CN203396784U - Seepage flow velocity monitoring test device for porous-medium structural body - Google Patents

Abstract

The utility model discloses a seepage flow velocity monitoring test device for a porous-medium structural body. The seepage flow velocity monitoring test device comprises a heating system (1), a distributed optical-fiber temperature sensing system (2), a porous-medium structural body model groove (3) with embedded optical fibers and a water outlet system (4). The heating system (1), the distributed optical-fiber temperature sensing system (2) and the water outlet system (4) are connected with the porous-medium structural body model groove (3). A monitoring period is a whole optical-cable heating temperature-rising period according to the unconventional optical-fiber seepage monitoring method, a linear correlation between seepage flow velocity and an average thermal conductivity is accurately pinpointed, and monitoring precision is reliably guaranteed.

Description

Seepage velocity monitoring test device for porous media structure

technical field

The invention relates to a porous medium structure body seepage flow velocity monitoring test device and method. the

Background technique

The No. 1 document of the central government on water conservancy construction has accelerated the pace of my country's water conservancy construction. The main problems faced by my country's earth-rock dam projects include leakage, piping, collapse, cracks, landslides, slope protection damage, and erosion cavitation. Seepage is an important factor affecting the safety of dams. If the hidden danger of leakage is not discovered in time and the seepage control measures are not in place, it is very likely to cause seepage damage and dam slope instability, which will seriously affect the safety of the project and even cause the dam to fail. According to statistics, more than one-third of the damage in earth-rock dam projects is caused by various degrees of leakage and various problems derived from leakage; more than 90% of embankment failures are caused by leakage damage. the

A large amount of engineering experience shows that strengthening the real-time positioning and quantitative monitoring of seepage and seepage deformation of earth-rock dams is of great significance to ensure the safe operation of the project. While the traditional monitoring technology is continuously improved and developed, more and more New technologies have been introduced into the field of dam safety monitoring, and research on the monitoring principles, implementation methods, and technologies of new technologies in the field of dam engineering has become a hot scientific research topic; The spatial discontinuity and missing measurement of the measured value, the distributed and continuous real-time monitoring and measurement of dam leakage by distributed optical fiber temperature sensing technology have attracted great attention from the engineering and academic circles, but the application of this technology in leakage monitoring The theory is not yet mature, especially the quantitative relationship model between the temperature rise of optical fiber heating and seepage flow velocity, ambient temperature, and heating power has not been established. Therefore, it is of great significance to carry out theoretical research and model tests on the seepage flow velocity monitoring of earth-rock dams. the

Contents of the invention

Purpose of the invention: The purpose of the present invention is to provide an efficient and accurate monitoring test device for seepage flow velocity of porous media structures in view of the deficiencies in the prior art. the

Technical solution: The porous media structure seepage velocity monitoring test device of the present invention includes a heating system, a distributed optical fiber temperature sensing system, a porous media structure model tank embedded with a monitoring optical fiber, and a water outlet system; the heating system, distributed optical fiber The temperature sensing system and the water outlet system are respectively connected with the model tank of the porous medium structure. the

The heating system is a parallel circuit mainly composed of an AC power supply, a voltage regulator and a load heating resistance wire. The monitoring optical fiber is heated through the load heating resistance wire, and the heating power is controlled by controlling the voltage through the voltage regulator. the

The distributed optical fiber temperature sensing system includes a distributed optical fiber temperature measurement host and a linear multi-mode temperature-sensing optical cable, and the distributed optical fiber temperature measurement host is connected to the linear multi-mode temperature-sensing optical cable through a pulse laser device and outputs optical pulses ; The tail of the linear multimode temperature-sensing optical cable is connected with the optical fiber connector. the

The water outlet system includes a water tank, a flow rate control valve, a water pump, and a circulating pool; the position of the water tank is higher than the circulating pool, and the upper water level of the water tank is connected to the circulating pool through an overflow pipe; the circulating pool Water is transported into the water tank by a water pump; the bottom of the water tank is connected with the porous medium structure model tank through a pipeline; the flow rate control valve is respectively arranged between the water tank and the porous medium structure model tank and the circulating pool on the pipe. the

