張建偉,楊 燦,黃錦林,曹克磊,葉合欣,李紫瑜
基于傳遞熵的泵站管道振動傳遞路徑特性分析
張建偉1,楊 燦1,黃錦林2,曹克磊1,葉合欣3,李紫瑜1
(1. 華北水利水電大學(xué)水利學(xué)院,鄭州 450046;2. 廣東省水利水電科學(xué)研究院,廣州 510635;3. 廣東省水利水電技術(shù)中心,廣州 510635)
泵站管道因結(jié)構(gòu)復(fù)雜,產(chǎn)生多種振源,且振動的傳遞路徑難以確定,對輸水管道的安全運行具有較大威脅。針對此問題,以某泵站管道為研究對象,結(jié)合原型觀測數(shù)據(jù)與傳遞熵方法識別主振源的振動傳遞路徑;并以信息傳遞率為定量標準,驗證管道振動傳遞路徑的有效性。結(jié)果表明:穩(wěn)定運行及開機時,葉頻引起的振動為主振源,并由彎管或三通管處向其他部位傳遞,其信息傳遞率均值分別為27.2%與42%;關(guān)機時,水流脈動及管-水耦合引起的振動為主振源,且振動主要在閥門與彎管或三通管之間呈周期性傳遞,信息傳遞率均值為51.4%;穩(wěn)定運行時信息傳遞率較低,表明在鎮(zhèn)墩控制下,管道穩(wěn)定運行時傳遞能量較少,但開關(guān)機時,管道閥門、彎管及三通管處仍有較大振動能量傳遞。本研究方法受管道結(jié)構(gòu)影響較小,能準確識別管道主振源,且從能量角度識別振動傳遞路徑,相較于傳統(tǒng)方法更加高效、直觀。研究結(jié)果有助于準確識別泵站管道主振源的振動傳遞路徑,展現(xiàn)管道各工況下的危險部位,并提出減振措施,為泵站管道運行管理提供理論依據(jù)。
泵;振動;傳遞路徑;傳遞熵;信息傳遞率;振源分析
近年來,隨著水利事業(yè)迅速發(fā)展,大流量、高揚程梯級輸水泵站的修建日益增多,能夠滿足跨流域供水的需求,降低水資源匱乏地區(qū)用水壓力。壓力管道是跨流域調(diào)水工程中不可或缺的重要組成部分,其運行狀態(tài)關(guān)系到農(nóng)業(yè)生產(chǎn)灌溉等用水問題,管道的安全穩(wěn)定運行極為重要[1-4]。由于水力學(xué)的復(fù)雜特性與管道結(jié)構(gòu)的自身特點,泵站管道在各工況下產(chǎn)生的振動十分強烈;但管道振動來源復(fù)雜,振動傳遞路徑難以分析;管道的安全運行存在隱患,管道結(jié)構(gòu)損傷逐漸積累,耐久性不斷下降,進而引發(fā)安全事故[5-6]。因此,解決管道振源分析及傳遞路徑識別問題,對農(nóng)業(yè)、石油、化工等領(lǐng)域獲得持久經(jīng)濟效益,極為重要。管道振動系統(tǒng)包括振源、振動傳遞路徑和受振體。其中管道主振源的能量通常在全部振動能量中占有較大比例,是管道振動傳遞路徑研究的關(guān)鍵[7-8]。但壓力管道結(jié)構(gòu)復(fù)雜,產(chǎn)生的振源多樣且難以區(qū)分,振動傳遞路徑更加復(fù)雜,管道主振源的振動傳遞路徑識別存在較大困難[9],對管道的安全運行極為不利。針對此問題,王海軍等[10]基于結(jié)構(gòu)聲強理論測得水電站廠房振動傳遞路徑;歐陽金惠等[11]利用脈動壓力測試得出抽水蓄能電站廠房振動原因;伍鶴皋等[12]通過解析計算和數(shù)值模擬相結(jié)合的方法得到水電站廠房振動傳遞路徑;職保平等[13]基于振動基本理論、矩陣微分理論等方法分析軸流式水輪機振動傳遞路徑。盡管上述研究在振動傳遞路徑上取得一定成果,但大多是對水電站廠房振動傳遞路徑識別;泵站管道結(jié)構(gòu)與水電站廠房這類大體積混凝土結(jié)構(gòu)不同,水電站廠房振動一般由尾水傳遞至支墩;而泵站管道較長且彎管、叉管較多,振動來源復(fù)雜,振動傳遞識別困難,并且將傳遞熵用于泵站管道結(jié)構(gòu)振動傳遞路徑的研究成果幾乎空白。
本文以某灌區(qū)提水泵站管道為研究對象,依據(jù)原型觀測數(shù)據(jù),利用傳遞熵與信息傳遞率識別泵站管道結(jié)構(gòu)振源及振動傳遞路徑。首先通過原型試驗觀測數(shù)據(jù),繪制頻譜圖并計算能量占比,獲得泵站管道不同工況下的振源組成,并確定主振源;然后使用傳遞熵方法識別該泵站管道不同工況下主振源傳遞路徑,確定振動傳遞方向;最后在傳遞熵基礎(chǔ)上利用信息傳遞率定量描述泵站管道主振源的傳遞規(guī)律,并提出優(yōu)化管道運行方法及減振措施。
由于該灌區(qū)提水泵站管道的鋪設(shè)方式具有代表性,并且便于檢測,能夠得到精確的原始數(shù)據(jù)。以7泵站管道作為試驗對象,管道平面布置如圖1所示。管道共連接3臺機組,額定轉(zhuǎn)速均為600 r/min;在泵站管道關(guān)鍵位置布置10個測點,每個測點均放置3個拾振器(、、方向),分別位于支管、主管及兩者交匯處,如圖1a所示。由工程經(jīng)驗可知,管道開關(guān)機時管道振動劇烈,且為與穩(wěn)定運行工況對比,在原型試驗測試4種工況,工況、采樣時間及頻率見表1。
