阅读说明：本技术 流体速度的处理方法与装置 (Method and device for processing fluid velocity ) 是由 朱一丁 于 2021-09-01 设计创作，主要内容包括：本发明公开了一种流体速度的处理方法与装置。其中,该方法包括：获取粒子图像,其中,粒子图像中包括流体区域和固体区域,且流体区域与固体区域的交界处为近壁面区域；在粒子图像中的固体区域添加伪静态粒子图像,得到待测速图像；依据待测速图像,确定近壁面区域的流体速度。本发明解决了相关技术中在处理近流体/固体交界面区域时会出现很大计算误差的技术问题。(The invention discloses a method and a device for processing fluid velocity. Wherein, the method comprises the following steps: acquiring a particle image, wherein the particle image comprises a fluid region and a solid region, and the boundary of the fluid region and the solid region is a near-wall region; adding a pseudo static particle image in a solid area in the particle image to obtain an image to be measured; and determining the fluid velocity of the near-wall area according to the image to be measured. The invention solves the technical problem that great calculation errors can occur when a near fluid/solid interface region is processed in the related art.)

1. A method of processing fluid velocity, comprising:

acquiring a particle image, wherein the particle image comprises a fluid region and a solid region, and the boundary of the fluid region and the solid region is a near-wall region;

adding a pseudo static particle image to the solid area in the particle image to obtain an image to be tested;

and determining the fluid velocity of the near-wall surface area according to the image to be measured.

2. The method of claim 1, wherein acquiring a particle image comprises:

and collecting an image of the particles scattered into the fluid to obtain the particle image.

3. The method of claim 2, wherein after acquiring an image of the particles dispersed into the fluid and obtaining the image of the particles, further comprising:

determining a boundary between a fluid and a solid in the particle image;

dividing the particle image into the fluid region and the solid region according to the boundary.

4. The method according to claim 3, further comprising, after dividing the particle image into the fluid region and the solid region according to the boundary:

and determining the solid area as a wall area, and determining the junction of the fluid area and the solid area as the near-wall area.

5. The method according to claim 1, wherein adding a pseudo-static particle image to the solid region in the particle image to obtain an image to be velocimetry comprises:

acquiring a pseudo-static particle image, wherein pseudo-static particles in the pseudo-static particle image are randomly distributed, and the average light intensity of the pseudo-static particles is the same as the average light intensity of the particles in the fluid region;

and adding the pseudo static particle image into the solid area to generate the image to be tested.

6. The method according to any one of claims 1 to 5, wherein determining the fluid velocity of the near-wall region from the image to be measured comprises:

and processing the image to be measured by using a particle image speed measurement algorithm to obtain the fluid speed of the near-wall surface area.

7. The method according to claim 6, wherein in the processing of the image to be velocimated using a particle image velocimetry algorithm, further comprising:

and setting the speed corresponding to the solid area in the image to be tested to be zero according to the pseudo static particle image.

8. A fluid velocity management apparatus, comprising:

the particle image acquisition module is used for acquiring a particle image, wherein the particle image comprises a fluid region and a solid region, and the boundary of the fluid region and the solid region is a near-wall surface region;

the adding module is used for adding a pseudo static particle image in the solid area in the particle image to obtain an image to be measured;

and the determining module is used for determining the fluid speed of the near-wall surface area according to the image to be measured.

9. A computer-readable storage medium, comprising a stored program, wherein the program, when executed, controls an apparatus in which the computer-readable storage medium is located to perform the fluid velocity processing method according to any one of claims 1 to 7.

10. A processor for running a program, wherein the program when running performs the method of fluid velocity processing of any one of claims 1 to 7.

Technical Field

The invention relates to the technical field of particle image processing, in particular to a method and a device for processing fluid velocity.

