磁流變阻尼器 ppt.ppt

1、Products of LORD,Audi TT (￥ 400,000-700,000) Audi R8 (￥ 2320,000-2780,000) Buick Lucerne (￥ 300,000-500,000) Ferrari 599GTB (￥ 5000,000) Holden HSV Commodore (￥ 1200,000-2000,000),地勢,MRF-122EG Magneto-Rheological Fluid, Fast Response Time responds instantly and reversibly to changes in a magnetic fi

2、eld. Dynamic Yield Strength provides high yield strength in the presence of a magnetic field and very low yield strength in the absence of a magnetic field; allows for a wide range of controllability. Temperature Resistant performs consistently throughout a broad temperature range, meeting the requi

3、rements of demanding applications such as automotive shock absorbers. Hard Settling Resistant provides high resistance to hard settling; easily redispersed(重分散). Non-Abrasive(零磨損) formulated to not abrade(損傷) the devices in which the MR fluid is used.,Features and Benefits,What are magneto rheologic

4、al fluids?,Magnetorheological fluids belong to the group of so called controllable fluids. This means that they exhibit a significant change in their rheological behaviour when an external magnetic field(外部磁場) is applied to them. They are indeed composed of micron-sized magnetic particles(微米級磁粒), lo

5、cated inside a liquid carrier, that form chain-like structures when the external magnetic field is applied, resulting in an increase of the apparent viscosity(粘性) of the fluid (Fig. 1 and 2).,Fig. 1 : Chain-like structures formation in the MR fluid underan externally applied magnetic field (from LOR

6、D corporation),Fig. 2: Chains formation in a drop of MR fluid (from ISC Fraunhofer),The rheological behaviour of MR fluids is often represented as a Bingham plastic model with a variable yield strength depending on the applied magnetic field H (Fig. 3a and 3b). The flow is governed by the equation:

7、where is the shear stress, is the shear strain and is the viscosity of the fluid. The operating range is the shaded area in Fig. 3c. Below the yield stress (at strains of the order of 10-3), the MR fluid behaves viscoelastically:,Where G is the complex material modulus. This model is also a good app

8、roximation for MR devices. However, the actual behaviour is more complicated and includes stiction(靜摩擦) and hysteresis(磁滯現(xiàn)象) such such as shown in Fig. 3.d,Fig. 3 : (a) and (b) Bingham plastic model, (c) Operating range, (d) Hysteretic behaviour in MR fluid devices,磁滯現(xiàn)象在鐵磁性材料中是被廣泛認知的。是指在磁化和去磁過程中，鐵磁質(zhì)

9、的磁化強度不僅依賴于外磁場強度，還依賴于原先磁化強度的現(xiàn)象。 當外加磁場施加于鐵磁質(zhì)時，其原子的偶極子按照外加場自行排列。即使當外加場被撤離，部分排列仍保持：此時，該材料被磁化。在該材料中，磁場強度（H）和磁感應強度（B）之間的關(guān)系是非線性的。如果在增強場強條件下，此二者關(guān)系將呈曲線上升到某點，到達此點后，即使場強H繼續(xù)增加，磁感應強度B也不再增加。該情況被稱為磁飽和（magnetic saturation）。 如果此時磁場線性降低，該線性關(guān)系將以另一條曲線返回到0場強的某點，該點的B將被初始曲線的磁感應強度量BR叫做剩磁感應強度或剩磁（remanent flux density）相抵消。 如

10、果繪制以外加磁場的全部強度的二者關(guān)系圖，將為S形的回路。S的中間厚度描述了磁滯量，該量與材料的矯頑力相關(guān)。 該現(xiàn)象的實際影響可為，例如，當通過磁芯的外加電流被撤離，由于殘留磁場繼續(xù)吸引電樞，而引起滯后從而延遲磁能的釋放。,磁滯現(xiàn)象 Hysteresis,磁流變阻尼器的力學模型雖然多種多樣, 而且有些能很精確模擬阻尼器的動態(tài)特性, 但是無法直接反映阻尼器的逆向動態(tài)特性。由于磁流變阻尼器的研究涉及到電磁學、流體力學、熱力學以及機械學等多學科, 這些學科的交叉和融合為研究帶來了挑戰(zhàn), 但這些研究是使磁流阻尼在工程應用中不可缺少的關(guān)鍵技術(shù)。,B-H loop,對于晶粒取向電材料的一組B-H環(huán)路（BR

