附 錄 A 1. 關(guān)于軟件接口連接 UG 為三位建模軟件，有較為完善的分析功能，在獨(dú)立建模是可進(jìn)行質(zhì)量，面積，體積，強(qiáng)度等多方面計(jì)算，可自行編程進(jìn)行導(dǎo)入式分析。 UG 軟件近幾年在國內(nèi)開始運(yùn)用，仍存在許多不足，在本次畢業(yè)設(shè)計(jì)中所體現(xiàn)的主要問題在于軟件的不完全兼容， UG 建模軟件與 ANSYS 分析軟件存在結(jié)構(gòu)稍復(fù)雜模型不可執(zhí)行布爾操作及分析，主要原因通過解讀導(dǎo)入程序得知，在 ANSYS 分析軟件中對 UG實(shí)體建模程序轉(zhuǎn)換不完全，所導(dǎo)致建模文件丟失性較大。存在軟件版本配合問題，同為高版本軟件時(shí)導(dǎo)入文件出現(xiàn)丟失情況較小。如 UG7.5與 ANSYS12.0之間導(dǎo)入文件時(shí)僅丟失少部分文件，同平面建模相對導(dǎo)入性較好。適于結(jié)構(gòu)簡單模型進(jìn)行運(yùn)用。 2. 模態(tài)實(shí)驗(yàn)應(yīng)考慮的問題 實(shí)驗(yàn)?zāi)B(tài)分析就是以控制理論為基礎(chǔ)，從所測得的輸入、輸出信息中去辨識結(jié)構(gòu)的模態(tài)參數(shù)。近幾年來，實(shí)驗(yàn)?zāi)B(tài)技術(shù)發(fā)展很快，各種測試手段日益更新，模態(tài)參數(shù)識別軟件也層出不窮，這為我們獲得結(jié)構(gòu)的較為準(zhǔn)確的模態(tài)參數(shù)帶來極大方便。 （ 1）激振方法 激振方法的選擇包括兩方面內(nèi)容：采用什么樣的激振信號；采用單點(diǎn)激振還是多點(diǎn)激振。問題的中心在于是否能夠提供足夠的能量，把需要 的頻段中的模態(tài)全部激發(fā)出來。激勵信號可采用隨機(jī)信號、脈沖信號等。隨機(jī)信號可用白噪聲發(fā)生器產(chǎn)生，試驗(yàn)中選用了 0-160Hz白噪聲信號，其優(yōu)點(diǎn)是，能量均勻分布在頻帶上，且在較寬頻率范圍內(nèi)對結(jié)構(gòu)進(jìn)行激勵，總的激振力水平，便如平均值、均方值等是可以控制的；其缺點(diǎn)是泄漏誤差大。用錘擊法提供脈沖信號，該方法的優(yōu)點(diǎn)是設(shè)備簡單，不需要精心設(shè)計(jì)安裝激振器的夾具，便于現(xiàn)場測試或在線測試；激振點(diǎn)可以靈活，敲擊力方向可以任意；測試精度能滿足一定要求，高于隨機(jī)激勵。缺點(diǎn)是激振力頻率范圍不易控制；僅適合于低頻，高頻模態(tài)不易激出來；由于 振動能量分散，從而信噪比??；錘擊有時(shí)可能過載，使結(jié)構(gòu)進(jìn)入非線性范圍。固定的激振點(diǎn)是經(jīng)過多點(diǎn)試敲后選定的。模態(tài)分析的頻域法有兩種：單點(diǎn)激振法和多點(diǎn)激振法。多點(diǎn)激振法需要昂貴的多點(diǎn)激振設(shè)備，試驗(yàn)過程復(fù)雜，但計(jì)算比較簡單；單點(diǎn)激振法所需設(shè)備簡單，試驗(yàn)也較容易，但計(jì)算方法要復(fù)雜上些。在本次實(shí)驗(yàn)中根據(jù)現(xiàn)有條件，采用單點(diǎn)激振法。 （ 2）固定方式 在進(jìn)行部件模態(tài)實(shí)驗(yàn)分析時(shí)，首先要確定被測物體的固定方式。固定方式一般有兩種：一種是按照其實(shí)際工作狀的方式約束，這種固定方式主要是用于較波折部件或在振動臺上進(jìn)行試 驗(yàn)；二是懸吊式。由于本次實(shí)驗(yàn)對象是車架，不可能選擇實(shí)際工作狀態(tài)方式，故采用橡皮繩懸吊式，使其處于自由狀態(tài)下進(jìn)行分析。結(jié)構(gòu)處于自由狀態(tài)具有最多的自由度，這樣得到的模態(tài)參數(shù)便于與其他部件一起進(jìn)行整體結(jié)構(gòu)的綜合模態(tài)分析。具體懸吊方江是：車架左右縱梁前后端各用一根橡皮繩將整個車架吊掛在大型吊架上，即為四點(diǎn)懸吊式。經(jīng)實(shí)測，車架掛上后，系統(tǒng)的固有頻率（所謂的 “ 剛體模態(tài)頻率 ” ）中的最高者為 0.816Hz，小于第一階彈性模態(tài)頻率（ FI=20.67Hz）的 1/5，可近似認(rèn)為被吊的車架處于自由狀態(tài)，這樣可以防止懸掛的剛體模戊與 車架的彈性模態(tài)發(fā)生耦合。 （ 3）激勵方式 采用電磁式激振器，最大激振力為 200N。激振器的推桿頂端連接一個力傳感器，力傳感器固定在車架后橫梁右下部。為了保證測試精度，不能讓被測物體有附加約束而產(chǎn)生其它外力，例如，對結(jié)構(gòu)激振時(shí)，除了產(chǎn)生垂直振動外，還將產(chǎn)生回轉(zhuǎn)（轉(zhuǎn)角），這時(shí)如果因?yàn)橛屑ふ衿鬟B接限制其轉(zhuǎn)動，就會產(chǎn)生附加的彎矩。為了解決這一問題，激振器和被測物體之間的推桿需要有一定的側(cè)向彈性，這樣既能保證在激振方向有一定的剛度，不影響激振力的傳遞，雙能減少在側(cè)向?qū)剞D(zhuǎn)的約束。另外，推力桿的自振 頻率應(yīng)遠(yuǎn)離被測物體的模態(tài)頻率。在試驗(yàn)中要求頂桿與車架之間不能脫離，頂桿與力傳感器間不能有任何松動和間隙。此次試驗(yàn)采用頂桿與力傳感器間通過螺紋連接。為防止頂桿與車架脫離，將力傳感器固定在一個小底座上，該底座用螺紋與一磁鐵相聯(lián)，同時(shí)將磁鐵塊吸附在車架上。還應(yīng)注意激振點(diǎn)不應(yīng)與測試頻段內(nèi)任何一階振型的節(jié)點(diǎn)相重合。因此在進(jìn)行正式試驗(yàn)以前應(yīng)先進(jìn)行預(yù)測。 ? （ 4）試驗(yàn)頻段的選擇 試驗(yàn)頻段的選擇應(yīng)考慮到汽車在運(yùn)行條件下可能的激振頻率范圍，通常認(rèn)為，遠(yuǎn)離振源頻帶的模態(tài)對結(jié)構(gòu)的實(shí)際振動影響（貢獻(xiàn)量）較小。通俗 的說法就是 “ 低頻激勵激不出高頻模態(tài) ” 。事實(shí)上，高頻模態(tài)貢獻(xiàn)的大小，除與激振頻率有關(guān)外，還與激振力的分布狀況有關(guān)。此外，如果部件進(jìn)行綜合分析，以求整體結(jié)構(gòu)的模態(tài)，為使整體模態(tài)具有更高的精確度，部件模態(tài)試驗(yàn)的頻段也應(yīng)適當(dāng)放寬，以求得稍多的模態(tài)?？傊的昴B(tài)過少，而各部件之間的連接點(diǎn)較少時(shí)，就不便于對整車進(jìn)行綜合分析。 考慮到汽車的運(yùn)行速度與路面條件以及車架與其他部件進(jìn)行綜合分析的需要，選取 0-120Hz作為其試驗(yàn)頻段。 （ 5）測點(diǎn)布置 測點(diǎn)布置原則是：布置在懸架支點(diǎn)，縱、橫梁連接點(diǎn)和 剛度變化較顯著的點(diǎn)上；盡可能使車架縱梁布點(diǎn)均勻，左右對稱布置。這樣，既便于今后的模態(tài)綜合，又不致使識別的模態(tài)失真。測點(diǎn)布置、測點(diǎn)數(shù)量的選擇還應(yīng)考慮到以下兩方面的要求：能夠明確顯示在試驗(yàn)頻段內(nèi)所有模態(tài)的基本特征及互相間的區(qū)別；保證所關(guān)心的結(jié)構(gòu)點(diǎn)（如與其它結(jié)構(gòu)的連接點(diǎn)），都在所選的測量點(diǎn)之中。