Bubble curtain system for prevention of seawater intrusion in coastal aquifers

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1 Available online at Advances in Applied Science Research, 013, 4(4):81-90 ISSN: CODEN (USA): AASRFC Bubble curtain sstem for prevention of seawater intrusion in coastal aquifers Mehdi Nehad Naderi, Masoud Rea Hessami Kermani and Gholam-Abbas Barani Department of Civil Engineering, Shahid Bahonar Universit, Kerman, Iran ABSTRACT A bubble curtain is a sstem that produces bubbles in a deliberate arrangement in water. This technique is based on bubbles of air (gas) under the water surface that act commonl as a barrier. When the bubbles rise the act as a barrier or a curtain. This paper paid to applications of this sstem for prevention of the advance of seawater and protection of environment of offshore. The multiphase flow is simulated b computational fluid dnamics method. During high level of tide bubble curtain sstem can be used simultaneous in several parallel rows of air inection in across the offshore. During low level of tide air inection rate and use of the bubble curtain sstem is reduced. The results of the numerical models show that increasing air inection rate is caused to reduce seawater. Kewords: bubble curtain, multiphase flow, computational fluid dnamic method, Prevention of seawater intrusion, Fluent Software. INTRODUCTION Bubble curtain, in its simplest form, is a circle or square tube with holes in it that air is inected under pressure into the tube and the bubbles will create a curtain of bubbles. Components needed to create a barrier bubbles: 1 - compressed air from a compressor station, - pipe with special noles incorporated and anchor blocs, 3 - levels produced b bubble curtains and 4- drain valve at the end of the nole tubes. The subects epressed about the use of bubble curtains to protect the marine environment. Saltwater intrusion in estuaries of tidal rivers is causing environmental damage. Construction of bubble curtain must be checed in across river as a wa for prevention of saltwater intrusion in estuaries of tidal rivers. In this paper is paid to two-phase flow simulation b software Fluent6.3 that freshwater input is from the left side, saltwater on the right side of the entrance and the air from vertical duct. B using of miture model and - turbulence model in software the two-phase miture is dissolved. At first the air inlet velocit is considered 0.6 meters per second then is reduced to 0. meters per second. As ou can see using of air (bubbles) curtain can be prevent from saltwater intrusion and also reduce densit in estuaries of tidal rivers. In this stud, flow is unstead with two-dimensional turbulence form. Velocit and pressure are a function of time and space. To model of the velocit and pressure fluctuations is the integrated from the Navier Stoes equation at time. In this stud, flow is stead with two-dimensional turbulence form. To model of the velocit and pressure fluctuations is the integrated from the Navier Stoes equation at time. Integration of Navier Stoes equations at time is nown Renolds equations []. Turbulence model equations are two equation models - (Standard) that have be averaged in depth [3]. equation is as one of the main sources of the limitations of accurac of the standard version of the - model and the Renolds stress model. It is interesting that - model includes a correction term that is dependent to strain with c13 constant in the equation of RNG model [4]. WillCo provided turbulence equations of -ω (standard) model [5]. 81

2 Mehdi Nehad Naderi et al Adv. Appl. Sci. Res., 013, 4(4): Figure 1 - View of a bubble curtain in place of berthing the ship in Vancouver of Canada to reduce noise pollution [1]. Figure - Barriers (bubble) to prevent the spread of spilled oil on the water surface Figure 3- from the right 1 - the compressor station, - pipe with special noles incorporated and anchor blocs, 3 - level generated b bubble curtains to the surface, 4 - the discharge valves on end of the nole tube. MATERIALS AND METHODS 0 = w v u (1) P v f uw uv uu t u c = () P u f vw vv uv t v c = (3) g P ww vw uw t w = (4)

