Magnetic field simulation of pinch mode magnetorheological fluid valve

This thesis presents the magnetic field simulation of magnetorheological fluid using finite element method. Magnetorheological fluid (MRF) is a smart material fluid carrying small magnetic particles. There are four operational mode of MRF that is squeeze mode, valve mode, shear mode and pinch mode. This thesis will focus on pinch mode which is named as magnetic gradient pinch mode (MGP). The objective of this thesis is to develop a design concept of a magnetic gradient pinch mode valve. It is very important to develop a concept design because it can help in finding the possible design configuration in producing a magnetic gradient pinch shape inside the valve from the reaction of the electromagnetic. From the concept design, simulation was conducted using Finite Element Method Magnetics (FEMM) software to get the magnetic flux density, B and magnetic field intensity, H produced by MGP valve. By getting the magnetic flux density from the finite element analysis, magnetic saturation was prevented in the valve. Magnetic saturation happened when the magnetic flux density at the valve gap is more than the maximum magnetic flux density of the MRF at 0.78 T. Magnetic field intensity, H, determine the generated maximum yield stress. One of the proposed design which is the third design, was exhibit highest magnetic flux density, B than other two design. Therefore, the thrird design is suitable for MGP valve due to abality to produce highest yield stress, thus, can withstand higher pressure when applied

Design, Modelling and Sensing Possibilities of Magneto-Rheological Based Devices

This thesis has been put in place during the development of an innovative medical device which consists in an intelligent footwear for foot plantar pressure redistribution in diabetic patients. In fact, despite the several sophisticated techniques developed in the last twenty years, diabetes remains one of the first causes of non-traumatic lower limb amputation worldwide. This is mainly due to the combination of peripheral neuropathy, which determines the loss of pain sensation in the lower extremities, and high plantar pressures, both recurrent among diabetic patients. The target application imposes severe constraints for what concerns the system requirements because of the high plantar pressure magnitude and dynamics achieved by diabetic people during walking. Furthermore, the need to maintain the offloading system portable requires at the same time a high level of miniaturisation and a reduced power consumption. Within a so challenging scenario, a regulating principle relying on Magneto-Rheological (MR) fluids, may represent a good solution. In fact, MR-based systems offer as main and common advantages high sustainable loads, high dynamic ranges of operation, low complexity, high reliability and low power consumption. MR fluids are a particular group of smart materials whose rheological properties (mainly the fluid internal yield stress which in turn determines the apparent viscosity of the fluid itself) can be controlled by and external magnetic field. With increasing levels of exciting field higher values of viscosity can be obtained, with the consequent possibility to control the material transition from the liquid to the semi-solid state. The research work presented in this thesis focuses on MR valves, the core element of the offloading system conceived. Nevertheless, the analysis has been conducted in order to be as broad as possible and most of the concepts presented can be extended to all MR-based devices. The development of an enhanced magnetic equivalent circuit to take into account relevant fringing and leakage phenomena is firstly addressed. High accuracy, flexibility and computational efficiency characterise the proposed approach which can be generalised to any axisymmetric structure. Analytical models are developed to describe three MR valves configurations and the analysis steps followed can be used as guidelines to define a design methodology. A dimensioning routine is implemented to shape the valves structures in order to fulfil some imposed design requirements and/or compare the different valves performances. A qualitatively consistent attempt for the dynamic modelling of MR valves is presented through considerations on energy exchanges between the different physical domains involved. This analysis underlined that MR-based systems behave like transducers and their sensing possibilities are demonstrated experimentally. Finally, all the contents addressed contribute to the conception and realisation of a miniature MR soft shock absorber, the basic constitutive element of the variable stiffness sole conceived. The research activities and the related results presented in this thesis do not pretend to definitely clarify and fix all points still open to question. The aim of this work is rather to provide some further elements and concepts to improve the design and modelling of MR- based devices

Dynamic response of poroelastic materials containing Bingham fluid: Application to electrorheological fluids

