On The Validity Extent Of Linear Viscoelastic Models Of Human Brain

Characterization of human brain material properties in the form of computationally feasible mathematical models is a complex problem; especially when the models are used in complicated Finite Element simulations. Various models have been proposed to include the tissue’s hyper-viscoelasticity, most of which are quite complicated and therefore only suited to Software-based Finite Element methods. Use of linear material models simplifies the problem and saves much time and effort, allowing the researcher to verify the results of more sophisticated models with lower computational cost. However, the preciseness of the results from such models is subject to special conditions. This study proposes and validates a Generalized Maxwell linear viscoelastic model with five constants to be used as an acceptable computational method to simulate brain’s viscoelastic behavior at low strain rates. To this end, an explicit numerical integration scheme is used to simulate the single-DOF tissue response with a Generalized Maxwell viscoelastic model. Using the material constants of a previous hyper-viscoelastic model, the results are compared with those obtained from a previous experiment. The comparison shows that the linear GM viscoelastic model is predicting the low-strain-rate behavior of the brain tissue with acceptable error

IMECE2011-63108 ANALYTICAL SOLUTIONS FOR THE STATIC INSTABILITY OF MICRO/NANO MIRRORS UNDER THE COMBINED EFFECT OF CAPILLARY FORCE AND CASIMIR FORCE

ABSTRACT This paper deals with the problem of static instability of Micro/Nano mirrors under the combined effect of capillary force and Casimir force. At the First the governing equations of the statical behavior of Micro/Nano mirrors under the combined effect of capillary force and casimir force is obtained. The dependency of the critical tilting angle on the physical and geometrical parameters of the nano/micromirror and its supporting torsional beams is investigated. It is found that existence of casimir force can considerably reduce the stability limits of nano/micromirror. It is also found that rotation angle of the mirror due to capillary force highly depends on the casimir force applied to the mirror. Finally analytical tool Homotopy Perturbation Method (HPM) is utilized for prediction of the mirror's behaviour under combined capillary and casimir forces. It is observed that a sixth order perturbation approximation accurately predicts the rotation angle and stability limits of the mirror. Results of this paper can be used for successful fabrication of nano/micromirrors using wet etching process where capillary force plays a major role in the system.

Robust Adaptive Control of a Micro Telemanipulation System Using Sliding Mode-Based Force Estimation

Abstract-Piezoelectric actuators are widely used in micro manipulation applications. However, hysteresis nonlinearity limits the accuracy of these actuators. This paper presents a novel approach for utilizing a piezoelectric nano-stage as the slave manipulator of a teleoperation system based on a sliding mode controller. The Prandtl-Ishlinskii (PI) model is used to model actuator hysteresis in feedforward scheme to cancel out this nonlinearity. The presented approach requires full state and force measurements at both the master and slave sides. Such a system is costly and also difficult to implement. Therefore, sliding mode unknown input observer (UIO) is proposed for full state and force estimations. Furthermore, the effects of uncertainties in the constant parameters on the estimated external forces should be eliminated. So, a robust adaptive controller is proposed and its stability is guaranteed through the Lyapunov criterion. Performance of the proposed control architecture is verified through experiments

IMECE2011-63112 CLOSED FORM SOLUTIONS FOR THE PROBLEM OF STATICAL BEHAVIOR OF NANO/MICROMIRRORS UNDER THE EFFECT OF CAPILLARY FORCE AND VAN DER WAALS FORCE

ABSTRACT The current paper deals with the problem of static instability of Micro/Nano mirrors under the combined effect of capillary force and van der Waals force. First the governing equations of the statical behavior of Micro/Nano mirrors under the combined effect of capillary force and casimir force is obtained using the newtons first law of motion. The dependence of the critical tilting angle on the physical and geometrical parameters of the nano/micromirror and its supporting torsional beams is investigated. It is found that existence of vdW torque can considerably reduce the stability limits of the nano/micromirror. It is also found that rotation angle of the mirror due to capillary force highly depends on the vdW toque applied to the mirror. Finally analytical tool Homotopy Perturbation Mehtod (HPM) is utilized for prediction of the nano/micromirror behaviour under combined capillary and vdW force. It is observed that a sixth order perturbation approximation accurately predicts the rotation angle and stability limits of the mirror. Results of this paper can be used for successful fabrication of nano/micromirrors using wet etching process where capillary force plays a major role in the system

