This document summarizes a student's dissertation using the MAESTRO finite element program to conduct a preliminary hull strength assessment of a double hull oil tanker based on the Common Structural Rules (CSR). The student created a finite element model of the tanker's midship section in MAESTRO and applied loading conditions according to the CSR. The model was assessed under two loading conditions (B8 and B11) to analyze the structural strength. The MAESTRO program helped streamline the modeling, loading application, and stress assessment stages of the preliminary CSR procedure.

1. Preliminary Hull Strength Assessment with MAESTRO Linear Finite Element
Modelling
By
Kang Jing ,Tay
A dissertation submitted in
Fulfilment of the partial requirements
for the degree of
Bachelor of Engineering in
Naval Architecture
School of Marine Science and Technology
Newcastle University
July 2016
Declaration
No part of the work presented in this thesis has been submitted in support of an application for another
degree or qualification of this or any other university or other institute of learning.

2. ABSTRACT
MAESTRO finite element program is used in an attempt
to conduct a preliminary FEM Common Structural Rules
hull strength assessment procedure for a double hull oil
tanker. MAESTRO is designed specifically for floating
structures, including ship structures. Rapid structural
modelling features takes advantage of uniformity in ship
structures. Ship based loading and loading management
features for multiple environmental and cargo loading
conditions. Comprehensive structural evaluation features
for stress and buckling assessment. A program tailored
for ship structures such as MAESTRO can potentially be
used for all stages of ship design and assessment
efficiently and effectively to achieve desired outcomes.
Utilisation of functions designed in MAESTRO in this
project has allowed substantial success in streamlining
and saving of effort and time in the CSR preliminary
assessment procedure. This project presents an example
of assessing the integrity of a working ship structure
design using the functions in MAESTRO to streamline
the lengthy and complicated preliminary procedure
recommended in the Common Structural Rules.
Keywords
FEM, Structure, IACS, Common Structural Rules,
MAESTRO
1. Introduction
The objective of classification of ships is to assess the
structural integrity of a ship. Classification has played an
integral role in the maritime industry where being in class
has become a ‘quality stamp’ for a ship’s structure,
showing that the structure is designed, constructed, and
is compliant with class rules. Today, close to all ships are
in class with a classification society.
Classification societies develops their own structural
rules and applies them to ships that are in class with them
or wants to be in class with them. A group of 12
classification societies have come together to form the
International Association of Classification Societies
(IACS). Together, these 12 classification societies cover
more than 90% of the world’s cargo tonnage.(IACS
2011) In an effort by IACS to harmonise the rules and
standards of ship classifications, the Common Structural
Rules (CSR) is produced. The CSR sets a basis for ship
assessment and is the product of the technical expertise
and experience of members of the IACS. (IACS 2016)
In assessing a ship, the classification society conducts a
range of surveys, ranging from visual to computational.
Accordance to Section 9/2.1 of the CSR for oil tankers, a
FE assessment is to be conducted to assess the structural
integrity of the hull structure. This assessment is done
accordance to the procedure laid out in the CSR and
verifies the hull structure against the required strength of
each components in the hull structure stated in the CSR.
(IACS 2010)
In this project, Finite Element program, MAESTRO, is
used to conduct the FEM assessment procedure in the
CSR to assess the integrity of a hull structure. This
project will provide some insight into utilising the
functions available in MAESTRO to streamline and
conduct the assessment procedure in the sections of
modelling, loading, constraining and stress assessment.
2. Modelling
2.1 Modelling
The design ship is a 183m Oil Product tanker. The
principal dimensions of the ship is shown in Table 1.
Table. 1 Principal Dimensions of design ship
Principal Dimensions
Length Overall (LOA) 183m
Length Between Perpendiculars (LBP) 174m
Breadth (Moulded) 32.2m
Depth (Moulded) 19.1m
Designed draft (Moulded) 11.0m
Scantling draft (Moulded) 13.0m
The model is created using MAESTRO Ship Design
program ver.11.2.0. The choice of MAESTRO is because
the program is specifically designed for floating
structures, including ship structures. The program can
potentially be used in all stages of ship design, with
functions of modelling, analysing and optimization.
