View
18
Download
0
Category
Preview:
Citation preview
STRUCTURAL ANALYSIS OF 11000 DWT SULPHUR BITUMEN TANKER
Yaşar GÜL, Levent KAYDIHAN, Osman BEDEL DELTA MARINE Engineering Co.
y.gul@deltamarine.com.tr, l.kaydihan@deltamarine.com.tr, o.bedel@deltamarine.com.tr
In this work, a sulphur and bitumen carrying tanker ship that has independent cargo tanks is in
scope of the analysis. Main structure, independent internal cargo tank structure and interaction
between the main structure and independent cargo tanks are investigated in perspective of stress
limits against hydrostatic and hydrodynamic worst-case scenario load cases.
INTRODUCTION
Sulphur or bitumen carrying tankers are special ships due to their complicated constructions
caused by integrated or independent cargo tanks. Choice of which cargo tank scheme to be used
in the ship depends on the temperature of the liquid to be carried. Sulphur tankers carry the
sulphur or bitumen in high temperatures because of the required viscosity value to storage and
control. The temperature value can be rise up to 250 C.
In case of integrated tanks scheme is chosen, there could be high stress values in tank structure
due to the difference between the outside sea and internal liquid temperature. For this case some
structural modifications can be applied to the model and stress concentration problems can be
solved. Generally, this configuration is used for the liquid temperature of up to 180 C.
In case of independent tank configuration is chosen, isolated independent internal cargo tanks are
placed into the ship structure. Therefore, thermal expansion induced stresses and damages over
the main structural components are avoided. The liquid temperature in isolated tanks could be up
to 250 C. The deficiency of this configuration is %20 to 30 decrement of the total carrying
capacity due to the space between internal cargo tank and main structure.
The Design of an 11000 DWT Molten Sulphur & Bitumen tanker is requested by French
Company called Fauquet Sacop Maritime. The ship is to be designed with double hull main
structure, one propeller and main engine features. The ship is to be intended to carry Sulphur &
Bitumen with the maximum temperature of 250 C and liquid density of 1.8 3mt . Therefore,
independent cargo tank configuration is to be used for this sulphur tanker.
The ship is designed by Delta Marine and built by Yardımcı Shipyard as Hull number 40. Main
dimensions are as given below and general view and arrangement of ship can be seen Fifures 1
and 2 below.
Main Dimensions Length Overall = 129.00 m
Length Between P.P. = 123.90 m
Breadth Moulded = 22.00 m
Depth Moulded = 12.50 m
Scanting Draught = 8.20 m
Deadweight = 11000 Dwt
Speed = 14 Knot
Figure 1 – General View of the Ship
Figure 2 – General Arrangement
The aim of this work is to investigate the structural endurance of midship cargo area construction
and internal cargo tanks of this sulphur tanker. Therefore, two finite element are developed to
analyse the main and internal tank structural components, transverse and longitudinal corrugated
bulkheads against the inertial internal pressure loading, maximum sea loading and test case
loading in perspective of stress criteria and results are presented.
MODELLING STAGE
The structural finite element models of following three-cargo area with a pump room and
internal cargo tank are developed for analyses. The extension of the model can be seen in Figure
3 below. Ansys 8.0 general purpose finite element software is used for all modelling, analysing
and post-processing operations.
Figure 3 – Extension of the Finite Element Model
Two finite element models are developed. The first model consists of only the three-cargo area
and pump room to analyse main structure and the half model is developed by taking into account
the symmetry feature along the longitudinal-vertical plane. The second model consists both of
the main cargo areas, pump room and a internal tank structure to analyse internal tank and
internal and main structure interaction. This model is fully developed with both port and
starboard sides.
The interaction between the internal tank and main structure is obtained by using the contact
feature of Ansys software.
The internal tank is restricted by contact elements as Ulepsi material in vertical direction, by the
block structure placed at the centre longitudinal double bottom girder and deck girder in lateral
direction and a block web frame in each cargo area restricts the internal tank in longitudinal
direction. Block structures can be seen in solid model figures.
