Method for evaluating vibration fatigue life of disc pump under internal flow action

Abstract

The invention provides a method for evaluating the vibration fatigue life of a disc pump under the action of internal flow, and belongs to the technical field of offshore oil engineering. Comprising the following steps: establishing a disc pump model; transient fluid-solid coupling calculation is carried out on the pump body structure to obtain a pump body internal flow pulsating pressure time domain load, and the pump body internal flow pulsating pressure time domain load serves as input to obtain a pump body displacement time domain load through ANSYS calculation; the pump body displacement time domain load is processed through software, and the pump body acceleration power spectral density is obtained; aNSYS is used for harmonic response analysis, and a pump body acceleration load frequency response curve is obtained; and evaluating the fatigue life of the pump body based on the pump body acceleration power spectral density and the material SN curve. According to the method, the model between vibration and fatigue caused by the internal flow pulsating pressure is established, the fatigue life of the disc pump is accurately evaluated through a finite element software simulation calculation method, the design quality of the disc pump can be improved, the maintenance cost can be reduced, and the service life of the disc pump can be prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of offshore oil engineering, and particularly relates to a vibration fatigue life evaluation method of a disc pump under internal flow action. BACKGROUND

[0002] A disc pump is a fluid conveying device widely used in the fields of offshore oil and gas, deep-sea mining, chemical industry, and water treatment. Its working principle is to generate negative pressure through the rotation or oscillation of the disc, thereby sucking and discharging the liquid. The disc pump is favored due to its compact structure, high working efficiency, wear resistance, and ability to transport large particles. During operation, the disc pump often suffers from vibration, which may be caused by factors such as imbalance, mechanical friction, and fluid turbulence. Long-term vibration can lead to material fatigue of the disc pump, affecting the service life of the equipment, and even causing the failure of the equipment. Evaluating the fatigue life of the disc pump is crucial to ensure its reliability and safety. Traditional fatigue life prediction methods often rely on experimental data and empirical formulas, which cannot fully reflect the complex working environment and actual operating conditions. Currently, many fatigue life evaluation methods do not consider the complexity and variability of vibration, resulting in insufficient accuracy and reliability of the evaluation results. At the same time, with the continuous development of new materials and new technologies, existing methods need to be updated and improved. Therefore, it is of great significance to develop a new evaluation method. SUMMARY

[0003] Therefore, the present application aims to provide a vibration fatigue life evaluation method of a disc pump under internal flow action, which can accurately evaluate the fatigue life of the disc pump by establishing a model between the vibration caused by internal flow pulsating pressure and fatigue, and using finite element software simulation calculation method, thereby improving the design quality of the disc pump, reducing maintenance costs, and prolonging the service life of the disc pump.

[0004] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows: a vibration fatigue life evaluation method of a disc pump under internal flow action, comprising the following steps: Step 1: establishing a disc pump model; Step 2: performing transient fluid-structure coupling calculation on the pump body structure to obtain the internal flow pulsating pressure time domain load of the pump body, and using ANSYS to calculate the pump body displacement time domain load based on the input; Step 3: using Matlab software and origin software to process the pump body displacement time domain load to obtain the pump body acceleration power spectral density; Step 4: using ANSYS to perform harmonic response analysis to obtain the pump body acceleration load frequency response curve; Step 5: based on the pump body acceleration power spectral density and the material SN curve, performing fatigue life evaluation of the pump body.

[0005] Further, step 2 comprises: Step 21, using computer finite element simulation software ANSYS Fluent module and static structure analysis module to calculate the transient fluid-structure coupling of the pump body structure, and calculate the numerical value of the pressure change with time at different positions in the pump body internal flow area; Step 22, exporting the finite element analysis result file in step 21, importing ANSYS CFD-Post module for data processing, setting several monitoring points in the rotor area, oil suction area and oil discharge area of the disc pump, and extracting the pressure change with time; Step 23, comparing the pressure change curves of each monitoring point with time, selecting the area with the largest change for analysis; using the pressure change curve extracted in step 22 as the load input, using computer finite element simulation software ANSYS to perform static structure analysis, and obtaining the displacement time domain load of the pump body.

