Method for realizing mixing test by using transfer functionTechnical Field
The invention relates to a method for realizing a mixing test by using a transfer function, belonging to the technical field of real-time mixing test vibration tables.
Background
The real-time mixing test (hereinafter referred to as mixing test) is applied to the civil engineering field, wherein one part of the mixing test is a physical test substructure and is executed by a loading system; the other part is a numerical value substructure, the numerical value substructure operates in a computer, signals of the sensor on the physical test piece are transmitted to a numerical value model, the numerical value model calculates commands in a simulation step length and outputs the commands to a loading system, and the commands act on the physical test piece to complete closed-loop interactive simulation. The relevant principle and introduction of the hybrid test can be seen in "openeses hybrid simulation test technology development and application", published in 2012, 11/25, of the university of general engineering, institute of civil engineering.
At present, most of civil mixed tests need to be composed of a Windows upper computer, a real-time target machine and a controller. The price of a computing platform is relatively high, and the transmission of closed loop signals is complex, because a finite element numerical model (a finite element model for short) and a signal processing algorithm need to be operated on an upper computer and a real-time target machine respectively.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a method for realizing a mixing test by using a transfer function, and the specific technical scheme is as follows:
the invention aims to provide a method for realizing a mixing test by using a transfer function and a method for realizing the mixing test in a controller (short for mixing test controller) by using the transfer function. It mainly comprises: finite element modeling, white noise displacement excitation identification, white noise force excitation identification, transfer function fitting, transfer function superposition and the like.
Finite element modeling, namely establishing a numerical substructure model of an object by using a common finite element modeling software OpenSees in a hybrid test. Modeling requires determining the tangent plane of the numerical substructure and the physical substructure in the mixing test; determining the position and the quality of a node in a finite element; determining the rigidity, damping and direction of materials in elements in the finite element model; the seismic waves of the load are determined. The numerical substructure has two inputs and one output in the hybrid test, wherein one input is the displacement input of seismic waves and is also called displacement excitation; one is the force input and the feedback force of the physical substructure, also called force actuation.
In the transfer function fitting module, the transfer function fitting is performed according to corresponding input and output by using Matlab software.
The white noise displacement excitation identification is to load the generated white noise seismic wave time interval on the corresponding node in the finite element model and collect the displacement response of the node of the segmentation surface under the condition of no other excitation. Fitting a displacement excitation transfer function G according to the displacement excitation time course of the white noise seismic wave and the displacement response of the segmentation surface node1The transfer function expresses the displacement action relation of displacement excitation on the node of the division plane in the finite element model.
White noise force excitation identification is to apply the generated white noise to the node of the segmentation surface of the numerical substructure in the form of node force input under the condition of no other excitation, and collect the displacement response of the node of the segmentation surface. Fitting a force excitation transfer function G according to the force excitation time interval of white noise and the displacement response of the node of the segmentation surface2The transfer function expresses the action relation of force excitation of the finite element model node on the displacement of the node of the division plane.
Transfer function superposition, namely fitting the previous step to a displacement excitation transfer function G1Force excitation transfer function G2And directly adding to obtain the final transfer function G equivalent to the finite element model.
G=G1+G2。
When the hybrid test is carried out, the compiled executable file is imported into a controller of the hybrid test, the controller carries out calculation, the input of the model is the displacement excitation of seismic waves and the reaction force of a physical test piece, and the output of the model is a displacement instruction acting on an actuator.
A method for performing a mixing experiment using a transfer function, comprising the steps of:
step one, building a frame model in finite element modeling software to obtain a finite element model;
generating two white noise time courses, namely x (t) and e (t), by using finite element analysis software;
step three, storing and converting the generated white noise time interval into a file format and a sampling step length identified by finite element software, and loading x (t) into a finite element model in a displacement excitation mode, and recording a displacement response obtained due to the displacement excitation, wherein the value of r is1(t); e (t) loading the finite element model in the form of force excitation, and recording the displacement response caused by the force excitation, wherein the value is r2(t);
Step four, mixing x (t), e (t), r1(t)、r2(t) substituting into transfer function fitting module to obtain G1And G2,G1As a displacement excitation transfer function, G2A transfer function is excited for the force; wherein, the transfer function fitting module is a transfer function fitting program of Matlab.