Solid Modelling Stage
The solid models are prepared in Ansys software and can be seen in Figures 3 to 6 below. In
these Figures different colours indicate different thickness values and the detailed outputs of
thickness values can be seen in Appendix I. In the definition stage of the thickness values, the
deduction of corrosion additions are also taken into account according to BV Rules, Part B,
Chapter 4, Section 2, [3] Table 2.
Figure 4 – Solid Model of Main Structure
Figure 5 – Solid Model of Main Structure
Figure 6 – Solid Model of Internal Tank
2.2 Mesh Modelling Stage Ansys solid models are meshed by using the Ansys specific elements Shell63 and Contact52.
Shell63 element is used for all plating parts, web frames and for HP profile’s webs. Contact52
element is used as vertically contact material for interaction between the internal tank and main
structure. The properties of these finite elements are given below.
The first model, which consists of only the three-cargo area and pump room, is finely meshed
because of the response of the main structure in scope of the analysis. Half of the ship is
developed for this model by taking into account the symmetry feature along the longitudinal-
vertical plane. Details of the mesh density can be seen in Figures from 7 to 10.
In the second model, which consists of both main cargo areas, pump room and an internal tank
structure, only the internal tank is finely meshed because of the response of the internal tank
structure in scope of the analysis. This model is fully developed with both port and starboard
sides.
Figure 7 – Mesh Density of the Main Structure Finite Element Model
Figure 8 – Main Structure Finite Element Model
Figure 9 – Finite Element Model with Internal Tank
Figure 10 – Finite Element Model with Internal Tank ( Main Structure has coarse mesh )
Material Properties The material for the steel used in the ship is St 42 grade shipbuilding steel and its properties are
given below
• Elasticity modulus = 210000 N/mm2
• Poission ratio = 0.30
• Density = 7850 kg/m3
BOUNDARY & LOADING CONDITIONS
Boundary Conditions
For main structure finite element model;
The nodes at the aft and fore end cross sections are coupled to section’s centre nodes near to the
natural axis and simple supported boundary conditions ( ux, uy, uz, Rx, Rz are fixed for aft end
and uy and uz are fixed for fore end ) are applied. For the longitudinal-vertical centre plane,
symmetry boundary conditions ( y, Rx,Rz ) are applied.
For finite element model with internal tank;
The nodes at the aft and fore end cross sections are coupled to section’s centre nodes near to the
natural axis and simple supported boundary conditions are applied.
These centre nodes are also to be used to apply the global bending and wave induced moment
values. Boundary conditions can be seen in Figure 11 below.
Figure 11 – Boundary Conditions For the Main Structure Finite Element Model
Loading Conditions
It is aimed to get the worst loading condition for internal tank’s transverse and longitudinal
corrugated bulkhead structure, main structure web frames and girders. It is seen from the Table 1
which is obtained from pre-calculations, the load case b with the inertial internal pressure is the
worst loading case for interaction between the internal tank and main structure, for ulepsi
material, main structure web frames and internal tank bulkheads and girders. A+ loading case is
worst loading case for longitudinal girders. Lateral and longitudinal accelerations are also
important for the effects of internal tank over the main structure. Only the alternate loading
condition is allowed during the voyage. But the unsymmetrical loading can be occur when the
ship is in harbour.
Table 1 – Pressure values for load cases ( kN/m2 )
Therefore, Five different load cases are applied to the finite element models and the solutions
obtained. These are;
• Load Case 1: Load Case b
• Load Case 2: Load Case a+
• Load Case 3: Longitudinal Acceleration Case
• Load Case 4: Lateral Acceleration Case
• Load Case 5: Unsymmetrical Loading
Load Case 1 –Load Case b
Load case “b” according to the BV Rules is applied to the model as alternate loading condition
by assuming that it is worst case for main structure web frames and internal tank bulkheads and
girders. In order to obtain alternate loading condition cargo tanks 4 and 5 which are in the middle
cargo area are fully loaded according to the inertial pressure loading rules in Pt B, Ch 5, Sec 6
with the liquid density of 1.8 3mt , pressure set valve value of 0.17 bar, Xa = 0.983 2sm and
Za = 3.438 2sm .
