Analytical Hierarchy Process (AHP) for Selecting and Designing a Mini LNG Plant: A Case Study of Batam Indonesia

Increase in demand for clean energy is one of the strategic issues in Indonesia nowadays, considering the significant economic growth of the country. A conventional LNG supply chain is not the best solution taking into consideration its high investment. The possibility of using a small scale LNG supply chain concept (Mini LNG) is recently sought by the government and private sectors in Indonesia. It is even more promising when we consider the amounts and number of stranded gas fields in the country. One of the main obstacles to the development plan is the geographical position of Indonesia as an archipelagic country. This paper presents a case study of LNG supply chain model of 10 mmscfd Gas Sales Agreement (GSA) in Batam and its design of LNG transportation model from Batam to Siantan-West Kalimantan [1]. The distance between Batam and Siantan is approximately 392 nautical miles. Two main objectives are covered in this paper. The first one is an implementation of the Analytical Hierarchy Process (AHP) to select the best location for mini LNG plant, and the second one is to design the LNG supply chain model based on optimization approach. The AHP model uses a pairwise comparison of 4 (four) qualitative attributes and 14 (fourteen) sub-attributes. 3 alternatives of location for mini LNG plant are evaluated, namely: Tanjung Uncang, Pemping Island and Janda Berhias Island. A sensitivity analysis by varying the weight of some critical attributes is also conducted to ensure that preferred location is sensitively selected with minimum error. The optimization of the LNG supply chain model is carried out by means of Gradually Reduced Gradient (GRG) methods. The Objective is to attain one design that will minimize investment (cost). Decision variables of the model are LNG plant capacity, storage tank capacity in loading and receiving terminal, vessel size, number of round trip, number of operating vessels, regasification capacity at the receiving terminal, and others.

The Research of Statistic Prediction for Wave Loads Based on Three Dimensional Method

The exact prediction of wave loads for ship or other marine structure is the key to its design and the assessment of structural strength, reliability and security. The short-term and long-term prediction of wave loads are always used in direct calculation for structural strength, fatigue strength assessment and so on based on spectral analysis method. In this paper, the numerical calculation method for statistic prediction is discussed firstly, including the Weibull distribution fitted method and the stack method. Further more, it is necessary to find a quick solution in order to improve the efficiency to compute the nonlinear equation in the second method. Then, some main factors that may influence the long-term or short-term prediction are discussed, such as wave spectrum, wave scatter diagram, incident wave angle interval and frequency interval. Finally, the wave loads prediction for a series of typical bulk carriers and oil tankers are calculated by the uniform predict method discussed above base on three dimensional wave loads calculation theory. The results showed that the method used in this paper can predict the statistic value of wave loads induced by irregular incident waves conveniently and efficiently. A rule to choose a series of uniform factors is confirmed for statistic prediction and some empirical formulas for long-term value of wave bending moment are concluded which are very useful in marine engineering.

Deformation Analysis and Reliability Assessment of the Ship Hull in Irregular Waves

When the ship navigates in the sea, the dynamic deformation of the ship hull will be induced by the waves. The relative large deformation of the ship hull induced by the waves may affect the operation of some certain equipment. In order to keep the equipment operating normally, the influence of the ship deformation should be evaluated. The method for the calculation and analysis of the ship deformation is discussed here. The wave loads of the ship in unit regular wave amplitude are calculated based on 3-D linear potential flow theory. The sea pressure and inertial force of the ship are obtained and applied to the global finite element model of the ship. Under the quasi-static assumption, the structural deformation response in unit regular wave amplitude is calculated with the use of finite element analysis. Then, the amplitude frequency response of the relative deformation between two arbitrary positions in the hull is achieved. The history of the deformation can be obtained based on the simulation of deformation response in irregular waves or the modal superposition method. With the help of spectral analysis method, the spectrum of the relative deformation between two arbitrary positions in the hull may be obtained. The statistical analysis of ship hull deformation in the short-term sea state is realized. Considering the critical value of ship deformation, the reliability analysis method is adopted to assess the ability of hull to resist the deformation.

Efficient Derivation of the Probability Distribution of the Extreme Values of Offshore Structural Response: Comparison of Three Different Methods

Offshore structures are exposed to random wave loading in the ocean environment and hence the probability distribution of the extreme values of their response to wave loading is required for their safe and economical design. To this end, the conventional (Monte Carlo) time simulation technique (CTS) is frequently used for predicting the probability distribution of the extreme values of response. However, this technique suffers from excessive sampling variability and hence a large number of simulated extreme responses (hundreds of simulated response records) are required to reduce the sampling variability to acceptable levels. In this paper, three different versions of a more efficient time simulation technique (ETS) are compared by exposing a test structure to sea states of different intensity. The three different versions of the ETS technique take advantage of the good correlation between extreme responses and their corresponding surface elevation extreme values, or quasi-static and dynamic linear extreme responses.