3 Mehdi Nehad Naderi et al Adv. Appl. Sci. Res., 013, 4(4):81-90 Known two-equation model of - (Standard) are presented for averaged form in depth as follows [3]: h U h ν t = [( ν ) h ] hp hpv h (5) t σ h U h νt = [( ν ) h ] hc1 t σ P hp v hc t = c, P ν t Si. Si (7) ν µ = u f 1 c cµ u f v = c, c =, P, c, c 1 v = c = 3 f = = c h e* σ t c 4 u v w f f µ = 0.09, c1 = 1.44, c = 1.9, σ = 1.0, σ = 1.31 P c P v and P v are production terms as result of non-uniform distribution velocit in depth that is stronger near-bed. P is production term of turbulent inetic energ averaged in depth as result of velocit gradients in the plan. ν t is the vorte viscosit. Turbulence model is used for calculation of lateral flow into one channel and is achieved much better results in comparison with ν t for fied parameters of rotational flow [7]. c f is the bed friction coefficient. σ t is Schmidt number that shows relationship between turbulence viscosit and turbulent diffusion coefficient according to the following equation: ν t d = (9) σ t Amount ofσ t is considered 0.5 [8]. Although values of σ t are 0.5 to in variable references [9]. e * is coefficient that gives turbulence diffusion coefficient in depth b following equation [8]. d = e * hu f (10) Direct measurement of color broadcasting in the fied-width channels offers 0.15 for e *. Although Keller and Rodi achieved better solutions for the velocit and stress within the composite channels [8]. On the other hand Biglari and Sturm have been assumed e * equaled to 0.3 to get the better answer within the composite channels [9]. MCGuri 1 and Rodi have considered equaled to 3.6 [7]. In equation of RNG model includes a correction term c 1 e * σ t that is constant strain-dependent [4]. For - (RNG), we have: h U h = t c µ = , c * 1 = c ν t [( ν ) h ] hc σ 1 η η(1 ) η0, c 3 1 βη 1 * 1 P hp = 1.68, σ v 1 (. ) η = Ei Ei, η0 = Onl constant β is adustable, high levels of turbulent data are obtained near-wall. All other constants are calculated eplicitl as part of the RNG process. hc = 1.39, β = 0.01, c 1 = 1.4, n h g 1 3 (6) (8) (11) (1) h t U h = ν t ν ) h ] P σ P h [( b (13) 83

4 Mehdi Nehad Naderi et al Adv. Appl. Sci. Res., 013, 4(4):81-90 h U h = t η c1 = Ma[0.43, ], η = s, s = η s ν t [( ν ) h ] hc1 P hc1s hc S (14) σ ν, µ = hc µ t T 1 * P = µ t s, Pb = βgi, µ t = cµ, cµ =, U = s, Pr * isi Ωi Ωi t i KU A0 As 1 1 sis si Ω = Ω, 4.04, 6 cos, cos ( 6 ),, ~ i i iω A0 = As = Φ Φ = ω ω = 3 ~ s = s 3 is s 1 u ui 1 P si = ( ), c1 = 1.44, c = 1.9, σ = 1, σ = 1., β = ( ) p,prt = 0.85 T i s s i i t µ ', P = uiu WillCo, turbulence model -ω (standard) equation to be provided as follows [6]: U t ω U t Ui * * = i β ω [( ν σ ν T ) ] (16) ω ω = α i U i βω ω 5 3 * 9 1 * ν t =, α =, β =, β =, σ =, = β ω ω ω [( ν σν T ) ] The values of the phsical properties of water are considered 998., , 418 and 0.6, respectivel, for densit, viscosit, heat capacit and thermal conductivit. Solutions of all governing equations are subect to assignment of variables correctl in the boundar nodes. In stead state problems required onl boundar condition but in unstead state problems is required the initial conditions for all nodes in the networ. Common boundar conditions in hdraulic issues include [10]: A- Inlet boundar condition: numerical models can fit the model b means of the various boundar conditions such as velocit, mass flow, etc. For eample, in modeling of flow inside a closed or open channel can be used velocit inlet as input boundar condition. B- The outlet boundar condition is considered pressure outlet equals the atmospheric pressure. If the output is chosen at a far distance from geometric constraints, and no change in direction of flow then the flow state is developed full. Using this model is caused the output surface is perpendicular to the flow and gradient is ero in the perpendicular direction on the output surface [10]. C - Wall boundar condition: the wall boundar condition is used to limit the area of between fluid and solid. The model is read for simulation b Solutions set and defining the model. The following steps show the simulation process [11]: selection methods of discretiation equation: In this paper first order upstream difference method is used for discretiation of momentum,, and ω equations and the standard method is used to find the pressure. Selection methods of the relation velocit - Pressure: this step is onl be studied segregated. In this paper is used from SIMPLE method for velocit - pressure coupling. Determine the discount factors: the discount factor values are used for control of calculated variables in the each iteration. In this paper, the default values 0.3, 1, 0.7, 0.8, 0.8 and 1 is used respectivel for the pressure, densit, momentum,, and turbulent viscosit. In this paper, the initial values of the relative pressure is considered ero And the initial values of velocit components close to the average values presented in the input stream. B completing the steps in the numerical model, we can start the introduced process of problem b defining of repeat process. The frequenc of reporting of results can be introduced before computing the numerical model. During solution process can be seen convergence of solution b the control of residues, integral of surface, statistics and values of the force. After finishing solution the computation of the unnown quantities and the results can be calculated at an point of the field and can be displaed b vector in the form, contour and profile [11]. In this paper for solution of flow is usuall introduced initial number repeat 1000 with report of ever step of the calculation that conditions for convergence of the unnown parameters were satisfied after 300 to 350 iterations. Gambit software version.3.16 is used to generate the channel geometr and meshing [1]. Model of the networ is used Quad element and the tpes of Map and Pave for pages and He elements and tpes of Map of Cooper for volumes. Inlet and outlet and wall boundar conditions and smmetr were introduced in the software. ' u ' i, i, (15) (17) 84

