Method for improving a fluid dynamic profile of a marine vessel, a marine vessel having an improved fluid dynamic profile, and a coating system for improving the fluid dynamic profile

Abstract

A method for improving a fluid dynamic profile and fouling properties of a marine vessel with a welding seam which forms a cap protruding above a surface being under the waterline of a vessel. The method comprising amending the welding seam by applying a fairing to the underwater surface, e.g. by use of filler. A vessel with a fairing, and a coating system for a vessel and including a fairing.

Claims

1. A method for improving a fluid dynamic profile of a marine vessel, the method comprising the step of identifying at least one welding seam forming a cap protruding above an underwater surface of the marine vessel, and amending a profile of the marine vessel by applying a fairing to the underwater surface and to the at least one welding seam, wherein the fairing is applied to the underwater surface and to the at least one welding seam by applying unsolidified filler to the underwater surface and to the at least one welding seam, shaping the filler, and solidifying the filler.

2. The method according to claim 1, wherein the unsolidified filler is applied from a pump into an application tool configured to be moved over the underwater surface and configured to define a shape of the fairing.

3. The method of claim 1, comprising the step of applying a fairing having a triangular shape forming a lower surface against the underwater surface and two top surfaces extending from a top point above the at least one welding seam and sloping from that top point downwards towards the lower surface.

4. The method of claim 3, comprising the step of applying a fairing having the shape of an isosceles triangle.

5. The method according to claim 1, wherein the fairing is applied to cover the at least one welding seam and a heat affected zone (HAZ) of the at least one welding seam.

6. The method according to claim 1, wherein the fairing is applied symmetrically about the at least one welding seam.

7. The method according to claim 1, wherein the fairing is applied over the at least one welding seam between a primer layer and a topcoat.

8. The method according to claim 1, wherein the fairing is covered with a fouling control surface coating system.

9. The method according to claim 1, comprising identifying at least one longitudinal welding seam extending on the underwater surface in a longitudinal direction in which the marine vessel is designed to sail, identifying at least one transverse welding seam extending on the underwater surface in a transverse direction being transverse to the longitudinal direction, and applying the fairing to the at least one transverse welding seam without applying a fairing to the at least one longitudinal welding seam.

10. The method according to claim 9, wherein the fairing is applied exclusively to at least one welding seam extending in a direction being perpendicular to the longitudinal direction.

11. The method according to claim 1, wherein the fairing is applied only on a downstream side of the at least one welding seam facing backwards relative to a sailing direction of the marine vessel.

12. The method according to claim 1, wherein the fairing is applied at most on at least one welding seam in a forward half part of the underwater surface of the marine vessel, the forward half part of the underwater surface extending from a front end pointing forward the sailing direction and half the way towards a rear end of the marine vessel.

13. The method according to claim 1, wherein the marine vessel is operated with a speed through water with the fairing applied to the underwater surface and at least one welding seam.

14. A marine vessel having a hull forming a welding seam extending along an underwater surface and forming a cap projecting a seam-height in an outwards direction away from the underwater surface, the marine vessel further comprising a fairing extending in an axial direction and projecting a fairing-height in the outwards direction and covering at least a part of the welding seam and underwater surface.

15. The marine vessel according to claim 14, wherein the fairing-height decreases in a width direction along the underwater surface away from the welding seam.

16. The marine vessel according to claim 14, wherein the fairing-height is between 90 and 110 percent of the seam-height.

17. The marine vessel according to claim 14, wherein the fairing terminates in two side edges extending in the axial direction on opposite sides of the welding seam.

18. A The marine vessel according to claim 17, wherein at least one of the side edges extends at a distance of at least 5 times the fairing-height from the welding seam.

19. The marine vessel according to claim 17, wherein the distance from one side edge to the welding seam equals the distance from the other side edge to the welding seam.

