CN104267097A - Determination method of fan blade crack position - Google Patents

Abstract

The invention discloses a method for determining the crack position of a fan blade. The method comprises the following steps: S1, simulating the occurrence of crack faults at different positions of the blade, and calculating the first three natural frequencies; The relative depth of the crack and the relative radial position of the crack are the coordinate axes, and the natural frequency solution surface diagram is drawn to construct the fault sample library; S3. During the fault diagnosis of the blade, the first three natural frequencies of the blade are obtained by calculation, and they are reversely input to the The fault sample library; S4, using the contour method to solve the problem, and obtain the depth and radial position of the crack. The method of the present invention uses the contour line method to solve the position of the blade crack, not only realizes the timely diagnosis of the fan blade crack, but also realizes the quantitative analysis of the fan blade crack position, the diagnosis speed is fast and the result is reliable, and it provides equipment maintenance. a strong guarantee.

Description

A method for determining the location of cracks in fan blades

technical field

The invention relates to the technical field of equipment fault diagnosis, and more particularly relates to a method for determining the crack position of a fan blade.

Background technique

Fans are widely used in ventilation, dust removal and cooling in factories, mines, tunnels, cooling towers, ships and buildings because of their characteristics of stable wind pressure, large air volume, high efficiency and low noise, providing a basic guarantee for safe production. The fan impeller system is the core component of the fan, and it is responsible for the important task of converting electrical energy into mechanical energy. During the working process, the impeller bears the comprehensive effects of centrifugal force, fluid power, vibration, temperature difference, working medium, etc., and the stress condition is relatively complicated. Especially in actual work, the working environment of the blade is even worse. Not only do they have to go through start-up and shutdown, but they often operate under non-design conditions. The complex airflow excitation force and changing centrifugal force caused by these stable and unstable factors cause the blade to have resonance damage due to the consistency of the natural frequency and the frequency of the excitation source. In addition, due to the comprehensive influence of manufacturing, installation errors and processing stress, etc. The anti-fatigue ability of the blade will cause the fatigue damage of the blade and cause cracks, which will pose a serious threat to the safe operation of the entire unit, and even lead to major accidents.

There is often strong background noise in the working environment of the fan, and the status signal of the fan obtained by the sensor is often accompanied by the interference of the environmental noise. The existing blade crack diagnosis methods, whether based on acoustic emission technology or relying on spectrum analysis of the acquired vibration signals, can only diagnose whether there is a crack in the blade, but cannot specifically detect the location of the crack, and cannot effectively avoid blade cracks. The economic losses caused by cracks also increase the difficulty of equipment maintenance.

Contents of the invention

(1) Technical problems to be solved

The technical problem to be solved by the invention is how to determine whether a crack occurs in the blade and where the crack occurs.

(2) Technical solutions

In order to solve the above technical problems, the present invention provides a method for determining the location of a fan blade crack, comprising the following steps:

S1. Simulate the occurrence of crack faults at different positions of the blade, and calculate the first three natural frequencies;

S2. Taking the natural frequency of each order, the relative depth of the crack, and the relative radial position of the crack as coordinate axes, draw a natural frequency solution surface diagram, and construct a fault sample library;

S3. During blade fault diagnosis, obtain the first three natural frequencies of the blade through calculation, and reversely input it into the fault sample library;

S4. Using the contour method to solve the problem, the radial position and depth of the crack are obtained.

Preferably, in the step S2, the relative radial position α of the crack is the ratio of the radial position l of the crack to the length L of the blade α=l/L, wherein the radial position l starts from the root of the blade close to the impeller Calculate, the value range is 0<l<L.

Preferably, in the step S2, the relative depth β of the crack is the ratio of the depth b of the crack to the thickness h of the blade β=b/h, wherein the depth b is calculated from the suction surface of the blade, and the value range is 0< b<h.

Preferably, in the step S2, the relative radial position α of the crack is taken as the x-axis, the relative depth β of the crack is taken as the y-axis, and the natural frequency ω of each order of the blade is taken as the z-axis.

Preferably, in the step S2, the natural frequency solution surface is the relationship between the i-th order natural frequency ω _i and the relative radial position α and the relative depth β, and the relative radial position α and the relative depth β as variables, fitted into the surface.

Preferably, in the step S4, the process of solving by the contour line method is to substitute the natural frequency of each order into the fault sample library, draw the corresponding frequency contour map, and then use the three The frequency contour map is drawn on the same plane, and the obtained intersection coordinates correspond to the relative radial position and relative depth of the crack, and finally the radial position and depth of the crack are obtained by calculation.

(3) Beneficial effects

The invention provides a method for determining the location of a fan blade crack. Compared with the prior art, the invention uses the contour line method to solve the position of the blade crack, which not only realizes the timely diagnosis of the fan blade crack, but also realizes the fan Quantitative analysis of blade crack location, fast diagnosis and reliable results, provides a strong guarantee for equipment maintenance, and is used for early warning and quantitative detection of fan blade crack failures, reducing unplanned production shutdowns caused by failures, thereby reducing economic losses.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is a flow chart of a method for determining the location of a fan blade crack in the present invention;

Figure 2a is a schematic structural view of a fan blade;

Fig. 2b is A-A sectional view in Fig. 2a;

Fig. 3 is a schematic diagram of the natural frequency solution surface of a method for determining the position of a fan blade crack in the present invention;

Fig. 4 is a three-dimensional schematic diagram of contour lines of a method for determining the position of a fan blade crack in the present invention;

Fig. 5 is a schematic diagram of a contour plane of a method for determining a crack location of a fan blade according to the present invention.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments. The following examples are used to illustrate the present invention, but should not be used to limit the scope of the present invention.

