Proceedings of SNAME Student Paper Competition SNAME February 27,, MIT, Boston, Massachusetts, USA CONCEPT DESIGN Javier Moreno Department of Mechanical Engineering University of Maine Orono, Maine, 04469 Email: javier.moreno@maine.edu Razieh Zangeneh Department of Mechanical Engineering University of Maine Orono, Maine, 04469 Email: razieh.zangeneh1@maine.edu ABSTRACT Expectations that the U.S. would become a major importer of liquefied natural gas (LNG) have been replaced by the possibility of the U.S. becoming a major LNG exporter as a result of a continued growth in shale gas production [1]. To become a major exporter, the deployment of new facilities, such as floating liquefied natural gas () platforms, becomes increasingly important. Such work is already underway, for example, the world s largest project will be commissioned in 2018 in the Gulf of Mexico, near Venice, Louisiana, U.S. This paper will present an overview design analysis of a barge-based. The consists of a liquefaction facility and 200,000 cubic meters of LNG storage capacity. The will be designed to operate off the coast of Maine. Commercial codes for hydrostatic and time domain analysis will be used to evaluate stability, mooring, system and global performance of the facility. 1 INTRODUCTION The U.S natural gas supply is more than adequate to meet both the future U.S domestic demand as well as the capacity to export to other countries [1]. Development of shale gas and improvements in drilling technologies have lead to an increase in natural gas production. The Energy Information Administration (EIA) estimates an increase in dry gas production of 32% from 2012 to 2025 [1] and this increase in production is expected to grow faster that the natural gas demand, which allow for exports. However, the U.S needs the required infrastructure to become a major exporter. The construction of new floating liquefied natural gas () platforms is the best solution to achieve this task rather than an onshore facility [2]. Therefore, the construction and deployment of terminals along the U.S. coast should be the primary task to achieve the export plan. This task was started started with the U.S. approval of construction of the Main Pass Energy Hub deepwater port (MPEH Port), which could be the world largest LNG export project with 24 million of tons per anum (MTPA). This project will include six units, with each capable of producing four MTPA and with a storage capacity of 200,000 cubic meters. This paper presents an overview of the first iteration in the design spiral of an unit. The stability, mooring system and global performance are evaluated using commercial software for hydrostatic and time domain analysis. Problem description The facility will be located approximately 1 mile off the coast of Robbinston, Maine in Passamaquoddy Bay with a water depth of about 40 m. It will consist on a rectangular barge with a two MTPA liquefaction capacity and with a storage capacity of 200,000 cubic meters. The main characteristics of the are presented in Table 1. Figure 1 shows the general arrangement of the barge. GTT no.96 membrane tanks are used to store the LNG. The LNG is storage at -163C therefore INVAR material (36% Ni- Steel) is used due to its low thermal contraction coefficient to absorb the thermal stresses 1. Two-row tanks were used instead of one row to significantly reduce sloshing due to roll motion [3]. Also once the first sizing of the tanks was finished, an initial check of possible sloshing problems in tanks was done using the ABS guidance for 1 GTT NO 96 Membrane System, http://www.gtt.fr/content.php?cat=34&menu=60
