一种小作用力的磁流变阻尼器.doc

A Low Force Magneto-rheological (MR) Fluid Damper: Design, Fabrication and CharacterizationGOKHAN AYDAR,1 CAHIT A. EVRENSEL,1,*FARAMARZ GORDANINEJAD1 AND ALAN FUCHS21Mechanical Engineering Department University of Nevada, Reno, Reno, NV, USA 2Chemical Engineering Department University of Nevada, Reno, Reno, NV, USAABSTRACT: This study focuses on the theoretical analysis, design, fabrication and characterization of a small Magneto-Rheological (MR) fluid damper. It can be potentially applied to a horizontal axis, front-loading washing machine. In such washing machines, although washing cycle is slow, spin cycle is much faster. During acceleration from washing cycle to spin cycle, the tub passes through its resonant speed requiring relatively high damping. On the other hand, high damping results in increased force transmission to the housing and noise at high-speed spin cycle. Controllability of the MR fluid damper allows adjustment of damping requirements for different cycles and helps to reduce the noise at high speed spin cycle while limiting the tub motion at resonance. A patented geometry of an MR valve developed by Composite and Intelligent Materials Laboratory at the University of Nevada, Reno is used as the basis of this new design to satisfy the requirements of the application. Fabricated prototype damper is characterized using harmonic displacement input. Test results are in good agreement with the theoretical predictions and design values.Key Words: magnetorheological (MR) fluid; controllable damper; MR damper; washing machine.INTRODUCTION One of the major problems associated with high- speed front-loading washing machines is high levels of vibration and noise. The tub of a front-loading washing machine is supported by a pair of springs and pair of dampers. While the dampers help limit amplitude of vibrations at resonance, they result in higher force transmitted to the housing and increased noise at spin cycle. The goal of this study is to design, fabricate and characterize a small Magneto-Rheological Fluid (MRF) damper that can be potentially used for a front loading washing machine. It is desired to minimize the amplitude of oscillations at resonance without resulting in relatively high force transmitted to the housing at high-speed spin cycle. MRF are suspensions of micron-sized intensely polarized particles in a carrier fluid (Sassi and Cherif, 2005). These particles diameters are in the range of 110mm (Kavlicoglu et al., 2002). Recent developments led to MR fluids with desirable properties such as low viscosity, high yield strength, and stable hysteretic characteristic over a wide temperature scale (Sassi and Cherif, 2005). Since MRF dampers do not add energy to the system but dissipate, they do not have the destabilizing potential active devices may have. Their power requirement is much lower compared to active devices. This force controllability of MRF dampers makes them very attractive in vibration isolation applications (Symans and Constantinou, 1997). Better understanding of the characteristics and benefits of the MRF at the end of the 1980s and beginning of 1990s resulted in greatly increased interest in this technology (Sassi and Cherif, 2005). List of devices that utilize MR fluids is continually expanding and include vibration isolators, shock absorbers, brakes, clutches, etc (Kavlicoglu et al., 2002). There are number of earlier work that discusses MR fluid dampers with low force range targeted in this study with different applications. For example Carlson (1998) introduced a novel application of MR fluids for washing machine vibration isolation in which the fluid is storedin an absorbent matrix. These MR sponge devices use MR fluid that is restrained by capillary movement in an absorbent matrix like a sponge, open celled felt, foam or fabric (Carlson, 1998; Carlson, 1999; Carlson, 2000; Carlson, 2001; Chrzan and Carlson, 2001; Sandrin and Carlson, 2001; Carlson, 2002a). Also, there are other patented MRF devices that are claimed to be applicable to washing machines (Hopkins et al., 2001; Carlson, 2002b,c). Durazzani and Valent (1999) developed a method for active damping of the washing machine vibration using a controllable MR fluid device. A more recent study by Choi et al. (2005) discusses a conventional MR damper and its control for possible application in vibration isolation of avionic packages. This study aims design, fabrication and characteriza- tion of an MRF damper with possible application in front-loading washing machines. In order to limit the tub displacement near resonance and minimize the noise at high-speed spin cycle, the damper it is desired to be active with