為提高信噪比，測點(diǎn)不應(yīng)選在各階振型節(jié)點(diǎn)附近；在研究的主要部位，測點(diǎn)布置應(yīng)較為密集。用壓電式加速度傳感器測量各測點(diǎn)在垂直方向上的振動加速度響應(yīng)，并將信號記錄在磁帶機(jī)上（錘擊法時(shí)），或現(xiàn)場采集信號，實(shí)時(shí)處理得到頻響函數(shù)，存儲于 微機(jī)硬盤（白噪聲激勵時(shí)）。 測振時(shí)加速度計(jì)安裝正確與否，對測量結(jié)果的正確性有很大的影響。安裝方式多種多樣，我們根據(jù)測試頻段及車架的構(gòu)造，采用永久磁鐵吸附法的安裝方式以求簡便、準(zhǔn)確。 （ 6）為提高測試精度應(yīng)采取的措施 1） 仔細(xì)標(biāo)定系統(tǒng)靈敏度。在機(jī)械阻抗測量時(shí)，我們校正的不僅是單個傳感器的靈敏度，而是力傳感器與加速度傳感器靈敏度的相對比值。具體方法見參考文獻(xiàn)。 2） 沖擊力的大小決定于激起各階模態(tài)所需之能量水平，但過大的沖擊力會造成局部非線性，所以錘擊時(shí)要控制沖擊力的大小。 同時(shí)錘擊的動作要迅速，不能抖動，特別要防止試件反彈造成二次沖擊。 3)為了減少譜泄漏，在處理時(shí)應(yīng)采用數(shù)據(jù)窗。對沖擊激勵函數(shù)分析，采用指數(shù)衰減數(shù)據(jù)窗可以減少噪聲總電平。 4)為檢查模態(tài)參數(shù)可靠性，可采取互易性來檢驗(yàn)，即根據(jù)阻抗矩陣的對稱性，在 P點(diǎn)激振、 L點(diǎn)測振的響應(yīng)與 L點(diǎn)激振、 P點(diǎn)測振的響應(yīng)相同。 5） 進(jìn)行數(shù)據(jù)處理時(shí)，首先需要確定觸發(fā)系統(tǒng)。脈沖信號采用信號觸發(fā)。即當(dāng)有一脈沖信號過來時(shí)，才進(jìn)行一次觸發(fā)平均。為減少隨機(jī)誤差，應(yīng)進(jìn)行多次平均。 6） 考慮到架結(jié)構(gòu)的阻尼較小，頻響函數(shù) 的半功率帶較窄，故應(yīng)盡量提高頻率分辨率。 7） 傳遞函數(shù)可信性檢驗(yàn)。所有時(shí)域信號均在微機(jī)上顯示，正常時(shí)才往下進(jìn)行。每個傳遞函數(shù)都用相干函數(shù)檢驗(yàn)，相干函數(shù)絕大多數(shù)都在 0.85以上。 8） 力譜要符合要求，幅值差不大于 3dB。 附 錄 B for software interfaces connection UG for three modeling software, there are more complete analysis, in the modeling is available to the area, volume, quality and strength for the various programming for import by itself, but in the analysis. UG software in the past few years at home and begin to use many. at the graduation design by the main problem lies in the software is not entirely compatible, modeling and UG ANSYS analysis software is a model not perform complicated structure and analysis, boolean The main reason by interpreting the importer, the analysis software ANSYS UG entity modeling applications for conversion, not by modeling papers missing. there is sexual older version match, with the high edition software import file a missing information. as a smaller UG7. 5 and ANSYS12.0 between the import file was missing document, with a plane model in the import of the better. for simple model be applied. Modal test should consider Experimental modal analysis is to control theory, from the measured input and output information to identify structural modal parameters. In recent years, experimental modal technology has developed rapidly, growing a variety of test methods updated modal parameter identification software is also another, which as we get more accurate structure of the modal parameters of a great convenience. excitation method Exciting choice of methods, including two aspects: what kind of excitation signal； excitation using a single point or multi point excitation. Question is whether the center can provide enough energy, the band needed to stimulate all the modes. Excitation signal can be random signals, pulse signals. Random white noise generator signal is available, test the selected 0-160Hz white noise signal, its advantage is that energy is uniformly distributed in the band, and a wide frequency range of the structure of incentives, the total level of the exciting force, just like a mean, mean square values, etc. can be controlled； its major drawback is that leakage error. Provide pulses with the hammer method, this method has the advantage of simple equipment, do not install the exciter fixture designed for easy field testing or online testing； excitation point can be flexible, percussion force direction can be arbitrary； test accuracy can meet