振动试验中的加速度数据判读方法研究

2018年第2期 导 弹 与 航 天 运 载 技 术 No.2 2018 总第360期 MISSILES AND SPACE VEHICLES Sum No.360Received 2018-01-03于韶明（1986-），男，工程师，主要研究方向为动力学试验 Yu Shao-ming (1986-), male, engineer, mainly focus on dynamic test文章编号：1004-7182(2018)02-0121-06 DOI ：10.7654/j.issn.1004-7182.20180224Research on the Interpretation Method of Acceleration Data inVibration TestYu Shao-ming 1, Gao Zhi-yong 2, Li Xin-miao 1, Wei Guo 1, Guo Dao-jun 1(1.Beijing Institute of Structure and Environment Engineering, Beijing, 100076;2. Air Force Military Representative Office in CALT, Beijing, 100076)Abstract: The interpretation of acceleration data and the processing of abnormal data in vibration test, which need richengineering experience and solid theoretical foundation as support are the embodiment of test ability of engineers in vibration laboratory. This paper introduces the interpretation methods of vibration response normal data, the interpretation of abnormal data and the solutions to the problems of vibration response normal data in vibration test are introduced respectively, and theoretical analysis is carried out. Using the correct acceleration data response interpretation method can significantly improve the test efficiency, and at the same time, it can help to get accurate and reliable data and ensure the effectiveness of the test.Key words: Vibration test; Acceleration response; Data interpretation振动试验中的加速度数据判读方法研究于韶明1，高志勇2，李鑫淼1，卫 国1，呙道军1（1.北京强度环境研究所，北京，100076；2.空军驻航天一院军事代表办公室，北京，100076）摘要：振动试验中加速度数据判读及异常数据的处理是振动实验室工程人员试验能力的体现，需要丰富的工程经验和扎实的理论功底作为支撑。

分别介绍了振动试验中振动响应正常数据的判读方法、异常数据的判读及问题的解决方法，并从理论上进行了分析研究。

采用正确的加速度数据响应判读方法，能够明显提高试验效率，同时能够有利于得到准确可靠的数据，确保试验的有效性。

关键词：振动试验；加速度响应；数据判读中图分类号：V416.2 文献标识码：A0 IntroductionVibration environment is widespread in aerospace, aviation, navigation, motor, bridge and other industries. It can cause strength failure, fatigue damage, etc. The US Air Force headquarters made a survey of the coastal base and found that 14% of the damaged products were caused by the vibration environment [1]. The products failure caused by vibration environment has caused enormous economic and social losses, which has received extensive attention. In order to improve the adaptability of products vibration environment, vibration tests are widely used in product design, transportation, storage and other stages.With the improvement of manufacturing level inChina and the acceleration of localization process of vibration equipment, vibration laboratory has sprung up,and vibration tests have been widely carried out. According to statistics, nearly 40 companies in Xi'an area were engaged in vibration test industry by 2017. Vibration test technology is the key factor to determine the ability of laboratory vibration test.The acceleration response is the main data in vibration test, interpretation and processing of acceleration data is the key to the success of the experiment. The interpretation of acceleration data involves not only the theory of vibration mechanics, signal analysis and processing, but also requires a lot of导 弹 与 航 天 运 载 技 术 2018年122vibration test engineering experience. Data processing in vibration test reflects the level and ability of the primary engineering personnel and vibration laboratory.This paper mainly introduces several methods of acceleration data interpretation in vibration test, and to research and analyze the causes of abnormal data, and then based on the causes of abnormal data, corresponding processing method is put forward.1 The Interpretation of Normal DataThe acceleration response of products is the specific response products of vibration stimulation to products, which includes not only information of vibration excitation signal, but also the embodiment of product structure characteristics [2]. Vibration test is mainly divided into two kinds, assessment test and performance test. The purpose of acceleration data interpretation is to confirm whether the test meets the requirements in the assessment test and get the structural characteristics of the product from the response of the characteristic test. 1.1 Time Domain and Frequency Domain Data ofRandom VibrationVibration is a form of reciprocating movement of objects around a balanced position. The motion, which can only describe the law of vibration by probability and statistics is called random vibration, which cannot be used as a definite function [3,4]. At present, the random vibration of the normal distribution of the probability density function is usually used in the vibration