Background

Particle image velocimetry is based on scattering particles in a fluid and recording a time sequence of particle images with a camera. And dividing the particle image into orthogonal grids according to a rectangular coordinate, and obtaining the distribution of the corresponding fluid velocity by using a window correlation algorithm to the displacement of the particle image in each grid between adjacent moments.

Fig. 1 is a schematic diagram of a particle image of a fluid velocity processing method according to the prior art, and as shown in fig. 1, a window search algorithm has a large calculation error when processing a near fluid/solid interface region, mainly because: strong shear exists in wall surface flowing; the solid portion has no image information (black area), causing the calculation to be an extrapolation problem from the fluid to the solid, causing misconvergence.

In view of the above-mentioned problem of the related art that a large calculation error occurs when processing a near fluid/solid interface region, no effective solution has been proposed at present.

Disclosure of Invention

The embodiment of the invention provides a method and a device for processing the fluid velocity, which at least solve the technical problem that great calculation errors occur when a near fluid/solid interface region is processed in the related art.

According to an aspect of an embodiment of the present invention, there is provided a method for processing a fluid velocity, including: acquiring a particle image, wherein the particle image comprises a fluid region and a solid region, and the boundary of the fluid region and the solid region is a near-wall region; adding a pseudo static particle image to the solid area in the particle image to obtain an image to be tested; and determining the fluid velocity of the near-wall surface area according to the image to be measured.

Optionally, acquiring a particle image comprises: and collecting an image of the particles scattered into the fluid to obtain the particle image.

Optionally, after acquiring an image of the particles scattered into the fluid and obtaining the particle image, the method further includes: determining a boundary between a fluid and a solid in the particle image; dividing the particle image into the fluid region and the solid region according to the boundary.

Optionally, after dividing the particle image into the fluid region and the solid region according to the boundary, the method further includes: and determining the solid area as a wall area, and determining the junction of the fluid area and the solid area as the near-wall area.

Optionally, adding a pseudo static particle image to the solid region in the particle image to obtain an image to be measured, where the obtaining includes: acquiring a pseudo-static particle image, wherein pseudo-static particles in the pseudo-static particle image are randomly distributed, and the average light intensity of the pseudo-static particles is the same as the average light intensity of the particles in the fluid region; and adding the pseudo static particle image into the solid area to generate the image to be tested.

Optionally, determining the fluid velocity of the near-wall surface region according to the image to be measured includes: and processing the image to be measured by using a particle image speed measurement algorithm to obtain the fluid speed of the near-wall surface area.

Optionally, in the process of processing the image to be speed-measured by using the particle image speed-measuring algorithm, the method further includes: and setting the speed corresponding to the solid area in the image to be tested to be zero according to the pseudo static particle image.

According to another aspect of the embodiments of the present invention, there is also provided a fluid velocity processing apparatus, including: the particle image acquisition module is used for acquiring a particle image, wherein the particle image comprises a fluid region and a solid region, and the boundary of the fluid region and the solid region is a near-wall surface region; the adding module is used for adding a pseudo static particle image in the solid area in the particle image to obtain an image to be measured; and the determining module is used for determining the fluid speed of the near-wall surface area according to the image to be measured.

According to another aspect of the embodiments of the present invention, there is also provided a computer-readable storage medium, which includes a stored program, wherein when the program runs, the apparatus where the computer-readable storage medium is located is controlled to execute the fluid velocity processing method according to any one of the above items.

According to another aspect of the embodiments of the present invention, there is also provided a processor for executing a program, wherein the program is executed to perform the fluid velocity processing method according to any one of the above.

