Study On Sloshing And Slamming Load In The Tank Design Of The FLNG System

Recently, a new development mode for liquefied natural gas (LNG) in the deep water or marginal gas fileds has attracted considerable attention in both the offshore gas exploration industry and academia. Since China plans to develop deepwater gas exploitation, it has a potential application in South China Sea. To produce, liquefy, store and transfer LNG, floating liquefid natural gas (FLNG) facility is one of the most important equipments in the new development mode. But there is no FLNG built. And only a few numbers of foreign companies have the abilities to design and manufacture FLNG. China needs to develop the corresponding technology to build its own FLNG.The main goals of this research are to study the slamming load in the large-scaled tank, the tank design of FLNG system and the suppression of slamming. The main work and the corresponding conclusions are summarized as follows:1 Experimental investigation of slamming load in the large-scaled tankExperimental approach is efficient and accurate to reveal the complicated physical phenomenon during liquid slamming. Due to the compressibility of liquid and gas, slamming load instantaneously increases dramatically. So, accurate measurement of the impact pressure is one of the key issues in experimental investigation. In this study, a large-scale platform and large-scale model tanks (rectangular tanks and GTT tanks) were employed. Furthermore, the measurement of slamming pressure was investgated. The uncertainty analysis of the measured pressure was conducted to make sure the results were accurate and reliable. According to the temporal and spatial distributions of impact pressure, the pressure monitoring module was designed to measure the impact pressure. The aboved research provides a reference to select pressure sensors and arrange their positions in the large-scaled sloshing model test.2 Experimental investigation of the effect of model size on slamming phenomena in GTT tanksDue to the complicated physical phenomena during liquid slamming, the effect of model size on slamming phenomena and slamming parameters remain unclear. Furthermore, one of the challenges in the model text is how to properly transfer the slamming load from model scale to prototy scale. Many scholars consider the Froude law is conservative for estimating the slamming force in the tanks. But this idea has not been proved by experiments. In this study, the non-similarity sloshing-induced slamming in the geometric similar GTT type tank was investigated. The effect of model size on the slamming phenomena and slamming force were analyzed. Then, it is found that Froude law is conservative for estimating the slamming force in the tanks from a statistical point of view.3 Experimental investigation of slamming load in the two-dimensional rectangular tankThe slamming load in the two-dimensional rectangular tank was experimentally studied. The effect of excitation parameters on the slamming load subjected to regular motion was investigated. Based on the slamming pressure from the experiments under long-time irregular excitation, the characteristics of slamming load were studied. According to the occurence of slamming, the corresponding slamming pressure peak and impact time were obtained. Then, a simplifid triangular time history of the impact pressure was quantitatively given. This load model could be a load reference for the LNG tank structural analysis.4 The study of tank design for GTT NO96According to the conceptual design of the GTT NO96 membrane tank and the conclusions form the aboved two chapters, numerical method was applied to study the shape and dimension of the tank. From the perspective of reducing the sloshing load, the optimal corner type and the optimal position of the corner were provided. According to the results mentioned, a new tank, which could reduce the sloshing load and satisfy the requirement of the tank capacity at the same time, was proposed. In order to avoid the slamming, the lowest natural frequency of the free surface in the tank should be far away from the frequency of the ship motion. Therefore, the reasonable range of the tank dimension and the optimized dimension of one tank were given.5 Experimental investigation of the mechanism of suppressing shallow-water slamming with centralized slat-screens of high solidity ratiosThe investigation of suppression the free-surface elevations and slamming pressures in shallow-liquid conditions with a large forcing amplitude were experimentally studied. A new wave system scenario has been recognized and characterized for a small forcing period and large amplitude for the clean tank and the tanks with four considered screens. This result extends the existing wave scenarios in a sloshing tank under shallow-water depth conditions and provides a new stress form of the slat-screen. Furthermore, it was experimentally found that the slat-screens of high solidity ratio could effectively reduce the free-surface elevation and suppress slamming load on the sidewalls in the applied forced frequency range. Our finding suggests that an optimal solidity ratio is approximately 0.6-0.7 for the applied filling level and excitation amplitude in the examined forced frequency range.The conclusions of this thesis have potential applications in areas such as swash bulkhead design and liquefied-cargo tank design in the FLNG facilities.