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FINITE ELEMENT MODELING AND JACKET LAUCH ANALYSIS USING A BARGE
Dinh Quang Cuong (1); Ngo Tuan Dung (2)
(1) ln.slilule of Conslruclion for Offshore Engineering (ICOFFSHORE) University of Civil Engineering - 55 Giai Phong Street - Hanoi (2) PclroVietnam Marine Shipyard J/S Company (PVshipyard),
No 65A2, 30/4 Street. Vung Tau; Email: dqcSjhn.vnn.vn
llicre jacket - barge syslcin models can be using Software system, which have currently on the world and in Vietnam to calculating. SlruCAD*3D.
SlabC AD: NFPTLW E Developed by Zenlech USA: MOSES (Miilti Operaliomil Structiiral Engineering Sinnilalion) and SA CS {Structural Analy.M.s Computer Sy.slem), Program Manual- Engineering Dynamic. Inc.
USA. but their use often by foreigners The most important problem is the .system simulation includes barge and jacket. This paper presents method numerically simulate ihe barge -jacket sy.slem for calculating the jacket launch process us'ing a barge by finite elements software, desire to affirm the ability of our engineers m the calculafion of the problems mentioned above
PHUONG PHAP Pl IAN TU' I lULJ HAN GIAI BAI TOAN VAN CHUYEN.
DANH CHIM Kl lOI Cl IAN DE CONG TRINH BIEN TU' SA LAN
Cd ihe dimg cdc chuang trinh phdn mem theo phuang phdp phdn ui huu ha, dd giai bdi lodn vdn chuyen. ddnh chim khdi chdn de fir xd lan. Cdc chuang trinh phdn mem ndi tren Id: SlruCAD*3D. SlrabCAD, SASC,... dd dugc trang bi lgi Viet Nam. tuy nhien hau nhu vdn chi do nguai nuac ngodi sic dung Vdn de quan trgng nhdt khi thuc hien bdi todn la su thdng nhdt ve mdt phuang phdp md phdng he thdng kef cdu khdi chdn de vd sd lan trong qud trinh van chuyen, ddnh chim. Bdo cdo ndy trinh bdy viec md phdng he thdng ket cdu theo phicang phdp phdn tic hicu hgn vd mdt sd ket qud ban ddu khi linh loan van chuyen. ddnh chim khdi chdn de cdng trinh bien bdng thep tic sd lan bdng chuang trinh phdn mem theo phuang phdp phdn tic hiru hgn, v&i mong mudn khdng dinh khd ndng ciia cdc ky ste ciia chiing ta cd the gidi cdc bdi todn neu tren ddy.
I. Introduction
The launch process Is broadly divided into four dynamically distinct phases:
Phase 1: Jacket sliding over the launch-way of the barge towards the rocker arm
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Phase 2: Jacket sliding on the rocker ami and rotating with respect to the rocker pin
Phase 3: Jacket tipping on one side of the barge i Phase 4: Separation of the jacket from Ihe barge ; During each phase, the equations of motion are developed and solved using a powcrliil 1
variable time step algorithm [IJ [2]. In the launch formulation, the barge-jacket inlcracliuii effect is incorporated and barge and jacket motions (including displaeemonl. velocity, mui acceleration) are computed for each time step, and the reaction forces and hydrodynamic forces are summarized. Bottom clearance for the jacket can also be checked during he launch process.
CuiTcnlly. the program assumes the lateral symmetry of the barge-jacket system, . nd thus only Phase 1, Phase 2. and Phase 4 are simulated by the program. Although the I'ILSI two phases of jacket motion are constrained lo Ihe vertical plane of Ihe barge, ilic hydrodynamic forces of the barge and jacket are considered in three dimensions.
2. Simulate the system
2.1, Coordinate Systems: There are five major coordinate systems:
2.1.I.The input coordinate system
The input coordinate system is Ihe coordinate system used to generate barge and jiiLket models and to enter launch data. In general, the input coordinate system is also known as j the structural global system when generating the jacket structural model. The x-axis oi' [he 1 input coordinate system should be parallel lo water surface and run along the center of ihc i barge toward the rocker arm, i.e., Ihe launch direction. It is recommended that the x-axis of the input coordinate system be chosen along the keel of the launch barge.
2.1.2. The barge body coordinate system
The barge body coordinate systems are fixed in the body with the origin located at ihe barge Center of Gravity (CO.), respectively (Figure 2). The barge body coordinate system j is also used to describe relative motions between jacket and barge during the first two phases of the launch process.
