Is a unit with a floating deck system supported by columns (vertical structural elements) and pontoons (horizontal structural elements) that allow more flexible response, and independent of wave motion characteristics of a good response.
With such a configuration structure, some important notes on performansinya include the following: (1) on the deck structure, pontoon, columns and elements of its branches (bracings) occurs across the force and torque, (2) equipment layout elements are integrated in - structural elements such as the deck box, the column and pontoon, (3) the details of local connections are vulnerable to high voltage and fatigue, (4) required a high strength steel (high tensile steel) to reduce the weight of the structure, (5) construction of the structure requires types of full penetrated weld welding and special welding procedures and (6) there is the air gap between surface water and the deck to allow the waves on the deck structure (slamming).
A floating object will move depending on the direction of the waves, winds and currents. So with this Floating Structure. To make this object relatively moving anywhere, it is necessary straps or known by the mooring line. Mooring was placed around the platform so that the floating structure for the condition without the influence of waves, winds and currents will be in a position of equilibrium for the vertical and horizontal directions. Mooring numbers ranged from 9 to 13, depending on the type of platform. Each mooring is tied at two locations. The first location was in itself a floating structure (attached mooring place is known by the name Fairlead) while the second location are embedded in the seabed. So that now the forces acting on the platform is no longer just the waves, winds and currents, but involves the force (top tension) of each mooring is attached around this platform.
To take the oil and gas on the seabed, it is necessary transport equipment known as the Riser. Riser There are many models, but there are widely recognized 2 types, namely SCR (Steel Catenary Riser) and TTR (Top Tension Riser). Like the mooring line, this line Riser length of the platform to the seabed. For this type of SCR, Riser curvature of the line is similar to the curvature of the Mooring line. While TTR is a vertical type Riser (perpendicular) from the platform to the seabed. The number of SCR and TTR depending on the wells located on the seabed. Meanwhile, drilled wells will depend on the amount of reserves and production of the desired daily basis. With additional resulted Riser style styles other than the above mentioned working on the platform.
Thus for the analysis of movement of the floating structure to see the force components acting on both the vertical platform (weight, buoyancy and the vertical tension of each of Mooring and Riser) or horizontal (waves, wind, currents, and the horizontal tension of each Mooring and Riser). To design, but must take into account the factors above, also must take into account the amount of oil and gas reserves will be taken (how many barrels per day), so this will affect the number and selection of Riser diameter to be used. Another factor to be reckoned with is the location where the offshore oil rigs will operate for Environment Condition will be different if we are designing for the Gulf of Mexico or to Makassar Strait. So that information about MetOcean be important for this initial process.
Viv can be formed around Riser for current flow or also around Spar because the flow of waves, winds and currents. To Riser (especially type TTR) is a challenge because of the amount of TTR is more than one and its position adjacent (Riser spacing generally ranges from 10 ft in length is more than 3000ft vertical direction) should be anticipated that each Riser did not collide. This paper will be more focused on issues surrounding Viv Spar (Spar, where the movement is also influenced by Viv caused by Riser).
Spar is a type banguan floating offshore shaped like a standing cylinder (see Figure 1). If there is a stream of silent object (eg a cylinder) then the flow of these items will be broken so that the vortex and the wake will be formed. Vortex formation and release on the left and right cylinder alternately to each other regularly with time (periodic). Because the flow pattern is not symmetric then the pressure distribution is not symmetrical and change with time periodically, so the cylinder will experience a net force which fluctuates periodically. Release of this vortex is marked with a Strouhal number of about 0.20. (King, 1977 and Winarto, 2003)
For building a floating offshore, it is not stationary but still flexible because the forces that worked earlier. When the waves, winds and currents flow and cause the force on the object then there will be interaction between the mechanism of vortex formation behind a moving object with this structure. When the two frequencies caused by the fluid and it has the same value (nearly equal) is called with "lock-in". In this condition, the movement of objects to be excited strongly and when the force created in excess of the maximum force that can be arrested by Mooring Mooring will result in termination of that.
To reduce the effects of VIV can be done two methods. First, the structure approach, namely by increasing the frequency of personality through the distribution of the object or objects to add rigidity (stiffness) or by adding a damper to absorb energy. Second, using the forms of aerodynamic body to reduce vortex formation around the object. Vortex breaker tool among others by adding helical strakes or cable around the cylinder, so that will affect the location or the location of flow separation (Zdravkovich, 1981).