[0006] Further, step 3 comprises: Step 31, comparing the displacement time domain loads of the several monitoring points set in step 22, selecting the monitoring point with the largest displacement time domain load, and extracting the displacement time domain load of the pump body at this point; Step 32, using computer origin drawing software to perform second-order differential processing on the pump body displacement change curve in step 31, and obtaining the acceleration change curve with time; Step 33, using Matlab software to perform fast Fourier transform on the acceleration change curve with time, obtaining the acceleration frequency domain load, and further calculating the acceleration power spectrum density.

[0007] Further, step 4 comprises: Step 41, using ANSYS software to perform modal analysis on the pump body structure of the disc pump, and giving the disc pump support fixed constraint; Step 42, performing harmonic response analysis on the pump body of the disc pump, applying unit g transverse acceleration load, using the modal analysis results in step 41 as the initial condition for analysis, and obtaining the acceleration load frequency response curve of the disc pump.

[0008] Further, step 5 comprises: using the harmonic response analysis results in step 4 as the initial condition, using ANSYS n-Code module, defining the input pump body acceleration power spectrum density, defining the material attribute mapping of the pump body, and performing fatigue life calculation to obtain the pump body loss cloud map and fatigue life cloud map, which can evaluate the vibration fatigue life of the disc pump body.

[0009] Compared with the prior art, the disc pump vibration fatigue life evaluation method under the action of internal flow has the following advantages: the model between the vibration caused by the internal flow pulsating pressure and the fatigue is established, the fatigue life of the disc pump is accurately evaluated by the finite element software simulation calculation method, the design quality of the disc pump is improved, the maintenance cost is reduced, and the service life of the disc pump is prolonged.

[0010] (1) For the method of evaluating the fatigue life of the pump body by using the empirical formula in the past, the finite element software is used to establish the fatigue calculation model of the pump body under the action of internal flow, so that the fatigue evaluation has more reference significance; (2) The computer finite element simulation software ANSYS Fluent module and the static structure analysis module are used to perform transient fluid-structure coupling calculation on the pump body structure, so that the extracted pump body displacement time domain load is more accurate, and a foundation is laid for subsequent accurate fatigue life evaluation; (3) The ANSYS n-Code module is used to define the input pump body acceleration power spectral density, define the material attribute mapping of the pump body, and perform fatigue life calculation, in which the statistical properties of the power spectral density are more suitable for the fatigue life evaluation of the pump body working in the frequency domain internal random vibration environment. BRIEF DESCRIPTION OF DRAWINGS

[0011] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application, and are incorporated in and constitute a part of this application. The embodiments of the present application illustrated in the drawings and their descriptions are used to explain the present application, and do not constitute an improper limitation on the present application. In the drawings: Figure 1 The technical flowchart of the method described in the present application; Figure 2 The finite element model of the disc pump; Figure 3 The material SN curve diagram of the disc pump; Figure 4 The model diagram of the disc pump after fixing the bottom support; Figure 5 The pump body rotor area monitoring point pressure pulsation curve diagram; Figure 6 The pump body harmonic response analysis load definition; Figure 7 The pump body frequency response curve diagram; Figure 8 The pump body fatigue life calculation result diagram; Figure 9 The pump body fatigue damage calculation result diagram. DETAILED DESCRIPTION

[0012] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein may be combined with each other.