2.1.3. The jacket body coordinate system
The jacket body coordinate systems are fixed in the body with the origin located at the jacket Center of Gravity respectively (Figure 2).
2.1.4. The rocker arm coordinate system
The rocker arm coordinate system is fixed in the rocker arm, with its origin at the rocker pin (Figure 3). The rocker arm coordinate system is mainly used lo describe phase 2 motion and jacket-barge interaction forces.
2.1.5. The global (water surface) coordinate system
The global coordinate system, which is an inertial system fixed in space, that the origin is at the water surface directly above the barge center of gravity before the launch process begins. The global coordinate system has the same positive directions (X, Y, and Z) as the
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input cobrdinalc system (Figure 1). The barge and jacket motions and hydrodynamic forces are described in the global coordinate system.
Originally, all the x-axes are in the direction of the barge bow lo stern (i.e., in the launch direction), and all z-axes are vertical upward. The y-axis is determined by the righl-hand rule. By specifying the jacket leading points, trailing points, and trailing edge distance, the program automatically puts the jacket on the top of the launch runner based the the assumption thai the launch runner is parallel lo the barge keel.
2.2. Mathematical Formulation
The forces acting on the jackcl-barge system due to inertial, gravitational, friclional, and hydrostatic and hydrodynamic forces are evaluated, and the equations of motion in the fomi
MX + CX + KX = F(t) arc established. (1) M: Total mass matrix of the global coordinate system; C: Damping matrix;
K: Structural stiffness matrix; F(t): Force vector; X;X;X: Vector of accelerations, velocities and displacements.
Thus the equations of motion are non-linear and the time domain method of analysis is inevitable.
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Fisure 1 Coordinate Svstems and Initial Position ("Before Eauilibrium'l
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Figure 2 Initial Equilibrium Position of the Jacket and Barge System
Figure 3: Rocker Arm Coordinate Systems
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Figure 4 Jacket and Barge Models in tlie Input Coordinate Systems
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Figure 5 Reference Systems for Forces and Moments
2.3. Model Generation
Other typical input which includes Ihe barge C O . , simulation time and time step, jacket
initial position relative to launch runner, and rocker arm data. I Hie barge geometry is modeled by 'PANEL' cards. Each panel is a flat area described
by connecling lines of up to 8 points. All the joints in the panel must be in the same plane.
The order of the connecling nodes, whether clockwise or counter-clockwise, will determine the direction of the panel in accordance with the right hand rule. All the panels must have inward normal (i.e., the direction of the panel) to form a complete enclosed body, i.e., the hull of the launch barge.
The jacket model can be generated in any orientation in the input coordinate system (Figure 4). By defining the contacting surface of the jacket on the barge, the program will re-orient the jacket. The initial position of the jacket ean be determined by further specifying the initial trailing edge position and the height of rocker pin and rocker arm in Ihe input coordinate system. ^Since it is assumed that the barge-jacket system is laterally symmetric, it is not necessary to specify the relative position in the y-direction.
The contacting surface of the jacket on the barge is defined by specifying four typical points, i e., the leading starboard point, the leading port point, the trailing starboard point, and the trailing port point (Figure 1). These points are used to determine the coordinate system associated with the contacting surface, and the contacting length of jacket structure members on the launch runner.
Therefore, the trailing points should be the aft-most points of the jacket structure members that contact the barge launch runner.
2.4. Initial Equilibrium Position
The barge-jacket system is assumed to be in static equilibrium under the effect of gravity and hydrostatic forces when the launch simulation begins. T h e initial equilibrium position ean be obtained by the program based upon mass matrices, geometry, and the relative
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position (if ihc jacket and barge. However, s'ou can also choose lo cnler ihe milial dral't and irim o f i h e barge lo define ihe initial equilibrium position. In ihj.s case, ihe program will not check Ihe unbalanced forces and momenls. il an\ Therefore, uui need Lo make suic lo enlei the coireel initial equilibrium po.silion ihal con'csponds wilh other input dala.
2.5. Mass Properties
In addition lo slruclural gcomelr). the mass properties oi" ihe barge and the jacket arc also required for launch a n a h s i s . While the mass matrix of the jacket slrucluie is calculated inlernaily by ihc program, you must enter the mass matrix of ihe barge )ourself.
16. Winch Effect
A s\slcni of "winches'" may be used to slide ihe jacket along ihe launch runner louard ihc rocker arm. In ibis case, il is assumed ihal a constant winch speed is applied and the winch process is slow enough thai Us d>namic effect can be neglected. Winching proceeds until the jacket sliding \elocily is greater than the winch speed, 'fhis makes the jacket slide along the launch runner by its own weight.
