DEVELOPMENT OF A TRAINING SIMULATOR FOR OIL SPILL RESPONSE. Universidade Federal do Rio de Janeiro LabOceano, COPPE-UFRJ Rio de Janeiro, RJ, Brazil

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1 Proceedings of the ASME rd International Conference on Ocean, Offshore and Arctic Engineering OMAE2014 June 8-13, 2014, San Francisco, California, USA OMAE DEVELOPMENT OF A TRAINING SIMULATOR FOR OIL SPILL RESPONSE Vinicius L. Vileti Paulo de Tarso T. Esperança Albino Ribeiro Neto Sergio H. Sphaier Joel S. Sales Jr. Leonardo S. Antunes Maciel OceanPact ABSTRACT The paper describes the development of a training simulator for boats used on Oil Spill response at sea. The simulator models the dynamics of tug boats pulling an oil boom under waves, wind and current. The boom is modeled as a flexible line connected by lumped masses and its flotation characteristics and loads are calculated by Morison equation. A simplified model is used to simulate the oil itself and its interface with the boom line. The verification process was applied and its outcomes are discussed. Also, some case study scenarios are presented and the results are used to evaluate the applicability of the simulator as a training system. of the boats during the operation. Also, after the boom is around the oil, the system must keep it trapped for some time to allow the skimming process. A picture of an oil boom with the skimmer is shown on Figure 1 below. INTRODUCTION Offshore oil production brings the risk of oil spill to the environment. Recent disasters of different amplitudes show that a fast response capacity is crucial for the minimization of the effects of such incidents to the environment and to the economy[1]. To date an important part of response plans is based on the use of boats pulling oil booms that trap the oil spills so that it can be removed by an oil skimmer. The booms are flexible floating lines that carry surfaces designed to avoid the oil from passing through. Their dynamics interact with the boat dynamics and the environmental loads, i.e., waves, current and wind. The success of this operation relies on the correct judgment of the personnel involved on the approaching of the boats to the oil spill, the launching of the equipment and the maneuvering Figure 1 - Oil boom and oil skimmer In Brazil, few boats are equipped with oil booms and only their crews are constantly trained to operate the related equipment. However, training routines are subject to the boats and equipment operational windows, which restrict the training capacity. Also, in the case of an incident, additional boats may be needed to attend a response plan, and non-trained people probably will get to be involved as well. So, the use of ship 1 Copyright 2014 by ASME

2 bridge simulators is both a good tool to give the inexperienced crews a basic training on the response procedures and also an alternative to give specialized oil spill response crews maintenance trainings without having to wait for the real equipment availability. Many commercial ship bridge simulators and oil spill-boom interactions codes are available [2, 3], but we did not find a full solution containing the bridges, the boom and the oil spill. Besides, our need to have a program with scenarios dedicated to the equipment and procedures found in Brazil motivated us to develop new software to be used as a training tool. We used a time domain Runge-Kutta integrator to solve the dynamics of the boats, the boom and the simplified oil spill movements. Also, we developed a graphical interface to interact with the simulator system in order to use it as a training simulator. At end, we tested the system for verification, by comparing its outputs with data available from other software. Results showed good correlation for motions on boats and for limited operation of the boom. Further development is still needed for the oil spill motions and for the interaction between the boom and waves. DEVELOPMENT OF THE RESPONSE SIMULATOR Background There is a large volume of published studies describing the role of an oil spill accident. A considerable amount of literature has been published concerning the impact on the environment, physical aspects of the oil in the sea, and also concerning the behavior of the equipment applied to contain the oil spill. A summary of the state of art of oil spill modeling can be found in [4], and a series of tests to identify the relevant parameters on the seakeeping of an oil boom is presented on [5]. Mathematical Model For the time domain integration we used a Runge-Kutta 4 th order method, with time steps of 0.1 seconds. At each time step, the following equations were solved: The oil spill interaction with the oil boom was modelled by means of a change on the boundaries of the former due to the contact with the latter. The slipping of the oil was modeled by defining an efficiency coefficient for the boom capacity of trapping the oil. The following sub-sections explain each of the equations described above. 6DOF motions of the boats The equations of motions for the boats were: where: Mass and Inertias Matrix (including added masses) Position vector for each boat Forces due to waves, calculated from RAO input files obtained from 3D Potential Theory model. Forces due to winds, calculated from drag coefficients for tugs. Forces due to current, calculated from drag coefficients for tugs. Forces due to maneuvering, calculated from maneuvering coefficients for low speed maneuvers for tugs Forces due to propulsion system, calculated from bollard pull values for commercial propulsion systems. Forces due to oil boom, input from oil boom model 3D motions of boom We modeled the boom as a set of lumped masses connected by springs and dampers (Figure 2). 6 DOF motions of the boats; 3D motions of nodes at oil boom; 2D mean position of Oil Spill; Although those three set of equations were solved separately, the interaction between then was imposed. For instance, the extremes nodes at oil boom applied forces at the connection points of the boats, and these loads were computed on the boats equations of motions. The motions of the boats were then updated on the Runge-Kutta steps and the 3D position of the connection points were input on the nodes so that in the next step the equations of motions for each node could be calculated. Fn-1 Node n Node n+1 Fn+1 Fmorison Figure 2 Boom model discretization 2 Copyright 2014 by ASME

