Illinois Technograph v. 106, iss. 4 Summer 1991

published or submitted for publicatio

Mathematical Modelling of LNG Dispersion Under Various Conditions

The global demand of liquefied natural gas (LNG) has risen rapidly in recent years. A new modelling method, direct CFD simulation method, was developed, due to the risks associated in handling, storage and transport of LNG. This method was shown to accurately model a LNG spill, pool formation and dispersion; and has been used to study the effect of (a) Impoundments, (b) Sea and air temperature and; (c) Sea and air stability

Study of Cryogenic Vaporization Source-Term Due to Heat Transfer from the Solid Substrate

U.S. regulation requires LNG facilities to demonstrate a safe exclusion zone for public safety. European safety case also requires that the facility will demonstrate their risk level within a tolerable limit. Thus, cryogenic liquids (i.e., LNG) release scenarios needs to be modeled to determine consequence severity and perceived risk level. The existing models and tools are very sensitive to the inputs, also known as source-terms. Inaccurate inputs might result in an amplified or subdued consequence severity and may change the estimated risk level and/or safety exclusion zone. Accurate prediction of the source-terms is complex due to the presence of boiling regimes and requires validated models of boiling regimes. A CFD-based approach is taken to model film boiling using Rayleigh-Taylor instability and volume of fluid (VOF) methods. Film boiling simulations for LN2, LO2, and LNG are conducted with a various degree of wall superheat. The simulated results were compared with Berenson and Klimenko correlations to demonstrate that CFD model overcomes the limitations of these correlations. To extend the applicability of these simulations, a first principle model is proposed to enable a faster calculation of heat transfer to cryogenic pool boiling. Medium-scale cryogenic spill experiments have been conducted on an instrumented concrete substrate where LN2, LO2, and liquid air are used. The vaporization rate, temperature, and heat flux profiles are recorded during the experiments. It is found that the effect of the mixture on the LN2 vaporization rate is not significant and the heat conduction inside the concrete substrate is unidirectional. The proposed CFD-based film boiling models for LN2 and LO2 are validated using medium-scale experimental data and are in agreement for higher wall superheats but slightly deviates for the lower wall superheats. The deviation in experimental data can be attributed to the surface roughness and change in boiling regime from film to nucleate. The model for LNG is validated against the experimental data reported in the literature. It is found that the model can capture the vaporization rate reported from the Maplin Sands experiments and other laboratory tests on film boiling

Theoretical Analysis and CFD Simulation of the Solid Ball Kill Process in Offshore Blowout Wells

Well blowout results in massive disaster especially for offshore well. The risk for blowout is increasing as drilling for oil and gas moves into more complex and challenging environment. The damages from blowout incident include life, environment and economy. Conventional well kill methods are either not effective or too slow. Thus, fast and reliable well kill method is needed. This research project is based on the well killing method invented by Xianhua Liu which uses heavy kill balls to be released into the well. These balls will block and suppress the flow of blowout fluids. This method is fast and reliable. The purpose of this project is to study theoretically on the interaction of kill balls with blowout fluids inside the well and also to simulate the behavior of kill balls by using Computational Fluid Dynamics simulation. This research process starts with literature review on blowout incidents and available well killing methods. Then, fluid mechanics theory and calculation are used for theoretical study. After that ANSYS 14 software is used for simulation purpose. Finally, the results from the study and simulation are analyzed. Kill balls are expected to suppress and significantly reduce the flow velocity of blowout fluids so that the well can be completely killed. The outcome of this project will benefits in solving well blowout problems fast and effectively so that to minimize the property loss of the petroleum company and environmental damage

Ambit of Multiphase CFD in Modelling Transport Processes Related to Oil Spill Scenario and Microfluidics

During the ‘Deepwater Horizon’ accident in the deep sea in 2010, about 4.9 million barrels of oil was released into the Gulf of Mexico, making the spill one of the worst ocean spills in recent times. To mitigate the ill effects of the event on the environment, subsea injection of dispersants was carried out. Dispersant addition lowers the interfacial tension at oil/water interface and presence of local turbulence enhances the droplet disintegration process. The oil droplets contain a plethora of hydrocarbons which are soluble in water. In deep spill scenarios, droplets spend large amounts of time in water column; hence, the dissolution process of soluble hydrocarbons becomes important. In this study, our focus is to exploit the capabilities of multiphase CFD in developing an integrated numerical model which accounts for various transport processes and hence would effectively guide us in predicting the fate of oil mass. In the initial stages, studies were conducted to understand these transport processes at a very fundamental level where the effect of surfactant, on the dynamics of crude oil, droplet rising in a stagnant column, was investigated. To capture the subsurface dissolution of hydrocarbons from oil droplet, a unique experiment was devised wherein a binary organic mixture, representing a pseudo oil droplet comprising of volatile and non-volatile hydrocarbons, was employed to study the effect of unsteady mass transport on the overall dynamics of the droplet. In the next phase of project, we developed a numerical model, by integrating traditional multiphase CFD models and turbulence models, with a population balance (PB) approach, for predicting the droplet size distribution resulting from the interaction of turbulent oil jets with the surrounding quiescent environment. Apart from the simulations specific to oil spill related situations, the multiphase CFD was also employed to study the fluid flow in micro-channels. The mass transfer mechanisms in micro-channels for immiscible fluids in squeezing and dripping regimes were studied by employing the numerical model, which couples the features of the traditional Volume of fluid method and the Continuous Species transport approach for evaluating the concentration fields inside dispersed and continuous phase