Sea pressures are applied according to the Pt B, Ch 5, Sec 5 2.1.1 pressure for upright ship
conditions. Wave pressure load case “b” is taken into account for this analysis as indicated in Pt
B, Ch 5, Sec 4 2 Table 1.
Hull girder moments are applied to the model according to the BV Pt B, Ch 7, App 1, 4.3.1
Table 5 with the still water bending moment value of 250000 kNm and vertical wave bending
moment value of 465356 kNm for sagging condition. Total bending moment is obtained by
applying the difference between the total moment value and existing moment occurred by the
loading on finite element model. Final total moment distribution can be seen Figure 12 below.
Sea pressure load case and internal and sea pressure values can be seen in Figures 13 to 16
Load Case
A+ A - B
Internal Pressure at Internal Tank Bottom 178.7473 178.7473 254.9047
Sea Pressure at the Bottom 115.6486 49.25747 99.05084
0
100000
200000
300000
400000
500000
600000
0 10000 20000 30000 40000 50000 60000 70000 80000
Length ( mm )
Mo
me
nt
( k
Nm
)
Figure 12 – Final Moment Distribution Along the Finite Element Model
.Figure 13 – Wave Pressure Distribution in Load Case “b”
Figure 14 – Internal Inertial Pressure Loading Values ( N/m2 )
Figure 15 – Sea Pressure Loading Values ( N/m2 )
Figure 16 – Pressure Loading Values on Deck ( 28000 N/m2 )
Load Case 2 – Load Case a+
Load case “a” with positive h1 is applied to the model as alternate loading condition by
assuming that it is worst case for empty tanks and longitudinal girders. In order to obtain
alternate loading condition, cargo tanks 4 and 5 are fully loaded by using the liquid density of 1.8 3mt and pressure set valve value of 0.17 bar.
Sea pressures are applied according to the Pt B, Ch 5, Sec 5 2.1.1 pressure for upright ship
conditions. Wave pressure load case “a” is taken into account for this analysis as indicated in Pt
B, Ch 5, Sec 4 2 Table 1. Therefore, the worst loading case for empty tanks is obtained. Wave
Pressure Distribution in Load Case “a” can be seen in Figure 17 below.
Hull girder moments are applied to the model according to the BV Pt B, Ch 7, App 1, 4.3.1
Table 5 with the still water bending moment value of 350000 kNm and vertical wave bending
moment value of 428691 kNm for hogging condition. Total bending moment is obtained by
applying the difference between the total moment value and existing moment occurred by the
loading. Final total moment distribution can be seen Figure 18 below.
Figure 17 – Wave Pressure Distribution in Load Case “a”
Figure 18 – Final Moment Distribution Along the Finite Element Model
-700000
-600000
-500000
-400000
-300000
-200000
-100000
0
0 10000 20000 30000 40000 50000 60000 70000 80000
Length ( mm )
Mo
me
nt
( k
Nm
)
Sea pressure load case and internal and sea pressure values can be seen in Figures 19 to 21.
Figure 19 – Internal Pressure Loading Values ( N/m2 )
Figure 20 – Sea Pressure Loading Values ( N/m2 )
Figure 21 – Pressure Loading Values on Deck ( 28000 N/m2 )
Load Case 3: Longitudinal Acceleration Case In this loading case, a longitudinal force value, which caused by maximum longitudinal
acceleration value is applied to the longitudinal internal tank supports on the inner bottom by
distributing over the structure. The longitudinal acceleration is Xa = 0.983 2sm . Distributed
forces are 640 kN and 320 kN for 28 nodes at inner bottom supports and 2161 kN for 8 nodes at
the deck. Details can be seen in Figure 22 and 23 below.
