• Journal of the Society of Naval Architects of Korea
• /
• v.48 no.5
• /
• pp.451-456
• /
• 2011

To ensure structural integrity of membrane type LNG tank, the rational assessment of the sloshing impact responses of tank structures should be preceded. The sloshing impact pressures acting on the insulation system of LNG tank are typical irregular loads and the resulting structural responses show very complex behaviors accompanied with fluid structure interaction. So it is not easy to estimate them accurately and immense time consuming calculation process would be necessary. In this research, a simplified method to analyse the dynamic structural responses of LNG tank insulation system under pressure time histories obtained by sloshing model test or numerical analysis was studied. The proposed technique based on the concept of linear combination of the triangular response functions which are the transient responses of structures under the unit triangular impact pressure acting on structures. The validity of suggested method was verified through the example calculations and applied to the dynamic structural response analysis of a real Mark III membrane type insulation system using the sloshing impact pressure time histories obtained by model test.

• Journal of Ocean Engineering and Technology
• /
• v.31 no.5
• /
• pp.357-363
• /
• 2017

The sloshing pressure acting on a membrane-type LNG CCS is a typical irregular impact load, and the structural response of a tank system induced by sloshing also shows very complex behavior, including fluid structure interaction. Therefore, it is not easy to accurately estimate the sloshing impact pressures and resulting structural response. Moreover, a huge time consuming process to deal with the enormous pressure data obtained during a model tank test and the following structural analysis would be inevitable. To reduce the computation time for structural analysis, in this study, a rational structural modeling strategy was considered, and a simplified scheme to analyze the dynamic structural responses of an LNG CCS was introduced, which was based on the concept of the linear combination of the triangular response functions obtained by a transient response analysis of structures under unit triangular impact pressure. A structural analysis of a real Mark III membrane type insulation system under the sloshing impact pressure time histories obtained by model tests was performed using the various proposed structural models and simplified analysis scheme. The results were investigated in detail, including the elastic support effects of the hull structure.

• Journal of Ocean Engineering and Technology
• /
• v.26 no.4
• /
• pp.50-56
• /
• 2012

When a liquid cargo tank is partially filled with fluid, internal impact loads can be occurred from the vessel's motions. In this study, liquid sloshing problems with a thin top layer of particles with a lighter density than water and the coupling effects of the liquid-sloshing/vessel-motion were investigated in order to reduce the sloshing-induced impact loads. The PNU-MPS (Pusan-National-University-modified Moving Particle Simulation) method for solving the liquid motion inside a tank and the CHARM3D BEM (Boundary Element Method) based time-domain ship motion analysis program for vessel-motion simulation were coupled. From the simulation results, we could see that the floaters seemed to be quite effective at reducing the sloshing impact loads in the case of tank-only sloshing problems, but not as much for the coupling problem with vessel motion.

• Journal of the Society of Naval Architects of Korea
• /
• v.50 no.6
• /
• pp.390-398
• /
• 2013

In this paper, an experimental study on sloshing problems in an independent B-type tank of STX Offshore and Shipbuilding Co. is described. Recently STX Offshore and Shipbuilding Co. introduced a new design of an independent B-type tank in order to reduce sloshing impact loads on LNG CCS. This tank has many internal members, so that sloshing flow and the resultant hydrodynamic loads are very different from those in typical membrane tanks. In this study, a series of sloshing experiment have been carried out for 1/50 scale model, and the main characteristics of sloshing load on the independent tank are observed. The properly scaled internal members such as swash bulkhead, center bulkhead and stringers have been installed in the test tank model, but sloshing pressures are measured on the tank walls only. The forced excitation signals have been generated by using the predicted ship motion in irregular sea states. The characteristics of sloshing loads on this tank have been observed in different filling levels with various heading angles, and sea states. In this paper, some key findings from the model tests are discussed.

• Journal of Ocean Engineering and Technology
• /
• v.26 no.1
• /
• pp.54-59
• /
• 2012

This study presents investigation on ullage effect in sloshing experiment. The experiment was done with two dimensional tank. Sloshing experiments were carried out in the tank with 6 different ullage pressures. The tested filling ratio was 30% of the tank height. The flow field was recorded with high speed camera. The sloshing impact pressure were measured at 18 locations. It was shown that the variation of ullage pressures influences the magnitude of pressure and flow field. This study demonstrated the importance of ullage pressure in sloshing test.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.35 no.5
• /
• pp.299-308
• /
• 2022