20. The marine vessel according to claim 14, wherein the fairing has an outer surface facing away from the underwater surface, the outer surface being convex in a cross-section transverse to the axial direction.

21. A coating system for an underwater surface of a marine vessel, the coating system comprising at least one layer of a primer applied to the underwater surface, a fairing configured to amend the profile of the underwater-surface at a welding seam and applied in accordance with claim 1, the fairing being applied to the primer, and a top coat applied to the fairing.

22. The coating system according to claim 21, further comprising a layer of a tie-coat applied between the fairing and the top coat.

23. The coating system according to claim 21, wherein the top coat comprises at least one layer of a fouling control surface coating system.

Description

LIST OF DRAWINGS

(1) FIGS. 1-3 illustrate cross-sectional views of a steel plate under the waterline of a vessel;

(2) FIGS. 4-6 illustrate top views of the steel plates;

(3) FIG. 7 illustrates a top view of a bottom surface of a vessel;

(4) FIGS. 8a-8e illustrate different profiles of fairings;

(5) FIGS. 9-13 illustrate results of different tests, and

(6) FIGS. 14-16 illustrate aspects related to CFD simulation.

DESCRIPTION OF EMBODIMENTS

(7) FIG. 1 illustrates steel plate forming an underwater surface of a marine vessel. The outer surface 1, which is in contact with water, is illustrated upwards, and the inner surface 2 faces inwards, e.g. towards ballast tanks etc. The plate is constituted by two separate sheets 3, 4 of metal which are joined by welding. The welding joint forms a cap 5 projecting a seam-height in an outwards direction away from the underwater surface. The height is illustrated by the arrow h.

(8) FIG. 2a illustrates the plate from FIG. 1 where a fairing 6 is made by applying filler over the welding seam. The fairing extends in the axial direction inwards and outwards of the plane defined by the cross-section. The axial direction is illustrated by the arrow 7.

(9) The fairing projects a fairing-height, p, in the outwards direction and covers the welding seam and a part of the underwater surface.

(10) FIG. 2b illustrates an enlarged cross-section of the fairing. The fairing has a triangular shape forming a lower surface illustrated by the dotted line 8 against the underwater surface. The lower surface 8 is interrupted by the cone shape 9 created by the cap of the welding. Within the meaning of this document, the fairing is, however, noted as being triangular. The triangle also forms the two top surfaces 10, 11 extending from the top point 12 above the welding seam and sloping from that top point downwards towards the lower surface at the corners 13. The illustrated fairing has the shape of an isosceles triangle, i.e. having at least two sides of equal length.

(11) FIG. 3 illustrates a fairing 14 forming a separate component having a shape which is pre-defined and which is attached adhesively to the welding seam and underwater surface.

(12) FIG. 4 illustrates the welding seam from FIG. 1 but seen above the outer surface, i.e. above the surface which is in contact with the water when the vessel is launched. In this view, two HAZ 15, 16 are illustrated on opposite sides of the welding cap. The two HAZ are a result of the excessive heat input from the welding process.

(13) FIG. 5 illustrates the welding seam from FIG. 4 and with a fairing 17 covering not only the welding cap but also the two HAZ. The fairing thereby provides a smooth surface with reduced drag and increases the protection of the welding and HAZ.

(14) In FIGS. 4 and 5, the arrow 7 indicates the axial direction of the welding seam, and arrow 18 (and arrow 24 in FIG. 7) indicates the sailing direction for the vessel also referred to as the longitudinal direction. The invention may generally be applied to any of the welding seams on underwater surfaces. However, as illustrated in FIG. 6, the invention may be particularly useful when the fairing is applied exclusively to weld lines extending transverse to the sailing direction, herein referred to as “in the transverse direction”. In FIG. 6, this is illustrated by the longitudinal welding seam 19 and HAZ 20, 21. Whereas the transverse welding seam 5 is covered by the fairing 17, the other, longitudinal, welding seam 19 extends in the sailing direction and is not covered. At the uncovered welding seam, the HAZ 20, 21 also extend uncovered.

