Method for measuring barnacle adhesion on surface of marine antifouling coating
Technical Field
The invention belongs to the technical field of antifouling coating performance test.
Background
Marine biofouling of surfaces of hulls, equipment, etc. in the ocean causes significant economic losses to the marine industry. The development of antifouling coatings for application to these underwater surfaces is an effective antifouling approach. During the development of marine antifouling coatings, it is necessary to evaluate the antifouling properties of antifouling coatings, and a common experimental method comprises: bacterial adhesion tests, algae adhesion tests, marine true sea coupon tests, and the like. In addition, a test method is also frequently used by researchers, namely barnacle attachment experiments. A large number of barnacles attached to and growing on seaside rocks can be frequently seen, and the adhesion capability of the barnacles on the surface of the coating can better show the antifouling performance of the coating because the barnacles have very strong adhesion capability and the adhesion force can reach 1 MPa. However, adhesion measurement of barnacles is very difficult. In order to solve this problem, ASTM D5618-94(2011) "Standard Test Method for measuring of Barnacle addition Strength in Shear" Standard provides a Method of using a metal cylinder, using epoxy resin as a bonding agent, adhering the metal cylinder as a "virtual Barnacle" (Pseudobarnacle) on the surface of a coating layer, pulling the virtual Barnacle apart under Shear under water, and recording the pulling force during separation by a tensile force meter, thereby obtaining the maximum Adhesion force. Although effective, this method is in quasi-static conditions for both the coating and the virtual barnacles. In a marine environment, the water flow scouring barnacles is under hydrodynamic conditions, and in some cases, such as barnacles on the surface of a propeller, the stress is more complicated. The method has very important significance in measuring the barnacle desorption force under hydrodynamic conditions. On the other hand, real barnacles cannot be measured by the ASTM D5618-94(2011) standard because they are small in size and cannot be easily connected by a tension meter.
Disclosure of Invention
In the 'GB/T7789-2007 dynamic test method for antifouling performance of antifouling paint for ships' a dynamic antifouling test apparatus is described (see fig. 1), the apparatus mainly comprises a water tank, a motor, a polyhedron for installing a coating, the polyhedron is connected with the motor, and the impact effect of water flow on the coating is simulated by rotation under the driving of the motor. Since the device is widely used, the invention describes a method for measuring the barnacle adhesion on the surface of the underwater antifouling coating based on the device.
The dynamic antifouling test equipment is described in GB/T7789-2007 and mainly comprises: the device comprises a motor 1, a connecting shaft 2, a polyhedron 3, a transparent water tank 4 and a motor controller 6; the polyhedron 3 is connected with the motor 1 through the connecting shaft 2, the motor 1 is arranged above the transparent water tank 4, the polyhedron 3 is placed in the transparent water tank 4, the motor controller 6 is used for controlling the on-off and the rotating speed of the motor,
to implement the measurement method of the present invention, only 2 or more high-speed cameras 5 (e.g., Phantom TMX 7510) need to be added and placed around or above the tank.
(1) Adhesion measurement of real barnacles
During the measurement, the surface of the polyhedron 3 is first provided or coated with an anti-fouling coating 7, which is ignored in the calculation since the coating is typically thin, in the hundreds of microns. The polyhedrons are then immersed in seawater containing juvenile, or adult barnacles, to attach the barnacles to the surface of the coating 7 (fig. 3).
The polyhedron 3 is immersed in the artificial seawater, the rotating speed of the motor 1 is gradually increased, when the rotating speed of the motor reaches a certain speed, the barnacles are separated from the surface of the coating, and due to the limitation of human eyes, a video recording that the barnacles are separated is recorded by the high-speed camera 5, so that the time when the barnacles are separated is obtained, and the rotating speed omega of the motor at the time can be found.
For real barnacles it can be seen as a sphere of radius r, with mass m (fig. 4).
