Research on Energy Efficiency Design Index for Sea-going LNG Carriers

This paper describes the characteristics of liquefied natural gas （LNG） carriers briefly. The LNG carrier includes power plant selection, vapor treatment, liquid cargo tank type, etc. Two parameters fuel substitution rate and recovery of boil of gas （BOG） volume to energy efficiency design index （EEDI） formula are added, and EEDI formula of LNG carriers is established based on ship EEDI formula. Then, based on steam turbine propulsion device of LNG carriers, mathematical models of LNG carriers＇ reference line value are established in this paper. By verification, the EEDI formula of LNG carriers described in this paper can provide a reference for LNG carrier EEDI calculation and green shipbuilding.

Quantitative Analysis of Frosting Characteristics on the Drip Tray of A Cryogenic Valve for LNG Ships

Cryogenic valves play a crucial role in the production and transportation of liquefied natural gas(LNG),and are primarily responsible for efficiently controlling the inflow and outflow of LNG and regulating pressure.However,due to their operation in low-temperature and high-humidity environments,crucial components such as drip trays are susceptible to frosting,which may lead to LNG leakage,thereby causing severe safety incidents.In this study,the user-defined function(UDF)is employed to redevelop Fluent,which integrates the frost growth model with the Eulerian multiphase flow model,to conduct a quantitative analysis of frosting on drip trays of cryogenic valves.The effects of environmental parameters,such as wind speed,ambient temperature,air humidity,and cold surface temperature on the growth of the frost layer were analyzed.This study reveals a limiting wind speed between 1 m/s and 2 m/s.Upon reaching this limit speed,the growth of the frost layer reaches its maximum,and further increases in the wind speed have no significant effect on the growth of the frost layer.Furthermore,the influence of the change in the flow field on droplet impingement and freezing during the growth of the frost layer is considered through the coupling method of the kinematic characteristics of water droplets and the collection coefficient of water droplets.This study identifies the influence of different parameters on the droplet impact efficiency,leading to the modification of the frost layer on the drip tray.

Smoothed-Particle Hydrodynamics Simulation of Ship Motion and Tank Sloshing under the Effect of Regular Waves

Predicting the response of liquefied natural gas(LNG)contained in vessels subjected to external waves is extremely important to ensure the safety of the transportation process.In this study,the coupled behavior due to ship motion and liquid tank sloshing has been simulated by the Smoothed-Particle Hydrodynamics(SPH)method.Firstly,the sloshing flow in a rectangular tank was simulated and the related loads were analyzed to verify and validate the accuracy of the present SPH solver.Then,a three-dimensional simplified LNG carrier model,including two prismatic liquid tanks and a wave tank,was introduced.Different conditions were examined corresponding to different wave lengths,wave heights,wave heading angles,and tank loading rates.Finally,the effects of liquid tank loading rate on LNG ship motions and sloshing loading were analyzed,thereby showing that the SPH method can effectively provide useful indications for the design of liquid cargo ships.

Enabling a Viable Technique for the Optimization of LNG Carrier Cargo Operations

In this study, we optimize the loading and discharging operations of the Liquefied Natural Gas(LNG) carrier. First, we identify the required precautions for LNG carrier cargo operations. Next, we prioritize these precautions using the analytic hierarchy process(AHP) and experts' judgments, in order to optimize the operational loading and discharging exercises of the LNG carrier, prevent system failure and human error, and reduce the risk of marine accidents. Thus, the objective of our study is to increase the level of safety during cargo operations.

Fatigue reliability for LNG carrier

The procedure of reliability-based fatigue analysis of liquefied natural gas(LNG) carrier of membrane type under wave loads is presented. The stress responses of the hotspots in regular waves with different wave heading angles and wave lengths are evaluated by global ship finite element method(FEM) . Based on the probabilistic distribution function of hotspots' short-term stress-range using spectral-based analysis,Weibull distribution is adopted and discussed for fitting the long-term probabilistic distribution of stress-range. Based on linear cumulative damage theory,fatigue damage is characterized by an S-N relationship,and limit state function is established. Structural fatigue damage behavior of several typical hotspots of LNG middle ship section is clarified and reliability analysis is performed. It is believed that the presented results and conclusions can be of use in calibration for practical design and initial fatigue safety evaluation for membrane type LNG carrier.

Research on Temperature Field of the Support Structure for the Independent LNG Tank

The independent LNG(Liquified Nature Gas)containment is widely used for small or medium-sized LNG carrier and ship using LNG as fuels.The common tank pattern includes single-spherical-cylindrical tank and double-spherical-cylindrical tank,which is the key to design the hull structure and its support.The support is designed to connect the hull structure and LNG tank.Its main functions are heat transferring and force loading.This paper focus on the temperature field distribution of hull and its support structure.The thermal boundary conditions are simulated according to the heat transfer action,such as thermal convection,heat conduction and thermal radiation.The method on how to carry out thermal analysis is presented for an independent LNG containment.The case study is carried out with two typical independent LNG tanks.One is a tank with double spherical cylindrical in the LNG carrier,and the other is a tank with single spherical cylindrical on the deck of the ship using LNG as fuels.The result shows the method presented in this paper is a good reference for the structural design with independent LNG containment.

