Dear all, beberapa waktu yang lalu iseng berselancar di dunia ghaib (maya) dan menemukan artikel yg menurut saya bagus. Gak tau juga kalau menurut kamu, terutama untuk rekan2 yg concern di bidang floating structure especially untuk analisis mooring atau tali tambat.
Artikel ini pengarang aslinya kalau saya baca2 dy wong Londo, dr Delf University di Holland (CMIIW). Berisi tentang konsep dasar dalam melakukan sebuah mooring analysis, pemahaman dan konsep yg ditulis juga mudah untuk dipahami.
Pendalamannya bisa dilakukan di kampus, atau belajar sendiri kalau ente mau. Almamater saya di ITS, sudah sangat jamak mahasiswa tingkat akhir yg ngambil bidang keahlian ini. Bpk2 dosennya juga sangat kompeten dalam membimbing anak buahnya, tp anak buahnya kadang mblendes koyok aku :))
Sok ah, monggo dibaca dan diartikan sendiri. Pakai gugle translate juga silaken, ayo dinikmati...
-------------------------------------------------Introduction---------------------------------------------------
This website is built to give a stepwise overview of how to moor an FPSO. This was done by Benno Poppelaars and Julien Mos, two students at the Delft University of Technology for the course OE5664 (Offshore moorings).
The different steps necessary for designing a mooring system can be found via the picture below as well as the index on the left side.
This site gives an explanation of all forces working on a mooring system, the boundary conditions that have to be taken into account and the possible mooring systems that result from this
Do not use this site without consulting specialists in the field of mooring an FPSO. This is purely made to act as a guideline and to provide some background information.
We hope the site is useful for you, enjoy!
Best regards,
Benno Poppelaars & Julien Mos
-------------------------------------------------Mooring types-----------------------------------------------------------
In this part of the site you can find all different types of mooring systems. For different conditions different mooring systems are required. In the left frame you can click on the type of mooring system and herewith additional information comes up. Also the special features of the different types will be displayed.
Types of mooring systems:
Spread
Internal turret
External turret
CALM
SALM
DP (Dynamic Positioning)
Tower
---------------------------------------------------------------Spread Mooring--------------------------------------------------
Spread moored systems are mooring systems that allow tankers to moor at a fixed location at a fixed heading and allows tankers to (off)load their products.
Spread Mooring Systems utilize four groups of anchor legs, normally arranged in a symmetrical pattern, attached to the bow and stern of the vessel. This style of mooring maintains the vessel on location with a fixed heading. Thus, its application is dependent on a site where the prevailing severe weather is highly directional.
Spread moorings can be used in applications requiring long service life, in any water depth, and on any size of vessel. Since the vessel is held essentially at a constant heading, the requirement for a turret structure with a large capacity slewing bearing, as well as the associated swivel stack for fluid, gas, chemical, hydraulic power, electrical power and control transfer is not needed. Virtually all types of anchor leg configurations can be used with this system. Typically, risers and control umbilicals are located amidships on both sides of the vessel. This arrangement provides ample room to accommodate a large number of risers and umbilicals. In applications with highly directional prevailing weather, the shuttle tanker offloading facilities are typically located at the stern or the bow; other deepwater applications may require a dedicated buoy terminal for cargo transfer.
Features:
• Uses traditional shipboard mooring equipment
• Turret structure and bearing are not needed
• Fluid and gas swivels are not needed
• Electrical power and control swivels are not needed
• Easily accommodates a large number of risers and umbilicals
Drawbacks:
• The dynamic motions of the FPSO are transferred directly to the SCR at the hang-off positions. This leads to fatigue life issues in the riser touchdown point on the seabed, which govern the cross-sectional design of the pipes.
• With increasing water depth, the length of mooring line required and the cost of the mooring system also increase; hence there are significant savings to be made by optimization of the mooring system.
