TRANSPORTATION ANALYSIS OF STEEL JACKET SUBSTRUCTURE USING MOSES SOFTWARE
NORHAMIMI BINTI MOHD HANAFIAH
A report submitted in partial fulfillment of the requirements for the award of the degree of Bachelor of Civil Engineering
Faculty of Civil Engineering Universiti Teknologi Malaysia
MEI 2009
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ABSTRACT
For many years, offshore structure has been transported on flat topped of bargelaunched type or on its own buoyancy from fabrication yard to offshore installation site. The final year project emphasises on the transportation analysis of steel jacket substructure using MOSES software. The result of analysis will give a better insight in regard to the motion stability of the jacket and the transportation barge. The process of transporting the jacket by barge need to be evaluated thoroughly by the design engineer for the purpose of selecting the most economical transportation method. This can be seamlessly done by considering the acceleration, motions, forces and moments during the transportation. The barge selected for transportation procedure must be robust and can greatly withstand the structure total weight as well as the environmental forces experienced during voyage to installation site. The analysis is based on the actual data of a project in Malaysia which the jacket is to be transported to the Malaysia’s oilfield. MOSES, an acronym for Multi Operational Structural Engineering Simulator, is a simulation and modelling language with great capability of motion analysis. The software can be utilised to generate the result of motions, forces and moments of the jacket members placed on the selected barge due to wave, wind and current effects. The analysis procedure covers two barges which is the required standard dimension of barge and an alternative barge as a comparison. The selection of the alternative barge will be done using trial and error method as for optimization purpose. The selected barge will be deployed for the jacket transportation as the analysis result satisfies the required compatibility, limit state condition as well as safety aspects throughout the journey.
ABSTRAK
Selama beberapa tahun, struktur luar pantai telah diangkut di atas barj permukaan rata jenis peluncuran atau dengan apungannya sendiri dari tempat pembuatan ke tapak pemasangan luar pantai.
Projek tahun akhir ini merangkumi analisis
pengangkutan substruktur jaket besi menggunakan perisian MOSES. Hasil analisis ini akan memberikan pemahaman yang lebih baik berdasarkan kestabilan pergerakan jaket dan barj. Proses pengangkutan jaket menggunakan barj perlu dinilai dengan teliti oleh Jurutera Rekabentuk bagi tujuan memilih kaedah pengangkutan yang paling ekonomik. Ini boleh dijalankan secara tersusun dengan mempertimbangkan pecutan, gerakan, daya dan momen semasa proses pengangkutan.
Barj yang dipilih untuk prosedur analisis
pengakutan ini haruslah boleh menanggung berat keseluruhan struktur termasuklah daya persekitaran yang dihadapi semasa pelayaran ke tapak pemasangan. Analisis ini adalah berdasarkan data sebenar satu projek di Malaysia dimana jaket itu akan diangkut ke lapangan minyak di Malaysia. MOSES adalah akronim bagi Simulator Pelbagai Operasi Kejuruteraan Struktur dimana ia menggunakan bahasa simulasi dan permodelan dengan keupayaan yang tinggi untuk analisis gerakan.
Perisian ini boleh digunakan untuk
menghasilkan keputusan bagi pergerakan, daya dan momen yang dihasilkan oleh anggota jaket yang diletakkan di atas barj yang dipilih berdasarkan keadaan ombak, angin dan keadaan semasa. Prosedur analisis merangkumi dua barj yang mana satu daripadanya adalah mengikut dimensi standard barj manakala satu lagi sebagai barj alternatif bagi tujuan perbandingan. Pemilihan barj alternatif akan dilakukan dengan cara cuba jaya bagi tujuan pengoptimisan.
Barj yang dipilih akan digunakan untuk
pengangkutan jaket kerana keputusan analisis telah memenuhi keperluan kesesuaian, keadaan had limit dan termasuklah aspek keselamatan sepanjang perjalanan.