A Numerical Study on Optimization of Side-by-Side Mooring System of Floating LNG Bunkering Terminal with LNG Carrier in Operation Condition

In this study, we perform a series of numerical calculations on two vessels in the time domain. One vessel maintains its position using an internal turret and catenary mooring lines, while the other is moored to the former vessel via an STS （ship-to-ship） mooring system. We obtain hydrodynamic forces using the HOBEM （higher-order boundary element method）. Then, we determine their coefficients using the convolution function method in the time domain. We model the catenary mooring lines using the finite element method, and the STS mooring lines are treated as linear SPs （springs） with constraints. To optimize the STS system, we conduct parametric studies on STS mooring systems. Finally, we compare the motion and structural responses of the initial and modified configurations.

Research on the navigational risk of liquefied natural gas carriers in an inland river based on entropy:A cloud evaluation model

Due to the flammability and explosive nature of liquefied natural gas(LNG),an extremely strict process is followed for the transporta-tion of LNG carriers in China.Particularly,no LNG carriers are operating in inland rivers within the country.Therefore,to ensure the future navigation safety of LNG carriers entering the Yangtze River,the risk sources of LNG carriers’navigation safety must be identi-fied and evaluated.Based on the Delphi and expert experience method,this paper analyses and discusses the navigation risk factors of LNG carriers in the lower reaches of the Yangtze River from four aspects(human,ship,environment and management),identifies 12 risk indicators affecting the navigation of LNG carriers and establishes a risk evaluation index system.Further,an entropy weight fuzzy model is utilized to reduce the influence of subjective judgement on the index weight as well as to conduct a segmented and overall evaluation of LNG navigation risks in the Baimaosha Channel.Finally,the cloud model is applied to validate the consistent feasibility of the entropy weight fuzzy model.The research results indicate that the method provides effective technical support for further study on the navigation security of LNG carriers in inland rivers.

Some Insights in Novel Risk Modeling of Liquefied Natural Gas Carrier Maintenance Operations

This study discusses the analysis of various modeling approaches such as genetic algorithms, fuzzy logic and evidential reasoning, and maintenance techniques applicable to the liquefied natural gas （LNG） carrier operations in the maritime environment. The usefulness of these algorithms in the LNG carrier industry in the areas of risk assessment and maintenance modeling as a standalone or hybrid algorithm are identified. This is evidenced with illustrative case studies.

Quantitative analysis of the efficiency dynamics of global liquefied natural gas shipping under COVID-19

Investigating how COVID-19 has influenced Liquefied Natural Gas(LNG)is significant for benefits evaluation for shipping companies and safety management for sustainable LNG shipping in case of accidents.This paper proposes a quantitative method to model the impact of COVID-19 on global LNG shipping efficiency based on the spatiotemporal characteristics of behavior mining for LNG ships.The time cost for LNG carriers serving inside LNG terminals is calculated based on the status of LNG carriers specifically based on arrival and departure times.Then,the time series analysis method is employed to extract the statistical characteristics of the COVID-19 severity index and time cost for LNG carriers inside LNG terminals.Finally,the impact of COVID-19 on global LNG shipping is explored through the Vector Autoregressive Model(VAR)combined with the sliding window.The results demonstrate that the COVID-19 pandemic has a certain influence on the service time for LNG carriers with time lags worldwide.The impact is spatial heterogeneity on a large scale or small scale across global,countries,and trading terminals.It can be used for decision-making in energy safety and LNG intelligent shipping management under unexpected global public health events in the future.The results provide support for intelligent decision-making for safety management under unexpected public health events,such as reducing the seafarer’s explosion to risk events and taking efficient actions to ensure the shipping flow to avoid the energy supply shortage.

Research on Temperature Field and Thermal Stress of Liquefied Natural Gas Carrier with Incomplete Insulation

The insulation of membrane type liquefied natunal gas （LNG） carrier is composed of plywood boxes filled with perlite. Within the service period, considering of the effects of load conditions, such as sloshing, wave load, it is possible to have some damage of the plywood box, leakage of perlite, and failure of the insulation box. LNG carrier without whole protection of effective insulation is dangerous. Hull structure is extremely fragile when exposed to ultra-low temperature. In order to solve these problems, firstly a study on insulation boxes＇ character and work condition is carried out and some presuppositions of partial disabled insulation are put forward. Secondly the thermal system of LNG carrier is analyzed to find out an effective way to simulate the thermal action of close air between outer and inner hull. Then a calculation about temperature field and thermal stress is done by MSC/PATRAN＆NASTRAN. At the end it is concluded that LNG carrier with incomplete insulation is dangerous and needs to be avoided.

Nonlinear roll damping of a barge with and without liquid cargo in spherical tanks

Damping plays a significant role on the maximum amplitude of a vessel’s roll motion,in particular near the resonant frequency.It is a common practice to predict roll damping using a linear radiation-diffraction code and add that to a linearized viscous damping component,which can be obtained through empirical,semi-empirical equations or free decay tests in calm water.However,it is evident that the viscous roll damping is nonlinear with roll velocity and amplitude.Nonlinear liquid cargo motions inside cargo tanks also contribute to roll damping,which when ignored impedes the accurate prediction of maximum roll motions.In this study,a series of free decay model tests is conducted on a barge-like vessel with two spherical tanks,which allows a better understanding of the nonlinear roll damping components considering the effects of the liquid cargo motion.To examine the effects of the cargo motion on the damping levels,a nonlinear model is adopted to calculate the damping coefficients.The liquid cargo motion is observed to affect both the linear and the quadratic components of the roll damping.The flow memory effect on the roll damping is also studied.The nonlinear damping coefficients of the vessel with liquid cargo motions in spherical tanks are obtained,which are expected to contribute in configurations involving spherical tanks.