• The potential for interference between the SCRs, mooring lines of the FPU, and mooring lines of neighboring platforms. A typical FPSO is the centerpiece of a deepwater field with wellhead platform and offloading buoy mooring lines in close proximity.
• The minimal ability for a spread moored FPU to weather vane into the direction of the environment if the dominant environmental conditions are on the side of the vessel.
• Long installation times for SCRs, resulting in a large delay between the arrival of the FPU on site and the first oil date.
-----------------------------------------------Internal Turret---------------------------------------------
The Internal Turret Mooring system is integrated into the forward end of a tanker or barge and is supported on a large roller bearing, located either inside a moonpool towards the bottom of the vessel, or at deck level. The outer rotating race of the bearing is connected to the vessel, while the inner race is attached to the fixed part of the turret. Above deck level, a manifold structure enables connection between the lower turret and the swivel stack.
Features:
• Permanent and disconnectable systems
• Moderate to harsh environment
• Deep water applications
-----------------------------------External Turret--------------------------
The External Turret Mooring system comprises a steel box type structure that can be close or extended some distance from the bow or stern of the vessel, providing a foundation for a rotating bearing arrangement and a turret. The bearing accommodates a fixed chaintable to which mooring chains and fluid transfer hoses are attached. The chain legs are anchored to the seabed either by anchors or piles. Product and utility connections are made between the facilities on the tanker and the seabed via a swivel stack in the turret, allowing the tanker to weather vane around the fixed part whilst continuing production. External turret systems are less expensive than internal turret designs and can be delivered in a shorter period of time, making them an excellent choice for many applications. They can be attached to the bow and the stern of ships.
Features:
• Fluid and gas swivels are needed
• Electrical power and control swivels needed
• Limited number of risers and umbilicals
---------------------------Catenary Anchor Leg Mooring------------------------
After more than 40 years of use, the Catenary Anchor Leg Mooring (CALM) system remains one of the most flexible, cost-effective, safe and reliable offshore loading/offloading systems. Environmentally friendly, this cost-saving "instant port" solution provides a trustworthy system that satisfies most offshore loading and offloading requirements. This concept has been utilised for a wide range of applications, water depths and vessel ranging from small product carriers to the largest ULCCs.
Features:
• Short term mooring: for import and export of fluids between onshore or offshore facilities and a tanker
• Permanent Mooring: for production and storage systems
• Semi-permanent Mooring: permanent mooring with easy disconnect capability to evacuate the facility in case of severe weather conditions
-----------------------------Single Anchor Leg Mooring-------------------------
A mooring facility dedicated to the offshore petroleum discharge system. Once installed, it permits a tanker to remain on station and pump in much higher sea states than is possible with a spread moor.
The Single Anchor Leg Mooring or SALM: Prevents collision damage to the swivels by placing them underwater and below the keel level of the tanker. Any damage should then only affect the simple surface buoy and be relatively cheap to repair. The underwater swivels do however have maintenance disadvantages. To prevent the flexible loading pipe clashing with the mooring chains the catenary is replaced by a single, nominally vertical, tensioned chain mooring leg. In shallow water the fluid swivels are on the base. In deep water the fluid swivels could be attached part way up the mooring leg. This would ease maintenance of the swivels and the flexible pipes from the swivels to the tanker.
Fluids flow either through a flexible pipe from the base on the seabed directly to the ship or flow through the base and the tubular column, via a swivel to the ship. The submarine hoses are long enough to adapt to all the motions of the buoy. The fluids are transferred between the buoy and the FPSO through one or more floating hoses. The flow through the buoy goes via a swivel, which allows flow between the geostatic parts and the rotating parts of the buoy.
Features:
• All weather
• Great range of water depths
• Fast installation and cost effective
• High reliability
--------------------------------Dynamic Positioning ------------------------------------
DP means dynamic positioning. This means to keep a floating structure stationary by means of controlling the magnitude and the direction of thrust, based on position feedback.