In the embodiment of the invention, a particle image is obtained, wherein the particle image comprises a fluid region and a solid region, and the boundary of the fluid region and the solid region is a near-wall region; adding a pseudo static particle image in a solid area in the particle image to obtain an image to be measured; the method comprises the steps of determining the fluid speed of a near-wall surface area according to an image to be measured, adding a pseudo static particle image into a solid area in the particle image to obtain the image to be measured, determining the fluid speed of the near-wall surface area by using the image to be measured, and achieving the purpose of changing the fluid speed calculation of the near-wall surface area from extrapolation to interpolation, thereby achieving the technical effects of reducing calculation errors and improving calculation accuracy, and further solving the technical problem that great calculation errors occur when a near-fluid/solid interface area is processed in the related technology.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limiting the invention. In the drawings:

FIG. 1 is a schematic illustration of a particle image of a fluid velocity processing method according to the prior art;

FIG. 2 is a flow chart of a method of processing fluid velocity according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of an original particle image and a wall region added pseudo-static particle image in accordance with an alternative embodiment of the present invention;

FIG. 4 is a schematic illustration of the distribution of flow rate (abscissa) along the height of a wall (ordinate) according to an alternative embodiment of the invention;

FIG. 5 is a schematic diagram of a fluid velocity processing apparatus according to an embodiment of the present invention.

Detailed Description

In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

Example 1

In accordance with an embodiment of the present invention, there is provided an embodiment of a method of fluid velocity processing, it being noted that the steps illustrated in the flowchart of the figure may be performed in a computer system, such as a set of computer-executable instructions, and that while a logical order is illustrated in the flowchart, in some cases the steps illustrated or described may be performed in an order different than presented herein.

Fig. 2 is a flow chart of a fluid velocity processing method according to an embodiment of the present invention, as shown in fig. 2, the method including the steps of:

step S202, acquiring a particle image, wherein the particle image comprises a fluid region and a solid region, and the boundary of the fluid region and the solid region is a near-wall region;

the near-wall surface region is a region in the vicinity of a boundary between the fluid region and the solid region, and the fluid region is a partial region in the vicinity of the solid region.

In an alternative embodiment, acquiring an image of a particle comprises: and collecting an image of the particles scattered into the fluid to obtain the particle image.

In an alternative embodiment, after acquiring an image of particles dispersed in a fluid and obtaining the image of the particles, the method further includes: determining a boundary between a fluid and a solid in the particle image; dividing the particle image into the fluid region and the solid region according to the boundary.

In an alternative embodiment, after dividing the particle image into the fluid region and the solid region according to the boundary, the method further includes: and determining the solid area as a wall area, and determining the junction of the fluid area and the solid area as the near-wall area.

Step S204, adding a pseudo static particle image in a solid area in the particle image to obtain an image to be measured;

in an optional embodiment, adding a pseudo static particle image to the solid region in the particle image to obtain an image to be velocimetry, includes: acquiring a pseudo-static particle image, wherein pseudo-static particles in the pseudo-static particle image are randomly distributed, and the average light intensity of the pseudo-static particles is the same as the average light intensity of the particles in the fluid region; and adding the pseudo static particle image into the solid area to generate the image to be tested.

And step S206, determining the fluid velocity of the near-wall area according to the image to be measured.

In an alternative embodiment, determining the fluid velocity in the near-wall region according to the image to be measured includes: and processing the image to be measured by using a particle image speed measurement algorithm to obtain the fluid speed of the near-wall surface area.

In an optional implementation manner, in the process of processing the image to be veloped by using the particle image velocimetry algorithm, the method further includes: and setting the speed corresponding to the solid area in the image to be tested to be zero according to the pseudo static particle image.

Through the steps, a particle image can be obtained, wherein the particle image comprises a fluid area and a solid area, and the boundary of the fluid area and the solid area is a near-wall area; adding a pseudo static particle image in a solid area in the particle image to obtain an image to be measured; the method comprises the steps of determining the fluid speed of a near-wall surface area according to an image to be measured, adding a pseudo static particle image into a solid area in the particle image to obtain the image to be measured, determining the fluid speed of the near-wall surface area by using the image to be measured, and achieving the purpose of changing the fluid speed calculation of the near-wall surface area from extrapolation to interpolation, thereby achieving the technical effects of reducing calculation errors and improving calculation accuracy, and further solving the technical problem that great calculation errors occur when a near-fluid/solid interface area is processed in the related technology.

