

c10.59

F10.1475

p1.025

y, flat bars1.6

For (a) calculation, Z value is:-Z = 0.043 s k hT1 le2 F1Z = 0.043(900)(0.78)(2.7)(2.7)2 (0.1475)Z = 84.27 cm4

where :-Z - Longitudinal section modulusL - Length rule (96% of extreme length of summer load waterline)S - Spacing transverselyFD - FD is 0.67 for longitudinal stiffenerF1 - equals to 0.25c1 (0.25*0.524) = 0.1475c1 - equals to 60/(225 165FD) - 60/(225 165*0.67) = 0.524le - effective length of stiffening memberhT1 - equals to L1/70, (190/70) = 2.7k - k = kL , tensile steel factor, 0.78 (High Tensile Steel) s1 - s1 = s (spacing at longitudinally)L1 - L1 = L but not taken greater than 190m

1

3.6 Strength AssessmentExample of Calculation :Table 3.1 : Calculation of MidshipSection ModulusL x TZ x AZ x 1STL/2 x Sin(ANGLE )

NOSTRUCTUREDESCRIPTIONLTZA1ST MOMENT2ND MOMENTloTYPEANGLEh

(m)(mm)(m From Keel)(m.mm)(m2.mm)(m3.mm)(m3.mm)(deg)(m)

1BOTTOM PLATE16.3140228.2000HP--

2INNER BOTTOM PLATE13.6122.3163.2375.36863.330HP--

3TRUNK DECK PLATE181221.02164536.0095256.000HP--

4UPPER DECK PLATE2.41218.728.8538.5610071.070HP--

5INNER DECK PLATE14.1719.498.71914.7837146.730HP--

6SIDE PLATE17.81211.5213.62456.4028248.6067677.02VP--

7SIDE BULKHEAD PLATE10.21211.1122.41358.6415080.9012734.50VP

8DECK GIRDER1.61220.219.2387.847834.3749.15VP

9CENTER GIRDER2.3201.154652.9060.84243.34VP--

10SIDE GIRDER X 32.3141.1596.6111.09127.75170.34VP--

11LOWER HOPPER5.2124.1462.4258.251068.8270.32IP451.839

12UPPER HOPPER4.61217.8355.2984.0217541.7048.68IP451.627

13BILGE PLATE PART 10.9120.02410.80.260.010.00IP30.024

14BILGE PLATE PART 20.9120.21110.82.280.480.09IP210.161

15BILGE PLATE PART 30.9120.68910.87.445.130.30IP400.289

16BILGE PLATE PART 40.9121.29010.813.9317.970.55IP600.390

17BILGE PLATE PART 50.9122.14210.823.1349.540.70IP790.442

18DECK LONGI X 1620.97515.36322.186757.880Sec--

19INNER DECK LONGI X 1519.4008.4162.963161.420Sec--

20BOTTOM LONGI X 160.06832.482.200.150Sec--

21INNER BOTTOM LONGI X 132.326.5261.00140.290Sec--

22UPPER HOPPER LONGI X 517.73.969.031221.830Sec--

23LOWER HOPPER LONGI X 54.38.737.41160.860Sec--

24SIDE LONGI X 1410.710.92116.841250.230Sec--

25SIDE BULKHEAD LONGI X 1111.18.5895.241057.140Sec--

26BILGE LONGI 1 X 34.26.0925.58107.430Sec--

27BILGE LONGI 2 X 50.910.159.148.220Sec--

1535.4013922.46227238.7180995.08

A 1ST MOMENT 2ND MOMENT lo

From calculation above, value obtained: A = 1535.40 m.mm 1ST MOMENT = 13922.46 m2.mm 2ND MOMENT = 227238.71 m3.mm lo = 80995.08 m3.mm

Table 3.2 : Calculation of Actual Section ModulusFORMULAITEMVALUEUNITVALUEUNIT

a ATotal Area =1535.40m.mm

b 1ST MOMENTTotal 1st. Moment =13922.46m2.mm

cb / aDist of NA from Keel =9.07m

d 2ND MOMENTTotal 2nd. Moment =227238.71m3.mm2272387.06m2.cm2

e loTotal Io =80995.08m3.mm809950.82m2.cm2

fd + eTotal I about Keel =3082337.88m2.cm2

gf - (a*(c^2))Total I about NA =2956093.92m2.cm2

hMeasureHeight of Deck =13.6m

ih - c or c Max y (y deck or y keel) =4.53or 8.909.07m

whichever greater

jg / iSection Modulus (Half) =326004.58m.cm2

kj x 2Section Modulus (Full) =652009.15m.cm265.20m3

Calculation of Required Section Modulus (Lloyds Rules) :

