CN107748055A - Water surface flow field acquisition method - Google Patents

Abstract

The invention relates to the technical field of hydraulic model tests, and discloses a method for collecting a water flow surface flow field. A single-lens reflex camera is fixed above the model of the flow field to be collected, the lens of the single-lens reflex camera is arranged downward, and the focal length, Aperture and exposure time; tracer particles are sown on the water surface of the model, and the tracer particles on the surface of the water flow are collected continuously and for a long time by a SLR camera, and the position of the tracer particles at different moments is tracked and superimposed, and reflected in the On the same picture, the trajectory of each tracer particle during the period of exposure and collection is displayed on the picture, and the trajectory of the tracer particle is the trajectory of the water flow during the period of exposure and collection. In this way, the efficiency of the collection test of the flow field on the surface of the water flow is improved, errors caused by post-processing are effectively avoided, the flow trajectory of the surface of the water flow is intuitively reflected, and more realistic visualization results are provided for studying the impact of engineering construction on the flow field of the water flow.

Description

Acquisition method of surface flow field of water flow

technical field

The invention relates to the technical field of hydraulic model tests, in particular to a method for collecting flow fields on the surface of water flow.

Background technique

Model test is an important research method and expertise in scientific experiments, and it is widely used. The hydraulic physical model test is to use the knowledge of river dynamics, according to the similar principle of water flow and sediment movement mechanics, to simulate the boundary conditions and dynamic conditions similar to the prototype, to study the river in the case of natural rivers or in the case of hydraulic structures A method for downstream flow structure, riverbed evolution, and engineering program effects.

The space occupied by the fluid motion is called the flow field. In order to study the flow field and its changes on the surface of the water flow, in the hydraulic model test, reflective particles that can float on the water surface are added to the water flow to trace the water flow, simulate the shape of the flow field of the water flow, and visualize it through different technologies.

At present, in the hydraulic model test, tracer particles are sown on the surface of the water flow, the range of the flow field to be observed is covered by a single or multiple cameras, the shutter duration and interval are set, and the cameras are used to take pictures (generally no more than 5). Analyze the photos taken at adjacent times (T1, T2, T3, T4, T5), match the positions of tracer particles A, B... in the picture at different times, and connect the positions of a tracer particle at different times in series , as its motion path, calculate the motion elements (flow velocity, Flow direction), through homogenization, and finally express the shape of the flow field on the surface of the water flow at T1 in the form of arrows.

However, the above method has the following disadvantages:

(1) The time for the camera to collect data is very short. Due to the quality and performance of the camera, the general collection time is 0.04 seconds, and then the next picture is taken after a period of time (usually 0-0.16 seconds), and finally multiple The images are superimposed and the paths of the tracer particles are calculated. Since there are many tracer particles distributed on the surface of the water flow, the adjacent tracer particles will be confused during superposition processing, especially when the flow velocity is high and there are many tracer particles, the A1 display at T1 time (the first photo) When matching with the second photo at T2, the corresponding A2 tracer particle was not found, but the B2 tracer particle was matched, resulting in the distortion of the final surface flow state, which was not similar to the prototype.

(2) Only the superimposed motion trajectory can be averaged to express the motion parameters (flow velocity and flow direction) at a certain moment (such as T1 time), but cannot express the flow trajectory in the T1-T5 time period.

(3) After the superposition and generalization processing, the horizontal and vertical homogeneous arrangement is carried out within the boundary range of the flow field, and the actual collected data is interpolated, which is not the original real flow state reproduction of the tracer particles.

(4) Post-processing takes a long time and is inefficient. A large number of screening processes are required, and manual judgment is required to delete unreasonable data.

Referring to Figure 1, when multiple photos are superimposed by CCD technology, the tracer particles A and B are close together, and the actual positions of the tracer particles are A1-A4 and B1-B4 at time T1-T4, respectively. When the photos at T1 and T2 are matched, A1 does not capture A2 correctly, but captures B2, causing the trajectory of tracer particle A to change to A1-B2-B3-B4, as shown in Figure 2, after homogenization The flow field expression of becomes Va.

Referring to Fig. 3, multiple cameras are used to collect water flow tracer particle motion, and the combined surface flow field is averaged.

Contents of the invention

The method for collecting the surface flow field of the water flow provided by the present invention aims to solve the problem that in the prior art, the time for the camera to collect data is short, and when the collected photos are superimposed, it is easy to confuse adjacent tracer particles, resulting in traces Wrong, it cannot truly reflect the surface flow field of water flow.

The present invention is achieved in that a single-lens reflex camera is fixed above the model of the flow field to be collected, the lens of the single-lens reflex camera is arranged downwards, and the focal length, aperture and exposure time of the single-lens reflex camera are adjusted; The tracer particles are sown on the surface of the water flow, and the tracer particles on the surface of the water flow are collected continuously and for a long time by the SLR camera, and the positions of the tracer particles at different moments are tracked and superimposed, and reflected in the same picture On the picture, the trajectory of each tracer particle during the period of exposure and acquisition is displayed on the picture, and the trajectory of the tracer particle is the trajectory of the water flow during the period of exposure and acquisition.

Further, the tracer particles are evenly arranged on the surface of the water flow of the model.

Further, the color of the tracer particles is white.

Further, the maximum exposure time of the SLR camera is not less than 2 seconds.

Further, the SLR camera is set directly above the model.