No additional sea pressure, internal pressure and girder moments are applied because of only the
longitudinal internal tank support structure is being investigated.
Figure 22 – Forces at the Inner Bottom Supports
Figure 23 – Forces at the Deck Supports
Load Case 4: Lateral Acceleration Case In this loading case, a lateral force value, which caused by maximum transverse acceleration
value is applied to the lateral internal tank supports on inner bottom centre and deck centre by
distributing over the structure. The lateral acceleration is Ya = 3.423 2sm . Distributed forces are
257 kN for 27 nodes at the inner bottom. Details can be seen in Figure 24 below.
No additional sea pressure, internal pressure and hull girder moments are applied because of only
the lateral internal tank support structures are being investigated.
Figure 24 – Forces at the Inner Bottom Supports
Load Case 5: Unsymmetrical Loading
In this loading case, unsymmetrical loading at the cargo 4 and 5 is taken into account. Although
the unsymmetrical loading is not allowed during the voyage, it can be occur in the harbour
condition when it is being loaded. Cargo tank 4 port side and cargo tank 5 starboard side is fully
loaded by using the liquid density of 1.8 3mt and without the pressure set valve value. The
pressure distribution can be seen in Figure 25.
No additional sea pressure and hull girder moments are applied because of only the internal tank
structure is being investigated.
Figure 25 – Internal Pressure Loading Values ( N/m2 )
4. ANALYSES & RESULTS
4.1 Structural Analysis
The solution strategy of the finite element models for load cases b and a+ is as explained below;
• First stage: Solution of the second model with the internal tank ( Internal tank is fine
meshed and main structure coarse meshed ) by using the all internal and sea pressures and
moment which are explained in load cases chapter. Internal tanks structure investigation is
the objective this analysis.
• Second Stage: From the results of the first stage, obtain the vertical force values transmitted by Ulepsi materials from internal tank to main structure. Check these force
values whether they are under the Ulepsi material force limit of 320 kN. In case of any
exceeding force is obtained, by using a gap value between internal tank and Ulepsi material
solve the first stage again and obtain the optimised solution.
• Third stage: Solution of first finite element model, which consists only the finely meshed main structure. By applying the optimised force values transmitted by Ulepsi
material to the main structure and the sea pressures and moments as explained in load cases
chapter, obtain the results. Main structure investigation is the objective this analysis.
As can be seen from the load cases, the worst case loading at the internal tanks and therefore at
the Ulepsi material is obtained in Load Case b, which has maximum inertial internal pressures.
Therefore the optimisation in the second analyse stage is only obtained for Load case b and the
resulting gap values are used for the rest of the analyses. Results for the Load Case b and Load
Case a+ are presented below.
For the longitudinal and lateral acceleration loading cases the fine meshed finite element model
is used and results are presented.
In unsymmetrical loading case the second finite element model is used and the stress results at
the internal tank structure are presented.
Load Case 1
Resulting maximum stress values can be seen in Tables 1 to 5 below in MPa.