This work examines the dynamic response to harmonic loading of a disk of poroelastic material containing non-Newtonian Bingham fluid which exhibits a yield stress. Biot\u27s poroelasticity equations and modified Darcy\u27s law for non-Newtonian fluids exhibiting a yield stress are combined together to obtain the governing equations of the system for quasi-static case. Dissipation due to friction arising from the flow of fluid relative to the solid is taken into account but inertia effects are neglected. The response and the complex modulus of the system are calculated using the finite element method taking into account the nonlinear nature of Bingham fluid. As an application of the model developed, the behavior of electrorheological (ER) fluids in poroelastic media is investigated. The storage modulus and loss tangent are obtained for different electric field strengths. The results suggest that ER fluid-porous solid device can be tuned to provide optimum stiffness and damping as excitation or resonant frequencies change

磁性流体を用いたバックドライブ可能な油圧アクチュエータの開発

早大学位記番号:新7478早稲田大

성능-침강안정성 상충 문제 해결을 위한 복합체 기반 자기유변유체에 대한 연구

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 재료공학부, 2021. 2. 서용석.Magnetorheological (MR) fluids are smart materials composed of magnetic particles dispersed in magnetically-insulating carrier medium. With magnetic field, chain-like structures are formed due to dipole-induced magnetostatic interaction between magnetic particles, and the structures inhibit the flow and increase the viscosity of MR fluids in very short time. This characteristic enables the rheological properties of MR fluids to be easily tailored with magnetic field strength. Due to this unique response, MR fluids can be used for actuator systems like power steering pumps haptic devices, and active suspensions, and damper systems in automobile, bridges, buildings and so on. A huge obstacle for application of MR fluids is their poor long-term stability against the sedimentation of magnetic particles. The large difference in the density between heavy magnetic particles and light medium make magnetic particles quickly go down to bottom, reducing the MR fluids length of life. One of the strategies for improvement of the long-term stability was to reduce the density of magnetic particles by synthesizing magnetic composite materials. Fabrication of magnetic composites using light materials such as polymer, silica, carbon materials efficiently have reduced the density mismatch between magnetic materials and carrier medium, enhancing the long-term stability of MR fluids. However, there was trade-off between long-term stability and performance of MR fluids because use of light materials is equivalent to the deterioration in magnetic properties. In this study, various magnetic composites with different composition and structures were fabricated for the objective of producing MR fluids having excellent performance and long-term stability simultaneously. As a first step, hollow structured polymer-Fe3O4 composite particles were synthesized using SiO2 as sacrificial template. With cavity inside, the hollow magnetic composite particles showed the density only 40 % of bare Fe3O4 and the large improvement in long-term stability of MR suspensions could be observed. To avoid huge decline in MR performance with non-magnetic polymers, hierarchically-structured Fe3O4 nanoparticles were prepared with simple electrospraying process. By excluding polymers, hierarchically-structured Fe3O4 had magnetization value very closed to its primary nanoparticles, leading to MR performance higher more than 3 times of hollow structured polymer-Fe3O4 suspensions. At the same time, the pores inside reduced the density of the structured particles by 23 %, resulting in better long-term stability of hierarchically-structured Fe3O4 suspension than bare Fe3O4 suspension. To minimize the trade-off between MR performance and long-term stability (density of magnetic particles), non-spherical, CoFeNi-based magnetic composites were fabricated and applied for MR fluids. CNT-Co0.4Fe0.4Ni0.2 composite was produced by synthesizing Co0.4Fe0.4Ni0.2 on the surface of functionalized CNTs. Much higher magnetization of Co0.4Fe0.4Ni0.2 compared to Fe3O4 enabled CNT-Co0.4Fe0.4Ni0.2 suspension to have much superior MR performance than Fe3O4 composite-based MR fluids. Also, due to high aspect ratio of CNTs, outstanding long-term stability of 22 % light transmission was observed with formation of 3-dimensional network structures. Finally, magnetically non-active CNTs were replaced by magnetizable, flake-shaped sendust. The high drag coefficient of flake sendust, combined with roughened surface due to attached Co0.4Fe0.4Ni0.2 nanoparticles, resulted in excellent stability with 23 % of light transmission despite of the high density of sendust-Co0.4Fe0.4Ni0.2 composite particles. Also, because both constituents of sendust-Co0.4Fe0.4Ni0.2 are both magnetic materials with high magnetization value, the MR fluids retained very high yield stress value자기유변유체는 자성입자가 비자성 매개액에 분산된 현탁액 형태의 스마트물질이다. 