TABLE 1: MAIN DIMENSIONS L (m) 202.00 B (m) 69.00 D (m) 30.00 T (m) 13.27 Displacement (t) 189,584 L tank (m) 37.00 B tank (m) 30.00 D tank (m) 23.00 TABLE 2: NATURAL PERIODS Pitch (s) Roll (s) 12 14.4 TABLE 3: LNG TANKS FLUID MOTION NATURAL PERI- ODS level of tank (d0) T pitch T roll 0.10 2.30 15.69 12.76 0.20 4.60 11.30 9.27 0.30 6.90 9.49 7.89 0.40 9.20 8.52 7.18 0.50 11.50 7.95 6.79 0.60 13.80 7.58 6.56 0.70 16.10 7.35 6.42 0.80 18.40 7.20 6.34 0.90 20.70 7.10 6.28 1.00 23.00 7.03 6.25 Regulations applied During the design process the considered regulations were: FIGURE 1: GENERAL ARRANGEMENT in Chapter 3-3-11. The sizing of the tanks was done so that there was no synchronize of the natural periods of the barge and the natural periods of the LNG inside the tank (the natural periods of the fluid motions in the tank, for each of the anticipated filling levels, should be at least 20% greater or smaller than that of the relevant vessels motion). Natural periods of the barge in Table 2 where obtained analytically in first approximation using ABS formulation [4]. Table 3 presents the roll and pitch natural periods of the LNG tanks for different filling levels. Cells in grey represent those periods that are near the natural periods of the (where sloshing problems can occur). It can be seen that by using a two-row tanks sloshing problem due to roll motion is eliminated (Sloshing problems for a 10% filling level are neglectable). For a filling level of 20% there might be sloshing problems in pitch motion, the design of the length of the tanks should be optimized in the second iteration of the spiral design in order to increase o reduce its natural period. 1. ABS regulations for Floating Offshore Liquefied Gas Terminals [4] 2. ABS regulations for Offshore Drilling Units [5] 3. IMO regulations (SOLAS 74/78 [6], MARPOL 73-78 [7] and International Gas Code (IGC) [8] ) STABILITY ANALYSIS This section presents the stability calculations and evaluation of the barge according to the regulations listed above. This includes: 1. The compartment definition of the 2. The specification of each of the load cases 3. Intact stability calculations 4. Damage stability calculations For the evaluation of the stability of the barge Hydromax Software (MARINE), a module of MAXSURF, was used. Trim by stern was considered a positive trim, a density of water of 1.025 t/m 3 and a density of LNG of 0.45 t/m 3 was considered throughout the entire calculations. 2
TABLE 4: EQUILIBRIUM CONDITIONS FOR EACH LOAD CASE FIGURE 2: COMPARTMENT DEFINITION Compartment definition of the In this first cycle of the project design spiral, a simplified compartment definition was done by defining the LNG tanks, water ballast tanks and all the adjacent compartments including the machinery compartments Figure 2. Load cases specification For the evaluation of the stability two load cases were considered: 1. Fully loaded case: Case in which the LNG tanks are 98% loaded, and all the water ballast tanks are unloaded (0%). 2. Water ballasted case: In this case the LNG tanks are 2% loaded. Normally some quantity of LNG remains in tanks (usually around 2%) to maintain a lower temperature of the tanks. Therefore a cooling process is not needed before loading tanks, which reduces loading time. Water ballast tanks will be fully loaded (98%). Table 4 shows the equilibrium condition for each of the load cases. Intact stability calculations According to [5], Part 3, Chapter 3, Section 2, Point 1.3.1, the should have sufficient stability (righting stability) to withstand the heeling moment equivalent to a wind speed of not less than 36 m/sec (70 kn) for normal drilling and transit conditions. In addition, the unit is to be capable of withstanding a severe storm condition applying a wind speed of not less than 51.5 m/s (100 kn). FULLY LOADED WATER BALLASTED Draft Amidsh. (m) 13.139 13.022 Displacement (tonne) 187746 186072 Trim (m) 0.19 1.488 WL Length (m) 202 202.01 WL Beam (m) 69 69 Waterpl. Area (m 2 ) 13938.01 20995.846 KB (m) 6.57 6.518 KG fluid (m) 18.631 18.932 BMt (m) 13.196 30.469 GMt (m) 15.076 18.054 KMt (m) 36.766 36.987 Immersion (TPc) 142.892 142.896 To evaluate the wind pressure the equation in Part 3, Chapter 1, Section 3, Point 1.3.2 of the [5] was used: P = f V k 2 C h C s N/m 2, (1) Where f is 0.611, V k is the wind velocity in m/s, C k is the height coefficient from 3-1-3/Table 2 [5] and C s is the shape coefficient from 3-1-3/Table 1 [5]. Three different sections were taken into account to evaluate the wind pressure Table 5: TABLE 5: COEFFICIENTS FOR WIND LOAD CALCULA- TION Hull Accommodation Liquefaction module Z g 8.02 m 26.044 m 23.434 m C h 1 1.1 1.1 C s 1 1 1 The wind speeds selected for each conditions and the wind pressure obtained, once the equation 1 was applied, are presented in Table 6: 3