A Procedure For Performance Experimental Analysis Of A Globe Control Valve

Control valves are known as the final control element in hydraulic closed/open loops of modern process industries around the world. Proper selection of control valve leads to enhanced performance curve of the hydraulic systems and therefore increases the efficiency, reliability, profitability and safety of the system. Flow coefficient (CV) of a control valve describes the relation between the pressure drop across the valve and the flow passing through it. Despite many computational efforts for calculating the exact value and curve of CV, the experimental procedure of the CV test has not been documented well. We used a control valve test-set up designed based on the standards ANSI/ISA-75.02-1996 and IEC 60534-2-3 (2013) to evaluate the performance of a 3 in. control valve. Upon extracting the results in terms of inlet, and outlet pressure and flow, the characteristic parameters such as CV and opening percentage were derived and compared with an ideal curve. Error analysis was performed to account for the tolerance of the measured parameters by the measuring devices. The results show acceptable agreement within the criteria of a reference standard approving the validity of the design method

IMECE2009-12186 APPLICATION OF THE EXTENDED KANTOROVICH METHOD TO THE VIBRATIONAL ANALYSIS OF ELECTRICALLY ACTUATED MICROPLATES

ABSTRACT This paper presents an extended Kantorovich approach to investigate the vibrational behavior of electrically actuated rectangular microplates. The model accounts for the electric force of the excitation and for the applied in plane loads. Starting from a one term Galerkin approximation and following the extended Kantorovich procedure, the partial differential equation governing the microplate vibration, is discretized to two ordinary differential equation with constant coefficients. These equations are then solved analytically and iteratively with a rapid convergence procedure for finding microplate natural frequencies and modeshapes. Results in some specific cases are validated against other theoretical results reported in the literature. It is shown that rapid convergence, high precision and independency of initial guess function make the EKM an effective and accurate design tool for design optimization

Analytical and numerical simulations of energy harvesting using MEMS devices operating in nonlinear regime

While macro-scale piezoelectric generators require base excitations with moderately large amplitudes to transit from the linear regime of vibration to the nonlinear one, for a MEMS harvester due to its small dimensions, this transition can occur at oscillatory base motions even smaller than a few microns, which necessitates the nonlinear analysis of MEMS harvesting devices in most environments. In this paper the coupled electromechanical behavior of a typical MEMS-based piezoelectric harvester in the nonlinear regime is investigated. Lagrange’s equations are used in accordance to the assumed mode method to extract the coupled nonlinear equations of motion governing the lateral deflection and output voltage. An analytical solution to the derived equations is performed employing the perturbation method of multiple scales providing the nonlinear frequency responses of the output power. Results indicate that although the effect of nonlinear inertia increases due to utilizing large tip masses in these harvesters, nonlinear curvature is still the dominant effect leading to hardening behavior of the response. The comparison of the responses of the nonlinear and linear devices shows a considerable enhancement of the frequency bandwidth in the nonlinear regime. Also a nonlinear coupled electromechanical FE simulation of the harvester is conducted using the ABAQUS software where a very good agreement is observed between the results of this simulation with both analytical and numerical solutions of the governing equations

Human Intraocular Thermal Field in Action with Different Boundary Conditions Considering Aqueous Humor and Vitreous Humor Fluid Flow

In this study, a validated 3D finite volume model of human eye is developed to study the fluid flow and heat transfer in the human eye at steady state conditions. For this purpose, discretized bio-heat transfer equation coupled with Boussinesq equation is analyzed with different anatomical, environmental, and physiological conditions. It is demonstrated that the fluid circulation is formed as a result of thermal gradients in various regions of eye. It is also shown that posterior region of the human eye is less affected by the ambient conditions compared to the anterior segment which is sensitive to the ambient conditions and also to the way the gravitational field is defined compared to the geometry of the eye making the circulations and the thermal field complicated in transient states. The effect of variation in material and boundary conditions guides us to the conclusion that thermal field of a healthy and non-healthy eye can be distinguished via computer simulations

Laser Keratoplasty in Human Eye Considering the Fluid Aqueous Humor and Vitreous Humor Fluid Flow

In this paper, conventional laser Keratoplasty surgeries in the human eye are studied. For this purpose, a validated 3D finite volume model of the human eye is introduced. In this model the fluid flow has also been considered. The discretized domain of the human eye incorporates a bio-heat transfer equation coupled with a Boussinesq equation. Both continuous and pulsed lasers have been modeled and the results are compared. Moreover, two different conventional surgical positions that are upright and recumbent are compared for these laser therapies. The simulation results show that in these conventional surgeries, the temperature rises above the critical values at the laser insertion areas. However, due to the short duration and the localized nature, the potential damages are restricted to very small regions and can be ignored. The conclusion is that the present day lasers are acceptably safe to the human eye