(15) FIG. 7 illustrates a bottom 22 of a vessel. The vessel has a rounded stern 23 and is intended for the sailing direction indicated by the arrow 24 thereby also indicating the longitudinal direction. The vessel comprises a number of transverse welding seams 25 extending perpendicular to the sailing direction, and at least two longitudinal welding seams 26 extending in the sailing direction.

(16) The fairings 27 of filler are applied only on welding seams in a forward half part of the underwater surface of the vessel. This is indicated by the distance indication X/2 for each of the two subsequent sections in the length direction.

(17) FIGS. 8a-8e illustrate different profiles of fairings.

(18) In FIG. 8a, the fairing 28 has a height below 100 pct. of the height of the cap of the welding seam and the cap therefore extends through the fairing. Even though the welding seam is visible through the fairing, the fairing protects and changes the flow conditions at the welding seam.

(19) In FIG. 8b, the fairing 29 has a height above 100 pct. of the height of the cap of the welding seam but it is only arranged to cover the part of the welding seam and HAZ pointing downstream away from the sailing direction indicated by the arrow 30. By this type of fairing, the flow conditions are amended particularly downstream of the welding seam where fouling is sometimes experienced. The change in flow conditions caused by the fairing downstream the welding seam may reduce the fouling.

(20) In FIG. 8c, the fairing 31 has a height below 100 pct. of the height of the cap of the welding seam and it is only arranged to cover the part of the welding seam and HAZ pointing downstream away from the sailing direction indicated by the arrow 30. The welding seam therefore extends through the fairing but the fairing still protects and changes the flow conditions at the welding seam.

(21) In FIG. 8d, the fairing 32 has a height of exactly 100 pct. of the height of the cap of the welding seam and it has a concave shape.

(22) In FIG. 8e, the fairing 33 has a height of exactly 100 pct. of the height of the cap of the welding seam and that part of the fairing pointing in the sailing direction has a concave shape, and that part pointing rearwards relative to the sailing direction has a convex shape.

EXAMPLES

Example 1—Towing Tank Test

(23) To investigate the effect on the resistance due to protruding welding seams on ship hulls, three resistance tests with flat plates with and without protrusions representing welding seams were performed in order to measure the added resistance from the welding seams.

(24) Two different profiles were tested: one with an arc type cross section as illustrated in FIG. 1 corresponding to a welding seam without a fairing, and one with a smooth transition over the welding seam (as illustrated in FIG. 2a) simulating a fairing. The arc type welding seam had a cross section with a width of 12 mm and height 3 mm, and faired protrusion had the same height but a width of 60-100 mm.

(25) Force measurements on thin flat plates were performed by FORCE Technology, Hjortekærsvej 99, DK-2800 Kongens Lyngby. The measurements were made in a 240 meter long towing tank with 5.5 meter deep water. The thin, flat 2.5×0.6 meter large plates were submerged from the rig and the drag forces were measured at speed from 3 to 7 m/s, from which the skin friction force and skin friction coefficient (Cf) was determined.

(26) Three 5 mm anodized aluminium plates were prepared for the test program. A fairing was applied to the leading edge to reduce the wave making resistance and a 25 mm wide vertical sandpaper tape was located, on both sides, 0.1 m aft of the leading edge of the plate in order to stimulate a fully turbulent flow on the remaining part of the plate downstream. Before any testing with plates the air resistance of the test rig was identified by running test runs with the rig alone.

(27) One welding seam were placed symmetrically on each sides of the plates, 1 m aft the leading edge, with the following dimensions:

(28) TABLE-US-00001 Welding type Height [mm] Width [mm] Length [mm] Arc 3 12 485 Faired arc 3 60-80 485
Initially one smooth reference plate was tested without any protuberances in order to validate the test setup and determine the reference frictional resistance. Then the plate with the arc welding seam was tested and subsequently the plate with the fairing over the welding seam was tested. After the tests with the protrusions the smooth reference plate was tested again.