Step five, fitting the well-fitted G1、G2Putting the model into a Simulink model for superposition operation to obtain G, wherein G is a transfer function; defining input and output interfaces of a Simulink model, and compiling the input and output interfaces into an executable file;
putting the executable file into an upper computer of a controller, playing a seismic wave time course, and starting a hybrid test;
and step seven, finishing the mixing test and finishing the test data.
As an improvement of the above technical solution, in the step one, the finite element modeling software is openses software.
As an improvement of the above technical solution, in the second step, the finite element analysis software is Matlab software.
In the second step, the bandwidth of the white noise is larger than the test bandwidth of the physical and numerical model in the mixing test.
As an improvement of the above technical solution, in the second step, the duration of the white noise is several times of the mixing test time.
As an improvement of the above technical solution, in step four, the algorithm formula of the transfer function fitting module is:
as an improvement of the above technical solution, in step five, G ═ G1+G2。
The invention has the beneficial effects that:
the invention can replace a complex linear finite element simulation model with a simple transfer function, thereby simplifying a mixed test model under the condition of ensuring the test effect, greatly reducing the performance requirement of the model on a real-time platform and saving the cost.
The invention has the advantages that:
1. under the condition of ensuring the accuracy of the test, the threshold of the hybrid test on the hardware of the simulator is reduced.
2. The signal closed loop of the hybrid test is simplified, the hybrid test can be carried out without an upper computer of finite element operation and a real-time simulator of signal interpolation, and the possibility is provided for developing the hybrid test of a small-sized portable teaching test bed.
3. The numerical model (the transfer function) is convenient to modify, and parameters of the transfer function can be directly adjusted in an upper computer of the controller without recompilation.
4. The operation process is simple and convenient, the mixing test and the receipt collection can be completed only by corresponding software operation on the upper computer of the controller, and the simulation starting of the finite element software and the simulation starting of the target machine are not needed.
5. The development cycle is short, only the development work is needed on the controller, and the algorithm development and compiling of the real-time simulator are not needed.
Drawings
FIG. 1 is a diagram comparing a mixing test and a transfer function based mixing test control signal loop commonly used in the civil field;
FIG. 2 is a schematic diagram of a hybrid test signal loop using a transfer function model in the controller;
FIG. 3 is a comparison of the interaction between the conventional finite element mixture test numerical physical interaction and the interaction between the transfer function and the physical model;
FIG. 4 is a schematic diagram of the fitting of a transfer function by a transfer function fitting module;
FIG. 5 is a graph comparing responses of simultaneous excitation and separate excitation in a verification test of the principle of superposition of finite element models;
FIG. 6 is a graph comparing the force excitation and the displacement excitation induced displacement response when excited separately in a validation test of the finite element model stacking principle;
FIG. 7 is a time domain comparison of the response of the transfer function using a finite element model and using a controller under the same excitation;
FIG. 8 is a plot of a frequency domain comparison of the response of the transfer function using a finite element model and using a controller under the same excitation.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
The method for realizing the mixing test by using the transfer function comprises the following steps:
step one, building a frame model in finite element modeling software, and obtaining a finite element model as shown in figure 3; the finite element modeling software is preferably OpenSees software.
Generating two white noise time courses, namely x (t) and e (t), by using finite element analysis software; the finite element analysis software is preferably Matlab software. The frequency bandwidth of the white noise is greater than the test frequency band of the physical and numerical models in the mixing test, so as to fully identify the frequency response of the system and ensure that the identified transfer function is accurate and effective in the frequency range concerned in the mixing test. The duration of the white noise is several times of the time of the mixing test so as to ensure the accuracy of the subsequent identification transfer function.
Step three, storing and converting the generated white noise time interval into a file format and sampling identified by finite element softwareStep length, x (t), is loaded into the finite element model in the form of displacement excitation, and the displacement response obtained by the displacement excitation is recorded, and the value is r1(t); e (t) loading the finite element model in the form of force excitation, and recording the displacement response caused by the force excitation, wherein the value is r2(t) as shown in FIG. 4.