MAESTRO’s modelling functions allows coarse mesh
finite element structures to be created rapidly, along with
fine meshing capabilities when needed. Analysis of
structures is by linear FEM, and this is sufficient
according to IACS Common Structural Rules for Oil
Tankers structural strength assessment procedure, which
this project will be based on. (MAESTRO) (MAESTRO
2015)
The finite element midship model created is of full
breadth and depth, and spans 3 identical cargo tanks
length, with the stools of the transverse corrugated
bulkheads at both ends modelled entirely, shown in
Figure 1.
Fig. 1 Starboard side of Full Breadth Tanker Model
The model is created with 3 or 4 nodes plate elements
and the stiffeners are created as beam elements using the
girder or stiffener functions. The mesh size follows the
longitudinal stiffening system and 3 panels between each
transverse web shown in Figure 2. To simplify the
modelling process, some structures, including stiffeners
and hopper have been adjusted slightly to match the
stiffener spacing and hence mesh sizes of other structures
as shown in Figure 3 and Figure 4.
The reduced thickness of all elements is calculated and
applied to all plating and stiffener elements according to
the formula:
𝑡 𝐹𝐸𝑀−𝑛𝑒𝑡50 = 𝑡 𝑔𝑟𝑠 − 0.5𝑡 𝑐𝑜𝑟𝑟

3. 2
Fig. 2 Mesh size according to stiffener spacing
Fig. 3 Displaced Stiffener to simplify model
Fig. 4 Adjusted Hopper to match Girders Mesh
Corrugated bulkheads and bulkhead stools are modelled
using shell and beam elements. The shell element mesh
follows the mesh size of the inner bottom and the inner
side longitudinal, the shape of the stool and corrugation,
and the stiffeners in the stools, are adjusted to match the
meshing as shown in Figure 5.
Fig. 5 Mesh Size and Geometrical Shape of Corrugation
and stool
Most openings in the model are not required to be
modelled according to the criteria stated in the CSR,
except the openings on the transverse web in the double
bottom and the top stool, and the web ring opening.
However, none of the openings are modelled as the
openings on the transverse webs exceeds the criteria only
slightly as shown in Table 2. For the web ring openings,
due to the number of stiffeners at the area, it is not
practical to model the web ring opening using coarse
mesh finite elements. The web ring opening can be
incorporated by use of the MAESTRO/Rhino to create
the mesh and importing the geometry into the model.
Table. 2 CSR criteria for openings
Criteria
Openings do not need to
be modelled
H0/h<0.35 and g0<1.2
Openings in double
bottom web
H0/h=0.37 and g0=1.07
Openings in top stool H0/h=0.38 and g0=1.27
With completion of the model, the model is checked for
element connectivity, for free edges and for aspect ratio
of less than 3. The model is also checked for accuracy of
geometrical shape by comparing the model’s second
moment of area (Izz) and location of vertical neutral axis
(ȳ) with the original structural drawing. The small
difference in the two second moment of area and location
of vertical neutral axis shown in Table 3 may be due to
the simplifications in the modelling process, but is within
acceptable range.
Table. 3 Comparison of model and drawing geometry
2.2 Loading conditions
Standard design load combinations listed in the CSR are
to be used in the structural analysis. These load
combinations are separated into Sea-going load cases,
and Harbour and tank testing load cases, where Sea-
going load cases consists of static and dynamic loading,
and Harbour load cases only consist of static loading. In
this study, the model will only be tested in 2 of the
Harbour and Tank testing load cases, B8 and B11, shown
in Figure 6.
Fig. 6 Loading Combinations
Model Calculated
Izz (mm4
) 1.85397 x 1014
1.79 x 1014
ȳ (mm) 8.25 x 103
8.35 x 103

4. 3
This two loading patterns will give sufficient insight into
the procedure of assessing structural strength of a tanker.
2.3 Application of loads
For Habour and Tank testing loading, only the static
loads are applied. These includes ship structural weight
distribution, weight of cargo and ballast, and static sea
pressure. The application of each loads is done according
to the CSR, but using the loading functions in
MAESTRO.
Ship structural weight distribution can be automatically
incorporated into the loading conditions in MAESTRO
as an option on the loading cases dialogue. Weight of
cargo and ballast can be represented with created volume
parts in the model and filling up the volume, stating the
percentage of tank filled and the density of cargo. This
automatically loads the model with the weight of the
cargo and applies the equivalent pressure on the tank
walls as shown in Figure 7 and 8.