Zmin = f1 kL C1 L2 B ( Cb + 0.7) X 10-6 Zmin = 1.0 (0.78)*(10.11)*(226.5)2 *(38.7)*(0.74 + 0.7) *10-6 Zmin = 22.54 m3Where :- F1 - 1.0B - breath of ship*C1 - for ship length of 90m < L < 300m, C1 = 10.75 [ (300 L) /100]1.5 - 10.75 [(300 226.5)/100]1.5 = 10.11L - length of ship*KL - tensile steel factor, 0.78 (High Tensile Steel)Cb - block coefficient of ship *Note: * taken from ship particular

Table 3.3 : Calculation of Safety Factor SM actual =65.20m3 Calculated based on actual section modulus

SM required =22.54m3 Calculated based on emphirical formula

SF = SM actual / SM required =2.89acceptable but overly design

4. MIDSHIP STRUCTURE DRAWING

TOLONG PASTE DARI AUTOCAD.. KALAU XNAK PADAM LA PAGE NIE.. HEHEHE

5. RESULT5.1 Data Specification

5.1.1 Plate Thickness

Table 5.1 : Plate ThicknessPlateThickness(mm)

Bottom Plate14

Inner Bottom Plate12

Trunk Deck Plate12

Upper Deck Plate12

Inner Deck Plate7

Side Plate12

Side Bulkhead Plate12

Deck Girder12

Center Girder20

Side Girder14

Lower Hopper Plate12

Upper Hopper Plate12

Bilge Plate12

5.1.2 Longitudinal Stiffening Members

Table 5.2 : Longitudinal Stiffening MembersStiffenerDimension (dw,bf,t) (mm)

Deck Longitudinal50,30,12

Inner Deck Longitudinal50,30,7

Bottom Longitudinal100,45,14

Inner Bottom Longitudinal110,60,12

Upper Hopper Longitudinal100,45,12

Lower Hopper Longitudinal45,20,12

Side Longitudinal45,20,12

Side Bulkhead Longitudinal45,20,12

Bilge Longitudinal100,45,12

5.2 Strength Assessment Table 5.3 Strength AssessmentSection Modulus Actual65.20 m3

Section Modulus Required22.54 m3

Safety Factor2.89

4.3 Scantling Drawing

The midship scantling drawing A3 size is attached with the report.

6. DISCUSSION

To complete this project, Lloyd's Register rules are used as a guideline. All the calculation is based on the formula provided by the rules. Also, the general structure is based on the General Arrangement and Lines Plan from the previous course, SMK 4532 Ship Design II. The scope of the project only involve around the midship area only.

In this project, there are many assumptions being made to complete the project. The first assumption made in this project is the spacing between the secondary supporting members, s, is 0.9 meter and the spacing between the primary members, S, is three times s which is 2.7 meter. The second assumption is that the local scantling deduction factor, FB and FD are 0.75and 0.67 for plate and longitudinal respectively. Besides that, some assumptions had to be made to solve the problem easily for example is the calculation of the sectional modulus, Z. Then, the shape of the longitudinal is a T shape is assumed to ease the calculation. The value obtained from thickness calculation of all plating and stiffening members are not really exact hence, to avoid any misconception during production process and to achieve production friendly status, we assumed all the plate and stiffening members thickness are to be the same. The values of bf and dw is changing as the iteration process goes to obtain an appropriate value of Z. The number had to be in between 0.5 until 1.0 so we must be creative enough to manipulate it. Another assumption is the tw = tf tp. This is another example of assumption that is made to make the calculation process to be less complicated since as an engineer good estimation is important in solving problem with lots of unknown.

Based on the result calculated, the value of the safety factor is 2.89 which are in range of 2 until 5.

7. CONCLUSION

The midship scantling of a Liquefied Natural Gas (LNG) vessel is done with a safety factor of 2.89. Although the value of safety factor is in range, the design can be improved by reducing the dimension of the major and minor structures. All the design including plate thickness and section modulus are calculated based on formula provided by the Lloyds Register Rules and Regulations. The drawing of the LNG vessel midship scantling is provided with this report in A3 size.

8. REFERENCE

i. YahyaSamian (2005). Structural Design and Strength Assessement, Lecture Note. UniversitiTeknologi Malaysia.ii. Lloyds Register (1997). Classification of Ships, Rules and Regulation

9. ACKNOWLEDGEMENT

The success and final outcomes of this project required a lot of guidance and assistance from many people and we extremely fortunate to have got this all along the completion of our project work. Whatever we have done is only due to such guidance and assistance and we would not forget to thank them. Our deepest thanks to lecturers, Tn Hj Yahya Samian and Dr. Yasser for giving us an opportunity to do this project and providing us all support and guidance which made us complete on time. We also extremely grateful to both of them for providing such a nice support though they had a busy schedule managing their work affairs.We also wish to thank to our family for their tremendous contributions and support both morally and financially towards the completion of this project. Last but not least, we also show our gratitude to our friends and who contributed in one way or other in the course of the project.

10. APPENDIXES