test. The probability density function is shown as follows:22()2()x P x µσ−− （1）The probability distribution function is presented as follow:22()20()d x x p x exµσ−−（2）Where µis the average value of random vibration ()x t ,0µ=generally in engineering, σ is the root meansquare acceleration of random vibration. In the random vibration test, σis the root mean square acceleration, the probability of the corresponding time domain acceleration falling in the range (σ−,σ) is 68.3%, and the other interval probability is shown in Tab.1. In engineering, thetime domain acceleration is basically in the interval of (3σ−,3σ), and the interval is reached of (5σ−,5σ)at a very specific time. In the random vibration test, the peak acceleration in time domain is generally 3 times that of the vibration square root acceleration, and the extreme individual condition is 5 times.Tab.1 Time Domain Acceleration’s Distribution Probability ofRandom VibrationRange Probability（σ−,σ） 68.26894%（2σ−,2σ） 95.44997%(3σ−,3σ) 99.73002%(4σ−,4σ) 99.99366%（5σ−,5σ） 99.99994%1.2 Resonance Frequency InterpretationThe structure characteristics of aerospace, aviation and other aircraft, have great impact on the performance and the safety of flight. Such as damper, its structural characteristics are the key parameters [5~7]. Before the product is delivered, a characteristic test is required to obtain the response characteristics of the product structure in a particular environment, such as the resonant frequency and amplification factor.When the product characteristics are tested, the acceleration sensor is generally placed at the key position of the structure. The ratio between the acceleration signal and the control signal is obtained, and the transmission curve of the key position is obtained. The resonant frequency and amplification factor of the structure are identified through the transmission curve.The transfer function curve of a certain type of rubber damper is shown in Fig.1.Fig.1 Transfer Curve of a Certain Type of DamperAs shown in Fig.1, it can be easily obtained that the于韶明等 振动试验中的加速度数据判读方法研究123第2期resonant frequency of this type of damper in a specific vibration environment is 35 Hz, and the amplification factor at this frequency is 3.547.1.3 Vibration ModeModal analysis of general large structures is obtained through modal test and finite element method, while small and medium-sized structures are seldom tested for modal tests, and vibration tests are carried out. However, the modal parameters of the small and medium-sized structures sometimes have a great impact on the performance of the product. Some modal information of the structure can be read in the vibration test, which provides the basis for the design of the structure.The modal information obtained in vibration test is mainly frequency, through the test point products the key position of the resonant frequency of the interpretation. Comparing several points’ resonant frequency, it is the overall modal frequency if the resonant frequency is found jointly, while it is the local modal frequency if the resonant frequency is found singly. In the product design, the sensitive frequency of the structure needs to be avoided by the overall modal frequency and the local modal frequency of the installation position.Through the resonant frequency of each measuring point, we can roughly read out the first few modes of the structure, which requires rich engineering experience and theoretical knowledge as backing.Of course, through the vibration test interpretation structure modal information has its limitations. the first is limited to the acceleration measurement, because the position of the measuring points and the number of the measuring points influence the interpretation results. In addition the vibration excitation direction limitation may omit some modes of the structure. However it can still serve as additional data for vibration test, providing valuable information for structure as much as possible, and it can also be verified with modal test and finite element method.2 Interpretation of Abnormal DataThe interpretation of normal data in the test is the basic work of the engineering staff, and it is the basic requirement to carry out the test. It can meet the requirements by simple training. The interpretation and resolution of abnormal data is the key criterion to reflect the qualification of an engineer.The following are several common outliers, which are analyzed, interpreted, tested and studied. Based on the causes of abnormal