외부 자기장 하에서 자성입자들 사이의 쌍극자로 인한 정자기성 상호작용으로 체인 형태의 구조가 형성되고, 이 구조가 유체의 흐름을 막아 매우 짧은 시간 내에 점도가 크게 향상되게 된다. 이러한 성질로 인해 자기유변유체의 유변특성을 외부 자기장을 통해 쉽게 조절하는 것이 가능하다. 이러한 외부자장에 대한 톡특한 반응성으로 인해, 햅틱 디바이스 파워스티어링 펌프, 그리고 자동차, 다리, 건물 등의 충격 방지 시스템에 자기유변유체를 이용할 수 있다. 하지만 자기유변유체의 활용은 자성입자의 침전에 대한 안정성의 부족함으로 인해 크게 제한 될 수 있다. 밀도가 높은 자성입자와 밀도가 낮은 매개액 사이의 큰 밀도차이로 인해 자성입자가 빠르게 가라앉게 되면, 자기유변유체의 수명이 크게 감소하게 된다. 이러한 문제를 해결하기 위한 한가지 방법으로 자성물질과 밀도가 낮은 물질(고분자, 실리카 탄소물질 등)을 결합하여 자성복합입자를 합성함으로써, 자성입자의 밀도를 낮추고 자기유변유체의 침강안정성을 높이는 연구들이 진행되어 왔다. 하지만 이러한 경우 복합자성입자의 자기적 성질이 저하되기 때문에 자기유변유체의 침강안정성과 성능이 서로 상충관계에 있다는 문제점을 가지고 있다. 본 논문에서는 뛰어난 성능과 침강안정성을 가지는 자기유변유체를 제조하기 위해 다양한 물질구성과 구조를 가지는 합성하였다. 첫 단계로 실리카를 템플레이트로 사용하여 할로우 구조를 가지는 고분자-Fe3O4 복합자성입자를 합성하였다. 할로우 구조 내부의 공동으로 인해, 입자의 밀도가 순수 Fe3O4 대비 40 % 수준까지 감소하였고, 이로 인해 자기유변유체의 침강안정성이 크게 상승하였다. 다음 연구로, 비자성 고분자로 인한 자기유변유체 성능의 감소를 최소화하기 위해, 간단한 전기방사 방법을 통해 계층구조를 가지는 Fe3O4 나노입자들을 제조하였다. 앞의 연구와 대비하여, 고분자의 배제를 통해 높은 자화값을 가지는 Fe3O4 나노구조입자들을 얻을 수 있었고, 이를 자기유변유체에 적용하여 할로우 고분자-Fe3O4 입자 기반 자기유변유체 대비 3배 이상의 성능을 가지는 자기유변유체를 얻을 수 있었다. 이와 동시에 Fe3O4 나노구조입자 내부에 생성된 기공들로 인해 순수 Fe3O4 대비 밀도가 약 23 % 정도 감소하였고, 이로 인해 침 Fe3O4 나노구조입자기반 자기유변유체의 침강안정성이 향상됨을 확인할 수 있었다. 자기유변유체의 성능과 침강안정성사이의 상충성을 최소화 하기 위해서 비구형의, CoFeNi 합금기반 자성 복합입자를 합성하고 자기유변유체에 적용하였다. 먼저 개질된 카본나노튜브 표면에 CoFeNi를 합성하는 방법을 통해 카본나노튜브-CoFeNi 복합체를 합성하였다. Fe3O4 대비 높은 CoFeNi의 자화값으로 인해 카본나노튜브-CoFeNi 복합체 기반 자기유변유체는 Fe3O4 복합체기반 유체 대비 3배에서 10배 이상의 뛰어난 유변성능을 보였다. 또한 종횡비가 높은 카본나노튜브로 인해 복합체가 유체 내에서 3차원 네트워크 구조를 형성하여, 빛 투과도 22 %의 매우 뛰어난 침강안정성을 보였다. 마지막으로 비자성 물질인 카본나노튜브를, 자성물질인 플레이크형 센더스트로 대체한 센더스트-CoFeNi 복합입자를 합성하여 자기유변유체에 적용하였다. 플레이크형 센더스트의 높은 종횡비로 인해 나타나는 높은 항력계수로 인해, 해당 자기유변유체는 빛 투과도 23 %의, 높은 입자밀도 대비 매우 뛰어난 침강안정성을 보였다. 동시에, 센더스트 CoFeNi 모두 높은 자화값을 가지는 자성물질이기 때문에, 센더스트-CoFeNi 기반 자기유변유체의 성능이 카본나노튜브-CoFeNi 유체 대비 크게 향상되는 것을 확인할 수 있었다.Contents Abstract ………………………………………………………..........i Contents ……………………………………………………….........v List of Tables ………………………………………………….........x List of Figures ………………………………………………..........xi Chapter 1. Introduction ……………………………………............1 1. 1. Magnetorheological (MR) Fluids and Applications………………….........1 1. 2. Long-Term Stability Problem and Proposed Solutions ……………...........4 1. 3. Research Objectives ………………………………………………….…...7 References ………………………………...........................................................9 Chapter 2. Backgrounds …………………….……………….......16 2. 1. Definition of Terms …………..................................................................16 2. 1. 1. Shear Stress …………........................................................................16 2. 1 .2. Shear Rate …………..........................................................................16 2. 1. 3. Shear Viscosity……............................................................................17 2. 1 .4. Viscoelastic Behavior .........................................................................17 2. 1. 4. 1. Storage Modulus and Loss Modulus ..........................................17 2. 2. Yield Stress of MR Fluids …………........................................................18 2. 2. 1. Rheological Models for Prediction of Dynamic and Static Yield Stress ………….............................................................................................................19 2. 2 .2. Yield Stress Dependency on the Magnetic Field Strength .................22 2. 3. Mechanism of Structures Evolution .........................................................25 References ………............................................................................................27 Chapter 3. Suspensions of Hollow Polydivinylbenzene Nanoparticles Decorated with Fe3O4 Nanoparticles as Magnetorheological Fluids for Microfluidics Applications ........31 3. 1. Introduction ………....................................................................................31 3. 2. Experimental Section ...............................................................................34 3. 2. 1. Synthesis of Hollow Polydivinylbezene (h-PDVB) Particles ............34 3. 2. 2. Deposition of Fe3O4 onto Hollow PDVB Particles ............................36 3. 2. 3. Characterization ..................................................................................37 3. 3. Results and Discussion .............................................................................41 3. 3. 1 Morphology and Structures ..................................................................41 3. 3. 2. Magnetorheological Behaviors ............................................................48 3. 3. 