Asymmetric monohull ship for floating production
By designing asymmetric monohulls, using the projections or straits to provide additional buoyancy and optimize rolling motion, the rolling motion problem caused by traditional monohull FPSOs in deep water environments is solved, achieving lower production downtime and higher productivity.
Patent Information
- Application Number
- CN202380074111.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-10-27
- Filing Date
- 2023-01-31
- Publication Date
- 2025-06-27
AI Technical Summary
The rolling motion caused by lateral unbalanced loads and surges in deep water environments leads to unsatisfactory load capacity, increased structural fatigue, unqualified production and frequent treatment shutdowns, thereby increasing production downtime and maintenance costs.
An asymmetric monohull is designed with a raised or a strait on one side of the hull to provide additional buoyancy to offset lateral unbalanced loads and is configured to optimize roll motion performance and reduce resonant roll motion.
Through the asymmetric design, the natural cycle of rolling motion of the floating ship is effectively improved, avoiding the resonant ship rolling motion caused by surges, minimizing production downtime and maintenance costs, and improving productivity and net present value.
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Figure CN120225423A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a single-hull ship for floating production, which may include storage and unloading functions. Background Art
[0002] Floating Production Storage and Offloading (FPSO) operations involve the production and processing of hydrocarbons and minerals, such as crude oil, water, and natural gas, at sea. In deep waters, floating vessels are typically used for such operations. Such operations are also commonly referred to as floating production. Hydrocarbons produced from subsea wells are transported to the floating vessel via subsea pipelines, riser systems, etc., and may be processed by facilities at the top of the floating vessel. The floating vessel can be used to store the processed products, such as crude oil. Then, the processed products can be offloaded onto shuttle tankers. If the operation only involves storage and offloading, it is called a Floating Production Storage and Offloading (FSO) operation. The hull of an FPSO can be converted from an oil tanker or can be specifically built for the operation. A single-hull FPSO is also known as a ship-shaped FPSO, which typically has a symmetric hull similar to a ship. For operation, the floating vessel is designed to be stationed at a specific location with the required storage capacity and support a large topside payload while reducing production downtime.
[0003] To date, symmetric hull or single-hull FPSOs S have been widely installed in the offshore industry. A paper titled "FPSO Design to Minimise Operational Downtime due to Adverse Metocean Conditions off North-West Australia" discussed the overall performance design optimization of a conventional single-hull FPSO as shown in Figure 1 S which was presented and exhibited at the Deep Offshore Technology International Conference & Exhibition held in Perth, Australia from November 27th to 29th, 2012. When a conventional single-hull FPSO suspends a large number of deepwater risers on one side, due to the lateral imbalance of the riser and structural loads, its load-bearing capacity, ballast, and cargo operations are not ideal, and there are other defects.
[0004] FPSO SThe metocean environment is typically characterized by waves and swells. Waves are locally generated due to wind conditions, while swells are mainly caused by ocean storms, such as in the Southern Ocean. Under non-tropical cyclone forcing, the typical peak period of waves is between 2 and 7 seconds, and the wave height is between 0 and 4 meters. The typical peak wave period of swells and many severe storms is in the range of 12 to 18 seconds. Persistent swells are the main cause of S resonant roll motion occurring in many conventional FPSOs.
[0005] For example, the Santos Basin offshore Brazil and the North West Shelf offshore Australia are affected by persistent Southern Ocean swells. In some cases, under metocean conditions, the roll motion amplitude caused by swells is greater than 12 degrees. It is worth noting that the actual roll motion observed on site usually exceeds the design prediction, and the roll motion under operating metocean conditions may be greater than that under severe metocean conditions.
[0006] The large-amplitude ship motions caused by long-wave period swells and strong storms pose problems for the installation and operation of FPSOs S , including riser damage, increased structural fatigue, production non-conformance, and frequent process shutdowns. All these problems and issues result in a large amount of downtime during the operation of the FPSO and lead to losses in productivity and net present value (NPV) over its entire service life.
[0007] In view of the above, it is worth noting that the motion characteristics of the floating vessel have a significant impact on the downtime of the production plant and the mooring and riser systems. Therefore, any economic benefits obtained during the conversion or construction of the floating vessel may be quickly offset if the hull design cannot adapt to the on-site environmental conditions and frequent shutdowns result in production losses or high maintenance costs for the process facilities, mooring, and riser systems.