Fig. 7 Tank wall pressure for loading pattern B8
Fig. 8 Tank wall pressure for loading pattern B11
Static sea pressure is applied using the immersion
function, by applying the relevant immersion depth for
each of the load cases, 1/3Tsc for B8 and Tsc for B11.
Applying immersion for the load cases automatically
applies static sea pressure on the model bottom and side
plating, shown in Figure 9 for loading pattern B11.
Fig. 9 Immersion pressure for loading pattern B11
Some modifications are done to achieve the load cases
criteria in Figure 6. For loading case B8, the cargo tank
is only filled up to 70% to lighten the model to 1/3Tsc,
while for loading case B11, the density of cargo is
increased to 1.35 x10-9
tonne/mm3
to achieve the Tsc
criteria.
2.4 Adjusting hull girder shear forces and
bending moments
After applying the static loadings, each of the loading
cases have to be adjusted to meet the Still Water Shear
Force (SWSF) and Bending Moment (SWBM) criteria
stated Figure 6. The target values of the SWSF and
SWBM are provided by the designer as the permissible
hull girder positive and negative SWSF and SWBM
limits for both seagoing and harbour operations. Since
the loading conditions used in this project are both
harbour cases, the permissible hull girder SWSF and
SWBM for harbour operations are used as the target
loadings.
In achieving the target SWSF and SWBM criteria, the
SWSF and SWBM of the 3 tank length model should
look approximately equivalent to Figure 10 for B8, and
Figure 11 for B11.
Fig. 10 Target SWSF and SWBM for B8
Fig. 11 Target SWSF and SWBM for B11
It should be noted that the sign convention used for SF
and BM in MAESTRO is the opposite of those used in
the CSR, hence the values of the SWSF and SWBM are
all with a factor of -1.

5. 4
2.4.1 Adjusting Shear Forces (SWSF)
In B8, from Figure 6, the target SWSF is 100% of the
maximum permissible sagging SF and for B11 100% of
the maximum permissible hogging SF, both referred as
Qtarg. The procedure stated in the CSR is modified
slightly to utilise the loading functions in MAESTRO.
The modified procedure is as follows:
1. Required adjustments are calculated using the
SWSF values obtained from the static loaded
model,
∆𝑄 𝑎𝑓𝑡 = −𝑄𝑡𝑎𝑟𝑔 − 𝑄 𝑎𝑓𝑡
∆𝑄 𝑓𝑤𝑑 = 𝑄𝑡𝑎𝑟𝑔 − 𝑄 𝑓𝑤𝑑
2. Total adjusting shear force for each of the pair
of cargo tanks along the longitudinal axis is
calculated by modifying the formula in the
CSR,
𝑊1 =
∆𝑄 𝑎𝑓𝑡(2𝑙 − 𝑙2 − 𝑙3) + ∆𝑄 𝑓𝑤𝑑(𝑙2 + 𝑙3)
2𝑙 − 𝑙1 − 2𝑙2 − 𝑙3
𝑊2 = 𝑊1 + 𝑊3 = ∆𝑄 𝑎𝑓𝑡 − ∆𝑄 𝑓𝑤𝑑
𝑊3
=
−∆𝑄 𝑓𝑤𝑑(2𝑙 − 𝑙1 − 𝑙2) − ∆𝑄 𝑎𝑓𝑡(𝑙1 + 𝑙2)
2𝑙 − 𝑙1 − 2𝑙2 − 𝑙3
3. Shear force distribution factors are calculated
using the formula stated in the CSR Table B.2.8,
shown in Figure 12.
Fig. 12 Shear Force Distribution Factors
4. The amount of adjusting load to be applied to
each structural part of the transverse section is
then calculated according to Figure 12 and
Table 4.
Fig. 13 Structural members under consideration
Table. 4 Distribution of adjusting load
Structural Member Applied Load Fs
Side Shell 𝑓. 𝑊𝑛
Longitudinal bulkhead
including bottom girder
beneath
𝑓. 𝑊𝑛
Inner hull longitudinal
bulkhead (vertical part)
𝑓. 𝑊𝑛 .