通過拾振器在泵站管道上采集數(shù)據(jù),對所有測點振動信號進行頻譜圖分析,獲得各測點振動主頻。由于泵站管道結(jié)構(gòu)、邊界條件,機械條件,水力條件復(fù)雜多樣,泵站管道產(chǎn)生振動的原因難以確定。根據(jù)以往研究可知,振動主要從3個方面進行分析:水力方面、機械方面和電磁方面[14-18]。由于泵站管道不同結(jié)構(gòu)產(chǎn)生的振動特性各不相同,在計算管道內(nèi)各振源及其所占比例時可采用式(1)。
式中為不同振源的能量,J;為總能量,J;x為不同振源能量所占比例。
表1 管道原型試驗測試工況
1.3.1 傳遞熵方法
泵站管道內(nèi)部結(jié)構(gòu)復(fù)雜、邊界條件、水體與管道的耦合作用,使其振動傳遞路徑識別產(chǎn)生困難。而傳遞熵作為度量不同時間序列之間的耦合關(guān)系以及信息傳遞關(guān)系的熵函數(shù),是一個動態(tài)過程關(guān)于另一個動態(tài)過程所產(chǎn)生的傳遞信息。傳遞熵的計算,不需要考慮物體的結(jié)構(gòu),而是從振動過程中不同位置振動信息傳遞熵值的大小,判斷信息之間相關(guān)程度,來揭示振動傳遞的方向。傳遞熵計算方式簡單、識別敏感性與可靠度較高、適用于線性與非線性數(shù)據(jù),對解決管道振動傳遞路徑識別問題具有較大優(yōu)勢。
按照Schreiber定義的傳遞熵[19],如果在與這兩個穩(wěn)定的傳遞過程中,對的作用影響概率為,這個過程表示為式(2)。為了減少計算傳遞熵時繁瑣的高維概率密度函數(shù),在不影響利用傳遞熵判斷傳遞的方向和關(guān)聯(lián)程度的前提下,Nichols等[20]和Overbey等{21]假設(shè)過程和過程均為一階馬爾可夫過程,即==1。式(2)可以化簡為式(3)。
其中:
1.3.2 信息傳遞率方法
為了更全面地描述管道振動的傳遞路徑,利用信息傳遞率[21](Information Translate Rate,ITR),ITR來計算管道振動能量傳遞效率。信息傳遞率通過兩點傳遞熵值計算,對振動信號之間的傳遞效率進行定量描述,可以更進一步描繪管道振動傳遞路徑。對于管道振動傳遞過程和,信息傳遞率計算過程為式(7),其中(y→x)與(x→y)與式(2)相同,表示與兩點間的傳遞熵:
式中ITR為信號到的傳遞率;|(y→x)(x→y)|為到的振動信息凈傳遞量。
泵站管道在開關(guān)機時振動較為劇烈,可以檢測到具有代表性的振動頻率,本文以開關(guān)機工況時靠近泵站機組的兩測點為例,方便檢測更全面的頻率。圖2為工況2和工況4下兩拾振器信號頻譜圖。由圖2a知,3機組開機時,7#拾振器幅值最大為59.38 Hz,是引起管道振動的主頻,69.25、29.69 Hz等為次頻;同理可知,1、2機組關(guān)機瞬間,其主頻為39.63、69.38 Hz。
統(tǒng)計泵站管道4種工況下各測點振動主頻出現(xiàn)次數(shù)并列表,表2為4種工況下主頻出現(xiàn)次數(shù)統(tǒng)計。由表2可知,測點頻率在0~2、9.9、19.8、29.7、39.6、49.5、59.4及60 Hz以上均有分布。
由式(1)結(jié)合振動信號頻譜圖與表2,參考已有研究[22]計算得出泵站管道振源??偨Y(jié)如下:1)低頻成分。泵站管道穩(wěn)定運行時,低流速的水流沖擊管道引起的低頻脈動, 頻率在10 Hz以下;2)葉頻、轉(zhuǎn)頻。泵機運行時,高速水流與機組葉片摩擦,使管道產(chǎn)生中高頻振動,由泵機參數(shù)計算,該泵站機組葉頻為60 Hz左右,屬于中高頻率,存在管道各種工況下所有位置,多為振動主頻,且比較突出;3)管-水耦合產(chǎn)生的高頻。泵站開關(guān)機瞬間,由于水錘作用,管道內(nèi)產(chǎn)生高速水流沖擊管道產(chǎn)生高頻振動。
表2 各工況主要頻率出現(xiàn)次數(shù)統(tǒng)計表
在研究該灌區(qū)提水泵站管道的振源對管道的影響時,參考Zhang等[23-24]對管道振動的研究,結(jié)合上述振源實測分析與振源組成計算,得出7 泵站管道不同工況下影響管道振動的主振源:1)機組穩(wěn)定運行時,葉頻、轉(zhuǎn)頻倍頻產(chǎn)生的振動能量占比最大,是管道振動的主振源。2)機組開機時,葉頻仍是主振源。3)機組關(guān)機時,低頻水流與管-水耦合引起的高頻振動占比最大,為管道主振源。
2.2.1 傳遞熵識別管道振動傳遞路徑
在泵站管道中,彎管及三通管、閥門等應(yīng)力集中部位與水流作用產(chǎn)生強烈激振力,引起彎管及三通管處產(chǎn)生汽蝕和空蝕,加大管道表面摩擦力,進而增強彎管及三通管處振動;并且在機組開關(guān)機時,流體流速變化較大,管道內(nèi)形成水錘,產(chǎn)生壓力波與反射波,在閥門與其余部位產(chǎn)生具有一定周期的振動,沿著管道傳遞。
基于上述對泵站管道振源研究,結(jié)合CEEMDAN和SVD方法[25]進行主振源特征信息提取,得到泵站管道 4種工況下的主振源及其對應(yīng)頻率;并利用傳遞熵方法對各工況下相鄰測點間主振源振動傳遞路徑進行識別。泵站管道在三通管與彎管間的振動較為明顯,為研究泵站管道振動傳遞路徑規(guī)律,以工況2下16測點至13與19測點間的傳遞熵為例分析開機時三通管傳遞至直管與彎管的傳遞路徑,以工況4下10測點至7測點、9測點至3測點分析關(guān)機時三通管傳遞至直管與彎管的傳遞路徑。7泵站管道在工況2與工況4下,上述兩測點之間的傳遞熵值隨時間的變化曲線分別見圖3、圖4。