Table 1 – Stress Values at the Frames At the Middle of Tanks ( MPa )
Frame No Y Direction Stress Z Direction Stress YZ Shear Stress Von Mises
Min Max Min Max Min Max Max
44 -107 83.3 -103 48.7 -35 65 133
46 -102 38.9 -102 44.2 30.8 64 128
48 -98.2 62.3 -104 44 -26.3 55.7 121
50 -80.1 20.5 -70.9 32.5 -23.1 38.3 47.1
52 -64.9 2.2 -79.6 27.4 36.4 25.9 93.9
59 -60.3 36.7 -80.6 61.4 -36 49.3 93.9
61 -82.4 35.1 -134 60.3 -45.8 34.9 127
63 -133 74.3 -109 78.6 -57.9 36.3 125
65 -141 48.8 -80 72.5 -46.5 56.5 138
67 -180 108 -113 105 -79.6 64.9 198
69 -180 59.9 -77.1 79.3 -26.3 55.7 177
71 -209 130 -128 116 88.2 55.9 186
73 -210 71.6 -78.7 81.5 -50.2 79.3 176
75 -203 120 -123 115 -87 58 181
77 -210 71.6 -78.7 81.5 -56.3 57.7 160
79 -155 92.6 -97.2 101 -92.3 42.2 174
81 -122 50.5 -78.6 74.5 -49.8 39.7 133
83 -98.9 53.9 -83.8 71 -55.7 35.1 109
85 -82.4 36.7 -84.8 52.9 -41.8 28.8 86.3
87 -62.8 52.2 -79.2 85.3 -35.3 29.9 127
90 -36.6 10.7 -71.8 43.8 -35.9 13 71.9
91 -53.9 25.2 -64.1 21.8 -17.2 34.1 79.1
93 -85.6 79.1 -85.3 40.3 -32.3 54.4 121
95 -128 65.3 -93.2 49.2 -35.9 13 131
97 -183 143 -112 144 -59.5 81.7 201
99 -125 132 -132 73.8 -47.8 70 140
101 -178 196 -145 74.9 -73.4 79.5 191
103 -142 155 -146 77.3 -53.1 78.8 163
105 -185 209 -151 78.1 -77 81.7 206
107 -141 151 -145 75.1 -53.5 78.2 158
109 -171 183 -143 71.1 -72.6 78.4 185
Table 2 – Stress Values at the Longitudinal Girders ( MPa )
Table 3 – Stress Values at the Side Girders ( MPa )
Table 4 – Stress Values at the Main Deck Plating ( MPa )
Table 5 – Stress Values at the Hull Plating ( MPa )
Von-Mises Results at the Frame 44 ( N/m2 )
X Direction Stress Y Direction Stress XY shear stress Von Mises
Min Max Min Max Min Max Max
3400 mm -101.0 126.0 -140.0 74.3 -33.0 62.5 151.0
6200 mm -90.0 62.6 -153.0 95.2 -55.3 77.8 167.0
9700 mm -121.0 27.3 -41.5 52.6 -39.2 31.5 116.0
X Direction Stress Z Direction Stress Von Mises
Min Max Min Max Max
-156.0 81.9 -105.0 -117.0 187.0
X Direction Stress Y Direction Stress XY shear stress XZ shear stress Von Mises
Min Max Min Max Min Max Min Max Max
-180.0 180.0 -150.0 150.0 -85.1 77.8 -80.0 80.0 175.0
X Direction Stress Z Direction Stress XZ shear stress Von Mises
Min Max Min Max Min Max Max
Center Girder -213.0 213.0 -177.0 161.0 -101.0 91.5 200.0
Middle Girder -221.0 185.0 -118.0 149.0 -60.3 96.7 218.0
Inner Side -159.0 140.0 -185.0 108.0 -70.8 56.6 187.0
YZ Shear Results at the Frame 44
Von-Mises Results at the Center Girder
X Direction Stress Results at the Center Girder
XZ Shear Stress Results at the Center Girder
Von-Mises Stress Results at the Side Girder at 3400 mm from BL
Von-Mises Stress Results at the Hull
Internal Tank Von-Mises Results at the Frame 59
Internal Tank Von-Mises Results at the Frame 63
Load Case 2
Von Mises Stress Results at Middle Girder ( N/m2 )
XZ Shear Stress Results at Middle Girder ( N/m2 )
XZ Shear Stress Results at Side Girder ( N/m2 )
Load Case 3
Von Mises Stress Values ( N/m2 )
Von Mises Stress Values ( N/m2 )
Load Case 4
Von Mises Stress Values ( N/m2 )
Load Case 5
Internal Tank Longitudinal Bulkhead Von Mises Stress Results ( N/m2 )
Internal Tank Longitudinal Bulkhead Z direction Stress Results ( N/m2 )
Recommended