An alternative embodiment of the invention is described in detail below.

Fig. 3 is a schematic diagram of an original particle image and a wall area added pseudo-static particle image according to an alternative embodiment of the invention, as shown in fig. 3, fig. 3(a) is the original particle image, specifically, the result of a conventional window query algorithm without image preprocessing, and fig. 3(b) is the wall area added pseudo-static particle image, specifically, the pseudo-static particles are added in the lower solid area. The region will be calculated by the query algorithm as velocity 0, changing the near wall region velocity field calculation from extrapolation to interpolation problem, thereby reducing the calculation error.

The specific implementation method comprises the following steps: 1) on the image of the particle that has been obtained, the boundary between the fluid and the solid is first found; 2) the solid part is added with a pseudo-static particle image which is randomly distributed, and the average light intensity of the pseudo-static particle image is consistent with that of the fluid part.

It should be noted that the original measured Image has no particles in the solid portion, and the solid portion is considered to have no measured value after being sent to a Particle Image Velocimetry (PIV) query program, so that interpolation to the solid portion is necessarily an extrapolation value. In contrast, in the above embodiment of the present invention, if the stationary particles are artificially added to the solid portion, the PIV query program will set the velocity signal of the solid portion to 0 based on the information of the stationary particles, so that the solid portion has a value and the velocity at the fluid-solid interface is interpolated. The implementation method has the advantages of simplicity and practicability, and the existing PIV query program does not need to be modified.

In comparison with a given particle image expansion algorithm, fig. 4 is a schematic diagram of the distribution of the flow velocity (abscissa) along the wall height (ordinate) according to an alternative embodiment of the present invention, as shown in fig. 4, a smooth curve is a given velocity curve, and a dotted line is a calculation result, where fig. 4(a) is the addition of pseudo-static particles, and fig. 4(b) is the non-addition, it can be clearly seen that the calculation error is greatly reduced after the pseudo-static particle image is added.

Example 2

According to another aspect of the embodiments of the present invention, there is also provided a fluid velocity processing apparatus, and fig. 5 is a schematic view of the fluid velocity processing apparatus according to the embodiments of the present invention, as shown in fig. 5, the fluid velocity processing apparatus includes: an acquisition module 52, an addition module 54, and a determination module 56. The fluid velocity processing apparatus will be described in detail below.

An obtaining module 52, configured to obtain a particle image, where the particle image includes a fluid region and a solid region, and a boundary between the fluid region and the solid region is a near-wall region;

an adding module 54, connected to the obtaining module 52, configured to add a pseudo static particle image to the solid region in the particle image to obtain an image to be speed-measured;

and the determining module 56 is connected to the adding module 54 and is used for determining the fluid velocity of the near-wall surface area according to the image to be measured.

It should be noted that the above modules may be implemented by software or hardware, for example, for the latter, the following may be implemented: the modules can be located in the same processor; and/or the modules are located in different processors in any combination.

In the above embodiment, the processing device of the fluid velocity may obtain an image to be measured by adding the pseudo static particle image to the solid region in the particle image, and determine the fluid velocity of the near-wall region by using the image to be measured, so as to achieve the purpose of changing the calculation of the fluid velocity of the near-wall region from extrapolation to interpolation, thereby achieving the technical effects of reducing the calculation error and improving the calculation accuracy, and further solving the technical problem of a large calculation error when processing the near-fluid/solid interface region in the related art.

It should be noted here that the above-mentioned obtaining module 52, adding module 54 and determining module 56 correspond to steps S202 to S206 in embodiment 1, and the above-mentioned modules are the same as the examples and application scenarios realized by the corresponding steps, but are not limited to what is disclosed in embodiment 1 above.

Optionally, the obtaining module 52 includes: and the acquisition unit is used for acquiring the image of the particles scattered in the fluid to obtain the particle image.