(29) The drag measured during the test runs with welding seams was first subtracted by the air resistance and smooth plate resistance to arrive at the drag increment due to the welding seam. The drag coefficients of the plates are presented in FIG. 9 and the model scale drag increment is presented in FIG. 10. It illustrates that the transverse arc welding seams increase the smooth plate resistance by 6.5-9.2% where the fairing over the welding seam gave about 2% increase.

(30) TABLE-US-00002 TABLE 1 Summary of the results showing the drag resistance of the plates with transverse welding seams. Local Reynolds reynolds number number Test Re Re.sub.X Mean STD Run ID Speed (U*L/ny) U*X/ny Drag drag Cd * Comments — — m/s — — N N — — 13 — 3.000 7.04E+06 0.21 0.07 1.74E−05 Air resistance 14 — 4.002 9.39E+06 0.34 0.18 1.64E−05 Air resistance 15 — 5.003 1.17E+07 0.30 0.33 9.25E−06 Air resistance 16 — 6.004 1.41E+07 0.80 0.11 1.70E−05 Air resistance 17 — 7.017 1.65E+07 1.06 0.13 1.64E−05 Air resistance 27 1 3.001 7.04E+06 38.98 0.24 3.29E−03 Reference plate, 29 1 4.001 9.39E+06 66.61 0.53 3.16E−03 Reference plate, 30 1 5.002 1.17E+07 102.60 0.52 3.12E−03 Reference plate, 31 1 6.005 1.41E+07 143.99 0.81 3.03E−03 Reference plate, 32 1 7.011 1.65E+07 189.05 1.38 2.92E−03 Reference plate, 54 1 3.001 7.04E+06 38.77 0.27 3.27E−03 Reference plate, 56 1 4.001 9.39E+06 66.11 0.40 3.13E−03 Reference plate, 58 1 5.002 1.17E+07 102.21 0.78 3.11E−03 Reference plate, 60 1 6.004 1.41E+07 143.07 0.52 3.01E−03 Reference plate, 63 1 7.005 1.64E+07 187.79 1.06 2.90E−03 Reference plate, 33 2 3.001 7.04E+06 2.82E+06 42.41 0.37 3.59E−03 Vertical welding seams, Arc, 1 m, — 35 2 4.001 9.39E+06 3.76E+06 72.14 0.36 3.44E−03 Vertical welding seams, Arc, 1 m, — 36 2 5.002 1.17E+07 4.70E+06 110.36 0.39 3.37E−03 Vertical welding seams, Arc, 1 m, — 37 2 6.003 1.41E+07 5.64E+06 153.30 0.50 3.25E−03 Vertical welding seams, Arc, 1 m, — 39 2 7.007 1.64E+07 6.58E+06 200.63 0.62 3.12E−03 Vertical welding seams, Arc, 1 m, — 43 4 3.000 7.04E+06 2.82E+06 39.46 0.33 3.35E−03 Vertical welding seams, Faired, 1 m, — 45 4 4.001 9.39E+06 3.76E+06 68.63 0.30 3.27E−03 Vertical welding seams, Faired, 1 m, — 47 4 5.002 1.17E+07 4.70E+06 103.78 0.27 3.17E−03 Vertical welding seams, Faired, 1 m, — 49 4 6.003 1.41E+07 5.64E+06 145.04 0.63 3.07E−03 Vertical welding seams, Faired, 1 m, — 51 4 7.004 1.64E+07 6.58E+06 191.78 1.42 2.98E−03 Vertical welding seams, Faired, 1 m, — * (based on the wetted surface)

(31) The drag coefficient is defined as

(32) $C_D=\frac{D}{\mathrm{hlq}}$

(33) Where

(34) D is the drag

(35) h is the height of the protuberance (welding seam)