the maximum damping force up to about 1.4 times the resonant tub rotational speed. It should be in in-active state with minimum damping at higher speeds. To achieve this, following criteria are used for the design of the controllable MRF damper:Maximum activated damping force should be at least 150N at resonance. Passive (no-current) damping force should be as low as possible.DESIGN OF THE MRF DAMPERGeometryThe geometry of the design is selected so that nonmagnetic materials, such as plastics, can be used for as many parts of the damper as possible while satisfying the required magnetic field strength and distribution. The motivation behind this is to minimize the manufacturing cost. A modified version of the patented geometry of the MR valve developed by the University of Nevada, Reno is used as the basis of this new design (Gordaninejad and Breese, 2000). Figure 1 shows the schematic of our design. Gray area represents MR fluid. Lm is the length of MR gap that is between two parallel disks. Although disk type MR valve is very efficient it results in increased off-state pressure drop due to this specific geometry and sharp turns, especially at high speeds. As it may be apparent from the scaled drawing the gap between the shaft and the cylinder is relatively small in order to minimize the off-state force by reducing the fluid velocity. This, naturally, reduces the effective area for the damper force. Since the disk type MR valve is very efficient, increase in the magneticfield strength increases the on-state pressure drop and compensates for the reduced effective area.Fluid Mechanics DesignFor the theoretical force calculations of the damper pressure drops due to viscous losses, minor losses and MR force are calculated separately and added together to find the total damper force. For the viscous pressure drop calculations, fluid is assumed to be an incompres- sible Newtonian fluid, flow to be steady and laminar. In this design, there are two main sources for the viscous pressure drops: (i) Fluid flow between parallel disks, identified as MR channel, or gap; (ii) Fluid flow through the channel inside the core. Pressure drop for the radial, laminar, steady flow of a Newtonian fluid through the gap between two parallel disks is given as (Dogruer et al., 2004)P visgap =6Qh3lnr2r1, (1) where Q is the volumetric flow rate, h is the gap height, r1 is the outer radius of the disk (Dpisin/2 in Figure 1), r2 is the inner radius of the disk (Dcorein/2 in Figure 1), and is viscosity of the fluid. Minor losses are one of the major pressure drop sources of this design and they are given in the general form (Dogruer et al., 2004) P minor =v2kL2 , (2)where KL is the overall minor pressure loss coefficient, is the fluid density and V is the average velocity of the fluid. The pressure drop through a single-stage disk type MR valve is given as (Dogruer et al., 2004) Pdiskmr = 2.85yhr2-r1 , (3)where y is the yield stress of the fluid due to the applied magnetic field, h is the gap height. Yield stress of the fluid can be approximately calculated as (Gordaninejad and Kelso, 2000) yp=1.03 105B(T), (4)where B(T) is the magnetic flux density in Tesla unit.Magnetorheological Polymer GelA new generation of MRFs, known as magnetorheo- logical polymer gels (MRPGs) are used in vibration control and damping devices (Wilson et al., 2002; Fuchs et al., 2003). Because the polymer gel distributes between the carrier fluid and the surface of the magnetic particles, these fluids have the advantage of providing controllable viscosity as well as reducing the settling of magnetic particles in the fluid. In this respect, the MRPGs are significantly different from traditional MRFs. Polyurethane MRPG has been developed with lower settling rates and better remixing, lower viscosity and higher dynamic yield stress compared to commercially available MR fluids. This is accomplished by particle surface treatment using polymers. Variation of yield stress with the magnetic field for the MRPG used in this study is shown in Figure 2. MRPG, similar to other MRF, exhibits shear-thinning behavior. At higher shear strain rates, the viscosity decreasesultimately reaching a constant value (Fuchs et al., 2004).Electromagnetic DesignElectromagnetic finite element analysis code Ansoft and fluid mechanics models are utilized to minimize the off-state viscous force while providing the necessary force in the on-state. The result of electromagnetic finite element analysis of the selected damper design is presented in Figure 3. As it can be seen in this figure, the maximum magnetic field is about 0.47T in the MR valve area (05r517.5mm) for input current of 3A. As discussed in the