由圖3可知:(16→19)的傳遞熵值明顯大于(19→16);(16→13)的傳遞熵值明顯大于(13→16)。表明在2號泵機開機期間,由葉頻引起的振動通過彎管或三通管傳向其余支路的信息量明顯較多,可以判斷泵站管道在開機狀況下葉頻振動由彎管或三通管傳至其他部位;同理,由圖 4 傳遞熵值關(guān)系可以得出:當(dāng)1號、2號泵機關(guān)機時,水流脈動和管-水耦合振動,在關(guān)機瞬間閘門附近由于水錘使振動增強,稍高于彎管處;并在短時間內(nèi)在閘門附近與彎管或三通管之間進行周期性傳遞。通過對泵站管道各個工況相鄰測點的傳遞熵值進行計算分析,得出與上述結(jié)果一致結(jié)論,限于篇幅不再贅述。
2.2.2 信息傳遞率識別管道振動傳遞路徑
在傳遞熵基礎(chǔ)上使用信息傳遞率對7泵站管道相鄰測點之間主振源的能量傳遞進行定量分析。以工況2與工況4測點的信息傳遞率為例,所選測點原則與計算傳遞熵時原因一致,不再贅述。表3為兩工況不同測點之間主振源的信息傳遞率。
表3 工況2與工況4相鄰測點之間的信息傳遞率
由表3可知:工況2泵站管道信號在3組測點之間的傳遞率分別為37.3%、44.8%與28.6%,表明彎管處很大一部分能量傳至管道其余部位;工況4泵站管道信號在3組測點之間的傳遞率分別為59.6%、27.0%與45.6%。表明關(guān)機時,短暫時間內(nèi)振動由閥門傳至彎管部位,能量較高的部位在閥門附近,振動在閥門彎管及三通管之間傳遞。
結(jié)合表4泵站管道各工況對應(yīng)的管道主要位置主振源信息傳遞率均值所占比例可知:泵站機組穩(wěn)定運行時,葉頻,轉(zhuǎn)頻引起的振動傳遞到彎管及三通管處產(chǎn)生了更強的耦合振動,信息傳遞率均值為27.2%,穩(wěn)定運行時傳遞率相對較低,主要是鎮(zhèn)墩、支墩等裝置起到了一定的減振消能;泵站機組開機時,葉頻振動主要從彎管及三通管向管道其他部位傳遞,信息傳遞率均值為42.0%,表明開機時彎管及三通管處較多能量傳遞至管道其它部位;泵站管道關(guān)機時,管道內(nèi)低頻水流脈動及由水擊引起的高頻振動,在閥門附近與彎管及三通管之間周期性傳遞,信息傳遞率均值為51.4%,表明閥門與彎管及三通管處較多能量傳遞至管道其它部位。結(jié)果證明,從信息傳遞率角度定量分析各工況下主振源的傳遞方向與傳遞熵值分析結(jié)果一致,表明信息傳遞率能有效識別泵站管道振動傳遞方向。
表4 不同工況下兩測點之間信息傳遞率及其均值對比
通過上述分析可知,在管道不同工況下,彎管、三通管與閥門是振動最為劇烈的部位,在危險位置提出減振措施對管道安全運行與泵站管道結(jié)構(gòu)設(shè)計尤為重要。如利用粒子阻尼為動力裝置基座減振;利用磁流變減振技術(shù)控制管道低頻振動。此外還可以通過增加彎管半徑、減少彎頭個數(shù)等方式來降低彎管、三通管、閥門的振動。且由上述研究結(jié)合表4分析可得,機組開關(guān)機時,與之相鄰機組管道中,中高頻振動比例及振動傳遞率明顯增加,管道開關(guān)機會加劇多個管道之間振動的相互作用。因此可通過避免同時開啟多個機組等方式來優(yōu)化開關(guān)機模式。
通過該泵站管道原型觀測資料結(jié)合傳遞熵與信息傳遞率方法對管道振動的傳遞路徑特性進行研究,可得如下結(jié)論:
1)泵站機組穩(wěn)定運行時:管道內(nèi)葉頻、轉(zhuǎn)頻倍頻引起的振動為主振源,振動主要從彎管及三通管向其它部位傳遞,信息傳遞率均值為27.2%,穩(wěn)定運行時傳遞率相對較低,主要是鎮(zhèn)墩、支墩等裝置起到了一定的減振消能。
2)泵站機組開機時:管道內(nèi)葉頻引起的振動為主振源,振動主要從彎管及三通管向管道其它部位傳遞,信息傳遞率均值為42.0%,表明開機時彎管及三通管處較多能量傳遞至管道其它部位。
3)泵站機組關(guān)機時:管道內(nèi)低頻水流脈動及管-水耦合引起的高頻振動為主振源,振動主要在閥門與彎管及三通管之間進行周期性傳遞,信息傳遞率均值為51.4%,表明閥門與彎管及三通管處較多能量傳遞至管道其它部位。
傳遞熵與信息傳遞率能準確描繪管道振動的傳遞路徑,確定管道危險部位,且能為管道減振與優(yōu)化開關(guān)機方法提出建議。
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Analysis of the pipeline transfer path characteristics of pumping stations based on transfer entropy
Zhang Jianwei1, Yang Can1, Huang Jinlin2, Cao Kelei1, Ye Hexin3, Li Ziyu1
(1.,,450046,; 2.,510635,; 3.510635,)