3. Long-Term Stability of Suspensions ...................................................62 3. 4. Conclusion ……….....................................................................................65 References ……….............................................................................................67 Chapter 4. Hierarchically Structured Fe3O4 Nanoparticles for High-Performance Magnetorheological Fluids with Long-Term Stability …………………….………………...................................74 4. 1. Introduction ………...................................................................................74 4. 2. Experimental Section ................................................................................77 4. 2. 1. Synthesis of Citric Acid-Capped Fe3O4 ..............................................77 4. 2. 2. Fabrication of HS-Fe3O4 with Electrospraying Process .....................78 4. 2. 3. Characterization ..................................................................................79 4. 3. Results and Discussion .............................................................................82 4. 3. 1. Morphology and Structures ................................................................82 4. 3. 2. Magnetorheological Behaviors ...........................................................89 4. 3. 3. Long-Term Stability of Suspensions .................................................103 4. 4. Conclusion ………..................................................................................106 References ………..........................................................................................108 Chapter 5. High-Performance Magnetorheological Fluids of Carbon Nanotube-CoFeNi Composites with Enhanced Long-Term Stability…………………….……………….................................116 5. 1. Introduction ………...............................................................................116 5. 2. Experimental Section ............................................................................119 5. 2. 1. Functionalization of Carbon Nanotubes ..........................................119 5. 2. 2. Synthesis of Co0.4¬Fe0.4Ni0.2 and CNT-Co0.4¬Fe0.4Ni0.2 .......................119 5. 2. 3. Characterization ...............................................................................120 5. 3. Results and Discussion ...........................................................................123 5. 3. 1. Morphology and Structures ..............................................................123 5. 3. 2. Magnetorheological Behaviors .........................................................130 5. 3. 3. Long-Term Stability of Suspensions .................................................142 5. 4. Conclusion ………..................................................................................145 References ………..........................................................................................146 Chapter 6. Sendust-CoFeNi Magnetic-Magnetic Composites-Based Magnetorheological Fluids for Simultaneous Improvement of Performance and Long-Term Stability ……………………..154 6. 1. Introduction ………................................................................................154 6. 2. Experimental Section .............................................................................157 6. 2. 1. Synthesis of Citric Acid-Capped Fe3O4 ...........................................157 6. 2. 2. Characterization ...............................................................................157 6. 3. Results and Discussion ...........................................................................159 6. 3. 1. Morphology and Structures ..............................................................159 6. 3. 2. Magnetorheological Behaviors ........................................................163 6. 3. 3. Long-Term Stability of Suspensions ................................................176 6. 4. Conclusion ………..................................................................................179 References ………..........................................................................................181 Chapter 7. Conclusions ………………………………………....188 7. 1. Overall conclusion ………......................................................................188 7. 2. Further works ………..............................................................................194 References ………...........................................................................................195 국문초록 ………...............................................................................................196 List of Publication ………………………………………….......199 Appendix …………………………………………..........…........201 Appendix A. Nonisothermal Crystallization Behaviors of Structure-Modified Polyamides (Nylon 6s) ...............................................................................201Docto

