KR102202569B1 - Apparatus and method for measuring drag on an object entering water - Google Patents

Abstract

The present invention relates to a device and a method for measuring drag which is applied to an object entering water by water. According to the present invention, the method for measuring the drag in accordance with temperature of the object entering the water comprises: a heating step of heating an object to be measured; a water entering step of dropping the object to be measured into water; a temperature measurement step of measuring temperature of the object entering the water; and a bubble measurement step of measuring a size of a cavity bubble generated in wake in an advancing direction of the object to be measured after the object enters the water.

Description

Device and method for measuring drag according to the temperature of the object being obtained {APPARATUS AND METHOD FOR MEASURING DRAG ON AN OBJECT ENTERING WATER}

The present invention relates to a measuring device and method, and more particularly to a device and method for measuring the drag force exerted by water on an object to be obtained.

Since the drag reduction of an object acquired underwater has a great advantage in terms of energy saving, there are various fields that can be applied. For example, it can be widely applied to defense fields such as torpedoes hung underwater, aircraft landing on wet surfaces, various industrial fields such as the bow part of ships colliding with waves, inkjet printers, sprayers, and water sports such as swimwear for divers. At the time of receipt, factors affecting the drag force generated between the water and the surface of the object being received include the surface roughness, velocity, temperature, and physical properties of the fluid.

In order to reduce the drag force, it is necessary to measure the drag force caused by water acting on the object. On the other hand, it is known that the drag of water against an object to be obtained is affected by the size, shape, speed, and surface roughness of the object as well as the surface temperature of the object.

Therefore, in order to measure the drag force of water against an object, at least a means for heating the object and a means for measuring the temperature of the object are required. However, since this object is moving, heating and temperature measurement are not easy. For example, a thermocouple widely used for temperature measurement is a type of contact sensor, so it must be attached to an object to be measured.Since this thermocouple constitutes a part of the object's external shape, there is a problem that it is impossible to measure the drag acting only on the object. . In addition, the means for heating the object must also directly contact the object, and there is also a problem that the time required for heating is relatively long.
Prior art: drag measuring device (application number 10-2017-0003773)

The present invention has been conceived to solve the above problems, and aims to provide a series of measuring devices and methods for measuring and controlling the instantaneous temperature of a measurement object, and observing and controlling the drag of water against the measurement object after acquisition. do.

Other objects, specific advantages and novel features of the present invention will become more apparent from the following detailed description and preferred embodiments associated with the accompanying drawings.

The technical problem to be achieved by the present invention is not limited to the technical problems mentioned above, and other technical problems that are not mentioned can be clearly understood by those of ordinary skill in the technical field to which the present invention belongs from the following description. There will be.

In order to achieve the above object, the drag measurement method according to the temperature of an object to be obtained according to the present invention includes a heating step of heating a measurement object, an acquisition step of dropping the measurement object into water, and A temperature measurement step of measuring a temperature, and a bubble measurement step of measuring the size of a cavity bubble generated in a wake in a traveling direction of the measurement object after acquisition.

In the drag measurement method according to the temperature of an object to be obtained according to the present invention, in the heating step, a laser beam may be irradiated to the object to be measured to heat it, and in particular, the laser beam is applied to the object to be measured from directly below the object You can investigate.

In the drag measurement method according to the temperature of an object to be obtained according to the present invention, in the temperature measuring step, the measuring object may be photographed with an infrared camera, and prior to the measuring step, the infrared camera is calibrated and the emissivity is measured. It may further include, wherein the adjusting step includes measuring a temperature with a contact sensor while heating the measurement object, and a result obtained by photographing the measurement object with the infrared camera with the temperature obtained from the contact sensor. It may include a step of contrasting.

In the method for measuring drag according to the temperature of an object to be obtained according to the present invention, the bubble measuring step may include photographing an image when the object to be measured is received with a high-speed camera.