Optionally, the obtaining module 52 further includes: the first determining unit is used for determining a boundary between the fluid and the solid in the particle image after acquiring an image of the particles scattered in the fluid to obtain the particle image; and a dividing unit for dividing the particle image into a fluid region and a solid region according to a boundary.

Optionally, the obtaining module 52 further includes: a second determining unit configured to determine the solid area as a wall area after dividing the particle image into the fluid area and the solid area according to a boundary, and determine a boundary between the fluid area and the solid area as a near-wall area.

Optionally, the adding module 54 includes: the acquiring unit is used for acquiring a pseudo-static particle image, wherein the pseudo-static particles in the pseudo-static particle image are randomly distributed, and the average light intensity of the pseudo-static particles is the same as the average light intensity of the particles in the fluid region; and the adding unit is used for adding the pseudo static particle image into the solid area and generating an image to be measured.

Optionally, the determining module 56 includes: and the processing unit is used for processing the image to be measured by utilizing a particle image velocimetry algorithm to obtain the fluid velocity of the near-wall surface area.

Optionally, the determining module 56 further includes: and the setting unit is used for setting the speed corresponding to the solid area in the image to be tested to be zero according to the pseudo static particle image in the process of processing the image to be tested by utilizing the particle image velocimetry.

Example 3

According to another aspect of the embodiments of the present invention, there is also provided a computer-readable storage medium including a stored program, wherein when the program runs, the apparatus where the computer-readable storage medium is located is controlled to execute the fluid velocity processing method of any one of the above.

Optionally, in this embodiment, the computer-readable storage medium may be located in any one of a group of computer terminals in a computer network and/or in any one of a group of mobile terminals, and the computer-readable storage medium includes a stored program.

Optionally, the program when executed controls an apparatus in which the computer-readable storage medium is located to perform the following functions: acquiring a particle image, wherein the particle image comprises a fluid region and a solid region, and the boundary of the fluid region and the solid region is a near-wall region; adding a pseudo static particle image in a solid area in the particle image to obtain an image to be measured; and determining the fluid velocity of the near-wall area according to the image to be measured.

Optionally, acquiring a particle image comprises: and collecting an image of the particles scattered into the fluid to obtain a particle image.

Optionally, after acquiring an image of the particles scattered into the fluid and obtaining the particle image, the method further includes: determining the boundary between the fluid and the solid in the particle image; the particle image is divided into a fluid region and a solid region according to a boundary.

Optionally, after dividing the particle image into the fluid region and the solid region according to a boundary, the method further includes: and determining the solid area as a wall area, and determining the boundary of the fluid area and the solid area as a near-wall area.

Optionally, adding a pseudo static particle image to a solid region in the particle image to obtain an image to be measured, where the method includes: acquiring a pseudo-static particle image, wherein the pseudo-static particles in the pseudo-static particle image are randomly distributed, and the average light intensity of the pseudo-static particles is the same as the average light intensity of the particles in the fluid region; and adding the pseudo static particle image into the solid area to generate an image to be measured.

Optionally, determining the fluid velocity in the near-wall region according to the image to be measured includes: and processing the image to be measured by using a particle image velocimetry algorithm to obtain the fluid velocity of the near-wall surface area.

Optionally, in the process of processing the image to be measured by using the particle image velocimetry algorithm, the method further includes: and setting the speed corresponding to the solid area in the image to be tested to be zero according to the pseudo static particle image.

Example 4

According to another aspect of the embodiments of the present invention, there is also provided a processor for executing a program, wherein the program executes a method for processing a fluid velocity according to any one of the above methods.

The embodiment of the invention provides equipment, which comprises a processor, a memory and a program which is stored on the memory and can run on the processor, wherein the processor executes the program and realizes the following steps: acquiring a particle image, wherein the particle image comprises a fluid region and a solid region, and the boundary of the fluid region and the solid region is a near-wall region; adding a pseudo static particle image in a solid area in the particle image to obtain an image to be measured; and determining the fluid velocity of the near-wall area according to the image to be measured.