certain requirements, higher than the random excitation. The disadvantage is difficult to control the frequency range of exciting force； only suitable for low frequency, high-frequency modes is not easy to shock them； vibrational energy spread due to noise ratio is small； hammer can sometimes overload the structure into the nonlinear range. The excitation point is fixed multi-point try after the selected after the knock. Modal analysis of frequency-domain method in two ways: single-point excitation method and multi-point excitation method. Multi-point excitation method requires expensive multi-point excitation equipment, the testing process complex, but the calculation is relatively simple； single-point excitation method required simple equipment, the test is relatively easy, but on a more complicated calculation. In this experiment, under the existing conditions, using single-point excitation method. Fixation During the experimental modal analysis of components, the first object to be measured to determine a fixed way. Fixed the way to have two: one is shaped in accordance with the actual work the way constraints, this fixation is mainly used for more twists and turns parts or the vibration table and tested； second is suspended. As the object of this experiment is the frame, means the state can not choose the actual work, so use rubber rope suspended, it is in a free state for analysis. Structure in a free state with the largest degree of freedom, so easy to obtain the modal parameters together with other parts of the overall structure of a comprehensive modal analysis. Jiang is the specific suspension side: left and right frame rails front and back of the rubber with a hanging rope to the frame in a large hanger, that is, four suspended. After measurement, the frame mount, the systems natural frequency (the so-called rigid body mode frequency) in the highest of 0.816Hz, less than the first order elastic modal frequency (FI = 20.67Hz), 1 / 5 , can be approximated that the frame was hanging in a free state, which would prevent suspension rigid with the frame of the elastic modulus E mode coupling occurs. Incentives Using electromagnetic shaker, maximum exciting force of 200N. Exciter putting the top connected to a force sensor, force sensors fixed on the bottom right of the frame after the beams. In order to ensure test accuracy, so that the measured object can not have additional constraints arising from other external forces, for example, excitation of the structure, in addition to generate vertical vibration, it will also produce rotation (angle), then if the connection limit because of the exciter its rotation, will produce additional moments. To solve this problem, between the exciter and the measured object putter need to have some lateral flexibility, so that can guarantee a certain direction in the excitation of stiffness does not affect the transmission of the exciting force, can reduce the double In the lateral constraints on the rotation. In addition, the thrust rod natural frequency away from the modal frequency of the measured object. Required in the test between the ejector and the frame can not be separated from the mandrel and the force between the sensor does not have any loose and gaps. The test used by the ejector and the threaded connection between the force sensor. To prevent the mandrel and the frame out, the force sensor fixed on a small