The test method for monitoring seepage flow rate of porous media structure includes the following steps:

(1) Constructing a model groove of a porous medium structure embedded with a monitoring optical fiber. Based on different test requirements, a porous medium structure model tank with monitoring optical fiber is built according to the specific design. the

(2) Adjust the outlet system to form a uniform and stable seepage field. Adjust the valve of the water outlet system to a certain position, and then continuously monitor the outflow of the water outlet system. When the outflow is stable, it is considered that a uniform and stable seepage field has been formed. the

(3) Based on the distributed optical fiber temperature sensing system, the temperature monitoring of the monitoring optical fiber buried in the model groove is carried out; both Raman scattering and Brillouin scattering are sensitive to temperature and can be used to measure temperature. Considering Brillouin scattering It is greatly affected by other factors such as stress, so Raman scattering is mainly used to measure temperature. The temperature value is calculated by Stokes light and anti-Stokes light:

$\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; wxya</span>}}{\mathrm{<span\; class="notranslate">\; K</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; ln</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; as</span>}}}{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}<span\; class="notranslate">\; ,</span>$

式中：C为真空中的光速，n为光纤的折射率。  Among them, in the formula: l _as is the anti-Stokes light intensity; l _s is the Stokes light intensity; α is the temperature correlation coefficient; h is the Planck coefficient; C is the speed of light in vacuum; V is Raman translation; K is the Boltzmann constant; T is the absolute temperature value. The temperature value of the optical cable can be obtained through the above method. Technically, it is also necessary to know the position value corresponding to the temperature value. Optical time domain reflectometry (OTDR) can solve this problem. By measuring the time difference Δt between the incident light and the reflected light, the distance X between the reflection point and the transmitting end can be known:

In the formula: C is the speed of light in vacuum, and n is the refractive index of the fiber.

(4) After being monitored by the distributed optical fiber temperature sensing system for 10 minutes, the target optical fiber is energized and heated through the heating system. The fixed steel wire in the monitoring optical cable is heated by the single-line heat source method, and the solution model of the temperature field under the influence of the uniform and constant seepage field in the single-line heat source method is as follows:

$\left\{\begin{array}{cc}\frac{{\&PartialD;}^{2}T}{{\&PartialD;x}^2}+\frac{{\&PartialD;}^{2}T}{{\&PartialD;\mathrm{the\; y}}^2}-d\frac{\&PartialD;T}{\&PartialD;x}=0& (x,\mathrm{the\; y})\&Element;\mathrm{\&Omega;}\\ -\mathrm{\&lambda;}\frac{\&PartialD;T(x,\mathrm{the\; y})}{\&PartialD;\mathrm{no}}=q& (x,\mathrm{the\; y})\&Element;{\mathrm{\&Gamma;}}_1\\ T(x,\mathrm{the\; y})=T_0& (x,\mathrm{the\; y})\&Element;{\mathrm{\&Gamma;}}_0\end{array}\right.,$ In the formula: Ω is the model area; Γ ₁ is the inner boundary oabc of the model; Γ ₀ is the outer boundary OABC of the model; λ is the thermal conductivity of the medium; n represents the outer normal direction somewhere on the boundary surface. At the same time, the distributed temperature of the target optical cable is continuously monitored and the heating power and the monitoring file name of the initial heating time are recorded, so as to provide a basis for data sorting in the future. After a monitoring period is completed, the heating power is changed, and the temperature rise curve of different heating powers at the seepage velocity is measured.