(36) l is the length of the protuberance (welding seam)

(37) q is the dynamic pressure, defined as q=½ρV.sup.2

(38) The effective dynamic pressure is defined as

(39) $\frac{q_{eff}}{q}\approx 0.75\sqrt[3]{h/\delta }$

(40) Where

(41) δ is the maximum boundary layer thickness

(42) Using the principle of effective dynamic pressure, the independent drag coefficient (C.sub.D.sub.ind) can be derived representing a drag coefficient in a free flow:

(43) $C_{D_{\mathrm{i𝔫d}}}=\frac{C_D}{0.75\sqrt[3]{h/\delta }}$

(44) By applying this theory to the test results, the independent drag coefficient, C.sub.D.sub.ind, of the different kinds of protrusions can be established:

(45) TABLE-US-00003 TABLE 2 Model test results represented as independent drag coefficients (C.sub.D.sub.ind) and the relative reduction of C.sub.D Measured Additional Cd_measured/m Relative Local Re drag (2D) delta/x delta q_eff/q Cd_ind reduction Text Run Test — N — — m — — Cd 0 33 2 2.8E+06 3.53 0.279 0.018 0.018 0.409 0.683 Vertical welding seams, Arc, 1 m, — 35 2 3.8E+06 5.76 0.256 0.018 0.018 0.415 0.618 Vertical welding seams, Arc, 1 m, — 36 2 4.7E+06 7.70 0.219 0.017 0.017 0.419 0.523 Vertical welding seams, Arc, 1 m, — 37 2 5.6E+06 10.19 0.201 0.017 0.017 0.423 0.476 Vertical welding seams, Arc, 1 m, — 39 2 6.6E+06 12.23 0.177 0.016 0.016 0.426 0.416 Vertical welding seams, Arc, 1 m, — 43 3 2.8E+06 0.60 0.048 0.018 0.018 0.409 0.117 83% Vertical welding seams, Faired, 1 m, — 45 3 3.8E+06 2.24 0.100 0.018 0.018 0.415 0.240 61% Vertical welding seams, Faired, 1 m, — 47 3 4.7E+06 1.14 0.032 0.017 0.017 0.419 0.077 85% Vertical welding seams, Faired, 1 m, — 49 3 5.6E+06 1.95 0.039 0.017 0.017 0.423 0.091 81% Vertical welding seams, Faired, 1 m, — 51 3 6.6E+06 3.54 0.051 0.016 0.016 0.426 0.120 71% Vertical welding seams, Faired, 1 m, —

(46) The results in table 2 are presented in FIG. 11. The welding seams with an altered profile, i.e. covered by a fairing according to the invention thus reduce the drag independent coefficient by 61-85% compared to a welding seam without fairing.

Example 2—Full Scale Extrapolation

(47) The effective pressure principle from example 1 is used to estimate drag increment on a full scale ship. In order to estimate the full scale effect of the transverse welding seams an example has worked out for a 350 m containership. In this example the velocity along the hull outside the boundary layer is assumed to be constant along the hull. The transverse welding seams are assumed to extend along the entire girth for every 5 m from 50 m to 300 m from FP, i.e. transverse welding length per section 2×11 m+42.8 m=64.8 m. In this example the independent welding seam resistance coefficient for the arc is 0.5 and for the welding seam with a fairing, the resistance coefficient was 0.15. The vessel has the following characteristics that will be used in the analysis:

(48) TABLE-US-00004 Full scale Water line length Lwl 350 m Beam B 42.8 m Draught T 11 m Wetted surface S 16534.67 m.sup.2 Seam height h 0.003 m Horizontal distance 5 m between vertical welding seams Kinematic viscosity ny 1.188E−06 s/m.sup.2 (15° C.) Density rho 1025.88 kg/m.sup.3 (15° C.)

(49) At 16 knots, the added resistance due to each welding seam is listed in table 3. The sum of the increase in resistance compared to total calm water resistance shows a relative increase of 3.73% for arc welding seams.