[0008] Therefore, it is very important to find solutions to the above problems. In other words, the design of the floating production vessel should optimize the ballast and cargo-carrying performance, as well as the motion performance under the metocean conditions at a specific location, to minimize production downtime. The novel asymmetric monohull described in this article has been proven to have advantages. Summary of the Invention
[0009] According to various embodiments, an asymmetric monohull design for floating production is provided. The asymmetric monohull has a raised portion or sponson on one side of the hull such that the raised portion or sponson is configured to provide additional buoyancy to the floating vessel to counteract a lateral imbalance load shifted to one side of the hull. The raised portion or sponson is also configured to act as an effective roll motion reduction attachment to optimize the roll motion performance of the floating vessel.
[0010] According to various embodiments, the asymmetric catamaran may further include ballast tanks within the hull such that the raised portion or sponson is in fluid communication with the ballast tanks.
[0011] According to various embodiments, the floating vessel may further include a riser platform extending from one side of the hull, wherein the lateral imbalance load includes a riser load, and wherein the riser platform is for attaching and supporting the riser load. BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Figure 1A A schematic view of a conventional floating vessel during floating production, storage and offloading (FPSO) operations is shown.
[0013] Figure 1B Shows Figure 1A A schematic cross-sectional view of a conventional single-hull floating vessel for FPSO operations in
[0014] Figure 2 A schematic cross-sectional view of an exemplary embodiment of an asymmetric catamaran for floating production is shown.
[0015] Figure 3 Examples of the asymmetric catamaran under different load conditions are shown.
[0016] Figure 4 Compares the resonance and optimized roll response amplitude operator (RAO Figure 2 ) of a conventional floating vessel with the asymmetric vessel shown in S with the wave energy distribution within the wave period.
[0017] Figure 5 For Figure 3 the various load conditions shown in Figure 2 a table of exemplary roll natural period values of a conventional floating vessel and an optimized asymmetric floating vessel in DETAILED DESCRIPTION
[0018] Figure 1A A schematic view of a conventional floating vessel 10 (commonly referred to as an FPSO) during floating production, storage and offloading (FPSO) operations is shown. The floating vessel 10 has a mooring system 20 that positions the floating vessel 10 and an attached riser system 30 for transporting fluid between the floating vessel 10 and a nearby platform 40.
[0019] Figure 1B Shows Figure 1A A schematic cross-sectional view of the hull 12 of the conventional floating vessel 10 for FPSO operations in Figure 1B As shown in SSimilarly, the hull 12 of the exemplary floating vessel 10 is symmetric about the vertical axis 10P.
[0020] Figure 2 FIG. shows a schematic cross-sectional view of an exemplary embodiment of an asymmetric single-hull vessel 100 for floating production. The asymmetric hull shape is asymmetric about a vertical plane 100V that divides the port side 110D and the starboard side 110E of the floating vessel 100. Specifically, the floating vessel 100 is an asymmetric single-hull vessel that includes a hull 110, and one side of the hull 110 (e.g., the port side 110D or the starboard side 110E) has a raised portion 120, as Figure 2 shown. The raised portion can be a sponson integrated through tanker conversion. The raised portion or sponson 120 provides additional buoyancy to the floating vessel and is configured to counteract any lateral imbalance loads, including riser loads and structural and facility loads biased to one side. This is one of the most obvious advantages of the novel asymmetric single-hull design.
[0021] The additional displacement of the raised portion or sponson 120 can be 1.5 times the static riser load, which also provides a greater FPSO weight and storage growth margin. Importantly, due to the more balanced lateral buoyancy and load distribution, the floating vessel 100 has improved ballast capacity (e.g., a draft depth of more than 14.5 meters to improve fire pump suction and reduce slamming), ballast efficiency, cargo operation flexibility, offloading availability, and damage stability margin.