The biggest difference between the single-line heat source method and the double-line heat source method is that the single-line method only needs one heat source fiber to invert the seepage velocity, while the two-line method requires a heat source fiber and a temperature field temperature sensing fiber. In the seepage monitoring of earth-rock dams and embankments, the single-line heat source method only needs to arrange a temperature-measuring optical fiber in the seepage field area, and use the DTS thermometer to measure the stable temperature T ₁ and initial temperature of the target optical fiber (that is, the environment during heating temperature) T ₀ and the heating power q of the target fiber. Using the above data, the seepage flow velocity v can be inverted by the single-line heat source method. Assuming that the cable embedding direction is perpendicular to the seepage direction, the temperature field and model diagram generated by the heating of the target fiber in the single-line heat source method are shown in Figure 3. In the figure, a represents the temperature contour, b represents the target fiber, and c represents the heating power P. The modeling area is selected as a space cylinder with the optical cable as the axis and r as the radius. In a space cylinder with a length of 1m, the seepage velocity can be regarded as a constant that does not change with the position. In order to determine the influence range of the heating fiber after heating, the test of the saturated non-seepage condition was carried out, and the initial temperature and stable temperature of the heat source fiber under different heating power were obtained, and the analysis module of the stable temperature field in the Marc finite element analysis software was used , invert the radius r of the cylinder, and finally determine the square two-dimensional area with the optical cable as the center and side length 2r=15c as the modeling area, which not only conforms to the inversion results of numerical calculations, but also conforms to actual test results. The specific inversion method See attached drawing 4.

在点(x_i,y_j)上用差商表示二阶导数，即：  The schematic diagram of the optical fiber flow velocity inversion model is shown in Figure 6, in which the optical cable is simplified into a square area of 1 cm × 1 cm. The entire model solution interval and its subdivision form meet the requirements of the finite difference method. The solution model of the temperature field under the influence of the constant seepage field, respectively record the set of points in the grid and boundary points as Ω _h and

Use the difference quotient to express the second order derivative on the point ( _xi , y _j ), namely:

${\frac{{<span\; class="notranslate">\; \&PartialD;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; T</span>}}{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; |</span>}_{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

${\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; T</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; |</span>}_{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

Substitute the above two equations into the differential equation

$\frac{{<span\; class="notranslate">\; \&PartialD;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; T</span>}}{<span\; class="notranslate">\; \&PartialD;</span>{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; +</span>\frac{{<span\; class="notranslate">\; \&PartialD;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; T</span>}}{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; d</span>}\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; T</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>$

The difference equation can be obtained

$\begin{array}{c}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>\\ <span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; d</span>}\frac{\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}\end{array}$

Using T _{i, j} to represent T( _xi , y _j ), then the above formula can be expressed as

$(1+\frac{\mathrm{ah}}{2})T_{i-1,j}+T_{i,j-1}-{4T}_{i,j}+T_{i,j+1}+(1-\frac{\mathrm{ah}}{2})T_{i+1,j}=0$ This formula is the five-point difference scheme of the temperature field solution model under the influence of the uniform steady seepage field in the single-line heat source method. How many nodes with unknown temperature are in the solution domain, that is, how many difference equations will be established, and then solved.

(5) After measuring the temperature rise curves of different heating powers under the condition of stable seepage, change the flow rate control valve opening of the water outlet system to change the seepage field. After the seepage field is stable, repeat the above steps to measure different seepage fields The temperature rise curve of different heating power. the

式中：θ为光缆绝对温升，θ=T-T₀，T为时间τ时光缆的温度，T₀为加热初始光缆温度；q为单位长度加热功率，单位为W/m；λ为导热系数，单位为W·m^-1·K^-1；τ为加热时间；a为热扩散系数，单位为m²/s；r₀为热线半径；C为比热容，单位J·kg^-1·K^-1，上式即为建立的瞬态热线法测量导热系数的基本方程。  (6) Construct a thermal conductivity calculation model based on the hot wire method; as the mainstream method for measuring the thermal conductivity of liquids, the transient hot wire method has been recognized as the best thermal conductivity measurement method, and its ideal model is a radial one in an infinite medium. dimensional unsteady heat conduction problem, in an infinite medium with uniform initial temperature distribution, a constant heating power is applied to the hot wire arranged in it, since the radius of the hot wire is very small, so as long as the time τ is long enough, the expression of the surface temperature rise θ of the hot wire can be expressed as Simplified to

In the formula: θ is the absolute temperature rise of the optical cable, θ=TT ₀ , T is the temperature of the cable at the time τ, T ₀ is the initial temperature of the cable during heating; q is the heating power per unit length, in W/m; λ is the thermal conductivity, The unit is W·m ^-1 ·K ^-1 ; τ is the heating time; a is the thermal diffusivity, the unit is m ² /s; r ₀ is the radius of the heating line; C is the specific heat capacity, the unit is J·kg ^-1 ·K ^-1 , the above formula is the basic equation for measuring the thermal conductivity established by the transient hot wire method.

通过前面推导的热线法计算模型进而可以计算出其导热系数。  (7) Calculate the thermal conductivity of the medium where the optical cable is located. According to the basic equation of measuring the thermal conductivity by the transient hot wire method, based on the experimental analysis, draw the relationship diagram of θ～lnτ, find out the straight line segment and calculate its slope, and calculate the thermal conductivity λ from the slope value and the heating power q , where the expression of λ is:

The thermal conductivity can be calculated through the calculation model of the hot wire method deduced above.

(8) The nominal thermal conductivity under the corresponding seepage field is obtained through the temperature rise process diagram. The nominal thermal conductivity is proposed for the first time in this application, and the temperature rise process line of the hot wire (that is, the optical cable heated by electricity) in the seepage field is analyzed, and the relationship between θ～lnτ is drawn. Observing the line diagram of the temperature rise process, it can be found that, like the traditional hot-line method, there is also a straight line segment in the figure, and a slope can be fitted by using the data in the line segment interval, and then a corresponding thermal conductivity can be calculated. Compared with the traditional hot wire method, a thermal conductivity coefficient including the influence of seepage on the hot wire is proposed for the first time, which is called the nominal thermal conductivity. the

The thermal conductivity is not the thermal conductivity of an infinite homogeneous medium in the traditional sense without seepage, but a thermal conductivity in the seepage field that includes the influence of seepage on the hot line. The nominal thermal conductivity includes both the traditional thermal conductivity section, also covers the effect of percolation on the hot wire. For different seepage fields, the corresponding nominal thermal conductivity must be different. There is a certain relationship between the two. A slope can be fitted by using the data of the straight line interval, and the slope can be substituted into the thermal conductivity calculation model. Calculate a corresponding nominal thermal conductivity. the

(9) Construct the mathematical model of the relationship between nominal thermal conductivity and seepage flow velocity, so that the seepage velocity values at various flow velocities can be obtained from the nominal thermal conductivity of different seepage fields. the

For different seepage fields, the corresponding nominal thermal conductivity must be different. Accordingly, the nominal thermal conductivity can be used as a new physical parameter to reflect the characteristics of the corresponding seepage field; based on the nominal thermal conductivity under different heating powers, various The different values under the flow rate; through the experimental analysis and theoretical research, the relationship between the seepage flow rate and the average thermal conductivity is obtained. The linear correlation between the seepage flow rate and the average nominal thermal conductivity is very obvious, and thus the empirical calculation formula of the seepage flow rate is obtained. The linear correlation is very obvious. the

渗流场影响下的三维导热方程可以写为下列形式：  ${\&dtri;}^{2}T-\frac{c_w{\mathrm{\&rho;}}_w}{\mathrm{\&lambda;}}[v_x\frac{\&PartialD;T}{\&PartialD;x}+v_y\frac{\&PartialD;T}{\&PartialD;y}+v_z\frac{\&PartialD;T}{\&PartialD;z}]=0,$ 令 $-\frac{c_w{\mathrm{\&rho;}}_w}{\mathrm{\&lambda;}}{v}_x=a1,-\frac{c_w{\mathrm{\&rho;}}_w}{\mathrm{\&lambda;}}{v}_y=a2,$ $-\frac{c_w{\mathrm{\&rho;}}_w}{\mathrm{\&lambda;}}{v}_z=a3.$ 则可以化简为 ${\&dtri;}^{2}T+a1\frac{\&PartialD;T}{\&PartialD;x}+a2\frac{\&PartialD;T}{\&PartialD;y}+a3\frac{\&PartialD;T}{\&PartialD;z}=0,$ 该式即为只考虑渗流对温度影响、渗流流速为常数的监测模型方程式。可以看出，对于给定的边值条件，温度场的分布只与系数a1、a2、a3有关，而对于某一特定介质，