Optionally, acquiring a particle image comprises: and collecting an image of the particles scattered into the fluid to obtain a particle image.

Optionally, after acquiring an image of the particles scattered into the fluid and obtaining the particle image, the method further includes: determining the boundary between the fluid and the solid in the particle image; the particle image is divided into a fluid region and a solid region according to a boundary.

Optionally, after dividing the particle image into the fluid region and the solid region according to a boundary, the method further includes: and determining the solid area as a wall area, and determining the boundary of the fluid area and the solid area as a near-wall area.

Optionally, adding a pseudo static particle image to a solid region in the particle image to obtain an image to be measured, where the method includes: acquiring a pseudo-static particle image, wherein the pseudo-static particles in the pseudo-static particle image are randomly distributed, and the average light intensity of the pseudo-static particles is the same as the average light intensity of the particles in the fluid region; and adding the pseudo static particle image into the solid area to generate an image to be measured.

Optionally, determining the fluid velocity in the near-wall region according to the image to be measured includes: and processing the image to be measured by using a particle image velocimetry algorithm to obtain the fluid velocity of the near-wall surface area.

Optionally, in the process of processing the image to be measured by using the particle image velocimetry algorithm, the method further includes: and setting the speed corresponding to the solid area in the image to be tested to be zero according to the pseudo static particle image.

The invention also provides a computer program product adapted to perform a program for initializing the following method steps when executed on a data processing device: acquiring a particle image, wherein the particle image comprises a fluid region and a solid region, and the boundary of the fluid region and the solid region is a near-wall region; adding a pseudo static particle image in a solid area in the particle image to obtain an image to be measured; and determining the fluid velocity of the near-wall area according to the image to be measured.

Optionally, acquiring a particle image comprises: and collecting an image of the particles scattered into the fluid to obtain a particle image.

Optionally, after acquiring an image of the particles scattered into the fluid and obtaining the particle image, the method further includes: determining the boundary between the fluid and the solid in the particle image; the particle image is divided into a fluid region and a solid region according to a boundary.

Optionally, after dividing the particle image into the fluid region and the solid region according to a boundary, the method further includes: and determining the solid area as a wall area, and determining the boundary of the fluid area and the solid area as a near-wall area.

Optionally, adding a pseudo static particle image to a solid region in the particle image to obtain an image to be measured, where the method includes: acquiring a pseudo-static particle image, wherein the pseudo-static particles in the pseudo-static particle image are randomly distributed, and the average light intensity of the pseudo-static particles is the same as the average light intensity of the particles in the fluid region; and adding the pseudo static particle image into the solid area to generate an image to be measured.

Optionally, determining the fluid velocity in the near-wall region according to the image to be measured includes: and processing the image to be measured by using a particle image velocimetry algorithm to obtain the fluid velocity of the near-wall surface area.

Optionally, in the process of processing the image to be measured by using the particle image velocimetry algorithm, the method further includes: and setting the speed corresponding to the solid area in the image to be tested to be zero according to the pseudo static particle image.

The above-mentioned serial numbers of the embodiments of the present invention are merely for description and do not represent the merits of the embodiments.

In the above embodiments of the present invention, the descriptions of the respective embodiments have respective emphasis, and for parts that are not described in detail in a certain embodiment, reference may be made to related descriptions of other embodiments.

In the embodiments provided in the present application, it should be understood that the disclosed technology can be implemented in other ways. The above-described embodiments of the apparatus are merely illustrative, and for example, the division of the units may be a logical division, and in actual implementation, there may be another division, for example, multiple units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, units or modules, and may be in an electrical or other form.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, functional units in the embodiments of the present invention may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.

The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a removable hard disk, a magnetic or optical disk, and other various media capable of storing program codes.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.