[0022] See Figure 2 , for the asymmetric single-hull vessel 100, the raised portion or sponson 120 extends only from one side of the hull 110 (e.g., the port side 110D) and does not protrude from the other side (e.g., the starboard side 110E). When the floating vessel 100 is operating in water, the raised portion or sponson 120 is designed to be submerged in water, i.e., below the waterline 100W of the floating vessel 100. Therefore, the raised portion or sponson 120 is disposed near the bottom 110B of the hull 110. As Figure 2 shown, the height of the raised portion or sponson 120 is a part of the height of the hull 110. In other words, the raised portion or sponson 120 does not extend along the entire height of the hull 110. The raised portion or sponson 120 can extend parallel to the longitudinal axis 110L along the entire length of the hull 110 or only along a part of the hull length (e.g., 80% of the length of the hull 110), which mainly depends on the additional displacement required to counteract the lateral imbalance riser and structural loads. The additional buoyancy provided by the raised portion or sponson 120 can be converted into a greater storage capacity or top weight bearing capacity of the floating vessel 100. The raised portion or sponson 120 can extend downward from the lower side 110U of the hull 110 and extend outward from the hull 110. Those skilled in the art should be clear that the raised portion or sponson 120 can extend from one side and the lower side 110U.
[0023] An important design consideration for the shape of the bulges or sponsons 120 is their impact on roll motion. The bulges or sponsons 120 can be configured to act as effective roll reduction appendages to optimize the motion performance of the floating vessel 100. As described later, the bulges or sponsons 120 change the resonant roll period of the floating vessel 100 and avoid resonance of the vessel with environmental waves having high energy concentration.
[0024] The floating vessel 100 includes a ballast system within the hull 110, and the ballast system has ballast tanks 130. The ballast system is configured to control the distribution of water within the ballast tanks 130. The bulges or sponsons 120 are hollow. The bulges or sponsons 120 can be hollow or can be in fluid communication with the ballast tanks 130 so that water in the ballast tanks 130 can flow into the bulges or sponsons 120 to increase the ballast capacity. The bulges or sponsons 120 can even be constructed as part of the ballast tanks 130. The floating vessel 100 can include storage tanks 140 within the hull 110.
[0025] Reference Figure 2 , the floating vessel 100 can include a riser suspension platform or riser platform 150 that extends from one side of the hull 110 and extends from near the top side 110P of the hull 110. The riser loads are applied to the vessel through the riser platform 150. The topside facilities of the floating vessel 100 are installed above the deck of the floating vessel 100. As Figure 2 shown, the riser platform 150 extends from the same side as where the bulges or sponsons 120 extend.
[0026] The floating vessel 100 can be built from scratch or converted from a ship. The bulges or sponsons 120 can be designed and manufactured in an integrated form with the hull 110, in which case it will become an integral part of the main hull 110. If the floating vessel 100 is converted from an existing ship, the sponsons 120 can be manufactured separately and attached to the main hull 110 of the ship to form the bulges 120.
[0027] Figure 3 Shows one design solution of the asymmetric single-hull floating vessel 100 under various load conditions. In the example, the load conditions are checked based on a topside weight of 48,000 tons. Under the first load condition (i.e., the ballast condition) in row 302 of the table 300, the floating vessel 100 has no cargo, but the ballast tanks 130 are filled with water, weighing 88,260 tons. As shown, the bulges or sponsons 120 are also filled with water. Under the second load condition (i.e., the intermediate condition) in row 304, the floating vessel 100 has a cargo of 780,000 barrels (bbls) of oil, and water is pumped out of the ballast tanks 130 to reduce the ballast weight to 32,600 tons. Under the third load condition in row 306, i.e., the full load condition, the floating vessel 100 is fully loaded with a cargo volume of 1,400,000 barrels, and the ballast tanks 130 and the bulges or sponsons 120 are empty.