Compared with the prior art, the method for collecting the surface flow field of the water flow provided by the present invention fixes the SLR camera above the model, arranges the lens of the SLR camera facing down and adjusts the focal length, aperture, and exposure time. The tracer particles are sown on the surface, and the continuous and long-term exposure collection of the SLR camera is used to track and superimpose the position of the tracer particles at different moments, and reflect it on the same picture, so as to show that each tracer particle is at the time of exposure and collection. The movement trajectory of a certain period of time, the movement trajectory is the trajectory of the water flow during the period of exposure acquisition. In this way, the efficiency of the collection test of the flow field on the surface of the water flow is improved, and errors caused by post-processing are effectively avoided. The time is short, and when the collected photos are superimposed, it is easy to confuse adjacent tracer particles, resulting in trace errors, which cannot truly reflect the problem of the flow field on the surface of the water flow.

Description of drawings

1 is a schematic diagram of the real trajectory of the tracer particles and the matched trajectory of the method for collecting the surface flow field of the water flow provided by the embodiment of the present invention;

2 is a schematic diagram of the real flow field expression of the tracer particles and the flow field expression after homogenization treatment of the method for collecting the flow field on the water surface provided by the embodiment of the present invention;

Fig. 3 is a schematic diagram of the surface flow field of the water flow synthesized by homogenizing the movement of particles of the water flow collected by multiple cameras in the method for collecting the surface flow field of the water flow provided by the embodiment of the present invention;

4 is a schematic diagram of the real flow state of the surface flow field of the water flow directly collected by the single-lens reflex camera of the method for collecting the surface flow field of the water flow provided by the embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

The implementation of the present invention will be described in detail below in conjunction with specific embodiments.

In the drawings of this embodiment, the same or similar symbols correspond to the same or similar components; The indicated orientation or positional relationship is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, or in a specific orientation. Construction and operation, so the words describing the positional relationship in the drawings are only for illustrative purposes, and should not be construed as limitations on this patent. Those of ordinary skill in the art can understand the specific meanings of the above terms according to specific situations.

Referring to Fig. 3-4, it is a preferred embodiment provided by the present invention.

The method for collecting the surface flow field of the water flow provided by the present invention is used for collecting the surface flow field of the water flow, and can also be used for collecting the surface flow field of other types of liquids, and is not limited to this embodiment.

The surface flow field acquisition method of the water flow is to fix a SLR camera above the model of the flow field to be collected, with the lens of the SLR camera facing down and adjust the focal length, aperture, and exposure time, sow tracer particles on the surface of the water flow of the model, and pass the SLR camera The camera collects continuous and long-term exposures to track and superimpose the position of the tracer particles at different times, and reflect it on the same picture, thereby displaying the trajectory of each tracer particle during the exposure collection period.

Since the exposure time of the SLR camera is long and can be set according to actual needs, the time of exposure acquisition can be set to a longer time, for example, the time of exposure acquisition is set to 2 seconds, and the SLR camera will continuously track and superimpose during this period The position of the tracer particles at different times is reflected on the same picture, showing the trajectory of each tracer particle during the period of 0-2s. In fluid research, it is called the trace of the time period of 0-2s. , that is, the trajectory of the water flow during this period of time. In this way, the efficiency of the collection test of the flow field on the surface of the water flow is improved, and errors caused by post-processing are effectively avoided. The time is short, and when the collected photos are superimposed, it is easy to confuse adjacent tracer particles, resulting in trace errors, which cannot truly reflect the problem of the flow field on the surface of the water flow.

Figure 4 shows the real flow state of the surface flow field of the water flow directly collected by the SLR camera. Compared with Figure 3, Figure 4 captured by the SLR camera can directly feed back the flow state of the water flow surface.

Specifically, the tracer particles are evenly arranged on the surface of the water flow in the model, that is, the tracer particles are spread as evenly as possible on the surface of the water flow at the beginning of the simulation test, so that the tracer particles can freely float with the water flow, It reduces the deformation of the tracer particle trajectory caused by the collision and extrusion between the tracer particles, making the test results more accurate.

Specifically, the color of the tracer particles is white. The white tracer particles have a good reflective effect and are easy to be captured by the SLR camera. In this way, the SLR camera can better track the tracer particles, thereby accurately simulating the shape of the flow field on the surface of the water flow.

In this embodiment, the maximum exposure time of the SLR camera is not less than 2 seconds. The maximum exposure time of the SLR camera determines the maximum exposure acquisition time it can achieve. If the maximum exposure time of the SLR camera is too short, the trajectory of each tracer particle will be too short, which is not conducive to simulating the surface flow field of the water flow. , in general, choose a SLR camera with a relatively long maximum exposure time.

In this embodiment, the SLR camera is set directly above the model. Setting the SLR camera directly above the model can capture the tracer particles more clearly and accurately, avoiding the unclear trajectory of the tracer particles due to the angle, and making the test results more accurate.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (5)

1. The method for collecting the flow field on the water surface is characterized in that a single-lens reflex camera is fixed above the model of the flow field to be collected, the lens of the single-lens reflex camera is arranged downwards, and the focal length, aperture and exposure of the single-lens reflex camera are adjusted time; tracer particles are sown on the surface of the water flow of the model, the tracer particles on the surface of the water flow are continuously and long-time exposed and collected by the SLR camera, and the positions of the tracer particles at different moments are tracked and superimposed, and the Its reaction is on the same picture, and the trajectory of each tracer particle during the period of exposure and collection is displayed on the picture, and the trajectory of the tracer particle is the water flow movement during the period of exposure and collection. track route. 2 . The method for collecting surface flow field of water flow according to claim 1 , wherein the tracer particles are evenly arranged on the surface of the water flow of the model. 3 . 3. The method for collecting water surface flow field according to claim 1, characterized in that the color of the tracer particles is white. 4. The method for collecting water surface flow field according to claim 1, characterized in that the maximum exposure time of the SLR camera is not less than 2 seconds. 5. The method for collecting water surface flow field according to any one of claims 1 to 4, wherein the single-lens reflex camera is arranged directly above the model.