11、表示剩磁，而HC為矯頑力。）,Working modes of magneto rheological fluids,Magnetorheological fluids can be operated in three distinct modes,Valve mode,Direct shear mode,Squeeze mode,Fig.4 Working modes of MR fluids,The fluid is located between a pair of stationary poles. The resistance to the fluid flow is control

12、led by modifying the magnetic field between the poles, in a direction perpendicular to the flow (Fig. 4a). Devices using this mode of operation include servo-valves, dampers, shock absorbers and actuators.,(a) Valve mode閥,valve mode is the most widely used of the three modes. An MR device is said to

13、 operate in valve mode when the MR fluid is used to impede阻礙 the flow of MR fluid from one reservoir儲存?zhèn)} to another.,Figure 5. MR fluid used in valve mode,The fluid is located between a pair of moving poles (translation or rotation motion). The relative displacement is parallel to the poles (Fig. 4b)

14、. The apparent viscosity, and thus the “drag force” applied by the fluid to the moving surfaces can be controlled by modifying the magnetic field between the poles . Devices using this mode of operation include clutches離合器, brakes, locking devices and dampers.,(b) Direct shear mode剪切,An MR fluid dev

15、ice is said to operate in shear mode when a thin layer ( 0.005 to 0.015 in.) of MR fluid is sandwiched between two paramagnetic順磁性 moving surfaces. Shear mode (see Figure 6) is useful primarily for dampers that are not required to produce large forces and for clutches and brakes.,Figure 6. MR fluid

16、used in shear mode,The fluid is located between a pair of moving poles. The relative displacement is perpendicular to the direction of the fluid flow (Fig. 4c). The compression force applied to the fluid is varying periodically間歇性. Displacements are small compared to the other modes (in the order of

17、 millimetres) but resistive forces are high. As for the two other modes, the magnitude of these resistive forces can be controlled by modifying the magnetic field between the poles. While less well understood than the other modes, the squeeze mode has been explored for use in small amplitude vibrati

18、on and impact dampers.,(c) Squeeze mode擠壓,A device that uses squeeze mode has a thin film (on the order of 0.020 in.) of MR fluid that is sandwiched between paramagnetic pole surfaces as shown in Figure1.,Figure 7. MR fluid used in squeeze mode,There are three types of control: passive, active and s

19、emi -active. A passive controller is a system that does not require power to operate and directly damps vibration or movement. Active control requires significant power to run and applies a force directly into the system to damp vibration. Semi-active control requires minimal power and it applies a

20、force that changes the systems physical properties, therefore damping the vibration . The MR damper is a semi -active control device .,MR damper,結(jié)構(gòu)振動的主動質(zhì)量驅(qū)動AMD（Active Mass Driver）控制系統(tǒng),When MR fluid is used in the valve mode, the areas where the MR fluid is exposed to magnetic flux lines are usually

21、referred to as “choking points” (see Figure 4). In the case of the damper depicted in Figure 4, MR fluid restricts the flow of fluid from one side of the piston to the other when the fluid is in the Vicinity鄰近的 of the “choking points” shown. Varying the magnetic field strength has the effect of chan

22、ging the apparent viscosity of the MR fluid. The phrase “apparent viscosity” is used since the carrier fluid exhibits no change in viscosity as the magnetic field strength is varied. Upon exposure to a magnetic field, the MR fluid as (a whole) will appear to have undergone a change in viscosity. As

23、the magnetic field strength increases, the resistance to fluid flow at the choking points increases until the saturation point飽和點 has been reached. The saturation point is the point where any increase in magnetic field strength fails to yield an increase in damper resistance. This resistance to move

