• Smart Structures and Systems
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• 제16권1호
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• pp.141-162
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• 2015

The magneto-rheological visco-elastomer (MRVE) is used as a smart core to control the stochastic micro-vibration of a sandwich plate with supported mass. The micro-vibration response of the sandwich plate with MRVE core and supported mass under stochastic support motion excitations is studied and compared to evaluate the vibration suppression capability. The effects of the supported mass and localized magnetic field on the stochastic micro-vibration response of the MRVE sandwich plate are taken into account. The dynamic characteristics of the MRVE core in micro-vibration are described by a non-homogeneous complex modulus dependent on vibration frequency and controllable by applied magnetic fields. The partial differential equations for the coupled transverse and longitudinal motions of the MRVE sandwich plate with supported mass are derived from the dynamic equilibrium, constitutive and geometric relations. The simplified ordinary differential equations are obtained for the transverse vibration of the MRVE sandwich plate under localized magnetic fields. A frequency-domain solution method for the stochastic micro-vibration response of sandwich plates with supported mass is developed based on the Galerkin method and random vibration theory. The expressions of frequency-response functions, response power spectral densities and root-mean-square velocity responses of the plate in terms of the one-third octave frequency band are obtained for micro-vibration evaluation. Finally, numerical results are given to illustrate the large response reduction capacity of the MRVE sandwich plate with supported mass under stochastic support motion excitations, and the influences of MRVE parameters, supported mass and localized magnetic field placement on the micro-vibration response.

• Smart Structures and Systems
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• 제19권1호
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• pp.21-31
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• 2017

To control the stochastic vibration of a vibration-sensitive instrument supported on a beam, the beam is designed as a sandwich structure with magneto-rheological visco-elastomer (MRVE) core. The MRVE has dynamic properties such as stiffness and damping adjustable by applied magnetic fields. To achieve better vibration control effectiveness, the optimal bounded parametric control for the MRVE sandwich beam with supported mass under stochastic and deterministic support motion excitations is proposed, and the stochastic and shock vibration suppression capability of the optimally controlled beam with multi-mode coupling is studied. The dynamic behavior of MRVE core is described by the visco-elastic Kelvin-Voigt model with a controllable parameter dependent on applied magnetic fields, and the parameter is considered as an active bounded control. The partial differential equations for horizontal and vertical coupling motions of the sandwich beam are obtained and converted into the multi-mode coupling vibration equations with the bounded nonlinear parametric control according to the Galerkin method. The vibration equations and corresponding performance index construct the optimal bounded parametric control problem. Then the dynamical programming equation for the control problem is derived based on the dynamical programming principle. The optimal bounded parametric control law is obtained by solving the programming equation with the bounded control constraint. The controlled vibration responses of the MRVE sandwich beam under stochastic and shock excitations are obtained by substituting the optimal bounded control into the vibration equations and solving them. The further remarkable vibration suppression capability of the optimal bounded control compared with the passive control and the influence of the control parameters on the stochastic vibration suppression effectiveness are illustrated with numerical results. The proposed optimal bounded parametric control strategy is applicable to smart visco-elastic composite structures under deterministic and stochastic excitations for improving vibration control effectiveness.

• 한국축산식품학회지
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• 제39권1호
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• pp.23-34
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• 2019

Fat reduction in the formulation of cheese emulsion causes problems in its flowability and functional characteristics during spray-dried cheese powder production. In order to eliminate these problems, the potential of using microparticulated whey protein (MWP) in cheese emulsions was examined in this study. Reduced-fat white-brined cheese emulsions (RF) with different dry-matters (DM) (15%, 20%, and 25% excluding emulsifying salt) were produced using various MWP concentrations (0%-20% based on cheese DM of emulsion). Their key characteristics were compared to full-fat cheese emulsion (FF). MWP addition had no influence on prevention of the phase separation observed in the instable group (RF 15). The most notable effect of using MWP was a reduction in apparent viscosity of RF which significantly increased by fat reduction. Moreover, increasing the amount of MWP led to a decrease in the values of consistency index and an increase in the values of flow behavior index. On the other hand, using high amounts of MWP made the emulsion more liquid-like compared to full-fat counterpart. MWP utilization also resulted in similar lightness and yellowness parameters in RF as their full-fat counterparts. MWP in RF increased glossiness and flowability scores, while decreased mouth coating scores in sensory analyses. Fat reduction caused a more compact network, while a porous structure similar to FF was observed with MWP addition to RF. In conclusion, MWP showed a good potential for formulation of reduced-fat cheese emulsions with rheological and sensorial characteristics suitable to be used as the feeding liquid in the spray drying process.

