Numerical and experimental analysis on motion performance of new sandglass-type floating body in waves

Outline

• Abstract
• Keywords
• 1. Introduction
• 2. Description of New Sandglass-Type Fpso
• 3. Effects of Shape Parameters on Motion Performance of Sandglass-Type Model
• 3.1. Sandglass-Type Shape and Numerical Model of Floating Body
• 3.2. Hydrodynamic Analysis of Floating Models with Different Parameters
• 4. Further Discussion on Heave Motion Performance of Sandglass-Type Floating Body
• 4.1. Influence of Viscous Damping and Nonlinear Stiffness on Heave Motion Rao
• 4.2. Deduction for Estimation Expression of Frequency Versus Minimum Heave Motion Rao
• 4.2.1. Heave Incident Wave Force
• 4.2.2. Heave Diffraction Wave Force
• 4.2.3. Frequency Versus Minimum Heave Motion Rao
• 4.3. Design Guideline and Scheme of Floating Body
• 5. Validation of Test Cases and Discussion
• 5.1. Verification for Design Guideline and Scheme of Sandglass-Type Floating Body
• 5.2. Comparison of Cylindrical and New Sandglass-Type Floating Models
• 5.2.1. Motion Performance Raos of Two Floating Models
• 5.2.2. Motion Response of Two Floating Models in the Sea Condition of Once in a Year
• 5.2.3. Stability of Two Floating Models
• 6. Conclusion
• Acknowledgment
• References

Conclusions

In order to solve the performance limitations of traditional ship-type and cylindrical FPSO, this paper presents a new concept FPSO with innovative sandglass-type floating body. Then the hydrodynamic performances of new floating model are studied by the qualitative and quantificational analysis. Furthermore, based on the design scheme and functions of cylindrical FPSO “Sevan Piranema”, a new sandglass-type floating body can be achieved and discussed by numerical and experimental methods. Finally, many useful conclusions can be made as follows.

1. The engineering estimation expressions of heave wave excitation force and frequency corresponding to the minimum heave motion RAO are derived by potential flow theory. Furthermore, the relative error between estimation results and numerical solutions is less than 10%, which shows that the engineering estimation expression can meet the precision requirement of practical engineering and it will be further chosen as a design guideline to control the heave motion performance of sandglass-type floating body.

2. Based on the guideline and scheme, a new sandglass-type floating body is designed and compared with “Sevan Piranema” cylindrical model by numerical and experimental methods.

3. The design of sandglass-type floating body can make the maximum peak of heave motion RAO away from the frequency bandwidth of wave spectrum with high energy, and thus can significantly improve the heave motion performance. For the full-load FPSO under sea condition of once in a year, the new model can reduce to about 1/3the heave motion response of cylindrical model. Furthermore because the FPSO with drilling function is much concerned about the heave motion response, therefore the shape design of sandglass-type model in this paper can provide a potential effective solution to improve the heave motion performance of FDPSO.

4. The design of sandglass-type floating body can greatly increase added mass and radiation damping of pitch (roll) motion, which can effectively restrain the occurrence of maximum peak in the high wave frequency and thus improve the pitch motion performance. For the full-load FPSO under sea condition of once in a year, the new sandglass-type model can decrease by about 50% the pitch motion response of cylindrical model. Therefore the new floating model can not only efficiently improve both the working performance and the safety of FPSO but also reduce the difficulty of COG control in the general arrangement.

5. The design of sandglass-type floating body can not only achieve smaller natural frequency of pitch motion but also provide the larger maximum restoring moment and endure the larger limiting wind moment. Thus the new floating model can support better stability characteristic for severe deep-water environment.

In summary, the design scheme of sandglass-type floating body in this paper is effective and valid, which can take the maximum peak of heave motion RAO away from the concentration zone of wave energy. Thus the new sandglass-type floating body based on the design scheme can significantly improve the performance (heave motion, pitch motion, stability, etc.), and thus can be applied in deepwater oil and gas exploitation as an efficient engineering platform. Furthermore, this paper tentatively introduces the control and optimization of hydrodynamic performance into the shape design of floating body, which can form a more scientific and reasonable design guideline and scheme to provide the reference and experience for the design of other ocean floating structures.