24、ment that the iron particles exhibit is what allows us to use MR fluid in electrically controlled viscous dampers.,Figure 9. Typical MR damper.,近似磁感線,磁性線圈,Figure 10. Monotube MR damper section view.,Monotube單管 and Twin Tube雙管 Magneto-Rheological Dampers,Double-ended MR damper,The double-ended MR dam

25、per (see Figure 11) is one that has piston rods of the same diameter直徑 that protrude through伸出 both ends of the damper. Since there is no change in volume as the piston rod moves, the double-ended damper does not require an accumulator or other similar device. Double-ended MR dampers have been used

26、for bicycle applications, gun recoil applications, and for stabilizing buildings during earthquakes.,Figure 11. Double-ended MR damper,磁流變阻尼器在建筑結(jié)構(gòu)減振中的應用,傳統(tǒng)的建筑抗震主要是加強結(jié)構(gòu)自身的強度來抵御外來動力作用；被動控制很難滿足地震作用下隨機動力的作用；主動控制雖然能滿足抗震要求，但所需外部能量較大，耗資大，在地震時很難保證能源供給，因此在實際工程中較難被應用。隨著土木工程領(lǐng)域內(nèi)學者的深入研究，近十幾年，使用磁流變阻尼器的半主動控制已被應用于各

27、種不同建筑結(jié)構(gòu)的減振中。實踐證明將磁流變阻尼器用于建筑結(jié)構(gòu)的減振控制中能取得較好效果。,1995年，美國Lord 公司在第五屆電磁流變體國際會議上展示了具有高性能參數(shù)的電/磁流變液和相應研制成功的幾種性能優(yōu)良的小型磁流變液阻尼裝置，引起了學術(shù)界很大的振動，從而掀起了磁流變液及其裝置的研究熱潮。從那年開始，兩年一屆的國際電流變會議易名為國際電磁流變會議。 1996年以來，Spencer等人研究了磁流變阻尼器的阻尼力模 型、結(jié)構(gòu)磁流變阻尼器的地震反應。美國NotreDame大學的G.Yang等人將磁流變阻尼器用于土木工程中的大型結(jié)構(gòu)地震響應的控制中。許多學者對安裝了磁流變阻尼器的高層建筑進行減振分

28、析：,1 周 云, 吳志遠, 梁興文. 磁流變阻尼器對高層建筑風振反應的半主動控制J. 地震工程與工程振動,2001,21(4)：159-162. 2 周 云, 鄧雪松, 吳志遠. 磁流變阻尼器對高層建筑風振的舒適度的半主動控制分析J. 地震工程與工程振動,2002,22(6)：135-141. 3 涂建維, 瞿偉廉. 設(shè)置磁流變阻尼器的高層鋼架支撐體系的地震反應研究J. 工程抗震與加固改造,2006,28(2)：73-77.,郭安薪等將磁流變阻尼器和粘滯阻尼器相結(jié)合用于上海廣暢國際大廈的減振分析，結(jié)果表明該方案能夠很好的控制結(jié)構(gòu)在地震作用下的響應。2005年薛素鐸，卞曉芳將SMA-MR阻尼器

29、用于大跨度挑棚結(jié)構(gòu)的減振控制中。磁流變阻尼器還被用于空間結(jié)構(gòu)和大平臺多塔樓結(jié)構(gòu)的減振分析中，其中大平臺多塔樓結(jié)構(gòu)在磁流變阻尼器半主動控制策略下，使結(jié)構(gòu)的基底剪力與平臺層間位移比隔震結(jié)構(gòu)減小17%-20% 左右。,為了能夠更有效的抑制結(jié)構(gòu)的地震反應，大批學者投入到MRFD 半主動控制系統(tǒng)的技術(shù)改善研究中，探討了利用Soong等人提出的移相法對MRFD 半主動控制系統(tǒng)的遲滯進行補償，并做了帶有磁流變阻尼器的結(jié)構(gòu)振動實時控制實驗。韓國Inha 大學的S.B.CHOI等人深入研究了磁流變阻尼器磁流變阻尼力的滯后模型。還有一些學者對磁流變阻尼器在建筑結(jié)構(gòu)的減振控制策略進行改進和優(yōu)化。Ribakov和Gl