This study was conducted to predict the tendency for heat exchange and boil-off gas (BOG) in a liquefied hydrogen tank under sloshing excitation. First, athe fluid domain excited by sloshing was modeled using a multiphase-thermal flow domain in which liquid hydrogen and hydrogen gas are in the saturated state. Both the the volume of fluid (VOF) and Eulerian-based multi-phase flow methods were applied to validate the accuracy of the pressure prediction. Second, it was indirectly shown that the fluid velocity prediction could be accurate by comparing the free surface and impact pressure from the computational fluid dynamics with those from the experimental results. Thereafter, the heat ingress from the external convective heat flux was reflected on the outer surfaces of the hydrogen tank. Eulerian-based multiphase-heat flow analysis was performed for a two-dimensional Type-C cylindrical hydrogen tank under rotational sloshing motion, and an inflation technique was applied to transform the fluid domain into a computational grid model. The heat exchange and heat flux in the hydrogen liquid-gas mixture were calculated throughout the analysis,, whereas the mass transfer and vaporization models were excluded to account for the pure heat exchange between the liquid and gas in the saturated state. In addition, forced convective heat transfer by sloshing on the inner wall of the tank was not reflected so that the heat exchange in the multiphase flow of liquid and gas could only be considered. Finally, the effect of sloshing on the amount of heat exchange between liquid and gas hydrogen was discussed. Considering the heat ingress into liquid hydrogen according to the presence/absence of a sloshing excitation, the amount of heat flux and BOG were discussed for each filling ratio.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2011.04a
• /
• pp.544-551
• /
• 2011

As the cargo tank size and configuration of Liquefied Natural Gas carriers(LNGC) grows in response to the global increase in demands for LNG and the necessities of its economical transportation, impact loading from sloshing may become one of the most important factors in the structural safety of LNG Cargo Containment Systems(CCS). The objective of this study is to demonstrate the procedure of the structural safety assessment of MARK III membrane type CCS under sloshing impact loading using local zooming analysis technique of LS-DYNA code.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.15 no.1
• /
• pp.147-154
• /
• 2002

The dynamic load caused by sloshing of internal fluid severely affects the structural and control stabilities of cylindrical liquid containers accelerating vertically. If the sloshing frequency of fluid is near the frequency of control system or the tank structure, large dynamic force and moment act on launching vehicles. For the suppression of such dynamic effects, generally flexible ring-type baffles are employed. In this paper, we perform the numerical analysis to evaluate the dynamic suppression effects of baffle. The parametric analysis is performed with respect to the baffle inner-hole diameter and two different baffle spacing types : equal spacing with respect to the tank and one with respect to the fluid height. The ALE (arbitrary Lagrangin-Eulerian) numerical method is adopted for the accurate and effective simulation of the hydrodynamic interaction between fluid and elastic structure.

• Journal of the Society of Naval Architects of Korea
• /
• v.50 no.2
• /
• pp.120-128
• /
• 2013

This paper presents the results of sloshing experiments having different fluids in model tanks with various density ratios. The experimental model consisting water and air at ambient, which has been commonly used, is not consistent in density ratio with that of an actual LNG cargo tank. Therefore, an advanced experimental scheme is developed to consider the same density ratio of LNG and NG by using a mixed gas of sulfur hexafluoride ($SF_6$) and nitrogen ($N_2$). For experimental observation, a two-dimensional model tank of 1/40 scale and a three-dimensional model tank of 1/50 scale have been manufactured and tested at various conditions. Two different fillings with various excitation frequencies under regular motions have been considered for the two-dimensional model tank, and three different filling levels under irregular motions have been imposed for the three-dimensional model tank. The density ratio between gas and liquid varies from the ratio of the ambient air and water to that of the actual LNG cargo container, and the different composition of gas is used for this variation. Based on the present experimental results, it is found that the decrease of sloshing pressure is predicted when the density ratio increases.

• Journal of Ocean Engineering and Technology
• /
• v.29 no.2
• /
• pp.154-162
• /
• 2015

In this study, experimental and numerical methods were applied to observe sloshing impact phenomena. A two-dimensional rectangular tank filled with water and air was considered with a specific excitation condition that induced a hydrodynamic impact without an air pocket at the top corner of the tank. High-speed cameras and a pressure measurement system were synchronized, and a particle image velocimetry (PIV) technique was applied to measure the velocity field and corresponding pressure. The experimental condition was implemented in a numerical computation to solve incompressible two-phase flows using a Cartesian-grid method. The discretized solution was obtained using the finite difference and constraint-interpolation-profile (CIP) methods, which adopt a fractional step scheme for coupling the pressure and velocity. The tangent of the hyperbola for interface capturing (THINC) scheme was used with the weighed line interface calculation (WLIC) method to capture the interface between the air and water. The calculated impact pressures and velocity fields were compared with experimental data, and the relationship between the local velocity and pressure was investigated based on the computational results.