The drag measurement device according to the temperature of an object to be obtained according to the present invention includes a water tank disposed under the object to be measured and filled with water, a holding portion capable of selectively holding and releasing the object to be measured, and the object to be measured. And a heating unit capable of heating, a temperature measuring unit capable of measuring the temperature of the measurement object, and a photographing unit capable of photographing the measurement object obtained from the water tank and a cavity bubble formed in the trailing direction thereof. I can.

In the drag measuring apparatus according to the temperature of an object to be obtained according to the present invention, the gripping unit may suction and hold the object to be measured.

In addition, the temperature measurement unit may include an infrared camera that photographs the measurement object, and the heating unit includes at least a laser oscillator and at least for converting a travel path to guide a laser beam from the laser oscillator to the measurement object. It may contain one mirror. Here, the wavelength band recognized by the infrared camera and the wavelength band of the laser beam from the laser oscillator may be different from each other.

Meanwhile, in the drag measuring apparatus according to the temperature of an object to be obtained according to the present invention, the heating unit further includes a stop for adjusting the diameter of the laser beam from the laser oscillator, and further includes a laser beam from the laser oscillator. It may further include a lens for diffusing or condensing.

In the drag measuring apparatus according to the temperature of an object to be obtained according to the present invention, the photographing unit includes a high-speed camera installed to face the water tank, and a wavelength band including a wavelength of a laser beam from the laser oscillator installed on the high-speed camera. It may include a filter to block. Here, the photographing unit may further include illumination disposed on the opposite side of the high-speed camera centering on the water tank, and the illumination may include a planar light source and provide illumination of a wavelength other than a wavelength band blocked by the filter.

According to the present invention, it is possible to relatively compare the drag force of water according to the size, shape, and temperature of various measurement objects by observing the temperature at the time of receipt of the measurement object and the cavity bubble formed in the downstream after the receipt.

In addition, since the object to be measured can be heated with a laser beam, it does not use a heat source such as electricity or flame, and can be heated within a short time. Also, since the laser has high permeability to water, the laser beam passes through the water tank to control the object to be measured. It can also be heated directly underneath.

In addition, since the temperature of the object to be measured can be measured in a non-contact manner when the object to be measured is received using an infrared camera, accurate drag measurement is possible without affecting the appearance of the object to be measured.

The effects of the present invention are not limited to the above effects, and should be understood to include all effects that can be deduced from the configuration of the invention described in the detailed description or claims of the present invention.

1 is a flowchart of an embodiment of a method of measuring drag according to the temperature of an object to be obtained according to the present invention.
2 is a schematic configuration diagram of an embodiment of an apparatus for measuring drag according to the temperature of an object to be obtained according to the present invention.
3 is a configuration diagram for measuring the emissivity of the object to be measured in order to measure the temperature when measuring the temperature of the object to be measured with an infrared camera in the device and method for measuring drag according to the temperature of an object to be obtained according to the present invention .

Hereinafter, the present invention will be described with reference to the accompanying drawings. However, the present invention may be implemented in various different forms, and therefore is not limited to the embodiments described herein. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and similar reference numerals are assigned to similar parts throughout the specification.

Throughout the specification, when a part is said to be "connected (connected, contacted, bonded)" with another part, it is not only "directly connected", but also "indirectly connected" with another member in the middle. "Including the case. In addition, when a part "includes" a certain component, it means that other components may be further provided, rather than excluding other components unless specifically stated to the contrary.

The terms used in the present specification are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or a combination thereof described in the specification, but one or more other features. It is to be understood that the presence or addition of elements or numbers, steps, actions, components, parts, or combinations thereof, does not preclude in advance.

1 is a flowchart of an embodiment of a method of measuring drag according to the temperature of an object to be obtained according to the present invention.

First, the object to be measured is heated (heating step, S110). The heated measurement object is then dropped into the water contained in the water tank (intake step, S120). At this time, it is preferable to heat the lower surface of the measurement object that comes into contact with the water surface first. The heating step (S110) may be followed even while the measurement object is falling. It is preferable to heat the lower surface of the measurement object using a laser beam in the above heating step (S110) so that the moving measurement object can also be easily heated. To this end, the laser beam may be guided to irradiate the object to be measured from directly below the object to be measured through water contained in the water tank.

The temperature when the object to be measured is obtained is measured (temperature measurement step, S130). In this case, the object to be measured is moving, and in the case of a contact-type sensor, since it has to be directly mounted on the object to be measured, there is a problem of changing the shape of the object to be measured. Since precise emissivity measuring devices using FTIR (Fourier transform infrared spectroscopy) or monochromatic spectroscopy are known, they can be used as a means for measuring temperature in a non-contact manner. However, these are large or expensive, and they are often less versatile. On the other hand, an infrared camera can be easily secured, and it has the advantage of being able to estimate the temperature of the object to be measured through an electrical signal or image output as a result of simply photographing the object to be measured, so it has excellent utility. In any case, the means for measuring the temperature of the object to be measured may be utilized to determine how much the object to be measured is heated in the heating step (S110).

In this process, in order to improve the measurement accuracy of the infrared camera, adjustment steps for calibration and emissivity measurement may be further performed. In this adjustment step, for example, as illustrated in FIG. 3, while placing the measurement object 50 on the heating block 70 made of carbon steel and heating the heating block 70 through the induction heater 80, contact such as a thermocouple The temperature of the measurement object 50 is measured by the expression sensor 60. At the same time, an image of the measurement object 50 is photographed with the infrared camera 130 to measure the emissivity. By comparing the result obtained from the infrared camera 130 with the temperature measured by the contact sensor 60, it is possible to obtain an accurate temperature of the object to be measured, and this temperature is at least with the contact sensor 60, for example, a thermocouple used here. They can have the same level of accuracy. Such an adjustment step is sufficient if it is performed prior to the temperature measurement step (S130), and may be performed before the heating step (S110).

When the object to be measured is received as water, a cavity bubble is formed in the wake thereof, and the shape or size of the cavity bubble can be an index representing the drag received from the water. Therefore, by measuring the size of the cavity bubble formed in the downstream after the object to be measured is obtained (bubble measurement step, S140), the drag of the water acting on the object to be measured can be estimated. In order to measure the size of the cavity bubble as described above, a high-speed camera may be used. When one measurement object and its wake are photographed with a high-speed camera, the relative size of the cavity bubble can be measured by comparing at least the image of the other measurement object and its wake. Furthermore, it is possible to quantitatively estimate the absolute size such as the volume of the cavity bubble from the size of the object to be measured within the same image. The drag coefficient for the object to be measured can be estimated through the relative size or absolute size of the cavity bubble.

By passing through or repeating this process, the size of the cavity bubble can be measured at the same or different temperature for one measurement object or a plurality of different measurement objects, and the accumulated measurement value indicates the drag force that the object receives in water. It can have high utilization value in research to reduce it.

Meanwhile, in the process of repeating the above process, the temperature of water contained in the water tank may be maintained at room temperature. When the temperature of the water changes over time or repeatedly, the size of the cavity bubble finally obtained varies, and thus the error may be reflected in the estimated drag coefficient. However, if the temperature change of water is, for example, ±5°, there is no significant error. In order to further reduce the error, it is also possible to further consider the difference between the temperature of the object to be measured and the temperature of the water in the water tank obtained in the temperature measurement step (S130), or to minimize the temperature change of the water by sufficiently increasing the total heat capacity of water in the water tank. It is possible.

2 is a schematic configuration diagram of an embodiment of an apparatus for measuring drag according to the temperature of an object to be obtained according to the present invention.

The water tank 140 is disposed below the measurement object 50 and is filled with water. In FIG. 2, the inverted triangle mark 10 indicates the water surface, but the height of the water surface may be arbitrarily selected according to necessity and may be positioned at a different height from that illustrated. In addition, the wall constituting the water tank 140 may be at least partially light-transmitting because the laser beam needs to pass therethrough, as described below.