2.7. Hydrodynamic Forces and Coefficients
While Moilson's equation is applied to calculate the hydrodynamic forces on ihe jacket, the h)'drod}naniic forces acting on the barge are described by added mass and damping cocrncienls, .You can choose lo enter these hydrodynamic coel'ficienls to override the dcfLiull values assigned by the program (Currently not available) Both added mass and damping cocfncients must be entered in a non-dimensional form.
Non-dimensional added mass coefficients are defined as follows'
• for surge, sway, and hca\-e: A,,/ Mass. i = 1. 2. 3
• For roll, pitch, and yaw: A,,/!,,. i ^ 4, 5, 6 Non-dimensional damping coefficients are defined as follows:
• For surge, sway, and hca\'e: B,, / Mass * (L/g) i = 1. 2, 3
• For roll, pitch, and yaw: B,,/ Mass * (L/g) '^^ * (1/L)". i = 4, 5, 6 Where 1,, is mass moment of inertial, L is the length of the barge, and g is the acceleration due lo gravity.
2.8. Load Generation
Each program-generated load case, which corresponds to each time point specified may include parts or ail of the following loads: Buoyancy, hydrodynamic forces, barge-jacket interaction forces, and inertial forces. Member buoyancy and hydrodynamic forces are generally transformed lo member distributed loads, except thai when only avery small number of Ihc members is submerged, and member concentrated loads are therefore used.
Fo generate barge-jacket interaction loads, the jacket structure joints lying on the launch runner thai is to receive the launch runner reaction is defined. Based upon these structural joints, the program will search for ihe structural members contacting the launch runner, and subsequently map the interaction forces onto these members. The program assumes that the rocker arm is rclalively rigid with respect to the jacket, and therefore interaction
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forces arc distributed uniformly along the slruclural members contacting the rocker arm and barge launch runner.
3. Program Output
There are tuo levels of output In Ihc Summary Output, Launch Parameters, Initial Position. Weight and Buoyancy. Phase-wise Motion Summary, and the 1 leighl to Water Surface reports arc included. The Detail Report includes Ihc Rigid Dody Position Resull 6 Degrees of Freedom (DOF). the Velocity of .lackcl and Barge (6 DOF). tho Acceleration of Jacket and Barge {6 DOF). Ihe Rocker Arm Forces, and Forces and Moments acting on Ihc Launch System.
You also have an option lo choose output lime steps for each phase, which can be different from Ihe simulation lime steps.
'fo help you better understand the Launch program, sample launch outputs are explained report-byreporl on Ihe following pages
3.1. Jacket Mass Matrix Report
The Jacket Mass Matrix and Jacket Radius of Gyration are reported in the Input Coordinate System with Ihe jacket at its original position, i.e., before Ihe jacket is reoriented and put on the launch way (Figruc 4).
3.2. Launch Parameters and Barge Data Report
The barge-jacket system is assumed to be in static equilibrium under the effect of gravity and hydrostatic forces when the launch simulation begins. The initial equilibrium position (wilh the jacket already on the launch way) is defined by the draft al Ihe barge center of gravity, and barge Irim and heel (Figure 2).
The Barge Radius of Gyration is relative to the body-fixed Barge Coordinate System. The Rocker Pin location is reported in the Input Coordinate System with the barge launch way still parallel to the X axis of the Input Coordinate System, i.e., before the barge-jacket system achieves its initial equilibrium position (Figure 4).
3.3. Weights and Buoyancy and Initial Position Data Report
In the Input Coordinate System, the jacket weight and buoyancy are reported with the jacket at its original position, i.e., before Ihe jacket is re-oriented and put on the launch way (Figure 4). However, in Ihe Global Coordinate System, the jacket weight and buoyancy are reported with the barge-jacket system in its initial equilibrium position (Figure 2).
The initial position data of barge - jacket system are reported in the Global Coordinate System (Figure 2,4).
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3.4. Rigid Body Position Results
The barge rigid body position (six degrees of freedom) is reported in the Global Coordinate System, which is fixed in the space with its X-Y plane coinciding wilh the water plane. The jacket rigid body posifion (six degrees of freedom) is reporled both in the Global Coordinate System and in the Barge Coordinate System, which is fixed in the barge wilh its origin at the barge CO.
For Phase 1, the only non-zero relative motion between the jacket and barge is in the barge Xdircetion. since the jacket is sliding on the launch way.
