Liping Sun

Bio: Liping Sun is an academic researcher from Harbin Engineering University. The author has contributed to research in topics: Mooring & Frequency domain. The author has an hindex of 4, co-authored 26 publications receiving 63 citations.

The Simulation of Dropped Objects on the Offshore Structure

Abstract: Dropped objects accidents frequently happen during offshore structures operating. In this paper models of dropped objects on the platform were built to simulate the whole falling process by nonlinear FEM software. The shape of dropped objects, the horizontal velocity of dropped objects, dropped into water, different boundary conditions etc. were considered. The safety and feasibility of an approximate method that simplified a stiffened plate into an equivalent panel were also discussed. According to the simulation, it is found that the effective contact area, the velocity of the dropping objects and dropping position are the main factors to the safety of the structure. The simulation with the Fluid-Solid approach was also be verified to be more conservative. Based on the calculation results, it’s proved that the simplified equivalent panel can not be substituted for the stiffened plate, because the girders and stiffeners on the plate promote the crashworthiness of the plate.

Truncation Design and Model Testing of a Deepwater FPSO Mooring System

Abstract: Limitation of offshore basin dimensions is a great challenge for model tests of deepwater mooring system. The mooring system cannot be modeled entirely in the basin with a reasonable model scale. A classical solution is based on hybrid model tests for the truncated mooring system. An efficient truncation method is proposed in this paper taking advantage of the mechanical characteristics of catenary mooring system. Truncation procedures are presented both in vertical and horizontal directions. A turret moored floating production storage and offloading (FPSO) is analyzed, and its mooring system is truncated from the original 914 m water depth to 736 m and 460 m, respectively. Numerical simulations are performed based on catenary theory and lumped mass model to these three systems, including the original untruncated system and two truncated systems. The static characteristics and dynamic response are investigated, and the results are compared between the truncated and untruncated system, and good agreements are obtained, verifying the preliminary truncation design. Model tests are conducted to the three mooring system configurations in the deepwater basin of the Harbin Engineering University. The static and dynamic properties are found to be mostly consistent between the untruncated system and two truncated systems, except for some discrepancy in 460 m system. It indicates that the truncation design is successful when the truncation factor is large, while difference still exists when the truncation factor is small. Numerical reconstruction to the model test in 460 m and extrapolation to 914 m are also implemented. The results are found to be consistent with those in 914 m, verifying the robustness and necessity of the hybrid model testing, especially for the mooring system with large truncation.

Dynamic truncation method for mooring lines with tension estimation combined in the time and frequency domains

Abstract: An improved truncation method for a deepwater mooring system based on the dynamic similarity of the mooring line in the time domain is proposed in this paper. The optimisation algorithm NSGA-II (non-dominated sorting genetic algorithm) is combined with the slender rod model to optimise the mooring line parameters in the static and dynamic analysis of the truncated system. A reliable fitness function is created in the frequency domain by transferring the mooring forces from the time domain with FFT, which makes the dynamic similarity between the truncated and full-depth mooring systems available and effective. An floating production storage and offloading unit (FPSO) mooring system working in 1500 m water depth is truncated to 1050 m and 700 m. The harmonic forced motions as well as the global response and mooring forces of the mooring system under irregular waves are consistent with each other across different water depths, thereby validating the proposed truncation method.

Model test and coupled dynamic analysis of a deepwater fpso with internal turret mooring system

Abstract: Model test is an effective way to verify numerical dynamic analysis of floating system. The diffraction and radiation analysis is carried out in frequency domain based on potential theory to predict motion response of rigid platform. The quasi static and dynamic methods are usually adopted to simulate mooring system, which determines if the whole system is coupled within the analysis. Here model tests are performed to indicate the accuracy of potential theory and quasi static and dynamic methods for the whole system. A FPSO is tested under regular waves to find its RAO. The FPSO with internal turret mooring system under irregular wave, wind and current are also studied in the deepwater basin of Harbin Engineering University. The results are compared between the model test and numerical models, which show the model test results agree well with the coupled numerical model, while the maximum mooring tensions are under estimated in quasi static analysis.

Offshore floating vertical axis wind turbines, dynamics modelling state of the art. Part II: Mooring line and structural dynamics

Abstract: The need to exploit enhanced wind resources far offshore as well as in deep waters requires the use of floating support structures to become economically viable. The conventional three-bladed horizontal axis wind turbine may not continue to be the optimal design for floating applications. Therefore it is important to assess alternative concepts in this context that may be more suitable. Vertical axis wind turbines (VAWTs) are a promising concept, and it is important to first understand the coupled and relatively complex dynamics of floating VAWTs to assess their technical feasibility. As part of this task, a series of articles have been developed to present a comprehensive literature review covering the various areas of engineering expertise required to understand the coupled dynamics involved in floating VAWTs. This second article focuses on the modelling of mooring systems and structural behaviour of floating VAWTs, discussing various mathematical models and their suitability within the context of developing a model of coupled dynamics. Emphasis is placed on computational aspects of model selection and development as computational efficiency is an important aspect during preliminary design stages. This paper has been written both for researchers new to this research area, outlining underlying theory whilst providing a comprehensive review of the latest work, and for experts in this area, providing a comprehensive list of the relevant references where the details of modelling approaches may be found.

Experimental Study on Motion Characterisation of CALM Buoy Hose System under Water Waves

Abstract: The application of marine bonded hoses has increased in recent times, due to the need for more flexible conduits and flexible applications in the offshore industry. These marine structures include Catenary Anchor Leg Moorings (CALM) buoys and ocean monitoring buoys. Their attachments include floating hoses, submarine hoses and submarine cables. However, the structural performance challenges of a CALM buoy system from its hydrodynamics water waves and other global loadings, have led to the need for this investigation. In this study, a detailed presentation on the motion characterisation of the CALM buoy hose system is presented. The CALM buoy is a structure with six degrees of freedom (6DoF). A well-detailed experimental presentation on the CALM buoy hose model conducted in Lancaster University Wave Tank is presented using three novel techniques, which are: a digital image captured using Imetrum systems, using an Akaso 4K underwater camera, using wave gauges arranged in a unique pattern and using underwater Bluetooth sensors. The buoy model was also found to respond uniquely for each motion investigated under water waves. The results showed that the higher the profile, the higher the response of the buoy. Thus, this study confirms the existence of flow patterns of the CALM buoy while floating on the water body.