The power management system provides all the power needed for the positioning of the vessel. It consists of two circuits. A high voltage circuit for the power supply of the thrusters and a low voltage circuit for the control systems. There are four kinds of thrusters that are used in DP systems. These are described below. These thrusters must be able to create thrust in the longitudinal and transverse direction and torque around a vertical axis at the ships centre of gravity in order to keep the vessel at its specified position. A position reference system provides the control system with information on the location of the vessel at any time. There are several different systems, such as satellite navigation, acoustic position measurement, radio ranging, laser beam ranging etc. For redundancy purposes more than one system is used.
The DP-control system has to keep the vessel on station and at a fixed heading, resisting environmental loads. It includes sensor systems, other that the position reference system, for example for the measurement of wind velocity or for measurement of roll and pitch of the vessel. These sensor data is processed. Inconsistent data is rejected, high frequency components of position signals are filtered and the required forces on the ship are determined. The required forces are then allocated to the available thrusters, keeping power and thrust limitations into account.
Features:
• Suitable for harsh environment
• Great range of depth possibilities
• Many risers possible
• High buying costs, high user costs
-----------------------------------Tower Mooring----------------------------
Tower moorings are a cost effective way of permanent FPSO moorings in shallow waters. A turntable is fastened to the tower with a roller bearing to allow the vessel to freely weathervane around the tower. A turntable is fastened to the tower with a roller bearing to allow the vessel to freely weathervane about the tower. A yoke is connected to the turntable with pitch and roll joints to allow the vessel to pitch and to roll. The yoke includes a large ballast tank filled with water to provide the necessary restoring force to minimize vessel motions. The two mooring links suspend the tank from a support structure mounted on the vessel.
Product is transferred from the tower across swivels located on the turntable and through hoses from the turntable to the vessel. Ample deck space is available on the tower for manifolding, pigging, and auxiliary equipment. Access to the tower can be made along walkways from the vessel across the yoke.
Features:
• It eliminates the need for submarine hoses and provides a simple fluid transfer via jumper hoses from the tower to the tanker
• It provides direct access to the tower structure from the storage tanker
• Only minor tanker modifications are required
• All mechanical equipment is located above sea level
---------------------------------------Forces----------------------------
When trying to keep a floating object at sea in position it will have to resist the environment. It will need a mooring system to oppose the forces subjected to it by wind waves and current. In this case wind will act on the exposed area of the FPSO and waves and wind and current act on the hull, risers and mooring system. In the picture below the exciting forces and the restoring forces are shown. These will be handled separately.
The maximum design conditions are put into the dynamic equation of the total system:
• 100 year waves, with associated wind and current
• 100 year wind, with associated waves and current
• 100 year current, with associated waves and wind
source
This website is built to give a stepwise overview of how to moor an FPSO. This was done by Benno Poppelaars and Julien Mos, two students at the Delft University of Technology for the course OE5664 (Offshore moorings).
The different steps necessary for designing a mooring system can be found via the picture below as well as the index on the left side.
Do not use this site without consulting specialists in the field of mooring an FPSO. This is purely made to act as a guideline and to provide some background information.
We hope the site is useful for you, enjoy!
Best regards,
Benno Poppelaars & Julien Mos
-------------------------------------------------Mooring types-----------------------------------------------------------
In this part of the site you can find all different types of mooring systems. For different conditions different mooring systems are required. In the left frame you can click on the type of mooring system and herewith additional information comes up. Also the special features of the different types will be displayed.
Types of mooring systems:
Spread
Internal turret
External turret
CALM
SALM
DP (Dynamic Positioning)
Tower
---------------------------------------------------------------Spread Mooring--------------------------------------------------
Spread moored systems are mooring systems that allow tankers to moor at a fixed location at a fixed heading and allows tankers to (off)load their products.
Spread Mooring Systems utilize four groups of anchor legs, normally arranged in a symmetrical pattern, attached to the bow and stern of the vessel. This style of mooring maintains the vessel on location with a fixed heading. Thus, its application is dependent on a site where the prevailing severe weather is highly directional.