TABLE OF CONTENT
CHAPTER
1
TITLE
PAGE
DECLARATION
ii
DEDICATION
iii
ABSTRACT
iv
ABSTRAK
v
TABLE OF CONTENT
vi
LIST OF TABLES
xi
LIST OF FIGURES
xiii
LIST OF ABBREVIATIONS
xiv
LIST OF SYMBOLS
xv
LIST OF APPENDICES
xvi
INTRODUCTION
1.1
Introduction
1
1.2
Problem Statement
2
1.3
Objectives
3
1.4
Scope of Study
4
1.5
Significance of Study
5
2
LITERATURE REVIEW
2.1
Introduction
6
2.2
General Informartion
8
2.2.1
Sea State Criteria
8
2.2.2
MOSES Sign Convention, Coordinate System, Units 9
2.2.3 2.3
2.4
2.5
2.6
Sign Convention
9
Environmental Criteria
12
2.3.1
Basic Considerations
12
2.3.2
Risk Levels
12
2.3.3
Reduced Criteria
13
2.3.4
Practical Application
14
2.3.5
Long Transportation
15
2.3.6
Statistical Reservations
16
Motion Criteria
17
2.4.1
Empirical Approach
17
2.4.2
Analytical Methods
18
2.4.2.1 Design Storm
18
Motion Responses
19
2.5.1
Periods
19
2.5.2
Motions Response on Computer Programs
20
Strength Criteria
21
2.6.1
Loadings
21
2.6.2
Overhang
22
2.6.3
Fatigue
22
2.6.4
Seafastening
22
2.6.5
Cribbing
23
2.7
Stability
23
2.7.1
Intact Stability
23
2.7.1.1 Wind Overtuning
24
2.7.1.2 Wind Velocity
24
2.7.1.3 Angle of Downflooding
24
Damage Stability
25
2.7.2.1 Range of stability
25
2.7.2.2 Wind Overtuning
25
2.7.2.3 Wind Velocity
25
2.7.2
3
METHODOLOGY
3.1
Introduction
26
3.2
Barge Selection
27
3.3
Computer Modelling
28
3.3.1
Modifications
28
3.3.2
Boundary Condition
29
3.3.3
Design Criteria for Transportation
30
3.3.4
Other Consideration
31
3.4
Loads 3.4.1
3.5
3.6
31 Basic Load Cases
32
Transportation Analysis
33
3.5.1
Weight Grown Factors
33
3.5.2
Design Load Factors
34
3.5.3
Load Combinations
34
Hydrostatic and Stability Computations
36
3.6.1
Tow Condition
36
3.6.2
Stability Assessment
36
3.6.3
Intact Stability
37
3.6.4
Damage Stability
38
3.7
MOSES Output
40
3.7.1
Motion, force and Moment
40
3.7.2
Summary of Single Amplitude Motion
40
3.7.3
Summary of Single Amplitude Forces and Moments 40
4
3.7.4
Summary of Acceleration
40
3.7.5
Flow Chart of Work Procedures
41
RESULTS AND DISCUSSIONS
4.1
Introduction
42
4.2
Barge Selection Result
42
4.3
Barge Information
45
4.3.1
Standard Barge
45
4.3.2
Alternative Barge
46
4.4
4.5
4.6
4.7
Payloads Data
47
4.4.1
47
Substructure
Radii of Gyration and Windage Area for Substructure
48
4.5.1
Accordance to Standard Barge
48
4.5.2
Accordance to Alternative Barge
49
Hydrostatic and Stability Computations
50
4.6.1
Tow Condition
50
4.6.1.1 Substructure on Standard barge
50
4.6.1.2 Substructure on Alternative Barge
50
Tow Condition Summary 4.7.1
51
Tow Condition of Substructure on Standard Barge 51
4.7.2
Tow Condition of Substructure on Alternative Barge 52
4.8
Summary of Hydrostatic and Stability Analysis
53
4.8.1
Accordance to Standard Barge
53
4.8.1.1 Intact Stability Check
53
4.8.1.2 Damage Stability Check
54
Accordance to Alternative Barge
55
4.8.2.1 Intact Stability Check
55
4.8.2.2 Damage Stability Check
56
4.8.2
4.9
Motion Output
57
4.9.1
Motion, Force and Moment
57
4.9.2
Summary of Single Amplitude Motion
58
4.9.2.1 Accordance to Standard Barge
58
4.9.2.2 Accordance to Alternative Barge
59
4.9.3
4.9.4
4.10
5
Summary of Single Amplitude Forces and Moments 60 4.9.3.1 Accordance to Standard Barge
60
4.9.3.2 Accordance to Alternative Barge
61
Summary of Acceleration
62
4.9.4.1 Accordance to Standard Barge
62
4.9.4.2 Accordance to Alternative Barge
63
MOSES Output
64
4.10.1 Accordance to Standard Barge
64
4.10.2 Accordance to Alternative Barge
76
CONCLUSIONS
5.1
Introduction
88
5.2
Conclusion
89
5.3
Recommendation for Future Research
91
REFERENCES
92
APPENDICES
94
LIST OF TABLES
TABLE NO.