The transmission path of vibration difficult to determine has posed a great threat to the safe operation of water transmission pipeline, due mainly to the complex structure of pump station pipeline, where there are many vibration sources. In this study, an attempt was made to analyze the pipeline transfer path characteristics of pumping stations using transfer entropy. The pipeline of 7 pump stations in an irrigation area was also taken as the research object. Firstly, a prototype test was carried out to obtain the spectrum diagram, and energy proportion, thereby analyzing the main vibration source of pipeline vibration. Then, a transmission entropy method was used to identify the vibration transmission path of the main vibration source in the pump station pipeline under various working conditions. The effectiveness of the pipeline vibration transmission path was finally verified when taking the information transmission rate as the quantitative standard. The results show that: 1) The main vibration source was caused by the blade frequency and frequency doubling in the pipeline, mainly transmitting from the elbow and tee pipe to other parts when the pumping station unit operated stably. Furthermore, the average information transmission rate was 27.2%. More importantly, the transmission rate was relatively low during stable operation, mainly because the anchor block, buttress, and other devices played a critical role in the vibration reduction and energy dissipation. 2) The main vibration source was also caused by the blade frequency in the pipeline, mainly transmitted from the elbow and tee to other parts of the pipeline, when the pump station unit starting up. The average information transmission rate was 42%. It was found that a large part of the energy at the elbow and tee was transmitted to other parts of the pipeline during startup. 3) The main vibration source was the high-frequency vibration caused by low-frequency water flow pulsation and pipe water coupling in the pipeline when the pump station unit was shut down. The vibration was mainly transmitted periodically between the valve, elbow, and tee. The average information transmission rate was 51.4%. It can be seen that a large part