The gripping part 110 is for selectively gripping or releasing the measurement object 50 from the upper side of the water tank 140, and holds the measurement object before starting the measurement, and then the measurement object 50 is placed in the tank 140 It can fall inside. In the embodiment of FIG. 2, the gripping unit 110 is illustrated as including a holder 111 and a vacuum pump 112 connected to the holder 111. In this case, the gripping part 110 suctions and grips the measurement object 50 with a vacuum pressure, and may release the gripping by releasing the vacuum pressure. In contrast, when the object to be measured 50 is a magnetic material, an electromagnet may be included in the holder 111, and other configurations may be used as the gripping unit 110 if the object to be measured 50 is selectively gripped. .

The heating unit is for heating the measurement object 50, and in particular, it is preferable to heat the measurement object 50 in a non-contact manner. To this end, a laser beam may be used. In this case, the heating unit may include a laser oscillator 121 and a mirror 122 for converting or guiding a traveling path of the laser beam from the laser oscillator 121. Two or more mirrors 122 may be included if the traveling path of the laser beam is to be converted two or more times. Meanwhile, the measurement object 50 may have different sizes, and a stop 123 for adjusting the laser beam to have a cross-sectional diameter suitable for the size of the measurement object 50 may be additionally disposed. In addition, a lens for diffusing or condensing the laser beam may be disposed in place of the stop 123 or in addition to the stop 123. In order for the heating unit to directly heat the lower surface of the measurement object 50, the laser beam may have to pass through the water. At this time, since the attenuation rate of the laser beam is relatively small in water, there is an additional advantage that it is less affected by heating the measurement object 50 even when passing through the water.

The temperature measuring unit is for measuring the temperature of the object 50 to be measured, which is illustrated in the form of a camera in FIG. 2, and may be an infrared camera that senses a wavelength in an infrared region, particularly a Medium Wave Infreared (MWIR) camera. As described above, the temperature of the measurement object 50 can be estimated from an electrical signal or image obtained as a result of photographing the measurement object 50 with the infrared camera 130. In addition, in order to improve the measurement accuracy of the infrared camera 130, it has been described above that calibration and emissivity measurement may be performed before use. On the other hand, when the heating unit includes the laser oscillator 121, a part of the laser beam irradiated from the laser oscillator 121 may proceed to the infrared camera 130 by refraction, reflection, scattering, etc., but the wavelength of the laser beam If the infrared camera 130 falls within a recognizable wavelength band, a significant error may occur in temperature measurement. To prevent this, a wavelength band recognized by the infrared camera 130 and a wavelength band of the laser beam irradiated by the laser oscillator 121 may be selected differently from each other.

The photographing unit is for photographing a measurement object obtained from a water tank and a cavity bubble formed in a downstream thereof, and may include a high-speed camera 151. Here, the high-speed camera 151 may take a still picture as well as a video. Meanwhile, when the laser beam irradiated from the laser oscillator 121 enters the high-speed camera 151, noise may be intervened in the image. In particular, when the measurement object 50 and the size of the cavity bubble are small, in order to remove noise, the high-speed camera 151 may block a ray of a specific wavelength range, for example, a ray of a wavelength in which the wavelength of the laser beam from the laser oscillator 121 belongs. A filter that can be provided may be provided.

When the photographing unit includes a high-speed camera 151, a lighting 152 is added to prevent image quality from deteriorating due to low light intensity, and to clearly discriminate particularly small measurement objects 50 and cavity bubbles. Can be. The lighting 152 may be disposed opposite to the high-speed camera of the photographing unit with the water tank 140 in the center. In addition, the illumination 152 may include a planar light source to obtain a uniform image. Obviously, it is preferable that the light emitted by the lighting 152 can pass through a filter that can be installed in a high-speed camera.

4 and 5 are exemplary images obtained by the device and method for measuring drag according to the temperature of an object obtained according to the present invention, respectively.