Spread moorings can be used in applications requiring long service life, in any water depth, and on any size of vessel. Since the vessel is held essentially at a constant heading, the requirement for a turret structure with a large capacity slewing bearing, as well as the associated swivel stack for fluid, gas, chemical, hydraulic power, electrical power and control transfer is not needed. Virtually all types of anchor leg configurations can be used with this system. Typically, risers and control umbilicals are located amidships on both sides of the vessel. This arrangement provides ample room to accommodate a large number of risers and umbilicals. In applications with highly directional prevailing weather, the shuttle tanker offloading facilities are typically located at the stern or the bow; other deepwater applications may require a dedicated buoy terminal for cargo transfer.
• Uses traditional shipboard mooring equipment
• Turret structure and bearing are not needed
• Fluid and gas swivels are not needed
• Electrical power and control swivels are not needed
• Easily accommodates a large number of risers and umbilicals
Drawbacks:
• The dynamic motions of the FPSO are transferred directly to the SCR at the hang-off positions. This leads to fatigue life issues in the riser touchdown point on the seabed, which govern the cross-sectional design of the pipes.
• With increasing water depth, the length of mooring line required and the cost of the mooring system also increase; hence there are significant savings to be made by optimization of the mooring system.
• The potential for interference between the SCRs, mooring lines of the FPU, and mooring lines of neighboring platforms. A typical FPSO is the centerpiece of a deepwater field with wellhead platform and offloading buoy mooring lines in close proximity.
• The minimal ability for a spread moored FPU to weather vane into the direction of the environment if the dominant environmental conditions are on the side of the vessel.
• Long installation times for SCRs, resulting in a large delay between the arrival of the FPU on site and the first oil date.
-----------------------------------------------Internal Turret---------------------------------------------
The Internal Turret Mooring system is integrated into the forward end of a tanker or barge and is supported on a large roller bearing, located either inside a moonpool towards the bottom of the vessel, or at deck level. The outer rotating race of the bearing is connected to the vessel, while the inner race is attached to the fixed part of the turret. Above deck level, a manifold structure enables connection between the lower turret and the swivel stack.
Features:
• Permanent and disconnectable systems
• Moderate to harsh environment
• Deep water applications
-----------------------------------External Turret--------------------------
The External Turret Mooring system comprises a steel box type structure that can be close or extended some distance from the bow or stern of the vessel, providing a foundation for a rotating bearing arrangement and a turret. The bearing accommodates a fixed chaintable to which mooring chains and fluid transfer hoses are attached. The chain legs are anchored to the seabed either by anchors or piles. Product and utility connections are made between the facilities on the tanker and the seabed via a swivel stack in the turret, allowing the tanker to weather vane around the fixed part whilst continuing production. External turret systems are less expensive than internal turret designs and can be delivered in a shorter period of time, making them an excellent choice for many applications. They can be attached to the bow and the stern of ships.
• Fluid and gas swivels are needed
• Electrical power and control swivels needed
• Limited number of risers and umbilicals
---------------------------Catenary Anchor Leg Mooring------------------------
After more than 40 years of use, the Catenary Anchor Leg Mooring (CALM) system remains one of the most flexible, cost-effective, safe and reliable offshore loading/offloading systems. Environmentally friendly, this cost-saving "instant port" solution provides a trustworthy system that satisfies most offshore loading and offloading requirements. This concept has been utilised for a wide range of applications, water depths and vessel ranging from small product carriers to the largest ULCCs.
• Short term mooring: for import and export of fluids between onshore or offshore facilities and a tanker
• Permanent Mooring: for production and storage systems
• Semi-permanent Mooring: permanent mooring with easy disconnect capability to evacuate the facility in case of severe weather conditions
-----------------------------Single Anchor Leg Mooring-------------------------
A mooring facility dedicated to the offshore petroleum discharge system. Once installed, it permits a tanker to remain on station and pump in much higher sea states than is possible with a spread moor.