TABLE 6: WIND SPEEDS CASE WIND SPEED PRESSURE UNRESTRICTED SERVICE 40 m/s 3128.32 Pa SEVERE STORM CONDITION 60 m/s 7038.72 Pa Static stability is evaluated by the righting lever curve. This curve represents at any heel angle the righting lever (GZ) for a particular loading condition of the vessel. Dynamic stability is important to evaluate the ability of the vessel to withstand the effect of gusts and severe wind and rolling. The area under the righting lever curve multiplied by the displacement represents the dynamic stability of the vessel. ABS [5] and [9] described in Part A, Chapter 2, were used to assess the static and dynamic stability of the for each of the loading conditions. The calculations of the righting lever curve and wind heeling moment for each load case of the were performed within Hydromax software using the Large Angle Stability analysis case. Figure 3 shows the righting lever curve for the fully loaded and the water ballasted conditions and for a wind speed of 60 m/s. It can be seen that the water ballasted condition has better stability than the fully loaded condition since the initial GM is bigger as well as the righting energy. Also it can be seen that the has enough righting energy to withstand the wind heel moment in both cases for the severe storm condition. The Table 7 presents the results of the static and dynamic stability analysis of the barge according to the regulations listed above. It can be seen that all the requirements are accomplished which demonstrates the great performance of the in stability. (a) Fully loaded condition. Wind speed 60 m/s (b) Water ballasted condition. Wind speed 60 m/s FIGURE 3: RIGHTING LEVER CURVES TABLE 7: INTACT STABILITY RESULTS CRITERIA LIMITED VALUE FULLY LOADED WATER BALLASTED PASS AREA 0-30 [m rad] (>=) 0.055 2.228 2.623 YES AREA 0-40 [m rad] (>=) 0.09 3.6 4.28 YES AREA 30-40 [m rad] (>=) 0.03 1.372 1.657 YES GZ MAX [m] (>=) 0.2 9.737 9.63 YES ANG. GZ MAX [ ](>=) 25 31.4 32.27 YES GM0 [m] (>=) 0.15 15.076 18.054 YES 40 m/s WIND HEELING (A+B/B+C) (>=) 1.4 YES YES YES 60 m/s WIND HEELING (A+B/B+C) (>=) 1.4 YES YES YES 4
Damage stability calculations Once the intact stability of the was evaluated, a number of damages cases were assumed to asses the damage stability of the barge. ABS [5] in Part 3, Chapter 3, Section 2 defines the extents of damages that should be considered. However the International Gas Code [8] regulations are more restrictive in their proppossed damages. Therefore this regulation was followed to assess the damage stability of the. Three damage cases were considered and are presented in Figure 4. The extent of damage considered in Case 1 affects LNG tank #1 (S), and the surrounding water ballast tanks (#1 WB tk. (S), #1 Bottom WB tk. (S) and Fwd. WB tk. (S)). In Damage Case 2, #2 and #3 LNG tk.(s) are damaged as well as #2 and #3 WB tk. (S) and #2 and #3 Bottom WB tk (S). Finally, Damage Case 3 affects #4 LNG tk. (S), Machinery room (S), #4 WB tk. (S) and #4 Bottom WB tk. (S). According to [5] a permeability of 0.95 was considered for all of the tanks and 0.85 for the machinery room. Hydromax uses the Lost buoyancy method rather than Added mass when performing the damage calculations. Any tank fluids are treated as having been completely replaced by seawater up to the equilibrium waterline, and flooding is considered to be instantaneous up to sea level [10]. The load condition with least stability (Fully loaded condition) was considered in the calculations to asses the damage stability of the barge. Also a wind heeling moment equivalent to a 30 m/s wind speed was considered for the dynamic stability calculations. Table8 shows the results of the damage static and dynamic stability calculations. It can be seen that the accomplishes with all the requirements for all of the damage cases. (a) Damage Case 1 (b) Damage Case 2 (c) Damage Case 3 FIGURE 4: DAMAGE CASES TABLE 8: DAMAGE STABILITY RESULTS CRITERIA LIMITED VALUE DAMAGE 1 DAMAGE 2 DAMAGE 3 PASS RANGE OF POSITIVE STABILITY [deg](>=) 20 68.2 62.9 65 YES RESIDUAL RIGHTING LEVER [m](>=) 0.1 5.84 4.795 5.279 YES AREA UNDER GZ [m rad](>) 0.018 0.968 0.665 0.766 YES ANGLE OF EQUILIBRIUM [ ](<) 30 4.6 2.9 2.4 YES DECK INMERSION - NO NO NO YES 30 m/s WIND HEELING (A+B/B+C) (>=) 1.4 YES YES YES YES 5