A guide to the equipment, methods and procedures for the prevention of risks, emergency response and mitigation of the consequences of accidents: Part I

This report is the first part of a dilogy which aims to be a compendium for regulators without a specific background in risk and safety assessment. It describes the state-of-the-art of the safety-related equipment, methods, procedures and projects available nowadays for the prevention of risks, the emergency response and the mitigation of the consequences of accidents. While the present report addresses the above topics from a generic perspective, the second part, currently in preparation, focuses on the particular challenges of the Nordic Seas. The review is based on the retrieval and analysis of a large number of open source information, along with personal contacts with Authorities and HSE representatives of several major oil and gas operators. This helps the reader go into further details and better appreciate the latest technological advancements in offshore safety as a consequence of the lessons learnt from the Macondo Accident.JRC.C.3-Energy Security, Distribution and Market

Evolving time surfaces and tracking mixing indicators for flow visualization

The complexity of large scale computational fluid dynamic simulations (CFD) demands powerful tools to investigate the numerical results. To analyze and understand these voluminous results, we need to visualize the 3D flow field. We chose to use a visualization technique called Time Surfaces. A time surface is a set of surfaces swept by an initial seed surface for a given number of timesteps. We use a front tracking approach where the points of an in initial surface are advanced in a Lagrangian fashion. To maintain a smooth time surface, our method requires surface refinement operations that either split triangle edges, adjust narrow triangles, or delete small triangles. In the conventional approach of edge splitting, we compute the length of an edge, and split that edge if it has exceeded a certain threshold length. In our new approach, we examine the angle between the two vectors at a given edge. We split the edge if the vectors are diverging from one another. This vector angle criterion enables us to refine an edge before advancing the surface front. Refining a surface prior to advancing it has the effect of minimizing the amount of interpolation error. In addition, unlike the edge length criterion which yields a triangular mesh with even vertex distribution throughout the surface, the vector angle criterion yields a triangular mesh that has fewer vertices where the vector field is flat and more vertices where the vector field is curved. Motivated by the evaluation and the analysis of flow field mixing quantities, this work explores two types of quantitative measurements. First, we look at Ottino\u27s mixing indicators which measure the degree of mixing of a fluid by quantifying the rate at which a sample fluid blob stretches in a flow field over a period of time. Using the geometry of the time surfaces we generated, we are able to easily evaluate otherwise complicated mixing quantities. Second, we compute the curvature and torsion of the velocity field itself. Visualizing the distribution and intensity of the curvature and torsion scalar fields enables us to identify regions of strong and low mixing. To better observe these scalar fields, we designed a multi-scale colormap that emphasizes small, medium, and large values, simultaneously. We test our time surface method and analyze fluid flow mixing quantities on two CFD datasets: a stirred tank simulation and a BP oil spill simulation

Modeling Magnetic Separation of Oil Spill Clean Up to Enhance Virtual Laboratory Learning in the Classroom

This thesis links an applied mathematics study of oil spill cleanup to a mathematics education study of the efficacy of virtual laboratory activities in physical and mathematical sciences. Oil spills will be investigated using a multi-phase Navier-Stokes Direct Numerical Simulation (DNS) code for magnetic fluids, also known as ferrofluids. Simulations model cases that are not possible to study in a laboratory experiment or in the real world. Simulation results show that scaling up this process involves fluid mechanical obstacles and that real world effects, such as seawater contamination, will also impact cleanup effectiveness. A physics laboratory classroom curriculum based on fluid dynamics virtual laboratory simulations is designed to provide an educational experience of oil spill cleanup without safety risks or other physical challenges, such as inaccessibly large or small length or time scales. Students’ development of intuition for fluid dyanmics, scaling and magnetic manipulation were tested, both directly and virtually. In-depth interviews indicate that a virtual lab provides a good substitute for a hands-on magnetic fluids lab of this type

Maritime Computing Transportation, Environment, and Development: Trends of Data Visualization and Computational Methodologies

This research aims to characterize the field of maritime computing (MC) transportation, environment, and development. It is the first report to discover how MC domain configurations support management technologies. An aspect of this research is the creation of drivers of ocean-based businesses. Systematic search and meta-analysis are employed to classify and define the MC domain. MC developments were first identified in the 1990s, representing maritime development for designing sailboats, submarines, and ship hydrodynamics. The maritime environment is simulated to predict emission reductions, coastal waste particles, renewable energy, and engineer robots to observe the ocean ecosystem. Maritime transportation focuses on optimizing ship speed, maneuvering ships, and using liquefied natural gas and submarine pipelines. Data trends with machine learning can be obtained by collecting a big data of similar computational results for implementing artificial intelligence strategies. Research findings show that modeling is an essential skill set in the 21st century

Committee V.1: Accidental Limit States

Concern for accidental scenarios for ships and offshore structures and for their structural components leading to limit states. Types of accidental scenarios shall include collision, grounding, dropped objects, explosion, and fire. Attention shall be given to hazard identification, accidental loads and nonlinear structural consequences including strength reduction, affecting the probability of failure and related risks. Uncertainties in the use of accidental scenarios for design and analysis shall be highlighted. Consideration shall be given to the practical application of methods and to the development of ISSC guidance for quantitative assessment and management of accidental risks