The Single Anchor Leg Mooring or SALM: Prevents collision damage to the swivels by placing them underwater and below the keel level of the tanker. Any damage should then only affect the simple surface buoy and be relatively cheap to repair. The underwater swivels do however have maintenance disadvantages. To prevent the flexible loading pipe clashing with the mooring chains the catenary is replaced by a single, nominally vertical, tensioned chain mooring leg. In shallow water the fluid swivels are on the base. In deep water the fluid swivels could be attached part way up the mooring leg. This would ease maintenance of the swivels and the flexible pipes from the swivels to the tanker.
Fluids flow either through a flexible pipe from the base on the seabed directly to the ship or flow through the base and the tubular column, via a swivel to the ship. The submarine hoses are long enough to adapt to all the motions of the buoy. The fluids are transferred between the buoy and the FPSO through one or more floating hoses. The flow through the buoy goes via a swivel, which allows flow between the geostatic parts and the rotating parts of the buoy.
Features:
• All weather
• Great range of water depths
• Fast installation and cost effective
• High reliability
--------------------------------Dynamic Positioning ------------------------------------
DP means dynamic positioning. This means to keep a floating structure stationary by means of controlling the magnitude and the direction of thrust, based on position feedback.
The power management system provides all the power needed for the positioning of the vessel. It consists of two circuits. A high voltage circuit for the power supply of the thrusters and a low voltage circuit for the control systems. There are four kinds of thrusters that are used in DP systems. These are described below. These thrusters must be able to create thrust in the longitudinal and transverse direction and torque around a vertical axis at the ships centre of gravity in order to keep the vessel at its specified position. A position reference system provides the control system with information on the location of the vessel at any time. There are several different systems, such as satellite navigation, acoustic position measurement, radio ranging, laser beam ranging etc. For redundancy purposes more than one system is used.
The DP-control system has to keep the vessel on station and at a fixed heading, resisting environmental loads. It includes sensor systems, other that the position reference system, for example for the measurement of wind velocity or for measurement of roll and pitch of the vessel. These sensor data is processed. Inconsistent data is rejected, high frequency components of position signals are filtered and the required forces on the ship are determined. The required forces are then allocated to the available thrusters, keeping power and thrust limitations into account.
• Suitable for harsh environment
• Great range of depth possibilities
• Many risers possible
• High buying costs, high user costs
-----------------------------------Tower Mooring----------------------------
Tower moorings are a cost effective way of permanent FPSO moorings in shallow waters. A turntable is fastened to the tower with a roller bearing to allow the vessel to freely weathervane around the tower. A turntable is fastened to the tower with a roller bearing to allow the vessel to freely weathervane about the tower. A yoke is connected to the turntable with pitch and roll joints to allow the vessel to pitch and to roll. The yoke includes a large ballast tank filled with water to provide the necessary restoring force to minimize vessel motions. The two mooring links suspend the tank from a support structure mounted on the vessel.
Product is transferred from the tower across swivels located on the turntable and through hoses from the turntable to the vessel. Ample deck space is available on the tower for manifolding, pigging, and auxiliary equipment. Access to the tower can be made along walkways from the vessel across the yoke.
Features:
• It eliminates the need for submarine hoses and provides a simple fluid transfer via jumper hoses from the tower to the tanker
• It provides direct access to the tower structure from the storage tanker
• Only minor tanker modifications are required
• All mechanical equipment is located above sea level
---------------------------------------Forces----------------------------
When trying to keep a floating object at sea in position it will have to resist the environment. It will need a mooring system to oppose the forces subjected to it by wind waves and current. In this case wind will act on the exposed area of the FPSO and waves and wind and current act on the hull, risers and mooring system. In the picture below the exciting forces and the restoring forces are shown. These will be handled separately.
• 100 year waves, with associated wind and current
• 100 year wind, with associated waves and current
• 100 year current, with associated waves and wind
source
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