[0013] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0014] like Figures 1-9 As shown, the present invention is a method for evaluating the vibration fatigue life of a disc pump under the action of internal flow, which mainly includes using numerical simulation to obtain the power spectrum density (PSD) spectrum of the pump body, obtaining the vibration frequency response curve of the pump body based on harmonic response analysis, and evaluating the fatigue life of the pump body based on the PSD spectrum and the material SN curve. Without relying on experiments, the vibration fatigue life of the disc pump can be directly evaluated by the numerical simulation method, which can effectively avoid dangerous frequencies and dangerous working conditions during the use of the disc pump and extend the service life. Specifically, the method includes the following steps: Step 1, establish a disc pump model; Step 2: Perform transient fluid-solid coupling calculation on the pump structure to obtain the time-domain load of the pump body internal flow pulsation pressure. Using this as input, use ANSYS to calculate the pump body displacement time-domain load. Specifically, it includes: Step 21, using the computer finite element simulation software ANSYS Fluent module and the static structural analysis module to perform transient fluid-solid coupling calculations on the pump structure, and calculate the pressure values ​​at different locations in the flow area inside the pump that change with time; Step 22: export the finite element analysis result file in step 21, import it into the ANSYS CFD-Post module for data processing, set several monitoring points in the disc pump rotor area, oil suction area, and oil discharge area, and extract the pressure change over time; In step 23, the pressure variation curves of each monitoring point are compared with time, and the area with the largest variation is selected for analysis. The pressure variation curve extracted in step 22 is used as the load input, and a static structural analysis is performed using the computer finite element simulation software ANSYS to obtain a pump displacement cloud map that varies with time, i.e., the pump displacement time domain load.

[0015] Step 3: Use Matlab and Origin software to process the pump displacement time domain load to obtain the pump acceleration power spectrum density (PSD spectrum); specifically, it includes: Step 31, comparing the displacement time-domain loads of several monitoring points set in step 22, selecting the monitoring point with the largest displacement time-domain load change, and extracting the displacement time-domain load of the pump body at this monitoring point; Step 32, using computer origin drawing software to perform second-order differential processing on the pump displacement versus time curve in step 31 to obtain the acceleration versus time curve; Step 33: Use Matlab software to perform a Fast Fourier Transform (FFT) on the acceleration-time curve to obtain the acceleration frequency domain load and further calculate the acceleration power spectrum density (PSD) spectrum. The basic FFT transformation code is as follows: clc; Data15 = xlsread('acc.xlsx') y=Data15 (:,2) Fs=1000 T=1 / Fs N=length(y) t=(0:1:N-1)*T t=t' figure plot(t,y) xlabel('time') ylabel('Signal value') Y=fft(y) Y=Y(1:N / 2+1) A=abs(Y) f=(0:1:N / 2)*Fs / N f=f' A_adj=zeros(N / 2+1,1) A_adj(1)=A(1) / N A_adj(end)=A(end) / N A_adj(2:end-1)=2*A(2:end-1) / N figure plot(f,A_adj) xlabel('Frequency(Hz)') ylabel('amplitude') Step 4: Use ANSYS to perform harmonic response analysis to obtain the pump body acceleration load frequency response curve, that is, the pump body vibration frequency response curve; specifically, including: Step 41, using ANSYS software to perform modal analysis on the pump body structure of the disc pump, and setting the disc pump support fixed constraint; Step 42 , performing harmonic response analysis on the disc pump body, applying a lateral acceleration load of unit g, and performing analysis using the result of the modal analysis in step 41 as the initial condition to obtain a disc pump acceleration load frequency response curve.

[0016] After the modal analysis result of the last step is verified that there is no resonance phenomenon, according to the frequency response curve, it can be obtained that when the acceleration load frequency is in which frequency section, the pump body life of the disc pump is more affected.