为常数，所以温度场的分布只与渗流流速v有关系，流速v会和温度场形成一一对应关系。  When assuming that the porous medium is isotropic, that is, λ _x = λ _y = λ _z = constant; only consider the fiber within the range of positioning accuracy of the fiber (that is, the range of 1m fiber length) and the field distribution within a certain radius centered on the fiber; seepage The field is a stable seepage field, that is, the seepage velocity does not change with time and position, and is a constant. In three-dimensional coordinates, it can be decomposed into V _x , V _y , V _z (constant); the passive sink term is Q _T =0; only the stable temperature field is considered, namely

The three-dimensional heat conduction equation under the influence of the seepage field can be written in the following form: ${\&dtri;}^{2}T-\frac{c_w{\mathrm{\&rho;}}_w}{\mathrm{\&lambda;}}[v_x\frac{\&PartialD;T}{\&PartialD;x}+v_{\mathrm{the\; y}}\frac{\&PartialD;T}{\&PartialD;\mathrm{the\; y}}+v_z\frac{\&PartialD;T}{\&PartialD;z}]=0,$ make $-\frac{c_w{\mathrm{\&rho;}}_w}{\mathrm{\&lambda;}}{v}_x=a1,-\frac{c_w{\mathrm{\&rho;}}_w}{\mathrm{\&lambda;}}{v}_{\mathrm{the\; y}}=a2,$ $-\frac{c_w{\mathrm{\&rho;}}_w}{\mathrm{\&lambda;}}{v}_z=a3.$ can be simplified to ${\&dtri;}^{2}T+a1\frac{\&PartialD;T}{\&PartialD;x}+a2\frac{\&PartialD;T}{\&PartialD;\mathrm{the\; y}}+a3\frac{\&PartialD;T}{\&PartialD;z}=0,$ This formula is a monitoring model equation that only considers the influence of seepage on temperature and the seepage velocity is constant. It can be seen that for a given boundary value condition, the distribution of the temperature field is only related to the coefficients a1, a2, a3, and for a specific medium,

is a constant, so the distribution of the temperature field is only related to the seepage flow velocity v, and the flow velocity v will form a one-to-one correspondence with the temperature field.

Compared with the prior art, the present invention has the beneficial effects as follows: 1. The method of the present invention breaks through the conventional optical fiber seepage monitoring method in which the monitoring period is the temperature rise period of the entire optical cable heating, and accurately locates the linear correlation between the seepage velocity and the average thermal conductivity performance, and the monitoring accuracy is reliably guaranteed. 2. The invention has passed theoretical research and experimental verification. It is the first to propose a nominal thermal conductivity that includes the influence of seepage on the hot wire. The results of the invention are true and reliable, and it is of great significance for the monitoring of the seepage velocity of buried optical cables in practical projects that need to be studied urgently. 3. The present invention solves the problem of monitoring the seepage velocity in the distributed optical fiber temperature sensing technology, and provides the possibility for its practical engineering application. the

Description of drawings

Fig. 1 is a schematic diagram of the porous media structure seepage velocity monitoring test device of the present invention;

Fig. 2 is the schematic diagram of the water supply system of the porous media structure seepage velocity monitoring test device;

Figure 3 is a schematic diagram of the temperature field and model generated by the heating of the target optical fiber in the single-line heat source method;

Figure 4 is a schematic diagram of the single-line method inversion flow velocity;

Figure 5 is a schematic diagram of the heating system of the porous media structure seepage velocity monitoring test device;

Figure 6 is a schematic diagram of the optical fiber flow velocity inversion model;

Fig. 7 is the front view of the model tank of the porous media structure seepage velocity monitoring test device;