data, corresponding processing methods are taken.2.1 Joint Loosing and Adhesive LoosingIn the process of the actual test, hard to avoid abnormal equipment installation problems, especially the measurement system, include sensors, measuring line, control instrument and other equipment, the equipment of the interface between connections due to improper operation or used for a long time will produce abnormal, affect the normal use.The experienced engineers will estimate the cause of the data anomaly according to the interpretation of the measured data, and save the time for the system to debug.More common measurement problems are sensor joint loosening, sensor loss and so on. The following is a description of the characteristics of these two situations. 2.1.1 Joint looseningAs the needle type sensor connector, and fixed by screw threads. After loosening of the screw structure, the pin will vibrate with the test. The pin is a cantilever structure, its amplitude will be very large at the resonant frequency, which will affect the contact and lead to the abnormal measurement data. In the non resonant frequency section, it is related to the relaxation degree of the pin.The sensor joint loosening test is carried out and two sensors are pasted at the same place for random vibration test. One of the sensor joints is loose, and the other sensor is normal. The test contrast data is shown in Fig.2, in which the curve 1 is the normal sensor data curve, and the curve 2 is the curve of the sensor joint loosening measurement data. The loosening of the sensor joint will result in the low measurement data of the whole frequency range and the significant decrease of the needle’s resonance frequency. When similar conditions are found in the test process, we should focus on finding the joint loosening of the sensor and eliminating the fault.导弹 与 航 天 运 载 技 术 2018年124Fig.2 Contrast Curves of Sensor Joint Loosening Test2.1.2 Adhesive looseningGenerally sensors are pasted at the product key position in the actual test. Due to the position is hard to observe, the best way is interpreting data in advance if it is pasted not firmly, which can not only reduce the inspection workload, but also ensure the accuracy of the collected data, avoiding to find that the data is not available after test.The sensor dropped test is carried out. Two sensors are pasted at the same place for random vibration test. One of the sensors is loosened, and the other sensor is normal. The test contrast data is shown in Fig.3, in which the curve 1 is the normal sensor’s data curve, and the curve 2 is the loosened sensor’s data curve. The sensor is loosened, which leads to the sensor’s high frequency energy loss. In the course of the test, it is found that similar situation, should focus on finding the sensor stickup, loosening and other problems, troubleshooting.Fig.3 Contrast curves of sensor adhesive loosening test2.2 Low frequency rising upIn the process of vibration test, the problem of low frequency warping of measured data is often encountered, which affects the accurate collection of data [8]. There aretwo main reasons for the low-frequency warping problem in vibration test. One is the impact of other signals such as percussion in the test, and the other is the measurement of sensors.2.2.1 PercussionIn the vibration test, the test frequency range is generally below 2000 Hz. According to the different types of sensors, the random vibration time domain vibrationrange is 100g , 200g , 500g , 1000g and so on. The RMS in the frequency domain is generally about 1/3 in the time domain.During the test, if the structure is loose or otherobjects near the sensor cause the tapping signal, thefrequency of the percussion signal is higher, and the vibration test is less affected. Percussion signal frequency generally is too high to affect the test. While once the percussion signal magnitude is over the range of the sensor, it will be clipping processing to the signal which may lead to a high frequency signal into low frequency hybrid vibration signal mixed in the measured data, causing the low frequency to rise up. The data of a certain type of pipeline vibration test is raised at low frequency is shown in Fig.4.As shown in Fig.4, the data response of the channel X, Y , and Z are measured in three directions of the X, Y , and Z respectively. Low frequency data raised up serious, and high frequency data is normal, this is the typical test curve of low-frequency rising up caused by percussion signal clipping. In fact, it is found