Numerical modelling for hydrodynamic behavior of round shape FLNG interacting with LNG carrier

The diffraction potential theory is an efficient and accurate method to predict the hydrodynamic characteristic of a large floating structure. However, this theory under-estimates the damping coefficient as the viscous effect is ignored. This weakness causes the diffraction potential theory to be less accurate in predicting the motion of floating structure in damping dominant region. Therefore, this research aims to propose a method to improve the estimation of hydrodynamic characteristic of free floating round shape Floating Liquefied Natural Gas (FLNG) carrier when it is alone and when it is interacting with another structure which is arranged in parallel head-sea condition. The proposed method was developed by modifying the diffraction potential theory and improving with the application of drag equation. The proposed method was also further developed by using motion’s energy dissipation concept and Huygens Principle to predict the influence of wave generated by the motion of nearby structure to the response amplitude operator (RAO) of the FLNG. To validate the proposed method, motion experiments in regular wave were conducted in selected conditions. Comparative study was also conducted by using FLNG’s RAO result predicted by ANSYS AQWA software. Over-estimation of peak heave RAO of single FLNG case is reduced from 2.42 to 1.74 by the proposed method as the method considered the viscous damping in its calculation. In interaction cases, the peak heave RAO is increased to 2.1 due to the effect of radiating waves. Besides, the interaction effect also induces sway and roll motion. The peak sway RAO estimated by both proposed method and experiment is around 0.22. The interaction effects on heave RAO and roll RAO are stronger around the motions' natural period as the damping coefficients are reduced around motion natural period. The research results showed that the proposed method improved the accuracy of the simulation by reducing the amount of over-prediction on the floating structure’s RAO in damping dominant region

Risk assessment of building fire evacuation with stochastic obstructed emergency exit

Fire evacuation simulation for buildings has greatly enhance the safety of escaping efficiently and give valuable insight for better layout permutation. The aim of this article is to evaluate the safety risk of fire evacuation given a random chance that emergency exits are obstructed. A case study of evacuation pathway was evaluated against fire safety codes and practices in Malaysia. AnyLogic was used to simulate fire evacuation, assuming peak occupancy, with three randomly obstructed emergency exit pathways. Results show that though the floorplan fulfils safety criteria, the risk was high which requires adjustment. Monte Carlo analysis indicates the performance of risk of obstruction of all three emergency exits at one percent probability. Risk assessment points to the need of a minimum number of emergency exits by floor area per exit basis and a reconfiguration of floorplan layout

Sloshing in a closed domain under unidirectional excitation

1145-1153Sloshing is a phenomenon where a partially filled tank is exerted into various environmental sea conditions, such as wave and wind. Sloshing in a tank of liquefied natural gas carrier can lead to structural damage of tank structures and motion instability of the carrier. Thus, sloshing analysis needs to be conducted beforehand to minimize the risk of damages. This paper presents experimental and numerical study on sloshing phenomenon in a prismatic membrane tank model under unidirectional excitation with 30% water filling condition. A regular wave motion stimulated by the linear actuator was applied to the model tank and recorded by a video camera. Meanwhile, OpenFoam software was used to simulate the sloshing numerically in a volume of fluid method based on Navier-Stokes theorem. The sloshing patterns and free surface elevation in the prismatic membrane model tank, with the same input amplitude and frequency, were investigated for both cases. Both experimental and simulation results showed reasonable agreement on the sloshing profile, while the internal free surface elevation in the closed domain indicated a deviation with maximum absolute error of 4.9 cm

Dynamic behavior of water intake riser for ocean thermal energy conversion system

Renewable energy has been regarded as an alternative to generate electricity. One of the examples for this energy is the Ocean Thermal Energy Conversion (OTEC) system which harnesses the temperature difference between sea surface and deeper ocean layer. Most research on OTEC is related to system efficiency but does not address the behavior of subsystem such as its water intake riser (WIR). Thus, this research aims to identify the dynamic behavior of water intake riser in terms of its vertical displacement and tension in order to investigate the sensitivity of key parameters of water intake riser design. The study covers the dynamic behavior of a derived mathematical model with reference to its vertical displacement and tension ratios result in which the length of the riser needs to be suitably designed particularly during the riser excitation period. A stiffer material of the riser has to be selected to obtain small vertical displacement and tension ratios while the diameter of the WIR only needs to be taken into account if the efficiency of the OTEC is of major concern. This study could aid in designing the suitable WIR to be implemented for the OTEC system

Experimental Scours by Impinging Twin-Propeller Jets at Quay Wall

Experiments were conducted to investigate the seabed scour holes due to the interaction between the twin-propeller jet and quay wall. Vertical quay wall was modelled by using a polyvinyl chloride (PVC) plastic plate in a water tank. The relationship between the positions of the propeller and the vertical quay wall was designed according to the actual working conditions of a ship entering and leaving a port. Propeller-to-wall distance and rotational speed were changed to observe the various scour conditions. The scour depth was measured by using an Acoustic Doppler Velocimeter (ADV). Primary scour hole was found within the jet downstream and secondary scour hole occurred beneath of the propeller. Third scour hole was found close to the quay wall due to horseshoe vortices. The maximum scour position of this third scour hole was found at the jet centre near the quay wall. Temporal formation of scour holes can be divided into three stages: axial scour formation, obstructed scour expansion and equilibrium stages. The quantitative relationships for six characteristic parameters of the scour pit were established including the maximum scour depth (εmax,q), maximum scour depth position (Xm,q), maximum scour width (Wm,q), length of main scour pit (XS,q), maximum deposition height (ZD,q), and location of maximum deposition height (XD,q)