[0017] Harmonic response analysis is used to determine the steady-state response of a linear structure subjected to sinusoidal loads varying in amplitude with frequency. The frequency response function of a single degree of freedom structure H(w) can be obtained. In engineering, the amplitude and phase can be described respectively, and the complex form can also be described:

[0018] The amplitude of the frequency response function is the ratio of the input and output amplitudes, that is:

[0019] The ratio of the imaginary part and the real part of the frequency response function is equal to the tangent of the phase angle, that is:

[0020] According to the random vibration theory, the response RPSD of the power spectral density is calculated by multiplying the input power spectral density by the transfer function, and the formula is as follows:

[0021] In the formula, is the spectral density input (from the input PSD curve); is the spectral density response; is the single degree of freedom input; is the single degree of freedom output obtained by analysis; is the single degree of freedom frequency response function; is the imaginary unit; and A are the same designator, both of which are the real part of the frequency response function; and B are the same designator, both of which are the imaginary part of the frequency response function; is the phase angle.

[0022] Step 5, based on the PSD spectrum and the material SN curve, the fatigue life of the pump body is evaluated, specifically: The harmonic response analysis result in step 4 is used as the initial condition, the ANSYS n-Code module is used, the input acceleration power spectral density PSD spectrum is defined, the pump body material properties are assigned, the material SN curve is defined, and the fatigue life calculation is performed. The pump body loss cloud and the fatigue life cloud are obtained, that is, the vibration fatigue life of the disc pump pump body can be evaluated.

[0023] The present application obtains the vibration response of the pump body under the action of internal and external flow through harmonic response analysis, mainly the unstable flow in the centrifugal pump significantly affects the energy conversion and hydraulic performance of the pump, and the pressure pulsation in the fluid is the main excitation source causing vibration; in view of the deep water operation environment, the flow velocity of the bottom sea current is small, and the vibration caused by the external flow is mainly transmitted to the pump body part through the wave-induced vibration of the riser section. In view of the above problems, the vibration fatigue life evaluation method of the disc pump under the action of internal flow of the present application establishes the relationship model between vibration and fatigue by analyzing the vibration of the pump body caused by the change of the internal flow pulsation pressure of the disc pump, and calculates the fatigue life of the disc pump by using the finite element simulation software. The method of the present application can evaluate the vibration fatigue life of the disc pump according to the numerical simulation method, and given the material properties and working conditions of the pump body, the vibration fatigue life of the disc pump under the working condition can be evaluated, which will help to improve the design quality of the equipment, reduce the maintenance cost and prolong the service life.

[0024] Embodiment

[0025] In this example, a disc pump prototype is selected as the analysis model, and the pump body part parameters are as follows: design head: 150 m, inlet diameter: 150 mm, outlet diameter: 80 mm, rated speed: 1800 rpm, and the pump body material is selected from a certain stainless steel, and the material parameters are as follows: tensile strength: 880 MPa, yield strength: 410 MPa; the internal fluid is mud, and the specific parameters are as follows: mud specific gravity: 1100-1400 kg / m, mud flow Q: 3270 m3 / h (4500 L / min), drilling fluid funnel viscosity (s): 50-60 s, drilling fluid viscosity (PV): 20-40 mPa.s, and drilling fluid viscosity (YP): 15-30 Pa.

[0026] Modeling and finite element calculation are performed using ANSYS.

[0027] 1. Component: establish a disc pump model, as shown in Figure 2 .

[0028] 2. Material properties: the values are as above when setting parameters, and the SN curve is as shown in Figure 3 ; it can be seen from Figure 3 that the fatigue life of the pump body material under different stress levels.

[0029] 3. Boundary conditions: fix the bottom support, as shown in Figure 4 .

[0030] 4. Load conditions: the internal flow pulsation pressure curve calculated by fluid-structure interaction is as shown in Figure 5 ; it can be seen from Figure 5 that the change of the internal flow pulsation pressure of the pump body with time; the harmonic response analysis transverse acceleration load g is as shown in Figure 6 .

[0031] 5. Meshing: select the appropriate number of mesh.

