RU107353U1 - DEVICE FOR DETERMINING HYDRODYNAMIC RESISTANCE OF THE NETWORK CLOTH WITH LONGITUDINAL FLOW - Google Patents

Abstract

 A device for determining the hydrodynamic resistance of a mesh web during longitudinal flow, including a reservoir with water, above which there is a horizontal guide for flexible communication with the rollers installed on it with the edge and in the middle part, a test specimen of the mesh web immersed in the tank, enclosed in a frame, to which a flexible connection is thrown over the rollers, branched at the end, with a suspended load at its other end, characterized in that the frame with a sample of net web in the tank mounted vertically, its upper rib is equipped with eyes to which a flexible connection is attached, and the branching point of the flexible connection is fixed with a stabilizing float, ensuring the vertical position of the frame's static equilibrium when moving it.

Description

The utility model relates to the field of hydrodynamic testing. The device is designed to determine the values of the hydrodynamic drag coefficients of the net web during its longitudinal flow used in conducting research work on the hydrodynamic resistance of fishing nets.

A known installation for the study of hydrodynamic resistance (RF patent No. 2285906, IPC G01M 10/00, publ. 10/20/2006), including a disk connected to a vertical shaft and placed in a tank with water, the main and auxiliary loads that can move in vertical position at a strictly defined distance, a flexible cable, providing the transition of the translational movement of the load into the rotational movement of the disk in the water. Stop fixes the initial position of the system. In the study, disks coated with various substances are used, the time of lowering the load during the rotation of each disk is determined, and a comparative analysis of the coatings for hydrodynamic resistance is carried out.

The disadvantages of the setup described above include the fact that the experimental results are of a purely qualitative nature and can only be used for comparative analysis, which is not enough to conduct more accurate hydrodynamic studies of various materials, for example, net webs, for which it is necessary to know the numerical values of the hydrodynamic drag coefficients of the material.

A device is known for determining the hydrodynamic resistance of a net web (RU, patent No. 95838, IPC G01M 10/00, published July 10, 2010), including a test sample immersed in a water tank over which a horizontal guide with rollers mounted on it is placed moreover, the extreme roller is fixed motionless, and the next is mounted with the possibility of horizontal movement. The test specimen of the net web, enclosed in a frame, is immersed in a water tank. The load suspended on flexible connection has the possibility of vertical movement by means of rollers. The frame, mounted horizontally, to exclude possible warping during movement, is equipped with flexible connections symmetrically located around its perimeter, connected to a flexible link thrown through rollers with a suspended load. A flexible connection is established vertically passing through the center of gravity of the test sample with the frame and is equipped with a lock washer at the junction.

The device does not allow determining the hydrodynamic drag coefficients of the net web during its longitudinal flow, since the frame with the net web sample is located horizontally in the tank, i.e. when the frame moves, its plane is perpendicular to the incoming liquid flow.

The utility model solves the problem of determining the numerical values of the hydrodynamic drag coefficients of the net webs during longitudinal flow, by providing the possibility of translational movement of the plane of the test specimen of the net web parallel to the oncoming liquid flow.

To obtain the necessary technical result in a known device for determining the hydrodynamic resistance of a mesh web, including a reservoir with water, above which a horizontal guide is placed for flexible communication with the rollers installed on it with the edge and in the middle part, a test specimen of the mesh web immersed in the reservoir with water, enclosed in a frame to which a flexible connection is thrown across the rollers, branched at the end, with a suspended load at its other end, a frame with a sample m, set the net web in the tank vertically, provide its upper rib with eyes to which to attach the flexible connection, and fix the branching point of the flexible connection with a stabilizing float, ensuring the vertical position of the frame's static equilibrium when moving it.

The attached to the description of the diagram shows the proposed device.

The following notation is used in the diagram:

1 - a tank of water;

2 - horizontal guide for flexible communications;

3 - rollers fixed on the guide;

4 - frame;

5 - eyes;

6 - stabilizing float;

7 - flexible communication;

8 - removable load;

9 - water level in the tank;

10 - separate communication branches attached to the eyes;

11 - net cloth;

1'-1 ', 2'-2', 3'-3 ', K' - markers on flexible communication;

K 'is a control marker.

The proposed device includes: a tank 1 with water, a horizontal guide 2 for flexible connection 7, with two rollers 3 fixed on it, one in the middle part, the second closer to the edge of the guide. The test sample of the net web 11 is enclosed in a frame 4. A load is suspended on a flexible connection 7. A flexible connection 7 is passed through the rollers 3. Separate branches of a flexible connection 7 are attached to the eyes 5. The branching point of the flexible connection is fixed with a stabilizing float 6. At the other end, a flexible Ties 7 are suspended removable loads 8 of variable mass.

A specific example of the operation of the device.

The tank 1 is a parallelepiped-shaped container filled with water to a height of H = 1.0 m. The guide 2 is made in the form of a wooden beam, to which the rollers 3 and 4 are attached. Frame 4 with a net web 11 is installed vertically in the tank and to its upper a flexible connection 10 is attached to the rib provided with eyes 5. A stabilizing float 6 fixes the branching point of the flexible connection 7 and provides a stable longitudinal flow around the plane of the frame with a mesh web, a fluid flow. Using interchangeable weights 8, the weight of the frame 4 with the net in water is determined, which corresponds to the position of the static equilibrium of the system. Then, with different masses of additional removable weights 8, the time for lifting the frame with the net to the calculated height is determined. The estimated height is set by markers on a flexible thread. Three markers are applied to the flexible thread: the first marker 1'-1 ', when the lower edge of the frame touches the bottom; a second marker 2'-2 ', corresponding to a distance of 0.1 m of the frame from the bottom of the tank, and a third marker 3'-3' at a distance of 0.675 m from the second. The distance N _p = 0.675 m is calculated. When the second marker on the flexible thread during movement of the frame coincides with the control marker K 'on the extreme guide roller 3, the stopwatch is turned on. When the third marker on the flexible thread coincides with the control marker on the outermost guide roller, the stopwatch turns off. Knowing the lifting time of the frame 4 with the web 11, the lifting height, the mass of the removable weights 8 at which the test object moves, it is possible to directly determine the velocity values from the experiment by calculation, and then the values of the hydrodynamic drag coefficients, which are a function of speed.

For example, the mass of the removable load m ₁ = 358 g, the average time of lifting the frame with the net to the estimated height N _p = 0.675 m corresponds to t _cp = 4.14 s. Then we repeat the experiment, lowering the frame without the net into the water tank. We select the load so that the frame lifting time equals, as in the first experiment, t _cp = 4.14 s. The mass of the cargo in this case is m ₂ = 350 g.

The resistance force R _x will be equal to

R _x = (m ₁ -m ₂ ) g = (0.358-0.350) 9.8 = 0.078 H,

where g = 9.8 m / s ² - acceleration of gravity;

m ₁ is the mass of the frame with a net cloth;

m ₂ is the mass of the frame without netting.

We determine the lifting speed by the formula

V = H / t = 0.675 / 4.14 = 0.163 m / s.

After which we find the hydrodynamic drag coefficient C _x of the mesh web sample

C _x = 2R _x / s _n ρV ² = 2 ∗ 0.078 / 0.0118 ∗ 10 ³ ∗ (0.163) ² = 0.497;

where ρ = 10 ³ kg / m ³ is the density of water;

s _n = 0,0118 m ² - the area of the threads in the grid.

Thus, the proposed utility model allows an extremely simple and cheap way to determine the values of the hydrodynamic coefficients of the net, so that they can be used later in the study of the hydrodynamic resistance of net webs of fishing gear.

It is the vertical installation of the frame with a sample of the net web in the tank and the supply of its upper rib with eyes located in the plane of attachment of the net web and rigidly fixed in the corners of the frame, as well as the presence of a stabilizing float, which ensure a stable longitudinal flow of liquid around the plane of the frame with the net web and the possibility determining the values of the coefficients of hydrodynamic resistance in this type of movement.

Claims (1)

A device for determining the hydrodynamic resistance of a mesh web during longitudinal flow, including a reservoir with water, above which there is a horizontal guide for flexible communication with the rollers installed on it with the edge and in the middle part, a test specimen of the mesh web immersed in the tank, enclosed in a frame, to which a flexible connection is thrown over the rollers, branched at the end, with a suspended load at its other end, characterized in that the frame with a sample of net web in the tank mounted vertically, its upper rib is equipped with eyes to which a flexible connection is attached, and the branching point of the flexible connection is fixed with a stabilizing float, ensuring the vertical position of the frame's static equilibrium when moving it.