GLOBAL PERFORMANCE. FREQUENCY DOMAIN To investigate the hydrodynamic performances of the system the numerical Simulation were carried out of the system subjected to a 100-year return extreme sea state of irregular waves combined with steady wind and current. The random wave environment is described by a three-parameter JONSWAP spectrum with a significant wave height of 2.0 meters, and a peak enhancement factor of 3.0. To simulate the wind load, steady flow is assumed. The mean wind velocity at the reference height of 10 meters for one hour is 4.0 m/s. The current velocity near free surface is 2.0 m/s. The hydrodynamic performances of the within the wave range from 0.02 rad/s to.2 rad/s were investigated, with the frequency density near the resonance field intensified. Theories used in these simulations are summarized as follows: FIGURE 5: SURGE RAO OF [M + a(ω)] ζ +C(ω) ζ + Kx = F(ω) (2) Where M is the generalized mass matrix for the ship hull, a(ω) is the added mass matrix, K is stiffness matrix and F(ω) is the external force vector. It follows from the equation that the body motions corresponding to the first-order wave exciting forces can now be written as [11]: ζ (1) (ω) = RAO(ω)F (1) (ω) (3) Where superscripts (1) represents the first order variables, and RAO(ω) represents the operator which can be expressed as: FIGURE 6: HEAVE RAO OF RAO(ω) = {( ω 2 [M + a(ω)] iωc(ω) + K} 1 (4) The RAOs of the surge, heave, roll and pitch motions of the in fully loaded condition are calculated over the wave frequency from 0.2 rad/s to 1.5 rad/s, the following figures present the results as a function of the wave period. Fig.?? shows that surge motion stays at the low resonant also it can be seen that the surge motion would generate larger response in waves with longer period. It can be found from Fig. 6 that the heave motion responses are sensitive to wave headings. In the beam wave the peak value of the heave motion responses would achieve 13.35 s that is far from significant period of wave spectrum (10 s). However much attention should be put on the heave motion in the beam sea. Fig.7 shows that roll motion responses is very small. The resonant period is far from the significant period of wave spectrum. As can be seen from fig pitch motion responses are sensitive to wave heading and the resonant period is far from the significant period of the wave. Figure 8 shows the pitch RAOs in 0 degree and 45 degree and wave spectrum. Pitch natural period in the beam sea is 12 s and significant period is 10 s. GLOBAL PERFORMANCE. TIME DOMAIN ANALYSIS The coupled analysis of the ship motions and the loads acting on the mooring lines are calculated with the wave and wind and current. The coupled equation adopted in the time domain analysis can be written as follows [12]: [M + a( )]{ ζ t } + [h(t τ)]{ ζ }dt + K{ζ } (5) Where M and K have been previously defined. a( ) indicates the added mass in infinite frequency. h(t) refers to radiation 6
FIGURE 7: ROLL RAO OF FIGURE 9: HEAVE TIME SERIES OF MOTION FOR THE FIGURE 8: PITCH RAO OF function matrix, which means the influence of the memory effect in the free surface. This can be obtained by the following equation: h i j (t) = 2 π 0 C i j (ω)cosωt dω (6) The statics result of vessel motions are summarized in Figures 9-12 for the simulation with jetty mooring system in the head sea. Figure 9 and 10 show the maximum values measured for the heave and pitch motions are 3.325 m 0.595 and witch are in safe range of operation. The extreme amplitude for heave and pitch motions are 4.519 m and 6.044 m respectively, which is acceptable for the system in extreme sea state [13]. From fig.11, we can see that the extreme value of the roll motion which of the great concern for us is 0.02 in the 100-year return storms with the wave heading angle of 180. This verifies the feasibil- FIGURE 10: PITCH TIME SERIES OF MOTION FOR THE ity of designs of the hull with the jetty mooring system, which aims to avoid sever roll motion in extreme sea sates. Figure 12 shows the Surge response motion in time domain. From the statistical prediction of surge motion, we get the maximum surge motion is -7.810 m. MOORING SYSTEM The design of a fender system is based on the law of conservation of energy. The amount of energy being introduced into the system must be determined, and then a means devised to absorb the energy within the force and stress limitations of the ship s hull and the fender. At the first we should calculate the effective berthing energy to pick out fender candidates witch absorb the calculated energy from catalog. The berthing energy to be 7