[0028] Figure 4 shows Figure 1B the conventional hull 12 of the floating vessel 10 shown, and Figure 2 the resonance and optimized roll response amplitude operator (RAO S ) of the asymmetric floating vessel 100 shown, compared with the wave energy distribution within the wave period in FIG. 400. Curve 452 represents the wave spectrum under the design conditions. This example shows a typical double-model wave spectrum of sea waves and swells. Curve 454 represents Figure 1B the variation of the roll RAO of the conventional hull 12 of the floating vessel 10 shown with respect to the wave period, and curve 456 represents Figure 2 the roll RAO of the floating vessel 100 shown. As Figure 4 shown, the maximum energy wave period of the swell is in the range of 12 - 18 seconds, and the wave energy density peaks at around 15 seconds, while the peak period of the roll RAO of the conventional hull 12 of the floating vessel 10 (as Figure 1B shown) is also about 15 seconds. This results in high-amplitude roll motion of the conventional floating vessel, which in turn leads to increased structural fatigue, production non-conformance, and frequent handling of shutdowns, ultimately resulting in long-term downtime of the conventional floating vessel. As Figure 2 shown, the natural roll period of the asymmetric floating vessel 100 at the peak of the roll RAO is about 19 to 21 seconds, which is higher than the swell period range. The floating vessel 100 effectively avoids the resonant roll motion of the vessel caused by the swell. Generally speaking, for a turret mooring system, the natural roll period should be 2 - 3 seconds higher than the peak period of the most adverse wave environment, and for a spread mooring system, the natural roll period should be 3 - 5 seconds higher than the peak period of the most adverse wave environment. The design of the floating vessel 100 is suitable for both systems.
[0029] The dynamic design principle of the floating vessel 100 can be expressed by the following mathematical formula to calculate the natural roll period of the vessel:
[0030]
[0031] Where:
[0032] T is the natural period of the roll motion of the floating vessel;
[0033] I is the inertia of the roll motion of the floating vessel;
[0034] a is the additional inertia caused by the roll motion;
[0035] ρ is the density of seawater;
[0036] g is the acceleration due to gravity;
[0037] is the displacement of the vessel;
[0038] GM is the metacentric height.
[0039] Referring to the above formula, due to the raised portion or sponson 120, the hull 110 is asymmetric, so the natural period of the rolling motion of the floating vessel 100 is effectively increased due to the increase in additional inertia. The design of the hull 110 of the floating vessel 100 is configured to avoid resonant ship rolling motion under the wave conditions at a specific location. It is necessary to identify the natural period of the ship and achieve the target natural period by determining and optimizing the main dimensions of the hull 110 and the dimensions of the raised portion or sponson 120.
[0040] Figure 5 Shows Figure 3 under various load conditions as shown Figure 2 Table 500 of the exemplary roll natural period values of a conventional floating vessel and the optimized asymmetric floating vessel 100 in. The readings in the table are obtained by performing a motion analysis on a conventional floating vessel and a floating vessel 100 with an asymmetric hull 110. Under various load conditions, i.e., ballast, intermediate load, and full load, as Figure 1B shown, the natural period of the conventional hull 12 of the floating vessel 10 is about 15 seconds. However, the natural period of the floating vessel 100 is about 19 seconds. As mentioned above, the natural period of the conventional floating vessel coincides with the swell period range, and there is a problem of resonant ship rolling motion caused by swells. On the other hand, the natural period of the floating vessel 100 effectively avoids the swell period range, avoiding the resonant ship rolling motion caused by swells.
[0041] The asymmetric floating vessel 100 with optimized motion performance has many beneficial effects. It minimizes the possibility of ship motion exceeding the standard, thus providing a larger window of operability and usability, such as handling plant operations, unloading operations, crew comfort, and helicopter operations. It can also minimize the fatigue caused by cumulative motion, thereby reducing the maintenance and repair of handling, structures, risers, and mooring systems. It reduces the frequency of unqualified production and process downtime. Overall, the problems and issues that result in a significant loss of productivity and net present value (NPV) of the floating vessel throughout its life cycle are alleviated.
[0042] Those skilled in the art should understand that the features described in one example may not be limited to that example and may be combined with any other example.
[0043] The present invention relates to an asymmetric single-hull ship for floating operations, generally as described, referenced, and / or shown herein in the accompanying drawings.
Claims
1. An asymmetric catamaran for floating production, comprising: A hull, the hull including a raised portion or sponson on one side of the hull, wherein the raised portion or the sponson is configured to provide additional buoyancy to the floating vessel to counteract a lateral imbalance load offset to the one side of the hull, and wherein the raised portion or the sponson is further configured to act as an effective roll motion reduction attachment to optimize the roll motion performance of the floating vessel.
2. The floating ship according to claim 1 further includes a ballast tank within the hull, wherein, The raised portion or the sponson is in fluid communication with the ballast tank.
3. The floating ship according to claim 1, wherein, The floating vessel further includes a riser platform extending from the one side of the hull, wherein the lateral imbalance load includes a riser load, and wherein the riser platform is for attaching risers and supporting the riser load.