Magnetorheological fluids for extreme environments : stronger, lighter, hotter

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 270-275).The controllable properties of magnetorheological (MR) fluids offer reliable and efficient actuation means to a number of far-ranging engineering applications. In this thesis we are motivated by the applications of MR fluids in oil & gas exploration and production. These applications also bring about a number of operational requirements for the fluid such as generating large magnetically induced shift in rheological properties with tolerance to elevated temperatures and low fluid density in order to maintain manageable hydrostatic downhole pressures. In this thesis we investigate a number of these fluid design constraints. Firstly, the evolution of the rheological properties of MR fluids over a wide range of magnetic field and temperature was investigated. A magnetorheometry fixture with a unique combination of high-field and high-temperature capability was manufactured. With the experimental measurements and the results from a numerical model of interparticle magnetic interaction, a scaling law was identified between the applied magnetic field and the resulting MR yield stress. The aggregation phenomena and the evolution of fluid microstructure were also investigated in microfluidic geometries with strong particle-wall interactions. The results of this study highlighted design features and operational techniques that can improve the performance of MR fluid valves. Investigation of fluid flow in non-uniform magnetic fields showed that in these regions the motion of the particle phase is governed by a balance between hydrodynamic and magnetophoretic forces. Finally, the flow of MR fluids in spatially-inhomogeneous magnetic and deformation fields was studied. A slit-flow magnetorheometer was manufactured to measure the bulk MR response of the fluid under non-uniform fields. In order to understand the parameters governing these flows and to develop a predictive tool for further investigations, a two-fluid suspension-balance constitutive model was developed which captures the key features of multi-phase flow and fluid anisotropy. The model was numerically implemented using the finite element method and was used to study the transport of MR fluids in spatially-inhomogeneous flows such as those encountered in contraction and expansion channels. This model provides insight into the design and optimization of MR fluid devices that can enhance the magnetically-controlled gain in flow resistance under downhole conditions.by Murat Ocalan.Ph.D

Magnetorheological fluid dynamics for high speed energy absorbers

Fluids with a controllable yield stress allow rapid variations in viscous force in response to an externally applied field. These fluids are used in adaptive energy dissipating devices, which have a controllable force response, reducing shock and vibration loads on occupants and structures. This thesis investigates the physics of these fluids at high speeds and shear rates, through particle modeling and fluid dynamics. The focus is on the experimentally observed reduction in controllable force at high speeds seen in magnetorheological (MR) fluid, a suspension of magnetizable particles that develop a yield stress when a magnetic field is applied. After ruling out particle dynamic effects, this dissertation takes the first rigorous look at the fluid dynamics of a controllable yield stress fluid entering an active region. A simplified model of the flow is developed and, using computational fluid dynamics to inform a control volume analysis, we show that the reduction in high speed controllable force is caused by fluid dynamics. The control volume analysis provides a rigorous criteria for the onset of high speed force effects, based purely on nondimensional fluid quantities. Fits for pressure loss in the simplified flow are constructed, allowing yield force prediction in arbitrary flow mode geometries. The fits are experimentally validated by accurately predicting yield force in all of the known high speed devices. These results should enable the design of a next generation of high performance adaptive energy absorbers