FIGURE 11: ROLL TIME SERIES OF MOTION FOR THE FIGURE 13: JETY MOORING SYSTEM IN AQWA FOR THE FIGURE 14: TOTAL FORCE OF THE FENDER FIGURE 12: SURGE TIME SERIES OF MOTION FOR THE absorbed by rubber fenders can be calculated by multiplying the vessels total kinetic energy by a series of coefficients: E = 0.5 M V 2 C e C h C s (7) Where M is displacement of the supply vessel, V is the relative speed, C e is the eccentricity coefficient accounting for the ships rotation, C h is the virtual mass coefficient accounting for added mass due to entrained water and C s is the softness ratio accounting for the relative stiffness of the vessel hull and the rubber fenders. Based on calculated effective energy absorption, MCN 700 with G4 Rubber grade absorbs 223 kn-m and is a suitable for our design [14]. The fender system with 7 fenders simulated by AQWA?? (fig.13), the total Reaction Force was calculated. The results is shown in Fig.14. The maximum total force is 532012 N. That is less than reaction force of this type of fender 601000 N. This indicates that the mooring system of the system would be safe enough even in the extreme sea states in the Maine sea. CONCLUSIONS The International Energy Agency has forecasted that the global energy demand will double between 2005 and 2030. Therefore, the demand for supply of gas must increase by five times to meet the projected global energy demand. Meanwhile, the lack of suitable sites for onshore gas plants and the pressure on the energy supply chain are expected to boost demand for a facility. The hydrodynamic characteristics of the system are of great importance to the efficient exploitation of the stranded. The global performance analysis gives a basic concept of how the will perform in actual offshore environment. Conclusions can be drawn from the simulation results that the jetty mooring system can survive safely the 100-year 8
return storms in Passamaquoddy Bay, ME. This would provide guidance for the ongoing projects of systems REFERENCES [1] Outlook, A. E., 2014. AEO 214 early release overview. Tech. rep. [2] Williams, N., 2012. Overview of world s first floating LNG liquefaction, regasification and storage unit (FLRSU) project.. [3] Deybach, F., de Seze, P., Cayuela, J., and Sigaudes, J., 2009. Going offshore with membrane containment systems. GAZTRANSPORT & TECHNIGAZ. [4] ABS, 2013. RULES FOR BUILDING AND CLASS- ING FLOATING OFFSHORE LIQUEFIED GAS TERMI- NALS. [5] ABS, 2014. RULES FOR BUILDING AND CLASSING MOBILE OFFSHORE DRILLING UNITS. [6] SOLAS, I., 2003. International convention for the safety of life at sea. london. International Maritime Organization. [7] IMO, M., 2003. 73/74, regulation 13G of annex i. Revised edition. [8] Code, I. G. C., 1990. International code for the construction and equipment of ships carrying liquefied gases in bulk. IMO, London. [9] Edition, S. C., 2004. Consolidated text of the international convention of safety of life at sea, 1974, and its protocol of 1988: articles, annexes and certificates. IMO, London. [10] MARINE. HYDROMAX User Manual V11. [11] Zhao, W. H., Yang, J. M., Hu, Z. Q., and Wei, Y. F., 2011. Recent developments on the hydrodynamics of floating liquid natural gas (). Ocean engineering, 38(14), p. 1555 1567. [12] Zhao, W.-h., Yang, J.-m., Hu, Z.-q., Xiao, L.-f., and Peng, T., 2012. Investigation on the hydrodynamic performance of an ultra deep turret-moored system. China Ocean Engineering, 26, p. 77 93. [13] Zhao, W., Yang, J., Hu, Z., Xiao, L., and Peng, T., 2013. Experimental and numerical investigation of the roll motion behavior of a floating liquefied natural gas system. Science China Physics, Mechanics and Astronomy, 56(3), p. 629 644. [14] Maritime International, 2013. MCN cone fender catalogue. 9