4 shows three images taken immediately after acquisition of a metal sphere with a diameter of 2 mm by changing its surface temperature. The surface temperature of the metal sphere was measured from the left to 21°C, 209°C, and 256°C, respectively, and the speed of the metal sphere immediately before acquisition. Is 1.5m/s. 5 shows four images taken at surface temperatures of 21° C., 135° C., 165° C., and 199° C. for a metal sphere having the same diameter of 2 mm, and the speed of the metal sphere immediately before acquisition is 3.23 m/s. Through this, it can be seen that, first of all, according to the present invention, it is possible to easily change the surface temperature of a metal sphere as a measurement object, and to obtain a clear image of the measurement object immediately after acquisition. In addition, referring to FIGS. 4 and 5, it can be seen that as the surface temperature of the metal sphere increases, the volume of the cavity bubble formed in the downstream thereof increases, and then decreases rapidly when the temperature exceeds a certain temperature. Here, the formation of the cavity bubble can be interpreted as having a positive effect on the drag reduction.

Embodiments of the present invention described above and illustrated in the drawings should not be construed as limiting the technical idea of the present invention. The protection scope of the present invention is limited only by the matters described in the claims, and those of ordinary skill in the technical field of the present invention can improve and change the technical idea of the present invention in various forms. Therefore, such improvements and changes will fall within the scope of the present invention as long as it is apparent to those of ordinary skill in the art.

Claims (16)

A heating step of heating the measurement object,
An acquisition step of dropping the measurement object into water,
A temperature measurement step of measuring the temperature of the obtained measurement object,
Bubble measurement step of measuring the size of the cavity bubble generated in the flow direction of the measurement object after acquisition
Containing, the drag measurement method according to the temperature of the object to be obtained. The method of claim 1,
The heating step is a method of measuring drag according to the temperature of the object to be obtained by irradiating a laser beam to the object to be heated. The method of claim 2,
The laser beam irradiates the object to be measured from directly below the object to be measured. The method of claim 1, wherein in the temperature measuring step, the measurement object is photographed with an infrared camera. The method of claim 4,
The infrared camera further comprises an adjusting step of calibrating and measuring emissivity prior to the temperature measuring step,
The adjustment step,
Measuring the temperature with a contact sensor while heating the measurement object,
And comparing the result obtained by photographing the measurement object with the infrared camera with the temperature obtained from the contact sensor. The method of claim 1, wherein the bubble measuring step comprises photographing an image with a high-speed camera when the object to be measured is received. A water tank placed under the object to be measured and filled with water,
A holding portion capable of selectively holding and releasing the object to be measured,
A heating unit capable of heating the measurement object,
A temperature measuring unit capable of measuring the temperature of the object to be measured,
A device for measuring drag according to the temperature of the object to be obtained, comprising a photographing unit capable of photographing the object to be measured acquired through the water tank and the cavity bubble formed in the downstream of the moving direction. The apparatus of claim 7, wherein the gripping unit is capable of holding the measurement object by vacuum suction. The method of claim 7, wherein the temperature measuring unit,
A drag measuring device according to the temperature of an object to be obtained, comprising an infrared camera for photographing the measurement object. The method of claim 7, wherein the heating unit,
Laser oscillator,
At least one mirror for converting a travel path to guide the laser beam from the laser oscillator to the measurement object. The method of claim 10, wherein the temperature measurement unit comprises an infrared camera for photographing the object to be measured, wherein a wavelength band recognized by the infrared camera and a wavelength band of the laser beam from the laser oscillator are different from each other at a temperature of the object to be obtained. According to the drag measuring device. The method of claim 10, wherein the heating unit,
Further comprising a stop for adjusting the diameter of the laser beam from the laser oscillator, the drag measuring device according to the temperature of the obtained object. The method of claim 10, wherein the heating unit,
A device for measuring drag according to the temperature of an object to be obtained, further comprising a lens for diffusing or condensing the laser beam from the laser oscillator. The method of claim 10, wherein the photographing unit,
A high-speed camera installed to face the tank,
A device for measuring drag according to the temperature of an object to be obtained, including a filter installed in the high-speed camera to block a wavelength band including a wavelength of a laser beam from the laser oscillator. The method of claim 14, wherein the photographing unit,
A device for measuring drag according to the temperature of an object to be obtained, further comprising a light disposed on the opposite side of the high-speed camera around the water tank. The apparatus of claim 15, wherein the illumination includes a planar light source and provides illumination of a wavelength other than the wavelength band blocked by the filter.

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