The attached barnacles were subjected to stress analysis, see figure 5. In the direction vertical to the water surface, it is subjected to gravity G and buoyancy FFloating bodyThe function of (1):
G=mg (1)
for an object floating in water, the gravity and the buoyancy are equal. In this case, however, since barnacles adhere to the coating surface, the resultant force of gravity and buoyancy thereof is not necessarily 0, and the direction thereof is uncertain. However, this does not affect the calculation of the resultant force thereof, the resultant force F of the twoVerticalThe size is as follows:
Fvertical=|FFloating body-G| (3)
When the barnacle is separated from the surface of the coating, the rotating speed of the motor is omega, the distance from the edge of the polyhedral surface to the center is R, and the centripetal force F of the barnacle in the direction vertical to the coating is realized because the polyhedron 3 rotates along with the motor 1To the direction ofThe centripetal force is:
Fto the direction of=mω2(R+r) (4)
When the barnacle rotates along with the coating in water, the resistance F of the water body is receivedResistance deviceComprises the following steps:
in the formula (5), C is a resistance coefficient, rho is the density of water, v is the water flow velocity at barnacles, and S is the sectional area of the barnacles in the moving direction, so that the formula can be converted into:
in equation (6), the coefficient of resistance C is unknown, and to find this value, the flow of the water flow outside the polyhedron is equated to a flow inside a smooth pipe 9 (fig. 3), with a characteristic length d (i.e. the width of the polyhedron), according to the fluid resistance coefficient formula proposed by Prandtl (Prandtl):
in formula (7), Re is a Reynolds number:
Re=ρvd/μ (8)
in the formula (8), ρ is the velocity of water, v is the velocity of water flow at barnacles, μ is the viscosity coefficient of water, and therefore the formula (8) is variable:
Re=ρω(R+r)d/μ (9)
the coefficient of resistance C can be solved from equations (7) and (9), and F in equation (6) can be calculatedResistance device。
As can be seen from FIG. 5, the resultant force F in the vertical directionVerticalCentripetal force FTo the direction ofAnd resistance F of water flow to barnaclesResistance deviceThe three forces are perpendicular to each other in the spatial direction, so that the resultant force F of the three forcesCombination of Chinese herbsComprises the following steps:
when barnacles adhere to the surface of the coating, the adhesion is balanced with the resultant of the other three forces, and is therefore numerically FAttached with=FCombination of Chinese herbsThe two directions are opposite; the maximum adhesion of a barnacle is numerically equal to the resultant F of the other three forces when the barnacle is detachedCombination of Chinese herbs,FAttached with=FCombination of Chinese herbsThe dynamic adhesive force F of the barnacle can be obtainedAttached with。
(2) Adhesion measurement of virtual barnacles
During the measurement, the surface of the polyhedron 3 is first provided or coated with an anti-fouling coating 7, which is ignored in the calculation since the coating is typically thin, in the hundreds of microns. A virtual barnacle (i.e. a metal cylinder) is then adhered to the surface of the coating 7 using epoxy (fig. 3).
Immerse the polyhedron 3 in artifical sea, increase the 1 rotational speed of motor gradually, when the motor speed reached certain speed, virtual barnacle breaks away from the coating surface, because the limitation of people's eye, adopts high-speed camera 5 to write down the video that the barnacle breaks away from to acquire the moment when breaking away from, can look into the motor speed omega at this moment.
The radius of the bottom surface of the virtual barnacle cylinder is r, the length is l, and the mass is m (figure 6).
The maximum adhesion force when the virtual barnacles are detached from the coating surface is numerically equal to Fq,
Fvertical=|FFloating body-G| (12)
FFloating body=ρgπr2l (13)
G=mg (14)
In the above formula, ρ is the density of water, g is the gravity acceleration, μ is the viscosity coefficient of water, the C resistance coefficient is obtained by combining (17) and (18), Re is the reynolds number, and d is the characteristic length of a smooth pipe 9 equivalent to the flow outside a certain plane of the polyhedron.
The invention has the beneficial effects that:
(1) the invention realizes the barnacle adhesion measurement under hydrodynamic force condition;
(2) the method is suitable for both real barnacles and virtual barnacles because a tension meter is not used;
(3) the dynamic antifouling test equipment of GB/T7789-2007 has a wide application foundation, and the measurement is more convenient on the basis of the existing equipment.