that the structure of the pipe joint is loose and the knocking signal is produced. After improving the pipeline structure, the phenomenon of low frequency rising up is disappearing.Fig.4 Vibration Response Curves of a Certain Type of PipelineIn order to theoretically verify that the vibration于韶明等 振动试验中的加速度数据判读方法研究125第2期response of the pipeline is raised at low frequency due to clipping, the 400 Hz sinusoidal signal is verified and analyzed by clipping. The FFT is performed on the signal before clipping (as shown in formula 1) and after clipping (as shown in formula 2). The frequency spectrum curves before and after clipping is shown in Fig.5. The red line is the frequency spectrum before clipping, only 400 Hz has a frequency response. The blue line is the frequency spectrum after clipping, which produces a new 200 Hz frequency response.)400π2sin(5t Y ×= （3）5sin(2π400) 5sin(2π400)33 5sin(2π400)3t t Y t ⎧××≤⎪=⎨×>⎪⎩， ，（4）Fig.5 Frequency Spectrum Curves Before and After Clipping2.2.2 SensorThe second kind of reason for low frequency rising up problem is that the sensitivity of the sensor is not up to the other measurement in the low frequency and low magnitude vibration test. About low frequency rising up problem in the low frequency vibration test, the Beijing Institute of Structure and Environment has carried out in-depth research in this area, and has obtained a reasonable solution from the aspects of sensors, control devices and control methods, so as to solve the problem of low frequency rise in low frequency vibration test. The study of "Improving the Control Standard Rate of Low Frequency Vibration Test" was evaluated as " Six Sigma excellent project of quality technology award of ChinaQuality Association in 2016". Here is only an analysis of the sensor selection to produce low frequency rising up.There are many varieties of acceleration sensors for vibration test. Several common sensors are as shown inFig.6.Fig.6 Acceleration Sensor for Vibration TestBasically, the larger the sensor is, the higher the sensitivity is, the more suitable for low frequency and lowmagnitude vibration test. The smaller the sensor is, thelarger the range is, and the more suitable for highfrequency and high magnitude vibration test. Fig.7 is the low frequency vibration test curve of two kinds of acceleration sensors.a ）Control by Sensor of BK4370Vb ）Control by Sensor of 356B21Fig.7 Low Frequency Vibration Curves of VariousAcceleration Sensors导弹与航天运载技术 2018年126Because the test vibration magnitude is very low, the low frequency sensor of small sensitivity rises seriously. In the test, the acceleration sensor must be selected reasonably according to the test requirements.3 SummaryIn the vibration test, the measurement of acceleration data is the key step of the test, which is related to the success or failure of the vibration test.The interpretation of acceleration data in vibration test is a basic requirement for a vibration test engineer. Through the acceleration response data of product vibration test, the transmission characteristics, resonance frequency and even modal information of products can be identified. The interpretation of abnormal data should be based on correct theories and rich engineering experiences. Abnormal data from the acceleration response may be resuled from various factors, such as measuring channel loosening, sensor installation error, percussion.References[1] Xing T H. Dynamics Environment Test Techniques[M]. Xi'an: China Xi'anTechnological University Press, 2003.[2] Yang Z Y, Jia Y. The identification of dynamic loads[J]. Advances inMechanics, 2015, 2(45):29-54.[3] Zeng C H. Random vibration[J]. Chinese Journal of Nature, 1982,4(5):285-287．[4] Han Q H, Ye F, Xu J. Review of random fatigue research in civilengineering[J]. Journal of Tianjin University(Science and Technology)，2016, 7(49):143-151.[5] Zhang Z L, Li S Q, Zhu W G, et al. New quasi-equal strength and highdamping isolator for spacecraft payload[J]. Journal of Vibration and Shock, 2012, 31(11):1-6.[6] Li X Y, Wang J Y, Zhao Y F, et al. Damping design for electric equipment[J]. Aerospace Materials & Technology, 2013(1):39-41.[7] Yu S M, Wei G, Lu T, et al. Research on dampers’ acceleration-vibrationenvironment test[J] Equipment Environmental Engineering, 2015, 12(6):70-75.[8] Yang W Y. Analysis of PSD curve rising up at low frequency in randomvibrating test[J]. Equipment Environmental Engineering, 2010, 4(7):25-28.长征三号乙/远征一号成功发射北斗三号工程第四组卫星3月30日1点56分，长征三号乙/远征一号运载火箭托举北斗全球卫星导航系统的两颗卫星在西昌卫星发射中心成功发射。