2.1
TITLE
PAGE
Tows from Peninsular Malaysia to Sabah waters for 1-year Return period 8
3.1
Towing Metocean Criteria
30
3.2
Transportation Analysis Basic Load Cases
32
3.3
Weight Growth Factors
33
3.4
LRFD Load Factors
34
3.5
Load combinations
35
4.1
Dimension and result of selected barges
43
4.2
Result of towing condition
44
4.3
Particulars of Standard barge
45
4.4
Particulars of Alternative barge
46
4.5
Ballast pattern of Standard barge
50
4.6
Ballast pattern of Alternative barge
51
4.7
Summary of single amplitude motion on Standard barge
58
4.8
Summary of single amplitude motion on Alternative barge
59
4.9
Summary of single amplitude forces and moments on Standard barge 60
4.10
Summary of single amplitude forces and moments on Alternative barge 61
4.11
Summary of acceleration on Standard barge
62
4.12
Summary of acceleration on Alternative barge
63
5.1
Dimension of selected barges
89
5.2
Result of ballast pattern of selected barges
90
LIST OF FIGURE
FIGURE NO.
2.1
TITLE
Barge Coordinate System
PAGE
11
LIST OF ABBREVIATIONS
MOSES
-
Multi Operational Structural Engineering Simulator
API-RP2A
-
American Petroleum Institute
ISSC
-
International Ship Structure Congress
SES
-
Standard Engineering Specifications
SACS
-
Structural Analysis Computer System
COG
-
Centre of Gravity
LIST OF SYMBOLS
+ve
-
Positive
-ve
-
Negative
%
-
Percent
’
-
Inch
TP
-
Peak Period
G
-
Gravity
°
-
Degree
-
Heel Angle
LIST OF APPENDICES
APPENDIX
TITLE
PAGE
A
User Interface before run the software (input)
94
B
User Interface after run the software (output)
96
C
AutoCAD Modelling
98
CHAPTER 1
INTRODUCTION
1.1
Introduction
Offshore structures used for oil and gas extraction have the common function of providing a safe, dry working environment for the equipment and personnel who operate the platform (Yahaya, 2008). The traditional offshore installation shown an utilises a welded steel, tubular framework jacket to support the topside facilities. The single jacket installation is typical of the rig found in deep water environment. An offshore structure installation usually consists of four project phases which is loadout, seafastening, offshore transportation and installation (Yahaya, 2008).
Offshore transportation phase will comprises the tow to the location offshore and the analysis to confirm the resistance of the structure and the barge toward the related load like acceleration, motions, forces and moments during the transportation as well as the ballast for positioning procedure. Transportation analysis will be done after the steel jacket placed on the barge and be start towing to the oilfield by considering the sea-state criteria and related environmental load (Chakabarti, 1994).