Drawings
FIG. 1 is a schematic measurement;
FIG. 2 is a polyhedral 3D diagram;
FIG. 3 is a schematic diagram of coating installation and barnacle/virtual barnacle attachment;
FIG. 4 is a simplified spherical model of a barnacle;
FIG. 5 stress analysis of barnacles/virtual barnacles during rotational movement of the surface of the underwater device;
fig. 6 the virtual barnacle is a cylinder.
Detailed Description
The technical solution of the invention is further explained and illustrated in the form of specific embodiments.
In the 'GB/T7789-2007 dynamic test method for antifouling performance of antifouling paint for ships' a dynamic antifouling test apparatus is described (see fig. 1), the apparatus mainly comprises a water tank, a motor, a polyhedron for installing a coating, the polyhedron is connected with the motor, and the impact effect of water flow on the coating is simulated by rotation under the driving of the motor. Since the device is widely used, the invention describes a method for measuring the barnacle adhesion on the surface of the underwater antifouling coating based on the device.
The dynamic antifouling test equipment is described in GB/T7789-2007 and mainly comprises: the device comprises a motor 1, a connecting shaft 2, a polyhedron 3, a transparent water tank 4 and a motor controller 6. To implement the measurement method of the present invention, only 2 or more high-speed cameras 5 (e.g., Phantom TMX 7510) need to be added and placed around or above the tank.
(1) Adhesion measurement of real barnacles
During the measurement, the surface of the polyhedron 3 is first provided or coated with an anti-fouling coating 7, which is ignored in the calculation since the coating is typically thin, in the hundreds of microns. The polyhedrons are then immersed in seawater containing young, or adult barnacles, and after a period of time (e.g. a few days) the barnacles are allowed to adhere to the surface of the coating 7 (fig. 3).
The polyhedron 3 is immersed in the artificial seawater, the rotating speed of the motor 1 is gradually increased, when the rotating speed of the motor reaches a certain speed, the barnacles are separated from the surface of the coating, and due to the limitation of human eyes, a video recording that the barnacles are separated is recorded by the high-speed camera 5, so that the time when the barnacles are separated is obtained, and the rotating speed omega of the motor at the time can be found.
For real barnacles it can be seen as a sphere of radius r, with mass m (fig. 4).
The attached barnacles were subjected to stress analysis, see figure 5. In the direction vertical to the water surface, it is subjected to gravity G and buoyancy FFloating bodyThe function of (1):
G=mg (19)
for an object floating in water, the gravity and the buoyancy are equal. In this case, however, since barnacles adhere to the coating surface, the resultant force of gravity and buoyancy thereof is not necessarily 0, and the direction thereof is uncertain. However, this does not affect the calculation of the resultant force thereof, the resultant force F of the twoVerticalThe size is as follows:
Fvertical=|FFloating body-G| (21)
When the barnacle is separated from the surface of the coating, the rotating speed of the motor is omega, the distance from the edge of the polyhedral surface to the center is R, and the centripetal force F of the barnacle in the direction vertical to the coating is realized because the polyhedron 3 rotates along with the motor 1To the direction ofThe centripetal force is:
Fto the direction of=mω2(R+r) (22)
When the barnacle rotates along with the coating in water, the resistance F of the water body is receivedResistance deviceComprises the following steps:
in the formula (5), C is a resistance coefficient, rho is the density of water, v is the water flow velocity at barnacles, and S is the sectional area of the barnacles in the moving direction, so that the formula can be converted into:
in equation (6), the drag coefficient C is unknown, and to find this value, the flow of the water flow outside the polyhedron is equated to a flow inside a smooth pipe 9 (fig. 3) with a characteristic length d (i.e. the width of the polyhedron), according to the fluid drag coefficient formula proposed by Prandtl (Prandtl):
in formula (7), Re is a Reynolds number:
Re=ρvd/μ (26)
in the formula (8), ρ is the velocity of water, v is the velocity of water flow at barnacles, μ is the viscosity coefficient of water, and therefore the formula (8) is variable:
Re=ρω(R+r)d/μ (27)
the coefficient of resistance C can be solved from equations (7) and (9), and F in equation (6) can be calculatedResistance device。
As can be seen from FIG. 5, the resultant force F in the vertical directionVerticalCentripetal force FTo the direction ofAnd resistance F of water flow to barnaclesResistance deviceThe three forces are perpendicular to each other in the spatial direction, so that the resultant force F of the three forcesCombination of Chinese herbsComprises the following steps:
when barnacles adhere to the surface of the coating, the adhesion is balanced with the resultant of the other three forces, and is therefore numerically FAttached with=FCombination of Chinese herbsThe two directions are opposite; the maximum adhesion of a barnacle is numerically equal to the resultant F of the other three forces when the barnacle is detachedCombination of Chinese herbs,FAttached with=FCombination of Chinese herbsThe dynamic adhesive force F of the barnacle can be obtainedAttached with。
(2) Adhesion measurement of virtual barnacles
During the measurement, the surface of the polyhedron 3 is first provided or coated with an anti-fouling coating 7, which is ignored in the calculation since the coating is typically thin, in the hundreds of microns. A virtual barnacle (i.e. a metal cylinder) is then adhered to the surface of the coating 7 using epoxy (fig. 3).
Immerse the polyhedron 3 in artifical sea, increase the 1 rotational speed of motor gradually, when the motor speed reached certain speed, virtual barnacle breaks away from the coating surface, because the limitation of people's eye, adopts high-speed camera 5 to write down the video that the barnacle breaks away from to acquire the moment when breaking away from, can look into the motor speed omega at this moment.
The radius of the bottom surface of the virtual barnacle cylinder is r, the length is 1, and the mass is m (figure 6).
The attached virtual barnacles were subjected to stress analysis, see figure 4. In the direction vertical to the water surface, the water surface is subjected to the action of gravity G and buoyancy F:
G=mg (29)
Ffloating body=ρgπr2l (30)
For an object floating in water, the gravity and the buoyancy are equal. In this case, however, since the virtual barnacles adhere to the coating surface, the resultant force of gravity and buoyancy thereof is not necessarily 0, and the direction thereof is uncertain. However, this does not affect the calculation of the resultant force thereof, the resultant force F of the twoVerticalThe size is as follows:
Fvertical=|FFloating body-G| (31)
When the virtual barnacle is separated from the coating, the rotating speed of the motor is omega, the distance from the edge of the polyhedron surface to the center is R, and the polyhedron 3 rotates along with the motor 1, so that the centripetal force F of the virtual barnacle in the direction vertical to the coating is generatedTo the direction ofThe centripetal force is:
when the virtual barnacle rotates along with the coating in water, the water body resistance F is receivedResistance deviceComprises the following steps:
in the above equation, the coefficient of resistance C is unknown, and to find this value, the flow of the water flow outside the polyhedron is equivalent to the flow inside a smooth pipe 9 (fig. 3), with a characteristic length d, according to the fluid resistance coefficient formula proposed by Prandtl:
in the above formula, Re is Reynolds number: re ═ ρ vd/μ
ρ is the density of water, v is the velocity of water flow at the virtual barnacle, μ is the viscosity coefficient of water, so the above equation can be changed as:
the resistance coefficient C is solved by the joint type (17) and the formula (18).
As can be seen from FIG. 5, the resultant force F in the vertical directionVerticalCentripetal force FTo the direction ofAnd resistance F of water flow to the virtual barnacleResistance deviceThe three forces are perpendicular to each other in the spatial direction, so that the resultant force F of the three forcesCombination of Chinese herbsComprises the following steps:
when the virtual barnacles are attached to the surface of the coating, the resultant force is 0, and the adhesive force is FAttached with=FCombination of Chinese herbsThe two directions are opposite. The maximum adhesion force at detachment of the virtual barnacles is therefore numerically equal to FCombination of Chinese herbsSo that the dynamic adhesion F of the virtual barnacle can be obtainedAttached with。