next section this satisfies the maximum design force requirement.Theoretical CalculationsA theoretical prediction of the MR damper perfor- mance for harmonic input with 3Hz frequency and 5cm peak-to-peak amplitude is given in Figure 4. This case represents expected resonance criteria for the intended application. The results show that the design meets the maximum force criteria at 3A. Also, the damper fabricated based on this design is shown in Figure 5.MRF DAMPER CHARACTERIZATIONThe characterization tests of the MRF damper are performed on the Instron 8821s hydraulic shaker. Figure 6 shows the test equipment and the damper. A power supply is used to provide the required current up to 3.0A for the damper. Force-displacement and force velocity behaviors of the damper are given in Figures 7 and 8. Harmonic input applied, 7.5Hz frequency and 2.0cm peak-to-peak amplitude, represents the samevelocity input for the resonance case given as 3Hz frequency and 5cm peak-to-peak amplitude as discussed above. These values are selected due to limitations of the test equipment. Comparison of Figure 4 with Figure 7 shows that the theoretical predictions are in reasonably good agreement with the experimental measurements. The force requirement of 150N can be achieved with a 2.1A applied current. Also, as it can be seen from Figure 8, the force increases gradually with increasing velocity. The force is almost flat after piston changes direction for the off-state case. This indicates that the main source of the force is the seal friction rather than the major and minor losses due to narrow channels and sharp turns on the flow path inside the damper.SUMMARY AND CONCLUSIONSIn this study, a novel design of a low force damper with design criteria of 150N maximum force is presented. Potential application of this damper is in a front-loading washing machine. Design geometry and dimensions are selected to fulfill the requirements of the application by using fluid mechanics principles and electro-magnetic finite element analysis. Test results of the fabricated damper are in good agreement with the theoretical predictions. They also show that design objectives are satisfied:Electromagnetic design is optimized to allow the use of nonmagnetic materials, such as plastic, for majority of the damper parts. This permits alternative manufacturing techniques and materials to reduce manufacturing cost.Entire damper, with the exception of the piston core is manufactured from Aluminum to successfully test the above criteria.Maximum force required is achieved at 2.1A activa- tion current. Forcevelocity test results indicate that off-state pressure drop does not increase much with increasing velocity as expected and off-state force is dominated by the seal friction. This indicates a potential for reducing the off-state force by optimization of the damper seal system without changing the main core design. Since the maximum force is achieved at a current lower than the maximum value of 3A, which the damper is designed for, reduction in the damping force can be compensated.一种小作用力的磁流变阻尼器的设计、制作和描述摘要：本研究侧重于理论分析，设计，和一个小的磁流变（MR）阻尼器的制作研究。它可应用于水平轴，滚筒洗衣机。在对于这种洗衣机，尽管它的洗涤周期是缓慢的，但自旋周期很快。在洗衣周期不断地旋转加速过程中，缸桶因为它的共振速度要求比较高的阻尼。另一方面，在高速旋转周期内，高阻尼导致传递到住房的力增加以及产生噪声。磁流变阻尼器的可控性允许根据不同周期的要求调整阻尼，并且有助于减少当缸桶运动限制在共振速度时因高速旋转而产生的噪声。使用一种由内华达大学里诺校区复合材料和智能材料实验室申请的MR阀几何专利在作为这个新设计的基础上，以满足应用需求的发展。原型阻尼器的制作利用到谐波输入特征。试验结果与理论预测结果与设计值吻合良好。关键词：磁流变（MR）液；可控阻尼器；磁流变阻尼器；洗衣机。简介一个有关高转速滚筒洗衣机的主要问题是振动和噪声的峰值。滚筒洗衣机的桶是由一对弹簧和一对阻尼器支撑。当阻尼器辅助对共振限幅时，振动会导致在旋转周期有更高的力传递到住房并且增加噪声。本研究的目的是设计，制造和描述可用于洗衣机的小体积磁流变液（MRF）减振器。设计的目的是减少在产生共振时振动的振幅，不会导致在高速旋转周期内相对较高的力传递到外壳上。磁流变液是由微米级强烈极化粒子混合在载体流体中形成的悬浮液（Sassi和Cherif，2005）。这些颗粒的直径在110mm的范围内（kavlicoglu等人，2002）。现在的科技发展使磁流变液在很宽的温度范围内具有理想的性能，如低粘度、高屈服强度和稳定的滞回特性（Sassi和Cherif，2005）。由于磁流变阻尼器没有能量供给就无法工作，他们不可能有潜在地不稳定的供能设备。它们的能量需求相比于很多的有源器件要低很多。磁流变阻尼器的可控性使其在振动隔离应用领域极具吸引力（Symans和Constantinou，1997）。由于在1980年底和1990年初对MRF的特点和效益有了更好的理解导致人们大大增加了对这项技术的兴趣（Sassi和Cherif，2005）。利用磁流变液的设备名单不断扩大，包括减振器、制动器、离合器等（kavlicoglu等人，2002）。一些早期的工作，针对不同的应用研究探讨了磁流变液阻尼器的小作用力范围。例如Carlson（1998）介绍了磁流变液的新应用洗衣机的振动隔离中的流体中吸收矩阵。这些设备使用的磁流变液的海绵先生是由像海绵一样吸收基质毛细管运动约束，开孔的感觉，泡沫或织物（Carlson，1998；1999；卡尔森，卡尔森，2000；2001；卡尔森，存在和Carlson，2001；2001；sandrin和卡尔森，卡尔森，2002a）。同时，还有其他专利MRF设备声称适用于洗衣机（霍普金斯等人。，2001；卡尔森，b，c）。durazzani和价（1999）开发了一种洗衣机振动采用可控磁流体装置有源阻尼法。Choi等人最近的研究。（2005）讨论了常规MR阻尼器对航空包裹隔离振动可能应用控制。本研究的目的是设计，可能应用在滚筒洗衣机的磁流变阻尼器的制备及表征方法。为了限制近共振盆位移和减少在高速自旋周期噪声，减振器要主动与最大阻尼力高达约1.4倍谐振桶转速。它应该处于活跃状态的最小阻尼在更高的速度。要做到这一点，以下的标准用于可控磁流变减振器的设计：活性最大阻尼力至少应为150N共振。被动（无电流）阻尼力应尽可能低。磁流变液阻尼器设计几何几何形状的设计选择，非磁性材料，如塑料，可用于作为阻尼器的很多部分同时尽可能满足所需的磁场强度及其分布。这背后的动机是为了减少制造成本。一个修改的MR阀由内华达大学里诺校区开发的专利几何版本作为这个新设计的基础（gordaninejad和布里斯，2000）。图1显示了我们的设计原理。灰色区域表示磁流体。我是先生的差距，两平行圆盘之间的长度。虽然盘式磁流变阀是非常有效的