5 Mehdi Nehad Naderi et al Adv. Appl. Sci. Res., 013, 4(4): Meshing model Gambit software version.3.16 is used to generate the channel geometr and meshing. Model of the networ is used Quad element and the tpes of Map and Pave for pages and He elements and tpes of Map of Cooper for volumes. Inlet and outlet and wall boundar conditions and smmetr were introduced in the software. RESULTS AND DISCUSSION The results of the numerical models show that increasing air inection rate is caused to reduce seawater intrusion to estuar of tidal rivers as figure 4 to 8. Figure 4- meshing of model and boundar conditions Figure 5- a- Velocit magnitude contours for the two phase flow for seawater intrusion from right input, bubble curtain channel and freshwater from left input (air velocit is 0.6 m/s) 85

6 Mehdi Nehad Naderi et al Adv. Appl. Sci. Res., 013, 4(4):81-90 Figure 5- b- the velocit contours for the two-phase flow in the direction, (air velocit is 0.6 m/s) Figure 5- c- the velocit contours for the two-phase flow in the direction (air velocit is 0.6 m/s) 86

7 Mehdi Nehad Naderi et al Adv. Appl. Sci. Res., 013, 4(4):81-90 Figure 6-a- the velocit magnitude contours for the two-phase flow (air velocit is 0. m/s) Figure 6- b- the velocit contours for the two-phase flow in the direction (air velocit is 0. m/s) 87

8 Mehdi Nehad Naderi et al Adv. Appl. Sci. Res., 013, 4(4):81-90 Figure 6- c- the velocit contours for the two-phase flow in the direction, (air velocit is 0. m/s) Figure 7-a- the pressure contours for the two-phase flow (air velocit is 0. m/s) 88

9 Mehdi Nehad Naderi et al Adv. Appl. Sci. Res., 013, 4(4):81-90 Figure 7-b- the pressure contours for the two-phase flow (air velocit is 0.6 m/s) Figure 8-a- the densit contours for the two-phase (air velocit is 0. m/s) 89

10 Mehdi Nehad Naderi et al Adv. Appl. Sci. Res., 013, 4(4):81-90 Figure 8- b- the densit contours for the two-phase flow (air velocit is 0.6 m/s) CONCLUSION A bubble curtain is a sstem that produces bubbles in a deliberate arrangement in water. Bubble curtain is applied for breaing the propagation of waves or prevention of the spreading of particles and other contaminants. In this paper is paid to two-phase flow simulation b software Fluent6.3 that freshwater input is from the left side, saltwater on the right side of the entrance and the air from vertical duct. B using of miture model and - turbulence model in software the two-phase miture is dissolved. At first the air inlet velocit is considered 0.6 meters per second then is reduced to 0. meters per second. The results of the numerical models show that increasing air inection rate is caused to reduce seawater intrusion. As ou can see using of air (bubbles) curtain can be prevent from saltwater intrusion and also reduce densit. REFERENCES [1] Swanson,., 004. Fish ills drive techniques for placing bridge piles. in Jun 3, 004 issue of Dail Journal of Commerce (Portland, OR). [] Renolds, O. On the Dnamical Theor of Incompressible Viscous Fluids and the Determination of the Criterion, Phil. Trans. Ro. Soc. London, 1986, [3] Rastogi, A. K., and Rodi, W. Journal of Hdraulics Division, ASCE, 1978, 104(3), [4] Yahot, V., Orsag, S.A., Thangam, S., Gatsi, T. B., and speiale, C. G. Phsics of Fluids A, 199, Vol. 4, No. 7, pp [5] Wilco, D. C. AIAA Journal, 1988, vol. 6, pp [6] McGuri, J. J., and Rodi, W. A Journal of Fluid Mechanics, 1978, 864, [7] Keller, R. J., and Rodi, W. Journal of Hdraulic Research, IAHR, 1988, 6(4), [8] Gibson, M. M., and Launder, B. E. Journal of Fluid Mechanics, 1978, 86, [9] Biglari, B., and Sturm, T. W. Journal of Hdraulic Engineering, ASCE, 1998, 14(), [10] Soltani, M. V. and Rahimi Asl,R. Computational Fluid Dnamics b Fluent Software, Tehran, Tarrah issues, 003. [11] Versteeg, H. K. and Malalaseera, W. An Introduction to Computational Fluid Dnamics, [1] GAMBIT. User s Guide, September,