Fig. 8 is a left view sectional view of the model tank of the porous media structure seepage velocity monitoring test device;

Figure 9 is the graph of θ～lnτ under different heating powers under v=0.0571×10-3m/s;

Figure 10 is the graph of θ～lnτ under different heating powers at v=0.0730×10 ^-3 m/s;

Figure 11 is the graph of θ～lnτ under different heating powers at 0.1515×10 ^-3 m/s;

Figure 12 is the graph of θ～lnτ under different heating powers under v=0.0974ⅹ10 ^-3 m/s;

Figure 13 is the graph of θ～lnτ under different heating powers under v=0.1964ⅹ10 ^-3 m/s;

Figure 14 is a graph showing the relationship between seepage velocity and thermal conductivity. the

Detailed ways

The technical solutions of the present invention will be described in detail below, but the protection scope of the present invention is not limited to the embodiments. the

Embodiment 1: The porous medium structure seepage flow rate monitoring test device according to the present invention, the schematic diagram of which is shown in Figure 1, includes a heating system 1, a distributed optical fiber temperature sensing system 2, and a porous medium structure embedded with monitoring optical fibers Body model tank 3 and water outlet system 4; the heating system 1, distributed optical fiber temperature sensing system 2 and water outlet system 4 are respectively connected to the porous medium structure model tank 3. the

The heating system, as shown in Figure 5, is mainly composed of a parallel circuit consisting of an AC power supply 9, a voltage regulator 10, and a load heating resistance wire 11. The monitoring optical fiber is heated by the load heating resistance wire 11, and the voltage is controlled by the voltage regulator 10 so that Control the heating power; the distributed optical fiber temperature sensing system includes a distributed optical fiber temperature measurement host and a linear multi-mode temperature sensing optical cable, and the distributed optical fiber temperature measurement host is connected to the linear multimode temperature sensing optical cable through a pulse laser device And output optical pulses; the tail of the linear multimode temperature-sensing optical cable is connected with the optical fiber connector; the water outlet system as shown in Figure 2 includes a water tank 5, a flow control valve 6, a water pump 7 and a circulating pool 8; the water tank The position of 5 is higher than that of the circulating pool 8, and the upper part of the water level line of the water tank 5 is connected with the circulating pool 8 through an overflow pipe; the circulating pool 8 delivers water to the water tank 5 through the water pump 7; the water tank 5. The bottom is connected to the porous medium structure model tank 3 through a pipeline; the flow rate control valve 6 is respectively arranged on the pipeline between the water tank 5, the porous medium structure model tank 3 and the circulating water pool 8. the

The porous medium structure body seepage velocity monitoring test method of the present invention comprises the following steps:

(1) Different flow rates and heating power conditions in the design test. Different flow rate conditions in the test are designed by controlling the water outlet system; different heating power conditions in the test are designed by controlling the heating system. Since the heating circuit is the same, the control voltage is used to control different heating power conditions. Six different flow velocity conditions were designed in this experiment: 0m/s, 0.0571×10-3m/s, 0.0730×10-3m/s, 0.1515×10-3m/s, 0.0974×10-3m/s, 0.1964×10 -3m/s. Since the heating circuit is the same, voltage is used to control the heating power, and 6 different heating voltages are used: 7V, 9V, 11V, 13V, 15V, 17V;

(2) Construct the model groove of the porous medium structure embedded with the monitoring optical fiber. Based on different test requirements, according to the specific design, a model tank to be monitored of a porous medium structure with an optical fiber is built. In this embodiment, a model tank with a length of 2.6m, a width of 1m, and a height of 1.15m is mainly built, and it is built with M5 cement mortar. M10 mortar plastering; plastic film is laid on the inner wall of the pool as a further anti-seepage material, and two water outlets with an outer diameter of 50mm are reserved on the lengthwise wall with a height of 1m. The water inlet and outlet are connected to the water inlet pipe 12, the water outlet pipe 13, the interface between the pressure measuring pipe 14 and the optical cable 15 and the plastic film is sealed and waterproof with rubber tightening and 502 glue; a 30cm reverse filter layer composed of various particle sizes is laid on the bottom of the pool 16; Lay reverse filter screen 17 above the reverse filter layer; Lay 55cm thick fine sand 18 on it, still be reverse filter screen 17 and reverse filter layer 16 above the fine sand; In the center of two width direction faces of pond, height is A wall hole for the layout of the target optical fiber 15 is reserved at the position of 65 cm. See attached drawings 7 and 8 for details. the