3 We solved the equations of motion for each node, as follows: where: To construct the virtual simulation environment maps and georeferenced terrain elevations of Guanabara Bay we used GoogleSketchup program to capture an area of approximately 20 square kilometers (Figure 3) and imported the file to 3Ds Max format (Figure 4). Force from previous element, calculated from EA (E is the Young s Modulus and A is the section area of the element) and structural damping Force from next element, calculated from EA and structural damping equation Hydrodynamic forces calculated from Morison 2D motions of Oil Spill We applied a simplification of the oil spill motions, just to have a graphic representation of it moving with waves, wind and current. The oil spill model was an elliptical area with moving center, and with velocity calculated using the following equation: Figure 3: Capturing maps of elevations using Sketchup process. where: Wave velocity contribution coefficient Wind velocity contribution coefficient Current velocity contribution coefficient Wave propagation vector Wind velocity vector Current velocity vector The borders of the spill interact with the boom when they encounter. System architecture and Graphic Design The development of synthetic environments in Virtual Reality is a response to a growing demand for training at a lower cost for different types of requirements and different areas. The development of simulators using Virtual Reality has proved to be an effective tool to implement training programs [6]. The development and testing of methodologies and technologies for creating immersive virtual environments assist in the study of cognitive processes. Figure 4: Geo-referenced images with terrain elevations of Guanabara Bay cut in 3Ds Max. Interactivity was implemented through 3D real-time application development software, ideal for applications in Virtual Reality. This was performed through visual programming scheme, allowing three-dimensional models, textures, and other various Medias and creation of executables or web applications. We used physics engine on graphic elements to allow realistic and widely configurable physical environment. The simulator dynamically generates shadows in real time, including a system for generating climate with rain, snow and clouds, sun positioning in several times of the day and wind speed for better realism in operations so that the operator has an image as close as possible to the real. Sounds were configured according to their geographical position within the simulator, thus every sound came from a specific direction within the simulation, that is, the closer the operator was to a vessel the greater was the sound heard. Three dimensional sky was a sphere with sky texture and clouds applied, and sun image with overlaid artificial light. 3 Copyright 2014 by ASME

4 Primitive collision geometry was applied using various boxes so that the application could take less computational resources. The model of the vessel used as reference for the threedimensional modeling in 3Ds Max was an Oil Spill Recovery Vessel as in Figure 5. Figure 5: Three-dimensional Oil Spill Recovery Vessel The interactivity of the barrier with the oil slick occurs with the principles of Newtonian Physics present in the engine used in the development of the simulator. To accomplish it, the motions of both the boom and the oil spill are updated by the mathematical model module, which sends this information to the collision model, and then this last adapts the oil spill shape. The collision geometry chosen is shown on Figure 6. Figure 7 - Shafts oil stain and blot (colored) interactivity with the barrier (in yellow). We used Shader 3.0 resource for the wave s representation. The skimmer is shown in figure 9 and the boom elements modeling in figure 10. Figure 6 - Shafts barrier and geometry primitive collision. Figure 9: Three-dimensional model of the Skimmer. This geometry of primitive collision consumes less computational resources and provides a good end result. Through this collision was possible to perform realistically the simulation of boom for oil slicks, as presented on Figure 7. Figure 10: Three-dimensional model representation of boom element. 4 Copyright 2014 by ASME

5 VERIFICATION OF THE SYSTEM Verification procedure For verification of the software, we tested at first the different models of the system separately for internal consistency of the sub-routines and inputs and output. The boom model was checked against the commercial code ORCAFLEX with current loads. One extreme of the boom was fixed and the opposite was moving to mimic the pull of the tug. For boats motions we used WAMIT RAOs and checked the response spectra of outputs from time series against input values. We checked also the maneuvering behavior of the tugs comparing the simulations with an in-house code developed for offloading simulations [7]. The final verification was done comparing the general behavior of the system with reports of training operations that we had access to. SIMULATION RESULTS A comparison of the behavior of the boom with ORCAFLEX made during verification process is shown in figure 11. Figure 11 Oil Boom nodes motions in horizontal plane verification (red- ORCAFLEX, blue present model). Figure 12 presents 6DOF motions results for one OSRV (Oil Spill Recovery Vessel) in time domain. In this plots the Surge, Sway and Yaw were determined by maneuvering model coefficients, while Heave, Roll and Pitch were obtained using RAO curves. The dashed red line shows the target for the Dynamic Positioning System and the blue line is the simulated motion of the OSRV. Both Simulations (ORCAFLEX and the present simulator) used the same motions to verify the oil boom behavior. Figure 12 Verification of 6DOF motions for OSRV simulation 5 Copyright 2014 by ASME

