Multi Interference Analysis And Model Establishment Of High Speed Train Surface Fluctuation Pressure Test Sensor

With the continuous development of high-speed train technology in China,the continuous increase of train speed and the lightweight design of vehicle body,the interaction between train and air is intensified,and the neglected train aerodynamic problems under low-speed operation are gradually highlighted.The aerodynamic performance of the train directly affects the aerodynamic drag,aerodynamic lift,aeroacoustics,transverse vibration and pressure fluctuation on the train.The deteriorated aerodynamic performance not only affects the comfort of passengers and increases energy consumption,but also severely annoys the residents along the railway.The surface fluctuation pressure of high-speed train is the direct cause of aeroacoustics,vibration and other problems.Therefore,it is necessary to deeply study the surface fluctuation pressure of high-speed train.Real train test is the most directed method to study the surface fluctuation pressure of high-speed train.However,it is difficult to extract the fluctuation pressure effectively,due to the surface fluctuation pressure of high-speed train has the characteristics of low amplitude and wide frequency band,and wind sand caused by high-speed near ground movement,pressure reference changes due to changes in line altitude,strong electromagnetic interference,vibration,temperature and other multi factor interference,resulting in low signal-to-noise ratio of test signal.At present,the average pressure can only be extracted by low-pass filtering of test signal,and the fluctuation pressure can not be accurately separated.Therefore,it is very necessary to study the test principle,signal extraction method and characteristics of train surface fluctuation pressure.In this paper,the theoretical analysis and experimental research are combined to study the single factor effect of pressure,temperature and vibration on the piezoresistive pressure sensor,the interaction mechanism among the three factors and the separation method of fluctuation pressure.The main research work of this paper is as follows:(1)The model of high-speed train and its surrounding flow field is established.Using the method of large eddy simulation,the surface fluctuation pressure of high-speed train running at 300km/h and 350km/h is simulated by CFD software.The surface pressure test system of real train running on the line is built to test the surface pressure of high-speed train under the actual operation condition of 300km/h～350km/h.By comparing the time domain and frequency spectrum characteristics of the simulated train surface fluctuating pressure signal with the measured train surface pressure signal,combined with the specific test environment of the real train test on the high-speed train line,the causes of the inaccurate measurement of the fluctuating pressure of the high-speed train are analyzed.(2)The relationship among three factors that affect the output of piezoresistive pressure sensor,pressure,temperature and vibration is analyzed.Combined with the elastic theory of thin film structure and the piezoresistive theory of semiconductor materials,the state space equation between the output of piezoresistive pressure sensor and the input of pressure,vibration,temperature and other interference is established through theoretical derivation.(3)The sensor structure for the surface fluctuation pressure test of high-speed train is designed.The real motion state of the pressure sensor excited by different frequency vibration loads is simulated by the large mass method.The output voltage of the pressure sensor excited by different vibration loads is obtained through the electrical structure joint simulation.By analyzing the output voltage of the sensor under different vibration loads,it is found that the output results of the sensor under the excitation of the same amplitude and different frequency vibration loads are different with the variation of the excitation frequency(4)The dynamic equation of forced vibration of thin plate structure is deduced theoretically,and the corresponding state space model is established.The vibration-pressure experiment device is built,and the input and output signals of the piezoresistive pressure sensor excited by different pressure loads and vibration loads are obtained through vibrationpressure experiment device.The parameters of the input-output state space model of the piezoresistive pressure sensor under vibration excitation are obtained by the method of system identification.The vibration effect calculated by the identification model is basically consistent with the vibration effect measured by the test.(5)The film structure of piezoresistive pressure sensor is established,and the mechanical characteristics of the film structure at different temperatures are calculated in the FE software.With the change of temperature,the stress distribution of the film structure of the sensor sensitive element will also change,and the corresponding temperature strain will be generated in the vertical direction of the film.Using the method of electrical structure joint simulation,the output of the sensor at different temperatures(different piezoresistive coefficient and resistivity)is calculated by FE software.With the increase of temperature,the piezoresistive coefficient of semiconductor resistance decreases,and the sensitivity of the sensor decreases.(6)The mathematical formulas of strain sensitivity,temperature drift and temperature pressure cross sensitivity of piezoresistive pressure sensor are deduced theoretically.The temperature-pressure experiment device is built,and the input and output signals of the piezoresistive pressure sensor under different pressure and temperature loads are obtained through the temperature-pressure experiment device.Combined with theoretical analysis,the mathematical equation of the influence of temperature on the output of the sensor is obtained by using the method of surface fitting.The surface fitting results based on the theoretical model proposed in this paper are better than the traditional surface fitting results in correcting the temperature effect.(7)Based on the study of the influence of single factor of vibration and temperature,a multi input single output(MISO)model of piezoresistive pressure sensor is established.The input and output characteristics of piezoresistive pressure sensor under different vibration,temperature and pressure loads are studied on the vibration temperature pressure coupling testbed,and the input and output signals of each sensor under different air pressure,temperature and vibration loads are obtained.The accuracy of the MISO model is verified.