Abstract: The development of micro-electro-mechanical systems (MEMS) faces a great challenge in commercial application with respect to lubrication issue recently. Short life time of lubricated MEMS is primarily caused by the failure of the lubrication. In this study, the use of superhydrophobic material applied on one or both of the opposing surfaces in lubricated MEMS was introduced to reduce this type of failure. The optimum parameter of the superhydrophobic effect that provides the greatest load support in MEMS was obtained using numerical analysis. A modified Reynolds equation combined with cavitation model was derived. The slip length model was used to address the superhydrophobic effect for the hydrodynamic analysis. It was shown that in the absence of the wedge effect, load support can be obtained using the superhydrophobic surface. In addition, the numerical analysis showed that the performance of MEMS using such surface depends on cavitation.
Abstract: Magnetorheological (MR) valve is one of the basic ways to apply and accommodate the MR fluid (MRF) into most of hydraulic applications. MRF can change its rheological properties controllably, reversibly and instantaneously by exposing it to the magnetic field, where the viscosity of the fluid increased variably proportionate to the intensity of the magnetic field applied to the fluid. Within the MR valve, the region where the MRF is allowed to be flown and exposed to the magnetic field is called the effective region, and the longer the effective region is in the MR valve, the higher the pressure drop can be, which means that the valve can withstand higher pressure from input and output of the valve. Hence, lots of studies and previous researches have been focused on improving the performance of MR valve by elongating the effective region in the valve. This paper presents one of the ways to increase the effective region in the MR valve by using the serpentine flux path method. This method is a way to weave the magnetic flux into the effective region of MR valve by alternating the magnetic and non-magnetic materials to guide the magnetic flux to be exposed into the effective region. In this paper, the method is simulated by using Finite Element Method Magnetics (FEMM) software for analyzing the magnetic flux path and flux density in the valve, to see the various effects of length and gap size of effective region, electromagnetic circuits and geometrical placements of magnetic and non-magnetic materials in the valve before it can be applied into real hardware for experimentation.
Abstract: Probability occurrence between two successive 2-d granular materials configuration, which are related to their entropy, can be used to check history line of the materials configurations. As an example, a well-known Brazil-nut effect will be presented. In small region it seems that this effect violates principle of minimum energy but not as the whole system, where the energy does decrease. In this work effect of temperature is considered constant since the configurations are observed in frozen states instead of dynamic or fluidized states.
Abstract: Investigation of local plastic deformation between rough surfaces in mechanical components such as gears, camshaft and bearings is very important. Contact between real surfaces occurs at the summits of the highest asperities which vary in height and radius. The plastic deformation of the contact between two asperities was studied in this paper. Asperity contact was modelled as a contact between hemispheres. The commercial finite element software, ABAQUS, was employed to perform the numerical contact analysis of the elastic perfectly-plastic deforming hemispheres with the ratios of radii (R2/R1) from 1 to 7. Normal loads of 5000 N, 8000 N and 11000 N were applied to the frictionless contact of the hemispheres. It was shown that the plastic deformation ratio (ωp1/ωp2) decreases as the radii ratio increases. The higher normal load showed a lower plastic deformation ratio for high radii ratio. The results indicate that the radii ratio contributes to the severity of the plastic deformation and the total displacement of the contacting asperities.
Abstract: Rotary forcespinning is one of techniques used for fabrication of polymer fiber. In this paper optimization of several parameters for synthesis of Polyvinyl Alcohol (PVA) fiber using rotary forcespinning technique was described. In order to obtain PVA fiber with smallest diameter the optimization parameters of solvent system and polymer concentration were performed. The results show that PVA dissolved in water as a single solvent produced fiber with high wettability. A mixture of water and ethanol as a solvent system was developed with variation in ethanol content. The effects of ethanol content on fiber diameter were investigated. Rotary forcespinning using solvent with ethanol content below 30% resulted in PVA fiber with high wettability, while solvent ethanol content of more than 70% was unable to dissolve PVA completely. The effect of PVA concentration on the fiber morphology was investigated by adjusting PVA concentration in the range of 9 to 13 weight %. The diameter of the PVA fiber was uniform and could be controlled by adjusting the PVA concentration.
Abstract: In principle gravity will affect everything. Although practically negligible it is legitimate to inquire the effect of gravity on the electromagnetic properties of materials which can be expressed as the relation between (d,b) fields (electric displacement and magnetic induction) with the (e,h) fields (electric and magnetic field strength). A sample of material in a weak gravitational field is equivalent with placing the sample in an accelerating reference field (which is the statement of the equivalence principle). By using the relation between the accelerating frame with the inertial frame we can compute the electromagnetic properties with the assistance of CAS (Computer Algebra System) Reduce due to the tedious algebraic manipulations needed to accomplish the task. The linear and isotropic relation in inertial frame (free of gravity), although still linear, becomes unisotropic and mixed up between electric and magnetic fields.
Abstract: We promote a finite volume method to solve a water hammer problem numerically. This problem is of the type of fast transient pipe flow. The mathematical model governing the problem is a system of two simultaneous partial differential equations. As the system is hyperbolic, our choice of numerical method is appropriate. In particular, we consider water flows through a pipe from a pressurized water tank at one end to a valve at the other end. We want to know the pressure and velocity profile in the pipe when the valve closes as a function of time. We find that the finite volume method is very robust to solve the problem.
Abstract: Focusing on the cigar-shaped trap model, we provide longitudinal profiles of a weakly outcoupled atom laser propagation both inside and outside the Bose-Einstein condensate regions. The propagation itself is generally represented by inhomogeneous Schrödinger equation which is derived from a set of Gross-Pitaevskii equations by applying the available conditions. We also show that by imposing boundary condition and using quantum oscillator model, energy of the outcoupled atom laser outside the Bose-Einstein condensate region is quantized while there is no analytical solution for the propagation of the outcoupled atom laser inside the Bose-Einstein condensate region.
Abstract: Simulation studies on a new concept of modular Magnetorheological (MR) valve using annular-radial gap combination are discussed in this paper. This study predicts and compares the performance of MR valve module with three different commercial kind MR fluids namely the MRF-122EG, MRF-132DG, and MRF140CG. Magnetorheological effect in various types of MR fluid is analyzed using finite element method (FEM) software in term of simulation magnetic field density within the valve module. The approximated functions of permeability and field dependent yield stress for each kind of MR fluid are derived and presented in this paper as a prerequisite for simulation works. The result has shown that the highest pressure drop rating is reached by applying an MR fluid type MRF140CG, for another kind has shown smallest of pressure drop rating because of the ability to produce the achievable pressure drop highly depends on MR fluid properties.