(3) Adjust the outlet system to form a uniform and stable seepage field. Based on the test conditions of different designs, the valves of the water supply system are adjusted to a certain position after several times of debugging, and then the outflow of the water outlet system is continuously monitored. When the outflow is stable, it can be considered that a uniform and stable seepage field has been formed. the

(4) Based on the distributed optical fiber temperature sensing system, the temperature monitoring of the monitoring optical fiber buried in the model groove is carried out; the Sentinel DTS-LR type distributed optical fiber temperature measurement host produced by the British Sensornet company is used, and the Sentinel DTS is equipped with a pulse laser A device that connects to a 50/125 multimode fiber and outputs a 10 nanosecond optical pulse whose tail is connected to an E2000 fiber optic connector. the

(5) Determine the heating method. In this embodiment, the single-line heat source method is used for heating. In the seepage monitoring of earth-rock dams and embankments, the biggest difference between the single-line heat source method and the double-line heat source method is that the single-line heat source method only needs to arrange a temperature-measuring optical fiber in the seepage field area. The DTS thermometer measures the stable temperature T ₁ of the target fiber, the initial temperature (that is, the ambient temperature during heating) T ₀ and the heating power q of the 1# fiber. Using the above data, the seepage flow velocity v can be inverted by the single-line heat source method.

(6) Conduct electric heating operation on the target optical fiber through the heating system. If a relatively large heating power is required, a large current is required, so when selecting a voltage regulator, the rated current of the voltage regulator must be considered. This device adopts TDGC2-5 single-phase voltage regulator, and the adjustable voltage AC power supply can choose a voltage regulator. And set up the anti-tripping start-up loading circuit; after being monitored by the distributed optical fiber temperature sensing system for 10 minutes, the fixed steel wire in the target optical cable will be heated by the single-ended heating method, and the distributed temperature of the target optical cable will be continuously monitored and recorded. The heating power and the monitoring file name of the initial heating time will provide the basis for the data sorting in the future. After a monitoring period is completed, the heating power is changed, and the temperature rise curve of different heating powers at the seepage velocity is measured. the

(7) After measuring the temperature rise curves of different heating powers under the condition of stable seepage, change the flow rate of the water supply system to control the valve opening and change the seepage field. After the seepage field is stable, repeat the above steps to measure different seepage flows. The temperature rise curve of different heating power under the field. the

(8) Construct a thermal conductivity calculation model based on the hot wire method. The expression of the surface temperature rise θ of the hot wire can be simplified as In the formula: θ is the absolute temperature rise of the optical cable, θ=TT ₀ , T is the temperature of the cable at the time τ, T ₀ is the initial temperature of the cable during heating; q is the heating power per unit length, in W/m; λ is the thermal conductivity, The unit is W·m ^-1 ·K ^-1 ; τ is the heating time; a is the thermal diffusivity, the unit is m ² /s; r ₀ is the radius of the heating line; C is the specific heat capacity, the unit is J·kg ^-1 ·K ^-1 , the above formula is the basic equation for measuring the thermal conductivity established by the transient hot wire method.

通过前面推导的热线法计算模型进而可以计算出其导热系数。  (9) Calculate the thermal conductivity of the medium where the cable is located. According to the basic equation of measuring the thermal conductivity by the transient hot wire method, based on the experimental analysis, draw the relationship diagram of θ～lnτ, find out the straight line segment and calculate its slope, and calculate the thermal conductivity λ from the slope value and the heating power q , where the expression of λ is:

The thermal conductivity can be calculated through the calculation model of the hot wire method deduced above.