6 Simulation of response procedures - Case studies scenarios We defined the starting of the response procedure as the approach of the oil spill by the OSRV. The main parameters influencing the actions to be implemented by the captain are related to the size of the spill and the weather conditions (Wind, Wave and Current). For this work we consider the case of one OSRV (main boat) acting together with a smaller boat, i.e., a tug. The former is the one launching the boom while the later will be responsible for pulling the end segment of the boom. The operation was divided into the following stages: 1. Approaching of the OSRV against the drift direction of the spill (figures 13 and 14); 2. Launching of the boom and approaching of the boat (figure 15); 3. Maneuvering of the tug to give an "U" shape configuration of the boom (figure 16); 4. Maneuvering of the tug to give an "J" shape of the boom to allow skimmer operation (figure 17); 5. Maneuvering for re-collecting the boom (figure 18). Figure 15 - Launching of the boom and approaching of the small boat Figure 16 - Maneuvering for "U" shape configuration Figure 13 - Approaching of the OSRV Figure 17 - Maneuvering "J" configuration for the skimmer launching Figure 14 - Approaching of the OSRV 6 Copyright 2014 by ASME

7 The system was verified for internal consistency checking purposes and its results were compared with commercial software. We concluded that the simulator was adequate for use in basic procedures training purposes of oil spill responses. Moreover, if one makes further developments mainly on the oil boom model, the system will be able to simulate more complex scenarios like breaking of oil boom and other issues related to boom handling during the response. ACKNOWLEDGMENTS The authors acknowledge the financial support from Brazil Innovation Agency FINEP, National Agency of Petroleum ANP and OCEANPACT. Figure 18 - Maneuvering for re-collecting the boom REFERENCES DISCUSSION The validation process requires further development, especially with the input of experimental and field data to check the coherence of the system. We concluded that the boom model was adequate to mimic the behavior of the equipment during basic procedures of training simulations as the one showed on this paper. However, a more detailed model would be needed for other more complex scenarios as: breaking of one segment; slipping of the oil underneath the boom and losing of capacity of trapping due to waves. For maneuvering simulations in the horizontal plane further development is still needed, since the comparisons for verification purposes were performed with hydrodynamic derivatives used for tankers-like hulls. CONCLUSION We developed a simulator for an oil spill response system consisting of OSRVs boats that handle an oil spill boom under waves, wind and current environment, in the presence of a visual oil spill. The system was constructed to allow interaction with an operator controlling the boats so that training on oil spill response can be performed. [1] Maggi, P., Morgado, C. D. V., and de Almeida, J. C. N., 2013, "Offshore Oil Spill Incidents in Brazil," Progress in Environmental Protection and Processing of Resource, Pts 1-4, , pp [2] Cho, Y. S., Kim, T. K., Jeong, W., and Ha, T., 2012, "Numerical Simulation of Oil Spill in Ocean," Journal of Applied Mathematics, p. 15. [3] Yang, X. F., and Liu, M. B., 2013, "Numerical modeling of oil spill containment by boom using SPH," Science China- Physics Mechanics & Astronomy, 56(2), pp [4] Reed, M., Johansen, O., Brandvik, P. J., Daling, P., Lewis, A., Fiocco, R., Mackay, D., and Prentki, R., 1999, "Oil spill modeling towards the close of the 20th century: Overview of the state of the art," Spill Science & Technology Bulletin, 5(1), pp [5] Kim, M., Muralidharan, S., Kee, S., Johnson, R., and Seymour, R., 1998, "Seakeeping performance of a containment boom section in random waves and currents," Ocean Engineering, 25(2-3), pp [6] Neto, A. R., Cunha, G. G., and Landau, L., 2013, "Development of Port Equipment Simulators using Virtual Reality," Virtual Reality Journal, 6, pp [7] Sales, J. S., Matter, G. B., Sphaier, S. H., Machado,R.R. and Correa, S.H.S., 2002, "A simulation program to support decisions in offloading operations," Proceedings of the 12 th International Offshore and Polar Engineering Conference, ISOPE. 7 Copyright 2014 by ASME