𝐴𝑙ℎ−𝑛𝑒𝑡50
𝐴2−𝑛𝑒𝑡50
Hopper plate 𝑓. 𝑊𝑛 .
𝐴 𝐻𝑃−𝑛𝑒𝑡50
𝐴2−𝑛𝑒𝑡50
Upper slope plating of
inner hull
𝑓. 𝑊𝑛 .
𝐴 𝑈𝑠𝑝−𝑛𝑒𝑡50
𝐴2−𝑛𝑒𝑡50
Outboard Girder 𝑓. 𝑊𝑛 .
𝐴 𝑂𝑔−𝑛𝑒𝑡50
𝐴2−𝑛𝑒𝑡50
5. A plate group is created for each structural part,
and the respective adjusting load is applied to
each of the corresponding groups.
If a load is applied to a group, MAESTRO distributes the
load evenly throughout all the nodes in the group. Hence,
using this function, there is no need to calculate the
amount of load to be applied to each of the nodes as in
the original CSR procedure. This modified procedure can
save much effort and time in both calculations and
loading of the model, while achieving the same objective.
The adjusted SWSF for both B8 and B11 loading
conditions is shown in Figure 14 and Figure 15
respectively, attaining the required Qtarg of 64MN at both
bulkheads fore and aft of the middle tank.
Fig. 14 B8 Loading Pattern SWSF
Fig. 15 B11 Loading Pattern SWSF
-80
-60
-40
-20
0
20
40
60
80
0 20 40 60
ShearForce(MN)
Length (m)
B8 Shear Force (Sagging)
Adjusted Static
-80
-60
-40
-20
0
20
40
60
80
0 20 40 60
ShearForce(MN)
Length (m)
B11 Shear Force (Hogging)
Static Adjusted

6. 5
2.4.2 Adjusting Bending moments
(SWBM)
In both B8 and B11 load cases, the still water bending
moment required is 100% of the maximum sagging and
minimum hogging permissible bending moment
respectively.
Similar to adjusting SWSF, the CSR procedure is
modified to utilise the loading functions in MAESTRO.
The required SWBM adjustments are calculated from the
following equation in the CSR:
𝑀𝑣−𝑒𝑛𝑑 = 𝑀𝑣−𝑡𝑎𝑟𝑔 − 𝑀𝑣−𝑝𝑒𝑎𝑘
The additional vertical bending moment is then
distributed evenly on both ends of the model using the
end moment loading function. This works well for
loading B8, however the bending moment still fall short
of target for loading B11, hence, the vertical bending
moment for loading B11 is increased from
5.503E+11Nmm to 7.030E+11Nmm per end of model to
achieve the target loading.
Since both loading cases are for Harbour and Tank
testing loading conditions, there is no need for horizontal
bending moments, hence the procedures for adjustments
of horizontal bending moments are not applicable to this
project. The adjustment of the SWBM are shown in
Figure 16 for B8 to the required -169MNm and Figure 17
for B11 to the required 164MNm.
Fig. 16 B8 Bending Moment Diagram
Fig. 17 B11 Bending Moment Diagram
2.5 Boundary conditions
2.5.1 Method of constrains
In defining boundary conditions of the model, ground
spring elements and rigid spline elements are used.
Ground spring elements are springs with one end
constrained in all 6 degrees of freedom, as defined in the
CSR. The global co-ordinate system used in this project
is accordance to the system used in MAESTRO, with y
axis upwards, and z axis towards the port side.
Ground spring elements with spring stiffness in the
global z degree of freedom is applied to nodes along the
deck, inner bottom and bottom shell.
Ground spring elements with spring stiffness in the
global y degree of freedom is applied to nodes along the
vertical parts of the side shells, inner hull longitudinal
bulkheads and oil-tight longitudinal bulkheads.
Each of the fixed ends of the ground springs are then
connected, using a rigid spline element, to an
independent point which is as close to the neutral axis as
possible. The independent point at the aft end is then
constrained in the x degree of freedom, with the
independent point at the fore end free to translate in all
directions.
The locations and directions of the boundary spring
elements and the independent point are shown in Figure
18. Figure 19 shows the constrained model.
Fig. 18 Boundary conditions and independent point
Fig. 19 Constrained Model
2.5.2 Spring Stiffness
Each of the spring stiffness, c, of the ground spring
elements are calculated using the formula provided in the
CSR,
𝑐 = (
𝐸
1 + 𝑣
)
𝐴 𝑠−𝑛𝑒𝑡50
𝑙 𝑡𝑘 𝑛
= 0.77
𝐴 𝑠−𝑛𝑒𝑡50 𝐸
𝑙 𝑡𝑘 𝑛
𝑁/𝑚𝑚
The calculated spring stiffness are shown in Table 5.
-200
-150
-100
-50
0
0 20 40 60
BendingMoment(MNm)
Length (m)
B8 BendingMoment
Adjusted static
-50
0
50
100
150
200
0 20 40 60
BendingMoment(MNm)
Length (m)
B11 BendingMoment
Static Adjusted

7. 6
Fig. 20 Vertical Springs structural members
Fig. 21 Horizontal Springs structural members
Table. 5 Boundary Spring stiffness
Spring Stiffness
Spring Stiffness Units Directio
n
Cside shell 34868.73 N/mm +Y
Cinner longitudinal 28733.31 N/mm +Y
Ccenter 55720.66 N/mm +Y
Cdeck 57472.97 N/mm +Z
Cinner bottom 68264.51 N/mm +Z
Cdouble bottom 85133.21 N/mm +Z
It should be noted, as stated in the CSR, that the
thickness of the corrugated bulkheads used for the
calculation of the required spring stiffness is calculated
according to Section 4/2.6.4 of the CSR.
3. Results Evaluation
Stress assessment on the FE model is done by comparing
the von Mises stress, σvm, against the permissible values
calculated according to Table 9.2.1 of the CSR, shown in
Figure 22.
Fig. 22 Stress assessment criteria
Since the model has tens of thousands of elements, it is
not practical to manage the stress values using a text
processor, hence the highest stress value present in the
model is obtained visually using the coloured stress
representation in MAESTRO, shown in Figure 23.
As the corrugated bulkheads are not modelled with its
exact geometrical shape, the axial stress in the flange of
the corrugation is corrected according the formula given
in the CSR, where the constants for the model are
inserted into the formula, the formula becomes
𝜎𝑓𝑙−𝑎𝑐𝑡 = 1.255 × 𝜎𝑓𝑙−𝐹𝐸𝑀
Fig. 23 Von Mises Stress of a model section
As shown in Table 6, a comparison of permissible stress
and the highest von Mises stress obtained visually from
the model shows that the model is within the
permissible criteria for both B8 and B11 loading
conditions except for the transverse bulkhead in the B11
loading condition. However, this is due to a stress
concentration, which is also present in multiple places
in the model, most of them around or on the transverse
corrugated bulkheads, highly likely due to sharp edges.
The stress concentration at the connection of the
transverse and longitudinal corrugated bulkhead is
shown in Figure 24.
Table. 6 Comparison of permissible stress and model
von Mises Stress for B8 and B11
Stress Evaluation B8 B11
Item
Permissible
stress
N/mm
Final
stress
N/mm
Pass/
Fail
Final
stress
N/mm
Pass/
Fail
Deck 169.2 50.78 Pass 112.93 Pass
Sides 169.2 98.60 Pass 112.04 Pass
Inner side 169.2 110 Pass 128.96 Pass
Hopper 226.8 95 Pass 55.76 Pass
Bilge 169.2 57.53 Pass 51.21 Pass
CL
bulkhead
252 158.38 Pass 237.19 Pass
Girders 226.8 112 Pass 196 Pass
Webs 169.2 107.68 Pass 57.38 Pass
Inner
bottom
201.6 44.13 Pass 50.18 Pass
Bottom 150.4 56.64 Pass 51.76 Pass
Transverse
bulkhead
201.6 106.46 Pass 264.8 Fail

8. 7
Fig. 24 Stress Concentration at intersection of
transverse and longitudinal corrugated bulkhead
These stress concentrations could easily be addressed
with the use of brackets to remove the edges of the
geometry. These brackets are present in the design
drawing but are not included in this coarse mesh model.