Fig. 1 is the flow chart of a kind of blower fan blade crack location determination method of the present invention; The method that this method buys that method comprises the following steps:

S1. Simulate the occurrence of crack faults at different positions of the blade, and calculate the first three natural frequencies;

S2. Taking the natural frequency of each order, the relative depth of the crack, and the relative radial position of the crack as coordinate axes, draw a natural frequency solution surface diagram, and construct a fault sample library;

S3. During blade fault diagnosis, obtain the first three natural frequencies of the blade through calculation, and reversely input it into the fault sample library;

S4. Using the contour method to solve the problem, the depth and radial position of the crack are obtained.

The invention uses the contour line method to solve the position of the blade crack, not only realizes the timely diagnosis of the fan blade crack, but also realizes the quantitative analysis of the fan blade crack position, the diagnosis speed is fast and the result is reliable, and it provides a powerful tool for equipment maintenance. Assure.

In the step S2, the relative radial position α of the crack is the ratio of the radial position l of the crack to the length L of the blade α=l/L, wherein the radial position l is calculated from the blade root 1 close to the impeller, and the value is The range is 0<l<L, as shown in Figure 2a; the relative depth β of the crack is the ratio β=b/h of the depth b of the crack to the thickness h of the blade, wherein the depth b is calculated from the suction surface 2 of the blade, The value range is 0<b<h, as shown in Figure 2b, 3 is the pressure surface; the relative radial position α of the crack is the x-axis, the relative depth β of the crack is the y-axis, and the The natural frequency ω is the z axis, and the natural frequency solution surface diagram is fitted by spline surface fitting technology; the natural frequency solution surface is the i-th order natural frequency ω _i with the relative radial position α and the relative The relationship between the depth β, and the relative radial position α and the relative depth β are used as variables to fit a curved surface, as shown in FIG. 3 .

When calculating the natural frequency of the faulty blade, the blade can be simplified as a rectangular cross-section beam, then the theoretical solution of the first three natural frequencies is:

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; 1.875</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; EI</span>}}{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; 4.694</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; EI</span>}}{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; 7.855</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; EI</span>}}{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}}}<span\; class="notranslate">\; ,</span>$

Among them, E is the elastic modulus of the blade, L is the length of the blade, I is the section moment of inertia of the blade, is the mass per unit length of the blade. Other calculation methods can also be used to calculate the first three natural frequencies of the faulty blade, and are not limited to the above methods.

Preferably, the process of solving by the contour method in the step S4 is to substitute the natural frequencies of the first three orders into the fault sample library, draw a corresponding frequency contour map, as shown in Figure 4, and then The three frequency contour maps are drawn on the same plane, as shown in Figure 5, at this time the x-axis represents the relative radial position α of the crack, the y-axis represents the relative depth β of the crack, and the ω-axis is the natural frequency, In the plane view shown in Figure 5, there must be an intersection point that characterizes the crack parameters, and the coordinates of the intersection point correspond to the relative radial position and relative depth of the crack, and finally calculate the radial position and depth of the crack; if no intersection point is obtained, Indicates that no cracks exist.

The method provided by the invention realizes the quantitative analysis of the crack position, the diagnosis speed is fast and the result is reliable, which provides a strong guarantee for equipment maintenance. Unplanned shutdowns, thereby reducing economic losses.

The above embodiments are only used to illustrate the present invention, but not to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that various combinations, modifications or equivalent replacements of the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all should cover Within the scope of the claims of the present invention.

Claims (6)

1. a fan blade crack position defining method, is characterized in that, comprises the following steps:

S1, simulation blade diverse location generation crack fault, and calculate its first three rank natural frequency;

S2, with natural frequency, the relative depth of crackle, the fractional radial position of crackle described in every rank for coordinate axis, draw natural frequency solution surface chart, structure fault sample storehouse;

When S3, blade fault diagnosing, by calculating first three the rank natural frequency obtaining blade, it is oppositely input to described fault sample storehouse;

S4, utilize contouring method to solve, obtain radial position and the degree of depth at crackle place.

2. method according to claim 1, it is characterized in that, in described step S2, the fractional radial position α of crackle is the radial position l of crackle and the ratio α=l/L of length of blade L, wherein, described radial position l calculates from the root of blade near impeller, and span is 0<l<L.

3. method according to claim 1, it is characterized in that, in described step S2, the relative depth β of crackle is the degree of depth b of crackle and the ratio β=b/h of vane thickness h, wherein said degree of depth b calculates from the suction surface of blade, and span is 0<b<h.

4. the method according to claim 1 or 2 or 3, is characterized in that, in described step S2, with described crackle fractional radial position α for x-axis, with described crackle relative depth β for y-axis, with natural frequency ω described in the every rank of blade for z-axis.

5. method according to claim 5, is characterized in that, in described step S2, natural frequency solution surface is for by natural frequency ω described in the i-th rank _iwith the relation of described fractional radial position α and described relative depth β, and with described fractional radial position α and described relative depth β for variable, the curved surface fitted to.

6. method according to claim 1, it is characterized in that, in described step S4, the process that contouring method solves is, natural frequency described in every rank is updated in described fault sample storehouse, draws out corresponding frequency contour map, then frequency contour map described in three width is drawn at grade, the fractional radial position of the corresponding crackle of the intersecting point coordinate obtained and relative depth, finally calculate radial position and the degree of depth of crackle.