Tubular steel jackets are completely fabricated onshore prior to transportation to site by dumb barge. The smaller jackets may be lifted in place by a floating crane whilst the larger jackets may employ floatation devices to assist in their installation once launched from the barge (Mather, 2000). The floatation devices are sequentially flooded to enable the jacket to sink slowly into its final resting place. Once located on the seabed the jackets are normally secured by foundation piles.
Transportation analysis is one of an important phase to be done during analysis process as one step closer to installation process (Guy, Clifford, 1980). These analysis need to be undertaken to calculate acceleration, motions, forces and moments faced by the structure and the barge during transportation. All the values were used to determine whether the barge selected were able to retain the structure total lift weight during the transportation.
1.2
Problem Statement
To choose the right size of barge is very important depend on the size of the structure since there is a variety size of barge in the region. If the barge selected is too big the structure for sure is safe for the transportation but in is not sustain in term of its cost. The barge selected has to be sure can resist the structure total weight with the environmental force faced during the transportation.
In order to minimize the associated risk and secure safe transportation from the fabrication yard to the offshore site, it is important to plan the transportation operation
carefully by considering the aspect required by the procedure. There is also some guideline from API-RP2A that should be considered like previous experience along the tow route, seasonal weather system and also appropriate return period for determining design wind, wave and current condition, characteristic of the tow such as size, structure, sensitivity and cost.
With the ballast value required known to obtain the required degree of pitch, towing procedure will run smoothly. If the ballast analysis is not taken during analysis stage, the structure may be failed during positioning stage and the barge will have a risk of overturning.
1.3
Objectives
The objective of the transportation analysis is to demonstrate whether the structure can resist the forces induced by the motions of the combined structure and barge system without exceeding the allowable stresses. The analysis was carried out to achieve following specific objectives:
1. To select the most economical and sustainable barge to transport the jacket compared to required dimension of barge.
2. To calculate the ballast value based on tow condition. 3. To determine hydrostatic and stability value for towing condition.
4. To determine the acceleration, motions, forces and moments during transportation by considering environmental load.
1.4
Scope of Study
The scope of the research will be focus on the outcome of the analysis using marine software program MOSES. MOSES software will be used in designing and analysis process. MOSES, an acronym for Multi Operational Structural Engineering Simulator, is a simulation and modelling language. The analysis is based on the actual data of a project in Malaysia which the jacket is to be transported to the Malaysia’s oilfield. Motions, forces and moments are derived using ISSC spectrum using specification sea state of 6.20 m (20.34 ft) significant wave height and mean period of 12.20 sec. These represent the tow condition for Sabah/Sarawak summer tow. The result will be run on a selected barge and a barge with requirement size (SES 10.1). No seafastening will be considered in the computer model as a preparation for worst case scenario.
The motion forces and moments were generated using MOSES. These forces and moments, coupled with the corresponding motion accelerations. A full motion analysis of the barge was performed with results of maximum barge responses, payload o
o
o
forces and moments obtained for beam (90 ), quartering (135 ) and head (180 ) seas.
The analysis will be undertaken at ProEight Offshore Engineering Sdn. Bhd. with supervision by Design Engineers as a collaboration project with MMC Oil and Gas Engineering Sdn. Bhd. Guidelines for the transportation have been made with
referenced to Sarawak Shell Berhad Standard Engineering Specification on Transportation of Substructure and Platform Components and General Transport.
1.5
Significance of Study
The research will show a result of transportation analysis using MOSES software and the result is commonly used to make an analysis for offshore structure transportation and as a preliminary study for installation phase. The result will show the compatibility of the selected barge with the structure based on the acceleration, motions, forces and moments as the outcome of MOSES.
This research summarized analyses undertaken for the generation of motion accelerations and forces due to the transportation of steel jacket substructure. The structure is to be transported to the existing oilfield in Sarawak.
The selection of the transportation barges were based on the feasibility studies done earlier before running the transportation analysis. The resultant centre of rotation and relative centre of gravity, as well as the location of the substructure will be shown in a drawing that will be included in this research report.
