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

Numerical analysis of point absorber for wave energy conversion in Malaysian seas

Wave energy conversion by using point absorber has recently gained intensive research in renewable energy. However, a majority of research works only focused on the regions with high wave heights, which may not be readily achievable in Malaysian seas condition. As the technology of point absorber facing the concern on less-applicability in low wave height conditions in Malaysia, a numerical modeling to understand the maximum potential power output to be generated by point absorber is now in demand to predict the power capture ability of point absorber in Malaysian waters. In order to complete this research gap, this paper is aiming to determine the sensitivity of different configurations of power take-off system in point absorber and to numerically analyze the potential maximum power output to be generated by the point absorber in Malaysian water, under regular wave motion. The significance of this study leads to a better understanding of the envelope of power output generated by point absorber in Malaysian seas. The methodology is conducted with theoretical modeling of point absorber, developing a numerical model of power take-off system to identify the maximum magnetic flux density of different stator-translator configuration, and simulating the power output of point absorber in time-domain under regular wave condition based on Malaysia seas data. The results show that power output of point absorber can be increased by a double-sided stator. The envelope of maximum power output to be generated has been identified. This research provides a further understanding of the development of point absorber technologies in Malaysian seas condition

Wave energy for electricity generation in Malaysia - Merang shore, Terengganu

Malaysian government introduced Small Renewable Energy Power (SREP) Program in 2001. In this paper, it dis cussed the possibility to utilize ocean wave in Merang shore, Terengganu, Malaysia. Besides, this paper also discusses the current technologies have been used to convert wave energy to electricity. The work principle of the devices also present in this paper. After that, sea condition in Malaysia was explored to study the possibility of utilization of wave energy in Malaysia. Finally, It is found Merang shore is the idea location to utilize the wave energy in Malaysia. Mean wave height and mean wave period at the location are 0.95 meter and 3.5 second. Also, attenuator type wave converter developed by Wave Star was considered as one of the possible devices to install at the location. From the calculation, the research obtained that the total r ate of electrical power possible to grid is 649 MWh a year if only on e set of C5 Wave star device install at Merang shore, Terengganu

Stability of mobile floating harbor container crane

Stability of the mobile floating harbor is an important criterion to avoid an accident in port operation during lifting, loading, and uploading container. The stability of a mobile floating harbor which completed with a container crane was analyzed by study the structure's rolling amplitude at several sea conditions. Factors considered in the study as follows: size and height of crane and the location of the container during loading and unloading. The mobile floating harbor was constructed using a semi-submersible model on a scale of 1:70 with a specified gantry crane with maximum outreach length 65 meters (Actual size). Using the model, inclining test, swing and oscillating tests was carried out to obtain hydrostatic particulars. By using the experimental result, the roll amplitude for several sea conditions was simulated using the Morison equation. The simulation results showed that the highest roll amplitude occurs when the crane for mobile floating harbor loaded with container in any sea condition

Gap distance analysis of floating structures in tandem arrangement

This paper proposed an empirical method to predict the minimum gap between two floating structures in tandem arrangement. The minimum distance is the shortest distance between two structures achieved due to surge motions induced by wave. This proposed empirical equation is created based on the experimental data between TLP and Semi-submersible. The experimental results indicate that the minimum gap length between TLP and Semi-submersible is highly depended on the structures' response. The empirical equation developed here is to estimate the minimal gap between structures in the functions of structures' response, wave height, wavelength and initial gap distance. Besides, this empirical method was shown well fixed with experimental results. The result showed that gap between structures changes in non-linear function to the wavelength. Finally, this suggested equation also can be used to define the safety of structures' arrangement in preliminary study

Identification of hazardous encounter scenarios using AIS data for collision avoidance system testing

The rise of artificial intelligence and advanced automation techniques have supported the development of Maritime Autonomous Surface Ships (MASS). Countries and companies are competing and collaborating to become leaders in this arising market. The Collision Avoidance System (CAS) replicates the human operator with its decision-making ability to ensure navigational safety of MASS. The CAS employs advanced algorithms to implement a wide spectrum of functions from collision avoidance to route optimization. However, the verification of the CAS dependability is highly reliant on the coverage of implemented scenarios during testing, which directly influences its trustworthiness. Scenarios in previous research from manually designed approaches have a limited coverage, while those from simulation-based approaches based on algorithms are disconnected from the scenarios occurring in the actual operational contexts. Others from real data-based approaches using Automatic Identification System (AIS) data propose an unbearably large number of scenarios. Considering that critical risk scenarios can constitute the basis for the development of CAS testing, this study proposes a method for identifying critical encounter scenarios based on AIS data. The method uses safety indices to identify hazardous encounter scenarios. Then, a muti-ship encounter scenario classification method based on COLREGs is proposed to categorize these scenarios. For each category, the risk value of each scenario is evaluated by Time-varying Risk Vectors (TRV). Scenarios with the lowest and highest risk are then used as representative for the whole. In this study, AIS data from Singapore Strait covering one month of operation is used for scenario identification. The results are discussed indicating good effectiveness in identifying critical scenarios in water area.Peer reviewe