Nonlinear vibration analysis and optimal damping design of sandwich cylindrical shells with viscoelastic and ER-fluid treatments

Viscoelastic and smart fluid materials such as electro-rheological (ER) and magneto-rheological fluids have been used in many applications in industry to suppress vibration in sandwich shell structures. The main objective of this dissertation is to investigate and develop analysis models and design optimization strategies to optimally suppress the vibration of cylindrical shell/panel type structures using both passive and semi-active treatments. This dissertation constitutes two major related parts. In the first part, passive treatment using viscoelastic layer is studied for sandwich cylindrical shell using semi-analytical finite element modeling. In order to provide more accuracy a higher order Taylor’s expansion of transverse and in-plane displacement fields is developed for the core layer of sandwich cylindrical shell structures including the least number of degrees of freedom. The developed model is then employed to formulate cut and partial treatment modeling which are applied to increase damping and reduce the weight of the structure. The formulations are also modified in order to consider the slippage between layers at the interfaces. A systematic parametric study is presented to investigate the effect of main parameters such as temperature, vibration amplitude, pre-stress components, slippage and etc on vibration damping characteristics of sandwich shell structure. The temperature distribution at each layer is obtained by solving the transient heat transfer equation for axisymmetric cylindrical structure based on the finite difference method using irregular grid. Finally, by combining the semi-analytical finite element method and the optimization algorithms a design optimization methodology has been formulated to maximize the damping characteristics in sandwich cylindrical shell using the optimal number and location of cuts and partial treatments with the optimal thicknesses of the treating layers. In the second part of the dissertation, semi-active treatment using smart ER fluid layer is studied. The shear stress response and the dynamic mechanical properties of the ER fluid created by dispersing cornstarch into corn oil are experimentally explored for small/large shear strain amplitude, moderate range of frequencies and different field intensities. A new constitutive model has been also proposed to predict accurately the measured experimental data in both frequency and time domains. Then, the nonlinear vibration analysis of sandwich shell/panel structure with constrained electrorheological (ER) fluid is investigated for different boundary conditions using the finite element method. In order to reduce the computational costs, a new notation referred to as H-notation is also developed over the two well known notations referred to as B and N notations in order to represent the nonlinear equations of motion. Finally, a design optimization methodology has been presented to maximize damping in sandwich cylindrical panel using both unconstrained viscoelastic and constrained ER fluid damping layers. The unconstrained viscoelastic layer is employed in order to practically seal the constrained ER fluid patches and boundaries of the ER based sandwich structure. Then, an optimization problem has been formulated to find simultaneously the optimum number and distribution of unconstrained viscoelastic and constrained ER fluid patches, electric field intensity and thickness ratios of the treating layers

Bingham-Papanastasiou and Approximate Parallel Models Comparison for the Design of Magneto-Rheological Valves

Magneto-Rheological Fluids (MRFs) are smart materials whose physical properties can be controlled by an exciting magnetic field. MRFs are described as Bingham plastics with variable magnetic field dependent yield stress. Thanks to their particular features, MRFs have been largely employed to realize controllable power dissipating devices and, among them, regulable valves without moving parts. The most commonly configuration used for MRF based valves consists on fluid flow through an annular duct. The conception of such valves implies to deal with different physics. In particular, the magnetic circuit is usually designed and verified by mean of FE (Finite Element) analysis, while the duct geometry is usually dimensioned using an approximated formula based on fluid flow between parallel plates. In the presented work, a complete and detailed derivation of the analytical model is discussed in order to describe the flow of MRFs through an annulus using an approximate parallel plate geometry. Successively, the Bingham-Papanastasiou regularization is chosen as the mean to accurately describe the continuous non-linear yield stress and shear dependent viscosity of a commercially available MRF and it is then implemented into a FE software. This step allows to built a complete multiphysics problem for the design of MRFs based devices. Results obtained from the analytical model and FE analysis are then compared and the different steps in the proposed approaches are validated