4. Conclusion
This project has successfully implemented the FEM
procedure in the CSR with MAESTRO ship design
program. Utilising the functions in MAESTRO, some of
the procedures stated in the CSR are streamlined as
shown in the relevant sections. Streamlining has not
affected the other sections of the procedure with the other
non-streamlined procedures still achieving the desired
outcome. Hence, this project has shown that MAESTRO
is not only capable of assessing a hull structure according
to the CSR, use of the MAESTRO functions in the
correct way can also save much time and effort in the
FEM assessment.
According to this preliminary assessment, this hull
structural design is proven to be viable in the portion of
stress assessment. However as mentioned in the results
evaluation section, there are some noticeable stress
concentrations due to the edges in the coarse mesh
model. This could be due to imperfections in the
modelling process or the absence of the designed
brackets which will have to be assessed with the local
fine mesh assessments. Unfortunately, MAESTRO has
limited capability of modelling complex shaped brackets
and structures in the coarse mesh model, hence the next
part of the hull structure assessment, local fine mesh
structural strength analysis, may hold more importance
than usual in the overall assessment procedure.
5. Further Work
This project has only completed the first of many steps
in the numerical assessment procedure of a hull structure.
Since MAESTRO has shown to have limited capability
in modelling complex shapes in the coarse mesh model,
leading firstly to the omission of the web ring opening
and then other structural components, incorporation of
finer meshes in the model should be explored and if
possible included into the model. The remaining steps of
the CSR assessment procedure should be conducted and
will be important in assessing the integrity of the hull
structure in other areas of failure including buckling and
fatigue failure.
Acknowledgements
Special thanks to Professor Dow for guidance, to Bing
Bing Ke for her patience in teaching me to read the ship
design drawing, and to Justin from MAESTRO support
team for his patience in answering my many questions
about MAESTRO.
Reference
IACS (2010). Common Structural Rules for Oil Tankers. http://www.iacs.org.uk/, IACS.
IACS (2011). Classification Societies - What, Why and How? www.iacs.org.uk.
IACS (2016). "IACS Common Structural Rules Homepage." Retrieved 2 May, 2016.
MAESTRO, M. "Capabilities Overview." Retrieved 26 April, 2016.
MAESTRO, M. (2015). "MAESTRO Manual."

9. 8
Definitions of terms used in equations
Section 2.1
𝑡 𝑔𝑟𝑠 Proposed new building gross thickness excluding owner’s extras
𝑡 𝑐𝑜𝑟𝑟 Corrosion thickness addition
Section 2.4.1
ΔQaft Required adjustment in shear force at the aft bulkhead of middle tank
ΔQfwd Required adjustment in shear force at the fwd bulkhead of middle tank
Qaft Shear force due to static loads at the aft bulkhead of middle tank
Qfwd Shear force due to static loads at the fwd bulkhead of middle tank
W1 Total evenly distributed vertical load applied to the aft tank of the model
W2 Total evenly distributed vertical load applied to the middle tank of the model
W3 Total evenly distributed vertical load applied to the fore tank of the model
l Total length of model
l1 Total length of aft cargo tank
l2 Total length of middle cargo tank
l3 Total length of fore cargo tank
Fs Total load applied to individual structural member under consideration
n 1, 2, or 3
f Shear force distribution factor of structural part
Alh-net50 Plate sectional area of individual inner hull longitudinal bulkhead
AHp-net50 Plate sectional area of individual hopper plate
AUsp-net50 Plate sectional area of individual upper slope plate of inner hull
AOg-net50 Plate sectional area of individual outboard girder
A2-net50 Plate sectional area of individual inner hull longitudinal bulkhead including hopper slope plate, double bottom
side girder in way and upper slope plating
Section 2.4.2
Mv-end additional vertical bending moment to be applied at both ends of the model
Mv-targ Required Hogging or Sagging bending moment
Mv-peak Maximum or minimum Bending moment within the length of the middle tank due to static loads
Section 2.5.2
As-net50 Shearing area of the individual structural member under consideration, in mm2
, shown in Figure 20 and Figure 21
E Modulus of Elasticity, in N/mm2
v Poisson ratio of material, 0.3 for this project
ltk Length of the middle cargo tank
n number of nodal points to which the spring elements are applied to the structural member under consideration
Section 3
σfl-act Corrected Axial Stress
σfl-FEM Axial Stress obtained from FEM