(50) For welding seams with a fairing, the relative increase in resistance is 1.12%. FIG. 12 illustrates the added resistance along the container ship from 50 m to 300 m at two different speeds, 16 knots and 18 knots, for both arc welding seams and welding seams with a fairing.

(51) These results clearly show the effect of altering the profile of an arc welding seam to a more smooth profile.

(52) TABLE-US-00005 TABLE 3 The relative increase in resistance of arc welding seams on a full scale container ship, by extrapolation. V δ/x x δ q.sub.eff/q C.sub.d.sub.—.sub.ind C.sub.d.sub.—.sub.local/m R.sub.weld R.sub.tot R.sub.increase knots — m m — — — N kN — 16 0.93% 50 0.464 0.140 0.5 0.070 944 941 0.10% 16 0.92% 55 0.504 0.136 0.5 0.068 919 941 0.10% 16 0.90% 60 0.543 0.133 0.5 0.066 896 941 0.10% 16 0.89% 65 0.581 0.130 0.5 0.065 876 941 0.09% 16 0.88% 70 0.619 0.127 0.5 0.063 857 941 0.09% 16 0.88% 75 0.657 0.124 0.5 0.062 841 941 0.09% 16 0.87% 80 0.694 0.122 0.5 0.061 825 941 0.09% 16 0.86% 85 0.731 0.120 0.5 0.060 811 941 0.09% 16 0.85% 90 0.768 0.118 0.5 0.059 798 941 0.08% 16 0.85% 95 0.804 0.116 0.5 0.058 786 941 0.08% . . . . . . . . . . 16 0.72% 300  2.115 0.084 0.5 0.042 566 941 0.08% 16 35063  941 3.73%

(53) The relative increase was measured at speeds of 16, 18, 20 and 22 knots for both arc welding seams and welding seams with a fairing. The results are illustrated in FIG. 13. The relative increase in resistance is constant, at all speeds. The result shows the effect of altering the profile of an arc welding seam to a more smooth profile is reducing the drag resistance even when increasing or lowering the speed.

(54) CFD Calculations

(55) A 2-D rectangular geometry was used for the simulations (see below) with the water flowing from left to right at different speeds. The dimensions of the computational domain are illustrated in FIG. 14.

(56) Simulations have been performed in steady state with the boundary conditions illustrated in FIG. 15. The simulations were performed by the Department of Fluid Mechanics, EEBE, Polytechnic University of Catalonia (UPC).

(57) The k-ε and k-w models were used to model turbulence. With regards to the mesh far from the welding seams, a triangular grid was used with 94713 cells. The shape of the protuberance determines the refining necessary for an acceptable description of the wakes and re-circulations and, hence, the eventual increase of the total resistance Close to the welding seam, the mesh was refined as per the below.

(58) The results are as follows. Note that the absolute values reported below are not relevant since the aim was not to describe the turbulence itself, but rather the influence of the turbulence on the mean flow (i.e. relative values).

(59) TABLE-US-00006 Total filler area 6 Total filler area 26 Unmodified cm cm Height of Total Total Total the welding resistance resistance Relative resistance Relative seam (N/M) (N/M) Savings (N/M) Savings 3 mm 113.48 110.40 2.7% 108.39 4.5% 9 mm 125.44 114.27 8.9% 109.36 12.8%

(60) The influence of the speed was also assessed (see below for the 3 mm welding seams):

(61) TABLE-US-00007 Total filler area 6 Total filler area 26 Unmodified cm cm Total Total Total resistance resistance Relative resistance Relative Speed (m/s) (N/M) (N/M) Savings (N/M) Savings 6.18 113.48 110.40 2.7% 108.39 4.5% 8.23 193.29 187.90 2.8% 184.21 4.7% 10.29 292.94 284.40 2.9% 278.66 4.9%