For Phase 2, the jacket has relative skid and rotational motion wilh respect to the barge.
These relative motion components are described as motion in 'X', 'Z' and 'Pitch' in the Barge Coordinate System.
For Phase 4. the jacket has been separated from the barge. Thus no relative motion is reporled.
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Figure 8. Phase 4 Motion Figure 9: Height to Water Surface and Bottom Clearance
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3.5. Velocity and Acceleration of Jacket and Barge
Ihc barue \elocily is reporled in the Global Coordinate System, which is lixej in space with ils X-Y plane coinciding «ilh the natcr plane.
Ihc jacket I'clocils is reported in both Ihe Global Coordinate System and in iho Bartic Coordinate S>slem. which s fixed in the barge wilh ils origin al the barge C.G.
3.6. Force Table
The total contacting forces bclucen the jacket and barge are reported in the rocker ami coordinate syslem, \\hich is fixed in Ihc rocker arm wilh Ihe local z direction alwjys perpendicular lo Ihc rocker arm top and Ihe x-dircclion originally in the launch dirccliiin (I'iuure 3). Note Ihal the rocker arm Y-dircclion is determined by the right hand rule.
3.7 I'orces and Moments acting on the Launch System
All Ihe forces and momenls acting on the barge are reported in the coordinale syslem, which origin is located al Ihe barge C.G. and Ihc X-Y-Z axes in Ihe same direelion as those of the Global Coordinale System (Figure 5).
All the forces and momenls acting on Ihc jacket arc reported in Ihc cootdinate system, which origin is located at the jacket C.G, and the X-Y-Z axes in the same direction as those
of the (ilobal Coordinale Syslem (Figure 5). j 3.S. Phase 1 Motion Report
In this report, the barge motions are reported in the Global Coordinate System. Since the only relative motion between lire jacket and the barge is in the x-dircclion of the Barge Coordinate System (fixed in the barge), the jacket motions are better described as relative motion. Note that the x-dircction of Ihc Barge Coordinate System will be different from that of the Global Coordinate System if the barge has a non-zero pitch/trim angle.
Only the most important barge motions, i.e.. surge, heave, and pitch, are included in this summary report. The other motion information can be found in the detail report.
3.9. Phase 2 Motion Report
For Phase 2, both the barge and jacket motions arc reported in the Global Coordinale System. The relative skid velocity is reported in the Rocker Arm System (fixed in the rocker arm). The relative position (X-direction) is still reported in Barge Coordinale System to be consistent wilh the Phase 1 relative motion. In addition, the rocker arm rotating angle and rocker arm contacting force in Ihe rocker arm z-direetion are also reporled. The rocker arm force in Ihe rocker arm y-direction can be found in Ihe detail report. Note that the x-direction of the Rocker Arm Coordinate System will be different from that of Ihe Global in Barge Coordinate System if rocker arm has a non-zero angle.
Only the most important barge and jacket motions, i.e., surge, heave, and pitch are included in tills siuranary report. The oilier motion infoiTnation can be found in the detail report.
3.10. Phase 4 Motion Report
For Phase 4, both Ihe barge and jacket motions are reported in the Global Coordinate System Since the jacket has separated from Ihc barge, no relative motion will be reported.
The bottom clearance is calculated based upon the refercncejoints you define.
Only the most important bai-ge and jacket motions, i.e., surge, heave, and pitch ai'e included in
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this summary report Ihe other motion infomiahon can be found in the detail report.
3.11. Height lo Water Surface and Bottom Clearance of Jacket
The "I leighl to Water Surface' is positive if the joints arc above Ihc water surface, fhc "Deepest PoinI" is calculated based upon the refercncejoints you define.
4. Conclusions
fhcrc jacket - barge system models can be using Software system, which have currently in ICOI'i'Sl IOR1-; to calculating: StruCAD*3D; SlabCAD; NEPTUNE Developed b>
Zenlech I'SA. SACS, Slruclural Analysis Computer System. Program Manual- lingineering Dynamic. Inc. USA.
5. Reference
1. Bathe. K. J -Finite I:lcment Procedures in Engineering Analysis-1992.
2. Bathe .K.J - Finite l-Tenient Procedures - USA-1996.
3. Peter Belles - Infinite element - London - 1993
4. Sol'tvvarcs: StruCAD*3D, SlrabCAD; NcpTune developed by Zenlech - USA 5. SACS. Structural Analysis Computer Syslem, Program Manual- Engineering Dynamic,
Inc. USA.