30、uck于2002年發(fā)表了題為Selective controlled bade isola-tion system with magnetorheological dampers的文章，對五種在不同位置安裝MR阻尼器的基礎(chǔ)隔震結(jié)構(gòu)進行了分析。周麗等使用神經(jīng)網(wǎng)絡(luò)技術(shù)實現(xiàn)了磁流變阻尼器對結(jié)構(gòu)振動的優(yōu)化控制。,磁流變阻尼器在橋梁工程減振中的應用,斜拉索是斜拉橋中重要的承重構(gòu)件，由于柔性大，阻尼小，易于產(chǎn)生各種類型的振動。傳統(tǒng)的方法均是在斜拉索上安裝被動阻尼器，由于被動阻尼器的阻尼系數(shù)是恒定的，不可能對每根索都有良好的減震效果。為了有效的控制橋梁結(jié)構(gòu)的地震反應，近年來國內(nèi)外學者投入了大量的研究。,例如

31、，中國第一座三塔斜拉橋洞庭湖大橋安裝了磁流變阻尼器并進行了試驗，實驗結(jié)果顯示安裝磁流變阻尼器的減振效果明顯優(yōu)于傳統(tǒng)的減振方法。廣東省地震工程與應用重點實驗室進行了高速公路跨線橋地震反應的智能磁流變控制。中國地震研究所的李小軍等建立橋梁的有限元模型，在橋梁的支座和伸縮縫處共安裝8組磁流變阻尼器對箱型梁橋地震反應半主動控制進行分析。香港理工大學的段元鋒等設(shè)計了專門用于索承結(jié)構(gòu)中斜拉索開環(huán)振動控制的磁流變阻尼器。Goudaninejad 等于1998年研究了設(shè)置兩個MR阻尼器的兩跨橋梁的減振能力。湖南岳陽洞庭湖大橋的風雨振控制試驗, 結(jié)論表明將磁流變阻尼器應用于橋梁結(jié)構(gòu)的減振控制能取得接近與主動控制

32、的效果，是一種經(jīng)濟、可行的減振方案。,目前比較典型的一種控制原理： 利用加速度或力傳感器測量拉索的振動信號，經(jīng)過信號放大，AD轉(zhuǎn)換后，將信號送入控制器，用一定的控制算法對信號進行處理輸出的信號經(jīng)DA轉(zhuǎn)換，通過調(diào)節(jié)閥調(diào)節(jié)可控流體的電場或磁場強度，使可控流體實現(xiàn)自由流動、粘滯流動和半固態(tài)的交替變化導致可控流體屈服剪應力的變化，從而調(diào)整阻尼器的驅(qū)動力；另一方面阻尼器的驅(qū)動力反作用到拉索，抑制拉索的振動從而實現(xiàn)對拉索振動的反饋控制。此控制過程可用下圖表示：,由上圖可以看出，裝有MR阻尼器的半主動控制結(jié)構(gòu)與原結(jié)構(gòu)相比，最大位移和最大速度分別減少了74和79，從而說明MR阻尼器是一種非常有效的半主動控制裝置；但與主動控制相比還不能達到主動控制的效果，這是因為半主動控制的控制力的大小和阻尼器的狀態(tài)有關(guān)，不能隨意調(diào)整。,磁流變阻尼器模型研究中存在的問題,目前國內(nèi)外所研究的磁流變阻尼器參數(shù)化模型都是想通過對某一型號的磁流變阻尼器在一定頻率的激勵下多次實驗, 再根據(jù)實驗數(shù)據(jù), 采用優(yōu)化方法對實驗曲線(應力-應變曲線、示功曲線、力-速度曲線)進行曲線擬合從而得到相應的模型參數(shù)。實驗發(fā)現(xiàn)阻尼器的輸出特性不僅跟電壓(或者電流)有關(guān), 而且與激振頻率也有關(guān)。所以這樣得出的模型用于實際振動控制中存在很多不足。,在給定位移和電壓(或電流)下, 通過這些模型可以很容易求得阻尼器產(chǎn)生的力, 但是它們都存在某些缺陷: