JP3046558B2 - Oscillating flow generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston-driven closed-type oscillatory flow generator used for hydraulic experiments such as drifting sand and turbulence.

[0002]

2. Description of the Related Art Phenomena such as drifting sand and turbulence on the sea floor are caused by the formation of an oscillating flow field on the sea floor by waves. Therefore, in order to conduct a hydraulic experiment on these phenomena or to conduct an experiment for studying the ecology of living things in an oscillating flow field on the sea floor, a device for artificially generating an oscillating flow is required.

Conventionally, when conducting such an experiment, as shown in FIG. 1, a piston disk 5 is indicated by an arrow in the figure in an annular closed system pipe 3 having an observation part 9 in a part thereof. Reciprocated by the piston disk drive means 7 in the range of E
A piston-driven oscillating flow generator 1 that generates a reciprocating flow (oscillating flow) traveling in both forward and reverse directions in a pipeline 3.
Is often used.

[0004]

In the above experiment, it is extremely important to control the flow velocity waveform of the oscillating flow arbitrarily and accurately, so that a desired oscillating flow is generated in the pipeline. It is desirable to control the reciprocating motion of the piston disk by calculating beforehand the driving speed of the piston disk required to cause the generation using a computer.

[0005] However, in the piston-driven vibratory flow generating device according to the above-described structure, as shown in FIG. 2, when the piston disk 5 is driven, for example, when the piston disk 5 is pushed in the direction of J when the piston disk 5 is driven. Since the fluid leaks in the Z direction from a slight gap between the piston board 5 and the inner wall 3a of the pipeline, the generated flow velocity is lost. That is, the flow velocity waveform (input waveform) of the oscillating flow input to the computer for reproduction and the control of the reciprocating motion of the piston board by the computer based on the input value result in the oscillating flow actually generated in the pipe line. There is a problem that a deviation occurs from the flow velocity waveform (output waveform). As is clear from the graph of FIG. 3, the loss of the flow velocity is particularly remarkable at the peak of the flow velocity.

Therefore, in order to eliminate the above-described loss of the generated flow velocity and to make the input waveform of the flow velocity coincide with the output waveform, a packing 13 of a Teflon resin film type as shown in FIG. Attempts have been made to mount the packing 15 of the cotton grease type as shown and fill the gap between the pipe inner wall 3a and the piston disc 5 to prevent the fluid from leaking. However, by installing the packing as described above around the piston disk, the escape of fluid from the gap between the piston disk 5 and the pipe inner wall 3a was suppressed, and an output waveform close to the input waveform was obtained. As shown in the graph of FIG. 6, it has been clarified that a fluctuation component of about several Hz is inevitably generated in the output waveform due to friction between the packing mounted on the piston board 5 and the pipe inner wall 3a.

As described above, if an attempt is made to reduce the gap between the piston disk and the inner wall of the pipe in order to avoid the problem of flow velocity loss due to the passage of fluid, the output waveform fluctuates due to friction. It is very difficult to control the flow velocity waveform of an arbitrary oscillating flow with high accuracy because there is a contradictory problem that if the gap is provided to avoid the flow, the flow velocity will be lost due to the passage of the fluid. Met.

SUMMARY OF THE INVENTION The present invention has been made to avoid the above-described problems. In order to remove a fluctuation component of an output waveform, instead of installing a packing, a space is provided between a piston disk and an inner wall of a pipeline. To provide an oscillating flow generator capable of positively providing a gap, theoretically predicting the escape of fluid from this gap, and controlling the output flow velocity to a predetermined arbitrary waveform by deforming the input waveform in advance. With the goal.

[0009]

In order to achieve the above object, an oscillatory flow generating device according to the present invention has an observing section capable of observing the inside from the outside and an annular closed system pipe filled with fluid, A piston disk arranged in the pipeline to close the pipeline, a piston disk drive means for reciprocating the piston disk along an inner wall of the pipeline, and a waveform of an oscillating flow to be reproduced is specified. Based on the value input in order to determine the driving speed of the piston disk required to generate the oscillating flow of the waveform in the pipeline, the reciprocating motion of the piston disk is determined based on the determined value. A computer recording a program for sending a signal for control to the piston disk drive means, and a vibration flow generator comprising a gap between an inner wall of the pipe and the piston disk. On the other hand, the computer records a program for determining a driving speed of the piston disk required to generate a desired oscillating flow in the observation unit in consideration of an amount of fluid slipping through the gap when driving the piston disk. It is characterized by having.

That is, in the present invention, since a gap is provided between the inner wall of the pipeline and the piston disk, the output waveform can be prevented from fluctuating due to friction between the inner wall of the pipeline and the piston disk. Since the driving speed of the piston disk required to generate the desired oscillating flow is determined in consideration of the amount of the fluid passing through the gap, the output waveform of the oscillating flow can be controlled with extremely high accuracy.

The width of the gap provided between the inner wall of the pipe and the piston board is 0.5 mm to 1.5 mm.
Is preferably set to. This means that the larger the width of the gap, the greater the amount of fluid that slips through the gap, and the maximum velocity of fluid that can be generated in the pipeline when the piston disk drive is operated at the maximum output (maximum speed). This is because there is a problem that the output flow velocity) becomes small. In addition, although there is a problem of accuracy, when the width of the gap is set to 0.
If the diameter is smaller than 5 mm, the piston disk may come into contact with the inner wall of the conduit when the piston disk is driven, which causes a problem that a fluctuation component occurs in the output waveform.

[0012]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an oscillating flow generator according to the present invention. FIG.
1 is an external perspective view of an oscillating flow generator 1 according to the present invention. Reference numeral 3 denotes a closed system pipe line, which is filled with a fluid. An observation unit 9 is provided in a part of the pipeline 3. The observing section 9 has a linear shape with a length of about 5 m and a rectangular cross section. The observing section 9 has transparent windows on the upper and side surfaces, so that the inside can be observed. Numeral 5 denotes a piston disc, which is arranged so as to close the pipe 3 in the pipe 3. As shown in FIG. 9, a gap is provided between the piston disc 5 and the pipe inner wall 3a. Have been. In this embodiment, the width of the gap is set to 1 mm.

Reference numeral 7 denotes a piston disk driving means, which is driven by a built-in hydraulic servo system (not shown) or the like.
By driving the piston disk 5 back and forth, an oscillating flow is generated in the pipeline 3. Numeral 11 denotes a computer in which a control program is recorded, which determines the driving speed of the piston disk 5 based on the input values and controls the reciprocating motion of the piston disk 5 by sending a control signal to the piston disk driving means 7. Is what you do.

Next, a specific procedure for generating (reproducing) a desired vibration flow using the vibration flow generator 1 according to the present invention will be described. First, as a prerequisite for operating the device,
A device-specific constant required for the calculation is input to the computer 11. The device-specific constants include a pipe length, a cross-sectional area of a fluid in each region, a loss coefficient, and the like.

Next, the waveform of the oscillating flow to be reproduced is set and input to the computer 11. The setting of the waveform of the oscillating flow is performed by specifying the velocity v ₁ of the fluid in the pipeline in relation to the time t. For example, when it is desired to reproduce the motion of sand on the sea floor, the velocity v ₁ of the fluid in the pipeline is required.
Are set to have a time waveform as shown in FIG. In addition, the setting of the flow velocity may be a mathematical expression, or may be a discrete numerical value input per unit time as shown in the following table.

(Input Example) Time t (second) Flow velocity v ₁ (meter / second) ──────────────────────── 10.2 20 .4 3 0.8 4 1.0 5 0.7

Subsequently, the value v _P of the driving speed of the piston disk 5 necessary for reproducing the oscillating flow having a desired waveform is represented by:
The computer 11 is caused to calculate while considering the amount of fluid that slips through the gap between the piston board 5 and the inner wall of the pipe 3.
Specifically, by using the relational expressions velocity v ₁ of the fluid velocity v _P and conduit of the piston plate 5 as follows (the formula 1 formula 3), obtaining the value of v _P.

[0018]

(Equation 1)

[0019]

(Equation 2)

[0020]

(Equation 3)

Then, based on the obtained value v _P , the computer 11 sends a control signal to the piston disk drive means 7 to control the driving speed of the piston disk 5. As a result, the piston disk 5 is driven at the speed v _P in the pipe 3, and an oscillating flow of fluid is generated in the pipe 3. The velocity of the fluid in the conduit 3 v ₁ becomes, the desired oscillating flow is reproduced.

Next, in order to determine the driving speed v _P of the piston disk 5 necessary for reproducing a desired oscillating flow (flow rate = v ₁ ),
The basis for using the above formulas 1 to 3 will be described.

Here, the basic equations for the oscillating flow field in the pipe 3 are derived and necessary definitions are made. First, in consideration of the fact that fluid escapes from the gap between the piston board 5 and the inner wall of the pipe 3, the oscillating flow field in the pipe 3 is set to the pipe length L from the front face 5 a to the rear face 5 b of the piston board 5. (A pipe region) and a gap region (gap region) between the piston board 5 and the inner wall of the pipeline 3. Then, as shown in FIG. 9, the sectional area of the fluid in the pipeline region is defined as A ₁ and its flow velocity is defined as v _1, and similarly, the sectional area of the fluid in the gap region is defined as A ₂ and its flow velocity is defined as v ₂ . . In addition, piston board 5
The area of the front surface 5a and the rear surface 5b of the above and the cross-sectional area of the fluid pushed out to the piston board 5 are defined as A _P , and the driving speed of the piston board 5 and the speed of the fluid pushed out to the piston board 5 are defined as v _P.

Then, a continuous equation of the entire pipeline and a basic equation composed of the unsteady Bernoulli's theorem whose section is averaged are simultaneously solved. Specifically, the following equation is given.

[0025]

(Equation 4)

[0026]

(Equation 5)

Here, p is a pressure (a hydrostatic pressure is subtracted), g is a gravitational acceleration, s is a flow axis direction, A (s) is a pipe cross-sectional area, Q is a flow rate, and α is an energy correction coefficient ( = 1.
1), β is the momentum correction coefficient (= 1.0), and h _l is the energy loss head. In order to apply the above equation (5) to the pipeline area, when the above equation (5) is integrated over the pipe length L in the flow axis direction from the front surface 5a to the rear surface 5b of the piston board 5, the following equation is derived.

[0028]

(Equation 6)

Here, Δp ₁ is the pressure difference before and after the piston disk 5, h _l1 is the head of energy loss in the pipeline area, and m ₁ is defined as follows.

[0030]

(Equation 7)

On the other hand, the gap region can be described as follows by using Equation 5 as in the case of the pipeline region.

[0032]

(Equation 8)

Here, m ₂ is obtained by setting the integral range in Equation 7 to the gap region. H _l2 is the energy loss head in the gap region.

Next, the pressure term is deleted from Equations 6 and 8, and 2g is multiplied on both sides to obtain the following equation.

[0035]

(Equation 9)

Here, the energy loss head term in each region is expressed in a form proportional to the square of the velocity in each region, as is generally used. Therefore, the proportional coefficients K ₁ and K ₂ are represented by the sum of various losses that occur in the pipeline region and the gap region. In this embodiment, the friction loss, the gradual expansion loss, and the bending loss coefficient are summed up for the pipe region. On the other hand, in the clearance area, it is difficult to evaluate the loss coefficient because the piston disk moves relative to the pipe inner wall surface and the end shape of the piston disk is not actually linear. Therefore, an empirically derived value may be set based on the reproducibility of the measured flow velocity waveform.

Then, when v ₂ is deleted and rearranged according to Equations 4 and 9, the relational expressions of Equations 1 to 3 are obtained.

[0038]

As described above, according to the present invention,
Fluctuations in the output waveform due to friction between the piston disk and the inner wall of the pipeline can be avoided, and a gap is positively provided between the piston disk and the inner wall of the pipeline so that the computer determines the driving speed of the piston disk. Since the amount of fluid passing through the gap is taken into account, the output waveform can be controlled with extremely high accuracy.

According to the second aspect of the present invention, the width of the gap provided between the piston disk and the inner wall of the pipeline is 0.5
Since it is set to 1.5 mm to 1.5 mm, not only can the reduction of the maximum output flow velocity be avoided, but also the contact between the piston disk and the inner wall of the pipeline can be prevented, and the mixing of new fluctuation components in the output waveform can be prevented. it can.

[Brief description of the drawings]

FIG. 1 is a plan view of a conventional oscillatory flow generator.

FIG. 2 is a partial cross-sectional view of the oscillating flow generator of FIG.

FIG. 3 is a diagram showing a difference between an input waveform and an output waveform of an oscillating flow by a conventional oscillating flow generating device.

FIG. 4 is a view showing a state in which packing is mounted on a piston board in a conventional oscillatory flow generator.

FIG. 5 is a view showing a state in which packing is mounted on a piston board in a conventional vibration flow generating device.

FIG. 6 is a diagram showing an example of an output waveform of an oscillating flow by a conventional oscillating flow generator.

FIG. 7 is an external perspective view of the vibration flow generator 1 according to the present invention.

FIG. 8 is a diagram showing an example of an input waveform of an oscillating flow.

FIG. 9 is a partial sectional view of the oscillating flow generator 1 according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Oscillation flow generator 3 ... Pipe 3a ... Pipe inner wall 5 ... Piston board 7 ... Piston board drive means 9 ... Observation part 11 ... Computer 13 ... Teflon resin film type packing 15 ... Cotton grease type packing

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01M 10/00

Claims (2)

(57) [Claims] An annular closed system pipe having an observation part capable of observing the inside from the outside and filled with a fluid; a piston disk arranged in the pipe so as to close the pipe; Piston disk drive means for reciprocating the piston disk along the inner wall of the pipe, and the vibration flow of the waveform is introduced into the pipe based on a value input to specify the waveform of the vibration flow to be reproduced. A computer recording a program for determining a driving speed of the piston disk required to cause the piston disk to send a signal for controlling reciprocation of the piston disk to the piston disk driving means based on the determined value; A gap between the inner wall of the pipe and the piston board, and the computer slips through the gap when driving the piston board. Flow generator, characterized in that a program for determining a driving speed of a piston disk required to generate a desired vibration flow in the observation unit is recorded in consideration of an amount of fluid to be generated. 2. The vibration according to claim 1, wherein a width of a gap provided between an inner wall of the pipe and the piston board is set to 0.5 mm to 1.5 mm. Flow generator.