base, the base with a thread associated with a magnet while the magnet adsorption on the frame. Excitation point should also note that the band should not be testing any vibration mode of the nodes coincide. Therefore, during the trial to be preceded by the official forecast. ? the choice of test frequency Test frequency selection should take into account vehicle operating conditions possible in the excitation frequency range, generally considered, away from the local oscillator frequency of modal vibration of the structure of the actual impact (contribution amount) is small. Popular saying that no high-frequency low-frequency laser excitation modes. In fact, the size of the contribution of high-frequency modes, in addition with the excitation frequency, but also with the distribution of the exciting force. In addition, if parts of a comprehensive analysis, the overall structure of the mode in order for the overall mode has a higher accuracy, the test frequency modal components should also be relaxed, in order to achieve slightly more modal. Modal value was too small, and the connection point between the various components when there are fewer, not to facilitate a comprehensive analysis of the vehicle. Taking into account the cars speed and road conditions, and other parts of the frame with a comprehensive analysis of needs, select 0-120Hz band as its pilot. measuring points Measuring points principle is: arranged in the suspension pivot, vertical, beam stiffness of the connection point and the more significant point； distribution frame rails as far as possible uniform, symmetrical layout. In this way, both for the future of the modal synthesis, modal identification without causing distortion. Measuring points, measuring points of the selection should also take into account the following two requirements: the ability to clearly show the band in the test mode all the basic characteristics and differences between each other； to ensure the structural point of interest (such as with the other structures connection point), are among the selected measurement points. To improve the signal to noise ratio, the measuring point should be selected in the vicinity of the first vibration mode node； the main part in the study, measuring points should be more intensive. Piezoelectric acceleration sensor with the measuring points in the vertical vibration acceleration response, and the signal recorded on the tape drive (when the hammer method), or on-site signal acquisition, real-time processing to get frequency response function, stored on computer hard disk (white noise excitation). Vibration when the accelerometer is installed correctly or not, the accuracy of the measurement results have great impact. Install a variety of ways, we test the frequency and the frame according to the structure, the use of permanent magnets in order to assay the installation simple and accurate. To improve test accuracy measures to be taken 1) careful calibration of the system sensitivity. In the mechanical impedance measurements, we corrected the sensitivity of the sensor is not only the individual, but force sensor and acceleration sensor relative sensitivity ratio. Specific methods see reference. 2) The impact depends on the size of the order provoked modal energy level required, but the impact is too large will result in local non-linear, so when the hammer impact force to control the siz