• Smart Structures and Systems
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• 제24권3호
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• pp.303-317
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• 2019

Magneto-rheological fluid (MRF) rotatory dampers are normally used for controlling the constant rotation of machines and engines. In this research, such a device is proposed to act as variable stiffness device to alleviate the rotational oscillation existing in the many engineering applications, such as motor. Under such thought, the main purpose of this work is to characterize the nonlinear torque-angular displacement/angular velocity responses of an MRF based variable stiffness device in oscillatory motion. A rotational hysteresis model, consisting of a rotatory spring, a rotatory viscous damping element and an error function-based hysteresis element, is proposed, which is capable of describing the unique dynamical characteristics of this smart device. To estimate the optimal model parameters, a modified whale optimization algorithm (MWOA) is employed on the captured experimental data of torque, angular displacement and angular velocity under various excitation conditions. In MWOA, a nonlinear algorithm parameter updating mechanism is adopted to replace the traditional linear one, enhancing the global search ability initially and the local search ability at the later stage of the algorithm evolution. Additionally, the immune operation is introduced in the whale individual selection, improving the identification accuracy of solution. Finally, the dynamic testing results are used to validate the performance of the proposed model and the effectiveness of the proposed optimization algorithm.

• Composites Research
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• 제35권3호
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• pp.153-160
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• 2022

목재 섬유 기반의 셀룰로오스 나노피브릴(cellulose nanofibrils, CNF)은 생체적합특성이 우수하여 조직 공학용 스캐폴드, 약물 운반체, 상처 치유용 겔 등의 생체 의료 분야에서 많은 관심을 받고 있다. 하지만, 셀룰로오스 나노피브릴은 상대적으로 약한 기계적 강도를 나타내기 때문에 높은 기계적 특성을 요구하는 응용 분야에 사용되기 어렵다는 한계를 가지고 있다. 따라서 본 연구에서는 셀룰로오스 나노피브릴의 기계적 강도를 향상시키기 위해 TEMPO (2,2,6,6-tetramethylpiperidin-oxyl) 산화 처리된 셀룰로오스 나노피브릴에 금속 양이온을 도입하여 금속-카르복실레이트 배위 결합을 가지는 하이드로겔을 제조하였다. 또한, 큰 진폭 진동 전단(large amplitude oscillatory shear) 측정과 Live/Dead 세포 시험을 통해 하이드로겔의 비선형 점탄성 거동과 세포 생존 능력을 분석하였다. 특히, 첨가된 금속염의 종류에 따라 세포의 증식 및 생존 능력이 변화하였고, 이는 하이드로겔들의 유변 물성 특성에도 영향을 미쳤다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.73-75
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• 2002

Recently, remarkable agreement has been reported between nonequilibrium molecular dynamics simulation and high-pressure Couette rheometry on squalane. We utilized the parameters obtained from this unique collaboration along with high-pressure viscometer measurements to calculate the elastohydrodynamic traction curve. A comparison with measured traction at 1.29 GPa shows excellent agreement, confirming the validity of the measurements and simulations. It should no longer be necessary to invoke a different rheological response to explain film thickness and traction.

• 터널과지하공간
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• 제8권1호
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• pp.1-7
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• 1998

In order to get the information of the deformational behavior of rock masses with time in waste disposal repository, it is necessary to measure the relationships between stress and strain and time for temperature. A creep law is used in conjunction with the elastic moduli to calculate stress and displacement following waste emplacement. Exponential-time law's parameters consist of stress and temperature. In this study, thermal creep test was carried out for Whangdeung granite. The measured creep deformation behavior was well explained by exponential time law and generalized Kelvin's rheological model. Mechanicla coefficients for exponential-time creep law showed the clear tendency of temperature dependent while those for Kelvein's model didn't.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1993년도 추계학술대회 논문집
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• pp.402-405
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• 1993

This paper presents design.dynamic modeling and control issues of a novel type of an ER valve-cylinder system incorporating with an electro-rheological(ER) fluid. The yield stress of the ER fluid to be employed to the proposed system is evaluated as a function of applied electric fields. The design and manufacturing process of the ER valve which features fast system response and simple mechanism are undertaken on the basis of model parameters. The governing equation for the hydraulic and pneumatic model is constructed by incorporation with the field-dependent Bingham behavior of the ER fluid. An effective neuro controller is proposed to realize an accurate position control.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1422-1427
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• 2007

MR fluid is a suspension of micrometer-sized magnetizable particles in silicon oil and a functional fluid whose apparent viscosity can be controlled by the applied magnetic field strength. In this paper, a rotary brake using MR fluid called MR brake for tension control of precision machinery such as roll-to-roll printing machinery is presented. First, to obtain the higher performance than conventional powder brake, a MR brake with a modified rotor shape is newly designed and analyzed using FEM. Second, the prototype of MR brake is fabricated with the optimized structural parameters and an experimental apparatus is constructed. Then, basic characteristics of the MR brake are investigated with the different MR fluids. Finally, the validity of the developed MR brake is verified through the comparison with the conventional powder brake.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.565-568
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• 1995

This paper presents the position control of a closed-loop cylinder system using ER(electro-rheological)valve actuators. Following the field-dependent pressure analysis of the ER valve actuators on the basis of Bingham model of ER fluids, a 3 d.o.f. close-loop sylinder system having the heave, roll and pitch motions is proposed. The governing equations of motion are derived using Lagrange's equation, and a control model is established by considering system uncertain parameters such as load conditions. A sliding mode controller which has inherent robustness to system uncertainties is adopted to achieve robust tracking control performance. Tracking control results for sinusoidal trajectory were presented in order to demonstrate the effectiveness of the proposed control system.