of the energy from the valve, elbow, and tee was transmitted to other parts of the pipeline. Correspondingly, the information transmission rate of each working condition showed that a large part of vibration energy at the pipeline valve, elbow, and tee pipe was still transmitted to other parts. Whether the machine was switched on or off, the energy transmitted by the pipeline during the stable operation was less under the control of vibration reduction measures, such as anchor block. Therefore, the prototype observation data was selected to analyze the source of vibration through the spectrum diagram and energy proportion, where quantitatively determine the transmission relationship between vibration from the perspective of energy with the help of transmission entropy and information transmission rate, as well as the direction of vibration transmission. It was more efficient and intuitive than before, indicating great advantages in the application of vibration transmission path recognition. Consequently, this research can greatly contribute to accurately identify the vibration transmission path of the main vibration source in the pump station pipeline, thereby identifying the dangerous parts of the pipeline under different working conditions, where the vibration reduction measures can be further proposed. This finding can provide a promising theoretical basis for the operation and management of the pump station pipeline
pumps; vibration; transmission path; transfer entropy; information transmission rate; vibration source analysis
張建偉,楊燦,黃錦林,等. 基于傳遞熵的泵站管道振動傳遞路徑特性分析[J]. 農(nóng)業(yè)工程學(xué)報,2021,37(15):47-52.doi:10.11975/j.issn.1002-6819.2021.15.006 http://www.tcsae.org
Zhang Jianwei, Yang Can, Huang Jinlin, et al. Analysis of the pipeline transfer path characteristics of pumping stations based on transfer entropy[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2021, 37(15): 47-52. (in Chinese with English abstract) doi:10.11975/j.issn.1002-6819.2021.15.006 http://www.tcsae.org
2021-04-29
2021-08-05
國家自然科學(xué)基金(51679091);廣東省水利科技創(chuàng)新項目(2020-18);廣州市科技計劃(2020-ky34)
張建偉,博士,教授,研究方向為水利水電工程。Email:zjwcivil@126.com
10.11975/j.issn.1002-6819.2021.15.006
TV93; TB53
A
1002-6819(2021)-15-0047-06