[0032] The frequency response curve is calculated by using ANSYS harmonic response analysis, and the result is shown in Figure 7 From the result, it can be seen that the acceleration load frequency has an influence on the service life of the disc pump body at different frequency bands. Figure 7 The PSD load input is defined, and the input is set at the corresponding input module of N-CODE. The simplified acceleration power spectral density is shown in Table 1. The material properties are assigned, the material SN curve is defined, and the finite element calculation is performed by using ANSYS n-Code software. The fatigue life calculation result is shown in Figure 8 , Figure 9 From the result, it can be seen that the fatigue life calculation result of the pump body is distributed as shown in the figure. The fatigue failure occurs first at the connecting position of the bottom support and the pump shell, and the calculation result at this position is the fatigue life of the pump body. Figure 8 From the result, it can be seen that the maximum fatigue damage of the pump body is located at the connecting position of the bottom support and the pump shell. Figure 9

[0033] Table 1. Simplified acceleration power spectral density

[0034]

[0035] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.​

Claims

1. A method for evaluating the vibration fatigue life of a disc pump under internal flow, characterized in that: The following steps are involved: Step 1, establish a disc pump model; Step 2: Perform transient fluid-solid coupling calculation on the pump structure to obtain the time-domain load of the pump body internal flow pulsation pressure. Using this as input, use ANSYS to calculate the pump body displacement time-domain load. Step 3: Use Matlab software and origin software to process the pump displacement time domain load and obtain the pump acceleration power spectrum density; Step 4: Use ANSYS to perform harmonic response analysis and obtain the pump body acceleration load frequency response curve; Step 5: Evaluate the fatigue life of the pump body based on the pump body acceleration power spectrum density and material SN curve.

2. The method for evaluating the vibration fatigue life of a disc pump under internal flow according to claim 1, characterized in that: Step 2 includes: Step 21, using the computer finite element simulation software ANSYS Fluent module and the static structural analysis module to perform transient fluid-solid coupling calculations on the pump structure, and calculate the pressure values ​​at different locations in the flow area inside the pump that change with time; Step 22: export the finite element analysis result file in step 21, import it into the ANSYS CFD-Post module for data processing, set several monitoring points in the disc pump rotor area, oil suction area, and oil discharge area, and extract the pressure change over time; In step 23, the pressure variation curves of each monitoring point are compared with time, and the area with the largest variation is selected for analysis; the pressure variation curve extracted in step 22 is used as the load input, and a static structural analysis is performed using the computer finite element simulation software ANSYS to obtain the pump body displacement time domain load.

3. The method for evaluating the vibration fatigue life of a disc pump under internal flow according to claim 1, characterized in that: Step 3 includes: Step 31, comparing the displacement time-domain loads of several monitoring points set in step 22, selecting the monitoring point with the largest displacement time-domain load change, and extracting the displacement time-domain load of the pump body at this monitoring point; Step 32, using computer origin drawing software to perform second-order differential processing on the pump displacement versus time curve in step 31 to obtain the acceleration versus time curve; Step 33: Use Matlab software to perform fast Fourier transform on the acceleration-time curve to obtain the acceleration frequency domain load and further calculate the acceleration power spectrum density.

4. The method for evaluating the vibration fatigue life of a disc pump under internal flow according to claim 1, characterized in that: Step 4 includes: Step 41, using ANSYS software to perform modal analysis on the pump body structure of the disc pump, and setting the disc pump support fixed constraint; Step 42 , performing harmonic response analysis on the disc pump body, applying a lateral acceleration load of unit g, and performing analysis using the result of the modal analysis in step 41 as the initial condition to obtain a disc pump acceleration load frequency response curve.

5. The method for evaluating the vibration fatigue life of a disc pump under internal flow according to claim 1, characterized in that: Step 5 includes: using the harmonic response analysis results in step 4 as initial conditions, using the ANSYS n-Code module, defining the input pump body acceleration power spectrum density, defining the material property mapping of the pump body, performing fatigue life calculations, and obtaining the pump body loss cloud map and fatigue life cloud map, thereby evaluating the vibration fatigue life of the disc pump body.

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