Step four, mixing x (t), e (t), r1(t)、r2(t) substituting into transfer function fitting module to obtain G1And G2,G1As a displacement excitation transfer function, G2Exciting a transfer function for the force; wherein, the transfer function fitting module is a transfer function fitting program of Matlab. The transfer function fitting module comprises an algorithm formula as follows:
step five, fitting the well-fitted G1、G2Putting the model into a Simulink model for superposition operation to obtain G, wherein G is a transfer function; defining input and output interfaces of a Simulink model, and compiling the input and output interfaces into an executable file; wherein G is G1+G2。
Putting the executable file into an upper computer of a controller, playing a seismic wave time course, and starting a mixing test;
and step seven, finishing the mixing test, collating the test data and analyzing the recorded data.
Example 2
Fig. 1 is a comparison diagram of a signal loop control of a hybrid test (based on openseeopenfresco) and a hybrid test based on a transfer function, which are commonly used in the civil field, and as can be seen from fig. 1, the present invention obviously simplifies the signal closed loop of the hybrid test, can carry out the hybrid test without an upper computer of finite element operation and a real-time simulator of signal interpolation, and provides a possibility for developing the hybrid test of a small-sized portable teaching test bed.
Fig. 2 is a schematic diagram of a signal loop of a mixing test using a transfer function model in a controller, and fig. 2 illustrates a signal transmission flow of the mixing test using a fitted transfer function, which is a framework of the test.
FIG. 3 is a comparison of the conventional finite element mixture test numerical physical interaction mode and the transfer function to physical model interaction mode, the left side of FIG. 3 is the conventional finite element mixture test numerical physical interaction mode, and the right side of FIG. 3 is the transfer function to physical model interaction mode according to the present invention. As can be seen from fig. 3: the invention can replace a complex linear finite element simulation model by a simple transfer function, simplifies a mixed test model and greatly reduces the performance requirement of the model on a real-time platform.
The principle of superposition of finite element models can be verified, the test A is that the finite element models are input simultaneously, namely displacement and force are input simultaneously, and the test A is used for investigating response and errors of simultaneous excitation; the test B is that the displacement and the force are respectively input and superposed, and the test B inspects the response and the error of the respective excitation. Analysis of FIG. 5 reveals that: meanwhile, the response contrast trend of the excitation and the response contrast trend of the respective excitation are the same, and the error difference is not large.
In test B, the displacement response by the force excitation and the displacement response by the displacement excitation were also examined, and the results are shown in fig. 6. FIGS. 5 and 6 further illustrate that the finite element model conforms to the superposition principle, the transfer function G1、G2Are superposable.
The finite element blending test of FIG. 7 is referred to as a conventional blending test, using a finite element model; the transfer function mixing test refers to a method for realizing the mixing test by using the transfer function by a controller of the mixing test, namely the transfer function. The mixing test using the finite element model in fig. 8 refers to the conventional mixing test, which is referred to as the finite element mixing test for short; the transfer function mixing test is a method for realizing the mixing test by using the transfer function, and is called the transfer function mixing test for short.
As can be seen from fig. 7 and 8, under the same excitation (which means that the force excitation and the displacement excitation are the same), the corresponding response, whether time domain contrast or frequency domain contrast, is the same when the existing finite element model is compared with the controller using the transfer function, as shown in fig. 7 and 8; that is, the results of the present invention are the same, with almost no difference in error, compared to the conventional mixing tests; this therefore demonstrates that the mixing test of the invention is of sufficiently high accuracy that it is comparable to existing mixing tests. Therefore, the threshold of the hybrid test on the hardware of the simulator is reduced under the condition of ensuring the test accuracy.
In addition, it should be noted that: if the transfer functions are not superposed, the mixing test can be carried out, but the expected test effect cannot be achieved, and although the closed loop of the mixing test can be formed, the test simulation is inconsistent with the real situation. Since for a numerical model there are two inputs required, a superposition is necessary if the model is fitted to a transfer function. Transfer function stacking is also an integral part of the solution to more comprehensive substitution of finite element models.
In the above embodiments, the present invention is directed to simplify a simulation hardware platform of a hybrid test, simplify a signal transmission circuit, and reduce the cost of developing the hybrid test. Complex finite element models and algorithms in the upper computer and the real-time simulator are fitted into a simple transfer function form, the fitted transfer function is put into a model simulation module of the controller to serve as a numerical model, and then effective real-time mixing tests can be carried out without the upper computer and the real-time simulator.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.