(10) The first to propose the nominal thermal conductivity under the corresponding seepage field. Extract the effective data at the 5m position of the monitoring optical fiber in this test, obtain the temperature change process line at this point under different flow rate conditions, and draw the θ～lnτ relationship diagram, see Figures 9-13. Observing the line diagram of the temperature rise process, it can be found that, like the traditional hot-line method, there is also a straight line segment in the figure, and a slope can be fitted by using the data in the line segment interval, and then a corresponding thermal conductivity can be calculated. Compared with the traditional hot wire method, a thermal conductivity coefficient including the influence of seepage on the hot wire is proposed, which is called the nominal thermal conductivity. the

The thermal conductivity is not the thermal conductivity of an infinite homogeneous medium in the traditional sense without seepage, but a thermal conductivity in the seepage field that includes the influence of seepage on the hot line. The nominal thermal conductivity includes both the traditional thermal conductivity section, also covers the effect of percolation on the hot wire. For different seepage fields, the corresponding nominal thermal conductivity must be different. There is a certain relationship between the two. A slope can be fitted by using the data of the straight line interval, and the slope can be substituted into the thermal conductivity calculation model. Calculate a corresponding nominal thermal conductivity, and the calculation results are shown in Attached Table 1. the

Table 1 Calculation table of nominal thermal conductivity under different working conditions

(11) Determine the mathematical model of the relationship between nominal thermal conductivity and seepage velocity. For different seepage fields, the corresponding nominal thermal conductivity must be different. Take the seepage velocity as the y-axis and the average thermal conductivity as the x-axis. Draw a scatter diagram, see attached drawing 14; it can be seen from attached drawing 14 that the seepage velocity The linear correlation with the average nominal thermal conductivity is very obvious; the calculation formula of the seepage flow velocity v=5.5848λ-2.7727 is obtained by linear fitting of the scatter diagram; where: v is the seepage velocity, and the unit is 10 ^-3 m/s; λ is the nominal thermal conductivity, the unit is W(m·k); the complex correlation coefficient R=0.9877, and the linear correlation between the two is very obvious. Based on this, the mathematical model of the relationship between the nominal thermal conductivity and the seepage velocity is established.

As stated above, while the invention has been shown and described with reference to certain preferred embodiments, this should not be construed as limiting the invention itself. Various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. the

Claims (2)

1. A porous media structure seepage velocity monitoring test device, characterized in that it includes a heating system (1), a distributed optical fiber temperature sensing system (2), and a porous media structure model tank (3) embedded with monitoring optical fibers and a water outlet system (4); the heating system (1), the distributed optical fiber temperature sensing system (2) and the water outlet system (4) are respectively connected to the porous medium structure model tank (3). 2. The porous media structure seepage velocity monitoring test device according to claim 1, characterized in that: The heating system is a parallel circuit mainly composed of an AC power supply (9), a voltage regulator (10) and a load heating resistance wire (11). The monitoring optical fiber is heated through the load heating resistance wire (11), and the voltage regulator ( 10) Control the voltage to control the heating power; The distributed optical fiber temperature sensing system includes a distributed optical fiber temperature measurement host and a linear multi-mode temperature-sensing optical cable, and the distributed optical fiber temperature measurement host is connected to the linear multi-mode temperature-sensing optical cable through a pulse laser device and outputs optical pulses ; The tail of the linear multimode temperature-sensing optical cable is connected to the optical fiber connector; The water outlet system includes a water tank (5), a flow rate control valve (6), a water pump (7) and a circulating water pool (8); the water tank (5) is located higher than the circulating water pool (8), and the water tank ( The upper part of the water level line of 5) is connected to the circulating pool (8) through an overflow pipe; the circulating pool (8) delivers water to the water tank (5) through the water pump (7); the bottom of the water tank (5) passes through The pipeline is connected to the porous medium structure model tank (3); the flow rate control valve (6) is respectively arranged between the water tank (5) and the porous medium structure model tank (3) and the circulating water pool (8) on the pipeline.

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