With such a configuration structure, some important notes on performansinya include the following: (1) on the deck structure, pontoon, columns and elements of its branches (bracings) occurs across the force and torque, (2) equipment layout elements are integrated in - structural elements such as the deck box, the column and pontoon, (3) the details of local connections are vulnerable to high voltage and fatigue, (4) required a high strength steel (high tensile steel) to reduce the weight of the structure, (5) construction of the structure requires types of full penetrated weld welding and special welding procedures and (6) there is the air gap between surface water and the deck to allow the waves on the deck structure (slamming).
A floating object will move depending on the direction of the waves, winds and currents. So with this Floating Structure. To make this object relatively moving anywhere, it is necessary straps or known by the mooring line. Mooring was placed around the platform so that the floating structure for the condition without the influence of waves, winds and currents will be in a position of equilibrium for the vertical and horizontal directions. Mooring numbers ranged from 9 to 13, depending on the type of platform. Each mooring is tied at two locations. The first location was in itself a floating structure (attached mooring place is known by the name Fairlead) while the second location are embedded in the seabed. So that now the forces acting on the platform is no longer just the waves, winds and currents, but involves the force (top tension) of each mooring is attached around this platform.
To take the oil and gas on the seabed, it is necessary transport equipment known as the Riser. Riser There are many models, but there are widely recognized 2 types, namely SCR (Steel Catenary Riser) and TTR (Top Tension Riser). Like the mooring line, this line Riser length of the platform to the seabed. For this type of SCR, Riser curvature of the line is similar to the curvature of the Mooring line. While TTR is a vertical type Riser (perpendicular) from the platform to the seabed. The number of SCR and TTR depending on the wells located on the seabed. Meanwhile, drilled wells will depend on the amount of reserves and production of the desired daily basis. With additional resulted Riser style styles other than the above mentioned working on the platform.
Thus for the analysis of movement of the floating structure to see the force components acting on both the vertical platform (weight, buoyancy and the vertical tension of each of Mooring and Riser) or horizontal (waves, wind, currents, and the horizontal tension of each Mooring and Riser). To design, but must take into account the factors above, also must take into account the amount of oil and gas reserves will be taken (how many barrels per day), so this will affect the number and selection of Riser diameter to be used. Another factor to be reckoned with is the location where the offshore oil rigs will operate for Environment Condition will be different if we are designing for the Gulf of Mexico or to Makassar Strait. So that information about MetOcean be important for this initial process.
Viv can be formed around Riser for current flow or also around Spar because the flow of waves, winds and currents. To Riser (especially type TTR) is a challenge because of the amount of TTR is more than one and its position adjacent (Riser spacing generally ranges from 10 ft in length is more than 3000ft vertical direction) should be anticipated that each Riser did not collide. This paper will be more focused on issues surrounding Viv Spar (Spar, where the movement is also influenced by Viv caused by Riser).
Spar is a type banguan floating offshore shaped like a standing cylinder (see Figure 1). If there is a stream of silent object (eg a cylinder) then the flow of these items will be broken so that the vortex and the wake will be formed. Vortex formation and release on the left and right cylinder alternately to each other regularly with time (periodic). Because the flow pattern is not symmetric then the pressure distribution is not symmetrical and change with time periodically, so the cylinder will experience a net force which fluctuates periodically. Release of this vortex is marked with a Strouhal number of about 0.20. (King, 1977 and Winarto, 2003)
For building a floating offshore, it is not stationary but still flexible because the forces that worked earlier. When the waves, winds and currents flow and cause the force on the object then there will be interaction between the mechanism of vortex formation behind a moving object with this structure. When the two frequencies caused by the fluid and it has the same value (nearly equal) is called with "lock-in". In this condition, the movement of objects to be excited strongly and when the force created in excess of the maximum force that can be arrested by Mooring Mooring will result in termination of that.
To reduce the effects of VIV can be done two methods. First, the structure approach, namely by increasing the frequency of personality through the distribution of the object or objects to add rigidity (stiffness) or by adding a damper to absorb energy. Second, using the forms of aerodynamic body to reduce vortex formation around the object. Vortex breaker tool among others by adding helical strakes or cable around the cylinder, so that will affect the location or the location of flow separation (Zdravkovich, 1981).
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