Experimental Study on Water Damping Effects of Hybrid Floating Structure

In this study, in order to evaluate water damping effects of hybrid pontoon system with cylinders, experimental studies were carried out. At first, in order to evaluate oscillatory motions, three small-scale models of hybrid, tapered, and pontoon were fabricated and tested under the still-water condition. Four acceleration gauges were attached on the top edges and acceleration of top edge were measured during the oscillation. Then, oscillatory motions of oscillation period and stabilizing time to steady-state were analyzed. Finally, based on the oscillatory motions, damping properties of the logarithmic decrement, damping ratio, and natural frequency of damped system were calculated and compared with each other. As the results of this study, it was found that hybrid model presented about 3.67 times higher decay rate of amplitude of the oscillatory motion than the pontoon model. Also, hybrid model presented about 3.67 times higher damping ratio than the pontoon model. Whereas the natural frequency of the pontoon and tapered model were nearly same with the natural frequency of undamped system, that of the hybrid model presented some difference with the that of the undamped system. In addition, periods of floating body at the wet mode presented about 1.5∼3.0 times longer periods than the dry mode, and it was expected that there was not possibility for the resonance. Therefore, it was expected that the hybrid model of this study should contribute to improve serviceability and safety of offshore floating structures as decreasing oscillatory motions.

Global Trends in Extreme Wind Speed and Wave Height

Satellite observations of the ocean surface provide a powerful method for acquiring global data on wind speed and wave height. Radar altimeters have now been in operation for more than 25 years, providing a reasonably long term data set with global coverage. This paper presents data from a fully calibrated and validated altimeter dataset. The dataset provides the basis for obtaining a global perspective of a number of parameters critical to ocean engineering design, ship operations and global climate change. Analysis of the data provides ocean climatology of mean monthly values of wind speed and wave height useful for ship operations. The data set is also sufficiently long to provide extreme value (i.e. 100-year return period) estimates of wind speed and wave height. The paper presents such values and describes the approaches most appropriate to obtain statistically significant extreme value estimates from such satellite data. With a data set of this length, it is possible to investigate whether there have been statistically significant changes in the wind and wave climates over the period. Careful trend analysis of the extensive data set shows that there has been a statistically significant increasing trend in mean wind speed over the period. The corresponding increase in wave height is less clear. There is also evidence to suggest that extreme wind speeds and wave heights are increasing and the data set is analysed to investigate these trends. The paper clearly shows the value of this dataset and its application to a range of engineering problems.

Fracture Resistance of Ship Longitudinal Members Including Fatigue Crack

This study investigates the fracture failure of longitudinal members including cracks. Specifically, this study employs the failure assessment diagram methodology to assess the conditions of failure at the crack tip. Based on various crack configurations, this study establishes the analytical formulations of the crack-tip condition that are validated using finite element analyses. In addition, the material toughness is expressed in terms of crack-tip opening displacement. This study evaluates the failure stress of representative cracked members as a function of the crack length. This enables determining critical crack lengths corresponding to the maximum stresses derived from extreme loads. Finally, this study uses simplified fatigue crack growth analyses to characterize the critical crack length in terms of fatigue life. For members located in the deck and bottom regions, the critical crack lengths correspond to the end of the assessed fatigue life. Therefore, the fracture resistance of the longitudinal members is satisfactory as it will not cause the premature loss of the component. This study also provides analytical formulations for crack-tip conditions that could be employed in a reliability study linking fatigue crack growth and fracture under extreme loads.

Stability Requirements of Multi-Purpose Ships for Heavy Lifts

New minimum intact stability criteria are presented to ensure safety against capsizing invoked by sudden loss of crane load during heavy lifts at sea, followed by typical sample stability assessments for a lifting operation on four multipurpose ships. For added stability, two of these ships had a pontoon attached at their sides opposite the lift. Two numerical time-domain methods assessed the transient dynamic heel after a sudden loss of crane load. With the ship at equilibrium, both analyses started by releasing the crane load, simulating a sudden failure of the lifting gear. The first method solved the roll motion equation as a one-degree-of-freedom system; the second method used a Reynolds-averaged Navier-Stokes equations solver. The first method relied on appropriately chosen linearized roll damping coefficients, and the nonlinearity of the righting moment function had to be accounted for. The second method required creating extensive numerical grids to idealize the ship’s hull, including the counter balancing stability pontoon, rudder and bilge keels, as well as all parts of the ship’s superstructure that effect the righting moment at large heeling angles.

Risk and Reliability Analyses for Innovative LNG Offshore Floating Units

The development of the Liquefied Natural Gas (LNG) offshore industry is viewed as a major improvement in the exploitation of the world’s energy resources. Most energy analysts agree that significant increases in Natural Gas (NG) demand is expected in the next decades due to relatively low prices and an important gas quantity worldwide. In order to develop the use of this resource, many innovative offshore floating installations have been developed and are currently deployed all over the world. However, hazards linked to LNG and due to hydrocarbon releases are not always so well understood or controlled. Thus, in order to quantify and understand these risks associated to LNG treatment or containment as well as their consequences, a number of different types of risk and reliability engineering techniques can be used at different stages of the project. The following will present specific analyses that have been performed on innovative LNG Offshore floating units to provide a qualitative and quantitative hazard assessment by predicting the consequences and the frequencies of these hazards, while improving the reliability of the installation and its availability. The paper will first introduce the LNG offshore industry outlining the different installations possibilities and the associated hazards. Then, based on recent projects, it will detail the risk-based methodology applied to ensure the safety and the profitability of such innovative installations when no rules are able to frame fully the development of these projects. Finally, after having pointed out the ins and outs of risk studies, a case study using most of the methods presented previously will be developed.